The electron, gamma and neutron radiation degradation of III-V semiconductors and heterojunction bipolar transistors (HBTs) is investigated in this thesis. Particular attention is paid to InP and InGaAs materials and InP/InGaAs abrupt single HBTs (SHBTs). Complete process sequences for fabrication of InP/InGaAs HBTs are developed and subsequently employed to produce the devices, which are then electrically characterized and irradiated with the different types of radiation. A comprehensive analytical HBT model is developed and radiation damage calculations are performed to model the observed radiation-induced degradation of SHBTs. The most pronounced radiation effects found in SHBTs include reduction of the common-emitter DC current gain, shift of the collector-emitter (CE) offset voltage and increase of the emitter, base and collector parasitic resistances. Quantitative analysis performed using the developed model demonstrates that increase of the neutral bulk and base-emitter (BE) space charge region (SCR) components of the base current are responsible for the observed current gain degradation. The rise of the neutral bulk recombination is attributed to decrease in a Shockley-Read-Hall (SRH) carrier lifetime, while the SCR current increase is caused by rising SCR SRH recombination and activation of a tunneling-recombination mechanism. On the material level these effects are explained by displacement defects produced in a semiconductor by the incident radiation. The second primary change of the SHBT characteristics, CE offset voltage shift, is induced by degradation of the base-collector (BC) junction. The observed rise of the BC current is brought on by diffusion and recombination currents which increase as more defects are introduced in a semiconductor. Finally, the resistance degradation is attributed to deterioration of low-doped layers of a transistor, and to degradation of the device metal contacts. / Graduation date: 2001

Although most research on bipolar I disorder has focused on biological models, recent investigation has elucidated the importance of psychosocial predictors of the course of illness. Theories of the Behavioral Activation System?s role in affect have helped unify biological and environmental explanations of the disorder. Along these lines, researchers have proposed that goal striving and attainment predict manic symptoms. In the current study, experience-sampling methodology was used to assess the relationship between fluctuations in goal striving and affect among 12 persons with bipolar I disorder and 12 without a history of mood disorder (control group). Participants completed measures of goal striving and affect three times each day for a period of three weeks. It was hypothesized that moving more quickly than expected toward a given goal would result in decreased subsequent effort toward that goal (coasting) for the control group, and increased subsequent effort (anti-coasting) for those with bipolar I disorder, with positive affect mediating the relationship in both cases. Results indicated that those in the bipolar I disorder group were significantly more likely to anti-coast than those in the control group. This finding, however, was explained primarily by gender, as men in the bipolar I disorder group showed no evidence of anti-coasting. In addition, there was no evidence of the mediating role of positive affect in these phenomena. Implications of the findings, limitations, and future directions are discussed.

Bipolar I disorder (BD) is one of the leading causes of disability among adults. Despite the fact that those with BD are at significantly greater risk for experiencing psychosocial hardship, many with the disorder function quite well. Researchers have shown this variability in quality of life to be partly explained by symptom severity, educational attainment, illness characteristics, and cognitive variables (e.g., executive function). The current study extends this research by examining the role of emotional intelligence in the quality of life and social and occupational functioning of people with BD. I hypothesized a significant proportion of the variance in quality of life and social and occupational functioning would be explained by emotional intelligence, above and beyond the variance explained by the aforementioned variables. Forty-two participants with BD were recruited and completed a battery of measures to assess quality of life, cognition, and emotional intelligence. Results indicated that emotional intelligence, as measured by the Mayer-Salovey-Caruso Emotional Intelligence Test, did not explain any unique variance in quality of life. Self-reported emotional intelligence, on the other hand, did explain unique variance in both subjective well-being and social functioning.

