面波产生的地震动转动分量的试验验证

迄今为止,地面运动转动分量主要是通过弹性波动理论方法间接由平动分量获得,但并未得到证实。首次运用面波试验验证了这种求取转动分量的方法的合理性。重锤击落地面,在半无限空间弹性介质的地表附近,可产生面波(瑞利波和乐夫波),合理布置拾振器位置,测得产生面波的时程,利用两点差原理可以测得地面近似转动分量;将实测转动分量和用理论方法求得的转动分量的时程曲线以及傅立叶谱进行对比,由两种方法得到的转动分量加速度时程在振动持续时间内的开始阶段、强震阶段和衰减阶段基本一致;Fourier谱峰值、峰值点个数、峰值出现的位置以及谱曲线的形状走向是接近的。     

Experimental measurements of orientation and rotation of dense 3D packings of spheres

Many recent advances in the study of granular media have stemmed from the improved capability to image and track individual grains in two and three dimensions. While two-dimensional systems readily yield both translational and rotational motion, a challenge in three-dimensional experiments is the tracking of rotational motion of isotropic particles. We propose an extension of the refractive index matched scanning technique as a method of measuring individual particle rotation. Initial measurements indicate that shear-driven rotational motion may stem from gear-like motion within the shear zone.     

Constitutive relations for a planar,simple shear flow of rough disks

Stresses developed in a rapid simple shear flow of disks are quantified. Collisional momentum transfer is considered to be the dominant stress generating mechanism. The disks are inelastic and frictional. The restitution coefficient and the coefficient of friction together determine the transfer of momentum and dissipation of energy during a collision. The frictional coefficient generates and maintains a rotational motion of disks. The total fluctuation motion of disks consists of two translational modes and one rotational mode. The rotational mode is found to depend on both the restitution and the friction coefficient. Equipartition of energy among all modes of motion is absent. The mean rotation depends only on the mean flow gradient. The analysis assumes fluctuation modes all have constant magnitudes. Comparison with a computer simulated disk flow shows good agreement. This implies that the distribution of velocity magnitude may not be crucial to the quantification of stresses.     

Uniform rotational motion compensation for inverse synthetic aperture radar with non-cooperative targets

In the current scenario of high-range resolution radars, the rotational motion of the target usually generates migration through resolution cells (MTRC) in the inverse synthetic aperture radar (ISAR) images. A technique to correct the MTRC in the case of uniform rotation rate is proposed. An estimation of the rotation vector of the non-cooperative targets is not required. The approach compensates the rotational motion in two steps: the slant-range rotation compensation (SRRC) and the cross-range rotation compensation (CRRC). CRRC is based on an extension of phase difference (PD) and on a robust method to delete outliers. The technique is verified both with simulated and live data from a millimetre-wave linear frequency-modulated continuous wave radar. A comparison with a minimum entropy-based technique is also made.     

Stokes flow with slip caused by the axisymmetric motion of a sphere bisected by a free surface bounding a semi-infinite micropolar fluid

The first part of this paper investigates the motion of a solid spherical particle in an incompressible axisymmetric micropolar Stokes flow. A linear slip, Basset-type, boundary condition has been used. Expressions for the drag force and terminal velocity has been obtained in terms of the parameter characterizing the slip friction. In the second part, we consider the flow of an incompressible axisymmetrical steady semi-infinite micropolar fluid arising from the motion of a sphere bisected by a free surface bounding a semi-infinite micropolar fluid. Two cases are considered for the motion of the sphere: perpendicular translation to the free surface and rotation about a diameter which is also perpendicular to the free surface. The speed of the translational motion and the angular speed for the rotational motion of the sphere are assumed to be small so that the nonlinear terms in the equations of motion can be neglected under the usual Stokesian approximation. Also a linear slip, Basset-type, has been used. The analytical expressions for velocity and microrotation components are determined in terms of modified Bessel functions of second kind and Legendre polynomials. The drag for the translation case and the couple for the rotational motion on the submerged half sphere are calculated and expressed in terms of nondimensional coefficients whose variation is studied numerically. The variations of the drag and couple coefficients with respect to the micropolarity parameter and slip parameter are tabulated and displayed graphically.     

