scholarly journals Note: Scale-free center-of-mass displacement correlations in polymer films without topological constraints and momentum conservation

2011 ◽  
Vol 135 (18) ◽  
pp. 186101 ◽  
Author(s):  
J. P. Wittmer ◽  
N. Schulmann ◽  
P. Polińska ◽  
J. Baschnagel
Keyword(s):  
Polymer Films ◽  
Center Of Mass ◽  
Momentum Conservation ◽  
Scale Free ◽  
Topological Constraints ◽  
Mass Displacement

scholarly journals Reactive Postural Responses to Continuous Yaw Perturbations in Healthy Humans: The Effect of Aging

Sensors ◽  
2019 ◽  
Vol 20 (1) ◽  
pp. 63 ◽  
Author(s):  
Ilaria Mileti ◽  
Juri Taborri ◽  
Stefano Rossi ◽  
Zaccaria Del Prete ◽  
Marco Paoloni ◽  
...  
Keyword(s):  
Older Adults ◽  
Balance Control ◽  
Center Of Mass ◽  
Community Dwelling ◽  
Body Segments ◽  
Healthy Humans ◽  
Eyes Closed ◽  
Age Related ◽  
Postural Responses ◽  
Mass Displacement

Maintaining balance stability while turning in a quasi-static stance and/or in dynamic motion requires proper recovery mechanisms to manage sudden center-of-mass displacement. Furthermore, falls during turning are among the main concerns of community-dwelling elderly population. This study investigates the effect of aging on reactive postural responses to continuous yaw perturbations on a cohort of 10 young adults (mean age 28 ± 3 years old) and 10 older adults (mean age 61 ± 4 years old). Subjects underwent external continuous yaw perturbations provided by the RotoBit1D platform. Different conditions of visual feedback (eyes opened and eyes closed) and perturbation intensity, i.e., sinusoidal rotations on the horizontal plane at different frequencies (0.2 Hz and 0.3 Hz), were applied. Kinematics of axial body segments was gathered using three inertial measurement units. In order to measure reactive postural responses, we measured body-absolute and joint absolute rotations, center-of-mass displacement, body sway, and inter-joint coordination. Older adults showed significant reduction in horizontal rotations of body segments and joints, as well as in center-of-mass displacement. Furthermore, older adults manifested a greater variability in reactive postural responses than younger adults. The abnormal reactive postural responses observed in older adults might contribute to the well-known age-related difficulty in dealing with balance control during turning.

Center of mass displacement and relaxation times of linear alkynes

Tetrahedron ◽  
1985 ◽  
Vol 41 (15) ◽  
pp. 3063-3069 ◽  
Author(s):  
J.M. Bernassau ◽  
M. Bertranne ◽  
C. Collongues ◽  
M. Fetizon
Keyword(s):  
Center Of Mass ◽  
Relaxation Times ◽  
Mass Displacement

THE FUZZY BAG MODEL REVISITED

2002 ◽  
Vol 17 (09) ◽  
pp. 543-553 ◽  
Author(s):  
F. PILOTTO ◽  
C. A. Z. VASCONCELLOS ◽  
H. T. COELHO
Keyword(s):  
Functional Form ◽  
Potential Model ◽  
Center Of Mass ◽  
Momentum Conservation ◽  
Radial Dependence ◽  
Bag Model ◽  
New Feature ◽  
The Masses ◽  
Relativistic Potential ◽  
Energy Momentum Conservation

In this work we develop a new version of the fuzzy bag model. The new feature is the inclusion of energy–momentum conservation. This turns the model into a "real" bag model, as opposed to a relativistic potential model. One immediate consequence is that the bag constant B will acquire a radial dependence, B = B(r), whose functional form can be completely fixed without any arbitrariness. Such a feature is of importance in the study of neutron stars, where a radial dependence of B is usually put in by hand. The parameters of the model are found by fitting the masses of the baryon octet. We include center-of-mass, one-gluon exchange and pion exchange corrections for these masses.

A Comparison of Computation Methods for Leg Stiffness During Hopping

2014 ◽  
Vol 30 (1) ◽  
pp. 154-159 ◽  
Author(s):  
Hiroaki Hobara ◽  
Koh Inoue ◽  
Yoshiyuki Kobayashi ◽  
Toru Ogata
Keyword(s):  
Ground Reaction Force ◽  
Stance Phase ◽  
Center Of Mass ◽  
Reaction Force ◽  
Sine Wave ◽  
Phase Method ◽  
Leg Stiffness ◽  
Mass Displacement ◽  
Male Subjects ◽  
Oscillation Method

Despite the presence of several different calculations of leg stiffness during hopping, little is known about how the methodologies produce differences in the leg stiffness. The purpose of this study was to directly compareKlegduring hopping as calculated from three previously published computation methods. Ten male subjects hopped in place on two legs, at four frequencies (2.2, 2.6, 3.0, and 3.4 Hz). In this article, leg stiffness was calculated from the natural frequency of oscillation (method A), the ratio of maximal ground reaction force (GRF) to peak center of mass displacement at the middle of the stance phase (method B), and an approximation based on sine-wave GRF modeling (method C). We found that leg stiffness in all methods increased with an increase in hopping frequency, butKlegvalues using methods A and B were significantly higher than when using method C at all hopping frequencies. Therefore, care should be taken when comparing leg stiffness obtained by method C with those calculated by other methods.

