Thin-film solar cells based on an absorber layer of chalcogenide compounds (CIGS, CdTe) are today among the most promising photovoltaic technologies due to their long-term ability to gain a foothold in mass commercial production as an alternative to conventional Si solar cells. Despite this success, the physical origin of the defects present in the thin films are still insufficiently elucidated, especially in the compounds of the chalcopyrite family Cu(In_{1x},Ga_{x})(S_{y},Se_{1y})_{2}. The research focuses on the identification and analysis of microstructural defects responsible for the electrical instability of chalcopyrite-based thin-film solar cells with a typical heterostructure arrangement ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se_{2}/Mo. The non-uniform polycrystalline nature of semiconductor materials in this complex multilayer structure requires a comprehensive analysis of electro-optical, structural and compositional properties associated with the actual morphology at the macroscopic, microscopic or even nanoscopic level. The observed predominant ohmic or non-ohmic current conduction in the dark transport characteristics was also reflected in the slope deviations of the excessive noise fluctuations, which were in the spectral domain exclusively in the form of flicker noise with dependency S_{i} ~ f^{1}. Spatially resolved electroluminescence based on stimulated photon emission by charge carriers injecting into the depletion region, not only showed a significantly inhomogeneous distribution of intensity in planar heterojunction under forward bias, but also revealed light emitting local spots in reverse bias due to a trap-assisted radiative recombination through the high density of defect states. Microscopic examination of the defect-related light emitting spots revealed rather extensive defective complexes with many interruptions through the layers, especially at the heterojunction CdS/Cu(In,Ga)Se_{2} interface. Besides, the high leakage current via these defective complexes subsequently led to a considerable local overheating, which caused a clearly observable structural and morphological changes, such as deviations in absorber layer stoichiometry due to Cu–In–Ga–Se segregation, Cu-rich and Ga-rich grains formation with an occurrence of Se-poor or Cu_{x}Se_{y} secondary phases regions, material redeposition accompanied by evaporation of ZnO:Al/i-ZnO/CdS layers together with the formation of Se structures on the surface around the defects. Within the research, analytical modelling of transport characteristics was implemented with parameters extraction of individual transport mechanisms to understand the non-ohmic shunt behaviour due to leakage current. In addition to the proper current path along the main heterojunction, the proposed model contains parasitic current pathways as a consequence of recombination-dominated charge transport or current conduction facilitated by multi-step tunnelling via high density of mid-gap defect states in the depletion region, ohmic leakage current caused by pinholes or low-resistance paths along grain boundaries in Cu(In,Ga)Se_{2}, or space-charge limited current due to metals diffusion from the ZnO:Al layer and grid Ag contacts through disruptions in i-ZnO/CdS layers.

Modern power systems require multiple conversions between DC and AC to deliver power from renewable energy sources. Recent growth in DC loads result in increased system costs and reduced efficiency, due to redundant conversions. Advances in DC microgrid systems demonstrate superior performance by reducing conversion stages. The literature reveals practical DC microgrid systems composed of wind and solar power to replace existing fossil fuel technologies for residential consumers. Although higher efficiencies are achieved, some household appliances require AC power; thus, the need for highly efficient DC to AC converters is imperative in establishing DC microgrid systems. Resonant inverter topologies exhibit zero current switching (ZCS); hence, eliminate switching losses leading to higher efficiencies in comparison to hard switched topologies. Resonant inverters suffer severe limitations mainly attributed to a load dependent resonant frequency. Recent advancements in power electronics propose an electronically tunable inductor suited for low frequency applications [24], [25]; as a consequence, frequency stability in resonant inverters is achievable within a limited load range. This thesis characterizes the operational characteristics of a low-frequency series loaded resonant inverter using a manually tunable inductor to achieve frequency stability and determine feasibility of utilization. Simulation and hardware results demonstrate elimination of switching losses via ZCS; however, significant losses are observed in the resonant inductor which compromises overall system efficiency. Additionally, harmonic distortion severely impacts output power quality and limits practical applications.

Submitted text deals with a power amplifier intended for usage in music electronics. First part is related to the common problems of low-frequency amplifiers including principles and individual circuit wiring types. Next part is related to description of self-made power amplifier including wiring scheme diagram. The end of the text concerns about mechanical construction of mounting box and design of possible module layout inside a device.

Presents results of research in the field of low-level electromagnetic fields interacting with the higher organisms, in the frequency band from 0,01 to 30 Hz effect on the individual or social group. Provides a description of the methodology of measuring and evaluating the impact of workplace assembled measuring low-level electromagnetic fields, extremely low frequency (ELF) on a sample of respondents. It was proposed measuring device for monitoring and evaluating how respondents' reactions to changes in the geomagnetic or external - external magnetic / electromagnetic field and to work for the measurement and evaluation of changes in external magnetic fields very low levels (ELF). This work is designed to process and evaluate implemented within experimental research into the influence of low-level magnetic fields in the Earth's resonator psychophysiological parameters of human organism and its behavior and decision-making. The work confirmed the influence of low-level magnetic fields on the psychophysiological parameters of the organism to be simultaneously confirmed the hypothesis established in accordance with the objectives of work.

