The increasing demand on wood and wood products, and the simultaneously decreasing quality of wood as a raw material leads to the increasing significance of wood-based composites such as particleboard or flakeboard. The resulting mechanical and physical properties are to the large extend dictated by the densification of the wood component. To be able to predict the density of the material, the behavior of structural elements must be known. A theory developed for rigid plastic foams was modified and applied to the deformation of wood in transverse compression. A testing procedure for high strain compression over a range of temperatures was developed. In addition, a stochastic model for prediction of high strain behavior was developed. Wood of yellow poplar (<i>Liriodendron tulipuera</i>) was used as the experimental material. / Master of Science

Nitrogenase-catalyzed nitrogen fixation is a biochemically and genetically complex process requiring the participation of a number of different nif (nitrogen fixation) gene products. The nifF (electron transport), nifA (nif gene regulation) and nifE (FeMo-cofactor biosynthesis) genes from <i>Azotobacter vinelandii</i> were genetically analyzed. The nucleotide sequence of the nifF gene, which encodes a flavodoxin, was determined. Specific mutation strains indicated that in <i>A vinelandii</i> flavodoxin is not the unique physiological electron donor to nitrogenase. The nifF gene appears to be constitutively expressed but under nitrogen fixing conditions nifF gene expression is stimulated. / Master of Science

A finite element modeling and geometrically nonlinear static analysis of glued-laminated timber domes is presented. The modeling and analysis guidelines include: the generation of the geometry, the selection of finite elements to model the components of a dome (beams, purlins, connections, and tension ring), the specification of boundary conditions, the specification of material properties, the determination of a sufficiently accurate mesh, the determination of design loads and the specification of load combinations, the application of analysis procedures to trace the complete response of the structure, and the evaluation of the response. The modeling assumptions and analysis procedures are applied to a dome model whose geometry is based on an existing glulam timber dome of 133 ft span and 18 ft rise above the tension ring. This dome consists of triangulated networks of curved southern pine glulam members connected by steel hubs. The members lie on great circles of a spherical surface of 133.3 ft radius. The dome is covered with a tongue-and-groove wood decking, which is not considered in this study. Therefore, the surface pressures are converted into member loads and then discretized into nodal concentrated loads. A geometrically nonlinear, 3-d, 3-node, isoparametric beam element for glulam beams is formulated, and a program is developed for the analysis of rigid-jointed space frames that can trace the response of the structure by the modified Newton-Ralphson and the modified Risk-Wempner methods. The material is assumed to be continuous, homogeneous, and transversely isotropic. The material properties are assumed to be constant through the volume of the element. The transverse isotropy assumption is validated for southern pine by testing small samples in torsion. The accuracy of the modeling assumptions for southern pine glulam beams is experimentally verified by testing full-size, curved and straight, glulam beams under combined loads. The results show that the isobeam element can accurately represent the overall linear response of the beams. However, to analyze glulam domes with the program, connector elements to model the joints and a truss element to model the tension ring must be added. Therefore, the finite element program ABAQUS is used for the analysis of the dome model. Three dead-load/snow-load combinations are considered in the analysis of the dome model. The space frame joints and the purlin-to-beam connections are modeled with 2-node isobeam elements. A 3-d, 2-node, truss element is used to model the tension ring. Three distinct analyses are considered for rigid and flexible joints: a linear analysis to check the design adequacy of the members. A linearized eigenvalue buckling prediction analysis to estimate the buckling load, which provided accurate estimates of the critical loads when rigid joints were specified. Finally, an incremental, iterative, geometrically nonlinear analysis to trace the complete response of the structure up to failure. It is shown that elastic instability, which is governed by geometric nonlinearities, is the dominant failure mode of the test dome. At the critical load, the induced element stresses remained below the proportional limit of the material. A discussion of the results is presented, and recommendations for future extensions are included. / Ph. D.

In this work, we investigate numerically the evolution of perturbed Vlasov equilibria. according to the full nonlinear system with particular emphasis on analyzing the asymptotic states towards which the system evolves. The simulations are carried out with the numerical code that we have implemented on the Cray X-MP of the Pittsburgh Supercomputing Center and which is based on the splitting scheme algorithm. Maxwellian symmetric and one-sided bump-on-tail and two-stream type of equilibrium distributions are considered: the only distribution which seems to evolve towards a BGK equilibrium is the two-stream while the asymptotic states for the other distributions are better described by superpositions of possible BGK modes. Perturbations with wave-like dependence in space and both symmetric and non-symmetric dependence on velocity are considered. For weakly unstable modes, the problem of the discrepancy between different theoretical models about the scaling of the saturation amplitude with the growth rate is addressed for the first time with the splitting scheme algorithm. The results are in agreement with the ones obtained in the past with less accurate algorithms and do not exhibit spurious numerical effects present in those. Finally, collisions are included in the splitting scheme in the form of the Krook model and some simulations are performed whose results are in agreement with existing theoretical models. / Ph. D.

