Дисертації з теми "Méthodes de connectivité"
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Bellec, Pierre. "Etude longitudinale des réseaux cérébraux à large échelle en IRMf : méthodes et application à l'étude de l'apprentissage moteur." Paris 11, 2006. http://www.theses.fr/2006PA112011.
Повний текст джерелаSkill learning in human healthy volunteers is thought to induce a reorganization of cerebral activity. Such process of cerebral plasticity involves the modulation of functional interactions within networks of spatially distributed brain regions, or large-scale networks. Various measures of connectivity exist that allow one to quantify these functional interactions using functional magnetic resonance imaging (fMRI), which enables the non-invasive, yet indirect, measure of cerebral activity. I developed a series of methods that allows to characterize the reorganization of large-scale networks in the brain when considering an fMRI longitudinal study of a single subject or group of subjects, at various stages of a learning process. First, the regions of the network involved in the execution of the task under scrutiny are built and identified from the functional data in an exploratory way, by using a competitive region growing method, which segments the gray matter into functionally homogeneous regions, then followed by a statistical classification procedure. A statistical method is then designed to assess which interactions are significantly modulated within the network during the plasticity process. This method is based on a non-parametric bootstrap technique, taking the temporal auto-correlation of fMRI time series into account, and controling the false discovery rate. These methods have been validated and evaluated on both synthetic and real datasets. Two real datasets were studied, which involved learning of a sensorimotor adaptation task and of a motor sequence task, respectively
Essaid, Mohand. "Modélisation et simulation de la connectivité des flux logistiques dans les réseaux manufacturiers." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2008. http://tel.archives-ouvertes.fr/tel-00783593.
Повний текст джерелаGélin, Pauline. "Délimitation d'espèces et connectivité chez les coraux du genre Pocillopora dans l'Indo-Pacifique." Thesis, La Réunion, 2016. http://www.theses.fr/2016LARE0041/document.
Повний текст джерелаThis work focuses on the connectivity among populations of the coral genus Pocillopora in the Southwestern Indian Ocean and the Southwestern Pacific Ocean. These corals are widely distributed throughout the tropical fringe of the Indian and Pacific oceans. Traditionally, species were identified on the basis of morphological criteria [17 species described in Veron (2000)]. Different studies using genetic data revealed that the delimitation of species was sometimes blurred in these corals. Thus, in this work, the use of species delineation methods from mitochondrial (ABGD, GMYC, PTP) and nuclear (haplowebs) DNA, 16 primary species hypotheses (PSH) were identified. These PSHs were then confronted to assignment tests from microsatellite loci, revealing a minimum of 18 secondary species hypotheses (SSH). Once the species hypotheses are defined, it is possible to conduct connectivity studies. In this work, two SSHs with different ecologies were chosen to carry out these analyses. The first, Pocillopora damicornis type β (SSH05) was sampled in the lagoons and the second, Pocillopora eydouxi (SSH09) was sampled on the outer slope. The estimation of the genetic structure of the populations made possible to estimate the reproductive modes (sexual or asexual) in these two SSHs and the connectivity analyzes revealed complex structuring patterns for each of the SSHs
Marrelec, Guillaume. "Méthodes bayésiennes pour l'analyse de la réponse hémodynamique et de la connectivité fonctionnelle en IRM fonctionnelle : apport à l'étude de la plasticité dans la chirurgie des gliomes de bas grade intracérébraux." Paris 11, 2003. http://www.theses.fr/2003PA112260.
Повний текст джерелаBOLD functional MRI (fMAI) is a recent imaging technique that can be used to dynamically and non-invasively study brain hemodynamic evolutions induced by neuronal activity. Use of fMRI could in particular allow for a better understanding of the plasticity phenomena that occur in the pathology of law-grade gliomas. To this end, development of new mathematical models is necessary. We first briefly introduce functional neuroimaging and the methodological framework of our work. We then develop our research on two complementary models, whose common goal is the study of brain plasticity. The first model considers the brain as a black box characterized by its response function, the so-called hemodynamic response. We proposed a robust Bayesian method to inter this response, through introduction of basic yet relevant a priori information about the underlying physiological process. This method was then generalized to account for most event-related fMRI acquisitions. A second model considers the interactions between regions involved in a given task. We developed a novel model, relying on the theory of independence graphs, that enables the quantification of interactions within this network. We also proposed a Bayesian procedure to estimate these quantities. We finally show that both approaches can be considered as two special cases within a more general model whose further development would allow for a better understanding of brain functional processes as measured by fMRI. Both methods developed were applied to clinical data to investigate brain plasticity observed among patients with law-grade brain gliomas. Most results obtained agree with the litterature. Some cast a new light on the functional reorganization that occurs among patients
Faivre, Anthony. "Etude de la réorganisation de la connectivité cérébrale au repos dans la sclérose en plaques." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM5022/document.
