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0707.4173

i

it is well - known that environmental processes play a significant role in shaping the evolution of galaxies as they assemble onto clusters . with the aid of hubble space telescope ( _ hst _ ) imaging and deep optical spectroscopy , recent studies have quantified this evolution in galaxy properties , painting a picture where the fraction of early - type ( elliptical and s0 ) galaxies and the fraction of passive non - star - forming galaxies both grow with time , and at a rate that seems to depend sensitively on the local density of galaxies @xcite . yet there are a wide variety of physical processes that may be responsible for these evolutionary trends including galaxy mergers , galaxy - galaxy harassment , gas stripping by the icm , or tidal processes @xcite . observationally , it has so far been impossible to fully separate the effects of the various physical processes , in large part due to the overlapping regimes of influence for each of the proposed mechanisms ( see * ? ? ? further complicating the picture , the large scale assembly states of clusters show considerable variety @xcite , such that the dominant forces acting on galaxies are likely to vary from cluster to cluster , or over the course of an individual cluster s assembly history . but gaining an understanding of the complex interplay between a variable icm , the properties of assembling galaxies , and the overall cluster dynamical state is crucial if we are to have a complete picture of the growth and evolution of galaxies in a hierarchical universe . in this paper , we combine optical ( _ hst _ ) and uv ( _ galex _ ) imaging of two @xmath4 galaxy clusters with ground - based spectroscopy of member galaxies , in an attempt to trace directly the buildup of passive early - type galaxies via a detailed ` case study ' of the galaxy population across each cluster . the two studied clusters , cl 0024 + 17 ( @xmath5 ) and ms 0451 ( @xmath3 ) , are part of a long - term campaign to trace the evolution of galaxies in wide fields ( @xmath6 mpc diameter ) centered on both clusters , using a variety of methods . by undertaking an in - depth , wide - field comparative study of two prominent clusters , we hope to provide a complement to other observational ( e.g. , * ? ? ? * ; * ? ? ? * ) and theoretical investigations ( e.g. , * ? ? ? * ) which trace with a broad brush the evolution in star formation rate and the buildup of structure in the universe . the first paper in our series , @xcite ( hereafter paper i ) , introduced our panoramic _ hst _ imaging of cl 0024 and began our ongoing discussion of the physical processes that may be acting on galaxies within clusters . in several subsequent papers , whose results are summarized in 2 , we have added extensive optical spectroscopy to the program , allowing targeted investigations of galaxy stellar populations and star formation rates as a function of cluster - centric radius , local density , and morphology . our goal for this paper is to bring our complete survey data set to bear on the question of how galaxies are affected by their environment , as a function of both the overall cluster properties and of local environment within each cluster . for maximum clarity and deductive power , we focus our investigation on several key populations of ` transition galaxies ' in the clusters galaxies whose stellar populations or dynamical states indicate a recent or ongoing change in morphology or star formation rate . lcclcccc cl 0024 & 6.65125 & 17.162778 & @xmath7 & @xmath8 & 0.395 & @xmath9 & 3.5@xmath10 + ms 0451 & 73.545417 & -3.018611 & 2.6 & @xmath11 & 0.540 & @xmath12 & 10.0@xmath13 + in evaluating cluster galaxies for signs of evolution , we have adopted a strategy to make maximal use of our _ hst_-based morphologies by characterizing signs of recent evolution in spirals and early - types separately . this approach is similar to using the color - magnitude relation to divide our sample into ` red sequence ' and ` blue cloud ' galaxies , but it provides additional leverage to identify galaxies in transition . early - type galaxies that have either been newly transformed or prodded back into an active phase , or spiral galaxies where star formation is being suppressed or enhanced will all stand out in our sample . at the same time , their morphologies reveal important information about their formation histories prior to their current transition state , information that colors alone do not provide . our strategy also has the benefit of allowing us to directly investigate the hypothesis that many cluster spirals transform into s0s between @xmath4 and today @xcite an investigation that will form the basis of this paper . in the next section , we outline our rationale for selecting cl 0024 and ms 0451 , describe the large - scale properties of each cluster , and give a summary of what we have concluded so far in our study of galaxy evolution in both clusters . in 3 , we describe new data not covered in previous papers in our series . in 4 , we will investigate the properties of ` passive spirals ' across the two clusters , suggesting that they are in the process of transforming into s0 galaxies . we confirm in 5 that this is the case , via identification of newly created s0s that we believe reflect the distinct passive spiral populations found in each cluster . in 6 , we consider the environments of these galaxies in transition , and begin to investigate the physical mechanisms that may be responsible for these transformations . in 7 , we outline a model of how galaxy evolution proceeds in each cluster . we consider the fundamental plane as a way to further constrain the physical mechanisms at work , and derive similar constraints from the populations of compact emission line galaxies in both clusters . finally , in 8 , we summarize our conclusions about the transformation of spirals into s0s at @xmath4 . in this paper , we adopt a standard @xmath14cdm cosmology with @xmath15 km s@xmath16 mpc@xmath16 , @xmath17 , and @xmath18 .

hst _ optical and _ galex _ uv imaging with keck spectroscopy of member galaxies , we identify and study several key classes of ` transition objects ' whose stellar populations or dynamical states indicate a recent or ongoing change in morphology and star formation rate . for the first time , we have been able to conclusively identify spiral galaxies in the process of transforming into s0 galaxies .

we present new results from our comprehensive comparative survey of two massive , intermediate redshift galaxy clusters , cl @xmath0 ( @xmath1 ) and ms @xmath2 ( @xmath3 ) . combining _ hst _ optical and _ galex _ uv imaging with keck spectroscopy of member galaxies , we identify and study several key classes of ` transition objects ' whose stellar populations or dynamical states indicate a recent or ongoing change in morphology and star formation rate . for the first time , we have been able to conclusively identify spiral galaxies in the process of transforming into s0 galaxies . this has been accomplished by locating both spirals whose star formation is being quenched as well as their eventual successors , the recently created s0s . differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation . combined with other diagnostics that are sensitive to either icm - driven galaxy evolution or galaxy - galaxy interactions including the residuals from the fundamental plane and the properties of ` signpost ' compact emission line galaxies we describe a self - consistent picture of galaxy evolution in clusters . we find that spiral galaxies within infalling groups have already begun a slow process of conversion into s0s primarily via gentle galaxy - galaxy interactions that act to quench star formation . the fates of spirals upon reaching the core of the cluster depend heavily on the cluster icm , with rapid conversion of all remaining spirals into s0s via ram - pressure stripping in clusters where the icm is dense . in the presence of a less - dense icm , the conversion continues at a slower pace , with galaxy - galaxy interactions continuing to play a role along with ` starvation ' by the icm . we conclude that the buildup of the local s0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments from cluster outskirts to cores .

0707.4173

c

in this paper , we have presented new results from our comprehensive comparative survey of two massive , intermediate redshift galaxy clusters , cl @xmath0 ( @xmath1 ) and ms @xmath2 ( @xmath3 ) . we have identified and studied several key classes of transition objects in the clusters : the passive spirals and the young s0s . through uv imaging and measurements of spectral line indices , we have concluded that some passive spirals have experienced a decline in star formation over a @xmath149 gyr timescale , mostly in cl 0024 , while others , mostly in ms 0451 , have experienced a more rapid truncation in star formation . for the first time , we have been able to conclusively identify spiral galaxies in the process of transforming into s0 galaxies , by directly linking the passive spirals in each cluster with their descendant s0s . having established that the transformation from spiral to s0 galaxies is taking place in each cluster , we have leveraged the differences between clusters in the timescales and spatial location of the conversion process , in order to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation . combined with other diagnostics that are sensitive to either icm - driven galaxy evolution or galaxy - galaxy interactions including the residuals from the fundamental plane and the properties of ` signpost ' compact emission line galaxies we paint a tentative but remarkably self - consistent picture of galaxy evolution in clusters . we find that spiral galaxies within infalling groups have already begun a slow process of conversion into s0s primarily via gentle galaxy - galaxy interactions that act to quench star formation , perhaps aided by interaction with the intra - group gas . the fates of spirals upon reaching the core of the cluster depend heavily on the cluster icm , with rapid conversion of all remaining spirals into s0s via ram - pressure stripping in clusters where the pressure of the icm is @xmath231 of that needed to strip a canonical milky way - like spiral . in the presence of a less - dense icm , the conversion continues at a slower pace , with galaxy - galaxy interactions continuing to play a role , perhaps along with ` starvation ' or gentle stripping by the icm . several authors have raised objections to a scenario where s0s are created via simple fading of spiral disks . first , s0s are observed to have higher bulge to disk ratios than their supposed spiral progenitors ( e.g. , * ? ? ? * ) , suggesting that if the spiral to s0 conversion takes place , significant redistribution of mass or significant new star formation is required @xcite . second , other authors have noted that the local abundance of s0s is only weakly correlated with environment , such that processes like ram pressure stripping that act only in cluster cores can not be responsible for the entire buildup of s0s @xcite . we have here demonstrated , however , that simple stripping of gas does _ not _ build up the entire population of cluster s0s . rather , a combination of gas effects and galaxy interactions are responsible , in ratios that vary widely and depend on both the cluster dynamical state and the location within the cluster or its outskirts . the buildup of bulges through new star formation @xcite that is expected from harassment - like encounters could potentially balance out the expected fading of disks after ram pressure stripping has run its course . it may still be necessary to invoke significant obscured star formation to bridge the observed gap between the bulges of spirals and s0s @xcite ; the higher detection rate of such systems in cl 0024 compared to ms 0451 @xcite may indicate that such obscured starbursts are part of the pre - processing that occurs before galaxies encounter a dense icm . furthermore , the wide distribution of passive spirals across both clusters , and their association with groups in the cluster outskirts , indicates that the resulting s0s will likely be spread across a wide range of environments . the typical densities of infalling groups at @xmath4 are likely realized even in isolated groups by @xmath130 @xcite , and so it seems that , though a variety of mechanisms are responsible , passive spirals could be the progenitors of most local s0s . in @xcite , a rough assessment of the frequency of passive spirals and their expected lifetimes in cl 0024 suggested that passive spirals could account for the entire buildup of s0s between @xmath217 and @xmath130 . in ms 0451 , we observe a similar number of spirals currently in the passive phase , but we have shown that the timescale for conversion is much shorter than in cl 0024 . this suggests that all existing spirals should be converted to s0 in ms 0451 even _ before _ @xmath130 , and the rate of any future buildup should be limited by the infall rate of new galaxies . as ms 0451 is a remarkably well - evolved system at @xmath3 , comparable in mass to virgo or coma ( @xmath232 and @xmath233 , respectively , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , this is perhaps not surprising . it suggests , however , that there may exist a generic tipping point in the evolution of a massive cluster : beyond the threshold in ram pressure strength that we have identified here ( which is reached through some combination of cluster mass and icm density ) , spirals are transformed so rapidly upon infall that they will be essentially absent . by @xmath130 , many clusters have likely reached this threshold , as evidenced by their low spiral fractions @xcite . this sort of dichotomy between well - evolved and still - assembling clusters could , for example , explain why some clusters , like coma , reveal few signs of evolution in their massive galaxies @xcite , while others , like virgo , have a rich population of passive spirals and galaxies with other signs of recent evolution ( e.g. , * ? ? ? regardless , the results presented here indicate that the abundant cluster spirals found at intermediate redshift , _ do _ , in fact , transform into the equally abundant s0 population seen today . the transformation process at @xmath234 , as we have seen , is beginning to operate even in groups at the cluster outskirts . as a result , the conversion of passive spirals to s0s can account for the evolution of the morphology density relation at both the cluster and group scale from intermediate redshift to today . we thank the referee , a. boselli , for insightful comments , especially on the various physical processes and their timescales , which were helpful in revising the discussion of these issues . smm would like to thank t. heckman , g. kauffmann , s. yi , & members of the _ galex _ science team for valuable discussions . faint object spectroscopy at keck observatory is made possible with lris and deimos thanks to the dedicated efforts of j. cohen , p. amico , s. faber and g. wirth . we acknowledge use of the gauss - hermite pixel fitting software developed by r. p. van der marel . the analysis pipeline used to reduce the deimos data was developed at uc berkeley with support from nsf grant ast-0071048 . tt acknowledges support from the nsf through career award nsf-0642621 , and from the sloan foundation through a sloan research fellowship . rse acknowledges financial support from nsf grant ast-0307859 and stsci grants hst - go-08559.01-a and hst - go-09836.01-a . irs and gps acknowledge support from the royal society . abraham , r. g. , et al . 1996 , apj , 471 , 694 balogh , m. l. , morris , s. l. , yee , h. k. c. , carlberg , r.g . , & ellingson , e. 1999 , apj , 527 , 54 bekki k. , couch , w.j . , & shioya , y. 2002 , apj , 577 , 651 bertin , e. & arnouts , s. 1996 , a&as , 117 , 393 biviano , a. girardi , m. , giuricin , g. , mardirossian , f. & mezzetti , m. 1993 , apj , 376 , 458 blanton , m. r. , et al . 2003 , aj , 125 , 2348 boselli , a. & gavazzi , g. 2006 , pasp , 118 , 517 boselli , a. , boissier , s. , cortese , s. , gil de paz , a. , seibert , m. , madore , b. f. , buat , v. & martin , d. c. 2006 , apj , 651 , 811 bruzual , g. , & charlot , s. 2003 , mnras , 344 , 1000 burstein , d. , ho , l. c. , huchra , j. p. , & macri , l. m. 2005 , apj , 621 , 246 . christlein , d. & zabludoff , a. i. 2004 , apj , 616 , 192 chung , a. , van gorkom , j. h. , kenney , j. d. p. , & vollmer , b. 2007 , apj , 659 , l115 cooper , m. c. , et al . 2007 , mnras , 376 , 1445 cortese , l. , et al . 2007 , mnras , 376 , 157 couch , w. j , barger , a. j. , smail , i. , ellis , r. s. & sharples , r. m. 1998 , apj , 497 , 188 cowie , l. l. & songaila , a. 1977 , nature , 266 , 501 czoske , o. , kneib , j .- p . , soucail , g. , bridges , t. j. , mellier , y. , & cuillandre , j .- c . 2001 , a&a , 372 , 391 czoske , o. , moore , b. , kneib , j .- , & soucail , g. 2002 , a&a , 386 , 31 davis , m. , et al . 2003 , spie , 4834 , 161 de filippis , e. , sereno , m. , bautz , m. , & longo , g. 2005 , apj , 625 , 108 de lucia , g. , springel , v. , white , s. d. , croton , d. , & kauffmann , g. 2006 , mnras , 366 , 499 donahue , m. , gaskin , j. a. , patel , s. k. , joy , m. , clowe , d. , & hughes , j. p. 2003 , apj , 598 , 190 dressler , a. 1980 , apj , 236 , 351 dressler , a. 2004 , in carnegie observatories centennial symposia , eds : j.s . mulchaey , a. dressler , & a. oemler , ( cambridge university press : cambridge , uk ) , 206 dressler , a. & gunn , j. e. 1983 , apj , 270 , 7 dressler , a. & shectman , s. a. 1988 , aj , 95 , 985 dressler , a. , smail , i. , poggianti , b. , butcher , h. , couch , w. j. , ellis , r. s. , & oemler , a. , jr . 1999 , apjs , 122 , 51 dressler , a. , et al . 1997 , apj , 490 , 577 ellingson , e. , yee , h. k. c. , abraham , r. g. , morris , s. l. , & carlberg , r. g. 1998 , apjs , 116 , 247 fouqu , p. solanes , j. m. , sanchis , t. & balkowski , c. 2001 , a&a , 375 , 770 fujita , y. 1998 , apj , 509 , 587 fujita , y. 2004 , pasj , 56 , 29 fujita , y. & nagashima , m. 1999 , apj , 516 , 619 gavazzi , g. , boselli , a. , cortese , l. , arosio , i. , gallazzi , a. , pedotti , p. , & carrasco , l. 2006 , a&a , 446 , 839 gavazzi , g. , zaccardo , a. , sanvito , g. , boselli , a. , & bonfanti , c. 2004 , a&a , 417 , 499 geach , j. e. , et al . 2006 , apj , 649 , 661 geller , m. j. , diaferio , a. , & kurtz , m. j. 1999 , apj , 517 , l23 gunn , j. e. & gott , j. r. 1972 , apj , 176 , 1 hester , j. a. 2006 , apj , 647 , 910 jee , m. j. , et al . 2007 , apj , in press jeltema , t. e. , mulchaey , j. s. , lubin , l. m. , & fassnacht , c. d. 2007 , apj , 658 , 865 kauffmann , g. , et al . 2003 , mnras , 341 , 33 kelson , d. d. , illingworth , g. d. , van dokkum , p. g. , & franx , m. 2000 , apj , 531 , 184 kneib , j - p . , 2003 , , 598 , 804 ( paper ii ) kodama , t. & smail , i. 2001 , mnras , 326 , 637 koo , d.,guzmn , r. , faber , s. m. , illingworth , g. d. , bershady , m. a. , kron , r. g. , & takamiya , m. 1995 , apj , 440 , 49 larson , r. b. , tinsley , b. m. , & caldwell , c. n. 1980 , apj , 237 , 692 lucey , j.r . , guzmn , r . , carter , d. , & terlevich , r. j. 1991 , mnras , 253 , 584 martin , d. c. , et al . 2005 , apj , 619 , l1 mihos , c. 2004 , in iau symposium no . 217 , recycling interstellar and intergalactic matter , ed . duc , j braine , e brinks , ( san francisco : asp ) , 390 moore , b. , lake , g. , quinn , t. , & stadel , j. 1999 , mnras , 304 , 465 moran , s. m. , ellis , r. s. , treu , t. , salim , s. , rich , r. m. , smith , g. p. & kneib , j - p . 2006 , apj , 641 , l97 moran , s. m. , ellis , r. s. , treu , t. , smail , i. , dressler , a. coil , a. l. & smith , g. p .. 2005 , apj , 634 , 977 ( paper iii ) moran , s. m. , miller , n. , treu , t. , ellis , r. s. & smith , g. p. 2007 , apj , 659 , 1138 mulchaey , j. 2000 , ara&a , 38 , 289 noeske , k. g. , koo , d. c. , phillips , a. c. , willmer , c. n. a. , melbourne , j. , de paz , a. g. , & papaderos , p. 2006 , apj 640 , l143 nulsen , p. e. j. 1982 , mnras , 198 , 1007 okamoto , t. & nagashima , m. 2003 , apj , 587 , 500 ota , n. , pointecouteau , e. , hattori , m. , & mitsuda , k. 2004 , apj , 601 , 120 peng , c. y. , ho , l. c. , impey , c. d. , & rix , h. 2002 , aj , 124 , 266 poggianti , b. m. & barbaro , g. , 1997 , a&a , 325 , 1025 poggianti , b. m. & barbaro , g. , 1996 , a&a , 314 , 379 poggianti , b. m. , bridges , t. j. , komiyama , y. , yagi , m. , carter , d. , mobasher , b. , okamura , s. , & kashikawa , n. 2004 , apj , 601 , 197 poggianti , b. m. , smail , i. , dressler , a. , couch w. j. , barger , a. j. , butcher , h. , ellis , r. s. , & oemler , a. , jr . 1999 , apj , 518 , 576 poggianti , b. m. , et al . 2001 , apj , 563 , 118 poggianti , b. m. , et al . 2006 , apj , 642 , 188 postman , m. , et al . 2005 , apj , 623 , 721 quilis , v. , moore , b. , & bower , r. 2000 , science , 288 , 1617 rawat , a. , kembhavi , a. k. , hammer , f. , flores , h. , & barway , s. 2007 , a&a , in press roettiger , k. , burns , j. , & loken , c. 1996 , , 473 , 651 schlegel , d.j . , finkbeiner , d. p. , & davis , m. 1998 , apj , 500 , 525 smith , g. p. , treu , t. , ellis , r. s. , moran , s. m. , & dressler , a. 2005a , apj , 620 , 78 smith , g. p. , et al . 2005b , mnras , 359 , 417 treu , t. , ellis , r. s. , kneib , j - 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we present new results from our comprehensive comparative survey of two massive , intermediate redshift galaxy clusters , cl @xmath0 ( @xmath1 ) and ms @xmath2 ( @xmath3 ) . combining _ differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation . combined with other diagnostics that are sensitive to either icm - driven galaxy evolution or galaxy - galaxy interactions including the residuals from the fundamental plane and the properties of ` signpost ' compact emission line galaxies we describe a self - consistent picture of galaxy evolution in clusters . we find that spiral galaxies within infalling groups have already begun a slow process of conversion into s0s primarily via gentle galaxy - galaxy interactions that act to quench star formation . the fates of spirals upon reaching the core of the cluster depend heavily on the cluster icm , with rapid conversion of all remaining spirals into s0s via ram - pressure stripping in clusters where the icm is dense . in the presence of a less - dense icm , the conversion continues at a slower pace , with galaxy - galaxy interactions continuing to play a role along with ` starvation ' by the icm .

we present new results from our comprehensive comparative survey of two massive , intermediate redshift galaxy clusters , cl @xmath0 ( @xmath1 ) and ms @xmath2 ( @xmath3 ) . combining _ hst _ optical and _ galex _ uv imaging with keck spectroscopy of member galaxies , we identify and study several key classes of ` transition objects ' whose stellar populations or dynamical states indicate a recent or ongoing change in morphology and star formation rate . for the first time , we have been able to conclusively identify spiral galaxies in the process of transforming into s0 galaxies . this has been accomplished by locating both spirals whose star formation is being quenched as well as their eventual successors , the recently created s0s . differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation . combined with other diagnostics that are sensitive to either icm - driven galaxy evolution or galaxy - galaxy interactions including the residuals from the fundamental plane and the properties of ` signpost ' compact emission line galaxies we describe a self - consistent picture of galaxy evolution in clusters . we find that spiral galaxies within infalling groups have already begun a slow process of conversion into s0s primarily via gentle galaxy - galaxy interactions that act to quench star formation . the fates of spirals upon reaching the core of the cluster depend heavily on the cluster icm , with rapid conversion of all remaining spirals into s0s via ram - pressure stripping in clusters where the icm is dense . in the presence of a less - dense icm , the conversion continues at a slower pace , with galaxy - galaxy interactions continuing to play a role along with ` starvation ' by the icm . we conclude that the buildup of the local s0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments from cluster outskirts to cores .

1702.08383

i

the narrow - line seyfert 1 ( nls1 ) galaxies , a subclass of active galactic nuclei ( agn ) have been the centre of interest because of their extreme variability in the x - ray band @xcite . the defining properties of this class of agn are : balmer lines with full width at half - maximum fwhm(h@xmath11 ) @xmath12 km s@xmath13 @xcite , strong permitted optical / uv fe ii emission lines @xcite and weaker [ oiii ] emission @xmath14\lambda5007}{h_{\beta}}\leq3 $ ] @xcite . the x - ray spectra of seyfert galaxies show a power - law like primary continuum which is thought to arise due to thermal comptonization of the optical / uv seed photons in a corona of hot electrons surrounding the central supermassive black hole ( e.g.@xcite ) . the optical / uv photons are thought to arise from an accretion disk but direct observational evidence is lacking . similarly , the interplay between the accretion disk and the hot corona is not well understood . many type 1 agn also show strong ` soft x - ray excess ' emission over the power - law continuum below @xmath15 kev in their x - ray spectra . the existence of this component ( @xmath16 kev ) was discovered around 30 years ago ( e.g. @xcite ) and its origin is still controversial . initially , it was considered to be the high energy tail of the accretion disk emission ( @xcite ) , but the temperature of the soft excess is in the range @xmath17 kev which is much higher than the maximum disk temperature expected in agn . it was then speculated that the soft excess may result from the compton up - scattering of the disk photons in an optically thick , warm plasma ( e.g. @xcite ) . currently , there are two competing models for the soft x - ray excess emission in terms of optically thick thermal comptonization @xcite and blurred reflection from partially ionized accretion disk @xcite . however , these models sometimes lead to spectral degeneracy because of the presence of multiple spectral components in the energy spectra of nls1 galaxies @xcite . one efficient approach to overcome the spectral model degeneracy is to study the root mean square ( rms ) spectrum which links the energy spectrum with variability and has been successfully applied in a number of agn ( mcg6 - 30 - 15 : @xcite , 1h 0707495 : @xcite , rx j1633.3 + 4719 : @xcite ) . observational evidence for the emission in different bands such as uv , soft and hard x - rays during large variability events may help us to probe the connection between the disk , hot corona and the soft excess emitting regions . in this manuscript , we investigate the origin of the soft x - ray excess emission , rapid x - ray variability and uv / x - ray connection in pg 1404 + 226 with the use of both model dependent and model independent techniques . pg 1404 + 226 is a narrow - line seyfert 1 galaxy at a redshift @xmath18 = 0.098 with fwhm(h@xmath11 ) @xmath19 km s@xmath13 @xcite . previously , the source was observed with _ rosat _ ( @xcite ) , _ asca _ ( @xcite ) , _ chandra _ ( @xcite ) and _ xmm - newton _ ( @xcite ) . from the _ asca _ observation , the 2 - 10 kev spectrum was found to be quite flat ( @xmath20 ) with flux @xmath21 erg @xmath22 s@xmath13 @xcite . the detection of an absorption edge at @xmath23 kev was claimed in previous studies and interpreted as high velocity ( 0.2 - 0.3 @xmath24 ) outflow of ionized oxygen @xcite . the source is well - known for its strong soft excess and large - amplitude x - ray variability on short time scales ( @xcite ) . here we explore the energy spectrum , rms spectrum , flux flux plot and uv / x - ray connection through a new @xmath25 ks _ xmm - newton _ observation of pg 1404 + 226 .

we use this variability event to investigate the origin of the soft x - ray excess emission and the connection between the disk , hot corona and the soft excess emitting region through uv / x - ray cross - correlation , time - resolved spectroscopy and root mean square ( rms ) spectral modelling . the weakly variable uv emission ( @xmath2=3.9@xmath3 ) the strong soft x - ray excess below 1 kev seen in the mean x - ray spectrum as well as in the time - resolved spectra is well described by both the intrinsic disk comptonization and the blurred reflection models .

we present results from a detailed analysis of our 2016 _ xmm - newton _ observation of the narrow - line seyfert 1 galaxy pg 1404 + 226 which showed a large - amplitude , rapid x - ray variability by a factor of @xmath0 in @xmath1 ks . we use this variability event to investigate the origin of the soft x - ray excess emission and the connection between the disk , hot corona and the soft excess emitting region through uv / x - ray cross - correlation , time - resolved spectroscopy and root mean square ( rms ) spectral modelling . the weakly variable uv emission ( @xmath2=3.9@xmath3 ) appears to lead the strongly variable x - ray emission ( @xmath4=89.0@xmath5 ) by @xmath6 ks . such a uv lead is consistent with the crossing time ( @xmath7 ks ) of the seed photons from the disk to a compact ( @xmath8 ) hot corona and the time required for their thermal comptonization ( @xmath9 ks ) giving rise to the x - ray power - law emission . the strong soft x - ray excess below 1 kev seen in the mean x - ray spectrum as well as in the time - resolved spectra is well described by both the intrinsic disk comptonization and the blurred reflection models . the soft excess emission is found to vary together with the power - law component as @xmath10 . the x - ray fractional rms spectrum shows an increase in variability with energy which can be described only in the framework of blurred reflection model in which both the intrinsic continuum and the reflected emission are highly variable in normalization only and are perfectly coupled with each other . our results suggest that accretion disk provides the seed photons for thermal comptonization giving rise to the x - ray power - law component which in turn illuminates the innermost accretion disk and gives rise to the soft x - ray excess emission . [ firstpage ]

1702.08383

r

the top panel of figure [ fig1 ] shows the background subtracted epic - pn light curve of pg 1404 + 226 with time bins of 500 s. the x - ray time series clearly shows a short - term , large - amplitude variability event in which pg 1404 + 226 varied by a factor of @xmath0 in @xmath1 ks during the 2016 observation . the fractional root mean square ( rms ) variability amplitude estimated in the 0.3@xmath3310 kev band is @xmath4=89.0@xmath34 ( the uncertainty on @xmath35 was calculated in accordance with @xcite ) . based on the variability pattern , we divided the entire 73 ks light curve into five intervals . int 1 consists of the first 38 ks of the time series and had the lowest flux with mean count rate of @xmath36 counts s@xmath13 and moderate fractional rms variability of @xmath37=12.5@xmath38 . in int 2 , the x - ray flux increases exponentially by a factor of @xmath39 with fractional rms variability of @xmath40=47.5@xmath41 . the duration and mean flux level of int 2 are @xmath42 ks and 0.51@xmath43 counts s@xmath13 , respectively . during int 3 , the source was in the highest flux state , with mean count rate of 1.38@xmath44 counts s@xmath13 and fractional rms amplitude of @xmath45=11.8@xmath46 . the source was in the brightest state only for @xmath47 ks and then count rate started decreasing . in int 4 , the source flux drops by a factor of @xmath48 in @xmath47 ks with @xmath49=47.2@xmath38 . during the end of the observation , the source was moderately variable with @xmath50=13.3@xmath51 . in the bottom panel of fig . [ fig1 ] , we show the uvw1 light curve of pg 1404 + 226 simultaneous with the x - ray light curve . the amplitude of the observed uv variability is only @xmath52 of the mean count rate on timescales of @xmath53 ks . the fractional rms variability amplitude in the uvw1 band is , @xmath2=3.9@xmath3 which is much less compared to the x - ray variability . the x - ray and uv variability patterns appear significantly different suggesting lack of any correlation between the x - ray and uv emissions at zero time - lag . the duration and fractional rms amplitude for each interval are listed in table [ table0 ] . the upper and middle panels of figure [ fig2 ] show the background - subtracted soft ( 0.3@xmath331 kev ) and hard ( 1@xmath3310 kev ) x - ray light curves , respectively , with time bins of 2 ks . the soft band is observed to be brighter than the hard band , however the variability pattern and amplitude ( @xmath54 and @xmath55 ) in these two bands are found to be comparable during the observation . the peak - to - trough ratio of the variability amplitudes in the soft and hard bands are of the order of @xmath56 and @xmath57 , respectively . in the bottom panel of fig . [ fig2 ] , we have shown the hardness ratio as a function of time . a constant model fitted to the hardness ratio curve provided statistically poor fit ( @xmath58/d.o.f=47/31 ) , implying the presence of moderate spectral variability and the source became harder in the beginning of the large amplitude variability . [ table0 ] to investigate the connection between the x - ray and uv emitting regions , we calculated the cross - correlation function ( ccf ) between the uvw1 and x - ray ( 0.3@xmath3310 kev ) light curves using the z - transformed discrete correlation function ( zdcf ) @xcite . in the zdcf method , all pairs from two time series are ordered according to their time difference , @xmath59 . the ordered list is then divided into time lag bins , each comprising of a minimum of @xmath60 pairs . the cross - correlation for each lag bin is calculated as @xmath61 where @xmath60 is the number of pairs in a time lag bin , @xmath62 , @xmath63 are the bin averages , and @xmath64 , @xmath65 are the bin standard deviations . the zdcf method uses the fishers z - transformation of @xmath66 to estimate the confidence intervals of a measured bin correlation coefficients . the zdcf method also determines the peak of the ccf and the corresponding lag uncertainty based on the monte carlo simulations @xcite . we have used minimum of 22 data points in a time bin and 10000 realizations for monte carlo runs to estimate the time - lag . figure [ ccf ] shows the zdcf for the observed uvw1 and x - ray light curves with @xmath67 bins . the time - lag was estimated relative to the uvw1 band and the positive lag implies that the uv is leading the x - ray variations . we observed both positive and negative correlations between the uv and x - ray bands with ccf@xmath68 and @xmath69 at time - lags of @xmath6 ks and @xmath70 ks , respectively . we estimated the time - lag in the range @xmath71 to 60 ks using the maximum likelihood method ( plike code , @xcite ) . the lag of x - rays by uvw1 is @xmath72 ks , where the errors represent the 1-@xmath73 confidence intervals . to determine the significance of the observed time - lag and ccf peak , we generated @xmath74 pair of simulated light curves by bootstrapping method using astropy v.1.3 @xcite . we estimated the zdcf and time - lag for each pair of simulated light curves . the resulting ccf and lag distributions are shown in figure [ ccf_lag ] . clearly , the detection of the uv lead corresponding to the positive correlation is statistically robust . to check the accuracy of the estimated time - lag , we have generated the distribution of the time - lag from @xmath75 realizations of the data using javelin cross - correlation program @xcite in the range of @xmath76 ks . [ lag ] shows the probability distribution of the x - ray time - lag with respect to the uvw1 band . the estimated time - lag is @xmath77 ks . we performed the spectral analysis of pg 1404 + 226 using xspec v.12.8.2 @xcite . we employed the @xmath58 statistic and quote the errors at the @xmath78 confidence limit for a single parameter corresponding to @xmath79 , unless otherwise specified . we begin our spectral analysis by fitting the 1@xmath338 kev epic - pn spectrum using a continuum model ( zpowerlw ) multiplied by the galactic absorption ( tbabs ) . we fixed the galactic column density at @xmath80 @xmath22 @xcite . this model provided @xmath58=71 for 50 degrees of freedom ( d.o.f ) with @xmath81 and can be considered as a good baseline model to describe the hard x - ray emission from the source . then we extrapolated our 1@xmath338 kev absorbed power - law model ( tbabs@xmath82zpowerlw ) down to 0.3 kev . this extrapolation reveals the presence of a strong soft excess emission below 1 kev with @xmath58/d.o.f = 11837/160 . the ratio of the observed epic - pn data and the absorbed power - law model is shown in figure [ fig4 ] ( left ) . the fitting of the 0.3@xmath338 kev data with the absorbed power - law model ( tbabs@xmath82zpowerlw ) resulted in a poor fit with @xmath58/d.o.f = 1126.5/158 . the residual plot demonstrates a sharp dip around @xmath23 kev and excess emission below 1 kev . initially , we modelled the soft excess emission using a simple blackbody model ( zbbody ) . the addition of the zbbody model improved the fit to @xmath58/d.o.f = 232.1/156 ( @xmath83=@xmath33894.4 for 2 additional free parameters ) . in xspec , the model reads as tbabs@xmath82(zbbody@xmath84zpowerlw ) . the deviations of the observed epic - pn data from the absorbed blackbody and power - law model is shown in fig . [ fig4 ] ( right ) . the estimated blackbody temperature @xmath85 ev is consistent with the temperature of the soft excess emission observed in seyfert 1 and qsos @xcite . in order to model the absorption feature @xmath23 kev , we used one ionized absorber model ( zxipcf ) which has 4 free parameters : column density ( @xmath86 ) , covering fraction ( c@xmath87 ) , redshift ( @xmath18 ) and ionization parameter ( @xmath88 , where @xmath89 , @xmath90 is the source luminosity , @xmath60 is the hydrogen density and @xmath66 is the distance between the source and cloud ) . we assumed that the absorbing cloud to cover the x - ray source fully and fixed the covering fraction at 1 . the inclusion of the warm absorber significantly improved the fit from @xmath58/d.o.f = 232.1/156 to 176.5/154 ( @xmath83=@xmath3355.6 for 2 additional free parameters ) . to test the presence of out - flow , we varied the redshift of the absorbing cloud which further improved the fit to @xmath58/d.o.f = 168.1/153 ( @xmath83=@xmath338.4 for 1 additional free parameter ) . in xspec , the 0.3@xmath338 kev best - fitting model reads as tbabs@xmath82zxipcf(zbbody@xmath84zpowerlw ) . the epic - pn spectral data , the best - fitting model and the deviations of the observed data from the best - fitting model are shown in figure [ fig5 ] ( left ) . the best - fitting values for the column density , ionization parameter and outflow velocity ( determined from the redshift of the cloud relative to the rest frame ) of the warm absorber are @xmath91 , @xmath88(erg cm s@xmath92 and @xmath93 , respectively . in order to search for spectral variability on shorter timescales , we performed time - resolved spectroscopy . first we applied our best - fitting mean spectral model to the 5 epic - pn spectra extracted from the five intervals ( see section 3.1 ) . we tied all the parameters except the normalization of the power - law and blackbody components which we set to vary independently . this resulted in statistically acceptable fit with @xmath58/d.o.f = 337.7/269 = 1.25 and without strong residual . if we allow the blackbody temperature and photon - index of the power - law to vary , we did not find any significant improvement in the fit with @xmath58/d.o.f = 327.7/261 = 1.25 ( @xmath83=@xmath3310 for 8 free parameters ) . the 5 epic - pn spectral data - sets , the best - fitting model and residuals are shown in fig . [ fig5 ] ( right ) . the best - fitting spectral model parameters for both time - averaged and time - resolved spectra are listed in table [ table1 ] . [ table1 ] [ table2 ] [ table3 ] in order to examine the origin of the soft x - ray excess emission , we have tested two different physical models thermal comptonization in an optically thick , warm medium and blurred reflection from a partially ionized accretion disk . first , we have used the intrinsic disk comtonization model ( optxagnf ) ( @xcite ) which assumes that the gravitational energy released in the disk at each radius is radiated as a blackbody emission from the outer disk radius , @xmath94 to the coronal radius , @xmath95 . inside the coronal radius , the gravitational energy is dissipated to produce the soft excess component in an optically thick , warm ( @xmath96 kev ) corona and the hard x - ray power - law tail in an optically thin , hot ( @xmath97 kev ) corona above the disk . thus , this model represents an energetically self - consistent model . the four parameters which determine the normalization of the model are the following : black hole mass ( @xmath98 ) , dimensionless spin parameter ( @xmath99 ) , eddington ratio ( @xmath100 ) and proper distance ( @xmath101 ) . we fitted the 0.3@xmath338 kev epic - pn time - averaged spectrum with the optxagnf model modified by the galactic absorption tbabs . we fixed the black hole mass , outer disk radius and proper distance at @xmath102 @xcite , 400@xmath103 and 397 mpc , respectively . we assumed a maximally rotating black hole as concluded by @xcite and fixed the spin parameter at @xmath104 . this model resulted in statistically unacceptable fit with @xmath58/d.o.f = 237.2/154 and a sharp dip around 1 kev in the residual spectrum . as before , we used the warm absorber model ( zxipcf ) which significantly improved the fit from @xmath58/d.o.f = 237.2/154 to 177.5/152 ( @xmath83=@xmath3359.7 for 2 additional free parameters ) . we then left the redshift of the absorbing medium to vary freely in order to justify the presence of out - flow , which further improved the fit to @xmath58/d.o.f = 168.3/151 = 1.11 ( @xmath83=@xmath339.2 for 1 additional free parameter ) . the epic - pn mean spectrum , the best - fitting absorbed disk comptonization model ( tbabs@xmath82zxipcf@xmath82optxagnf ) and the deviations of the observed data from the model are shown in figure [ fig5a ] ( left ) . the best - fitting values for the eddington rate , coronal radius , electron temperature , optical depth and spectral index are @xmath105 , @xmath106 , @xmath107 kev , @xmath108 and @xmath109 , respectively . then we jointly fitted the five time - resolved spectral data - sets with the absorbed disk comptonization model and kept all the parameters tied to their mean spectral best - fitting values except the eddington rate . this provided statistically acceptable fit with @xmath58/d.o.f = 364.3/279 = 1.3 and we did not notice any strong feature in the residual spectra . the 5 epic - pn spectral data - sets , the best - fitting disk comptonization model and residuals are shown in fig . [ fig5a ] ( right ) . the best - fitting spectral model parameters for both mean and time - resolved spectra are listed in table [ table2 ] . the origin of the soft excess emission could be the blurred reflection from the ionized accretion disk @xcite . hence we modelled the soft x - ray excess using the reflection model reflionx @xcite convolved with the model kdblur which blurs the spectrum due to general relativistic effects close to the rapidly rotating smbh @xcite . then we fitted the 0.3@xmath338 kev epic - pn mean spectrum with the incident power - law ( zpowerlw ) and blurred reflection ( kdblur@xmath110reflionx ) models after correcting for the galactic absorption ( tbabs ) . the parameters of the reflionx model are iron abundance ( fe / solar ) , ionization parameter ( @xmath111 , @xmath112 is the total illuminating flux , @xmath60 is hydrogen density ) , normalization ( @xmath113 ) of the reflected spectrum and photon - index ( @xmath114 ) of the incident power - law . the convolution model kdblur has four free parameters : emissivity index ( @xmath115 , where emissivity of the reflected emission is defined by @xmath116 ) , inner disk radius ( @xmath117 ) , outer disk radius ( @xmath94 ) and disk inclination angle ( @xmath118 ) . the outer disk radius was fixed at @xmath119 . in xspec , the 0.3@xmath338 kev model reads as tbabs@xmath82(kdblur@xmath110reflionx@xmath84zpowerlw ) which provided reasonably good fit with @xmath58/d.o.f = 191.9/152 . however , the residual spectrum shows an absorption feature @xmath23 kev which was modelled with the ionized absorber model ( zxipcf ) . the multiplication of the warm absorber model improved the fit to @xmath58/d.o.f = 165.8/150 = 1.1 ( @xmath83=@xmath3326.1 for 2 additional free parameters ) . in xspec , the 0.3@xmath338 kev best - fitting model reads as tbabs@xmath82zxipcf@xmath82(kdblur@xmath110reflionx@xmath84zpowerlw ) . the epic - pn mean spectrum , the best - fitting absorbed blurred reflection model and the deviations of the observed data from the best - fitting model are shown in figure [ fig5b ] ( left ) . the best - fitting values for the emissivity index , inner disk radius , disk ionization parameter , inclination angle and spectral index are @xmath120 , @xmath121 , @xmath122 erg cm s@xmath13 , @xmath123 and @xmath124 , respectively . we also fitted the five time - resolved spectra jointly with the blurred reflection model and tied every parameter to its mean spectral best - fitting value except the normalization ( @xmath113 ) of the reflection component . this provided an unacceptable fit with @xmath58/d.o.f = 380.2/279 = 1.36 . we then set the normalization ( @xmath125 ) of the illuminating continuum to vary between the 5 spectra and obtain a noticeable improvement in the fitting with @xmath58/d.o.f = 334.7/274 = 1.22 ( @xmath83=@xmath3345.5 for 5 additional free parameters ) . if we leave the spectral index ( @xmath114 ) of the primary continuum to vary , we did not get any significant improvement in the fitting . the results obtained from both time - averaged and time - resolved spectroscopy are listed in table [ table3 ] . the 5 epic - pn spectral data - sets , the best - fitting blurred reflection model and residuals are shown in fig . [ fig5b ] ( right ) . the flux@xmath33flux analysis is a model - independent approach to distinguish the main components responsible for the observed spectral variability and was pioneered by @xcite and @xcite . on the basis of our x - ray spectral modelling , we identified the 0.3@xmath331 kev and 1@xmath3310 kev energy bands as representatives of the soft excess and primary emission , respectively . then we constructed the 0.3@xmath331 vs 1@xmath3310 kev flux@xmath33flux plot which is shown in figure [ fig6 ] ( top panel ) . the mean count rate in the soft and hard bands are @xmath126 counts s@xmath13 and @xmath127 counts s@xmath13 , respectively . we begin our analysis by fitting the flux@xmath33flux plot with a linear relation of the from , @xmath128 , where @xmath129 and @xmath130 represent the 1@xmath3310 kev and 0.3@xmath331 kev band count rates , respectively . the straight line model provided statistically unacceptable fit with @xmath58/d.o.f = 56.7/31 and implied that the immanent relationship between the soft excess and primary emission is not linear . therefore we fit the flux@xmath33flux plot with a power - law plus constant ( plc ) model of the form , @xmath131 ( where @xmath132 and @xmath133 count rates ) following the approach of @xcite . the plc model explains the data statistically well with @xmath58/d.o.f @xmath134 . the best - fitting plc model is shown as a solid line in fig . [ fig6 ] ( top ) . the best - fitting power - law normalization , slope and constant values are @xmath135 counts s@xmath13 , @xmath136 and @xmath137 counts s@xmath13 , respectively . the plc best - fitting slope is significantly greater than unity which indicates the presence of intrinsic variability in the source . the detection of positive ` c'-value in the flux@xmath33flux plot implies the existence of a distinct spectral component which is less variable than the primary x - ray continuum and contributes @xmath138 of the 1@xmath3310 kev count rate at the mean flux level . in order to investigate this issue further , we computed the unabsorbed ( without the galactic and intrinsic absorption ) primary continuum and soft excess flux in the full 0.3@xmath338 kev band for all 5 intervals using xspec convolution model cflux and plotted the intrinsic primary power - law flux as a function of the soft excess flux which is shown in fig . [ fig6 ] ( bottom ) . the best - fitting normalization , slope and constant parameters , obtained by fitting the @xmath139 vs @xmath140 plot with a plc model , are @xmath141 erg @xmath22s@xmath13 , @xmath142 and @xmath143 erg @xmath22s@xmath13 , respectively . interestingly , we found steeping in the @xmath139 vs @xmath140 plot with an apparent positive constant which is in agreement with the 0.3@xmath331 vs 1@xmath3310 kev flux@xmath33flux plot . our flux@xmath33flux analysis suggests that the primary continuum and soft excess emission are well correlated with each other , although they vary in a non - linear fashion . mos 0.3@xmath338 kev fractional rms spectrum of pg 1404 + 226 . the solid red line represents the best - fitting fractional rms which consists of a ` two - component phenomenological ' model in which both soft excess ( zbbody ) and primary emission ( zpowerlw ) are variable in normalization only and are correlated with each other . bottom : the deviation of the observed fractional rms from the best - fitting model and is given with reference to @xmath144=(data - model)/@xmath73 . the solid straight line is the best - fitting residual corresponding to @xmath145 . ] in order to estimate the percentage of variability in the primary continuum and soft excess emission , and also to quantify the variability relation between them , we derived and modelled the fractional rms variability spectrum of pg 1404 + 226 . first we extracted background subtracted light curves in different energy bands from the simultaneous and equal length ( @xmath146 ) combined epic - pn+mos data with a timing resolution of @xmath147 ks . then we computed the frequency - averaged ( @xmath148[@xmath149@xmath150 hz ) fractional rms , @xmath151 in each light curve using the method described in @xcite . the source shows an increase in fractional variability with energy which can be explained in the framework of two components : soft excess and primary hard x - ray emission with decreasing relative importance of soft excess and increasing dominance of intrinsic primary emission with energy . we constructed fractional rms spectral model using our best - fitting phenomenological and physical mean spectral models in isis v.1.6.2 - 32 @xcite . first we explored the phenomenological fractional rms spectral model in which both soft excess ( zbbody ) and primary emission ( zpowerlw ) are variable in normalization only and are coupled with each other . using the equation 4 of @xcite , we obtained the expression for theoretical fractional rms spectral model : @xmath152}}{f_{\rm pl}(a_{\rm pl},e)+f_{\rm bb}(a_{\rm bb},e ) } \label{eu1}\ ] ] where @xmath153 and @xmath154 represent fractional changes in the normalization of the primary power - law , @xmath155 and blackbody , @xmath156 components respectively . @xmath157 measures the correlation or coupling between @xmath155 and @xmath156 . we then fitted the 0.3@xmath338 kev fractional rms spectrum of pg 1404 + 226 using this ` two - component phenomenological ' model ( equation [ eu1 ] ) and the best - fitting mean spectral model parameters as the input parameters for the above model . this model describes the data reasonably well with @xmath58/d.o.f = 3.48/4 = 0.87 . the best - fitting rms model parameters are : @xmath153=83.9@xmath158 , @xmath154=78.5@xmath159 and @xmath160 . the fractional rms variability spectrum , the best - fitting ` two - component phenomenological ' model and residuals are shown in figure [ fig7a ] . in pg 1404 + 226 , the soft excess was modelled by two different physical models : intrinsic disk comptonization and blurred reflection from the ionized accretion disk . in order to break the degeneracy between these two possible physical scenarios , we made fractional rms spectral model considering our best - fitting disk comptonization and blurred reflection models to the time - averaged spectrum . in the disk comptonization scenario , the observed variability in pg 1404 + 226 was driven by variation in the accretion rate as inferred from the joint fitting of 5 epic - pn spectra . therefore the expression for theoretical fractional rms ( see @xcite ) can be written as @xmath161 where @xmath162 represents the best - fitting optxagnf model and @xmath163 is the scaled accretion rate which is the only variable free parameter in the model . the fitting of the 0.3@xmath338 kev fractional rms spectrum using this model ( equation [ eu2 ] ) resulted in statistically poor fit with @xmath58/d.o.f = 15.3/6 = 2.6 . the fractional variability spectrum , the ` one - component disk comptonization ' model and residuals are shown in figure [ fig7b ] ( left ) . then we investigated the blurred reflection scenario where the origin of soft excess was explained in terms of disk irradiation @xcite . in this scenario , the rapid variability in pg 1404 + 226 can be described due to changes in the normalization of the reflection component and illuminating power - law continuum as evident from the time - resolved spectroscopy . thus , we constructed the ` two - component blurred reflection ' model where both reflection ( kdblur@xmath110reflionx ) and intrinsic continuum ( zpowerlw ) are variable in normalization only and are perfectly coupled with each other . mathematically , the expression for fractional rms can be written as @xmath164 where @xmath165 here @xmath166 and @xmath167 represent the best - fitting incident power - law ( zpowerlw ) and blurred reflection ( kdblur@xmath110reflionx ) components , respectively . the two free parameters of this model are @xmath125 and @xmath113 . we then fitted the observed fractional rms spectrum using that model ( equation [ eu3 ] ) and obtained statistically acceptable fit with @xmath58/d.o.f = 4.35/5 = 0.87 . the fractional rms variability spectrum , the best - fitting ` two - component blurred reflection ' model and residuals are shown in figure [ fig7b ] ( right ) . the fractional variations in the normalization of the illuminating continuum and reflected emission are @xmath168 and @xmath169 respectively .

the x - ray fractional rms spectrum shows an increase in variability with energy which can be described only in the framework of blurred reflection model in which both the intrinsic continuum and the reflected emission are highly variable in normalization only and are perfectly coupled with each other . [ firstpage ]

we present results from a detailed analysis of our 2016 _ xmm - newton _ observation of the narrow - line seyfert 1 galaxy pg 1404 + 226 which showed a large - amplitude , rapid x - ray variability by a factor of @xmath0 in @xmath1 ks . we use this variability event to investigate the origin of the soft x - ray excess emission and the connection between the disk , hot corona and the soft excess emitting region through uv / x - ray cross - correlation , time - resolved spectroscopy and root mean square ( rms ) spectral modelling . the weakly variable uv emission ( @xmath2=3.9@xmath3 ) appears to lead the strongly variable x - ray emission ( @xmath4=89.0@xmath5 ) by @xmath6 ks . such a uv lead is consistent with the crossing time ( @xmath7 ks ) of the seed photons from the disk to a compact ( @xmath8 ) hot corona and the time required for their thermal comptonization ( @xmath9 ks ) giving rise to the x - ray power - law emission . the strong soft x - ray excess below 1 kev seen in the mean x - ray spectrum as well as in the time - resolved spectra is well described by both the intrinsic disk comptonization and the blurred reflection models . the soft excess emission is found to vary together with the power - law component as @xmath10 . the x - ray fractional rms spectrum shows an increase in variability with energy which can be described only in the framework of blurred reflection model in which both the intrinsic continuum and the reflected emission are highly variable in normalization only and are perfectly coupled with each other . our results suggest that accretion disk provides the seed photons for thermal comptonization giving rise to the x - ray power - law component which in turn illuminates the innermost accretion disk and gives rise to the soft x - ray excess emission . [ firstpage ]

1702.08383

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we presented results from our _ xmm - newton _ observation of the nls1 galaxy pg 1404 + 226 and studied the large - amplitude x - ray variability , the uv / x - ray connection , the origin of the soft x - ray excess and its connection with the intrinsic power - law emission through a detailed analysis of the time - resolved x - ray spectra , frequency - averaged ( @xmath148[@xmath149@xmath150 hz ) x - ray fractional rms spectrum and uv / x - ray cross - correlation . below we summarize our results : 1 . pg 1404 + 226 showed large - amplitude ( a factor of @xmath0 in about 11 ks ) x-ray variability with fractional rms @xmath4=89.0@xmath5 . the rapid x - ray variability had been observed in a few nls1 galaxies ( e.g. ngc 4051 : @xcite , 1h 0707495 : @xcite , mrk 335 : @xcite ) . the uv emission form pg 1404 + 226 is much less variable ( @xmath2=3.9@xmath3 ) compared to the x - ray variability and is observed to lead the x - ray emission by @xmath6 ks . the source exhibited a strong soft excess below @xmath23 kev , which was modelled by intrinsic disk comptonization as well as blurred reflection component . the x - ray ( 0.3@xmath338 kev ) spectra revealed the presence of a highly ionized ( @xmath170 erg cm s@xmath13 ) absorbing cloud along the line - of - sight with column density of @xmath171 @xmath22 . 3 . the time - resolved spectroscopy shows significant variability in the soft excess and primary power - law flux , although there was no noticeable variations in the soft excess temperature ( @xmath172 kev ) and photon index ( @xmath173 ) of the primary continuum . 4 . in the disk comptonization scenario , the rapid x - ray variability can be attributed to a change in the mass accretion rate as indicated by time - resolved spectroscopy . however , the modelling of the x - ray fractional rms spectrum using ` one - component disk comptonization ' model can not reproduce the observed x - ray variability pattern and indicates reflection origin for the soft excess emission ( see fig . [ fig7b ] ) . 5 . in the reflection scenario , we found that the observed large - amplitude x - ray variability was predominantly due to two components : illuminating continuum and reflected emission which are variable in normalization only ( see fig . [ fig7b ] ) . 6 . the inner disk radius estimated from the blurred reflection model is @xmath174 which implies a rapidly rotating black hole at the center of pg 1404 + 226 and is consistent with the measurement performed by @xcite . the non - detection of the 6.4 kev iron emission line is perhaps due to its smearing into the broad shape in the spectrum . we found that the soft ( 0.3@xmath331 kev ) and hard ( 1@xmath3310 kev ) band count rates are correlated with each other and vary in a non - linear manner as suggested by the steepening of the flux - flux plot . the fitting of the hard - vs - soft counts plot with a power - law plus constant ( plc ) model reveals a significant positive offset at high energies which can be interpreted as corroboration for the presence of a less variable reflection component ( probably smeared iron emission line ) in the hard band . the observed uv variability in pg 1404 + 226 is weak with @xmath2=3.9@xmath3 only , whereas the x - ray variability is much stronger ( @xmath4=89.0@xmath5 ) . we found that the uv variations lead the x - ray variations by @xmath175 in pg 1404 + 226 . similar behaviour had also been observed in another seyfert 1 galaxy mcg-6 - 30 - 15 @xcite . the time - lag between the uv and x - ray variations in mcg-6 - 30 - 15 was found to be @xmath176 ks and interpreted as a signature of the accretion flow propagation . the uv lead observed in pg 1404 + 226 is much shorter than that seen in mcg-6 - 30 - 15 , although pg 1404 + 226 is hosting more massive ( a factor of 10 ) black hole than mcg-6 - 30 - 15 . the observed lead of @xmath175 for variations in the uv emission compared to the variations in the x - ray emission is likely to be the result of the thermal comptonization of the uv seed photons in a compact hot corona . in this process , the uv lead can occur due to ( i ) the light - crossing time between the uv emitting region of the disk and the compact hot corona , and ( ii ) the time required for the multiple inverse compton scattering of uv photons into x - ray photons . the light - crossing time required by the uv photons to reach the compact hot corona can be written as @xcite @xmath177 where @xmath178 is the scaled mass accretion rate , @xmath98 is the central black hole mass in units of @xmath179 and @xmath180 is the effective wavelength where the disk emission peaks . in the case of pg 1404 + 226 , @xmath181 , @xmath182 ( calculated from the unabsorbed flux in the energy band @xmath183 kev using the convolution model cflux in xspec ) and @xmath184 for uvw1 filter . therefore the light crossing time between the x - ray source and the disk is @xmath185 ks , which corresponds to the peak disk emission radius of @xmath186 . recent results on x - ray reprocessing lags @xcite have shown that the agn disks are larger than that predicted for the standard disks . however , we did not observe the reprocessing lag . the uv emission from pg 1404 + 226 is most likely to be dominated by the intrinsic emission from the disk . in the framework of compton up - scattering , a uv photon with energy @xmath187 after @xmath188 scatterings produces an x - ray photon of energy @xcite @xmath189 where @xmath190 , @xmath191 and @xmath192 and @xmath193 are the electron temperature and rest mass , respectively . if @xmath194 is the time delay between successive scattering and the x - ray photons are produced within the optically thin , hot corona after n scatterings , then the comptonization timescale is @xmath195 for an optically thin ( @xmath196 ) , hot ( @xmath197 kev ) corona of size @xmath198 , the estimated comptonization timescale is @xmath199 ks . thus the observed uv lead of @xmath175 can indeed correspond to the sum of the light - crossing time ( @xmath185 ks ) between the disk and power - law emitting region and the comptonization timescale ( @xmath200 ks ) of the uv seed photons within the hot corona . in the intrinsic disk comptonization ( optxagnf ) model , the soft excess emission results from the compton up - scattering of the uv seed photons by optically thick , warm ( @xmath201 kev ) electron plasma in the inner disk ( below @xmath95 ) itself . however , if the optically - thick corona is the inner disk , it is unlikely that it will intercept significant amount of seed photons from intermediate or outer disk . thus , the seed photons for the optically - thick thermal comptonization must arise from the inner regions of the standard cold disk . hence , the soft excess emission from the comptonized inner disk and the intrinsic uv emission from the intermediate regions of standard cold disk are likely to be connected only via the propagation of accretion rate fluctuations , and the intrinsic uv emission from the standard disk should lead the soft excess by the propagation fluctuation timescale . assuming that the fluctuations in the accretion rate propagate with the speed of sound waves in the radial direction , the timescale of propagation fluctuation @xmath202 can be written as @xcite @xmath203 where the dynamical time scale @xmath204 , @xmath205 is the disk height at the radius @xmath206 for the observed uv emission . if we consider a thin disk for which height - to - radius ratio , @xmath207 @xcite , the propagation fluctuation timescale at this emission radius ( @xmath208 ) is of the order of @xmath209 s which is much longer than the observed uv lead hence , the observed uv lead is unlikely to be due to the propagation of accretion rate fluctuations . unlike the comptonized inner disk in the optxagnf model , the hot corona is likely spherical and can intercept significant fraction of uv seed photons . thus , in the framework of optxagnf model , the uv lead is entirely due to the comptonization of seed photons in the hot corona . in this case , it is difficult to explain the correlation between the soft excess and the power - law components unless the variability is intrinsic resulting from simultaneous gravitational energy release both to the inner , comptonized disk and the hot corona . however , it is difficult to explain the uv x - ray connection as the propagation fluctuation timescale is longer compared to the observed uv lead . therefore the only possible explanation for the observed uv lead is that the uv seed photons from the disk travel all the way up to the hot electron plasma , get compton up - scattered within the compact hot corona and produces the x - ray power - law component . pg 1404 + 226 shows strong x - ray variability with increase in overall fractional rms with energy . we attempted to explain the observed rapid variability of pg 1404 + 226 in the framework of two possible physical scenarios : intrinsic disk comptonization and blurred reflection from the ionized accretion disk . in the disk comptonization scenario , if the rapid x - ray variability is due to the mass accretion rate changes which is favoured by the time - resolved spectroscopy , then it can not explain the rms variability pattern below 0.4 kev and in the hard band ( see fig . [ fig7b ] , left ) . therefore , it is unlikely that the rapid x - ray variability is caused by variations in the mass accretion rate alone . on the other hand , the soft excess and primary continuum vary non - linearly ( as @xmath10 ) which indicates that the soft excess is coupled and reciprocating with the primary continuum variations . this is in agreement with the smeared reflection scenario which is further supported by the high emissivity index ( @xmath210 ) . moreover , the fractional variability spectrum of pg 1404 + 226 is best described by two components illuminating continuum and reflected emission which vary in normalization only and perfectly coupled with each other . the variations in the reflected component and primary continuum are @xmath211 and @xmath212 , respectively . in the blurred reflection model , the soft excess is a consequence of the disc irradiation by a hot , compact corona close to the black hole . the correlated , non - linear variability between the illuminating continuum and soft excess emission is consistent with the light bending model @xcite . our results indicate that the thermal comptonization of the uv seed photons from the accretion disk produces the x - ray power - law component which in turn illuminates the innermost accretion disk giving rise to the soft x - ray excess emission in pg 1404 + 226 .

we present results from a detailed analysis of our 2016 _ xmm - newton _ observation of the narrow - line seyfert 1 galaxy pg 1404 + 226 which showed a large - amplitude , rapid x - ray variability by a factor of @xmath0 in @xmath1 ks . appears to lead the strongly variable x - ray emission ( @xmath4=89.0@xmath5 ) by @xmath6 ks . such a uv lead is consistent with the crossing time ( @xmath7 ks ) of the seed photons from the disk to a compact ( @xmath8 ) hot corona and the time required for their thermal comptonization ( @xmath9 ks ) giving rise to the x - ray power - law emission . the soft excess emission is found to vary together with the power - law component as @xmath10 . our results suggest that accretion disk provides the seed photons for thermal comptonization giving rise to the x - ray power - law component which in turn illuminates the innermost accretion disk and gives rise to the soft x - ray excess emission .

we present results from a detailed analysis of our 2016 _ xmm - newton _ observation of the narrow - line seyfert 1 galaxy pg 1404 + 226 which showed a large - amplitude , rapid x - ray variability by a factor of @xmath0 in @xmath1 ks . we use this variability event to investigate the origin of the soft x - ray excess emission and the connection between the disk , hot corona and the soft excess emitting region through uv / x - ray cross - correlation , time - resolved spectroscopy and root mean square ( rms ) spectral modelling . the weakly variable uv emission ( @xmath2=3.9@xmath3 ) appears to lead the strongly variable x - ray emission ( @xmath4=89.0@xmath5 ) by @xmath6 ks . such a uv lead is consistent with the crossing time ( @xmath7 ks ) of the seed photons from the disk to a compact ( @xmath8 ) hot corona and the time required for their thermal comptonization ( @xmath9 ks ) giving rise to the x - ray power - law emission . the strong soft x - ray excess below 1 kev seen in the mean x - ray spectrum as well as in the time - resolved spectra is well described by both the intrinsic disk comptonization and the blurred reflection models . the soft excess emission is found to vary together with the power - law component as @xmath10 . the x - ray fractional rms spectrum shows an increase in variability with energy which can be described only in the framework of blurred reflection model in which both the intrinsic continuum and the reflected emission are highly variable in normalization only and are perfectly coupled with each other . our results suggest that accretion disk provides the seed photons for thermal comptonization giving rise to the x - ray power - law component which in turn illuminates the innermost accretion disk and gives rise to the soft x - ray excess emission . [ firstpage ]

cond-mat0011100

r

it is well known that for a sample of type - ii superconductor with pinning , the critical current i@xmath2 decreases monotonically with the increase in h and goes to zero at the irreversibility field ( h@xmath7h@xmath5 ) . this is shown schematically in fig . 1 ( a ) . however , for superconductors showing pe , i@xmath2(h ) shows a peak or local maximum at an intermediate h value before finally going to zero at h@xmath8 ( see fig . 1(a ) ) . the signature of pe will appear in the field dependence of r(h ) , depending on the magnitude of the measuring current i@xmath3 . if i@xmath9i@xmath10 ( see fig . 1(a ) ) , r(h ) will show zero value up to ( depending on the exact value of i@xmath3 ) almost h@xmath11 ( see fig . 1(b ) ) . for h@xmath12 h@xmath13 , r(h ) will show flux - flow resistivity leading to the normal state behaviour for h@xmath14h@xmath5 . on the other hand if i@xmath15i@xmath16(h ) ( see fig . 1(a ) ) , flux - flow resistivity will start at lower field . in either of these cases , the r(h ) will not bear any signature of the pe . the signature of pe will appear in r(h ) if i@xmath17 ( see fig . 1(a ) ) . in such a situation a flux - flow resistance is observed with increasing h where i@xmath15i@xmath2(h ) but r(h ) will fall back to zero in the pe regime where i@xmath18i@xmath2(h ) before increasing again at higher field ( see fig . 1(b ) ) . while a direct measurement of the field dependence of i@xmath2 would have been very illuminating for the present study of pe in v@xmath0si , the lack of a suitable current source ( with i@xmath19 100 ma ) constrained us to the study of r(h ) only . adjusting the measuring current i@xmath3 accordingly , we present in fig . 2 r vs h plots for v@xmath0si at various t showing a distinct signature of pe . the ( h , t ) regime where pe is observed , roughly agrees with that obtained earlier in magnetic measurements @xcite . the finer quantitative discrepancy can be attributed to the different residual resistivity ratio of the samples used in the earlier measurement @xcite which leads to a small but perceptible change in h@xmath5(t ) . ( it should be noted here that the normal state resistance of the present v@xmath0si sample above h@xmath5(t ) is @xmath20 40 micro ohm as shown in figs . 2 - 5 . ) the distinct signature in pe disappears in the h dependence of r(h ) for t@xmath1415k . the r vs h plots do not show the _ reentrant _ zero - resistance behaviour for any pre - decided value of i@xmath3 between 10ma and 100ma at t=15.5k , although a subtle minimum in r(h ) is observed for i@xmath3=20ma ( see fig.3).it should be noted here that the existence of pe in v@xmath0si was not at all clear in this t regime in the magnetic measurements as well @xcite . the pe and the associated features have been very well studied in recent years in the c15-laves phase superconductor ceru@xmath1 @xcite . a very distinct history dependence of pe while cycling h or t was observed in ceru@xmath1 and it was suggested that at the onset of the pe regime , the field cooled ( fc ) flux - line lattice or the superconducting vortex state of ceru@xmath1 was more disordered than the corresponding zfc state @xcite . we shall now investigate the possibility of the same in the present sample of v@xmath0si . for this , we measure r vs h at various t following the fc protocol ( described above in the experimental section ) , and the results of such a study are shown in fig.4 . the r(h ) measured with the fc protocol is found to be zero even for h - values at which measuring current i@xmath3 gave rise to the intermediate h flux - flow regime in the measurements following the zfc protocol ( see fig.2 ) . this clearly indicates that in the fc mode i@xmath2(h)is greater than i@xmath3 in this intermediate h regime , while the opposite is true in the zfc mode . thus i@xmath21 is higher in the fc mode than in the zfc mode and this is represented schematically in fig.1c . to the best of our knowledge this history dependent property of the flux - line lattice of v@xmath0si has not been reported in the literature so far . the field cooled fll at the onset of the pe regime in ceru@xmath1 was reported to be quite metastable in nature @xcite . we shall now focus on the fc fll of v@xmath0si and check for the metastable behaviour in various h regime . we subject the sample to small field cycling subsequent to the initial fc measurement with an applied h at a particular t. the results of such experiments are shown in fig.5 . we find that within the intermediate h regime , the zero resistance state obtained in the fc mode is destroyed readily on field cycling and the flux - flow resistance corresponding to zfc state is recovered . this clearly shows the metastability of fc state in the intermediate h regime just below the pe regime . we also note that the minimum value of the cycling field ( @xmath22 ) to destroy the metastable fc state , decreases as we move away from the pe regime towards lower field . while we required @xmath23h=25 mt at h=3.2 t to reach the flux - flow resistance of the corresponding zfc state ( see fig . 5 ) , the recorded value of @xmath22 at h=2.4 t is 5 mt . below h=1.8 t where both zfc and fc r(h ) show zero resistance , the fc state is quite stable and not sensitive to any external field cycling . inside the pe regime also the field cycling does not have any effect on the fc state . so , it is clear that in the intermediate h regime ( where the fc fll is inferred to be more disordered than the zfc fll ) , the fc state is metastable in nature .

the field variation of the electrical resistance in the flux - line lattice prepared by different experimental path , namely zero field cooling ( zfc ) and field cooling ( fc ) , shows a distinct path dependence in the vicinity of the peak - effect regime . in the field

we present results of transport properties measurement on a single crystal of v@xmath0si showing distinct signature of peak - effect in its vortex state . the field variation of the electrical resistance in the flux - line lattice prepared by different experimental path , namely zero field cooling ( zfc ) and field cooling ( fc ) , shows a distinct path dependence in the vicinity of the peak - effect regime . in the field cooled state , small cycling of magnetic field modifies the resistance drastically around the peak - effect regime , highlighting the metastable nature of that state in the concerned regime .

