scholarly journals Humans optimally anticipate and compensate for an uneven step during walking

2020 ◽  
Author(s):  
Osman Darici ◽  
Arthur D. Kuo
Keyword(s):  
Energy Input ◽  
Human Subjects ◽  
Mechanical Energy ◽  
Selection Criterion ◽  
Time Of Arrival ◽  
Forward Speed ◽  
Dynamic Prediction ◽  
Simple Task ◽  
Average Speed ◽  
Walking Dynamics

ABSTRACTThe simple task of walking up a sidewalk curb is actually a dynamic prediction task. The curb is a disturbance that causes a loss of momentum, to be anticipated and compensated for. For example, the compensation might regain momentum and ensure undisturbed time of arrival. But without a selection criterion, there are infinite possible strategies. Here we show that humans compensate with an anticipatory pattern of forward speed adjustments, with a criterion of minimizing mechanical energy input. This is predicted by optimal control for a simple model of walking dynamics, with each leg’s push-off work as input. Optimization predicts a tri-phasic trajectory of speed (and thus momentum) adjustments, including an anticipatory, feedforward phase. In experiment, human subjects successfully regain time relative to undisturbed walking, with the predicted tri-phasic trajectory. They also scale the pattern with up- or down-steps, and inversely with average speed, as also predicted by model. Humans can reason about the dynamics of walking to plan anticipatory and economical control, even with a sidewalk curb in the way.

scholarly journals Humans optimally anticipate and compensate for an uneven step during walking

eLife ◽  
2022 ◽  
Vol 11 ◽  
Author(s):  
Osman Darici ◽  
Arthur D Kuo
Keyword(s):  
Human Subjects ◽  
Mechanical Energy ◽  
Bipedal Walking ◽  
Time Of Arrival ◽  
Dynamic Prediction ◽  
Simple Task ◽  
Model Predictions ◽  
Steady Level ◽  
Speed Fluctuation ◽  
Energy Economy

The simple task of walking up a sidewalk curb is actually a dynamic prediction task. The curb is a disturbance that could cause a loss of momentum if not anticipated and compensated for. It might be possible to adjust momentum sufficiently to ensure undisturbed time of arrival, but there are infinite possible ways to do so. Much of steady, level gait is determined by energy economy, which should be at least as important with terrain disturbances. It is, however, unknown whether economy also governs walking up a curb, and whether anticipation helps. Here we show that humans compensate with an anticipatory pattern of forward speed adjustments, predicted by a criterion of minimizing mechanical energy input. The strategy is mechanistically predicted by optimal control for a simple model of bipedal walking dynamics, with each leg's push-off work as input. Optimization predicts a tri-phasic trajectory of speed (and thus momentum) adjustments, including an anticipatory phase. In experiment, human subjects ascend an artificial curb with the predicted tri-phasic trajectory, which approximately conserves overall walking speed relative to undisturbed flat ground. The trajectory involves speeding up in a few steps before the curb, losing considerable momentum from ascending it, and then regaining speed in a few steps thereafter. Descending the curb entails a nearly opposite, but still anticipatory, speed fluctuation trajectory, in agreement with model predictions that speed fluctuation amplitudes should scale linearly with curb height. The fluctuation amplitudes also decrease slightly with faster average speeds, also as predicted by model. Humans can reason about the dynamics of walking to plan anticipatory and economical control, even with a sidewalk curb in the way.

scholarly journals Exploring the utility of robots in exposure studies

2019 ◽  
Author(s):  
Elisabeth Feld-Cook ◽  
Rahul Shome ◽  
Rosemary T. Zaleski ◽  
Krishnan Mohan ◽  
Hristiyan Kourtev ◽  
...  
Keyword(s):  
New Product Development ◽  
Human Subjects ◽  
New Product ◽  
Health Science ◽  
Exposure Model ◽  
Proof Of Concept ◽  
Simple Task ◽  
Research Ethics Review ◽  
Exposure Data ◽  
Volatile Organic

AbstractObtaining valid, reliable quantitative exposure data can be a significant challenge for industrial hygienists, exposure scientists, and other health science professionals. In this proof-of-concept study, a robotic platform was programmed to perform a simple task as a plausible alternative to human subjects in exposure studies for generating exposure data. The use of robots offers several advantages over the use of humans. Research can be completed more efficiently and there is no need to recruit, screen, or train volunteers. In addition, robots can perform tasks repeatedly without getting tired allowing for collection of an unlimited number of measurements using different chemicals to assess exposure impacts from formulation changes and new product development. The use of robots also eliminates concerns with intentional human exposures while removing health research ethics review requirements which are time consuming. In this study, a humanoid robot was programmed to paint drywall, while volatile organic compounds were measured in air for comparison to model estimates. The measured air concentrations generally agreed with more advanced exposure model estimates. These findings suggest that robots have potential as a methodology for generating exposure measurements relevant to human activities, but without using human subjects.

