Although it was once thought that neurons solely rely on glucose as a substrate for cellular energy production, it is now known that small monocarboxylate molecules, like pyruvate, lactate, and ketone bodies, are also utilized. Monocarboxylates are transported across plasma membranes via facilitated diffusion using a family of transport proteins known as monocarboxylate transporters (MCTs). Four MCTs (MCT1, MCT2, MCT3, and MCT4) are expressed within neural tissues. Expression of the MCTs has been tied to co-expression of a cell adhesion molecule belonging to the Basigin subset of the immunoglobulin superfamily (IgSF). Basigin gene products are known to interact with MCT1 and MCT4 in the mammalian neural retina and this association is essential to support the cellular energy needs of photoreceptors. A previous study indicated that Basigin gene products use hydrophobic amino acids within specific regions of the transmembrane domain to interact with MCT1. In the present study, it is hypothesized that the same amino acids within the transmembrane domain are used to interact with MCT4, but that no association exists with MCT2, which typically interacts with a different member of the IgSF subset. Therefore, the purpose of the present study was to assess the association between Basigin gene products and MCT4, and with MCT2. Recombinant proteins corresponding to the transmembrane domain of Basigin gene products were used in in vitro binding assays with endogenous MCT2 and MCT4 from mouse brain protein lysates. Contrary to the hypothesis, it was determined that the transmembrane domain of Basigin gene products binds to both MCT2 and MCT4 in vitro. Different amino acids within the transmembrane domain of Basigin gene products are used for each association and the pattern is different from that used in the association with MCT1. The data suggest that Basigin plays multiple roles in the nervous system.

Le volume grandissant de vidéos a suscité le besoin de nouveaux outils d'aide à l'indexation. Un des outils possibles est le résumé de vidéo qui permet de fournir un aperçu rapide à l'usager. L'objectif de cette thèse est d'extraire, à partir d'informations visuelles, un résumé de vidéo contenant le « message » de la vidéo. Nous avons choisi d'étudier trois nouvelles méthodes de résumé de vidéo utilisant différentes informations visuelles.<br />La première méthode de résumé repose sur des caractéristiques de bas niveau (couleur, orientation et mouvement). La combinaison de ces index qui s'appuie sur un système d'inférence floue a permis de construire un résumé hiérarchique. Nous avons montré l'intérêt d'un tel résumé dans une application de la recherche par l'exemple.<br />La deuxième méthode de résumé est construite à partir du mouvement de caméra. Cette caractéristique de plus haut niveau sémantique est réfléchie par le réalisateur et induit une information sur le contenu. Une méthode de classification des mouvements basée sur le Modèle des Croyances Transférables est élaborée. La méthode de résumé est alors établie selon des règles sur l'amplitude et l'enchaînement des mouvements de caméra identifiés.<br />La troisième méthode de résumé est développée à partir de l'attention visuelle. Connaître les endroits où le regard se porte lors du visionnage de la vidéo est une information de plus haut niveau sémantique et pertinente pour créer le résumé. Un modèle spatio-temporel d'attention visuelle est proposé, puis utilisé pour détecter le changement de contenu au cours du temps afin de construire le résumé.

L'électronique de puissance d'aujourd'hui est de plus en plus exigeante vis à vis des dispositifs semi-conducteurs. Es doivent être performants tant en statique qu'en dynamique: faibles pertes en conduction et en commutation, vitesses élevées, grandes capacités en surcharge... . Grâce à sa structure, associant le thyristor avec le MOS, le MCT offre une faible tension directe et une grande facilité de commande. H est l'un des nouveaux dispositifs pouvant éventuellement répondre aux exigences actuelles. Ce mémoire est composé de deux parties. Dans la première nous présentons une étude du comportement individuel du MCT dans les différents modes de commutation (commutation dure, commutations douce ZVS, ZCS) et en cas de surcharge (pouvoir de coupure et aire de sécurité). Cette étude comportementale est réalisée par deux voies distinctes et complémentaires: la voie expérimentale en utilisant le Simulateur Analogique de l'Electronique de Puissance et la voie physique interne basée sur une modélisation simplifiée et qualitative. Dans la deuxième partie nous intéressons à l'association du MCT dans la mise en série et dans la mise en parallèle. Cette étude fait le point sur l'ensemble des problèmes et présente les solutions envisageables pour la réalisation des commutateurs haute tension et forts courants avec le MCT.

