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Note on Redshift Distortion in Fourier Space

Chinese Journal of Astronomy and Astrophysics 2007年第1期7卷 51-62页

作者： Yan-chuan cai Jun Pan Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

We explore features of redshift distortion in Fourier analysis of N-body simulations. The phases of the Fourier modes of dark matter density fluctuation are generally shifted by the peculiar motion along the line of sight, the induced phase shift is stochastic and has a probability distribution function （PDF） that is symmetric about the peak at zero shift and whose exact shape depends on the wave vector, except on very large scales where phases are invariant by linear perturbation theory. Analysis of the phase shifts motivates our phenomenological models for the bispectrum in redshift space. Comparison with simulations shows that our toy models are very successful in modeling bispectrum of equilateral and isosceles trian- gles at large scales. In the second part we compare the monopole of the power spectrum and bispectrum in the radial and plane-parallel distortion to test the plane-parallel approximation. We confirm the results of Scoccimarro that difference of power spectrum is at the level of 10%, and, in the reduced bispectrum, the difference is as small as a few percent. However, on the plane perpendicular to the line of sight of kz = 0, the difference in power spectrum be- tween the radial and plane-parallel approximation can be more than - 10%, and even worse on very small scales. Such difference is prominent for bispectrum, especially for configura- tions of tilted triangles. Non-Ganssian signals under the radial distortion on small scales are systematically biased downside than are in the plane-parallel approximation, with amplitudes depending on the opening angle of the sample point to the observer. This observation gives warning to the practice of using the power spectrum and bispectrum measured on the kz = 0 plane as estimates of the real space statistics.

关键词： cosmology theory-large-scale structure of universe-methods statistical

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A Preconditioned Recycling GMRES Solver for Stochastic Helmholtz Problems

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Communications in Computational Physics 2009年第7期6卷 342-353页

作者： Chao Jin Xiao-chuan cai Cadence Design Systems 555 River Oaks ParkwaySan JoseCA 95134USA Department of Computer Science University of Colorado at BoulderBoulderCO 80309USA

We present a parallel Schwarz type domain decomposition preconditioned recycling Krylov subspace method for the numerical solution of stochastic indefinite elliptic equations with two random ***-Loeve expansions are used to represent the stochastic variables and the stochastic Galerkin method with double orthogonal polynomials is used to derive a sequence of uncoupled deterministic *** show numerically that the Schwarz preconditioned recycling GMRES method is an effective technique for solving the entire family of linear systems and,in particular,the use of recycled Krylov subspaces is the key element of this successful approach.

关键词： Recycling GMRES domain decomposition additive Schwarz preconditioner stochastic Helmholtz equation

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A Parallel Domain Decomposition Algorithm for Simulating Blood Flow with Incompressible Navier-Stokes Equations with Resistive Boundary Condition

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Communications in Computational Physics 2012年第4期11卷 1279-1299页

作者： Yuqi Wu Xiao-chuan cai Department of Applied Mathematics University of Colorado at BoulderBoulderCO 80309USA Department of Computer Science University of Colorado at BoulderBoulderCO 80309USA

We introduce and study a parallel domain decomposition algorithm for the simulation of blood flow in compliant arteries using a fully-coupled system of nonlinear partial differential equations consisting of a linear elasticity equation and the incompressible Navier-Stokes equations with a resistive outflow boundary *** system is discretized with a finite element method on unstructured moving meshes and solved by a Newton-Krylov algorithm preconditioned with an overlapping restricted additive Schwarz *** resistive outflow boundary condition plays an interesting role in the accuracy of the blood flow simulation and we provide a numerical comparison of its accuracy with the standard pressure type boundary *** also discuss the parallel performance of the implicit domain decomposition method for solving the fully coupled nonlinear system on a supercomputer with a few hundred processors.

