Basierend auf dem Reaktordynamikcode DYN3D für LWR, wurde die Codeversion DYN3D-HTR für das Blockkonzept eines graphit-moderierten, helium-gekühlten Hochtemperaturreaktors entwickelt. Diese Entwicklung umfasst die: • methodische Weiterentwicklung der 3D stationären Neutronenflussberechnung für hexagonale Geometrie (HTR-Brennelement-Blöcke), • Generierung von Wirkungsquerschnittsdaten unter Berücksichtigung der doppelten Heterogenität, • Modellierung der Wärmeleitung und des Wärmetransports in der Graphitmatrix. Die nodale SP3-Neutronentransport-Methode in DYN3D wurde auf hexagonale Brennelementgeometrie erweitert. Es wird eine Unterteilung der Hexagone in Dreiecke vorgenommen, so dass die Verfeinerung hexagonaler Strukturen untersucht werden kann. Die Verifikation erfolgte durch Vergleiche mit Monte-Carlo-Referenzlösungen. Für die Behandlung der doppelten Heterogenität der Brennelementstruktur bei Homogenisierung der Wirkungsquerschnitte wurden neue Methoden entwickelt. Zum einen wurde ein zweistufiges Homogenisierungsverfahren basierend auf der Methode der sog. Reactivity Equivalent Transformation (RPT) weiterentwickelt. Zum anderen ermöglichte die Verfügbarkeit des neuen Monte-Carlo-Codes SERPENT die Anwendung eines einstufigen Verfahrens, wobei die 3D heterogenen Strukturen in einem Rechenschritt konsistent erfasst werden können. Weiterhin wur-de in DYN3D ein 3D Wärmeleitungsmodell implementiert, das den radialen und axialen Wärmetransport in der Graphitmatrix beschreiben kann. DYN3D-HTR wurde schließlich anhand der Testfälle für Reaktivitätstransienten erprobt. Die Verifikation erfolgte durch Vergleich zwischen 3D und 1D Berechnung der Wärmeleitung. Schließlich wurde DYN3D mit dem CFD-Code ANSYS-CFX gekoppelt, um auch dreidimensionale Strömungen in Reaktorkernen berechnen zu können. Der Kern wird als poröser Körper modelliert. Die Kopplung wurde an anhand von 2 Testbeispielen, dem Auswurf eines Steuerstabes und einer lokalen Strömungsblockade in einem Brennelement, erprobt.

Engineers often view variability as undesirable and seek to minimize it, such as when they employ transistor-matching techniques to improve circuit and system performance. Biology, however, makes no discernible attempt to avoid this variability, which is particularly evident in biological nervous systems whose neurons exhibit marked variability in their cellular properties. In previous studies, this heterogeneity has been shown to have mixed consequences on network rhythmicity, which is essential to locomotion and other oscillatory neural behaviors. The systems that produce and control these stereotyped movements have been optimized to be energy efficient and dependable, and one particularly well-studied rhythmic network is the central pattern generator (CPG), which is capable of generating a coordinated, rhythmic pattern of motor activity in the absence of phasic sensory input. Because they are ubiquitous in biological preparations and reveal a variety of physiological behaviors, these networks provide a platform for studying a critical set of biological control paradigms and inspire research into engineered systems that exploit these underlying principles. We are directing our efforts toward the implementation of applicable technologies and modeling to better understand the combination of these two concepts---the role of heterogeneity in rhythmic networks of neurons. The central engineering theme of our work is to use digital and analog platforms to design and build Hodgkin--Huxley conductance-based neuron models that will be used to implement a half-center oscillator (HCO) model of a CPG. The primary scientific question that we will address is to what extent this heterogeneity affects the rhythmicity of a network of neurons. To do so, we will first analyze the locations, continuities, and sizes of bursting regions using single-neuron models and will then use an FPGA model neuron to study parametric and topological heterogeneity in a fully-connected 36-neuron HCO. We found that heterogeneity can lead to more robust rhythmic networks of neurons, but the type and quantity of heterogeneity and the population-level metric that is used to analyze bursting are critical in determining when this occurs.

