Natural Coordinates Research Articles

Pre-clinical assessment of an intuitive prosthetic elbow control strategy using residual limb motion with osseo-integrated patients

Most transhumeral amputees deplore that their prosthesis lacks functionality due to control-related limitations. Externally powered prosthetic devices are commonly controlled via myoelectric control whereby biceps and triceps contractions drive sequentially the prosthetic joints. Because of a complex control scheme, transhumeral amputees are generally equipped with a 1-degree-of-freedom myoelectric hand, a myoelectric wrist rotator, and a manually locked elbow, despite the commercialization of more advanced devices. This results in the development of compensatory strategies to overcome the prosthesis’ lack of mobility. An alternative control strategy relates the residual limb motions to the prosthetic elbow motion using the natural coordination between shoulder and elbow observed in healthy movements. However, conventional external sockets tend to prevent the residual limb mobility, limiting the potentiality of this novel control strategy. Osseo-integration enables a stable attachment of the prosthetic device and frees the residual limb. This study focuses on the performance of three osseo-integrated patients using an automatically driven prosthesis. A prosthesis prototype including a myoelectric hand, a wrist rotator, and a motorized elbow was mounted on the participants’ abutment from the osseo-integrated implant system. The subjects were asked to point at targets while the motorized elbow was controlled by residual limb movements based on a model of healthy shoulder/elbow coordination. For comparison purposes, the task was also performed with conventional sequential myoelectric control. Body movements were assessed with the data recorded with a motion capture system. Large trunk compensatory movements were measured during pointing gesture with a myoelectrically driven elbow. Automatic control of the elbow enabled a more natural body behavior whereby the trunk displacements were small, and the shoulder and the prosthetic elbow were moving synchronously. The study shows that osseo-integration made possible residual limb movements of large amplitudes, allowing the participants to achieve the pointing task with a prosthetic elbow driven by the residual limb motions. Moreover, simultaneous control of elbow and end-effector was achieved by one subject. Hence, this work highlights the interest of combining osseo-integration with an automatic control strategy for intermediate joints in terms of compensatory movement reduction and control intuitiveness gain.

The emergence of city-regions and their implications for contemporary spatial governance: Evidence from Ghana

Over the years, urbanization has triggered complex spatial processes, such as the evolution of city-regions that defy traditional administrative regional boundaries. However, despite the growing body of research on city-regions, the evolution of this phenomenon and its implications for contemporary spatial governance remains a huge gap in urban planning literature, while approaches to their delineation have largely been restricted to commuting patterns data and approximations. This research examines the emergence of city-regions and their implications for contemporary spatial governance using Ghana as an illustrative case. In the process, inspired by Tobler's first law of geography and the concept of distance decay, the study engages a unique methodological approach that uses spatial mapping of rural-urban population continuum, transportation network, built-up patterns and GIS techniques for the delineation of city-region. The research finds a gap between the rapidly emerging spatial structure of Accra and the operational governance framework, as there is no provision in the latter for the planning and management of the evolving city-region which, territorially, spans multiple administrative regions. At the local context, while making the lagging spatial governance system more responsive to the dynamically evolving spatial structure, it is imperative that urban policy recognises city-regions, such as the Accra City Region (ACR), and their diverse opportunities; plan for them through joint development planning boards; and foster natural coordination even among local planning authorities across different administrative regions. At the global scale, the research practically illustrates that alternative methodologies based on spatial mapping and GIS techniques could provide useful insights into the study of city-regions.

