The single crystals and powder of a Yavapaiite Structure phosphate,namely,PbSb0.5Fe0.5(PO4)2,were synthesized by solid state method and characterized by X-ray single-crystal diffraction and powder diffraction.The ti...The single crystals and powder of a Yavapaiite Structure phosphate,namely,PbSb0.5Fe0.5(PO4)2,were synthesized by solid state method and characterized by X-ray single-crystal diffraction and powder diffraction.The title compound crystallizes in the monoclinic system,space group C2/c(No.15) with a = 16.716(4),b = 5.186(7),c = 8.130(2)A,β = 114.93(6)°,Z = 4,R(I 〉 2s(I)) = 0.0430,R indices(all data) = 0.0460,and T = 293(2) K.The title compound belongs to the Yavapaiite Structure A^(Ⅱ)M^(Ⅳ)(PO4)2 compounds,and the Sb1 atom and Fe1 atoms occupy the same site(M) and their occupancy factors are refined to be 0.5 and 0.5 having a sum occupancy factor of 1.0.Its structure consists of [M(PO)4]n^2n- layers running parallel to the(b,c) plane built up of cornerconnected MO6 octahedra and PO4 tetrahedra.Additionally,the calculations of energy band structure,and density of states have been performed with the density functional theory method.The studies of computational calculation and UV experimental results show that the new compound is an indirect band-gap insulator.展开更多
In this paper, we study the computative structure of computable function - a structure of computative tree, and, by analysis on it, got the most general algorithm and model for computation on computable functions.
This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenv...This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenvectors are transformed into multiple parameter forms,and the second-order perturbation sensitivity matrices of eigenvalues and eigenvectors are developed.With these formulations,the efficient methods based on the second-order Taylor expansion and second-order perturbation are obtained to estimate changes of eigenvalues and eigenvectors when the design parameters are changed. The presented method avoids direct differential operation,and thus reduces difficulty for computing the second-order sensitivity matrices of eigenpairs.A numerical example is given to demonstrate application and accuracy of the proposed method.展开更多
Two 3-D numerical models of the discrete element method (DEM) for impact problems are proposed. The models can calculate not only the impact problems of continuum and non-continuum, but also the transient process fr...Two 3-D numerical models of the discrete element method (DEM) for impact problems are proposed. The models can calculate not only the impact problems of continuum and non-continuum, but also the transient process from continuum to non-continuum. The stress wave propagation in a concrete block and a dynamic splitting process of a marble disc under impact loading are numerically simulated with the proposed models. By comparing the numerical results with the corresponding results obtained by the finite element method (FEM) and the experiments, it is proved that the models are reliable for three-dimensional impact problems.展开更多
For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics...For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.展开更多
The direct band gap ZnTe with transition metal (TM) impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson (mBJ) functional fo...The direct band gap ZnTe with transition metal (TM) impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson (mBJ) functional for performing the structural computations and detailed investigations of the optical characters in Zn1_xTMxTe (TM = Fe, Co) alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn1_xTMxTe (TM = Fe, Co) have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.展开更多
Objective image quality assessment(IQA)plays an important role in various visual communication systems,which can automatically and efficiently predict the perceived quality of images.The human eye is the ultimate eval...Objective image quality assessment(IQA)plays an important role in various visual communication systems,which can automatically and efficiently predict the perceived quality of images.The human eye is the ultimate evaluator for visual experience,thus the modeling of human visual system(HVS)is a core issue for objective IQA and visual experience optimization.The traditional model based on black box fitting has low interpretability and it is difficult to guide the experience optimization effectively,while the model based on physiological simulation is hard to integrate into practical visual communication services due to its high computational complexity.For bridging the gap between signal distortion and visual experience,in this paper,we propose a novel perceptual no-reference(NR)IQA algorithm based on structural computational modeling of HVS.According to the mechanism of the human brain,we divide the visual signal processing into a low-level visual layer,a middle-level visual layer and a high-level visual layer,which conduct pixel information processing,primitive information processing and global image information processing,respectively.The natural scene statistics(NSS)based features,deep features and free-energy based features are extracted from these three layers.The support vector regression(SVR)is employed to aggregate features to the final quality prediction.Extensive experimental comparisons on three widely used benchmark IQA databases(LIVE,CSIQ and TID2013)demonstrate that our proposed metric is highly competitive with or outperforms the state-of-the-art NR IQA measures.展开更多
The wave-induced seepage force is investigated on marine structures resting on or buried in the seabed.The bed is modelled as a poroelastic medium containing a nearly saturated water.The governing equations are solved...The wave-induced seepage force is investigated on marine structures resting on or buried in the seabed.The bed is modelled as a poroelastic medium containing a nearly saturated water.The governing equations are solved with Finite Element Method.For a pipeline buried in the seabed,agreement between the present numerical results and that of Cheng H.D.(1986)is quite satisfactory.展开更多
