1,120 research outputs found

    A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars

    Full text link
    Context: The solution of the nonlocal thermodynamical equilibrium (non-LTE) radiative transfer equation usually relies on stationary iterative methods, which may falsely converge in some cases. Furthermore, these methods are often unable to handle large-scale systems, such as molecular spectra emerging from, for example, cool stellar atmospheres. Aims: Our objective is to develop a new method, which aims to circumvent these problems, using nonstationary numerical techniques and taking advantage of parallel computers. Methods: The technique we develop may be seen as a generalization of the coupled escape probability method. It solves the statistical equilibrium equations in all layers of a discretized model simultaneously. The numerical scheme adopted is based on the generalized minimum residual method. Result:. The code has already been applied to the special case of the water spectrum in a red supergiant stellar atmosphere. This demonstrates the fast convergence of this method, and opens the way to a wide variety of astrophysical problems.Comment: 13 pages, 9 figure

    Sur un Dictionnaire de la Commune

    Get PDF

    Varicella-Zoster virus ORF9p: role in viral envelopment and cell-cell fusion

    Full text link
    Varicella-Zoster virus is a double-stranded DNA virus belonging to the Herpesviridae family. Its genome encodes 72 ORFs among which ORF9p, the most expressed protein during the lytic cycle of the virus. Previous work in our laboratory showed that ORF9p plays a role in viral envelopment and that it may interact with the cellular Adaptor Protein-1 (AP-1) complex to do so. The aim of this work was to better characterize the role of ORF9p during secondary envelopment and to understand the importance of the ORF9p/AP-1 interaction in this process. First, we confirmed the ORF9p/AP-1 interaction in an infection context and identified the residue leucine 231 of ORF9p as critical for this interaction. We showed that alanine substitution of this residue led to a mislocalization of ORF9p in infected cells as well as a strong replication defect of the virus. Then, we showed that the L231A mutation was also associated with a lack of cell-cell fusion usually seen upon infection by the Wild-type virus. Moreover, naturally occurring compensatory mutations in the coding sequences of gE and/or gH not only restored the fusion phenotype, but also increased cell-cell fusion compared to the Wild-type virus. We have also demonstrated that ORF9p favored the formation of glycoproteins complexes around gE and gH and that the ORF9p L231A mutation destabilized these complexes. Finally, we propose a model explaining the potential role of ORF9p in secondary envelopment of VZV as well as in the cell-cell fusion process

    Les fondamentaux de la valeur des entreprises en Europe

    Full text link
    peer reviewe

    NLTE water lines in Betelgeuse-like atmospheres

    Full text link
    The interpretation of water lines in red supergiant stellar atmospheres has been much debated over the past decade. The introduction of the so-called MOLspheres to account for near-infrared "extra" absorption has been controversial. We propose that non-LTE effects should be taken into account before considering any extra-photospheric contribution. After a brief introduction on the radiative transfer treatment and the inadequacy of classical treatments in the case of large-scale systems such as molecules, we present a new code, based on preconditioned Krylov subspace methods. Preliminary results suggest that NLTE effects lead to deeper water bands, as well as extra cooling.Comment: 9 pages, 5 figures, Proceedings of the Betelgeuse Workshop, Paris, 201

