California horses incur a bone fragility syndrome manifested by pathologic fractures. This study investigated gross, radiographic, and histologic features of the disorder as well as relationships with silicosis and levels of heavy metals and trace minerals through a postmortem study of 9 affected and 3 unaffected horses. Bones and soft tissues were evaluated grossly and histologically. Bones, lymph nodes, and lung tissue were evaluated radiographically. Tissues were evaluated for silicon levels, intracytoplasmic crystals, heavy metals, and trace minerals. All 9 affected horses had osteoporosis and clinical or subclinical pulmonary disease due to silicosis (8/9) or pneumoconiosis (1/9). All affected horses had radiographic findings consistent with osteopenia and histologic evidence of osteoporosis characterized by osteopenia, numerous resorption cavities, cement lines, and a mosaic lamellar pattern indicative of multiple remodeling events. Silicosis was characterized by widespread pulmonary granuloma formation with fibrosis; variable tracheobronchiolar and mediastinal granulomatous lymphadenitis; intracellular crystals within lung and lymph node macrophages; and pronounced lymph node fibrosis, focal necrosis, and dystrophic calcification. Crystals in lung (6/9) and lymph node (8/9) tissues were identified as cytotoxic silica dioxide polymorphs. Lung and liver tissue from affected horses had elevated levels of elemental silicon. Osteoporosis was highly correlated (r = 0.8, P < .01) with silicosis. No abnormalities in heavy metal or trace minerals were detected. This evaluation indicated that horses with bone fragility disorder have systemic osteoporosis associated with fibrosing pulmonary silicosis. The etiopathogenesis of the bone fragility syndrome is unknown; however, this study provides circumstantial evidence for a silicate associated osteoporosis.

for his invaluable advice and tireless assistance throughout, Robb Kulin for his technical input and high-speed camera expertise, Tsukasa Takahashi for his commiseration and encouragement, and Hesham-Heesh‖ Khalifa for all the questions he answered and wisdom he shared. I would not have finished without their help. My family, who with their prayers kept me alive, and my friends, who despite my complaining supported me, deserve any and all remaining credit for my success. Chapter 1, in part, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. Chapter 2, in part, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. Chapter 3, in part, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. Chapter 4, in part, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. Chapter 5, in part, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. Chapter 6, in full, is currently being prepared for submission for publication of the material. The dissertation author was the primary investigator and author of this material. xviii

The fatigue behavior of a conditioned short glass-fiber reinforced polyamide 6 was studied and the effect of the cyclic frequency investigated. Load controlled fatigue tests were performed, and the strains and surface temperature of specimens were recorded continuously. The number of cycles to failure was found to be dependent upon cyclic creep rate, as is typical for short glass fiber reinforced polyamides in the conditioned state. A strong reduction of fatigue strength was observed for increasing cyclic load frequency. This was mainly related to the specimen temperature increase due to hysteretic self heating and its effect on the cyclic creep speed. A frequency superposition method is proposed, expressing the relationship between temperature rise, applied stress, and cyclic creep speed in terms of a parameter derived from the Larson-Miller steady creep parameter. POLYM. COMPOS.,

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