No description available.

Coherent X-ray diffraction and X-ray Intensity Fluctuation Spectroscopy (XIFS) are ideal methods and techniques to perform measurements on the dynamics of fluctuations in condensed matter materials. To investigate more systems and faster fluctuations by being able to tune the coherence length, we use a zone plate to change the coherence length and beam size but keep most of the intensity. Using the zone plate, experiments were carried out to measure the properties of the focused beam. We applied a formalism to calculate the effect of optics on coherence. We tested our results by doing measurement at Advanced Photon Source. We measured the focal properties of the zone plate, speckle sizes and contrast, obtained by using coherent X-ray diffraction from an disordered Fe3Al crystals. Our theoretical calculations are compared with the experimental results.

The crystal structure of caesium permanganate has been determined. CsMn0₄ crystallises in the orthorhombic space group Pnma. There are four molecules per unit cell with a = 10.0692 Å, b = 5.8080 Å, c = 7.9470 Å. The structure was determined by Fourier syntheses on the (010) and (001) projections and refined by two-dimensional difference syntheses. The structure is similar to that of KMn0₄. The manganese is surrounded by four oxygen atoms at an average distance of 1.629 Å arranged in a slightly distorted tetrahedron. The caesium is surrounded by eight manganese atoms at an average distance of 4.381 Å.

M.Sc. (Geology) / This study involves the quantitative analysis of fluorspar-containing slurries by two X-ray diffraction methods, whereby these two methods of on-stream analysis are compared. The first method involves a single counter with a diffracted beam monochromator, and the second method involves a fixed geometry with an incident beam monochromator. The second method is a cheaper and more robust apparatus, which can withstand the harsh environment of the flotation plants. A new algorithm was developed for a more accurate calibration method. Programmes for calibration, recalibration and measuring of unknown samples were developed. The measuring apparatus was interfaced with a microcomputer for computerised operation of the system. Results from both methods were comparable, with more accurate results obtained for the feed and tailings than for the concentrate samples. The single detector apparatus can thus be replaced by the fixed geometry model, which is less expensive and more robust.

M.Phil. (Energy Studies) / Non-destructive investigations of unusual natural polycrystalline diamond samples are reported. The samples originate from various international locations discovered in soils and sediments and may have been formed by di erent mechanisms which are the subject of debate. Analysis techniques include scanning electron microscopy, with energy dispersive spectroscopy and X-ray di raction. Sample composition, structure and surface stresses were investigated. The samples (two Egyptian nodules, two Brazillian carbonados, two Venetian ballas diamonds and a polycrystalline diamond compact sample consisting of a polycrystalline diamond layer sintered onto a Co-cemented tungsten carbide support) are cubic diamonds, with varying amounts of minority phases. In most cases the minority phases could not be identi ed unambiguously due to their low intensities and the overlap of Bragg peaks. The Egyptian nodule samples in particular showed a large presence of oxygen that could not be linked to speci c metal oxides. The Ballas samples had the lowest impurity content. Using a Rietveld based quanti cation analysis, the crystalline cubic diamond contents were determined respectively as 99 wt.%, 98 wt.% and 76 wt.% in the Ballas, Brazilian carbonado and Egyptian nodule samples. A signi cant result from this study is the substantial inhomogeneous peak broadening observed in the X-ray diffraction patterns of the Egyptian samples. This is indicative of the presence of nano-crystalline diamond grains in addition to substantial mechanical deformation with extensive accumulation of dislocations and crystalline defects. These observations are supportive of a recently proposed impact mechanism for their formation.

No description available.

The crystal structure of dibenzothiophene has been determined by X-ray diffraction. Mo-Kα [subscript omitted] scintillation counter data were used for this analysis; the sulfur atom position was determined by means of a Patterson function; the carbon atoms were located from a Fourier synthesis, and the hydrogen atoms, from a difference synthesis. Refinement of positional and thermal parameters was by least-squares methods. The molecule is slightly folded, the dihedral angles between the five-membered ring and the six-membered rings being 0.4° and 1.2°. The bond distances and valency angles are similar to those in related molecules. The C-S bond length is 1.740 A, and the C-S-C angle is 91.5°. The crystal structure of DL-ornithine hydrobromide has been determined by means of visual Cu-Kα [subscript omitted] data. The bromine ion position was found by Patterson methods; carbon, nitrogen, and oxygen atoms were located on Fourier summations and the hydrogen atoms, on a difference synthesis. The positional and thermal parameters were refined by least-squares. The ornithine molecule is a zwitterion, with both nitrogens accepting protons. The mean bond distances are C-0, 1.249 A; C-N, 1.469 A; C-C, 1.532 A. The structure is held together by a system of N—H …… 0 (2.84, 2.84, 2.89 A) and N—H…..Br (3.29, 3.36,.3.46 A) hydrogen bonds. The crystal and molecular structure of histamine diphosphate monohydrate has been determined with scintillation counter Mo-Kα [subscript omitted] data. The positions of the phosphorus atoms were determined by Patterson methods; the carbon, nitrogen and oxygen atoms were located by means Fourier syntheses; the hydrogen atoms were found on a difference synthesis. The thermal and positional parameters were refined by least-squares. The atoms of this histamine cation lie in two almost perpendicular planes, the plane of the imidazole ring and that of the side chain. The bond lengths and angles are similar to the corresponding values in histidine hydrochloride monohydrate. The dimensions of the two P0₂(OH) ₂⁻ ions are P-0 1.51 A, P-OH 1.57 A, O-P-0 115.5°, and HO-P-OH 107.0°. The most important feature of the packing is a complex system of 0-H.....0 and N-H...0 hydrogen bonds. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis: B.S., Massachusetts Institute of Technology, Department of Biology, 1976 / Includes bibliographical references. / by Ann B. Mansfield. / B.S. / B.S. Massachusetts Institute of Technology, Department of Biology

Recent hardware developments of automated, high speed, portable X-ray diffraction instrumentation have not yet resulted in widespread use of the technique in industry despite its potentials. We suggest that these hardware developments require an equivalent development in the training of instrument operators in order to guarantee the integrity of the resulting data, as well as to enhance the understanding of such materials characterization data. The hurdle to date is the variety of skills necessary in a wide range of scientific and engineering disciplines and which are not commonly found in a single individual. We suggest that a computer-based system, integrating visualization tools, knowledge bases and analysis-capabilities and which is focused on the operator performance can provide an efficient solution to this problem, as it changes the enactment of the stress determination work process. / Master of Science

M.S.