0903.0800

c

we have presented a mathematical framework for cortical spreading depolarizations that unifies existing activator - inhibitor models as special cases @xcite . within this framework the reaction - diffusion mechanism of sd is extended by nonlocal coupling as an integral part of the phenomenon necessary to describe the emergence and transitions of two - dimensional sd wave patterns . as a framework it provides a flexible procedure for analysing sd patterns observed in both experimental migraine and stroke models , and clinical data @xcite . this framework is aimed at providing basic insights needed to understand cortical susceptibility to transient sd wave propagation in terms of nonlinear science . in particular , we focus on bifurcations in the dynamics of cortical homeostasis caused by cortical circuits and neurovascular coupling represented as nonlocal transmission schemes . a long term goal is to provide control strategies based on bifurcation theory for both traditional pharmacological treatments and biomedical engineered devices that intelligently target the occurrence of sd waves . a mathematical model that involves only two species with activator - inhibitor dynamics is undoubtedly a very crude macroscopic level of cortical homeostasis . activator - inhibitor dynamics is the minimal requirement that leads to a description of sd as a traveling wave pattern with a trailing edge . in two spatial dimensions , these waves take a characteristic form that reveals much about cortical susceptibility to sd . yet , little insight into microscopic mechanisms of sd is offered by such minimal dynamic systems . there are much more sophisticated mathematical descriptions of sd on a detailed microscopic level that try to resolve the mechanism of sd @xcite . in our framework , these microscopic mechanism are hidden inside the box labeled as `` firing rate '' ( fig . [ fig : sdpathways ] ) . proposing a conceptual framework at this macroscopic level must be justified by showing that this approach avoids deficiencies that would arise if sd wave propagation is modeled on a microscopic level . from the clinical perspective , the macroscopic scale , in particular , the two - dimensional pattern on the cortical surface , is highly relevant . in migraine , the whole spectrum of aura subtypes could depend critically on whether sd can break away from a focus point , and , if it does , whether sd waves take the shape of a particle - like wave and therefore limit the extent of a full - scale attack to certain cortical regions ( fig . [ fig : brains ] ( d ) ) , or , in the worst case , sd becomes a persistent activity pattern ( fig . [ fig : persistent ] ) . in stroke , outcome depends on sd as these waves are suspected to contribute to the loss of potentially salvageable tissue , i.e. , tissue at risk of infarction . since re - entrant pattern increase the total number of waves , the emergence of these patterns need to be understood . none of these questions can be addressed in a cellular model of sd including only one or several neurons , let alone the semantic objection against applying the term _ spreading _ to such models because they are not meant to model the spread @xcite . microscopic models include several ion channel types in a single neuron , and its dendritic tree . these models also consider surrounding compartments , and can therefore also describe changes in intra- and extracelluar ion concentrations @xcite . to obtain the continuum limit of such discrete microscopic cellular models is by no means straightforward . the problem is to match the very detailed and accurate knowledge of microscopic processes involved in the depolarization cycle of sd by an equally detailed description of volume transmission and wiring transmission needed to provide the spatial coupling for transition to the continuum limit . mismatching these levels of description by merely using a diffusion term as in eq . ( [ eq : d ] ) to simulate spatial coupling by extracellular potassium would be like attaching the wheels of a carriage on a mercedes . efforts have been made to address this problem by accounting not only for interstitial ionic diffusion but also for ionic movement through a neuronal syncytium of cells connected by gap junctions and for cells that are allowed to expand in response to osmotic pressure . from these it was concluded that cytosolic diffusion via gap junctions and osmotic forces are important mechanisms underlying sd @xcite . yet , to compute the spatio - temporal development of sd across the cortical surface on a centimeter scale and investigate the emergence of retracting , re - entrant , and stationary sd waves , coupling schemes other than local schemes must be accounted for . there are important nonlocal transmission schemes in the cortex hat provide spatial coupling over a long range or lead to time delays . example are ( i ) the functional and structural cortical connectivity , in the continuum limit described by neural fields @xcite , ( ii ) the cortical energy state maintained by a segmental blood perfusion from the arteries to smaller arterioles and finally branching capillaries leading to a complex hemodynamic response that is regulated by smooth muscle cells ( arterioles ) and pericytes ( capillaries ) @xcite , and ( iii ) the topology of the network of the neuronal syncytium that will be compromised by disseminate neuronal injury during ischemia @xcite . there are more transmission schemes , but the effect of these ( i)-(iii ) are the ones we have considered in a first approximation by ( i ) long - range connections , ( ii ) global coupling , and ( iii ) spatial diversity . future investigations have to relate the quantitative values of the parameters in macroscopic model that successfully describe the bifurcations observed in the spatio - temporal characteristics of sd to the cellular level . this will open up this approach for the design of both drug treatments @xcite and engineered devices utilizing transcranial stimulation @xcite with the aim to target sd intelligently . migraine and stroke are found in specific genetic disorders giving clues to genetic factors that hint at differences in the cortical network activity . such hints may provide means to bridge the gap between the macroscopic and microscopic level of sd . similar hints of changed network activity are coming from psychophysics describing abnormal cortical processing in migraine by concepts like hyper- and hypoexcitability , heightened responsiveness , a lack of habituation and/or a lack of intra - cortical inhibition @xcite . our framework provides means by which such statements on cortical excitability in migraine can be investigated , in particular how abnormal cortical nonlocal connectivity changes susceptibility to sd . although it seems tempting to suggest that cortical hyperexcitability increases susceptibility to sd or even that neurons prone to hyperexcitabilty trigger sd , such a simple relation can not be expected , and a detailed bifurcation analysis will be important for the thorough understanding of sd as a nonlinear pattern formation process . 10 url # 1#1urlprefix d. w. dodick and j. j. gargus : _ why migraines strike _ , sci . am . * 299 * , 56 ( 2008 ) . a. a. p. leo : _ spreading depression of activity in the cerebral cortex _ , j. neurophysiol . * 7 * , 359 ( 1944 ) . m. milner : _ note on a possible correspondence between the scotomas of migraine and spreading depression of leo _ , electroencephalogr . clin . * 10 * , 705 ( 1958 ) . m. lauritzen : _ cortical spreading depression as a putative migraine mechanism _ , trends in neurosciences * 10 * , 8 ( 1987 ) . n. hadjikhani , m. sanchez del . , o. wu , d. schwartz , d. bakker , b. fischl , k. k. kwong , f. m. cutrer , b. r. rosen , r. b. tootell , a. g. sorensen , and m. a. moskowitz : _ mechanisms of migraine aura revealed by functional mri in human visual cortex _ , proc . usa * 98 * , 4687 ( 2001 ) . m. a. moskowitz : _ the 2006 thomas willis lecture : the adventures of a translational researcher in stroke and migraine _ , stroke * 38 * , 1645 ( 2007 ) . k. a. hossmann : _ periinfarct depolarizations _ , brain metab . rev . * 8 * , 195 ( 1996 ) . a. j. strong , m. fabricius , m. g. boutelle , s. j. hibbins , s. e. hopwood , r. jones , m. c. parkin , and m. lauritzen : _ spreading and synchronous depressions of cortical activity in acutely injured human brain _ , stroke * 33 * , 2738 ( 2002 ) . m. fabricius , s. fuhr , r. bhatia , m. boutelle , p. hashemi , a. j. strong , and m. lauritzen : _ cortical spreading depression and peri - 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dependent effects of tetraethylammonium on circling spreading depressions in chicken retina _ , j. neurosci . 51 * , 85 ( 1998 ) . s. d. silberstein , a. stiles , and w. b. young ( editors ) : _ atlas of migraine and other headaches _ ( taylor & francis , london , 2005 ) . c. s. rebert : _ spreading depression in squirrel monkey lissencephalic cortex _ , physiology & behavior * 5 * , 239 ( 1967 ) . f. wilkinson : _ auras and other hallucinations : windows on the visual brain _ , prog . brain res . * 144 * , 305 ( 2004 ) . m. vincent and n. hadjikhani : _ migraine aura and related phenomena : beyond scotomata and scintillations _ , cephalalgia * 27 * , 1368 ( 2007 ) . m. f. james , m. i. smith , k. h. bockhorst , l. d. hall , g. c. houston , n. g. papadakis , j. m. smith , a. j. williams , d. xing , a. a. parsons , c. l. huang , and t. a. carpenter : _ cortical spreading depression in the gyrencephalic feline brain studied by magnetic resonance imaging _ , j. physiol . ( lond . ) * 519 pt 2 * , 415 ( 1999 ) . k. krischer and a. mikhailov : _ bifurcation to traveling spots in reaction - diffusion systems _ , phys . * 73 * , 3165 ( 1994 ) . t. sakurai , e. mihaliuk , f. chirila , and k. showalter : _ design and control of wave propagation patterns in excitable media _ , science * 296 * , 2009 ( 2002 ) . e. mihaliuk , t. sakurai , f. chirila , and k. showalter : _ feedback stabilization of unstable propagating waves _ e * 65 * , 065602 ( 2002 ) . a. karma : _ universal limit of spiral wave propagation in excitable media _ , phys . . lett . * 66 * , 2274 ( 1991 ) . v. hakim and a. karma : _ theory of spiral wave dynamics in weakly excitable media : asymptotic reduction to a kinematic model and applications _ e * 60 * , 5073 ( 1999 ) . e. schll : _ nonlinear spatio - temporal dynamics and chaos in semiconductors _ ( cambridge university press , cambridge , 2001 ) . g. stegemann and e. schll : _ two - dimensional spatiotemporal pattern formation in the double - barrier resonant tunneling diode _ , new j. phys . * 9 * , 55 ( 2007 ) . e. schll : _ pattern formation and time - delayed feedback control at the nano - scale _ , in _ nonlinear dynamics of nanosystems _ , edited by g. radons , b. rumpf , and h. g. schuster ( wiley - vch , weinheim , 2009 ) . m. a. dahlem and e. p. chronicle : _ a computational perspective on migraine aura _ , prog . neurobiol . * 74 * , 351 ( 2004 ) . hossmann : _ pathophysiology and therapy of experimental stroke _ , cell . * 26 * , 1055 ( 2006 ) . e. leniger - follert and d. w. lbbers : _ regulation of microflow and behaviour of local tissue po2 during activation and anoxia of the brain cortex _ , bibl anat pp . 345349 ( 1977 ) . e. glatt , m. gassel , and f. kaiser : _ variability - induced transition in a net of neural elements : from oscillatory to excitable behavior _ , phys . e * 73 * , 066230 ( 2006 ) . e. glatt , m. gassel , and f. kaiser : _ variability - sustained pattern formation in subexcitable media _ , phys . e * 75 * , 026206 ( 2007 ) . h. kager , w. j. wadman , and g. g. somjen : _ simulated seizures and spreading depression in a neuron model incorporating interstitial space and ion concentrations _ , j. neurophysiol . * 84 * , 495 ( 2000 ) . j. makarova , j. m. ibarz , s. canals , and o. herreras : _ a steady - state model of spreading depression predicts the importance of an unknown conductance in specific dendritic domains _ , biophys . j. * 92 * , 4216 ( 2007 ) . b. e. shapiro : _ osmotic forces and gap junctions in spreading depression : a computational model _ , j. comput . * 10 * , 99 ( 2001 ) . h. r. wilson and j. d. cowan : _ a mathematical theory of the functional dynamics of cortical and thalamic nervous tissue . _ , kybernetik * 13 * , 55 ( 1973 ) . s. hanyu , u. ito , y. hakamata , and i. nakano : _ topographical analysis of cortical neuronal loss associated with disseminated selective neuronal necrosis and infarction after repeated ischemia _ , brain res . * 767 * , 154 ( 1997 ) . d. liebetanz , f. fregni , k. k. monte - silva , m. b. oliveira , a. amncio - dos santos , m. a. nitsche , and r. c. guedes : _ after - effects of transcranial direct current stimulation ( tdcs ) on cortical spreading depression _ , 398 * , 85 ( 2006 ) . a. j. shepherd : _ increased visual after - effects following pattern adaptation in migraine : a lack of intracortical excitation ? _ , brain * 124 * , 2310 ( 2001 ) .

we present spatio - temporal characteristics of spreading depolarizations ( sd ) in two experimental systems : retracting sd wave segments observed with intrinsic optical signals in chicken retina , and spontaneously occurring re - entrant sd waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry . a mathematical framework of reaction - diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns . pattern formation , reaction - diffusion , spiral waves , migraine , stroke

we present spatio - temporal characteristics of spreading depolarizations ( sd ) in two experimental systems : retracting sd wave segments observed with intrinsic optical signals in chicken retina , and spontaneously occurring re - entrant sd waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry . a mathematical framework of reaction - diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns . our prediction is that the observed patterns are reaction - diffusion patterns controlled and modulated by weak nonlocal coupling . the described spatio - temporal characteristics of sd are of important clinical relevance under conditions of migraine and stroke . in stroke , the emergence of re - entrant sd waves is believed to worsen outcome . in migraine , retracting sd wave segments cause neurological symptoms and transitions to stationary sd wave patterns may cause persistent symptoms without evidence from noninvasive imaging of infarction . pattern formation , reaction - diffusion , spiral waves , migraine , stroke

astro-ph9703087

c

does the presence of wc stars lead to the high excitation of the gas , and thus the nebular emission as suggested by schaerer ( 1996 ) ? at the age of region _ a _ ( estimated from its large value of w ( ) ) the models of schaerer ( 1996 ) predict an important _ nebular _ contribution to the total @xmath34686 emission due to the large fraction of wc stars in the burst . given the weakness of the 4686 line in this region , its width is quite uncertain . the presence of strong nebular lines of [ ] @xmath34658 and [ ] @xmath134711,4740 indicating high excitation resembles closely the cases of pox 4 ( cf . kunth & sargent 1981 ; vc92 ) and mkr 1271 ( contini 1996 ) where the distinction between broad stellar and nebular is unclear . the observations of region _ a _ are thus compatible with wc stars as the origin of nebular emission . at the age corresponding to region _ b _ the models of schaerer ( 1996 ) predict only broad emission , in agreement with the observations . compared to _ a _ , the weakness of the forbidden lines also indicates a lower excitation . _ the ionizing clusters : _ as pointed out by ksrwr97 the brightest uv cluster ( their uv1 which is included in our region _ b _ ) does not provide enough ionizing flux to explain the surface brightness of ngc 5253 corresponding to @xmath24 photons s@xmath25 ( martin & kennicutt 1995 ) derived assuming a constant extinction of @xmath11 0.47 . our observations , however , clearly reveal that region _ a _ ( corresponding to the optical maximum and also approximately to the emission peak ) contains a larger number of o stars than region _ b_. from we obtain an ionizing lyman continuum flux of @xmath26 and @xmath27 photon s@xmath25 for regions _ a _ and _ b _ respectively . a _ is of higher extinction and thus clearly dominates the production of ionizing photons as compared to the brightest region in the uv . in view of the possible underestimation of extinction ( cf . beck et al . 1996 ) and the strong spatial extinction variations ( ksrwr97 , calzetti et al . 1997 ) we suspect that the close area surrounding region _ ( possibly including also _ h _ ) may well produce enough ionizing photons to explain the total observed surface brightness . _ wr stars and the chemical enrichment : _ local overabundance of nitrogen in several regions of ngc 5253 is well established ( wr87 , wr89 , ksrwr97 ) . the recent hst observations of ksrwr97 show n enrichment in two locations ( called hii-1 and hii-2 ) close to the peak of emission (= our region _ a _ ) , while n / o in their region uv1 ( included in our region _ b _ ) seems to be typical for metal - poor galaxies . assuming that wr stars eject a significant amount of nitrogen , our likely detection of wr stars in _ a _ provides a plausible source of n in the very proximity of the n - enriched regions . region _ a _ , overlooked by ksrwr97 due to its low uv brightness , is thus most likely the `` hidden '' cluster containing the sources of the observed pollution . more generally , the detection of wr stars of both wn and wc subtypes in both of our regions raises several questions . the earlier finding of a possible carbon overabundance by wr89 , which originally lead these authors to suggest the presence of wc stars , was not confirmed by the results of ksrwr97 . if the overabundance of n ( in the regions close to _ a _ ) is due to wn stars , why are the ejecta of wc stars ( presumably mostly he , c and o ) not detected ? furthermore , why does region _ b _ ( = uv1 ) , which also harbours wr stars , not show any significant overabundance ? abundance differences between these two regions might be related to their age difference : maybe mixing processes in _ b _ had time to dilute the ejecta with the ambient medium , whereas the younger region _ a _ is currently in a phase of heavy pollution . hopefully a study of ngc 5253 will not only tell us its history of star formation but also more about still poorly understood nucleosynthetic yields in massive stars and mixing processes in the ism . ds thanks daniela calzetti , rosa gonzlez - delgado , claus leitherer , gerhard meurer , and bill vacca for stimulating and useful discussions . dk thanks eline tolstoy for a careful reading of the manuscript . daniela calzetti also kindly provided us with hst images of ngc 5253 . ds acknowledges a fellowship from the swiss national foundation of scientific research and partial support from the directors discretionary research fund of the stsci . beck , s.c . , turner , j.l . , ho , p.t.p . , lacy , j.h . , kelly , d.m . , 1996 , , 457 , 610 burnstein , d. , heiles , c. , 1984 , , 54 , 33 campbell , a. , terlevich , r. , melnick , j. , 1986 , , 223 , 811 calzetti , d. , et al . , 1997 , in preparation conti , p. , 1991 , , 377 , 115 conti , p. , vacca , w.d.w . , 1994 , , 423 , l97 contini , t. , 1996 , in `` wr stars in the framework of stellar evolution '' , 33rd lige int . , eds . j.m . vreux et al . , esteban , c. , peimbert , m. , 1995 , , 300 , 78 gorjian , v. , 1996 , , 112 , 1886 izotov , y.i . , thuan , t.x . , lipovetsky , v.a . , 1994 , , 435 , 647 izotov , y.i . , thuan , t.x . , lipovetsky , v.a . , 1997 , , in press kingsburgh , r.l . , barlow , m.j . , storey , p.j . , 1995 , , 295 , 75 kobulnicky , h.a . , skillman , e.d . , roy , j.r . , walsh , j.r . , rosa , m.r . , 1997 , , in press ( ksrwr97 ) kunth , d. , sargent , w.l.w . , 1981 , , 101 , l5 maeder , a. , 1983 , , 120 , 113 martin , c.l . , kennicutt , r.c . , 1995 , , 447 , 171 meurer , g. , heckman , t.m . , leitherer , c. , kinney , a. , robert , c. , garnett , d.r . , 1995 , , 110 , 2665 meynet , g. , 1995 , , 298 , 767 pagel , b.e.j . , simonson , e.a . , terlevich r.j . , edmunds , m.g . , 1992 , , 255 , 325 sandage , a. , saha , a. , labhardt , l. , schwengeler , h. , panagia , n. , macchetto , f.d . , 1994 , , 423 , l13 schaerer , d. , 1996 , , 467 , l17 schaerer , d. , vacca , w.d.w . , 1996 , in `` wr stars in the framework of stellar evolution '' , 33rd lige int . astroph . , eds . j.m . vreux et al . , p. 641 seaton , m.j . , 1979 , , 187 , 73p smith , l.f . , shara , m.m . , moffat , a.f.j . , 1990 , , 358 , 229 smith , l.f . , shara , m.m . , moffat , a.f.j . , 1996 , , 281 , 163 vacca , w.d . , conti , p. , 1992 , , 401 , 543 walsh , j.r . , roy , j - r . , 1987 , , 319 , l57 ( wr87 ) walsh , j.r . , roy , j - r . , 1989 , , 239 , 297 ( wr89 ) lrrrrrrr hei & 4471 & 45.8 & 52.1 & 36.0 & 38.4 & 55.2 & 69.8 niii / ciii & 4645 & ( 6.2 ) & ( 6.7 ) & ( 39.3 ) & ( 40.7 ) & ( 35.4 ) & ( 40.1 ) [ feiii ] & 4658 & 13.0 & 13.8 & 19.1 & 19.8 & 22.7 & 25.5 heii & 4686 & 8.3 & 8.8 & 54.8 & 56.3 & 150.3 & 166.3 [ ariv ] & 4711 & 16.1 & 16.9 & ( 21.9 ) & ( 22.3 ) & ( 48.3 ) & ( 52.6 ) [ ariv ] & 4740 & 10.1 & 10.5 & ( 10.8 ) & ( 11.1 ) & ( 12.7 ) & ( 13.6 ) hei & 4922 & 10.0 & 9.8 & 10.9 & 10.7 & 10.1 & 9.7 [ oiii ] & 4959 & 2123.0 & 2059.7 & 1564.1 & 1538.8 & 1779.4 & 1685.1 [ oiii ] & 5007 & 6375.6 & 6103.1 & 4695.2 & 4589.0 & 5322.4 & 4917.1 [ ni ] & 5199 & 7.4 & 6.7 & 7.4 & 7.0 & & [ feiii ] & 5271 & 4.8 & 4.2 & 6.4 & 6.0 & & [ cliii ] & 5518 & 4.0 & 3.3 & 4.6 & 4.1 & & [ cliii ] & 5538 & 2.9 & 2.4 & & & & [ nii ] & 5755 & 5.4 & 4.3 & ( 2.8 ) & ( 2.4 ) & & civ & 5808 & 7.2 & 5.6 & 33.0 & 29.0 & & hei & 5876 & 142.2 & 109.5 & 127.6 & 111.0 & 126.9 & 79.2 [ oi ] & 6300 & 26.8 & 19.0 & 34.7 & 28.8 & 33.5 & 17.9 [ siii ] & 6312 & 40.2 & 28.4 & 24.7 & 20.6 & 22.1 & 11.8 [ oi ] & 6364 & 8.8 & 6.2 & 10.5 & 8.7 & 10.0 & 5.2 & & & & & & & @xmath10 & & 0.44 & & 0.20 & & 0.85 & @xmath28 & & 294 & & 109 & & 87 & @xmath29 & & 70.6 & 229.8 & 29.8 & 55.8 & 13.1 & 109.6

the region of maximum optical emission is found to provide the dominant contribution of the ionizing flux as opposed to the less extinguished region of maximum uv brightness . the presence of wr stars near the n - enriched regions found by walsh & roy ( 1987 , 1989 ) and kobulnicky et al .

we present spectroscopic observations of the central star clusters in ngc 5253 the aim of which is to search for wc stars . our observations show the presence of wolf - rayet ( wr ) stars not only of wn but also of wc subtype in two star forming regions corresponding to the maximum optical and uv emission . the massive star population we derive is consistent with young bursts of @xmath0 3 and 4 myr . the region of maximum optical emission is found to provide the dominant contribution of the ionizing flux as opposed to the less extinguished region of maximum uv brightness . the presence of wr stars near the n - enriched regions found by walsh & roy ( 1987 , 1989 ) and kobulnicky et al . ( 1997 ) suggests they are a possible source of n. it is presently unclear whether or not our detection of wc stars is compatible with the normal observed he / o and c / o abundance ratios . _ apj letter , in press ( received : 2 november 1996 , accepted : 13 march 1997 ) _ # 1#2@xmath1 2c16o@xmath2

1307.4287

c

gaseous nebulae , mainly pne and h ii regions , are useful probes of the past chemical composition of the interstellar medium ( ism ) . the @xmath1-element abundances of a pn reflect those in the ism at the time when the progenitor star formed , while the @xmath1-element abundances of a sample of h ii regions provide a ` snapshot ' of the current status of chemical evolution of galaxies . comparison of the abundances of pne and h ii regions on the disk of a spiral galaxy helps to study the chemical history and production processes of the elements . furthermore , studying the relations between abundances of different @xmath1-elements helps to constrain the production processes and the relative yields of each element . ratios of different @xmath1-element abundances also reflect the enrichment by the progenitor stars . figures[noratio_o][aro_o ] show the abundance correlations in our sample as well as the m31 disk and bulge pne from the literature , in the logarithmic scale . figure[noratio_o ] presents the @xmath69(n / o ) versus @xmath69(o / h ) abundance relation . also overplotted are the m31 disk pne from @xcite and the m31 bulge and disk sample observed by @xcite . also presented in the plot are the solar values from @xcite and the nebular abundances of orion from @xcite . figure[noratio_o ] shows that there is no obvious trend in the @xmath69(n / o ) versus @xmath69(o / h ) ratio in our sample . figure[ne_o ] displays a positive correlation between @xmath69(ne / h ) and @xmath69(o / h ) . that confirms the tight relation between these two elements , which have by far been observed for pne in both the mw and m31 . the neon - oxygen abundance distribution of our sample agree with the slope of other m31 pne within the errors . figure[neo_o ] shows that there is no obvious correlation between the ne / o ratio and o / h . figure[s_o ] shows @xmath69(s / h ) versus @xmath69(o / h ) , and figure[so_o ] is @xmath69(s / o ) versus @xmath69(o / h ) . the sulphur - oxygen correlation shows larger scatter than neon ( figure[ne_o ] ) . as pointed out by @xcite as well as by earlier studies , the determination of sulphur abundances in the pne of m31 is very challenging : 1 ) ionization correction introduces uncertainties because of the ions that can not be observed in the optical , e.g. s@xmath62 ; and 2 ) the lines from both s@xmath49 and the predominant ionization state s@xmath48 are faint , or absent , in the m31 pne . our observations ( in pn3 ) confirm the results of @xcite that derived sulphur abundances for the m31 pne are lower than that of the sun . the [ s ii ] line is only observed in pn3 , and figures[s_o ] and [ so_o ] show that our abundance ratios lie within the ranges of @xcite . the behavior of argon is similar to that of neon , as shown in figure[ar_o ] , and pn3 is located well within the argon - oxygen correlation of @xcite . there is no obvious correlation between @xmath69(ar / o ) and @xmath69(o / h ) , as indicated by figure[aro_o ] . the distribution of oxygen abundance with the galactocentric distance of the m31 pne and h ii regions is shown in figure[gradient ] . the m31 disk sample observed by @xcite and our three northern spur pne are both given in the plot . also presented are the m31 pne observed by @xcite and nine h ii regions on the disk of m31 observed by @xcite . all galactocentric distances have been rectified for the effects of projection on the sky plane and reduced in units of @xmath70 which is 22.4 kpc for m31 @xcite . the galactocentric distances ( in kpc ) of our three pne have been rectified using the formula @xmath71 given by @xcite . here we assumed that the three northern spur pne are all located on the disk of m31 . @xmath72 and @xmath73 are distances to the galactic center projected on the major and minor axes , respectively . the inclination angle @xmath74 of the m31 disk to the plane of the sky is 77.7@xmath3 as adopted from @xcite . the @xmath72 and @xmath73 values were calculated from the ra and dec of a pn as well as the position angle ( pa ) of the m31 main axis ( 37.7@xmath75 ; @xcite ) . it can be seen from figure[gradient ] that the oxygen abundances of the m31 disk pne observed by @xcite are generrally higher than those of @xcite . however , the radial distribution of the sample of @xcite is more restricted . in our sample , pn3 has a higher oxygen abundance than the m31 disk pne at similar galactocentric distances . this pn also has the best - quality spectrum among the three . that indicates our sample , at least pn3 , might be different from the m31 disk population . abundances of the sample observed by @xcite show very large scatter and systematically lower than those of @xcite . the nine h ii regions in the disk of m31 observed by @xcite were derived from the direct @xmath28-based method . these h ii regions seem to have steeper oxygen gradient than @xcite , but they are spatially restricted and too few sample . judging from the spatial distribution of our three northern spur pne ( figure[orbit ] ) , pn3 may be more associated with this substructure , although all three pne have already been identified by @xcite as belonging to the northern spur ; the other two pne are located more close to the major axis of m31 . if the orbital model of @xcite is correct , i.e. the northern spur of m31 is connected to the southern stream , our observations of pn3 seem to be in line with the postulation that the northern spur substructure is composed of the tidal debris of the m31 s satellite galaxies . the origin of northern spur is still largely unclear , although large - area photometric observations of m31 had been carried out more than 10 years ago . previous studies of the substructure in m31 have revealed that northern spur is metal - rich . however , those results are only based on color information . quantitative spectroscopy are needed to confirm that nature . @xcite was among the first to formally propose the possible origin of northern spur , i.e. it might be associated with the southern stream , although that had been inferred by @xcite and @xcite . using the kinematic information of pne in the disk of m31 and based on the studies of @xcite and @xcite , @xcite constructed an orbit model of the stellar stream that connects the northern spur to the southern stream . in this model , the area of the northern spur encompasses the turning point of the orbit which is strongly warped near the center of m31 ( see figure@xmath76 of @xcite ; see also figure[orbit ] in this paper which is constructed based on figure2 of @xcite , with permission of the authors ) . judging from the projected position and kinematics of m32 , @xcite hypothesized that this satellite might be a parent of the stream , although the exact position of m32 with respect to m31 is still an open question . figure[orbit ] shows this orbit in the @xmath72-@xmath73 coordinate system in an m31-based reference frame , where @xmath72 lies along the major axis of m31 and increases toward the south - west , and @xmath73 lies along the minor axis and increases toward the north - west . both coordinates are calculated following the geometric transformations of @xcite . also presented in figure[orbit ] is the projection of this orbit in the line - of - sight velocity with respect to to m31 , @xmath77 , versus distance along the major and minor axes . spatial and kinematic distribution of the m31 pne observed by @xcite are presented along with the orbit . pne in the region of northern spur identified by ( * ? ? ? * see figure32 therein ) as well as those identified by the same authors as forming a continuation of the southern stream are highlighted with different symbols in figure[orbit ] . the three northern spur pne studied in the current paper are also highlighted . in the lower panel of figure[orbit ] ( i.e. @xmath77 versus @xmath72 ) , dispersion in the line - of - sight velocities of the northern spur pne with respect to the projected orbit is relatively large , indicating the orbit in this section might be of large uncertainty . that is expected because the orbit model of @xcite is based on a limited number of pne ( @xmath220 ) and relatively simple assumptions . considering the fact that pn3 in our sample has relatively higher oxygen abundance than the m31 disk sample at similar galactocentric distances ( figure[gradient ] ) , our observations seem to be in line with the postulation of @xcite . also noticeable in figure[orbit ] ( also figure@xmath78 in @xcite ) is that the 20 pne ( two of them might be the northern spur candidates , as indicated by @xcite ) associated with the southern stream generally well fit the orbit model . future spectroscopy of these pne will help to confirm their true nature . the kinematics of pne in the northern spur region are indistinguishable from those of the disk , and @xcite suggests that this substructure is related to the disk , perhaps indicative of a warp . however , deep spectroscopy of more pne in this region is definitely needed so that they can be chemically distinguished from those in the disk . figure[orbit ] here is to visually demonstrate the position of the northern spur pne relative to the model orbit of @xcite . as to the origin of the northern spur , observations of more pne therein and the pne in the southern stream may help to confirm whether these two substructures linked . observations of the pne m32 may also help to understand the interaction between m32 and m32 and assess whether the northern spur and southern stream both originate from m32 . currently , observations of pne in m32 are scarce @xcite and results inconclusive . more high - quality spectroscopic observations are preferred .

, we observed relatively higher oxygen abundance compared to the disk sample in m31 at similar galactocentric distances . the results of at least one of the three northern spur pne might be in line with the proposed possible origin of the northern spur substructure of m31 , i.e. the northern spur is connected to the southern stream and both substructures comprise the tidal debris of the satellite galaxies of m31 .

we present spectroscopy of three planetary nebulae ( pne ) in the northern spur of the andromeda galaxy ( m31 ) obtained with the double spectrograph on the 5.1 m hale telescope at the palomar observatory . the samples are selected from the observations of merrett et al . our purpose is to investigate formation of the substructures of m31 using pne as a tracer of chemical abundances . the [ o iii ] @xmath04363 line is detected in the spectra of two objects , enabling temperature determinations . ionic abundances are derived from the observed collisionally excited lines , and elemental abundances of nitrogen , oxygen , and neon as well as sulphur and argon are estimated . correlations between oxygen and @xmath1-element abundance ratios are studied , using our sample and the m31 disk and bulge pne from the literature . in one of the three pne , we observed relatively higher oxygen abundance compared to the disk sample in m31 at similar galactocentric distances . the results of at least one of the three northern spur pne might be in line with the proposed possible origin of the northern spur substructure of m31 , i.e. the northern spur is connected to the southern stream and both substructures comprise the tidal debris of the satellite galaxies of m31 .

1307.4287

i

we present deep spectroscopy of three pne in the northern spur of m31 using dbsp on the 5.1 m hale telescope at the palomar observatory . the sample is selected from @xcite . this is the first chemical study of pne in this substructure . the [ o iii ] @xmath04363 auroral line is detected in the spectra of two objects after meticulous work on the subtraction of sky background . electron temperatures were determined for two pne . ionic abundances of heavy elements were derived from the [ n ii ] , [ o iii ] , [ ne iii ] , [ s ii ] and [ ar iii ] cels detected in the spectra . the n / h , o / h , ne / h , s / h and ar / h elemental abundances were estimated . correlations between oxygen and @xmath79-element abundance ratios were studied , using our sample and other m31 pne from the literature . one of the three northern spur pne has relatively higher oxygen abundance than both the m31 disk pne at similar galactocentric distances and the average abundance of the m31 disk sample . our study is thus seems to be in line with the postulation that the northern spur might be connected to the southern stream and are metal - enriched . more observations of pne at different substructures , in combination with the kinematic information , are needed to assess the properties of those substructures and further constrain the possible origins of the northern spur .

we present spectroscopy of three planetary nebulae ( pne ) in the northern spur of the andromeda galaxy ( m31 ) obtained with the double spectrograph on the 5.1 m hale telescope at the palomar observatory . the [ o iii ] @xmath04363 line is detected in the spectra of two objects , enabling temperature determinations . correlations between oxygen and @xmath1-element abundance ratios are studied , using our sample and the m31 disk and bulge pne from the literature . in one of the three pne

we present spectroscopy of three planetary nebulae ( pne ) in the northern spur of the andromeda galaxy ( m31 ) obtained with the double spectrograph on the 5.1 m hale telescope at the palomar observatory . the samples are selected from the observations of merrett et al . our purpose is to investigate formation of the substructures of m31 using pne as a tracer of chemical abundances . the [ o iii ] @xmath04363 line is detected in the spectra of two objects , enabling temperature determinations . ionic abundances are derived from the observed collisionally excited lines , and elemental abundances of nitrogen , oxygen , and neon as well as sulphur and argon are estimated . correlations between oxygen and @xmath1-element abundance ratios are studied , using our sample and the m31 disk and bulge pne from the literature . in one of the three pne , we observed relatively higher oxygen abundance compared to the disk sample in m31 at similar galactocentric distances . the results of at least one of the three northern spur pne might be in line with the proposed possible origin of the northern spur substructure of m31 , i.e. the northern spur is connected to the southern stream and both substructures comprise the tidal debris of the satellite galaxies of m31 .

1302.0009

c

we present multiwavelength observations of ps1 - 10afx at redshift @xmath0 , perhaps the most luminous sn yet discovered . the combination of observables presents strict constraints on any theoretical interpretation . these are : * a peak bolometric luminosity of 4.1@xmath410@xmath5 erg s@xmath6 * an observed rise time of @xmath312 d * a fast light curve decay , with @xmath122@xmath123= @xmath162 mag * at least 7@xmath410@xmath126 erg of optical radiation emitted , with a total likely closer to 10@xmath15 erg * red color near maximum light ( @xmath163 k ) , although @xmath102 may be closer to @xmath99 k * constant uv color before maximum light * photospheric velocities near maximum light of @xmath3@xmath8 km s@xmath6 * spectra that most closely resemble normal sne ic , with deep p - cygni absorption * photometric and spectroscopic evidence for some line blanketing in the nuv from iron - peak elements , although not as much as for sne ia * a massive ( @xmath32@xmath410@xmath13 m@xmath12 ) host galaxy that is unlikely to have an extremely low metallicity we surveyed existing models for slsne and found that none were acceptable . in particular , the large inferred @xmath128 near maximum light is very hard to reconcile with the fast observed rise time and the measured photospheric velocities because the sn ejecta need too much time to reach such large radii . the magnetar models that match the peak luminosity and rise time do so by producing a much higher temperature at a smaller radius . these flaws are generic to models powered by internal energy sources , although if the onset of the internal energy source can be sufficiently delayed after the initial explosion , then maybe the conflict between the velocities and radii can be avoided . shock breakout scenarios invoking dense csm provide a promising solution by allowing the sn to explode well before the optical emission is detectable . if the csm is sufficiently dense out to @xmath35@xmath410@xmath10 cm , then the light curve will only rise after the ejecta have had time to reach that radius . however , these models leave the normal sn ic - like spectrum unexplained and are in apparent conflict with the observed color evolution before maximum light . more detailed radiative transfer calculations of the models are necessary to know whether these flaws can be avoided . in addition , it is not clear how to produce the special csm structure that has to be assumed ( a truncated wind or a shell ) . ps1 - 10afx was initially identified as an object of interest due to its unusual colors ( @xmath164 2 mag at peak ) and would not have been found without the ps1 observation strategy , which includes regular @xmath29 and @xmath30 observations as part of the search . at redshifts below @xmath31 , an object like ps1 - 10afx would have a strong detection in @xmath28 and would not stand out without knowing the redshift . unlike many of the sn 2005ap - like sne , the time - dilated light curve of a ps1 - 10afx - like sn at lower redshift would not be unusually long and would not be associated with the attention - grabbing lack of a visible host galaxy . however , ps1 - 10afx was more than a magnitude brighter than its host galaxy , which potentially provides a selection criterion to increase the odds of finding similar objects in the future . in the sample of slsne found by ps1 , sn 2005ap - like objects @xcite outnumber ps1 - 10afx by at least an order of magnitude . our poor understanding of spectroscopic incompleteness and the relevant selection effects precludes a more precise estimate of rates at this time . an additional complication to be considered is the role of metallicity . the massive host of ps1 - 10afx is in contrast with the low - mass @xcite and low - metallicity @xcite hosts of known hydrogen - poor slsne . the natal composition of the progenitor could have an indirect effect on the explosion through stellar evolutionary processes or it could directly affect the appearance through the opacity in the outer ejecta ( could sn 2005ap - like events with higher metal abundances exhibit line - blanketed spectra like ps1 - 10afx ? ) . most of the published slsne that lack hydrogen in their spectra are similar to sn 2005ap and scp06f6 @xcite . sn 2007bi @xcite and a couple of as - yet unpublished objects @xcite were the only known exceptions . they exhibited rather different spectra and had very slow light curve decays , which were interpreted by @xcite to be the result of decay of a large amount of radioactive @xmath21ni produced in a pair - instability explosion . this result has been challenged on theoretical grounds by @xcite , who show that the observations do not match theoretical expectations for pair - instability sne . with the discovery of ps1 - 10afx , we now have further evidence that the most luminous sne are a heterogeneous lot , even when just considering the objects lacking hydrogen . a key question for future investigations is whether these diverse outcomes of stellar evolution can be produced by variations on a single underlying physical model or whether multiple pathways exist to produce sne of these extraordinary luminosities . ps1 - 10afx differs from existing slsne - i in almost every observable except for the peak luminosity . it is hard to understand how all of these differences could be produced with only small modifications to a single model , and may indicate that ps1 - 10afx is the first example of a different channel for producing slsne . this paper includes data gathered with the 6.5-m magellan telescopes located at las campanas observatory , chile . we thank the staffs at ps1 , gemini , magellan , and the vlt for their assistance with performing these observations . we are grateful for the grants of dd time at gemini and the vlt . we acknowledge j. strader for obtaining some fourstar observations , as well as the mmirs observers who helped obtained some of the data here during the fall 2010 queue observations : m. kriek , i. labbe , j. roll , d. sand , and s. wuyts . sjs acknowledges funding from the european research council under the european union s seventh framework programme ( fp7/2007 - 2013)/erc grant agreement n@xmath165 291222 . the pan - starrs1 surveys ( ps1 ) have been made possible through contributions of the institute for astronomy , the university of hawaii , the pan - starrs project office , the max - planck society and its participating institutes , the max planck institute for astronomy , heidelberg and the max planck institute for extraterrestrial physics , garching , the johns hopkins university , durham university , the university of edinburgh , queen s university belfast , the harvard - smithsonian center for astrophysics , the las cumbres observatory global telescope network incorporated , the national central university of taiwan , the space telescope science institute , and the national aeronautics and space administration under grant no . nnx08ar22 g issued through the planetary science division of the nasa science mission directorate . some observations were obtained under program ids gn-2010b - q-5 ( pi : berger ) , gs-2010b - q-4 ( pi : berger ) , and gn-2010b - dd-2 ( pi : chornock ) at the gemini observatory , which is operated by the association of universities for research in astronomy , inc . , under a cooperative agreement with the nsf on behalf of the gemini partnership : the national science foundation ( united states ) , the science and technology facilities council ( united kingdom ) , the national research council ( canada ) , conicyt ( chile ) , the australian research council ( australia ) , ministrio da cincia , tecnologia e inovao ( brazil ) and ministerio de ciencia , tecnologa e innovacin productiva ( argentina ) . some observations were collected at the european organisation for astronomical research in the southern hemisphere , chile under ddt programme 286.d-5005 ( pi : smartt ) . the national radio astronomy observatory is a facility of the national science foundation operated under cooperative agreement by associated universities , inc . some of the archival data presented in this paper were taken under programs go-5623 and go-9114 ( pi : kirshner ) and were obtained from the mikulski archive for space telescopes ( mast ) . stsci is operated by the association of universities for research in astronomy , inc . , under nasa contract nas5 - 26555 . some of the computations in this paper were run on the odyssey cluster supported by the fas science division research computing group at harvard university . tonry , j. , & onaka , p. 2009 , advanced maui optical and space surveillance technologies conference , proceedings of the advanced maui optical and space surveillance technologies conference , ed . : s. ryan , p.e40 .

our extensive optical and near - infrared observations indicate that the bolometric light curve of ps1 - 10afx rose on the unusually fast timescale of @xmath312 d to the extraordinary peak luminosity of 4.1@xmath410@xmath5 erg s@xmath6 ( @xmath7 mag ) and subsequently faded rapidly . equally important , the sed is unusually red for a slsn , with a color temperature of @xmath36800 k near maximum light , in contrast to previous hydrogen - poor slsne , which are bright in the ultraviolet ( uv ) . the spectra more closely resemble those of a normal sn ic than any known slsn , with a photospheric velocity of @xmath3@xmath8 km s@xmath6 and evidence for line blanketing in the rest - frame uv . despite the fast rise , these parameters imply a very large emitting radius ( @xmath95@xmath410@xmath10 cm ) . the host galaxy is well detected in pre - explosion imaging with a luminosity near @xmath11 , a star formation rate of @xmath315 m@xmath12yr@xmath6 , and is fairly massive ( @xmath32@xmath410@xmath13 m@xmath12 ) , with a stellar population age of @xmath310@xmath14 yr , also in contrast to the young dwarf hosts of known hydrogen - poor slsne .

we present the discovery of ps1 - 10afx , a unique hydrogen - deficient superluminous supernova ( slsn ) at redshift @xmath0 . the light curve peaked at @xmath1 mag , making ps1 - 10afx comparable to the most luminous known sne , with @xmath2 mag . our extensive optical and near - infrared observations indicate that the bolometric light curve of ps1 - 10afx rose on the unusually fast timescale of @xmath312 d to the extraordinary peak luminosity of 4.1@xmath410@xmath5 erg s@xmath6 ( @xmath7 mag ) and subsequently faded rapidly . equally important , the sed is unusually red for a slsn , with a color temperature of @xmath36800 k near maximum light , in contrast to previous hydrogen - poor slsne , which are bright in the ultraviolet ( uv ) . the spectra more closely resemble those of a normal sn ic than any known slsn , with a photospheric velocity of @xmath3@xmath8 km s@xmath6 and evidence for line blanketing in the rest - frame uv . despite the fast rise , these parameters imply a very large emitting radius ( @xmath95@xmath410@xmath10 cm ) . we demonstrate that no existing theoretical model can satisfactorily explain this combination of properties : ( i ) a nickel - powered light curve can not match the combination of high peak luminosity with the fast timescale ; ( ii ) models powered by the spindown energy of a rapidly - rotating magnetar predict significantly hotter and faster ejecta ; and ( iii ) models invoking shock breakout through a dense circumstellar medium can not explain the observed spectra or color evolution . the host galaxy is well detected in pre - explosion imaging with a luminosity near @xmath11 , a star formation rate of @xmath315 m@xmath12yr@xmath6 , and is fairly massive ( @xmath32@xmath410@xmath13 m@xmath12 ) , with a stellar population age of @xmath310@xmath14 yr , also in contrast to the young dwarf hosts of known hydrogen - poor slsne . ps1 - 10afx is distinct from known examples of slsne in its spectra , colors , light - curve shape , and host galaxy properties , suggesting that it resulted from a different channel than other hydrogen - poor slsne .

astro-ph0611330

c

cy 2201 - 3201 is an edge - on galaxy lens . such systems offer the possibility of decomposing the relative mass contributions of the disk , bulge and halo . in our optical images cy 2201 - 3201 appears as a bulgeless edge - on spiral galaxy , producing two images of a background @xmath1 qso . we have therefore modeled the system with one ( disk ) and two ( disk+halo ) mass components , neglecting the bulge . all viable models explored produce either three or four visible images . however , our optical images only show two images of the qso ( fig [ fig2 ] ) . we observe the two images that are farther away from the disk but miss the third ( and in some configurations the fourth ) image located very close to the disk . we have investigated whether dust extinction could be responsible for this missing image . the colors of the qso images a and b ( table [ tab2 ] ) are in fact redder than expected for a typical qso at that redshift . although low in signal - to - noise ratioand covering a small wavelength range , the qso spectrum does not reveal indication of strong intrinsic absorption in the qso itself . one is then led to conclude that the redder colors are due to dust extinction between the qso and the observer . the most probable source of attenuation comes from the disk itself . we have computed the amount of dust extinction at the galaxy redshift ( @xmath82 ) necessary to explain the observed colors assuming a mean qso spectrum at this redshift , no intrinsic absorption at the qso itself and the value of the local galactic extinction @xmath83 @xcite . we find that the qso image a requires an extinction by the galaxy disk of @xmath84 and the image b an extinction of @xmath85 . images a and b are seen at a projected distance of 0.35 and 0.47 ( 1.7 and 2.2 @xmath86 kpc ) of the disk plane respectively . the inferred values of the extinction by the disk are then likely taking into account thee projected distances to the disk . our @xmath21 band image is the one with the highest signal - to - noise detection of the qso images . we have inserted a third image of the qso in our model images at the position given by our lens models and verify through our mcmc method the maximum flux it could have without being significantly detected . if the ratio of expected flux to maximum observed flux are completely due to absorption by dust at the lens galaxy , then there are at least 3 mag of extinction more at the position of the third image than at the brightest . taking into account the possible extinction at the brightest image , the third image would suffer @xmath87 of extinction going through the lens galaxy . in our models of the lens , we have first explored the assumption that the mass distribution has the same ellipticity as the light . we have tried three one - mass component models fixing the galaxy center , axis ratio and position angle to those observed in the optical . we have fit an sie , an exponential and an nfw model . all three models reproduce the two qso images and predict a third image that is unobserved . the predicted rotational velocities are consistent with the observed value at the 1 @xmath81 level for the sie model and at the 2 @xmath81 level for the exponential and elliptical nfw models . we have also tried other methods to estimate the galaxy mass . we have fit the observed galaxy photometry with the pegase synthesis evolutionary models @xcite . we obtain an absolute magnitude of @xmath88 , adding an evolutionary correction . ] which is a factor 3 fainter than l@xmath89 @xcite . the stellar mass - to - light ratio(@xmath90/@xmath91 ) of the best fitting model is @xmath92 , so its stellar mass would be @xmath93 @xmath94 @xmath95 . the expected rotational velocity for such a mass at 2.7 times the scale radius is @xmath96 km s@xmath3 ( depending on the mass model ) . the stellar mass by itself is thus insufficient to produce the observed ( or predicted ) rotational velocity . if we assume the local tully - fisher relation @xcite neglecting evolution and the measured absolute magnitude , we obtain a value for the expected rotational velocity of @xmath97 km s@xmath3 , which is consistent with the measured rotational velocity . we have also studied more realistic models . the galaxy does not appear to have a bulge in the optical images , and therefore we have modelled the system with two mass components : one for the disk and one for the halo . we have tried an sie+sis model and an exponential+nfw model . these models reproduce the positions and fluxes of the two observed qso images . however , the sie+sis model predicts four visible images and the best fitting exponential+nfw predicts three visible images . none of these predicted additional images are seen in our images ( see above ) . we measure a rotational velocity of @xmath2 km s@xmath3 at 2.7 disk scale radius for the lens galaxy . the sie+sis model predicts values of the rotational velocity consistent with this value for certain combinations of the relative contributions of the sie and sis components ( see 3.3 ) . however , the exponential+nfw model predicts higher values of the rotational velocity if we fit the observed position and fluxes of the qso images . our magellan spectroscopic data were obtained on three different nights with two different settings . as explained in 2.5 , we have four sets of same night / grating data . the individual fits to the rotational velocity at 2.7@xmath44 for each set of data are @xmath98 , @xmath99,@xmath100 , and @xmath101 ( low - resolution september 7 , low - resolution september 9 , high - resolution september 7 and high - resolution september 8 , respectively ) . the relative dispersion of these values may hint at a possible underestimation of the errors . it this were the case , the range of allowed @xmath46 values would be larger and the exponential+nfw model prediction would still be viable . we have also explored other effects that can affect our modeling . our system is likely to be influenced by some external shear which will contribute to the image separation but not to the rotational velocity of the lens galaxy . in fact , cy2201 - 3201 lies 7 away from the hickson compact group hcg 90 . we have computed what would be the external shear produced by the group assuming it is modeled with a sie with the same velocity dispersion as measured from the galaxy members . hcg 90 is relatively small and the external shear induced in the cy 2201 - 3201 system is negligible for our purposes . apart from hcg 90 , cy 2201 - 3201 appears to be isolated and not in any group , cluster , or obvious large - scale structure . in fact , as part of the cyder survey we have obtained spectra of several sources in the field and , with the limited spectroscopic data we have , not found any sign of a massive structure . another possible flaw in our modeling could be that the galaxy center is miscalculated . if the galaxy center is much closer to the qso images than the position we have measured then most of the discussed configurations would no longer apply and the system would display other image configurations , which can in fact place tighter constraints on the relative contribution of the halo and disk to the total mass budget in the central regions of the lens galaxy . however , the seeing and pixel size of our images and the consistency of the galaxy center in our different filter images make us believe that the true center if different from the one measured should not be very far off .

the geometry of the system is favorable to separate the relative mass contribution of the disk and halo in the inner parts of the galaxy . we also model the system with two mass components , disk and halo . the detection of the third image and a more accurate measurement of the rotational velocity would help to set tighter constraints on the mass distribution of this edge - on spiral galaxy .

we present the cxocy j220132.8 - 320144 system , which is composed of an edge - on spiral galaxy at @xmath0 lensing a @xmath1 background quasar . two images of the quasar are seen . the geometry of the system is favorable to separate the relative mass contribution of the disk and halo in the inner parts of the galaxy . we model the system with one elliptical mass component with the same ellipticity as the light distribution and manage to reproduce the quasar image positions and fluxes . we also model the system with two mass components , disk and halo . again , we manage to reproduce the quasar image positions and fluxes . however , all models predict at least a third visible image close to the disk that is not seen in our images . we speculate that this is most likely due to extinction by the disk . we also measure the rotational velocity of the galaxy at 2.7 disk scale radius to be @xmath2 km s@xmath3 from the [ oii ] emission lines . when adding the rotational velocity constraint to the models , we find that the contribution to the rotational velocity of the disk is likely to be equal to or larger than the contribution of the halo at this radius . the detection of the third image and a more accurate measurement of the rotational velocity would help to set tighter constraints on the mass distribution of this edge - on spiral galaxy .

astro-ph0611330

c

we have presented the discovery and subsequent follow up observations of the cy2201 - 3201 system composed of an edge - on spiral at @xmath82 splitting a background @xmath102 qso into two observed images each at opposite sides of the disk . we have modeled the system with one ( disk ) and two ( disk+halo ) mass components . the most likely configuration is the `` disk''configuration with three images of the qso one at each side of the disk and the fainter one approximately behind the disk . there are also possible configurations that produce four or even five ( this one unlikely ) observable images . however we only observe two images . we have discussed the possibility that the third ( and fourth , if existent ) image is extincted by the disk . we estimate that an @xmath87 at th epredicted position of the third image at the galaxy lens redshift is required to be consistent with our observations . we have measured the rotational velocity of the lens galaxy to be @xmath103 km s@xmath3 at a radius 2.7 times the scale radius of the galaxy exponential light distribution . if we use an sie+sis model to fit the qso image positions and fluxes and this value of the rotational velocity , we find that the contribution by the sie ( disk ) to the @xmath46 at this radius is required to be the same or larger than the contribution of the sis ( halo ) . if we use an exponential+nfw model then we are unable to reproduce this value of the rotational velocity if we fit the positions and fluxes of the qso images . we have speculated whether we have underestimated the error in our determination of the @xmath46 which would make the exponential+nfw model viable . cy 2201 - 3201 is the best lensing spiral galaxy known to date that can be used to disentangle the contributions of its different mass components . unfortunately our current follow up observations are not constraining enough to elucidate between different possible models . more accurate image source positions , the discovery or not of the predicted third image and the measurement of its properties and a precise rotational velocity would make this system fulfill its potential . cy 2201 - 3201 has been awarded _ hubble space telescope _ ( hst ) acs time in cycle 13 . we have also been awarded more spectroscopic time at magellan . we expect that the higher quality images and extra spectra will help us improve our modeling and place strong constraints on the relative contribution of the disk and halo mass components . we thank c. keeton for making public his gravlens code and replying to our questions . we thank paul schechter for his encouragement and helpful discussions . we thank all observatory staff for their help during observations . we thank the anonymous referee for his / her comments that have helped us improve the paper . f.j.c . acknowledges support from the spanish ministerio de educacin y ciencia ( mec ) , project aya2005 - 09413-c02 - 01 with ec - feder funding and from the research project 2005sgr00728 from the generalitat de catalunya . j.m . gratefully acknowledges support from the chilean centro de astrofsica fondap 15010003 . f.j.c . and j.m . acknowledge support from a `` convenio bilateral csic - universidad de chile '' . e.g. is supported by the national science foundation under grant ast 02 - 01667 .

we present the cxocy j220132.8 - 320144 system , which is composed of an edge - on spiral galaxy at @xmath0 lensing a @xmath1 background quasar . however , all models predict at least a third visible image close to the disk that is not seen in our images . we speculate that this is most likely due to extinction by the disk . we also measure the rotational velocity of the galaxy at 2.7 disk scale radius to be @xmath2 km s@xmath3 from the [ oii ] emission lines . when adding the rotational velocity constraint to the models , we find that the contribution to the rotational velocity of the disk is likely to be equal to or larger than the contribution of the halo at this radius .

we present the cxocy j220132.8 - 320144 system , which is composed of an edge - on spiral galaxy at @xmath0 lensing a @xmath1 background quasar . two images of the quasar are seen . the geometry of the system is favorable to separate the relative mass contribution of the disk and halo in the inner parts of the galaxy . we model the system with one elliptical mass component with the same ellipticity as the light distribution and manage to reproduce the quasar image positions and fluxes . we also model the system with two mass components , disk and halo . again , we manage to reproduce the quasar image positions and fluxes . however , all models predict at least a third visible image close to the disk that is not seen in our images . we speculate that this is most likely due to extinction by the disk . we also measure the rotational velocity of the galaxy at 2.7 disk scale radius to be @xmath2 km s@xmath3 from the [ oii ] emission lines . when adding the rotational velocity constraint to the models , we find that the contribution to the rotational velocity of the disk is likely to be equal to or larger than the contribution of the halo at this radius . the detection of the third image and a more accurate measurement of the rotational velocity would help to set tighter constraints on the mass distribution of this edge - on spiral galaxy .

1603.05299

i

most stars are born spinning rapidly . observations of young clusters reveal a wide range of rotation rates , with some stars spinning more than 100 times faster than the sun ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? this scatter is generally attributed to the vortical nature of the turbulent interstellar clouds from which these stars form . though much of the initial angular momentum is lost during the gravitational collapse of a protostellar core , the dramatic decrease in the moment of inertia during the collapse is enough to impart a substantial rotational velocity in a large fraction of young stars . as the stars age , torques from magnetized stellar winds cause them to spin down and this reduces the scatter of the general population @xcite . the rapid rotation of young stars can have a dramatic influence on their internal structure and dynamics . in the most extreme cases , the centrifugal force can alter the stars shape , causing it to be significantly oblate . models of rotating stars suggest that the effects of rapid rotation and oblateness can alter the stars s convective and radiative heat transport , reduce their luminosities , induce shearing instabilities and global circulations , and modify their rotational and compositional evolution @xcite . much of this work has focused on high - mass stars because of their short lifetimes , which makes them intrinsically more likely for fast rotation to play an important evolutionary role from birth to death , when they explode as supernovae and enrich the galaxy with heavy elements . high - mass stars are also luminous and large , which makes them relatively easy to observe . in the last fifteen years , researchers have been able to directly detect the oblate shapes of several rapidly - rotating , massive stars by means of optical and infrared interferometry @xcite . more direct detections are likely to be made in the future as observations continue to improve @xcite . one of the major theoretical predictions that has been addressed by these observations is the phenomenon of gravity darkening , which was introduced nearly a century ago in a pioneering paper by @xcite . for a massive star with a radiative outer envelope , von zeipel argued that the effective temperature of the stellar surface should scale as @xmath1 , where @xmath2 and @xmath3 is the effective gravity , equal to the newtonian gravity plus the centrifugal force . this in turn implies that the radiative energy flux emitted from the stellar surface scales as @xmath4 . since the centrifugal force acts to reduce @xmath3 at the equator , gravity darkening predicts that the equatorial regions should be darker than the polar regions . though observations have confirmed the existence of gravity darkening , they suggest that the exponent may be somewhat less than predicted , with @xmath5 0.13 - 0.25 @xcite . lower - mass , late - type stars with convective envelopes are also expected to exhibit gravity darkening but again , with a smaller latitudinal variation than that predicted by von zeipel , with @xmath6 possibly as low as 0.08 @xcite . however , these expectations are based on simplified models of convection , with little observational guidance . substantial progress has been made in recent years in modeling the structure of rapidly rotating stars . a number of models have been used to investigate the effects of oblateness on stellar structure and evolution , with implications for asteroseismology @xcite . though these models are ostensibly @xmath7 , the thermodynamic quantities only depend on the effective gravitational potential . furthermore , like most stellar structure models , these models do not address the internal dynamics of oblate stars ; they solve only for the hydrostatic structure using a mixing - length formulation for convection , though some do include idealized cylindrical or shellular differential rotation profiles . @xcite took a somewhat different approach , calculating the non - spherical shape and internal structure of a rapidly rotating gaseous body using a three - dimensional , finite - element code with an unstructured grid . but again , the fluid dynamics was not considered . other analytical and numerical work on fluid dynamics in ellipsoidal geometries has focused on flows induced by precession ; for a recent example that employs a finite - element approach see @xcite . the first numerical model ( to our knowledge ) capable of capturing the internal dynamics of oblate stars is the ester ( evolution stellaire en rotation ) code @xcite . ester solves the axisymmetric , steady - state fluid equations self - consistently , taking into account nuclear energy generation , differential rotation and meridional circulation . however , convection is still treated using either a turbulent diffusion approximation @xcite or an isentropic approximation @xcite in which the effective convective heat flux is inferred from the nuclear energy generation and radiative heat flux under the assumption of a steady state . furthermore , published ester simulations are currently limited to high - mass stars with convective cores ( @xmath8 ) ; they have not yet considered convective envelopes . there have been many global 3d hydrodynamic ( hd ) and magnetohydrodynamic ( mhd ) simulations of convection in the envelopes of lower - mass stars that address the rapid rotation regime ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? . however , these do not take into account the oblateness caused by the centrifugal force . in this study , we present the first 3d hd simulations of convection in the oblate envelopes of rapidly - rotating solar - type stars . these simulations are performed using the compressible high - order unstructured spectral difference ( chorus ) code recently introduced by ( * ? ? ? * hereafter wlm15 ) . we focus in particular on the influence of the oblateness on the convective structure , heat transport , mean flows , and the thermodynamic stratification . this paper is organized as follows . in section [ sec : mp ] we discuss the chorus code and its application to model oblate spheriodal geometries . we follow this in section [ sec : setup ] with a description of the numerical experiments that we have performed , which compare oblate simulations at varying rotation rates with their spherical counterparts . we consider rotation rates up to @xmath9 where @xmath10 is the critical angular velocity at which the outward centrifugal force at the equator equals the inward gravitational force . we then present our results , focusing first on the convective structure and energetics ( section [ sec : con ] ) , then on the energy transport ( section [ sec : transport ] ) and finally on the mean flows and associated thermal gradients ( section [ sec : mean ] ) . we summarize our results , conclusions and future plans in section [ sec : summary ] .

we present the first global 3d simulations of thermal convection in the oblate envelopes of rapidly - rotating solar - type stars . we consider rotation rates up to 85% of the critical ( breakup ) rotation rate , which yields an equatorial radius that is up to 17% larger than the polar radius .

we present the first global 3d simulations of thermal convection in the oblate envelopes of rapidly - rotating solar - type stars . this has been achieved by exploiting the capabilities of the new compressible high - order unstructured spectral difference ( chorus ) code . we consider rotation rates up to 85% of the critical ( breakup ) rotation rate , which yields an equatorial radius that is up to 17% larger than the polar radius . this substantial oblateness enhances the disparity between polar and equatorial modes of convection . we find that the convection redistributes the heat flux emitted from the outer surface , leading to an enhancement of the heat flux in the polar and equatorial regions . this finding implies that lower - mass stars with convective envelopes may not have darker equators as predicted by classical gravity darkening arguments . the vigorous high - latitude convection also establishes elongated axisymmetric circulation cells and zonal jets in the polar regions . though the overall amplitude of the surface differential rotation , @xmath0 , is insensitive to the oblateness , the oblateness does limit the fractional kinetic energy contained in the differential rotation to no more than 61% . furthermore , we argue that this level of differential rotation is not enough to have a significant impact on the oblateness of the star .

1603.05299

i

we have preformed the first global 3d hydrodynamic simulations of convection in the oblate envelopes of rapidly - rotating solar - type stars using the recently introduced compressible high - order unstructured spectral difference ( chorus ) code ( wlm15 ) . the chorus code employs unstructured grids , giving it the capability to deal with oblate spheroidal shell geometries . this unique tool allows us to investigate the influence of the oblateness on the convection and mean flows , including heat transport , differential rotation , and the thermal structure of the convective envelope . we have found that the influence of rotation and oblateness leads to an enhancement of the emerging heat flux in the polar and equatorial regions . this is in stark contrast to the conventional concept of gravity darkening and has important observational implications ; oblate , low - mass stars with convective envelopes may not exhibit gravity darkening in the same way that higher - mass stars do . in particular , the minimum suface brightness might occur at mid - latitudes rather than at the equator . the enhancement of the polar heat flux due to oblateness arises for essentially the same reason as in classical gravity darkening arguments ; the stronger effective gravity relative to lower latitudes enhances thermal gradients ( see section [ sec : flux ] ) . this makes the convection more vigorous . however , the secondary peak in the emergent heat flux at the equator arises from physical effects that are not taken into account in the classical models of @xcite , @xcite , and @xcite . oblate stars are rapidly - rotating by nature , implying strong rotational constraints on the convective motions ( low rossby numbers ) . in these parameter regimes , the convection in the equatorial region ( outside the tangent cylinder ) is dominated by banana cells , columnar convective modes aligned with the rotation axis . these banana cells can transport heat more efficiently than at mid - latitudes . in short , the convective heat transport peaks at the poles and at the equator because this is where the convective structures can most easily organize themselves to mitigate the strong rotational constraints : vertical plumes at high latitudes and banana cells at low latitudes . furthermore , though banana cells are essentially laminar flow features , this fundamental argument also extends to more turbulent parameter regimes ( higher rayleigh and reynolds numbers ) . for example , in the high - resolution boussinesq simulations of @xcite , the convective columns break up into vortex sheets as the diffusion is decreased . however , these vortex sheets are still aligned with the rotation axis outside the tangent cylinder and would still be expected to yield an enhancement of the equatorial heat flux . thus , we expect that the general latitudinal dependence of the emergent heat flux in oblate solar - type stars to be similar to that found here , with maxima at the poles and equator . however , as discussed in section [ sec : darkening ] , we may be overestimating the magnitude of the variation , which here is on the order of 40% ( see figure [ fig : fu_so ] ) . the latitudinal dependence of the emergent heat flux is a symptom of the more general tendency for convection in rapidly - rotating spherical or spheroidal shells to separate into distinct polar and equatorial modes , inside and outside the tangent cylinder . we find that the oblateness enhances this dichotomy , causing the polar regions to largely decouple from the equatorial regions ( figs . [ fig : con_pattern ] , [ fig : vn_so ] ) . however , other aspects of the convective structure such as the power spectrum and the width of banana cells , are insensitive to the oblateness . another notable result from our simulations is the presence of banded zonal jets at high latitudes ( section [ sec : mean ] ) . remarkably , these only occur in the oblate simulations , so they are clearly induced by the oblateness . they appear to be due to narrow , axisymmetric convective modes that are approximately aligned with the rotation axis but significantly tilted ( fig . [ fig : mc_120 ] ) . each jet is about 4 - 5@xmath392 wide and many persist for over 100 rotation periods , though they meander in latitude ( figure [ fig : df_o120 ] ) . it is unclear whether or not these jets would persist in the presence of magnetic fields . all stars are ionized and , given the extreme parameter regimes , all stellar convection zones are expected to undergo vigorous dynamo action . dynamo - generated magnetic fields might suppress the polar jets directly by means of magnetic tension or indirectly by inhibiting the intrinsic self - organization processes of rapidly - rotating hydrodynamic turbulence ( e.g. the inverse cascade of kinetic energy and the anisotropic suppression of this cascade that gives rise to the rhines scale ) . however , these jets do not appear to arise from the inverse cascade of smaller - scale vorticies . whether or not they occur in the presence of magnetism is a topic for future work . though chorus does not currently have the capability to solve the full set of mhd equations , we intend to implement this capability in the future . the amplitude of the differential rotation is not very sensitive to either the rotation rate or the oblateness . if we decrease @xmath14 and @xmath42 as we increase the rotation rate in order to mainin a roughly constant supercriticality , we find that the differential rotation scales as @xmath393 . this result is for spherical ( non - oblate ) simulations and is qualitatively consistent with previous global convection simulations and stellar observations ( section [ sec : dr1 ] ) . alternatively , if @xmath14 and @xmath42 are held constant , we find no clear scaling of @xmath0 versus @xmath326 ( fig . [ fig : delta_omega ] ) . however , the fraction of the total kinetic energy contained in the differential rotation , drke / ke , does increase monotonically in these same spherical simulations as @xmath326 is increased from 0.526 in case @xmath144 to 0.681 to case @xmath145 ( table [ tab : diagnostics ] ) . it is interesting that the oblateness tends to suppress this increase of drke / ke with @xmath326 . for the oblate series of simulations , @xmath146 through @xmath147 , the drke / ke ratio saturates at a maximum value of 0.61 for @xmath344 ( table [ tab : diagnostics ] ) . this trend is also visible in the surface differential rotation @xmath0 , which decreases slightly beyond about @xmath394 ( fig . [ fig : delta_omega ] ) . the fractional differential rotation @xmath395 decreases with increasing rotation for both the spherical and the oblate stars . furthermore , we argue that the differential rotation is likely to be too weak to have a significant effect on the oblateness ( appendix [ appen : a ] ) . we acknowledge that our simulations certainly have their limitations , the most important being the relatively laminar parameter regimes and the absence of magnetic fields . however , as the first simulations of their kind , we regard these as a baseline for future work . we have identified interesting features that warrant further study , such as a departure from the classical gravity darkening paradigm for late - type stars and the presence of polar jets induced by oblateness . and , we have demonstrated some of the potential of the new chorus code , which promises to be a unique and powerful tool for the ongoing investigation of stellar and planetary convection . we thank matthias rempel and the anonymous referee for helpful comments on the manuscript . junfeng wang is funded by a newkirk graduate fellowship from the national center for atmospheric center ( ncar ) . chunlei liang is grateful for the faculty start - up fund provided by the george washington university and a recent career award ( award number 1554005 ) from the national science foundation . ncar is operated by the university of corporation for atmospheric research under sponsorship of the national science foundation .

this has been achieved by exploiting the capabilities of the new compressible high - order unstructured spectral difference ( chorus ) code . we find that the convection redistributes the heat flux emitted from the outer surface , leading to an enhancement of the heat flux in the polar and equatorial regions . furthermore , we argue that this level of differential rotation is not enough to have a significant impact on the oblateness of the star .

we present the first global 3d simulations of thermal convection in the oblate envelopes of rapidly - rotating solar - type stars . this has been achieved by exploiting the capabilities of the new compressible high - order unstructured spectral difference ( chorus ) code . we consider rotation rates up to 85% of the critical ( breakup ) rotation rate , which yields an equatorial radius that is up to 17% larger than the polar radius . this substantial oblateness enhances the disparity between polar and equatorial modes of convection . we find that the convection redistributes the heat flux emitted from the outer surface , leading to an enhancement of the heat flux in the polar and equatorial regions . this finding implies that lower - mass stars with convective envelopes may not have darker equators as predicted by classical gravity darkening arguments . the vigorous high - latitude convection also establishes elongated axisymmetric circulation cells and zonal jets in the polar regions . though the overall amplitude of the surface differential rotation , @xmath0 , is insensitive to the oblateness , the oblateness does limit the fractional kinetic energy contained in the differential rotation to no more than 61% . furthermore , we argue that this level of differential rotation is not enough to have a significant impact on the oblateness of the star .

astro-ph9710371

r

the highest s / n images of the silhouettes obtained by mo96 were through a narrow - band h@xmath0 ( @xmath46565 ) filter , admitting the full emission line flux from the bright orion nebula region , while minimizing continuum emission from the central stars , or in the case of 114 - 426 , its polar lobes . the brightest near - ir counterpart is the pa@xmath0 line at 1.87 , which can not be detected from the ground due to atmospheric absorption . for typical region ionization parameters ( 10@xmath5k , 10@xmath5@xmath6 , case b ) and @xmath7@xmath2 foreground to the nebula , the detected photon flux at pa@xmath0 should be @xmath260% of that at h@xmath0 : the brightest equivalent line available to ground - based observers ( br@xmath8 at 2.16 ) would be a further factor of ten fainter ( osterbrock 1989 ) . the pa@xmath0 1.87 image of 114 - 426 is shown in figure 1 with the h@xmath0 ( @xmath46565 ) image from mo96 . the s / n in the p@xmath0 image is poor ( @xmath95:1 ) since the integration time was short ( 288 sec ) , and the nic1 image scale of 0.0432 arcsec / pixel over - resolved the 0.19 arcsec fwhm diffraction - limited resolution of the telescope at 1.87 . nevertheless , the silhouette is clearly detected , allowing a preliminary measurement of its size . the data were binned by a factor of two to better match the appropriate pixel size ( 2 pixels per fwhm ) and then averaged across the minor axis . the resulting 1d major axis profile had high enough s / n to show the two ends of the disk as sharp dips separated by 1.8 arcsec . as discussed in detail by mo96 , the apparent size and structure of a silhouette disk is a convolution of its real form with the instrumental point spread function , and following mo96 , we adjusted the parameters of a model edge - on disk convolved with a model hst+nicmos psf calculated using the tinytim software ( krist & hook 1997 ) until the major axis length was reproduced . the resulting best - fit model disk has a major axis size of @xmath10800au at 1.87 , @xmath220% less than the 1012au measured at 0.6 ( mo96 ) . the same procedure used on the 2 continuum image ( section [ sec : continuum ] ) yielded the same result to within 5% . finally , we verified the overall procedure by degrading the high s / n [ oiii ] image from mo96 to the same spatial resolution and s / n as the pa@xmath0 image , then performing the same fitting process , before retrieving the correct size for the disk at optical wavelengths . the optical continuum image of 114 - 426 showed faint polar lobes , interpreted as reflection nebulae of tenuous dust above and below the plane of the disk , illuminated by the otherwise unseen central star ( mo96 ) . similar reflection nebulae are seen above and below the plane of an edge - on disk in the hh30 system ( burrows 1996 ) . the wavelength dependent morphology and polarization structure of the lobes in 114 - 426 should allow us to probe the underlying form of the disk , the geometry of polar cavities , the grain size , and scattering function . the near - ir broad - band continuum images , along with the f547 m image from mo96 , are shown in figure 2 in grayscale and contour forms . as the wavelength increases , three effects are seen . first , the initially fainter se polar lobe increases in brightness until it equals then outshines the intensity of the nw lobe . the peak intensities in the lobes ( after background subtraction ) are in the ratios 7.3:1 , 2.2:1 , 1.2:1 , and 0.85:1 for the nw : se lobes , at 0.57 , 1.1 , 1.6 , and 2.0 respectively . second , the nebulae move closer together , as the reduced extinction allows us to probe closer to the disk midplane : the separations of the peak pixels in the two lobes are at 0.64 , 0.43 , 0.40 , and 0.32 arcsec at 0.57 , 1.1 , 1.6 , and 2.0 respectively . third , the nebulae appear to flatten from conical to slab - like . these features can be compared to model disks and envelopes ( lazareff , pudritz , & monin 1990 ; whitney & hartmann 1992 [ wh92 ] , 1993 [ wh93 ] ; fischer , henning , & yorke 1996 [ fhy96 ] ) . the general broad fan shape and increasing flatness of the nebulae are best reproduced by model sh of fhy96 , a thin , massless disk ( in comparison to the central star ) in keplerian rotation , with an envelope and broad polar cavities . models with thick , massive disks have more polar material and result in images with too much elongation perpendicular to the disk . the same is true of models with just a narrow , cylindrical polar hole rather than a broader , so - called `` streamline '' cavity ( wh93 ) . since the central star in 114 - 426 is not seen , the disk must lie within a few degrees of edge - on , as the thin disk of the sh model does not occult the central star unless this condition is met ( fhy96 ) . this degree of alignment is also argued for on the grounds that the two lobes have nearly equal brightness in the near - ir . the asymmetry between the two lobes in the optical continuum ( figure 2a ) can probably explained by asymmetries in the outer , more diffuse parts of the envelope , perhaps due to external effects in the region .

continuum images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predictions for reflection nebulae in a diffuse envelope with large polar cavities , surrounding a thin , massless , keplerian disk , centered on an otherwise hidden central star .

we present the first high - resolution near - infrared images of the edge - on silhouette circumstellar disk , orion 114 - 426 , made using nicmos on the _ hubble space telescope_. images taken against the bright nebular background of the ionized hydrogen pa@xmath0 line at 1.87 show the major axis of the disk to be approximately 20% smaller than at 0.6 , from which we deduce the structure of the edge of the disk . continuum images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predictions for reflection nebulae in a diffuse envelope with large polar cavities , surrounding a thin , massless , keplerian disk , centered on an otherwise hidden central star . we make use of our observations and reasonable assumptions about the underlying disk structure to show that the disk mass is at least 10 and plausibly @xmath1 . 6.25 in 8.9 in subject headings : accretion , accretion disks circumstellar matter ism : individual ( orion nebula ) stars : formation , pre - main sequence infrared : ism : continuum , lines and bands

astro-ph9710371

c

the disk appears @xmath220% smaller at 1.87 than at 0.6 , and thus we are clearly resolving structure in its outer parts . in order to understand the implications of these observations , we need to examine the theoretical expectations . for a thin , massless , keplerian disk that is hydrostatically supported and vertically isothermal ( shakura & sunyaev 1973 ; pringle 1981 ; lazareff 1990 ) , the density @xmath11 as a function of radius , @xmath12 , and height above the midplane , @xmath13 , is : @xmath14 \label{eq : one } \ ] ] where @xmath15 is the midplane density at the outer disk radius , @xmath16 , and @xmath17 is the disk scale - height : @xmath18 where @xmath19 is the scale - height at @xmath16 . the disk surface density is then : @xmath20 for typical orion nebula dust grains ( r=5 ; cardelli , clayton , & mathis 1989 ) , the extinction at 1.87 is one sixth of that at 0.6 , and thus achieving the same effective optical depth requires six times higher column density at the longer wavelength . for a face - on disk with unity optical depth at 0.6 at 506au radius , eq.[eq : three ] shows that the equivalent optical depth at 1.87 would occur at 46au , the disk would appear much smaller in the near - ir . for an edge - on disk , the calculation is harder : we are probing the midplane density of the disk , not the surface density , and the line - of - sight through the disk at a given `` impact parameter '' ( the distance off - center ) integrates over different densities at different radii . assuming the disk is truncated at some outer radius , we can integrate the total column density through the midplane as a function of the impact parameter , @xmath21 . we have calculated profiles for disks in which the midplane density scales as @xmath22 , with @xmath23 and @xmath24 ( figure 3 ) . these values were chosen since simple analytical integrals exist in each case , but they also closely correspond to plausible disk models : @xmath25 would yield a surface density independent of radius ; @xmath26 yields the canonical @xmath27 ; @xmath28 yields @xmath29 , a commonly assumed density law for more massive circumstellar disks ( adams , shu , & lada 1988 ) . rough power laws can be fit to the inner section of each curve in fig.3 , with the column density increasing as @xmath30 , and @xmath31 , and @xmath32 corresponding to @xmath23 and @xmath24 respectively . in the canonical case of @xmath33 , a disk with unity optical depth at 506au at 0.6 would have the same optical depth at 84au at 1.87 . thus , even though an edge - on disk will shrink less with wavelength than a face - on one , it is clear that for 114 - 426 , the observed decrease in size of only 20% ( @xmath34dex ) for an increase in density of six ( 0.78dex ) would require @xmath35 , and thus @xmath36 and @xmath37 , quite inconsistent with conventional understanding of disk structure . the exception comes near the edge of a disk , where the integrated column density rises sharply as the path length increases most rapidly . indeed , fig.3 shows that in the @xmath38 case , the density _ does _ increase by the required factor of six within 80% of the outer radius , as observed . thus , the observed shift between the optical edge at 506au and the infrared edge at 400au could still be consistent with the midplane density following the canonical power law for a thin , massless disk , _ as long as _ the disk is physically truncated somewhere near the optical edge . as discussed by mo96 , it seems plausible that the disk may be truncated due to physical processes present in the orion nebula region and/or trapezium cluster , and it may be possible to ascertain which particular process is responsible from our future hst observations , which will trace the radial structure of 114 - 426 over a full order of magnitude in limiting column density . the mass of the 114 - 426 disk remains unknown : in particular , does it exceed the @xmath20.01 of the minimum mass solar nebula ( mmsn ) , is it massive enough to form a planetary system similar to our own ? odell & wen ( 1994 ) and mo96 discuss how the mass of a silhouette disk can be roughly estimated , noting that the minimum intensity seen towards it is typically @xmath210% of that of the background region . assuming this to be background emission attenuated by the disk , a line - of - sight column density is calculated for each point in the silhouette , and summing over the whole disk area , a total mass is estimated . however , virtually all of this `` disk light '' is an artifact , as the the background emission is blended into the disk by the instrumental psf ( mo96 ) . thus the usefulness of the `` transmission technique '' is diminished , but it at least provides an absolute _ lower - limit _ mass , an important counterpoint to the results from millimeter interferometry which are , as yet , generally provide only _ upper - limit _ masses for disks in the trapezium cluster ( mundy , looney , & lada 1995 ; lada 1996 ) . mo96 used the transmission technique to estimate lower - limit masses for the six silhouette disks based on their optical images . the masses were small , typically several orders of magnitude less than the mmsn . the most massive was 114 - 426 at 0.002 , but we must report here that an error was made in calculating the area and thus mass of 114 - 426 in mo96 : its minimum mass should be revised downwards to @xmath39 . ( the masses for the other disks given in table 2 of mo96 remain unaffected by this error ) . in principle , the transmission technique could be applied to our new near - ir images of 114 - 426 , resulting in a significantly _ higher _ estimate of the minimum mass . since the disk is only marginally smaller at 1.87 , the reduced near - ir extinction should lead to a higher mass , on the order of the factor of six in @xmath40 . however , the present images are not good enough to make such estimates : the pa@xmath0 image has very poor s / n , making a reliable measure of the disk / background flux ratio impossible , and while the continuum images have much higher s / n , the silhouette is contaminated by the reflection nebulae , making it difficult to measure the underlying disk / background flux ratio and the true silhouette area . such calculations must wait until higher - quality pa@xmath0 data are available . in the interim , alternative approaches to estimating the disk mass can be taken . the non - detection of the central star in the pol 2 continuum image can be used to set a lower limit on the total column density through the disk midplane , depending on the intrinsic brightness of the star . the integrated flux from the two reflection nebulae is = , which clearly only represents a fraction of the flux we would see from the central star if it had no disk . some estimate of this fraction can be made from wh92 and wh93 , who tabulate @xmath41 ( the total flux observed as a fraction of the flux that would be seen if the star had no disk or envelope ) for a variety of models . while @xmath41 ranges from 0.0110% depending on the disk and envelope structure , inclination angle , grain properties , and total opacity , @xmath21% is typical for models inferred for 114 - 426 ( near edge - on flared disk , wh92 models 3,4 with @xmath42 , perhaps with a tenuous envelope with broad polar cavities , wh93 models 58 ) . the inferred intrinsic brightness of the central star is then @xmath2 , corresponding to a 1myr old , @xmath21.5 star at 450pc ( dantona & mazzitelli 1994 ) . since the star is undetected in the 2 image to a 5@xmath43 point source detection limit of = , the implied line - of - sight extinction towards it is @xmath44 at 2 , or @xmath45 . assuming the disk is exactly edge - on , the corresponding column density through the disk midplane to the central star is @xmath46@xmath47 ( assuming 1@xmath48@xmath47 ) . the disk outer radius , @xmath49au , is known from the data of mo96 . the same data can be used to determine @xmath19 , the scale - height at @xmath16 : we fit a 1d average minor axis profile across the [ oiii ] image of 114 - 426 ( fig.4 of mo96 ) with a gaussian characterized by eq.[eq : two ] , yielding @xmath50au . finally , we assume the disk inner radius , @xmath51au : since the surface density increases towards the center with a power @xmath52 , our results are not too sensitive to this assumption . integrating eq.[eq : one ] ( with @xmath53 ) through the midplane , we calculate the midplane density at the outer edge , @xmath54@xmath6 . then integrating eq.[eq : three ] between @xmath16 and @xmath55 , the total number of particles ( hi+2h@xmath56 ) is @xmath57 , yielding a mass estimate of @xmath58 g or @xmath59 . although it is clear that very little mass is required to render the central star invisible , the disk mass is likely to be significantly greater . using the analytical solution for the total column density seen through the midplane of an edge - on disk in the @xmath33 case ( section [ sec : structure ] ) , and assuming @xmath60@xmath6 at an outer radius of 506au , we obtain values @xmath61@xmath47 or @xmath62 just inside the edge . yet the disk must have a significantly higher column density there to be _ seen _ as an edge : the results of mo96 show that the attenuation at the edge of the disk is at least 85% , equivalent to @xmath63 , in turn implying @xmath64@xmath6 . this is a plausible value if ( for example ) the location of the disk edge is set by pressure balance with the surrounding region : assuming a temperature and density for the latter of 10@xmath5k and 10@xmath5@xmath6 and an outer disk temperature of 10100k , densities at the disk edge of @xmath65@xmath66@xmath6 would be predicted . inserting @xmath64@xmath6 into eq.[eq : three ] along with our other derived disk parameters yields a disk mass of @xmath67 g or @xmath1 . while still considerably less than the mmsn , this is a lower limit , and the disk might be more massive . however , our present simple calculations based on lower - limit extinction measurements alone can not be pushed much further . burrows ( 1996 ) have shown for hh30 that more realistic mass estimates can be made by fitting the structure of the polar reflection nebulae , in particular the width of the dark lane of obscuration between them , and such an approach will be taken with 114 - 426 when our higher s / n and resolution cycle 7 hst data are available . ultimately , the most meaningful estimate of disk mass must come from measurements of optically thin tracers at millimeter wavelengths : such observations have been obtained for 114 - 426 and will be discussed in a future paper .

