411 research outputs found
Self-Diffusion in Random-Tiling Quasicrystals
The first explicit realization of the conjecture that phason dynamics leads
to self-diffusion in quasicrystals is presented for the icosahedral Ammann
tilings. On short time scales, the transport is found to be subdiffusive with
the exponent , while on long time scales it is consistent
with normal diffusion that is up to an order of magnitude larger than in the
typical room temperature vacancy-assisted self-diffusion. No simple finite-size
scaling is found, suggesting anomalous corrections to normal diffusion, or
existence of at least two independent length scales.Comment: 11 pages + 2 figures, COMPRESSED postscript figures available by
anonymous ftp to black_hole.physics.ubc.ca directory outgoing/diffuse (use bi
for binary mode to transfer), REVTeX 3.0, CTP-TAMU 21/9
Introduction to Arithmetic Mirror Symmetry
We describe how to find period integrals and Picard-Fuchs differential
equations for certain one-parameter families of Calabi-Yau manifolds. These
families can be seen as varieties over a finite field, in which case we show in
an explicit example that the number of points of a generic element can be given
in terms of p-adic period integrals. We also discuss several approaches to
finding zeta functions of mirror manifolds and their factorizations. These
notes are based on lectures given at the Fields Institute during the thematic
program on Calabi-Yau Varieties: Arithmetic, Geometry, and Physics
On the Two Species Asymmetric Exclusion Process with Semi-Permeable Boundaries
We investigate the structure of the nonequilibrium stationary state (NESS) of
a system of first and second class particles, as well as vacancies (holes), on
L sites of a one-dimensional lattice in contact with first class particle
reservoirs at the boundary sites; these particles can enter at site 1, when it
is vacant, with rate alpha, and exit from site L with rate beta. Second class
particles can neither enter nor leave the system, so the boundaries are
semi-permeable. The internal dynamics are described by the usual totally
asymmetric exclusion process (TASEP) with second class particles. An exact
solution of the NESS was found by Arita. Here we describe two consequences of
the fact that the flux of second class particles is zero. First, there exist
(pinned and unpinned) fat shocks which determine the general structure of the
phase diagram and of the local measures; the latter describe the microscopic
structure of the system at different macroscopic points (in the limit L going
to infinity in terms of superpositions of extremal measures of the infinite
system. Second, the distribution of second class particles is given by an
equilibrium ensemble in fixed volume, or equivalently but more simply by a
pressure ensemble, in which the pair potential between neighboring particles
grows logarithmically with distance. We also point out an unexpected feature in
the microscopic structure of the NESS for finite L: if there are n second class
particles in the system then the distribution of first class particles
(respectively holes) on the first (respectively last) n sites is exchangeable.Comment: 28 pages, 4 figures. Changed title and introduction for clarity,
added reference
Evolution of high-frequency gravitational waves in some cosmological models
We investigate Isaacson's high-frequency gravitational waves which propagate
in some relevant cosmological models, in particular the FRW spacetimes. Their
time evolution in Fourier space is explicitly obtained for various metric forms
of (anti--)de Sitter universe. Behaviour of high-frequency waves in the
anisotropic Kasner spacetime is also described.Comment: 14 pages, 8 figures, to appear in Czech. J. Phy
Remodeling the B-model
We propose a complete, new formalism to compute unambiguously B-model open
and closed amplitudes in local Calabi-Yau geometries, including the mirrors of
toric manifolds. The formalism is based on the recursive solution of matrix
models recently proposed by Eynard and Orantin. The resulting amplitudes are
non-perturbative in both the closed and the open moduli. The formalism can then
be used to study stringy phase transitions in the open/closed moduli space. At
large radius, this formalism may be seen as a mirror formalism to the
topological vertex, but it is also valid in other phases in the moduli space.
We develop the formalism in general and provide an extensive number of checks,
including a test at the orbifold point of A_p fibrations, where the amplitudes
compute the 't Hooft expansion of Wilson loops in lens spaces. We also use our
formalism to predict the disk amplitude for the orbifold C^3/Z_3.Comment: 83 pages, 9 figure
An exact solution of the moving boundary problem for the relativistic plasma expansion in a dipole magnetic field
An exact analytic solution is obtained for a uniformly expanding, neutral,
highly conducting plasma sphere in an ambient dipole magnetic field with an
arbitrary orientation of the dipole moment in the space. Based on this solution
the electrodynamical aspects related to the emission and transformation of
energy have been considered. In order to highlight the effect of the
orientation of the dipole moment in the space we compare our results obtained
for parallel orientation with those for transversal orientation. The results
obtained can be used to treat qualitatively experimental and simulation data,
and several phenomena of astrophysical and laboratory significance.Comment: 7 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:physics/060323
Mirror Manifolds in Higher Dimension
We describe mirror manifolds in dimensions different from the familiar case
of complex threefolds. We emphasize the simplifying features of dimension three
and supply more robust methods that do not rely on such special characteristics
and hence naturally generalize to other dimensions. The moduli spaces for
Calabi--Yau -folds are somewhat different from the ``special K\"ahler
manifolds'' which had occurred for , and we indicate the new geometrical
structures which arise. We formulate and apply procedures which allow for the
construction of mirror maps and the calculation of order-by-order instanton
corrections to Yukawa couplings. Mathematically, these corrections are expected
to correspond to calculating Chern classes of various parameter spaces (Hilbert
schemes) for rational curves on Calabi--Yau manifolds. Our results agree with
those obtained by more traditional mathematical methods in the limited number
of cases for which the latter analysis can be carried out. Finally, we make
explicit some striking relations between instanton corrections for various
Yukawa couplings, derived from the associativity of the operator product
algebra.Comment: 44 pages plus 3 tables using harvma
Motion of a driven tracer particle in a one-dimensional symmetric lattice gas
We study the dynamics of a tracer particle subject to a constant driving
force in a one-dimensional lattice gas of hard-core particles whose
transition rates are symmetric. We show that the mean displacement of the
driven tracer grows in time, , as , rather than the linear
time dependence found for driven diffusion in the bath of non-interacting
(ghost) particles. The prefactor is determined implicitly, as the
solution of a transcendental equation, for an arbitrary magnitude of the
driving force and an arbitrary concentration of the lattice gas particles. In
limiting cases the prefactor is obtained explicitly. Analytical predictions are
seen to be in a good agreement with the results of numerical simulations.Comment: 21 pages, LaTeX, 4 Postscript fugures, to be published in Phys. Rev.
E, (01Sep, 1996
King Pin? A Case Study of a Middle Market Drug Broker
The article is concerned with 'middle market' drug distribution, based on research that involved prison interviews with middle and upper level drug dealers and interviews with a range of enforcement personnel. It offers a preliminary discussion of different definitions of the 'middle market', where various forms of drug brokerage connect up different levels of drug markets. It goes on to provide a detailed case study of a single middle market drug distribution network, illustrating the complexity of such operations, the way in which drug brokers work as free trading entrepreneurs, and the often misunderstood role of violence in serious crime networks such as these
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