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1. Mono([8]annulene)Uranium(4) half-sandwich complexes, 2. Novel syntheses of symmetrically substituted cyclooctatetetraenes
A reproducible, high-yield synthesis of mono([8]annulene)uranium(4)dichloride (1) is reported, along with the X-ray crystal structural of the bis(pyridine) adduct. Metathesis reactions of the half-sandwich complex 1 with a variety of simple alkyl and alkoxy reagents failed to generate any isolable mono-ring complexes. Reactions of 1 with polydentate, delocalized anions did produce stable derivatives, including mono([8]annulene)uranium(4)bis(acetylacetonate) (4). An X-ray crystal structure of 4 is reported.
Date:
October 1, 1991
Creator:
Boussie, T. R.
System:
The UNT Digital Library
1: Redox chemistry of bimetallic fulvalene complexes; 2: Oligocyclopentadienyl complexes
The electrochemistry of the heterobimetallic complexes (fulvalene)WFe(CO){sub 5} (30) and (fulvalene)WRu(CO){sub 5} (31) has been investigated. Compound 30 is reduced in two one-electron processes, and this behavior was exploited synthetically to prepare a tetranuclear dimer by selective metal reduction. Complex 31 displayed a distinction between the metals upon reoxidation of the dianion, allowing the formation of a dimer by selective metal anion oxidation. The redox behavior of 30 led to an investigation of the use of electrocatalysis to effect metal-specific ligand substitution. It was found that reduction of 30 with a catalytic amount of CpFe(C{sub 6}Me{sub 6}) (97) in the presence of excess P(OMe){sub 3} or PMe{sub 3} led to the formation of the zwitterions (fulvalene)[W(CO){sub 3}{sup {minus}}][Fe(CO)PR{sub 3}{sup +}] (107, R = P(OMe){sub 3}; 108, R = PMe{sub 3}). Compound 31 also displayed unique behavior with different reducing agents, as the monosubstituted zwitterion (fulvalene)[W(CO){sub 3}{sup {minus}}][Ru(CO){sub 2}(PMe{sub 3}){sup +}] was obtained when 97 was used while the disubstituted complex (fulvalene) [W(CO){sub 3}{sup {minus}}] [Ru(CO)(PMe{sub 3}){sub 2}{sup +}] was produced when Cp*Fe(C{sub 6}Me{sub 6}) was the catalyst. Potential synthetic routes to quatercyclopentadienyl complexes were also explored. Various attempts to couple heterobimetallic fulvalene compounds proved to be unsuccessful. 138 refs.
Date:
November 1, 1993
Creator:
Brown, D. S.
System:
The UNT Digital Library
10 microsecond time resolution studies of Cygnus X-1
Time variability analyses have been applied to data composed of event times of X-rays emitted from the binary system Cygnus X-1 to search for unique black hole signatures. The X-ray data analyzed was collected at ten microsecond time resolution or better from two instruments, the High Energy Astrophysical Observatory (HEAO) A-1 detector and the Rossi X-ray Timing Explorer (XTE) Proportional Counter Array (PCA). HEAO A-1 and RXTE/PCA collected data from 1977--79 and from 1996 on with energy sensitivity from 1--25 keV and 2--60 keV, respectively. Variability characteristics predicted by various models of an accretion disk around a black hole have been searched for in the data. Drop-offs or quasi-periodic oscillations (QPOs) in the Fourier power spectra are expected from some of these models. The Fourier spectral technique was applied to the HEAO A-1 and RXTE/PCA data with careful consideration given for correcting the Poisson noise floor for instrumental effects. Evidence for a drop-off may be interpreted from the faster fall off in variability at frequencies greater than the observed breaks. Both breaks occur within the range of Keplerian frequencies associated with the inner edge radii of advection-dominated accretion disks predicted for Cyg X-1. The break between 10--20 Hz is also …
Date:
June 1, 1997
Creator:
Wen, H.C.
