Maximizing energy deposition by shaping few-cycle laser pulses

We experimentally investigate the impact of pulse shape on the dynamics of laser-generated plasma in rare gases. Fast-rising triangular pulses with a slower decay lead to early ionization of the gas and depose energy more efficiently than their temporally reversed counterparts. As a result, in both argon and krypton, the induced shockwave as well as the plasma luminescence are stronger. This is due to an earlier availability of free electrons to undergo inverse Bremsstrahlung on the pulse trailing edge. Our results illustrate the ability of adequately tailored pulse shapes to optimize the energy deposition in gas plasmas

N-3 polyunsaturated fatty acid and neuroinflammation in aging and Alzheimer's disease

The innate immune system of the brain is mainly composed of microglial cells, which play a key role in the maintenance of synapses and the protection of neurons against noxious agents or lesions owing to their phagocytic activity. In the healthy brain, microglia are highly motile and strongly interact with neurons either by physical contact, induction of oxidative stress or through specific mediators, such as chemokines and cytokines. In response to inflammatory insult however, microglial cells get activated and produce inflammatory cytokines. The action of cytokines on specific receptors expressed in the brain triggers the development of sickness behavior and altered cognitive and emotional processes. The effects are acute and reversible as normal behavior is restored once the synthesis of inflammatory brain cytokines returns to baseline after a few hours. However, in pathological situations, these cytokines may reach toxic levels and have irreversible consequences such as neuronal death, as observed in neurodegenerative disorders such as Alzheimer’s disease. Omega-3 (n-3) polyunsaturated fatty acids (PUFAs) are essential nutrients and fundamental components of neuronal and glial cell membranes. They accumulate in the brain during the perinatal period in a dietary supply-dependent fashion. Their brain levels may diminish with age, but can be increased by diets enriched in n-3 PUFAs. Changes in the immune profile have been associated with n-3 PUFAs intake in humans and animal models. Therefore, the increasing exposure of the population to diets low in n-3 PUFAs could contribute to the deleterious effects of the chronic activation of microglia in the brain

The SIB Swiss Institute of Bioinformatics' resources: focus on curated databases

The SIB Swiss Institute of Bioinformatics (www.isb-sib.ch) provides world-class bioinformatics databases, software tools, services and training to the international life science community in academia and industry. These solutions allow life scientists to turn the exponentially growing amount of data into knowledge. Here, we provide an overview of SIB's resources and competence areas, with a strong focus on curated databases and SIB's most popular and widely used resources. In particular, SIB's Bioinformatics resource portal ExPASy features over 150 resources, including UniProtKB/Swiss-Prot, ENZYME, PROSITE, neXtProt, STRING, UniCarbKB, SugarBindDB, SwissRegulon, EPD, arrayMap, Bgee, SWISS-MODEL Repository, OMA, OrthoDB and other databases, which are briefly described in this article

Coherent control of excited states: molecular discrimination & Kramers-Hennberger states

Cette thèse s'inscrit dans le cadre général de la spectroscopie non-linéaire assistée par la mise en forme d'impulsion ultra courte. Nous appliquons le façonnage d'impulsion femtoseconde dans les longueurs d'ondes de l'ultraviolet profond ainsi que sur une large bande spectrale allant du visible au proche infrarouge. Au travers d'une première expérience, nous décrivons une technique tout optique résolue en temps reposant sur la déplétion d'états de fluorescence excités. Cette technique permet la détection et l'identification d'acides aminés essentiels et d'hormones sur un fond fluorescent. Dans une seconde expérience, nous démontrons expérimentalement la présence d'états de Kramers-Henneberger (KH) (atomes habillés) dans des gaz nobles par l'application d'impulsions femtoseconde modulées par une phase spécifique. Cette modulation de la phase qui opère sur une bande spectrale extrêmement large nous permet de révéler des raies spectrales résonnantes spécifiques à un atome habillé par un champ laser intense

Probing ultrafast thermalization with field-free molecular alignment

International audienceThe rotation-translation thermalization of CO2 gas is investigated 500 ps after its preheating by a nonresonant short and intense laser pulse. The temperature of thermalization is optically determined with two additional short laser pulses enabling a field-free molecular alignment process and its probing, respectively. The measurements are performed for various intensities of the preheat pulse, leading to the observation of different temperatures which are in very good agreement with classical molecular dynamics simulations. The results can be regarded as a step towards real-time tracking of ultrafast relaxation pathways in molecular motion

Triggering filamentation using turbulence

We study the triggering of single filaments due to turbulence in the beam path for a laser of power below the filamenting threshold. Turbulence can act as a switch between the beam not filamenting and producing single filaments. This 'positive' effect of turbulence on the filament probability, combined with our observation of off-axis filaments suggests the underlying mechanism is modulation instability caused by transverse perturbations. We hereby experimentally explore the interaction of modulation instability and turbulence, commonly associated with multiple-filaments, in the single-filament regime

Dynamical System Modeling of Self-Regulated Systems Undergoing Multiple Excitations: First Order Differential Equation Approach

This article proposes a dynamical system modeling approach for the analysis of longitudinal data of self-regulated homeostatic systems experiencing multiple excitations. It focuses on the evolution of a signal (e.g., heart rate) before, during, and after excitations taking the system out of its equilibrium (e.g., physical effort during cardiac stress testing). Such approach can be applied to a broad range of outcomes such as physiological processes in medicine and psychosocial processes in social sciences, and it allows to extract simple characteristics of the signal studied. The model is based on a first order linear differential equation with constant coefficients defined by three main parameters corresponding to the initial equilibrium value, the dynamic characteristic time, and the reaction to the excitation. Assuming the presence of interindividual variability (random effects) on these three parameters, we propose a two-step procedure to estimate them. We then compare the results of this analysis to several other estimation procedures in a simulation study that clarifies under which conditions parameters are accurately estimated. Finally, applications of this model are illustrated using cardiology data recorded during effort tests

Habitat durable : approches critiques

Ce numéro de Sciences de la Société vise à saisir dans quelle mesure il devient possible d’adresser un certain nombre de critiques au développement et à l’habitat durables. De telles critiques pourront aider à mieux comprendre les problèmes rencontrés par l’habitat durable – que se disputent les acteurs individuels (habitants, professionnels, bailleurs, architectes, etc.) ou collectifs (entreprises, institutions, associations, etc.) –, depuis la « production » de cet artefact à sa « consommation ». Il s’agit alors dans cette livraison, de mettre en perspective non seulement les forces mais aussi les ambiguïtés ou les apories d’un tel « habitat durable », que celui-ci soit tour à tour considéré comme l’expression d’une « totalité en acte » ; d’un système incluant l’ensemble des éléments qui le constituent – des conditions de sa production à sa fonction d’usage ; ou bien encore comme une « catégorie de la pratique ». Comment encore un tel « habiter » peut-il reconfigurer notre rapport au monde – autrement que par une injonction à la ville durable – et ainsi réinterroger des enjeux environnementaux, sociaux, économiques, culturels ou de gouvernance ? Ce numéro de Sciences de la Société fait l’hypothèse que les critiques, aujourd’hui portées à l’endroit de l’habitat durable, pourront aider à des éléments de réponse à la mesure de ces enjeux