Effect of the Twin Jetties as A Regulating Structure at the Tao-er Estuary     

LU  Peidong 《中国海洋工程》2002,16(2):219-226

The phase one project of the twin jetties at the Tao-er Estuary yields no effect on the flow, and there is a large area of deposition. A numerical model is employed to simulate the flow field, and the scouring and silting in the channel be-tween the two jetties are analyzed. The results show that the effective tidal flux between the two jetties is reduced due to the notch located at the heel of the east jetty, and the effect of contraction-flush is not obvious. As for the regulation of this kind of estuary under the tide action, the capability of tidal flux should be fully used.  相似文献   

“地震预警”法律概念的构成及延展     

李一行  陈华静 《中国地震》2021,37(3):641-648

“地震预警”法律概念是讨论和规范地震预警相关行为的基础,也是地震预警立法首先要明确的问题。目前,国家层面尚未制定专门的地震预警法律法规,地方已经颁布的管理办法中对“地震预警”法律概念的规定也不完全一致。随着地震预警立法进程的不断推进,“地震预警”法律概念的确定和统一愈发重要和迫切。“地震预警”法律概念应涵括其技术属性和社会属性,秉持完整规范、避免歧义的原则,将时间、空间、机理和影响等要素排列组合而成。为深入理解这一概念,本文还讨论了发布主体、预警客体、技术服务、法律责任等地震预警法律规范的基本内容。  相似文献   

地下水库调蓄能力综合评价的指标体系与模糊集方法   总被引：2，自引：0，他引：2       下载免费PDF全文

郑德凤  王本德  年廷凯 《水科学进展》2005,16(5):720-725

从维护生态平衡与水资源可持续开发利用的角度定义了地下水库的调蓄能力,提出地下水库调蓄能力综合评价的指标体系。并在模糊模式识别理论与模型的基础上,去除指标间的相关性,建立一种适合于对多指标体系的地下水库调蓄能力进行综合评价的多层模糊模式识别交叉迭代模型。实例应用表明,该模型具有能同时考虑定性与定量指标,又能将迭代结果与决策者经验知识相结合来确定多指标权重的优点,便于推广应用。  相似文献   

奎屯河流域冰雹天气发生规律及防御措施   总被引：2，自引：0，他引：2  

宋玉玲  冯永新 《沙漠与绿洲气象(新疆气象)》2005,28(4):23-24

根据1989～2003年奎屯河流域中小尺度强对流冰雹天气资料,统计分析了其发生规律,给出了雹暴发生源地、移动路径和基本类型,探讨了地形和下垫面的作用,并提出了综合防御措施.  相似文献   

对“十五”期间防震减灾社会需求的分析     

王云基 《四川地震》2002,(2):1-7

分析了“十五”期间社会，政府对防震减灾工作的需求，联系工作实际进行了全面论述和分析，并对推进防震减灾提出了一些有益的政策建议。  相似文献   

VS型垂直摆倾斜仪的安装调试与标定要点   总被引：1，自引：0，他引：1  

秦家林  佟国刚 《东北地震研究》2002,18(3):20-21

本文总结了铁岭地震台安装，调试与标定VS型垂直倾仪的经验。  相似文献   

岷江干旱河谷三种主要灌丛地上生物量的分布规律   总被引：24，自引：1，他引：24  

刘国华  张洁瑜  张育新  周建云  关文彬  马克明  傅伯杰 《山地学报》2003,21(1):24-32

灌丛是岷江干旱河谷主要的植被类型之一,也是该地区相对稳定的生态系统类型。在岷江干旱河谷的水土保持中发挥着重要的作用。本文通过野外样地调查和实验,研究了岷江干旱河谷分布最为广泛的莸灌丛、小花滇紫草灌丛和川甘亚菊灌丛3种灌丛类型的地上生物量,并探讨了其分布规律和影响因素。结果表明:(1)在3种灌丛类型中,川甘亚菊灌丛的平均地上生物量最大,达4819 8kg·hm-2,其次是莸灌丛,为1652 9kg·hm-2,而滇紫草灌丛的平均地上生物量最小,仅为1407 2kg·hm-2;(2)在同一灌丛类型中,不同样地的灌丛地上生物量存在着差异,其中莸灌丛的地上生物量的变化幅度最大,为304 2～5804 7kg·hm-2;滇紫草灌丛地上生物量的变化幅度为241 1～3889 2kg·hm-2;川甘亚菊灌丛地上生物量的变化幅度相对较小,为2089 8～6457 5kg·hm-2;说明川甘亚菊灌丛的群落结构相对稳定。(3)莸灌丛的地上生物量随海拔的上升而减少,而小花滇紫草灌丛和川甘亚菊灌丛的地上生物量则随海拔梯度的升高而增加,但三者都呈现出较好的相关性。(4)在3种灌丛类型中,莸灌丛的土壤水分条件相对较好,其次为小花滇紫草灌丛,川甘亚菊灌丛的土壤水分条件最差。3种灌丛中,小花滇紫草灌丛和川甘亚菊灌丛的地上生物量受土壤水分条件的影响较大,表现为随着土壤水  相似文献   

Salt tolerance of Microcoleus vaginatus Gom., a cyanobacterium isolated from desert algal crust, was enhanced by exogenous carbohydrates     

Lanzhou Chen  Dunhai Li  Yongding Liu 《Journal of Arid Environments》2003,55(4):381

Microcoleus vaginatus isolated from a desert algal crust of Shapotou was cultured in BG-11 medium containing 0.2 mol l⁻¹ NaCl or 0.2 mol l⁻¹ NaCl plus 100 mg l⁻¹ sucrose, extracellular polymeric substances (EPS) or hot water-soluble polysaccharides (HWP), respectively. Photosynthetic oxygen evolution rates, photosystem II activity (Fv/Fm) and dark respiration of NaCl-stressed cells were enhanced significantly by the added sucrose or EPS under salt stress conditions (0.2 mol l⁻¹ NaCl). Compared with cells treated with salt alone, sodium contents in cells reduced significantly; the content of cellular total carbohydrate did not change, and intracellular sucrose, water-soluble sugar increased significantly following the addition of exogenous carbohydrates. Sucrose synthase (SS) activity of NaCl-stressed cells increased following the addition of sucrose, and sucrose phosphate synthase (SPS) activity of NaCl-stressed cells increased following the addition of exogenous sucrose, EPS or HWP compared with cells stressed with NaCl only. The results suggested that the extruded EPS might be re-absorbed by cells of M. vaginatus as carbon source, they could increase salt tolerance of M. vaginatus through the changes of carbohydrate metabolism and the selective uptake of sodium ions.  相似文献   

Pressures on an intensive irrigated cash-crop system in coastal Ghana     

Gina Porter  Einir Young  Akrofi Dzietror 《Geoforum》1997,28(3-4)

This paper outlines the results of recent interdisciplinary fieldwork in Anloga on Keta Lagoon, Ghana. Vegetable production has been undertaken at Anloga since the nineteenth century and is now highly intensive and carefully regulated. Farmers produce shallots and other crops utilising irrigation water, mostly from wells which tap a shallow fresh-water perched aquifer. However, farmers have been expanding their cultivation activities from the lagoon-side, encouraged by a World Bank supported programme which provides for well-sinking and some electric pumps. The project has environmental and socio-economic implications which give cause for concern. The research employs field investigation to explore both the physical and political economy context and implications of recent change and considers the opportunities for community-based water and crop regulation.  相似文献   

Streeter-Phelps模型参数估计的遗传算法   总被引：3，自引：0，他引：3       下载免费PDF全文

王黎  马光文 《水科学进展》1997,8(1):32-36

提出Streeter-Phelps模型参数估计的新方法--遗传算法(Genetic Algorithm),它不同于常规参数估计方法,其优点在于,从多个初始点开始寻优,并采用交迭和变异运算避免过早地收敛到局部最优解,可获得全局最优解,且不受初始值影响.该方法不必求导计算,编程简单快捷.给出了实例计算及与其他方法相比较的结果.  相似文献