2,951,150 research outputs found
Comment on "Evidence for nontrivial ground-state structure of 3d +/- J spin glasses"
In a recent Letter [Europhys. Lett. 40, 429 (1997)], Hartmann presented
results for the structure of the degenerate ground states of the
three-dimensional +/- J spin glass model obtained using a genetic algorithm. In
this Comment, I argue that the method does not produce the correct
thermodynamic distribution of ground states and therefore gives erroneous
results for the overlap distribution. I present results of simulated annealing
calculations using different annealing rates for cubic lattices with
N=4*4*4spins. The disorder-averaged overlap distribution exhibits a significant
dependence on the annealing rate, even when the energy has converged. For fast
annealing, moments of the distribution are similar to those presented by
Hartmann. However, as the annealing rate is lowered, they approach the results
previously obtained using a multi-canonical Monte Carlo method. This shows
explicitly that care must be taken not only to reach states with the lowest
energy but also to ensure that they obey the correct thermodynamic
distribution, i.e., that the probability is the same for reaching any of the
ground states.Comment: 2 pages, Revtex, 1 PostScript figur
Gravitating Brane Systems: Some General Theorems
Multidimensional gravity interacting with intersecting electric and magnetic
-branes is considered for fields depending on a single variable. Some
general features of the system behaviour are revealed without solving the field
equations. Thus, essential asymptotic properties of isotropic cosmologies are
indicated for different signs of spatial curvature; a no-hair-type theorem and
a single-time theorem for black holes are proved (the latter makes sense in
models with multiple time coordinates). The validity of the general
observations is verified for a class of exact solutions known for the cases
when certain vectors, built from the input parameters of the model, are either
orthogonal in minisuperspace, or form mutually orthogonal subsystems. From the
non-existence of Lorentzian wormholes, a universal restriction is obtained,
applicable to orthogonal or block-orthogonal subsystems of any -brane
system.Comment: 13 pages, Latex2e, 1 Latex figure, uses bezier.st
2-Local derivations on algebras of locally measurable operators
The paper is devoted to 2-local derivations on the algebra of all
locally measurable operators affiliated with a type I von Neumann
algebra We prove that every 2-local derivation on is a derivation.Comment: arXiv admin note: substantial text overlap with arXiv:1110.155
Relativistic Kinetic Equations for Finite Domains and Freeze-out Problem
The relativistic kinetic equations for the two domains separated by the
hypersurface with both space- and time-like parts are derived. The particle
exchange between the domains separated by the time-like boundaries generates
source terms and modifies the collision term of the kinetic equation. The
correct hydrodynamic equations for the ``hydro+cascade'' models are obtained
and their differences from existing freeze-out models of the hadronic matter
are discussed
Role of Fe substitution on the anomalous magnetocaloric and magnetoresistance behavior in Tb(Ni1-xFex)2 compounds
We report the magnetic, magnetocaloric and magnetoresistance results obtained
in Tb(Ni1-xFex)2 compounds with x=0, 0.025 and 0.05. Fe substitution leads to
an increase in the ordering temperature from 36 K for x=0 to 124 K for x=0.05.
Contrary to a single sharp MCE peak seen in TbNi2, the MCE peaks of the Fe
substituted compounds are quite broad. We attribute the anomalous MCE behavior
to the randomization of the Tb moments brought about by the Fe substitution.
Magnetic and magnetoresistance results seem to corroborate this proposition.
The present study also shows that the anomalous magnetocaloric and
magnetoresistance behavior seen in the present compounds is similar to that of
Ho(Ni,Fe)2 compounds
Neutral and charged matter in equilibrium with black holes
We study the conditions of a possible static equilibrium between spherically
symmetric, electrically charged or neutral black holes and ambient matter. The
following kinds of matter are considered: (1) neutral and charged matter with a
linear equation of state p_r = w\rho (for neutral matter the results of our
previous work are reproduced), (2) neutral and charged matter with p_r \sim
\rho^m, m > 1, and (3) the possible presence of a "vacuum fluid" (the
cosmological constant or, more generally, anything that satisfies the equality
T^0_0 = T^1_1 at least at the horizon). We find a number of new cases of such
an equilibrium, including those generalizing the well-known Majumdar-Papapetrou
conditions for charged dust. It turns out, in particular, that ultraextremal
black holes cannot be in equilibrium with any matter in the absence of a vacuum
fluid; meanwhile, matter with w > 0, if it is properly charged, can surround an
extremal charged black hole.Comment: 12 pages, no figures, final version published in PR
Effect of plasma inhomogeneity on plasma wakefield acceleration driven by long bunches
Effects of plasma inhomogeneity on self-modulating proton bunches and
accelerated electrons were studied numerically. The main effect is the change
of the wakefield wavelength which results in phase shifts and loss of
accelerated particles. This effect imposes severe constraints on density
uniformity in plasma wakefield accelerators driven by long particle bunches.
The transverse two stream instability that transforms the long bunch into a
train of micro-bunches is less sensitive to density inhomogeneity than are the
accelerated particles. The bunch freely passes through increased density
regions and interacts with reduced density regions.Comment: 7 pages, 10 figure
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