Teses / dissertações sobre o tema "Approche par LMI"
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Scorletti, Gérard. "Approche Unifiée de l'Analyse et de la Commande des Systèmes par Optimisation LMI". Phd thesis, Université Paris Sud - Paris XI, 1997. http://tel.archives-ouvertes.fr/tel-00009249.
Texto completo da fonteScorletti, Gérard. "Approche unifiee de l'analyse et de la commande des systemes par formulation lmi". Paris 11, 1997. https://tel.archives-ouvertes.fr/tel-00009249.
Texto completo da fonteManceaux-Cumer, Christelle. "Techniques de commande robuste : approche par multiplicateurs et approche stochastique". Toulouse, ENSAE, 1998. http://www.theses.fr/1998ESAE0003.
Texto completo da fonteZarudniev, Mykhailo. "Synthèse de fréquence par couplage d'oscillateurs spintroniques". Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00804561.
Texto completo da fonteCaldas, Alex. "Contribution à la manipulation dextre : prise en compte d'incertitudes de modèle et de saisie dans la commande". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066069/document.
Texto completo da fonteThis thesis deals with grasping and dexterous manipulation with multifingered hands, with the robustness to uncertain environments as a common denominator.The first contribution of the present work is a new measure of the grasp quality, which is used to evaluate the stability of a grasp. In the footsteps of the most known methods which consist in determining the reachable wrench space, our measure aims to evaluate this space whatever the uncertainty which affects the gripper/object system. This new space is called Reachable Wrench Space under Uncertainty (RWSU). Two algorithms are proposed to find respectively an upper and a lower bound of the RWSU.The second contribution concerns the application of robust control algorithms for dexterous manipulation. The first control method is composed of as a state-space feedback, which enables a manipulation task, and of an additional dynamic action, allowing to respect the grasp constraints. The state-space feedback is designed for a robust regional pole placement by the resolution of an optimization problem under LMI constraints. The LMI constraints define the dynamic response of the system in closed loop, and ensure the robustness with respect to model uncertainties. A second control method, based on eigenstructure assignment, is proposed to improve the trajectory tracking for the MIMO system. The eigenstructure assignment decouples the movement of the task from the disturbing movements resulting from the dynamic coupling between the axes
Falcón, Prado Ricardo. "Active vibration control of flexible structures under input saturation through delay-based controllers and anti-windup compensators". Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASG042.
Texto completo da fonteIn this work, the problem of active vibration control of flexible mechanical structures is addressed through infinite and finite dimensional techniques. The compared approaches are adjusted for an output feedback controller based on delayed proportional actions,through a quasipolynomial-based approach, and an optimalH∞ controller design computed with an LMI approach.They are shown in order to analyze their capabilities to damp some vibrational modes in the frequency band with of interest, and to avoid the so called “spillover”phenomenon. These controllers are synthetized through a finite dimensional model, derived from a finite element analysis of the mechanical structure, combined with some reduction methods.The flexible structures considered here are, firstly, aflexible aluminium beam in the Euler-Bernoulli configuration,and secondly, an axysimmetric membrane. Bothof them are equipped with two piezoelectric patches that are bounded and collocated on each face of the structure.We intend to examine and discuss the aforementioned performances in both simulation and experimental environments
Chadli, Mohammed. "Stabilité et commande de systèmes décrits par des multimodèles". Phd thesis, Vandoeuvre-les-Nancy, INPL, 2002. http://www.theses.fr/2002INPL089N.
Texto completo da fonteBensmaine, Fayçal. "Modélisation et commande d'un système de stockage d'énergie à base de supercondensateur pour l'hybridation des groupes électrogènes". Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2341.
