The relation of structure to lack of superconductivity in Pr-Ba-Cu-O was systematically investigated. First, the phase equilibria of this system was studied to find the processing parameters which maximize the cation-site ordering between Pr and Ba ions. Second, a comparative study between superconducting Nd-Ba-Cu-0 and non- superconducting Pr-Ba-Cu-0 was performed by forming solid-solution Nd- Pr-Ba-Cu-0. The relation between structure and superconductivity in Nd{sub 1{minus}x}Pr{sub x}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} is investigated. {Tc} decreases monotonically with increasing {times} and superconductivity disappears at around x=0.3-0.4. {Tc} is enhanced by 10K when the sample is processed at an oxygen partial pressure (PO{sub 2}) of 0.01 atm, followed by oxygenation at 450C. Depression of {Tc} as a function of {times} and PO {sub 2} is explained in terms of a charge-transfer model. It is suggested that destruction of superconductivity in the RE{sub 1{minus}x}Pr{sub x}Ba{sub 2}CU{sub 3}O{sub 7{minus}{delta}} (RE=rare-earth) system can be viewed as disruption of four-fold planar coordinated Cu ions in the chain-site due to permanent occupation of extra Pr ions on Ba sites.

Kinetic data for elimination of silylene supports formation of a ``tighter`` transition state, indicating a silacyclopropene intermediate. This extends the silacyclopropene mechanism to the cyclicdialkyne system and validates the consistency of the mechanism for silylakynes, in general. Investigation into the other possible silacyclopropene product established the instability of the product. The work with silylketenes proved that an inherent difference exists between reactivity of monosilyl-substituted ketenes and polysilyl-substituted ketenes. Although the mechanism for thermal decomposition of bis(silyl)ketenes can be modified to account for the unexpected silylene elimination products, reasons for the difference are limited to speculation. The photochemistry of silylketenes has not been previously studied, so a model system does not exist for comparison with our polysilylketene work. The photochemical experimentation suggests that the photochemistry and thermochemistry of polysilylketenes is not the same. A more extensive study of the mechanism of the systems covered in this research as well as with monosilyl-substituted systems is needed.

Mechanisms and associated energetics for adatom diffusion on the (100) and (110) surfaces of Ni, Cu, Rh, Pd, and Ag are investigated. Self-diffusion was studied on (100) and (I 10) surfaces of Ni, Cu, Pd and Ag using corrected effective medium method (CEM) and approximation to CEM used for molecular dynamics and Monte Carlo studies (MD/MC-CEM). Self-diffusion on Pd(100), Ag(100), Ni(110), Cu(110), Pd(110), and Ag(110) is accomplished by classical diffusion: the adatom hops from its equilibrium adsorption site over an intervening bridge site to an adjacent equilibrium site. Self-diffusion on Ni(100) and Cu(100) proceeds by atomic-exchange diffusion: the adatom on the surface displaces an atom in the first surface layer. Aside from explicit inclusion of the kinetic-exchange-correlation energy, it is critical to include enough movable atoms in the calculation to insure correct energetics. Distortions induced by these diffusion mechanisms, especially atomic exchange, are long ranged in surface plane, owing to small distortions of many atoms being energetically favored over large distortions of few atoms. Energetics and rates of heterogeneous adatom diffusion on the (100) surfaces of Ni, Cu, Rh, Pd, and Ag show that the final state energies differ due to variation of metallic bonding with coordination for different types …

Role of H spillover to the silica support was studied using chemisorption; a strongly bound component of spilled over H was found in the silica support which interfered with accurate measurements of active metal sites via volumetric strong H chemisorption. The volumetric chemisorption technique was modified so that measurement times were reduced from 12--36 h to 1 h. The active Ru surface was characterized means of changes in proton spin counts and NMR Knight shifts vs alkali loading. Na, K blocked the active surface of Ru metal, but Cs was pushed off by H chemisorption. The alkali promoters restricted H mobility on both metal surface and at the metal support interfaces; this is consistent with effects on Fischer-Tropsch synthesis. {sup 1}H NMR was used to study the effect of the active metal and promoter on support hydroxyl groups. The OH group density in the silica support decreased with metal and/or promoter loading, but not on a one-to-one basis; the exchange efficiency of the hydroxyls decreased with atomic size of the alkali metal. An additional downfield proton resonance was detected which was assigned to the alkali hydroxide species in the support.

