Theses and Dissertations - Department of Physics & Astronomy

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Browsing Theses and Dissertations - Department of Physics & Astronomy by Author "Bakker, Martin G."

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    Bacterium E. coli- and phage P22-templated synthesis of semiconductor nanostructures
    (University of Alabama Libraries, 2010) Shen, Liming; Gupta, Arunava; University of Alabama Tuscaloosa
    The properties of inorganic materials in the nanoscale are found to be size- and shape-dependent due to quantum confinement effects, and thereby nanomaterials possess properties very different from those of single molecules as well as those of bulk materials. Assembling monodispersed nanoparticles into highly ordered hierarchical architectures is expected to generate novel collective properties for potential applications in catalysis, energy, biomedicine, etc. The major challenge in the assembly of nanoparticles lies in the development of controllable synthetic strategies that enable the growth and assembly of nanoparticles with high selectivity and good controllability. Biological matter possesses robust and precisely ordered structures that exist in a large variety of shapes and sizes, providing an ideal platform for synthesizing high-performance nanostructures. The primary goal of this thesis work has been to develop rational synthetic strategies for high-performance nanostructured materials using biological templates, which are difficult to achieve through traditional chemical synthetic methods. These approaches can serve as general bio-inspired approaches for synthesizing nanoparticle assemblies with desired components and architectures. CdS- and TiO_2 -binding peptides have been identified using phage display biopanning technique and the mechanism behind the specific affinity between the selected peptides and inorganic substrates are analyzed. The ZnS- and CdS-binding peptides, identified by the phage display biopanning, are utilized for the selective nucleation and growth of sulfides over self-assembled genetically engineered P22 coat proteins, resulting in ordered nanostructures of sulfide nanocrystal assemblies. The synthetic strategy can be extended to the fabrication of a variety of other nanostructures. A simple sonochemical route for the synthesis and assembly of CdS nanostructures with high yield under ambient conditions has been developed by exploiting the chemical characteristics and structure of permeabilized E. coli bacteria. The crystal phase, morphology, micro/nanostructure, optical absorption, and photocatalytic properties of the CdS nanostructures are tailored over a wide range by merely changing the synthetic conditions. Photoanodes fabricated using the nanoporous hollow CdS microrods exhibit excellent performance for the photocatalytic hydrogen production. This facile approach has been extended to the synthesis and assembly of other semiconducting sulfides, including PbS, ZnS, and HgS.
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    A Monte Carlo approach to 7Be solar neutrino analysis with KamLAND
    (University of Alabama Libraries, 2012) Grant, Christopher; Piepke, Andreas; University of Alabama Tuscaloosa
    Terrestrial measurements of neutrinos produced by the Sun have been of great interest for over half a century because of their ability to test the accuracy of solar models. The first solar neutrinos detected with KamLAND provided a measurement of the ^8B solar neutrino interaction rate above an analysis threshold of 5.5 MeV. This work describes efforts to extend KamLAND's detection sensitivity to solar neutrinos below 1 MeV, more specifically, those produced with an energy of 0.862 MeV from the ^7Be electron-capture decay. Many of the difficulties in measuring solar neutrinos below 1 MeV arise from backgrounds caused abundantly by both naturally occuring, and man-made, radioactive nuclides. The primary nuclides of concern were ^210Bi, ^85Kr, and ^39Ar. Since May of 2007, the KamLAND experiment has undergone two separate purification campaigns. During both campaigns a total of 5.4 ktons (about 6440 m^3) of scintillator was circulated through a purification system, which utilized fractional distillation and nitrogen purging. After the purification campaign, reduction factors of 1.5 x 10^3 for ^210Bi and 6.5 x 10^4 for ^85Kr were observed. The reduction of the backgrounds provided a unique opportunity to observe the ^7Be solar neutrino rate in KamLAND. An observation required detailed knowledge of the detector response at low energies, and to accomplish this, a full detector Monte Carlo simulation, called KLG4sim, was utilized. The optical model of the simulation was tuned to match the detector response observed in data after purification, and the software was optimized for the simulation of internal backgrounds used in the ^7Be solar neutrino analysis. The results of this tuning and estimates from simulations of the internal backgrounds and external backgrounds caused by radioactivity on the detector components are presented. The first KamLAND analysis based on Monte Carlo simulations in the energy region below 2 MeV is shown here. The comparison of the Δχ^2 between the null hypothesis and the existence of the ^7Be solar neutrino signal in the data shows a change of 27.9 units, providing evidence that the signal is statistically favored. This analysis reports a measured interaction rate from ^7Be solar neutrinos of R = 343.3 ± 65.0(stat) ± 99.2(syst) events/(kton·day), which corresponds to a total flux of ɸ = (3.41 ±; 1.18) x 10^9 cm^-2 s^-1. The ^7Be solar neutrino flux reported in this work is only the second measurement made of this quantity worldwide. It provides an important cross-check of the Borexino experiment. The flux measurement reported here agrees within 1σ with the standard solar model predictions thus validating our basic understanding of solar fusion reaction processes.
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    Theory and practice of brine processing by industrial-scale magnetic ion polarization and optimization of personal-scale passive solar desalination
    (University of Alabama Libraries, 2010) Wofsey, Michael Henry; Tipping, Richard H.; University of Alabama Tuscaloosa
    In the first section of this work we hope to add to the science of brine management in desalination. We have undertaken a feasibility analysis of a method of brine processing where the ions in solution are transported by an axial magnetic field in a long pipe, and an off-center cross-section of the flow is extracted with a lower ion concentration than that near the edges of the pipe. We constructed an apparatus that examines this process and allows us to measure the change in voltage in a solution during treatment. The goal of this process is to separate brine effluent from the desalination system into two components; one close to ocean water which can be safely injected back into the ocean or reprocessed into potable water using standard desalination techniques. The second component will have an ion concentration higher than typical waste brine, and can be more economically treated using a conventional process such as an evaporation pond or solar drying. This research addresses an emerging problem, the Achilles' heel of large-scale desalination. Specifically, systems for municipal-sized water demands can produce desalinated water in quantities exceeding a million liters per day. A basic mass balance shows that all the freshwater that is extracted from seawater will leave a nearly equal quantity of high-salt brine. Ejected brine from commercial-scale desalination facilities has been shown to cause distress and damage to marine organisms and possibly even saline gradient inversions, which lead to unpredictable solar heating of littoral ocean waters. In the second section of this work we add to the general knowledge of the science of solar desalination. We have used common and straightforward measurement techniques, physical analyses and quantitative analyses to optimize efficient methods of personal-scale solar desalination. In this research we have used simple modifications to stills of our own design that increase efficiency and output of distilled water. We also examine a theoretical efficiency model that may be useful in determining the efficiency of solar stills and offer potential predictor of solar still output efficiency.