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STABLE FOURTH-ORDER STREAM-FUNCTION METHODS FOR INCOMPRESSIBLE FLOWS WITH BOUNDARIES

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Journal of Computational Mathematics 2009年第4期27卷 441-458页

作者： thomas y.hou BrianR.Wetton Department of Applied and Computational Mathematics California Institute of TechnologyPasadenaCA91125 USA Department of Mathematics University of British ColumbiaVancouverBCV6T 1Z2Canada

Fourth-order stream-function methods are proposed for the time dependent, incom- pressible Navier-Stokes and Boussinesq equations. Wide difference stencils are used instead of compact ones and the boundary terms are handled by extrapolating the stream-function values inside the computational domain to grid points outside, up to fourth-order in the noslip condition. Formal error analysis is done for a simple model problem, showing that this extrapolation introduces numerical boundary layers at fifth-order in the stream-function. The fourth-order convergence in velocity of the proposed method for the full problem is shown numerically.

关键词： Incompressible flow Stream-function formulation Finite difference methods.

Multiscale Domain Decomposition Methods for Elliptic Problems with High Aspect Ratios

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Acta Mathematicae Applicatae Sinica 2002年第1期18卷 63-76页

作者： JφrgAarnes thomas y.hou Department of Mathematics University of BergenJohs.Brunsgt.125008 BergenNorwayApplied Mathematics217-50CaltechPasadenaCA 91125

In this paper we study some nonoverlapping domain decomposition methods for solving a class of elliptic problems arising from composite materials and flows in porous media which contain many spatial scales. Our preconditioner differs from traditional domain decomposition preconditioners by using a coarse solver which is adaptive to small scale heterogeneous features. While the convergence rate of traditional domain decomposition algorithms using coarse solvers based on linear or polynomial interpolations may deteriorate in the presence of rapid small scale oscillations or high aspect ratios, our preconditioner is applicable to multiple-scale problems without restrictive assumptions and seems to have a convergence rate nearly independent of the aspect ratio within the substructures. A rigorous convergence analysis based on the Schwarz framework is carried out, and we demonstrate the efficiency and robustness of the proposed preconditioner through numerical experiments which include problems with multiple-scale coefficients, as well problems with continuous scales.

关键词： Multiscale elliptic problems Domain decomposition Schwarz methods Porous media

An Adaptive ANOVA-Based Data-Driven Stochastic Method for Elliptic PDEs with Random Coefficient

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Communications in Computational Physics 2014年第8期16卷 571-598页

作者： Zhiwen Zhang Xin Hu thomas y.hou Guang Lin Mike yan Computing and Mathematical Sciences California Institute of TechnologyPasadenaCA 91125USA. Pacific Northwest National Laboratory RichlandWA 99352USA.

In this paper,we present an adaptive,analysis of variance(ANOVA)-based data-driven stochastic method(ANOVA-DSM)to study the stochastic partial differential equations(SPDEs)in the multi-query *** new method integrates the advantages of both the adaptive ANOVA decomposition technique and the data-driven stochastic *** handle high-dimensional stochastic problems,we investigate the use of adaptive ANOVA decomposition in the stochastic space as an effective dimension-reduction *** improve the slow convergence of the generalized polynomial chaos(gPC)method or stochastic collocation(SC)method,we adopt the data-driven stochastic method(DSM)for speed *** essential ingredient of the DSM is to construct a set of stochastic basis under which the stochastic solutions enjoy a compact representation for a broad range of forcing functions and/or boundary *** ANOVA-DSM consists of offline and online *** the offline stage,the original high-dimensional stochastic problem is decomposed into a series of lowdimensional stochastic subproblems,according to the ANOVA decomposition ***,for each subproblem,a data-driven stochastic basis is computed using the Karhunen-Lo`eve expansion(KLE)and a two-level preconditioning optimization *** trial functions are used to enrich the stochastic basis and improve the *** the online stage,we solve each stochastic subproblem for any given forcing function by projecting the stochastic solution into the data-driven stochastic basis constructed *** our ANOVA-DSM framework,solving the original highdimensional stochastic problem is reduced to solving a series of ANOVA-decomposed stochastic subproblems using the *** adaptive ANOVA strategy is also provided to further reduce the number of the stochastic subproblems and speed up our *** demonstrate the accuracy and efficiency of our method,numerical examples are presented for one-and two-dimensional elliptic PDEs with rando

关键词： Analysis of variance stochastic partial differential equations data-driven methods Karhunen-Loeve expansion uncertainty quantification model reduction.

