1,655 research outputs found
Effects of Galaxy Formation on Thermodynamics of the Intracluster Medium
We present detailed comparisons of the intracluster medium (ICM) in
cosmological Eulerian cluster simulations with deep Chandra observations of
nearby relaxed clusters. To assess the impact of galaxy formation, we compare
two sets of simulations, one performed in the non-radiative regime and another
with radiative cooling and several physical processes critical to various
aspects of galaxy formation: star formation, metal enrichment and stellar
feedback. We show that the observed ICM properties outside cluster cores are
well-reproduced in the simulations that include cooling and star formation,
while the non-radiative simulations predict an overall shape of the ICM
profiles inconsistent with observations. In particular, we find that the ICM
entropy in our runs with cooling is enhanced to the observed levels at radii as
large as half of the virial radius. We also find that outside cluster cores
entropy scaling with the mean ICM temperature in both simulations and Chandra
observations is consistent with being self-similar within current error bars.
We find that the pressure profiles of simulated clusters are also close to
self-similar and exhibit little cluster-to-cluster scatter. The X-ray
observable-total mass relations for our simulated sample agree with the Chandra
measurements to \~10%-20% in normalization. We show that this systematic
difference could be caused by the subsonic gas motions, unaccounted for in
X-ray hydrostatic mass estimates. The much improved agreement of simulations
and observations in the ICM profiles and scaling relations is encouraging and
the existence of tight relations of X-ray observables, such as Yx, and total
cluster mass and the simple redshift evolution of these relations hold promise
for the use of clusters as cosmological probes.Comment: 14 pages, 6 figures. Matches version accepted to Ap
Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma
Equations describing the linear evolution of a non-dissipative Langmuir wave
in inhomogeneous nonstationary anisotropic plasma without magnetic field are
derived in the geometrical optics approximation. A continuity equation is
obtained for the wave action density, and the conditions for the action
conservation are formulated. In homogeneous plasma, the wave field E
universally scales with the electron density N as E ~ N^{3/4}, whereas the
wavevector evolution varies depending on the wave geometry
Two-eigenfunction correlation in a multifractal metal and insulator
We consider the correlation of two single-particle probability densities
at coinciding points as a function of the
energy separation for disordered tight-binding lattice models
(the Anderson models) and certain random matrix ensembles. We focus on the
models in the parameter range where they are close but not exactly at the
Anderson localization transition. We show that even far away from the critical
point the eigenfunction correlation show the remnant of multifractality which
is characteristic of the critical states. By a combination of the numerical
results on the Anderson model and analytical and numerical results for the
relevant random matrix theories we were able to identify the Gaussian random
matrix ensembles that describe the multifractal features in the metal and
insulator phases. In particular those random matrix ensembles describe new
phenomena of eigenfunction correlation we discovered from simulations on the
Anderson model. These are the eigenfunction mutual avoiding at large energy
separations and the logarithmic enhancement of eigenfunction correlations at
small energy separations in the two-dimensional (2D) and the three-dimensional
(3D) Anderson insulator. For both phenomena a simple and general physical
picture is suggested.Comment: 16 pages, 18 figure
Classical Cepheids and the spiral structure of the Milky Way
We use the currently most complete collection of reliable Cepheid positions
(565 stars) out to ~5 kpc based mostly on our photometric data to outline the
spiral pattern of our Galaxy. We find the pitch-angle to be equal to 9--10
degrees with the most accurate estimate (i=9.5 +/-0.1 degrees) obtained
assuming that the spiral pattern has a four-armed structure, and the solar
phase angle in the spiral pattern to be chi_0 = 121+/-3 degrees. The pattern
speed is found to be Omega_P=25.2+/-0.5km/s/kpc based on a comparison of the
positions of the spiral arms delineated by Cepheids and maser sources and the
age difference between these objects.Comment: 21 pages, 11 figures. To appear in Astronomy Letter
Level statistics inside the core of a superconductive vortex
Microscopic theory of the type of Efetov's supermatrix sigma-model is
constructed for the low-lying electron states in a mixed superconductive-normal
system with disorder. The developed technique is used for the study of the
localized states in the core of a vortex in a moderately clean superconductor
(1/\Delta << \tau << 1/\omega_0 = E_F/\Delta^2). At sufficiently low energies E
<< \omega_{Th}, the energy level statistics is described by the
"zero-dimensional" limit of this supermatrix theory, with the effective
"Thouless energy" \omega_{Th} \sim (\omega_0/\tau)^{1/2}. Within this energy
range the result for the density of states is equivalent to that obtained
