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Freezing is a very common method of food preservation around the world. Accurate simulation of the freezing process in food materials is very important for the design of superior freezing processes and more efficient refrigeration equipment. The accuracy of numerical methods is very significant for reliable prediction of temperature history in food materials during freezing. However, accurate simulation of the freezing process in foods is difficult due to its inherent nonlinearity. In this study, a technique was presented and used to assess the accuracy of the Crank-Nicolson and the Two-Step methods in solving this nonlinear problem. Overall, the accuracy of the Two-Step method was higher than that of the Crank-Nicolson method. These numerical methods were also implemented to simulate one-dimensional freezing experiments. Again, the results of the Two-Step method exhibited better agreement with the experimental data than the Crank-Nicolson results. The thermal properties of food materials change substantially with temperature during freezing. The estimation of these properties is very important in simulating freezing and determining the freezing time of foods. Mathematical modeling of the thermal properties of foods has been an appealing alternative to experimental methods. These models are generally based on the assumption that food materials are ideal binary solutions. One of the goals of this research study is to estimate thermal properties of aqueous solutions of basic food substances (sucrose, methyl-cellulose, and wheat gluten) during freezing. Temperature data from one-dimensional freezing experiments were used to estimate the temperature dependent thermal properties of these materials during freezing using the Modified Box-Kanemasu estimation method. The estimated thermal properties were then compared with models from the literature. Generally, the estimated thermal properties did not agree well with the predicted properties using the models from the literature, especially in the case of methyl-cellulose and wheat gluten. Hence, the models examined in this research study need to be modified to account for the chemical and the physical processes that occur during freezing. / Ph. D.

Este trabalho é uma contribuição às análises de forças de aprisionamento óptico exercidas sobre partículas esféricas por superposições discretas de feixes de Bessel. Um estudo teórico-numérico foi realizado no regime de óptica geométrica, completando as pesquisas já realizadas com tais feixes e no caso escalar, tanto no regime de Rayleigh quanto através de um formalismo eletromagnético completo. Investigam-se padrões longitudinais de intensidade de possível interesse prático, com potenciais de fornecer múltiplas armadilhas ópticas simultâneas utilizando dois métodos de análise. O primeiro parte da observação de que no regime paraxial todos os raios associados aos feixes se encontram quase paralelos entre si quando se toma como aproximação uma superposição de raios paralelos que incidem completamente sobre um hemisfério do espalhador. Tal método, entretanto, é naturalmente restrito pelas forças transversais. O segundo, que torna mais confiáveis e precisas as predições acerca da componente longitudinal de força, adota procedimentos mais robustos que levam em consideração tanto a contribuição da pressão de radiação (força de espalhamento) quanto a força gradiente devido a gradientes locais de intensidade associados a raios não-paralelos. Assim, acredita-se que este trabalho traz como contribuição um reforço a esta classe específica e promissora de feixes não difrativos como feixes de luz interessantes para aplicações em aprisionamento e micromanipulação óptica. / This work is a contribution to the analyses of optical trapping forces exerted on spherical particles by discrete superpositions of Bessel beams. A theoretical-numerical study has been carried out in the ray optics regime, completing the pre-existing research performed with such beams, in the scalar case, both in the Rayleigh regime and through a complete electromagnetic formalism. We investigate longitudinal intensity patterns of possible practical interest with potential to provide multiple simultaneous optical traps, by using two methods of analysis. The first assumes that, in the paraxial regime, all rays associated to the beams are almost parallel to each other, taking a superposition of parallel rays that are completely incident on a hemisphere of the scatterer as a suitable approximation. Such a method, however, is naturally constrained by the transverse forces. The second one, which makes the predictions about the longitudinal force component more reliable and accurate, adopts more robust procedures that take into consideration the contribution of the radiation pressure (scattering force) as well as the gradient force due to local intensity gradients associated to non-parallel rays. Thus it is hoped that this work will contribute to reinforce this specific and promising class of non-diffractive beams as interesting light beams for applications in optical trapping and micromanipulation.

