A stress control design protocol was developed to minimize coal mine bumps, which are the explosive failure of highly stressed pillars. The protocol was developed for room-and-pillar retreat mining conducted with available continuous miner technology. The inability of existing coal pillar equations to accurately represent the wide total extraction pillars required, forced the development of the pseudoductile coal pillar strength model. A confined pillar core is assumed to reach a maximum stress when surrounded by a yielded perimeter. The width of the yielded perimeter is assumed to increase linearly with increased coalbed thickness. The pseudoductile model was employed in the development of supercritical and subcritical width section design criteria. The supercritical design procedure assumes an infinitely long pillar line, composed of uniformly sized pillars, extracted against an infinitely wide gob area. Tributary area theory was combined with a linear shear angle concept to estimate the loads applied to total extraction pillars adjacent to gob areas. The boundary element code MULSIM/NL was utilized in the development and implementation of a systematic subcritical design procedure to apply the stress shield concept to retreat room-and-pillar coal mining, under bump hazard. The complex distribution of gob side abutment load between the side abutment pillars and the chain pillars in the total extraction zone made computer simulation a necessity. Section layouts were determined for the mining of a 6 ft thick coalbed under overburden up to 2,200 ft thick. The sections consist of total extraction areas separated by continuous abutment pillars. A spreadsheet program LAYOUT was created to summarize and provide for efficient utilization of the bump control design protocol. Based on overburden thickness, coalbed thickness, abutment load linear shear angle, and pillar dimensions entered by the user, LAYOUT calculates a stability factor for the first and second pillar row outbye the expanding gob for supercritical width sections. If the overburden and coalbed thickness conditions do not allow a supercritical section design, LAYOUT develops a subcritical design. / Ph. D.

This dissertation investigates two problems in the function theory of one complex variable. In Chapter 1, we study the asymptotics and zero distribution of solutions of the differential equation wⁿ + A(z)w = 0, where A(z) is a transcendental entire function of very slow growth. The result parallels the classical case when A(z) is assumed to be a polynomial. An analogue concerning the case when A(z) is a transcendental entire function whose series expansion satisfies the Hadamard gap condition is given. In Chapter 2, we give upper bounds for the number of deficient functions of entire functions of completely regular growth and entire functions whose zeros have angular densities. In particular, the bound is 2λ + 1 if the entire function is of completely regular growth with order λ, 0 < λ < ∞. / Ph. D.

Organizations today place great emphasis on the selection of their managerial and supervisory personnel. Consequently, the need to develop strong predictors of leadership for use in selection tests is immense. Theoretically and historically, intelligence, dominance, masculinity-femininity, and self-monitoring have been strong indicators of leadership. Accordingly, biographical questionnaires and personality inventories were administered to 1137 Air Force officers attending Squadron Officer School to determine their levels of intelligence, dominance, femininity, and self-monitoring. These traits and individual difference variables were then used in a discriminant analysis to predict the subject's classification into one of four leadership categories. Analyses showed differences between leaders and nonleaders for intelligence, dominance, and femininity, but not for self-monitoring. However, a discriminant analysis and associated cross validation resulted in no predictive capability. A possible reason for the lack of classification capability was the uniqueness of the military sample. Since military individuals seem to share very common experiences and beliefs, the sample appeared to be quite homogeneous making differences between leaders and nonleaders extremely difficult to detect. Future studies should address this potential problem / Ph. D.

Increasing use of fiber reinforced ceramic matrix composites (CMC's) materials is needed, especially for hostile environments such as elevated temperatures. However, some fundamental issues regarding how these materials should be made for optimized performance are far from being settled. This study focuses on the modeling of the tensile behavior of unidirectional CMC using statistical methods and micro-mechanical analysis, based on laboratory observations. The model can be used to examine the effect of performance-influencing parameters on the strength of unidirectional CMC, thus shed light on how such material should be put together. The tensile strength model was then modified such that the behavior of unidirectioal CMC under cyclic tensile load can be studied. Results from the tensile strength model suggest that the Weibull modulus, <i>m</i>, of the strength of the reinforcing fibers and the fiber/matrix interfacial shear stress both have significant effect on the strength and toughness of the unidirectional composite: a higher <i>m</i> value and a lower interfacial shear stress result in a lower strength; a lower value of <i>m</i> and a higher interfacial shear stress results in a higher strength but lower toughness. Calculations from the tensile fatigue model suggest that a lower <i>m</i> value results in a longer fatigue life. / Ph. D.

