Proefschrift--Utrecht. / "Stellingen": [2] p. inserted. Summary in Dutch. Bibliography: p. 115-120.

Given the importance of simulation techniques in automotive engineering, there is a lack of implementation regarding these techniques in the acoustics of damping materials for air-borne sound. Biot’s calculations have proven its abilities to simulate the acoustic characteristics of these damping materials. However, the characterisation of essential structural parameters, such as Young’s modulus and loss factor, in order to conduct Biot’s calculations have been inconclusive. Thus, the primary research objective of this study is to propose a new measurement system for the structural Biot parameters. After a comprehensive literature review has been undertaken on damping materials, as well as measurement apparatuses for Young’s modulus and loss factor of damping materials, two causes of measurement errors have been identified. Unknown stresses in measurement apparatuses and inhomogeneous, polytrophic and viscoelastic behaviour of specimens. A new measurement system that does not affect the specimens with unknown stresses and accounts for their complex behaviour required investigation. Non-contact ultrasound had been selected as a solution to determine the aforementioned parameters, since these methods do not necessarily touch or compress the specimen, which led to unknown stresses and neglection of the complex specimen behaviour with the aforementioned techniques. Although ultrasound had been used to determine structural parameters on various types of materials, it has never been used to measure soft porous damping materials. In order to find possible solutions, various sources using ultrasonics to investigate struc- tural parameters had been reviewed. In order to calculate structural parameters, the longitudinal and transversal wave velocity inside the specimen had to be determined. The main findings showed that non-contact ultrasound will be able to evaluate the Young’s modulus, loss factor as well as Poisson’s ratio. Consequently, it was shown that longitudinal velocity measurements could be conducted using well known transmission measurements. However, well known approaches would not be sufficient measuring the transversal wave velocity in soft damping materials. This problem was addressed with a special gas to be used, with lower sound speed velocity in the fluid than in the solid. Moreso, a new method determining the transversal wave velocity had been found, as it would enable the use of an even larger range of damping materials, especially ones with heavy frames and lower porosity. It will use refracted waves inside the specimen and the determination of the convertion position of the transversal to the longitudinal wave at the rear specimen surface. At the end of the study, hardware components were selected and a test rig was constructed, which should be able to prove that a determination of structural Biot parameters with non-contact ultrasound is possible with less errors instead of using mechanical transfer function systems. The development of measurement software as well as the testing of the measurement system and its validation was not under investigation in this dissertation. This study has expanded on the body of literature knowledge regarding non-contact ultrasound. Furthermore, a significant contribution has been made towards a new measurement system measuring Young’s modulus and loss factor which circumvents errors in mechanical transfer function systems. This will contribute to more precise simulations of damping materials and damped enclosures, which may ultimately result in enhanced efficiency of damping materials as well as the acoustic packaging of cars.

Thin elastic objects, including leaves, flowers, plastic sheets and sails, are ubiquitous in nature and their technological applications are growing with the introduction of hydrogel thin-films, flexible electronics and environmentally responsive gels. The intricate rippling and buckling patterns are postulated to be the result of minimizing an elastic energy. In this dissertation, we investigate the role of regularity in minimizing the elastic energy. Though there exist smooth isometric immersions of arbitrarily large subsets of H2 into R3, we show that the introduction of weakly-irregular singularities, of smoothness class C^{1,1}, significantly reduces the energy; we provide numerical evidence supporting an upper bound on the asymptotic scaling of the minimum energy over C^{1,1} isometries which is an exponentially large improvement as compared to the conjectured lower bound over C2 surfaces. This work provides insight into the quantitative nature of the Hilbert-Efimov theorem. The introduction of such singularities is energetically inexpensive, and so too is their relocation. Therefore, isometries are "floppy" or easily-deformable, motivating a shift in focus from finding the exact minimizers of the elastic energy in favor of understanding the statistical mechanics of the collection of zero-stretching immersions.

We present an elastic orthotropic plate theory in plane strain and axisym-metric deformations by first developing their uniform asymptotic expansions of the exact solutions for the basic governing boundary value problems. Then, the establishment of the necessary conditions for decaying states, both explicitly and asymptotically, enables us to determine the outer solution without reference to the inner solution and clarify the precise meaning of the well known St.Venant's principle under the circumstances considered here. The possible existence of corner stress singularities was examined by establishing and solving three transcendental governing equations. By developing a generalized Cauchy type singular integral equation for the plane strain deformation and an integral equation of the second kind for the axi-symmetric deformation and taking the corner stress singularities into consideration, we obtained accurate numerical solutions for all canonical boundary value problems which are needed in the asymptotic necessary conditions for decaying states. Finally, the accuracy of the numerical solutions of canonical boundary value problems and the efficiency of the plate theory were confirmed through the applications of solving two physical problems and comparing with the existing results. / Science, Faculty of / Mathematics, Department of / Graduate

The dissertation identifies and responds to two gaps in the current literature on the elasticity of taxable income (ETI). Firstly, there is a lack of a deep understanding of the process underlying behavioral responses of taxable income to taxation. Secondly, there is a lack of inquiry into the functional form of the ETI. This dissertation seeks to fill these gaps in the ETI literature. It constructs a theoretical framework for behavioral responses of taxable income to taxation, based on a review of the literature on taxpayer compliance behavior. The dissertation also introduces a new approach to estimating the ETI. This study is the first attempt to fill in the gap of the ETI for a lack of studying the functional form of the ETI and factors determining the ETI function. Using the functional form derived from the Allingham-Sandmo model and empirical data on the function's arguments in the years 1979, 1982, 1985, and 1988, the dissertation studies behavior of the declared income elasticity function. / Ph. D.

