Auto-parametric resonance of a continuous-beam-bridge model under two-point periodic excitation:an experimental investigation and stability analysis

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study.An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns.The parametric vibration equation is established for the test model using the finite-element method.The auto-parametric resonance stability of the structure is analyzed by using Newmark's method and the energy-growth exponent method.The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model.Compared with the experiment,the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena,and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones.For a continuous beam bridge,when the ratio of multipoint excitation frequency(applied to the columns)to natural frequency of the continuous girder is approximately equal to 2,the continuous beam may undergo a strong auto-parametric resonance.Combined with the present experiment and analysis,a hypothesis of Volgograd Bridge's serpentine vibration is discussed.

Analytical Modeling and Mechanism Analysis of Time-Varying Excitation for Surface Defects in Rolling Element Bearings

Surface defects,including dents,spalls,and cracks,for rolling element bearings are the most common faults in rotating machinery.The accurate model for the time-varying excitation is the basis for the vibration mechanism analysis and fault feature extraction.However,in conventional investigations,this issue is not well and fully addressed from the perspective of theoretical analysis and physical derivation.In this study,an improved analytical model for time-varying displacement excitations(TVDEs)caused by surface defects is theoretically formulated.First and foremost,the physical mechanism for the effect of defect sizes on the physical process of rolling element-defect interaction is revealed.According to the physical interaction mechanism between the rolling element and different types of defects,the relationship between time-varying displacement pulse and defect sizes is further analytically derived.With the obtained time-varying displacement pulse,the dynamic model for the deep groove bearings considering the internal excitation caused by the surface defect is established.The nonlinear vibration responses and fault features induced by surface defects are analyzed using the proposed TVDE model.The results suggest that the presence of surface defects may result in the occurrence of the dual-impulse phenomenon,which can serve as indexes for surface-defect fault diagnosis.

A simple semiempirical model for the static polarizability of electronically excited atoms and molecules

We present a semiempirical analytical model for the static polarizability of electronically excited atoms and molecules,which requires very few readily accessible input data,including the ground-state polarizability,elemental composition,ionization potential,and spin multiplicities of excited and ground states.This very simple model formulated in a semiclassical framework is based on a number of observed trends in polarizability of electronically excited compounds.To adjust the model,both accurate theoretical predictions and reliable measurements previously reported elsewhere for a broad range of multielectron species in the gas phase are utilized.For some representative compounds of general concern that have not yet attracted sufficient research interest,the results of our multireference second-order perturbation theory calculations are additionally engaged.We show that the model we developed has reasonable(given the considerable uncertainties in the reference data)accuracy in predicting the static polarizability of electronically excited species of arbitrary size and excitation energy.These findings can be useful for many applications,where there is a need for inexpensive and quick assessments of the static gas-phase polarizability of excited electronic states,in particular,when building the complex nonequilibrium kinetic models to describe the observed optical refractivity(dielectric permittivity)of nonthermal reacting gas flows.

Functional Integrals and Collective Excitations in Boson-Fermion Model

In this paper, collective excitations in the boson-fermion model are investigated by means of functional integration method. The equations of energy gap and excitation spectrum are derived. Moreover, the Bose energy spectrum of zero wave vector Fermi fields is also calculated.

Functional Integrals and Excitation Energy in Three-Band Hubbard Model

The normal and anomalous Green＇s functions of antiferromagnetie state in three-band Hubbard model are studied by using functional integrals and temperature Green＇s function method. The equations of energy spectrum are derived. In addition, excitation energy of Fermi fields are calculated under long wave approximation.

Two-proton radioactivity of the excited state within the Gamow-like and modified Gamow-like models

In this study,we systematically investigated the two-proton(2p)radioactivity half-lives from the excited state of nuclei near the proton drip line within the Gamowlike model(GLM)and modified Gamow-like model(MGLM).The calculated results were highly consistent with the theoretical values obtained using the unified fission model[Chin.Phys.C 45,124105(2021)],effective liquid drop model,and generalized liquid drop model[Acta Phys.Sin 71,062301(2022)].Furthermore,utilizing the GLM and MGLM,we predicted the 2p radioactivity halflives from the excited state for some nuclei that are not yet available experimentally.Simultaneously,by analyzing the calculated results from these theoretical models,it was found that the half-lives are strongly dependent on Qand l.

Distinct neuronal excitability alterations of medial prefrontal cortex in early-life neglect model of rats

Object:Early-life neglect has irreversible emotional effects on the central nervous system.In this work,we aimed to elucidate distinct functional neural changes in me-dial prefrontal cortex(mPFC)of model rats.Methods:Maternal separation with early weaning was used as a rat model of early-life neglect.The excitation of glutamatergic and GABAergic neurons in rat mPFC was recorded and analyzed by whole-cell patch clamp.Results:Glutamatergic and GABAergic neurons of mPFC were distinguished by typi-cal electrophysiological properties.The excitation of mPFC glutamatergic neurons was significantly increased in male groups,while the excitation of mPFC GABAergic neurons was significant in both female and male groups,but mainly in terms of rest membrane potential and amplitude,respectively.Conclusions:Glutamatergic and GABAergic neurons in medial prefrontal cortex showed different excitability changes in a rat model of early-life neglect,which can contribute to distinct mechanisms for emotional and cognitive manifestations.