The H2/air micro PEMFC stacks were designed and fabricated in-house through MEMS (Micro-Electro-Mechanical System) technology with deep UV lithography manufacturing processes (SU-8 photoresist) and micro electroforming manufacturing processes to construct a novel metallic bipolar plate. The effect of different operating parameters on micro PEMFC stacks performance was experimentally investigated for serpentine flow-field configuration. Experiments were conducted through a serious laboratory experiments with different operating conditions of temperature (25oC, 35 oC and 50 oC), anode backpressures (97kPa, 153kPa, 207kPa) as well as anode humidifier temperature (25oC, 35 oC and 50 oC). Experimental results are presented in the form of polarization VI curves and PI curves under above operating conditions. The influence of the aforementioned parameters was presented and discussed.

Psychologists face challenges on a daily basis. Among the challenges they face are making diagnostic decisions. Recently, bipolar disorder has shown an increase in diagnosis in children and adolescents. Once felt to be an adult disorder, journals are describing the use of the diagnosis with children and adolescents. While the diagnosis has been considered as relevant, no psychological measures have been developed to make an accurate diagnosis. Developing a new psychological measure for bipolar disorder in children is critical. Due to the lack of data on what constitutes normal behavior as well as the absence of an accurate measurement of early-onset bipolar disorder, it is necessary to develop such a measure. The purpose of this study was to evaluate a newly developed measure based on the literature on bipolar disorder in children. The measure was developed through a review of the current literature, DSMIV-TR criteria for bipolar disorder, and ideas developed within a bipolar disorder research team at Texas A&M University. Because of the item content, the new measure is entitled the Mania Assessment Scale for Children (MASC). The first steps in understanding a new measure for early-onset bipolar disorder is to determine the factor structure of the scale as well as the reliability and validity. Results indicated that the MASC is best understood as a measure with a single score, or factor. Once the underlying structure of the MASC was determined, the study evaluated which behaviors of typically developing children may be misconstrued as indicative of bipolar disorder. Group differences on the measure are also evaluated. Results from statistical analysis showed that there were significant group differences between age groups, but not gender and ethnic groups. In addition, there was a statistically significant difference between clinical and non-clinical groups. To conclude, a discussion of the findings and recommendations for future research is presented. Overall, it is hoped that the study will help psychologists better understand the complexity of behaviors associated with the diagnosis of bipolar disorder in children and adolescents.

The retina is able to adjust its signaling over a wide range of light levels. A functional result of this is increased visual acuity at brighter luminance levels, such as during the day, due to changes in the organization of retinal receptive fields. This process is commonly referred to as light adaptation. These organizational changes have been shown to occur at the level of the ganglion cells, the output neurons of the retina, which have shifts in their excitatory center-inhibitory surround receptive fields that increase their sensitivity to small stimuli. Recent work supports the idea that light-adapted changes in ganglion cell spatial sensitivity are due in part to inner retinal signaling changes, possibly including changes to inhibition onto bipolar cells, the interneurons at the center of retinal signal processing. However, it is unknown how inhibition to the bipolar cells changes with light adaptation, how any changes affect the light signal or what mediates the changes to the bipolar cells that have been suggested by previous reports. To determine how light adaptation affects bipolar cell inhibition, the inhibitory inputs to OFF bipolar cells were measured. OFF bipolar cells, which respond to the offset of light, in particular may be involved in retinal adaptation as they bridge dim- and bright-light retinal pathways. Their inputs were compared between dark- and light-adapted conditions to determine how any inhibitory changes affects their output onto downstream ganglion cells. We found that there was a compensatory switch from primarily glycinergic-mediated inhibition to OFF bipolar cells in the dark to primarily GABAergic-mediated inhibition in the light. Since glycinergic and GABAergic inhibition perform very different roles and are mediated by morphologically different cells, it is likely this switch underlies a change in the spatial distribution of inhibition to these cells. We found that the spatial inhibitory input to OFF bipolar cells became significantly smaller and narrower with light adaptation, translating to smaller inhibitory surrounds of the OFF bipolar cell receptive fields. Through a model, our data suggested that the OFF bipolar cell output to downstream ganglion cells was stronger in the light, due to the narrowing and reduction in the spatial input, to small light stimuli. This would effectively be one way the retina could use to increase visual acuity. Additionally, we found that the inhibitory changes to OFF bipolar cells with light-adaptation are partially mediated by dopamine D1 receptor signaling. Dopamine is released in the light and has been shown to be an important modulator of retinal light-adaptation. However, there are likely other factors involved in mediating inhibitory changes to OFF bipolar cells. Through these studies, we show that light adaptation heavily influences inner retina inhibition and likely plays a prominent role in determining and shaping light signals under different ambient light conditions which may ultimately be one mechanism for increasing visual sensitivity and acuity.

