Abstract Photoreceptors convert the energy of light into an electric signal to be processed by the visual system. Photoreceptors of nocturnal insects are adapted for night vision by sacrificing spatial and temporal resolution for improved sensitivity. While the sensitivity-increasing optical adaptations and the temporal properties of light responses have been studied earlier, the intermediate biophysical mechanisms responsible for shaping the captured light into voltage responses were previously not known in detail in any nocturnal species. Using electrophysiological tools and computer simulations the photoreceptors of the nocturnal cockroach (Periplaneta americana) were studied by characterising 1) the electrical properties responsible for shaping the light responses, 2) the properties of light responses at different stages of light and dark adaptation and 3) properties of low-intensity light stimuli and how they are processed by the photoreceptors. The high input resistance and whole-cell capacitance were typical for a nocturnal insect, but the two voltage-dependent potassium conductances were closer to those found in diurnal species. The dominant sustained conductance typically associated with day-light vision activated during simulated light responses whereas the lesser transient conductance previously linked to low-light vision did not. Light responses were persistently slow regardless of the adapting light level and saturated at low intensities, indicating a strong adaptation to vision in dim light. Simulations showed that at such low light levels the physical noise caused by random photons determines the information rate and the biological noise, caused by random latency and amplitude of single photon responses, has only a minor effect. At higher intensities the latency variability degraded the information rates but the amplitude variability did not. Thus, photoreceptors of nocturnal animals can sacrifice phototransduction precision in their natural illumination without compromising their coding performance.

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De nos jours, les batteries lithium-ion sont les plus utilisées pour alimenter les appareils électroniques et les véhicules électriques. Les accumulateurs électrochimiques basés sur le lithium ont une meilleure densité d'énergie et une plus grande fiabilité que toutes les autres méthodes d'accumulation d'énergie. Les batteries au lithium utilisées dans les applications de haute puissance et énergie sont généralement constitué d'un grand nombre de cellules, ce qui amène de nouveaux défis. Une méthodologie de dimensionnement facile et rapide a été identifiée comme un besoin à combler dans l'état de l'art. Ce travail vise à développer un tel outil permettant d'identifier rapidement les arrangements séries-parallèle respectant les objectifs de conception que sont le volume, le poids, l'énergie, le coût et la durée de vie, pour définir un espace de recherche. Ceci a pour but d'accélérer le processus de conception et assurant une meilleure prise de décision dès le début d'un projet. Une des nouveautés de ce travail est l'introduction de la représentation des performances système en cartes iso-performance, permettant une évaluation rapide et intuitive des tendances et de l'impact des compromis d'ingénierie. Le modèle sur lequel la méthodologie s'appuie assume le comportement statique en régime permanent pour estimer la puissance, le courant et la température d'opération et établir la durée de vie projetée d'un produit. En plus de la méthode de dimensionnement, un modèle transitoire électrothermique (MET) semi-empirique a été élaboré dans le formalisme de modélisation de la Représentation Énergétique Macroscopique (REM) sous MATLAB/Simulink\textregistered, contribuant à l'art de ce domaine. Celui-ci a été utilisé pour simuler le comportement du système d'accumulation d'énergie. Ce document vise à faire le pont entre tous les aspects principaux à considérer dans la conception d'une batterie, en présentant une nouvelle palette d'outils pouvant être utilisés par les ingénieurs de système. La flexibilité de l'application des outils à divers types de projets a été démontrée par l'application de la méthode à trois cas d'étude: une voiture urbaine électrique, un camion de livraison léger et un système stationnaire. / Abstract : Nowadays lithium-ion batteries have become the most popular technology to power portable electronic devices and battery powered electric vehicles. Lithium based electrochemical energy storage systems have far greater energy density and reliability than any other energy storage systems. Scaling up lithium-ion from small single cell batteries to large multi-cell systems comes with many new challenges. The need for a straightforward and easy-to-follow battery sizing methodology was identified as an area of improvement to the art. This work aims to provide such a tool to identify electrical arrangements that respect all design objectives, such as volume, mass, energy, cost and lifetime, to define a constraint bounded searchspace, speeding the process and ensuring a good decision right from the begining of a project. The novelty of this work is to present system level performances using iso-performance plots, allowing for quick and intuitive asssesment of design compromises and tendencies. The underlying model assumes steady-state operation of the system, to estimate temperature and lifetime prognosis. In addition to the battery sizing method, a transient semi-empirical electro-thermal battery model was constructed to run within MATLAB/Simulink® into the Energetic Macroscopic Representation (EMR) modeling formalism framework, bringing new art to the field. With it energy storage system performances were validated by simulation. This document aims to bridge the gap between most of the aspects of battery design, presenting a new set of tools to be used by system engineers. Three different design scenarios have been studied : an Urban electric car, a light duty delivery truck and a stationary system; to show how the tools can be used to any type of battery design project.

