Mitigating the Jahn-Teller distortion driven by the spin-orbit coupling of lithium manganate cathode

Spinel LiMn_(2)O_(4)is recognized as one of the most competitive cathode candidates for lithium-ion batteries ascribed to environmentally benign and rich sources.However,the wholesale application of LiMn_(2)O_(4)is predominately plagued by its severe capacity degradation,mainly associated with the innate Jahn-Teller effect.Herein,single-crystalline LiMn_(2)O_(4)with Eu^(3+) doping is rationally designed to mitigate the detrimental Jahn-Teller distortion by tuning the chemical environment of MnO_(6) octahedra and accommodating localized electron,based on the unique aspheric flexible 4f electron orbit of rare-earth metal ions.Notably,the stretching of MnO_(6) octahedron stemmed from the Jahn-Teller effect in Eu-doped LiMn_(2)O_(4)is effectively suppressed,confirmed by theoretical calculation.Meanwhile,the structural stability of the material has been significantly enhanced due to the robust Mn–O band coherency and weakened phase transition,proved by synchrotron radiation absorption spectrum and operando X-ray diffraction.The corresponding active cathode manifests superior long-cycle stability after 300 loops at 2C and displays only a 0.011%capacity drop per cycle even at 5C.Given this,this modification tactic sheds new light on achieving superior long-cycle performances by suppressing distortion in various cathode materials.

Theoretical Investigations of the Local Structure Distortion and EPR Parameter for Ni2＋-doped Perovskite Fluorides

By analyzing the optical spectra and electron paramagnetic resonance parameter D, the local structure distortion of （NiF6）4- clusters in AMF3 （A=K, Rb; M=Zn, Cd, Ca） and K2ZnF4 series are studied using the complete energy matrix based on the double spin-orbit coupling parameter model for configuration ions in a tetragonal ligand field. The results indicate that the contribution of ligand to spin-orbit coupling interaction should be considered for our studied systems. Moreover, the relationships between D and the spin-obit coupling coefficients as well as the average parameter and the divergent parameter are discussed.

Lattice distortion in disordered antiferromagnetic XY models

The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin-phonon coupling in the adiabatic limit. It is found that lattice distortion relies on the strength of the random modulation. For strong or weak enough spin phonon couplings, the average lattice distortion may decrease or increase as the random modulation is strengthened. This may be the result of competition between the random magnetic modulation and the spin phonon coupling.

Design and application of a new kind of rolling coupling

Based on Hertz theory of elastic contact and the design theory of ball bearings, a new type of rolling coupling was designed. The two halves of the rolling coupling can be moved relatively by a small axial force when a great moment is exerted on it. The rolling coupling was used to connect the principal axis and the decelerator of continuous extrusion machine and it can greatly decrease the harmful axial forces on the continuous machine. The engineering formulas for the contact stress and distance of apporach of the rolling elements were deduced and the method for designing the rolling couplings was proposed. The formulas for the forces exerted on the rolling element were verified by the experiment.

Colossal structural distortion and interlayer-coupling suppression in a van der Waals crystal induced by atomic vacancies

The interlayer coupling in van der Waals(vdW)crystals has substantial effects on the performance of materials.However,an indepth understanding of the microscopic mechanism on the defect-modulated interlayer coupling is often elusive,owing partly to the challenge of atomic-scale characterization.Here we report the native Se-vacancies in a charge-density-wave metal 2HNbSe2,as well as their influence on the local atomic configurations and interlayer coupling.Our low-temperature scanning tunneling microscopy(STM)measurements,complemented by density functional theory calculations,indicate that the Sevacancies in few-layer NbSe2 can generate obvious atomic distortions due to the Jahn-Teller effect,thus breaking the rotational symmetry on the nanoscale.Moreover,these vacancies can locally generate an in-gap state in single-layer NbSe2,and more importantly,lead to a colossal suppression of interlayer coupling in the bilayer system.Our results provide clear structural and electronic fingerprints around the vacancies in vdW crystals,paving the way for developing functional vdW devices.

Lattice distortion in disordered antiferromagnetic XY models

The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin–phonon coupling in the adiabatic limit. It is found that lattice distortion relies on the strength of the random modulation. For strong or weak enough spin–phonon couplings, the average lattice distortion may decrease or increase as the random modulation is strengthened. This may be the result of competition between the random magnetic modulation and the spin–phonon coupling.

