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An examination of oxidation products of the pterin cofactor in the formate dehydrogenase of Methanobacterium formicicum revealed that the cofactor is a 6-substituted pterin similar to the molybdopterin of xanthine oxidase. In contrast to the molybdopterin from xanthine oxidase the formate dehydrogenase cofactor was unable to complement the cofactor-deficient nitrate reductase of Neurospora crassa mutant nit-1 and possessed two phosphate groups. Incubation of oxidized formate dehydrogenase with cyanide resulted in an irreversible loss of enzyme activity which could not be restored by treatment with sulfide. Equimolar amounts of thiocyanate were released from cyanide-treated formate dehydrogenase suggesting the loss of one terminal sulfur ligand to molybdenum. These results along with electron paramagnetic resonance spectroscopy of the cyanide-inactivated formate dehydrogenase suggest that the the molybdenum ligands of the enzyme are similar to those of xanthine oxidase. The concentration of molybdenum and the level of formate dehydrogenase activity in extracts of hydrogen-grown Methanobacterium formicicum decreased by at least 10- fold when the organism was grown for several transfers in molybdenum-deficient media or with added tungstate. Immunochemical analysis showed that both subunits of the formate dehydrogenase were produced regardless of the growth condition. However the amount of formate dehydrogenase protein decreased more than 10-fold when the amount of molybdenum in the cell was low. The pterin cofactor was present in the inactive enzyme from tungstategrown cells; however the protein contained less than 0.05 molecules of molybdenum or tungsten per formate dehydrogenase. Messenger RNA specific for fdh gene was detected in high amount in cells grown without added molybdenum and in low amount in cells that contained high amounts of molybdenum. These results suggest that molybdenum is required for the synthesis of a stable formate dehydrogenase and that a molybdenum-dependent repressor may be required for the termination of fdh transcription. / Ph. D.

Field experiments were conducted in the Coastal Plain and Ridge and Valley regions of Virginia during the 1981-82 through 1985-86 winter wheat growing seasons. The treatments in all experiments consisted of varying amounts of N fertilizer rates applied at Zadoks' growth stages 25 (GS 25) and 30 (GS 30). The research was divided into three studies. The first study was conducted to assess the effect of N fertilizer rates and climatic conditions on the amounts and patterns of the crop N uptake. Dry matter production and total N concentration were measured in total above ground plant material at different growth stages, as well as in leaves, stems, and spikes. Plant N uptake was affected by the climatic conditions in the different growing seasons. Temperature and precipitation variations in early spring determined the differences in amounts and patterns of the N uptake by whole plants and by the various plant portions. Maximum N uptake daily rates were obtained in the period immediately after GS 30 suggesting that this is the wheat growth stage in which the highest efficiency of N fertilizer use could be expected. Crop N uptake at GS 30 also appeared to be a potentially good indicator of the plant N requirements. The second study was designed to develop models for determining critical N levels and optimum N fertilizer rates for winter wheat. Two nonlinear models were successfully developed to determine critical N levels at GS 30 utilizing plant N concentration at GS 30 (N%30) and crop N uptake at GS 30 (NUP30). The R² values for the models utilizing N%30 and NUP30 as independent variables were 0.87, and 0.82, respectively. Simple regression models were successfully developed to predict N rates required at GS 30 to obtain either maximum or economically optimum grain yields. The models utilized NUP30 as the independent variable and had high correlation coefficients and good predicting ability. The objective of the third study was to determine the recommended amount of N fertilizer to be applied at GS 25 that would optimize the use of the simple linear regression models developed in the second study. Quadratic programming models were developed with the objective of maximizing marginal profit with N fertilizer application. The models were then solved to determine the amounts of N at GS 25 and at GS 30 that would produce the maximum attainable profit. Four recommended nitrogen fertilizer rates at GS 25 (N25) were evaluated: 0, 30, 60, and 100 kg N ha⁻¹. The difference (D) between the yields with maximum attainable profit (Y) and the yields when N25 was forced to be 0, 30, 60, and 100 kg N ha⁻¹ (Υ^R) was then calculated (D = Y - Y^R). The best N25 recommendation was the one that minimized the mean value, standard deviation, and coefficient of variation of D. This methodology was used for 3 nitrogen fertilizer : wheat price ratios (2.0, 4.0, and 8.0). The results indicated that the best recommendations for N25 were 50 - 60 kg N ha⁻¹ for N fertilizer : wheat price ratios of 2.0 - 4.0, and 40 - 50 kg N haha⁻¹ for a price ratio of 8.0. Sensitivity analysis was then performed to study the effect of variations in the N fertilizer : wheat price ratio on the recommended N rates. The results indicated that the recommended N rates were essentially insensitive to the variations in the price ratio of N fertilizer : wheat / Ph. D.

