华北地区气候变化及其对水资源的影响   总被引：10，自引：0，他引：10  

Gao Ge  Huang Chaoying 《大气科学进展》2001,18(5):718-732

根据华北地区近50年的气候、水资源、旱涝灾害面积等资料，对该地区的气候特点及变化趋势、水资源的变化规律与气候变化的相互关系、极端气候事件对水资源的影响及气候变化对农业旱涝的影响进行了分析，并在气候模式预测结果的基础上，简要分析了华北地区未来气候变化对水资源的可能影响，提出了相应的对策建议，从而为实现水资源可持续利用提供科学依据。  相似文献   

城市边缘区景观变化与人为影响的空间分异研究   总被引：38，自引：5，他引：38  

陈浮  葛小平  陈刚  彭补拙 《地理科学》2001,21(3):210-216

利用1988、1993、1998年的遥感影像，应用最大似然法和概率松弛法对马山景观组分进行了测量，在此基础上，对分类结果进行比较求得研究区景观变化的转移短也阵，分析了人为改造活动与景观组分之间的对应关系和空间变化过程，马山区已经从1988年的传统农业景观转化为1998年的城郊混合景观，人口、经济、产业结构均发生了巨大变化，借助人为影响指数，利用网格采样和地统计学分析，研究了马山1988-1998年间景观的人为开发利用活动，揭示人为活动的空间变异强度分布及景观转变过程的社会驱动力。  相似文献   

The Sudbury Structure (Ontario,Canada): a tectonically deformed multi-ring impact basin     

A. Deutsch  R. A. F. Grieve  M. Avermann  L. Bischoff  P. Brockmeyer  D. Buhl  R. Lakomy  V. Müller-Mohr  M. Ostermann  D. Stöffler 《International Journal of Earth Sciences》1995,84(4):697-709

The occurrence of shock metamorphic features substantiates an impact origin for the 1.85 Ga old Sudbury Structure, but this has not been universally accepted. Recent improvements in knowledge of large-scale impact processes, combined with new petrographic, geochemical, geophysical (LITHOPROBE) and structural data, allow the Sudbury Structure to be interpreted as a multi-ring impact structure. The structure consists of the following lithologies: Sudbury Breccia —dike breccias occurring up to 80 km from the Sudbury Igneous Complex (SIC); Footwall rocks and Footwall Breccia — brecciated, shocked crater floor materials, in part thermally metamorphosed by the overlying SIC; Sublayer and Offset Dikes, Main Mass of the SIC and Basal Member of the Onaping Formation (OF) — geochemically heterogeneous coherent impact melt complex ranging from inclusion-rich basal unit through a dominantly inclusion-free to a capping inclusion-rich impact melt rock; Grey Member of OF — melt-rich impact breccia (suevite); Green Member of OF — thin layer of fall back ejecta; Black Member of OF — reworked and redeposited breccia material; Onwatin and Chelmsford Formations — post-impact sediments. Observational and analytical data support an integrated step-by-step impact model for the genesis of these units. Analysis of the present spatial distribution of various impact-related lithologies and shock metamorphic effects result in an estimated original rim-to-rim diameter of the final crater of 200 or even 280 km for the Sudbury Structure, prior to tectonic thrusting and deformation during the Penokean orogeny.  相似文献   

海洋环境沉积物输运研究进展   总被引：6，自引：0，他引：6  

蒋东辉  高抒 《地球科学进展》2003,18(1):100-108

海洋环境中沉积物的输运涉及复杂的过程和机制。20世纪后半叶发展起来的悬沙输运数学模型已经成为海洋沉积动力学的一个有力的研究工具。悬沙输运数学模型的有效运行需要正确的数值解法和模型中所含参数的确定,包括悬沙沉降速度、扩散系数、底床糙度和切应力,以及底边界上的沉降-再悬浮通量。由于复杂的水动力条件、屏蔽效应以及海底生物扰动等因素的作用,海洋环境推移质输运的经验、半经验公式具有一定的局限性。因此,充分考虑以上各种因素是正确预测海洋环境中推移质输运的关键。海洋环境沉积物输运理论的进一步发展需要着重进行各种过程和机制的研究,而这项工作依赖于高精度、高分辨率现场观测仪器的发展和更先进的颗粒态物质运动理论的建立。  相似文献   

Validation of a model for impact breakage incorporating particle size effect     

Fengnian Shi  Toni Kojovic 《International Journal of Mineral Processing》2007

Investigation of a breakage probability model published by Vogel and Peukert [Vogel, L. and Peukert, W., 2004. Determination of material properties relevant to grinding by practicable labscale milling tests. Int. J. Miner. Process., 74S, 329–338.] has led to a modification of their model to describe the degree of impact breakage, t₁₀. The modified model takes a form similar to the JKMRC prior art breakage model, but with particle size and breakage properties incorporated explicitly in the model.  相似文献   

