Showing papers on "Degrees of freedom published in 2002"

Repositioning and reorientation of master/slave relationship in minimally invasive telesurgery

Abstract: The invention provides robotic surgical systems which allow selectable independent repositioning of an input handle of a master controller and/or a surgical end effector without corresponding movement of the other. In some embodiments, independent repositioning is limited to translational degrees of freedom. In other embodiments, the system provides an input device adjacent a manipulator supporting the surgical instrument so that an assistant can reposition the instrument at the patient's side.

Tachyon Matter

Abstract: It is shown that classical decay of unstable D-branes in bosonic and superstring theories produces pressureless gas with non-zero energy density. The energy density is stored in the open string fields, even though around the minimum of the tachyon potential there are no open string degrees of freedom. We also give a description of this phenomenon in an effective field theory.

Motion capture assisted animation: texturing and synthesis

Abstract: We discuss a method for creating animations that allows the animator to sketch an animation by setting a small number of keyframes on a fraction of the possible degrees of freedom. Motion capture data is then used to enhance the animation. Detail is added to degrees of freedom that were keyframed, a process we call texturing. Degrees of freedom that were not keyframed are synthesized. The method takes advantage of the fact that joint motions of an articulated figure are often correlated, so that given an incomplete data set, the missing degrees of freedom can be predicted from those that are present.

A Motorcycle Multi-Body Model for Real Time Simulations Based on the Natural Coordinates Approach

Abstract: This paper presents an eleven degrees of freedom, non-linear, multi-body dynamics model of a motorcycle. Front and rear chassis, steering system, suspensions and tires are the main features of the model. An original tire model was developed, which takes into account the geometric shape of tires and the elastic deformation of tire carcasses. This model also describes the dynamic behavior of tires in a way similar to relaxation models. Equations of motion stem from the natural coordinates approach. First, each rigid body is described with a set of fully cartesian coordinates. Then, links between the bodies are obtained by means of algebraic equations. This makes it possible to obtain simple equations of motion, even though the coordinates are redundant. The model was implemented in a Fortran code, named FastBike. In order to test the code, both simulated and real slalom and lane change maneuvers were carried out. A very good agreement between the numerical simulations and experimental test was found. The co...

Open Strings from Script N = 4 Super Yang-Mills

Abstract: Exploiting insights on strings moving in pp-wave backgrounds, we show how open strings emerge from = 4 SU(N) Yang-Mills theory as fluctuations around certain states carrying R-charge of order N. These states are dual to spherical D3-branes of AdS5 × S5 and we reproduce the spectrum of small fluctuations of these states from Yang-Mills theory. We discuss the emergence of the G2 light degrees of freedom expected when G such D3-branes nearly coincide. The open strings running between the branes can be quantized easily in a Penrose limit of the spacetime. Taking the corresponding large charge limit of the Yang-Mills theory, we reproduce the open string worldsheets and their spectra from field theory degrees of freedom.

Open Strings from N=4 Super Yang-Mills

Abstract: Exploiting insights on strings moving in pp-wave backgrounds, we show how open strings emerge from N = 4 SU(M) Yang-Mills theory as fluctuations around certain states carrying R-charge of order M. These states are dual to spherical D3-branes of AdS_5 x S^5 and we reproduce the spectrum of small fluctuations of these states from Yang Mills theory. When G such D3-branes coincide, the expected G^2 light degrees of freedom emerge. The open strings running between the branes can be quantized easily in a Penrose limit of the spacetime. Taking the corresponding large charge limit of the Yang-Mills theory, we reproduce the open string worldsheets and their spectra from field theory degrees of freedom.

Microwrist system for surgical procedures

Abstract: A medical robotic system with a handle assembly that is used to control a medical instrument. The handle assembly and medical instrument have five degrees of freedom. Five degrees of freedom may provide greater dexterity than medical robotic systems of the prior art with four or less degrees of freedom. Five degrees of freedom reduces the size and complexity of the instrument.

