Research Scholars Theses
Recent Submissions
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Simpson, Ashley (September 30, 2009)[more][less]
Abstract: ABSTRACT The Effects of Alcohol, and Age on Astrocytes in Female Rats Following an Inflammatory Stimulus (May 2006) Ashley N. Simpson Department of Biology Texas A&M University Research Advisor: Dr. Farida Sohrabji Department of Neuroscience and Experimental Therapeutics Astrocytes are an important support cell within the central nervous system and are an integral part of the blood brain barrier. They participate in inflammatory processes in the brain and may also be influenced by alcohol and age. Thus, the objective of this research was to determine the relationship between alcohol and age following a lipopolysaccharide-induced (LPS) insult in astrocytes derived from young adult and reproductively senescent female rats. To understand the effects of age on astrocytes, primary cultures were derived from reproductively-competent young adult female rats or reproductively senescent female rats. The reproductive senescent females are physiologically similar to human menopause. Thus, our aging model is based on ovarian, not chronological, age. In this study, LPS increased both nitric oxide production and matrix metalloproteinase 9 (MMP-9) activity in young adult and reproductive senescent-derived astrocytes. Matrix metalloproteinases are enzymes that degrade extracellular matrix (ECM) molecules in which cells adhere within the brain. Degradation of the ECM allows for cell migration, but prolonged activation can potentially lead to blood brain barrier degradation. In young adult-derived astrocytes, LPS increased MMP-9 and this was not affected by ethanol. However, in reproductive senescent female-derived astrocytes, the LPS induced increase in MMP-9 was exacerbated in the presence of ethanol. Interestingly, in astrocytes derived from young adults and reproductive senescent females ethanol had no effect on the LPS-induced increase in nitric oxide (NO). Inflammation is a necessary process for the brain to fight infection or viruses and to remove cellular debris following injury. Prolonged inflammation, however, can lead to neurodegeneration. This data suggests that, in female adult rat astrocytes, LPS is able to stimulate NO in the presence or absence of ethanol. However, matrix metalloproteinase activity may be differentially regulated in these two physiologically distinct female populations. Thus ethanol may potentially have a more detrimental impact on the mobility of astrocytes and on the blood brain barrier in the aging brain. URI: http://handle.tamu.edu/1969.1/88045 Files in this item: 1
FinalThesis.pdf (249.7Kb) -
Pritchard, Megan; Tsvetkov, Pavel (September 30, 2009)[more][less]
Abstract: Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems. URI: http://handle.tamu.edu/1969.1/88044 Files in this item: 1
MPritchardUGRS.pdf (659.8Kb) -
Perry, Regina (September 30, 2009)[more][less]
Abstract: This research focuses on the analysis of microfossils from deep-sea sediments. I am investigating a series of deep-sea sediment cores from the South Pacific. The cores are a vertical timeline of sedimentation, with each centimeter layer representing approximately 1,000 to 5,000 years of deposition. I subsampled each core by removing 10cc of sediment every 150 cm. Each subsample spans 2cm. After recording the mass of each sample, I washed and agitated each in purified water and sodium metaphosphate (disaggregant) solution to break up any clays adhering to the fragile fossil material. After rinsing over a 63m sieve, the samples were dried, and then transferred to a storage vial. Each sample was examined under a low-power binocular microscope to identify and quantify the assemblage of microfossils. I also analyzed the microfossil specimens using the scanning electron microscope to aid in identification and capture images of the important specimens. Results document changes in the composition of microfossil shells and faunal assemblages through time. In general, the dominant sediment lithology is red clay. However, several cores contain evidence of significant sediment variability through time. Typically, South Pacific deep waters are corrosive to calcium carbonate, so the preservation of carbonate fossils in the sediments reflects intervals of anomalous ocean chemistry that in turn may reflect changes in atmospheric CO inventories. These results show that over a relatively short geologic period, the ocean level at the coring site fluctuated between shallower nutrient rich waters and deeper carbonate rich waters. Future work, in collaboration with colleagues at the University of Michigan and Boise State University, will focus on more precise determinations of the sediment layer ages and geochemical analyses of the microfossils to determine ancient oceanic and atmospheric circulation patterns. URI: http://handle.tamu.edu/1969.1/88043 Files in this item: 1
Thesis revised.doc (5.541Mb) -
Evetts, Elizabeth A.; Peterson, Jacqueline A. (September 30, 2009)[more][less]
Abstract: The above- and below-ground litter from fallen foliage and root exudates and their decomposition has an impact on forest soil. The objective of this research project was to determine the effect of above- and below-ground litter manipulation on the retention and release of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate and ammonium in the soil profile at 0-5 and 5-15 cm depths. The soils were obtained from a Long Term Ecological Research site in the Sikfokut Forest in Hungary. The site is a mature oak forest and the soil has no organic layer; the leaf litter sits directly on the A horizon. There are six treatments applied to the soil: doubling of annual leaf litter (DL), doubling of annual wood litter (DW), removal of annual leaf litter (NL), removal of roots (NR), removal of leaf and roots (NI) and control (C). Each plot is 7 x 7 m, and each soil sample taken was 15 x 15 cm square. A stock solution of leaf litter was added in different concentrations to soils from each treatment in a 50 mL centrifuge tube. Because I was investigating retention or release of carbon and nitrogen, I inverted the tube gently over a period of 2 hours prior to centrifugation and removal of supernatant. The supernatant solution was analyzed for DOC, DON, ammonium and nitrate to determine retention and release values for each dependant upon the different treatments. The results of the study were interesting. Dissolved organic nitrogen was neither retained nor released in the 0-5 cm layer for any treatment yet nitrate, typically considered a mobile anion showed retention and release in this layer. In the 5-15 cm layer we had no retention or release of nitrate but dissolved organic nitrogen was retained and released between the solid and solution phases. URI: http://handle.tamu.edu/1969.1/88040 Files in this item: 1
Evetts_Approved_Thesis.pdf (131.3Kb) -
Koss, James R. (September 30, 2009)[more][less]
Abstract: The objective of this study is to demonstrate the ability to detect the presence of energetic materials by analyzing the bending response of an electrically heated micro-cantilever thermal bi-morph array. Heating the cantilevers that are made of materials with different coefficients of thermal expansion affects the bending and is measured using an optical device in real time. The detection scheme is based on the threshold value of current that results in a deviation (from the control value) of the actuation of the micro-cantilver. This threshold current is found to provide a unique signature to identify an equilibrium concentration of iso-propyl alcohol, acetone or gasoline vapors at room temperature. The threshold current is proportional with the vapor pressure of the volatile species and the ignition temperature. This shows sensors can be used for specific detection of different energetic material. The sensor array can be used to detect and identify volatile combustibles species in real time. Further, the sensor array can be multiplexed (i.e., detect multiple explosives simultaneously) and also allows redundancy checks so that false positive or false negative results can be eliminated. The sensor permits detection without coming in contact with the contaminated surface or source of the combustible material because it detects the vapors effused by the explosive materials. Thus it can be used at a nominal distance away from the source. URI: http://handle.tamu.edu/1969.1/88039 Files in this item: 1
Koss_THESIS_UGRSP_2008.pdf (496.2Kb)
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