In this thesis, optimization techniques for a joint admission control and radio resource allocation are developed for multicasting over high altitude platforms. First, a primary system model in a multicellular high altitude platform system is considered, in which each user can receive any requested multicast session in its cell from no more than only one HAP antenna simultaneously. All the users have equal priority for admission. The users are selected to join the respective multicast groups and the power, subchannels and time slots are allocated such that the spectrum utilization is maximized while satisfying the quality of service requirements. Lagrangian relaxation and the subgradient algorithm are used to obtain solution bounds for the primary system model problem formulation. These bounds were then used in the branch and bound algorithm for pruning of nodes. The numerical results illustrate the goodness of the bounds for different constraint set dualizations and for different subgradient step size rules. The system model is then extended to allow the multicast group users to receive a session's transmission from more than one antenna simultaneously at different frequencies. This also allows the user to receive multicast sessions transmitted in neighboring cells too, not just those transmitted in the cell which the user resides in. The users have different priority levels of admission and the objective is to maximize the admission of highest priority users to the system. A much efficient formulation is obtained for the extended model in terms of size, as compared to the primary model. Linear outer approximation using McCormick underestimators are used for the relaxation of the mixed binary quadratically constrained problem. The solution method is based on branch and cut scheme in which cutting planes, domain propagation and heuristics are integrated. Various branching schemes are considered and a presolving reformulation linearization scheme for a specific set of quadratic constraints is considered. The numerical experiments compare the performances in terms of the duality gap, number of nodes, number of iterations, the number of iterations per node, the time needed to obtain the first feasible solution and the percentage of instances a feasible solution was found. / October 2016

Ascent to altitude presents a significant challenge to the human body. Specifically, it is associated with an increased ventilation and pulmonary vasoconstriction. In healthy subjects these are related such that a high ventilatory drive is associated with blunted pulmonary vasoconstriction. Adults born prematurely and given supplemental oxygen at birth have a blunted ventilatory response to hypoxia. We hypothesized that the hypoxic ventilatory and pulmonary vasoconstrictor responses would be unrelated following perinatal supplemental oxygen exposure. To test our hypothesis, we used a well-established rat model of 80% O2 (80%) exposure for 14 days post-natally, with 21% O2 exposure as a control (21%). We assessed the ventilatory response to graded hypoxia using barometric plethysmography 6-9 months post hyperoxia exposure. The left and right ventricles were catheterized to evaluate the hemodynamic response to 10 minutes of 12% O2 (hypoxia). To our surprise we found that 80% animals did not demonstrate a depressed ventilatory response to hypoxia. However, these animals experienced increased right ventricular systolic pressure in response to 12% O2. An increase in cardiac output was the primary driving force behind the increase in right ventricular end systolic pressure, not an increase in vascular resistance. We found no relationship between the hypoxic ventilatory drive and right ventricular pressure. In 21% animals exposed to hypoxia, the increase in right ventricular pressure was driven primarily by vasoconstriction and, as previous studies have shown, there was a relationship between the ventilatory and pressure responses. These data suggest that neonatal supplemental oxygen alters the hemodynamic response to hypoxia, possibly through enhanced sympathetic drive. The relationship between ventilation and pulmonary pressure may not translate to individuals born prematurely.

This study resulted from the identification of gaps in the literature pertaining to the morphological descriptions of the tadpoles occurring at high altitudes in the Drakensberg Mountains in South Africa. These tadpoles are exposed to low temperatures, high desiccation risk, elevated ultraviolet radiation, competition, and predation and inhabit the clear, flowing streams and marsh areas of the mountain. Highly varying environmental conditions caused tadpoles to have considerable intraspecific variation. The high degree of plasticity necessitated extensive descriptive studies of tadpole morphology in order to document intraspecific variation and set up reliable keys for species identification. Specified adaptations to the extreme montane conditions are present in tadpoles of certain species. An especially interesting adaptation is the elygium, a hemispherical pigmented area above the eye, which apparently protects the retina from harmful ultraviolet radiation. There are no known studies of elygium plasticity in tadpole eyes in relation to variation in ultraviolet radiation. Particular attention was given to the functionality and cytology of this structure. Detailed measurements of tadpoles of six frog species of the high altitude Drakensberg Mountains were made. Morphological adaptations were described on the basis of these measurements. The cytological origin of the elygium of Amietia vertebralis was revealed through histological and cellular ultrastructure studies. The change in elygium morphology over time was studied as a function of ultraviolet intensity by exposing tadpoles to different levels of ultraviolet radiation. From the detailed morphological descriptions a more reliable binomial key was constructed, which made it possible to distinguish between Amietia umbraculata and A. vertebralis. A new amended definition of the epidermal elygium can now be given as an area of melanophores originating from the pigmented epithelium of the retina, forming a hemispherical shape from the dorsal margin of the iris. It is positioned in such a way as to protect the retina when light enters directly from above. This empirical study of the functional significance of the elygium showed that elygium morphology was considerably plastic, and that there were differences in elygium area and base length in the presence or absence of UVB radiation. In the presence of high UV radiation tadpoles produced an elygium with a broader base rather than longer elygia with a larger area. A wider elygium base shaded the pupil more effectively, thus protecting the retina from harmful UV radiation. The presence of a ventral elygium was also discovered. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