Introdução: Os efeitos metabólicos do uso combinado dos triglicerídeos de cadeia média (TCM) e do óleo de peixe (OP) na esteatose hepática ainda não estão totalmente esclarecidos. Objetivo: O presente estudo teve o objetivo de verificar os efeitos da combinação dos TCMs e OP na esteatose hepática e estresse oxidativo induzidos pela dieta hiperlipídica (HL+) termolizada em ratos. Material e Métodos: Foram utilizados no total 50 ratos machos da linhagem Wistar. O grupo Controle (n=10) recebeu a dieta controle. Os grupos HL+ receberam a dieta contendo 50% de gordura animal (GA) termolizada e 50% de ração. A adaptação às dietas HL+ foi realizada durante 5 dias. Os grupos HL+GA, HL+TCM, HL+OP e HL+TCM/OP (n=10) receberam a dieta HL+ com 50% de lipídios (gordura animal termolizada) durante 30 dias. Após este período, os grupos HL+TCM, HL+OP e HL+OP/TCM receberam as dietas HL+ adicionadas de óleo de TCM (OTCM), OP e OTCM + OP, respectivamente, durante 20 dias. As análises realizadas foram a gordura hepática total, frações lipídicas hepáticas e séricas, glicemia, vitamina E e retinol séricos, glutationa reduzida (GSH) e malondialdeído (MDA) sérico e hepático e aminotransferases séricas. Resultados: Os grupos HL+ apresentaram acúmulo significativo de gordura total e triglicerídeos hepáticos, exceto o HL+OP. Apenas o grupo HL+TCM não apresentou acúmulo significativo de colesterol total hepático (CT). Este mesmo grupo apresentou valores maiores de CT e HDLcol séricos e menor razão triglicerídeos/HDLcol. Os valores séricos de aminotransferases foram significativamente maiores nos grupos que receberam os OTCM e/ou OP. A peroxidação lipídica (LPO) hepática foi maior foi nos grupos HL+, exceto o HL+TCM. Apenas o grupo HL+GA apresentou maior LPO sérica. Verificou-se que a GSH foi maior nos grupos HL+GA, HL+TCM e HL+OP/TCM, a vitamina E sérica foi menor nos grupos HL+GA, HL+OP e HL+OP/TCM e o retinol sérico foi maior nos grupos HL+GA e HL+TCM. Conclusões: As alterações séricas não refletiram as alterações hepáticas em relação aos lipídios, estresse oxidativo e antioxidantes. O uso do óleo de TCM e óleo de peixe em associação na dieta HL+ resultou em efeito negativo devido ao maior acúmulo de gordura hepática tanto na forma de triglicerídeos quanto de colesterol, maior peroxidação lipídica hepática e menor vitamina E sérica. / Introduction: The metabolic effects of combined use of medium chain triglycerides (MCT) and fish oil (FO) on non alcoholic hepatic steatosis are not fully understood. Objective: The aim of this study was to investigate the effects of the combination of MCT and FO on hepatic steatosis and oxidative stress induced by high fat (HF+) thermolyzed diet in rats. Methodology: Fifty wistar male rats were studied. The Control group (n = 10) received the standard diet. The HF+ groups received diet with 50% of thermolyzed animal fat (AF) and 50% of ration. Five days were dedicated for adaptation to high-fat diets. The groups HF+AF, HF+MCT, HF+FO and HF+MCT/FO (n = 10) received HF+ diet with 50% thermolyzed fat during 30 days. After this period, the groups HF+MCT, HF+FO and HF+MCT/FO received HF+ diets with MCT oil (MCTO), FO and MCTO + OP, respectively, during 20 days. Analysis of total liver fat, liver and serum lipid fractions, serum glucose, vitamin E and retinol, serum and liver reduced glutathione (GSH) and malondialdehyde (MDA), and serum aminotransferases (AST and ALT) were performed. Results: The groups HF+ showed higher total fat and triglycerides, except HF+FO. Only HF+MCT group didn´t have higher liver total colesterol (TC). This same group had higher serum TC and HDLcol and lower triglycerides/HDLcol ratio. The groups fed with MCTO and/or FO had higher serum aminotransferase. Liver lipid peroxidation (LPO) was higher in HF+ groups, except HF+MCT. Serum LPO was higher in HF+AF. The hepatic GSH was higher in the groups HF+AF, HF+MCT and HF+MCT/FO, serum vitamin E was lower in groups HF+AF, HF+FO and HF+MCT/FO, and serum retinol was higher in groups HF+AF and HF+MCT. Conclusions: Lipids, oxidative stress and antioxidant serum and liver alterations didnt correspond. The association of MCTO with FO in HF+ diet resulted in a negative effect when it concerns liver fat, triglyceride and cholesterol accumulation, higher liver lipid peroxidation and lower serum vitamin E.