Focused ion beam (FIB) technique uses a focused beam of ions to scan the surface of aspecimen, analogous to the way scanning electron microscope (SEM) utilizes electrons. Recent developments in the FIB technology have led to beam spot size below 10 nm,which makes FIB suitable for nanofabrication. This project investigated thenanofabrication aspect of the FIB technique, with device applications perspective inseveral directions. Project work included construction of an in-situ FIB electricalmeasurement system and development of its applications, direct measurements ofnanometer scale FIB cuts and fabrication and testing of lateral field emission devices. Research work was performed using a number of materials including Al, Cr, SiO2, Si3N4and their heterostructures. Measurements performed included in-situ resistometricmeasurements, which provided milled depth information by monitoring the resistancechange of a metal track while ion milling it. The reproducibly of this method wasconfirmed by repeating experiments and accuracy was proven by atomic force microscopy(AFM). The system accurately monitored the thickness of 50 nm wide and 400 nm thick(high aspect ratio) Nb tracks while ion milling them. Direct measurements of low aspectratio nanometer scale FIB cuts were performed using AFM on single crystal Si,polycrystalline Nb and an amorphous material. These experiments demonstrated theimportance of materials aspects for example the presence of grains for cuts at this scale. Anew lateral field emission device (in the plane of the chip) was fabricated, as FIB offersseveral advantages for these devices such as control over sharpness and decrease in anodeto-cathode spacing. FIB fabrication achieved field emission tip sharpness below 50 nm andanode-to-cathode spacing below 100 nm. For determining the field emission characteristicsof the devices, a low current (picoampere) measurement system was constructed anddevices operated in ultra high vacuum (10-9 mbar) in picoampere range. One devicefabricated using a FIB sharpening process had a turn on voltage of 57 V.

Biodiesel purification processes generate wastewater streams that require a large amount of energy when distillation is used as a treatment technology. Process simulation software was used to show that an alternative water treatment process involving ion exchange would require only 31% of the energy used by distillation. Experiments showed that multiple washing stages were required to meet the standard specification for sodium, an impurity present in crude biodiesel, when washing biodiesel made from used frying oil. A comparison was made between washing biodiesel in a cross-current washing configuration and a counter-current configuration. Both configurations met the specification for sodium within three washing stages; however, the counter-current configuration required less water, making it the more efficient process. Lastly, the removal of sodium from wastewater samples using an ion exchange resin was experimentally investigated. The results validated the use of ion exchange to reduce energy consumption in biodiesel purification.

This thesis describes a simple method for the separation of strontium from an excess of barium using ion exchange techniques. This process has been applied to the separation of strontium and rubidium in barites. The resin used is Dowex-50 (200-400 mesh, hydrogen form) and the column dimensions are 1.1 by 8 cm. The column is eluted at room temperature with 1.5 M hydrochloric acid at a flow rate of approximately 1 ml/ min. Strontium and rubidium from two samples of barites were analysed using a solid-source mass spectrometer to determine strontium-87/strontium-86 ratios. The above chemical techniques have also been employed in the separation of strontium and rubidium from galenas. The concentration of strontium in one sample of galena (U.B.C. No. 1) has been determined using isotope dilution techniques. The results show an absence of strontium in the galena sample studied. Finally the common strontium ratios of two barite samples are compared with common lead ratios of associated galenas (Slawson and Austin, 1962) and a possible correlation between these ratios has been observed. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The major purpose of this study was to examine the physiological basis of the differences in the early life histories of pink Oncorhynchus gorbuscha, chum O. keta, coho O. kisutch, chinook O. tshawytscha and sockeye O. nerka. To this end, the following working hypotheses were tested: (i) the embryo, alevin and fry of pink and chum salmon are euryhaline, whereas the same life stages of coho, chinook and sockeye are stenohaline and (ii) the euryhalinity of pink and chum is due not to high tissue tolerance but to their ability to regulate the osmotic and ionic concentrations in their blood, whereas the stenohalinity of coho, chinook and sockeye stems from their inability to osmoregulate and ion regulate. The results did not completely support these hypotheses. The LD₅₀ values and the osmoregulatory data obtained from embryos indicated that pink and chum are not euryhaline as hypothesized but like coho, chinook and sockeye embryos are stenohaline. However, pink and chum embryos showed significantly greater salinity resistance and osmoregulatory ability than embryos of the other species. The data obtained from alevins also did not support the working hypothesis for alevins of all five species were found to be stenohaline. But, as in the case for embryos, pink and chum alevins showed greater salinity resistance and osmoregulatory abilities than coho and sockeye alevins. This ability of pink and chum was correlated with better ionic regulation of sodium and chloride. Although chinook alevins survived considerably longer in 31.8 °/oo sea water than coho and sockeye alevins , their ability to osmoregulate and ion regulatewas not very different from that of coho and sockeye alevins. It was concluded, therefore, that the greater salinity resistance of chinook alevins was due to high tissue tolerance. Contrary to the results with embryos and alevins, the data obtained from fry supported the working hypotheses. The results showed that pink and chum were euryhaline and that this condition was due to their ability to osmoregulate and control the levels of sodium and chloride in the blood. Coho, chinook and sockeye fry were found to be stenohaline and were unable to regulate the osmotic and ionic concentrations in their blood. As in the case of alevins, chinook fry, due to higher tissue tolerance, manifested greater salinity resistance than coho and sockeye. When the data for all species of embryos and fry were grouped and compared to the alevins taken as a group, the LD₅₀ values of embryos and fry were found to be significantly greater than those of the alevins . The blood osmotic concentrations of embryos and fry exposed for the same duration in 31.8 °/oo sea water were significantly lower than the blood osmotic concentrations for alevins. It was included, therefore, that embryos and fry have greater salinity resistance than alevins because of the greater osmoregulatory ability of embryos and fry. On the basis of these results as well as information obtained from the literature, speculations were made on the phylogenetic relations within the genus Oncorhynchus. / Science, Faculty of / Zoology, Department of / Graduate

