Maxwell-Bloch modeling of an x-ray pulse amplification in a 1D photonic crystal

We present an implementation of the Maxwell-Bloch (MB) formalism for the study of x-ray emission dynamics from periodic multilayer materials whether they are artificial or natural. The treatment is based on a direct Finite-Difference-Time-Domain (FDTD) solution of Maxwell equations combined with Bloch equations incorporating a random spontaneous emission noise. Besides periodicity of the material, the treatment distinguishes between two kinds of layers, those being active (or resonant) and those being off-resonance. The numerical model is applied to the problem of $K\alpha$ emission in multilayer materials where the population inversion could be created by fast inner-shell photoionization by an x-ray free-electron-laser (XFEL). Specificities of the resulting amplified fluorescence in conditions of Bragg diffraction is illustrated by numerical simulations. The corresponding pulses could be used for specific investigations of non-linear interaction of x-rays with matter

Line shape diagnostics for solid density plasmas produced by ultra intense subpicosecond laser

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87325/2/158_1.pd

Une méthode Galerkin discontinue d'ordre élevé pour la propagation d'ondes sismiques en milieu viscoélastique

We present a high-order discontinuous Galerkin method for the simulation of P-SV seismic wave propagation in heterogeneous media and two dimensions of space. The first-order velocity-stress system is obtained by assuming that the medium is linear, isotropic and viscoelastic, thus considering intrinsic attenuation. The associated stress-strain relation in the time domain being a convolution, which is numerically intractable, we consider the rheology of a generalized Maxwell body replacing the convolution by differential equations. This results in a velocity-stress system which contains additional equations for the anelastic functions including the strain history of the material. Our numerical method, suitable for complex triangular unstructured meshes, is based on a centered numerical flux and a leap-frog time-discretization. The extension to high order in space is realized by Lagrange polynomial functions, defined locally in each element. The inversion of a global mass matrix is avoided since an explicit scheme in time is used and because of the local nature of the discontinuous Galerkin formulation. The method is validated through numerical simulations including comparisons with a finite difference scheme.Nous présentons une méthode Galerkin discontinue d'ordre élévé pour la simulation de la propagation d'ondes sismiques P-SV en milieu hétérogène et en deux dimensions d'espace. Le système vitesse-contraintes du premier ordre est obtenu en supposant un milieu linéaire, isotrope et viscoélastique, prenant ainsi en compte l'atténuation intrinsèque du milieu. La relation contraintes-déformations dans le domaine temporel étant une convolution, qui nécessiterait une approximation numérique très coûteuse, nous considérons la rhéologie d'un "generalized Maxwell body" (GMB) remplaçant la convolution par un jeu d'équations différentielles. Il en résulte un système vitesse-contraintes contenant des équations supplémentaires pour les fonctions anélastiques qui traduisent l'historique de déformation du matériau. Notre méthode numérique, applicable à des maillages triangulaires non structurés, est basée sur des flux centrés et un schéma saute-mouton en temps. L'extension en espace à l'ordre élevé est obtenue grâce à des polynômes de Lagrange, définis localement dans chaque élément. La méthode étant explicite, elle ne nécessite pas d'inversion de matrice de masse globale. La méthode est validée via des simulations numériques, notamment des comparaisons avec un schéma aux différences finies

Opacity calculation for target physics using the ABAKO/RAPCAL code

Radiative properties of hot dense plasmas remain a subject of current interest since they play an important role in inertial confinement fusion (ICF) research, as well as in studies on stellar physics. In particular, the understanding of ICF plasmas requires emissivities and opacities for both hydro-simulations and diagnostics. Nevertheless, the accurate calculation of these properties is still an open question and continuous efforts are being made to develop new models and numerical codes that can facilitate the evaluation of such properties. In this work the set of atomic models ABAKO/RAPCAL is presented, as well as a series of results for carbon and aluminum to show its capability for modeling the population kinetics of plasmas in both LTE and NLTE regimes. Also, the spectroscopic diagnostics of a laser-produced aluminum plasma using ABAKO/RAPCAL is discussed. Additionally, as an interesting application of these codes, fitting analytical formulas for Rosseland and Planck mean opacities for carbon plasmas are reported. These formulas are useful as input data in hydrodynamic simulation of targets where the computation task is so hard that in line computation with sophisticated opacity codes is prohibitive

X‐ray spectroscopy of hot solid density plasmas produced by subpicosecond high contrast laser pulses at 1018–1019 W/cm2

Analysis is presented of K‐shell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 μm) at 1018–1019 W/cm2. Stark broadening measurements of He‐like and Li‐like lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce x‐ray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest x‐ray pulse at a given wavelength is relatively narrow. Lower intensity produces a short x‐ray pulse but low brightness. The x‐ray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximately 6% of the laser energy is coupled to the target at 1018 W/cm2 (1% in thermal electrons with Te≊0.6 keV and 5% in suprathermal electrons with Th≊25 keV). At Iλ2=1018 W μm2/cm2 (no prepulse) around 1010 photons are emitted per laser shot, in 2π srd in cold Kα radiation (2–9 Å, depending on the target material) and up to 2×1011 photons are obtained in 2π srd with the unresolved transition array (UTA) emission from the Ta target. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69900/2/PHPAEN-2-5-1702-1.pd

