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Penetration of high velocity is of concern for both civilian and military research for decades, and computerized simulation is the scholar's focus in recent years. This study presents a study on the Discrete Element Method (DEM) simulation of plain concrete target's behavior under high-velocity penetration of rigid projectile. In this thesis, different types of research works including empirical, analytical and numerical methods in penetration by the previous scholars were carefully reviewed. A DEM-based concrete model was established by using software PFC3D. The major micro-variables of the simulation program were calibrated according to the required macro-mechanical parameters. Meanwhile, their correlations within the concrete range were studied, with the sensitivity analysis and the corresponding regression equations. With the established digital concrete model, penetration simulation tests were carried out. The results of penetration depth versus impact velocity were compared with the experimental and empirical calculated results from Forrestal's work in 1994. A good agreement was obtained. Some other simulation studies, like projectile mass, geometry, penetrating acceleration, concrete response stress, strain, and strain-rate were also conducted to study the constitutive properties in this thesis. / Master of Science

The skin is an amazingly resilient and relatively impermeable barrier that provides protective, perceptive and communication functions to the body (Ramachandran & Fleisher, 2000). The stratum corneum is widely accepted as the barrier of the skin - limiting the transport of molecules into and across the skin. One of the bottlenecks in the successful development of transdermal drug delivery devices is the fact that the skin (more accurately, the stratum corneum - SC) tends to control the rate of drug transport. This makes it very difficult to influence or regulate the transdermal drug absorption kinetics from outside, Le. by means of the vehicle. A possible, and even elegant, solution may be the use of so-called "penetration enhancers", thereby suppressing the dominant role of the stratum corneum penetration barrier (Bodde et al., 1990). For this study 5-fluorouracil (5-FU), a polar hydrophilic drug, was chosen as model drug to study its penetration through the stratum corneum. Terpenes used as possible penetration enhancers for 5-FU were menthol, isomenthol, menthone, l3-myrcene, limonene and 1,8-cineole. In previous studies, terpenes with low skin irritancy and low systemic toxicity, were found to be effective penetration enhancers for a number of hydrophilic and lipophillic drugs (Cornwell & Barry, 1994; Cornwell et a/., 1996; Godwin & Michniak, 1999). The objective of this study was to determine the different flux rates of 5-FU in the absence of any pre-treatment of the stratum corneum and also through ethanol and selected terpene pre-treated SC. The effect of each terpene on the penetration of 5-FU was determined. The penetration of the selected terpenes themselves through the human stratum corneum was also determined in vitro permeation studies were performed using vertical Franz diffusion cells with human skin (stratum corneum). A saturated aqueous solution of 5-fluorouracil in the absence and presence of pre-treatment of the SC was used as the donor phase. Pre-treatment was performed by applying a 5 % terpene solution or absolute ethanol to the SC half an hour before the saturated III solution was applied in the donor compartment. A 50/50 ethanol/water solution was used as the receptor phase. All the experiments were conducted over a 24 h period. The 37°C temperature was held constant by means of a water bath. For the analysis of 5-FU flux rates, samples from the receptor compartment were obtained and were analysed by means of high-pressure liquid chromatography (HPLC). In order to determine the cumulative percentage of terpenes penetrated through human stratum corneum, the samples were analysed by gas chromatography (GC). In this study, only menthol and isomenthol (both oxygen-containing terpenes) showed a statistically significant increase on the flux of 5-FU, with flux values of 1.13 +- 0.38 and 1.45 +- 0.68 ug/cm2/h, respectively, compared to untreated skin with a flux value of 0.54 +- 0.23 ug/cm2/h for 5-FU. It was also proved that ethanol itself had an enhancing effect on 5-FU and showed synergistic effects on the enhancement activities of all the terpenes. It was found that all the terpenes (applied as a 5 % solution in ethanol) penetrated through the stratum corneum in the absence of 5-fluorouracil. 5-Fluorouracil had either an increasing or decreasing effect on the penetration of the terpenes. From these findings, it could be concluded that oxygen-containing terpenes had the best penetration enhancing effect on 5-FU and that menthol and isomenthol were the most effective penetration enhancers, although the extend of penetration enhancement is not large enough for clinical application. All the terpenes have the ability to penetrate through human stratum corneum, and 5-FU either had an increasing or decreasing effect on their penetration. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.

