2,608 research outputs found
Microcanonical Lattice Gas Model for Nuclear Disassembly
Microcanonical calculations are no more difficult to implement than canonical
calculations in the Lattice Gas Model. We report calculations for a few
observables where we compare microcanonical model results with canonical model
results.Comment: 7 pages, Revtex, 3 postscript figure
Velocity distributions in dissipative granular gases
Motivated by recent experiments reporting non-Gaussian velocity distributions
in driven dilute granular materials, we study by numerical simulation the
properties of 2D inelastic gases. We find theoretically that the form of the
observed velocity distribution is governed primarily by the coefficient of
restitution and , the ratio between the average number of
heatings and the average number of collisions in the gas. The differences in
distributions we find between uniform and boundary heating can then be
understood as different limits of , for and
respectively.Comment: 5 figure
Extraction of shear viscosity in stationary states of relativistic particle systems
Starting from a classical picture of shear viscosity we construct a
stationary velocity gradient in a microscopic parton cascade. Employing the
Navier-Stokes ansatz we extract the shear viscosity coefficient . For
elastic isotropic scatterings we find an excellent agreement with the analytic
values. This confirms the applicability of this method. Furthermore for both
elastic and inelastic scatterings with pQCD based cross sections we extract the
shear viscosity coefficient for a pure gluonic system and find a good
agreement with already published calculations.Comment: 17 pages, 7 figure
Number-conserving master equation theory for a dilute Bose-Einstein condensate
We describe the transition of weakly interacting atoms into a
Bose-Einstein condensate within a number-conserving quantum master equation
theory. Based on the separation of time scales for condensate formation and
non-condensate thermalization, we derive a master equation for the condensate
subsystem in the presence of the non-condensate environment under the inclusion
of all two body interaction processes. We numerically monitor the condensate
particle number distribution during condensate formation, and derive a
condition under which the unique equilibrium steady state of a dilute, weakly
interacting Bose-Einstein condensate is given by a Gibbs-Boltzmann thermal
state of non-interacting atoms
Feasibility of intraventricular administration of etoposide in patients with metastatic brain tumours
As the systemic administration of etoposide is effective in the treatment of relapsed and metastatic brain tumours, a pilot trial was designed to study the feasibility of intraventricular administration of etoposide in such patients. 14 patients aged 2.1 to 33.2 years were treated with intraventricular etoposide simultaneously with either oral or intravenous chemotherapy with trofosfamide or carboplatin and etoposide. In 59 courses (1–12/patient) 0.5 mg etoposide was administered daily via an indwelling subcutaneous reservoir for 5 consecutive days every 2–5 weeks over a period of 0–11 months. During 15 courses in 5 patients serial CSF samples were obtained and etoposide levels were determined by reversed-phase HPLC. Side effects included transient headache and bacterial meningitis, each during 2 courses. Pharmacokinetic data analysis in the CSF (11 courses, 4 patients) revealed a terminal half-life of 7.4±1.2 hours and an AUC of 25.0 ± 9.5 μg h ml–1(mean ± standard deviation). The volume of distribution at steady state and total clearance exhibited a large interindividual variability with mean values of 0.16 l and 0.46 ml min–1respectively. Intraventricularly administered etoposide is well tolerated. CSF peak levels exceed more than 100-fold those achieved with intravenous infusions. Further studies should be focused on optimizing the dose and schedule and on determining the effectiveness of intraventricularly administered etoposide. © 2001 Cancer Research Campaign http://www.bjcancer.co
Caloric Curves for small systems in the Nuclear Lattice Gas Model
For pedagogical reasons we compute the caloric curve for 11 particles in a
lattice. Monte-Carlo simulation can be avoided and exact results are
obtained. There is no back-bending in the caloric curve and negative specific
heat does not appear. We point out that the introduction of kinetic energy in
the nuclear Lattice Gas Model modifies the results of the standard Lattice Gas
Model in a profound way.Comment: 12 pages, Revtex, including 4 postscript figure
Quantum Interactive Proofs with Competing Provers
This paper studies quantum refereed games, which are quantum interactive
proof systems with two competing provers: one that tries to convince the
verifier to accept and the other that tries to convince the verifier to reject.
We prove that every language having an ordinary quantum interactive proof
system also has a quantum refereed game in which the verifier exchanges just
one round of messages with each prover. A key part of our proof is the fact
that there exists a single quantum measurement that reliably distinguishes
between mixed states chosen arbitrarily from disjoint convex sets having large
minimal trace distance from one another. We also show how to reduce the
probability of error for some classes of quantum refereed games.Comment: 13 pages, to appear in STACS 200
Dynamic roughening and fluctuations of dipolar chains
Nonmagnetic particles in a carrier ferrofluid acquire an effective dipolar
moment when placed in an external magnetic field. This fact leads them to form
chains that will roughen due to Brownian motion when the magnetic field is
decreased. We study this process through experiments, theory and simulations,
three methods that agree on the scaling behavior over 5 orders of magnitude.
The RMS width goes initially as , then as before it
saturates. We show how these results complement existing results on polymer
chains, and how the chain dynamics may be described by a recent non-Markovian
formulation of anomalous diffusion.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Thermodynamic entropy of a many body energy eigenstate
It is argued that a typical many body energy eigenstate has a well defined
thermodynamic entropy and that individual eigenstates possess thermodynamic
characteristics analogous to those of generic isolated systems. We examine
large systems with eigenstate energies equivalent to finite temperatures. When
quasi-static evolution of a system is adiabatic (in the quantum mechanical
sense), two coupled subsystems can transfer heat from one subsystem to another
yet remain in an energy eigenstate. To explicitly construct the entropy from
the wave function, degrees of freedom are divided into two unequal parts. It is
argued that the entanglement entropy between these two subsystems is the
thermodynamic entropy per degree of freedom for the smaller subsystem. This is
done by tracing over the larger subsystem to obtain a density matrix, and
calculating the diagonal and off-diagonal contributions to the entanglement
entropy.Comment: 18 page
Continuous Time Monte Carlo and Spatial Ordering in Driven Lattice Gases: Application to Driven Vortices in Periodic Superconducting Networks
We consider the two dimensional (2D) classical lattice Coulomb gas as a model
for magnetic field induced vortices in 2D superconducting networks. Two
different dynamical rules are introduced to investigate driven diffusive steady
states far from equilibrium as a function of temperature and driving force. The
resulting steady states differ dramatically depending on which dynamical rule
is used. We show that the commonly used driven diffusive Metropolis Monte Carlo
dynamics contains unphysical intrinsic randomness that destroys the spatial
ordering present in equilibrium (the vortex lattice) over most of the driven
phase diagram. A continuous time Monte Carlo (CTMC) is then developed, which
results in spatially ordered driven states at low temperature in finite sized
systems. We show that CTMC is the natural discretization of continuum Langevin
dynamics, and argue that it gives the correct physical behavior when the
discrete grid represents the minima of a periodic potential. We use detailed
finite size scaling methods to analyze the spatial structure of the steady
states. We find that finite size effects can be subtle and that very long
simulation times can be needed to arrive at the correct steady state. For
particles moving on a triangular grid, we find that the ordered moving state is
a transversely pinned smectic that becomes unstable to an anisotropic liquid on
sufficiently large length scales. For particles moving on a square grid, the
moving state is a similar smectic at large drives, but we find evidence for a
possible moving solid at lower drives. We find that the driven liquid on the
square grid has long range hexatic order, and we explain this as a specifically
non-equilibrium effect. We show that, in the liquid, fluctuations are diffusive
in both the transverse and longitudinal directions.Comment: 29 pages, 35 figure
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