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The relative fission yields of the isotopes of krypton and xenon have been determined mass spectrometrically. Abnormal fission yields, resulting in fine structure in the mass fission yield curve, have been found in both mass ranges. A shift of the fine structure to lower masses has been observed in going from U^235 + n fission to U^238 + n fission. From this shift in fine structure, it has been possible to determine the proportion of U^235 and U^236 neutron fission that have occurred in the sample. Evidence is presented to show that the observed fine structure and the shift in this fine structure is the result of a combination of two effects involved the extra stability of closed neutron shells of 50 and 82 neutrons which fall in the Kr and Xe ranges respectively. The capture of thermal neutrons by Xe^135, which modifies the fission yields in the 135 and 136 mass chains, has been studied so that the observed fission yields at these masses may be suitably corrected. Finally, the branching ratio between the isomeric states of Kr^85 and the half-life of the long-lived isomer have been re-determined and found to be 0.29 and 10.27 ± 0.18 yrs. respectively. / Thesis / Doctor of Philosophy (PhD)

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Despite the fact that most firms are late entrants in any product market, research on how to achieve a late-mover advantage is limited and lags behind the theoretical work on first-mover advantage. The strategic choice a late mover can utilize to compete against the pioneer is largely underdeveloped. Further, extant studies provide contradictory arguments and predictions regarding the efficacy of two basic late entry strategies: an enhancing strategy (providing a late entrant with enhanced features along existing product attributes) and a distinctive strategy (adding new or unique features to a late entrant' offering). The goal of this dissertation is to better understand the underlying behavioral mechanisms that enable a late entrant to compete with a successful pioneer and thereby address this inconsistency in the literature. Taking a category-based learning perspective, it is proposed that new brands are learned through a comparison process with existing brands. In the process, common features are evaluated in a category-based mode while unique features are processed in a piecemeal fashion. Two behavioral mechanisms are identified — discrepancy effects (i.e., perceived differentiation) which add to the late entrant's visibility and attractiveness, and ambiguity effects (comparison difficulty and perceived performance risk) that lessen the late entrant's attractiveness. Product category familiarity is proposed as the key moderator that affects the salience of each behavioral mechanism and hence the effectiveness of late entry strategies. Three experiments were designed to test the proposed perspective. It was found that common features are the focus of comparison in unfamiliar product classes and unique features receive particular attention in familiar product classes. Accordingly, ambiguity effects become more salient in unfamiliar product categories while differentiation effects are more prominent in familiar product cases. Further, a distinctive strategy is both more differentiated and more ambiguous than an enhancing strategy. Thus, a distinctive strategy is more effective in a familiar product class due to its attention-grabbing nature. An enhancing strategy is more successful in a novel or unfamiliar product class because of low levels of ambiguity. These findings provide important implications for product entry and positioning strategies as well as for further research. / Ph. D.

Over the last decade, rapidly growing world energy consumption is leading to supply difficulties, exhaustion of fossil energy resources, and global environmental deterioration. More than one-third of energy expenditure is attributable to buildings. Urbanization is intensifying these trends with tighter spatial interrelationships among buildings. This is escalating building energy consumption due to the mutual impact of buildings on each other and, as a result, exacerbating Urban Heat Island (UHI) effects. I sought solutions to this significant engineering issue from nature, and discovered a similar heat island effect in flowers, namely the micro-greenhouse effect. However, a special cooling effect has been observed in a peculiar temperate flower, Galanthus nivalis, which generates cooler intrafloral temperatures. In this research, I studied the special retro-reflectance of the flower petals, which has been suggested as a possible contributor to this cooling effect, and implemented a bio-inspired retro-reflective pattern for building envelopes. I conducted cross-regional energy simulation of building networks in a dynamic simulation environment in order to examine its thermal-energy impact. I found that building surface temperatures dropped considerably when neighboring buildings were retrofitted with my bio-inspired retro-reflective facade. I concluded that my bio-inspired retro-reflective pattern for building envelopes; (1) lessens the reflected heat of solar radiation in spatially-proximal buildings leading to reduced UHI, and (2) reduces the energy required for cooling and, therefore, energy consumption. The research has further implications and contributions on building design, urban planning, development of retro-reflective technology, and environmental conservation. / Master of Science

The environmental fate and transport of engineered nanomaterials have been broadly investigated and evaluated in many published studies. Silver nanoparticles (AgNPs) represent one of the most widely manufactured nanomaterials. They are currently being incorporated into a wide range of consumer products due to their purported antimicrobial properties. However, either the AgNPs themselves or dissolved Ag+ ions has a significant potential for the environmental release. The safety issues for nanoparticles are continuously being tested because of their potential danger to the environment and human health. Studies have explored the toxicity of AgNPs to a variety of organisms and have shown such toxicity is primarily driven by Ag+ ion release. Dissolution of nanoparticles is an important process that alters their properties and is a critical step in determining their safety. Therefore, studying nanoparticles' dissolution can help in the current move towards safer design and application of nanoparticles. This research endeavor sought to acquire comprehensive kinetic data of AgNP dissolution to aid in the development of quantitative risk assessments of AgNP fate. To evaluate the dissolution process in the absence of nanoparticle aggregation, AgNP arrays were produced on glass substrates using nanosphere lithography (NSL). Changes in the size and shape of the prepared AgNP arrays were monitored during the dissolution process by atomic force microscopy (AFM). The dissolution of AgNP is affected by both internal and external factors. First, surface coating effects were investigated by using three different coating agents (BSA, PEG1000, and PEG5000). Capping agent effects nanoparticle transformation rate by blocking reactants from the nanoparticle surface. Coatings prevented dissolution to different extents due to the various way they were attached to the AgNP surface. Evidence for the existence of bonds between the coating agents and the AgNPs was obtained by surface enhanced Raman spectroscopy. Moreover, to study the size effects on AgNP dissolution, small, medium, and large sized AgNPs were used. The surrounding medium and temperature were the two variables that were included in the size effects study. Relationships were established between medium concentration and dissolution rate for three different sized AgNP samples. By using the Arrhenius equation to plot the reaction constant vs. reaction temperature, the activation energy of AgNPs of different sizes were obtained and compared. / Doctor of Philosophy / Nanomaterials, defined as materials with at least one characteristic dimension less than 100 nm, often have useful attributes that are distinct from the bulk material. The novel physical, chemical, and biological properties enable the promising applications in various manufacturing industry. Silver nanoparticles (AgNPs) represent one of the most widely manufactured nanomaterials and has been used as the antimicrobial agent in a wide range of consumer products. However, either the AgNPs themselves or dissolved Ag+ ions has a significant potential for the environmental release. The environmental fate and transport of AgNPs drawn considerable attentions because of the potential danger to environment and human health. Dissolution of nanoparticles is an important process that alters their properties and is a critical step in determining their safety. Ag+ ions migrate from the nanoparticle surface to the bulk solution when an AgNP dissolves. Studying nanoparticles' dissolution can help in the current move towards safer design and application of nanoparticles. This research aimed to acquire comprehensive kinetic data of AgNP dissolution to aid in the development of quantitative risk assessments of AgNP fate. AgNP arrays were produced on glass substrates using nanosphere lithography (NSL) and changes in the size and shape during the dissolution process were monitored by atomic force microscopy (AFM). First, surface coating effects were investigated by using three different coating agents. Coatings prevented dissolution to different extents due to the various way they were attached to the AgNP surface. Moreover, small, medium, and large sized AgNPs were used to study the size effects on AgNP dissolution. The surrounding medium concentration and temperature were the two variables that were included in the size effects study.