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0704.1201 | Evaluation of the Axial Vector Commutator Sum Rule for Pion-Pion
Scattering | We consider the sum rule proposed by one of us (SLA), obtained by taking the
expectation value of an axial vector commutator in a state with one pion. The
sum rule relates the pion decay constant to integrals of pion-pion cross
sections, with one pion off the mass shell. We remark that recent data on
pion-pion scattering allow a precise evaluation of the sum rule. We also
discuss the related Adler--Weisberger sum rule (obtained by taking the
expectation value of the same commutator in a state with one nucleon),
especially in connection with the problem of extrapolation of the pion momentum
off its mass shell. We find, with current data, that both the pion-pion and
pion-nucleon sum rules are satisfied to better than six percent, and we give
detailed estimates of the experimental and extrapolation errors in the closure
discrepancies.
| hep-ph |
0704.1202 | Colour pairs for constraining the age and metallicity of stellar
populations | Using a widely used stellar population synthesis model, we study the ability
of using pairs of AB system colours to break the well-known stellar
age--metallicity degeneracy and give constraints on the two stellar-population
parameters (age and metallicity). The relative age and metallicity
sensitivities of AB system colours that relate to u, B, g, V, r, R, i, I, z, J,
H, and K bands are presented, and the abilities of various colour pairs for
breaking the age--metallicity degeneracy are quantified by an uncertainty
parameter (UP) method. Our results suggest that a few pairs of colours can be
used to constrain the two above stellar-population parameters. This will be
very useful for exploring the stellar populations of distant galaxies. In
detail, colour pairs [(r-K), (u-R)] and [(r-K), (u-r)] are shown to be the best
pairs for estimating stellar ages and metallicities. They can constrain two
stellar-population parameters on average with age uncertainties less than 3.89
Gyr and metallicity uncertainties less than 0.34 dex for typical uncertainties
in colours. Some other colour pairs, such as [(R-K), (u-R)], [(I-K), (u-R)],
[(R-K), (u-r)] and [(i-J), (u-R)], can possibly be used for constraining the
two parameters, too. As a whole, our results suggest that colours relating to
both UBVRIJHK and ugriz magnitudes are much better than either UBVRIJHK colours
or ugriz colours for breaking the well-known degeneracy. The results also show
that the stellar ages and metallicities of galaxies observed by the Sloan
Digital Sky Survey (SDSS) and the Two-Micron All-Sky Survey (2MASS) can be
estimated via photometry data. It is also shown that the colours can be used in
conjunction with line indices to measure stellar-population parameters.
| astro-ph |
0704.1203 | On the Fine Structure of QCD Confining String | This paper had been withdrawn because the prime reported effect had not been
confirmed in further investigations (see arXiv:0812.4488 [hep-lat]).
| hep-lat hep-ph |
0704.1204 | The effect of supernova asymmetry on coalescence rates of binary neutron
stars | We study the effect of the kick velocity -- neutron star spin alignment
observed in young radio pulsars on the coalescence rate of binary neutron
stars. The effect is shown to be especially strong for large kick amplitudes
and tight alignments, reducing the galactic rate of binary neutron star
coalescences up to an order of magnitude with respect to the rates calculated
for random kicks. The spin-kick correlation also leads to much narrower NS
spin-orbit misalignments compared to random kicks.
| astro-ph |
0704.1205 | Electronic structure of the zigzag spin-chain compound In$_2$VO$_5$ | Band structure calculations within the local spin-density approximation are
presented in order to investigate the electronic and magnetic properties of the
zigzag spin-chain compound In$_2$VO$_5$. The essential structural feature of
the system is a double chain of VO$_6$-octahedra, which leads to competing
intrachain and interchain magnetic couplings. Frustration of the spin-chains is
expected for the proposed antiferromagnetic ordering at low temperatures.
However, the band calculations show that the experimental room temperature
crystal structure is incompatible with antiferromagnetism. Both the intrachain
and interchain coupling is found to be ferromagnetic.
| cond-mat.str-el |
0704.1206 | Elasticity with Arbitrarily Shaped Inhomogeneity | A classical problem in elasticity theory involves an inhomogeneity embedded
in a material of given stress and shear moduli. The inhomogeneity is a region
of arbitrary shape whose stress and shear moduli differ from those of the
surrounding medium. In this paper we present a new, semi-analytic method for
finding the stress tensor for an infinite plate with such an inhomogeneity. The
solution involves two conformal maps, one from the inside and the second from
the outside of the unit circle to the inside, and respectively outside, of the
inhomogeneity. The method provides a solution by matching the conformal maps on
the boundary between the inhomogeneity and the surrounding material. This
matching converges well only for relatively mild distortions of the unit circle
due to reasons which will be discussed in the article. We provide a comparison
of the present result to known previous results.
| cond-mat.mtrl-sci |
0704.1207 | Asymptotic profiles of solutions to viscous Hamilton-Jacobi equations | The large time behavior of solutions to Cauchy problem for viscous
Hamilton-Jacobi equation is classified. The large time asymptotics are given by
very singular self-similar solutions on one hand and by self-similar viscosity
solutions on the other hand
| math.AP |
0704.1208 | Asymptotic profiles of solutions to convection-diffusion equations | The large time behavior of zero mass solutions to the Cauchy problem for a
convection-diffusion equation. We provide conditions on the size and shape of
the initial datum such that the large time asymptotics of solutions is given
either by the derivative of the Guass-Weierstrass kernel or by a self-similar
solution or by a hyperbolic N-wave
| math.AP |
0704.1209 | Characterization of fragment emission in ^{20}Ne (7 - 10 MeV/nucleon) +
^{12}C reactions | The inclusive energy distributions of the complex fragments (3 $\leq$ Z
$\leq$ 7) emitted from the bombardment of ^{12}C by ^{20}Ne beams with incident
energies between 145 and 200 MeV have been measured in the angular range
10$^{o} \leq \theta_{lab} \leq$ 50^{o}. Damped fragment yields in all the cases
have been found to be the characteristic of emission from fully energy
equilibrated composites. The binary fragment yields are compared with the
standard statistical model predictions. Enhanced yields of entrance channel
fragments (5 $\leq$ Z $\leq$ 7) indicate the survival of orbiting-like process
in ^{20}Ne + ^{12}C system at these energies.
| nucl-ex |
0704.1210 | The dynamics of Jupiter and Saturn in the gaseous proto-planetary disk | We study the possibility that the mutual interactions between Jupiter and
Saturn prevented Type II migration from driving these planets much closer to
the Sun. Our work extends previous results by Masset and Snellgrove (2001), by
exploring a wider set of initial conditions and disk parameters, and by using a
new hydrodynamical code that properly describes for the global viscous
evolution of the disk. Initially both planets migrate towards the Sun, and
Saturn's migration tends to be faster. As a consequence, they eventually end up
locked in a mean motion resonance. If this happens in the 2:3 resonance, the
resonant motion is particularly stable, and the gaps opened by the planets in
the disk may overlap. This causes a drastic change in the torque balance for
the two planets, which substantially slows down the planets' inward migration.
If the gap overlap is substantial, planet migration may even be stopped or
reversed. As the widths of the gaps depend on disk viscosity and scale height,
this mechanism is particularly efficient in low viscosity, cool disks. We
discuss the compatibility of our results with the initial conditions adopted in
Tsiganis et al. (2005) and Gomes et al. (2005) to explain the current orbital
architecture of the giant planets and the origin of the Late Heavy Bombardment
of the Moon.
| astro-ph |
0704.1211 | Kinetic Theory for Binary Granular Mixtures at Low-Density | Many features of granular media can be modelled as a fluid of hard spheres
with {\em inelastic} collisions. Under rapid flow conditions, the macroscopic
behavior of grains can be described through hydrodynamic equations. At
low-density, a fundamental basis for the derivation of the hydrodynamic
equations and explicit expressions for the transport coefficients appearing in
them is provided by the Boltzmann kinetic theory conveniently modified to
account for inelastic binary collisions. The goal of this chapter is to give an
overview of the recent advances made for binary granular gases by using kinetic
theory tools. Some of the results presented here cover aspects such as
transport properties, energy nonequipartition, instabilities, segregation or
mixing, non-Newtonian behavior, .... In addition, comparison of the analytical
results with those obtained from Monte Carlo and molecular dynamics simulations
is also carried out, showing the reliability of kinetic theory to describe
granular flows even for strong dissipation.
| cond-mat.stat-mech cond-mat.soft |
0704.1212 | Optical carrier wave shocking: detection and dispersion | Carrier wave shocking is studied using the Pseudo-Spectral Spatial Domain
(PSSD) technique. We describe the shock detection diagnostics necessary for
this numerical study, and verify them against theoretical shocking predictions
for the dispersionless case. These predictions show Carrier Envelope Phase
(CEP) and pulse bandwidth sensitivity in the single-cycle regime. The flexible
dispersion management offered by PSSD enables us to independently control the
linear and nonlinear dispersion. Customized dispersion profiles allow us to
analyze the development of both carrier self-steepening and shocks. The results
exhibit a marked asymmetry between normal and anomalous dispersion, both in the
limits of the shocking regime and in the (near) shocked pulse waveforms.
Combining these insights, we offer some suggestions on how carrier shocking (or
at least extreme self-steepening) might be realised experimentally.
| physics.optics |
0704.1213 | Spin-polarized transport through weakly coupled double quantum dots in
the Coulomb-blockade regime | We analyze cotunneling transport through two quantum dots in series weakly
coupled to external ferromagnetic leads. In the Coulomb blockade regime the
electric current flows due to third-order tunneling, while the second-order
single-barrier processes have indirect impact on the current by changing the
occupation probabilities of the double dot system. We predict a zero-bias
maximum in the differential conductance, whose magnitude is conditioned by the
value of the inter-dot Coulomb interaction. This maximum is present in both
magnetic configurations of the system and results from asymmetry in cotunneling
through different virtual states. Furthermore, we show that tunnel
magnetoresistance exhibits a distinctively different behavior depending on
temperature, being rather independent of the value of inter-dot correlation.
