Smoothed Particle Hydrodynamics (SPH) is a Lagrangian-based numerical method used for simulating problems in fluid and solid mechanics. In this thesis, a basic introduction to particle and Smoothed Particle (SP) approximations is given first. Application of SP approximations to Euler and Navier-Stokes equations is discussed, followed by an improvement to restore first order consistency in SPH. Then, simulations of 2D free-surface waves in a weakly incompressible fluid are conducted. If the artificial viscosity used is small, results indicate that the accuracy of SPH scheme is reasonably good; however, a low artificial viscosity leads to a rugged air-water interface. Furthermore, application of the LES filter has negligible effects. It is also observed that the use of Renormalized SPH (R-SPH) increases diffusivity but does not increase accuracy significantly. Hence, for 2D surface waves in weakly incompressible fluids, basic SPH formulation without any modification is as good as the R-SPH or LES-SPH methods.

Surface tension of a polymer melt in a supercritical fluid is a principal factor in determining cell nucleation and growth in polymer microcellular foaming. Previous work has presented the surface tension of the amorphous polymer, polystyrene (PS), in supercritical CO2 determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), together with theoretical calculations for a corresponding system. The dependences of the surface tension on temperature, pressure and polymer molecular weight were discussed and the physical mechanisms for three main experimental trends were explained using Self Consistent Field Theory (SCFT). This thesis introduces recent work on the surface tension measurement of the crystalline polymer, high density polyethylene (HDPE), in supercritical N2 under various temperatures and pressures. The surface tension was determined by ADSA-P and the results were compared with those of the amorphous polymer PS. The dependence of the surface tension on temperature and pressure, at temperatures above the HDPE melting point, ~125°C, was found to be similar to that of PS; that is, the surface tension decreased with increasing temperature and pressure. Below 125°C and above 100°C, HDPE underwent a process of crystallization, where the surface tension dependence on temperature was different from that above the melting point, i.e., decreased with decreasing temperature. Differential Scanning Calorimetry (DSC) characterization of the polymer was carried out to reveal the process of HDPE crystallization and relate this to the surface tension behavior. It was found that the amount of the decrease in surface tension was related to the rate of temperature change and hence the extent of polymer crystallization. In the second part of the thesis, surface tension dependences on temperature, pressure and clay concentrations were studied for HDPE nano-clay composites (HNC) and compared with pure HDPE. It was found the trends with temperature and pressure were the same with PS in CO2 and HDPE in N2; that is, the surface tension decreased with increasing temperature and pressure. In all nanocomposite samples, the surface tension decreased compared with pure HDPE. This could be a good explanation for the better polymer foaming quality with the addition of clay in the polymer. A minimum surface tension was found with the sample at ~3% concentration of clay. The degree of crystallinity of HNC was analyzed by Differential Scanning Calorimetry (DSC) at different clay concentrations. A minimumz crystallinity was also found at the clay concentration of 3%. The possible relationship between surface tension and polymer crystallinity was discussed.

Current understanding of sensitivity and sensation experienced across the ocular surface remains limited. This project explored the regional variation of corneal sensitivity and transducer function, interaction of sensory and autonomic nerves in the lacrimal functional unit, and the ocular surface sensitivity in Dry Eye and with silicone hydrogel (SH) lens wear. Experiments were undertaken, using Belmonte esthesiometer to deliver pneumatic mechanical, chemical and thermal stimuli and Cochet-Bonnet esthesiometer for tactile stimuli, to the cornea and conjunctiva. Psychophysical methods were used to determine the thresholds of stimulus detection, and the magnitude of sensations to suprathreshold stimulation was estimated assuming Steven’s power law. Additionally, tear secretion in response to corneal sensory input was determined by tear meniscus height measured using Optical Coherence Tomography. Sensitivity to pneumatic cool and mechanical stimuli varied slightly across the cornea while chemical sensitivity was not different between regions. The transducer function was also similar between central and peripheral cornea but different between stimulus modalities. In comparison, the reflex tearing response to suprathreshold stimuli was greater with central corneal stimulation. Also, corneal and conjunctival hypersensitivity was found in the dry eye symptomatic group, and it appeared to be associated with symptom severity, tear film stability and corneal epitheliopathy. Refitting with SH lenses after an initial no-lens interval led to increased conjunctival pneumatic mechanical sensitivity, while corneal tactile sensitivity showed a decrease. In addition, corneal staining induced by certain lens-solution combination appeared to be accompanied by increased corneal and conjunctival sensitivity. In conclusion, the position-invariant corneal sensitivity to pneumatic mechanical, chemical and thermal stimuli suggests that the distribution of human corneal sensory fibres may be more homogeneous than previously hypothesised. The mechanisms mediating the sensory aspect of corneal nociception may be similar across the cornea, while, perhaps due to the importance of the visual axis, the tear reflex response to central and peripheral cornea seems to be driven by different neural circuitry, perhaps at the higher levels of the sensory processing pathway. It appears that alteration in sensory processing of the ocular surface occurs in Dry Eye and accompanies SH lens-solution-induced corneal staining. This altered sensitivity seems to be more prominent in the conjunctiva than in the cornea.