Based on the principle of virtual displacements, the incremental equations of motion of a continuous medium are formulated by using the total Lagrangian description. After linearization of the incremental equations of motion, the displacement finite element model is obtained, which is solved iteratively. From this displacement finite element model, four different elements, i.e. degenerated shell element, degenerated curved beam element, 3-D continuum element and solid-shell transition element, are developed for the geometric nonlinear analysis of general shell-type structures, anisotropic as well as isotropic. Compatibility and completeness requirements are stressed in modelling the general shell-type structures in order to assure the convergence of the finite-element analysis. For the transient analysis Newmark scheme is adopted for time discretization. An iterative solution procedure, either Newton-Raphson method or modified Riks/Wempner method, is employed to trace the nonlinear equilibrium path. The latter is also used to perform post-buckling analysis. A variety of numerical examples are presented to demonstrate the validity and efficiency of various elements separately and in combination. The effects of boundary conditions, lamination scheme, transverse shear deformations and geometric nonlinearity on static and transient responses are also investigated. Many of the numerical results of general shell-type structures presented here could serve as references for future investigations. / Ph. D.

Significant advances in understanding early stages of transitional flows have been achieved by studying secondary instabilities in selected prototype flows. These secondary instabilities can be modeled as parametric instabilities of the nearly periodic flow that consists of the prototype velocity profile and a superposed finite-amplitude TS-wave (wavelength λ). The generally three dimensional secondary instabilities are governed by a linearized system of partial differential equations with periodic coefficients which are reduced to an algebraic eigenvalue problem through the application of a spectral collocation method Following Floquet theory, previous analysis looked for subharmonic (wavelength 2 λ) and fundamental (wavelength λ) types of solutions. We extend the Floquet theory to solutions having arbitrary wavelengths, hence including the previous solutions as special cases. Modes with wavelength in between the subharmonic and fundamental values are called detuned modes. Detuned modes lead to combination resonance which has been observed in controlled transition experiments. Knowledge of the bandwidth of amplified detuned or (combination) modes is very important for clarification of the selectivity of the early stages of transition with respect to initial disturbances. We have selected two flows: the Blasius boundary layer flow and the hyperbolic-tangent free-shear flow as prototypes of wall bounded Hows and unbounded Hows, respectively. In the Blasius flow we have concentrated on studying detuned modes. We found the growth rates of modes slightly detuned from the subharmonic wavelength to be almost as large as the growth rate of the subharmonic itself. This result is consistent with both the broadband spectra centered at subharmonic frequency observed in the "biased" experiment of Kachanov & Levchenko, wherein only the TS frequency was introduced, and with the large band-width of resonance in the "controlled" experiments, wherein a TS wave and the detuned modes were introduced simultaneously. In the free-shear flow, our goals were three-fold. The first was to investigate whether the Floquet analysis based on the shape assumption for TS waves would provide results consistent with results for the stability of Stuart vortices. Second, we aimed at revealing the effect of viscosity on these results. Finally, we wanted to evaluate a group of spectral methods for the numerical treatment of the flow in an unbounded domain. We have made a detailed analysis of subharmonic, fundamental, and detuned modes. Results display the basically inviscid, convective character of the secondary instabilities, and their broadband nature in the streamwise and spanwise directions. In the inviscid limit, and for neutral TS waves, a detailed comparison is made with the closely related study on stability of Stuart vortices by Pierrehumbert & Widnall. Good quantitative agreement is obtained. For a wide range of Reynolds numbers and amplitudes of the 2-D primary wave, results reveal that the most unstable subharmonic modes are two-dimensional (vortex pairing). On the other hand, the most unstable fundamental modes are three-dimensional, with short spanwise wavelengths. Detuned modes have characteristics in between, being most unstable in the two-dimensional or three-dimensional form depending on the detuning value. Comparisons of our results for a superposed TS wave of constant amplitude with results obtained by numerical simulations suggested that the growth of the TS wave may have a significant effect on the secondary disturbance growth. To check this hypothesis, we have developed a numerical method that accounts for small variations in the TS amplitude. However, the results indicate that the discrepancies are due to other yet concealed effects. / Ph. D. / incomplete_metadata

