This study examines the relationship between firm and facility characteristics and environmental compliance rates. A framework to help analyze this relationship is provided by deterrence theory which suggests that given the same level of government monitoring and enforcement, facilities with higher compliance costs will have lower compliance rates. The literature implies that firms and facilities with certain characteristics face higher costs to ensure compliance with regulations. For example, it has been proposed that plants that are part of large firms, multi-facility firms, or publicly traded firms will incur higher agency costs monitoring employees to make sure they are complying with regulations. Similarly, it is thought that large facilities and facilities located in a different state than the firms headquarters will also face higher agency costs. In addition, it is suggested that foreign-owned plants will confront higher costs developing the expertise to comply with domestic regulations. Understanding the nature of these costs and how they relate to firm and facility characteristics could assist policymakers with developing more targeted environmental compliance strategies. The current study uses data collected on a sample of chemical facilities to analyze whether these characteristics affect facility violation rates, as measured by compliance with air permits. The results suggest that plants with more employees and plants that are part of multi-facility firms are more likely to be out of compliance. Plants that are part of firms with out-of- state headquarters were unexpectedly found to have lower violation rates. None of the other firm and facility characteristics were found to be significant predictors of facility violation rates.

This dissertation reports the study of defects in Cadmium Zinc Telluride (CZT) and Cadmium Manganese Telluride (CMT) nuclear detectors. In this dissertation I studied the defects associated with surface processing of detectors as well as the extended defects present in the crystals. Synchrotron radiation, Infrared microscopy and Atomic Force Microscopy were employed to identify and study the defects. Detector response and performance from x-ray mapping and external sources was correlated with the observed defects. The Pockels electro-optic effect was used to observe non-uniformities of the internal electric field caused by defects. This collection of data was employed to produce a counting algorithm to show the expected performance of detectors based on sizes, concentration and distribution of inclusions. An optimal surface processing method combining polishing and chemical etching was established. Finally the first response of a CMT detector to high energy gamma radiation was demonstrated.

Electro-osmotic (EO) pumps directly convert electrical energy into fluids kinetic energy, which have many advantages such as a simple and compact structure, no mechanical moving parts, and easy integration. In general, it is easy for EO pumps to generate enough pressure but it has been a challenge for EO pumps to produce a high flowrate. EO pumps have found applications in various micro-/nano-electro-mechanical systems (MEMS/NEMS) and have the potential to impact a variety of engineering fields including microelectronics cooling and bio-analytical systems. This dissertation focuses on the design, fabrication and characterization of EO pumps based on two novel porous membrane materials: SiO2-coated anodic porous alumina and SiNx-coated porous silicon. High quality porous alumina membranes of controllable pore diameters in the range of 30-100 nm and pore lengths of 60-100 &181;m were fabricated by electrochemical anodization. The pores are straight, uniform and hexagonally close-packed with a high porosity of up to 50%. The inner surface of the pore was coated with a thin layer (~5 nm) of SiO2 conformally to achieve a high zeta potential. The EO pumping flowrate of the fabricated anodic alumina membranes, coated and uncoated, was experimentally measured. Results indicate that the high zeta potential of the SiO2 coating increases the pumping flowrate even though the coating reduces the porosity of the membrane. The nanostructured SiO2-coated porous anodic alumina membranes can provide a normalized flowrate of 0.125 ml/min/V/sq. cm. under a low effective applied voltage of 3 V, which sets a record high normalized flowrate under low applied voltage. To realize field effect control of EO pumping, we designed and fabricated SiNx-coated porous silicon membranes with the silicon core as the electrode to apply a transverse gate potential. The gate potential will modulate the zeta potential of the pore wall and thereby provide control over the EO flowrate. The membranes were fabricated out of heavily doped silicon wafers using microfabrication techniques. The pores have a 15 &181;m &215; 40 &181;m cross sectional area with a thin layer of SiNx coated conformally over the pores by low-pressure chemical vapor deposition (LPCVD). The range of gate voltages applied was from -45 V to +40 V. For Vg < 0, current leakage through the SiNx film was observed whereas negligible leaking current was detected for Vg > 0. This current rectification effect is known as electrolytic rectification, as a result of which a greater EO flow control, nearly 70% reduction in flow velocity, was observed for positive gate bias and 15% flow velocity enhancement under negative gate bias of similar magnitude. Ionic current is closely related to EO flow and the last part of the dissertation is devoted to ionic current measurements through commercially made nanoporous glass membranes (4 nm average pore diameter). This study was motivated by a molecular dynamics (MD) simulation highlighting an unusual ionic current trend in a 3 nm diameter pore having high surface charge density at high electrolyte concentrations. The ionic current was measured with two kinds of electrolytes NaCl and KCl. The experimental results, however, indicated an expected linear trend of ionic current for electrolyte concentrations beyond 1 M, contrary to the results of the MD simulation study, which was attributed to a low surface charge density measured for the porous glass membranes.

