Tolerance to ethanol is an endophenotype of alcoholism, allowing the study of a complex psychiatric condition using animal models. To identify new genes involved in the acquisition of tolerance, I designed an automated and high-throughput tolerance assay and screened a collection of deficiency mutants for the inability to develop tolerance. The screen yielded several “regions of interest” where more than one overlapping deficiency failed to develop tolerance. One of these regions comprised nine genes, and testing the expression levels of each gene revealed that diazepam binding inhibitor (Dbi) showed grossly increased expression in the deficiency mutant compared to wild type. Another mutant stock, with a P-element transposon inserted downstream of the Dbi gene, both failed to develop tolerance and showed further increased expression of Dbi. There are two insulator binding sites flanking Dbi, and the P-element transposon also contains insulator binding sites. Based on these results, it was hypothesized that an insulator complex kept Dbi expression low in wild type flies and that disrupting the insulator complex allowed aberrantly high expression of Dbi in the mutants. Furthermore, we assumed that induction of Dbi blocked tolerance by making the mutants resistant prior to the first sedation. A UAS-DBI transgene was constructed to over-express Dbi. Induction of the UAS-DBI with a heat shock gal4 driver induced resistance to ethanol sedation; a similar response was observed in the parental control, but the effect was smaller. Although driving UAS-DBI with the neural elav-gal4 driver did not block tolerance, the experimental stock was resistant to ethanol sedation compared to the parental controls, indicating that increased Dbi expression produced “pre-tolerance.” To confirm the theory that insulator disruption was responsible for the increase in Dbi and the resulting no-tolerance phenotype, the P-element in the second mutant was mobilized by introducing a transposase source. These offspring lines were analyzed using qualitative PCR to determine whether the transposon excised precisely, left a portion of the transposon behind, or removed some of the flanking region. A precise excision mutant was identified, but this mutation did not rescue tolerance as predicted. This result might indicate that genetic background was the cause of the no-tolerance phenotype, or it might indicate that the excision was not exactly precise and removed the native insulator binding site, causing the insulator complex to remain disrupted. / text

Hydrogen, one of the cleanest energies, is very attractive in the near future. However, it could be hazardous to store, transport and use hydrogen gas because leakage can cause explosion if sparks appear. Therefore, it is essential to develop sensors to detect the hydrogen leakage in order to prevent potential accidents. In this research, Metal-Insulator-Semiconductor (MIS) Schottky-diode hydrogen sensors with different gate insulators (Ta2O5, La2O3, LaTiON, and HfTiO) or substrates (Si, SiC, and InGaN/GaN MQW) were prepared in order to study their hydrogen sensing performances. Firstly, two sensors based on Si and SiC with Ta2O5 as gate insulator were prepared and compared. Owing to high permittivity (~25), good thermal stability and low electrical defects, Ta2O5 was chosen as the insulator. The differences in sensitivity and response time between the two sensors were ascribed to the difference in the surface morphology of Ta2O5 between the SiC sensor (mean surface roughness was 0.39 nm) and its Si counterpart (mean surface roughness was 0.22 nm). Secondly, due to the high permittivity (~25) and good thermal stability of La2O3, the high permittivity (~20), low interface-state density, and low leakage current of LaTiON, Si sensors with these two dielectrics as gate insulator were developed. The sensitivity of the La2O3 sensor could exceed 7.0 at 150 oC, and the sensor exhibited good hydrogen sensing performance at up to 250 oC. On the other hand, the maximum sensitivity of the LaTiON sensor could reach 2.5 at 100 oC. For the LaTiON sensor, the Poole-Frenkel model controlled the carrier transport at high temperatures (150 ~ 200 oC) while the thermionic emission was the dominant conduction mechanism at lower temperatures (from room temperature to 150 oC). For the La2O3 sensor, the hydrogen reaction kinetics was confirmed, and an activation energy of 10.9 kcal/mol was obtained for this sensor. Thirdly, the La2O3 gate insulator used in the previous work was applied to make MIS sensor on SiC substrate for higher-temperature applications. Its maximum sensitivity and response time at high temperature (260 oC) are 4.6 and 20 s, respectively. The electrical conduction mechanisms were explained in terms of Fowler-Nordheim tunneling (below 120 oC) and the Poole-Frenkel effect (above 120 oC). Finally, in order to see whether the unique structure of InGaN/GaN multiple quantum wells (MQWs) can be utilized for the MIS Schottky-diode hydrogen sensor, three sensors were made on InGaN/GaN MQWs substrate, one without gate insulator, one Finally, in order to see whether the unique structure of InGaN/GaN multiple quantum wells (MQWs) can be utilized for the MIS Schottky-diode hydrogen sensor, three sensors were made on InGaN/GaN MQWs substrate, one without gate insulator, one In summary, the quality of the gate insulator plays an important part in the performance of the hydrogen sensors. SiC and InGaN/GaN MQW substrates are suitable for high-temperature (from ~200 to ~500 oC) applications while the low-cost sensors based on Si substrate can function well below about 200 oC. Hydrogen sensors with these high-k materials (Ta2O5, La2O3, LaTiON, and HfTiO) as gate insulator can produce good electrical characteristics, high sensitivity, and fast response. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

