No description available.

In wheat (Triticum aestivum L), high molecular weight glutenin subunits (HMW -GS) are synthesized by the loci Glu-A1, Glu-B1, and Glu-D1 on the long arm of group 1 chromosome, and their variants play a significant role in the functional properties of flour; hence dough properties and tortilla quality. This study was conducted to understand the effects of HMW-GS on dough properties and tortilla quality using 40 different wheat lines from two different locations; Texas Agrilife Experiment Station at McGregor, and at Castroville, Texas, in 2010. Wheat lines in which one or more of these loci were absent (deletion lines) and non-deletion lines were used. Flours were evaluated for insoluble polymeric protein (IPP) content and mixograph properties. Dough properties; compression force, stress relaxation test, and dough extensibility, were determined using a texture analyzer. Tortillas were produced by hot-pressed method and evaluated for physical properties and textural change during 16 days of storage. Flour from deletion lines had lower average IPP content (38.4%) than non-deletion lines (41.9%). Dough from deletion lines were more extensible (44.8 mm) and required lower equilibrium force from stress relaxation test (4.91 N) compared to non-deletion lines (34.2 mm, and 6.56 N, respectively). Deletion lines produced larger diameter tortillas (177 mm) than non-deletion lines (165 mm) and had lighter color (L* = 82.3) than tortillas from non-deletion lines (L* = 81.0). Most of the deletion lines interestingly produced tortillas with acceptable flexibility scores on day 16 of storage (>= 3.0). Flour IPP content (r = -0.57) and equilibrium force (r = -0.80) were negatively correlated with tortilla diameter, but positively correlated with 16 day flexibility scores (r = 0.72, and r = 0.68, respectively). In general, deletion at Glu-A1 or Glu-D1 or presence of 2+12 instead of 5+10 allelic pair at Glu-D1 locus produced large diameter tortillas, but with poor day 16 flexibility. However, combination of 7+9 at Glu-B1 locus with deletions at Glu-A1 or Glu-D1 or 2+12 at Glu-D1 consistently produced tortillas that had large diameter and retained good flexibility scores during 16 days of storage. The results indicate the presence of 7+9 at Glu-B1 may play a crucial role in selection of wheat varieties for tortilla making.

This thesis focuses on how the properties of polymer thin films depend on the film thickness and molecular weight (Mw). Previous studies of polystyrene (PS) films coated on silica with Mw of 2.4 and 212 kg/mol found that the viscosity of the films decreases with decreasing film thickness. A two-layer model assuming a 3 nm thick mobile layer situated at the top surface of the film and hydrodynamically coupled to a bulklike inner layer is able to describe the viscosity of the films. To better understand the dynamics exhibited by the surface mobile layer, this work extends the measurement to various other Mw up to 2316 kg/mol. The result shows that the viscosity of the films also decreases with decreasing film thickness and can be described by the same two-layer model. But there are exceptional findings as well. Specifically, the viscosity of the high-Mw films (> 60 kg/mol) exhibit a Mw^0 dependence, distinctly different from the Mw^3.4 dependence exhibited by the viscosity of the bulk polymer. Moreover, the surface chains in the high-Mw films, as inferred from the two-layer model, are in an unphysically stretched state. These observations led to the conjecture that the viscosity reduction in the high-Mw films is due to a different mechanism from that in the lower Mw films which is directly tied to the surface mobile layer as in the two-layer model. To scrutinize this conjecture, viscosity measurement is extended to PS films doped with Dioctyl phthalate (DOP). A previous experiment showed that the influence of the surface on the overall dynamics in this system is likely to be much smaller than in the undoped films. The measurement results are examined to determine, among other things, whether the viscosity reduction relative to that in the undoped films is weaker in the low-Mw than in the high-Mw regime.

No description available.

No description available.

No description available.

No description available.

