Nonlocal effects in the shot noise of diffusive superconductor - normal-metal systems

A cross-shaped diffusive system with two superconducting and two normal electrodes is considered. A voltage $eV < \Delta$ is applied between the normal leads. Even in the absence of average current through the superconducting electrodes their presence increases the shot noise at the normal electrodes and doubles it in the case of a strong coupling to the superconductors. The nonequilibrium noise at the superconducting electrodes remains finite even in the case of a vanishingly small transport current due to the absence of energy transfer into the superconductors. This noise is suppressed by electron-electron scattering at sufficiently high voltages.Comment: 4 pages, RevTeX, 2 eps figure

Hydrodynamic instabilities in gaseous detonations: comparison of Euler, Navier–Stokes, and large-eddy simulation

A large-eddy simulation is conducted to investigate the transient structure of an unstable detonation wave in two dimensions and the evolution of intrinsic hydrodynamic instabilities. The dependency of the detonation structure on the grid resolution is investigated, and the structures obtained by large-eddy simulation are compared with the predictions from solving the Euler and Navier–Stokes equations directly. The results indicate that to predict irregular detonation structures in agreement with experimental observations the vorticity generation and dissipation in small scale structures should be taken into account. Thus, large-eddy simulation with high grid resolution is required. In a low grid resolution scenario, in which numerical diffusion dominates, the structures obtained by solving the Euler or Navier–Stokes equations and large-eddy simulation are qualitatively similar. When high grid resolution is employed, the detonation structures obtained by solving the Euler or Navier–Stokes equations directly are roughly similar yet equally in disagreement with the experimental results. For high grid resolution, only the large-eddy simulation predicts detonation substructures correctly, a fact that is attributed to the increased dissipation provided by the subgrid scale model. Specific to the investigated configuration, major differences are observed in the occurrence of unreacted gas pockets in the high-resolution Euler and Navier–Stokes computations, which appear to be fully combusted when large-eddy simulation is employed

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors

Reactive Rayleigh-Taylor Turbulence

The Rayleigh-Taylor (RT) instability develops and leads to turbulence when a heavy fluid falls under the action of gravity through a light one. We consider this phenomenon accompanied by a reactive transformation between the fluids, and study with Direct Numerical Simulations (DNS) how the reaction (flame) affects the turbulent mixing in the Boussinesq approximation. We discuss "slow" reactions where the characteristic reaction time exceeds the temporal scale of the RT instability. In the early turbulent stage, effects of the flame are distributed over a maturing mixing zone, whose development is weakly influenced by the reaction. At later times, the fully mixed zone transforms into a conglomerate of pure-fluid patches of sizes proportional to the mixing zone width. In this "stirred flame'' regime, temperature fluctuations are consumed by reactions in the regions separating the pure-fluid patches. This DNS-based qualitative description is followed by a phenomenology suggesting that thin turbulent flame is of a single-fractal character, and thus distribution of the temperature field is strongly intermittent.Comment: 14 pages, 4 figure

Production primaire et relations trophiques chez les invertébrés des communautés halophiles de Camargue

Les biomasses végétales mesurées dans les zones émergées de la sansouire camarguaise sont relativement élevées dans le Sali cornietum fruticosae, de l’ordre de 3 kg de matière sèche par m2 alors qu’elles n’atteignent que 0,4 kg/m2 dans Y Arthrocnemetum. La production primaire annuelle du S. fruticosae se situe entre 0,5 et 1 kg de matière sèche par m2, soit du même ordre que celle d’un peuplement à Quercus ilex étudié sous le même climat. Elle est réalisée pour l’essentiel en trois mois, de mai à juillet. Ensuite l’abaissement de la nappe aquifère, conséquence de la forte évapo ration estivale, se traduit par une chute du potentiel hydrique et par une régulation efficace de la transpiration. L’étude des niveaux de consommation chez les Invertébrés terrestres montre, qu’en dehors de périodes exceptionnelles de pullulation des chenilles de deux espèces de microlépidoptères, la forte production primaire de S. fruticosae n’est pas utilisée directement. Les détritivores (Coléoptères, Collemboles) et les décomposeurs jouent un rôle essentiel. Dans les zones à submersion temporaire l’abondance des débris végétaux desséchés pendant l’été qui s’ajoute à la production alguale pendant l’inondation hivernale permet la pullulation des Crustacés planctoniques, en particulier celle des Copépodes Cala nides filtreurs dont plusieurs espèces de tailles différentes peuvent proliférer ensemble. Ces populations de Crustacés ainsi que les larves aquatiques d’insectes procurent lors de l’assèchement une nourriture abondante pour la communauté ripicole où les Coléoptères Carabiques sont bien représentés.The above-ground plant biomass in the emerged zones of the Camargue “ sansouire ” is relatively high in Salicornietum fruticosae, about 3 kg of dry matter per square metre, whereas it only reaches 0.4 kg/m2 in Arthrocnemetum. The above-ground annual primary production of Salicornietum fruticosae ranges from 0.5 to 1.0 kg/m2/year, which is approximately equal to that of Quercus ilex stands in the same climate. Production essentially takes place during a three month period from May to July. Afterwards the lowering of the water table resulting from the high level of evaporation during the summer is marked by a decrease in water potential and by an efficient regulation of transpiration. Aside from exceptional outbreaks of caterpillars of two species of microlepidoptera, the primary production of Salicornia is not used by primary consumers, but by detritus feeders (beetles and springt ails) and decomposers. In the areas temporarily flooded, algal production during winter flooding and the accumulation of dried plant debris in summer, allow planktonic Crustacea, Calanoid Copepods particularly, to reach high population densities. These Copepods, together with the larvae of aquatic insects, provide an abundant food for Carabid beetles and other riparian invertebrates when water recedes and the “ sansouire ” dries out

