An analytical model for the thermal conductivity of silicon nanostructures

A simple model of thermal conductivity, based on the harmonic theory of solids, is used to study the heat transfer in nanostructures. The thermal conductivity is obtained by summing the contribution of all the vibration modes of the system. All the vibrational properties (dispersion curves and relaxation time) that are used in the model are obtained using the data for bulk samples. The size effeect is taaken into account through the sampling of the Brillouin zone and the distance that a wave vector can travel between two boundaries in the structure. The model is used to predict the thermal conductivity of silicon nanowires and nanofilms, and demonstrates a good agreement with experimental results. Finally, using this model, the quality of the silicon interatomic potential, used for molecular-dynamics simulations of heat transfer, is evaluate

Thermal conductivity and thermal boundary resistance of nanostructures

International audienceWe present a fabrication process of low-cost superlattices and simulations related with the heat dissipation on them. The influence of the interfacial roughness on the thermal conductivity of semiconductor/semiconductor superlattices was studied by equilibrium and non-equilibrium molecular dynamics and on the Kapitza resistance of superlattice's interfaces by equilibrium molecular dynamics. The non-equilibrium method was the tool used for the prediction of the Kapitza resistance for a binary semiconductor/metal system. Physical explanations are provided for rationalizing the simulation results

Détermination expérimentale des paramètres d’un modèle macroscopique de couplage thermique de solides en contact glissant

La détermination du champ de température dans les systèmes comportant des solides en contact et en mouvement relatif est un problème important. En effet, la température des surfaces de contact est un des facteurs prépondérants qui conditionnent leur comportement tribologique. Un modèle de couplage thermique de solides en contact glissant est un outil particulièrement utile pour réaliser des calculs prédictifs. Dans le cadre du GDR 916 CNRS-CNES- SNECMA division SEP concernant le “Comportement des roulements en ambiance cryotechnique”, un cryotribomètre bidisque a été réalisé. Il a permis d’étudier les variations du coefficient de traction en fonction des conditions thermiques ainsi que le modèle de couplage thermique

Diffusion model for austenite formation kinetics during inter-critical annealing of dual-phase steels

cited By 0A numerical solution for the ferrite-to-austenite phase transformation in a ternary iron alloy is proposed that predicts austenite formation during isothermal treatment. As the solution ensures perfect mass conservation of the solutes, it can be applied for long holding times until the system reaches final thermodynamic equilibrium. The solution was validated using previous experimental results on Fe-Ni-Cr alloys. Comparison with experimental data for a low-C, low-alloyed dual-phase steel enabled investigation of the effect of the initial concentration of the substitutional solute in cementite and the dissolution of cementite on the austenite formation kinetics. © 2019 IOP Publishing Ltd

HAEMOGLOBIN MESSENGER RNA

Abstract This is a short review on the isolation and translation in heterologous Systems of a 9 s RNA which carries the information of haemoglobin. Rabbit haemodobin (Hb) messenger RNA (mRNA) was the first eukaryotic genetic message t o be isolated, quite a long time ago (1). This was mainly due t o the fact that mammalian reticulocytes offer the favourable opportunity of being highly specialized cells whose protein synthesis is almost totally concerned with haemoglobin. Haemoglobin mRNA should amount to about 90 % of total polysomal mRNA. Furthermore, and ß globin chains have such lengths that their mRNAs must sediment at approximately 9s. Isolation of the latter by sucrose gradient centrifugation was therefore quite easy (Hb mRNA must sediment between the 4 s region and the 18s ribosomal RNA region if one analyzes total reticulocyte polysomal RNA). These criteria and others allowed us to isolate from rabbit reticulocyte polyribosomes a 9 s RNA fraction presenting several properties the globin mRNA must possess (1) (2). The putative mRNA could also be detached as a specific 1 4 s ribonucleoprotein when polyribosomes were dissociated by EDTA or CMC treatment (3). This 14s mRNP has been extensively studied in our laboratory (4) and its obtention now constitutes the first step in the preparation of 9s Hb mRNA. But the definitive proof that the 9 s RNA fraction was or contained Hb message could only be obtained if this RNA would direct Hb synthesis when added to an heterologous protein synthesizing system. A preliminary indication in this direction was obtained by SCHAPIRA and coworkers (5) but the first clearcut result was presented by LOCKARD and LINGREL in 1969 (6). They added mouse polysomd 9 s RNA to a rabbit reticulocyte cell-free system and identified the mouse globin P chain in the synthesized products. Somewhat later, GURDON and coworkers showed that 9 s rabbit reticulocyte RNA could be extensively translated into a and 0 globin chains when injected into frog oocytes (7). Translation could proceed for several days. The synthesized ~r o d u c t s were characterized by gel filtration, ion exchange chromatography (7) and finger printing (8). JONES and LINGREL also showed that the 9 s RNA fraction isolated from mouse reticulocyte polyribosomes

3D simulation of a power ramp including oxygen thermo-diffusion and its impact on thermochemistry

International audienceThis paper presents the coupling of the thermochemical solver ANGE (Advanced Gibbs Energy Minimizer) with an oxygen thermo-diffusion model. The coupling is implemented within the fuel performance code ALCYONE co-developed by CEA, EDF and FRAMATOME within the PLEIADES environment. An application to a 3D simulation of a power ramp on a Cr-doped UO 2 fuel is developed. Post-ramp EPMA measurements of chromia doped fuel show reduction of chromium and molybdenum oxides in the central part of the pellet, indicative of thermo-diffusion of oxygen. These phenomena are well reproduced by the coupled thermo-chemical-mechanical simulations. Impact of oxygen redistribution on speciation of fission products is then studied. Chemical state of caesium, iodine and tellurium is important as regard PCI, as they can form gaseous species (CsI$_{(g),}$ I $_{(g),}$ I$_{(2g),}$ TeI$_{(2g)}$) that can react with the cladding and induce SCC. Release of gaseous species and concentration of chemically reactive iodine compounds near the cladding are calculated in order to investigate I-SCC