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51.
金安桥水电站下闸蓄水后,陡升的库水位将对导流洞结构稳定造成不利影响。为保障堵头封堵前的导流洞结构稳定性,运用三维弹塑性损伤有限元,在模拟进水口边坡及导流洞开挖支护的基础上,计算汛前下闸水位时的岩体渗流场,对导流洞围岩和衬砌在岩体渗流作用下的结构稳定性进行复核分析。分析结果表明,导流洞的围岩稳定性在蓄水后仍有保障,衬砌结构受力较小,现有环向配筋满足结构内力要求,但在进水口变截面和导流洞变截面部位沿水流方向的拉应力较大,使得衬砌出现开裂。进一步分析表明,上述区域的开裂范围有限,对整体衬砌结构影响较小。 相似文献
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Huimin Yang Murray Unkovich Ann McNeill Xianzhi Wang 《Biology and Fertility of Soils》2011,47(4):377-385
Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil
mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in
an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18
permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3− by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year.
We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher
than that of non-N2 fixing species examined. 相似文献
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ZHANG Xu LIU Ming-ming CHENG Ming XU Jin WANG Shu-he WANG Hui REN Ya-li XIU Rui-juan WANG Su-xia 《园艺学报》2015,31(8):1520
AIM: To investigate the ultrastructural changes of islet microvascular endothelial cells in STZ-induced type 1 diabetic mice. METHODS: BALB/c mice were randomly divided into diabetic group and control group. The expression of insulin and platelet-endothelial cell adhesion molecule-1 (CD31) in islet microvessels was detected by immunohistochemical staining. The ultrastructural changes of islet β cells and islet microvessels were observed under transmission electron microscope. RESULTS: Compared with control group, the number of islet β cells, ratio of β cells/α cells, average number of secretory granules in β cells and insulin expression area per islet in diabetic group were significantly decreased (P<0.01). Besides, diabetic group had fewer microvessels with lower expression of CD31 (P<0.01). Mitochondria in islet microvascular endothelial cells and pericytes in diabetic group were swelling. The basement membrane of islet microvessels became thicker in diabetic group (P<0.01). CONCLUSION: Islet microvascular endothelial cells were impaired in type 1 diabetic mice. 相似文献
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The effects of ammonia and nitrite on vigour, survival rate, moulting rate of zoea of blue swimming crab, Portunus pelagicus, were studied. A total of five nitrite-N treatments (26.67, 53.34, 106.68, 213.36, 426.72 mg/l) and a control (no nitrite-N added) were
set up for the acute nitrite-N toxicity experiment; a total of five ammonia-N treatments (8.43, 16.86, 33.72, 67.44, 134.88 mg/l)
and a control (no ammonia-N added) were set up for the acute ammonia-N toxicity experiment. The results showed that the vigour,
survival rate and moulting rate of zoea of the blue swimming crabs exposed to over 53.34 mg/l were significantly different
(P < 0.05) from the control group. The zoea LC50 values (mg/l) of nitrite-N were 179.47, 76.56, 66.70, 37.49, 25.01, 25.35, 25.34 mg/l for 24, 36, 48, 60, 72, 84, 96 h, respectively.
The vigour, survival rate and moulting rate of zoea of the blue swimming crabs exposed to over 16.86 mg/l were significantly
different (P < 0.05) from the control group. The zoea LC50 values (mg/l) of ammonia-N were 51.04, 39.62, 38.72, 24.43, 16.90, 13.42, 11.16 mg/l for 24, 36, 48, 60, 72, 84, 96 h, respectively.
The zoeae are highly sensitive to ammonia and nitrite, and the toxicity of ammonia and nitrite on Portunus pelagicus decrease with development of this crab. 相似文献