Shock Waves and the Interpretation of the Chromospheric Calcium K-line

1972 ◽  
Vol 2 (3) ◽  
pp. 146-147 ◽  
Author(s):  
L. E. Cram
Keyword(s):  
Energy Source ◽  
Shock Waves ◽  
Energy Loss ◽  
Temperature Rise ◽  
Energy Input ◽  
Mechanical Energy ◽  
Theoretical Models ◽  
Radiative Energy ◽  
Heating Process ◽  
Radiative Energy Loss

Dissipation of shock waves has often been proposed as the energy source required to sustain the outward temperature rise in the solar atmosphere. Theoretical models for the heating process have been developed by equating the mechanical energy input to the radiative energy loss at each height, but neither of these processes is well understood, and the lack of data means that the models are necessarily crude.

scholarly journals Stellar population of the superbubble N 206 in the LMC

2017 ◽  
Vol 609 ◽  
pp. A7 ◽  
Author(s):  
Varsha Ramachandran ◽  
R. Hainich ◽  
W.-R. Hamann ◽  
L. M. Oskinova ◽  
T. Shenar ◽  
...  
Keyword(s):  
Energy Input ◽  
Large Scale ◽  
Massive Stars ◽  
Mechanical Energy ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
High Mass ◽  
Clear Correlation ◽  
Physical Parameters ◽  
X Ray

Context. Massive stars severely influence their environment by their strong ionizing radiation and by the momentum and kinetic energy input provided by their stellar winds and supernovae. Quantitative analyses of massive stars are required to understand how their feedback creates and shapes large scale structures of the interstellar medium. The giant H ii region N 206 in the Large Magellanic Cloud contains an OB association that powers a superbubble filled with hot X-ray emitting gas, serving as an ideal laboratory in this context. Aims. We aim to estimate stellar and wind parameters of all OB stars in N 206 by means of quantitative spectroscopic analyses. In this first paper, we focus on the nine Of-type stars located in this region. We determine their ionizing flux and wind mechanical energy. The analysis of nitrogen abundances in our sample probes rotational mixing. Methods. We obtained optical spectra with the multi-object spectrograph FLAMES at the ESO-VLT. When possible, the optical spectroscopy was complemented by UV spectra from the HST, IUE, and FUSE archives. Detailed spectral classifications are presented for our sample Of-type stars. For the quantitative spectroscopic analysis we used the Potsdam Wolf-Rayet model atmosphere code. We determined the physical parameters and nitrogen abundances of our sample stars by fitting synthetic spectra to the observations. Results. The stellar and wind parameters of nine Of-type stars, which are largely derived from spectral analysis are used to construct wind momentum − luminosity relationship. We find that our sample follows a relation close to the theoretical prediction, assuming clumped winds. The most massive star in the N 206 association is an Of supergiant that has a very high mass-loss rate. Two objects in our sample reveal composite spectra, showing that the Of primaries have companions of late O subtype. All stars in our sample have an evolutionary age of less than 4 million yr, with the O2-type star being the youngest. All these stars show a systematic discrepancy between evolutionary and spectroscopic masses. All stars in our sample are nitrogen enriched. Nitrogen enrichment shows a clear correlation with increasing projected rotational velocities. Conclusions. The mechanical energy input from the Of stars alone is comparable to the energy stored in the N 206 superbubble as measured from the observed X-ray and Hα emission.

Wind Stress Dependence on Ocean Surface Velocity: Implications for Mechanical Energy Input to Ocean Circulation

2006 ◽  
Vol 36 (2) ◽  
pp. 202-211 ◽  
Author(s):  
Thomas H. A. Duhaut ◽  
David N. Straub
Keyword(s):  
Wind Stress ◽  
Ocean Circulation ◽  
Energy Input ◽  
Mechanical Energy ◽  
Quadratic Function ◽  
Ocean Surface ◽  
Power Source ◽  
Surface Velocity ◽  
Stress Dependence ◽  
Scaling Arguments

Abstract It is pointed out that accounting for an ocean surface velocity dependence in the wind stress τ can lead to a significant reduction in the rate at which winds input mechanical energy to the geostrophic circulation. Specifically, the wind stress is taken to be a quadratic function of Ua − uo, where Ua and uo are the 10-m wind and ocean surface velocity, respectively. Because |Ua| is typically large relative to |uo|, accounting for a uo dependence leads only to relatively small changes in τ. The change to the basin-averaged wind power source, however, is considerably larger. Scaling arguments and quasigeostrophic simulations in a basin setting are presented. They suggest that the power source (or rate of energy input) is reduced by roughly 20%–35%.

