径向电场对离子温度梯度模稳定性的影响

为了理解托卡马克装置中给定径向电场对离子温度梯度模(ITG)稳定性的影响,基于非线性回旋动理学理论和气球模表象推导了环位形下包含径向电场引起的极向流和密度扰动影响的ITG的本征模方程,并分别在长/短波长极限下研究了高能量粒子诱发测地声模(EGAM)所伴随的径向电场对ITG的本征频率、增长率和平行模结构的影响.不仅对该本征模方程进行了理论研究,还使用本征矩阵法对其进行数值求解,以便对理论结果进行验证.研究发现EGAM伴随的电场引起的极向转动会大幅降低ITG的增长率,而极向模数m=1的密度扰动对ITG的线性稳定性影响很小.这一结果与一般认为的带状流通过极向流剪切抑制湍流的结果是一致的.除此之外,使用本文发展的一般性方法也可以研究高能量粒子激发的阿尔芬不稳定性与漂移波湍流通过阿尔芬不稳定性激发带状结构发生的间接非线性相互作用,即带状结构所伴随的径向电场通过极向转动和密度扰动影响ITG的稳定性.该间接非线性通道可以作为对主导背景等离子体输运的微观湍流和主导高能量粒子输运的阿尔芬不稳定性之间的直接相互作用通道的补充.

基于立体视觉的移动机器人自主导航定位系统

描述了一种基于立体视觉的移动机器人自主导航定位系统。该系统采用双目立体视觉完成环境特征的 3D信息提取 ,实时计算出机器人相对作业目标的位姿 (6D)关系 ,导引移动机器人控制系统按目标导向进行运动。系统在相对位姿计算中采用旋动(Screw)理论 ,将带约束的多变量函数的非线性优化问题转化为线性方程组的最小二乘问题 ,简化了计算复杂性。实验表明 ,这个导航定位系统在定位精度和数据处理速度上均可满足机器人导航的要求。

基于空间向量的三维基准转换模型

从空间几何角度出发,利用空间向量的关系研究坐标转换,提出一种新的三维基准转换模型。通过模拟算例和在工程中的实际应用证明:该模型不受坐标转换旋转角大小的约束,能适用于任意角度;计算结果可靠,精度较高,与现有模型相比,有着简便、效率高的特点。

DYNAMICS ANALYSIS OF 2-DOF SPHERICAL PARALLEL MECHANISM

The analytical formulations of the velocity and the acceleration of a 2-DOF spherical parallel mechanism are derived by the screw theory. Based on building its dynamics model by the principle of virtual work and reciprocal product of the screw, the equation of the motor moment is obtained. Through the transformation of dynamics model, the configuration space method of the dynamics equation and the corresponding coefficients are presented. Finally, the result of an example shows that the inertia moment and the gravity play a more important role than the coriolis and centrifugal moment, and the former is ten times of the latter in the magnitude. So, the latter can be neglected only when the velocity of mechanism is very slow.

Spin-Spin Interactions in Gauge Theory of Gravity, Violation of Weak Equivalence Principle and New Classical Test of General Relativity

For a long time, it has been generally believed that spin-spin interactions can only exist in a theory where Lorentz symmetry is gauged, and a theory with spin-spin interactions is not perturbatively renormalizable. But this is not true. By studying the motion of a spinning particle in gravitational field, it is found that there exist spin-spin interactions in gauge theory of gravity. Its mechanism is that a spinning particle will generate gravitomagnetic field in space-time, and this gravitomagnetic field will interact with the spin of another particle, which will cause spin-spin interactions. So, spin-spin interactions are transmitted by gravitational field. The form of spin-spin interactions in post Newtonian approximations is deduced. This result can also be deduced from the Papapetrou equation. This kind of interaction will not affect the renormalizability of the theory. The spin-spin interactions will violate the weak equivalence principle, and the violation effects are detectable. An experiment is proposed to detect the effects of the violation of the weak equivalence principle.

The Calculations of Propeller Induced Velocity by RANS and Momentum Theory

In order to provide instructions for the calculation of the propeller induced velocity in the study of the hull-propeller interaction using the body force approach,three methods were used to calculate the propeller induced velocity：1） Reynolds-Averaged Navier-Stokes（RANS） simulation of the self-propulsion test,2） RANS simulation of the propeller open water test,and 3） momentum theory of the propeller.The results from the first two methods were validated against experimental data to assess the accuracy of the computed flow field.The thrust identity method was adopted to obtain the advance velocity,which was then used to derive the propeller induced velocity from the total velocity field.The results computed by the first two approaches were close,while those from the momentum theory were significantly overestimated.The presented results could prove to be useful for further calculations of self-propulsion using the body force approach.

The kinematics modeling based on Spinor theory for CT-guided hybrid robot

This paper focused on a simplified method for solving the hybrid robot kinematics in CT-guided （computerized tomography, CT） surgery. By position constraint introduced, the hybrid robot can be transformed as a redundant serial 7-DOF robot. The forward displacement calculation was developed based on the product-of-exponential formula （POE）. Because of the kinematics complexity of the hybrid and redundant robot, the combination technique of Ulrich two-step iteration method and paul variables detachment method （UTI-PVD） was introduced to fulfill the inverse kinematics of redundant robot, the novelty of which lay in the flexibility of various robots structures and in high calculation efficiency for realtime control. The process of solving the inverse displacement was analyzed. The UTI-PVD method can be applicable to kinematics of many robots, especially for redundant robots with more than 6DOF. The kinematics simulation was provided, and robot dexterity analysis was presented. The results indicated that the hybrid robot could implement the minimally invasive CT-guided surgery.

