Natural history of the ERVWE1 endogenous retroviral locus

BACKGROUND: The human HERV-W multicopy family includes a unique proviral locus, termed ERVWE1, whose full-length envelope ORF was preserved through evolution by the action of a selective pressure. The encoded Env protein (Syncytin) is involved in hominoid placental physiology. RESULTS: In order to infer the natural history of this domestication process, a comparative genomic analysis of the human 7q21.2 syntenic regions in eutherians was performed. In primates, this region was progressively colonized by LTR-elements, leading to two different evolutionary pathways in Cercopithecidae and Hominidae, a genetic drift versus a domestication, respectively. CONCLUSION: The preservation in Hominoids of a genomic structure consisting in the juxtaposition of a retrotransposon-derived MaLR LTR and the ERVWE1 provirus suggests a functional link between both elements

Femtosecond laser-induced sub-wavelength plasma inside dielectrics: I. Field enhancement

The creation of high energy density ($\gtrsim10^6$ joules per cm$^3$) over-critical plasmas in a large volume has essential applications in the study of warm dense matter, being present in the hot cores of stars and planets. It was recently shown that femtosecond Bessel beams enable creating over-critical plasmas inside sapphire with sub-wavelength radius and several tens of micrometers in length. Here, the dependence of field structure and absorption mechanism on the plasma density transverse profile are investigated by performing self-consistent Particle-In-Cell (PIC) simulations. Two { limiting} cases are considered: one is a homogeneous step-like profile, that can sustain plasmon formation, the second is an inhomogeneous Gaussian profile, where resonance absorption occurs. Comparing experimental absorption measures to analytical predictions allows determining the plasma parameters used in PIC simulations. The PIC simulation results are in good agreement with experimental diagnostics of total absorption, near-field fluence distribution, and far-field radiation pattern. We show that in each case an ambipolar field forms at the plasma surface due to the expansion of the hot electrons and that electron sound waves propagate into the over-critical region.Comment: 13 pages, 10 figures, published in Physics of Plasma

Propagation et rétrodiffusion d'un faisceau laser lissé dans un plasma de fusion thermonucléaire

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Velocities of speckles in a smoothed laser beam propagating in a plasma

International audienceBy means of three-dimensional simulations, the paraxial propagation of a laser beam in a nonlinearplasma modeled by ion-acoustic waves is examined. The beam speckles are smoothed by aone-dimensional transverse spectral dispersion technique. In the case of weak smoothing and whenthe incident speckle velocity is subsonic, the propagation in the plasma is found to exhibit anasymptotic speckle velocity and to enhance filamentation. With contrary conditions, it is found toreduce simply the speckle velocity

Deux entreprises publiques devant leur avenir Air-France et S.N.C.F. Preface de Charles Detbascn.

(Travaux et Memoires de la Faculte deDroit et de Scienc? " Politique d'Aix-Marseille. N 18)!B.11

Maxwell solvers for the simulations of the laser-matter interaction

With the advent of high intensity laser beams, solving the Maxwell equations with a free-dispersive algorithm is becoming essential. Several Maxwell solvers, implemented in Particle-In-Cell codes, have been proposed. We present here some of them by describing their computational stencil in two-dimensional geometry and defining their stability area as well as their numerical dispersion relation. Numerical simulations of Backward Raman amplification and laser wake-field are presented to compare these different solvers

Les fluides charges relativistes : approches hydrodynamique et cinetique

Available at INIST (FR), Document Supply Service, under shelf-number : RM 1448 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Femtosecond laser-induced sub-wavelength plasma inside dielectrics. II. Second-harmonic generation

International audienceSecond-harmonic emission at a frequency that is twice the laser frequency is an important diagnostic for nonlinear laser–plasma interaction. It is forbidden for centrosymmetric materials such as the bulk of sapphire. The symmetry, however, can be broken by dielectric discontinuities as a result of plasma generation inside a solid dielectric. In the present work, we explore the basic characteristics of experimentally observed second-harmonic emission during focusing a femtosecond Bessel beam inside sapphire. We employ three-dimensional particle-in-cell simulations and theHelmholtz wave equation for theoretical investigations. We analyze how the efficiency of second-harmonic generation and its polarization depend on the plasma parameters. We find that the second-harmonic is generated either due to the coalescence of two-surface electromagnetic waves or nonlinear interaction between the transverse electromagnetic wave and the longitudinal electron plasma wave driven by linear mode conversion. Experimental results agree with the theoretical predictions and confirm the existence of over-critical plasma inside the sapphire that is essential for the resonance of plasma waves or excitation of surface plasmons