Learning of chemistry of solution with help of computer simulation

Le présent article rend compte d'une expérimentation utilisant des simulations informatiques de titrages acide-base dans des situations didactiques d'apprentissage basées sur l'investigation et la participation de l'apprenant dans la construction de son savoir. Deux approches dans l'utilisation des simulations de titrages pH-métriques à l'aide du logiciel «SIMULTI2» sont mises en place et évaluées avec un groupe d'enseignants en formation continue et un groupe d'élèves-professeurs en formation initiale. On montre que les simulations informatiques créent un contexte pédagogique favorisant l'apprentissage par la découverte ou l'exploration basée sur les conflits cognitifs

An efficient algorithm to calculate intrinsic thermoelectric parameters based on Landauer approach

The Landauer approach provides a conceptually simple way to calculate the intrinsic thermoelectric (TE) parameters of materials from the ballistic to the diffusive transport regime. This method relies on the calculation of the number of propagating modes and the scattering rate for each mode. The modes are calculated from the energy dispersion (E(k)) of the materials which require heavy computation and often supply energy relation on sparse momentum (k) grids. Here an efficient method to calculate the distribution of modes (DOM) from a given E(k) relationship is presented. The main features of this algorithm are, (i) its ability to work on sparse dispersion data, and (ii) creation of an energy grid for the DOM that is almost independent of the dispersion data therefore allowing for efficient and fast calculation of TE parameters. The inclusion of scattering effects is also straight forward. The effect of k-grid sparsity on the compute time for DOM and on the sensitivity of the calculated TE results are provided. The algorithm calculates the TE parameters within 5% accuracy when the K-grid sparsity is increased up to 60% for all the dimensions (3D, 2D and 1D). The time taken for the DOM calculation is strongly influenced by the transverse K density (K perpendicular to transport direction) but is almost independent of the transport K density (along the transport direction). The DOM and TE results from the algorithm are bench-marked with, (i) analytical calculations for parabolic bands, and (ii) realistic electronic and phonon results for $Bi_{2}Te_{3}$.Comment: 16 Figures, 3 Tables, submitted to Journal of Computational electronic

Cross-plan Si/SiGe superlattice acoustic and thermal properties measurement by picosecond ultrasonics

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Thermoelectric quadrupole of a leg to model transient state

International audienceThe transient heat transfer in a thermoelectric leg is modelled. The Thomson effect is into account, whereas it is often neglected in other studies. Thanks to the expressions of the temperature and the heat flux expressed in the Laplace domain, a semi-analytical technique, the so-called quadrupole method is performed. No mesh is required. The whole matrix formulation is given for different initial conditions. It will allow, for instance, to evaluate easily the efficiency or the coefficient of performance of the thermoelement or use it as inverse method, for instance, to perform estimations

Harmonic regime analysis and inverse method applied to the simultaneous determination of thermoelectric properties

An AC harmonic analysis of thermoelectric phenomena is presented in this work. It deals with the modification of the suspended sample configuration used in the Harman method, by using pure sine wave electrical excitation. Heat transfer in the sample and its interfaces are described using the thermal quadrupoles method. The fundamental harmonic response in the sample voltage is analytically calculated. The model sensitivity coefficients show that all the properties concerned in the figure of merit i.e. the Seebeck coefficient, the thermal conductivity and the electric resistivity can be simultaneously estimated. This is a novel skill in thermoelectrics properties characterization. Main aspects for an optimal experimental design in an inverse problem point of view are given. The advantages of the harmonic regime upon the classical DC regime are studied in detai

Harmonic regime analysis and inverse method applied to the simultaneous determination of thermoelectric properties

International audienceAn AC harmonic analysis of thermoelectric phenomena is presented in this work. It deals with the modification of the suspended sample configuration used in the Harman method, by using pure sine wave electrical excitation. Heat transfer in the sample and its interfaces are described using the thermal quadrupoles method. The fundamental harmonic response in the sample voltage is analytically calculated. The model sensitivity coefficients show that all the properties concerned in the figure of merit i.e. the Seebeck coefficient, the thermal conductivity and the electric resistivity can be simultaneously estimated. This is a novel skill in thermoelectrics properties characterization. Main aspects for an optimal experimental design in an inverse problem point of view are given. The advantages of the harmonic regime upon the classical DC regime are studied in detai

Determination of Thermophysical Properties of Si/SiGe Superlattices with a Pump-Probe Technique

A Time Domain Thermo-Reflectance technique (TDTR) is used for the non-destructive evaluation of thermal and acoustic properties of Si/SiGe superlattices (SL) at room temperature. In particular, this technique allows the determination of the SL cross-plan thermal conductivity, the thermal boundary resistance at the interface between the metallic film and the SL, and the longitudinal sound velocity inside the SL. We discuss the effect of both transducer thickness and pump power on the measurements and then on values of the extracted thermophysical properties of the superlattice