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chinese Science Bulletin 1999年第13期44卷 1224-1228页

作者： xu jiongxininstitute of geography, chinese academy of sciences , Beijing 100101, china Institute of geography Chinese Academy of Sciences Beijing China

Based on data from more than 100 alluvial rivers, a systematic comparison of flow shear stress and energy expenditure has been made between sand- and gravel-bed rivers, by plotting the relationships between channel shape (i.e. channel width-depth ratio) and hydraulic indices in a two-dimensional plane. These relationships show clearly that the four channel patterns, i.e. sand-bed meandering, sand-bed braided, gravel-bed meandering and gravel-bed braided, are located in 4 different areas that can be divided by 2 straight lines.

关键词： sand-bed river gravel-bed river channel pattern channel pattern discrimination.

COMPLICATED FILL-SCOURBEHAVIORS OF THE YELLOW RIVER ANDTHE CHANNEL-FORMING PROCESSES

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International Journal of Sediment Research 1999年第2期14卷 259-266页

作者： xu JiongXin (1 Institute of geography, chinese {3. of {3., Beijing 100101, china)

Based on the data from 159 events at the Tongguan station on the Yellow River, we have found the rule to describe the complicated relationship between the fill-scour features and the event-maximum suspended concentration (C_max). The depth of scour is large if the C_max is low. and is small if C_max is high. However, if C_max increases to the ranges of hyperconcentrated flows, scour occurs again. Controlled by the foregoing complicated fill-scour behaviors, the channel adjustment of the Yellow River is also complicated. When the suspended concentration is low, channel scour occurs, and thereby the channel shape tends to be narrower and deeper, and the thalweg more sinuous. When the suspended concentration increases, channel fill occurs, leading to an increase in the channel width-depth ratio and a decrease in the channel sinuosity. However, when the suspended concentration further increases and exceeds a certain threshold, channel scour occurs again, and the adjustment of channel morphology turns to the opposite direction. The rules outlined in the paper for the channel adjustment of the lower Yellow River may provide a new thinking for the regulation of the channel morphology of the lower Yellow River after the closure of the Xiaolangdi Dam, through the regulation of the lower Yellow River’s water and sediment by choosing some specific operation modes of the reservoir Either by releasing clear water or by releasing man-made hyperconcentrated flows, the downstream channel may tend to be narrowed, deeper and more sinuous.

关键词： Channel adjustment Fill-scour behavior Hyperconcentrated flows Lower Yellow River

Modified conceptual model for predicting the tendency of alluvial channel adjustment induced by human activities

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chinese Science Bulletin 2001年第S1期46卷 51-57页

作者： xu jiongxininstitute of Geographical sciences and Natural Resources Research, {3. {3. of sciences, Beijing 100101, china (e-mail: xujxin?***) Institute of Geographical sciences and Natural Resources Research Chinese Academy of Sciences Beijing China

After a discussion about some limitations of Schumm’s conceptual model for prediction of river metamorphosis, this study introduces the channel boundary material as an independent variable, and thereby establishes a conceptual model that can be used to predict the direction of channel adjustment induced by human activities. This model has been tested by data from natural rivers and a laboratory model river, and can be used to explain the complex behavior of channel adjustment after reservoir construction.

关键词： human influence on channels channel boundary condi- tions feedback in channel system prediction of channel adjustment.

Plausible impact of global climate change on water resources in the Tarim River Basin

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Science china Earth sciences 2005年第1期48卷 65-73页

作者： CHEN Yaning & xu Zongxue Xinjiang Institute of Ecology & geography, {3. academy of {3., Urumqi 83.011, china College of Environmental {3., Beijing Normal University, Beijing 100875, china Xinjiang Institute of Ecology & geography Chinese Academy of Sciences Urumqi China College of Environmental sciences Beijing Normal University Beijing China