关键词： Fluid-structure interaction blood flow mesh movement resistive boundary condition additive Schwarz domain decomposition parallel computing

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Algorithm development for extreme-scale computing

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National Science Review 2016年第1期3卷 26-27页

作者： Jiachang Sun Chao Yang Xiao-chuan cai Institute of Software Chinese Academy of Sciences State Key Laboratory of Computer Science Chinese Academy of Sciences Department of Computer Science University of Colorado Boulder

The rapid advances of supercomputing and the growing needs of extreme-scale applications pose great challenges in the development of highly efficient and scalable parallel *** addition to the traditional homogeneous c... 详细信息

关键词： PDEs Algorithm development for extreme-scale computing GPU code

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Development of metal-organic deposition-derived second-generation high-temperature superconductor tapes and artificial flux pinning

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Advances in Manufacturing 2023年第3期11卷 523-540页

作者： Dong-Xu Wang Jing Chen Di-Fan Zhou chuan-Bing cai Shanghai Key Laboratory of High Temperature Superconductors Shanghai Frontiers Science Center of Quantum and Superconducting Matter StatesDepartment of PhysicsShanghai UniversityShanghai 200444People's Republic of China Shanghai Creative Superconductor Technologies Co.Ltd. Shanghai 201401People's Republic of China

The second-generation high-temperature superconductor tape(2G-HTS,also known as a coated conductor)based on REBaCuO(REBa_(2)Cu_(3)O_(7-δ))exhibits high current density and potential cost-effective price/performance,compared with conventional superconducting *** commercial 2G-HTS tapes,more than a dozen cable vendors had been manufacturing REBCO cables,such as the latest kilometer-class REBCO cable,which was incorporated into a civil grid on December 2021,as part of the recordbreaking 35-kV-voltage superconductor cable demonstration project in downtown *** paper describes the development of HTS-coated conductors,then outlines the various technological routes for their preparation,reviews the artificial flux pinning of coated conductors,and finally summarizes the technological breakthroughs,the latest research advances,and provides an outlook on their application prospects.

关键词： High-temperature superconductors RE123 superconductor tapes Chemical solution deposition Flux pinning

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Neutral C–H bond vs. electron pair of N(sp^2): A binding site effect study of macrocycle anion receptor

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Chinese Chemical Letters 2014年第8期25卷 1125-1131页

作者： chuan-cai Fan Li-Jin Xu Han-Yuan Gong Department of Chemistry Renmin University of China College of Chemistry Beijing Normal University

To evaluate the effect of neutral C–H bond or electron pair of nitrogen atom with sp2hybridization（N（sp2）） involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine） [2]（1,3-dimethylenebenzene）（14＋）, and cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine）[2]（2,6-di methylenepyridine）（24＋）were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl,N3, NO3, and H2PO4. The host–guest interactions were characterized via1 H NMR spectroscopy,electrospray ionization mass spectrometry（ESI-MS） and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites（14＋with neutral C–H vs. 24＋with N（sp2）） vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.

关键词： Macrocycle Anion binding Neutral C-H bond N(sp2) Hydrogen bond

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A Scalable Numerical Method for Simulating Flows Around High-Speed Train Under Crosswind Conditions

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Communications in Computational Physics 2014年第4期15卷 944-958页

作者： Zhengzheng Yan Rongliang Chen Yubo Zhao Xiao-chuan cai Shenzhen Institutes of Advanced Technology Chinese Academy of SciencesShenzhen 518055P.R.China Department of Computer Science University of Colorado BoulderBoulderCO 80309USA

This paper presents a parallel Newton-Krylov-Schwarz method for the numerical simulation of unsteady flows at high Reynolds number around a high-speed train under *** a realistic train geometry,a realistic Reynolds number,and a realistic wind speed,this is a very challenging computational *** of the limited parallel scalability,commercial CFD software is not suitable for supercomputers with a large number of *** develop a Newton-KrylovSchwarz based fully implicit method,and the corresponding parallel software,for the 3D unsteady incompressible Navier-Stokes equations discretized with a stabilized finite element method on very fine unstructured *** test the algorithm and software for flows passing a train modeled after China’s high-speed train CRH380B,and we also compare our results with results obtained from commercial CFD *** algorithm shows very good parallel scalability on a supercomputer with over one thousand processors.

