No description available.

No description available.

No description available.

It is believed that the noise produced in squeaking dashboards is caused by the drop in friction force during the transition from static to kinetic conditions between the mating plastic components of the dashboard. The frictional behavior of a polymer determines whether there is a drop in friction force during this transition. This study investigates the frictional behavior of polymers under dry sliding conditions. Various compositions of ABS plastic along with Polypropylene were tested in a flat-on-flat configuration. There appears to be no consistent evidence of surface roughness effects on the magnitude of the drop in friction force. The surface roughness did have an effect on the frictional behavior of the polymers as did the material composition. A new test apparatus was designed to study the transition from static to kinetic conditions more closely. A computer model was developed to simulate this transition. The computer model was used to illustrate the effect of the friction-velocity curve on the frictional behavior of a surface interaction. A few conclusions are made about which friction mechanisms are in control of the polymer-on-polymer tribological system. / Master of Science

M.S.

This thesis is the study of the effects of several commercial admixtures on the properties of concrete in the plastic and the hardened state. The project is divided into two parts. Part I deals with the laboratory investigation and Part II takes into account the theoretical study of Part I. Three standard concrete mixtures at different water-cement ratios and approximately at constant slump were designed without the addition of admixtures to serve as a parameter for the test mixtures. Eighteen different test mixtures were made with local aggregates. Three test mixtures for each individual admixture and combination admixtures were used for comparison purposes. From the results obtained in the laboratory study, it was found that all the admixture used, separately and in combination, the test mixtures with an air entraining agent produced the greatest improvement in the plastic state as compared with their standard. In the hardened state, the cement dispersing agent (normal set) and the accelerator produced the greatest increase in the compressive strengths at all ages of testing as compared with their standard. It is further revealed that the accelerator imparted the greatest influence when used in rich mixture. In the theoretical study, by making alterations in the water-cement ratio so as to obtain a desired slump of four inches, the theoretical test mixtures so designed predicted a further increase in the compressive strengths, except in the case of the accelerator. It is noteworthy that the accelerator produced the same magnitude of compressive strength as was produced by the cement dispersing agent (normal set) at 28 days in the rich mixture, but in the case of the poor mixture, the latter was more effective. / Master of Science