Moreover, we find negative TMR in some range of the bias voltage.
| cond-mat.mes-hall cond-mat.mtrl-sci |
0704.1214 | Possible origin of Larson's lows | It was found that approximately constant column densities of giant molecular
clouds (Larson's low) can be explained as cloud existence condition in external
(galactic) gravitational field. This condition can be also applied to objects
(clumps and cores) embedded into the cloud and its gravitational field. Derived
existence condition do not rely on any internal dynamic of a cloud and embedded
objects.
| astro-ph |
0704.1215 | Double Neutron Stars: Evidence For Two Different Neutron-Star Formation
Mechanisms | Six of the eight double neutron stars known in the Galactic disk have low
orbital eccentricities (< 0.27) indicating that their second-born neutron stars
received only very small velocity kicks at birth. This is similar to the case
of the B-emission X-ray binaries, where a sizable fraction of the neutron stars
received hardly any velocity kick at birth (Pfahl et al. 2002). The masses of
the second-born neutron stars in five of the six low-eccentricity double
neutron stars are remarkably low (between 1.18 and 1.30 Msun). It is argued
that these low-mass, low-kick neutron stars were formed by the electron-capture
collapse of the degenerate O-Ne-Mg cores of helium stars less massive than
about 3.5 Msun, whereas the higher-mass, higher kick-velocity neutron stars
were formed by the collapses of the iron cores of higher initial mass. The
absence of low-velocity single young radio pulsars (Hobbs et al. 2005) is
consistent with the model proposed by Podsiadlowski et al. (2004), in which the
electron-capture collapse of degenerate O-Ne-Mg cores can only occur in binary
systems, and not in single stars.
| astro-ph |
0704.1216 | Large Scale Self-Similar Skeletal Structure of the Universe | An analysis of the redshift maps of galaxies and quasars has revealed
large-scale self-similar skeletal structures of the Universe of the same
topology which had been found earlier in a wide range of phenomena, spatial
scales and environments. The "cartwheel" type of structure with diameter ~ 1.5
10^27 cm is discovered in this analysis by means of the method of multi-level
dynamical contrasting. Similar skeletal structures in size up to 1.5 10^28 cm
are found also in the redshift maps of quasars.
| astro-ph |
0704.1217 | The Manin conjecture in dimension 2 | These lecture notes describe the current state of affairs for Manin's
conjecture in the context of del Pezzo surfaces.
| math.NT math.AG |
0704.1218 | The impact of radio feedback from active galactic nuclei in cosmological
simulations: Formation of disk galaxies | In this paper, we present a new implementation of feedback due to active
galactic nuclei (AGN) in cosmological simulations of galaxy formation. We
assume that a fraction of jet energy, which is generated by an AGN, is
transferred to the surrounding gas as thermal energy. Combining a theoretical
model of mass accretion onto black holes with a multiphase description of
star-forming gas, we self-consistently follow evolution of both galaxies and
their central black holes. The novelty in our model is that we consider two
distinct accretion modes: standard radiatively efficient thin accretion disks
and radiatively inefficient accretion flows which we will generically refer to
as RIAFs; motivated by theoretical models for jet production in accretion
disks, we assume that only the RIAF is responsible for the AGN feedback. We
find that, after an initial episode of bursting star formation, the accretion
rate onto the central black hole drops so that the accretion disk switches to a
RIAF structure. At this point, the feedback from the AGN becomes efficient and
slightly suppresses star formation in the galactic disk and almost completely
halts star formation in the bulge. As a result, the nucleus becomes a
stochastically fuelled low-luminosity AGN (Seyfert galaxy) with recurrent
short-lived episodes of activity after the star bursts. Our model predicts
several properties of the low-luminosity AGN including the bolometric
luminosity, jet powers, the effect on kpc-scale of the radio jet and the AGN
lifetime, which are in broad agreement with observations of Seyfert galaxies
and their radio activity. We also find that the mass ratios between the central
black hole and the the host spheroid at z = 0 are ~10^{-3} regardless of the
strength of either supernova feedback or AGN feedback. (abridged)
| astro-ph |
0704.1219 | Y-formalism and $b$ ghost in the Non-minimal Pure Spinor Formalism of
Superstrings | We present the Y-formalism for the non-minimal pure spinor quantization of
superstrings. In the framework of this formalism we compute, at the quantum
level, the explicit form of the compound operators involved in the construction
of the $b$ ghost, their normal-ordering contributions and the relevant
relations among them. We use these results to construct the quantum-mechanical
$b$ ghost in the non-minimal pure spinor formalism. Moreover we show that this
non-minimal $b$ ghost is cohomologically equivalent to the non-covariant $b$
ghost.
| hep-th |
0704.1220 | A multi-transition molecular line study of candidate massive young
stellar objects associated with methanol masers | We characterize the molecular environment of candidate massive young stellar
objects (MYSOs) signposted by methanol masers. Single pixel observations of 10
transitions of HCO^+, CO and CS isotopomers were carried out, using the IRAM
30m telescope. We studied a sample of 28 targets for which the 6.7GHz maser
emission positions are known with a sub-arcsecond accuracy. The systemic
velocity inferred from the optically thin lines agrees within 3km/s with the
central velocity of the maser emission for most of the sources. About 64% of
the sources show line wings in one or more transitions of CO, HCO^+ and CS
species, indicating the presence of molecular outflows. Comparison of the
widths of line wings and methanol maser emission suggests that the 6.7GHz maser
line traces the environment of MYSO of various kinematic regimes. Therefore
conditions conducive for the methanol maser can exist in the inner parts of
molecular clouds or circumstellar discs as well as in the outer parts
associated with molecular outflows. Calculations of the physical conditions
based on the CO and HCO^+ lines and the CS line intensity ratios refine the
input parameters for maser models.
| astro-ph |
0704.1221 | Dynamics of the Tippe Top via Routhian Reduction | We consider a tippe top modeled as an eccentric sphere, spinning on a
horizontal table and subject to a sliding friction. Ignoring translational
effects, we show that the system is reducible using a Routhian reduction
technique. The reduced system is a two dimensional system of second order
differential equations, that allows an elegant and compact way to retrieve the
classification of tippe tops in six groups as proposed in [1] according to the
existence and stability type of the steady states.
| math.DS |
0704.1222 | Plasmaneutrino spectrum | Spectrum of the neutrinos produced in the massive photon and longitudal
plasmon decay process has been computed with four levels of approximation for
the dispersion relations. Some analytical formulae in limiting cases are
derived. Interesting conclusions related to previous calculations of the energy
loss in stars are presented. High energy tail of the neutrino spectrum is shown
to be proportional to exp(-E/kT), where E is the neutrino energy and kT is the
temperature of the plasma.
| astro-ph |
0704.1223 | Quadratic BSDEs with random terminal time and elliptic PDEs in infinite
dimension | In this paper we study one dimensional backward stochastic differential
equations (BSDEs) with random terminal time not necessarily bounded or finite
when the generator F(t,Y,Z) has a quadratic growth in Z. We provide existence
and uniqueness of a bounded solution of such BSDEs and, in the case of infinite
horizon, regular dependence on parameters. The obtained results are then
applied to prove existence and uniqueness of a mild solution to elliptic
partial differential equations in Hilbert spaces.
| math.PR |
0704.1224 | Non-minimal Wu-Yang wormhole | We discuss exact solutions of three-parameter non-minimal Einstein-Yang-Mills
model, which describe the wormholes of a new type. These wormholes are
considered to be supported by SU(2)-symmetric Yang-Mills field, non-minimally
coupled to gravity, the Wu-Yang ansatz for the gauge field being used. We
distinguish between regular solutions, describing traversable non-minimal
Wu-Yang wormholes, and black wormholes possessing one or two event horizons.
The relation between the asymptotic mass of the regular traversable Wu-Yang
wormhole and its throat radius is analysed.
| gr-qc astro-ph hep-ph hep-th |
0704.1225 | Patterns of dominant flows in the world trade web | The large-scale organization of the world economies is exhibiting
increasingly levels of local heterogeneity and global interdependency.
Understanding the relation between local and global features calls for
analytical tools able to uncover the global emerging organization of the
international trade network. Here we analyze the world network of bilateral
trade imbalances and characterize its overall flux organization, unraveling
local and global high-flux pathways that define the backbone of the trade
system. We develop a general procedure capable to progressively filter out in a
consistent and quantitative way the dominant trade channels. This procedure is
completely general and can be applied to any weighted network to detect the
underlying structure of transport flows. The trade fluxes properties of the
world trade web determines a ranking of trade partnerships that highlights
global interdependencies, providing information not accessible by simple local
analysis. The present work provides new quantitative tools for a dynamical
approach to the propagation of economic crises.
| q-fin.GN cond-mat.dis-nn physics.soc-ph |
0704.1226 | Hydrogen 2p--2s transition: signals from the epochs of recombination and
reionization | We propose a method to study the epoch of reionization based on the possible
observation of 2p--2s fine structure lines from the neutral hydrogen outside
the cosmological H {\sc ii} regions enveloping QSOs and other ionizing sources
in the reionization era. We show that for parameters typical of luminous
sources observed at $z \simeq 6.3$ the strength of this signal, which is
proportional to the H {\sc i} fraction, has a brightness temperature $\simeq 20
\mu K$ for a fully neutral medium. The fine structure line from this redshift
is observable at $\nu \simeq 1 \rm GHz$ and we discuss prospects for the
detection with several operational and future radio telescopes. We also compute
the characteristics of this signal from the epoch of recombination: the peak
brightness is expected to be $\simeq 100 \mu K$; this signal appears in the
frequency range 5-10 MHz. The signal from the recombination era is nearly
impossible to detect owing to the extreme brightness of the Galactic emission
at these frequencies.
| astro-ph |
0704.1227 | Superconductor strip in a closed magnetic environment: exact analytic
representation of the critical state | An exact analytic representation of the critical state of a current-carrying
type-II superconductor strip located inside a cylindrical magnetic cavity of
high permeability is derived. The obtained results show that, when the cavity
radius is small, penetration of magnetic flux fronts is strongly reduced as
compared to the situation in an isolated strip. From our generic representation
it is possible to establish current profiles in closed cavities of various
other geometries too by means of conformal mapping of the basic configuration
addressed.
| cond-mat.supr-con cond-mat.mtrl-sci |
0704.1228 | Near- and Far-Infrared Counterparts of Millimeter Dust Cores in the Vela
Molecular Ridge Cloud D | The aim of this paper is to identify the young protostellar counterparts
associated to dust millimeter cores of the Vela Molecular Ridge Cloud D through
new IR observations (H_2 narrow-band at 2.12 micron and N broad band at 10.4
micron) along with an investigation performed on the existing IR catalogues.
