Individual Leg and Joint Work during Sloped Walking for People with a Transtibial Amputation Using Passive and Powered Prostheses

Directory of Open Access Journals (Sweden)

Jana R. Jeffers

2017-12-01

Full Text Available People with a transtibial amputation using passive-elastic prostheses exhibit reduced prosthetic ankle power and push-off work compared to non-amputees and compensate by increasing their affected leg (AL hip joint work and unaffected leg (UL ankle, knee, and hip joint and leg work during level-ground walking. Use of a powered ankle–foot prosthesis normalizes step-to-step transition work during level-ground walking over a range of speeds for people with a transtibial amputation, but the effects on joint work during level-ground, uphill, and downhill walking have not been assessed. We investigated how use of passive-elastic and powered ankle–foot prostheses affect leg joint biomechanics during level-ground and sloped walking. 10 people with a unilateral transtibial amputation walked at 1.25 m/s on a dual-belt force-measuring treadmill at 0°, ±3°, ±6°, and ±9° using their own passive-elastic and a powered prosthesis (BiOM T2, BionX Medical Technologies, Inc., Bedford, MA, USA while we measured kinematic and kinetic data. We calculated AL and UL prosthetic, ankle, knee, hip, and individual leg positive, negative, and net work. Use of a powered compared to passive-elastic ankle–foot prosthesis resulted in greater AL prosthetic and individual leg net work on uphill and downhill slopes. Over a stride, AL prosthetic positive work was 23–30% greater (p < 0.05 during walking on uphill slopes of +6°, and +9°, prosthetic net work was up to 10 times greater (more positive (p ≤ 0.005 on all uphill and downhill slopes and individual leg net work was 146 and 82% more positive (p < 0.05 at uphill slopes of +6° and +9°, respectively, with use of the powered compared to passive-elastic prosthesis. Greater prosthetic positive and net work through use of a powered ankle–foot prosthesis during uphill and downhill walking improves mechanical work symmetry between the legs, which could decrease metabolic cost and improve functional

Influence of neuromuscular noise and walking speed on fall risk and dynamic stability in a 3D dynamic walking model.

Science.gov (United States)

Roos, Paulien E; Dingwell, Jonathan B

2013-06-21

Older adults and those with increased fall risk tend to walk slower. They may do this voluntarily to reduce their fall risk. However, both slower and faster walking speeds can predict increased risk of different types of falls. The mechanisms that contribute to fall risk across speeds are not well known. Faster walking requires greater forward propulsion, generated by larger muscle forces. However, greater muscle activation induces increased signal-dependent neuromuscular noise. These speed-related increases in neuromuscular noise may contribute to the increased fall risk observed at faster walking speeds. Using a 3D dynamic walking model, we systematically varied walking speed without and with physiologically-appropriate neuromuscular noise. We quantified how actual fall risk changed with gait speed, how neuromuscular noise affected speed-related changes in fall risk, and how well orbital and local dynamic stability measures predicted changes in fall risk across speeds. When we included physiologically-appropriate noise to the 'push-off' force in our model, fall risk increased with increasing walking speed. Changes in kinematic variability, orbital, and local dynamic stability did not predict these speed-related changes in fall risk. Thus, the increased neuromuscular variability that results from increased signal-dependent noise that is necessitated by the greater muscular force requirements of faster walking may contribute to the increased fall risk observed at faster walking speeds. The lower fall risk observed at slower speeds supports experimental evidence that slowing down can be an effective strategy to reduce fall risk. This may help explain the slower walking speeds observed in older adults and others. Copyright © 2013 Elsevier Ltd. All rights reserved.

Does dynamic stability govern propulsive force generation in human walking?

Science.gov (United States)

Browne, Michael G; Franz, Jason R

2017-11-01

Before succumbing to slower speeds, older adults may walk with a diminished push-off to prioritize stability over mobility. However, direct evidence for trade-offs between push-off intensity and balance control in human walking, independent of changes in speed, has remained elusive. As a critical first step, we conducted two experiments to investigate: (i) the independent effects of walking speed and propulsive force ( F P ) generation on dynamic stability in young adults, and (ii) the extent to which young adults prioritize dynamic stability in selecting their preferred combination of walking speed and F P generation. Subjects walked on a force-measuring treadmill across a range of speeds as well as at constant speeds while modulating their F P according to a visual biofeedback paradigm based on real-time force measurements. In contrast to improvements when walking slower, walking with a diminished push-off worsened dynamic stability by up to 32%. Rather, we find that young adults adopt an F P at their preferred walking speed that maximizes dynamic stability. One implication of these findings is that the onset of a diminished push-off in old age may independently contribute to poorer balance control and precipitate slower walking speeds.

Walking Robots Dynamic Control Systems on an Uneven Terrain

Directory of Open Access Journals (Sweden)

MUNTEANU, M. S.

2010-05-01

Full Text Available The paper presents ZPM dynamic control of walking robots, developing an open architecture real time control multiprocessor system, in view of obtaining new capabilities for walking robots. The complexity of the movement mechanism of a walking robot was taken into account, being a repetitive tilting process with numerous instable movements and which can lead to its turnover on an uneven terrain. The control system architecture for the dynamic robot walking is presented in correlation with the control strategy which contains three main real time control loops: balance robot control using sensorial feedback, walking diagram control with periodic changes depending on the sensorial information during each walk cycle, predictable movement control based on a quick decision from the previous experimental data. The results obtained through simulation and experiments show an increase in mobility, stability in real conditions and obtaining of high performances related to the possibility of moving walking robots on terrains with a configuration as close as possible to real situations, respectively developing new technological capabilities of the walking robot control systems for slope movement and walking by overtaking or going around obstacles.

Dynamic balance during walking adaptability tasks in individuals post-stroke.

Science.gov (United States)

Vistamehr, Arian; Balasubramanian, Chitralakshmi K; Clark, David J; Neptune, Richard R; Fox, Emily J

2018-04-24

Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Community ambulation requires performance of steady-state level walking as well as tasks that require walking adaptability. Prior studies on balance control post-stroke have mainly focused on steady-state walking, but walking adaptability tasks have received little attention. The purpose of this study was to quantify and compare dynamic balance requirements during common walking adaptability tasks post-stroke and in healthy adults and identify differences in underlying mechanisms used for maintaining dynamic balance. Kinematic data were collected from fifteen individuals with post-stroke hemiparesis during steady-state forward and backward walking, obstacle negotiation, and step-up tasks. In addition, data from ten healthy adults provided the basis for comparison. Dynamic balance was quantified using the peak-to-peak range of whole-body angular-momentum in each anatomical plane during the paretic, nonparetic and healthy control single-leg-stance phase of the gait cycle. To understand differences in some of the key underlying mechanisms for maintaining dynamic balance, foot placement and plantarflexor muscle activation were examined. Individuals post-stroke had significant dynamic balance deficits in the frontal plane across most tasks, particularly during the paretic single-leg-stance. Frontal plane balance deficits were associated with wider paretic foot placement, elevated body center-of-mass, and lower soleus activity. Further, the obstacle negotiation task imposed a higher balance requirement, particularly during the trailing leg single-stance. Thus, improving paretic foot placement and ankle plantarflexor activity, particularly during obstacle negotiation, may be important rehabilitation targets to enhance dynamic balance during post-stroke community ambulation. Copyright © 2018. Published by Elsevier Ltd.

Walking on high heels changes muscle activity and the dynamics of human walking significantly

DEFF Research Database (Denmark)

Simonsen, Erik B; Svendsen, Morten Bo Søndergaard; Nørreslet, Andreas

2012-01-01

The aim of the study was to investigate the distribution of net joint moments in the lower extremities during walking on high-heeled shoes compared with barefooted walking at identical speed. Fourteen female subjects walked at 4 km/h across three force platforms while they were filmed by five...... digital video cameras operating at 50 frames/second. Both barefooted walking and walking on high-heeled shoes (heel height: 9 cm) were recorded. Net joint moments were calculated by 3D inverse dynamics. EMG was recorded from eight leg muscles. The knee extensor moment peak in the first half of the stance...... phase was doubled when walking on high heels. The knee joint angle showed that high-heeled walking caused the subjects to flex the knee joint significantly more in the first half of the stance phase. In the frontal plane a significant increase was observed in the knee joint abductor moment and the hip...

Effect of exoskeletal joint constraint and passive resistance on metabolic energy expenditure: Implications for walking in paraplegia.

Directory of Open Access Journals (Sweden)

Sarah R Chang

Full Text Available An important consideration in the design of a practical system to restore walking in individuals with spinal cord injury is to minimize metabolic energy demand on the user. In this study, the effects of exoskeletal constraints on metabolic energy expenditure were evaluated in able-bodied volunteers to gain insight into the demands of walking with a hybrid neuroprosthesis after paralysis. The exoskeleton had a hydraulic mechanism to reciprocally couple hip flexion and extension, unlocked hydraulic stance controlled knee mechanisms, and ankles fixed at neutral by ankle-foot orthoses. These mechanisms added passive resistance to the hip (15 Nm and knee (6 Nm joints while the exoskeleton constrained joint motion to the sagittal plane. The average oxygen consumption when walking with the exoskeleton was 22.5 ± 3.4 ml O2/min/kg as compared to 11.7 ± 2.0 ml O2/min/kg when walking without the exoskeleton at a comparable speed. The heart rate and physiological cost index with the exoskeleton were at least 30% and 4.3 times higher, respectively, than walking without it. The maximum average speed achieved with the exoskeleton was 1.2 ± 0.2 m/s, at a cadence of 104 ± 11 steps/min, and step length of 70 ± 7 cm. Average peak hip joint angles (25 ± 7° were within normal range, while average peak knee joint angles (40 ± 8° were less than normal. Both hip and knee angular velocities were reduced with the exoskeleton as compared to normal. While the walking speed achieved with the exoskeleton could be sufficient for community ambulation, metabolic energy expenditure was significantly increased and unsustainable for such activities. This suggests that passive resistance, constraining leg motion to the sagittal plane, reciprocally coupling the hip joints, and weight of exoskeleton place considerable limitations on the utility of the device and need to be minimized in future designs of practical hybrid neuroprostheses for walking after paraplegia.

Kinematics and dynamics analysis of a quadruped walking robot with parallel leg mechanism

Science.gov (United States)

Wang, Hongbo; Sang, Lingfeng; Hu, Xing; Zhang, Dianfan; Yu, Hongnian

2013-09-01

It is desired to require a walking robot for the elderly and the disabled to have large capacity, high stiffness, stability, etc. However, the existing walking robots cannot achieve these requirements because of the weight-payload ratio and simple function. Therefore, Improvement of enhancing capacity and functions of the walking robot is an important research issue. According to walking requirements and combining modularization and reconfigurable ideas, a quadruped/biped reconfigurable walking robot with parallel leg mechanism is proposed. The proposed robot can be used for both a biped and a quadruped walking robot. The kinematics and performance analysis of a 3-UPU parallel mechanism which is the basic leg mechanism of a quadruped walking robot are conducted and the structural parameters are optimized. The results show that performance of the walking robot is optimal when the circumradius R, r of the upper and lower platform of leg mechanism are 161.7 mm, 57.7 mm, respectively. Based on the optimal results, the kinematics and dynamics of the quadruped walking robot in the static walking mode are derived with the application of parallel mechanism and influence coefficient theory, and the optimal coordination distribution of the dynamic load for the quadruped walking robot with over-determinate inputs is analyzed, which solves dynamic load coupling caused by the branches’ constraint of the robot in the walk process. Besides laying a theoretical foundation for development of the prototype, the kinematics and dynamics studies on the quadruped walking robot also boost the theoretical research of the quadruped walking and the practical applications of parallel mechanism.

Trapping photons on the line: controllable dynamics of a quantum walk

Science.gov (United States)

Xue, Peng; Qin, Hao; Tang, Bao

2014-04-01

Optical interferometers comprising birefringent-crystal beam displacers, wave plates, and phase shifters serve as stable devices for simulating quantum information processes such as heralded coined quantum walks. Quantum walks are important for quantum algorithms, universal quantum computing circuits, quantum transport in complex systems, and demonstrating intriguing nonlinear dynamical quantum phenomena. We introduce fully controllable polarization-independent phase shifters in optical pathes in order to realize site-dependent phase defects. The effectiveness of our interferometer is demonstrated through realizing single-photon quantum-walk dynamics in one dimension. By applying site-dependent phase defects, the translational symmetry of an ideal standard quantum walk is broken resulting in localization effect in a quantum walk architecture. The walk is realized for different site-dependent phase defects and coin settings, indicating the strength of localization signature depends on the level of phase due to site-dependent phase defects and coin settings and opening the way for the implementation of a quantum-walk-based algorithm.

Economy, Movement Dynamics, and Muscle Activity of Human Walking at Different Speeds

DEFF Research Database (Denmark)

Raffalt, Peter Christian; Guul, Martin Kjær; Nielsen, A. N.

2017-01-01

The complex behaviour of human walking with respect to movement variability, economy and muscle activity is speed dependent. It is well known that a U-shaped relationship between walking speed and economy exists. However, it is an open question if the movement dynamics of joint angles and centre...... of mass and muscle activation strategy also exhibit a U-shaped relationship with walking speed. We investigated the dynamics of joint angle trajectories and the centre of mass accelerations at five different speeds ranging from 20 to 180% of the predicted preferred speed (based on Froude speed) in twelve...... healthy males. The muscle activation strategy and walking economy were also assessed. The movement dynamics was investigated using a combination of the largest Lyapunov exponent and correlation dimension. We observed an intermediate stage of the movement dynamics of the knee joint angle and the anterior...

Treadmill walking of the pneumatic biped Lucy: Walking at different speeds and step-lengths

Science.gov (United States)

Vanderborght, B.; Verrelst, B.; Van Ham, R.; Van Damme, M.; Versluys, R.; Lefeber, D.

2008-07-01

Actuators with adaptable compliance are gaining interest in the field of legged robotics due to their capability to store motion energy and to exploit the natural dynamics of the system to reduce energy consumption while walking and running. To perform research on compliant actuators we have built the planar biped Lucy. The robot has six actuated joints, the ankle, knee and hip of both legs with each joint powered by two pleated pneumatic artificial muscles in an antagonistic setup. This makes it possible to control both the torque and the stiffness of the joint. Such compliant actuators are used in passive walkers to overcome friction when walking over level ground and to improve stability. Typically, this kind of robots is only designed to walk with a constant walking speed and step-length, determined by the mechanical design of the mechanism and the properties of the ground. In this paper, we show that by an appropriate control, the robot Lucy is able to walk at different speeds and step-lengths and that adding and releasing weights does not affect the stability of the robot. To perform these experiments, an automated treadmill was built

Passivity analysis of higher order evolutionary dynamics and population games

KAUST Repository

Mabrok, Mohamed

2017-01-05

Evolutionary dynamics describe how the population composition changes in response to the fitness levels, resulting in a closed-loop feedback system. Recent work established a connection between passivity theory and certain classes of population games, namely so-called “stable games”. In particular, it was shown that a combination of stable games and (an analogue of) passive evolutionary dynamics results in stable convergence to Nash equilibrium. This paper considers the converse question of necessary conditions for evolutionary dynamics to exhibit stable behaviors for all generalized stable games. Using methods from robust control analysis, we show that if an evolutionary dynamic does not satisfy a passivity property, then it is possible to construct a generalized stable game that results in instability. The results are illustrated on selected evolutionary dynamics with particular attention to replicator dynamics, which are also shown to be lossless, a special class of passive systems.

Dynamic physiological responses to the incremental shuttle walk test in adults

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Evandro Fornias Sperandio

Full Text Available Abstract Introduction: Understanding the normal dynamic physiological responses to the incremental shuttle walk test might enhance the interpretation of walking performance in clinical settings. Objective: To assess dynamic physiological responses to the incremental shuttle walk test and its predictors in healthy adults. Methods: We assessed the simultaneous rates of changes of Δoxygen uptake/Δwalking velocity (ΔVO 2 /ΔWV, Δheart rate/Δoxygen uptake (ΔHR/ΔVO 2 , Δventilation/Δcarbon dioxide production (ΔVE/ΔVCO 2 , and Δtidal volume/Δlinearized ventilation (ΔVT/ΔlnVE during the incremental shuttle walk test in 100 men and women older than 40 years. Fat and lean body masses (bioimpedance were also evaluated. Results: We found that the dynamic relationships were not sex-dependent. Participants aged ≥ 70 presented declines in ΔVO 2 /ΔWV slope compared to those aged 40-49 (215 ± 69 vs. 288 ± 84 mL.min-1.km.h-1. Obese participants presented shallower slopes for ΔVO 2 /ΔWV (2.94 ± 0.90 vs. 3.84 ± 1.21 mL.min-1.kg-1.km.h-1 and ΔVT/ΔlnVE (0.57 ± 0.20 vs. 0.67 ± 0.26. We found negative influence of fat body mass on ΔVT/ΔlnVE (R2 = 0.20 and positive influence of lean body mass on ΔVO 2 /ΔWV (R2 = 0.31, ΔHR/ΔVO2 (R2 = 0.25, and ΔVT/ΔlnVE (R2 = 0.44. Conclusion: Dynamic relationships during walking were slightly influenced by age, but not sex-dependent. Body composition played an important role in these indices. Our results may provide better interpretation of walking performance in patients with chronic diseases.

Effects of upper body parameters on biped walking efficiency studied by dynamic optimization

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Kang An

2016-12-01

Full Text Available Walking efficiency is one of the considerations for designing biped robots. This article uses the dynamic optimization method to study the effects of upper body parameters, including upper body length and mass, on walking efficiency. Two minimal actuations, hip joint torque and push-off impulse, are used in the walking model, and minimal constraints are set in a free search using the dynamic optimization. Results show that there is an optimal solution of upper body length for the efficient walking within a range of walking speed and step length. For short step length, walking with a lighter upper body mass is found to be more efficient and vice versa. It is also found that for higher speed locomotion, the increase of the upper body length and mass can make the walking gait optimal rather than other kind of gaits. In addition, the typical strategy of an optimal walking gait is that just actuating the swing leg at the beginning of the step.

Dynamical correlations for vicious random walk with a wall

International Nuclear Information System (INIS)

Nagao, Taro

2003-01-01

A one-dimensional system of nonintersecting Brownian particles is constructed as the diffusion scaling limit of Fisher's vicious random walk model. N Brownian particles start from the origin at time t=0 and undergo mutually avoiding motion until a finite time t=T. Dynamical correlation functions among the walkers are exactly evaluated in the case with a wall at the origin. Taking an asymptotic limit N→∞, we observe discontinuous transitions in the dynamical correlations. It is further shown that the vicious walk model with a wall is equivalent to a parametric random matrix model describing the crossover between the Bogoliubov-deGennes universality classes

Characterizing Dynamic Walking Patterns and Detecting Falls with Wearable Sensors Using Gaussian Process Methods

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Taehwan Kim

2017-05-01

Full Text Available By incorporating a growing number of sensors and adopting machine learning technologies, wearable devices have recently become a prominent health care application domain. Among the related research topics in this field, one of the most important issues is detecting falls while walking. Since such falls may lead to serious injuries, automatically and promptly detecting them during daily use of smartphones and/or smart watches is a particular need. In this paper, we investigate the use of Gaussian process (GP methods for characterizing dynamic walking patterns and detecting falls while walking with built-in wearable sensors in smartphones and/or smartwatches. For the task of characterizing dynamic walking patterns in a low-dimensional latent feature space, we propose a novel approach called auto-encoded Gaussian process dynamical model, in which we combine a GP-based state space modeling method with a nonlinear dimensionality reduction method in a unique manner. The Gaussian process methods are fit for this task because one of the most import strengths of the Gaussian process methods is its capability of handling uncertainty in the model parameters. Also for detecting falls while walking, we propose to recycle the latent samples generated in training the auto-encoded Gaussian process dynamical model for GP-based novelty detection, which can lead to an efficient and seamless solution to the detection task. Experimental results show that the combined use of these GP-based methods can yield promising results for characterizing dynamic walking patterns and detecting falls while walking with the wearable sensors.

Random walk in dynamically disordered chains: Poisson white noise disorder

International Nuclear Information System (INIS)

Hernandez-Garcia, E.; Pesquera, L.; Rodriguez, M.A.; San Miguel, M.

1989-01-01

Exact solutions are given for a variety of models of random walks in a chain with time-dependent disorder. Dynamic disorder is modeled by white Poisson noise. Models with site-independent (global) and site-dependent (local) disorder are considered. Results are described in terms of an affective random walk in a nondisordered medium. In the cases of global disorder the effective random walk contains multistep transitions, so that the continuous limit is not a diffusion process. In the cases of local disorder the effective process is equivalent to usual random walk in the absence of disorder but with slower diffusion. Difficulties associated with the continuous-limit representation of random walk in a disordered chain are discussed. In particular, the authors consider explicit cases in which taking the continuous limit and averaging over disorder sources do not commute

Effects of an attention demanding task on dynamic stability during treadmill walking

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Troy Karen L

2008-04-01

Full Text Available Abstract Background People exhibit increased difficulty balancing when they perform secondary attention-distracting tasks while walking. However, a previous study by Grabiner and Troy (J. Neuroengineering Rehabil., 2005 found that young healthy subjects performing a concurrent Stroop task while walking on a motorized treadmill exhibited decreased step width variability. However, measures of variability do not directly quantify how a system responds to perturbations. This study re-analyzed data from Grabiner and Troy 2005 to determine if performing the concurrent Stroop task directly affected the dynamic stability of walking in these same subjects. Methods Thirteen healthy volunteers walked on a motorized treadmill at their self-selected constant speed for 10 minutes both while performing the Stroop test and during undisturbed walking. This Stroop test consisted of projecting images of the name of one color, printed in text of a different color, onto a wall and asking subjects to verbally identify the color of the text. Three-dimensional motions of a marker attached to the base of the neck (C5/T1 were recorded. Marker velocities were calculated over 3 equal intervals of 200 sec each in each direction. Mean variability was calculated for each time series as the average standard deviation across all strides. Both "local" and "orbital" dynamic stability were quantified for each time series using previously established methods. These measures directly quantify how quickly small perturbations grow or decay, either continuously in real time (local or discretely from one cycle to the next (orbital. Differences between Stroop and Control trials were evaluated using a 2-factor repeated measures ANOVA. Results Mean variability of trunk movements was significantly reduced during the Stroop tests compared to normal walking. Conversely, local and orbital stability results were mixed: some measures showed slight increases, while others showed slight decreases

Optimal Passive Dynamics for Physical Interaction: Catching a Mass

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Kevin Kemper

2013-05-01

Full Text Available For manipulation tasks in uncertain environments, intentionally designed series impedance in mechanical systems can provide significant benefits that cannot be achieved in software. Traditionally, the design of actuated systems revolves around sizing torques, speeds, and control strategies without considering the system’s passive dynamics. However, the passive dynamics of the mechanical system, including inertia, stiffness, and damping along with other parameters such as torque and stroke limits often impose performance limitations that cannot be overcome with software control. In this paper, we develop relationships between an actuator’s passive dynamics and the resulting performance for the purpose of better understanding how to tune the passive dynamics for catching an unexpected object. We use a mathematically optimal controller subject to force limitations to stop the incoming object without breaking contact and bouncing. The use of an optimal controller is important so that our results directly reflect the physical system’s performance. We analytically calculate the maximum velocity that can be caught by a realistic actuator with limitations such as force and stroke limits. The results show that in order to maximize the velocity of an object that can be caught without exceeding the actuator’s torque and stroke limits, a soft spring along with a strong damper will be desired.

The walking behaviour of pedestrian social groups and its impact on crowd dynamics.

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Mehdi Moussaïd

Full Text Available Human crowd motion is mainly driven by self-organized processes based on local interactions among pedestrians. While most studies of crowd behaviour consider only interactions among isolated individuals, it turns out that up to 70% of people in a crowd are actually moving in groups, such as friends, couples, or families walking together. These groups constitute medium-scale aggregated structures and their impact on crowd dynamics is still largely unknown. In this work, we analyze the motion of approximately 1500 pedestrian groups under natural condition, and show that social interactions among group members generate typical group walking patterns that influence crowd dynamics. At low density, group members tend to walk side by side, forming a line perpendicular to the walking direction. As the density increases, however, the linear walking formation is bent forward, turning it into a V-like pattern. These spatial patterns can be well described by a model based on social communication between group members. We show that the V-like walking pattern facilitates social interactions within the group, but reduces the flow because of its "non-aerodynamic" shape. Therefore, when crowd density increases, the group organization results from a trade-off between walking faster and facilitating social exchange. These insights demonstrate that crowd dynamics is not only determined by physical constraints induced by other pedestrians and the environment, but also significantly by communicative, social interactions among individuals.

Random walk on random walks

NARCIS (Netherlands)

Hilário, M.; Hollander, den W.Th.F.; Sidoravicius, V.; Soares dos Santos, R.; Teixeira, A.

2014-01-01

In this paper we study a random walk in a one-dimensional dynamic random environment consisting of a collection of independent particles performing simple symmetric random walks in a Poisson equilibrium with density ¿¿(0,8). At each step the random walk performs a nearest-neighbour jump, moving to

Local dynamic stability of lower extremity joints in lower limb amputees during slope walking.

Science.gov (United States)

Chen, Jin-Ling; Gu, Dong-Yun

2013-01-01

Lower limb amputees have a higher fall risk during slope walking compared with non-amputees. However, studies on amputees' slope walking were not well addressed. The aim of this study was to identify the difference of slope walking between amputees and non-amputees. Lyapunov exponents λS was used to estimate the local dynamic stability of 7 transtibial amputees' and 7 controls' lower extremity joint kinematics during uphill and downhill walking. Compared with the controls, amputees exhibited significantly lower λS in hip (P=0.04) and ankle (P=0.01) joints of the sound limb, and hip joints (P=0.01) of the prosthetic limb during uphill walking, while they exhibited significantly lower λS in knee (P=0.02) and ankle (P=0.03) joints of the sound limb, and hip joints (P=0.03) of the prosthetic limb during downhill walking. Compared with amputees level walking, they exhibited significantly lower λS in ankle joints of the sound limb during both uphill (P=0.01) and downhill walking (P=0.01). We hypothesized that the better local dynamic stability of amputees was caused by compensation strategy during slope walking.

The effect of walking speed on local dynamic stability is sensitive to calculation methods

DEFF Research Database (Denmark)

Stenum, Jan; Bruijn, Sjoerd M; Jensen, Bente Rona

2014-01-01

Local dynamic stability has been assessed by the short-term local divergence exponent (λS), which quantifies the average rate of logarithmic divergence of infinitesimally close trajectories in state space. Both increased and decreased local dynamic stability at faster walking speeds have been...... reported. This might pertain to methodological differences in calculating λS. Therefore, the aim was to test if different calculation methods would induce different effects of walking speed on local dynamic stability. Ten young healthy participants walked on a treadmill at five speeds (60%, 80%, 100%, 120......% and 140% of preferred walking speed) for 3min each, while upper body accelerations in three directions were sampled. From these time-series, λS was calculated by three different methods using: (a) a fixed time interval and expressed as logarithmic divergence per stride-time (λS-a), (b) a fixed number...

Simulating continuous-time Hamiltonian dynamics by way of a discrete-time quantum walk

International Nuclear Information System (INIS)

Schmitz, A.T.; Schwalm, W.A.

2016-01-01

Much effort has been made to connect the continuous-time and discrete-time quantum walks. We present a method for making that connection for a general graph Hamiltonian on a bigraph. Furthermore, such a scheme may be adapted for simulating discretized quantum models on a quantum computer. A coin operator is found for the discrete-time quantum walk which exhibits the same dynamics as the continuous-time evolution. Given the spectral decomposition of the graph Hamiltonian and certain restrictions, the discrete-time evolution is solved for explicitly and understood at or near important values of the parameters. Finally, this scheme is connected to past results for the 1D chain. - Highlights: • A discrete-time quantum walk is purposed which approximates a continuous-time quantum walk. • The purposed quantum walk could be used to simulate Hamiltonian dynamics on a quantum computer. • Given the spectra decomposition of the Hamiltonian, the quantum walk is solved explicitly. • The method is demonstrated and connected to previous work done on the 1D chain.

Dynamic random walks theory and applications

CERN Document Server

Guillotin-Plantard, Nadine

2006-01-01

The aim of this book is to report on the progress realized in probability theory in the field of dynamic random walks and to present applications in computer science, mathematical physics and finance. Each chapter contains didactical material as well as more advanced technical sections. Few appendices will help refreshing memories (if necessary!).· New probabilistic model, new results in probability theory· Original applications in computer science· Applications in mathematical physics· Applications in finance

Dynamic optimization of a biped model: Energetic walking gaits with different mechanical and gait parameters

Directory of Open Access Journals (Sweden)

Kang An

2015-05-01

Full Text Available Energy consumption is one of the problems for bipedal robots walking. For the purpose of studying the parameter effects on the design of energetic walking bipeds with strong adaptability, we use a dynamic optimization method on our new walking model to first investigate the effects of the mechanical parameters, including mass and length distribution, on the walking efficiency. Then, we study the energetic walking gait features with the combinations of walking speed and step length. Our walking model is designed upon Srinivasan’s model. Dynamic optimization is used for a free search with minimal constraints. The results show that the cost of transport of a certain gait increases with the increase in the mass and length distribution parameters, except for that the cost of transport decreases with big length distribution parameter and long step length. We can also find a corresponding range of walking speed and step length, in which the variation in one of the two parameters has no obvious effect on the cost of transport. With fixed mechanical parameters, the cost of transport increases with the increase in the walking speed. There is a speed–step length relationship for walking with minimal cost of transport. The hip torque output strategy is adjusted in two situations to meet the walking requirements.

Random walk of passive tracers among randomly moving obstacles

OpenAIRE

Gori, Matteo; Donato, Irene; Floriani, Elena; Nardecchia, Ilaria; Pettini, Marco

2016-01-01

Background: This study is mainly motivated by the need of understanding how the diffusion behaviour of a biomolecule (or even of a larger object) is affected by other moving macromolecules, organelles, and so on, inside a living cell, whence the possibility of understanding whether or not a randomly walking biomolecule is also subject to a long-range force field driving it to its target. Method: By means of the Continuous Time Random Walk (CTRW) technique the topic of random walk in random en...

Obesity May Not Induce Dynamic Stability Disadvantage during Overground Walking among Young Adults.

Science.gov (United States)

Liu, Zhong-Qi; Yang, Feng

2017-01-01

Obesity has been related to postural instability during static standing. It remains unknown how obesity influences stability during dynamic movements like gait. The primary aim of this study was to investigate the effects of obesity on dynamic gait stability control in young adults during gait. Forty-four young adults (21 normal-weight and 23 obese) participated in this study. Participants walked five times at their self-selected gait speeds on a linear walkway. Their full-body kinematics were gathered by a motion capture system. Compared with normal-weight group, individuals with obesity walked more slowly with a shorter but wider step. People with obesity also spent an elongated double stance phase than those with normal weight. A reduced gait speed decreases the body center of mass's velocity relative to the base of support, leading to a reduction in dynamic stability. On the other hand, a shortened step in accompanying with a less backward-leaning trunk has the potential to bring the center of mass closer to the base of support, resulting in an increase in dynamic stability. As the result of these adaptive changes to the gait pattern, dynamic gait stability among people with obesity did not significantly differ from the one among people with normal weight. Obesity seems to not be inducing dynamic stability disadvantage in young adults during level overground walking. These findings could provide insight into the mechanisms of stability control among people affected by obesity during dynamic locomotion.

Quantized Passive Dynamic Output Feedback Control with Actuator Failure

Directory of Open Access Journals (Sweden)

Zu-Xin Li

2016-01-01

Full Text Available This paper investigates the problem of passive dynamic output feedback control for fuzzy discrete nonlinear systems with quantization and actuator failures, where the measurement output of the system is quantized by a logarithmic quantizer before being transferred to the fuzzy controller. By employing the fuzzy-basis-dependent Lyapunov function, sufficient condition is established to guarantee the closed-loop system to be mean-square stable and the prescribed passive performance. Based on the sufficient condition, the fuzzy dynamic output feedback controller is proposed for maintaining acceptable performance levels in the case of actuator failures and quantization effects. Finally, a numerical example is given to show the usefulness of the proposed method.

The role of series ankle elasticity in bipedal walking.

Science.gov (United States)

Zelik, Karl E; Huang, Tzu-Wei P; Adamczyk, Peter G; Kuo, Arthur D

2014-04-07

The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active work demands on the plantarflexor muscles in series. However, this does not explain why or when this ankle work, whether by muscle or tendon, needs to be performed during gait. We therefore employ a simple bipedal walking model to investigate how ankle work and series elasticity impact economical locomotion. Our model shows that ankle elasticity can use passive dynamics to aid push-off late in single support, redirecting the body's center-of-mass (COM) motion upward. An appropriately timed, elastic push-off helps to reduce dissipative collision losses at contralateral heelstrike, and therefore the positive work needed to offset those losses and power steady walking. Thus, the model demonstrates how elastic ankle work can reduce the total energetic demands of walking, including work required from more proximal knee and hip muscles. We found that the key requirement for using ankle elasticity to achieve economical gait is the proper ratio of ankle stiffness to foot length. Optimal combination of these parameters ensures proper timing of elastic energy release prior to contralateral heelstrike, and sufficient energy storage to redirect the COM velocity. In fact, there exist parameter combinations that theoretically yield collision-free walking, thus requiring zero active work, albeit with relatively high ankle torques. Ankle elasticity also allows the hip to power economical walking by contributing indirectly to push-off. Whether walking is powered by the ankle or hip, ankle elasticity may aid walking economy by reducing collision losses. Copyright © 2013 Elsevier Ltd. All rights reserved.

Moving-window dynamic optimization: design of stimulation profiles for walking.

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Dosen, Strahinja; Popović, Dejan B

2009-05-01

The overall goal of the research is to improve control for electrical stimulation-based assistance of walking in hemiplegic individuals. We present the simulation for generating offline input (sensors)-output (intensity of muscle stimulation) representation of walking that serves in synthesizing a rule-base for control of electrical stimulation for restoration of walking. The simulation uses new algorithm termed moving-window dynamic optimization (MWDO). The optimization criterion was to minimize the sum of the squares of tracking errors from desired trajectories with the penalty function on the total muscle efforts. The MWDO was developed in the MATLAB environment and tested using target trajectories characteristic for slow-to-normal walking recorded in healthy individual and a model with the parameters characterizing the potential hemiplegic user. The outputs of the simulation are piecewise constant intensities of electrical stimulation and trajectories generated when the calculated stimulation is applied to the model. We demonstrated the importance of this simulation by showing the outputs for healthy and hemiplegic individuals, using the same target trajectories. Results of the simulation show that the MWDO is an efficient tool for analyzing achievable trajectories and for determining the stimulation profiles that need to be delivered for good tracking.

Activity of upper limb muscles during human walking.

Science.gov (United States)

Kuhtz-Buschbeck, Johann P; Jing, Bo

2012-04-01

The EMG activity of upper limb muscles during human gait has rarely been studied previously. It was examined in 20 normal volunteers in four conditions: walking on a treadmill (1) with unrestrained natural arm swing (Normal), (2) while volitionally holding the arms still (Held), (3) with the arms immobilized (Bound), and (4) with the arms swinging in phase with the ipsilateral legs, i.e. opposite-to-normal phasing (Anti-Normal). Normal arm swing involved weak rhythmical lengthening and shortening contractions of arm and shoulder muscles. Phasic muscle activity was needed to keep the unrestricted arms still during walking (Held), indicating a passive component of arm swing. An active component, possibly programmed centrally, existed as well, because some EMG signals persisted when the arms were immobilized during walking (Bound). Anti-Normal gait involved stronger EMG activity than Normal walking and was uneconomical. The present results indicate that normal arm swing has both passive and active components. Copyright © 2011 Elsevier Ltd. All rights reserved.

Resolvent-based modeling of passive scalar dynamics in wall-bounded turbulence

Science.gov (United States)

Dawson, Scott; Saxton-Fox, Theresa; McKeon, Beverley

2017-11-01

The resolvent formulation of the Navier-Stokes equations expresses the system state as the output of a linear (resolvent) operator acting upon a nonlinear forcing. Previous studies have demonstrated that a low-rank approximation of this linear operator predicts many known features of incompressible wall-bounded turbulence. In this work, this resolvent model for wall-bounded turbulence is extended to include a passive scalar field. This formulation allows for a number of additional simplifications that reduce model complexity. Firstly, it is shown that the effect of changing scalar diffusivity can be approximated through a transformation of spatial wavenumbers and temporal frequencies. Secondly, passive scalar dynamics may be studied through the low-rank approximation of a passive scalar resolvent operator, which is decoupled from velocity response modes. Thirdly, this passive scalar resolvent operator is amenable to approximation by semi-analytic methods. We investigate the extent to which this resulting hierarchy of models can describe and predict passive scalar dynamics and statistics in wall-bounded turbulence. The support of AFOSR under Grant Numbers FA9550-16-1-0232 and FA9550-16-1-0361 is gratefully acknowledged.

The efficacy of the Ankle Mimicking Prosthetic Foot prototype 4.0 during walking: Physiological determinants.

Science.gov (United States)

De Pauw, Kevin; Cherelle, Pierre; Roelands, Bart; Lefeber, Dirk; Meeusen, Romain

2018-04-01

Evaluating the effectiveness of a novel prosthetic device during walking is an important step in product development. To investigate the efficacy of a novel quasi-passive ankle prosthetic device, Ankle Mimicking Prosthetic Foot 4.0, during walking at different speeds, using physiological determinants in transtibial and transfemoral amputees. Nonrandomized crossover design for amputees. Six able-bodied subjects, six unilateral transtibial amputees, and six unilateral transfemoral amputees underwent a 6-min walk test at normal speed, followed by series of 2-min walking at slow, normal, and fast speeds. The intensity of effort and subjective measures were determined. Amputees performed all walking tests on a treadmill with current and novel prostheses. Shapiro-Wilk normality tests and parametric and nonparametric tests were conducted (p 4.0 is a novel quasi-passive ankle prosthesis with state-of-the-art technological parts. Subjective measures show the importance of this technology, but the intensity of effort during walking still remains higher compared to current passive prostheses, especially in transfemoral amputees.

Comparison of inverse dynamics calculated by two- and three-dimensional models during walking

DEFF Research Database (Denmark)

Alkjaer, T; Simonsen, E B; Dyhre-Poulsen, P

2001-01-01

recorded the subjects as they walked across two force plates. The subjects were invited to approach a walking speed of 4.5 km/h. The ankle, knee and hip joint moments in the sagittal plane were calculated by 2D and 3D inverse dynamics analysis and compared. Despite the uniform walking speed (4.53 km....../h) and similar footwear, relatively large inter-individual variations were found in the joint moment patterns during the stance phase. The differences between individuals were present in both the 2D and 3D analysis. For the entire sample of subjects the overall time course pattern of the ankle, knee and hip...... the magnitude of the joint moments calculated by 2D and 3D inverse dynamics but the inter-individual variation was not affected by the different models. The simpler 2D model seems therefore appropriate for human gait analysis. However, comparisons of gait data from different studies are problematic...

Bifurcation and chaos in the simple passive dynamic walking model with upper body.

Science.gov (United States)

Li, Qingdu; Guo, Jianli; Yang, Xiao-Song

2014-09-01

We present some rich new complex gaits in the simple walking model with upper body by Wisse et al. in [Robotica 22, 681 (2004)]. We first show that the stable gait found by Wisse et al. may become chaotic via period-doubling bifurcations. Such period-doubling routes to chaos exist for all parameters, such as foot mass, upper body mass, body length, hip spring stiffness, and slope angle. Then, we report three new gaits with period 3, 4, and 6; for each gait, there is also a period-doubling route to chaos. Finally, we show a practical method for finding a topological horseshoe in 3D Poincaré map, and present a rigorous verification of chaos from these gaits.

Bifurcation and chaos in the simple passive dynamic walking model with upper body

Energy Technology Data Exchange (ETDEWEB)

Li, Qingdu; Guo, Jianli [Key Laboratory of Industrial Internet of Things and Networked Control, Ministry of Education, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Yang, Xiao-Song, E-mail: yangxs@hust.edu.cn [Department of Mathematics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2014-09-01

We present some rich new complex gaits in the simple walking model with upper body by Wisse et al. in [Robotica 22, 681 (2004)]. We first show that the stable gait found by Wisse et al. may become chaotic via period-doubling bifurcations. Such period-doubling routes to chaos exist for all parameters, such as foot mass, upper body mass, body length, hip spring stiffness, and slope angle. Then, we report three new gaits with period 3, 4, and 6; for each gait, there is also a period-doubling route to chaos. Finally, we show a practical method for finding a topological horseshoe in 3D Poincaré map, and present a rigorous verification of chaos from these gaits.

Bifurcation and chaos in the simple passive dynamic walking model with upper body

International Nuclear Information System (INIS)

Li, Qingdu; Guo, Jianli; Yang, Xiao-Song

2014-01-01

We present some rich new complex gaits in the simple walking model with upper body by Wisse et al. in [Robotica 22, 681 (2004)]. We first show that the stable gait found by Wisse et al. may become chaotic via period-doubling bifurcations. Such period-doubling routes to chaos exist for all parameters, such as foot mass, upper body mass, body length, hip spring stiffness, and slope angle. Then, we report three new gaits with period 3, 4, and 6; for each gait, there is also a period-doubling route to chaos. Finally, we show a practical method for finding a topological horseshoe in 3D Poincaré map, and present a rigorous verification of chaos from these gaits

A passive exoskeleton with artificial tendons: design and experimental evaluation.

Science.gov (United States)

van Dijk, Wietse; van der Kooij, Herman; Hekman, Edsko

2011-01-01

We developed a passive exoskeleton that was designed to minimize joint work during walking. The exoskeleton makes use of passive structures, called artificial tendons, acting in parallel with the leg. Artificial tendons are elastic elements that are able to store and redistribute energy over the human leg joints. The elastic characteristics of the tendons have been optimized to minimize the mechanical work of the human leg joints. In simulation the maximal reduction was 40 percent. The performance of the exoskeleton was evaluated in an experiment in which nine subjects participated. Energy expenditure and muscle activation were measured during three conditions: Normal walking, walking with the exoskeleton without artificial tendons, and walking with the exoskeleton with the artificial tendons. Normal walking was the most energy efficient. While walking with the exoskeleton, the artificial tendons only resulted in a negligibly small decrease in energy expenditure. © 2011 IEEE

Biomechanical parameters in lower limbs during natural walking and Nordic walking at different speeds.

Science.gov (United States)

Dziuba, Alicja K; Żurek, Grzegorz; Garrard, Ian; Wierzbicka-Damska, Iwona

2015-01-01

Nordic Walking (NW) is a sport that has a number of benefits as a rehabilitation method. It is performed with specially designed poles and has been often recommended as a physical activity that helps reduce the load to limbs. However, some studies have suggested that these findings might be erroneous. The aim of this paper was to compare the kinematic, kinetic and dynamic parameters of lower limbs between Natural Walking (W) and Nordic Walking (NW) at both low and high walking speeds. The study used a registration system, BTS Smart software and Kistler platform. Eleven subjects walked along a 15-metre path at low (below 2 m⋅s-1) and high (over 2 m⋅s-1) walking speeds. The Davis model was employed for calculations of kinematic, kinetic and dynamic parameters of lower limbs. With constant speed, the support given by Nordic Walking poles does not make the stroke longer and there is no change in pelvic rotation either. The only change observed was much bigger pelvic anteversion in the sagittal plane during fast NW. There were no changes in forces, power and muscle torques in lower limbs. The study found no differences in kinematic, kinetic and dynamic parameters between Natural Walking (W) and Nordic Walking (NW). Higher speeds generate greater ground reaction forces and muscle torques in lower limbs. Gait parameters depend on walking speed rather than on walking style.

Humanoid Walking Robot: Modeling, Inverse Dynamics, and Gain Scheduling Control

Directory of Open Access Journals (Sweden)

Elvedin Kljuno

2010-01-01

Full Text Available This article presents reference-model-based control design for a 10 degree-of-freedom bipedal walking robot, using nonlinear gain scheduling. The main goal is to show concentrated mass models can be used for prediction of the required joint torques for a bipedal walking robot. Relatively complicated architecture, high DOF, and balancing requirements make the control task of these robots difficult. Although linear control techniques can be used to control bipedal robots, nonlinear control is necessary for better performance. The emphasis of this work is to show that the reference model can be a bipedal walking model with concentrated mass at the center of gravity, which removes the problems related to design of a pseudo-inverse system. Another significance of this approach is the reduced calculation requirements due to the simplified procedure of nominal joint torques calculation. Kinematic and dynamic analysis is discussed including results for joint torques and ground force necessary to implement a prescribed walking motion. This analysis is accompanied by a comparison with experimental data. An inverse plant and a tracking error linearization-based controller design approach is described. We propose a novel combination of a nonlinear gain scheduling with a concentrated mass model for the MIMO bipedal robot system.

Observation of quasiperiodic dynamics in a one-dimensional quantum walk of single photons in space

Science.gov (United States)

Xue, Peng; Qin, Hao; Tang, Bao; Sanders, Barry C.

2014-05-01

We realize the quasi-periodic dynamics of a quantum walker over 2.5 quasi-periods by realizing the walker as a single photon passing through a quantum-walk optical-interferometer network. We introduce fully controllable polarization-independent phase shifters in each optical path to realize arbitrary site-dependent phase shifts, and employ large clear-aperture beam displacers, while maintaining high-visibility interference, to enable 10 quantum-walk steps to be reached. By varying the half-wave-plate setting, we control the quantum-coin bias thereby observing a transition from quasi-periodic dynamics to ballistic diffusion.

Biomechanics and muscle coordination of human walking. Part I: introduction to concepts, power transfer, dynamics and simulations.

Science.gov (United States)

Zajac, Felix E; Neptune, Richard R; Kautz, Steven A

2002-12-01

Current understanding of how muscles coordinate walking in humans is derived from analyses of body motion, ground reaction force and EMG measurements. This is Part I of a two-part review that emphasizes how muscle-driven dynamics-based simulations assist in the understanding of individual muscle function in walking, especially the causal relationships between muscle force generation and walking kinematics and kinetics. Part I reviews the strengths and limitations of Newton-Euler inverse dynamics and dynamical simulations, including the ability of each to find the contributions of individual muscles to the acceleration/deceleration of the body segments. We caution against using the concept of biarticular muscles transferring power from one joint to another to infer muscle coordination principles because energy flow among segments, even the adjacent segments associated with the joints, cannot be inferred from computation of joint powers and segmental angular velocities alone. Rather, we encourage the use of dynamical simulations to perform muscle-induced segmental acceleration and power analyses. Such analyses have shown that the exchange of segmental energy caused by the forces or accelerations induced by a muscle can be fundamentally invariant to whether the muscle is shortening, lengthening, or neither. How simulation analyses lead to understanding the coordination of seated pedaling, rather than walking, is discussed in this first part because the dynamics of pedaling are much simpler, allowing important concepts to be revealed. We elucidate how energy produced by muscles is delivered to the crank through the synergistic action of other non-energy producing muscles; specifically, that a major function performed by a muscle arises from the instantaneous segmental accelerations and redistribution of segmental energy throughout the body caused by its force generation. Part II reviews how dynamical simulations provide insight into muscle coordination of walking.

Relation between random walks and quantum walks

Science.gov (United States)

Boettcher, Stefan; Falkner, Stefan; Portugal, Renato

2015-05-01

Based on studies of four specific networks, we conjecture a general relation between the walk dimensions dw of discrete-time random walks and quantum walks with the (self-inverse) Grover coin. In each case, we find that dw of the quantum walk takes on exactly half the value found for the classical random walk on the same geometry. Since walks on homogeneous lattices satisfy this relation trivially, our results for heterogeneous networks suggest that such a relation holds irrespective of whether translational invariance is maintained or not. To develop our results, we extend the renormalization-group analysis (RG) of the stochastic master equation to one with a unitary propagator. As in the classical case, the solution ρ (x ,t ) in space and time of this quantum-walk equation exhibits a scaling collapse for a variable xdw/t in the weak limit, which defines dw and illuminates fundamental aspects of the walk dynamics, e.g., its mean-square displacement. We confirm the collapse for ρ (x ,t ) in each case with extensive numerical simulation. The exact values for dw themselves demonstrate that RG is a powerful complementary approach to study the asymptotics of quantum walks that weak-limit theorems have not been able to access, such as for systems lacking translational symmetries beyond simple trees.

Passivity analysis of higher order evolutionary dynamics and population games

KAUST Repository

Mabrok, Mohamed; Shamma, Jeff S.

2017-01-01

Evolutionary dynamics describe how the population composition changes in response to the fitness levels, resulting in a closed-loop feedback system. Recent work established a connection between passivity theory and certain classes of population

Addition of Passive Dynamics to a Flapping Airfoil to Improve Performance

Science.gov (United States)

Asselin, Daniel; Young, Jay; Williamson, C. H. K.

2017-11-01

Animals which fly or swim typically employ flapping motions of their wings and fins in order to produce thrust and to maneuver. Small, unmanned vehicles might also exploit such motions and are of considerable interest for the purposes of surveillance, environmental monitoring, and search and rescue. Flapping refers to a combination of pitch and heave and has been shown to provide good thrust and efficiency (Read, et al. 2003) when both axes are independently controlled (an Active-Active system). In this study, we examine the performance of an airfoil actuated only in the heave direction but allowed to pitch passively under the control of a torsion spring (an Active-Passive system). The presence of the spring is simulated in software using a force-feedback control system called Cyber-Physical Fluid Dynamics, or CPFD (Mackowski & Williamson 2011, 2015, 2016). Adding passive pitch to active heave provides significantly improved thrust and efficiency compared with heaving alone, especially when the torsion spring stiffness is selected so that the system operates near resonance (in an Active-Passive system). In many cases, values of thrust and efficiency are comparable to or better than those obtained with two actively controlled degrees of freedom. By using carefully-designed passive dynamics in the pitch direction, we can eliminate one of the two actuators, saving cost, complexity, and weight, while maintaining performance. This work was supported by the Air Force Office of Scientific Research Grant No. FA9550-15-1-0243, monitored by Dr. Douglas Smith.

Computational fluid dynamics (CFD) simulation of a newly designed passive particle sampler.

Science.gov (United States)

Sajjadi, H; Tavakoli, B; Ahmadi, G; Dhaniyala, S; Harner, T; Holsen, T M

2016-07-01

In this work a series of computational fluid dynamics (CFD) simulations were performed to predict the deposition of particles on a newly designed passive dry deposition (Pas-DD) sampler. The sampler uses a parallel plate design and a conventional polyurethane foam (PUF) disk as the deposition surface. The deposition of particles with sizes between 0.5 and 10 μm was investigated for two different geometries of the Pas-DD sampler for different wind speeds and various angles of attack. To evaluate the mean flow field, the k-ɛ turbulence model was used and turbulent fluctuating velocities were generated using the discrete random walk (DRW) model. The CFD software ANSYS-FLUENT was used for performing the numerical simulations. It was found that the deposition velocity increased with particle size or wind speed. The modeled deposition velocities were in general agreement with the experimental measurements and they increased when flow entered the sampler with a non-zero angle of attack. The particle-size dependent deposition velocity was also dependent on the geometry of the leading edge of the sampler; deposition velocities were more dependent on particle size and wind speeds for the sampler without the bend in the leading edge of the deposition plate, compared to a flat plate design. Foam roughness was also found to have a small impact on particle deposition. Copyright © 2016 Elsevier Ltd. All rights reserved.

Real-time feedback of dynamic foot pressure index for gait training of toe-walking children with spastic diplegia.

Science.gov (United States)

Pu, Fang; Ren, Weiyan; Fan, Xiaoya; Chen, Wei; Li, Shuyu; Li, Deyu; Wang, Yu; Fan, Yubo

2017-09-01

The aim of this study was to determine whether and how real-time feedback of dynamic foot pressure index (DFPI) could be used to correct toe-walking gait in spastic diplegic children with dynamic equinus. Thirteen spastic diplegic children with dynamic equinus were asked to wear a monitoring device to record their ambulation during daily gait, conventional training gait, and feedback training gait. Parameters based on their DFPI and stride duration were compared among the three test conditions. The results with feedback training were significantly better for all DFPI parameters in comparison to patients' daily gait and showed significant improvements in DFPI for toe-walking gait and percentage of normal gait in comparison to conventional training methods. Moreover, stride duration under two training gaits was longer than patient's daily gait, but there was no significant difference between the two training gaits. Although the stride duration for the two training gaits was similar, gait training with real-time feedback of DFPI did produce noticeably superior results by increasing heel-loading impulse of toe-walking gait and percentage of normal gait in comparison to convention training methods. However, its effectiveness was still impacted by the motion limitations of diplegic children. Implications for Rehabilitation The DFPI-based gait training feedback system introduced in this study was shown to be more effective at toe-walking gait rehabilitation training over conventional training methods. The feedback system accomplished superior improvement in correcting toe-walking gait, but its effectiveness in an increasing heel-loading impulse in normal gait was still limited by the motion limitations of diplegic children. Stride duration of normal gait and toe-walking gait was similar under conventional and feedback gait training.

Complex networks: when random walk dynamics equals synchronization

International Nuclear Information System (INIS)

Kriener, Birgit; Anand, Lishma; Timme, Marc

2012-01-01

Synchrony prevalently emerges from the interactions of coupled dynamical units. For simple systems such as networks of phase oscillators, the asymptotic synchronization process is assumed to be equivalent to a Markov process that models standard diffusion or random walks on the same network topology. In this paper, we analytically derive the conditions for such equivalence for networks of pulse-coupled oscillators, which serve as models for neurons and pacemaker cells interacting by exchanging electric pulses or fireflies interacting via light flashes. We find that the pulse synchronization process is less simple, but there are classes of, e.g., network topologies that ensure equivalence. In particular, local dynamical operators are required to be doubly stochastic. These results provide a natural link between stochastic processes and deterministic synchronization on networks. Tools for analyzing diffusion (or, more generally, Markov processes) may now be transferred to pin down features of synchronization in networks of pulse-coupled units such as neural circuits. (paper)

Walking to health.

