Les élastomères silicones sont déjà largement utilisés dans l'isolation électrique extérieure grâce à la bonne tenue aux contraintes climatiques et à la hydrophobicité. Ils commencent aujourd'hui à être utilisés dans l'isolation volumique pour des applications haute tension. L'objectif de cette thèse était d'analyser plus profondément les propriétés diélectriques et électriques, peu connues, dans ces polymères.<br />L'originalité de ces études porte sur la gamme importante de température étudiée (100-430K), la mesure des propriétés diélectriques dans des très basses fréquences (10-4Hz–1MHz), la mesure de charges d'espace par un dispositif de type ‘onde de pression' et la mesure de courants faibles (jusqu'à 50fA). Deux familles d'élastomères silicones ont été étudiées : des RTV et des LSR comportant des charges de renfort de silice. L'évolution de ces propriétés lorsque ces matériaux sont soumis à des contraintes électrothermiques (16 kV/mm à 353K) pendant un an est également menée. <br />Des comportements classiquement observés dans les polymères ont été identifiés comme l'injection de charges d'espace, de type Schottky. Cependant, des comportements plus spécifiques ont été identifiés : (i) des courants de conduction sub-linéaires, (ii) des courants de dépolarisation qui s'inversent et qui présentent une réponse chaotique, (iii) des réponses diélectriques de type loi de puissance fractionnelle, (iv) de la dispersion dans les basses fréquences après vieillissement. Ces comportements particuliers sont principalement attribués à des effets d'électrode bloquante et des mécanismes de conduction dans les clusters présents aux interfaces PDMS–silice.<br />L'étude en spectroscopie diélectrique dans les très basses fréquences s'est avérée être un outil précieux de caractérisation de l'ensemble de ces phénomènes.

Multiprotocol Label Switching (MPLS) fuses the intelligence of routing with the performance of switching and provides significant benefits to networks with a pure IP architecture as well as those with IP and ATM or a mix of ther Layer 2 technologies. MPLS technology is key to scalable virtual private networks (VPNs) and end-to-end quality of service (QoS), enabling efficient utilization of existing networks to meet future growth. The technology also helps to deliver highly scalable, differentiated end-to-end IP services with simpler configuration, management, and provisioning for both Internet providers and end-users. However, MPLS is a connection-oriented architecture. In case of failure MPLS first has to establish a new label switched path (LSP) and then forward the packets to the newly established LSP. For this reason MPLS has a slow restoration response to a link or node failure on the LSP.The thesis provides a description of MPLS-based architecture as a preferred technology for integrating ATM and IP technologies, followed by a discussion of the motivation for the fast and reliable restoration mechanism in an MPLS network. In this thesis first we address the fast rerouting mechanisms for MPLS networks and then we focus on the problem of packet loss, packet reordering and packet delay for protected LSP in MPLS-based network for a single node/link failure. In order to deliver true service assurance for guaranteed traffic on a protected LSP we use the fast rerouting mechanism with a preplanned alternative LSP. We propose enhancements to current proposals described in extant literature. Our fast rerouting mechanism avoids packet disorder and significantly reduces packet delay during the restoration period.An extension of the Fast Rerouting proposal, called Reliable and Fast Rerouting (RFR), provides some preventive actions for the protected LSP against packet loss during a failure. RFR maintains the same advantages of Fast Rerouting while eliminating packet losses, including those packet losses due to link or node failure (circulating on the failed links), which were considered to be "inevitable" up to now.For the purpose of validating and evaluating the behavior of these proposals a simulation tool was developed. It is based on the NS, a well-known network simulator that is being used extensively in research work. An extension featuring the basic functionality of MPLS (MNS) is also available for the NS, and this is the basis of the developed simulation tool.Simulation results allow the comparison of Fast Rerouting and RFR with previous rerouting proposals.In addition to this we propose a mechanism for multiple failure recovery in an LSP. This proposal combines the path protection, segment protection and local repair methods. In addition to the multiple link/node failure protection, the multiple fault tolerance proposal provides a significant reduction of delay that the rerouted traffic can experience after a link failure, because the repair action is taken close to the point of failure.Then we proceed to address an inherent problem of the preplanned alternative LSP. As alternative LSPs are established together with the protected LSP it may happen that the alternative is not the optimal LSP at the time the failure occurs. To overcome this undesired behavior, we propose the Optimal and Guaranteed Alternative Path (OGAP). The proposal uses a hybrid of fast-rerouting and a dynamic approach to establish the optimal alternative LSP while rerouting the affected traffic using the preplanned alternative LSP. This hybrid approach provides the best of the fast rerouting and the dynamic approaches.At the same time we observed that the protection path becomes in fact unprotected from additional failures after the traffic is rerouted onto it.To address this we propose a guarantee mechanism for protection of the new protected LSP carrying the affected traffic, by establishing an alternative LSP for the rerouted traffic after a failure, avoiding the vulnerability problem for the protected traffic.Finally, we present a further optimization mechanism, adaptive LSP, to enhance the existing traffic engineering for Quality of Services (QoS)provision and improve network resource utilization. The adaptive LSP proposal allows more flexibility in network resource allocation and utilization by adapting the LSP to variations in all network loads,resulting in an enhancement of existing MPLS traffic engineering.