Background: Pulmonary arterial hypertension (PAH) is a condition with severe morbidity and mortality. It is associated with an increase in incidence of all forms of arrhythmias which further increase morbidity and mortality. The monocrotaline (MCT) model of pulmonary hypertension (PH) in the rat is analogous to PAH in humans and was used to study how PH causes arrhythmias. Methods: A single injection of MCT or a volume matched saline injection (control) was given to the rats on day 0 of the protocol. The hearts of both groups of rats were studied in vivo with echocardiography (echo) and electrocardiogram (ECG). The rat’s condition was monitored and they were electively sacrificed when they showed symptoms or on day 28. Live cardiac tissue was studied using the Langendorff preparation and a right atrial preparation that incorporated the sinoatrial (SA) and atrioventricular (AV) nodes. Molecular biology techniques including reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry were used identify changes in the heart caused by PH. The effects of macitentan, an endothelin receptor antagonist used in the treatment of PAH, on the MCT injected rats was assessed using echo and ECGResults: Echo demonstrated that the MCT treated rats developed severe pulmonary hypertension with a decreased pulmonary artery acceleration time (P<0.005) and an increased pulmonary artery deceleration (P<0.005). The MCT treated rats also developed right ventricular hypertrophy (P<0.05) and dilation (P<0.005). The in vivo ECG demonstrated QT prolongation (P<0.005). Ex vivo functional experiments demonstrated QT prolongation (P<0.005) and prolonged ventricular effective refractory period (P<0.005). AV node dysfunction was also seen in the ex vivo experiments with an increased AV effective refractory period (P<0.05), AV functional refractory period (P<0.05) and incidence of complete heart block (P<0.05). RT-qPCR demonstrated significant changes in the mRNA expression of several ion channels and exchanges, Ca2+ handling proteins and autonomic receptors including a downregulation of HCN4 and CaV1.2 in the AV nodal tissues (P<0.05). Treatment of established pulmonary hypertension led to a reduction in the prolongation of the QT interval caused by MCT administration at day 21 (P<0.05).Conclusions: PH causes arrhythmogenic changes including prolonged repolarisation in the working myocardium and AV node dysfunction. These changes may be caused by dysregulation of ion channels and Ca2+ handling proteins. These ion channels and Ca2+handling proteins may play a key role in both physiological and pathological processes within the AV node.

Operational characteristics and performance of two mass spectrometers incorporating improved versions of the Very High Yield Electron Impact (VHY-EI) ion source are described. The ionizers are designed around a large volume, low pressure, hot cathode Penning geometry and operate at source pressures of 10⁻⁵ torr and below. In combination with low spherical aberration focusing optics, mass analyzed ion currents 100 to 1000 times more intense than those produced by conventional ionizers operated under identical or comparable conditions of resolution, analyzer type, sample pressure, and electron impact energy are obtained. In addition, high ionization-mass analysis efficiencies have been demonstrated for a variety of organic compounds with sample mass flow rates approaching 1 mg/min. Typical electron impact spectra are obtained with no evidence of pyrolysis or ion molecule reactions. Unusually intense spectra can be produced with low energy electrons.