    Étude du potentiel de création de formes du quantron

    Get PDF
    RÉSUMÉ Ce travail consiste en l’étude du potentiel de création de formes du quantron, un modèle récent de neurone artificiel qui décrit la transmission de l’information aux synapses des neurones à l’aide de processus stochastiques. Celui-ci a auparavant été le sujet de différentes tentatives d’approximations mathématiques dans le but d’applications futures au domaine des réseaux de neurones. Nous proposons plutôt une implémentation informatique fidèle au modèle original qui nous permet d’étudier ses caractéristiques. Dans le cadre de la reconnaissance de formes, nous explorons les capacités du quantron et de réseaux formés à partir de celui-ci à créer des images binaires à deux dimensions. Plus spécifiquement, nous nous sommes donnés comme objectif de déterminer les architectures et les paramètres des réseaux qui permettent de produire les 26 lettres majuscules de l’alphabet. D’abord en variant les paramètres de quantrons uniques selon des règles déterminées par notre connaissance préalable du fonctionnement du modèle, nous obtenons une grande quantité d’images que nous arrivons à assembler pour obtenir quelques premières lettres. En procédant à l’analyse des fonctionnements internes des quantrons qui produisent les lettres, nous arrivons à améliorer leur esthétisme et par le fait même acquérons une meilleure compréhension du modèle, ce qui nous mène à découvrir et démontrer des caractéristiques nouvelles lui donnant un puissant potentiel de production d’images. Des limites et contraintes sont aussi mises à jour, nous suggérons par la suite comment elles peuvent être contournées. Le souci de fidélité au modèle original du quantron est conservé tout au long du travail et les effets des approximations inhérentes à l’implémentation numérique sont étudiés. Nous proposons finalement des équations pour déterminer les paramètres de réseaux produisant n’importe quelle image désirée et les utilisons pour compléter la banque de lettres de l’alphabet. Les résultats obtenus suggèrent un avenir prometteur au modèle et différentes avenues sont suggérées pour tirer profit.----------ABSTRACT This document presents the study of pattern creation capacities of the quantron, a recent model of artificial neuron that describes the transmission of information at synapses with stochastic processes. Earlier works have been dedicated to the development of mathematical approximations that aim at the applicability of the model within the neural network domain. Rather, we propose an informatics implementation true to the original mathematical model that enables us to study its characteristics. Within the guidelines of pattern recognition, we explore the capacities of quantrons and of networks of quantrons to produce binary two dimensional images. Specifically, we had as an objective to determine the architectures and parameters of networks able to produce the 26 capital letters of the alphabet. First by varying the parameters of single quantrons within limits and rules determined by our prior understanding of the model, we obtain a great quantity of images which we are able to assemble in order to create a few first letters. By proceeding to the analysis of the inner workings of the quantrons producing the letters, we are able to improve their esthetics and at the same time obtain a better understanding of the model, which leads us to discover and demonstrate different new characteristics that give it strong image production capacities. Limitations are also brought to light for which we suggest ways to work around. In order to support the precision of the numeric approximations of the model, its effects are studied and carefully monitored. Finally, we propose equations that enable us to find parameter values that produce any desired image and make use of them in order to complete our collection of letters of the alphabet. The results suggest a promising future to the model and different avenues are suggested for later work to benefit from it

    Screening robust water infrastructure investments and their trade-offs under global change: A London Example

    Get PDF
    AbstractWe propose an approach for screening future infrastructure and demand management investments for large water supply systems subject to uncertain future conditions. The approach is demonstrated using the London water supply system. Promising portfolios of interventions (e.g., new supplies, water conservation schemes, etc.) that meet London’s estimated water supply demands in 2035 are shown to face significant trade-offs between financial, engineering and environmental measures of performance. Robust portfolios are identified by contrasting the multi-objective results attained for (1) historically observed baseline conditions versus (2) future global change scenarios. An ensemble of global change scenarios is computed using climate change impacted hydrological flows, plausible water demands, environmentally motivated abstraction reductions, and future energy prices. The proposed multi-scenario trade-off analysis screens for robust investments that provide benefits over a wide range of futures, including those with little change. Our results suggest that 60 percent of intervention portfolios identified as Pareto optimal under historical conditions would fail under future scenarios considered relevant by stakeholders. Those that are able to maintain good performance under historical conditions can no longer be considered to perform optimally under future scenarios. The individual investment options differ significantly in their ability to cope with varying conditions. Visualizing the individual infrastructure and demand management interventions implemented in the Pareto optimal portfolios in multi-dimensional space aids the exploration of how the interventions affect the robustness and performance of the system
    • …
    corecore