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Synthesis of heterocycles: Indolo (2,1-a) isoquinolines, renewables, and aptamer ligands for cellular imaging

Description: In this thesis, we explore both total syntheses and methodologies of several aromatic heterocyclic molecules. Extensions of the Kraus indole synthesis toward 2-substituted and 2,3-disubstituted indoles, as well as biologically attractive indolo[2,1-a]isoquinolines are described. Recent renewable efforts directed to commodity maleic acid and the first reported furan-based ionic liquids are described. Our total synthesis of mRNA aptamer ligand PDC-Gly, and its dye coupled forms, plus aminoglycoside dye coupled ligands used in molecular imaging, are described.
Date: May 7, 2013
Creator: Beasley, Jonathan
Partner: UNT Libraries Government Documents Department

Templated synthesis of nickel nanoparticles: Toward heterostructured nanocomposites for efficient hydrogen storage

Description: The world is currently facing an energy and environmental crisis for which new technologies are needed. Development of cost-competitive materials for catalysis and hydrogen storage on-board motor vehicles is crucial to lead subsequent generations into a more sustainable and energy independent future. This thesis presents work toward the scalable synthesis of bimetallic heterostructures that can enable hydrogen to compete with carbonaceous fuels by meeting the necessary gravimetric and volumetric energy densities and by enhancing hydrogen sorption/desorption kinetics near ambient temperatures and pressures. Utilizing the well-known phenomenon of hydrogen spillover, these bimetallic heterostructures could work by lowering the activation energy for hydrogenation and dehydrogenation of metals. Herein, we report a novel method for the scalable synthesis of silica templated zero-valent nickel particles (Ni⊂SiO{sub 2}) that hold promise for the synthesis of nickel nanorods for use in bimetallic heterostructures for hydrogen storage. Our synthesis proceeds by chemical reduction of a nickel-hydrazine complex with sodium borohydride followed by calcination under hydrogen gas to yield silica encapsulated nickel particles. Transmission electron microscopy and powder X-ray diffraction were used to characterize the general morphology of the resultant nanocapsules as well as the crystalline phases of the incorporated Ni{sup 0} nanocrystals. The structures display strong magnetic behavior at room temperature and preliminary data suggests nickel particle size can be controlled by varying the amount of nickel precursor used in the synthesis. Calcination under different environments and TEM analysis provides evidence for an atomic migration mechanism of particle formation. Ni⊂SiO{sub 2} nanocapsules were used as seeds to induce heterogeneous nucleation and subsequent growth within the nanocapsule via electroless nickel plating. Nickel nanoparticle growth occurs under high temperature alkaline conditions, however silica nanocapsule integrity is not maintained due to the incompatibility of silica with the growth conditions. Silica nanocapsule integrity is maintained under low temperature neutral conditions, but ...
Date: May 7, 2013
Creator: Nelson, Nicholas Cole
Partner: UNT Libraries Government Documents Department

Solid state NMR method development and studies of biological and biomimetic nanocomposites

Description: This thesis describes application and development of advanced solid-state nuclear magnetic resonance techniques for complex materials, in particular organic-inorganic nanocomposites and thermoelectric tellurides. The apatite-collagen interface, essential for understanding the biomineralization process in bone and engineering the interface for controlled bio-mimetic synthesis and optimized mechanical properties, is buried within the nanocomposite of bone. We used multinuclear solid-state NMR to study the composition and structure of the interface. Citrate has been identified as the main organic molecule strongly bound to the apatite surface with a density of 1/(2 nm){sup 2}, covering 1/6 of the total surface area in bovine bone. Citrate provides more carboxylate groups, one of the key functional groups found to affect apatite nucleation and growth, than all the non-collagenous proteins all together in bone; thus we propose that citrate stabilizes apatite crystals at a very small thickness of {approx}3 nm (4 unit cells) to increase bone fracture tolerance. The hypothesis has been confirmed in vitro by adding citrate in the bio-mimetic synthesis of polymerhydroxyapatite nanocomposites. The results have shown that the size of hydroxyapatite nanocrystals decreases as increasing citrate concentration. With citrate concentrations comparable to that in body fluids, similar-sized nanocrystals as in bone have been produced. Besides the dimensions of the apatite crystals, the composition of bone also affects its biofunctional and macroscopic mechanical properties; therefore, our team also extended its effort to enhance the inorganic portion in our bio-mimetic synthesis from originally 15 wt% to current 50 wt% compared to 65 wt% in bovine bone, by using Lysine-Leucine hydroxyapatite nucleating diblock co-polypeptide, which forms a gel at very low concentration. In this thesis, various advanced solid state NMR techniques have been employed to characterize nanocomposites. Meanwhile, we have developed new methods to achieve broadband high resolution NMR and improve the accuracy of inter-nuclear distance measurements involving ...
Date: February 7, 2011
Creator: Hu, Yanyan
Partner: UNT Libraries Government Documents Department

