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The influence of the wake of a flapping wing on the production of aerodynamic forces

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Acta Mechanica Sinica 2005年第5期21卷 411-418页

作者： Jianghao wu Mao sun Ministry-of-Education Key Laboratory of Fluid Mechanics Institute of Fluid Mechanics Beihang University Beijing 100083 China

The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the method of computational fluid dynamics. The wake effect is isolated by comparing the forces and flows of the starting stroke （when the wake has not developed） with those of a later stroke （when the wake has developed）. The following has been shown. （1） The wake effect may increase or decrease the lift and drag at the beginning of a half-stroke （downstroke or upstroke）, depending on the wing kinematics at stroke reversal. The reason for this is that at the beginning of the half-stroke, the wing “impinges” on the spanwise vorticity generated by the wing during stroke reversal and the distribution of the vorticity is sensitive to the wing kinematics at stroke reversal. （2） The wake effect decreases the lift and increases the drag in the rest part of the half-stroke. This is because the wing moves in a downwash field induced by previous half-stroke＇s starting vortex, tip vortices and attached leading edge vortex （these vortices form a downwash producing vortex ring）. （3） The wake effect decreases the mean lift by 6%-18% （depending on wing kinematics at stroke reversal） and slightly increases the mean drag. Therefore, it is detrimental to the aerodynamic performance of the flapping wing.

关键词： Insect. Flapping. Unsteady aerodynamics.Wing/wake interaction. CFD analysis

非厄米PT对称多通道光波导体系的调控及动力学

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原子与分子物理学报 2025年第1期42卷 108-117页

作者：孙武叶伏秋张光成吉首大学物理与机电工程学院吉首416000

宇称-时间(PARITY-TIME PT)对称光学波导系统中有关PT对称性的调控主要通过周期性变化的复折射率材料来实现.本文中我们给出了一种对于已耦合的双通道波导体系中额外引入周期调制的中性波导操纵PT对称性的构型,通过高频近似将系统转换... 详细信息

宇称-时间(PARITY-TIME PT)对称光学波导系统中有关PT对称性的调控主要通过周期性变化的复折射率材料来实现.本文中我们给出了一种对于已耦合的双通道波导体系中额外引入周期调制的中性波导操纵PT对称性的构型,通过高频近似将系统转换为重整化参数后的等效未调制系统后,发现可以通过额外引入单频周期调制的光波导去调控体系的PT对称性,并且讨论了周期调制的非厄米三通道波导体系的能谱特性.最后通过解析和数值的方法给出了光在非厄米三通道光学波导中的动力学演化.

关键词： PT对称非厄米三通道波导

Building Height Trends and Their Influencing Factors under China’s Rapid Urbanization:A Case Study of Guangzhou,1960–2017

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Chinese Geographical Science 2020年第6期30卷 993-1004页

作者： sun wu LI Tao School of Geography South China Normal UniversityGuangzhou 510631China Northwest Land and Resource Research Center Shaanxi Normal UniversityXi'an 710119China

Understanding the spatiotemporal patterns of three-dimensional urban forms,especially building height,can have important implications for improving urban air quality and mitigating the urban heat island effect by optimizing urban planning and management *** study investigated building height evolution and its influencing factors over approximately half a century(1960–2017)in Guangzhou,*** results indicated that the logarithmic declines in height,quantity,and area of urban buildings followed Zapf’s law,which restricts the three-dimensional shape of the urban *** urban building height decreased from the center to the periphery of the city and decreased with decreasing altitude and increasing distance from main *** characteristics constituted the three main spatial differentiation rules of building height in the central district of Guangzhou,and all exhibited a logarithmic decrease,which gradually strengthened over *** development of a double-layered height structure of low-rise and high-rise buildings between 1990 and 2017 was a notable manifestation of the increase in vertical urban height over *** three factors of city center,altitude,and accessibility,which represent centrality,low relief,proximity to water,and proximity to road networks,highlighted the roles of traffic accessibility and commercial attraction in building height *** importance of location macroscopically depends on the combined effect of the geographical pattern,urban planning,and market forces of cities located on a plain near hill or by a *** principle of profit orientation restricted spatiotemporal building height patterns.

关键词： building height urban form altitude road formative mechanism Guangzhou,China

Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles

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Journal of University of Science and Technology Beijing 2008年第6期15卷 769-774页

作者： Qianlin wu Yangshan sun Guoqing Li School of Material Science and Engineering Southeast University Nanjing 211189 China

The electroslag remelting （ESR） layer reinforced by TiC particles was obtained by electroslag remelting. The microstructure and wear properties of the ESR layer were studied by means of scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis （SHS） reaction during the electroslag remelting process. The size of TiC particles is in the range of 1-10 μm, and the distribution of TiC particles is uniform, from outside to inside of the ESR layer, and the volume fraction and the size of TiC particles decrease gradually. Molten iron and slag flow into porosity due to the SHS process leading to rapid densification and the elimination of porosity in the ESR layer during the ESR process. TiC particles enhance the wear resistance of the ESR layer, whereas CaF2 can improve the high temperature lubricating property of the ESR layer.