No description available.

Aim of the work 1. To analyze the methods used for the quality and resource assessment of complex insulation; 2. To develop the models for the assessment and analysis of polarization features, dielectric parameters and moisture content in oil- paper insulation; 3. To develop the method for the assessment of moisture quantity by measuring the polarization characteristics; 4. To analyze the impact of water quantity on dielectric parameters of transformer insulation; 5. To classify the quality criteria of oil-paper insulation; 6. To identify the tendencies in variation of insulation’s dielectric parameters and moisture quantity; 7. To implement the developed models and methods in the electricity industry of Lithuania for the assessment of the transformers’ insulation quality and resource.

The thesis constitutes a systematic theoretical and experimental investigation into impulse breakdown voltage-time curves of coaxial-cylinder gaps in SF(,6) and a 50% SF(,6) - 50% N(,2) mixture. The breakdown time delay probability is treated as a bivariate distribution in statistical and formative time lags. A method is developed to deduce the marginal breakdown voltage probability curve from statistics of time delay. The experimental work was performed on 2.54/7.0-cm diameter, 60-cm long coaxial-cylinder electrodes using SF(,6) or SF(,6)-N(,2) mixtures at pressures of 0.1 - 0.3 MPa subjected to 0.5/50-(mu)s and 1.2/50-(mu)s impulses of both polarities. The effect of a spherical conducting particle attached to the central electrode of the coaxial-cylinder gap on the voltage-time characteristics is also investigated.

performance of high voltage outdoor insulators can be greatly affected by weather conditions. The weather conditions under investigation are cold temperatures coupled with high humidity levels. Weather data from a number of coastal stations around South Africa was analyzed to determine whether surface condensation was likely on outdoor insulators under these weather conditions. A heat transfer equation was used to determine the response of the insulator surface temperature to the environmental temperature. It was found that surface condensation would occur on the insulator surfaces which would lead to sudden, heavy wetting of the surface. Outdoor insulators in coastal environments are often heavily polluted, due to salt spray, and when wet, a conductive layer can form on the insulator surface. This conductive layer can result in appreciable leakage currents flowing on the insulator surface, often leading to premature failure. The finite element method program, Maxwcll, was used to simulate the outdoor insulators both under these polluted, wet conditions and under unpolluted conditions. Both cases were simulated for a silicone rubber, glass cap-and-pin and two EPDM outdoor insulators. The polluted insulators were simulated with varying pollution severities. The results of the simulations are analyzed and the surface resistances of the wet polluted insulators were calculated. An experiment was' set up to mask the environmental weather conditions found which would lead to surface condensation. The insulators under test were placed in a chilled weather chamber which introduced a steam fog to simulate the humidity. The leakage current was measured and recorded for comparison with the simulation results. The results of the weather chamber test showed that surface condensation resulted in more severe wetting than manual wetting. The weather chamber surface resistances calculated were much lower than those calculated by the Maxwcll simulations. This was due to the difference it humid particle temperature in the condensation rate equations used for the Maxwell simulations, and the humid particle temperature of the steam fog used in the weather chamber. Polluted coastal outdoor insulators exposed to the above weather conditions will experience larger than normal leakage currents which will lead to premature failure of the units. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

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No description available.

No description available.