Повний текст джерелаResting-state fMRI (rs-fMRI) may provide important clue concerning disability in multiple sclerosis (MS) by exploring the spontaneous BOLD fluctuations at rest in the whole brain. The aim of this work is to depict the functional reorganization of resting-state networks in MS patients and to assess its potential relationships with disability.In the first part, we performed an fMRI protocol combining a rs-fMRI and task-associated fMRI during a motor task, in a group of early MS patients. This study evidenced a direct association between reorganization of connectivity at rest and during activation in the motor system of patients. In the second rs-fMRI study, we evidenced an increased of the global level of connectivity in most of the rs-networks, strongly associated with the level of disability of patients. In the third part, we evidenced in a 2-year longitudinal study using graph theoretical approach that MS patients exhibited a dynamical alteration of functional brain topology that significantly correlated with disability progression. In the last part, we evidenced that the transient clinical improvement following physical rehabilitation in MS patients is associated with reversible plasticity mechanisms located in the default mode network, the central executive network and in the left fronto-orbital cortex. These works evidence that MS patients exhibit a complex and dynamical functional reorganization of rs-networks, significantly associated with disability progression. This PhD thesis confirms that rs-fMRI is a relevant biomarker of pathophysiology leading to disability in MS and represents a promising tool for therapeutic assessment of MS patients in the future
Bonneau, François. "Inclusion de données indirectes dans la simulation de réseaux de fractures discrets." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0144/document.
Повний текст джерелаThe stochastic simulation of discrete fracture network is based on the sampling of distribution law that describes the geometry of natural fracture networks. It generally simulates each fracture by selecting the position, the geometry and the dimensions of a planar object. The general organization of the discrete fracture network emerges from this stationary and stochastic process. This thesis explores a pseudo genetic and stochastic approach using rules that drive the seeding and the propagation of non planar objects, and allow the emergence of a fractal organization. The simulation mimics the natural fracturing process by considering the constraint accumulation zone and the shadow zone associated to each fracture already simulated in the fracture seeding, growth and linkage. We explore the impact of the method on the fractal dimension of discrete fracture network models, and we quantify its impact on both the connectivity and the percolation threshold. The validation of the stochastic approach is based on the realism of models both in terms of geometry and impact on its physical behavior. Our approach constrains the geometry of discrete fracture networks at fracture and at fracture network scales using statistic distribution laws and mechanical concepts. Mechanical discontinuities can also be described by indirect data that quantify the response of the fractured rock volume to dynamic or mechanical stimulation. We propose an efficient way to take into account flow information recorded from tracer tests and microseismic events that trigger after a hydraulic stimulation. The method is integrated during the stochastic simulation in order to remove the need of an optimization process that may be time consuming or may impact the fractal organization of the network
Bader, El Dine Kamil. "Uterine synchronization analysis during pregnancy and labor using graph theory, classification based on machine learning." Thesis, Compiègne, 2022. http://www.theses.fr/2022COMP2680.
Повний текст джерелаThe overall objective of this thesis is to study the phenomenon of the propagation of uterine electrical activity by a approach based on graph theory. The first step in this thesis is to find new parameters extracted from the graphs which are suitable to represent the physio-pathological evolutions of the uterus. These parameters will be tested directly on th EHG signals recorded at the level of the abdomen then at the level of the sources identified from the EHGs. This analysis will be applied to the EHG signal i) globally (using the entire contraction) and ii) dynamically (using time windows in the contraction to characterize each time the corresponding graph). The second step will be to develop a new method based on neural networks and apply it on all the parameters already used in order to select the best parameters that can differentiate pregnancy and labor contractions. The expected results will be used both to enrich scientific knowledge in this field and to try to improve the performance of the prediction of prematurity in women
Messé, Arnaud. "Caractérisation de la relation structure-fonction dans le cerveau humain à partir de données d'IRM fonctionnelle et de diffusion : méthodes et applications cognitive et clinique." Phd thesis, Université de Nice Sophia-Antipolis, 2010. http://tel.archives-ouvertes.fr/tel-00845014.
Повний текст джерелаAnquez, Pierre. "Correction et simplification de modèles géologiques par frontières : impact sur le maillage et la simulation numérique en sismologie et hydrodynamique." Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0069/document.
