The knowledge of particle size and size distribution are important parameters for understanding the behavior of numerous colloid systems. These areas include for example, clays, viruses, paints and blood. Until recently this information could be obtained only by the use of expensive, slow and complex instrumentation. Hydrodynamic chromatography provides a means of investigating particles in the submicron and micron region. The separation mechanism of this method is based upon the flow parameters with which the solute particles interact as they pass through a packed column. In the past the interpretation of these chromatograms has been based upon the mathematical modeling of the column parameters. We have developed a new multiwavelength detector system to be used in conjunction with hydrodynamic chromatography which provides size and concentration information of the eluant directly. The result is a rugged system that provides size and size distribution information rapidly and at low cost. / Ph. D.

Consumers rely on sources of information to learn about products and make informed purchasing decisions. In fact, one of the first factors consumer consider when evaluating product information, is the source of that information. Yet despite the importance of the source, research on this topic is sporadic, leaving my unanswered questions. This dissertation advances our understanding of how three different sources of information influence consumers' perceptions and decision making. In the first study, we examine two sources (consumer originated and third party) to determine which one dominates in a persuasion episode. We find consumers overwhelmingly prefer consumer originated versus third party sources because they believe fellow consumers convey information that is diagnostic of future product experiences. In our second study, we show how a subtle firm-dominated characteristic, firm size, influences manufacturing assumptions and purchase behavior. We find consumers prefer small to large firms for unique products, because they assume small firms have a high degree of human intervention in the manufacturing process. / Doctor of Philosophy / Consumers rely on sources of information to learn about products and make informed purchasing decisions. In fact, one of the first factors consumer consider when evaluating product information, is the source of that information. Yet despite the importance of the source, research on this topic is sporadic, leaving my unanswered questions. This dissertation advances our understanding of how three different sources of information influence consumers' perceptions and decision making. In the first study, we examine two sources (consumer originated and third party) to determine which one dominates in a persuasion episode. We find consumers overwhelmingly prefer consumer originated versus third party sources because they believe fellow consumers convey information that is diagnostic of future product experiences. In our second study, we show how a subtle firm-dominated characteristic, firm size, influences manufacturing assumptions and purchase behavior. We find consumers prefer small to large firms for unique products, because they assume small firms have a high degree of human intervention in the manufacturing process.

The beef cattle industry has placed increased focus on mature cow size as a result of its influence on production efficiency and profitability. The objectives of this study were to evaluate relationships among lifetime measures of body weight (BW) and frame score (FS) in commercial beef females, and to assess the value of immature measures as predictors of mature cow size. Measurements of BW, hip height (HH), body condition score (BCS), and calculated FS were recorded at weaning (WN), breeding at 13 mo age (BR), and 8 subsequent periods, ceasing at approximately 5 yr of age for 232 Angus-cross females born 2004 through 2008. Correlation analysis revealed significant (P < 0.001) relationships among BW taken at WN and BR with BW measurements taken at 2.5, 3.8, and 4.8 yr of age (WN r = 0.70, 0.51, 0.61; BR r = 0.65, 0.57, 0.64, respectively). Significant relationships (P < 0.001) existed between FS collected at WN and BR, and FS at 2.5 and 3.8 yr (WN= 0.70, 0.72; BR= 0.79, 0.82, respectively). Repeatability of lifetime FS measures was 0.73. BCS was a significant (P < 0.001) source of variation in mature BW, with a unit change in BCS accounting for 41 kg BW change at 4.8 yr (P < 0.001). BW and FS were moderately to strongly related (P < 0.001) at WN, BR, 2.5, 3.8, and 4.8 yr (r = 0.62, 0.49, 0.62, 0.62, and 0.47 respectively). Prediction models for BW at 4.8 yr were similar using weaning BW alone, or with inclusion of both weaning BW and HH (R2 = 0.57 and 0.56). Similarly, breeding BW and HH were non-additive for prediction of 4.8 yr BW (R2 = 0.68, 0.58, and 0.68 for BW, HH, and BW +HH respectively). Performance at immature ages proves to be a satisfactory indicator of mature size, supporting continued incorporation of immature BW and HH and/or FS measurements into selection practices. / Master of Science

Threshold leak sizes and leak rates were calculated for a number of liquid food products exhibiting a wide range of surface tension and viscosity values. From this data, one can see that mathematically, under typical pressure differentials generated in food packages (less than or equal to ±34.5 kPa), a leak will never start through a 2 μm defect. The calculated leak rates were compared to calculated evaporation rates. The evaporation rate exceeds the leak rate at lower sized microholes (2, and 5 μm diameter) under typical pressure differentials found in food packages. If the liquid, typically aqueous in food products, is evaporating off faster than the leak itself, then there will be solids left behind that could effectively plug the leak. The critical leak size is the size micro-defect that allows microbial penetration into the package. The critical leak size of air-filled defects was found to be 7 μm at all pressures tested. This size is considerably important to food packagers because this is when sterility of the package is lost. Previous leak studies have shown that the critical leak size for liquid-filled defects coincide with the threshold leak size and pressure. If this is in fact true, then air-filled defects should exhibit a larger critical leak size than the liquid-filled defects. In this study, air-filled defects were examined. A bioaerosol exposure chamber was used to test micro-defects, nickel microtubes of known diameters 2, 5, 7, 10, 20, and 50 μm hydraulic diameters, against pressure differentials of 0, -6.9, -13.8, and -34.5 kPa. / Master of Science

