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Search for disappearing tracks in proton-proton collisions at sqrt(s) = 8 TeV
No full textSubmitted to JHEP ; see paper for full list of authorsInternational audienceA search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. Disappearing tracks are identified as those with little or no associated calorimeter energy deposits and with missing hits in the outer layers of the tracker. The search uses proton-proton collision data recorded at sqrt(s) = 8 TeV that corresponds to an integrated luminosity of 19.5 inverse femtobarns. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking (AMSB) model. The number of observed events is in agreement with the background expectation, and limits are set on the cross section of direct electroweak chargino production in terms of the chargino mass and mean proper lifetime. At 95% confidence level, AMSB models with a chargino mass less than 260 GeV, corresponding to a mean proper lifetime of 0.2 ns, are excluded
On the convergence of the iterates of "FISTA"
No full textInternational audienceFISTA is a classical optimization algorithm to minimize convex functions. The article gives new results on the properties of the sequences generated by this algorithm for non classical choices of parameters. The main result is the proof of the convergence of the iterates of the algorithm.FISTA est un algorithme classique d'optimisation des fonctions convexes. Cet article propose de nouveaux résultats sur les suites générées par cet algorithme pour des choix de paramètres qui ne sont pas ceux classiquement utilisés. Le résultat principal est la preuve de convergence des itérés de l'algorithme pour des choix adéquats des paramètre
Gaining insight into regional coastal changes on La Réunion island through a Bayesian data mining approach
No full textInternational audienceRecent works have highlighted the interest in coastal geographical databases - collected for coastal management purposes - for obtaining insight into current shoreline changes. On La Réunion, a tropical volcanic high island located in the Southern Indian Ocean, a dataset is available which describes shoreline changes, the coastal geomorphology and the presence of anthropic structures. This database is first supplemented with information on the exposure of each coastal segment to energetic waves and to estuarine sediment inputs. To incorporate relative sea-level changes along the coast in the database, levelling data are analysed in combination with GPS, satellite altimetry and sea-level reconstructions. Finally, a method based on Bayesian networks is used to assess the probabilistic relationships between the variables in the database. The results highlight the high degree of dependency between variables: a retrospective model is able to reproduce 81% of the observations of shoreline mobility. Importantly, we report coastal ground motions for La Réunion island of the order of 1 to 2 mm/year along the coast. However, the resulting differing rates of relative sea-level rise do not significantly impact on shoreline changes. Instead, the results suggest a major control of geological processes and local coastal geomorphic settings on shoreline evolution. While any exploration of a coastal database needs to be complemented with human reasoning to interpret the results in terms of physical processes, this study highlights the significance of revisiting other datasets to gain insight into coastal processes and factors causing shoreline changes, including sea-level changes
Rare event simulation using reversible shaking transformations
No full textWe introduce random transformations called reversible shaking transformations which we use to design two schemes for estimating rare event probability. One is based on interacting particle systems (IPS) and the other on time-average on a single path (POP) using ergodic theorem. We discuss their convergence rates and provide numerical experiments including continuous stochastic processes and jump processes. Our examples cover rather important situations related to insurance, queueing system and random graph for instance. Both schemes have good performance, with a seemingly better one for POP
Trip-timing decisions and congestion with household scheduling preferences
No full textInternational audienceMost traffic congestion models assume that agents make trip-timing decisions independently and receive payoffs at the origin and destination that do not depend on whether other agents are present. We depart from this paradigm by considering a variant of Vickrey׳s bottleneck model of the morning commute in which individuals live as couples and value time at home more when together than when alone. We show that the costs of congestion can be higher than for a comparable population of individuals living alone. The costs can be even higher if spouses collaborate with each other when choosing their departure times. To calibrate the model we estimate trip-timing preferences for married and unmarried men and women in the Greater Paris region
Ductile shear zone rheology : the viewpoint of experimentally crept lower crustal rocks and analogues
No full textInternational audienc
ETUDE DE NANOFILS DE SILICIUM HORIZONTAUX D’UN MODE DE CROISSANCE SOLIDE-LIQUIDE-SOLIDE ET LEUR AUTO-ORGANISATION DANS DISPOSITIFS ELECTRONIQUES