Nucleon—Pair Shell Model：Magnetic Excitations for Ba Isotopes

Magnetic excitations for Ba isotopes are discussed within the nucleon-pair shell model truncated in the SD subspace. With the SD pair determined by a surface- interaction, M1 transitions for are well fitted. The M1 and M3 transitions for and are also predicted. It is shown that the statement, the collective magnetic properties are due to the orbital motion of nucleons, is approximately valid.

Generation Model of Particle Physics with Excited Rishon States

It is proposed that the Generation Model (GM) of particle physics, which describes the elementary particles, the six leptons, the six quarks and the three weak bosons, of the Standard Model (SM) as composite particles in terms of three kinds of rishons and their antiparticles may be mimicking a simpler model, employing only two kinds of rishons and their antiparticles.

Operational Modal Analysis of a Ship Model in the Presence of Harmonic Excitation

A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm （NExT-ERA） is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.

Method for Evaluating Bolt Competitive Failure Life Under Composite Excitation

In this study,the competitive failure mechanism of bolt loosening and fatigue is elucidated via competitive failure tests on bolts under composite excitation.Based on the competitive failure mechanism,the mode prediction model and“load ratio-life prediction curve”(ξ-N curve)of the bolt competitive failure are established.Given the poor correlation of theξ-N curve,an evaluation model of the bolt competitive failure life is proposed based on Miner’s linear damage accumulation theory.Based on the force analysis of the thread surface and simulation of the bolt connection under composite excitation,a theoretical equation of the bolt competitive failure life is established to validate the model for evaluating the bolt competitive failure life.The results reveal that the proposed model can accurately predict the competitive failure life of bolts under composite excitation,and thereby,it can provide guidance to engineering applications.

Changes in Excitability of the Motor Cortex Associated with Internal Model Formation during Intrinsic Visuomotor Learning in the Upper Arm

Previous studies have shown that the primary motor cortex (M1) may drive part of the feed forward control of well learnt simple movements by specifying patterns of muscle activation. This study explored the role of the M1 in the feed forward control of newly formed movement patterns after motor adaptation. Ten healthy right-handed subjects performed planar, centre-out arm reaching movement trials with a robotic manipulandum in three phases: a null force field (baseline), a velocity-dependent force field (adaptation;25 Nsm-1) and again in a null force field (deadaptation). Reaching error and voluntary EMG were recorded from the biceps and triceps before, during and after motor adaptation. We also explored the effects of motor adaptation on evoked responses to single and paired pulse Transcranial Magnetic Stimulation from the same muscles at different delays after a visual go command, but before the onset of voluntary muscle activity. After the force field was removed, subjects produced reaching overshoot characteristic of adaptive internal model formation. Following motor adaptation, there was a significant increase in corticospinal excitability, reduction in short interval intracortical inhibition and increase in short interval intracortical facilitation that was associated with a sustained increase in voluntary muscle activity in the biceps. The adaptation-driven increase in reaching overshoot coupled with the increase in voluntary activity, corticospinal and intracortical excitability in the biceps suggests that the M1 may specify some of the feed forward components of newly learnt internal models through the control of specific muscles.

Four-Level Decay Model of^6P_(7/2) Excited State of Eu^(2+) Ion in KMgF_3

A four-level decay model of ~6P_(7/2) excited state of Eu^(2+_ ion in KMgF_3: Eu^(2+) has been proposed. The decay profiles of the ~6P_(7/2) excited state of Eu^(2+) are two exponential and the physical implication of each term in the fit equation responsible for the model is interpreted. The data obtained spectroscopically are in good agreement with the fit results.

Critical Behavior of the Energy Gap and Its Relation with the Berry Phase Close to the Excited State Quantum Phase Transition in the Lipkin Model

In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.

Excitation and power spectrum analysis of electromagnetic radiation for the plasma wake of reentry vehicles

The plasma wake of reentry vehicles has the advantages of extensive space range and long traceability,which provides new possibilities for the detection and monitoring of reentry vehicles.Based on the Zakharov model,this work investigates the excitation and power spectrum characteristics of electromagnetic radiation for the plasma wake of a typical reentry vehicle.With the aid of parametric decay instability,the excitation condition of electromagnetic radiation for a typical plasma wake is evaluated first.The power spectrum characteristics of electromagnetic radiation,including the effects of both the flight parameters and incident wave parameters are analyzed in detail.The results show that when the phenomenon of excited electromagnetic radiation occurs,plasma wakes closer to the bottom of the vehicle and with faster speeds require higher incident frequencies and thresholds of the electric field.As the frequency of the incident wave increases,peaks appear in the power spectra of plasma wakes,and their magnitudes increase gradually.The frequency shifts of the secondary peaks are equal,whereas,the peaks of the downshifted spectral lines are generally larger than those of the upshifted spectral lines.The work in this paper provides a new idea and method for the tracking of reentry vehicles,which has potential application value in the field of reentry vehicle detection.

