1,809 research outputs found
Nouveau dictionnaire des difficultés du français moderne, Joseph Hanse, 1994, Éditions De Boek - Duculot, 983 p.
Data Assimilation for hyperbolic conservation laws. A Luenberger observer approach based on a kinetic description
Developing robust data assimilation methods for hyperbolic conservation laws
is a challenging subject. Those PDEs indeed show no dissipation effects and the
input of additional information in the model equations may introduce errors
that propagate and create shocks. We propose a new approach based on the
kinetic description of the conservation law. A kinetic equation is a first
order partial differential equation in which the advection velocity is a free
variable. In certain cases, it is possible to prove that the nonlinear
conservation law is equivalent to a linear kinetic equation. Hence, data
assimilation is carried out at the kinetic level, using a Luenberger observer
also known as the nudging strategy in data assimilation. Assimilation then
resumes to the handling of a BGK type equation. The advantage of this framework
is that we deal with a single "linear" equation instead of a nonlinear system
and it is easy to recover the macroscopic variables. The study is divided into
several steps and essentially based on functional analysis techniques. First we
prove the convergence of the model towards the data in case of complete
observations in space and time. Second, we analyze the case of partial and
noisy observations. To conclude, we validate our method with numerical results
on Burgers equation and emphasize the advantages of this method with the more
complex Saint-Venant system
An Empirical Investigation of Information Systems Departments’ Configurations
This empirical study focuses on IS departments, investigates their configurations, and assesses their performance. It adopts the configurational approach to cluster IS departments based on their strategy and structure attributes. A nation-wide survey of 217 IS departments was conducted in Canadian business organizations. Cluster analysis was performed, which led to the emergence of three IS department configurations. The more strategy- and structure-oriented departments are, the higher their performance is. IS departments with a medium performance are the ones that focus more on their strategy than on their structure, whereas those who put more emphasis on their structure and less on their strategy achieve the lowest performance
Les technologies de l'autonomie et de la santé : entre progrès et régressions
Ce rapport résulté d'une recherche pour l'IRES-CGT et anlyse les enjeux sociétaux, politiques, éthiques et juridiques dud éveloppement des technologies de l'autonomie et de la santé. Il analyse les enjeux d'usage et d'acceptabilité tant pour les publics destinataires -notamment personnes âgées en perte d'autonomie- que pour les professionnels du soin et de l'accompagnement
Realistic wireless communication simulations for VANETS
International audienceVehicular AdÂhoc NETworks (VANETs) are mainly evaluated through simulations in which the choice of a realistic wireless channel model is a central point. Deterministic channel models bring good realism but need huge simulation time, whereas with statistical models the computational effort is reduced, but sadly so is the realism of the model. In this paper, we present a semiÂdeterministic channel model, called UMÂCRT, based on a deterministic channel simulator, CRT (Communication Ray Tracer) and a statistical channel model, SCME-UM (Spatial Channel Model Extended - Urban Microcell). To integrate it into the NSÂ2 network simulator, we couple it to selfÂdeveloped fully compliant 802.11p and 802.11n physical layers. Simulations in urban environment show both a good realism and a reduced computation time indicating that UMÂCRT is adapted for VANETs simulations
UM-CRT : Un modèle de canal semi-déterministe pour les VANETs
National audienceLe choix d'un modèle de canal efficace pour la simulation des VANETs (Vehicular Ad-hoc NETworks) est difficile. Avec un modèle de canal purement déterministe les simulations sont réalistes mais prennent un temps très long, voire prohibitif. Dans le cas d'un modèle purement statistique, les simulations sont rapides mais le réalisme obtenu est limité. Dans ce papier nous proposons UM-CRT, un modèle de canal semi- déterministe basé sur un simulateur 3D déterministe de canal et sur le modèle statistique géométrique de canal SCME-UM (Spatial Channel Model Extended - Urban Micro). Nous avons intégré ce modèle dans le simulateur de réseaux NS-2 et montré qu'il fournit des résultats proches de ceux du modèle déterministe en un temps très nettement réduit
A survey of V2V channel modeling for VANET simulations
International audienceMost Vehicle to Vehicle (V2V) network protocols are evaluated by simulation. However in most network simulators, the physical layer suffers from a lack of realism. Therefore, realistic V2V channel modeling has become a crucial issue in Intelligent Transportation Systems (ITS) networks. V2V channels are known to exhibit specific features which imply the design of new simulation models. In this survey paper, we first recall the main physical features of such wireless time and frequency dispersive channels. Next, three "simulation-ready" V2V channel models found in the literature are reviewed. Finally, two complete VANET simulation frameworks are presented. They illustrate the importance of a realistic channel and physical layer modeling in vehicular networking
A semi-deterministic channel model for VANETs simulations
International audienceIn this paper we propose a semi-deterministic channel propagation model for VANETs (Vehicular Ad-hoc NETworks) called UM-CRT. It is based on CRT (Communication Ray Tracer) and SCME-UM (Spatial Channel Model Extended - Urban Micro) which are respectively a deterministic channel simulator and a statistical channel model. It uses a process which adjusts the SCME-UM model using relevant parameters extracted from CRT. In order to evaluate this new model, we incorporate it into the NS-2 network simulator. Our results show that UM-CRT is adapted to VANETs simulations as it approximates in a realistic manner channel propagation mechanisms while improving simulation time
Organic semiconductor laser biosensor : design and performance discussion
Organic distributed feedback lasers can detect nanoscale materials and are therefore an attractive sens- ing platform for biological and medical applications. In this paper, we present a model for optimizing such laser sensors and discuss the advantages of using an organic semiconductor as the laser material in comparison to dyes in a matrix. The structure of the sensor and its operation principle are described. Bulk and surface sensing exper- imental data using oligofluorene truxene macromolecules and a conjugated polymer for the gain region is shown to correspond to modeled values and is used to assess the biosensing attributes of the sensor. A comparison between organic semiconductor and dye-doped laser sensitivity is made and analyzed theoretically. Finally, experimental and theoretical specific biosensing data is provided and methods for improving sensitivity are discussed
Micro-LED waveguide for fluorescence applications
A micro-LED-coupled multimode slab waveguide is reported for fluorescence sensing. The device consists of a 1-dimensional micro-LED array coupled to a sub-mm polymeric slab for evanescent excitation of fluorescent analytes present on the surface. Proof-principle detection of semiconductor nanocrystals down to 0.2 pM/cm2 is demonstrated
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