PMR polyimides with improved high temperature performance

Studies were performed to investigate the effect of substituting a hexafluoro isopropyl idene connecting group for a carbonyl group of a PMR polyimide monomeric reactant on the thermo-mechanical properties processability of graphite fiber reinforced PMR polyimide composites. Composites were fabricated utilizing PMR methodology. Monomeric reactant solutions of various stoichiometric ratios were used to impregnate Hercules HTS graphite fiber. The processing characteristics and elevated temperature (600 F) mechanical properties of the composites are described

Bears in Big South Fork: A Spatially Explicit Density Estimate of a Reintroduced Population

Black bears (Ursus americanus) were extirpated from the Cumberland Plateau (CP) in the late 19th to early 20th century due to habitat loss and overexploitation. After the Kentucky Department of Fish and Wildlife Resources, Tennessee Wildlife Resources Agency, and the National Park Service showed interest in reintroducing bears into Big South Fork National River and Recreation Area (BSF), Eastridge and Clark (2001) experimentally translocated black bears from the Great Smoky Mountains National Park to BSF. Since the reintroduction, this population has been monitored with capture-recapture studies using genetic identification. A current and accurate estimate of density and abundance were needed to direct future management of the population as it expands beyond the boundaries of BSF. American black bears (Ursus americanus) were extirpated from the Cumberland Plateau in Tennessee and Kentucky in the late 19th to early 20th centuries due to habitat loss and overexploitation. After the Kentucky Department of Fish and Wildlife Resources, Tennessee Wildlife Resources Agency, and the National Park Service showed interest in reintroducing bears into Big South Fork National River and Recreation Area (BSF), Eastridge and Clark (2001) experimentally translocated 14 female black bears from the Great Smoky Mountains National Park to BSF from 1996 to 1997. In 2010–2012, a population estimate based on DNA extracted from hair samples collected at barbed wire hair traps revealed that the population expanded to 190 individuals in Tennessee and 38 in Kentucky. Based on the Tennessee estimate alone, this was an 18.3% annual increase since reintroduction. The bear population was thought to have expanded its range in the Cumberland Plateau since that estimate was conducted, so a more current estimate of bear density and abundance was needed across a wider spatial extent to direct future management of this population. American black bears (Ursus americanus) were extirpated from the Cumberland Plateau in Tennessee and Kentucky in the late 19th to early 20th centuries due to habitat loss and overexploitation. Eastridge and Clark (2001) experimentally translocated 14 female black bears from Great Smoky Mountains National Park to Big South Fork National river and Recreation Area (BSF) from 1996 to 1997. In 2010–2012, a population estimate based on DNA extracted from hair samples collected at barbed wire hair traps revealed that the population had expanded to 190 individuals in Tennessee and 38 in Kentucky. The population was thought to have expanded its range in the Cumberland Plateau, so an updated estimate of bear density and abundance was needed across a wider spatial extent to direct future management. I used spatially explicit capture-recapture (SECR) to estimate bear density and abundance within and surrounding BSF in northern Tennessee and southern Kentucky. Barbed-wire sampling stations (i.e., hair traps) were constructed in a 3- × 3-trap layout per cluster with 2 km between hair traps within a cluster and 16 km between cluster centers. I used DNA from hair samples obtained from hair traps to identify individual bears and establish genetic capture histories. I utilized spatial covariates to model inhomogeneous densities within the study area. Population abundance estimates across the 36,035-km2 study area were 436.2 males (95% CI = 234.1–812.5) and 450.9 females (95% CI = 295.0–689.1) for a total of 887.1 (95% CI 607.5–1,295.3) bears, excluding cubs. Average density estimates were 0.012 (95% CI = 0.007–0.023) male bears/km2 and 0.013 (95% CI = 0.008–0.020) female bears/km2, totaling 0.025 (95% CI = 0.017–0.037) bears/km2. The mean annual growth rate was 20.4% since 1998. Based on my population estimates, growth rates, and harvest reports, harvest rates in Kentucky averaged 4.2% from 2013 to 2019 ranging from 1.8% to 6.1% annually. In Tennessee, harvest rates from 2014 to 2019 averaged 12.2% ranging from 4.8% to 23.5%. Kentucky has seen greater population growth than Tennessee (31.1% and 15.0% respectively), possibly due to more restrictive harvest regulations and availability of contiguous forested federal lands

The Determinants and Impact of Property Rights: Land Titles on the Brazilian Frontier

This paper provides new empirical results regarding the demand and supply of title, its impact on land value, and its effects on agricultural investment on Brazilian frontiers. We use survey data from 1992 and 1993 from the state of Par  with data on the characteristics of the settlers, land tenure, land agencies involved, land values, and investment. We then turn to census data from the Brazilian agricultural census from 1940 through 1985, with observations at the municipio (county) level to examine the development of property rights to land in the southern state of Paran  during the agricultural boom between 1940 and 1970 and in the Amazon state of Par  during the period of rapid migration to the region after 1970. By examining frontiers we can follow the rise in land values, the increase in the demand for title, and the response of government. The empirical findings support the predictions of the theory regarding the effects of title and investment on land value, the role of expected change in value on demand for title, and the contribution of title in promoting investment. Governments, however, have not exactly followed the predictions of the analytical framework in supplying title. Political and bureaucratic factors play an important role in the government response to demands for title. This result suggests that researchers must pay special attention to the complex political process by which property rights are assigned in studying the emergence of tenure institutions.

