Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Adipose tissue. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

Transition between different regimes of rf glow discharges

Abstract: A self-consistent fluid model of radio-frequency glow discharges has been used to analyze the existence of two different discharge regimes and the transition between them The existence of these regimes had been previously established by Levitskii [Sov Phys Tech Phys 2, 887 (1958)] The self-sustaining and power-deposition mechanisms that characterize each of these regimes are drastically different In the first regime, termed as the ``wave-riding regime'' corresponding to low discharge power, most of the power deposition is due to bulk plasma electrons heated by the sheath expansions In the second regime termed as the ``secondary electron regime'' corresponding to higher discharge power, the discharge is sustained mainly by electrons emitted by the electrodes under ion bombardment and avalanching in the sheath regions The numerical results are in good agreement with previous experimental measurements by Godyak and Kanneh [IEEE Trans Plasma Sci PS-14, 112 (1986)] The results presented in this paper form the first self-consistent description of these different regimes and of the transition between them The validity domain of the model is restricted to pressure higher than a fraction of Torr and frequency less than a few tens of MHz The gas being considered is helium and the discharge power varies between 0 and 700 mW ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ The model is based on solutions of electron and ion fluid equations describing charged particle transport coupled with Poisson's equation for the electric field A realistic description of the electron kinetics has been obtained by considering separately two electron groups representing, respectively, the tail and the bulk of the electron distribution function The validity of the two-electron group fluid model has been checked with Monte Carlo simulations

Monge-Ampère equations in big cohomology classes

Abstract: We define non-pluripolar products of an arbitrary number of closed positive (1, 1)-currents on a compact Kahler manifold X. Given a big (1, 1)-cohomology class α on X (i.e. a class that can be represented by a strictly positive current) and a positive measure μ on X of total mass equal to the volume of α and putting no mass on pluripolar sets, we show that μ can be written in a unique way as the top-degree self-intersection in the non-pluripolar sense of a closed positive current in α. We then extend Kolodziedj’s approach to sup-norm estimates to show that the solution has minimal singularities in the sense of Demailly if μ has L1+e-density with respect to Lebesgue measure. If μ is smooth and positive everywhere, we prove that T is smooth on the ample locus of α provided α is nef. Using a fixed point theorem, we finally explain how to construct singular Kahler–Einstein volume forms with minimal singularities on varieties of general type.

Algal and cyanobacterial secondary metabolites in freshwaters: a comparison of allelopathic compounds and toxins

Abstract: Summary 1. The photoautotrophic micro-organisms collectively termed ‘micro-algae’ (including micro-eukaryotes and cyanobacteria) are known to produce a wide range of secondary metabolites with various biological actions. A small subset of these compounds has been identified. Some of them, termed allelopathic compounds, have been shown to play a role in allelopathy, defined here as inhibitory effects of secondary metabolites against either competitors or predators. Freshwater cyanobacteria also produce some secondary metabolites, termed toxins, which are highly toxic for animals. 2. While allelopathic compounds play a role in the interactions between the emitter organisms and their direct competitors or predators, toxins are categorised according to their toxic effect on several organisms, including some that may not be present in their immediate environment. However, these two definitions are not mutually exclusive. This review considers the evolutionary, ecological and physiological aspects of the production of allelopathic compounds by micro-algae in freshwaters, and compares the characteristics of allelopathic compounds with those of toxins. 3. Allelopathic compounds include alkaloids, cyclic peptides, terpens and volatile organic compounds. Toxins include alkaloids, cyclic peptides and lipopolysaccharides. No allelopathic compound type is associated with a particular phylogenetic group of algae. In contrast, freshwater toxins are only produced by cyanobacteria belonging to a restricted number of genera. Allelopathic compounds have various modes of action, from inhibition of photosynthesis to oxidative stress or cellular paralysis. Toxins are often enzyme inhibitors, or interfere with cell membrane receptors. 4. The ecological roles of allelopathic compounds have been well identified in several cases, but those of toxins are still debated. In the light of descriptions of negative effects of toxins on both micro-invertebrates and photoautotrophic organisms, we suggest that at least some toxins should actually be considered as allelopathic compounds. Further research on toxic secondary metabolites in freshwaters is now needed, with emphasis on the ecological effects of the compounds in the immediate environment of the emitter algae.