Posttraumatic epilepsy is a common consequence of brain trauma. However, little is known about how long-term changes in local excitatory and inhibitory synaptic networks contribute to epilepsy after closed-head brain injury. This study adapted a widely used model of experimental brain injury as a mouse model of posttraumatic epilepsy. Behavioral seizure activity and alterations in synaptic circuitry in the dentate gyrus were examined in mice after experimental cortical contusion brain injury. Spontaneous behavioral seizures were observed in 20% of mice after moderate injury and 36-40% of mice weeks after severe injury. In the dentate gyrus, most mice displayed regionally localized mossy fiber reorganization ipsilateral to the injury that was absent in control mice or sections contralateral to the injury. Extracellular field and whole-cell patch clamp recordings were performed in acute brain slice preparations of the dentate gyrus. Dentate granule cells displayed spontaneous and evoked activity that was consistent with network synchronization and the formation of recurrent excitatory network only in slices that had posttraumatic mossy fiber sprouting. The excitability of surviving hilar GABAergic interneurons, which provide important feedback inhibition to granule cells, was examined at similar time points. Cell-attached and whole-cell voltage-clamp recordings revealed increased spontaneous and glutamate photostimulation-evoked excitatory input to hilar GABA neurons ipsilateral to the injury, versus control and contralateral slices. Despite increased excitatory synaptic input to interneurons, whole-cell voltage-clamp recordings revealed a reduction in inhibitory synaptic input to granule cells. These findings suggest that there are alterations in excitatory and inhibitory circuits in mice with posttraumatic mossy fiber sprouting and seizures after cortical contusion head injury.

An average-value model of a rotating rectifier circuit in a brushless excitation system is set forth, where a detailed simulation is required to extract the essential averaged-model parameters using numerical averaging. In the proposed approach, a synchronous machine model with saturation and cross saturation and an arbitrary rotor network representation that uses a voltage-behind-reactance representation for the field winding of the main machine is proposed. This allows the field winding to be represented as branches in a circuit solver, permitting straightforward simulation with connected circuitry. Also a brushless exciter model is introduced to be compatible with the averaged-model, where the exciter armature windings are represented using a voltage-behind-reactance formulation. The resulting average-value model is verified in time domain against detailed simulation, and its validity is demonstrated in all rectifier modes of operation.

L'étude de la sécurité sismique des grands barrages-voûtes existants ou devant être construits dans des zones sujettes à des tremblements de terres nécessite une modélisation numérique des différents éléments intervenants dans son comportement dynamique. Les sols de fondation ainsi que l'eau du réservoir jouent un rôle important dans l'analyse dynamique des barrages. On parle ainsi souvent d'un système barrage-réservoir-fondation. Le choix des différents paramètres de modélisation devient alors primordial pour l'obtention d'un modèle représentatif de la réalité. L'OFEN (Office fédéral de l'énergie en Suisse) a entrepris des études et recherches à long terme sur les principaux barrages suisses. Un réseau d'accélérographes permettant d'enregistrer l'amplitude des mouvements à différents points des barrages lors de tremblements de terres a été installé. Trois barrages-voûtes suisses seront ainsi modélisés ; soit le barrage Mauvoisin qui a une hauteur de 250 mètres, le barrage d'Émosson d'une hauteur de 180 mètres ainsi que le barrage Punt-dal-Gal qui a pour sa part une hauteur de 130 mètres. La modélisation des barrages sera réalisée à l'aide du logiciel EADC-3D-2008 qui est spécialisé dans la modélisation des barrages et qui permet de considérer l'interaction barrage-réservoir-fondation. Pour évaluer l'efficacité des modèles à l'étude, les simulations seront comparées aux données réellement enregistrées par les accélérographes lors de tremblements de terre. Afin de déterminer l'influence de chaque paramètre de modélisation, une étude paramétrique des différents modèles sera réalisée. Trois tailles de modèles seront ainsi générés ; soit un grossier, un intermédiaire et un raffiné. Un paramètre sera modifié tout en gardant les autres invariables. La rigidité ainsi que l'amortissement du barrage et du sol seront analysés en tenant compte de l'amortissement du réservoir par propagation d'onde. Pour la sollicitation, l'hypothèse d'excitation simultanée des supports sera considérée car la base de données disponible pour des analyses qui tiennent compte de l'excitation variable est encore insuffisante. Finalement, l'influence de la rigidité du sol et du barrage ainsi que celle de l'amortissement du barrage et de la fondation sur l'altération de la réponse sismique des modèles, en fonction de la taille du maillage, seront démontrées.

