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A Remark on the Symplectic Blow-up in Dimension 4

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Acta Mathematica Sinica,English Series 1996年第4期12卷 379-384页

作者： Ma Renyi department of Applied Mathematics tsinghua University beijing, {3. china department of Applied Mathematics Tsinghua University Beijing China

In this note, we prove that the symplectic blow-up or blow-down in the dimension 4 is rigid, i.e. the symplectic area of the divisor does not exceed the symplectic radius of the neighbourhood on which we do the blow-u... 详细信息

关键词： J-Holomorphic disc Contact manifold Symplectic blow-up

Centralizers and Iterate Radicals of Morse-Smale Diffeomorphisms of the Circle

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Acta Mathematica Sinica,English Series 1995年第1期11卷 1-11页

作者： Zhang Meirong department of Applied Mathematics tsinghua University beijing,{3. china department of Applied Mathematics Tsinghua University Beijing People's Republic of China

In this paper,we will use the embedding flows in[1],[2]to give a complete descrip- tion of the smooth centralizers and iterate radicals of all C^r(r≥2)Morse-Smale diffeomorphisms of the circle S^*** a result,we prove... 详细信息

关键词： Centralizers and Iterate Radicals of Morse-Smale Diffeomorphisms of the Circle TDFs

DYNAMIC AND KINEMATIC WAVE MODELSFOR 1-D RILL FLOW: A COMPARISON

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International Journal of Sediment Research 1999年第2期14卷 95-105页

作者： SHAO Xuejun (department of Hydraulic Engineering, tsinghua University, beijing 100084, {3.)

Overland flows on hillslopes due to rainfall excess are numerically simulated with a simplified strip microtopography which has one single straight rill, and comparisons are made between predictions of a dynamic wave model (DWM) and a kinematic wave model (KWM). Overland flow on the strip is treated as one-dimensional and interrill flow is not simulated. The DWM is based on the Saint-Venant equation, and the KWM is derived using the Chezy formula. A numerical scheme is developed which solves the non-linear DWM equations in a similar way to that of solving the KWM equations, *** the basis of the method of characteristics. This scheme greatly reduces the complexity of the solution procedure and therefore allows the use of DWM in process-based catchment models involving a large number of topographical elements, i.e., hillslopes. Simulation result shows that. in terms of the predicted flow velocity V and depth h, the *** model is an accurate approximation to the dynamic one for broad sheet overland flows resulted from normal rainfall excess rates (1-3.mm/min). However. for small rill width, e.g. B<20cm. or if the rainfal excess rate is extremely large (e.g.. 20 mm/min). differences of V and h between the two models will be significant. In general, the KWM tends to underestimate rill flow depth but overestimate its velocity, especially for small rill width. though it does give the same steady discharge per unit width, q =V h, as that predicted by DWM for steady rainfall excess rate. At the rising stage of the hydrograph, KWM predicts higher unit width discharge q, which leads to overestimation of rill detachment as a stream power function method is used.

关键词： Overland flow Rill flow Kinematic wave model Method of characteristics

HIGH TEMPERATURE OXIDATION AND STRUCTURE OF SCALE AND WHISKERS FOR Fe-Ni-Cr SEALING ALLOYS

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Acta Metallurgica Sinica(English Letters) 1993年第8期6卷 147-150页

作者： DONG Zhili MA Jusheng TANG Xiangyun YOU Liang tsinghua University,beijing,china lecturer {3. of Materials Science and Engineering,tsinghua University,beijing 100084,china tsinghua Univ Beijing China

The oxidation rate,the growth,morphology and structure of oxide scale and whiskers for Fe-Ni-Cr sealing alloys in H_2-H_2O atmosphere at high temperatures have been studied. The growth rate of scale is controlled by *... 详细信息

关键词： oxidation oxide scale oxide whisker Fe-Ni-Cr sealing alloy

Fuzzy tolerance quotient spaces and fuzzy subsets

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Science china(Information Sciences) 2010年第4期53卷 704-714页

作者： ZHANG Ling1 & ZHANG Bo2,3.4* 1Computer Science & Technology College, Anhui University, Anhui 23.03., china 2State Key Laboratory of Intelligent Technology and Systems, beijing 100084, china 3.3. National Laboratory of Information Science & Technology, beijing 100084, china 4Information Science & Technology College, Computer Science & Technology department, {3. University, beijing 100084, china 1. Computer Science & Technology College Anhui University Anhui 230039 China2. State Key Laboratory of Intelligent Technology and Systems Beijing 100084 China3. Tsinghua National Laboratory of Information Science & Technology Beijing 100084 China4. Information Science & Technology College Computer Science & Technology Department Tsinghua University Beijing 100084 China

The structure and characteristic of fuzzy subsets are discussed by using the concepts of granulation and hierarchy in quotient space theory. First, the equivalence relation based quotient space theory is extended to the fuzzy tolerance relation. Second, the isomorphism and its discriminant of fuzzy tolerance relations are discussed. Finally, by using the fuzzy tolerance relation to define the fuzzy subset, its properties are addressed. The main results are given below: (1) several equivalent statements of fuzzy tolerance relations; (2) the definition of isomorphism of fuzzy tolerance relations; (3. the isomorphic discriminant of fuzzy tolerance relations; (4) the definition and properties of fuzzy subsets based on the fuzzy tolerance relations; and (5) the necessary and sufficient condition of the isomorphism of fuzzy subsets. These results will help us further comprehend the concepts of fuzzy tolerance relations and fuzzy subsets.

