Kinematic Restrictions Research Articles

Kinematics of primate midfoot flexibility

This study describes a unique assessment of primate intrinsic foot joint kinematics based upon bone pin rigid cluster tracking. It challenges the assumption that human evolution resulted in a reduction of midfoot flexibility, which has been identified in other primates as the "midtarsal break." Rigid cluster pins were inserted into the foot bones of human, chimpanzee, baboon, and macaque cadavers. The positions of these bone pins were monitored during a plantarflexion-dorsiflexion movement cycle. Analysis resolved flexion-extension movement patterns and the associated orientation of rotational axes for the talonavicular, calcaneocuboid, and lateral cubometatarsal joints. Results show that midfoot flexibility occurs primarily at the talonavicular and cubometatarsal joints. The rotational magnitudes are roughly similar between humans and chimps. There is also a similarity among evaluated primates in the observed rotations of the lateral cubometatarsal joint, but there was much greater rotation observed for the talonavicular joint, which may serve to differentiate monkeys from the hominines. It appears that the capability for a midtarsal break is present within the human foot. A consideration of the joint axes shows that the medial and lateral joints have opposing orientations, which has been associated with a rigid locking mechanism in the human foot. However, the potential for this same mechanism also appears in the chimpanzee foot. These findings demonstrate a functional similarity within the midfoot of the hominines. Therefore, the kinematic capabilities and restrictions for the skeletal linkages of the human foot may not be as unique as has been previously suggested.

CHIPS_TPT models for exclusive Geant4 simulation of neutron-nuclear reactions at low energies

A novel TPT code (Toolkit for Particle Transport), which is included in CHIPS_TPT physics list for Geant4 simulations, is briefly overviewed. Underlying concept of exclusive modelling is introduced and its beneficial features are illustrated with several examples. Widely used neutron Monte Carlo codes, MCNP and Geant4/HP, are based on inclusive algorithms that independently model neutron state change and secondary particles production while tracking. The exclusive approach implemented in TPT overcomes this unphysical separation and makes it possible to allow for kinematic restrictions as well as correlated emission of gamma-rays and secondaries.

Steering the Last Trailer as a Virtual Tractor for Reversing Vehicles With Passive On- and Off-Axle Hitches

The paper reports on a practical backward motion strategy for a vehicle pushing several passive trailers with any combination of on- and off-axle hitches. The last trailer is defined as a virtual tractor that can be guided along paths of varying curvature like a single non-holonomic vehicle. Then, kinematic relationships are proposed to translate the resulting motion commands to the actual tractor. The paper extends previous work by specifically addressing propagation of virtual set-points through on-axle hitches. This case is difficult because direct propagation cannot be achieved due to kinematic restrictions imposed by current joint angles. The method has been experimentally applied for both autonomous path-tracking and online operator steering using a tracked mobile robot with two different off- and on-axle combinations of dissimilar trailers. Results indicate applicability in autonomous vehicles and advanced driver assistance systems.

A two‐scale failure model for heterogeneous materials: numerical implementation based on the finite element method

SUMMARYIn the first part of this contribution, a brief theoretical revision of the mechanical and variational foundations of a Failure‐Oriented Multiscale Formulation devised for modeling failure in heterogeneous materials is described.The proposed model considers two well separated physical length scales, namely: (i) the macroscale where nucleation and evolution of a cohesive surface is considered as a medium to characterize the degradation phenomenon occurring at the lower length scale, and (ii) the microscale where some mechanical processes that lead to the material failure are taking place, such as strain localization, damage, shear band formation, and so on. These processes are modeled using the concept of Representative Volume Element (RVE). On the macroscale, the traction separation response, characterizing the mechanical behavior of the cohesive interface, is a result of the failure processes simulated in the microscale. The traction separation response is obtained by a particular homogenization technique applied on specific RVE sub‐domains. Standard, as well as, Non‐Standard boundary conditions are consistently derived in order to preserve objectivity of the homogenized response with respect to the micro‐cell size.In the second part of the paper, and as an original contribution, the detailed numerical implementation of the two‐scale model based on the finite element method is presented. Special attention is devoted to the topics, which are distinctive of the Failure‐Oriented Multiscale Formulation, such as: (i) the finite element technologies adopted in each scale along with their corresponding algorithmic expressions, (ii) the generalized treatment given to the kinematical boundary conditions in the RVE, and (iii) how these kinematical restrictions affect the capturing of macroscopic material instability modes and the posterior evolution of failure at the RVE level.Finally, a set of numerical simulations is performed in order to show the potentialities of the proposed methodology, as well as, to compare and validate the numerical solutions furnished by the two‐scale model with respect to a direct numerical simulation approach. Copyright © 2013 John Wiley & Sons, Ltd.