Le générateur de vapeur a un rôle d'échangeur thermique et de sûreté nucléaire. L'énergie du fluide primaire est transférée au circuit secondaire via un faisceau de tubes en U soutenus par des plaques entretoise. Un dépôt modifie les conditions de liaison et l'écoulement du fluide secondaire. Le tube peut alors entrer en instabilité fluide-élastique, qui aboutit à une ruine rapide. Cette thèse vise à mieux comprendre l'effet de la non-linéarité de contact sur la dynamique d'un tube en air rentrant en contact intermittent avec les entretoises et ses conséquences en présence d'une instabilité. La discrétisation des conditions de contact entre le tube et les plaques, par des obstacles circulaires répartis sur l'épaisseur, ainsi que l'utilisation de bases de réductions enrichies permettent des résolutions numériques non-linéaires fiables et rapides, numériquement valides pour de fortes non-linéarités et des amortissements modaux négatifs, et bien corrélées avec les mesures correspondantes. On analyse les évolutions du contenu spectral (DSP) en fonction de l'amplitude d'excitation : remplissage des anti-résonances, décalage et étalement des pics ; puis on met en évidence la pertinence d'une notion de raideur apparente d'un contact bilatéral permanent qui permet de décrire ces transitions. En présence d'un système libre instable, on montre enfin que la non-linéarité conduit à des réponses bornées ou stabilisées ouvrant ainsi la voie vers une extension des travaux réalisés vers des applications avec fluide réel ou simulé.

Teleoperation of hydraulic manipulators is of potential when the presence of the operator, in a remote location, is inconvenient or dangerous. Augmenting such teleoperated systems using haptic sensation will further enhance performance, safety, and convenience. The advantage of using haptic force becomes more evident when it is employed to compensate for undesirable phenomena such as existence of a delayed and lossy communication channel or excitation of the manipulator base. The focus of this thesis is on haptic-enabled control of base-excited hydraulic manipulators that are controlled through a wireless communication channel. The targeted application is live transmission line maintenance. Both unilateral and bilateral controls of teleoperated hydraulic manipulators are studied. On the unilateral front, position error is shown to be an important issue, especially when the position accuracy of the slave manipulator is violated due to fast motion of the operator’s hand at the master site, lack of responsiveness in actuation system, or poor quality of communication channel. With respect to bilateral control, three main challenges are identified, and solutions to these challenges are investigated: (i) accurate control of the slave manipulator when the communication channel is delayed and/or lossy, (ii) control of the teleoperated system when the slave manipulator is mounted atop a moving platform, and (iii) transparent force feedback to improve the position tracking of the system. First, effects of network quality and slave manipulator base excitation are examined on performance of the teleoperated system. The position error between the haptic device implement and the hydraulic manipulator end-effector is shown to increase when the network is delayed and lossy. Next, excitation of the slave manipulator base deviates the end-effector from its reference trajectory, and the position error therefore becomes larger. To alleviate the position inaccuracy, a position referenced force feedback scheme is proposed. The scheme makes the input dynamics a better match with the slave dynamics. Combined with the virtual fixture force, the virtual fixture is shown to aid the operator in following a predefined virtual fixture trajectory. Due to complexity of dynamics, performance evaluations are mostly conducted using experimental validations on actual system in a laboratory setting.

NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

No description available.

Quantification of natural organic matter (NOM) in water is limited by the complex and varied nature of compounds found in natural waters. Current characterization techniques, which identify and quantify fractions of NOM, are often expensive and time consuming suggesting the need for rapid and accurate characterization methods. In this work, principal component analysis of fluorescence excitation-emission matrices (FEEM-PCA) was investigated as a NOM characterization technique. Through the use of jar tests and disinfection by-product formation tests, FEEM-PCA was shown to be a good surrogate for disinfection by-product precursors. FEEM-PCA was also applied in order to characterize differences in humic-like, protein-like, and Rayleigh scattering between multiple source waters and due to differing treatment processes. A decrease in Rayleigh scattering influence was observed for a deep lake intake, and multiple processes were found to significantly affect humic-like substances, protein-like, and Rayleigh scattering fractions.

Quantification of natural organic matter (NOM) in water is limited by the complex and varied nature of compounds found in natural waters. Current characterization techniques, which identify and quantify fractions of NOM, are often expensive and time consuming suggesting the need for rapid and accurate characterization methods. In this work, principal component analysis of fluorescence excitation-emission matrices (FEEM-PCA) was investigated as a NOM characterization technique. Through the use of jar tests and disinfection by-product formation tests, FEEM-PCA was shown to be a good surrogate for disinfection by-product precursors. FEEM-PCA was also applied in order to characterize differences in humic-like, protein-like, and Rayleigh scattering between multiple source waters and due to differing treatment processes. A decrease in Rayleigh scattering influence was observed for a deep lake intake, and multiple processes were found to significantly affect humic-like substances, protein-like, and Rayleigh scattering fractions.