This research effort involved the application of indirect- and direct-contact, freeze-thaw conditioning techniques for improving the dewatering characteristics of both wastewater and water treatment sludges. Sludges tested included waste activated sludge, primary sewage sludge, waste activated/primary sewage sludge mixtures and alum sludge. The direct-freeze methods examined were the use of a secondary refrigerant (butane) evaporated in the sludge and the use of gas hydrate or clathrate formation by addition of Freon 12 under appropriate temperature and pressure conditions. Sludges were also frozen solid using indirect freezing methods, thawed and tested for comparative purposes. Particle size distribution and floc density measurements were used to determine changes in particle characteristics; specific resistance values and dewatered dry solids concentration were used to assess dewatering characteristics. Results of direct- and indirect-contact, freeze-thaw conditioning were compared to the effects of polymer conditioning. The results indicated that direct-freeze methods do not appear technically or economically competitive with currently accepted conditioning methods. The superior results obtained with the indirect-contact, freeze-thaw process when compared to the direct-contact processes suggested that the extent and rate of freezing may greatly influence the particle characteristics of the conditioned sludge, and thus its dewatering characteristics. / Ph. D.

In this paper consider the problem of controlling a thermoviscoelastic system. We present a semigroup setting for this system, and prove the well-posedness by applying a general theorem which is given in this paper. We also study the stability of the system. We give a finite element/averaging scheme to approximate the linear quadratic regulator problem governed by the system. We prove that yields faster convergence. We give a proof of convergence of the simulation problem for singular kernels and of the control problem for L2 kernels. We carry on the numerical computation to investigate the effect of heat transfer on damping and the closed-loop system. / Ph. D.

The interactions of O-isopropyl-N-ethylthionocarbamate (IPETC) and O-isobutyl-N-ethoxycarbonylthionocarbamate (IBECTC) with Cu₂S, CuFeS₂ and FeS₂ have been characterized using thermodynamic calculations, electrochemistry, microflotation tests, contact angle measurements, FTIR, and UV spectroscopy. Pearson’s theory of hard and soft acids and bases (HSAB) has also been applied to these flotation systems, through the use of Drago’s acid-base concept and flow microcalorimetry. The results of the thermodynamic calculations and electrochemical measurements suggest that IPETC and IBECTC adsorption on copper and chalcocite are dependent on potential. This has been verified by contact angle and in-situ spectroelectrochemical measurements. Microflotation tests with these thionocarbamates show that the floatability of Cu₂S and CuFeS₂ is dependent on pH. The floatability of FeS₂ only becomes significant at acidic conditions and high collector additions. Spectroscopic measurements also show that thionocarbamate adsorption is dependent on pH and is most favored on Cu₂S followed by CuFeS₂ and FeS₂. FTIR results indicate that IPETC is adsorbed on Cu°, Cu₂S, and CuFeS₂ through a coordination of the sulfur atom with the surface Cu. IBECTC adsorption on these substrates involves the coordination of Cu with both sulfur and oxygen atoms to form a six-membered chelate ring. Adsorption of these collectors cannot remove or prevent the formation of sulfoxy oxidation products on the FeS₂ surface, unlike the case with the xanthate-pyrite system. This may explain the improved selectivity of IPETC and IBECTC over xanthates. Infrared reflection-absorption spectroscopic studies show that KEX is preferentially adsorbed on Cu° over IPETC and IBECTC. Between IPETC and IBECTC, the latter is more favorably adsorbed than the former. Kinetic studies using UV spectroscopy show that the rate of thionocarbamate adsorption is highest on Cu₂S followed by CuFeS₂ and FeS₂. IBECTC adsorption on each sulfide mineral is relatively faster than IPETC, indicating the higher collecting power of IBECTC. The HSAB concept suggests that the interaction of thionocarbamates (soft bases) with sulfide minerals that are classified as soft acids should be favored. The C/E ratios of Cu₂S and FeS₂ were determined to be 0.86 and 0.52, respectively. This indicates that FeS₂ is a harder acid than Cu₂S, thus providing an explanation for the observed selectivity of both IPETC and IBECTC against FeS₂. / Ph. D.