Combining the temperature and precipitation data from 77 climatological stations and the climatic and hydrological change data from three headstreams of the Tarim River: Hotan, Yarkant, and Aksu in the study area, the plausible association between climate change and the variability of water resources in the Tarim River Basin in recent years was investigated, the long-term trend of the hydrological time series including temperature, precipitation, and streamflow was detected, and the possible association between the El Ni(n)o/Southern Oscillation (ENSO) and these three kinds of time series was tested. The results obtained in this study show that during the past years, the temperature experienced a significant monotonic increase at the speed of 5%, nearly 1℃ rise; the precipitation showed a significant decrease in the 1970s, and a significant increase in the1980s and 1990s, the average annual precipitation was increased with the magnitude of 6.8 mm per decade. A step change occurred in both temperature and precipitation time series around 1986, which may be influenced by the global climate change. Climate change resulted in the increase of the streamflow at the headwater of the Tarim River, but the anthropogenic activities such as over-depletion of the surface water resulted in the decrease of the streamflow at the lower reaches of the Tarim River. The study result also showed that there is no significant association between the ENSO and the temperature, precipitation and streamflow.

关键词： climate change, hydrological change, temperature, precipitation, streamflow, Tarim River.

Simulation of aerodynamic performance affected by vortex generators on blunt trailing-edge airfoils

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Science china(Technological sciences) 2010年第1期53卷 1-7页

作者： YANG Ke1,2,ZHANG Lei1,3.& xu JianZhong1,2 1 Institute of Engineering Thermophysics,chinese academy of {3.,Beijing 100190,{3. 2 Key Laboratory of Wind Energy Utilization,chinese academy of {3.,Beijing 100190,{3. 3.Graduate School of chinese academy of {3.,Beijing 100190,{3. Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing China Key Laboratory of Wind Energy Utilization Chinese Academy of Sciences Beijing China Graduate School of chinese academy of sciences Beijing China

An investigation was carried out by numerical simulation on a wind turbine airfoil and a blunt trailing-edge airfoil with and without vortex generators (VGs), and the performance of the airfoils was analyzed. By the simulation of airfoil DU 91-W2-250 it was verified that the numerical method and model were credible. Based on this airfoil, a new one with a blunt trailing edge of 6% chord was blended by symmetrically adding thickness, and its characteristics curves were obtained through computing at key angles of attack. Additionally, the pressure distribution on blended airfoil was analyzed by comparing to the airfoil without blend. The interaction of streamwise vortices induced by VGs with trailing vortex or separation vortex was considered, followed by the uncovery of how VGs can suppress the boundary layer separation.

关键词： vortex generators airfoil blunt trailing-edge

SOME NONLINEAR APPROXIMATIONS FOR MATRIX-VALUED FUNCTIONS

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Journal of Computational Mathematics 2003年第6期21卷 801-814页

作者： Guo-liang xu(academy of Mathematics and System sciences, {3. academy of sciences,Beijing 100080, china) academy of Mathematics and System sciences Chinese Academy of Sciences 北京 100080

Some nonlinear approximants, i.e., exponential-sum interpolation with equal distance or at origin, (0,1)-type, (0,2)-type and (1,2)-type fraction-sum approximations, for matrix-valued functions are introduced. All these approximation problems lead to a same form system of nonlinear equations. Solving methods for the nonlinear system are discussed. Conclusions on uniqueness and convergence of the approximants for certain class of functions are given.

关键词： Matrix-valued function Nonlinear approximation Interpolation.

Relative importance of water, energy, and heterogeneity in determining regional pteridophyte and seed plant richness in china

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Journal of Systematics and Evolution 2011年第2期49卷 95-107页

作者： 1,2,3.Sheng-Bin CHEN § 1 Gao-Ming JIANG 3.Zhi-Yun OUYANG 3.Wei-Hua xu 3.Yi XIAO 1 (State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, chinese academy of {3., Beijing 100093.{3.) 2 (Graduate University of the chinese academy of {3., Beijing 100049,{3.) 3.(State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental {3., chinese academy of {3., Beijing 100085,{3.) (State Key Laboratory of Vegetation and Environmental Change Institute of Botany Chinese Academy of Sciences Beijing 100093 China) (Graduate University of the chinese academy of sciences Beijing 100049 China) (State Key Laboratory of Urban and Regional Ecology Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Beijing 100085 China)