Ammonium ionenes are macromolecules with quaternized nitrogen groups in the main chain. Ionenes are commonly referred to as x,y-ionene, where x and y represent the number of methylene groups between quaternized nitrogens. Synthesis of aliphatic ammonium ionenes has been studied since the early twentieth century; however, absolute molecular weight characterization has only been performed using extensive light scattering and viscosity experiments. Performing aqueous size exclusion chromatography (SEC) on ammonium ionenes provides absolute molecular weight determinations while eliminating the need for separate viscosity and light scattering experiments. We developed a mobile phase composition that provides reliable separation of aliphatic ammonium ionenes using aqueous SEC. For the first time, we report absolute molecular weights of aliphatic ammonium ionenes using this technique. We investigated the influence of charge density and structural symmetry on thermal and mechanical properties of ammonium 6,6-, 12,6- and 12,12-ionenes. Thermal properties were measured using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and mechanical properties were measured using dynamic mechanical analysis (DMA) and an Instron. Incorporating low molecular weight polymer segments into the main chain of the ionene allows tailoring of polymer characteristics. Poly (tetramethylene oxide) segments decrease hydrophilicity and increase elastomeric character. Linear PTMO based ionenes have been synthesized previously, and we were interested in how branching affected thermal and mechanical properties. We synthesized bis(dimethylamino) poly(tetramethylene oxide) segments, and subsequently, synthesized linear and branched ionenes to study the effects of topology on thermal and mechanical properties. Polymers were analyzed using DMA, DSC, TGA, SAXS, and an Instron. / Master of Science

Barriers to fish movement can cause aquatic habitat fragmentation by reducing the amount of available habitat. The primary goal of my research was to investigate applications of population genetic analysis tools as indicators of barrier effects on brook trout populations in fragmented subwatersheds. In chapter1, I tested the hypothesis that brook trout population genetic differentiation (FST) above and below barriers will differ in relation to barrier height and gradient. I also tested the hypothesis that average gene diversity per locus (H) and the numbers of alleles (A) differed between samples below and above each barrier. There was no significant difference in average number of alleles (A) or average gene diversity per locus (H) between the above- and below-barrier samples, but linear regression identified a statistically significant relationship between barrier height and FST values. Unrooted neighbor-joining consensus trees of Cavalli-Sforza and Edwards (1967) chord distances provided evidence of genetic differentiation between samples of resident brook trout above and below natural barriers. Additionally, average total allelic diversity (A), average gene diversity per locus (H), average number of private alleles per locus per sample, and total alleles per sample differed between Level III Ecoregions. In chapter 2 I tested the hypothesis that the presence of a barrier, total habitat potentially isolated above a barrier (km), road density, and percent forest cover within a subwatershed (USGS 6th-level Hydrologic Units) were significant habitat fragmentation factors affecting the effective population size (Ne) of brook trout in the Blue Ridge Level III Ecoregion. Multivariable linear regression indicated that total habitat above the barrier (km) and road density were significant variables retained in the model to predict Ne. In chapter 3, the objective of the study was to infer relationships between barriers and family structure in brook trout populations. Maximum likelihood analysis of pairwise kinship relationships between above- and below-barrier individuals indicated the presence of parent-offspring relationships between above- and below-barrier individuals at six sites in the Blue Ridge Level III Ecoregion and five sites in the Northern Lakes and Forests Level III Ecoregion, which indicated movement of individuals between the above- and below-barrier locations. / Ph. D.

Local school districts throughout the country are experiencing declining enrollment, frequently resulting in the need to close elementary schools. Often, the decision on which school to close is dependent on the size (enrollment) of the schools being considered. The purpose of this study was to examine the relationship between size of elementary school and academic achievement. The sample used in this study was composed of grade 3 and 5 students in the Montgomery County (Maryland) Public Schools who were administered the Iowa Tests of Basic Skills and Cognitive Abilities Test during the 1977-78 school year and attended an elementary school with grades K-6 (approximately 13,000 pupils). Vari.ables which have been found in previous studies to have a relationship with achievement were employed in this study as control variables. These were aptitude, percentage of low-income pupils, race, sex, highest degree status of professional staff, years of experience of teachers, and class size. The statistical methodology employed in this study was multiple regression analysis. This technique was selected to evaluate the contribution of a single variable, school size, to academic achievement while controlling for other, confounding variables. Twelve multiple regression analyses were conducted--one for each of the five Iowa Tests of Basic Skills major skill areas (vocabulary, reading comprehension, language skills, work-study skills, and mathematics skills) and composite scores for both grades 3 and 5. It was found, for all the analyses that elementary school size did not make a significant contribution to the variance in academic achievement. Also, on the basis of the data available and for the students tested, it was concluded that there is no elementary school size which maximizes academic achievement, nor is there a minimum or maximum elementary school size beyond which academic achievement is adversely affected. Therefore, it was recommended that the decision on which elementary school(s) to close should not rest on a perceived relationship between school size and academic achievement. Other factors, such as financial considerations, transportation implications, and utilization and condition of the school plant, should be of primary concern. / Ph. D.