O objetivo do presente trabalho foi avaliar o efeito de aditivos químicos e microbianos sobre as perdas de matéria seca, perfil fermentativo, valor nutritivo e estabilidade aeróbia da silagem de cana-de-açúcar. A variedade utilizada para confeccionar os silos laboratoriais foi RB-72454 com 12 meses de idade fisiológica. O experimento foi desenvolvido em delineamento inteiramente casualizado, sendo seis tratamentos, com quatro repetições cada. Além da silagem de cana-de-açúcar controle, foram utilizados dois aditivos microbianos: Lactobacillus plantarum e o conjunto de bactérias L. plantarum + Streptococcus faecium + Pediocccus acidilactici (BAL). Esses dois aditivos microbianos também foram aplicados associados a duas doses de benzoato de sódio, 0,01 e 0,05% da massa verde (MV). Os aditivos microbianos foram aplicados à contagem de 5 x 104 ufc/g de forragem. As variáveis analisadas foram: perdas totais e gasosas, produção de efluente, recuperação de matéria seca, perfil fermentativo, estabilidade aeróbia e valor nutritivo no momento da abertura dos silos e durante o ensaio de estabilidade aeróbia. As maiores perdas fermentativas e gasosas foram observadas para o tratamento da associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV. No entanto, não houve diferença entre os tratamentos para as variáveis do perfil fermentativo. Com relação ao valor nutritivo, as silagens que foram tratadas com associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, apresentaram no momento da abertura maior concentração de componentes fibrosos e menores coeficientes de digestibilidade da matéria seca. A maioria dos tratamentos apresentou desempenho semelhante ao tratamento controle no valor nutritivo no momento da abertura dos silos. Com relação ao ensaio de estabilidade aeróbia na associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, foi observado o menor acúmulo de temperatura nos primeiros cinco dias após abertura (ADITE-5) e menor pico de temperatura da massa exposta ao ar. Da mesma forma, as silagens tratadas com esses aditivos mantiveram estável o valor de pH e apresentaram maior recuperação de matéria seca das silagens nos primeiros cinco dias pós-abertura. Todavia, não houve diferenças significativas entres os tratamentos para as outras variáveis analisadas na fase aeróbia. Com relação ao valor nutritivo das silagens no momento da abertura, associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV apresentou menores valores da fração fibrosa e maior digestibilidade da matéria seca nos primeiros cinco dias da fase aeróbia. Para a avaliação químico-bromatológicas, não foram encontradas diferença nos teores de carboidratos solúveis e proteína bruta entre os tratamentos. De forma geral, a analise conjunta dos experimentos mostra que as silagens tratadas com associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, apresentaram melhor desempenho na fase aeróbia que na fase fermentativa. / The objective of this study was to evaluate the effect of chemical and microbial additives on dry matter losses, fermentative profile, nutritive value and aerobic stability of sugarcane silages. The variety used to ensiling was RB-72454, harvested with 12 months of regrowth. It was analyzed as a completely randomized model, with six treatments and four replications for each treatment. Besides the control sugarcane silage, were tested two types of microbial additives: Lactobacillus plantarum and the association of L. plantarum and Streptococcus faecium and Pediocccus acidilactici (BAL). Moreover these two microbial additives were associated with two levels of sodium benzoate, 0.01 or 0.05% of fresh matter. The microbial additives were applied trying to reach 5 x 104 UFC/g of forage. The variables analyzed were: total dry matter losses, gases losses, effluent yield, dry matter recovery rate, fermentative profile, aerobic stability and nutritive value when the silos were opened and during the aerobic stability trial. The greatest fermentative and gaseous losses were observed in silages treated with L. plantarum associated with 0.05% of sodium benzoate. However, there is no difference among treatments regarding the fermentative profile. The silages added with L. plantarum associated to 0.05% of sodium benzoate showed highest cell wall content and lowest in vitro dry matter digestibility. Most of the treatments showed similar nutritive value as control silages. Regarding the aerobic stability assay, L. plantarum associated to 0.05% of sodium benzoate had highest accumulated temperature in the first five days (ADITE-5) and the lowest temperature pick. Similarly, these silages remained the pH stable and showed highest dry matter recovery rate in the first five days during aerobic trial. Although, there were no differences in the other variables in aerobic assay. In terms of nutritive value, the treatment of L. plantarum associated 0.05% of sodium benzoate, showed lowest fiber content and highest in vitro dry matter digestibility during the first five days of aerobic stability trial. There were no differences in the water soluble carbohydrates and crude protein content among treatments. In general, considering the whole trial, the treatment with L. platarum associated with 0.05% of sodium benzoate had better performance during the aerobic phase than the fermentative one.

Lithium-ion batteries (LIBs) are the most commonly used type of rechargeable batteries with a global market estimated at $11 billion, which is predicted to grow to $60 billion by 2020. The global commercialization of Li-ion batteries is impeded by issues such as poor cycle life (5000 cycles achieved in some LIBs) in high energy and power density applications because of the rising internal resistance due to aging and safety concerns such as overcharge which ultimately leads to thermal runaway and explosions. A battery’s performance mainly depends on external factors such as electrode thickness and degree of compacting, and the type of conductive additive and electrolyte mixture used, and internal factors such as its internal temperature and state of charge. The performance suffers due to aging or erroneous mechanisms such as decomposition of the electrode or electrolyte material affecting the lifetime. In this thesis, an attempt is made to improve the lifetimes of the Li-ion batteries by incorporating suitable electrolyte additives, which were incorporated in the battery electrolyte to prevent overcharge. Also, several conductive electrode additives were incorporated as filler materials in an anode to explore the effects on its discharge capacities.

Thesis (MSc (Agric)(Production Management)) -- University of Pretoria, 2007. / Includes bibliographical references.