Reaction front propagation in a turbulent flow

The propagation of reaction fronts was studied by direct numerical simulations. The velocity field was obtained by integrating the Navier-Stokes equation. The structure of the reaction front and the enhancement of the front propagation speed were investigated. The ratio of eddy turnover times and of the characteristic chemical time scale was determined

Biodiversity of the Collembola Fauna of Wetland Kerkini (N. Greece), with description of the sexual dimorphism of Entomobrya atrocincta Schött 1896 (Collembola: Entomobryomorpha)

A report on the results of a research into some aspects of the collembolan fauna of the Greek Nature Reserve associated with Lake Kerkini, known as Wetland Kerkini, is presented. The nature reserve is large and includes a wide variety of habitats, many of which were not included in this preliminary survey. From the areas sampled we recorded 44 species, of which 39 were previously described, two (Folsomia potapovi Jordana & Baquero n. sp., Entomobrya naziridisi Jordana & Baquero n. sp.), are new to science, while three are identifi ed to generic level; a further 21 are new records for Greece, and an additional 11 species are new records to the Greek Mainland. Sampling with Berlese- Tullgren funnels and Malaise traps allowed us to capture species typical of soil and species present over vegetation. This summary is based on the records held in the online database of the Fauna Europaea Project

Differentially expressed profiles in the larval testes of Wolbachia infected and uninfected Drosophila

BACKGROUND: Wolbachia are endosymbiotic bacteria that are frequently found in arthropods and nematodes. These maternally inherited bacteria manipulate host reproduction by several mechanisms including cytoplasmic incompatibility (CI). CI is the most common phenotype induced by Wolbachia and results in the developmental arrest of embryos derived from crosses between Wolbachia-infected males and uninfected females. Although the molecular mechanisms of CI are currently unknown, several studies suggest that host sperm is modified by Wolbachia during spermatogenesis. RESULTS: We compared the gene expression of Drosophila melanogaster larval testes with and without the wMel strain of Wolbachia to identify candidate genes that could be involved in the interaction between Wolbachia and the insect host. Microarray, quantitative RT-PCR and in situ hybridization analyses were carried out on D. melanogaster larval testes to determine the effect of Wolbachia infection on host gene expression. A total of 296 genes were identified by microarray analysis to have at least a 1.5 fold change [q-value < 5%] in expression. When comparing Wolbachia-infected flies to uninfected flies, 167 genes were up-regulated and 129 genes down-regulated. Differential expression of genes related to metabolism, immunity, reproduction and other functions were observed. Quantitative RT-PCR (qRT-PCR) confirmed 12 genes are differentially expressed in the testes of the 3rd instar larvae of Wolbachia-infected and uninfected flies. In situ hybridization demonstrated that Wolbachia infection changes the expression of several genes putatively associated with spermatogenesis including JH induced protein-26 and Mst84Db, or involved in immune (kenny) or metabolism (CG4988-RA). CONCLUSIONS: Wolbachia change the gene expression of 296 genes in the larval testes of D. melanogaster including genes related to metabolism, immunity and reproduction. Interestingly, most of the genes putatively involved in immunity were up-regulated in the presence of Wolbachia. In contrast, most of the genes putatively associated with reproduction (especially spermatogenesis) were down-regulated in the presence of Wolbachia. These results suggest Wolbachia may activate the immune pathway but inhibit spermatogenesis. Our data provide a significant panel of candidate genes that may be involved in the interaction between Wolbachia and their insect hosts. This forms a basis to help elucidate the underlying mechanisms of Wolbachia-induced CI in Drosophila and the influence of Wolbachia on spermatogenesis