Motion capture assisted animation

Abstract: We discuss a method for creating animations that allows the animator to sketch an animation by setting a small number of keyframes on a fraction of the possible degrees of freedom. Motion capture d...

Lectures on Chaotic Dynamical Systems

Abstract: Basic concepts Zero-dimensional dynamics One-dimensional dynamics Two-dimensional dynamics Systems with 1.5 degrees of freedom Systems generated by three-dimensional vector fields Lyapunov exponents Appendix Bibliography Index.

Modal Reduction of a Nonlinear Rotating Beam Through Nonlinear Normal Modes

Abstract: A method for determining reduced-order models for rotating beams is presented. The approach is based on the construction of nonlinear normal modes that are defined in terms of invariant manifolds that exist for the system equations of motion. The beam considered is an idealized model for a rotor blade whose motions are dominated by transverse vibrations in the direction perpendicular to the plane of rotation (known as flapping). The mathematical model for the rotating beam is relatively simple, but contains the nonlinear coupling that exists between transverse and axial deflections. When one employs standard modal expansion or finite element techniques to this system, this nonlinearity causes slow convergence, leading to models that require many degrees of freedom in order to achieve accurate dynamical representations. In contrast, the invariant manifold approach systematically accounts for the nonlinear coupling between linear modes, thereby providing models with very few degrees of freedom that accurately capture the essential dynamics of the system. Models with one and two nonlinear modes are considered, the latter being able to handle systems with internal resonances. Simulation results are used to demonstrate the validity of the approach and to exhibit features of the nonlinear modal responses. @DOI: 10.1115/1.1426071#

The concept of jogging JOHNNIE

Abstract: Within the large variety of existing and still newly emerging biped walking machines Jogging JOHNNIE represents a fundamental study on fast walking and on especially adapted foot-dynamics. Air phases are possible with two feet lifted off the ground. Each foot possesses six degrees of freedom with respect to the body and additionally seven degrees of freedom within the local foot environment. The overall system includes 23 degrees of freedom. It is 1.80 m, large and weighs 40 kg. Up to now stable walking has been achieved.

Calibration of flux-gate magnetometers using relative motion

Abstract: A simple analytical model for the calibration of a flux-gate magnetometer using relative sensor motion in a constant magnitude magnetic field (B) is presented. Sensor motion is parametrized in terms of elementary rotations about one axis. The number of elementary rotations constitutes the number of degrees of freedom of the motion. A generalization is performed by investigating cases with known/unknown B, one/several different values of B, one/several degrees of freedom. The maximum number of calibration parameters, which can be determined in each case, is established. The conclusion is that the determination of all calibration parameters, i.e. an absolute calibration of the instrument, is already possible if the relative motion has at least two degrees of freedom at a known, constant B value. Two experimental applications of the model are described briefly.

Jumping in frogs: assessing the design of the skeletal system by anatomically realistic modeling and forward dynamic simulation.

Abstract: Comparative musculoskeletal modeling represents a tool to understand better how motor system parameters are fine-tuned for specific behaviors. Frog jumping is a behavior in which the physical properties of the body and musculotendon actuators may have evolved specifically to extend the limits of performance. Little is known about how the joints of the frog contribute to and limit jumping performance. To address these issues, we developed a skeletal model of the frog Rana pipiens that contained realistic bones, joints and body-segment properties. We performed forward dynamic simulations of jumping to determine the minimal number of joint degrees of freedom required to produce maximal-distance jumps and to produce jumps of varied take-off angles. The forward dynamics of the models was driven with joint torque patterns determined from inverse dynamic analysis of jumping in experimental frogs. When the joints were constrained to rotate in the extension-flexion plane, the simulations produced short jumps with a fixed angle of take-off. We found that, to produce maximal-distance jumping, the skeletal system of the frog must minimally include a gimbal joint at the hip (three rotational degrees of freedom), a universal Hooke's joint at the knee (two rotational degrees of freedom) and pin joints at the ankle, tarsometatarsal, metatarsophalangeal and iliosacral joints (one rotational degree of freedom). One of the knee degrees of freedom represented a unique kinematic mechanism (internal rotation about the long axis of the tibiofibula) and played a crucial role in bringing the feet under the body so that maximal jump distances could be attained. Finally, the out-of-plane degrees of freedom were found to be essential to enable the frog to alter the angle of take-off and thereby permit flexible neuromotor control. The results of this study form a foundation upon which additional model subsystems (e.g. musculotendon and neural) can be added to test the integrative action of the neuromusculoskeletal system during frog jumping.

