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Microstructure Characteristics of the Eutectics of Die Cast AM60B Magnesium Alloy

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Journal of Materials Science & Technology 2011年第12期27卷 1150-1156页

作者： MengwuWu Shoumei xiong Department of Mechanical Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Automobile Safety and Energy Tsinghua University Beijing 100084 China

Under the cold-chamber high pressure die casting （HPDC） process, samples were produced with AM60B magnesium alloy to investigate the microstructure characteristics of the eutectics, especially focusing on the constitution, morphology and distribution of the eutectics over cross section of the castings. Attentions were also paid to study the effect of heat treatment on the eutectics in the die castings. Based on experimental analysis using optical microscopy （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectroscopy （EDS）, it was determined that fully divorced eutectics consisting of c^-Mg and l%MglzA112 appeared at the grain boundary of the primary c^-Mg in the as-cast microstructure. Islands and networks of β-Mg17Al12 phase were observed in the central region of the castings, while the β-Mg17Al12 phase revealed a more dispersed and granular morphology on the surface layer. The two phases ratio β/α in the central region of the castings was approximately 10%, which was higher than that on the surface layer. Besides, the defect bands contained a higher percentage of the eutectics than the adjacent regions. After aging treatment （T6）, only α-Mg phase was detected by XRD in the AM60B magnesium alloy, though a small amount of precipitated β-MgITAI12 phase was observed at the grain boundary. In contrast to the microstructure of die cast AZ91D magnesium alloy under the same T0 heat treatment, no discontinuous precipitation of the β-MgITAI12 phase was observed in AMO0B magnesium alloy die castings.

关键词： AM60B magnesium alloy High pressure die casting Fully divorced eutectic Heat treatment

Revising Space Groups from Simulated SHELXfcf Structure Factors. More Examples of Incorrect Space Groups, an Example of a Chemically-Incorrect Structure and the Special Case of Pgl to PRevisions

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Chinese Journal of Structural Chemistry 2003年第6期22卷 691-699页

作者： NgSeikWeng XIEZhao-xiong DepartmentofChemistry UniversityofMalaya50603KualaLumpurMalaysia StateKeyLaboratoryforPhysicalChemistryofSolidSurfaces XiamenUniversityXiamen361005China

The structure factors of any crystal structure can be simulated from its atomic coordinates (and temperature factors) in a SHELXL-97 run on a dummy hkl in which only the scale factor is refined. The squares of the structure factors are retrieved from the fcf, and such simulated data are used in the revision of the space groups of several incorrectly-refined crystal structures. Two cases, a P1 to P1 revision and a chemically-incorrect structure that is refined in a correct space group, are discussed.

关键词： space-group correction crystal structure revision simulated structure factors

Rapid Springback Compensation for Age Forming Based on Quasi Newton Method

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Chinese Journal of Mechanical Engineering 2014年第3期27卷 551-557页

作者： xiong Wei GAN Zhong xiong Shipeng XIA Yushan Department of Mechanical Engineering Guilin University of Aerospace Technology Key Laboratory of Contemporary Design and Integrated Manufacturing Technology of Ministry of Education Northwestern Polytechnical University

Iterative methods based on finite element simulation are effective approaches to design mold shape to compensate springback in sheet metal forming. However, convergence rate of iterative methods is difficult to improve greatly. To increase the springback compensate speed of designing age forming mold, process of calculating springback for a certain mold with finite element method is analyzed. Springback compensation is abstracted as finding a solution for a set of nonlinear functions and a springback compensation algorithm is presented on the basis of quasi Newton method. The accuracy of algorithm is verified by developing an ABAQUS secondary development program with MATLAB. Three rectangular integrated panels of dimensions 710 mmx750 mm integrated panels with intersected ribs of 10 mm are selected to perform case studies. The algorithm is used to compute mold contours for the panels with cylinder, sphere and saddle contours respectively and it takes 57%, 22% and 33% iterations as compared to that of displacement adjustment （DA） method. At the end of iterations, maximum deviations on the three panels are 0.618 4 mm, 0.624 1 mm and 0.342 0 mm that are smaller than the deviations determined by DA method （0.740 8 mm, 0.740 8 mm and 0.713 7 mm respectively）. In following experimental verification, mold contour for another integrated panel with 400 ram^380 mm size is designed by the algorithm. Then the panel is age formed in an autoclave and measured by a three dimensional digital measurement devise. Deviation between measuring results and the panel＇s design contour is less than 1 mm. Finally, the iterations with different mesh sizes （40 mm, 35 mm, 30 mm, 25 mm, 20 mm） in finite element models are compared and found no considerable difference. Another possible compensation method, Broyden-Fletcher-Shanmo method, is also presented based on the solving nonlinear fimctions idea. The Broyden-Fletcher-Shanmo method is employed to compute mold contour for the second panel. It

关键词： age forming quasi Newton method springback compensation mold design displacement adjustment method

Corrections of Original CFPREV Control in LCC-HVDC Links and Analysis of Its Inherent Plateau Effect

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CSEE Journal of Power and Energy Systems 2022年第1期8卷 10-16页

作者： Dachuan Tian Xiaofu xiong College of Automation Chongqing University of Posts and TelecommunicationsChongqing 400065China School of Electrical Engineering Chongqing UniversityChongqing 400044China

The most effective approach to suppressing the first commutation failure(CF)of the LCC-HVDC link at fault inception is to advance firings of the inverter,and the commutation failure prevention(CFPREV)control is the most commonly used method in practical ***,it is discovered in this study that there exist a few serious defects in its original scheme,and thus targeted vital corrections were ***,an interesting phenomenon termed the plateau effect,which states that an excessive advancement of firings will contrarily and inevitably lead to more commutation failures,is also revealed and *** turns out that the inherent commutation dents of the Graetz bridge should be primarily responsible,which bridges the knowledge gap and further enhances the cognition of the limitation of CFPREV control,and it may also be conducive to the design of related control *** results then validate the necessity of these presented corrections and confirm the existence of the plateau effect.