The complex interaction between cement and chemical/mineral admixtures in concrete mixtures sometimes leads to unpredictable concrete performance in the field which is generally defined as concrete incompatibilities. Cement paste rheology measurements instead of traditional workability tests (i.e., slump cone test) can have great potential in detecting those incompatibilities in concrete before the concrete is placed, which can, in turn, avoid related workability problems and setting time as well as heat evolution abnormalities. The objectives of the present study were to examine the applicability of the dynamic shear rheometer (DSR) to measure cement paste rheology, and to identify cement and mineral/chemical admixture incompatibilities, based on the determined rheological parameters. The DSR was modified and optimized for cement paste rheology measurements. Two different modes of operations (i.e., static and dynamic methods) with the modified DSR were investigated to measure representative rheological parameters as well as to identify cement and chemical/mineral admixture incompatibility. The conventional plastic viscosity and yield stress are measured in static mode and storage modulus curve, as a function of time, is measured in dynamic mode. The rate of change of plastic viscosity (RPV) as another static rheological parameter and the modeled magnitude parameter ?, from the dynamic rheological method, showed great potentialities as acceptance criteria to identify incompatible mixtures. The heat of hydration data from isothermal conduction calorimeter tests and setting time results for the studied mixtures have strongly supported the rheology based observations as supporting tools. Based on the main tests results, the acceptance criteria were set up using the rheological parameters in accordance with heat of hydration data. This will ultimately help material suppliers, concrete producers, and other users to detect problematic combinations of concrete ingredients before a given concrete mixture is placed.

The structure and the energy band gap of hydrogenated amorphous silicon carbide are theoretically revised. In the light of defect pool model, density of states distribution is investigated for various regions of mobility gap. The films are deposited by plasma enhanced chemical vapor deposition system with various gas concentrations at two different, lower (30 mW/cm2) and higher (90 mW/cm2), radio frequency power densities. The elemental composition of hydrogenated amorphous silicon carbide films and relative composition of existing bond types are analyzed by x-ray photoelectron spectroscopy measurements. The thicknesses, deposition rates, refractive indices and optical band gaps of the films are determined by ultraviolet visible transmittance measurements. Uniformity of the deposited films is analyzed along the radial direction of the bottom electrode of the plasma enhanced chemical vapor deposition reactor. The molecular vibration characteristics of the films are reviewed and analyzed by Fourier transform infrared spectroscopy measurements. Electrical characteristics of the films are analyzed by dc conductivity measurements. Conduction mechanisms, such as extended state, nearest neighbor and variable range hopping in tail states are revised. The hopping conductivities are analyzed by considering the density of states distribution in various regions of mobility gap. The experimentally measured activation energies for the films of high carbon content are too low to be interpreted as the difference between Fermi level and relevant band edge. This anomaly has been successfully removed by introducing hopping conduction across localized tail states of the relevant band. In other words, the second contribution lowers the mobility edge towards the Fermi level.

Selective stimulation and conduction block of specific nerve fibers has been a major area of research in neuroscience. The potential clinical and neurophysiological applications have warranted reliable techniques for transiently blocking conduction through nerves. High Frequency Alternating Current (HFAC) waveforms have been found to induce a reversible and repeatable block in peripheral nerves; however the effect of these waveforms on the neural activity of individual fiber types is currently unknown. Understanding this effect is critical if clinical applications are to be pursued. This dissertation work utilized extracellular electrophysiological techniques to characterize the activity of different fiber type populations in peripheral nerves during application of HFAC waveforms. First, we investigated the phenomenon in the homogeneous unmyelinated nerves of the sea-slug, Aplysia californica. Although complete reversible block was demonstrated in these nerves, a non-monotonic relationship of block threshold to frequency was found which differed from previously published work in the field. We then investigated the effect of HFAC waveforms on amphibian mixed nerves and studied the response of specific fiber types by isolating different components of the compound action potential. We validated our results from the Aplysia nerves by determining the block thresholds of the larger diameter, myelinated A-fibers and comparing them with those of the smaller diameter, unmyelinated C-fibers. We also showed that block threshold behavior during application of the HFAC waveform depends on the nerve fiber type, and this property can be used to selectively block specific fiber types. Finally, we examined the recovery time after block induction in unmyelinated nerves and found that recovery from block was dependent on the duration of application of the HFAC waveform. The time-dependent distribution of the recovery time and the non-monotonic threshold behavior in the smaller diameter unmyelinated nerves indicate that multiple mechanisms are involved in block induction using HFAC waveforms, and these mechanisms are dependent not only on the blocking stimulus but also on the characteristics of the nerve fiber. Overall, this work demonstrates that HFAC waveforms may enable inherent peripheral nerve properties to be exploited for potential clinical applications related to the treatment of unwanted neural activity.

