Femtosecond Laser-Produced Plasma X-Rays from Periodically Modulated Surface Targets

We have studied theoretically and experimentally the x-ray production above 1 keV from femtosecond laser plasmas generated on periodically modulated surface targets. Laser energy coupling to plasma surface waves has been modeled using a numerical differential method. Almost total absorption of incident laser radiation is predicted for optimized interaction conditions. Silicon gratings have been irradiated by a 120fs Ti:sapphire laser at irradiances in excess of 1016 W/cm2. X-ray intensities above 1.5 keV (K-shell lines) have been measured as a function of the incidence angle. Results show a distinct x-ray emission maximum for the first order diffraction angle and are in good qualitative agreement with our theoretical predictions

Role of Histone Acetylation in the Stimulatory Effect of Valproic Acid on Vascular Endothelial Tissue-Type Plasminogen Activator Expression

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Active transport of L-proline in the protozoan parasite Trypanosoma brucei brucei.

The characteristics of L-proline transport in the procyclic form of Trypanosoma brucei were studied by using L-[14C]proline and a quick separation technique by centrifugation through an oil mixture. L-Proline uptake displayed typical Michaelis-Menten kinetics, with a Km of 19 microM and a maximum transport velocity of 17 nmol/min per 10(8) cells at 27 degrees C. The maximum concentration gradient factor obtained after 1 min of incubation was 270-fold in 0.02 mM proline. Cells permeabilized with 80 microM digitonin were still able to accumulate 14C label, but to a lower extent. The temperature-dependence of proline uptake gave an apparent activation energy of 74.9 kJ.mol-1. In competition studies with a 10-fold excess of structural analogues, L-alanine, L-cysteine and L-azetidine-2-carboxylate were found to inhibit L-proline uptake. Variation of pH or addition of the protonophore carbonyl cyanide m-chlorophenylhydrazone ('CCCP') did not affect proline transport, showing that it is not driven by a protonmotive force. The absence of Na+, with or without monensin, did not affect proline transport. The absence of K+ and the addition of the Na+,K(+)-ATPase inhibitor ouabain had no significant effect on proline uptake activity. The thiol-modifying reagent iodoacetate (10 mM) decreased proline uptake by half. KCN (1 mM) inhibited proline uptake to a lesser extent, and the degree of inhibition was proportional to the intracellular ATP concentration. Preliminary experiments on proline transport in plasma-membrane vesicles of the cells, using a filtration technique, showed an uptake of proline (0.67 nmol/mg of protein) by the vesicles, but only in the presence of intravesicular ATP. The results thus obtained suggest that the proline carrier system in T. brucei is ATP-driven and independent of Na+, K+ or H+ co-transport

Profils de chercheurs primo entrepreneurs et croissance de la jeune entreprise innovante

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Profils de chercheurs primo entrepreneurs et croissance de la jeune entreprise innovante

International audienc

DIAGNOSTICS OF GOLD LASER PLASMAS

Dans le but d'étudier un schéma de laser X dans les nickeloïdes, on a besoin d'un modèle pour déterminer les paramètres qui décrivent les plasmas d'ions lourds fortement ionisés. Le sujet de ce travail est d'étudier les plasmas d'or créés par laser et de comparer les résultats expérimentaux aux prédictions d'un modele collisionnel-radiatif dans les nickeloïdes. La température et la densité électronique sont mesurées à partir des raies d'emission d'un traceur d'aluminium, et sont comparées aux valeurs obtenues avec le modèle collisionnel-radiatif pour un plasma d'or pur. Les résultats montrent que l'on peut estimer la température et la densité électronique dans un plasma d'or pur.In order to achieve a nickel-like X ray laser scheme we need a tool to determine the parameters which characterise the high-2 plasma. The aim of this work is to study gold laser plasmas and to compare experimental results to a collisional-radiative model which describes nickel-like ions. The electronic temperature and density are measured by the emission of an aluminium tracer. They are compared to the predictions of the nickel-like model for pure gold. The results show that the density and temperature can be estimated in a pure gold plasma

High dynamic range streak camera for subpicosecond time-resolved x-ray spectroscopy

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Epigenetic Regulation of Tissue-Type Plasminogen Activator in Human Brain Tissue and Brain-Derived Cells

The serine protease tissue-type plasminogen activator (t-PA) is involved in both vital physiological brain processes, such as synaptic plasticity, and pathophysiological conditions, such as neurodegeneration and ischemic stroke. Recent data suggest that epigenetic mechanisms play an important role in the regulation of t-PA in human endothelial cells. However, there are limited data on epigenetic regulation of t-PA in human brain-derived cells. We demonstrate that treatment of cultured human neurons and human astrocytes with the histone deacetylase inhibitors trichostatin A (TSA) and MS-275 resulted in a two- to threefold increase in t-PA mRNA and protein expression levels. Next, we performed a chromatin immunoprecipitation assay on treated astrocytes with antibodies directed against acetylated histones H3 and H4 (both markers of gene activation). Treatment with MS-275 and TSA for 24 hours resulted in a significant increase in H3 acetylation, which could explain the observed increase in t-PA gene activity after the inhibition of histone deacetylation. Furthermore, DNA methylation analysis of cultured human neurons and astrocytes, as well as human postmortem brain tissue, revealed a stretch of unmethylated CpG dinucleotides in the proximal t-PA promoter, whereas more upstream CpGs were highly methylated. Taken together, these results implicate involvement of epigenetic mechanisms in the regulation of t-PA expression in the human brain