System:
The UNT Digital Library
Abraham Lincoln and the American Romantic Writers: Embodiment and Perpetuation of an Ideal
The American Romantic writers laid a broad foundation for the historic and heroic Abraham Lincoln who has evolved as our national myth. The writers were attracted to Lincoln by his eloquent expression of the body of ideals and beliefs they shared with him, especially the ideal of individual liberty and the belief that achievement of the ideal would bring about an amelioration of the human condition. The time, place and conditions in which they lived enhanced the attraction, and Lincoln's able leadership during the Civil War strengthened their estimation of him. His martyrdom was the catalyst which enabled the Romantic writers to lay the foundation of the Lincoln myth which has made his name synonymous with individual freedom everywhere even today.
Date:
December 1992
Creator:
Hicks, Mary G. (Mary Geraldine)
System:
The UNT Digital Library
AC microcalorimetry of adsorbates on evaporated metal films: Orientational ordering of H₂ multilayers
We have improved and extended a novel ac calorimetric technique for measuring the heat capacity of adsorbates on evaporated metal films. Metallic substrates are of particular interest in current studies of the thermodynamics of adsorbed molecules. The method described in the present work is only calorimetric technique which allows measurements of molecules on simple metallic surfaces. Among other improvements, we have achieved significant progress in the preparation and characterization of the evaporated metal film. We have applied this novel technique to a study of hydrogen multilayers on gold and sapphire substrates. We have shown that samples of normal-hydrogen with a nominal coverage n of approximately 25 monolayers (ML) undergo a bulk-like orientational ordering transition. The transition is suppressed as the coverage is decreased, and no sign of the transition remains above 1.6 K for n {approx} 1 ML. For n {approx_lt} 8 ML, the peak in the heat capacity exhibits signs of finite-size effects. At higher coverages, finite-size effects are not observed, and the shape of the peak depends strongly on the substrate. We conclude that the peak is inhomogeneously broadened for n {approx_lt} 8 ML. This work represents the first measurements of the heat capacity due to orientational ordering …
Date:
November 1, 1991
Creator:
Phelps, R. B.
System:
The UNT Digital Library
Academic Achievement Among Language-Impaired Children as a Function of Intensive Preschool Language Intervention
Parents and professionals are concerned about the long-term effects of language problems on later academic, communicative and behavioral functioning of children. The purpose of this study was to examine the relationship of level of language impairment with type of class placement, reading achievement, and social emotional functioning. Subjects were 19 children, aged 4 years, 10 months through 10 years, 4 months, who had previously been enrolled in a preschool language development program. Statistical analyses were performed on data from the Kaufman Assessment Battery for Children (K-ABC), Test of Early Reading Ability (TERA), and the Achenbach Child Behavior Checklist (CBC). Results do not support a relationship between level of language impairment and academic or social/emotional functioning.
Date:
August 1990
Creator:
McCormack, Sarah (Sarah Smith)
System:
The UNT Digital Library
Academic Achievement: Examining the Impact of Community Type at a Small Liberal Arts College in Texas
Hierarchical regression was used to determine if high school community type is an effective predictor of academic success when controlling for demographics, prior academic achievement, socioeconomic status, and current commitment or work habits for students entering Austin College in 1992,1993, and 1994 . Findings revealed that there is a relationship between attending high school in community types of rural and independent town controlling for the effects of SAT scores, high school rank, sex, and late application deposit on first semester grade point average.
