Robustness: a new SLIP model based criterion for gait transitions in bipedal locomotion

Bipedal locomotion is a phenomenon that still eludes a fundamental and concise mathematical understanding. Conceptual models that capture some relevant aspects of the process exist but their full explanatory power is not yet exhausted. In the current study, we introduce the robustness criterion which defines the conditions for stable locomotion when steps are taken with imprecise angle of attack. Intuitively, the necessity of a higher precision indicates the difficulty to continue moving with a given gait. We show that the spring-loaded inverted pendulum model, under the robustness criterion, is consistent with previously reported findings on attentional demand during human locomotion. This criterion allows transitions between running and walking, many of which conserve forward speed. Simulations of transitions predict Froude numbers below the ones observed in humans, nevertheless the model satisfactorily reproduces several biomechanical indicators such as hip excursion, gait duty factor and vertical ground reaction force profiles. Furthermore, we identify reversible robust walk-run transitions, which allow the system to execute a robust version of the hopping gait. These findings foster the spring-loaded inverted pendulum model as the unifying framework for the understanding of bipedal locomotion.Comment: unpublished, in preparatio

Tapping into rhythm generation circuitry in humans during simulated weightlessness conditions

An ability to produce rhythmic activity is ubiquitous for locomotor pattern generation and modulation. The role that the rhythmogenesis capacity of the spinal cord plays in injured populations has become an area of interest and systematic investigation among researchers in recent years, despite its importance being long recognized by neurophysiologists and clinicians. Given that each individual interneuron, as a rule, receives a broad convergence of various supraspinal and sensory inputs and may contribute to a vast repertoire of motor actions, the importance of assessing the functional state of the spinal locomotor circuits becomes increasingly evident. Air-stepping can be used as a unique and important model for investigating human rhythmogenesis since its manifestation is largely facilitated by a reduction of external resistance. This article aims to provide a review on current issues related to the ‘locomotor’ state and interactions between spinal and supraspinal influences on the central pattern generator circuitry in humans, which may be important for developing gait rehabilitation strategies in individuals with spinal cord and brain injuries

In silico case studies of compliant robots: AMARSI deliverable 3.3

In the deliverable 3.2 we presented how the morphological computing ap- proach can significantly facilitate the control strategy in several scenarios, e.g. quadruped locomotion, bipedal locomotion and reaching. In particular, the Kitty experimental platform is an example of the use of morphological computation to allow quadruped locomotion. In this deliverable we continue with the simulation studies on the application of the different morphological computation strategies to control a robotic system

Extended Einstein-Cartan theory a la Diakonov: the field equations

Diakonov formulated a model of a primordial Dirac spinor field interacting gravitationally within the geometric framework of the Poincar\'e gauge theory (PGT). Thus, the gravitational field variables are the orthonormal coframe (tetrad) and the Lorentz connection. A simple gravitational gauge Lagrangian is the Einstein-Cartan choice proportional to the curvature scalar plus a cosmological term. In Diakonov's model the coframe is eliminated by expressing it in terms of the primordial spinor. We derive the corresponding field equations for the first time. We extend the Diakonov model by additionally eliminating the Lorentz connection, but keeping local Lorentz covariance intact. Then, if we drop the Einstein-Cartan term in the Lagrangian, a nonlinear Heisenberg type spinor equation is recovered in the lowest approximation.Comment: 13 pages, no figure

Efficiency of Lift Production in Flapping and Gliding Flight of Swifts

Many flying animals use both flapping and gliding flight as part of their routine behaviour. These two kinematic patterns impose conflicting requirements on wing design for aerodynamic efficiency and, in the absence of extreme morphing, wings cannot be optimised for both flight modes. In gliding flight, the wing experiences uniform incident flow and the optimal shape is a high aspect ratio wing with an elliptical planform. In flapping flight, on the other hand, the wing tip travels faster than the root, creating a spanwise velocity gradient. To compensate, the optimal wing shape should taper towards the tip (reducing the local chord) and/or twist from root to tip (reducing local angle of attack). We hypothesised that, if a bird is limited in its ability to morph its wings and adapt its wing shape to suit both flight modes, then a preference towards flapping flight optimization will be expected since this is the most energetically demanding flight mode. We tested this by studying a well-known flap-gliding species, the common swift, by measuring the wakes generated by two birds, one in gliding and one in flapping flight in a wind tunnel. We calculated span efficiency, the efficiency of lift production, and found that the flapping swift had consistently higher span efficiency than the gliding swift. This supports our hypothesis and suggests that even though swifts have been shown previously to increase their lift-to-drag ratio substantially when gliding, the wing morphology is tuned to be more aerodynamically efficient in generating lift during flapping. Since body drag can be assumed to be similar for both flapping and gliding, it follows that the higher total drag in flapping flight compared with gliding flight is primarily a consequence of an increase in wing profile drag due to the flapping motion, exceeding the reduction in induced drag

