2,970 research outputs found
Non equilibrium effects in fragmentation
We study, using molecular dynamics techniques, how boundary conditions affect
the process of fragmentation of finite, highly excited, Lennard-Jones systems.
We analyze the behavior of the caloric curves (CC), the associated thermal
response functions (TRF) and cluster mass distributions for constrained and
unconstrained hot drops. It is shown that the resulting CC's for the
constrained case differ from the one in the unconstrained case, mainly in the
presence of a ``vapor branch''. This branch is absent in the free expanding
case even at high energies . This effect is traced to the role played by the
collective expansion motion. On the other hand, we found that the recently
proposed characteristic features of a first order phase transition taking place
in a finite isolated system, i.e. abnormally large kinetic energy fluctuations
and a negative branch in the TRF, are present for the constrained (dilute) as
well the unconstrained case. The microscopic origin of this behavior is also
analyzed.Comment: 21 pages, 11 figure
The dispersive self-dual Einstein equations and the Toda lattice
The Boyer-Finley equation, or -Toda equation is both a reduction
of the self-dual Einstein equations and the dispersionlesslimit of the
-Toda lattice equation. This suggests that there should be a dispersive
version of the self-dual Einstein equation which both contains the Toda lattice
equation and whose dispersionless limit is the familiar self-dual Einstein
equation. Such a system is studied in this paper. The results are achieved by
using a deformation, based on an associative -product, of the algebra
used in the study of the undeformed, or dispersionless,
equations.Comment: 11 pages, LaTeX. To appear: J. Phys.
Interaction of vortices in thin superconducting films and Berezinskii-Kosterlitz-Thouless transition
The precondition for the BKT transition in thin superconducting films, the
logarithmic intervortex interaction, is satisfied at distances short relative
to , is the London penetration depth of the
bulk material and is the film thickness. For this reason, the search for
the transition has been conducted in samples of the size . It is
argued below that film edges turn the interaction into near exponential
(short-range) thus making the BKT transition impossible. If however the
substrate is superconducting and separated from the film by an insulated layer,
the logarithmic intervortex interaction is recovered and the BKT transition
should be observable.Comment: 4 pages, no figure
The Moyal bracket and the dispersionless limit of the KP hierarchy
A new Lax equation is introduced for the KP hierarchy which avoids the use of
pseudo-differential operators, as used in the Sato approach. This Lax equation
is closer to that used in the study of the dispersionless KP hierarchy, and is
obtained by replacing the Poisson bracket with the Moyal bracket. The
dispersionless limit, underwhich the Moyal bracket collapses to the Poisson
bracket, is particularly simple.Comment: 9 pages, LaTe
Inference of disease associations with unmeasured genetic variants by combining results from genome-wide association studies with linkage disequilibrium patterns in a reference data set
Results from whole-genome association studies of many common diseases are now available. Increasingly, these are being incorporated into meta-analyses to increase the power to detect weak associations with measured single-nucleotide polymorphisms (SNPs). Imputation of genotypes at unmeasured loci has been widely applied using patterns of linkage disequilibrium (LD) observed in the HapMap panels, but there is a need for alternative methods that can utilize the pooled effect estimates from meta-analyses and explore possible associations with SNPs and haplotypes that are not included in HapMap
Molecular dynamics simulations of oxide memory resistors (memristors)
Reversible bipolar nano-switches that can be set and read electronically in a
solid-state two-terminal device are very promising for applications. We have
performed molecular-dynamics simulations that mimic systems with oxygen
vacancies interacting via realistic potentials and driven by an external bias
voltage. The competing short- and long-range interactions among charged mobile
vacancies lead to density fluctuations and short-range ordering, while
illustrating some aspects of observed experimental behavior, such as memristor
polarity inversion.Comment: 15 pages, 5 figure
The algebraic and Hamiltonian structure of the dispersionless Benney and Toda hierarchies
The algebraic and Hamiltonian structures of the multicomponent dispersionless
Benney and Toda hierarchies are studied. This is achieved by using a modified
set of variables for which there is a symmetry between the basic fields. This
symmetry enables formulae normally given implicitly in terms of residues, such
as conserved charges and fluxes, to be calculated explicitly. As a corollary of
these results the equivalence of the Benney and Toda hierarchies is
established. It is further shown that such quantities may be expressed in terms
of generalized hypergeometric functions, the simplest example involving
Legendre polynomials. These results are then extended to systems derived from a
rational Lax function and a logarithmic function. Various reductions are also
studied.Comment: 29 pages, LaTe
Effective temperatures in a simple model of non-equilibrium, non-Markovian dynamics
The concept of effective temperatures in nonequilibrium systems is studied
within an exactly solvable model of non-Markovian diffusion. The system is
coupled to two heat baths which are kept at different temperatures: one
('fast') bath associated with an uncorrelated Gaussian noise and a second
('slow') bath with an exponential memory kernel. Various definitions of
effective temperatures proposed in the literature are evaluated and compared.
The range of validity of these definitions is discussed. It is shown in
particular, that the effective temperature defined from the
fluctuation-dissipation relation mirrors the temperature of the slow bath in
parameter regions corresponding to a separation of time scales. On the
contrary, quasi-static and thermodynamic definitions of an effective
temperature are found to display the temperature of the fast bath in most
parameter regions
Hydrodynamic reductions of the heavenly equation
We demonstrate that Pleba\'nski's first heavenly equation decouples in
infinitely many ways into a triple of commuting (1+1)-dimensional systems of
hydrodynamic type which satisfy the Egorov property. Solving these systems by
the generalized hodograph method, one can construct exact solutions of the
heavenly equation parametrized by arbitrary functions of a single variable. We
discuss explicit examples of hydrodynamic reductions associated with the
equations of one-dimensional nonlinear elasticity, linearly degenerate systems
and the equations of associativity.Comment: 14 page
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