Date:
August 1995
Creator:
Rutherford, Janis Pruitt
System:
The UNT Digital Library
Academic Achievement of National Social Fraternity Pledges Compared to Non-Fraternity Students
This study examined the academic achievement of national social fraternity pledges compared to non-fraternity students at the University of Texas at Arlington. It was done to determine whether significant differences existed between the grade point averages of pledges of social fraternities and those of students who did not pledge a social fraternity, and to determine whether significant differences existed among fraternities when compared with each other with respect to academic achievement. This study was meant to provide a research design that could be used by other colleges and universities with fraternities to conduct the same comparison of academic performance. In the fall semester of 1989, 164 pledges were selected as the population for the study to be matched with non-fraternity students based on Scholastic Aptitude Test (SAT) scores, age, sex, classification, academic major, and number of hours attempted. A T-test of like groups was performed on the entire population with no significant difference found at the .05 level between all the fraternity pledges and all the matched pairs. A T-test of like groups was performed on the pledges from each separate organization and there was a significant difference among three of the fraternities. Two of the fraternities had significantly higher …
Date:
August 1990
Creator:
Gardner, Kent Lee
System:
The UNT Digital Library
Academic, Behavioral, and Social Competency Characteristics of Non-Handicapped, Learning Disabled, and Emotionally/Behaviorally Disordered Adjudicated Juveniles
The juvenile justice system is society's response to juvenile misconduct. In spite of numerous federal, state, and local programs, the problem of juvenile delinquency persists. An increasing number of juveniles are being taken into custody and placed in institutional settings. Although juvenile delinquents share a number of common general characteristics (e.g., sex, minority, lower socioeconomic status, a history of school failure), they are not a homogeneous group. Effective educational interventions with delinquent juveniles can meet their unique academic, vocational, and social skills deficits. Handicapped juveniles are disproportionately represented among juvenile correctional facility populations. The identification of handicapped juveniles among delinquent populations is compounded as they share many of the same general characteristics. Federal statutes require individualized educational programs for all handicapped juveniles. This research investigated academic, behavioral, and social competencies of non-handicapped and handicapped adjudicated youth. Specifically, this investigation assessed measures of academic performance, classroom behavior, self-esteem, and social behavior. ANOVA indicated statistically significant differences between non-handicapped, learning disabled, and emotionally/behaviorally disordered adjudicated juveniles in reading achievement, mathematics achievement, and teacher generated measures of classroom behavior.
Date:
August 1990
Creator:
Campbell, Robert E. (Robert Eugene)
System:
The UNT Digital Library
Academic Lineage and Student Performance in Medical School
This research investigated the association between academic lineage and student performance in medical school. The purposes of the study were to: (1) determine whether the Carnegie classifications of medical school applicants' institutions of origin are associated with academic performance in medical school; (2) consider the relationship between the admission selectivity of the schools of origin and the academic performance of medical school students; (3) compare the performance of medical students from institutions under public governing control with students from privately controlled institutions; and (4) establish a model by which the relative academic strengths of applicants from a variety of undergraduate institutions can be understood more clearly based on the previous performance of medical students from schools with similar institutional characteristics. A review of the literature on medical school admissions was completed and used to develop this research. Medical students from the University of Texas Southwestern Medical Center at Dallas who enrolled between the years 1990 and 1994 and graduated or were dismissed between the years 1994 and 1998 were selected as the sample for the study (n=933). The undergraduate institution of origin for each student was coded based on its Carnegie classification, admissions selectivity group, and whether its governing control …
Date:
August 1999
Creator:
Wright, James Scott
System:
The UNT Digital Library
Accelerated hygrothermal stabilization of composite materials
Experimentation validated a simple moisture conditioning scheme to prepare Gr/Ep composite parts for precision applications by measuring dimensional changes over 90 days. It was shown that an elevated temperature moisture conditioning scheme produced a dimensionally stable part from which precision structures could be built/machined without significant moisture induced dimensional changes after fabrication. Conversely, that unconditioned Gr/Ep composite panels exhibited unacceptably large dimensional changes (i.e., greater than 125 ppM). It was also shown that time required to produce stable parts was shorter, by more than an order of magnitude, employing the conditioning scheme than using no conditioning scheme (46 days versus 1000+ days). Two final use environments were chosen for the experiments: 50% RH/21C and 0% RH/21C. Fiberite 3034K was chosen for its widespread use in aerospace applications. Two typical lay-ups were chosen, one with low sensitivity to hygrothermal distortions and the other high sensitivity: [0, {plus_minus} 45, 90]s, [0, {plus_minus} 15, 0]s. By employing an elevated temperature, constant humidity conditioning scheme, test panels achieved an equilibrium moisture content in less time, by more than an order of magnitude, than panels exposed to the same humidity environment and ambient temperature. Dimensional changes, over 90 days, were up to 4 times lower …
Date:
May 1, 1994
Creator:
Gale, J. A.