La chaîne himalayenne constitue le paradigme actuel des chaînes de collision. Cependant, les processus de formation de cette chaîne sont toujours en discussion. Bien que fondamentales pour comprendre la formation de la chaine, les klippes de Haut Himalaya Cristallin (HHC) sont paradoxalement assez peu intégrées dans les différents modèles. Dans la klippe de Jaljala (Centre – Ouest Népal) la combinaison d’études structurales pétrographiques et géochronologiques (40Ar/39Ar) ont permis de caractériser près du front de l’Himalaya la géométrie et la cinématique du Main Central Thrust (MCT) et d'une zone de cisaillement top vers le nord : la zone de cisaillement de Jaljala, failles qui encadrent le HHC. Les résultats montrent que le MCT et la zone de cisaillement de Jaljala ont été replissés et que le que la zone de cisaillement de Jaljala est proche du MCT au nord de la klippe. Une faille normale intra – séquences téthysiennes (TH) a été découverte, faille interprétée comme étant la zone de cisaillement de Jaljala sur le flanc sud de la klippe. Les données pétrographiques montrent une augmentation progressive de la température entre 350 et 550 °C au travers du MCT dans le Haut Himalaya Cristallin alors qu’elle atteint plus de 650 °C au Nord dans les zones internes. Les pseudosections montrent que ce pic de température est atteint après un échauffement isobare à desvaleurs de pression variant entre 7 à 9 kbars. Les âges 40Ar/39Ar sur micas montrent trois populations : environ 20, environ 40 et environ 100 Ma dans le HHC et dans les séquences téthysiennes. Deux hypothèses peuvent être proposées : soit l’exhumation est marquée par les âges à 40 Ma ce qui représente une date relativement ancienne pour l’exhumation du Haut Himalaya Cristallin au front de la chaîne, soit elle est datée à 20 Ma ce qui représente des âges plus communs d’exhumation sur le MCT et sous le STD (South Tibetan Detachment). La nature des roches observées, leurs déformations ainsi que les corrélations avec les résultats des autres klippes montrent que la zone de cisaillement de Jaljala ne peut être connecté au STD des zones internes. Le MCT et le STD ne peuvent se rejoindre en profondeur au front de la klippe ce qui exclut le modèle de prisme tectonique. Enfin la continuité des pressions et températures des zones internes avec les roches de la klippe va à l’encontre du modèle de fluage de croûte chenalisée puisqu’il n’y a pas de fusion partielle dans la klippe de Jaljala. Les structures, les conditions métamorphiques et les âges seraient plutôt compatibles avec la formation d’un duplex de Haut Himalaya Cristallin dont la géométrie est cependant mal contrainte et qui nécessiterait de présenter un système de plat – rampe frontal pour transférer les écailles les plus internes sur le front de la chaîne et ainsi former les klippes comme la klippe de Jaljala qui seront ensuite isolées de la zone interne par la formation d’un duplex Moyen Himalaya. / The Himalayan belt is the actual paradigm of collision mountain belt. However, formation model remains still under discussion. Even fundamental to understand the belt formation, the High Himalaya Cristalline (HHC) klippen are poorly integrated to the different existing models. In the Jaljala klippe (Western Central Nepal) a combination of structural, petrographic and geochronological (40Ar/39Ar) studies have allowed to caracterise close to the Himalaya front, the Main Central Thrust (MCT) and a top - to - the North shear zone : the Jaljala shear zone geometry and kinematics, faults that bordered the HHC. Results show that the MCT and the Jaljala shear zone have been refolded and the Jaljala shear zone is close to the MCT in the North of the klippe. An intra téthyan sequences (TH) have been discovered and interpreted as the Jaljala shear zone in the southern flank of the klippe. Petrographic datas show a progressive augmentation of temperature between 350 and 550 ° C cross to the MCT in High Himalaya Cristalline instead of 650 °C in the internal zones. Pseudosections show this temperature peak is achieved after an isobaric warming at pressure varying between 7 and 9 bars. 40Ar/39Ar ages on micas show three ages populations : about 20, about 40 and about 100 Myrs in the HHC and in Tethyan sequences. Two hypothesis can be proposed : on the one hand, the exhumation can be testified by 40 Myrs ages which represent an ancient age for the High Himalaya Crystalline in the front belt, on the other hand, it is dated at 20 Myrs which represent more commons ages for exhumation on MCT and under STD (South Tibetan Detachment). Rock lithology and their deformations and correlations with results for other klippen show that the STD in the Jaljala klippe cannot be connected width the STD in internal zones. The MCT and the STD cannot converge in depth at the front that excluded the tectonic wedge model. Finally, the pressures and temperature continuities in internal zones and with the klippe rocks excluded the channel flow model because partial melting is absent in the Jaljala klippe. Structures, metamorphic conditions and ages are more compatible with High Himalaya Crystalline duplex formation whose geometry is still poorly constrained and which necessitate a frontal flat - ramp system to transfer crustal nape on the front of the belt and then to form klippe as the Jaljala klippe that will then isolated from internal zones by Lesser Himalaya duplex formation.

