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Anisotropic magnetothermal transport and spin Seebeck effect
No full textÉquipe 101 : Nanomagnétisme et électronique de spinInternational audienceThe anisotropic properties of thermal transport in insulating or conducting ferromagnets are derived on the basis of the Onsager reciprocity relations applied to a magnetic system. It is shown that the angular dependence of the temperature gradient takes the same form as that of the anisotropic magnetoresistance, including anomalous and planar Hall contributions. The measured thermocouple generated between the extremities of the nonmagnetic electrode in thermal contact to the ferromagnet follows this same angular dependence. The sign and amplitude of the magnetovoltaic signal is controlled by the difference of the Seebeck coefficients of the thermocouple
Obstructions to weak decomposability for simplicial polytopes
No full textInternational audienceProvan and Billera introduced notions of (weak) decomposability of simplicial complexes as a means of attempting to prove polynomial upper bounds on the diameter of the facet-ridge graph of a simplicial polytope. Recently, De Loera and Klee provided the first examples of simplicial polytopes that are not weakly vertex-decomposable. These polytopes are polar to certain simple transportation polytopes. In this paper, we refine their analysis to prove that these -dimensional polytopes are not even weakly -decomposable. As a consequence, (weak) decomposability cannot be used to prove a polynomial version of the Hirsch Conjecture
Modeling wind effect on the motion of leaves in a tree: from single leaf mechanics to global quantities
No full textCommunication oraleCommunication oraleabsen
Shear strength of rock discontinuities reinforced by passive rockbolt, Proc. International Conference on Rock Slope Stability (RSS 2014), Marrakech, Morocco.
No full textInternational audienc
Métrologie des harmoniques élevées ensemencée doux rayons X Laser Basé sur Solid-plasma Amplificateur
No full textUltrashort coherent soft x-ray lasers (SXRL) are adequate to capture dynamics in atoms, molecules, surfaces and materials at the ultrashort time-scales. In current dissertation, we numerically and experimentally studied on a table-top fully coherent SXRL source. The main idea is to seed high harmonic pulse into laser-induced plasma achieving significant energy amplification. The first attempt was tested using neon-like titanium plasma (32.6 nm) at LASERIX facility. Then wave front of this seeded SXRL beam (18.9 nm) was measured approaching diffraction-limited (λ=14) using Hartmann wave front sensor at Colorado State University. Numerical studying on short plasma with large cross-sectional area demonstrated 10s of μJ and ~80 f s SXRL pulse. Further modelling of the amplification process revealed a rapid depletion (< 300 f s) of the gain followed by a full recovery after about 1.5 ps. A novel x-ray pump/x-ray probe experiment was successfully conducted to verify it. This inspired the X-ray chirped pulse amplification (CPA) concept. It promises GW fully coherent SXRL (several mJ) with a capability of reaching Fourier-limited beam (~100 f s).Les lasers émettant des rayons X-mous sous forme d’impulsions cohérentes ultracourtes (SXRL pour soft X-ray laser en anglais) sont des outils appropriés à l’étude de la dynamique ultrarapide des atomes, molécules, surfaces et matériaux. Le présent manuscrit expose des travaux numériques et expérimentaux sur l’injection par harmonique élevée d’un amplificateur SXRL compact. Des essais sur l’installation LASERIX montrèrent une amplification limitée dans un plasma d’ions néonoïdes du titane (32.6 nm), due à la réfraction du faisceau harmonique injecté. Le front d’onde d’un SXRL à 18.9 nm fut ensuite mesuré au Colorado State University (CSU), en fonction de différents paramètres d’amplification. L’étude numérique d’un plasma à grande section efficace démontra la génération d’impulsion SXRL de plusieurs dizaines de μJ et d’une durée 80 f s. Une modélisation pluspoussée du processus d’amplification a révélé une déplétion rapide (< 300 f s) du gain suivie par une reprise après environ 1.5 ps, vérifiée xpérimentalement durant une expérience pompe-sonde (rayons X / rayons X) effectuée au CSU. Ceci a inspiré le concept d’amplification à dérive de fréquence dans les rayons X. Une modélisation complète annonce une émission SXRL totalement cohérente de l’ordre du GW (200 f s, plusieurs mJ)
Understanding the amorphous-to-microcrystalline silicon transition in SiF4/H2/Ar gas mixtures
No full textInternational audienc
Influence of low energy argon plasma treatment on the moisture barrier performance of hot wire-CVD grown SiN x multilayers Influence of low energy argon plasma treatment on the moisture barrier performance of hot wire-CVD grown SiN x multilayers
No full textInternational audienceThe reliability and stability are key issues for the commercial utilization of organic photovoltaic devices based on flexible polymer substrates. To increase the shelf-lifetime of these devices, transparent moisture barriers of silicon nitride (SiN x) films are deposited at low temperature by hot wire CVD (HW-CVD) process. Instead of the conventional route based on organic/inorganic hybrid structures, this work defines a new route consisting in depositing multilayer stacks of SiN x thin films, each single layer being treated by argon plasma. The plasma treatment allows creating smoother surface and surface atom rearrangement. We define a critical thickness of the single layer film and focus our attention on the effect of increasing the number of SiN x single-layers on the barrier properties. A water vapor transmission rate (WVTR) of 2 ' 10 %4 g/(m 2 &day) is reported for SiN x multilayer stack and a physical interpretation of the plasma treatment effect is given
Diode-pumped Yb:CaF 2 multipass amplifier producing 50 mJ with dynamic analysis for high repetition rate operation
No full textInternational audienceThe dynamic thermal issues of the Yb:CaF 2 crystals within a multi-tens-mJ-energy multipass amplifier operating in the 20–100 Hz repetition rate range and pumped in quasi-cw regime have been studied at different timescales. Thermal response times of the system have been precisely investigated and analyzed, for the first time to our best knowledge in such amplifiers. This study includes a dual timescale analysis: in the long-timescale (second) with direct thermography mapping and in the millisecond range with thermal lensing in a pump-probe configuration. Very atypical positive lens behavior with fluorites will also be presented and discussed. This complete analysis is used to demonstrate the capability of Yb:CaF 2 multipass amplifier systems for operating the amplifier at 20 Hz with 57 mJ and 100 Hz with 32-mJ stable regime. Indeed, high repetition rate multipass amplifier has been realized for the first time with Yb:CaF 2 and for this energy. The results have been analyzed precisely to take into account the thermal issues and excellent beam quality, with a M 2 of 1.1. The pointing stability of 20 lrad has been measured documenting the reliability of the high repetition rate mJ amplifier
Finite Temperature Infrared Spectra from Polarizable Molecular Dynamics Simulations
No full textInternational audienceInfrared spectra of biomolecules are obtained from molecular dynamics simulations at finite temperature using the AMOEBA force field. Diverse examples are presented such as N-methylacetamide and its derivatives and a helical peptide. The computed spectra from polarizable molecular dynamics are compared in each case to experimental ones at various temperatures. The role of high-level electrostatic treatment and explicit polarization, including parameters improvements, is highlighted for obtaining spectral sensitivity to the environment including hydrogen bonds and water molecules and a better understanding of the observed experimental band
Multi-path Extension for the Optimized Link State Routing Protocol version 2 (OLSRv2)
No full textIETF Internet Draft (I-D), MANET WG Documen