Ph.D.,Dept. of Orthopaedic Surgery, Faculty of Health Sciences, University of the Witwatersrand, 2009. / Total hip replacement (THR) is an effective method of treatment for patients with hip disability. The procedure is capable of providing long-term functional improvement with excellent control of pain and restoration of function. Sir J Charnley developed a concept of low friction arthroplasty, which was based on use of ultra-high molecular weight polyethylene acetabular and stainless steel femoral components. The components were attached to bone with the use of polymethylmethacrylate (PMMA) bone cement. This concept has been very successful, and is considered the gold standard of THR. Aseptic loosening of the prosthetic components remains the single most important reason for failure of THRs. Wear to the ultra high molecular weight polyethylene (UHMWPE) acetabular cup is a well-known cause of osteolysis and aseptic loosening of the components. Thus, substantial improvement to the wear resistance of UHMWPE could extend the clinical life span of total hip replacements. In an attempt to reduce polyethylene wear and subsequent osteolysis, a method was developed in the early seventies in South Africa to improve polyethylene quality by means of gamma ray cross-linking. The acetabular cup was irradiated with 100 Kilogray in an acetylene environment, which was used as a cross-linking gas material, resulting in improvement of UHMWPE wear resistance. Influenced by the world trend and with the advent of a ceramic bearing surface, the Project of cross-linking was, to a certain extent, forgotten. Patients followed up in the late 1990s, showed minimal or total absence of wear after 15 years or longer. 3 Based on my preliminary studies, and anticipating the world trend of acceptance of cross- link UHMWPE, the aim of this research is to consolidate the results from the largest long term group of patients with acetylene cross-link UHMWPE, to study polyethylene gamma irradiated in the presence of a cross-linking acetiylene gas and the effects of it, in vitro, using a hip simulator. I was planning to communicate with as many patients as possible from the group operated on from 1977 until 1983 in whom cross-link UHMWPE was used. This group of over thousand patients represents the largest group of patients with cross-linked UHMWPE acetabular components in the world, with the longest clinical follow up of over 20 years on average. The first part of the research is a retrospective study: The goal was to contact as many patients as possible who were operated on during the period 1977 to 1983 when cross-linked polyethylene was used. To qualified for the study each patient had to have an early postoperative and the latest follow up radiograph. The radiological study consisted of the radiological measurement of wear. For this purpose the Hip Analysis Suite program was used. This is a software program designed by Dr John M. Martell from the University of Chicago, which is widely used and internationally accepted for that purpose. Image analysis offers significant improvements in reproducibility and accuracy when compared to manual analysis. 4 The final results were compared with results of polyethylene wear in patients in whom conventional UHMWPE was used. For this comparison only patients with acetabular components made from the same UHMWPE material and from the same supplier were used. The conventional UHMWPE is a component of the gold standard of hip replacement surgery. World-wide published follow up studies of 15 years and longer using conventional UHMWPE were compared to the cross-link UHMWPE group. If revision surgery was indicated for whatever reason in patients in with cross-linked UHMWPE acetabular components, the retrieved prosthesis was analyzed. The analysis consisted of examination of the articular surface of the cross-linked acetabular component for micro wear phenomena using a Scanning Electron Microscope (SEM). In order to perform an objective analysis of the retrieved components, two independent laboratories were used, namely: Peterson Tribology Laboratory, Loma Linda University, California, and Biomechanical Laboratory, Faculty of Engineering, University of Pretoria. The analyses were possible thanks to collaboration with Dr Ian Clark from Peterson Tribology Laboratory and Dr NDL Burger in charge of the Biomechanical Laboratory at the Department of Engineering, University of Pretoria