we present the first high - resolution near - infrared images of the edge - on silhouette circumstellar disk , orion 114 - 426 , made using nicmos on the _ hubble space telescope_. images taken against the bright nebular background of the ionized hydrogen pa@xmath0 line at 1.87 show the major axis of the disk to be approximately 20% smaller than at 0.6 , from which we deduce the structure of the edge of the disk . we make use of our observations and reasonable assumptions about the underlying disk structure to show that the disk mass is at least 10 and plausibly @xmath1 . 6.25 in 8.9 in subject headings : accretion , accretion disks

we present the first high - resolution near - infrared images of the edge - on silhouette circumstellar disk , orion 114 - 426 , made using nicmos on the _ hubble space telescope_. images taken against the bright nebular background of the ionized hydrogen pa@xmath0 line at 1.87 show the major axis of the disk to be approximately 20% smaller than at 0.6 , from which we deduce the structure of the edge of the disk . continuum images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predictions for reflection nebulae in a diffuse envelope with large polar cavities , surrounding a thin , massless , keplerian disk , centered on an otherwise hidden central star . we make use of our observations and reasonable assumptions about the underlying disk structure to show that the disk mass is at least 10 and plausibly @xmath1 . 6.25 in 8.9 in subject headings : accretion , accretion disks circumstellar matter ism : individual ( orion nebula ) stars : formation , pre - main sequence infrared : ism : continuum , lines and bands

hep-lat0008004

i

one of the main objects in the yang mills theory is the wilson loop or holonomy ; it is defined as a path - ordered exponent , w_r= ida_^at^a , [ wl1]where @xmath3 with @xmath4 parametrizes the closed contour , @xmath5 is the yang mills field ( or connection ) and @xmath6 are the generators of the gauge group in a given representation @xmath7 whose dimension is @xmath8 . it is generally believed that in three and four dimensions the average of the wilson loop in a pure yang mills quantum theory exhibits an area behavior for large and simple contours ( like flat rectangular ) . this should be true not for all representations but those with ` @xmath9-ality ' nonequal zero ; in the simplest case of the @xmath10 gauge group these are representations with half - integer spin @xmath11 . one of the difficulties in proving the asymptotic area law for the wilson loop in half - integer representations ( and proving that in integer representations it is absent ) is that the wilson loop is a complicated object by itself : it is impossible to calculate it analytically in a general non - abelian background field . meanwhile , it is sometimes easier to average a quantity over an ensemble than to calculate it for a specific representative . however , in case of the wilson loop the path - ordering is a serious obstacle on that way . a decade ago we have suggested a formula for the wilson loop in a given background belonging to any gauge group and any representation @xcite . in this formula the path ordering along the loop is removed , but at the price of an additional functional integration over all gauge transformations of the given non - abelian background field . this formula is discussed below , in section 2 . furthermore , the wilson loop can be presented in a form of a surface integral @xcite , see section 3 . we call this representation the non - abelian stokes theorem . it is quite different from previous interesting statements @xcite also called by their authors ` non - abelian stokes theorems ' but which involve surface ordering . our formula has no surface ordering . a classification of ` non - abelian stokes theorems ' for arbitrary groups and their representations has been given recently by kondo et al . @xcite who used the naturally arising techniques of flag manifolds . though these formulae usually do not facilitate finding wilson loops in particular backgrounds , they can be used to average over ensembles of yang mills configurations , and in more general settings , see e.g. @xcite . our formula for the wilson loop have been recently questioned by faber , ivanov , troitskaya and zach ( fitz ) @xcite . in section 4 we show that all points of their criticism are due to mistakes in mathematics , which we thoroughly locate , one by one . an alternative formula for the wilson loop proposed by fitz is also mathematically inconsistent , and we pinpoint their concrete errors . finally , in section 5 we present a variant of our formula for the wilson loop in lattice regularization . it appears to be very similar to that presented in section 2 .

its validity has been recently questioned by faber , ivanov , troitskaya and zach . we demonstrate that all points of their criticism are based on mistakes in mathematics . finally , we derive a variant of our formula for the wilson loop in lattice regularization .

we present the non - abelian stokes theorem for the wilson loop in various forms and discuss its meaning . its validity has been recently questioned by faber , ivanov , troitskaya and zach . we demonstrate that all points of their criticism are based on mistakes in mathematics . finally , we derive a variant of our formula for the wilson loop in lattice regularization . nordita-2000/64 he 2true cm * on the non - abelian stokes theorem * 1.5true cm * dmitri diakonov@xmath0 and victor petrov@xmath1 * + 1true cm @xmath2 _ nordita , blegdamsvej 17 , dk-2100 copenhagen , denmark _ + .5true cm @xmath1 _ st.petersburg nuclear physics institute , gatchina 188 350 , russia _ + .5true cm e - mail : diakonov@nordita.dk , victorp@thd.pnpi.spb.ru 1.5true cm

astro-ph0310626

c

@xcite , @xcite suggested , from the available material at these times , that ll and belongs to a class of dwarf novae with large outburst amplitudes . this identification , however , becomes dubious upon closer examination of the present material . firstly , @xcite used the maximum outburst magnitude of @xmath10 = 13.8 , which is clearly an overestimated caused by an incorrect zero point . the present observation , calibrated on the modern @xmath4 scale , suggests a much fainter outburst maximum of @xmath4 = 14.314.5 . the bright magnitude quoted by @xcite needs to be treated with special caution , because the observation probably used blue - sensitive plates ( hence would not adequately represent visual magnitudes ) , and because the published magnitudes were very likely only preliminary measurements with probable errors of @xmath01 mag . secondly , the quiescent magnitude in @xcite , @xcite was likely underestimated . the object is already readily recognized on paper reproduction of poss i red and blue prints ( section [ sec : intro ] ) , which suggests a significantly brighter magnitude than @xmath11 20 . the modern magnitude estimates ( usno b1.0 : @xcite ) give red and blue magnitudes of 19.26 and 19.5919.78 , respectively . these measurements are in line with the author s estimate on poss i paper prints . the usno b1.0 magnitude correspond to @xmath4 = 19.4 . the outburst frequency looks like to be small . the only recorded outbursts up to now were in 1979 september @xcite and in 1993 december ( this work ) . in spite of intensive monitoring mainly by the vsnet @xcite members , no definite outburst has been recorded up to 2003 . even considering the unavoidable seasonal observational gaps , the detected outbursts are much less frequent than in most dwarf novae , and may be comparable to those of the wz sge - type dwarf novae . very recently , @xcite reported the detection of photometric periodicity of 0.055053(6 ) d. assuming that this periodicity represents the orbital period ( @xmath12 ) , = 0.055053(6 ) d to likely represent @xmath12 because of its proximity to what would be expected from the superhump period using the known relation @xcite . ] the fractional superhump excess @xmath13 amounts to 3.5(1 ) % . this value is exceptionally large for an su uma - type system with @xmath14 = 0.05697 d ( cf . this conclusion seems to further support the presence of a rather massive secondary star @xcite , and is likely incompatible with the earlier claim of a brown - dwarf secondary @xcite . as shown in subsection [ sec : outprop ] , the outburst cycle length of ll and is likely comparable to rarely outbursting wz sge - type dwarf novae . the short superhump period ( 0.05697 d ) is also comparable to those of wz sge - type dwarf novae @xcite . the object , however , shows remarkable difference from typical wz sge - type dwarf novae in its small ( @xmath0 5 mag ) outburst amplitude ( compared to @xmath0 8 mag for wz sge - type dwarf novae ) , short ( 9@xmath12 d ) duration of the superoutburst ( compared to @xmath1520 d for wz sge - type dwarf novae , cf . @xcite ; @xcite ; @xcite ; @xcite ) . the combination of long outburst cycle length , low outburst amplitude , and short duration of a superoutburst resembles that of an unusual su uma - type dwarf nova go com ( a. imada et al . , in preparation ) . in go com , the small scale of the recorded outburst , in spite of the long preceding quiescence , is interpreted as the possible consequence of the extraction of disk mass ( e.g. via evaporation ) during quiescence ( a. imada et al . , in preparation ) . this scenario was initially proposed by @xcite to explain the long outburst intervals in systems resembling wz sge - type stars , but now looks more applicable to systems such as go com and ll and [ see also discussions by @xcite ; @xcite on the difficulty of reproducing wz sge - like outbursts with a leaky " accretion disk , as in @xcite ] . by adopting the large fractional superhump excess ( subsection [ sec : shexcess ] ) , the secondary star of ll and is likely slightly too massive for this period ( figure [ fig : excess ] ) . we know at least two well - established examples of such short - period dwarf novae with unusually massive or luminous secondaries ( ei psc : @xcite ; @xcite ; @xcite and qz ser : @xcite ) . both objects have low outburst frequencies than would be expected from their binary parameters . @xcite and @xcite suggested that ei psc may be the first identified object following the hypothetical evolutionary track @xcite containing an mass donor having an evolved core . ll and may be an object filling the evolutionary missing link between qz ser and ei psc ( see also figure 4 in @xcite ) , and finally to the double - degenerate am cvn stars ( @xcite ; @xcite ) . further spectroscopic determination of the orbital parameters is encouraged . the author is grateful to t. vanmunster for promptly notifying us of the rare outburst of ll and . we are also grateful to a number of observers who have been reporting their observations to the vsnet , and to dr . t. takata for helping the observation . this work is partly supported by a grant - in - aid ( 13640239 , 15037205 ) from the japanese ministry of education , culture , sports , science and technology . this research has made use of the digitized sky survey producted by stsci , and the vizier catalogue access tool .

although ll and has been proposed to be a wz sge - type dwarf nova based on its low outburst frequency , our new analysis indicates that the outburst amplitude ( @xmath0 5 mag ) and outburst duration ( 9@xmath12 d ) are much smaller and shorter than in typical wz sge - type dwarf novae . we suspect that the unusual outburst properties of ll and might be explained by assuming a leaky disk " in quiescence , which was originally proposed to explain the prototypical wz sge - type outbursts . by combination with the recent suggestion of the orbital period , the fractional superhump excess is found to be 3.5(1 ) % , which is unusually large for this short - period system . ll and may be an object filling the gap in the evolutionary track , which has recently been proposed to explain the unusual ultracompact binaries with an evolved mass donor .

we present time - resolved ccd photometry of ll and during its 1993 outburst . the observation revealed the presence of superhumps with a period of 0.05697(3 ) d. this period is one of the smallest among the hydrogen - rich dwarf novae . although ll and has been proposed to be a wz sge - type dwarf nova based on its low outburst frequency , our new analysis indicates that the outburst amplitude ( @xmath0 5 mag ) and outburst duration ( 9@xmath12 d ) are much smaller and shorter than in typical wz sge - type dwarf novae . we suspect that the unusual outburst properties of ll and might be explained by assuming a leaky disk " in quiescence , which was originally proposed to explain the prototypical wz sge - type outbursts . by combination with the recent suggestion of the orbital period , the fractional superhump excess is found to be 3.5(1 ) % , which is unusually large for this short - period system . ll and may be an object filling the gap in the evolutionary track , which has recently been proposed to explain the unusual ultracompact binaries with an evolved mass donor .

1006.0169

i

activity in galactic nuclei is fuelled by a reservoir of low angular momentum gas , but it is unclear how such reservoirs build up . fast outflows from ob stars , supernovae or agn activity can clear out nuclear ism @xcite . gas in the nucleus can also be quickly consumed by star formation @xcite or driven outwards by positive gravitational torques @xcite . if the gas in the reservoir originates outside the nucleus , multiple mechanisms operating on different distance- and time - scales , such as bars feeding nuclear rings @xcite , radiation drag @xcite or interactions @xcite are required . from observations , around @xmath3 of all galactic nuclei in the local universe exhibit low luminosity nuclear activity @xcite , so the mechanism promoting nuclear gas build up is likely to be simple and on - going . in this letter we propose a new mechanism for delivery of gas to the galactic nucleus . we show that the impact of a warm halo cloud ( whc ) , containing @xmath4 , on the central regions of a galaxy will fuel nuclear activity . we develop a simplistic model of this phenomenon to demonstrate its likely importance . while there remains considerable uncertainty in whc parameters , we show that for plausible input parameters , a direct hit by a single whc on the center of a galaxy will supply fuel for star formation and radiatively inefficient accretion onto the central black hole . since whc bombardment of galaxies must occur , some fraction of the low luminosity activity observed in galactic nuclei must be due to whc impacts on galactic nuclei .

we propose a new mechanism for the delivery of gas to the heart of galactic nuclei . the impact of an accreting warm halo cloud originating far in the galactic halo can , depending on mixing , produce a nuclear starburst of low metallicity stars as well as low luminosity accretion onto the central black hole .

we propose a new mechanism for the delivery of gas to the heart of galactic nuclei . we show that warm halo clouds must periodically impact galactic centers and potentially deliver a large ( @xmath0 ) mass of gas to the galactic nucleus in a singular event . the impact of an accreting warm halo cloud originating far in the galactic halo can , depending on mixing , produce a nuclear starburst of low metallicity stars as well as low luminosity accretion onto the central black hole . based on multiphase cooling around a @xmath1cdm distribution of halos we calculate the nuclear impact rate , the mass captured by the central black hole and the fraction of active nuclei for impacting cloud masses in the range @xmath2 . if there is moderate braking during cloud infall , our model predicts an average fraction of low luminosity active nuclei consistent with observations .

1006.0169

c

in this letter we introduce a new mechanism that delivers large quantities of gas to galactic nuclei on astrophysically interesting timescales . we show that a single warm halo cloud ( whc ) impact on a galactic bulge could potentially deliver a large mass ( @xmath4 ) of gas to the central regions of a galactic nucleus , in a singular event . although there are considerable uncertainties in the parameters of warm halo clouds , some representative numbers suggest that the impacts occur on astrophysically interesting timescales and at a rate that must account for some or even all of the low luminosity activity observed in galactic nuclei in the local universe . based on analytic @xmath1cdm calculations of cooling halos , our model predicts an impact rate relatively independent of galaxy mass . our model also predicts that larger mass black holes ( @xmath82 ) can capture significant fractions of the impacting cloud mass at some critical value depending on the nuclear braking ( @xmath49 ) . at this critical value , our model predicts the highest eddington ratios . below this critical mass , our model predicts that most of the cloud mass will not accrete onto the black hole . instead , this material will mix with the ism in the nuclear bulge or induce star formation , which may lead to delayed episodes of high eddington ratio accretion . finally , our model predicts that , for a reasonable range of cloud masses , densities and braking , the fraction of supermassive black holes accreting at very low eddington ratios in the local universe could be around @xmath83 , which agrees with observations @xcite .

we show that warm halo clouds must periodically impact galactic centers and potentially deliver a large ( @xmath0 ) mass of gas to the galactic nucleus in a singular event . if there is moderate braking during cloud infall , our model predicts an average fraction of low luminosity active nuclei consistent with observations .

we propose a new mechanism for the delivery of gas to the heart of galactic nuclei . we show that warm halo clouds must periodically impact galactic centers and potentially deliver a large ( @xmath0 ) mass of gas to the galactic nucleus in a singular event . the impact of an accreting warm halo cloud originating far in the galactic halo can , depending on mixing , produce a nuclear starburst of low metallicity stars as well as low luminosity accretion onto the central black hole . based on multiphase cooling around a @xmath1cdm distribution of halos we calculate the nuclear impact rate , the mass captured by the central black hole and the fraction of active nuclei for impacting cloud masses in the range @xmath2 . if there is moderate braking during cloud infall , our model predicts an average fraction of low luminosity active nuclei consistent with observations .

cmp-lg9705005

i

we are concerned here with the issue of classifying documents into categories . more precisely , we begin with a number of categories ( e.g. , ` tennis , soccer , skiing ' ) , each already containing certain documents . our goal is to determine into which categories newly given documents ought to be assigned , and to do so on the basis of the distribution of each document s words . many methods have been proposed to address this issue , and a number of them have proved to be quite effective ( e.g.,@xcite ) . the simple method of conducting hypothesis testing over word - based distributions in categories ( defined in section 2 ) is not efficient in storage and suffers from the _ data sparseness problem _ , i.e. , the number of parameters in the distributions is large and the data size is not sufficiently large for accurately estimating them . in order to address this difficulty , @xcite have proposed using distributions based on what we refer to as _ hard clustering _ of words , i.e. , in which a word is assigned to a single cluster and words in the same cluster are treated uniformly . the use of hard clustering might , however , degrade classification results , since the distributions it employs are not always precise enough for representing the differences between categories . we propose here to employ _ soft clustering _ , i.e. , a word can be assigned to several different clusters and each cluster is characterized by a specific word probability distribution . we define for each category a _ finite mixture model _ , which is a linear combination of the word probability distributions of the clusters . we thereby treat the problem of classifying documents as that of conducting statistical hypothesis testing over finite mixture models . in order to accomplish hypothesis testing , we employ the em algorithm to efficiently and approximately calculate from training data the maximum likelihood estimates of parameters in a finite mixture model . our method overcomes the major drawbacks of the method using word - based distributions and the method based on hard clustering , while retaining their merits ; it in fact includes those two methods as special cases . experimental results indicate that our method outperforms them . although the finite mixture model has already been used elsewhere in natural language processing ( e.g. @xcite ) , this is the first work , to the best of knowledge , that uses it in the context of document classification .

we propose a new method of classifying documents into categories . we define for each category a _ finite mixture model _ based on _ soft clustering _ of words . we treat the problem of classifying documents as that of conducting statistical hypothesis testing over finite mixture models , and employ the em algorithm to efficiently estimate parameters in a finite mixture model .

we propose a new method of classifying documents into categories . we define for each category a _ finite mixture model _ based on _ soft clustering _ of words . we treat the problem of classifying documents as that of conducting statistical hypothesis testing over finite mixture models , and employ the em algorithm to efficiently estimate parameters in a finite mixture model . experimental results indicate that our method outperforms existing methods .

hep-th0406193

i

studies of interactions between d - branes and closed strings are quite important from various points of view . the interactions play a crucial role in finding non - trivial relationships between open strings and closed strings such as ads / cft @xcite and recently - proposed open - closed dualities @xcite , for example . studies of the interactions are also important to analyze the dynamics of the systems of multiple d - branes . however , almost all analyses of the interactions have been carried out by considering static d - branes , and it is a long - standing problem to describe the back reaction of the d - branes . a d - brane in the worldsheet description is just a boundary of the worldsheet with dirichlet boundary condition , and the d - brane is treated as an infinitely heavy classical source of closed strings ; the position , or the collective coordinate , of the d - brane is fixed at a point in the target space in the dirichlet direction . there are several attempts to describe the back reaction of d - branes . some of them are based on the conformal field theory on the worldsheet @xcite . in ref . @xcite , the disk amplitude for the scattering of closed string states from a d - particle is computed in the bosonic string theory in which the collective coordinate of the d - particle is quantized . the current conservation condition of the d - particle is obtained by demanding the conformal invariance of the amplitude in that work . momentum conservation condition between the closed strings and the d - particle is described by using the zero - mode integral in the path integral of the trajectory of the d - particle . attempts to obtain the momentum conservation condition between closed strings and a d - brane from the viewpoint of conformal invariance can be found in refs . an annulus amplitude for the scattering of the closed strings from the d - brane is considered and a variant of the fischler - susskind mechanism is proposed there ; the infrared ( ir ) divergence in the open string channel of the annulus amplitude is canceled by adding an appropriate operator to the boundary of the worldsheet . the momentum conservation condition between the closed strings and the d - particle is explicitly obtained in refs . @xcite by demanding the conformal invariance of the total amplitude . in ref . @xcite , the ir divergence is canceled by adding a logarithmic operator @xcite that represents the recoil of the d - particle @xcite . however , it is also pointed out in ref . @xcite that the divergence does not exist in the case of d@xmath0-brane with @xmath1 . in ref . @xcite , the energy conservation condition is also obtained as well as the momentum conservation condition in the case of d - particle , explicitly . however , there is still room to clarify how to define the initial momentum of the d - particle there . further investigation along the ideas of refs . @xcite is still important for deeper understanding of recoil of d - branes . some applications of d - brane recoil to other topics , and related works are found in refs . @xcite . a target - space theory that handles second - quantized closed strings with dynamical d - branes may provide us a description of back reaction of d - branes . some arguments on back reaction and recoil of d - branes along this approach is found in ref . @xcite . in the present work , we propose an alternative method to describe the scattering process between a d - brane and closed strings together with the back reaction of the d - brane in the bosonic string theory . the impact of the closed strings in this method is represented by a source term of the low - energy effective worldvolume theory of the d - brane , and the initial and the final velocity of the d - brane are described by the time derivative of the expectation values of the massless scalar fields of the worldvolume theory . we utilize the following approximations to justify our approach : 1 . field theory limit , namely @xmath2 where @xmath3 is the typical momentum of the open strings on the d - brane . elastic limit , namely the momenta of the closed strings are small enough and no massive open - string mode is excited on the d - brane . we also assume that the closed strings do not lose their total momentum in the worldvolume directions of the d - brane , and no internal field on the d - brane gets momentum from the closed strings . non - relativistic limit , namely the velocity of the d - brane is very small . tree level approximation in the string theory , namely the string coupling is very small . the above conditions 3 and 4 means that the tension of the d - brane is very large . this is also consistent with the condition 1 . a nontrivial problem is how to represent the source term of the worldvolume theory in terms of the quantities of the closed strings . the basic idea is as follows . we consider a scattering process between the d - brane and the closed strings that creates @xmath4 massless scalar particles on the worldvolume of the d - brane . we calculate the probability of the creation of the @xmath4 massless scalar particles in the two different frameworks : one of them is the worldvolume theory of the d - brane with the source term and the other is the perturbative string theory . by comparing the two results , we obtain the relationship between the source term and the momenta of the closed strings , and we obtain the momentum conservation condition between the closed strings and the d - brane up to the relative sign of the momentum of the d - brane . one of the distinction between the present work and those in refs . @xcite is that all the diagrams we consider in the string theory are disk diagrams and we need not annulus diagrams . the organization of this article is as follows . we consider bosonic strings , and we start by considering a recoiling d - particle for simplicity . in section 2 , we consider the worldvolume theory of the d - particle and review some basic facts necessary for the later discussions . we calculate the amplitude of the creation of the @xmath4 massless particles explicitly . in section 3 , we consider the scattering process between the d - particle and the closed strings and calculate the amplitude of the process that creates @xmath4 massless open string modes on the d - particle in the framework of the string theory . in section 4 , we compare the results obtained in section 2 with those in section 3 . we show that the absolute value of the total momentum transfer from the closed strings is exactly equal to the absolute value of the change of the d - particle s momentum , within the above approximations . we also comment on the distribution of the probability of the @xmath4 massless particle creation . we see that the expectation value of the total energy of the created particles gives the kinetic energy of the d - particle , correctly . in section 5 , we generalize the results obtained for the d - particle to the case of higher dimensional d - branes . we compactify the worldvolume of the d - brane to make its mass finite , and we obtain the momentum conservation condition between the closed strings and the d - brane up to the relative sign of the momentum of the d - brane , again . we provide conclusion , several open problems and discussions in the last section .

we utilize the low - energy effective field theory on the worldvolume of the d - brane , and the velocity of the d - brane is described by the time derivative of the expectation values of the massless scalar fields on the worldvolume . the effects of the closed strings are represented by a source term for the massless fields in this method . the momentum conservation condition between the closed strings and the d - brane is derived up to the relative sign of the momentum of the d - brane . plus

we propose a new method to describe a recoiling d - brane that is elastically scattered by closed strings in the non - relativistic region . we utilize the low - energy effective field theory on the worldvolume of the d - brane , and the velocity of the d - brane is described by the time derivative of the expectation values of the massless scalar fields on the worldvolume . the effects of the closed strings are represented by a source term for the massless fields in this method . the momentum conservation condition between the closed strings and the d - brane is derived up to the relative sign of the momentum of the d - brane . plus 0.2pt minus 0.1pt addtoresetequationsection

1002.0127

i

light plays an essential role in quantum communication and is indispensable in most practical applications , for example quantum cryptography . photons are attractive carriers of quantum information because the interactions of light with the surroundings are normally weak , but for the same reason it is generally difficult to prepare , manipulate , and measure quantum states of light in a nondestructive way . repeated interactions provide a method to increase the effective coupling strength between light and matter , and the backreflection of light in a cavity thus constitutes an interesting tool , in particular , because experiments are currently moving into the strong coupling regime @xcite , where coherent dynamics takes place on a faster time scale than dissipative dynamics . in this paper we propose a versatile setup consisting of an array of cavities and passive optical elements ( beam splitters and phase shifters ) , which allows for quantum state engineering , quantum state purification , and non - destructive number resolving photon detection . the setup builds on two basic ingredients : the hong - ou - mandel interference effect @xcite generalized to input pulses containing an arbitrary number of photons and the possibility of projection onto the subspace of even or the subspace of odd photon - number states by use of cavity quantum electrodynamics in the strong coupling regime . regarding quantum state engineering , the basic setup provides a possibility to conditionally generate photon - number correlated states . more specifically , the setup allows us to project an arbitrary photonic two - mode input state onto the subspace spanned by the state vectors @xmath0 with @xmath1 . we denote this subspace by @xmath2 . the scheme is probabilistic as it is conditioned on a specific measurement outcome . the success probability equals the norm of the projection of the input state onto @xmath2 and is thus unity if the input state already lies in @xmath2 . in other words , the setup may be viewed as a filter @xcite , which removes all undesired components of the quantum state but leaves the desired components unchanged . we may , for example , use two independent coherent states as input and obtain a photon - number correlated state as output . photon - number correlated states , for example einstein - podolsky - rosen ( epr ) entangled states @xcite , are an important resource for quantum teleportation @xcite , entanglement swapping @xcite , quantum key distribution @xcite , and bell tests @xcite . in practice , however , the applicability of these states is hampered by noise effects such as photon losses . real - world applications require therefore entanglement purification . the proposed setup is very attractive for detection of losses and can in particular be used to purify photon - number entangled states on site . if a photon - number correlated state , for example an epr state , is used as input , the desired state passes the setup with a certificate , while states which suffered from photon losses are detected and can be rejected . photon losses are an especially serious problem in quantum communication over long distances . it is not only a very common source of decoherence which is hard to avoid , but also typically hard to overcome . the on - site purification protocol mentioned above can easily be adopted to a communication scenario such that it allows for the purification of a photon - number correlated state after transmission to two distant parties . purification of two mode entangled states has been shown experimentally for qubits @xcite and in the continuous variable ( cv ) regime @xcite . ( cv - entanglement purification is especially challenging @xcite . nevertheless , several proposals have been made to accomplish this task @xcite , and very recently takahashi _ et al . _ succeeded in an experimental demonstration @xcite . ) a special advantage of our scheme lies in the fact that it does not only allow for detection of arbitrary photon losses , but is also applicable to many modes such that entanglement can be distributed and purified in a network . with a small modification , the basic setup can be used for number resolved photon detection . the ability to detect photons in a number resolved fashion is highly desirable in the fields of quantum computing and quantum communication . for example , linear optics quantum computation relies crucially on photon number resolving detectors @xcite . moreover , the possibility to distinguish different photon - number states allows for conditional state preparation of nonclassical quantum states @xcite , and plays a role in bell experiments @xcite and the security in quantum cryptographic schemes @xcite . other applications include interferometry @xcite and the characterization of quantum light sources @xcite . existing technologies for photon counting @xcite such as avalanche photodiodes , cryogenic devices , and quantum dots typically have scalability problems and can not reliably distinguish high photon numbers , destroy the quantum state of light in the detection process , or do not work for optical photons . here , we present a non - destructive number resolving photo detection scheme in the optical regime . this quantum - non - demolition measurement of the photon number allows for subsequent use of the measured quantum state of light . an advantage of the counting device put forward in this work compared to other theoretical proposals for qnd measurements of photon numbers @xcite is the ability to detect arbitrarily high photon numbers with arbitrary resolution . the scheme is based on testing successively all possible prime factors and powers of primes and the resources needed therefore scale moderately with ( width and mean of the ) photon number distribution . in particular , a very precise photon number measurement can be made even for very high photon numbers by testing only few factors if the approximate photon number is known . the paper is structured as follows . we start with a brief overview of the main results in sec . [ overview ] . in sec . [ filter ] , we explain how the conditional projection onto @xmath2 can be achieved and discuss some properties of the proposed setup in the ideal limit , where the atom - cavity coupling is infinitely strong and the input pulses are infinitely long . in sec . [ detector ] , we show that a modified version of the setup can act as a non - destructive photon number resolving detector , and in sec . [ purification ] , we investigate the possibility to use the setup to detect , and thereby filter out , losses . in sec . [ nonideal ] , we consider the significance of finite input pulse length and finite coupling strength , and we obtain a simple analytical expression for the optimal choice of input mode function for coherent state input fields . section [ conclusion ] concludes the paper .

we propose and analyze a multi - functional setup consisting of high finesse optical cavities , beam splitters , and phase shifters . the basic scheme projects arbitrary photonic two - mode input states onto the subspace spanned by the product of fock states @xmath0 with @xmath1 . this protocol does not only provide the possibility to conditionally generate highly entangled photon number states as resource for quantum information protocols but also allows one to test and hence purify this type of quantum states in a communication scenario , which is of great practical importance . the scheme is especially attractive as a generalization to many modes allows for distribution and purification of entanglement in networks . in an alternative working mode

we propose and analyze a multi - functional setup consisting of high finesse optical cavities , beam splitters , and phase shifters . the basic scheme projects arbitrary photonic two - mode input states onto the subspace spanned by the product of fock states @xmath0 with @xmath1 . this protocol does not only provide the possibility to conditionally generate highly entangled photon number states as resource for quantum information protocols but also allows one to test and hence purify this type of quantum states in a communication scenario , which is of great practical importance . the scheme is especially attractive as a generalization to many modes allows for distribution and purification of entanglement in networks . in an alternative working mode , the setup allows of quantum non demolition number resolved photodetection in the optical domain .

hep-ph9608311

i

neutrino flavor oscillations in vacuum @xcite represent a viable solution @xcite to the observed deficit of the solar neutrino flux @xcite as compared to the predictions of the standard solar model @xcite . if the oscillations have a wavelength comparable to the earth orbit radius ( just - so oscillations @xcite ) , then significant distortions could arise both in the neutrino energy spectrum @xcite ( as a result of the energy - dependence of the oscillation probability ) and in the time structure of the signal @xcite ( as a result of the earth s orbit eccentricity @xcite ) . the combination of these two effects , namely time - dependent spectral distortions , could also be observable @xcite . the four pioneering solar neutrino experiments have not observed such effects . the three radiochemical experiments @xcite can not observe _ a priori _ spectral distortions since they detect only energy - integrated signals @xcite , and do not show evidence for periodic variations of the detected rates associable to just - so oscillations ( see , e.g. , @xcite ) . the neutrino - electron scattering experiment kamiokande @xcite shows no evidence for distortions in the spectrum of the scattered electrons @xcite either . however , these are low - statistics experiments , and possible vacuum oscillation effects could be hidden by the relatively large uncertainties . much higher statistics ( thousands of events per year ) will be collected with the second - generation experiments superkamiokande @xcite and sudbury neutrino observatory ( sno ) @xcite . these real - time experiments can test variations in the time structure of the signal , as well as deviations of the solar neutrino energy spectrum from its standard shape . in particular , information about the @xmath1b solar neutrino spectrum @xmath2 @xcite can be gained through the observation of the electron spectrum @xcite from the reactions @xmath3 \nu_e + d & \;\rightarrow\ ; & p+p + e^- \text { ( sno)}\ . \label{eq : snoreac}\end{aligned}\ ] ] in this work we study a specific signal of just - so oscillations which involves both time variations and shape distortions of the electron kinetic energy spectrum expected at superkamiokande and sno . we propose to separate the events detected when the earth is nearest to the sun ( perihelion @xmath0 3 months ) from those detected when the earth is farthest from the sun ( aphelion @xmath0 3 months ) . in sec . ii we introduce a near - far asymmetry @xmath4 , which is non - zero if just - so oscillations occur . in sec . iii and iv we apply our calculations of @xmath4 to the kinetic energy spectra of electrons in the superkamiokande and sno experiments respectively . we show how the sensitivity to the neutrino oscillation parameters can be increased by probing the near - far asymmetry in selected parts of the electron energy spectra . in sec . v we summarize our work and draw our conclusions . some technical aspects of our calculations are discussed in the appendices a and b.

we introduce a solar model independent near - far asymmetry , which is non - zero if just - so oscillations occur . we apply our calculations to the kinetic energy spectra of electrons induced by @xmath1b solar neutrino interactions in the superkamiokande and sudbury neutrino observatory experiments . we show that the sensitivity to the neutrino oscillation parameters can be increased by probing the near - far asymmetry in selected parts of the electron energy spectra .

we propose to study possible signals of just - so oscillations in new - generation solar neutrino experiments by separating the events detected when the earth is nearest to the sun ( perihelion @xmath0 3 months ) from those detected when the earth is farthest from the sun ( aphelion @xmath0 3 months ) . we introduce a solar model independent near - far asymmetry , which is non - zero if just - so oscillations occur . we apply our calculations to the kinetic energy spectra of electrons induced by @xmath1b solar neutrino interactions in the superkamiokande and sudbury neutrino observatory experiments . we show that the sensitivity to the neutrino oscillation parameters can be increased by probing the near - far asymmetry in selected parts of the electron energy spectra .

hep-ph9608311

i

we have studied the signals of just - so oscillations that can be observed in the superkamiokande and sno solar neutrino experiments by separating the events detected when the earth is nearest to the sun ( perihelion @xmath0 3 months ) from those detected when the earth is farthest from the sun ( aphelion @xmath0 3 months ) . we have calculated the asymmetry @xmath4 between the near and far signals by factorizing out the trivial geometrical variation of the signal , and using the entire electron energy spectrum as well as representative spectrum bins . the calculations involve the integration of the @xmath15 survival probability over time and energy . the time integration over half - year can be performed analitically . compact expressions for the near - far asymmetry have been given for @xmath67 and @xmath52 oscillations . the value of @xmath4 is solar model independent , and is different from zero if just - so oscillations occur . in the case of @xmath67 oscillations , it has been shown that measurements of the near - far asymmetry at sno and superkamiokande can probe the range @xmath153 ev@xmath51 for sufficiently large values of the mixing angle @xmath45 . a similar range of @xmath130 and @xmath35 can be probed in the presence of @xmath52 oscillations with one relevant mass scale , provided that the second mixing angle @xmath46 is not large . the sno experiment appears to be about twice as sensitive as superkamiokande to the near - far asymmetry , due to the different energetics of the @xmath114-@xmath145 absorption and @xmath114-@xmath115 scattering reactions . in both experiments , measurements of @xmath4 in selected bins of the electron energy spectrum may increase the sensitivity to the neutrino oscillation parameters . since the selection of a bin implies a loss of statistics , the net gain of binning the spectrum in measurements of @xmath4 can be assessed only after the experiments have run for some time and the data and their uncertainties are well understood . we thank p. i. krastev for useful discussions . one of us ( b.f . ) thanks the dipartimento di fisica and sezione infn di bari for kind hospitality . the work of e.l . was supported in part by infn and in part by the institute for advanced study through a hansmann membership . this work has been performed under the auspices of the european theoretical astroparticle network ( tan ) .

we propose to study possible signals of just - so oscillations in new - generation solar neutrino experiments by separating the events detected when the earth is nearest to the sun ( perihelion @xmath0 3 months ) from those detected when the earth is farthest from the sun ( aphelion @xmath0 3 months ) .

we propose to study possible signals of just - so oscillations in new - generation solar neutrino experiments by separating the events detected when the earth is nearest to the sun ( perihelion @xmath0 3 months ) from those detected when the earth is farthest from the sun ( aphelion @xmath0 3 months ) . we introduce a solar model independent near - far asymmetry , which is non - zero if just - so oscillations occur . we apply our calculations to the kinetic energy spectra of electrons induced by @xmath1b solar neutrino interactions in the superkamiokande and sudbury neutrino observatory experiments . we show that the sensitivity to the neutrino oscillation parameters can be increased by probing the near - far asymmetry in selected parts of the electron energy spectra .

1207.4218

i

many quantum computing applications @xcite and quantum communication protocols @xcite , such as quantum teleportation @xcite , are based on the sharing of entangled two - photon states between two distant receiving stations . the paired photons can be distributed through free space transmission channels , or alternatively , through single - mode fiber optical links . indeed , fiber optical links are the most practical way to share entanglement between a large number of users . the polarization degree of freedom is the most widely used resource to generate entanglement between two distant parties . polarization - entangled photons can be generated by means of spontaneous parametric down - conversion ( spdc ) , a nonlinear optical process in which two lower - frequency photons ( signal and idler ) are generated when a strong pump interacts with the atoms of a nonlinear material . subsequently to the generation , each photon constituting a pair can propagate through a different single - mode fiber , with the initial degree of entanglement between the photons being preserved over long distances @xcite . one application that is attracting a lot of interest due its potential key role in the newly emerging quantum communication networks is the multi - user quantum key distribution ( qkd ) @xcite . in order to implement a multi - user qkd network , various frequency channels can expediently be employed for transmitting individual entangled pairs . in this way , one can re - route on demand specific channels between users located in different sites of the optical network . similar schemes , considering the emission of photon pairs in different spectral and spatial modes , have been presented in @xcite for an on - demand single - photon source based on a single crystal . to prepare polarization - entangled paired photons in many frequency channels at the same time , one needs to engineer an spdc process with an ultra - broad spectrum . usually type - i or type-0 configurations are preferred . with the type - ii phase - matching , the two down - converted photons have different polarizations and consequently different group velocities , which reduces dramatically their bandwidth . for instance , the fwhm bandwidth of an spdc process in a type - ii periodically - poled ( pp ) ktp crystal at @xmath0 nm is given by @xmath1 , where @xmath2 is the length of the crystal @xcite . for @xmath3 mm , the bandwidth is @xmath4 nm . on the other hand , in a type-0 ppln configuration with the same crystal length @xmath3 mm , lim et al . @xcite achieved an approximate tenfold increase of the bandwidth @xmath5 nm . even though one can always reduce the length of the nonlinear crystal in a type - ii configuration to achieve an increase of the bandwidth , this results in a reduction of the spectral brightness of the source . alternatively to short bulk crystals , bragg reflection waveguides ( brws ) based on iii - v ternary semiconductor alloys ( al@xmath6ga@xmath7as ) offer the possibility to generate polarization - entangled photons with an ultra - large bandwidth . the most striking feature of the use of brw as a photon source is the capability of controlling the dispersive properties of all interacting waves in the spdc process , which in turn allows the tailoring of the bandwidth of the down - converted photons : from narrowband ( @xmath8 nm ) to ultra - broadband ( hundreds of nm ) @xcite , considering both type - i and type - ii configurations . therefore , one can design a type - ii spdc process in brws with a bandwidth typical for type - i or type-0 processes . the utilization of bragg reflection waveguide ( brw ) has further advantages over other conventional spdc sources due to the large nonlinear coefficient of semiconductors ( @xmath9 pm / v ) @xcite , broad transparency window ( @xmath10 - @xmath11 m ) and mature fabrication technologies that can be used for integration of the source of entangled photons with a light source and other optical elements . additionally , a laser based on brws has already been demonstrated @xcite , opening a door for the integration in a single chip of the pump light source together with the brw , where the down - converted photons are generated @xcite . al@xmath6ga@xmath7as is an optically isotropic semiconductor , precluding birefringent phase matching . however , the modal phase - matching of the interacting waves ( pump , signal and idler ) can be achieved by letting each wave propagate in a different type of mode supported by the waveguide . for instance , the phase - matching can be successfully achieved if the pump propagates in the waveguide in a bragg mode , whereas the signal and idler photons propagate in total - internal - reflection ( tir ) modes @xcite .

we put forward a new highly efficient source of paired photons entangled in polarization with an ultra - large bandwidth . the photons are generated by means of a conveniently designed spontaneous parametric down - conversion process in a semiconductor type - ii bragg reflection waveguide . 99 a. serafini , s. mancini , and s. bose , `` distributed quantum computation via optical fibers , '' phys . j. i. cirac , a. k. ekert , s. f. huelga , and c. macchiavello , `` distributed quantum computation over noisy channels , '' phys . g. ribordy , j. brendel , j. gautier , n. gisin , and h. zbinden , `` long - distance entanglement - based quantum key distribution , '' phys . a. k. ekert , `` quantum cryptography based on bell s theorem , '' phys . m. hillery , v. buek , and a. berthiaume , `` quantum secret sharing , '' phys . t. s. humble , and w. p. grice , `` spectral effects in quantum teleportation , '' phys . t. e. chapuran , p. toliver , n. a. peters , j. jackel , m. s. goodman , r. j. runser , s. r. mcnown , n. dallmann , r. j. hughes , k. p. mccabe , j. e. nordholt , c. g. peterson , k. t. tyagi , l. mercer , and h. dardy , `` optical networking for quantum key distribution and quantum communications , '' new j. phys . * 11 * , 105001 ( 2009 ) . . j. h. shapiro , and f. n. wong , `` on - demand single - photon generation using a modular array of parametric downconverters with electro - optic polarization controls , '' opt . a. fedrizzi , t. herbst , a. poppe , t. jennewein , and a. zeilinger , `` a wavelength - tunable fiber - coupled source of narrowband entangled photons , '' opt . d. kang and a. s. helmy , `` generation of polarization entangled photons using concurrent type - i and type-0 processes in algaas ridge waveguides , '' opt . lett . * b. j. bijlani , and a. s. helmy , `` bragg reflection waveguide diode lasers , '' opt . lett . * 34 * , 37343736 ( 2009 ) . r. horn , p. abolghasem , b. j. bijlani , d. kang , a. s. helmy , and g. weihs , `` monolithic source of photon pairs , '' phys . j. p. torres , k. banaszek , and i. a. walmsley , `` engineering nonlinear optic sources of photonic entanglement , '' prog . s. v. zhukovsky , l. g. helt , d. kang , p. abolghasem , a. s. helmy , and j. e. sipe , `` generation of maximally - polarization - entangled photons on a chip , '' phys . j. p. torres , m. hendrych , and a. valencia , `` angular dispersion : an enabling tool in nonlinear and quantum optics , '' adv . opt a. ling , a. lamas - linares , and c. kurtsiefer , `` absolute emission rates of spontaneous parametric down - conversion into single transverse gaussian modes , '' phys . t. yu , and j. h. eberly , `` quantum open system theory : bipartite aspects , '' phys .

we put forward a new highly efficient source of paired photons entangled in polarization with an ultra - large bandwidth . the photons are generated by means of a conveniently designed spontaneous parametric down - conversion process in a semiconductor type - ii bragg reflection waveguide . the proposed scheme aims at being a key element of an integrated source of polarization - entangled photon pairs highly suitable for its use in a multi - user quantum - key - distribution system . 99 a. serafini , s. mancini , and s. bose , `` distributed quantum computation via optical fibers , '' phys . . lett . * 96 * , 010503 ( 2006 ) . j. i. cirac , a. k. ekert , s. f. huelga , and c. macchiavello , `` distributed quantum computation over noisy channels , '' phys . rev . a * 59 * , 42494254 ( 1999 ) . g. ribordy , j. brendel , j. gautier , n. gisin , and h. zbinden , `` long - distance entanglement - based quantum key distribution , '' phys . rev . a * 63 * , 012309 ( 2000 ) . a. k. ekert , `` quantum cryptography based on bell s theorem , '' phys . rev . lett . * 67 * , 661663 ( 1991 ) . m. hillery , v. buek , and a. berthiaume , `` quantum secret sharing , '' phys . rev . a * 59 * , 18291834 ( 1999 ) . c. h. bennett , g. brassard , c. crepeau , r. jozsa , a. peres , and w. k. wootters , `` teleporting an unknown quantum state via dual classical and einstein - podolsky - rosen channels , '' phys . . lett . * 70 * , 18951899 ( 1993 ) . t. s. humble , and w. p. grice , `` spectral effects in quantum teleportation , '' phys . rev . a * 75 * , 022307 ( 2007 ) . h. hubel , m. r. vanner , t. lederer , b. blauensteiner , t. lorunser , a. poppe , and a. zeilinger , `` high - fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber , '' opt . express * 15 * , 78537862 ( 2007 ) . t. e. chapuran , p. toliver , n. a. peters , j. jackel , m. s. goodman , r. j. runser , s. r. mcnown , n. dallmann , r. j. hughes , k. p. mccabe , j. e. nordholt , c. g. peterson , k. t. tyagi , l. mercer , and h. dardy , `` optical networking for quantum key distribution and quantum communications , '' new j. phys . * 11 * , 105001 ( 2009 ) . a. l. migdall , d. branning , and s. castelletto , `` tailoring single - photon and multiphoton probabilities of a single - photon on - demand source , '' phys . rev . a * 66 * , 053805 ( 2002 ) . j. h. shapiro , and f. n. wong , `` on - demand single - photon generation using a modular array of parametric downconverters with electro - optic polarization controls , '' opt . lett . * 32 * , 26982700 ( 2007 ) . a. fedrizzi , t. herbst , a. poppe , t. jennewein , and a. zeilinger , `` a wavelength - tunable fiber - coupled source of narrowband entangled photons , '' opt . express * 15 * , 1537715386 ( 2007 ) . h. c. lim , a. yoshizawa , h. tsuchida , and k. kikuchi , `` wavelength - multiplexed distribution of highly entangled photon - pairs over optical fiber , '' opt . express * 26 * , 2209922104 ( 2008 ) . p. abolghasem , j. han , b. j. bijlani , a. arjmand , and a. s. helmy , `` continuous - wave second harmonic generation in bragg reflection waveguides , '' opt . lett . * 34 * , 94609467 ( 2009 ) . k. thyagarajan , r. das , o. alibart , m. micheli , d. b. ostrowsky , and s. tanzilli , `` increased pump acceptance bandwidth in spontaneous parametric downconversion process using bragg reflection waveguides , '' opt . express * 16 * , 35773582 ( 2008 ) . d. kang and a. s. helmy , `` generation of polarization entangled photons using concurrent type - i and type-0 processes in algaas ridge waveguides , '' opt . lett . * 37 * , 14811483 ( 2012 ) . i. shoji , t. kondo , a. kitamoto , m. shirane , r. ito , `` absolute scale of second - order nonlinear - optical coefficients , '' j. opt . soc . am . b * 14 * , 22682294 ( 1997 ) . b. j. bijlani , and a. s. helmy , `` bragg reflection waveguide diode lasers , '' opt . lett . * 34 * , 37343736 ( 2009 ) . r. horn , p. abolghasem , b. j. bijlani , d. kang , a. s. helmy , and g. weihs , `` monolithic source of photon pairs , '' phys . rev . lett . * 108 * , 153605 ( 2012 ) . a. s. helmy , b. bijlani , and p. abolghasem , `` phase matching in monolithic bragg reflection waveguides , '' opt . lett . * 32 * , 23992401 ( 2007 ) . j. p. torres , k. banaszek , and i. a. walmsley , `` engineering nonlinear optic sources of photonic entanglement , '' prog . optics * 56 * , 227331 ( 2011 ) . s. v. zhukovsky , l. g. helt , d. kang , p. abolghasem , a. s. helmy , and j. e. sipe , `` generation of maximally - polarization - entangled photons on a chip , '' phys . rev . a * 85 * , 013838 ( 2012 ) . j. p. torres , m. hendrych , and a. valencia , `` angular dispersion : an enabling tool in nonlinear and quantum optics , '' adv . opt . photon . * 2 * , 319369 ( 2010 ) . j. jin , _ the finite element method in electromagnetics , 2nd edition _ , ( wiley - ieee press , 2002 ) . s. gehrsitz , f . k. reinhart , c. gourgon , n. herres , a. vonlanthan , and h. sigg , `` the refractive index of al(x)ga(1-x)as below the band gap : accurate determination and empirical modeling , '' j. appl . phys . * 87 * , 78257837 ( 2000 ) . a. ling , a. lamas - linares , and c. kurtsiefer , `` absolute emission rates of spontaneous parametric down - conversion into single transverse gaussian modes , '' phys . rev . a * 77 * , 043834 ( 2008 ) . s. hill , and w. k. wootters , `` entanglement of a pair of quantum bits , '' phys . rev . lett . * 78 * , 50225025 ( 1997 ) . k. wootters , `` entanglement of formation of an arbitrary state of two qubits , '' phys . rev . lett . * 80 * , 22452248 ( 1998 ) . t. yu , and j. h. eberly , `` quantum open system theory : bipartite aspects , '' phys . rev . lett . * 97 * , 140403 ( 2006 ) . y kim , and w. p. grice , `` reliability of the beam - splitter based bell - state measurement , '' phys . rev . a * 68 * , 062305 ( 2003 ) . p. p. rohde , and t. c. ralph , `` frequency and temporal effects in linear optical quantum computing , '' phys . rev . a * 71 * , 032320 ( 2005 ) . w. drexler , `` ultrahigh - resolution optical coherence tomography , '' j. biomedical opt . * 9 * , 4774 ( 2004 ) .

1207.4218

r

( a ) .(a ) parameters of the structure : @xmath58 - core thickness ; @xmath59 - thicknesses of the alternating layers of the bragg reflector ; @xmath60 - aluminium concentration in the core ; @xmath61 - aluminium concentrations in the reflector s layers ; @xmath62 - the refractive index in the core ; @xmath63 - refractive indices in the reflector s layers ; @xmath64 -the inverse group velocity of the signal ( idler ) photon . the structure is optimized for the collinear type - ii spdc . ( b ) profile of the refractive index along the _ y_-axis of the brw . [ cols="^,^",options="header " , ] ( b ) [ fig_tab_1 ] in the waveguide structure considered , the pump wavelength is @xmath65 nm . the frequency spacing between channels is @xmath66 ghz and the bandwidth of each channel is @xmath67 ghz , which corresponds approximately to @xmath68 nm at @xmath69 nm . the channel width and the spacing between channels were chosen according to the typical values used in commercial wdm systems . channel @xmath70 corresponds to the wavelength @xmath71 nm in the upper path and to @xmath72 nm in the lower path . in order to reach a high number of frequency channels , the brw structure must be designed in such way , so as to permit the generation of signal - idler pairs with an ultra - broad spectrum in the type - ii configuration . this is achieved when the group velocities of the te and tm modes are equal @xcite , i.e. , @xmath73 . the modes of the structure and its propagation constants are obtained as a numerical solution of the maxwell equations inside the waveguide using the finite element method @xcite . the waveguide design has been optimized by a genetic algorithm according to the requirements . the final brw design is composed of two bragg reflectors , one placed above and one below the core . each reflector contains 8 bi - layers . the sellmeier equations for the refractive indices of the layers were taken from @xcite . table 1 summarizes the main parameters of the structure . of the biphoton generated in the bragg reflection waveguide for type - ii phase - matching ( @xmath74 ) . ] inspection of eq . ( [ sigma ] ) shows that the effective nonlinearity @xmath75 of the waveguide spdc process depends on the effective area ( @xmath76 ) , which is related to the spatial overlap of the pump , signal and idler modes . for the structure considered , the effective area exhibits only minimal frequency dependence in the bandwidth of interest and it is equal to @xmath77 @xmath78 . despite the fact that the large effective area will reduce the strength of the interaction , the high nonlinear coefficient still results in an efficiency that is a much higher than for other phase - matching platforms in waveguides or in bulk media . the total emission rate @xcite can be expressed using eq . ( [ state1 ] ) as @xmath79 . for our brw , the emission rate is @xmath80 @xmath81 . for comparison , for a typical ppln waveguide ( type-0 ) similar to the one used in @xcite , we obtain @xmath82 @xmath81 . the intensity of the joint spectral amplitude , given by eq . ( [ eg3 ] ) , is displayed in fig . even though we are considering a type - ii configuration , the width ( fwhm ) of the spectrum is a staggering @xmath83 nm . the degree of entanglement in each spectral channel can be quantified by calculating the concurrence @xmath84 of the biphoton @xcite . the concurrence is equal to 0 for a separable state and to 1 for a maximally entangled state . for the density matrix of eq . ( [ state3 ] ) we obtain @xcite @xmath85 so the degree of entanglement depends on the symmetry of the spectral amplitude @xmath86 , i.e. , if @xmath87 the concurrence is maximum . ( solid line ) , @xmath88 ( dashed line ) and @xmath89(dotted - and - dashed line ) as a function of the frequency channel . ] figure [ fig4 ] shows the values of @xmath88 , @xmath89 and @xmath84 for the first 200 channels . @xmath90 is reached for the first 179 channels . the decrease ( increase ) of the parameters @xmath89 ( @xmath88 ) reflects the fact that for frequency channels with a large detuning from the central frequency , one of the two polarization components of the polarization entangled state , @xmath91 or @xmath92 , shows a greater amplitude probability . in this case , one of the two options predominates . therefore , if the goal is to generate a quantum state of the form @xmath93 in a specific frequency channel with @xmath94 , one can always modify the diagonal elements of the density matrix with a linear transformation optical system , keeping unaltered the degree of entanglement . the number of frequency channels available depends on the concurrence required for the specific application . a good example is a linear optical gate relying on the interference of photons on a beam splitter @xcite . this would be especially important for the implementation of quantum teleportation , where the fidelity of the protocol depends strongly on the spectral indistinguishably between polarizations of the entangled state @xcite . in fig . [ fig5 ] we plot the number of frequency channels available as a function of the minimum concurrence required . for instance , if we select only frequency channels with @xmath95 , we have at our disposal @xmath96 channels , while for @xmath97 this number is reduced to @xmath98 channels . in the implementation of the system considered here in a _ real _ fiber - optics network , the number of frequency channels available can be limited by several factors . for instance , it can be limited by the operational bandwidth of the demultiplexer ( see fig.1 ) . this device should be designed to operate with the same broad spectral range of the photon pairs generated in the brw waveguide . when using a large number of channels , inspection of fig . [ fig2 ] shows that channels far apart from the central frequency will exhibit a lower brightness . in this case , spectral shapers or appropriately designed filters , should be used to flatten the emission spectrum , similarly to the case of broadband gain - flattened erbium doped fiber amplifiers ( edfa ) . notwithstanding , this might introduce some losses in the generation process , especially when considering a large number of channels , deteriorating the flux rate of the source . interestingly , a similar problem appears in the context of optical coherence tomography ( oct ) , where large bandwidths are required to increase the imaging resolution . in oct , spectral shapers are used to obtain an optimum ( gaussian - like ) spectral shape @xcite . finally , we should mention that the generation of polarization - entangled photons with the large bandwidths considered here require a precise control the group velocities of the interacting waves , which in turn requires a precise control of the waveguide parameters : refractive index and layer widths . the effective number of available frequency channels in a specific application is inevitably linked to the degree of control of the fabrication process . since both down - converted photons are propagating as tir modes , they are more resistant to fabrication imperfections . for example , a change of about 10@xmath99 in the aluminium concentration in the core will reduce the spectral bandwidth to @xmath100 nm . notwithstanding , it has to be stressed that the phase - matching condition for interacting waves is highly sensitive to any fabrication imperfection , therefore any small change of the structural parameters will lead to a shift of the central ( phase - matched ) wavelength .

. lett . * 96 * , 010503 ( 2006 ) . rev . a * 59 * , 42494254 ( 1999 ) . rev . a * 63 * , 012309 ( 2000 ) . rev . lett . * 67 * , 661663 ( 1991 ) . rev . a * 59 * , 18291834 ( 1999 ) . c. h. bennett , g. brassard , c. crepeau , r. jozsa , a. peres , and w. k. wootters , `` teleporting an unknown quantum state via dual classical and einstein - podolsky - rosen channels , '' phys . . lett . * 70 * , 18951899 ( 1993 ) . rev . a * 75 * , 022307 ( 2007 ) . express * 15 * , 78537862 ( 2007 ) . rev . a * 66 * , 053805 ( 2002 ) lett . * 32 * , 26982700 ( 2007 ) . express * 15 * , 1537715386 ( 2007 ) . express * 26 * , 2209922104 ( 2008 ) . * 34 * , 94609467 ( 2009 ) . 37 * , 14811483 ( 2012 ) . soc . am . b * 14 * , 22682294 ( 1997 ) . rev . lett . * 108 * , 153605 ( 2012 ) . optics * 56 * , 227331 ( 2011 ) . rev . a * 85 * , 013838 ( 2012 ) . j. jin , _ the finite element method in electromagnetics , 2nd edition _ , ( wiley - ieee press , 2002 ) . s. gehrsitz , f . k. reinhart , c. gourgon , n. herres , a. vonlanthan , and h. sigg , `` the refractive index of al(x)ga(1-x)as below the band gap : accurate determination and empirical modeling , '' j. appl . phys . * 87 * , 78257837 ( 2000 ) . rev . a * 77 * , 043834 ( 2008 ) . lett . * 78 * , 50225025 ( 1997 ) . rev . lett . * 80 * , 22452248 ( 1998 ) . rev . lett . * 97 * , 140403 ( 2006 ) . rev . a * 68 * , 062305 ( 2003 ) . rev . a * 71 * , 032320 ( 2005 ) . w. drexler , `` ultrahigh - resolution optical coherence tomography , '' j. biomedical opt . * 9 * , 4774 ( 2004 ) .

we put forward a new highly efficient source of paired photons entangled in polarization with an ultra - large bandwidth . the photons are generated by means of a conveniently designed spontaneous parametric down - conversion process in a semiconductor type - ii bragg reflection waveguide . the proposed scheme aims at being a key element of an integrated source of polarization - entangled photon pairs highly suitable for its use in a multi - user quantum - key - distribution system . 99 a. serafini , s. mancini , and s. bose , `` distributed quantum computation via optical fibers , '' phys . . lett . * 96 * , 010503 ( 2006 ) . j. i. cirac , a. k. ekert , s. f. huelga , and c. macchiavello , `` distributed quantum computation over noisy channels , '' phys . rev . a * 59 * , 42494254 ( 1999 ) . g. ribordy , j. brendel , j. gautier , n. gisin , and h. zbinden , `` long - distance entanglement - based quantum key distribution , '' phys . rev . a * 63 * , 012309 ( 2000 ) . a. k. ekert , `` quantum cryptography based on bell s theorem , '' phys . rev . lett . * 67 * , 661663 ( 1991 ) . m. hillery , v. buek , and a. berthiaume , `` quantum secret sharing , '' phys . rev . a * 59 * , 18291834 ( 1999 ) . c. h. bennett , g. brassard , c. crepeau , r. jozsa , a. peres , and w. k. wootters , `` teleporting an unknown quantum state via dual classical and einstein - podolsky - rosen channels , '' phys . . lett . * 70 * , 18951899 ( 1993 ) . t. s. humble , and w. p. grice , `` spectral effects in quantum teleportation , '' phys . rev . a * 75 * , 022307 ( 2007 ) . h. hubel , m. r. vanner , t. lederer , b. blauensteiner , t. lorunser , a. poppe , and a. zeilinger , `` high - fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber , '' opt . express * 15 * , 78537862 ( 2007 ) . t. e. chapuran , p. toliver , n. a. peters , j. jackel , m. s. goodman , r. j. runser , s. r. mcnown , n. dallmann , r. j. hughes , k. p. mccabe , j. e. nordholt , c. g. peterson , k. t. tyagi , l. mercer , and h. dardy , `` optical networking for quantum key distribution and quantum communications , '' new j. phys . * 11 * , 105001 ( 2009 ) . a. l. migdall , d. branning , and s. castelletto , `` tailoring single - photon and multiphoton probabilities of a single - photon on - demand source , '' phys . rev . a * 66 * , 053805 ( 2002 ) . j. h. shapiro , and f. n. wong , `` on - demand single - photon generation using a modular array of parametric downconverters with electro - optic polarization controls , '' opt . lett . * 32 * , 26982700 ( 2007 ) . a. fedrizzi , t. herbst , a. poppe , t. jennewein , and a. zeilinger , `` a wavelength - tunable fiber - coupled source of narrowband entangled photons , '' opt . express * 15 * , 1537715386 ( 2007 ) . h. c. lim , a. yoshizawa , h. tsuchida , and k. kikuchi , `` wavelength - multiplexed distribution of highly entangled photon - pairs over optical fiber , '' opt . express * 26 * , 2209922104 ( 2008 ) . p. abolghasem , j. han , b. j. bijlani , a. arjmand , and a. s. helmy , `` continuous - wave second harmonic generation in bragg reflection waveguides , '' opt . lett . * 34 * , 94609467 ( 2009 ) . k. thyagarajan , r. das , o. alibart , m. micheli , d. b. ostrowsky , and s. tanzilli , `` increased pump acceptance bandwidth in spontaneous parametric downconversion process using bragg reflection waveguides , '' opt . express * 16 * , 35773582 ( 2008 ) . d. kang and a. s. helmy , `` generation of polarization entangled photons using concurrent type - i and type-0 processes in algaas ridge waveguides , '' opt . lett . * 37 * , 14811483 ( 2012 ) . i. shoji , t. kondo , a. kitamoto , m. shirane , r. ito , `` absolute scale of second - order nonlinear - optical coefficients , '' j. opt . soc . am . b * 14 * , 22682294 ( 1997 ) . b. j. bijlani , and a. s. helmy , `` bragg reflection waveguide diode lasers , '' opt . lett . * 34 * , 37343736 ( 2009 ) . r. horn , p. abolghasem , b. j. bijlani , d. kang , a. s. helmy , and g. weihs , `` monolithic source of photon pairs , '' phys . rev . lett . * 108 * , 153605 ( 2012 ) . a. s. helmy , b. bijlani , and p. abolghasem , `` phase matching in monolithic bragg reflection waveguides , '' opt . lett . * 32 * , 23992401 ( 2007 ) . j. p. torres , k. banaszek , and i. a. walmsley , `` engineering nonlinear optic sources of photonic entanglement , '' prog . optics * 56 * , 227331 ( 2011 ) . s. v. zhukovsky , l. g. helt , d. kang , p. abolghasem , a. s. helmy , and j. e. sipe , `` generation of maximally - polarization - entangled photons on a chip , '' phys . rev . a * 85 * , 013838 ( 2012 ) . j. p. torres , m. hendrych , and a. valencia , `` angular dispersion : an enabling tool in nonlinear and quantum optics , '' adv . opt . photon . * 2 * , 319369 ( 2010 ) . j. jin , _ the finite element method in electromagnetics , 2nd edition _ , ( wiley - ieee press , 2002 ) . s. gehrsitz , f . k. reinhart , c. gourgon , n. herres , a. vonlanthan , and h. sigg , `` the refractive index of al(x)ga(1-x)as below the band gap : accurate determination and empirical modeling , '' j. appl . phys . * 87 * , 78257837 ( 2000 ) . a. ling , a. lamas - linares , and c. kurtsiefer , `` absolute emission rates of spontaneous parametric down - conversion into single transverse gaussian modes , '' phys . rev . a * 77 * , 043834 ( 2008 ) . s. hill , and w. k. wootters , `` entanglement of a pair of quantum bits , '' phys . rev . lett . * 78 * , 50225025 ( 1997 ) . k. wootters , `` entanglement of formation of an arbitrary state of two qubits , '' phys . rev . lett . * 80 * , 22452248 ( 1998 ) . t. yu , and j. h. eberly , `` quantum open system theory : bipartite aspects , '' phys . rev . lett . * 97 * , 140403 ( 2006 ) . y kim , and w. p. grice , `` reliability of the beam - splitter based bell - state measurement , '' phys . rev . a * 68 * , 062305 ( 2003 ) . p. p. rohde , and t. c. ralph , `` frequency and temporal effects in linear optical quantum computing , '' phys . rev . a * 71 * , 032320 ( 2005 ) . w. drexler , `` ultrahigh - resolution optical coherence tomography , '' j. biomedical opt . * 9 * , 4774 ( 2004 ) .