Science.gov (United States)

Morris, J N; Hardman, A E

1997-05-01

Walking is a rhythmic, dynamic, aerobic activity of large skeletal muscles that confers the multifarious benefits of this with minimal adverse effects. Walking, faster than customary, and regularly in sufficient quantity into the 'training zone' of over 70% of maximal heart rate, develops and sustains physical fitness: the cardiovascular capacity and endurance (stamina) for bodily work and movement in everyday life that also provides reserves for meeting exceptional demands. Muscles of the legs, limb girdle and lower trunk are strengthened and the flexibility of their cardinal joints preserved; posture and carriage may improve. Any amount of walking, and at any pace, expends energy. Hence the potential, long term, of walking for weight control. Dynamic aerobic exercise, as in walking, enhances a multitude of bodily processes that are inherent in skeletal muscle activity, including the metabolism of high density lipoproteins and insulin/glucose dynamics. Walking is also the most common weight-bearing activity, and there are indications at all ages of an increase in related bone strength. The pleasurable and therapeutic, psychological and social dimensions of walking, whilst evident, have been surprisingly little studied. Nor has an economic assessment of the benefits and costs of walking been attempted. Walking is beneficial through engendering improved fitness and/or greater physiological activity and energy turnover. Two main modes of such action are distinguished as: (i) acute, short term effects of the exercise; and (ii) chronic, cumulative adaptations depending on habitual activity over weeks and months. Walking is often included in studies of exercise in relation to disease but it has seldom been specifically tested. There is, nevertheless, growing evidence of gains in the prevention of heart attack and reduction of total death rates, in the treatment of hypertension, intermittent claudication and musculoskeletal disorders, and in rehabilitation after heart

Lévy walks

Science.gov (United States)

Zaburdaev, V.; Denisov, S.; Klafter, J.

2015-04-01

Random walk is a fundamental concept with applications ranging from quantum physics to econometrics. Remarkably, one specific model of random walks appears to be ubiquitous across many fields as a tool to analyze transport phenomena in which the dispersal process is faster than dictated by Brownian diffusion. The Lévy-walk model combines two key features, the ability to generate anomalously fast diffusion and a finite velocity of a random walker. Recent results in optics, Hamiltonian chaos, cold atom dynamics, biophysics, and behavioral science demonstrate that this particular type of random walk provides significant insight into complex transport phenomena. This review gives a self-consistent introduction to Lévy walks, surveys their existing applications, including latest advances, and outlines further perspectives.

Continuous-time quantum random walks require discrete space

International Nuclear Information System (INIS)

Manouchehri, K; Wang, J B

2007-01-01

Quantum random walks are shown to have non-intuitive dynamics which makes them an attractive area of study for devising quantum algorithms for long-standing open problems as well as those arising in the field of quantum computing. In the case of continuous-time quantum random walks, such peculiar dynamics can arise from simple evolution operators closely resembling the quantum free-wave propagator. We investigate the divergence of quantum walk dynamics from the free-wave evolution and show that, in order for continuous-time quantum walks to display their characteristic propagation, the state space must be discrete. This behavior rules out many continuous quantum systems as possible candidates for implementing continuous-time quantum random walks

Continuous-time quantum random walks require discrete space

Science.gov (United States)

Manouchehri, K.; Wang, J. B.

2007-11-01

Quantum random walks are shown to have non-intuitive dynamics which makes them an attractive area of study for devising quantum algorithms for long-standing open problems as well as those arising in the field of quantum computing. In the case of continuous-time quantum random walks, such peculiar dynamics can arise from simple evolution operators closely resembling the quantum free-wave propagator. We investigate the divergence of quantum walk dynamics from the free-wave evolution and show that, in order for continuous-time quantum walks to display their characteristic propagation, the state space must be discrete. This behavior rules out many continuous quantum systems as possible candidates for implementing continuous-time quantum random walks.

Human Skeleton Model Based Dynamic Features for Walking Speed Invariant Gait Recognition

Directory of Open Access Journals (Sweden)

Jure Kovač

2014-01-01

Full Text Available Humans are able to recognize small number of people they know well by the way they walk. This ability represents basic motivation for using human gait as the means for biometric identification. Such biometrics can be captured at public places from a distance without subject's collaboration, awareness, and even consent. Although current approaches give encouraging results, we are still far from effective use in real-life applications. In general, methods set various constraints to circumvent the influence of covariate factors like changes of walking speed, view, clothing, footwear, and object carrying, that have negative impact on recognition performance. In this paper we propose a skeleton model based gait recognition system focusing on modelling gait dynamics and eliminating the influence of subjects appearance on recognition. Furthermore, we tackle the problem of walking speed variation and propose space transformation and feature fusion that mitigates its influence on recognition performance. With the evaluation on OU-ISIR gait dataset, we demonstrate state of the art performance of proposed methods.

An inverse dynamics model for the analysis, reconstruction and prediction of bipedal walking

NARCIS (Netherlands)

Koopman, Hubertus F.J.M.; Grootenboer, H.J.; de Jongh, Henk J.; Huijing, P.A.J.B.M.; de Vries, J.

1995-01-01

Walking is a constrained movement which may best be observed during the double stance phase when both feet contact the floor. When analyzing a measured movement with an inverse dynamics model, a violation of these constrains will always occur due to measuring errors and deviations of the segments

Quantum walks, quantum gates, and quantum computers

International Nuclear Information System (INIS)

Hines, Andrew P.; Stamp, P. C. E.

2007-01-01

The physics of quantum walks on graphs is formulated in Hamiltonian language, both for simple quantum walks and for composite walks, where extra discrete degrees of freedom live at each node of the graph. It is shown how to map between quantum walk Hamiltonians and Hamiltonians for qubit systems and quantum circuits; this is done for both single-excitation and multiexcitation encodings. Specific examples of spin chains, as well as static and dynamic systems of qubits, are mapped to quantum walks, and walks on hyperlattices and hypercubes are mapped to various gate systems. We also show how to map a quantum circuit performing the quantum Fourier transform, the key element of Shor's algorithm, to a quantum walk system doing the same. The results herein are an essential preliminary to a Hamiltonian formulation of quantum walks in which coupling to a dynamic quantum environment is included

Magnetic field line random walk in two-dimensional dynamical turbulence

Science.gov (United States)

Wang, J. F.; Qin, G.; Ma, Q. M.; Song, T.; Yuan, S. B.

2017-08-01

The field line random walk (FLRW) of magnetic turbulence is one of the important topics in plasma physics and astrophysics. In this article, by using the field line tracing method, the mean square displacement (MSD) of FLRW is calculated on all possible length scales for pure two-dimensional turbulence with the damping dynamical model. We demonstrate that in order to describe FLRW with the damping dynamical model, a new dimensionless quantity R is needed to be introduced. On different length scales, dimensionless MSD shows different relationships with the dimensionless quantity R. Although the temporal effect affects the MSD of FLRW and even changes regimes of FLRW, it does not affect the relationship between the dimensionless MSD and dimensionless quantity R on all possible length scales.

Influence of Neuromuscular Noise and Walking Speed on Fall Risk and Dynamic Stability in a 3D Dynamic Walking Model

OpenAIRE

Roos, Paulien E.; Dingwell, Jonathan B.

2013-01-01

Older adults and those with increased fall risk tend to walk slower. They may do this voluntarily to reduce their fall risk. However, both slower and faster walking speeds can predict increased risk of different types of falls. The mechanisms that contribute to fall risk across speeds are not well known. Faster walking requires greater forward propulsion, generated by larger muscle forces. However, greater muscle activation induces increased signal-dependent neuromuscular noise. These speed-r...

Population Games, Stable Games, and Passivity

Directory of Open Access Journals (Sweden)

Michael J. Fox

2013-10-01

Full Text Available The class of “stable games”, introduced by Hofbauer and Sandholm in 2009, has the attractive property of admitting global convergence to equilibria under many evolutionary dynamics. We show that stable games can be identified as a special case of the feedback-system-theoretic notion of a “passive” dynamical system. Motivated by this observation, we develop a notion of passivity for evolutionary dynamics that complements the definition of the class of stable games. Since interconnections of passive dynamical systems exhibit stable behavior, we can make conclusions about passive evolutionary dynamics coupled with stable games. We show how established evolutionary dynamics qualify as passive dynamical systems. Moreover, we exploit the flexibility of the definition of passive dynamical systems to analyze generalizations of stable games and evolutionary dynamics that include forecasting heuristics as well as certain games with memory.

Trunk motion visual feedback during walking improves dynamic balance in older adults: Assessor blinded randomized controlled trial.

Science.gov (United States)

Anson, Eric; Ma, Lei; Meetam, Tippawan; Thompson, Elizabeth; Rathore, Roshita; Dean, Victoria; Jeka, John

2018-05-01

Virtual reality and augmented feedback have become more prevalent as training methods to improve balance. Few reports exist on the benefits of providing trunk motion visual feedback (VFB) during treadmill walking, and most of those reports only describe within session changes. To determine whether trunk motion VFB treadmill walking would improve over-ground balance for older adults with self-reported balance problems. 40 adults (75.8 years (SD 6.5)) with self-reported balance difficulties or a history of falling were randomized to a control or experimental group. Everyone walked on a treadmill at a comfortable speed 3×/week for 4 weeks in 2 min bouts separated by a seated rest. The control group was instructed to look at a stationary bulls-eye target while the experimental group also saw a moving cursor superimposed on the stationary bulls-eye that represented VFB of their walking trunk motion. The experimental group was instructed to keep the cursor in the center of the bulls-eye. Somatosensory (monofilaments and joint position testing) and vestibular function (canal specific clinical head impulses) was evaluated prior to intervention. Balance and mobility were tested before and after the intervention using Berg Balance Test, BESTest, mini-BESTest, and Six Minute Walk. There were no significant differences between groups before the intervention. The experimental group significantly improved on the BESTest (p = 0.031) and the mini-BEST (p = 0.019). The control group did not improve significantly on any measure. Individuals with more profound sensory impairments had a larger improvement on dynamic balance subtests of the BESTest. Older adults with self-reported balance problems improve their dynamic balance after training using trunk motion VFB treadmill walking. Individuals with worse sensory function may benefit more from trunk motion VFB during walking than individuals with intact sensory function. Copyright © 2018 Elsevier B.V. All rights reserved.

More symmetrical gait after split-belt treadmill walking does not modify dynamic and postural balance in individuals post-stroke.

Science.gov (United States)

Miéville, Carole; Lauzière, Séléna; Betschart, Martina; Nadeau, Sylvie; Duclos, Cyril

2018-04-24

Spontaneous gait is often asymmetrical in individuals post-stroke, despite their ability to walk more symmetrically on demand. Given the sensorimotor deficits in the paretic limb, this asymmetrical gait may facilitate balance maintenance. We used a split-belt walking protocol to alter gait asymmetry and determine the effects on dynamic and postural balance. Twenty individuals post-stroke walked on a split-belt treadmill. In two separate periods, the effects of walking with the non-paretic leg, and then the paretic one, on the faster belt on spatio-temporal symmetry and balance were compared before and after these perturbation periods. Kinematic and kinetic data were collected using a motion analysis system and an instrumented treadmill to determine symmetry ratios of spatiotemporal parameters and dynamic and postural balance. Balance, quantified by the concepts of stabilizing and destabilizing forces, was compared before and after split-belt walking for subgroups of participants who improved and worsened their symmetry. The side on the slow belt during split-belt walking, but not the changes in asymmetry, affected balance. Difficulty in maintaining balance was higher during stance phase of the leg that was on the slow belt and lower on the contralateral side after split-belt walking, mostly because the center of pressure was closer (higher difficulty) or further (lower difficulty) from the limit of the base of support, respectively. Changes in spatiotemporal parameters may be sought without additional alteration of balance during gait post-stroke. Copyright © 2018 Elsevier Ltd. All rights reserved.

On the pertinence to Physics of random walks induced by random dynamical systems: a survey

International Nuclear Information System (INIS)

Petritis, Dimitri

2016-01-01

Let be an abstract space and a denumerable (finite or infinite) alphabet. Suppose that is a family of functions such that for all we have and a family of transformations . The pair (( S_a)_a , ( p_a)_a ) is termed an iterated function system with place dependent probabilities. Such systems can be thought as generalisations of random dynamical systems. As a matter of fact, suppose we start from a given ; we pick then randomly, with probability p_a (x) , the transformation S_a and evolve to S_a (x) . We are interested in the behaviour of the system when the iteration continues indefinitely. Random walks of the above type are omnipresent in both classical and quantum Physics. To give a small sample of occurrences we mention: random walks on the affine group, random walks on Penrose lattices, random walks on partially directed lattices, evolution of density matrices induced by repeated quantum measurements, quantum channels, quantum random walks, etc. In this article, we review some basic properties of such systems and provide with a pathfinder in the extensive bibliography (both on mathematical and physical sides) where the main results have been originally published. (paper)

Characteristics and classification of hippocampal θ rhythm induced by passive translational displacement.

Science.gov (United States)

Xie, Kangning; Yan, Yili; Fang, Xiaolei; Gao, Shangkai; Hong, Bo

2012-04-25

Theta rhythms in the hippocampus are believed to be the "metric" relating to various behavior patterns for free roaming rats. In this study, the theta rhythms were studied while rats either walked or were passively translated by a toy car on a linear track (referred to as WALK and TRANS respectively). For the similar running speeds in WALK and TRANS conditions, theta frequency and amplitude were both reduced during TRANS. Theta modulation of pyramidal cells during TRANS was reduced compared to that during WALK. Theta frequency was positively correlated with translation speed during TRANS. Theta rhythm remained apparent during TRANS and WALK after large dose of atropine sulfate (blocking the cholinergic pathway) was injected compared to still states. The present study demonstrated the patterns of theta rhythm induced by passive translation in rats and suggested that the Type I theta rhythm could occur during non-voluntary locomotion. We further argued that the perception of actual self-motion may be the underlying mechanism that initiates and modulates type I theta. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Dynamic Characteristics of Ventilatory and Gas Exchange during Sinusoidal Walking in Humans.

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Yoshiyuki Fukuoka

Full Text Available Our present study investigated whether the ventilatory and gas exchange responses show different dynamics in response to sinusoidal change in cycle work rate or walking speed even if the metabolic demand was equivalent in both types of exercise. Locomotive parameters (stride length and step frequency, breath-by-breath ventilation (V̇E and gas exchange (CO2 output (V̇CO2 and O2 uptake (V̇O2 responses were measured in 10 healthy young participants. The speed of the treadmill was sinusoidally changed between 3 km·h-1 and 6 km·h-1 with various periods (from 10 to 1 min. The amplitude of locomotive parameters against sinusoidal variation showed a constant gain with a small phase shift, being independent of the oscillation periods. In marked contrast, when the periods of the speed oscillations were shortened, the amplitude of V̇E decreased sharply whereas the phase shift of V̇E increased. In comparing walking and cycling at the equivalent metabolic demand, the amplitude of V̇E during sinusoidal walking (SW was significantly greater than that during sinusoidal cycling (SC, and the phase shift became smaller. The steeper slope of linear regression for the V̇E amplitude ratio to V̇CO2 amplitude ratio was observed during SW than SC. These findings suggested that the greater amplitude and smaller phase shift of ventilatory dynamics were not equivalent between SW and SC even if the metabolic demand was equivalent between both exercises. Such phenomenon would be derived from central command in proportion to locomotor muscle recruitment (feedforward and muscle afferent feedback.

Dynamic Simulation and Analysis of Human Walking Mechanism

Science.gov (United States)

Azahari, Athirah; Siswanto, W. A.; Ngali, M. Z.; Salleh, S. Md.; Yusup, Eliza M.

2017-01-01

Behaviour such as gait or posture may affect a person with the physiological condition during daily activities. The characteristic of human gait cycle phase is one of the important parameter which used to described the human movement whether it is in normal gait or abnormal gait. This research investigates four types of crouch walking (upright, interpolated, crouched and severe) by simulation approach. The assessment are conducting by looking the parameters of hamstring muscle joint, knee joint and ankle joint. The analysis results show that based on gait analysis approach, the crouch walking have a weak pattern of walking and postures. Short hamstring and knee joint is the most influence factor contributing to the crouch walking due to excessive hip flexion that typically accompanies knee flexion.

Quantifying collective effervescence: Heart-rate dynamics at a fire-walking ritual

DEFF Research Database (Denmark)

Xygalatas, Dimitris; Konvalinka, Ivana; Roepstorff, Andreas

2011-01-01

Collective rituals are ubiquitous and resilient features of all known human cultures. They are also functionally opaque, costly, and sometimes dangerous. Social scientists have speculated that collective rituals generate benefits in excess of their costs by reinforcing social bonding and group...... solidarity, yet quantitative evidence for these conjectures is scarce. Our recent study measured the physiological effects of a highly arousing Spanish fire-walking ritual, revealing shared patterns in heart-rate dynamics between participants and related spectators. We briefly describe our results...

To what extent does not wearing shoes affect the local dynamic stability of walking?: effect size and intrasession repeatability.

Science.gov (United States)

Terrier, Philippe; Reynard, Fabienne

2014-04-01

Local dynamic stability (stability) quantifies how a system responds to small perturbations. Several experimental and clinical findings have highlighted the association between gait stability and fall risk. Walking without shoes is known to slightly modify gait parameters. Barefoot walking may cause unusual sensory feedback to individuals accustomed to shod walking, and this may affect stability. The objective was therefore to compare the stability of shod and barefoot walking in healthy individuals and to analyze the intrasession repeatability. Forty participants traversed a 70 m indoor corridor wearing normal shoes in one trial and walking barefoot in a second trial. Trunk accelerations were recorded with a 3D-accelerometer attached to the lower back. The stability was computed using the finite-time maximal Lyapunov exponent method. Absolute agreement between the forward and backward paths was estimated with the intraclass correlation coefficient (ICC). Barefoot walking did not significantly modify the stability as compared with shod walking (average standardized effect size: +0.11). The intrasession repeatability was high (ICC: 0.73-0.81) and slightly higher in barefoot walking condition (ICC: 0.81-0.87). Therefore, it seems that barefoot walking can be used to evaluate stability without introducing a bias as compared with shod walking, and with a sufficient reliability.

Froude number fractions to increase walking pattern dynamic similarities: application to plantar pressure study in healthy subjects.

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Moretto, P; Bisiaux, M; Lafortune, M A

2007-01-01

The purpose of this study was to determine if using similar walking velocities obtained from fractions of the Froude number (N(Fr)) and leg length can lead to kinematic and kinetic similarities and lower variability. Fifteen male subjects walked on a treadmill at 0.83 (VS(1)) and 1.16ms(-1) (VS(2)) and then at two similar velocities (V(Sim27) and V(Sim37)) determined from two fractions of the N(Fr) (0.27 and 0.37) so that the average group velocity remained unchanged in both conditions (VS(1)=V (Sim27)andVS(2)=V (Sim37)). N(Fr) can theoretically be used to determine walking velocities proportional to leg lengths and to establish dynamic similarities between subjects. This study represents the first attempt at using this approach to examine plantar pressure. The ankle and knee joint angles were studied in the sagittal plane and the plantar pressure distribution was assessed with an in-shoe measurement device. The similarity ratios were computed from anthropometric parameters and plantar pressure peaks. Dynamically similar conditions caused a 25% reduction in leg joint angles variation and a 10% significant decrease in dimensionless pressure peak variability on average of five footprint locations. It also lead to heel and under-midfoot pressure peaks proportional to body mass and to an increase in the number of under-forefoot plantar pressure peaks proportional to body mass and/or leg length. The use of walking velocities derived from N(Fr) allows kinematic and plantar pressure similarities between subjects to be observed and leads to a lower inter-subject variability. In-shoe pressure measurements have proven to be valuable for the understanding of lower extremity function. Set walking velocities used for clinical assessment mask the effects of body size and individual gait mechanics. The anthropometric scaling of walking velocities (fraction of N(Fr)) should improve identification of unique walking strategies and pathological foot functions.

Physical implementation of quantum walks

CERN Document Server

Manouchehri, Kia

2013-01-01

Given the extensive application of random walks in virtually every science related discipline, we may be at the threshold of yet another problem solving paradigm with the advent of quantum walks. Over the past decade, quantum walks have been explored for their non-intuitive dynamics, which may hold the key to radically new quantum algorithms. This growing interest has been paralleled by a flurry of research into how one can implement quantum walks in laboratories. This book presents numerous proposals as well as actual experiments for such a physical realization, underpinned by a wide range of

Frontal joint dynamics when initiating stair ascent from a walk versus a stand.

Science.gov (United States)

Vallabhajosula, Srikant; Yentes, Jennifer M; Stergiou, Nicholas

2012-02-02

Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair treads were recorded simultaneously as ten healthy young adults ascended a custom-built staircase. Data were collected from two starting conditions of stair ascent, from a walk (speed: 1.42 ± 0.21 m/s) and from a stand. Results showed that subjects generated greater peak knee abductor moment and greater peak hip abductor moment when initiating stair ascent from a walk. Greater peak joint moments and powers at all joints were also seen while ascending the second ipsilateral step. Particularly, greater peak hip abductor moment was needed to avoid contact of the contralateral limb with the intermediate step by counteracting the pelvic drop on the contralateral side. This could be important for therapists using stair climbing as a testing/training tool to evaluate hip strength in individuals with documented frontal plane abnormalities (i.e. knee and hip osteoarthritis, ACL injury). Copyright © 2011 Elsevier Ltd. All rights reserved.

Modeling the 3-DOF dynamics of an electrodynamic Maglev suspension system with a passive sled

NARCIS (Netherlands)

Boeij, de J.; Gutierrez, H.M.; Agarwal, R.; Steinbuch, M.

2003-01-01

A model that describes the 3-DOF dynamics of a passively levitated electro-dynamic maglevsystem is presented. The model is based on the flux-current-force interactions and the geometricrelationships between the levitation coils and the permanent magnets on the sled. The model ispresented in a

Changes in gait and posture as factors of dynamic stability during walking in pregnancy.

Science.gov (United States)

Krkeljas, Zarko

2018-04-01

Changes in gait and postural control during pregnancy may lead to increased fall rates during walking relative to non-pregnant women. Due to lack of empirical evidence on balance and postural control in dynamic conditions, the primary aim of this study was investigate the changes in gait and postural control as factors of stability during walking. Gait and posture of thirty-five (35) pregnant women (27 ± 6.1 years) were analysed at self-selected walking speed, and at different stage of pregnancy. The results indicate that although the gait kinematics did not differ between the trimesters, significant associations were noted between the step width, the lateral trunk lean, and the medio-lateral deviations in centre of gravity and centre of pressure. In contrast to the static conditions, anterior-posterior postural sway is not present during walking, whereas the lateral trunk lean is the primary factor women use in pregnancy to keep the centre of gravity closer to the base of support. Postural changes and those in gait kinematics were largely affected by the relative mass gain, rather than the absolute mass. Considering the importance of relative mass gain, more attention during healthy pregnancy should be given to monitoring the timing of onset of musculoskeletal changes, and design of antenatal exercise programs targeting core strength and pelvic stability. Copyright © 2017 Elsevier B.V. All rights reserved.

Fractal fluctuations in spatiotemporal variables when walking on a self-paced treadmill.

Science.gov (United States)

Choi, Jin-Seung; Kang, Dong-Won; Seo, Jeong-Woo; Tack, Gye-Rae

2017-12-08

This study investigated the fractal dynamic properties of stride time (ST), stride length (SL) and stride speed (SS) during walking on a self-paced treadmill (STM) in which the belt speed is automatically controlled by the walking speed. Twelve healthy young subjects participated in the study. The subjects walked at their preferred walking speed under four conditions: STM, STM with a metronome (STM+met), fixed-speed (conventional) treadmill (FTM), and FTM with a metronome (FTM+met). To compare the fractal dynamics between conditions, the mean, variability, and fractal dynamics of ST, SL, and SS were compared. Moreover, the relationship among the variables was examined under each walking condition using three types of surrogates. The mean values of all variables did not differ between the two treadmills, and the variability of all variables was generally larger for STM than for FTM. The use of a metronome resulted in a decrease in variability in ST and SS for all conditions. The fractal dynamic characteristics of SS were maintained with STM, in contrast to FTM, and only the fractal dynamic characteristics of ST disappeared when using a metronome. In addition, the fractal dynamic patterns of the cross-correlated surrogate results were identical to those of all variables for the two treadmills. In terms of the fractal dynamic properties, STM walking was generally closer to overground walking than FTM walking. Although further research is needed, the present results will be useful in research on gait fractal dynamics and rehabilitation. Copyright © 2017 Elsevier Ltd. All rights reserved.

XPED2: A passive exoskeleton with artificial tendons

NARCIS (Netherlands)

van Dijk, Wietse; van der Kooij, Herman

2014-01-01

Wearable exoskeletons might reduce human effort during walking. However, many of the current exoskeletons rely on heavy actuators and/or external power supplies; this has a negative impact on their efficiency and operation range. As an alternative, (quasi)passive exoskeletons have been developed.

Instantaneous Metabolic Cost of Walking: Joint-Space Dynamic Model with Subject-Specific Heat Rate.

Directory of Open Access Journals (Sweden)

Dustyn Roberts

Full Text Available A subject-specific model of instantaneous cost of transport (ICOT is introduced from the joint-space formulation of metabolic energy expenditure using the laws of thermodynamics and the principles of multibody system dynamics. Work and heat are formulated in generalized coordinates as functions of joint kinematic and dynamic variables. Generalized heat rates mapped from muscle energetics are estimated from experimental walking metabolic data for the whole body, including upper-body and bilateral data synchronization. Identified subject-specific energetic parameters-mass, height, (estimated maximum oxygen uptake, and (estimated maximum joint torques-are incorporated into the heat rate, as opposed to the traditional in vitro and subject-invariant muscle parameters. The total model metabolic energy expenditure values are within 5.7 ± 4.6% error of the measured values with strong (R2 > 0.90 inter- and intra-subject correlations. The model reliably predicts the characteristic convexity and magnitudes (0.326-0.348 of the experimental total COT (0.311-0.358 across different subjects and speeds. The ICOT as a function of time provides insights into gait energetic causes and effects (e.g., normalized comparison and sensitivity with respect to walking speed and phase-specific COT, which are unavailable from conventional metabolic measurements or muscle models. Using the joint-space variables from commonly measured or simulated data, the models enable real-time and phase-specific evaluations of transient or non-periodic general tasks that use a range of (aerobic energy pathway similar to that of steady-state walking.

Quantitative dynamic reliability evaluation of AP1000 passive safety systems by using FMEA and GO-FLOW methodology

International Nuclear Information System (INIS)

Hashim Muhammad; Yoshikawa, Hidekazu; Matsuoka, Takeshi; Yang Ming

2014-01-01

The passive safety systems utilized in advanced pressurized water reactor (PWR) design such as AP1000 should be more reliable than that of active safety systems of conventional PWR by less possible opportunities of hardware failures and human errors (less human intervention). The objectives of present study are to evaluate the dynamic reliability of AP1000 plant in order to check the effectiveness of passive safety systems by comparing the reliability-related issues with that of active safety systems in the event of the big accidents. How should the dynamic reliability of passive safety systems properly evaluated? And then what will be the comparison of reliability results of AP1000 passive safety systems with the active safety systems of conventional PWR. For this purpose, a single loop model of AP1000 passive core cooling system (PXS) and passive containment cooling system (PCCS) are assumed separately for quantitative reliability evaluation. The transient behaviors of these passive safety systems are taken under the large break loss-of-coolant accident in the cold leg. The analysis is made by utilizing the qualitative method failure mode and effect analysis in order to identify the potential failure mode and success-oriented reliability analysis tool called GO-FLOW for quantitative reliability evaluation. The GO-FLOW analysis has been conducted separately for PXS and PCCS systems under the same accident. The analysis results show that reliability of AP1000 passive safety systems (PXS and PCCS) is increased due to redundancies and diversity of passive safety subsystems and components, and four stages automatic depressurization system is the key subsystem for successful actuation of PXS and PCCS system. The reliability results of PCCS system of AP1000 are more reliable than that of the containment spray system of conventional PWR. And also GO-FLOW method can be utilized for reliability evaluation of passive safety systems. (author)

Dynamics of a Dispersion-Managed Passively Mode-Locked Er-Doped Fiber Laser Using Single Wall Carbon Nanotubes

Directory of Open Access Journals (Sweden)

Norihiko Nishizawa

2015-07-01

Full Text Available We investigated the dynamics of a dispersion-managed, passively mode-locked, ultrashort-pulse, Er-doped fiber laser using a single-wall carbon nanotube (SWNT device. A numerical model was constructed for analysis of the SWNT fiber laser. The initial process of passive mode-locking, the characteristics of the output pulse, and the dynamics inside the cavity were investigated numerically for soliton, dissipative-soliton, and stretched-pulse mode-locking conditions. The dependencies on the total dispersion and recovery time of the SWNTs were also examined. Numerical results showed similar behavior to experimental results.

Robust and efficient walking with spring-like legs

Energy Technology Data Exchange (ETDEWEB)

Rummel, J; Blum, Y; Seyfarth, A, E-mail: juergen.rummel@uni-jena.d, E-mail: andre.seyfarth@uni-jena.d [Lauflabor Locomotion Laboratory, University of Jena, Dornburger Strasse 23, 07743 Jena (Germany)

2010-12-15

The development of bipedal walking robots is inspired by human walking. A way of implementing walking could be performed by mimicking human leg dynamics. A fundamental model, representing human leg dynamics during walking and running, is the bipedal spring-mass model which is the basis for this paper. The aim of this study is the identification of leg parameters leading to a compromise between robustness and energy efficiency in walking. It is found that, compared to asymmetric walking, symmetric walking with flatter angles of attack reveals such a compromise. With increasing leg stiffness, energy efficiency increases continuously. However, robustness is the maximum at moderate leg stiffness and decreases slightly with increasing stiffness. Hence, an adjustable leg compliance would be preferred, which is adaptable to the environment. If the ground is even, a high leg stiffness leads to energy efficient walking. However, if external perturbations are expected, e.g. when the robot walks on uneven terrain, the leg should be softer and the angle of attack flatter. In the case of underactuated robots with constant physical springs, the leg stiffness should be larger than k-tilde = 14 in order to use the most robust gait. Soft legs, however, lack in both robustness and efficiency.

Robust and efficient walking with spring-like legs

International Nuclear Information System (INIS)

Rummel, J; Blum, Y; Seyfarth, A

2010-01-01

The development of bipedal walking robots is inspired by human walking. A way of implementing walking could be performed by mimicking human leg dynamics. A fundamental model, representing human leg dynamics during walking and running, is the bipedal spring-mass model which is the basis for this paper. The aim of this study is the identification of leg parameters leading to a compromise between robustness and energy efficiency in walking. It is found that, compared to asymmetric walking, symmetric walking with flatter angles of attack reveals such a compromise. With increasing leg stiffness, energy efficiency increases continuously. However, robustness is the maximum at moderate leg stiffness and decreases slightly with increasing stiffness. Hence, an adjustable leg compliance would be preferred, which is adaptable to the environment. If the ground is even, a high leg stiffness leads to energy efficient walking. However, if external perturbations are expected, e.g. when the robot walks on uneven terrain, the leg should be softer and the angle of attack flatter. In the case of underactuated robots with constant physical springs, the leg stiffness should be larger than k-tilde = 14 in order to use the most robust gait. Soft legs, however, lack in both robustness and efficiency.

Dynamic walking stability of the TUlip robot by means of the extrapolated center of mass

NARCIS (Netherlands)

Bouwman, W.M.; van Oort, Gijs; Dertien, Edwin Christian; Broenink, Johannes F.; Carloni, Raffaella

The TUlip robot was created to participate in the teensize league of Robocup. The TUlip robot is a bipedal robot intended for dynamic walking. It has six degrees of freedom for each leg: three for the hip, one for the knee and two for the ankle. This paper elaborates on the algorithm for the

Neuromorphic walking gait control.

Science.gov (United States)

Still, Susanne; Hepp, Klaus; Douglas, Rodney J

2006-03-01

We present a neuromorphic pattern generator for controlling the walking gaits of four-legged robots which is inspired by central pattern generators found in the nervous system and which is implemented as a very large scale integrated (VLSI) chip. The chip contains oscillator circuits that mimic the output of motor neurons in a strongly simplified way. We show that four coupled oscillators can produce rhythmic patterns with phase relationships that are appropriate to generate all four-legged animal walking gaits. These phase relationships together with frequency and duty cycle of the oscillators determine the walking behavior of a robot driven by the chip, and they depend on a small set of stationary bias voltages. We give analytic expressions for these dependencies. This chip reduces the complex, dynamic inter-leg control problem associated with walking gait generation to the problem of setting a few stationary parameters. It provides a compact and low power solution for walking gait control in robots.

The effects of gravity on human walking: a new test of the dynamic similarity hypothesis using a predictive model.

Science.gov (United States)

Raichlen, David A

2008-09-01

The dynamic similarity hypothesis (DSH) suggests that differences in animal locomotor biomechanics are due mostly to differences in size. According to the DSH, when the ratios of inertial to gravitational forces are equal between two animals that differ in size [e.g. at equal Froude numbers, where Froude = velocity2/(gravity x hip height)], their movements can be made similar by multiplying all time durations by one constant, all forces by a second constant and all linear distances by a third constant. The DSH has been generally supported by numerous comparative studies showing that as inertial forces differ (i.e. differences in the centripetal force acting on the animal due to variation in hip heights), animals walk with dynamic similarity. However, humans walking in simulated reduced gravity do not walk with dynamically similar kinematics. The simulated gravity experiments did not completely account for the effects of gravity on all body segments, and the importance of gravity in the DSH requires further examination. This study uses a kinematic model to predict the effects of gravity on human locomotion, taking into account both the effects of gravitational forces on the upper body and on the limbs. Results show that dynamic similarity is maintained in altered gravitational environments. Thus, the DSH does account for differences in the inertial forces governing locomotion (e.g. differences in hip height) as well as differences in the gravitational forces governing locomotion.

Effect of noise and filtering on largest Lyapunov exponent of time series associated with human walking.

Science.gov (United States)

Mehdizadeh, Sina; Sanjari, Mohammad Ali

2017-11-07

This study aimed to determine the effect of added noise, filtering and time series length on the largest Lyapunov exponent (LyE) value calculated for time series obtained from a passive dynamic walker. The simplest passive dynamic walker model comprising of two massless legs connected by a frictionless hinge joint at the hip was adopted to generate walking time series. The generated time series was used to construct a state space with the embedding dimension of 3 and time delay of 100 samples. The LyE was calculated as the exponential rate of divergence of neighboring trajectories of the state space using Rosenstein's algorithm. To determine the effect of noise on LyE values, seven levels of Gaussian white noise (SNR=55-25dB with 5dB steps) were added to the time series. In addition, the filtering was performed using a range of cutoff frequencies from 3Hz to 19Hz with 2Hz steps. The LyE was calculated for both noise-free and noisy time series with different lengths of 6, 50, 100 and 150 strides. Results demonstrated a high percent error in the presence of noise for LyE. Therefore, these observations suggest that Rosenstein's algorithm might not perform well in the presence of added experimental noise. Furthermore, findings indicated that at least 50 walking strides are required to calculate LyE to account for the effect of noise. Finally, observations support that a conservative filtering of the time series with a high cutoff frequency might be more appropriate prior to calculating LyE. Copyright © 2017 Elsevier Ltd. All rights reserved.

Navigation by anomalous random walks on complex networks.

Science.gov (United States)

Weng, Tongfeng; Zhang, Jie; Khajehnejad, Moein; Small, Michael; Zheng, Rui; Hui, Pan

2016-11-23

Anomalous random walks having long-range jumps are a critical branch of dynamical processes on networks, which can model a number of search and transport processes. However, traditional measurements based on mean first passage time are not useful as they fail to characterize the cost associated with each jump. Here we introduce a new concept of mean first traverse distance (MFTD) to characterize anomalous random walks that represents the expected traverse distance taken by walkers searching from source node to target node, and we provide a procedure for calculating the MFTD between two nodes. We use Lévy walks on networks as an example, and demonstrate that the proposed approach can unravel the interplay between diffusion dynamics of Lévy walks and the underlying network structure. Moreover, applying our framework to the famous PageRank search, we show how to inform the optimality of the PageRank search. The framework for analyzing anomalous random walks on complex networks offers a useful new paradigm to understand the dynamics of anomalous diffusion processes, and provides a unified scheme to characterize search and transport processes on networks.

Navigation by anomalous random walks on complex networks

Science.gov (United States)

Weng, Tongfeng; Zhang, Jie; Khajehnejad, Moein; Small, Michael; Zheng, Rui; Hui, Pan

2016-11-01

Anomalous random walks having long-range jumps are a critical branch of dynamical processes on networks, which can model a number of search and transport processes. However, traditional measurements based on mean first passage time are not useful as they fail to characterize the cost associated with each jump. Here we introduce a new concept of mean first traverse distance (MFTD) to characterize anomalous random walks that represents the expected traverse distance taken by walkers searching from source node to target node, and we provide a procedure for calculating the MFTD between two nodes. We use Lévy walks on networks as an example, and demonstrate that the proposed approach can unravel the interplay between diffusion dynamics of Lévy walks and the underlying network structure. Moreover, applying our framework to the famous PageRank search, we show how to inform the optimality of the PageRank search. The framework for analyzing anomalous random walks on complex networks offers a useful new paradigm to understand the dynamics of anomalous diffusion processes, and provides a unified scheme to characterize search and transport processes on networks.

A study on the multiple dynamic wavelength distribution for gigabit capable passive optical networks

Directory of Open Access Journals (Sweden)

Gustavo Adolfo Puerto Leguizamón

2014-04-01

Full Text Available This paper presents a data traffic based study aiming at evaluating the impact of dynamic wavelength allocation on a Gigabit capable Passive Optical Network (GPON. In Passive Optical Networks (PON, an Optical Line Terminal (OLT feeds different PONs in such a way that a given wavelength channel is evenly distributed between the Optical Network Units (ONU at each PON. However, PONs do not specify any kind of dynamic behavior on the way the wavelengths are allocated in the network, a completely static distribution is implemented instead. In thispaper we evaluate the network performance in terms of packet losses and throughput for a number of ONUs being out-of-profile while featuring a given percentage of traffic in excess for a fixed wavelength distribution and for multiple dynamic wavelength allocation. Results show that for a multichannel operation with four wavelengths, the network throughput increases up to a rough value of 19% while the packet losses drop from 22 % to 1.8 % as compared with a static wavelength distribution.

Design Considerations of a Lower Limb Exoskeleton System to Assist walking and Load-Carrying of Infantry Soldiers

Directory of Open Access Journals (Sweden)

Seungnam Yu

2014-01-01

Full Text Available This paper describes the development of a wearable exoskeleton system for the lower extremities of infantry soldiers and proposes appropriate design criteria based on existing case studies. Because infantry soldiers carry a variety of equipment, the interference with existing equipment and additional burden of the exoskeleton support system should be minimized. Recent studies have shown that a user only needs to be supported in the gravitational direction when walking on flat terrain; however, active joints are necessary to support walking over rough and sloped terrain such as mountains. Thus, an underactuated exoskeleton system was considered: passive joints are applied to the hip and ankle joints, and active joints are applied to the knee joints to exploit the dynamic coupling effect of the link structure and muscular activation patterns when the user is going up and down stairs. A prototype of the exoskeleton system was developed and validated through a simple stair-climbing experiment.

Fermionic entanglement via quantum walks in quantum dots

Science.gov (United States)

Melnikov, Alexey A.; Fedichkin, Leonid E.

2018-02-01

Quantum walks are fundamentally different from random walks due to the quantum superposition property of quantum objects. Quantum walk process was found to be very useful for quantum information and quantum computation applications. In this paper we demonstrate how to use quantum walks as a tool to generate high-dimensional two-particle fermionic entanglement. The generated entanglement can survive longer in the presence of depolorazing noise due to the periodicity of quantum walk dynamics. The possibility to create two distinguishable qudits in a system of tunnel-coupled semiconductor quantum dots is discussed.

Passivation and control of partially known SISO nonlinear systems via dynamic neural networks

Directory of Open Access Journals (Sweden)

Reyes-Reyes J.

2000-01-01

Full Text Available In this paper, an adaptive technique is suggested to provide the passivity property for a class of partially known SISO nonlinear systems. A simple Dynamic Neural Network (DNN, containing only two neurons and without any hidden-layers, is used to identify the unknown nonlinear system. By means of a Lyapunov-like analysis the new learning law for this DNN, guarantying both successful identification and passivation effects, is derived. Based on this adaptive DNN model, an adaptive feedback controller, serving for wide class of nonlinear systems with an a priori incomplete model description, is designed. Two typical examples illustrate the effectiveness of the suggested approach.

Big power from walking

Science.gov (United States)

Illenberger, Patrin K.; Madawala, Udaya K.; Anderson, Iain A.

2016-04-01

Dielectric Elastomer Generators (DEG) offer an opportunity to capture the energy otherwise wasted from human motion. By integrating a DEG into the heel of standard footwear, it is possible to harness this energy to power portable devices. DEGs require substantial auxiliary systems which are commonly large, heavy and inefficient. A unique challenge for these low power generators is the combination of high voltage and low current. A void exists in the semiconductor market for devices that can meet these requirements. Until these become available, existing devices must be used in an innovative way to produce an effective DEG system. Existing systems such as the Bi-Directional Flyback (BDFB) and Self Priming Circuit (SPC) are an excellent example of this. The BDFB allows full charging and discharging of the DEG, improving power gained. The SPC allows fully passive voltage boosting, removing the priming source and simplifying the electronics. This paper outlines the drawbacks and benefits of active and passive electronic solutions for maximizing power from walking.

Possible biomechanical origins of the long-range correlations in stride intervals of walking

Science.gov (United States)

Gates, Deanna H.; Su, Jimmy L.; Dingwell, Jonathan B.

2007-07-01

When humans walk, the time duration of each stride varies from one stride to the next. These temporal fluctuations exhibit long-range correlations. It has been suggested that these correlations stem from higher nervous system centers in the brain that control gait cycle timing. Existing proposed models of this phenomenon have focused on neurophysiological mechanisms that might give rise to these long-range correlations, and generally ignored potential alternative mechanical explanations. We hypothesized that a simple mechanical system could also generate similar long-range correlations in stride times. We modified a very simple passive dynamic model of bipedal walking to incorporate forward propulsion through an impulsive force applied to the trailing leg at each push-off. Push-off forces were varied from step to step by incorporating both “sensory” and “motor” noise terms that were regulated by a simple proportional feedback controller. We generated 400 simulations of walking, with different combinations of sensory noise, motor noise, and feedback gain. The stride time data from each simulation were analyzed using detrended fluctuation analysis to compute a scaling exponent, α. This exponent quantified how each stride interval was correlated with previous and subsequent stride intervals over different time scales. For different variations of the noise terms and feedback gain, we obtained short-range correlations (α1.0). Our results indicate that a simple biomechanical model of walking can generate long-range correlations and thus perhaps these correlations are not a complex result of higher level neuronal control, as has been previously suggested.

Design of a Fully-Passive Transfemoral Prosthesis Prototype

NARCIS (Netherlands)

Behrens, Sebastiaan Maria; Behrens, S.M.; Ünal, Ramazan; Unal, R.; Hekman, Edsko E.G.; Carloni, Raffaella; Stramigioli, Stefano; Koopman, Hubertus F.J.M.

In this study, we present the mechanical design of a prototype of a fully-passive transfemoral prosthesis for normal walking. The conceptual working principle at the basis of the design is inspired by the power flow in human gait, with the main purpose of realizing an energy efficient device. The

A painless and constraint-free method to estimate viscoelastic passive dynamics of limbs' joints to support diagnosis of neuromuscular diseases.

Science.gov (United States)

Venture, Gentiane; Nakamura, Yoshihiko; Yamane, Katsu; Hirashima, Masaya

2007-01-01

Though seldom identified, the human joints dynamics is important in the fields of medical robotics and medical research. We present a general solution to estimate in-vivo and simultaneously the passive dynamics of the human limbs' joints. It is based on the use of the multi-body description of the human body and its kinematics and dynamics computations. The linear passive joint dynamics of the shoulders and the elbows: stiffness, viscosity and friction, is estimated simultaneously using the linear least squares method. Acquisition of movements is achieved with an optical motion capture studio on one examinee during the clinical diagnosis of neuromuscular diseases. Experimental results are given and discussed.

Quantum random walks and their convergence to Evans–Hudson ...

Indian Academy of Sciences (India)

Quantum dynamical semigroup; Evans–Hudson flow; quantum random walk. 1. Introduction. The aim of this article is to investigate convergence of random walks on von Neumann algebra to Evans–Hudson flows. Here the random walks and Evans–Hudson flows are gene- ralizations of classical Markov chains and Markov ...

Using dynamic walking models to identify factors that contribute to increased risk of falling in older adults.

Science.gov (United States)

Roos, Paulien E; Dingwell, Jonathan B

2013-10-01

Falls are common in older adults. The most common cause of falls is tripping while walking. Simulation studies demonstrated that older adults may be restricted by lower limb strength and movement speed to regain balance after a trip. This review examines how modeling approaches can be used to determine how different measures predict actual fall risk and what some of the causal mechanisms of fall risk are. Although increased gait variability predicts increased fall risk experimentally, it is not clear which variability measures could best be used, or what magnitude of change corresponded with increased fall risk. With a simulation study we showed that the increase in fall risk with a certain increase in gait variability was greatly influenced by the initial level of variability. Gait variability can therefore not easily be used to predict fall risk. We therefore explored other measures that may be related to fall risk and investigated the relationship between stability measures such as Floquet multipliers and local divergence exponents and actual fall risk in a dynamic walking model. We demonstrated that short-term local divergence exponents were a good early predictor for fall risk. Neuronal noise increases with age. It has however not been fully understood if increased neuronal noise would cause an increased fall risk. With our dynamic walking model we showed that increased neuronal noise caused increased fall risk. Although people who are at increased risk of falling reduce their walking speed it had been questioned whether this slower speed would actually cause a reduced fall risk. With our model we demonstrated that a reduced walking speed caused a reduction in fall risk. This may be due to the decreased kinematic variability as a result of the reduced signal-dependent noise of the smaller muscle forces that are required for slower. These insights may be used in the development of fall prevention programs in order to better identify those at increased risk of

Using Dynamic Walking Models to Identify Factors that Contribute to Increased Risk of Falling in Older Adults

Science.gov (United States)

Roos, Paulien E.; Dingwell, Jonathan B.

2013-01-01

Falls are common in older adults. The most common cause of falls is tripping while walking. Simulation studies demonstrated that older adults may be restricted by lower limb strength and movement speed to regain balance after a trip. This review examines how modeling approaches can be used to determine how different measures predict actual fall risk and what some of the causal mechanisms of fall risk are. Although increased gait variability predicts increased fall risk experimentally, it is not clear which variability measures could best be used, or what magnitude of change corresponded with increased fall risk. With a simulation study we showed that the increase in fall risk with a certain increase in gait variability was greatly influenced by the initial level of variability. Gait variability can therefore not easily be used to predict fall risk. We therefore explored other measures that may be related to fall risk and investigated the relationship between stability measures such as Floquet multipliers and local divergence exponents and actual fall risk in a dynamic walking model. We demonstrated that short-term local divergence exponents were a good early predictor for fall risk. Neuronal noise increases with age. It has however not been fully understood if increased neuronal noise would cause an increased fall risk. With our dynamic walking model we showed that increased neuronal noise caused increased fall risk. Although people who are at increased risk of falling reduce their walking speed it had been questioned whether this slower speed would actually cause a reduced fall risk. With our model we demonstrated that a reduced walking speed caused a reduction in fall risk. This may be due to the decreased kinematic variability as a result of the reduced signal-dependent noise of the smaller muscle forces that are required for slower. These insights may be used in the development of fall prevention programs in order to better identify those at increased risk of

Applied reliability assessment for the passive safety systems of nuclear power plants (NPPs) using system dynamics (SD)

International Nuclear Information System (INIS)

Kim, Yun Il; Woo, Tae Ho

2018-01-01

The passive system by the free-fall is investigated in the accident of nuclear power plants (NPPs). The complex algorithm of the system dynamics (SD) modeling is done in the passive cooling system. The nuclear passive system by free-fall is successfully modeled for the loss of coolant accident (LOCA). Conventional passive system of gravity or natural circulation is working only when the piping systems is in the good condition. The external coolant supply system is introduced in the case of the piping system failure. The water is poured into the reactor through the guiding piping or tube. If the explosion happens, the coolants could be showering into the reactor core and its building. New kind of passive system is expected successfully in the on-site black out where the drone could be operated by battery or engine.

Neuromechanical Control for Dynamic Bipedal Walking with Reduced Impact Forces

DEFF Research Database (Denmark)

Widenka, Johannes; Xiong, Xiaofeng; Matthias Braun, Jan

2016-01-01

Human walking emerges from an intricate interaction of nervous and musculoskeletal systems. Inspired by this principle, we integrate neural control and muscle-like mechanisms to achieve neuromechanical control of the biped robot RunBot. As a result, the neuromechanical controller enables RunBot t......Bot to perform more human-like walking and reduce impact force during walking, compared to original neural control. Moreover, it also generates adaptive joint motions of RunBot; thereby allowing it to deal with different terrains...

Velocity dependent passive sampling for monitoring of micropollutants in dynamic stormwater discharges

DEFF Research Database (Denmark)

Birch, Heidi; Sharma, Anitha Kumari; Vezzaro, Luca

2013-01-01

Micropollutant monitoring in stormwater discharges is challenging because of the diversity of sources and thus large number of pollutants found in stormwater. This is further complicated by the dynamics in runoff flows and the large number of discharge points. Most passive samplers are non......-ideal for sampling such systems because they sample in a time-integrative manner. This paper reports test of a flow-through passive sampler, deployed in stormwater runoff at the outlet of a residential-industrial catchment. Momentum from the water velocity during runoff events created flow through the sampler...... resulting in velocity dependent sampling. This approach enables the integrative sampling of stormwater runoff during periods of weeks to months while weighting actual runoff events higher than no flow periods. Results were comparable to results from volume-proportional samples and results obtained from...

Identifying particular places through experimental walking

Directory of Open Access Journals (Sweden)

Henrik Schultz

2016-11-01

Full Text Available Experimental walking can be used to identify particular places, design strategies and spatial visions for urban landscapes. Walking designers can explore sites and, in particular, their temporal dynamics and atmospheric particularities – both essential elements in making particular places. This article illustrates the benefits of this method, using the changing German city of Freiburg as an example.

Static and Dynamic Water Motion-Induced Instability in Oxide Thin-Film Transistors and Its Suppression by Using Low-k Fluoropolymer Passivation.

Science.gov (United States)

Choi, Seungbeom; Jo, Jeong-Wan; Kim, Jaeyoung; Song, Seungho; Kim, Jaekyun; Park, Sung Kyu; Kim, Yong-Hoon

2017-08-09

Here, we report static and dynamic water motion-induced instability in indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) and its effective suppression with the use of a simple, solution-processed low-k (ε ∼ 1.9) fluoroplastic resin (FPR) passivation layer. The liquid-contact electrification effect, in which an undesirable drain current modulation is induced by a dynamic motion of a charged liquid such as water, can cause a significant instability in IGZO TFTs. It was found that by adopting a thin (∼44 nm) FPR passivation layer for IGZO TFTs, the current modulation induced by the water-contact electrification was greatly reduced in both off- and on-states of the device. In addition, the FPR-passivated IGZO TFTs exhibited an excellent stability to static water exposure (a threshold voltage shift of +0.8 V upon 3600 s of water soaking), which is attributed to the hydrophobicity of the FPR passivation layer. Here, we discuss the origin of the current instability caused by the liquid-contact electrification as well as various static and dynamic stability tests for IGZO TFTs. On the basis of our findings, we believe that the use of a thin, solution-processed FPR passivation layer is effective in suppressing the static and dynamic water motion-induced instabilities, which may enable the realization of high-performance and environment-stable oxide TFTs for emerging wearable and skin-like electronics.

Measuring In-Home Walking Speed using Wall-Mounted RF Transceiver Arrays

Science.gov (United States)

Jacobs, Peter G.; Wan, Eric A.; Schafermeer, Erich; Adenwala, Fatema; Paul, Anindya S.; Preiser, Nick; Kaye, Jeffrey

2014-01-01

In this paper we present a new method for passively measuring walking speed using a small array of radio transceivers positioned on the walls of a hallway within a home. As a person walks between a radio transmitter and a receiver, the received signal strength (RSS) detected by the receiver changes in a repeatable pattern that may be used to estimate walking speed without the need for the person to wear any monitoring device. The transceivers are arranged as an array of 4 with a known distance between the array elements. Walking past the first pair of transceivers will cause a peak followed by a second peak when the person passes the second pair of transceivers. The time difference between these peaks is used to estimate walking speed directly. We further show that it is possible to estimate the walking speed by correlating the shape of the signal using a single pair of transceivers positioned across from each other in a hallway or doorframe. RMSE performance was less than 15 cm/s using a 2-element array, and less than 8 cm/s using a 4-element array relative to a gait mat used for ground truth. PMID:25570108

Infrared dynamics of Minimal Walking Technicolor

DEFF Research Database (Denmark)

Del Debbio, Luigi; Lucini, Biagio; Patella, Agostino

2010-01-01

We study the gauge sector of Minimal Walking Technicolor, which is an SU(2) gauge theory with nf=2 flavors of Wilson fermions in the adjoint representation. Numerical simulations are performed on lattices Nt x Ns^3, with Ns ranging from 8 to 16 and Nt=2Ns, at fixed \\beta=2.25, and varying...

