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impact of land-use change on hydrological processes in the Maying River basin, China

Science China Earth Sciences 2006年第10期49卷 1098-1110页

作者： WANG Genxu1,3, ZHANG Yu2, LIU Guimin2 & CHEN Lin3 1. Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China 2. Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China 3. Resource and Environment School, Lanzhou University, Lanzhou 730000, China Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu China Resource and Environment School Lanzhou University Lanzhou China Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Lanzhou China

Since the 1960s, dramatic changes have taken place in land-use patterns characterized by the persistent expansion of cultivated land and a continuous decrease in natural woodland and grassland in the arid inland river basins of China. It is very important to assess the effects of such land-use changes on the hydrological processes so vital for water resource management and sustainable development on the catchment scale. The Maying River catchment, a typical arid inland watershed located in the middle of the Hexi Corridor in northwest China, was the site chosen to investigate the hydrological responses to land-use changes. The annual runoff, base flow, maximum peak flow, and typical seasonal runoff in both spring and autumn flood periods were selected as the variables in the hydrological processes. Statistical-trend analysis and curvilinear regression were utilized to detect the trends in hydrological variables while eliminating the climatic influence. The relationship between cultivated land-use and hydrological variables was analyzed based on four periods of land-use variation data collected since 1965. A runoff model was established composed of two factors, i.e., cultivated land use and precipitation. The impact of land use changes, especially in the large ar- eas of upstream woodland and grassland turned into cultivated lands since 1967, has resulted in a mean annual runoff decrease of 28.12%, a base flow decline of 35.32%, a drop in the maximum peak discharge of 35.77%, and mean discharge decreases in spring and autumn of 36.05% and 24.87% respectively, of which the contribution of cultivated land expansion to the influence of annual runoff amounts to 77%-80%, with the contribution to the influence of spring discharge being 73%-81%, and that to the influence of base flow reaching 62%-65%. Thus, a rational regulation policy of land use patterns is vitally important to the sustainable use of water resources and the proper development of the entire catchment.

关键词： land-use change, arid inland river catchment, hydrological process, impact, Maying River.

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The numerical method for three-dimensional impact with friction of multi-rigid-body system

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Science China(Physics,Mechanics & Astronomy) 2006年第1期49卷 102-118页

作者： ZHAO Zhen1,2, LIU Caishan2 & CHEN Bin2 1. Beijing Institute of Graphic Communication, Beijing 102600, China 2. Department of Mechanics & Engineering Science, Peking University, Beijing 100871, China Beijing Institute of Graphic Communication Beijing China Department of Mechanics & Engineering Science Peking University Beijing China

The differential equations for planar impacts reduce to an algebraic form, and can be easily solved. For three dimensional impacts with friction, there is no closed-form solution, and numerical integration is required due to the swerve behavior of tangential impulse during collisions. The dynamic governing equations in the impact process are built up in impulse space based on the Lagrangian equation in this paper. The coefficient of restitution defined by Poisson is used as the condition of impact termination. A valid nu- merical method for solving three-dimensional frictional impact of multi-rigid body system is established. The singular cases of tangential movement in sticking point are especially noticed and analyzed. Several examples are present to reveal the different kinds of tan- gential movement modes varied with the normal impulse during collision.

关键词： multi-rigid body, impact, friction.

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Stress waves propagation in solids under high-speed liquid impact

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Science China(Physics,Mechanics & Astronomy) 2004年第6期47卷 752-766页

作者： J.E.Field Cavendish Laboratory Cambridge UniversityMadingly RoadCambridge CB3 0HEUK

An experiment of impact between 450 m/s water jets and polymethylme- thacrylate (PMMA) materials with complex surface geometry was conducted. The testing surfaces were a corner, step change, surface-breaking notch, inclined surface, etc. Stress waves propagation in the solid such as reflection, interference and diffraction was observed using polarized optics and an Imacon high speed camera (operating at both of 106 and 5×105 framing rates per second, fps). A damage test by the impact of the side jetting of an 850 m/s water jet was also carried out. It was found that stress waves propagation in solids depends not only on the surface geometry but also on the contact situation between liquid and solid. It was shown that the side jetting has sufficient damage potential although its head may consist of finer droplets. The results of this paper are useful to further analyze the dynamic stress state of solids under high-speed liquid impact.

关键词： high-speed liquid/solid impact, stress waves, mechanical property of solid, high-speed photography.

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Strategies for farmers and policy makers to control nitro-gen losses whilst maintaining crop production

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Science China(Life Sciences) 2005年第Z2期48卷 710-719页

作者： Keith W.T.Goulding Agriculture and the Environment Division Rothamsted Research HarpendenHertfordshireAL5 2JQUK

The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeochemical N cycle. However, intensive agricultural production, industry and vehicle use have more tem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems.

关键词： Nitrogen cycle, farm systems, best management, environmental impact, productivity.

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Tensile Properties of Fiber Materials under Different Strain Rates

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Journal of Donghua University(English Edition) 2002年第2期19卷 54-58页

作者：熊杰顾伯洪王善元 College of Materials and Textiles Zhejiang Institute Science and Technology Hangzhou 310033 China College of Textiles Dong Hua University Shanghai 200051

The quasi-static and dynamic tensile tests of aramid and high strength PVA fiber bundles are carried out under a wider range of strain rate by use of MTS (Materials Testing System) and bar-bar tensile impact apparatus. The influences of strain rate on mechanical properties of aramid and high strength polyvinyl alcohol fibers are studied. Micro failure mechanisms of fibers at different strain rates are examined by means of SEM.

关键词： aramid fiber, polyvinyl alcohol fiber, tensile impact, high strain rate

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脆性单颗粒之动态损伤和破碎

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岩石力学与工程学报 2003年第Z1期22卷 2138-2144页

作者：周锦添武生智黄凯珠

Breakage, comminution, crushing and fragmentation of brittle solids under dynamic impacts are an important applied mechanics and rock mechanics problem. In civil engineering applications, impact-induced-fragmentation relates to crushing of rock mass during mining process, tunneling, and aggregate production. The main objective of this paper is to outline some of our recent experimental, analytical and numerical efforts in studying the dynamic fragmentation process in brittle particle. First, an analytical solution of a solid sphere compressed dynamically between two rigid flat platens is derived analytically. Secondly, a sequence of double impact tests on spheres were conducted using an impactor Dynatup 8250 at HKUST, with both impact velocity and contact force at the impactor measured accurately. Finally, a newly developed computer program, DIFAR, is used to investigate the mechanism of dynamic fragmentation. The paper will summarize and discuss briefly all three aspects of our comprehensive approach.

关键词： damage mechanics, fragmentation, dynamic impact, brittle particles

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