The oscillatory characteristics of a 2C60/CNT oscillator system

The authors have studied, using molecular dynamic (MD) simulations, the oscillatory characteristics of a 2C60/CNT oscillator system, in which two C60 fullerenes oscillate inside a single walled carbon nanotube (CNT) in two basic modes, i.e., the symmetric and non-symmetric motions. In the symmetric mode, with each oscillation the two fullerenes move symmetrically from the CNT ends towards the CNT center where they bounce off each other and head back towards the ends. In the non-symmetric mode, the two fullerenes move back and forth inside the CNT crossing the center point of the CNT together with each oscillation. The simulations show that the non-symmetric oscillation mode is stable for the prescribed initial (maximum) velocities up to 300 m/s, while the symmetric oscillation mode however, experiences dynamic instabilities for a prescribed initial (maximum) velocity larger than 250 m/s. The instability takes place as a result of the transfer of energy from the translational to the rotational motion of the fullerenes. This characteristic differentiates 2C60/CNT oscillators from double-walled CNT oscillators. The rotation is primarily caused by the inter-colliding of the two fullerenes, which subjects the fullerenes to large van der Waals repelling forces. These repelling forces are not necessarily aligned perfectly along the CNT axis nor precisely pointing towards the mass centers of the fullerenes. These misalignments cause the fullerenes to rock around the CNT's axis, while their offsets from the mass centers cause the fullerenes to rotate. The rocking motion, being severely confined by the CNT, does not gain much energy itself, but instead, channels energy from translational to rotational motion. The energy channeling is found to be reversed in some very short time intervals, but the rotational motion always gains energies from the translational motion over a time interval that is long enough at the MD time scale. This feature, contrary to our experiences in the macroscopic world, appears to be unique for such nanoscopic mechanical systems.     

自立式微波通讯塔在复合地震动作用下的随机反应分析

本文建立了自立式微波通讯塔在复合地震动作用下的振动方程,给出了计算弹性结构反应统计量的有关公式。应用给出的地震动转动分量的随机模型及修正的Kanai-Tajimi 平动模型,对山西某地的微波通讯塔进行了平稳随机反应分析,得到了一些对实际工程有意义的结果。最后对某些问题进行了讨论。     

确定建筑物刚心的一种动测方法

介绍一种利用实测振动记录确定已有建筑物的刚度中心的方法。该方法以建筑物刚度中心处的平移运动与扭转运动的相干函数最小为依据，分别对建筑物不同位置的运动作对于扭转的相干函数并积分求面积，面积最小所对应的结构坐标即为建筑特的刚度中心。     

Molecular dynamics simulation of pressure effect on phase transition behaviour and dynamics in the isotropic and discotic nematic phases

Molecular dynamics simulation was performed at constant temperature and pressure to investigate the effect of pressure on molecular dynamics for disc-shaped molecules. The generic Gay-Berne model, GB(0.345, 5.0, 1, 3), was used to study the phase transition behaviour, and translational and rotational dynamics, under two different reduced pressures P^?, 10.0 and 20.0. Obvious shifts were detected in the transition temperatures. Both systems have the same phase sequence with different pressures: isotropic, discotic nematic and columnar phases. Translational motion is characterised by the parallel and perpendicular components of diffusion coefficients, with respect to the director in the orientational ordered phase. With regard to rotational dynamics, the correlation time of the first-rank orientational time autocorrelation function, which corresponds to end-over-end rotational motion of a molecule, has been investigated. A clear jump in the temperature dependence of the correlation time has been found at the isotropic-nematic phase transition point. The retardation factor g_|| as a function of the reduced temperature T^?/T_NI^? shows an apparent pressure effect on the rotational dynamics.     

Translational and rotational dynamics of methane in ZSM-5 zeolite: A quasi-elastic neutron scattering study

The translational and rotational motions of methane adsorbed at different loadings in NaZSM-5 have been studied by quasi-elastic neutron scattering at two temperatures: 200 and 250 K. The translational motion does not simply follow Fick's law, but a jump diffusion model with a Gaussian distribution of jump lengths satisfactorily simulates the experimental results. The diffusion coefficient that is obtained for long-range translational motion does not vary much on the loading in the range that was studied: it is of ⋍ 2.7 × 10⁻⁵ cm² s⁻¹ at 200 K and ⋍ 5.5 × 10⁻⁵ cm² s⁻¹ at 250 K. Good agreement is found between the neutron and n.m.r. results for this motion, but large discrepancies are observed with the macroscopic measurements. The rotational motion is well described by an isotropic rotational diffusion model, and this motion is found to be much slower in the zeolite than in physisorbed layers or in bulk solid methane.     