One of the most important and interesting unsolved problems of science is the nature of glassy dynamics and the glass transition. It is quite an old problem, and starting from the early20th century there have been many efforts towards a sound understanding of the phenomenon. As a result, there are a number of theories in the field, which do not entirely contradict each other, but between which the connection is not entirely clear. In the last couple of decades or so, there has been significant progress and currently we do understand many facets of the problem. But a unified theoretical framework for the varied phenomena associated with glassiness is still lacking. Mode-coupling theory, an extreaordinarily popular approach, came from Götze and co-workers in the early eighties. The theory was originally developed to describe the two¬ step decay of the time-dependent correlation functions in a glassy fluid observed near the glass transition temperature(Tg). The theory went beyond that and made a number of quantitative predictions that can be tested in experiments and simulations. However, one of the drawback of the theory is its prediction of a strong ergodic to non-ergodic transition at a temperature TMCT; no such transition exists in real systems at the temperatures at which MCT predicts it. Consequently, the predictions of the theory like the power-law divergences of the transport quantities (e.g., viscosity and relaxation time) fail at low enough temperature and the theory can not be used below TMCT. It is well understood now that MCT is some sort of a mean-field theory of the real phenomenon, and in real systems the transition predicted by MCT is at best avoided due to finite dimensions and activated processes, neither of which is taken into account in standard MCT. Despite its draw backs, even the most severe critic of the theory will be impressed by its power and the predictions in a regime where it works. Even though the non-ergodic transition predicted by the theory is averted, the MCT mechanism for the increase of viscosity and relaxation time is actually at work in real systems. The status of MCT for glass transition is ,perhaps, similar to the Curie-Weiss theory of magnetic phase transition and it will require hard work and perhaps a conceptual breakthrough to go beyond this mean-field picture. Discussion of such a theoretical framework and its possible directions are, however, beyond the scope of this thesis. In the first part of this work, we have extended the mode coupling theory to three important physical situations: the properties of fluids under strong confinement, a sheared fluid and for the growth kinetics of glassy domains. In the second part, we have studied a different class of non equilibrium phenomenon in arrested systems, the fluctuation relations for yielding. In the first chapter, we talk about some general phenomenology of the glass transition problem and a few important concepts in the field. Then we briefly discuss the physical problems to be addressed in detail later on in the thesis followed by a brief account of some of the important existing theories in the field. This list is by no means exhaustive but is intended to give a general idea of the theoretical status of the problem. We conclude this chapter with a detailed derivation of MCT and its successes and failures. This derivation is supposed to serve as a reference for the details of the calculations in later chapters. The second chapter deals with a simple theory of an important problem of lubrication and dynamics of fluid at nanoscopic scales. When a fluid is confined between two smooth surfaces down to a few molecular layers and an normal force is applied on the upper surface, it is found that one layer of fluid gets squeezed out of the geometry at a time. The theory to explain this phenomenon came from Persson and Tosatti. However, due to a mathematical error, the in-plane viscosity term played no role in the original calculation. We re-do this calculation and show that the theory is actually more powerful than was suggested originally by its proponents. In the third chapter, we work out a detailed theory for the dynamics of fluid under strong planar confinement. This theory is based on mode-coupling theory. The walls in our theory enter in terms of an external potential that impose a static inhomogeneous background density. The interaction of the density fluctuation with this static background density makes the fluid sluggish. The theory explains how the fluid under strong confinement can undergo a glassy transition at a higher temperature or lower density than the corresponding bulk fluid as has been found in experiments and simulations. One of the interesting findings of the theory is the three-step relaxation that has also been found in a variety of other cases. The fourth chapter consists of a mode-coupling calculation of a sheared fluid through