Development and Analysis of Improved Thermoelectric Materials

Thermoelectric cooling devices, also called Peltier coolers, are devices based on the thermoelectric effect of materials and act in cooling mode. By adding an electrical potential on two sides of the material, a temperature gradient will be created. Thermoelectric cooling devices have many advantages, when compared to the commonly used compression-used refrigerators. For example, refrigerant-free, vibration free and compact. However, a vital disadvantage of thermoelectric cooling device is that it has a much lower device efficiency, comparing to compressor-based refrigerators. Thermoelectric coolers offer around 10-15% efficiency of ideal Carnot cycle, while compressor-based refrigerators provide 40-60% efficiency ideal Carnot cycle. The efficiency of thermoelectric cooler is influenced by the performance of thermoelectric used. Therefore, the purpose of this project was to improve the thermoelectric performance of Bi-Sb alloy. Bi-Sb alloys are of interest for thermoelectric cooling devices and it is believed that their heat pump efficiency can be enhanced by using CuBr resonant impurities. This project involves the synthesis of polycrystalline Bi-Sb alloys with different amounts of CuBr prepared via ingot casting. A concentrated master sample, with 0.5% CuBr, was developed first. Then, 2 times, 5 times and 10 times diluted samples was developed by diluting the master sample. After measurement, the master sample was found to have best thermoelectric performance, with a ZT of 0.27. The second step was to develop a single-crystalline sample via zone melting with the master sample mentioned above. The single-crystalline sample was found to have huge enhancement in thermoelectric performance, the ZT value of it was found to be 0.41. The results prove that CuBr dopant does enhanced the heat pump efficiency of Bi-Sb alloy. However, it is not as much as expected. Further effort can be done to improve the efficiency even more.No embargoAcademic Major: Mechanical Engineerin

Mobile Search Strategies and Detection Analysis of Nuclear Radiation Sources

This work focuses on detection analysis and search strategies for nuclear radiation sources in metropolitan areas with mobile sensor networks. A mobile sensor detecting a stationary nuclear source experiences continually changing statistics. In this work we provide an analysis of the probability of detection of a nuclear source that incorporates these continual changes. We apply the analysis technique to several patterns of motion including linear and circular paths. Analysis is also presented for cases in which there is a significant vertical offset between source and mobile sensor (the three-dimensional problem). The resulting expressions are computationally simple to evaluate and have application to both analysis and simulation of nuclear detection systems in a variety of scenarios. In metropolitan areas, with vehicles equipped with detectors and Global Position System (GPS) devices, we consider the design of a robust detection system to provide consistent surveillance. Various strategies for providing this surveillance with a mobile sensor network are considered and the results are compared. Both time-from-last-visit based algorithms and detection algorithms that utilize both time and probability-of-miss estimates are considered. The algorithms are shown to perform well in a variety of scenarios, and it is further shown that the algorithms that utilize probability information outperform those that do not

Statistical analysis of sleep patterns in Drosophila melanogaster

“Sleep is one of the most preserved and restorative behaviors of animals and is important in human health. Lack of sleep may cause numerous diseases. So the study of sleep rhythms is very essential and complicated. In order to simplify the process of studying sleep, the fruit fly Drosophila melanogaster, is utilized as a model organism for several reasons. Some of the molecular mechanisms that contribute to the circadian clock in the fruit fly were also found to generate similar cycles in mammals. In order to study sleep patterns in the fruit fly, experiments were designed and performed to observe the differences between genotypes and gender of flies. Sleep was also monitored under different environment conditions. Experiments last four days long, with sleep status recorded at each minute. Several variables can be derived from the original data for further statistical analysis. Ultimately it is of interest to characterize the sleep behavior of flies by identifying sleep-related variables based on the four days of sleep. We will investigate if these differ among fly types and genders. So cluster analysis and discriminant analysis has been applied to figure out the key features that would affect sleep cycle of flies. Also, an exponential model of current sleep duration based on past sleep and wake durations is fit to check differences of the parameter estimators between cluster groups”--Abstract, page iii