This dissertation develops and applies an integrated framework for embedding flexibility in an engineered system architecture. Systems are constantly faced with unpredictability in the operational environment, threats from competing systems, obsolescence of technology, and general uncertainty in future system demands. Current systems engineering and risk management practices have focused almost exclusively on mitigating or preventing the negative consequences of uncertainty. This research recognizes that high uncertainty also presents an opportunity to design systems that can flexibly respond to changing requirements and capture additional value throughout the design life. There does not exist however a formalized approach to designing appropriately flexible systems. <p>This research develops a three stage integrated flexibility framework based on the concept of architecture options embedded in the system design. Stage One defines an eight step systems engineering process to identify candidate architecture options. This process encapsulates the operational uncertainty though scenario development, traces new functional requirements to the affected design variables, and clusters the variables most sensitive to change. The resulting clusters can generate insight into the most promising regions in the architecture to embed flexibility in the form of architecture options. Stage Two develops a quantitative option valuation technique, grounded in real options theory, which is able to value embedded architecture options that exhibit variable expiration behavior. Stage Three proposes a portfolio optimization algorithm, for both discrete and continuous options, to select the optimal subset of architecture options, subject to budget and risk constraints. Finally, the feasibility, extensibility and limitations of the framework are assessed by its application to a reconnaissance satellite system development problem. Detailed technical data, performance models, and cost estimates were compiled for the Tactical Imaging Constellation Architecture Study and leveraged to complete a realistic proof-of-concept.

White light-emitting diodes (LEDs) have attracted great interest recently due to their capability for higher efficiency and longer lifetimes compared to other current lighting technologies. In pursuit of a white LED that has improved characteristics over commercial white LEDs, the focus of this dissertation is on the optical properties of white-light emitting cadmium selenide (CdSe) nanocrystals. Phosphor-based LEDs typically require an encapsulant to protect the phosphor from heating and photo-oxidation, as well as to inhibit particle aggregation. In this dissertation, a number of encapsulant materials were tested to determine which material would mix well with the nanocrystals in solution before deposition, cure properly as a film, and maintain the optical properties of the CdSe nanocrystals. A biphenylperfluorocylcobutyl (BP-PFCB) polymer performed the best of the encapsulants tested, with over twice the emission intensity of the next best encapsulant as well as a much higher percentage of UV excitation light absorbed at a certain thickness. In addition, several methods to improve the device efficiency of these LEDs were investigated, including experimentally optimizing the LED excitation wavelength, film thickness, and nanocrystal concentration in the film. The optimum device parameters were found to be a 365 nm or 385 nm LED exciting a film of 60-140 μm in thickness with a nanocrystal weight concentration in BP-PFCB of 10%, resulting in a luminous efficacy of 1 lm/W, CIE coordinates of (0.35, 0.37), and a color rendering index (CRI) of 86. Furthermore, while scattering from micron-sized phosphors used in LEDs can cause significant losses, the scattering cross section for ultrasmall CdSe nanocrystals was found to be five orders of magnitude lower than the absorption cross section, thus scattering from nanocrystals can be neglected. Finally, a more accurate approach to determining the nanocrystal concentration of a solution and extinction coefficient was investigated. These results represent the initial steps towards building an ultrasmall CdSe nanocrystal-based, photoluminescent LED, and with further improvements could result in higher quality lighting products.

The oxides of rare-earth elements (rare-earth sesquioxide: RE2O3) are known for their optical and dielectric properties. Europium oxide is known for characteristic red luminescence and gadolinium oxide has excellent insulating properties (band gap: 5.5 eV). Development of ultra-small nanocrystals (sub-3 nm diameter) of these rare-earth oxides and investigation of their optical and dielectric properties are explored in this dissertation. A new synthesis process was developed successfully to produce ultra-small colloidal nanocrystals, which were capped with oleic acid. Europium oxide nanocrystals exhibited a new luminescence peak because of the occupation of Eu3+ ions in a surface site. The nanocrystals were assembled into films from their suspensions in hexane by electrophoretic deposition. Films of europium oxide were highly transparent in visible spectral region because of minimal scattering losses within the films and exhibited characteristic red luminescence. Gadolinium oxide nanocrystals exhibited charge-storage properties when integrated in a metal-insulator-semiconductor structure. Layered heterostructures of carbon nanotubes and nanocrystals were fabricated and their charge-storage properties were studied.

