检索结果-南通市图书馆

Methodology to determine regional water demand for instream flow and its application in the Yellow River Basin

Journal of Environmental Sciences 2006年第5期18卷 1031-1039页

作者： ZHANG Yuan yang zhi-feng Wang Xi-qin School of Environmental Sciences State Key Laboratory of Water Environment Simulation Beijing Normal University Beijing 100875 China Chinese Research Academy of Environmental Sciences Beijing 100012 China School of Natural Resources and Environment Renmin Universitiy of China Beijing 100872 China

In order to realistically reflect the difference between regional water demand for instream flow and river ecological water demand as well as to resolve the problem that water demand may be counted repeatedly, a concept of regional water demand for minimum instream flow have been developed. The concept was used in the process of determining river functions and calculating ecological water demand for a river. The Yellow River watershed was used to validate the calculation methodology for regional water demand. CaIculation results indicate that there are significant differences in water demands among the different regions. The regional water demand at the downstream of the Yellow River is the largest about 14.893 × 10^9 m^3/a. The regional water demand of upstream, Lanzhou-Hekou section is the smallest about -5.012 × 10^9 m^3/a. The total ecological water demand of the Yellow River Basin is 23.06 × 10^9 m^3/a, about the 39% of surface water resources of the water resources should not exceed 61% in the Yellow River Basin. Yellow River Basin. That means the maximum available surface The regional river ecological water demands at the Lower Section of the Yellow River and Longyangxia-Lanzhou Section exceed the surface water resources produced in its region and need to be supplemented from other regions through the water rational planning of watershed water resources. These results provides technical basis for rational plan of water resources of the Yellow River Basin.

关键词： regional water demand instream flow environmental flow methodology the Yellow River Basin

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Prediction of the concentration of chlorophyll-α for Liuhai urban lakes in Beijing City

引用

Journal of Environmental Sciences 2006年第4期18卷 827-831页

作者： ZENG Yong yang zhi-feng LIU Jing-ling State Key Laboratory of Water Environment Simulation School of-Environmental Beijing Normal University Beijing 100875 China Key Laboratory for Water and Sediment Sciences of Ministry of Education School of Environment Beijing Normal University Beijing 100875 China

The weekly water quality monitor data of Liuhai lakes between April 2003 and November 2004 in Beijing City were used as an example to build an artificial neural networks （ANN） model and a multi-varieties regression model respectively for predicting the fresh water algae bloom. The different predicted abilities of the two methods in Liuhai lakes were compared. A principle analysis method was first used to select the input variables of the models to avoid the phenomenon of collinearity in the data. The results showed that the input variables for the artificial neural networks were T, TP, transparency（SD）, DO, chlorophyll-a （Chl-a）,pH and the output variable was Chl-a. A three layer Levenberg-Marguardt feed forward leaming algorithm in ANN was used to model the eutrophication process of Liuhai lakes. 20 nodes in hidden layer and 1 node of output for the ANN model had been optimized by trial and error method. A sensitivity analysis of the input variables was performed to evaluate their relative significance in determining the predicted values. The correlation coefficient between predicted value and observed value in all data and in test data were 0.717 and 0.816 respectively in the artificial neural networks. The stepwise regression method was used to simulate the linear relation between Chl-a and temperature, of which the correlation coefficient was 0.213. By comparing the results of the two models, it was found that neural network models were able to simulate non-linear behavior in the water eutrophication process of Liuhai lakes reasonably and could successfully estimate some extreme values from calibration and test data sets.

关键词： artificial neural networks eutrophication multi-varieties regression forecast Liuhai lakes Beijing City

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Estimation of the radionuclide distribution in sediment in coast area

引用

Journal of Environmental Sciences 2001年第4期13卷 398-400页

作者： SHEN Zhen-yao yang zhi-feng LI Wei-juan NI Shi-wei YAO Lang-gen CAI Yuan Institute of Environmental Science Beijing Normal UniversityState Key Joint Laboratory of Environmental Simulation and Pollution ControlBeijing 100875China China Institute for Radiation Protection Key Laboratory of Nuclear Radiation Environmental SimulationTaiyuan 030006China

The study of the radionuelide distribution in sediment is a very important aspect in environmental impact of the low level radioactive liquid waste (LLW) from coastal nuclear facilities or nuclear power plant. Even now we do not know much about it. In this paper, a simple and useful method is put forward and it is used to estimate the nuclide distribution in sediment. The result showed that the LLW from nuclear facility or nuclear power plant will do a little harm to the sediment nearby. But the harm is not very serious. Much works have to be done before full understanding of the situation.