Bingham fluids: deformation and energy dissipation in triangular cross section tube flow

Flow of Bingham plastics through straight, long tubes with non-circular cross-sections is studied by means of an analytical method that allows to model a wide spectrum of tube geometries. Shear stress normal to equal velocity lines, velocity field and plug zones are explored, in particular in a tube with equilateral triangular cross-section for small values of the Bingham number Bi, and they are compared with corresponding numerical solutions. We show that a circular plug is present at the center of the triangular tube cross-section, consistent with numerical simulations as well as with previous results in the literature, if calculations up to and including first order in the shape perturbation parameter $$\epsilon$$ are taken into account. However with the inclusion of the second order terms in the algorithm this structure is no longer present and no plug zone is predicted for the same pressure drop. We find that in that case normal shear stresses are always greater than the yield stress of the fluid. As a result, the central region becomes a pseudo-plug since it presents small but non-vanishing relative deformations and does not move as a rigid core. The energy dissipation function for the Bingham fluid flow is written in terms of natural coordinates. Its distribution depends only on the normal shear stress at any point with Bingham number as a parameter.

Modifying upper-limb inter-joint coordination in healthy subjects by training with a robotic exoskeleton

BackgroundThe possibility to modify the usually pathological patterns of coordination of the upper-limb in stroke survivors remains a central issue and an open question for neurorehabilitation. Despite robot-led physical training could potentially improve the motor recovery of hemiparetic patients, most of the state-of-the-art studies addressing motor control learning, with artificial virtual force fields, only focused on the end-effector kinematic adaptation, by using planar devices. Clearly, an interesting aspect of studying 3D movements with a robotic exoskeleton, is the possibility to investigate the way the human central nervous system deals with the natural upper-limb redundancy for common activities like pointing or tracking tasks.MethodsWe asked twenty healthy participants to perform 3D pointing or tracking tasks under the effect of inter-joint velocity dependant perturbing force fields, applied directly at the joint level by a 4-DOF robotic arm exoskeleton. These fields perturbed the human natural inter-joint coordination but did not constrain directly the end-effector movements and thus subjects capability to perform the tasks. As a consequence, while the participants focused on the achievement of the task, we unexplicitly modified their natural upper-limb coordination strategy. We studied the force fields direct effect on pointing movements towards 8 targets placed in the 3D peripersonal space, and we also considered potential generalizations on 4 distinct other targets. Post-effects were studied after the removal of the force fields (wash-out and follow up). These effects were quantified by a kinematic analysis of the pointing movements at both end-point and joint levels, and by a measure of the final postures. At the same time, we analysed the natural inter-joint coordination through PCA.ResultsDuring the exposition to the perturbative fields, we observed modifications of the subjects movement kinematics at every level (joints, end-effector, and inter-joint coordination). Adaptation was evidenced by a partial decrease of the movement deviations due to the fields, during the repetitions, but it occurred only on 21% of the motions. Nonetheless post-effects were observed in 86% of cases during the wash-out and follow up periods (right after the removal of the perturbation by the fields and after 30 minutes of being detached from the exoskeleton). Important inter-individual differences were observed but with small variability within subjects. In particular, a group of subjects showed an over-shoot with respect to the original unexposed trajectories (in 30% of cases), but the most frequent consequence (in 55% of cases) was the partial persistence of the modified upper-limb coordination, adopted at the time of the perturbation. Temporal and spatial generalizations were also evidenced by the deviation of the movement trajectories, both at the end-effector and at the intermediate joints and the modification of the final pointing postures towards targets which were never exposed to any field.ConclusionsSuch results are the first quantified characterization of the effects of modification of the upper-limb coordination in healthy subjects, by imposing modification through viscous force fields distributed at the joint level, and could pave the way towards opportunities to rehabilitate pathological arm synergies with robots.

Mechatronics of a ball screw drive using an N degrees of freedom dynamic model

High-performance position control in machine tools can only be achieved modeling the dynamic behavior of the mechatronic system composed by the motor, transmission and control during the design stage. In this work, a complex analytical model of a ball screw drive is presented and integrated in a mechatronic model of the actuator to predict the dynamic behavior and analyze the impact of each component of the transmission. First, a simple 2-dof model is presented, and its analysis sets the basis for the development of a more complex model of several degrees of freedom, whose resulting fundamental transfer functions are represented using natural and modal coordinates. The modeling in modal coordinates carries a reduction of the transfer function that reduces computational work. The two models are compared and experimentally validated in time and frequency domains by means of experimental tests carried out on a specifically developed ball screw drive test bench.

