检索结果-南通市图书馆

A distributed hydrological model with its application to the Jinghe watershed in the Yellow River Basin

在线全文

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2004年第z1期47卷 60-71页

作者： WANG Zhonggen1, ZHENG Hongxing1, LIU Changming1, , WU Xianfeng2 2 & ZHAO Weimin3.1. Key Laboratory of Water Cycle & Related Land Surface Processes, institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, beijing 100101, china 2. institute of Environmental Science, beijing Normal University, beijing 100875, china 3. Water Resources Conservation Committee of Yellow River, Zhengzhou 450003. china Key Laboratory of Water Cycle & Related Land Surface Processes Institute of Geographic Science and Natural Resources Research Chinese Academy of Sciences institute of Environmental Science Beijing Normal University

For the purpose of water resources management in the Yellow River Basin with highly spatial difference, a daily distributed hydrological model was proposed, of which the determination of spatially-distributed parameters and model inputs processing were performed by means of GIS/RS. In the model, the computation of runoff yield was based on the topography index method and flow routing was modeled by Maskingum method. The operation of the model is followed by means of “command structure” technique based upon the topography of river network. A case study using the model was conducted for the Jinghe watershed, which locates at the middle Yellow River Basin. The simulation of the hydrological processes in 1996 has shown that water quantity balance errors were less than 5% and the Nash-Sutcliffe coefficient arrived at 0.7, indicating that the model structure is justifiable, and the precision of the model can satisfy the purpose of water resources management.

关键词： distributed hydrological model, structure and equation, GIS and RS, Jinghe Basin, Yellow River Basin.

A formal model of fair exchange protocols

在线全文

学校读者我要写书评

暂无评论

Science in china(Series F) 2005年第4期48卷 499-512页

作者： QING Sihan1,2,3.& LI Gaicheng1,2,3.1. Engineering Research Center for Information Security Technology, institute of Software, Chinese Aca- demy of Sciences, beijing 100080, china 2. beijing Zhongke Ansheng Corporation of Information Technology, beijing 100080, china 3. Graduate School of the Chinese Academy of Sciences, beijing 10003., china Engineering Research Center for Information Security Technology Institute of Software Chinese Aca- demy of Sciences beijing Zhongke Ansheng Corporation of Information Technology Graduate School of the Chinese Academy of Sciences

Based on the study of existing fair exchange protocols, this paper sets up an accurate formal model by stepwise refinement. In the process of refinement an unreliable channel is employed to simulate an attack behavior. The model provides a novel formal definition of exchanged items, and presents the formal goals for fairness, accountability, etc., reflecting the inherent requirements for fair exchange protocols across-the-board. In order to check, prove, and design fair exchange protocols effectively and efficiently, the model puts forward a novel property of abuse-freeness which applies to all fair exchange protocols, gives a formal definition for trust strand of the third party, and presents general criteria of designing a secure and effective fair exchange protocol. Taking a typical fair exchange protocol as an example, this paper presents the analysis steps of fair exchange protocols appealing to our model. An unknown attack is uncovered. The analysis reveals the process of a complete attack, discovering deeper reasons for causing an attack. Finally, we modify the flawed protocol and the revised protocol ensures the desirable properties.

关键词： events local causal relation local temporal relation global relation exchanged item security goals.

Reconstruction of precipitation variation from tree rings in recent 1000 years in Delingha, Qinghai

在线全文

学校读者我要写书评

暂无评论

Science china Earth Sciences 2005年第7期48卷 939-949页

作者： SHAO Xuemei1, HUANG Lei1, LIU Hongbin2, LIANG Eryuan1, FANG Xiuqi3.& WANG Lili1 1. institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, beijing 100101, china 2. National Climate Center, beijing 100081, china 3. beijing Normal University, beijing 100875, china institute of Geographic Sciences Natural Resources Research Chinese Academy of Sciences Beijing 100101 China National Climate Center Beijing 100081 China beijing Normal University Beijing 100875 China