回转运动坐标定位精度的检测与误差补偿模型

在对回转运动坐标定位精度的干涉测量原理和方法进行深入研究的基础上,采用激光干涉法检测混联机床C轴的定位精度和重复定位精度,并做出了基于测量数据的混联机床C轴单向均位偏差特性曲线,推导出了C轴顺、逆时针旋转定位误差数学模型。利用最小二乘法拟合得到了机床回转运动坐标目标位置的均值误差补偿数学模型,提出了一种回转运动坐标定位精度的激光干涉测量方法和误差补偿模型的建模方法。     

Revealing Rotational Modes of Functionalized Gold Nanorods on Live Cell Membranes

A full understanding of cell mechanics requires knowledge of both translational and rotational dynamics. The single particle orientation and rotational tracking (SPORT) technique is combined here with correlation analysis to identify the fundamental rotational modes: in‐plane rotation and out‐of‐plane tilting, as well as other more complex rotational patterns, from the vast image data captured at a temporal resolution of 5 ms for single gold nanorod probes in live cell imaging experiments. The unique capabilities of visualizing and understanding rotational motions of functional nanoparticles on live cell membranes allow correlation of the rotational and translational dynamics in unprecedented detail and provide new insights into complex membrane processes. Particles with functionalized surfaces, which interact with the membrane in fundamentally different ways, can exhibit distinct rotational modes and are, for the first time, directly visualized, and these show the early events for membrane approach and attachment.     

基于序列图像中二次曲线对应的纯旋转运动参数估计算法

采用特征对应的视觉运动分析方法，建立了基于二次曲线的刚体纯旋转运动方程，提出了求解刚体纯旋转运动参数的算法。在刚体纯旋转运动分析中，最少利用前后两幅图像中7对匹配二次曲线，就可用线性方程组求解刚体旋转运动参数，线性算法的提出使旋转运动参数的求解精度得到很大提高。最后利用合成数据和真实图像对纯旋转运动估计算法的精度和有效性进行了验证，表明该算法能准确、可靠地估计旋转运动参数。     

Rotating fullerene chains in carbon nanopeapods

The rotation of fullerene chains in SWNT peapods is studied using low-voltage high resolution transmission electron microscopy. Anisotropic fullerene chain structures (i.e., C300) are formed in situ in carbon nanopeapods via electron beam induced coalescence of individual fullerenes (i.e., C60). A low electron accelerating voltage of 80 kV is used to prevent damage to the SWNT. The large asymmetric C300 fullerene structure exhibits translational motion inside the SWNT and unique corkscrew like rotation motion. Another asymmetric fullerene chain containing mixed fullerene species is prepared by fusing smaller C60 fullerenes to a larger Sc@C82 fullerene, and this also exhibits corkscrew rotational motion. Chains of Sc3C2@C80 in SWNT peapods adopt a zigzag packing structure, and the entire zigzag chain rotates inside the SWNT to induce structural modifications to the SWNT diameter and cross-sectional shape of the SWNT. The expansion and contraction of the diameter of the SWNT is measured as 17%, demonstrating nanoactuation behavior in carbon nanopeapods.     

复式行星齿轮传动系统综合动力学模型及振动特性研究

建立了复式行星齿轮传动综合动力学模型,模型考虑了各构件的平移和扭转振动及静态传递误差。系统分析了复式行星齿轮传动系统的固有振动特性,研究了其固有频率的带状分布特点,根据中心构件及行星轮的振动特点,将系统振型分为三类,即中心构件平移-行星轮随机振动模式、中心构件扭转-行星轮相同振动模式、中心轮静止-相邻行星轮反向振动模式。     

埋置块式基础地基阻抗函数的简化计算方法研究

目前关于地基阻抗的分析和计算方法都比较繁琐,不易为工程设计人员所掌握.基于此,提出了埋置基础地基阻抗函数的简化计算方法.首先,采用锥体模型分析均质半空间内埋置圆盘一维振动波的传播过程,得到了平动和转动时的地基阻抗.在此基础上,利用埋置圆盘组来模拟埋置基础,分析得到了埋置基础地基阻抗函数.最后,通过算例表明此方法计算效率高,误差小,适用于工程计算.     

Tensor Properties of Added-mass and Damping Coefficients

It has been shown that in the context of a linear theory for a floating body with six degrees of freedom each of the 6× 6 added-mass and damping matrices contains three distinct Cartesian second-order tensors in regard to translational, rotational and interaction between translational and rotational oscillations. As a result of this, a new technique based on the transformation law of second-order tensors is introduced for motion analysis of offshore platforms which can be used as an alternative to the common methods in offshore engineering.     

Direct simultaneous measurement of rotational and translational accomodation coefficients

When molecules of a low density diatomic gas strike a solid surface both translational energy and the internal energy modes of rotation and vibration will contribute the energy exchange that occurs. Theoretical studies indicate that accomodation coefficient for rotational energy should be less than that for translational energy, and this is confirmed by experimental results. The experimental apparatus described in this paper uses the electron bream fluorescence detector to measure simultaneously both rotational and translational energy accommodation coefficients of room temperature nitrogen reflecting from a solid surface. A bakeable ultra high vacuum system was built to provide a clean vacuum environment for control of the solid surface properties. In addition to being the only known direct measurement of rotational accomodation coefficient the system offers an advantage over some previous methods of translational accommodation measurement in that there are few restrictions on solid surface temperature or composition.