464 research outputs found
Adiabatic invariance with first integrals of motion
The construction of a microthermodynamic formalism for isolated systems based
on the concept of adiabatic invariance is an old but seldom appreciated effort
in the literature, dating back at least to P. Hertz [Ann. Phys. (Leipzig) 33,
225 (1910)]. An apparently independent extension of such formalism for systems
bearing additional first integrals of motion was recently proposed by Hans H.
Rugh [Phys. Rev. E 64, 055101 (2001)], establishing the concept of adiabatic
invariance even in such singular cases. After some remarks in connection with
the formalism pioneered by Hertz, it will be suggested that such an extension
can incidentally explain the success of a dynamical method for computing the
entropy of classical interacting fluids, at least in some potential
applications where the presence of additional first integrals cannot be
ignored.Comment: 2 pages, no figures (REVTeX 4
Steady non-ideal detonations in cylindrical sticks of expolsives
Numerical simulations of detonations in cylindrical rate-sticks of highly
non-ideal explosives are performed, using a simple model with a weakly pressure
dependent rate law and a pseudo-polytropic equation of state. Some numerical issues
with such simulations are investigated, and it is shown that very high resolution
(hundreds of points in the reaction zone) are required for highly accurate (converged)
solutions. High resolution simulations are then used to investigate the qualitative
dependences of the detonation driving zone structure on the diameter and degree of
confinement of the explosive charge. The simulation results are used to show that,
given the radius of curvature of the shock at the charge axis, the steady detonation
speed and the axial solution are accurately predicted by a quasi-one-dimensional
theory, even for cases where the detonation propagates at speeds significantly below
the Chapman-Jouguet speed. Given reaction rate and equation of state models, this
quasi-one-dimensional theory offers a significant improvement to Wood-Kirkwood
theories currently used in industry
The Approach to Ergodicity in Monte Carlo Simulations
The approach to the ergodic limit in Monte Carlo simulations is studied using
both analytic and numerical methods. With the help of a stochastic model, a
metric is defined that enables the examination of a simulation in both the
ergodic and non-ergodic regimes. In the non-ergodic regime, the model implies
how the simulation is expected to approach ergodic behavior analytically, and
the analytically inferred decay law of the metric allows the monitoring of the
onset of ergodic behavior. The metric is related to previously defined measures
developed for molecular dynamics simulations, and the metric enables the
comparison of the relative efficiencies of different Monte Carlo schemes.
Applications to Lennard-Jones 13-particle clusters are shown to match the model
for Metropolis, J-walking and parallel tempering based approaches. The relative
efficiencies of these three Monte Carlo approaches are compared, and the decay
law is shown to be useful in determining needed high temperature parameters in
parallel tempering and J-walking studies of atomic clusters.Comment: 17 Pages, 7 Figure
Proton propagation in nuclei studied in the (e,e’p) reaction
Proton propagation in nuclei was studied using the (e,e’p) reaction in the quasifree region. The coincidence (e,e’p) cross sections were measured at an electron angle of 50.4° and proton angles of 50.1°, 58.2°, 67.9°, and 72.9° for 12C, 27Al, 58Ni, and 181Ta targets at a beam energy of 779.5 MeV. The average outgoing proton energy was 180 MeV. The ratio of the (e,e’p) yield to the simultaneously measured (e,e’) yield was compared to that calculated in the plane-wave impulse approximation and an experimental transmission defined. These experimental transmissions are considerably larger (a factor of ∼2 for 181Ta) than those one would calculate from the free N-N cross sections folded into the nuclear density distribution. A new calculation that includes medium effects (N-N correlations, density dependence of the N-N cross sections and Pauli suppression) accounts for this increase
Cell shape analysis of random tessellations based on Minkowski tensors
To which degree are shape indices of individual cells of a tessellation
characteristic for the stochastic process that generates them? Within the
context of stochastic geometry and the physics of disordered materials, this
corresponds to the question of relationships between different stochastic
models. In the context of image analysis of synthetic and biological materials,
this question is central to the problem of inferring information about
formation processes from spatial measurements of resulting random structures.
We address this question by a theory-based simulation study of shape indices
derived from Minkowski tensors for a variety of tessellation models. We focus
on the relationship between two indices: an isoperimetric ratio of the
empirical averages of cell volume and area and the cell elongation quantified
by eigenvalue ratios of interfacial Minkowski tensors. Simulation data for
these quantities, as well as for distributions thereof and for correlations of
cell shape and volume, are presented for Voronoi mosaics of the Poisson point
process, determinantal and permanental point processes, and Gibbs hard-core and
random sequential absorption processes as well as for Laguerre tessellations of
polydisperse spheres and STIT- and Poisson hyperplane tessellations. These data
are complemented by mechanically stable crystalline sphere and disordered
ellipsoid packings and area-minimising foam models. We find that shape indices
of individual cells are not sufficient to unambiguously identify the generating
process even amongst this limited set of processes. However, we identify
significant differences of the shape indices between many of these tessellation
models. Given a realization of a tessellation, these shape indices can narrow
the choice of possible generating processes, providing a powerful tool which
can be further strengthened by density-resolved volume-shape correlations.Comment: Chapter of the forthcoming book "Tensor Valuations and their
Applications in Stochastic Geometry and Imaging" in Lecture Notes in
Mathematics edited by Markus Kiderlen and Eva B. Vedel Jense
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
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