The skin is an amazingly resilient and relatively impermeable barrier that provides protective, perceptive and communication functions to the body (Ramachandran & Fleisher, 2000). The stratum corneum is widely accepted as the barrier of the skin - limiting the transport of molecules into and across the skin. One of the bottlenecks in the successful development of transdermal drug delivery devices is the fact that the skin (more accurately, the stratum corneum - SC) tends to control the rate of drug transport. This makes it very difficult to influence or regulate the transdermal drug absorption kinetics from outside, Le. by means of the vehicle. A possible, and even elegant, solution may be the use of so-called "penetration enhancers", thereby suppressing the dominant role of the stratum corneum penetration barrier (Bodde et al., 1990). For this study 5-fluorouracil (5-FU), a polar hydrophilic drug, was chosen as model drug to study its penetration through the stratum corneum. Terpenes used as possible penetration enhancers for 5-FU were menthol, isomenthol, menthone, l3-myrcene, limonene and 1,8-cineole. In previous studies, terpenes with low skin irritancy and low systemic toxicity, were found to be effective penetration enhancers for a number of hydrophilic and lipophillic drugs (Cornwell & Barry, 1994; Cornwell et a/., 1996; Godwin & Michniak, 1999). The objective of this study was to determine the different flux rates of 5-FU in the absence of any pre-treatment of the stratum corneum and also through ethanol and selected terpene pre-treated SC. The effect of each terpene on the penetration of 5-FU was determined. The penetration of the selected terpenes themselves through the human stratum corneum was also determined in vitro permeation studies were performed using vertical Franz diffusion cells with human skin (stratum corneum). A saturated aqueous solution of 5-fluorouracil in the absence and presence of pre-treatment of the SC was used as the donor phase. Pre-treatment was performed by applying a 5 % terpene solution or absolute ethanol to the SC half an hour before the saturated III solution was applied in the donor compartment. A 50/50 ethanol/water solution was used as the receptor phase. All the experiments were conducted over a 24 h period. The 37°C temperature was held constant by means of a water bath. For the analysis of 5-FU flux rates, samples from the receptor compartment were obtained and were analysed by means of high-pressure liquid chromatography (HPLC). In order to determine the cumulative percentage of terpenes penetrated through human stratum corneum, the samples were analysed by gas chromatography (GC). In this study, only menthol and isomenthol (both oxygen-containing terpenes) showed a statistically significant increase on the flux of 5-FU, with flux values of 1.13 +- 0.38 and 1.45 +- 0.68 ug/cm2/h, respectively, compared to untreated skin with a flux value of 0.54 +- 0.23 ug/cm2/h for 5-FU. It was also proved that ethanol itself had an enhancing effect on 5-FU and showed synergistic effects on the enhancement activities of all the terpenes. It was found that all the terpenes (applied as a 5 % solution in ethanol) penetrated through the stratum corneum in the absence of 5-fluorouracil. 5-Fluorouracil had either an increasing or decreasing effect on the penetration of the terpenes. From these findings, it could be concluded that oxygen-containing terpenes had the best penetration enhancing effect on 5-FU and that menthol and isomenthol were the most effective penetration enhancers, although the extend of penetration enhancement is not large enough for clinical application. All the terpenes have the ability to penetrate through human stratum corneum, and 5-FU either had an increasing or decreasing effect on their penetration. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.

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published_or_final_version / Applied Geosciences / Master / Master of Science

Analytical three-dimensional temperature field in the liquid and heat-affected zones and prediction of the three-dimensional fusion zone shape around the keyhole produced by a moving high-intensity beam are provided. Determination of the fusion zone shapes is of fundamental and practical importance to understand properties and microstructures of joints. In this work, the keyhole is idealized by a paraboloid of revolution in a finite workpiece subject to an incident flux of a Gaussian distribution.Introducing analytical solutions of three-dimensional analytical temperature field, the dimensionless width, leading and rear edges, and depth of the fusion zone are analytically found to be a function of the dimensionless parameters governing beam power per unit penetration, location of the workpiece surface and shape of the keyhole. The dimensionless parameters governing the keyhole shape can be evaluated from a force balance at the keyhole base. The results show the effects of welding parameters, such as the dimensionless beam power, Peclet number, cavity opening radius, Biot number, thickness of workpiece, and the parameter approximating convection, on the shape of the fusion zone and the temperature of keyhole surface. A significant difference in the fusion zone shapes predicted between the line-source solution and this work indicates the strong effects of three-dimensional heat transfer. Agreement between the prediction from this work and available experimental data is achieved.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 244-247). Available also in a digital version from Dissertation Abstracts.

No description available.