No description available.

No description available.

In this thesis, the features of electric field signatures of narrow bipolar pulses (NBPs) generated by cloud flashes are investigated and their effects on wireless communication systems are studied. A handful amount of NBPs (14.5%) have been observed to occur as part of cloud-to-ground flashes in South Malaysia. Occurrence of NBPs in Sweden has been reported for the first time in this thesis. The electric field waveform characteristics of NBPs as part of cloud-to-ground flashes were similar to isolated NBPs found in Sweden and South Malaysia and also to those isolated NBPs reported by previous studies from various geographical areas. This is a strong indication that their breakdown mechanisms are similar at any latitudes regardless of geographical areas. A comparative study on the occurrence of NBPs and other forms of lightning flashes across various geographical areas ranging from northern regions to the tropics is presented. As the latitude decreased from Uppsala, Sweden (59.8°N) to South Malaysia (1.5°N), the percentage of NBP emissions relative to the total number of lightning flashes increased significantly from 0.13% to 12%. Occurrences of positive NBPs were more common than negative NBPs at all observed latitudes. However, as latitudes decreased, the negative NBP emissions increased significantly from 20% (Sweden) to 45% (South Malaysia). Factors involving mixed-phase region elevations and vertical extents of thundercloud tops are invoked to explain the observed results. These factors are fundamentally latitude dependent. In this thesis, the interaction between microwave radiations emitted by cloud-to-ground and cloud flashes events and bits transmission in wireless communication networks are also presented. To the best of our knowledge, this is the first time such effects are investigated in the literature. Narrow bipolar pulses were found to be the strongest source of interference that interfered with the bits transmission.

Transmission Electron Microscope (TEM) studies have been carried out of emitter regions in polysilicon contacted emitter bipolar transistors. The preparation of suitable TEM thin foils is described. In addition a technique is developed for the observation and quant jtative interpretation of the break-up of the interfacial oxide layers observed in these samples. The effect of annealing the samples prior to emitter dopant implantation (pre-annealing) is investigated for phosphorus and arsenic doped samples, implanted into a polysilicon layer 0.4μm thick, with a dose of 1x10¹⁶cm². Two wafer pre-cleans have been used prior to polysilicon deposition to produce a thin oxide (0-8Å) and a thicker oxide (14Å). In the presence of the thinner oxide, the phosphorus doped samples enhance epitaxial regrowth of the polysilicon layer compared with the arsenic doped or undoped samples. In the presence of the thicker oxide, no difference is observed between the samples. A mechanism is proposed to explain this. The mechanisms controlling the gain of a phosphorus doped device are investigated and a model proposed to explain the observed electrical characteristics. It is concluded that there are two mechanisms responsible for the observed supression of hole current. Firstly tunnelling through the interfacial oxide and secondly some blocking effect of the interface. Carrier transport in the polysilicon is not believed to contribute to this supression. A dopant sensitive etch has been applied to TEM thin foils containing fully processed emitters in state-of-the-art devices. The shape of the emitter dopant distribution is revealed in such devices for the first time, and a 2-D profile is obtained from the emitter. It is shown that reduction in the emitter depth to 8OOÅ or less does not alter the emitter dopant geometry. The technique is demonstrated to be capable of resolving spatial separations of dopant iso-concentration contours of 100Å or less.