1207.4218

c

in conclusion , we have presented a new type of highly efficient waveguide source for generating polarization - entangled photon pairs for its use in multi - frequency qkd networks . in spite of being a type - ii spdc source , the achieved bandwidth is even larger than the bandwidth usually obtained with type - i or type-0 sources . the key enabling factor that allows us to achieve high efficiency of the nonlinear process together with a bandwidth increase is the fact that we can use a longer nonlinear material in a type - ii configuration , while at the same time keeping the broadband nature of the spdc process through the appropriate design of the bragg reflection waveguide structure . even though _ conventional _ sources based on the use of more common nonlinear materials , such as ktp or linbo@xmath101 , might also generate entangled pairs of photons with a large bandwidth , brws based on algaas compounds offer two main advantages : an enhanced capability to tailor the general properties of the downconverted photons , and the possibility of integration of different elements ( pump source , nonlinear waveguide and diverse optical elements ) in a chip platform based on an already mature technology , which could pave the way for entanglement - based technologies in _ out - of - the - lab scenarios_.

the proposed scheme aims at being a key element of an integrated source of polarization - entangled photon pairs highly suitable for its use in a multi - user quantum - key - distribution system . h. hubel , m. r. vanner , t. lederer , b. blauensteiner , t. lorunser , a. poppe , and a. zeilinger , `` high - fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber , '' opt . a. l. migdall , d. branning , and s. castelletto , `` tailoring single - photon and multiphoton probabilities of a single - photon on - demand source , '' phys . p. abolghasem , j. han , b. j. bijlani , a. arjmand , and a. s. helmy , `` continuous - wave second harmonic generation in bragg reflection waveguides , '' opt . lett . k. thyagarajan , r. das , o. alibart , m. micheli , d. b. ostrowsky , and s. tanzilli , `` increased pump acceptance bandwidth in spontaneous parametric downconversion process using bragg reflection waveguides , '' opt . i. shoji , t. kondo , a. kitamoto , m. shirane , r. ito , `` absolute scale of second - order nonlinear - optical coefficients , '' j. opt . k. wootters , `` entanglement of formation of an arbitrary state of two qubits , '' phys .

we put forward a new highly efficient source of paired photons entangled in polarization with an ultra - large bandwidth . the photons are generated by means of a conveniently designed spontaneous parametric down - conversion process in a semiconductor type - ii bragg reflection waveguide . the proposed scheme aims at being a key element of an integrated source of polarization - entangled photon pairs highly suitable for its use in a multi - user quantum - key - distribution system . 99 a. serafini , s. mancini , and s. bose , `` distributed quantum computation via optical fibers , '' phys . . lett . * 96 * , 010503 ( 2006 ) . j. i. cirac , a. k. ekert , s. f. huelga , and c. macchiavello , `` distributed quantum computation over noisy channels , '' phys . rev . a * 59 * , 42494254 ( 1999 ) . g. ribordy , j. brendel , j. gautier , n. gisin , and h. zbinden , `` long - distance entanglement - based quantum key distribution , '' phys . rev . a * 63 * , 012309 ( 2000 ) . a. k. ekert , `` quantum cryptography based on bell s theorem , '' phys . rev . lett . * 67 * , 661663 ( 1991 ) . m. hillery , v. buek , and a. berthiaume , `` quantum secret sharing , '' phys . rev . a * 59 * , 18291834 ( 1999 ) . c. h. bennett , g. brassard , c. crepeau , r. jozsa , a. peres , and w. k. wootters , `` teleporting an unknown quantum state via dual classical and einstein - podolsky - rosen channels , '' phys . . lett . * 70 * , 18951899 ( 1993 ) . t. s. humble , and w. p. grice , `` spectral effects in quantum teleportation , '' phys . rev . a * 75 * , 022307 ( 2007 ) . h. hubel , m. r. vanner , t. lederer , b. blauensteiner , t. lorunser , a. poppe , and a. zeilinger , `` high - fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber , '' opt . express * 15 * , 78537862 ( 2007 ) . t. e. chapuran , p. toliver , n. a. peters , j. jackel , m. s. goodman , r. j. runser , s. r. mcnown , n. dallmann , r. j. hughes , k. p. mccabe , j. e. nordholt , c. g. peterson , k. t. tyagi , l. mercer , and h. dardy , `` optical networking for quantum key distribution and quantum communications , '' new j. phys . * 11 * , 105001 ( 2009 ) . a. l. migdall , d. branning , and s. castelletto , `` tailoring single - photon and multiphoton probabilities of a single - photon on - demand source , '' phys . rev . a * 66 * , 053805 ( 2002 ) . j. h. shapiro , and f. n. wong , `` on - demand single - photon generation using a modular array of parametric downconverters with electro - optic polarization controls , '' opt . lett . * 32 * , 26982700 ( 2007 ) . a. fedrizzi , t. herbst , a. poppe , t. jennewein , and a. zeilinger , `` a wavelength - tunable fiber - coupled source of narrowband entangled photons , '' opt . express * 15 * , 1537715386 ( 2007 ) . h. c. lim , a. yoshizawa , h. tsuchida , and k. kikuchi , `` wavelength - multiplexed distribution of highly entangled photon - pairs over optical fiber , '' opt . express * 26 * , 2209922104 ( 2008 ) . p. abolghasem , j. han , b. j. bijlani , a. arjmand , and a. s. helmy , `` continuous - wave second harmonic generation in bragg reflection waveguides , '' opt . lett . * 34 * , 94609467 ( 2009 ) . k. thyagarajan , r. das , o. alibart , m. micheli , d. b. ostrowsky , and s. tanzilli , `` increased pump acceptance bandwidth in spontaneous parametric downconversion process using bragg reflection waveguides , '' opt . express * 16 * , 35773582 ( 2008 ) . d. kang and a. s. helmy , `` generation of polarization entangled photons using concurrent type - i and type-0 processes in algaas ridge waveguides , '' opt . lett . * 37 * , 14811483 ( 2012 ) . i. shoji , t. kondo , a. kitamoto , m. shirane , r. ito , `` absolute scale of second - order nonlinear - optical coefficients , '' j. opt . soc . am . b * 14 * , 22682294 ( 1997 ) . b. j. bijlani , and a. s. helmy , `` bragg reflection waveguide diode lasers , '' opt . lett . * 34 * , 37343736 ( 2009 ) . r. horn , p. abolghasem , b. j. bijlani , d. kang , a. s. helmy , and g. weihs , `` monolithic source of photon pairs , '' phys . rev . lett . * 108 * , 153605 ( 2012 ) . a. s. helmy , b. bijlani , and p. abolghasem , `` phase matching in monolithic bragg reflection waveguides , '' opt . lett . * 32 * , 23992401 ( 2007 ) . j. p. torres , k. banaszek , and i. a. walmsley , `` engineering nonlinear optic sources of photonic entanglement , '' prog . optics * 56 * , 227331 ( 2011 ) . s. v. zhukovsky , l. g. helt , d. kang , p. abolghasem , a. s. helmy , and j. e. sipe , `` generation of maximally - polarization - entangled photons on a chip , '' phys . rev . a * 85 * , 013838 ( 2012 ) . j. p. torres , m. hendrych , and a. valencia , `` angular dispersion : an enabling tool in nonlinear and quantum optics , '' adv . opt . photon . * 2 * , 319369 ( 2010 ) . j. jin , _ the finite element method in electromagnetics , 2nd edition _ , ( wiley - ieee press , 2002 ) . s. gehrsitz , f . k. reinhart , c. gourgon , n. herres , a. vonlanthan , and h. sigg , `` the refractive index of al(x)ga(1-x)as below the band gap : accurate determination and empirical modeling , '' j. appl . phys . * 87 * , 78257837 ( 2000 ) . a. ling , a. lamas - linares , and c. kurtsiefer , `` absolute emission rates of spontaneous parametric down - conversion into single transverse gaussian modes , '' phys . rev . a * 77 * , 043834 ( 2008 ) . s. hill , and w. k. wootters , `` entanglement of a pair of quantum bits , '' phys . rev . lett . * 78 * , 50225025 ( 1997 ) . k. wootters , `` entanglement of formation of an arbitrary state of two qubits , '' phys . rev . lett . * 80 * , 22452248 ( 1998 ) . t. yu , and j. h. eberly , `` quantum open system theory : bipartite aspects , '' phys . rev . lett . * 97 * , 140403 ( 2006 ) . y kim , and w. p. grice , `` reliability of the beam - splitter based bell - state measurement , '' phys . rev . a * 68 * , 062305 ( 2003 ) . p. p. rohde , and t. c. ralph , `` frequency and temporal effects in linear optical quantum computing , '' phys . rev . a * 71 * , 032320 ( 2005 ) . w. drexler , `` ultrahigh - resolution optical coherence tomography , '' j. biomedical opt . * 9 * , 4774 ( 2004 ) .

astro-ph0108049

i

supernovae are thought to be one of the main sources of the hot coronal gas in the interstellar medium ( ism ) @xcite . there have been few absorption - line observations of the hot gas in individual supernova remnants ( snrs ) , however , so global descriptions of the ism have been forced to rely on models of evolving snrs to reproduce the characteristics observed in absorption line studies of the galactic disk and halo @xcite . in particular , the @xmath7 1032 , 1038 lines are very important probes of collisionally ionized gas near 3@xmath810@xmath9k . while several snrs have been observed in @xcite , few have been studied in absorption . @xcite detected absorption in the vela supernova remnant with the _ copernicus _ satellite , but since then the opportunities to observe the spectral region containing the lines have been limited . with the launch of the _ far ultraviolet spectroscopic explorer ( fuse ) _ @xcite , this spectral window has been reopened . hd 5980 ( sk78 , av 229 , @xmath10 , @xmath11 ) is a luminous blue variable / wolf - rayet star on the edge of the region ngc346 ( n66 ) in the small magellanic cloud ( smc ) . de boer & savage ( 1980 ) first noticed an absorption system at v@xmath12 kms@xmath1 arising in a highly ionized cloud in _ international ultraviolet explorer _ spectra of this star . @xcite suggested that the cloud might be an snr moving toward hd 5980 at @xmath5150 kms@xmath1 . this interpretation was confirmed by a radio detection of an snr in n66 , snr00577226 @xcite coinciding with the x - ray source ikt18 @xcite . high velocity h@xmath13 emission was also seen at this position by @xcite . @xcite observed hd 5980 with the space telescope imaging spectrograph ( stis ) on the _ hubble space telescope ( hst)_. they detected the snr in ultraviolet absorption lines , and were able to separate the absorption into two components at v@xmath14 and @xmath15 kms@xmath1 ( v@xmath12 and @xmath16 kms@xmath1 ) in some of the lines . they also detected excess absorption at v@xmath17 and + 64 kms@xmath1 ( v@xmath18 and @xmath19 kms@xmath1 ) , suggesting that the high velocity gas is located on the far side of an expanding structure . the stis spectrum contains absorption features of and , which probe gas at @xmath52@xmath2010@xmath9 k and @xmath51@xmath2010@xmath9 k , respectively . in this paper we present @xmath3 data on even hotter gas in snr00577226 .

we report a detection of far ultraviolet absorption from the supernova remnant snr 0057 7226 in the small magellanic cloud ( smc ) . the absorption is seen in the _ far ultraviolet spectroscopic explorer ( fuse ) _ spectrum of the lbv / wr star hd 5980 . the @xmath6()/@xmath6 ( ) ratio for the snr absorption is in the range of 0.120.17 , similar to the value seen in the milky way disk , and lower than the halo value , supporting models in which snrs produce the highly ionized gas close to the plane of the galaxy , while other mechanisms occur in the halo .

we report a detection of far ultraviolet absorption from the supernova remnant snr 0057 7226 in the small magellanic cloud ( smc ) . the absorption is seen in the _ far ultraviolet spectroscopic explorer ( fuse ) _ spectrum of the lbv / wr star hd 5980 . absorption from @xmath01032 and @xmath0977 is seen at a velocity of + 300 kms@xmath1 with respect to the galactic absorption lines , + 170 kms@xmath1 with respect to the smc absorption . the @xmath01038 line is contaminated by h@xmath2 absorption , but is present . these lines are not seen in the @xmath3 spectrum of sk80 , only @xmath4 ( @xmath517 pc ) away from hd 5980 . no blue - shifted @xmath01032 absorption from the snr is seen in the @xmath3spectrum . the @xmath01032 line in the snr is well described by a gaussian with fwhm=75kms@xmath1 . we find log @xmath6()=14.3314.43 , which is roughly 50% of the rest of the column in the smc ( excluding the snr ) and greater than the column in the milky way halo along this sight line . the @xmath6()/@xmath6 ( ) ratio for the snr absorption is in the range of 0.120.17 , similar to the value seen in the milky way disk , and lower than the halo value , supporting models in which snrs produce the highly ionized gas close to the plane of the galaxy , while other mechanisms occur in the halo . the @xmath6()/@xmath6 ( ) ratio is also lower than the smc ratio along this sight line , suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the smc . the , , and apparent column density profiles suggest the presence of a multi - phase shell followed by a region of higher temperature gas .

astro-ph0108049

r

figure 1 shows the observed absorption profiles of and in the spectra of hd 5980 and sk80 . the two stars are separated by @xmath24 , or @xmath517 pc , assuming a distance of 59 kpc to the smc @xcite . absorption features of @xmath01032 and @xmath0977 are detected at + 300 kms@xmath1 in the @xmath3 spectrum of hd 5980 , but no similar features are seen in the sk80 spectrum . the edge of the radio snr extends very close to the projected position of sk80 @xcite . either the + 300kms@xmath1 absorbing region does not extend as far as sk80 , or sk80 is in front of the absorbing gas . absorption from hot gas in the milky way and the smc is also seen in the spectra of both stars , and will be the subject of a future paper . the @xmath01038 line at @xmath25 kms@xmath1 is contaminated by two h@xmath2 lines , p(1)5 - 0 and r(2)5 - 0 , but it is clearly much stronger in the hd 5980 spectrum than in sk80 . the milky way and smc @xmath01032 profiles in the hd 5980 and sk80 spectra look very similar . figure 2 shows an overlay of the two spectra , as well as the hd 5980 spectrum divided by the spectrum of sk80 ( the stellar continua near the @xmath01038 and @xmath0977 did not match as well ) . the milky way and smc components divide out almost completely . the + 300kms@xmath1 absorption toward hd 5980 remains , and is well described by a gaussian with a fwhm of 75kms@xmath1 . this corresponds to a temperature of @xmath52@xmath2010@xmath26 k if the line is broadened solely by thermal motions . we do not see any absorption from the approaching side of the snr in the divided spectrum , identified in the stis spectrum by @xcite . @xcite detected two red - shifted components associated with the snr in low ions , a strong component at v@xmath12 kms@xmath1 and a weaker component at v@xmath27 kms@xmath1 . the absorption in the @xmath3spectrum is located at v@xmath28 kms@xmath1 , corresponding to the strong component . we do not detect the v@xmath27 kms@xmath1component in or . the absorption lines from this component seen by @xcite were very weak , so this component may be blended with the main absorption system at + 300kms@xmath1 in the @xmath3data . @xcite detected a weak component at + 325kms@xmath1 , which if present in the @xmath3 data would be blended with the broad + 300kms@xmath1component . table 1 lists the measured equivalent widths and column densities for the and lines , and upper limits on and . no or h@xmath2 absorption is seen at + 300kms@xmath1 . the and lines in the @xmath3 bandpass are blended with other absorption lines , so we can not determine whether any high velocity absorption is present . column densities were calculated by integrating the apparent column density per unit velocity over the velocity range given , an approach which is valid if the intrinsic line width is comparable to or broader than the instrumental line spread function ( lsf ) @xcite . at temperatures of 3@xmath2010@xmath9k , where the abundance of peaks in collisional ionization equilibrium @xcite , the line width from thermal broadening ( @xmath29kms@xmath1 ) is larger than the @xmath3 lsf width ( @xmath30kms@xmath1 ) , so the condition is most likely satisfied . the abundance peaks at a lower temperature ( @xmath31 k ) , and it is possible that unresolved saturated absorption exists . in this case the measured column density of is a lower limit to the true value . the uncertainty estimates in table 1 include statistical noise fluctuations and modest continuum placement uncertainty @xcite . for the very faint line , continuum placement may dominate the uncertainty , so its effects were evaluated by varying the continuum fit . we have reanalyzed the stis data taken with the e140 m grating from @xcite so that the equivalent widths could be measured over the same velocity ranges used for the @xmath3 data . these values are also given in table 1 ( lines with @xmath32 were measured from stis data ) . we also measured the equivalent width and column density toward hd 5890 using the spectrum that had been divided by the sk80 spectrum . using the divided spectrum , we place an upper limit ( 3@xmath33 ) of log @xmath6()@xmath34 on the approaching side , @xmath35% of the column density of the receding side .

absorption from @xmath01032 and @xmath0977 is seen at a velocity of + 300 kms@xmath1 with respect to the galactic absorption lines , + 170 kms@xmath1 with respect to the smc absorption . the @xmath01038 line is contaminated by h@xmath2 absorption , but is present . these lines are not seen in the @xmath3 spectrum of sk80 , only @xmath4 ( @xmath517 pc ) away from hd 5980 . no blue - shifted @xmath01032 absorption from the snr is seen in the @xmath3spectrum . the @xmath01032 line in the snr is well described by a gaussian with fwhm=75kms@xmath1 . the , , and apparent column density profiles suggest the presence of a multi - phase shell followed by a region of higher temperature gas .

we report a detection of far ultraviolet absorption from the supernova remnant snr 0057 7226 in the small magellanic cloud ( smc ) . the absorption is seen in the _ far ultraviolet spectroscopic explorer ( fuse ) _ spectrum of the lbv / wr star hd 5980 . absorption from @xmath01032 and @xmath0977 is seen at a velocity of + 300 kms@xmath1 with respect to the galactic absorption lines , + 170 kms@xmath1 with respect to the smc absorption . the @xmath01038 line is contaminated by h@xmath2 absorption , but is present . these lines are not seen in the @xmath3 spectrum of sk80 , only @xmath4 ( @xmath517 pc ) away from hd 5980 . no blue - shifted @xmath01032 absorption from the snr is seen in the @xmath3spectrum . the @xmath01032 line in the snr is well described by a gaussian with fwhm=75kms@xmath1 . we find log @xmath6()=14.3314.43 , which is roughly 50% of the rest of the column in the smc ( excluding the snr ) and greater than the column in the milky way halo along this sight line . the @xmath6()/@xmath6 ( ) ratio for the snr absorption is in the range of 0.120.17 , similar to the value seen in the milky way disk , and lower than the halo value , supporting models in which snrs produce the highly ionized gas close to the plane of the galaxy , while other mechanisms occur in the halo . the @xmath6()/@xmath6 ( ) ratio is also lower than the smc ratio along this sight line , suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the smc . the , , and apparent column density profiles suggest the presence of a multi - phase shell followed by a region of higher temperature gas .

astro-ph0108049

c

models of evolving snr @xcite predict the production of in gas heated to @xmath36 k by shocks . the existence of in the snr requires shock speeds of at least @xmath37 kms@xmath1 @xcite . if the absorption seen in the @xmath3 spectrum traces only the receding side of the shell , and the systemic velocity of the snr is + 176 kms@xmath1 @xcite , then the expansion velocity is at least 124kms@xmath1 , and may be higher if the sight line is offset from the center of the remnant . @xcite detected h@xmath13 emission separated from the smc emission by + 170kms@xmath1 , so shock velocities this high certainly seem plausible . assuming that @xmath6()/@xmath6(o ) @xmath38 0.2 @xcite , and using log [ o / h ] @xmath39 for ngc346 @xcite , we find that @xmath6(h@xmath40 ) @xmath41 @xmath42 . the 3-@xmath33 upper limit on from the stis spectrum is @xmath6()@xmath43 @xmath42 , which corresponds to @xmath6()@xmath44 @xmath42 , so h@xmath40/h@xmath45 @xmath46 38 . @xcite estimated @xmath6(h ) @xmath47 @xmath42 in the shell , close to our estimated value of @xmath6(h@xmath40 ) , so most of the gas in the shell may be ionized if the h@xmath45 and h@xmath40 are cospatial . figure 3 compares the apparent column density profile with those of , , , and convolved with a 15 kms@xmath1 fwhm gaussian to approximate the @xmath3 resolution . the red sides of the profiles of the high ions have similar shapes , while on the blue side the higher ions extend over progressively larger velocity ranges , so that in terms of v@xmath48 , the velocity of the blue edge of the profile , v@xmath48 ( ) @xmath23 v@xmath48 ( ) @xmath23 v@xmath48 ( ) . the has a distinct tail of absorption to negative relative velocities that extends almost as far as the absorption . near @xmath25 kms@xmath1 , the / ratio implies temperatures @xmath49 k , while the / ratio suggests @xmath50 k if the gas is in ionization equilibrium @xcite . there appears to be gas at several different temperatures at this velocity , a conclusion supported by the presence of , , and . the and absorption at @xmath51 kms@xmath1 , along with the absence of absorption by lower ionization lines , suggests that this material is dominated by hot gas . a possible interpretation of this ionization structure is a multi - phase shell of swept - up ism moving at the highest velocity ( @xmath25 kms@xmath1 ) , with the cavity behind it filled with hot gas . the / ratio is @xmath55 in the shell , similar to that seen in the old snr radio loop iv , and on the high side of the ism average of @xmath52 @xcite . the line ratios imply temperatures lower than that indicated by the line width , suggesting that non - thermal motions contribute to the line broadening . table 2 lists the observed @xmath6()/@xmath6 ( ) and @xmath6()/@xmath6 ( ) ratios for snr00577226 , for the smc and milky way along this sight line , and the general disk and halo values . also listed are the predictions of models of different mechanisms for producing high ions . the observed @xmath6()/@xmath6 ( ) ratio in snr00577226 agrees well with the predicted ranges of models of evolving snrs . the observed value of @xmath6()/@xmath6 ( ) for snr00577226 is close to the milky way disk value , and very different from the halo value . the @xmath6()/@xmath6 ( ) ratio in the snr also agrees with the disk value . while there may be a metallicity effect on the observed ratios , the observed values for snr 0057 7226 lend support to models of hot gas production @xcite in which supernovae are largely responsible for the highly ionized gas in the galactic disk , while different processes such as turbulent mixing layers @xcite and radiatively cooling fountain gas @xcite are responsible for the hot gas in the upper halo . the observed snr ratios are also quite different from the general smc ratios along this sight line , suggesting that mechanisms other than evolving snr , such as those listed in table 2 , contribute to the extended hot gas in the smc . the column density of in the snr is @xmath54065% of the column in the smc component ( excluding the snr ) . thus , only three such supernova remnants would be needed to explain all of the in the smc in this direction . since this sight line is in the star - forming region ngc346 , it is quite plausible that multiple snrs may exist along this sight line . the column density of in the snr is greater than that in the entire galactic component in this direction . if snr00577226 is representative of supernova remnants in general , then they may be able to account for much of the observed in the ism of the milky way . this project benefitted from discussions with charles danforth . we thank alex fullerton and the @xmath3 hot star team for reducing the @xmath3 data . this work is based on data obtained for the guaranteed time team by the nasa - cnes - csa fuse mission operated by the johns hopkins university . financial support has been provided by nasa contract nas5 - 32985 . lcccc @xmath01031.93 & 2.14 & @xmath53 & @xmath54 & @xmath55 + @xmath01031.93 & 2.14 & @xmath53 & @xmath56 & @xmath57 + @xmath01031.93 & 2.14 & @xmath58 & @xmath59 & @xmath60 + @xmath0977.02 & 2.87 & @xmath61 & @xmath62 & @xmath63 + @xmath0933.38 & 2.61 & @xmath61 & @xmath64 & @xmath65 + @xmath01144.94 & 2.08 & @xmath61 & @xmath66 & @xmath67 + @xmath01122.52 & 1.95 & @xmath61 & @xmath68 & @xmath69 + @xmath01548.20 & 2.47 & @xmath53 & @xmath70 & @xmath71 + @xmath01550.77 & 2.17 & @xmath53 & @xmath72 & @xmath73 + @xmath01242.80 & 1.99 & @xmath53 & @xmath74 & @xmath75 + @xmath01302.17 & 1.80 & @xmath53 & @xmath76 & @xmath77 + lcc snr 00577226 & 0.120.17 & 2.04.5 + smc ( toward hd 5980 ) & @xmath460.71 & @xmath465.1 + mw ( toward hd 5980 ) & @xmath51.3 & @xmath56.8 + mw ( disk ) & 0.080.26 & @xmath53.8 + mw ( halo ) & 0.461.91 & 4.37.0 + mixing layer & 1.03.4 & 7.828 + cooling fountain & 0.10.5 & 2.26.8 + conductive interface & 0.20.4 & 1.82.6 + snr models & 0.10.2 & 1.92.3 +

we find log @xmath6()=14.3314.43 , which is roughly 50% of the rest of the column in the smc ( excluding the snr ) and greater than the column in the milky way halo along this sight line . the @xmath6()/@xmath6 ( ) ratio is also lower than the smc ratio along this sight line , suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the smc .

we report a detection of far ultraviolet absorption from the supernova remnant snr 0057 7226 in the small magellanic cloud ( smc ) . the absorption is seen in the _ far ultraviolet spectroscopic explorer ( fuse ) _ spectrum of the lbv / wr star hd 5980 . absorption from @xmath01032 and @xmath0977 is seen at a velocity of + 300 kms@xmath1 with respect to the galactic absorption lines , + 170 kms@xmath1 with respect to the smc absorption . the @xmath01038 line is contaminated by h@xmath2 absorption , but is present . these lines are not seen in the @xmath3 spectrum of sk80 , only @xmath4 ( @xmath517 pc ) away from hd 5980 . no blue - shifted @xmath01032 absorption from the snr is seen in the @xmath3spectrum . the @xmath01032 line in the snr is well described by a gaussian with fwhm=75kms@xmath1 . we find log @xmath6()=14.3314.43 , which is roughly 50% of the rest of the column in the smc ( excluding the snr ) and greater than the column in the milky way halo along this sight line . the @xmath6()/@xmath6 ( ) ratio for the snr absorption is in the range of 0.120.17 , similar to the value seen in the milky way disk , and lower than the halo value , supporting models in which snrs produce the highly ionized gas close to the plane of the galaxy , while other mechanisms occur in the halo . the @xmath6()/@xmath6 ( ) ratio is also lower than the smc ratio along this sight line , suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the smc . the , , and apparent column density profiles suggest the presence of a multi - phase shell followed by a region of higher temperature gas .

1501.01663

i

the observation of a relation between the masses of supermassive black holes at the centers of galaxies and the stellar velocity dispersion ( @xmath2 relation ; * ? ? ? * ; * ? ? ? * ) suggests a direct link between black holes and their host galaxies . energy and momentum driven out from the central regions push gas and dust away , halting star formation and stopping agn fueling (; see for a review ) . the action of agn feedback could be achieved through the powerful radio jets in the kinetic mode . in the radiative mode , accretion disks drive powerful winds that could contribute significantly to the energy budget of the bh - galaxy system . observing the properties of such a wind is of great importance , particularly in x - rays where most of the radiation from the expelled material is produced . although warm absorber winds are common in the x - ray spectra of agn , with outflow velocities of @xmath3 and column densities of @xmath4 @xmath5 , they are weak , providing only @xmath6 of the agn bolometric luminosity . the more powerful winds seen in several objects with outflow velocities of @xmath7 and column densities of @xmath8 @xmath5 could carry power that is a few percent of the bolometric luminosity . these ultra - fast outflows ( ufo ) seem to be present in at least @xmath9 of observed agn in x - rays . however , this number could be an overestimate when alternative modeling and more conservative statistical analyses are considered @xcite . establishing how common these outflows are , their physical and geometrical properties is therefore crucial to understanding their contribution to the energy and momentum budget of black holes and their hosts . in this letter , we present analysis of the _ nustar_@xcite observation of the quasar pg 1211 + 143 . _ nustar_band ( @xmath10 kev ) with the unprecedented sensitivity at hard ( @xmath11 kev ) x - rays , fixes the continuum and thus allows a meaningful search for blue - shifted absorption below 10 kev . pg 1211 + 143(@xmath12 ) is the archetypical case for the ultra - fast outflows in active galaxies . the first observation with _ xmm - newton _ in 2001 showed evidence for highly blue - shifted absorption lines that are reminiscent of mildly relativistic disk winds ( @xmath7 ; * ? ? ? the same dataset was analyzed by @xcite who find a best fit outflow velocity of 3000 instead of the high 24,000 . letg observation showed two redshifted ( instead of blueshifted ! ) absorption lines at 4.56 and 5.33 kev in the source frame @xcite , which , when identified as the h - like k@xmath13 lines corresponds to inflowing velocities of @xmath14 . later _ xmm - newton _ observations in 2004 and 2007 showed weaker lines but seem to be consistent with the original observations @xcite , or possibly with no absorption lines at all

the putative flow would carry away a high mass flux and kinetic power , with broad implications for feedback and black hole - galaxy co - evolution . we discuss the statistics and the implications of these results in terms of connections between accretion onto quasars , seyferts , and stellar - mass black holes , and feedback into their host environments . .

we report on four epochs of observations of the quasar pg 1211 + 143using _ nustar_. the net exposure time is 300 ks . prior work on this source found suggestive evidence of an `` ultra - fast outflow '' ( or , ufo ) in the fe k band , with a velocity of approximately @xmath0 . the putative flow would carry away a high mass flux and kinetic power , with broad implications for feedback and black hole - galaxy co - evolution . _ nustar_detects pg 1211 + 143out to 30 kev , meaning that the continuum is well - defined both through and above the fe k band . a characteristic relativistic disk reflection spectrum is clearly revealed , via a broad fe k emission line and compton back - scattering curvature . the data offer only weak constraints on the spin of the black hole . a careful search for ufo s show no significant absorption feature above @xmath1 confidence . the limits are particularly tight when relativistic reflection is included . we discuss the statistics and the implications of these results in terms of connections between accretion onto quasars , seyferts , and stellar - mass black holes , and feedback into their host environments . .

1501.01663

c

we have analyzed a deep 300 ks observation of the quasar pg 1211 + 143 , obtained with _ nustar_in four time intervals spanning six months . when fit with a simple power - law model , the total spectrum shows clear signatures of disk reflection ( fig . [ fig : lc_spec]-right ) . fits with the newest , most sophisticated reflection models currently available provide significantly improved fits . the residuals to fits with simple reflection show an excess around @xmath39 kev indicating that relativistic blurring is required , clearly signaling that x - ray emission probes the very innermost portion of the accretion flow in pg 1211 + 143 . the data do not permit a strong constraint on the spin of the black hole , but when reverberation delays seen previously in _ xmm - newton _ data are considered , a solution with a small inner radius ( @xmath43 , corresponding to a black hole spin of @xmath44 ) is supported by the data . we thoroughly examined the _ nustar_data both in segments and in total , and the spectra show no compelling evidence of a steady or variable ultra - fast outflow seen previously in this source . the limits are particularly tight once disk reflection has been modeled . _ nustar_clearly has the sensitivity and spectral resolution required to detect extraordinary outflows , when they are present . observations of pds 456 , for instance , reveal a likely p - cygni profile in that quasar , signaling a massive and powerful outflow from that black hole into its host galaxy ( nardini et al . 2014 , submitted ) . _ nustar_spectra from observations of ngc 1365 were able to disentangle variable absorption , outflows , and disk reflection in that source , leading to a robust measure of the black hole spin @xcite . at the opposite end of the mass scale , _ nustar_observations of the black hole candidate 4u 1630@xmath45472 revealed strong absorption that may be a ufo - like outflow , in addition to disk reflection @xcite . the true extent of these ultra - fast outflows and their persistence is unclear . the non - detection of ultra - fast outflows in the prototypical object pg 1211 + 143 in the current observation ( and also previous observations subsequent to the first _ xmm - newton _ detection ) raises several questions on how common these might be in this and other sources . systematic searches suggest that @xmath46 of objects observed with _ xmm - newton _ and _ suzaku _ show them . this number could be much lower if a careful statistical search is performed that takes into account physical baseline models along with their observational uncertainties . this comes in the form of including the best fit uncertainties in simulating spectra during the monte carlo tests and also allowing for that uncertainty when fitting for narrow features at arbitrary energies in the spectrum . the true extent of ufo s could be affected by the significance of any single detection , which we have discussed , and also by their variability . a non - detection could simply be due to the fact they are transient in nature as suggested by the the simulations @xcite . the case of pg 1211 + 143shows that the ufo is seen in one out of eleven observations ( _ xmm - newton _ , _ suzaku _ , _ chandra _ and _ nustar _ ) between 2001 and 2014 . with the caveat that we still have small numbers , if one assumes the observations are done randomly as far as the agn is concerned , it appears that a variability argument would also suggest that the contribution of ufo s is an order of magnitude lower than previously inferred .

we report on four epochs of observations of the quasar pg 1211 + 143using _ nustar_. the net exposure time is 300 ks . _ nustar_detects pg 1211 + 143out to 30 kev , meaning that the continuum is well - defined both through and above the fe k band . the data offer only weak constraints on the spin of the black hole . a careful search for ufo s show no significant absorption feature above @xmath1 confidence . the limits are particularly tight when relativistic reflection is included .

we report on four epochs of observations of the quasar pg 1211 + 143using _ nustar_. the net exposure time is 300 ks . prior work on this source found suggestive evidence of an `` ultra - fast outflow '' ( or , ufo ) in the fe k band , with a velocity of approximately @xmath0 . the putative flow would carry away a high mass flux and kinetic power , with broad implications for feedback and black hole - galaxy co - evolution . _ nustar_detects pg 1211 + 143out to 30 kev , meaning that the continuum is well - defined both through and above the fe k band . a characteristic relativistic disk reflection spectrum is clearly revealed , via a broad fe k emission line and compton back - scattering curvature . the data offer only weak constraints on the spin of the black hole . a careful search for ufo s show no significant absorption feature above @xmath1 confidence . the limits are particularly tight when relativistic reflection is included . we discuss the statistics and the implications of these results in terms of connections between accretion onto quasars , seyferts , and stellar - mass black holes , and feedback into their host environments . .

astro-ph9809404

i

the hubble deep field @xcite provided unprecedented information on the nature of the universe at high redshifts ( e.g. abraham et al . 1996 , steidel et al . 1996 , madau et al . a similar study of a southern field in the hst continuous viewing zone has just been completed . a primary goal of the hubble deep field south ( hdf - s ) project will be to further our understanding of the relationship between galaxies and quasar absorption line systems and the hst field will be centred on a bright high redshift quasar . the position of the hdf - s field was determined by the location of the bright ( @xmath3 ) @xmath4 qso j2233606 , discovered by one of us ( pch ) and m j irwin using apm scans of a ukst objective prism plate , with confirmation of the object by the aat @xcite . the main reasons for centring the hdf - s on a high redshift quasar are to compare the absorption line spectrum of the quasar with the redshifts of the galaxies identified in the field , and to probe the quasar environment . initial spectral observations of j2233606 have already been reported by sealey , webb & drinkwater and savaglio . sealey et al . combined observations made with the anu 2.3 m telescope with hst stis observations to yield a low resolution spectrum ( @xmath5 ) over the wide wavelength range @xmath6 . savaglio reported on intermediate - resolution ( @xmath7 ) observations obtained with the emmi spectrograph on the eso 3.6 m telescope in the wavelength region @xmath8 . in this paper we report on high - resolution observations ( @xmath9 ) of j2233606 made with the university college of london echelle spectrograph ( ucles ) at the anglo - austrlian telescope ( aat ) . these observations cover the important wavelength region @xmath10 , comprising much of the key ly@xmath11 forest region . this data also largely bridges the gap between the hst stis ( @xmath12 ) observations and the existing emmi observations ( @xmath13 ) providing nearly contiguous spectral coverage at resolution of at least @xmath14 over the full wavelength range @xmath15 .

we report on high resolution observations ( @xmath0 ) of the hubble deep field south qso j2233 - 606 obtained with the university college london echelle spectrograph at the aat . the data has a mean signal - to - noise ratio in the continuum of approximately 15 per 0.05 resolution element at @xmath2 3700 . quasars : absorption line systems quasars : individual : j2233 - 606

we report on high resolution observations ( @xmath0 ) of the hubble deep field south qso j2233 - 606 obtained with the university college london echelle spectrograph at the aat . we present spectral data and an associated absorption line list for the wavelength region 3530@xmath1 4390 . the data has a mean signal - to - noise ratio in the continuum of approximately 15 per 0.05 resolution element at @xmath2 3700 . quasars : absorption line systems quasars : individual : j2233 - 606

1011.4433

i

to summarize , our experiments clearly demonstrate that , both , linear and circular mpge in gaas / algaas qw structures result from spin and orbital contributions . our experiments show that for most quantum well widths the mpge is mainly driven by spin - related mechanisms , which result in a photocurrent proportional to the @xmath0 factor . for structures with a vanishingly small @xmath0 factor , however , the mpge caused by orbital mechanisms is clearly observed . our work demonstrates that a variation of the electron @xmath0 factor by different means , like varying the qw width , as it is done here , doping with magnetic impurities or using narrow band materials , where @xmath0 and the spin - orbit interaction are enhanced , can be used for the separation of these qualitatively different mechanisms . moreover , the orbital mpge can be studied independently in materials with a vanishingly small spin - orbit interaction , like si - based metal - oxide - semiconductor low dimensional structures . we thank s.a . tarasenko and e.l . ivchenko for fruitful discussions and support , as well as m. schmalzbauer . this work is supported by the dfg via programs spp 1285 , sfb 689 , by the linkage grant of ib of bmbf at dlr , russian ministry of education and sciences , rfbr and `` dynasty '' foundation icfpm . v. v. belkov and s. d. ganichev , _ zero - bias spin separation _ , in _ handbook of spintronic semiconductors _ , edited by w. m. chen and i. a. buyanova ( pan stanford publishing , singapore 2010 ) . s. d. ganichev , v. v. belkov , s. a. tarasenko , s. n. danilov , s. giglberger , c. hoffmann , e. l. ivchenko , d. weiss , w. wegscheider , c. gerl , d. schuh , j. stahl , j. de boek , g. borghs and w. prettl , nature physics * 2 * , 609 ( 2006 ) . v. v. belkov , p. olbrich , s. a. tarasenko , d. schuh , w. wegscheider , t. korn , c. schller , d. weiss , w. prettl , and s. d. ganichev , phys . lett . * 100 * , 176806 ( 2008 ) . s. d. ganichev , petra schneider , v. v. belkov , e. l. ivchenko , s. a. tarasenko , w. wegscheider , d. weiss , d. schuh , b. n. murdin , p. j. phillips , c. r. pidgeon , d. g. clarke , m. merrick , p. murzyn , e. v. beregulin , and w. prettl , phys . b. * 68 * , 081302 ( 2003 ) . s. giglberger , l. e. golub , v. v. belkov , s. n. danilov , d. schuh , ch . gerl , f. rohlfing , j. stahl , w. wegscheider , d. weiss , w. prettl , and s. d. ganichev , phys . b * 75 * 035327 ( 2007 ) . v. lechner , l. e. golub , p. olbrich , s. stachel , d. schuh , w. wegscheider , v. v. belkov , and s. d. ganichev , appl . . lett . * 94 * , 242109 ( 2009 ) . c. l. yang , j. dai , w. k. ge , and x. cui , appl . * 96 * , 152109 ( 2010 ) . m. i. dyakonov and v. i. perel , sov . - jetp * 33 * , 1053 ( 1971 ) . e. a. de andrada e silva , g. c.la rocca , and f. bassani , phys . b * 55 * , 16293 ( 1997 ) . note , that @xmath152 of the sample with @xmath153 nm is twice as large as in the other samples , therefore sia and consequently the sia - induced current is enhanced compared to the samples with larger @xmath7 . c. drexler , v. v. belkov , b. ashkinadze , p. olbrich , c. zoth , v. lechner , ya . v. terentev , d. r. yakovlev , g. karczewski , t. wojtowicz , d. schuh , w. wegscheider , and s. d. ganichev , appl . 97 * , 182107 ( 2010 ) . note , that comparing our mpge data obtained at room temperature with the @xmath154-factor behavior measured at low temperatures , we do not consider the weak temperature dependence @xmath0-factor , @xcite which may result in a small shift of its zero crossing . v. v. belkov , s. d. ganichev , e. l. ivchenko , s. a. tarasenko , w. weber , s. giglberger , m. olteanu , h .- tranitz , s. n. danilov , petra schneider , w. wegscheider , d. weiss , and w. prettl , j. phys . c : condens . matter * 17 * , 3405 ( 2005 ) . here and latter the calculations are limited to rather narrow quantum wells , for which only one subband is occupied . in a wider qws other subbands should be taken into account which is out of scope of this paper . we note , that recently an additional possible root of the spin - galvanic effect has been addressed in ref . . instead of sge due to band spin splitting considered in ref . , it is based on the spin - dependent scattering given by eq . . however , this mechanism also yields a contribution proportional to the zeeman splitting and does not qualitatively change the discussion of the mpge variation upon the qw width change .

our experiments show that , for most quantum well widths , the mpges are mainly driven by spin - related mechanisms , which results in a photocurrent proportional to the @xmath0 factor . in structures with a vanishingly small @xmath0 factor , however , linear and circular mpge are also detected , proving the existence of orbital mechanisms .

we report on the study of the linear and circular magneto - gyrotropic photogalvanic effect ( mpge ) in gaas / algaas quantum well structures . using the fact that in such structures the land - factor @xmath0 depends on the quantum well ( qw ) width and has different signs for narrow and wide qws , we succeeded to separate spin and orbital contributions to both mpges . our experiments show that , for most quantum well widths , the mpges are mainly driven by spin - related mechanisms , which results in a photocurrent proportional to the @xmath0 factor . in structures with a vanishingly small @xmath0 factor , however , linear and circular mpge are also detected , proving the existence of orbital mechanisms .

1403.3409

i

the last decade has witnessed the arrival of unprecedented amounts of high quality imaging data from the sloan digital sky survey ( sdss ) . thanks to the depth and the exquisite stability of the sdss broad - band photometry across thousands of square degrees on the sky , previously unseen low - level fluctuations in the galactic stellar density field have been unearthed ( see e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? in the milky way halo one striking example of a small - scale over - density is the gd-1 stellar stream @xcite , only a fraction of a degree in width , but running over 60 degrees from end to end in the sdss footprint . such stellar trails are formed in the process of a satellite disruption in the tidal field of the galaxy . the mechanics of the stream formation and the subsequent dynamical evolution in the host potential have been carefully studied ( e.g. * ? ? ? * ; * ? ? ? the consensus that has emerged from both theoretical considerations and admittedly , very few tests on the actual data ( e.g. * ? ? ? * ) , is that these structures can be used to yield powerful , unbiased constraints of the matter distribution in the galaxy . in principle there exists a methodology to model the entire spectrum of tidal debris in the galactic halo ( see e.g. * ? ? ? * ) , from very narrow structures like gd-1 to broad luminous streams like that of sgr ( exposed in e.g. * ? ? ? * ) , including the stellar over - densities that do not necessarily even trace out a stream ( e.g. * ? ? ? however , the thinnest streams appear doubly interesting . first , given that these are not affected by the progenitor s gravity , methods are now in place to infer the galactic potential without the need to resort to approximating the stellar tracks with a single orbit ( e.g. * ? ? ? * ; * ? ? ? second , along these narrow tidal tails it is easiest to observe density fluctuations due to interactions with dark matter sub - halos in the galaxy ( see e.g. * ? ? ? * ; * ? ? ? * ) , provided that so - called epicyclic feathering is taken care of ( see e.g. * ? ? ? sdss data has already been thoroughly mined to yield a handful of cold stellar streams . these include , for example , the tails of the pal 5 globular cluster @xcite , as well as tails around ngc 5466 @xcite , ngc 5053 @xcite , pal 14 @xcite and pal 1 @xcite . in addition @xcite found a group of narrow streams acheron , cocytos , lethe and more recently the discovery of the pisces stellar stream was announced @xcite . in this paper we present the discovery of a new stellar stream in the southern celestial hemipshere based on photometry from data release 1 ( dr1 ) of the vst atlas survey @xcite . atlas is one of the three imaging surveys being currently undertaken within the remit of the eso vst public surveys program , the other two being kids @xcite and vphas+ ( drew et al 2014 ) . the aim of the atlas survey is to obtain photometry in the sdss @xmath3 filters down to @xmath4 for approximately 4,500 square degrees of the southern sky . the primary motiviation for the survey is to identify large numbers of @xmath5 qsos and luminous red galaxies out to redshifts of @xmath6 for studies of the cosmological matter power spectrum . the ability to use this data to also detect low - level galactic halo stellar sub - structure spanning several hundred square degree survey fields is testament to the quality and the stability of the atlas photometric and astrometric calibration . section 2 briefly describes the data being used , while section 3 gives the details of the newly discovered stream . the final section summarises the main results .

we report the discovery of a narrow stellar stream crossing the constellations of sculptor and fornax in the southern celestial hemisphere . the portion of the stream detected in the data release 1 photometry of the atlas survey is at least 12 degrees long , while its width is @xmath0 0.25 deg .

we report the discovery of a narrow stellar stream crossing the constellations of sculptor and fornax in the southern celestial hemisphere . the portion of the stream detected in the data release 1 photometry of the atlas survey is at least 12 degrees long , while its width is @xmath0 0.25 deg . the color magnitude diagram of this halo sub - structure is consistent with a metal - poor @xmath1}\lesssim -1.4 $ ] stellar population located at a heliocentric distance of 20 @xmath2 2 kpc . there are three globular clusters that could tentatively be associated with the stream : ngc 7006 , ngc 7078 ( m15 ) and pyxis , but ngc 7006 and 7078 seem to have proper motions incompatible with the stream orbit . [ firstpage ] galaxy : fundamental parameters galaxy : halo galaxy : kinematics and dynamics stars : main sequence stars

cond-mat9407094

i

the fundamental statistical physics describing systems which are so far out of equilibrium that the notion of a partition function is not valid is currently not well understood . our goal is to study the structural response of very simple systems as they are driven between two distinct steady - state configurations , using time - resolved x - ray scattering . the particular experimental systems we chose to study are the charge - density - waves ( cdws ) found in quasi - one - dimensional metals . the structure of the pinned cdw state has been measured at high resolution . theory and experiment are in excellent agreement@xcite . on the other hand , the dynamics of cdw systems are less well understood , particularly the structural aspects . although a large number of electronic transport experiments have been performed , the results of these experiments are difficult to interpret in terms of microscopic models and time - resolved structural data are limited and restricted primarily to the k@xmath6mo@xmath7 system.@xcite in order to acquire the data , we developed a time - resolved , high - resolution x - ray scattering system capable of measuring the time - evolution of the structure of the sliding @xmath8 charge - density - wave in nbse@xmath7 as the direction of the driving electric field is reversed . we are able to interpret our data using an equation of motion for the phase of the cdw order parameter which pertains at low temperatures and at large applied fields . in the next section of this paper , we review the elementary physics describing cdws in one - dimensional metals and discuss the structure of both stationary and sliding cdws . in the third section , we review the standard theory describing x - ray scattering from cdw systems and develop some of the extensions necessary to describe evolving systems . we explicitly solve an equation of motion describing the wave number of the cdw . in the fourth section , we review the details of our nbse@xmath7 samples and our experimental apparatus . in section five , we present our time - resolved x - ray scattering data . we conclude with a brief discussion of our results and an appendix of mathematical details .

we report time - resolved x - ray scattering measurements of the transient structural response of the sliding * q*@xmath0 charge - density - wave ( cdw ) in nbse@xmath1 to a reversal of the driving electric field . the observed time scale characterizing this response at 70k varies from @xmath2 15 msec for driving fields near threshold to @xmath2 2 msec for fields well above threshold . the position and time - dependent strain of the cdw is analyzed in terms of a phenomenological equation of motion for the phase of the cdw order parameter .

we report time - resolved x - ray scattering measurements of the transient structural response of the sliding * q*@xmath0 charge - density - wave ( cdw ) in nbse@xmath1 to a reversal of the driving electric field . the observed time scale characterizing this response at 70k varies from @xmath2 15 msec for driving fields near threshold to @xmath2 2 msec for fields well above threshold . the position and time - dependent strain of the cdw is analyzed in terms of a phenomenological equation of motion for the phase of the cdw order parameter . the value of the damping constant , @xmath3 ev @xmath4 seconds @xmath4 @xmath5 , is in excellent agreement with the value determined from transport measurements . as the driving field approaches threshold from above , the line shape becomes bimodal , suggesting that the cdw does not depin throughout the entire sample at one well - defined voltage .

1507.01979

i

manganese pnictides of the hexagonal nias structure type ( _ e.g. _ mnas , mn@xmath1sb , mnbi ; figure [ fig : structure ] ) display a wealth of functional magnetic properties . the class of materials includes potential candidates for rare earth - free permanent magnets,@xcite magneto - optical data storage,@xcite and magnetic refrigeration.@xcite manganese antimonide is known to only exist as a manganese - rich phase , mn@xmath1sb.@xcite the wide compositional region shown on the equilibrium phase diagram extends from @xmath7,@xcite with excess mn occupying the interstitial site ( figure [ fig : structure]b ) in trigonal bipyramidal coordination by sb . increasing amounts of interstitial mn ( mn@xmath0 ) lengthen the @xmath8 and shorten the @xmath9 lattice parameters , which accompanies reductions of the saturation magnetization , spin - reorientation temperature ( @xmath10),@xcite and the curie temperature ( @xmath11).@xcite magnetic ordering of the primary mn sites occurs parallel to @xmath9 at high temperature , but it changes to the @xmath12 plane below @xmath10.@xcite although the bulk magnetic properties are well known , the microscopic nature of the magnetism associated with mn@xmath0 has been equivocal . a straightforward explanation of the reduced magnetization in more mn - rich samples is that mn@xmath0 is aligned antiparallel to the ferromagnetic mn@xmath13 atoms , that is , mn@xmath1sb is ferrimagnetic . ( here we use krger vink notation to differentiate interstitial mn@xmath0 and nominal mn@xmath13 atoms . ) nonpolarized neutron diffraction studies are consistent with this expectation.@xcite however , polarized neutron scattering analyses have suggested that mn@xmath0 has no moment . @xcite the reduction of magnetization is then explained on the basis of greater orbital overlap between mn atoms upon reduction of the @xmath9 lattice constant , and to a local perturbation of the mn moment when in proximity to mn@xmath0.@xcite , with mn on 2@xmath8 at ( 0,0,0 ) and bi on 2@xmath9 at ( @xmath14 ) ] , and inelastic neutron scattering data collected at 4k from a single crystal of mnbi . ( b ) structure of mn@xmath1sb highlighting the fractionally occupied , trigonal bipyramidal coordination environment of interstitial mn [ mn@xmath0 , on 2@xmath15 site at ( @xmath16 ) ] . note that mn@xmath0 is also in trigonal prismatic coordination with respect to the primary ( fully occupied ) mn@xmath13 site . inelastic neutron scattering data collected at 10k on a single crystal of mn@xmath17sb shows a pronounced diffuse component that is not observed for mnbi . inelastic scattering figures adapted from taylor _ et al . _ , reference .,width=316 ] the question of whether mn@xmath0 carries a moment was recently re - addressed by taylor _ _ via a combination of nonpolarized elastic and inelastic neutron scattering on an mn@xmath17sb single crystal.@xcite a critical feature of the modeling strategies adopted in previous _ polarized _ neutron studies was the use of a highly aspherical magnetic form factor for mn.@xcite in the recent work of taylor and co - workers it was shown that such a model provides an inferior description of the magnetic reflections particularly at low @xmath18 where magnetic scattering is strongest relative to a model employing a spherical magnetic form factor and antiferromagnetic coupling between mn@xmath0 and mn@xmath13.@xcite density functional calculations enlisting small supercells further supported mn@xmath1sb as a ferrimagnet . additionally , a pronounced and gapless diffuse magnetic component was observed across all temperature regimes in the inelastic spectrum ( figure [ fig : structure]b ) , centered at ( 001 ) . similar or related features have also been noted by other groups.@xcite the location of the diffuse component is intriguing because the ( 001 ) reflection should be systematically absent from the structure factor ; there is no diffuse scattering observed for stoichiometric ( interstitial - free ) mnbi ( figure [ fig : structure]a ) . two plausible explanations were suggested : the diffuse scattering could arise from ( @xmath19 ) correlated structural or magnetic disorder , or ( @xmath20 ) modification of the neighboring mn@xmath13 moments by mn@xmath0.@xcite an essential feature of the mn@xmath1sb system that has been largely unaccounted for , both experimentally and computationally , is the local structure around mn@xmath0 . it has long been recognized that the equatorial mn@xmath0sb contacts of the crystallographic mn@xmath0 site in the mn@xmath1sb unit cell are quite short.@xcite however , few studies have attempted to model the presumed structural relaxation.@xcite yamaguchi and watanabe approximated that mn@xmath0 would be accommodated by distortions of only the sb positions , the magnitude of the local displacements being derived from the concentration dependence of the lattice parameters.@xcite this assumption was used in their analysis of polarized neutron diffuse scattering data . models with no mn@xmath0 moment , but containing reduced moments on the first or second nearest - neighbor mn atoms in proximity to mn@xmath0 , were compared against calculated scattering for a model with mn@xmath0 aligned antiparallel . although the best agreement was obtained for a reduction of the six nearest - neighbor mn moments , an aspherical mn magnetic form factor appears to have contributed to the result.@xcite the utility of density functional modeling in describing local structural effects and defect physics is well demonstrated . a variety of approaches can be used to simulate defects ( substitutional , interstitial , antisite , vacancy ) and random alloying , the validity of which is reflected in agreement with a variety of experimental probes of local bonding arrangements , including nuclear magnetic resonance ( nmr),@xcite extended x - ray absorption fine structure ( exafs),@xcite and pair distribution function ( pdf ) data obtained from total scattering . @xcite when the concentration of defects is low , an effective strategy is to model a defect in a sufficiently large supercell such that the defect is approximately isolated ( _ i.e. _ , limiting the interaction between defects when periodic boundary conditions are applied).@xcite at higher levels of substitution , the creation of models on the basis of chemically reasonable , ordered supercells can be an elegant strategy to assess plausible bonding motifs.@xcite random alloys are inherently challenging systems to model in the framework of density functional theory ( dft ) , since even large supercells will necessarily contain elements of periodicity that are absent in a truly random structure , but strategies such as stochastic mixing and the special quasirandom structures approach often provide adequate approximations.@xcite mn@xmath1sb can be regarded as a type of random alloy , with a distribution of interstitials and vacancies over the crystallographic mn@xmath0 site . in the present contribution , we examine local structural relaxation in mn@xmath1sb using synchrotron x - ray total scattering and pdf analysis coupled with density functional modeling . the use of x rays rather than neutrons allows us to base our analysis on the local nuclear structure without interference from magnetic scattering . particular attention is devoted to the mn@xmath0 environment and its calculated magnetic moment , as well as the compositional and structural influence on the moment of ferromagnetically aligned mn@xmath13 . structural relaxation has a pronounced effect on the mn@xmath0 environment and enhances electronic localization by a lengthening of equatorial sb contacts , but it does not appear to influence the moments on mn@xmath13 or sb . a weak diffuse signal is observed near the symmetry - forbidden ( 001 ) bragg position , suggestive of correlated disorder associated with clustering of mn@xmath0 . these results are discussed in light of the recent work of taylor _ _

we report x - ray total scattering and pair distribution function ( pdf ) studies of the structural relaxation around interstitial manganese ( mn@xmath0 ) in ferromagnetic mn@xmath1sb ( @xmath2 ) alloys , guided by density functional theory ( dft ) . observation of a weak diffuse signal near the symmetry - forbidden ( 001 ) reflection position is indicative of correlated disorder from the clustering of mn@xmath0 .

we report x - ray total scattering and pair distribution function ( pdf ) studies of the structural relaxation around interstitial manganese ( mn@xmath0 ) in ferromagnetic mn@xmath1sb ( @xmath2 ) alloys , guided by density functional theory ( dft ) . refinements to the experimental pdf using a crystallographically constrained structural model indicate an expansion in the equatorial plane of the mn@xmath0sb@xmath3 trigonal bipyramidal site , which introduces significant positional disorder in addition to the nominally - random occupation of interstitial voids . observation of a weak diffuse signal near the symmetry - forbidden ( 001 ) reflection position is indicative of correlated disorder from the clustering of mn@xmath0 . density functional relaxation of supercells approximating the @xmath4 , @xmath5 and @xmath6 compositions provides improved models that accurately describe the short - range structural distortions captured in the pdfs . such structural relaxation increases the dft calculated moment on mn@xmath0 , which aligns antiparallel to the primary mn moments , but leads to insubstantial changes in the average mn and sb moments and moments of mn and sb proximal to interstitials , thus providing a more accurate description of the observed bulk magnetic properties .

1507.01979

c

analysis of x - ray total scattering data collected on polycrystalline powders of mn@xmath1sb ( @xmath2 ) reveals signatures of structural relaxation associated with the accommodation of interstitial atoms . in particular , the trigonal bipyramidal site of mn@xmath0 is better described by longer equatorial mn@xmath0sb distances than reflected by the crystallographic unit cell . density functional relaxation of large supercells for compositions close to @xmath4 , @xmath93 , and @xmath6 , provides excellent structural descriptions of the short - range disorder induced by mn@xmath0 , evidenced by improved fits to the experimental pdfs . relaxation has a pronounced effect on the calculated moment of mn@xmath0 , which aligns antiparallel to mn@xmath13 , but our results suggest that mn@xmath0 has effectively no influence on the moments of mn@xmath13 in proximity to interstitials . the observation of a diffuse signal near the ( 001 ) reflection position , which is systematically absent when mn@xmath0 is distributed completely randomly , indicates that some degree of _ correlated _ disorder exists in mn@xmath1sb .

density functional relaxation of supercells approximating the @xmath4 , @xmath5 and @xmath6 compositions provides improved models that accurately describe the short - range structural distortions captured in the pdfs . such structural relaxation increases the dft calculated moment on mn@xmath0 , which aligns antiparallel to the primary mn moments , but leads to insubstantial changes in the average mn and sb moments and moments of mn and sb proximal to interstitials , thus providing a more accurate description of the observed bulk magnetic properties .

we report x - ray total scattering and pair distribution function ( pdf ) studies of the structural relaxation around interstitial manganese ( mn@xmath0 ) in ferromagnetic mn@xmath1sb ( @xmath2 ) alloys , guided by density functional theory ( dft ) . refinements to the experimental pdf using a crystallographically constrained structural model indicate an expansion in the equatorial plane of the mn@xmath0sb@xmath3 trigonal bipyramidal site , which introduces significant positional disorder in addition to the nominally - random occupation of interstitial voids . observation of a weak diffuse signal near the symmetry - forbidden ( 001 ) reflection position is indicative of correlated disorder from the clustering of mn@xmath0 . density functional relaxation of supercells approximating the @xmath4 , @xmath5 and @xmath6 compositions provides improved models that accurately describe the short - range structural distortions captured in the pdfs . such structural relaxation increases the dft calculated moment on mn@xmath0 , which aligns antiparallel to the primary mn moments , but leads to insubstantial changes in the average mn and sb moments and moments of mn and sb proximal to interstitials , thus providing a more accurate description of the observed bulk magnetic properties .

1405.7786

i

multi - dimensional or multi - way data is prevalent nowadays , which can be represented by tensors . an @xmath0th - order tensor is a multi - way array of size @xmath1 , where the @xmath2th dimension or mode is of size @xmath3 . for example , a tensor can be induced by the discretization of a multivariate function @xcite . given a multivariate function @xmath4 defined on a domain @xmath5^n$ ] , we can get a tensor with entries containing the function values at grid points . for another example , we can obtain tensors based on observed data @xcite . we can collect and integrate measurements from different modalities by neuroimaging technologies such as functional magnetic resonance imaging ( fmri ) and electroencephalography ( eeg ) : subjects , time , frequency , electrodes , task conditions , trials , and so on . furthermore , high - order tensors can be created by a process called tensorization or quantization @xcite , by which a large - scale vectors and matrices are reshaped into higher - order tensors . however , it is impossible to store a high - order tensor because the number of entries , @xmath6 when @xmath7 , grows exponentially as the order @xmath0 increases . this is called the `` curse - of - dimensionality '' . even for @xmath8 , with @xmath9 we obtain @xmath10 entries . such a huge storage and computational costs required for high dimensional problems prohibit the use of standard numerical algorithms . to make high dimensional problems tractable , there were developed approximation methods including sparse grids @xcite and low - rank tensor approximations @xcite . in this paper , we focus on the latter approach , where computational operations are performed on tensor formats , i.e. , low - parametric representations of tensors . in this paper , we consider several tensor formats , especially the tensor train ( tt ) format , which is one of the simplest tensor networks developed with the aim of overcoming the curse - of - dimensionality . extensive overviews of the modern low - rank tensor approximation techniques are presented in @xcite . the tt format is equivalent to the matrix product states ( mps ) for open boundary conditions proposed in computational physics , and it has taken a key role in density matrix renormalization group ( dmrg ) methods for simulating quantum many - body systems @xcite . it was later re - discovered in numerical analysis community @xcite . the tt - based numerical algorithms can accomplish algorithmic stability and adaptive determination of ranks by employing the singular value decomposition ( svd ) @xcite . its scope of application is quickly expanding for addressing high - dimensional problems such as multi - dimensional integrals , stochastic and parametric pdes , computational finance , and machine learning @xcite . on the other hand , a comprehensive survey on traditional low - rank tensor approximation techniques for cp and tucker formats is presented in @xcite . despite the large interest in high - order tensors in tt format , mathematical representations of the tt tensors are usually limited to the representations based on scalar operations on matrices and vectors , which leads to complex and tedious index notation in the tensor calculus . for example , a tt tensor is defined by each entry represented as products of matrices @xcite . on the other hand , representations of traditional low - rank tensor formats have been developed based on multilinear operations such as the kronecker product , khatri - rao product , hadamard product , and mode-@xmath2 multilinear product @xcite , which enables coordinate - free notation . through the utilization of the multilinear operations , the traditional tensor formats expanded the area of application to chemometrics , signal processing , numerical linear algebra , computer vision , data mining , graph analysis , and neuroscience @xcite . in this work , we develop extended definitions of multilinear operations on tensors . based on the tensor operations , we provide a number of new and useful representations of the tt format . we also provide graphical representations of the tt format , motivated by @xcite , which are helpful in understanding the underlying principles and tt - based numerical algorithms . based on the tt representations of large - scale vectors and matrices , we show that the basic numerical operations such as the addition , contraction , matrix - vector product , and quadratic form are conveniently described by the suggested representations . we demonstrate the usefulness of the proposed tensor operations in tensor calculus by giving a proof of orthonormality of the so - called frame matrices . moreover , we derive explicit representations of localized linear maps in tt format that have been implicitly presented in matrix forms in the literature in the context of alternating linear scheme ( als ) for solving various optimization problems . the suggested mathematical operations and tt representations can be further applied to describing tt - based numerical methods such as the solutions to large - scale systems of linear equations and eigenvalue problems @xcite . this paper is organized as follows . in section 2 , we introduce notations for tensors and definitions for tensor operations . in section 3 , we provide the mathematical and graphical representations of the tt format . we also review mathematical properties the tt format as a low - rank approximation . in section 4 , we describe basic numerical operations on tensors in tt format such as the addition , hadamard product , matrix - vector multiplication , and quadratic form in terms of the multilinear operations and tt representations . discussion and conclusions are given in section 5 .

we review and introduce new representations of tensor train decompositions for large - scale vectors , matrices , or low - order tensors . we provide extended definitions of mathematical multilinear operations such as kronecker , hadamard , and contracted products , with their properties for tensor calculus . then we introduce an effective low - rank tensor approximation technique called the tensor train ( tt ) format with a number of mathematical and graphical representations . we also provide a brief review of mathematical properties of the tt format as a low - rank approximation technique . with the aim of breaking the curse - of - dimensionality in large - scale numerical analysis , we describe basic operations on large - scale vectors and matrices in tt format . the suggested representations can be used for describing numerical methods based on the tt format for solving large - scale optimization problems such as the system of linear equations and eigenvalue problems .

we review and introduce new representations of tensor train decompositions for large - scale vectors , matrices , or low - order tensors . we provide extended definitions of mathematical multilinear operations such as kronecker , hadamard , and contracted products , with their properties for tensor calculus . then we introduce an effective low - rank tensor approximation technique called the tensor train ( tt ) format with a number of mathematical and graphical representations . we also provide a brief review of mathematical properties of the tt format as a low - rank approximation technique . with the aim of breaking the curse - of - dimensionality in large - scale numerical analysis , we describe basic operations on large - scale vectors and matrices in tt format . the suggested representations can be used for describing numerical methods based on the tt format for solving large - scale optimization problems such as the system of linear equations and eigenvalue problems .

1206.2854

i

closely spaced double layer electron systems possess an additional , layer degree of freedom , which in certain conditions stabilizes ground states with no counterpart in the single layer case . notable examples include fractional quantum hall states ( qhs ) at even denominator fillings , such as @xmath0 @xcite and @xmath1 @xcite , or a peculiar qhs at total filling factor @xmath2 ( layer filling factor 1/2 ) @xcite . the @xmath2 qhs in interacting double layers displays striking transport properties such as enhanced inter - layer tunneling @xcite and counterflow superfluidity @xcite , and has been likened to a bcs exciton condensate @xcite . dipolar superfluidity has been posited to also occur at zero magnetic field @xcite in spatially separated , closely spaced two - dimensional electron and hole systems , thanks to the pairing of carriers in opposite layers . although remarkable progress has been made in the realization of high mobility electron - hole bilayers @xcite , an unambiguous signature of electron - hole pairing remains to be experimentally observed . the common thread in these phenomena is the inter - layer coulomb interaction being comparable in strength to the intra - layer interaction , leading to many - particle ground states involving the carriers of _ both _ layers . the emergence of graphene @xcite as an electronic material has opened fascinating avenues in the study of the electron physics in reduced dimensions . thanks to its atomically thin vertical dimension , graphene allows separate two - dimensional electron systems to be brought in close proximity , at separations otherwise not accessible in other heterostructures , and tantalizing theoretical predictions are based on this property @xcite . in light of these observations , it is of interest to explore electron physics in closely spaced graphene double layers . here we discuss the fabrication , and key electron transport properties in this system , namely individual layer resistivity and coulomb drag . we introduce a model to describe the layer density dependence on gate and inter - layer bias , and show that calculations agree well with experimental results in zero and high magnetic fields . coulomb drag measurements reveal two distinct regimes : ( i ) diffusive drag at elevated temperatures , and ( ii ) mesoscopic fluctuations - dominated drag at low temperatures . while we focus here on graphene double layers separated by a thin metal - oxide dielectric , a system with which the authors are most familiar with @xcite , we also note recent progress in graphene double layers separated by hexagonal boron nitride @xcite .

we outline a simple band structure model relating the layer densities to the applied gate and inter - layer biases , and show that calculations and experimental results are in excellent agreement both at zero and in high magnetic fields . coulomb drag measurements , which probe the electron - electron scattering between the two layers reveal two distinct regime : ( i ) diffusive drag at elevated temperatures , and ( ii ) mesoscopic fluctuation - dominated drag at low temperatures . we discuss the coulomb drag results within the framework of existing theories .

we review the fabrication and key transport properties of graphene double layers , consisting of two graphene monolayers placed in close proximity , independently contacted , and separated by an ultra - thin dielectric . we outline a simple band structure model relating the layer densities to the applied gate and inter - layer biases , and show that calculations and experimental results are in excellent agreement both at zero and in high magnetic fields . coulomb drag measurements , which probe the electron - electron scattering between the two layers reveal two distinct regime : ( i ) diffusive drag at elevated temperatures , and ( ii ) mesoscopic fluctuation - dominated drag at low temperatures . we discuss the coulomb drag results within the framework of existing theories . = 1 graphene , double layer , coulomb drag , quantum hall 73.22.pr , 73.43.-f , 73.22.gk , 71.35.-y

cond-mat0208455

i

properties of systems with long range interactions are to a large extent only poorly understood although they concern a wide range of problems in physics . recently , the disclosure of new methodologies to approach the study of these systems has revealed its importance also in a trans - disciplinary perspective ( astrophysics , nuclear physics , plasmas physics , bose - einstein condensates , atomic clusters , hydrodynamics , ... ) . the main challenge is represented by the construction of a thermodynamic treatment of systems with long range forces and by the understanding of analogies and differences among the numerous domains of applications . some promising results in this direction have been recently obtained in the attempt of combining tools developed in the framework of standard statistical mechanics with concepts and methods of dynamical systems . particularly arduous , but very exciting , is the understanding of phase transitions ( negative specific heat , non extensive thermodynamics , ... ) for such systems as well as all the aspects related to non - equilibrium phenomena and their description in terms of dynamical concepts ( self - consistent chaos , slow relaxation , formation and role of structures , ... ) . finally this fundamental and methodological study should help us to detect the depth and the origin of the analogies found in the different domains mentioned above or on the contrary emphasize their specificities . in particular , we would like to put a special emphasis on bose einstein condensation ( bec ) which could be the main field of applications , since experiments and theoretical ideas have reached an impressive quality in the last decade . in that domain , many inequivalences between ensembles have been reported and should be clarified . moreover , long range interactions in bec have opened very exciting new perspectives to consider bec as a model for other systems .

we review theoretical results obtained recently in the framework of statistical mechanics to study systems with long range forces . this fundamental and methodological study leads us to consider the different domains of applications in a trans - disciplinary perspective ( astrophysics , nuclear physics , plasmas physics , metallic clusters , hydrodynamics , ... ) with a special emphasis on bose - einstein condensates .

we review theoretical results obtained recently in the framework of statistical mechanics to study systems with long range forces . this fundamental and methodological study leads us to consider the different domains of applications in a trans - disciplinary perspective ( astrophysics , nuclear physics , plasmas physics , metallic clusters , hydrodynamics , ... ) with a special emphasis on bose - einstein condensates .

math0212061

i

calabi - yau manifolds of dimensions @xmath2 and @xmath3 , i.e. elliptic curves and k3-surfaces , have a long and successful tradition in geometry and number theory . in the 1980 s , in connection with developments in string theory , calabi - yau manifolds of dimension @xmath4 moved to the forefront . emphasis has been on their complex and symplectic geometry , and in particular on the variation of the hodge structure for calabi - yau threefolds near the so - called large complex structure limit . this is the first of a series of papers in which we want to describe certain aspects of the arithmetic geometry of families of ordinary calabi - yau threefolds and analogies with complex calabi - yau threefolds near the large complex structure limit . more specifically , this paper discusses the associated crystals , i.e. modules with an integrable connection , like the gauss - manin connection on the cohomology of a family of calabi - yau threefolds . crystals which originate from geometry come with a hodge filtration , which is not preserved by the connection but instead satisfies griffiths transversality . crystals which originate from geometry in characteristic @xmath1 additionally carry an action of frobenius operators behaving in an appropriate way with respect to the connection and the hodge filtration : they are divisible hodge @xmath5-crystals . for so - called divisible _ hodge @xmath5-crystals the space of flat sections decomposes into eigenspaces for the frobenius operators . the position of the hodge filtration with respect to this eigenspace decomposition is the source for the canonical coordinates and the yukawa coupling : see theorems [ thmstructure ] , [ cy3structure ] , [ integralities ] . the ordinariness requirement implies , exactly as the requirement of maximally unipotent local monodromy in the traditional analysis of complex calabi - yau threefolds near the large complex structure limit @xcite , that there is a _ filtration which is opposite to the hodge filtration and is invariant under the gauss - manin connection and whose associated graded is of hodge - tate type _ @xcite prop.1.3.6 , @xcite 6 ) . the theory of ordinary hodge @xmath5-crystals has its origins in dwork s work on the variation of the zeta function in a family of varieties over a finite field @xcite and in the work of serre and tate on the formal moduli of deformations of an ordinary elliptic curve over a field of positive characteristic . in @xcite deligne and illusie present a general theory of ordinary hodge @xmath5-crystals and apply it to investigate the formal moduli of ordinary abelian varieties and ordinary k3-surfaces . the general theory works equally well for ordinary cy3 crystals , i.e. crystals of the kind that arises as the crystalline cohomology of ordinary calabi - yau threefolds in characteristic @xmath0 . thus , exactly as in @xcite , there are canonical coordinates on the formal moduli space . in section [ section 1 ] we briefly recall the general theory of @xcite . in section 2 we take the same algebraic path as bryant , griffiths , morrison and deligne @xcite in their analysis of the variation of the hodge structure of complex calabi - yau threefolds near a maximally degenerate ( @xmath6 maximally unipotent local monodromy @xmath6 large complex structure ) boundary point of the moduli space . in particular we find for ordinary cy3 crystals an exact analog of the cubic form of bryant - griffiths ( @xmath6 yukawa coupling ) . interestingly , besides the standard characterization ( [ eq : yukawa ] ) of the prepotential of this cubic form we find a characterization ( [ eq : yukinnerproduct ] ) by means of the action of the canonical lift of frobenius . the latter characterization remains valid if there are no parameters , i.e. if @xmath7 in ( [ eq : a ] ) , while in that case the former description is vacuous . also for the canonical coordinates the formalisms in the ordinary and the large complex structure situations match very well , but the match is not perfect : in the ordinary case the canonical coordinates take the value @xmath2 at the origin of the deformation space ( cf . ( [ eq : canorig ] ) ) , whereas the canonical coordinates at the large complex structure limit point vanish . the standard algorithms ( cf . @xcite ) for computing canonical coordinates and yukawa coupling for complex calabi - yau threefolds near the `` maximally unipotent local monodromy boundary point '' use special solutions of the picard - fuchs equations associated with the family of cy3 s and a nowhere vanishing global @xmath4-form . in remark [ picard - fuchs ] we point out that in the ordinary case one has basically the same relation between canonical coordinates , yukawa coupling and special solutions of the picard - fuchs equations ( although explicit computations seem here out of reach ) . the present paper is a survey of structures none which except maybe ( [ eq : yukinnerproduct ] ) and ( [ eq : yukinteger ] ) is new by itself , but which appear in the literature in different contexts . so we hope that there is an inspiring and cross - fertilizing effect from putting them into one ( con)text . for instance , being alerted that for the deformation theory of ordinary calabi - yau threefolds the cubic form of bryant - griffiths ( yukawa coupling ) should be relevant , one may wonder how that shows up in connection with the hodge - tate decomposition of @xmath1-adic tale cohomology as in @xcite p. 109 . the original motivation for our work was to find a general method of proof for the integrality conjectures in mirror symmetry by reducing them to known results or easy to check conditions on the crystalline cohomology for families of calabi - yau threefolds in positive characteristics : it has been observed in many examples in the literature on mirror symmetry for calabi - yau threefolds , that the coefficients in appropriate expansions of the canonical coordinates and of the prepotential of the yukawa coupling are integers . in the famous example of the quintics in @xmath8 ( see @xcite ) one has for instance @xmath9 where @xmath10 is the parameter and @xmath11 is the canonical coordinate of the family @xmath12 the yukawa coupling @xmath13 is given by @xmath14 @xmath15 the prepotential @xmath16 is defined ( up to terms of order @xmath17 in @xmath18 ) by @xmath19 and has an expansion @xmath20 where @xmath21 is the trilogarithm function . according to the mirror symmetry conjecture @xcite the number @xmath22 is the number of rational curves of degree @xmath23 on a generic quintic hypersurface in @xmath8 . for the integrality conjecture one is interested in the less astonishing , but still highly non - trivial fact that these numbers are integers . now one may note that the numbers @xmath22 are integers if and only if for every prime number @xmath1 @xmath24\ ] ] where @xmath25 is the ring of @xmath1-adic integers . in this paper we show that @xmath1-adic analogues of the integrality conjectures , in particular an analogue of ( [ eq : exa.quintic ] ) , hold true for ordinary cy3 crystals ; see formulas ( [ eq : qprops ] ) and ( [ eq : yukinteger ] ) .. ] throughout this paper the prime @xmath1 is fixed and the constructions involve choices which may depend on @xmath1 . for the integrality conjectures for families of calabi - yau threefolds , like the above quintics , one must however deal with all primes . thus one is confronted with the challenge to ` glue ' or to ` synchronize ' those choices for the various primes @xmath1 . in @xcite we will describe the beginnings of such a synchronized set - up for `` ordinariness '' . the present paper starts at the fairly abstract heights of @xmath5-crystals and wants to find out from there whether the path of ordinariness leads to interesting vistas . in @xcite we will start at a less abstract more geometric level .

we show that crystals with the properties of crystalline cohomology of ordinary calabi - yau threefolds in characteristic @xmath0 , exhibit a remarkable similarity with the well known structure on the cohomology of complex calabi - yau threefolds near a boundary point of the moduli space with maximal unipotent local monodromy . in particular , there are canonical coordinates and an analogue of the prepotential of the yukawa coupling . moreover in formulas ( [ eq : qprops ] ) and ( [ eq : yukinteger ] ) we show @xmath1-adic analogues of the integrality properties for the canonical coordinates and the prepotential of the yukawa coupling , which have been observed in the examples of mirror symmetry .

we show that crystals with the properties of crystalline cohomology of ordinary calabi - yau threefolds in characteristic @xmath0 , exhibit a remarkable similarity with the well known structure on the cohomology of complex calabi - yau threefolds near a boundary point of the moduli space with maximal unipotent local monodromy . in particular , there are canonical coordinates and an analogue of the prepotential of the yukawa coupling . moreover in formulas ( [ eq : qprops ] ) and ( [ eq : yukinteger ] ) we show @xmath1-adic analogues of the integrality properties for the canonical coordinates and the prepotential of the yukawa coupling , which have been observed in the examples of mirror symmetry .

hep-th0609094

i

larmor s formula of electromagnetism @xcite states that an electric charge in uniform motion does not radiate . however , there are two ways to have radiation from a charge moving with constant velocity . the first way is to have a particle moving in a medium with velocity exceeding the phase velocity of light in that medium . this gives rise to the well - known vavilov - cherenkov radiation @xcite . the second way is to consider charge motion in inhomogeneous media . ginzburg and frank @xcite first discussed this effect by investigating a particle in uniform motion which crosses a planar interface between two media with dissimilar refractive index . this kind of radiation is known as transition radiation @xcite . more generally , any motion near finite - size objects also induces radiation , in a process called diffraction radiation @xcite . one of the first experimental verifications on this effect was provided by smith and purcell @xcite . the smith - purcell experimental set - up consisted of an electron moving close to the surface of a metal diffraction grating at right angles to the rulings . the theory of the smith - purcell effect has been discussed by several authors @xcite . the aim of this paper is to show the existence of gravitational diffraction radiation ( gdr ) and discuss its physical effects . the model under consideration is a braneworld scenario @xcite such as , for example , the randall - sundrum i model @xcite . braneworld models have attracted a lot of interest in recent years , revolutionizing our view of how our universe may be described . the central idea of braneworld scenarios is that the visible universe is restricted to a four - dimensional brane inside a higher - dimensional space , called the bulk . the additional dimensions are taken to be compact and other branes may be moving through the bulk . interactions of the visible brane with the bulk and hidden branes introduce effects not seen in standard physics . in this set - up , a particle in uniform motion on the visible brane radiates gravitational waves due to the presence of a second ( hidden ) brane at finite distance , which plays the role of the metal diffraction grating of the smith - purcell experiment . gdr on the visible brane is generated by inhomogeneities on the hidden brane due , for example , to bulk - brane interactions and brane fluctuations @xcite . we will show that the amount of gdr depends on the size of extra dimensions and the length scale of brane perturbations . this result is general and independent on the fine details of the model . without loss of generality , in our computations we will consider a flat five - dimensional spacetime with the extra dimension taking values within the interval @xmath0 $ ] . the distance between the particle and the diffraction grating , @xmath1 , is the distance between the two branes located at the orbifold fixed points . the model is illustrated pictorially in fig . [ braneworld1 ] . the generalization to higher - dimensions is trivial and is discussed at the end of this letter . is identified with the brane at @xmath2 . the visible brane is located at @xmath3 . the particle moves on the visible brane along @xmath4 with constant velocity @xmath5 . only one transverse coordinate , @xmath6 , is shown . the right panel shows the wrapping around the extra dimension @xmath7 . if the two halves of the cylinder are identified , the randall - sundrum model i @xcite is obtained.,title="fig:",scaledwidth=45.0% ] is identified with the brane at @xmath2 . the visible brane is located at @xmath3 . the particle moves on the visible brane along @xmath4 with constant velocity @xmath5 . only one transverse coordinate , @xmath6 , is shown . the right panel shows the wrapping around the extra dimension @xmath7 . if the two halves of the cylinder are identified , the randall - sundrum model i @xcite is obtained.,title="fig:",scaledwidth=30.0% ]

we show that if the visible universe is a membrane embedded in a higher - dimensional space , particles in uniform motion radiate gravitational waves because of spacetime lumpiness . the role of the metallic grating is played by the inhomogeneities of the extra - dimensional space , such as a hidden brane . we derive a general formula for gravitational diffraction radiation and apply it to a higher - dimensional scenario with flat compact extra dimensions . this allows to set stringent limits on the scale of brane perturbations . physical effects of gravitational diffraction radiation are briefly discussed .