考虑约束扭转二次剪力流影响的箱梁畸变效应分析

为了揭示箱梁约束扭转和畸变之间的耦联关系,研究约束扭转对箱梁畸变效应的影响,根据约束扭转二次剪力流形成的畸变荷载,建立了考虑约束扭转的箱梁畸变控制微分方程.基于乌曼斯基第二理论,提出约束扭转剪力流是基于约束扭转引起的畸变效应修正后的总扭矩布雷特剪力流,并通过Ansys有限元模型和能量法计算结果对理论公式进行了验证.数值算例结果表明:2种不同约束扭转剪力流分解方法计算所得结果完全一致;不同计算点处的约束扭转剪应力与Ansys有限元法计算结果吻合良好;扭转畸变翘曲总正应力、畸变翘曲正应力均与按能量法计算所得结果吻合良好,误差不超过10%.计入约束扭转二次剪应力的影响能够更准确地计算箱梁畸变效应.

Quantifying structural distortion manipulation for desired perovskite phase:PartⅡ.Three-step workflow to reveal phase evolution logic

Distortion manipulation emerges as an efficient approach to obtain desired perovskite phases for various applications.In part I of this study,we propose a paradigm to quantify the structural distortion manipulation,which enables us to obtain desired perovskite phases by translating relevant materials research into a single mathematical question.As part II of this continuous study,we construct normalized structures by introducing all possible couplings of dominant distortions into a cubic supercell and then compare them with variously shaped primitive/conventional cells known in the database.The structure comparison demonstrates that distortions are the only cause for phase and property variations.This confirms that our proposed distortion parameters can be directly used to construct phases,providing theoretical support for the paradigm in Part I.Given the limited number of distortion types,we identify that the positional relations involved in distortion arrangements and couplings are the keys to describe numerous phases.Furtherly,a three-step workflow is proposed with core contents related to the positional relation,distortion hierarchy,and distortion-component-generation ordering in spatial dimension,respectively.The definition basis and value changes of distortion/model parameters in this workflow illustration provide guidelines about how to reveal the logic behind the perovskite phase evolution.

长波红外差分干涉仪光栅低温安装结构设计与优化

长波红外差分干涉仪在低温工况下会因光学元件受到非均匀应力作用产生干涉条纹的畸变,从而降低干涉仪系统性能。本文为解决低温工况干涉条纹弯曲畸变问题,基于长波红外差分干涉仪光机系统进行了干涉条纹畸变影响因素分析,结合光-机-热耦合分析方法,对干涉仪系统低温工作状态进行仿真。随后设计了针对影响条纹畸变的关键元件——光栅元件的低温微应力动态稳定支撑安装结构,结构优化后的光栅表面面形均方根(Root Mean Square,RMS)值为3.89×10^(-2) nm,面形峰谷值(Peak to Valley,PV)值为2.21×10^(-1) nm,分别较优化前初始系统的分析结果减小了5个数量级,系统仿真干涉条纹畸变小于1个探测器像元。全系统低温验证试验表明,优化结构可有效抑制干涉条纹畸变,畸变量小于2个探测器像元,试验与仿真计算结果一致性较好,验证了优化分析方法的有效性。该优化方案对提升反射式光学系统结构低温稳定性,提高系统工作能力有较大意义和价值。

A thermo-mechanical damage constitutive model for deep rock considering brittleness-ductility transition characteristics

This paper developed a statistical damage constitutive model for deep rock by considering the effects of external load and thermal treatment temperature based on the distortion energy.The model parameters were determined through the extremum features of stress−strain curve.Subsequently,the model predictions were compared with experimental results of marble samples.It is found that when the treatment temperature rises,the coupling damage evolution curve shows an S-shape and the slope of ascending branch gradually decreases during the coupling damage evolution process.At a constant temperature,confining pressure can suppress the expansion of micro-fractures.As the confining pressure increases the rock exhibits ductility characteristics,and the shape of coupling damage curve changes from an S-shape into a quasi-parabolic shape.This model can well characterize the influence of high temperature on the mechanical properties of deep rock and its brittleness-ductility transition characteristics under confining pressure.Also,it is suitable for sandstone and granite,especially in predicting the pre-peak stage and peak stress of stress−strain curve under the coupling action of confining pressure and high temperature.The relevant results can provide a reference for further research on the constitutive relationship of rock-like materials and their engineering applications.