关键词： electroslag remelting (ESR) TiC particles porosity wear resistance lubricating property

Neutronic analysis of deuteron-driven spallation target

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Nuclear Science and Techniques 2021年第9期32卷 52-60页

作者： Wei-Wei Qiu wu sun Jun Su Sino-French Institute of Nuclear Engineering and Technology Sun Yat-sen UniversityZhuhai 519082China

Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission *** this study,the Geant4 toolkit was used to simulate the inter-action between a deuteron beam at 500 MeV and a com-posite target composed of alternating lead-bismuth eutectic(LBE)and *** water was used because it may be employed as a target *** energy spectrum,neu-tron yield,average energy,and total energy of the emitted neutrons were calculated for different thicknesses and thickness ratios between the LBE and *** a constant target thickness,the neutron yield increases with an increasing thickness ratio of LBE to H 2 O,while the aver-age energy of the emitted neutrons decreases with an increasing in the aforementioned thickness *** two aspects support the use of a pure target,either LBE or ***,with an increasing LBE-to-H 2 O thickness ratio,the total energy of the emitted neutrons increases and then *** result supports the addition of water into the LBE *** angular distributions of the emitted neutrons show that the rear of the target is suit-able for loading nuclear waste containing minor actinides and long-lifetime fission products.

关键词： Long-lived nuclear waste product Accelerator-driven sub-critical system Deuteron-induced spallation target Neutron spectrum

Degenerate Orbit Flip Homoclinic Bifurcations with Higher Dimensions

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Acta Mathematica Sinica,English Series 2006年第6期22卷 1651-1656页

作者： Ran Chao wu Jian Hua sun Department of Mathematics Nanjing University Nanjing 210093 P. R. China

Bifurcations of a degenerate homoclinic orbit with orbit flip in high dimensional system are studied. By establishing a local coordinate system and a Poincare map near the homoclinic orbit, the existence and uniqueness of 1-homoclinic orbit and 1-periodic orbit are given. Also considered is the existence of 2-homoclinic orbit and 2-periodic orbit. In additon, the corresponding bifurcation surfaces are given.

关键词： Orbit flip Homoclinic bifurcations Poincaré map

Magnetic moments of odd-A aluminum isotopes in covariant density functional theory

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Communications in Theoretical Physics 2020年第5期72卷 58-64页

作者： Jian Li wu-Ji sun College of Physics Jilin UniversityChangchun 130012China Department of Physics Western Michigan UniversityKalamazooMI 49008United States of America

The ground-state properties,especially the magnetic moments,of odd-A aluminum isotopes have been studied and well reproduced in covariant density functional theory after considering the rotational *** present calculations support the rotational structure in the ground state of odd-A aluminum isotopes,*** ground state 5/2^+is built on the intrinsic state 5/2[202].In addition,the contribution from the time-odd fields is also discussed.

关键词： nuclear magnetic moment covariant density functional theory aluminum isotopes rotational coupling time-odd fields

Energy staggering parameters in nuclear magnetic rotational bands

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Chinese Physics C 2019年第9期43卷 83-89页

作者： wu-Ji sun Jian Li College of Physics Jilin University

This study presents the systematics of energy staggering for magnetic rotational bands with M1 and E2 transition properties,which are strictly consistent with the features of good candidates of magnetic rotational bands in the A^80,110,130,and 190 mass *** regularities exhibited by these bands with respect to the staggering parameter,which increases with increasing spin,are in agreement with the semiclassical description of shears ***,the abnormal behaviour in the backbend regions or close to band termination has also been *** the magnetic dipole bands with same configuration in three N=58 isotones,i.e.,103Rh,105Ag,and 107In,as examples,the transition from chiral to magnetic rotation with the proton number approaching Z=50 is ***,the self-consistent tilted axis and principle axis cranking relativistic mean-field theories are applied to investigate the rotational mechanism in the dipole band of 105Ag.

关键词： energy staggering magnetic rotational band shears mechanism cranking relativistic mean-field theory

Ranking approach of cross-efficiency based on improved TOPSIS technique

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Journal of Systems Engineering and Electronics 2011年第4期22卷 604-608页

作者： Jie wu Jiasen sun Yong Zha Liang Liang School of Management University of Science and Technology of China Hefei 230026 R R. China

The cross-efficiency evaluation method is reviewed which is developed as a data envelopment analysis （DEA） extensive tool. The cross-efficiency evaluation method is utilized to identify the decision making unit （DMU） with the best practice and to rank the DMUs by their respective cross-efficiency scores. The main drawbacks of the cross-efficiency evaluation method when the ultimate average cross-efficiency scores are used to evalu- ate and rank the DMUs are also pointed out. With the research gap, an improved technique for order preference by similarity to ideal solution （TOPSIS） is introduced to rank the crossfficiency by eliminating the average assumption. Finally, an empirical example is illustrated to examine the validity of the proposed method.

关键词： data envelopment analysis (DEA) cross-efficiency,improved technique for order preference by similarity to ideal solu-tion (TOPSIS) decision making unit (DMU).