System:
The UNT Digital Library
Acceleration of electrons using an inverse free electron laser auto- accelerator
We present data from our study of a device known as the inverse free electron laser. First, numerical simulations were performed to optimize the design parameters for an experiment that accelerates electrons in the presence of an undulator by stimulated absorption of radiation. The Columbia free electron laser (FEL) was configured as an auto-accelerator (IFELA) system; high power (MW`s) FEL radiation at {approximately}1.65 mm is developed along the first section of an undulator inside a quasi-optical resonator. The electron beam then traverses a second section of undulator where a fraction of the electrons is accelerated by stimulated absorption of the 1.65 mm wavelength power developed in the first undulator section. The second undulator section has very low gain and does not generate power on its own. We have found that as much as 60% of the power generated in the first section can be absorbed in the second section, providing that the initial electron energy is chosen correctly with respect to the parameters chosen for the first and second undulators. An electron momentum spectrometer is used to monitor the distribution of electron energies as the electrons exit the IFELA. We have found; using our experimental parameters, that roughly 10% of …
Date:
July 1, 1992
Creator:
Wernick, I. K. & Marshall, T. C.
System:
The UNT Digital Library
Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions
The existence of singly, doubly, and triply charged diatomic molecular ions was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF^3+ was measured.
Date:
December 1994
Creator:
Kim, Yong-Dal
System:
The UNT Digital Library
Accounting Measurement Bias and Executive Compensation Systems
This dissertation presents empirical evidence intended to help answer two research questions. The first question asks whether executive compensation systems appear to exploit the bias in accounting-based performance measures in order to reduce the volatility in executive compensation and to allocate incentives more effectively across the range of activities performed by the executive. The second question asks whether compensation systems systematically differ between firms that use alternative accounting methods and whether any such systematic difference helps explain accounting choice. Parameters estimated in fixed-effects endogenous switching regression models were used to test the risk-shielding and incentive-allocation hypotheses. The models were estimated across a dataset consisting of 1151 executive-year observations of annual compensation paid to 222 top-level executives in 40 oil and gas firms. The dataset was partitioned by accounting method and separate models estimated for the full cost and successful efforts partitions. The tests provided modest support for the risk-shielding and incentive-allocation hypotheses, revealing that accounting measurement bias is used to focus incentives for effort in the exploration activity and to reduce executives' exposure to production risk. The design also allowed an estimate of the proportional change in compensation that was realized from the accounting choice actually made.
Date:
December 1994
Creator:
Boone, Jeffery Paul
System:
The UNT Digital Library
Accounting Regulation and Information Asymmetry in the Capital Markets: An Empirical Study of Accounting Standard SFAS no 87
This study uses both basic and self-selection regression models to test three hypotheses about the effect of SFAS 87 disclosures on information asymmetry during 1985- 1987. Both types of models test the hypotheses after controlling for changes in the inventory holding and order processing costs of the spread, while the self-selection models also control for potential self-selection bias.
