115,825 research outputs found
Study of the Fully Frustrated Clock Model using the Wang-Landau Algorithm
Monte Carlo simulations using the newly proposed Wang-Landau algorithm
together with the broad histogram relation are performed to study the
antiferromagnetic six-state clock model on the triangular lattice, which is
fully frustrated. We confirm the existence of the magnetic ordering belonging
to the Kosterlitz-Thouless (KT) type phase transition followed by the chiral
ordering which occurs at slightly higher temperature. We also observe the lower
temperature phase transition of KT type due to the discrete symmetry of the
clock model. By using finite-size scaling analysis, the higher KT temperature
and the chiral critical temperature are respectively estimated as
and . The results are in favor of the double
transition scenario. The lower KT temperature is estimated as .
Two decay exponents of KT transitions corresponding to higher and lower
temperatures are respectively estimated as and
, which suggests that the exponents associated with the KT
transitions are universal even for the frustrated model.Comment: 7 pages including 9 eps figures, RevTeX, to appear in J. Phys.
A Multiwavelength Study on the Fate of Ionizing Radiation in Local Starbursts
The fate of ionizing radiation is vital for understanding cosmic ionization,
energy budgets in the interstellar and intergalactic medium, and star formation
rate indicators. The low observed escape fractions of ionizing radiation have
not been adequately explained, and there is evidence that some starbursts have
high escape fractions. We examine the spectral energy distributions of a sample
of local star-forming galaxies, containing thirteen local starburst galaxies
and ten of their ordinary star-forming counterparts, to determine if there
exist significant differences in the fate of ionizing radiation in these
galaxies. We find that the galaxy-to-galaxy variations in the SEDs is much
larger than any systematic differences between starbursts and non-starbursts.
For example, we find no significant differences in the total absorption of
ionizing radiation by dust, traced by the 24um, 70um, and 160um MIPS bands of
the Spitzer Space Telescope, although the dust in starburst galaxies appears to
be hotter than that of non-starburst galaxies. We also observe no excess
ultraviolet flux in the GALEX bands that could indicate a high escape fraction
of ionizing photons in starburst galaxies. The small H-alpha fractions of the
diffuse, warm ionized medium in starburst galaxies are apparently due to
temporarily boosted H-alpha luminosity within the star-forming regions
themselves, with an independent, constant WIM luminosity. This independence of
the WIM and starburst luminosities contrasts with WIM behavior in non-starburst
galaxies and underscores our poor understanding of radiation transfer in both
ordinary and starburst galaxies.Comment: 10 pages, 8 figures, accepted to ApJ 10/11/1
Radial distribution of RNA genome packaged inside spherical viruses
The problem of RNA genomes packaged inside spherical viruses is studied. The
viral capsid is modeled as a hollowed sphere. The attraction between RNA
molecules and the inner viral capsid is assumed to be non-specific and occurs
at the inner capsid surface only. For small capsid attraction, it is found that
monomer concentration of RNA molecules is maximum at the center of the capsid
to maximize their configurational entropy. For stronger capsid attraction, RNA
concentration peaks at some distance near the capsid. In the latter case, the
competition between the branching of RNA secondary struture and its adsorption
to the inner capsid results in the formation of a dense layer of RNA near
capsid surface. The layer thickness is a slowly varying (logarithmic) function
of the capsid inner radius. Consequently, for immediate strength of RNA-capsid
interaction, the amount of RNA packaged inside a virus is proportional to the
capsid {\em area} (or the number of proteins) instead of its volume. The
numerical profiles describe reasonably well the experimentally observed RNA
nucleotide concentration profiles of various viruses.Comment: 5 pages, 2 figures. Abstract, introduction rewritten. Comparison to
actual virus profiles added. Submitted to PR
F-wave versus P-wave Superconductivity in Organic Conductors
Current experimental results suggest that some organic quasi-one-dimensional
superconductors exhibit triplet pairing symmetry. Thus, we discuss several
potential triplet order parameters for the superconducting state of these
systems within the functional integral formulation. We compare weak spin-orbit
coupling , , and symmetries via several thermodynamic
quantities. For each symmetry, we analyse the temperature dependences of the
order parameter, condensation energy, specific heat, and superfluid density
tensor.Comment: 5 pages, 4 figure
Crystal vs glass formation in lattice models with many coexisting ordered phases
We present here new evidence that after a quench the planar Potts model on
the square lattice relaxes towards a glassy state if the number of states q is
larger than four. By extrapolating the finite size data we compute the average
energy of these states for the infinite system with periodic boundary
conditions, and find that it is comparable with that previously found using
fixed boundary conditions. We also report preliminary results on the behaviour
of these states in the presence of thermal fluctuationsComment: 7 pages with 5 figure
Phase transition in a super superspin glass
We here confirm the occurrence of spin glass phase transition and extract
estimates of associated critical exponents of a highly monodisperse and densely
compacted system of bare maghemite nanoparticles. This system has earlier been
found to behave like an archetypal spin glass, with e.g. a sharp transition
from paramagnetic to non-equilibrium behavior, suggesting that this system
undergoes a spin-glass phase transition at a relatively high temperature,
140 K.Comment: 4 pages, 3 figure
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