The association of mm continuum emission with infrared sources from catalogues
(IRAS, MSX, 2MASS), JHK data from the literature and new observations, has been
established according to spatial coincidence, infrared colours and spectral
energy distributions. Only 7 out of 29 resolved mm cores (and 16 out of the 26
unresolved ones) do not exhibit signposts of star formation activity. The other
ones are clearly associated with: far-IR sources, H_2 jets or near-IR objects
showing a high intrinsic colour excess. The distribution of the spectral
indices pertaining to the associated sources is peaked at values typical of
Class I objects, while three objects are signalled as candidates Class 0
sources. We remark the high detection rate (30%) of H_2 jets driven by sources
located inside the mm-cores. They appear not driven by the most luminous
objects in the field, but rather by less luminous objects in young clusters,
testifying the co-existence of both low- and intermediate-mass star formation.
The presented results reliably describe the young population of VMR-D. However,
the statistical evaluation of activity vs inactivity of the investigated cores,
even in good agreement with results found for other star forming regions, seems
to reflect the limiting sensitivity of the available facilities rather than any
property intrinsic to the mm-condensations.
| astro-ph |
0704.1229 | High-precision covariant one-boson-exchange potentials for np scattering
below 350 MeV | All realistic potential models for the two-nucleon interaction are to some
extent based on boson exchange. However, in order to achieve an essentially
perfect fit to the scattering data, characterized by a chi2/Ndata ~ 1, previous
potentials have abandoned a pure one boson-exchange mechanism (OBE). Using a
covariant theory, we have found a OBE potential that fits the 2006 world np
data below 350 MeV with a chi2/Ndata = 1.06 for 3788 data. Our potential has
fewer adjustable parameters than previous high-precision potentials, and also
reproduces the experimental triton binding energy without introducing
additional irreducible three-nucleon forces.
| nucl-th |
0704.1230 | Pseudodifferential operators and weighted normed symbol spaces | In this work we study some general classes of pseudodifferential operators
whose symbols are defined in terms of phase space estimates.
| math.OA math.AP |
0704.1231 | Entwining Structures in Monoidal Catrgories | Interpreting entwining structures as special instances of J. Beck's
distributive law, the concept of entwining module can be generalized for the
setting of arbitrary monoidal category. In this paper, we use the distributive
law formalism to extend in this setting basic properties of entwining modules.
| math.QA math.RA |
0704.1232 | CP Violation and Arrows of Time Evolution of a Neutral $K$ or $B$ Meson
from an Incoherent to a Coherent State | We study the evolution of a neutral $K$ meson prepared as an incoherent equal
mixture of $K^0$ and $\bar{K^0}$. Denoting the density matrix by $\rho(t) =
{1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] $, the norm of the state
$N(t)$ is found to decrease monotonically from one to zero, while the magnitude
of the Stokes vector $|\vec{\zeta}(t)|$ increases monotonically from zero to
one. This property qualifies these observables as arrows of time. Requiring
monotonic behaviour of $N(t)$ for arbitrary values of $\gamma_L, \gamma_S$ and
$\Delta m$ yields a bound on the CP-violating overlap $\delta =
\braket{K_L}{K_S}$, which is similar to, but weaker than, the known unitarity
bound. A similar requirement on $|\vec{\zeta}(t)|$ yields a new bound,
$\delta^2 < {1/2} (\frac{\Delta \gamma}{\Delta m}) \sinh (\frac{3\pi}{4}
\frac{\Delta \gamma}{\Delta m})$ which is particularly effective in limiting
the CP-violating overlap in the $B^0$-$\bar{B^0}$ system. We obtain the Stokes
parameter $\zeta_3(t)$ which shows how the average strangeness of the beam
evolves from zero to $\delta$. The evolution of the Stokes vector from
$|\vec{\zeta}| = 0$ to $|\vec{\zeta}| = 1$ has a resemblance to an order
parameter of a system undergoing spontaneous symmetry breaking.
| hep-ph |
0704.1233 | Residual entropy in a model for the unfolding of single polymer chains | We study the unfolding of a single polymer chain due to an external force. We
use a simplified model which allows to perform all calculations in closed form
without assuming a Boltzmann-Gibbs form for the equilibrium distribution.
Temperature is then defined by calculating the Legendre transform of the
entropy under certain constraints. The application of the model is limited to
flexible polymers. It exhibits a gradual transition from compact globule to
rod. The boundary line between these two phases shows reentrant behavior. This
behavior is explained by the presence of residual entropy.
| cond-mat.stat-mech |
0704.1234 | Generalization of Einstein-Lovelock theory to higher order dilaton
gravity | A higher order theory of dilaton gravity is constructed as a generalization
of the Einstein-Lovelock theory of pure gravity. Its Lagrangian contains terms
with higher powers of the Riemann tensor and of the first two derivatives of
the dilaton. Nevertheless, the resulting equations of motion are quasi-linear
in the second derivatives of the metric and of the dilaton. This property is
crucial for the existence of brane solutions in the thin wall limit. At each
order in derivatives the contribution to the Lagrangian is unique up to an
overall normalization. Relations between symmetries of this theory and the
O(d,d) symmetry of the string-inspired models are discussed.
| hep-th hep-ph |
0704.1235 | Fluctuations of the partial filling factors in competitive RSA from
binary mixtures | Competitive random sequential adsorption on a line from a binary mix of
incident particles is studied using both an analytic recursive approach and
Monte Carlo simulations. We find a strong correlation between the small and the
large particle distributions so that while both partial contributions to the
fill factor fluctuate widely, the variance of the total fill factor remains
relatively small. The variances of partial contributions themselves are quite
different between the smaller and the larger particles, with the larger
particle distribution being more correlated. The disparity in fluctuations of
partial fill factors increases with the particle size ratio. The additional
variance in the partial contribution of smaller particle originates from the
fluctuations in the size of gaps between larger particles. We discuss the
implications of our results to semiconductor high-energy gamma detectors where
the detector energy resolution is controlled by correlations in the cascade
energy branching process.
| cond-mat.dis-nn cond-mat.stat-mech |
0704.1236 | Sur les repr\'esentations du groupe fondamental d'une vari\'et\'e
priv\'ee d'un diviseur \`a croisements normaux simples | Given a projective variety X over an algebraically closed field of
characteristic zero, we show that finite parabolic bundles along a fixed simple
normal crossings divisor D are in one to one correspondence with
representations of the \'etale fundamental group of X-D.
| math.AG |
0704.1237 | Infrared High-Resolution Spectroscopy of Post-AGB Circumstellar Disks.
I. HR 4049 - The Winnowing Flow Observed? | High-resolution infrared spectroscopy in the 2.3-4.6 micron region is
reported for the peculiar A supergiant, single-lined spectroscopic binary HR
4049. Lines from the CO fundamental and first overtone, OH fundamental, and
several H2O vibration-rotation transitions have been observed in the
near-infrared spectrum. The spectrum of HR 4049 appears principally in emission
through the 3 and 4.6 micron region and in absorption in the 2 micron region.
The 4.6 micron spectrum shows a rich 'forest' of emission lines. All the
spectral lines observed in the 2.3-4.6 micron spectrum are shown to be
circumbinary in origin. The presence of OH and H2O lines confirm the
oxygen-rich nature of the circumbinary gas which is in contrast to the
previously detected carbon-rich material. The emission and absorption line
profiles show that the circumbinary gas is located in a thin, rotating layer
near the dust disk. The properties of the dust and gas circumbinary disk and
the spectroscopic orbit yield masses for the individual stars, M_AI~0.58 Msolar
and M_MV~0.34 Msolar. Gas in the disk also has an outward flow with a velocity
of $\gtrsim$ 1 km/s. The severe depletion of refractory elements but near-solar
abundances of volatile elements observed in HR 4049 results from abundance
winnowing. The separation of the volatiles from the grains in the disk and the
subsequent accretion by the star are discussed. Contrary to prior reports, the
HR 4049 carbon and oxygen isotopic abundances are typical AGB values:
12C/13C=6^{+9}_{-4} and 16O/17O>200.
| astro-ph |
0704.1238 | Tannakian Categories attached to abelian Varieties | Starting from certain perverse sheaves on an abelian variety, including the
intersection cohomology sheaves of curves and smooth ample divisors, we
construct a semisimple super-Tannakian category.
| math.AG |
0704.1239 | On the Entropy Function and the Attractor Mechanism for Spherically
Symmetric Extremal Black Holes | In this paper we elaborate on the relation between the entropy formula of
Wald and the "entropy function" method proposed by A. Sen. For spherically
symmetric extremal black holes, it is shown that the expression of extremal
black hole entropy given by A. Sen can be derived from the general entropy
definition of Wald, without help of the treatment of rescaling the AdS_2 part
of near horizon geometry of extremal black holes. In our procedure, we only
require that the surface gravity approaches to zero, and it is easy to
understand the Legendre transformation of f, the integration of Lagrangian
density on the horizon, with respect to the electric charges. Since the Noether
charge form can be defined in an "off-shell" form, we define a corresponding
entropy function, with which one can discuss the attractor mechanism for
extremal black holes with scalar fields.
| hep-th |
0704.1240 | Dynamical layer decoupling in a stripe-ordered, high T_c superconductor | In the stripe-ordered state of a strongly-correlated two-dimensional
electronic system, under a set of special circumstances, the superconducting
condensate, like the magnetic order, can occur at a non-zero wave-vector
corresponding to a spatial period double that of the charge order. In this
case, the Josephson coupling between near neighbor planes, especially in a
crystal with the special structure of La_{2-x}Ba_xCuO_4, vanishes identically.