关键词： radionuclide coast area deposit characteristic sediment

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

NuMED CHEATHAM-PLATINUM STENT AND BALLOON IN BALLOON DELIVERY CATHETER FOR TREATMENT OF NATIVE COARCTATION OF THE AORTA

引用

Chinese Medical Sciences Journal 2006年第1期21卷 65-67页

作者： Guang-yi Wang Bo yang zhi-feng Wang Jun Guo Lu-yue Gai Guang zhi Department of Cardiology General Hospital of People＇s Liberation Army Beijing 100853

COARCTATION of the aorta (CoA) is a congenital heart defect involving a narrowing of the *** narrowed segment called coarctation is most likely to happen in the segment just after the aortic *** narrowing can be removed by surgery or sometimes by a nonsurgical balloon ***, aortic coarctation may recur even after successful surgery or balloon ***, coarctation can now be treated with nonsurgical balloon dilation associated with implanting a stent using cardiac *** we reported our experience in a 19-year-old boy with CoA who underwent successful covered Cheatham-Platinum (CP) stent implantation for the coarctation.

关键词： covered stent coarctation of the aorta catheter intervention

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

T-CELL RESPONSE OF ADVANCED AIDS PATIENTS AFTER HIGHLY ACTIVE ANTIRETROVIRAL THERAPY

引用

Chinese Medical Sciences Journal 2005年第4期20卷 223-225,页

作者： Ai-xia Wang Tai-sheng Li Yun-zhen Cao yang Han zhi-feng Qiu Jing Xie Department of Medicine Infectious Diseases Section Peking Union Medical College Hospital Chiness Academy of Medical Sciences ＆ Peking Union Medical College Beijing 100730

Objective To investigate the response on late stage Chinese AIDS patients after highly active antiretroviral therapy （HAART）. Methods From October 2002 to March 2004, 20 cases of late stage Chinese AIDS patients were selected to participate in this opened and randomised study, we purposely chose those with CD4＋ T cell counts 〈 100/mm^3. All of them had one or two opportunistic infections and none had been treated with anti-HIV drugs. All patients were tested with CD4＋（naive CD4＋ T cell defined by CD45RA＋ and CD62L＋, memory CD4＋ T cell defined by CD45RA-）, CD8＋ T cell, plasma HIV viral load, and clinical manifestations on before, during, and after HAART （5 different regimes） on 1, 3, 6, 9, and 12 months. Before HAART mean CD4＋ T cell counts were 32 ± 31 （range 2-91）/mm^3, and plasma HIV viral load were 5.07 ± 0.85（range 2.04-5.70） log copies/mL. In 1 month＇s time patients treated with HAAT had mean CD4＋ and CD8＋ T cell counts increasing rapidly. After 1 month the increasing speed turned to slow down, but HIV viral load decreased predominantly within the first 3 months. The major part of increasing CD4＋ T cells were memory CD4＋ T cells, as for naive CD4＋ T cells increasing low and slow. Clinical symptoms and signs improved, and opportunistic infections reduced. The quality of life will be far much better than before. Each patient was followed for 12 months, and had finished 12 months＇ HAAT. Conclusion This is the first report in China that late stage Chinese AIDS patients after HAART could have their immune reconstitution. The regular pattern is similar to what had been reported in Western countries and also in China. So it is worth to treat late stage Chinese AIDS patients with HAAT.

关键词： acquired immune deficiency syndrome highly active antiretroviral therapy immune reconstitution

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A HIGH-ORDER-ACCURATE DIFFERENCE SCHEME WITH UNCONDITIONAL STABILITY FOR THE DIFFUSION EQUATION ON NONUNIFORM GRIDS

引用

Journal of Hydrodynamics 2001年第1期13卷 92-98页

作者： Wang Xuan, yang zhi-feng State Key Laboratory of Environment Simulation and Pollution Control, Institute of Environmental Sciences, Beijing Normal University, Beijing 100875, China[WT5”HZ] Beijing Normal Univ. Beijing 100875 China

WT5”BZ]A high-order-accurate difference scheme with unconditional stability is developed for the diffusion equation on nonuniform grids. The theoretical analysis shows that the accuracy of this scheme is between third order and fourth order, and fourth-order accuracy is achieved in the case of the same grid steps being used within the computational domain. Two numerical examples are given to demonst ate the advantages of the proposed scheme. Compared with the conventional difference scheme, more accurate numerical solution can be obtained by using the proposed scheme even with relatively larger grid sizes. It is also pointed out that the appropriate structure of the nonuniform grid can not only make the proposed scheme more practical, but lead to a solution superior to that for a uniform grid structure. [WT5”HZ]

关键词： ]finite difference scheme diffusion equation nonuniform grid high accuracy computational fluid dynamics

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A MACRO-SCALE SEMI-DISTRIBUTED HYDROLOGICAL MODEL AND APPLICATION TO THE DATONG RIVER VALLEY