Palladium(Ⅱ)-Catalyzed Markovnikov Hydroalkynylation of Unactivated Terminal Alkenes

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Chinese Journal of Chemistry 2024年第1期42卷 29-34页

作者： Chuanqi hou Pinhong Chen Guosheng Liu Sstate Key Laboratory of Organometallic Chemistry and Shanghai Hongkong Joint Laboratory in Chemical SynthesisCenter for Excellence in Molecular SynthesisShanghai Institute of Organic ChemistryUniversity of Chinese Academy of SciencesChinese Academy of SciencesShanghai 200032China Chang-Kung Chuang Institute East China Normal UniversityShanghai 200062China

Alkynes are versatile synthons in organic synthesis,as well as important structural moieties in bioactive ***,transition metal-catalyzed hydroalkynylation of alkenes has been developed with reactive alkenes and alkenes bearing directing ***,the regioselective hydroalkynylation of simple alkenes is still ***,we have developed a palladium-catalyzed Markovnikov hydroalkynylation of unactivated terminal alkenes,which provides an efficient approach for the synthesis of branched alkynyl compounds under mild *** reaction features excellent functional group tolerance,good reaction yields and excellent ***,the asymmetric hydroalkynylation reaction has also been achieved with moderate enantioselectivity by introducing a sterically bulky chiral Pyox ligand.

关键词： Palladium catalysis Alkynylpalladation Unactivated terminal alkenes Markovnikov hydroalkynylation

Hierarchical vectorization for facial images

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Computational Visual Media 2024年第1期10卷 97-118页

作者： Qian Fu Linlin Liu Fei hou ying He School of Computer Science and Engineering Nanyang Technological University639798SingaporeSingapore Data61 Commonwealth Scientific and Industrial Research OrganisationSydney2015Australia Interdisciplinary Graduate School Nanyang Technological University and Alibaba Group639798SingaporeSingapore State Key Laboratory of Computer Science Institute of SoftwareChinese Academy of SciencesBeijing100190China University of Chinese Academy of Sciences Beijing100049China

The explosive growth of social media means portrait editing and retouching are in high *** portraits are commonly captured and stored as raster images,editing raster images is non-trivial and requires the user to be highly *** at developing intuitive and easy-to-use portrait editing tools,we propose a novel vectorization method that can automatically convert raster images into a 3-tier hierarchical *** base layer consists of a set of sparse diffusion curves(DCs)which characterize salient geometric features and low-frequency colors,providing a means for semantic color transfer and facial expression *** middle level encodes specular highlights and shadows as large,editable Poisson regions(PRs)and allows the user to directly adjust illumination by tuning the strength and changing the shapes of *** top level contains two types of pixel-sized PRs for high-frequency residuals and fine details such as pimples and *** train a deep generative model that can produce high-frequency residuals *** to the inherent meaning in vector primitives,editing portraits becomes easy and *** particular,our method supports color transfer,facial expression editing,highlight and shadow editing,and automatic *** quantitatively evaluate the results,we extend the commonly used FLIP metric(which measures color and feature differences between two images)to consider *** new metric,illumination-sensitive FLIP,can effectively capture salient changes in color transfer results,and is more consistent with human perception than FLIP and other quality measures for portrait *** evaluate our method on the FFHQR dataset and show it to be effective for common portrait editing tasks,such as retouching,light editing,color transfer,and expression editing.

关键词： face editing vectorization Poisson editing color transfer illumination editing expression editing

Evidence of guide field magnetic reconnection in flapping current sheets

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Earth and Planetary Physics 2024年第4期8卷 650-658页

作者： yunTian hou SuPing Duan Lei Dai Chi Wang State Key Laboratory of Space Weather National Space Science CenterChinese Academy of SciencesBeijing 100190China Key Laboratory of Solar Activity and Space Weather National Space Science CenterChinese Academy of SciencesBeijing 100190China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

Based on current sheet flapping motion on 27 August 2018 in the dusk flank magnetotail,as recorded by instruments aboard Magnetospheric Multiscale(MMS)spacecraft,we present the first study of guide field reconnection observed in the flux rope embedded in kink-like flapping current sheets near the dusk-side flank of the *** more common magnetotail reconnections,which are symmetric,these asymmetric small-scale(λ_(i)~650 km)reconnections were found in the highly twisted current sheet when the direction normal to the sheet changes from the Z direction into the y *** unique feature of this unusual reconnection is that the reconnection jets are along the Z direction-different from outflow in the X direction,which is the more usual *** vertical reconnection jet is parallel or antiparallel to the up-and-down motion of the tail’s current *** normalized reconnection rate R is estimated to be~*** results indicate that such asymmetric reconnections can significantly enlarge current sheet flapping,with large oscillation *** letter presents direct evidence of guide field reconnection in a highly twisted current sheet,characterized by enlarged current sheet flapping as a consequence of the reconnection outflow.