The longitudinal response function of the deuteron in chiral effective field theory

We use chiral effective field theory (χEFT) to make predictions for the longitudinal electromagnetic response function of the deuteron, f L , which is measured in d(e, e′N) reactions. In this case the impulse approximation gives the full χEFT result up to \(\mathcal{O}(P^4 )\) relative to leading order. By varying the cutoff in the χEFT calculation between 0.6 and 1 GeV we conclude that the calculation is accurate to better than 10% for values of q 2 within 4 fm−2 of the quasi-free peak, up to final-state energies E np = 60 MeV. In these regions χEFT is in reasonable agreement with predictions for f L obtained using the Bonn potential. We also find good agreement with existing experimental data on f L , albeit in a more restricted kinematic domain.

Dispersive approach to QCD and inclusiveτlepton hadronic decay

The dispersive approach to QCD is applied to the study of the inclusive $\ensuremath{\tau}$ lepton hadronic decay. This approach provides the unified integral representations for the hadronic vacuum polarization function, related $R$ function, and Adler function. These representations account for the intrinsically nonperturbative constraints, which originate in the kinematic restrictions on the functions on hand, and retain the effects due to hadronization, which play a valuable role in the analysis of the strong interaction processes at low energies. The dispersive approach proves to be capable of describing recently updated ALEPH and OPAL experimental data on inclusive $\ensuremath{\tau}$ lepton hadronic decay in vector and axial-vector channels. The vicinity of values of the QCD scale parameter obtained in both channels testifies to the potential ability of the developed approach to describe the aforementioned data in a self-consistent way.

Gamow–Teller strength extraction from (3He, t) reactions

Abstract Details of Gamow–Teller (GT) and Fermi (F) strength extraction from charge-exchange reactions at intermediate energies, as well as the concept of using the phenomenological effective interaction for the description of the reactions are reviewed. The focus lies on high-resolution ( 3 He, t ) data, yet new data on ( d , 2 He) charge-exchange reactions are presented as well to indicate the connection and the similarity of both probes to the elementary ( p , n ) , resp. ( n , p ) reactions. We show that for the extraction of B ( GT ) and B ( F ) strength a proper extrapolation of the charge-exchange cross section to the zero momentum transfer point, q = 0 , gets to be increasingly important for medium to high-mass target nuclei and at moderate excitation energies of a few MeV. Numerous ( 3 He, t ) and ( p , n ) spectra are being compared, and, once adjusted for the different momentum transfers, they reveal a remarkable similarity up to the highest measured excitation energies of ≈ 25 MeV . Further, we remark that the precision, with which GT and F transition strengths can be extracted, is limited by the relatively poor knowledge of the absorption processes, and a more thorough theoretical understanding of the nuclear structure leading to absorption in charge-exchange reactions, especially in the restricted kinematic region of low-momentum transfers, is warranted. Finally, B ( GT ) values for the 136 Xe( 3 He, t ) are being re-evaluated in the light of the present discussion.

Three-dimensional Route Planning for Unmanned Aerial Vehicles in a Risk Environment

This paper introduces a new approach for three-dimensional flight path optimization for unmanned aerial vehicles. It considers the performance of the air vehicle as well as mission specific requirements including the avoidance of no-fly areas, risk reduction in threat environments by terrain following flight or terrain masking low-level flight, and other regulations such as fixed release and approach vectors at the start and destination locations. The focus of the approach is on a proper discretization of the airspace by a network which allows the application of standard algorithms of combinatorial optimization. In contrast to conventional discretizations by grids or grid-like graphs, our network is non-regular since created by some random process. Moreover, each path in the network corresponds to a twice continuously differentiable trajectory which obeys the kinematic restrictions of the air vehicle and which is feasible with respect to the operational requirements of the mission. With suitable costs defined on the edges of the network, a minimum-cost path calculation allows to identify a trajectory of shortest length, shortest flight time, minimum flight height, or minimum visibility from the ground. The latter objectives aim to minimize the probability of being detected by hostile forces, hence increasing the survivability of the air vehicle.

An optimal control strategy for two-dimensional motion camouflage with non-holonimic constraints

Motion camouflage is a stealth behaviour observed both in hover-flies and in dragonflies. Existing controllers for mimicking motion camouflage generate this behaviour on an empirical basis or without considering the kinematic motion restrictions present in animal trajectories. This study summarises our formal contributions to solve the generation of motion camouflage as a non-linear optimal control problem. The dynamics of the system capture the kinematic restrictions to motion of the agents, while the performance index ensures camouflage trajectories. An extensive set of simulations support the technique, and a novel analysis of the obtained trajectories contributes to our understanding of possible mechanisms to obtain sensor based motion camouflage, for instance, in mobile robots.