we show that if the visible universe is a membrane embedded in a higher - dimensional space , particles in uniform motion radiate gravitational waves because of spacetime lumpiness . this phenomenon is analogous to the electromagnetic diffraction radiation of a charge moving near to a metallic grating . in the gravitational case , the role of the metallic grating is played by the inhomogeneities of the extra - dimensional space , such as a hidden brane . we derive a general formula for gravitational diffraction radiation and apply it to a higher - dimensional scenario with flat compact extra dimensions . gravitational diffraction radiation may carry away a significant portion of the particle s initial energy . this allows to set stringent limits on the scale of brane perturbations . physical effects of gravitational diffraction radiation are briefly discussed .

hep-ph9609204

i

the discovery of the top quark at fermilab fulfilled the three - family quark picture in the standard electroweak model . up to now , some knowledge on the mass spectra of @xmath2 and @xmath3 quarks has been accumulated through both experimental and theoretical ( or phenomenological ) attempts @xcite . the ratios of quark mass eigenvalues are obtainable after one renormalizes them to a common reference scale , e.g. , @xmath4 gev or @xmath5 . there exists a clear mass hierarchy in each quark sector : @xmath6 in comparison , the masses of three charged leptons manifest a similar hierarchical pattern @xcite . quark mass eigenstates are related to quark weak ( flavor ) eigenstates by the kobayashi - maskawa ( km ) matrix @xmath7 @xcite , which provides a quite natural description of flavor mixings and @xmath1 violation in the standard model . to date , many experimental constraints on the magnitudes of the km matrix elements have been achieved . the unitarity of @xmath7 together with current data requires a unique hierarchy among the nine matrix elements @xcite : @xmath8 here @xmath9 is a necessary condition for the presence of @xmath1 violation in the km matrix . how to understand the hierarchies of quark masses and flavor mixings is an important but unsolved problem in particle physics . a natural approach to the final solution of this problem is to look for the most favorable pattern of quark mass matrices ( see , e.g. , refs . @xcite ) , which can account for all low - energy phenomena of quark mixings and @xmath1 violation . the relevant symmetries hidden in such phenomenological schemes are possible to provide useful hints toward the dynamical details of fermion mass generation . it has been speculated by some authors that the realistic fermion mass matrices could arise from the flavor permutation symmetry and its spontaneous or explicit breaking @xcite . under exact @xmath10 symmetry the mass spectrum for either up or down quark sector consists of only two levels : one is of 2-fold degeneracy with vanishing mass eigenvalues , and the other is nondegenerate ( massive ) . an appropriate breakdown of the above symmetry may lead to the observed mass hierarchy and flavor mixings . although the way to introduce the minimum number of free parameters for permutation symmetry breaking is technically trivial , its consequences on quark mixings and @xmath1 violation may be physically instructive and may even shed some light on the proper relations between the km matrix elements and quark mass ratios . indeed there has not been a satisfactory symmetry breaking pattern with enough predictive power in the literature . in this work we first stress that some observed properties of the km matrix can be interpreted by the quark mass hierarchy without the assumption of specific mass matrices . in the quark mass limits such as @xmath11 , @xmath12 or @xmath13 , we find that simple but instructive relations between the km matrix elements and quark mass ratios are suggestible from current experimental data . then we present a new quark mass _ ansatz _ through the explicit breakdown of flavor permutation symmetry at the weak scale ( @xmath14 gev ) . this _ ansatz _ contains seven free parameters , thus it can give rise to three predictions for the phenomena of quark mixings and @xmath1 violation . the typical results are @xmath15 , @xmath16 and @xmath17 in the leading order approximation . prescribing the same _ ansatz _ at the supersymmetric grand unified theory ( gut ) scale ( @xmath18 gev ) , we derive the renormalized quark mass matrices at @xmath5 for small @xmath19 ( the ratio of higgs vacuum expectation values in the minimal supersymmetric model ) . we also renormalize some relations between the km matrix elements and quark mass ratios at @xmath5 for arbitrary @xmath19 , and find that the relevant results are in good agreement with experimental data . the scale - independent predictions of our _ ansatz _ for the characteristic measurables of @xmath1 asymmetries in weak @xmath20 decays , i.e. , @xmath21 , @xmath22 and @xmath23 , can be tested at the forthcoming kek and slac @xmath20-meson factories . the remaining part of this paper is organized as follows . some qualitative implications of the quark mass hierarchy on the km matrix elements , which are almost independent of the specific forms of quark mass matrices , are discussed in section 2 . in section 3 we suggest a new quark mass _ ansatz _ from the flavor permutation symmetry breaking at the weak scale , and study its various consequences on flavor mixings and @xmath1 violation . the same _ ansatz _ is prescribed at the supersymmetric gut scale in section 4 . by use of the one - loop renormalization group equations , we run the mass matrices from @xmath24 to @xmath5 and then discuss the renormalized relations between the km matrix elements and quark mass ratios . section 5 is devoted to a brief summary of this work .

we stress that the observed pattern of flavor mixings can be partly interpreted by the quark mass hierarchy without the assumption of specific quark mass matrices . we prescribe the same _ ansatz _ at the supersymmetric grand unified theory scale , and find that its all low - energy consequences on flavor mixings and @xmath1 violation are in good agreement with current experimental data . = 17.1 cm = 24.71 cm = -15.mm = -11 mm plus 1pt minus 1pt * dpnu-96 - 39 + august 1996 * * implications of the quark mass hierarchy on flavor mixings * zhi - zhong xing _ department of physics , nagoya university , chikusa - ku , nagoya 464 - 01 , japan _ pacs number(s ) : 12.15.ff , 11.30.hv , 11.30.pb , 12.10.dm

we stress that the observed pattern of flavor mixings can be partly interpreted by the quark mass hierarchy without the assumption of specific quark mass matrices . the quantitatively proper relations between the kobayashi - maskawa matrix elements and quark mass ratios , such as @xmath0 \ ; , \ ] ] are obtainable from a simple _ ansatz _ of flavor permutation symmetry breaking at the weak scale . we prescribe the same _ ansatz _ at the supersymmetric grand unified theory scale , and find that its all low - energy consequences on flavor mixings and @xmath1 violation are in good agreement with current experimental data . = 17.1 cm = 24.71 cm = -15.mm = -11 mm plus 1pt minus 1pt * dpnu-96 - 39 + august 1996 * * implications of the quark mass hierarchy on flavor mixings * zhi - zhong xing _ department of physics , nagoya university , chikusa - ku , nagoya 464 - 01 , japan _ pacs number(s ) : 12.15.ff , 11.30.hv , 11.30.pb , 12.10.dm

nucl-th0101061

i

the possibility of getting information about the thermodynamics of nuclear matter from the analysis of intermediate energies heavy ion collisions has triggered a lot of interest in this field . starting from the pioneering work of the purdue group , when for the first time a power law was used to fit the mass spectra resulting from highly excited nuclear systems and thus suggesting that a critical phenomena was taking place , it has open the study of a rather new branch of thermodynamics i.e the study of phase transitions ( liquid - vapor ) in finite systems@xcite . one of the most challenging features that nuclear multi - fragmentation phenomena presents , is that signals of phase transitions of different orders can be extracted from experimental data . on one hand , the analogy between the nuclear force and a van der waals interaction suggests that the nuclear equation of state should reproduce the main features that characterize a liquid - gas phase transition . different indications of this kind of transition have been reported @xcite . on the other , signatures of a second order phase transition or critical behavior have been obtained assuming fisher - like scaling relations for fragment distributions @xcite . moreover , in recent works @xcite is suggested that the observed critical behavior is compatible with a first order phase transition , and it is due exclusively to finite size effects . an important point to be kept in mind is that the above mentioned approaches to the fragmentation problem are based on descriptions where not only the concept of thermodynamical equilibrium , but also the macroscopic constraints imposed to the system play a relevant role . for example , several statistical descriptions of the nuclear multi - fragmentation process , e.g. the statistical multifragmentation model ( smm ) @xcite and the microcanonical metropolis monte carlo model ( mmmc ) @xcite , employ the concept of a _ freeze - out volume _ inside of which the existence of a thermodynamical equilibrated ensemble of fragments is assumed . these statistical models have been widespreadly used by the nuclear community in a successful manner to described some experimental observations . however , from the experience gained in numerical simulations , such a concept as _ freeze - out volume _ , even as an approximation , does not seem to be completely correct . it is then important to study which kind of differences arise as a consequence of not assumming a finite volume scenario , as it is not _ a priori _ evident that the evolution of a fragmenting system confined in a finite volume would produced the same macroscopic observable when compared with a non confined one , in which an expansive motion is present as an extra collective degree of freedom . in previous works @xcite we have studied the fragmentation of a simple classical system where the dynamics is governed by a hamiltonian with a two body interaction lennard - jones term . a microscopic description , employing molecular dynamics techniques , was used in order to adequately handle the possible presence of a non equilibrium behavior . it was shown that a fragmentation time can be defined , after which a certain degree of local equilibrium is achieved in the system . this fact allowed us to calculate a caloric curve for our expanding - fragmenting system , which is characterized by the absence of a vapor branch . the aim of the present communication is to study how the restriction of a finite volume , and then the imposition of equilibration , affects some of the results obtained in the unconstrained case . we will show that one of the main effects is seen in the behavior of the caloric curve ( cc ) . for the constrained system it clearly shows a vapor - branch , which is absent in the free expanding case . this behavior is a direct consequence of the presence of a confining volume , which destroys the velocity correlations that , in the case of the free expanding system , build up an expansive flux that acts as a heat sink . nevertheless for both cases ( at rather low densities for the constrained system ) a local maximum and a loop in the cc can be seen . this feature can be associated with a negative branch in the corresponding thermal response function ( trf ) , that might signal a phase transition of first order . a gradual smoothing of the mentioned indicators is observed for the confined system at higher densities . differences in fragment mass distributions are also reported and related to the microscopic origin of such behavior . this paper is organized as follows . in section [ numsim ] we will describe the model used in our simulations . a brief review of the results already obtained for the unconstrained expanding system is included . section [ seccc ] is devoted to the study of the caloric curves . in section [ secvfo ] we study possible choices for the freeze out volume for the constrained case . in section [ sectrf ] we calculate the thermal response functions and the kinetic energy fluctuations in order to signal the presence of possible phase transitions . a microscopic correlations study is performed in section [ secspectra ] analyzing the results of two different clusterization algorithms . finally , in section [ secconclu ] , conclusions are drawn .

we study , using molecular dynamics techniques , how boundary conditions affect the process of fragmentation of finite , highly excited , lennard - jones systems . this branch is absent in the free expanding case even at high energies . the microscopic origin of this behavior is also analyzed .

we study , using molecular dynamics techniques , how boundary conditions affect the process of fragmentation of finite , highly excited , lennard - jones systems . we analyze the behavior of the caloric curves ( cc ) , the associated thermal response functions ( trf ) and cluster mass distributions for constrained and unconstrained hot drops . it is shown that the resulting cc s for the constrained case differ from the one in the unconstrained case , mainly in the presence of a `` vapor branch '' . this branch is absent in the free expanding case even at high energies . this effect is traced to the role played by the collective expansion motion . on the other hand , we found that the recently proposed characteristic features of a first order phase transition taking place in a finite isolated system , i.e. abnormally large kinetic energy fluctuations and a negative branch in the trf , are present for the constrained ( dilute ) as well the unconstrained case . the microscopic origin of this behavior is also analyzed .

cond-mat0102521

i

phase ordering dynamics describes the way in which domains of an ordered state develop when an initially disordered system is placed in an environment which promotes ordering . for instance , when a simple ferromagnet or alloy is quenched rapidly from very high to very low temperatures @xmath14 , domains of equilibrium low-@xmath14 ordered phases form and grow to macroscopic sizes . a quantitative description of the ordering process is provided by the time development of the two - point correlation function ; asymptotically , it is a function only of the separation scaled by a length which increases with time , typically as a power law @xcite . new phenomena and effects can arise when we deal with phase ordering in systems which are approaching _ nonequilibrium _ steady states . in this paper , we study a coupled - field nonequilibrium system in which one field evolves autonomously and influences the dynamics of the other . the system shows phase ordering of a new sort , whose principal characteristic is that fluctuations are very strong and do not damp down in the thermodynamic limit hence the term fluctuation - dominated phase ordering ( fdpo ) . in usual phase ordering systems such as ferromagnetic ising model , if one considers a finite system and waits for infinite time , then the system reaches a state with magnetization per site very close to the two possible values of the spontaneous magnetization , @xmath15 or @xmath16 , with very infrequent transitions between the two . this is reflected in a probability distribution for the order parameter which is sharply peaked at these two values , with the width of the peaks approaching zero in the thermodynamic limit ( fig . [ fdpo](a ) ) . by contrast , in the fdpo steady state , the system continually shows strong fluctuations in time without , however , losing macroscopic order . accordingly , the order parameter shows strong variations in time , reflected eventually in a probability distribution which remains broad even in the thermodynamic limit ( fig . [ fdpo](b ) ) . the physical system we study consists of an independently stochastically fluctuating surface of zero average slope , on which reside particles which tend to slide downwards guided by the local slopes of the surface . somewhat surprisingly , a state with uniform particle density is unstable towards large scale clustering under the action of surface fluctuations . eventually it is driven to a phase - ordered state with macroscopic inhomogeneities of the density , of the fdpo sort . besides exhibiting a broad order parameter distribution , this state shows unusual scaling of two - point correlation functions and cluster distributions . it turns out that much of the physics of this type of ordering is also captured by a simpler model involving a coarse - grained characterization of the surface alone , and we study this as well . a brief account of some of our results has appeared in @xcite . in the remainder of the introduction , we first discuss the characteristics of fdpo _ vis a vis _ normal phase - ordered states . we then discuss , in a qualitative way , the occurrence of fdpo in the surface - driven models under study . the layout of the rest of the paper is as follows . in section [ fdpo_cd ] , we define and study the coarsening and steady states of three different coarse - grained depth models of the fluctuating surfaces . in section [ understandfdpo ] , we demonstrate the existence of a power - law in the cluster size distribution , and show how it can give rise to fdpo . in section [ fdpo_sp ] , we discuss ordering of sliding particles on fluctuating surfaces . in section [ robust ] , we explore the robustness of fdpo with respect to changes in various rates defining the nonequilibrium process . finally , in section [ conclusion ] we summarize our principal results , and discuss the possible occurrence of fdpo in models of other physical systems . with the aim of bringing out the features of fluctuation dominated phase ordering ( fdpo ) in nonequilibrium systems , let us recall some familiar facts about phase ordered states in equilibrium statistical systems . we first discuss different characterizations of spontaneous ordering , following the paper of griffiths @xcite on the magnetization of idealized ferromagnets . we follow this with a discussion of fluctuations about the ordered state . * ( a ) * in the absence of a conservation law , the magnetization @xmath17 is an indicator of the ordering : m= 1 l^d _ n s_n [ defm11 ] where @xmath18 is the linear size , @xmath19 is the dimension and @xmath20 is spin at site @xmath21 . in the thermodynamic limit , the thermal average of the absolute value m_1= lim_l |m| ( nonconserved ) [ defm1 ] with boltzmann - gibbs weights for configurations provides an unequivocal measure of the order . this is because in the low - temperature ordered phase , the probability @xmath22 of occurrence of magnetization @xmath17 is peaked at @xmath23 and @xmath16 ; the peak widths approach zero in the thermodynamic limit @xmath24 , so that the average value @xmath25 coincides with the peak value @xmath15 ( fig . [ fdpo]@xmath26 ) . for the conserved order parameter case , the value of the magnetization is a constant and is same in both the disordered and ordered phase . one therefore needs a quantity that is sensitive to the difference between order and disorder . the simplest such quantity is the lowest nonzero fourier mode of the density @xcite |q| = 1 l|_n e^2i n / l(1+s_n)2| [ defq*1 ] where @xmath27 denotes the average magnetization in the @xmath28-dimensional plane @xmath21 oriented perpendicular to the @xmath29 direction . the modulus in eq . [ defq*1 ] above leads to the same value for all states which can be reached from each other by a translational shift . in the low-@xmath14 ordered phase , @xmath30 is expected to be a sharply peaked function , with peak widths vanishing in the thermodynamic limit . then the mean value @xmath31 defined by q_1= lim_l |q| ( conserved ) [ defq * ] serves as an order parameter . a disordered state corresponds to @xmath32 , while a perfectly ordered state with @xmath33 in half of the system and @xmath34 in the other half corresponds to @xmath35 * ( b ) * another characterization of the order is obtained from the asymptotic value of the 2-point spatial correlation function @xmath36 . at large separations @xmath37 , @xmath38 is expected to decouple : s_o s_o+r= s_o s_o+r = m_c^2 . [ defmc ] a finite value of @xmath39 indicates that the system has long - range order . a value @xmath40 would indicate a perfectly ordered pure phase without any droplets of the other species ( like the @xmath41 state of an ising ferromagnet ) , while @xmath42 would indicate that the phase has an admixture of droplets of the other species ( like the state of an ising ferromagnet for @xmath43 ) . in a finite system , @xmath44 is a function only of the scaled variable @xmath45 in the asymptotic scaling limit @xmath46 ( see also * ( d ) * below ) . an operational way to find the value of @xmath39 is then to read off the intercept ( @xmath47 ) in a plot of @xmath44 versus @xmath45 ; it gives @xmath48 in the @xmath24 limit . in equilibrium systems of the type discussed above , @xmath25 ( defined in eq . [ defm1 ] ) and @xmath39 coincide . * ( c ) * with a conserved scalar order parameter , the low-@xmath14 state is phase - separated , with each phase occupying a macroscopically large region , and separated from the other phase by an interface of width @xmath49 . the interfacial region is quite distinct from either phase , and on the scale of system size , it is structureless and sharp . * ( d ) * customarily in phase - ordered steady states , the spatial correlation function @xmath38 has a scaling form in @xmath50 , for @xmath51 where @xmath18 is the size of the system . in the limit @xmath52 , @xmath38 follows the form @xcite c(r ) m_c^2(1 - 2|r / l| ) ( |r / l| 0 ) [ porodr ] the origin of the linear fall in eq . [ porodr ] is easy to understand in systems where phases are separated by sharp boundaries on the scale of the system size , as in * ( c ) * above : a spatial averaging of @xmath53 produces @xmath54 with probability @xmath55 ( within a phase ) and @xmath56 with probability @xmath50 ( across phases ) . the linear drop with @xmath50 implies that the structure factor @xmath57 , which is the fourier transform of @xmath38 , is given , for large wave - vectors @xmath58 ) , by : ~1 ^d+1 . [ porod ] this form of the decay of the structure factor for scalar order parameters is known as the porod law . it is worth remarking that the forms eqs . [ porodr ] and [ porod ] also describe the behaviour of the two - point correlation function in an infinite system undergoing phase ordering starting from an initially disordered state . in such a case , @xmath18 denotes the coarsening time - dependent length scale which is the characteristic size of an ordered domain . * ( e ) * for usual phase - ordered systems , spatial fluctuations are negligible in the limit of the system size going to infinity . hence the averages of 1-point and 2-point functions over an ensemble of configurations are well represented by a spatial average for a single configuration in a large system . the phase ordering of interest in this paper occurs in certain types of nonequilibrium systems , and the resulting steady state differs qualitatively from the ordered state of equilibrium systems and other types of nonequilibrium systems considered earlier @xcite . the primary difference lies in the effects of fluctuations . customarily , fluctuations lead to large variations of the order parameter which scale sublinearly with the volume , and so are negligible in the thermodynamic limit . fluctuation effects are much stronger here , and lead to variations of the order parameter in time , without , however , losing the fact of ordering . below we discuss how the properties * ( a)-(e ) * discussed above are modified . * ( a ) * nonzero values of the averages @xmath59 and @xmath31 ( eqs . [ defm1 ] and [ defq * ] ) continue to indicate the existence of order , but no longer provide an unequivocal measure of the order parameter . this is because the probability distributions @xmath22 and @xmath30 remain broad even in the limit @xmath60 ( as shown schematically in fig [ fdpo]@xmath61 ) . * ( b ) * the measure @xmath62 of long - range order is nonzero , and its value can be found from the intercept @xmath63 . however , the value of @xmath39 is , in general , quite different from @xmath25 . * ( c ) * as with usual ordered states , the regions of pure phases are of the order of system size @xmath18 . but in contrast to the usual situation , there need not be a well - defined interfacial region , distinct from either phase . rather , the region between the two largest phase stretches is typically a finite fraction of the system size , and has a lot of structure ; this region itself contains stretches of pure phases separated by further such regions , and the pattern repeats . representative spin configurations @xmath64 for the two cases are depicted schematically in fig . [ cusp1 ] . this nested structure is consistent with a power - law distribution of cluster sizes , and thus of a critical state . the crucial extra feature of the fdpo state is that the largest clusters occupy a finite fraction of the total volume , and it is this which leads to a finite value of @xmath39 as in ( b ) above . representative spin configurations @xmath64 for the two cases are depicted schematically in fig . [ cusp1 ] . * ( d ) * the ensemble - averaged spatial correlation function @xmath38 continues to show a scaling form in @xmath50 . however , in contrast to eq . [ porod ] it exhibits a cusp ( fig . [ cusp1 ] ) at small values of @xmath50 : c(r ) m_c^2(1 - b|r l|^ ) . [ scale ] this implies that the scaled structure factor varies as ~1 ^d+ [ cusp ] with @xmath65 . this represents a marked deviation from the porod law ( eq . [ porod ] ) . we will demonstrate in some cases that this deviation is related to the power - law distribution of clusters in the interfacial region separating the domains of pure phases , as discussed in * ( c ) * above . * ( e ) * the spatial average of 1-point functions ( @xmath17 or @xmath66 ) and the 2-point function @xmath44 as a function of @xmath50 in a single configuration of a large system typically do not represent the answers obtained by averaging over an ensemble of configurations . this reflects the occurrence of macroscopic fluctuations . having described the general nature of fluctuation - dominated phase ordering , we now discuss the model systems that we have studied and which show fdpo . we consider physical processes defined on a fluctuating surface with zero average slope . the surface is assumed to have no overhangs , and so is characterized by a single - valued local height variable @xmath67 at position @xmath29 at time @xmath68 as shown in fig . the evolution of the height profile is taken to be governed by a stochastic equation . the height - height correlation function has a scaling form @xcite for large separations of space and time : ^2~|x - x|^2f(|t - t| |x - x|^z ) . [ hhcorr ] here @xmath69 is a scaling function , and @xmath70 and @xmath2 are the roughness and dynamical exponents , respectively . a common value of these exponents and scaling function for several different models of surface fluctuations indicate a common universality class for such models . in this paper we will study one - dimensional surfaces belonging to three such universality classes of surface growth . similar studies of two - dimensional surfaces @xcite show that similar fluctuation - dominated phase - ordered states arise in these cases as well . before turning to the physical model of particles sliding on such fluctuating surfaces , we address the notion of phase ordering in coarse - grained depth models associated with these surface fluctuations . in fig . [ sur1 ] we show the function @xmath71 which take values @xmath72 , @xmath73 and @xmath74 depending on whether the height is below , above or at the same level as some reference height @xmath75 . explicitly , we have @xmath76 . different definitions of @xmath77 define variants of the model ; these are studied in section ii . starting from initially flat surfaces , we study the coarsening of of up - spin or down spin phases , which arise from the evolution of surface profiles . with the passage of time , the surface gets rougher up to some length scale @xmath78 . the profile has hills and valleys , the base lengths of which are of the order of @xmath78 , implying domains of like - valued @xmath79 whose size is of the same order . once the steady state is reached , there are landscape arrangements of the order of the system size @xmath18 which occur on a time scale @xmath80 . however , these landscape fluctuations do not destroy long - range order , but cause large fluctuations in its value . now let us turn to the problem of hard - core particles sliding locally downwards under gravity on these fluctuating surfaces . figure [ par1 ] depicts the evolution of particles falling to the valley bottoms under gravity . when a local valley forms in a region ( fig . 3(a ) @xmath81 fig . 3(b ) ) , particles in that region tend to fall in and cluster together . the point is that particles stay together even when there is a small reverse fluctuation ( valley @xmath82 hill as in fig . [ par1](b ) @xmath82 ( c ) ) ; declustering occurs only if there is a rearrangement on length scales larger than the size of the valley . the combination of random surface fluctuations and the external force due to gravity drive the system towards large - scale clustering . results of our numerical studies show that in the coarsening regime , the typical scale of ordering in the particle - hole system is comparable to the length scale over which surface rearrangements take place . further , the steady state of the particle system exhibits uncommonly large fluctuations , reflecting the existence of similar fluctuations in the underlying coarse - grained depth models of the hill - valley profile . similar effects are seen in 1-point and 2-point correlation functions .

we study a new kind of phase ordering phenomenon in coarse - grained depth models of the hill - valley profile of fluctuating surfaces with zero overall tilt , and for hard - core particles sliding on such surfaces under gravity . the particles on the gbdt surface show conventional coarsening ( porod ) behavior with @xmath13 . 0.5 cm pacs numbers : 05.70.ln , 05.40.-a , 02.50.-r , 64.75.+g # 1#2#3 = 0.75 2

we study a new kind of phase ordering phenomenon in coarse - grained depth models of the hill - valley profile of fluctuating surfaces with zero overall tilt , and for hard - core particles sliding on such surfaces under gravity . we find that several such systems approach an ordered state with large scale fluctuations which make them qualitatively different from conventional phase ordered states . we consider surfaces in the edwards - wilkinson ( ew ) , kardar - parisi - zhang ( kpz ) and golubovic - bruinsma - das sarma - tamborenea ( gbdt ) universality classes . for ew and kpz surfaces , coarse - grained depth models of the surface profile exhibit coarsening to an ordered steady state in which the order parameter has a broad distribution even in the thermodynamic limit , the distribution of particle cluster sizes decays as a power - law ( with an exponent @xmath0 ) , and the 2-point spatial correlation function has a cusp ( with an exponent @xmath1 ) at small values of the argument . the latter feature indicates a deviation from the porod law which holds customarily , in coarsening with scalar order parameters . we present several numerical and exact analytical results for the coarsening process and the steady state . for linear surface models with dynamical exponent @xmath2 , we show that @xmath3 for @xmath4 , @xmath5 for @xmath6 , and there are logarithmic corrections for @xmath7 , implying @xmath1 for the ew surface and @xmath8 for the gbdt surface . within the independent interval approximation we show that @xmath9 . we also study the dynamics of hard - core particles sliding locally downwards on these fluctuating one - dimensional surfaces and find that the surface fluctuations lead to large - scale clustering of the particles . we find a surface - fluctuation driven coarsening of initially randomly arranged particles ; the coarsening length scale grows as @xmath10 . the scaled density - density correlation function of the sliding particles shows a cusp with exponent @xmath11 , and @xmath12 for the ew and kpz surfaces . the particles on the gbdt surface show conventional coarsening ( porod ) behavior with @xmath13 . 0.5 cm pacs numbers : 05.70.ln , 05.40.-a , 02.50.-r , 64.75.+g # 1#2#3 = 0.75 2

cond-mat0102521

c

in this paper we have discussed the possibility of phase ordering of a sort which is dominated by strong fluctuations . in steady state , these fluctuations lead to variations of the order parameter of order unity , but the system stays ordered in the sense that with probability one , a finite fraction of the system is occupied by a single phase . the value of this fraction fluctuates in time , leading to a broad probability distribution of the order parameter . we demonstrated these features in two types of models having to do with surface fluctuations the first , a coarse - grained depth ( cd ) model where we could establish these properties analytically , and the second a model of sliding particles ( sp ) on the surface in question . for these models we found that besides ( a ) the broad probability distribution of the order parameter ( which we may take to be the defining characteristic of fdpo ) , the steady state was also characterised by ( b ) power laws of cluster size distributions and ( c ) cusps in the scaled two - point correlation function , associated with the breakdown of the porod law . the connection between ( b ) and ( c ) was elucidated using the independent interval approximation . further , an extremal statistics argument showed that the largest cluster drawn from the power law distribution is of the order of the system size ; this implies a macroscopic ordered region , so that within our models , properties ( a ) and ( b ) are connected . there are several open questions . does fluctuation - dominated phase ordering occur in other , completely different types of systems as well ? are properties ( b ) and ( c ) necessarily concomitant with the defining property ( a ) of fdpo ? can one characterize quantitatively the dynamical behaviour in the fdpo steady state ? our model of particles sliding on a fluctuating surface relates to several physical systems of interest . first , it describes a new mechanism of large scale clustering in vibrated granular media , provided the vibrations are random both in space and time . second , it describes a special case ( the passive scalar limit ) of a crystal driven through a dissipative medium , for instance a sedimenting colloidal crystal @xcite . finally , related models describe the formation of domains in growing binary films @xcite . it would be interesting to see if ideas related to fdpo play a role in any of these systems . it would also be interesting to examine fluctuating phase - ordered states in other nonequilibrium systems from the point of view of fdpo . for instance , in a study of jamming in the bus - route model studied in @xcite , the largest empty stretch in front of a bus was found to be of order @xmath18 , and it is argued that such a stretch survives for a time which is proportional to @xmath371 for a nonvanishing rate of arrival of the passengers . these features are reminescent of the behaviour of the cd and sp models derived from the edwards - wilkinson model discussed above . however , more work is required to make a clear statement about fdpo in the bus - route model . in general , fluctuation - dominated phase ordering is evidently a possibililty that should be kept in mind when discussing new situations involving phase ordering in nonequilibrium systems , both in theory and in experiment .

in which the order parameter has a broad distribution even in the thermodynamic limit , the distribution of particle cluster sizes decays as a power - law ( with an exponent @xmath0 ) , and the 2-point spatial correlation function has a cusp ( with an exponent @xmath1 ) at small values of the argument .

we study a new kind of phase ordering phenomenon in coarse - grained depth models of the hill - valley profile of fluctuating surfaces with zero overall tilt , and for hard - core particles sliding on such surfaces under gravity . we find that several such systems approach an ordered state with large scale fluctuations which make them qualitatively different from conventional phase ordered states . we consider surfaces in the edwards - wilkinson ( ew ) , kardar - parisi - zhang ( kpz ) and golubovic - bruinsma - das sarma - tamborenea ( gbdt ) universality classes . for ew and kpz surfaces , coarse - grained depth models of the surface profile exhibit coarsening to an ordered steady state in which the order parameter has a broad distribution even in the thermodynamic limit , the distribution of particle cluster sizes decays as a power - law ( with an exponent @xmath0 ) , and the 2-point spatial correlation function has a cusp ( with an exponent @xmath1 ) at small values of the argument . the latter feature indicates a deviation from the porod law which holds customarily , in coarsening with scalar order parameters . we present several numerical and exact analytical results for the coarsening process and the steady state . for linear surface models with dynamical exponent @xmath2 , we show that @xmath3 for @xmath4 , @xmath5 for @xmath6 , and there are logarithmic corrections for @xmath7 , implying @xmath1 for the ew surface and @xmath8 for the gbdt surface . within the independent interval approximation we show that @xmath9 . we also study the dynamics of hard - core particles sliding locally downwards on these fluctuating one - dimensional surfaces and find that the surface fluctuations lead to large - scale clustering of the particles . we find a surface - fluctuation driven coarsening of initially randomly arranged particles ; the coarsening length scale grows as @xmath10 . the scaled density - density correlation function of the sliding particles shows a cusp with exponent @xmath11 , and @xmath12 for the ew and kpz surfaces . the particles on the gbdt surface show conventional coarsening ( porod ) behavior with @xmath13 . 0.5 cm pacs numbers : 05.70.ln , 05.40.-a , 02.50.-r , 64.75.+g # 1#2#3 = 0.75 2

1312.2405

c

in this paper , we showed that eulerian coherent structures and lagrangian coherent structures give very different information of the dynamics and structure of astrophysical plasma flows . eulerian coherent structures give instantaneous information of plasma dynamics and structure at a given time , whereas lagrangian coherent structures account for the integrated effect of plasma dynamics and structure in a finite - time interval . arguably , instantaneous quantities may be considered inappropriate to understand inherently transient phenomenon since such quantities may not properly convey the integrated behavior of constantly changing flow . lcs typically account for such integrated behavior more naturally by considering the integrated fluid motion to reveal organizing flow features . in the context of photospheric turbulence , we showed in figure [ fig euler ] that the eulerian analysis is able to differentiate two types of coherent structures arising from either deformation or vorticity . an enlargement of the rectangle region indicated at figure [ fig euler ] at 12-dec-2006 18:24 ut is depicted in figure [ fig zoomeuler2d ] . the pattern of streamlines in figure [ fig zoomeuler2d](a ) identifies the localized region of a vortex in the photospheric flow . figures [ fig zoomeuler2d](c ) and [ fig zoomeuler2d](d ) show that this vortex region is characterized by high values of the modulus of both deformation and vorticity . figure [ fig zoomeuler2d](b ) shows that the q - criterion can differentiate clearly two subregions : one being the deformation eulerian coherent structures ( blue subregion ) and the other being the vortical eulerian coherent structures ( red subregion ) . for the sake of clarity , a corresponding 3d view of figure [ fig zoomeuler2d ] is presented in figure [ fig zoomeuler3d ] . our eulerian analysis shows that , on average , in the plage region the deformation eulerian coherent structures dominate over the vortical eulerian coherent structures in the turbulent photospheric flows , as seen in figure [ fig pdfeuler ] . the lagrangian analysis is able to provide further information of magnetic and velocity fields of the photospheric turbulence missing in the eulerian analysis . yeates et al . ( 2012 ) demonstrated that it is possible to make the link between the squashing q - factor and the maximum lyapunov exponent @xmath39 of the repelling lagrangian coherent structures , since both quantities are similar measures of the local rate of stretching at a given point and defined by the norm of the cauchy - green tensor of the deformation imposed by the field - line mapping . note , however , that there are some differences between these two quantities . while the squashing q - factor uses the frobenius norm of the tensor , @xmath61 uses the spectral norm ; while the squashing q - factor is dimensionless , @xmath61 has units of inverse time and includes the logarithm in its definition in eq . the close similarity of these two quantities is shown in figure [ fig squash2d ] , where the squashing q - factor calculated for the same region of the photosphere under study is shown in figure [ fig squash2d](a ) and the corresponding repelling lagrangian coherent structures are shown in figure [ fig squash2d](b ) . both figures [ fig squash2d](a ) and [ fig squash2d](b ) are computed for @xmath26 = 12-dec-2006 14:24 ut and @xmath30 = + 12 h , the same as figure [ fig lcs](c ) . figure [ fig squash2d](a ) adopts the logarithmic scaling since certain trajectories typically become exponentially separated in time , which shows the emergence of thin ridges of high values of the squashing q - factor representing the quasi - separatrix layers . these ridges are interspersed by regions of low values of the squashing q - factor . figure [ fig squash2d](b ) shows the emergence of thin ridges of high positive values of @xmath39 , representing the locally strongest repelling material surfaces in the photospheric flow . these ridges are interspersed by regions of negative @xmath39 that represent converging trajectories of the plasma transport . evidently , the ridges of the quasi - separatrix layers in figure [ fig squash2d](a ) are co - spatial with the ridges of the photospheric flow in figure [ fig squash2d](b ) . for the sake of clarity , a 3d view of the rectangle regions of figure [ fig squash2d ] is presented in figure [ fig squash3d ] . note that the spiky features seen in figure [ fig squash3d](a ) may be related to numerical issues which can be smoothed by applying a refined numerical procedure @xcite . as mentioned in section 1 , the lagrangian analysis based on corks can provide insight into the relationship between magnetic fields and plasma flows in the photosphere . roudier et al . ( 2009 ) used a 48 h time sequence of the horizontal velocity data from the solar optical telescope ( sot ) onboard hinode to study the interactions between granular to supergranular scales in a quiet region of the photosphere . they showed that the tree of fragmenting granules plays a crucial role in the advection of the magnetic field and in the build - up of the magnetic network . in particular , the long time sequence of their analysis shows that the trajectory of plasma flows traced by corks matches exactly the position of the highest magnetic flux concentration of the network , which lies on supergranule boundaries . our technique of lagrangian coherent structures is closely related to corks , but gives additional important information missing in the cork - based studies as demonstrated below . figure [ fig blcs2d ] shows a comparison of the line - of - sight magnetic field @xmath11 measured by hinode / sot at @xmath62 = 13-dec-2006 02:24 ut ( figure [ fig blcs2d](a ) , same as figure [ fig euler ] ) and the attracting lagrangian coherent structures computed for @xmath26 = 13-dec-2006 02:24 ut and @xmath30 = -12 h ( figure [ fig blcs2d](b ) , same as figure [ fig lcs](f ) ) . it is possible to identify similar patterns in figures [ fig blcs2d](a ) and [ fig blcs2d](b ) . for example , a superposition of the rectangle regions marked in figures [ fig blcs2d](a)-(b ) is shown in figure [ fig blcs2d](c ) ( where the thresholded b - ftle with @xmath63 is plotted ) that shows clearly the proximity of the trajectory of plasma flows to the magnetic field , similar to the cork results of roudier et al . in addition , figure [ fig blcs2d](b ) shows the emergence of thin ridges of high positive values of @xmath39 , representing the locally strongest attracting material surfaces in the photospheric flow . these ridges are interspersed by regions of negative @xmath39 that represent diverging trajectories of the plasma transport . for the sake of clarity , a 3d view of the rectangle regions of figure [ fig blcs2d ] is presented in figure [ fig blcs3d ] . in order to confirm the validity of figures [ fig blcs2d ] and [ fig blcs3d ] , we performed 3d numerical simulations of large - scale dynamos in turbulent compressible convection with uniform horizontal shear and rotation . the dimensionless compressible magnetohydrodynamics equations are solved in a simulation box divided into three layers , an upper cooling layer , a convectively unstable layer , and a stable overshoot layer , with constant gravity in the vertical direction , as described by @xcite . the box has dimensions @xmath64 , where @xmath65 is the depth of the convectively unstable layer , and shearing periodic boundary conditions are used in the horizontal direction . in the vertical direction we use stress - free boundary conditions for the velocity field and vertical field conditions for the magnetic field . in our simulations we adopt dimensionless quantities , setting @xmath66 , where @xmath67 is gravity , distance is in units of @xmath65 , density in units of the initial value at the base of convective layer @xmath68 , time in units of the free fall time @xmath69 , velocity in units of @xmath70 and magnetic field in units of @xmath71 . the physical parameters ( e.g. kinematic viscosity , resistivity , heat conductivity , rotation velocity , etc . ) are chosen to ensure the onset of a large - scale magnetic field in a moderately turbulent velocity field . for a detailed setup , we direct the reader to run d2 in @xcite . the model is solved with the pencil code , which employes sixth - order finite - differences in space and third - order variable step runge - kutta integration in time . figure [ fig blcs_sim2d](a ) shows a 2d image of the vertical component of the magnetic field @xmath11 near the top of the convective layer at a time @xmath26 when the magnetic energy growth has already saturated . this figure shows that the simulated large - scale turbulent dynamo reproduces the pattern of convective cells , similar to granulations in the photosphere . in particular , it shows that the network of high concentration of magnetic flux is located in the boundaries between the convective cells , corresponding to the intergranular lanes . the elongated convective cells in figure [ fig blcs_sim2d ] result from the shear . since there is an imposed large - scale flow in the @xmath72 direction , it is expected that the convective cells would be elongated along this direction . this is more pronounced after a strong large - scale magnetic field develops due to the dynamo mechanim . figure [ fig blcs_sim2d](b ) shows the b - ftle computed for the horizontal velocity field @xmath73 at @xmath26 using @xmath74 time units . the ridges of high values of b - ftle in figure [ fig blcs_sim2d](b ) indicate the locations of converging plasma flows . in figure [ fig blcs_sim2d](c ) we plot the superposition of the thresholded b - ftle ( with @xmath75 ) on top of @xmath11 . for the sake of clarity , a 3d view of the rectangle regions of figure [ fig blcs_sim2d ] is given in figure [ fig blcs_sim3d ] , where the modulus of @xmath11 is plotted in comparison with the b - ftle . evidently , figures [ fig blcs_sim2d ] and [ fig blcs_sim3d ] render support for the results of figures [ fig blcs2d ] and [ fig blcs3d ] that there is correspondence of the network of high magnetic flux concentration to the attracting lcs in the photospheric velocity . in conclusion , we extended the observational study by @xcite of lagrangian coherent structures in the photospheric velocity to show that in addition to the correspondence of the network of quasi - separatrix layers in the repelling lcs demonstrated by @xcite , there is a correspondence of the network of high magnetic flux concentration to the attracting lcs in the photospheric flows , confirmed by both observations and numerical simulations . hence , the repelling and attracting lcs of the photospheric velocity provide complementary informations of the local dynamics and topology of solar magnetic fields . although the corks coincide with the network of magnetic flux , they are not the best way to find the transport barriers and the directions of the flow convergence . we showed that the attracting lcs are more suitable for these tasks because they trace continuous curves ( material lines ) that are the explicit structures potentially responsible for observed physical patterns and at the same time measure the local rate of contraction / expansion in the flow . while eulerian coherent structures provide useful insights of the snapshot of the photospheric flows , they fail to reveal the fine structures of the transport barriers and the local dynamics of the flows that are readily provided by the repelling and attracting lagrangian coherent structures . a.c.l.c . acknowledges the support of cnpq , the award of a marie curie fellowship by the european commission , and the hospitality of paris observatory . elr acknowledges the financial support of cnpq ( brazil ) and fapesp ( brazil ) . we thank petri kpyl for providing the configuration files for the pencil code mhd simulations . cadavid , a. c. , lawrence , j. k. , christian , d. j. , jess , d. b. , & mathioudakis , m. 2012 , in `` magnetic fields from the photosphere to the corona '' , t. r. rimmele , m. collados vera , et al . ( eds . ) , asp conf . series , vol . 75 - 82 * pdf of eulerian coherent structures ( ecs ) as a function of : ( a ) * @xmath21 , * ( b ) * @xmath22 , * ( c ) * q - criterion ; at 12-dec-2006 14:24 ut ( green ) , 12-dec-2006 18:24 ut ( yellow ) , 12-dec-2006 22:24 ut ( red ) , 13-dec-2006 02:24 ut ( black ) . ] = 13-dec-2006 02:24 ut and * ( b ) * the b - ftle for @xmath26 = 13-dec-2006 02:24 ut and @xmath30 = -12 h. a superposition of the rectangle regions of ( a ) and ( b ) ( green ) is shown in * ( c ) * , where the thresholded @xmath63 is applied to b - ftle . ]

we study coherent structures in solar photospheric flows in a plage in the vicinity of the active region ar 10930 using the horizontal velocity data derived from hinode / sot magnetograms . our analysis indicates that , on average , the deformation eulerian coherent structures dominate over the vortical eulerian coherent structures in the plage region . we demonstrate the correspondence of the network of high magnetic flux concentration to the attracting lagrangian coherent structures ( a - lcs ) in the photospheric velocity based on both observations and numerical simulations .

we study coherent structures in solar photospheric flows in a plage in the vicinity of the active region ar 10930 using the horizontal velocity data derived from hinode / sot magnetograms . eulerian and lagrangian coherent structures are detected by computing the q - criterion and the finite - time lyapunov exponents of the velocity field , respectively . our analysis indicates that , on average , the deformation eulerian coherent structures dominate over the vortical eulerian coherent structures in the plage region . we demonstrate the correspondence of the network of high magnetic flux concentration to the attracting lagrangian coherent structures ( a - lcs ) in the photospheric velocity based on both observations and numerical simulations . in addition , the computation of a - lcs provides a measure of the local rate of contraction / expansion of the flow .

1606.07030

c

quantum wires electrically conducting wires with diameters in the nanometer range in which quantum effects strongly influence the transport properties offer insights into fundamental questions of many - body physics as well as possible avenues to new electronic devices . it is therefore important to develop numerical and analytical tools to investigate the properties of such systems . in this paper we have studied , in particular , the simplest quantum wire device : an interacting quantum wire contacted by non - interacting leads . contrary to most previous studies , we model the lead - wire junction microscopically and include electron scattering at the junction . the latter is ignored in the most commonly used field theoretical description of this setup where the junctions between leads and quantum wire are assumed to be perfectly adiabatic . our microscopic approach starts from the opposite limit of a sharp junction leading to models of inhomogeneous tight - binding chains where parameters such as the hopping amplitude , the chemical potential , and the screened coulomb interactions abruptly change on the scale of the lattice spacing . to numerically investigate lead - wire junctions we have generalized a quantum monte carlo algorithm based on the stochastic series expansion technique which has been used previously for homogeneous systems.@xcite this method allows us to calculate response functions in imaginary time . we calculate the linear response to an infinitesimal drop in electric or magnetic field . after a fourier transformation to discrete matsubara frequencies we have shown that at sufficiently low temperatures a reliable extrapolation to zero frequency is possible , giving access to the charge and spin conductance near zero temperature . to test the validity and accuracy of this approach we have studied different homogeneous and inhomogeneous setups where the conductances are known exactly . in all those test cases we have found very good agreement of the numerical data with the exact results , establishing this method as a reliable tool to study quantum wire devices . as a first application , we have studied the conductance across a lead - wire junction in a spinless fermion system . in two previous publications,@xcite we have predicted by field theoretical means that non - trivial perfectly conducting fixed points exist despite the inhomogeneity of the system on the scale of the lattice spacing . at these fixed points the amplitude of the relevant backscattering process exactly vanishes . for the half - filled spinless fermion system we have predicted this to happen when the velocities of the excitations in lead and wire exactly match . previously , we have only been able to provide indirect numerical evidence for this fixed point by studying friedel oscillations and autocorrelations near the junction . here we have directly calculated the conductance and shown that the result near the fixed point can be well fitted by the field theory formula requiring only a single fitting parameter . next , we have also studied the conductance in inhomogeneous spinless fermion wires away from half - filling . in this case , field theory predicts that conducting fixed points still exist , however , the condition for perfect conductance is no longer a simple velocity matching . we have verified this prediction here numerically as well ; values close to perfect conductance are obtained for all fillings investigated . while spinless fermions are easiest to study by field theory , the spinful case is the experimentally more relevant one . to study whether or not non - trivial conducting fixed points still exist once the spin degree of freedom is included we have analyzed the inhomogeneous hubbard chain without magnetic field using bosonization . this analysis provided evidence for a fundamental difference to the spinless case : while the amplitude of the relevant backscattering process is always real for spinless fermions it is complex , in general , for the spinful case . for the @xmath64 symmetric inhomogeneous hubbard chain , in particular , we find to lowest order in the hubbard interaction that the imaginary part of the backscattering amplitude only vanishes at half - filling ( particle - hole symmetric case ) . if we conjecture that this holds to all orders in the interaction , then non - trivial conducting fixed points only exist for the half - filled system . numerically , we have been able to show the existence of a conducting fixed point at half - filling for the inhomogeneous hubbard model where the spin conductance takes it ideal value @xmath214 while the charge conductance will vanish in the thermodynamic limit due to the charge gap induced for repulsive interactions by a relevant bulk umklapp scattering term . on the other hand , a non - trivial fixed point was not found for several lead - wire setups away from half - filling . there seem to be therefore two main setups in which these conducting fixed points described by a rather unusual boundary conformal field theory@xcite can possibly be investigated experimentally . on the one hand , one might consider a quantum wire of spin polarized electrons which is effectively described by a spinless fermion model . on the other hand , it might be possible to use a spinful quantum wire with a low - energy band structure which can be tuned to a particle - hole symmetric filling by a gate electrode . in both cases the field theory predicts that for a sufficiently sharp junction a non - trivial conducting fixed point should be accessible by tuning the effective bandwidths and chemical potentials of the leads . for the half - filled spinful model , in particular , a fixed point with perfect spin conductance can be found for repulsive interactions while perfect charge conductance is expected for attractive interactions with backscattering at the junction being always irrelevant in the latter case . finally , we note that the experiment described in ref . has recently been analyzed using the bosonic model but without the local backscattering term .@xcite in these studies the authors find backscattering of a wavepacket injected into the lead at a lead - wire junction . we want to stress that this result is not in contradiction to the results presented here . while a wavepacket is indeed scattered at the junction in an inhomogeneous luttinger model even without a single electron backscattering term being present , the conductance will be ideal in this case as has already been stressed in ref . . j.s . acknowledges support by the natural sciences and engineering research council ( nserc , canada ) and by the deutsche forschungsgemeinschaft ( dfg ) via research unit for 2316 . this research was supported by the dfg via transregio 49 , transregio 173 , and transregio 185 ( s.e . and d.m . ) . support for this research at michigan state university ( n.s . ) was provided by the institute for mathematical and theoretical physics with funding from the office of the vice president for research and graduate studies . we are grateful for computation time at ahrp .

we study electron and spin transport in interacting quantum wires contacted by noninteracting leads . we theoretically model the wire and junctions as an inhomogeneous chain where the parameters at the junction change on the scale of the lattice spacing . we first consider an inhomogeneous spinless fermion model with a nearest - neighbor interaction and then generalize our results to a spinful model with an onsite hubbard interaction .

we study electron and spin transport in interacting quantum wires contacted by noninteracting leads . we theoretically model the wire and junctions as an inhomogeneous chain where the parameters at the junction change on the scale of the lattice spacing . we study such systems analytically in the appropriate limits based on luttinger liquid theory and compare the results to quantum monte carlo calculations of the conductances and local densities near the junction . we first consider an inhomogeneous spinless fermion model with a nearest - neighbor interaction and then generalize our results to a spinful model with an onsite hubbard interaction .

1608.08087

i

we study elementary geometric operations on triangles defined as follows . let @xmath0 be a triangle , and @xmath1 be a real number . let @xmath2 , and @xmath3 be division points of the edges @xmath4 , and @xmath5 by @xmath6 respectively , namely , @xmath7 let @xmath8 ( @xmath9 or @xmath10 ) be the intersection of the lines @xmath11 and @xmath12 ( @xmath12 and @xmath13 or @xmath13 and @xmath11 respectively ) . define _ equisection operators _ @xmath14 and @xmath15 , where @xmath15 can be defined when @xmath16 , by @xmath17 the operators @xmath14 have been studied in articles such as @xcite , _ et . al . _ ] 0.4 cm ] in this note we study the equivalence relation ( denoted by @xmath18 ) of the set of triangles ( denoted by @xmath19 ) generated by similarity and @xmath20 , which we shall call _ equisectional equivalence_. the equivalence relation generated by similarity and @xmath21 shall be called _ rational equisectional equivalence _ and denoted by @xmath22 . we say two triangles @xmath23 and @xmath24 are _ equisectionally equivalent _ ( or _ rational equisectionally equivalent _ ) if @xmath25 ( or @xmath26 respectively ) . we remark that we use the term `` similarity '' as the equivalence under orientatipon preserving homothetic transformation in this article . we say two triangles are reversely similar if they are equivalent under orientation reversing homothetic transformation . nakamura and oguiso introduced the moduli space of similarity classes of triangles in @xcite , which is a strong tool for the study of @xmath14 and @xmath15 . using their results ( explained in section [ section_no ] ) , we give ( projective ) geometric characterization of equisectionally equivalent triangles . namely , two triangles with a common base , say @xmath27 , with the third vertices , say @xmath28 and @xmath29 , in the same side of the base are equisectionally equivalent if and only if @xmath28 and @xmath29 are on the same circle of apollonius with foci being two vertices ( denoted by @xmath30 and @xmath31 ) of regular triangles with the common base @xmath27 . therefore , each equisectional equivalence class with a given base @xmath27 corresponds to a circle of apollonius with foci @xmath30 and @xmath31 . it is an element of a hyperbolic pencil of circles defined by @xmath30 and @xmath31 from a projective geometric viewpoint . we then study properties of triangles of the following three special types , right triangles , isosceles triangles , and trianges with sides in arithmetic progression ( which shall be denoted by _ sap _ triangles ) , that appear in the same equisectional equivalence class . there are ( at most ) two similarity classes of such triangles for each type , which are reversely similar in the case of right or sap triangles , or the base angles of which satisfy @xmath32 in the case of isosceles triangles . for each type we explicitly give the ratio @xmath1 such that @xmath14 maps one to the other in the same equisectional equivalence class , which implies that a pair of triangles @xmath23 and @xmath24 of one of the above special types with rational edges satisfies @xmath33 if and only if @xmath34 . we finally study compass and straightedge constructibility of @xmath1 for a given pair of triangles .

we study equivalence relation of the set of triangles generated by similarity and operation on a triangle to get a new one by joining division points of three edges with the same ratio . using the moduli space of similarity classes of triangles introduced by nakamura and oguiso , we also study rationality problem and constructibility problem .

we study equivalence relation of the set of triangles generated by similarity and operation on a triangle to get a new one by joining division points of three edges with the same ratio . using the moduli space of similarity classes of triangles introduced by nakamura and oguiso , we give characterization of equivalent triangles in terms of circles of apollonius ( or hyperbolic pencil of circles ) and properties of special equivalent triangles . we also study rationality problem and constructibility problem . 2010 _ mathematics subject classification _ : 51m04 .

1412.6200

c

in this work we have studied massive charged fermionic perturbations on the background of two - dimensional charged dilatonic black holes , and we have computed the reflection and transmission coefficients , and the absorption cross section , and we have shown numerically that the absorption cross section vanishes at the low and high frequency limits . therefore , a wave emitted from the horizon , with low or high frequency , does not reach infinity and is totally reflected , since the fraction of particles penetrating the potential barrier vanishes ; however , we have shown that there is a range of frequencies where the absorption cross section is not null . the reflection coefficient is 1 at the low frequency limit and null for the high frequency limit , demonstrating behavior opposite of the transmission coefficient , with @xmath106 . it is worth mentioning that these results , greybody factors , are consistent with other geometries of dilatonic black holes @xcite . also , we have studied the effect of the electric charge of the fermionic field over the absorption cross section , and we have observed different behaviors depending on the sign and the value of the product of the charges @xmath128 . that is , for @xmath111 we have found that the absorption cross section decreases when @xmath112 increases , due to the electric repulsion . however , for @xmath113 we have found that the absorption cross section does not depend on the value of @xmath112 , and for this case we obtain the same value of the absorption cross section as for the case @xmath129 . also , we have found that the absorption cross section increases if the mass of the fermionic field increases ; however , beyond a certain value of the frequency , the absorption cross section is constant . also , we have found that the absorption cross section for massive charged fermionic fields in a charged two - dimensional dilatonic black hole does not depend on the mass of the black hole .

then , we compute the reflection and transmission coefficients and the absorption cross section for massive charged fermionic fields , and we show that the absorption cross section vanishes at the low and high frequency limits . however , there is a range of frequencies where the absorption cross section is not null . furthermore , we study the effect of the mass and electric charge of the fermionic field over the absorption cross section .

we study massive charged fermionic perturbations in the background of a charged two - dimensional dilatonic black hole , and we solve the dirac equation analytically . then , we compute the reflection and transmission coefficients and the absorption cross section for massive charged fermionic fields , and we show that the absorption cross section vanishes at the low and high frequency limits . however , there is a range of frequencies where the absorption cross section is not null . furthermore , we study the effect of the mass and electric charge of the fermionic field over the absorption cross section .

0712.3767

c

in conclusion , contrary to the common believe that spin - orbit interaction is weak and insignificant in carbon materials , we have shown that the situation is actually much richer and that spin - orbit interaction can be very important in nanotubes . we have studied spin relaxation and decoherence caused by electron - lattice and spin - orbit interaction and predict striking non - monotonic effects induced by magnetic fields @xmath0 . for particular values of @xmath0 , destructive interference occurs resulting in ultralong spin relaxation times @xmath1 exceeding tens of seconds . for small phonon frequencies @xmath2 , we find a @xmath3 spin - phonon noise spectrum a novel dissipation channel for spins in quantum dots which can reduce @xmath1 by many orders of magnitude . we show that nanotubes exhibit zero - field level splitting caused by spin - orbit interaction . this enables an all - electrical and phase - coherent control of spin the hallmark of spintronics . we thank g. burkard , s. ilani , l. kouwenhoven , and l. vandersypen for useful discussions and e. klinovaya for pointing out several typos . we acknowledge support from the swiss nsf , nccr nanoscience , onr , and jst icorp .

we study spin relaxation and decoherence in nanotube quantum dots caused by electron - lattice and spin - orbit interaction and predict striking effects induced by magnetic fields @xmath0 . for particular values of @xmath0 , destructive interference occurs resulting in ultralong spin relaxation times @xmath1 exceeding tens of seconds . for small phonon frequencies @xmath2 , we find a @xmath3 spin - phonon noise spectrum a dissipation channel for spins in quantum dots which can reduce @xmath1 by many orders of magnitude . we show that nanotubes exhibit zero - field level splitting caused by spin - orbit interaction . this enables an all - electrical and phase - coherent control of spin .

we study spin relaxation and decoherence in nanotube quantum dots caused by electron - lattice and spin - orbit interaction and predict striking effects induced by magnetic fields @xmath0 . for particular values of @xmath0 , destructive interference occurs resulting in ultralong spin relaxation times @xmath1 exceeding tens of seconds . for small phonon frequencies @xmath2 , we find a @xmath3 spin - phonon noise spectrum a dissipation channel for spins in quantum dots which can reduce @xmath1 by many orders of magnitude . we show that nanotubes exhibit zero - field level splitting caused by spin - orbit interaction . this enables an all - electrical and phase - coherent control of spin .

1204.2611

i

since many systems in science and engineering are approximately linear , linear inverse problems have attracted great attention in the signal processing community . an input signal @xmath0 is recorded via a linear operator under additive noise : @xmath1 where @xmath2 is an @xmath3 matrix and @xmath4 denotes the noise . the goal is to estimate @xmath5 from the measurements @xmath6 given knowledge of @xmath2 and a model for the noise @xmath7 . when @xmath8 , the setup is known as compressed sensing ( cs ) and the estimation problem is commonly referred to as recovery or reconstruction ; by posing a sparsity or compressibility requirement on the signal and using this requirement as a prior during recovery , it is indeed possible to accurately estimate @xmath5 from @xmath6 @xcite . on the other hand , we might need more measurements than the signal length when the signal is dense or the noise is substantial . wu and verd @xcite have shown that independent and identically distributed ( i.i.d . ) gaussian sensing matrices achieve the same phase - transition threshold as optimal nonlinear encoding , for any discrete continuous mixture . hence , in cs the acquisition can be designed independently of the particular signal prior through the use of randomized gaussian matrices @xmath2 . nevertheless , the majority of ( if not all ) existing recovery algorithms require knowledge of the sparsity structure of @xmath5 , i.e. , the choice of a _ sparsifying transform _ @xmath9 that renders a sparse coefficient vector @xmath10 for the signal . the large majority of recovery algorithms pose a sparsity prior on the signal @xmath5 , e.g. , @xcite . a second , separate class of bayesian cs recovery algorithms poses a probabilistic prior for the coefficients of @xmath5 in a known transform domain @xcite . given a probabilistic model , some related message passing approaches learn the parameters of the signal model and achieve the minimum mean squared error ( mmse ) in some settings ; examples include em - gm - amp - mos @xcite , turbogamp @xcite , and amp - mixd @xcite . as a third alternative , complexity - penalized least square methods @xcite can use arbitrary prior information on the signal model and provide analytical guarantees , but are only computationally efficient for specific signal models , such as the independent - entry laplacian model @xcite . for example , donoho et al . @xcite relies on kolmogorov complexity , which can not be computed @xcite . as a fourth alternative , there exist algorithms that can formulate dictionaries that yield sparse representations for the signals of interest when a large amount of training data is available @xcite . when the signal is non - i.i.d . , existing algorithms require either prior knowledge of the probabilistic model @xcite or the use of training data @xcite . in certain cases , one might not be certain about the structure or statistics of the source prior to recovery . uncertainty about such structure may result in a sub - optimal choice of the sparsifying transform @xmath9 , yielding a coefficient vector @xmath11 that requires more measurements to achieve reasonable estimation quality ; uncertainty about the statistics of the source will make it difficult to select a prior or model for bayesian algorithms . thus , it would be desirable to formulate algorithms to estimate @xmath5 that are agnostic to the particular statistics of the signal . therefore , we shift our focus from the standard sparsity or compressibility priors to _ universal _ priors @xcite . such concepts have been previously leveraged in the kolmogorov sampler universal denoising algorithm @xcite , which minimizes kolmogorov complexity @xcite . related approaches based on minimum description length ( mdl ) @xcite minimize the complexity of the estimated signal with respect to some class of parametric sources . unfortunately , mdl can provide a suitable algorithmic recovery framework primarily for parametric sources @xcite . alternative approaches for non - parametric sources based on kolmogorov complexity are not computable in practice @xcite . to address this computational problem , we confine our attention to stationary ergodic sources and develop an algorithmic framework for universal signal estimation in cs systems , which can be applied to general linear inverse problems where more measurements might be needed . our framework leverages the fact that for stationary ergodic sources , both the per - symbol empirical entropy and kolmogorov complexity converge asymptotically almost surely to the entropy rate of the source @xcite . we aim to minimize the empirical entropy ; our minimization is regularized by introducing a log likelihood for the noise model , which is equivalent to the standard least squares under additive white gaussian noise . other noise distributions are readily supported . we make several contributions toward our universal cs framework . first , we apply a specific quantization grid to a maximum _ a posteriori _ ( map ) estimator driven by a universal prior , providing a finite - computation universal estimation scheme ; our scheme can also be applied to general linear inverse problems where more measurements might be needed . second , we propose a recovery algorithm based on markov chain monte carlo ( mcmc ) @xcite to approximate this estimation procedure . third , we prove that for a sufficiently large number of iterations the output of our mcmc recovery algorithm converges to the correct map estimate . fourth , we identify computational bottlenecks in the implementation of our mcmc estimator and show approaches to reduce their complexity . fifth , we develop an adaptive quantization scheme that tailors a set of reproduction levels to minimize the quantization error within the mcmc iterations and that provides an accelerated implementation . sixth , we propose a framework that adaptively adjusts the cardinality ( or size for short ) of the adaptive quantizer to match the complexity of the input signal , in order to further reduce the quantization error and computation . we note in passing that averaging over the outputs of different runs of the same signal with the same measurements will yield lower mean squared error ( mse ) for our proposed algorithm . to showcase the potential of our universal estimation approach , fig . [ fig : m4 ] illustrates recovery results from gaussian measurement matrices for a four - state markov source of length @xmath12 that generates the pattern @xmath13 with 3% errors in state transitions , resulting in the signal switching from @xmath14 to @xmath15 or vice versa either too early or too late ( see section [ sec : numerical ] for details on the simulation setup ) . note that the reconstruction algorithm does not know that this source is a binary source . while it is well known that sparsity - promoting recovery algorithms @xcite can recover sparse sources from linear measurements , the aforementioned switching source is not sparse in conventional sparsifying bases ( e.g. , fourier , wavelet , and discrete cosine transforms ) , rendering such sparsifying transforms not applicable . signals generated by this markov source can be sparsified using an averaging analysis matrix @xcite whose diagonal and first three lower sub - diagonals are filled with @xmath15 , and all other entries are @xmath16 ; this transform yields @xmath17 non - zeros in the sparse coefficient vector . however , even if this matrix is known _ a priori _ , existing algorithms based on analysis sparsity @xcite do not perform satisfactorily , yielding mean signal - to - distortion ratios below @xmath18 db ( cf . section [ sec : numerical ] ) . in contrast , our size- and level - adaptive mcmc ( sla - mcmc , cf . section [ sec : adaptive ] ) algorithm estimates this source with high fidelity when a moderate number of measurements @xmath19 are available . we provide more experimental results in section [ sec : numerical ] to show that the performance of mcmc is comparable to and in many cases better than existing algorithms . for different signal - to - noise ratio ( snr ) values ( @xmath12 ) . existing cs algorithms fail at reconstructing this signal , because it is not sparse . _ [ fig : m4],width=302 ] this paper is organized as follows . section [ sec : setting ] provides background content . section [ sec : theory ] overviews map estimation , quantization , and introduces universal map estimation . section [ sec : mcmc ] formulates an initial mcmc algorithm for universal map estimation , section [ sec : adaptive ] describes several improvements to this initial algorithm , and section [ sec : numerical ] presents experimental results . we conclude in section [ sec : conclusions ] . the proof of our main theoretical result appears in the appendix .

we study the compressed sensing ( cs ) signal estimation problem where an input signal is measured via a linear matrix multiplication under additive noise . while this setup usually assumes sparsity or compressibility in the input signal during recovery , the signal structure that can be leveraged is often not known _ a priori_. in this paper , we consider _ universal _ cs recovery , where the statistics of a stationary ergodic signal source are estimated simultaneously with the signal itself . inspired by kolmogorov complexity and minimum description length , we focus on a maximum _ a posteriori _ ( map ) estimation framework that leverages universal priors to match the complexity of the source . our framework can also be applied to general linear inverse problems where more measurements than in cs might be needed . we incorporate some techniques to accelerate the algorithm while providing comparable and in many cases better reconstruction quality than existing algorithms . compressed sensing , map estimation , markov chain monte carlo , universal algorithms .

we study the compressed sensing ( cs ) signal estimation problem where an input signal is measured via a linear matrix multiplication under additive noise . while this setup usually assumes sparsity or compressibility in the input signal during recovery , the signal structure that can be leveraged is often not known _ a priori_. in this paper , we consider _ universal _ cs recovery , where the statistics of a stationary ergodic signal source are estimated simultaneously with the signal itself . inspired by kolmogorov complexity and minimum description length , we focus on a maximum _ a posteriori _ ( map ) estimation framework that leverages universal priors to match the complexity of the source . our framework can also be applied to general linear inverse problems where more measurements than in cs might be needed . we provide theoretical results that support the algorithmic feasibility of universal map estimation using a markov chain monte carlo implementation , which is computationally challenging . we incorporate some techniques to accelerate the algorithm while providing comparable and in many cases better reconstruction quality than existing algorithms . experimental results show the promise of universality in cs , particularly for low - complexity sources that do not exhibit standard sparsity or compressibility . compressed sensing , map estimation , markov chain monte carlo , universal algorithms .

1402.4210

i

the increasing demand for accurate control of quantum devices using high - fidelity control protocols@xcite , has stimulated interest in the study of the dynamics of quantum systems in response to slowly varying hamiltonian . moreover , rapid progress in the field of adiabatic quantum computing has fueled further interest in and need for more careful analysis of the dynamics of quantum systems whose parameters vary slowly in time.@xcite in addition , decoherence in any real quantum system sets a rigid constraint on the time interval during which a quantum protocol must be carried out , limiting all protocols to intermediate time intervals that are shorter than the decoherence time . at these intermediate time scales , both non - adiabatic corrections and coupling to the environment become equally important . the previous analysis@xcite of the qubit dynamics with time - dependent hamiltonians was based on the lindblad master equation@xcite that describes the interaction with environment in terms of dephasing and transition processes characterized by phenomenological decoherence rates . an alternative microscopic approach , formulated as a perturbative theory for a quantum system with a time - independent hamiltonian interacting with its environment , introduces the bloch redfield ( br ) master equation@xcite . if the hamiltonian of the system changes in time , the br approach has to be modified to properly account for a non - adiabatic corrections . in this paper we extend the br approach to account for slow evolution of the system hamiltonian in the presence of the environment . the main concept of the br theory is based on the identification of decoherence processes in terms of the matrix elements for transitions caused by environment in the eigenstate basis of the quantum system.@xcite for the hamiltonian that varies with time , one can still use a basis defined by eigenvectors of the hamiltonian@xcite , where the hamiltonian is always represented by a diagonal matrix @xmath0 , where the unitary transformation @xmath1 denotes a transition from the original basis to the eigenstate basis . time - dependence of @xmath1 produces an extra term in the time evolution of the quantum system that is effectively described by the new hamiltonian @xmath2 . this expression is not necessarily diagonal and another basis transformation is required . such series of diagonalization transformations can be continued indefinitely , but for slowly changing hamiltonian , the series can be truncated after a finite number of transformations neglecting terms of the higher order in time - derivatives of the parameters in the hamiltonian . in addition to changes in the effective spectrum of the system , matrix elements representing coupling between the quantum system and its environment are also modified , resulting in a redefinition of the transition rates for the system . we focus our analysis on the dynamics of a two - level quantum system a qubit or a spin-1/2 system in the presence of time - dependent field , which we refer to below as the control field of the qubit . we study the dynamical response of the transverse magnetization to quench velocity of the control field . the transverse magnetization measurements can provide the value of the berry curvature of a quantum system @xcite and , consequently , characterize topological properties of a ground state of the system . since any real qubit is always coupled to its environment , it is necessary to perform detailed analysis of the non - adiabatic dynamics of a qubit system in the presence of dissipation . to this end , we investigate the effect of pure dephasing and energy relaxation due to the ohmic bath on the qubit polarization . our results indicate that the decoherence suppresses the transient wiggles of the out - of - plane qubit projection , thereby bringing up the linear relation between the qubit response and the quench velocity . thus , the dissipation facilitates the berry curvature measurement based on the non - adiabatic response , proposed in ref . @xcite . furthermore , this study is also related to the measurement technique of the berry phase in qubits , which are based on an interference experiment where the drive parameter was changed slowly @xcite , see also refs . @xcite for theoretical analysis of the influence of environment on the berry phase . we also apply the modified br equation to the landau zener ( lz ) problem@xcite in a qubit coupled to environment at arbitrary temperature . the lz problem in a quantum system coupled to its environment has attracted significant interest recently , where the environment was considered either as a source of classical noise@xcite , or quantum fluctuations that cause transitions between qubit states @xcite , or pure dephasing@xcite . more recently , the lz interferometry has attracted a growing interest@xcite . here we focus on the role of quantum fluctuations in the environment that cause transitions between the eigenstates of the qubit in the lz problem . we argue that during the lz transition , the matrix elements of the coupling between the qubit and its environment must be considered in the basis of eigenstates of the full qubit hamiltonian and therefore , the matrix elements acquire an explicit time dependence due to rotation of the eigenstate basis in addition to straightforward dependence on the energy difference between the eigenstates . this treatment modifies the previous results of refs . @xcite and generalizes the results of refs . @xcite , where a similar basis transformation was naturally included in the calculations . we disregard the effect of the lamb stark shift on the qubit spectrum due to coupling to the environment , considered in ref . @xcite , since this can be included in the redefined control field of the qubit . we focus solely on the transition effects due to non - unitary evolution of the qubit density matrix . we consider the quantum fluctuations of the environment that are fixed along the direction of the control field at very long initial and final moments of the lz transition so that the matrix element that characterizes the transition between qubit states at long times is absent and environment produces dephasing only . for arbitrary direction of the fluctuating field , the transition remains effective over long time and will effectively bring the qubit to the ground state for zero temperature environment . we also consider `` dephasing '' coupling@xcite when the quantum fluctuations occur only in the direction parallel to the direction of the control field in the parameter space of the qubit hamiltonian . our result is in agreement with ref . @xcite of the same problem within lindblad master equation , in the limit of a high - temperature environment . this paper is organized as follows . in section [ sec2 ] , we present a formalism of the br equations in transformed basis for time - dependent hamiltonians . in section [ sec3 ] , we study the evolution of a qubit whose control field rotates in a plane with a constant magnitude and consider different directions of the environmental coupling field . in section [ sec4 ] , we consider the lz problem in the presence of zero and finite temperature environment and show that transition is dominated by thermal excitation of the qubit at finite temperatures . in section [ sec5 ] , we analyze the non - adiabatic effects within the lindblad formalism . we end with conclusions in section [ sec6 ] .

we study the dynamics of a two - level system described by a slowly varying hamiltonian and weakly coupled to the ohmic environment . ( 1 ) we consider a qubit , or a spin-1/2 , in a rotating magnetic field . ( 2 ) we re - examine the landau zener transition for a system coupled to environment at arbitrary temperature . we also apply the lindblad master equations to these two problems and compare results with those obtained from the bloch redfield equations .

we study the dynamics of a two - level system described by a slowly varying hamiltonian and weakly coupled to the ohmic environment . we follow the bloch redfield perturbative approach to include the effect of the environment on qubit evolution and take into account modification of the spectrum and matrix elements of qubit transitions due to time - dependence of the hamiltonian . we apply this formalism to two problems . ( 1 ) we consider a qubit , or a spin-1/2 , in a rotating magnetic field . we show that once the rotation starts , the spin has a component perpendicular to the rotation plane of the field that initially wiggles and eventually settles to the value proportional to the product of angular rotation velocity of the field and the berry curvature . ( 2 ) we re - examine the landau zener transition for a system coupled to environment at arbitrary temperature . we show that as temperature increases , the thermal excitation and relaxation become leading processes responsible for transition between states of the system . we also apply the lindblad master equations to these two problems and compare results with those obtained from the bloch redfield equations .

