黄河河口拦门沙发育动态   总被引：5，自引：0，他引：5  

叶青超 《地理研究》1996,15(1):58-65

河口拦门沙发育主要取决于河口边界、径流、海洋动力、海面增减水以及河口疏浚等环境要素的相互作用。拦门沙在口门附近呈扇状分布隆起的沙坝,沉积结构为紧密的“铁板沙”.1984-1987年拦门沙自然发育时期,拦门沙长度为7km以上,年平均推进速度1.30km,沙顶高程为-0.1-0.5m;1988-1992年拦门沙人为疏浚发育时期,通过河口疏浚后,拦门沙增长有所减缓,其长度减为4-6km,年平均推进速度降为1.26km,沙顶平均高程下降到-0.7m,相应地减轻了河口地区的防洪压力。  相似文献   

席状岩浆房中的岩浆冷却及动力稳定性   总被引：4，自引：0，他引：4  

张正阶  宋谢炎 《岩石学报》1996,12(1):1-16

关于岩浆房中岩浆的结晶分异方式一直存在着争议，其基本矛盾在于对岩浆冷却历史及热不稳定性可能引起的对流形式的理解各不相同。本文在充分考虑席状岩浆房的基本物理特征的基础上，建立了稳定岩浆体系的动态冷却模型，并以攀枝花层状岩体为例，计算了相应的温度场、密度场及粘度场。同时，提出了一种基于能量守恒的、对热不稳定性进行分析的新方法。计算了热不稳定性可能引起的对流强度、对流区域及对流时间，并深入讨论了在一定的热不稳定状态下，不同的岩浆屈服强度对对流特征参量的影响。结果表明，在该岩体的整个固化过程中，如果曾发生过自发对流，其对流也是极微弱而短暂的，不会影响中下部岩浆房中岩浆的固化和结晶。这一结论与对该岩体的实际观察相符。  相似文献   

MODIS数据在乌鲁木齐地区植被景观动态监测中的应用   总被引：2，自引：0，他引：2  

李聪肖继东  宫恒瑞石玉 冯志敏 《沙漠与绿洲气象(新疆气象)》2005,28(3):27-29

根据EOS／MODIS卫星时次高覆盖面广的特征，选取从4．10月的MODIS晴空资料，对整个乌鲁木齐地区植被景观进行动态监测，利用植被指数最大合成法制作了每月植被指数专题图。为了能够结合物候更好地分析乌鲁木齐地区植被随季节变化趋势以及不同时期植被生长状况，我们还制作了植被景观专题图及其变化评价图。评价图的优势在于能直观地反映植被变化的趋势，并能将变化的程度数字化，还可以根据不同的评价图叠加DEM做相应的分析。为乌鲁木齐地区植被变化研究提供有效的依据。  相似文献   

Seismic earth pressures on rigid and flexible retaining walls     

P.N. Psarropoulos  G. Klonaris  G. Gazetas 《Soil Dynamics and Earthquake Engineering》2005,25(7-10):795-809

While limiting-equilibrium Mononobe–Okabe type solutions are still widely used in designing rigid gravity and flexible cantilever retaining walls against earthquakes, elasticity-based solutions have been given a new impetus following the analytical work of Veletsos and Younan [23]. The present paper develops a more general finite-element method of solution, the results of which are shown to be in agreement with the available analytical results for the distribution of dynamic earth pressures on rigid and flexible walls. The method is then employed to further investigate parametrically the effects of flexural wall rigidity and the rocking base compliance. Both homogeneous and inhomogeneous retained soil is considered, while a second soil layer is introduced as the foundation of the retaining system. The results confirm the approximate convergence between Mononobe–Okabe and elasticity-based solutions for structurally or rotationally flexible walls. At the same time they show the beneficial effect of soil inhomogeneity and that wave propagation in the underlying foundation layer may have an effect that cannot be simply accounted for with an appropriate rocking spring at the base.  相似文献   

Effects of inertial and kinematic interaction on seismic behavior of pile with embedded foundation   总被引：4，自引：0，他引：4  

Kohji Tokimatsu  Hiroko Suzuki  Masayoshi Sato 《Soil Dynamics and Earthquake Engineering》2005,25(7-10):753-762

Effects of inertial and kinematic forces on pile stresses are studied based on large shaking table tests on pile-structure models with a foundation embedded in dry and liquefiable sand deposits. The test results show that, if the natural period of the superstructure, T_b, is less than that of the ground, T_g, the ground displacement tends to be in phase with the inertial force from the superstructure, increasing the shear force transmitted to the pile. In contrast, if T_b is greater than T_g, the ground displacement tends to be out of phase with the inertial force, restraining the pile stress from increasing. With the effects of earth pressures on the embedded foundation and pile incorporated in, pseudo-static analysis is conducted to estimate maximum moment distribution in pile. It is assumed that the maximum moment is equal to the sum of the two stresses caused by the inertial and kinematic effects if T_b<T_g or the square root of the sum of the squares of the two if T_b>T_g. The estimated pile stresses are in good agreement with the observed ones regardless of the occurrence of soil liquefaction.  相似文献   

The role of the seismic trigger in the Calitri landslide (Italy): historical reconstruction and dynamic analysis   总被引：2，自引：0，他引：2  

Salvatore Martino  Gabriele Scarascia Mugnozza 《Soil Dynamics and Earthquake Engineering》2005,25(12):933-950

The study covered by this paper was focused on the historical case of the Calitri landslide, which was repeatedly reactivated by earthquakes, as reported since 1694. The town of Calitri (Southern Italy) is located on a ridge whose southern slope, from its top to the Ofanto river valley floor, has been historically affected by major landsliding. The last record of recurrence of the Calitri landslide leads back to the 1980 Irpinia earthquake, which caused significant damage to the town and had pervasive and visible ground effects. Based on a detailed historical reconstruction of landsliding and seismicity at Calitri, the study analysed the current static and dynamic stability of the landsliding slope by means of a finite-difference numerical analysis, taking into account the various factors of landslide initiation and kinematics. The results of the numerical analysis: (i) were consistent with the roto-translational mechanism observed upon the latest reactivation of the landslide; (ii) demonstrated that excess pore pressure redistribution caused a lag between the seismic trigger and the initiation of landsliding; and (iii) showed the impact of seismic input frequency on propagation and depth of slope instability.  相似文献   

Combining European Earth Observation products with Dynamic Global Vegetation Models for estimating Essential Biodiversity Variables     

Mateus Dantas de Paula  Marta Gómez Giménez  Aidin Niamir  Martin Thurner  Thomas Hickler 《International Journal of Digital Earth》2020,13(2):262-277

ABSTRACT

Global, fast and accessible monitoring of biodiversity is one of the main pillars of the efforts undertaken in order to revert it loss. The Group on Earth Observations Biodiversity Observation Network (GEO-BON) provided an expert-based definition of the biological properties that should be monitored, the Essential Biodiversity Variables (EBVs). Initiatives to provide indicators for EBVs rely on global, freely available remote sensing (RS) products in combination with empirical models and field data, and are invaluable for decision making. In this study, we provide alternatives for the expansion and improvement of the EBV indicators, by suggesting current and future data from the European Space Agencýs COPERNICUS and explore the potential of RS-integrated Dynamic Global Vegetation Models (DGVMs) for the estimation of EBVs. Our review found that mainly due to the inclusion of the Sentinel constellation, Copernicus products have similar or superior potential for EBV indicator estimation in relation to their NASA counterparts. DGVMs simulate the ecosystem level EBVs (ecosystem function and structure), and when integrated with remote sensing data have great potential to not only offer improved estimation of current states but to provide projection of ecosystem impacts. We suggest that focus on producing EBV relevant outputs should be a priority within the research community, to support biodiversity preservation efforts.  相似文献   

论板块运动的驱动力          下载免费PDF全文

谢鸣一  谢鸣谦 《地质科学》1987,(3):209-220

本文从动力学的角度讨论了板块运动的驱动机理,并提出了计算板块扩张速度的公式,然后求出了不同类型板块的扩张速度。用此公式所计算出的板块扩张速度与实际观测速度很符合。  相似文献   

An aspect of indivisible land development with a reservation level of revenue     

A. A.?BatabyalEmail author  S. J.?Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(3):216-218

Recently, Batabyal and Yoo (2003) have studied aspects of indivisible and divisible land development in a dynamic and stochastic framework. In this note, we complement the analysis in this paper by examining an aspect of the indivisible land development decision when a landowner has an exogenously given reservation level of revenue. In particular, we show that the magnitude of the first record (largest offer) that exceeds the landowners reservation revenue is independent of the time at which this record is received by the landowner.  相似文献   

潜水不完整井取样保持氡值稳定的初探     

吴广琳 《山西地震》1998,(2):48-51

水氡观测作为地震活动的一种前兆观测项目,由于受地下水动力条件的影响,会出现不稳定的因素。通过对潜水不完整井氡值变化规律的研究,运用地下水动力学原理,得出潜水不完整井在达到动态平衡状态时取样,可保持氡含量的相对稳定的结论。  相似文献