Random walks of oriented particles on fractals

International Nuclear Information System (INIS)

Haber, René; Prehl, Janett; Hoffmann, Karl Heinz; Herrmann, Heiko

2014-01-01

Random walks of point particles on fractals exhibit subdiffusive behavior, where the anomalous diffusion exponent is smaller than one, and the corresponding random walk dimension is larger than two. This is due to the limited space available in fractal structures. Here, we endow the particles with an orientation and analyze their dynamics on fractal structures. In particular, we focus on the dynamical consequences of the interactions between the local surrounding fractal structure and the particle orientation, which are modeled using an appropriate move class. These interactions can lead to particles becoming temporarily or permanently stuck in parts of the structure. A surprising finding is that the random walk dimension is not affected by the orientation while the diffusion constant shows a variety of interesting and surprising features. (paper)

A scaling law for random walks on networks

Science.gov (United States)

Perkins, Theodore J.; Foxall, Eric; Glass, Leon; Edwards, Roderick

2014-10-01

The dynamics of many natural and artificial systems are well described as random walks on a network: the stochastic behaviour of molecules, traffic patterns on the internet, fluctuations in stock prices and so on. The vast literature on random walks provides many tools for computing properties such as steady-state probabilities or expected hitting times. Previously, however, there has been no general theory describing the distribution of possible paths followed by a random walk. Here, we show that for any random walk on a finite network, there are precisely three mutually exclusive possibilities for the form of the path distribution: finite, stretched exponential and power law. The form of the distribution depends only on the structure of the network, while the stepping probabilities control the parameters of the distribution. We use our theory to explain path distributions in domains such as sports, music, nonlinear dynamics and stochastic chemical kinetics.

Some Passive Damping Sources on Flooring Systems besides the TMD

DEFF Research Database (Denmark)

Pedersen, Lars

2010-01-01

Impulsive loads and walking loads can generate problematic structural vibrations in flooring-systems. Measures that may be taken to mitigate the problem would often be to consider the implementation of a tuned mass damper or even more advanced vibration control technologies; this in order to add...... damping to the structure. Basically also passive humans on a floor act as a damping source, but it also turns out from doing system identification tests with a floor strip that a quite simple set-up installed on the floor (cheap and readily at hand) might do a good job in terms of reducing vertical floor...... vibrations for some floors. The paper describes the tests with the floor strip, and the results, in terms of dynamic floor behaviour, are compared with what would be expected had the floor instead been equipped with a tuned mass damper....

Interlimb communication following unexpected changes in treadmill velocity during human walking

DEFF Research Database (Denmark)

Stevenson, Andrew James Thomas; Geertsen, Svend Sparre; Sinkjær, Thomas

2015-01-01

Interlimb reflexes play an important role in human walking, particularly when dynamic stability is threatened by external perturbations or changes in the walking surface. Interlimb reflexes have recently been demonstrated in the contralateral biceps femoris (cBF) following knee joint rotations...... applied to the ipsilateral leg (iKnee) during the late stance phase of human gait (Stevenson et al. 2013). This interlimb reflex likely acts to slow the forward progression of the body in order to maintain dynamic stability following the perturbations. We examined this hypothesis by unexpectedly...... to slow the forward progression of the body and maintaining dynamic stability during walking, thus signifying a functional role for interlimb reflexes....

Elements of random walk and diffusion processes

CERN Document Server

Ibe, Oliver C

2013-01-01

Presents an important and unique introduction to random walk theory Random walk is a stochastic process that has proven to be a useful model in understanding discrete-state discrete-time processes across a wide spectrum of scientific disciplines. Elements of Random Walk and Diffusion Processes provides an interdisciplinary approach by including numerous practical examples and exercises with real-world applications in operations research, economics, engineering, and physics. Featuring an introduction to powerful and general techniques that are used in the application of physical and dynamic

Using Efference Copy and a Forward Internal Model for Adaptive Biped Walking

DEFF Research Database (Denmark)

Schröder-Schetelig, Johannes; Manoonpong, Poramate; Wörgötter, Florentin

2010-01-01

an application of this for our dynamic walking robot RunBot. We use efference copies of the motor commands with a simple forward internal model to predict the expected self-generated acceleration during walking. The difference to the actually measured acceleration is then used to stabilize the walking...... on terrains with changing slopes through its upper body component controller. As a consequence, the controller drives the upper body component (UBC) to lean forwards/backwards as soon as an error occurs resulting in dynamical stable walking. We have evaluated the performance of the system on four different...

Mobile Device Passive Localization Based on IEEE 802.11 Probe Request Frames

Directory of Open Access Journals (Sweden)

Lin Sun

2017-01-01

Full Text Available This paper presents a novel passive mobile device localization mode based on IEEE 802.11 Probe Request frames. In this approach, the listener can discover mobile devices by receiving the Probe Request frames and localize them on his walking path. The unique location of the mobile device is estimated on a geometric diagram and right-angled walking path. In model equations, site-related parameter, that is, path loss exponent, is eliminated to make the approach site-independent. To implement unique localization, the right-angled walking path is designed and the optimal location is estimated from the optional points. The performance of our method has been evaluated inside the room, outside the room, and in outdoor scenarios. Three kinds of walking paths, for example, horizontal, vertical, and slanted, are also tested.

Dynamically adjustable foot-ground contact model to estimate ground reaction force during walking and running.

Science.gov (United States)

Jung, Yihwan; Jung, Moonki; Ryu, Jiseon; Yoon, Sukhoon; Park, Sang-Kyoon; Koo, Seungbum

2016-03-01

Human dynamic models have been used to estimate joint kinetics during various activities. Kinetics estimation is in demand in sports and clinical applications where data on external forces, such as the ground reaction force (GRF), are not available. The purpose of this study was to estimate the GRF during gait by utilizing distance- and velocity-dependent force models between the foot and ground in an inverse-dynamics-based optimization. Ten males were tested as they walked at four different speeds on a force plate-embedded treadmill system. The full-GRF model whose foot-ground reaction elements were dynamically adjusted according to vertical displacement and anterior-posterior speed between the foot and ground was implemented in a full-body skeletal model. The model estimated the vertical and shear forces of the GRF from body kinematics. The shear-GRF model with dynamically adjustable shear reaction elements according to the input vertical force was also implemented in the foot of a full-body skeletal model. Shear forces of the GRF were estimated from body kinematics, vertical GRF, and center of pressure. The estimated full GRF had the lowest root mean square (RMS) errors at the slow walking speed (1.0m/s) with 4.2, 1.3, and 5.7% BW for anterior-posterior, medial-lateral, and vertical forces, respectively. The estimated shear forces were not significantly different between the full-GRF and shear-GRF models, but the RMS errors of the estimated knee joint kinetics were significantly lower for the shear-GRF model. Providing COP and vertical GRF with sensors, such as an insole-type pressure mat, can help estimate shear forces of the GRF and increase accuracy for estimation of joint kinetics. Copyright © 2016 Elsevier B.V. All rights reserved.

A passive UHF RFID tag with a dynamic-Vth-cancellation rectifier

International Nuclear Information System (INIS)

Shen Jinpeng; Wang Bo; Liu Shan; Wang Xin'an; Ruan Zhengkun; Li Shoucheng

2013-01-01

This paper presents a passive UHF RFID tag with a dynamic-V th -cancellation (DVC) rectifier. In the rectifier, the threshold voltages of MOSFETs are cancelled by applying gate bias voltages, which are dynamically changed according to the states of the MOSFETs. The DVC rectifier enables both low ON-resistance and small reverse leakage of the MOSFETs, resulting in high power conversion efficiency (PCE). An area-efficient demodulator with a novel average detector is also designed, which takes advantage of the rectifier's first stage as the envelope detector. The whole tag chip is implemented in a 0.18 μm CMOS process with a die size of 880 × 950 μm 2 . Measurement results show that the rectifier achieves a maximum PCE of 53.7% with 80 kΩ resistor load. (semiconductor integrated circuits)

Nordic Walking Health-improving and Training Impact on the Human Body

Directory of Open Access Journals (Sweden)

Alexander А. Fedyakin

2012-11-01

Full Text Available The article deals with the relatively new trend of fitness - Nordic walking. The data describing the Nordic walking impact is compared to Terrainkur. The main indicator is the dynamics and the heart rate in the course the Terrainkur walking with poles and without them.

Random-walk enzymes

Science.gov (United States)

Mak, Chi H.; Pham, Phuong; Afif, Samir A.; Goodman, Myron F.

2015-09-01

Enzymes that rely on random walk to search for substrate targets in a heterogeneously dispersed medium can leave behind complex spatial profiles of their catalyzed conversions. The catalytic signatures of these random-walk enzymes are the result of two coupled stochastic processes: scanning and catalysis. Here we develop analytical models to understand the conversion profiles produced by these enzymes, comparing an intrusive model, in which scanning and catalysis are tightly coupled, against a loosely coupled passive model. Diagrammatic theory and path-integral solutions of these models revealed clearly distinct predictions. Comparison to experimental data from catalyzed deaminations deposited on single-stranded DNA by the enzyme activation-induced deoxycytidine deaminase (AID) demonstrates that catalysis and diffusion are strongly intertwined, where the chemical conversions give rise to new stochastic trajectories that were absent if the substrate DNA was homogeneous. The C →U deamination profiles in both analytical predictions and experiments exhibit a strong contextual dependence, where the conversion rate of each target site is strongly contingent on the identities of other surrounding targets, with the intrusive model showing an excellent fit to the data. These methods can be applied to deduce sequence-dependent catalytic signatures of other DNA modification enzymes, with potential applications to cancer, gene regulation, and epigenetics.

A Control Scheme That Uses Dynamic Postural Synergies to Coordinate a Hybrid Walking Neuroprosthesis: Theory and Experiments.

Science.gov (United States)

Alibeji, Naji A; Molazadeh, Vahidreza; Dicianno, Brad E; Sharma, Nitin

2018-01-01

A hybrid walking neuroprosthesis that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton can be used to restore walking in persons with paraplegia. It provides therapeutic benefits of FES and torque reliability of the powered exoskeleton. Moreover, by harnessing metabolic power of muscles via FES, the hybrid combination has a potential to lower power consumption and reduce actuator size in the powered exoskeleton. Its control design, however, must overcome the challenges of actuator redundancy due to the combined use of FES and electric motor. Further, dynamic disturbances such as electromechanical delay (EMD) and muscle fatigue must be considered during the control design process. This ensures stability and control performance despite disparate dynamics of FES and electric motor. In this paper, a general framework to coordinate FES of multiple gait-governing muscles with electric motors is presented. A muscle synergy-inspired control framework is used to derive the controller and is motivated mainly to address the actuator redundancy issue. Dynamic postural synergies between FES of the muscles and the electric motors were artificially generated through optimizations and result in key dynamic postures when activated. These synergies were used in the feedforward path of the control system. A dynamic surface control technique, modified with a delay compensation term, is used as the feedback controller to address model uncertainty, the cascaded muscle activation dynamics, and EMD. To address muscle fatigue, the stimulation levels in the feedforward path were gradually increased based on a model-based fatigue estimate. A Lyapunov-based stability approach was used to derive the controller and guarantee its stability. The synergy-based controller was demonstrated experimentally on an able-bodied subject and person with an incomplete spinal cord injury.

A Control Scheme That Uses Dynamic Postural Synergies to Coordinate a Hybrid Walking Neuroprosthesis: Theory and Experiments

Directory of Open Access Journals (Sweden)

Naji A. Alibeji

2018-04-01

Full Text Available A hybrid walking neuroprosthesis that combines functional electrical stimulation (FES with a powered lower limb exoskeleton can be used to restore walking in persons with paraplegia. It provides therapeutic benefits of FES and torque reliability of the powered exoskeleton. Moreover, by harnessing metabolic power of muscles via FES, the hybrid combination has a potential to lower power consumption and reduce actuator size in the powered exoskeleton. Its control design, however, must overcome the challenges of actuator redundancy due to the combined use of FES and electric motor. Further, dynamic disturbances such as electromechanical delay (EMD and muscle fatigue must be considered during the control design process. This ensures stability and control performance despite disparate dynamics of FES and electric motor. In this paper, a general framework to coordinate FES of multiple gait-governing muscles with electric motors is presented. A muscle synergy-inspired control framework is used to derive the controller and is motivated mainly to address the actuator redundancy issue. Dynamic postural synergies between FES of the muscles and the electric motors were artificially generated through optimizations and result in key dynamic postures when activated. These synergies were used in the feedforward path of the control system. A dynamic surface control technique, modified with a delay compensation term, is used as the feedback controller to address model uncertainty, the cascaded muscle activation dynamics, and EMD. To address muscle fatigue, the stimulation levels in the feedforward path were gradually increased based on a model-based fatigue estimate. A Lyapunov-based stability approach was used to derive the controller and guarantee its stability. The synergy-based controller was demonstrated experimentally on an able-bodied subject and person with an incomplete spinal cord injury.

Impaired gait function in adults with cerebral palsy is associated with reduced rapid force generation and increased passive stiffness

DEFF Research Database (Denmark)

Geertsen, Svend Sparre; Kirk, Henrik; Lorentzen, Jakob

2015-01-01

analysis of the ankle joint during treadmill walking was obtained by 3-D motion analysis. RESULTS: Passive stiffness was significantly increased in adults with CP compared to controls. Passive stiffness and RFDdf were correlated to reduced toe lift. RFDpf provided the best correlation to push-off velocity...

Association between stride time fractality and gait adaptability during unperturbed and asymmetric walking.

Science.gov (United States)

Ducharme, Scott W; Liddy, Joshua J; Haddad, Jeffrey M; Busa, Michael A; Claxton, Laura J; van Emmerik, Richard E A

2018-04-01

Human locomotion is an inherently complex activity that requires the coordination and control of neurophysiological and biomechanical degrees of freedom across various spatiotemporal scales. Locomotor patterns must constantly be altered in the face of changing environmental or task demands, such as heterogeneous terrains or obstacles. Variability in stride times occurring at short time scales (e.g., 5-10 strides) is statistically correlated to larger fluctuations occurring over longer time scales (e.g., 50-100 strides). This relationship, known as fractal dynamics, is thought to represent the adaptive capacity of the locomotor system. However, this has not been tested empirically. Thus, the purpose of this study was to determine if stride time fractality during steady state walking associated with the ability of individuals to adapt their gait patterns when locomotor speed and symmetry are altered. Fifteen healthy adults walked on a split-belt treadmill at preferred speed, half of preferred speed, and with one leg at preferred speed and the other at half speed (2:1 ratio asymmetric walking). The asymmetric belt speed condition induced gait asymmetries that required adaptation of locomotor patterns. The slow speed manipulation was chosen in order to determine the impact of gait speed on stride time fractal dynamics. Detrended fluctuation analysis was used to quantify the correlation structure, i.e., fractality, of stride times. Cross-correlation analysis was used to measure the deviation from intended anti-phasing between legs as a measure of gait adaptation. Results revealed no association between unperturbed walking fractal dynamics and gait adaptability performance. However, there was a quadratic relationship between perturbed, asymmetric walking fractal dynamics and adaptive performance during split-belt walking, whereby individuals who exhibited fractal scaling exponents that deviated from 1/f performed the poorest. Compared to steady state preferred walking

Neuromechanical Control for Hexapedal Robot Walking on Challenging Surfaces and Surface Classification

DEFF Research Database (Denmark)

Xiong, Xiaofeng; Wörgötter, Florentin; Manoonpong, Poramate

2014-01-01

The neuromechanical control principles of animal locomotion provide good insights for the development of bio-inspired legged robots for walking on challenging surfaces. Based on such principles, we developed a neuromechanical controller consisting of a modular neural network (MNN) and of virtual...... agonist–antagonist muscle mechanisms (VAAMs). The controller allows for variable compliant leg motions of a hexapod robot, thereby leading to energy-efficient walking on different surfaces. Without any passive mechanisms or torque and position feedback at each joint, the variable compliant leg motions...... are achieved by only changing the stiffness parameters of the VAAMs. In addition, six surfaces can be also classified by observing the motor signals generated by the controller. The performance of the controller is tested on a physical hexapod robot. Experimental results show that it can effectively walk...

Autonomous exoskeleton reduces metabolic cost of human walking.

Science.gov (United States)

Mooney, Luke M; Rouse, Elliott J; Herr, Hugh M

2014-11-03

Passive exoskeletons that assist with human locomotion are often lightweight and compact, but are unable to provide net mechanical power to the exoskeletal wearer. In contrast, powered exoskeletons often provide biologically appropriate levels of mechanical power, but the size and mass of their actuator/power source designs often lead to heavy and unwieldy devices. In this study, we extend the design and evaluation of a lightweight and powerful autonomous exoskeleton evaluated for loaded walking in (J Neuroeng Rehab 11:80, 2014) to the case of unloaded walking conditions. The metabolic energy consumption of seven study participants (85 ± 12 kg body mass) was measured while walking on a level treadmill at 1.4 m/s. Testing conditions included not wearing the exoskeleton and wearing the exoskeleton, in both powered and unpowered modes. When averaged across the gait cycle, the autonomous exoskeleton applied a mean positive mechanical power of 26 ± 1 W (13 W per ankle) with 2.12 kg of added exoskeletal foot-shank mass (1.06 kg per leg). Use of the leg exoskeleton significantly reduced the metabolic cost of walking by 35 ± 13 W, which was an improvement of 10 ± 3% (p = 0.023) relative to the control condition of not wearing the exoskeleton. The results of this study highlight the advantages of developing lightweight and powerful exoskeletons that can comfortably assist the body during walking.

Comparison of the Effects of Seated, Supine, and Walking Interset Rest Strategies on Work Rate.

Science.gov (United States)

Ouellette, Kristen A; Brusseau, Timothy A; Davidson, Lance E; Ford, Candus N; Hatfield, Disa L; Shaw, Janet M; Eisenman, Patricia A

2016-12-01

Ouellette, KA, Brusseau, TA, Davidson, LE, Ford, CN, Hatfield, DL, Shaw, JM, and Eisenman, PA. Comparison of the effects of seated, supine, and walking interset rest strategies on work rate. J Strength Cond Res 30(12): 3396-3404, 2016-The idea that an upright posture should be maintained during the interset rest periods of training sessions is pervasive. The primary aim of this study was to determine differences in work rate associated with 3 interset rest strategies. Male and female members of the CrossFit community (male n = 5, female n = 10) were recruited to perform a strenuous training session designed to enhance work capacity that involved both cardiovascular and muscular endurance exercises. The training session was repeated on 3 separate occasions to evaluate 3 interset rest strategies, which included lying supine on the floor, sitting on a flat bench, and walking on a treadmill (0.67 m·s). Work rate was calculated for each training session by summing session joules of work and dividing by the time to complete the training session (joules of work per second). Data were also collected during the interset rest periods (heart rate [HR], respiratory rate [RR], and volume of oxygen consumed) and were used to explain why one rest strategy may positively impact work rate compared with another. Statistical analyses revealed significant differences (p ≤ 0.05) between the passive and active rest strategies, with the passive strategies allowing for improved work rate (supine = 62.77 ± 7.32, seated = 63.66 ± 8.37, and walking = 60.61 ± 6.42 average joules of work per second). Results also suggest that the passive strategies resulted in superior HR, RR, and oxygen consumption recovery. In conclusion, work rate and physiological recovery were enhanced when supine and seated interset rest strategies were used compared with walking interset rest.

Non-linear dynamics of the passivity breakdown of iron in acidic solutions

CERN Document Server

Sazou, D

2003-01-01

Breakdown of the iron passivity in acid solutions accompanied by current oscillations was investigated by using electrochemical techniques, which reveal the non-linear dynamical response of the system in the current-potential (I-E) and current-time (I-t) planes. Current oscillations of the Fe-electrolyte electrochemical system were studied in the (a) absence and (b) presence of chlorides. In case (a) two oscillatory regions were distinguished; one at low potentials associated with the formation-dissolution of a ferrous salt and another at higher potentials associated with the formation-breakdown of the oxide film. Chaotic oscillations appear in the former region whereas periodic oscillations of a relaxation type appear in the latter region. In case (b), complex periodic and aperiodic oscillations are induced by small amounts of chlorides due to pitting corrosion. Pitting corrosion is a multistage localized process of a great technological importance. It consists of a local breakdown of the passive oxide film ...

Large deviation principle for one-dimensional random walk in dynamic random environment: attractive spin-flips and simple symmetric exclusion

NARCIS (Netherlands)

Avena, L.; Hollander, den W.Th.F.; Redig, F.H.J.

2010-01-01

Consider a one-dimensional shift-invariant attractive spin-flip system in equilibrium, constituting a dynamic random environment, together with a nearest-neighbor random walk that on occupied sites has a local drift to the right but on vacant sites has a local drift to the left. In previous work we

Visual evoked responses during standing and walking

Directory of Open Access Journals (Sweden)

Klaus Gramann

2010-10-01

Full Text Available Human cognition has been shaped both by our body structure and by its complex interactionswith its environment. Our cognition is thus inextricably linked to our own and others’ motorbehavior. To model brain activity associated with natural cognition, we propose recording theconcurrent brain dynamics and body movements of human subjects performing normal actions.Here we tested the feasibility of such a mobile brain/body (MoBI imaging approach byrecording high-density electroencephalographic (EEG activity and body movements of subjectsstanding or walking on a treadmill while performing a visual oddball response task. Independentcomponent analysis (ICA of the EEG data revealed visual event-related potentials (ERPs thatduring standing, slow walking, and fast walking did not differ across movement conditions,demonstrating the viability of recording brain activity accompanying cognitive processes duringwhole body movement. Non-invasive and relatively low-cost MoBI studies of normal, motivatedactions might improve understanding of interactions between brain and body dynamics leadingto more complete biological models of cognition.

Adaptive random walks on the class of Web graphs

Science.gov (United States)

Tadić, B.

2001-09-01

We study random walk with adaptive move strategies on a class of directed graphs with variable wiring diagram. The graphs are grown from the evolution rules compatible with the dynamics of the world-wide Web [B. Tadić, Physica A 293, 273 (2001)], and are characterized by a pair of power-law distributions of out- and in-degree for each value of the parameter β, which measures the degree of rewiring in the graph. The walker adapts its move strategy according to locally available information both on out-degree of the visited node and in-degree of target node. A standard random walk, on the other hand, uses the out-degree only. We compute the distribution of connected subgraphs visited by an ensemble of walkers, the average access time and survival probability of the walks. We discuss these properties of the walk dynamics relative to the changes in the global graph structure when the control parameter β is varied. For β≥ 3, corresponding to the world-wide Web, the access time of the walk to a given level of hierarchy on the graph is much shorter compared to the standard random walk on the same graph. By reducing the amount of rewiring towards rigidity limit β↦βc≲ 0.1, corresponding to the range of naturally occurring biochemical networks, the survival probability of adaptive and standard random walk become increasingly similar. The adaptive random walk can be used as an efficient message-passing algorithm on this class of graphs for large degree of rewiring.

A Review: Passive System Reliability Analysis – Accomplishments and Unresolved Issues

Energy Technology Data Exchange (ETDEWEB)

Nayak, Arun Kumar, E-mail: arunths@barc.gov.in [Reactor Engineering Division, Reactor Design and Development Group, Bhabha Atomic Research Centre, Mumbai (India); Chandrakar, Amit [Homi Bhabha National Institute, Mumbai (India); Vinod, Gopika [Reactor Safety Division, Reactor Design and Development Group, Bhabha Atomic Research Centre, Mumbai (India)

2014-10-10

Reliability assessment of passive safety systems is one of the important issues, since safety of advanced nuclear reactors rely on several passive features. In this context, a few methodologies such as reliability evaluation of passive safety system (REPAS), reliability methods for passive safety functions (RMPS), and analysis of passive systems reliability (APSRA) have been developed in the past. These methodologies have been used to assess reliability of various passive safety systems. While these methodologies have certain features in common, but they differ in considering certain issues; for example, treatment of model uncertainties, deviation of geometric, and process parameters from their nominal values. This paper presents the state of the art on passive system reliability assessment methodologies, the accomplishments, and remaining issues. In this review, three critical issues pertaining to passive systems performance and reliability have been identified. The first issue is applicability of best estimate codes and model uncertainty. The best estimate codes based phenomenological simulations of natural convection passive systems could have significant amount of uncertainties, these uncertainties must be incorporated in appropriate manner in the performance and reliability analysis of such systems. The second issue is the treatment of dynamic failure characteristics of components of passive systems. REPAS, RMPS, and APSRA methodologies do not consider dynamic failures of components or process, which may have strong influence on the failure of passive systems. The influence of dynamic failure characteristics of components on system failure probability is presented with the help of a dynamic reliability methodology based on Monte Carlo simulation. The analysis of a benchmark problem of Hold-up tank shows the error in failure probability estimation by not considering the dynamism of components. It is thus suggested that dynamic reliability methodologies must be

Spectral dynamics of square pulses in passively mode-locked fiber lasers

Science.gov (United States)

Semaan, Georges; Komarov, Andrey; Niang, Alioune; Salhi, Mohamed; Sanchez, François

2018-02-01

We investigate experimentally and numerically the spectral dynamics of square pulses generated in passively mode-locked fiber lasers under the dissipative soliton resonance. The features of the transition from the single-peak spectral profile to the doublet spectrum with increasing pump power are studied. The used master equation takes into account the gain saturation, the quadratic frequency dispersion of the gain and the refractive index, and the cubic-quintic nonlinearity of the losses and refractive index. Experimental data are obtained for an Er:Yb-doped fiber ring laser. The theoretical and experimental results are in good agreement with each other.

Large deviation principle for one-dimensional random walk in dynamic random environment : attractive spin-flips and simple symmetric exclusion

NARCIS (Netherlands)

Avena, L.; Hollander, den W.Th.F.; Redig, F.H.J.

2009-01-01

Consider a one-dimensional shift-invariant attractive spin-ip system in equilibrium, constituting a dynamic random environment, together with a nearest-neighbor random walk that on occupied sites has a local drift to the right but on vacant sites has a local drift to the left. In [2] we proved a law

Numerical and experimental study of the virtual quadrupedal walking robot-semiquad

International Nuclear Information System (INIS)

Aoustin, Yannick; Chevallereau, Christine; Formal'sky, Alexander

2006-01-01

SemiQuad is a prototyped walking robot with a platform and two double-link legs. Thus, it is a five-link mechanism. The front leg models identical motions of two quadruped's front legs, the back leg models identical motions of two quadruped's back legs. The legs have passive (uncontrolled) feet that extend in the frontal plane. Due to this the robot is stable in the frontal plane. This robot can be viewed as a 'virtual' quadruped. Four DC motors drive the mechanism. Its control system comprises a computer, hardware servo-systems and power amplifiers. The locomotion of the prototype is planar curvet gait. In the double support our prototype is statically stable and over actuated. In the single support it is unstable and under actuated system. There is no flight phase. We describe here the scheme of the mechanism, the characteristics of the drives and the control strategy. The dynamic model of the planar walking is recalled for the double, single support phases and for the impact instant. An intuitive control strategy is detailed. The designed control strategy overcomes the difficulties appeared due to unstable and under actuated motion in the single support. Due to the control algorithm the walking regime consists of the alternating different phases. The sequence of these phases is the following. A double support phase begins. A fast bend and unbend of the front leg allows a lift-off of the front leg. During the single support on the back leg the distance between the two leg tips increases. Then an impact occurs and a new double support phase begins. A fast bend and unbend of the back leg allows the lift-off of the back leg. During the single support on the front leg the distance between the two leg tips decreases to form a cyclic walking gait. The experiments give results that are close to those of the simulation

Maintenance of muscle strength retains a normal metabolic cost in simulated walking after transtibial limb loss

Science.gov (United States)

Russell Esposito, Elizabeth

2018-01-01

Recent studies on relatively young and fit individuals with limb loss suggest that maintaining muscle strength after limb loss may mitigate the high metabolic cost of walking typically seen in the larger general limb loss population. However, these data are cross-sectional and the muscle strength prior to limb loss is unknown, and it is therefore difficult to draw causal inferences on changes in strength and gait energetics. Here we used musculoskeletal modeling and optimal control simulations to perform a longitudinal study (25 virtual “subjects”) of the metabolic cost of walking pre- and post-limb loss (unilateral transtibial). Simulations of walking were first performed pre-limb loss on a model with two intact biological legs, then post-limb loss on a model with a unilateral transtibial prosthesis, with a cost function that minimized the weighted sum of gait deviations plus metabolic cost. Metabolic costs were compared pre- vs. post-limb loss, with systematic modifications to the muscle strength and prosthesis type (passive, powered) in the post-limb loss model. The metabolic cost prior to limb loss was 3.44±0.13 J/m/kg. After limb loss, with a passive prosthesis the metabolic cost did not increase above the pre-limb loss cost if pre-limb loss muscle strength was maintained (mean -0.6%, p = 0.17, d = 0.17). With 10% strength loss the metabolic cost with the passive prosthesis increased (mean +5.9%, p loss cost for all subjects with strength losses of 10% and 20%, but increased for all subjects with strength loss of 30% (mean +5.9%, p loss, and that a gait with minimal deviations can be achieved when muscle strength is sufficiently high, even when using a passive prosthesis. PMID:29329344

Shifty: A Weight-Shifting Dynamic Passive Haptic Proxy to Enhance Object Perception in Virtual Reality.

Science.gov (United States)

Zenner, Andre; Kruger, Antonio

2017-04-01

We define the concept of Dynamic Passive Haptic Feedback (DPHF) for virtual reality by introducing the weight-shifting physical DPHF proxy object Shifty. This concept combines actuators known from active haptics and physical proxies known from passive haptics to construct proxies that automatically adapt their passive haptic feedback. We describe the concept behind our ungrounded weight-shifting DPHF proxy Shifty and the implementation of our prototype. We then investigate how Shifty can, by automatically changing its internal weight distribution, enhance the user's perception of virtual objects interacted with in two experiments. In a first experiment, we show that Shifty can enhance the perception of virtual objects changing in shape, especially in length and thickness. Here, Shifty was shown to increase the user's fun and perceived realism significantly, compared to an equivalent passive haptic proxy. In a second experiment, Shifty is used to pick up virtual objects of different virtual weights. The results show that Shifty enhances the perception of weight and thus the perceived realism by adapting its kinesthetic feedback to the picked-up virtual object. In the same experiment, we additionally show that specific combinations of haptic, visual and auditory feedback during the pick-up interaction help to compensate for visual-haptic mismatch perceived during the shifting process.

Dynamic optimization of walker-assisted FES-activated paraplegic walking: simulation and experimental studies.

Science.gov (United States)

Nekoukar, Vahab; Erfanian, Abbas

2013-11-01

In this paper, we propose a musculoskeletal model of walker-assisted FES-activated paraplegic walking for the generation of muscle stimulation patterns and characterization of the causal relationships between muscle excitations, multi-joint movement, and handle reaction force (HRF). The model consists of the lower extremities, trunk, hands, and a walker. The simulation of walking is performed using particle swarm optimization to minimize the tracking errors from the desired trajectories for the lower extremity joints, to reduce the stimulations of the muscle groups acting around the hip, knee, and ankle joints, and to minimize the HRF. The results of the simulation studies using data recorded from healthy subjects performing walker-assisted walking indicate that the model-generated muscle stimulation patterns are in agreement with the EMG patterns that have been reported in the literature. The experimental results on two paraplegic subjects demonstrate that the proposed methodology can improve walking performance, reduce HRF, and increase walking speed when compared to the conventional FES-activated paraplegic walking. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

Molecular dynamics study of solid-liquid heat transfer and passive liquid flow

Science.gov (United States)

Yesudasan Daisy, Sumith

High heat flux removal is a challenging problem in boilers, electronics cooling, concentrated photovoltaic and other power conversion devices. Heat transfer by phase change is one of the most efficient mechanisms for removing heat from a solid surface. Futuristic electronic devices are expected to generate more than 1000 W/cm2 of heat. Despite the advancements in microscale and nanoscale manufacturing, the maximum passive heat flux removal has been 300 W/cm2 in pool boiling. Such limitations can be overcome by developing nanoscale thin-film evaporation based devices, which however require a better understanding of surface interactions and liquid vapor phase change process. Evaporation based passive flow is an inspiration from the transpiration process that happens in trees. If we can mimic this process and develop heat removal devices, then we can develop efficient cooling devices. The existing passive flow based cooling devices still needs improvement to meet the future demands. To improve the efficiency and capacity of these devices, we need to explore and quantify the passive flow happening at nanoscales. Experimental techniques have not advanced enough to study these fundamental phenomena at the nanoscale, an alternative method is to perform theoretical study at nanoscales. Molecular dynamics (MD) simulation is a widely accepted powerful tool for studying a range of fundamental and engineering problems. MD simulations can be utilized to study the passive flow mechanism and heat transfer due to it. To study passive flow using MD, apart from the conventional methods available in MD, we need to have methods to simulate the heat transfer between solid and liquid, local pressure, surface tension, density, temperature calculation methods, realistic boundary conditions, etc. Heat transfer between solid and fluids has been a challenging area in MD simulations, and has only been minimally explored (especially for a practical fluid like water). Conventionally, an

Observed diurnal variations in Mars Science Laboratory Dynamic Albedo of Neutrons passive mode data

Science.gov (United States)

Tate, C. G.; Moersch, J.; Jun, I.; Mitrofanov, I.; Litvak, M.; Boynton, W. V.; Drake, D.; Fedosov, F.; Golovin, D.; Hardgrove, C.; Harshman, K.; Kozyrev, A. S.; Kuzmin, R.; Lisov, D.; Maclennan, E.; Malakhov, A.; Mischna, M.; Mokrousov, M.; Nikiforov, S.; Sanin, A. B.; Starr, R.; Vostrukhin, A.

2018-06-01

The Mars Science Laboratory Dynamic Albedo of Neutrons (DAN) experiment measures the martian neutron leakage flux in order to estimate the amount of water equivalent hydrogen present in the shallow regolith. When DAN is operating in passive mode, it is sensitive to neutrons produced through the interactions of galactic cosmic rays (GCR) with the regolith and atmosphere and neutrons produced by the rover's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). During the mission, DAN passive mode data were collected over the full diurnal cycle at the locations known as Rocknest (sols 60-100) and John Klein (sols 166-272). A weak, but unexpected, diurnal variation was observed in the neutron count rates reported at these locations. We investigate different hypotheses that could be causing these observed variations. These hypotheses are variations in subsurface temperature, atmospheric pressure, the exchange of water vapor between the atmosphere and regolith, and instrumental effects on the neutron count rates. Our investigation suggests the most likely factors contributing to the observed diurnal variations in DAN passive data are instrumental effects and time-variable preferential shielding of alpha particles, with other environmental effects only having small contributions.

Molecular dynamics simulation for PBR pebble tracking simulation via a random walk approach using Monte Carlo simulation.

Science.gov (United States)

Lee, Kyoung O; Holmes, Thomas W; Calderon, Adan F; Gardner, Robin P

2012-05-01

Using a Monte Carlo (MC) simulation, random walks were used for pebble tracking in a two-dimensional geometry in the presence of a biased gravity field. We investigated the effect of viscosity damping in the presence of random Gaussian fluctuations. The particle tracks were generated by Molecular Dynamics (MD) simulation for a Pebble Bed Reactor. The MD simulations were conducted in the interaction of noncohesive Hertz-Mindlin theory where the random walk MC simulation has a correlation with the MD simulation. This treatment can easily be extended to include the generation of transient gamma-ray spectra from a single pebble that contains a radioactive tracer. Then the inverse analysis thereof could be made to determine the uncertainty of the realistic measurement of transient positions of that pebble by any given radiation detection system designed for that purpose. Copyright © 2011 Elsevier Ltd. All rights reserved.

Kinematic Gait Changes Following Serial Casting and Bracing to Treat Toe Walking in a Child With Autism.

Science.gov (United States)

Barkocy, Marybeth; Dexter, James; Petranovich, Colleen

2017-07-01

To evaluate the effectiveness of serial casting in a child with autism spectrum disorder (ASD) exhibiting a toe-walking gait pattern with equinus contractures. Although many children with ASD toe walk, little research on physical therapy interventions exists for this population. Serial casting has been validated for use in idiopathic toe walking to increase passive dorsiflexion and improve gait, but not for toe walking in children with ASD. Serial casting followed by ankle-foot orthosis use was implemented to treat a child with ASD who had an obligatory equinus gait pattern. Gait analysis supported improvements in kinematic, spatial, and temporal parameters of gait, and the child maintained a consistent heel-toe gait at 2-year follow-up. STATEMENT OF CONCLUSION AND RECOMMENDATIONS FOR CLINICAL PRACTICE:: Serial casting followed by ankle-foot orthosis use is a viable treatment option for toe walking in children with ASD.

Random walk theory and exchange rate dynamics in transition economies

Directory of Open Access Journals (Sweden)

Gradojević Nikola

2010-01-01

Full Text Available This paper investigates the validity of the random walk theory in the Euro-Serbian dinar exchange rate market. We apply Andrew Lo and Archie MacKinlay's (1988 conventional variance ratio test and Jonathan Wright's (2000 non-parametric ranks and signs based variance ratio tests to the daily Euro/Serbian dinar exchange rate returns using the data from January 2005 - December 2008. Both types of variance ratio tests overwhelmingly reject the random walk hypothesis over the data span. To assess the robustness of our findings, we examine the forecasting performance of a non-linear, nonparametric model in the spirit of Francis Diebold and James Nason (1990 and find that it is able to significantly improve upon the random walk model, thus confirming the existence of foreign exchange market imperfections in a small transition economy such as Serbia. In the last part of the paper, we conduct a comparative study on how our results relate to those of other transition economies in the region.

Design and Control of a Powered Hip Exoskeleton for Walking Assistance

Directory of Open Access Journals (Sweden)

Qingcong Wu

2015-03-01

Full Text Available The wearable powered exoskeleton is a human-robot cooperation system that integrates the strength of a robot with human intelligence. This paper presents the research results into a powered hip exoskeleton (PH-EXOS designed to provide locomotive assistance to individuals with walking impediments. The Bowden cable actuated exoskeleton has an anthropomorphic structure with six degrees of freedom (DOF in order to match the human hip anatomy and enable natural interaction with the user. The mechanical structure, the actuation system, and the interaction kinematics of PH-EXOS are optimized to achieve preferable manoeuvrability and harmony. For the control of the exoskeleton, a real-time control system is established in xPC target environment based on Matlab/RTW. A Cascaded PID controller is developed to perform the trajectories tracking tasks in passive control mode. Besides, based on the pressure information on the thigh, a fuzzy adaptive controller is developed to perform walking assistance tasks in active control mode. Preliminary treadmill walking experiments on a healthy subject were conducted to verify the effectiveness of the proposed device and control approaches in reducing walking effort.

Partition-based discrete-time quantum walks

Science.gov (United States)

Konno, Norio; Portugal, Renato; Sato, Iwao; Segawa, Etsuo

2018-04-01

We introduce a family of discrete-time quantum walks, called two-partition model, based on two equivalence-class partitions of the computational basis, which establish the notion of local dynamics. This family encompasses most versions of unitary discrete-time quantum walks driven by two local operators studied in literature, such as the coined model, Szegedy's model, and the 2-tessellable staggered model. We also analyze the connection of those models with the two-step coined model, which is driven by the square of the evolution operator of the standard discrete-time coined walk. We prove formally that the two-step coined model, an extension of Szegedy model for multigraphs, and the two-tessellable staggered model are unitarily equivalent. Then, selecting one specific model among those families is a matter of taste not generality.

Mathematical model of the 5-DOF sled dynamics of an electrodynamic Maglev system with a passive sled

NARCIS (Netherlands)

Boeij, de J.; Steinbuch, M.; Gutierrez, H.M.

2005-01-01

A model that describes the five-degrees-of-freedom (5-DOF) dynamics of a passively levitated electrodynamic maglev system is presented. The model is based on the flux-current-force interactions and the geometric relationships between the levitation coils and the permanent magnets on the sled. The

Comparison of trunk activity during gait initiation and walking in humans.

Directory of Open Access Journals (Sweden)

Jean-Charles Ceccato

Full Text Available To understand the role of trunk muscles in maintenance of dynamic postural equilibrium we investigate trunk movements during gait initiation and walking, performing trunk kinematics analysis, Erector spinae muscle (ES recordings and dynamic analysis. ES muscle expressed a metachronal descending pattern of activity during walking and gait initiation. In the frontal and horizontal planes, lateroflexion and rotation occur before in the upper trunk and after in the lower trunk. Comparison of ES muscle EMGs and trunk kinematics showed that trunk muscle activity precedes corresponding kinematics activity, indicating that the ES drive trunk movement during locomotion and thereby allowing a better pelvis mobilization. EMG data showed that ES activity anticipates propulsive phases in walking with a repetitive pattern, suggesting a programmed control by a central pattern generator. Our findings also suggest that the programs for gait initiation and walking overlap with the latter beginning before the first has ended.

Dynamic Passive Dosing for Studying the Biotransformation of Hydrophobic Organic Chemicals: Microbial Degradation as an Example

DEFF Research Database (Denmark)

Smith, Kilian E. C.; Rein, Arno; Trapp, Stefan

2012-01-01

Biotransformation plays a key role in hydrophobic organic compound (HOC) fate, and understanding kinetics as a function of (bio)availability is critical for elucidating persistence, accumulation, and toxicity. Biotransformation mainly occurs in an aqueous environment, posing technical challenges...... for producing kinetic data because of low HOC solubilities and sorptive losses. To overcome these, a new experimental approach based on passive dosing is presented. This avoids using cosolvent for introducing the HOC substrate, buffers substrate depletion so biotransformation is measured within a narrow...... also similar for both PAHs, but decreased by around 2 orders of magnitude with increasing dissolved concentrations. Dynamic passive dosing is a useful tool for measuring biotransformation kinetics at realistically low and defined dissolved HOC concentrations....

Electrocortical correlates of human level-ground, slope, and stair walking.

Science.gov (United States)

Luu, Trieu Phat; Brantley, Justin A; Nakagome, Sho; Zhu, Fangshi; Contreras-Vidal, Jose L

2017-01-01

This study investigated electrocortical dynamics of human walking across different unconstrained walking conditions (i.e., level ground (LW), ramp ascent (RA), and stair ascent (SA)). Non-invasive active-electrode scalp electroencephalography (EEG) signals were recorded and a systematic EEG processing method was implemented to reduce artifacts. Source localization combined with independent component analysis and k-means clustering revealed the involvement of four clusters in the brain during the walking tasks: Left and Right Occipital Lobe (LOL, ROL), Posterior Parietal Cortex (PPC), and Central Sensorimotor Cortex (SMC). Results showed that the changes of spectral power in the PPC and SMC clusters were associated with the level of motor task demands. Specifically, we observed α and β suppression at the beginning of the gait cycle in both SA and RA walking (relative to LW) in the SMC. Additionally, we observed significant β rebound (synchronization) at the initial swing phase of the gait cycle, which may be indicative of active cortical signaling involved in maintaining the current locomotor state. An increase of low γ band power in this cluster was also found in SA walking. In the PPC, the low γ band power increased with the level of task demands (from LW to RA and SA). Additionally, our results provide evidence that electrocortical amplitude modulations (relative to average gait cycle) are correlated with the level of difficulty in locomotion tasks. Specifically, the modulations in the PPC shifted to higher frequency bands when the subjects walked in RA and SA conditions. Moreover, low γ modulations in the central sensorimotor area were observed in the LW walking and shifted to lower frequency bands in RA and SA walking. These findings extend our understanding of cortical dynamics of human walking at different level of locomotion task demands and reinforces the growing body of literature supporting a shared-control paradigm between spinal and cortical

A soft robotic exosuit improves walking in patients after stroke.

Science.gov (United States)

Awad, Louis N; Bae, Jaehyun; O'Donnell, Kathleen; De Rossi, Stefano M M; Hendron, Kathryn; Sloot, Lizeth H; Kudzia, Pawel; Allen, Stephen; Holt, Kenneth G; Ellis, Terry D; Walsh, Conor J

2017-07-26

Stroke-induced hemiparetic gait is characteristically slow and metabolically expensive. Passive assistive devices such as ankle-foot orthoses are often prescribed to increase function and independence after stroke; however, walking remains highly impaired despite-and perhaps because of-their use. We sought to determine whether a soft wearable robot (exosuit) designed to supplement the paretic limb's residual ability to generate both forward propulsion and ground clearance could facilitate more normal walking after stroke. Exosuits transmit mechanical power generated by actuators to a wearer through the interaction of garment-like, functional textile anchors and cable-based transmissions. We evaluated the immediate effects of an exosuit actively assisting the paretic limb of individuals in the chronic phase of stroke recovery during treadmill and overground walking. Using controlled, treadmill-based biomechanical investigation, we demonstrate that exosuits can function in synchrony with a wearer's paretic limb to facilitate an immediate 5.33 ± 0.91° increase in the paretic ankle's swing phase dorsiflexion and 11 ± 3% increase in the paretic limb's generation of forward propulsion ( P exosuit was sufficient to facilitate more normal walking in ambulatory individuals after stroke. Future work will focus on understanding how exosuit-induced improvements in walking performance may be leveraged to improve mobility after stroke. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Reverse Non-Equilibrium Molecular Dynamics Demonstrate That Surface Passivation Controls Thermal Transport at Semiconductor-Solvent Interfaces.

Science.gov (United States)

Hannah, Daniel C; Gezelter, J Daniel; Schaller, Richard D; Schatz, George C

2015-06-23

We examine the role played by surface structure and passivation in thermal transport at semiconductor/organic interfaces. Such interfaces dominate thermal transport in semiconductor nanomaterials owing to material dimensions much smaller than the bulk phonon mean free path. Utilizing reverse nonequilibrium molecular dynamics simulations, we calculate the interfacial thermal conductance (G) between a hexane solvent and chemically passivated wurtzite CdSe surfaces. In particular, we examine the dependence of G on the CdSe slab thickness, the particular exposed crystal facet, and the extent of surface passivation. Our results indicate a nonmonotonic dependence of G on ligand-grafting density, with interfaces generally exhibiting higher thermal conductance for increasing surface coverage up to ∼0.08 ligands/Å(2) (75-100% of a monolayer, depending on the particular exposed facet) and decreasing for still higher coverages. By analyzing orientational ordering and solvent penetration into the ligand layer, we show that a balance of competing effects is responsible for this nonmonotonic dependence. Although the various unpassivated CdSe surfaces exhibit similar G values, the crystal structure of an exposed facet nevertheless plays an important role in determining the interfacial thermal conductance of passivated surfaces, as the density of binding sites on a surface determines the ligand-grafting densities that may ultimately be achieved. We demonstrate that surface passivation can increase G relative to a bare surface by roughly 1 order of magnitude and that, for a given extent of passivation, thermal conductance can vary by up to a factor of ∼2 between different surfaces, suggesting that appropriately tailored nanostructures may direct heat flow in an anisotropic fashion for interface-limited thermal transport.

Effects of Active and Passive Control Techniques on Mach 1.5 Cavity Flow Dynamics

Directory of Open Access Journals (Sweden)

Selin Aradag

2017-01-01

Full Text Available Supersonic flow over cavities has been of interest since 1960s because cavities represent the bomb bays of aircraft. The flow is transient, turbulent, and complicated. Pressure fluctuations inside the cavity can impede successful weapon release. The objective of this study is to use active and passive control methods on supersonic cavity flow numerically to decrease or eliminate pressure oscillations. Jet blowing at several locations on the front and aft walls of the cavity configuration is used as an active control method. Several techniques are used for passive control including using a cover plate to separate the flow dynamics inside and outside of the cavity, trailing edge wall modifications, such as inclination of the trailing edge, and providing curvature to the trailing edge wall. The results of active and passive control techniques are compared with the baseline case in terms of pressure fluctuations, sound pressure levels at the leading edge, trailing edge walls, and cavity floor and in terms of formation of the flow structures and the results are presented. It is observed from the results that modification of the trailing edge wall is the most effective of the control methods tested leading to up to 40 dB reductions in cavity tones.

Dynamics of temporally localized states in passively mode-locked semiconductor lasers

Science.gov (United States)

Schelte, C.; Javaloyes, J.; Gurevich, S. V.

2018-05-01

We study the emergence and the stability of temporally localized structures in the output of a semiconductor laser passively mode locked by a saturable absorber in the long-cavity regime. For large yet realistic values of the linewidth enhancement factor, we disclose the existence of secondary dynamical instabilities where the pulses develop regular and subsequent irregular temporal oscillations. By a detailed bifurcation analysis we show that additional solution branches that consist of multipulse (molecules) solutions exist. We demonstrate that the various solution curves for the single and multipeak pulses can splice and intersect each other via transcritical bifurcations, leading to a complex web of solutions. Our analysis is based on a generic model of mode locking that consists of a time-delayed dynamical system, but also on a much more numerically efficient, yet approximate, partial differential equation. We compare the results of the bifurcation analysis of both models in order to assess up to which point the two approaches are equivalent. We conclude our analysis by the study of the influence of group velocity dispersion, which is only possible in the framework of the partial differential equation model, and we show that it may have a profound impact on the dynamics of the localized states.

Fire-Walking

Science.gov (United States)

Willey, David

2010-01-01

This article gives a brief history of fire-walking and then deals with the physics behind fire-walking. The author has performed approximately 50 fire-walks, took the data for the world's hottest fire-walk and was, at one time, a world record holder for the longest fire-walk (www.dwilley.com/HDATLTW/Record_Making_Firewalks.html). He currently…

Multiport optical circulator by using polarizing beam splitter cubes as spatial walk-off polarizers.

Science.gov (United States)

Chen, Jing-Heng; Chen, Kun-Huang; Lin, Jiun-You; Hsieh, Hsiang-Yung

2010-03-10

Optical circulators are necessary passive devices applied in optical communication systems. In the design of optical circulators, the implementation of the function of spatial walk-off polarizers is a key technique that significantly influences the performance and cost of a device. This paper proposes a design of a multiport optical circulator by using polarizing beam splitter cubes as spatial walk-off polarizers. To show the feasibility of the design, a prototype of a six-port optical circulator was fabricated. The insertion losses are 0.94-1.49 dB, the isolations are 25-51 dB, and return losses are 27.72 dB.

Biomechanically Excited SMD Model of a Walking Pedestrian

DEFF Research Database (Denmark)

Zhang, Mengshi; Georgakis, Christos T.; Chen, Jun

2016-01-01

Through their biomechanical properties, pedestrians interact with the structures they occupy. Although this interaction has been recognized by researchers, pedestrians' biomechanical properties have not been fully addressed. In this paper, a spring-mass-damper (SMD) system, with a pair of biomech......Through their biomechanical properties, pedestrians interact with the structures they occupy. Although this interaction has been recognized by researchers, pedestrians' biomechanical properties have not been fully addressed. In this paper, a spring-mass-damper (SMD) system, with a pair...... produced the pedestrian's center of mass (COM) trajectories from the captured motion markers. The vertical COM trajectory was approximated to be the pedestrian SMD dynamic responses under the excitation of biomechanical forces. SMD model parameters of a pedestrian for a specific walking frequency were...... estimated from a known walking frequency and the pedestrian's weight, assuming that pedestrians always walk in displacement resonance and retain a constant damping ratio of 0.3. Thus, biomechanical forces were extracted using the measured SMD dynamic responses and the estimated SMD parameters. Extracted...

A generalized model via random walks for information filtering

Energy Technology Data Exchange (ETDEWEB)

Ren, Zhuo-Ming, E-mail: zhuomingren@gmail.com [Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg (Switzerland); Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, ChongQing, 400714 (China); Kong, Yixiu [Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg (Switzerland); Shang, Ming-Sheng, E-mail: msshang@cigit.ac.cn [Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, ChongQing, 400714 (China); Zhang, Yi-Cheng [Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700, Fribourg (Switzerland)

2016-08-06

There could exist a simple general mechanism lurking beneath collaborative filtering and interdisciplinary physics approaches which have been successfully applied to online E-commerce platforms. Motivated by this idea, we propose a generalized model employing the dynamics of the random walk in the bipartite networks. Taking into account the degree information, the proposed generalized model could deduce the collaborative filtering, interdisciplinary physics approaches and even the enormous expansion of them. Furthermore, we analyze the generalized model with single and hybrid of degree information on the process of random walk in bipartite networks, and propose a possible strategy by using the hybrid degree information for different popular objects to toward promising precision of the recommendation. - Highlights: • We propose a generalized recommendation model employing the random walk dynamics. • The proposed model with single and hybrid of degree information is analyzed. • A strategy with the hybrid degree information improves precision of recommendation.

A generalized model via random walks for information filtering

International Nuclear Information System (INIS)

Ren, Zhuo-Ming; Kong, Yixiu; Shang, Ming-Sheng; Zhang, Yi-Cheng

2016-01-01

There could exist a simple general mechanism lurking beneath collaborative filtering and interdisciplinary physics approaches which have been successfully applied to online E-commerce platforms. Motivated by this idea, we propose a generalized model employing the dynamics of the random walk in the bipartite networks. Taking into account the degree information, the proposed generalized model could deduce the collaborative filtering, interdisciplinary physics approaches and even the enormous expansion of them. Furthermore, we analyze the generalized model with single and hybrid of degree information on the process of random walk in bipartite networks, and propose a possible strategy by using the hybrid degree information for different popular objects to toward promising precision of the recommendation. - Highlights: • We propose a generalized recommendation model employing the random walk dynamics. • The proposed model with single and hybrid of degree information is analyzed. • A strategy with the hybrid degree information improves precision of recommendation.

Randomized random walk on a random walk

International Nuclear Information System (INIS)

Lee, P.A.

1983-06-01

This paper discusses generalizations of the model introduced by Kehr and Kunter of the random walk of a particle on a one-dimensional chain which in turn has been constructed by a random walk procedure. The superimposed random walk is randomised in time according to the occurrences of a stochastic point process. The probability of finding the particle in a particular position at a certain instant is obtained explicitly in the transform domain. It is found that the asymptotic behaviour for large time of the mean-square displacement of the particle depends critically on the assumed structure of the basic random walk, giving a diffusion-like term for an asymmetric walk or a square root law if the walk is symmetric. Many results are obtained in closed form for the Poisson process case, and these agree with those given previously by Kehr and Kunter. (author)

Dynamics of Passive Lateral Pressure in Granular Mass during Discontinual Movement of Retaining Structure

Czech Academy of Sciences Publication Activity Database

Koudelka, Petr; Valach, Jaroslav

2006-01-01

Roč. 10, I (2006), s. 271-276 ISSN 1335-2393. [ICE Experimental stress analysis 2006. Červený Kláštor, xx.06.2006] R&D Projects: GA ČR(CZ) GA103/05/2130; GA AV ČR(CZ) IAA2071302 Institutional research plan: CEZ:AV0Z2071913; CEZ:AV0Z20710524 Keywords : dynamics of passive lateral (earth) pressure * rotation about the top * retaining structure * history of both pressure component Subject RIV: JM - Building Engineering

Numerical modeling of dynamics of heart rate and arterial pressure during passive orthostatic test

Science.gov (United States)

Ishbulatov, Yu. M.; Kiselev, A. R.; Karavaev, A. S.

