The availability and abundance of surface water on the Manyeleti Game Reserve was quantified to provide information towards the development of a water provision policy. A total of 696 water source sites were located with a mean distance of 223.3 m apart. The water source sites (natural and artificial) were monitored seasonally to describe the seasonal availability of surface water on the Manyeleti Game Reserve. There were significant relationships between seasonal rainfall and the number of water source sites and maximum distance between sites. The large number of water sources is regulated by climatic progression and thus water provision on the Manyeleti Game Reserve follows a natural cycle linked primarily to rainfall. Water sources that dry up towards the dry seasons need to be supplied with water during drought periods in order to maintain game numbers without causing rangeland degradation. A water provision model that incorporates all the variables of the Greater Kruger Park Conservation Area, with particular reference to the smaller conservation areas within it, should become a research priority.

This paper presents two new schemes for interpolating missing samples in satellite diurnal temperature cycles (DTCs). The first scheme, referred to here as the cosine model, is an improvement of the model proposed in [2] and combines a cosine and exponential function for modelling the DTC. The second scheme uses the notion of a Reproducing Kernel Hilbert Space (RKHS) interpolator [1] for interpolating the missing samples. The application of RKHS interpolators to the DTC interpolation problem is novel. Results obtained by means of computer experiments are presented.

This thesis explores the fundamental chemistry of selective oxidation reactions on gold and silver surfaces, developing a predictive framework for oxidative catalysis, which is crucial for rational design of catalytic systems. We begin with an introduction covering the history of precious metal catalyst development, with emphasis on the roles of silver and gold (Chapter 1). Next, we explore selectivity control for oxidative reactions on gold. Specifically, we address the role of coadsorbed oxygen with respect to stability and selectivity control in the reaction of adsorbed acetate (Chapters 2 and 3), the importance of van der Waals forces in controlling the selectivity for cross-coupling reactions (Chapter 4), and the influence of CF3 on alkoxide stability on gold (Chapter 5). Further, we study various oxidative coupling and partial oxidation reactions on silver. In each case we elucidate reaction mechanisms, with attention to control of reaction selectivity. First, we establish oxidative coupling between dimethylamine and formaldehyde to form dimethylformamide (Chapter 6). Then we explore the role of hydroxyl in oxidative reactions silver, establishing its reactivity as a nucleophile in reaction with formaldehyde (Chapter 7). Finally, we directly compare the reactivity of gold and silver, in the acetylation of dimethylamine using acetaldehyde (Chapter 8). Appendices are included which investigate the oxidation of dimethylamine on silver (Appendix A), selectivity control for alcohol and aldehyde coupling on silver (Appendix B), and reactivity of hydroxyl on silver as a Bronsted base (Appendix C). A MATLAB code, which was developed for quantitative analysis of temperature program reaction spectroscopy experiments is also presented (Appendix D), as well as Supporting Material (Appendix E). / Engineering and Applied Sciences

Objective: Topography, chemistry, and energy of titanium (Ti) implants alter cell response through variations in protein adsorption, integrin expression, and downstream cell signaling. However, the contribution of surface energy on cell response is difficult to isolate because altered hydrophilicity can result from changes in surface chemistry or microstructure. Our aim was to examine a unique system of wettability gradients created on microstructured Ti on osteoblast maturation and phenotype. Method: A surface energy gradient was created on sand-blasted/acid-etched (SLA) Ti surfaces. Surfaces were treated with oxygen plasma for 2 minutes, and then allowed to age for 1, 12, 80, or 116 hours to generate a wettability gradient. Surfaces were characterized by contact angle and SEM. MG63 cells were cultured on SLA or experimental SLA surfaces to confluence on TCPS. Osteoblast differentiation (IBSP, RUNX2, ALP, OCN, OPG) and integrin subunits (ITG2, ITGA5, ITGAV, ITGB1) measured by real-time PCR (n=6 surfaces per variable analyzed by ANOVA/Bonferroni’s modified Student’s t-test). Result: After plasma treatment, SLA surface topography was retained. A gradient of wettability was obtained, with contact angles of 32.0° (SLA116), 23.3° (SLA80), 12.5° (SLA12), 7.9° (SLA1). All surfaces were significantly more hydrophilic than the original SLA surface (126.8°). Integrin expression was affected by wettability. ITGA2 was higher on wettable surfaces than on SLA, but was highest on SLA1. ITGAV and ITGB1 were decreased on hydrophilic surfaces, but ITGA5 was not affected. IBSP, RUNX2, and ALP increased and OPG decreased with increasing wettability. OCN decreased with increasing wettability, but levels on the most wettable surface were similar to SLA. Conclusion: Here we elucidated the role of surface energy on cell response using surfaces with the same topography and chemistry. The results show that osteoblastic maturation was regulated in a wettability-dependent manner and suggest that the effects are mediated by integrins.