the microscopic approach first suggested by Zaccarelli et al[J. Phys.: Condens. Matter 14,2413(2002)]. The various assumptions of the theory are quite clear in this approach. The main aim of this calculation is to understand how FDR enters with in the theory. The only new result is the modified form of Yvon-Born-Green(YBG) equations for a sheared fluid. Then we extend the theory for the case of a confined fluid under steady shear and show that a confined fluid will show shear thinning at a much lower shear rate than the bulk fluid. When a system is quenched past a phase transition point, phase ordering kinetics begins. The properties of the system show “aging” with time, and the characteristic length scale of the quenched system grows as one waits. The analogous question for glasses has also been asked in the contexts of various numerical and experimental works. We formulate a theory in chapter five for rationalizing these findings. We find that MCT, surprisingly, offers an answer to this key question in glass forming liquids. The challenge of this theory is that care must be taken in using some equilibrium relations like the fluctuation-dissipation relation(FDR), which is one of the key steps in most of the derivations of MCT. We find that the qualitative, and some times even the quantitative, picture is in agreement with numerical findings. A similar calculation for the spin-glass case also predicts increase of the correlation volume with the waiting time, but with a smaller exponent than the structural glass case. We extended this theory to the case of shear and find that shear cuts off the growth of the length-scale of glassy correlations when the waiting time becomes of the order of the inverse shear rate. For the case of sheared fluid, if we take the limit of the infinite waiting time, the system will reach a steady state. Then, the resulting theory will describe a fluid in sheared steady state. The advantage of this theory over the existing mode-coupling theories for a sheared fluid is that FDR has not been used in any stage. This is an important development since the sheared steady state is driven away from equilibrium. Interestingly, the theory captures a suitably-defined effective temperature and gives results that are consistent with numerical experiments of steady state fluids(both glass and granular materials). We give the details of a theoretical model for jamming and large deviations in micellar gel in the sixth chapter. This theory is motivated by experiments. Through the main ingredient of the attachment-detachment kinetics and some simple rules for the dynamics, the theory is capable of capturing all the experimental findings. The novel prediction of this work is that in a certain parameter range, the fluctuation relations may be violated although the large deviation function exists. We argue that a wider class of physical systems can be understood in terms of the present theory. In the final chapter, we summarize the problems studied in this thesis and point out some future directions.

This qualitative case study provided a narrative portrait of 12 students in the 11th grade in one north Texas district who failed the initial administration of the Texas Educational Assessment of Minimum Skills (TEAMS) exit-level test. It also presented an account of their perceptions of the test and their efforts to overcome this educational hurdle. The following conclusions were drawn from the study. Limited English proficiency (LEP) students had difficulty mastering the language arts section of the test. A majority of the students reported that TEAMS failure had no social impact. Most of the students declined district-offered remediation. Students tended to perceive the test as a personal challenge. Those students who attended remedial tutoring sessions performed better on the following retest than those who declined remediation. Hispanic and Asian students expressed additional study as being the key to passing the test. Black students felt that the key to passing was to spend sufficient time while taking the test. Those students who were more verbal during their interviews tended to be more successul in passing the language arts section of the TEAMS. The following recommendations were made from the study: (a) students who fail the TEAMS by minimal margins should be encouraged to take remediation; (b) an intensive remedial English course for LEP students should be offered; (c) "high interest" TEAMS mini-lessons should be presented daily for several weeks as a lead-up to the TEAMS; (d) a TEAMS ex it-level orientation program which stresses the importance of the test for the student's future should be implemented; and (e) additional research should be conducted on older students' verbal responses to see if a rich language approach in English classes including listening, reading, writing, and speaking will develop higher level language skills.