Drill cores through the Lower to Middle Cambrian Shady Dolomite carbonate platform (600 to 1200 m thick) in the Austinville, Virginia, region allow the evolution of the carbonate platform from a gently sloping ramp, to a high relief, rimmed shelf to be documented. The Shady Dolomite forms the initial carbonate foundation for the overlying Cambrian-Ordovician carbonate shelf sequence, which persisted for about 30 m.a. until it was destroyed by incipient collision during the Early Ordovician. The Shady Dolomite records several episodes of dolomitization during burial, coeval with late Paleozoic deformation. Rare relict corcs of zone 1 dolomite were replaced and overgrown by zone 2A dolomite, the dominant replacement phase. After replacement dolomitization, the sequence was subjected to dissolution and fracturing, followed by Pb-Zn mineralization, zones 2B, 3 and 4 dolomite cement, sphalerite, quartz, and calcite. Zone 1 dolomite apparently has similar isotopic and trace element composition as zone 2A dolomite. Zone 2A dolomite (δ¹⁸O = -10.2 to -7.0 °/oo PDB; δ¹³C = +1.0 to +1.6 °/oo PDB) is depleted in ¹⁸O and enriched in ¹³C relative to marine cements (δ¹⁸O = -7.5 to -6.1; δ¹³C = +0.2 to +0.8), reflecting precipitation at elevated temperatures from fluids in equilibrium with the host limestone. Zone 2B dolomite cement has identical δ¹⁸O values as zone 2A dolomite, indicating precipitation from similar fluids for the two dolomite generations. The Mn and Fe contents of zones 2A and 2B dolomite likely reflect a pH control over the fluid Mn and Fe chemistry; their similar low total Sr and nonradiogenic ⁸⁷Sr/⁸⁶Sr, imply that Sr was largely derived from the limestone precursor. Zones 3 and 4 dolomite cements (δ¹⁸O = -13.8 to -11.3; δ¹³C = -0.7 to +0.9) are depleted in δ¹⁸O relative to previous dolomites, recording hotter fluids. Zone 3 dolomite is depleted in Fe, due to pyrite precipitation whereas zone 4 dolomite cement has relatively high Mn and Fe contents. Zones 3 and 4 dolomite cements and later calcite are enriched in total Sr and have high ⁸⁷Sr/⁸⁶Sr, indicating late radiogenic Sr-enriched brines. Fluid inclusions indicate that zones 2A and 2B dolomite precipitated from warm (100-175°C), saline (23-26 wt.% NaC1 equiv.) fluids, followed by later hotter (175-225°C) more saline (30-33 wt.% NaCl equiv.) fluids. Pressure solution of the Knox Group dolomites during overthrusting provided much of the Mg²⁺ for dolomitization, this Mg²⁺ was transported by regional gravity-driven fluid flow that developed in response to tectonic uplift. / Ph. D.

A method is presented for the efficient analytical prediction of the two dimensional laminar or turbulent compressor or turbine cascade blade-to-blade flow field and wake. The scheme utilizes a viscous-inviscid interaction routine combining a two-dimensional full potential cascade flow solver with a two-dimensional compressible boundary layer analysis. The boundary layer analysis can compute in the direct mode with pressure gradient specified or in the inverse mode with "boundary layer mass flux" specified. When calculating with the inverse mode, flow separation can be handled easily. Turbulent flow is treated using an algebraic eddy viscosity model with the modified Levy—Lees transformation applied to capture the growth of laminar and turbulent boundary layers. The boundary layer solution is fully implicit and formally second order accurate. The viscous inviscid coupling is performed utilizing thin airfoil theory. Numerical solutions are presented for several numerical test cases and compared with published test data. / Ph. D.

This dissertation reports the findings of an investigation aiming to the incorporation of the transition elements: cobalt, vanadium, and molybdenum into AlPO₄-5 molecular sieves, to the study of the redox properties of the resulting materials and to the potential application of these compounds in the partial oxidation of methane to methanol and formaldehyde. AlPO₄-5 molecular sieves containing Co, V, and Mo were synthesized by hydrothermal crystallization of typical aluminophosphate gels with the adequate metal substrates at temperatures of 200°C, 150°C, and 150°C respectively. Samples of each material were calcined in oxidant, reducing and inert atmospheres and the properties of the treated solids studied by different characterization techniques. The significant feature of the Co and V containing AlPO₄-5, CoAPO-5 and VAPO-5, is that they exhibit different colors depending on the treatment atmosphere. Evidence for cobalt contained in framework positions of CoAPO-5 is obtained by the change in its unit cell volume relative to AlPO₄-5, and by diffuse reflectance spectroscopy. CoAPO-5 also contains an appreciable quantity of extra-framework cobalt occluded in the pores, and/or as balancing cations. Evidence for this was obtained from ion exchange, and from oxygen and argon adsorption. Pentavalent vanadium incorporation is inferred from the change in the unit cell volume of VAPO-5 relative to AlPO₄-5, from pH measurements of the reaction vessel contents before and after heating, from oxygen and argon adsorption, chemical analysis, SEM, XPS, NMR, and diffuse reflectance spectroscopy. A scheme for the substitution of V into AlPO₄-5 is postulated based on the acidity observed in VAPO-5 by ion exchange, and potentiometrlc titration. Only a very small amount of Mo was found in the molybdenum containing AlPO₄-5. Evidence for Mo incorporation into the framework was not obtained. The use of CoAPO-5 and VAPO-5 as redox catalysts for the partial oxidation of methane to methanol and formaldehyde lead mostly to oxides of carbon. / Ph. D.