The operation and properties of semiconductor devices depends critically on a materials electronic structure. Point defects, such as vacancy and interstitial defects that arise from operation in radiative atmospheres or during less-than-ideal growth processes, have a significant influence on electronic material properties and tend to degrade device operation. Here we show that a novel ultrafast time-resolved pump-probe technique, known as coherent acoustic phonon spectroscopy, is capable of non-destructive, quantitative, depth-dependent measurement of point defect profiles arising from ion irradiation in gallium arsenide. In the CAP response, defects are observable through reduction of the CAP oscillation amplitude, which is demonstrated to be connected to a decrease in the photoelastic constant at the 1.42 eV GaAs band-edge caused by defect-induced lattice strain. Finally, we present theoretical calculations that support our proposed model and agree well with experimental observations

Multiple sclerosis (MS) is characterized as an autoimmune neurodegenerative disease. The disease manifests as demyelination or degradation of the myelin sheath in the central nervous system. The Major Histocompatibility Complex (MHC) was associated with MS in the mid-1970s; the association was later refined to the HLA-DRB1*1501-DQB*0602 haplotype. The MHC region is riddled with complicating factors including high gene content, extreme levels of polymorphism, and a dense pattern of linkage disequilibrium (LD). These characteristics make this region difficult for differentiating whether a single allele or an entire haplotype contributes to disease association. Despite these challenges it is clear that the MHC region harbors MS susceptibility loci in addition to the HLA-DRB1*1501 region. Using the strong LD in this region we can test a model that predicts residual odds ratios (ORs) for a marker in LD with a disease allele such as HLA-DRB1*1501. Comparing the correlation between the observed OR and the calculated OR for multiple SNPs in the MHC region, we hypothesize those SNPs that appear as outliers are suggestive of additional effects independent from the HLA-DRB1*1501 region. We examined ~2,300 SNPs in 1,479 cases and 1,482 controls in the 28 Mb to 36 Mb region on chromosome 6 containing the MHC. The ORs for the SNPs were grouped based on the amount of LD with the HLA-DRB1 surrogate SNP (rs3135388). We identified nine outlying SNPs, which had observed ORs much larger than the calculated OR. These nine SNPs are in six different genes that suggest susceptibility to MS independent of HLA-DRB1*1501.

The monoamine neurotransmitter serotonin (5-HT) is an essential component of vertebrate cognitive function and the autonomous nervous system, regulating body temperature, sleep, appetite, and mood. Abnormal 5-HT signaling is implicated in a variety of disorders such as depression, anxiety, alcoholism, and obsessive-compulsive disorder. Synaptic serotonergic activity is primarily regulated by the recycling of 5-HT from the synaptic cleft by the presynaptic 5-HT transporter (SERT), a target for many psychostimulants and anti-depressants such as MDMA (Ecstasy) and Fluoxetine (Prozac). In the model system Caenorhabditis elegans (C. elegans), 5-HT is an active participant in a variety of motor, autonomic, and behavioral functions including egg-laying, pharyngeal pumping, locomotion, male mating, aging, and enhanced slowing. The goal of this work is to use the C. elegans model system to manipulate the SERT homolog (MOD-5) and examine regulatory genes controlling MOD-5 trafficking, localization, and activity. We characterized the behavioral phenotypes of endogenous 5-HT activity in C. elegans and in 5-HT transporter deletion mutants, especially those pertaining to locomotor function. We also describe a novel, food dependent immobilization phenotype and use genetic and pharmacological approaches to establish the role of 5-HT and MOD-5 within this phenotype. These techniques provide the necessary tools for use of this phenotype as the basis for a forward genetic screen which will provide unbiased assessments of transporter regulatory molecules. This work provides the foundation for elucidation of proteins that regulate determinants of serotonin transporter function and support normal serotonin transporter activity.

The goal of this work was to determine the luminescent lifetime of these phosphor materials as a function of temperature. Cerium-doped yttrium aluminum garnet and europium-doped pyrochlores were synthesized using combustion synthesis. The phosphors were characterized using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Lifetime measurements were taken over a range of temperatures. The garnet materials exhibited thermal quenching between 30-125 ◦ C . In contrast, the pyrochlore materials did not exhibit thermal quenching until well past 300 ◦ C . The results presented in this work have shown that high energy states, such as the charge transfer state or the d -orbitals, play a key role in the thermal quenching properties of materials. For Ce-doped materials, our results indicate that materials which cause the splitting of the d -orbitals to increase will cause the emission from the d1 → 4 f transition to thermally quench at higher temperatures. The lifetime of the 5 D0 → 4 f emission line of Eu3+ is dependent on the location of the charge transfer state. We suggest that the reason higher quenching temperature are observed in materials such as YBO3 : Eu and the other pyrochlores is because these materials have high-energy charge transfer states. Tuning Eu3+ materials to maximize the energy of the charge transfer state may improve thermal quenching properties of thermographic phosphors.