Despite formidable advances in virology and medicine in recent decades, we know remarkably little about the dynamics of the influenza virus in the environment during transmission between hosts. There is still controversy over the relative importance of various transmission routes, and the seasonality of influenza remains unexplained. This work focuses on developing new knowledge about influenza transmission via the airborne route and the virus' inter-host dynamics in droplets and aerosols. We measured airborne concentrations of influenza A viruses (IAVs) and size distributions of their carrier aerosols in a health center, a daycare center, and airplanes. Results indicate that the majority of viruses are associated with aerosols smaller than 2.5 µm and that concentrations are sufficient to induce infection. We further modeled the fate and transport of IAV-laden droplets expelled from a cough into a room, as a function of relative humidity (RH) and droplet size. The model shows that airborne concentrations of infectious IAV vary with RH through its influence on virus inactivation and droplet size, which shrinks due to evaporation. IAVs associated with large droplets are removed mostly by settling, while those associated with aerosols smaller than 5 µm are removed mainly by ventilation and inactivation. To investigate the relationship between RH and influenza transmission further, we measured the viability of IAV in droplets at varying RHs. Results suggest that there exist three regimes defined by RH: physiological conditions (~100% RH) with high viability, concentrated conditions (~50% to ~99% RH) with lower viability, and dry conditions (<~50% RH) with high viability. A droplet's extent of evaporation, which is determined by RH, affects solute concentrations in the droplet, and these appear to influence viability. This research considerably advances the current understanding of the dynamics of the influenza virus while it is airborne and provides an explanation for influenza's seasonality. Increased influenza activity in winter in temperate regions could be due to greater potential for IAV carrier aerosols to remain airborne and higher viability of IAV at low RH. In tropical regions, transmission could be enhanced due to better survival of IAV at extremely high RH. / Ph. D.

Cellular processes critical to sustaining physiology, including growth, division and differentiation, are carefully governed by intricate control systems. Deregulations in these systems often result in complex diseases such as cancer. Hence, it is crucial to understand the interactions between molecular players of these control systems, their emergent network dynamics, and, ultimately, the overall contribution to cellular physiology. In this dissertation, we have developed a mathematical framework to understand two such cellular systems: an early checkpoint (START) in the budding yeast cell cycle (Chapter 1), and the canonical Wnt signaling pathway involved in cell proliferation and differentiation (Chapter 2). START transition is an important decision point where the cell commits to one round DNA replication followed by cell division. Several years of experimental research have gone into uncovering molecular details of this process, but a unified understanding is yet to emerge. In chapter one, we have developed a comprehensive mathematical model of START transition that incorporates several findings including information about the phosphorylation state of key START proteins and their subcellular localization. In the second chapter, we focus on modeling the canonical Wnt signaling pathway, a cellular circuit that plays a key role in cell proliferation and differentiation. The Wnt pathway is often deregulated in colon cancers. Based on some evidence of bistability in the Wnt signaling pathway, we proposed the existence of a positive feedback loop underlying the activation and inactivation of the core protein complex of the pathway. Bistability is a common feature of biological systems that toggle between ON and OFF states because it ensures robust switching back and forth between the two states. To study and explain the behavior of this dynamical system, we developed a mathematical model. Based on experimentally determined interactions, our simple model recapitulates the observed phenomena of bimodality (bistability) and hysteresis under the effects of the physiological signal (Wnt), a Wnt-mimic (LiCl), and a stabilizer of one of the key members of core complex (IWR-1). Overall, we believe that cell biologists and molecular geneticists can benefit from our work by using our model to make novel quantitative predictions for experimental verification. / Ph. D.

The purpose of this inquiry was to determine if specific situational factors influence the manner in which number of children affect family life quality. Situational factors examined were: congruence between ideal number of children and actual; and secondly, expressed differences in family life quality by sex given similar conditional influences. Data were drawn from five recent U.S. national surveys. Sample one, which was used in examining the congruence concept, contained 778 individuals. The sample was divided into four groups, each represented varying degrees and direction of congruence between ideal number of children and actual. Dunn-Bonferroni a priori comparisons were used to compare mean family life satisfaction scores for selected groups. Findings indicated that differing degrees of congruence between ideal and actual number of children did not affect family life quality. A second sample of 1091 respondents was used to determine if women with young children reported lower family life satisfaction than comparable males. A t-test showed significant differences existed between males and females if a young child was present in the home. These findings indicate that young children have a detrimental effect on perceived family life quality for females. The two situational factors examined indicate that degree and direction of congruence between ideal and actual number of children does not influence family life quality. Secondly, young children inhibit perceived family life satisfaction among females. / Master of Science