We propose that this is the underlying cause of the dynamical decoupling of the
layers recently observed in transport measurements at x=1/8.
| cond-mat.str-el cond-mat.supr-con |
0704.1241 | Cooling and heating by adiabatic magnetization in the
Ni$_{50}$Mn$_{34}$In$_{16}$ magnetic shape memory alloy | We report on measurements of the adiabatic temperature change in the inverse
magnetocaloric Ni$_{50}$Mn$_{34}$In$_{16}$ alloy. It is shown that this alloy
heats up with the application of a magnetic field around the Curie point due to
the conventional magnetocaloric effect. In contrast, the inverse magnetocaloric
effect associated with the martensitic transition results in the unusual
decrease of temperature by adiabatic magnetization. We also provide
magnetization and specific heat data which enable to compare the measured
temperature changes to the values indirectly computed from thermodynamic
relationships. Good agreement is obtained for the conventional effect at the
second-order paramagnetic-ferromagnetic phase transition. However, at the first
order structural transition the measured values at high fields are lower than
the computed ones. Irreversible thermodynamics arguments are given to show that
such a discrepancy is due to the irreversibility of the first-order martensitic
transition.
| cond-mat.mtrl-sci |
0704.1242 | Giant Fluctuations of Coulomb Drag in a Bilayer System | We have observed reproducible fluctuations of the Coulomb drag, both as a
function of magnetic field and electron concentration, which are a
manifestation of quantum interference of electrons in the layers. At low
temperatures the fluctuations exceed the average drag, giving rise to random
changes of the sign of the drag. The fluctuations are found to be much larger
than previously expected, and we propose a model which explains their
enhancement by considering fluctuations of local electron properties.
| cond-mat.mes-hall cond-mat.dis-nn cond-mat.mtrl-sci |
0704.1243 | Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In | Applying a magnetic field to a ferromagnetic Ni$_{50}$Mn$_{34}$In$_{16}$
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.
| cond-mat.mtrl-sci |
0704.1244 | SN 2003du: 480 days in the Life of a Normal Type Ia Supernova | An extensive set of optical and NIR photometry and low-resolution spectra the
Type Ia supernova (SN Ia) 2003du was obtained using a number of facilities. The
observations started 13 days before B-band maximum light and continued for 480
days with exceptionally good time sampling. The optical photometry was
calibrated through the S-correction technique.
The UBVRIJHK light curves and the color indices of SN 2003du closely resemble
those of normal SNe Ia. SN 2003du reached a B-band maximum of 13.49 (+/-0.02)
mag on JD2452766.38 (+/-0.5). We derive a B-band stretch parameter of 0.988
(+/-0.003), which corresponds to dM15=1.02 (+/-0.05), indicative of a SN Ia of
standard luminosity. The reddening in the host galaxy was estimated by three
methods, and was consistently found to be negligible. We estimate a distance
modulus of 32.79 (+/-0.15) mag to the host galaxy, UGC 9391. The peak UVOIR
bolometric luminosity of 1.35(+/-0.20) 10^43 erg/s and Arnett's rule implies
that M(Ni56)=0.68 (+/-0.14)M_sun of Ni56 was synthesized during the explosion.
Modeling of the UVOIR bolometric light curve also indicates M(Ni56) in the
range 0.6-0.8 M_sun. The spectral evolution of SN 2003du at both optical and
NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si II
ratio at maximum R(Si II)=0.22 (+/-0.02) and the time evolution of the
blueshift velocities of the absorption line minima are typical. The pre-maximum
spectra of SN 2003du showed conspicuous high-velocity features in the Ca II H&K
doublet and infrared triplet, and possibly in Si II 6355, lines. We compare the
time evolution of the profiles of these lines with other well-observed SNe Ia
and we suggest that the peculiar pre-maximum evolution of Si II 6355 line in
many SNe Ia is due to the presence of two blended absorption components.
| astro-ph |
0704.1245 | Outflow and Infall in a Sample of Massive Star Forming Regions | We present single pointing observations of SiO, HCO$^+$ and H$^{13}$CO$^+$
from the James Clerk Maxwell Telescope towards 23 massive star forming regions
previously known to contain molecular outflows and ultracompact HII regions. We
detected SiO towards 14 sources and suggest that the non-detections in the
other nine sources could be due to those outflows being older and without
ongoing shocks to replenish the SiO. We serendipitously detected SO$_2$ towards
17 sources in the same tuning as HCO$^+$. We detected HCO$^+$ towards all
sources, and suggest that it is tracing infall in nine cases. For seven infall
candidates, we estimate mass infall rates between 1$\times10^{-2}$ and
2$\times10^{-5}$ M$_{\odot}$ yr$^{-1}$. Seven sources show both SiO detections
(young outflows) and HCO$^+$ infall signatures. We also find that the abundance
of H$^{13}$CO$^+$ tends to increase along with the abundance of SiO in sources
for which we could determine abundances. We discuss these results with respect
to current theories of massive star formation via accretion. From this survey,
we suggest that perhaps both models of ionized accretion and halted accretion
may be important in describing the evolution of a massive protostar (or
protostars) beyond the formation of an HII region.
| astro-ph |
0704.1246 | Invariants of Welded Virtual Knots Via Crossed Module Invariants of
Knotted Surfaces | We define an invariant of welded virtual knots from each finite crossed
module by considering crossed module invariants of ribbon knotted surfaces
which are naturally associated with them. We elucidate that the invariants
obtained are non trivial by calculating explicit examples. We define welded
virtual graphs and consider invariants of them defined in a similar way.
| math.GT hep-th math.QA |
0704.1247 | A Rational Approach to Resonance Saturation in large-Nc QCD | We point out that resonance saturation in QCD can be understood in the
large-Nc limit from the mathematical theory of Pade Approximants to meromorphic
functions. These approximants are rational functions which encompass any
saturation with a finite number of resonances as a particular example,
explaining several results which have appeared in the literature. We review the
main properties of Pade Approximants with the help of a toy model for the
<VV-AA> two-point correlator, paying particular attention to the relationship
among the Chiral Expansion, the Operator Product Expansion and the resonance
spectrum. In passing, we also comment on an old proposal made by Migdal in 1977
which has recently attracted much attention in the context of AdS/QCD models.
Finally, we apply the simplest Pade Approximant to the <VV-AA> correlator in
the real case of QCD. The general conclusion is that a rational approximant may
reliably describe a Green's function in the Euclidean, but the same is not true
in the Minkowski regime due to the appearance of unphysical poles and/or
residues.
| hep-ph hep-lat hep-th nucl-th |
0704.1248 | Unification and Fermion Mass Structure | Grand Unified Theories predict relationships between the GUT-scale quark and
lepton masses. Using new data in the context of the MSSM, we update the values
and uncertainties of the masses and mixing angles for the three generations at
the GUT scale. We also update fits to hierarchical patterns in the GUT-scale
Yukawa matrices. The new data shows not all the classic GUT-scale mass
relationships remain in quantitative agreement at small to moderate tan beta.
However, at large tan beta, these discrepancies can be eliminated by finite,
tan beta-enhanced, radiative, threshold corrections if the gluino mass has the
opposite sign to the wino mass.
| hep-ph |
0704.1249 | Cluster tilting for one-dimensional hypersurface singularities | In this article we study Cohen-Macaulay modules over one-dimensional
hypersurface singularities and the relationship with the representation theory
of associative algebras using methods of cluster tilting theory. We give a
criterion for existence of cluster tilting objects and their complete
description by homological methods, using higher almost split sequences and
results from birational geometry. We obtain a large class of 2-CY tilted
algebras which are finite dimensional symmetric and satisfy $\tau^2=\id$. In
particular, we compute 2-CY tilted algebras for simple and minimally elliptic
curve singularities.
| math.RT math.AG |
0704.1250 | Gemini Mid-IR Polarimetry of NGC1068: Polarized Structures Around the
Nucleus | We present diffraction limited, 10um imaging polarimetry data for the central
regions of the archetypal Seyfert AGN, NGC1068. The position angle of
polarization is consistent with three dominant polarizing mechanisms. We
identify three distinct regions of polarization: (a) north of the nucleus,
arising from aligned dust in the NLR, (b) south, east and west of the nucleus,
consistent with dust being channeled toward the central engine and (c) a
central minimum of polarization consistent with a compact (<22pc) torus. These
observations provide continuity between the geometrically and optically thick
torus and the host galaxy's nuclear environments. These images represent the
first published mid-IR polarimetry from an 8-m class telescope and illustrate
the potential of such observations.