IMPROVING SUPERVISORY CONTROL WATER DISTRIBUTION OF IRRIGATION CANALS RECLAMATION SYSTEMS

Цель. Изучить вопросы диспетчерского управления водораспределением на каналах мелиоративных систем с использованием системного подхода.Материалы и методы. Для управления водораспределением на оросительных каналах активно разрабатываются и внедряются интегрированные автоматизированные системы управления. При автоматизации водораспределения в системе открытых каналов мелиоративной сети необходимо учитывать динамические процессы течения воды. Имитационное математическое моделирование водораспределения при неустановившемся режиме движения представляет собой процесс изучения динамических свойств рассматриваемых автоматизированных систем управления на основе аналитических решений дифференциальных уравнений в частных производных.Результаты. Реализованы алгоритмы и математические модели в виде программного комплекса, описывающая поведение объекта управления в зависимости от его состояния, управляющих воздействий и возможных возмущений. Приводятся элементы функциональной математической модели водораспределения, построенной на основе алгоритмов управления с учётом работы большей части водопотребителей «по требованию».Заключение. На основе проведенных имитационных и полевых исследований предложены рекомендации по расчету времени распространения волны возмущения в открытых руслах, по выбору и назначению оптимальных параметров каналов и сооружений на них, длин расчетных участков, уклонов дна распределительных каналов, напоров и величин открытий затворов на сооружениях, выбору створов сечений каналов для установки средств регулирования при неустановившемся режиме движения воды.Background: Examine issues of dispatching management of water distribution systems in the reclamation channels using a systematic approach.Materials and methods: Integrated automated control systems are actively developed implemented to manage water distribution in irrigation canals. It needs to take into account the dynamic processes of water flow while the automation of water distribution in open channel irrigation network system must. Imitating mathematical modeling of water distribution during transient driving mode is the process of studying the dynamic properties of these automated control systems on the basis of analytic solutions of differential equations in partial derivatives.Results: Algorithms and mathematical models in the form of a software package, which describes the behavior of object of control, while it’s depending on its condition, control actions and possible disturbances. The elements functional water distribution mathematical model constructed on the basis of control algorithms taking into account the work of the majority of water consumers “on demand”.Conclusion: Based on the simulation and field research there were presented recommendations on the calculation of the propagation time of the disturbance waves in open channels, regarding the selection and appointment of the optimum parameters of channels and structures on them, the lengths of the calculated areas, slope of the bottom of the distribution channels, pressures and quantities shutter opens on structures, the choice of cross-sections sections of the channels for the installation of control equipment at unsteady flow regime

Neck muscle vibration makes walking humans accelerate in the direction of gaze

We studied the effect of the continuous vibration of symmetrical dorsal neck muscles in seven normal subjects during (a) quiet standing, (b) stepping in place movements and (c) walking on the treadmill. The experiments were performed in a darkened room and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by feedback from the subject's current position. Head, trunk and leg motion were recorded at 100 Hz.In normal standing, neck vibration elicited a prominent forward body sway. During stepping in place, neck vibration produced an involuntary forward stepping at about 0.3 m s−1 without modifying the stepping frequency. If the head was turned horizontally 45 and 90 deg to the right or to the left, neck muscle vibration caused stepping approximately in the direction of the head naso-occipital axis. For lateral eye deviations, the direction of stepping was roughly aligned with gaze direction.In treadmill locomotion, neck vibration produced an involuntary step-like increase of walking speed (by 0.1–0.6 m s−1), independent of the initial walking speed. During backward locomotion, the walking speed tended to decrease during neck vibration.Thus, continuous neck vibration evokes changes in the postural reference during quiet standing and in the walking speed during locomotion. The results suggest that the proprioceptive input from the neck is integrated in the control of human posture and locomotion and is processed in the context of a viewer-centred reference frame

Control of foot trajectory in walking toddlers: adaptation to load changes

On earth, body weight is an inherent constraint, and accordingly, load-regulating mechanisms play an important role in terrestrial locomotion. How do toddlers deal with the effects of their full body weight when faced with the task of independent upright locomotion for the first time? Here we studied the effect of load variation on walking in 12 toddlers during their first unsupported steps, 15 older children (1.3-5 yr), and 10 adults. To simulate various levels of body weight, an experimenter held the trunk of the subject with both hands and supplied an approximately constant vertical force during stepping on a force platform. During unsupported stepping, the shape of the foot path in toddlers (typically single-peak toe trajectory) was different from that of adults and older children (double-peak trajectory). In contrast to adults and older children, who showed only limited changes in kinematic coordination, the "reduced-gravity" condition considerably affected the shape of the foot path in toddlers: they tended to make a high lift and forward foot overshoot at the end of swing. In addition, stepping at high levels of body unloading was characterized by a significant change in the initial direction of foot motion during early swing. Intermediate walkers (1.5-5 mo after walking onset) showed only partial improvement in foot trajectory characteristics. The results suggest that, at the onset of walking, changes in vertical body loads are not compensated accurately by the kinematic controllers; compensation necessitates a few months of independent walking experience

Development of independent walking in toddlers

Surprisingly, despite millions of years of bipedal walking evolution, the gravity-related pendulum mechanism of walking does not seem to be implemented at the onset of independent walking, requiring each toddler to develop it. We discuss the precursor of the mature locomotor pattern in infants as an optimal starting point strategy for gait maturation