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The Retinal Prosthesis project is a three year project conducted in part at the Lawrence Livermore National Laboratory and funded by the Department of Energy to create an epiretinal microelectrode array for stimulating retinal cells. The implant must be flexible to conform to the retina, robust to sustain handling during fabrication and implantation, and biocompatible to withstand physiological conditions within the eye. Using poly(dimethyl siloxane) (PDMS), LLNL aims to use microfabrication techniques to increase the number of electrodes and integrate electronics. After the initial designs were fabricated and tested in acute implantation, it became obvious that there was a need to characterize and understand the mechanical and electrical properties of these new structures. This knowledge would be imperative in gaining credibility for polymer microfabrication and optimizing the designs. Thin composite microfabricated devices are challenging to characterize because they are difficult to handle, and exhibit non-linear, viscoelastic, and anisotropic properties. The objective of this research is to device experiments and protocols, develop an analytical model to represent the composite behavior, design and fabricate test structures, and conduct experimental testing to determine the mechanical and electrical properties of PDMS-metal composites. Previous uniaxial stretch tests show an average of 7% strain before failure …

n-Butane selective oxidation over the VPO catalyst to maleic anhydride is the first and only commercialized process of light alkane selective oxidation. The mechanism of this reaction is still not well known despite over twenty years of extensive studies, which can partially be attributed to the extreme difficulties to characterize catalytic reactions real-time under typical reaction conditions. In situ spectroscopic characterization techniques such as Infrared spectroscopy and laser Raman spectroscopy were used in the current mechanistic investigations of n-butane oxidation over VPO catalysts. To identify the reaction intermediates, oxidation of n-butane, 1,3-butadiene and related oxygenates on the VPO catalyst were monitored using FTIR spectroscopy under transient conditions. n-Butane was found to adsorb on the VPO catalyst to form olefinic species, which were further oxidized to unsaturated, noncyclic carbonyl species. The open chain dicarbonyl species then experienced cycloaddition to form maleic anhydride. VPO catalyst phase transformations were investigated using in situ laser Raman spectroscopy. This report contains Chapter 1: General introduction; Chapter 2: Literature review; and Chapter 5: Conclusion and recommendations.

This dissertation focuses on the development of methods for stable isotope metabolic tracer studies in living systems using inductively coupled plasma single and dual quadrupole mass spectrometers. Sub-nanogram per gram levels of molybdenum (Mo) from human blood plasma are isolated by the use of anion exchange alumina microcolumns. Million-fold more concentrated spectral and matrix interferences such as sodium, chloride, sulfate, phosphate, etc. in the blood constituents are removed from the analyte. The recovery of Mo from the alumina column is 82 {+-} 5% (n = 5). Isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) is utilized for the quantitative ultra-trace concentration determination of Mo in bovine and human blood samples. The average Mo concentration in reference bovine serum determined by this method is 10.2 {+-} 0.4 ng/g, while the certified value is 11.5 {+-} 1.1 ng/g (95% confidence interval). The Mo concentration of one pool of human blood plasma from two healthy male donors is 0.5 {+-} 0.1 ng/g. The inductively coupled plasma twin quadrupole mass spectrometer (ICP-TQMS) is used to measure the carbon isotope ratio from non-volatile organic compounds and bio-organic molecules to assess the ability as an alternative analytical method to gas chromatography combustion isotope ratio mass spectrometry …

Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, the author synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, they were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of the studies, he synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led them to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides. This report contains the Introduction; ``Chapter 6: Isomerization of Propargylic Alcohols to Enones and Enals Catalyzed by Methylrhenium Trioxide``; and Conclusions.

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This thesis consists of three main parts. The first one relates to boron neutron capture therapy. It summarizes the guidelines obtained by numerical simulations for the treatment of shallow and deep-seated brain tumors, as well as the results on the design of beam-shaping assemblies to moderate D-D and D-T neutrons to epithermal energies. The second part is about boron neutron capture synovectomy for the treatment of rheumatoid arthritis. Optimal neutron energy for treatment and beam-shaping assembly designs are summarized in this section. The last part is on the development of the sealed neutron generator, including experimental results on the prototype ion source and the prototype accelerator column.

Helium, with its two electrons and one nucleus, is a three-body system. One of the models for investigating correlated electron motion in this system is autoionization, produced via double excitation of the electrons. Predictions about the autoionization spectrum of helium have differed from each other and from preliminary experimental data. However, previous experiments have not been able to distinguish among the theoretical predictions because their energy resolution is not high enough to resolve the narrow linewidths of quasi-forbidden peaks and the resonances that appear in the highest excited states. Consequently, a team of researchers at Lawrence Berkeley National Laboratory have embarked on a project for building a high-resolution Fourier-Transform Soft X-ray (or VUV) interferometer (FTSX) to provide definitive data to answer remaining questions about the autoionization spectrum of helium. The design and construction of this interferometer is described in detail below, including the use of a flexure stage to provide the large path length difference necessary for high resolution measurements, the manufacture of x-ray beamsplitters, a description of the software, and the solution to the problems of stick-slip, vibration, and alignment. Current progress of its development is also described, as well as future goals.