699 research outputs found
Glassy behavior of the site frustrated percolation model
The dynamical properties of the site frustrated percolation model are
investigated and compared with those of glass forming liquids. When the density
of the particles on the lattice becomes high enough, the dynamics of the model
becomes very slow, due to geometrical constraints, and rearrangement on large
scales is needed to allow relaxation. The autocorrelation functions, the
specific volume for different cooling rates, and the mean square displacement
are evaluated, and are found to exhibit glassy behavior.Comment: 8 pages, RevTeX, 11 fig
Dynamic heterogeneities in attractive colloids
We study the formation of a colloidal gel by means of Molecular Dynamics
simulations of a model for colloidal suspensions. A slowing down with gel-like
features is observed at low temperatures and low volume fractions, due to the
formation of persistent structures. We show that at low volume fraction the
dynamic susceptibility, which describes dynamic heterogeneities, exhibits a
large plateau, dominated by clusters of long living bonds. At higher volume
fraction, where the effect of the crowding of the particles starts to be
present, it crosses over towards a regime characterized by a peak. We introduce
a suitable mean cluster size of clusters of monomers connected by "persistent"
bonds which well describes the dynamic susceptibility.Comment: 4 pages, 4 figure
Two channel model for optical conductivity of high mobility organic crystals
We show that the temperature dependence of conductivity of high mobility
organic crystals Pentacene and Rubrene can be quantitatively described in the
framework of the model where carriers are scattered by quenched local
impurities and interact with phonons by Su-Schrieffer-Hegger (SSH) coupling.
Within this model, we present approximation free results for mobility and
optical conductivity obtained by world line Monte Carlo, which we generalize to
the case of coupling both to phonons and impurities. We find fingerprints of
carrier dynamics in these compounds which differ from conventional metals and
show that the dynamics of carriers can be described as a superposition of a
Drude term representing diffusive mobile particles and a Lorentz term
associated with dynamics of localized charges.Comment: 6 pages, 5 figure
Comment on ``Two Time Scales and Violation of the Fluctuation-Dissipation Theorem in a Finite Dimensional Model for Structural Glasses''
In cond-mat/0002074 Ricci-Tersenghi et al. find two linear regimes in the
fluctuation-dissipation relation between density-density correlations and
associated responses of the Frustrated Ising Lattice Gas. Here we show that
this result does not seem to correspond to the equilibrium quantities of the
model, by measuring the overlap distribution P(q) of the density and comparing
the FDR expected on the ground of the P(q) with the one measured in the
off-equilibrium experiments.Comment: RevTeX, 1 page, 2 eps figures, Comment on F. Ricci-Tersenghi et al.,
Phys. Rev. Lett. 84, 4473 (2000
Irreversible Opinion Spreading on Scale-Free Networks
We study the dynamical and critical behavior of a model for irreversible
opinion spreading on Barab\'asi-Albert (BA) scale-free networks by performing
extensive Monte Carlo simulations. The opinion spreading within an
inhomogeneous society is investigated by means of the magnetic Eden model, a
nonequilibrium kinetic model for the growth of binary mixtures in contact with
a thermal bath. The deposition dynamics, which is studied as a function of the
degree of the occupied sites, shows evidence for the leading role played by
hubs in the growth process. Systems of finite size grow either ordered or
disordered, depending on the temperature. By means of standard finite-size
scaling procedures, the effective order-disorder phase transitions are found to
persist in the thermodynamic limit. This critical behavior, however, is absent
in related equilibrium spin systems such as the Ising model on BA scale-free
networks, which in the thermodynamic limit only displays a ferromagnetic phase.
The dependence of these results on the degree exponent is also discussed for
the case of uncorrelated scale-free networks.Comment: 9 pages, 10 figures; added results and discussion on uncorrelated
scale-free networks; added references. To appear in PR
Glass transition in models with controlled frustration
A class of models with self-generated disorder and controlled frustration is
studied. Between the trivial case, where frustration is not present at all, and
the limit case, where frustration is present over every length scale, a region
with local frustration is found where glassy dynamics appears. We suggest that
in this region, the mean field model might undergo a p-spin like transition,
and increasing the range of frustration, a crossover from a 1-step replica
symmetry breaking to a continuous one might be observed.Comment: 4 pages, 6 figure
'I dont' know the anwer to that question': A Corpus-assisted Discourse Analysis of White House Press Briefings
White House Press Briefings, daily meetings with the press held by the White House Press Secretary, are the main information conduit for the White House (Kumar 2007). They are considered a ‘political chess game’ where the Press Secretary and the press face a ‘wrestling match’ (Partington 2006: 16).
Our analysis is carried out on a corpus comprising all the Press Briefings across three presidencies from Clinton to Obama. The additional mark-up includes information about individual speakers and their role, allowing us to compare different discourse strategies adopted by the participants in the briefings at different points in time. This leads us to determine the extent of the differences in the patterns found as well as the nature of the variation from one participant to the next one.
Starting from a phraseological perspective (Granger and Meunier 2008), our analysis will focus on avoidance strategies enacted by the podium with the main purpose of preserving face and yet ‘doing the job’ (Partington 2003: 80). We will show how the cluster ‘I don’t know’ can be exploited by various podiums, mainly in accordance with strategic communication choices made by the US administrations, highlighting differences in the podium’s attitude towards the press
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