Monte Carlo transient phonons transport in silicon and germanium at nanoscales

Heat transport at nanoscales in semiconductors is investigated with a statistical method. The Boltzmann Transport Equation (BTE) which characterize phonons motion and interaction within the crystal lattice has been simulated with a Monte Carlo technique. Our model takes into account media frequency properties through the dispersion curves for longitudinal and transverse acoustic branches. The BTE collisional term involving phonons scattering processes is simulated with the Relaxation Times Approximation theory. A new distribution function accounting for the collisional processes has been developed in order to respect energy conservation during phonons scattering events. This non deterministic approach provides satisfactory results in what concerns phonons transport in both ballistic and diffusion regimes. The simulation code has been tested with silicon and germanium thin films; temperature propagation within samples is presented and compared to analytical solutions (in the diffusion regime). The two materials bulk thermal conductivity is retrieved for temperature ranging between 100 K and 500 K. Heat transfer within a plane wall with a large thermal gradient (250 K-500 K) is proposed in order to expose the model ability to simulate conductivity thermal dependence on heat exchange at nanoscales. Finally, size effects and validity of heat conduction law are investigated for several slab thicknesses

Protection of stainless-steels against corrosion in sulphidizing environments by Ce oxide coatings: X-ray absorption and thermogravimetric studies

In this paper a study is reported concerning ceramic coatings containing cerium oxide, prepared by the sol-gel method, used to protect Incoloy 800H against sulphidation. When the coating is sintered in air at 850°C good protection is obtained. In an X-ray absorption spectroscopic study of the coatings it was observed that the best protective coating contains all cerium as CeIV after pretreatment. After sulphidizing cerium was reduced to CeIII. Possible mechanisms to explain the protective properties are discussed

Modeling semi-conductor thermal properties. The dispersion role

We study heat transport in semiconductor nanostructures by solving the Boltzmann Transport Equation (BTE) by means of the Discrete Ordinate Method (DOM). Relaxation time and phase and group velocitiy spectral dependencies are taken into account. The Holland model of phonon relaxation time is revisited and recalculated from dispersion relations (taken in litterature) in order to match bulk silicon and germanium values. This improved model is then used to predict silicon nanowire and nanofilm thermal properties in both ballistic and mesoscopic regimes

The Nearby Supernova Factory

The Nearby Supernova Factory (SNfactory) is an ambitious project to find and study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at redshifts 0.03<z<0.08. This program will provide an exceptional data set of well-studied SNe in the nearby smooth Hubble flow that can be used as calibration for the current and future programs designed to use SNe to measure the cosmological parameters. The first key ingredient for this program is a reliable supply of Hubble-flow SNe systematically discovered in unprecedented numbers using the same techniques as those used in distant SNe searches. In 2002, 35 SNe were found using our test-bed pipeline for automated SN search and discovery. The pipeline uses images from the asteroid search conducted by the Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction techniques and analysis have allowed us to increase our effective SN discovery rate to ~12 SNe/month in 2003.Comment: 7 pages, 3 figures to be published in New Astronomy Review

In vivo study of the GC90/IRIV vaccine for immune response and autoimmunity into a novel humanised transgenic mouse

Parathyroid hormone-related protein (PTH-rP), a secreted protein produced by prostate carcinoma and other epithelial cancers, is considered a key agent for the development of bone metastases. We investigated the construct GC90/IRIV, composed of immunopotentiating reconstituted influenza virosomes (IRIV) containing PTH-rP gene plasmids (GC90), as a potential tool for human anticancer immunotherapy into humanised mice transgenic for HLA-A(*)02.01, the human-β2 microglobulin, and the human CD8α molecule. Intranasal administration of GC90/IRIV resulted in the induction of a PTH-rP-specific multiepitope cytotoxic T-cell (CTL) response. Cytotoxic T cells derived from vaccinated mice were capable of lysing in vitro syngenic murine PTH-rP transfectants and human HLA-A(*)02.01+/PTH-rP+ prostate carcinoma LNCaP cells as well. The immune response capacity and the absence of any sign of toxicity and/or autoimmunity in vivo suggest the GC90/IRIV vaccine as a valid tool for active specific immunotherapy of human cancers and metastases overexpressing PTH-rP

Linking Spatial and Temporal Dynamic of Bacterioplankton Communities With Ecological Strategies Across a Coastal Frontal Area