2018-04-01

A model of human cardiovascular system is proposed to describe the main heart rhythm, influence of autonomous regulation on frequency and strength of heart contractions and resistance of arterial vessels; process of formation of arterial pressure during systolic and diastolic phases; influence of respiration; synchronization between loops of autonomous regulation. The proposed model is used to simulate the dynamics of heart rate and arterial pressure during passive transition from supine to upright position. Results of mathematical modeling are compared to original experimental data.

Nine Walks

DEFF Research Database (Denmark)

2013-01-01

Based on studies of, among others, the Situationists and their theories regarding walks as an artistic method and expression nine master students from “Studio Constructing an Archive”, Aarhus School of Architecture, Denmark performed nine walks as part of the exhibition. These walks relate...... to the students’ individual mappings of Behind the Green Door, its structure and content. They highlight a number of motifs found in the exhibition which are of particular interest to the students. The walks represented reflections on the walk as an artistic method and expression. Each walk is an individual...

On the Necessity of Including Joint Passive Dynamics in the Impedance Control of Robotic Legs

Directory of Open Access Journals (Sweden)

Juan Carlos Arevalo

2014-07-01

Full Text Available Bioinspired quadruped robots are among the best robot designs for field missions over the complex terrain encountered in extraterrestrial landscapes and disaster scenarios caused by natural and human-made catastrophes, such as those caused by nuclear power plant accidents and radiological emergencies. For such applications, the performance characteristics of the robots should include high mobility, adaptability to the terrain, the ability to handle a large payload and good endurance. Nature can provide inspiration for quadruped designs that are well suited for traversing complex terrain. Horse legs are an example of a structure that has evolved to exhibit good performance characteristics. In this paper, a leg design exhibiting the key features of horse legs is briefly described. This leg is an underactuated mechanism because it has two actively driven degrees of freedom (DOFs and one passively driven DOF. In this work, two control laws intended to be use in the stan ce phase are described: a control law that considers passive mechanism dynamics and a second law that neglects these dynamics. The performance of the two control laws is experimentally evaluated and compared. The results indicate that the first control law better achieves the control goal; however, the use of the second is not completely unjustified.

Modeling, simulation and optimization of bipedal walking

CERN Document Server

Berns, Karsten

2013-01-01

The model-based investigation of motions of anthropomorphic systems is an important interdisciplinary research topic involving specialists from many fields such as Robotics, Biomechanics, Physiology, Orthopedics, Psychology, Neurosciences, Sports, Computer Graphics and Applied Mathematics. This book presents a study of basic locomotion forms such as walking and running is of particular interest due to the high demand on dynamic coordination, actuator efficiency and balance control. Mathematical models and numerical simulation and optimization techniques are explained, in combination with experimental data, which can help to better understand the basic underlying mechanisms of these motions and to improve them. Example topics treated in this book are Modeling techniques for anthropomorphic bipedal walking systems Optimized walking motions for different objective functions Identification of objective functions from measurements Simulation and optimization approaches for humanoid robots Biologically inspired con...

Design, Modeling and Control of a Biped Line-Walking Robot

Directory of Open Access Journals (Sweden)

Ludan Wang

2010-12-01

Full Text Available The subject of this paper is the design and analysis of a biped line walking robot for inspection of power transmission lines. With a novel mechanism the centroid of the robot can be concentrated on the axis of hip joint to minimize the drive torque of the hip joint. The mechanical structure of the robot is discussed, as well as forward kinematics. Dynamic model is established in this paper to analyze the inverse kinematics for motion planning. The line-walking cycle of the line-walking robot is composed of a single-support phase and a double-support phase. Locomotion of the line-walking robot is discussed in details and the obstacle-navigation process is planed according to the structure of power transmission line. To fulfill the demands of line-walking, a control system and trajectories generation method are designed for the prototype of the line-walking robot. The feasibility of this concept is then confirmed by performing experiments with a simulated line environment.

Scaling Limit of Symmetric Random Walk in High-Contrast Periodic Environment

Science.gov (United States)

Piatnitski, A.; Zhizhina, E.

2017-11-01

The paper deals with the asymptotic properties of a symmetric random walk in a high contrast periodic medium in Z^d, d≥1. From the existing homogenization results it follows that under diffusive scaling the limit behaviour of this random walk need not be Markovian. The goal of this work is to show that if in addition to the coordinate of the random walk in Z^d we introduce an extra variable that characterizes the position of the random walk inside the period then the limit dynamics of this two-component process is Markov. We describe the limit process and observe that the components of the limit process are coupled. We also prove the convergence in the path space for the said random walk.

Influence of dynamic topography on landscape evolution and passive continental margin stratigraphy

Science.gov (United States)

Ding, Xuesong; Salles, Tristan; Flament, Nicolas; Rey, Patrice

2017-04-01

Quantifying the interaction between surface processes and tectonics/deep Earth processes is one important aspect of landscape evolution modelling. Both observations and results from numerical modelling indicate that dynamic topography - a surface expression of time-varying mantle convection - plays a significant role in shaping landscape through geological time. Recent research suggests that dynamic topography also has non-negligible effects on stratigraphic architecture by modifying accommodation space available for sedimentation. In addition, dynamic topography influences the sediment supply to continental margins. We use Badlands to investigate the evolution of a continental-scale landscape in response to transient dynamic uplift or subsidence, and to model the stratigraphic development on passive continental margins in response to sea-level change, thermal subsidence and dynamic topography. We consider a circularly symmetric landscape consisting of a plateau surrounded by a gently sloping continental plain and a continental margin, and a linear wave of dynamic topography. We analyze the evolution of river catchments, of longitudinal river profiles and of the χ values to evaluate the dynamic response of drainage systems to dynamic topography. We calculate the amount of cumulative erosion and deposition, and sediment flux at shoreline position, as a function of precipitation rate and erodibility coefficient. We compute the stratal stacking pattern and Wheeler diagram on vertical cross-sections at the continental margin. Our results indicate that dynamic topography 1) has a considerable influence on drainage reorganization; 2) contributes to shoreline migration and the distribution of depositional packages by modifying the accommodation space; 3) affects sediment supply to the continental margin. Transient dynamic topography contributes to the migration of drainage divides and to the migration of the mainstream in a drainage basin. The dynamic uplift

Estimation of numerical uncertainty in computational fluid dynamics simulations of a passively controlled wave energy converter

DEFF Research Database (Denmark)

Wang, Weizhi; Wu, Minghao; Palm, Johannes

2018-01-01

for almost linear incident waves. First, we show that the computational fluid dynamics simulations have acceptable agreement to experimental data. We then present a verification and validation study focusing on the solution verification covering spatial and temporal discretization, iterative and domain......The wave loads and the resulting motions of floating wave energy converters are traditionally computed using linear radiation–diffraction methods. Yet for certain cases such as survival conditions, phase control and wave energy converters operating in the resonance region, more complete...... dynamics simulations have largely been overlooked in the wave energy sector. In this article, we apply formal verification and validation techniques to computational fluid dynamics simulations of a passively controlled point absorber. The phase control causes the motion response to be highly nonlinear even...

Walking stability during cell phone use in healthy adults.

Science.gov (United States)

Kao, Pei-Chun; Higginson, Christopher I; Seymour, Kelly; Kamerdze, Morgan; Higginson, Jill S

2015-05-01

The number of falls and/or accidental injuries associated with cellular phone use during walking is growing rapidly. Understanding the effects of concurrent cell phone use on human gait may help develop safety guidelines for pedestrians. It was shown previously that older adults had more pronounced dual-task interferences than younger adults when concurrent cognitive task required visual information processing. Thus, cell phone use might have greater impact on walking stability in older than in younger adults. This study examined gait stability and variability during a cell phone dialing task (phone) and two classic cognitive tasks, the Paced Auditory Serial Addition Test (PASAT) and Symbol Digit Modalities Test (SDMT). Nine older and seven younger healthy adults walked on a treadmill at four different conditions: walking only, PASAT, phone, and SDMT. We computed short-term local divergence exponent (LDE) of the trunk motion (local stability), dynamic margins of stability (MOS), step spatiotemporal measures, and kinematic variability. Older and younger adults had similar values of short-term LDE during all conditions, indicating that local stability was not affected by the dual-task. Compared to walking only, older and younger adults walked with significantly greater average mediolateral MOS during phone and SDMT conditions but significantly less ankle angle variability during all dual-tasks and less knee angle variability during PASAT. The current findings demonstrate that healthy adults may try to control foot placement and joint kinematics during cell phone use or another cognitive task with a visual component to ensure sufficient dynamic margins of stability and maintain local stability. Copyright © 2015 Elsevier B.V. All rights reserved.

Electrocortical correlates of human level-ground, slope, and stair walking.

Directory of Open Access Journals (Sweden)

Trieu Phat Luu

Full Text Available This study investigated electrocortical dynamics of human walking across different unconstrained walking conditions (i.e., level ground (LW, ramp ascent (RA, and stair ascent (SA. Non-invasive active-electrode scalp electroencephalography (EEG signals were recorded and a systematic EEG processing method was implemented to reduce artifacts. Source localization combined with independent component analysis and k-means clustering revealed the involvement of four clusters in the brain during the walking tasks: Left and Right Occipital Lobe (LOL, ROL, Posterior Parietal Cortex (PPC, and Central Sensorimotor Cortex (SMC. Results showed that the changes of spectral power in the PPC and SMC clusters were associated with the level of motor task demands. Specifically, we observed α and β suppression at the beginning of the gait cycle in both SA and RA walking (relative to LW in the SMC. Additionally, we observed significant β rebound (synchronization at the initial swing phase of the gait cycle, which may be indicative of active cortical signaling involved in maintaining the current locomotor state. An increase of low γ band power in this cluster was also found in SA walking. In the PPC, the low γ band power increased with the level of task demands (from LW to RA and SA. Additionally, our results provide evidence that electrocortical amplitude modulations (relative to average gait cycle are correlated with the level of difficulty in locomotion tasks. Specifically, the modulations in the PPC shifted to higher frequency bands when the subjects walked in RA and SA conditions. Moreover, low γ modulations in the central sensorimotor area were observed in the LW walking and shifted to lower frequency bands in RA and SA walking. These findings extend our understanding of cortical dynamics of human walking at different level of locomotion task demands and reinforces the growing body of literature supporting a shared-control paradigm between spinal and

Active and passive spatial learning in human navigation: acquisition of survey knowledge.

Science.gov (United States)

Chrastil, Elizabeth R; Warren, William H

2013-09-01

It seems intuitively obvious that active exploration of a new environment would lead to better spatial learning than would passive visual exposure. It is unclear, however, which components of active learning contribute to spatial knowledge, and previous literature is decidedly mixed. This experiment tests the contributions of 4 components to metric survey knowledge: visual, vestibular, and podokinetic information and cognitive decision making. In the learning phase, 6 groups of participants learned the locations of 8 objects in a virtual hedge maze by (a) walking, (b) being pushed in a wheelchair, or (c) watching a video, crossed with (1) making decisions about their path or (2) being guided through the maze. In the test phase, survey knowledge was assessed by having participants walk a novel shortcut from a starting object to the remembered location of a test object, with the maze removed. Performance was slightly better than chance in the passive video condition. The addition of vestibular information did not improve performance in the wheelchair condition, but the addition of podokinetic information significantly improved angular accuracy in the walking condition. In contrast, there was no effect of decision making in any condition. The results indicate that visual and podokinetic information significantly contribute to survey knowledge, whereas vestibular information and decision making do not. We conclude that podokinetic information is the primary component of active learning for the acquisition of metric survey knowledge. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Gait Selection and Transition of Passivity-Based Bipeds with Adaptable Ankle Stiffness

Directory of Open Access Journals (Sweden)

Yan Huang

2012-10-01

Full Text Available Stable bipedal walking is one of the most important components of humanoid robot design, which can help us better understand natural human walking. In this paper, to study gait selection and gait transition of efficient bipedal walking, we proposed a dynamic bipedal walking model with an upper body, flat feet and compliant joints. The model can achieve stable cyclic motion with different walking gaits. The hip actuation and ankle stiffness behavior of the model are quite similar to those of human normal walking. In simulation, we studied the influence of hip actuation and ankle stiffness on walking performance of each gait. The effects of ankle stiffness on gait selection are also analyzed. Gait transition is realized by adjusting ankle stiffness during walking.

Walk Score(TM), Perceived Neighborhood Walkability, and walking in the US.

Science.gov (United States)

Tuckel, Peter; Milczarski, William

2015-03-01

To investigate both the Walk Score(TM) and a self-reported measure of neighborhood walkability ("Perceived Neighborhood Walkability") as estimators of transport and recreational walking among Americans. The study is based upon a survey of a nationally-representative sample of 1224 American adults. The survey gauged walking for both transport and recreation and included a self-reported measure of neighborhood walkability and each respondent's Walk Score(TM). Binary logistic and linear regression analyses were performed on the data. The Walk Score(TM) is associated with walking for transport, but not recreational walking nor total walking. Perceived Neighborhood Walkability is associated with transport, recreational and total walking. Perceived Neighborhood Walkability captures the experiential nature of walking more than the Walk Score(TM).

Biomechanics of stair walking and jumping.

Science.gov (United States)

Loy, D J; Voloshin, A S

1991-01-01

Physical activities such as stair walking and jumping result in increased dynamic loading on the human musculoskeletal system. Use of light weight, externally attached accelerometers allows for in-vivo monitoring of the shock waves invading the human musculoskeletal system during those activities. Shock waves were measured in four subjects performing stair walking up and down, jumping in place and jumping off a fixed elevation. The results obtained show that walking down a staircase induced shock waves with amplitude of 130% of that observed in walking up stairs and 250% of the shock waves experienced in level gait. The jumping test revealed levels of the shock waves nearly eight times higher than that in level walking. It was also shown that the shock waves invading the human musculoskeletal system may be generated not only by the heel strike, but also by the metatarsal strike. To moderate the risk of degenerative joint disorders four types of viscoelastic insoles were utilized to reduce the impact generated shock waves. The insoles investigated were able to reduce the amplitude of the shock wave by between 9% and 41% depending on the insole type and particular physical activity. The insoles were more effective in the reduction of the heel strike impacts than in the reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping trials than in the stair walking studies. The insoles were ranked in three groups on the basis of their shock absorbing capacity.

Walking pattern classification and walking distance estimation algorithms using gait phase information.

Science.gov (United States)

Wang, Jeen-Shing; Lin, Che-Wei; Yang, Ya-Ting C; Ho, Yu-Jen

2012-10-01

This paper presents a walking pattern classification and a walking distance estimation algorithm using gait phase information. A gait phase information retrieval algorithm was developed to analyze the duration of the phases in a gait cycle (i.e., stance, push-off, swing, and heel-strike phases). Based on the gait phase information, a decision tree based on the relations between gait phases was constructed for classifying three different walking patterns (level walking, walking upstairs, and walking downstairs). Gait phase information was also used for developing a walking distance estimation algorithm. The walking distance estimation algorithm consists of the processes of step count and step length estimation. The proposed walking pattern classification and walking distance estimation algorithm have been validated by a series of experiments. The accuracy of the proposed walking pattern classification was 98.87%, 95.45%, and 95.00% for level walking, walking upstairs, and walking downstairs, respectively. The accuracy of the proposed walking distance estimation algorithm was 96.42% over a walking distance.

Seismic passive earth resistance using modified pseudo-dynamic method

Science.gov (United States)

Pain, Anindya; Choudhury, Deepankar; Bhattacharyya, S. K.

2017-04-01

In earthquake prone areas, understanding of the seismic passive earth resistance is very important for the design of different geotechnical earth retaining structures. In this study, the limit equilibrium method is used for estimation of critical seismic passive earth resistance for an inclined wall supporting horizontal cohesionless backfill. A composite failure surface is considered in the present analysis. Seismic forces are computed assuming the backfill soil as a viscoelastic material overlying a rigid stratum and the rigid stratum is subjected to a harmonic shaking. The present method satisfies the boundary conditions. The amplification of acceleration depends on the properties of the backfill soil and on the characteristics of the input motion. The acceleration distribution along the depth of the backfill is found to be nonlinear in nature. The present study shows that the horizontal and vertical acceleration distribution in the backfill soil is not always in-phase for the critical value of the seismic passive earth pressure coefficient. The effect of different parameters on the seismic passive earth pressure is studied in detail. A comparison of the present method with other theories is also presented, which shows the merits of the present study.

Passive cavitation imaging with ultrasound arrays.

Science.gov (United States)

Salgaonkar, Vasant A; Datta, Saurabh; Holland, Christy K; Mast, T Douglas

2009-12-01

A method is presented for passive imaging of cavitational acoustic emissions using an ultrasound array, with potential application in real-time monitoring of ultrasound ablation. To create such images, microbubble emissions were passively sensed by an imaging array and dynamically focused at multiple depths. In this paper, an analytic expression for a passive image is obtained by solving the Rayleigh-Sommerfield integral, under the Fresnel approximation, and passive images were simulated. A 192-element array was used to create passive images, in real time, from 520-kHz ultrasound scattered by a 1-mm steel wire. Azimuthal positions of this target were accurately estimated from the passive images. Next, stable and inertial cavitation was passively imaged in saline solution sonicated at 520 kHz. Bubble clusters formed in the saline samples were consistently located on both passive images and B-scans. Passive images were also created using broadband emissions from bovine liver sonicated at 2.2 MHz. Agreement was found between the images and source beam shape, indicating an ability to map therapeutic ultrasound beams in situ. The relation between these broadband emissions, sonication amplitude, and exposure conditions are discussed.

Effects of nasal positive expiratory pressure on dynamic hyperinflation and 6-minute walk test in patients with COPD.

Science.gov (United States)

Wibmer, Thomas; Rüdiger, Stefan; Heitner, Claudia; Kropf-Sanchen, Cornelia; Blanta, Ioanna; Stoiber, Kathrin M; Rottbauer, Wolfgang; Schumann, Christian

2014-05-01

Dynamic hyperinflation is an important target in the treatment of COPD. There is increasing evidence that positive expiratory pressure (PEP) could reduce dynamic hyperinflation during exercise. PEP application through a nasal mask and a flow resistance device might have the potential to be used during daily physical activities as an auxiliary strategy of ventilatory assistance. The aim of this study was to determine the effects of nasal PEP on lung volumes during physical exercise in patients with COPD. Twenty subjects (mean ± SD age 69.4 ± 6.4 years) with stable mild-to-severe COPD were randomized to undergo physical exercise with nasal PEP breathing, followed by physical exercise with habitual breathing, or vice versa. Physical exercise was induced by a standard 6-min walk test (6 MWT) protocol. PEP was applied by means of a silicone nasal mask loaded with a fixed-orifice flow resistor. Body plethysmography was performed immediately pre-exercise and post-exercise. Differences in mean pre- to post-exercise changes in total lung capacity (-0.63 ± 0.80 L, P = .002), functional residual capacity (-0.48 ± 0.86 L, P = .021), residual volume (-0.56 ± 0.75 L, P = .004), S(pO2) (-1.7 ± 3.4%, P = .041), and 6 MWT distance (-30.8 ± 30.0 m, P = .001) were statistically significant between the experimental and the control interventions. The use of flow-dependent expiratory pressure, applied with a nasal mask and a PEP device, might promote significant reduction of dynamic hyperinflation during walking exercise. Further studies are warranted addressing improvements in endurance performance under regular application of nasal PEP during physical activities.

Differences in physical-fitness test scores between actively and passively recruited older adults : Consequences for norm-based classification

NARCIS (Netherlands)

van Heuvelen, M.J.G.; Stevens, M.; Kempen, G.I.J.M.

This study investigated differences in physical-fitness test scores between actively and passively recruited older adults and the consequences thereof for norm-based classification of individuals. Walking endurance, grip strength, hip flexibility, balance, manual dexterity, and reaction time were

Effect of orientation dynamics on the growth of a passive vector in a family of model flows

International Nuclear Information System (INIS)

Gonzalez, M

2014-01-01

The stretching properties of a parameterized model flow used to study the fast dynamo (Tanner and Hughes 2003 Astrophys. J. 586 685–91) are analyzed by paying special attention to the dependence of the growth rate of a passive vector on its orientation with respect to strain principal axes. More specifically, the study brings out that, rather than strain intensity, it is the dynamics of orientation resulting from the alternating tilting of the strain principal axes that explains the evolution of the passive vector mean growth rate in this class of flows. On a more general level, this view of stretching may bring an alternative understanding of the growth mechanisms of vectors such as the magnetic field vector. (paper)

Signatures of active and passive optimized Lévy searching in jellyfish.

Science.gov (United States)

Reynolds, Andy M

2014-10-06

Some of the strongest empirical support for Lévy search theory has come from telemetry data for the dive patterns of marine predators (sharks, bony fishes, sea turtles and penguins). The dive patterns of the unusually large jellyfish Rhizostoma octopus do, however, sit outside of current Lévy search theory which predicts that a single search strategy is optimal. When searching the water column, the movement patterns of these jellyfish change over time. Movement bouts can be approximated by a variety of Lévy and Brownian (exponential) walks. The adaptive value of this variation is not known. On some occasions movement pattern data are consistent with the jellyfish prospecting away from a preferred depth, not finding an improvement in conditions elsewhere and so returning to their original depth. This 'bounce' behaviour also sits outside of current Lévy walk search theory. Here, it is shown that the jellyfish movement patterns are consistent with their using optimized 'fast simulated annealing'--a novel kind of Lévy walk search pattern--to locate the maximum prey concentration in the water column and/or to locate the strongest of many olfactory trails emanating from more distant prey. Fast simulated annealing is a powerful stochastic search algorithm for locating a global maximum that is hidden among many poorer local maxima in a large search space. This new finding shows that the notion of active optimized Lévy walk searching is not limited to the search for randomly and sparsely distributed resources, as previously thought, but can be extended to embrace other scenarios, including that of the jellyfish R. octopus. In the presence of convective currents, it could become energetically favourable to search the water column by riding the convective currents. Here, it is shown that these passive movements can be represented accurately by Lévy walks of the type occasionally seen in R. octopus. This result vividly illustrates that Lévy walks are not necessarily

Who walks? Factors associated with walking behavior in disabled older women with and without self-reported walking difficulty.

Science.gov (United States)

Simonsick, E M; Guralnik, J M; Fried, L P

1999-06-01

To determine how severity of walking difficulty and sociodemographic, psychosocial, and health-related factors influence walking behavior in disabled older women. Cross-sectional analyses of baseline data from the Women's Health and Aging Study (WHAS). An urban community encompassing 12 contiguous zip code areas in the eastern portion of Baltimore City and part of Baltimore County, Maryland. A total of 920 moderately to severely disabled community-resident women, aged 65 years and older, identified from an age-stratified random sample of Medicare beneficiaries. Walking behavior was defined as minutes walked for exercise and total blocks walked per week. Independent variables included self-reported walking difficulty, sociodemographic factors, psychological status (depression, mastery, anxiety, and cognition), and health-related factors (falls and fear of falling, fatigue, vision and balance problems, weight, smoking, and cane use). Walking at least 8 blocks per week was strongly negatively related to severity of walking difficulty. Independent of difficulty level, older age, black race, fatigue, obesity, and cane use were also negatively associated with walking; living alone and high mastery had a positive association with walking. Even among functionally limited women, sociocultural, psychological, and health-related factors were independently associated with walking behavior. Thus, programs aimed at improving walking ability need to address these factors in addition to walking difficulties to maximize participation and compliance.

A Control Framework for Anthropomorphic Biped Walking Based on Stabilizing Feedforward Trajectories.

Science.gov (United States)

Rezazadeh, Siavash; Gregg, Robert D

2016-10-01

Although dynamic walking methods have had notable successes in control of bipedal robots in the recent years, still most of the humanoid robots rely on quasi-static Zero Moment Point controllers. This work is an attempt to design a highly stable controller for dynamic walking of a human-like model which can be used both for control of humanoid robots and prosthetic legs. The method is based on using time-based trajectories that can induce a highly stable limit cycle to the bipedal robot. The time-based nature of the controller motivates its use to entrain a model of an amputee walking, which can potentially lead to a better coordination of the interaction between the prosthesis and the human. The simulations demonstrate the stability of the controller and its robustness against external perturbations.

Human-Robot Interaction: Does Robotic Guidance Force Affect Gait-Related Brain Dynamics during Robot-Assisted Treadmill Walking?

Directory of Open Access Journals (Sweden)

Kristel Knaepen

Full Text Available In order to determine optimal training parameters for robot-assisted treadmill walking, it is essential to understand how a robotic device interacts with its wearer, and thus, how parameter settings of the device affect locomotor control. The aim of this study was to assess the effect of different levels of guidance force during robot-assisted treadmill walking on cortical activity. Eighteen healthy subjects walked at 2 km.h-1 on a treadmill with and without assistance of the Lokomat robotic gait orthosis. Event-related spectral perturbations and changes in power spectral density were investigated during unassisted treadmill walking as well as during robot-assisted treadmill walking at 30%, 60% and 100% guidance force (with 0% body weight support. Clustering of independent components revealed three clusters of activity in the sensorimotor cortex during treadmill walking and robot-assisted treadmill walking in healthy subjects. These clusters demonstrated gait-related spectral modulations in the mu, beta and low gamma bands over the sensorimotor cortex related to specific phases of the gait cycle. Moreover, mu and beta rhythms were suppressed in the right primary sensory cortex during treadmill walking compared to robot-assisted treadmill walking with 100% guidance force, indicating significantly larger involvement of the sensorimotor area during treadmill walking compared to robot-assisted treadmill walking. Only marginal differences in the spectral power of the mu, beta and low gamma bands could be identified between robot-assisted treadmill walking with different levels of guidance force. From these results it can be concluded that a high level of guidance force (i.e., 100% guidance force and thus a less active participation during locomotion should be avoided during robot-assisted treadmill walking. This will optimize the involvement of the sensorimotor cortex which is known to be crucial for motor learning.

Human-Robot Interaction: Does Robotic Guidance Force Affect Gait-Related Brain Dynamics during Robot-Assisted Treadmill Walking?

Science.gov (United States)

Knaepen, Kristel; Mierau, Andreas; Swinnen, Eva; Fernandez Tellez, Helio; Michielsen, Marc; Kerckhofs, Eric; Lefeber, Dirk; Meeusen, Romain

2015-01-01

In order to determine optimal training parameters for robot-assisted treadmill walking, it is essential to understand how a robotic device interacts with its wearer, and thus, how parameter settings of the device affect locomotor control. The aim of this study was to assess the effect of different levels of guidance force during robot-assisted treadmill walking on cortical activity. Eighteen healthy subjects walked at 2 km.h-1 on a treadmill with and without assistance of the Lokomat robotic gait orthosis. Event-related spectral perturbations and changes in power spectral density were investigated during unassisted treadmill walking as well as during robot-assisted treadmill walking at 30%, 60% and 100% guidance force (with 0% body weight support). Clustering of independent components revealed three clusters of activity in the sensorimotor cortex during treadmill walking and robot-assisted treadmill walking in healthy subjects. These clusters demonstrated gait-related spectral modulations in the mu, beta and low gamma bands over the sensorimotor cortex related to specific phases of the gait cycle. Moreover, mu and beta rhythms were suppressed in the right primary sensory cortex during treadmill walking compared to robot-assisted treadmill walking with 100% guidance force, indicating significantly larger involvement of the sensorimotor area during treadmill walking compared to robot-assisted treadmill walking. Only marginal differences in the spectral power of the mu, beta and low gamma bands could be identified between robot-assisted treadmill walking with different levels of guidance force. From these results it can be concluded that a high level of guidance force (i.e., 100% guidance force) and thus a less active participation during locomotion should be avoided during robot-assisted treadmill walking. This will optimize the involvement of the sensorimotor cortex which is known to be crucial for motor learning.

Experimental identification and analytical modelling of human walking forces: Literature review

Science.gov (United States)

Racic, V.; Pavic, A.; Brownjohn, J. M. W.

2009-09-01

Dynamic forces induced by humans walking change simultaneously in time and space, being random in nature and varying considerably not only between different people but also for a single individual who cannot repeat two identical steps. Since these important aspects of walking forces have not been adequately researched in the past, the corresponding lack of knowledge has reflected badly on the quality of their mathematical models used in vibration assessments of pedestrian structures such as footbridges, staircases and floors. To develop better force models which can be used with more confidence in the structural design, an adequate experimental and analytical approach must be taken to account for their complexity. This paper is the most comprehensive review published to date, of 270 references dealing with different experimental and analytical characterizations of human walking loading. The source of dynamic human-induced forces is in fact in the body motion. To date, human motion has attracted a lot of interest in many scientific branches, particularly in medical and sports science, bioengineering, robotics, and space flight programs. Other fields include biologists of various kinds, physiologists, anthropologists, computer scientists (graphics and animation), human factors and ergonomists, etc. It resulted in technologically advanced tools that can help understanding the human movement in more detail. Therefore, in addition to traditional direct force measurements utilizing a force plate and an instrumented treadmill, this review also introduces methods for indirect measurement of time-varying records of walking forces via combination of visual motion tracking (imaging) data and known body mass distribution. The review is therefore an interdisciplinary article that bridges the gaps between biomechanics of human gait and civil engineering dynamics. Finally, the key reason for undertaking this review is the fact that human-structure dynamic interaction and

Mobile dynamic passive sampling of trace organic compounds: Evaluation of sampler performance in the Danube River.

Science.gov (United States)

Vrana, Branislav; Smedes, Foppe; Allan, Ian; Rusina, Tatsiana; Okonski, Krzysztof; Hilscherová, Klára; Novák, Jiří; Tarábek, Peter; Slobodník, Jaroslav

2018-03-29

A "dynamic" passive sampling (DPS) device, consisting of an electrically driven large volume water pumping device coupled to a passive sampler exposure cell, was designed to enhance the sampling rate of trace organic compounds. The purpose of enhancing the sampling rate was to achieve sufficient method sensitivity, when the period available for sampling is limited to a few days. Because the uptake principle in the DPS remains the same as for conventionally-deployed passive samplers, free dissolved concentrations can be derived from the compound uptake using available passive sampler calibration parameters. This was confirmed by good agreement between aqueous concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) derived from DPS and conventional caged passive sampler. The DPS device enhanced sampling rates of compounds that are accumulated in samplers under water boundary layer control (WBL) more than five times compared with the conventionally deployed samplers. The DPS device was deployed from a ship cruising downstream the Danube River to provide temporally and spatially integrated concentrations. A DPS-deployed sampler with surface area of 400cm 2 can reach sampling rates up to 83Ld -1 . The comparison of three passive samplers made of different sorbents and co-deployed in the DPS device, namely silicone rubber (SR), low density polyethylene (LDPE) and SDB-RPS Empore™ disks showed a good correlation of surface specific uptake for compounds that were sampled integratively during the entire exposure period. This provided a good basis for a cross-calibration between the samplers. The good correlation of free dissolved PAHs, PCBs and HCB concentration estimates obtained using SR and LDPE confirmed that both samplers are suitable for the identification of concentration gradients and trends in the water column. We showed that the differences in calculated aqueous concentrations between sampler types

Design and Characterization of a Quasi-Passive Pneumatic Foot-Ankle Prosthesis.

Science.gov (United States)

Lee, Jeffrey D; Mooney, Luke M; Rouse, Elliott J

2017-07-01

The majority of commercially available passive prosthetic feet are not capable of providing joint mechanics that match that of the intact human ankle. Due to their cantilever design, their stiffness characteristics contrast with what has been observed in the biological ankle, namely, an increase in stiffness during the stance phase of walking. In this paper, we introduce the design and control of a pneumatic foot-ankle prosthesis that attempts to provide biomimetic mechanics. The prosthesis is comprised of a pneumatic cylinder in series with a fiberglass leaf spring, and a solenoid valve to control the flow of air between the two sides of the cylinder. The solenoid valve acts as a mechanical clutch, enabling resetting of the ankle's equilibrium position. By adjusting the pressure inside the cylinder, the prosthesis can be customized to provide a range of ankle mechanics. A mechanical testing machine is used to compare the torque-angle curve of the pneumatic prosthesis with a low-profile passive prosthetic foot. Finally, data are presented of one transtibial amputee walking with the prosthesis at 1.2 m/s. The testing shows that the pneumatic prosthesis is capable of providing an appropriate range of motion as well a maximum torque of 94 Nm, while returning approximately 11.5 J of energy.

Counting the corners of a random walk and its application to traffic flow

International Nuclear Information System (INIS)

Knorr, Florian; Schreckenberg, Michael

2012-01-01

We study a system with two types of interacting particles on a one-dimensional lattice. Particles of the first type, which we call ‘active’, are able to detect particles of the second type (called ‘passive’). By relating the problem to a discrete random walk in one dimension with a fixed number of steps we determine the fraction of active and detected particles for both open and periodic boundary conditions as well as for the case where passive particles interact with both or only one neighbors. In the random walk picture, where the two particles types stand for steps in opposite directions, passive particles are detected whenever the resulting path has a corner. For open boundary conditions, it turns out that a simple mean field approximation reproduces the exact result if the particles interact with one neighbor only. A practical application of this problem is heterogeneous traffic flow with communicating and non-communicating vehicles. In this context communicating vehicles can be thought of as active particles which can by front (and rear) sensors detect the vehicle ahead (and behind) although these vehicles do not actively share information. Therefore, we also present simulation results which show the validity of our analysis for real traffic flow. (paper)

Foot deformation during walking: differences between static and dynamic 3D foot morphology in developing feet.

Science.gov (United States)

Barisch-Fritz, Bettina; Schmeltzpfenning, Timo; Plank, Clemens; Grau, Stefan

2014-01-01

The complex functions of feet require a specific composition, which is progressively achieved by developmental processes. This development should take place without being affected by footwear. The aim of this study is to evaluate differences between static and dynamic foot morphology in developing feet. Feet of 2554 participants (6-16 years) were recorded using a new scanner system (DynaScan4D). Each foot was recorded in static half and full weight-bearing and during walking. Several foot measures corresponding to those used in last construction were calculated. The differences were identified by one-way ANOVA and paired Student's t-test. Static and dynamic values of each foot measure must be considered to improve the fit of footwear. In particular, footwear must account for the increase of forefoot width and the decrease of midfoot girth. Furthermore, the toe box should have a more rounded shape. The findings are important for the construction of footwear for developing feet.

Shared and task-specific muscle synergies of Nordic walking and conventional walking.

Science.gov (United States)

Boccia, G; Zoppirolli, C; Bortolan, L; Schena, F; Pellegrini, B

2018-03-01

Nordic walking is a form of walking that includes a poling action, and therefore an additional subtask, with respect to conventional walking. The aim of this study was to assess whether Nordic walking required a task-specific muscle coordination with respect to conventional walking. We compared the electromyographic (EMG) activity of 15 upper- and lower-limb muscles of 9 Nordic walking instructors, while executing Nordic walking and conventional walking at 1.3 ms -1 on a treadmill. Non-negative matrix factorization method was applied to identify muscle synergies, representing the spatial and temporal organization of muscle coordination. The number of muscle synergies was not different between Nordic walking (5.2 ± 0.4) and conventional walking (5.0 ± 0.7, P = .423). Five muscle synergies accounted for 91.2 ± 1.1% and 92.9 ± 1.2% of total EMG variance in Nordic walking and conventional walking, respectively. Similarity and cross-reconstruction analyses showed that 4 muscle synergies, mainly involving lower-limb and trunk muscles, are shared between Nordic walking and conventional walking. One synergy acting during upper limb propulsion is specific to Nordic walking, modifying the spatial organization and the magnitude of activation of upper limb muscles compared to conventional walking. The inclusion of the poling action in Nordic walking does not increase the complexity of movement control and does not change the coordination of lower limb muscles. This makes Nordic walking a physical activity suitable also for people with low motor skill. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

The development and study on passive natural circulation

International Nuclear Information System (INIS)

Zhou Tao; Li Jingjing; Ju Zhongyun; Huang Yanping; Xiao Zejun

2013-01-01

Passive natural circulation is getting more and more important in the field of nuclear power engineering. This article cited a passive natural circulation in the nuclear power system application, analyzed the potential problems during operation, described current mathematical research methods of the reliability of passive natural cycle analysis, briefly summarized the advantages and disadvantages of these methods, and finally got an outlook of the direction of passive natural circulation. Since the presence of passive natural circulation may get failure, sufficient attention and active research should be paid in response to the physical process failure of the running passive natural circulation system and its reliability. To ensure system security during the operation, the operation process should combine active with non-dynamic; while selecting an accurate model, perfect passive reliability analysis methods to achieve accurate theoretical calculations and experimental verification. (authors)

Functionality of the contralateral biceps femoris reflex response during human walking

DEFF Research Database (Denmark)

Stevenson, Andrew James Thomas; Geertsen, Svend Sparre; Sinkjaer, Thomas

2014-01-01

of the body in order to maintain dynamic equilibrium during walking. Therefore, we hypothesized that if we suddenly slowed the treadmill participants were walking on, the cBF reflex would be inhibited because the necessity to break the forward progression of the body would be decreased. Conversely, if we...... the treadmill velocity was altered concurrently or 50 ms after knee perturbation onset. These results, together with the finding that the cBF reflex response is under some cortical control [1], strongly suggest a functional role for the cBF reflex during walking that is adaptable to the environmental situation....

Disordered-quantum-walk-induced localization of a Bose-Einstein condensate

International Nuclear Information System (INIS)

Chandrashekar, C. M.

2011-01-01

We present an approach to induce localization of a Bose-Einstein condensate in a one-dimensional lattice under the influence of unitary quantum-walk evolution using disordered quantum coin operation. We introduce a discrete-time quantum-walk model in which the interference effect is modified to diffuse or strongly localize the probability distribution of the particle by assigning a different set of coin parameters picked randomly for each step of the walk, respectively. Spatial localization of the particle or state is explained by comparing the variance of the probability distribution of the quantum walk in position space using disordered coin operation to that of the walk using an identical coin operation for each step. Due to the high degree of control over quantum coin operation and most of the system parameters, ultracold atoms in an optical lattice offer opportunities to implement a disordered quantum walk that is unitary and induces localization. Here we present a scheme to use a Bose-Einstein condensate that can be evolved to the superposition of its internal states in an optical lattice and control the dynamics of atoms to observe localization. This approach can be adopted to any other physical system in which controlled disordered quantum walk can be implemented.

Random Walks on Homeo( S 1)

Science.gov (United States)

Malicet, Dominique

2017-12-01

In this paper, we study random walks {g_n=f_{n-1}\\ldots f_0} on the group Homeo ( S 1) of the homeomorphisms of the circle, where the homeomorphisms f k are chosen randomly, independently, with respect to a same probability measure {ν}. We prove that under the only condition that there is no probability measure invariant by {ν}-almost every homeomorphism, the random walk almost surely contracts small intervals. It generalizes what has been known on this subject until now, since various conditions on {ν} were imposed in order to get the phenomenon of contractions. Moreover, we obtain the surprising fact that the rate of contraction is exponential, even in the lack of assumptions of smoothness on the f k 's. We deduce various dynamical consequences on the random walk ( g n ): finiteness of ergodic stationary measures, distribution of the trajectories, asymptotic law of the evaluations, etc. The proof of the main result is based on a modification of the Ávila-Viana's invariance principle, working for continuous cocycles on a space fibred in circles.

Design of a Quasi-Passive Parallel Leg Exoskeleton to Augment Load Carrying for Walking

National Research Council Canada - National Science Library

Valiente, Andrew

2005-01-01

.... The exoskeleton structure runs parallel to the legs, transferring payload forces to the ground. In an attempt to make the exoskeleton more efficient, passive hip and ankle springs are employed to store and release energy throughout the gait cycle...

Image-Based Method for Determining Better Walking Strategies for Hexapods

Directory of Open Access Journals (Sweden)

Kazi Mostafa

2015-05-01

Full Text Available An intelligent walking strategy is vital for multi-legged robots possessing no a priori information of an environment when traversing across discontinuous terrain. Six-legged robots outperform other multi-legged robots in static and dynamic stability. However, hexapods require careful planning to traverse across discontinuous terrain. A hexapod walking strategy can be accomplished using a vision-based navigation system to identify the surrounding environment. This paper presents an image-based technique to achieve better walking strategies for a hexapod walking on a special terrain containing irregular, restricted regions. The properties of the restricted regions were acquired beforehand by using reliable surveillance means. Moreover, simplified forward gaits, better rotational gaits, and adaptive gait selection strategies for walking on discontinuous terrain were proposed. The hexapod can effectively switch the gait sequences and types according to the environment involved. The boundary of standing zones can be successfully labelled by applying the greyscale erosion comprising a structuring element similar in shape and size to the foot tip of the hexapod. The experimental results demonstrated that the proposed image-based technique significantly improved the walking strategies of hexapods traversing on discontinuous terrain.

Dynamic Characteristics of Rotors on Passive and Active Thrust Fluid-film Bearings with Fixed Pads

Directory of Open Access Journals (Sweden)

Babin Alexander

2018-01-01

Full Text Available Application of fluid-film bearings in rotor machines in many cases could have no alternative due to obvious advantages when compared to roller element bearings. Integration of information technology in mechanical engineering resulting in emergence of a new field of research – mechatronic bearings which allowed tracking condition of the most important parts of a machine and adjusting operational parameters of the system. Application of servo valves to control the flow rate through a fluid-film bearing is the most universal and simple way of rotor’s position control due to relative simplicity of modelling and absence of need to radically change the design of conventional hydrodynamic bearings. In the present paper numerical simulations of passive (conventional as opposed to mechatronic and active hybrid thrust fluid-film bearings with a central feeding chamber are presented, that are parts of a mechatronic rotor-bearing node. Numerical model of an active thrust bearing is based on solution of equations of hydrodynamics, rotor dynamics and an additional model of a servo valve. Various types of control have been investigated: P, PI and PID control, and the dynamic behaviour of a system has been estimated under various loads, namely static, periodic and impulse. A design of a test rig has been proposed to study passive and active thrust fluid-film bearings aimed at, among other, validation of numerical results of active bearings simulation.

GLOBAL RANDOM WALK SIMULATIONS FOR SENSITIVITY AND UNCERTAINTY ANALYSIS OF PASSIVE TRANSPORT MODELS

Directory of Open Access Journals (Sweden)

Nicolae Suciu

2011-07-01

Full Text Available The Global Random Walk algorithm (GRW performs a simultaneoustracking on a fixed grid of huge numbers of particles at costscomparable to those of a single-trajectory simulation by the traditional Particle Tracking (PT approach. Statistical ensembles of GRW simulations of a typical advection-dispersion process in groundwater systems with randomly distributed spatial parameters are used to obtain reliable estimations of the input parameters for the upscaled transport model and of their correlations, input-output correlations, as well as full probability distributions of the input and output parameters.

An online gait generator for quadruped walking using motor primitives

Directory of Open Access Journals (Sweden)

Chunlin Zhou

2016-11-01

Full Text Available This article presents implementation of an online gait generator on a quadruped robot. Firstly, the design of a quadruped robot is presented. The robot contains four leg modules each of which is constructed by a 2 degrees of freedom (2-DOF five-bar parallel linkage mechanism. Together with other two rotational DOF, the leg module is able to perform 4-DOF movement. The parallel mechanism of the robot allows all the servos attached on the body frame, so that the leg mass is decreased and motor load can be balanced. Secondly, an online gait generator based on dynamic movement primitives for the walking control is presented. Dynamic movement primitives provide an approach to generate periodic trajectories and they can be modulated in real time, which makes the online adjustment of walking gaits possible. This gait controller is tested by the quadruped robot in regulating walking speed, switching between forward\\backward movements and steering. The controller is easy to apply, expand and is quite effective on phase coordination and online trajectory modulation. Results of simulated experiments are presented.

Joint forces and torques when walking in shallow water.

Science.gov (United States)

Orselli, Maria Isabel Veras; Duarte, Marcos

2011-04-07

This study reports for the first time an estimation of the internal net joint forces and torques on adults' lower limbs and pelvis when walking in shallow water, taking into account the drag forces generated by the movement of their bodies in the water and the equivalent data when they walk on land. A force plate and a video camera were used to perform a two-dimensional gait analysis at the sagittal plane of 10 healthy young adults walking at comfortable speeds on land and in water at a chest-high level. We estimated the drag force on each body segment and the joint forces and torques at the ankle, knee, and hip of the right side of their bodies using inverse dynamics. The observed subjects' apparent weight in water was about 35% of their weight on land and they were about 2.7 times slower when walking in water. When the subjects walked in water compared with walking on land, there were no differences in the angular displacements but there was a significant reduction in the joint torques which was related to the water's depth. The greatest reduction was observed for the ankle and then the knee and no reduction was observed for the hip. All joint powers were significantly reduced in water. The compressive and shear joint forces were on average about three times lower during walking in water than on land. These quantitative results substantiate the use of water as a safe environment for practicing low-impact exercises, particularly walking. Copyright © 2011 Elsevier Ltd. All rights reserved.

Passivation Effects in Copper Thin Films

International Nuclear Information System (INIS)

Wiederhirn, G.; Nucci, J.; Richter, G.; Arzt, E.; Balk, T. J.; Dehm, G.

2006-01-01

We studied the influence of a 10 nm AlxOy passivation on the stress-temperature behavior of 100 nm and 1 μm thick Cu films. At low temperatures, the passivation induces a large tensile stress increase in the 100 nm film; however, its effect on the 1 μm film is negligible. At high temperatures, the opposite behavior is observed; while the passivation does not change the 100 nm film behavior, it strengthens the 1 μm film by driving it deeper into compression. These observations are explained in light of a combination of constrained diffusional creep and dislocation dynamics unique to ultra-thin films

Finite element analysis of high modal dynamic responses of a composite floor subjected to human motion under passive live load

Directory of Open Access Journals (Sweden)

Arash Behnia

Full Text Available Light weight and long span composite floors are common place in modern construction. A critical consequence of this application is undesired vibration which may cause excessive discomfort to occupants. This work investigates the composite floor vibration behavior of an existing building based on a comprehensive study of high modal dynamic responses, the range of which has been absent in previous studies and major analytical templates, of different panels under the influence of loads induced by human motion. The resulting fundamental natural frequency and vibration modes are first validated with respect to experimental and numerical evidences from literature. Departing from close correlation established in comparison, this study explores in detail the effects of intensity of passive live load as additional stationary mass due to crowd jumping as well as considering human structure interaction. From observation, a new approach in the simulation of passive live load through the consideration of human structure interaction and human body characteristics is proposed. It is concluded that higher vibration modes are essential to determine the minimum required modes and mass participation ratio in the case of vertical vibration. The results indicate the need to consider 30 modes of vibration to obtain all possible important excitations and thereby making third harmonic of load frequency available to excite the critical modes. In addition, presence of different intensities of passive live load on the composite floor showed completely different behavior in each particular panel associated with load location of panel and passive live load intensity. Furthermore, implementing human body characteristics in simulation causes an obvious increase in modal damping and hence better practicality and economical presentation can be achieved in structural dynamic behavior.

Functional roles of lower-limb joint moments while walking in water.

Science.gov (United States)

Miyoshi, Tasuku; Shirota, Takashi; Yamamoto, Shin-Ichiro; Nakazawa, Kimitaka; Akai, Masami

2005-02-01

To clarify the functional roles of lower-limb joint moments and their contribution to support and propulsion tasks while walking in water compared with that on land. Sixteen healthy, young subjects walked on land and in water at several different speeds with and without additional loads. Walking in water is a major rehabilitation therapy for patients with orthopedic disorders. However, the functional role of lower-limb joint moments while walking in water is still unclear. Kinematics, electromyographic activities in biceps femoris and gluteus maximums, and ground reaction forces were measured under the following conditions: walking on land and in water at a self-determined pace, slow walking on land, and fast walking in water with or without additional loads (8 kg). The hip, knee, and ankle joint moments were calculated by inverse dynamics. The contribution of the walking speed increased the hip extension moment, and the additional weight increased the ankle plantar flexion and knee extension moment. The major functional role was different in each lower-limb joint muscle. That of the muscle group in the ankle is to support the body against gravity, and that of the muscle group involved in hip extension is to contribute to propulsion. In addition, walking in water not only reduced the joint moments but also completely changed the inter-joint coordination. It is of value for clinicians to be aware that the greater the viscosity of water produces a greater load on the hip joint when fast walking in water.

Towards Quantification of Glacier Dynamic Ice Loss through Passive Seismic Monitoring

Science.gov (United States)

Köhler, A.; Nuth, C.; Weidle, C.; Schweitzer, J.; Kohler, J.; Buscaino, G.

2015-12-01

Global glaciers and ice caps loose mass through calving, while existing models are currently not equipped to realistically predict dynamic ice loss. This is mainly because long-term continuous calving records, that would help to better understand fine scale processes and key climatic-dynamic feedbacks between calving, climate, terminus evolution and marine conditions, do not exist. Combined passive seismic/acoustic strategies are the only technique able to capture rapid calving events continuously, independent of daylight or meteorological conditions. We have produced such a continuous calving record for Kronebreen, a tidewater glacier in Svalbard, using data from permanent seismic stations between 2001 and 2014. However, currently no method has been established in cryo-seismology to quantify the calving ice loss directly from seismic data. Independent calibration data is required to derive 1) a realistic estimation of the dynamic ice loss unobserved due to seismic noise and 2) a robust scaling of seismic calving signals to ice volumes. Here, we analyze the seismic calving record at Kronebreen and independent calving data in a first attempt to quantify ice loss directly from seismic records. We make use of a) calving flux data with weekly to monthly resolution obtained from satellite remote sensing and GPS data between 2007 and 2013, and b) direct, visual calving observations in two weeks in 2009 and 2010. Furthermore, the magnitude-scaling property of seismic calving events is analyzed. We derive and discuss an empirical relation between seismic calving events and calving flux which for the first time allows to estimate a time series of calving volumes more than one decade back in time. Improving our model requires to incorporate more precise, high-resolution calibration data. A new field campaign will combine innovative, multi-disciplinary monitoring techniques to measure calving ice volumes and dynamic ice-ocean interactions simultaneously with terrestrial laser

Nonlinear dynamic behaviour of a rotor-foundation system coupled through passive magnetic bearings with magnetic anisotropy - Theory and experiment

DEFF Research Database (Denmark)

Enemark, Søren; Santos, Ilmar F.

2016-01-01

In this work, the nonlinear dynamic behaviour of a vertical rigid rotor interacting with a flexible foundation by means of two passive magnetic bearings is quantified and evaluated. The quantification is based on theoretical and experimental investigation of the non-uniformity (anisotropy......) of the magnetic field and the weak nonlinearity of the magnetic forces. Through mathematical modelling the nonlinear equations of motion are established for describing the shaft and bearing housing lateral dynamics coupled via the nonlinear and non-uniform magnetic forces. The equations of motion are solved...

Two-particle quantum walks applied to the graph isomorphism problem

International Nuclear Information System (INIS)

Gamble, John King; Friesen, Mark; Zhou Dong; Joynt, Robert; Coppersmith, S. N.

2010-01-01

We show that the quantum dynamics of interacting and noninteracting quantum particles are fundamentally different in the context of solving a particular computational problem. Specifically, we consider the graph isomorphism problem, in which one wishes to determine whether two graphs are isomorphic (related to each other by a relabeling of the graph vertices), and focus on a class of graphs with particularly high symmetry called strongly regular graphs (SRGs). We study the Green's functions that characterize the dynamical evolution single-particle and two-particle quantum walks on pairs of nonisomorphic SRGs and show that interacting particles can distinguish nonisomorphic graphs that noninteracting particles cannot. We obtain the following specific results. (1) We prove that quantum walks of two noninteracting particles, fermions or bosons, cannot distinguish certain pairs of nonisomorphic SRGs. (2) We demonstrate numerically that two interacting bosons are more powerful than single particles and two noninteracting particles, in that quantum walks of interacting bosons distinguish all nonisomorphic pairs of SRGs that we examined. By utilizing high-throughput computing to perform over 500 million direct comparisons between evolution operators, we checked all tabulated pairs of nonisomorphic SRGs, including graphs with up to 64 vertices. (3) By performing a short-time expansion of the evolution operator, we derive distinguishing operators that provide analytic insight into the power of the interacting two-particle quantum walk.

Welfare assessment in broiler farms: transect walks versus individual scoring.