| astro-ph |
0704.1251 | Coupling between magnetic ordering and structural instabilities in
perovskite biferroics: A first-principles study | We use first-principles density functional theory-based calculations to
investigate structural instabilities in the high symmetry cubic perovskite
structure of rare-earth (R $=$ La, Y, Lu) and Bi-based biferroic chromites,
focusing on $\Gamma$ and $R$ point phonons of states with para-, ferro-, and
antiferromagnetic ordering. We find that (a) the structure with G-type
antiferromagnetic ordering is most stable, (b) the most dominant structural
instabilities in these oxides are the ones associated with rotations of oxygen
octahedra, and (c) structural instabilities involving changes in Cr-O-Cr bond
angle depend sensitively on the changes in magnetic ordering. The dependence of
structural instabilities on magnetic ordering can be understood in terms of how
super-exchange interactions depend on the Cr-O-Cr bond angles and Cr-O bond
lengths. We demonstrate how adequate buckling of Cr-O-Cr chains can favour
ferromagnetism. Born effective charges (BEC) calculated using the Berry phase
expression are found to be anomalously large for the A-cations, indicating
their chemical relevance to ferroelectric distortions.
| cond-mat.mtrl-sci |
0704.1252 | LNRF-velocity hump-induced oscillations of a Keplerian disc orbiting
near-extreme Kerr black hole: A possible explanation of high-frequency QPOs
in GRS 1915+105 | At least four high-frequency quasiperiodic oscillations (QPOs) at frequencies
41Hz, 67Hz, 113Hz, and 167Hz were reported in a binary system GRS 1915+105
hosting near-extreme Kerr black hole with a dimensionless spin a>0.98. We use
the idea of oscillations induced by the hump of the orbital velocity profile
(related to locally non-rotating frames - LNRF) in discs orbiting near-extreme
Kerr black holes, which are characterized by a "humpy frequency" f_h, that
could excite the radial and vertical epicyclic oscillations with frequencies
f_r, f_v. Due to non-linear resonant phenomena the combinational frequencies
are allowed as well. Assuming mass M=14.8M_sun and spin a=0.9998 for the GRS
1915+105 Kerr black hole, the model predicts frequencies f_h=41Hz, f_r=67Hz,
(f_h+f_r)=108Hz, (f_v-f_r)=170Hz corresponding quite well to the observed ones.
For black-hole parameters being in good agreement with those given
observationally, the forced resonant phenomena in non-linear oscillations,
excited by the "hump-induced" oscillations in a Keplerian disc, can explain
high-frequency QPOs in GRS 1915+105 within the range of observational errors.
| astro-ph |
0704.1253 | Compton thick AGN in the Suzaku era | Suzaku observations of two hard X-ray (> 10 keV) selected nearby Seyfert 2
galaxies are presented. Both sources were clearly detected with the PIN Hard
X-ray Detector up to several tens of keV, allowing for a fairly good
characterization of the broad band X-ray continuum. Both sources are heavily
obscured, one of which (NGC 5728) being Compton thick, while at lower energies
the shape and intensity of the scattered/reflected continuum is very different.
Strong iron Kalpha lines are detected in both sources. There are also hints for
the presence of a broad relativistic iron line in NGC 4992.
| astro-ph |
0704.1254 | Spin-dependence of Ce $4f$ hybridization in magnetically ordered
systems: A spin-resolved photoemission study of Ce/Fe(110) | Spin- and angle-resolved resonant (Ce $4d\to4f$) photoemission spectra of a
monolayer Ce on Fe(110) reveal spin-dependent changes of the Fermi-level peak
intensities. That indicate a spin-dependence of $4f$ hybridization and, thus,
of $4f$ occupancy and local moment. The phenomenon is described in the
framework of the periodic Anderson model by $4f$ electron hopping into the
exchange split Fe 3d derived bands that form a spin-gap at the Fermi energy
around the $\bar{\Gamma}$ point of the surface Brillouin zone.
| cond-mat.str-el |
0704.1255 | Two-way coupling of FENE dumbbells with a turbulent shear flow | We present numerical studies for finitely extensible nonlinear elastic (FENE)
dumbbells which are dispersed in a turbulent plane shear flow at moderate
Reynolds number. The polymer ensemble is described on the mesoscopic level by a
set of stochastic ordinary differential equations with Brownian noise. The
dynamics of the Newtonian solvent is determined by the Navier-Stokes equations.
Momentum transfer of the dumbbells with the solvent is implemented by an
additional volume forcing term in the Navier-Stokes equations, such that both
components of the resulting viscoelastic fluid are connected by a two-way
coupling. The dynamics of the dumbbells is given then by Newton's second law of
motion including small inertia effects. We investigate the dynamics of the flow
for different degrees of dumbbell elasticity and inertia, as given by
Weissenberg and Stokes numbers, respectively. For the parameters accessible in
our study, the magnitude of the feedback of the polymers on the macroscopic
properties of turbulence remains small as quantified by the global energy
budget and the Reynolds stresses. A reduction of the turbulent drag by up to
20% is observed for the larger particle inertia. The angular statistics of the
dumbbells shows an increasing alignment with the mean flow direction for both,
increasing elasticity and inertia. This goes in line with a growing asymmetry
of the probability density function of the transverse derivative of the
streamwise turbulent velocity component. We find that dumbbells get stretched
referentially in regions where vortex stretching or bi-axial strain dominate
the local dynamics and topology of the velocity gradient tensor.
| physics.flu-dyn nlin.CD |
0704.1256 | A Novel String Derived Z' With Stable Proton, Light-Neutrinos and
R-parity violation | The Standard Model indicates the realization of grand unified structures in
nature, and can only be viewed as an effective theory below a higher energy
cutoff. While the renormalizable Standard Model forbids proton decay mediating
operators due to accidental global symmetries, many extensions of the Standard
Model introduce such dimension four, five and six operators. Furthermore,
quantum gravity effects are expected to induce proton instability, indicating
that the higher energy cutoff scale must be above 10^{16}GeV. Quasi-realistic
heterotic string models provide the arena to explore how perturbative quantum
gravity affects the particle physics phenomenology. An appealing explanation
for the proton longevity is provided by the existence of an Abelian gauge
symmetry that suppresses the proton decay mediating operators. Additionally,
such a low-scale U(1) symmetry should: allow the suppression of the left-handed
neutrino masses by a seesaw mechanism; allow fermion Yukawa couplings to the
electroweak Higgs doublets; be anomaly free; be family universal. These
requirements render the existence of such U(1) symmetries in quasi-realistic
heterotic string models highly non-trivial. We demonstrate the existence of a
U(1) symmetry that satisfies all of the above requirements in a class of
left-right symmetric heterotic string models in the free fermionic formulation.
The existence of the extra Z' in the energy range accessible to future
experiments is motivated by the requirement of adequate suppression of proton
decay mediation. We further show that while the extra U(1) forbids dimension
four baryon number violating operators it allows dimension four lepton number
violating operators and R-parity violation.
| hep-ph hep-th |
0704.1257 | Complexity of Janet basis of a D-module | We prove a double-exponential upper bound on the degree and on the complexity
of constructing a Janet basis of a $D$-module. This generalizes a well known
bound on the complexity of a Gr\"obner basis of a module over the algebra of
polynomials. We would like to emphasize that the obtained bound can not be
immediately deduced from the commutative case.
| math.AP math.RA |
0704.1258 | Evidence for a merger of binary white dwarfs: the case of GD 362 | GD 362 is a massive white dwarf with a spectrum suggesting a H-rich
atmosphere which also shows very high abundances of Ca, Mg, Fe and other
metals. However, for pure H-atmospheres the diffusion timescales are so short
that very extreme assumptions have to be made to account for the observed
abundances of metals. The most favored hypothesis is that the metals are
accreted from either a dusty disk or from an asteroid belt. Here we propose
that the envelope of GD 362 is dominated by He, which at these effective
temperatures is almost completely invisible in the spectrum. This assumption
strongly alleviates the problem, since the diffusion timescales are much larger
for He-dominated atmospheres. We also propose that the He-dominated atmosphere
of GD 362 is likely to be the result of the merger of a binary white dwarf.
| astro-ph |
0704.1259 | Intersection local time for two independent fractional Brownian motions | We prove the existence of the intersection local time for two independent, d
-dimensional fractional Brownian motions with the same Hurst parameter H.
Assume d greater or equal to 2, then the intersection local time exists if and
only if Hd<2.
| math.PR |
0704.1260 | Lapse of transmission phase and electron molecules in quantum dots | The puzzling behavior of the transition phase through a quantum dot can be
understood in a natural way via a formation of the electron molecule in the
quantum dot. In this case the resonance tunneling takes place through the
quasi-stationary (doorway) state, which emerges when the number of electrons
occupying the dot reaches a certain ``critical'' value, $N_{cr}$. Our
estimation of this quantity agrees with the experimental data. The dependence
of $N_{cr}$ on the dot's size is predicted as well.
| cond-mat.mes-hall quant-ph |
0704.1261 | Quantum-corrected black hole thermodynamics to all orders in the Planck
length | We investigate the effects to all orders in the Planck length from a
generalized un- certainty principle (GUP) on black holes thermodynamics. We
calculate the corrected Hawking temperature, entropy, and examine in details
the Hawking evaporation process. As a result, the evaporation process is
accelerated and the evaporation end-point is a zero entropy, zero heat capacity
and finite non zero temperature black hole remnant (BHR). In particular we
obtain a drastic reduction of the decay time, in comparison with the results
obtained in the Hawking semi classical picture and with the GUP to leading
order in the Planck length.
| gr-qc |
0704.1262 | Symmetry Breaking Study with Deformed Ensembles | A random matrix model to describe the coupling of m-fold symmetry in
constructed. The particular threefold case is used to analyze data on
eigenfrequencies of elastomechanical vibration of an anisotropic quartz block.