An experimental study of a low-frequency transcritical thermoacoustic device has been conducted at Purdue University's Maurice J. Zucrow Laboratories. The purpose of this study was to characterize the thermoacoustic response of transcritical R-218 and asses it's feasibility for energy extraction and waste heat removal. This rig operated as a standing-wave configuration and achieved pressure amplitudes as high as 690 KPa (100 psi) at a temperature difference of 150 K and a bulk pressure of 1.3 P/P_cr(3.43 MPa). To the author's knowledge, this is the highest ever thermoacoustic pressure amplitude achieved in a non-reacting flow. The thermoacoustic response was characterized by varying temperature difference and bulk pressure parametrically. The effect of resonator length was characterized in a set of tests where resonator length and bulk pressure was varied parametrically at a single temperature difference. Finally, the feasibility for energy extraction was assessed in a set of tests which characterized the ability of the working fluid to pump itself through a recirculation line with check valves. This set of tests showed that the working fluid was able to create self-sustained circulation by inducing a pressure differential across the check valves with the thermoacoustic response. This circulation was induced while still maintaining a significant pressure amplitude, demonstrating promising results as a feasible method for energy extraction and waste heat removal.

Thesis: M.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1980 / Includes bibliographical references. / by Tarek Mohamed Habashy. / M.S. / M.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

The aims of this study were to evaluate the influence of an extremely low-frequency electromagnetic field (ELF-EMF) on [3H]glucose uptake in the peripheral tissues and organs of rats. Rats were exposed to ELF-EMF (frequency-10 Hz, induction -1.8-3.8 mT) one hour daily for 14 consecutive days. Control animals were sham exposed. On the 15th day (24 hours after last exposure) rats were injected with D-[3H]-6-glucose 500μCi/kg IP. Fifteen minutes later animals were sacrificed by decapitation and peripheral tissues were excised and examined for radioactivity (desintegrations per minute, DPM/ 100 mg wet tissue weight), which expressed [3H]glucose uptake. In most of the examined tissues and organs, such as liver, kidney, heart muscle, cartilage, connective tissue, tendon and skin, [3H]glucose uptake in ELF-EMF-exposed animals was significantly higher as compared to that in the sham control. Exposure to ELF-EMF did not influence [3H]glucose uptake in the thoracic aorta and the skeletal muscle. It is concluded that ELF-EMF impacts tissue glucose uptake by facilitating glucose transport via cell membranes, dependent and probably also independent of its role in increasing insulin action in insulin-dependent tissues.

No description available.

A dissertation submitted to the Faculty of Health Sciences, University of Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Masters of Science. Johannesburg 2012 / Background: The detrimental effects of prolonged mechanical ventilation (MV) on the respiratory muscles, especially the diaphragm, are well documented and it is crucial that MV should be discontinued as soon as possible to prevent added complications and additional risks to patients with critical illness. The spontaneous breathing stage of MV can be managed as a rehabilitation and conditioning phase for the respiratory muscles due to the fact that the respiratory muscles are more active during this stage of MV. Weaning strategies that provide insufficient respiratory work, too high a respiratory muscle load or insufficient respiratory muscle rest may lead to respiratory muscle fatigue and consequently failed weaning and extubation. The aim of this research project was to develop an individualised continuous positive airway pressure (CPAP) weaning programme and test its effects on the outcomes of extubation in the adult ventilated patient. Method: An experimental, prospective, non-randomised, sequential study of two groups of subjects was performed. Forty eight subjects [group one: n =24 (control) and group two: n = 24 (intervention)], who were mechanically ventilated for longer than 48 hours, in an open adult, general intensive care unit were recruited. Subjects in the control group were weaned according to the standard weaning programme of the test setting at the time; and those in the intervention group were weaned according to an individualised CPAP programme. This weaning programme was developed utilising three principles of muscle rehabilitation namely; daily stepwise progression, sufficient rest and recovery periods and adapted to the individual needs and progression of each subject. Objective measurements such as the rapid shallow breathing index (RSBI), RSBI rate and the maximum inspiratory pressure (MIP) were used to determine the subjects in group two’s readiness for a spontaneous breathing trial. The primary outcomes assessed were time spent in the different stages of MV, rate of failure to sustain spontaneous breathing in stage 3 of MV, successful extubation and mortality rate. Results and Discussion: The difference in rate of failure to sustain spontaneous breathing between the two groups was statistically significant (p = 0.01) with 10 events of failure in group one and three in group two. The rate of successful extubation from MV between groups one and two was 70.8% and 91.7% iv respectively (p=0.52). The mortality rate was 33.3% for group one and 8.3% for group two (p = 0.02). The difference in the total time spent on MV (days) did not differ significantly (group one = 8.6 (± 0.40) days; group two = 9.3 (±0.32) days; p = 0.75). The results yielded from this study suggest that the use of a multidisciplinary team model and an individualised CPAP programme aids successful extubation from MV as the success rate was much higher in the intervention group than in the control group without adding additional time on MV. Conclusion: Results from this study showed that the implementation of an individualised CPAP programme during the spontaneous breathing stage of MV may improve the outcomes of extubation in adult ventilated patients.

No description available.