1402.4210

c

in conclusion , we have presented a detailed analysis of the dynamics of an open quantum system in the presence of time - varying control field . specifically , we applied the bloch - redfield formalism to a spin-1/2 system whose hamiltonian varies slowly with time and investigated two problems . in the first problem , we studied the response of a qubit to a rotating control field of the qubit with a fixed magnitude . we noted that when the qubit basis is transformed to keep the effective hamiltonian in the diagonal form , which is required for proper perturbative analysis of the coupling between the qubit and its environment , the transformed hamiltonian acquires extra gauge terms . the gauge terms result in the modification of the qubit environment coupling and are related to the renormalization of the mass and friction terms due to changing parameters of the hamiltonian , cf . the exact form of the renormalization depends on a particular orientation of the control field with respect to the fluctuating environment field . we have illustrated this scenario by considering different orientations of the environment field : ( 1 ) control field and fluctuations are always perpendicular to each other , and the corresponding relaxation rates are time - independent ; ( 2 ) control and fluctuation fields are parallel only at some moments of time , in which case the relaxation rates significantly oscillate in time ; ( 3 ) fluctuations are always along the direction of the control field , then the relaxation rates are small in the parameter given by the ratio of the rotation velocity and level separation . our analysis offers a clear evidence of robustness of topological features against external noises . to see this one needs to consider a long time limit where the qubit density matrix reaches a steady state solution that at zero temperature coincides with the ground state of the effective hamiltonian . when this ground - state qubit configuration is looked at in the original laboratory basis , the qubit has a constant projection in the direction perpendicular to the plane of rotation and the magnitude of the projection is proportional to the product of rotation velocity of the control field and the berry curvature of the qubit ground state . in the long time limit , this response is unaffected by the environmental coupling field , at least for zero temperature environment . this relation of the response at long times and the berry curvature can be utilized as a practical method for measurements of the chern number@xcite of a quantum system . we also considered an environment with a very sharp spectral function . we represent this environment by a quantum harmonic oscillator that has internal relaxation . in this case we solve the lindblad master equation for the system of coupled qubit and oscillator and find that the results are qualitatively similar to the solution of the br equation with properly chosen relaxation rates . in the second example , we revisited the landau zener problem . in this case , the modification of the matrix elements for transitions between eigenstates of the qubit hamiltonian is essential , even though it was not always taken into account.@xcite the eigenstate basis that is necessary to use in treatment of interaction of the qubit with its environment is also convenient for numerical evaluation because in this basis the system behavior during the landau zener level crossing is represented by a smooth function that quickly reaches its long - time asymptotic value . for a qubit weakly coupled to the environment , the evolution , long after the level crossing , reduces to suppression of the off - diagonal elements of the density matrix and relaxation of the excited state to the ground state , the latter is accurately described by the rate equations . for the fluctuating field along the asymptotic direction of the control field , the relaxation rate decreases as the level separation increases due to suppression of the matrix elements of qubit transition between eigenstates caused by the environment . however , this suppression is not sufficient to cut the relaxation in the long time limit , and the relaxation results in a power law decay of the excited state , until the separation between the qubit states exceeds the ultra - violet cutoff of the environment . at finite temperature , in addition to enhancement of decoherence rates for the qubit , the excitation processes produce transitions from the ground to the excited qubit states , eventually increasing the probability for the qubit to appear in the excited state after the transition . the br equations accurately describe the crossover for the landau zener transition in an isolated quantum system , eq . , with unitary evolution , to the open system at arbitrary temperature , see sec . [ sec4 ] . furthermore , we compare the results obtained from the generalized br equations with that from the lindblad master equation . in particular , we focused on the case of pure dephasing lindblad superoperators,@xcite that are equivalent to the longitudinal coupling of the environment ( fluctuating field of the environment is along the control field ) . we found that the two results are consistent in the high temperature limit , when the lindblad and br equations are equivalent , but application of the lindblad equation for a system coupled to low temperature environment may result in unphysical solutions . finally , we note that the generalization of the bloch redfield equations can be applied to accurately evaluate the fidelity of quantum gates . by taking into account proper modification of the transition and dephasing rates caused by time - varying parameters in the hamiltonian , optimization techniques for gate operations can be further improved . similarly , the br equations for time - dependent hamiltonian are also required for accurate description of protocols for adiabatic quantum computing and the berry phase measurement in recent experiments . @xcite we thank i. aleiner , a. glaudell , f. nori , a. polkovnikov , s. shevchenko and a. levchenko for fruitful discussions . the work was supported by nsf grants no . dmr-1105178 and dmr-0955500 , aro and lps grant no . w911nf-11 - 1 - 0030 .

redfield perturbative approach to include the effect of the environment on qubit evolution and take into account modification of the spectrum and matrix elements of qubit transitions due to time - dependence of the hamiltonian . we apply this formalism to two problems . we show that once the rotation starts , the spin has a component perpendicular to the rotation plane of the field that initially wiggles and eventually settles to the value proportional to the product of angular rotation velocity of the field and the berry curvature .

we study the dynamics of a two - level system described by a slowly varying hamiltonian and weakly coupled to the ohmic environment . we follow the bloch redfield perturbative approach to include the effect of the environment on qubit evolution and take into account modification of the spectrum and matrix elements of qubit transitions due to time - dependence of the hamiltonian . we apply this formalism to two problems . ( 1 ) we consider a qubit , or a spin-1/2 , in a rotating magnetic field . we show that once the rotation starts , the spin has a component perpendicular to the rotation plane of the field that initially wiggles and eventually settles to the value proportional to the product of angular rotation velocity of the field and the berry curvature . ( 2 ) we re - examine the landau zener transition for a system coupled to environment at arbitrary temperature . we show that as temperature increases , the thermal excitation and relaxation become leading processes responsible for transition between states of the system . we also apply the lindblad master equations to these two problems and compare results with those obtained from the bloch redfield equations .

0907.3667

i

understanding of star formation and its feedback effects in the high - redshift universe is a key to unravelling how the primeval universe has evolved into the variety of luminous objects we observe today . recent numerical studies have indicated that the first stars , or pop iii.1 stars ( oshea et al . 2008 ) , presumably have typical mass of @xmath7 m@xmath8 ( abel , bryan & norman 2002 ; bromm , coppi & larson 2002 ; omukai & palla 2003 ; yoshida et al . copious amounts of radiation from such very massive stars photo - ionize hydrogen atoms and photo - dissociate molecular hydrogen in their surroundings ( kitayama et al . 2004 ; whalen et al . 2004 ) . as well as the radiative feedback , the first star deaths have an impact on subsequent star formation around them . the ultimate fate of metal - free stars is determined by their mass . stellar evolution models predict that stars with @xmath9 @xmath10 m@xmath8 finally collapse into black holes without supernovae , while those with @xmath4 @xmath9 m@xmath8 or @xmath10 @xmath11 m@xmath8 explode as type ii supernovae or pair - instability supernovae ( pisne ) , respectively ( heger & woosley 2002 ; umeda & nomoto 2002 ) . if the first star dies without supernova , the hii region is left over around a remnant black hole . at the centre of the fossil hii region , h@xmath12 is quickly replenished owing to a large amount of electrons , which are the catalysts for the h@xmath12 formation reaction . the resultant fast radiative cooling allows a small portion of the gas to re - collapse and turn into the next - generation stars , provided that no external ultraviolet ( uv ) radiation effectively dissociates h@xmath12 and the dark halo mass is higher than @xmath13 m@xmath8 ( nagakura & omukai 2005 ) . in addition , deuterated hydrogen ( hd ) molecules abundantly form in such regions and further reduce the gas temperature to that of the cmb . the re - collapsing gas fragments with typical mass of @xmath14 m@xmath8 ( yoshida et al . 2007 ) , which is an order of magnitude lower than that of the first stars ( see also , uehara & inutsuka 2000 ; nakamura & umemura 2002 ) . if the first star explodes as a supernova , the surrounding medium is severely affected by the blast wave . the blast wave removes most of the gas from a low - mass halo ( @xmath15 m@xmath8 ) even for the explosion energy as low as @xmath16 erg ( kitayama & yoshida 2005 ; whalen et al . 2008 ) , because the gas density has been decreased to @xmath17 @xmath18 @xmath19 inside the hii region . evacuation of the gas from the halo quenches subsequent star formation in the same halo without a substantial gas supply through merging with other haloes ( greif et al . 2007 ) . for a supernova in higher - mass haloes ( @xmath20 m@xmath8 ) , the situations are quite different . the halo gas remains in the hii region owing to a deeper dark matter potential well ( kitayama et al . the blast wave stagnates inside the halo and sweeps a considerable amount of gas into a dense shell ( whalen et al . such a shell is a potential site for next - generation star formation . the stability analyses of linear perturbations on an expanding and decelerating thin shell predict that small density perturbations can grow to trigger gravitational instabilities , provided that the temperature in the shell becomes low enough and sufficient gas is taken into the shell ( elmegreen 1994 ; whitworth et al . some authors have investigated the possibility of star formation triggered by the first supernova explosions ( ferrara 1998 ; mackey , bromm & hernquist 2003 ; bromm , yoshida & hernquist 2003 ; salvaterra , ferrara & schneider 2004 ; machida et al . 2005 ; vasiliev , vorobyov & shchekinov 2008 ; whalen et al . 2008 ) . applying a classical supernova remnant ( snr ) model to a primordial gas , salvaterra et al . ( 2004 ) and machida et al . ( 2005 ) found the combination of the explosion energy and the ambient density where the shell fragmentation occurs , and discussed the typical mass of the stars forming in the shell . however , their results are somewhat different because of different one - zone modelling . to solve this uncertainty , more detailed calculation is needed . supernovae also disperse heavy elements into the intergalactic medium ( igm ) ( e.g. , kitayama & yoshida 2005 ) . greif et al . ( 2007 ) showed that the metals are preferentially transfered into voids , while some of them collide with neighbouring haloes and mix with the gas in them through hydrodynamical instabilities such as kelvin - helmholtz instability . cen & riquelme ( 2008 ) showed that the mixing occurs only at the edge of haloes of @xmath21 at @xmath22 . however , irradiation of ionizing photons from neighbouring haloes , which was omitted from their analysis , may enhance the metal enrichment of lower - mass haloes at higher redshifts . turbulent motions excited by hierarchical mergers also causes the efficient metal mixing ( wise & abel 2007 ; grief et al . metals contribute to the radiative cooling of gas , having an effect on dynamical evolution of snrs . thornton et al . ( 1998 ) investigated this issue for a wide metallicity range with the intention of including the sn feedback in galaxy - formation simulations . they showed that the metal cooling modifies the redistribution of supernova energy to the surroundings for metallicity @xmath23 . however , they paid no attention to the structure and evolution of the supernova - driven shell nor to the possibility of subsequent fragmentation . the aim of this paper is to find the condition where the supernova - driven shell fragments and triggers subsequent star formation in young galaxies . towards this end , we study the evolution of supernova remnants in the low - metallicity interstellar medium by way of hydrodynamics with spherical symmetry . this paper is organized as follows : in section [ sec : models ] , we describe the numerical method and input physics . the results are presented in section [ sec : results ] , where we first describe dynamical evolution of an snr and the structure of the shell , focusing on the roles of metals , and then discuss the possibility of the shell fragmentation using the linear stability analysis by elmegreen ( 1994 ) . in section [ sec : discuss ] , by using the above result , we constrain the mass range of haloes where the triggered star formation occurs . in addition , we discuss effects of processes not included in our analysis . finally , we summarize our study in section [ sec : summary ] . throughout this paper , we adopt a flat @xmath24cdm model with parameters @xmath25 , @xmath26 , @xmath27 , and hubble parameter @xmath28 ( spergel et al . 2003 ) .

we study the evolution of supernova remnants in a low - metallicity medium @xmath0 @xmath1 in the early universe , using one - dimensional hydrodynamics with non - equilibrium chemistry . once a post - shock layer is able to cool radiatively , a dense shell forms behind the shock . [ firstpage ] cosmology : theory galaxies : formation high - redshift ism : supernova remnants shock waves stars : formation

we study the evolution of supernova remnants in a low - metallicity medium @xmath0 @xmath1 in the early universe , using one - dimensional hydrodynamics with non - equilibrium chemistry . once a post - shock layer is able to cool radiatively , a dense shell forms behind the shock . if this shell becomes gravitationally unstable and fragments into pieces , next - generation stars are expected to form from these fragments . to explore the possibility of this triggered star formation , we apply a linear perturbation analysis of an expanding shell to our results and constrain the parameter range of ambient density , explosion energy , and metallicity where fragmentation of the shell occurs . for the explosion energy of @xmath2 , the shell fragmentation occurs for ambient densities higher than @xmath3 ( @xmath4 @xmath5 , respectively ) . this condition depends little on the metallicity in the ranges we examined . we find that the mode of star formation triggered occurs only in massive ( @xmath6 ) haloes . [ firstpage ] cosmology : theory galaxies : formation high - redshift ism : supernova remnants shock waves stars : formation

0907.3667

r

we first present the result for the parameter set of @xmath109 erg , @xmath110 @xmath19 , and @xmath111 , which we hereafter call the fiducial run . [ fig1 ] shows the snapshots of ( a ) the density , ( b ) temperature , ( c ) pressure , and ( d ) velocity distribution as a function of the radius . the numbers in fig . [ fig1 ] represent the structures at time ( 1 ) @xmath112 , ( 2 ) @xmath113 , ( 3 ) @xmath114 , ( 4 ) @xmath115 , ( 5 ) @xmath116 , ( 6 ) @xmath117 , and ( 7 ) @xmath118 yr . a contact discontinuity forms quite early at the boundary between the stellar remnants and the surrounding medium , which is consistent with the previous studies ( chevalier 1974 ; cioffi , mckee & bertschinger 1988 ; thornton et al . however , this discontinuity disappears before the state ( 1 ) because the heat transfer causes the gas slightly outside it to flow into a hot interior bubble while smoothing out the boundary . the strong shock evolves adiabatically until @xmath119 yr . the post - shock density is @xmath120 times as high as that of the ambient medium . the shock front moves outwards in conformity with the canonical power - law form ; @xmath121 , where the exponent @xmath122 during the sedov - taylor ( st ) phase . the expansion time of the shock front , @xmath123 , increases linearly with the time elapsed during the st phase , while the radiative cooling time in the post - shock layer , @xmath124 , continues to decrease . after the cooling time becomes shorter than the expansion time at @xmath119 yr , the post - shock temperature quickly plunges to a low value and the gas in the post - shock layer is compressed to a thin shell . the mean pressure in the hot bubble is several orders of magnitude higher than that of the ambient medium at this moment ( fig . [ fig1 ] c ) , and drives the outward motion of the shell . this is called the pressure - driven snowplough ( pds ) phase . an analytic model of a point - source explosion exhibits @xmath125 in the absence of radiative cooling in the hot bubble ( mckee & ostriker 1977 ) . the power - law index of our results , however , deviates from that of the analytic model @xmath126 because the interior pressure at the st phase slightly increases the effective value of @xmath127 ( cioffi et al . 1988 ; see whalen et al . 2008 , in detail ) . note that the expansion law of the bubble will change with more realistic density distribution in the relic hii region , e.g. , clumpiness , and radial density gradient . these effects should be separately examined in future studies . this phase continues as long as the mean interior pressure is much higher than the ambient pressure . radiative cooling is inefficient inside the bubble because of the extremely low density , and the gas loses thermal energy through adiabatic expansion instead . the mean interior pressure continues to decrease and becomes comparable to the ambient pressure at @xmath128 myr . the motion of the shell is then driven by its momentum . this is a so - called momentum - conserving snowplough ( mcs ) phase . the thin shell model predicts that @xmath129 , but it is slightly higher in our results because of the contribution of finite pressure in the bubble ( cioffi et al . the shell s expansion velocity eventually falls to the sound speed of the ambient medium . in reality , the shell loses its identity thereafter and mixes with the ism . this is the end of the lifetime of the shell . the results of the other runs are similar to the fiducial one . in all cases , the snrs enter the mcs phase before the end of the shell lifetime . this is because the ambient temperature monotonically decreases to a low value by radiative cooling . if the ambient matter is heated , for example , by external radiation , the mcs phase is unlikely to be reached . [ fig2 ] shows time evolution of the internal structure of the shell . radial density and temperature profiles are presented against column density of hydrogen nuclei measured from the center . the column density of the shell increases as the shock front sweeps up the ambient materials , whereas the column density of the bubble decreases with time , because the mean density in the bubble quickly falls by the expansion . the mean density in the shell gradually decreases over the snowplough phase this is because the shock strength becomes weaker and weaker as the bubble expands . the minimum temperature in the shell decreases with time . note that it eventually falls below the cmb value . to see the physical processes , we plot in fig . [ fig3 ] the evolutionary trajectories of some typical fluid elements on the temperature - density diagram . these elements are taken into the shell in the snowplough phase . after they slightly drop from the initial location at @xmath130 by radiative cooling , the temperatures suddenly rise with the shock arrival . due to fast cooling from atomic hydrogen , the post - shock layer can not be resolved until the temperature falls back to @xmath131 , where the post - shock pressure balances with the ram pressure . however , our insufficient resolution there does not affect the evolution thereafter because the time - scale for the atomic cooling is very small compared with the entire evolutionary time - scale of the shell . for element ( 4 ) in fig . [ fig3 ] , the radiative cooling rate and the chemical fractions are shown in figures [ fig4 ] and [ fig5 ] , respectively . following the shock heating , the gas cools to somewhat below @xmath93 k through the ly @xmath94 emission . by this time , abundant h@xmath12 has formed as a result of a large amount of available electrons . the h@xmath12 abundance reaches as high as @xmath132 ( fig . [ fig5 ] ) , about an order of magnitude higher than that formed in an almost neutral gas . below @xmath133 8000 k , the h@xmath12 becomes the most important coolant ( fig . [ fig4 ] ) . the h@xmath12 cooling reduces the temperature down to @xmath134 k , giving rise to compression of the gas . the metal line cooling has a negligible effect during this phase because of the low abundance of metals ( fig . [ fig4 ] ) . below @xmath135 k , the h@xmath12 cooling rate significantly drops and the other coolants can not compensate for the inefficiency . at this moment , radiative cooling can not reduce the shell pressure rapidly , while the ram pressure decreases faster than the shell pressure . as a result , the shell pressure becomes higher than the ram pressure and the shell begins to gradually distend to maintain the balance of pressure . this is seen in fig . [ fig3 ] as the turn - around of the trajectories at @xmath134 k. the adiabatic expansion phase continues for @xmath136 @xmath137 yr , which is much greater than a typical time - scale for the h@xmath12 cooling phase ( @xmath138 @xmath139 yr ) , until the shell dissolves into the ambient medium . at low temperatures ( @xmath140 k ) , hd is known to form abundantly via the rightward reaction of @xmath141 although the temperature falls below the threshold for hd formation in our case , the density within the shell decreases as well . the reaction [ eq : hdfd2 ] thus proceeds slower than the evolutionary time - scale of the shell , and the hd fraction is frozen to the final abundance of @xmath142 , which is an order of magnitude smaller than the total deuterium abundance ( fig . [ fig5 ] ) . the gradual density decrease causes the hd cooling to be inefficient . for @xmath143 , the cmb heating via hd lines is weak and the trajectories in fig . [ fig3 ] exhibit the relation for the adiabatic expansion , @xmath144 , except the highest density case of trajectory 1 . note that the cooling time in the post - shock gas lengthens for smaller shock velocity , and reaches @xmath136 yr for a gas entering the shell during the mcs phase . thus , the temperature at the outer edge of the shell remains high ( fig . [ fig2 ] b ) . we use this result to explore the conditions for the shell fragmentation in section [ sec : fragment ] . for a high metallicity gas , metal cooling or heating becomes important at low temperatures ( @xmath145 k ) . in this section , we elaborate on this effect on the evolution of the shell . [ fig6 ] shows the thermal evolution of some fluid elements for the parameters @xmath109 ergs , @xmath110 @xmath19 , and @xmath146 , which is 100 times higher in metallicity than in the fiducial case . the trajectories are almost the same as those in the fiducial run until they reach @xmath134 k where the h@xmath12 cooling rate sharply decreases . in this case , the oi and then ci become the dominant coolants for @xmath147 k and @xmath148k , respectively ( fig . [ fig7 ] ) . unlike in the fiducial case , the temperatures approach the cmb value through radiative cooling rather than through the adiabatic expansion . with a rapid decrease in the radiative cooling rate near the cmb temperature , the shell begins to distend in a manner similar to the fiducial case . owing to the metal cooling , the temperatures at which the shell starts to swell are lower than those in the fiducial case . when the temperature falls below the cmb value , the radiative heating via ci lines is effective enough to keep the temperature nearly constant at @xmath149 k , although with a gradual decrease in the temperatures . thus , the final temperatures are somewhat higher than in the fiducial case . how much metallicity is needed to affect the evolution of the shell ? to answer this question , we performed other simulations with metallicity @xmath150 , and found that the metal cooling remains below that of hd molecules . hence , in this case , the evolution of the shell is almost the same as in the fiducial case . we conclude that the minimum metallicity necessary to affect the thermal evolution of the shell is @xmath151 . we will mention its influence on the conditions for the shell fragmentation in section [ sec : fragment ] . here , we discuss whether the supernova - driven shell fragments into pieces before it dissolves into the ambient medium . when the shell fragments by gravitational instability , the next - generation stars are expected to form from the fragments . conditions for fragmentation of an expanding and decelerating shell have been studied by several authors both analytically ( vishniac 1983 ; nishi 1992 ; elmegreen 1994 ; whitworth et al . 1994 ) and numerically ( yoshida & habe 1992 ; mac low & norman 1993 ) . the linear analysis by elmegreen ( 1994 ) showed that the instantaneous growth rate of density perturbations for transverse motion at wavenumber @xmath152 is given by @xmath153 where r , v , @xmath154 , and @xmath155 are the radius , velocity , unperturbed column density , and sound speed of the shell , respectively . here , the perturbations are assumed to grow in a way similar to @xmath156 . the seeds of density perturbations are generated , for instance , by the decelerating shock instability ( mac low & norman 1993 ) , or by the shock propagation into the inhomogeneous medium . the perturbations grow by collecting the ambient medium , while the new mass accretion onto the shell increases total transverse momentum . in addition , the spherical expansion stretches and attenuates perturbations . these processes are taken into account via the @xmath157 terms in equation ( [ eq : grate ] ) and the net effect acts to hinder growth of the perturbations . the maximum growth rate , @xmath158 is attained at wavenumber @xmath159 the shell becomes gravitationally unstable if @xmath160 , i.e. , @xmath161 where @xmath162 , @xmath163 , and @xmath164 are the shell expansion time , free - fall time in the shell , and the sound crossing time for the shell width , respectively . even when the shell becomes gravitationally unstable , it takes some time for the perturbations to grow to induce the fragmentation . the time - scale for fragmentation can be roughly estimated by @xmath165 . it should be noted , however , that the growth rate for a fixed wavenumber changes with time because @xmath157 and @xmath154 in equation ( [ eq : grate ] ) are modified by the mass accretion . to evaluate the typical fragmentation scale , we keep track of all the modes that attain the maximum growth rate during the shell history . for those modes , we define the fragmentation time @xmath166 as : @xmath167 where @xmath168 is the time when the mode @xmath152 first becomes unstable . namely , @xmath166 is the time for the perturbation to grow @xmath33 times the initial value . when condition ( [ eq : tfrag ] ) is met , the shell is assumed to fragment into pieces with scales corresponding to @xmath169 ( ehlerov et al . 1997 ; elmegreen , palou & ehlerov 2002 ) . we evaluate the fragment mass by @xmath170 where @xmath171 . the shell loses its identity when it slows down to the sound speed of the ambient medium . for triggering subsequent star formation , fragmentation must occur within the lifetime of the shell . in this section , we use the result of the linear analysis to find the conditions for fragmentation of a supernova - driven shell . the dispersion relation ( [ eq : maxrate ] ) is derived with one - zone approximation to the shell , whereas the shell has a stratified structure in our simulations . the application of the linear analysis to our result is , therefore , not straightforward . if the stratified structure is maintained until the shell disappears , the gravitational instability seems to occur first in a cold layer of the shell due to its low temperature . however , this is not the case because the mass of the cooled gas is not sufficient to trigger the gravitational instability . on the contrary , the coldest layer tends to gradually expand as discussed in section [ result2 ] , indicating that the self - gravity is not important there . in reality , the gravitational instability most easily occurs at the scale comparable to the width of the shell because the column density of the layer must be high enough for fragmentation . we then simply estimate a representative temperature by taking mass - weighted average over the whole shell . in fig . [ fig8 ] , we show the parameter range of ( @xmath172 where the shell fragments within its lifetime for runs with @xmath102 and @xmath173 . metallicity affects the result only for @xmath174 , where the @xmath175 run satisfies condition ( [ eq : fragcon ] ) but not ( [ eq : tfrag ] ) before the dissolution of the shell . for high ambient density , the shell accumulates a large amount of gas within the lifetime and fragments even in the case of @xmath175 . thus , the metallicity dependence disappears for such high ambient densities . in the cases of @xmath176 , the shell fragmentation occurs for both metallicities at the ambient density @xmath177 @xmath19 . for lower explosion energy @xmath178 , this threshold density increases to @xmath179 . in fig . [ fig8 ] , we also plot the conditions for shell fragmentation found by salvaterra et al . ( 2004 ) and machida et al . ( 2005 ) for comparison . the discrepancy among their conditions stems from the difference in their adopted shell temperatures and criteria for fragmentation . our result almost coincides with that by salvaterra et al . ( 2004 ) because their assumed temperature is almost the same as ours . as long as the mean temperature falls to @xmath180 @xmath181 k through h@xmath12 cooling , the total amount of gas swept up into the shell does matter for fragmentation . thus , the conditions for fragmentation rely heavily on the ambient density as well as explosion energy , but little on the metallicity . in table [ tab : timef ] , we show the properties of the shell at fragmentation time @xmath166 . there is a range of the fragment mass because some unstable modes fulfill the condition ( [ eq : tfrag ] ) soon after @xmath166 . this means that the fragmentation scale depends largely on the shape of initial perturbation , or that the shell fragments with a wide range of mass scales . the fragment mass for models with @xmath182 @xmath19 is in the range @xmath183 @xmath184 m@xmath8 , while that for a model with @xmath185 @xmath19 is an order of magnitude lower . because the wavelength @xmath186 lengthens for the smaller column density ( see equation [ eq : kmax ] ) , the fragment mass becomes higher for lower ambient density .

if this shell becomes gravitationally unstable and fragments into pieces , next - generation stars are expected to form from these fragments . to explore the possibility of this triggered star formation , we apply a linear perturbation analysis of an expanding shell to our results and constrain the parameter range of ambient density , explosion energy , and metallicity where fragmentation of the shell occurs . for the explosion energy of @xmath2 , the shell fragmentation occurs for ambient densities higher than @xmath3 ( @xmath4 @xmath5 , respectively ) . this condition depends little on the metallicity in the ranges we examined .

we study the evolution of supernova remnants in a low - metallicity medium @xmath0 @xmath1 in the early universe , using one - dimensional hydrodynamics with non - equilibrium chemistry . once a post - shock layer is able to cool radiatively , a dense shell forms behind the shock . if this shell becomes gravitationally unstable and fragments into pieces , next - generation stars are expected to form from these fragments . to explore the possibility of this triggered star formation , we apply a linear perturbation analysis of an expanding shell to our results and constrain the parameter range of ambient density , explosion energy , and metallicity where fragmentation of the shell occurs . for the explosion energy of @xmath2 , the shell fragmentation occurs for ambient densities higher than @xmath3 ( @xmath4 @xmath5 , respectively ) . this condition depends little on the metallicity in the ranges we examined . we find that the mode of star formation triggered occurs only in massive ( @xmath6 ) haloes . [ firstpage ] cosmology : theory galaxies : formation high - redshift ism : supernova remnants shock waves stars : formation

1301.6831

i

topological insulators ( tis)@xcite , as a class of materials with insulating bulk states , but conducting surface states , have been theoretically proposed@xcite and experimentally realized both in two dimensions , such as hgte quantum wells@xcite , and three dimensions@xcite , such as bi@xmath0se@xmath1 family of materials@xcite . for three dimensional ( 3d ) tis , for example , bi@xmath0se@xmath1 , the surface state consisting of a single two dimensional ( 2d ) dirac cone with the gapless dirac point protected by time reversal symmetry since the two components of the dirac cone are kramers partners . for simplicity , we can regard these two components as `` spin '' . the 2d surface state exhibits a novel `` spin - momentum locking''@xcite , in the sense that the `` spin '' is locked and points perpendicularly to the momentum , forming a left - hand helical texture in the momentum space . therefore , the surface state of tis is also dubbed `` helical metals '' ( hms)@xcite . for a finite fermi energy @xmath2 , the hm possesses a plasmon excitation similar to graphene with the dispersion @xmath3 in the long wavelength limit ( the momentum @xmath4 ) . but different from graphene , this plasmon excitation is coupled to the spin wave due to the helical nature , leading to a novel `` spin - plasmon '' mode@xcite . another intriguing feature of a hm is the hall response due to the lift of the degeneracy at the dirac point by the breaking of time reversal symmetry , when the surface of tis is coated by a ferromagnetic layer , or doped with magnetic atoms , which provide magnetization normal to the surface . if the fermi surface lies inside the magneto - bandgap , the hall conductance is half quantized as @xmath5 , known as `` half quantum hall effect''@xcite . in case of a finite fermi surface , the hall conductance is no longer quantized , but still non - zero . for a non - zero hall response , the longitudinal and transverse electromagnetic self - excitations are coupled , forming a magnetoplasmon , similar to that in the conventional metals in a strong magnetic field@xcite . it is interesting to ask what is the behavior of the `` spin - plasmon '' mode in the magnetically doped hms . in this paper , we investigate the interaction between electromagnetic fields and hms on the surface of a ti with magnetic doping , focusing on the plasmon excitation . in sec . ii , we derive the correlation function for a 2d single layer of hms and discuss how the `` spin - plasmon '' mode is affected by the magnetic doping . the electromagnetic waves exist in three dimensions and can not interact strongly with the 2d hms , so we consider a model with multilayers of hms , with an alternating stacking of tis and normal insulators . based on the dielectric function of this model , we discuss the propagating modes of the electromagnetic waves in hms , in sec . the conclusion is drawn in sec .

, we find a `` spin - plasmon '' mode with the rotating spin texture due to the combination of the spin - momentum locking of `` helical metals '' and the hall response from magnetization . for the multilayers case , we investigate the electromagnetic response due to the plasmon excitations , including the faraday rotation for the light propagating normal to the helical metal layers and an additional optical mode with the frequency within the conventional plasmon gap for the light propagating along the helical metal layers .

we study the plasmon excitations and the electromagnetic response of the magnetically doped single layer and multilayer of `` helical metals '' , which emerge at the surfaces of topological insulators . for the single layer case , we find a `` spin - plasmon '' mode with the rotating spin texture due to the combination of the spin - momentum locking of `` helical metals '' and the hall response from magnetization . for the multilayers case , we investigate the electromagnetic response due to the plasmon excitations , including the faraday rotation for the light propagating normal to the helical metal layers and an additional optical mode with the frequency within the conventional plasmon gap for the light propagating along the helical metal layers .

1005.0994

i

the new family of the charmonium or charmonium - like states include @xmath5 , @xmath6 , @xmath7 , @xmath8 , @xmath9 , @xmath10 , @xmath11 , @xmath12 , @xmath13 , @xmath14 and @xmath15 etc @xcite . many states sit on the the threshold of two charmed mesons , which inspired some of them ( especially those charged ones ) to be candidates of heavy moleculues @xcite . in the heavy quark limit , the s - wave and p - wave heavy mesons can be categorized into three doublets : @xmath16 , @xmath17 , @xmath18 . we collect their masses from pdg in table [ hs ] . the bottom mesons in the @xmath19 doublet are still missing experimentally . thus , we will adopt the theoretical predictions of the bottom meson masses in the @xmath19 doublet when we study the heavy flavor molecular system composed of the bottom and anti - bottom mesons . in the framework of the meson exchange model , we have investigated the possible loosely bound molecular states composed of a pair of heavy mesons in refs . @xcite . in this work , we will investigate the possible heavy molecular system constructed by the charmed and anti - charmed mesons , where one meson is in the @xmath20 doublet and the other one is in the @xmath19 doublet . in the following , we denote the heavy flavor molecular system as the @xmath21 system for the convenience . the @xmath22 system can be categorized into four subsystems : @xmath23 $ ] , @xmath24 $ ] , @xmath25 $ ] and @xmath26 $ ] . they correspond to different quantum number combinations @xmath27 , @xmath28 , @xmath29 and @xmath30 , respectively . since charmed mesons belong to the fundamental representation of flavor @xmath31 , the system constructed by the charmed meson and anti - charmed meson forms an octet and a singlet : @xmath32 as illustrated in table [ wavefunction ] . the parameter @xmath33 in the flavor wave functions corresponds to the charge parity @xmath34 respectively for the neutral systems as pointed out in refs . @xcite . this paper is organized as follows . we review the formalism in section [ sec2 ] and present the results in section [ sec3 ] . the last section is a short summary .

we study the possible heavy molecular states composed of a pair of charm mesons in the h and s doublets . since the p - wave charm - strange mesons @xmath0 and @xmath1 are extremely narrow , the future experimental observation of the possible heavy molecular states composed of @xmath2 and @xmath3 may be feasible if they really exist .

we study the possible heavy molecular states composed of a pair of charm mesons in the h and s doublets . since the p - wave charm - strange mesons @xmath0 and @xmath1 are extremely narrow , the future experimental observation of the possible heavy molecular states composed of @xmath2 and @xmath3 may be feasible if they really exist . especially the possible @xmath4 states may be searched for via the initial state radiation technique .

cond-mat9607188

i

after a long history in which a large number of experimental groups around the world contributed to the development of succesful methods to master stabilization and cooling of dilute bose gases , last year the aim of achieving bose - einstein condensation in such a system was finally reached . indeed , a macroscopic occupation of the one - particle ground state was irrefutably observed in magnetically trapped and evaporatively cooled alkali gas samples of @xmath1rb and @xmath2na using relatively simple time - of - flight measurements @xcite . the transition that was claimed to be seen in an experiment using @xmath3li was less convincing @xcite . in the latter case , the interatomic interaction is effectively attractive and the potential has a negative scattering length @xmath4 . therefore , bose - einstein condensation in this system is preempted by a first order phase transition to a liquid or solid phase in the homogeneous case @xcite . nevertheless , for inhomogeneous gas samples the trapping potential has a stabilizing influence and a macroscopic occupation of the ground state is possible in principle . however , when the condensate contains more than some 1500 particles under the conditions of the @xmath3li experiment @xcite , the condensate is still expected to collapse @xcite . after these first experiments , which were primarily aimed at proving the existence of a bose condensate , many experimental groups are now building or improving on their experimental setups to be able to perform much more precise measurements of various interesting properties of the gas in the degenerate regime . superfluidity @xcite , the condensate density and its profile , the dynamics of condensate formation @xcite , the josephson effect @xcite , vortex dynamics , collective excitations @xcite and the precise value of the critical temperature are examples of phenomena and quantities of interest . other types of experiments will presumably also study the properties of mixtures of atomic gases . in this respect one might think of two bosonic species with a different sign of the scattering length , or mixtures of bosons and fermions , or mixtures uniting both aspects . in the case of a pure fermionic gas of @xmath5li atoms , a bcs transition to a superfluid state is predicted to occur and should be within reach of the current experimental technology @xcite . furthermore , in some cases the magnitude and even the sign of the scattering length can be changed by varying the applied magnetic field . this opens the road to yet another type of experiment . it is clear from these possibilities that a large number of experiments are expected to be performed in the near future , which clearly makes the degenerate dilute bose gas also a very interesting subject for theoretical studies . indeed , this field of research has rapidly expanded during the last year . however , most approaches to the dilute bose gas use the bogoliubov ( or popov ) theory and are therefore of mean - field type and susceptible to improvements , both from a practical as well as a fundamental point of view . in these approaches one mostly uses the so - called two - body @xmath6matrix , or equivalently the scattering length @xmath4 . technically , this important quantity describes the collisions taking place in the dilute bose gas by summing all possible two - body scattering processes , i.e. all ladder diagrams , without taking into account the fact that the surrounding gaseous medium has an effect on these collisions . however , we have recently shown that the many - body corrections arising from the surrounding gas may be important @xcite , and are even essential for solving the problem connected to the order of the phase transition which is found to be of first order when using the two - body @xmath6matrix @xcite . including quantatively the same many - body corrections in the case of a highly inhomogeneous gas sample has at this point not yet been done . moreover , introducing the effect of the medium on two - particle collisions also in the condensed phase by means of the many - body @xmath6matrix leads to fundamental problems if we want to describe the physics at long wavelengths correctly as the ladder diagrams contain infrared divergencies in this case . using renormalization group techniques , we expect in principle to be capable of resolving these infrared problems as with this method a correct resummation of diagrams is automatically performed , eliminating any potentially troublesome large distance behavior of the individual diagrams . furthermore , a renormalization group calculation can be used to improve the usual mean - field approaches and the many - body @xmath6matrix theory in the critical region . indeed , we recently predicted by these means for example that the critical temperature in the @xmath1rb and @xmath2na experiments can , due to interaction effects only , be raised with as much as 10 % compared to the ideal gas value found from the criterion @xmath7 @xcite , which is identical to the criterion also found using mean - field calculations @xcite . here @xmath8 is the density and @xmath9 the thermal de broglie wavelength of the atoms in the gas . therefore , it is very well conceivable that in the critical region also other properties of the dilute bose gas , such as the superfluid and condensate densities , will significantly change when going beyond the mean - field level or beyond the many - body @xmath6matrix theory . the renormalization group method is a very powerful method which was in first instance developed by wilson @xcite to study the universal properties of second order phase transitions . the basic idea is to perform the trace in the grand canonical partition function @xmath10 gradually , starting with the high momentum states . after each step one tries to find a new effective hamiltonian such that @xmath11 and the trace is limited to the low momentum states which have not been reached yet . one proceeds until the complete sum has been performed . besides the partition function one in this manner also ends up with the effective hamiltonian describing the long distance properties of the system . the renormalization group method has been applied to the dilute bose gas @xcite before , but without actually performing an extensive quantitative study of this system . this is due to the fact that in general the quantities of nonuniversal nature , such as the critical temperature and the superfluid and condensate densities , depend on the microscopic details of the system considered . put differently , they depend on the ultraviolet cutoff @xmath12 of the theory and this quantity is usually unknown . however , due to the diluteness of the gas the nonuniversal properties are in the present and forthcoming experiments the most interesting ones , and therefore we are in this paper mainly interested in these aspects . the reason that it is nevertheless possible to perform a quantitative study of the dilute bose gas using the renormalization group method , is that for this system we do have sufficient information about the microscopic details to calculate and predict the nonuniversal properties . thus we can , by correctly applying this knowledge , use the renormalization group method and eliminate the cutoff dependence at the same time . we will come back to this point in sec . ii . furthermore , we will show that , in contrast to regular perturbation theory , the problems related to the infrared divergencies are in principle indeed resolved , but lead nevertheless to some problems whose solution requires further investigation . however , these problems are only of importance when the interaction energy is no longer negligible compared to the kinetic energy of the particles . the dimensionless parameter reflecting this aspect is @xmath13 . therefore , we will in this paper first concentrate on the regime where @xmath0 . we treat here only the homogeneous bose gas with effectively repulsive interactions , i.e. with a positive scattering length . however , as in all experiments up till now the number of particles @xmath14 is so large that the critical temperature @xmath15 is much larger than the energy splitting @xmath16 between subsequent levels , one can practically for all temperatures use a local density approximation to describe the gas in the trap . the criterion for this description to be valid is that the correlation length should be smaller than the typical length scale on which the atomic density varies . therefore , a local density approximation breaks down close to the edge of the gas cloud , which is for most practical purposes an unimportant region , but also in the center of the trap if the temperature approaches the critical temperature and the diverging correlation length starts to exceed the typical dimensions of the trap . the temperature interval where this occurs has a width of @xmath17 around the critical temperature . as this region is very small , we conclude that the results we find in this paper for the homogeneous gas are essentially also valid for the inner part of the trapped bose gases , and in particular pertain to the @xmath1rb and @xmath2na experiments . furthermore , we want to remark here that it would in principle also be possible to set up a renormalization group calculation for the inhomogeneous bose gas . of course , there is no real second order phase transition present in this system because the correlation length @xmath18 can never become infinite , but the techniques of renormalization group as presented in this article can still be used to calculate the ( nonuniversal ) properties also in this case . the paper is organized as follows . in sec . ii we briefly discuss the theoretical description of the dilute bose gas and the renormalization group method . in sec . iii we first apply the renormalization group to the uncondensed phase of the bose gas because the flow equations are relatively simple and easy to understand in this case . in sec . iv we then go over to the degenerate bose gas and again describe the gas properties following from the renormalization group approach . finally , in sec . v we end with some concluding remarks . in the numerical calculations we always use @xmath2na as an example , because the experiment with this atomic species is closest to the conditions of homogeneity @xcite . we take in these cases the most up - to - date value of @xmath19 for the two - body scattering length @xcite .

we study the three - dimensional atomic bose gas using renormalization group techniques . using our knowledge of the microscopic details of the interatomic interaction , we can predict for instance the critical temperature of the gas and the superfluid and condensate density of the bose - einstein condensed phase in the regime @xmath0 .

we study the three - dimensional atomic bose gas using renormalization group techniques . using our knowledge of the microscopic details of the interatomic interaction , we determine the correct initial values of our renormalization group equations and thus obtain also information on nonuniversal properties . as a result , we can predict for instance the critical temperature of the gas and the superfluid and condensate density of the bose - einstein condensed phase in the regime @xmath0 .

1011.4172

i

driven many - particle systems are often affected by strongly nonlinear fluctuations which can lead to dramatic phenomena such as self - organized density waves @xcite , jamming @xcite , and spontaneous segregation @xcite . in inhomogeneous type - ii superconductors , nonlinear phenomena resulting from the motion of magnetic flux quanta ( vortices ) have been investigated , for instance , in the context of dendritic flux instabilities stemming from the breakdown of the bean critical state @xcite . in a superconductor , vortices are subjected to the lorentz force induced by an applied current density @xmath0 and to the pinning force produced by sample inhomogeneities . a dissipative dynamical state of moving vortices is established at the critical current @xmath1 when the lorentz force overcomes pinning.@xcite just above @xmath1 , motion is usually plastic with vortices moving at different velocities , which results in a nonlinear velocity - force ( voltage - current ) characteristic . at a stronger drive , the pinning potential is washed out and the corresponding dynamical state , coined _ flux flow _ , is essentially linear . these dynamical regimes have been extensively investigated in disordered superconductors @xcite and , more recently , in films with periodic arrays of nanoengineered pinning centers.@xcite however , much less attention has been given to the dynamics of vortices in arrays of obstacles ( or antipinning centers).@xcite because in this configuration vortices are not trapped individually , it renders a very small critical current , which , in principle , has limited interest for applications . on the other hand a small @xmath1 allows for investigation of vortex motion in a much wider current range . moreover , vortices may be forced into meandering paths inducing strong lateral fluctuations that can give rise to novel dynamical phases . in this paper , we demonstrate the breakdown of the flux - flow state in a superconducting film with an array of obstacles into a vortex - density wave state and , subsequently , into a fully jammed phase . evidence of density waves in vortex systems have previously been found in the context of current - depaired vortices and antivortices in clean superconductors @xcite and turbulence in superfluids @xcite . in contrast , the phenomena we present here are collective states of the moving vortex matter resulting from the interplay of vortex - vortex interactions and the friction induced by the obstacles . as we shall see in this paper , these competing interactions lead to a critical profile of the density waves where distinct dynamical phases , as well as a jammed phase , coexist . the paper is organized as follows . in sec [ sec.model ] , we give the details of our model and numerical procedure . in sec . [ sec.dynph ] , we present the main results of our molecular dynamics simulations and discuss the dynamical phases . an analytical model is proposed in sec . [ sec.mf ] to explain the conditions for formation and stabilization of vortex - density waves and how this leads to a constant voltage regime . [ sec.mf ] is devoted to illustrating an application of the interplay between the moving and jammed phases , namely , the negative absolute resistance effect . finally , our main findings and final remarks are summarized in sec . [ sec.concl ] .

these waves are formed by a self - assembled phase separation process induced by strongly nonlinear density fluctuations of the moving vortex matter above a certain critical driving current . at high vortex concentrations , the waves move at an approximately current - independent speed resulting in a wide plateau in the voltage - current characteristics . at stronger drives , the vortex system enters into a fully jammed ( zero - voltage ) phase . by combining ac and dc drives

we study theoretically dynamical phases of vortices in superconducting films with arrays of obstacles . by performing a series of molecular dynamics simulations and analytical calculations , we demonstrate the existence of a phase of soliton - like vortex - density waves existing in a wide range of parameters . these waves are formed by a self - assembled phase separation process induced by strongly nonlinear density fluctuations of the moving vortex matter above a certain critical driving current . at high vortex concentrations , the waves move at an approximately current - independent speed resulting in a wide plateau in the voltage - current characteristics . at stronger drives , the vortex system enters into a fully jammed ( zero - voltage ) phase . by combining ac and dc drives , the interplay between the vortex - density - wave and jammed phases leads to the observation of negative absolute mobility of vortices , which induces the superconducting film into a negative resistance state .

1011.4172

c

in conclusion , we studied novel dynamical phases of vortices in a patterned superconducting film . by molecular dynamics calculations we demonstrated , for a wide range of parameters , the existence of vortex - density waves propagating at a constant speed @xmath80 larger than the mean vortex velocity @xmath134 and essentially force - independent for long - range vortex - vortex interactions . the waves consist of well - defined regions of coexisting moving phases , where vortices assist each other to either dodge or overcome the barriers , and are intercalated by regions of trapped vortices . our mean - field analysis revealed that these waves stem from fluctuations in the vortex distribution induced by a highly nonlinear friction force . a density bump produced by such fluctuations turns into a stable moving wave when it reaches a certain critical profile . it is precisely this critical shape of the waves that results in a force independent wave velocity , thereby naturally accounting for the voltage plateau observed in the md simulations . we have also demonstrated the feasibility of a superconducting device which exhibits negative absolute resistance . this is achieved by exploring a combination of ac and dc excitations in such a way as to conveniently switch the system between the moving and fully - jammed phases . this prediction could be promptly tested using conventional transport measurement techniques on a nanostructured sample with a pattern similar to that proposed here . finally , it is worth pointing out that , given the generality of our mean field model , the main results predicted here can also be applied to other systems of interacting particles , such as colloids and pedestrians . an advantage of the vortex system proposed here is that interactions can easily be tuned . in typical nanostructured superconducting films , @xmath12 can be varied from a fraction to several lattice spacings by controlling the film temperature near @xmath24 @xcite , thereby allowing for experimentally accessing our predictions in both long and short range cases . in additional modern imaging techniques could be used to identify the vortex density waves . we would like to thank alejandro v. silhanek , giovani l. vasconcelos , and leonardo r. e. cabral for useful suggestions and enlightening discussions . this work was supported by the brazilian science agencies cnpq and facepe ( grant no . apq-0589 - 1.05/08 ) .

we study theoretically dynamical phases of vortices in superconducting films with arrays of obstacles . by performing a series of molecular dynamics simulations and analytical calculations , we demonstrate the existence of a phase of soliton - like vortex - density waves existing in a wide range of parameters .

we study theoretically dynamical phases of vortices in superconducting films with arrays of obstacles . by performing a series of molecular dynamics simulations and analytical calculations , we demonstrate the existence of a phase of soliton - like vortex - density waves existing in a wide range of parameters . these waves are formed by a self - assembled phase separation process induced by strongly nonlinear density fluctuations of the moving vortex matter above a certain critical driving current . at high vortex concentrations , the waves move at an approximately current - independent speed resulting in a wide plateau in the voltage - current characteristics . at stronger drives , the vortex system enters into a fully jammed ( zero - voltage ) phase . by combining ac and dc drives , the interplay between the vortex - density - wave and jammed phases leads to the observation of negative absolute mobility of vortices , which induces the superconducting film into a negative resistance state .

1307.3512

i

in summary , we have investigated thermal transport in temperature - biased extended josephson tunnel junctions under the influence of an in - plane magnetic field . we have shown , in particular , that the heat current through the junction displays _ coherent diffraction _ , in full analogy with the josephson critical current . in an electrically - open junction configuration , minimization of the josephson coupling energy imposes the quantum phase difference across the junction to undergo @xmath0 slips in suitable magnetic flux intervals , the latter depending on the specific junction geometry . finally , we have proposed and analyzed a hybrid superconducting microstructure , easily implementable with current technology , which would allow to demonstrate diffraction of thermal currents . we wish further to stress that the described temperature detection is uniquely suited to reveal the hidden physical properties of the quantum phase in electrically - open tunnel junctions of whatever geometry otherwise more difficult to access with electric - type transport measurement . the effects here predicted could serve to enhance the flexibility to master thermal currents in emerging coherent caloritronic nanocircuitry . we would like to thanks c. altimiras for useful discussions . m.j.m .- p . acknowledges the fp7 program no . 228464 `` microkelvin '' , the italian ministry of defense through the pnrm project `` terasuper '' , and the marie curie initial training action ( itn ) q - net 264034 for partial financial support . p.s . acknowledges financial support from firb - futuro in ricerca 2012 under grant no . rbfr1236vv hybridnanodev . 99 f. giazotto , t. t. heikkil , a. luukanen , a. m. savin , and j. p. pekola , rev . mod . phys . * 78 * , 217 ( 2006 ) . y. dubi and m. di ventra , rev . * 83 * , 131 ( 2011 ) . o .- saira , m. meschke , f. giazotto , a. m. savin , m. mttnen , and j. p. pekola , phys . . lett . * 99 * , 027203 ( 2007 ) . j. p. pekola , f. giazotto , and o .- p . saira , phys . lett . * 98 * , 037201 ( 2007 ) . m. meschke , w. guichard , and j. p. pekola , nature * 444 * , 187 ( 2006 ) . e. v. bezuglyi and v. vinokur , phys . lett . * 91 * , 137002 ( 2003 ) . j. eom , c .- j . chien , and v. chandrasekhar , phys . lett . * 81 * , 437 ( 1998 ) . v. chandrasekhar , supercond . * 22 * , 083001 ( 2009 ) . v. v. ryazanov and v. v. schmidt , solid state commun . * 42 * , 733 ( 1982 ) . g. i. panaitov , v. v. ryazanov , and v. v. schmidt , phys . lett . * 100 * , 301 ( 1984 ) . p. virtanen and t. t. heikkil , appl . a * 89 * , 625 ( 2007 ) . m. j. martnez - prez and f. giazotto , appl . . lett . * 102 * , 182602 ( 2013 ) . f. giazotto , t. t. heikkil , g. p. pepe , p. helisto , a. luukanen , and j. p. pekola , appl . . lett . * 92 * , 162507 ( 2008 ) . f. giazotto , f. taddei , r. fazio , and f. beltram , appl . phys 80 * , 3784 ( 2002 ) . k. maki and a. griffin , phys . rev . lett . * 15 * , 921 ( 1965 ) . g. d. guttman , b. nathanson , e. ben - jacob , and d. j. bergman , phys . b * 55 * , 3849 ( 1997 ) . g. d. guttman , e. ben - jacob , and d. j. bergman , phys . b * 57 * , 2717 ( 1998 ) . e. zhao , t. lfwander , and j. a. sauls , phys . * 91 * , 077003 ( 2003 ) . e. zhao , t. lfwander , and j. a. sauls , phys . b * 69 * , 134503 ( 2004 ) . d. golubev , t. faivre , and j. p. pekola , phys . b * 87 * , 094522 ( 2013 ) . f. giazotto and m. j. martnez - prez , appl . * 101 * , 102601 ( 2012 ) . m. j. martnez - prez and f. giazotto , appl . 102 * , 092602 ( 2013 ) . f. giazotto and m. j. martnez - prez , nature * 492 * , 401 ( 2012 ) . r. w. simmonds , nature * 492 * , 358 ( 2012 ) . langer , v. ambegaokar , phys . rev . * 164 * , 498 ( 1967 ) . zaikin , d.s . golubev , a. van otterlo , g.t . zimanyi , phys . lett . * 78 * , 1552 ( 1997 ) . o. v. astafiev , l. b. ioffe , s. kafanov , yu . a. pashkin , k. yu . arutyunov , d. shahar , o. cohen , and j. s. tsai , nature * 484 * , 355 ( 2012 ) . arutyunov , d.s . golubev and a.d . zaikin , physics reports * 464 * , 1 ( 2008 ) . when this condition is no longer satisfied the total magnetic penetration depth has to be replaced with an effective thickness ( @xmath175 ) given by @xmath176 @xcite . m. weihnacht , phys . status solidi * 32 * , k169 ( 1969 ) . b. frank and w. krech , phys . a * 235 * , 281 ( 1997 ) . m. tinkham , _ introduction to superconductivity 2nd edn . _ ( mcgraw - hill , new york , 1996 ) . a. barone and g. patern , _ physics and applications of the josephson effect _ ( wiley , new york , 1982 ) . n. martucciello and r. monaco , phys . b * 53 * , 3471 ( 1996 ) . s. v. kuplevakhsky and a. m. glukhov , phys . rev . b * 73 * , 024513 ( 2006 ) . c. nappi , phys . rev . b * 55 * , 82 ( 1997 ) . throughout our analysis we added a small imaginary part to the energy in @xmath177 and @xmath178 to account for smearing , i.e. , @xmath179 , where @xmath180 @xcite . r. c. dynes , j. p. garno , g. b. hertel , and t. p. orlando , phys . lett . * 53 * , 2437 ( 1984 ) . j. p. pekola , t. t. heikkil , a. m. savin , j. t. flyktman , f. giazotto , and f. w. j. hekking , phys . lett . * 92 * , 056804 ( 2004 ) . j. p. pekola , v. f. maisi , s. kafanov , n. chekurov , a. kemppinen , yu . a. pashkin , o .- p . saira , m. mttnen , and j. s. tsai , phys . * 105 * , 026803 ( 2010 ) . a. v. timofeev , c. p. garcia , n. b. kopnin , a. m. savin , m. meschke , f. giazotto , and j. p. pekola , phys . * 102 * , 017003 ( 2009 ) . d. r. schmidt , r. j. schoelkopf , and a. n. cleland , phys . 93 * , 045901 ( 2004 ) .

we theoretically investigate heat transport in temperature - biased josephson tunnel junctions in the presence of an in - plane magnetic field . in full analogy with the josephson critical current , the phase - dependent component of the heat flux through the junction displays _ notably , minimization of the josephson coupling energy requires the quantum phase difference across the junction to undergo @xmath0 _ slips _ in suitable intervals of magnetic flux . an experimental setup suited to detect thermal diffraction

we theoretically investigate heat transport in temperature - biased josephson tunnel junctions in the presence of an in - plane magnetic field . in full analogy with the josephson critical current , the phase - dependent component of the heat flux through the junction displays _ coherent diffraction_. thermal transport is analyzed in three prototypical junction geometries highlighting their main differences . notably , minimization of the josephson coupling energy requires the quantum phase difference across the junction to undergo @xmath0 _ slips _ in suitable intervals of magnetic flux . an experimental setup suited to detect thermal diffraction is proposed and analyzed .

0706.0208

i

using 5 n - body simulations with different sized boxes and particle loads we considered the abundance , clustering and assembly histories of high mass halos at high redshift . we present results specifically for @xmath4 , but the evolution of the populations is smooth and the results will be similar at slightly higher and lower redshift . like the halos of rich groups or clusters today the halos we consider are in the process of forming , growing rapidly through accretions and mergers . we found that they had larger velocity dispersions than a naive application of the virial theorem would predict , due to a surface pressure from infalling material . being recently formed , the halos were not very centrally concentrated , leading to a factor of two difference between fof(0.2 ) masses and @xmath32 . when measured against @xmath32 we found our halo abundances were closer to the press - schechter fitting formula than that of @xcite , though the simulations had more high mass halos than the analytic form . if fof(0.2 ) masses were used instead , the mass function approached that of @xcite , in agreement with earlier work . this discrepancy indicates that analytic models which assign an observable to halos of a given size need to pay particular attention to the marker of halo size employed . the high mass halos were significantly clustered , and we calculated the halo bias by taking the halo - mass cross correlation and dividing by the matter auto - correlation function . our rare halos were more clustered than the recent models of @xcite and closer to the models of @xcite . merging is common , though not ubiquitous , in high mass halos at @xmath4 . major mergers , with progenitor mass ratios less than 1:3 , occurred within @xmath75myr of @xmath4 for more than half of halos with @xmath121 . we looked at the fraction of halos undergoing mergers for a variety of lookback times and progenitor ratios , finding more mergers for more massive halos , longer lookback times or less extreme merger events . mass gains , parameterized by @xmath76 , showed similar trends even though not all merger events were two body within our @xmath26myr time step . the eps model provides a reasonable description of the progenitor mass distribution , though it underpredicts the number of low mass progenitors and diverges as @xmath126 . the mass accretions histories predicted by eps , as calculated by @xcite , provide only a qualitative guide to the mean mass accretion histories seen in our simulations . at @xmath4 reionization is expected to be underway due to photon production from astrophysical objects which formed in collapsed halos . within the context of a simple model which associates mergers with an increase in photon production rate the photon production distribution developed a high rate tail due to recently merged halos . including these photon production enhancements will likely drive scatter in photon production at fixed halo mass . since the number of massive halos within a typical ionized bubble can be small , this scatter in photon production could well translate into additional scatter in bubble sizes and it would be very interesting to include this effect in approximate models of reionization . if the recently merged halos are not spatially biased with respect to other halos of the same mass , including these effects in models , even those without merger trees , should be straightforward . jdc would like to thank d. holz and s. koushiappas for conversations . we thank o. zahn for helpful comments on an early draft , and s. furlanetto , c.p . ma , l. miller , e. neistein and j. zhang for comments on the final draft . the simulations were analyzed on the supercomputers at the national energy research scientific computing center . mw was supported by nasa . we thank the referee for encouraging us to run the @xmath18mpc box .

we use a suite of high - resolution n - body simulations to study the properties , abundance and clustering of high mass halos at high redshift , including their mass assembly histories and mergers . if rare , high mass halos contribute significantly to the photon production rates , the scatter in photon production rate can translate into additional scatter in the sizes of ionized bubbles .

we use a suite of high - resolution n - body simulations to study the properties , abundance and clustering of high mass halos at high redshift , including their mass assembly histories and mergers . we find that the analytic form which best fits the abundance of halos depends sensitively on the assumed definition of halo mass , with common definitions of halo mass differing by a factor of two for these low concentration , massive halos . a significant number of massive halos are undergoing rapid mass accretion , with major merger activity being common . we compare the mergers and mass accretion histories to the extended press - schechter formalism . we consider how major merger induced star formation or black hole accretion may change the distribution of photon production from collapsed halos , and hence reionization , using some simplified examples . in all of these , the photon distribution for a halo of a given mass acquires a large scatter . if rare , high mass halos contribute significantly to the photon production rates , the scatter in photon production rate can translate into additional scatter in the sizes of ionized bubbles . -1 cm

astro-ph0605025

i

stellar streams in the milky way halo produced by the accretion of smaller galaxies are a standard prediction of hierarchical merging cosmogonies ( e.g. , * ? ? ? * and references therein ) . the most spectacular example is the disrupting sagittarius dwarf spheroidal ( sgr dsph ) , originally discovered by ibata , gilmore & irwin ( 1995 ) . it has a heliocentric distance of @xmath2 kpc and is centered at galactic coordinates of @xmath3 and @xmath4 @xcite . it is dominated by an intermediate age population ( between 6 and 9 gyrs , bellazzini et al . 2006 ) , but there is evidence for a much older population ( @xmath5 10 gyrs ) as well @xcite . the metallicity [ fe / h ] ranges from very metal - poor ( as low as -2 based on the globular clusters ) up to approximately solar , with probably a mean of @xmath6 ( * ? ? ? * and references therein ) . it was realised early on that there was some tidal debris in the neighbourhood of the sgr dsph @xcite and that the distribution of this material traced the sgr dsph orbit . subsequently , @xcite used sloan digital sky survey ( sdss ) first - year commissioning data to identify an over - density of blue a - type stars in two strips located at ( @xmath7 ) = ( @xmath8 , @xmath9 , 46 kpc ) and ( @xmath10 , @xmath11 , 33 kpc ) , which were then matched with the sgr stream @xcite . likewise , @xcite noticed that clumps of rr lyrae stars in sdss commissioning data lay along the sgr stream s orbit . the best panorama of the sgr stream to date was obtained by @xcite using m giants selected from the two micron all - sky survey ( 2mass ) . they saw the trailing tidal tail very clearly in the southern galactic hemisphere , as well as part of the leading arm reaching towards the north galactic cap . here , we use sdss data release 5 ( dr5 ) to provide a picture of the leading arm of the sgr stream in the vicinity of the north galactic cap with remarkable clarity , together with a number of other notable stellar structures in the field . [ cols="<,^,^,^,^,^,^,^,^,^,^,^,^,^,^,^,^,^,^,^",options="header " , ]

we use sloan digital sky survey ( sdss ) data release 5 ( dr5 ) @xmath0 photometry to study milky way halo substructure in the area around the north galactic cap . a simple color cut ( @xmath1 ) reveals the tidal stream of the sagittarius dwarf spheroidal , as well as a number of other stellar structures in the field .

we use sloan digital sky survey ( sdss ) data release 5 ( dr5 ) @xmath0 photometry to study milky way halo substructure in the area around the north galactic cap . a simple color cut ( @xmath1 ) reveals the tidal stream of the sagittarius dwarf spheroidal , as well as a number of other stellar structures in the field . two branches ( a and b ) of the sagittarius stream are clearly visible in an rgb - composite image created from 3 magnitude slices , and there is also evidence for a still more distant wrap behind the a branch . a comparison of these data with numerical models suggests that the shape of the galactic dark halo is close to spherical .

astro-ph0605025

c

we used a simple color cut @xmath1 to map out the distribution of stars in sdss dr5 . the `` field of streams '' is an rgb - composite image composed of magnitude slices of the stellar density of these stars . it reveals a super - abundance of galactic substructure , including the leading arm of the sgr stream , as well as a number of sibling streams ( some hitherto unknown ) . part of the sgr stream has previously been seen in the northern hemisphere by majewski et al . ( 2003 ) . here , we have mapped out the continuation of the stream , as it passes by the galactic cap and returns to the galactic plane . at least two branches of the stream labelled a and b have been identified , corresponding to material torn off at different epochs . there is also evidence for a still more distant structure behind the a branch . the sgr stream provides a probe of the shape of the galactic halo . previous work has been hampered by the absence of data in the most important regions of the sky . for example , @xcite provides simulations of the sgr stream for a range of halo shapes from extreme oblate to prolate , all of which broadly agree with the data available at that time . our data covers the critical region where the models differ substantially . examination of the simulations displayed in figure 2 of @xcite enables some preliminary conclusions to be drawn . in oblate haloes , the sgr stream is much fatter and the stars much more scattered than shown in our figure 1 . only the spherical and very mildly prolate haloes ( @xmath47 , where @xmath48 is the axis ratio in the potential ) seem reasonable matches to the data . in both these simulations , the sgr stream shows the same bifurcation and overall morphology as in the sdss data . we suggest that this may be a powerful discriminant of halo shape ( fellhauer et al . 2006 ) . we thank m. bellazzini and the anonymous referee for helpful discussions . funding for the sdss and sdss - ii has been provided by the alfred p. sloan foundation , the participating institutions , the national science foundation , the u.s . department of energy , the national aeronautics and space administration , the japanese monbukagakusho , the max planck society , and the higher education funding council for england . the sdss web site is http://www.sdss.org/. the sdss is managed by the astrophysical research consortium for the participating institutions . the participating institutions are the american museum of natural history , astrophysical institute potsdam , university of basel , cambridge university , case western reserve university , university of chicago , drexel university , fermilab , the institute for advanced study , the japan participation group , johns hopkins university , the joint institute for nuclear astrophysics , the kavli institute for particle astrophysics and cosmology , the korean scientist group , the chinese academy of sciences ( lamost ) , los alamos national laboratory , the max - planck - institute for astronomy ( mpia ) , the max - planck - institute for astrophysics ( mpa ) , new mexico state university , ohio state university , university of pittsburgh , university of portsmouth , princeton university , the united states naval observatory , and the university of washington .

two branches ( a and b ) of the sagittarius stream are clearly visible in an rgb - composite image created from 3 magnitude slices , and there is also evidence for a still more distant wrap behind the a branch . a comparison of these data with numerical models suggests that the shape of the galactic dark halo is close to spherical .

we use sloan digital sky survey ( sdss ) data release 5 ( dr5 ) @xmath0 photometry to study milky way halo substructure in the area around the north galactic cap . a simple color cut ( @xmath1 ) reveals the tidal stream of the sagittarius dwarf spheroidal , as well as a number of other stellar structures in the field . two branches ( a and b ) of the sagittarius stream are clearly visible in an rgb - composite image created from 3 magnitude slices , and there is also evidence for a still more distant wrap behind the a branch . a comparison of these data with numerical models suggests that the shape of the galactic dark halo is close to spherical .

astro-ph0612078

c

at @xmath13 , there is a strong association between the presence , but not the power , of faint radio and x - ray emission . the extended radio emission is starburst - dominated in 3/4 of the objects @xcite whilst 18 of the x - ray sources are hard enough and bright enough to be agn2 @xcite . 11 of these x - ray agn2 have radio starburst characteristics . their radio emission mechanisms must be dominated by star - formation whilst the agn provides most of the x - ray luminosity . the high-@xmath0 population of @xmath1jy radio sources contains a significant fraction of starbursts an order of magnitude more active and more extended than local ulirgs , and they simultaneously host highly x - ray - luminous obscured agn . , d. m. , et al . , 2003 , aj , 126 , 539 , d. m. , bauer , f. e. , chapman , s. c. , a smail , i. , blain , a. w. , brandt , w. n. , ivison , r. j. 2005 , apj , 632 , 736 , 2002 , aj , 124 , 2351 borys , c. , scott , d. , chapman , s. , halpern , m. , nandra , k. , pope , a. 2004 , mnras , 355 , 485 , m. a. , 2002 , a&a , 384 , l19 , d. , et al . , cesarsky , c. j. , chanial , p. , aussel , h. , franceschini , a. , fadda , d. , chary , r. r. , 2002 , a&a , 384 , 848 giavalisco , m. et al . , 2004 , apj , 600 , l93 , t. w. b. , et al . , 2005 , mnras , 358 , 1159 , p. , allen , m. g. , rosati , p. , walton , n. a. , 2004 , a&a , 424 , 545 richards , e. a. , kellermann , k. i. , fomalont , e. b. , windhorst , r. a. , partridge , r. b. , 1998 , aj , 116 , 1039 serjeant , s. et al . , 2003 , mnras , 344 , 887

we use virtual observatory methods to investigate the association between radio and x - ray emission at high redshifts . chandra _ , of which 18 are hard enough and bright enough to be obscured agn . the high-@xmath0 population of @xmath1jy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at @xmath2 and at least a quarter of these simultaneously host highly x - ray - luminous obscured agn .

we use virtual observatory methods to investigate the association between radio and x - ray emission at high redshifts . fifty - five of the 92 hdf(n ) sources resolved by combining merlin+vla data were detected by _ chandra _ , of which 18 are hard enough and bright enough to be obscured agn . the high-@xmath0 population of @xmath1jy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at @xmath2 and at least a quarter of these simultaneously host highly x - ray - luminous obscured agn .

1208.2621

i

the bifurcation of limit cycles by perturbing a planar system which has a continuous family of _ cycles _ , i.e. periodic orbits , has been an intensively studied phenomenon ; see for instance @xcite and references therein . the simplest planar system having a continuous family of cycles is the linear center , and a special family of its perturbations is given by the generalized polynomial linard systems : @xmath0 where @xmath1 , @xmath2 , @xmath3 , @xmath4 and @xmath5 are polynomials for @xmath6 , and @xmath7 is a small parameter . the classical and generalized linard systems appear very often in several branches of science and engineering , as biology , chemistry , mechanics , electronics , etc . see for instance @xcite and references therein . in particular linard systems are frequent specially in physiological processes , see for instance @xcite . in addition , the family of generalized polynomial linard systems is one of the most considered families in the study of limit cycles , see @xcite . we assume that @xmath8 , @xmath9 , @xmath10 , and @xmath11 . for a small enough @xmath7 , let @xmath12 be the maximum number of limit cycles of that bifurcate from cycles of the _ linear center _ @xmath13 , i.e. the maximum number of _ medium amplitude limit cycles _ which can bifurcate from @xmath13 under the perturbation . if @xmath14 , then @xmath15 does not depend on @xmath16 ; hence we only write @xmath17 . the main problem concerning @xmath12 is finding its exact value . we know from @xcite that @xmath18 $ ] , where @xmath19 $ ] denotes the integer part function . moreover , by following ( * ? ? ? * theorem 3.1 ) we can prove that @xmath20 $ ] for @xmath21 ; theorem [ mth1 ] ( below ) is a generalization of this result . also , we know from @xcite that @xmath22 $ ] , @xmath23 , \left[m/2\right]+\left[n/2\right]-1\right\}$ ] , and @xmath24 - 1 $ ] . however , the exact values of @xmath25 , @xmath26 , and @xmath27 were not reported there . in this paper we give the exact value of @xmath12 for two subfamilies of . more precisely , we will give the exact value of @xmath28 and @xmath29 , where @xmath28 is the value of @xmath12 by assuming that @xmath4 is odd for @xmath30 , and @xmath29 is the value of @xmath12 by assuming that @xmath5 is even for @xmath31 , where @xmath32 with @xmath33 is the smallest integer such that @xmath34 . of course , if @xmath35 , then @xmath36 . our main result is the following : [ mth1 ] @xmath37 @xmath38 $ ] . @xmath39 @xmath29 is either @xmath40 $ ] if @xmath41 is odd or @xmath42 + \left[\frac{n}{2}\right]-1 $ ] if @xmath41 is even . the assumptions on @xmath4 and @xmath5 in definitions of @xmath28 and @xmath29 , respectively , are necessary . otherwise , we can construct systems having more medium amplitude limit cycles , see remark 1 in section [ sec3 ] . theorem [ mth1](@xmath43 ) is a generalization of theorem 1.1 in @xcite , where the case @xmath44 was considered . we note that in such a case @xmath45 . hence theorem 1@xmath39 ( ( * ? ? ? * theorem 1.1 ) ) gives the exact value of @xmath46 . the proof of theorem [ mth1 ] is based on computing the maximum number of isolated zeros of the first non - vanishing poincar pontryagin melnikov function of the displacement function of , by taking into account the restrictions : @xmath4 odd for @xmath30 and @xmath5 even for @xmath47 , respectively . the paper is organized as follows . in section [ ppmf ] we recall the definition of the displacement function of , as well as the algorithm to compute the poincar pontryagin melnikov functions . preliminary results that allow us to provide elementary proofs of the main results are given in section [ sec3 ] . finally , in section [ sec4 ] we will prove theorem [ mth1 ] .

we will consider two special families of polynomial perturbations of the linear center . for the resulting perturbed systems , which are generalized linard systems , we provide the exact upper bound for the number of limit cycles that bifurcate from the periodic orbits of the linear center . limit cycle , linard system , periodic orbit

we will consider two special families of polynomial perturbations of the linear center . for the resulting perturbed systems , which are generalized linard systems , we provide the exact upper bound for the number of limit cycles that bifurcate from the periodic orbits of the linear center . limit cycle , linard system , periodic orbit

0802.1546

i

we have discussed the problem of spacetime geometry fluctuations using the riemann tensor correlation function , first near flat spacetime , and then in black hole spacetime . in the former case , we noted some of the operational signatures of spacetime geometry fluctuation : luminosity fluctuations , line broadening , and angular blurring . however , the main interest is in the problem of black hole horizon fluctuations . the hawking derivation of black hole radiance invokes transplanckian modes , which must remain extremely close to the event horizon for a very long time , as measured by an external observer . here extremely close means far less than one planck length as measured by an infalling observer . this suggests that quantum fluctuations of the horizon might drastically alter black hole radiance . if this were the case , then the connection between black hole physics and thermodynamics might only be preserved by going to a `` mode - regeneration '' picture based upon a non - linear , non - lorentz invariant dispersion relation . however , a previous study @xcite of active fluctuations from gravitons in a vacuum state indicated that the vacuum level horizon fluctuations will not upset the hawking derivation for black holes more massive than the planck mass . in the present paper , we have summarised an investigation @xcite which goes further and considers both active and passive fluctuations from squeezed states . this has the advantage that the level of the fluctuations can be increased by increasing the squeeze parameter . indeed , we did find that one can the fractional fluctuation in the geodesic deviation vector approach order unity . however , in all of the models discussed in this paper , the contribution to the quantity @xmath104 come only from the @xmath36-component of @xmath32 , not the @xmath43-component . if we refer to figure [ fig : blackhole2 ] , we see that it would require @xmath43-component fluctuations to cause serious problems with modes being prematurely ejected or captured by the black hole . fluctuations in the @xmath36-component do influence when a given wave packet arrives at @xmath105 . however , this is likely to be unobservable when the quantum state before collapse is the vacuum state . these fluctuations could alter stimulated emission , and hence are in principle observable , but would require a state containing particles with transplanckian energies if the stimulated emission is to be observed well after the collapse . in summary , although it is possible to enhance spacetime geometry fluctuations by use of squeezed states , these enhanced fluctuations do not seem to alter the thermal hawking radiation . thus we conclude that hawking s derivation of black hole radiance is remarkably robust , and that there may be no transplanckian `` problem '' .

we will discuss selected physical effects of spacetime geometry fluctuations , especially the operational signatures of geometry fluctuations and their effects on black hole horizons . the operational signatures which we discuss involve the effects of the fluctuations on images , and include luminosity variations , spectral line broadening and angular blurring . we find that this thermal character is remarkably robust , and that hawking s original derivation using transplanckian modes does not seem to be sensitive even to enhanced horizon fluctuations .

we will discuss selected physical effects of spacetime geometry fluctuations , especially the operational signatures of geometry fluctuations and their effects on black hole horizons . the operational signatures which we discuss involve the effects of the fluctuations on images , and include luminosity variations , spectral line broadening and angular blurring . our main interest will be in black hole horizon fluctuations , especially horizon fluctuations which have been enhanced above the vacuum level by gravitons or matter in squeezed states . we investigate whether these fluctuations can alter the thermal character of a black hole . we find that this thermal character is remarkably robust , and that hawking s original derivation using transplanckian modes does not seem to be sensitive even to enhanced horizon fluctuations .