Using magnetic susceptibility to find Precambrian impact ejecta: A proposal     

Dallas Abbott  Rajat Mazumder 《Gondwana Research》2007,12(4):571-575

Layers with high magnetic susceptibility contain heavy minerals that are the most likely to preserve signatures of impact in metamorphosed Precambrian rocks. The following impact indicators are resistant to alteration and metamorphism and are likely to be found in heavy mineral layers: impact diamond, SiC, shocked zircon, high-pressure TiO₂ phases, reidite, and high-pressure chromite. Coesite and stishovite could also be present but are not likely to be preserved in rocks metamorphosed above the greenschist facies. Looking for layers with high magnetic susceptibility will also identify layers that might contain concentrations of zircon for dating.  相似文献   

对2005年盛夏十堰市一次连续强降水天气过程的分析     

朱明  姚道强  徐远波  谭永秀  董如根  王立华 《湖北气象》2007,26(3):236-240

使用2005年8月14～23日各层(850、700、500 hPa等)天气图资料,以及有关物理量场资料、雷达回波资料和卫星云图资料,采取天气诊断分析方法,对2005年盛夏十堰市一次连续强降水天气过程进行了分析。结果表明:此次过程是在西太平洋副热带高压、"珊瑚"台风、东南急流、南支低槽、中低层低涡切变线等系统共同影响下形成的;贝加尔湖低槽持续分裂冷空气与副热带高压边缘暖湿气流对峙是该过程能够维持的基本条件;短带状强回波与新生的强对流窄回波带相叠加并维持较长时间,中-β尺度云团在本地发展为中-α尺度云团且受地形作用维持近5 h,使得灾情更趋严重。  相似文献   

城市小区规划对大气环境影响的评估研究   总被引：5，自引：3，他引：5  

苗世光  王晓云  蒋维楣  奚文  季崇萍  刘凤辉  陈鲜艳 《高原气象》2007,26(1):92-97

不同城市小区规划方案对大气环境的影响不同。本文在已建城市小区尺度气象和污染扩散模式的基础上,针对城市小区规划对气象及大气环境的影响,提出了一套以人为本的客观、科学、可操作的影响评估指标及方法,并以北京市某小区两种规划方案为例,具体评估了它们对气象及大气环境的不同影响。结果表明:由于第二种规划方案在小区中部有一条较宽的东西向道路,并且道路中绿化较多,这条道路是气流东西向流动的重要通道,道路附近风速较大、气温较低、污染较轻,并且对整个小区的气象和大气环境都有改善。由此可见,基于城市小区尺度模式,对城市小区规划对大气环境的影响进行评估是必要和可行的。本文提出的人体舒适度、行人舒适度、地面污染物浓度、最高建筑高度以下污染物浓度、建筑物表面污染物浓度及扩散能力等六项评估指标,并分别给予该6种指标的权重系数为0.2,0.1,0.1,0.1,0.1及0.4,然后再加权平均的评估方法是合理可行的。  相似文献   

Numerical predictions of water–air wave slam using incompressible–compressible smoothed particle hydrodynamics     

《Applied Ocean Research》2015

The high-speed impact between a body and water is an important practical problem, whether due to wave impact on a structural deck or wall, or due to a moving body such as a ship or aircraft hitting water. The very high pressures exerted are difficult to predict and the role of air may be significant. In this paper, numerical simulations are undertaken to investigate the impact of a rigid horizontal plate onto a wave crest and, in the limit, onto a flat water surface. A two-phase incompressible–compressible smoothed particle hydrodynamics (SPH) method for water and air, respectively, is applied where the water phase imposes kinematics on the air phase at the air–water interface and the air phase imposes pressures on the water at the interface. Results are compared with experimental measurements undertaken using a drop rig positioned over a wave flume so that a horizontal plate impacts the water surface in free flight. Numerical predictions of impact pressure are quite accurate; air is shown to have a significant cushioning effect for impact on to flat water and this reduces for waves as the ratio of wave height to wavelength increases.  相似文献   

Ultimate Load Capacity of Offshore Pipeline with Arbitrary Shape Corrosion Defects     

陈严飞  张娟  张宏  刘啸奔  李昕  周晶  曹静 《海洋工程》2015,29(2):241-252

A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anisotropic material characteristics in longitudinal and circumferential direction of pipeline are also considered in the proposed equations. Simplified numerical method is used to solve the generalized expressions. The comparisons of numerical results based generalized solutions and full-scale experimental results are carried out. The predicted results agree reasonably well with the experiment results. Meanwhile, the effects of corrosion shapes and locations on the ultimate load capacity are studied.  相似文献