Повний текст джерелаNumerical geological models help to understand the spatial organization of the subsurface. They are also designed to perform numerical simulations to study or predict the rocks physical behavior. The internal structures of geological models are commonly discretized using meshes to solve the physical governing equations. The quality of the meshes can be, however, considerably degraded due to the mismatch between, on the one hand, the geometry and the connectivity of the geological objects to be discretized and, on the other hand, the constraints imposed on number, shape and size of the mesh elements. As a consequence, it may be desirable to modify a geological model in order to generate good quality meshes that allow realization of reliable physical simulations in a reasonable amount of time. In this thesis, I developed strategies for repairing and simplifying 2D geological models, with the goal of easing mesh generation and simulation of physical processes on these models. I propose tools to detect model elements that do not meet the specified validity and level of detail requirements. I present a method to repair and simplify geological cross-sections locally, thus limiting the extension of modifications. This method uses operations to edit both the geometry and the connectivity of the geological model features. Two strategies are thus explored: geometric modifications (local enlargements of the layer thickness) and topological modifications (deletions of small components and local fusions of thin layers). These editing operations produce a model on which it is possible to generate a mesh and to realize numerical simulations more efficiently. But the simplifications of geological models inevitably lead to the modification of the numerical simulation results. To compare the advantages and disadvantages of model simplifications on the physical simulations, I present three applications of the method: (1) the simulation of seismic wave propagation on a cross-section within the Lorraine coal basin, (2) the site effects evaluation related to the seismic wave amplifications in the basin of the lower Var river valley, and (3) the simulation of fluid flows in a fractured porous medium. I show that (1) it is possible to use the physical simulation parameters, like the seismic resolution, to constrain the magnitude of the simplifications and to limit their impact on the numerical simulations, (2) my method of model simplification is able to drastically reduce the computation time of numerical simulations (up to a factor of 55 in the site effects case study) while preserving an equivalent physical response, and (3) the results of numerical simulations can be changed depending on the simplification strategy employed (in particular, changing the connectivity of a fracture network can lead to a modification of fluid flow paths and overestimation or underestimation of the quantity of produced resources)
Zahran, Saeed. "Source localization and connectivity analysis of uterine activity." Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2469.
Повний текст джерелаThe technique of EHGI allows a noninvasive reconstruction of the electrical potential on the uterus surface based on electrical potential measured on the body surface and anatomical data of the torso. EHGI provides very precious information about the uterus condition since it is able to provide refined spatial description of the electrical wave pathway and magnitude on the uterus surface. This may help a lot in different clinical interventions. The scientific algorithms behind any EHGI tool are able to preprocess the anatomical data of the patient in order to provide a computational mesh, filter noisy measurements of the electrical potential and solve an inverse problem. The inverse problem in uterus electrohysterography (electrohysterography imaging (EHGI)) is a new and a powerful diagnosis technique. This non-invasive technology interests more and more medical industries. The success of this technology would be considered as a breakthrough in the uterus diagnosis. However, in many cases the quality of reconstructed electrical potential is not accurate enough. The difficulty comes from the fact that the inverse problem in uterus electrohysterography is well known as a mathematically ill-posed problem. Different methods based on Thikhnov regularization have been used in order to regularize the problem. We have conducted our analysis by using a realistic uterus model and have aimed at identifying the spatial extent of the sources
Mheich, Ahmad. "Méthodes de classification des graphes : application à l’identification des réseaux fonctionnels impliqués dans les processus de mémoire." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S115/document.
Повний текст джерелаThe human brain is a "large-scale" network consisting of distributed and functionally interconnected regions. The information processing in the brain is a dynamic process that involves a fast reorganization of functional brain networks in a very short time scale (less than one second). In the field of cognitive neuroscience, two big questions remain about these networks. Firstly, is it possible to follow the spatiotemporal dynamics of the brain networks with a temporal resolution significantly higher than the functional MRI? Secondly, is it possible to detect a significant difference between these networks when the brain processes stimuli (visual, for example) with different characteristics? These two questions are the main motivations of this thesis. Indeed, we proposed new methods based on dense electroencephalography. These methods allow: i) to follow the dynamic reconfiguration of brain functional networks at millisecond time scale and ii) to compare two activated brain networks under specific conditions. We propose a new algorithm benefiting from the excellent temporal resolution of EEG to track the fast reconfiguration of the functional brain networks at millisecond time scale. The main objective of this algorithm is to segment the brain networks into a set of "functional connectivity states" using a network-clustering approach. The algorithm is based on K-means and was applied on the connectivity graphs obtained by estimation the functional connectivity values between the considered regions of interest. The second challenge addressed in this work falls within the measure of similarity between graphs. Thus, to compare functional connectivity networks, we developed an algorithm (SimNet) that able to quantify the similarity between two networks whose node coordinates is known. This algorithm maps one graph to the other using different operations (insertion, deletion, substitution of nodes and edges). The algorithm is based on two main parts, the first one is based on calculating the nodes distance and the second one is to calculate the edges distance. This algorithm provides a normalized similarity index: 0 for no similarity and 1 for two identical networks. SimNet was evaluated with simulated graphs and was compared with previously-published graph similarity algorithms. It shows high performance to detect the similarity variation between graphs involving a shifting of the location of nodes. It was also applied on real data to compare different brain networks. Results showed high performance in the comparison of real brain networks obtained from dense EEG during a cognitive task consisting in naming items of two different categories (objects vs. animals)
Ndoye, El Hadji Malick. "Réseaux de capteurs sans fil linéaires : impact de la connectivité et des interférences sur une méthode d'accès basée sur des jetons circulants." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22661/document.