Using seven well-replicated Qilian juniper (Sabina przewalskii Kom.) ring-width chronologies developed at Zongwulong and Shalike Mts. in the northeastern part of the Qaidam Basin annual precipitation from previous July to current June in the recent 1000 years was re- constructed for Delingha. The reconstruction can capture 63.1% of precipitation variance and the equation was stable over time. For the reconstructed precipitation, wet periods occurred in AD1520—163. and 193.—2001, whereas dry intervals in 1429—1519 and 163.—1741. In ad- dition, the magnitude in precipitation variation was lower before 143. with about 15 mm, but it increased to 3. mm during the period of 143. to 1850. After 1850, the precipitation variance de- creased again. In contrast to the increase in temperature, a decrease in annual precipitation was evident since the 1990s. The agreement in low-frequency variation between the reconstruction and the glacier accumulation and particulate content in Dunde ice cores during the recent several hundred years suggested that the precipitation reconstructed in this study was rather reliable, and represented a regional signal. This 1000-year reconstruction could benefit our understanding of climatic variation in decadal to century-scale in this region, and provide basic data to climate models and to prediction of future climate in the 21st century.

关键词： northeastern part of the Qaidam Basin tree-ring width series of Qilian juniper precipitation reconstruction in 1000 years.

Preparation of a Novel Micro/nano Tubes via Electrospun Fiber as a Template

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2004年第5期20卷 613-616页

作者： Taiqi LIUSchool of Materials and Chemical Engineering, beijing institute of Petro-chemical Technology, beijing 102617,{3. Sch. of Mat. and Chem. Eng. Beijing Inst. of Petrochem. Technol. Beijing 102617 China

Poly (para-xylylene) hollow fibers with inner diameters can be prepared via template fibers electrospun from solutions. The PPX is deposited from the vapor phase and the template fiber is selectively removed by heat treatment or solvent extraction. The PPX is partially crystalline and the crystal modification depending on the route is used to extract the template fiber. The thermal stability of the hollow fibers is only slightly reduced relative to the bulk material and the same holds for the UV-stability.

关键词： Electrospinning Fiber Chemical vapor deposition Physical vapor deposition Crystal Conductivity

Relationships between tree-ring width index and NDVI of grassland in Delingha

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2006年第9期51卷 1106-1114页

作者： HE Jicheng1,3.& SHAO Xuemei1,21. institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, beijing 100101, china 2. institute of Tibetan Plateau Research, Chinese Academy of Sciences, beijing 100085, china 3. Graduate School of Chinese Academy of Sciences, beijing 10003., china institute of Geographical Sciences and Natural Resources Research Chinese Academy of Sciences Beijing China Graduate School of Chinese Academy of Sciences Beijing China institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China

Using five well-replicated Qilian juniper (Sabina przewalskii Kom.) tree-ring width index se- ries, monthly normalized difference vegetation index (NDVI) of grassland, and climatic data from 1982 to 2001, the relationships between tree-ring width index, NDVI of grassland, and climatic data were analyzed firstly. Then, the relationship between tree-ring width index and NDVI of grassland was explored. The re- sults showed that: (1) Temperature and precipitation in June influenced tree-ring width index and NDVI of grassland deeply in Delingha. (2) There were sig- nificant relationships between five tree-ring width index series (DLH1-DLH5) and monthly NDVI of grassland from June to September, with the most significant relationship being between tree-ring width index series and NDVI of grassland in August. (3. The PC1 (the first principal component derived from DLH1-DLH5 series) exhibited good agreement with monthly NDVI of grassland in the grass growth sea- son (from June to September) and the averaged NDVI in the growth season, which was attributed to their common responses to water-supply limit in Delingha. This study may allow an increase in studying the past dynamics of grassland in Delingha in that the variation of grassland NDVI during the last millennium has been reconstructed from PC1.