Supervised dimension reduction of intrinsically low-dimensional data

Abstract: High-dimensional data generated by a system with limited degrees of freedom are often constrained in low-dimensional manifolds in the original space. In this article, we investigate dimension-reduction methods for such intrinsically low-dimensional data through linear projections that preserve the manifold structure of the data. For intrinsically one-dimensional data, this implies projecting to a curve on the plane with as few intersections as possible. We are proposing a supervised projection pursuit method that can be regarded as an extension of the single-index model for nonparametric regression. We show results from a toy and two robotic applications.

Computer having a monitor that has multiple degrees of freedom with respect to the base of the computer

Abstract: A computer monitor is movably attached to stanchions that are pivotally attached to a base of the computer. The monitor can be moved toward and away from the base and can be angularly adjusted with respect to the base of the computer whereby the monitor has a plurality of degrees of freedom and adjustment with respect to the base of the computer.

Smooth Macro-Elements Based on Powell–Sabin Triangle Splits

Abstract: Macro-elements of smoothness Cr on Powell–Sabin triangle splits are constructed for all r≥0. These new elements are improvements on elements constructed in [13] in that certain unneeded degrees of freedom have been removed.

On various solutions of the coupled KP equation

Abstract: The coupled KP (cKP) equation possesses N-soliton solutions with many more degrees of freedom than the solitons for the usual KP equation have. In comparison, cKP solutions can therefore be expected to model far more complex interactions than their KP counterparts. In this paper we present some typical solutions for the cKP system (and for some of its reductions: a complex coupled KdV equation and a coupled Boussinesq equation) and we analyse their interaction and asymptotic properties.

Effective Lagrangians for physical degrees of freedom in the Randall–Sundrum model

Abstract: We derive the second variation Lagrangian of the Randall–Sundrum model with two branes, study its gauge invariance and diagonalize it in the unitary gauge. We also show that the effective four-dimensional theory looks different on different branes and calculate the observable mass spectra and the couplings of the physical degrees of freedom of five-dimensional gravity to matter.

On the absence of simultaneous reflection and transmission in integrable impurity systems

Abstract: We establish that the Yang-Baxter equations in the presence of an impurity can in general only admit solutions of simultaneous tranmission and reflection when the transmission and reflection amplitudes commute in the defect degrees of freedom with an additional exchange of the corresponding rapidities. In the absence of defect degrees of freedom we show in complete generality, that the only exceptions to this are theories which possess rapidity independent bulk scattering matrices. In particular bulk theories with diagonal scattering matrices, can only be the free Boson and Fermion, the Federbush model and their generalizations. These anyonic solutions do not admit the possibility of excited impurity states.

Rate constants for the CH4 + H → CH3 + H2 reaction calculated with a generalized reduced-dimensionality method

Abstract: We present calculations of rate constants for the CH4 + H → CH3 + H2 reaction. Calculations were performed using a reduced-dimensionality model with four degrees of freedom and two different method...

Real-time trajectory generation for omnidirectional vehicles

Abstract: We discuss a method of generating near-optimal trajectories for a robot with omnidirectional drive capabilities, taking the second-order dynamics of the vehicle into account. The relaxation of optimality results in immense computational savings, critical in dynamic environments. In particular, a decoupling strategy for each of the three degrees of freedom of the vehicle is presented, along with a method for coordinating the degrees of freedom. A nearly optimal trajectory for the vehicle can typically be calculated in less than 1000 floating point operations, which makes it attractive for real-time control in dynamic and uncertain environments.

