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121.
四川旱涝灾害时间分布序列的分形特征研究 总被引:12,自引:2,他引:12
本文采用分形理论计算了四川旱涝灾害时间分布序列的分数维,其结果初步证实了四川旱涝灾害时间分布在一定区间范围内的无标度性。无标度区的跨度及相应的分形维数可作为四川旱涝灾害自组织程度的量度。 相似文献
122.
胜利油田位于我国黄河三角洲地区,潜水位高,水的矿化度大。生态环境恶劣,对植物尤其对木本植物的生长不利,整个地区生长的多是抗盐碱能力强的草本植物。针对油田的特殊环境条件,综合有关资料,介绍了以沙枣为代表的植物特性,特别强调了其抗盐碱、降低土壤矿化度和潜水位、增加土壤有机质和引起植被变化的特性。指出黄河三角洲也有些土质较好的、适于作物和木本植物生长的地区,改良盐碱地可以以这些地区为基点,放射性地向外逐步试验沙枣的种植,以探索改善生态环境的途径。努力做到边发展经济,边改善环境,达到经济效益、社会效益和环境效益三统一。 相似文献
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Summary The distributions of mountain hare (Lepus timidus) and European hare (L. europaeus) overlap in central Sweden, but they occupy separate food niches in winter. In Scandinavia, the European hare is mainly a grazer while mountain hare is a predominant browser. Browse contain high amounts of secondary metabolites, such as phenols, compared to grass. This raises the question if the two hare species differ in their metabolic tolerance of plant phenols and that these differences influence their food choice.Phenolic excretion in urine increased significantly with phenolic intake in both species. Excretion of glucuronic acid conjugates, one of the major pathways of elimination of phenols in both hare species, is positively correlated to phenolic intake and excretion. However, the extent of excretion of phenolics by this route was different in the two species of hare. European hares excreted substantially more glucuronic acid per amount of phenolics than mountain hare. The phenols were metabolized to a larger extent in the mountain hare, indicating a higher detoxification capacity. From these results it is likely that European hare have a higher cost for the detoxification of plant phenols compared to mountain hare. This cost and negative effect on sodium balance when feeding on browse may prevent exploitation of forest habitats by European hares, whereas mountain hare are better able to do so. 相似文献
124.
DAKA Erema Ransome 《环境科学学报(英文版)》2006,18(2):364-368
Introduction Pollution-induced stress indices at various levels of organization, from sub-cellular to organism al level, have been investigated as a m eans of identifying and m onitoring environm ental contam ination. Since changes elicited by toxic m aterials m ust occur at the biochem ical, cellular and tissue levels of organization before effects w ould be observed at the organism al level, such m easures have been suggested as potential short-term , functional indices w hich can be used to… 相似文献
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根据Paris公式推导出适用于B级钢圆角细节耐久性分析的 ,在一定裂纹尺寸范围内的裂纹扩展速率公式及其检验方法 ,笔者模拟货车B级钢转 8A侧架的导框弯角内侧 (A区 )的圆角细部进行耐久性实验 ;以试验数据的检验证明 ,在 0 .4~ 4mm的尺寸范围内 ,选用的断裂力学模型是合理的 ;同时为建立合理的检修周期和寿命体系提供理论模型和安全评价基础。 相似文献
127.
ABSTRACT: Customarily, it has been assumed that hydraulic conductivity is a stationary, homogeneous stochastic process with a finite variance for stochastic analysis of solute transport in the subsurface. That the distribution of hydraulic conductivity may have a fractal behavior with long range correlations was suggested from field data analyses. This motivates us to further investigate how the fractal behavior of permeability distribution impacts solute transport in porous media. This study provides longitudinal and transverse macrodispersivity coefficients and the variance of the solute concentration. Longitudinal and transverse macrodispersivity coefficients are found to depend strongly on the fractal dimension (D) of logarithmic hydraulic conductivity (logK). The longitudinal and transverse macrodispersivity coefficients are the highest when D = 1, and the values decrease monotonically to zero at D = 2. Both coefficients correspond to the characteristic length scale of the logK distribution, thus are scale dependent parameters. The ratio of the transverse to the longitudinal macrodispersivity coefficient is on the order of 10‐1 to 10‐4. Concentration variance also decreases with the fractal dimension of logK. There is no spatial spreading of solute for D = 2, and the concentration variance reaches zero for this case. 相似文献
128.
用于结构振动控制的电流变阻尼器的设计 总被引:1,自引:0,他引:1
地震是一种随机振动 ,一旦发生将影响结构的安全。ER智能材料是一种可控流体 ,它在电场作用下可从牛顿流体变为剪切屈服应力较高的粘塑性体 ,且这种转变连续、可逆、迅速 ,因此 ,可用它来制作可调阻尼器 ,实现对工程结构地震反应的半主动控制。本文在简要介绍了ER电流材料的基本性能和ER可调阻尼器的工作原理的基础上设计了一个具有较大可调范围和较高阻尼力的ER电流变阻尼器 相似文献
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