Texto completo da fonteThe research in this thesis are part of study and control of a new concept of hybrid generator to reduce the power of the diesel engine (downsizing) in order to save fuel and improve the behavior of the synchronous generator during transients. The adopted solution is to place in parallel with the synchronous generator an energy storage system. The latter consists of an inverter with a super capacitor on the DC bus. The aim of the thesis was to scale the entire supercapacitor / static converter and to develop a control law having the best performance with the best compromise between the energy exchanged in the supercapacitor, efficiency, the group speed and voltage amplitude of the generator. A feedback control condition with integration of the deviation using LMI's approach has been established for the synthesis of loop current regulators from the inverter.A second control law was developed to regulate the variable voltage across the supercapacitor. A simulator combining generator and storage system has been developed to test these commands.All validations were made on an experimental test rig specifically developed for this thesis. The tests were conducted with an electric drive motor in the test platform of the LIAS and with a diesel in that of the Leroy Somer Motors company.Finally, experimental tests have highlighted the significant contribution of this hybridization on the diesel speed variationsand on the terminal voltage of the alternator during impact or load shedding
Cabanial, Jean-Marc. "Convergence du filtrage par densités approchées". Rouen, 1998. http://www.theses.fr/1998ROUES014.
Texto completo da fonteLemaire, Anne-Sophie. "Une approche par mélange des lois L 1-symetriques et estimation d'un paramètre de position". Rouen, 1997. http://www.theses.fr/1997ROUES081.
Texto completo da fonteSenga, Kiessé Tristan. "Approche non-paramétrique par noyaux associés discrets des données de dénombrement". Phd thesis, Université de Pau et des Pays de l'Adour, 2008. http://tel.archives-ouvertes.fr/tel-00372180.
Texto completo da fonteLévesque, Martin. "Modélisation du comportement mécanique de matériaux composites viscoélastiques non linéaires par une approche d'homogénéisation". Paris, ENSAM, 2004. https://pastel.archives-ouvertes.fr/pastel-00001237.
Texto completo da fonteThe main objective of this thesis is to develop a model, based on homogenisation, for predicting the mechanical response of nonlinear viscoelastic composites. The model is applied to a glass beads reinforced polypropylene in which the beads are randomly distributed. The initial part of the thesis is concerned with the development of a three dimensional nonlinear viscoelastic constitutive law that can be applied to this polypropylene composite. The second stage of the thesis deals with the development and identification of the homogenisation model while this theoretical model is presented in Chapter Three. This approach allows material models, for which the response does not depend on the load history, to be applied to nonlinear viscoelastic materials. The approach involves transforming the initial nonlinear viscoelastic problem into one which is linear viscoelastic with a history of stress-free deformations. This problem is solved with the linear viscoelastic correspondence principle and Laplace-Carson transforms. Chapter Four deals with the numerical implementation of such a model. The implementation is achieved in such a way that the comparison materials, which represent the new linear viscoelastic problem, satisfy all thermodynamic requirements. Moreover, a new algorithm has been developed to numerically invert the Laplace-Carson transforms with good accuracy. The final part of the thesis validates the theoretical model through means of finite element models of typical microstructures and the numerical implementation of the nonlinear viscoelastic constitutive law. Comparisons are also presented between the predictions of the homogenisation model, the fi(…)
Ait, Ighil Mehdi. "Simulateur de canal de propagation basé sur une approche physico-statistique et adapté à la modélisation des multitrajets pour les systèmes de navigation par satellite". Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0001/document.
Texto completo da fonteThis PhD work deals with land mobile satellite channel modelling and addresses the specific issue of satellite navigation systems in urban environments with a particular focus on multipath modelling and wide-band representation of the channel. The developed land mobile satellite channel simulator, SCHUN (Simplified CHannel for Urban Navigation), is based on a hybrid physical-statistical approach satisfying fast computation requirements. The statistical component of the modelling is mainly used during the virtual city synthesis step based on known statistical distributions of building height and street width. The rest of the modelling comes from deterministic methods using simplified electromagnetic interaction models reproducing building macro-scattering (3CM model (Three Component Model)) and building blockage of the direct path. The main underlying electromagnetic methods are the physical optics and the uniform theory of diffraction. The SCHUN simulator now opens interesting perspectives for the modelling of wide-band land mobile satellite propagation channel in dense urban environments. Optimised for pseudo real-time constraints, it uses both physical and statistical approaches. Furthermore, the SCHUN simulator has been designed and validated against measurements to answer specific needs of satellite diversity, receiving diversity, polarisation diversity or frequency diversity for satellite navigation applications
Toubal, Lotfi. "Approches analytique et expérimentale de l'endommagement par fatigue d'un composite carbone/epoxy". Toulouse 3, 2004. http://www.theses.fr/2004TOU30231.