Anomalously interacting new extra vector bosons and their first LHC constraints

In this review phenomenological consequences of the Standard Model extension by means of new spin-1 chiral fields with the internal quantum numbers of the electroweak Higgs doublets are summarized. The prospects for resonance production and detection of the chiral vector $Z^*$ and $W^{*\pm}$ bosons at the LHC energies are considered. The $Z^*$ boson can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distributions in the same way as the well-known extra gauge $Z'$ bosons. However, the $Z^*$ bosons have unique signatures in transverse momentum, angular and pseudorapidity distributions of the final leptons, which allow one to distinguish them from other heavy neutral resonances. In 2010, with 40 pb$^{-1}$ of the LHC proton-proton data at the energy 7 TeV, the ATLAS detector was used to search for narrow resonances in the invariant mass spectrum of $e^+e^-$ and $\mu^+\mu^-$ final states and high-mass charged states decaying to a charged lepton and a neutrino. No statistically significant excess above the Standard Model expectation was observed. The exclusion mass limits of 1.15 TeV$/c^2$ and 1.35 TeV$/c^2$ were obtained for the chiral neutral $Z^*$ and charged $W^*$ bosons, respectively. These are the first direct limits on the $W^*$ and $Z^*$ boson production. For almost all currently considered exotic models the relevant signal is expected in the central dijet rapidity region. On the contrary, the chiral bosons do not contribute to this region but produce an excess of dijet events far away from it. For these bosons the appropriate kinematic restrictions lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump expected in the most exotic models.

Trajectory planning of mobile robots using indirect solution of optimal control method in generalized point-to-point task

This paper presents an optimal control strategy for optimal trajectory planning of mobile robots by considering nonlinear dynamic model and nonholonomic constraints of the system. The nonholonomic constraints of the system are introduced by a nonintegrable set of differential equations which represent kinematic restriction on the motion. The Lagrange’s principle is employed to derive the nonlinear equations of the system. Then, the optimal path planning of the mobile robot is formulated as an optimal control problem. To set up the problem, the nonlinear equations of the system are assumed as constraints, and a minimum energy objective function is defined. To solve the problem, an indirect solution of the optimal control method is employed, and conditions of the optimality derived as a set of coupled nonlinear differential equations. The optimality equations are solved numerically, and various simulations are performed for a nonholonomic mobile robot to illustrate effectiveness of the proposed method.

Exponential Fields Formulation for WMR Navigation

In this manuscript, an autonomous navigation algorithm for wheeled mobile robots (WMR) operating in dynamic environments (indoors or structured outdoors) is formulated. The planning scheme is of critical importance for autonomous navigational tasks in complex dynamic environments. In fast dynamic environments, path planning needs algorithms able to sense simultaneously a diversity of obstacles, and use such sensory information to improve real-time navigation control, while moving towards a desired goal destination. The framework tackles 4 issues. 1) Reformulation of the Social Force Model (SFM) adapted to WMR; 2) the cohesion of a general inertial scheme to represents motion in any coordinate system; 3) control of actuators rotational speed as a general model regardless kinematic restrictions; 4) assuming detection of features (obstacles/goals), adaptive numeric weights are formulated to affect navigational exponential components. Simulation and experimental outdoors results are presented to show the feasibility of the proposed framework.

Exponential fields formulation for WMR navigation

In this manuscript, an autonomous navigation algorithm for wheeled mobile robots WMR operating in dynamic environments indoors or structured outdoors is formulated. The planning scheme is of critical importance for autonomous navigational tasks in complex dynamic environments. In fast dynamic environments, path planning needs algorithms able to sense simultaneously a diversity of obstacles, and use such sensory information to improve real-time navigation control, while moving towards a desired goal destination. The framework tackles 4 issues. 1 Reformulation of the Social Force Model SFM adapted to WMR; 2 the cohesion of a general inertial scheme to represents motion in any coordinate system; 3 control of actuators rotational speed as a general model regardless kinematic restrictions; 4 assuming detection of features obstacles/goals, adaptive numeric weights are formulated to affect navigational exponential components. Simulation and experimental outdoors results are presented to show the feasibility of the proposed framework.

Digital volume correlation: what are the limits to the spatial resolution?

Most of the norms used in the field of digital image (and volume) correlation to register two images (or volumes) lead to ill-posed problems. One of the frequent solutions is to enforce a restricted kinematics requiring a compromise between the richness of the solution (i.e., the spatial resolution) and the measurement uncertainty. An alternative route is to use a displacement norm that permits to alleviate this compromise by the means of a mechanical regularization used when the gray levels do not give enough information. It is then possible to compute a displacement vector for each pixel or voxel, inducing lower residuals (in terms of experimental data) while decreasing the noise sensitivity. The resolution performance of these different approaches is discussed, and compared for the analysis of a tensile test on a cast iron specimen based on a pair of tomographic images. As representative reconstructed volumes lead to a large number of degrees of freedom, a dedicated GPU computational strategy has been developed and implemented.