It is suggested that such experimental/theoretical study may supply powerful
means to discern intrinsic symmetries in physical systems.
| physics.data-an cond-mat.other nlin.CD nucl-th |
0704.1263 | The Measurement Calculus | Measurement-based quantum computation has emerged from the physics community
as a new approach to quantum computation where the notion of measurement is the
main driving force of computation. This is in contrast with the more
traditional circuit model which is based on unitary operations. Among
measurement-based quantum computation methods, the recently introduced one-way
quantum computer stands out as fundamental.
We develop a rigorous mathematical model underlying the one-way quantum
computer and present a concrete syntax and operational semantics for programs,
which we call patterns, and an algebra of these patterns derived from a
denotational semantics. More importantly, we present a calculus for reasoning
locally and compositionally about these patterns.
We present a rewrite theory and prove a general standardization theorem which
allows all patterns to be put in a semantically equivalent standard form.
Standardization has far-reaching consequences: a new physical architecture
based on performing all the entanglement in the beginning, parallelization by
exposing the dependency structure of measurements and expressiveness theorems.
Furthermore we formalize several other measurement-based models:
Teleportation, Phase and Pauli models and present compositional embeddings of
them into and from the one-way model. This allows us to transfer all the theory
we develop for the one-way model to these models. This shows that the framework
we have developed has a general impact on measurement-based computation and is
not just particular to the one-way quantum computer.
| quant-ph |
0704.1264 | Aharonov-Bohm oscillations in the presence of strong spin-orbit
interactions | We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring
structure defined by local anodic oxidation on a p-type GaAs heterostructure
with strong spin-orbit interactions. Clear beating patterns observed in the raw
data can be interpreted in terms of a spin geometric phase. Besides h/e
oscillations, we resolve the contributions from the second harmonic of AB
oscillations and also find a beating in these h/2e oscillations. A resistance
minimum at B=0T, present in all gate configurations, is the signature of
destructive interference of the spins propagating along time-reversed paths.
| cond-mat.mes-hall |
0704.1265 | Radio and X-ray nebulae associated with PSR J1509-5850 | We have discovered a long radio trail at 843 MHz which is apparently
associated with middle age pulsar PSR J1509-5850. The radio trail has a length
of ~7 arcmin. In X-rays, Chandra observations of PSR J1509-5850 reveal an
associated X-ray trail which extends in the same orientation as the radio
trail. Moreover, two clumpy structures are observed along the radio trail. The
larger one is proposed to be the supernova remnant (SNR) candidate MSC
319.9-0.7. Faint X-ray enhancement at the position of the SNR candidate is
found in the Chandra data.
| astro-ph |
0704.1266 | Branching fraction and charge asymmetry measurements in B to J/psi pi pi
decays | We study the decays B0 to J/psi pi+pi- and B+ to J/psi pi+pi0, including
intermediate resonances, using a sample of 382 million BBbar pairs recorded by
the BaBar detector at the PEP-II e+e- B factory. We measure the branching
fractions B(B0 ->J/psi rho0) = (2.7 +/- 0.3 +/- 0.17) x 10-5 and B(B+ ->J/psi
rho+) = (5.0 +/- 0.7 +/-0.31) x 10-5.
We also set the following upper limits at the 90% confidence level: B(B0 ->
J/psi pi+ \pi- non-resonant) < 1.2 x 10-5, B(B0 -> J/psi f_2(1270)) < 4.6 x
10-6, and B(B+ -> J/psi pi+ pi0 non-resonant) < 4.4 x 10-6. We measure the
charge asymmetry in charged B decays to J/psi rho to be -0.11 +/- 0.12 +/-
0.08.
| hep-ex |
0704.1267 | Text Line Segmentation of Historical Documents: a Survey | There is a huge amount of historical documents in libraries and in various
National Archives that have not been exploited electronically. Although
automatic reading of complete pages remains, in most cases, a long-term
objective, tasks such as word spotting, text/image alignment, authentication
and extraction of specific fields are in use today. For all these tasks, a
major step is document segmentation into text lines. Because of the low quality
and the complexity of these documents (background noise, artifacts due to
aging, interfering lines),automatic text line segmentation remains an open
research field. The objective of this paper is to present a survey of existing
methods, developed during the last decade, and dedicated to documents of
historical interest.
| cs.CV |
0704.1268 | On the interpretation of muon-spin-rotation experiments in the mixed
state of type-II superconductors | We argue that claims about magnetic field dependence of the magnetic field
penetration depth lambda, which were made on the basis of moun-spin-rotation
studies of some superconductors, originate from insufficient accuracy of
theoretical models employed for the data analysis. We also reanalyze some of
already published experimental data and demonstrate that numerical calculations
of Brandt [E.H. Brandt, Phys. Rev. B 68, 54506 (2003)] may serve as a reliable
and powerful tool for the analysis of the data collected in experiments with
conventional superconductors. Furthermore, one can use this approach in order
to distinguish between conventional and unconventional superconductors. It is
unfortunate that these calculations have practically never been employed for
such analyses.
| cond-mat.supr-con |
0704.1269 | Phase Transitions in the Coloring of Random Graphs | We consider the problem of coloring the vertices of a large sparse random
graph with a given number of colors so that no adjacent vertices have the same
color. Using the cavity method, we present a detailed and systematic analytical
study of the space of proper colorings (solutions).
We show that for a fixed number of colors and as the average vertex degree
(number of constraints) increases, the set of solutions undergoes several phase
transitions similar to those observed in the mean field theory of glasses.
First, at the clustering transition, the entropically dominant part of the
phase space decomposes into an exponential number of pure states so that beyond
this transition a uniform sampling of solutions becomes hard. Afterward, the
space of solutions condenses over a finite number of the largest states and
consequently the total entropy of solutions becomes smaller than the annealed
one. Another transition takes place when in all the entropically dominant
states a finite fraction of nodes freezes so that each of these nodes is
allowed a single color in all the solutions inside the state. Eventually, above
the coloring threshold, no more solutions are available. We compute all the
critical connectivities for Erdos-Renyi and regular random graphs and determine
their asymptotic values for large number of colors.
Finally, we discuss the algorithmic consequences of our findings. We argue
that the onset of computational hardness is not associated with the clustering
transition and we suggest instead that the freezing transition might be the
relevant phenomenon. We also discuss the performance of a simple local Walk-COL
algorithm and of the belief propagation algorithm in the light of our results.
| cond-mat.dis-nn cond-mat.stat-mech cs.CC |
0704.1270 | Core-Corona Separation in Ultra-Relativistic Heavy Ion Collisions | Simple geometrical considerations show that the collision zone in high energy
nuclear collisions may be divided into a central part (``core''), with high
energy densities, and a peripheral part (``corona''), with smaller energy
densities, more like in pp or pA collisions. We present calculations which
allow to separate these two contributions, and which show that the corona
contribution is quite small (but not negligible) for central collisions, but
gets increasingly important with decreasing centrality. We will discuss
consequences concerning results obtained in heavy ion collisions at the
Relativistic Heavy Ion Collider (RHIC) and the Super Proton Synchrotron (SPS).
| nucl-th astro-ph hep-ph nucl-ex |
0704.1271 | Numerical Evaluation of Six-Photon Amplitudes | We apply the recently proposed amplitude reduction at the integrand level
method, to the computation of the scattering process 2 photons -> 4 photons,
including the case of a massive fermion loop. We also present several
improvements of the method, including a general strategy to reconstruct the
rational part of any one-loop amplitude and the treatment of vanishing
Gram-determinants.
| hep-ph |
0704.1272 | Dynamics of shear homeomorphisms of tori and the Bestvina-Handel
algorithm | Sharkovskii proved that the existence of a periodic orbit in a
one-dimensional dynamical system implies existence of infinitely many periodic
orbits. We obtain an analog of Sharkovskii's theorem for periodic orbits of
shear homeomorphisms of the torus. This is done by obtaining a dynamical order
relation on the set of simple orbits and simple pairs. We then use this order
relation for a global analysis for a quantum chaotic physical system called the
kicked accelerated particle.
| math.GT math.DS |
0704.1273 | Coniveau over $p$-adic fields and points over finite fields | If the $\ell$-adic cohomology of a projective smooth variety, defined over a
$\frak{p}$-adic field $K$ with finite residue field $k$, is supported in
codimension $\ge 1$, then any model over the ring of integers of $K$ has a
$k$-rational point. This slightly improves our earlier result math/0405318: we
needed there the model to be regular (but then our result was more general: we
obtained a congruence for the number of points, and $K$ could be local of
characteristic $p>0$).
| math.NT math.AG |
0704.1274 | Parametric Learning and Monte Carlo Optimization | This paper uncovers and explores the close relationship between Monte Carlo
Optimization of a parametrized integral (MCO), Parametric machine-Learning
(PL), and `blackbox' or `oracle'-based optimization (BO). We make four
contributions. First, we prove that MCO is mathematically identical to a broad
class of PL problems. This identity potentially provides a new application
domain for all broadly applicable PL techniques: MCO. Second, we introduce
immediate sampling, a new version of the Probability Collectives (PC) algorithm
for blackbox optimization. Immediate sampling transforms the original BO
problem into an MCO problem. Accordingly, by combining these first two
contributions, we can apply all PL techniques to BO. In our third contribution
we validate this way of improving BO by demonstrating that cross-validation and
bagging improve immediate sampling. Finally, conventional MC and MCO procedures
ignore the relationship between the sample point locations and the associated
values of the integrand; only the values of the integrand at those locations
are considered. We demonstrate that one can exploit the sample location
information using PL techniques, for example by forming a fit of the sample
locations to the associated values of the integrand. This provides an
additional way to apply PL techniques to improve MCO.