Environmental variables, such as ambient energy, water availability, and environmental heterogeneity have been frequently proposed to account for species diversity gradients. How taxon-specific functional traits define large-scale richness gradients is a fundamental issue in understanding spatial patterns of species diversity, but has not been well documented. Using a large dataset on the regional flora from china, we examine the contrast spatial patterns and environmental determinants between pteridophytes and seed plants which differ in dispersal capacity and environmental requirements. Pteridophyte richness shows more pronounced spatial variation and stronger environmental associations than seed plant richness. Water availability generally accounts for more spatial variance in species richness of pteridophytes and seed plants than energy and heterogeneity do, especially for pteridophytes which have high dependence on moist and shady environments. Thus, pteridophyte richness is disproportionally affected by water-related variables; this in turn results in a higher proportion of pteridophytes in regional vascular plant floras (pteridophyte proportion) in wet regions. Most of the variance in seed plant richness, pteridophyte richness, and pteridophyte proportion explained by energy is included in variation that water and heterogeneity account for, indicating the redundancy of energy in the study extent. However, heterogeneity is more important for determining seed plant distributions. Pteridophyte and seed plant richness is strongly correlated, even after the environmental effects have been removed, implying functional linkages between them. Our study highlights the importance of incorporating biological traits of different taxonomic groups into the studies of macroecology and global change biology.

关键词： habitat heterogeneity pteridophytes seed plants species richness water-energy hypothesis.

Uncertainty in magnetic activity indices

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Science china(Technological sciences) 2008年第10期51卷 1659-1664页

作者： xu WenYao Institute of Geology and Geophysics, chinese academy of {3., Beijing 100029,{3. Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China

Magnetic activity indices are widely used in theoretical studies of solar-terrestrial coupling and space weather prediction. However, the indices suffer from various uncertainties, which limit their application and even mislead to incorrect conclu-sion. In this paper we analyze three most popular indices, Kp, AE and Dst. Three categories of uncertainties in magnetic indices are discussed: "data uncertainty" originating from inadequate data processing, "station uncertainty" caused by in-complete station covering, and "physical uncertainty" stemming from unclear physical mechanism. A comparison between magnetic disturbances and related indices indicate that the residual Sq will cause an uncertainty of 1―2 in K meas-urement, the uncertainty in saturated AE is as much as 50%, and the uncertainty in Dst index caused by the partial ring currents is about a half of the partial ring cur-rent.

关键词： magnetic activity indices Kp AE Dst solar-terrestrial coupling space weather

Applications of URANS on predicting unsteady turbulent separated flows

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Acta Mechanica Sinica 2009年第3期25卷 319-324页

作者： Jinglei xu Huiyang Ma Department of Physics, Graduate University of the chinese academy of {3., 100049 Beijing,{3. Department of Physics Graduate University of the Chinese Academy of Sciences Beijing China

Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3.900 is numerically investigated by using the technique of unsteady RANS （URANS）. Some typical linear and nonlinear eddy viscosity turbulence models （LEVM and NLEVM） and a quadratic explicit algebraic stress model （EASM） are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.

关键词： URANS Nonlinear eddy viscosity turbulencemodel ,Separated flows Circular cylinder

Trace element characteristics and origin of intergranular components in mantle peridotites

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chinese Science Bulletin 2000年第7期45卷 643-649页

作者： xu YigangGuangzhou Institute of Geochemistry, chinese academy of {3., Guangzhou 510640,{3. Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou China

Leaching experiment has been carried out on mantle xenoliths with different petrographic features in order to directly characterize the nature of intergranular components. ICP-MS analyses of leachates show that they are characterized by high LREE concentrations with strong depletion of Ta. The total REE contents and whether the negative Rb, Ba and Nb anomalies are present or not in intergranular components are largely dependent upon the nature of mantle metasomatism experienced by its host rock. It is proposed that intergranular components may represent residues of small volume metasomatic melts.

关键词： peridotite xenoliths intergranular components trace elements upper mantle.