The purpose of this study was to examine intrafamily relationship variables which constitute the frame of reference for person perception. A model was proposed to conceptualize how the variables interact and influence the process. Specifically, the proposed model was developed to investigate how adolescent person perception is influenced by congruence between the mother and adolescent in: (a) communication, (b) dyadic relationships, and (c) adolescent self-image. One hundred forty-six mother-adolescent dyads participated in the study. Fifty-nine males and 87 females (M = 14.6 years) represented the adolescent sample. Two communication subscales from The Parent-Adolescent Communication Scale were used to measure mother-adolescent congruence: Open and Problem Family Communication (Barnes & Olson, 1982). Congruence in four aspects of dyadic relationships was measured with the Family Assessment Measure-Dyadic Relationship Scale (Skinner, Steinhauer & Santa-Barbara, 1984). The four dyadic relationship subscales were: (a) task accomplishment, (b) role performance, (c) affective interaction, and (d) control. Congruence between the adolescent's own self-image and the perception of the adolescent held by the mother was measured with The Offer Self-Image Questionnaire For Adolescents (Offer, 1977), and The Offer Parent-Adolescent Questionnaire (Offer, 1982). Adolescent person perception was measured using the Adapted Modified Role Reperatory Test-(AMRRT) (Vacc & Vacc, 1982). The results indicated a significant path coefficient between mother-adolescent congruence in adolescent social self-image and adolescent person perception ability. Contrary to expected outcomes, high percentages of mother-adolescent congruence were associated with less self and other role differentiation by the adolescent and accounted for 6% of the total variance in the model. These data indicate that the unexpected high percentages of congruence occurring in the mother's and adolescent's perceptions of the adolescent's social self-image could have represented an enmeshed relationship, thus inhibiting the adolescent's self and other role differentiation. Additionally, the dispersion of scores on the AMRRT indicated possible random responding on the instrument by the adolescent which could have contributed to a large variance, and subsequently, the loss of path linkages in the proposed model. / Ph. D.

Molecular weight control and endgroup functionalization in poly(arylene ether sulfones) has been achieved by two synthetic routes. The first utilizes DMSO/sodium hydroxide and aminophenol to introduce the amine functionality. This route, though synthetically useful, suffers from serious limitations, such as hydrolytic side reactions and oxidation of the end capping reagent. An alternative route utilized K₂CO₃/NMP as base and solvent respectively. This approach has been used with great success in the preparation of both high molecular weight polymers and functionalized oligomers. We have extended this method to include amine terminated oligomers through the use of a novel aminophenolic compound 2-p-aminophenyl-2-p-hydroxyphenylpropane or MBA. The use of MBA to introduce terminal amine functionality allowed a simpler, 1-step synthesis of controlled molecular weight oligomers to be realized. Our investigations focused on bisphenol-A based systems, but this technique may be also utilized with other bisphenols. The synthesis and characterization of a wide variety of derivatives of these functionally terminated oligomers was demonstrated. A number of potential post reactions involving these oligomeric diamines were investigated and synthetic techniques to prepare novel block and segmented copolymers were defined. As the molecular weight of the sulfone oligomer was varied, the percent sulfone character in a given polymeric material could be systematically changed. The effect was studied in block copolymers with poly(arnide sulfones) and in novel modified epoxy and bismaleimide thermosetting systems. / Ph. D.

