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First-principles study of the structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing various imperfections

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Chinese Physics B 2016年第5期25卷 410-417页

作者：张研段理 Vincent Ji 徐可为 School of Materials Science and Engineering Chang'an University Xi 'an 710061 China ICMMO/SP2M UMR CNRS 8182 Universite Paris- Sud 91405 Orsay Cedex France State Key Laboratory for Mechanical Behavior of Materials Xi' an Jiaotong University Xi' an 710049 China

The structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing eight different imperfections of FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, V_（Fe）, V_（Re）, VOor V_（Sr） vacancies have been studied by using the first-principles projector augmented wave（PAW） within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction（GGA＋U）. No obvious structural changes are observed for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, or VSrvacancy defects. However, the six（eight） nearest oxygen neighbors of the vacancy move away from（close to） VFeor V_（Re）（VO） vacancies. The half-metallic（HM） character is maintained for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re4 interchange, V_（Fe）,VO or V_（Sr） vacancies, while it vanishes when the Fe1–Re1 interchange or VRevacancy is presented. So the Fe1–Re1 interchange and the VRevacancy defects should be avoided to preserve the HM character of Sr_2FeReO_6 and thus usage in spintronic devices. In the FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges cases, the spin moments of the Fe（Re）cations situated on Re（Fe） antisites are in an antiferromagnetic coupling with those of the Fe（Re） cations on the regular sites. In the V_（Fe）, V_（Re）, VO, or V_（Sr） vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice,while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μtot（μB/f.u.） of the imperfect Sr_2FeReO_6 containing eight different defects decrease in the sequence of VSrvacancy（3.50）, VRevacancy（3.43）,FeReantisite（2.74）, VOvacancy（2.64）, VFevacancy（2.51）, ReFeantisite（2.29）, Fe1–Re4 interchange（1.96）, Fe1–Re1interchange（1.87）, and the mechanisms of the saturation magnetization reduction have been analyzed.

关键词： double perovskite imperfections electronic properties magnetic properties

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THE INFLUENCE OF imperfections UPON THE CRITICAL LOAD OF STRUCTURES

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Applied Mathematics and Mechanics(English Edition) 1999年第10期20卷 1108-1115页

作者：朱正佑丛玉豪 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai P R China Department of Mathematics Shanghai University Shanghai P R China College of Mathematical Sciences Shanghai Normal University Shanghai P R China

By means of the theory of universal unfolding, the influence of multi-imperfections upon the critical load of structure in engineering is analysed in this paper. For the pitchfork problem, a lower bound of increments of the critical loads caused by imperfections of the structures is given. A simple and available numerical method for computing the lower bound is described.

关键词： imperfections critical load pitchfork universal unfolding

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Buckling and post-buckling of rotationally restrained columns with imperfections

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Science China(Physics,Mechanics & Astronomy) 2012年第8期55卷 1519-1522页

作者： CAI JianGuo XU YiXiang FENG Jian ZHANG Jin Key Lab of C&PC Structures of Education of Ministry Southeast University Nanjing 210096 China National Engineering Research Center for Prestress Southeast University Nanjing 210096 China Department of Civil Engineering Strathclyde University Glasgow UK

The stability of imperfect columns has been studied by many researchers. Often the ends of a column are not necessarily fixed or pin-ended for practical structures. Therefore, rotationally restrained columns having an initial imperfection in an asymmetric mode have been studied in this paper. An elastic formula using the large deflection theory was given, and the shooting method was used to obtain the equilibrium paths and critical loads. Then the relationship between the end rotation and rotational restraints has been studied and discussed followed by a detailed discussion on the influence of imperfection on the column behaviour.

关键词： columns buckling imperfections structural stability supports

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Numerical Analysis of Physical and Geometrical imperfections in Cellular Beams

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Open Journal of Civil Engineering 2017年第1期7卷 116-129页

作者： Carlos Humberto Martins Felipe Piana Vendramell Ferreira Alexandre Rossi Eduardo Vicente Wolf Trentini State University of Maringá Maringá Brazil

Cellular beams are appropriate for large spans with relatively small loads or for conditions in which strain dictates dimensioning. Another important advantage of cellular beams is the possibility of passing utility ducts through the openings, which avoids cutting through the web of the beam or increasing the construction height, which occurs when the ducts pass under the beams. Geometrical imperfections result from a lack of straightness during fabrication of rolled profiles. Geometric imperfections are represented numerically by an initial curvature. Additionally, the physical imperfections of rolled profiles result from the appearance of residual stresses. The condition that creates residual stresses in steel is the result of thermal and mechanical industrial processes. In this study, numerical analyses are performed with cellular beams using Finite Element Method software. During the simulations, through non-linear geometric and physical analyses, geometric imperfections were varied, where lateral torsional buckling in cellular beams was considered as a function of the unrestrained length. In the boundary, conditions were restrained displacements in the axis X, Y, Z and rotation about X-axis, thus simulating the fork support. The beams are submitted to uniform bending and concentrated load. The results from the numerical analyses were compared with the calculation procedures, which verified that the results were significant.

