Jurnal Edukasi
Not a member yet
4879 research outputs found
Sort by
Proof nets and semi-star-autonomous categories
No full textInternational audienceIn this paper it is proved that Girard’s proof nets for multiplicative linear logic characterise free semi-⋆-autonomous-categories
Energy management method for an electric vehicle
No full textThe invention relates to a method for managing energy consumption for an automobile having an electric battery and a heat engine, said method making it possible to select the use phases of said engine along a given route so as to minimize the fuel consumption of said vehicle. The main characteristic of the method according to the invention is that it includes the following steps: a step of cutting the road network, which is taken into consideration for a given route, into a plurality of segments, each segment being defined by an input node and by an output node; a step of calculating, from a speed associated with said segment, the probability of a speed transition between a speed at an input node and a speed at an output node of a segment, while taking a plurality of speeds at the input node and a plurality speeds at the output node into consideration, said step being carried out gradually over all of the segments of the route; a step of applying a stochastic optimization algorithm taking all the possible transition scenarios between each input node and each output node, and the probability associated therewith, into account, and taking a fuel consumption model between two successive nodes into account, said step being carried out over all of the segments of the route; and a step of selecting use phases of the heat engine along the route
Possible climates on terrestrial exoplanets
No full textInternational audienceWhat kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance, to optimize future telescopic observations or to assess the probability of habitable worlds. To begin with, climate primarily depends on (i) the atmospheric composition and the volatile inventory; (ii) the incident stellar flux; and (iii) the tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes, which are difficult to model: origins of volatiles, atmospheric escape, geochemistry, photochemistry, etc. We discuss physical constraints, which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using global climate models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components, such as a 'dynamical core', a radiative transfer solver, a parametrization of subgridscale turbulence and convection, a thermal ground model and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive feedbacks. They can drive planets with very similar forcing and volatile inventory to completely different states. For instance, the coupling among temperature, volatile phase changes and radiative properties results in instabilities, such as runaway glaciations and runaway greenhouse effect. © 2014 The Author(s) Published by the Royal Society
Two methods for retrieving UV index for all cloud conditions from sky imager products or total SW radiation measurements
No full textInternational audienceCloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (60°). Similarly, local short-time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%). Cloud effects on UV Index (UVI) and total solar radiation (TR) are assessed. The role of cloud cover and sunny conditions (from sky images) and of solar zenith angle is investigated. The analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds affect TR more than UVI, both in reducing and enhancing the cloud-free radiation. From the analyses, two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Methods' estimations are compared with measurements. © 2014 The American Society of Photobiology
Extraction de motifs dans les graphes de workflows scientifiques
No full textLa quantité de données données biologiques est en pleine croissance. Une fois ces données brutes collectées, il faut les analyser et les comparer aux données existantes pour obtenir de nouvelles connaissances. Cette analyse se fait grâce à l'utilisation de différents outils, scripts ou programmes que l'on peut aujourd'hui utiliser et enchaîner en utilisant un système de gestion de workflows scientifique. L'utilisation des systèmes de workflows est en plein essor, donnant lieu à un important développement des bases de données pour stocker ces workflows. Cependant, très peu de techniques ont été mises en œuvre pour pouvoir aider les utilisateurs dans la conception des workflows scientifiques, notamment pour les aider à tirer au mieux partie des workflows existants dans les bases qui pourraient être réutilisés. Un besoin fort est présent dans la communauté bioinformatique pour proposer des techniques pour guider les utilisateurs dans leur choix d'ensemble d'outils à (ré)utiliser. C'est dans ce cadre que s'articule les travaux de mon stage académique. Plus précisément, notre objectif est d'extraire des workflows scientifiques des sous-structures fréquentes et intéressantes et constituer des librairies de motifs. Dans nos travaux, nous avons étudié de façon approfondie les structures (grands graphes) des workflows scientifiques et nous avons fait un état de l'art des approches existantes d'extraction de motifs à base de graphes. Nous avons choisi d'étudier plus particulièrement les résultats fournis par deux algorithmes d'extraction qui ont fait leurs preuves sur des données réelles. Nous avons proposé d'utiliser et nous avons adapté au contexte plusieurs métriques pour rendre compte de la qualité des motifs extraits. Nos contributions sont les suivantes : (i) nous avons mis en évidence des caractéristiques structurelles des workflows scientifiques ayant un impact sur le problème de l'extraction de motifs dans les workflows ; (ii) nous proposons une étude comparative quantitative et qualitative des résultats obtenus par deux algorithmes d'extraction de motifs
Error-correcting pairs: a new approach to code-based cryptography
No full textInternational audienceMcEliece proposed the first public-key cryptosystem based on linear error-correcting codes. A code with an efficient bounded distance decoding algorithm is chosen as secret key. It is assumed that the chosen code looks like a random code. The known efficient bounded distance decoding algorithms of the families of codes proposed for code-based cryptography, like Reed-Solomon codes, Goppa codes, alternant codes or algebraic geometry codes, can be described in terms of error-correcting pairs (ECP). That means that, the McEliece cryptosystem is not only based on the intractability of bounded distance decoding but also on the problem of retrieving an error-correcting pair from the public code. In this article we propose the class of codes with a t-ECP whose error-correcting pair that is not easily reconstructed from of a given generator matrix
Systèmes oscillants chaotiques en biologie
No full textInternational audienceOn montrera un exemple simple de système chaotique déterministe, et pourquoi on peut dire qu'il est chaotique. On étudiera ensuite un réseau de régulation transcriptionnelle oscillant et un système analogue de type "proie-prédateur" et on montrera le caractère chaotique de la période de leurs oscillations. On utilisera diverses méthodes calculatoires dans chacun de ces exemples: méthodes déterministes et stochastiques, en différenciant le chaos de la stochasticité. On discutera enfin de l'interêt du chaos pour les systèmes vivants
On the Gap and Time Interval between the First Two Maxima of Long Random Walks
No full text52 pages, 8 figures. Published version (typos corrected).International audienceIn the context of order statistics of discrete time random walks (RW), we investigate the statistics of the gap, , and the number of time steps, , between the two highest positions of a Markovian one-dimensional random walker, starting from , after time steps (taking the -axis vertical). The jumps are independent and identically distributed random variables drawn from a symmetric probability distribution function (PDF), , the Fourier transform of which has the small behavior , with . For , the variance of the jump distribution is finite and the RW (properly scaled) converges to a Brownian motion. For , the RW is a L\'evy flight of index . We show that the joint PDF of and converges to a well defined stationary bi-variate distribution as the RW duration goes to infinity. We present a thorough analytical study of the limiting joint distribution , as well as of its associated marginals and , revealing a rich variety of behaviors depending on the tail of (from slow decreasing algebraic tail to fast decreasing super-exponential tail). We also address the problem for a random bridge where the RW starts and ends at the origin after time steps. We show that in the large limit, the PDF of and converges to the {\it same} stationary distribution as in the case of the free-end RW. Finally, we present a numerical check of our analytical predictions. Some of these results were announced in a recent letter [S. N. Majumdar, Ph. Mounaix, G. Schehr, Phys. Rev. Lett. {\bf 111}, 070601 (2013)]
Structure fractale tridimensionnelle avec une transformation conforme 1/O dans l'ensemble des Octonions -section tridimensionnelle-
No full textTridimensional fractal structure with a 1/O conformal transformation in the Octonionic space -tridimensional cross-section- (Structure fractale tridimensionnelle avec une transformation conforme 1/O dans l'ensemble des Octonions -section tridimensionnelle-
Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth
No full textInternational audienceThe low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality