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22.
强降雨条件下土质边坡瞬态稳定性分析 总被引:9,自引:1,他引:8
基于实际降雨气象资料,设计了单峰降雨和8个不同时间间隔的双峰降雨计算方案,利用非饱和土力学理论,对边坡的瞬态稳定性进行了计算和分析,研究了水分在坡体内的运移对边坡稳定性的时间空间影响效应,同时考察了降雨入渗造成的土性渗透特性的改变。分析发现:一次降雨的影响历时约12 d,降雨后约0.5 d该类土质边坡最危险;不同时间间隔的两次降雨对边坡稳定的影响比单峰降雨的最小安全系数滞后约0.3 d~0.8 d,影响历时基本保持不变;土体物理力学性质、边坡最危险滑动面及其对应的安全系数随水分在坡体内渗透运移而变化。 相似文献
23.
报道用室内实验方法对鲢鱼摄食强度和摄食节律的研究结果,探讨了影响它们的因子。提出鲢鱼在不同水温、不同花粉密度及不同鱼规格下的摄食量的统计分析。指出:食粒密度和水温与摄食量正相关,而鱼规格与摄食量负相关;食粒密度对摄食量影响最大(P<0.01),其次为水温;水温和食粒密度在影响摄食量的过程中可能有一定的交互作用。鲢鱼摄食强度在室内条件下也具明显的昼夜节律。在食粒规格较小、密度较低且溶氧充足条件下,鲢鱼夜晚非但不停食且出现摄食率次高峰。在本实验条件下,鲢鱼的日摄食节律与水温和光照无关,可能受饵料可得性和自身的生物钟节律等制约。 相似文献
24.
尝试性地将南黄海灾害地质因素分为4大类。同时参考地貌沉积界线和其他因素将南黄海分成4个灾害地质区:即海岸带、苏北浅滩、海州湾和南黄海东部灾害地质区,并时各灾害地质区进行了定性评价,苏北浅滩灾害地质区是研究区内灾害地质环境最不稳定的区域。 相似文献
25.
From the experimental studies in recent years, it has become known that when a wave breaks directly on a vertical faced coastal structure, high magnitude impact pressures are produced. The theoretical and experimental studies show that the dynamic response of such structures under wave impact loading is closely dependent on the magnitude and duration of the load history. The dynamic analysis and design of a coastal structure can be succeeded provided the design load history for the wave impact is available. Since these types of data are very scarce, it is much more convenient to follow a method which is based on static analysis for the dynamic design procedure. Therefore, to facilitate the dynamic design of a vertical plate that is exposed to breaking wave impact, a multiplication factor called “dynamic magnification factor” is herein presented which is defined as the ratio of the maximum value of the dynamic response to that found by static analysis. The computational results of the present study show that the dynamic magnification factor is a useful ratio to transfer the results of static analysis to the dynamic design of a coastal plate for the maximum impact pressure conditions of pmax/γH0≤18. 相似文献
26.
This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific, the oceanic region centered on the eastern Pacific warm pool, but also including the equatorial cold tongue and equatorial current system, and summarizes what is known about oceanographic influences on seabirds and cetaceans there. The eastern tropical Pacific supports on the order of 50 species of seabirds and 30 species of cetaceans as regular residents; these include four endemic species, the world’s largest populations for several others, three endemic sub-species, and a multi-species community that is relatively unique to this ecosystem. Three of the meso-scale physical features of the region are particularly significant to seabirds and cetaceans: the Costa Rica Dome for blue whales and short-beaked common dolphins, the Equatorial Front for planktivorous seabirds, and the countercurrent thermocline ridge for flocking seabirds that associate with mixed-species schools of spotted and spinner dolphins and yellowfin tuna. A few qualitative studies of meso- to macro-scale distribution patterns have indicated that some seabirds and cetaceans have species-specific preferences for surface currents. More common are associations with distinct water masses; these relationships have been quantified for a number of species using several different analytical methods. The mechanisms underlying tropical species–habitat relationships are not well understood, in contrast to a number of higher-latitude systems. This may be due to the fact that physical variables have been used as proxies for prey abundance and distribution in species–habitat research in the eastern tropical Pacific.Though seasonal and interannual patterns tend to be complex, species–habitat relationships appear to remain relatively stable over time, and distribution patterns co-vary with patterns of preferred habitat for a number of species. The interactions between seasonal and interannual variation in oceanographic conditions with seasonal patterns in the biology of seabirds and cetaceans may account for some of the complexity in species–habitat relationship patterns.Little work has been done to investigate effects of El Niño-Southern Oscillation cycles on cetaceans, and results of the few studies focusing on oceanic seabirds are complex and not easy to interpret. Although much has been made of the detrimental effects of El Niño events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time. 相似文献
27.
Abstract. A test of the niche width variation hypothesis was conducted in the three Mediterranean littoral species of the family Trochidae: Monodonta turbinata, M. turbiformis and Gibbula richardi. Allozymic variation encoded by 26 gene loci was analyzed, and the levels of polymorphism (P), heterozygosity (H) and allele diversity per locus (A) were estimated and appear to support the niche-width variation hypothesis. The broad-niche species, M. turbiformis and G. richardi are more polymorphic and heterozygous than the relatively narrow-niche M. turbinata (P = 0.571; 0.731 and 0.417; H = 0.108; 0.116 and 0.078; A = 2.025; 2.489 and 1.965, respectively). 相似文献
28.
29.
Fishing, selection, and phenotypic evolution 总被引:10,自引:9,他引:10
30.
邱燕 《海洋地质与第四纪地质》2007,27(5):1-7
利用南海中南部表层沉积物151个样品中黏土矿物的测试数据,计算了主要黏土矿物含量的平均值并编制分布图,据此分析黏土矿物的分布特征及其控制因素。南海中南部表层沉积物中的黏土矿物组合类型为伊利石-蒙脱石-高岭石-绿泥石,含量平均值依次为47%、19%、17%和16%。高岭石含量分布具有北部低、南部高的特点,与之对应的是蒙脱石矿物含量呈现北部高、南部低的趋势。伊利石和绿泥石含量分布规律不甚明显。前者呈现北部略高、南部稍低的分布趋势,含量变化起伏较大;后者的含量变化呈西北陆坡区稍偏低,其他部位含量分布均匀的趋势。伊利石/高岭石含量的比值变化与高岭石含量变化呈明显的负相关关系。从黏土矿物含量的分布规律来看,控制本区黏土矿物分布的主要因素有物源的搬运和输送、水动力条件变化、海底火山活动、地球化学环境影响等。 相似文献