Jurnal Edukasi
Not a member yet
4879 research outputs found
Sort by
Foundational Proof Certificates
No full textInternational audienceConsider a world where exporting proof evidence into a well defined,universal, and permanent format is taken as "feature zero" forcomputational logic systems. In such a world, provers willcommunicate and share theorems and proofs; libraries will archive andorganize proofs; and marketplaces of proofs would be open to anyprover that admits checkable proof objects. In that world, proofcheckers will be the new gatekeepers: they will be entrusted with thetask of checking that claimed proof evidence elaborates into a formalproof.Logicians and proof theorists have worked on defining notions of proofthat are not based on technology and do not have version numbersattached to them. There are many such proof systems in theliterature: Hilbert-Frege proofs, Gentzen's sequent calculus proofs,Prawitz's natural deduction proofs, etc. Each of these proof systemshave been given precise syntax and meaning. While such well studiedproof descriptions exist, a quick review of the current state ofautomated and interactive theorem provers reveals that provers seldomoutput their "proof evidence" using such proof systems. While thereis a lot of interest in having provers share and trust each other'sproofs most of that work has been based on building bridges betweentwo specific provers: a change in the version number of one prover cancause that bridge to collapse.The ProofCert project has as one of its goals the development of aflexible framework for defining the semantics of a wide range of proofevidence in such a way that provers would define the meaning of theirown proof evidence and trusted proof checkers would be able tointerpret that meaning and check its formal correctness. To achievethis goal, we must first be able to separate proof evidence from itsprovenance and then provide a formal and clear framework for definingthe semantics of proof evidence. The ProofCert project is focused onthe problem of checking formal proof: there is no assumption made thatsuch formal proofs are actually readable by humans
A study of the impact of climate on the optimal geometry of a LCPV system
No full textInternational audienceThe inter-row spacing of classical photovoltaic (PV) plants is generally chosen to avoid shading during periods of significant solar radiation. The installation results in widely-spaced rows, and the inter-row space is illuminated during periods of high solar resource. The addition of inter-row reflectors augments the direct and diffuse flux reaching the PV cells while resulting in a lower inter-row spacing, which is advantageous for both large-scale and rooftop installations. The project aims to explore the benefits of equipping the inter-row space with highly reflective surfaces, and develop clear rules for optimal settings of the PV+Reflector system in a specified location and climate. An integrated model of the system was developed and validated with a demonstrator installed on the SIRTA meteorology platform (Palaiseau, France, 48.71°N, 2.21°E). The model was applied on three cities with similar latitudes but different climates: St. Johns, Palaiseau and Bratislava. The locations were compared based on achievable gains and optimal settings
Cross-sectional investigations on epitaxial silicon solar cells by Kelvin and Conducting Probe Atomic Force Microscopy: Effect of illumination
No full textNational audienc
How to use the elasticity of a badminton racket to increase its speed by 80%?
No full textInternational audienc
Hydrophobie dynamique et Dynamiques hydrophobes
No full textThis work focuses on situations in which movement and liquid repellency are combined. First, we study dynamic hydrophobicity, a phenomenon created by the horizontal movement of a flat surface, here a rotating plate of bare aluminum. When the surface reaches a critical velocity, approaching droplets cannot penetrate the boundary layer of air that covers the surface, thus protected from wetting. Droplets that are gently deposited on the substrate levitate a few micrometers above the surface, while falling droplets can bounce off, much faster than in other non-wetting situations. If the plate moves fast enough, all liquids can be repelled, creating an omniphobic surface.In a second part, we investigate the dynamics of drops in contact with surfaces textured at a microscopic scale, which makes them water-repellent. We show that viscous drops deposited on a moving superhydrophobic surface are not immediately carried away, but accelerate and start to spin very rapidly. As the substrate velocity increases, the spinning makes the drops loose their spherical shape and turn into bilobes, and sometimes trilobes. We also study the impact of water droplets on superhydrophobic surfaces macrotextured by a straight wire or a marble of same repellency, with a typical size of 100 mm. The bouncing dynamics are dramatically modified in presence of the macrotexture : on a wire drops take-off as 1, 2 or 4 independent sub-units while in presence of a marble they exhibit surprising doughnut shapes. This affects the contact time, which takes discrete values with increasing impact velocity. At high velocity it is divided by a factor of 2 compared to a non-textured surface, which enhances anti-icing properties.Nous considérons dans cette thèse des situations qui lient mouvement et non-mouillage.L’hydrophobie dynamique est une propriété étonnante engendrée par le simple mouvement d’une surface, ici un plateau d’aluminium en rotation. Dès lors que le solide atteint une vitesse suffisante, les gouttes qui s’en approchent sont repoussées par la couche limite d’air qui couvre le solide, ainsi protégé du mouillage. Les gouttes délicatement posées restent en lévitation à quelques dizaines de micromètres de hauteur, alors que celles qui tombent sur le substrat rebondissent, et beaucoup plus rapidement que dans d’autres situations de non-mouillage. Si la vitesse du plateau est assez élevée, tous les liquides peuvent être chassés, conférant au substrat des propriétés omniphobes.Nous explorons également les dynamiques hydrophobes de gouttes au contact de surfaces rendues non mouillantes grâce à une texturation. Nous montrons que des gouttes visqueuses entrainées par une surface superhydrophobe en mouvement sont mises en rotation ce qui les amène à prendre des formes à deux, et parfois même à trois lobes lorsque la vitesse du substrat augmente. Nous nous sommes aussi intéressés aux caractéristiques du rebond sur des surfaces hydrophobes macrotexturées par un fil ou par une bille dix fois plus petits queles gouttes qui les approchent. L’étalement et la rétraction du liquide en présence des textures suivent des dynamiques inhabituelles : selon la macrotexture (fil ou bille), les gouttes peuvent prendre soit une forme à 1, 2 ou 4 sous-unités, soit une forme de tore lorsqu’elles quittent la surface. Cela joue sur le temps de contact, qui diminue par paliers, pour tomber à des valeurs deux fois inférieures à ce que l’on observe sansmacrotexture, ce qui donne à ces surfaces de potentielles propriétés anti-givre