| cs.LG |
0704.1275 | On the Structure and Properties of Differentially Rotating Main-Sequence
Stars in the 1-2 M_sun Range | We conduct a systematic examination of the properties of models for
chemically homogeneous, differentially rotating, main-sequence stars of mass
1-2 M_sun. The models were constructed using a code based on a reformulation of
the self-consistent field method of computing the equilibrium stellar structure
for a specified conservative internal rotation law. [abridged] Relative to
nonrotating stars of the same mass, these models all have reduced luminosities
and effective temperatures, and flattened photospheric shapes (i.e., decreased
polar radii) with equatorial radii that can be larger or smaller, depending on
the degree of differential rotation. For a fixed ratio of the axial rotation
rate to the surface equatorial rotation rate, increasingly rapid rotation
generally deepens convective envelopes, shrinks convective cores, and can lead
to the presence of a convective core (envelope) in a 1 M_sun (2 M_sun) model, a
feature that is absent in a nonrotating star of the same mass. The positions of
differentially rotating models for a given mass M in the H-R diagram can be
shifted in such a way as to approximate the nonrotating ZAMS over ranges in
luminosity and effective temperature that correspond to a mass interval between
M and about 0.7 M. We briefly note a few of the implications of these results,
including (i) possible ambiguities arising from similarities between the
properties of rotating and nonrotating models of different masses, (ii) a
reduced radiative luminosity for a young, rapidly rotating Sun, (iii) the
nuclear destruction of lithium and other light metallic species in the layers
beneath an outer convective envelope, and (iv), the excitation of solar-like
oscillations and the operation of a solar-like hydromagnetic dynamo in some
1.5-2 M_sun stars.
| astro-ph |
0704.1276 | SDSS J102146.44+234926.3: New WZ Sge-type dwarf nova | We report CCD photometry and spectroscopy during 2006 outburst of the dwarf
nova SDSS J102146.44+234926.3 (SDSS J1021). The photographic plates from the
MAO, SAI and CrAO plate archives, which cover the position of the SDSS J1021,
were inspected for the presence of previous outbursts. We also present the
BVRcIc photometric calibration of 52 stars in SDSS J1021 vicinity, which have
V-magnitude in the range of 11.21-17.23m and can serve as comparison stars. The
large amplitude of the SDSS J1021 outburst of 7m, superhumps with a period
below the ''period gap'', rebrightening during the declining stage of
superoutburst, rarity of outbursts and obtained spectrum allow to classify this
object as a WZ Sge type dwarf nova.
| astro-ph |
0704.1277 | Discrete phase space and minimum-uncertainty states | The quantum state of a system of qubits can be represented by a Wigner
function on a discrete phase space, each axis of the phase space taking values
in a finite field. Within this framework, we show that one can make sense of
the notion of a "rotationally invariant state" of any collection of qubits, and
that any such state is, in a well defined sense, a state of minimum
uncertainty.
| quant-ph |
0704.1278 | Turbulent Mixing in the Surface Layers of Accreting Neutron Stars | During accretion a neutron star (NS) is spun up as angular momentum is
transported through its surface layers. We study the resulting differentially
rotating profile, focusing on the impact this has for type I X-ray bursts. The
predominant viscosity is likely provided by the Tayler-Spruit dynamo. The
radial and azimuthal magnetic field components have strengths of ~10^5 G and
~10^10 G, respectively. This leads to nearly uniform rotation at the depths of
interest for X-ray bursts. A remaining small shear transmits the accreted
angular momentum inward to the NS interior. Though this shear gives little
viscous heating, it can trigger turbulent mixing. Detailed simulations will be
required to fully understand the consequences of mixing, but our models
illustrate some general features. Mixing has the greatest impact when the
buoyancy at the compositional discontinuity between accreted matter and ashes
is overcome. This occurs at high accretion rates, at low spin frequencies, or
may depend on the ashes from the previous burst. We then find two new regimes
of burning. The first is ignition in a layer containing a mixture of heavier
elements from the ashes. If ignition occurs at the base of the mixed layer,
recurrence times as short as ~5-30 minutes are possible. This may explain the
short recurrence time of some bursts, but incomplete burning is still needed to
explain these bursts' energetics. When mixing is sufficiently strong, a second
regime is found where accreted helium mixes deep enough to burn stably,
quenching X-ray bursts. We speculate that the observed change in X-ray burst
properties near one-tenth the Eddington accretion rate is from this mechanism.
The carbon-rich material produced by stable helium burning would be important
for triggering and fueling superbursts. (abridged)
| astro-ph |
0704.1279 | Wide-bandwidth, tunable, multiple-pulse-width optical delays using slow
light in cesium vapor | We demonstrate an all-optical delay line in hot cesium vapor that tunably
delays 275 ps input pulses up to 6.8 ns and 740 input ps pulses up to 59 ns
(group index of approximately 200) with little pulse distortion. The delay is
made tunable with a fast reconfiguration time (hundreds of ns) by optically
pumping out of the atomic ground states.
| physics.optics |
0704.1280 | Controllable Quantum Switchboard | All quantum information processes inevitably requires the explicit state
preparation of an entangled state. Here we present the construction of a
quantum switchboard which can act both as an optimal quantum cloning machine
and a quantum demultiplexer based on the preparation of a four-qubit state.
| quant-ph |
0704.1281 | The Galactic Center | In the past decade high resolution measurements in the infrared employing
adaptive optics imaging on 10m telescopes have allowed determining the three
dimensional orbits stars within ten light hours of the compact radio source at
the center of the Milky Way. These observations show the presence of a three
million solar mass black hole in Sagittarius A* beyond any reasonable doubt.
The Galactic Center thus constitutes the best astrophysical evidence for the
existence of black holes which have long been postulated, and is also an ideal
`lab' for studying the physics in the vicinity of such an object. Remarkably,
young massive stars are present there and probably have formed in the innermost
stellar cusp. Variable infrared and X-ray emission from Sagittarius A* are a
new probe of the physical processes and space-time curvature just outside the
event horizon.
| astro-ph |
0704.1282 | A geometric proof that $e$ is irrational and a new measure of its
irrationality | We give a simple geometric proof that $e$ is irrational, using a construction
of a nested sequence of closed intervals with intersection $e$. The proof leads
to a new measure of irrationality for $e$: if $p$ and $q$ are integers with $q
> 1$, then $|e - p/q| > 1/(S(q)+1)!$, where $S(q)$ is the smallest positive
integer such that $S(q)!$ is a multiple of $q$. We relate this measure for $e$
to a known one and to the greatest prime factor of an integer. We make two
conjectures and recall a theorem of Cantor that can be proved by a similar
construction.
| math.HO math.NT |
0704.1283 | Scanning tunnelling microscopy for ultracold atoms | We propose a novel experimental probe for cold atomic gases analogous to the
scanning tunnelling microscope (STM) in condensed matter. This probe uses the
coherent coupling of a single particle to the system. Depending on the
measurement sequence, our probe allows to either obtain the \emph{local}
density, with a resolution on the nanometer scale, or the single particle
correlation function in real time. We discuss applications of this scheme to
the various possible phases for a two dimensional Hubbard system of fermions in
an optical lattice.
| cond-mat.str-el |
0704.1284 | Center Manifold and Lie Symmetry Calculations on a Quasi-chemical Model
for Growth-death Kinetics in Food | Food scientists at the U.S. Army's Natick Solider Center have developed a
model for the lifecyle of the bacteria Staphylococcus aureus in intermediate
moisture bread. In this article, we study this model using dynamical systems
and Lie symmetry methods. We calculate center manifolds and Lie symmetries for
different cases of parameter values and compare our results to those of the
food scientists.
| math.DS |
0704.1285 | Absence of commensurate ordering at the polarization flop transition in
multiferroic DyMnO3 | Ferroelectric spiral magnets DyMnO3 and TbMnO3 show similar behavior of
electric polarization in applied magnetic fields. Studies of the field
dependence of lattice modulations on the contrary show a completely different
picture. Whereas in TbMnO3 the polarization flop from P||c to P||a is
accompanied by a sudden change from incommensurate to commensurate wave vector
modulation, in DyMnO3 the wave vector varies continuously through the flop
transition. This smooth behavior may be related to the giant magnetocapacitive
effect observed in DyMnO3.
| cond-mat.str-el |
0704.1286 | Study of a finite volume - finite element scheme for a nuclear transport
model | We consider a problem of nuclear waste contamination. It takes into account
the thermal effects. The temperature and the contaminant's concentration
fulfill convection-diffusion-reaction equations. The velocity and the pressure
in the flow satisfy the Darcy equation, with a viscosity depending on both
concentration and temperature. The equations are nonlinear and strongly
coupled. Using both finite volume and nonconforming finite element methods, we
introduce a scheme adapted to this problem. We prove the stability and
convergence of this scheme and give some error estimates.
| math.NA |
0704.1287 | Realizable Hamiltonians for Universal Adiabatic Quantum Computers | It has been established that local lattice spin Hamiltonians can be used for
universal adiabatic quantum computation. However, the 2-local model
Hamiltonians used in these proofs are general and hence do not limit the types
of interactions required between spins. To address this concern, the present
paper provides two simple model Hamiltonians that are of practical interest to
experimentalists working towards the realization of a universal adiabatic
quantum computer. The model Hamiltonians presented are the simplest known
QMA-complete 2-local Hamiltonians. The 2-local Ising model with 1-local
transverse field which has been realized using an array of technologies, is
perhaps the simplest quantum spin model but is unlikely to be universal for
adiabatic quantum computation. We demonstrate that this model can be rendered
universal and QMA-complete by adding a tunable 2-local transverse XX coupling.