Dynamics Automatic Design of Planar Linkage Mechanism Based on Genetic Program

Regarded planar linkage mechanism kinematic target and execution of kinematic pair constraint reaction restrictions as the quantitative objectives, established the comprehensive dynamic design fitness function with the distance between a kinematics target and execution of a set of practical movement points, and the difference between actual constraint reaction of kinematic pair and its limit. According to multi-branch tree expression and random configuration method to create mechanical initial population, driven by the fitness function, made the mechanical population evolution towards the target requirements by the use of copy, crossover and mutation operators of genetic program. In the evolutionary process, inserted kinematics and dynamics automatic analysis technique, design examples indicated that using a genetic program can search parallel in different mechanical configuration space, dimension space and inertia space, automatically searched to such kinds of mechanisms approximate kinematics target and dynamics requirements, thus fulfilling the dynamics automatic design.

Production ofJ/ψ-meson pairs and4ctetraquark at the LHC

Theoretical predictions for the $pp\ensuremath{\rightarrow}2J/\ensuremath{\psi}+X$ cross section at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ with different kinematical restrictions are presented. Results are compared with the first LHCb data available. Special attention is paid to a possible signal from novel particles---tetraquarks build from two valence $c$-quarks and two valence $\overline{c}$-quarks. According to our estimates, it is quite possible to observe at least one of these states (tensor tetraquark) experimentally under LHCb conditions.

Lattice QCD and the Timelike Pion Form Factor

We present a formula that allows one to calculate the pion form factor in the timelike region 2m(π) ≤ √(s) ≤ 4m(π) in lattice QCD. The form factor quantifies the contribution of two-pion states to the vacuum polarization. It must be known very accurately in order to reduce the theoretical uncertainty on the anomalous magnetic moment of the muon. At the same time, the formula constitutes a rare example where, in a restricted kinematic regime, the spectral function of a conserved current can be determined from Euclidean observables without an explicit analytic continuation.

Some analytic results for two-loop scattering amplitudes

We present analytic results for the finite diagrams contributing to the two-loop eight-point MHV scattering amplitude of planar $ \mathcal{N} = 4 $ SYM. We use a recently proposed representation for the integrand of the amplitude in terms of (momentum) twistors and focus on a restricted kinematics in which the answer depends only on two independent cross-ratios. The theory of motives can be used to vastly simplify the results, which can be expressed as simple combinations of classical polylogarithms.

Detection of satellite remnants in the Galactic Halo with Gaia - II. A modified great circle cell method

We propose an extension of the GC3 streamer finding method of Johnston et al. 1996 that can be applied to the future Gaia database. The original method looks for streamers along great circles in the sky, our extension adds the kinematical restriction that velocity vectors should also be constrained to lie along these great circles, as seen by a Galactocentric observer. We show how to use these combined criteria starting from heliocentric observables. We test it by using the mock Gaia catalogue of Brown et al. 2005, which includes a realistic Galactic background and observational errors, but with the addition of detailed star formation histories for the simulated satellites. We investigate its success rate as a function of initial satellite luminosity, star formation history and orbit. We find that the inclusion of the kinematical restriction vastly enhances the contrast between a streamer and the background, even in the presence of observational errors, provided we use only data with good astrometric quality (fractional errors of 30 per cent or better). The global nature of the method diminishes the erasing effect of phase mixing and permits the recovery of merger events of reasonable dynamical age. Satellites with a star formation history different to that of the Galactic background are also better isolated. We find that satellites in the range of 10^8-10^9 Lsun can be recovered even for events as old as ~10 Gyr. Even satellites with 4-5x10^7 Lsun can be recovered for certain combinations of dynamical ages and orbits.

Motion teaching method for complex robot links using motor current

Conventional robot motion teaching methods use a teaching pendant or a motion capture device and are not the most convenient or intuitive ways to teach a robot sophisticated and fluid movements such as martial arts motions. Ideally, a robot could be set up as if it were a clothing mannequin that has light limbs and flexible yet frictional joints which can be positioned at desirable shape and hold all the positions. To do the same with a robot, an operator could pull or push the links with minor forces until the desired robot posture is attained. For this, a robot should measure the applied external force by using torque sensors at the robot joints. However, torque sensors are bulky and expensive to install in every DOF joints while keeping a compact design, which is essential to humanoid robots. In this paper, we use only motor current readings to acquire joint torques. The equations used to compensate for the effect of gravity on the joint torques and the self-calibration method to earn link parameters are presented. Additionally, kinematic restrictions can be imposed on the robot’s arms to simplify the motion teaching. Here, we teach the Kendo training robot with this method and the robot’s learnt martial art motions are demonstrated.