20,413 research outputs found
Heat transport in stochastic energy exchange models of locally confined hard spheres
We study heat transport in a class of stochastic energy exchange systems that
characterize the interactions of networks of locally trapped hard spheres under
the assumption that neighbouring particles undergo rare binary collisions. Our
results provide an extension to three-dimensional dynamics of previous ones
applying to the dynamics of confined two-dimensional hard disks [Gaspard P &
Gilbert T On the derivation of Fourier's law in stochastic energy exchange
systems J Stat Mech (2008) P11021]. It is remarkable that the heat conductivity
is here again given by the frequency of energy exchanges. Moreover the
expression of the stochastic kernel which specifies the energy exchange
dynamics is simpler in this case and therefore allows for faster and more
extensive numerical computations.Comment: 21 pages, 5 figure
On the derivation of Fourier's law in stochastic energy exchange systems
We present a detailed derivation of Fourier's law in a class of stochastic
energy exchange systems that naturally characterize two-dimensional mechanical
systems of locally confined particles in interaction. The stochastic systems
consist of an array of energy variables which can be partially exchanged among
nearest neighbours at variable rates. We provide two independent derivations of
the thermal conductivity and prove this quantity is identical to the frequency
of energy exchanges. The first derivation relies on the diffusion of the
Helfand moment, which is determined solely by static averages. The second
approach relies on a gradient expansion of the probability measure around a
non-equilibrium stationary state. The linear part of the heat current is
determined by local thermal equilibrium distributions which solve a
Boltzmann-like equation. A numerical scheme is presented with computations of
the conductivity along our two methods. The results are in excellent agreement
with our theory.Comment: 19 pages, 5 figures, to appear in Journal of Statistical Mechanics
(JSTAT
Rancang Bangun Sistem Peringkasan Teks Multi-Dokumen
Seiring dengan bertumbuhnya jumlah dokumen digital yang sangat pesat, membuat pengguna membutuhakan suatu sistem yang dapat melakukan peringkasan teks. Pada penelitian ini diusulkan sebuah rancangan peringksan teks multi-dokumen berbasis pendekatan clustering dan pemilihan kalimat. Metode yang digunakan proses clustering kalimat adalah Latent Semantic Indexing (LSI) dan Similarity Based Histogram Clustering (SHC). Metode LSI dilakukan untuk menghitung tingkat kemiripan antarpasangan kalimat dan metode SHC digunakan untuk mengelompokkan kalimat-kalimat ke dalam cluster. Sedangkan metode yang digunakan dalam pemilihan kalimat adalah Sentences Information Density (SID). Metode tersebut merupakan metode pemilihan berbasis positional text graph. Kombinasi metode tersebut mampu menghasilkan sebuah peringkasan teks multi-dokumen yang mengandung coverage, diversity dan koherensi yang tinggi
“An ethnographic seduction”: how qualitative research and Agent-based models can benefit each other
We provide a general analytical framework for empirically informed agent-based simulations. This methodology provides present-day agent-based models with a sound and proper insight as to the behavior of social agents — an insight that statistical data often fall short of providing at least at a micro level and for hidden and sensitive populations. In the other direction, simulations can provide qualitative researchers in sociology, anthropology and other fields with valuable tools for: (a) testing the consistency and pushing the boundaries, of specific theoretical frameworks; (b) replicating and generalizing results; (c) providing a platform for cross-disciplinary validation of results
Level density of a Fermi gas and integer partitions: a Gumbel-like finite-size correction
We investigate the many-body level density of gas of non-interacting
fermions. We determine its behavior as a function of the temperature and the
number of particles. As the temperature increases, and beyond the usual
Sommerfeld expansion that describes the degenerate gas behavior, corrections
due to a finite number of particles lead to Gumbel-like contributions. We
discuss connections with the partition problem in number theory, extreme value
statistics as well as differences with respect to the Bose gas.Comment: 5 pages, 1 figure, one figure added, accepted for publication in
Phys. Rev.
Persistence effects in deterministic diffusion
In systems which exhibit deterministic diffusion, the gross parameter
dependence of the diffusion coefficient can often be understood in terms of
random walk models. Provided the decay of correlations is fast enough, one can
ignore memory effects and approximate the diffusion coefficient according to
dimensional arguments. By successively including the effects of one and two
steps of memory on this approximation, we examine the effects of
``persistence'' on the diffusion coefficients of extended two-dimensional
billiard tables and show how to properly account for these effects, using walks
in which a particle undergoes jumps in different directions with probabilities
that depend on where they came from.Comment: 7 pages, 7 figure
Non-classical correlations in non-Markovian continuous variable systems
We consider two identical and non-interacting harmonic oscillators coupled to
either two independent bosonic baths or to a common bosonic bath. Under the
only assumption of weak coupling, we analyze in details the non-Markovian short
time-scale evolution of intensity correlations, entanglement and quantum
discord for initial two-mode squeezed-thermal vacuum states. In the independent
reservoirs case we observe the detrimental effect of the environment for all
these quantities and we establish a hierarchy for their robustness against the
environmental noise. In the common reservoir case, for initial uncorrelated
states, we find that only quantum discord can be created via interaction with
the bath, while entanglement and sub shot noise intensity correlations remain
absent.Comment: 10 pages, 5 figure
Kinematic Masses of Super Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy
Using high-resolution (R~22,000) near-infrared (1.51 -- 1.75 microns) spectra
from Keck Observatory, we measure the kinematic masses of two super star
clusters in M82. Cross-correlation of the spectra with template spectra of cool
evolved stars gives stellar velocity dispersions of sigma_r=15.9 +/- 0.8 km/s
for MGG-9 and sigma_r=11.4 +/- 0.8 km/s for MGG-11. The cluster spectra are
dominated by the light of red supergiants, and correlate most closely with
template supergiants of spectral types M0 and M4.5. We fit King models to the
observed profiles of the clusters in archival HST/NICMOS images to measure the
half-light radii. Applying the virial theorem, we determine masses of 1.5 +/-
0.3 x 10^6 M_sun for MGG-9 and 3.5 +/- 0.7 x 10^5 M_sun for MGG-11. Population
synthesis modelling suggests that MGG-9 is consistent with a standard initial
mass function, whereas MGG-11 appears to be deficient in low-mass stars
relative to a standard IMF. There is, however, evidence of mass segregation in
the clusters, in which case the virial mass estimates would represent lower
limits.Comment: 16 pages, 8 figures; ApJ, in pres
Log-periodic drift oscillations in self-similar billiards
We study a particle moving at unit speed in a self-similar Lorentz billiard
channel; the latter consists of an infinite sequence of cells which are
identical in shape but growing exponentially in size, from left to right. We
present numerical computation of the drift term in this system and establish
the logarithmic periodicity of the corrections to the average drift
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