This study resulted from the identification of gaps in the literature pertaining to the morphological descriptions of the tadpoles occurring at high altitudes in the Drakensberg Mountains in South Africa. These tadpoles are exposed to low temperatures, high desiccation risk, elevated ultraviolet radiation, competition, and predation and inhabit the clear, flowing streams and marsh areas of the mountain. Highly varying environmental conditions caused tadpoles to have considerable intraspecific variation. The high degree of plasticity necessitated extensive descriptive studies of tadpole morphology in order to document intraspecific variation and set up reliable keys for species identification. Specified adaptations to the extreme montane conditions are present in tadpoles of certain species. An especially interesting adaptation is the elygium, a hemispherical pigmented area above the eye, which apparently protects the retina from harmful ultraviolet radiation. There are no known studies of elygium plasticity in tadpole eyes in relation to variation in ultraviolet radiation. Particular attention was given to the functionality and cytology of this structure. Detailed measurements of tadpoles of six frog species of the high altitude Drakensberg Mountains were made. Morphological adaptations were described on the basis of these measurements. The cytological origin of the elygium of Amietia vertebralis was revealed through histological and cellular ultrastructure studies. The change in elygium morphology over time was studied as a function of ultraviolet intensity by exposing tadpoles to different levels of ultraviolet radiation. From the detailed morphological descriptions a more reliable binomial key was constructed, which made it possible to distinguish between Amietia umbraculata and A. vertebralis. A new amended definition of the epidermal elygium can now be given as an area of melanophores originating from the pigmented epithelium of the retina, forming a hemispherical shape from the dorsal margin of the iris. It is positioned in such a way as to protect the retina when light enters directly from above. This empirical study of the functional significance of the elygium showed that elygium morphology was considerably plastic, and that there were differences in elygium area and base length in the presence or absence of UVB radiation. In the presence of high UV radiation tadpoles produced an elygium with a broader base rather than longer elygia with a larger area. A wider elygium base shaded the pupil more effectively, thus protecting the retina from harmful UV radiation. The presence of a ventral elygium was also discovered. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

Tinamous (Tinamidae) have the smallest heart in relation to body mass compared to any other flying bird today (Bishop 1997). This means that heart size is likely to restrict aerobic metabolism. Tinamous inhabit areas from sea level to 4800 m a.s.l., which means that the high altitude living species, Nothoprocta ornata (NO), is exposed to hypoxia. In this study the activity of the two metabolic enzymes Lactate Dehydrogenase (LDH) and Citrate Synthase (CS) was measured and the ratio between the enzyme activities calculated to examine if the small heart of the tinamous affects their aerobic/anaerobic metabolism. The activity of the two enzymes was measured in the heart and the gastrocnemius muscle in the three species Nothoprocta ornata (NO), Nothoprocta perdicaria (NP) and Gallus gallus (GG). CS activity was significantly higher in the heart compared to the skeletal muscle and LDH activity was significant higher in the skeletal muscle than in the heart in all three species. The LDH/CS ratio was significantly higher in NO’s skeletal muscle than in chickens but there was no significant difference between species in the heart. The higher ratio in NO´s muscle could be a sign of a higher anaerobic metabolism that is used in the muscles to compensate for the small heart NO have. In conclusion, the Tinamous

Some animals have adapted to hypoxia by increasing their haemoglobin affinity for oxygen, but in vitro studies have not shown any change of haemoglobin affinity for oxygen in human high altitude natives or lowlanders acutely acclimatized to high altitude. We conducted the first in vivo study of the oxyhaemoglobin dissociation curve by progressively reducing arterial PO2 while maintaining normocapnia in lowlanders at sea level, lowlanders sojourning at 3600m for two weeks and native Andeans at the same altitude. We found that the in vivo PO2 at which haemoglobin is half-saturated (P50) is higher in lowlanders at sea level (32 mmHg) than that measured in vitro (27 mmHg) and that lowlanders and highlanders do significantly increase the in vivo affinity of their haemoglobin for oxygen with exposure to high altitude. These results indicate the value of an in vivo approach for studying the oxyhaemoglobin dissociation curve.