No description available.

No

An exact solution for the stress field within a rectangular slab of orthotropic material is found using a two-dimensional Fourier series formulation. The material is required to be in plane stress, with general stress boundary conditions, and the principle axes of the material must be parallel to the sides of the rectangle. Two load cases similar to those encountered in materials testing are investigated using the solution. The solution method developed is seen to have potential uses in stress analysis of composite structures. / Master of Science

This study investigated the demand patterns of poor households during a period of rising prices. Focus was on three main constructs namely the poor, rising prices and the demand patterns. The study was on Bophelong, a township in South Africa. This study was conducted from an empirical, quantitative approach which was preceded by a literature review. The main objective of conducting the literature review was to provide a theoretical framework for questionnaire design and empirical work. Cross sectional data was collected at Bophelong households. On completion of the survey, the poor were selected from the non-poor by means of a poverty line. The poor were further divided into two categories, namely moderately poor and the very poor. Moderately poor households were categorised by an income ranging 50% to 99% inclusively of their household poverty line. The very poor households were categorised by an income in the range of 0 to 49% inclusively of their poverty line. Using the above division, the total poverty rate was 56% of the total sample, 26% being moderately poor and 30% very poor. The poverty gap ratio for all the poor in the sample was 0.48, meaning that on average, the poor needed 48% of their current income to reach their poverty line. This ratio was 0.29 for the moderately poor households and 0.69 for the very poor households. A logistic regression done on the determinants of poverty in Bophelong showed that household size, age of the household head, monthly household income and the employment status of the household head were significant in determining poverty. The monthly average household income in Bophelong was R2 910. For the moderately poor households it was R1 641 for the and R932 for the very poor households. Household size was 3.96 for the whole sample size, 2.97 for the non-poor households, 4.2 for the moderately poor households and 4.7 for the very poor households. The study revealed that demand patterns of the poor differ from those of the non-poor. In addition the moderately poor households‟ demand patterns differ from the very poor An analysis of the poor‟s demand patterns during rising prices: the case of Bophelong household. The greatest part of income of the poor is spent on basic food stuffs. The very poor spent more than half of their income (53%) on food. The study indicated that bread is a giffen good only to the very poor households where quantity demanded moves in the same direction with price. In the non-poor households, bread is regarded inferior. A commodity can be overly a necessity, but the degree of necessity differs with a households‟ economic status. In some cases, a commodity was a necessity in the very poor households but a luxury in the non-poor. The way households substitute one good for another depends on their income levels. In conclusion, the study recommends that for poverty alleviation policies to effectively target the very poor in reducing malnutrition and hunger, these very poor should be studied separetely from the poor households. This is because households of different poverty levels face different challenges. A more detailed and deeper study relating to the demand structure of the poor is recommended. There is also a need to explore the survival means of the poor as to direct policy actions aimed at alleviating poverty among the poor in general. / Thesis (PhD (Economics))--North-West University, Vaal Triangle Campus, 2013

This study investigated the demand patterns of poor households during a period of rising prices. Focus was on three main constructs namely the poor, rising prices and the demand patterns. The study was on Bophelong, a township in South Africa. This study was conducted from an empirical, quantitative approach which was preceded by a literature review. The main objective of conducting the literature review was to provide a theoretical framework for questionnaire design and empirical work. Cross sectional data was collected at Bophelong households. On completion of the survey, the poor were selected from the non-poor by means of a poverty line. The poor were further divided into two categories, namely moderately poor and the very poor. Moderately poor households were categorised by an income ranging 50% to 99% inclusively of their household poverty line. The very poor households were categorised by an income in the range of 0 to 49% inclusively of their poverty line. Using the above division, the total poverty rate was 56% of the total sample, 26% being moderately poor and 30% very poor. The poverty gap ratio for all the poor in the sample was 0.48, meaning that on average, the poor needed 48% of their current income to reach their poverty line. This ratio was 0.29 for the moderately poor households and 0.69 for the very poor households. A logistic regression done on the determinants of poverty in Bophelong showed that household size, age of the household head, monthly household income and the employment status of the household head were significant in determining poverty. The monthly average household income in Bophelong was R2 910. For the moderately poor households it was R1 641 for the and R932 for the very poor households. Household size was 3.96 for the whole sample size, 2.97 for the non-poor households, 4.2 for the moderately poor households and 4.7 for the very poor households. The study revealed that demand patterns of the poor differ from those of the non-poor. In addition the moderately poor households‟ demand patterns differ from the very poor An analysis of the poor‟s demand patterns during rising prices: the case of Bophelong household. The greatest part of income of the poor is spent on basic food stuffs. The very poor spent more than half of their income (53%) on food. The study indicated that bread is a giffen good only to the very poor households where quantity demanded moves in the same direction with price. In the non-poor households, bread is regarded inferior. A commodity can be overly a necessity, but the degree of necessity differs with a households‟ economic status. In some cases, a commodity was a necessity in the very poor households but a luxury in the non-poor. The way households substitute one good for another depends on their income levels. In conclusion, the study recommends that for poverty alleviation policies to effectively target the very poor in reducing malnutrition and hunger, these very poor should be studied separetely from the poor households. This is because households of different poverty levels face different challenges. A more detailed and deeper study relating to the demand structure of the poor is recommended. There is also a need to explore the survival means of the poor as to direct policy actions aimed at alleviating poverty among the poor in general. / Thesis (PhD (Economics))--North-West University, Vaal Triangle Campus, 2013