441 research outputs found
Structural properties of silicon dioxide thin films densified by medium-energy particles
Classical molecular-dynamics simulations have been carried out to investigate
densification mechanisms in silicon dioxide thin films deposited on an
amorphous silica surface, according to a simplified ion-beam assisted
deposition (IBAD) scenario. We compare the structures resulting from the
deposition of near-thermal (1 eV) SiO particles to those obtained with
increasing fraction of 30 eV SiO particles. Our results show that there
is an energy interval - between 12 and 15 eV per condensing SiO unit on
average - for which the growth leads to a dense, low-stress amorphous
structure, in satisfactory agreement with the results of low-energy ion-beam
experiments. We also find that the crossover between low- and high-density
films is associated with a tensile to compressive stress transition, and a
simultaneous healing of structural defects of the {\em a-}SiO network,
namely three- and four-fold rings. It is observed, finally, that densification
proceeds through significant changes at intermediate length scales (4--10 \AA),
leaving essentially unchanged the ``building blocks'' of the network, viz. the
Si(O) tetrahedra. This latter result is in qualitative agreement
with the mechanism proposed to explain the irreversible densification of
amorphous silica recovered from high pressures ( 15--20 GPa).Comment: 12 pages including 10 postscript figures; submitted to Phys. Rev. B;
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Discrete-time port-Hamiltonian systems: A definition based on symplectic integration
International audienceWe introduce a new definition of discrete-time port-Hamiltonian systems (PHS), which results from structure-preserving discretization of explicit PHS in time. We discretize the underlying continuous-time Dirac structure with the collocation method and add discrete-time dynamics by the use of symplectic numerical integration schemes. The conservation of a discrete-time energy balance-expressed in terms of the discrete-time Dirac structure-extends the notion of symplecticity of geometric integration schemes to open systems. We discuss the energy approximation errors in the context of the presented definition and show that their order is consistent with the order of the numerical integration scheme. Implicit Gauss-Legendre methods and Lobatto IIIA/IIIB pairs for partitioned systems are examples for integration schemes that are covered by our definition. The statements on the numerical energy errors are illustrated by elementary numerical experiments
Pseudo-spectral methods for the spatial symplectic reduction of open systems of conservation laws
International audienceA reduction method is presented for systems of conservation laws with boundary energy flow. It is stated as a generalized pseudo-spectral method which performs exact differentiation by using simultaneously several approximation spaces generated by polynomials bases and suitable choices of port-variables. The symplecticity of this spatial reduction method is proved when used for the reduction of both closed and open systems of conservation laws, for any choice of collocation points (i.e. for any polynomial bases). The symplecticity of some more usual collocation schemes is discussed and finally their accuracy on approximation of the spectrum, on the example of the ideal transmission line, is discussed in comparison with the suggested reduction scheme
Decontamination of Solid and Powder Foodstuffs using DIC Technology
International audienc
Vers des machines exaflopiques vertes
National audienceMoving to exascale era can not be done without taking into account the energy consumption of such systems. In this paper, we wonder if the solutions found for the petascale era will still be available for the exascale era. We propose to adapt some of them within a green framework.Les superordinateurs ont connu une croissance rapide en particulier ces dernieÌres anneÌes. AÌ peine avons-nous franchi l'eÌchelle du petaflop que l'on s'inteÌresse deÌjaÌ aÌ concevoir des machines pouvant atteindre 1 exaflop par seconde et ce, afin d'eÌtre en mesure de satisfaire les besoins importants en terme de performances qu'expriment les scientifiques dans divers domaines. Cependant, pour concevoir des machines exaflopiques, il faut au preÌalable relever certains deÌfis dont le principal est d'eÌtre capable de reÌduire les importants couÌts de consommations eÌnergeÌtiques dans ces machines. Dans cet article, nous nous demandons si les solutions existantes pour reÌduire la consommation eÌnergeÌtique au niveau peÌta- flopique resteront valables aÌ l'eÌchelle exaflopique et dans quelles mesures il est possible de les adap- ter pour qu'elles puissent passer aÌ l'eÌchelle. Nous proposons eÌgalement des solutions nouvelles pour l'eÌchelle exaflopique, qui deÌbouchent sur une architecture verte pour les machines exaflopiques
SystÚmes de compréhension et de traduction de la parole (vers une approche unifiée dans le cadre de la portabilité multilingue des systÚmes de dialogue)