Texto completo da fonteFatigue failure is by far the most common type of failure in service loading of structural materials, including composites. The phenomenon of fatigue becomes thus one of the principal factors of dimensioning. It is what explains the interest of the industrialists with respect to research in fatigue. This work was financed by an allowance MNER. The origin of this study lies within the framework of an industrial agreement to study the behaviour of composite materials (carbon/epoxy) used in structural work in the field of aeronautics. In order to anticipate possible problems of mechanical resistance and life span on these materials, a series of static fatigue tests and finite element studies have been planned. In traction (instrumented by cameras CCD and ESPI) to determine the elastic properties and the stresses with rupture of material, in fatigue (instrumented by infra-red camera) to determine a criterion of damage. The whole of resulted resulting from the tests was compared with numerical simulations, they presents a good correlation, which made it possible to judge validity of the assumptions retained within the framework of this research
Renault, Norbert. "Etude du couplage thermomécanique du PEHD par essais mécaniques et inversion d'images infrarouges". Thesis, Vandoeuvre-les-Nancy, INPL, 2007. http://www.theses.fr/2007INPL100N/document.
Texto completo da fonteThis research aims at looking further into current knowledge of the mechanical behavior of semi-crystalline polymers at multiple scales. It relies on the simultaneous acquisition of coupled information relating to me-chanical, thermal and microstructural behaviors. For this purpose, we have studied the response of High Density Polyethylene (HDPE) under tensile tests with controlled strain rates, using three optical techniques : (i) Vidéotraction®, a videoextensemeter to access the true stress and strain. (ii) Infrared thermography to access the thermal sources evolution. (iii) Backscattering of Incoherent Light (ISLT technique) to access information on damage mechanisms. The core of the research concerns the reconstruction of the 2D thermal sources starting from temperature fields maps measured during the test. This ill-posed problem has been solved with two different methods : A constrained optimization based on the adjoint formulation and a minimization based on a reduced spectral model. The regularization tools used in the problem are detailed for each method. The ISLT technique allows to monitor damaging processes due to crazing : the creation of isotropic micro-cavities followed by the development of a strong anisotropy during the hardening phase. We show that these information at microstructural level confirm the evolutions of the heat source thermal. All these experimental information are finally considered within a thermodynamical framework used for deri-ving constitutive laws. A sensitivity analysis applied to the parameters of our law led to a reduced model that is more appropriate for their proper estimation
Dufreche, Jérôme. "Écoulement à travers une couche poreuse limitée par une paroi perforée : comparaison entre approche de Darcy et simulations numériques à l'échelle microscopique". Toulouse, INPT, 2000. http://www.theses.fr/2000INPT037H.
Texto completo da fonteRuiz, Virginie. "Estimation et prédiction d'un système évoluant de façon non linéaire : filtrage par densités approchées". Rouen, 1993. http://www.theses.fr/1993ROUE5018.
Texto completo da fonteDestribats, Alain. "Les cycles pathologiques Ko de la théorie des cinq éléments : tentative d'explication de 5 syndromes par le raisonnement acupunctural, parallèle occidental à cette approche". Bordeaux 2, 1992. http://www.theses.fr/1992BOR2M082.
Texto completo da fonteTamatoro, Johng-Ay. "Approche stochastique de l'analyse du « residual moveout » pour la quantification de l'incertitude dans l'imagerie sismique". Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3044/document.
