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Sustainable fusion power is within reach; however, more research is needed in the field of material science and engineering. One critical component of a fusion reactor is the plasma facing material. Very little literature exists on the sustainability of tungsten as a plasma facing material (PFM). During operation, PFM must withstand harsh conditions with combined effects from high temperature, mechanical stress, irradiation, transmutation, and the production of hydrogen (H) and helium (He) from nuclear reactions. Therefore, this thesis will focus on co-implantation of H and He into tungsten to investigate the mechanical and microstructural material response. For the first part of this study, Molecular Dynamics (MD) was used to qualitatively understand defect migration and mechanical property changes in tungsten. A Brinell hardness test was simulated using MD in tungsten to study the dependence on void size and void density hardness. It was found that hardness changes vary as the square root of the void size and void density. Also the movement of dislocations and its interaction with voids were investigated. For the second part of the study, H and He were co-implanted into tungsten to look at the mechanical and microstructural changes. Hardness changes were measured using a nano-indenter ex-situ on post-irradiated specimen. Results show that the hardness of tungsten after co-implantation is proportional to the square root of the fluence. Additionally, the microstructure of irradiated tungsten samples was investigated by using a Transmission Electron Microscope (TEM). It was observed that the defect microstructure in tungsten, after co-implantation, is quite complex, with a number of intriguing features, such as the presence of the nano-bubbles and dislocation loops. Also it was observed that there was an effect that H has on the nucleation of He nano-bubbles. The results from this work suggest that the effect of co-implanting H and He into tungsten is crucial to fully understand its viability as a PFM.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains ix, 59 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Orientador: Jaime Maia dos Santos / Banca: Arlindo Leal Boiça Júnior / Banca: Vilmar Gonzaga / Banca: Rita de Cassia Panizzi / Banca: Clélia Aparecida Iunes Lapera / Resumo: Foi objetivo desta pesquisa: 1) Quantificar a população de nematóides e fungos em amostras de sementes procedentes dos principais Estados produtores do Brasil; 2) Estudar a taxonomia dos nematóides; 3) Estudar o processo de infecção de sementes de Brachiaria brizantha por nematóides; 4) Avaliar a eficácia da irradiação com 60Co e do tratamento químico para o controle dos nematóides. Amostras de 237 lotes de sementes de diferentes gramíneas forrageiras foram examinadas nos Laboratórios de Nematologia e de Fitossanidade da UNESP/FCAV, Câmpus de Jaboticabal, quanto à ocorrência de fungos e nematóides. No tratamento químico, usouse um lote de sementes infectadas por 1.350 Aphelenchoides sp. por 10 g. As sementes foram tratadas com doses de diferentes produtos, e como testemunha usaram-se sementes não-tratadas do mesmo lote. O experimento foi conduzido a campo em duas regiões distintas. Para irradiação, empregaram-se doses de 60Co, no Centro de Energia Nuclear na Agricultura (CENA), Piracicaba - SP, sendo que 160 g de sementes de B. brizantha foram irradiadas com a taxa de dose de 186,8 Gy/h. Em outro experimento, 10 g de sementes de B. brizantha, isentas de nematóide, foram colocadas em gerbox, sobre areia autoclavada. Em seguida, foram inoculados 10 mL de uma suspensão contendo 3.000 indivíduos de Aphelenchoides sexlineatus (partenogenética). Os tratamentos tanto químico quanto com 60Co demonstraram não ter efeito sobre a população do nematóide. Confirmou-se, neste estudo, que os nematóides infectam as sementes após elas caírem no solo. Nematóides e fungos são encontrados infectando sementes de diferentes espécies forrageiras. / Abstract: It was the objective of this study: 1) To quantify the population of nematodes and fungi in samples of seeds from the main producer states of Brazil, 2) study the taxonomy of nematodes, 3) To study the process of infection of seeds of tropical grasses by nematodes, 4) Evaluate the effectiveness of irradiation with 60Co and chemical treatment to control nematodes. Samples of 237 seed lots of different grasses were examined in the Nematologia and Fitopatologia laboratory of UNESP / FCAV, from Jaboticabal Câmpus as the occurrence of fungi and nematodes. In the chemical treatment, used to a lot of seeds infected by 1350 Aphelenchoides sp. for 10 g. The seeds were treated with doses of different products and used it as a witness if untreated seeds from the same batch. The experiment was conducted under field conditions in two separate regions. For irradiation, using doses of 60Co, in the Centro de Energia Nuclear na Agricultura (CENA) Piracicaba - SP, of which 160 g of seeds of B. brizantha were irradiated with a dose rate of 186.8 Gy / h. In another experiment, 10 g of seeds of B. brizantha, free of nematode, were placed in gerbox on autoclaved sand. It was then inoculated 10 mL of a suspension containing 3000 specimens of Aphelenchoides sexlineatus. The both treatments, chemist and with 60Co showed no effect on the nematode population. It was confirmed in this study that the nematodes infect the seeds after they fall on the ground. Nematodes and fungi are found infected seeds of different forage species. / Doutor

Read the abstract in the section 00front of this document. / Thesis (DPhil (Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

The effects of irradiation dose (0, 0.5 and 1.0 kGy), various gas atmospheres and storage temperature (5, 15 and 25$ sp circ$C) on the physical, chemical, microbiological, and organoleptic changes in fresh pork were studied using factorial design experiments. The effects on toxin production by Clostridium botulinum were also investigated using challenge studies. Shelf life could be extended to 21 d when product was packaged in 0% O$ sb2$, irradiated at 1.0 kGy and stored at 5$ sp circ$C compared to 4 d for control samples. While the presence of O$ sb2$ in the package headspace enhanced the antimicrobial effects of low-dose irradiation, it adversely affected the organoleptic qualities of pork. Botulinum toxin was detected after only 2 d in all inoculated treatments stored at 25$ sp circ$C. At 15$ sp circ$C, toxin was produced faster when pork was initially packaged with O$ sb2$ or low levels of CO$ sb2$ (15-30%) as compared to 100% N$ sb2$. Higher levels of CO$ sb2$ (45-75%) delayed toxin production. In most treatments, spoilage preceded toxigenesis. Models were developed relating the above factors to the time until toxin production and to the probability of toxigenesis. Temperature, initial O$ sb2$ and irradiation were all significant factors.

Graduation date: 1961

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains iii, 50 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph.D.)(Food Science)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xi, 87 p. : ill. Vita. Includes abstract. Includes bibliographical references.