Science.gov (United States)

Marchewka, J; Watanabe, T T N; Ferrante, V; Estevez, I

2013-10-01

Current scientific approaches to welfare assessment in broilers are based on individual sampling that can be time consuming under field conditions. On the other hand, farmers conduct routine checks based on walks through the house to screen birds' health condition. We adapted the walks through following line transect methodology used in wildlife studies to explore their feasibility as a welfare assessment tool. The aim of this study was to compare broiler welfare assessed by individual sampling and transect walks. We evaluated 6 identically managed flocks. For individual sampling, we collected measures on 150 birds, including weight, breast dirtiness, hock and footpad dermatitis, lameness, and immobility. Transect observations were conducted by slowly walking on randomized paths within each house recording: immobility, lameness, back dirtiness, sickness, agony, and dead. Transect walks allowed detection of small variations (P < 0.003) in the prevalence of most welfare indicators considered with consistency in interobserver reliability (P ≥ 0.05). In addition, assessments across transects were highly consistent (P ≥ 0.05). Individual sampling was also sensitive to differences across houses (P < 0.01) with the exception of immobility (P = 0.783). No differences were found across sampling locations (P ≥ 0.05). However, both methods differed greatly in the frequency of the incidence of the parameters considered. For example, immobility varied from 0.2 ± 0.02% for transect walks to 4 ± 2.3% for individual sampling, whereas lameness varied between 0.8 ± 0.07% and 24.2 ± 4.7% for transect and samplings, respectively. It is possible that the transect approach may have overlooked walking deficiencies because a large number of birds were scored, although if this was the case, the consistency obtained in the scoring across observers and transects would be surprising. Differences may also be related to possibly biased individual sampling procedures, where less mobile

The Effect of Foot Progression Angle on Knee Joint Compression Force during Walking

DEFF Research Database (Denmark)

Baldvinsson, Henrik Koblauch; Heilskov-Hansen, Thomas; Alkjær, Tine

2013-01-01

males walked at a fixed speed of 4.5 km/h under three conditions: Normal walking, internally rotated and externally rotated. All gait-trials were recorded by six infrared cameras. Net joint moments were calculated by 3D inverse dynamics. The results revealed that the medial knee joint compartment......It is unclear how rotations of the lower limb affect the knee joint compression forces during walking. Increases in the frontal plane knee moment have been reported when walking with internally rotated feet and a decrease when walking with externally rotated feet. The aim of this study...... was to investigate the knee joint compressive forces during walking with internal, external and normal foot rotation and to determine if the frontal plane knee joint moment is an adequate surrogate for the compression forces in the medial and lateral knee joint compartments under such gait modifications. Ten healthy...

Swing-Leg Retraction for Limit Cycle Walkers Improves Disturbance Rejection

NARCIS (Netherlands)

Hobbelen, D.G.E.; Wisse, M.

2008-01-01

Limit cycle walkers are bipeds that exhibit a stable cyclic gaitwithout requiring local controllability at all times during gait. A well-known example of limit cycle walking is McGeer’s “passive dynamic walking,” but the concept expands to actuated bipeds as involved in this study. One of the

The effect of ankle foot orthosis stiffness on the energy cost of walking: a simulation study.

Science.gov (United States)

Bregman, D J J; van der Krogt, M M; de Groot, V; Harlaar, J; Wisse, M; Collins, S H

2011-11-01

In stroke and multiple sclerosis patients, gait is frequently hampered by a reduced ability to push-off with the ankle caused by weakness of the plantar-flexor muscles. To enhance ankle push-off and to decrease the high energy cost of walking, spring-like carbon-composite Ankle Foot Orthoses are frequently prescribed. However, it is unknown what Ankle Foot Orthoses stiffness should be used to obtain the most efficient gait. The aim of this simulation study was to gain insights into the effect of variation in Ankle Foot Orthosis stiffness on the amount of energy stored in the Ankle Foot Orthosis and the energy cost of walking. We developed a two-dimensional forward-dynamic walking model with a passive spring at the ankle representing the Ankle Foot Orthosis and two constant torques at the hip for propulsion. We varied Ankle Foot Orthosis stiffness while keeping speed and step length constant. We found an optimal stiffness, at which the energy delivered at the hip joint was minimal. Energy cost decreased with increasing energy storage in the ankle foot orthosis, but the most efficient gait did not occur with maximal energy storage. With maximum storage, push-off occurred too late to reduce the impact of the contralateral leg with the floor. Maximum return prior to foot strike was also suboptimal, as push-off occurred too early and its effects were subsequently counteracted by gravity. The optimal Ankle Foot Orthosis stiffness resulted in significant push-off timed just prior to foot strike and led to greater ankle plantar-flexion velocity just before contralateral foot strike. Our results suggest that patient energy cost might be reduced by the proper choice of Ankle Foot Orthosis stiffness. Copyright © 2011 Elsevier Ltd. All rights reserved.

Groups, graphs and random walks

CERN Document Server

Salvatori, Maura; Sava-Huss, Ecaterina

2017-01-01

An accessible and panoramic account of the theory of random walks on groups and graphs, stressing the strong connections of the theory with other branches of mathematics, including geometric and combinatorial group theory, potential analysis, and theoretical computer science. This volume brings together original surveys and research-expository papers from renowned and leading experts, many of whom spoke at the workshop 'Groups, Graphs and Random Walks' celebrating the sixtieth birthday of Wolfgang Woess in Cortona, Italy. Topics include: growth and amenability of groups; Schrödinger operators and symbolic dynamics; ergodic theorems; Thompson's group F; Poisson boundaries; probability theory on buildings and groups of Lie type; structure trees for edge cuts in networks; and mathematical crystallography. In what is currently a fast-growing area of mathematics, this book provides an up-to-date and valuable reference for both researchers and graduate students, from which future research activities will undoubted...

Stable walking with asymmetric legs

International Nuclear Information System (INIS)

Merker, Andreas; Rummel, Juergen; Seyfarth, Andre

2011-01-01

Asymmetric leg function is often an undesired side-effect in artificial legged systems and may reflect functional deficits or variations in the mechanical construction. It can also be found in legged locomotion in humans and animals such as after an accident or in specific gait patterns. So far, it is not clear to what extent differences in the leg function of contralateral limbs can be tolerated during walking or running. Here, we address this issue using a bipedal spring-mass model for simulating walking with compliant legs. With the help of the model, we show that considerable differences between contralateral legs can be tolerated and may even provide advantages to the robustness of the system dynamics. A better understanding of the mechanisms and potential benefits of asymmetric leg operation may help to guide the development of artificial limbs or the design novel therapeutic concepts and rehabilitation strategies.

Multipulse dynamics of a passively mode-locked semiconductor laser with delayed optical feedback

Science.gov (United States)

Jaurigue, Lina; Krauskopf, Bernd; Lüdge, Kathy

2017-11-01

Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an ever-increasing degree of multistability between mode-locked solutions due to the frequency pulling effect.

KidsWalk-to-School: A Guide To Promote Walking to School.

Science.gov (United States)

Center for Chronic Disease Prevention and Health Promotion (DHHS/CDC), Atlanta, GA.

This guide encourages people to create safe walking and biking routes to school, promoting four issues: physically active travel, safe and walkable routes to school, crime prevention, and health environments. The chapters include: "KidsWalk-to-School: A Guide to Promote Walking to School" (Is there a solution? Why is walking to school important?…

Walking training with cueing of cadence improves walking speed and stride length after stroke more than walking training alone: a systematic review.

Science.gov (United States)

Nascimento, Lucas R; de Oliveira, Camila Quel; Ada, Louise; Michaelsen, Stella M; Teixeira-Salmela, Luci F

2015-01-01

After stroke, is walking training with cueing of cadence superior to walking training alone in improving walking speed, stride length, cadence and symmetry? Systematic review with meta-analysis of randomised or controlled trials. Adults who have had a stroke. Walking training with cueing of cadence. Four walking outcomes were of interest: walking speed, stride length, cadence and symmetry. This review included seven trials involving 211 participants. Because one trial caused substantial statistical heterogeneity, meta-analyses were conducted with and without this trial. Walking training with cueing of cadence improved walking speed by 0.23 m/s (95% CI 0.18 to 0.27, I(2)=0%), stride length by 0.21 m (95% CI 0.14 to 0.28, I(2)=18%), cadence by 19 steps/minute (95% CI 14 to 23, I(2)=40%), and symmetry by 15% (95% CI 3 to 26, random effects) more than walking training alone. This review provides evidence that walking training with cueing of cadence improves walking speed and stride length more than walking training alone. It may also produce benefits in terms of cadence and symmetry of walking. The evidence appears strong enough to recommend the addition of 30 minutes of cueing of cadence to walking training, four times a week for 4 weeks, in order to improve walking in moderately disabled individuals with stroke. PROSPERO (CRD42013005873). Copyright © 2014 Australian Physiotherapy Association. Published by Elsevier B.V. All rights reserved.

Complementarity and quantum walks

International Nuclear Information System (INIS)

Kendon, Viv; Sanders, Barry C.

2005-01-01

We show that quantum walks interpolate between a coherent 'wave walk' and a random walk depending on how strongly the walker's coin state is measured; i.e., the quantum walk exhibits the quintessentially quantum property of complementarity, which is manifested as a tradeoff between knowledge of which path the walker takes vs the sharpness of the interference pattern. A physical implementation of a quantum walk (the quantum quincunx) should thus have an identifiable walker and the capacity to demonstrate the interpolation between wave walk and random walk depending on the strength of measurement

Folding in and out: passive morphing in flapping wings.

Science.gov (United States)

Stowers, Amanda K; Lentink, David

2015-03-25

We present a new mechanism for passive wing morphing of flapping wings inspired by bat and bird wing morphology. The mechanism consists of an unactuated hand wing connected to the arm wing with a wrist joint. Flapping motion generates centrifugal accelerations in the hand wing, forcing it to unfold passively. Using a robotic model in hover, we made kinematic measurements of unfolding kinematics as functions of the non-dimensional wingspan fold ratio (2-2.5) and flapping frequency (5-17 Hz) using stereo high-speed cameras. We find that the wings unfold passively within one to two flaps and remain unfolded with only small amplitude oscillations. To better understand the passive dynamics, we constructed a computer model of the unfolding process based on rigid body dynamics, contact models, and aerodynamic correlations. This model predicts the measured passive unfolding within about one flap and shows that unfolding is driven by centrifugal acceleration induced by flapping. The simulations also predict that relative unfolding time only weakly depends on flapping frequency and can be reduced to less than half a wingbeat by increasing flapping amplitude. Subsequent dimensional analysis shows that the time required to unfold passively is of the same order of magnitude as the flapping period. This suggests that centrifugal acceleration can drive passive unfolding within approximately one wingbeat in small and large wings. Finally, we show experimentally that passive unfolding wings can withstand impact with a branch, by first folding and then unfolding passively. This mechanism enables flapping robots to squeeze through clutter without sophisticated control. Passive unfolding also provides a new avenue in morphing wing design that makes future flapping morphing wings possibly more energy efficient and light-weight. Simultaneously these results point to possible inertia driven, and therefore metabolically efficient, control strategies in bats and birds to morph or recover

Physiological aspect walking and Nordic walking as adequate kinetic activities.

OpenAIRE

BENEŠ, Václav

2010-01-01

This bachelor thesis on the topic of The Physiological Aspect of Walking and Nordic Walking as an adequate physical activity focuses on chosen physiological changes of an organism during a five-month training cycle. In the theoretical part I describe the physiological changes of organism during a regularly repeated strain, and also the technique of walking, Nordic walking and health benefits of these activities are defined here. The research part of the thesis describes the measurement method...

Walking Beliefs in Women With Fibromyalgia: Clinical Profile and Impact on Walking Behavior.

Science.gov (United States)

Peñacoba, Cecilia; Pastor, María-Ángeles; López-Roig, Sofía; Velasco, Lilian; Lledo, Ana

2017-10-01

Although exercise is essential for the treatment of fibromyalgia, adherence is low. Walking, as a form of physical exercise, has significant advantages. The aim of this article is to describe, in 920 women with fibromyalgia, the prevalence of certain walking beliefs and analyze their effects both on the walking behavior itself and on the associated symptoms when patients walk according to a clinically recommended way. The results highlight the high prevalence of beliefs related to pain and fatigue as walking-inhibitors. In the whole sample, beliefs are associated with an increased perception that comorbidity prevents walking, and with higher levels of pain and fatigue. In patients who walk regularly, beliefs are only associated with the perception that comorbidity prevents them from walking. It is necessary to promote walking according to the established way (including breaks to prevent fatigue) and to implement interventions on the most prevalent beliefs that inhibit walking.

Random walks on generalized Koch networks

International Nuclear Information System (INIS)

Sun, Weigang

2013-01-01

For deterministically growing networks, it is a theoretical challenge to determine the topological properties and dynamical processes. In this paper, we study random walks on generalized Koch networks with features that include an initial state that is a globally connected network to r nodes. In each step, every existing node produces m complete graphs. We then obtain the analytical expressions for first passage time (FPT), average return time (ART), i.e. the average of FPTs for random walks from node i to return to the starting point i for the first time, and average sending time (AST), defined as the average of FPTs from a hub node to all other nodes, excluding the hub itself with regard to network parameters m and r. For this family of Koch networks, the ART of the new emerging nodes is identical and increases with the parameters m or r. In addition, the AST of our networks grows with network size N as N ln N and also increases with parameter m. The results obtained in this paper are the generalizations of random walks for the original Koch network. (paper)

Effects of Nordic walking and walking on spatiotemporal gait parameters and ground reaction force.

Science.gov (United States)

Park, Seung Kyu; Yang, Dae Jung; Kang, Yang Hun; Kim, Je Ho; Uhm, Yo Han; Lee, Yong Seon

2015-09-01

[Purpose] The purpose of this study was to investigate the effects of Nordic walking and walking on spatiotemporal gait parameters and ground reaction force. [Subjects] The subjects of this study were 30 young adult males, who were divided into a Nordic walking group of 15 subjects and a walking group of 15 subjects. [Methods] To analyze the spatiotemporal parameters and ground reaction force during walking in the two groups, the six-camera Vicon MX motion analysis system was used. The subjects were asked to walk 12 meters using the more comfortable walking method for them between Nordic walking and walking. After they walked 12 meters more than 10 times, their most natural walking patterns were chosen three times and analyzed. To determine the pole for Nordic walking, each subject's height was multiplied by 0.68. We then measured the spatiotemporal gait parameters and ground reaction force. [Results] Compared with the walking group, the Nordic walking group showed an increase in cadence, stride length, and step length, and a decrease in stride time, step time, and vertical ground reaction force. [Conclusion] The results of this study indicate that Nordic walking increases the stride and can be considered as helping patients with diseases affecting their gait. This demonstrates that Nordic walking is more effective in improving functional capabilities by promoting effective energy use and reducing the lower limb load, because the weight of the upper and lower limbs is dispersed during Nordic walking.

Walking drawings and walking ability in children with cerebral palsy.

Science.gov (United States)

Chong, Jimmy; Mackey, Anna H; Stott, N Susan; Broadbent, Elizabeth

2013-06-01

To investigate whether drawings of the self walking by children with cerebral palsy (CP) were associated with walking ability and illness perceptions. This was an exploratory study in 52 children with CP (M:F = 28:24), mean age 11.1 years (range 5-18), who were attending tertiary level outpatient clinics. Children were asked to draw a picture of themselves walking. Drawing size and content was used to investigate associations with clinical walk tests and children's own perceptions of their CP assessed using a CP version of the Brief Illness Perception Questionnaire. Larger drawings of the self were associated with less distance traveled, higher emotional responses to CP, and lower perceptions of pain or discomfort, independent of age. A larger self-to-overall drawing height ratio was related to walking less distance. Drawings of the self confined within buildings and the absence of other figures were also associated with reduced walking ability. Drawing size and content can reflect walking ability, as well as symptom perceptions and distress. Drawings may be useful for clinicians to use with children with cerebral palsy to aid discussion about their condition. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Game Design Document Format For Video Games With Passive Dynamic Difficulty Adjustment

Directory of Open Access Journals (Sweden)

Pratama Wirya Atmaja

2016-07-01

satisfaction of its players is the primary mean to measure its quality. One important element of player’s satisfaction is a proper difficulty level, which is neither too easy nor too hard. The current state-of-the-art way to implement it is with Dynamic Difficulty Adjustment (DDA, which allows the difficulty level of a video game to be adjusted at run-time. Currently, the most popular type of DDA is the passive one. Meanwhile, Game Design Document (GDD is an important artefact in the development process of a video game software, and there is still no GDD format that supports the design of passive DDA mechanism. The aim of this research was to find a new GDD format that supports the mechanism. We modified a general purpose GDD format by adding new parts for designing passive DDA mechanism. We tested the usefulness of the modified format in a testing process involving developers and players. The developers developed video games using the modified GDD format and the general purpose one. Their development processes were observed and evaluated to know if there were any difficulties. The resulting video games were played by the players to find which are better in terms of passive DDA mechanism. The result of developer testing showed that the modified format is better than the general purpose one. The result of player testing showed that the video games made with the modified format are better than their counterparts, albeit by an insignificant margin. Based on the results, we declare that the modified GDD format is successful.Keywords: Video game, requirement engineering, game design document, dynamic difficulty adjustment, software development.

Walking performance: correlation between energy cost of walking and walking participation. new statistical approach concerning outcome measurement.

Directory of Open Access Journals (Sweden)

Marco Franceschini

Full Text Available Walking ability, though important for quality of life and participation in social and economic activities, can be adversely affected by neurological disorders, such as Spinal Cord Injury, Stroke, Multiple Sclerosis or Traumatic Brain Injury. The aim of this study is to evaluate if the energy cost of walking (CW, in a mixed group of chronic patients with neurological diseases almost 6 months after discharge from rehabilitation wards, can predict the walking performance and any walking restriction on community activities, as indicated by Walking Handicap Scale categories (WHS. One hundred and seven subjects were included in the study, 31 suffering from Stroke, 26 from Spinal Cord Injury and 50 from Multiple Sclerosis. The multivariable binary logistical regression analysis has produced a statistical model with good characteristics of fit and good predictability. This model generated a cut-off value of.40, which enabled us to classify correctly the cases with a percentage of 85.0%. Our research reveal that, in our subjects, CW is the only predictor of the walking performance of in the community, to be compared with the score of WHS. We have been also identifying a cut-off value of CW cost, which makes a distinction between those who can walk in the community and those who cannot do it. In particular, these values could be used to predict the ability to walk in the community when discharged from the rehabilitation units, and to adjust the rehabilitative treatment to improve the performance.

Random walk centrality for temporal networks

International Nuclear Information System (INIS)

Rocha, Luis E C; Masuda, Naoki

2014-01-01

Nodes can be ranked according to their relative importance within a network. Ranking algorithms based on random walks are particularly useful because they connect topological and diffusive properties of the network. Previous methods based on random walks, for example the PageRank, have focused on static structures. However, several realistic networks are indeed dynamic, meaning that their structure changes in time. In this paper, we propose a centrality measure for temporal networks based on random walks under periodic boundary conditions that we call TempoRank. It is known that, in static networks, the stationary density of the random walk is proportional to the degree or the strength of a node. In contrast, we find that, in temporal networks, the stationary density is proportional to the in-strength of the so-called effective network, a weighted and directed network explicitly constructed from the original sequence of transition matrices. The stationary density also depends on the sojourn probability q, which regulates the tendency of the walker to stay in the node, and on the temporal resolution of the data. We apply our method to human interaction networks and show that although it is important for a node to be connected to another node with many random walkers (one of the principles of the PageRank) at the right moment, this effect is negligible in practice when the time order of link activation is included. (paper)

Random walk centrality for temporal networks

Science.gov (United States)

Rocha, Luis E. C.; Masuda, Naoki

2014-06-01

Nodes can be ranked according to their relative importance within a network. Ranking algorithms based on random walks are particularly useful because they connect topological and diffusive properties of the network. Previous methods based on random walks, for example the PageRank, have focused on static structures. However, several realistic networks are indeed dynamic, meaning that their structure changes in time. In this paper, we propose a centrality measure for temporal networks based on random walks under periodic boundary conditions that we call TempoRank. It is known that, in static networks, the stationary density of the random walk is proportional to the degree or the strength of a node. In contrast, we find that, in temporal networks, the stationary density is proportional to the in-strength of the so-called effective network, a weighted and directed network explicitly constructed from the original sequence of transition matrices. The stationary density also depends on the sojourn probability q, which regulates the tendency of the walker to stay in the node, and on the temporal resolution of the data. We apply our method to human interaction networks and show that although it is important for a node to be connected to another node with many random walkers (one of the principles of the PageRank) at the right moment, this effect is negligible in practice when the time order of link activation is included.

Results from the dynamic albedo of neutrons (DAN) passive mode experiment: Yellowknife Bay to Amargosa Valley (Sols 201-753)

Science.gov (United States)

Tate, C. G.; Moersch, J.; Mitrofanov, I.; Litvak, M.; Bellutta, P.; Boynton, W. V.; Drake, D.; Ehresmann, B.; Fedosov, F.; Golovin, D.; Hardgrove, C.; Harshman, K.; Hassler, D. M.; Jun, I.; Kozyrev, A. S.; Lisov, D.; Malakhov, A.; Ming, D. W.; Mischna, M.; Mokrousov, M.; Nikiforov, S.; Sanin, A. B.; Starr, R.; Vostrukhin, A.; Zeitlin, C.

2018-01-01

The Mars Science Laboratory (Curiosity rover) Dynamic Albedo of Neutrons (DAN) experiment detects neutrons for the purpose of searching for hydrogen in the shallow subsurface of Mars. DAN has two modes of operation, active and passive. In passive mode, the instrument detects neutrons produced by Galactic Cosmic Ray interactions in the atmosphere and regolith and by the rover's Multi-Mission Radioisotope Thermoelectric Generator. DAN passive data from Yellowknife Bay to Amargosa Valley (sols 201 through 753) are presented and analyzed here. Water equivalent hydrogen (WEH) estimates from this portion of Curiosity's traverse range from 0.0 wt. % up to 15.3 wt. %. Typical uncertainties on these WEH estimates are ∼0.5 wt. % but in some cases can be as high as ∼4.0 wt. % depending on the specific circumstances of a given measurement. Here we also present a new way of reporting results from the passive mode of the experiment, the DAN passive geochemical index (DPGI). This index is sensitive to some key geochemical variations, but it does not require assumptions about the abundances of high thermal neutron absorption cross section elements, which are needed to estimate WEH. DPGI variations in this section of the traverse indicate that the shallow regolith composition is changing on both the local (∼meters) and regional (∼100 s of meters) scales. This variability is thought to be representative of the diverse composition of source regions for sediments within the crater floor. Kolmogorov-Smirnov Tests on the populations of WEH estimates and DPGI values demonstrate there are statistically significant differences between nearly all of the geologic units investigated along the rover's traverse. We also present updated previous DAN passive results from Bradbury Landing to John Klein that make use of revised DAN active mode results for calibration, however, no qualitative changes in the interpretations made in Tate et al. (2015b) are incurred.

Random walk to a nonergodic equilibrium concept

Science.gov (United States)

Bel, G.; Barkai, E.

2006-01-01

Random walk models, such as the trap model, continuous time random walks, and comb models, exhibit weak ergodicity breaking, when the average waiting time is infinite. The open question is, what statistical mechanical theory replaces the canonical Boltzmann-Gibbs theory for such systems? In this paper a nonergodic equilibrium concept is investigated, for a continuous time random walk model in a potential field. In particular we show that in the nonergodic phase the distribution of the occupation time of the particle in a finite region of space approaches U- or W-shaped distributions related to the arcsine law. We show that when conditions of detailed balance are applied, these distributions depend on the partition function of the problem, thus establishing a relation between the nonergodic dynamics and canonical statistical mechanics. In the ergodic phase the distribution function of the occupation times approaches a δ function centered on the value predicted based on standard Boltzmann-Gibbs statistics. The relation of our work to single-molecule experiments is briefly discussed.

Nordic walking versus walking without poles for rehabilitation with cardiovascular disease: Randomized controlled trial.

Science.gov (United States)

Girold, Sébastien; Rousseau, Jérome; Le Gal, Magalie; Coudeyre, Emmanuel; Le Henaff, Jacqueline

2017-07-01

With Nordic walking, or walking with poles, one can travel a greater distance and at a higher rate than with walking without poles, but whether the activity is beneficial for patients with cardiovascular disease is unknown. This randomized controlled trial was undertaken to determine whether Nordic walking was more effective than walking without poles on walk distance to support rehabilitation training for patients with acute coronary syndrome (ACS) and peripheral arterial occlusive disease (PAOD). Patients were recruited in a private specialized rehabilitation centre for cardiovascular diseases. The entire protocol, including patient recruitment, took place over 2 months, from September to October 2013. We divided patients into 2 groups: Nordic Walking Group (NWG, n=21) and Walking Group without poles (WG, n=21). All patients followed the same program over 4 weeks, except for the walk performed with or without poles. The main outcome was walk distance on the 6-min walk test. Secondary outcomes were maximum heart rate during exercise and walk distance and power output on a treadmill stress test. We included 42 patients (35 men; mean age 57.2±11 years and BMI 26.5±4.5kg/m 2 ). At the end of the training period, both groups showed improved walk distance on the 6-min walk test and treatment stress test as well as power on the treadmill stress test (PNordic walking training appeared more efficient than training without poles for increasing walk distance on the 6-min walk test for patients with ACS and PAOD. Copyright © 2017. Published by Elsevier Masson SAS.

Kinematic control of walking.

Science.gov (United States)

Lacquaniti, F; Ivanenko, Y P; Zago, M

2002-10-01

The planar law of inter-segmental co-ordination we described may emerge from the coupling of neural oscillators between each other and with limb mechanical oscillators. Muscle contraction intervenes at variable times to re-excite the intrinsic oscillations of the system when energy is lost. The hypothesis that a law of coordinative control results from a minimal active tuning of the passive inertial and viscoelastic coupling among limb segments is congruent with the idea that movement has evolved according to minimum energy criteria (1, 8). It is known that multi-segment motion of mammals locomotion is controlled by a network of coupled oscillators (CPGs, see 18, 33, 37). Flexible combination of unit oscillators gives rise to different forms of locomotion. Inter-oscillator coupling can be modified by changing the synaptic strength (or polarity) of the relative spinal connections. As a result, unit oscillators can be coupled in phase, out of phase, or with a variable phase, giving rise to different behaviors, such as speed increments or reversal of gait direction (from forward to backward). Supra-spinal centers may drive or modulate functional sets of coordinating interneurons to generate different walking modes (or gaits). Although it is often assumed that CPGs control patterns of muscle activity, an equally plausible hypothesis is that they control patterns of limb segment motion instead (22). According to this kinematic view, each unit oscillator would directly control a limb segment, alternately generating forward and backward oscillations of the segment. Inter-segmental coordination would be achieved by coupling unit oscillators with a variable phase. Inter-segmental kinematic phase plays the role of global control variable previously postulated for the network of central oscillators. In fact, inter-segmental phase shifts systematically with increasing speed both in man (4) and cat (38). Because this phase-shift is correlated with the net mechanical power

Alzheimer random walk

Science.gov (United States)

Odagaki, Takashi; Kasuya, Keisuke

2017-09-01

Using the Monte Carlo simulation, we investigate a memory-impaired self-avoiding walk on a square lattice in which a random walker marks each of sites visited with a given probability p and makes a random walk avoiding the marked sites. Namely, p = 0 and p = 1 correspond to the simple random walk and the self-avoiding walk, respectively. When p> 0, there is a finite probability that the walker is trapped. We show that the trap time distribution can well be fitted by Stacy's Weibull distribution b(a/b){a+1}/{b}[Γ({a+1}/{b})]-1x^a\\exp(-a/bx^b)} where a and b are fitting parameters depending on p. We also find that the mean trap time diverges at p = 0 as p- α with α = 1.89. In order to produce sufficient number of long walks, we exploit the pivot algorithm and obtain the mean square displacement and its Flory exponent ν(p) as functions of p. We find that the exponent determined for 1000 step walks interpolates both limits ν(0) for the simple random walk and ν(1) for the self-avoiding walk as [ ν(p) - ν(0) ] / [ ν(1) - ν(0) ] = pβ with β = 0.388 when p ≪ 0.1 and β = 0.0822 when p ≫ 0.1. Contribution to the Topical Issue "Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook", edited by Ryszard Kutner and Jaume Masoliver.

Cognitive processing for step precision increases beta and gamma band modulation during overground walking

DEFF Research Database (Denmark)

Oliveira, Anderson Souza; Arguissain, Federico Gabriel; Andersen, Ole Kæseler

2018-01-01

The aim of this study was to investigate whether cognitive processing for defining step precision during walking could induce changes in electrocortical activity. Ten healthy adults (21-36 years) were asked to walk overground in three different conditions: (1) normal walking in a straight path (N...... activity in cognitive, motor and sensorimotor areas may be relevant to produce patterned and safe locomotion through challenging paths.......The aim of this study was to investigate whether cognitive processing for defining step precision during walking could induce changes in electrocortical activity. Ten healthy adults (21-36 years) were asked to walk overground in three different conditions: (1) normal walking in a straight path (NW....../sensorimotor regions, a phase in the gait cycle in which participants define the correct foot placement for the next step. These results suggest that greater cognitive demands during precision stepping influences electrocortical dynamics especially towards step transitions. Therefore, increased electrocortical...

Psychosocial and environmental correlates of active and passive transport behaviors in college educated and non-college educated working young adults.

Science.gov (United States)

Simons, Dorien; De Bourdeaudhuij, Ilse; Clarys, Peter; De Cocker, Katrien; de Geus, Bas; Vandelanotte, Corneel; Van Cauwenberg, Jelle; Deforche, Benedicte

2017-01-01

This study aimed to examine potential differences in walking, cycling, public transport and passive transport (car/moped/motorcycle) to work and to other destinations between college and non-college educated working young adults. Secondly, we aimed to investigate which psychosocial and environmental factors are associated with the four transport modes and whether these associations differ between college and non-college educated working young adults. In this cross-sectional study, 224 working young adults completed an online questionnaire assessing socio-demographic variables (8 items), psychosocial variables (6 items), environmental variables (10 items) and transport mode (4 types) and duration to work/other destinations. Zero-inflated negative binomial regression models were performed in R. A trend (pyoung adults participated in cycling and public transport. However, another trend indicated that cycle time and public transport trips were longer and passive transport trips were shorter in non-college compared to college educated working young adults. In all working young adults, high self-efficacy towards active transport, and high perceived benefits and low perceived barriers towards active and public transport were related to more active and public transport. High social support/norm/modeling towards active, public and passive transport was related to more active, public and passive transport. High neighborhood walkability was related to more walking and less passive transport. Only in non-college educated working young adults, feeling safe from traffic and crime in their neighborhood was related to more active and public transport and less passive transport. Educational levels should be taken into account when promoting healthy transport behaviors in working young adults. Among non-college educated working young adults, focus should be on increasing active and public transport participation and on increasing neighborhood safety to increase active and public

Validity and reliability of the 10-m walk test and the 6-min walk test in spinal cord injury patients.

Science.gov (United States)

Scivoletto, G; Tamburella, F; Laurenza, L; Foti, C; Ditunno, J F; Molinari, M

2011-06-01

The 10-m walk test (10MWT) and the 6-min walk test (6MWT) have been recommended for assessment of walking in spinal cord injury (SCI) patients. The study was designed on test-retest analysis of the 10MWT and 6MWT. The objective of this study was to assess validity/reliability of different methods of performing the tests. The study was set at an SCI unit of a rehabilitation hospital. A total of 37 patients; whose median age was 58.5 years (interquartile range 40-66, full range 19-77); median time since onset of SCI was 24 months (interquartile range 16.25-70.5, full range 6-109). Non-traumatic etiology in 20 out of 37 patients; level: 12C, 14T and 11L; American Spinal Injury Association Impairment Scale grade: 35D/2C. Assessment with the 10MWT (with or without dynamic start) and the 6MWT (short or long track) by two blinded raters to evaluate inter/intra-rater reliabilities. The 10MWT was performed in a median of 19 s (25th-75th interquartile range 13-28) with the dynamic start and of 18.4 s (25th-75th interquartile range 12.6-29.9) with the static start (P=0.092). The correlation between the results of the two methods was between 0.98 and 0.99. The inter- and intra-rater reliabilities were between 0.95 and 0.99 for both the methods. The 6MWT showed significant differences according to the track length: patients walked a median of 226.7 m (25th-75th interquartile range 123.2-319) on the longer track and of 187.6 m (25th-75th interquartile range 69.7-240.6) on the short one (P<0.001). The correlation between the results of the two methods was between 0.91 and 0.93. The inter- and intra-rater reliabilities were between 0.98 and 0.99. The 10MWT shows high inter/intra-rater reliability and shows comparable results with both dynamic and static start. The different testing conditions of the 6MWT (track/turns) results in significant differences that need standardization for use in future trials.

Dynamic legged locomotion in robots and animals

Science.gov (United States)

Raibert, Marc; Playter, Robert; Ringrose, Robert; Bailey, Dave; Leeser, Karl

1995-01-01

This report documents our study of active legged systems that balance actively and move dynamically. The purpose of this research is to build a foundation of knowledge that can lead both to the construction of useful legged vehicles and to a better understanding of how animal locomotion works. In this report we provide an update on progress during the past year. Here are the topics covered in this report: (1) Is cockroach locomotion dynamic? To address this question we created three models of cockroaches, each abstracted at a different level. We provided each model with a control system and computer simulation. One set of results suggests that 'Groucho Running,' a type of dynamic walking, seems feasible at cockroach scale. (2) How do bipeds shift weight between the legs? We built a simple planar biped robot specifically to explore this question. It shifts its weight from one curved foot to the other, using a toe-off and toe-on strategy, in conjunction with dynamic tipping. (3) 3D biped gymnastics: The 3D biped robot has done front somersaults in the laboratory. The robot changes its leg length in flight to control rotation rate. This in turn provides a mechanism for controlling the landing attitude of the robot once airborne. (4) Passively stabilized layout somersault: We have found that the passive structure of a gymnast, the configuration of masses and compliances, can stabilize inherently unstable maneuvers. This means that body biomechanics could play a larger role in controlling behavior than is generally thought. We used a physical 'doll' model and computer simulation to illustrate the point. (5) Twisting: Some gymnastic maneuvers require twisting. We are studying how to couple the biomechanics of the system to its control to produce efficient, stable twisting maneuvers.

The effects of powered ankle-foot orthoses on joint kinematics and muscle activation during walking in individuals with incomplete spinal cord injury

Directory of Open Access Journals (Sweden)

Domingo Antoinette

2006-02-01

Full Text Available Abstract Background Powered lower limb orthoses could reduce therapist labor during gait rehabilitation after neurological injury. However, it is not clear how patients respond to powered assistance during stepping. Patients might allow the orthoses to drive the movement pattern and reduce their muscle activation. The goal of this study was to test the effects of robotic assistance in subjects with incomplete spinal cord injury using pneumatically powered ankle-foot orthoses. Methods Five individuals with chronic incomplete spinal cord injury (ASIA C-D participated in the study. Each subject was fitted with bilateral ankle-foot orthoses equipped with artificial pneumatic muscles to power ankle plantar flexion. Subjects walked on a treadmill with partial bodyweight support at four speeds (0.36, 0.54, 0.72 and 0.89 m/s under three conditions: without wearing orthoses, wearing orthoses unpowered (passively, and wearing orthoses activated under pushbutton control by a physical therapist. Subjects also attempted a fourth condition wearing orthoses activated under pushbutton control by them. We measured joint angles, electromyography, and orthoses torque assistance. Results A therapist quickly learned to activate the artificial pneumatic muscles using the pushbuttons with the appropriate amplitude and timing. The powered orthoses provided ~50% of peak ankle torque. Ankle angle at stance push-off increased when subjects walked with powered orthoses versus when they walked with passive-orthoses (ANOVA, p Two of the five subjects were able to control the orthoses themselves using the pushbuttons. The other three subjects found it too difficult to coordinate pushbutton timing. Orthoses assistance and maximum ankle angle at push-off were smaller when the subject controlled the orthoses compared to when the therapist-controlled the orthoses (p Conclusion Mechanical assistance from powered ankle-foot orthoses improved ankle push-off kinematics without

The Rh-1 Full-Size Humanoid Robot: Design, Walking Pattern Generation and Control

Directory of Open Access Journals (Sweden)

M. Arbulú

2009-01-01

Full Text Available This paper is an overview of the humanoid robot Rh-1, the second phase of the Rh project, which was launched by the Robotics Lab at the Carlos III University of Madrid in 2002. The robot mechanical design includes the specifications development in order to construct a platform, which is capable of stable biped walking. At first, the robots’ weights were calculated in order to obtain the inverse dynamics and to select the actuators. After that, mechanical specifications were introduced in order to verify the robot’s structural behaviour with different experimental gaits. In addition, an important aspect is the joints design when their axes are crossed, which is called ‘Joints of Rectangular Axes’ (JRA. The problem with these joints is obtaining two or more degrees of freedom (DOF in small space. The construction of a humanoid robot also includes the design of hardware and software architectures. The main advantage of the proposed hardware and software architectures is the use of standardised solutions frequently used in the automation industry and commercially available hardware components. It provides scalability, modularity and application of standardised interfaces and brings the design of the complex control system of the humanoid robot out of a closed laboratory to industry. Stable walking is the most essential ability for the humanoid robot. The three dimensional Linear Inverted Pendulum Model (3D-LIPM and the Cart-table models had been used in order to achieve natural and dynamic biped walking. Humanoid dynamics is widely simplified by concentrating its mass in the centre of gravity (COG and moving it following the natural inverted pendulum laws (3D-LIPM or by controlling the cart motion (Cart-table model. An offline-calculated motion pattern does not guarantee the walking stability of the humanoid robot. Control architecture for the dynamic humanoid robot walking was developed, which is able to make online modifications of the

Walking strategies of visually impaired people on trapezoidal- and sinusoidal-section tactile groundsurface indicators.

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Ranavolo, A; Conte, C; Iavicoli, S; Serrao, M; Silvetti, A; Sandrini, G; Pierelli, F; Draicchio, F

2011-03-01

The visual system in walking serves to perceive feedback or feed-forward signals. Therefore, visually impaired persons (VIP) have biased motor control mechanisms. The use of leading indicators (LIs) and long canes helps to improve their walking efficiency. The aims of this study were to compare the walking efficiency of VIP on trapezoidal- and sinusoidal-section LIs using an optoelectronic motion analysis system. VIP displayed a significantly longer stance phase, a shorter swing phase and shorter step and stride lengths when they walked on the sinusoidal LI than when they walked on the trapezoidal LI. Compared with the trapezoidal LI, VIP walking on the sinusoidal LI displayed significantly lower joint ranges of motion. The centre of mass lateral displacement was wider for VIP walking on the sinusoidal LI than on the trapezoidal LI. Some significant differences were also found in sighted persons walking on both LIs. In conclusion, the trapezoidal shape enabled visually impaired subjects to walk more efficiently, whereas the sinusoidal shape caused dynamic balance problems. STATEMENT OF RELEVANCE: These findings suggest that VIP can walk more efficiently, with a lower risk of falls, on trapezoidal-section than on sinusoidal-section LIs. These results should be considered when choosing the most appropriate ground tactile surface indicators for widespread use.

Walking modality, but not task difficulty, influences the control of dual-task walking.

Science.gov (United States)

Wrightson, J G; Smeeton, N J

2017-10-01

During dual-task gait, changes in the stride-to-stride variability of stride time (STV) are suggested to represent the allocation of cognitive control to walking [1]. However, contrasting effects have been reported for overground and treadmill walking, which may be due to differences in the relative difficulty of the dual task. Here we compared the effect of overground and treadmill dual-task walking on STV in 18 healthy adults. Participants walked overground and on a treadmill for 120s during single-task (walking only) and dual-task (walking whilst performing serial subtractions in sevens) conditions. Dual-task effects on STV, cognitive task (serial subtraction) performance and perceived task difficulty were compared between walking modalities. STV was increased during overground dual-task walking, but was unchanged during treadmill dual-task walking. There were no differences in cognitive task performance or perceived task difficulty. These results show that gait is controlled differently during overground and treadmill dual-task walking. However, these differences are not solely due to differences in task difficulty, and may instead represent modality dependent control strategies. Copyright © 2017 Elsevier B.V. All rights reserved.

The influence of gait speed on the stability of walking among the elderly.

Science.gov (United States)

Fan, Yifang; Li, Zhiyu; Han, Shuyan; Lv, Changsheng; Zhang, Bo

2016-06-01

Walking speed is a basic factor to consider when walking exercises are prescribed as part of a training programme. Although associations between walking speed, step length and falling risk have been identified, the relationship between spontaneous walking pattern and falling risk remains unclear. The present study, therefore, examined the stability of spontaneous walking at normal, fast and slow speed among elderly (67.5±3.23) and young (21.4±1.31) individuals. In all, 55 participants undertook a test that involved walking on a plantar pressure platform. Foot-ground contact data were used to calculate walking speed, step length, pressure impulse along the plantar-impulse principal axis and pressure record of time series along the plantar-impulse principal axis. A forward dynamics method was used to calculate acceleration, velocity and displacement of the centre of mass in the vertical direction. The results showed that when the elderly walked at different speeds, their average step length was smaller than that observed among the young (p=0.000), whereas their anterior/posterior variability and lateral variability had no significant difference. When walking was performed at normal or slow speed, no significant between-group difference in cadence was found. When walking at a fast speed, the elderly increased their stride length moderately and their cadence greatly (p=0.012). In summary, the present study found no correlation between fast walking speed and instability among the elderly, which indicates that healthy elderly individuals might safely perform fast-speed walking exercises. Copyright © 2016 Elsevier B.V. All rights reserved.

Creating cat states in one-dimensional quantum walks using delocalized initial states

International Nuclear Information System (INIS)

Zhang, Wei-Wei; Gao, Fei; Goyal, Sandeep K; Sanders, Barry C; Simon, Christoph

2016-01-01

Cat states are coherent quantum superpositions of macroscopically distinct states and are useful for understanding the boundary between the classical and the quantum world. Due to their macroscopic nature, cat states are difficult to prepare in physical systems. We propose a method to create cat states in one-dimensional quantum walks using delocalized initial states of the walker. Since the quantum walks can be performed on any quantum system, our proposal enables a platform-independent realization of the cat states. We further show that the linear dispersion relation of the effective quantum walk Hamiltonian, which governs the dynamics of the delocalized states, is responsible for the formation of the cat states. We analyze the robustness of these states against environmental interactions and present methods to control and manipulate the cat states in the photonic implementation of quantum walks. (paper)

Biomechanical analysis of rollator walking

DEFF Research Database (Denmark)

Alkjaer, T; Larsen, Peter K; Pedersen, Gitte

2006-01-01

The rollator is a very popular walking aid. However, knowledge about how a rollator affects the walking patterns is limited. Thus, the purpose of the study was to investigate the biomechanical effects of walking with and without a rollator on the walking pattern in healthy subjects.......The rollator is a very popular walking aid. However, knowledge about how a rollator affects the walking patterns is limited. Thus, the purpose of the study was to investigate the biomechanical effects of walking with and without a rollator on the walking pattern in healthy subjects....

Dynamic interaction between rotor and axially-magnetized passive magnetic bearing considering magnetic eccentricity

DEFF Research Database (Denmark)

Enemark, Søren; Santos, Ilmar

2014-01-01

with a multibody system composed of rigid rotor and flexible foundation. The magnetic eccentricities of the shaft magnets are modelled using the distances (amplitudes) and directions (phase angles) between the shaft axis and the centre of the magnetic fields generated. A perturbation method, i.e. harmonic......-linear stiffness. In this investigation passive magnetic bearings using axially- aligned neodymium cylinder magnets are investigated. The cylinder magnets are axially magnetised for rotor as well as bearings. Compared to bearings with radial magnetisation, the magnetic stiffness of axially-aligned bearings...... is considerably lower, nevertheless they allow for asymmetric stiffness mounting, and it could be beneficial for rotor stabilization. A theoretical model is proposed to describe the non-linear rotor-bearing dynamics. It takes into account non-linear behaviour of the magnetic forces and their interaction...

Entanglement in coined quantum walks on regular graphs

International Nuclear Information System (INIS)

Carneiro, Ivens; Loo, Meng; Xu, Xibai; Girerd, Mathieu; Kendon, Viv; Knight, Peter L

2005-01-01

Quantum walks, both discrete (coined) and continuous time, form the basis of several recent quantum algorithms. Here we use numerical simulations to study the properties of discrete, coined quantum walks. We investigate the variation in the entanglement between the coin and the position of the particle by calculating the entropy of the reduced density matrix of the coin. We consider both dynamical evolution and asymptotic limits for coins of dimensions from two to eight on regular graphs. For low coin dimensions, quantum walks which spread faster (as measured by the mean square deviation of their distribution from uniform) also exhibit faster convergence towards the asymptotic value of the entanglement between the coin and particle's position. For high-dimensional coins, the DFT coin operator is more efficient at spreading than the Grover coin. We study the entanglement of the coin on regular finite graphs such as cycles, and also show that on complete bipartite graphs, a quantum walk with a Grover coin is always periodic with period four. We generalize the 'glued trees' graph used by Childs et al (2003 Proc. STOC, pp 59-68) to higher branching rate (fan out) and verify that the scaling with branching rate and with tree depth is polynomial

Image-based fall detection and classification of a user with a walking support system

Science.gov (United States)

Taghvaei, Sajjad; Kosuge, Kazuhiro

2017-10-01

The classification of visual human action is important in the development of systems that interact with humans. This study investigates an image-based classification of the human state while using a walking support system to improve the safety and dependability of these systems.We categorize the possible human behavior while utilizing a walker robot into eight states (i.e., sitting, standing, walking, and five falling types), and propose two different methods, namely, normal distribution and hidden Markov models (HMMs), to detect and recognize these states. The visual feature for the state classification is the centroid position of the upper body, which is extracted from the user's depth images. The first method shows that the centroid position follows a normal distribution while walking, which can be adopted to detect any non-walking state. The second method implements HMMs to detect and recognize these states. We then measure and compare the performance of both methods. The classification results are employed to control the motion of a passive-type walker (called "RT Walker") by activating its brakes in non-walking states. Thus, the system can be used for sit/stand support and fall prevention. The experiments are performed with four subjects, including an experienced physiotherapist. Results show that the algorithm can be adapted to the new user's motion pattern within 40 s, with a fall detection rate of 96.25% and state classification rate of 81.0%. The proposed method can be implemented to other abnormality detection/classification applications that employ depth image-sensing devices.

Random walk in genome space: A key ingredient of intermittent dynamics of community assembly on evolutionary time scales

KAUST Repository

Murase, Yohsuke

2010-06-01

Community assembly is studied using individual-based multispecies models. The models have stochastic population dynamics with mutation, migration, and extinction of species. Mutants appear as a result of mutation of the resident species, while migrants have no correlation with the resident species. It is found that the dynamics of community assembly with mutations are quite different from the case with migrations. In contrast to mutation models, which show intermittent dynamics of quasi-steady states interrupted by sudden reorganizations of the community, migration models show smooth and gradual renewal of the community. As a consequence, instead of the 1/f diversity fluctuations found for the mutation models, 1/f2, random-walk like fluctuations are observed for the migration models. In addition, a characteristic species-lifetime distribution is found: a power law that is cut off by a "skewed" distribution in the long-lifetime regime. The latter has a longer tail than a simple exponential function, which indicates an age-dependent species-mortality function. Since this characteristic profile has been observed, both in fossil data and in several other mathematical models, we conclude that it is a universal feature of macroevolution. © 2010 Elsevier Ltd.

Random walk in genome space: A key ingredient of intermittent dynamics of community assembly on evolutionary time scales

KAUST Repository

Murase, Yohsuke; Shimada, Takashi; Ito, Nobuyasu; Rikvold, Per Arne

2010-01-01

Community assembly is studied using individual-based multispecies models. The models have stochastic population dynamics with mutation, migration, and extinction of species. Mutants appear as a result of mutation of the resident species, while migrants have no correlation with the resident species. It is found that the dynamics of community assembly with mutations are quite different from the case with migrations. In contrast to mutation models, which show intermittent dynamics of quasi-steady states interrupted by sudden reorganizations of the community, migration models show smooth and gradual renewal of the community. As a consequence, instead of the 1/f diversity fluctuations found for the mutation models, 1/f2, random-walk like fluctuations are observed for the migration models. In addition, a characteristic species-lifetime distribution is found: a power law that is cut off by a "skewed" distribution in the long-lifetime regime. The latter has a longer tail than a simple exponential function, which indicates an age-dependent species-mortality function. Since this characteristic profile has been observed, both in fossil data and in several other mathematical models, we conclude that it is a universal feature of macroevolution. © 2010 Elsevier Ltd.

Adults' Daily Walking for Travel and Leisure: Interaction Between Attitude Toward Walking and the Neighborhood Environment.

Science.gov (United States)

Yang, Yong; Diez-Roux, Ana V

2017-09-01

Studies on how the interaction of psychological and environmental characteristics influences walking are limited, and the results are inconsistent. Our aim is to examine how the attitude toward walking and neighborhood environments interacts to influence walking. Cross-sectional phone and mail survey. Participants randomly sampled from 6 study sites including Los Angeles, Chicago, Baltimore, Minneapolis, Manhattan, and Bronx Counties in New York City, and Forsyth and Davidson Counties in North Carolina. The final sample consisted of 2621 persons from 2011 to 2012. Total minutes of walking for travel or leisure, attitude toward walking, and perceptions of the neighborhood environments were self-reported. Street Smart (SS) Walk Score (a measure of walkability derived from a variety of geographic data) was obtained for each residential location. Linear regression models adjusting for age, gender, race/ethnicity, education, and income. Attitude toward walking was positively associated with walking for both purposes. Walking for travel was significantly associated with SS Walk Score, whereas walking for leisure was not. The SS Walk Score and selected perceived environment characteristics were associated with walking in people with a very positive attitude toward walking but were not associated with walking in people with a less positive attitude. Attitudes toward walking and neighborhood environments interact to affect walking behavior.

Modeling spatial segregation and travel cost influences on utilitarian walking: Towards policy intervention.

Science.gov (United States)

Yang, Yong; Auchincloss, Amy H; Rodriguez, Daniel A; Brown, Daniel G; Riolo, Rick; Diez-Roux, Ana V

2015-05-01

We develop an agent-based model of utilitarian walking and use the model to explore spatial and socioeconomic factors affecting adult utilitarian walking and how travel costs as well as various educational interventions aimed at changing attitudes can alter the prevalence of walking and income differentials in walking. The model is validated against US national data. We contrast realistic and extreme parameter values in our model and test effects of changing these parameters across various segregation and pricing scenarios while allowing for interactions between travel choice and place and for behavioral feedbacks. Results suggest that in addition to income differences in the perceived cost of time, the concentration of mixed land use (differential density of residences and businesses) are important determinants of income differences in walking (high income walk less), whereas safety from crime and income segregation on their own do not have large influences on income differences in walking. We also show the difficulty in altering walking behaviors for higher income groups who are insensitive to price and how adding to the cost of driving could increase the income differential in walking particularly in the context of segregation by income and land use. We show that strategies to decrease positive attitudes towards driving can interact synergistically with shifting cost structures to favor walking in increasing the percent of walking trips. Agent-based models, with their ability to capture dynamic processes and incorporate empirical data, are powerful tools to explore the influence on health behavior from multiple factors and test policy interventions.

Walking, sustainability and health: findings from a study of a Walking for Health group.

Science.gov (United States)

Grant, Gordon; Machaczek, Kasia; Pollard, Nick; Allmark, Peter

2017-05-01

Not only is it tacitly understood that walking is good for health and well-being but there is also now robust evidence to support this link. There is also growing evidence that regular short walks can be a protective factor for a range of long-term health conditions. Walking in the countryside can bring additional benefits, but access to the countryside brings complexities, especially for people with poorer material resources and from different ethnic communities. Reasons for people taking up walking as a physical activity are reasonably well understood, but factors linked to sustained walking, and therefore sustained benefit, are not. Based on an ethnographic study of a Walking for Health group in Lincolnshire, UK, this paper considers the motivations and rewards of group walks for older people. Nineteen members of the walking group, almost all with long-term conditions, took part in tape-recorded interviews about the personal benefits of walking. The paper provides insights into the links between walking as a sustainable activity and health, and why a combination of personal adaptive capacities, design elements of the walks and relational achievements of the walking group are important to this understanding. The paper concludes with some observations about the need to reframe conventional thinking about adherence to physical activity programmes. © 2017 John Wiley & Sons Ltd.

A Novel Technology for Motion Capture Using Passive UHF RFID Tags

DEFF Research Database (Denmark)

Krigslund, Rasmus; Popovski, Petar; Pedersen, Gert Frølund

2013-01-01

Although there are several existing methods for human motion capture, they all have important limitations and hence there is the need to explore fundamentally new approaches. Here we present a method based on a Radio Frequency IDentification (RFID) system with passive Ultra High Frequency (UHF...... walking. The reference joint angles for the validation were obtained by an optoelectronic system. Although the method is in its initial phase of development, the results of the validation are promising and show that the movement information can be extracted from the RFID response signals....

A Solution of Time Dependent Schrodinger Equation by Quantum Walk

International Nuclear Information System (INIS)

Sekino, Hideo; Kawahata, Masayuki; Hamada, Shinji

2012-01-01

Time Dependent Schroedinger Equation (TDSE) with an initial Gaussian distribution, is solved by a discrete time/space Quantum Walk (QW) representing consecutive operations corresponding to a dot product of Pauli matrix and momentum operators. We call it as Schroedinger Walk (SW). Though an Hadamard Walk (HW) provides same dynamics of the probability distribution for delta-function-like initial distributions as that of the SW with a delta-function-like initial distribution, the former with a Gaussian initial distribution leads to a solution for advection of the probability distribution; the initial distribution splits into two distinctive distributions moving in opposite directions. Both mechanisms are analysed by investigating the evolution of the both amplitude components. Decoherence of the oscillating amplitudes in central region is found to be responsible for the splitting of the probability distribution in the HW.

Prefrontal, posterior parietal and sensorimotor network activity underlying speed control during walking

Directory of Open Access Journals (Sweden)

Thomas C Bulea

2015-05-01

Full Text Available Accumulating evidence suggests cortical circuits may contribute to control of human locomotion. Here, noninvasive electroencephalography (EEG recorded from able-bodied volunteers during a novel treadmill walking paradigm was used to assess neural correlates of walking. A systematic processing method, including a recently developed subspace reconstruction algorithm, reduced movement-related EEG artifact prior to independent component analysis and dipole source localization. We quantified cortical activity while participants tracked slow and fast target speeds across two treadmill conditions: an active mode that adjusted belt speed based on user movements and a passive mode reflecting a typical treadmill. Our results reveal frequency specific, multi-focal task related changes in cortical oscillations elicited by active walking. Low γ band power, localized to the prefrontal and posterior parietal cortices, was significantly increased during double support and early swing phases, critical points in the gait cycle since the active controller adjusted speed based on pelvis position and swing foot velocity. These phasic γ band synchronizations provide evidence that prefrontal and posterior parietal networks, previously implicated in visuo-spatial and somotosensory integration, are engaged to enhance lower limb control during gait. Sustained μ and β band desynchronization within sensorimotor cortex, a neural correlate for movement, was observed during walking thereby validating our methods for isolating cortical activity. Our results also demonstrate the utility of EEG recorded during locomotion for probing the multi-regional cortical networks which underpin its execution. For example, the cortical network engagement elicited by the active treadmill suggests that it may enhance neuroplasticity for more effective motor training.