Surprising structures hiding in Penrose’s future null infinity

Since the late1950s, almost all discussions of asymptotically flat (Einstein–Maxwell) space-times have taken place in the context of Penrose’s null infinity, In addition, almost all calculations have used the Bondi coordinate and tetrad systems. Beginning with a known asymptotically flat solution to the Einstein–Maxwell equations, we show first, that there are other natural coordinate systems, near (analogous to light-cones in flat-space) that are based on (asymptotically) shear-free null geodesic congruences (analogous to the flat-space case). Using these new coordinates and their associated tetrad, we define the complex dipole moment, (the mass dipole plus i times angular momentum), from the l = 1 harmonic coefficient of a component of the asymptotic Weyl tensor. Second, from this definition, from the Bianchi identities and from the Bondi–Sachs mass and linear momentum, we show that there exists a large number of results—identifications and dynamics—identical to those of classical mechanics and electrodynamics. They include, among many others, , spin, Newton’s second law with the rocket force term (v) and radiation reaction, angular momentum conservation and others. All these relations take place in the rather mysterious H-space rather than in space-time.This leads to the enigma: ‘why do these well known relations of classical mechanics take place in H-space?’ and ‘What is the physical meaning of H-space?’

Algorithm for solving the inverse vibronic problem on the basis of SVL fluorescence spectra

Computer methods whereby the inverse vibronic problem is solved on the basis of resonance fluorescence spectra with the use of modern quantum-mechanical methods for constructing structuraldynamic models of polyatomic molecules are discussed. An algorithm is proposed for solving the inverse vibronic problem according to resonance fluorescence spectra under laser excitation, and the corresponding calculation programs are constructed. The initial program data are acquired by means of an original software package which implements the scaling of quantum-mechanical force fields in two electronic states. The Duschinsky matrix and the initial matrix of shifts in normal coordinates caused by electron excitation are calculated in the Cartesian and natural vibrational coordinates. The program data are taken from quantum-molecular models based on calculations performed via ab initio modern quantum-mechanical methods and density functional theory. The algorithm is tested through the calculation of a model molecular system.

Coordination of metabolic pathways: Enhanced carbon conservation in 1,3-propanediol production by coupling with optically pure lactate biosynthesis

Metabolic engineering has emerged as a powerful tool for bioproduction of both fine and bulk chemicals. The natural coordination among different metabolic pathways contributes to the complexity of metabolic modification, which hampers the development of biorefineries. Herein, the coordination between the oxidative and reductive branches of glycerol metabolism was rearranged in Klebsiella oxytoca to improve the 1,3-propanediol production. After deliberating on the product value, carbon conservation, redox balance, biological compatibility and downstream processing, the lactate-producing pathway was chosen for coupling with the 1,3-propanediol-producing pathway. Then, the other pathways of 2,3-butanediol, ethanol, acetate, and succinate were blocked in sequence, leading to improved d-lactate biosynthesis, which as return drove the 1,3-propanediol production. Meanwhile, efficient co-production of 1,3-propanediol and l-lactate was also achieved by replacing ldhD with ldhL from Bacillus coagulans. The engineered strains PDL-5 and PLL co-produced over 70g/L 1,3-propanediol and over 100g/L optically pure d-lactate and l-lactate, respectively, with high conversion yields of over 0.95mol/mol from glycerol.

Trajectory planning with residual vibration suppression for space manipulator based on particle swarm optimization algorithm

Space manipulator suffers from vibration problems mainly due to the flexibility of joints and links in a microgravity environment. This article presents a new optimization method of trajectory planning with minimum residual vibration for space manipulator system which is modeled by absolute coordinate-based method. First, absolute nodal coordinate formulation, which can describe large rotation and large deformation of flexible bodies precisely, is used to describe the deformation of flexible links, and natural coordinate formulation with nonlinear torsion stiffness function is used to model flexible joints. Then, joint rotation trajectory resulting from the planned end-effector trajectory by inverse kinematics theory is discrete through the proposed cosine-based function that has been validated to suppress the residual vibration. The particle swarm optimization algorithm is employed to achieve minimum residual vibration by optimizing redundant coefficients of movement derived from inverse kinematics theory. The effectiveness of the proposed method is illustrated via simulation of a planar three-link manipulator taking large deformation and large rotation into account. Results show that the optimized method can exhibit better features for the residual vibration suppression as compared to those of the original cosine-based trajectory.