Texto completo da fonteThe main goal of the seismic imaging for oil exploration and production as it is done nowadays is to provide an image of the first kilometers of the subsurface to allow the localization and an accurate estimation of hydrocarbon resources. The reservoirs where these hydrocarbons are trapped are structures which have a more or less complex geology. To characterize these reservoirs and allow the production of hydrocarbons, the geophysicist uses the depth migration which is a seismic imaging tool which serves to convert time data recorded during seismic surveys into depth images which will be exploited by the reservoir engineer with the help of the seismic interpreter and the geologist. During the depth migration, seismic events (reflectors, diffractions, faults …) are moved to their correct locations in space. Relevant depth migration requires an accurate knowledge of vertical and horizontal seismic velocity variations (velocity model). Usually the so-called Common-Image-Gathers (CIGs) serve as a tool to verify correctness of the velocity model. Often the CIGs are computed in the surface offset (distance between shot point and receiver) domain and their flatness serve as criteria of the velocity model correctness. Residual moveout (RMO) of the events on CIGs due to the ratio of migration velocity model and effective velocity model indicates incorrectness of the velocity model and is used for the velocity model updating. The post-stacked images forming the CIGs which are used as data for the RMO analysis are the results of an inverse problem and are corrupt by noises. An uncertainty analysis is necessary to improve evaluation of the results. Dealing with the uncertainty is a major issue, which supposes to help in decisions that have important social and commercial implications. The goal of this thesis is to contribute to the uncertainty analysis and its quantification in the analysis of various parameters computed during the seismic processing and particularly in RMO analysis. To reach these goals several stages were necessary. We began by appropriating the various geophysical concepts necessary for the understanding of:- the organization of the seismic data ;- the various processing ;- the various mathematical and methodological tools which are used (chapters 2 and 3). In the chapter 4, we present different tools used for the conventional RMO analysis. In the fifth one, we give a statistical interpretation of the conventional RMO analysis and we propose a stochastic approach of this analysis. This approach consists in hierarchical statistical model where the parameters are: - the variance which express the noise level in the data ;- a functional parameter which express coherency of the amplitudes along events ; - the ratio which is assume to be a random variable and not an unknown fixed parameter as it is the case in conventional approach. The adjustment of data to the model done by using smoothing methods of data, combined with the using of the wavelets for the estimation of allow to compute the posterior distribution of given the data by the empirical Bayes methods. An estimation of the parameter is obtained by using Markov Chain Monte Carlo simulations of its posterior distribution. The various quantiles of these simulations provide different estimations of . The proposed methodology is validated in the sixth chapter by its application on synthetic data and real data. A sensitivity analysis of the estimation of the parameter was done. The using of the uncertainty of this parameter to quantify the uncertainty of the spatial positions of reflectors is presented in this thesis
Audibert, Jean-Yves. "Théorie statistique de l'apprentissage : une approche PAC-Bayésienne". Paris 6, 2004. http://www.theses.fr/2004PA066003.
Texto completo da fonteSchmitt, Bénédicte. "Conception de techniques d'interaction mixtes dédiées aux environnements virtuels hétérogènes : approche centrée sur les usages et guidée par les modèles". Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2460/.
Texto completo da fonte3D environments are increasingly present in our life (games, cultural situation, or professional applications). At the same time, new interaction techniques continuously appear to improve the user interaction with systems. Evaluations are usually proposed to assess the implementation of an interaction technique in a specific type of environment for elementary tasks (e. G. Selection or navigation) to determine the consistency of the technique in terms of performance and satisfaction. Our works aim at defining an evaluation method in 3D environment that is based on the standard ISO 9241-9. To answer to issues of linked multi-views systems, we adapt the standard ISO 9241-9 to a heterogeneous environment that mixes 2D and 3D
Faure, Xavier. "Approche formelle pour la simulation interactive de modèles mixtes". Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10177/document.
Texto completo da fonteInteractive simulation of the human body is a crucial issue in medical computer sciences. There are many approaches to reach this goal. Reducing the computation time is the leitmotiv of a large number of efforts in recent years. For researches which use physical models derived from continuum mechanics for the simulation of deformable objects, it is primarily the internal forces and their derivatives which are the subject of study for improving computation time. We chose to develop the Tensor Mass Method, a physical model often used for its good computation time vs accuracy trade-off. Our first contribution is the use of computer algebra to generate the internal forces and their derivatives. Our second contribution is the parallelization of this physical model by computing the generated equations on the GPU. Our third contribution is an extension of this physical model to other elements : triangle, quandrangle , hexahedron, prism and pyramid. Considering deformations to use the most effective constitutive law in terms of computation time whenever possible is a good strategy that we started developing. In the same idea, we take the geometry of the simulated model into account to introduce more complex elements, albeit in reduced numbers. To use these strategies, we have developed mixed models in constitutive laws and elements. Our research was performed in the framework of the ETOILE project, to develop a biomechanical model of the respiratory system
Rigal, Claire. "Comportement de fluides complexes sous écoulement : approche expérimentale par résonance magnétique nucléaire et techniques optiques et simulations numériques". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0091/document.