Mobility and constant-orientation workspace analysis of 4UPS-UPU parallel mechanism

One of the key issues for parallel mechanism is the kinematic characteristics,especially the workspace which varies with configuration parameters.A kind of 4UPS-UPU parallel mechanism is designed and its workspace is studied in this paper.First,the mobility of the 4UPS-UPU parallel mechanism is analyzed based on the reciprocal screw theory,and the motion and constraint screw systems of the parallel mechanism are obtained.Then the inverse kinematics is derived by the closed-form kinematics chain.The boundary search method in the polar coordinate system is presented to analyze the constant-orientation workspace of the parallel mechanism.Finally,the influence factors relevant to the workspace,such as the structural parameters and kinematics parameters are analyzed in detail.The relationship between the workspace volume and different parameters are obtained.The conclusions can be used for parameters optimization and path planning of the parallel mechanism.

Coupling Between Spin and Gravitational Field and Equation of Motion of Spin

In general relativity, the equation of motion of the spin is given by the equation of parallel transport, which is a result of the space-time geometry. Any result of the space-time geometry cannog be directly applied to gauge theory of gravity. In gauge theory of gravity, based on the viewpoint of the coupling between the spin and gravitational field, an equation of motlon of the spin is deduced. In the post Newtonian approximation, it is proved that this equation gives the same result as that of the equation of parallel transport. So, in the post Newtonian approximation, gauge theory of gravity gives out the same prediction on the precession of orbiting gyroscope as that of general relativity.

Anguilliform Fish Propulsion of Highest Hydrodynamic Efficiency

It is hypothesized that steady anguilliform swimming motion of aquatic animals is purely reactive such that no net vortex wake is left downstream. This is versus carangiform and tunniform swimming of fish, where vortex streams are shed from tail, fins, and body. But there the animal movements are such to produce partial vortex cancellation downstream in maximizing propulsive efficiency. In anguilliform swimming characteristic of the eel family, it is argued that the swimming motions are configured by the animal such that vortex shedding does not occur at all. However, the propulsive thrust in this case is higher order in the motion amplitude, so that relatively large coils are needed to produce relatively small thrust; the speeds of anguilliform swimmers are less than the carangiform and tunniforrn, which develop first order thrusts via lifting processes. Results of experimentation on live lamprey are compared to theoretical prediction which assumes the no-wake hypothesis. Two-dimensional analysis is first performed to set the concept. This is followed by three-dimensional analysis using slender-body theory. Slender-body theory has been applied by others in studying anguilliform swimming, as it is ideally suited to the geometry of the lamprey and other eel-like animals. The agreement between this new approach based on the hypothesis of wakeless swimming and the experiments is remarkably good in spite of the physical complexities.

Multiconfigurational Study of the Electronic Structure of Negatively Charged Fullerens

Multiconfigurational second order perturbation theory was employed in order to describe the ground and excited states of C60^-n. Different choices of the active spaces are discussed and the possibility to apply multiconfigurational theory to study C12o is investigated. The calculations were performed for all possible spin states （for selected charge） and show the preference of low spin state. The energy difference between two C60^-3 and pairs C60^-1- C60^-5 and C60^-2- C60^-4 shows that the probability to create a charge alternation in fullerides is small.

Type synthesis of the rotational decoupled parallel mechanism based on screw theory

With the gradual deepening of study on the parallel mechanism,the difficulty brought by the existence of coupling to the theoretical analysis and practical application of parallel mechanisms is becoming increasingly apparent.The research on the decoupled parallel mechanism is currently one of the hot fields.Though most of the rotational parallel mechanisms,which has been widely used in spatial orientation fields,are not decoupled.It is comparative difficult for the synthesis of fully decoupled rotational parallel mechanisms,and the number of the existing parallel mechanisms which can realize rotational decoupling is limited.In addition,most of the existing rotational decoupled parallel mechanism are obtained depending on the experience of the researcher,and don't possess the general theoretical significance.Based on the screw theory,this paper presents the rotational conditions of the parallel mechanism through the analysis of the relationship between the degree of freedom of the parallel mechanism and its limbs.The synthesis rule of the limbs for decoupled rotational parallel mechanism is established according to the twist screw system of the limbs,which assures the decoupling of the rotations in each limb.The selection principle of the input pairs for the rotation driven limbs is proposed,then the type synthesis method for rotational decoupled parallel mechanisms is formed.With this type synthesis method,synthesis of the rotational decoupled parallel mechanisms is performed,which can provide a reference for the development of the novel type parallel mechanisms with independent intellectual property rights.

Reconfigurable parallel mechanisms with planar five-bar metamorphic linkages

This paper presents the idea of constructing reconfigurable limbs by integrating metamorphic linkages as subchains.The planar five-bar metamorphic linkages that have three phases resulting from locking of motors are considered.Under the assumption that the constraint exerted by the reconfigurable limb can switch between no constraint,a constraint force,and a constraint couple,the output motions of the metamorphic linkage in its two planar four-bar linkage phases are identified.By adding an appropriate joint to planar four-bar linkages with translational output,four planar five-bar linkages that can be employed in the construction of reconfigurable limbs are enumerated.Serial chains that can provide a constraint couple and a constraint force are synthesized based on screw theory.Reconfigurable limbs that have three configurations associated with the three distinct phases of the metamorphic linkages are assembled with planar five-bar metamorphic linkages and serial chains with four degrees of freedom.A class of reconfigurable parallel mechanisms are constructed by connecting a moving platform and a base with three identical reconfigurable limbs.The degrees of freedom of the reconfigurable parallel mechanism in different configurations with the metamorphic linkages in different phases are given.Finally,the actuation scheme for this kind of mechanisms is addressed.