We also show the universality and QMA-completeness of spin models with only
1-local Z and X fields and 2-local ZX interactions.
| quant-ph |
0704.1288 | Quantitative size-dependent structure and strain determination of CdSe
nanoparticles using atomic pair distribution function analysis | The size-dependent structure of CdSe nanoparticles, with diameters ranging
from 2 to 4 nm, has been studied using the atomic pair distribution function
(PDF) method. The core structure of the measured CdSe nanoparticles can be
described in terms of the wurtzite atomic structure with extensive stacking
faults. The density of faults in the nanoparticles ~50% . The diameter of the
core region was extracted directly from the PDF data and is in good agreement
with the diameter obtained from standard characterization methods suggesting
that there is little surface amorphous region. A compressive strain was
measured in the Cd-Se bond length that increases with decreasing particle size
being 0.5% with respect to bulk CdSe for the 2 nm diameter particles. This
study demonstrates the size-dependent quantitative structural information that
can be obtained even from very small nanoparticles using the PDF approach.
| cond-mat.soft cond-mat.mtrl-sci |
0704.1289 | Brane-world Quantum Gravity | The Arnowitt-Deser-Misner canonical formulation of general relativity is
extended to the covariant brane-world theory in arbitrary dimensions. The
exclusive probing of the extra dimensions makes a substantial difference,
allowing for the construction of a non-constrained canonical theory. The
quantum states of the brane-world geometry are defined by the
Tomonaga-Schwinger equation, whose integrability conditions are determined by
the classical perturbations of submanifolds contained in the Nash's
differentiable embedding theorem. In principle, quantum brane-world theory can
be tested by current experiments in astrophysics and by near future laboratory
experiments at Tev energy. The implications to the black-hole information loss
problem, to the accelerating cosmology, and to a quantum mathematical theory of
four-sub manifolds are briefly commented.
| gr-qc |
0704.1290 | Isospin diffusion in thermal AdS/CFT with flavor | We study the gauge/gravity dual of a finite temperature field theory at
finite isospin chemical potential by considering a probe of two coincident
D7-branes embedded in the AdS-Schwarzschild black hole background. The isospin
chemical potential is obtained by giving a vev to the time component of the
non-Abelian gauge field on the brane. The fluctuations of the non-Abelian gauge
field on the brane are dual to the SU(2) flavor current in the field theory.
For the embedding corresponding to vanishing quark mass, we calculate all Green
functions corresponding to the components of the flavor current correlator. We
discuss the physical properties of these Green functions, which go beyond
linear response theory. In particular, we show that the isospin chemical
potential leads to a frequency-dependent isospin diffusion coefficient.
| hep-th hep-ph nucl-th |
0704.1291 | Projective Hilbert space structures at exceptional points | A non-Hermitian complex symmetric 2x2 matrix toy model is used to study
projective Hilbert space structures in the vicinity of exceptional points
(EPs). The bi-orthogonal eigenvectors of a diagonalizable matrix are
Puiseux-expanded in terms of the root vectors at the EP. It is shown that the
apparent contradiction between the two incompatible normalization conditions
with finite and singular behavior in the EP-limit can be resolved by
projectively extending the original Hilbert space. The complementary
normalization conditions correspond then to two different affine charts of this
enlarged projective Hilbert space. Geometric phase and phase jump behavior are
analyzed and the usefulness of the phase rigidity as measure for the distance
to EP configurations is demonstrated. Finally, EP-related aspects of
PT-symmetrically extended Quantum Mechanics are discussed and a conjecture
concerning the quantum brachistochrone problem is formulated.
| math-ph cond-mat.other math.MP quant-ph |
0704.1292 | Excitation of the dissipationless Higgs mode in a fermionic condensate | The amplitude mode of a fermionic superfluid, analogous to the Higgs Boson,
becomes undamped in the strong coupling regime when its frequency is pushed
inside the BCS energy gap. We argue that this is the case in cold gases due to
the energy dispersion and nonlocality of the pairing interaction, and propose
to use the Feshbach resonance regime for parametric excitation of this mode.
The results presented for the BCS pairing dynamics indicate that even weak
dispersion suppresses dephasing and gives rise to persistent oscillations. The
frequency of oscillations extracted from our simulation of the BCS dynamics
agrees with the prediction of the many-body theory.
| cond-mat.supr-con cond-mat.mes-hall |
0704.1293 | Two characterizations of crooked functions | We give two characterizations of crooked functions: one based on the minimum
distance of a Preparata-like code, and the other based on the
distance-regularity of a crooked graph.
| math.CO |
0704.1294 | A Disciplined Approach to Adopting Agile Practices: The Agile Adoption
Framework | Many organizations aspire to adopt agile processes to take advantage of the
numerous benefits that it offers to an organization. Those benefits include,
but are not limited to, quicker return on investment, better software quality,
and higher customer satisfaction. To date however, there is no structured
process (at least in the public domain) that guides organizations in adopting
agile practices. To address this problem we present the Agile Adoption
Framework. The framework consists of two components: an agile measurement
index, and a 4-Stage process, that together guide and assist the agile adoption
efforts of organizations. More specifically, the agile measurement index is
used to identify the agile potential of projects and organizations. The 4-Stage
process, on the other hand, helps determine (a) whether or not organizations
are ready for agile adoption, and (b) guided by their potential, what set of
agile practices can and should be introduced.
| cs.SE |
0704.1295 | Electronic structure of the noncentrosymmetric superconductor
Mg10Ir19B16 | Electronic structure of a novel superconducting noncentrosymmetric compound
Mg10Ir19B16 was calculated using the Korringa-Kohn-Rostoker method. Electronic
part of the electron-phonon coupling constant, McMillan-Hopfield parameters,
were calculated using the rigid-muffin-tin approximation (RMTA). The magnitude
of the electron-phonon coupling constant, analysing atomic contributions, is
discussed. Our results show, that superconductivity in Mg10Ir19B16 is
presumably mediated by electron-phonon interaction.
| cond-mat.supr-con |
0704.1296 | Prospects of using simulations to study the photospheres of brown dwarfs | We discuss prospects of using multi-dimensional time-dependent simulations to
study the atmospheres of brown dwarfs and extrasolar giant planets, including
the processes of convection, radiation, dust formation, and rotation. We argue
that reasonably realistic simulations are feasible, however, separated into two
classes of local and global models. Numerical challenges are related to
potentially large dynamic ranges, and the treatment of scattering of radiation
in multi-D geometries.
| astro-ph |
0704.1297 | The exceptionally extended flaring activity in the X-ray afterglow of
GRB 050730 observed with Swift and XMM-Newton | We present the results of a detailed spectral and temporal analysis of Swift
and XMM-Newton observations of the high redshift (z=3.969) GRB 050730. The
X-ray afterglow of GRB 050730 was found to decline with time with superimposed
intense flaring activity that extended over more than two orders of magnitude
in time. Seven distinct re-brightening events starting from 236 s up to 41.2 ks
after the burst were observed. The underlying decay of the afterglow was well
described by a double broken power-law model with breaks at t_1= 237 +/- 20 s
and t_2 = 10.1 (-2.2) (+4.6) ks. The temporal decay slopes before, between and
after these breaks were alpha_1 = 2.1 +/- 0.3, alpha_2 = 0.44 (-0.08) (+0.14)
and alpha_3 = 2.40 (+0.07) (-0.09), respectively. The spectrum of the X-ray
afterglow was well described by a photoelectrically absorbed power-law with an
absorbing column density N_H=(1.28 +/- 0.26) 10^22 cm^-2 in the host galaxy.
Strong X-ray spectral evolution during the flaring activity was present. In the
majority of the flares (6/7) the ratio Delta_t/t_p between the duration of the
event and the time when the flare peaks was nearly constant and about 0.6-0.7.
We showed that the observed spectral and temporal properties of the first three
flares are consistent with being due both to high-latitude emission, as
expected if the flares were produced by late internal shocks, or to refreshed
shocks, i.e. late time energy injections into the main afterglow shock by slow
moving shells ejected from the central engine during the prompt phase. The
event fully satisfies the E_p-E_iso Amati relation while is not consistent with
the E_p-E_jet Ghirlanda relation.
| astro-ph |
0704.1298 | The obscured quasar population from optical, mid-infrared, and X-ray
surveys | Over the last few years, optical, mid-infrared and X-ray surveys have brought
to light a significant number of candidate obscured AGN and, among them, many
Type 2 quasars, the long-sought after "big cousins'' of local Seyfert 2
galaxies. However, despite the large amount of multi-wavelength data currently
available, a proper census and a panchromatic view of the obscured AGN/quasar
population are still missing, mainly due to observational limitations. Here we
provide a review of recent results on the identification of obscured AGN,
focusing primarily on the population of Type 2 quasars selected in the optical
band from the Sloan Digital Sky Survey.
| astro-ph |
0704.1299 | The Realm of the First Quasars in the Universe: the X-ray View | We review the X-ray studies of the highest redshift quasars, focusing on the
results obtained with Chandra and XMM-Newton. Overall, the X-ray and broad-band
properties of z>4 quasars and local quasars are similar, suggesting that the
small-scale X-ray emission regions of AGN are insensitive to the significant
changes occurring at z=0-6.
| astro-ph |
0704.1300 | The obscured X-ray source population in the HELLAS2XMM survey: the
Spitzer view | Recent X-ray surveys have provided a large number of high-luminosity,
obscured Active Galactic Nuclei (AGN), the so-called Type 2 quasars. Despite
the large amount of multi-wavelength supporting data, the main parameters
related to the black holes harbored in such AGN are still poorly known. Here we
present the results obtained for a sample of eight Type 2 quasars in the
redshift range 0.9-2.1 selected from the HELLAS2XMM survey, for which we used
Ks-band, Spitzer IRAC and MIPS data at 24 micron to estimate bolometric
corrections, black hole masses, and Eddington ratios.
| astro-ph |