Texto completo da fonteThis thesis is an experimental and numerical study of structured fluids bidimensional flows in a cylindrical pipe with singularity and in an annular geometry with eccentric cylinders. The objective of this thesis is to characterize the influence of the shear thinning properties on the recirculation zones by using efficient and non-intrusive techniques: particle image velocimetry and velocimetry by nuclear magnetic resonance imaging. Materials are xanthane solutions at different concentrations. In the first part, we determine the rheological and viscoelastic properties of the fluids used. The second part concerns the measured velocity field. It is shown that the shear thinning behavior have a strongly influence on the structure and the morphology of these flows and the pattern of the recirculation zones. Simultaneously, numerical simulations performed by Fluent and using the rheological behavior. A good concordance is observed between the experimental and numerical results. For the flows considered here, this comparison allows to validate the computational code and the behavior law used in the numerical simulations and modelling by a Cross model
Batiot, Benjamin. "Etude expérimentale et numérique de la décomposition thermique du bois résineux". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2014. http://www.theses.fr/2014ESMA0009/document.
Texto completo da fonteFires are complex and a variety of phenomena are involved. In order to study them, the up-scaling approach separates all the processes.Among them, the solid thermal decomposition has an important role to play. Source term, it reflects the amount, rate and nature of volatile compounds emitted and its numerical description is essential. The models used currently are formed by a law of variable speed (the Arrhenius law) coupled with a conversion function of mass for each species and a kinetic mechanism organizing all reactions between them. However, this model is based on the theories used in the gas phase and serious doubts might be raised with regard to the representativeness for application in the condensed phase.The thesis works exposed in this report are focused on the model development departing from the reactions and the processes the more fundamental in the condensed phase in order to permit the simulation of the solid kinetic decomposition. The second aspect concerns the study of this model to determine the resolution and the optimization method the most appropriate, the role of each parameter, the possible compensation mechanisms and the uniqueness of the solution.Finally, the entire process is applied to a complex material, the wood. The results obtained from a new approach developed in this work, show a significant improvement of the model to the physical and chemical aspects of the thermal degradation of solid materials
Kreczanik, Paul. "Étude de la fiabilité et du vieillissement d'un système de stockage par supercondensateurs pour l'alimentation partielle et ponctuelle d'un trolleybus grâce à la récupération de l'énergie de freinage : approche du composant au système de stockage". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00656058.
Texto completo da fonteSow, Libasse. "Approche couplée expérimentation - modélisation multi-échelle pour la détermination du comportement mécanique des graves routières traitées aux liants : Application à la valorisation des Mâchefers d'Incinération de Déchêts Non Dangereux". Thesis, Rennes, INSA, 2018. http://www.theses.fr/2018ISAR0001/document.
