This thesis presents the analysis of flow and heat transfer for the SPND (Self-Powered Neutron Detector) system used within the nuclear reactor core in the U.S. Evolutionary Power Reactor developed by AREVA. The SPND system is composed of six individual detectors which are used for in-core measurement of thermal neutron flux. The study of the SPND system is important since this system provides information and signals necessary for safe reactor operation and control. The main goal of the project was to determine the maximum temperature for the SPND detectors under three different operating scenarios. The maximum temperature of the detectors is of special interest, since if it exceeds a limiting temperature of 622 K then the accuracy of the information provided by the system is reduced. All of the flow and heat transfer simulations were performed using the commercial software Fluent. The first scenario that was studied was for the system under normal operating conditions. For this case, the maximum temperature for a detector was determined to be 603.4 K, which is within the proper range of operation. It was also important to determine the maximum temperature of the fluid within the SPND assembly in order to ascertain that boiling does not occur within the system during normal operation. The maximum fluid temperature was found to be 613.7 K, which is below the boiling temperature of water (618.05 K) at an operating pressure of 2250 psi. The second scenario involved an increase in the power of the reactor's core by a factor of 17% in a 30 second period. The results of the unsteady calculation indicated that the maximum temperature for a detector was 608.5 K. The results also indicate that no boiling occurs inside of the SPND system. The third scenario involved a loss of coolant flow in the SPND system. This reduction in flow rate caused the maximum temperature of the detectors to reach 619.6 K. For this case, boiling occurs within the guide tube and protection tube. / Master of Science

For over forty years, researchers have attempted to refine the Fourier heat equation to model heat transfer in engineering materials. The equation cannot accurately predict temperatures in some applications, such as during transients in microscale (< 10^-12 s) situations. However, even in situations where the time duration is relatively large, the Fourier heat equation might fail to predict observed non-Fourier behavior. Therefore, non-Fourier models must be created for certain engineering applications, in which accurate temperature modeling is necessary for design purposes. In this thesis, we use the Fourier heat equation to create a general non-Fourier, but diffusive, equation that governs the matrix temperature in a composite material. The composite is composed of a matrix with embedded particles. We let the composite materials be governed by Fourier's law and let the heat transfer between the matrix and particles be governed by contact conductance. After we make certain assumptions, we derive a general integro-differential equation governing the matrix temperature. We then non-dimensionalize the general equation and show that our model reduces to that used by other researchers under a special limit of a non-dimensional parameter. We formulate an initial-boundary-value problem in order to study the behavior of the general matrix temperature equation. We show that the thermalization time governs the transition of the general equation from its small-time limit to its large-time limit, which are both Fourier heat equations. We also conclude that our general model cannot accurately describe temperature changes in an experimental sand composite. / Master of Science

Turbine manufacturers continually seek to gain efficiency by increasing operating temperatures well above the maximum temperature of component alloys. This increase in temperature must be accounted for in the cooling of components by examining the heat transfer from these crucial components. This study specifically examines the effect of a contoured endwall on the heat transfer of a scaled-up stator vane. Understanding the three-dimensional effects of contoured endwalls on vane heat transfer can lead to prolonging blade life. The results of a combined experimental and computational study of heat transfer along the surface of a turbine vane that incorporates a contoured endwall are discussed in detail. A commercially available computational fluid dynamics code was used to design a contoured endwall and simulate an engine representative pressure distribution for a turbine vane cascade placed in a low-speed wind tunnel. A significant flow acceleration caused by the contour increased heat transfer over 40% of the vane span compared to the vane far from the contoured endwall. The effects of freestream turbulence with respect to the contour were examined. Results showed a significant increase in heat transfer at elevated freestream turbulence levels at each span location. The effects of the contour were minimal compared to the effects of increased turbulence. The boundary layer transition location moved further upstream with increasing turbulence. Trip wires were used to model the effect of film-cooling holes on the boundary layer development. The heat transfer increased locally at the trip and either remained elevated if the boundary layer remained turbulent or the heat transfer decreased as the boundary layer relaminarized due to flow acceleration. These results are beneficial to turbine manufacturers interested in effective placement of film-cooling holes. / Master of Science

