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Inverse minimum spanning tree problem and reverse shortest-path problem with discrete values

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progress in Natural Science:Materials International 2006年第6期16卷 649-655页

作者： LIU Longcheng and HE Yong (department of Mathematics, zhejiang university, hangzhou 310027, china State Key Laboratory of CAD & CG, zhejiang university, hangzhou 310027, china) [a]department of Mathematics Zhejiang University Hangzhou China [b]State Key Laboratory of CAD & CG Zhejiang University Hangzhou China

In this paper, we consider two network improvement problems with given discrete values: the inverse minimum spanning tree problem and the reverse shortest-path problem, where the decrements of the weight of the edges are given discrete values. First, for the three models of the inverse minimum spanning tree problem (the sum-type, the bottleneck-type and the constrained bottleneck-type), we present their respective strongly polynomial algorithms. Then, we show that the reverse shortest-path problem is strongly Np-complete.

关键词： minimum spanning tree shortest-path problem inverse problem reverse problem computational complexity.

LOCAL WELL-pOSEDNESS AND ILL-pOSEDNESS ON THE EQUATION OF TYpE □u= u^k(u)~α

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Chinese Annals of Mathematics,Series B 2005年第3期26卷 361-378页

作者： FANGDAOYUAN wangCHENGBO departmentofMathematics ZhejiangUniversityHangzhou310027China

This paper undertakes a systematic treatment of the low regularity local well-posedness and ill-posedness theory in H3 and Hs for semilinear wave equations with polynomial nonlinearity in u and (?)u. This ill-posed re... 详细信息

关键词： Semilinear wave equation Low regularity Local well-posedness Ill-posedness

EFFECTS OF STOICHIOMETrIC rATIO ON STrUCTUrE AND ELECTrODE pErFOrMANCE OF HYDrOGEN STOrAGE ALLOYS

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中国有色金属学会会刊：英文版 1998年第3期8卷 72-76页

作者： Chen Weixiang department of Materials Science and Engineering, zhejiang university, hangzhou 310027, p. r. china department of Materials Science and Engineering Zhejiang University Hangzhou 310027 China

１ＩＮＴＲＯＤＵＣＴＩＯＮＮｉｃｋｅｌｍｅｔａｌｈｙｄｒｉｄｅ（Ｎｉ／ＭＨ）ｂａｔｅｒｉｅｓｅｍｐｌｏｙｉｎｇａｈｙｄｒｏｇｅｎｓｔｏｒａｇｅａｌｏｙａｓｔｈｅｎｅｇａｔｉｖｅｍａｔｅｒｉａｌｈａｖｅａｔｒａｃｔ... 详细信息

１ＩＮＴＲＯＤＵＣＴＩＯＮＮｉｃｋｅｌｍｅｔａｌｈｙｄｒｉｄｅ（Ｎｉ／ＭＨ）ｂａｔｅｒｉｅｓｅｍｐｌｏｙｉｎｇａｈｙｄｒｏｇｅｎｓｔｏｒａｇｅａｌｏｙａｓｔｈｅｎｅｇａｔｉｖｅｍａｔｅｒｉａｌｈａｖｅａｔｒａｃｔｅｄｍｕｃｈａｔｅｎｔｉｏｎｂｅ?..

关键词： hydrogen storage alloy stoichiometric ratio structure thermodynamic property

Wake structures of two spheres in tandem arrangement at various gaps for re=300

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progress in Natural Science:Materials International 2005年第2期15卷 37-41页

作者： ZOU Jianfeng*, rEN Anlu, DENG Jian and CHEN Wenqu(department of mechanics, zhejiang university, hangzhou 310027, china) department of mechanics Zhejiang University Hangzhou 310027 China

The virtual boundary method is extended to a 3D application and used to simulate the flow field of two spheres in tandem arrangement for a reynolds number of 300. The wake structures and flow spectra at various gaps are investigated. The numerical results show that for small gaps (≈1.5), due to the mutual suppress between the wakes of the two spheres, the full flow field is stable and axisymmetric. As the gap is increased to 2.0, an asymmetric but stable flow is constructed through a certain bifurcation. The downstream wake structure is characterized by a double-thread vortex structure that comprises two slender parallel vortex tubes. The double-thread structure has a planar symmetry at gap 2.0. The hairpin-shape vortices are periodically shed from the downstream sphere at gap 2.5, but the planar symmetry persists. The vortex structures at gaps ranging from 3.0 to 4.0 are irregular and the flow field is undergoing a kind of 3D transition. It is up to the large gap 5.0 that the hairpin-shape structures are reconstructed behind the upstream and the downstream sphere, and the planar symmetry is resumed. All these numerical computations were performed on an SGI Origin3900 machine at the Center for Engineering and Scientific Computation of zhejiang university.