Influence of Energy Input on Suspension Properties

2010 ◽  
Vol 62 ◽  
pp. 141-146 ◽  
Author(s):  
Anja Meyer ◽  
Kerstin Lenzner ◽  
Annegret Potthoff
Keyword(s):  
Energy Input ◽  
Molar Mass ◽  
Mechanical Energy ◽  
Particle Surface ◽  
Significant Loss ◽  
Polymer Chains ◽  
Background Solution ◽  
Electrosteric Stabilization ◽  
Before And After ◽  
Nanoscale Range

Electrosteric stabilization of a commercially available boehmite powder in water was investigated to perform milling experiments and reduce the particle size to the nanoscale range. The effect of three sodium polyacrylate dispersants (Na-PA) with different molar masses (2,100, 8,000, 15,000 g/mol) on the suspension properties before and after milling experiments was assessed by electroacoustic measurements in comparison with rheological tests. A significant loss of the stabilizing effect of the sodium polyacrylates due to the application of mechanical energy was detectable. Measurements of the adsorbed amount of the dispersants after milling via detection of the COD in the background solution show a considerable desorption from the particle surface. Accessorily performed analyses of the molar mass of the polymers yielded a destruction of the polymer chains due to the mechanical energy.

scholarly journals Mechanical energy input to the world oceans due to atmospheric loading

2006 ◽  
Vol 51 (3) ◽  
pp. 327-330 ◽  
Author(s):  
Wei Wang ◽  
Qian Chengchun ◽  
Huang Ruixin
Keyword(s):  
Energy Input ◽  
Mechanical Energy ◽  
Atmospheric Loading ◽  
The World

scholarly journals Single-phase friction riveting: metallic rivet deformation, temperature evolution, and joint mechanical performance

2019 ◽  
Vol 64 (1) ◽  
pp. 47-58 ◽  
Author(s):  
Gonçalo Pina Cipriano ◽  
Aakash Ahiya ◽  
Jorge F. dos Santos ◽  
Pedro Vilaça ◽  
Sergio T. Amancio-Filho
Keyword(s):  
Energy Input ◽  
Single Phase ◽  
Mechanical Performance ◽  
Mechanical Energy ◽  
Tensile Force ◽  
Energy Conditions ◽  
Two Phase ◽  
Axial Forces ◽  
Joint Properties ◽  
Riveting Process

Abstract The present work explores the feasibility of single-phase friction riveting on unreinforced thermoplastics. In single phase, the load is kept constant throughout the process, avoiding the forging phase with higher axial force, used in the conventional process. This process variant can constitute an answer when payload restrictions exist. The results demonstrate the feasibility of single-phase friction riveting on unreinforced polyetherimide plates joined by AA2024 rivets with 5 mm of diameter. A Box-Behnken design of experiments and analysis of variance were used to set parameter matrix and understand the correlations between parameters and joint properties. A large variation of the mechanical energy input was observed (151–529 J). Over-deformation and material rupture were observed in higher energy conditions. Lower energy input yielded a bell-shaped rivet plastic deformation, corresponding to the best performance. The maximum process temperatures varied between 461 and 509 °C. This friction riveting process variant allowed a considerable high mechanical strength to be achieved, with ultimate tensile force of 7486 N, comparable with the two-phase friction riveting process, albeit applying lower axial forces, such as 2400 N. Within the investigated conditions, this study proves the feasibility of the single-phase process, achieving good global mechanical performance and energetically efficient conditions, without forging phase.

Tillage Mechanical Energy Input and Soil-Crop Response

1981 ◽  
Vol 24 (6) ◽  
pp. 1412-1419 ◽  
Author(s):  
Dan Wolf ◽  
Thomas H. Garner ◽  
Jack W. Davis
Keyword(s):  
Energy Input ◽  
Mechanical Energy ◽  
Crop Response

Modeling the Efficiency of Movement: From Individual Muscles to Whole Organism

2009 ◽  
Author(s):  
Brian R. Umberger ◽  
Alexis D. Gidley
Keyword(s):  
Energy Consumption ◽  
Energy Input ◽  
Mechanical Energy ◽  
Human Movement ◽  
Metabolic Energy ◽  
Energy Output ◽  
Whole Body ◽  
Similar Data ◽  
Invasive Approach

In the context of human movement, efficiency is defined as the ratio of mechanical energy output (work) to metabolic energy input [1,2]. It is straightforward to determine whole-body efficiency in a task such as pedaling a bicycle ergometer. In this case, work is computed from the ergometer load and pedaling cadence, and metabolic energy is determined from pulmonary gas exchange. It is also relatively straightforward to determine the efficiency of contraction in isolated muscle preparations, where the work done is easily measured, and energy input can be inferred from heat production or oxygen consumption. However, our understanding of the efficiency of muscle function during locomotion, and how this contributes to organismal efficiency, is incomplete [1]. The ability to determine efficiency of individual muscles as they perform work in vivo would greatly enhance our understating in this area. Experimental measurement of both work and metabolic energy consumption in muscles during dynamic activities is currently limited to isolated applications in non-human animals [3]. Similar data could be obtained using computational modeling and simulation techniques, provided that estimates could be obtained for both muscle work and muscle metabolic energy consumption. This non-invasive approach would open the door to investigations in humans as well as other species. Therefore, the primary purpose of this study was to determine efficiency at both the organismal and muscular levels for bicycle pedaling, using a musculoskeletal modeling approach. A secondary purpose was to identify factors that account for between-muscle differences in efficiency.

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