Modélisation d’impulsions lasers ultra-brèves

Des méthodes de caractérisation d’impulsions lasers femtoseconde sont développées afin d’étudier leur propagation dans la matière. De telles impulsions présentent obligatoirement un étalement spectral considérable, et donc difficiles à utiliser. Ce travail consiste à étudier la propagation d’impulsions lasers ultra-brèves dans un matériau transparent. Notre travail est devisé en deux parties : la première partie sera consacrée à l’analyse par la méthode des ondes planes. La deuxième partie consiste à élaborer un model mathématique basé sur la technique d’ondelettes pour bien décrire les effets de dispersion chromatique, du facteur de propagation k(w) sur le profil et la phase. Cette dernière méthode s’avère être un outil très puissant pour résoudre ce problème de dispersion chromatique.Mots-clés : Indice de réfraction, impulsion femtoseconde, dispersion chromatique, chirp, analyse de Fourier, decomposition en ondelettes

Time-Frequency Decomposition of an Ultrashort Pulse: Wavelet Decomposition

An efficient numerical algorithm is presented for the numerical modeling of the propagation of ultrashort pulses with arbitrary temporal and frequency characteristics through linear homogeneous dielectrics. The consequences of proper sampling of the spectral phase in pulse propagation and its influence on the efficiency of computation are discussed in detail. The numerical simulation presented here is capable of analyzing the pulse in the temporal-frequency domain. As an example, pulse propagation effects such as temporal and spectral shifts, pulse broadening effects, asymmetry and chirping in dispersive media are demonstrated for wavelet decomposition

The Triassic-Liassic volcanic sequence and rift evolution in the Saharan Atlas basins (Algeria). Eastward vanishing of the Central Atlantic magmatic province

We investigate the Triassic-Liassic sequence in ten diapirs from the Saharan Atlas (Algeria). Based on detailed mapping, two episodes are identified. The first one consists of a volcano-sedimentary sequence in which three volcanic units were identified (lower, intermediate and upper units). They are interlayered and sometimes imbricated with siliciclastic to evaporitic levels which record syn-sedimentary tectonics. This sequence was deposited in a lagoonal-continental environment and is assigned to the Triassic magmatic rifting stage. The second episode, lacking lava flows (post magmatic rifting stage), consists of carbonate levels deposited in a lagoonal to marine environment during the Rhaetian-Hettangian. The volcanic units consist of several thin basaltic flows, each 0.5 to 1m thick, with a total thickness of 10–15m. The basalts are low-Ti continental tholeiites, displaying enrichment in large ion lithophile elements and light rare earth elements [(La/Yb)n= 2.5-6] with a negative Nb anomaly. Upwards decrease of light-rare-earth-elements enrichment (e.g. La/Yb) is modelled through increasing melting rate of a spinel-bearing lherzolite source from the lower (6–10wt.%) to the upper (15–20wt.%) unit. The lava flows from the Saharan Atlas share the same geochemical characteristics and evolution as those from the Moroccan Atlas assigned to the Central Atlantic magmatic province. They represent the easternmost witness of this large igneous province so far known

Wavefront correction with a ferrofluid deformable mirror: experimental results and recent developments

We present the research status of a deformable mirror made of a magnetic liquid whose surface is actuated by a triangular array of small current carrying coils. We demonstrate that the mirror can correct a 11 microns low order aberrated wavefront to a residual RMS wavefront error 0.05 microns. Recent developments show that these deformable mirrors can reach a frequency response of several hundred hertz. A new method for linearizing the response of these mirrors is also presented.Comment: To appear in "Ground-based and Airborne Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200

Evaluation multicritère pour la rénovation thermique des bâtiments en maçonnerie.

In Algeria, the residential and tertiary sectors are the ones with the highest energy consumption, making use of 34% of the total energy ; consequently, the government has launched a thermal renovation program for existing buildings to reduce this consumption. Knowing that the existing stock has 1.050.000 of masonry dwelling built before 1945 and that these same dwellings are subject to a rehabilitation program, thermal renovation of these would both guarantee their preservations and reduce energy consumption. Thermal renovation of masonry buildings is a complex decision, it needs a comprehensive approach as it simultaneously involves a multitude of criteria (energy consumption, investment cost, etc) including risks related to the heritage preservation as the loss of building historic aesthetic features and the fabric decay in the walls, floor or roof due to moisture accumulation. This paper presents a decision aid method based on the Preference Ranking Organization Method for Enrichment Evaluation, Promethee methods for the thermal renovation of masonry buildings with a heritage value. The aim of this method is to rank the different thermal renovation solution. The method uses a multi-criteria approach that includes risks related to the heritage preservation. A case study was investigated to test the method, as expected the method works, it was possible to get a full ranking of the thermal renovation

Dynamic node allocation in Network Virtualization

International audienceNetwork virtualization is a new technology that provides a transparent abstraction of the networking resources. The most important challenge in network virtualization is the allocation of the physical substrate network among the pool of the active virtual networks (VNs). Our work in progress aims at allocating the node resources in a virtualized networking infrastructure. We believe that this allocation should be dynamic to lead to higher performance and better utilization of the physical resources. In this paper, we propose two models for dynamic node allocation for multiple VNs. The first model uses game theory and market-based approach in order to better allocate the physical node. The second one proposes a dynamic weighted round robin (WRR) approach where each VN receives a fraction of the physical node according to an estimation of its current number of waiting packets and its weight. Both models use a distributed approach to minimize the packet delays inside the physical router and to fairly allocate the nodes between different VN