A method for computing the skin-stiffener interface stresses in stiffened composite panels is developed. Both geometrically linear and nonlinear analyses are considered. Particular attention is given to the flange termination region where stresses are expected to exhibit unbounded characteristics. The method is based on a finite-element analysis and an elasticity solution. The finite-element analysis is standard, while the elasticity solution is based on an eigenvalue expansion of the stress functions. The eigenvalue expansion is assumed to be valid in the local flange termination region and is coupled with the finite-element analysis using collocation of stresses on the local region boundaries. In the first part of the investigation the accuracy and convergence of the local elasticity solution are assessed using a geometrically linear analysis. It is found that the finite-element/local elasticity solution scheme produce a very accurate interface stress representation in the local flange termination region. The use of 10 to 15 eigenvalues, in the eigenvalue expansion series, and 100 collocation points results in a converged local elasticity solution. In the second part of the investigation, the local elasticity solution is extended to include geometric nonlinearities. Using this analysis procedure, the influence of geometric nonlinearities on skin-stiffener interface stresses is evaluated. It is found that in flexible stiffened skin structures, which exhibit out-of-plane deformation on the order of 2 to 4 times the skin thickness, inclusion of geometrically nonlinear effects in the calculation of interface stresses is very important. Thus, the use of a geometrically linear analysis, rather than a nonlinear analysis, can lead to considerable error in the computation of the interface stresses. Finally, using the analytical tool developed in this investigation, it is possible to study the influence of stiffener parameters on the state of interface stresses. / Ph. D.

This experiment examines the effects of financial reporting bases (GAAP and income tax) and service levels offered by external accountants (audits and reviews) on loan officers. The effects are measured using a loan approval decision and four perceptions: (1) appropriate interest premium, (2) likelihood of default, (3) confidence in the financial report, and (4) usefulness of the financial report. Analysis of variance techniques are used to ascertain the effects of accounting reports on the perceptions of loan officers; legit model development is used to isolate the effects on loan approval decisions. Reviews result in higher interest premiums than audits. Loan officers also associate higher default risks with reviews and tax-basis financial reports. Loan officers are most confident with audited GAAP-basis financial reports and least confident with audited income tax basis financial reports. In addition, loan officers indicate that GAAP-basis financial reports are more useful than income-tax-basis financial reports. Neither reporting basis nor service level affected their loan-approval decisions, however. Confirmatory and exploratory factor analyses are used to develop surrogates for decision usefulness using Statement of Financial Accounting Concepts (SFAC) Number 2. The most dependable surrogate for decision usefulness developed involves two characteristics that SFAC Number 2 suggests as being nonessential to accounting information: certainty and precision. The reporting basis affected this surrogate and decision usefulness itself in the same manner; in both cases, GAAP-basis financial reports are more useful than tax-basis financial reports. Managers, accountants, and loan officers should be aware that using income-tax-basis financial reports can detrimentally affect loan officer perceptions of default risk, confidence, and decision usefulness. Further, using a review rather than an audit may affect loan officer perceptions of confidence and interest rates. Future research could introduce additional independent variables. These variables include the effects of a statement of changes in financial position, financial ratios, industries, or differential reporting. Research using qualitative characteristics of accounting information could lead to strong measures of decision usefulness that would be beneficial in ascertaining effects on loan-officer perceptions and decisions. / Ph. D.

A method for predicting unsteady, subsonic aeroelastic responses has been developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The angle of attack is limited only by the occurrence of stall or vortex bursting near the wing. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flowfield are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion. / Ph. D.