含感应加热电源的电网电压畸变信号智能判别研究

感应加热电源运行过程中,受光伏电网周边环境扰动的影响,造成线路谐波引起电压畸变。提出含感应加热电源的光伏电网母线电压畸变信号判别方法,以期保证光伏电网的稳定运行。建立谐波耦合导纳矩阵模型,完成含感应加热电源的电网电压畸变情况分析;通过波形包络阈值线在时域、小波域、频域上提取电网电压扰动信号特征;基于支持向量机方法完成电压畸变信号的判别。实验结果表明,所提方法在单一扰动信号和多种扰动信号情况下,均具有较高的电压畸变信号识别正确率和效率。

牵引供电系统的谐波渗透机理分析及治理研究

通过分析机车谐波电流特性及牵引网谐波对车载变压器的渗透机理,提出一种LC滤波器参数设计方案,并将其应用于某实际运行的线路,通过现场测试效果良好,谐波问题得到有效治理。

Vertical-horizontal coupling nonlinear vibration characteristics of rolling mill under mixed lubrication

Considering the dynamic influence of the roll vibration on the lubricant film thickness in the rolling deformation area,nonlinear dynamic rolling forces related to film thickness in the vertical and horizontal directions were obtained based on the Karman balance theory.Based on these dynamic rolling forces and the mechanical vibration of the rolling mill,a vertical-horizontal coupling nonlinear vibration dynamic model was established.The amplitude-frequency equation of the main resonance was derived by using the multiple-scale method.At last,the parameters of the 1780 rolling mill were used for numerical simulation,and the time-domain response curves of the system’s vibration displacement and lubricating film thickness under the steady and unsteady conditions were analyzed.The influences of parameters such as interface contact ratio,nonlinear parameters and external disturbances on the primary resonance frequency characteristics were obtained,which provided a theoretical reference for the suppression of rolling mill vibration.

政府科技投入、资本扭曲与“科技-金融”耦合系统效率:基于市场化程度的调节作用机制

为进一步厘清政府科技投入对“科技-金融”耦合系统效率的作用机制、促进耦合系统效率提升,鉴于目前缺乏将政府科技投入、资本扭曲、市场化程度与“科技-金融”耦合系统效率置于同一研究框架且缺乏变量间内部作用机制的讨论,因此在分析政府科技投入对“科技-金融”耦合系统效率作用机制中考虑资本扭曲的中介作用以及市场化程度的调节作用,以中国30个省份相关面板数据为样本,基于非期望产出超效率SBM模型测算耦合系统效率,并采用固定效应模型和有调节的中介模型进行实证分析。结果表明:政府科技投入与“科技-金融”耦合系统效率之间存在倒“U”型影响关系,政府科技投入能够缓解资本扭曲提升耦合系统效率;随着市场化程度的提升,政府科技投入在其直接作用路径中,对耦合系统效率的促进作用减弱,在由资本扭曲中介过程的后半路径中,资本扭曲对耦合系统效率的抑制作用减弱。最后,根据理论分析和实证结果,为促进我国“科技-金融”耦合系统效率提升,从厘清市场和政府的边界、防范过度政府科技投入,加快推进金融体制深化改革、促进金融业务多元化,以及完善基础设施建设、主动吸收先进技术和推动产业结构优化升级等三大方面提出相关对策建议。

薄壁方管轴向压溃的相似性研究

薄壁方管由于其几何特性导致相似性研究中,厚度无法与长度、宽度按照同一比例进行结构缩放,从而产生几何畸变,造成传统的相似律失效。为了解决这一问题,基于轴压冲击问题的响应方程、能量守恒方程,采用方程分析和量纲分析,推导了受轴压冲击作用下理想弹塑性薄壁方管几何畸变时动态响应的相似律。讨论了缩比模型与原型选取同种和不同种材料时的速度比例因子,并在理想弹塑性材料的基础上进一步修正了考虑应变率、应变硬化效应时的速度比例因子。建立有限元模型验证了畸变模型相似律的有效性。结果表明,缩比模型在采用提出的受轴压冲击薄壁方管的相似律进行缩放后,能够准确预测原型的载荷、能量等动态响应,相似性较好。