In the modern era there exist applications that require very high resources and generate a tremendous amount of traffic so they require considerable amount of bandwidth and QOS to operate and perform correctly. MPLS is a new and a fast technology that offers much remuneration both in terms of providing trouble-free and efficient security together with the high speed of switching. MPLS not only guarantees quality of service of IP networks but in addition to provides scope for traffic engineering it offers many enhanced features of IP networks as it does not replace IP routing, but works along with existing and future routing technologies to provide high-speed data forwarding between label-switched routers (LSRs) together with QOS. Many network carriers are facing the problem of how to accommodate such ever-growing demands for bandwidth. And the static nature of current routing algorithms, such as OSPF or IS-IS, the situation is going even worse since the traffic is concentrated on the &quot;least cost&quot; paths which causes the congestion for some links while leaving other links lightly loaded. Therefore, MPLS traffic engineering is proposed and by taking advantage of MPLS, traffic engineering can route the packets through explicit paths to optimize network resource utilization and traffic performance. MPLS provides a robust quality of service control feature in the internet. MPLS class of service feature can work in accordance with other quality of service architectures for IP networks.

Block characters are often used when filling out forms, for example when writing ones personal number. The question of whether or not there is recoverable, biometric (identity related) information within individual digits of hand written personal numbers is then relevant. This thesis investigates the question by using both handcrafted features and extracting features via Deep learning (DL) models, and successively limiting the amount of available training samples. Some recent works using DL have presented semi-supervised methods using Generative adveserial network (GAN) generated data together with a modified Label smoothing regularization (LSR) function. Using this training method might improve performance on a baseline fully supervised model when doing authentication. This work additionally proposes a novel modified LSR function named Bootstrap label smooting regularizer (BLSR) designed to mitigate some of the problems of previous methods, and is compared to the others. The DL feature extraction is done by training a ResNet50 model to recognize writers of a personal numbers and then extracting the feature vector from the second to last layer of the network.Results show a clear indication of recoverable identity related information within the hand written (personal number) digits in boxes. Our results indicate an authentication performance, expressed in Equal error rate (EER), of around 25% with handcrafted features. The same performance measured in EER was between 20-30% when using the features extracted from the DL model. The DL methods, while showing potential for greater performance than the handcrafted, seem to suffer from fluctuation (noisiness) of results, making conclusions on their use in practice hard to draw. Additionally when using 1-2 training samples the handcrafted features easily beat the DL methods.When using the LSR variant semi-supervised methods there is no noticeable performance boost and BLSR gets the second best results among the alternatives.

Le récepteur LSR est un acteur important du métabolisme hépatique, puisqu'il joue un rôle dans la clairance des lipoprotéines à ApoB/ApoE riches en triglycérides durant la période postprandiale. Dans cette étude, nous avons montré qu'un traitement in vitro par DHA peut augmenter les niveaux de protéine et d'activité LSR dans les cellules d'hépatome de souris Hepa 1-6. En toute cohérence, un régime supplémenté en DHA a conduit à élever les niveaux de protéine LSR hépatique chez la souris. Mais aucune de ces deux études n'a montré de changement au niveau des ARNm. Ceci suggère que l'enrichissement en DHA influe positivement sur le microenvironnement de LSR et son ancrage à la surface de la cellule. Nous avons ensuite étudié le rôle du récepteur PPAR[alpha] dans la régulation du gène lsr. Une analyse in silico nous a permis d'identifier des éléments PPRE dans la région 5' régulatrice du gène humain et de ses homologues de souris et de rat. Des traitements pharmacologiques par des agoniste et antagoniste spécifiques de PPAR[alpha] ont montré que ce récepteur est impliqué dans la régulation transcriptionnelle de l'expression du LSR dans les cellules Hepa 1 6. Enfin, une analyse transcriptomique a révélé une diminution de l'expression de PPAR[alpha] et d'autres gènes impliqués dans le métabolisme lipidique hépatique chez la souris LSR+/- sous régime standard ou riche en graisses. En conclusion, toutes ces études indiquent que l'activité LSR hépatique est sous le contrôle de facteurs nutritionnels capables d'activer divers mécanismes de régulation, faisant du LSR une cible d'intérêt potentiel pour des stratégies nutritionnelles ou thérapeutiques destinées à prévenir ou traiter les dyslipidémies / Lipolysis stimulated lipoprotein receptor (LSR) plays an important role in the clearance of ApoB/ApoE containing triglyceride-rich lipoproteins during postprandial phase. In this study, we demonstrated that in vitro treatment of mouse hepatoma cells, Hepa 1-6, with docosahexaenoic acid (DHA) led to an increase in LSR protein levels as well as its activity. Furthermore, the mice placed on the diet supplemented with DHA showed an increase in hepatic LSR protein. However, the mRNA levels remained unchanged in both in vitro and in vivo studies, suggesting that DHA enrichment may result in changes in LSR microenvironment that could affect its anchorage at the surface of cell membrane. Specific peroxisome proliferator response elements were identified in the upstream region of human, mouse and rat lsr gene by in silico analysis. We therefore sought to determine the role of the transcription factor, peroxisome proliferator-activated receptor (PPAR[alpha]), in LSR regulation. In vitro pharmacological studies using PPAR[alpha]-selective agonist and antagonist agents demonstrated that PPAR[alpha] is indeed involved in the transcriptional regulation of LSR expression. Furthermore, qPCR array analysis revealed the downregulation of PPAR[alpha] and various genes involved in hepatic lipid metabolism in LSR+/- mice on standard and high-fat diets. In conclusion, these studies show that the hepatic LSR activity is controlled by dietary factors that can activate various pathways involved in regulating lipid homeostasis, therefore representing LSR as a potential target for either nutritional or therapeutic strategies towards the prevention or treatment of dyslipidemia