This thesis on multicarrier effects in the magnetotransport and optical properties of Mercury Cadmium Telluride (MCT or HgCdTe) covers mainly: design, construction and calibration of a 12T 4K and 19T 77K pulsed high magnetic field systems; temperature dependent magnetotransport measurements upto 15T performed on the home-built pulsed magnet systems; computational techniques developed to extract densities and mobilities of various carriers, especially low mobility heavy holes, participating in conduction; theoretical analysis of heavy hole mobility based on Boltzmann transport equation; temperature dependent optical absorption experiments in the Mid and Far-IR on bulk and thin film samples; and theoretical modelling of optical absorption below bandgap. The work essentially probes the low and high frequency conductivity of the semiconductor alloy Hg1?xCdxTe by performing microscopic calculations of scattering related phenomena of its free carriers at higher temperatures (200 K–300 K) and comparing with experimental data. Special attention is given to properties of heavy holes as the effects due to these carriers appear only at higher magnetic fields. It is demonstrated that in this temperature range and at high magnetic fields, taking both measured resistivity and derived conductivity in the multicarrier analysis gives better results which are then applied to explain both heavy hole mobility as well as free carrier absorption without further fitting parameters and using a minimal set of necessary intrinsic properties. The agreement thus obtained with experimental data is shown to be excellent. The bulk and epilayer samples used in this thesis were grown by the MCT group headed by R. K. Sharma (SSPL, Delhi). The organization of the thesis is as follows: Chapter 1 The importance of Mercury Cadmium Telluride as a narrow gap semiconductor for infrared detection is introduced. The relevant physical and material properties of HgCdTe are reviewed. Chapter 2 A low cost 12T pulsed magnet system has been integrated with a closed-cycle Helium refrigerator (CCR) for performing magnetotransport measurements. Minimal delay between pulses and AC current excitation with software lock-in to reduce noise enable quick but accurate measurements to be performed at temperatures 4K-300K upto 12T. An additional pulsed magnet operating with a liquid nitrogen cryostat extends the range upto 19T. The instrument has been calibrated against a commercial superconducting magnet by comparing quantum Hall effect data in a p-channel SiGe/Si heterostructure and common issues arising out of pulsed magnet usage have been addressed. The versatility of the system is demonstrated through magnetotransport measurements in a variety of samples such as heterostructures, narrow gap semiconductors and those exhibiting giant magnetoresistance. Chapter 3 The necessity of employing multicarrier methods in magnetotransport of narrow gap semiconductors is brought out. In these materials, mixed conduction is seen to exist at nearly all temperatures of interest. Methods of extracting two of the most important transport parameters of device interest, density and mobility, from the variable magnetic field Hall and magnetoresistance measurements are elaborated. Improvements have been made to the conventional non-linear least squares fitting procedure and are demonstrated. Chapter 4 Magnetotransport measurements in pulsed fields upto 15 Tesla have been performed on Mercury Cadmium Telluride (Hg1?xCdxTe, x?0.2) bulk as well as liquid phase epitaxially grown samples to obtain the resistivity and conductivity tensors in the temperature range 220K to 300 K. Mobilities and densities of various carriers participating in conduction have been extracted using both conventional multicarrier fitting (MCF) and Mobility Spectrum Analysis(MSA). The fits to experimental data, particularly at the highest magnetic fields, were substantially improved when MCF is applied to minimize errors simultaneously on both resistivity and conductivity tensors. The semiclassical Boltzmann Transport Equation (BTE) has been solved without using adjustable parameters by incorporating the following scattering mechanisms to fit the mobility: ionized impurity, polar and nonpolar optical phonon, acoustic deformation potential and alloy disorder. Compared to previous estimates based on the relaxation time approximation with out-scattering only, polar optical scattering and ionized impurity scattering limited mobilities are shown to be larger due to the correct incorporation of the in-scattering term taking into account the overlap integrals in the valence band. Chapter 5 Optical absorption measurements have been performed on bulk Mercury Cadmium Telluride (Hg1?xCdxTe, x?0.2) samples between 4K and 300 K. After fitting the Urbach part of the spectrum in the mid-infrared, below bandgap absorption is modeled using only basic processes and mechanisms, i.e. intervalence transitions and free carrier absorption (FCA). The additive FCA coefficients for individual carriers have been calculated using known quantum mechanically derived expressions for scattering due to polar and nonpolar optical phonons, ionized impurities and acoustic deformation potential mechanisms found to be relevant for electrical transport in this temperature range. The densities of carriers used in the calculations are derived from a modified multicarrier fitting (MCF) procedure on both resistivity and conductivity tensors from magnetotransport measurements in pulsed fields upto 15 Tesla from 220K to 300 K, thus making hole density more reliable. It is found that such a treatment is sufficient to model the absorption spectra below bandgap quite accurately without introducing any additional mechanical or compositional defect related phenomena. Chapter 6 A summary of the work carried out in this thesis is presented. Some future directions including preliminary work to measure carrier mobilities at high electric fields and effect of hydrogen passivation in MCT are briefly discussed.

