Surface layer coatings, which are thin films in the range of micrometer and nanometer are of utmost importance. These layers have many applications and control processes like corrosion, friction, wearing and adhesion. Therefore the search for layers with satisfactory surface properties for different applications is needed. Thickness measurements were evaluated in this study using PIXE in conjunction with RBS. Different samples were evaluated using both the solid-state chamber and the nuclear microprobe. The energies of 2.0 MeV alpha particles, 2.5 MeV and 3.0 MeV protons were used in this study. RBS when compared to PIXE showed low sensitivity towards light elements. The High purity Germanium detector also found it difficult to resolve peaks of elements (Magnesium and. Aluminum) that were close to one another. The GeoPIXE software showed inconsistent results for all the measurements. However the results showed good agreement between the two techniques. The overall observation of the study was that PIXE has shown its ability to measure thickness and that the inconsistency in the results from GeoPIXE software makes it difficult to trust the software for analysis of the results. / MSc (ARST) North-West University, Mafikeng Campus, 2003

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Background: Alzheimer's disease (AD) prevalence has grown 68% in that timeframe, and has risen to the sixth leading cause of death in the United States. Hispanics are at increased risk of acquiring cardiovascular risk factors that contribute to AD pathology and are minimally 1.5 times more likely at any age to be diagnosed with AD. Identifying the roots of this ethnic disparity can lead to more effective personalized health interventions. Aim: To compare indices of vascular health to measures of gray matter integrity in middle-aged Hispanic and Caucasian adults. As a secondary outcome, we will examine these health statuses in relation to cognitive function. Methods: Sixty subjects in Caucasian (n=30) and Hispanic (n=30) groups were matched across racial classification by age, gender, years of education, and cognitive status. Participants' arterial stiffness (carotid-femoral pulse-wave velocity and [beta]-stiffness index), arterial wave reflection (augmentation index), endothelial function (flow-mediated dilation), and atherosclerosis (carotid arterial wall intima-media thickness) were characterized. Magnetic resonance imaging (MRI) estimated cortical thickness in a priori cortical regions of interest known to be susceptible to vascular risk factors. Cognitive function was assessed with a comprehensive cognitive battery covering the domains of global cognitive function, language function, visuo-spatial abilities, memory function and attention-executive function. Results: Carotid-femoral pulse wave velocity (cfPWV) (p=0.02), Carotid artery [beta]-stiffness index (p=0.01), and augmentation index (Aix) (p=0.05) were significantly greater in Hispanics than in Caucasians. Carotid intima-media thickness (IMT) and flow-mediated dilation (FMD) were not different between the groups. Hispanics exhibited thinner left inferior frontal gyrus (LIFG) cortical thickness (p=0.04) with concurrently lower language (p=0.02), memory (p=0.03), and attention-executive functioning (p=0.02). Conclusion: Hispanics exhibited significantly greater cfPWV, Aix, and [beta]-stiffness index as well as selective cortical thinning of the LIFG. Additionally, language, working memory and attention-executive domains of cognition were lower in the Hispanic group compared to their age-, gender-, education- and cognitive status-matched Caucasian counterparts. These results may form a basis for future investigations that aim to explain the increased prevalence and earlier onset of symptoms of AD in the Hispanic population through cardiovascular health. / text

For many decades gas turbine engineers have investigated methods to improve engine efficiency further. These methods include advances in the composition and processing of materials, intricate cooling techniques, and the use of protective coatings. Thermal barrier coatings (TBCs) are the most promising development in superalloy coatings research in recent years with the potential to reduce metal surface temperature, or increase turbine entry temperature, by 70-200°C. In order for TBCs to be exploited to their full potential, they need to be applied to the most demanding of stationary and rotating components, such as first stage blades and vanes. Comprehensive reviews of coating processes indicate that this can only be achieved on rotating components by depositing a strain-tolerant layer applied by the electron beam-physical vapour deposition (EB-PVD) coating process. A computer program has been developed in Visual c++ based on the Knudsen cosine law and aimed at calculating the coating thickness distribution around any component, but typically turbine blades. This should permit the controlled deposition to tailor the TBC performance and durability. Various evaporation characteristics have been accommodated by developing a generalised point source evaporation model that involves real and virtual sources. Substrates with complex geometry can be modelled by generating an STL file from a CAD package with the geometric information of the component, which may include shadow-masks. Visualisation of the coated thickness distributions around components was achieved using OpenGL library functions within the computer model. This study then proceeded to verify the computer model by first measuring the coating thickness for experimental trial runs and then comparing the calculated coating thickness to that measured using a laboratory coater. Predicted thickness distributions are in good agreement even for the simplified evaporation model, but can be improved further by increasing the complexity of the source model.