Continuum spin foam model for 3d gravity

Abstract: An example illustrating a continuum spin foam framework is presented. This covariant framework induces the kinematics of canonical loop quantization, and its dynamics is generated by a renormalized sum over colored polyhedra. Physically the example corresponds to 3d gravity with cosmological constant. Starting from a kinematical structure that accommodates local degrees of freedom and does not involve the choice of any background structure (e.g., triangulation), the dynamics reduces the field theory to have only global degrees of freedom. The result is projectively equivalent to the Turaev–Viro model.

Spin-Space Entanglement Transfer and Quantum Statistics

Abstract: Both the topics of entanglement and particle statistics have aroused enormous research interest since the advent of quantum mechanics. Using two pairs of entangled particles we show that indistinguishability enforces a transfer of entanglement from the internal to the spatial degrees of freedom without any interaction between these degrees of freedom. Moreover, subensembles selected by local measurements of the path will, in general, have different amounts of entanglement in the internal degrees of freedom depending on the statistics (either fermionic or bosonic) of the particles involved.

Diversity and freedom: a fundamental tradeoff in multiple antenna channels

Abstract: Multiple antennas can be used for increasing the amount of diversity or the number of degrees of freedom in wireless communication systems We propose the point of view to study the tradeoff between the two types of gains In this paper, we present the complete results on the optimal tradeoff, and give a brief discussion on the techniques used to get the results

Electronic structure of Pu monochalcogenides and monopnictides

Abstract: The electronic and magnetic properties of Pu monopnictides and monochalcogenides, PuX (X = N, P, As, Sb, Bi, O, S, Se, Te, Po), are studied using the ab initio>"> self-interaction-corrected local spin-density approximation This approach allows for an integer number of f-states to be localized, while the remaining f-electron degrees of freedom are available for band formation By varying the relative proportions of localized and delocalized f-states, the energetically most favourable (groundstate) configuration can be established We show that the experimental data can be interpreted in terms of the coexistence of both localized and delocalized f-states

Multiloop Kinematotropic Mechanisms

Abstract: Starting from single-loop kinematic chains whose pairs present different connectivities when the chains are displaced in different positions, the paper shows how to assemble multiloop chains with numbers of degrees of freedom that change due to continuous variations in the position variables of the chains. This special mobility property is called kinematotropy. The paper provides a method (based on the displacement group theory) to form chains that allow any desired change in the number of degrees of freedom, with a sudden or gradual increment of this number. Several examples are presented and applications are discussed.Copyright © 2002 by ASME

New special wave boundary elements for short wave problems

Abstract: The theory of special boundary elements which incorporate wave shapes into the element shape functions is described. The new boundary elements are applied to the classical problem of plane waves scattered by a circular cylinder. The new boundary elements demonstrate reduced errors, for a given number of degrees of freedom, of three to five orders of magnitude. No difficulties were encountered in the implementation of the new elements. It is concluded that this is a powerful new method for scattering of short waves. Copyright © 2002 John Wiley & Sons, Ltd.

Use of extra degrees of freedom in multilevel drives

Abstract: Multilevel converters with series connection of semiconductors allow power electronics to reach medium voltages (1-10 kV) with relatively standard components. The increase of the number of semiconductors provides extra degrees of freedom, which can be used to improve different characteristics. This paper is focused on variable-speed drives and it is shown that with the proposed multilevel direct torque control strategy (DiCoIF) the tradeoff between the performances of the drive (harmonic distortions, torque dynamics, voltage step gradients, etc.) and the switching frequency of the semiconductors is improved. Then, a slightly modified strategy reducing common-mode voltage and bearing currents is presented.