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Diffusion filtering in image processing based on wavelet transform

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Science in China(Series F) 2006年第4期49卷 494-503页

作者： liu feng Department of Information Science School of Mathematical Science Xi'an Jiaotong University Xi'an 710049 China

The nonlinear diffusion filtering in image processing bases on the heat diffusion equations. Its key is the control of diffusion amount. In the previous models, the diffusivity depends on the gradients of images. So it is easily affected by noises. This paper first gives a new multiscale computational technique for diffusivity. Then we proposed a class of nonlinear wavelet diffusion （NWD） models that are used to restore images. The NWD model has strong ability to resist noise. But it, like the previous models, requires higher computational effort. Thus, by simplifying the NWD, we establish linear wavelet diffusion （LWD） models that consist of advection and diffusion. Since there exists the advection, the LWD filter is anisotropic, and hence can well preserve edges although the diffusion at edges is isotropic. The advantage is that the LWD model is easy to be analyzed and has lesser computational load. Finally, a variety of numerical experiments compared with the previous model are shown.

关键词： image restoration diffusion filtering wavelet transform.

Stabilization of switched linear systems with bounded disturbances and unobservable switchings

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Science in China(Series F) 2007年第5期50卷 711-718页

作者： liu feng School of Electronics and Information Engineeing Beijing Jiaotong University Beijing 100044 China

This paper studies the stabilization problem of switched linear systems with bounded disturbances. It is assumed that the system switches among an Infinite set of uniformly controllable linear systems, and that the switching signals are not observable, but the switching duration has a lower bound. It will be shown that by combining on-line adaptive estimation and control in the controller design, a feedback control law can be constructed which makes the switched linear system globally stable.

关键词： switched systems uniform controllability estimation stabilization

Three-dimensional structure of the antennal lobe in the Southern house mosquito Culex quinquefasciatus

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Insect Science 2021年第1期28卷 93-102页

作者： Zi Ye feng liu Nannan liu Department of Biological Sciences Vanderbilt UniversityNashvilleTennesseeUSA Department of Entomology and Plant Pathology Auburn UniversityAuburnAlabamaUSA

The Southern house mosquito Culex quinquefasciatus relies on its olfactory system to locate the human hosts for blood meals,by which several deadly diseases are *** sensory neurons(OSNs)housed in the sensilla on the olfactory appendages send their axons into the antennal lobes(ALs),the primary olfactory center in the brain,where the OSNs expressing the same olfactory receptors converge upon the same spherical structures known as glomeruli in the *** structure of the antennal lobe,that is,the spatial organization of the glomeruli,governs the insect's odor identification and *** studies have demonstrated the specific connections between receptors and glomeruli based on the 3D structure of the antennal lobe,deepening our understanding of the relationships between glomerular activities and behaviors,but as yet the structure of the *** antennal lobe remains *** therefore constructed a 3D model of the *** antennal lobe using nc82 antibody staining,identifying 62 and 44 glomeruli in the female and male mosquito antennal lobe,respectively,with a significant sexual dimorphism in terms of the antennal lobe volume and glomerulus *** results demonstrate the structural basis of mosquito odor coding and provide a platform for future studies of the mosquito olfactory signal processing mechanism.

关键词： 3D-reconstruction antennal lobe Culex quinquefasciatus glomerulus olfaction

Theoretical study of reduction mechanism of Fe_(2)O_(3) by H_(2) during chemical looping combustion

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Chinese Journal of Chemical Engineering 2021年第9期34卷 175-183页

作者： feng liu Jing liu Yu Li Ruixue Fang State Key Laboratory of Coal Combustion School of Energy and Power EngineeringHuazhong University of Science and TechnologyWuhan 430074China