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No description available.

Student Number : 0001361N - MSc(Eng) dissertation - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment / Thick composite cylinders are important structural elements which cannot be analysed by traditional techniques due to through-thickness effects. This work presents analyses for thick composite tubes of finite length including through-thickness shear. A numerical thermal analysis is implemented for the determination of the transient through-thickness behaviour of tubes. A me- chanical analysis, based on the Rayleigh-Ritz technique, is presented which analyses finite length, composite tubes under a variety of loadings. The anal- yses are shown to be accurate and efficient and are validated against existing results. Results are presented for two ring-stiffened tubes under pressure and thermal loading and also for the transient thermal behaviour of these tubes. It was found that both the through-thickness and transient effects are of im- portance as the stress variation through the thickness and with time was significant for both tubes.

"This project investigates the effect of membrane thickness on the performance and durability of a Direct Methanol Fuel Cell (DMFC) using a commercially available Celtec®P-1000 PBI-based membrane electrode assembly (MEA). The PBI-based membranes tested were the 100µm, the standard thickness, 200µm and 250µm thick. With various methanol feed concentrations and cathode feeds, oxygen and air, the PBI-based MEAs were operated between 160 and 180°C with vaporized methanol feed. Results showed that the DMFC performance increased with temperature and with PBI membrane thickness. The optimal concentration for the 100µm membrane was at 5M while the best performance with the 200µm membrane was obtained at 3M. The 250µm membrane looked like it could have had better performance than the 200µm, but unfortunately experimental issues didn’t allow completion of these results."

Liquid films falling under the influence of gravity are widely encountered in a variety of industrial two-phase flow applications (distillation columns, nuclear reactor cores, etc.). In addition, the falling annular film represents a fundamental limiting case of the annular flow regime of two-phase gas-liquid flows. The literature on annular falling films is dominated by studies concerning the average film thickness. Information on more detailed characteristics of the film thickness variations and information on the velocity profile within the film and wall shear stress are much less common. The statistical description of the film thickness is complicated by the fact that practically all flows of interest occur in the turbulent regime. Due to the complex and unsteady nature of the turbulent annular falling film, no complete theories or models have yet been developed on the subject. Experimental studies are needed to gain insight into the basic mechanisms that govern this complex flow.<p>The primary purpose of this thesis research was to characterise the film thickness of falling annular films at high and very high Reynolds numbers using non-intrusive imaging techniques. Another objective was to develop ray-tracing techniques to reduce optical distortion and obtain high-quality experimental data. <p>Instantaneous film thickness measurements of falling annular films were extracted at five different Reynolds numbers in the range Re = 1000 ~ 6000 for the fully developed turbulent regime using an automated optical measurement technique. From visual observation of the images obtained it was found that waves were not axisymmetric, i.e., there was substantial azimuthal variation in film thickness. The turbulent waves appeared to be similar in appearance to very large breaking ocean waves driven by strong winds. The random nature of these falling annular films was subjected to statistical analysis.<p>Statistical characteristics of film thickness were studied at Reynolds numbers in the range Re = 1000 ~ 6000. A correlation for dimensionless mean film thickness was obtained in the turbulent flow regime. The dimensionless mean film thickness obtained here was found to be in reasonable agreement with the other established experimental and theoretical studies. It was shown that the Reynolds number influences the statistical characteristics of film thickness such as standard deviation and coefficient of variation. The additional data obtained here shows that the standard deviation continues to increase in proportion to the mean film thickness in the turbulent regime. In other words, in the lower turbulent zones the films are thin and less wavy, whereas in the higher turbulent zones the films are thicker and extremely wavy in nature.<p>The probability density distributions were also obtained. It was found that the measured probability density distributions were asymmetric. They all had a maximum peak and were skewed to the right hand side with a long tail that stretched to over six times the peak value. The maximum peak could be considered to represent the modal value of the film thickness or the substrate film thickness. The increase in skewness and the decrease in the height of the peak with liquid Reynolds number could be attributed to the presence of large disturbance waves which ride on the substrate film. This enhances the waviness of the film.<p>A common problem in imaging flows in cylindrical tubes is the optical distortion caused by the wall curvature. To minimize this problem the cylindrical tube was surrounded by an optical correction box with flat walls filled with water. In addition, an advanced ray tracing model was employed to reduce optical distortion effects in the cylindrical tube. This technique increased the accuracy of the imaging technique and enabled quantitative measurements of film thickness to be made.