Modelisation et simulation d'un PON (Passive Optical Network) base ...

African Journals Online (AJOL)

English Title: Modeling and simulation of a PON (Passive Optical Network) Based on hybrid technology WDM/TDM. English Abstract. This development is part of dynamism of design for a model combining WDM and TDM multiplexing in the optical network of PON (Passive Optical Network) type, in order to satisfy the high bit ...

Quantum walk computation

International Nuclear Information System (INIS)

Kendon, Viv

2014-01-01

Quantum versions of random walks have diverse applications that are motivating experimental implementations as well as theoretical studies. Recent results showing quantum walks are “universal for quantum computation” relate to algorithms, to be run on quantum computers. We consider whether an experimental implementation of a quantum walk could provide useful computation before we have a universal quantum computer

Scattering quantum random-walk search with errors

International Nuclear Information System (INIS)

Gabris, A.; Kiss, T.; Jex, I.

2007-01-01

We analyze the realization of a quantum-walk search algorithm in a passive, linear optical network. The specific model enables us to consider the effect of realistic sources of noise and losses on the search efficiency. Photon loss uniform in all directions is shown to lead to the rescaling of search time. Deviation from directional uniformity leads to the enhancement of the search efficiency compared to uniform loss with the same average. In certain cases even increasing loss in some of the directions can improve search efficiency. We show that while we approach the classical limit of the general search algorithm by introducing random phase fluctuations, its utility for searching is lost. Using numerical methods, we found that for static phase errors the averaged search efficiency displays a damped oscillatory behavior that asymptotically tends to a nonzero value

Increasing Walking in the Hartsfield-Jackson Atlanta International Airport: The Walk to Fly Study.

Science.gov (United States)

Fulton, Janet E; Frederick, Ginny M; Paul, Prabasaj; Omura, John D; Carlson, Susan A; Dorn, Joan M

2017-07-01

To test the effectiveness of a point-of-decision intervention to prompt walking, versus motorized transport, in a large metropolitan airport. We installed point-of-decision prompt signage at 4 locations in the airport transportation mall at Hartsfield-Jackson Atlanta International Airport (Atlanta, GA) at the connecting corridor between airport concourses. Six ceiling-mounted infrared sensors counted travelers entering and exiting the study location. We collected traveler counts from June 2013 to May 2016 when construction was present and absent (preintervention period: June 2013-September 2014; postintervention period: September 2014-May 2016). We used a model that incorporated weekly walking variation to estimate the intervention effect on walking. There was an 11.0% to 16.7% relative increase in walking in the absence of airport construction where 580 to 810 more travelers per day chose to walk. Through May 2016, travelers completed 390 000 additional walking trips. The Walk to Fly study demonstrated a significant and sustained increase in the number of airport travelers choosing to walk. Providing signage about options to walk in busy locations where reasonable walking options are available may improve population levels of physical activity and therefore improve public health.

Walk Score® and Transit Score® and Walking in the Multi-Ethnic Study of Atherosclerosis

Science.gov (United States)

Hirsch, Jana A.; Moore, Kari A.; Evenson, Kelly R.; Rodriguez, Daniel A; Diez Roux, Ana V.

2013-01-01

Background Walk Score® and Transit Score® are open-source measures of the neighborhood built environment to support walking (“walkability”) and access to transportation. Purpose To investigate associations of Street Smart Walk Score and Transit Score with self-reported transport and leisure walking using data from a large multi-city and diverse population-based sample of adults. Methods Data from a sample of 4552 residents of Baltimore MD; Chicago IL; Forsyth County NC; Los Angeles CA; New York NY; and St. Paul MN from the Multi-Ethnic Study of Atherosclerosis (2010–2012) were linked to Walk Score and Transit Score (collected in 2012). Logistic and linear regression models estimated ORs of not walking and mean differences in minutes walked, respectively, associated with continuous and categoric Walk Score and Transit Score. All analyses were conducted in 2012. Results After adjustment for site, key sociodemographic, and health variables, a higher Walk Score was associated with lower odds of not walking for transport and more minutes/week of transport walking. Compared to those in a “walker’s paradise,” lower categories of Walk Score were associated with a linear increase in odds of not transport walking and a decline in minutes of leisure walking. An increase in Transit Score was associated with lower odds of not transport walking or leisure walking, and additional minutes/week of leisure walking. Conclusions Walk Score and Transit Score appear to be useful as measures of walkability in analyses of neighborhood effects. PMID:23867022

Effects of walking and strength training on walking capacity in individuals with claudication: meta-analysis

Directory of Open Access Journals (Sweden)

Alessandra de Souza Miranda

2013-06-01

Full Text Available CONTEXT: Over the past few years, several clinical trials have been performed to analyze the effects of exercise training on walking ability in patients with intermittent claudication (IC. However, it remains unclear which type of physical exercise provides the maximum benefits in terms of walking ability. OBJECTIVE: To analyze, by means of a meta-analysis, the effects of walking and strength training on the walking capacity in patients with IC. METHODS: Papers analyzing the effects of walking and strength training programs in patients with IC were browsed on the Medline, Lilacs, and Cochrane databases. Randomized clinical trials scoring >4 on the Physiotherapy Evidence Database (PEDro scale and assessing claudication distance (CD and total walking distance (TWD were included in the review. RESULTS: Walking and strength training yielded increases in CD and TWD (P < 0.05. However, walking training yielded greater increases than strength training (P = 0.02. CONCLUSION: Walking and strength training improve walking capacity in patients with IC. However, greater improvements in TWD are obtained with walking training.

Random walks of a quantum particle on a circle

International Nuclear Information System (INIS)

Fjeldsoe, N.; Midtdal, J.; Ravndal, F.

1987-07-01

When the quantum planar rotor is put on a lattice, its dynamics can be approximated by random walks on a circle. This allows for fast and accurate Monto Carlo simulations to determine the topological charge of different configurations of the system and thereby the Θ-dependency of the lowest energy levels

Walking economy during cued versus non-cued self-selected treadmill walking in persons with Parkinson's disease.

Science.gov (United States)

Gallo, Paul M; McIsaac, Tara L; Garber, Carol Ewing

2014-01-01

Gait impairments related to Parkinson's disease (PD) include variable step length and decreased walking velocity, which may result in poorer walking economy. Auditory cueing is a common method used to improve gait mechanics in PD that has been shown to worsen walking economy at set treadmill walking speeds. It is unknown if auditory cueing has the same effects on walking economy at self-selected treadmill walking speeds. To determine if auditory cueing will affect walking economy at self-selected treadmill walking speeds and at speeds slightly faster and slower than self-selected. Twenty-two participants with moderate PD performed three, 6-minute bouts of treadmill walking at three speeds (self-selected and ± 0.22 m·sec-1). One session used cueing and the other without cueing. Energy expenditure was measured and walking economy was calculated (energy expenditure/power). Poorer walking economy and higher energy expenditure occurred during cued walking at a self-selected and a slightly faster walking speed, but there was no apparent difference at the slightly slower speed. These results suggest that potential gait benefits of auditory cueing may come at an energy cost and poorer walking economy for persons with PD at least at some treadmill walking speeds.

The six-spot-step test - a new method for monitoring walking ability in patients with chronic inflammatory polyneuropathy

DEFF Research Database (Denmark)

Kreutzfeldt, Melissa; Jensen, Henrik B; Ravnborg, Mads

2017-01-01

OBJECTIVE: To evaluate whether the Six-Spot-Step-Test (SSST) is more suitable for monitoring walking ability in patients with chronic inflammatory polyneuropathy than the Timed-25-Foot-Walking test (T25FW). METHOD: In the SSST, participants have to walk as quickly as possible across a field...... of effect size, standardized response means and relative efficiency. Both ambulation tests correlated moderately to PGIC. CONCLUSION: The SSST may be superior to the T25FW in terms of dynamic range, floor effect and responsiveness which makes the SSST a possible alternative for monitoring walking ability...

Toe Walking in Children

Science.gov (United States)

... prone to damage and weaken over time. This diagnosis might be more likely if your child initially walked normally before starting to toe walk. Autism. Toe walking has been linked to autism spectrum ...

Shoe-Insole Technology for Injury Prevention in Walking

Directory of Open Access Journals (Sweden)

Hanatsu Nagano

2018-05-01

Full Text Available Impaired walking increases injury risk during locomotion, including falls-related acute injuries and overuse damage to lower limb joints. Gait impairments seriously restrict voluntary, habitual engagement in injury prevention activities, such as recreational walking and exercise. There is, therefore, an urgent need for technology-based interventions for gait disorders that are cost effective, willingly taken-up, and provide immediate positive effects on walking. Gait control using shoe-insoles has potential as an effective population-based intervention, and new sensor technologies will enhance the effectiveness of these devices. Shoe-insole modifications include: (i ankle joint support for falls prevention; (ii shock absorption by utilising lower-resilience materials at the heel; (iii improving reaction speed by stimulating cutaneous receptors; and (iv preserving dynamic balance via foot centre of pressure control. Using sensor technology, such as in-shoe pressure measurement and motion capture systems, gait can be precisely monitored, allowing us to visualise how shoe-insoles change walking patterns. In addition, in-shoe systems, such as pressure monitoring and inertial sensors, can be incorporated into the insole to monitor gait in real-time. Inertial sensors coupled with in-shoe foot pressure sensors and global positioning systems (GPS could be used to monitor spatiotemporal parameters in real-time. Real-time, online data management will enable ‘big-data’ applications to everyday gait control characteristics.

Attention demanding tasks during treadmill walking reduce step width variability in young adults

Directory of Open Access Journals (Sweden)

Troy Karen L

2005-08-01

Full Text Available Abstract Background The variability of step time and step width is associated with falls by older adults. Further, step time is significantly influenced when performing attention demanding tasks while walking. Without exception, step time variability has been reported to increase in normal and pathologically aging older adults. Because of the role of step width in managing frontal plane dynamic stability, documenting the influence of attention-demanding tasks on step width variability may provide insight to events that can disturb dynamic stability during locomotion and increase fall risk. Preliminary evidence suggests performance of an attention demanding task significantly decreases step width variability of young adults walking on a treadmill. The purpose of the present study was to confirm or refute this finding by characterizing the extent and direction of the effects of a widely used attention demanding task (Stroop test on the step width variability of young adults walking on a motorized treadmill. Methods Fifteen healthy young adults walked on a motorized treadmill at a self-selected velocity for 10 minutes under two conditions; without performing an attention demanding task and while performing the Stroop test. Step width of continuous and consecutive steps during the collection was derived from the data recorded using a motion capture system. Step width variability was computed as the standard deviation of all recorded steps. Results Step width decreased four percent during performance of the Stroop test but the effect was not significant (p = 0.10. In contrast, the 16 percent decrease in step width variability during the Stroop test condition was significant (p = 0.029. Conclusion The results support those of our previous work in which a different attention demanding task also decreased step width variability of young subjects while walking on a treadmill. The decreased step width variability observed while performing an attention

Talk the Walk: Does Socio-Cognitive Resource Reallocation Facilitate the Development of Walking?

Science.gov (United States)

Geva, Ronny; Orr, Edna

2016-01-01

Walking is of interest to psychology, robotics, zoology, neuroscience and medicine. Human's ability to walk on two feet is considered to be one of the defining characteristics of hominoid evolution. Evolutionary science propses that it emerged in response to limited environmental resources; yet the processes supporting its emergence are not fully understood. Developmental psychology research suggests that walking elicits cognitive advancements. We postulate that the relationship between cognitive development and walking is a bi-directional one; and further suggest that the initiation of novel capacities, such as walking, is related to internal socio-cognitive resource reallocation. We shed light on these notions by exploring infants' cognitive and socio-communicative outputs prospectively from 6-18 months of age. Structured bi/tri weekly evaluations of symbolic and verbal development were employed in an urban cohort (N = 9) for 12 months, during the transition from crawling to walking. Results show links between preemptive cognitive changes in socio-communicative output, symbolic-cognitive tool-use processes, and the age of emergence of walking. Plots of use rates of lower symbolic play levels before and after emergence of new skills illustrate reductions in use of previously attained key behaviors prior to emergence of higher symbolic play, language and walking. Further, individual differences in age of walking initiation were strongly related to the degree of reductions in complexity of object-use (r = .832, p developments, form an integrated adaptable composite, which possibly enables proactive internal resource reallocation, designed to support the emergence of new developmental milestones, such as walking.

A generalized model via random walks for information filtering

Science.gov (United States)

Ren, Zhuo-Ming; Kong, Yixiu; Shang, Ming-Sheng; Zhang, Yi-Cheng

2016-08-01

There could exist a simple general mechanism lurking beneath collaborative filtering and interdisciplinary physics approaches which have been successfully applied to online E-commerce platforms. Motivated by this idea, we propose a generalized model employing the dynamics of the random walk in the bipartite networks. Taking into account the degree information, the proposed generalized model could deduce the collaborative filtering, interdisciplinary physics approaches and even the enormous expansion of them. Furthermore, we analyze the generalized model with single and hybrid of degree information on the process of random walk in bipartite networks, and propose a possible strategy by using the hybrid degree information for different popular objects to toward promising precision of the recommendation.

Active and passive spatial learning in human navigation: acquisition of graph knowledge.

Science.gov (United States)

Chrastil, Elizabeth R; Warren, William H

2015-07-01

It is known that active exploration of a new environment leads to better spatial learning than does passive visual exposure. We ask whether specific components of active learning differentially contribute to particular forms of spatial knowledge-the exploration-specific learning hypothesis. Previously, we found that idiothetic information during walking is the primary active contributor to metric survey knowledge (Chrastil & Warren, 2013). In this study, we test the contributions of 3 components to topological graph and route knowledge: visual information, idiothetic information, and cognitive decision making. Four groups of participants learned the locations of 8 objects in a virtual hedge maze by (a) walking or (b) watching a video, crossed with (1) either making decisions about their path or (2) being guided through the maze. Route and graph knowledge were assessed by walking in the maze corridors from a starting object to the remembered location of a test object, with frequent detours. Decision making during exploration significantly contributed to subsequent route finding in the walking condition, whereas idiothetic information did not. Participants took novel routes and the metrically shortest routes on the majority of both direct and barrier trials, indicating that labeled graph knowledge-not merely route knowledge-was acquired. We conclude that, consistent with the exploration-specific learning hypothesis, decision making is the primary component of active learning for the acquisition of topological graph knowledge, whereas idiothetic information is the primary component for metric survey knowledge. (c) 2015 APA, all rights reserved.

Allegheny County Walk Scores

Data.gov (United States)

Allegheny County / City of Pittsburgh / Western PA Regional Data Center — Walk Score measures the walkability of any address using a patented system developed by the Walk Score company. For each 2010 Census Tract centroid, Walk Score...

Talk the Walk: Does Socio-Cognitive Resource Reallocation Facilitate the Development of Walking?

Directory of Open Access Journals (Sweden)

Ronny Geva

Full Text Available Walking is of interest to psychology, robotics, zoology, neuroscience and medicine. Human's ability to walk on two feet is considered to be one of the defining characteristics of hominoid evolution. Evolutionary science propses that it emerged in response to limited environmental resources; yet the processes supporting its emergence are not fully understood. Developmental psychology research suggests that walking elicits cognitive advancements. We postulate that the relationship between cognitive development and walking is a bi-directional one; and further suggest that the initiation of novel capacities, such as walking, is related to internal socio-cognitive resource reallocation. We shed light on these notions by exploring infants' cognitive and socio-communicative outputs prospectively from 6-18 months of age. Structured bi/tri weekly evaluations of symbolic and verbal development were employed in an urban cohort (N = 9 for 12 months, during the transition from crawling to walking. Results show links between preemptive cognitive changes in socio-communicative output, symbolic-cognitive tool-use processes, and the age of emergence of walking. Plots of use rates of lower symbolic play levels before and after emergence of new skills illustrate reductions in use of previously attained key behaviors prior to emergence of higher symbolic play, language and walking. Further, individual differences in age of walking initiation were strongly related to the degree of reductions in complexity of object-use (r = .832, p < .005, along with increases, counter to the general reduction trend, in skills that serve recruitment of external resources [socio-communication bids before speech (r = -.696, p < .01, and speech bids before walking; r = .729, p < .01]. Integration of these proactive changes using a computational approach yielded an even stronger link, underscoring internal resource reallocation as a facilitator of walking initiation (r = .901, p<0

Hydrogen passivation of polycrystalline Si thin film solar cells

International Nuclear Information System (INIS)

Gorka, Benjamin

2010-01-01

Hydrogen passivation is a key process step in the fabrication of polycrystalline Si (poly-Si) thin film solar cells. In this work a parallel plate rf plasma setup was used for the hydrogen passivation treatment. The main topics that have been investigated are (i) the role of plasma parameters (like hydrogen pressure, electrode gap and plasma power), (ii) the dynamics of the hydrogen treatment and (iii) passivation of poly-Si with different material properties. Passivation was characterized by measuring the open-circuit voltage V OC of poly-Si reference samples. Optimum passivation conditions were found by measurements of the breakdown voltage V brk of the plasma for different pressures p and electrode gaps d. For each pressure, the best passivation was achieved at a gap d that corresponded to the minimum in V brk . Plasma simulations were carried out, which indicate that best V OC corresponds to a minimum in ion energy. V OC was not improved by a larger H flux. Investigations of the passivation dynamic showed that a plasma treatment in the lower temperature range (≤400 C) is slow and takes several hours for the V OC to saturate. Fast passivation can be successfully achieved at elevated temperatures around 500 C to 600 C with a plateau time of 10 min. It was found that prolonged hydrogenation leads to a loss in V OC , which is less pronounced within the observed optimum temperature range (500 C-600 C). Electron beam evaporation has been investigated as an alternative method to fabricate poly-Si absorbers. The material properties have been tuned by alteration of substrate temperature T dep =200-700 C and were characterized by Raman, ESR and V OC measurements. Largest grains were obtained after solid phase crystallization (SPC) of a-Si, deposited in the temperature range of 300 C. The defect concentration of Si dangling bonds was lowered by passivation by about one order of magnitude. The lowest dangling bond concentration of 2.5.10 16 cm -3 after passivation was

Regional passive seismic monitoring reveals dynamic glacier activity on Spitsbergen, Svalbard

Directory of Open Access Journals (Sweden)

Andreas Köhler

2015-12-01

Full Text Available Dynamic glacier activity is increasingly observed through passive seismic monitoring. We analysed near-regional-scale seismicity on the Arctic archipelago of Svalbard to identify seismic icequake signals and to study their spatial–temporal distribution within the 14-year period from 2000 until 2013. This is the first study that uses seismic data recorded on permanent broadband stations to detect and locate icequakes in different regions of Spitsbergen, the main island of the archipelago. A temporary local seismic network and direct observations of glacier calving and surging were used to identify icequake sources. We observed a high number of icequakes with clear spectral peaks between 1 and 8 Hz in different parts of Spitsbergen. Spatial clusters of icequakes could be associated with individual grounded tidewater glaciers and exhibited clear seasonal variability each year with more signals observed during the melt season. Locations at the termini of glaciers, and correlation with visual calving observations in situ at Kronebreen, a glacier in the Kongsfjorden region, show that these icequakes were caused dominantly by calving. Indirect evidence for glacier surging through increased calving seismicity was found in 2003 at Tunabreen, a glacier in central Spitsbergen. Another type of icequake was observed in the area of the Nathorstbreen glacier system. Seismic events occurred upstream of the glacier within a short time period between January and May 2009 during the initial phase of a major glacier surge. This study is the first step towards the generation and implementation of an operational seismic monitoring strategy for glacier dynamics in Svalbard.

Screen time and passive school travel as independent predictors of cardiorespiratory fitness in youth.

Science.gov (United States)

Sandercock, Gavin R H; Ogunleye, Ayodele A

2012-05-01

The most prevalent sedentary behaviours in children and adolescents are engagement with small screen media (screen-time) and passive travel (by motorised vehicle). The objective of this research was to assess the independence of these behaviours from one another and from physical activity as predictors of cardiorespiratory fitness in youth. We measured cardiorespiratory fitness in n=6819 10-16 year olds (53% male) who self-reported their physical activity (7-day recall) school travel and screen time habits. Travel was classified as active (walking, cycling) or passive; screen time as 4 h. The multivariate odds of being fit were higher in active travel (Boys: OR 1.32, 95% CI: 1.09-1.59; Girls: OR 1.46, 1.15-1.84) than in passive travel groups. Boys reporting low screen time were more likely to be fit than those reporting >4 h (OR 2.11, 95% CI: 1.68-2.63) as were girls (OR 1.66, 95% CI: 1.24-2.20). These odds remained significant after additionally controlling for physical activity. Passive travel and high screen time are independently associated with poor cardiorespiratory fitness in youth, and this relationship is independent of physical activity levels. A lifestyle involving high screen time and habitual passive school travel appears incompatible with healthful levels of cardiorespiratory fitness in youth. Copyright © 2012 Elsevier Inc. All rights reserved.

Kineziologická charakteristika Nordic Walking

OpenAIRE

Pospíšilová, Petra

2009-01-01

Title: Functional a physiological characteristics of Nordic Walking Purposes: The aim of the thesis is to describe and summarize current knowledge about Nordic Walking Methods: Literature analysis Key words: Nordic Walking, free bipedal walk, health benefits, functional indicator changes

An Estimation of a Passive Infra-Red Sensor Probability of Detection

International Nuclear Information System (INIS)

Osman, E.A.; El-Gazar, M.I.; Shaat, M.K.; El-Kafas, A.A.; Zidan, W.I.; Wadoud, A.A.

2009-01-01

Passive Infera-Red (PIR) sensors are one of many detection sensors are used to detect any intrusion process of the nuclear sites. In this work, an estimation of a PIR Sensor's Probability of Detection of a hypothetical facility is presented. sensor performance testing performed to determine whether a particular sensor will be acceptable in a proposed design. We have access to a sensor test field in which the sensor of interest is already properly installed and the parameters have been set to optimal levels by preliminary testing. The PIR sensor construction, operation and design for the investigated nuclear site are explained. Walking and running intrusion tests were carried out inside the field areas of the PIR sensor to evaluate the sensor performance during the intrusion process. 10 trials experimentally performed for achieving the intrusion process via a passive infra-red sensor's network system. The performance and intrusion senses of PIR sensors inside the internal zones was recorded and evaluated.

Effects of jumping skill training on walking balance for children with mental retardation and Down's syndrome.

Science.gov (United States)

Wang, W Y; Chang, J J

1997-08-01

In the present study, we hypothesized that the enhancements obtained from the practice of jumping activity could be transferred to improve the walking balance in children with mental retardation (MR) and Down's syndrome (DS). Fourteen children with the diagnosis of MR or DS, aged 3 to 6 years, were recruited from a day care institution. They were ambulant but without jumping ability. Sixty-one non-handicapped children was used to serve as a normative comparison group. Before the training program, the performances of walking balance, jump skills and jumping distances were assessed individually by one physical therapist. The balance sub-test in the Bruininks Oseretsky Test of Motor Proficiency (BOTMP) was administered to assess the walking balance. Motor Skill Inventory (MSI) was used to assess the qualitative levels of jumping skills. A jumping skill training lesson that included horizontal jumps and vertical jumps was designed and integrated into the educational program. The recruited children received 3 sessions of training per-week for 6 weeks. A post-training test and a follow-up test were administered to the handicapped children. In BOTMP scores, statistical differences exited between the pre-training and post-training tests in the tested items of floor walk and beam walk. However, no significant difference was found in the items of floor stand, beam stand and floor heel-toe walk. MSI scales revealed there were significant differences between pre-training and post-training tests. There was no significant difference between the scores of post-training test and the follow-up test. The results implicated that the jumping activity might effectively evoke the automatic and dynamic postural control. Moreover, the significant improvements of the floor walk and beam walk performances might be due to the transferred effects via the practice of dynamic jumping activity. Furthermore, implications and suggestions are discussed.

A Comparative Study of Biologically Inspired Walking Gaits through Waypoint Navigation

Directory of Open Access Journals (Sweden)

Umar Asif

2011-01-01

Full Text Available This paper investigates the locomotion of a walking robot by delivering a comparative study of three different biologically inspired walking gaits, namely: tripod, ripple, and wave, in terms of ground slippage they experience while walking. The objective of this study is to identify the gait model which experiences the minimum slippage while walking on a ground with a specific coefficient of friction. To accomplish this feat, the robot is steered over a reference path using a waypoint navigation algorithm, and the divergence of the robot from the reference path is investigated in terms of slip errors. Experiments are conducted through closed-loop simulations using an open dynamics engine which emphasizes the fact that due to uneven and unsymmetrical distribution of payload in tripod and ripple gait models, the robot experiences comparatively larger drift in these gaits than when using the wave gait model in which the distribution of payload is even and symmetrical on both sides of the robot body. The paper investigates this phenomenon on the basis of force distribution of supporting legs in each gait model.

Fast visual prediction and slow optimization of preferred walking speed.

Science.gov (United States)

O'Connor, Shawn M; Donelan, J Maxwell

2012-05-01

People prefer walking speeds that minimize energetic cost. This may be accomplished by directly sensing metabolic rate and adapting gait to minimize it, but only slowly due to the compounded effects of sensing delays and iterative convergence. Visual and other sensory information is available more rapidly and could help predict which gait changes reduce energetic cost, but only approximately because it relies on prior experience and an indirect means to achieve economy. We used virtual reality to manipulate visually presented speed while 10 healthy subjects freely walked on a self-paced treadmill to test whether the nervous system beneficially combines these two mechanisms. Rather than manipulating the speed of visual flow directly, we coupled it to the walking speed selected by the subject and then manipulated the ratio between these two speeds. We then quantified the dynamics of walking speed adjustments in response to perturbations of the visual speed. For step changes in visual speed, subjects responded with rapid speed adjustments (lasting 300 s). The timing and direction of these responses strongly indicate that a rapid predictive process informed by visual feedback helps select preferred speed, perhaps to complement a slower optimization process that seeks to minimize energetic cost.

An Approach to Stable Walking over Uneven Terrain Using a Reflex-Based Adaptive Gait

Directory of Open Access Journals (Sweden)

Umar Asif

2011-01-01

Full Text Available This paper describes the implementation of an adaptive gait in a six-legged walking robot that is capable of generating reactive stepping actions with the same underlying control methodology as an insect for stable walking over uneven terrains. The proposed method of gait generation uses feedback data from onboard sensors to generate an adaptive gait in order to surmount obstacles, gaps and perform stable walking. The paper addresses its implementation through simulations in a visual dynamic simulation environment. Finally the paper draws conclusions about the significance and performance of the proposed gait in terms of tracking errors while navigating in difficult terrains.

Quantum walks with entangled coins

International Nuclear Information System (INIS)

Venegas-Andraca, S E; Ball, J L; Burnett, K; Bose, S

2005-01-01

We present a mathematical formalism for the description of un- restricted quantum walks with entangled coins and one walker. The numerical behaviour of such walks is examined when using a Bell state as the initial coin state, with two different coin operators, two different shift operators, and one walker. We compare and contrast the performance of these quantum walks with that of a classical random walk consisting of one walker and two maximally correlated coins as well as quantum walks with coins sharing different degrees of entanglement. We illustrate that the behaviour of our walk with entangled coins can be very different in comparison to the usual quantum walk with a single coin. We also demonstrate that simply by changing the shift operator, we can generate widely different distributions. We also compare the behaviour of quantum walks with maximally entangled coins with that of quantum walks with non-entangled coins. Finally, we show that the use of different shift operators on two and three qubit coins leads to different position probability distributions in one- and two-dimensional graphs

Finite Memory Walk and Its Application to Small-World Network

Science.gov (United States)

Oshima, Hiraku; Odagaki, Takashi

2012-07-01

In order to investigate the effects of cycles on the dynamical process on both regular lattices and complex networks, we introduce a finite memory walk (FMW) as an extension of the simple random walk (SRW), in which a walker is prohibited from moving to sites visited during m steps just before the current position. This walk interpolates the simple random walk (SRW), which has no memory (m = 0), and the self-avoiding walk (SAW), which has an infinite memory (m = ∞). We investigate the FMW on regular lattices and clarify the fundamental characteristics of the walk. We find that (1) the mean-square displacement (MSD) of the FMW shows a crossover from the SAW at a short time step to the SRW at a long time step, and the crossover time is approximately equivalent to the number of steps remembered, and that the MSD can be rescaled in terms of the time step and the size of memory; (2) the mean first-return time (MFRT) of the FMW changes significantly at the number of remembered steps that corresponds to the size of the smallest cycle in the regular lattice, where ``smallest'' indicates that the size of the cycle is the smallest in the network; (3) the relaxation time of the first-return time distribution (FRTD) decreases as the number of cycles increases. We also investigate the FMW on the Watts--Strogatz networks that can generate small-world networks, and show that the clustering coefficient of the Watts--Strogatz network is strongly related to the MFRT of the FMW that can remember two steps.

Muscle coordination in healthy subjects during floor walking and stair climbing in robot assisted gait training.

Science.gov (United States)

Hussein, S; Schmidt, H; Volkmar, M; Werner, C; Helmich, I; Piorko, F; Krüger, J; Hesse, S

2008-01-01

The aim of gait rehabilitation is a restoration of an independent gait and improvement of daily life walking functions. Therefore the specific patterns, that are to be relearned, must be practiced to stimulate the learning process of the central nervous system (CNS). The Walking Simulator HapticWalker allows for the training of arbitrary gait trajectories of daily life. To evaluate the quality of the training a total of 9 subjects were investigated during free floor walking and stair climbing and during the same tasks in two different training modes on the HapticWalker: 1) with and 2) without vertical center of mass (CoM) motion. Electromyograms (EMG) of 8 gait relevant muscles were measured and muscle activation was compared for the various training modes. Besides the muscle activation as an indicator for the quality of rehabilitation training the study investigates if a cancellation of the vertical CoM movement by adaption of the footplate trajectory is feasible i.e. the muscle activation patterns for the two training modes on the HapticWalker agree. Results show no significant differences in activation timing between the training modes. This indicates the feasibility of using a passive patient suspension and emulate the vertical CoM motion by trajectory adaption of the footplates. The muscle activation timing during HapticWalker training shows important characteristics observed in physiological free walking though a few differences can still remain.

Walking for Well-Being: Are Group Walks in Certain Types of Natural Environments Better for Well-Being than Group Walks in Urban Environments?

Directory of Open Access Journals (Sweden)

Sara L. Warber

2013-10-01

Full Text Available The benefits of walking in natural environments for well-being are increasingly understood. However, less well known are the impacts different types of natural environments have on psychological and emotional well-being. This cross-sectional study investigated whether group walks in specific types of natural environments were associated with greater psychological and emotional well-being compared to group walks in urban environments. Individuals who frequently attended a walking group once a week or more (n = 708 were surveyed on mental well-being (Warwick Edinburgh Mental Well-being Scale, depression (Major Depressive Inventory, perceived stress (Perceived Stress Scale and emotional well-being (Positive and Negative Affect Schedule. Compared to group walks in urban environments, group walks in farmland were significantly associated with less perceived stress and negative affect, and greater mental well-being. Group walks in green corridors were significantly associated with less perceived stress and negative affect. There were no significant differences between the effect of any environment types on depression or positive affect. Outdoor walking group programs could be endorsed through “green prescriptions” to improve psychological and emotional well-being, as well as physical activity.

Feedback Control Design for a Walking Athlete Robot

Directory of Open Access Journals (Sweden)

Xuan Vu Trien Nguyen

2017-06-01

Full Text Available In the paper, authors generalized the dynamic model of an athlete robot with elastic legs through Lagrange method. Then, a feed-back controller was designed to control the robot through a step-walking. The research just focused on stance phase – the period that robot just touched one leg on the ground. The simulation results showed that system worked well with the designed controller.

Optical transitions driven by self-induced walk-off in nematic liquid crystals

International Nuclear Information System (INIS)

Brasselet, E.

2004-01-01

Optical field induced reorientation of a nematic liquid crystals film is investigated for finite cross-section of the excitation beam. An approach based on self-induced walk-off between extraordinary and ordinary waves is proposed, including the geometrical aspect ratio between the beam diameter and the cell thickness in a perturbative fashion. The bifurcation scenario when the intensity is taken as the control parameter is calculated in the case of a circularly polarized excitation beam at normal incidence. The sudden appearance of a new saddle-node bifurcation is predicted for a walk-off corresponding to realistic experimental conditions. Changes of the light angular momentum transfer induced by walk-off are singled out as a valid candidate to explain observed nonlinear dynamics whose origin is not yet well understood

In situ passivation of GaAsP nanowires.

Science.gov (United States)

Himwas, C; Collin, S; Rale, P; Chauvin, N; Patriarche, G; Oehler, F; Julien, F H; Travers, L; Harmand, J-C; Tchernycheva, M

2017-12-08

We report on the structural and optical properties of GaAsP nanowires (NWs) grown by molecular-beam epitaxy. By adjusting the alloy composition in the NWs, the transition energy was tuned to the optimal value required for tandem III-V/silicon solar cells. We discovered that an unintentional shell was also formed during the GaAsP NW growth. The NW surface was passivated by an in situ deposition of a radial Ga(As)P shell. Different shell compositions and thicknesses were investigated. We demonstrate that the optimal passivation conditions for GaAsP NWs (with a gap of 1.78 eV) are obtained with a 5 nm thick GaP shell. This passivation enhances the luminescence intensity of the NWs by 2 orders of magnitude and yields a longer luminescence decay. The luminescence dynamics changes from single exponential decay with a 4 ps characteristic time in non-passivated NWs to a bi-exponential decay with characteristic times of 85 and 540 ps in NWs with GaP shell passivation.

In situ passivation of GaAsP nanowires

Science.gov (United States)

Himwas, C.; Collin, S.; Rale, P.; Chauvin, N.; Patriarche, G.; Oehler, F.; Julien, F. H.; Travers, L.; Harmand, J.-C.; Tchernycheva, M.

2017-12-01

We report on the structural and optical properties of GaAsP nanowires (NWs) grown by molecular-beam epitaxy. By adjusting the alloy composition in the NWs, the transition energy was tuned to the optimal value required for tandem III-V/silicon solar cells. We discovered that an unintentional shell was also formed during the GaAsP NW growth. The NW surface was passivated by an in situ deposition of a radial Ga(As)P shell. Different shell compositions and thicknesses were investigated. We demonstrate that the optimal passivation conditions for GaAsP NWs (with a gap of 1.78 eV) are obtained with a 5 nm thick GaP shell. This passivation enhances the luminescence intensity of the NWs by 2 orders of magnitude and yields a longer luminescence decay. The luminescence dynamics changes from single exponential decay with a 4 ps characteristic time in non-passivated NWs to a bi-exponential decay with characteristic times of 85 and 540 ps in NWs with GaP shell passivation.

Beam walking can detect differences in walking balance proficiency across a range of sensorimotor abilities.

Science.gov (United States)

Sawers, Andrew; Ting, Lena H

2015-02-01

The ability to quantify differences in walking balance proficiency is critical to curbing the rising health and financial costs of falls. Current laboratory-based approaches typically focus on successful recovery of balance while clinical instruments often pose little difficulty for all but the most impaired patients. Rarely do they test motor behaviors of sufficient difficulty to evoke failures in balance control limiting their ability to quantify balance proficiency. Our objective was to test whether a simple beam-walking task could quantify differences in walking balance proficiency across a range of sensorimotor abilities. Ten experts, ten novices, and five individuals with transtibial limb loss performed six walking trials across three different width beams. Walking balance proficiency was quantified as the ratio of distance walked to total possible distance. Balance proficiency was not significantly different between cohorts on the wide-beam, but clear differences between cohorts on the mid and narrow-beams were identified. Experts walked a greater distance than novices on the mid-beam (average of 3.63±0.04m verus 2.70±0.21m out of 3.66m; p=0.009), and novices walked further than amputees (1.52±0.20m; p=0.03). Amputees were unable to walk on the narrow-beam, while experts walked further (3.07±0.14m) than novices (1.55±0.26m; p=0.0005). A simple beam-walking task and an easily collected measure of distance traveled detected differences in walking balance proficiency across sensorimotor abilities. This approach provides a means to safely study and evaluate successes and failures in walking balance in the clinic or lab. It may prove useful in identifying mechanisms underlying falls versus fall recoveries. Copyright © 2015 Elsevier B.V. All rights reserved.

Force encoding in muscle spindles during stretch of passive muscle.

Directory of Open Access Journals (Sweden)

Kyle P Blum

2017-09-01

Full Text Available Muscle spindle proprioceptive receptors play a primary role in encoding the effects of external mechanical perturbations to the body. During externally-imposed stretches of passive, i.e. electrically-quiescent, muscles, the instantaneous firing rates (IFRs of muscle spindles are associated with characteristics of stretch such as length and velocity. However, even in passive muscle, there are history-dependent transients of muscle spindle firing that are not uniquely related to muscle length and velocity, nor reproduced by current muscle spindle models. These include acceleration-dependent initial bursts, increased dynamic response to stretch velocity if a muscle has been isometric, and rate relaxation, i.e., a decrease in tonic IFR when a muscle is held at a constant length after being stretched. We collected muscle spindle spike trains across a variety of muscle stretch kinematic conditions, including systematic changes in peak length, velocity, and acceleration. We demonstrate that muscle spindle primary afferents in passive muscle fire in direct relationship to muscle force-related variables, rather than length-related variables. Linear combinations of whole muscle-tendon force and the first time derivative of force (dF/dt predict the entire time course of transient IFRs in muscle spindle Ia afferents during stretch (i.e., lengthening of passive muscle, including the initial burst, the dynamic response to lengthening, and rate relaxation following lengthening. Similar to acceleration scaling found previously in postural responses to perturbations, initial burst amplitude scaled equally well to initial stretch acceleration or dF/dt, though later transients were only described by dF/dt. The transient increase in dF/dt at the onset of lengthening reflects muscle short-range stiffness due to cross-bridge dynamics. Our work demonstrates a critical role of muscle cross-bridge dynamics in history-dependent muscle spindle IFRs in passive muscle

Force encoding in muscle spindles during stretch of passive muscle.

Science.gov (United States)

Blum, Kyle P; Lamotte D'Incamps, Boris; Zytnicki, Daniel; Ting, Lena H

2017-09-01

Muscle spindle proprioceptive receptors play a primary role in encoding the effects of external mechanical perturbations to the body. During externally-imposed stretches of passive, i.e. electrically-quiescent, muscles, the instantaneous firing rates (IFRs) of muscle spindles are associated with characteristics of stretch such as length and velocity. However, even in passive muscle, there are history-dependent transients of muscle spindle firing that are not uniquely related to muscle length and velocity, nor reproduced by current muscle spindle models. These include acceleration-dependent initial bursts, increased dynamic response to stretch velocity if a muscle has been isometric, and rate relaxation, i.e., a decrease in tonic IFR when a muscle is held at a constant length after being stretched. We collected muscle spindle spike trains across a variety of muscle stretch kinematic conditions, including systematic changes in peak length, velocity, and acceleration. We demonstrate that muscle spindle primary afferents in passive muscle fire in direct relationship to muscle force-related variables, rather than length-related variables. Linear combinations of whole muscle-tendon force and the first time derivative of force (dF/dt) predict the entire time course of transient IFRs in muscle spindle Ia afferents during stretch (i.e., lengthening) of passive muscle, including the initial burst, the dynamic response to lengthening, and rate relaxation following lengthening. Similar to acceleration scaling found previously in postural responses to perturbations, initial burst amplitude scaled equally well to initial stretch acceleration or dF/dt, though later transients were only described by dF/dt. The transient increase in dF/dt at the onset of lengthening reflects muscle short-range stiffness due to cross-bridge dynamics. Our work demonstrates a critical role of muscle cross-bridge dynamics in history-dependent muscle spindle IFRs in passive muscle lengthening conditions

Quantum logic using correlated one-dimensional quantum walks

Science.gov (United States)

Lahini, Yoav; Steinbrecher, Gregory R.; Bookatz, Adam D.; Englund, Dirk

2018-01-01

Quantum Walks are unitary processes describing the evolution of an initially localized wavefunction on a lattice potential. The complexity of the dynamics increases significantly when several indistinguishable quantum walkers propagate on the same lattice simultaneously, as these develop non-trivial spatial correlations that depend on the particle's quantum statistics, mutual interactions, initial positions, and the lattice potential. We show that even in the simplest case of a quantum walk on a one dimensional graph, these correlations can be shaped to yield a complete set of compact quantum logic operations. We provide detailed recipes for implementing quantum logic on one-dimensional quantum walks in two general cases. For non-interacting bosons—such as photons in waveguide lattices—we find high-fidelity probabilistic quantum gates that could be integrated into linear optics quantum computation schemes. For interacting quantum-walkers on a one-dimensional lattice—a situation that has recently been demonstrated using ultra-cold atoms—we find deterministic logic operations that are universal for quantum information processing. The suggested implementation requires minimal resources and a level of control that is within reach using recently demonstrated techniques. Further work is required to address error-correction.

The advantages of a rolling foot in human walking.

Science.gov (United States)

Adamczyk, Peter G; Collins, Steven H; Kuo, Arthur D

2006-10-01

The plantigrade human foot rolls over the ground during each walking step, roughly analogous to a wheel. The center of pressure progresses on the ground like a wheel of radius 0.3 L (leg length). We examined the effect of varying foot curvature on the mechanics and energetics of walking. We controlled curvature by attaching rigid arc shapes of various radii to the bottoms of rigid boots restricting ankle motion. We measured mechanical work performed on the center of mass (COM), and net metabolic rate, in human subjects (N=10) walking with seven arc radii from 0.02-0.40 m. Simple models of dynamic walking predict that redirection of COM velocity requires step-to-step transition work, decreasing quadratically with arc radius. Metabolic cost would be expected to change in proportion to mechanical work. We measured the average rate of negative work performed on the COM, and found that it followed the trend well (r2=0.95), with 2.37 times as much work for small radii as for large. Net metabolic rate (subtracting quiet standing) also decreased with increasing arc radius to a minimum at 0.3 L, with a slight increase thereafter. Maximum net metabolic rate was 6.25 W kg(-1) (for small-radius arc feet), about 59% greater than the minimum rate of 3.93 W kg(-1), which in turn was about 45% greater than the rate in normal walking. Metabolic rate was fit reasonably well (r2=0.86) by a quadratic curve, but exceeded that expected from COM work for extreme arc sizes. Other factors appear to increase metabolic cost for walking on very small and very large arc feet. These factors may include effort expended to stabilize the joints (especially the knee) or to maintain balance. Rolling feet with curvature 0.3 L appear energetically advantageous for plantigrade walking, partially due to decreased work for step-to-step transitions.

Dynamic Electromechanical Coupling of Piezoelectric Bending Actuators

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Mostafa R. A. Nabawy

2016-01-01

Full Text Available Electromechanical coupling defines the ratio of electrical and mechanical energy exchanged during a flexure cycle of a piezoelectric actuator. This paper presents an analysis of the dynamic electromechanical coupling factor (dynamic EMCF for cantilever based piezoelectric actuators and provides for the first time explicit expressions for calculation of dynamic EMCF based on arrangement of passive and active layers, layer geometry, and active and passive materials selection. Three main cantilever layer configurations are considered: unimorph, dual layer bimorph and triple layer bimorph. The actuator is modeled using standard constitutive dynamic equations that relate deflection and charge to force and voltage. A mode shape formulation is used for the cantilever dynamics that allows the generalized mass to be the actual mass at the first resonant frequency, removing the need for numerical integration in the design process. Results are presented in the form of physical insight from the model structure and also numerical evaluations of the model to provide trends in dynamic EMCF with actuator design parameters. For given material properties of the active and passive layers and given system overall damping ratio, the triple layer bimorph topology is the best in terms of theoretically achievable dynamic EMCF, followed by the dual layer bimorph. For a damping ratio of 0.035, the dynamic EMCF for an example dual layer bimorph configuration is 9% better than for a unimorph configuration. For configurations with a passive layer, the ratio of thicknesses for the passive and active layers is the primary geometric design variable. Choice of passive layer stiffness (Young’s modulus relative to the stiffness of the material in the active layer is an important materials related design choice. For unimorph configurations, it is beneficial to use the highest stiffness possible passive material, whereas for triple layer bimorph configurations, the passive

Minimal Walking Technicolor

DEFF Research Database (Denmark)

Foadi, Roshan; Frandsen, Mads Toudal; A. Ryttov, T.

2007-01-01

Different theoretical and phenomenological aspects of the Minimal and Nonminimal Walking Technicolor theories have recently been studied. The goal here is to make the models ready for collider phenomenology. We do this by constructing the low energy effective theory containing scalars......, pseudoscalars, vector mesons and other fields predicted by the minimal walking theory. We construct their self-interactions and interactions with standard model fields. Using the Weinberg sum rules, opportunely modified to take into account the walking behavior of the underlying gauge theory, we find...... interesting relations for the spin-one spectrum. We derive the electroweak parameters using the newly constructed effective theory and compare the results with the underlying gauge theory. Our analysis is sufficiently general such that the resulting model can be used to represent a generic walking technicolor...

Walking - Sensing - Participation

DEFF Research Database (Denmark)

Bødker, Mads; Meinhardt, Nina Dam; Browning, David

2014-01-01

Building on ethnographic research and social theory in the field of ‘mobilities’, this workshop paper suggests that field work based on simply walking with people entails a form of embodied participation that informs technological interventions by creating a space within which to address a wider ...... set of experiential or ‘felt’ qualities of living with mobile technologies. Moving from reflections on the value of walking with people, the paper outlines some affordances of a smartphone application built to capture place experiences through walking.......Building on ethnographic research and social theory in the field of ‘mobilities’, this workshop paper suggests that field work based on simply walking with people entails a form of embodied participation that informs technological interventions by creating a space within which to address a wider...

Age-Related Imbalance Is Associated With Slower Walking Speed: An Analysis From the National Health and Nutrition Examination Survey.

Science.gov (United States)

Xie, Yanjun J; Liu, Elizabeth Y; Anson, Eric R; Agrawal, Yuri

Walking speed is an important dimension of gait function and is known to decline with age. Gait function is a process of dynamic balance and motor control that relies on multiple sensory inputs (eg, visual, proprioceptive, and vestibular) and motor outputs. These sensory and motor physiologic systems also play a role in static postural control, which has been shown to decline with age. In this study, we evaluated whether imbalance that occurs as part of healthy aging is associated with slower walking speed in a nationally representative sample of older adults. We performed a cross-sectional analysis of the previously collected 1999 to 2002 National Health and Nutrition Examination Survey (NHANES) data to evaluate whether age-related imbalance is associated with slower walking speed in older adults aged 50 to 85 years (n = 2116). Balance was assessed on a pass/fail basis during a challenging postural task-condition 4 of the modified Romberg Test-and walking speed was determined using a 20-ft (6.10 m) timed walk. Multivariable linear regression was used to evaluate the association between imbalance and walking speed, adjusting for demographic and health-related covariates. A structural equation model was developed to estimate the extent to which imbalance mediates the association between age and slower walking speed. In the unadjusted regression model, inability to perform the NHANES balance task was significantly associated with 0.10 m/s slower walking speed (95% confidence interval: -0.13 to -0.07; P imbalance mediates 12.2% of the association between age and slower walking speed in older adults. In a nationally representative sample, age-related balance limitation was associated with slower walking speed. Balance impairment may lead to walking speed declines. In addition, reduced static postural control and dynamic walking speed that occur with aging may share common etiologic origins, including the decline in visual, proprioceptive, and vestibular sensory and

Hydrogen passivation of polycrystalline Si thin film solar cells

Energy Technology Data Exchange (ETDEWEB)

Gorka, Benjamin

2010-12-15

Hydrogen passivation is a key process step in the fabrication of polycrystalline Si (poly-Si) thin film solar cells. In this work a parallel plate rf plasma setup was used for the hydrogen passivation treatment. The main topics that have been investigated are (i) the role of plasma parameters (like hydrogen pressure, electrode gap and plasma power), (ii) the dynamics of the hydrogen treatment and (iii) passivation of poly-Si with different material properties. Passivation was characterized by measuring the open-circuit voltage V{sub OC} of poly-Si reference samples. Optimum passivation conditions were found by measurements of the breakdown voltage V{sub brk} of the plasma for different pressures p and electrode gaps d. For each pressure, the best passivation was achieved at a gap d that corresponded to the minimum in V{sub brk}. Plasma simulations were carried out, which indicate that best V{sub OC} corresponds to a minimum in ion energy. V{sub OC} was not improved by a larger H flux. Investigations of the passivation dynamic showed that a plasma treatment in the lower temperature range ({<=}400 C) is slow and takes several hours for the V{sub OC} to saturate. Fast passivation can be successfully achieved at elevated temperatures around 500 C to 600 C with a plateau time of 10 min. It was found that prolonged hydrogenation leads to a loss in V{sub OC}, which is less pronounced within the observed optimum temperature range (500 C-600 C). Electron beam evaporation has been investigated as an alternative method to fabricate poly-Si absorbers. The material properties have been tuned by alteration of substrate temperature T{sub dep}=200-700 C and were characterized by Raman, ESR and V{sub OC} measurements. Largest grains were obtained after solid phase crystallization (SPC) of a-Si, deposited in the temperature range of 300 C. The defect concentration of Si dangling bonds was lowered by passivation by about one order of magnitude. The lowest dangling bond concentration

Kinematic effects of inertia and friction added by a robotic knee exoskeleton after prolonged walking.

Science.gov (United States)

Shirota, C; Tucker, M R; Lambercy, O; Gassert, R

2017-07-01

The capabilities of robotic gait assistive devices are ever increasing; however, their adoption outside of the lab is still limited. A critical barrier for the functionality of these devices are the still unknown mechanical properties of the human leg during dynamic conditions such as walking. We built a robotic knee exoskeleton to address this problem. Here, we present the effects of our device on the walking pattern of four subjects. We assessed the effects after a short period of acclimation as well as after a 1.5h walking protocol. We found that the knee exoskeleton decreased (towards extension) the peak hip extension and peak knee flexion of the leg with the exoskeleton, while minimally affecting the non-exoskeleton leg. Comparatively smaller changes occurred after prolonged walking. These results suggest that walking patterns attained after a few minutes of acclimation with a knee exoskeleton are stable for at least a couple of hours.

On the energetics of the walking gait of a human operator using a passive exoskeleton apparatus

Science.gov (United States)

Lavrovskii, E. K.

2015-01-01

We study the energy expenditures and the peak values of control torques which a human operator must apply in the process of exoskeleton displacement for various types of regular, plane, and single-support gaits. The obtained results allow us to estimate the performance of the passive exoskeleton apparatus.

Passivity-Based Control of a Class of Blondel-Park Transformable Electric Machines

Directory of Open Access Journals (Sweden)

Per J. Nicklasson

1997-10-01

Full Text Available In this paper we study the viability of extending, to the general rotating electric machine's model, the passivity-based controller method that we have developed for induction motors. In this approach the passivity (energy dissipation properties of the motor are taken advantage of at two different levels. First, we prove that the motor model can be decomposed as the feedback interconnection of two passive subsystems, which can essentially be identified with the electrical and mechanical dynamics. Then, we design a torque tracking controller that preserves passivity for the electrical subsystem, and leave the mechanical part as a "passive disturbance". In position or speed control applications this procedure naturally leads to the well known cascaded controller structure which is typically analyzed invoking time-scale separation assumptions. A key feature of the new cascaded control paradigm is that the latter arguments are obviated in the stability analysis. Our objective in this paper is to characterize a class of machines for which such a passivity-based controller solves the output feedback torque tracking problem. Roughly speaking, the class consists of machines whose nonactuated dynamics are well damped and whose electrical and mechanical dynamics can be suitably decoupled via a coordinate transformation. The first condition translates into the requirement of approximate knowledge of the rotor resistances to avoid the need of injecting high gain into the loop. The latter condition is known in the electric machines literature as Blondel-Park transformability, and in practical terms it requires that the air-gap magnetomotive force must be suitably approximated by the first harmonic in its Fourier expansion. These conditions, stemming from the construction of the machine, have a clear physical interpretation in terms of the couplings between its electrical, magnetic and mechanical dynamics, and are satisfied by a large number of practical

The Effects of Walking or Walking-with-Poles Training on Tissue Oxygenation in Patients with Peripheral Arterial Disease

Directory of Open Access Journals (Sweden)

Eileen G. Collins

2012-01-01

Full Text Available This randomized trial proposed to determine if there were differences in calf muscle StO2 parameters in patients before and after 12 weeks of a traditional walking or walking-with-poles exercise program. Data were collected on 85 patients who were randomized to a traditional walking program ( or walking-with-poles program ( of exercise training. Patients walked for 3 times weekly for 12 weeks. Seventy-one patients completed both the baseline and the 12-week follow-up progressive treadmill tests ( traditional walking and walking-with-poles. Using the near-infrared spectroscopy measures, StO2 was measured prior to, during, and after exercise. At baseline, calf muscle oxygenation decreased from % prior to the treadmill test to % at peak exercise. The time elapsed prior to reaching nadir StO2 values increased more in the traditional walking group when compared to the walking-with-poles group. Likewise, absolute walking time increased more in the traditional walking group than in the walking-with-poles group. Tissue oxygenation decline during treadmill testing was less for patients assigned to a 12-week traditional walking program when compared to those assigned to a 12-week walking-with-poles program. In conclusion, the 12-week traditional walking program was superior to walking-with-poles in improving tissue deoxygenation in patients with PAD.