The goal of this study is to develop and test a conceptual framework of the impact of selected human factors on acquired firm lower level employees' perception toward acquisition success. The variables selected for inclusion in the framework have been identified from the following relevant literature in the (1) post acquisition integration area, (2) management area, and (3) strategy implementation area. The framework incorporates direct effects of employees' involvement in the integration process, extent of employees being informed about integration activities, and the amount of company support on employees' perceptions toward acquisition success. In addition, the level of integration has been included in the framework as a possible moderating variable. Based on two acquisitions , made by one firm in the U. S. banking industry, the study examines the above relationships with a number of statistical techniques. These techniques includes correlation analysis, t-test, and regression analysis. Two hundred and fifty four respondents completed the study employees' questionnaire. / Ph. D.

Four sol-gel systems (alumina, aluminum hydroxide, zirconia, and magnesia) were investigated, primarily by laser spectroscopy, on several series of materials prepared by systematically varying the synthesis procedures. Key material phases analyzed were: (1) nanocrystalline boehmite [AlO(OH)]; (2) bayerite, nordstrandite, and gibbsite [Al(OH)₃ polymorphs]; (3) amorphous zirconia [a-ZrO₂]; and (4) magnesite [MgCO₃], hydromagnesite [4MgCO₃·Mg(OH)₂·5H₂0], and magnesia [MgO]. Crystal nucleation and crystal growth kinetics were studied in several cases, with x-ray experiments carried out to calibrate the Raman-scattering technique I developed for monitoring crystallite size. Nanocrystalline boehmite, γ-AlO(OH), was found to be the principal component in the sol-gel alumina system. Materials were prepared by the hot-water hydrolysis/condensation of Al(OC₄H₉)₃, the Yoldas process, as a function of process variables such as the time spent in the sol phase. Small but systematic changes, as a function of sol aging time, were discovered in the lineshape and position of the dominant boehmite Raman band observed in the alumina hydrogels. These spectral changes were interpreted in terms of nanocrystallinity-induced finite-size effects associated with the slow growth of AlO(OH) nanocrystals in the sol. X-ray diffraction experiments were used to determine nanocrystal sizes (as small as 3 nm for gels prepared from fresh sols) and to estimate growth kinetics from the Raman-lineshape results. These results appear to be among the first available for crystallite growth kinetics (ripening) in the near-atomic-scale nanocrystal regime. The Raman peak-position shift is proportional to L^-α, where L is the average nanocrystal size and α is a Raman-versus-size scaling exponent. For AlO(OH), I determined α to be 1.0, close to the scaling-exponent values reported for graphite and BN and different from the values (about 1.5) that describe the reported behavior of Si, Ge, and GaAs. The trihydroxide polymorph system is closely related to the sol-gel alumina system. The processing temperature and the method of hydrolysis were varied, in order to determine their effect on the trihydroxide phase mix. The trihydroxide phase mix does not change with time; it depends only on the initial hydrolysis conditions. Bayerite is the primary phase present for materials processed at 25 C, while nordstrandite is the primary phase present for materials processed at 60 C. It is shown that the trihydroxide crystal nucleation kinetics are responsible for the Al(OH)₃ phase mix. Hydroxide/oxyhydroxide phase-mix kinetics were also studied; this ratio increases with time. The associated rate constant decreases with increasing temperature. Sol-gel zirconia was prepared by using atmospheric water to hydrolyze a mixture of zirconium propoxide, acetic acid, and n-propanol. This produces a clear gel. Hydrogen peroxide was found to chemically react with the gels. Clean Raman spectra reveal a broad-band structure (the full width at half maximum is 150 cm⁻¹) centered at about 460 cm⁻¹. This band is interpreted as the signature of an amorphous phase of zirconia. Raman and luminescent spectra (both obtained on the Raman spectrometer) were used to monitor the conversion of magnesium-carbonate-based materials to magnesium oxide, as a function of temperature. This new phase-determination technique utilizes the krypton 674.1 nm laser line so that the carbonate symmetric-stretch band and the MgO:Cr⁺⁺⁺ luminescence band are readily observable on the same spectrum. / Ph. D.

This work presents the modeling and analyses of multiple-output forward converters with weighted voltage control. Based upon the analyses, the systematic design methodologies and design tools are provided. A power stage de model including all the major parasitics, which are detrimental to the output voltages, is derived. A nonlinear programming based design tool is developed to search for the weighting factors. Five methods of stacking secondaries to improve cross-regulation are presented, and the improvement of cross-regulation is quantified. A small-signal model of the multiple-output converters with coupled output filter inductors and weighted voltage control is established. The small-signal characteristics are studied, and the model shows that the system behavior is very sensitive to the coupling coefficient, which has been reported, but never been quantified. The pole-zero interlaced condition is derived. A current-mode control small-signal model is also presented, which can predict all the observed phenomena of current-mode control. Compensator design is discussed for different types of power stage transfer functions for both voltage-mode and current-mode control. / Ph. D.

