Seismic anisotropy, structures and geodynamics of continents Shear-wave splitting in the Appalachians and the Pyrenees: importance of the inherited tectonic fabric of the lithosphere

International audienceSplitting of teleseismic shear waves has been measured in the Appalachians (eastern USA) and the Pyrenees (western Europe) using data recorded by permanent and portable stations. From a comparison of the results, it appears that an interpretation of the recorded seismic anisotropy in terms of geodynamics is not straightforward. Successive geodynamic events have generated structures that may have resulted in a similar pattern of mantle flow and that therefore may have contributed in the development of the recorded anisotropy. Combining geological and geophysical arguments, it appears that the mantle anisotropy measured across the Appalachians and the Pyrenees may not be systematically Appalachian or Pyrenean in age but may be mainly due to a lithospheric structure formed during earlier major tectonic events, i.e. the Grenvillian and the Hercynian orogenies, respectively. We suggest that during major episodes of continent assembly, a pervasive tectonic fabric is developed in the lithospheric mantle. In the subsequent evolution of the continent, this fabric may induce a significant mechanical anisotropy that will drastically influence the mechanical behaviour of the Iithosphere when submitted to new tectonic events

Tailoring Chirp in Spin-Lasers

The usefulness of semiconductor lasers is often limited by the undesired frequency modulation, or chirp, a direct consequence of the intensity modulation and carrier dependence of the refractive index in the gain medium. In spin-lasers, realized by injecting, optically or electrically, spin-polarized carriers, we elucidate paths to tailoring chirp. We provide a generalized expression for chirp in spin-lasers and introduce modulation schemes that could simultaneously eliminate chirp and enhance the bandwidth, as compared to the conventional (spin-unpolarized) lasers.Comment: 4 pages, 3 figure

Why do continents break-up parallel to ancient orogenic belts?

International audienceThe frequently observed parallelism between rifts and the pre­ existing orogenic fabric of continents suggests that the inherited tectonic fabric of the lithosphere influences the rupture of continents. We propose that the existence of a pervasive fabric in the lithospheric mantle induces an anisotropie strength in the lithosphere, that guides the propagation of continental rifts. Subcrustal mantle mechanical anisotropy is supported by (i) the anisotropie strength of olivine, (ii) an ubiquitous tectonic fabric in exposed mantle rocks, and (iii) measurements of seismic and electrical anisotropy. During major episodes of continent Rifting parallel to orogenic belts Ocean-opening through rifting and continent break-up is frequently related to the occurrence ofhotspots. There is, howevcr, a discrepancy between hot­ spots acting as pin point sources of heat and the linear extent of rifts over thou­ sands ofkilometres. Moreover rifts tend to parallel pre-existing orogenic fab

Transient response of a sandwich structure damped with a fibrous core material

International audienceThis paper investigates the effect of a fibrous core material on the transient response of a sandwich structure. The core material studied is made of entangled carbon fibers cross-linked with epoxy resin. In order to understand its complex behavior, the material is characterized in shear oscillation, and the obtained shear-stress loops are described using Dahl’s dynamic hysteresis model. Then, the transient response of a single-degree-of-freedom system including this material is simulated and the amplitude dependency of the response is analyzed. Sandwich beams with the fibrous core material are tested experimentally with a impact hammer and compared with classical honeycomb and foam cored sandwich beams. The entangled cross-linked fibers are shown to provide high damping resulting in a fast return to the equilibrium position. Both theoretical and experimental studies showed nonlinear damping. In the amplitude range studied, the material is more interesting at high impact amplitude

Scénarios d’ajustement du solde courant américain : une évaluation avec différentes calibrations de NiGEM.

L’article propose un examen de différents scénarios d’ajustement du déficit courant américain et une mesure des coûts associés pour les économies des États-Unis et de leurs partenaires.déficit courant américain, ajustement par le change, ajustement par une réduction de la demande intérieure américaine.

Low temperature tunneling current enhancement in silicide/Si Schottky contacts with nanoscale barrier width

The low temperature electrical behavior of adjacent silicide/Si Schottky contacts with or without dopant segregation is investigated. The electrical characteristics are very well modeled by thermionic-field emission for non-segregated contacts separated by micrometer-sized gaps. Still, an excess of current occurs at low temperature for short contact separations or dopant-segregated contacts when the voltage applied to the device is sufficiently high. From two-dimensional self-consistent non-equilibrium Green's function simulations, the dependence of the Schottky barrier profile on the applied voltage, unaccounted for in usual thermionic-field emission models, is found to be the source of this deviation

Macroscopic urban dynamics: Analytical and numerical comparisons of existing models

In this paper we compare a single reservoir model and a trip-based model under piecewise linear MFD and a piecewise constant demand. These assumptions allow to establish the exact solution of the accumulation-based model, and continuous approximations of the trip-based model at any order using Taylor series