A Study of Effect of Walking Pole on the Walking Exercise

OpenAIRE

加藤, 麻樹; 下平, 佳江; 佐藤, 健

2010-01-01

So-called metabolic syndrome is one of the medical problems in our country, because many of people have difficulty at lack of exercises. Ministry of Health, Labor and Welfare suggest healthy life by exercise and moderate foods. Walking is one of the effective exercises to keep health in everyday life. Walking with poles, the exercise method of cross country skiing, is noticed as the effective exercise nowadays. Some studies show the effect of the pole walking exercise from view points of c...

Tailoring discrete quantum walk dynamics via extended initial conditions

Energy Technology Data Exchange (ETDEWEB)

Valcarcel, German J de; Roldan, Eugenio [Departament d' Optica, Universitat de Valencia, Dr Moliner 50, 46100-Burjassot, Spain, EU (Spain); Romanelli, Alejandro, E-mail: german.valcarcel@uv.es, E-mail: eugenio.roldan@uv.es, E-mail: alejo@fing.edu.uy [Instituto de Fisica, Facultad de IngenierIa, Universidad de la Republica, CC 30, CP 11000, Montevideo (Uruguay)

2010-12-15

We study the evolution of initially extended distributions in the coined quantum walk (QW) on the line. By analysing the dispersion relation of the process, continuous wave equations are derived whose form depends on the initial distribution shape. In particular, for a class of initial conditions, the evolution is dictated by the Schroedinger equation of a free particle. As that equation also governs paraxial optical diffraction, all of the phenomenology of the latter can be implemented in the QW. This allows us, in particular, to devise an initially extended condition leading to a uniform probability distribution whose width increases linearly with time, with increasing homogeneity.

Tailoring discrete quantum walk dynamics via extended initial conditions

International Nuclear Information System (INIS)

Valcarcel, German J de; Roldan, Eugenio; Romanelli, Alejandro

2010-01-01

We study the evolution of initially extended distributions in the coined quantum walk (QW) on the line. By analysing the dispersion relation of the process, continuous wave equations are derived whose form depends on the initial distribution shape. In particular, for a class of initial conditions, the evolution is dictated by the Schroedinger equation of a free particle. As that equation also governs paraxial optical diffraction, all of the phenomenology of the latter can be implemented in the QW. This allows us, in particular, to devise an initially extended condition leading to a uniform probability distribution whose width increases linearly with time, with increasing homogeneity.

Piping reliability improvement through passive seismic supports

International Nuclear Information System (INIS)

Baltus, R.; Rubbers, A.

1999-01-01

The nuclear plants designed in the 1970's were equipped with large quantities of snubbers in auxiliary piping systems. The experience revealed a poor performance of snubbers during periodic inspection, while non-nuclear facility piping survived through strong earthquakes. Consequently, seismic design rules evolved towards more realistic criteria and passive dynamic supports were developed to reduce snubber quantities. These solutions improve the pipe reliability during normal operation while reducing the radiation exposure in a sample line is presented with the impact on pipe stresses compared to the results obtained with passive supports named Limit Stops. (author)

CHECKING OF TECHNICAL BRIDGES’ STATE BY PASSIVE VIBRATIONAL DYNAMICS METHODS

Directory of Open Access Journals (Sweden)

V. P. Redchenko

2010-03-01

Full Text Available In the article the results of studies of the passive vibration test methods and the possibilities of using them for determining and monitoring of technical condition of bridges are presented.

On the Disambiguation of Passively Measured In-home Gait Velocities from Multi-person Smart Homes.

Science.gov (United States)

Austin, Daniel; Hayes, Tamara L; Kaye, Jeffrey; Mattek, Nora; Pavel, Misha

2011-01-01

In-home monitoring of gait velocity with passive PIR sensors in a smart home has been shown to be an effective method of continuously and unobtrusively measuring this important predictor of cognitive function and mobility. However, passive measurements of velocity are nonspecific with regard to who generated each measurement or walking event. As a result, this method is not suitable for multi-person homes without additional information to aid in the disambiguation of gait velocities. In this paper we propose a method based on Gaussian mixture models (GMMs) combined with infrequent clinical assessments of gait velocity to model in-home walking speeds of two or more residents. Modeling the gait parameters directly allows us to avoid the more difficult problem of assigning each measured velocity individually to the correct resident. We show that if the clinically measured gait velocities of residents are separated by at least 15 cm/s a GMM can be accurately fit to the in-home gait velocity data. We demonstrate the accuracy of this method by showing that the correlation between the means of the GMMs and the clinically measured gait velocities is 0.877 (p value < 0.0001) with bootstrapped 95% confidence intervals of (0.79, 0.94) for 54 measurements of 20 subjects living in multi-person homes. Example applications of using this method to track in-home mean velocities over time are also given.

An Improved Walk Model for Train Movement on Railway Network

International Nuclear Information System (INIS)

Li Keping; Mao Bohua; Gao Ziyou

2009-01-01

In this paper, we propose an improved walk model for simulating the train movement on railway network. In the proposed method, walkers represent trains. The improved walk model is a kind of the network-based simulation analysis model. Using some management rules for walker movement, walker can dynamically determine its departure and arrival times at stations. In order to test the proposed method, we simulate the train movement on a part of railway network. The numerical simulation and analytical results demonstrate that the improved model is an effective tool for simulating the train movement on railway network. Moreover, it can well capture the characteristic behaviors of train scheduling in railway traffic. (general)

Walking the Everyday

Directory of Open Access Journals (Sweden)

Matthew Bissen

2014-11-01

Full Text Available Since 2010, @matthewalking (Bissen, 2013 has published real-time public texts of walks in the city. This text-based Twitter feed has developed a narrative of a particular everyday life and developed a space of interface with others that represents a centering of perspective within an urban landscape. Walking the city provides a spatial, tactile, social, and embodied knowledge of the environment as each of us emerges into a space, orients ourselves, and determines a path that is highly localized, but is in connection with distant spaces and cultures. According to Ben Jacks in “Walking the City: Manhattan Projects,” “for urban dwellers and designers, walking is a fundamental tool for laying claim to, understanding, and shaping a livable city. Walking yields bodily knowing, recovers place memory, creates narrative, prioritizes human scale, and reconnects people to places” (75. @matthewalking’s walks, at times for as long as 5 hours, attempt to center an experience of an urban existence in a spatial narrative of the city that at once prioritizes a connection to place, but also is projected outward into a mediated relationship with others. The project is a series of unbounded walks, or dérives (drift, through the city that are logged on Twitter and traced to create an archive map of a set of particular urban experiences. The dérive concept as outlined in “The Theory of the Dérive,” by Guy Debord is when “one or more persons during a certain period drop their relations, their work and leisure activities, and all their other usual motives for movement and action, and let themselves be drawn by the attractions of the terrain and the encounters they find there” (62.

Cellular automaton simulation of pedestrian counter flow with different walk velocities

International Nuclear Information System (INIS)

Weng, W. G.; Chen, T.; Yuan, H. Y.; Fan, W. C.

2006-01-01

This paper presents a cellular automaton model without step back for pedestrian dynamics considering the human behaviors which can make judgments in some complex situations. This model can simulate pedestrian movement with different walk velocities through update at different time-step intervals. Two kinds of boundary conditions including periodic and open boundary for pedestrian counter flow are considered, and their dynamical characteristics are discussed. Simulation results show that for periodic boundary condition there are three phases of pedestrian patterns, i.e., freely moving phase, lane formation phase, and perfectly stopped phase at some certain total density ranges. In the stage of lane formation, the phenomenon that pedestrians exceed those with lower walk velocity through a narrow walkway can be found. For open boundary condition, at some certain entrance densities, there are two steady states of pedestrian patterns; but the first is metastable. Spontaneous fluctuations can break the first steady state, i.e., freely moving phase, and run into the second steady state, i.e., perfectly stopped phase

Dog ownership, dog walking, and leisure-time walking among Taiwanese metropolitan and nonmetropolitan older adults.

Science.gov (United States)

Liao, Yung; Huang, Pin-Hsuan; Chen, Yi-Ling; Hsueh, Ming-Chun; Chang, Shao-Hsi

2018-04-04

This study examined the prevalence of dog ownership and dog walking and its association with leisure-time walking among metropolitan and nonmetropolitan older adults. A telephone-based cross-sectional survey targeting Taiwanese older adults was conducted in November 2016. Data related to dog ownership, time spent dog walking (categorized as non-dog owner, non-dog walkers, and dog walkers), and sociodemographic variables were obtained from 1074 older adults. Adjusted binary logistic regression was then performed. In this sample, 12% of Taiwanese older adults owned a dog and 31% of them walked their dogs for an average of 232.13 min over 5.9 days/week (standard deviation = 2.03). Older adults living in nonmetropolitan areas were more likely to own a dog (14.7% vs. 9.1%) but less likely to walk their dog (25.9% vs. 39.6%) than were those living in metropolitan areas. Compared with non-dog owners, only older adults living in nonmetropolitan areas who were dog walkers achieved 150 min of leisure-time walking (odds ratio: 3.03, 95% confidence interval: 1.05-8.77), after adjustment for potential confounders. Older Taiwanese adults living in nonmetropolitan areas who owned and walked their dogs were more likely to achieve health-enhancing levels of leisure-time walking. Tailored physical activity interventions for promoting dog walking should be developed for older adults who are dog owners living in nonmetropolitan areas and who do not engage in dog walking.

Humanoids Learning to Walk: A Natural CPG-Actor-Critic Architecture.

Science.gov (United States)

Li, Cai; Lowe, Robert; Ziemke, Tom

2013-01-01

The identification of learning mechanisms for locomotion has been the subject of much research for some time but many challenges remain. Dynamic systems theory (DST) offers a novel approach to humanoid learning through environmental interaction. Reinforcement learning (RL) has offered a promising method to adaptively link the dynamic system to the environment it interacts with via a reward-based value system. In this paper, we propose a model that integrates the above perspectives and applies it to the case of a humanoid (NAO) robot learning to walk the ability of which emerges from its value-based interaction with the environment. In the model, a simplified central pattern generator (CPG) architecture inspired by neuroscientific research and DST is integrated with an actor-critic approach to RL (cpg-actor-critic). In the cpg-actor-critic architecture, least-square-temporal-difference based learning converges to the optimal solution quickly by using natural gradient learning and balancing exploration and exploitation. Futhermore, rather than using a traditional (designer-specified) reward it uses a dynamic value function as a stability indicator that adapts to the environment. The results obtained are analyzed using a novel DST-based embodied cognition approach. Learning to walk, from this perspective, is a process of integrating levels of sensorimotor activity and value.

Humanoids Learning to Walk: a Natural CPG-Actor-Critic Architecture

Directory of Open Access Journals (Sweden)

CAI eLI

2013-04-01

Full Text Available The identification of learning mechanisms for locomotion has been the subject of much researchfor some time but many challenges remain. Dynamic systems theory (DST offers a novel approach to humanoid learning through environmental interaction. Reinforcement learning (RL has offered a promising method to adaptively link the dynamic system to the environment it interacts with via a reward-based value system.In this paper, we propose a model that integrates the above perspectives and applies it to the case of a humanoid (NAO robot learning to walk the ability of which emerges from its value-based interaction with the environment. In the model,a simplified central pattern generator (CPG architecture inspired by neuroscientific research and DST is integrated with an actor-critic approach to RL (cpg-actor-critic. In the cpg-actor-critic architecture, least-square-temporal-difference (LSTD based learning converges to the optimal solution quickly by using natural gradient and balancing exploration and exploitation. Futhermore, rather than using a traditional (designer-specified reward it uses a dynamic value function as a stability indicator (SI that adapts to the environment.The results obtained are analyzed and explained by using a novel DST embodied cognition approach. Learning to walk, from this perspective, is a process of integrating sensorimotor levels and value.

Aerobic treadmill plus Bobath walking training improves walking in subacute stroke: a randomized controlled trial.

Science.gov (United States)

Eich, H-J; Mach, H; Werner, C; Hesse, S

2004-09-01

To evaluate the immediate and long-term effects of aerobic treadmill plus Bobath walking training in subacute stroke survivors compared with Bobath walking training alone. Randomized controlled trial. Rehabilitation unit. Fifty patients, first-time supratentorial stroke, stroke interval less than six weeks, Barthel Index (0-100) from 50 to 80, able to walk a minimum distance of 12 m with either intermittent help or stand-by while walking, cardiovascular stable, minimum 50 W in the bicycle ergometry, randomly allocated to two groups, A and B. Group A 30 min of treadmill training, harness secured and minimally supported according to patients' needs, and 30 min of physiotherapy, every workday for six weeks, speed and inclination of the treadmill were adjusted to achieve a heart rate of HR: (Hrmax-HRrest)*0.6+HRrest; in group B 60 min of daily physiotherapy for six weeks. Primary outcome variables were the absolute improvement of walking velocity (m/s) and capacity (m), secondary were gross motor function including walking ability (score out of 13) and walking quality (score out of 41), blindly assessed before and after the intervention, and at follow-up three months later. Patients tolerated the aerobic training well with no side-effects, significantly greater improvement of walking velocity and capacity both at study end (p =0.001 versus p =0.002) and at follow-up (p Bobath walking training in moderately affected stroke patients was better than Bobath walking training alone with respect to the improvement of walking velocity and capacity. The treatment approach is recommended in patients meeting the inclusion criteria. A multicentre trial should follow to strengthen the evidence.

The Walking Renaissance: A Longitudinal Analysis of Walking Travel in the Greater Los Angeles Area, USA

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Kenneth Joh

2015-07-01

Full Text Available Promoting walking travel is considered important for reducing automobile use and improving public health. Recent U.S. transportation policy has incentivized investments in alternative, more sustainable transportation modes such as walking, bicycling and transit in auto-oriented cities such as Los Angeles. Although many past studies have analyzed changes in walking travel across the U.S., there is little clarity on the drivers of change. We address this gap by conducting a longitudinal analysis of walking travel in the greater Los Angeles area from 2001 to 2009. We use travel diary and household data from regional and national surveys to analyze changes in walking trip shares and rates across our study area. Results show that walking has significantly increased across most of Los Angeles, and that increases in walking trips generally correspond with increases in population, employment, and transit service densities. Estimates from fixed-effects regression analysis generally suggest a positive association between population density and walking, and that higher increases in transit stop density are correlated with increased walking trips to and from transit stops. These findings illustrate how regional planning efforts to pursue a coordinated land use-transit planning strategy can help promote walking in auto-oriented or vehicle adopting cities.

Pedestrian and Evacuation Dynamics 2012

CERN Document Server

Kirsch, Uwe; Schreckenberg, Michael

2014-01-01

The 6th International Conference on Pedestrian and Evacuation Dynamics conference (PED2012) showcased research on human locomotion. This book presents the proceedings of PED2012. Humans have walked for eons; our drive to settle the globe began with a walk out of Africa. However, much remains to discover. As the world moves toward sustainability while racing to assess and accommodate climate change, research must provide insight on the physical requirements of walking, the dynamics of pedestrians on the move and more. We must understand, predict and simulate pedestrian behaviour, to avoid dangerous situations, to plan for emergencies, and not least, to make walking more attractive and enjoyable. PED2012 offered 70 presentations and keynotes and 70 poster presentations covering new and improved mathematical models, describing new insights on pedestrian behaviour in normal and emergency cases and presenting research based on sensors and advanced observation methods. These papers offer a starting point for innova...

A Realization of a Quasi-Random Walk for Atoms in Time-Dependent Optical Potentials

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Torsten Hinkel

2015-09-01

Full Text Available We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential that forces the atom into a non-trivial motion, strongly resembling a discrete random walk behavior between lattice sites. We provide both numerical and analytical analysis of such a quasi-random walk behavior.

Effect of uphill and downhill walking on walking performance in geriatric patients using a wheeled walker.

Science.gov (United States)

Lindemann, Ulrich; Schwenk, Michael; Schmitt, Syn; Weyrich, Michael; Schlicht, Wolfgang; Becker, Clemens

2017-08-01

Wheeled walkers are recommended to improve walking performance in older persons and to encourage and assist participation in daily life. Nevertheless, using a wheeled walker can cause serious problems in the natural environment. This study aimed to compare uphill and downhill walking with walking level in geriatric patients using a wheeled walker. Furthermore, we investigated the effect of using a wheeled walker with respect to dual tasking when walking level. A total of 20 geriatric patients (median age 84.5 years) walked 10 m at their habitual pace along a level surface, uphill and downhill, with and without a standard wheeled walker. Gait speed, stride length and cadence were assessed by wearable sensors and the walk ratio was calculated. When using a wheeled walker while walking level the walk ratio improved (0.58 m/[steps/min] versus 0.57 m/[steps/min], p = 0.023) but gait speed decreased (1.07 m/s versus 1.12 m/s, p = 0.020) when compared to not using a wheeled walker. With respect to the walk ratio, uphill and downhill walking with a wheeled walker decreased walking performance when compared to level walking (0.54 m/[steps/min] versus 0.58 m/[steps/min], p = 0.023 and 0.55 m/[steps/min] versus 0.58 m/[steps/min], p = 0.001, respectively). At the same time, gait speed decreased (0.079 m/s versus 1.07 m/s, p walker improved the quality of level walking but the performance of uphill and downhill walking was worse compared to walking level when using a wheeled walker.

[Objective evaluation of arterial intermittent claudication by the walking tolerance test. Comparative study of physiological walking and walking on a conveyor belt (author's transl)].

Science.gov (United States)

Bouchet, J Y; Franco, A; Morzol, B; Beani, J C

1980-01-01

Two methods are used to evaluate the walking distance: physiological walking along a standard path (0% - 6 mk/h) and walking on a tread mill (10% - 3 km/h). In both tests, four data are checked: -- initial trouble distance, -- cramp or walking-distance, -- localisation of pain, -- recovery time. These tests are dependable for the diagnosis of arterial claudication, reproducible and well tolerated. Their results have been compared: there is no correlation between the initial trouble distance and the cramp distance. However there is a correlation between the cramp distance by physiological walking and on treadmill. Recovery time, if long, is a criteria of gravity. Interests of both methods are discussed.

Simulation of quantum dynamics with integrated photonics

Science.gov (United States)

Sansoni, Linda; Sciarrino, Fabio; Mataloni, Paolo; Crespi, Andrea; Ramponi, Roberta; Osellame, Roberto

2012-12-01

In recent years, quantum walks have been proposed as promising resources for the simulation of physical quantum systems. In fact it is widely adopted to simulate quantum dynamics. Up to now single particle quantum walks have been experimentally demonstrated by different approaches, while only few experiments involving many-particle quantum walks have been realized. Here we simulate the 2-particle dynamics on a discrete time quantum walk, built on an array of integrated waveguide beam splitters. The polarization independence of the quantum walk circuit allowed us to exploit the polarization entanglement to encode the symmetry of the two-photon wavefunction, thus the bunching-antibunching behavior of non interacting bosons and fermions has been simulated. We have also characterized the possible distinguishability and decoherence effects arising in such a structure. This study is necessary in view of the realization of a quantum simulator based on an integrated optical array built on a large number of beam splitters.

Topology Optimization of Passive Micromixers Based on Lagrangian Mapping Method

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Yuchen Guo

2018-03-01

Full Text Available This paper presents an optimization-based design method of passive micromixers for immiscible fluids, which means that the Peclet number infinitely large. Based on topology optimization method, an optimization model is constructed to find the optimal layout of the passive micromixers. Being different from the topology optimization methods with Eulerian description of the convection-diffusion dynamics, this proposed method considers the extreme case, where the mixing is dominated completely by the convection with negligible diffusion. In this method, the mixing dynamics is modeled by the mapping method, a Lagrangian description that can deal with the case with convection-dominance. Several numerical examples have been presented to demonstrate the validity of the proposed method.

The effects of smartphone multitasking on gait and dynamic balance.

Science.gov (United States)

Lee, Jeon Hyeong; Lee, Myoung Hee

2018-02-01

[Purpose] This study was performed to analyze the influence of smartphone multitasking on gait and dynamic balance. [Subjects and Methods] The subjects were 19 male and 20 female university students. There were 4 types of gait tasks: General Gait (walking without a task), Task Gait 1 (walking while writing a message), Task Gait 2 (walking while writing a message and listening to music), Task Gait 3 (walking while writing a message and having a conversation). To exclude the learning effect, the order of tasks was randomized. The Zebris FDM-T treadmill system (Zebris Medical GmbH, Germany) was used to measure left and right step length and width, and a 10 m walking test (10MWT) was conducted for gait velocity. In addition, a Timed Up and Go test (TUG) was used to measure dynamic balance. All the tasks were performed 3 times, and the mean of the measured values was analyzed. [Results] There were no statistically significant differences in step length and width. There were statistically significant differences in the 10MWT and TUG tests. [Conclusion] Using a smartphone while walking decreases a person's dynamic balance and walking ability. It is considered that accident rates are higher when using a smartphone.

Random walks and diffusion on networks

Science.gov (United States)

Masuda, Naoki; Porter, Mason A.; Lambiotte, Renaud

2017-11-01

Random walks are ubiquitous in the sciences, and they are interesting from both theoretical and practical perspectives. They are one of the most fundamental types of stochastic processes; can be used to model numerous phenomena, including diffusion, interactions, and opinions among humans and animals; and can be used to extract information about important entities or dense groups of entities in a network. Random walks have been studied for many decades on both regular lattices and (especially in the last couple of decades) on networks with a variety of structures. In the present article, we survey the theory and applications of random walks on networks, restricting ourselves to simple cases of single and non-adaptive random walkers. We distinguish three main types of random walks: discrete-time random walks, node-centric continuous-time random walks, and edge-centric continuous-time random walks. We first briefly survey random walks on a line, and then we consider random walks on various types of networks. We extensively discuss applications of random walks, including ranking of nodes (e.g., PageRank), community detection, respondent-driven sampling, and opinion models such as voter models.

The effect of shoe type on static and dynamic balance during treadmill walking in young healthy women.

Science.gov (United States)

Kim, Mi-Kyoung; Kong, Byung-Sun; Yoo, Kyung-Tae

2017-09-01

[Purpose] The purpose of this study was to analyze the effect of various shoes on the static and dynamic balance of young women in their 20s. [Subjects and Methods] The subjects of the study were 15 healthy young women and repeated measured design. The subjects walked on the treadmill at a speed of 4 km/h for 30 minutes wearing three types of shoes: sneaker, rain boots, and combat boots. Balance was measured by a Romberg test and a limits of stability test. One-way ANOVA was used for statistical analysis. [Results] As the results of the Romberg test, the main effect of time was shown in the EO-COG area, EO-COG length, and EO-COG velocity. As the results of the limits of stability test, the main effects of time in LT, RT, FW, and total. There were significant differences in the LT in the sneaker group, the rain boots group, and the LT and RT in the combat boots group between the pre- and post-test. [Conclusion] The characteristics of shoes such as the materials, hardness, and thickness of the soles, the coefficient of friction of the outsoles, and the collar height affected the static and dynamic balance.

A comparison of at-home walking and 10-meter walking test parameters of individuals with post-stroke hemiparesis.

Science.gov (United States)

Nagano, Katsuhito; Hori, Hideaki; Muramatsu, Ken

2015-02-01

[Purpose] The purpose of this study was to clarify the difference in gait parameters of at-home walking and the 10-meter walking test results of individuals with hemiparesis. [Subjects] A total of 14 hemiparetic stroke recovery patients participated in this study. Inclusion criteria were: living at home, the ability to walk independently, and demonstrated low extremity on recovery stages III-V on the Brunnstrom Approach. The average age of the subjects was 66 years. [Methods] We used video surveillance and the inked footprint technique to record usual walking speed and maximum speed patterns both in subjects' homes and during the 10-meter walking test. From these methods, walking speed, stride length, and step rate were calculated. [Results] While both usual and maximum walking speeds of the 10-meter walking test correlated with stride length and step rate, at-home walking speeds only significantly correlated with stride length. [Conclusion] Walking patterns of the 10-meter walking test are quantifiably distinct from those demonstrated in patients' homes, and this difference is mainly characterized by stride length. In order to enhance in-home walking ability, exercises that improve length of stride rather than step rate should be recommended.

Non-Markovian decoherent quantum walks

International Nuclear Information System (INIS)

Xue Peng; Zhang Yong-Sheng

2013-01-01

Quantum walks act in obviously different ways from their classical counterparts, but decoherence will lessen and close this gap between them. To understand this process, it is necessary to investigate the evolution of quantum walks under different decoherence situations. In this article, we study a non-Markovian decoherent quantum walk on a line. In a short time regime, the behavior of the walk deviates from both ideal quantum walks and classical random walks. The position variance as a measure of the quantum walk collapses and revives for a short time, and tends to have a linear relation with time. That is, the walker's behavior shows a diffusive spread over a long time limit, which is caused by non-Markovian dephasing affecting the quantum correlations between the quantum walker and his coin. We also study both quantum discord and measurement-induced disturbance as measures of the quantum correlations, and observe both collapse and revival in the short time regime, and the tendency to be zero in the long time limit. Therefore, quantum walks with non-Markovian decoherence tend to have diffusive spreading behavior over long time limits, while in the short time regime they oscillate between ballistic and diffusive spreading behavior, and the quantum correlation collapses and revives due to the memory effect

Validity and Reliability of Dynamic Visual Acuity (DVA) Measurement During Walking

Science.gov (United States)

Deshpande, Nandini; Peters, Brian T.; Bloomberg, Jacob J.

2014-01-01

DVA is primarily subserved by the vestibulo-ocular reflex mechanism. Individuals with vestibular hypofunction commonly experience highly debilitating illusory movement or blurring of visual images during daily activities possibly, due to impaired DVA. Even without pathologies, gradual age-related morphological deterioration is evident in all components of the vestibular system. We examined the construct validity to detect age-related differences and test-retest reliability of DVA measurements performed during walking. METHODS: Healthy adults were recruited into 3 groups: 1. young (20-39years, n=18), 2. middle-aged (40-59years, n=14), and 3. older adults (60-80years, n=15). Randomly selected seven participants from each group (n=21) participated in retesting. Participants were excluded if they had a history of vestibular or neuromuscular pathologies, dizziness/vertigo or >1 falls in the past year. Older persons with MMSE scores reliability. RESULTS: The three age groups were not different in their height, weight and normal walking speed (p>0.05). The post hoc analyses for DVA measurements demonstrated that each group was significantly different from the other two groups for Near as well as FarDVA (preliability. FarDVA at 0.8 m/s and 1.0 m/s demonstrated good test-retest reliability (ICCs 0.71 and 0.77, respectively).

Human H-reflexes are smaller in difficult beam walking than in normal treadmill walking.

Science.gov (United States)

Llewellyn, M; Yang, J F; Prochazka, A

1990-01-01

Hoffman (H) reflexes were elicited from the soleus (SOL) muscle while subjects walked on a treadmill and on a narrow beam (3.5 cm wide, raised 34 cm from the floor). The speed of walking on the treadmill was selected for each subject to match the background activation level of their SOL muscle during beam walking. The normal reciprocal activation pattern of the tibialis anterior and SOL muscles in treadmill walking was replaced by a pattern dominated by co-contraction on the beam. In addition, the step cycle duration was more variable and the time spent in the swing phase was reduced on the beam. The H-reflexes were highly modulated in both tasks, the amplitude being high in the stance phase and low in the swing phase. The H-reflex amplitude was on average 40% lower during beam walking than treadmill walking. The relationship between the H-reflex amplitude and the SOL EMG level was quantified by a regression line relating the two variables. The slope of this line was on average 41% lower in beam walking than treadmill walking. The lower H-reflex gain observed in this study and the high level of fusimotor drive observed in cats performing similar tasks suggest that the two mechanisms which control the excitability of this reflex pathway (i.e. fusimotor action and control of transmission at the muscle spindle to moto-neuron synapse) may be controlled independently.

Fundamental studies of passivity and passivity breakdown

International Nuclear Information System (INIS)

Macdonald, D.D.; Urquidi-Macdonald, M.; Song, H.; Biaggio-Rocha, S.; Searson, P.

1991-11-01

This report summarizes the findings of our fundamental research program on passivity and passivity breakdown. During the past three and one half years in this program (including the three year incrementally-funded grant prior to the present grant), we developed and experimentally tested various physical models for the growth and breakdown of passive films on metal surfaces. These models belong to a general class termed ''point defects models'' (PDMs), in which the growth and breakdown of passive films are described in terms of the movement of anion and cation vacancies

Nordic Walking Can Be Incorporated in the Exercise Prescription to Increase Aerobic Capacity, Strength, and Quality of Life for Elderly: A Systematic Review and Meta-Analysis.

Science.gov (United States)

Bullo, Valentina; Gobbo, Stefano; Vendramin, Barbara; Duregon, Federica; Cugusi, Lucia; Di Blasio, Andrea; Bocalini, Danilo Sales; Zaccaria, Marco; Bergamin, Marco; Ermolao, Andrea

2018-04-01

The aim of this systematic review and meta-analysis was to summarize and analyze the effects of Nordic Walking on physical fitness, body composition, and quality of life in the elderly. Keyword "Nordic Walking" associated with "elderly" AND/OR "aging" AND/OR "old subjects" AND/OR "aged" AND/OR "older adults" were used in the online database MEDLINE, Embase, PubMed, Scopus, PsycINFO, and SPORTDiscus. Only studies written in English language and published in peer-reviewed journals were considered. A meta-analysis was performed and effect sizes calculated. Fifteen studies were identified; age of participants ranged from 60 to 92 years old. Comparing with a sedentary group, effect sizes showed that Nordic Walking was able to improve dynamic balance (0.30), functional balance (0.62), muscle strength of upper (0.66) and lower limbs (0.43), aerobic capacity (0.92), cardiovascular outcomes (0.23), body composition (0.30), and lipid profile (0.67). It seemed that Nordic Walking had a negative effect on static balance (-0.72). Comparing with a walking (alone) training, effect sizes showed that Nordic Walking improved the dynamic balance (0.30), flexibility of the lower body (0.47), and quality of life (0.53). Walking training was more effective in improving aerobic capacity (-0.21). Comparing Nordic Walking with resistance training, effect sizes showed that Nordic Walking improved dynamic balance (0.33), muscle strength of the lower body (0.39), aerobic capacity (0.75), flexibility of the upper body (0.41), and the quality of life (0.93). Nordic Walking can be considered as a safe and accessible form of aerobic exercise for the elderly population, able to improve cardiovascular outcomes, muscle strength, balance ability, and quality of life.

Race walking gait and its influence on race walking economy in world-class race walkers.

Science.gov (United States)

Gomez-Ezeiza, Josu; Torres-Unda, Jon; Tam, Nicholas; Irazusta, Jon; Granados, Cristina; Santos-Concejero, Jordan

2018-03-06

The aim of this study was to determine the relationships between biomechanical parameters of the gait cycle and race walking economy in world-class Olympic race walkers. Twenty-One world-class race walkers possessing the Olympic qualifying standard participated in this study. Participants completed an incremental race walking test starting at 10 km·h -1 , where race walking economy (ml·kg -1 ·km -1 ) and spatiotemporal gait variables were analysed at different speeds. 20-km race walking performance was related to race walking economy, being the fastest race walkers those displaying reduced oxygen cost at a given speed (R = 0.760, p < 0.001). Longer ground contact times, shorter flight times, longer midstance sub-phase and shorter propulsive sub-phase during stance were related to a better race walking economy (moderate effect, p < 0.05). According to the results of this study, the fastest race walkers were more economi cal than the lesser performers. Similarly, shorter flight times are associated with a more efficient race walking economy. Coaches and race walkers should avoid modifying their race walking style by increasing flight times, as it may not only impair economy, but also lead to disqualification.

Walking and child pedestrian injury: a systematic review of built environment correlates of safe walking.

Science.gov (United States)

Rothman, Linda; Buliung, Ron; Macarthur, Colin; To, Teresa; Howard, Andrew

2014-02-01

The child active transportation literature has focused on walking, with little attention to risk associated with increased traffic exposure. This paper reviews the literature related to built environment correlates of walking and pedestrian injury in children together, to broaden the current conceptualization of walkability to include injury prevention. Two independent searches were conducted focused on walking in children and child pedestrian injury within nine electronic databases until March, 2012. Studies were included which: 1) were quantitative 2) set in motorized countries 3) were either urban or suburban 4) investigated specific built environment risk factors 5) had outcomes of either walking in children and/or child pedestrian roadway collisions (ages 0-12). Built environment features were categorized according to those related to density, land use diversity or roadway design. Results were cross-tabulated to identify how built environment features associate with walking and injury. Fifty walking and 35 child pedestrian injury studies were identified. Only traffic calming and presence of playgrounds/recreation areas were consistently associated with more walking and less pedestrian injury. Several built environment features were associated with more walking, but with increased injury. Many features had inconsistent results or had not been investigated for either outcome. The findings emphasise the importance of incorporating safety into the conversation about creating more walkable cities.

Walking and Sensing Mobile Lives

DEFF Research Database (Denmark)

Bødker, Mads; Meinhardt, Nina Dam

In this position paper, we discuss how mindful walking with people allow us to explore sensory aspects of mobile lives that are typically absent from research. We present an app that aids researchers collect impressions from a walk.......In this position paper, we discuss how mindful walking with people allow us to explore sensory aspects of mobile lives that are typically absent from research. We present an app that aids researchers collect impressions from a walk....

Human treadmill walking needs attention

Directory of Open Access Journals (Sweden)

Daniel Olivier

2006-08-01

Full Text Available Abstract Background The aim of the study was to assess the attentional requirements of steady state treadmill walking in human subjects using a dual task paradigm. The extent of decrement of a secondary (cognitive RT task provides a measure of the attentional resources required to maintain performance of the primary (locomotor task. Varying the level of difficulty of the reaction time (RT task is used to verify the priority of allocation of attentional resources. Methods 11 healthy adult subjects were required to walk while simultaneously performing a RT task. Participants were instructed to bite a pressure transducer placed in the mouth as quickly as possible in response to an unpredictable electrical stimulation applied on the back of the neck. Each subject was tested under five different experimental conditions: simple RT task alone and while walking, recognition RT task alone and while walking, walking alone. A foot switch system composed of a pressure sensitive sensor was placed under the heel and forefoot of each foot to determine the gait cycle duration. Results Gait cycle duration was unchanged (p > 0.05 by the addition of the RT task. Regardless of the level of difficulty of the RT task, the RTs were longer during treadmill walking than in sitting conditions (p 0.05 was found between the attentional demand of the walking task and the decrement of performance found in the RT task under varying levels of difficulty. This finding suggests that the healthy subjects prioritized the control of walking at the expense of cognitive performance. Conclusion We conclude that treadmill walking in young adults is not a purely automatic task. The methodology and outcome measures used in this study provide an assessment of the attentional resources required by walking on the treadmill at a steady state.

'It was not just a walking experience': reflections on the role of care in dog-walking.

Science.gov (United States)

Degeling, Chris; Rock, Melanie

2013-09-01

Research into physical activity and human health has recently begun to attend to dog-walking. This study extends the literature on dog-walking as a health behaviour by conceptualizing dog-walking as a caring practice. It centres on qualitative interviews with 11 Canadian dog-owners. All participants resided in urban neighbourhoods identified through previous quantitative research as conducive to dog-walking. Canine characteristics, including breed and age, were found to influence people's physical activity. The health of the dog and its position in the life-course influenced patterns of dog-walking. Frequency, duration and spatial patterns of dog-walking all depended on relationships and people's capacity to tap into resources. In foregrounding networks of care, inclusive of pets and public spaces, a relational conceptualization of dog-walking as a practice of caring helps to make sense of heterogeneity in patterns of physical activity among dog-owners.

Pedestrian Walking Behavior Revealed through a Random Walk Model

Directory of Open Access Journals (Sweden)

Hui Xiong

2012-01-01

Full Text Available This paper applies method of continuous-time random walks for pedestrian flow simulation. In the model, pedestrians can walk forward or backward and turn left or right if there is no block. Velocities of pedestrian flow moving forward or diffusing are dominated by coefficients. The waiting time preceding each jump is assumed to follow an exponential distribution. To solve the model, a second-order two-dimensional partial differential equation, a high-order compact scheme with the alternating direction implicit method, is employed. In the numerical experiments, the walking domain of the first one is two-dimensional with two entrances and one exit, and that of the second one is two-dimensional with one entrance and one exit. The flows in both scenarios are one way. Numerical results show that the model can be used for pedestrian flow simulation.

Ascending and Descending in Virtual Reality: Simple and Safe System Using Passive Haptics.

Science.gov (United States)

Nagao, Ryohei; Matsumoto, Keigo; Narumi, Takuji; Tanikawa, Tomohiro; Hirose, Michitaka

2018-04-01

This paper presents a novel interactive system that provides users with virtual reality (VR) experiences, wherein users feel as if they are ascending/descending stairs through passive haptic feedback. The passive haptic stimuli are provided by small bumps under the feet of users; these stimuli are provided to represent the edges of the stairs in the virtual environment. The visual stimuli of the stairs and shoes, provided by head-mounted displays, evoke a visuo-haptic interaction that modifies a user's perception of the floor shape. Our system enables users to experience all types of stairs, such as half-turn and spiral stairs, in a VR setting. We conducted a preliminary user study and two experiments to evaluate the proposed technique. The preliminary user study investigated the effectiveness of the basic idea associated with the proposed technique for the case of a user ascending stairs. The results demonstrated that the passive haptic feedback produced by the small bumps enhanced the user's feeling of presence and sense of ascending. We subsequently performed an experiment to investigate an improved viewpoint manipulation method and the interaction of the manipulation and haptics for both the ascending and descending cases. The experimental results demonstrated that the participants had a feeling of presence and felt a steep stair gradient under the condition of haptic feedback and viewpoint manipulation based on the characteristics of actual stair walking data. However, these results also indicated that the proposed system may not be as effective in providing a sense of descending stairs without an optimization of the haptic stimuli. We then redesigned the shape of the small bumps, and evaluated the design in a second experiment. The results indicated that the best shape to present haptic stimuli is a right triangle cross section in both the ascending and descending cases. Although it is necessary to install small protrusions in the determined direction, by

Prosthetic ankle push-off work reduces metabolic rate but not collision work in non-amputee walking

OpenAIRE

Caputo, Joshua M.; Collins, Steven H.

2014-01-01

Individuals with unilateral below-knee amputation expend more energy than non-amputees during walking and exhibit reduced push-off work and increased hip work in the affected limb. Simple dynamic models of walking suggest a possible solution, predicting that increasing prosthetic ankle push-off should decrease leading limb collision, thereby reducing overall energy requirements. We conducted a rigorous experimental test of this idea wherein ankle-foot prosthesis push-off work was incrementall...

Continuous-Time Random Walk with multi-step memory: an application to market dynamics

Science.gov (United States)

Gubiec, Tomasz; Kutner, Ryszard

2017-11-01

An extended version of the Continuous-Time Random Walk (CTRW) model with memory is herein developed. This memory involves the dependence between arbitrary number of successive jumps of the process while waiting times between jumps are considered as i.i.d. random variables. This dependence was established analyzing empirical histograms for the stochastic process of a single share price on a market within the high frequency time scale. Then, it was justified theoretically by considering bid-ask bounce mechanism containing some delay characteristic for any double-auction market. Our model appeared exactly analytically solvable. Therefore, it enables a direct comparison of its predictions with their empirical counterparts, for instance, with empirical velocity autocorrelation function. Thus, the present research significantly extends capabilities of the CTRW formalism. Contribution to the Topical Issue "Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook", edited by Ryszard Kutner and Jaume Masoliver.

Exploring Muscle Activation during Nordic Walking: A Comparison between Conventional and Uphill Walking.

Directory of Open Access Journals (Sweden)

Barbara Pellegrini

Full Text Available Nordic Walking (NW owes much of its popularity to the benefits of greater energy expenditure and upper body engagement than found in conventional walking (W. Muscle activation during NW is still understudied, however. The aim of the present study was to assess differences in muscle activation and physiological responses between NW and W in level and uphill walking conditions. Nine expert Nordic Walkers (mean age 36.8±11.9 years; BMI 24.2±1.8 kg/m2 performed 5-minute treadmill trials of W and NW at 4 km/h on inclines of 0% and 15%. The electromyographic activity of seven upper body and five leg muscles and oxygen consumption (VO2 were recorded and pole force during NW was measured. VO2 during NW was 22.3% higher at 0% and only 6.9% higher at 15% than during W, while upper body muscle activation was 2- to 15-fold higher under both conditions. Lower body muscle activation was similarly increased during NW and W in the uphill condition, whereas the increase in erector spinae muscle activity was lower during NW than W. The lack of a significant increase in pole force during uphill walking may explain the lower extra energy expenditure of NW, indicating less upper body muscle activation to lift the body against gravity. NW seemed to reduce lower back muscle contraction in the uphill condition, suggesting that walking with poles may reduce effort to control trunk oscillations and could contribute to work production during NW. Although the difference in extra energy expenditure between NW and W was smaller in the uphill walking condition, the increased upper body muscle involvement during exercising with NW may confer additional benefit compared to conventional walking also on uphill terrains. Furthermore, people with low back pain may gain benefit from pole use when walking uphill.

Exploring Muscle Activation during Nordic Walking: A Comparison between Conventional and Uphill Walking.

Science.gov (United States)

Pellegrini, Barbara; Peyré-Tartaruga, Leonardo Alexandre; Zoppirolli, Chiara; Bortolan, Lorenzo; Bacchi, Elisabetta; Figard-Fabre, Hélène; Schena, Federico

2015-01-01

Nordic Walking (NW) owes much of its popularity to the benefits of greater energy expenditure and upper body engagement than found in conventional walking (W). Muscle activation during NW is still understudied, however. The aim of the present study was to assess differences in muscle activation and physiological responses between NW and W in level and uphill walking conditions. Nine expert Nordic Walkers (mean age 36.8±11.9 years; BMI 24.2±1.8 kg/m2) performed 5-minute treadmill trials of W and NW at 4 km/h on inclines of 0% and 15%. The electromyographic activity of seven upper body and five leg muscles and oxygen consumption (VO2) were recorded and pole force during NW was measured. VO2 during NW was 22.3% higher at 0% and only 6.9% higher at 15% than during W, while upper body muscle activation was 2- to 15-fold higher under both conditions. Lower body muscle activation was similarly increased during NW and W in the uphill condition, whereas the increase in erector spinae muscle activity was lower during NW than W. The lack of a significant increase in pole force during uphill walking may explain the lower extra energy expenditure of NW, indicating less upper body muscle activation to lift the body against gravity. NW seemed to reduce lower back muscle contraction in the uphill condition, suggesting that walking with poles may reduce effort to control trunk oscillations and could contribute to work production during NW. Although the difference in extra energy expenditure between NW and W was smaller in the uphill walking condition, the increased upper body muscle involvement during exercising with NW may confer additional benefit compared to conventional walking also on uphill terrains. Furthermore, people with low back pain may gain benefit from pole use when walking uphill.

Quantum walks based on an interferometric analogy

International Nuclear Information System (INIS)

Hillery, Mark; Bergou, Janos; Feldman, Edgar

2003-01-01

There are presently two models for quantum walks on graphs. The ''coined'' walk uses discrete-time steps, and contains, besides the particle making the walk, a second quantum system, the coin, that determines the direction in which the particle will move. The continuous walk operates with continuous time. Here a third model for quantum walks is proposed, which is based on an analogy to optical interferometers. It is a discrete-time model, and the unitary operator that advances the walk one step depends only on the local structure of the graph on which the walk is taking place. This type of walk also allows us to introduce elements, such as phase shifters, that have no counterpart in classical random walks. Several examples are discussed

Bio-Inspired Optimal Control Framework to Generate Walking Motions for the Humanoid Robot iCub Using Whole Body Models

Directory of Open Access Journals (Sweden)

Yue Hu

2018-02-01

Full Text Available Bipedal locomotion remains one of the major open challenges of humanoid robotics. The common approaches are based on simple reduced model dynamics to generate walking trajectories, often neglecting the whole-body dynamics of the robots. As motions in nature are often considered as optimal with respect to certain criteria, in this work, we present an optimal control-based approach that allows us to generate optimized walking motions using a precise whole-body dynamic model of the robot, in contrast with the common approaches. The optimal control problem is formulated to minimize a set of desired objective functions with respect to physical constraints of the robot and contact constraints of the walking phases; the problem is then solved with a direct multiple shooting method. We apply the formulation with combinations of different objective criteria to the model of a reduced version of the iCub humanoid robot of 15 internal DOF. The obtained trajectories are executed on the real robot, and we carry out a discussion on the differences between the outcomes of this approach with the classic approaches.

Active and Passive Microrheology: Theory and Simulation

Science.gov (United States)

Zia, Roseanna N.

2018-01-01

Microrheological study of complex fluids traces its roots to the work of the botanist Robert Brown in the early nineteenth century. Indeed, passive microrheology and Brownian motion are one and the same. Once thought to reveal a fundamental life force, the phenomenon was ultimately leveraged by Einstein in proof of the atomic nature of matter ( Haw 2006 ). His work simultaneously paved the way for modern-day passive microrheology by connecting observable particle motion—diffusion—to solvent properties—the viscosity—via the well-known Stokes-Einstein relation. Advances in microscopy techniques in the last two decades have prompted extensions of the original model to generalized forms for passive probing of complex fluids. In the last decade, active microrheology has emerged as a means by which to interrogate the nonequilibrium behavior of complex fluids, in particular, the non-Newtonian rheology of dynamically heterogeneous and microscopically small systems. Here we review theoretical and computational approaches and advances in both passive and active microrheology, with a focus on the extent to which these techniques preserve the connection between single-particle motion and flow properties, as well as the rather surprising recovery of non-Newtonian flow behavior observed in bulk rheology.

A Regulatory Perspective on the Performance and Reliability of Nuclear Passive Safety Systems

International Nuclear Information System (INIS)

Quan, Pham Trung; Lee, Sukho

2016-01-01

Passive safety systems have been proven to enhance the safety of NPPs. When an accident such as station blackout occurs, these systems can perform the following functions: the decay heat removal, passive safety injection, containment cooling, and the retention of radioactive materials. Following the IAEA definitions, using passive safety systems reduces reliance on active components to achieve proper actuation and not requiring operator intervention in accident conditions. That leads to the deviations in boundary conditions of the critical process or geometric parameters, which activate and operate the system to perform accident prevention and mitigation functions. The main difficulties in evaluation of functional failure of passive systems arise because of (a) lack of plant operational experience; (b) scarcity of adequate experimental data from integral test facilities or from separate effect tests in order to understand the performance characteristics of these passive systems, not only at normal operation but also during accidents and transients; (c) lack of accepted definitions of failure modes for these systems; and (d) difficulty in modeling certain physical behavior of these systems. Reliability assessment of the PSS is still one of the important issues. Several reliability methodologies such as REPAS, RMPS and ASPRA have been applied to the reliability assessments. However, some issues are remained unresolved due to lack of understanding of the treatment of dynamic failure characteristics of components of the PSS, the treatment of dynamic variation of independence process parameters such as ambient temperature and the functional failure criteria of the PSS. Dynamic reliability methodologies should be integrated in the PSS reliability analysis to have a true estimate of system failure probability. The methodology should estimate the physical variation of the parameters and the frequency of the accident sequences when the dynamic effects are considered

Passivity-Based Control of Rotational and Translational Timoshenko Arms

Directory of Open Access Journals (Sweden)

Minoru Sasaki

2012-01-01

Full Text Available It is shown that the alternate passivity-based control schemes can be designed which explicitly exploit the passivity properties of the Timoshenko model. This approach has the advantage over the conventional methods in the respect that it allows one to deal directly with the system's partial differential equations without resorting to approximations. Numerical results for the tracking control of a translational and rotational flexible Timoshenko arm are presented and compared. They verify that the proposed control schemes are effective at controlling flexible dynamical systems.

Dynamics and stability of rigid rotors levitated by passive cylinder-magnet bearings and driven/supported axially by pointwise contact clutch

DEFF Research Database (Denmark)

Andersen, Søren Bøgh; Enemark, Søren; Santos, Ilmar

2013-01-01

A stable rotor—supported laterally by passive magnetic bearings and longitudinally by magnetic forces and a clutch—loses suddenly its contact to the clutch and executes abruptly longitudinal movements away from its original equilibrium position as a result of small increases in angular velocity...... by MCMB using several configurations of magnet distribution are described based on an accurate nonlinear model able to reliably reproduce the rotor-bearing dynamic behaviour. Such investigations lead to: (a) clear physical explanation about the reasons for the rotor's unstable behaviour, losing its...

An Integrated Passive (Battery-Free) Seals-and-Tag for International Safeguards

International Nuclear Information System (INIS)

Nekoogar, F.; Dowla, F.

2015-01-01

The ability to reliably and securely automate the monitoring of SNM is an important goal in Safeguards. Although item level monitoring of SNM requires both seal and tag technologies, the two technologies thus far have been developed more or less independently, and had been a lack of an integrated compact system. An integrated seal-and-tag approach not only aids inspectors to perform their tasks effectively, this approach also allows real-time inspection in large scale facilities. A typical facility could be the size of a large warehouse with hundreds or thousands of items that need to be sealed and monitored in real-time. Previously we reported on advanced secure RF passive (battery-less) tags with special features including, long-range interrogation of passive tags, communicating with passive tags with strong encryption and dynamic authentication features, and the ability to place the tags directly on metal objects. In this paper, we report on a novel secure passive tag integrated with fibre optics seal that allows real-time monitoring of items through secure wireless communications that employs AES encryption and dynamic authentication. Furthermore, the devices can be networked for large scale operations. The proposed passive seal has the same capabilities as active seals in that it allows realtime monitoring. However, the battery lifetimes of conventional active seals are limited or unpredictable. As the long-term storage of SNM might last for several years, these passive seals having been integrated with passive RF tags, extends the lifetime of the physical seals and tags indefinitely, while getting the same performance of active seals and tags. The integrated seal-and-tag is transformational in addressing a critical need in Safeguards area for long-term real-time monitoring. (author)

The Effects of Aging and Dual Tasking on Human Gait Complexity During Treadmill Walking: A Comparative Study Using Quantized Dynamical Entropy and Sample Entropy.

Science.gov (United States)

Ahmadi, Samira; Wu, Christine; Sepehri, Nariman; Kantikar, Anuprita; Nankar, Mayur; Szturm, Tony

2018-01-01

Quantized dynamical entropy (QDE) has recently been proposed as a new measure to quantify the complexity of dynamical systems with the purpose of offering a better computational efficiency. This paper further investigates the viability of this method using five different human gait signals. These signals are recorded while normal walking and while performing secondary tasks among two age groups (young and older age groups). The results are compared with the outcomes of previously established sample entropy (SampEn) measure for the same signals. We also study how analyzing segmented and spatially and temporally normalized signal differs from analyzing whole data. Our findings show that human gait signals become more complex as people age and while they are cognitively loaded. Center of pressure (COP) displacement in mediolateral direction is the best signal for showing the gait changes. Moreover, the results suggest that by segmenting data, more information about intrastride dynamical features are obtained. Most importantly, QDE is shown to be a reliable measure for human gait complexity analysis.

Negligible motion artifacts in scalp electroencephalography (EEG during treadmill walking

Directory of Open Access Journals (Sweden)

Kevin eNathan

2016-01-01

Full Text Available Recent Mobile Brain/Body Imaging (MoBI techniques based on active electrode scalp electroencephalogram (EEG allow the acquisition and real-time analysis of brain dynamics during active unrestrained motor behavior involving whole body movements such as treadmill walking, over-ground walking and other locomotive and non-locomotive tasks. Unfortunately, MoBI protocols are prone to physiological and non-physiological artifacts, including motion artifacts that may contaminate the EEG recordings. A few attempts have been made to quantify these artifacts during locomotion tasks but with inconclusive results due in part to methodological pitfalls. In this paper, we investigate the potential contributions of motion artifacts in scalp EEG during treadmill walking at three different speeds (1.5, 3.0, and 4.5 km/h using a wireless 64 channel active EEG system and a wireless inertial sensor attached to the subject’s head. The experimental setup was designed according to good measurement practices using state-of-the-art commercially-available instruments, and the measurements were analyzed using Fourier analysis and wavelet coherence approaches. Contrary to prior claims, the subjects’ motion did not significantly affect their EEG during treadmill walking although precaution should be taken when gait speeds approach 4.5 km/h. Overall, these findings suggest how MoBI methods may be safely deployed in neural, cognitive, and rehabilitation engineering applications.

Equivalence of Szegedy's and coined quantum walks

Science.gov (United States)

Wong, Thomas G.

2017-09-01

Szegedy's quantum walk is a quantization of a classical random walk or Markov chain, where the walk occurs on the edges of the bipartite double cover of the original graph. To search, one can simply quantize a Markov chain with absorbing vertices. Recently, Santos proposed two alternative search algorithms that instead utilize the sign-flip oracle in Grover's algorithm rather than absorbing vertices. In this paper, we show that these two algorithms are exactly equivalent to two algorithms involving coined quantum walks, which are walks on the vertices of the original graph with an internal degree of freedom. The first scheme is equivalent to a coined quantum walk with one walk step per query of Grover's oracle, and the second is equivalent to a coined quantum walk with two walk steps per query of Grover's oracle. These equivalences lie outside the previously known equivalence of Szegedy's quantum walk with absorbing vertices and the coined quantum walk with the negative identity operator as the coin for marked vertices, whose precise relationships we also investigate.

Mixed random walks with a trap in scale-free networks including nearest-neighbor and next-nearest-neighbor jumps

Science.gov (United States)

Zhang, Zhongzhi; Dong, Yuze; Sheng, Yibin

2015-10-01

Random walks including non-nearest-neighbor jumps appear in many real situations such as the diffusion of adatoms and have found numerous applications including PageRank search algorithm; however, related theoretical results are much less for this dynamical process. In this paper, we present a study of mixed random walks in a family of fractal scale-free networks, where both nearest-neighbor and next-nearest-neighbor jumps are included. We focus on trapping problem in the network family, which is a particular case of random walks with a perfect trap fixed at the central high-degree node. We derive analytical expressions for the average trapping time (ATT), a quantitative indicator measuring the efficiency of the trapping process, by using two different methods, the results of which are consistent with each other. Furthermore, we analytically determine all the eigenvalues and their multiplicities for the fundamental matrix characterizing the dynamical process. Our results show that although next-nearest-neighbor jumps have no effect on the leading scaling of the trapping efficiency, they can strongly affect the prefactor of ATT, providing insight into better understanding of random-walk process in complex systems.