Texto completo da fonteIn this work, the feasibility of a valorisation in road engineering of non-hazardous waste incineration bottom ash aggregates (NHWI) is investigated. This study is first based on an experimental determination of the elastic properties of the bottom ash particles. These properties serve as input data for hierarchical multi-scale modelling developed to study the mechanical behaviour of aggregates treated with binders (cement and bitumen). The original experimental campaign on the bottom ash particles allowed them to be mapped to the Scanning Electron Microscope (SEM). For the particles, a mean reduced modulus of elasticity in between 15 and 68 GPa was found by means of indentation tests and applying the "Olivier and Phan method. The chemical analysis of the aggregates was obtained using qualitative point chemical analyzes (OHS). Based on a 0/25 particle size distribution of NHWI, which was the subject of an experimental study [BEC 07] , we have implemented two 30 models < road materials treated with binders in Representative Elementary Volumes (REV). These models are based on a hierarchical multi-scale modelling strategy. Two types of binder are studied: cement CEM I 42.5 R and bitumen of [NGU 08]. For both types of binder, the treated aggregates we divided into two REV, at respectively the sub-mesoscale (0/6 mm) and the mesoscale (6/25 mm). An application to the valorisation of NHWI bottom ashes in road engineering is studied in both cases. With a 3% cement treatment, a numerical simulation campaign "Virtual Laboratory" was conducted. At the sub-mesoscale, the input parameters for the Concrete Damaged Plasticity Model used at the mesoscale are determined. At the mesoscale, the mechanical characteristics of the road materials usually determined through experiments have been found. The developed simulation strategy has been validated by comparing our numerical results and son experimental results of [BEC 07]. With a 5% bitumen treatment, stress relaxation tests carried out at the two scales enable one to obtain the thermo-rheological properties of the Bitumen Bound Gravel. These properties are the Prony series at a reference temperature of 0°C and the Williams-Landei- Ferry (WLF) law constants. Prony series are obtained by means of standardized elastic moduli. The obtained WLF law constants are Cl = 20 °C-1 and C2 = 130 °C. The numeric simulations have been validated by comparing the responses of heterogeneous and corresponding homogeneous materials
Kreczanik, Paul. "Étude de la fiabilité et du vieillissement d’un système de stockage par supercondensateurs pour l’alimentation partielle et ponctuelle d’un trolleybus grâce à la récupération de l'énergie de freinage : approche du composant au système de stockage". Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10069/document.
Texto completo da fonteThe first objective of the HYBUS project is to integrate a supercapacitor storage system in a trolleybus in order to ensure the continuity of onboard electrical systems supply. The aim is to integrate an energy storage system, composed by a huge number of supercapacitors, for the recovery of the braking energy of trolleybus and allow autonomy for several meters. Our work concerns the study of the lifetime of the storage system. Several accelerated aging tests on supercapacitors were developed in the AMPERE aboratory. These tests have shown that as far as ageing are concerned; the cycling is the major responsible. However, these changes are partially reversible during the rest time when regeneration phenomena are observed. A method based on the observed damage during cycling and the damage after regeneration, leads to a formal equation for the evolution of internal parameters of supercapacitors. An endurance test of complete storage systems was also performed in the laboratory. Experimental results show the heterogeneity of aging due to the existence of significant temperature gradients between components. As a result, a new balancing strategy to equalize the lifetime of each supercapacitors has been developed. In conclusion, our study has contributed to a better comprehension and evaluation of supercapacitors aging in order to improve the lifetime of this type of energy storage system. A method for the estimation of the supercapacitor lifetime has been also proposed
Hoareau, Johan. "Utilisation d'une approche couplée hydrogéophysique pour l'étude des aquifères : application aux contextes de socle et côtier sableux". Phd thesis, Grenoble 1, 2009. http://www.theses.fr/2009GRE10301.
Texto completo da fonteThe pertinence of any aquifer management plan relies o nthe knowledge of this system, and therefore on the information used to chearacterize it. The aim of this thesis is to quantify the improvement of this characterization when geophysical methods are used complementary to hydrogeological techniques. Two hydrogeological contexts have been selected for the study, as their characterization is often difficult while they gather important populations : cristalline hard rock aquifers, and the freshwater lens of sandy coastal aquifers. The results of a numerical study and its validation on two study site located in India reveal that the information brought by electrical resistivity tomography (ERT) and magnetic resonance soundings (MRS) enable to precise the interpretation of pumping tests in hard rock areas. The uncertainly on transmissivity is reduced by an average of 39 % and by an average of 34 % for storativity. In a sandy coastal area, the combined use of water level measurements, Archie's law, time domain electromagnetism (TDEM) and MRS soundings enable to quantify the available freshwater volume. This volume would have been overstimated by 23 % with a more classical approach. Time lapse geophysics also enable to quantify the net recharge of the aquifer for 2008, as 142 mm (for a total rainfall of 2030 mm). As the site present an important geomagnetic field heterogeneity, a new protocol for the acquisition and the interpretation of MRS data has been tested and validated. It is based on the measurements of spin echo signals. It enables to constrain the estimation of water content on this site, which under-estimate by 29 % by the classicla protocol
Todeschini, Adrien. "Probabilistic and Bayesian nonparametric approaches for recommender systems and networks". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0237/document.