Este trabalho é uma contribuição às análises de forças de aprisionamento óptico exercidas sobre partículas esféricas por superposições discretas de feixes de Bessel. Um estudo teórico-numérico foi realizado no regime de óptica geométrica, completando as pesquisas já realizadas com tais feixes e no caso escalar, tanto no regime de Rayleigh quanto através de um formalismo eletromagnético completo. Investigam-se padrões longitudinais de intensidade de possível interesse prático, com potenciais de fornecer múltiplas armadilhas ópticas simultâneas utilizando dois métodos de análise. O primeiro parte da observação de que no regime paraxial todos os raios associados aos feixes se encontram quase paralelos entre si quando se toma como aproximação uma superposição de raios paralelos que incidem completamente sobre um hemisfério do espalhador. Tal método, entretanto, é naturalmente restrito pelas forças transversais. O segundo, que torna mais confiáveis e precisas as predições acerca da componente longitudinal de força, adota procedimentos mais robustos que levam em consideração tanto a contribuição da pressão de radiação (força de espalhamento) quanto a força gradiente devido a gradientes locais de intensidade associados a raios não-paralelos. Assim, acredita-se que este trabalho traz como contribuição um reforço a esta classe específica e promissora de feixes não difrativos como feixes de luz interessantes para aplicações em aprisionamento e micromanipulação óptica. / This work is a contribution to the analyses of optical trapping forces exerted on spherical particles by discrete superpositions of Bessel beams. A theoretical-numerical study has been carried out in the ray optics regime, completing the pre-existing research performed with such beams, in the scalar case, both in the Rayleigh regime and through a complete electromagnetic formalism. We investigate longitudinal intensity patterns of possible practical interest with potential to provide multiple simultaneous optical traps, by using two methods of analysis. The first assumes that, in the paraxial regime, all rays associated to the beams are almost parallel to each other, taking a superposition of parallel rays that are completely incident on a hemisphere of the scatterer as a suitable approximation. Such a method, however, is naturally constrained by the transverse forces. The second one, which makes the predictions about the longitudinal force component more reliable and accurate, adopts more robust procedures that take into consideration the contribution of the radiation pressure (scattering force) as well as the gradient force due to local intensity gradients associated to non-parallel rays. Thus it is hoped that this work will contribute to reinforce this specific and promising class of non-diffractive beams as interesting light beams for applications in optical trapping and micromanipulation.

Theoretical part of the thesis is a scientific research of latest articles about frozen shoulder syndrome with accent to immunohistochemical level. At the same time, based on scientific literature it aims to clarify and statistically prove multifactorial causes of this syndrome especially in women going through hormonal changes. Psychosocial factors are also taken into account in this study and examined by unique questionnaire that was made expressly for this thesis. The questionnaire originates from internationally accepted clinimetrics such as VAS, SPADI, DASH score and most importantly SF-36. The theoretical research part also consists of "Therapy" chapter which describes latest trending treatment method for this condition. Experimental part, which consists of few case reports, focuses on a group of female patients who underwent range of motion measurement including functional testing of the affected limb. Next step followed was consecutive twelve minutes exercise on bicycle. They were controlled not to cross over anaerobic threshold. Level of exercise was controlled by predicted heart rate and estimation of the threshold by basic calculation and also by subjective Borg's scale of effort determined by the patient. After the bicycle exercise the range of motion was measured again and compared to the...

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Thesis (M.Sc. Agriculture (Agricultural Economics)) -- University of Limpopo, 2022 / The agricultural sector is dominated by broiler production and it is the key source of animal proteins followed by beef. South Africa is described as a net importer of chicken meat, given that broiler consumption of broiler is greater than supply. Additionally, the South African Poultry industry has raised concerns regarding the high influx of cheap broiler imports into the domestic market. This led to an increase of the ad valorem tariff charged on poultry imports in April 2020 from a previous adjustment in September 2013. It is vital to understand how import tariff changes affect the broiler sector since little is known about how domestic broiler production is responding to an increased tariff. The study, therefore, attempted to determine the relationship between domestic broiler production, import tariff, domestic prices, and import volume. The study aimed to investigate the long-run relationship between import tariff, import quantity, domestic production, and prices (retail and producer) in the broiler sector of South Africa for the period (April 2010 – June 2020). Brazilian frozen chicken imports were selected for study given their relatively high domestic demand in South Africa. In addition, Brazil primarily faces the import tariffs charged by South Africa as the main country of origin for South African imports. The Augmented Dickey-Fuller test, Johansen Cointegration tests, and the Error Correction Model were used as analytical tools in achieving the study objectives. The results for the Augmented Dickey-Fuller test and the Johansen cointegration test showed that all variables were stationary at first difference and cointegrated. The ECM results concluded the existence of a long-run relationship between domestic production, ad valorem tariff, and import volume. As the tariff charged changes, the domestic production increased by 4% in the long run which might be deemed a small advantage in terms of the production scale and therefore not sufficient. The study recommended that strategies that reduce barriers of entry for small-scale farmers such as reduced production costs be implemented to boost domestic production. Lastly, since domestic production is responding positively to tariff adjustment, a thorough investigation is necessary to prove dumping allegations against broiler importers as this will enable the country to impose anti-dumping duties on all countries. / Agri SETA