3,939 research outputs found
Existence of a critical point in the phase diagram of the ideal relativistic neutral Bose gas
We explore the phase transitions of the ideal relativistic neutral Bose gas
confined in a cubic box, without assuming the thermodynamic limit nor
continuous approximation. While the corresponding non-relativistic canonical
partition function is essentially a one-variable function depending on a
particular combination of temperature and volume, the relativistic canonical
partition function is genuinely a two-variable function of them. Based on an
exact expression of the canonical partition function, we performed numerical
computations for up to hundred thousand particles. We report that if the number
of particles is equal to or greater than a critical value, which amounts to
7616, the ideal relativistic neutral Bose gas features a spinodal curve with a
critical point. This enables us to depict the phase diagram of the ideal Bose
gas. The consequent phase transition is first-order below the critical pressure
or second-order at the critical pressure. The exponents corresponding to the
singularities are 1/2 and 2/3 respectively. We also verify the recently
observed `Widom line' in the supercritical region.Comment: 1+25 pages, 6 B/W figures: Comment on the Widom line added. Minor
improvement. Version to appear in `New Journal of Physics
Percolation properties of the 2D Heisenberg model
We analyze the percolation properties of certain clusters defined on
configurations of the 2--dimensional Heisenberg model. We find that, given any
direction \vec{n} in O(3) space, the spins almost perpendicular to \vec{n} form
a percolating cluster. This result gives indications of how the model can avoid
a previously conjectured Kosterlitz-Thouless phase transition at finite
temperature T.Comment: 4 pages, 3 eps figures. Revised version (more clear abstract, some
new references
Bacterial genome adaptation to niches: Divergence of the potential virulence genes in three Burkholderia species of different survival strategies
BACKGROUND: Two closely related species Burkholderia mallei (Bm) and Burkholderia pseudomallei (Bp) are serious human health hazards and are potential bio-warfare agents, whereas another closely related species Burkholderia thailandensis (Bt) is a non-pathogenic saprophyte. To investigate the genomic factors resulting in such a dramatic difference, we first identified the Bm genes responsive to the mouse environment, and then examined the divergence of these genes in Bp and Bt. RESULTS: The genes down-expressed, which largely encode cell growth-related proteins, are conserved well in all three species, whereas those up-expressed, which include potential virulence genes, are less well conserved or absent notably in Bt. However, a substantial number of up-expressed genes is still conserved in Bt. Bm and Bp further diverged from each other in a small number of genes resulting from unit number changes in simple sequence repeats (ssr) in the homologs. CONCLUSION: Our data suggest that divergent evolution of a small set of genes, rather than acquisition or loss of pathogenic islands, is associated with the development of different life styles in these bacteria of similar genomic contents. Further divergence between Bm and Bp mediated by ssr changes may reflect different adaptive processes of Bm and Bp fine-tuning into their host environments
Directed percolation with an absorbing boundary
We consider directed percolation with an absorbing boundary in 1+1 and 2+1
dimensions. The distribution of cluster lifetimes and sizes depend on the
boundary. The new scaling exponents can be related to the exponents
characterizing standard directed percolation in 1+1 dimension. In addition, we
investigate the backbone cluster and red bonds, and calculate the distribution
of living sites along the absorbing boundary.Comment: 10 latex pages, including 4 figure
Damage Spreading in the Ising Model
We present two new results regarding damage spreading in ferromagnetic Ising
models. First, we show that a damage spreading transition can occur in an Ising
chain that evolves in contact with a thermal reservoir. Damage heals at low
temperature and spreads for high T. The dynamic rules for the system's
evolution for which such a transition is observed are as legitimate as the
conventional rules (Glauber, Metropolis, heat bath). Our second result is that
such transitions are not always in the directed percolation universality class.Comment: 5 pages, RevTeX, revised and extended version, including 3 postscript
figure
Molecular dynamics simulations of oxide memristors: thermal effects
We have extended our recent molecular-dynamic simulations of memristors to
include the effect of thermal inhomogeneities on mobile ionic species appearing
during operation of the device. Simulations show a competition between an
attractive short-ranged interaction between oxygen vacancies and an enhanced
local temperature in creating/destroying the conducting oxygen channels. Such a
competition would strongly affect the performance of the memristive devices.Comment: submit/0169777; 6 pages, 4 figure
Towards Deconstruction of the Type D (2,0) Theory
We propose a four-dimensional supersymmetric theory that deconstructs, in a
particular limit, the six-dimensional theory of type . This 4d
theory is defined by a necklace quiver with alternating gauge nodes
and . We test this proposal by comparing the
6d half-BPS index to the Higgs branch Hilbert series of the 4d theory. In the
process, we overcome several technical difficulties, such as Hilbert series
calculations for non-complete intersections, and the choice of
versus gauge groups. Consistently, the result matches the Coulomb
branch formula for the mirror theory upon reduction to 3d
Elastic String in a Random Medium
We consider a one dimensional elastic string as a set of massless beads
interacting through springs characterized by anisotropic elastic constants. The
string, driven by an external force, moves in a medium with quenched disorder.
We present evidence that the consideration of longitudinal fluctuations leads
to nonlinear behavior in the equation of motion which is {\it kinematically}
generated by the motion of the string. The strength of the nonlinear effects
depends on the anisotropy of the medium and the distance from the depinning
transition. On the other hand the consideration of restricted solid on solid
conditions imposed to the growth of the string leads to a nonlinear term in the
equation of motion with a {\it diverging} coefficient at the depinning
transition.Comment: 9 pages, REVTEX, figures available upon request from
[email protected]
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