Non-Equilibrium Statistical Mechanics of Anharmonic Chains Coupled to Two Heat Baths at Different Temperatures

We study the statistical mechanics of a finite-dimensional non-linear Hamiltonian system (a chain of anharmonic oscillators) coupled to two heat baths (described by wave equations). Assuming that the initial conditions of the heat baths are distributed according to the Gibbs measures at two different temperatures we study the dynamics of the oscillators. Under suitable assumptions on the potential and on the coupling between the chain and the heat baths, we prove the existence of an invariant measure for any temperature difference, i.e., we prove the existence of steady states. Furthermore, if the temperature difference is sufficiently small, we prove that the invariant measure is unique and mixing. In particular, we develop new techniques for proving the existence of invariant measures for random processes on a non-compact phase space. These techniques are based on an extension of the commutator method of H\"ormander used in the study of hypoelliptic differential operators.Comment: 43 page

Entropy Production in Non-Linear, Thermally Driven Hamiltonian Systems

We consider a finite chain of non-linear oscillators coupled at its ends to two infinite heat baths which are at different temperatures. Using our earlier results about the existence of a stationary state, we show rigorously that for arbitrary temperature differences and arbitrary couplings, such a system has a unique stationary state. (This extends our earlier results for small temperature differences.) In all these cases, any initial state will converge (at an unknown rate) to the stationary state. We show that this stationary state continually produces entropy. The rate of entropy production is strictly negative when the temperatures are unequal and is proportional to the mean energy flux through the system

Bioceramics: spark plasma sintering (SPS) of calcium phosphates

Calcium phosphates (Ca-P) are major constituents of calcified tissues, and are also extensively used for the elaboration of biomaterials. However, the usual high-temperature sintering processes generally lead to strong alterations of their chemical, physical and biological properties. Spark plasma sintering (SPS) is a non-conventional sintering technique based on the use of pulsed current, enabling fast heating and cooling rates, and lower sintering temperatures are often observed. The sintering of several orthophosphates (DCPD, amorphous TCP, beta-TCP, OCP, HA and biomimetic nanocrystalline apatites) by SPS was investigated in order to track potential advantages of this technique over usual Ca-P sintering methods. Special attention was given to the SPS consolidation of highly bioactive nanocrystalline apatites

Intermediate Exchange Rate Regimes in Emerging Economies: The Case of Morocco

In this paper, we estimate the relative weights of each foreign currency in the basket of currencies comprising the dirham for the period 1973-2003 on monthly data. We show that before the advent of the euro, the exchange rate regime in Morocco was a "Crawling Basket (basket slippery). This basket reflects quite well the geographical distribution of foreign trade of the country, but also takes into account denominated debt. The birth of the euro has led, after 1999, a profound change in the exchange rate policy in Morocco. On the one hand, the automatic component of the adjustment of the exchange rate of dirham: slipping according to the inflation differential between Morocco and its partners has been abandoned; domestic inflation has been stabilized at a level comparable to that of developed economies. On the other hand, the substitution of European national currencies by the euro, synonymous with a decrease in the variety of currencies used in the composition of the basket, the tradeoff between stabilizing the debt burden and maintaining external competitiveness vis-à-vis European trade partners, have led the monetary Moroccan authorities to diversify the composition of the basket by introducing new currencies outside the European area, it is the British Pound and perhaps Franc Switzerland.Exchange rates, currency basket, policy shift

Managing tensions between evaluation and research: illustrative cases of developmental evaluation in the context of research

Developmental evaluation (DE), essentially conceptualized by Patton over the past 30 years, is a promising evaluative approach intended to support social innovation and the deployment of complex interventions. Its use is often justified by the complex nature of the interventions being evaluated and the need to produce useful results in real time. Despite its potential advantages, DE appears not to have been very widely used in research. The authors of this article decided to use this emergent approach in two evaluative research projects in health promotion. This article, coming out of their experiences, aims to assess the appropriateness of DE in research and describes issues related to its use. First, DE is presented, along with the potential advantages of its use in research. This is followed by a discussion of tensions related its application encountered in two studies carried out by the authors. The key issues are related to the links between academic and evaluative objectives, the dual role of researcher and consultant, and the temporality of the process. Finally, weighing the advantages of DE against its challenges, the authors conclude with a diagnosis regarding the application of this approach in research

Simulation numérique d'un écoulement de convection mixte en aval d'une marche

International audienceDes expériences numériques d'un écoulement en aval d'une marche horizontale sont menées en régime laminaire instationnaire, afin d'étudier les mécanismes thermodynamiques générés par la convection mixte dans un canal bidimensionnel de géométrie fixe. On se propose de quantifier l'influence de divers écarts de température dT entre la température de la base du canal et la température du fluide entrant. En analysant l'évolution temporelle de la température, on constate que l'écoulement est stationnaire lorsque dT est inférieur à 4 K, puis est périodique aux alentours de 5 K. Au-delà de cette valeur, le signal temporel de la température montre un comportement apériodique

