大口径相机主镜/次镜结构动力减振的研究

本文对大口径相机结构次镜相对主镜的振动进行了分析,并提出了次镜动力减振的减振方式,且对动力减振系统进行了分析。最后对某相机的动力减振结构进行了优化设计,并计算了一定冲击激励下原结构与带动力减振结构的响应时间历程。结果表明动力减振具有一定的减振效果,对相机高成象质量的保证具有一定的应用意义.     

Favoured superdeformed states in 89Tc

A superdeformed band consisting of a cascade of ten γ-ray transitions has been identified and assigned to the nucleus ⁸⁹Tc, close to the proton dripline. The quadrupole moment of the band (Q _t= 6.7^+3.0 _−2.3 eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the γ-ray flux in the ⁸⁹Tc exit channel, the band is among the most intense superdeformed bands observed to date. Received: 6 July 1999     

Effective Hubbard model for Zn-doped CuO2 plane

In the framework of the cell-perturbation method for the original p-d model an effective two-band Hubbard model for the CuO₂ plane with Zn impurities is derived. Zn impurities are modelled by Wannir oxygen one-hole states at vacant Cu sites. The model is based on the results of band structure calculations carried out within the local-density approximation. Further reduction to an extended t-J model shows a large ferromagnetic superexchange interaction between the Cu spin with the nearest virtual oxygen spin in the Zn cell. Received 17 November 1998     

Vibrational and correlation effects on properties of water

Large basis set, ab initio potential energy and property surfaces of water have been used with quantum Monte Carlo vibrational analysis in the evaluation of the molecule's rotational constants, zero-point energy, and dipole moment. While there are clearly differences in vibrational state parameters due to including correlation effects, the vibrational averaging effect on rotational constants is very nearly additive with the correlation effect. This has implications for evaluation and estimation of properties of molecules in specific vibrational states. Received: 9 February 1999 / Accepted: 11 February 1999 / Published online: 5 May 1999     

The analysis of arbitrarily-damped linear mechanical systems

Summary The analysis of arbitrarily-damped linear mechanical systems is the subject of this paper, the main issue being the analysis of nondecouplable systems. It is well known that decouplable systems occur when the damping matrix happens to be a linear combination of the mass and stiffness matrices. Systems with this type of damping are said to have proportional damping, which nevertheless seldom occurs in practice, but many a damped system is analyzed under the assumption that it is proportionally damped. In fact, this property allows the analyst to study these systems using the same approach as that applicable to their undamped counterparts. In this paper, we show that proportional damping need not be assumed in order to analyze the system at hand with the same approach as used to analyze undamped systems. Moreover, we propose an algorithm to determine the natural frequencies, the damped frequencies and the damping ratios of an n-degree-of-freedom damped system, that does not require the casting of the system into first-order form. In this way, the characteristic equation is derived naturally as a 2n-degree polynomial, computing its roots being then straightforward. Furthermore, we propose a semigraphical method to ease this calculation, which should be attractive to practicing engineers. Received 5 April 1999; accepted for publication 7 May 1999     

复式降噪块地铁车轮减振降噪特性

为探究一种复式降噪块装置及其组合形式对某S型辐板地铁车轮的减振降噪效果和机理,在半消声室内,分别对1种自由状态下的标准车轮和3种形式的复式降噪块车轮开展振动声辐射特性及阻尼特性试验,并通过有限元建模对其进行了模态计算。结果表明：复式降噪块装置可在全频段内提高车轮阻尼比,并对车轮各部位有良好的减振效果,以轮辋和踏面的减振效果最为显著;其中,6个制振阻尼片形式的降噪块对车轮的降噪效果最显著,径向激励下的降噪量为13.1dB(A),轴向激励下的降噪量为11.1dB(A),降噪频段主要集中在1000Hz以上中高频。该文研究结果是对列车降噪研究领域的补充和发展。     

Chiral magnetic effect for chiral fermion system

The chiral magnetic effect is concisely derived by employing the Wigner function approach in the chiral fermion system. Subsequently, the chiral magnetic effect is derived by solving the Landau levels of chiral fermions in detail. The second quantization and ensemble average leads to the equation of the chiral magnetic effect for righthand and lefthand fermion systems. The chiral magnetic effect arises uniquely from the contribution of the lowest Landau level. We carefully analyze the lowest Landau level and find that all righthand(chirality is +1) fermions move along the direction of the magnetic field, whereas all lefthand(chirality is-1) fermions move in the opposite direction of the magnetic field. Hence, the chiral magnetic effect can be explained clearly using a microscopic approach.     

Thermal buckling and free vibration of FG truncated conical shells with stringer and ring stiffeners using differential quadrature method

In this paper, thermal buckling and free vibration of orthogonally stiffened functionally graded truncated conical shells in thermal environment is investigated. Conical shell has been stiffened by rings and stringers, and the influences of the stiffeners are evaluated by the aid of smearing method. The material properties of the structure are assumed to be changed continuously in the thickness direction. First, the initial thermal stresses are obtained accurately by solving the thermoelastic equilibrium equations. Then, by taking into account the initial thermal stresses, equations of motion as well as boundary conditions are obtained, applying the Hamilton’s principle and the first-order shear deformation theory. The natural frequencies of the system have been achieved, solving these governing equations with considering Differential Quadrature Method (DQM). In addition to Eigen frequency analysis, the critical buckling-temperature of the conical shell has been computed. Moreover, the effects of geometrical parameters, number of stiffeners, thermal environment and various boundary conditions on natural frequency of the system have been investigated. Finally, in order to validate the present work, the results are compared with those of other researches available in literature.     

基于薄包层极大倾角光纤光栅的灵敏度增强型振动传感器

提出了一种薄包层极大倾角光纤光栅悬臂梁振动传感器,采用基于标准单模光纤的极大倾角光纤光栅,从理论上分析包层半径的减小对波导色散因子、包层模的有效折射率、轴向应变灵敏度因子、轴向应变灵敏度及模式阶数的影响,并进行数值仿真,为其振动传感增敏方法提供理论依据.然后使用氢氟酸腐蚀光纤包层,构成不同直径的极大倾角光纤光栅并进行相...     

在低频振动场中注塑成型iPP试样的结构与性能研究

利用自行研制的低频振动注塑成型装置进行等规聚丙烯(iPP)试样的结构与性能研究.实验中对常规注射和振动注射成型的试样力学性能和微观形态进行了对比实验.采用低频振动注塑成型工艺实现了IPP试样的自增强,在190℃下进行注射,强度由常规试样的41.3 MPa最大提高到振动试样的48.4 MPa(振幅PA=59.4 MPa,振频FR=0.7 Hz),强度提高了17.2%;SEM显示常规试样芯层结构主要由球晶构成,振动注射使球晶在流动方向上变形、取向,晶粒尺寸得到细化;DSC表明振动注射促进熔融峰向高温漂移,晶体结晶更加完善,结晶度最大提高了12.1%;WAXD显示低频大振幅振动注塑有利于γ晶型的生成,γ晶型有利于试样实现自增强.