within Altland-Zirnbauer random matrix model of class C. Nonzero modes of the
sigma-model increase the mean interlevel distance \omega_0 by the relative
amount of the order of [2\ln(1/\omega_0\tau)]^{-1}.Comment: 5 pages, RevTeX. One error is corrected, also two references are
added. Submitted to JETP Letter
Anomalously Weak Dynamical Friction in Halos
A bar rotating in a pressure-supported halo generally loses angular momentum
and slows down due to dynamical friction. Valenzuela & Klypin report a
counter-example of a bar that rotates in a dense halo with little friction for
several Gyr, and argue that their result invalidates the claim by Debattista &
Sellwood that fast bars in real galaxies require a low halo density. We show
that it is possible for friction to cease for a while should the pattern speed
of the bar fluctuate upward. The reduced friction is due to an anomalous
gradient in the phase-space density of particles at the principal resonance
created by the earlier evolution. The result obtained by Valenzuela & Klypin is
probably an artifact of their adaptive mesh refinement method, but anyway could
not persist in a real galaxy. The conclusion by Debattista & Sellwood still
stands.Comment: To appear in "Island Universes - Structure and Evolution of Disk
Galaxies" ed. R. S. de Jong, 8 pages, 4 figures, .cls and .sty files include
Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers
In this work we analyse the role of a thin Cr spacer between Fe and Gd layers
on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12
superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are
investigated using X-ray diffraction, polarized neutron and resonance X-ray
magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and
ferromagnetic resonance techniques. Magnetic properties are studied
experimentally in a wide temperature range 4-300K and analysed theoretically
using numerical simulation on the basis of the mean-field model. We show that a
reasonable agreement with the experimental data can be obtained considering
temperature dependence of the effective field parameter in gadolinium layers.
The analysis of the experimental data shows that besides a strong reduction of
the antiferromagnetic coupling between Fe and Gd, the introduction of Cr
spacers into Fe/Gd superlattice leads to modification of both structural and
magnetic characteristics of the ferromagnetic layers
Energy absorption in time-dependent unitary random matrix ensembles: dynamic vs Anderson localization
We consider energy absorption in an externally driven complex system of
noninteracting fermions with the chaotic underlying dynamics described by the
unitary random matrices. In the absence of quantum interference the energy
absorption rate W(t) can be calculated with the help of the linear-response
Kubo formula. We calculate the leading two-loop interference correction to the
semiclassical absorption rate for an arbitrary time dependence of the external
perturbation. Based on the results for periodic perturbations, we make a
conjecture that the dynamics of the periodically-driven random matrices can be
mapped onto the one-dimensional Anderson model. We predict that in the regime
of strong dynamic localization W(t) ln(t)/t^2 rather than decays exponentially.Comment: 6 pages, 1 figur
Topological universality of level dynamics in quasi-one-dimensional disordered conductors
Nonperturbative, in inverse Thouless conductance 1/g, corrections to
distributions of level velocities and level curvatures in quasi-one-dimensional
disordered conductors with a topology of a ring subject to a constant vector
potential are studied within the framework of the instanton approximation of
nonlinear sigma-model. It is demonstrated that a global character of the
perturbation reveals the universal features of the level dynamics. The
universality shows up in the form of weak topological oscillations of the
magnitude ~ exp(-g) covering the main bodies of the densities of level
velocities and level curvatures. The period of discovered universal
oscillations does not depend on microscopic parameters of conductor, and is
only determined by the global symmetries of the Hamiltonian before and after
the perturbation was applied. We predict the period of topological oscillations
to be 4/(pi)^2 for the distribution function of level curvatures in orthogonal
symmetry class, and 3^(1/2)/(pi) for the distribution of level velocities in
unitary and symplectic symmetry classes.Comment: 15 pages (revtex), 3 figure
Horizon in Random Matrix Theory, Hawking Radiation and Flow of Cold Atoms
We propose a Gaussian scalar field theory in a curved 2D metric with an event
horizon as the low-energy effective theory for a weakly confined, invariant
Random Matrix ensemble (RME). The presence of an event horizon naturally
generates a bath of Hawking radiation, which introduces a finite temperature in
the model in a non-trivial way. A similar mapping with a gravitational analogue
model has been constructed for a Bose-Einstein condensate (BEC) pushed to flow
at a velocity higher than its speed of sound, with Hawking radiation as sound
waves propagating over the cold atoms. Our work suggests a three-fold
connection between a moving BEC system, black-hole physics and unconventional
RMEs with possible experimental applications.Comment: 4 pages, no figures. PRL accepted versio
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