关键词： Three-dimensional unsteady incompressible flows high-speed train crosswind full Navier-Stokes equations Newton-Krylov-Schwarz algorithm parallel computing

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A review of thickness-induced evolutions of microstructure and superconducting performance of REBa2Cu3O7-δ coated conductor

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Advances in Manufacturing 2017年第2期5卷 165-176页

作者： Jian-Xin Lin Xu-Ming Liu chuan-Wei Cui chuan-Yi Bai Yu-Ming Lu Feng Fan Yan-Qun Guo Zhi-Yong Liu chuan-Bing cai Shanghai Key Laboratory of High Temperature Superconductors Shanghai University Shanghai 200444People's Republic of China

The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.

关键词： Thickness effect Superconducting film Critical current density Microstructure Epitaxial texture Pinning force

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DWT Power Spectrum of the Two-Degree Field Galaxy Redshift Survey

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Chinese Journal of Astronomy and Astrophysics 2008年第2期8卷 159-178页

作者： Yan-chuan cai Jun Pan Yong-Heng Zhao Long-Long Feng Li-Zhi Fang Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Department of Physics University of Arizona Tucson AZ 85721 US

The power spectrum of the two-degree Field Galaxy Redshift Survey （2dFGRS） sample is estimated with the discrete wavelet transform （DWT） method. The DWT power spectra within 0.035 〈 k 〈 2.2 h Mpc^-1 are measured for three volume-limited samples defined in consecutive absolute magnitude bins - 19 - - 18, - 20 - - 19 and - 21 - - 20. We show that the DWT power spectrum can effectively distinguish ACDM models of σ8 = 0.84 and σ8 = 0.74. We adopt maximum likelihood method to perform three-parameter fitting of the bias parameter b, pairwise velocity dispersion σpv and redshift distortion parameterβ = Ωm^0.6/b to the measured DWT power spectrum. The fitting results state that in a σ8 = 0.84 universe the best-fit values of Ωm given by the three samples are mutually consistent within the range 0.28 - 0.36, and the best fitted values of Opv are 398-27^＋35, 475-29^37 and 550 ± 20 km s^-1 for the three samples, respectively. In the model of σ8 = 0.74, our three samples give very different values of Ωm. We repeated the fitting using the empirical formula of redshift distortion. The result of the model of low σ8 is still poor, especially, one of the best-fit values of σpv is as large as 10^3 km s^-1. We also repeated our fitting by incorporating a scale-dependent galaxy bias. This gave a slightly lower value of Ωm. Differences between the models of σ8 = 0.84 and σ8 = 0.74 still exist in the fitting results. The power spectrum of 2dFGRS seems to disfavor models with low amplitude of density fluctuations if the bias parameter is assumed to be scale independent. For the fitting value of Ωm to be consistent with that given by WMAP3, strong scale dependence of the bias parameters is needed.

关键词： methods: data analysis -- methods: statistical : (cosmology:) cosmological parameters --(cosmology:) large-scale structure of universe

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Influence of Magnetic Scattering and Interface Transparency on Superconductivity Based on a Ferromagnet/Superconductor Heterostructure

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Chinese Physics Letters 2011年第8期28卷 281-284页

作者： PENG Lin LIU Yong-Sheng cai chuan-Bing ZHANG Jin-Cang Department of Physics Shanghai University of Electric PowerShanghai 200090 Department of Physics Shanghai UniversityShanghai 200444

We investigate an antiferromagnet/ferromagnet/superconductor/ferromagnet(AF/F/S/F)spin-valve system with nanoscopic scale,described by Usadel equations in the dirty *** results show that the superconducting characteristics in the system strongly depend not only on the mutual orientation and thickness of two ferromagnetic layers,but also on the interface transparency and the magnetic *** superconducting critical temperature can exhibit three types of characteristic behaviors with a variation of interface *** particular,the reentrance phenomenon of the superconductivity is observed at the interface transparencyγBξn/ξf=7.1,while the reentrance phenomenon disappears in the presence of magnetic *** addition,it is also found that the introduction of magnetic scattering results in the decrease of the spin-valve *** obtained results could provide some practical recommendations for the spin-valve effect in experimental observation.

关键词： transparency interface mutual

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