70,423 research outputs found
Particle simulation of lower hybrid waves in tokamak plasmas
Global particle simulations of the lower hybrid waves have been carried out
using fully kinetic ions and drift kinetic electrons with a realistic
electron-to-ion mass ratio. The lower hybrid wave frequency, mode structure,
and electron Landau damping from the electrostatic simulations agree very well
with the analytic theory. Linear simulation of the propagation of a lower
hybrid wave-packet in the toroidal geometry shows that the wave propagates
faster in the high field side than the low field side, in agreement with a ray
tracing calculation. Electromagnetic benchmarks of lower hybrid wave dispersion
relation are also carried out. Electromagnetic mode conversion are observed in
toroidal geometry, slow waves are launched at the plasma boundary and converts
to fast waves at the mode conversion layer, which is consistent with linear
theory.Comment: 8 pages, 11 figure
Using particle shape to induce tilted and bistable liquid crystal anchoring
We use Monte Carlo simulations of hard Gaussian overlap (HGO) particles symmetrically confined in slab geometry to investigate the role of particle-substrate interactions on liquid crystalline
anchoring. Despite the restriction here to purely steric interactions and smooth substrates, a range of behaviours are captured, including tilted anchoring and homeotropic-planar bistability. These macroscopic behaviours are all achieved through appropriate tuning of the microscopics of the HGO-substrate interaction, based upon non-additive descriptions for the HGO-substrate shape parameter.</p
Strangeness production in heavy ion collisions at SPS and RHIC within two-source statistical model
The experimental data on hadron yields and ratios in central Pb+Pb and Au+Au
collisions at SPS and RHIC energies, respectively, are analysed within a
two-source statistical model of an ideal hadron gas. These two sources
represent the expanding system of colliding heavy ions, where the hot central
fireball is embedded in a larger but cooler fireball. The volume of the central
source increases with rising bombarding energy. Results of the two-source model
fit to RHIC experimental data at midrapidity coincide with the results of the
one-source thermal model fit, indicating the formation of an extended fireball,
which is three times larger than the corresponding core at SPS.Comment: Talk at "Strange Quarks in Matter" Conference (Strangeness'2001),
September 2001, Frankfurt a.M., German
Drell-Yan Lepton Angular Distribution at Small Transverse Momentum
We investigate the dependence of the Drell-Yan cross section on lepton polar
and azimuthal angles, as generated by the lowest-order QCD annihilation and
Compton processes. We focus in particular on the azimuthal-angular
distributions, which are of the form cos(phi) and cos(2phi). At small
transverse momentum q_T of the lepton pair, q_T << Q, with Q the pair mass,
these terms are known to be suppressed relative to the phi-independent part of
the Drell-Yan cross section by one or two powers of the transverse momentum.
Nonetheless, as we show, like the phi-independent part they are subject to
large logarithmic corrections, whose precise form however depends on the
reference frame chosen. These logarithmic contributions ultimately require
resummation to all orders in the strong coupling. We discuss the potential
effects of resummation on the various angular terms in the cross section and on
the Lam-Tung relation.Comment: 13 pages, 2 figures; reference added, minor other changes, matches
version to be published in PR
CTMC calculations of electron capture and ionization in collisions of multiply charged ions with elliptical Rydberg atoms
We have performed classical trajectory Monte Carlo (CTMC) studies of electron
capture and ionization in multiply charged (Q=8) ion-Rydberg atom collisions at
intermediate impact velocities. Impact parallel to the minor and to the major
axis, respectively, of the initial Kepler electron ellipse has been
investigated. The important role of the initial electron momentum distribution
found for singly charged ion impact is strongly disminished for higher
projectile charge, while the initial spatial distribution remains important for
all values of Q studied.Comment: 3 pages, 5 figure
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
Exporting behavior of foreign affiliates: Theory and evidence
Firms have increasingly conducted different stages of production in different countries. In particular, they may set up operations in low-cost countries (those operations are referred to as foreign affiliates in those countries) either as platforms for export or serving the growing markets there. What is the exporting behavior of foreign affiliates? In this paper, using data from China, we find that among foreign affiliates exporters are less productive than non-exporters. We then offer a theoretical explanation by incorporating into the standard firm heterogeneity model the possibility that firms could have different stages of production in different countries. © 2010 Elsevier B.V.postprin
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