Implementation of the Immersed Boundary Method in the Weather Research and Forecasting model

Description: Accurate simulations of atmospheric boundary layer flow are vital for predicting dispersion of contaminant releases, particularly in densely populated urban regions where first responders must react within minutes and the consequences of forecast errors are potentially disastrous. Current mesoscale models do not account for urban effects, and conversely urban scale models do not account for mesoscale weather features or atmospheric physics. The ultimate goal of this research is to develop and implement an immersed boundary method (IBM) along with a surface roughness parameterization into the mesoscale Weather Research and Forecasting (WRF) model. IBM will be used in WRF to represent the complex boundary conditions imposed by urban landscapes, while still including forcing from regional weather patterns and atmospheric physics. This document details preliminary results of this research, including the details of three distinct implementations of the immersed boundary method. Results for the three methods are presented for the case of a rotation influenced neutral atmospheric boundary layer over flat terrain.
Date: December 7, 2006
Creator: Lundquist, K A
Partner: UNT Libraries Government Documents Department

Design of a rural water provision system to decrease arsenic exposure in Bangladesh

Description: Researchers at the Lawrence Berkeley National Laboratory have invented ARUBA (Arsenic Removal Using Bottom Ash) a material that effectively and affordably removes high concentrations of arsenic from contaminated groundwater. The technology is cost-effective because the substrate?bottom ash from coal fired power plants?is a waste material readily available in South Asia. During fieldwork in four sub-districts ofBangladesh, ARUBA reduced groundwater arsenic concentrations as high as 680 ppb to below the Bangladesh standard of 50 ppb. Key results from three trips in Bangladesh and one trip to Cambodia include (1) ARUBA removes more than half of the arsenic from contaminated water within the first five minutes of contact, andcontinues removing arsenic for 2-3 days; (2) ARUBA?s arsenic removal efficiency can be improved through fractionated dosing (adding a given amount of ARUBA in fractions versus all at once); (3) allowing water to first stand for two to three days followed by treatment with ARUBA produced final arsenic concentrations ten times lower than treating water directly out of the well; and (4) the amount of arsenic removed per gram of ARUBA is linearly related to the initial arsenic concentrationof the water. Through analysis of existing studies, observations, and informal interviews in Bangladesh, eight design strategies have been developed and used in the design of a low-cost, community-scale water treatment system that uses ARUBA to remove arsenic from drinking water. We have constructed, tested, and analyzed a scale version of the system. Experiments have shown that the system is capable of reducing high levels of arsenic (nearly 600 ppb) to below 50 ppb, while remaining affordable to people living on less than $2 per day. The system could be sustainably implemented as a public-private partnership in rural Bangladesh.
Date: January 7, 2009
Creator: Mathieu, Johanna
Partner: UNT Libraries Government Documents Department

Measurement of branching fractions of B decays to K1(1270)pi and K1(1400)pi and determination of the CKM angle alpha from B0 --> a1(1260) - pi-

Description: In the Standard Model, CP violation in weak interactions involving quarks is parameterized by an irreducible complex phase in the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing-matrix. The precise determination of the CKM elements is a necessary ingredient for a stringent test of the Standard Model predictions, and is a crucial input for reducing the theoretical error in many New Physics searches with flavor, e.g., in the kaon sector. The unitarity of the CKM matrix is typically expressed as a triangle relationship among its parameters, where the area of the so-called Unitarity Triangle visually depicts the amount of asymmetry between the decays of B particles and their antimatter counterparts. In the past few years, the BABAR and Belle experiments have been able to measure all three angles of the triangle from CP asymmetry measurements. The first asymmetry measurements in B particle decays, about ten years ago, allowed to determine {beta}, which is now known to better than 5% precision. The angles {alpha} and {gamma}, measured in much rarer processes, required several years of data taking before analyses could yield reliable answers. A remarkable feature is that the direct measurement of the angles of the Unitarity Triangle generates an area that is consistent with the area predicted by measurement of the sides. In this thesis we have presented the branching fraction measurements of charged and neutral B meson decays to K{sub 1}(1270){pi} and K{sub 1}(1400){pi}, obtained from a data sample of 454 million {Upsilon}(4S) {yields} B{bar B} events. This analysis is particularly challenging from the experimental side since the branching fractions involved are very low, at the level of 10{sup -6} - 10{sup -7}, and the signal is characterized by the simultaneous presence of two overlapping resonances, which exhibit sizeable interference effects. The combined K{sub 1}(1270){pi} and K{sub 1}(1400){pi} signal is therefore modeled with a ...
Date: February 7, 2011
Creator: Stracka, Simone & /SLAC, /Milan U.
Partner: UNT Libraries Government Documents Department

