11,404 research outputs found
Vortex-line solitons in a periodically modulated Bose gas
We study the nonlinear excitations of a vortex-line in a Bose-Einstein
condensate trapped in a one-dimensional optical lattice. We find that the
classical Euler dynamics of the vortex results in a description of the vortex
line in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which
allows for both bright and gray soliton solutions. We discuss these solutions
in detail and predict that it is possible to create vortex-line solitons with
current experimental capabilities.Comment: minor changes, updated/corrected references, 4 pages, 3 figure
Stationary quantum Markov process for the Wigner function
As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde
A Monte Carlo Approach to Measure the Robustness of Boolean Networks
Emergence of robustness in biological networks is a paramount feature of
evolving organisms, but a study of this property in vivo, for any level of
representation such as Genetic, Metabolic, or Neuronal Networks, is a very hard
challenge. In the case of Genetic Networks, mathematical models have been used
in this context to provide insights on their robustness, but even in relatively
simple formulations, such as Boolean Networks (BN), it might not be feasible to
compute some measures for large system sizes. We describe in this work a Monte
Carlo approach to calculate the size of the largest basin of attraction of a
BN, which is intrinsically associated with its robustness, that can be used
regardless the network size. We show the stability of our method through
finite-size analysis and validate it with a full search on small networks.Comment: on 1st International Workshop on Robustness and Stability of
Biological Systems and Computational Solutions (WRSBS
Single Crystal Growth and Characterization of the Iron-Based Superconductor KFe2As2 Synthesized by KAs Flux Method
Centimeter sized platelet single crystals of KFe2As2 were grown using a
self-flux method. An encapsulation technique using commercial stainless steel
container allowed the stable crystal growth lasting for more than 2 weeks.
Ternary K-Fe-As systems with various starting compositions were examined to
determine the optimal growth conditions. Employment of KAs flux led to the
growth of large single crystals with the typical size of as large as 15 mm x 10
mm x 0.4 mm. The grown crystals exhibit sharp superconducting transition at 3.4
K with the transition width 0.2 K, as well as the very large residual
resistivity ratio exceeding 450, evidencing the good sample quality.Comment: 4 pages, 6 Postscript figure
Radial Correlations between two quarks
In nuclear many-body problems the short-range correlation between two
nucleons is well described by the corresponding correlation in the {two}-body
problem. Therefore, as a first step in any attempt at an analogous description
of many-quark systems, it is necessary to know the two-quark correlation. With
this in mind, we study the light quark distribution in a heavy-light meson with
a static heavy quark. The charge and matter radial distributions of these
heavy-light mesons are measured on a lattice with a light quark mass about that
of the strange quark. Both distributions can be well fitted upto r approx 0.7
fm with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the
charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m \approx
0.24(2) fm. We also discuss the normalisation of the total charge (defined to
be unity in the continuum limit) and matter integrated over all space, finding
1.30(5) and 0.4(1) respectively for a lattice spacing approx 0.17 fm.Comment: 8 pages, 3 ps figure
Noncommutative Vortex Solitons
We consider the noncommutative Abelian-Higgs theory and investigate general
static vortex configurations including recently found exact multi-vortex
solutions. In particular, we prove that the self-dual BPS solutions cease to
exist once the noncommutativity scale exceeds a critical value. We then study
the fluctuation spectra about the static configuration and show that the exact
non BPS solutions are unstable below the critical value. We have identified the
tachyonic degrees as well as massless moduli degrees. We then discuss the
physical meaning of the moduli degrees and construct exact time-dependent
vortex configurations where each vortex moves independently. We finally give
the moduli description of the vortices and show that the matrix nature of
moduli coordinates naturally emerges.Comment: 22 pages, 1 figure, typos corrected, a comment on the soliton size is
adde
The Environment of ``E+A'' Galaxies
The violent star formation history of ``E+A'' galaxies and their detection
almost exclusively in distant clusters is frequently used to link them to the
``Butcher-Oemler effect'' and to argue that cluster environment influences
galaxy evolution. From 11113 spectra in the Las Campanas Redshift Survey, we
have obtained a unique sample of 21 nearby ``E+A" galaxies. Surprisingly, a
large fraction (about 75%) of these ``E+A''s lie in the field. Therefore,
interactions with the cluster environment, in the form of the ICM or cluster
potential, are not essential for ``E+A'' formation. If one mechanism is
responsible for ``E+A''s, their existence in the field and the tidal features
in at least 5 of the 21 argue that galaxy-galaxy interactions and mergers are
that mechanism. The most likely environments for such interactions are poor
groups, which have lower velocity dispersions than clusters and higher galaxy
densities than the field. In hierarchical models, groups fall into clusters in
greater numbers at intermediate redshifts than they do today. Thus, the
Butcher-Oemler effect may reflect the typical evolution of galaxies in groups
and in the field rather than the influence of clusters on star formation in
galaxies. This abstract is abridged.Comment: 39 uuencoded, compressed pages (except Fig 1), complete preprint at
ftp://ociw.edu/pub/aiz/eplusa.ps, ApJ, submitte
- …