L'étude des isotopes stables H, C, 0, à été entreprise dans le but de préciser le rôle et la nature des fluides associés au magmatisme leucogranitique du Haut Himalaya, ses roches sources et le Grand Chevauchement Central Himalayen (MCT), 290 analyses isotopiques de roches totales, de minéraux et d'inclusions fluides provenant des formations chevauchées (Moyen Pays), des formations chevauchantes (source du granite, Dalle du Tibet) et du granite du Manaslu, apportent certaines contraintes sur les processus métamorphiques et magmatiques. Les Formations du Moyen Pays ont des compositions isotopiques variables impliquant l'absence de circulation massive et pénétrante. La nature des roches majoritaires, très pauvres en C, implique que les fluides riches en CO2 présent dans les inclusions fluides sont libérés dans des niveaux plus profonds puis infiltrés dans les niveaux étudiés. La déshydratation des schistes atteint 20 à 40% de l'eau initiale dans les niveaux proches du MCT (maximum du métamorphisme) et s'accompagne d'une diminution des &D des schistes de l'ordre de 15 %0. On peut prévoir des volatilisations plus intenses (2 à 5 % poids suivant les niveaux) dans les zones plus profondes du chevauchement. Pour le granite, les &D musc varient entre -70 et -85 %0 et les & 180 RT de 10.9 à 12.8. Les fractionnements entre minéraux de l'hydrogène comme de l'oxygène sont compatibles avec des températures d'équilibre élevées et, pour l'oxygène, avec des évolutions en système fermé. Quelques échantillons provenant surtout du Bras filonien de Chhokang ont des &D très négatifs (> -180 %0) et des fractionnements biot.-musc. trop importants. Ces rares déséquilibres sont liés à la chloritisation et à des circulations tardives de fluides d'origine météorique, Les gneiss de la Dalle du Tibet (Formation l, source du granite) ont des &18 Oquartz variant de 12 à 14.3 %0 qui confirment la filiation du granite à la Formation I. Par contre les &D sont environ 20 %0 plus élevés que ceux du granite. Deux processus sont proposés pour expliquer cette différence (1) le dégazage magmatique accompagné d'un fractionnement du deutérium, (2) l'infiltration de fluides pauvres en deutérium dans la zone de fusion. Les fluides libérés au niveau du Moyen Pays pourraient concorder avec ce dernier processus car de nombreux niveaux du Moyen Pays ont des &D initiaux < -80 %0. La combinaison des données chimiques et isotopiques O, Sr, Nd du granite et de la Formation 1 confirme que les variations isotopiques et les relations des systèmes isotopiques dans le granite sont héritées de celles de la Formation 1. De plus ces données dans la Formation 1 reflètent le stade sédimentaire des gneiss et pour l'oxygène et le Nd la proportion des minéraux détritiques et des phyllosilicates.

In this thesis, theoretical and computer simulation studies of vibrational phase relaxation in various molecular liquids are presented. That includes liquid nitrogen, both along the coexistence line and the critical isochore, binary liquid mixture and liquid water. The focus of the thesis is to understand the dependence of the vibrational relaxation on the density, temperature, composition and the role of different interactions among the molecules. The density fluctuation of the solute particles in a solvent is studied systematically, where the computer simulation results are compared with the mode coupling theory (MCT). The classical density functional theory (DFT) is used to study the vibrational relaxation dynamics in molecular liquids with an aim to understand the heterogeneous nature of the dynamics commonly observed in experiments. Chapter 1 contains a brief overview of the earlier relevant theories, their successes and shortcomings in the light of the problems discussed in this thesis. This chapter discusses mainly the basic features of the vibrational dynamics of molecular liquids and portrays some of the theoretical frameworks and formalisms which are widely recognized to have contributed to our present understanding. Vibrational dephasing of nitrogen molecules is known to show highly interesting anomalies near its gas–liquid critical point. In Chapter 2, we present the results of extensive computer simulation studies and theoretical analysis of the vibrational phase relaxation of nitrogen molecules both along the critical isochore and the gas–liquid coexistence line. The simulation includes the different contributions (density (ρ), vibration–rotation (VR), and resonant transfer (Rs)) and their cross–correlations. Following Everitt and Skinner, we have included the vibrational coordinate (q) dependence of the inter–atomic potential, which is found to have an important contribution. The simulated results are in good agreement with the experiments. The linewidth (directly proportional to the rate of the vibrational phase relaxation) is found to have a lambda shaped temperature dependence near the critical point. As observed in the experimental studies, the calculated lineshape becomes Gaussian–like as the critical temperature (Tc) is approached while being Lorentzian–like at the temperatures away from Tc. Both the present simulation and a mode coupling theory (MCT) analysis show that the slow decay of the enhanced density fluctuations near the critical point (CP), probed at the sub–picosecond timescales by the vibrational frequency modulation, and an enhanced vibration–rotation coupling, are the