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L'interférence à l'ARN est un phénomène impliqué dans plusieurs processus biologiques, notamment dans l'intégrité génomique et le développement, qui est conservé dans l'évolution. Ce phénomène est induit par la présence d'un long ARNdb qui mène à la production de siARN (short-interfering ARN) d'environ 22 nucléotides de long qui sont parfaitement complémentaires à un ARNm cible. Ces siARN servent de guide aux protéines Argonautes qui utilisent leur activité catalytique pour cliver l'ARNm et ainsi diminuer son expression. Chez plusieurs organismes, notamment Caenorhabditis elegans, l'exposition à de l'ARN double-brin exogène permet la production de siARN. Par la suite, le signal de dégradation de l'ARNm ciblé se transmet de générations en générations sans que ces dernières n'aient été exposées à la molécule initiatrice par un mécanisme peu compris. Différentes études antérieures ont tenté de déterminer quels sont les facteurs physiques qui sont transmis aux générations subséquentes, mais ces études utilisent des transgènes comme cibles, ces derniers ayant été démontrés comme étant réprimés par des mécanismes indépendants de l'interférence à l'ARN induit par de l'ARN double-brin exogène. Le but du projet est donc de développer une méthode qui permet d'étudier ce phénomène dans un contexte endogène et de l'utiliser afin de déterminer quels facteurs moléculaires peuvent être transmis à la descendance selon le type de gamète (mâle ou femelle) et le type de tissu (somatique ou germinal) touché. En utilisant la méthode développée qui utilise comme cible un ARNm endogène qui possède une délétion silencieuse, l'étude a permis de déterminer que l'ARNm cible a besoin d'être présent chez le géniteur pour induire le processus de transmission de l'interférence à l'ARN à la descendance. De plus, l'étude a permis de déterminer qu'une accumulation de siARN double-brin chez le parent peut mener à une transmission à la descendance du signal de dégradation de l'ARNm et que cette transmission ne peut s'effectuer que si le parent hermaphrodite est exposé à la molécule d'ARN double-brin. En bref, cette étude a permis d'améliorer la compréhension de ce mécanisme épigénétique qu'est la transmission entre générations de l'interférence à l'ARN. / RNA interference is a phenomenon implicated in many biological processes, including genomic integrity and development, and it is conserved in evolution. This phenomenon is induced by the presence of double stranded RNA leading to the production of siRNAs (short-interfering RNAs) of about 22 nucleotides long that are perfectly complementary to a target mRNA. Those siRNAs guide Argonaute proteins to the target mRNA and use their catalytic activity to cleave the target and decrease its expression. In many organisms, including Caenorhabditis elegans, production of siRNAs by exposing cells to exogenous dsRNA induce a transmission of RNAi signal between generation without exposing progeny to initiator molecules by a poorly understood mechanism. Different studies have already tried to determine which physical factors can be transmitted to the next generation, but these studies have used transgenes as a mRNA target, who have been shown to be also repressed by a mechanism independent of RNA interference induced by a double-stranded RNA. Therefore the main purpose of the project is to develop a method who can be used to study this phenomenon in an endogenous context and to determine which molecular factors can be transmitted between generations depending on the gamete type (male or female) and the tissue type (somatic or germline tissue) targeted. Using the developed method which uses a mRNA that carries a silenced deletion mutation, the study has determined that the target mRNA must be present in the parent to induce transmission of RNA interference through generations. Also, the data has shown that a double-stranded RNA accumulation can lead to a transmission to the progeny of the mRNA degradation signal, but this transmission can only occur if the hermaphrodite parent is exposed to the double-stranded RNA. In short, this study helped to increase the understanding of this epigenetic mechanism that is the transmission between generations of RNA interference.