O objetivo do presente trabalho foi avaliar o efeito de aditivos químicos e microbianos sobre as perdas de matéria seca, perfil fermentativo, valor nutritivo e estabilidade aeróbia da silagem de cana-de-açúcar. A variedade utilizada para confeccionar os silos laboratoriais foi RB-72454 com 12 meses de idade fisiológica. O experimento foi desenvolvido em delineamento inteiramente casualizado, sendo seis tratamentos, com quatro repetições cada. Além da silagem de cana-de-açúcar controle, foram utilizados dois aditivos microbianos: Lactobacillus plantarum e o conjunto de bactérias L. plantarum + Streptococcus faecium + Pediocccus acidilactici (BAL). Esses dois aditivos microbianos também foram aplicados associados a duas doses de benzoato de sódio, 0,01 e 0,05% da massa verde (MV). Os aditivos microbianos foram aplicados à contagem de 5 x 104 ufc/g de forragem. As variáveis analisadas foram: perdas totais e gasosas, produção de efluente, recuperação de matéria seca, perfil fermentativo, estabilidade aeróbia e valor nutritivo no momento da abertura dos silos e durante o ensaio de estabilidade aeróbia. As maiores perdas fermentativas e gasosas foram observadas para o tratamento da associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV. No entanto, não houve diferença entre os tratamentos para as variáveis do perfil fermentativo. Com relação ao valor nutritivo, as silagens que foram tratadas com associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, apresentaram no momento da abertura maior concentração de componentes fibrosos e menores coeficientes de digestibilidade da matéria seca. A maioria dos tratamentos apresentou desempenho semelhante ao tratamento controle no valor nutritivo no momento da abertura dos silos. Com relação ao ensaio de estabilidade aeróbia na associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, foi observado o menor acúmulo de temperatura nos primeiros cinco dias após abertura (ADITE-5) e menor pico de temperatura da massa exposta ao ar. Da mesma forma, as silagens tratadas com esses aditivos mantiveram estável o valor de pH e apresentaram maior recuperação de matéria seca das silagens nos primeiros cinco dias pós-abertura. Todavia, não houve diferenças significativas entres os tratamentos para as outras variáveis analisadas na fase aeróbia. Com relação ao valor nutritivo das silagens no momento da abertura, associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV apresentou menores valores da fração fibrosa e maior digestibilidade da matéria seca nos primeiros cinco dias da fase aeróbia. Para a avaliação químico-bromatológicas, não foram encontradas diferença nos teores de carboidratos solúveis e proteína bruta entre os tratamentos. De forma geral, a analise conjunta dos experimentos mostra que as silagens tratadas com associação de L. plantarum com benzoato de sódio na dosagem de 0,05% da MV, apresentaram melhor desempenho na fase aeróbia que na fase fermentativa. / The objective of this study was to evaluate the effect of chemical and microbial additives on dry matter losses, fermentative profile, nutritive value and aerobic stability of sugarcane silages. The variety used to ensiling was RB-72454, harvested with 12 months of regrowth. It was analyzed as a completely randomized model, with six treatments and four replications for each treatment. Besides the control sugarcane silage, were tested two types of microbial additives: Lactobacillus plantarum and the association of L. plantarum and Streptococcus faecium and Pediocccus acidilactici (BAL). Moreover these two microbial additives were associated with two levels of sodium benzoate, 0.01 or 0.05% of fresh matter. The microbial additives were applied trying to reach 5 x 104 UFC/g of forage. The variables analyzed were: total dry matter losses, gases losses, effluent yield, dry matter recovery rate, fermentative profile, aerobic stability and nutritive value when the silos were opened and during the aerobic stability trial. The greatest fermentative and gaseous losses were observed in silages treated with L. plantarum associated with 0.05% of sodium benzoate. However, there is no difference among treatments regarding the fermentative profile. The silages added with L. plantarum associated to 0.05% of sodium benzoate showed highest cell wall content and lowest in vitro dry matter digestibility. Most of the treatments showed similar nutritive value as control silages. Regarding the aerobic stability assay, L. plantarum associated to 0.05% of sodium benzoate had highest accumulated temperature in the first five days (ADITE-5) and the lowest temperature pick. Similarly, these silages remained the pH stable and showed highest dry matter recovery rate in the first five days during aerobic trial. Although, there were no differences in the other variables in aerobic assay. In terms of nutritive value, the treatment of L. plantarum associated 0.05% of sodium benzoate, showed lowest fiber content and highest in vitro dry matter digestibility during the first five days of aerobic stability trial. There were no differences in the water soluble carbohydrates and crude protein content among treatments. In general, considering the whole trial, the treatment with L. platarum associated with 0.05% of sodium benzoate had better performance during the aerobic phase than the fermentative one.