Showing papers on "Degrees of freedom published in 1989"
TL;DR: The purpose of this chapter is to review this “traditional” approach in the area of nuclear forces and their applications to nuclear structure.
Abstract: Nowadays it has become customary in nuclear physics to denote by “tradition” the approach that considers nucleons and mesons as the relevant degrees of freedom. It is the purpose of this chapter to review this “traditional” approach in the area of nuclear forces and their applications to nuclear structure.
1,049 citations
TL;DR: In this paper, the uniqueness of the vector potential is given special attention, and a numerically stable finite-element scheme that performs well at low and high frequencies, does not require an unduly high number of degrees of freedom, and is capable of treating multiple connected conductors is presented.
Abstract: Various magnetic vector potential formulations for the eddy-current problem are reviewed. The uniqueness of the vector potential is given special attention. The aim is to develop a numerically stable finite-element scheme that performs well at low and high frequencies, does not require an unduly high number of degrees of freedom, and is capable of treating multiple connected conductors. >
720 citations
TL;DR: In this article, the authors investigated variational principles employing independent rotation fields, which lead to membrane elements with "drilling degrees of freedom" of practical use in shell analysis, and showed that convenient interpolatory patterns require modifications of the classical variational framework.
Abstract: Variational principles employing independent rotation fields are investigated. In the two-dimensional case these lead to membrane elements with “drilling degrees of freedom”, of practical use in shell analysis. We argue that convenient interpolatory patterns require modifications of the classical variational framework. Several formulations are proposed and shown to be convergent for displacement/rotation interpolations of all orders.
294 citations
TL;DR: In this paper, it was shown that edge elements, as vectorial finite-element approximations fields like e and h, can be used to solve scattering problems, which can be done in essentially two ways, according to which of the two fields d or b one most wishes to get in divergence-free form.
Abstract: It is shown that edge elements, as vectorial finite-element approximations fields like e and h, can be used to solve scattering problems. This can be done in essentially two ways, according to which of the two fields d or b one most wishes to get in divergence-free form. Apparent drawback of edge elements (due to the increased number of degrees of freedom in comparison with nodal elements) are more than compensated by economies due to greater sparsity. Moreover, they could help get rid of unwanted spurious modes when resonance frequencies of waveguides of complicated shape are computed. >
180 citations
TL;DR: In this paper, the load distribution problem for two coordinating industrial robots handling a single object is studied and optimal algorithms with and without a bound on the joint torques are investigated, and the results show that the algorithms are computationally complicated and not suitable for real-time applications.
Abstract: The load distribution problem for two coordinating industrial robots handling a single object is studied. When two industrial robots grasp a single object, the total number of degrees of freedom is usually greater than six. Thus, the joint torques of two robots for a required motion of the object is not unique. The redundant degrees of freedom may be used to optimize certain kind of performance. The least energy consumption is selected as the optimization criterion. Optimal algorithms without and with a bound on the joint torques are investigated. The results show that the algorithms are computationally complicated and not suitable for real-time applications. Alternatively, optimal algorithms are proposed for load distribution with minimum exerted forces on the object. These algorithms require less computational time, which makes them attractive for real-time applications. >
141 citations
TL;DR: In this article, a spherical DC servo motor with three degrees of freedom was proposed, and the dynamics of the spherical motor were investigated theoretically and experimentally, considering torque interference, gyro moment and gravity.
Abstract: A spherical DC servo motor with three degrees of freedom is proposed. First, the process of generating three-dimensional torque is analyzed to obtain the torque constant matrix. The matrix elements are shown to vary with rotor inclination, and winding currents are shown to interfere with each other. Then, the dynamics of the spherical motor are investigated theoretically and experimentally, considering torque interference, gyro moment and gravity. Finally, the trajectory of the prototype motor is shown in order to clarify its abilities. This new spherical motor is expected to produce a smaller, a lighter mechanism, since no gears or linkages are needed.
87 citations
TL;DR: In this paper, it was shown that any local quantum field theory admits thermodynamical equilibrium states (KMS-states) for all positive temperatures provided it satisfies a nuclearity condition, which restricts the admissible number of local degrees of freedom.