O polietileno de ultra alto peso molecular (UHMWPE) é um plástico de engenharia que tem várias aplicações atualmente, mormente em áreas específicas da indústria e da medicina. O UHMWPE pode ser utilizado ainda em outras aplicações: defensas portuárias; guias de corrente; revestimentos de caçambas, silos e calhas; engrenagens; buchas; guias de correias e próteses cirúrgicas. Esta gama de aplicações se deve ao fato das excelentes características técnicas que este material possui, como: alta resistência a abrasão, elevada resistência ao impacto, anti-aderência, atóxico, excelente resistência química, baixo peso específico, fácil usinagem e alta resistência a fadiga. Os tipos de polietileno de ultra alto peso molecular (UHMWPE) utilizados neste trabalho foram o UTEC 3041 e UTEC 6541 da Braskem. A reciclabilidade do UHMWPE ganhou interesse, porque a utilização desta matéria-prima na última década cresceu mais de 600%, tornando-se um dos plásticos de engenharia mais utilizados para obtenção de peças usinadas depois da poliamida. Com o crescimento na utilização deste polímero na confecção de peças para maquinários, o seu desperdício tem sido muito grande, porque o resto deste material é desprezado, geralmente não sendo reaproveitado. Este trabalho tem como objetivo reciclar o UHMWPE UTEC 3041 e estudar as propriedades deste material virgem e reciclado e comparar os resultados entre si e com o UHMWPE UTEC 6541, e com estes materiais submetidos a diferentes doses de radiação. / Ultra High Molecular Weight Polyethylene (UHMWPE) is an engineering plastic which has several applications, chiefly, in specific areas of the industry and medicine. UHMWPE can be even for other applications such as: port fenders, current guide, bucket coating, silos and gutters, plugs, pulleys and surgical prosthesis. This range of applications is due to the excellent technical characteristics that this material owns, such as; high resistance to wear, high resistance to impact, anti-adherence, non toxic, excellent chemical resistance, low specific weight, easy mill processing, and high resistance to fatigue. The UHMWPE type used in this work were UTEC 3041 and UTEC 6541 of the Braskem. The recycling process of UHMWPE raised much interest, because the utilization of this rawmaterial grew over 600% in the last decade, becoming one of the most used engineering plastics for attainment of mill processed parts after polyamide. As the utilization of this polymer in the manufacturing of parts for machinery has grown, its waste is very big, because the rest of this material is thrown out, usually not being reused. The goal of this work is to recycle the UHMWPE UTEC 3041 and study the properties of this recycled and virgin material and compare the results between both with these materials submitted to different radiation dose.

O polietileno de ultra alto peso molecular (UHMWPE) é um plástico de engenharia que tem várias aplicações atualmente, mormente em áreas específicas da indústria e da medicina. O UHMWPE pode ser utilizado ainda em outras aplicações: defensas portuárias; guias de corrente; revestimentos de caçambas, silos e calhas; engrenagens; buchas; guias de correias e próteses cirúrgicas. Esta gama de aplicações se deve ao fato das excelentes características técnicas que este material possui, como: alta resistência a abrasão, elevada resistência ao impacto, anti-aderência, atóxico, excelente resistência química, baixo peso específico, fácil usinagem e alta resistência a fadiga. Os tipos de polietileno de ultra alto peso molecular (UHMWPE) utilizados neste trabalho foram o UTEC 3041 e UTEC 6541 da Braskem. A reciclabilidade do UHMWPE ganhou interesse, porque a utilização desta matéria-prima na última década cresceu mais de 600%, tornando-se um dos plásticos de engenharia mais utilizados para obtenção de peças usinadas depois da poliamida. Com o crescimento na utilização deste polímero na confecção de peças para maquinários, o seu desperdício tem sido muito grande, porque o resto deste material é desprezado, geralmente não sendo reaproveitado. Este trabalho tem como objetivo reciclar o UHMWPE UTEC 3041 e estudar as propriedades deste material virgem e reciclado e comparar os resultados entre si e com o UHMWPE UTEC 6541, e com estes materiais submetidos a diferentes doses de radiação. / Ultra High Molecular Weight Polyethylene (UHMWPE) is an engineering plastic which has several applications, chiefly, in specific areas of the industry and medicine. UHMWPE can be even for other applications such as: port fenders, current guide, bucket coating, silos and gutters, plugs, pulleys and surgical prosthesis. This range of applications is due to the excellent technical characteristics that this material owns, such as; high resistance to wear, high resistance to impact, anti-adherence, non toxic, excellent chemical resistance, low specific weight, easy mill processing, and high resistance to fatigue. The UHMWPE type used in this work were UTEC 3041 and UTEC 6541 of the Braskem. The recycling process of UHMWPE raised much interest, because the utilization of this rawmaterial grew over 600% in the last decade, becoming one of the most used engineering plastics for attainment of mill processed parts after polyamide. As the utilization of this polymer in the manufacturing of parts for machinery has grown, its waste is very big, because the rest of this material is thrown out, usually not being reused. The goal of this work is to recycle the UHMWPE UTEC 3041 and study the properties of this recycled and virgin material and compare the results between both with these materials submitted to different radiation dose.