Percutaneous balloon angioplasty in an infant with obstructed total anomalous pulmonary vein return

This is a report of successful dilation of stenosis of the common trunk in a case of total anomalous pulmonary vein return into the left superior vena cava in a 3 month old infant. Percutaneous angioplasty was performed with a 6 mm diameter balloon catheter. Right ventricular systolic pressure decreased from 96 to 60 mm Hg, mean pulmonary vein pressure decreased from 26 to 14 mm Hg and left ventricular systolic pressure increased from 70 to 90 mm Hg

Nanocrystalline apatites: From powders to biomaterials

Non-stoichiometric nanocrystalline apatite powders are used to elaborate highly-bioactive biomaterials. Their exceptional surface reactivity arises from a structured but rather unstable hydrated layer involving ions in nonapatitic chemical environments, like in bone mineral. The initial powder characteristics can be tailored through precipitation parameters (pH, temperature, maturation time in solution). The drying of nanocrystalline apatite suspensions at very low temperature (4 °C) leads to ceramic-like materials exhibiting average mechanical properties (compressive strength 54 MPa) and a high porosity which could be exploited to entrap active organic compounds (e.g. growth factors). The consolidation at 150–200 °C of nanocrystalline apatite powders has also been studied using uni-axial pressing and spark plasma sintering (SPS). The results indicate only a limited alteration of the initial nanocrystals, and the bioceramics obtained show mechanical properties close to those reached with sintered stoichiometric HA. The high ion mobility in the hydrated layer of the nanocrystals can lead to “crystal fusion” processes. This capability to favor crystal–crystal interactions at low temperature, while preserving the non-stoichiometry and nanometer dimensions of apatite crystals, opens interesting perspectives for the elaboration of new resorbable and highly-bioactive bioceramics

Biomimetic apatite sintered at very low temperature by spark plasma sintering: Physico-chemistry and microstructure aspects

Nanocrystalline apatites analogous to bone mineral are very promising materials for the preparation of highly bioactive ceramics due to their unique intrinsic physico-chemical characteristics. Their surface reactivity is indeed linked to the presence of a metastable hydrated layer on the surface of the nanocrystals. Yet the sintering of such apatites by conventional techniques, at high temperature, strongly alters their physico-chemical characteristics and biological properties, which points out the need for "softer" sintering processes limiting such alterations. In the present work a non-conventional technique, spark plasma sintering, was used to consolidate such nanocrystalline apatites at non-conventional, very low temperatures (T° < 300 °C) so as to preserve the surface hydrated layer present on the nanocrystals. The bioceramics obtained were then thoroughly characterized by way of complementary techniques. In particular, microstructural, nanostructural and other major physico-chemical features were investigated and commented on. This work adds to the current international concern aiming at improving the capacities of present bioceramics, in view of elaborating a new generation of resorbable and highly bioactive ceramics for bone tissue engineering

Intérêt public, intérêt privé et discrimination

Nous considérons un service à qualité variable dont chaque usager consomme au plus une unité. Les coûts de production, fixe et variable, ne dépendent pas de la qualité : améliorer, dans certaines limites, la qualité, n’augmente pas les coûts de production. Chaque usager cependant apprécie d’autant plus le service que celui-ci est de meilleure qualité : la propension à payer de l’usager est une fonction linéaire croissante de la qualité du service.Chaque usager est seul à connaître sa propre propension à payer, alors que la distribution des propensions est connue de tous, producteurs et consommateurs. Nous étudions comment et pourquoi, dans ces conditions, une discrimination par les prix et les qualités peut être pratiquée par les producteurs. Nous montrons qu’un monopole recherchant la maximisation de son profit ne pratiquera pas de discrimination; en revanche, dans un large champ de situation, il n’est possible d’atteindre un optimum de Pareto sous contraintes — informationnelle et financière — qu’en discriminant : le gain qu’apporte la discrimination en tant que mécanisme d’autosélection l’emporte sur le gaspillage qu’il y a à produire au même coût une qualité moindre.Nous reformulons enfin notre modèle pour élargir son domaine d’application à des questions telles que la tarification de l’accès à un réseau téléphonique, le marchandage dans un contexte d’achats répétés, etc.We consider a service whose quality is variable and from which every consumer consumes either one unit or nothing. Production costs, both fixed and variable, do not depend on quality: a higher quality service is no more costly to produce than a lower quality one. On the consumption side however, higher quality is preferred: a consumer's willingness-to-pay for one unit of the service is an increasing and linear function of the service quality.A consumer's willingness-to-pay is private information to him, whereas the corresponding distribution over all consumers is public information, hence known to the producers. In this setting we investigate why and how producers might use price and quality discrimination. We show that a profit-maximising monopolist will not discriminate, whereas it is often the case that reaching a constrained Pareto optimum will not be possible without some recourse—which we precisely define—to discrimination: the improvement in welfare thus brought by self-selection is worth some waste of quality.In the last section we reformulate our model in order to include in the analysis such topics as network access pricing, selling strategies when buying is repeated, etc