Texto completo da fonteWe propose two novel approaches for recommender systems and networks. In the first part, we first give an overview of recommender systems and concentrate on the low-rank approaches for matrix completion. Building on a probabilistic approach, we propose novel penalty functions on the singular values of the low-rank matrix. By exploiting a mixture model representation of this penalty, we show that a suitably chosen set of latent variables enables to derive an expectation-maximization algorithm to obtain a maximum a posteriori estimate of the completed low-rank matrix. The resulting algorithm is an iterative soft-thresholded algorithm which iteratively adapts the shrinkage coefficients associated to the singular values. The algorithm is simple to implement and can scale to large matrices. We provide numerical comparisons between our approach and recent alternatives showing the interest of the proposed approach for low-rank matrix completion. In the second part, we first introduce some background on Bayesian nonparametrics and in particular on completely random measures (CRMs) and their multivariate extension, the compound CRMs. We then propose a novel statistical model for sparse networks with overlapping community structure. The model is based on representing the graph as an exchangeable point process, and naturally generalizes existing probabilistic models with overlapping block-structure to the sparse regime. Our construction builds on vectors of CRMs, and has interpretable parameters, each node being assigned a vector representing its level of affiliation to some latent communities. We develop methods for simulating this class of random graphs, as well as to perform posterior inference. We show that the proposed approach can recover interpretable structure from two real-world networks and can handle graphs with thousands of nodes and tens of thousands of edges
Oliveira, Neto Francisco de. "Caracterização estrutural e magnética do compósito cerâmico ZnO – CoFe2O4". Universidade Federal de Goiás, 2015. http://repositorio.bc.ufg.br/tede/handle/tede/5228.
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Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG
Multiferroic materials that simultaneously exhibit two or more physical properties have increasingly raised the interest of the scientific and technological community to develop new multifunctional materials. The discuss all stages of manufacturing, morphological, structural and magnetic characterization of a multifunctional composite containing zinc oxide and cobalt ferrite. Thus, studies of ZnO, and the CoFe2O4 composite (0,80ZnO+0,20 CoFe2O4) initiated by the synthesis of nanosized powders by combustion reaction phases were performed. The compounds studied were sintered at different temperatures (1100 to 1250°C) to obtain relative density near to 90% of the theoretical density. Analysis by scanning electron microscopy, spectroscopy energy dispersive, vibrating sample magnometry and diffraction ray-X were made. Measurements of magnetic properties were conducted at room temperature (22°C) and high temperature (22°C to 700°C). In the samples, formation of ceramic structures was verified, the stoichiometry of the proposed chemical compounds was maintained and possibly the formation of a mixed zinc and cobalt ferrite to composite samples. In the sample of the composite sintered at 1250°C there was the formation of cubic zinc oxide. The magnetic behavior and magnetic anisotropy of the samples were similar, however, significant differences were observed in the values of the Curie temperature, coercive field, can assume different origins for the magnetic CoFe2O4 and the composite (0,80ZnO+0,20CoFe2O4) due, perhaps to the formation of a mixed ferrite.