An atomic-level insight into the H_(2)adsorption and oxidation on the Fe_(2)O_(3)surface during chemicallooping combustion was provided on the basis of density functional theory calculations in this *** results indicated that H_(2)molecule most likely chemisorbs on the Fe_(2)O_(3)surface in a dissociative *** decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the *** particular,the H_(2)molecule adsorbed on an O top site could directly form H_(2)O precursor on the O_(3)-terminated ***,the newly formed H-O bond was activated,and the H atom could migrate from one O site to another,consequently forming the H_(2)O *** the H_(2)oxidation process,the decomposition of H_(2)molecule was the rate-determining step for the O_(3)-terminated surface with an activation energy of 1.53 ***,the formation of H_(2)O was the ratedetermining step for the Fe-terminated surface with an activation energy of 1.64 *** Feterminated surface is less energetically favorable for H_(2)oxidation than that the O_(3)-terminated surface owing to the steric hindrance of Fe *** results provide a fundamental understanding about the reaction mechanism of Fe_(2)O_(3)with H_(2),which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H_(2).

关键词： Chemical-looping combustion Fe_(2)O_(3)oxygen carrier H_(2)adsorption Density functional theory Reaction mechanism

Description of inverse energy cascade in homogeneous isotropic turbulence using an eigenvalue method

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Applied Mathematics and Mechanics(English Edition) 2021年第9期42卷 1233-1246页

作者： feng liu Hantao liu Hongkai ZHAO Pengfei LYU Research Center of Shanxi Province for Solar Energy Engineering and Technology School of Energy and Power EngineeringNorth University of ChinaTaiyuan 030051China National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power EngineeringBeihang UniversityBeijing 100191China

A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue *** show a special isotropic turbulence,in which the initial condition is constructed by reversing the velocity field in space,i.e.,the time-reversed *** is shown that the product of eigenvalues of the rate-of-strain tensor can quantitatively describe the backward energy transfer *** description is consistent to the velocity derivative skewness ***,compared with Sk,it is easier to be obtained,and it is expected to be extended to anisotropic ***,this description also works for the resolved velocity field,which means that it can be used in engineering turbulent *** description presented here is desired to inspire future investigation for the modeling of the backward energy transfer process and lay the foundation for the accurate prediction of complex flows.

关键词： inverse energy cascade homogeneous isotropic turbulence eigenvalue method turbulence model

Synthesis and Rheological Investigation of Model Symmetric 3-Arm Star Polyethylene

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Chinese Journal of Polymer Science 2014年第1期32卷 51-63页

作者： feng liu Dong Wan 唐涛 State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied ChemistryChinese Academy of Sciences Graduate School of the Chinese Academy of Sciences

A variety of linear and 3-arm star polyethylene （PE） model polymers covering a wide range of molecular weight are synthesized by the living polymerization of butadiene and the subsequent hydrogenation. Several rheological parameters of these model linear and 3-arm star PE samples are analyzed for detecting the long chain branching （LCB） structure. It is found that the analyses based on zero shear viscosity, vGP plot and flow activation energy are very sensitive to the 3-arm star PEs. The information on the presence of LCB can be obtained with these methods even for low molecular weight samples, which can not be determined by GPC-MALLS. However the information about the LCB structure can not be obtained by the rheological methods alone.

关键词： Long chain branching Rheology Star polymers Polyethylene Thermorheology.

Harmonizing models and observations: Data assimilation in Earth system science

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Science China Earth Sciences 2020年第8期63卷 1059-1068页

作者： Xin LI feng liu Miao FANG National Tibetan Plateau Data Center Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing 100101China CAS Center for Excellence in Tibetan Plateau Earth Sciences Chinese Academy of SciencesBeijing 100101China Key Laboratory of Remote Sensing of Gansu Province Northwest Institute of Eco-Environment and ResourcesChinese Academy of SciencesLanzhou 730000China

Models and observations are two fundamental methodological approaches in Earth system science(ESS). They evolve collaboratively and enhance one another. However, neither of these two approaches is perfect, and they have incompatibilities due to their methodological differences. The emergence of data assimilation(DA) has enabled these two approaches to develop in conjunction and form a harmonic ESS methodology. As a result, DA has shown a fresh vitality and applicability in ESS. This paper reviews the application of DA in the main branches of ESS, traces the coordinated evolution of DA with the methodologies of rationalism and empiricism, analyzes the relationships of DA with estimation theory and cybernetics, summarizes the advances of DA in China, and presents an outlook on the challenges facing the development of a uniform DA for ESS. DA theories and methods will continue to evolve and provide an increasingly mature methodology for enhancing the understanding and prediction of Earth as a system.