main causes of the observed anomalies. Dephasing time (тv) and the root mean square frequency fluctuation (Δ) in the supercritical region are calculated. The principal results are: 1. a crossover from a Lorentzian–like to a Gaussian–like lineshape is observed as the critical point is approached along the critical isochore, 2. the root mean square frequency fluctuation shows a non–monotonic dependence on the temperature along the critical isochore, 3. the temperature dependent linewidth shows a divergence–like (λ–shaped) behavior along the coexistence line and the critical isochore. It is found that the linewidth calculated from the time integral of the normal coordinate time correlation function (CQ(t)) is in good agreement with the known experimental results. The origin of the anomalous temperature dependence of linewidth can be traced to simultaneous effects of several factors, (i) the enhancement of the negative cross–correlations of ρ with VR and Rs and (ii) the large density fluctuations as the critical point (CP) is approached. Due to the negative cross–correlations of ρ with VR and Rs the total decay becomes faster (correlation times are in the femtosecond scale). The reason for the negative cross–correlation between ρ and VR is explored in detail. A mode coupling theory (MCT) analysis shows a slow decay of the enhanced density fluctuations near the critical point. The MCT analysis demonstrates that the large enhancement of VR–coupling near CP may arise from a non–Gaussian behavior of the equilibrium density fluctuations. This enters through a non–zero value of the triplet direct correlation function. Many of the complex systems found in nature and used routinely in industry are multi–component systems. In particular, binary mixtures are highly non–ideal and play an important role in the industry. The dynamic properties are strongly influenced by composition fluctuations which are absent in the one component liquids. In Chapter 3, isothermal–isobaric (NPT) ensemble molecular dynamics simulation studies of vibrational phase relaxation (VPR) in a model system are presented. The model considers strong attractive interaction between the dissimilar species to prevent phase separation. The model reproduces the experimentally observed non–monotonic, nearly symmetric, composition dependence of the dephasing rate. In addition, several other experimentally observed features, such as the maximum of the frequency modulation correlation time (т c) at a mole fraction near 0.5 and the maximum rate enhancement by a factor of about 3 above the pure component value, are also reproduced. The product of the mean square frequency modulation ((Δω2(0))) with тc indicates that the present model is in the intermediate regime of the inhomogeneous broadening. The non–monotonic composition (χ) dependence of тv is found to be primarily due to the non–monotonic χ dependence of тc, rather than due to a similar dependence in the amplitude of (Δω2(0)). The probability distribution of Δω shows a markedly non–Gaussian behavior at intermediate composition (χ - 0.5). We have also calculated the composition dependence of the viscosity (η∗) in order to explore the correlation between the viscosity with that of тv and тc. It is found that both the correlation times essentially follow the nature of the composition dependence of the viscosity. A mode coupling theory (MCT) analysis is presented to include the effects of the composition fluctuations in binary mixture. Water is an interesting and attractive object for research, not only because of its great importance in life processes but also due to its unusual and intriguing properties. Most of the anomalous properties of water are related to the presence of a three–dimensional network of hydrogen bonds, which is constantly changing at ultrafast, sub–picosecond timescales. Vibrational spectroscopy provides the means to study the dynamics of processes involving only certain chemical bonds. The dynamics of hydrogen bonding can be probed via its reflection on molecular vibrations, e.g., the stretching vibrational mode of the O–H bond. Recently developed femtosecond infrared vibrational spectroscopy has proved to be valuable to study water dynamics because of its unique temporal resolution. Recent studies have shown that the vibrational relaxation of the O–H stretch of HDO occurs at an extremely fast timescale with time constant being less than 100 femtosecond. Here, in Chapter 4, we investigate the origin of this ultrafast vibrational dephasing using computer simulation and appropriate theoretical analysis. In addition to the usual fast vibrational dynamics due to the hydrogen bonding excitations, we find two additional reasons: (a) the large amplitude of angular jumps of the water molecules (with 30–40 fs time intervals) provide large contribution to the mean square vibrational frequency and (b) the projected force along the O–H bond due to the solvent molecules, on the oxygen (FO(t)) and hydrogen (FH (t)) atoms of the O–H bond exhibit a large negative cross–correlation (NCC) between FO(t) and FH (t). This NCC is shown to be partly responsible for a weak, non–Arrhenius temperature dependence of the relaxation rate. In the concluding note, Chapter 5 starts with a brief summary of the outcome of this thesis and ends up with suggestions of a few relevant problems that may prove worthwhile to be addressed in the future.