Liquid films falling under the influence of gravity are widely encountered in a variety of industrial two-phase flow applications (distillation columns, nuclear reactor cores, etc.). In addition, the falling annular film represents a fundamental limiting case of the annular flow regime of two-phase gas-liquid flows. The literature on annular falling films is dominated by studies concerning the average film thickness. Information on more detailed characteristics of the film thickness variations and information on the velocity profile within the film and wall shear stress are much less common. The statistical description of the film thickness is complicated by the fact that practically all flows of interest occur in the turbulent regime. Due to the complex and unsteady nature of the turbulent annular falling film, no complete theories or models have yet been developed on the subject. Experimental studies are needed to gain insight into the basic mechanisms that govern this complex flow.<p>The primary purpose of this thesis research was to characterise the film thickness of falling annular films at high and very high Reynolds numbers using non-intrusive imaging techniques. Another objective was to develop ray-tracing techniques to reduce optical distortion and obtain high-quality experimental data. <p>Instantaneous film thickness measurements of falling annular films were extracted at five different Reynolds numbers in the range Re = 1000 ~ 6000 for the fully developed turbulent regime using an automated optical measurement technique. From visual observation of the images obtained it was found that waves were not axisymmetric, i.e., there was substantial azimuthal variation in film thickness. The turbulent waves appeared to be similar in appearance to very large breaking ocean waves driven by strong winds. The random nature of these falling annular films was subjected to statistical analysis.<p>Statistical characteristics of film thickness were studied at Reynolds numbers in the range Re = 1000 ~ 6000. A correlation for dimensionless mean film thickness was obtained in the turbulent flow regime. The dimensionless mean film thickness obtained here was found to be in reasonable agreement with the other established experimental and theoretical studies. It was shown that the Reynolds number influences the statistical characteristics of film thickness such as standard deviation and coefficient of variation. The additional data obtained here shows that the standard deviation continues to increase in proportion to the mean film thickness in the turbulent regime. In other words, in the lower turbulent zones the films are thin and less wavy, whereas in the higher turbulent zones the films are thicker and extremely wavy in nature.<p>The probability density distributions were also obtained. It was found that the measured probability density distributions were asymmetric. They all had a maximum peak and were skewed to the right hand side with a long tail that stretched to over six times the peak value. The maximum peak could be considered to represent the modal value of the film thickness or the substrate film thickness. The increase in skewness and the decrease in the height of the peak with liquid Reynolds number could be attributed to the presence of large disturbance waves which ride on the substrate film. This enhances the waviness of the film.<p>A common problem in imaging flows in cylindrical tubes is the optical distortion caused by the wall curvature. To minimize this problem the cylindrical tube was surrounded by an optical correction box with flat walls filled with water. In addition, an advanced ray tracing model was employed to reduce optical distortion effects in the cylindrical tube. This technique increased the accuracy of the imaging technique and enabled quantitative measurements of film thickness to be made.