Abstract: It is shown that any local quantum field theory admits thermodynamical equilibrium states (KMS-states) for all positive temperatures provided it satisfies a “nuclearity condition,” proposed by Wichmann and one of the authors, which restricts the admissible number of local degrees of freedom.
83 citations
TL;DR: In this paper, a sufficient condition for the non-existence of an additional global analytic integral is given for n-degrees of freedom Hamiltonians with a homogeneous potential, expressed quite simply in terms of the Kowalevski exponents (KE), which characterize the singularity structure of the solution in the complex t-plane.
67 citations
TL;DR: In this article, a detailed numerical simulation incorporating the many internal degrees of freedom of the DNA chain was performed to recover the experimental features of DNA in a gel under the application of a time-dependent field.
Abstract: The study of DNA in a gel under the application of a time‐dependent field has revealed some unexpected experimental features. These features are recovered by means of a detailed numerical simulation incorporating the many internal degrees of freedom of the DNA chain. These results can in turn be understood qualitatively by means of a model containing only four degrees of freedom.
63 citations
60 citations
TL;DR: In this article, Car and Parrinello's molecular dynamics method (1985) is analyzed and the authors show that the degrees of freedom associated with the electronic wavefunctions do not behave as classical degrees-of-freedom because their motions are damped by the constraint of normalisation of the wave-functions.
Abstract: A detailed analysis of Car and Parrinello's molecular dynamics method (1985) is presented. It is shown that the degrees of freedom associated with the electronic wavefunctions do not behave as classical degrees of freedom because their motions are damped by the constraint of normalisation of the wavefunctions. Therefore, the accuracy to which the electronic configuration remains on the Born-Oppenheimer surface and the ionic configuration evolves at constant energy during a dynamical simulation is not a result of treating the electronic degrees of freedom as classical degrees of freedom. Instead it is shown that the accuracy of the constant energy evolution of the ionic system in a molecular dynamics calculation is explained by the tendency for errors in the Hellmann-Feynman forces to cancel when the molecular dynamics equations of motion are used to evolve the electronic degrees of freedom. A quantitative analysis of this error cancellation is presented. By analysing the magnitude of the error in the electronic wavefunction, a criterion is developed for the maximum velocity of propagation of the ions at which the evolution of the electronic configuration remains stable.
TL;DR: The singular character of such perturbations is inevitable since it is stipulated by the general requirements of the type of relativistic invariance, the infiniteness of the number of degrees of freedom, by the short rangedness (6-potentials).
Abstract: The concept of singular bilinear form arose in connection with the question of giving mathematical meaning to formal expressions defining perturbations of Hamiltonians in models of quantum physics. The singular character of such perturbations is inevitable since it is stipulated by the general requirements of the type of relativistic invariance, the infiniteness of the number of degrees of freedom, by the short rangedness (6-potentials).
TL;DR: In this article, the design of an element which includes rotations normal to the plane of the element as additional degrees of freedom is described and shown to give virtually defect-free performance.
TL;DR: A brief introduction to the field is given together with an overview of the lectures given at the workshop on External Noise and its interaction with Spatial Degrees of Freedom in Nonlinear Dissipative Systems organized by the Center for Nonlinear Studies at Los Alamos.
Abstract: A brief introduction to the field is given together with an overview of the lectures given at the workshop on External Noise and its Interaction with Spatial Degrees of Freedom in Nonlinear Dissipative Systems organized by the Center for Nonlinear Studies at Los Alamos, March 28–31, 1988. It is hoped that the publication of papers presented at the workshop in a single issue of theJournal of Statistical Physics will help draw attention to the recent developments in this rapidly area of nonequilibrium phenomena.
Patent•
27 Nov 1989
TL;DR: In this article, a motion simulator for vehicle driver training is presented, which includes at least three actuators placed at the vertices of a triangle, connected to three connecting points arranged in a triangle for the fastening of a platform of a cabin by lever arms.