关键词： magnetic reconnection magnetotail current sheet

Dynamic ocean inverse modeling based on differentiable rendering

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Computational Visual Media 2024年第2期10卷 279-294页

作者： Xueguang Xie yang Gao Fei hou Aimin Hao Hong Qin State Key Lab of Virtual Reality Technology and Systems Beihang UniversityBeijing 100191China Qingdao Research Institute Beihang UniversityQingdao 266100Chinaand Peng Cheng LabShenzhen 518000China SKLCS Institute of SoftwareChinese Academy of SciencesBeijing 100190Chinaand University of Chinese Academy of SciencesBeijing 100049China Department of Computer Science Stony Brook University(SUNY at Stony Brook)Stony BrookNew York 11794-2424USA

Learning and inferring underlying motion patterns of captured 2D scenes and then re-creating dynamic evolution consistent with the real-world natural phenomena have high appeal for graphics and *** bridge the technical gap between virtual and real environments,we focus on the inverse modeling and reconstruction of visually consistent and property-verifiable oceans,taking advantage of deep learning and differentiable physics to learn geometry and constitute waves in a self-supervised ***,we infer hierarchical geometry using two networks,which are optimized via the differentiable *** extract wave components from the sequence of inferred geometry through a network equipped with a differentiable ocean ***,ocean dynamics can be evolved using the reconstructed wave *** extensive experiments,we verify that our new method yields satisfactory results for both geometry reconstruction and wave ***,the new framework has the inverse modeling potential to facilitate a host of graphics applications,such as the rapid production of physically accurate scene animation and editing guided by real ocean scenes.

关键词： inverse modeling surface reconstruction wave modeling ocean waves differentiable rendering(DR)

The corrosion characteristic and mechanism of Mg-5y-1.5Nd-xZn-0.5Zr(x=0,2,4,6 wt.%)alloys in marine atmospheric environment

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Journal of Magnesium and Alloys 2024年第1期12卷 139-158页

作者： Quantong Jiang Dongzhu Lu Liren Cheng Nazhen Liu Baorong hou CAS Key Laboratory of Marine Environmental Corrosion and Bio-fouling Institute of OceanologyChinese Academy of SciencesNo.7 Nanhai RoadQingdao 266071PR China State Key laboratory of Rare Earth Resource Utilization Changchun Institute of Applied ChemistryChinese Academy of SciencesNo.5625 Renmin StreetChangchun 130022PR China Open Studio for Marine Corrosion and Protection Pilot National Laboratory for Marine Science and Technology(Qingdao)No.1 Wenhai RoadQingdao 266071PR China Sanya Institute of Oceanology South China Sea Institute of OceanologyChinese Academy of SciencesZhenzhou RoadSanya 572000PR China

The microstructure and precipitated phases of as-cast Mg-5y-1.5Nd-x Zn-0.5Zr(x=0,2,4,6 wt.%)alloys were investigated by optical microscopy,scanning electron microscopy,energy-dispersive spectrometry and X-ray *** exposure corrosion experiment of these magnesium alloys was tested in South China Sea and KEXUE vessel atmospheric *** corrosion characteristic and mechanism of magnesium alloys of Mg-5y-1.5Nd-x Zn-0.5Zr(x=0,2,4,6 wt.%)alloys were analyzed by weight loss rate,corrosion depth,corrosion products and corrosion *** electrochemical corrosion tests were also measured in the natural *** comprehensive results showed that Mg-5y-1.5Nd-4Zn-0.5Zr magnesium alloy existed the best corrosion resistance whether in the marine atmospheric environment and natural seawater *** depended on the microstructure,type and distribution of precipitated phases in Mg-5y-1.5Nd-4Zn-0.5Zr magnesium *** quantity anodic precipitated phases in the microstructure of Mg-5y-1.5Nd-4Zn-0.5Zr alloy played the key role in the corrosion resistance.

关键词： Marine atmospheric environment Exposure corrosion Magnesium alloy Corrosion rate Corrosion mechanism

A multi-functional MgF_(2)/polydopamine/hyaluronan-astaxanthin coating on the biodegradable ZE21B alloy with better corrosion resistance and biocompatibility for cardiovascular application

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Journal of Magnesium and Alloys 2024年第3期12卷 1102-1116页

作者： yachen hou Xueqi Zhang Jingan Li Liguo Wang Shaokang Guan School of Materials Science and Engineering and Henan Key Laboratory of Advanced Magnesium Alloy and Key Laboratory of Materials Processing and Mold Technology(Ministry of Education) Zhengzhou UniversityZhengzhou 450001China

The cardiovascular diseases(CVD)continue to be the major threat to global public health over the years,while one of the effective methods to treat CVD is stent *** magnesium(Mg)alloys have great potential applications in cardiovascular stents benefit from their excellent biodegradability and ***,excessive degradation rate and the delayed surface endothelialization still limit their further *** this study,we modified a Mg-Zn-y-Nd alloy(ZE21B)by preparing MgF_(2) as the corrosion resistance layer,the dopamine polymer film(PDA)as the bonding layer,and hyaluronic acid(HA)loaded astaxanthin(ASTA)as an important layer to directing the cardiovascular cells *** electrochemical test results showed that the MgF_(2)/PDA/HA-ASTA coating improved the corrosion resistance of *** cytocompatibility experiments also demonstrated that this novel composite coating also selectively promoted endothelial cells proliferation,inhibited hyperproliferation of smooth muscle cells and adhesion of *** with the HAloaded rapamycin(RAPA)coating,our MgF_(2)/PDA/HA-ASTA coating showed better blood compatibility and cytocompatibility,indicating stronger multi-functions for the ZE21B alloy on cardiovascular application.

关键词： Biodegradable ZE21B alloy Reendothelialization Surface modification Hyaluronic acid Astaxanthin.