Plants of Senecio vulgaris L. were grown individually within pots to examine effects of maternal soil nutrient level on offspring. Genotypic variability among maternal plants was minimized by using only maternal plants derived from seed of a single inbred line. Significant (P < 0.05) maternal effects of the nutrient gradient were detected at four different levels. Maternal plants grown in lower soil nutrients produced: 1) seeds with lower individual mass; 2) seeds that germinated later; 3) seedling offspring that grew into smaller juvenile plants in nutrient‐impoverished soil; and 4) seedling offspring that survived longer in the absence of external nutrients. This last type of maternal effect is reported for the first time in the present study. These data suggest that a compensatory effect of relatively low maternal soil nutrient level may be conferred on the plant's offspring in the form of a “wait and tolerate” strategy through a longer “seedling dormancy” period. This appears to involve a high seedling tolerance threshold level for external nutrient deprivation. To account for these results, we propose two hypotheses based on two different causes of nutrient deprivation, and based on the assumption that if maternal plants experience nutrient deprivation, seedling offspring have a high probability of also experiencing the same cause of nutrient deprivation: 1) Under the “nutrient supply hypothesis,” the wait and tolerate strategy in seedling offspring represents an adaptation to selection factors associated with nutrient deprivation resulting from a low nutrient‐supplying power of the environment. 2) Under the “nutrient‐depletion hypothesis,” this strategy represents an adaptation to selection factors associated with nutrient depletion by neighbors.

Evolutionary pressures have led humans to walk in a highly efficient manner that conserves energy, making it difficult for exoskeletons to reduce the metabolic cost of walking. Despite the challenge, some exoskeletons have managed to lessen the metabolic expenditure of walking, either by adding or storing and returning energy. We show that the use of an exoskeleton that strategically removes kinetic energy during the swing period of the gait cycle reduces the metabolic cost of walking by 2.5 ± 0.8% for healthy male users while converting the removed energy into 0.25 ± 0.02 watts of electrical power. By comparing two loading profiles, we demonstrate that the timing and magnitude of energy removal are vital for successful metabolic cost reduction.

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Many inverter topologies have been proposed to eliminate the leakage current of transformerless Full Bridge Grid-Tied photovoltaic (PV) inverters. These include implementations such as the H5, H6, and HERIC topologies, among others. In this paper, a new full bridge topology synthesis method, called the MN synthesis method, is proposed. The MN method introduces two criteria that can be used to synthesize all of the possible topologies, including the existing topologies as well as new simplified topologies. This method concludes that there are only 15 simplified topologies available. Most simplified topologies from MN method have been verified by existing papers and patents.

This thesis discusses a power electronics module (PEM) that is used to extract power from a human energy harvesting generator according to the user's desired input power, and stores all of the extracted energy into an appropriately sized battery while staying within the charging limitations of the battery. The PEM can temporarily store the peak power produced by the generator allowing the reduction in the size of the battery required to the average power production level of the generator.The battery's safety and longevity is maintained by charging them at the constant current and constant voltage rate.The design of the two-stage PEM, the requirements of the Energy Storage Capacitor (ESC) and battery size are discussed. The two controllers that control the PEM are explained and the different operating modes of the controllers are reviewed. A two-stage prototype digitally controlled average current mode control Boost converter and average current mode controlled Buck converter were designed and experimental waveforms were captured to test and validate the control theories used in the PEM. A Voltage Adaptive Gain compensator was used to optimize the closed loop response of both the Boost and Buck converters over their respective output and input voltage ranges. The DC efficiency of the prototype was measured with the peak efficiency of the Boost converter equal to 93% and the peak efficiency of the Buck converter measured at 93.7%. The total PEM system efficiency was measured at 87.9% at an input power level of 10 watts. The AC efficiency of the PEM was also measured with a peak efficiency of 91% with V in = 15 V at R in = 60 Ω.The software considerations for an embedded system, including power consumption and timing of real time events are reviewed. A software flow chart and timing diagram are provided to help iii visualize the sequence of the code. A design chart for selection of the size and voltage rating of the ESC was created. An experimental comparison of a single stage design without energy storage capability and the current PEM design was performed, with a power limited source, in order to show the effectiveness of the PEM and controllers at maximizing the power extraction from the generator. The PEM design was able to extract 50% more power than the single stage converter without energy storage capability.iv Acknowledgements First of all I would like to thank not only my supervisor, but also my mentor through this process, Dr. Yan-Fei Liu. He has provided me with structure and encouragement throughout the duration of my degree. Secondly, I would like to give a special thanks to my partner in designing, prototyping, and testing of the human energy harvester. Michael Sherpertycky has been an excellent support as well as a good friend. I was also surrounded by great lab mates, who have become friends throughout the process, and offered valuable insight.