Groundwater discharge and phosphorus dynamics in a flood-pulse system: Tonle Sap Lake, Cambodia

Tonle Sap Lake (Cambodia), a classic example of a “flood pulse” system, is the largest freshwater lake in SE Asia, and is reported to have one of the highest freshwater fish productions anywhere. During the dry season (November–April) the lake drains through a tributary to the Mekong River. The flow in the connecting tributary completely reverses during the wet monsoon (May–October), adding huge volumes of water back to the lake, increasing its area about six fold. The lake is likely phosphorus limited and we hypothesized that groundwater discharge, including recirculated lake water, may represent an important source of P and other nutrients. To address this question, we surveyed hundreds of kilometers of the lake for natural 222Rn (radon), temperature, conductivity, GPS coordinates and water depth. All major inorganic nutrients and phosphorus species were evaluated by systematic sampling throughout the lake. Results showed that there were radon hotspots, all at the boundaries between the permanent lake and the floodplain, indicating likely groundwater inputs. A radon mass balance model indicates that the groundwater flow to Tonle Sap Lake is approximately 10km3/yr, about 25% as large as the floodwaters entering from the Mekong River during the wet monsoon. Our results suggest that the groundwater-derived dissolved inorganic phosphorus (DIP) contribution to Tonle Sap is more than 30% of the average inflows from all natural sources. Since the productivity of the lake appears to be phosphorus limited, this finding suggests that the role of groundwater is significant for Tonle Sap Lake and perhaps for other flood pulse systems worldwide.

ADVANCES IN SHAPE-FREE FINITE ELEMENT METHODS: A REVIEW

As the most important tool for simulation and computation, the finite element method has been widely applied in engineering and scientific problems. However, this powerful method still suffers from some inherent deficiencies, such as the sensitivity problem to mesh distortion and so on, which have not been completely solved yet. This paper systematacially introduces some research developments on new finite element methods, i.e., the shape-free finite element methods, including the hybrid stress-function elements for plane and 2D fracture problems, the hybrid displacement-function elements for Reissner-Mindlin plate bending problem, and new unsymmetric finite element for plane and 3D elasticity. Based on the existing hybrid stress and unsymmetric finite element methods, some advanced techniques, including the analytical trial function method, new natural coordinate method, generalized conforming technique, etc., were adopted in the aforementioned new approaches. The resulting new finite element models possess high precision and good robustness. In particular, they can keep their level of performance even in extremely distorted meshes. Furthermore, some historical challenges in the finite element method, such as the limitation defined by the MacNeal's theorem, the edge effect problem of the Resissner-Mindlin plate, were also successfully solved. At the end of this paper, some features of the new methods and further development are discussed.

Kinematics Simulation of Multi–rope Friction Winder Based on Flexible Multi-body Dynamics

In order to realize the formulaic modeling and precise solution of a flexible multi-body winder system, a dynamic model with Lagrange multipliers is established by natural coordinates. Based on RecurDyn software, a Rigid-Flexible Couple model was established through using the method of flexible multi-body dynamics, and the simulation of kinematical characteristics of the friction winder was carried out. By introducing the relative nodal method, the simplified dynamic equations have been derived via the virtual work principle and validated on a virtual prototype with the RecurDyn software package and ANSYS. Kinematics and dynamics characteristic date are obtained by computer-aided dynamic simulation of virtual Multi – rope friction winder. The research work will provide a powerful tool and useful method for the design of economic and credible elevator system. The approach can be generalized to analysis other flexible drive fields.