发电机定子环形励磁绕组寄生电容解析模型与容值降低方法

励磁控制器是调节发电机励磁电流,控制发电机电压的核心部件。采用宽禁带功率器件(例如碳化硅、氮化镓器件)的励磁控制器具有损耗低、开关频率高的优点,而电路中的寄生电容会影响功率管的开关性能,增加开关损耗,带来震荡和电磁干扰问题等。励磁绕组寄生电容是励磁控制电路的重要组成部分,降低其容值可有效提升控制器性能。为了探寻有效的容值降低方法,建立考虑匝间距离、匝到铁心距离和层间距离的多层绕组寄生电容解析模型;通过田口法计算参数灵敏度得到影响寄生电容的关键参数,研究寄生电容的变化规律;在考虑槽空间约束情况下得到降低多层定子环形励磁绕组寄生电容的有效方法;通过实验验证解析模型的准确性和降低寄生电容方法的有效性。

船模静水参激横摇阻尼测量实验研究

针对船舶参数横摇独特的运动特征,设计激励稳性参数的船模静水参激横摇实验,研究与船舶参数横摇特征吻合的横摇阻尼测量方法.基于船舶参数横摇机理,设计了由激励船模重心高度的激振器,控制电机与测量船模运动的测控仪为主要设备组成的实验系统.由阻尼耗散、激励释放和复原力矩三项能量的平衡,推导了横摇阻尼系数的计算公式.露天船模水池的静水参激横摇阻尼测量实验.结果表明:稳态响应的横摇幅值持续稳定,大幅横摇阻尼可测,实验测量的重复性好.

基于白鲨算法的七自由度机械臂动力学参数辨识

本文提出了基于白鲨算法(WSO)的关节机器人动力学参数辨识方法。首先,利用SYMORO+软件建立了七自由度机械臂的动力学模型并将其转换为可辨识模型。其次,利用关节机器人的性质提取摩擦力矩进行摩擦模型辨识。然后,设计激励轨迹并让机器人跟踪该轨迹,用辨识摩擦模型计算关节力矩信号中的摩擦项并补偿。进而,采用最小二乘法(LS)估计器确定白鲨算法的搜索空间,并由白鲨算法迭代获得最优动力学参数。最后,在Franka协作臂进行了实验验证,结果表明所提方法相较于传统算法在规避局部最优解方面具有更好的表现,且得到的参数更准确。

非正弦激励下高频变压器铁心动态磁滞特性模拟方法

高频变压器是DC/DC变换器的核心部件,其激励波形一般为非正弦波,工作频率可达数千赫兹以上,导致铁心损耗显著增加,准确模拟非正弦激励下高频变压器铁心动态磁滞特性,有助于铁心损耗计算以及变压器的电磁暂态分析。首先,该文考虑铁心磁化物理过程,利用系统级电力电子仿真软件PLECS中底层模块和语言编写程序,建立基于静态J-A磁滞模型和磁导-电容类比法的铁心静态磁滞磁导模型;然后,考虑高频条件下涡流效应与弛豫效应对铁心动态磁滞特性的影响,根据损耗统计理论建立铁心动态磁滞磁导模型;最后,基于模拟退火与Levinberg-Marquardt混合算法提取静态J-A磁滞模型参数,根据铁心损耗特性曲线采用最小二乘法提取动态损耗系数。对比分析不同占空比、高频方波电压激励下电流波形以及磁滞回线的仿真结果与实验测量结果,验证了模型的有效性。

多变运行工况下混合励磁轴向磁场永磁电机自适应模型预测电流控制

针对多变运行工况下混合励磁轴向磁场永磁(hybrid excited axial field permanent magnet,HE-AFPM)电机中电励磁磁场与电枢磁场之间矢量耦合、端部漏磁等导致的电机参数非线性变化问题,该文提出一种混合励磁轴向磁场永磁电机自适应模型预测电流控制方法。详细分析HE-AFPM电机拓扑结构及参数变化特性;引入多矢量模型预测电流控制,理论推导分析HE-AFPM电机参数对控制系统的敏感性。在此基础上,将多矢量预测模型作为自适应控制的可调模型,降低了控制算法的复杂度和控制系统的计算负荷,提高了控制系统响应速度;依据波波夫(Popov)超稳定理论,引入3个不等式稳定判据设计各参数的自适应律,可实现多变运行工况下的HE-AFPM电机磁链、自感、互感等参数的有效识别,提高了控制模型的准确性和电流跟踪性能。最后,通过实验验证所提出的自适应模型预测电流控制的有效性。