关键词： virtual boundary method flow past two spheres wake structure flow spectra

Local orthogonal transform for a class of acoustic waveguides

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progress in Natural Science:Materials International 2007年第10期17卷 1136-1146页

作者： Zhu Jianxin and Li peng(department of Mathematics, zhejiang university, hangzhou 310027, china) department of Mathematics Zhejiang University Hangzhou 310027 China

There are some curved interfaces in acoustic waveguides. To compute wave propagation along the waveguides with some marching methods, flattening of the internal interfaces is needed. In this paper, a local orthogonal coordinate transform and an equation transform are constructed to solve the two-dimensional Helmholtz equation for the waveguides bounded by a flat top, a flat bottom and two curved internal interfaces with three layered media. The curved internal interfaces are flattened by the local orthogonal coordinate transform, and the corresponding transformed Helmholtz equation can be solved by some marching methods. This treatment can be extended in multilayered medium waveguides. The one-way reformulation based on the Dirichlet-to-Neumann (DtN) map is then used to reduce the boundary value problem to an initial value problem. Numerical implementation of the resulting operator riccati equation uses a large range step method to discretize the range variable and a truncated local eigenfunction expansion to approximate the operators. This method is particularly useful for solving long range wave propagation problems in slowly varying waveguides with multilayered medium structure.

关键词： Helmholtz equation local orthogonal transform DtN reformulation marching method internal interface one-way reformulation.

Analysis on the environmental problems accompanying the high-speed urbanization of small towns in china

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Journal of Environmental Sciences 2002年第1期14卷 120-126页

作者： XU Lei, GE Jian, HUA Ying (department of Architecture, zhejiang university, hangzhou 310027, china department of Architecture Zhejiang University Hangzhou 310027 Chin

The environmental problems accompanying the rapid urbanization of many small towns like Keqiao, Shaoxing County of china and their countermeasures are presented. To settle these problems rationally as well as effectively will not only conduce to boost the environmental quality and life quality of cities, but also help to promote the development of regional economy and the realization of sustainable development.

关键词： environmental problems urbanization small towns

THE ESTIMATE AND MEASUrEMENT OF TrANSVErSE WAVE INTENSITY

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Acta Mechanica Solida Sinica 1997年第3期10卷 235-245页

作者： Ming ruisen, department of Architecture, zhejiang university, hangzhou 310027, china zhejiang UNIV DEPT ARCHITECTUREHANGZHOU 310027PEOPLES R CHINA

Transverse waves are a type of structural waves and should be considered in the analysis of high frequency vibration because the energy carried by transverse waves increases with the increase of frequency and becomes important at high frequencies. This paper studies the estimate theory and measuring technique of the transverse wave intensity in two-dimensional homogeneous structures. In general, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Each axial intensity component is proportional to two imaginary parts of cross spectral densities and its estimate is complicated. For the special case where transverse waves propagate in one direction, the intensity variation is zero and the estimate of the intensity is simplified. The intensity technique is formed based on the finite difference principle. Transverse wave intensity can be measured using a pair of two-transducer arrays lying in the orthogonal direction for the general case or a two-transducer array lying in the propagating direction for the special case. In order to assess the measurement accuracy of transverse wave intensify, the coupling loss factors from bending to transverse waves in building structures were measured using the intensity technique and compared with the results predicted and measured using the conventional method. It is shown that the agreement between the results measured using the intensity technique and that by the conventional method is good.

关键词： transverse wave intensity estimate theory measurement accuracy

rigidity for rational maps with Cantor Julia sets

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Science china Mathematics 2008年第1期51卷 79-92页

作者： ZHAI Yu department of Mathematics, zhejiang university, hangzhou 310027, china department of Mathematics Zhejiang University Hangzhou 310027 China

In this paper, we prove that two rational maps with the Cantor Julia sets are quasicon- formally conjugate if they are topologically conjugate.

关键词： Cantor Julia set rigidity puzzle piece bounded shape quasiconformally conjugate 37F12

NUMErICAL SIMULATION OF CAVITATION FLOW UNDEr HIGH prESSUrE AND TEMpErATUrE

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Journal of Hydrodynamics 2011年第3期23卷 289-294页

作者： ZHAO Wei-guo ZHANG Ling-xin SHAO Xue-ming department of mechanics Zhejiang University Hangzhou 310027 China State Key Laboratory of Fluid power Transmission and Control Zhejiang University Hangzhou 310027 China

The numerical simulation of cavitation flow on a 2D NACA0015 hydrofoil under high pressure and temperature is performed. The Singhal＇s cavitation model is adopted combined with an improved rNG k-ε turbulence model to study the cavitation flow. The thermal effect in the cavitation flow is taken into account by introducing the energy equation with a source term based on the latent heat transfer. The code is validated by a case of a hydrofoil under two different temperatures in a comparison between the simulation and the experiment. Computational results show that the latent heat of vaporization has a significant impact on the cavitation process in the high temperature state, and the cavity in the high temperature state is thinner and shorter than that in a normal state with the same cavitation number, due to the fact that the heat absorption in the cavitation area reduces the local temperature and the saturated vapor pressure. This numerical study provides some guidance for the design of machineries in the High pressure and Temperature （HpT） state.

关键词： cavitation NACA0015 thermodynamic CFD high pressure and temperature