Ocean frontal systems are widespread hydrological features defining the transition zone between distinct water masses. They are generally of high biological importance as they are often associated with locally enhanced primary production by phytoplankton. However, the composition of bacterial communities in the frontal zone remains poorly understood. In this study, we investigate how a coastal tidal front in Brittany (France) structures the free-living bacterioplankton communities in a spatio-temporal survey across four cruises, five stations and three depths. We used 16S rRNA gene surveys to compare bacterial community structures across 134 seawater samples and defined groups of co-varying taxa (modules) exhibiting coherent ecological patterns across space and time. We found that bacterial communities composition was strongly associated with the biogeochemical characteristics of the different water masses and that the front act as an ecological boundary for free-living bacteria. Seasonal variations in primary producers and their distribution in the water column appeared as the most salient parameters controlling heterotrophic bacteria which dominated the free-living community. Different dynamics of modules observed in this environment were strongly consistent with a partitioning of heterotrophic bacterioplankton in oligotroph and copiotroph ecological strategies. Oligotroph taxa, dominated by SAR11 Clade members, were relatively more abundant in low phytoplankton, high inorganic nutrients water masses, while copiotrophs and particularly opportunist taxa such as Tenacibaculum sp. or Pseudoalteromonas sp. reached their highest abundances during the more productive period. Overall, this study shows a remarkable coupling between bacterioplankton communities dynamics, trophic strategies, and seasonal cycles in a complex coastal environment

Différenciation hémisphérique auditive par analyse de potentiels évoqués auditifs

- Par opposition aux études subjectives adressant le problème de la spécialisation hémisphérique auditive, le but de ce travail est de proposer des mesures objectives permettant de différencier le comportement des deux hémisphères vis-à-vis des stimuli. Pour ce faire, nous disposons de signaux intracérébraux enregistrés en réponse à divers stimuli. Ce papier ne traite que des réponses aux sons verbaux voisé /ba/, non voisé /pa/ et à la voyelle /a/ et présente trois méthodes. La première calcule le coefficient de corrélation entre les réponses à deux stimuli, recueillies sur le même plot. La seconde porte sur l'évolution de la corrélation au cours du temps. Sur les valeurs de corrélation obtenues est effectuée une analyse factorielle des correspondances (AFC) suivie d'une classification hiérarchique ascendante appliquée sur les facteurs de l'AFC. Finalement, les réponses sont caractérisées selon le nombre d'extrema en fonction de l'hémisphère et du stimulus considérés. Les trois méthodes permettent de mettre en avant certains paramètres révélateurs de différence de comportement des deux hémisphères

Оценка осадков в прибрежных районах Антарктики в глобальной модели атмосферы LMDZ6 с использованием наземных радиолокационных наблюдений

In the current context of climate change in the poles, one of the objectives of the APRES3 (Antarctic Precipitation Remote Sensing from Surface and Space) project was to characterize the vertical structure of precipitation in order to better simulate it. Precipitation simulated by models in Antarctica is currently very widespread and it overestimates the data. Sensitivity studies have been conducted using a global climate model and compared to the observations obtained at the Dumont d’Urville coast station, obtained by a Micro Rain Radar (MRR). The LMDz/IPSL general circulation model, with zoomed configuration over Dumont d’Urville, has been considered for this study. A sensitivity study was conducted on the physical and numerical parameters of the LMDz model with the aim of estimating their contribution to the precipitation simulation. Sensitivity experiments revealed that changes in the sedimentation and sublimation parameters do not significantly impact precipitation rate. However, dissipation of the LMDz model, which is a numerical process that dissipates spatially excessive energy and keeps the model stable, impacts precipitation indirectly but very strongly. A suitable adjustment of the dissipation reduces significantly precipitation over Antarctic peripheral area, thus providing a simulated profile in better agreement with the MRR observations.В текущем тренде изменения климата на полюсах одна из задач проекта APRES3 (Дистанционное зондирование осадков в Антарктике с поверхности и из космоса) заключается в том, чтобы уточнить вертикальную структуру осадков и повысить качество их прогноза. Известные результаты моделирования осадков в Антарктиде базируются на данных с высокой степенью неопределенности и сильно разнятся. Исследование избирательной чувствительности расчета осадков проводилось на основе глобальной климатической модели и сопоставлялось с наблюдениями, полученными с помощью метеорадара (MRR) на береговой станции Дюмон-д’Юрвиль. Использовалась LMDz/IPSL-модель общей циркуляции с повышенной детализацией в районе станции Дюмон-д’Юрвиль. Была выполнена оценка вклада физических и численных параметров данной модели в расчет осадков. Вычислительные эксперименты показали, что изменения параметров седиментации и сублимации не влияют существенно на прогнозируемую скорость выпадения осадков. Однако диссипация, возникающая в модели LMDz в процессе вычислений, рассеивая пространственно избыточную энергию и обеспечивая устойчивость модели, хотя и косвенно, но очень сильно влияет на рассчитываемую величину осадков. Адекватная подгонка уровня рассеивания при моделировании значительно снижает количество осадков в периферийных районах Антарктики, обеспечивая таким образом лучшее согласование моделируемого профиля с данными метеорадарных наблюдений