The biochemical pathway for the anaerobic degradation of gallate, pyrogallol and phloroglucinol by Eubacterium oxidoreducens was investigated. Phloroglucinol reductase was purified 90-fold, from the soluble fraction of cell extract, to electrophoretic homogeneity. The enzyme was an α₂ homodimer with a native M_r of 78,000, did not contain metals or cofactors and was specific for phloroglucinol and NADPH with a K_m of 800 μM and 6.7 μM respectively at pH 6.8. The Km for phloroglucinol decreased with increasing pH. The enzyme catalyzed reaction was reversible and the equilibrium constant was 9.6. Dihydroresorcinol was a competitive inhibitor of the reverse reaction (K_i = 756 μM). Dihydrophloroglucinol produced in cell extract with H₂ as the reductant was identical to the compound produced by sodium borohydride reduction of phloroglucinol as shown by ¹H NMR spectroscopy. The ¹³C NMR spectrum was consistent with the structural assignment of dihydrophloroglucinol. The mechanism of the proposed enzymatically catalyzed reaction is proposed to involve transfer of a hydride equivalent from NADPH to the carbonyl carbon of the phloroglucinol dianion. Mutant strains of E. oxidoreducens that showed no gallate decarboxylase or dihydrophloroglucinol hydrolase activity were isolated after mutagenesis with ethylmethane sulfonate and emichment with ampicillin. The decarboxylase deficient mutants were unable to grow on gallate while pyrogallol and phloroglucinol supported growth. The hydrolase deficient mutants were unable to grow on any aromatic substrates and converted gallate to pyrogallol and dihydrophloroglucinol. The conversion of gallate to non-aromatic intermediates by cell extract of the wild-type stain was dependent on the presence of 1,2,3,5-benzenetetrol for the conversion of pyrogallol to phloroglucinol and on formate for the reduction of phloroglucinol to dihydrophloroglucinol. Transhydroxylase activity involved in the conversion of pyrogallol to phloroglucinol was induced by growth on aromatic substrates. The formate dehydrogenase was located in the soluble fraction of cell extract, and activity was protected from oxygen inactivation by sodium azide. The Km for formate and NADP was 290 μM and 140 μM respectively at pH 7.5. The pH optimum for activity was 7.5 and maximum activity was observed at a temperature of 50°C. / Ph. D.

Ecological theory states that forest succession is largely environmentally determined. Many investigators have suggested, however, that stochastic processes can frequently alter successional pathways. In particular, the colonization phase is thought to be very stochastic. This study utilizes a unique series of 6 naturally replicated sites on Brush Mountain (Montgomery Co., VA) to determine whether forest structure and species composition is primarily deterministic or stochastic in nature. Although the canopy stratum of the mature forest at these environmentally similar sites was very Similar in structure and species composition (p>0.05), the composition of the subcanopy strata vegetation differed Significantly among sites (p<0.05). This indicated that stochastic events (e.g. low intensity ground fires, deer browsing, cattle grazing) were were important factors during the development of understory and ground layer vegetation. Site-to-site differences in subcanopy species composition remained apparent during the first 2 years following disturbance (removal of canopy cover) of 4 sites. Brush Mountain lacked a significant seed bank (< 1 seed/m²), and the dominant sub canopy species reproduced largely by vegetative sprouting. Post-disturbance colonization of the sites was very stochastic, but had relatively little immediate effect on vegetation structure and composition. In the future, however, as colonist species reproduce and increase in density, stochastic colonization events may become an important aspect of forest development at some of the sites. / Ph. D.

This study deals with the vibration and stability analyses of laminated plates and shells, using classical, first-order and third-order equivalent single-layer theories and the layer-wise theory of Reddy. Analytical solutions of these theories for natural frequencies and critical buckling loads of plates and shells under various boundary conditions are developed using an improved analytical procedure. A solution for the transient response of viscously damped cross-ply laminated plates, subjected to a sonic-boom type loading, is developed using the third-order shear deformation plate theory of Reddy and the first-order shear deformation plate theory. The nonlinear dynamic equations of the first-order shear deformation plate theory and the third-order shear deformation plate theory of Reddy are reformulated in terms of a pair of equations describing the interior and the edge-zone problems of rectangular plates laminated of transversely isotropic layers. The pure—shear frequencies of the plate in linear and nonlinear problems are identified from the edge—zone equation. For certain boundary conditions the original system of equations are reduced to three in number, as in the classical plate theory. The frequency and buckling equations of symmetric plates laminated of transversely isotropic layers are obtained using the Levinson’s third—order shear deformation plate theory. Using the interior and the edge—zone equations, the frequency and buckling equations are also obtained according to the first—order shear deformation plate theory. The solution contribution of the edge—zone equation is analyzed. By introducing a mixed approach, the bending problem of laminated plates with various boundary conditions is studied according to the first—order and Reddy’s third-order shear deformation plate theories. / Ph. D.

