In this thesis, RXTE observations of 4U 1907+09 are presented. Timing analysis of these data sets have yielded quasi periodic oscillations (QPOs) at orbital phases corresponding to the two flares in every orbital period. Known continuous spin down trend and QPO behaviour at the flares strongly suggest that a transient accretion disk occurs at the flares. Our findings strongly suggested that neutron star passes through the equatorial wind of Be companion star. During these passages a transient disk forms around Be neutron star.

In this work the effect of rotation on oscillation frequencies have been inves- tigated . Rotation has been treated as a perturbation and detailed calculations were done on the infuence of second order rotation . We used an evolutionary model of DELTA-Scuti star V1162 Ori with a mass of 1:8 solar mass. The eigenfrequencies were calculated in two cases , the slow rotation case with vsini = 46km/s and the fast rotation case with vsini = 61.9km/s. Calculation were carried out by a modifed oscillation program and results were compared to observations .

In this study, forced convection cooling of package of 2-D parallel boards with heat generating chips is investigated. The main objective of this study is to determine the optimal board-to-board spacing to maintain the temperature of the components below the allowable temperature limit and maximize the rate of heat transfer from parallel heat generating boards cooled by forced convection under constant pressure drop across the package. Constant heat flux and constant wall temperature boundary conditions on the chips are applied for laminar and turbulent flows. Finite elements method is used to solve the governing continuity, momentum and energy equations. Ansys-Flotran computational fluid dynamics solver is utilized to obtain the numerical results. The solution approach and results are compared with the experimental, numerical and theoretical results in the literature. The results are presented for both the laminar and turbulent flows. Laminar flow results improve existing relations in the literature. It introduces the effect of chip spacing on the optimum board spacing and corresponding maximum heat transfer. Turbulent flow results are original in the sense that a complete solution of turbulent flow through the boards with discrete heat sources with constant temperature and constant heat flux boundary conditions are obtained for the first time. Moreover, optimization of board-to-board spacing and maximum heat transfer rate is introduced, including the effects of chip spacing.

Le but de cette thèse a été de mettre en évidence notre capacité à utiliser des boîtes quantiques semi-conductrices comme support à la réalisation de bits quantiques, briques élémentaires de l'information quantique. Nous avons ainsi démontré la possibilité de définir un système à deux niveaux, dont l'initialisation et le contrôle est réalisable au moyen d'impulsions lumineuses picosecondes et déterminé le temps durant lequel nous étions en mesure de conserver sa cohérence. Les oscillations de Rabi entre niveau fondamental et niveau excité permettent d'initialiser le système dans une superposition cohérente pouvant être ensuite manipulée par une deuxième impulsion au cours d'expériences de contrôle cohérent. Le temps de cohérence T2 du système n'est pas seulement limité par la durée de vie radiative T1 et reste très inférieur à la valeur théorique T2= 2T1. Les différents mécanismes de décohérence entrant en jeu ont dès lors été étudiés, en particulier le rôle des phonons acoustiques, responsables d'un fort amortissement des oscillations de Rabi et d'une diminution du temps de cohérence pour une partie des boîtes quantiques étudiées. Nous avons cependant dans certains cas mis en évidence la présence de mécanismes supplémentaires, liés aux fluctuations de l'environnement électrostatique des boîtes. Par ailleurs, une étude poussée de la polarisation de la luminescence émise par ces boîtes, dont la croissance a été réalisée en régime Stranski-Krastanov, a révélé une inclinaison des états propres de la structure fine de l'exciton, ainsi qu'une modification de leur intensité d'émission, témoignant d'un fort mélange des états lourds et légers de la bande de valence

Les oscil·lacions d'activitat neuronal són un fenomen omnipresent a l'escorça cerebral. La funció d'aquestes oscil·lacions, però, no està clara. ¿Són només un epifenomen de les elevades taxes de descàrrega de potencials d'acció, o representen un procés fonamental? Per tal d'aclarir aquesta qüestió, en aquest treball hem aplicat models computacionals basats en xarxes neurobiològicament plausibles per tal d'investigar alguns dels resultats experimentals recents més rellevants. Primerament, estudiem la rellevància de les oscil·lacions en processos d'atenció i després en un context més general de teoria d'informació. Els resultats donen suport a la idea que les oscil·lacions representen un mecanisme independent. Demostrem que l'atenció modula les oscil·lacions gamma de manera independent de la taxa de descàrrega de potencials d'acció. També es mostra que la transmissió d'informació entre àrees corticals depèn tant de la fase com de la potència espectral de les oscil·lacions. A més, la velocitat amb què es produeix aquesta transmissió d'informació augmenta en funció de la potència espectral en bandes de freqüències específiques. Aquests resultats suggereixen que les oscil·lacions representen un mecanisme biològicament plausible per mitjançar les interaccions entre àrees cerebrals i, per tant, per establir un vincle entre activitat neuronal i comportament. / Oscillatory neuronal activity is an omnipresent phenomenon in the cerebral cortex. However, the actual function of these oscillations remains unclear. Are they just an epiphenomenon of elevated firing rates or do they represent a fundamental process on their own? Based on experimental work, we apply computational modeling to address this question. We first study the role of oscillations in attentional processes and then in a more general, information theoretical context. Our results support the idea that oscillations represent an independent mechanism. In particular, we show that attention modulates gamma oscillations independently of rates and that the flow of information between brain areas depends both on the phase and on the spectral power of oscillations. Moreover, we show that the speed of information exchange increases as a function of spectral power in specific frequency bands. Taken together, these results suggest that oscillations are a mechanism employed by the brain to control actual interactions between brain areas and thus likely have a link to behavior.