Ultrafast x‐ray sources@f|

Time‐resolved spectroscopy (with a 2 psec temporal resolution) of plasmas produced by the interaction between solid targets and a high contrast subpicosecond table top terawatt (T3) laser at 1016 W/cm2, is used to study the basic processes which control the x‐ray pulse duration. Short x‐ray pulses have been obtained by spectral selection or by plasma gradient scalelength control. Time‐dependent calculations of the atomic physics [Phys. Fluids B 4, 2007, 1992] coupled to a Fokker–Planck code [Phys. Rev. Lett. 53, 1461, 1984] indicate that it is essential to take into account the non‐Maxwellian character of the electron distribution for a quantitative analysis of the experimental results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70417/2/PFBPEI-5-7-2676-1.pd

Nutritional omega-3 deficiency alters glucocorticoid receptor-signaling pathway and neuronal morphology in regionally distinct brain structures associated with emotional deficits

Extensive evidence suggests that long term dietary n-3 polyunsaturated fatty acids (PUFAs) deficiency results in altered emotional behaviour. We have recently demonstrated that n-3 PUFAs deficiency induces emotional alterations through abnormal corticosterone secretion which leads to altered dendritic arborisation in the prefrontal cortex (PFC). Here we show that hypothalamic-pituitary-adrenal (HPA) axis feedback inhibition was not compromised in n-3 deficient mice. Rather, glucocorticoid receptor (GR) signaling pathway was inactivated in the PFC but not in the hippocampus of n-3 deficient mice. Consequently, only dendritic arborisation in PFC was affected by dietary n-3 PUFAs deficiency. In addition, occlusion experiment with GR blockade altered GR signaling in the PFC of control mice, with no further alterations in n-3 deficient mice. In conclusion, n-3 PUFAs deficiency compromised PFC, leading to dendritic atrophy, but did not change hippocampal GR function and dendritic arborisation. We argue that this GR sensitivity contributes to n-3 PUFAs deficiency-related emotional behaviour deficits

Lettre ouverte à Lexis-Nexis : à propos de l’édito de M. Jean Hauser « Phéromones »

Ce texte est une réponse rédigé par plusieurs juristes en réaction à un édito publié dans la Semaine juridique et portant sur le harcèlement sexuel. Il analyse et dénonce les propos tenus dans cet édito comme étant porteurs de stéréotypes de genre et d'une banalisation des violences sexuelles.This text is an answer written by several jurists to react to an editorial about sexual harassment published by the French legal review Semaine juridique. It analyses and denounces this editorial witch conveys gender stereotypes and trivialise sexual violence

Neuroinflammatory processes in cognitive disorders:Is there a role for flavonoids and n-3 polyunsaturated fatty acids in counteracting their detrimental effects?

Neuroinflammatory processes are known to contribute to the cascade of events culminating in the neuronal damage that underpins neurodegenerative disorders such as Parkinson's and Alzheimer's disease. With the ageing population and increased cases of neurodegenerative diseases, there is a crucial need for the development of new strategies capable to prevent, delay the onset or treat brain dysfunction and associated cognitive decline. Growing evidence sheds light on the use of dietary polyphenols and n-3 long chain polyunsaturated fatty acids to improve cognitive performances and reduce the neuroinflammatory and oxidative stress responses occurring with age and neurodegenerative pathologies. This review will summarise the most recent information related to the impact and mechanisms underlying the neuroinflammatory processes in neurodegenerative disorders. We will also detail the current evidence indicating that flavonoids and n-3 polyunsaturated fatty acids are strong candidate in preventing neuroinflammation and modulating age-related memory decline, and will describe the potential mechanisms of action underlying their neuroprotective effects. As such, these dietary bioactives represent important precursor molecules in the quest to develop of a new generation of drugs capable of counteracting neuroinflammation and neurodegenerative diseases

Interplay between n-3 and n-6 long-chain polyunsaturated fatty acids and the endocannabinoid system in brain protection and repair.

The brain is enriched in arachidonic acid (ARA) and docosahexaenoic acid (DHA), long-chain polyunsaturated fatty acids (LCPUFA) of the n-6 and n-3 series, respectively. Both are essential for optimal brain development and function. Dietary enrichment with DHA and other long-chain n-3 PUFA, such as eicosapentaenoic acid (EPA) have shown beneficial effects on learning and memory, neuroinflammatory processes and synaptic plasticity and neurogenesis. ARA, DHA and EPA are precursors to a diverse repertoire of bioactive lipid mediators, including endocannabinoids. The endocannabinoid system comprises cannabinoid receptors, their endogenous ligands, the endocannabinoids, and their biosynthetic and degradation enzymes. Anandamide (AEA) and 2-archidonoylglycerol (2-AG) are the most widely studied endocannabinoids, and are both derived from phospholipid-bound ARA. The endocannabinoid system also has well established roles in neuroinflammation, synaptic plasticity and neurogenesis, suggesting an overlap in the neuroprotective effects observed with these different classes of lipids. Indeed, growing evidence suggests a complex interplay between n-3 and n-6 LCPUFA and the endocannabinoid system. For example, long-term DHA and EPA supplementation reduces AEA and 2-AG levels, with reciprocal increases in levels of the analogous endocannabinoid-like DHA and EPA-derived molecules. This review summarises current evidence of this interplay and discusses the therapeutic potential for brain protection and repair