关键词： Cellular Beams Physical imperfections Geometrical imperfections Lateral Torsional Buckling

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Buckling of composite cylindrical shells with ovality and thickness variation subjected to hydrostatic pressure

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Defence Technology（防务技术） 2022年第5期18卷 862-875页

作者： Zhun Li Ke-chun Shen Xin-hu Zhang Guang Pan School of Marine Science and Technology Northwestern Polytechnical UniversityXi'an710072China Key Laboratory for Unmanned Underwater Vehicle Northwestern Polytechnical UniversityXi'an710072China Structural Ceramics and Composites Engineering Research Center Shanghai Institute of CeramicsChinese Academy of SciencesShanghai200050China

The initial geometric imperfection is one of the primary factors affecting the buckling behaviors of composite cylindrical shells under hydrostatic *** this study,ovality and thickness variations as two representative types of the geometric imperfections are *** measuring the geometric imperfections,a typical carbon fiber reinforced polymers(CFRP)cylindrical shell is tested to obtain the buckling *** buckling behaviors of the shell sample are analyzed in combination with the strain *** using the nonlinear numerical analysis,the buckling shapes of the CFRP cylinder shells with different combinations of ovality and thickness variation are firstly *** rules of influence of such imperfections on the buckling pressure are then obtained by nonlinear regression ***,an empirical formula is proposed to predict the buckling pressure of the composite cylinder shells,and the calculated results from the formula are in good agreement with the numerical results.

关键词： Composite Cylindrical shell Buckling Hydrostatic pressure imperfections

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An improved differential evolution algorithm for learning high-fidelity quantum controls

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Science Bulletin 2019年第19期64卷 1402-1408页

作者： Xiaodong Yang Jun Li Xinhua Peng CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics University of Science and Technology of ChinaHefei230026China Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and TechnologyShenzhen518055China Center for Quantum Computing Peng Cheng LaboratoryShenzhen518055China Shenzhen Key Laboratory of Quantum Science and Engineering Southern University of Science and TechnologyShenzhen518055China Synergetic Innovation Centre of Quantum Information&Quantum Physics University of Science and Technology of ChinaHefei230026China

Precisely and efficiently designing control pulses for the preparation of quantum states and quantum gates are the fundamental tasks for quantum ***-based optimal control methods are the routine to design such ***,the gradient information is often difficult to calculate or measure,especially when the system is not well calibrated or in the presence of various ***-free evolutionary algorithm is an alternative choice to accomplish this task but usually with ***,we design an efficient mutation rule by using the information of the current and the former individuals *** leads to our improved differential evolution algorithm,called da *** demonstrate its performance,we numerically benchmark the pulse optimization for quantum states and quantum gates preparations on small-scale NMR *** numerical comparisons with conventional differential evolution algorithms show that da DE has great advantages on the convergence speed and robustness to several uncertainties including pulse imperfections and measurement errors.

关键词： Control pulses searching Differential evolution Quantum states and gates preparation Pulse imperfections Random measurement errors

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Plastic wrinkling prediction in thin-walled part forming process: A review

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Chinese Journal of Aeronautics 2016年第1期29卷 1-14页

作者： Liu Nan Yang He Li Heng Yan Siliang State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical University

The precision forming of thin-walled components has been urgently needed in aviation and aerospace field. However, the wrinkling induced by the compressive instability is one of the major defects in thin-walled part forming. The initiation and growth of the wrinkles are interac- tively affected by many factors such as stress states, mechanical properties of the material, geometry of the workpiece and boundary conditions. Especially when the forming process involves compli- cated boundary conditions such as multi-dies constrains, the perturbation of clearances between workpiece and dies and the contact conditions changing in time and space, etc., the predication of the wrinkling is further complicated. In this paper, the *** prediction methods were summa- rized including the static equilibrium method, the energy method, the initial imperfection method, the eigenvalue buckling analysis method, the static-implicit finite element method and the dynamic- explicit finite element method. Then, a systematical comparison and summary of these methods in terms of their advantages and limitations are presented. By using a combination of explicit FE method, initial imperfection and energy conservation, a hybrid method is recommended to predict plastic wrinkling in thin-walled part forming. Finally, considering the urgent requirements of com- plex thin-walled structures＇ part in aviation and aerospace field, the trends and challenges in wrin- kling prediction under complicated boundary conditions are presented.