SUMMARY Introduction: There has recently been a great deal of interest in the role of synchronous high-frequency gamma oscillations in brain function. This interest has been motivated by an increasing body of evidence, that oscillations which are synchronous in phase across separated neuronal populations, may represent an important mechanism by which the brain binds or integrates spatially distributed processing activity which is related to the same object. Many models of schizophrenia suggest an impairment in the integration of brain processing, such as a loosening of associations, disconnection, defective multiple constraint organization, or cognitive dysmetria. This has led to recent speculation that abnormalities of high-frequency gamma synchronization may reflect a core dimension of the disturbance underlying this disorder. However, examination of the phase synchronization of gamma oscillations in patients with schizophrenia has never been previously undertaken. Method: In this thesis a new method of analysis of gamma synchrony was introduced, which enables the phase relationships of oscillations in a specific frequency band to be examined across multiple scalp sites as a function of time. This enabled, for the first time, the phase synchronization of gamma oscillations across widespread regions, to be studied in electrical brain activity measured at the scalp in humans. Gamma synchrony responses were studied in electroencephalographic (EEG) data acquired during a commonly employed conventional auditory oddball paradigm. The research consisted of two sets of experiments. In the first set of experiments, data from 100 normal subjects, consisting of 10 males and 10 females in each age decade from 20 to 70, was examined. These experiments were designed to characterize the gamma synchonizations that occurred in response to target and background stimuli and their functional significance in normal brain activity, and to exclude the possibility of these findings being due to electromyogram (EMG) or volume conduction artifact. The examination of functional significance involved the development of an additional new analysis technique. In the second set of experiments, data acquired from 35 patients with schizophrenia and 35 matched normal controls was analyzed. The purpose of these experiments was to determine whether patients showed disturbances of gamma synchrony compared to controls, and to establish the relationship of any such disturbances to medication levels, symptom profiles, duration of illness, and a range of psychophysiological variables. Results: In the 100 normals, responses to target stimuli were characterized by two bursts of synchronous gamma oscillations, an early (evoked) and a late (induced) synchronization, with different topographic distributions. Only the early gamma synchronization was seen in response to background stimuli. The main variable modulating the magnitude of these gamma synchronizations from epoch to epoch was pre-stimulus EEG theta (3-7 Hz) and delta (1-3 Hz) power. Early and late gamma synchrony were also associated with N1 and P3 ERP component amplitude across epochs. Across subjects, the early gamma synchronization was associated with shorter latency of the ERP components P2, N2 and P3, smaller amplitude of N1 and P2, and smaller pre-stimulus beta power. The control analyses showed that these gamma responses were specific to a narrow frequency range (37 to 41 Hz), and were not present in adjacent frequency bands. The responses were not generated by EMG contamination or volume conduction. In the 35 patients with schizophrenia, significant abnormalities of both the early and late synchronizations were observed compared to the 35 normal controls, with distinctive topographic characteristics. In general, early gamma synchrony was increased in patients compared to controls, and late gamma synchrony was decreased. These gamma synchrony disturbances were not related to medication level or the four summed symptom profile scores (positive, negative, general and total). They were, however, associated with duration of illness, becoming less severe the longer the patient had suffered from the disorder. The disordered gamma synchrony in patients was not secondary to abnormalities in other psychophysiological variables, but appeared to represent a primary disturbance. Discussion: The early synchronization may relate to the binding of object representations in early sensory processing, or, given that a constant inter-stimulus interval was employed, may be anticipatory and related to active memory. The late response is probably involved in binding in relation to activation of the internal contextual model involved in late expectancy/contextual processing (context updating or context closure) for target stimuli. The across epochs effects may relate to whether the focus of attention immediately prior to stimulus presentation is internal or is directed at the task. The across subjects effects suggest that a larger magnitude of the early gamma synchronization might indicate that the subject maintains a more stable and less ambiguous internal representation of the environment, that reduces the complexity of input and facilitates target/background discrimination and subsequent processing. The early gamma synchronization findings in patients with schizophrenia suggest that anticipatory processing involving active memory and forward-prediction of the environment is subject to over-binding or the formation of inappropriate associations. The late synchronization disturbances may reflect a fragmentation of contextual processing, and an inability to maintain contextual models of the environment intact over time. Conclusion: This research demonstrates the potential importance of integrative network activity as indexed by gamma phase synchrony in relation to normal cognition, and the possible broad relevance of such activity in psychiatric disorders. In particular, the application in this study to patients with schizophrenia showed that an impairment of brain integrative activity (missing links) might be a key feature of this illness.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2113" Halim Meco. 12/19/2004. Report is also available in paper and microfiche from NTIS.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 190-195). Also available via the World Wide Web.

Thesis (M.Sc. (Applied Mathematics))--Mahidol University, 1986.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Singhose, William; Committee Member: Costello, Mark; Committee Member: Whiteman, Wayne