引用

Journal of Hydrodynamics 2005年第6期17卷 667-676页

作者： yang zhi-feng LIU Lu-liu SHEN Zhen-yao GORDON G. Huang State Key Laboratory of Water Environmental Simulation School of Environment Beijing Normal Uni- versity Beijing 100875 China National Climate Center Beijing 100081 China Faculty of Engineering University of Regina Canada

A daily distributed hydrological model was developed using routine hydro meteorological data on the basis of the raster DEM and land cover data. Then the model was used to model daily runoff of the Datong River Valley located in the upper catchment of the Yellow River Basin. The runoff comprises surface flow, subsurface flow and ground water flow. Evapotranspiration comprises canopy evaporation, snow sublimation and soil evapotranspiration. The infiltration to the soil was estimated with improved Green-Ampt model, and the potential evapotranspiration is estimated with Morton CRAE method, which only needs the routine meteorological data. Simulation results and the comparison with semi distributed SLURP hydrological model show that the structure of the model presented herein is reasonable.

关键词： hydrological model Yellow River GIS runoff

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A HIGH-ORDER FINITE DIFFERENCE METHOD FOR UNSTEADY CONVECTION-DIFFUSION PROBLEMS WITH SOURCE TERM

引用

Journal of Hydrodynamics 1999年第2期11卷 97-102页

作者： yang zhi-feng Wang Xuan(State Key Laboratory of Environment Simulation and Pollution Control, Institute of Environmental Sciences, Beijing Normal University, Beijing 100875, P. R. China.) Beijing Normal Univ Beijing China

The convection and diffusion are the basic processes in fluid flow and heat& mass transfer. The upwind and evolution functions for the convection term are introduced to give a comprehensive transformation to one-dimensional unsteady convection-diffusion equation involving source term. The corresponding compact fourth-order finite difference methed is developed. With the trans formation, the authors overcome the difficultyin dealing with the convection term, and the high-order expression for the convection-diffusion term can be conveniently obtained. The proposed difference scheme with thefourth-order accuracy and unconditional stability can fully reflect the upwind and evolutioneffects of the convection. The calculated results show that the errors of the referencescheme are 600 or 6000 times those of the proposed scheme for the same computationalgrid. With the one time decrease of the space grid, the errors of the proposed scheme andthe reference scheme reduce about 20 times and 2 times respectively. It is evident that theaccuracy of the proposed scheme is remarkably higher than that of the reference scheme.

关键词： convection-diffusion compact difference method comprehensive transformation unsteady computational fluid dynamics

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A PERTURBATIONAL FOURTH-ORDER UPWIND FINITE DIFFERENCE SCHEME FOR THE CONVECTION-DIFFUSION EQUATION

引用

Journal of Hydrodynamics 1993年第1期5卷 82-97页

作者： Chen Guo-qian yang zhi-feng Department of Mechanics,Peking University,Beijing 100871,P.R.China

In this study,a compact fourth-order upwind finite difference scheme for the con- vection-diffusion equation is developed,by the scheme perturbation technique and the compact second-order upwind scheme proposed by the *** basic fourth-order scheme,which like the classical upwind scheme is free of cell Reynolds-number limitation in terms of spurious oscil- lation and involves only immediate neighbouring nodal points,is presented for the one-dimen- sional equation,and subsequently generalized to multi-dimensional *** examples including one-to three-dimensional model equations,with available analytical solutions,of fluid flow and a problem,with benchmark solutions,of natural convective heat transfer are given to illustrate the excellent behavior in such aspects as accuracy,resolution to‘shock wave’-and ‘boundary layer’-effects in convection dominant cases,of the present ***,the fourth-order accuracy is specially verified using double precision arithmetic.

关键词： convection-diffusion equation finite difference scheme

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

THE COMPACT SECOND-ORDER UPWIND FINITE DIFFERENCE SCHEMES FOR THE CONVECTION-DIFFUSION EQUATIONS

引用

Journal of Hydrodynamics 1992年第4期4卷 32-42页

作者： Chen Guo-qian yang zhi-feng Department of Mechanics,Peking University,Beijing 100871,P.R.China

The compact second-order upwind finite difference schemes free of ceil Reynolds number limitation are developed in this paper for the one-to three-dimensional steady convection- diffusion equations,using a perturbational technique applied to the classical first-order upwind *** present second-order schemes take essentially the same form as those of the first- order schemes,but involve a simple modification to the diffusive *** exam- ples including one-to three-dimensional model equations of fluid flow and a problem of natural convection with boundary-layer effect are given to illustrate the excellent behavior of the present schemes.

关键词： convection-diffusion equations finite difference scheme perturbational technique

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：