Measurement and Modeling of Blocking Contacts for Cadmium Telluride Gamma Ray Detectors

Description: Gamma ray detectors are important in national security applications, medicine, and astronomy. Semiconductor materials with high density and atomic number, such as Cadmium Telluride (CdTe), offer a small device footprint, but their performance is limited by noise at room temperature; however, improved device design can decrease detector noise by reducing leakage current. This thesis characterizes and models two unique Schottky devices: one with an argon ion sputter etch before Schottky contact deposition and one without. Analysis of current versus voltage characteristics shows that thermionic emission alone does not describe these devices. This analysis points to reverse bias generation current or leakage through an inhomogeneous barrier. Modeling the devices in reverse bias with thermionic field emission and a leaky Schottky barrier yields good agreement with measurements. Also numerical modeling with a finite-element physics-based simulator suggests that reverse bias current is a combination of thermionic emission and generation. This thesis proposes further experiments to determine the correct model for reverse bias conduction. Understanding conduction mechanisms in these devices will help develop more reproducible contacts, reduce leakage current, and ultimately improve detector performance.
Date: January 7, 2010
Creator: Beck, P R
Partner: UNT Libraries Government Documents Department

Effect of surface structure on catalytic reactions: A sum frequency generation surface vibrational spectroscopy study

Description: In the results discussed above, it is clear that Sum Frequency Generation (SFG) is a unique tool that allows the detection of vibrational spectra of adsorbed molecules present on single crystal surfaces under catalytic reaction conditions. Not only is it possible to detect active surface intermediates, it is also possible to detect spectator species which are not responsible for the measured turnover rates. By correlating high-pressure SFG spectra under reaction conditions and gas chromatography (GC) kinetic data, it is possible to determine which species are important under reaction intermediates. Because of the flexibility of this technique for studying surface intermediates, it is possible to determine how the structures of single crystal surfaces affect the observed rates of catalytic reactions. As an example of a structure insensitive reaction, ethylene hydrogenation was explored on both Pt(111) and Pt(100). The rates were determined to be essentially the same. It was observed that both ethylidyne and di-{sigma} bonded ethylene were present on the surface under reaction conditions on both crystals, although in different concentrations. This result shows that these two species are not responsible for the measured turnover rate, as it would be expected that one of the two crystals would be more active than the other, since the concentration of the surface intermediate would be different on the two crystals. The most likely active intermediates are weakly adsorbed molecules such as {pi}-bonded ethylene and ethyl. These species are not easily detected because their concentration lies at the detection limit of SFG. The SFG spectra and GC data essentially show that ethylene hydrogenation is structure insensitive for Pt(111) and Pt(100). SFG has proven to be a unique and excellent technique for studying adsorbed species on single crystal surfaces under high-pressure catalytic reactions. Coupled with kinetic data obtained from gas chromatography measurements, it can give ...
Date: September 7, 2001
Creator: McCrea, Keith R.
Partner: UNT Libraries Government Documents Department