Accelerated reference systems in AdS space

We consider reference systems of uniformly accelerated observers in anti-de Sitter space. We construct coordinate transformations for the transition from an inertial reference system to a uniformly accelerated reference system for all acceleration values, both greater and less than critical. The basis for the construction are the Beltrami coordinates, natural coordinates for describing a uniformly accelerated motion because geodesics in anti-de Sitter space in these coordinates become straight lines, i.e., can be described by linear functions. Because translations of space–time coordinates in anti-de Sitter space are non-Abelian, a nontrivial problem of defining the comoving inertial reference system arises. Constructing the coordinate system of an accelerated observer using this auxiliary comoving inertial reference system requires additional transformations that not only equalize the velocities of the two systems but also equalize the system origins. The presence of a critical acceleration in anti-de Sitter space leads to a difference in explicit expressions in passing to an accelerated coordinate system for accelerations greater and less than critical.

Homoclinic tangles in the DIII-D tokamak from the map equations in natural canonical coordinates*

ABSTRACTTrajectories of magnetic field lines are a 1½ degree of freedom Hamiltonian system. The unperturbed separatrix and the perturbed separatrix in a divertor tokamak are fundamentally different. Magnetic asymmetries cause the separatrix to form extremely complicated structures known as homoclinic tangles. After each toroidal circuit, the perturbed separatrix manifolds meet in a fixed poloidal plane and intersect to form homoclinic tangle in order to preserve the topological invariants. This tangle becomes extremely complicated as the magnetic field lines take more and more toroidal turns. This effect is most pronounced near the X-point. The homoclinic tangles of the DIII-D tokamak separatrix from the magnetic perturbation representing the peeling-ballooning modes are studied. The homoclinic tangles can have important implications for the edge physics in divertor tokamaks.

Identification of simple reaction coordinates from complex dynamics.

Reaction coordinates are widely used throughout chemical physics to model and understand complex chemical transformations. We introduce a definition of the natural reaction coordinate, suitable for condensed phase and biomolecular systems, as a maximally predictive one-dimensional projection. We then show that this criterion is uniquely satisfied by a dominant eigenfunction of an integral operator associated with the ensemble dynamics. We present a new sparse estimator for these eigenfunctions which can search through a large candidate pool of structural order parameters and build simple, interpretable approximations that employ only a small number of these order parameters. Example applications with a small molecule's rotational dynamics and simulations of protein conformational change and folding show that this approach can filter through statistical noise to identify simple reaction coordinates from complex dynamics.

Real-time simulation of cable pay-out and reel-in with towed fishing gears

Achieving real-time simulation of fast cable pay-out and reel-in manoeuvres with towed fishing gears is a challenging task. This work presents two new simulation methods based on simplified cable models for this kind of application. First, three numerical techniques are proposed to enhance a classical spring-based cable model, increasing its computational efficiency in manoeuvres that involve reeling the cable around a winch drum. Second, the development of an efficient multibody modelling approach based on natural coordinates is reported. The performance of these methods was assessed with two realistic examples. The numerical experiments involved different values of cable axial stiffness and spatial discretization levels, since these parameters were found to have a major impact on computational efficiency. The proposed methods achieved real-time performance in the simulation of systems modelled with up to a few thousand variables. Each modelling approach has advantages and limitations that must be considered when addressing a given application.

Differential quadrature thermal buckling analysis of general quadrilateral orthotropic auxetic FGM plates on elastic foundations

Majority of the available research on buckling analysis of the plates, has been devoted to plates with well-behaved configurations, e.g., rectangular or circular geometries. In the present research, thermal buckling of general quadrilateral plates fabricated from heterogeneous, orthotropic, and auxetic (with negative Poisson ratio) materials resting on elastic Winkler-Pasternak elastic media is investigated. Edges of the plate may be either simply supported or clamped. Thus, the problem is a quite general one, from the material, boundary conditions, and to some extent, geometry points of view and may cover wide ranges of the practical applications, as special cases. The stability equations are derived through transformation of the governing equations of the plate from the geometric rectangular Cartesian coordinates to the computational natural coordinates and discretization of the resulting equations by means of the differential quadratic method. Buckling analysis has been accomplished through investigation of the pre-buckling and buckling onset situations. Finally, effects of the skew angles of the general quadrilateral plate, heterogeneity index, orthotropy angle, edge condition, foundation stiffness, and auxeticity of the material on the buckling temperature rises are investigated comprehensively.