关键词： Explicit algorithm Hybrid method imperfections Implicit algorithm Thin-walled part forming Wrinkling

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Dynamic Instability of Straight Bars Subjected to Impulsive Axial Loads Using the DEM

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Computer Modeling in Engineering & Sciences 2015年第2期104卷 87-104页

作者： Leticia Fleck Fadel Miguel Leandro Fleck Fadel Miguel Joao Kaminski Jr. Department of Mechanical Engineering UFRGSPorto AlegreRSBrazil Department of Civil Engineering UFSCFlorianopolisSCBrazil Department of Structures and Civil Construction UFSMSanta MariaRSBrazil

Since the half of the XX century,attention was given to the instability of structures under parametric excitation,especially under periodic *** the other hand,the instability of bars subjected to axial loads of impulsive type has been little studied,in spite of the practical importance of the ***,in Engineering Design it is frequently supposed,without tests or additional verifications,that an axial load of short duration can exceed the Euler critical load of the bar without inducing damage in the *** this context,this paper proposes the use of the truss-like Discrete Element Method(DEM)for determining the dynamic response of elastic straight bars subjected to axial loads defined by pulses of short *** proposed approach allows the consideration of initial imperfections,as well as large displacements and other non-linear *** influence of the pulse duration and other effects in the response of the bar are also ***,the performance of the proposed methodology is verified in static and dynamic instability problems of homogeneous bars without geometrical imperfections,by comparing the DEM results with analytical solutions available in the *** that,the DEM is employed to analyze more complex cases,including bars with initial imperfections and non-homogeneous bars,in which material properties,as Young’s modulus and mass density,are assumed to be correlated Gaussian random *** proposed methodology has proven to be a useful and easy tool for analysis of dynamic instability of bars and could therefore be used by designers for estimating the dynamic buckling load.

关键词： Dynamic Instability Critical Buckling Load Discrete Element Method Impulsive Load Stochastic Fields Mesh imperfections

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Model of Rotation Accuracy of High-Speed Spindles on Ball Bearings

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Engineering（科研） 2010年第7期2卷 477-484页

作者： Jeong-Du Kim Igor Zverv Keon-Beom Lee 不详

For the purpose to improve a design quality of high-speed spindle units, we have developed mathematical models and software to simulate a rotation accuracy of spindles running on ball bearings. In order to better understand the mechanics of ball bearings, the dynamic interaction of ball bearings and spindle unit, and the influence of the bearing imperfections on the spindle rotation accuracy, we have carried out computer aided analysis and experimental studies. When doing this, we have found that the spindle rotation accuracy can vary drastically with rotational speed. The influence of bearing preload has a secondary importance. Comparison of the results of these studies has demonstrated adequacy of the models developed to the real spindle units.

关键词： High-Speed Spindle Unit Ball Bearing Bearing imperfections Spindle Rotation Accuracy

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Pore Water Pressure Arising during Pile Drilling in Sand

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Journal of Civil Engineering and Architecture 2011年第4期5卷 331-340页

作者： Abdrabbo F. Khaled El-Sayed Gaaver Structural Engineering Department Faculty of Engineering Alexandria University Egypt

The pile working load depends on the imperfections which may be taken place in pile-soil system, during pile construction, among many other factors. This subject attracted the researcher＇s attention world wide in the last decades. Types of imperfections either geotechnical or structural are documented in literature and well explained. Nevertheless, the influence of these imperfections in pile load calculations is still ambiguous. The work presented herein is devoted to study soil disturbance during construction of piles using continuous flight auger, CFA. The study of soil disturbance due to drilling needs some evidence. The source of this evidence is field observations collected from four different construction sites, which are documented in this paper. The study concluded that the disturbed zone of soil by CFA has a conical shape and extending laterally to a distance equivalent to ten times of the pile diameter around the auger at the cutting bits and has an inclined surface of4：1 （vertical ： horizontal）. Furthermore excess pore water pressure was induced in soil in the vicinity of pile drilling. Due to this excess pore water pressure, 3.5% to 6.5% of piles constructed by CFA showed percolation of water from the top of the piles through fresh concrete. Also, subsidence of fresh concrete in pile hole was recorded in few of the constructed piles. Pile loading tests showed that the percolation of water and/or subsidence of fresh concrete have not appreciable influence on the load-displacement characteristics of the piles. Moreover, percolation of water at pile heads.

关键词： Pore water pressure pile drilling imperfections CFA water percolation

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