In this article,an effective technique is developed to efficiently obtain the output responses of parameterized structural dynamic problems.This technique is based on the conception of reduced basis method and the usa...In this article,an effective technique is developed to efficiently obtain the output responses of parameterized structural dynamic problems.This technique is based on the conception of reduced basis method and the usage of linear interpolation principle.The original problem is projected onto the reduced basis space by linear interpolation projection,and subsequently an associated interpolation matrix is generated.To ensure the largest nonsingularity,the interpolation matrix needs to go through a timenode choosing process,which is developed by applying the angle of vector spaces.As a part of this technique,error estimation is recommended for achieving the computational error bound.To ensure the successful performance of this technique,the offline-online computational procedures are conducted in practical engineering.Two numerical examples demonstrate the accuracy and efficiency of the presented method.展开更多
A finite volume(FV)method for simulating 3D Fluid-Structure Interaction(FSI)is presented in this paper.The fluid flow is simulated using a parallel unstructured multigrid preconditioned implicit compressible solver,wh...A finite volume(FV)method for simulating 3D Fluid-Structure Interaction(FSI)is presented in this paper.The fluid flow is simulated using a parallel unstructured multigrid preconditioned implicit compressible solver,whist a 3D matrix-free implicit unstructured multigrid finite volume solver is employed for the structural dynamics.The two modules are then coupled using a so-called immersed membrane method(IMM).Large-Eddy Simulation(LES)is employed to predict turbulence.Results from several moving boundary and FSI problems are presented to validate proposed methods and demonstrate their efficiency。展开更多
We study non-overlapping axis-parallel packings of 3D boxes with profits into a dedicated bigger box where rotation is either forbidden or permitted, and we wish to maximize the total profit. Since this optimization p...We study non-overlapping axis-parallel packings of 3D boxes with profits into a dedicated bigger box where rotation is either forbidden or permitted, and we wish to maximize the total profit. Since this optimization problem is NP-hard, we focus on approximation algorithms. We obtain fast and simple algorithms for the non-rotational scenario with approximation ratios 9 + ε and 8 + ε, as well as an algorithm with approximation ratio 7 + ε that uses more sophisticated techniques; these are the smallest approximation ratios known for this problem. Furthermore, we show how the used techniques can be adapted to the case where rotation by 90° either around the z-axis or around all axes is permitted, where we obtain algorithms with approximation ratios 6 + ε and 5 + ε, respectively. Finally our methods yield a 3D generalization of a packability criterion and a strip packing algorithm with absolute approximation ratio 29/4, improving the previously best known result of 45/4.展开更多
基金Supported by the National Natural Science Foundation of China(21101156 and 61376002)State Key Laboratory of Structure Chemistry(No.20150016)+1 种基金Outstanding Youth of Colleges and Universities of Department of Education,Fujian Province Natural Science Foundation for Youths(No.2016J05109)Fujian Education Department(No.JK2015056)
文摘The single crystals and powder of a Yavapaiite Structure phosphate,namely,PbSb0.5Fe0.5(PO4)2,were synthesized by solid state method and characterized by X-ray single-crystal diffraction and powder diffraction.The title compound crystallizes in the monoclinic system,space group C2/c(No.15) with a = 16.716(4),b = 5.186(7),c = 8.130(2)A,β = 114.93(6)°,Z = 4,R(I 〉 2s(I)) = 0.0430,R indices(all data) = 0.0460,and T = 293(2) K.The title compound belongs to the Yavapaiite Structure A^(Ⅱ)M^(Ⅳ)(PO4)2 compounds,and the Sb1 atom and Fe1 atoms occupy the same site(M) and their occupancy factors are refined to be 0.5 and 0.5 having a sum occupancy factor of 1.0.Its structure consists of [M(PO)4]n^2n- layers running parallel to the(b,c) plane built up of cornerconnected MO6 octahedra and PO4 tetrahedra.Additionally,the calculations of energy band structure,and density of states have been performed with the density functional theory method.The studies of computational calculation and UV experimental results show that the new compound is an indirect band-gap insulator.
基金Project supported by National Natural Science Foundation of China.
文摘In this paper, we study the computative structure of computable function - a structure of computative tree, and, by analysis on it, got the most general algorithm and model for computation on computable functions.
基金Project supported by the 985-Engineering Innovation of Graduate Students of Jilin Universitythe Science and Technology Development Foundation of Jilin Province(20070541)
文摘This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenvectors are transformed into multiple parameter forms,and the second-order perturbation sensitivity matrices of eigenvalues and eigenvectors are developed.With these formulations,the efficient methods based on the second-order Taylor expansion and second-order perturbation are obtained to estimate changes of eigenvalues and eigenvectors when the design parameters are changed. The presented method avoids direct differential operation,and thus reduces difficulty for computing the second-order sensitivity matrices of eigenpairs.A numerical example is given to demonstrate application and accuracy of the proposed method.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10572002 and 10732010.
文摘Two 3-D numerical models of the discrete element method (DEM) for impact problems are proposed. The models can calculate not only the impact problems of continuum and non-continuum, but also the transient process from continuum to non-continuum. The stress wave propagation in a concrete block and a dynamic splitting process of a marble disc under impact loading are numerically simulated with the proposed models. By comparing the numerical results with the corresponding results obtained by the finite element method (FEM) and the experiments, it is proved that the models are reliable for three-dimensional impact problems.