基于MVDR波束形成的FDA平台外干扰抑制

针对频控阵(frequency diverse array,FDA)在对与目标位置相近的平台外干扰进行抑制时,传统FDA与非线性频偏结合不能实现距离-角度去耦合、对数递增FDA主瓣展宽较大和汉明窗加权FDA距离维旁瓣过高的问题,在充分研究汉明窗加权的线性FDA(Hamming linear FDA,HL-FDA)方案的基础上,对4种频偏方案的性能进行了分析,提出采用FDA多输入多输出结构代替传统的一维均匀线性FDA结构,通过结合最小方差无失真响应(minimum variance distortion free respinse,MVDR)准则,将HL-FDA应用到MVDR自适应波束形成层面,对平台外干扰进行抑制。仿真验证了HL-FDA在结合MVDR自适应波束形成算法后能有效地对抗距离-角度二维平台外干扰。

电磁感应矫平工艺的多物理场耦合仿真研究

电磁感应矫平方法具有效率高、易操作的特点,在薄板矫平工艺中有良好的应用前景.以船厂使用的固定式一字型线圈感应矫平工艺为例,基于COMSOL Multiphysics有限元仿真软件建立了三维电磁-热-力耦合感应矫平有限元模型.该模型输入AH36钢板随温度变化的物理性能,以对接焊件残余应力与焊接变形作为初始状态,采用顺序耦合的方法计算矫平过程中电磁场、温度场与结构场的变化,从而验证了温度场与电磁场在矫平过程的双向耦合关系,得到焊接件在矫平后的变形量.通过自行搭建的感应矫平实验平台测试矫平工艺中的温度变化与变形量,验证了该有限元模型的准确性与有效性.

基于平板电路的无源互调耦合测试方法

无源互调(PIM)是一个吸引众多领域研究人员的课题,包括卫星、天线和智能终端等。本文提出一个非接触式PIM测量的新思路:使用一个经过近场重构的基片集成缝隙波导(SISW)作为互调信号的激励和接收路径,SISW通过对载波信号的远场抑制和近场测试区的优化,实现了一种针对没有射频端口的样品非线性特性的评估解决方案。该测试平台结合了近场天线的有限辐射特性和多敏度测试区在PIM评估中对收发系统和测试样片的适应性。实验结果表明,该测试方法在稳定性和分辨力方面具有相当大的工程应用潜力。

计及套管内气–液介质流体特性的高压直流电缆终端优化模型研究

为探究不同负荷条件下直流电缆终端内部的多物理场状态,基于电磁场、温度场、计算流体力学的基本理论搭建直流电缆终端的多物理场耦合模型,并且根据三场之间的关系对其进行双向全耦合。该文提出一种基于阻尼系数的变步长高度非线性求解方法,有效解决了求解时因时间尺度差异造成的计算收敛性与计算成本间的矛盾。通过红外热成像仪测量实验中带负荷±160k V高压直流电缆的套管表面温度,验证了该仿真模型的准确性。研究发现,温升所致的电场反转在过负荷时会引发应力锥根部电场畸变,此现象在导体最高温度70℃之后尤为明显,进而结合国家及行业的相关标准,可确定其载流量为1140A,略小于相同导体截面积直流电缆的载流量。该研究可为通过表面温度评估直流电缆终端的内部状态提供参考。

激光雷达IMU紧耦合的室内大范围SLAM方法

针对激光雷达SLAM算法在室内大范围场景中建图与定位精确度低、鲁棒性差的问题,提出一种激光雷达IMU紧耦合的SLAM方法。该方法基于LeGO-LOAM算法,在点云去畸变环节引入惯性测量单元(IMU)数据,将IMU预积分的结果作为初始位姿,消除点云畸变;在点云配准环节,将IMU预积分的结果作为迭代优化时的初始位姿,提升点云配准精度,从而提高机器人位姿估计的准确性;在后端优化环节,通过构建因子图的方式引入激光里程计因子、IMU预积分因子及回环因子,得到全局最优解,进一步提升建图与定位的精度。为验证所提方法的可行性,设计不同场景下LeGO-LOAM算法与改进SLAM算法的对比实验。实验结果表明,在室内大范围场景下,改进的SLAM算法能够减少轨迹波动,提升建图效果及轨迹精度,增强算法的鲁棒性。