关键词： Commutation failure CFPREV LCC-HVDC transmission plateau effect

Q-Learning-Based Target Selection for Bearings-Only Autonomous Navigation

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Journal of Systems Science & Complexity 2021年第4期34卷 1401-1425页

作者： xiong Kai WEI Chunling Science and Technology on Space Intelligent Control Laboratory Beijing Institute of Control EngineeringBeijing 100094China

This paper presents a Q-learning-based target selection algorithm for spacecraft autonomous navigation using bearing observations of known visible *** the considered navigation system,the position and velocity of the spacecraft are estimated using an extended Kalman filter(EKF)with the measurements of inter-satellite line-of-sight(LOS)vectors obtained via an onboard star *** paper focuses on the selection of the appropriate target at each observation period for the star camera adaptively,such that the performance of the EKF is *** derive an effective algorithm,a Q-function is designed to select a proper observation region,while a U-function is introduced to rank the targets in the selected *** the Q-function and the U-function are constructed based on the sequence of innovations obtained from the *** efficiency of the Q-learning-based target selection algorithm is illustrated via numerical simulations,which show that the presented algorithm outperforms the traditional target selection strategy based on a Cramer-Rao bound(CRB)in the case that the prior knowledge about the target location is inaccurate.

关键词： Bearings-only autonomous navigation convergence analysis extended Kalman filtering Q-Learning target selection

Influence of modeling approaches and structural parameters on impact resistance of the human porous cranium

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Acta Mechanica Sinica 2021年第6期37卷 910-928,I0001页

作者： Qianqian Wu Jian xiong Center for Composite Materials and Structures Harbin Institute of TechnologyHarbin150001China

Failure mechanism and impact resistance of a human porous cranium are studied in detail by means of theoretical and numerical *** is hypothesized that pore distribution of a cranium directly affects cranial energy absorption,and a stretched beam model and a real beam model are taken as the example for the ***,for the purpose of comparison with numerical results,a theoretical model is also proposed for the prediction of residual velocity and contact force of the impactor for an impacted *** with the real beam model,the stretched beam model containing through-thickness pores is easily deformed under the impact,thereby buffering well the external impact *** energy absorption efficiency of both the stretched beam model and real beam model is concerned with the threshold velocity for penetration which is directly related to the size of the structural damage ***,there is good agreement between numerical and theoretical *** addition,the effect of structural geometric parameters(shape and size of the impactor)on the impact resistance of the skull bone is theoretically *** study provides reference for the evaluation of the energy absorption and failure mechanism of the skull under impact loads.

关键词： Skull porous structure Impact resistance Modeling approach Theoretical prediction Influence of structural parameters

Chaos in a topologically transitive system

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Science China Mathematics 2005年第7期48卷 929-939页

作者： xiong Jincheng South China Normal University Guangzhou 510631 China

The chaotic phenomena have been studied in a topologically transitive system and it has been shown that the erratic time dependence of orbits in such a topologically transitive system is more complicated than what described by the well-known technology "Li-Yorke chaos". The concept "sensitive dependency on initial conditions" has been generalized, and the chaotic phenomena has been discussed for transitive systems with the generalized sensitive dependency property.

关键词： chaos, topological transitive, topologically dynamical systems, sensitive dependence.

Progressive damage behaviors of woven composite laminates subjected to LVI, TAI and CAI

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Chinese Journal of Aeronautics 2020年第10期33卷 2807-2823页

作者： Zhengqiang CHENG Junjiang xiong School of Transportation Science and Engineering Beihang UniversityBeijing 100083China

This paper seeks to deal with progressive damage behaviors of woven composite laminates subjected to low-velocity impact(LVI),tension-after-impact(TAI)and compression-afterimpact(CAI).The LVI,TAI and CAI tests were conducted on woven carbon fibre lamina3238 A/CF3052 and woven glass fibre lamina 3238 A/EW250 F,and the time-dependent LVI contact force and deflection curves,static TAI and CAI load versus displacement curves were determined and discussed.A modified progressive damage model was presented for explicit dynamic LVI and implicit static TAI and CAI analysis by using basic material properties and geometrical dimensions,and progressive damage LVI,TAI and CAI behaviors of woven composite laminates were simulated,demonstrating a good correlation between simulations and experiments.

关键词： Compression after impact Low velocity impact Progressive damage Tension after impact Woven composite laminates

Photoelectrochemical oxygen atom transfer enabling efficient selective oxygenation

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Science China Chemistry 2022年第1期65卷 5-6页

作者： Yujie xiong School of Chemistry and Materials Science University of Science and Technology of ChinaHefei 230026China

Photoelectrochemical(PEC)technique represents a promising approach to chemical transformation by harvesting sustainable solar *** the wide applications of PEC systems such as environmental remediation and solar energy conversion,the reported PEC reactions are dominated by the radical-based processes that are initiated by the single electron transfer between photo-induced carriers and adsorbed species on photoelectrode surface[1,2].For instance,hydroxyl radicals are often involved in the PEC oxidation *** well known,it is a grand challenge to control the formation and evolution rates of radicals,which inevitably leads to the unsatisfactory product selectivity of PEC ***,such a circumstance brings about a question to the research community whether a different mechanism can be established to sustain efficient and selective ***,based on their previous findings on PEC water oxidation[3,4],Zhao and coworkers[5]reported that many substrates can be oxidized in an oxygen atom transfer(OAT)pathway,a non-radical two electron process,to oxygenated products byα-Fe2O3 photoanodes.

关键词： transfer electrochemical radical