Adsorption at metal electrodes is usually a very fast process and it plays a most important role in many areas of industry. The thermodynamics of the process are well known for many systems. However, there is currently no good method that allows a determination of very fast kinetics of adsorption to be made. Previously, many attempts at evaluation of kinetic parameters of adsorption were made, but in moat cases, due to the inadequacy of the experimental methods used, the parameters obtained were much lower than expected. This thesis aims at providing the means for determining the kinetics of adsorption at metal electrodes. The methods herein described are based on two different experimental techniques. These techniques are: (i) fast cyclic voltammetry (FCV, potential sweep rate up to 100000 V/s) and (ii) high frequency AC and FFT SW (Fast Fourier Transform Square-wave) voltammetry (frequency up to 50 MHz) at ultramicroelectrodes (5 or 6.25 ìm in radius). A theoretical description of the adsorption process for both kinds of experiments is presented. A simulation program was written to provide a better understanding of the process and to elucidate the development of methods for determining the kinetics of adsorption. Thermodynamic and kinetic descriptions of the process are based on the Frumkin adsorption isotherm. Both the equilibrium constant and the adsorption rate constant are treated as functions of potential and the electrode coverage. Comparison of results for different systems is presented as an analysis of the dependence of the adsorption rate constant on the equilibrium constant. FCV proved to be useful in the evaluation of kinetics of chemisorption (standard rate constant in the range of 10⁶ s$\sp{-1})$ but the results for adsorption of aliphatic alcohols were unreliable. High frequency AC methods allowed the determination of kinetics of physical adsorption. It was found that the activation energy of the adsorption process can be expressed as a linear combination of the electrical component of the standard free energy of adsorption (a major contribution) and the energy of lateral interactions (a minor contribution). At the zero charge potential the rate constant reaches the maximum value of $\rm(4.6\pm0.3)10\sp9\ s\sp{-1}.$

Crevice corrosion generally occurs on the crevice surface while the exterior or bold surfaces are not damaged. However, for copper and its alloys, the opposite is true; the bold surface is corroded while the crevice remains relatively corrosion-free. This unique type of corrosion is referred to as reverse crevice corrosion (RCC). In this research, commercially pure copper was chosen as the target metal to investigate RCC. Based on electrochemical measurements and surface analysis, reverse crevice corrosion was found to occur at room temperature. At elevated temperature only uniform corrosion was observed while under a deoxygenated environment, as expected, no corrosion was observed.<p> A multiple crevice assembly and a working electrode were designed especially for this research. Exposure test experiments were first performed at room temperature and 50 ºC. Several types of electrochemical tests were conducted including open circuit potential measurement, potentiodynamic measurement and electrochemical impendence spectroscopy (EIS). Atomic Force Microscopy (AFM) and Raman Spectroscopy were used to analyze the surfaces of the copper coupon.<p>The results of the exposure tests showed that RCC occurred at room temperature, but not at elevated temperature. Only uniform corrosion was observed at elevated temperature and no corrosion was occurred under a deoxygenated environment. It was found, based on the open circuit potential measurement, that the RCC process can be divided into three steps, a uniform corrosion phase, a corrosion slow-down step and a reverse crevice corrosion step. The first two steps can be combined into one phase, incubation phase. This hypothesis is supported with the results from Raman spectra and AFM. The EIS measurements revealed that the diffusion process from bulk solution to copper coupon surface is the rate controlling step for incubation phase and this diffusion process combined with the reduction of Cu (I) oxide in the crevice are the rate-controlling step corresponding to the last step.

Activated Carbon (AC) is an amorphous carbon-based material characterized with a large surface area (~ 1,000 m2/g) and consists primarily of graphitic (sp2 hybrid) layers. Its amphoteric chemical property results because of the chemical treatment of the surface of AC with oxidizing agents, reducing agents, and grafting agents. β-cyclodextrin (β-CD) is a very interesting carbohydrate oligomer that provides very strong binding ability for small organic guest molecules in its inner cavity (6.0 ~ 6.5 Å) by van der Waals interactions and hydrogen bond formation between the guest molecules and the host. <p>Surface modification of AC with β-CD was synthesized by chemical methods: oxidation with HNO3, reduction with LiAlH4, and grafting β-CD onto the surface of AC via organic linkers such as glutaraldehyde and 1,4-phenylene diisocyanate. This surface grafted AC with β-CD, then, was evaluated for its surface area and sorption performance by using a solution dye sorption method using dye adsorbates. <p>Surface functional groups produced from oxidation (carboxylic acid, lactone, quinine, phenol, and nitro groups), reduction (alcohol and amine groups), and grafting (imine, hemiacetal, and urethane bonds) methods including microscopy of untreated, surface modified, and grafted ACs were characterized by various surface characterization methods: Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS), Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), Differential thermogravimetry (DTG), Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI TOF MS), and Electron spin resonance (ESR) spectroscopy. A chemical method, the Boehm method, was used for identifying surface bound acidic and basic functional groups. Nitrogen porosimetry was used to analyze the surface area and pore structure characteristics of AC, surface modified ACs, and grafted ACs. <p>p-nitrophenol (PNP) and methylene blue (MB) were used as adsorbates for the dye sorption method. PNP and MB were used to measure the sorption performance of grafted ACs at equilibrium using UV-vis spectrophotometry in aqueous solution. Sorption capacity (Qe), surface area (m2/g), and binding affinity characteristics [KF (L/g), KL (g/mol), and KBET (L/g)] were determined at equilibrium conditions using fundamental sorption models such as Langmuir, Freundlich, and BET isotherms. The sorption performance of grafted ACs and granular AC were different according to the difference in surface area and pore structure characteristics of each material.

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