Connecting dispersion models and wall temperature prediction for laminar and turbulent flows in channels

In a former paper, Drouin et al. (2010) proposed a model for dispersion phenomena in heated channels that works for both laminar and turbulent regimes. This model, derived according to the double averaging procedure, leads to satisfactory predictions of mean temperature. In order to derive dispersion coefficients, the so called ‘‘closure problem’’ was solved, which gave us access to the temperature deviation at sub filter scale. We now propose to capitalize on this useful information in order to connect dispersion modeling to wall temperature prediction. As a first step, we use the temperature deviation modeling in order to connect wall to mean temperatures within the asymptotic limit of well established pipe flows. Since temperature in wall vicinity is mostly controlled by boundary conditions, it might evolve according to different time and length scales than averaged temperature. Hence, this asymptotic limit provides poor prediction of wall temperature when flow conditions encounter fast transients and stiff heat flux gradients. To overcome this limitation we derive a transport equation for temperature deviation. The resulting two-temperature model is then compared with fine scale simulations used as reference results. Wall temperature predictions are found to be in good agreement for various Prandtl and Reynolds numbers, from laminar to fully turbulent regimes and improvement with respect to classical models is noticeable

Quelle indemnisation chômage pour les intermittents du spectacle?:Modélisation et évaluation d'un régime alternatif

Ce travail vise à étudier les effets de différents dispositif en matière d’indemnisation des intermittents du spectacle. Il s’agit à partir d’une modélisation et des données de la Caisse des congés spectacles (sur les contrats, les salaires, les durées d’emploi, les périodes de non emploi des intermittents), de mesurer les différences entre ces dispositifs en matière d’effectifs concernés, de cotisations perçues et d’allocations versées par l’assurance chômage. Pourquoi travailler sur les données de la Caisse des congés spectacles plutôt que sur celles de l’UNEDIC ? Parce que leur périmètre est plus large et qu’elles permettent de prendre en compte non seulement les intermittents indemnisés par Pôle Emploi mais aussi ceux qui ne le sont pas mais pourraient l’être en cas de changement des règles d’éligibilité (...)

Structural Optimization with FreeFem++

International audienceThe aim of this paper is to show that relatively small, simple and efficient shape optimization routines can be written using the free finite element software \texttt{FreeFem++}.This is illustrated by the implementation of two classical methods: the boundary variation method and the homogenization one.Even though these routines are simple enough so that their implementation can be assigned (partially or totally) as homework to graduate students, they yield results accurate enough to be useful tools for engineers orresearchers

Circadian glomerular function: from physiology to molecular and therapeutical aspects

Life on earth is rhythmic by essence due to day/night alternation, and many biological processes are also cyclic. The kidney has a special role in the organism, controlling electrolytes and water balance, blood pressure, elimination of metabolic waste and xenobiotics and the production of several hormones. The kidney is submitted to changes throughout 24 h with periods of intense activity followed by calmer periods. Filtration, reabsorption and secretion are the three components determining renal function. Here, we review circadian changes related to glomerular function and proteinuria and emphasize the role of the clock in these processe

ALTITUDE AND FOOTBALL: WHAT ARE NEW METHODS AND OPPORTUNITIES TO MAXIMIZE PLAYERS' FITNESS?

International audiencePlaying football competition at terrestrial altitude is not an isolated phenomenon. For instance, eight of the last 19 football FIFA World Cup tournaments were hosted by countries located at low-to-moderate altitude. While football-required fitness and technical qualities are affected by the development of neuromuscular fatigue at sea level, hypoxia-induced decrease in convective oxygen transport further hinders the aerobic capacity but also the ability to perform consecutive sprints, eventually impacting the outcome of a game. This results from the decrease in partial pressure of oxygen which reduces maximal aerobic power. The later, in turn, increases the relative intensity of any given absolute level of work, potentially delaying recovery of high-energy phosphates between high-intensity intermittent efforts. Despite reduction in air resistance (caused by the decrease in air density) could facilitate high-velocity running, it can also alter drag and lift, thereby impairing sensorimotor skills. Conversely, altitude/hypoxic training could help footballers preparing for competition at altitude, but also at sea level. Traditional altitude training camps involve chronic exposure to low-to-moderate terrestrial or simulated altitudes (14%) for improving oxygen-carrying capacity. While "live high-train high" or "live high-train low" paradigms are actually implemented by many elite club or national team football squads, the benefits they may have on (repeated-) sprint performance are still debated. The development of hypoxic technologies has led to the emergence of "live low-train high" methods, in isolation (i.e., the "repeated-sprint training in hypoxia" and "resistance training in hypoxia") or in combination with hypoxic/altitude residence (i.e., "live high-train low and high"). Today, the panorama of altitude/hypoxic training methods is wider than ever and includes also practices such as "blood flow restriction" or "ischemic preconditioning", which demonstrate encouraging preliminary results. The aims of this chapter are twofold: First, to summarize the effects of acute altitude/hypoxia exposure on football-specific qualities measured in the laboratory and/or during games at terrestrial altitude. Second, to discuss the potential benefits of each altitude/hypoxic training method in respect to sport-specific physiological and fitness development and/or in-game performance

Complete mapping of the spin-wave spectrum in vortex state nano-disk

We report a study on the complete spin-wave spectrum inside a vortex state nano-disk. Transformation of this spectrum is continuously monitored as the nano-disk becomes gradually magnetized by a perpendicular magnetic field and encouters a second order phase transition to the uniformly magnetized state. This reveals the bijective relationship that exists between the eigen-modes in the vortex state with the ones in the saturated state. It is found that the gyrotropic mode can be continuously viewed as a uniform phase precession, which uniquely softens (its frequency vanishes) at the saturation field to transform above into the Kittel mode. By contrast the other spin-wave modes remain finite as a function of the applied field while their character is altered by level anti-crossing

Comparative Measurements of Inverse Spin Hall and Magnetoresistance in YIG|Pt and YIG|Ta

We report on a comparative study of spin Hall related effects and magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements allow to estimate the characteristic transport parameters of both Pt and Ta layers juxtaposed to YIG: the spin mixing conductance $G_{\uparrow \downarrow}$ at the YIG$|$normal metal interface, the spin Hall angle $\Theta_{SH}$, and the spin diffusion length $\lambda_{sd}$ in the normal metal. The inverse spin Hall voltages generated in Pt and Ta by the pure spin current pumped from YIG excited at resonance confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we extract the spin diffusion length in Ta, found to be $\lambda_{sd}^\text{Ta}=1.8\pm0.7$ nm. Both the YIG|Pt and YIG|Ta systems display a similar variation of resistance upon magnetic field orientation, which can be explained in the recently developed framework of spin Hall magnetoresistance.Comment: 8 pages, 5 figures, 1 tabl

Detection of the microwave spin pumping using the inverse spin Hall effect

We report electrical detection of the dynamical part of the spin pumping current emitted during ferromagnetic resonance (FMR) using the inverse Spin Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The choice of YIG, a magnetic insulator, ensures that no charge current flows between the two layers and only pure spin current produced by the magnetization dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin pumping. To avoid measuring the parasitic eddy currents induced at the frequency of the microwave source, a resonance at half the frequency is induced using parametric excitation in the parallel geometry. Triggering this nonlinear effect allows to directly detect on a spectrum analyzer the microwave component of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession angles of a couple of degrees. This direct detection provides a novel efficient means to study magnetization dynamics on a very wide frequency range with great sensitivity