Cognitive science of science attempts to explain a range of phenomena familiar to philosophers of science, such as theory choice and scientific discovery. The appeal to cognitive science may be seen as an attempt to naturalize the philosophy of science. I examine and criticize several of the most important contributions to this new field. I argue that an unrecognized common defect of this work is its reliance on an explanatory approach that takes individuals’ cognitive capacities as its units of analysis. I introduce the term "cognitive individualism" to identify this position, and conclude by examining the position in detail and sketching alternative approaches to naturalizing philosophy stressing the social dimensions of science. In Chapter 1 I briefly describe the field of cognitive science, and outline the empirical resources it can provide a philosopher of science. I then outline key themes of current cognitive science of science. In the next four chapters I critically examine the work of four prominent cognitive scientists of science: Herbert Simon, Paul Thagard, Ronald Giere, and Paul Churchland. All share the same goals of naturalizing philosophy of science by using the empirical resources of cognitive science. I show that all four accounts ignore the important social nature of science, and share an adherence to cognitive individualism. In the final chapter I develop the notion of cognitive individualism in detail. I show that relying on empirical evidence from work in cognitive psychology on human judgment, and work in the sociology of science is more fruitful for explaining science than the current cognitive individualist approach. I conclude with several theses that act as guidelines for future research in naturalized philosophy of science. / Ph. D.

Theoretical and experimental studies of grain boundary structures were carried out to understand the grain boundary properties of Ni₃Al. Using various techniques of transmission electron microscopy, the geometry of grain boundaries was determined from a number of grain boundaries to obtain a distribution of grain boundary types in Ni₃Al. Five macroscopic parameters, including a misorientation between two grains and a grain boundary plane orientation, were considered in the grain boundary type. A distribution of grain boundary types in ductile Ni₃Al contained more low Σ boundaries than brittle Ni₃Al. In a distribution of grain boundary plane orientations, the trend of having high density plane of coincident sites was maintained on low Σ boundaries up to Σ = 9 and random orientations of grain boundary planes became dominant after Σ = 11. In ductile Ni₃Al, grain boundary accommodations of dislocations in the vicinity of grain boundaries were found, which were not shown in brittle Ni₃Al. Using CBED techniques, symmetry information of a single crystal was obtained. However, an extension to bicrystals was not successful. In order to study the possible disordering and segregation near grain boundaries, two different atomistic computer simulations, namely, molecular statics simulation and two dimensional lattice gas model, were carried out. Both results showed a similar trend of disordering near the grain boundary regardless of grain boundary composition and atomic interaction energy assumptions. However, segregation behavior near grain boundaries showed strong influences from grain boundary compositions and atomic interaction energy assumptions. / Ph. D.

A cellular cofferdam represents a challenging soil-structure interaction problem. The cellular system consists of a combination of a flexible structure formed from interlocking sheet piles that is filled with soil. In the past, the cellular cofferdam has been viewed as a temporary structure, and the design procedures have been based on empirical concepts. Basic to these approaches are assumptions of soil and structural behavior that have, at best, only a rough accounting for soil-structure interaction. In the last decade, work on cofferdams has improved our understanding of the behavior of these systems. Documentation of performance has increased, and in a few cases major instrumentation efforts have been undertaken. Concurrently, finite element methods have been introduced for the analysis of cofferdams. Where the finite element models have been properly calibrated by field performance, they have reasonably predicted the principal aspects of cofferdam behavior. Results of the finite element models have also served to help explain some aspects of the soil-structure interaction process in the cofferdam system. Two finite element programs are used in this research, AXISHL and GPS. The first of these is an axisymmetric analysis tool which is applicable to the case of filling of a main cell. The second program provides a simplified means of analyzing the main/arc cell and common wall system. Both programs are used in a series of parameter studies with the objective to provide information that will allow improvement of the state-of-the-art of design for cofferdams. An analytical solution is proposed which allows an insight to be developed as to how the clamping effect at the dredge line affects the behavior of the system. A simplified calculation procedure which has some of the characteristics of the finite element analysis is developed to supplement the need for a finite element analysis. / Ph. D.