Dans le contexte d'un contrat de la Délégation Générale pour l'Armement (DGA) avec la société Nexans, le CRTBT-CNRS a développé une bobine supraconductrice de stockage d'énergie, ou SMES Superconducting Magnetic Energy Storage), avec des rubans PIT Bi-2212 pour un fonctionnement à 20 K. L'utilisation d'un bobinage supraconducteur permet de stocker l'énergie électrique sous forme magnétique sans conversion d'énergie, ceci pendant des temps très longs. Le bobinage stocke 800!kJ à décharger en 1 s pour atteindre une puissance de 500 kW sur la charge, ce qui génère une tension maximale de 5 kV. La cryogénie est réalisée avec des pièces en cuivre qui relient les cryoréfrigérateurs et le bobinage, avec différence de température de 2 K au maximum. L'interface HT (Haute Tension) entre les drains et le bobinage a une tenue diélectrique de 5 kV et permet de refroidir efficacement les amenées de courant et les 26 galettes, soit 40 km de ruban. L'énergie dissipée dans le cuivre et le bobinage pendant la décharge représente 1 l'énergie stockée. Des mesures thermiques à 20 K ont été réalisées sur des échantillons pour mesurer l'interface!HT par exemple, puis sur un bobinage de dimensions réduites pour valider les solutions retenues. Le procédé de coétamage des rubans supraconducteurs développés par Nexans permet d'adapter la géométrie du conducteur à sa situation dans le bobinage. Les essais des dix premières galettes bobinées a validé la cryogénie développée. L'étude d'extrapolation pour un SMES de 20 MJ présente une géométrie torique adaptée à un refroidissement par thermosiphon avec un câble bi-étagé Rutherford / 6+1 en fils ronds de Bi-2212.

Certains dispositifs électrotechniques présentent une couche de faible conductivité et de faible épaisseur qui modifie considérablement les répartitions des potentiels et des champs électriques. Cette situation se rencontre, par exemple, dans l'étude des isolateurs pollués ou des traversées comportant un revêtement semi-conducteur. La zone conductrice a une épaisseur très faible devant les autres dimensions du système et il est difficile d'en tenir compte, telle quelle, dans une méthode numérique. Ce travail est consacré à la modélisation (2D et 3D axisymétrique) d'une couche conductrice présente à l'interface de deux diélectriques. Celle-ci est simulée par une surface munie d'une conductivité surfacique qui peut dépendre ou non du champ électrique. Les équations qui caractérisent le modèle ont été implantées dans un logiciel de calcul de champ basé sur la méthode des équations intégrales de frontière. Le premier chapitre décrit les divers phénomènes physiques liés à la présence d'une couche conductrice entre deux isolants. Le second chapitre rappelle d'abord les résultats très classiques sur les équations de Maxwell. Ensuite, il établit une équation de conservation de l'électricité au niveau de la zone conductrice. Le troisième chapitre passe en revue les différentes méthodes numériques généralement utilisées en électrotechnique. Le quatrième chapitre est consacré à la résolution numérique. Le cinquième chapitre présente les résultats et la validation du nouveau module logiciel. Les résultats obtenus, dans le cas d'une configuration simplifiée, sont en accord avec la solution analytique (problème linéaire) et la solution numérique (problème non linéaire).

