710 research outputs found
Dynamic heterogeneity in amorphous materials
Amorphous solids are mechanically rigid while possessing a disordered
structure similar to that of dense liquids. Recent research indicates that
dynamical heterogeneity, spatio-temporal fluctuations in local dynamical
behavior, might help understanding the statistical mechanics of glassy states.Comment: 7 pages; 5 figures -- "Trends" article published by Physics at
http://physics.aps.org/articles/v4/4
Equilibrium equation of state of a hard sphere binary mixture at very large densities using replica exchange Monte-Carlo simulations
We use replica exchange Monte-Carlo simulations to measure the equilibrium
equation of state of the disordered fluid state for a binary hard sphere
mixture up to very large densities where standard Monte-Carlo simulations do
not easily reach thermal equilibrium. For the moderate system sizes we use (up
to N=100), we find no sign of a pressure discontinuity near the location of
dynamic glass singularities extrapolated using either algebraic or simple
exponential divergences, suggesting they do not correspond to genuine
thermodynamic glass transitions. Several scenarios are proposed for the fate of
the fluid state in the thermodynamic limit.Comment: 10 pages, 8 fig
A critical test of the mode-coupling theory of the glass transition
The mode-coupling theory of the glass transition predicts the time evolution
of the intermediate scattering functions in viscous liquids on the sole basis
of the structural information encoded in two-point density correlations. We
provide a critical test of this property and show that the theory fails to
describe the qualitatively distinct dynamical behavior obtained in two model
liquids characterized by very similar pair correlation functions. Because we
use `exact' static information provided by numerical simulations, our results
are a direct proof that some important information about the dynamics of
viscous liquids is not captured by pair correlations, and is thus not described
by the mode-coupling theory, even in the temperature regime where the theory is
usually applied.Comment: 7 pages, 5 figures
The Stackelberg equilibrium as a consistent conjectural equilibrium
We consider a static game with conjectural variations where some firms make conjectures while others do not. Two propositions are proved. We first show that there exists a continuum of conjectural variations such that the conjectural equilibrium locally coincides with the Stackelberg equilibrium (Proposition 1). Second, we define the conditions under which a conjectural equilibrium is a locally consistent equilibrium (i.e. such that conjectures are fulfilled). The concept of (local) consistency is restricted to firms making conjectures. Two conditions on consistency are featured: consistency within a cohort and consistency among cohorts. The Stackelberg equilibrium fulfills only the latter condition (Proposition 2). An example is provided.Consistent conjectural variations, reaction functions, Stackelberg competition
Do followers really matter in Stackelberg competition?
In this note, we consider a generalized Tâstage Stackelberg oligopoly. We provide a proof and an interpretation that under the two necessary and sufficient conditions of linear aggregate demand and identical constant marginal costs, followers do not matter for leaders. Leaders act as rational myopic agents, voluntarily ignoring the number of followers and remaining stages, thereby behaving as Cournotian oligopolists. Strategies of incumbent firms are invariant to entry of new cohorts. Their profits can be studied by the way of two discount factors: the first impacting markup and the second impacting output supply. Some implications in terms of welfare and convergence toward competitive equilibrium are derived.Leaderâs markup discount factor, linear economy, followerâs output discount factor, myopic behavior
Increasing the density melts ultrasoft colloidal glasses
We use theory and simulations to investigate the existence of amorphous
glassy states in ultrasoft colloids. We combine the hyper-netted chain
approximation with mode-coupling theory to study the dynamic phase diagram of
soft repulsive spheres interacting with a Hertzian potential, focusing on low
temperatures and large densities. At constant temperature, we find that an
amorphous glassy state is entered upon compression, as in colloidal hard
spheres, but the glass unexpectedly melts when density increases further. We
attribute this re-entrant fluid-glass transition to particle softness, and
correlate this behaviour to previously reported anomalies in soft systems, thus
emphasizing its generality. The predicted fluid-glass-fluid sequence is
confirmed numerically.Comment: 4 pages, 3 fig
Spin ice under pressure: symmetry enhancement and infinite order multicriticality
We study the low-temperature behaviour of spin ice when uniaxial pressure
induces a tetragonal distortion. There is a phase transition between a Coulomb
liquid and a fully magnetised phase. Unusually, it combines features of
discontinuous and continuous transitions: the order parameter exhibits a jump,
but this is accompanied by a divergent susceptibility and vanishing domain wall
tension. All these aspects can be understood as a consequence of an emergent
SU(2) symmetry at the critical point. We map out a possible experimental
realisation
A Three Dimensional Kasteleyn Transition: Spin Ice in a [100] Field
We examine the statistical mechanics of spin-ice materials with a [100]
magnetic field. We show that the approach to saturated magnetisation is, in the
low-temperature limit, an example of a 3D Kasteleyn transition, which is
topological in the sense that magnetisation is changed only by excitations that
span the entire system. We study the transition analytically and using a Monte
Carlo cluster algorithm, and compare our results with recent data from
experiments on Dy2Ti2O7.Comment: 4 pages, 5 figure
Safe and Secure Support for Public Safety Networks
International audienceAs explained by Tanzi et al. in the first volume of this book, communicating and autonomous devices will surely have a role to play in the future Public Safety Networks. The âcommunicatingâ feature comes from the fact that the information should be delivered in a fast way to rescuers. The âautonomousâ characteristic comes from the fact that rescuers should not have to concern themselves about these objects: they should perform their mission autonomously so as not to delay the intervention of the rescuers, but rather to assist them efficiently and reliably.</p
Distribution of Interference in the Presence of Decoherence
We study the statistics of quantum interference for completely positive maps.
We calculate analytically the mean interference and its second moment for
finite dimensional quantum systems interacting with a simple environment
consisting of one or several spins (qudits). The joint propagation of the
entire system is taken as unitary with an evolution operator drawn from the
Circular Unitary Ensemble (CUE). We show that the mean interference decays with
a power law as function of the dimension of the Hilbert space of the
environment, with a power that depends on the temperature of the environment.Comment: 28 pages of pd
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