No full textThis is the first Ph.D. thesis on studying the growth of in-plane silicon nanowires (SiNWs) and developing a method for self-organising them for nano-electronics applications. The growth of in-plane SiNWs is based on plasma-enhanced chemical vapour deposition (PECVD) thin film techniques and results from the interaction between a metal droplet and a hydrogenated amorphous silicon (a-Si:H) thin film. This in-plane solid-liquid-solid (IPSLS) growth mode can be considered as a reactive-spreading and moving behaviour of indium droplet on a-Si:H activated by the establishment of a surface energy gradient due to the phase transition from a-Si:H at the advancing NP edge to c-Si at the NP receding edge. In order to integrate IPSLS SiNWs in nano-electronic devices it is of prime importance to organise them in a controllable way. We propose a growth-in-place strategy which enables the SiNWs to grow along pre-patterned guiding steps. Moreover, this technique is applied to form In NPs on the sidewall of buried ITO layers, which facilitates the localization of the step-guided SiNWs. This work sets the basis for the fabrication of SiNW field effect transistors on insulator, which also allows for gate engineering and the obtaining of Fully Depleted Silicon-On-Insulator (FD-SOI).Celle-ci est la première thèse sur la fabrication et caractérisation de nanofils de silicium (SiNWs) horizontaux basé sur des techniques de dépôt chimique en phase vapeur assisté par plasma (PECVD). La croissance de nanofils de silicium dans le plan de l’échantillon découle de l’interaction entre une goutte métallique et une couche de silicium amorphe hydrogéné (a-Si:H). Dans ce procédé la nanoparticule d’indium liquide (NP) se déplace sur un substrat couvert d’une couche d’a-Si:H. Lors de son déplacement la NP dissout et absorbe la couche d’a-Si:H sur sa face avant et précipite un nanofil de silicium cristallin (c-Si) par sa face arrière. Ce mode de croissance de nanofils, que nous avons appelé in-plane solid-liquid-solid (IPSLS), peut être considéré comme un processus de mouillage réactif dans lequel le déplacement de l’indium liquide sur le a-Si:H est activé par l’établissement d’un gradient d’énergie superficielle entre le a-Si:H en face avant de la NP et le c-Si à l’arrière. Afin d’intégrer les nanofils dans dispositifs électroniques (transistors), il est primordial de les organiser d’une manière contrôlée. Nous proposons une méthode pour guider la croissance des nanofils basée sur la formation de marches sur le substrat par des techniques de nanofabrication. Qui plus est, nous avons développé une technique de formation de NPs d’In à la surface d’une paroi d’oxyde d’indium et étain (ITO) enterrée. Ceci permet la localisation du point de départ des nanofils. Cette stratégie de croissance de nanofils établit les bases pour la fabrication de transistors à base de nanofils de silicium sur l’isolant, ce qui ouvre la voie à la réalisation de transistors complétement déplétés sur isolant (FD-SOI)
Laser-delayed double shock-wave generation in water-confinement regime
No full textInternational audienceThis paper investigates the different physical processes involved during laser-delayed double shock-wave generation in water-confined geometry. With this technique, two laser pulses, separated by a Δt duration, irradiate a target immersed in water at an intensity of a few GW/cm2 and form a high pressure plasma which results in a double shock-wave generation. This 2 pulses configuration is currently being investigated as an attractive method for improving the LASer Adhesion Test (LASAT) [L. M. Barker and R. E. Hollenbach, J. Appl. Phys. 43, 4669–4674 (1972)] technique by adapting the time delay Δt to the position of interfaces. The LASAT technique is a noncontact adhesion test allowing to generate a high-level tensile stress near interfaces with the use of laser-driven shock wave. The generation of two delayed high-intensity shock waves by laser plasma in the water-confinement regime has been investigated at 10ns@532 nm with the new Nd:YAG laser GAIA from Thales Laser company in the new facility HEPHAISTOS. For each incident Gaussian laser impulsion, the characterization of the high-amplitude laser-plasma-generated shock wave and its propagation through the target has been performed using a velocity interferometer system for any reflector [L. Berthe et al., “State-of-the-art laser adhesion test (LASAT),” Nondestr. Test. Eval. 26(3–4), 303–317 (2011)]. The new laser facility allows us a nanosecond-control of the time delay between the two laser pulses and a precise control of each laser maximum-intensity. Therefore, the influence of the first laser-induced plasma, on the second shock-wave generation has been studied by modifying different parameters such as the delay Δt and the intensity I1 and 12 of each pulse and different aluminum plate thicknesses from 0.2 to 1.5 mm. Preliminary tests show that the maximum pressure level of the second generated shock wave is sensitive to the time delay between the two impulsions and influenced by the plasma generated by the first laser pulse
Dynamic monitoring of cell mechanical properties using profile microindentation.
No full textInternational audienceWe have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells' actin is depolymerized using cytochalasin-D
Microstructural insight into the nonlinear swelling of argillaceous rocks
No full textInternational audienceArgillaceous rocks are chosen as possible host rocks for underground radioactive nuclear waste disposal. These rocks exhibit complex coupled thermo–hydro–chemo-mechanical behavior, the description of which would strongly benefit from an improved experimental insight on micro-scale. In this work we present some recent observations of the evolution of these rocks upon swelling on the scale of their composite microstructure, essentially made of a clay matrix with embedded grains of calcite and quartz with sizes ranging from a few to several hundreds of micrometers. The micro-scale experimental investigation was based on the combination of high definition and high resolution imaging in an environmental scanning electron microscope (ESEM) and digital image correlation techniques. Samples were held at a constant temperature of 2 °C while the vapor pressure in the ESEM chamber was varied from a few to several hundreds of Pascals, generating a relative humidity (RH) ranging from about 10% up to 99%. Results on micro-scale showed strongly heterogeneous deformation fields, which result from complex hydromechanical interactions between different components of argillaceous rocks. The swelling of argillaceous rocks is moderate at low RH but becomes significant at high RH. The observations demonstrated that the nonlinearity is related not only to the micro-cracking upon wetting, but also to the nonlinear swelling of the clay matrix itself that is governed by different mechanisms