Supervised Associative Learning in Spiking Neural Network

In this paper, we propose a simple supervised associative learning approach for spiking neural networks. In an excitatory-inhibitory network paradigm with Izhikevich spiking neurons, synaptic plasticity is implemented on excitatory to excitatory synapses dependent on both spike emission rates and spike timings. As results of learning, the network is able to associate not just familiar stimuli but also novel stimuli observed through synchronised activity within the same subpopulation and between two associated subpopulations

High-frequency electron paramagnetic resonance investigation of the Fe3+ impurity center in polycrystalline PbTiO3 in its ferroelectric phase

The intrinsic iron(III) impurity center in polycrystalline lead titanate was investigated by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy in order to determine the local-environment sensitive fine structure parameter D. At a spectrometer frequency of 190 GHz, spectral analysis of a powder sample was unambiguously possible. The observed mean value D = +35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the B-site of the perovskite ABO3 lattice forming a directly coordinated iron - oxygen vacancy defect associate. A consistent fit of the multi-frequency data necessitated use of a distribution of D values with a variance of about 1 GHz. This statistical distribution of values is probably related to more distant defects and vacancies.Comment: 6 pages, 3 figures, 1 table, to appear in J. App. Phys, 96 (2004

Correlation between glove use practices and compliance with hand hygiene in a multicenter study with elderly patients

In a study conducted in 11 health care settings for elderly patients, we demonstrated a significant negative correlation between the proportion of glove use outside any risk of exposure to body fluids and compliance with hand hygiene (P < .02). This result underscores a major limitation of strategies for controlling the spread of multidrug-resistant bacteria that recommend systematic glove use for each contact with carriers or their environment

Preparing multi-partite entanglement of photons and matter qubits

We show how to make event-ready multi-partite entanglement between qubits which may be encoded on photons or matter systems. Entangled states of matter systems, which can also act as single photon sources, can be generated using the entangling operation presented in quant-ph/0408040. We show how to entangle such sources with photon qubits, which may be encoded in the dual rail, polarization or time-bin degrees of freedom. We subsequently demonstrate how projective measurements of the matter qubits can be used to create entangled states of the photons alone. The state of the matter qubits is inherited by the generated photons. Since the entangling operation can be used to generate cluster states of matter qubits for quantum computing, our procedure enables us to create any (entangled) photonic quantum state that can be written as the outcome of a quantum computer.Comment: 10 pages, 4 figures; to appear in Journal of Optics

Fermionic field theory for directed percolation in (1+1) dimensions

We formulate directed percolation in (1+1) dimensions in the language of a reaction-diffusion process with exclusion taking place in one space dimension. We map the master equation that describes the dynamics of the system onto a quantum spin chain problem. From there we build an interacting fermionic field theory of a new type. We study the resulting theory using renormalization group techniques. This yields numerical estimates for the critical exponents and provides a new alternative analytic systematic procedure to study low-dimensional directed percolation.Comment: 20 pages, 2 figure

Rolling contact fatigue of railways wheels: Influence of steel grade and sliding conditions

AbstractThe aim of this work is to develop a numerical approach which is able to compare the different steel grades influence on rolling contact fatigue of railways wheels according to practical conditions. The main stages are the identification of the material behavior, the determination of the stress-strain fields and the application of a fatigue criterion. Two steels usually used for the manufacturing of wheels have been studied, R9T and 50CrMo4. Their influence has been numerically studied. Results show that the threshold of elastic and plastic shakedown differs depending on the steel grades and consequently the risk of damage can be affected. This methodology allows a classification of the material grades face the risk on rolling contact fatigue

Invasive alien species in the food chain : advancing risk assessment models to address climate change, economics and uncertainty

Economic globalization depends on the movement of people and goods between countries. As these exchanges increase, so does the potential for translocation of harmful pests, weeds, and pathogens capable of impacting our crops, livestock and natural resources (Hulme 2009), with concomitant impacts on global food security (Cook et al. 2011)

Dzyaloshinsky-Moriya Anisotropy in the Spin-1/2 Kagom\'e Compound ZnCu3_{3}(OH)6_{6}Cl2_{2}

We report the determination of the Dzyaloshinsky-Moriya interaction, the dominant magnetic anisotropy term in the \kagome spin-1/2 compound {\herbert}. Based on the analysis of the high-temperature electron spin resonance (ESR) spectra, we find its main component $|D_z|=15(1)$ K to be perpendicular to the \kagome planes. Through the temperature dependent ESR line-width we observe a building up of nearest-neighbor spin-spin correlations below $\sim$150 K.Comment: 4 pages, 3 figures, minor modification

Construction participative d’un modèle régional pour l’évaluation de la demande en eau agricole: un exemple dans le bassin de la Drôme

