About a hundred samples of y-manganese dioxide covering three materials coded SBP- A, Faradiser M and R2 have been reduced chemically by insertion of H through controlled additions of hydrazine hydrate solutions at about 1 °C. The H-inserted samples and the starting materials were subjected to chemical analysis for oxidation state, X-ray diffraction (XRD) for structure study and Fourier Transform Infrared (FTIR) spectroscopy to gain information on OH bonding. Additional techniques including FTIR spectroscopy at low temperature (~ -180 °C), electrode potential measurement and scanning electron microscopy (SEM) have also been applied. The intergrowth structure of the starting materials consisted of ramsdellite intercepted with pyrolusite layers, known as de Wolff faults, and quantified by the fraction of pyrolusite layers Pr. An additional structural parameter for these materials was the amount of micro twinning (Tw) across the 021/061 ramsdellite planes. This parameter, introduced by Pannetier, is given in percent. Values of (Pr , Tw) have been given as (0.41 , 17) for SBP-A, (0.70,10) for Faradiser M and (0.41, ~100) for R2. Upon H-insertion, the structure of the starting materials expanded homogeneously in a direction and to an extent which depended on the Pr and Tw parameters. Faradiser M, with high Pr and very low Tw, expanded homogeneously in the direction of the b lattice dimension up to an insertion level of 0.69 of s in MnOn/Hs. Above this level, the initial structure changed suddenly into the structure of the final product: the insertion then proceeded homogeneously in the new phase. The main changes were an expansion of the octahedra and a rotation leading to hinged tunnels. This is the first time that the existence of two solid solutions in the MnO2/H system has been noted. With SBP-A, the amount of microtwinning restricted the homogeneous expansion of SBP-A to s = 0.28, which occurred predominantly in the a direction. Further insertion broke the twinning boundary and formed a demicrotwinned phase of composition MnOn Ho.68 in which the tunnels were also hinged. Thereafter H-insertion proceeded heterogeneously from 0.28 to 0.68 in s. Above s = 0.68, the structure developed homogeneously towards that of the fully H-inserted product. The extensive microtwinning in R2 allowed for a homogeneous expansion, thought to be isotropic to maintain the microtwinned structure, up to s = 0.39. Higher insertion levels led to the expansion to proceed heterogeneously to a composition of MnOn Ho.63. Above s = 0.63, a new phase, the final product, was formed with fully demicrotwinned structure and fully hinged tunnels. R-insertion into y-manganese dioxide has never been reported to occur in three stages previously. The FTIR study at room temperature has shown absence of OH bond vibrations at insertion levels prior to the hinging of the tunnels, in contrast to their presence after the structure has rotated and the tunnels had hinged. This is seen as a strong indication of H mobility in the initial structure. The hinging is necessary for OH bonding as it brings the 02 and 01 oxygens closer allowing the proton to bond both covalently and by H-bonding. At low temperature, initially mobile hydrogen could be trapped and OR bonds formed only in H-inserted R2. This was linked to 061-microtwinning. The absence of OH bonds at low temperature in SBP-A and Faradiser M led to the conclusion that these materials have no 061 micro twinning faults. The absence of OH bonds at low temperature in the starting materials, particularly in R2, strongly questions the postulated OH groups in the structure of y-MnO2, according to the cation vacancy model. Electrode potential data supported the above conclusions in terms of the stages of the H-insertion. The battery activity of the materials seemed to be related to the extent at which the materials kept the initial structure with non-hinged tunnels. Comparison with previous works on the same materials suggested that the differences could be accounted for by the kinetics of the H-insertion. While protons in this work were released spontaneously on the surface of the MnO x , their diffusion into the bulk was slow due to the low temperature. In the compared literature, the reverse applies.

No description available.

This work is a part of a large project in our laboratory that is aimed toward characterization of prokaryotic transcription regulators from different families and their interactions with small-molecule effectors. My study was focused of IclR family of transcriprion regulators, specifically on its founding member Isocytrate Lyase Regulator (IclR) from E.coli and AllR regulator from E.coli, which share 42% sequence identity with IclR. I used a combination of biophysical, biochemical and structural biology techniques to explore the mechanisms by which IclR and AllR interact with their effectors. I performed site-directed mutagenesis experiments in order to research the role of individual amino acids in interaction of AllR regulator with its previously identified effector glyoxylate and to test whether oligomerization plays a role in effector-induced signal transduction by AllR. Using differential light scattering, which allows high-throughput screening of small molecules for thermostabilization of proteins, I identified potential effctors for the IclR regulator. The physiological relevance of these candidate molecules was tested in-vitro and in-vivo and their interaction with IclR was characterized by Isothermal Titration Calorimetry and X-ray Crystallography.

This work is a part of a large project in our laboratory that is aimed toward characterization of prokaryotic transcription regulators from different families and their interactions with small-molecule effectors. My study was focused of IclR family of transcriprion regulators, specifically on its founding member Isocytrate Lyase Regulator (IclR) from E.coli and AllR regulator from E.coli, which share 42% sequence identity with IclR. I used a combination of biophysical, biochemical and structural biology techniques to explore the mechanisms by which IclR and AllR interact with their effectors. I performed site-directed mutagenesis experiments in order to research the role of individual amino acids in interaction of AllR regulator with its previously identified effector glyoxylate and to test whether oligomerization plays a role in effector-induced signal transduction by AllR. Using differential light scattering, which allows high-throughput screening of small molecules for thermostabilization of proteins, I identified potential effctors for the IclR regulator. The physiological relevance of these candidate molecules was tested in-vitro and in-vivo and their interaction with IclR was characterized by Isothermal Titration Calorimetry and X-ray Crystallography.

No description available.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1970. / Bibliography: leaves [76]-79. / vi, 79 l maps, graphs, tables

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1970. / Bibliography: leaves 183-192. / xiii, 192 l illus., graphs, tables

<p>In this study we report on the effect of the deposition parameters on the morphology and structural properties of CNTs, synthesized by means of the hot-wire chemical vapour deposition technique. SEM, Raman and XRD results show that the optimum deposition conditions for the HWCVD synthesis of aligned MWCNTs, with diameters between 50 and 150 nm and lengths in the micrometer range are: Furnace temperature of 500 &ordm / C, deposition pressure between 150 and 200 Torr, methane/hydrogen dilution of 0.67 and a substrateto- filament distance of 10 cm.</p>

Coherent Diffractive Imaging (CDI) has become an increasingly popular frame work in which to solve the classic phase problem in imaging due to benefits in resolution and the facility of collecting data in this modality. In particular, there is considerable interest in using the short wavelength and high coherence of fourth generation x-ray sources with CDI techniques to phase non-crystalline, or nano-crystalline biomolecular samples. CDI provides an opportunity to determine the structure of proteins and other biological samples which are unable to be phased with the standard techniques of protein crystallography, typically due to lack of adequate crystalline samples. Methods of non-crystalline phase retrieval are legion, however many suffer from limitations in resolution or the inability to recover phase fields containing a pathological singularity. Wavefields containing phase singularities are common in optical fields. The creation of an x-ray wavefield containing a pathological phase singularity is demonstrated. In this thesis a form of CDI termed astigmatic diffraction is presented, that is able tophase uniquely this class of wavefield. This is achieved by illuminating the sample with beams containing known phase curvature. The theory of the method and simulations of its application to a nano-crystalline biomolecule are presented. The experimental recovery of the direction of the phase gradient of a sample illuminated with coherent x-rays produced by a synchrotron source is shown to verify this method.

Thesis (Ph. D. - Geosciences)--University of Arizona, 1983. / Includes bibliographical references (leaves 168-177).