Mn-salophen complex with superoxide-scavenging activity was prepared from manganese(III) acetate dihydrate and salophen in ethanol. Visible absorption spectrum of the red-brown solution exhibited a broad absorption band at 430 - 450 nm with two shoulders between 500 and 600 nm which were absent with either salophen or manganic acetate alone. Titration of salophen with manganese(III) was consistent with a 1:1 Mn to salophen stoichiometry of the complex based on changes in the absorbance at 500 nm or of superoxide scavenging activity. The SOD-like activity of the complex in the xanthine-xanthine oxidase/cytochrome <i>c</i> assay was 1450 units/mg salophen. The SOD activity of the complex was suppressed 50% in the presence of EDTA (1 mM), but was not altered in the presence of bovine serum albumin (1 mg/ml) or crude protein extract of <i>E. coli</i> QC779 <i>sodA sodB</i> (1 mg/ml). <i>E. coli</i> QC779 <i>sodA sodB</i> grew scantily after an 8 hour lag phase in aerobic M63 glucose minimal medium. / Ph. D.

A novel concept, the fracture efficiency, is proposed in this dissertation as a performance index of fracture specimen designs for adhesive bonds. Evaluated based on a simple quantity, the fracture efficiency parameter, the fracture efficiency represents how much crack driving force a certain specimen design can produce along the bondline for a given maximum non-singular stress in the adherends. In this dissertation, a study of membrane peeling specimens shows that various existing test geometries have little difference in the fracture efficiency. Furthermore, the study shows that it is unlikely to develop new n1embrane peeling tests with high fracture efficiency. Therefore, gross inelastic energy dissipation in the film specimen may occur when using the membrane peeling tests, and may result in large errors in the film adhesion measurement when only elastic material response is considered in the analysis. As a result, the use of a backing material for film adhesion measurement is suggested because of the significant increase in the fracture efficiency when a proper backing material is used. Besides the use as one of the guidelines for fracture specimen designs, it is also demonstrated in this dissertation that the fracture efficiency parameter can also be used to help one determine the validity of a measured bond fracture strength. The study of fracture efficiency leads to new analyses of several existing fracture test geometries, and contributes to a better understanding of the standard blister, island blister, peninsula blister, peel, and cracked lap shear tests. It is found that the island blister and peninsula blister tests can produce very high energy release rates at low pressures by using a small island radius or a small peninsula width. However, these so called "high energy release rate" tests also induce localized high stress concentrations near the debond front and therefore, yielding or rupturing may still unavoidable in such specimens. The significant localized inelastic effect on the measurement of the bond fracture strength is also demonstrated in the peninsula blister experiment for an adhesive tape specimen subjected to a relatively low pressure load. Another important conclusion drawn from the analyses of various membrane peeling tests is that the existing membrane blister tests are special cases of the peel test if compared very near the debond front. Besides analyses for membrane peeling specimens, this dissertation also reports a new closed form solution for the cracked lap shear specimen using a geometrically nonlinear beam-column approach. Excellent agreement for energy release rates has been shown between the closed form solution and geometrically nonlinear finite element analyses. The study also discusses how to design a cracked lap shear specimen of constant energy release rate and high fracture efficiency. / Ph. D.

Because the act of supervisory feedback can critically affect a subordinate's performance, it is imperative to explicate the various conditions in which the character of feedback is determined. The purpose of the following research was to model the conditions under which supervisors adopt a negative feedback bias (NFB). This bias was first described by Kahneman and Tversky (1973), when they noted that Israeli flight instructors found that praise of exceptionally good piloting was often followed by poorer performance, while criticism of exceptional poor flying was usually followed by improved performance. Thus, the flight instructors came to believe that negative feedback motivated people effectively, while positive feedback appeared ineffective. Of course, supervisors had erred by failing to recognize the natural variation of their students' performance. In general, this error applies primarily to the conditions under which supervisors acquire and interpret information. Two factors were hypothesized as responsible for the emergence of a NFB: (a) limitations caused by opportunity-based supervision, where only a certain amount of subordinate behavior can be sampled at any given moment, and (b) supervisors find it difficult to recognize the natural variation, random fluctuations, and regression to mean processes characteristic of performance governed by common causes (cf. Deming, 1982; Hogarth, 1980 and Kahneman & Tversky, 1973). Results indicated that NFB was an emergent process occurring over time and under conditions where (a) supervisors managed highly inconsistent subordinate performance and (b) supervisors had limited information regarding a subordinate's performance per evaluation episode. Since this experimental approach and set-up is relatively novel, the results are discussed from several conceptual perspectives. Finally, a discussion regarding the ecological approach to feedback research, and the importance of model building and testing is offered. / Ph. D.