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Nonlinear Absorption Initiated Laser-Induced Damage in [Gamma]-Irradiated Fused Silica, Fluorozirconate Glass and Cubic Zirconia

Description: The contributions of nonlinear absorption processes to laser-induced damage of three selected groups of transparent dielectrics were investigated. The studied materials were irradiated and non-irradiated fused silica, doped and undoped fluorozirconate glass and cubic zirconia stabilized with yttria. The laser-induced damage thresholds, prebreakdown transmission, and nonlinear absorption processes were studied for several specimens of each group. Experimental measurements were performed at wavelengths of 1064 nm and 532 nm using nanosecond and picosecond Nd:YAG laser pulses. In the irradiated fused silica and fluorozirconate glasses, we found that there is a correlation between the damage thresholds at wavelength λ and the linear absorption of the studied specimens at λ/2. In other words, the laser-induced breakdown is related to the probability of all possible two-photon transitions. The results are found to be in excellent agreement with a proposed two-photon-initiated electron avalanche breakdown model. In this model, the initial "seed" electrons for the formation of an avalanche are produced by two-photon excitations of E' centers and metallic impurity levels which are located within the bandgaps of irradiated Si02 and fluorozirconate glasses, respectively. Once the initial electrons are liberated in the conduction band, a highly absorbing plasma is formed by avalanche impact ionization. The resultant heating causes optical damage. In cubic zirconia, we present direct experimental evidence that significant energy is deposited in the samples at wavelength 532 nm prior to electron avalanche formation. The mechanism is found to be due to formation of color centers (F+ or F° centers) by the two-photon absorption process. The presence of these centers was directly shown by transmission measurements. The two-photon absorption (2PA) process was independently investigated and 2PA coefficients obtained. The accumulated effects of the induced centers on the nonlinear absorption measurements were also considered and the 2PA coefficients were measured using short pulses where this effect ...
Date: August 1988
Creator: Mansour, Nastaran
Partner: UNT Libraries

Evaluation of Text-Based and Image-Based Representations for Moving Image Documents

Description: Document representation is a fundamental concept in information retrieval (IR), and has been relied upon in textual IR systems since the advent of library catalogs. The reliance upon text-based representations of stored information has been perpetuated in conventional systems for the retrieval of moving images as well. Although newer systems have added image-based representations of moving image documents as aids to retrieval, there has been little research examining how humans interpret these different types of representations. Such basic research has the potential to inform IR system designers about how best to aid users of their systems in retrieving moving images. One key requirement for the effective use of document representations in either textual or image form is thedegree to which these representations are congruent with the original documents. A measure of congruence is the degree to which human responses to representations are similar to responses produced by the document being represented. The aim of this study was to develop a model for the representation of moving images based upon human judgements of representativeness. The study measured the degree of congruence between moving image documents and their representations, both text and image based, in a non-retrieval environment with and without task constraints. Multidimensional scaling (MDS) was used to examine the dimensional dispersions of human judgements for the full moving images and their representations.
Date: August 1997
Creator: Goodrum, Abby A. (Abby Ann)
Partner: UNT Libraries

A Delphi Study to Determine if SCANS Workplace Know-How Can Be Developed through the Achievement of National Standards for [Visual] Arts Education

Description: The purpose of this study was to provide a basis for understanding among Tech Prep and School-to-Work change agents, and educational leaders, of the role that Discipline-Based Art Education (DBAE) can perform as a part of the core curriculum, within the framework of these reform movements. The literature indicated that the federally supported Tech Prep and School-to-Work reform movements were not acquainted with DBAE reform initiative which were supported by the Getty Education Institute for the Arts through the work of Regional Institutes. Therefore, they had no ideas about the possible worth of art as an education core component. Also, DBAE was not acquainted with Tech Prep and School-to-Work and therefore had established no common terminology to communicate the power of what they do in a manner which was relevant to that audience. The DBAE Regional Institutes provided individuals to assist in the development and validation of the study tools, and to participate in the pilot study. The Regional Institutes also identified the 10 Discipline-Based Art Education experts who composed the national Delphi panel for the study. The findings were reported according to research questions. They show the national Delphi panels' perceptions of which SCANS skills can be developed by Content Standards and Performance Standards from the National Standards for [Visual] Arts Education. The study concluded that: 1) there is a relationship between the Content and Performance Standards taken from the National Standards for [Visual] Arts Education and the SCANS skills; 2) SCANS Basic skills, Thinking skills, Resources skills, Information skills and Systems skills could be developed through the achievement of the Performance Standards of the National Standards for [Visual] Arts Education; and 3) the relationship between the SCANS Workplace Know-How skills and the National Standards for [Visual] Art Education was validated by a national Delphi panel. Recommendations were made ...
Date: August 1997
Creator: Crews, Jan, 1959-
Partner: UNT Libraries

Role of α-Keto Acids In Cyanide Detoxification and Assimilation by Pseudomonas Bacteria

Description: Cyanide was rapidly removed when added to culture supernatants of seven different Pseudomonas. The ability to remove cyanide was correlated with the accumulation of α-keto acids (pyruvate and α-ketoglutarate). These compounds react with cyanide forming less toxic cyanohydrins, thus conferring a mechanism for bacterial cyanide tolerance. When added to growth media the α-keto acids were shown also to serve as effective cyanide antagonists. While all bacteria tested accumulated α-keto acids, only those capable of utilizing cyanide as a nutritional nitrogen source were able to metabolize cyanohydrins. In P. fluorescens NCIMB 11764, the same enzyme (cyanide oxygenase) shown previously to be involved in cyanide metabolism appears responsible for cyanohydrin transformation. Keto acid excretion is believed to represent a new mechanism of bacterial cyanide detoxification with further enzymatic metabolism of the cyanohydrins helping to explain how cyanide can satisfy the nitrogen requirement in cyanide-utilizing bacteria.
Date: December 1998
Creator: Pan, Guangliang
Partner: UNT Libraries

The Consideration of Visual Aspects of Art in Motion Picture Awards

Description: The writer, who, as an art student, has a special interest in the visual qualities of motion picture art, has undertaken to investigate the extent to which the visual aspect of art was outstanding in motion pictures receiving awards during the years 1951 through 1954. As a result of this investigation he hopes to reach some valid conclusions concerning the chronological and geographical distribution of visually excellent pictures during the period and to consider the consequences of those trends which can be identified.
Date: 1956
Creator: Jones, Billy Jack
Partner: UNT Libraries