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The ENSTA ParisTech, École nationale supérieure de techniques avancées , is one of the most prestigious and selective French grande école in engineering. It is a member of ParisTech .It is located in Palaiseau , next to École polytechnique.Every year about 150 engineers graduate from it.ENSTA offers its students general engineering training with the aim of enabling them to design, produce and oversee complex industrial systems, while meeting strict economic constraints and dealing with an international environment. To do this, the School provides high-level scientific and technological training, which is frequently updated to keep pace with changes in the leading edge technologies and supplemented by language, general culture, law and economics teaching.The teaching is given by research professors at ENSTA with the participation of numerous auxiliary teachers from the economic and industrial world familiar with the latest technical developments in a wide variety of fields.Research, which is one of the School's primary missions, makes a dynamic contribution in both the fundamental and applied fields, to the School's pedagogical project and to meeting the needs of business. Half is the responsibility of the School's research professors, and the other half is carried out by researchers from the CNRS, the INSERM and the École polytechnique working in ENSTA's premises.The general nature of the training given enables ENSTA graduates to find a career in a large number of sectors such as the automotive or naval industry, networks and telecommunications, space propulsion, robotics, oceanology and the environment. Most of the ENSTA graduate engineers are much sought-after by companies and generally find their first job in R&D departments and design offices, rapidly moving towards supervisory and project management posts.ENSTA is a public teaching and research establishment operating under the supervision of the Ministry of Defence. It is headed by a general officer of the Corps of Ordnance Ingineers . Some former graduates of École polytechnique attend ENSTA before joining the military Corps of Ordnance Ingineers, which staffs the DGA. Wikipedia.

Depresseux A.,ENSTA ParisTech
Nature Photonics | Year: 2015

The advent of X-ray free-electron lasers has granted researchers an unprecedented access to the ultrafast dynamics of matter on the nanometre scale. Aside from being compact, seeded plasma-based soft X-ray lasers (SXRLs) turn out to be enticing as photon-rich sources (up to 1015 per pulse) that display high-quality optical properties. Hitherto, the duration of these sources was limited to the picosecond range, which consequently restricts the field of applications. This bottleneck was overcome by gating the gain through ultrafast collisional ionization in a high-density plasma generated by an ultraintense infrared pulse (a few 1018 W cm-2) guided in an optically pre-formed plasma waveguide. For electron densities that ranged from 3 × 1018 cm-3 to 1.2 × 1020 cm-3, the gain duration was measured to drop from 7 ps to an unprecedented value of about 450 fs, which paves the way to compact and ultrafast SXRL beams with performances previously only accessible in large-scale facilities. © 2015 Nature Publishing Group

A thermodynamic approach is proposed to determine the dissociation conditions of salt hydrates and semiclathrate hydrates. The thermodynamic properties of the liquid phase are described with the SAFT-VRE equation of state, and the solid-liquid equilibria are solved by applying the Gibbs energy minimization criterion under stoichiometric constraints. The methodology is applied to water + halide salt systems, and an excellent description of the solid-liquid coexistence curves is obtained. The approach is extended to the water + tetra-n-butylammonium bromide (TBAB) binary mixture, and an accurate representation of the solid-liquid coexistence curves and dissociation enthalpies is obtained. The van der Waals-Platteeuw (vdW-P) theory combined with the new model for salt hydrates is used to determine the dissociation temperatures of semiclathrate hydrates of TBAB + carbon dioxide. A good description of the dissociation pressures of CO2 semiclathrate hydrates is obtained over wide temperature, pressure, and TBAB composition ranges (AAD = 10.5%). For high TBAB weight fractions the new model predicts a change of hydrate structure from type A to type B as the partial pressure of CO2 is increased. The model can also capture a change of behavior with respect to TBAB concentration, which has been observed experimentally: an increase of the TBAB weight fraction leads to a stabilization of the gas semiclathrate hydrate at low initial TBAB concentrations below the stoichiometric composition but leads to a destabilization of the hydrate at TBAB concentrations above the stoichiometric composition. © 2010 American Chemical Society.

Malka V.,ENSTA ParisTech
Physics of Plasmas | Year: 2012

This review article highlights the tremendous evolution of the research on laser plasma accelerators which has, in record time, led to the production of high quality electron beams at the GeV level, using compact laser systems. I will describe the path we followed to explore different injection schemes and I will present the most significant breakthrough which allowed us to generate stable, high peak current and high quality electron beams, with control of the charge, of the relative energy spread and of the electron energy. © 2012 American Institute of Physics.

Ciarlet Jr. P.,ENSTA ParisTech
Computers and Mathematics with Applications | Year: 2012

To solve variational indefinite problems, a celebrated tool is the Banach-Nečas-Babuška theory, which relies on the inf-sup condition. Here, we choose an alternate theory, T-coercivity. This theory relies on explicit inf-sup operators, both at the continuous and discrete levels. It is applied to solve Helmholtz-like problems in acoustics and electromagnetics. We provide simple proofs to solve the exact and discrete problems, and to show convergence under fairly general assumptions. We also establish sharp estimates on the convergence rates. © 2012 Elsevier Ltd. All rights reserved.

Pelanti M.,ENSTA ParisTech | Shyue K.-M.,National Taiwan University
Journal of Computational Physics | Year: 2014

We model liquid-gas flows with cavitation by a variant of the six-equation single-velocity two-phase model with stiff mechanical relaxation of Saurel-Petitpas-Berry (Saurel et al., 2009) [9]. In our approach we employ phasic total energy equations instead of the phasic internal energy equations of the classical six-equation system. This alternative formulation allows us to easily design a simple numerical method that ensures consistency with mixture total energy conservation at the discrete level and agreement of the relaxed pressure at equilibrium with the correct mixture equation of state. Temperature and Gibbs free energy exchange terms are included in the equations as relaxation terms to model heat and mass transfer and hence liquid-vapor transition. The algorithm uses a high-resolution wave propagation method for the numerical approximation of the homogeneous hyperbolic portion of the model. In two dimensions a fully-discretized scheme based on a hybrid HLLC/Roe Riemann solver is employed. Thermo-chemical terms are handled numerically via a stiff relaxation solver that forces thermodynamic equilibrium at liquid-vapor interfaces under metastable conditions. We present numerical results of sample tests in one and two space dimensions that show the ability of the proposed model to describe cavitation mechanisms and evaporation wave dynamics. © 2013 Elsevier Inc.

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