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Analysis of finite-element-based methods for reducing the ill-posedness in the reconstruction of fluorescence molecular tomography

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Progress in Natural Science:Materials International 2009年第4期19卷 501-509页

作者： Zhun Xu, Jing Bai Department of Biomedical Engineering, School of Medicine, tsinghua university, beijing 100084, china Department of Biomedical Engineering School of Medicine Tsinghua University Beijing 100084 China

The major issue in reconstruction of optical imaging might be the ill-posedness of the problem. In this paper, four different algorithms, including singular value decomposition (SVD), the truncated SVD, Tikhonov regularization and adaptive regularization, are analyzed and applied for solving the matrix equation generated from diffuse equation based on finite-element method in fluorescence molecular tomography. Results illustrate the need for either imposition of regularization term or elimination of too small singular values in reducing the illposedness. The results also suggest that the adaptive-regularization method offers superior performance in the reconstruction among the four methods in most cases even if the initially selected regularization parameter is not optimal, thus providing the convenience for the reconstruction.

关键词： Fluorescence molecular tomography Reconstruction Ill-posedness The truncated SVD Adaptive regularization

Fractal Characteristics of Round Jets in Steady Crossflow

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Communications in Nonlinear Science and Numerical Simulation 1998年第3期3卷 183-186页

作者： Yuhang LI Chaoquan CHEN and Chunbo JIANG(Hydraulic Department, tsinghua university, beijing 100084, china) Hydraulic Department Tsinghua University Beijing 100084 China

The fractal dimensions of turbulent round jets in steady crossflow has beenanalyzed by using planar laser-induced fluorescence (PLIF) method. The relation betweenthe fractal dimension and the momentum ratio, the variation of the fractal dimension withthe elevation of jet and the dilution have been investigated. The comparison of the fractalcharacteristics between the multiple jets and the signal jet has been carried out.

关键词： steady crossflow turbulent jet measurement of fractal dimension

Extremal functions for the Moser-Trudinger inequalities on compact Riemannian manifolds

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Science china Mathematics 2005年第5期48卷 618-648页

作者： LI Yuxiang Department of Mathematical Sciences, tsinghua university, beijing 100084, china Department of Mathematical Sciences Tsinghua University Beijing China

Let (M,g) be a compact Riemannian manifold without boundary, and (N,g) a compact Riemannian manifold with boundary. We will prove in this paper that the and can be attained. Our proof uses the blow-up analysis.

关键词： Moser-Trudinger inequality extremal function n-Lapalace Green function.

ADAPTIVE VARIABLE STRUCTURE CONTROLLERS AND APPLICATION TO ENGINE IDLE SPEED CONTROL SIMULATION

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Chinese Journal of Mechanical Engineering 2003年第2期16卷 171-174页

作者： Hui Qing Quyang MinggaoState Key Laboratory of AutomotiveSafety and Energy,tsinghua university,beijing 100084, china State Key Laboratory of Automotive Safety and Energy Tsinghua University Beijing 100084 China

A neural-network-based adaptive variable structure control methodology isproposed for the tracking problem of nonlinear discrete-time input-output systems. The unknowndynamics of the system are approximated via radial basis function neural networks. The control lawis based on sliding modes and simple to implement. The discrete-time adaptive law for tuning theweight of neural networks is presented using the adaptive filtering algorithm with residueupper-bound compensation. The application of the proposed controller to engine idle speed controldesign is discussed. The results indicate the validation and effectiveness of this approach.

关键词： variable structure control adaptive control neural networks nonlineardiscrete-time systems idle speed control

Stability of core-annular flow of power-law fluids in the presence of interfacial surfactant

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Science china(Physics,Mechanics & Astronomy) 2010年第5期53卷 933-943页

作者： SUN XueWei,PENG Jie & ZHU KeQin Department of Engineering Mechanics,tsinghua university,beijing 100084,china Department of Engineering Mechanics Tsinghua University Beijing 100084 China

The shear-thinning influence on the core-annular flow stability of two immiscible power-law fluids is considered by making a linear stability *** flow is driven by an axial pressure gradient in a straight pipe with the interface between the two fluids occupied by an insoluble *** the basic flow for this core-annular arrangement,the analytical solution is obtained with respect to the power-law fluid *** linearized equations for the evolution of infinitesimal disturbances are derived and the stability problem is formulated as a generalized matrix eigenvalue problem,which is solved by using the software package Matlab based on the QZ *** shear-thinning property is found to have marked influence on the power-law fluid core-annular flow stability,which is reflected in various ***,the capillary instability is magnified by the shear-thinning property,which may lead to an essential difference between power-law and Newtonian fluid *** when the interface is close to the pipe wall,the power-law fluid flow may be unstable while the Newtonian fluid flow is ***,under disturbances to the interface a velocity discontinuity at the interface appears which is destabilizing to the *** magnitude of this velocity discontinuity is affected by the power-law index and the flow stability is influenced ***,the shear-thinning property may induce new stability modes which do not appear in the Newtonian fluid *** flow stability shows much dependence on the interface location,the role of which was neglected in most previous *** shear-thinning fluid flow is more unstable to long wave disturbances when the interface is close to the pipe wall,while the Newtonian fluid flow is more unstable when the interface is close to the pipe *** this trend is changed by the addition of interfacial surfactant,for which the power-law fluid flow is more stable no matter where the interface is loca

