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Summary A mechanism for growth stress generation is studied which involves a contractive strain in the microfibril direction and swelling strain in the transverse direction in the developing wall of wood cells. A cylindrically anisotropic elastic model is used to calculate the accumulation of residual stresses in the S2 wall as it is formed. An explicit relation between the shrinkage/swelling strains in the growth increment of the cell wall and the resulting axial and circumferential stresses induced in the cell is derived. For gymnosperm cells the transition from tensile stress in normal wood cells to compressive stress in compression wood cells is found with increasing microfibril angle.  相似文献   
303.
Colic remains a significant problem in the horse in terms of welfare and economics; in some equine populations it is the single most common cause of death. Many causes of colic are cited in the equestrian and veterinary literature but little scientific evidence exists to substantiate these theories. Recent epidemiological investigations have confirmed that colic is complex and multi-factorial in nature. Studies have identified a number of factors that are associated with increased risk of colic including parasite burden, certain feed types, recent change in feeding practices, stabling, lack of access to pasture and water, increasing exercise and transport. These findings are reviewed together with examples of management practices that may be altered to reduce the incidence of specific types of colic. This is an opinionated, not a systematic, review focusing on those areas that are considered most relevant to the practitioner.  相似文献   
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Idiopathic focal eosinophilic enteritis (IFEE) is a rare disease in the horse and few cases have been reported in the literature. The objective of this paper was to describe the clinical, surgical, histological features and post-operative progress of 12 horses with IFEE, a disease that had not been identified in the authors' hospital population prior to 2000. Diagnosis of IFEE was made at laparotomy and confirmed by histological examination of resected abnormal small intestine. In all 12 horses colic was associated with jejunal obstruction involving visibly striking and palpably thickened serosal plaques or circumferential constrictions. Surgical resection of affected intestine was performed in 10 horses, of which seven completely recovered. In one horse, on which surgical resection was not performed, ingesta re-obstructed post-operatively at one of the lesions. Histological examination of resected intestines revealed, in all cases, severe transmural enteritis in which eosinophilic leucocytes were the predominant inflammatory cells. No helminths were identified and the cause of this lesion is not known. IFEE is an uncommon but significant cause of small intestinal obstruction for which surgical resection can be curative. The gross lesions may be under-recognised and histology is essential for diagnosis.  相似文献   
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