Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure

Adventices hôtes alternatifs de virus en culture de solanaceae en Côte D’Ivoire

Un inventaire de la flore adventice a été effectué dans des parcelles de piment, tomate et aubergine à Divo, Sinfra et Djebonoua durant l'année 2013. Au cours de ce recensement, 31 échantillons de feuilles de mauvaises herbes présentant des symptômes de viroses ont été prélevés. Les espèces dont les feuilles ont été prélevées sont : d'Ageratum  conyzoides, Boerhavia diffusa, Chromolaena odorata, Euphorbia heterophylla, Croton hirtus. Ces échantillons ont été soumis au test DAS-ELISA en vue de la la détection des virus. Ce travail a permis d'identifier le Cumcumber mosaic virus (CMV), le Peper veinal mosaic virus (PVMV) et le Potato virus Y (PVYN) chez Chromolaena odorata. Ces virus sont responsables de dégâts importants en culture de Solanaceae. Les mauvaises herbes : Chromolaena odorata, Ageratum conyzoides,  Boerhavia diffusa, Croton hirtus et Euphorbia heterophylla sont des réservoirs de ces virus. Les résultats de la présente étude mettent en évidence le rôle des adventices dans le maintien et la dissémination des virus en culture de Solanaceae.Mots-clés : Adventice, CMV, PVMV, PVYN, Solanaceae

Short Intense Laser Pulse Collapse in Near-Critical Plasma

It is observed that the interaction of an intense ultra-short laser pulse with an overdense gas jet results in the pulse collapse and the deposition of a significant part of energy in a small and well localized volume in the rising part of the gas jet, where the electrons are efficiently accelerated and heated. A collisionless plasma expansion over 150 microns at a sub-relativistic velocity (~c/3) has been optically monitored in time and space, and attributed to the quasistatic field ionization of the gas associated to the hot electron current. Numerical simulations in good agreement with the observations suggest the acceleration in the collapse region of relativistic electrons, along with the excitation of a sizeable magnetic dipole that sustains the electron current over several picoseconds. Perspectives of ion beam generation at high repetition rate directly from gas jets are discussed

Real-time monitoring via second-harmonic interferometry of a flow gas cell for laser wakefield acceleration

The use of a gas cell as a target for laser weakfield acceleration (LWFA) offers the possibility to obtain stable and manageable laser-plasma interaction process, a mandatory condition for practical applications of this emerging technique, especially in multi-stage accelerators. In order to obtain full control of the gas particle number density in the interaction region, thus allowing for a long term stable and manageable LWFA, real-time monitoring is necessary. In fact, the ideal gas law cannot be used to estimate the particle density inside the flow cell based on the preset backing pressure and the room temperature because the gas flow depends on several factors like tubing, regulators and valves in the gas supply system, as well as vacuum chamber volume and vacuum pump speed/throughput. Here, second-harmonic interferometry is applied to measure the particle number density inside a flow gas cell designed for LWFA. The results demonstrate that real-time monitoring is achieved, and that using low backing pressure gas (< 1 bar) and different cell orifice diameters (< 2 mm) it is possible to finely tune the number density up to the range well suited for LWFA

Facteurs Explicatifs de la Pratique Contraceptive Moderne des Femmes Fréquentant les Formations Sanitaires du District de Youwarou au Mali

