Within two minutes of global ischemia or focal stroke, a sudden loss of neuronal and glial membrane potential induces anoxic depolarization (AD) that propagates across gray matter of the cerebral hemispheres at 2-5 mm/min. It induces terminal neuronal damage, forming the initial ischemic core. In healthy gray matter, a milder version termed spreading depression (SD) does not cause tissue damage and generates the migraine aura, often a marching sensory deficit preceding the pain. AD and SD have been well studied in the cerebral and cerebellar cortices, but not the in the brainstem. We induced AD in coronal brain slices of mouse using oxygen/glucose deprived (OGD) saline. SD was induced by briefly elevating the extracellular K+ concentration. AD or SD propagation was imaged as a moving front of elevated light transmittance (LT) in cerebral and cerebellar cortices. Most ventral brainstem areas did not support AD or SD but in the dorsal brainstem some LT mini-fronts were observed in the superficial superior colliculus (SC), edges of inferior colliculus (IC), periaqueductal gray (PAG), tegmental nucleus (TN) and solitary nucleus (SolN). Their AD/SD characteristics were compared to those in the ‘higher’ brain regions. Although time of onset was not different, the present AD and SD propagated more slowly in brainstem gray matter. A non-specific glutamate receptor antagonist kynurenic acid (KYNA) successfully blocked the SD but not AD in PAG, TN and SolN. Two-photon laser scanning microscopy (2-PLSM) of live YFP+ mice brain slices showed that pyramidal neurons in ‘higher’ hippocamal CA1 irreversibly swelled and formed dendritic beads while neurons in the ‘lower’ mesencephalic trigeminal nucleus (Mes) of the midbrain-pons did not significantly swell or display any sign of injury. Finally, dendritic beading was induced in intact mouse neocortex and hippocampus by cardiac perfusion with OGD saline or ice-cold saline. However, dendrites in the brainstem from the same mice showed no obvious beading. Taken together, our study supports the concept that most brainstem regions are comparatively resistant to AD/SD compared to the ‘higher’ regions of cerebral and cerebellar cortices. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2012-10-01 13:42:14.325

No description available.

No description available.

Three seismic refraction profiles obtained between 42°N and 43°N along the median valley of the Gorda Ridge, an active spreading center, allow the computation of the velocity structure underlying the valley. Wide angle reflections which appear on the seismic records suggest the existence of a velocity inversion underlying layer 3 and were analyzed in combination with refraction arrivals. The resulting velocity model has a low velocity zone with a directly-determined velocity of 5.72 km/sec, between crust of velocity 6.48 km/sec and Moho of velocity 7.54 km/sec. The velocity inversion is 0.7 km thick and lies 3 km below acoustic basement. Consideration of the velocity structure of the Gorda Ridge, together with other information on processes involved in oceanic crustal formation, suggests a model which is consistent with current knowledge on oceanic spreading centers. In the proposed model, the rise of asthenospheric material on the ascending limb of a convection cell causes the generation of a small percentage of partial melt. The molten fraction tends to coalesce near the top of the ascending limb, forming a region of significant partial melt under the ridge crest. This molten material is the immediate source reservoir for mid-ocean ridge magmas. The geophysical expression of the reservoir is a region of low seismic velocity and low density. As the magma cools from the upper surface, heavy minerals tend to work their way downward, forming a layer of cumulate ultramafic rocks at the base of the crust, while the lighter constituents work upward to form the cumulate gabbros of oceanic layer 3. The injection and extrusion of magmatic material upward leads to the formation of layer 2. The crust under the median valley is in isostatic equilibrium with the partial melt during formation, but as it is displaced laterally from the magmatic center, the entire lithosphere becomes competent and the isostatic depth of compensation moves downward into the mantle. This is thought to cause the familiar ridge crest topography of a median valley and adjacent axial mountains observed at slowly spreading ridges. The features of this general model in the specific case of the northern Gorda Ridge between 42°N and 43°N have been tested by the comparison of theoretical and observed gravity and magnetic anomalies. The computation of the theoretical gravity anomaly for this model gives values which match the observed anomaly. The magnetic data show only the pattern of anomalies expected from sea floor spreading and magnetic field reversals. / Graduation date: 1978