Materiais multiferróicos que exibem simultaneamente duas ou mais propriedades físicas têm cada vez mais suscitado o interesse da comunidade científica e tecnológica para o desenvolvimento de novos materiais multifuncionais. Objetivou-se discutir todas as etapas de fabricação e caracterização morfológica, estrutural e magnética de um compósito multifuncional contendo óxido de zinco e ferrita de cobalto. Assim, foram realizados estudos sobre as fases das amostras de ZnO, CoFe2O4 e o compósito (0,80ZnO+0,20CoFe2O4) iniciados pela síntese de pós nanométricos por via de reação de combustão. Os compostos estudados foram sinterizados em diferentes temperaturas (1100 e 1250°C) obtendo densidades relativas próximas a 90% das densidades teóricas. Foram efetuadas análises por microscopia eletrônica de varredura, espectroscopia de energia dispersiva, difratometria de raio-X e magnometria de amostra vibrante. As medidas de propriedades magnéticas foram realizadas à temperatura ambiente (22°C) e em função da temperaturas (22°C à 700°C) (altas temperaturas). Em todas as amostras estudadas foi verificada a formação de estruturas cerâmicas, mantendo a estequiometria dos compostos químicos propostos e possivelmente a formação de uma ferrita mista de zinco e cobalto para as amostras do compósito. Para a amostra do compósito sinterizada a 1250°C verificou-se também a formação de óxido de zinco cúbico. O comportamento magnético e a anisotropia magnética das amostras foram similares, entretanto diferenças significativas foram observadas nos valores obtidos da temperatura de Curie, do campo coercitivo e do momento magnético total, podendo supor origens magnéticas diferentes para o CoFe2O4 e o compósito de 0,80ZnO+0,20CoFe2O4 devido a formação de uma ferrita mista.
Mnie, Filali Imane. "Distribution multi-contenus sur Internet". Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4068/document.
Texto completo da fonteIn this study, we focused on peer-to-peer protocols (P2P), which represent a promising solution for data dissemination and content delivery at low-cost in the Internet. We performed, initially, a behavioral study of various P2P protocols for file sharing (content distribution without time constraint) and live streaming. Concerning file sharing, we have shown the impact of Hadopi on users’ behavior and discussed the effectiveness of protocols according to content type, based on users’ choice. BitTorrent appeared as the most efficient approach during our study, especially when it comes to large content. As for streaming, we studied the quality of service of Sopcast, a live distribution network that accounts for more than 60% of P2P broadcast live events. Our in-depth analysis of these two distributionmodes led us to focus on the BitTorrent protocol because of its proven efficiency in file sharing and the fact that it is open source. In the second part of the thesis, we proposed and implemented a new protocol based on BitTorrent, in a controlled environment. The modifications that we proposed allow to increase the efficiency of the protocol through improved dissemination of metadata (the rarest piece), both for live and file sharing. An enhanced version is introduced with a push method, where nodes that lag behind receive an extra service so as to improve the overall performance
Lenormand, Maxime. "Initialiser et calibrer un modèle de microsimulation dynamique stochastique : application au modèle SimVillages". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00822114.
Texto completo da fonteLévesque, Martin. "Modélisation du comportement mécanique de matériaux composites viscolélastiques non linéaires par une approche d'homogénéisation". Phd thesis, 2004. http://pastel.archives-ouvertes.fr/pastel-00001237.
Texto completo da fonteNguyen, Thi Quynh Chi. "Construction de l’image organisationnelle réfractée par les journaux et les groupes de pression : le cas du gouvernement fédéral canadien dans la mise en œuvre du projet de loi C-38". Thèse, 2015. http://hdl.handle.net/1866/13999.
Texto completo da fonteOur research aimed to understand the emergent dimensions of an organization’s image construction. Following the review of existing research literature, we are interested in the refracted image, which is the image of an organization built by a specific public named external arbiters. These external arbiters are mandated organizations that disseminate information to the general public. By adopting a qualitative approach, we conducted a study about the case of the implementation of Bill C-38 by the Canadian Federal Government. Specifically, we examined the working process of two arbiters communities : journalists working for different newspapers, and environmental organizations’ members. The empirical study has allowed us to propose a conceptual model of the construction of the refracted image phenomenon. We thus suggested to observe this phenomenon through the actors’ working practices to understand the emergence of the image dynamics. Also, we emphasized the relevance to consider factors that constitute the framework within which the working process of the actors belonging to different public communities takes place. For it is these parameters that generate the various dynamics regulating the organizational image’s construction by each public community.
Hoareau, Johan. "Utilisation d'une approche couplée hydrogéophysique pour l'étude des aquifères - Applications aux contextes de socle et côtier sableux". Phd thesis, 2009. http://tel.archives-ouvertes.fr/tel-00470297.
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