Short-wavelength secondary instabilities in homogeneous and stably stratified shear flows

We present a numerical investigation of three-dimensional, short-wavelength linear instabilities in Kelvin-Helmholtz (KH) vortices in homogeneous and stratified environments. The base flow, generated using two-dimensional numerical simulations, is characterized by the Reynolds number and the Richardson number defined based on the initial one-dimensional velocity and buoyancy profiles. The local stability equations are then solved on closed streamlines in the vortical base flow, which is assumed quasi-steady. For the unstratified case, the elliptic instability at the vortex core dominates at early times, before being taken over by the hyperbolic instability at the vortex edge. For the stratified case, the early time instabilities comprise a dominant elliptic instability at the core and a hyperbolic instability strongly influenced by stratification at the vortex edge. At intermediate times, the local approach shows a new branch of instability (convective branch) that emerges at the vortex core and subsequently moves towards the vortex edge. A few more convective instability branches appear at the vortex core and move away, before coalescing to form the most unstable region inside the vortex periphery at large times. The dominant instability characteristics from the local approach are shown to be in good qualitative agreement with results from global instability studies for both homogeneous and stratified cases. Compartmentalized analyses are then used to elucidate the role of shear and stratification on the identified instabilities. The role of buoyancy is shown to be critical after the primary KH instability saturates, with the dominant convective instability shown to occur in regions with the strongest statically unstable layering. We conclude by highlighting the potentially insightful role that the local approach may offer in understanding the secondary instabilities in other flows.Comment: Submitted to J. Fluid Mech., 20 pages, 10 figure

Application de la formule de Manning et Strickler à des projets d'aménagement en Côte d'Ivoire

Dans le sud de la Côte d'Ivoire, les sols hydromorphes minéraux ou organiques couvrent 100 à 200 000 ha. Le drainage naturel y est faible en raison de l'obstruction des cours d'eau ou des marigots. Le maintien d'une nappe quasi permanente à la surface du sol fait de la majorité de ces sols des zones très peu exploitées par les villageois. L'expérience acquise de ces types de sols sur la station IRHO de La Mé à fait ressortir l'intérêt de leur mise en culture par le palmier à huile. Cette mise en valeur nécessite l'établissement d'un réseau d'assainissement constitué de fossés dont les dimensions dépendent de nombreux paramètres, en particulier la pente et les quantités d'eaux à évacuer. Cet article a pour objet de décrire la méthode de calcul des dimensions des fossé

Contrôle et maintien de la nappe phréatique sous culture de palmiers à huile en Côte d'Ivoire

L'extension des cultures de palmiers à huile en Côte d'Ivoire a permis de valoriser des unités de sols hydromorphes après création de fossés de drainage. Description de la méthode d'appréhension du niveau du plan d'eau par rapport à la surface du sol ainsi que des ouvrages simples permettant une régulation de ce nivea

Traspaso cultural sobre ruedas y asfalto

Ante la aparición de nuevos escenarios móviles, en los cuales se puede observar el traspaso cultural y deportivo con el paso del tiempo, se converge en los individuos la actividad motriz con el entorno físico y -en algunos casos- con la manipulación del objeto utilizado por los mismos. Aquí es pertinente situar la práctica del Longboarding inserto en un espacio físico exclusivo y social determinado, capaz de interpelar, transformar y regular la vida cotidiana de estos practicantes. Unificar este deporte extremo con la mirada social traerá acomplejado una riqueza de valores y vivencias propias en cuanto a lo que se desprende de su universo vocabular y capital simbólico. Surgiendo de esta manera como una invasión cultural que trae configuraciones de movimientos corporales que vinieron a mover -en los últimos siete años- el tablero sociocultural y deportivo establecido hasta entonce

Validation of an ontology of risk and disaster through a case study of the 1923 gerat Kanto Earthquake