关键词： Fuzzy tolerance relation quotient space isomorphism fuzzy subset

Local Gromov-Witten invariants of canonical line bundles of toric surfaces

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Science china Mathematics 2010年第6期53卷 1571-1582页

作者： YANG Fei & ZHOU Jian department of Mathematical Sciences,tsinghua University,beijing 100084,{3. 1. department of Mathematical Sciences Tsinghua University Beijing 100084 China

We define and compute by localizating the local equivariant Gromov-Witten invariants of the canonical line bundles of toric surfaces,not necessarily Fano.

关键词： local Gromov-Witten invariants localization partition function geometric engineering

The effect of hydrogen on the electronic structure of kink in bcc iron

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Science china(Technological Sciences) 2009年第5期52卷 1212-1218页

作者： CHEN LiQun1,QIU ZhengChen1,YU Tao2 & WANG ChongYu2,3.4 1 College of Sciences,Central South University of Forestry and Technology,Changsha 410004,china 2 Central Iron and Steel Research Institute,beijing 100081,china {3.,tsinghua University,beijing 100084,china 4 International Center for Materials physics,Chinese Academy of Sciences,Shenyang 110016,china 1. College of Sciences Central South University of Forestry and Technology Changsha 410004 China 2. Central Iron and Steel Research Institute Beijing 100081 China 3. department of physics Tsinghua University Beijing 100084 China 4. International Center for Materials physics Chinese Academy of Sciences Shenyang 110016 China

The electronic structures of kinks in the [100](010) and 1/2[111](-110) edge dislocations in bcc iron containing hydrogen are investigated by means of the first-principles DMol method and the discrete variational *** effects of hydrogen on the kinks are *** results show that hydro-gen forms weak bonding states with its neighboring host atoms,and since hydrogen draws charge from its neighboring host atoms,the interactions between most of the host atoms are weakened com-pared with those of the corresponding atomic pairs in the clean *** indicates that the migration of kink,*** motion of dislocation,is easier in the doping hydrogen kink than in the clean kink,which may be the solid solution softening effect resulting from the impurity hydrogen.

关键词： electronic structure dislocation kink impurity

Classification of hypersurfaces with parallel Mobius second fundamental form in S^(n+1)

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Science china Mathematics 2004年第3期47卷 417-430页

作者： HU Zejun LI Haizhong department of Mathematics, Zhengzhou University Zhengzhou 450052, china department of Mathematical Sciences, {3. University, beijing 100084, china department of Mathematics Zhengzhou University Zhengzhou China department of Mathematical Sciences Tsinghua University Beijing China

Let Mn(n≥2) be an immersed umbilic-free hypersurface in the(n+1)-dimensional unit sphere Sn+1. Then Mn is associated witha so-called M(o)bius metric g, and a M(o)bius second fundamental form Bwhich are invariants of Mn under the M(o)bius transformation groupof Sn+*** this paper, we classify all umbilic-free hypersurfaces withparallel M(o)bius second fundamental form.

关键词： parallel Mobius second fundamental form,hypersurface, Mobius metric, Mobius equivalence.

A land surface model incorporated with soil freeze/thaw and its application in GAME/Tibet

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Science china Earth Sciences 2006年第12期49卷 1311-1322页

作者： HU Heping1, YE Baisheng2, ZHOU Yuhua3.& TIAN Fuqiang1 1. department of Hydraulic Engineering, tsinghua University, beijing 100084, {3. 2. Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 73.000, {3. 3. department of Civil Engineering, Massachusetts Institute of Technology, USA 1. department of Hydraulic Engineering Tsinghua University Beijing 100084 China 2. Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Lanzhou 730000 China 3. department of Civil Engineering Massachusetts Institute of Technology USA

Land surface process is of great importance in global climate change, moisture and heat exchange in the interface of the earth and atmosphere, human impacts on the environment and eco- system, etc. Soil freeze/thaw plays an important role in cold land surface processes. In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied. A sophisti- cated land surface model is developed, the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux. The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil, but also demon- strates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone, which makes the model applicable for various circumstances. The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme. Finally, the model is applied to analyze the diurnal energy and water cycle char- acteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998. Heat and energy transfer simulation shows that: (i) There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux; (ii) during freezing period all three heat fluxes do not vary apparently, in spite of the fact that the negative soil temperature is higher than that not considering soil freeze; (iii) during thawing period, ground heat flux increases, and sensible heat flux decreases, but latent heat flux does not change much; and (iv) during freezing period, soil temperature decreases, though ground heat flux increases.

关键词： land surface model,soil freeze/thaw,GAME/Tibet,simultaneous liquid,vapor and heat transfer.