Les synapses formées par les fibres moussues (FM) sur les cellules principales de la région CA3 (FM-CA3) jouent un rôle crucial pour la formation de la mémoire spatiale dans l’hippocampe. Une caractéristique des FM est la grande quantité de zinc localisée avec le glutamate dans les vésicules synaptiques recyclées par la voie d’endocytose dépendante de l’AP3. En combinant l’imagerie calcique et l’électrophysiologie, nous avons étudié le rôle des vésicules contenant le zinc dans la neurotransmission aux synapses FM-CA3. Contrairement aux études précédentes, nous n’avons pas observé de rôle pour le zinc dans l’induction des vagues calciques. Nos expériences ont révélé que les vagues calciques sont dépendantes de l’activation des récepteurs métabotropiques et ionotropiques du glutamate. D’autre part, nos données indiquent que les vésicules dérivées de la voie dépendante de l’AP3 forment un groupe de vésicules possédant des propriétés spécifiques. Elles contribuent principalement au relâchement asynchrone du glutamate. Ainsi, les cellules principales du CA3 de souris n’exprimant pas la protéine AP3 avaient une probabilité inférieure de décharge et une réduction de la synchronie des potentiels d’action lors de la stimulation à fréquences physiologiques. Cette diminution de la synchronie n’était pas associée avec un changement des paramètres quantiques ou de la taille des groupes de vésicules. Ces résultats supportent l’hypothèse que deux groupes de vésicules sont présents dans le même bouton synaptique. Le premier groupe est composé de vésicules recyclées par la voie d’endocytose utilisant la clathrine et participe au relâchement synchrone du glutamate. Le second groupe est constitué de vésicules ayant été recyclées par la voie d’endocytose dépendante de l’AP3 et contribue au relâchement asynchrone du glutamate. Ces deux groupes de vésicules sont nécessaires pour l’encodage de l’information et pourraient être importants pour la formation de la mémoire. Ainsi, les décharges de courte durée à haute fréquence observées lorsque les animaux pénètrent dans les places fields pourraient causer le relâchement asynchrone de glutamate. Finalement, les résultats de mon projet de doctorat valident l’existence et l’importance de deux groupes de vésicules dans les MF qui sont recyclées par des voies d’endocytoses distinctes et relâchées durant différents types d’activités. / Mossy fiber-CA3 pyramidal cell synapses play a crucial role in the hippocampal formation of spatial memories. These synaptic connections possess a number of unique features substantial for its role in the information processing and coding. One of these features is presence of zinc co-localized with glutamate within a subpopulation of synaptic vesicles recycling through AP3-dependent bulk endocytosis. Using Ca2+ imaging and electrophysiological recordings we investigated role of these zinc containing vesicles in the neurotransmission. In contrast to previous reports, we did not observe any significant role of vesicular zinc in the induction of large postsynaptic Ca2+ waves triggered by burst stimulation. Moreover, our experiments revealed that Ca2+ waves mediated by Ca2+ release from internal stores are dependent not only on the activation of metabotropic, but also ionotropic glutamate receptors. Nevertheless, subsequent experiments unveiled that the vesicles derived via AP3-dependent endocytosis primary contribute to the asynchronous, but not synchronous mode of glutamate release. Futhermore, knockout mice lacking adaptor protein AP3 had a reduced synchronization of postsynaptic action potentials and impaired information transfer; this was not associated with any changes in the synchronous release quantal parameters and vesicle pool size. These findings strongly support the idea that within a single presynaptic bouton two heterogeneous pools of releasable vesicles are present. One pool of readily releasable vesicles forms via clathrin mediated endocytosis and mainly participates in the synchronous release; a second pool forms through bulk endocytosis and primarily supplies asynchronous release. The existence of two specialized pools is essential for the information coding and transfer within hippocampus. It also might be important for hippocampal memory formation. In contrast to low firing rates at rest, dentate gyrus granule cells tend to fire high frequency bursts once an animal enters a place field. These burst activities, embedded in the lower gamma frequency, should be especially efficient in the triggering of substantial asynchronous glutamate release. Therefore, the results of my PhD project for the first time provide strong evidence for the presence and physiological importance of two vesicle pools with heterogeneous release and recycling properties via separate endocytic pathways within the same mossy fiber bouton.

A computer program and an associated instruction manual were developed to fill a need for a useful learning tool for the study of transmission network power-flow programming techniques. Past programs were found to use techniques that did not give the student "hands-on" programming lessons, but instead gave them practice at using "pull-down menu" type of programming experience. The PFLOW program written is intended to be used "hands-on" with a complete instruction manual included to help the student use the program successfully and study the complete analysis technique. This includes network modelling, structure of input data, understanding program software, and correct meaning of outputs based on the complete knowledge of program solution methods. Sample input and outputs are also included to help get the student started, and to demonstrate the use of the PFLOW program. This program should prove beneficial to those with a general background in power transmission systems analysis.