7,122 research outputs found
Affinity and Fluctuations in a Mesoscopic Noria
We exhibit the invariance of cycle affinities in finite state Markov
processes under various natural probabilistic constructions, for instance under
conditioning and under a new combinatorial construction that we call ``drag and
drop''. We show that cycle affinities have a natural probabilistic meaning
related to first passage non-equilibrium fluctuation relations that we
establish.Comment: 30 pages, 1 figur
Local Detailed Balance : A Microscopic Derivation
Thermal contact is the archetype of non-equilibrium processes driven by
constant non-equilibrium constraints when the latter are enforced by reservoirs
exchanging conserved microscopic quantities. At a mesoscopic scale only the
energies of the macroscopic bodies are accessible together with the
configurations of the contact system. We consider a class of models where the
contact system, as well as macroscopic bodies, have a finite number of possible
configurations. The global system with only discrete degrees of freedom has no
microscopic Hamiltonian dynamics, but it is shown that, if the microscopic
dynamics is assumed to be deterministic and ergodic and to conserve energy
according to some specific pattern, and if the mesoscopic evolution of the
global system is approximated by a Markov process as closely as possible, then
the mesoscopic transition rates obey three constraints. In the limit where
macroscopic bodies can be considered as reservoirs at thermodynamic equilibrium
(but with different intensive parameters) the mesoscopic transition rates turn
into transition rates for the contact system and the third constraint becomes
local detailed balance ; the latter is generically expressed in terms of the
microscopic exchange entropy variation, namely the opposite of the variation of
the thermodynamic entropy of the reservoir involved in a given microscopic jump
of the contact system configuration. For a finite-time evolution after contact
has been switched on we derive a fluctuation relation for the joint probability
of the heat amounts received from the various reservoirs. The generalization to
systems exchanging energy, volume and matter with several reservoirs, with a
possible conservative external force acting on the contact system, is given
explicitly.Comment: 26 pages. arXiv admin note: substantial text overlap with
arXiv:1302.453
A parity breaking Ising chain Hamiltonian as a Brownian motor
We consider the translationally invariant but parity (left-right symmetry)
breaking Ising chain Hamiltonian \begin{equation} {\cal H} = -U_2\sum_{k}
s_{k}s_{k+1} - U_3\sum_{k} s_{k}s_{k+1}s_{k+3} \nonumber \end{equation} and let
this system evolve by Kawasaki spin exchange dynamics. Monte Carlo simulations
show that perturbations forcing this system off equilibrium make it act as a
Brownian molecular motor which, in the lattice gas interpretation, transports
particles along the chain. We determine the particle current under various
different circumstances, in particular as a function of the ratio and
of the conserved magnetization . The symmetry of the term
in the Hamiltonian is discussedComment: 11 pages, 4 figure
Density profiles in a classical Coulomb fluid near a dielectric wall. I. Mean-field scheme
The equilibrium density profiles in a classical multicomponent plasma near a
hard wall made with a dielectric material characterized by a relative
dielectric constant \ew are studied from the first Born-Green-Yvon equation
combined with Poisson equation in a regime where Coulomb coupling is weak
inside the fluid. In order to prevent the collapse between charges with
opposite signs or between each charge and its dielectric image inside the wall
when \ew >1, hard-core repulsions are added to the Coulomb pair interaction.
The charge-image interaction cannot be treated perturbatively and the density
profiles vary very fast in the vicinity of the wall when \ew \neq 1. The
formal solution of the associated inhomogeneous Debye-H\"uckel equations will
be given in Paper II, together with a systematic fugacity expansion which
allows to retrieve the results obtained from the truncated \bgy hierarchy. In
the present paper the exact density profiles are calculated analytically up to
first order in the coupling parameter. The expressions show the interplay
between three effects~: the geometric repulsion from the impenetrable wall; the
electrostatic effective attraction (\ew >1) or repulsion (\ew <1) due to
its dielectric response; and the Coulomb interaction between each charge and
the potential drop created by the electric layer which appears as soon as the
system is not symmetric. We exhibit how the charge density profile evolves
between a structure with two oppositely-charged layers and a three-layer
organization when \ew varies. (The case of two ideally conducting walls will
be displayed elsewhere)Comment: 32 pages, 11 figure
Reconstructing intelligible audio speech from visual speech features
This work describes an investigation into the feasibility of producing intelligible audio speech from only visual speech fea- tures. The proposed method aims to estimate a spectral enve- lope from visual features which is then combined with an arti- ficial excitation signal and used within a model of speech pro- duction to reconstruct an audio signal. Different combinations of audio and visual features are considered, along with both a statistical method of estimation and a deep neural network. The intelligibility of the reconstructed audio speech is measured by human listeners, and then compared to the intelligibility of the video signal only and when combined with the reconstructed audio
Voicing classification of visual speech using convolutional neural networks
The application of neural network and convolutional neural net- work (CNN) architectures is explored for the tasks of voicing classification (classifying frames as being either non-speech, unvoiced, or voiced) and voice activity detection (VAD) of vi- sual speech. Experiments are conducted for both speaker de- pendent and speaker independent scenarios. A Gaussian mixture model (GMM) baseline system is de- veloped using standard image-based two-dimensional discrete cosine transform (2D-DCT) visual speech features, achieving speaker dependent accuracies of 79% and 94%, for voicing classification and VAD respectively. Additionally, a single- layer neural network system trained using the same visual fea- tures achieves accuracies of 86 % and 97 %. A novel technique using convolutional neural networks for visual speech feature extraction and classification is presented. The voicing classifi- cation and VAD results using the system are further improved to 88 % and 98 % respectively. The speaker independent results show the neural network system to outperform both the GMM and CNN systems, achiev- ing accuracies of 63 % for voicing classification, and 79 % for voice activity detection
Density profiles in a classical Coulomb fluid near a dielectric wall. II. Weak-coupling systematic expansions
In the framework of the grand-canonical ensemble of statistical mechanics, we
give an exact diagrammatic representation of the density profiles in a
classical multicomponent plasma near a dielectric wall. By a reorganization of
Mayer diagrams for the fugacity expansions of the densities, we exhibit how the
long-range of both the self-energy and pair interaction are exponentially
screened at large distances from the wall. However, the self-energy due to
Coulomb interaction with images still diverges in the vicinity of the
dielectric wall and the variation of the density is drastically different at
short or large distances from the wall. This variation is involved in the
inhomogeneous Debye-H\"uckel equation obeyed by the screened pair potential.
Then the main difficulty lies in the determination of the latter potential at
every distance. We solve this problem by devising a systematic expansion with
respect to the ratio of the fundamental length scales involved in the two
coulombic effects at stake. (The application of this method to a plasma
confined between two ideally conducting plates and to a quantum plasma will be
presented elsewhere). As a result we derive the exact analytical perturbative
expressions for the density profiles up to first order in the coupling between
charges. The mean-field approach displayed in Paper I is then justified.Comment: 37 pages, 5 figure
Reasoning and Improving on Software Resilience against Unanticipated Exceptions
In software, there are the errors anticipated at specification and design
time, those encountered at development and testing time, and those that happen
in production mode yet never anticipated. In this paper, we aim at reasoning on
the ability of software to correctly handle unanticipated exceptions. We
propose an algorithm, called short-circuit testing, which injects exceptions
during test suite execution so as to simulate unanticipated errors. This
algorithm collects data that is used as input for verifying two formal
exception contracts that capture two resilience properties. Our evaluation on 9
test suites, with 78% line coverage in average, analyzes 241 executed catch
blocks, shows that 101 of them expose resilience properties and that 84 can be
transformed to be more resilient
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