关键词： core-annular flow power-law fluid interfacial surfactant linear stability analysis

Heat kernel estimates on effective resistance metric spaces

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Progress in Natural Science:Materials International 2007年第7期17卷 775-783页

作者： Hu Jiaxin Ji Yuan Wen Zhiying (Department of Mathematical Sciences,tsinghua university,beijing 100084,china) Department of Mathematical Sciences Tsinghua University Beijing 100084 China

We obtain two-sided estimates of heat kernels on effective-resistance metric spaces by using an analytic *** applications,such as on post-critically finite self-similar sets and on products of effective resistance spa... 详细信息

关键词： Heat kernel effective resistance Dirichlet form Green’s function

A normalized thoracic coordinate system for atlas mapping in 3D CT images

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Progress in Natural Science:Materials International 2008年第1期18卷 111-117页

作者： Hongkai Wang,Jing Bai*,Yonghong Zhang Department of Biomedical Engineering,tsinghua university,beijing 100084,china Department of Biomedical Engineering Tsinghua University Beijing 100084 China

In this paper,a normalized thoracic coordinate system(NTCS)is defined for rapidly mapping the 4D thoracic organ atlas into indi- vidual CT volume *** coordinate system is defined based on the thoracic *** coordinate values are normalized by the size of the individual thorax so that this coordinate system is universal to different *** compensating the respiratory motion of the organs,a 4D dynamic torso atlas is introduced.A method for mapping this dynamic atlas into the individual image using the NTCS is also *** this method,the dynamic atlas was mapped into the clinical thoracic CT images and rough positions of the organs were found *** NTCS-based 4D atlas mapping method may provide a novel way for estimating the thoracic organ positions in low-resolution molecular imaging modalities,as well as in modern 4D medical images.

关键词： Atlas mapping Registration Segmentation Molecular imaging

Measuring-basis-encrypted six-state quantum key distribution scheme

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Progress in Natural Science:Materials International 2006年第1期16卷 84-89页

作者： CHEN Pan1, DENG Fuguo1, WANG Pingxiao1 and LONG Guilu1,2 (Key Laboratory for Quantum Information and Measurements and Department of Physics, tsinghua university, beijing 100084, china 2. Key Laboratory for Atomic and Molecular NanoSciences, tsinghua university, beijing 100084, china) Key Laboratory for Quantum Information and Measurements and Department of Physics Tsinghua University Beijing 100084 China

A six-state quantum key distribution scheme with measuring-basis encryption technique, which is based on the six-state protocol and the MBE protocol, is proposed. In this modified six-state quantum key distribution protocol, Alice and Bob use a control key to synchronize the use of their measuring-basis so that they always use the same measuring-basis. This modified six-state quantum key distribution protocol retains the advantage of higher security and at the same time has a higher efficiency.

关键词： quantum key distribution measuring-basis encrypted six-state security.

Gas kinetic algorithm for flows in Poiseuille-like microchannels using Boltzmann model equation

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Science china(Physics,Mechanics & Astronomy) 2005年第4期48卷 496-512页

作者： LI Zhihui1,2, ZHANG Hanxin1 & FU Song2 ⒈ National Laboratory for CFD, Hypervelocity Aerodynamics Institute,china Aerodynamics Research and Development Center,Mianyang 621000,china 2.Department of Engineering Mechanics,tsinghua university,beijing 100084,china National Laboratory for CFD Hypervelocity Aerodynamics Institute China Aerodynamics Research and Development Center Mianyang China Department of Engineering Mechanics Tsinghua University Beijing China

The gas-kinetic unified algorithm using Boltzmann model equation have been extended and developed to solve the micro-scale gas flows in Poiseuille-like micro-channels from Micro-Electro-Mechanical Systems (MEMS). The numerical modeling of the gas kinetic boundary conditions suitable for micro-scale gas flows is presented. To test the present method, the classical Couette flows with various Knudsen numbers, the gas flows from short microchannels like plane Poiseuille and the pressure-driven gas flows in two-dimensional short microchannels have been simulated and compared with the approximate solutions of the Boltzmann equation, the related DSMC results, the modified N-S solutions with slip-flow boundary theory, the gas-kinetic BGK-Burnett solutions and the experimental data. The comparisons show that the present gas-kinetic numerical algorithm using the mesoscopic Boltzmann simplified velocity distribution function equation can effectively simulate and reveal the gas flows in microchannels. The numerical experience indicates that this method may be a powerful tool in the numerical simulation of micro-scale gas flows from MEMS.

关键词： Boltzmann model equation, discrete velocity ordinate method, finite-difference scheme, Couette flow, Poiseuille flow, gas flow in short-microchannel.