La gĂ©nĂ©ralisation de l usage des systĂšmes de dialogue homme-machine accroĂźt la nĂ©cessitĂ© du dĂ©veloppement rapide des diffĂ©rents composants de ces systĂšmes. Les systĂšmes de dialogue peuvent ĂȘtre conçus pour diffĂ©rents domaines d application et dans des langues diffĂ©rentes. La nĂ©cessitĂ© d une production rapide pour de nouvelles langues reste un problĂšme ouvert et crucial auquel il est nĂ©cessaire d apporter des solutions efficaces.Nos travaux s intĂ©ressent particuliĂšrement au module de comprĂ©hension de la parole et proposent des approches pour la portabilitĂ© rapide peu coĂ»teuse de ce module.Les mĂ©thodes statistiques ont montrĂ© de bonnes performances pour concevoir les modules de comprĂ©hension de la parole pour l Ă©tiquetage sĂ©mantique de tours de dialogue.Cependant ces mĂ©thodes nĂ©cessitent de larges corpus pour ĂȘtre apprises. La collecte de ces corpus est aussi coĂ»teuse en temps et en expertise humaine.Dans cette thĂšse, nous proposons plusieurs approches pour porter un systĂšme de comprĂ©hension d une langue vers une autre en utilisant les techniques de la traduction automatique. Les premiers travaux consistent Ă appliquer la traduction automatique Ă plusieurs niveaux du processus de portabilitĂ© du systĂšme de comprĂ©hension afin de rĂ©duire le coĂ»t liĂ© Ă production de nouvelles donnĂ©es d apprentissage. Les rĂ©sultats expĂ©rimentaux montrent que l utilisation de la traduction automatique permet d obtenir des systĂšmes performant avec un minimum de contribution humaine.Cette thĂšse traite donc Ă la fois de la traduction automatique et de la comprĂ©hension de la parole. Nous avons effectuĂ© une comparaison approfondie entre les mĂ©thodes utilisĂ©es pour chacune des tĂąches et nous avons proposĂ© un dĂ©codage conjoint basĂ© sur une mĂ©thode discriminante qui Ă la fois traduit une phrase et lui attribue ses Ă©tiquettes sĂ©mantiques. Ce dĂ©codage est obtenu par une approche Ă base de graphe qui permet de composer un graphe de traduction avec un graphe de comprĂ©hension. Cette reprĂ©sentation peut ĂȘtre gĂ©nĂ©ralisĂ©e pour permettre des transmissions d informations riches entre les composants du systĂšme de dialogueThe generalisation of human-machine dialogue system increases the need for a rapid development of the various components of these systems. Dialogue systems can be designed for different applications and in different languages. The need for a fast production of systems for new languages is still an open and crucial issue which requires effective solutions. Our work is particularly interested in speech understanding module and propose approaches for language portability of this module. The statistical methods showed good performance to design modules for speech understanding. However, these methods require large corpora to be trained. The collection of these corpora is expensive in time and human expertise. In this thesis, we propose several approaches to port an understanding system from one language to another using machine translation techniques. The experimental results show that the use of machine translation allows to produce efficient systems with minimal human effort. This thesis addresses both machine translation and speech understanding domain. We conducted a comparison between the methods used for each task and we have proposed a joint decoding between translation and understanding based on a discriminant method. This decoding is achieved by a graph-based approach which allows to compose a translation graph with an understanding graph. This representation can be generalized to allow a rich transmission of information between the components of the dialogue systemAVIGNON-Bib. numĂ©rique (840079901) / SudocSudocFranceF
DNA-inspired Scheme for Building the Energy Profile of HPC Systems
International audienceEnergy usage is becoming a challenge for the design of next generation large scale distributed systems. This paper explores an inno- vative approach of profiling such systems. It proposes a DNA-like solution without making any assumptions on the running applications and used hardware. This profiling based on internal counters usage and energy monitoring allows to isolate specific phases during the execution and enables some energy consumption control and energy usage prediction. First experimental validations of the system modeling are presented and analyzed
Beyond CPU Frequency Scaling for a Fine-grained Energy Control of HPC Systems
International audienceModern high performance computing subsystems (HPC) - including processor, network, memory, and IO - are provided with power management mechanisms. These include dynamic speed scaling and dynamic resource sleeping. Understanding the behavioral patterns of high performance computing systems at runtime can lead to a multitude of optimization opportunities including controlling and limiting their energy usage. In this paper, we present a general purpose methodology for optimizing energy performance of HPC systems consid- ering processor, disk and network. We rely on the concept of execution vector along with a partial phase recognition technique for on-the-fly dynamic management without any a priori knowledge of the workload. We demonstrate the effectiveness of our management policy under two real-life workloads. Experimental results show that our management policy in comparison with baseline unmanaged execution saves up to 24% of energy with less than 4% performance overhead for our real-life workloads
On Applying DTNs to a Delay Constrained Scenario in Wired Networks
International audienceThe Delay/Disruption Tolerant Networking (DTN) architecture has been successful in addressing communication issues such as disruption, variable delay, and network parti- tioning. DTN uses intermittently available links to communicate opportunistically regardless of delivery delay. In the literature, much work has been done mainly to improve the rate of message delivery and routing algorithms. However, previous work has not focused on guaranteeing the message delivery delay in a DTN scenario. In addition, real deployments of DTN systems have so far been mostly proof-of-concepts in research projects. We address the problem of delivery delay in a wired DTN scenario where messages are moved across a time-varying graph topology whose dynamics are known in advance and can be modified. We propose a framework that guarantees bounded delivery delay of users' data. To demonstrate the feasibility of our network management approach, we evaluate our framework on a 10-node wired DTN topology deployed on the Grid5000 platfor
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