1503.03954

c

this article presented a new paradigm for future cr by exploring the fd technology to allow the sus to simultaneously sense and access the vacant spectrum . novel protocol design and key parameter derivation have been explained in depth . both analytical and simulated results indicated that the proposed lat protocol can efficiently improve the spectrum utilization . feasible applications with fd enabled cr have been elaborated into centralized and distributed scenarios . the associated signal processing and spectrum access problems in these systems were also outlined . future work may further study the scenario with multiple pus and sus in crns , and introduce basic economic theories as a tool to study and analyze fd - crns , such as dynamic spectrum access and spectrum trading problems . j. choi , m. jain , k. srinivasan , p. levis , and s. katti , achieving single channel , full duplex wireless communication , " in _ the 16th annual international conference on mobile computing and networking ( mobicom ) _ , new york , ny , sep . 2010 . y. liao , t. wang , k. bian , l. song and z. han , `` decentralized dynamic spectrum access in full - duplex cognitive radio networks , '' in _ proc . ieee international conference on communications _ , london , uk , jun . t. wang , y. liao , l. song and b. zhang , `` joint spectrum access and power allocation in full - duplex cognitive cellular networks , '' in _ proc . ieee international conference on communications _ , london , uk , jun . x. zhang and k. g. shin , enabling coexistence of heterogeneous wireless systems : case for zigbee and wifi , " in _ proc . acm international symposium on mobile ad hoc networking and computing ( mobihoc ) _ , new york , us , may 2011 . t. riihonen and r. wichman , `` energy detection in full - duplex cognitive radios under residual self - interference , '' in _ proc . cognitive radio oriented wireless networks and communications ( crowncom ) _ , pp . 57 - 60 , oulu , finland , jun . 2014 . yun liao ( s14 ) has been pursuing her b.s . degree in school of electrical engineering and computer science in peking university since 2011 . her research interests mainly include cognitive radio networks , full - duplex communications , cooperative communications , wireless network virtualization , and optimization theory . lingyang song ( s03-m06-sm12 ) received his phd from the university of york , uk , in 2007 , where he received the k. m. stott prize for excellent research . he worked as a research fellow at the university of oslo , norway , and harvard university , until rejoining philips research uk in march 2008 . in may 2009 , he joined the school of electronics engineering and computer science , peking university , china , as a full professor . his main research interests include mimo , cognitive and cooperative communications , physical layer security , and wireless ad hoc / sensor networks . dr . song published extensively and wrote 3 text books . he is the recipient of 2012 ieee asia pacific ( ap ) young researcher award , and received 7 best paper awards , including the best paper award in ieee international conference on wireless communications , networking and mobile computing ( wcnm 2007 ) , the best paper award in the first ieee international conference on communications in china ( iccc 2012 ) , the best student paper award in the 7th international conference on communications and networking in china ( chinacom2012 ) , the best paper award in ieee wireless communication and networking conference ( wcnc2012 ) , the best paper awards in international conference on wireless communications and signal processing ( wcsp 2012 ) , the best paper awards in ieee international conference on communications ( icc 2014 ) , and the best paper awards in ieee global communication conferences ( globecom 2014 ) . dr . song is ieee senior member and ieee distinguished lecturer since 2015 . zhu han ( s01-m04-sm09-f14 ) received the b.s . degree in electronic engineering from tsinghua university , in 1997 , and the m.s . and ph.d . degrees in electrical engineering from the university of maryland , college park , in 1999 and 2003 , respectively . from 2000 to 2002 , he was an r@xmath26d engineer of jdsu , germantown , maryland . from 2003 to 2006 , he was a research associate at the university of maryland . from 2006 to 2008 , he was an assistant professor in boise state university , idaho . currently , he is an associate professor in electrical and computer engineering department at the university of houston , texas . his research interests include wireless resource allocation and management , wireless communications and networking , game theory , wireless multimedia , security , and smart grid communication . han is an associate editor of ieee transactions on wireless communications since 2010 . han is the winner of ieee fred w. ellersick prize 2011 . han is an nsf career award recipient 2010 . han is ieee distinguished lecturer since 2015 . yonghui li ( m04-sm09 ) received the ph.d . degree from beijing university of aeronautics and astronautics beijing , china , in 2002 . from 1999 to 2003 , he was affiliated with linkair communication inc , where he held a position of project manager with responsibility for the design of physical layer solutions for the las - cdma system . since 2003 , he has been with the centre of excellence in telecommunications , the university of sydney , sydney , n.s.w . , he is now an associate professor in school of electrical and information engineering , university of sydney . he was the australian queen elizabeth ii fellow and is currently the australian future fellow . his current research interests are in the area of wireless communications , with a particular focus on mimo , cooperative communications , coding techniques and wireless sensor networks . he holds a number of patents granted and pending in these fields . he is an executive editor for european transactions on telecommunications ( ett ) . he has also been involved in the technical committee of several international conferences , such as icc , globecom , etc .

this unfortunately results in two major problems : 1 ) transmission time reduction due to sensing , and 2 ) sensing accuracy impairment due to data transmission . to tackle these problems , in this paper we present a new design paradigm for future cr by exploring the full - duplex ( fd ) techniques to achieve the simultaneous spectrum sensing and data transmission . with fd radios equipped at the secondary users ( sus ) , sus can simultaneously sense and access the vacant spectrum , and thus , significantly improve sensing performances and meanwhile increase data transmission efficiency . several application scenarios with fd enabled cr are elaborated , and key open research directions and novel algorithms in these systems are discussed .

with the rapid growth of demand for ever - increasing data rate , spectrum resources have become more and more scarce . as a promising technique to increase the efficiency of the spectrum utilization , cognitive radio ( cr ) technique has the great potential to meet such a requirement by allowing un - licensed users to coexist in licensed bands . in conventional cr systems , the spectrum sensing is performed at the beginning of each time slot before the data transmission . this unfortunately results in two major problems : 1 ) transmission time reduction due to sensing , and 2 ) sensing accuracy impairment due to data transmission . to tackle these problems , in this paper we present a new design paradigm for future cr by exploring the full - duplex ( fd ) techniques to achieve the simultaneous spectrum sensing and data transmission . with fd radios equipped at the secondary users ( sus ) , sus can simultaneously sense and access the vacant spectrum , and thus , significantly improve sensing performances and meanwhile increase data transmission efficiency . the aim of this article is to transform the promising conceptual framework into the practical wireless network design by addressing a diverse set of challenges such as protocol design and theoretical analysis . several application scenarios with fd enabled cr are elaborated , and key open research directions and novel algorithms in these systems are discussed .

0707.1138

i

although strong and electromagnetic decays of @xmath0 have been extensively studied for several decades , both experimental and theoretical investigations of weak decays of @xmath0 are much behind . due to smallness of the strength of weak interaction , the weak decays of the @xmath0 are rare processes . sanchis - lonzano suggested to search for these rare decays whose sum of branching ratios were estimated to be at the order of @xmath4 @xcite . such processes hardly drew much attention because the database was far from reaching such accuracy . thus , for a long time , few further researches on this topic were done . thanks to the progress of accelerator and detector techniques , more accurate measurements may be carried out , thus the interest on weak decays of @xmath0 has been revived . the bes collaboration indeed starts to measure some rare weak decays of @xmath0 and eventually sets an upper bound on the branching ratio of @xmath5 at order of @xmath6 by using @xmath7 @xmath0 database @xcite . the forthcoming upgraded besiii can accumulate @xmath8 @xmath0 per year @xcite , which makes it marginally possible to measure such weak decays of @xmath0 , at least one may expect to observe not - null such events . thus , more careful theoretical investigation on these decays seems necessary . indeed , the weak decays of heavy quarkonium like @xmath0 offer an ideal opportunity of studying non - perturbative qcd effects , because such systems contain two heavy constituents of the same flavor . the situation is quite different from that for heavy mesons which contain only one heavy constituent , and the non - perturbative effects might be attributed to the light flavor , thus the heavy quark effective theory ( hqet ) applies . moreover , for the weak decay of a vector meson , the polarization effect may play a role to probe the underlying dynamics and hadron structure @xcite . the weak decay of @xmath0 is realized via the spectator mechanism that the charm quark ( antiquark ) decays and the antiquark ( quark ) acts as a spectator . the characteristic of the decay modes is that the final state contains a single charmed hadron . the theory of weak interactions has been thoroughly investigated and the effective hamiltonian at the quark level is perfectly formulated . the main job of calculating the rates of the semi - leptonic decays of @xmath0 is to properly evaluate the hadronic matrix elements for @xmath9 , namely the transition form factors which are obviously governed by non - perturbative qcd effects . the main aim of this work is to calculate the @xmath10 form factors in the qcd sum rules . the weak decay of heavy quarkonium has been studied by virtue of heavy quark spin symmetry @xcite . in that framework , the transition form factors of a heavy quarkonium to heavy pseudoscalar and vector mesons are parameterized by a universal function @xmath11 in analog to the isgur - wise function for the heavy meson transitions . however , the non - recoil approximation @xmath12 was used in ref.@xcite , which would bring up uncontrollable uncertainties to the estimation of decay widths . it seems helpful to re - investigate these processes based on a more rigorous theoretical framework . motivated by the arguments , in this work we will calculate the form factors for heavy quarkonium @xmath0 decays into a pseudoscalar or vector meson in the qcd sum rules . as a matter of fact , many authors have tried to evaluate the transition form factors for the heavy meson and quarkonium system in various approaches , such as the simple quark model @xcite , light - front approach @xcite , the qcd sum rules @xcite , the perturbative qcd approach @xcite and etc . the qcd sum - rule approach , which is rooted in the quantum field theory and fully relativistic , is considered to be one of the effective tools for analyzing hadronic processes @xcite . besides evaluation of hadron spectra , the qcd sum - rule technique has been applied to calculate the pion electromagnetic form factor at intermediate momentum transfer @xcite , various weak decay channels @xcite , the coupling constant of the strong interaction @xcite and even to determine the light cone distribution amplitudes of hadrons @xcite . the advantage of this method is that the non - perturbative qcd effects are included in a few parameters such as the quark- and gluon - condensates which have evident physical meaning @xcite . after this introduction , we will firstly display the effective hamiltonian relevant to the semi - leptonic decays of @xmath0 to @xmath13 , and the sum rules for form factors in section [ the standard procedure ] . the wilson coefficients of various operators which manifest the perturbative qcd effects are also calculated in this section with the help of operator product expansion ( ope ) technique . the numerical analysis on the form factors are performed in section [ numerical results ] . the decay rates of semi - leptonic decay @xmath14 and a comparison of our results with that obtained based on other approaches are presented in section [ decay rate ] . in the last section we draw our conclusion .

the various form factors of @xmath0 transiting to a single charmed meson ( @xmath1 ) are studied in the framework of the qcd sum rules . these form factors fully determine the rates of the weak semi - leptonic decays of @xmath0 and provide valuable information about the non - perturbative qcd effects .

within the standard model , we investigate the semi - leptonic weak decays of @xmath0 . the various form factors of @xmath0 transiting to a single charmed meson ( @xmath1 ) are studied in the framework of the qcd sum rules . these form factors fully determine the rates of the weak semi - leptonic decays of @xmath0 and provide valuable information about the non - perturbative qcd effects . our results indicate that the decay rate of the semi - leptonic weak decay mode @xmath2 is at order of @xmath3 .

astro-ph9907424

i

x - ray surveys have consistently indicated the existence of a moderately bright x - ray source near the galactic longitude 41.97@xmath4 and latitude @xmath5 . this source , which we refer to as x 1908 + 075 , was cataloged as 4u 1909 + 07 by uhuru , the first earth - orbiting mission dedicated to celestial x - ray astronomy ( forman et al . subsequent determinations were cataloged as 1 m 1912 + 077 with mit / oso 7 ( markert et al . 1979 ) , 3a 1907 + 074 with ariel 5 ( warwick et al . 1981 ; bell burnell & chiappetti 1984 ) , 1h 1907 + 074 with heao a-1/lass ( wood et al . 1984 ) , gps 1908 + 075 with exosat / me ( warwick et al . 1988 ) . there are large uncertainties in the position determinations of these survey instruments , as shown in fig . the heao a-2 experiment on heao-1 scanned this region and detected x - ray emission of @xmath6 mcrab in the 1.520 kev band ( heasarc archival data ) . the source was also detected with the modulation collimator experiment ( heao a-3 ) on heao-1 , with an 8@xmath7 detection in each of the two collimators for the energy range of 313 kev ( heasarc archival data ) . the heao a-3 instrument yields a multiplicity of relatively precise error regions which appear as a grid of diamonds in fig [ pos ] . the einstein imaging proportional counter ( ipc ) imaged a portion of this region and detected a source , 1e 1908.4 + 0730 , the brightest source in the center of the field , at a significance level of @xmath8 ( heasarc archival data ) . the ipc flux is about 0.3 mcrab ( 0.53.5 kev ) , possibly highly attenuated by interstellar absorption ( see table 1 ) . the position ( j2000 ) is @xmath9 and @xmath10 with a positional accuracy of @xmath11 . this position overlaps one of the heao a-3 `` diamonds '' . there are a few other 5-@xmath7 detections at the edge of the field of view ( @xmath12 square ) of the ipc , and these sources are located well beyond the celestial map provided in fig . [ pos ] . furthermore , none of these sources have positions that are consistent with the heao a-3 diamonds . it is thus highly likely that the einstein / ipc detection represents the same source as the x - ray survey detections . no optical counterpart has been identified within the error circle of 1e 1908.4 + 0730 . + + fig.1 positions of x 1908 + 075 and other x - ray sources detected previously , with reported error boxes superposed on an optical image taken from the digitized sky survey . the degenerated positions determined with heao a-3 can be seen as a grid of diamonds . the position of x 1908 + 075 used in the asm analysis was taken to be that of einstein / ipc source 1e 1908.4 + 0730 , represented as a small circle . [ pos ] the x - ray spectra and flux available from the hard x - ray survey detections are roughly consistent with each other as summarized in table 1 . the fluxes are about 5 mcrab in the 26 kev band and 714 mcrab in the 220 kev band . the spectrum of exosat / me observation of 4u 1909 + 07 in the @xmath13@xmath14 kev band ( at the uhuru position ) indicates excessive absorption at photon energy below @xmath15 kev compared with that of the crab nebula ( heasarc archival data ) . the observations from the ariel 5 spectrometer show that 3a 1907 + 074 has a hard spectrum which can be fitted with a power law of photon index @xmath16 , hydrogen column density of @xmath17 @xmath18 , and an iron line emission with equivalent width @xmath19 ev ( bell burnell & chiappetti 1984 ) . none of these pointed observations were long enough to investigate the long - term variability of this source . in this paper , we use the data from the all sky monitor ( asm ) ( levine et al . 1996 ) on board _ rxte _ ( bradt , rothschild , & swank 1993 ) to confirm the position and to study the nature of x 1908 + 075 . we show that the coded mask patterns for the asm , processed for the einstein / ipc position , yield a persistent @xmath1 mcrab x - ray source with a coherent @xmath20-day periodicity for over 3 years . we then discuss the implications of this discovery .

x 1908 + 075 is an optically unidentified and highly absorbed x - ray source that appears in early surveys such as uhuru , oso-7 , ariel v , heao-1 , and the exosat galactic plane survey . these surveys measured a source intensity in the range of 212 mcrab at 210 kev , and the position was localized to @xmath0 . we use the rossi x - ray timing explorer ( _ rxte _ ) all sky monitor ( asm ) to confirm our expectation that a particular einstein ipc detection ( 1e 1908.4 + 0730 ) provides the correct position for x 1908 + 075 . the analysis of the coded mask shadows from the asm for the position of 1e 1908.4 + 0730 yields a persistent intensity @xmath1 mcrab ( 1.512 kev ) over a 3 year interval beginning in 1996 february .

x 1908 + 075 is an optically unidentified and highly absorbed x - ray source that appears in early surveys such as uhuru , oso-7 , ariel v , heao-1 , and the exosat galactic plane survey . these surveys measured a source intensity in the range of 212 mcrab at 210 kev , and the position was localized to @xmath0 . we use the rossi x - ray timing explorer ( _ rxte _ ) all sky monitor ( asm ) to confirm our expectation that a particular einstein ipc detection ( 1e 1908.4 + 0730 ) provides the correct position for x 1908 + 075 . the analysis of the coded mask shadows from the asm for the position of 1e 1908.4 + 0730 yields a persistent intensity @xmath1 mcrab ( 1.512 kev ) over a 3 year interval beginning in 1996 february . furthermore , we detect a period of 4.400 @xmath2 0.001 days with a false alarm probability @xmath3 . the folded light curve is roughly sinusoidal , with an amplitude that is 22% of the mean flux . the x - ray period may be attributed to the scattering and absorption of x - rays through a stellar wind combined with the orbital motion in a binary system . we suggest that x 1908 + 075 is an x - ray binary with a high mass companion star .

astro-ph9907424

c

the x - ray emission detected by the asm has been found to arise from the immediate region of the einstein / ipc source , to exhibit a hard spectrum and intensity similar to the historical survey detections , and to be persistent over @xmath60 years . this together with the einstein ipc and heao a-3 positional correspondence strongly suggest that the position of 1e 1908.4 + 0730 is the accurate location of the sources seen in the historical x - ray surveys . it is natural to link the observed @xmath20-day period of x 1908 + 075 to the orbital period of a binary . the periods of x - rays from known sources are believed to be associated with one of the following ( white , nagase , & parmar 1995 ) : ( 1 ) rotational periods of neutron stars in x - ray pulsars , ranging between milliseconds to hundreds of seconds ; ( 2 ) orbital periods of binary systems , ranging from tens of minutes to tens of days , and possibly hundreds of days ; and ( 3 ) `` superorbital '' orbital periods from @xmath61 days to hundreds of days , which in some cases are believed to be the precession period of the accretion disk ( e.g. , levine & jernigan 1982 ) . it is clear that the coherence and the timescale of the @xmath20-day x - ray oscillation in x 1908 + 075 can be best interpreted as the orbital period of a binary system . we can then picture x 1908 + 075 as a binary system consisting of a compact object and a mass - donor companion star . an x - ray binary with a low mass companion ( lmxb ) is unlikely the scenario for x 1908 + 075 , since the known orbital periods of most lmxbs ( white et al . 1995 ) are on the order of hours , much shorter than the detected 4.4 days . there are only a few known lmxbs having orbital periods longer than a day , among them only cir x-1 ( @xmath62 d ) and her x-1 ( @xmath63 d , a possible lmxb ) exhibit orbital modulations in x - rays . the modulation in x - rays of cir x-1 manifests itself as periodic flares and dips likely due to a highly eccentric orbit , while her x-1 is an eclipsing system . such dramatic modulations are not evident in the orbital light curves of x 1908 + 075 . on the other hand , most hmxbs have orbital periods on the orders of days . the smooth and nearly sinusoidal modulations in x 1908 + 075 have a lot in common with a supergiant systems such as cyg x-1 . we therefore suggest that x 1908 + 075 is a high mass x - ray binary ( hmxb ) . we further suggest that the companion star is a supergiant rather than a be star for the following reasons . ( 1 ) the @xmath20-d orbital period fits in the range favored more by supergiant systems than by be - star systems , as the known orbital periods of the latter are much longer than @xmath20 days ( @xmath64-d ) ( white et al . ( 2 ) the known orbital light curves of be - star systems are all outburst - like rather than sinusoidal ( e.g. , exo 2030 + 375 ) , probably due to the enhanced accretion caused by the the compact object s periastron passage around the be star . ( 3 ) the orbital modulation of a supergiant system are known to be persistent while this is generally not true in be - star systems ( e.g. , 4u 0115 + 63 in asm light curves during 1996 march to 1998 november ) . the smooth and roughly sinusoidal orbital modulation in the x - rays of x 1908 + 075 suggests that the system could be embedded in a strong stellar wind from the companion star ( e.g. , a supergiant o or b star ) , which absorbs and scatters the x - rays . the x - ray modulation is then caused by changes in the optical depth along the line of sight to the x - ray source as a function of orbital phase . for x 1908 + 075 , absorption of x - rays probably dominates over scattering , as the amplitude of the modulation in the @xmath27@xmath29 kev band is larger than in the @xmath29@xmath30 kev band . to explain a modulation with an amplitude of nearly @xmath65 in the 512 kev band , the difference in the hydrogen column densities between phases 0 and 0.5 is expected to be more than @xmath66 @xmath18 for an absorption and scattering process . the mechanism of the orbital modulation of x 1908 + 075 could be very similar to that of cyg x-1 , wherein hard state orbital modulation in the asm light curves can be well explained with absorption and scattering in a stellar wind ( wen et al . another example of such a system could be the newly discovered x - ray pulsar xte j1855 - 026 ( corbet et al . 1999 ) . in this system , the orbital period is proposed to be 6.1-d as detected by the asm . the modulation is roughly sinusoidal with an amplitude about @xmath67 in the 1.512 kev band . it has also been proposed as a supergiant wind accretion system . the hydrogen column density @xmath68 can be used to estimate the optical extinction in the v band using the empirical relation between the @xmath68 and the color excess @xmath69 ( savage & mathis 1979 ) . it is found that @xmath70 for @xmath71 @xmath18 , as indicated from the ariel 5 observation of 3a 1907 + 074 . the optical objects within the einstein / ipc error circle have magnitudes @xmath72 in the palomar sky survey . to estimate the distance to x 1908 + 075 , we first investigated the possible range of the absolute v - band magnitudes @xmath73 ( from lang 1992 ) known for supergiant stars in binaries with known orbital periods . we found that @xmath74 . together with @xmath70 and @xmath75 , we obtained @xmath76 kpc as the lower - limit for the distance . the x - ray luminosity , estimated from the asm count rate ( 1.512 kev ) , is then @xmath77 erg s@xmath78 if we assume the ariel 5 spectrum . given the @xmath79 value , a more likely scenario is a distance @xmath80 7 kpc estimated from the formula provided by allen ( 1973 ) , where the relation between the extinction of the star light near the galactic plane and the distance is estimated based on the average properties of interstellar absorbing clouds and the grains between them . we obtained similar distance by comparing directly the @xmath81 value of x 1908 + 075 with that of another galactic plane source grs 1915 + 105 , which is @xmath82 away from x 1908 + 075 and is believed to have a kinetic distance of 12.5 kpc and @xmath83 @xmath84 ( chaty et al . 1996 ) . at the distance of 7 kpc , the estimated x - ray luminosity of x 1908 + 075 is @xmath85 erg s@xmath78 . finally , the detected @xmath47-d period seems to be caused by scattered solar x - ray contamination . we found from the asm light curve that three major flares happened at the times when the sun was near the field of view of this source , while flares with smaller amplitudes are evident when the sun is @xmath86 away from the source position . the latter may be caused by the back - scattering of the solar x - rays off the earth s atmosphere and the instrument .

the folded light curve is roughly sinusoidal , with an amplitude that is 22% of the mean flux . the x - ray period may be attributed to the scattering and absorption of x - rays through a stellar wind combined with the orbital motion in a binary system . we suggest that x 1908 + 075 is an x - ray binary with a high mass companion star .

x 1908 + 075 is an optically unidentified and highly absorbed x - ray source that appears in early surveys such as uhuru , oso-7 , ariel v , heao-1 , and the exosat galactic plane survey . these surveys measured a source intensity in the range of 212 mcrab at 210 kev , and the position was localized to @xmath0 . we use the rossi x - ray timing explorer ( _ rxte _ ) all sky monitor ( asm ) to confirm our expectation that a particular einstein ipc detection ( 1e 1908.4 + 0730 ) provides the correct position for x 1908 + 075 . the analysis of the coded mask shadows from the asm for the position of 1e 1908.4 + 0730 yields a persistent intensity @xmath1 mcrab ( 1.512 kev ) over a 3 year interval beginning in 1996 february . furthermore , we detect a period of 4.400 @xmath2 0.001 days with a false alarm probability @xmath3 . the folded light curve is roughly sinusoidal , with an amplitude that is 22% of the mean flux . the x - ray period may be attributed to the scattering and absorption of x - rays through a stellar wind combined with the orbital motion in a binary system . we suggest that x 1908 + 075 is an x - ray binary with a high mass companion star .

1406.4118

c

the observed evidence for the existence of strange stars has also led to observed masses and radii . these observations are used in this paper to obtain an interpolation function @xmath9 , which proved to be an effective model for strange stars . the subsequent analysis is based on the mit bag model and yields both the radial pressure @xmath10 and the transverse pressure @xmath11 , as well as the energy density of the strange star . subsequently , @xmath9 was used to show that a mass - radius relation due to buchdahl is satisfied in our model of a strange star . from our results we can predict some characteristics of a strange star of radius , say 9.9 km . one can see that we have set @xmath12 in our calculations . now , if one substitutes @xmath13 and @xmath14 into relevant equations , the value of the surface density of the predicted strange star of radius 9.9 km turns out to be @xmath15 gm @xmath16 . note that our model can not predict the central density since we can not get the values of the physical parameters less than 6.2 km radius . also , we can predict the mass of strange star of radius 9.9 km as @xmath17 . the compactness of the star will be 0.2548 and corresponding redshift is z=0.4285 . this high redshift is convenient for explaining strange stars . we can definitely state that our predicted strange star is more compact than neutron stars . in 2008 , cackett et al . @xcite reported that redshift of a strange star in the low - mass x - ray binary 4u 1820 - 30 is @xmath18 . this supports our prediction on strange stars in the low - mass x - ray binary 4u 1820 - 30 . recently , x - ray binaries xte j1739 - 285 were suggested as strange stars @xcite . we hope our method can be used to determine different characteristics of these strange stars .

the resulting general mass function becomes an effective model for a strange star . the analysis is based on the mit bag model and yields the energy density , as well as the radial and transverse pressures . using the interpolation function for the mass , it is shown that a mass - radius relation due to buchdahl is satisfied in our model . we find the surface redshift ( @xmath0 ) corresponding to the compactness of the stars . finally , from our results , we predict some characteristics of a strange star of radius 9.9 km . + pacs numbers : 04.20.jb , 98.62.gq , 95.36.+x

* abstract : * the observed evidence for the existence of strange stars and the concomitant observed masses and radii are used to derive an interpolation formula for the mass as a function of the radial coordinate . the resulting general mass function becomes an effective model for a strange star . the analysis is based on the mit bag model and yields the energy density , as well as the radial and transverse pressures . using the interpolation function for the mass , it is shown that a mass - radius relation due to buchdahl is satisfied in our model . we find the surface redshift ( @xmath0 ) corresponding to the compactness of the stars . finally , from our results , we predict some characteristics of a strange star of radius 9.9 km . + pacs numbers : 04.20.jb , 98.62.gq , 95.36.+x

1610.08589

i

we consider numerical inversion of a forward deformation vector field ( dvf ) from one image to another . very often the inverse dvf is needed along with the forward dvf to map medical images , structures , or doses back and forth throughout the process of 4d image reconstruction and adaptive radiotherapy @xcite . the inverse dvf may be obtained in different ways , such as through deformable registration with swapped inputs , simultaneous registration in both directions , or inverting the forward dvf from the reference image to the deformed target image . the latter option ( inverting the forward dvf ) is often preferred in clinical applications , due to several reasons : inversion is typically faster , empirically ; image quality can be quite different for the reference and target image sets , which may make the other approaches more error - prone @xcite ; and inversion can ensure consistency between forward and inverse dvfs @xcite . previously , chen _ et al . _ @xcite developed a fixed - point iteration method for dvf inversion . in this study , we aim to advance the dvf inversion approach further by improving its convergence behavior , in terms of convergence region and rate , using a feedback control . the problem of dvf inversion can be framed as follows . the reference and target images , denoted by @xmath3 and @xmath4 , respectively , can be related to one another by two non - linear transformations . the forward transformation , @xmath5 , maps the voxels of the reference image , @xmath3 , onto those of the target image , @xmath4 , via the forward deformation vector field , @xmath6 : @xmath7 where @xmath8 is the 3d displacement of the reference voxel at @xmath9 , and @xmath10 is the image domain . conversely , the backward transformation , @xmath11 , maps the voxels of @xmath4 back to @xmath3 , @xmath12 via @xmath13 , the reverse dvf . the problem of dvf inversion is to obtain @xmath14 given @xmath15 . the two transformations are the inverse of each other , i.e. , @xmath16 consequently , the forward and backward dvfs satisfy the _ simultaneous inverse consistency condition _ : [ eq : consistency - condition ] @xmath17 where @xmath18 . inverse consistency is of great importance to deformable registration and estimation of 4d dose accumulation , among other biomedical applications @xcite . the inverse consistency condition is commonly incorporated in deformable registration processes . for instance , christensen and johnson @xcite formulate image registration using objective functions symmetrically between the two images in both matching and regularization terms . et al . _ @xcite also treat the two images symmetrically , and use inverse consistency in approximating the unknown inverse fields . additional related studies on employing the consistency condition in simultaneous estimates of the forward and inverse dvf can be found in the survey by sotiras _ et al . _ @xcite . the study reported in this paper follows and improves upon the work of chen _ et al . _ the precursor work presented a fixed - point iteration method for dvf inversion , with regard to inverse consistency condition . the significance of that work lies not only in the simple iterative process , but also in the corresponding convergence condition . assuming @xmath6 is given , chen s iteration proceeds as , @xmath19 the initial guess , @xmath20 , is set to zero ; i.e. , @xmath21 . negating the forward dvf used to a prevailing approach for inverse dvf computation , but the resulting inverse estimate , @xmath22 , does not in general satisfy inverse consistency . this common misconception was made clear and amended by the fixed - point iteration solution of ( [ eq : fpim ] ) . with fixed - point method , the convergence behavior of the iterative inversion process can be analyzed , which is a substantial advancement from previous methods which solely relied on empirical studies . a sufficient convergence condition for ( [ eq : fpim ] ) is the contraction condition on @xmath6 : @xmath23 where @xmath24 is a well - defined distance metric in the 3d image domain , and @xmath25 is a lipschitz constant , @xmath26 . the convergence behavior of chen s iteration depends passively on this condition , which is not always met in clinical cases with large deformation . in this study , we introduce an iterative method with an active feedback control mechanism . at each step of the iteration , we compute a residual which measures the inconsistency between the forward dvf and the iterative inverse estimate , see ( [ eq : residual - r ] ) . the residual is incorporated into the next iterate after being modulated by the feedback control . the feedback control provides an extra handle for controlling and improving the convergence behavior . the rest of the document is organized as follows . in , we describe the new iterative method with feedback control , introduce a simple feedback control mechanism , and provide the underlying principle . in , we make experimental assessment of the new method with an analytic dvf pair and with numerical dvfs obtained via the 4d extended cardiac - torso ( xcat ) digital anthropomorphic phantom @xcite . in , we conclude the presented work and give additional remarks on extended feedback control .

* purpose : * the inverse of a deformation vector field ( dvf ) is often needed in deformable registration , 4d image reconstruction , and adaptive radiation therapy . this study aims at improving both the accuracy with respect to inverse consistency and efficiency of the numerical dvf inversion by developing a fixed - point iteration method with feedback control . + * method : * we introduce an iterative method with active feedback control for dvf inversion . the optimal parameter value is determined either analytically by a closed - form expression for analytical test data , or numerically for experimental data . the feedback control design is demonstrated and assessed with two data sets : an analytic dvf pair , and a dvf generated between two phases of the 4d extended cardiac - torso ( xcat ) digital anthropomorphic phantom . * conclusion : * the introduced iteration method for dvf inversion shows the previously unexplored possibility in exercising active feedback control in dvf inversion , and the unexploited potential in improving both numerical accuracy and computational efficiency . = 1 mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu

* purpose : * the inverse of a deformation vector field ( dvf ) is often needed in deformable registration , 4d image reconstruction , and adaptive radiation therapy . this study aims at improving both the accuracy with respect to inverse consistency and efficiency of the numerical dvf inversion by developing a fixed - point iteration method with feedback control . + * method : * we introduce an iterative method with active feedback control for dvf inversion . the method is built upon a previous fixed - point iteration method , which is represented as a particular passive instance in the new method . at each iteration step , we measure the inconsistency , namely the residual , between the iterative inverse estimate and the input dvf . the residual is modulated by a feedback control mechanism before being incorporated into the next iterate . the feedback control design is based on analysis of error propagation in the iteration process . the control design goal is to suppress estimation error progressively to make the convergence region as large as possible , and to make estimate errors vanish faster whenever possible . we demonstrated the feedback control with a single - parameter control mechanism . the optimal parameter value is determined either analytically by a closed - form expression for analytical test data , or numerically for experimental data . the feedback control design is demonstrated and assessed with two data sets : an analytic dvf pair , and a dvf generated between two phases of the 4d extended cardiac - torso ( xcat ) digital anthropomorphic phantom . * results : * the single - parameter feedback control improved both the convergence region and convergence rate of the iterative algorithm , for both datasets . with the analytic data , the iteration becomes convergent over the entire image domain , and the convergence is sped up substantially compared to the precursor method , which suffers from slow convergence or even divergence , as the deformation becomes larger . with the xcat dvf data , the new iteration method substantially outperforms the precursor method in both accuracy and efficiency ; feedback control reduced the 95th percentile of residual errors from @xmath0 mm to @xmath1 mm . additionally , convergence rate was accelerated by at least a factor of @xmath2 for both datasets . * conclusion : * the introduced iteration method for dvf inversion shows the previously unexplored possibility in exercising active feedback control in dvf inversion , and the unexploited potential in improving both numerical accuracy and computational efficiency . = 1 mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu

1610.08589

m

an iterative method with feedback control is first introduced for numerical dvf inversion . an analysis is then provided for steering the feedback mechanism to improve convergence behavior . at each iteration step , we get an iterative estimate , @xmath27 , of the inverse dvf , @xmath14 . we use the residual with respect to the consistency condition of ( [ eq : consistency - condition ] ) as the feedback : @xmath28 the residual can be obtained at each iteration step . this computationally available quantity allows us to monitor and control the ( unknown ) estimate error , @xmath29 which is to be reduced to zero , or sufficiently close to zero , via the iteration process . the residual @xmath30 is small when the error @xmath31 is small , and @xmath31 is zero when @xmath27 is equal to the inverse satisfying the consistency condition ( [ eq : consistency - condition ] ) . feedback control is introduced in the iteration process as follows . the residual for the @xmath32-th iterate , @xmath33 , is calculated , modulated by a nonsingular matrix @xmath34 , and used as an incremental correction , @xmath35 where @xmath36 is a @xmath37 matrix , local to each @xmath38 . feedback control is spatially homogeneous when @xmath34 does not vary with @xmath9 . there are many formulations or reformulations of a fixed - point equation . the formulation in ( [ eq : fpim - general ] ) is a general formulation for fixed - point iterations , with feedback control @xmath34 modifying and transforming the residual before it is fed back to @xmath39 . in this study , we focus on the feedback mechanism in its simplest form with a single parameter . we let @xmath40 , where @xmath41 is the identity matrix , and @xmath42 is a scalar which may be referred to as the relaxation parameter . the iteration process thus takes the simple form : @xmath43 when @xmath44 , the iteration of ( [ eq : fpim - single - parameter ] ) reduces to chen s iteration of ( [ eq : fpim ] ) . hereafter , we refer to the iteration procedure by chen _ _ as the iteration with feedback control @xmath45 . we first demonstrate how the feedback control can be designed for inverting the analytic dvfs introduced by chen _ et al . _ the forward and backward dvfs are expressed by the following closed - form formulas over a 2d spatial domain : [ eq:2d - analytic - dvfs ] @xmath46 where @xmath9 denotes cartesian coordinates in the 2d spatial domain @xmath47^{2}$ ] , and @xmath48 is the corresponding angular coordinate in the polar representation , @xmath49 . the dvf functions have two constant parameters , @xmath50 and @xmath51 . illustrates a source image and two target images ; the latter are related to the former by the analytic dvfs of ( [ eq:2d - analytic - dvfs ] ) . it is straightforward to verify that the analytic dvfs satisfy the consistency condition of ( [ eq : consistency - condition ] ) . when @xmath52 , there is no deformation . when @xmath53 and @xmath54 , the displacement ( forward or backward ) at @xmath9 is proportional to @xmath9 . with @xmath55 and @xmath56 , the deformation at @xmath9 remains in the radial direction , but its magnitude varies with @xmath50 and @xmath57 ; when @xmath50 is close to or larger than @xmath58 , the deformation becomes large at and near angles where @xmath59 . the iteration with control @xmath45 converges slowly when @xmath50 approaches @xmath58 from below , and becomes divergent when @xmath50 is greater than @xmath58 . in fact , the contraction condition ( [ eq : contraction - condition ] ) no longer holds at all @xmath48 values when @xmath60 . 1 iteration 5 iterations 10 iterations + to improve convergence , we begin by taking a closer look at how errors propagate through the iteration process . errors in two successive iteration steps are related by the following propagation equation : @xmath61 \cdot { \mathbf{e}}_{k } ( { \mathbf{x}}).\ ] ] our objective is to suppress the iterative error ( [ eq : error - propagation - customized ] ) at every step and make it vanish at a faster pace . when @xmath45 and @xmath60 , the error propagation factor is greater than one at and near angular locations where @xmath62 . wherever the factor is greater than @xmath0 , the iterative errors are magnified instead of suppressed at each iteration . this explains the divergent behavior with @xmath45 at certain polar angles when @xmath63 , as illustrated in . when @xmath45 and @xmath64 , the propagation factor is less than @xmath0 at any @xmath48 , and the iteration converges in theory . but as @xmath50 approaches to @xmath58 from below , the iteration becomes slower . further analysis , provided in , shows that the single - parameter feedback control can be employed to achieve convergence over the entire image domain with this analytic dvf pair . we claim specifically that , for any @xmath65 , there exists some @xmath66 which satisfies the following necessary and sufficient convergence condition : @xmath67 under this condition , the iteration ( [ eq : fpim - single - parameter ] ) converges over the entire image domain for any @xmath65 , with arbitrary initial guess . for @xmath68 , iteration with the feedback control @xmath45 fails to meet the necessary and sufficient condition . among the feasible values for the parameter @xmath42 , one may find , by the propagation factor in ( [ eq : error - propagation - customized ] ) , that some values of @xmath42 render faster convergence than others . in particular , we find the optimal value , @xmath69 we provide the proofs of ( [ eq : error - propagation - customized ] ) , ( [ eq : specific - mu - condition ] ) and ( [ eqn : optimal - mu - specific ] ) in . in this section , we will describe the basic principle , objectives and approach for feedback control , taking into consideration that , in practice , the forward dvf is provided in numerical values over a discrete spatial domain , not in a closed - form expression . the design of feedback control is based in principle on the error propagation analysis . for the iteration of ( [ eq : fpim - single - parameter ] ) with a single control parameter @xmath42 , the error propagation equation may be described in the first order form , @xmath70 where @xmath41 is the identity matrix , @xmath71 is a location in @xmath72 $ ] , @xmath73 denotes the jacobian of @xmath15 evaluated at @xmath74 , and @xmath75 denotes the error propagation matrix . in order to express the error propagation matrix in a first - order form , we assume that @xmath15 is smooth almost everywhere over the spatial domain and the jacobian can be well approximated from the numerical values of @xmath15 . the first control objective is to make the propagation matrix @xmath76 a contractor over the image domain of interest , which implies that the convergence region must span the entire image domain . when the feedback control , @xmath36 , is limited by a specific mechanism structure , one may consider making the convergence region in the image domain as large as possible . the second objective is to make the convergence as fast as possible . we describe in particular the control design approach with the single - parameter control mechanism . first , we find the feasible values of @xmath42 over which @xmath76 is a contractor over the spatial domain of interest , @xmath77 where @xmath78 is the spectral radius of the propagation matrix . if the feasible set is not empty , we next locate the values of @xmath42 that reach the fastest convergence speed possible . in , we have demonstrated how to achieve these objectives with analytic dvfs . in , we will introduce a simple approach to locate @xmath42 in practical situation where the dvf is numerically provided , without a closed - form expression .

the method is built upon a previous fixed - point iteration method , which is represented as a particular passive instance in the new method . at each iteration step , we measure the inconsistency , namely the residual , between the iterative inverse estimate and the input dvf . the residual is modulated by a feedback control mechanism before being incorporated into the next iterate . the feedback control design is based on analysis of error propagation in the iteration process . the control design goal is to suppress estimation error progressively to make the convergence region as large as possible , and to make estimate errors vanish faster whenever possible . we demonstrated the feedback control with a single - parameter control mechanism . * results : * the single - parameter feedback control improved both the convergence region and convergence rate of the iterative algorithm , for both datasets . with the analytic data , the iteration becomes convergent over the entire image domain , and the convergence is sped up substantially compared to the precursor method , which suffers from slow convergence or even divergence , as the deformation becomes larger . with the xcat dvf data , the new iteration method substantially outperforms the precursor method in both accuracy and efficiency ; feedback control reduced the 95th percentile of residual errors from @xmath0 mm to @xmath1 mm .

* purpose : * the inverse of a deformation vector field ( dvf ) is often needed in deformable registration , 4d image reconstruction , and adaptive radiation therapy . this study aims at improving both the accuracy with respect to inverse consistency and efficiency of the numerical dvf inversion by developing a fixed - point iteration method with feedback control . + * method : * we introduce an iterative method with active feedback control for dvf inversion . the method is built upon a previous fixed - point iteration method , which is represented as a particular passive instance in the new method . at each iteration step , we measure the inconsistency , namely the residual , between the iterative inverse estimate and the input dvf . the residual is modulated by a feedback control mechanism before being incorporated into the next iterate . the feedback control design is based on analysis of error propagation in the iteration process . the control design goal is to suppress estimation error progressively to make the convergence region as large as possible , and to make estimate errors vanish faster whenever possible . we demonstrated the feedback control with a single - parameter control mechanism . the optimal parameter value is determined either analytically by a closed - form expression for analytical test data , or numerically for experimental data . the feedback control design is demonstrated and assessed with two data sets : an analytic dvf pair , and a dvf generated between two phases of the 4d extended cardiac - torso ( xcat ) digital anthropomorphic phantom . * results : * the single - parameter feedback control improved both the convergence region and convergence rate of the iterative algorithm , for both datasets . with the analytic data , the iteration becomes convergent over the entire image domain , and the convergence is sped up substantially compared to the precursor method , which suffers from slow convergence or even divergence , as the deformation becomes larger . with the xcat dvf data , the new iteration method substantially outperforms the precursor method in both accuracy and efficiency ; feedback control reduced the 95th percentile of residual errors from @xmath0 mm to @xmath1 mm . additionally , convergence rate was accelerated by at least a factor of @xmath2 for both datasets . * conclusion : * the introduced iteration method for dvf inversion shows the previously unexplored possibility in exercising active feedback control in dvf inversion , and the unexploited potential in improving both numerical accuracy and computational efficiency . = 1 mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu mailto:[[`[`]author to whom correspondence should be addressed . electronic mail : ] lei.ren@duke.edu

hep-ph0208166

c

under the assumption that the neutrino system can interact with a pervasive environment , we have obtained neutrino probability formulae for three neutrino generations , taking into account quantum dissipative effects coming from the interaction with the medium on top of the oim mechanism . the damping terms were brought in through the quantum dynamical semigroup formalism . this approach is very useful , since no _ a priori _ assumption on the form of neutrino - medium interaction has to be made . some simplifications of the form of the dissipative matrix were adopted based on results in two generations . we have performed a qualitative analysis to test if the two generation decoherence solution to the atmospheric neutrino problem viewed in this hybrid three neutrino framework , can still explain the tendencies of the current experimental neutrino data . we have analyzed two different cases , the first one considering only pd and the second including a mixture of both conversion mechanisms , that is , decoherence plus oim . the second case was further subdivided into two cases , according to the choice of mixing matrix : i ) mass and mixing contributions connecting @xmath176 ; ii ) mass and mixing contribution connecting @xmath177 . we have observed that all of these cases are clearly disfavored by recent relevant experimental neutrino data . particularly , in the pd case , the fact that @xmath178 is not compatible with the constraint given by chooz combined with sk data ( @xmath97 and @xmath179 ) or with k2k results . for the hybrid case of decoherence plus non - null mixing in @xmath176 , the same prediction @xmath178 arises which is clearly not supported by sk data . in the case of decoherence plus mixing in @xmath177 , we have made a statistical analysis of chooz data using our theoretical expression for @xmath161 , with some simplifications . we have obtained that the best fit value for the decoherence solution to the atmospheric neutrino problem , @xmath180 gev@xmath174 , is highly disfavored by data . values of @xmath181 gev@xmath174 for @xmath158 consistent with the lma solution to the solar neutrino deficit are , in general , excluded at 99 % c.l .. although , the tests we have performed in the three neutrino scheme indicate a disagreement between data and theoretical expectations , this does not mean that dissipative effects can not exist as subleading processes , with the full three neutrino oim as the main mechanism for neutrino flavor conversion . in fact , the formulae developed here are interesting to be used to help establishing limits on the decoherence parameters or to try to detect their effects using an appropriate three neutrino description . also it is worth to stress that we have worked here in a simplified situation in which the dissipative matrix is diagonal . the presence of off - diagonal terms can certainly produce interesting effects on the probability expressions . our formulae can be easily modified to include these off - diagonal terms . however , any further qualitative or quantitative analysis in three generations will not be so direct . this work was supported by conselho nacional de desenvolvimento cientfico e tecnolgico ( cnpq ) and by fundao de amparo pesquisa do estado de so paulo ( fapesp ) . 99 e. b. davies , _ quantum theory of open systems _ , academic press , london ( 1976 ) . w. h. louisell , _ quantum statistical properties of radiation _ , jonh wiley & sons , new york ( 1973 ) . f. benatti and r. floreanini , jhep * 0002 * , 32 ( 2000 ) . f. benatti and r. floreanini , _ phys . d _ * 64 * , 085015 ( 2001 ) . a. m. gago , e. m. santos , w. j. c. teves and r. zukanovich funchal , _ phys . d _ * 63 * , 073001 ( 2001 ) . a. m. gago , e. m. santos , w. j. c. teves and r. zukanovich funchal , _ phys . d _ * 63 * , 113013 ( 2001 ) . e. lisi , a. marrone and , d. montanino , _ phys . * 85 * , 1166 ( 2000 ) . kamiokande collaboration , h. s. hirata _ _ , _ phys . * b 205 * , 416 ( 1988 ) ; _ ibid . _ * 280 * , 146 ( 1992 ) ; y. fukuda _ et al . _ , _ ibid._*335 * , 237 ( 1994 ) ; imb collaboration , r. becker - szendy _ et al . * 46 * , 3720 ( 1992 ) ; soudan-2 collaboration , w. w. m. allison _ * b 391 * , 491 ( 1997 ) ; super - kamiokande collaboration , y. fukuda _ et al . _ , _ phys . lett . _ * 81 * , 1562 ( 1998 ) ; _ phys . * b 436 * , 33 ( 1999 ) . homestake collaboration , k. lande _ et al . _ , _ astrophys . j. _ * 496 * , 505 ( 1998 ) ; _ nucl . * 77 * ( _ proc . suppl . _ ) , 13 ( 1999 ) ; gallex collaboration , w. hampel _ _ , _ phys . lett . _ * b 447 * , 127 ( 1999 ) ; gno collaboration , m. altmann _ _ , _ phys . _ * b 490 * , 16 ( 2000 ) ; sage collaboration , j. n. abdurashitov _ _ , _ phys . * c 60 * , 055801 ( 1999 ) ; v. n. gavrin , _ nucl . * 91 * ( _ proc _ ) , 36 ( 2001 ) ; super - kamiokande collaboration , y. fukuda _ et al . _ , _ phys . lett . _ * 81 * , 1158 ( 1999 ) , ( e ) _ ibid._*81 * , 4279 ( 1998 ) ; _ ibid._*82 * , 1810 ( 1999 ) ; _ ibid._*82 * , 2430 ( 1999 ) ; y. suzuki , _ nucl . * 91 * ( _ proc . _ ) , 29 ( 2001 ) ; sno collaboration , q. r. ahmad _ et al . _ , _ phys . lett . _ * 87 * , 071301 ( 2001 ) . sno collaboration , q. r. ahmad _ et al . _ , _ phys . * 89 * , 011301 ( 2002 ) ; _ ibid._*89 * , 011302 ( 2002 ) . r. alicki and k. lendi , _ quantum dynamical semigroups and applications _ , lect . notes phys . * 286 * , springer - verlag , berlin ( 1987 ) . g. lindblad , _ commun . phys . _ * 48 * , 119 ( 1976 ) . v. gorini , a. kossakowski and e. c. g. sudarshan , _ j. math * 17 * , 821 ( 1976 ) . m. gell - mann , _ phys . rev . _ * 125 * , 1067 ( 1962 ) . f. benatti and h. narnhofer , _ lett . * 15 * , 325 ( 1988 ) . v. gorini , a. frigerio , m. verri , a. kossakowski and e. c. g. sudarshan , _ rep . * 13 * , 149 ( 1978 ) . a. frigerio and v. gorini , _ j. math * 17 * , 2123 ( 1976 ) . a. kossakowski , _ rep . phys . _ * 3 * , 247 ( 1972 ) . r. s. ingarden and a. kossakowski , _ ann . _ * 89 * , 451 ( 1975 ) . e. b. davies , _ commun . phys . _ * 39 * , 91 ( 1974 ) . c. favre and p. a. martin , _ helv . . acta _ * 41 * , 333 ( 1968 ) . r. dmcke and h. spohn , _ b _ * 22 * , 419 ( 1979 ) . chooz collaboration , m. apollonio _ et al . _ , _ phys . * b 466 * , 415 ( 1999 ) . k2k collaboration , j. e. hill _ et al . _ , hep - ex/0110034 . super - kamiokande collaboration , m. shiozawa , talk at neutrino 2002 , http://neutrino2002.ph.tum.de/. t. kajita and y. totsuka , _ rev . * 73 * , 85 ( 2001 ) . super - kamiokande collaboration , s. fukuda _ et al . _ , _ phys . * b 539 * , 179 ( 2002 ) . a. dziewonski and d. anderson , _ phys . earth planet . inter . _ * 25 * , 297 ( 1981 ) .

in addition to the theoretical interest of the approach , at least from the completeness point of view , this extension of the formalism to the three flavors , provide us with a direct application : we can analyze qualitatively the consistency of the two generation pure decoherence solution to the atmospheric neutrino problem , accommodated within this enlarged scheme , with the mean tendencies observed for some of the current neutrino experimental data . our qualitative tests for decoherence with three neutrinos show a clear incompatibility between neutrino data and the theoretical expectations .

-1.1 cm using the open quantum system approach applied to the neutrino system , we derive three generations neutrino probability formulae considering the oscillation induced by mass plus quantum decoherence contributions . the introduction of these dissipative effects is done through the quantum dynamical semigroup formalism . in addition to the theoretical interest of the approach , at least from the completeness point of view , this extension of the formalism to the three flavors , provide us with a direct application : we can analyze qualitatively the consistency of the two generation pure decoherence solution to the atmospheric neutrino problem , accommodated within this enlarged scheme , with the mean tendencies observed for some of the current neutrino experimental data . this study was performed based on different choices of the @xmath0 mixing matrix selected in order to adjust the @xmath1 to the same form it has for the decoherence solution in two generations . our qualitative tests for decoherence with three neutrinos show a clear incompatibility between neutrino data and the theoretical expectations . 15truecm -0.4truecm 22truecm 1.truecm 1.truecm =

1506.00651

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the standard model ( sm ) is very successful in explaining almost all experimental data to date , culminating in the recent discovery of the long awaited higgs boson at the cern large hadron collider ( lhc ) @xcite . in the sm , all elementary particles acquire mass from a single higgs doublet that generates spontaneous electroweak symmetry breaking ( ewsb ) . all charged fermions have their masses and yukawa couplings to the higgs boson as correlated but free parameters . furthermore , there are no flavor changing neutral currents ( fcnc ) mediated by gauge interactions , nor by higgs interactions ( fcnh ) , at the tree level . the most important goals of the lhc , at run 2 and beyond , are the study of higgs properties and the search for signals , direct or indirect , of new physics beyond the sm . as the most massive particle ever discovered , the top quark might provide clues to better understand the mechanism of ewsb . a possible explanation for its heaviness could be provided by a special two higgs doublet model for the top quark ( t2hdm ) @xcite , where it is the only fermion that couples to a higgs doublet with a large vacuum expectation value ( vev ) . the second heaviest particle is the newly discovered higgs boson ( @xmath4 ) . with @xmath7 , it opens up the possibility of top quark decays into @xmath4 plus a charm quark . the branching fraction of @xmath8 in sm at one loop level is approximately @xmath9 @xcite for @xmath10 gev . if this decay is detected , it would indicate a large effective fcnh coupling of tree - level origins @xcite , or very large enhancement from beyond sm loop effects @xcite . in flavor conserving two higgs doublet models , a discrete symmetry @xcite is often imposed to distinguish the su(2 ) doublet fields @xmath11 from @xmath12 . without such a discrete symmetry , a general two higgs doublet model ( 2hdm ) should possess fcnh vertices . to study such interactions , we adopt the following lagrangian involving higgs bosons and fermions @xcite , @xmath13 h^0 + \left [ \kappa^fc_{\beta-\alpha}-\rho^fs_{\beta-\alpha } \right ] h^0 - i \ , { \rm sgn}(q_f)\rho^f a^0 \right\ } p_r f \nonumber \\ & & -\bar{u } \left [ v \rho^d p_r - \rho^{u\dagger } v p_l \right ] d h^+ -\bar{\nu } \left [ \rho^l p_r \right ] l h^+ + { \rm h.c . } \ , , \end{aligned}\ ] ] where @xmath14 , @xmath15 , @xmath16 , @xmath17 , and @xmath18 is the mixing angle between neutral higgs scalars in the type ii ( 2hdm - ii ) notation @xcite . @xmath19 matrices are diagonal and fixed by fermion masses to @xmath20 with @xmath21 gev , while @xmath22 matrices are free and have both diagonal and off - diagonal elements . we adopt a cp conserving higgs model and choose @xmath22 matrices to be real but not necessarily hermitian . @xmath23 , @xmath24 , @xmath25 and @xmath26 are vectors in flavor space ( @xmath27 , etc . ) . @xmath4 and @xmath2 are cp - even scalars ( @xmath28 ) , while @xmath3 is a cp - odd pseudoscalar . with the advent of the lhc , theoretical interest in search of fcnh top decays ( @xmath29 ) picked up @xcite , and the atlas and cms experiments have already placed the branching fraction limit @xmath30 @xcite , implying @xmath31 . for lhc at @xmath32 tev and integrated luminosity of @xmath33 fb@xmath34 , the atlas experiment expects @xcite to reach @xmath35 , i.e. probing down to @xmath36 . the flavor changing heavy higgs decay ( @xmath37 ) is complementary to fcnh top decay ( @xmath29 ) , since the coupling @xmath38 is proportional to @xmath5 while @xmath39 . higgs boson data from the lhc favor the decoupling limit @xcite or the alignment limit @xcite of a 2hdm . in this limit , fcnh couplings of @xmath4 are naturally suppressed by small @xmath5 , while off - diagonal couplings of @xmath2 , @xmath3 are sustained by @xmath40 . in this letter , we study the discovery potential of the lhc in the search for heavy higgs bosons @xmath2 or @xmath3 that decay into a top quark and a charm quark . the top quark then decays into a b quark , a charged lepton ( @xmath41 or @xmath42 ) , and a neutrino . taking lhc higgs data and @xmath43 physics constraints into account , we evaluate production rates with full tree - level matrix elements for both signal and background . we optimize the acceptance cuts to effectively reduce the latter with realistic @xmath44-tagging and mistag efficiencies . promising results are presented for the lhc with @xmath45 tev as well as @xmath46 tev .

a general two higgs doublet model ( 2hdm ) is adopted to study the signature of flavor changing neutral higgs ( fcnh ) decay @xmath0 , where @xmath1 could be a cp - even scalar ( @xmath2 ) or a cp - odd pseudoscalar ( @xmath3 ) . measurement of the light 125 gev neutral higgs boson ( @xmath4 ) couplings at the large hadron collider ( lhc ) favor the decoupling limit or the alignment limit of a 2hdm , in which gauge boson and diagonal fermion couplings of @xmath4 approach standard model values . in such limit , fcnh couplings of @xmath4 are naturally suppressed by a small mixing parameter @xmath5 , while the off - diagonal couplings of heavier neutral scalars @xmath1 are sustained by @xmath6 .

a general two higgs doublet model ( 2hdm ) is adopted to study the signature of flavor changing neutral higgs ( fcnh ) decay @xmath0 , where @xmath1 could be a cp - even scalar ( @xmath2 ) or a cp - odd pseudoscalar ( @xmath3 ) . measurement of the light 125 gev neutral higgs boson ( @xmath4 ) couplings at the large hadron collider ( lhc ) favor the decoupling limit or the alignment limit of a 2hdm , in which gauge boson and diagonal fermion couplings of @xmath4 approach standard model values . in such limit , fcnh couplings of @xmath4 are naturally suppressed by a small mixing parameter @xmath5 , while the off - diagonal couplings of heavier neutral scalars @xmath1 are sustained by @xmath6 . we study physics background from dominant processes with realistic acceptance cuts and tagging efficiencies . promising results are found for the lhc running at 13 or 14 tev collision energies .

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around 200 years ago , carnot revealed that thermodynamic efficiency in a cyclic process with two heat baths with inverse temperatures @xmath0 and @xmath1 ( @xmath2 ) is bounded by a universal function of these two temperatures , which was turned to be the celebrated carnot efficiency @xcite @xmath3 at the same time , carnot also showed that infinitely slow processes ( i.e. , zero power ) realize the maximum efficiency . an infinitely slow heat engine is however useless in practical sense , and thus a question naturally arises whether finite power engines attain the carnot efficiency , which is the opposite statement of the aforementioned one . contrary to its apparent triviality , this has still been an open problem in spite of enormous effort for investigation of large power @xcite , high efficiency @xcite , and both of them @xcite . we emphasize that although the question seems to be negative by intuition , it is hard to prove this rigorously in general setups . in fact , conventional thermodynamics provides no restriction on the speed of processes , and even in the linear response regime the linear irreversible thermodynamics neither prohibits engines at the carnot efficiency with finite power if time - reversal symmetry is broken @xcite . the latter work attracted renewed interest in this problem , and many researches are devoted to analyze specific models to find clues for capturing general properties on the relation between finite power and the carnot efficiency . one frequently - used setup to tackle the problem is a mesoscopic conducting system with non - interacting electrons under a magnetic field , where the incompatibility between finite power and the carnot efficiency is shown through deriving a novel restriction on the onsager matrix @xcite . owing to the newly - derived restriction , it is shown both theoretically @xcite and numerically @xcite that this system never attains the carnot efficiency at finite power in the linear response regime . another frequently - used setup is a periodically driven system , for which the onsager matrix can be defined and is in general asymmetric . utilizing the detailed information on microscopic dynamics , refs . @xcite and refs . @xcite respectively demonstrate the incompatibility for underdamped langevin particles with two heat baths and for isothermal driven systems . on the other hand , some researches proposed some ideas to realize these two simultaneously @xcite ( some comments on these studies are seen in ref . recently , inspired by the idea of partial entropy production @xcite , one of the authors has shown this incompatibility for general classical markovian heat engines beyond the linear response regime @xcite . however , non - markovian heat engines have not been addressed in the previous works though real experimental heat engines are inevitably non - markovian . on the basis of the recent experimental development of small quantum heat engines @xcite , a general result covering non - markovian heat engines is highly desired . in this paper , we establish a trade - off relation between efficiency and speed of operation , which leads to this no - go theorem for general quantum heat engines . we focus on the fact that most of the energy released from the engine to the cold heat bath remains in the region close to the engine , which leads to finite dissipation in the bath . to prove this intuitive picture rigorously , we employ the lieb - robinson bound @xcite , which claims that a commutator of two observables with different time acting on different regions far from each other can not be large . the lieb - robinson bound has recently used in various problems including problems on structure of a gapped ground state @xcite , the lieb - shultz - mattis theorem in higher dimensions @xcite , the quantum hall effect @xcite , and thermalization @xcite . using this bound , we establish a useful upper bound on the change in a local observable caused by an operation with finite time - interval far from the area on which the local observable acts . applying this bound , we find that the expectation value of energy in the cold bath far from the engine does not largely change . with help of the pythagorean theorem for quantum relative entropy and some relations on the quantum fisher information @xcite , we finally arrive at an upper bound for efficiency with the time interval of a cyclic process . this bound clearly manifests that the faster the engine is operated the less the maximum efficiency becomes . since the obtained inequality turns to be no more than the second law of thermodynamics in the markovian limit , in which the lieb - robinson velocity diverges , we treat markovian heat engines in a completely different way . we extend the result of classical markov processes shown in ref . @xcite to quantum markov processes , which denies the compatibility between finite power and the carnot efficiency . this paper is organized as follows . in sec . [ s : setup ] , we show the setup of quantum heat engines and state our main inequality on efficiency and the time interval of a cyclic process . in sec . [ s : proof ] , we prove our main inequality in the following four steps . first , in sec . [ s : eff - rel ] , we introduce an expression of efficiency in terms of quantum relative entropy , which is a corollary of the quantum fluctuation theorem . we explain the lieb - robinson bound in sec . [ s : lr ] , and next derive a helpful relation on the speed of information propagation from an operation with finite time interval in sec . [ s : info - prop ] . applying this relation , in sec . [ s : residual ] we rigorously show the lower bound for the energy increase in a region near the engine . finally , in sec . [ s : qig ] , we connect the relative entropy to the energy increase , which leads to the desired inequality . in sec . [ s : transient ] , we apply our analysis to a transient process and derive an extended version of the principle of maximum work . in sec . [ s : markov ] , we treat a quantum heat engine in markovian dynamics , to which our main inequality does not provide information more than the second law of thermodynamics . we state our setup in sec . [ s : markov - set ] and derive an inequality on efficiency and power for quantum markovian heat engines in sec . [ s : markov - claim ] .

a long standing open problem whether a heat engine with finite power achieves the carnot efficiency is investigated . we rigorously prove a general trade - off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines . in a first step , employing the lieb - robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable . this inequality provides a rigorous characterization of the following intuitive picture that most of the energy released from the engine to the cold bath remains near the engine when the cyclic process is finished . using the above description , we finally prove an upper bound on efficiency with the aid of quantum information geometry .

a long standing open problem whether a heat engine with finite power achieves the carnot efficiency is investigated . we rigorously prove a general trade - off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines . in a first step , employing the lieb - robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable . this inequality provides a rigorous characterization of the following intuitive picture that most of the energy released from the engine to the cold bath remains near the engine when the cyclic process is finished . using the above description , we finally prove an upper bound on efficiency with the aid of quantum information geometry . in addition , since our inequality falls down into the conventional second law of thermodynamics in markovian limit , we adopt a completely different treatment which is developed in the context of classical stochastic processes . our result generally excludes the possibility of a process with finite speed at the carnot efficiency in quantum heat engines . in particular , the obtained constraint covers engines evolving with non - markovian dynamics , which almost all previous studies on this topics fail to address . pacs numbers : : 03.67.-a , 05.30.-d , 05.70.ln , 87.10.ca ,

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s : markov s : markov - set our main result contains the operator norm of the local hamiltonian of the bath l in its rhs in the form of the lieb - robinson velocity @xmath45 . because the operator norm of the local hamiltonian in baths diverges and so does @xmath45 in markovian limit , our inequality falls down into the conventional second law in this limit . to avoid this insufficiency , we employ a completely different approach to the quantum markov process . we again treat an engine with two heat baths l and h with inverse temperatures @xmath0 and @xmath1 . it is straightforward to extend our analysis to the case with three or more baths and with particle baths . the initial state of the total system is again given by @xmath36 . the spectrum decomposition of the initial state of the engine reads @xmath176 . by denoting the energy eigenstates of the bath @xmath24 ( @xmath23h , l ) by @xmath177 , the basis @xmath178 diagonalizes @xmath179 . suppose that the total system evolves in a small time interval from @xmath76 to @xmath180 . the density matrix of the total system at @xmath180 is given by @xmath181 with the time evolution operator @xmath182 . the spectrum decomposition of the reduced density matrix reads @xmath183=\sum_a p_{{\mathit{\delta}}t}(a)\ket{\psi _ a}\bra{\psi _ a}$ ] , where the label of @xmath184 in @xmath185 is set as satisfying @xmath186 . suppose that we perform a projection measurement on @xmath187 with a basis @xmath188 , which does not affect the evolution of the system because the engine is diagonalized with this basis and the baths are not used in the subsequent evolution of the engine as explained later . s : markov - claim we here introduce the transition probability of a forward and its time - reversal process as @xmath189 where @xmath190 represents the time - reversal state of @xmath191 . time - reversal symmetry of unitary evolution implies @xmath192 it is known that the stochastic entropy production can be expressed as @xcite @xmath193 where we defined the heat release @xmath194 , the canonical distribution @xmath195 with the partition function @xmath196 , and the stochastic entropy @xmath197 , which reproduces the shannon entropy by taking its average . with these definitions , both the fluctuation theorem , @xmath198 , and the second law of thermodynamics , @xmath199 , are satisfied . we here require a physically plausible property that in sufficiently small time interval @xmath200 energy can not be transported directly from a bath to the other bath . in other words , @xmath201 turns to be zero if both @xmath202 and @xmath203 hold . we then safely define the transition rate induced by each bath as @xmath204 taking @xmath205 limit and defining @xmath206 , we have an expression of entropy production rate @xmath207 and heat flux as @xmath208 here , @xmath209 ( @xmath23h , l ) is a part of entropy production rate contributed from the bath @xmath24 , and @xmath210 is the energy expectation value of a state @xmath211 , which satisfies @xmath212 in @xmath205 limit due to the law of energy conservation . in line with ref . @xcite , we arrive at the main inequality for a quantum markov engine ( see appendix [ s : markov ] ) : @xmath213 here , @xmath214 is defined as @xmath215\ ] ] with energy fluctuation and activity : @xmath216 , \\ a^x _ { a , j_x ; a',j'_x}:=&p_0(a)p^x_{\rm can}(j_x ) p_{a , j_x \to a',j'_x } { \notag}\\ & + p_0(a')p^x_{\rm can}(j_x ) p_{{a}',{j}'_x \to { a},{j}_x}. \end{aligned}\ ] ] since the bath equilibrates extremely quick compared to the time scale of the engine , we argue that throughout a process in @xmath19 the heat bath is regarded as always in canonical distribution , which implies that eq . holds at any time @xmath28 by replacing @xmath217 and @xmath214 to @xmath218 and @xmath219 . the same assumption is seen in the born - markov approximation , which is used in a standard derivation of the lindblad equation @xcite . accepting this plausible requirement , we obtain the trade - off relation between power and efficiency for a cyclic process during @xmath19 with two heat baths with inverse temperatures @xmath0 and @xmath1 ( @xmath2 ) . the integration of eq . from @xmath76 to @xmath48 with the schwarz inequality leads to @xmath220 , where we defined time - averaging of @xmath221 as @xmath222 and entropy increase as @xmath223 . here , the change in the entropy of the engine is zero due to cyclicity . then , a thermodynamic relation @xmath224 suggests that the work @xmath225 and efficiency @xmath42 satisfies @xmath226 which clearly shows that a finite power heat engine never attains the carnot efficiency .

in addition , since our inequality falls down into the conventional second law of thermodynamics in markovian limit , we adopt a completely different treatment which is developed in the context of classical stochastic processes . our result generally excludes the possibility of a process with finite speed at the carnot efficiency in quantum heat engines . in particular , the obtained constraint covers engines evolving with non - markovian dynamics , which almost all previous studies on this topics fail to address .

a long standing open problem whether a heat engine with finite power achieves the carnot efficiency is investigated . we rigorously prove a general trade - off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines . in a first step , employing the lieb - robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable . this inequality provides a rigorous characterization of the following intuitive picture that most of the energy released from the engine to the cold bath remains near the engine when the cyclic process is finished . using the above description , we finally prove an upper bound on efficiency with the aid of quantum information geometry . in addition , since our inequality falls down into the conventional second law of thermodynamics in markovian limit , we adopt a completely different treatment which is developed in the context of classical stochastic processes . our result generally excludes the possibility of a process with finite speed at the carnot efficiency in quantum heat engines . in particular , the obtained constraint covers engines evolving with non - markovian dynamics , which almost all previous studies on this topics fail to address . pacs numbers : : 03.67.-a , 05.30.-d , 05.70.ln , 87.10.ca ,

1605.03711

c

based on these simulations , the theory hereby presented is shown to be compatible with the experimental findings : it accounts for the existence of multiple peaks , their appearance far away from the surface and their nature being related to the cdw structure of the sample . it is interesting to notice that the vortices appearing in our simulations have been described before in the context of cdw conduction noise @xcite , where their creation and movement justifies the phase slip near the cdw boundaries . in this sense , this theory lies in between these macroscopic effect and the simple one - dimensional model of defect pinning and phase slip @xcite , as is appropriate for a localized but extended perturbation . to conclude , i have presented a mechanism to explain peaks in the dissipation of a tip oscillating at specific distances above a cdw surface : these occur around instability points corresponding to the crossing of energy levels characterized by different winding numbers . numerical simulations in a system of reduced complexity support the validity of this mechanism . it would be interesting to investigate the same effect in other systems displaying cdw or even spin density waves , as well as systems where the origin of charge modulation is related to the fermi surface and not to other effects . _ acknowledgements _ the author thanks his collaborators g.e . santoro and e. tosatti . he acknowledges research support by snsf , through sinergia project crsii2 136287/1 , by erc advanced research grant n. 320796 modphysfrict , and by miur , through prin-2010llkjbx_001 vanossi a. , manini n. , urbakh m. , zapperi s. , and tosatti e. , rev . phys . * 85 * 529 ( 2013 ) . langer m. , kisiel m. , pawlak r. , pellegrini f. , santoro g.e . , buzio r. , gerbi a. , balakrishnan g. , baratoff a. , tosatti e. , and meyer e. , nature mater . * 13 * 173177 ( 2014 ) . grner g. , rev . phys . * 60 * 1129 ( 1988 ) . fukuyama h. , and lee p.a . b * 17 * 535 ( 1978 ) . lee p.a . , and rice t.m . , b * 19 * 3970 ( 1979 ) . tucker j.r . b * 40 * 5447 ( 1989 ) . ttt i. , and zawadowski a. , phys . b * 32 * 2449 ( 1985 ) . maki k. , phys . a * 202 * 313 ( 1995 ) . gorkov l.p . , zh . eksp . 86 * 1818 ( 1984 ) . mcmillan w.l . b * 12 * 1187 ( 1975 ) . press w.h . , teukolsky s.a . , vetterling w.t . , and flannery b.p . _ numerical recipes : the art of scientific computing ( 3rd ed . ) _ , cambridge university press ( 2007 ) . , verma g. , and maki k. , phys . lett . * 52 * 663 ( 1984 ) .

a mechanism is proposed to describe the occurrence of distance - dependent dissipation peaks in the dynamics of an atomic force microscope tip oscillating over a surface characterized by a charge density wave state . , experiments have started to single out the effects of microscopic probes in contact or near contact with different surfaces , and much theoretical effort has been devoted to the full understanding of such experiments @xcite . in particular , recently , a non - contact atomic force microscopy ( afm ) experiment @xcite on a nbse@xmath0 sample has shown dissipation peaks appearing at specific heights from the surface and extending up to @xmath1 nm far from it . a model is proposed explaining in detail the mechanism responsible for these peaks : the tip oscillations induce a charge perturbation in the surface right under the tip , but , due to the nature of the cdw order parameter , multiple stable charge configurations exist characterized by different `` topological '' properties .

a mechanism is proposed to describe the occurrence of distance - dependent dissipation peaks in the dynamics of an atomic force microscope tip oscillating over a surface characterized by a charge density wave state . the dissipation has its origin in the hysteretic behavior of the tip oscillations occurring at positions compatible with a localized phase slip of the charge density wave . this model is supported through static and dynamic numerical simulations of the tip surface interaction and is in good qualitative agreement with recently performed experiments on a nbse@xmath0 sample . the study of the microscopic mechanisms leading to energy dissipation and friction has very important theoretical and practical implications . in recent years , experiments have started to single out the effects of microscopic probes in contact or near contact with different surfaces , and much theoretical effort has been devoted to the full understanding of such experiments @xcite . in particular , the minimally invasive non - contact experiments offer a chance to investigate delicate surface properties and promise to bring new insight on localized effects and their interaction with the bulk . recently , a non - contact atomic force microscopy ( afm ) experiment @xcite on a nbse@xmath0 sample has shown dissipation peaks appearing at specific heights from the surface and extending up to @xmath1 nm far from it . these peaks were obtained with tips oscillating both parallel and perpendicular to the surface , and in a range of temperatures compatible with the surface charge density wave ( cdw ) phase of the sample . in this paper , a model is proposed explaining in detail the mechanism responsible for these peaks : the tip oscillations induce a charge perturbation in the surface right under the tip , but , due to the nature of the cdw order parameter , multiple stable charge configurations exist characterized by different `` topological '' properties . when the tip oscillates at distances corresponding to the crossover of this different manifolds , the system is not allowed to follow the energy minimum configuration , even at the low experimental frequencies of oscillation , and this gives rise to a hysteresis loop for the tip , leading to an increase in the dissipation . while the idea behind this dissipation mechanism has been proposed by the author and collaborators in the original paper @xcite , this article expands on the technical aspects of the model , highlighting details to appear in a future publication .