A hydrogel consists of a cross-linked polymer network and solvent molecules, capable of large, reversible deformation in response to a variety of external stimuli. In particular, diverse instability patterns have been observed experimentally in swelling hydrogels under mechanical constraints. The present study develops a general theoretical framework based on a variational approach, which leads to a set of governing equations coupling mechanical and chemical equilibrium conditions for swelling deformation of hydrogels, along with proper boundary conditions. A specific material model is employed for analytical and numerical studies, for which the nonlinear constitutive behavior of the hydrogel is derived from a free energy function combining rubber elasticity with a polymer solution theory. A finite element method is then developed and implemented as a user-defined material (UMAT) in the commercial package, ABAQUS. By numerical simulations, the effect of constraint on inhomogeneous swelling of substrate-attached hydrogel lines is elucidated. It is found that crease-like surface instability occurs when the width-to-height aspect ratio of the hydrogel line exceeds a critical value. Next, by considering a hydrogel layer on a rigid substrate, swell-induced surface instability is studied in details. A linear perturbation analysis is performed to predict the critical condition for onset of the surface instability. In contrast to previously suggested critical conditions, the present study predicts a range of critical swelling ratios, from about 2.5 to 3.4, depending on the material properties of the hydrogel system. A stability diagram is constructed with two distinct regions for stable and unstable hydrogels with respect to two dimensionless material parameters. Numerical simulations are presented to show the swelling process, with evolution of initial surface perturbations followed by formation of crease-like surface patterns. Furthermore, with combined swelling and mechanical compression, the stability analysis is extended to predict a general critical condition that unifies the swell-induced surface instability of hydrogels with mechanically induced surface instability of rubbers. The effect of surface tension is found to be critical in suppressing short-wavelength modes of surface instability, while the substrate confinement suppresses long-wavelength modes. With both surface tension and substrate confinement, an intermediate wavelength is selected at a critical swelling ratio for onset of surface instability. Both the critical swelling ratio and the characteristic wavelength depend on the initial thickness of the hydrogel layer as well as other material properties of the hydrogel. It is found that the hydrogel layer becomes increasingly stable as the initial layer thickness decreases. A critical thickness is predicted, below which the hydrogel layer swells homogeneously and remains stable at the equilibrium state. Finally, three-dimensional finite element models are developed to simulate swelling deformation of hydrogel lines. Depending on the aspect ratio of the cross section as well as the material properties of the hydrogel, two types of swell-induced instability patterns are envisaged, i.e., localized surface instability versus global buckling. / text

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Estimating S-wave velocities (Vs) from Rayleigh-wave velocities (VR) is widely used in field seismic testing for geotechnical engineering purposes. In this research, two widely used surface-wave methods, the Spectral-Analysis-of-Surface-Waves (SASW) and Multichannel-Analysis-of-Surface-Waves (MASW) methods, are evaluated and compared in field experiments. An experimental parametric study was undertaken of the SASW and MASW methods. Conventional seismic sources in the SASW method are sledge hammers, bulldozers and vibroseises. For MASW testing, sledge hammers and small shakers are usually used as the seismic sources. In this research, MASW testing was performed with traditional and non-traditional sources at a site owned by the City of Austin, Texas. Experimental dispersion curves and Vs profiles from SASW tests are used as references for the field parametric study with the MASW method. The source type, source offset, receiver spacing and number of receivers were varied to evaluate the impact of each variable on the field experimental dispersion curve. Two type of receivers, 1-Hz and 4.5-Hz natural-frequency geophones, were also compared in these tests. A second part of this research involved studying the use of characterizing geotechnical materials based on Vs. This work included two projects. The first project involved basalt on the Big Island of Hawaii. To develop empirical ground motion prediction models for the purpose of earthquake hazard mitigation and seismic design on the Big Island, the subsurface site conditions beneath 22 strong motion stations were investigated by SASW tests. Vs profiling was performed to depths of more than 100 ft. Vs30, the average Vs in the top 30 m, was also calculated to assign NEHRP site classes to different testing locations. Different materials, mainly thought to be stiff basalt, were characterized and grouped based on the Vs values. These groups were then compared with reference curves for sand and gravel (Menq, 2003) to differentiate the groups. The second project dealing with charactering geotechnical materials based on Vs involved of soil/rock profiles at a project site in British Columbia, Canada. The goals in terms of this research were to: (1) compare the Vs profiles from the different test locations to investigate the stiffnesses of different geologic materials, the variability in the material stiffnesses, and the estimated depth to bedrock, and (2) to compare the Vs profiles to existing geological and geotechnical information such as nearby boreholes, cone penetration tests and seismic cone penetration tests. Good agreement between SASW Vs profiles and boring records is expected when lateral variability at the site is low. However, when lateral variability is significant, then the difference between localized measurements, like borings and CPT results, and global measurements, like SASW Vs results, can further contribute to understanding the site conditions as shown at the site in British Columbia, Canada. / text

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No description available.