提出了一种图像编码算法ESPIHT(extended set partitioning in hierarchical trees).该算法能够通过以下3项措施提高SPIHT算法工作效率:(1) 全面引入快速提升小波变换;(2) 重新定义扩充零树结构;(3) 综合考虑人眼视觉特性.实验结果表明,...提出了一种图像编码算法ESPIHT(extended set partitioning in hierarchical trees).该算法能够通过以下3项措施提高SPIHT算法工作效率:(1) 全面引入快速提升小波变换;(2) 重新定义扩充零树结构;(3) 综合考虑人眼视觉特性.实验结果表明, ESPIHT算法是一种高效的图像压缩算法,其编解码速度、图像复原质量、内存需求量等关键技术指标均优于SPIHT等编码算法(特别是在低比特率下).展开更多
Topology optimization was developed as an advanced structural design methodology to generate innovative lightweight and high-performance configurations that are difficult to obtain with conventional ideas.Additive man...Topology optimization was developed as an advanced structural design methodology to generate innovative lightweight and high-performance configurations that are difficult to obtain with conventional ideas.Additive manufacturing is an advanced manufacturing technique building asdesigned structures via layer-by-layer joining material,providing an alternative pattern for complex components.The integration of topology optimization and additive manufacturing can make the most of their advantages and potentials,and has wide application prospects in modern manufacturing.This article reviews the main content and applications of the research on the integration of topology optimization and additive manufacturing in recent years,including multi-scale or hierarchical structural optimization design and topology optimization considering additive manufacturing constraints.Meanwhile,some challenges of structural design approaches for additive manufacturing are discussed,such as the performance characterization and scale effects of additively manufactured lattice structures,the anisotropy and fatigue performance of additively manufactured material,and additively manufactured functionally graded material issues,etc.It is shown that in the research of topology optimization for additive manufacturing,the integration of material,structure,process and performance is important to pursue high-performance,multi-functional and lightweight production.This article provides a reference for further related research and aerospace applications.展开更多
The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline （MTG） was studied. N2 adsorption-desorption res...The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline （MTG） was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2-20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.展开更多
Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agr...Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agriculture, and water and wastewater treatment. Their wide use is because of their many beneficial properties, such as framework and compositional flexibilities, physical and hydro‐thermal stabilities, non‐toxicity, high surface areas, exchangeable cations, and good cost‐benefit ratios. Although many zeolite applications depend on their microporous structures, this can cause diffusional constraints for bulky reactant and product molecules. There have been many efforts to overcome the intrinsic limitations of conventional zeolites by preparing nanosized and hierarchi‐cally structured zeolites. As a result of these efforts, several strategies have been established and the use of new zeolitic materials in various catalytic and adsorptive reactions has been investigated. Longer lifetimes, high catalytic performances, and postponed coking and catalyst deactivation can be achieved using hierarchical and nanosized zeolites. The aim of this review is to provide an over‐view of the enhanced properties of hierarchical and nanosized zeolites, and recent development methods for their synthesis. The advantages and disadvantages of each route are discussed, and the catalytic applications of nanozeolites and zeolites with secondary porosity, and a comparison with conventional zeolites, are briefly presented.展开更多
Researches on organization and structure in complex systems are academic and industrial fronts in modern sciences. Though many theories are tentatively proposed to analyze complex systems, we still lack a rigorous the...Researches on organization and structure in complex systems are academic and industrial fronts in modern sciences. Though many theories are tentatively proposed to analyze complex systems, we still lack a rigorous theory on them. Complex systems possess various degrees of freedom, which means that they should exhibit all kinds of structures. However, complex systems often show similar patterns and structures. Then the question arises why such similar structures appear in all kinds of complex systems. The paper outlines a theory on freedom degree compression and the existence of hierarchical self-organization for all complex systems is found. It is freedom degree compression and hierarchical self-organization that are responsible for the existence of these similar patterns or structures observed in the complex systems.展开更多
A variable-fidelity method can remarkably improve the efficiency of a design optimization based on a high-fidelity and expensive numerical simulation,with assistance of lower-fidelity and cheaper simulation(s).However...A variable-fidelity method can remarkably improve the efficiency of a design optimization based on a high-fidelity and expensive numerical simulation,with assistance of lower-fidelity and cheaper simulation(s).However,most existing works only incorporate‘‘two"levels of fidelity,and thus efficiency improvement is very limited.In order to reduce the number of high-fidelity simulations as many as possible,there is a strong need to extend it to three or more fidelities.This article proposes a novel variable-fidelity optimization approach with application to aerodynamic design.Its key ingredient is the theory and algorithm of a Multi-level Hierarchical Kriging(MHK),which is referred to as a surrogate model that can incorporate simulation data with arbitrary levels of fidelity.The high-fidelity model is defined as a CFD simulation using a fine grid and the lower-fidelity models are defined as the same CFD model but with coarser grids,which are determined through a grid convergence study.First,sampling shapes are selected for each level of fidelity via technique of Design of Experiments(DoE).Then,CFD simulations are conducted and the output data of varying fidelity is used to build initial MHK models for objective(e.g.C_D)and constraint(e.g.C_L,C_m)functions.Next,new samples are selected through infillsampling criteria and the surrogate models are repetitively updated until a global optimum is found.The proposed method is validated by analytical test cases and applied to aerodynamic shape optimization of a NACA0012 airfoil and an ONERA M6 wing in transonic flows.The results confirm that the proposed method can significantly improve the optimization efficiency and apparently outperforms the existing single-fidelity or two-level-fidelity method.展开更多
文摘提出了一种图像编码算法ESPIHT(extended set partitioning in hierarchical trees).该算法能够通过以下3项措施提高SPIHT算法工作效率:(1) 全面引入快速提升小波变换;(2) 重新定义扩充零树结构;(3) 综合考虑人眼视觉特性.实验结果表明, ESPIHT算法是一种高效的图像压缩算法,其编解码速度、图像复原质量、内存需求量等关键技术指标均优于SPIHT等编码算法(特别是在低比特率下).