Reproduction de : Thèse de doctorat : Structure et dynamique des systèmes réactifs : Lille 1 : 2005. / N° d'ordre (Lille 1) : 3660. Résumé en français et en anglais. Titre provenant de la page de titre du document numérisé. Bibliogr. à la suite de chaque chapitre.

Disertacijos objektas yra žmogaus širdies laidžiosios sistemos ir kitų širdies audinių morfologinių skirtumų tyrimas spektroskopiniais, histocheminiais ir proteominiais metodais. Disertacijoje pateikti žmogaus širdies laidžiosios sistemos ir kitų širdies audinių palyginamieji spektroskopiniai ir proteominiai tyrimai parodė aiškius struktūrinius šių audinių skirtumus. Baltymų elektroforezės metodu rasta baltymų grupė aptinkama tik širdies laidžiosios sistemos audinyje. Darbe konstatuojama, kad rasti fluorescenciniai ir baltyminės sudėties skirtumai tarp žmogaus širdies laidžiosios sistemos ir miokardo audinių leidžia manyti, kad bioelektrinio impulso sklidimo greičių skirtumus sąlygoja ne tik ląstelių išsidėstymas, skersmuo, bet ir specifiniai morfologiniai skirtumai. Pasinaudojus nustatytais morfologiniais skirtumais galima sukurti žmogaus širdies laidžiosios sistemos vaizdinimo metodiką, kuri leistų nustatyti širdies laidžiosios sistemos anatomines ypatybes. / The theme covered in the dissertation is about investigation of the morphological differences of the conduction system of the human heart and those of other heart tissues, applying spectroscopic, histochemical and proteomic methods. The described spectroscopical and proteomic investigations of the human heart conduction system and other heart tissues in the dissertation indicate clear structural differences between these tissues. Electrophoresis shows protein groups which may be detected only in a conduction system tissue. The dissertation concludes that estimated fluorescence and proteomic differences between His bundle and myocardium tissues may allow us to suggest that distinction of the bioelectrical impulse velocity in these tissues is determined by the specific morphological odds. According to these differences it is possible to create the visualization method of the conduction system.

The theme covered in the dissertation is about investigation of the morphological differences of the conduction system of the human heart and those of other heart tissues, applying spectroscopic, histochemical and proteomic methods. The described spectroscopical and proteomic investigations of the human heart conduction system and other heart tissues in the dissertation indicate clear structural differences between these tissues. Electrophoresis shows protein groups which may be detected only in a conduction system tissue. The dissertation concludes that estimated fluorescence and proteomic differences between His bundle and myocardium tissues may allow us to suggest that distinction of the bioelectrical impulse velocity in these tissues is determined by the specific morphological odds. According to these differences it is possible to create the visualization method of the conduction system. / Disertacijos objektas yra žmogaus širdies laidžiosios sistemos ir kitų širdies audinių morfologinių skirtumų tyrimas spektroskopiniais, histocheminiais ir proteominiais metodais. Disertacijoje pateikti žmogaus širdies laidžiosios sistemos ir kitų širdies audinių palyginamieji spektroskopiniai ir proteominiai tyrimai parodė aiškius struktūrinius šių audinių skirtumus. Baltymų elektroforezės metodu rasta baltymų grupė aptinkama tik širdies laidžiosios sistemos audinyje. Darbe konstatuojama, kad rasti fluorescenciniai ir baltyminės sudėties skirtumai tarp žmogaus širdies laidžiosios sistemos ir miokardo audinių leidžia manyti, kad bioelektrinio impulso sklidimo greičių skirtumus sąlygoja ne tik ląstelių išsidėstymas, skersmuo, bet ir specifiniai morfologiniai skirtumai. Pasinaudojus nustatytais morfologiniais skirtumais galima sukurti žmogaus širdies laidžiosios sistemos vaizdinimo metodiką, kuri leistų nustatyti širdies laidžiosios sistemos anatomines ypatybes.