Objectif : Mettre en exergue les déterminants de la pratique contraceptive moderne des femmes fréquentant les centres de santé du district de Youwarou au Mali. L’étude part du constat que la situation sanitaire est non satisfaisante avec un faible taux de fréquentation des centres de santé qui est de 15 %, exacerbée par la crise sécuritaire déclenchée en 2012. Ainsi, le taux d’utilisation des méthodes contraceptives modernes est également très faible soit 1,07%. En effet, l’utilisation de la contraception moderne selon la cinquième Enquête Démographique et de Santé du Mali (EDSM-5) est de 9,6% au niveau national et de 2,7% dans la région de Mopti. Méthode : Etude transversale quantitative dont l’enquête fut réalisée du 1er mai au 30 juin 2015, et a porté sur 200 femmes âgées de 15-49 ans fréquentant les 07 centres de santé dans le district de Youwarou. Les données collectées par un&nbsp;questionnaire ont été vérifiées, compilées à l’aide du logiciel le Sphinx Plus² version 4.5, puis transférées sur le logiciel stata 10 pour l’analyse statistique. Pour l’analyse des données, nous avons eu recours à deux méthodes dans ce travail : la méthode d’analyse descriptive (analyse bivariée) et la méthode d’analyse explicative (analyse multivariée). Résultats : L’étude montrent que la prévalence contraceptive moderne est de 8,8%. Les femmes de centre de Guidio-sare utilisent les contraceptives modernes plus que leurs consoeurs du district. Enfin les déterminants de la pratique contraceptive sont notamment l’ethnie, l’âge et le statut matrimonial de la femme. Conclusion : A la lumière de cette étude, nous suggérons qu’un accent particulier doit être mis sur les déterminants révélés afin de promouvoir les méthodes contraceptives modernes. Objective: Highlight the determinants of modern contraceptive practice among women attending health centers in the Youwarou health district of Mali. The study was carried out based on the observation that the health situation is unsatisfactory with a low utilization rate of health centers is 15%, exacerbated by the security crisis triggered in 2012. Thus, the rate of use of modern contraceptive methods is also very low is 1.07%. Indeed, the use of modern contraception according to the fifth Demographic and Health Survey of Mali (EDSM-5) is 9.6% at the national level and 2.7% in the Mopti region. Methods: A quantitative cross-sectional study was carried out from May 1th to June 30th 2015, and covered 200 women aged 15-49 attending the 07 health centers in the district of Youwarou. The data collected by a questionnaire was verified, compiled using the software Sphinx Plus² version 4.5, and then transferred to the Stata 10 software for statistical analysis. For data analysis, two methods were used in this work: the descriptive analysis&nbsp;method (bivariate analysis) and the explanatory analysis method (multivariate analysis). Results: The study shows that modern contraceptive prevalence is 8.8%. women of Guidio-sare Center use modern contraceptives more than their sisters of district. Finally, the determinants of contraceptive practice include the ethnicity, age and marital status of women. Conclusion: In the light of this study, we suggest that emphasis should be placed on the identified determinants in order to promote modern contraceptive methods

Persistence of magnetic field driven by relativistic electrons in a plasma

The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory

Consistency of projected drought over the Sahel with changes in the monsoon circulation and extremes in a regional climate model projections

As a step toward an increased understanding of climate change over West Africa, in this paper we analyze the relationship between rainfall changes and monsoon dynamics in high-resolution regional climate model experiments performed using the Regional Climate Model (RegCM3). Multidecadal simulations are carried out for present-day and future climate conditions under increased greenhouse gas forcing driven by the global climate model European Center/Hamburg 5 (ECHAM5). Compared to the present day, the future scenario simulation produces drier conditions over the Sahel and wetter conditions over orographic areas. The Sahel drying is accompanied by a weaker monsoon flow, a southward migration and strengthening of the African Easterly Jet, a weakening of the Tropical Easterly Jet, a decrease of the deep core of ascent between the jets, and reduced African Easterly Wave activity. These circulation changes are characteristics of dry periods over the Sahel and are similar to the conditions found in the late twentieth century observed drought over the region. Changes in extreme events suggest that the drier conditions over the Sahel are associated with more frequent occurrences of drought periods. The projected drought over the Sahel is thus physically consistent with changes in the monsoon circulation and the extreme indices (maximum dry spell length and 5 day precipitation)

A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator

Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately linear with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we measure a gamma-ray source size of less than 100 microns for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators

ORAL LESIONS OF HIV-INFECTED CHILDREN IN WEST AFRICA IN THE ERA OF ANTIRETROVIRAL TREATMENTS

Oral Communication presented at the "Forum des Jeunes Chercheurs", Brest (France) 2011