International audienceLa " gestion intégrée des ressources en eau " tente de rendre compte du fonctionnement d’" hydro-systèmes " qui rassemblent un ensemble de ressources et d’usages de l’eau en interaction au sein d’un territoire, qui lui-même recouvre diverses unités administratives ou politiques. Pour mettre en place cette gestion intégrée, certains pays ont opté pour une décentralisation : la gestion de l’eau est alors confiée à des organisations de bassin au sein desquels siègent des porte-parole des différents intérêts en jeu. Ces organisations soulignent le peu de support pour favoriser la concertation. Les outils disponibles mettent l’accent sur les processus biophysiques, mais proposent une représentation très simplifiée des usages notamment agricoles. Ces usages sont non seulement liés aux disponibilités en eau et à ses conditions d’accès, mais aussi au contexte technologique, économique, et institutionnel dans lequel les agriculteurs évoluent. Pour favoriser la concertation, nous proposons de construire avec les acteurs locaux une représentation du système dans lequel ils agissent, touchant à la fois aux aspects techniques, et économiques. L’objectif est de représenter les interactions entre ressource et usages (notamment agricoles), et d’évaluer les conséquences de scénarios imaginés à l’échelle du territoire. Ce modèle régional comprend donc (i) une caractérisation hydrologique simplifiée qui permet d’évaluer en entrée les disponibilités initiales de la ressource et de mesurer les impacts des prélèvements, (ii) un modèle bio-physique PILOT qui permet d’évaluer les consommations d’eau, et les rendements selon les pratiques agricoles et les conditions agroclimatiques, et (iii) un modèle technico-économique qui rend compte des choix techniques des agriculteurs et de leurs conséquences en termes économiques. Le modèle technicoéconomique des activités agricoles à l’échelle régionale s’appuie sur une typologie des exploitations et des ateliers de productions agricoles. Dans ce modèle, (i) les activités agricoles à l’échelle régionale sont la somme pondérée des activités des exploitations types (les pondérations correspondent aux effectifs d’exploitations), et (ii) les activités d’une exploitation type sont la somme pondérée d’ateliers de production types (les pondérations correspondent aux dimensions des ateliers). Cette structure permet d’agréger à l’échelle régionale les impacts des activités et de désagréger à l’échelle des exploitations et de leurs activités les conséquences de mesures globales. La construction participative du modèle régional s’appuie sur la mise en place dès le démarrage de l’étude d’un " groupe de pilotage ", composé des représentants des acteurs locaux. Ce groupe de pilotage participe à la modélisation en fournissant les données nécessaires et en validant chaque étape de la construction. Le modèle, construit et validé par Colloque - 13th IWRA World water congress, 1-4 september 2008, Montpellier tous les acteurs, peut alors contribuer à aider les décideurs locaux ou régionaux à élaborer des scénarios raisonnés pour définir des stratégies de gestion intégrée et durable de l’eau. Nous avons mis en oeuvre cette démarche dans le bassin de la Drôme dans le cadre du programme APPEAU financé par l’Agence Nationale de la Recherche (programme " Agriculture et Développement Durable "), et en nous appuyant sur les travaux du programme MIPAIS financé par l’Union Européenne (programme Interreg III Medoc). / The "integrated management of water resources" tries to convey the functioning of the "hydro-systems" which brings together a group of resources and uses of water. This group of resources and uses interacts within a territory, which itself includes various administrative or political units. In order to develop this integrated management, some countries have chosen decentralization: water management is then given to basin institutions within which representatives of the various key interests sit. These institutions emphasize the poor support they get to encourage the dialogue. Available tools emphasize biophysical process but provide a very simplified representation of uses, and particularly of farm uses. These uses are not only linked to water availabilities and to its conditions of access, but also to the technological, economic, and institutional background in which the farmers operate. With the local stakeholders, we suggest to build a model of the system in which they act. At the same time, this model includes the technical, economic, and environmental sides. Therefore, this regional model includes (i) a hydrological model, which enables to assess as input the initial resource availabilities and to measure the impacts of withdrawals, (ii) a biophysical model which enables to assess crop water needs, yields and environmental impacts according to agricultural practices and agro-climatic conditions, and (iii) a technical and economic model which conveys the technical choices of farmers and theirs economic consequences. The construction of the hydrological and biophysical models can be limited to the parameterization of pre-existing models. The technical and economic model of farm activities at the regional scale relies on a typology of farms and of farm production units; its structure has been designed to enable an aggregation and a desegregation of the results between various scales, which provides a detailed analysis of the studied scenarios. The participative construction of the regional model relies on the creation, from the start of the study, of a “steering group” compound of the representatives of local stakeholders. This steering group takes part in the modelling by supplying the necessary data and by validating each stage of the model construction. The model, build and validated by all the stakeholders, can then contribute to help the local or regional decision-makers to develop reasoned scenarios in order to define strategies of integrated and sustainable water management. We have implemented this approach in the Drôme basin within the framework of the APPEAU project funded by the "Agriculture et Développement Durable" program of the French National Research Agency, and by relying on the works of the MIPAIS project funded by the Programme Interreg III Medoc of the European Union. This paper presents the first results obtained

Finite-size and correlation-induced effects in Mean-field Dynamics

The brain's activity is characterized by the interaction of a very large number of neurons that are strongly affected by noise. However, signals often arise at macroscopic scales integrating the effect of many neurons into a reliable pattern of activity. In order to study such large neuronal assemblies, one is often led to derive mean-field limits summarizing the effect of the interaction of a large number of neurons into an effective signal. Classical mean-field approaches consider the evolution of a deterministic variable, the mean activity, thus neglecting the stochastic nature of neural behavior. In this article, we build upon two recent approaches that include correlations and higher order moments in mean-field equations, and study how these stochastic effects influence the solutions of the mean-field equations, both in the limit of an infinite number of neurons and for large yet finite networks. We introduce a new model, the infinite model, which arises from both equations by a rescaling of the variables and, which is invertible for finite-size networks, and hence, provides equivalent equations to those previously derived models. The study of this model allows us to understand qualitative behavior of such large-scale networks. We show that, though the solutions of the deterministic mean-field equation constitute uncorrelated solutions of the new mean-field equations, the stability properties of limit cycles are modified by the presence of correlations, and additional non-trivial behaviors including periodic orbits appear when there were none in the mean field. The origin of all these behaviors is then explored in finite-size networks where interesting mesoscopic scale effects appear. This study leads us to show that the infinite-size system appears as a singular limit of the network equations, and for any finite network, the system will differ from the infinite system