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Simulation study and function analysis of the dynamic aortic valve

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Progress in Natural Science:Materials International 2006年第5期16卷 512-517页

作者： XIA Dongdong and BAI Jing (dep.r.ment of Biomedical Engineering, tsinghua university, beijing 100084, china) dep.r.ment of Biomedical Engineering Tsinghua University Beijing 100084 China

The dynamic aortic valve (DAV) is a new left ventricular assist device, a micro-axial blood pump implemented at the position of the aortic valve, pumping blood from the left ventricle into the aortic artery. The present dynamic aortic valve operates at 7 different rotation speeds, ranging from 3000 r/min (speed 1) to 9000 r/min (speed 7). Because in vivo experiments need a lot of live animals and take a long period of time, modeling and simulation have been widely used to simulate and analyze hydra-dynamic property of the DAV and its assisting effects. With the measurements from the mock circulatory loop, a mathematic model of the DAV is established and embedded into the previously developed canine circulatory system. Using this model, the effect of the DAV on the failing heart at each rotation speed level is investigated. The vital cardiac variables are computed and compared with in vivo experimental results, which are in good agreement with an acceptable difference mostly 15%. The establishment of the DAV model and its simulation are useful for further improvement of the DAV device.

关键词： dynamic aortic valve mathematic model computer simulation.

Computational fluid dynamics modeling and hemolysis analysis of axial blood pumps with various impeller structures

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Progress in Natural Science:Materials International 2006年第9期16卷 993-997页

作者： XIA Dongdong, ZHAO Chunzhang, ZHANG Xiwen and BAI Jing ( dep.r.ment of Biomedical Engineering, tsinghua university, beijing 100084, china dep.r.ment of Engineering Mechanics, tsinghua university, beijing 100084, china) [a]dep.r.ment of Biomedical Engineering Tsinghua University Beijing China [b]dep.r.ment of Engineering Mechanics Tsinghua University Beijing China

The flow fields in the blood pump were analyzed three- dimensionally using computational fluid dynamics (CFD). Hemolysis of the pump was calculated based on the changes in shear stress and related exposure times along the particle trace lines using a forward Euler approach. In this "way, how different impeller structures and rotational speeds affect the hemolysis was particularly acquired. As a result, impeller with long-short alternant vanes behaved best in hemolysis property and can be utilized to axial blood pumps development and design.

关键词： axial blood pump computational fluid dynamics hemolysis.

Ar quivers,exceptional sequences and algorithms in derived Hall algebras

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Science china Mathematics 2010年第6期53卷 1609-1624页

作者： SHENG Jie dep.r.ment of Mathematical Sciences,tsinghua university,beijing 100084,china 1. dep.r.ment of Mathematical Sciences Tsinghua University Beijing 100084 China

Consider the canonical isomorphism between the positive part U+ of the quantum group Uq(g) and the Hall algebra H(Λ),where the semisimple Lie algebra g and the finite-dimensional hereditary algebra Λ share a Dynkin *** and Xiao have given two algorithms to decompose the root vectors into linear combinations of monomials of Chevalley generators of U+,respectively induced by the braid group action on the exceptional sequences of Λ-modules and the structure of the Auslander-reiten quiver of Λ.In this paper,we obtain the corresponding algorithms for the derived Hall algebra DH(Λ),which was introduced by *** show that both algorithms are applicable to the lattice algebra and Heisenberg double in the sense of *** the new recursive formulae have the same flavor with the quantum Serre relations.

关键词： derived Hall algebra exceptional sequence Ar quiver

rEGULArIZATION OF SINGULAr SYSTEMS BY OUTPUTFEEDBACK

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Journal of Computational Mathematics 2000年第1期18卷 43-60页

作者： De-lin Chu Da-yong Cai(dep.r.ment of Mathematical Sciences, tsinghua university, beijing 100084, china) 清华大学北京 100084

Presents a study which examined problem of regularization of a singular linear time-invariant system by derivative and proportional output feedback. reduced form for the system that can be computed using orthogonal tr... 详细信息

关键词： regularization singular systems output feedback

Effective elastic moduli of polymer-layered silicate nanocomposites

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Chinese Science Bulletin 2001年第13期46卷 1130-1133页

作者： FENG Xiqiaodep.r.ment of Engineering Mechanics, tsinghua university, beijing 100084, china dep.r.ment of Engineering Mechanics Tsinghua University Beijing China

Polymer-layered silicate (PLS) nanocomposites exhibit some mechanical properties that are much better than conventional polymer filled composites. A relatively low content of layered silicate yields a significant enhancement of material performance. After the volume fraction of clay reaches a relatively low 'critical value'; however, further increasing does not show a greater stiffening effect. This phenomenon is contrary to previous micromechanical predictions and is not understood well. Based on the analysis on the microstructures of PLS nanocomposites, the present note provides an insight into the physical micromechanisms of the above unexpected phenomenon. The Mori-Tanaka scheme and a numerical method are employed to estimate the effective elastic moduli of such a composite.

关键词： nanocomposites effective moduli microstructure Mori-Tanaka method.

