Rate of Converrgence for ergodic continuous Markov processes : Lyapunov versus Poincare

We study the relationship between two classical approaches for quantitative ergodic properties : the first one based on Lyapunov type controls and popularized by Meyn and Tweedie, the second one based on functional inequalities (of Poincar\'e type). We show that they can be linked through new inequalities (Lyapunov-Poincar\'e inequalities). Explicit examples for diffusion processes are studied, improving some results in the literature. The example of the kinetic Fokker-Planck equation recently studied by H\'erau-Nier, Helffer-Nier and Villani is in particular discussed in the final section

Mass or heat transfer inside a spherical gas bubble at low to moderate Reynolds number

Mass (or heat) transfer inside a spherical gas bubble rising through a stationary liquid is investigated by direct numerical simulation. Simulations were carried out for bubble Reynolds number ranging from 0.1 to 100 and for Péclet numbers ranging from 1 to 2000. The study focuses on the effect of the bubble Reynolds number on both the interfacial transfer and the saturation time of the concentration inside the bubble. We show that the maximum velocity Umax at the bubble interface is the pertinent velocity to describe both internal and external transfers. The corresponding Sherwood (or Nusselt) numbers and the saturation time can be described by a sigmoid function depending on the Péclet number Pemax = Umaxdb/D (db and D being the bubble diameter and the corresponding diffusion coefficient)

Experiments and modelling of a draft tube airlift reactor operated at high gas throughputs

One-dimensional modelling of global hydrodynamics and mass transfer is developed for an annulus sparged draft tube airlift reactor operating at high gas throughputs. In a first part, a specific closure law for the mean slip velocity of bubbles in the riser is proposed according for, in one hand, the collective effects on bubble rise velocity and, in the other hand, the size of the liquid recirculation in the airlift riser. This global hydrodynamics model is found towel explain the global gas volume fraction measurements in the airlift riser for a wide range of superficial gas velocity (0.6 ≤ Jg ≥10 cm sˉ¹). In a second part, mass transfer in the airlift has been studied by using the gassing-out method and a dual-tip optical probe to measure the bubble size distributions. As for bubble columns, in such airlift, the volumetric mass transfer coefficient appears to be quite proportional to the gas superficial velocity. Finally, as in Colombet et al. (2011), mass transfer at the bubble scale seems to be weakly influenced by an increase of gas volume fraction

Experiments and modelling of a draft tube airlift reactor operated at high gas throughputs

One-dimensional modelling of global hydrodynamics and mass transfer is developed for an annulus sparged draft tube airlift reactor operating at high gas throughputs. In a first part, a specific closure law for the mean slip velocity of bubbles in the riser is proposed according for, in one hand, the collective effects on bubble rise velocity and, in the other hand, the size of the liquid recirculation in the airlift riser. This global hydrodynamics model is found towel explain the global gas volume fraction measurements in the airlift riser for a wide range of superficial gas velocity (0.6 ≤ Jg ≥10 cm sˉ¹). In a second part, mass transfer in the airlift has been studied by using the gassing-out method and a dual-tip optical probe to measure the bubble size distributions. As for bubble columns, in such airlift, the volumetric mass transfer coefficient appears to be quite proportional to the gas superficial velocity. Finally, as in Colombet et al. (2011), mass transfer at the bubble scale seems to be weakly influenced by an increase of gas volume fraction

Theory for planetary exospheres: III. Radiation pressure effect on the Circular Restricted Three Body Problem and its implication on planetary atmospheres

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the stellar radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this third paper, we investigate the effect of the stellar radiation pressure on the Circular Restricted Three Body Problem (CR3BP), called also the photogravitational CR3BP, and its implication on the escape and the stability of planetary exospheres, especially for Hot Jupiters. In particular, we describe the transformation of the equipotentials and the location of the Lagrange points, and we provide a modified equation for the Hill sphere radius that includes the influence of the radiation pressure. Finally, an application to the hot Jupiter HD 209458b reveals the existence of a blow-off escape regime induced by the stellar radiation pressure

Theory for planetary exospheres: I. Radiation pressure effect on dynamical trajectories

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this first paper, we present the complete exact solutions of particles trajectories, which are not conics, under the influence of the solar radiation pressure. This problem was recently partly solved by Lantoine and Russell (2011) and completely by Biscani and Izzo (2014). We give here the full set of solutions, including solutions not previously derived, as well as simpler formulations for previously known cases and comparisons with recent works. The solutions given may also be applied to the classical Stark problem (Stark,1914): we thus provide here for the first time the complete set of solutions for this well-known effect in term of Jacobi elliptic functions

Distribution of Avalanches on the (n,k)-wheel

This paper deals with the sandpile model on the wheel, a lattice with particular boundary conditions. It presents how transducers applied to the language of recurrent configurations of the abelian sandpile model can help determining critical exponents of the underlying model. We present exact results for the avalanche distribution on the simple wheel, and give some clues for the multiple one where strange phenomena happen

Height-arrow Model

We study in this article the characteristics of the so-called Height-Arrow Model (HAM), introduced by physicists as an extension of the Abelian Sandpile Model and the Eulerian Walker. We show that recurrent configurations of this model form an Abelian group and that classical algorithms such as the recurrence criterion or the burning algorithm for the ASM could be extended to the HAM

Pilotage des flux communicationnels du centre e-learning HES-SO Cyberlearn

Le but de ce travail consiste à amener une réponse à la question de recherche suivante : « Où se situent les flux de communication du centre par rapport à ceux d’autres universités en matière de e-learning et comment développer un outil de pilotage qui permettra de résoudre la problématique ? »

Approches soignantes lors de troubles du sommeil associés aux troubles neurocognitifs chez l'aîné institutionnalisé: revue de la littérature

La prévalence des troubles du sommeil chez l’aîné ne cesse d’augmenter. Ces troubles se péjorent avec l’institutionnalisation et risquent de s’aggraver lorsqu’ils sont associés à des troubles neurocognitifs. Cependant, les troubles du sommeil peuvent passer inaperçus en regard de la modification normale de l’architecture du sommeil chez les aînés. Ainsi, ils ne sont ni diagnostiqués, ni traités. Le but de cette revue de la littérature est de déterminer quels pourraient être les moyens non pharmacologiques utiles et efficaces pour traiter ces troubles pour ainsi réinstaurer une qualité de sommeil chez les résidents tout en réduisant l’utilisation de benzodiazépines. Différentes bases de données consultées de 2016 à 2017 ainsi que l’association de mots clés ont permis d’obtenir des recherches de qualité. Au total, six études sont retenues et répondent aux critères d’inclusion suivants : la présence de troubles du sommeil et des moyens thérapeutiques utilisés. Les principaux résultats évoquent la haute prévalence de troubles du sommeil associés ou non à une démence de type Alzheimer. L’utilisation chronique et abusive de benzodiazépines chez les aînés institutionnalisés atteints d’insomnie est aussi relevée. Finalement, les auteurs soulignent la méconnaissance d’approches non pharmacologiques avec cependant une bonne efficacité si celles-ci sont employées de manière adéquate. En conclusion, il est ressorti que l’utilisation d’approches non pharmacologiques est peu utilisée car elles sont méconnues. Il est donc nécessaire d’approfondir les connaissances et les formations concernant ces moyens thérapeutiques afin de diminuer l’utilisation chronique de benzodiazépines