MESURE DES GRADIENTS DE DENSITÉ DANS L'INTERACTION LASER-PLASMA

Nous étudions la densité électronique et son gradient dans l'interaction d'un laser à CO2 avec une cible plane de polyéthylène, pour un flux laser de 1012 W/cm2. L'étude par interférométrie Jamin des profils de densité et la mesure strioscopique de son gradient, couplées à l'étude de l'image en rayons X du plasma conduisent à une valeur de 220 ± 80 µm de la longueur du gradient de densité. Ceci est confirmé par des mesures indirectes obtenues à partir du bilan optique de l'interaction et du seuil de génération de l'harmonique 3/2 ω0 du laser à CO2. Les conséquences de ces résultats sur les conditions de l'interaction sont discutées

Successive Solar Flares and Coronal Mass Ejections on 2005 September 13 from Noaa Ar 10808

We present a multiwavelength study of the 2005 September 13 eruption from NOAA 10808 that produced total four flares and two fast coronal mass ejections (CMEs) within 1.5 hours. Our primary attention is paid to the fact that these eruptions occurred in close succession in time, and that all of them were located along an S-shaped magnetic polarity inversion line (PIL) of the active region. In our analysis, (1) the disturbance created by the first flare propagated southward along the PIL to cause a major filament eruption that led to the first CME and the associated second flare underneath. (2) The first CME partially removed the overlying magnetic fields over the northern Delta spot to allow the third flare and the second CME. (3) The ribbon separation during the fourth flare would indicate reclosing of the overlying field lines opened by the second CME. It is thus concluded that this series of flares and CMEs are interrelated to each other via magnetic reconnections between the expanding magnetic structure and the nearby magnetic fields. These results complement previous works made on this event with the suggested causal relationship among the successive eruptions.Comment: 11 pages, 8 figures, 2 tables, accepted to The Astrophysical Journa

Acceleration of Relativistic Protons during the 20 January 2005 Flare and CME

The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far.We perform a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event of 20 January 2005. The intensity-time profile of the relativistic protons derived from the neutron monitor data indicates two successive peaks. We show that microwave, hard X-ray and gamma-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion decay gamma-rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures of particle acceleration in the corona within approximatively 1 solar radius above the photosphere, revealed by hard X-ray and microwave emissions of low intensity, and by the renewed radio emission of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration in the corona.Comment: 22 pages, 5 figure

Alexithymia may explain the relationship between autistic traits and eating disorder psychopathology

Background: Autistic people are disproportionately vulnerable to anorexia nervosa and other eating disorders (ED), and within the general population, autistic traits correlate with ED psychopathology. A putative mechanism which may underpin this heightened risk is alexithymia, a difficulty identifying and describing emotional states which is observed in both autism and ED. In two experiments with independent non-clinical samples, we explored whether alexithymia might mediate the heightened risk of eating psychopathology in individuals high in autistic traits. Methods: Our first experiment used the PROCESS macro for SPSS to examine relationships between alexithymia (measured by the Toronto Alexithymia Scale (TAS-20)), autistic traits (autism quotient (AQ)), and eating psychopathology (Eating Attitudes Test (EAT-26)) in 121 participants. Our second experiment (n = 300) replicated and furthered this analysis by examining moderating effects of sex and controlling for anxiety and depression as covariates. We also included an additional performance-based measure of alexithymia, the Levels of Emotional Awareness Scale (LEAS). Results: Study 1 suggested that TAS-20 scores mediated the relationship between heightened autistic traits and eating psychopathology. Replication and further scrutiny of this finding, in study 2, revealed that this mediation effect was partial and specific to the female participants in this sample. The mediation effect appeared to be carried by the difficulty identifying feelings subscale of the TAS-20, even when depression and anxiety were controlled for. LEAS scores, however, were not significantly related to autistic traits or eating psychopathology. Limitations: Cross-sectional data prevents any conclusions around the direction and causality of relationships between alexithymia, autistic traits, and eating psychopathology (alongside depression and anxiety), necessitating longitudinal research. Our non-clinical sample was predominantly Caucasian undergraduate students, so it remains to be seen if these results would extrapolate to clinical and/or autistic samples. Divergence between the TAS-20 and LEAS raises crucial questions regarding the construct validity of these measures. Conclusions: Our findings with respect to autistic traits suggest that alexithymia could partially explain the prevalence of ED in autistic people and may as such be an important consideration in the pathogenesis and treatment of ED in autistic and non-autistic people alike. Further research with clinical samples is critical to explore these ideas. Differences between men and women, furthermore, emphasize the importance of looking for sexspecific as well as generic risk factors in autistic and non-autistic men and women

Simplified rational approximations for Holtsmark and related functions

A single rational fraction, valid for any value of the electric field, closely approximates the Holtsmark distribution. This also applies to its derivative and its cumulative

Réponse du film SB aux rayons X de 0,1 à 10 keV

From reevaluated physical parameters of the Kodak SB film and with a revised theoretical formulation of its response to X-rays, available results of sensitometric calibration between 0.1 and 10 keV are gathered into a user-friendly semi-empirical model.Une réévaluation des caractéristiques physiques du film Kodak SB et une reformulation théorique de sa réponse aux rayons X permettent de réduire à un modèle semi-empirique très maniable les résultats disponibles d'étalonnage sensitométrique entre 0,1 et 10 keV

Recombinaison radiative directe le long de plusieurs séquences isoélectroniques

From results of specific calculations for ions with 0, 1 or 2 electrons, and from a critical compilation of literature data for other isoelectronic sequences, we establish a simple and accurate analytic approximation, over a wide range of charges and temperatures, for the total coefficient of direct radiative recombination of atomic ions with Maxwellian electrons.A l'aide de calculs spécifiques pour les ions ayant 0, 1 ou 2 électrons, et d'une compilation critique des données de la littérature pour d'autres séquences isoélectroniques, on établit une approximation analytique simple et précise, dans un vaste domaine de charges et de températures, pour le coefficient total de recombinaison radiative directe des ions atomiques avec des électrons maxwelliens

Élargissement Stark de raies hydrogénoïdes entre niveaux élevés d'ions multichargés

Stark broadening is studied theoretically for hydrogenic lines from multicharged ions, between highly excited levels, when perturbing ions contribute quasi-statically and électrons by impacts, especially by inelastic collisions. Its dependence upon charges and quantum numbers is outlined. This scaling allows a quick évaluation of any profile, from reduced numerical results that are presented. Theory is compared in détail with récent expérimental results.On étudie théoriquement l'élargissement Stark des raies hydrogénoïdes d'ions multichargés, entre niveaux d'énergie élevés, lorsque les ions perturbateurs agissent quasi-statiquement et les électrons par impacts, spécialement par collisions inélastiques. On en précise les lois de variation suivant les charges et les nombres quantiques. Ces lois permettent d'obtenir rapidement un profil quelconque, à partir des résultats numériques réduits qui sont présentés. On effectue une comparaison détaillée avec des résultats expérimentaux récents