This paper seeks to validate a factual ontology derived from an ontology of the domain of risk and catastrophe (Provitolo, Müller, Dubos-Paillard, 2009). The factual ontology is that part describing the structure and dynamics of the system, that is, the representation of an event and of on what it has a bearing. The objective is to show that the ontology is able to account for and allow comparison between complex stories (because of the diversity of event types and of their multi-scale description). The event used as the basis for validation of the ontology is the Great Kanto Earthquake of 1923. The account is that of P. Hadfield (1991) that provides a detailed description of the earthquake. Judgements by the actors involved of the system elements and events are excluded from this exercise, which is a first stage in validating the ontology. (Résumé d'auteur

The Josephson critical current in a long mesoscopic S-N-S junction

We carry out an extensive experimental and theoretical study of the Josephson effect in S-N-S junctions made of a diffusive normal metal (N) embedded between two superconducting electrodes (S). Our experiments are performed on Nb-Cu-Nb junctions with highly-transparent interfaces. We give the predictions of the quasiclassical theory in various regimes on a precise and quantitative level. We describe the crossover between the short and the long junction regimes and provide the temperature dependence of the critical current using dimensionless units $eR_{N}I_{c}/\epsilon_{c}$ and $k_{B}T/\epsilon_{c}$ where $\epsilon_{c}$ is the Thouless energy. Experimental and theoretical results are in excellent quantitative agreement.Comment: 5 pages, 4 figures, slighly modified version, publishe

ORIGAMIX, a CdTe-based spectro-imager development for nuclear applications

The Astrophysics Division of CEA Saclay has a long history in the development of CdTe based pixelated detection planes for X and gamma-ray astronomy, with time-resolved imaging and spectrometric capabilities. The last generation, named Caliste HD, is an all-in-one modular instrument that fulfills requirements for space applications. Its full-custom front-end electronics is designed to work over a large energy range from 2 keV to 1 MeV with excellent spectroscopic performances, in particular between 10 and 100 keV (0.56 keV FWHM and 0.67 keV FWHM at 13.9 and 59.5 keV). In the frame of the ORIGAMIX project, a consortium based on research laboratories and industrials has been settled in order to develop a new generation of gamma camera. The aim is to develop a system based on the Caliste architecture for post-accidental interventions or homeland security, but integrating new properties (advanced spectrometry, hybrid working mode) and suitable for industry. A first prototype was designed and tested to acquire feedback for further developments. In this study, we particularly focused on spectrometric performances with high energies and high fluxes. Therefore, our device was exposed to energies up to 700 keV (133Ba, 137Cs) and we measured the evolution of energy resolution (0.96 keV at 80 keV, 2.18 keV at 356 keV, 3.33 keV at 662 keV). Detection efficiency decreases after 150 keV, as Compton effect becomes dominant. However, CALISTE is also designed to handle multiple events, enabling Compton scattering reconstruction, which can drastically improve detection efficiencies and dynamic range for higher energies up to 1408 keV (22Na, 60Co, 152Eu) within a 1-mm thick detector. In particular, such spectrometric performances obtained with 152Eu and 60Co were never measured before with this kind of detector.Comment: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. Available online 9 January 2015, ISSN 0168-9002 (http://www.sciencedirect.com/science/article/pii/S0168900215000133). Keywords: CdTe; X-ray; Gamma-ray; Spectrometry; Charge-sharing; Astrophysics Instrumentation; Nuclear Instrumentation; Gamma-ray camera

Formes d'innovation des sous-traitants des filières automobile, plasturgie et microtechnique franc-comtoises

C es dernières années sont marquées par un essor important de la sous-traitance, de la co-traitance, des collaborations, des alliances entre les entreprises. " L'entreprise en réseau " est devenue la forme organisationnelle dominante, la mieux adaptée dans une économie fortement concurrentielle. Malgré cela, on sait peu de choses sur la façon dont les industries sous-traitantes régionales s'adaptent à l'évolution des marchés. Une enquête réalisée en 2008 par le laboratoire ThéMA/CEREQ dans le cadre d'une étude faite par la MSHE C.N. Ledoux pour le Secrétariat général aux affaires régionales de Franche-Comté apporte des éclairages intéressants