Effects of graphite fiber stability on the properties of PMR polyimide composites

The effect of the stability of graphite fibers on composite properties after exposure in air at 600 F was investigated. Composites were fabricated from PMR-15 and PMR-2 monomer solutions, using HTS-2 and Celion 6000 graphite fibers as the reinforcement. The effect of long-term exposure in air at 600 F on composite weight loss and mechanical properties was determined. These composites exhibited a significantly increased lifetime at that temperature compared to composites fabricated from HTS fiber sold prior to 1975. The effect of the PMR-15 and PMR-II resin compositions on long-term composite performance at 600 F is also discussed

Master of Science

thesisStabilization of the head is critical for running. Homo sapiens possess several anatomical features that are useful for head stabilization. In order to test the functional value of some of these features, namely the location of the center of mass and the muscular connection between the skull and shoulder girdle, mechanical models are created. These mechanical models are representative of Homo sapiens and their ancestors. These models are subject to the kinematics and dynamics of a complete running gait cycle. The results show that the location of the center of mass for the Homo sapiens is superior to that of its ancestors for the purposes of head stabilization. Furthermore, the results show that the muscular connection between the skull and the shoulder girdle of Homo sapiens permit the counter rotation of the shoulders to reduce the energy needed to stabilize the head during running

Stability of PMR-polyimide monomer solutions

The stability of alcohol solutions of norborneyl capped PMR-polyimide resins was monitored during storage at ambient and subambient temperatures. Chemical changes during storage were determined spectroscopically using nuclear magnetic resonance. Resin processability and cured resin quality were determined by fabrication of unidirectional, graphite fiber composites using aged solutions and testing of selected composite properties. PMR-15 solutions exhibit nominally two weeks of useful life and PMR-2 solutions exhibit nominally two days of useful life at ambient conditions. The limiting factor is precipitation of imide reaction produces from the monomer solutions. Both solutions exhibit substantially longer useful lifetimes in subambient storage. PMR-15 shows no precipitation after several months storage at subambient temperatures. PMR-2 solutions do exhibit precipitates after extended subambient storage, however, the precipitates formed under these conditions can be redissolved. The chemical implications of these observations are discussed

The Effects of the Food Stamp Program on Energy Balance and Obesity

The Effects of the Food Stamp Program on Energy Balance and ObesityFood Stamp Program (FSP), Supplemental Nutrition Assistance Program (SNAP), obesity, body mass index (BMI), nutrition assistance, Food Consumption/Nutrition/Food Safety, Q18, H53, I12, I18, I38,

The Effects of the Food Stamp Program on Energy Balance and Obesity

The Food Stamp Program (FSP) administered by the U.S. Department of Agriculture (USDA) is the cornerstone of the U.S. federal income and food safety net policy. The FSP has subsidized the food budget for millions of American households for over forty years, spending more than $60 billion per year in recent times. Prior research has demonstrated that women who participate in the FSP are more likely to be overweight or obese than eligible non-participants. This finding raises the concern that the additional income provided by FSP benefits induces participants to eat significantly more calories and gain weight, contributing to the U.S. obesity epidemic. Previous studies of the FSP have yielded mixed results. In this study we develop new conceptual and empirical models linking FSP participation, calorie consumption, physical activity, and weight gain, while controlling for genetic variation, weight history, and other physiological characteristics of individuals. The models enable us to test whether participants gained more weight, ate more calories, or engaged less in physical activity; or if previously omitted variables and individual health characteristics explain the higher prevalence of obesity among female FSP participants. We find a positive relationship between FSP participation and weight gain for a small subset of women. We do not find convincing evidence for the hypothesis that FSP participation causes obesity by increasing caloric consumption, decreasing physical activity, or some combination of the two. Our findings suggest that a positive association between FSP and weight exists, but we find no evidence of a direct causal link from one to the other. The association between weight and FSP likely results from confounding factors that make individuals more likely both to gain weight and to participate in the FSP.Food Stamp Program (FSP), Supplemental Nutrition Assistance Program (SNAP), obesity, body mass index (BMI), nutrition assistance, Agricultural and Food Policy, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Health Economics and Policy, Q18, H53, I12, I18, I38,