The glpD gene, which encodes aerobic sn-glycerol 3-phosphate dehydrogenase, and the glpR gene, which encodes a repressor that negatively regulates the expression of the g/p regulon, map near minute 75 on the linkage map of Escherichia coli K-12. In the present study, the nucleotide sequence of the 2895 base pair of DNA containing the glpD control region and the glpE, glpG, glpR genes was determined. The translation initiation codons with adjacent ribosome-binding sites were found for these four genes. The transcription start site of the glpD gene was identified 42 base pairs upstream from the proposed methionine start codon, preceded by a region containing typical -10 and -35 sequences found in bacterial promoters. A binding site for the cyclic AMP-cAMP receptor protein complex was located just upstream from the -35 sequence, centered at position -63. The interaction site for the glp repressor was identified by using DNase I footprinting. This region contained two tandemly repeated sequences which started at the -10 sequence and continued to position +38. The glp repressor contained 252 amino acid residues and had a molecular weight of 28,046 which was deduced from the nucleotide sequence. The position of the initiation codon was verified by determination of the amino acid sequence of the N-terminus of the purified gip repressor. The presumptive helix-turn-helix region of the repressor was located near the N-terminus (amino acids 22 to 41) at a poSition analogous to that found for the operator binding domain of other repressors such as the deo and Jac repressors. The recognition helix of the glp repressor and the nucleotide sequence of the glp operator were very similar to those of the deo system. The presumptive glpR recognition helix was changed to the deoR recognition helix and the sixth amino acid arginine of the recognition helix was changed to alanine by site-directed mutagenesis. The mutant forms of the repressor had a greatly reduced affinity for the glpD operators in vivo, determined by measuring β-galactosidase activity in a strain carrying a glpD-lacZ fusion. / Ph. D.

Materials comprising of two or more polymeric components have achieved considerable technological significance in the last decade or so due to the unique properties often not attainable in their homopolymeric counterparts. In the present work, two such systemsone involving modified thermosets and the other involving thermoplastic polymer blends, have been studied with regard to their morphological and thermal properties. Both systems take the advantage of not only the physical interactions between the components involved but also their themooxidative properties, giving rise to novel properties that have both fundamental and practical importance. The network system consists of a phenolic novolac based epoxy cured in the presence of low molecular weight poly (propylene oxide). The resulting morphology of these polymers has been studied with the help of scanning electron microscopy. / Ph. D.

A partial-wave analysis of K⁺-nucleon scattering has been performed. Energy-dependent and energy-independent solutions for the isoscalar and isovector amplitudes are generated by fitting data with a chi-squared minimization technique. The isoscalar amplitudes extend to a K⁺ incident lab kinetic energy of 1100 MeV; the isovector amplitudes extend to 2650 MeV. Due to the lack of a neutron target and scarcity of isoscalar data, K⁺-deuteron inelastic and elastic data are utilized in the analysis. The theories which incorporate the K⁺-deuteron data are fixed-scatterer, single-scattering impulse approximations. Two different techniques are employed to find preliminary energy-dependent isoscalar solutions for the scattering amplitudes. The first technique involves initializing to two different single-energy solutions of previous studies. The second technique consists of utilizing the energy-dependent parametrization to fit successively larger bins of data, starting from zero energy, until the entire energy range is covered. Two solutions result from these investigations since one of the solutions from the first technique agrees with the solution from the second technique. The partial-wave amplitudes are discussed. Resonance pole positions and scattering lengths are extracted from each solution and compared with predictions from theories and other analyses. Also, observables from each solution are compared and experiments are suggested to further refine the determination of the K⁺N partial-wave amplitudes. / Ph. D.

This study examined the structural and functional development of zooplankton communities in 12 new experimental ponds for one year and tested four predictions derived from the Random Placement Hypothesis (Coleman 1981). Physico-chemistry, zooplankton colonization dynamics, zooplankton community structure and function were analyzed every two weeks from 5 February 1988 to 10 February 1989. Ponds varied in physico-chemistry at points in time but followed similar patterns during the study year. Ponds were not colonized by zooplankton similarly. Some species occurred in all ponds with about the same timing, but many species exhibited variable timing among ponds or never occurred in more than a few ponds. Colonization curves varied among ponds and through time, and species accrual curves differed in both accrual rates and the numbers of species accrued. Observed colonization curves did not closely match the curve expected according to the Random Placement Hypothesis. Zooplankton community structure also varied among ponds. Multivariate analyses could not discern similar trends in zooplankton community structure among ponds due to the disparity of species trends among ponds. species data were pooled into taxa (Copepoda, Cladocera, Rotifera, ostracoda and Chaoborus) and analyzed. Rotifers dominated zooplankton communities in densities and biomass, and ponds differed in taxa densities and biomasses. Zooplankton community function was more similar among ponds than community structure. Multivariate analyses indicated ponds generally followed similar trajectories in zooplankton community function through the year. Zooplankton did not colonize experimental ponds equally and did not develop similar zooplankton community structure among ponds. Dispersal processes probably limited colonization and development of zooplankton community structure. Zooplankton community function was generally more similar among ponds than community structure, probably due to the functional redundancy of zooplankton species. Implications of these results for experimental pond studies are discussed. / Ph. D.