关键词：圆柏祁连山 NDVI 草原年轮宽度指数

Re-assessment and Optimization of the Ga-M (M=In, Sb,Pb) Systems with Chemsage

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 1998年第4期12卷 212-218页

作者： Xianran Xing Thiyu Qiao Herbert IPser( institute of Inorganic Chemistry, University of vienna,A-1090wien,Austria)( applied Science School, University of Science and Technology beijing, beijing 100083. china) institute of Inorganic Chemistry University of Vienna A-1090 Wien Austria applied Science School University of Science and Technology Beijing Beijing 100083 China

The thermodynamic properties and the phase diagrams of the systems Ga-M (M = In, Sb, Ph) were critically re-assessed and optimized employing the software package ChemSage for the calculation of thermodynamicequilibria. The Redlich-Kister/Margules formalism was employed for all solution phases and sets of self-consistentthermodynamic parameters were obtained. The results of re-assessment and optimization are compared with previous work, they are in excellent agreement with most experimental data.

关键词： phase diagram calculation CALPHAD method gallium-based alloy thermodynamic property

Full fermion-boson vertex function derived in terms of symmetry relations in Abelian gauge theory

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2008年第9期51卷 1206-1213页

作者： HE HanXin china institute of Atomic Energy, beijing 102413. china china institute of Atomic Energy Beijing China

Nonperturbative studies such as confinement and dynamical chiral symmetry breaking need the nonperturbative interacting vertex functions. In this paper, an approach to determining the full fermion-boson vertex function in four-dimensional Abelian gauge theory is presented: this full vertex function is derived in terms of a set of normal (longitudinal) and transverse Ward-Takahashi relations for the fer-mion-boson (vector) and axial-vector vertices in the momentum space in the case of massless fermion. Such a derived fermion-boson vertex function should be sat-isfied both perturbatively and nonperturbatively. The fact that such a derived full fermion-boson vertex function to one-loop order holds indeed is proven and the nonperturbative form of this vertex is also under discussion.

关键词： symmetry Ward-Takahashi relations full fermion-boson vertex function

Non-existence of positive solution to a quasilinear elliptic system and blow-up estimates for a reaction-diffusion system

在线全文

学校读者我要写书评

暂无评论

Communications in Nonlinear Science and Numerical Simulation 2001年第4期6卷 222-226页

作者： Zuodong YANG and Qishao LU Department of applied Mathematics, beijing University of Aeronautics and Astronautics, beijing 100083.{3. Department of applied Mathematics Beijing University of Aeronautics and Astronautics Beijing 100083 China

The non-existence result for radially nonincreasing positive solutions of the system is implied. By using this non-existence result. blow-up estimates for a class of quasilinear reaction-diffusion systems (non-Newtoni... 详细信息

关键词： blow-up. quasilinear reaction-diffusion system. positive radial solutions existence and non-existence

A mixed method for measuring low-frequency acoustic properties of macromolecular materials

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2006年第6期49卷 729-739页

作者： LIU Hongwei1,YAO Lei1,3.ZHAO Hong1,3.ZHANG Jichuan2,3.& XUE Zhaohong2 1. National Key Laboratory of Acoustics,institute of Acoustics,Chinese Academy of Sciences,beijing 100080,china 2. institute of Chemistry,Chinese Academy of Sciences,beijing 100080,china 3. Graduate University of Chinese Academy of Sciences,beijing 100049,china National Key Laboratory of Acoustics Institute of Acoustics Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China institute of Chemistry Chinese Academy of Sciences Beijing China

A mixed method for measuring low-frequency acoustic properties of macro-molecular materials is presented. The dynamic mechanical parameters of materials are first measured by using Dynamic Mechanical Thermal Apparatus(DMTA) at low frequen-cies,usually less than 100 Hz; then based on the Principles of Time-Temperature Super-position (TTS),these parameters are extended to the frequency range that acousticians are concerned about,usually from hundreds to thousands of hertz; finally the extended dynamic mechanical parameters are transformed into acoustic parameters with the help of acoustic measurement and inverse analysis. To test the feasibility and accuracy,we measure a kind of rubber sample in DMTA and acquire the basic acoustic parameters of the sample by using this method. While applying the basic parameters to calculating characteristics of the sample in acoustic pipe,a reasonable agreement of sound absorp-tion coefficients is obtained between the calculations and measurements in the acoustic pipe.

关键词： low-frequency acoustic properties,dynamic mechanical properties,Principles of Time-Temperature Superposition,acoustic pipe,sound absorption coefficient.