Some animals have adapted to hypoxia by increasing their haemoglobin affinity for oxygen, but in vitro studies have not shown any change of haemoglobin affinity for oxygen in human high altitude natives or lowlanders acutely acclimatized to high altitude. We conducted the first in vivo study of the oxyhaemoglobin dissociation curve by progressively reducing arterial PO2 while maintaining normocapnia in lowlanders at sea level, lowlanders sojourning at 3600m for two weeks and native Andeans at the same altitude. We found that the in vivo PO2 at which haemoglobin is half-saturated (P50) is higher in lowlanders at sea level (32 mmHg) than that measured in vitro (27 mmHg) and that lowlanders and highlanders do significantly increase the in vivo affinity of their haemoglobin for oxygen with exposure to high altitude. These results indicate the value of an in vivo approach for studying the oxyhaemoglobin dissociation curve.

xvii, 174 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / During acute altitude exposure, humans maintain higher skin temperature and lower core body temperature. However, the role of cutaneous vascular regulation in these thermoregulatory differences is unclear. Therefore, the purpose of these studies was to investigate the impact of altitude exposure on reflex control of skin blood flow and core temperature during cold exposure. In Chapter IV, the effects of hypoxia and hypocapnia on cutaneous vasoconstriction during mild cold exposure were investigated. We found that hypoxia stimulates cutaneous vasodilation in men whereas skin blood flow is unaltered in women. However, during whole body cooling skin blood flow is upward shifted in both sexes. The development of hypocapnia does not affect the vascular response to hypoxia in either sex, but reduces the magnitude of cutaneous vasoconstriction during cold exposure by 50% in women. In Chapter V, we studied the timecourse of α-adrenergic blockade by yohimbine in the cutaneous circulation and how the duration of cold exposure modulates cotransmitter-mediated vasoconstriction during cold stress. We found that yohimbine produces functional α-adrenergic blockade within 30 minutes of initial delivery and completely abolishes reflex cutaneous vasoconstriction during mild cold stress. This latter finding was surprising, and an additional protocol demonstrated that cotransmitter-mediated vasoconstriction only participates in the vascular response to cold stress when the exposure is more prolonged. In Chapter VI, the effects of hypoxia on cutaneous vasoconstrictor mechanisms and core cooling rate were tested during more prolonged and severe cold stress. In contrast to our findings during brief cold exposure, we showed that cutaneous vasoconstriction during prolonged cold stress is potentiated by hypoxia and abolishes hypoxic vasodilation. Moreover, increased cotransmitter-mediated vasoconstriction appears to account for this response. Hypoxia had no effect on core cooling rate during severe cold exposure. The selective potentiation of cotransmitter-mediated vasoconstriction observed during hypoxia in Chapter VI provided the basis for Chapter VII. This study was designed to test the effect of hypoxia on cutaneous vascular responsiveness to peripherally stimulated sympathetic vasoconstriction. The results demonstrated that α-adrenergic vasoconstrictor transduction is not affected by hypoxia, and that stimulation of adrenergic nerves with tyramine does not elicit cotransmitter-mediated vasoconstriction in skin. / Adviser: John R. Halliwill

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2010. / Stable and reliable source of electrical energy is a requirement for efficient operation of satellites. Several sources of electrical power for satellites exist such as fuel cells, nuclear or battery stored Direct Current energy but of late concentration has been on solar cells as the advantages compared to the other sources are many. Solar cells are p-n semiconductor devices which convert light energy into electrical energy by photovoltaic effect. The biggest drawback of solar cell energy system is the low light to electricity conversion efficiency. Apart from powering satellites, solar cells and panels have found other numerous applications such as in water pumping systems, rural electrification, street lightning. Photovoltaic principle of solar cells started way back in 1839 when Alexandre Edmund Becquerel observed that electrical currents arose from certain light induced chemical reactions. A comprehensive understanding of this phenomenon became clear when the science of quantum theory was unveiled in the early parts of the 20th century. Most solar cells and panels available today in the market are silicon based made of single junction technology. The disadvantage with single junction technology is that the p-n junction is made of a single type of solar cell material which absorbs a fraction of light wavelengths from the spectrum of light. The disability of the single p-n junction to convert all the light energy to electricity accounts for the low efficiency for the solar cells. One way to go around the problem of efficiency is to use multi-junction solar cells. Multijunction solar cells are designed to absorb a large fraction of the light spectrum and convert them to electrical energy. They are made of multiple p-n junctions made of different solar cell materials which absorb different parts of light spectrum and convert them to electrical energy. In this thesis, a design of a multi-junction solar cell for developing space solar panel is presented. The multi-junction cell has been designed from simulation results of different solar cell materials simulated with space conditions. Ideas and recommendations for future work are also presented.

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