The coordinated motion planning of a dual-arm space robot for target capturing

Robotica ◽  
2011 ◽  
Vol 30 (5) ◽  
pp. 755-771 ◽  
Author(s):  
Wenfu Xu ◽  
Yu Liu ◽  
Yangsheng Xu
Keyword(s):  
Center Of Mass ◽  
Momentum Conservation ◽  
Conservation Equation ◽  
Space Robot ◽  
Coordinated Motion ◽  
First Case ◽  
Solution Equation ◽  
Target Capturing ◽  
Dual Arm ◽  
Momentum Conservation Equation

SUMMARYIn this paper, autonomous motion control approaches to generate the coordinated motion of a dual-arm space robot for target capturing are presented. Two typical cases are studied: (a) The coordinated dual-arm capturing of a moving target when the base is free-floating; (b) one arm is used for target capturing, and the other for keeping the base fixed inertially. Instead of solving all the variables in a unified differential equation, the solution equation of the first case is simplified into two sub-equations and practical methods are used to solve them. Therefore, the computation loads are largely reduced, and feasible trajectories can be determined. For the second case, we propose to deal with the linear and angular momentums of the system separately. The linear momentum conservation equation is used to design the configuration and the mounted pose of a balance arm to keep the inertial position of the base's center of mass, and the angular momentum conservation equation is used to estimate the desired momentum generated by the reaction wheels for maintaining the inertial attitude of the base. Finally, two typical tasks are simulated. Simulation results verify the corresponding approaches.

Passive dynamics change leg mechanics for an unexpected surface during human hopping

2004 ◽  
Vol 97 (4) ◽  
pp. 1313-1322 ◽  
Author(s):  
Chet T. Moritz ◽  
Claire T. Farley
Keyword(s):  
Center Of Mass ◽  
Natural World ◽  
Knee Joints ◽  
Hard Surface ◽  
Leg Stiffness ◽  
Soft Surface ◽  
Mass Displacement ◽  
Joint Flexion ◽  
Stiffness And Damping ◽  
Surface Changes

Humans running and hopping maintain similar center-of-mass motions, despite large changes in surface stiffness and damping. The goal of this study was to determine the contributions of anticipation and reaction when human hoppers encounter surprise, expected, and random changes from a soft elastic surface (27 kN/m) to a hard surface (411 kN/m). Subjects encountered the expected hard surface on every fourth hop and the random hard surface on an average of 25% of the hops in a trial. When hoppers on a soft surface were surprised by a hard surface, the ankle and knee joints were forced into greater flexion by passive interaction with the hard surface. Within 52 ms after subjects landed on the surprise hard surface, joint flexion increased, and the legs became less stiff than on the soft surface. These mechanical changes occurred before electromyography (EMG) first changed 68–188 ms after landing. Due to the fast mechanical reaction to the surprise hard surface, center-of-mass displacement and average leg stiffness were the same as on expected and random hard surfaces. This similarity is striking because subjects anticipated the expected and random hard surfaces by landing with their knees more flexed. Subjects also anticipated the expected hard surface by increasing the level of EMG by 24–76% during the 50 ms before landing. These results show that passive mechanisms alter leg stiffness for unexpected surface changes before muscle EMG changes and may be critical for adjustments to variable terrain encountered during locomotion in the natural world.

Pelvic Kinematic Method for Determining Vertical Jump Height

2010 ◽  
Vol 26 (4) ◽  
pp. 508-511 ◽  
Author(s):  
Loren Z.F. Chiu ◽  
George J. Salem
Keyword(s):  
Vertical Jump ◽  
Center Of Mass ◽  
Reaction Force ◽  
Jump Height ◽  
Impulse Method ◽  
Vertical Jump Height ◽  
Reconstruction Methods ◽  
Kinematic Method ◽  
Mass Displacement ◽  
Vertical Jumps