文摘For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.
基金supported by the Deanship of Scientific Research at King Saud University(for Shahid M Ramay)(Grant No.RG 1435-004)the University of the Punjab,Lahore for financial support through Faculty Research Grant Program(for M Hassan)the HEC Pakistan(Grant No.21-261/SRGP/R&D/HEC/2014)(for M Yaseen)
文摘The direct band gap ZnTe with transition metal (TM) impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson (mBJ) functional for performing the structural computations and detailed investigations of the optical characters in Zn1_xTMxTe (TM = Fe, Co) alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn1_xTMxTe (TM = Fe, Co) have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.
基金This work was supported by National Natural Science Foundation of China(Nos.61831015 and 61901260)Key Research and Development Program of China(No.2019YFB1405902).
文摘Objective image quality assessment(IQA)plays an important role in various visual communication systems,which can automatically and efficiently predict the perceived quality of images.The human eye is the ultimate evaluator for visual experience,thus the modeling of human visual system(HVS)is a core issue for objective IQA and visual experience optimization.The traditional model based on black box fitting has low interpretability and it is difficult to guide the experience optimization effectively,while the model based on physiological simulation is hard to integrate into practical visual communication services due to its high computational complexity.For bridging the gap between signal distortion and visual experience,in this paper,we propose a novel perceptual no-reference(NR)IQA algorithm based on structural computational modeling of HVS.According to the mechanism of the human brain,we divide the visual signal processing into a low-level visual layer,a middle-level visual layer and a high-level visual layer,which conduct pixel information processing,primitive information processing and global image information processing,respectively.The natural scene statistics(NSS)based features,deep features and free-energy based features are extracted from these three layers.The support vector regression(SVR)is employed to aggregate features to the final quality prediction.Extensive experimental comparisons on three widely used benchmark IQA databases(LIVE,CSIQ and TID2013)demonstrate that our proposed metric is highly competitive with or outperforms the state-of-the-art NR IQA measures.
文摘The wave-induced seepage force is investigated on marine structures resting on or buried in the seabed.The bed is modelled as a poroelastic medium containing a nearly saturated water.The governing equations are solved with Finite Element Method.For a pipeline buried in the seabed,agreement between the present numerical results and that of Cheng H.D.(1986)is quite satisfactory.
基金supported by the National Natural Science Foundation of China (10802028)the Major State Basic Research Development Program of China (2010CB832705)the National Science Fund for Distinguished Young Scholars (10725208)
文摘In this article,an effective technique is developed to efficiently obtain the output responses of parameterized structural dynamic problems.This technique is based on the conception of reduced basis method and the usage of linear interpolation principle.The original problem is projected onto the reduced basis space by linear interpolation projection,and subsequently an associated interpolation matrix is generated.To ensure the largest nonsingularity,the interpolation matrix needs to go through a timenode choosing process,which is developed by applying the angle of vector spaces.As a part of this technique,error estimation is recommended for achieving the computational error bound.To ensure the successful performance of this technique,the offline-online computational procedures are conducted in practical engineering.Two numerical examples demonstrate the accuracy and efficiency of the presented method.
文摘A finite volume(FV)method for simulating 3D Fluid-Structure Interaction(FSI)is presented in this paper.The fluid flow is simulated using a parallel unstructured multigrid preconditioned implicit compressible solver,whist a 3D matrix-free implicit unstructured multigrid finite volume solver is employed for the structural dynamics.The two modules are then coupled using a so-called immersed membrane method(IMM).Large-Eddy Simulation(LES)is employed to predict turbulence.Results from several moving boundary and FSI problems are presented to validate proposed methods and demonstrate their efficiency。
基金supported in part by DFG Project, Entwicklung und Analyse von Approximativen Algorithmen für Gemischte und Verallgemeinerte Packungs-und überdeckungsprobleme, JA 612/10-1,in part by the German Academic Exchange Service DAAD,in part by project AEOLUS, under EU Contract No. 015964, and in part by a Grant "DAAD Doktorandenstipendium" of the GermanAcademic Exchange Service DAAD. Part of this work was done in duration of visit to the LIG, Grenoble University.
文摘We study non-overlapping axis-parallel packings of 3D boxes with profits into a dedicated bigger box where rotation is either forbidden or permitted, and we wish to maximize the total profit. Since this optimization problem is NP-hard, we focus on approximation algorithms. We obtain fast and simple algorithms for the non-rotational scenario with approximation ratios 9 + ε and 8 + ε, as well as an algorithm with approximation ratio 7 + ε that uses more sophisticated techniques; these are the smallest approximation ratios known for this problem. Furthermore, we show how the used techniques can be adapted to the case where rotation by 90° either around the z-axis or around all axes is permitted, where we obtain algorithms with approximation ratios 6 + ε and 5 + ε, respectively. Finally our methods yield a 3D generalization of a packability criterion and a strip packing algorithm with absolute approximation ratio 29/4, improving the previously best known result of 45/4.