Exploiting Hybrid Parallelism in the Kinematic Analysis of Multibody Systems Based on Group Equations

Computational kinematics is a fundamental tool for the design, simulation, control, optimization and dynamic analysis of multibody systems. The analysis of complex multibody systems and the need for real time solutions requires the development of kinematic and dynamic formulations that reduces computational cost, the selection and efficient use of the most appropriated solvers and the exploiting of all the computer resources using parallel computing techniques. The topological approach based on group equations and natural coordinates reduces the computation time in comparison with well-known global formulations and enables the use of parallelism techniques which can be applied at different levels: simultaneous solution of equations, use of multithreading routines, or a combination of both. This paper studies and compares these topological formulation and parallel techniques to ascertain which combination performs better in two applications. The first application uses dedicated systems for the real time control of small multibody systems, defined by a few number of equations and small linear systems, so shared-memory parallelism in combination with linear algebra routines is analyzed in a small multicore and in Raspberry Pi. The control of a Stewart platform is used as a case study. The second application studies large multibody systems in which the kinematic analysis must be performed several times during the design of multibody systems. A simulator which allows us to control the formulation, the solver, the parallel techniques and size of the problem has been developed and tested in more powerful computational systems with larger multicores and GPU.

The Spatial Hierarchy in the Poetics of Anna Akhmatova: Ontological, Mythological and Psychological Aspects

Objectives: The article aims at understanding the role of the space and time categories in the artistic world of Anna Akhmatova. The problem is considered in ontological, mythological and psychological aspects. Methods: In terms of methodology the article is based on research of the Russian Acmeism as a literary movement and creative works of Anna Akhmatova as one of its leading poets. We perceive Acmeism within the limits of a system-typological approach – not as a static reality, but as a tendency of purposes and principles common to a number of authors. The analysis used sociocultural, biographical, cultural-historical and comparative-typological methods of research. Findings: Anna Akhmatova as a representative of Russian Acmeism in her polemics with Symbolists and with their characteristic loci, both abstract and generalized, focused her attention on the concept of real life, on the image-motive embodiment of time and space. The external space in the lyrics of Akhmatova includes three areas – the space of home, of the city, and the nature, each of which is characterized by the materiality and the Artifact. There is a gradual evolution of mythological connotations, the formation of the semiotic opposition “top – down” and accentuation of the vertical axis of natural coordinates of “heaven – earth”. In the work of Anna Akhmatova dd.1930-1960-ies the disposition “top – down” remains, however the “top” begins to be associated with harmonious existence, and “bottom” – with death, grave. In those years the antique intertext starts to appear in her works, producing impression that the poet is going back to the origins of civilization, but it was associated with the Soviet ideology and its polytheistic pantheon headed by the “Father of all peoples”. Novelty: The space-time bases of Anna Akhmatova’s artistic world has been changing during her work, the transformation of semiotic opposition “top – bottom”, a shift from the abstract to the tangible materiality, from the external to the mental.

On the lubrication approximation for a class of viscoelastic fluids

We present a rigorous derivation of a dimensionally reduced Reynolds type equation for thin film flow lubrication of a class of viscoelastic fluids by employing a perturbation analysis on the upper-convected Maxwell model in natural orthogonal coordinates. This approximation accounts for the viscoelastic and curvature corrections to the classical Reynolds lubrication approximation. Comparison of our approximation with the classical Reynolds approximation suggests that viscoelasticity can have a significant influence on the lubrication characteristics, at least for certain values of the film thickness and of the eccentricity ratios of the journal bearing.