1203.5593

c

in the present paper we have considered a modified f(g ) gravity model with coupling between matter and geometry , described by the product of the lagrange density of the matter and an arbitrary function of the gauss - bonnet term . the proposed action represents the general extension of the standard hilbert action for the gravitational field , @xmath177l_m\}$ ] . the field equations and the equations of motion corresponding to this model show the non - conservation of the energy - momentum tensor , the presence of an extra - force acting on test particles and the non - geodesic motion . moreover , in the modified f(g ) gravity we have derived the energy conditions ( sec , nec , dec , wec ) when we consider @xmath75 and @xmath82 , respectively . for the sec and the nec , the raychaudhuri equation , which is the physical origin of them , has been used . from the derivation , we found equivalent results can be obtained by taking the transformations @xmath178 and @xmath179 into @xmath65 and @xmath66 . by means of these transformations , the dec and wec in the modified f(g ) gravity have been also obtained . in order to exemplify how to use these energy conditions to constrain the modified f(g ) gravity models , we have considered two specific models of f(g ) gravity , i.e. , @xmath110 and @xmath116 and given the corresponding constraints on the parameters in the @xmath110 and @xmath116 models . since there has been no reliable measurement for the snap parameter @xmath92 up to now , we only focus on the wec in this particular case . by analysis on figs.1 and 2 we have given the constraints on the parameters in the @xmath110 and @xmath116 models satisfying the weak energy conditions when @xmath75 . by the similar discussions to the case of @xmath75 , when @xmath82 the restrictions on the parameters @xmath106 , @xmath107 and @xmath108 have been also illustrated in figs.3 and 4 , from which we have found that in the two different forms of @xmath2 the constraints on the parameters for the @xmath110 model are nearly the same , but quite different for the @xmath116 model . furthermore , we have derived the stability criterion at the de sitter point for the modified f(g ) gravity models , which means that the modified f(g ) gravity models may be stable . in addition , we have researched the conditions for late - time cosmic accelerated expansion in the modified f(g ) gravity . concretely , for the two different forms of @xmath2 , the relationship among r , @xmath147 and n have been respectively given in the model @xmath180 , and by using the conditions of power - law accelerated expansion and the equation of state of matter less than @xmath0 , the constraints on the parameter n have been obtained , which are exactly the same in the two different forms of @xmath2 . the candidate for late - time cosmic accelerated expansion would be either the effective quintessence ( @xmath181 ) or the effective phantom ( @xmath171 ) , which could be determined by choosing n properly . of course , other forms of f(g ) gravity models with curvature - matter coupling will be considered in our following investigations . * acknowledgments * the research work is supported by the national natural science foundation of china ( 11147150 ) , the natural science foundation of education department of liaoning province ( l2011189 ) , the natural science foundation of liaoning province , china ( grant no.20102124 ) the nsfc ( 11175077 ) of p.r . china . riess , et al . j. 116 ( 1998 ) 1009 . s. perlmutter , et al . , astrophys . j. 517 ( 1999 ) 565 . copeland , m. sami , s. tsujikawa , int . d 15 ( 2006 ) 1753 - 1936 . c. brans , r.h . dicke , phys . 124 ( 1961 ) 925 ; + v. faraoni , cosmology in scalar - tensor gravity ( kluwer academic , dordrecht ) 2004 ; + dvali , et al . b 485 ( 2000 ) 208 ; + r. maartens , living rev . rel . 7 ( 2004 ) 7 ; + j.d . bekenstein , phys . rev . d 70 ( 2004 ) 083509 ; + t. jacobson , d. mattingly , phys . d 64 ( 2001 ) 024028 . s. capozziello , s. nojiri , s.d . odintsov and a. troisi , phys . b 639 ( 2006 ) 135 ; + l. amendola , d.polarskiands . tsujikawa , phys . 98 ( 2007 ) 131302 ; + s. capozziello , s. nojiri , s.d . odintsov and a. troisi , phys . b 639 ( 2006 ) 135 ; + s. nojiri and s.d . odintsov , phys . d 74 ( 2006 ) 086005 ; + j. santos , j.s . alcaniz , m.j . reboucas and f.c . carvalho , phys . d 76 ( 2007 ) 083513 ; + s. nojiri and s.d . odintsov , phys . b 652 ( 2007 ) 343 ; + s. tsujikawa , phys . rev . d 77 ( 2008 ) 023507 ; t.p . sotiriou , v. faraoni , rev . 82 ( 2010 ) 451 - 497 ; + s. nojiri , s.d . odintsov , econf c0602061 ( 2006 ) 06 ; int . j. geom . 4 ( 2007 ) 115 - 146 ; + s. capozziello , int . d 11 ( 2002 ) 483 ; + s. nojiri , s.d . odintsov , gen . rel . grav . 36 ( 2004 ) 1765 - 1780 ; + a.d . dolgov , m. kawasaki , phys . b 573 ( 2003 ) 1 ; + v. faraoni , phys . rev . d 74 ( 2006 ) 104017 ; + v. faraoni , phys . rev . d 76 ( 2007 ) 127501 . s. nojiri , s.d . odintsov , phys . b 631 ( 2005 ) 1 ; + g. cognola , e. elizalde , s. nojiri , s.d . odintsov , s. zerbini , phys . d 73 ( 2006 ) 084007 ; + g. cognola , e. elizalde , s. nojiri , s.d . odintsov , s. zerbini , phys . d 75 ( 2007 ) 086002 ; + b.j . barrow , d.f . mota , phys . d 76 ( 2007 ) 044027 ; + m. alimohammadi , a. ghalee , phys . rev . d 79 ( 2009 ) 063006 ; + c.g . boehmer , f.s.n . lobo , phys . d 79 ( 2009 ) 067504 ; + s.y . zhou , e.j.copeland , p.m. saffin , j. cosmol . astropart . phys . 0907 ( 2009 ) 009 ; + n. goheer , r. goswami , p.k.s . dunsby , k.ananda , phys . d 79 ( 2009 ) 121301 ; + j. sadeghi , m.r . setare , a. banijamali , phys . b 679 ( 2009 ) 302 .

a modified f(g ) gravity model with coupling between matter and geometry is proposed , which is described by the product of the lagrange density of the matter and an arbitrary function of the gauss - bonnet term . the field equations and the equations of motion corresponding to this model show the non - conservation of the energy - momentum tensor , the presence of an extra - force acting on test particles and the non - geodesic motion .

a modified f(g ) gravity model with coupling between matter and geometry is proposed , which is described by the product of the lagrange density of the matter and an arbitrary function of the gauss - bonnet term . the field equations and the equations of motion corresponding to this model show the non - conservation of the energy - momentum tensor , the presence of an extra - force acting on test particles and the non - geodesic motion . moreover , the energy conditions and the stability criterion at de sitter point in the modified f(g ) gravity models with curvature - matter coupling are derived , which can degenerate to the well - known energy conditions in general relativity . furthermore , in order to get some insight on the meaning of these energy conditions , we apply them to the specific models of f(g ) gravity and the corresponding constraints on the models are given . in addition , the conditions and the candidate for late - time cosmic accelerated expansion in the modified f(g ) gravity are studied by means of conditions of power - law expansion and the equation of state of matter less than @xmath0 .

1105.0445

i

the study of the final state of the gravitational collapse of initially regular distributions of matter is one of the open problems in classical general relativity , having attracted remarkable attention in past decades . when a sufficiently massive star exhausts all the thermonuclear sources of its energy , it would undergo a collapsing scenario due to its own gravity , without reaching a final state in terms of a neutron star or white dwarf . under a variety of circumstances , singularities will inevitably emerge ( geodesic incompleteness in space - time ) , matter densities and space - time curvatures diverging . albeit the singularity theorems @xcite state that there exist space - time singularities in a generic gravitational collapse , they provide no information on the nature of singularities : the problem of whether these regions are hidden by a space - time event horizon or can actually be observed , remains unsolved . the cosmic censorship conjecture ( ccc ) , as hypothesized by penrose @xcite , conveys that the singularities appearing at the collapse final outcome must be hidden within an event horizon and thus no distant observer could detect them . a black hole forms . although the ccc plays a crucial role in the physics of black holes , there is yet no proof of it , due to the lack of adequate tools to treat the global characteristics of the field equations . nevertheless , in the past 30 years many solutions to the field equations have been discovered , which exhibit the occurrence of naked singularities , where the matter content has included perfect and imperfect fluids @xcite , scalar fields @xcite , self - similar models @xcite and null strange quarks @xcite . basically , it is the geometry of trapped surfaces that decides the visibility or otherwise of the space - time singularity . in case the collapse terminates into a naked singularity , the trapped surfaces do not emerge early enough , allowing ( otherwise hidden ) regions to be visible to the distant observers . the gravitational collapse of scalar fields is of relevance @xcite , owing to the fact that they are able to mimic other types of behaviours , depending on the choice of the potentials . scalar field models have been extensively examined for studying ccc in spherically symmetric models @xcite , non - spherically symmetric models @xcite and also for static cases @xcite . their role in understanding the machinery governing the causal structure of space - time was available since the 90 s , when the numerical solutions exhibiting naked singularities were found numerically by choptuik @xcite and analytically by christodoulou @xcite . there are in the literature a few papers discussing gravitational collapse in the presence of a scalar field joined by a fluid for the matter content@xcite : in summary , a black hole forms in these collapsing situations . however , to our knowledge , a tachyon scalar field has not yet been considered regarding whether a black hole or naked singularity forms , that is to say , in the ccc context , together with a fluid . tachyon fields arise in the framework of string theory @xcite and have been of recent use in cosmology @xcite . the action for the tachyon field has a non - standard kinetic term @xcite , enabling for several effects whose dynamical consequences are different from those of a standard scalar field @xcite . namely , other ( anti-)friction features that can alter the outcome of a collapsing scenario . this constitutes a worthy motivation to investigate the scenario where a tachyon field is added to a barotropic fluid , both constituting the matter content present in the collapse process : on the one hand , the fluid will play the role of conventional matter from which a collapse can proceed into , whereas , on the other hand , the tachyon would convey , albeit by means of a simple framework , some intrinsic features from a string theory setting . restricting ourselves herein to the tachyon as the intrinsic string ingredient influencing the collapse , let us nevertheless point that many other string features could be incorporated in subsequent similar studies @xcite . our purpose , in this paper , by investigating the gravitational collapse of a barotropic fluid together with a tachyon field , is therefore to establish the types of final state that can occur ( i.e. , whether a black hole or a naked singularity emerges , in the context of the ccc ) , which matter component will determine the outcome . in particular , if the late time tachyon behaviour , possibly competing with the fluid and eventually becoming dominant , could allow interesting features to appear . we then organize this paper as follows . in section [ collapse ] we give a brief review on the gravitational collapse of a specific space - time , namely the marginally bounded case ( cf . @xcite ) . in section [ classic ] we study , by means of a dynamical system analysis , the gravitational collapse employing a tachyon and a barotropic fluid as the matter content . the analytical study is complemented by a careful numerical investigation . in section [ discussion ] we present our conclusions and a discussion of our results .

our purpose , by making use of the specific kinematical features of the tachyon , which are rather different from a standard scalar field , is to establish the several types of asymptotic behavior that our matter content induces . employing a dynamical system analysis , complemented by a thorough numerical study furthermore , these collapsing scenarios both have as final state the formation of a black hole .

a particular class of space - time , with a tachyon field , @xmath0 , and a barotropic fluid constituting the matter content , is considered herein as a model for gravitational collapse . for simplicity , the tachyon potential is assumed to be of inverse square form _ i.e. _ , @xmath1 . our purpose , by making use of the specific kinematical features of the tachyon , which are rather different from a standard scalar field , is to establish the several types of asymptotic behavior that our matter content induces . employing a dynamical system analysis , complemented by a thorough numerical study , we find classical solutions corresponding to a naked singularity or a black hole formation . in particular , there is a subset where the fluid and tachyon participate in an interesting tracking behaviour , depending sensitively on the initial conditions for the energy densities of the tachyon field and barotropic fluid . two other classes of solutions are present , corresponding respectively , to either a tachyon or a barotropic fluid regime . which of these emerges as dominant , will depend on the choice of the barotropic parameter , @xmath2 . furthermore , these collapsing scenarios both have as final state the formation of a black hole .

1105.0445

c

in this paper we considered a particular setting among the spherically symmetric class of models for gravitational collapse , with a tachyon field and a barotropic fluid as matter content . we restricted ourselves to the marginally bound case ( cf . @xcite for a description and details ) . the tachyon potential was assumed to be of an inverse square form . our objective was to establish ( i ) which final states would occur ( namely , a black hole or a naked singularity ) , ( ii ) how each matter component will compete ( the fluid being conventional , whereas the tachyon bringing some workable but intrinsic non - standard effects from string theory ) and , ( iii ) which will eventually be the determinant component at the end of the collapse process . more precisely , in our opinion it is of interest to assert , if and how , at later stages , effects induced by the tachyon ( a scalar field ( among others ) found in string theory context ) , could allow interesting features to be eventually discussed ( i.e. , what asymptotic behaviour emerges ) . as far as the tachyon field is concerned , from eq . ( [ field ] ) we can have that with @xmath304 and @xmath305 , @xmath258 terms act like an anti - friction contribution at a collapsing phase , within an uphill evolution for the @xmath306 potential for tachyon field ( i.e. , when @xmath307 ) . moreover , other terms ( i.e. the term including @xmath308 ) would have an anti - friction effect as well . determining therefore the outcome of the gravitational collapse in our system , i.e. , whether , e.g. , a black hole or naked singularity would form , was not a straightforward assessment . we considered an analytical description by means of a phase space analysis @xcite , discussing several asymptotic behaviours ; these were also subject to a careful study involving a numerical investigation , which added a clearer description of the possible dynamical evolutions . within this setting , for a spatially homogeneous interior space - time , we found a situation where the tachyon was dominant , with a black hole forming i.e. , @xmath309 . in both models , the collapsing systems lead to the black hole formation . ] . a cosmological framework involving only a frw geometry , with a tachyon field and a barotropic fluid , was investigated in @xcite , focusing on the late time ( dark energy like ) stages . it is interesting to note that while for a tachyon dominated regime , an inflationary - like ( i.e. , accelerated expansion ) scenario leads to violation of the strong energy condition ( sec ) . thus , the sec holds if @xmath310 . ] @xcite , in our collapse scenario we have instead a corresponding asymptotic stage , where tachyon dominance leads to black hole formation , satisfying the sec at the final state of the collapse ( cf . figure ( [ f3b ] ) ) . the same behaviour is observed in the fluid dominated regime , where for @xmath132 the sec is satisfied by the fluid , with a black hole formation . however , for the tracking solutions , where a naked singularity forms , i.e. , @xmath311 and @xmath214 , the sec is violated . moreover , in further comparison with the set of fixed points found in @xcite for an expanding ( accelerating ) universe ( @xmath312 ) , we have found analytically two additional critical points ( @xmath285 and @xmath313 ) for the collapse process which correspond to a barotropic dominated collapsing regime which ends in a black hole for @xmath132 , respecting the wec and sec . indeed , for the late - time acceleration of the universe , filled with a tachyon field and a fluid , the phase space analysis in @xcite predicted two class of solutions : a tachyon dominated solution ; and a tracking solution @xcite . rather differently , corresponding solutions herein our paper turn to be unstable towards the singularity in the collapse process . nevertheless , two other solutions are also provided in our collapsing scenario : a tachyon dominated solution where @xmath2 satisfies the range @xmath131 , initially ; and a barotropic dominated solution for which the barotropic parameter holds the range @xmath132 . all these solutions predict a black hole formation as collapse end state . further regarding the tracking solutions ( of a cosmological nature ) indicated in @xcite . in our collapsing system , a different and rather interesting set of states is found , within the context of tracking behavior for the barotropic fluid plus tachyon field content . being more concrete , these solutions have that a black hole or naked singularity forms . in particular , in this situation , we found that it is possible to define by a numerical appraisal in particular , the threshold @xmath314 , separating black hole and naked singularity solutions for the gravitational collapse . we have also discussed the specific conditions leading to the formation of a naked singularity . therefore , we concluded , that in our model , if the collapse starts with an unbalanced distribution of the matter content favoring the barotropic fluid , i.e. @xmath315 , then towards the final stage of the collapse they evolve until @xmath316 , when a naked singularity forms . however , since the nec is satisfied , the strong curvature condition along the null geodesics can be preserved and the singularity can be strong in the sense of @xcite . we think it is fair to indicate that we employed a @xmath306 potential for the tachyon , whereas for @xmath317 , the tachyon should not induce a divergent behavior as far as string theory advises @xcite . in fact , an exponential - like potential for the tachyon could bring a richer set of possible outcomes @xcite , including a better behaved and possibly a more realistic evolution when dealing with @xmath317 . finally , let us add that it will be of interest to investigate ( i ) other scenarios for the geometry of the interior space - time region , ( ii ) specific couplings between the tachyon and the fluid , within e.g. , a chamaleonic scenario for gravitational collapse and black hole production ( broadening the scope in @xcite ) , ( iii ) adding either axionic , dilatonic or other terms ( e.g. , curvature invariants ) that could be considered from a string setup , but at the price of making the framework severely less workable and ( iv ) whether explicit quantum effects can alter the outcomes presented in this paper . to this purpose latter , we plan to use ingredients brought from loop quantum gravity ( cf . ref .

a particular class of space - time , with a tachyon field , @xmath0 , and a barotropic fluid constituting the matter content , is considered herein as a model for gravitational collapse . for simplicity , the tachyon potential is assumed to be of inverse square form _ two other classes of solutions are present , corresponding respectively , to either a tachyon or a barotropic fluid regime .

a particular class of space - time , with a tachyon field , @xmath0 , and a barotropic fluid constituting the matter content , is considered herein as a model for gravitational collapse . for simplicity , the tachyon potential is assumed to be of inverse square form _ i.e. _ , @xmath1 . our purpose , by making use of the specific kinematical features of the tachyon , which are rather different from a standard scalar field , is to establish the several types of asymptotic behavior that our matter content induces . employing a dynamical system analysis , complemented by a thorough numerical study , we find classical solutions corresponding to a naked singularity or a black hole formation . in particular , there is a subset where the fluid and tachyon participate in an interesting tracking behaviour , depending sensitively on the initial conditions for the energy densities of the tachyon field and barotropic fluid . two other classes of solutions are present , corresponding respectively , to either a tachyon or a barotropic fluid regime . which of these emerges as dominant , will depend on the choice of the barotropic parameter , @xmath2 . furthermore , these collapsing scenarios both have as final state the formation of a black hole .

1311.2274

i

given the navarro - frenk - white density profile of halos , it was shown in ref . @xcite ( and confirmed in this paper ) that these halos posses some of the characteristics that could give rise to traversable wormholes . given that @xmath39 is the only allowed value in eq . ( [ e : start ] ) , we also obtained a partial converse : the existence of traversable wormholes helps determine the basic form of the navarro - frenk - white density profile . the shape function , obtained from this profile , meets the flare - out condition at the throat . such a throat always exists , but its location can not be determined from the geometry . however , using a method for calculating the deflection angle pioneered by bozza @xcite , it is shown that the deflection angle diverges at the throat . the resulting photon sphere has a radius of about 0.40 ly regardless of the location of the wormhole . detection may be possible using past data . since the dark matter in the halo region does not interact with light , a suitable vehicle would be ordinary light from the large magellanic cloud . f. rahaman , p.k.f . kuhfittig , s. ray , and n. islam , eur . j. c * 74 * , 2750 ( 2014 ) . navarro , c.s . frenk , and s.d.m . white , astroph . j. * 462 * , 563 ( 1996 ) . cramer , r.l . forward , m.s . morris , m. visser , g. benford , and g.a . landis , phys . d * 51 * , 3117 ( 1995 ) . m. safanova , d.f . torres , and g.e . romero , phys . d * 65 * , 023001 ( 2002 ) . torres , g.e . romero , and l.a . anchordoqui , phys . d * 58 * , 123001 ( 1998 ) . f. abe , astrophys . j. * 725 * , 787 ( 2010 ) . y. toki , t. kitamura , h. asada , and f. abe , astrophys . j. * 740 * , 121 ( 2010 ) . v. bozza , phys . rev d * 66 * , 103002 ( 2002 ) . tejeiro and e.a . larranaga , arxiv : gr - qc/0505054 . j.m . tejeiro and e.a . larranaga , rom . * 57 * , 736 ( 2012 ) . lemos , f.s.n . lobo , and s. quinet de oliveira , phys . d * 68 * , 064004 ( 2003 ) . f. rahaman , m. kalam , and s. chakraborty , chin . * 45 * , 518 ( 2007 ) . nandi , a.i . filippov , f. rahaman , s. ray , a.a . usmani , m. kalam , and a. debenedictis , mon . not . . soc . * 399 * , 2079 ( 2009 ) . morris and k.s . thorne , am . * 56 * , 395 ( 1988 ) . k.s . virbhadra and g.f.r . ellis , phys . rev d * 62 * , 084003 ( 2002 ) . g. gentile , p. salucci , u. klein , d. vergani , and p. kalberla , mon . not . . soc . * 351 * , 903 ( 2014 ) . c. tonini , a. lapi , and p. salucci , astroph . j. * 649 * , 591 ( 2006 ) . maccio et al . , apj lett . * 744 * , l9 ( 2012 ) .

, it is shown that the deflection angle diverges at the throat of the wormhole . the resulting photon sphere has a radius of about 0.40 ly . given the dark - matter background , detection may be possible from past data using ordinary light .

a recent study by rahaman et al . has shown that the galactic halo possesses the necessary properties for supporting traversable wormholes , based on two observational results , the navarro - frenk - white density profile and the observed flat rotation curves of galaxies . using a method for calculating the deflection angle pioneered by v. bozza , it is shown that the deflection angle diverges at the throat of the wormhole . the resulting photon sphere has a radius of about 0.40 ly . given the dark - matter background , detection may be possible from past data using ordinary light . + pacs numbers : 04.20.jb , 98.62.gq , 98.62.sb

cond-mat9711242

i

in contrast to conventional superconductivity and antiferromagnetism , metallic ferromagnetism is in general an intermediate or strong coupling phenomenon . since there do not exist systematic investigation schemes to solve such types of problems the stability of metallic ferromagnetism is still not sufficiently understood . this is true even within the simplest electronic correlation model , the one - band hubbard model,@xcite in spite of significant progress made recently . the hubbard interaction is very unspecific , i.e. , does not depend on the lattice structure or dimension . hence the dispersion , and thereby the shape of the density of states ( dos ) , is of considerable importance for the stability of ferromagnetism . this was recognized already by gutzwiller,@xcite hubbard,@xcite and kanamori@xcite in their initial work on the hubbard model . however , the approximations used in the early days of many - body theory were usually not reliable enough to provide definite conclusions . an exception are the exact results by nagaoka@xcite on the stability of ferromagnetism at @xmath4 in the case of one electron above or below half filling . they show an important lattice sensitivity but , unfortunately , are not applicable in the thermodynamic limit . over the years the stability of metallic ferromagnetism has turned out to be a particularly difficult many - body problem whose explanation requires subtle _ nonperturbative _ techniques . there has been an upsurge of interest in this topic most recently @xcite . these investigations confirm that ferromagnetism is favored in systems with ( i ) frustrated lattices ( which suppress antiferromagnetism ) and ( ii ) high spectral weight near the band edge closest to the fermi energy ( which improve the kinetic energy of the polarized electrons ) . taken together , these properties imply a strongly asymmetric dos of the electrons . ferromagnetism on bipartite lattices having a symmetric dos may still be possible , but seems to require very large values of @xmath0.@xcite with the exception of refs . all previous calculations refer to the ground state . it is therefore of interest to obtain an answer to the question : _ how does the distribution of spectral weight in the dos influence the stability regime of ferromagnetism at finite temperatures ? _ it should be noted that a strongly peaked , asymmetric dos is a considerably more complex condition for ferromagnetism than the stoner criterion . the latter merely asserts that , at @xmath5 , the critical interaction for the instability is determined by the inverse of the dos precisely _ at _ the fermi energy @xmath6 , @xmath7 , thus neglecting antiferromagnetism and the structure of the dos away from @xmath6 . stoner ( i.e. , hartree - fock@xcite ) theory is a purely static mean - field theory which ignores correlation effects , e.g. , the correlation - induced redistribution of momentum states and the dynamic renormalizations of the band shape and width . so the question remains : _ how essential are genuine correlation effects for the stability of itinerant ferromagnetism at finite temperatures ? _ a third question concerns the suitability of the hubbard model itself as a model for ferromagnetism . indeed there is no compelling _ a priori _ reason why the hubbard model should be a good model for ferromagnetism at all . not only does it neglect band degeneracy , a feature observed in all ferromagnetic transition metals ( fe , co , ni ) , it also ignores the ( weak ) direct heisenberg exchange interaction which is equivalent to a ferromagnetic spin - spin interaction and hence favors ferromagnetism in the most obvious way.@xcite the proposition by hirsch and coworkers@xcite that this interaction plays a key role in metallic ferromagnetism was disputed by campbell et al.@xcite so the controversial question is : _ how important is the direct heisenberg exchange interaction for the stability of itinerant ferromagnetism in the one - band hubbard model at finite temperatures ? _ in this paper quantitative answers to the three questions formulated above are given within the dynamical mean field theory ( dmft ) . the dmft , a nonperturbative approach , becomes exact in the limit of large coordination numbers.@xcite when applied to @xmath8 , where the coordination number is @xmath9 , the dmft has proven to yield accurate and reliable results , especially in the context of long - range magnetic order.@xcite it treats local correlations exactly while spatial fluctuations are neglected . in this situation the momentum integral entering in the local propagator will be replaced by an energy integral involving only the dos of the noninteracting electrons . the latter may be viewed as an input parameter . in our investigation the question concerning the importance of the distribution of spectral weight within the band for the stability of ferromagnetism will therefore be studied using a model dos of the noninteracting electrons whose shape can be changed continuously from symmetric to strongly asymmetric by varying an asymmetry parameter . the paper is structured as follows : in sec . ii we present the model under investigation , the dynamical mean - field equations , and the analytical and numerical steps needed to construct magnetic phase diagrams . the model dos is introduced in sec . the results of our investigation and quantitative answers to the questions posed above are presented in sec . iv . a discussion where these results are put into perspective ( sec . v ) closes the presentation .

a systematic investigation of the microscopic conditions stabilizing itinerant ferromagnetism of correlated electrons in a single - band model is presented . quantitative results are obtained by quantum monte carlo simulations for a model with hubbard interaction @xmath0 and direct heisenberg exchange interaction @xmath1 within the dynamical mean - field theory . special emphasis is placed on the investigation of ( i ) the distribution of spectral weight in the density of states , ( ii ) the importance of genuine correlations , and ( iii ) the significance of the direct exchange , for the stability of itinerant ferromagnetism at finite temperatures . the nearest - neighbor heisenberg exchange does not , in general , play a decisive role .

a systematic investigation of the microscopic conditions stabilizing itinerant ferromagnetism of correlated electrons in a single - band model is presented . quantitative results are obtained by quantum monte carlo simulations for a model with hubbard interaction @xmath0 and direct heisenberg exchange interaction @xmath1 within the dynamical mean - field theory . special emphasis is placed on the investigation of ( i ) the distribution of spectral weight in the density of states , ( ii ) the importance of genuine correlations , and ( iii ) the significance of the direct exchange , for the stability of itinerant ferromagnetism at finite temperatures . we find that already a moderately strong peak in the density of states near the band edge suffices to stabilize ferromagnetism at intermediate @xmath0-values in a broad range of electron densities @xmath2 . correlation effects prove to be essential : slater hartree - fock results for the transition temperature are both qualitatively and quantitatively incorrect . the nearest - neighbor heisenberg exchange does not , in general , play a decisive role . detailed results for the magnetic phase diagram as a function of @xmath0 , @xmath1 , @xmath2 , temperature @xmath3 , and the asymmetry of the density of states are presented and discussed . 2

cond-mat9711242

c

after more than three decades of research it has become clear at last@xcite that the hubbard model can describe itinerant ferromagnetism even on regular lattices and at moderate @xmath0-values for a wide range of electronic densities @xmath2 . since ferromagnetism is an intermediate to strong coupling problem the question concerning its `` mechanism '' has , in principle , no straightforward answer . this is in contrast to _ weak _ coupling phenomena , e.g. , conventional superconductivity , which can be explained within perturbation theory . nevertheless a good starting point for an understanding of the origin of itinerant ferromagnetism can be obtained in the strong coupling limit . at @xmath4 doubly occupied sites are excluded and the hubbard model reduces to a ( complicated ) kinetic energy . to avoid doubly occupied sites in a paramagnetic phase the dos is then necessarily strongly renormalized compared with the noninteracting case , whereas for the saturated ferromagnetic phase the interacting dos is the same as the noninteracting one except for a shift between the spin - up and -down bands . in this situation details of the structure of the noninteracting dos become relevant in selecting the state with the lowest energy . this physical picture is , in principle , similar to that underlying the nagaoka mechanism ; however , the latter only addresses the kinetic energy of a single hole and it was so far not possible to generalize it to thermodynamically relevant densities . our investigations within the dmft explicitly show that a moderately strong peak at the band edge closest to the fermi energy is sufficient to stabilize ferromagnetism . furthermore a strong asymmetry of the dos implies a nonbipartite lattice which frustrates the competing antiferromagnetism near half filling . the mechanism described above is completely different from the mere band shift of the hartree - fock theory . this weak coupling approach does not take into account the dynamical renormalization of the dos in the paramagnetic phase and thus predicts ferromagnetism for any dos , even at relatively small values of @xmath0 and for high temperatures . the comparison with dmft clearly shows that hartree - fock ( i ) overestimates transition temperatures by more than an order of magnitude , ( ii ) renders the dependence of @xmath65 on @xmath0 qualitatively incorrect , and ( iii ) predicts ferromagnetism for the symmetric dos , where ( at least for @xmath120 ) this is not found . these shortcomings of hartree - fock theory are due to the neglect of dynamical fluctuations which are at the heart of the correlation problem . the heisenberg exchange interaction , not considered in the pure hubbard model , provides another mechanism that may order the fluctuating local moments arising by the suppression of double occupancies . we found that for a symmetric dos rather large values of @xmath1 are needed to stabilize ferromagnetism . however , for an asymmetric dos with a peak near the band edge already small values of the exchange interaction may provide the final `` kick '' towards ferromagnetism . in any case it reduces the critical on - site interaction and increases the critical temperatures of the ferromagnetic phase boundary . while the dmft correctly describes the dynamic fluctuations of the interacting many - body system , it neglects spatial fluctuations and short - range order . hence one should suspect that this approach overestimates the transition temperatures @xmath65 . within dmft ulmke@xcite estimated @xmath65 for a three - dimensional fcc lattice to be of the order of 500 to 800 k which is in the range of realistic transition temperatures . we may expect spatial fluctuations to reduce these temperatures . on the other hand , band degeneracy , not considered in our model so far , is expected to increase @xmath65 . indeed , band degeneracy and hund s rule couplings which are clearly present in realistic systems can be rigorously shown to improve the stability of ferromagnetism at least for special parameter values.@xcite the incorporation of band degeneracy , for which the dmft also provides a suitable framework , is the most important feature that has to be included in future investigations of the hubbard model.@xcite the additional nearest - neighbor interactions discussed in the appendix may provide yet another mechanism for ferromagnetism and will be studied in the future . we are very grateful to m. kollar and m. ulmke for numerous helpful discussions . one of us ( n.b . ) thanks the fulbright commission for support and the department of physics at the university of illinois for hospitality . computations were performed on the cray t90 of the hlrz jlich .

we find that already a moderately strong peak in the density of states near the band edge suffices to stabilize ferromagnetism at intermediate @xmath0-values in a broad range of electron densities @xmath2 . detailed results for the magnetic phase diagram as a function of @xmath0 , @xmath1 , @xmath2 , temperature @xmath3 , and the asymmetry of the density of states are presented and discussed . 2

a systematic investigation of the microscopic conditions stabilizing itinerant ferromagnetism of correlated electrons in a single - band model is presented . quantitative results are obtained by quantum monte carlo simulations for a model with hubbard interaction @xmath0 and direct heisenberg exchange interaction @xmath1 within the dynamical mean - field theory . special emphasis is placed on the investigation of ( i ) the distribution of spectral weight in the density of states , ( ii ) the importance of genuine correlations , and ( iii ) the significance of the direct exchange , for the stability of itinerant ferromagnetism at finite temperatures . we find that already a moderately strong peak in the density of states near the band edge suffices to stabilize ferromagnetism at intermediate @xmath0-values in a broad range of electron densities @xmath2 . correlation effects prove to be essential : slater hartree - fock results for the transition temperature are both qualitatively and quantitatively incorrect . the nearest - neighbor heisenberg exchange does not , in general , play a decisive role . detailed results for the magnetic phase diagram as a function of @xmath0 , @xmath1 , @xmath2 , temperature @xmath3 , and the asymmetry of the density of states are presented and discussed . 2

1208.0206

i

applications of anti - de sitter space / conformal field theory ( ads / cft ) correspondence @xcite to statistical and condensed matter physics are hot topics in string theory . on the other hand , it is recognized that a new class of variational anzats in statistical physics , so called multiscale entanglement renormalization anzats ( mera ) , would be a discrete version of the ads / cft correspondence @xcite . both of them overcomes difficulties of real - space renormalization in critical systems . it is thus attracting attention to examine their complementarity in a mathematical level . the mera is a kind of tensor network ( product ) states ( tns , tps ) of quantum many - body systems on lattices @xcite . historically , the tns formalism was constructed so that the ground - state variational wave function satisfies the entanglement - entropy scaling . the examination was first developed for gapped cases . in the gapped cases , the entropy obeys the well - known area - law scaling @xcite . in spatially one dimension ( 1d ) , the wave function appropriate for the scaling is matrix product state ( mps ) . actually , the mps is numerically optimized by the density matrix renormalization group ( dmrg ) method , and the dmrg is known to be the most powerful method in quantum 1d systems @xcite . a natural generalizartion of the mps to higher dimensions is to make the tensor contraction that represents a set of short - range entangled pairs on bonds . in that sense , the tns is also called projected entangled pair state ( peps ) . when the tensor rank and the surrounding area of a partial system are @xmath0 and @xmath1 respectively , the entanglement entropy between the partial system and its enviromnent is given by @xmath2 . on the other hand , in critical cases , the area - law scaling violates logarithmically @xcite . then , we must take a large @xmath0 value of the order of the total sites @xmath3 , if we keep the basic tns structure . however , it is possible to construct a hierarchical tensor network in one higher dimension that has a managable size of the tensor rank and shows the logarithmic divergence of the entropy . that is a concept of the mera network . the mera network has its graphical representation as shown in fig . [ fig1 ] , and it is easy to visualize the entanglement structure inherent in the network . a key ingredient of mera is that the network is composed of layers , each of which has its own energy and length scales . the layered structure emerges as a result of repeating the block - spin transformation as well as disentangling transformation . in an another viewpoint , the tensors with large @xmath4 in the tns is decomposed into a set of tensors with smaller dimensions and with different functionalities . then , the total entanglement entropy is given by the sum of the entropy in each layer compatible with the area - law scaling . the reason for the appearance of the area law is that the smaller tensor rank represents more classical - like short - range correlation in this extended space . graphically , the sum corresponds to the outside area of the causal cone in the discrete ads space , and actually this is comparable to the ryu - takayanagi formula @xcite . in this paper , we focus on general tns and in particular mera at finite temperature . in comparison with the ground states , finite temperature properties of the tns are less understood . because of the potential complementarity of mera and ads / cft , the understanding also gives us deeper insight for application of the ads / cft to condensed matter physics @xcite . in the application , it is necessary to deform the asymptotically ads metric so that the ir geometry has a black hole solution . the black hole is a source of coarse graining , and determines the temperature at the conformal boundary of the ads space . then , we would like to know whether the black hole naturally emerges from the tns formalizm without any phenomenological assumptions . this is the purpose of this paper . in a viewpoint of the cft , the tns has rich functionalities . let us briefly look at a basic property of the mps that is the most primitive tns in 1d . the property is about a dicrete version of the calabrese - cardy formula for the entanglement entropy @xcite , the so called scaling of entanglement support given by @xmath5 , where @xmath6 is the central charge , @xmath7 is the finite - entanglement scaling exponent , and @xmath4 is the matrix dimension @xcite . it has been shown that the correlation length @xmath8 is given by @xmath9 . this means that the mps is a very simple structure but catches the essential feature of the cft . therefore , we expect that the black hole is also described by the tns . we will confirm this statement with use of the mera network . since the mera is a wave - function approach , it is straightforward to use thermofield dynamics ( tfd ) for finite - temperature formalism of quantum field theory ( the readers may be aware of equivalence between tfd and dual cft in a special case ) @xcite . for our purpose , we reformulate the original tfd so that the tfd wave function matches well with the tensor network representation . we will find that by this reformulation the event horizon naturally appears as a result of hidden quantum entanglement between the original hilbert space and its tilde space . the entanglement produces a combined tensor network , and we will examine the basic properties of the network . the paper is organized as follows . section ii is the main part of this paper . we first examine a single - site model , and find a method for constructing the tns formalism of the thermal state . then , we examine the finite - temperature mera network . we will present microscopic derivation of the black hole entropy , the event horizon , and the temperature at the conformal boundary of the ads space . in sec . iii and sec . iv , we discuss related topics and summarize our study .

a tensor network formalism of thermofield dynamics is introduced . the formalism relates the original hilbert space with its tilde space by a product of two copies of a tensor network . then , their interface becomes an event horizon , and the logarithm of the tensor rank corresponds to the black hole entropy . eventually , multiscale entanglement renormalization anzats ( mera ) reproduces an ads black hole at finite temperature . our finding shows rich functionalities of mera as efficient graphical representation of ads / cft correspondence .

a tensor network formalism of thermofield dynamics is introduced . the formalism relates the original hilbert space with its tilde space by a product of two copies of a tensor network . then , their interface becomes an event horizon , and the logarithm of the tensor rank corresponds to the black hole entropy . eventually , multiscale entanglement renormalization anzats ( mera ) reproduces an ads black hole at finite temperature . our finding shows rich functionalities of mera as efficient graphical representation of ads / cft correspondence .

cs0606073

i

polarimetric imagery consists in forming an image of the state of polarization of the light backscattered by a scene . we consider in this paper that the scene is artificially illuminated with coherent light ( laser ) . for example , this illumination is used in active imagery in order to combine night vision capability and to improve image resolution for a given aperture size . in practice , using a coherent illumination produces speckle noise that deteriorate the image @xcite . however , the backscattered light gives information about the capability of the scene to polarize or depolarize the emitted light and thus allows one to determine the medium that compose the scene . these information can be described by a scalar parameter : the degree of polarization of light . this quantity is obtained in standard configurations of polarimetric systems using four pair of angular rotations of both a compensator and a polarizer . four transmittance are thus recorded @xcite that lead to the estimation of the degree of polarization . however , this system is complex and it is interesting to develop methods to estimate the degree of polarization that could reduce the number of images to register . in @xcite , the authors proposed to estimate the degree of polarization with only two intensity images , however this method relies on the assumption that the measurements of the two components are uncorrelated which can be in some cases a too restrictive hypothesis . this paper extends the work of @xcite by taking into account the correlation of the different components . + let us first introduce the context of the study .

active polarimetric imagery is a powerful tool for accessing the information present in a scene . indeed the polarization properties of a scene are characterized by the degree of polarization . in standard polarimetric imagery system , four intensity images are needed to estimate this degree @xcite . however , this approach appears too restrictive in some cases .

active polarimetric imagery is a powerful tool for accessing the information present in a scene . indeed , the polarimetric images obtained can reveal polarizing properties of the objects that are not avalaible using conventional imaging systems @xcite . however , when coherent light is used to illuminate the scene , the images are degraded by speckle noise . the polarization properties of a scene are characterized by the degree of polarization . in standard polarimetric imagery system , four intensity images are needed to estimate this degree @xcite . if we assume the uncorrelation of the measurements , this number can be decreased to two images using the orthogonal state contrast image ( osci ) @xcite . however , this approach appears too restrictive in some cases . we thus propose in this paper a new statistical parametric method to estimate the degree of polarization assuming correlated measurements with only two intensity images . the estimators obtained from four images , from the osci and from the proposed method , are compared using simulated polarimetric data degraded by speckle noise .

1002.1005

i

in many application domains , software systems need to perpetually and rapidly evolve to cope with new user and technology requirements . being able to modify existing systems or redesign new systems to rapidly take in account new functionalities or preferences has led to the proposition of several software engineering approaches such as the agile software development methodology @xcite . one of the key principles of agile software development is to build software through an incremental and iterative process . each iteration adds a new feature and produces a fully working system by going through the whole the software lifecycle , _ i.e. , _ the analyze , develop and test phases . another particularity of agile development is that the testing activity is not just confined to the classical test phase but rather integrated throughout the entire lifecycle , meaning that the software is continuously tested throughout its development , from its specifications to the final running system , in order to augment the overall software system quality . another software engineering approach that contributes to facilitating the rapid development of software systems is the use of component - based software architectures . in this context , the overall structure of the application is first described with an architecture description language ( adl ) @xcite . such description highlights the needed components and their assembly , which facilitates the understanding and analysis of the application s properties , such as behavioral or quality of service properties . if the specifications are coherent , the application is eventually instantiated , deployed and executed to be tested . although agile software development and component - based software engineering ( cbse ) may appear quite different approaches , some works @xcite have identified that both approaches could benefit to each other , cbse bringing for example the capability of building large software and enhancing reusability , and agile development offering more flexible development processes for shorter time - to - market products . nevertheless we believe that there is still a bridge between these two approaches , one reason being the lack of component frameworks that allow incremental and iterative development processes , as well as throughout - lifecycle testing . to address this problematic , we have developed a model - based framework , named calico , that enables architects to design and test component - based systems in an iterative and uniformed process @xcite . calico allows software architects to specify their architectures as models , and to analyze them with respect to application and platform constraints . our approach enables the testing of the system throughout the system lifecycle . more concretely , calico analyses architecture models and creates contracts by composing contractual application properties , _ e.g. _ , behavioral , dataflow , qos properties . this composition allows compatible and incompatible interaction to be identified , as well as partially compatible interactions , which require runtime checking @xcite . when runtime checking is needed , calico automatically instruments the application to reify runtime information to complete the resolution of the partially compatible interaction contract and thus detects if the given interaction may lead to an error . by using this framework in iterative software design processes , architects get design feedback , _ i.e. , _ information on identified interaction errors , and can then modify the models accordingly . each modification performed on the model is propagated to the running system since calico ensures the synchronization between the model and the runtime system , both of which thus coexist during the whole application development . furthermore , the solution offered by calico is generic regarding underlying platforms , allowing component platforms to benefit from all the analyses integrated into calico . the rest of this paper is organized as follows . section [ sec : presentation ] gives an overview of the calico iterative and incremental development process . section [ sec : example ] illustrates with a concrete scenario the calico approach . finally , section [ sec : conclusion ] provides some information about the current status of our framework implementation .

agile development processes and component - based software architectures are two software engineering approaches that contribute to enable the rapid building and evolution of applications . nevertheless , few approaches have proposed a framework to combine agile and component - based development , allowing an application to be tested throughout the entire development cycle . to address this problematic , we have built calico , a model - based framework that allows applications to be safely developed in an iterative and incremental manner . the calico approach relies on the synchronization of a model view , which specifies the application properties , and a runtime view , which contains the application in its execution context . tests on the application specifications that require values only known at runtime , are automatically integrated by calico into the running application , and the captured needed values are reified at execution time to resume the tests and inform the architect of potential problems . any modification at the model level that does not introduce new errors is automatically propagated to the running system , allowing the safe evolution of the application . in this paper , we illustrate the calico development process with a concrete example and provide information on the current implementation of our framework .

agile development processes and component - based software architectures are two software engineering approaches that contribute to enable the rapid building and evolution of applications . nevertheless , few approaches have proposed a framework to combine agile and component - based development , allowing an application to be tested throughout the entire development cycle . to address this problematic , we have built calico , a model - based framework that allows applications to be safely developed in an iterative and incremental manner . the calico approach relies on the synchronization of a model view , which specifies the application properties , and a runtime view , which contains the application in its execution context . tests on the application specifications that require values only known at runtime , are automatically integrated by calico into the running application , and the captured needed values are reified at execution time to resume the tests and inform the architect of potential problems . any modification at the model level that does not introduce new errors is automatically propagated to the running system , allowing the safe evolution of the application . in this paper , we illustrate the calico development process with a concrete example and provide information on the current implementation of our framework .

0904.0140

c

an analysis of geological hazards associated to seismic and volcanic activity ( lava flows and ashfall ) was carried out at selected astronomical sites , namely el teide and roque de los muchachos in the canary islands , mauna kea in hawaii and the chilean observatory of paranal and the candidate site of cerro ventarrones . a common methodology was used to characterize the geological hazard , expressed in terms of probabilities of occurrence in the next 50 years , recalling that this period of time corresponds to the expected lifetime of a telescope . large telescopes have to withstand the effects associated to seismic activity , but they also have to minimize the loss of operational time , recalling the extreme precision in the alignment of mechanical and optical components . the hazard from lava flows is the damage or destruction by burying , crushing or burning astronomical facilities in their paths . burial by ash / tephra could collapse roofs , break power and communication lines , whereas suspension of fine - grained particles in air affects visibility , could damage unprotected machinery , cause short circuits in electrial facilities and affect comunications . tectonic and/or volcanic activity might also induce subtle ground tilt that could also result in the disalignment of mechanical and optical components , in particular in the case of interferometric observations . the lowest geological hazard in both seismic and volcanic activity was found at roque de los muchachos observatory , in the island of la palma . seismic hazard is also low at the other canarian site , el teide observatory , since seismic activity in the canary islands is low in both number and magnitude of earthquakes . on the contrary , seismic hazard is very high in paranal and ventarrones ( chile ) and in mauna kea ( hawaii ) . hazard associated to lava flows during a volcanic eruption is not significant at any site , as the result of low volcanic activity in the regions where the sites are emplaced , topographical protection or distance to the eruptive vents . hazard associated to volcanic ashfall is negligible at mauna kea and roque de los muchachos and low to moderate in tenerife and the central andes , depending on the prevailing winds and the still poorly known explosive volcanic activity in these regions . ground tilt induced by volcanic activity might be significant at mauna kea and el teide observatories , whereas tilt produced by fault dislocation is significant at the chilean observatories .

an analysis of the impact of seismic and volcanic activity was carried out at selected astronomical sites , namely the observatories of el teide ( tenerife , canary islands ) , roque de los muchachos ( la palma , canary islands ) , mauna kea ( hawaii ) and paranal ( chile ) and the candidate site of cerro ventarrones ( chile ) . hazard associated to volcanic activity is low or negligible at all sites , whereas seismic hazard is very high in chile and hawaii . the lowest geological hazard in both seismic and volcanic activity was found at roque de los muchachos observatory , in the island of la palma .

an analysis of the impact of seismic and volcanic activity was carried out at selected astronomical sites , namely the observatories of el teide ( tenerife , canary islands ) , roque de los muchachos ( la palma , canary islands ) , mauna kea ( hawaii ) and paranal ( chile ) and the candidate site of cerro ventarrones ( chile ) . hazard associated to volcanic activity is low or negligible at all sites , whereas seismic hazard is very high in chile and hawaii . the lowest geological hazard in both seismic and volcanic activity was found at roque de los muchachos observatory , in the island of la palma . [ firstpage ] site testing geological activity canary islands hawaii chile

1603.04299

c

we perform experiments , analytical computations and numerical simulations with the autocatalytic iodate arsenious acid reaction ( @xmath1 ) over a wide range of flow velocities around a solid disk . for the same set of control parameters , we observe two types of frozen fronts : an upstream @xmath0 which avoid the solid disk and a downstream @xmath0 with two symmetric branches emerging from the solid disk surface . we delineate the range over which we do observe these frozen fronts . we also revisit the so - called eikonal , thin front limit to describe the observed fronts and to select the frozen front shapes . + _ acknowledgements.- _ it is a pleasure to acknowledge agence nationale de la recherche for financial support of the project labocothep anr-12-monu-0011 .

we perform experiments , analytical computations and numerical simulations with the autocatalytic iodate arsenious acid reaction ( @xmath1 ) over a wide range of flow velocities around a solid disk . for the same set of control parameters , we observe two types of frozen fronts : an upstream @xmath0 which avoid the solid disk and a downstream @xmath0 with two symmetric branches emerging from the solid disk surface . we also address the relevance of the so - called eikonal , thin front limit to describe the observed fronts and select the frozen front shapes .

autocatalytic reaction fronts between two reacting species in the absence of fluid flow , propagate as solitary waves . the coupling between autocatalytic reaction front and forced hydrodynamic flow may lead to stationary front whose velocity and shape depend on the underlying flow field . we focus on the issue of the chemo - hydrodynamic coupling between forced advection opposed to self - sustained chemical waves which can lead to static stationary fronts , i.e frozen fronts , @xmath0 . towards that purpose , we perform experiments , analytical computations and numerical simulations with the autocatalytic iodate arsenious acid reaction ( @xmath1 ) over a wide range of flow velocities around a solid disk . for the same set of control parameters , we observe two types of frozen fronts : an upstream @xmath0 which avoid the solid disk and a downstream @xmath0 with two symmetric branches emerging from the solid disk surface . we delineate the range over which we do observe these frozen fronts . we also address the relevance of the so - called eikonal , thin front limit to describe the observed fronts and select the frozen front shapes .

1507.02334

i

unlike pristine noble metal or graphite basal - plane electrodes used in classical electric double layer ( edl ) studies,@xcite lithium ion battery ( lib ) electrodes generally exhibit complex interfaces.@xcite both electron ( @xmath5 ) and li@xmath0 transport can occur inside lib electrodes . in addition , solid thin films , on the order 1 - 50 nm thick , are ubiquitous on lib electrode surfaces and can become part of the edl ( fig . [ fig1]a - h ) . the edl is critical because key battery processes like li@xmath0 incorporation kinetics ( including li@xmath0 desolvation ) , parasitic reactions , li - plating , and degradation - inducing phase transformations on electrode surfaces most likely initiate within it . indeed , `` solid electrolyte interphase '' ( sei ) films@xcite covering anodes are relied upon as kinetic barriers that prevent thermodynamic equilibrium in batteries ; they are critical for lib which operate outside the redox stability window of the organic solvent electrolytes used . as discussed below , the edl is also crucial in computational work because it effectively determines the electrode potential ( henceforth `` applied voltage '' or simply `` voltage '' ) in the simulation cell . our work examines edl associated with thin - film coated electrode surfaces , and emphasizes the importance of creating electrode interface models that exhibit consistent electrochemical activities for both li@xmath0 and @xmath5 . examples of solid films on electrode surfaces include li@xmath3co@xmath1 layers formed on pristine cathode oxide surfaces;@xcite cathode - coating films made of electrolyte decomposition products;@xcite sei films on anodes arising from reductive decomposition of liquid electrolyte components;@xcite artificial protective / passivating coatings,@xcite including atomic layer deposition ( ald ) layers@xcite which can undergo phase transformations at low voltages;@xcite ald layers between solid electrolytes and electrodes in all - solid state batteries;@xcite and even li@xmath3o@xmath3 films deposited on cathodes during fast discharge of li - air batteries,@xcite the re - oxidation of which is accompanied by significant voltage hysteresis and is a root cause of the lack of a suitable liquid electrolyte in li - air batteries . detailed atomic lengthscale understanding of the interfaces and edl associated with such thin films has remained elusive , partly due to challenges in imaging buried interfaces at sub - nanometer resolution . even edls associated with liquid organic electrolyte in batteries have arguably only recently received systematic experimental studies.@xcite modeling efforts have made much progress in elucidating the structures of solid - solid@xcite and solid - vacuum@xcite interfaces . however , voltage dependences , particularly in processes involving @xmath5 transfer like parasitic reactions and undesirable metal plating , have arguably received less theoretical attention . in this work , we apply electronic density functional theory ( dft ) calculations to investigate how voltages affect the structures and stoichiometries of thin solid films , their interfaces , and their edl at atomic lengthscales . in view of the complexities of lib electrodes , we have adopted simple model systems . the liquid electrolyte is omitted , although a few solvent molecules are included as frozen monolayers in some models to illustrate their huge impact on the voltage . au(111 ) surfaces are adopted as model cathodes , instead of transition metal oxides typically found in batteries . au does not alloy with li under voltages considered in this work and is a convenient inert electrode . these systems might be realized in ultra - high vacuum ( uhv ) settings ; they dovetail with the use of copper@xcite and gold@xcite electrodes in recent fundamental battery science experimental studies . the model thin films examined in this work , in order of increasing complexity , are li@xmath1po@xmath2 ( 010 ) ( fig . [ fig2]a),@xcite li@xmath3co@xmath1 basal plane ( fig . [ fig2]b),@xcite and li@xmath4mn@xmath3o@xmath2 ( 111 ) ( fig . [ fig2]c).@xcite these are coated on au(111 ) on one side and face a vacuum region on the other . li@xmath1po@xmath2 is a non - redox - active solid electrolyte . it illustrates the correlation between interfacial dipole densities and voltages . li@xmath3co@xmath1 is often found on as - synthesized cathode surfaces . in lib studies , there is disagreement@xcite concerning whether li@xmath3co@xmath1 dissolves upon soaking in electrolyte,@xcite is formed at high voltages,@xcite or is removed at @xmath64 v.@xcite in li - air batteries , li@xmath3co@xmath1 is generally accepted to be oxidized and removed above @xmath74.5 v.@xcite our goal is not to elucidate the detailed reaction mechanism , but to study the electronic and structural signatures accompanying voltage increase . redox - active limn@xmath3o@xmath2 ( spinel lmo ) is not used as nanometer - thick films in batteries , but its inclusion here helps illustrate the diversity of interfacial behavior ( fig . [ fig1 ] ) . like most lib cathode materials , lmo is a polaron conductor because mn can exhibit multiple redox states . it also conducts li@xmath0 , but is not a band ( `` metallic '' ) conductor . by classical electrostatics definition , the interior of lmo is not instantaneously at a constant potential.@xcite our lmo / au interface model provides a well - defined fermi level ( @xmath8 ) to demonstrate how voltage control is achieved at atomic lengthscales , and how this affects ec oxidative decomposition on lmo surfaces.@xcite out of necessity , we critically examine the voltage calibration method used in the theortical lib literature ( sec . [ voltage ] ) . the same experimental voltage governs li@xmath0 and @xmath5 motion . indeed , in cyclic voltametry , it is difficult to distinguish currents arising from faradaic li - insertion or parasitic processes that involve undesired @xmath5 transfer to the liquid . but what is `` voltage '' at atomic lengthscales ? the absolute electrochemical potential for a charged particle in an atomic configuration is the ( free ) energy needed to transfer it into a given phase from infinity ( see , e.g. , ref . ) . there can be differences whether the particle is a li@xmath0 or a @xmath5 . in dft modeling , the electronic voltage ( @xmath9 ) governing electronic motion , and ionic voltage ( @xmath9 ) governing li@xmath0 motion , can and must be distinguished . first we focus on @xmath9 . under constant voltage experimental conditions , potentiostats directly control the @xmath5 ( not li ) content . when the phase is a metallic conductor with a well - defined @xmath8 , the voltage asociated with transferring @xmath5 from infinity , multiplied by the electronic charge , is equal to the work function ( @xmath10 ) modulo a constant , just like in photovoltaics ( pv)@xcite and electrocatalytic systems.@xcite @xmath10=@xmath11 , where @xmath12 is the vacuum level and @xmath8 is set to zero herein without loss of generality . if the electrode is immersed in liquid electrolyte , @xmath10 calculated for the electrode covered by a sufficiently thick liquid layer , divied by the electronic charge , also gives @xmath9.@xcite @xmath9 applies even under out - of - equilibrium conditions . it is readily computed in our model systems because vacuum regions exist and qualify as `` infinity . '' in commercial batteries , there is no vacuum . nevertheless , our focus on @xmath10 is formally correct and emphasizes the synergy between batteries , fuel cells,@xcite pv,@xcite and metal - semiconductor interfaces.@xcite in those research areas , dipoles at interfaces are recognized as properties of paramount importance . at battery liquid - solid interfaces , edl s are the manifestations of complex surface dipole distributions associated with applied voltages ; it is in effect our computational potentiostat . based on our calculations , we propose the manipulation of surface dipoles as a novel electrode passivating strategy ( fig . [ fig1]b ) . li@xmath0 ions are only indirectly controlled by potentiostats ; they slowly redistribute in response to changes in electronic configurations . we define the li `` voltage '' ( @xmath13 ) as the ( free ) energy difference between li chemical potential in a system and the lithium metal cohesive energy per li divided by @xmath14 . this definition is widely used as the sole voltage estimate in the lib theory literature.@xcite at equilibrium , when the voltage is pinned at the redox potential of li - insertion reactions , @xmath9 must be equal to @xmath13 . thus @xmath13 should be considered a self - consistent criterion at interfaces . by itself , @xmath13 can give incorrect voltages when modeling parasitic processes induced by @xmath5 transfer , and it may not govern the dynamics of li@xmath0 insertion processes adequately . fig . [ fig3]a - d offers a preview of our results , pertinent to issues discussed above . the rest of the paper is organized as follows . 2 discusses and reconciles different definitions of voltage in dft calculations in more detail . 3 describes the methods used . the results are given in sec . 4 and sec . 5 summarizes the paper . a supporting information ( s.i . ) document provides further details about our three model systems , compares the modeling of battery interfaces with geochemical@xcite and other liquid - oxide interfaces,@xcite and discusses li@xmath3co@xmath1 oxidation thermodynamics . experimentalist readers are encouraged to skip to sec . [ results ] .

battery electrode surfaces are generally coated with electronically insulating solid films of thickness 1 - 50 nm . we apply density functional theory ( dft ) to investigate how the applied voltage is manifested as changes in the edl at atomic lengthscales , including charge separation and interfacial dipole moments . illustrating examples include li@xmath1po@xmath2 , li@xmath3co@xmath1 , and li@xmath4mn@xmath3o@xmath2 thin - films on au(111 ) surfaces under ultrahigh vacuum conditions . we propose that manipulating surface dipoles , seldom discussed in battery studies , may be a viable strategy to improve electrode passivation . this distinction is critical for a comprehensive description of electrochemical activities on electrode surfaces , including li@xmath0 insertion dynamics , parasitic electrolyte decomposition , and electrodeposition at overpotentials .

battery electrode surfaces are generally coated with electronically insulating solid films of thickness 1 - 50 nm . both electrons and li@xmath0 can move at the electrode - surface film interface in response to the voltage , which adds complexity to the `` electric double layer '' ( edl ) . we apply density functional theory ( dft ) to investigate how the applied voltage is manifested as changes in the edl at atomic lengthscales , including charge separation and interfacial dipole moments . illustrating examples include li@xmath1po@xmath2 , li@xmath3co@xmath1 , and li@xmath4mn@xmath3o@xmath2 thin - films on au(111 ) surfaces under ultrahigh vacuum conditions . adsorbed organic solvent molecules can strongly reduce voltages predicted in vacuum . we propose that manipulating surface dipoles , seldom discussed in battery studies , may be a viable strategy to improve electrode passivation . we also distinguish the computed potential governing electrons , which is the actual or instantaneous voltage , and the `` lithium cohesive energy''-based voltage governing li content widely reported in dft calculations , which is a slower - responding self - consistency criterion at interfaces . this distinction is critical for a comprehensive description of electrochemical activities on electrode surfaces , including li@xmath0 insertion dynamics , parasitic electrolyte decomposition , and electrodeposition at overpotentials . keywords : lithium ion batteries ; voltage prediction ; density functional theory ; computational electrochemistry epsf

0807.2002

i

in recent years there has been great interest in the physics of bose - einstein condensates of dilute atomic gases confined in highly elongated traps @xcite . these systems are routinely produced experimentally by using microfabricated atom chips @xcite or tight optical lattices @xcite and have important applications in generation and manipulation of matter - wave solitons @xcite and in the design of highly sensitive quantum devices such as matter - wave interferometers @xcite . from a theoretical point of view , in the mean - field regime and zero temperature limit , they are accurately described in terms of a macroscopic wave function @xmath3 that satisfies the gross - pitaevskii equation ( gpe ) @xcite @xmath4 where @xmath5 is the number of atoms , @xmath6 is the interaction strength determined by the _ s_-wave scattering length @xmath7 , and @xmath8 is the potential of the confining trap . in this work we shall restrict ourselves to condensates with repulsive interatomic interactions ( @xmath9 ) . in highly anisotropic cigar - shaped traps the radial confinement can be so tight that the transversal motion becomes practically reduced to zero - point oscillations . under these circumstances , only the slow axial degrees of freedom are relevant and the condensate dynamics becomes effectively one - dimensional . this is the quasi-1d mean - field regime . more generally , a high anisotropy always induces two very different time scales . when the axial motion is sufficiently slow in space and time that the radial degrees of freedom can adjust practically instantaneously to the different axial configurations , the radial motion becomes irrelevant and one can still study the condensate dynamics in terms of an effective equation of lower dimensionality . several proposals have been made in recent years in this respect @xcite . by using the adiabatic approximation and the local chemical potential that follows from a suitable ansatz for the condensate local density @xcite , we derived in ref . @xcite an effective 1d equation of motion for the axial dynamics of cigar - shaped condensates with repulsive interatomic interactions . we demonstrated that this equation , which is also applicable to condensates containing an axisymmetric vortex of topological charge @xmath10 , is more accurate than previous proposals . it also has the advantage that it allows to obtain very accurate analytical expressions for a number of ground - state properties , and these expressions remain valid for condensates with an arbitrary number of particles . despite these merits , from a fundamental point of view it would be desirable to find a more systematic way of deriving this equation . in this work , by using a variational approach in combination with the adiabatic approximation we derive a new effective equation of motion which , for @xmath0 and @xmath1 , coincides exactly with our previous proposal . we also rederive the nonpolynomial schrdinger equation ( npse ) in terms of the adiabatic approximation . this provides a unified method for obtaining the different effective equations and allows appreciating clearly the differences and similarities between the various proposals . interestingly , it also demonstrates that in certain cases a variational approach based on the chemical - potential functional can produce more simple and accurate results than the usual variational approach based on the energy functional . we also obtain an expression for the _ axial healing length _ of cigar - shaped condensates and show that , in the local density approximation and in units of the axial oscillator length , it coincides with the inverse of the axial half - length . from this result it immediately follows the necessary condition for the validity of the local density approximation . finally , we obtain analytic formulas that give the frequency of the axial breathing mode of an elongated condensate with accuracy better than @xmath2 and remain valid in the crossover between the thomas - fermi ( tf ) and the quasi-1d mean - field regimes .

by using a variational approach in combination with the adiabatic approximation we derive a new effective 1d equation of motion for the axial dynamics of elongated condensates . for condensates with vorticity @xmath0 or @xmath1 , this equation coincides with our previous proposal [ a. muoz mateo and v. delgado , phys . rev . a * 77 * , 013617 ( 2008 ) ] . we also rederive the nonpolynomial schrdinger equation ( npse ) in terms of the adiabatic approximation . this provides a unified treatment for obtaining the different effective equations and allows appreciating clearly the differences and similarities between the various proposals . we also obtain an expression for the axial healing length of cigar - shaped condensates and show that , in the local density approximation and in units of the axial oscillator length , it coincides with the inverse of the condensate axial half - length . from this result it immediately follows the necessary condition for the validity of the local density approximation . finally , we obtain analytical formulas that give the frequency of the axial breathing mode with accuracy better than @xmath2 . these formulas can be relevant from an experimental point of view since they can be expressed in terms only of the axial half - length and remain valid in the crossover between the thomas - fermi and the quasi-1d mean - field regimes .

by using a variational approach in combination with the adiabatic approximation we derive a new effective 1d equation of motion for the axial dynamics of elongated condensates . for condensates with vorticity @xmath0 or @xmath1 , this equation coincides with our previous proposal [ a. muoz mateo and v. delgado , phys . rev . a * 77 * , 013617 ( 2008 ) ] . we also rederive the nonpolynomial schrdinger equation ( npse ) in terms of the adiabatic approximation . this provides a unified treatment for obtaining the different effective equations and allows appreciating clearly the differences and similarities between the various proposals . we also obtain an expression for the axial healing length of cigar - shaped condensates and show that , in the local density approximation and in units of the axial oscillator length , it coincides with the inverse of the condensate axial half - length . from this result it immediately follows the necessary condition for the validity of the local density approximation . finally , we obtain analytical formulas that give the frequency of the axial breathing mode with accuracy better than @xmath2 . these formulas can be relevant from an experimental point of view since they can be expressed in terms only of the axial half - length and remain valid in the crossover between the thomas - fermi and the quasi-1d mean - field regimes . we have corroborated the validity of our results by numerically solving the full 3d gross - pitaevskii equation .

1007.0529

i

since both of superconductivity and ferromagnetism are antagonistic ordered phases of matter , for a few decades after discovery of superconductivity , the interplay between superconductivity and ferromagnetism had not been a subject of intensive research interest . however , recently the study of interplay between superconductor and ferromagnet has been revived and , in particular , proximity effect and andreev reflection in superconductor - ferromagnet junctions has attracted much attention.@xcite when a singlet superconductor has placed in proximity to a ferromagnetic layer , one can find triplet pairing correlations in the ferromagnetic layer and this component of pairing provides interesting effects.@xcite on the other hand , spin - triplet superconductor have been extensively investigated due to its anomalous features.@xcite proximity of spin - triplet superconductor and ferromagnet is more interesting than the singlet one in the sense that both of spin - triplet superconductor and ferromagnet have a magnetic nature . . ] in refs.@xcite the authors demonstrated presence of both charge and spin currents in the systems consisting of a thin barrier of ferromagnet sandwiched between two triplet superconductors . they obtained a spin current due to the coupling of the ferromagnetic moment to the spin of triplet cooper pairs . also , they found a 0-@xmath0 transition in the triplet superconductor - ferromagnet - superconductor ( sfs ) josephson junction generated by the misalignment of the @xmath1-vectors of the triplet superconductors with respect to the magnetic moment of the ferromagnet . in contrast to refs.@xcite where the ferromagnet is modeled as @xmath2 function potential , in this paper we allow for arbitrary length of the ferromagnet , which is a more realistic modeling , based on the quasiclassical eilenberger equation . in this paper , we investigate a triplet sfs structure with arbitrary misalignment between magnetization of the ferromagnet and gap vector of superconductors ( fig.[fig1 ] ) , by changing the exchange field and thickness of ferromagnetic layer . we find that charge and spin currents show 0-@xmath0 transition except for the case that the two vectors are in nearly perpendicular configuration the organization of this paper is as follows . in sec.[2 ] the quasiclassical equations for green functions are presented . in sec.[3 ] , we calculate green functions of the system analytically , presenting the formulas for the green functions to calculate the charge and spin current densities . in sec.[4 ] , we show the results of spin and charge currents . the paper will be finished with the conclusions in sec.[5 ] . component of the charge current versus the phase difference @xmath3 for @xmath4 , @xmath5 , and different @xmath6 and @xmath7 . currents are given in units of @xmath8 . ] component of the charge current versus the phase difference @xmath3 for @xmath9 , @xmath5 , and different @xmath10 and @xmath7 . ]

charge and spin josephson currents in a ballistic superconductor - ferromagnet - superconductor junction with spin - triplet pairing symmetry are studied using the quasiclassical eilenberger equation . the gap vector of superconductors has an arbitrary relative angle with respect to magnetization of the ferromagnetic layer .

charge and spin josephson currents in a ballistic superconductor - ferromagnet - superconductor junction with spin - triplet pairing symmetry are studied using the quasiclassical eilenberger equation . the gap vector of superconductors has an arbitrary relative angle with respect to magnetization of the ferromagnetic layer . we clarify the effects of the thickness of ferromagnetic layer and magnitude of the magnetization on the josephson charge and spin currents . we find that 0-@xmath0 transition can occur except for the case that the exchange field and d - vector are in nearly perpendicular configuration . we also show how spin current flows due to misorientation between the exchange field and d - vector .

1007.0529

c

in this paper , we have investigated transport properties in triplet sfs josephson junction and clarified the effects of the thickness of ferromagnet , the exchange field , and misorientation angle between exchange field of ferromagnet and @xmath1-vector of superconductors on the josephson charge and spin currents . we found that 0-@xmath0 transition can occur except for the case that the exchange field and d - vector are in nearly perpendicular configuration . also , we showed how spin current flows due to misorientation between the exchange field and @xmath1-vector and found that it is absent when two vectors are parallel or perpendicular to each other .

we clarify the effects of the thickness of ferromagnetic layer and magnitude of the magnetization on the josephson charge and spin currents . we find that 0-@xmath0 transition can occur except for the case that the exchange field and d - vector are in nearly perpendicular configuration . we also show how spin current flows due to misorientation between the exchange field and d - vector .

charge and spin josephson currents in a ballistic superconductor - ferromagnet - superconductor junction with spin - triplet pairing symmetry are studied using the quasiclassical eilenberger equation . the gap vector of superconductors has an arbitrary relative angle with respect to magnetization of the ferromagnetic layer . we clarify the effects of the thickness of ferromagnetic layer and magnitude of the magnetization on the josephson charge and spin currents . we find that 0-@xmath0 transition can occur except for the case that the exchange field and d - vector are in nearly perpendicular configuration . we also show how spin current flows due to misorientation between the exchange field and d - vector .

math0210416

i

let @xmath1 be a complex semisimple lie algebra with adjoint group @xmath2 and write @xmath3 for the coadjoint orbit of @xmath2 through @xmath4 in @xmath5 . fix a borel subgroup @xmath6 of @xmath2 and let @xmath7 be the flag variety @xmath8 for a unipotent element @xmath9 , @xmath10 is the variety of flags in @xmath7 fixed by the action of @xmath11 . the orbit @xmath12 has a natural @xmath2-invariant symplectic structure and the kostant - kirillov method seeks to attach representations of @xmath2 to certain lagrangian subvarieties of @xmath12 ( see @xcite , @xcite , and @xcite ) . of particular importance is the set of orbital varieties , lagrangian subvarieties of @xmath13 that are fixed by a given borel subgroup of g. a result of spaltenstein identifies the set of orbital varieties for a given nilpotent orbit with the orbits of a finite group on the irreducible components of the corresponding unipotent variety @xcite . the main purpose of this paper is to provide new parameterizations of both , the orbital varieties contained in a given nilpotent orbit , as well as the irreducible components of the unipotent variety @xmath14 . in the case of classical groups , nilpotent coadjoint orbits are classified by partitions . because the number of orbital varieties contained in a given orbit is finite , one expects that both orbital varieties and the components of the unipotent variety should also admit combinatorial descriptions @xcite . this is most apparent when @xmath2 is of type @xmath0 . [ theorem : typea ] suppose that @xmath15 and the nilpotent orbit @xmath12 corresponds to the partition @xmath16 of @xmath17 . then the orbital varieties contained in @xmath12 as well as the set of components @xmath18 are both parameterized by the family of standard young tableaux of shape @xmath16 . in the setting of other classical groups , a method similar to the one used to obtain the above can also be employed to describe both families of objects . however , the resulting parametrization by subsets of signed domino tableaux is somewhat cumbersome ( see @xcite and @xcite ) . the following argument suggests a more appealing parameter set . let @xmath19 be the set of partitions indexing the unitary dual of @xmath20 , the weyl group of @xmath2 @xcite and write @xmath16 for a partition lying in @xmath19 . the dimension of the representation given by @xmath16 is precisely the number of standard domino tableaux of shape @xmath16 . if we choose a unipotent representative @xmath21 in the conjugacy class corresponding to @xmath16 , then springer s characterization of the representations @xmath22 in the top degree cohomology of @xmath23 @xcite indicates that @xmath24 this suggests that @xmath14 should correspond to a set of standard domino tableaux in a natural way . indeed , this is the case . the precise relationship between van leeuwen s parameter set for @xmath14 @xcite and the set of domino tableaux can be described in terms of garfinkle s notions of cycles and moving - through maps @xcite . after defining the notion of a _ cycle for a cluster of dominos , we show that moving through sets of distinguished cycles of open and closed clusters in van leeuwen s parameter set defines a bijection with the set of all domino tableaux of a given size . [ theorem1 ] suppose that @xmath2 is a complex classical simple lie group not of type @xmath0 . then the collection of irreducible components of the unipotent varieties for @xmath2 as the unipotent element ranges over all conjugacy classes is parameterized by @xmath25 , the set of standard domino tableaux of size @xmath17 . the action of the finite group @xmath26 on the irreducible components @xmath14 is described by @xcite . in the signed domino parametrization , it acts by changing the signs of open clusters . we exploit this to obtain a parametrization of orbital varieties by standard domino tableaux . this time , moving through the distinguished cycles of just the closed clusters in van leeuwen s parameter set defines the required bijection . the result is a little simpler to state if we consider nilpotent orbits of the isometry group of a nondegenerate bilinear form , @xmath27 . [ theorem2 ] suppose that @xmath2 is a complex classical simple lie group not of type @xmath0 and @xmath28 is the nilpotent orbit of @xmath27 that corresponds to the partition @xmath16 . then the set of orbital varieties contained in @xmath28 is parameterized by the set of standard domino tableaux of shape @xmath16 . parameterizations of orbital varieties by domino tableaux have been obtained in @xcite , by describing equivalence classes in the weyl group of @xmath2 , as well as in @xcite . we will address the compatibility of these parameterizations with the one above in another paper .

consider a complex classical semi - simple lie group along with the set of its nilpotent coadjoint orbits . when the group is of type @xmath0 , the set of orbital varieties contained in a given nilpotent orbit is described a set of standard young tableaux . we parameterize both , the orbital varieties and the irreducible components of unipotent varieties in the other classical groups by sets of standard domino tableaux .

consider a complex classical semi - simple lie group along with the set of its nilpotent coadjoint orbits . when the group is of type @xmath0 , the set of orbital varieties contained in a given nilpotent orbit is described a set of standard young tableaux . we parameterize both , the orbital varieties and the irreducible components of unipotent varieties in the other classical groups by sets of standard domino tableaux . the main tools are spaltenstein s results on signed domino tableaux together with garfinkle s operations on standard domino tableaux .

1101.4026

i

clusters of galaxies with steeply rising x - ray surface brightness profiles are known as cool core clusters , and require strong feedback from their central agn to offset cooling of the intracluster medium ( icm ) . for highly - luminous cool core clusters ( with @xmath4 ) , the central agn must be injecting on average @xmath5 into the surrounding medium . we do not know the black hole ( bh ) mass for most of these agn but we expect that they lie between @xmath6 and @xmath7 , based on the few reliable measurements in the literature ( e. g. m87 , ( * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * macchetto et al . 1997 ) ) . given that these objects are in an exceptional environment and are active continuously , it is not clear that the standard @xmath8 or @xmath9 relations are relevant for them . for @xmath10 , this means that these black holes must be operating at high enough eddington rates that they should be radiatively efficient ( see fig . [ fig1 ] ) . we would therefore expect to see an x - ray point source . we present a sample of strong cool core , highly - luminous clusters , for which there is _ _ n__o evidence of a nuclear x - ray point source in the @xmath1 images . using these images , we derive upper limits of the nuclear luminosities with the web interface of pimms ( ( * ? ? ? * ; * ? ? ? * mukai 1993 ) ) , which converts a count rate into an expected flux . we also investigate whether there is a hidden power law in the x - ray spectra , but find no such evidence in any of our objects . finally , we calculate the energy that must be injected by the agn in order to offset the cooling ( ) of the icm , and compare it with the nuclear luminosity of the agn . , then for @xmath10 the power exceeds @xmath11 , indicating that @xmath12 , i.e. we should see a nuclear point source . for @xmath13 , the power exceeds @xmath14 . here , @xmath15 could dominate over , if the black hole is in a low accretion state . ]

cool core clusters of galaxies require strong feedback from their central agn to offset cooling . all of the central galaxies host a radio source , indicating an active nucleus , and no obvious x - ray point source . for all clusters in the sample , the nucleus has an x - ray bolometric luminosity below 2 per cent of that of the entire cluster . ps . -.4 in

cool core clusters of galaxies require strong feedback from their central agn to offset cooling . we present a study of strong cool core , highly - luminous ( most with @xmath0 ) , clusters of galaxies in which the mean central agn jet power must be very high yet no central point x - ray source is detected . using the unique spatial resolution of @xmath1 , a sample of 13 clusters is analysed , including a1835 , a2204 , and one of the most massive cool core clusters , rxcj1504.1 - 0248 . all of the central galaxies host a radio source , indicating an active nucleus , and no obvious x - ray point source . for all clusters in the sample , the nucleus has an x - ray bolometric luminosity below 2 per cent of that of the entire cluster . we investigate how these clusters can have such strong x - ray luminosities , short radiative cooling - times of the inner intracluster gas requiring strong energy feedback to counterbalance that cooling , and yet have such radiatively - inefficient cores with , on average , @xmath2/@xmath3 exceeding 200 . explanations of this puzzle carry significant implications for the origin and operation of jets , as well as on establishing the importance of kinetic feedback for the evolution of galaxies and their surrounding medium . ps . -.4 in