Повний текст джерелаIn this thesis, we propose a MAC protocol that takes into account the specific characteristics of LSNs. This MAC protocol is based on tokens circulating that give the right to nodes to access to the transmission channel. We evaluate from this protocol the impact of interference and connectivity in the LSN. This evaluation allows us to propose clustering techniques in a LSN. We assume first a clustering based on a logical exploitation of the vicinity of the sensor nodes. In this case, we assume that a deterministic propagation model that does not take into account the complexity of the environment. Next, we consider a clustering technique wherein the propagation model takes into account the fluctuations that make complex the medium
Osman, Hoch Bachir. "Modelling of hydrogen diffusion in heterogeneous materials : implications of the grain boundary connectivity." Thesis, La Rochelle, 2015. http://www.theses.fr/2015LAROS030/document.
Повний текст джерелаThe diffusion of hydrogen in metals is a key factor for understanding the basic mechanisms of hydrogen embrittlement. However, the contribution of grain boundaries to the hydrogen diffusion is not well established. In this this work, we first investigated the effects of a heterogeneous grain boundary networks on the effective diffusivity in polycrystalline materials, using finite elements modeling. To do so, hydrogen diffusion through heterogeneous materials, modeled by a ternary continuum composite media, was simulated. We showed, by characterizing the grain-boundary connectivity, that there are strong correlations between the grain-boundary connectivity parameters and the effective diffusivity. It was found also that these correlations are more significant for nanocrystalline materials. Moreover, by using a homogenization method, it was evidenced that the percolation behavior of the effective diffusivity is controlled by the grain-boundary network evolution, without exhibiting the same percolation threshold than the latter. A second approach, using EBSD-based microstructures, was conducted to evaluate the effect of microstructural constraints on the grain boundary connectivity and to compare the effective diffusivity numerically obtained with experimental data on polycrystalline nickel from literature. In parallel, experimental analyses were performed to analyze the effects of the grain boundaries on the local hydrogen concentration. This highlighted the significant impact of grain-boundary character on the hydrogen distribution around grain boundaries, which can not be explained by the only diffusion process
Ngou, Jean. "Identification des antigènes du virus Epstein-Barr et caractérisation des anticorps correspondants dans la pathologie des connectivites par la méthode de l'immunoempreinte." Montpellier 1, 1990. http://www.theses.fr/1990MON13521.
Повний текст джерелаMahjoub, Meriem. "The Survivable Network Design Problems with High Node-Connectivity Constraints : Polyhedra and Algorithms." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLED046/document.
Повний текст джерелаGiven a weighted undirected graph and an integer k, the k-node-connected subgraph problem is to find a minimum weight subgraph which contains k-node-disjoint paths between every pair of nodes. We introduce new classes of valid inequalities and discuss their facial aspect. We also devise separation routines, investigate the structural properties of the linear relaxation and discuss some reduction operations that can be used in a preprocessing phase for the separation. Using these results, we devise a Branch-and-Cut algorithm and present some computational results. Then we present a new extended formulation for the the k-node-connected subgraph problem, along with a Branch-and-Cut-and-Price algorithm for solving the problem.Next, we investigate the hop-constrained version of the problem. The k node-disjoint hop-constrained network design problem is to find a minimum weight subgraph such that between every origin and destination there exist at least k node-disjoint paths of length at most L. We propose an integer linear programming formulation for L=2,3 and investigate the associated polytope. We introduce valid inequalities and devise separation algorithms. Then, we propose a B\&C algorithm for solving the problem along with some computational results
Yagoubi, Saïd. "Association d'ions uranyle et d'oxoanions molybdates ou tungstates : nouvelles architectures structurales et mobilité cationique." Lille 1, 2004. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2004/50376-2004-149.pdf.
Повний текст джерелаPour finir, nous avons complété ce travail par la caractérisation de deux nouveaux uranates de rubidium de formule Rb2U2O7 et Rb8U9O31. Cette étude confirme la complexité et l'intérêt de la cristallochimie des composés résultant de l'association d'ions uranyles et d'oxyanions. Cette complexité provient: - des différentes coordinations possibles à la fois de l'uranium et du métal de l"oxyanion. - des différentes possibilités de "polymérisation" de ces polyèdres à la fois de l'uranium (par exemple pour former des chaînes par la mise en commun d'arrêtes) et du métal de l'oxyanion (par exemple par des sommets pour former des chaînes ou des couche de types perovskite), - des différentes possibilités de connexion directe entre les polyèdres des coordination de l'uranium et du métal de l'oxyanion