Date:
August 1994
Creator:
Lin, Wen-shan
System:
The UNT Digital Library
Acculturation in African American College Women and Correlates of Eating Disorders
Although eating disorders have been the focus of much research, the inclusion of minority populations has been minimal. A recent review of the literature by Dolan (1991) has found that eating disorders were most likely to be present in non-White women who were exposed to Western societies and cultures. Thus, the purpose of this study was to examine personality, physical, and cultural correlates of bulimic symptomatology in a sample of African American college women. The Bulimia Test Revised (BULIT-R) was used to assess bulimia symptoms. The African American Acculturation Scale (AAAS), the Beliefs about Attractiveness Scale Revised (BAAR factors 1 and 2), the Rosenberg Self-Esteem Scale (SES), the Centers for Epidemiological Depression Scale (CES-D), Body Parts Satisfaction Scale (BPSS), and body mass were the independent variables hypothesized to predict bulimic symptoms. Hierarchical regression analysis revealed that body mass, depression, and low self-esteem were the best predictors of bulimic symptomatology, together accounting for 38% of the variance. Beliefs about attractiveness and body satisfaction were related to bulimic symptoms but not when considered simultaneously with the other variables. Acculturation was not predictive of bulimic symptoms. 0-ordered correlations revealed that beliefs about attractiveness and body satisfaction were correlated with bulimic symptoms. Acculturation was …
Date:
August 1996
Creator:
Lester, Regan
System:
The UNT Digital Library
O-Acetylserine Sulhydralase-A from Salmonella typhimurium LT-2: Thermodynamic Properties and SPectral Identification of Intermediates
O-Acetylserine Sulfhydrylase (OASS) is a pyridoxal phosphate enzyme that catalyzes the reaction of O-acetyl-Lserine with sulfide to give L-cysteine. OASS is present as two isoforms, designated -A and -B. The kinetic mechanism of OASS-A is well known and there is also much known concerning the acid-base chemistry of the enzyme. However, little is known concerning the location of the rate determining steps, the sequencing of chemical steps that occur at the active site, or the nature of the rate determining transition states. The studies performed to help elucidate these aspects of the OASS-A mechanism included determination of the thermodynamics of both half reactions, along with studies utilizing substrate analogs of OAS halting the reaction at specific points along the reaction pathway allowing the identification of reaction intermediates. The free energy change of the first half reaction was shown to be -5.7 Kcal/mole while the second half reaction was shown to be, for all intents and purposes, irreversible. Intermediates along the reaction pathway that have been previously identified include the internal Schiff base and the a-aminoacrylate. The external Schiff base was identified using the analogs cysteine, alanine, and glycine while the geminal diamine was identified using the analog serine. Formation of …
Date:
August 1993
Creator:
Simmons, James Walter
System:
The UNT Digital Library
Acoustic Resonance Characteristics of Rock and Concrete Containing Fractures
None
Date:
August 1, 1998
Creator:
Nakagawa, S.
System:
The UNT Digital Library
Actinide cation-cation complexes
The +5 oxidation state of U, Np, Pu, and Am is a linear dioxo cation (AnO{sub 2}{sup +}) with a formal charge of +1. These cations form complexes with a variety of other cations, including actinide cations. Other oxidation states of actinides do not form these cation-cation complexes with any cation other than AnO{sub 2}{sup +}; therefore, cation-cation complexes indicate something unique about AnO{sub 2}{sup +} cations compared to actinide cations in general. The first cation-cation complex, NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, was reported by Sullivan, Hindman, and Zielen in 1961. Of the four actinides that form AnO{sub 2}{sup +} species, the cation-cation complexes of NpO{sub 2}{sup +} have been studied most extensively while the other actinides have not. The only PuO{sub 2}{sup +} cation-cation complexes that have been studied are with Fe{sup 3+} and Cr{sup 3+} and neither one has had its equilibrium constant measured. Actinides have small molar absorptivities and cation-cation complexes have small equilibrium constants; therefore, to overcome these obstacles a sensitive technique is required. Spectroscopic techniques are used most often to study cation-cation complexes. Laser-Induced Photacoustic Spectroscopy equilibrium constants for the complexes NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, NpO{sub 2}{sup +}{center_dot}Th{sup 4+}, PuO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, …
Date:
December 1994
Creator:
Stoyer, N. J. & Seaborg, G. T.
System:
The UNT Digital Library
Active or Passive Voice: Does It Matter?