Abstract: A motion simulator for vehicle driver training, which includes at least three actuators placed at the vertices of a triangle, connected to at least three connecting points, arranged in a triangle, for the fastening of a platform of a cabin by lever arms, one end of each of these arms being connected to a corresponding actuator by a joint with two degrees of freedom, the other end of one of the lever arms being connected to a point for fastening the platform by the joint with two degrees of freedom, and the other end of the other lever arms being connected, at all times, to one of the other platform fastening points by a joint with at least four degrees of freedom.
Patent•
21 Mar 1989
TL;DR: A portable hair dryer assembly includes a battery that is recharged to operate the air moving system of the assembly as mentioned in this paper, and a cover for the air intake system, and a system for moving the air exhaust nozzle so that the assembly has a plurality of degrees of freedom.
Abstract: A portable hair dryer assembly includes a battery that is recharged to operate the air moving system of the assembly. The assembly further includes a cover for the air intake system, and a system for moving the air exhaust nozzle so that the assembly has a plurality of degrees of freedom.
TL;DR: In this paper, the authors present a method for the computation of time-dependent quantum correlation functions, where they calculate the temperature dependence of the correlation function at zero time and analytically continue to obtain the time dependence at finite temperature.
14 May 1989
TL;DR: An approach is presented which simplifies the programming of the algorithmic component for high-degree-of-freedom objects, and is applied to generate joint trajectories for a walking biped.
Abstract: The authors suggest that there are two components required in most control schemes: an algorithmic component which takes a high-level goal and generates joint trajectories, and a dynamics component which takes these joint trajectories and generates the required joint torques. The joint torques are then sent to the mechanism, which (it is hoped) achieves the high-level goal. An approach is presented which simplifies the programming of the algorithmic component for high-degree-of-freedom objects. Instead of supplying a complete set of joint trajectories as a function of time, the algorithm controls other, more intuitive, degrees of freedom. The degrees of freedom are automatically converted to the more conventional joint trajectories. The algorithm can underconstrain the object, in which case constrained optimization is used in converting to joint trajectories. This approach is applied to generate joint trajectories for a walking biped. The walking algorithm, is presented along with the results from testing with the authors' Newton simulation system (ibid., vol.3, p.1806-11). >
TL;DR: In this paper, a 4-node quadrilateral membrane element with one rotational and two translational degrees of freedom per node is presented, called QC9(8), which is formed by degeneration of the 9-node Lagrange element and condensation of the centre degree of freedom.
Abstract: An assessment is made of a 4‐node quadrilateral membrane element with one rotational and two translational degrees of freedom per node, as formulated by Taylor and Simo. The element, QC9, is formed by degeneration of the 9‐node Lagrange element and condensation of the centre degrees of freedom. An 8‐point, modified reduced integration scheme is implemented in this element, QC9(8), to improve on the 3 × 3 quadrature performance, yet avoid the additional rank deficiency due to reduced integration (2 × 2). QC9(8) performs as good or better than all elements surveyed. It is shown that a similar degeneration of the 16‐node Lagrangian element can be carried out, but that the resulting element fails the patch test.
TL;DR: In this paper, the authors consider a model problem with just two degrees of freedom for which the coordinate transformations become planar and therefore easily visualizable, and a set of plane diagrams is provided showing how the diagonalization is achieved for the model problem considered.
Abstract: The theory of small oscillations, when cast in matrix form, leads to an eigenvalue problem involving the simultaneous diagonalization of two real symmetric matrices. While a geometrical interpretation of this process exists, its visualization is generally hampered by the multidimensional nature of the coordinate transformations involved. I consider a model problem with just two degrees of freedom for which the coordinate transformations become planar and therefore easily visualizable. A set of plane diagrams is provided showing how the diagonalization is achieved for the model problem considered.
01 Mar 1989
TL;DR: In this paper, pure coherent squeezed states of many degrees of freedom are analyzed via a fluctuation matrix description and a symplectic group description, and a group description is used to analyze the properties of the squeezed states.
Abstract: Pure coherent squeezed states of many degrees of freedom are analyzed via a fluctuation matrix description and a symplectic group description.