A new chemodynamical tool to study the evolution of galaxies in the local Universe: a quick and accurate numerical technique to compute gas cooling rate for any chemical composition

We have developed a quick and accurate numerical tool to compute gas cooling whichever its chemical composition.Comment: 3 pages, 2 figures, to appear in the Proceedings of "Heating vs. Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching (Germany), Eds. Boehringer, Schuecker, Pratt, Finoguenov, Springer-Verlag series "ESO Astrophysics Symposia

A new chemodynamical tool to study the evolution of galaxies in the local Universe

We present some preliminary results obtained with a new galactic chemodynamical tool under development. In the framework of non-instantaneous recycling approach, we follow the interactions due to star formation and feedback processes. One of the main original features of our code is that we record the abundance evolution of several chemical elements. This allows us to build cooling functions dependent on the real abundances of individual elements. We illustrate the need for such metal-dependent cooling functions using a toy model made of a star cluster embedded in a two-phase gas cloud. Our results suggest that computing cooling rates according to individual abundances of chemical elements can influence the star formation rate.Comment: 6 pages, 4 figures, to appear in the proceedings of the CRAL-Conference Series I "Chemodynamics: from first stars to local galaxies", Lyon 10-14 July 2006, France, Eds. Emsellem, Wozniak, Massacrier, Gonzalez, Devriendt, Champavert, EAS Publications Serie

Cartographier des controverses pour apprendre la complexité des technosciences : l'étude des gaz de schiste en lycée agricole

Version longueInternational audienceCet article rend compte de l'adaptation à l'enseignement secondaire agricole de l'exercice universitaire de la cartographie des controverses. Les élèves de deux classes de première ont cartographié par groupe un corpus de documents relatifs à la problématique des gaz de schiste. Cette recherche vise à décrire et comprendre la manière dont les élèves ont représenté la complexité de la question socialement vive investiguée. L'analyse des cartes montre que la production de catégories permettant de structurer les informations sélectionnées est problématisée par les élèves, bien que la dichotomie « pour » / « contre » le gaz de schiste soit majoritairement utilisée par les élèves. L'analyse des cartes montre par contre que les informations sélectionnées sont faiblement problématisées, car elles sont peu mises en réseau et sont parfois contradictoires d'une carte à l'autre. Des perspectives sont ensuite données, tant du point de vue de la poursuite de l'ingénierie pédagogique que des questions de recherche qu'elle soulève

Aggregation of multiple prior opinions.

Experts are asked to provide their advice in a situation of uncertainty. They adopt the decision maker’s utility function, but each has a potentially different set of prior probabilities, and so does the decision maker. The decision maker and the experts maximize the minimal expected utility with respect to their sets of priors. We show that a natural Pareto condition is equivalent to the existence of a set Λ of probability vectors over the experts, interpreted as possible allocations of weights to the experts, such that (i) the decision maker’s set of priors is precisely all the weighted-averages of priors, where an expert’s prior is taken from her set and the weight vector is taken from Λ; (ii) the decision maker’s valuation of an act is the minimal weighted valuation, over all weight vectors in Λ, of the experts’ valuations.Aggregation of opinions, Ambiguity, Multiple priors;

Experimental evidence of a hydrodynamic soliton gas

We report on an experimental realization of a bi-directional soliton gas in a 34~m-long wave flume in shallow water regime. We take advantage of the fission of a sinusoidal wave to inject continuously solitons that propagate along the tank, back and forth. Despite the unavoidable damping, solitons retain adiabatically their profile, while decaying. The outcome is the formation of a stationary state characterized by a dense soliton gas whose statistical properties are well described by a pure integrable dynamics. The basic ingredient in the gas, i.e. the two-soliton interaction, is studied in details and compared favourably with the analytical solutions of the Kaup-Boussinesq integrable equation. High resolution space-time measurements of the surface elevation in the wave flume provide a unique tool for studying experimentally the whole spectrum of excitations.Comment: accepted for publication in Physical Review Letter

How performing a mental arithmetic task modify the regulation of centre of foot pressure displacements during bipedal quiet standing.

We investigated the effect of performing a mental arithmetic task with two levels of difficulty on the regulation of centre of foot pressure (COP) displacements during bipedal quiet standing in young healthy individuals. There was also a control condition in which no concurrent task was required. A space-time-domain analysis showed decreased COP displacements, along the antero-posterior axis, when participants concurrently performed the most difficult mental arithmetic task. Frequency-domain and stabilogram-diffusion analyses further suggested these decreased COP displacements to be associated with an increased stiffness and a reduction of the exploratory behaviours in the short term, respectively

The theory of photorefractive resonance for localized beams in two-carrier photorefractive systems

This paper extends the existing theory of two carrier photorefractivity resonance, which is generally applied to Iron doped Indium Phosphide (InP:Fe), to the case of low non-harmonic illumination. The space charge field profile is computed, and the variations of its amplitude, width and position are determined as functions of the background intensity. The effect of photorefractive resonance on these quantities is evidenced, contributing to the understanding of published experimental results in InP:Fe.Comment: Physical Review A: Atomic, Molecular and Optical Physics Accepted (2009) To be publishe

On the concatenated structures of a [49, 18, 12] binary abelian code

AbstractWe here introduce a new formalism for describing concatenated codes. Using this formalism, we show how any generalized concatenated code can be viewed as a first order concatenated code. Finally, we give an illustrative example: using Jensen's result (1985) which shows that any abelian code has a generalized concatenated structure, we first give the representation of the [49, 18, 12] abelian code introduced by Camion (1971) as a second order concatenated code; then using our description, we show that this code is also equal to the first order concatenation of two linear cyclic codes