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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Profile analysis of X-ray powder diffraction data.

Naicker, Vishnu Visvanathan. 07 November 2013 (has links)
Various strategies have been tested for obtaining integrated intensities from x-ray powder diffractometer data. An asymmetric pseudo-Voigt profile function was used to fit the pattern in the region above 2θ = 35̊ (Cu-Kα radiation). At lower angles where the asymmetry was strongest and the profile function not suitable the peaks were integrated numerically. A smooth background function was estimated from the regions of minimum intensity of the pattern. The profile parameters were initially refined in small ranges of about 10̊ 2θ in order to determine their 2θ-dependence. Thereafter final refinements of peak intensities were undertaken using the profile parameters thus determined. Analysis of data from the mineral Fe-akermanite, Ca₂Mg₀. ₄Fe₀. δSi₂O₇, generated 173 integrated intensities with 1 > 2δ(1) out of 187 positions separated in 2θ by more than 0,02̊. Of the total of 213 reflections in the range, those overlapping exactly or separated by < 0,02̊ were treated as single peaks. The structure was refined using an overall isotropic temperature parameter and a parameter to compensate for preferred orientation, giving an unweighted residual of 10,4% for 14 parameters. / Thesis (M.Sc.)-University of Durban-Westville, 1988.
22

Investigation of hydrogen and its role in dehydration processes in halloysite.

Harris, Billy Banks 05 1900 (has links)
No description available.
23

Temperature dependence of the low-energy electron diffraction from silver

Jones, Edwin R., January 1965 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
24

Problems associated with the construction of an electron diffraction unit

Marak, Eldon John. January 1951 (has links)
Call number: LD2668 .T4 1951 M373 / Master of Science
25

Wave propagation in an elastic half-space at high frequencies

Gridin, Dmitri January 1999 (has links)
No description available.
26

Characterization of liquid crystal surfaces by X-ray and neutron scattering

Phillips, Pepe Louise January 1997 (has links)
No description available.
27

High energy electron diffraction from transverse stacking faults

Jesson, D. E. January 1987 (has links)
No description available.
28

Studies of computer aided image interpretaion in high resolution electron microscopy

Tang, Dong January 1992 (has links)
No description available.
29

Extinction theorem analysis of diffraction anomalies in overcoated-gratings.

DeSandre, Lewis Francis. January 1989 (has links)
A rigorous analysis based upon the extinction theorem is presented to study anomalous resonance effects from single- and multilayer-overcoated, low-efficiency diffraction gratings. Anomalously high diffraction efficiency at resonance results from the coupling of the incident beam into guided waves that can be propagated within the composite structure. Both the traditional characteristic matrix technique and a recursive or R-matrix propagation technique are presented. The R-matrix propagation algorithm was found to be stable numerically, and computational results agree favorably with both experimental and other theoretical work. Numerical results are presented in order to investigate the influence of certain parameters (i.e., groove depth and shape and the number of high- and low-index overlayers) on the diffraction efficiency at resonance. In this analysis, a wavelength of 0.6328 μm and grating period of 0.7 μm were chosen so that only a -1 diffracted order other than the specular is reflected from the gratings. Perfect transfer of the grating relief to the film boundaries does not occur in all instances; it depends on the grating and film characteristics together with the conditions during deposition. Investigated in this work is the effect of nonreplication of the grating profile at film interfaces on anomalous diffraction; a transition from trapezoidal profile at the grating substrate to a rounded relief at the top surface of the multilayer structure is assumed. For the cases studied, it was found that nonreplication has the effect of reducing the strength of the resonance outcoupling. Finally, experimental results on anomalous resonance effects for multilayer-coated gratings are presented. Good agreement with computational results was attained.
30

Nonlinear grating structures in indium antimonide waveguides.

Ehrlich, Jeffrey Ellis. January 1989 (has links)
This dissertation describes various nonlinear grating coupling phenomena in InSb waveguides. InSb exhibits an opto-thermal, diffusive nonlinearity at 9.6μm. This nonlinearity strongly modifies the growth of a guided wave via the grating coupling of an incident, Gaussian signal. In particular, optical limiting and bistability in the coupled power were demonstrated for a detuned grating coupler. The limits on the detunings were also investigated. The experimental results showed qualitative agreement with a theory based upon a diffusive nonlinearity in the grating coupling process. Also demonstrated and theoretically explained was a new form of "butterfly" bistability in the output coupled signal from a nonlinear waveguide. In this situation, nonlinear interference effects in the substrate modified the proportion of power outcoupled into the cover and the substrate. The effects of a thermal nonlinearity on the response of a distributed feedback grating (DFB) were also studied. The DFB reflection response of an incident guided wave was modified either by varying the power of the incident guided wave or that of a second guided wave. Also, the effects of the DFB reflection were shown to enhance the bistable input grating coupling process by providing an additional feedback. This enhancement resulted in a smaller incident switching power required to obtain bistability in the input coupler.

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