Asymptotic stability in the energy space for dark solitons of the Landau-Lifshitz equation
No full textWe prove the asymptotic stability in the energy space of non-zero speed solitons for the one-dimensional Landau-Lifshitz equation with an easy-plane anisotropy ∂ t m + m × (∂ xx m − m 3 e 3) = 0 for a map m = (m 1 , m 2 , m 3) : R × R → S 2 , where e 3 = (0, 0, 1). More precisely, we show that any solution corresponding to an initial datum close to a soliton with non-zero speed, is weakly convergent in the energy space as time goes to infinity, to a soliton with a possible different non-zero speed, up to the invariances of the equation. Our analysis relies on the ideas developed by Martel and Merle for the generalized Korteweg-de Vries equations. We use the Madelung transform to study the problem in the hydrodynamical framework. In this framework, we rely on the orbital stability of the solitons and the weak continuity of the flow in order to construct a limit profile. We next derive a monotonicity formula for the momentum, which gives the localization of the limit profile. Its smoothness and exponential decay then follow from a smoothing result for the localized solutions of the Schrödinger equations. Finally, we prove a Liouville type theorem, which shows that only the solitons enjoy these properties in their neighbourhoods
Modélisation probabiliste et éco-évolutionnaire des communautés proies-prédateurs
No full textWe study the random modeling and the impact of natural selection on prey-predator communities. We first consider the coevolution of prey and predator phenotypes under the assumptions of adaptive dynamics (large population, rare and small mutations). The microscopic community evolves according to a multi-type birth and death process. In the rare mutation time scale, the community process jumps from an equilibrium state to another according to the mutations in the prey or in the predator population. Furthermore, when mutations have a small impact on phenotypes, the coevolution of the phenotypes follows a system of two coupled differential equations. Besides, we illustrate these results on a biologically relevant model including different prey defense mechanisms. In a second part we consider specific communities in which the predator demographic and phenotypic dynamics are faster than the prey dynamics (e.g. trees-insects). These time scale differences arise from the difference between the prey and the predator masses. We intoduce a piecewise deterministic markov process (PDMP) in which the prey population evolves as a birth and death process while the predator dynamics is a solution of a logistic deterministic equation. This process describes the demographic dynamics of the community when the predator population is infinite and we study its stationary behavior. In a limit of small predator mass, this slow-fast process converges toward an averaged process in which the predator population is always at its demographic equilibrium. In order to consider the phenotypic evolution of predators, we consider a piecewise deterministe process in infinite dimensions composed of a birth and death process coupled with the solution of a reaction-diffusion equation.We study the convergence of the slow prey process, in a limit of small predator mass, toward a birth and death process which only depends on the stationary eco-evolutionary equilibrium of the fast predator population.Cette thèse porte sur la modélisation mathématique et l'étude rigoureuse de l'impact de la sélection naturelle sur les communautés proies-prédateurs.Dans une première partie, nous étudions la coévolution de phénotypes des proies et des prédateurs sous les hypothèses des dynamiques adaptatives (grande population, mutations rares et de petite amplitude). A l'aide de différentes limites d'échelle d'un processus microscopique, nous introduisons successivement un processus de saut pur décrivant les états d'équilibres successifs de la dynamique coévolutive en fonction de l'arrivée des mutations des proies ou des prédateurs, puis un système de deux équations différentielles couplées représentant l'évolution des phénotypes lorsque les mutations sont de faible amplitude. Nous illustrons ces résultats sur un modèle écologique prenant en compte plusieurs types de défenses des proies.Dans une seconde partie, nous nous intéressons à des communautés dans lesquelles les dynamiques démographiques et évolutionnaires des prédateurs sont plus rapides que celles de leurs proies (e.g. arbres-insectes). Nous modélisons la communauté par un processus déterministe par morceaux (PDMP) dans lequel les proies évoluent selon un processus de naissance et mort et les prédateurs selon une équation différentielle logistique. Ce processus décrit les dynamiques démographiques de la communauté lorsque la population de prédateurs est infinie et nous étudions son comportement stationnaire. Dans une asymptotique de petite masse des prédateurs, le processus lent-rapide converge vers une processus moyenné, dans lequel la population de prédateurs est toujours à son équilibre démographique. Afin de prendre en compte l'évolution phénotypique de la population de prédateurs, nous considérons un processus lent-rapide en dimension infinie constitué d'un processus de naissance et mort couplé avec la solution d'une équation de réaction diffusion. Nous étudions la convergence,dans une limite de petite masse des prédateurs, du processus des proies vers un processus de naissance et mort dépendant uniquement de l'équilibre stationnaire de la population de prédateurs