Sacral marker and pelvis reconstruction methods have been proposed to approximate total body center of mass during relatively low intensity gait and hopping tasks, but not during a maximum effort vertical jumping task. In this study, center of mass displacement was calculated using the pelvic kinematic method and compared with center of mass displacement using the ground-reaction force-impulse method, in experienced athletes (n= 13) performing restricted countermovement vertical jumps. Maximal vertical jumps were performed in a biomechanics laboratory, with data collected using an 8-camera motion analysis system and two force platforms. The pelvis center of mass was reconstructed from retro-reflective markers placed on the pelvis. Jump height was determined from the peak height of the pelvis center of mass minus the standing height. Strong linear relationships were observed between the pelvic kinematic and impulse methods (R2= .86;p< .01). The pelvic kinematic method underestimated jump height versus the impulse method, however, the difference was small (CV = 4.34%). This investigation demonstrates concurrent validity for the pelvic kinematic method to determine vertical jump height.

scholarly journals Iliopectineal line: A valuable radiological reference for spino-pelvic parameters

2021 ◽  
Vol 0 ◽  
pp. 1-6
Author(s):  
Abdul M Baco ◽  
Khalid Mukhter ◽  
Isam Moghamis ◽  
Nasser Mehrab ◽  
Mohamed A Alhabash ◽  
...  
Keyword(s):  
Pelvic Tilt ◽  
Center Of Mass ◽  
Reference Points ◽  
Sacral Slope ◽  
Cross Sectional ◽  
Digital Radiology ◽  
Pelvic Parameters ◽  
Radiological Images ◽  
Mass Displacement ◽  
Spinal Imbalance

Objectives: Spinopelvic parameters are crucial to address sagittal spinal imbalance; such measurements require standardized lateral radiographs that include spine and hips, which are neither always available, nor readily feasible intra-operatively. The aim of this study was to describe pelvic radiological reference points that could provide reliable sagittal balance estimates from conventional lumbosacral lateral radiographs. Methods: A descriptive, cross-sectional, radiological-based study was conducted. Readings were taken from institute’s digital radiology library, blinded to personal and clinical data. The correlation was made to conventional pelvic incidence (CPI), conventional pelvic tilt (CPT), and sacral slope (SS), measured for the same patients, and from the same standardized standing radiographs that included femoral heads. Results: Radiological images for 140 adult subjects, with suspected or established spine problems were studied. The average lumbar lordosis (LL) of 3 readers was 47 ± 13 (13–81) with an interclass agreement of 0.9, SS was 41 ± 9 with an interclass agreement of 0.9, CPI was 53 ± 10 with an interclass agreement of 0.8, CPT was 14 ± 8 with an interclass agreement of 0.9, iliopectineal inclination (IPI) of 4 readers was 64 ± 8 with an interclass agreement of 0.7 and iliopectineal tilt (IPT) was 24 ± 8 with an interclass agreement of 0.8 LL was with 6° of CPI and 16° of IPI. The CPI was equal to (CPI = SS + [CPT + 1.2]) and (IPI = SS + [IPT + 0.6]). The IPI was negatively correlated with CPI –0.2 P = 0.006, and IPI was negatively correlated with CPT –0.333 P < 0.001. Conclusion: Iliopectineal line provides reproducible readings, closer values to LL, and addresses the center of mass displacement.

Movement screens: Are we measuring movement dysfunction or movement skill?

2018 ◽  
Vol 13 (5) ◽  
pp. 771-778
Author(s):  
Anthony D Vidal ◽  
Mimi Nakajima ◽  
Will FW Wu ◽  
James Becker
Keyword(s):  
Center Of Mass ◽  
Corrective Feedback ◽  
Screen Test ◽  
Camera Motion ◽  
Joint Angles ◽  
Verbal Cues ◽  
Verbal Instructions ◽  
Movement Screening ◽  
Mass Displacement ◽  
Injury Potential

Movement screens are commonly used for assessing athletic readiness or injury potential. However, these screens fail to distinguish between movement dysfunction and movement skill. The purpose of this study was to compare performance on a common movement screen test, the overhead squat, when using no instructions (Baseline), instruction from a commercial movement screen, and instructions which include verbal cues, demonstration, and practice (Instructions, Demonstration, and Practice [IDP]). Fourteen individuals performed the overhead squat under the three different conditions while their movements were recorded using a 12-camera motion capture system. Specific scoring criteria for the overhead squat such as joint angles, depth of squat, torso and shank orientation, and weight distribution were compared between instructional conditions. Compared to the Baseline and commercial movement screen conditions, IDP resulted in greater vertical center of mass displacement, better alignment of the torso and shank segments, and greater peak flexion at the hip and knee. These results show that incorporating verbal cues, providing demonstration, and allowing for practice during movement screening significantly improve performance in the overhead squat assessment. Based on these results, the authors recommend that coaches or clinicians using movement screens to identify movement dysfunction should provide demonstrations of the movement, allow the participant to practice, provide verbal instructions about the movement prior to assessment, and provide corrective feedback during practice. Excluding these elements limits the ability to distinguish between true dysfunctional movement patterns and a simple lack of movement skill.

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