基金supported by National Key Research and Development Program(2017YFB1102800)Key Project of NSFC(51790171,51761145111)NSFC for Excellent Young Scholars(11722219)。
文摘Topology optimization was developed as an advanced structural design methodology to generate innovative lightweight and high-performance configurations that are difficult to obtain with conventional ideas.Additive manufacturing is an advanced manufacturing technique building asdesigned structures via layer-by-layer joining material,providing an alternative pattern for complex components.The integration of topology optimization and additive manufacturing can make the most of their advantages and potentials,and has wide application prospects in modern manufacturing.This article reviews the main content and applications of the research on the integration of topology optimization and additive manufacturing in recent years,including multi-scale or hierarchical structural optimization design and topology optimization considering additive manufacturing constraints.Meanwhile,some challenges of structural design approaches for additive manufacturing are discussed,such as the performance characterization and scale effects of additively manufactured lattice structures,the anisotropy and fatigue performance of additively manufactured material,and additively manufactured functionally graded material issues,etc.It is shown that in the research of topology optimization for additive manufacturing,the integration of material,structure,process and performance is important to pursue high-performance,multi-functional and lightweight production.This article provides a reference for further related research and aerospace applications.
基金supported by the Fundamental Research Funds for the Central Universities, HUST (No. Z2009008)the National Natural Science Foundation of China (No. 20973068)
文摘The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline （MTG） was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2-20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.
文摘Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agriculture, and water and wastewater treatment. Their wide use is because of their many beneficial properties, such as framework and compositional flexibilities, physical and hydro‐thermal stabilities, non‐toxicity, high surface areas, exchangeable cations, and good cost‐benefit ratios. Although many zeolite applications depend on their microporous structures, this can cause diffusional constraints for bulky reactant and product molecules. There have been many efforts to overcome the intrinsic limitations of conventional zeolites by preparing nanosized and hierarchi‐cally structured zeolites. As a result of these efforts, several strategies have been established and the use of new zeolitic materials in various catalytic and adsorptive reactions has been investigated. Longer lifetimes, high catalytic performances, and postponed coking and catalyst deactivation can be achieved using hierarchical and nanosized zeolites. The aim of this review is to provide an over‐view of the enhanced properties of hierarchical and nanosized zeolites, and recent development methods for their synthesis. The advantages and disadvantages of each route are discussed, and the catalytic applications of nanozeolites and zeolites with secondary porosity, and a comparison with conventional zeolites, are briefly presented.
基金Supported by the Science Foundation of the Ministry of Education of China for the Returned Overseas Chinese Scholars
文摘Researches on organization and structure in complex systems are academic and industrial fronts in modern sciences. Though many theories are tentatively proposed to analyze complex systems, we still lack a rigorous theory on them. Complex systems possess various degrees of freedom, which means that they should exhibit all kinds of structures. However, complex systems often show similar patterns and structures. Then the question arises why such similar structures appear in all kinds of complex systems. The paper outlines a theory on freedom degree compression and the existence of hierarchical self-organization for all complex systems is found. It is freedom degree compression and hierarchical self-organization that are responsible for the existence of these similar patterns or structures observed in the complex systems.
基金sponsored by the National Natural Science Foundation of China(Nos.11772261 and 11972305)Aeronautical Science Foundation of China(No.2016ZA53011)Foundation of National Key Laboratory(No.JCKYS2019607005).
文摘A variable-fidelity method can remarkably improve the efficiency of a design optimization based on a high-fidelity and expensive numerical simulation,with assistance of lower-fidelity and cheaper simulation(s).However,most existing works only incorporate‘‘two"levels of fidelity,and thus efficiency improvement is very limited.In order to reduce the number of high-fidelity simulations as many as possible,there is a strong need to extend it to three or more fidelities.This article proposes a novel variable-fidelity optimization approach with application to aerodynamic design.Its key ingredient is the theory and algorithm of a Multi-level Hierarchical Kriging(MHK),which is referred to as a surrogate model that can incorporate simulation data with arbitrary levels of fidelity.The high-fidelity model is defined as a CFD simulation using a fine grid and the lower-fidelity models are defined as the same CFD model but with coarser grids,which are determined through a grid convergence study.First,sampling shapes are selected for each level of fidelity via technique of Design of Experiments(DoE).Then,CFD simulations are conducted and the output data of varying fidelity is used to build initial MHK models for objective(e.g.C_D)and constraint(e.g.C_L,C_m)functions.Next,new samples are selected through infillsampling criteria and the surrogate models are repetitively updated until a global optimum is found.The proposed method is validated by analytical test cases and applied to aerodynamic shape optimization of a NACA0012 airfoil and an ONERA M6 wing in transonic flows.The results confirm that the proposed method can significantly improve the optimization efficiency and apparently outperforms the existing single-fidelity or two-level-fidelity method.