关键词： Data assimilation Model Observation Earth system science Methodology Philosophy of science Synthesis

Insights into the stable and fast lithium storage performance of oxygen-deficient LiV_(3)O_(8) nanosheets

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Nano Research 2021年第3期14卷 814-822页

作者： Huanqiao Song feng liu Mingsheng Luo Department of Chemical Engineering Beijing Institute of Petrochemical TechnologyBeijing102617China Beijing Key Laboratory of Clean Fuels and Efficient Catalytic Emission Reduction Technology Beijing102617China

Oxygen-deficient LiV_(3)O_(8) is considered as one of the promising cathode materials for lithium ion batteries(LIBs)because of its high cycling stability and rate ***,it is very difficult to control and study the content and position of V^(4+)and oxygen vacancies in LiV_(3)O_(8),and therefore the mechanism of improving electrochemical performance of LiV_(3)O_(8) is still ***,we developed four LiV_(3)O_(8) nanosheets with different V^(4+)and oxygen vacancy contents and *** physicochemical and lithium storage properties indicate that the V^(4+)and oxygen vacancies in the surface layer increase the contribution of pseudocapacitive lithium storage on the nanosheet *** V^(4+)and oxygen vacancies in the lattice improve the electrical conductivity of LiV_(3)O_(8),and enhance the phase transformation and lithium ion diffusion *** adjusting the content of V^(4+)and oxygen vacancies,we obtained an oxygen-deficient LiV_(3)O_(8) nanosheet which maintained more than 93%of the initial reversible capacity after 300 cycles at 5,000 mA·g^(−1).The V^(4+)and oxygen vacancies play an important role in improving the stability and rapidity of lithium *** work is helpful to understand the stable and fast lithium storage mechanism of oxygen-deficient LiV_(3)O_(8),and might lay a foundation for further studies of other oxygen-deficient metal oxide electrodes for long-life and high-power LIBs.

关键词： oxygen-deficient LiV_(3)O_(8) fast lithium storage high stability tetravalent vanadium ion oxygen vacancy

An h-adaptive numerical manifold method for solid mechanics problems

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Science China(Technological Sciences) 2018年第6期61卷 923-933页

作者： YU ChangYi liu feng XU Ying State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil Engineering Tianjin University Tianjin 300072 China State Key Laboratory of Geomechanies and Geoteehnical Engineering Institute of Rock andSoil Mechanics Chinese Academy of Sciences Wuhan 430071 China

The numerical manifold method(NMM) features its dual cover systems, namely the mathematical cover and physical cover,which provide a unified framework for mechanics problems involving continuum and discontinuum deformation. Uniform finite element meshes can be and are usually used to construct the mathematical cover. Though this strategy can handle different kinds of problems in a unified way, it is not economical for cases with steep deformation gradients or singularities. In this paper, using the recovery-based error estimator, an h-adaptive NMM on quadtree meshes is proposed to deal with such cases. The quadtree meshes serve as the mathematical meshes, on which the local refinement is carried out. When the quadtree meshes are refined,the corresponding mathematical cover, physical cover and manifold elements are updated accordingly. To handle the hanging nodes in the quadtree meshes, we resort to mean value coordinates. Comparing to the refinement based on manifold elements,the proposed strategy guarantees consistent structured meshes throughout the adaptive process, thus retaining the unique feature of original NMM. In contrast with polygonal finite element method, an advantage of the proposed method is that the meshes do not need to conform to the crack face and material boundary, which means the adaptive NMM is very suitable for problems with complex geometric boundary. Several representative mechanics problems, including crack problems, are analyzed to investigate the effectiveness of the proposed method. It is demonstrated that the proposed adaptive NMM has higher accuracy and better performance comparing to uniform refinement strategy.

关键词： numerical manifold method (NMM) adaptive analysis quadtree meshes mean value coordinates cover refinement