493 research outputs found
Critical Behavior of O(n)-symmetric Systems With Reversible Mode-coupling Terms: Stability Against Detailed-balance Violation
We investigate nonequilibrium critical properties of -symmetric models
with reversible mode-coupling terms. Specifically, a variant of the model of
Sasv\'ari, Schwabl, and Sz\'epfalusy is studied, where violation of detailed
balance is incorporated by allowing the order parameter and the dynamically
coupled conserved quantities to be governed by heat baths of different
temperatures and , respectively. Dynamic perturbation theory and the
field-theoretic renormalization group are applied to one-loop order, and yield
two new fixed points in addition to the equilibrium ones. The first one
corresponds to and leads to model A critical
behavior for the order parameter and to anomalous noise correlations for the
generalized angular momenta; the second one is at and is
characterized by mean-field behavior of the conserved quantities, by a dynamic
exponent equal to that of the equilibrium SSS model, and by
modified static critical exponents. However, both these new fixed points are
unstable, and upon approaching the critical point detailed balance is restored,
and the equilibrium static and dynamic critical properties are recovered.Comment: 18 pages, RevTeX, 1 figure included as eps-file; submitted to Phys.
Rev.
Scaling of thermal conductivity of helium confined in pores
We have studied the thermal conductivity of confined superfluids on a
bar-like geometry. We use the planar magnet lattice model on a lattice with . We have applied open boundary conditions on the bar
sides (the confined directions of length ) and periodic along the long
direction. We have adopted a hybrid Monte Carlo algorithm to efficiently deal
with the critical slowing down and in order to solve the dynamical equations of
motion we use a discretization technique which introduces errors only
in the time step . Our results demonstrate the
validity of scaling using known values of the critical exponents and we
obtained the scaling function of the thermal resistivity. We find that our
results for the thermal resistivity scaling function are in very good agreement
with the available experimental results for pores using the tempComment: 5 two-column pages, 3 figures, Revtex
Critical Binder cumulant for isotropic Ising models on square and triangular lattices
Using Monte Carlo techniques, the critical Binder cumulant U* of isotropic
nearest-neighbour Ising models on square and triangular lattices is studied.
For rectangular shapes, employing periodic boundary conditions, U* is found to
show the same dependence on the aspect ratio for both lattice types. Similarly,
applying free boundary conditions for systems with square as well as circular
shapes for both lattices, the simulational findings are also consistent with
the suggestion that, for isotropic Ising models with short-range interactions,
U* depends on the shape and the boundary condition, but not on the lattice
structure.Comment: 7 pages, 4 figures, submitted to J. Stat. Mec
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Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life
The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats
Singularity in the boundary resistance between superfluid He and a solid surface
We report new measurements in four cells of the thermal boundary resistance
between copper and He below but near the superfluid-transition
temperature . For fits of to the data yielded ,
whereas a fit to theoretical values based on the renormalization-group theory
yielded . Alternatively, a good fit of the theory to the data could
be obtained if the {\it amplitude} of the prediction was reduced by a factor
close to two. The results raise the question whether the boundary conditions
used in the theory should be modified.Comment: 4 pages, 4 figures, revte
Recent Star Formation in Sextans A
We investigate the relationship between the spatial distributions of stellar
populations and of neutral and ionized gas in the Local Group dwarf irregular
galaxy Sextans A. This galaxy is currently experiencing a burst of localized
star formation, the trigger of which is unknown. We have resolved various
populations of stars via deep UBV(RI)_C imaging over an area with diameter \sim
5.'3. We have compared our photometry with theoretical isochrones appropriate
for Sextans A, in order to determine the ages of these populations. We have
mapped out the history of star formation, most accurately for times \lesssim
100 Myr. We find that star formation in Sextans A is correlated both in time
and space, especially for the most recent (\lesssim 12 Myr) times. The youngest
stars in the galaxy are forming primarily along the inner edge of the large H I
shell. Somewhat older populations, \lesssim 50 Myr, are found inward of the
youngest stars. Progressively older star formation, from \sim 50--100 Myr,
appears to have some spatially coherent structure and is more centrally
concentrated. The oldest stars we can accurately sample appear to have
approximately a uniform spatial distribution, which extends beyond a surface
brightness of \mu_B \simeq 25.9 mag arcsec^{-2} (or, a radius r \simeq 2.'3$).
Although other processes are also possible, our data provides support for a
mechanism of supernova-driven expansion of the neutral gas, resulting in cold
gas pileup and compression along the H I shell and sequential star formation in
recent times.Comment: 64 pages, 22 figures, to appear in A
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Spectroscopic results from the Life in the Atacama (LITA) project 2004 field season
Analysis of spectroscopy datasets from rover field tests in the Atacama Desert (Chile), focusing on the composition of the surface and identification of potential habitats for life
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