Abstract For reducing the interference of multi-path and multi-user access, we propose to design a spreading code with ideal auto-correlation and cross-correlation. In this paper, we will introduce a code with ideal auto-correlation and cross-correlation. Recently, there has been great interest in applying zero correlation spreading codes to reduce interference of different users or their multi-path. The set of sequences having zero auto-correlation and cross-correlation plays an important part in typical DS-CDMA systems. A periodic sequence with zero out-of-phase auto-correlation is called a perfect or an orthogonal sequence, it can mitigate the multi-path interference. Similarly, a set of periodic sequences with zero cross-correlation values is called a set of uncorrelated sequences. However, it is impossible to be found in single sequence spreading code. In this paper, we propose a new code for ideal auto-correlation and cross-correlation, and the code set size is equal to the number of flock size.

No description available.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on June 16, 2008). Includes bibliographical references.

Thesis (Doctoral)--University of Tokyo, 1973. / One folded plate in pocket. Includes bibliographical references (leaves 76-81).

Thesis--University of Connecticut. / Includes abstract (2 leaves). Includes bibliographical references (p. 86-94).

La compréhension des écoulements de fumées issus d’un foyer d’incendie au sein d’une station souterraine de métropolitain, en présence d’accès passagers et d’une ventilation mécanique forcée,constitue l’objectif principal de ce présent mémoire. Deux maquettes basées sur le nombre de Froude (Fr) et sur le rapport de quantité de mouvement (r) sont mises en place. La première, préexistante,représente une station complète à échelle 1/30e et l’incendie y est simulé par un brûleur air-butane. Cependant, l’analyse y est limitée à une approche globale et le manque d’information sur le développement des écoulements internes est préjudiciable. Une seconde maquette adonc été développée, version simplifiée de la précédente, permettant d’étudier finement (vitesse,température) la confrontation entre un jet chaud vertical et un écoulement froid traversier. Cette approche expérimentale est complétée par des simulations numériques LES permettant d’accéder aux champs 3D. Les études réalisées ont mis en évidence 4 paramètres influents couplés : la différence de hauteur station-tunnel (H/H0), le débit de ventilation, le nombre et la position des accès et le réseau hydraulique du tunnel amont. Quelle que soit la configuration, un débit d’extraction« critique » peut-être mis en place pour contrer la contamination thermique des accès, définissant ainsi un facteur r « critique ». De plus, les écoulements dans les accès et dans la station sont dépendants de leur nombre et de leur position : suivant les configurations, deux ou trois régimes sont obtenus. Enfin, la représentativité du réseau présente une forte influence sur les écoulements internes. / Smoke spreading in an underground subway station is analyzed and studied by taking into account parameters such as passenger accesses and forced ventilation systems. Two sub-scale models are considered to arise such analysis ; based on the Froude number (Fr) or momentum ratio(r). The first experiment based on Froude number conservation is conducted on a 1/30e scale modelof a realistic subway station with fire provided from an air-butane burner. Due to restricted access to local temperature and velocity measurements, a second model was entirely developed during the course of this work ; the main issue is to study momentum ratio and thermal spreading. Numerical studies were in parallel carried out from an house-code LES turbulent model.Four main parameters were thus identified : tunnel/station height ratio (H/H0), ventilation massflowrate, number and position of accesses and hydraulic network in which the subway station islocated. « Critical » flowrate can be imposed in order to avoid thermal speading within the passenger accesses and consequently a critical factor was defined. The air/smoke flow is strongly linked to the number and position of accesses and also of the geometrical configuration. Two or three regimes can be identified. Finally internal flows in the accesses and in the station are also strongly influenced by the pressure drop of the hydraulic network.