Mechanism and control of convective heat transfer——Coordination of velocity and heat flow fields

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Chinese Science Bulletin 2001年第7期46卷 596-599页

作者： QUO Zengyuandep.r.ment of Engineering Mechanics, tsinghua university, beijing 100084, china dep.r.ment of Engineering Mechanics Tsinghua University Beijing 100084 China

A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.

关键词： convective heat transfer coordination heat transfer enhancement.

DOPING LEVEL INCrEASE OF POLY(3-METHYLTHIOPHENE)FILM DUrING ELECTrOCHEMICAL POLYMErIZATION PrOCESS

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Chinese Journal of Polymer Science 2002年第5期20卷 425-430页

作者： Jing-kun Xu Gao-quan Shi Feng-en Chen Xiao-yin Hong dep.r.ment of chemistry and Bio-organic Phosphorous chemistry Laboratory tsinghua university beijing 100084, china tsinghua Univ Dept Chem Beijing 100084 Peoples R China tsinghua Univ Bioorgan Phosphorous Chem Lab Beijing 100084 Peoples R China

The raman spectra of poly(3-methylthiophene) (PMeT) films with different thicknesses, which have been electrochemically deposited on a flat stainless steel electrode surface by direct oxidation of 3-methylthiophene in boron trifluoride diethyl etherate (BFEE) at a constant applied potential of 1.38 V (versus SCE), have been investigated by excitation with a 633-nm laser beam. The spectroscopic results demonstrated that the doping level of PMeT film was increasing during film growth. This finding was also confirmed by electrochemical examination. Moreover, the raman bands assigned to radical cations and dications in doped PMeT films were found approximately at 1420 and 1400 cm(-1), respectively. radical cations and dications coexist on the backbone of PMeT as conductive species and their concentrations increase with the increase of doping level. Successive cyclic voltammetry was proved to be an effective approach to improving the doping level of as-grown thin compact PMeT film.

关键词： poly(3-methylthiophene) raman spectra doping level radical cations dications

The numbers of periodic orbits hidden at fixed points of 2-dimensional holomorphic mappings

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Science china Mathematics 2010年第3期53卷 863-886页

作者： ZHANG GuangYuan dep.r.ment of Mathematical Sciences, tsinghua university, beijing 100084, china 1. dep.r.ment of Mathematical Sciences Tsinghua University Beijing 100084 China

Let △n be the ball |x| < 1 in the complex vector space C n , let f :△n→ C n be a holomorphic mapping and let M be a positive integer. Assume that the origin 0 = (0, . . . , 0) is an isolated fixed point of both f a... 详细信息

Let △n be the ball |x| r space C n , let f :△n→ C n be a holomorphic mapping and let M be a positive integer. Assume that the origin 0 = (0, . . . , 0) is an isolated fixed point of both f and the M-th iteration f M of f. Then the (local) Dold index P M (f, 0) at the origin is well defined, which can be interpreted to be the number of virtual periodic points of period M of f hidden at the origin: any holomorphic mapping f 1 :△n→ C n sufficiently close to f has exactly P M (f, 0) distinct periodic points of period M near the origin, provided that all the fixed points of f M 1 near the origin are simple. Therefore, the number O M (f, 0) = P M (f, 0)/M can be understood to be the number of virtual periodic orbits of period M hidden at the fixed point. According to the works of Shub-Sullivan and Chow-Mallet-Paret-Yorke, a necessary condition so that there exists at least one virtual periodic orbit of period M hidden at the fixed point, i.e., O M (f, 0)≥1, is that the linear part of f at the origin has a periodic point of period M. It is proved by the author recently that the converse holds true. In this paper, we will study the condition for the linear part of f at 0 so that O M (f, 0)≥2. For a 2 × 2 matrix A that is arbitrarily given, the goal of this paper is to give a necessary and sufficient condition for A, such that O M (f, 0)≥2 for all holomorphic mappings f :△2 → C 2 such that f(0) = 0, Df(0) = A and that the origin 0 is an isolated fixed point of f M .

关键词： complex dynamical systems periodic points fixed point indices

GHG emission reductions and costs to achieve Kyoto target

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Journal of Environmental Sciences 2003年第4期15卷 541-547页

作者： CHEN Wen\|ying (Energy, Environment and Economy research Institute, tsinghua university, beijing 100084, china.) Energy Environment and Economy Research Institute Tsinghua University 北京 100084

Emission projection and marginal abatement cost curves(MACs) are the central components of any assessment of future carbon market, such as CDM (clean development mechanism) potentials, carbon quota price etc. However, they are products of very complex, dynamic systems driven by forces like population growth, economic development, resource endowments, technology progress and so on. The modeling approaches for emission projection and MACs evaluation were summarized, and some major models and their results were compared. Accordingly, reduction and cost requirements to achieve the Kyoto target were estimated. It is concluded that Annex I Parties' total reduction requirements range from 503—1304 MtC with USA participation and decrease significantly to 140—612 MtC after USA's withdrawal. Total costs vary from 21—77 BUSD with USA and from 5—36 BUSD without USA if only domestic reduction actions are taken. The costs would sharply reduce while considering the three flexible mechanisms defined in the Kyoto Protocol with domestic actions' share in the all mitigation strategies drops to only 0—16%.

关键词： Kyoto Protocol emission reduction abatement cost flexible mechanisms