Inertial fusion energy target injection, tracking, and beam pointing

Description: Several cryogenic targets must be injected each second into a reaction chamber. Required target speed is about 100 m/s. Required accuracy of the driver beams on target is a few hundred micrometers. Fuel strength is calculated to allow acceleration in excess of 10,000 m/s{sup 2} if the fuel temperature is less than 17 K. A 0.1 {mu}m thick dual membrane will allow nearly 2,000 m/s{sup 2} acceleration. Acceleration is gradually increased and decreased over a few membrane oscillation periods (a few ms), to avoid added stress from vibrations which could otherwise cause a factor of two decrease in allowed acceleration. Movable shielding allows multiple targets to be in flight toward the reaction chamber at once while minimizing neutron heating of subsequent targets. The use of multiple injectors is recommended for redundancy which increases availability and allows a higher pulse rate. Gas gun, rail gun, induction accelerator, and electrostatic accelerator target injection devices are studied, and compared. A gas gun is the preferred device for indirect-drive targets due to its simplicity and proven reliability. With the gas gun, the amount of gas required for each target (about 10 to 100 mg) is acceptable. A revolver loading mechanism is recommended with a cam operated poppet valve to control the gas flow. Cutting vents near the muzzle of the gas gun barrel is recommended to improve accuracy and aid gas pumping. If a railgun is used, we recommend an externally applied magnetic field to reduce required current by an order of magnitude. Optical target tracking is recommended. Up/down counters are suggested to predict target arrival time. Target steering is shown to be feasible and would avoid the need to actively point the beams. Calculations show that induced tumble from electrostatically steering the target is not excessive.
Date: March 7, 1995
Creator: Petzoldt, R.W.
Partner: UNT Libraries Government Documents Department

Synthesis, characterization and application of electrode materials

Description: It has been known that significant advances in electrochemistry really depend on improvements in the sensitivity, selectivity, convenience, and/or economy of working electrodes, especially through the development of new working electrode materials. The advancement of solid state chemistry and materials science makes it possible to provide the materials which may be required as satisfactory electrode materials. The combination of solid state techniques with electrochemistry expands the applications of solid state materials and leads to the improvement of electrocatalysis. The study of Ru-Ti{sub 4}O{sub 7} and Pt-Ti{sub 4}O{sub 7} microelectrode arrays as introduced in paper 1 and paper 4, respectively, focuses on their synthesis and characterization. The synthesis is described by high temperature techniques for Ru or Pt microelectrode arrays within a conductive Ti{sub 4}O{sub 7} ceramic matrix. The characterization is based on the data obtained by x-ray diffractometry, scanning electron microscopy, voltammetry and amperometry. These microelectrode arrays show significant enhancement in current densities in comparison to solid Ru and Pt electrodes. Electrocatalysis at pyrochlore oxide Bi{sub 2}Ru{sub 2}O{sub 7.3} and Bi{sub 2}Ir{sub 2}O{sub 7} electrodes are described in paper 2 and paper 3, respectively. Details are reported for the synthesis and characterization of composite Bi{sub 2}Ru{sub 2}O{sub 7.3} electrodes. Voltammetric data are examined for evidence that oxidation can occur with transfer of oxygen to the oxidation products in the potential region corresponding to anodic discharge of H{sub 2}O with simultaneous evolution of O{sub 2}. Paper 3 includes electrocatalytic activities of composite Bi{sub 2}Ir{sub 2}O{sub 7} disk electrodes for the oxidation of I{sup -} and the reduction of IO{sub 3}{sup -}.
Date: July 7, 1995
Creator: He, L.
Partner: UNT Libraries Government Documents Department

Matrix effects in inductively coupled plasma mass spectrometry

Description: The inductively coupled plasma is an electrodeless discharge in a gas (usually Ar) at atmospheric pressure. Radio frequency energy generated by a RF power source is inductively coupled to the plasma gas through a water cooled load coil. In ICP-MS the {open_quotes}Fassel{close_quotes} TAX quartz torch commonly used in emission is mounted horizontally. The sample aerosol is introduced into the central flow, where the gas kinetic temperature is about 5000 K. The aerosol is vaporized, atomized, excited and ionized in the plasma, and the ions are subsequently extracted through two metal apertures (sampler and skimmer) into the mass spectrometer. In ICP-MS, the matrix effects, or non-spectroscopic interferences, can be defined as the type of interferences caused by dissolved concomitant salt ions in the solution. Matrix effects can be divided into two categories: (1) signal drift due to the deposition of solids on the sampling apertures; and/or (2) signal suppression or enhancement by the presence of the dissolved salts. The first category is now reasonably understood. The dissolved salts, especially refractory oxides, tend to deposit on the cool tip of the sampling cone. The clogging of the orifices reduces the ion flow into the ICP-MS, lowers the pressure in the first stage of ICP-MS, and enhances the level of metal oxide ions. Because the extent of the clogging increases with the time, the signal drifts down. Even at the very early stage of the development of ICP-MS, matrix effects had been observed. Houk et al. found out that the ICP-MS was not tolerant to solutions containing significant amounts of dissolved solids.
Date: July 7, 1995
Creator: Chen, Xiaoshan
Partner: UNT Libraries Government Documents Department