G-300: The first French Getaway Special microgravity measurements of fluid thermal conductivity

Thermal conductivity measurements on liquids are difficult to perform on Earth because of thermal motions due to convection. In microgravity, the convection due to buoyancy is evanescent, and a strong reduction of Rayleigh and Nusselt numbers can be expected. Three low viscosity liquids are selected to carry out the measurements; distilled water (standard) and two silicone oils. A modified hot plate method with a simplified guard ring is used; the reduction of convective motions permitted the use in the experimental cells of larger interplate distances and/or temperature differences than in Earth measurements, improving the accuracy. Comparisons between Earth and orbit results may help to understand the convection occurrence in the cells. Thermal, vibrational, and EMI tests have proved that the design satisfies the NASA requirements

"Whose data is it anyway?" The implications of putting small area-level health and social data online

International audienceThe planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this second part of our work, we present here the density profiles of atomic Hydrogen in planetary exospheres subject to the radiation pressure. We first provide the altitude profiles of ballistic particles (the dominant exospheric population in most cases), which exhibit strong asymmetries that explain the known geotail phenomenon at Earth. The radiation pressure strongly enhances the densities compared with the pure gravity case (i.e. the Chamberlain profiles), in particular at noon and midnight. We finally show the existence of an exopause that appears naturally as the external limit for bounded particles, above which all particles are escaping

Amélioration de la gestion des périphériques d'un système embarqué

At CERN, experiments must gather huge amounts of data. The Data Acquisition System of the LHCb is therefore very large, and dedicated to this task. Hundreds of TELL1 boards provide the selection of relevant data and their transfer over a local area network in order to be saved. An embedded system, the Creditcard PC, allows physicists to monitor and program the TELL1 boards. This system runs a CERN release of the Linux operating system, and provides several libraries to handle the communication with the TELL1 board. Several users can work on the same TELL1 board simultaneously. This calls for process synchronization to control the access to the devices. Tests were made progressively, from some dedicated boards to a larger assembly, and then the solution has been distributed to the all TELL1 boards and to other boards using the Creditcard PC

Robust seismic velocity change estimation using ambient noise recordings

We consider the problem of seismic velocity change estimation using ambient noise recordings. Motivated by [23] we study how the velocity change estimation is affected by seasonal fluctuations in the noise sources. More precisely, we consider a numerical model and introduce spatio-temporal seasonal fluctuations in the noise sources. We show that indeed, as pointed out in [23], the stretching method is affected by these fluctuations and produces misleading apparent velocity variations which reduce dramatically the signal to noise ratio of the method. We also show that these apparent velocity variations can be eliminated by an adequate normalization of the cross-correlation functions. Theoretically we expect our approach to work as long as the seasonal fluctuations in the noise sources are uniform, an assumption which holds for closely located seismic stations. We illustrate with numerical simulations and real measurements that the proposed normalization significantly improves the accuracy of the velocity change estimation

Effects of curvature on hydrothermal waves instability of radial thermocapillary flows

URL: http://www-spht.cea.fr/articles/s01/006 Effets de courbure sur l'instabilité en ondes hydrothermales d'un écoulement thermocapillaire radialInternational audienceThe stability of a thermocapillary flow in an extended cylindrical geometry is analysed. This flow occurs in a thin liquid layer with a disk shape when a radial temperature gradient is applied along the horizontal free surface. Besides the aspect ratio, a second parameter related to the local curvature is introduced to describe completely the geometrical effects. We recover classical hydrothermal waves as predicted by Smith and Davis [1] but the properties of these waves are shown to evolve with the curvature parameter, thus leading to a non uniform pattern over the cell. Moreover, it is shown that the problem is not invariant with respect to the exchange of the hot and cold sides.Nous étudions la stabilité linéaire d'un écoulement thermocapillaire en géométrie cylindrique étendue. Un tel écoulement est produit dans un disque de fluide dont la surface libre horizontale est soumise à un gradient de température purement radial. Outre le rapport d'aspect, un second paramètre lié à la courbure locale est introduit pour caractériser la géométrie du problème. L'instabilité en ondes hydrothermales prédite par [1] est retrouvée mais les propriétés des ondes sont altérées par la courbure locale ce qui explique l'existence de structures non uniformes. La dissymétrie du problème vis-à-vis d'une inversion du gradient de température est aussi mise en évidence

Elementary structural building blocks encountered in silicon surface reconstructions

Driven by the reduction of dangling bonds and the minimization of surface stress, reconstruction of silicon surfaces leads to a striking diversity of outcomes. Despite this variety even very elaborate structures are generally comprised of a small number of structural building blocks. We here identify important elementary building blocks and discuss their integration into the structural models as well as their impact on the electronic structure of the surface

Western Mediterranean precipitation over the last 300 years from instrumental observations

The paper reports the results of the analysis of the 14 longest precipitation instrumental series, covering the last 300 years, that have been recovered in six subareas of the Western Mediterranean basin, i.e., Portugal, Northern and Southern Spain, Southern France, Northern and Southern Italy. This study extends back by one century our knowledge about the instrumental precipitation over theWestern Mediterranean, and by two centuries in some specific subareas. All the time series show repeated swings. No specific trends have been found over the whole period, except in a few cases, but with modest time changes and sometimes having opposite tendency. The same can be said for the most recent decades although with some more marked departures from the average. The correlation between the various Mediterranean subareas is generally not significant, or almost uncorrelated. The Wavelet Spectral Analysis applied to the precipitation identifies only a minor 56-year cycle in autumn, i.e., the same return period that has been found in literature for the Sea Surface Temperature over North Atlantic. A comparison with a gridded dataset reconstruction based on mixed multiproxy and instrumental observations, shows that the grid reconstruction is in good agreement with the observed data for the period after 1900, less for the previous period