This thesis reports on the use of active and passive voice in the workplace and classroom through analysis of surveys completed by 37 employees and 66 students. The surveys offered six categories of business writing with ten sets of two sentences each, written in active and passive voice. Participants selected one sentence from each set and gave a reason for each selection. The participants preferred active over passive 47 to 46 percent of opportunities, but they preferred mixed voice over both, 49 percent. The participants preferred active only for memos to supervisors; in the other five categories they preferred passive or mixed voice. Both males and females preferred mixed voice, and age appeared to influence the choices. They cited context as the most common reason for using passive.
Date:
December 1993
Creator:
Watson, Rose E. (Rose Elliott)
System:
The UNT Digital Library
The Activities of Disaster Relief Organizations During the Permanent Housing Phase of Recovery: a Case Study Analysis
This study investigates the recovery efforts provided for low income and ethnic minority populations by organizations during the permanent housing phase of recovery in Watsonville, California, following the Loma Prieta earthquake of October 17, 1989. The case study format is used to discover what activities were performed and why each organization chose to perform them. Dynes and Quarantelli's (1968) typology of organization is used to explain how and why established, expanding, extending and emergent organizations participated in the recovery efforts. The findings indicate that the type of organization dictated the kind of tasks each organization performed. Organizations maintained activities during recovery for which they had experience, expertise and proficiency.
Date:
August 1992
Creator:
Ephraim, Melinda M. H.
System:
The UNT Digital Library
Acts of Survival: the Plight and Prospects of Dallas Theatre
A comprehensive investigation examines the decline and changes that have affected Dallas regional theatre development from the dream of Margo Jones in the 1940s to the proliferation of emerging theatres in 1993. Changing economic conditions, lack of audience support, and shortages of performance space have contributed to an exodus of Dallas actors and artists. Reviewed are measures to reverse this trend, including funding changes, awareness campaigns, improved inter-theatre cooperation, and guidelines for audience development. The study's conclusion notes that theatres do, indeed, have a natural life cycle, but with renewed emphasis on audience development and self-sufficiency, theatres in Dallas can endure and contribute to an enlarged sense of civic pride.
Date:
December 1993
Creator:
Leeman, Patricia Diane
System:
The UNT Digital Library
N-Acylethanolamines and Plant Phospholipase D
Recently, three distinct isoforms of phospholipase D (PLD) were identified in Arabidopsis thaliana. PLD α represents the well-known form found in plants, while PLD β and γ have been only recently discovered (Pappan et al., 1997b; Qin et al., 1997). These isoforms differ in substrate selectivity and cofactors required for activity. Here, I report that PLD β and γ isoforms were active toward N-acylphosphatidylethanolamine (NAPE), but PLD α was not. The ability of PLD β and γ to hydrolyze NAPE marks a key difference from PLD α. N-acylethanolamines (NAE), the hydrolytic products of NAPE by PLD β and γ, inhibited PLD α from castor bean and cabbage. Inhibition of PLD α by NAE was dose-dependent and inversely proportional to acyl chain length and degree of unsaturation. Enzyme kinetic analysis suggested non-competitive inhibition of PLD α by NAE 14:0. In addition, a 1.2-kb tobacco (Nicotiana tabacum L.) cDNA fragment was isolated that possessed a 74% amino acid identity to Arabidopsis PLD β indicating that this isoform is expressed in tobacco cells. Collectively, these results provide evidence for NAE producing PLD activities and suggest a possible regulatory role for NAE with respect to PLD α.
Date:
December 1998
Creator:
Brown, Shea Austin
System:
The UNT Digital Library
Ádám's Conjecture and Its Generalizations
This paper examines idam's conjuecture and some of its generalizations. In terms of Adam's conjecture, we prove Alspach and Parson's results f or Zpq and ZP2. More generally, we prove Babai's characterization of the CI-property, Palfy's characterization of CI-groups, and Brand's result for Zpr for polynomial isomorphism's. We also prove for the first time a characterization of the CI-property for 1 SG, and prove that Zn is a CI-Pn-group where Pn is the group of permutation polynomials on Z,, and n is square free.
Date:
August 1990
Creator:
Dobson, Edward T. (Edward Tauscher)
System:
The UNT Digital Library