Role of passive body dynamics in micro-organism swimming in complex fluids

Science.gov (United States)

Thomases, Becca; Guy, Robert

2016-11-01

We investigate the role of passive body dynamics in the kinematics of swimming micro-organisms in complex fluids. Asymptotic analysis and linear theory are used to predict shape changes that result as body elasticity and fluid elasticity are varied. The analysis is compared with a computational model of a finite length swimmer in a Stokes-Oldroyd-B fluid. Simulations and theory agree quantitatively for small amplitude motions with low fluid elasticity (Deborah number). This may not be surprising as the theory is expected hold in these two regimes. What is more remarkable is that the predicted shape changes match the computational shape changes quantitatively for large amplitudes, even for large Deborah numbers. Shape changes only tell part of the story. Swimming speed depends on other effects as well. We see that shape changes can predict swimming speed well when either the amplitude is small (including large Deborah number) or when the Deborah number is small (including large amplitudes). It is only in the large De AND large amplitude regime where the theory breaks down and swimming speed can no longer be inferred from shape changes alone.

Why the null matters: statistical tests, random walks and evolution.

Science.gov (United States)

Sheets, H D; Mitchell, C E

2001-01-01

A number of statistical tests have been developed to determine what type of dynamics underlie observed changes in morphology in evolutionary time series, based on the pattern of change within the time series. The theory of the 'scaled maximum', the 'log-rate-interval' (LRI) method, and the Hurst exponent all operate on the same principle of comparing the maximum change, or rate of change, in the observed dataset to the maximum change expected of a random walk. Less change in a dataset than expected of a random walk has been interpreted as indicating stabilizing selection, while more change implies directional selection. The 'runs test' in contrast, operates on the sequencing of steps, rather than on excursion. Applications of these tests to computer generated, simulated time series of known dynamical form and various levels of additive noise indicate that there is a fundamental asymmetry in the rate of type II errors of the tests based on excursion: they are all highly sensitive to noise in models of directional selection that result in a linear trend within a time series, but are largely noise immune in the case of a simple model of stabilizing selection. Additionally, the LRI method has a lower sensitivity than originally claimed, due to the large range of LRI rates produced by random walks. Examination of the published results of these tests show that they have seldom produced a conclusion that an observed evolutionary time series was due to directional selection, a result which needs closer examination in light of the asymmetric response of these tests.

Problems facing the use of passive safety systems

International Nuclear Information System (INIS)

Burgazzi, L.

2012-01-01

This study will analyze the current state of the art in the reliability of passive systems for extensive use in future nuclear power plants. This case study uncovers the insights on the technological issues associated with the reliability of the systems based on thermal-hydraulics, for which, methods are still in developing phase. The paper is organized as follows: at first the current available methodologies are illustrated and compared, the open issues coming out from their analysis are identified. Five open issues have been identified: 1) the assessment of the uncertainties related to passive system performance; 2) the dependencies among parameters in thermo-hydraulics; 3) the integration of the passive systems within an accident sequence in combination with active systems; 4) the development of dynamic event tree to incorporate the evolution upon time of the physical processes; and 5) the comparison between active and passive systems, mainly on a functional viewpoint. For each open issue the state of the art and the outlook is presented; the relative importance of each of them within the evaluation process is presented as well. (authors)

Rhythmic walking interactions with auditory feedback

DEFF Research Database (Denmark)

Jylhä, Antti; Serafin, Stefania; Erkut, Cumhur

2012-01-01

of interactions based on varying the temporal characteristics of the output, using the sound of human walking as the input. The system either provides a direct synthesis of a walking sound based on the detected amplitude envelope of the user's footstep sounds, or provides a continuous synthetic walking sound...... as a stimulus for the walking human, either with a fixed tempo or a tempo adapting to the human gait. In a pilot experiment, the different interaction modes are studied with respect to their effect on the walking tempo and the experience of the subjects. The results tentatively outline different user profiles......Walking is a natural rhythmic activity that has become of interest as a means of interacting with software systems such as computer games. Therefore, designing multimodal walking interactions calls for further examination. This exploratory study presents a system capable of different kinds...

Quantum walks, deformed relativity and Hopf algebra symmetries.

Science.gov (United States)

Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo

2016-05-28

We show how the Weyl quantum walk derived from principles in D'Ariano & Perinotti (D'Ariano & Perinotti 2014Phys. Rev. A90, 062106. (doi:10.1103/PhysRevA.90.062106)), enjoying a nonlinear Lorentz symmetry of dynamics, allows one to introduce Hopf algebras for position and momentum of the emerging particle. We focus on two special models of Hopf algebras-the usual Poincaré and theκ-Poincaré algebras. © 2016 The Author(s).

Development of Matlab Simulink model for dynamics analysis of passive suspension system for lightweight vehicle

Science.gov (United States)

Jamali, M. S.; Ismail, K. A.; Taha, Z.; Aiman, M. F.

2017-10-01

In designing suitable isolators to reduce unwanted vibration in vehicles, the response from a mathematical model which characterizes the transmissibility ratio of the input and output of the vehicle is required. In this study, a Matlab Simulink model is developed to study the dynamic behaviour performance of passive suspension system for a lightweight electric vehicle. The Simulink model is based on the two degrees of freedom system quarter car model. The model is compared to the theoretical plots of the transmissibility ratios between the amplitudes of the displacements and accelerations of the sprung and unsprung masses to the amplitudes of the ground, against the frequencies at different damping values. It was found that the frequency responses obtained from the theoretical calculations and from the Simulink simulation is comparable to each other. Hence, the model may be extended to a full vehicle model.

Computational and experimental studies of microvascular void features for passive-adaptation of structural panel dynamic properties

Science.gov (United States)

Sears, Nicholas C.; Harne, Ryan L.

2018-01-01

The performance, integrity, and safety of built-up structural systems are critical to their effective employment in diverse engineering applications. In conflict with these goals, harmonic or random excitations of structural panels may promote large amplitude oscillations that are particularly harmful when excitation energies are concentrated around natural frequencies. This contributes to fatigue concerns, performance degradation, and failure. While studies have considered active or passive damping treatments that adapt material characteristics and configurations for structural control, it remains to be understood how vibration properties of structural panels may be tailored via internal material transitions. Motivated to fill this knowledge gap, this research explores an idea of adapting the static and dynamic material distribution of panels through embedded microvascular channels and strategically placed voids that permit the internal movement of fluids within the panels for structural dynamic control. Finite element model and experimental investigations probe how redistributing material in the form of microscale voids influences the global vibration modes and natural frequencies of structural panels. Through parameter studies, the relationships among void shape, number, size, and location are quantified towards their contribution to the changing structural dynamics. For the panel composition and boundary conditions considered in this report, the findings reveal that transferring material between strategically placed voids may result in eigenfrequency changes as great as 10.0, 5.0, and 7.4% for the first, second, and third modes, respectively.

A Passive Optical Location with Limited Range

Directory of Open Access Journals (Sweden)

Pavel Fiala

2008-01-01

Full Text Available We know active and passive methods of a location. This article deals only with a passive location of dynamic targets. The passive optics location is suitable just for tracking of targets with mean velocity which is limited by the hardware basis. The aim of this work is to recognize plasma, particles etc. It is possible to propose such kind of evaluation methods which improve the capture probability markedly. Suggested method is dealing with the short-distance evaluation of targets. We suppose the application of three independent principles how to recognize an object in a scanned picture. These principles use similar stochastic functions in order to evaluate an object location by means of simple mathematical operations. Methods are based on direct evaluation of picture sequence by the help of the histogram and frequency spectrum. We find out the probability of unidentified moving object in pictures. If the probability reaches a setting value we will get a signal.

Passivation process of X80 pipeline steel in bicarbonate solutions

Science.gov (United States)

Zhou, Jian-Long; Li, Xiao-Gang; Du, Cui-Wei; Pan, Ying; Li, Tao; Liu, Qian

2011-04-01

The passivation process of X80 pipeline steel in bicarbonate solutions was investigated using potentiodynamic, dynamic electrochemical impedance spectroscopy (DEIS), and Mott-Schottky measurements. The results show that the shape of polarization curves changes with HCO{3/-} concentration. The critical `passive' concentration is 0.009 mol/L HCO{3/-} for X80 pipeline steel in bicarbonate solutions. No anodic current peak exists in HCO3/- solutions when the concentration is lower than 0.009 mol/L, whereas there are one and two anodic current peaks when the HCO3/- concentration ranges from 0.009 to 0.05 mol/L and is higher than 0.1 mol/L, respectively. DEIS measurements show that there exist active dissolution range, transition range, pre-passive range, passive layer formation range, passive range, and trans-passive range for X80 pipeline steel in the 0.1 mol/L HCO{3/-} solutions. The results of DEIS measurements are in complete agreement with the potentiodynamic diagram. An equivalent circuit containing three sub-layers is used to explain the Nyquist plots in the passive range. Analyses are well made for explaining the corresponding fitted capacitance and impedance. The Mott-Schottky plots show that the passive film of X80 pipeline steel is an n-type semiconductor, and capacitance measurements are in good accordance with the results of DEIS experiment.

A voltage regulator system with dynamic bandwidth boosting for passive UHF RFID transponders

International Nuclear Information System (INIS)

Shen Jinpeng; Wang Xin'an; Liu Shan; Li Shoucheng; Ruan Zhengkun

2013-01-01

This paper presents a voltage regulator system for passive UHF RFID transponders, which contains a rectifier, a limiter, and a regulator. The rectifier achieves power by rectifying the incoming RF energy. Due to the huge variation of the rectified voltage, a limiter at the rectifier output is used to clamp the rectified voltage. In this paper, the design of a limiter circuit is discussed in detail, which can provide a stable limiting voltage with low sensitivity to temperature variation and process dispersion. The key aspect of the voltage regulator system is the dynamic bandwidth boosting in the regulator. By sensing the excess current that is bypassed in the limiter during periods of excess energy, the bias current as well as the bandwidth of the regulator are increased, the output supply voltage can recover quickly from line transients during the periods of no RF energy to a full blast of RF energy. This voltage regulator system is implemented in a 0.18 μm CMOS process. (semiconductor integrated circuits)

Movable shark scales act as a passive dynamic micro-roughness to control flow separation

International Nuclear Information System (INIS)

Lang, Amy W; Bradshaw, Michael T; Smith, Jonathon A; Wheelus, Jennifer N; Motta, Philip J; Habegger, Maria L; Hueter, Robert E

2014-01-01

Shark scales on fast-swimming sharks have been shown to be movable to angles in excess of 50°, and we hypothesize that this characteristic gives this shark skin a preferred flow direction. During the onset of separation, flow reversal is initiated close to the surface. However, the movable scales would be actuated by the reversed flow thereby causing a greater resistance to any further flow reversal and this mechanism would disrupt the process leading to eventual flow separation. Here we report for the first time experimental evidence of the separation control capability of real shark skin through water tunnel testing. Using skin samples from a shortfin mako Isurus oxyrinchus, we tested a pectoral fin and flank skin attached to a NACA 4412 hydrofoil and separation control was observed in the presence of movable shark scales under certain conditions in both cases. We hypothesize that the scales provide a passive, flow-actuated mechanism acting as a dynamic micro-roughness to control flow separation. (paper)

Consumer preference in ranking walking function utilizing the walking index for spinal cord injury II.

Science.gov (United States)

Patrick, M; Ditunno, P; Ditunno, J F; Marino, R J; Scivoletto, G; Lam, T; Loffree, J; Tamburella, F; Leiby, B

2011-12-01

Blinded rank ordering. To determine consumer preference in walking function utilizing the walking Index for spinal cord injury II (WISCI II) in individuals with spinal cord injury (SCI)from the Canada, the Italy and the United States of America. In all, 42 consumers with incomplete SCI (25 cervical, 12 thoracic, 5 lumbar) from Canada (12/42), Italy (14/42) and the United States of America (16/42) ranked the 20 levels of the WISCI II scale by their individual preference for walking. Subjects were blinded to the original ranking of the WISCI II scale by clinical scientists. Photographs of each WISCI II level used in a previous pilot study were randomly shuffled and rank ordered. Percentile, conjoint/cluster and graphic analyses were performed. All three analyses illustrated consumer ranking followed a bimodal distribution. Ranking for two levels with physical assistance and two levels with a walker were bimodal with a difference of five to six ranks between consumer subgroups (quartile analysis). The larger cluster (N=20) showed preference for walking with assistance over the smaller cluster (N=12), whose preference was walking without assistance and more devices. In all, 64% (27/42) of consumers ranked WISCI II level with no devices or braces and 1 person assistance higher than multiple levels of the WISCI II requiring no assistance. These results were unexpected, as the hypothesis was that consumers would rank independent walking higher than walking with assistance. Consumer preference for walking function should be considered in addition to objective measures in designing SCI trials that use significant improvement in walking function as an outcome measure.

Quantum walks on quotient graphs

International Nuclear Information System (INIS)

Krovi, Hari; Brun, Todd A.

2007-01-01

A discrete-time quantum walk on a graph Γ is the repeated application of a unitary evolution operator to a Hilbert space corresponding to the graph. If this unitary evolution operator has an associated group of symmetries, then for certain initial states the walk will be confined to a subspace of the original Hilbert space. Symmetries of the original graph, given by its automorphism group, can be inherited by the evolution operator. We show that a quantum walk confined to the subspace corresponding to this symmetry group can be seen as a different quantum walk on a smaller quotient graph. We give an explicit construction of the quotient graph for any subgroup H of the automorphism group and illustrate it with examples. The automorphisms of the quotient graph which are inherited from the original graph are the original automorphism group modulo the subgroup H used to construct it. The quotient graph is constructed by removing the symmetries of the subgroup H from the original graph. We then analyze the behavior of hitting times on quotient graphs. Hitting time is the average time it takes a walk to reach a given final vertex from a given initial vertex. It has been shown in earlier work [Phys. Rev. A 74, 042334 (2006)] that the hitting time for certain initial states of a quantum walks can be infinite, in contrast to classical random walks. We give a condition which determines whether the quotient graph has infinite hitting times given that they exist in the original graph. We apply this condition for the examples discussed and determine which quotient graphs have infinite hitting times. All known examples of quantum walks with hitting times which are short compared to classical random walks correspond to systems with quotient graphs much smaller than the original graph; we conjecture that the existence of a small quotient graph with finite hitting times is necessary for a walk to exhibit a quantum speedup

Quantum walks with infinite hitting times

International Nuclear Information System (INIS)

Krovi, Hari; Brun, Todd A.

2006-01-01

Hitting times are the average time it takes a walk to reach a given final vertex from a given starting vertex. The hitting time for a classical random walk on a connected graph will always be finite. We show that, by contrast, quantum walks can have infinite hitting times for some initial states. We seek criteria to determine if a given walk on a graph will have infinite hitting times, and find a sufficient condition, which for discrete time quantum walks is that the degeneracy of the evolution operator be greater than the degree of the graph. The set of initial states which give an infinite hitting time form a subspace. The phenomenon of infinite hitting times is in general a consequence of the symmetry of the graph and its automorphism group. Using the irreducible representations of the automorphism group, we derive conditions such that quantum walks defined on this graph must have infinite hitting times for some initial states. In the case of the discrete walk, if this condition is satisfied the walk will have infinite hitting times for any choice of a coin operator, and we give a class of graphs with infinite hitting times for any choice of coin. Hitting times are not very well defined for continuous time quantum walks, but we show that the idea of infinite hitting-time walks naturally extends to the continuous time case as well

Optimal speeds for walking and running, and walking on a moving walkway.

Science.gov (United States)

Srinivasan, Manoj

2009-06-01

Many aspects of steady human locomotion are thought to be constrained by a tendency to minimize the expenditure of metabolic cost. This paper has three parts related to the theme of energetic optimality: (1) a brief review of energetic optimality in legged locomotion, (2) an examination of the notion of optimal locomotion speed, and (3) an analysis of walking on moving walkways, such as those found in some airports. First, I describe two possible connotations of the term "optimal locomotion speed:" that which minimizes the total metabolic cost per unit distance and that which minimizes the net cost per unit distance (total minus resting cost). Minimizing the total cost per distance gives the maximum range speed and is a much better predictor of the speeds at which people and horses prefer to walk naturally. Minimizing the net cost per distance is equivalent to minimizing the total daily energy intake given an idealized modern lifestyle that requires one to walk a given distance every day--but it is not a good predictor of animals' walking speeds. Next, I critique the notion that there is no energy-optimal speed for running, making use of some recent experiments and a review of past literature. Finally, I consider the problem of predicting the speeds at which people walk on moving walkways--such as those found in some airports. I present two substantially different theories to make predictions. The first theory, minimizing total energy per distance, predicts that for a range of low walkway speeds, the optimal absolute speed of travel will be greater--but the speed relative to the walkway smaller--than the optimal walking speed on stationary ground. At higher walkway speeds, this theory predicts that the person will stand still. The second theory is based on the assumption that the human optimally reconciles the sensory conflict between the forward speed that the eye sees and the walking speed that the legs feel and tries to equate the best estimate of the forward

Passive solar technology

Energy Technology Data Exchange (ETDEWEB)

Watson, D

1981-04-01

The present status of passive solar technology is summarized, including passive solar heating, cooling and daylighting. The key roles of the passive solar system designer and of innovation in the building industry are described. After definitions of passive design and a summary of passive design principles are given, performance and costs of passive solar technology are discussed. Passive energy design concepts or methods are then considered in the context of the overall process by which building decisions are made to achieve the integration of new techniques into conventional design. (LEW).

High on walking

DEFF Research Database (Denmark)

Woythal, Bente Martinsen; Haahr, Anita; Dreyer, Pia

2018-01-01

a leg, and people who live with Parkinson’s disease. The analysis of the data is inspired by Paul Ricoeur’s philosophy of interpretation. Four themes were identified: (a) I feel high in two ways; (b) Walking has to be automatic; (c) Every Monday, I walk with the girls in the park; and (d) I dream...

Motor fatigue measurement by distance-induced slow down of walking speed in multiple sclerosis.

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Rémy Phan-Ba

Full Text Available BACKGROUND AND RATIONALE: Motor fatigue and ambulation impairment are prominent clinical features of people with multiple sclerosis (pMS. We hypothesized that a multimodal and comparative assessment of walking speed on short and long distance would allow a better delineation and quantification of gait fatigability in pMS. Our objectives were to compare 4 walking paradigms: the timed 25-foot walk (T25FW, a corrected version of the T25FW with dynamic start (T25FW(+, the timed 100-meter walk (T100MW and the timed 500-meter walk (T500MW. METHODS: Thirty controls and 81 pMS performed the 4 walking tests in a single study visit. RESULTS: The 4 walking tests were performed with a slower WS in pMS compared to controls even in subgroups with minimal disability. The finishing speed of the last 100-meter of the T500MW was the slowest measurable WS whereas the T25FW(+ provided the fastest measurable WS. The ratio between such slowest and fastest WS (Deceleration Index, DI was significantly lower only in pMS with EDSS 4.0-6.0, a pyramidal or cerebellar functional system score reaching 3 or a maximum reported walking distance ≤ 4000 m. CONCLUSION: The motor fatigue which triggers gait deceleration over a sustained effort in pMS can be measured by the WS ratio between performances on a very short distance and the finishing pace on a longer more demanding task. The absolute walking speed is abnormal early in MS whatever the distance of effort when patients are unaware of ambulation impairment. In contrast, the DI-measured ambulation fatigability appears to take place later in the disease course.

Effects of physical guidance on short-term learning of walking on a narrow beam

Science.gov (United States)

Domingo, Antoinette; Ferris, Daniel P.

2009-01-01

Physical guidance is often used in rehabilitation when teaching patients to re-learn movements. However, the effects of guidance on motor learning of complex skills, such as walking balance, are not clear. We tested four groups of healthy subjects that practiced walking on a narrow (1.27 cm) or wide (2.5 cm) treadmill-mounted balance beam, with or without physical guidance. Assistance was given by springs attached to a hip belt that applied restoring forces towards beam center. Subjects were evaluated while walking unassisted before and after training by calculating the number of times subjects stepped off of the beam per minute of successful walking on the beam (Failures per Minute). Subjects in Unassisted groups had greater performance improvements in walking balance from pre to post compared to subjects in Assisted groups. During training, Unassisted groups had more Failures per Minute than Assisted groups. Performance improvements were smaller in Narrow Beam groups than in Wide Beam groups. The Unassisted-Wide and Assisted-Narrow groups had similar Failures per Minute during training, but the Unassisted-Wide group had much greater performance gains after training. These results suggest that physical assistance can hinder motor learning of walking balance, assistance appears less detrimental for more difficult tasks, and task-specific dynamics are important to learning independent of error experience. PMID:19674900

Effects of physical guidance on short-term learning of walking on a narrow beam.

Science.gov (United States)

Domingo, Antoinette; Ferris, Daniel P

2009-11-01

Physical guidance is often used in rehabilitation when teaching patients to re-learn movements. However, the effects of guidance on motor learning of complex skills, such as walking balance, are not clear. We tested four groups of healthy subjects that practiced walking on a narrow (1.27 cm) or wide (2.5 cm) treadmill-mounted balance beam, with or without physical guidance. Assistance was given by springs attached to a hip belt that applied restoring forces towards beam center. Subjects were evaluated while walking unassisted before and after training by calculating the number of times subjects stepped off of the beam per minute of successful walking on the beam (Failures per Minute). Subjects in Unassisted groups had greater performance improvements in walking balance from pre to post compared to subjects in Assisted groups. During training, Unassisted groups had more Failures per Minute than Assisted groups. Performance improvements were smaller in Narrow Beam groups than in Wide Beam groups. The Unassisted-Wide and Assisted-Narrow groups had similar Failures per Minute during training, but the Unassisted-Wide group had much greater performance gains after training. These results suggest that physical assistance can hinder motor learning of walking balance, assistance appears less detrimental for more difficult tasks, and task-specific dynamics are important to learning independent of error experience.

Person Recognition Method using Sequential Walking Footprints via Overlapped Foot Shape and Center-Of-Pressure Trajectory

Directory of Open Access Journals (Sweden)

Jin-Woo Jung

2013-08-01

Full Text Available One emerging biometric identification method is the use of human footprint. However, in the previous research, there were some limitations resulting from the spatial resolution of sensors. One possible method to overcome this limitation is through the use additional information such as dynamic walking information in sequential walking footprint. In this study, we suggest a new person recognition scheme based on both overlapped foot shape and COP (Center Of Pressure trajectory during one-step walking. And, we show the usefulness of the suggested method, obtaining a 98.6% recognition rate in our experiment with eleven people. In addition, we show an application of the suggested method, automatic door-opening system for intelligent residential space.

Disorder and decoherence in coined quantum walks

International Nuclear Information System (INIS)

Zhang Rong; Qin Hao; Tang Bao; Xue Peng

2013-01-01

This article aims to provide a review on quantum walks. Starting form a basic idea of discrete-time quantum walks, we will review the impact of disorder and decoherence on the properties of quantum walks. The evolution of the standard quantum walks is deterministic and disorder introduces randomness to the whole system and change interference pattern leading to the localization effect. Whereas, decoherence plays the role of transmitting quantum walks to classical random walks. (topical review - quantum information)

Mechanical Energy Recovery during Walking in Patients with Parkinson Disease.

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Mariangela Dipaola

Full Text Available The mechanisms of mechanical energy recovery during gait have been thoroughly investigated in healthy subjects, but never described in patients with Parkinson disease (PD. The aim of this study was to investigate whether such mechanisms are preserved in PD patients despite an altered pattern of locomotion. We consecutively enrolled 23 PD patients (mean age 64±9 years with bilateral symptoms (H&Y ≥II if able to walk unassisted in medication-off condition (overnight suspension of all dopaminergic drugs. Ten healthy subjects (mean age 62±3 years walked both at their 'preferred' and 'slow' speeds, to match the whole range of PD velocities. Kinematic data were recorded by means of an optoelectronic motion analyzer. For each stride we computed spatio-temporal parameters, time-course and range of motion (ROM of hip, knee and ankle joint angles. We also measured kinetic (Wk, potential (Wp, total (WtotCM energy variations and the energy recovery index (ER. Along with PD progression, we found a significant correlation of WtotCM and Wp with knee ROM and in particular with knee extension in terminal stance phase. Wk and ER were instead mainly related to gait velocity. In PD subjects, the reduction of knee ROM significantly diminished both Wp and WtotCM. Rehabilitation treatments should possibly integrate passive and active mobilization of knee to prevent a reduction of gait-related energetic components.

Neighborhood Walking and Social Capital: The Correlation between Walking Experience and Individual Perception of Social Capital

Directory of Open Access Journals (Sweden)

Heechul Kim

2017-04-01

Full Text Available The purpose of this study was to analyze the relationship between people’s actual walking experience and their social capital levels in order to examine the possibility of restoring weakened social functions of streets and public spaces in a walking-friendly urban environment. Based on the survey data of 591 residents of Seoul, we empirically analyzed the relationship between walking experience for various purposes and individual perceptions of social capital using one-way ANOVA and OLS regression models. As a result of the analysis, we found that the levels of neighborly trust and networking of people who experienced leisure walking were higher than those of people who did not, while there was no difference in the level of social capital according to walking experiences for other purposes. This result is significant in that it shows the basis for the restoration of the social function of neighborhoods through social capital formation of people as an effect of walking. Hence, it is important to create a walking environment that supports leisure activities.

Walking on four limbs: A systematic review of Nordic Walking in Parkinson disease.

Science.gov (United States)

Bombieri, Federica; Schena, Federico; Pellegrini, Barbara; Barone, Paolo; Tinazzi, Michele; Erro, Roberto

2017-05-01

Nordic Walking is a relatively high intensity activity that is becoming increasingly popular. It involves marching using poles adapted from cross-country skiing poles in order to activate upper body muscles that would not be used during normal walking. Several studies have been performed using this technique in Parkinson disease patients with contradictory results. Thus, we reviewed here all studies using this technique in Parkinson disease patients and further performed a meta-analysis of RCTs where Nordic Walking was evaluated against standard medical care or other types of physical exercise. Nine studies including four RCTs were reviewed for a total of 127 patients who were assigned to the Nordic Walking program. The majority of studies reported beneficial effects of Nordic Walking on either motor or non-motor variables, but many limitations were observed that hamper drawing definitive conclusions and it is largely unclear whether the benefits persist over time. It would appear that little baseline disability is the strongest predictor of response. The meta-analysis of the 4 RCTs yielded a statistically significant reduction of the UPDRS-3 score, but its value of less than 1 point does not appear to be clinically meaningful. Well-designed, large RCTs should be performed both against standard medical care and other types of physical exercise to definitively address whether Nordic Walking can be beneficial in PD. Copyright © 2017. Published by Elsevier Ltd.

[Walking with canes and forearm-crutches (author's transl)].

Science.gov (United States)

Bergmann, G; Kölbel, R; Rauschenbach, N; Rohlmann, A

1978-02-01

Partial weight bearing is frequently prescribed but cannot be controlled adequately. In a previous paper the change of forces at the hip joint as effected by a one sided cane was determined by instrumentation of the cane and a mechanical analysis of gait on a walkway. In the present study we looked at the conditions for control of partial weightbearing when two forearm crutches are used. Instrumented crutches and a forceplate were used. In walking with two forearm crutches the total of the ground reaction forces and the force pattern differ from those in free walking. The total of two crutch forces plus the force at the leg with partial weightbearing exceeds that caused by body weight alone. This is due to mass accelerations in a changed gait pattern. When the maximal leg force is reduced from 100% body weight to zero, the additional dynamic forces exceed those caused by body weight alone by 4%-19%. Only 2% of the additional dynamic forces act on the controlateral crutch while the rest is transmitted through the ipsilateral crutch. The crutch force pattern on the ipsilateral side depends more on individual gait characteristics than does that on the controlateral side. Load reduction is more pronounced in the late stages of the stand phase than in the early ones.

A single-longitudinal-mode Brillouin fiber laser passively stabilized at the pump resonance frequency with a dynamic population inversion grating

International Nuclear Information System (INIS)

Spirin, V V; López-Mercado, C A; Kinet, D; Mégret, P; Fotiadi, A A; Zolotovskiy, I O

2013-01-01

We demonstrate a single-longitudinal-mode Brillouin ring fiber laser passively stabilized at the resonance frequency with a 1.7 m section that is an unpumped polarization-maintaining erbium-doped fiber. The two coupled all-fiber Fabry–Perot interferometers that comprise the cavity, in combination with the dynamical population inversion gratings self-induced in the active fiber, provide adaptive pump-mode selection and Stokes wave generation at the same time. The laser is shown to emit a single-frequency Stokes wave with a linewidth narrower than 100 Hz. (letter)

Heterogeneous continuous-time random walks

Science.gov (United States)

Grebenkov, Denis S.; Tupikina, Liubov

2018-01-01

We introduce a heterogeneous continuous-time random walk (HCTRW) model as a versatile analytical formalism for studying and modeling diffusion processes in heterogeneous structures, such as porous or disordered media, multiscale or crowded environments, weighted graphs or networks. We derive the exact form of the propagator and investigate the effects of spatiotemporal heterogeneities onto the diffusive dynamics via the spectral properties of the generalized transition matrix. In particular, we show how the distribution of first-passage times changes due to local and global heterogeneities of the medium. The HCTRW formalism offers a unified mathematical language to address various diffusion-reaction problems, with numerous applications in material sciences, physics, chemistry, biology, and social sciences.

"Four legs instead of two"--perspectives on a Nordic walking-based walking programme among people with arthritis.

Science.gov (United States)

O'Donovan, Rhona; Kennedy, Norelee

2015-01-01

Nordic Walking (NW) is growing in popularity among people with arthritis. The aim of this study was to explore the perspectives of participants with arthritis on a NW-based walking programme including factors contributing to sustained participation in the programme. Three semi-structured focus groups were conducted with a total of 27 participants with various types of arthritis. The groups consisted of participants who completed a NW-based walking programme in the previous 4 years. Only participants who had sustained involvement in the walking group were included. Groups were audio-recorded, transcribed verbatim and thematic analysis was performed. Participants reported that the walking programme offered numerous benefits. Two distinct themes emerged: (1) "four legs instead of two legs" and (2) "a support group". Theme 1 incorporates the physical, psychological and educational benefits that stem from involvement in a walking group while Theme 2 incorporates the benefits of social support in group-based activity. Several benefits of a NW-based walking programme from the perspectives of individuals with arthritis who engage in group-based walking programmes were identified. The benefits may encourage sustained participation and justify the promotion of NW as an intervention for people with arthritis. Considering how to sustain exercise participation is important to ensure continued benefits from physical activity participation. A community-based Nordic walking-based walking programme for people with arthritis improved exercise knowledge and confidence to exercise. Group exercise is valuable in providing support and motivation to continue exercising.

A gait stability investigation into FES-assisted paraplegic walking based on the walker tipping index.

Science.gov (United States)

Ming, Dong; Bai, Yanru; Liu, Xiuyun; Qi, Hongzhi; Cheng, Longlong; Wan, Baikun; Hu, Yong; Wong, Yatwa; Luk, Keith D K; Leong, John C Y

2009-12-01

The gait outcome measures used in clinical trials of paraplegic locomotor training determine the effectiveness of improved walking function assisted by the functional electrical stimulation (FES) system. Focused on kinematic, kinetic or physiological changes of paraplegic patients, traditional methods cannot quantify the walking stability or identify the unstable factors of gait in real time. Up until now, the published studies on dynamic gait stability for the effective use of FES have been limited. In this paper, the walker tipping index (WTI) was used to analyze and process gait stability in FES-assisted paraplegic walking. The main instrument was a specialized walker dynamometer system based on a multi-channel strain-gauge bridge network fixed on the frame of the walker. This system collected force information for the handle reaction vector between the patient's upper extremities and the walker during the walking process; the information was then converted into walker tipping index data, which is an evaluation indicator of the patient's walking stability. To demonstrate the potential usefulness of WTI in gait analysis, a preliminary clinical trial was conducted with seven paraplegic patients who were undergoing FES-assisted walking training and seven normal control subjects. The gait stability levels were quantified for these patients under different stimulation patterns and controls under normal walking with knee-immobilization through WTI analysis. The results showed that the walking stability in the FES-assisted paraplegic group was worse than that in the control subject group, with the primary concern being in the anterior-posterior plane. This new technique is practical for distinguishing useful gait information from the viewpoint of stability, and may be further applied in FES-assisted paraplegic walking rehabilitation.

A gait stability investigation into FES-assisted paraplegic walking based on the walker tipping index

Science.gov (United States)

Ming, Dong; Bai, Yanru; Liu, Xiuyun; Qi, Hongzhi; Cheng, Longlong; Wan, Baikun; Hu, Yong; Wong, Yatwa; Luk, Keith D. K.; Leong, John C. Y.

2009-12-01

The gait outcome measures used in clinical trials of paraplegic locomotor training determine the effectiveness of improved walking function assisted by the functional electrical stimulation (FES) system. Focused on kinematic, kinetic or physiological changes of paraplegic patients, traditional methods cannot quantify the walking stability or identify the unstable factors of gait in real time. Up until now, the published studies on dynamic gait stability for the effective use of FES have been limited. In this paper, the walker tipping index (WTI) was used to analyze and process gait stability in FES-assisted paraplegic walking. The main instrument was a specialized walker dynamometer system based on a multi-channel strain-gauge bridge network fixed on the frame of the walker. This system collected force information for the handle reaction vector between the patient's upper extremities and the walker during the walking process; the information was then converted into walker tipping index data, which is an evaluation indicator of the patient's walking stability. To demonstrate the potential usefulness of WTI in gait analysis, a preliminary clinical trial was conducted with seven paraplegic patients who were undergoing FES-assisted walking training and seven normal control subjects. The gait stability levels were quantified for these patients under different stimulation patterns and controls under normal walking with knee-immobilization through WTI analysis. The results showed that the walking stability in the FES-assisted paraplegic group was worse than that in the control subject group, with the primary concern being in the anterior-posterior plane. This new technique is practical for distinguishing useful gait information from the viewpoint of stability, and may be further applied in FES-assisted paraplegic walking rehabilitation.

Walking on fractals: diffusion and self-avoiding walks on percolation clusters

International Nuclear Information System (INIS)

Blavatska, V; Janke, W

2009-01-01

We consider random walks (RWs) and self-avoiding walks (SAWs) on disordered lattices directly at the percolation threshold. Applying numerical simulations, we study the scaling behavior of the models on the incipient percolation cluster in space dimensions d = 2, 3, 4. Our analysis yields estimates of universal exponents, governing the scaling laws for configurational properties of RWs and SAWs

Walking while performing working memory tasks changes the prefrontal cortex hemodynamic activations and gait kinematics

Directory of Open Access Journals (Sweden)

Ming-I Brandon Lin

2016-05-01

the narrow road was found to elicit a smaller decrement in HbO levels.ConclusionsThe current study provided direct evidence that, in young adults, neural correlates of executive function and dynamic postural control tend to be altered in response to the cognitive load imposed by the walking environment and the concurrent task during ambulation. A shift of brain activation patterns between functionally connected networks may occur when facing challenging cognitive-motor interaction.

Treadmill walking with body weight support

OpenAIRE

Aaslund, Mona Kristin

2012-01-01

Background: Rehabilitating walking in patients post-stroke with safe, task-specific, intensive training of sufficient duration, can be challenging. Body weight supported treadmill training (BWSTT) has been proposed as an effective method to meet these challenges and may therefore have benefits over training overground walking. However, walking characteristics should not be aggravated during BWSTT or require a long familiarisation time compared to overground walking. Objectives: To investi...

Interlimb coordination during forward walking is largely preserved in backward walking in children with cerebral palsy

NARCIS (Netherlands)

Meyns, P.; Molenaers, G.; Desloovere, K.; Duysens, J.E.J.

2014-01-01

OBJECTIVE: Limb kinematics in backward walking (BW) are essentially those of forward walking (FW) in reverse. It has been argued that subcortical mechanisms could underlie both walking modes. METHODS: Therefore, we tested whether participants with supraspinal/cortical deficits (i.e. cerebral palsy)

3D laser measurements of bare and shod feet during walking.

Science.gov (United States)

Novak, Boštjan; Možina, Janez; Jezeršek, Matija

2014-01-01

This article presents a new system for 3D foot-shape measurements during walking. It is based on the laser-triangulation, multiple-line-illumination and color-modulation techniques. It consists of a walking stage and four measuring modules that simultaneously acquire the foot shape from the top, bottom and side views. The measuring speed is 30 fps. Custom-developed software makes it possible to analyze the foot's dimensions at an arbitrary cross-section by means of the width, height, girth and section orientation. Six subjects were measured during bare and shod walking, and the bare foot and the outside dimensions of the footwear during the entire stance phase are presented. The relative measurement repeatability of a single subject is 0.5% for bare foot and 1% for shod foot. This means that it is possible to study the differences between various influences on the foot-shape dynamics, such as a bare/shod foot, different loading conditions and the shoe's stiffness condition. Copyright © 2014 Elsevier B.V. All rights reserved.

The VSPA Foot: A Quasi-Passive Ankle-Foot Prosthesis With Continuously Variable Stiffness.

Science.gov (United States)

Shepherd, Max K; Rouse, Elliott J

2017-12-01

Most commercially available prosthetic feet do not exhibit a biomimetic torque-angle relationship, and are unable to modulate their mechanics to assist with other mobility tasks, such as stairs and ramps. In this paper, we present a quasi-passive ankle-foot prosthesis with a customizable torque-angle curve and an ability to quickly modulate ankle stiffness between tasks. The customizable torque-angle curve is obtained with a cam-based transmission and a fiberglass leaf spring. To achieve variable stiffness, the leaf spring's support conditions can be actively modulated by a small motor, shifting the torque-angle curve to be more or less stiff. We introduce the design, characterize the available torque-angle curves, and present kinematics from a transtibial amputee subject performing level-ground walking, stair ascent/descent, and ramp ascent/descent. The subject exhibited a more normative range of motion on stairs and ramps at lower stiffness levels, and preferred different stiffness levels for each task. Paired with an appropriate intent recognition system, our novel ankle prosthesis could improve gait biomechanics during walking and many other mobility tasks.

More Adults Are Walking

Centers for Disease Control (CDC) Podcasts

This podcast is based on the August 2012 CDC Vital Signs report. While more adults are walking, only half get the recommended amount of physical activity. Listen to learn how communities, employers, and individuals may help increase walking.

Episodic reinforcement learning control approach for biped walking

Directory of Open Access Journals (Sweden)

Katić Duško

2012-01-01

Full Text Available This paper presents a hybrid dynamic control approach to the realization of humanoid biped robotic walk, focusing on the policy gradient episodic reinforcement learning with fuzzy evaluative feedback. The proposed structure of controller involves two feedback loops: a conventional computed torque controller and an episodic reinforcement learning controller. The reinforcement learning part includes fuzzy information about Zero-Moment- Point errors. Simulation tests using a medium-size 36-DOF humanoid robot MEXONE were performed to demonstrate the effectiveness of our method.

Effects of wide step walking on swing phase hip muscle forces and spatio-temporal gait parameters.

Science.gov (United States)

Bajelan, Soheil; Nagano, Hanatsu; Sparrow, Tony; Begg, Rezaul K

2017-07-01

Human walking can be viewed essentially as a continuum of anterior balance loss followed by a step that re-stabilizes balance. To secure balance an extended base of support can be assistive but healthy young adults tend to walk with relatively narrower steps compared to vulnerable populations (e.g. older adults and patients). It was, therefore, hypothesized that wide step walking may enhance dynamic balance at the cost of disturbed optimum coupling of muscle functions, leading to additional muscle work and associated reduction of gait economy. Young healthy adults may select relatively narrow steps for a more efficient gait. The current study focused on the effects of wide step walking on hip abductor and adductor muscles and spatio-temporal gait parameters. To this end, lower body kinematic data and ground reaction forces were obtained using an Optotrak motion capture system and AMTI force plates, respectively, while AnyBody software was employed for muscle force simulation. A single step of four healthy young male adults was captured during preferred walking and wide step walking. Based on preferred walking data, two parallel lines were drawn on the walkway to indicate 50% larger step width and participants targeted the lines with their heels as they walked. In addition to step width that defined walking conditions, other spatio-temporal gait parameters including step length, double support time and single support time were obtained. Average hip muscle forces during swing were modeled. Results showed that in wide step walking step length increased, Gluteus Minimus muscles were more active while Gracilis and Adductor Longus revealed considerably reduced forces. In conclusion, greater use of abductors and loss of adductor forces were found in wide step walking. Further validation is needed in future studies involving older adults and other pathological populations.

Clearing out a maze: A model of chemotactic motion in porous media

Science.gov (United States)

Schilling, Tanja; Voigtmann, Thomas

2017-12-01

We study the anomalous dynamics of a biased "hungry" (or "greedy") random walk on a percolating cluster. The model mimics chemotaxis in a porous medium: In close resemblance to the 1980s arcade game PAC-MA N ®, the hungry random walker consumes food, which is initially distributed in the maze, and biases its movement towards food-filled sites. We observe that the mean-squared displacement of the process follows a power law with an exponent that is different from previously known exponents describing passive or active microswimmer dynamics. The change in dynamics is well described by a dynamical exponent that depends continuously on the propensity to move towards food. It results in slower differential growth when compared to the unbiased random walk.

Quantum walk on a chimera graph

Science.gov (United States)

Xu, Shu; Sun, Xiangxiang; Wu, Jizhou; Zhang, Wei-Wei; Arshed, Nigum; Sanders, Barry C.

2018-05-01

We analyse a continuous-time quantum walk on a chimera graph, which is a graph of choice for designing quantum annealers, and we discover beautiful quantum walk features such as localization that starkly distinguishes classical from quantum behaviour. Motivated by technological thrusts, we study continuous-time quantum walk on enhanced variants of the chimera graph and on diminished chimera graph with a random removal of vertices. We explain the quantum walk by constructing a generating set for a suitable subgroup of graph isomorphisms and corresponding symmetry operators that commute with the quantum walk Hamiltonian; the Hamiltonian and these symmetry operators provide a complete set of labels for the spectrum and the stationary states. Our quantum walk characterization of the chimera graph and its variants yields valuable insights into graphs used for designing quantum-annealers.

Passive scalar dynamics near the turbulent/nonturbulent interface in a jet

Science.gov (United States)

Taveira, Rodrigo R.; da Silva, Carlos

2011-11-01

The present work uses several direct numerical simulations (DNS) of turbulent planar jets at Reynolds number ranging from Reλ = 120 to Reλ = 160 and Schmidt numbers raging from Sc = 0 . 7 to 7.0 to analyze the nature and properties of the ``scalar interface'' and to investigate the dynamics of turbulent mixing of a passive scalar. Specifically, we employ conditional statistics in relation to the distance from the T/NT interface in order to eliminate the intermittency that affects common turbulence statistics close to the jet edge. The physical mechanisms behind scalar mixing near the T/NT interfaces and their associated turbulent scales and topology are investigated. A sharp scalar interface exists separating the Turbulent and the irrotational flow regions. The thickness of this scalar interface δθ is also of the order of the Taylor micro-scale, λ. However, the thickness of the scalar gradient variance I (where Gj = ∂ θ / ∂xj) is much smaller. Very intense scalar gradient sheet structures along regions of intense strain, in particular at the T/NT interface. The scalar gradient transport equation is analyzed in order to further investigate the physical mechanism of scalar turbulent mixing at the jet edge. Almost all mixing takes place in a confined region close to the interface, beyond which they become reduced to an almost in perfect - balance between production and dissipation of scalar variance.

Walking Wheel Design for Lunar Rove-Rand and Its Application Simulation Based on Virtual Lunar Environment

Directory of Open Access Journals (Sweden)

Zhao Yibing

2014-05-01

Full Text Available The lunar rover design is the key problem of planet exploration. It is extraordinarily important for researchers to fully understand the lunar terrain and propose the reasonable lunar rover. In this paper, one new type of walking wheel modeled on impeller is presented based on vehicle terramechanics. The passive earth pressure of soil mechanics put forward by C. A. Coulomb is employed to obtain the wheel traction force. Some kinematics simulations are conducted for lunar rover model. Besides, this paper presents how to model lunar landing terrain containing typical statistic characteristic including craters and boulders; then, the second step is to construct basal lunar surface by using Brown Fractal Motion and the next is to add craters and boulders by means of known diameter algorithm and Random-create Diameter Algorithm. By means of importing 2D plain of lunar surface into UG, 3D parasolid is modeled and finally imported to ADAMS, which is available for lunar rover kinematics and dynamics simulation. Lastly, based on power spectrum curve of lunar terrain, the spectral characteristic of three different lunar terrain roughness is educed by using reverse engineering algorithm. Simulation results demonstrated the frequency of vibration mechanics properties of different roughness surfaces.

Validity of the MarkWiiR for kinematic analysis during walking and running gaits

Directory of Open Access Journals (Sweden)

Johnny Padulo

2014-11-01

Full Text Available The aim of this study was to validate the MarkWiiR (MW captured by the Nintendo Wii-Remote (100-Hz to assess active marker displacement by comparison with 2D video analysis. Ten participants were tested on a treadmill at different walking (1<6 km · h-1 and running (10<13 km · h-1 speeds. During the test, the active marker for MW and a passive marker for video analysis were recorded simultaneously with the two devices. The displacement of the marker on the two axes (x-y was computed using two different programs, Kinovea 0.8.15 and CoreMeter, for the camera and MW, respectively. Pearson correlation was acceptable (x-axis r≥0.734 and y-axis r≥0.684, and Bland–Altman plots of the walking speeds showed an average error of 0.24±0.52% and 1.5±0.91% for the x- and y-axis, respectively. The difference of running speeds showed average errors of 0.67±0.33% and 1.26±0.33% for the x- and y-axes, respectively. These results demonstrate that the two measures are similar from both the x- and the y-axis perspective. In conclusion, these findings suggest that the MarkWiiR is a valid and reliable tool to assess the kinematics of an active marker during walking and running gaits.

Dynamical systems

CERN Document Server

Sternberg, Shlomo

2010-01-01

Celebrated mathematician Shlomo Sternberg, a pioneer in the field of dynamical systems, created this modern one-semester introduction to the subject for his classes at Harvard University. Its wide-ranging treatment covers one-dimensional dynamics, differential equations, random walks, iterated function systems, symbolic dynamics, and Markov chains. Supplementary materials offer a variety of online components, including PowerPoint lecture slides for professors and MATLAB exercises.""Even though there are many dynamical systems books on the market, this book is bound to become a classic. The the

Learning to walk with an adaptive gain proportional myoelectric controller for a robotic ankle exoskeleton.

Science.gov (United States)

Koller, Jeffrey R; Jacobs, Daniel A; Ferris, Daniel P; Remy, C David

2015-11-04

Robotic ankle exoskeletons can provide assistance to users and reduce metabolic power during walking. Our research group has investigated the use of proportional myoelectric control for controlling robotic ankle exoskeletons. Previously, these controllers have relied on a constant gain to map user's muscle activity to actuation control signals. A constant gain may act as a constraint on the user, so we designed a controller that dynamically adapts the gain to the user's myoelectric amplitude. We hypothesized that an adaptive gain proportional myoelectric controller would reduce metabolic energy expenditure compared to walking with the ankle exoskeleton unpowered because users could choose their preferred control gain. We tested eight healthy subjects walking with the adaptive gain proportional myoelectric controller with bilateral ankle exoskeletons. The adaptive gain was updated each stride such that on average the user's peak muscle activity was mapped to maximal power output of the exoskeleton. All subjects participated in three identical training sessions where they walked on a treadmill for 50 minutes (30 minutes of which the exoskeleton was powered) at 1.2 ms(-1). We calculated and analyzed metabolic energy consumption, muscle recruitment, inverse kinematics, inverse dynamics, and exoskeleton mechanics. Using our controller, subjects achieved a metabolic reduction similar to that seen in previous work in about a third of the training time. The resulting controller gain was lower than that seen in previous work (β=1.50±0.14 versus a constant β=2). The adapted gain allowed users more total ankle joint power than that of unassisted walking, increasing ankle power in exchange for a decrease in hip power. Our findings indicate that humans prefer to walk with greater ankle mechanical power output than their unassisted gait when provided with an ankle exoskeleton using an adaptive controller. This suggests that robotic assistance from an exoskeleton can allow

Establishing the Range of Perceptually Natural Visual Walking Speeds for Virtual Walking-In-Place Locomotion

DEFF Research Database (Denmark)

Nilsson, Niels Christian; Serafin, Stefania; Nordahl, Rolf

2014-01-01

to virtual motion. This paper describes two within-subjects studies performed with the intention of establishing the range of perceptually natural walking speeds for WIP locomotion. In both studies, subjects performed a series of virtual walks while exposed to visual gains (optic flow multipliers) ranging...... from 1.0 to 3.0. Thus, the slowest speed was equal to an estimate of the subjects normal walking speed, while the highest speed was three times greater. The perceived naturalness of the visual speed was assessed using self-reports. The first study compared four different types of movement, namely...... proportional to the degree of underestimation of the virtual speeds for both treadmill-mediated virtual walking and WIP locomotion. Combined, the results constitute a first attempt at establishing a set of guidelines specifying what virtual walking speeds WIP gestures should produce in order to facilitate...

Coherent chemical kinetics as quantum walks. II. Radical-pair reactions in Arabidopsis thaliana

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Chia, A.; Górecka, A.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.

2016-03-01

We apply the quantum-walk approach proposed in the preceding paper [A. Chia et al., preceding paper, Phys. Rev. E 93, 032407 (2016), 10.1103/PhysRevE.93.032407] to a radical-pair reaction where realistic estimates for the intermediate transition rates are available. The well-known average hitting time from quantum walks can be adopted as a measure of how quickly the reaction occurs and we calculate this for varying degrees of dephasing in the radical pair. The time for the radical pair to react to a product is found to be independent of the amount of dephasing introduced, even in the limit of no dephasing where the transient population dynamics exhibits strong coherent oscillations. This can be seen to arise from the existence of a rate-limiting step in the reaction and we argue that in such examples, a purely classical model based on rate equations can be used for estimating the time scale of the reaction but not necessarily its population dynamics.

Variability in energy cost and walking gait during race walking in competitive race walkers.

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Brisswalter, J; Fougeron, B; Legros, P

1998-09-01

The aim of this study was to examine the variability of energy cost (Cw) and race walking gait after a 3-h walk at the competition pace in race walkers of the same performance level. Nine competitive race walkers were studied. In the same week, after a first test of VO2max determination, each subject completed two submaximal treadmill walks (6 min length, 0% grade, 12 km X h(-1) speed) before and after a 3-h overground test completed at the individual competition speed of the race walker. During the two submaximal tests, subjects were filmed between the 2nd and the 4th min, and physiological parameters were recorded between the 4th and the 6th min. Results showed two trends. On the one hand, we observed a significant and systematic increase in energy cost of walking (mean deltaCw = 8.4%), whereas no variation in the gait kinematics prescribed by the rules of race walking was recorded. On the other hand, this increase in metabolic energy demand was accompanied by variations of different magnitude and direction of stride length, of the excursion of the heel and of the maximal ankle flexion at toe-off among the race walkers. These results indicated that competitive race walkers are able to maintain their walking gait with exercise duration apart from a systematic increase in energy cost. Moreover, in this form of locomotion the effect of fatigue on the gait variability seems to be an individual function of the race walk constraints and the constraints of the performer.

Motor modules in robot-aided walking

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Gizzi Leonardo

2012-10-01

Full Text Available Abstract Background It is hypothesized that locomotion is achieved by means of rhythm generating networks (central pattern generators and muscle activation generating networks. This modular organization can be partly identified from the analysis of the muscular activity by means of factorization algorithms. The activity of rhythm generating networks is described by activation signals whilst the muscle intervention generating network is represented by motor modules (muscle synergies. In this study, we extend the analysis of modular organization of walking to the case of robot-aided locomotion, at varying speed and body weight support level. Methods Non Negative Matrix Factorization was applied on surface electromyographic signals of 8 lower limb muscles of healthy subjects walking in gait robotic trainer at different walking velocities (1 to 3km/h and levels of body weight support (0 to 30%. Results The muscular activity of volunteers could be described by low dimensionality (4 modules, as for overground walking. Moreover, the activation signals during robot-aided walking were bursts of activation timed at specific phases of the gait cycle, underlying an impulsive controller, as also observed in overground walking. This modular organization was consistent across the investigated speeds, body weight support level, and subjects. Conclusions These results indicate that walking in a Lokomat robotic trainer is achieved by similar motor modules and activation signals as overground walking and thus supports the use of robotic training for re-establishing natural walking patterns.

Energy-efficient orthogonal frequency division multiplexing-based passive optical network based on adaptive sleep-mode control and dynamic bandwidth allocation

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Zhang, Chongfu; Xiao, Nengwu; Chen, Chen; Yuan, Weicheng; Qiu, Kun

2016-02-01

We propose an energy-efficient orthogonal frequency division multiplexing-based passive optical network (OFDM-PON) using adaptive sleep-mode control and dynamic bandwidth allocation. In this scheme, a bidirectional-centralized algorithm named the receiver and transmitter accurate sleep control and dynamic bandwidth allocation (RTASC-DBA), which has an overall bandwidth scheduling policy, is employed to enhance the energy efficiency of the OFDM-PON. The RTASC-DBA algorithm is used in an optical line terminal (OLT) to control the sleep mode of an optical network unit (ONU) sleep and guarantee the quality of service of different services of the OFDM-PON. The obtained results show that, by using the proposed scheme, the average power consumption of the ONU is reduced by ˜40% when the normalized ONU load is less than 80%, compared with the average power consumption without using the proposed scheme.

Walking Behavior of Zoo Elephants: Associations between GPS-Measured Daily Walking Distances and Environmental Factors, Social Factors, and Welfare Indicators.

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Matthew R Holdgate