Background: Theoretically, balance is affected by the height of center of mass (COM) during quiet standing. However, no one examined this in humans with variables derived from the center of pressure (COP). Objects: We have conducted balance experiment to measure COP data during quiet standing, in order to examine how the COP measures were affected by the height of COM, vision, floor conditions, and gender. Methods: Twenty individuals stood still with feet together and arms at sides for 30 seconds on a force plate. Trials were acquired with three COM heights: 1% increased or decreased, and not changed, with two vision conditions: eyes closed (EC) and eyes open (EO), and with two floor conditions: unstable (foam pad) and stable (force plate) floor. Outcome variables included the mean distance, root mean square distance, total excursion, mean velocity, and 95% confidence circle area. Results: All outcome variables were associated with the COM height (p < 0.0005), vision (p < 0.0005), and floor condition (p < 0.003). The mean velocity and 95% confidence circle area were 5.7% and 21.8% greater, respectively, in raised COM than in lowered COM (24.6 versus 23.2 mm/s; 1,013.4 versus 832.3 mm2). However, there were no interactions between the COM height and vision condition (p > 0.096), and between the COM height and floor condition (p > 0.183) for all outcome variables. Furthermore, there was no gender difference in all outcome variables (p > 0.186). Conclusion: Balance was affected by the change of COM height induced by a weight belt in human. However, the effect was not affected by vision or floor condition. Our results should inform the design of balance exercise program to improve the outcome of the balance training.

Background: The consequences of falls are often debilitating, and prevention is important. In theory, the lower the center of mass (COM), the greater postural stability during standing, and a weight belt at the waist level may help to lower the COM and improve the standing balance. Objects: We examined how the limit of stability (LOS) was affected by the lowered center of mass with the weight belt. Methods: Twenty healthy individuals participated in the LOS test. After calculating each participant’s COM, a weight belt was fastened ten centimeters below the COM. Trials were acquired with five weight belt conditions: 0%, 2%, 4%, 6%, and 8% of body weight. Outcome measures included reaction time, movement velocity, endpoint excursion, maximum excursion, and directional control in 4 cardinal moving directions. Results: None of our outcome variables were associated with a weight belt (p > 0.075), but all of them were associated with moving direction (p < 0.01). On average, movement velocity of the COM and maximum excursion were 31% and 18% greater, respectively, in mediolateral than anteroposterior direction (5.4°/s vs. 4.1°/s; 97.5% vs. 82.6%). Conclusion: Our results suggest that postural stability was not affected by the weightinduced lowered COM, informing the development and improvement of balance training strategies.

In this study, vertical acceleration of center of mass was observed along normal gait phases in 9 healthy male volunteers (aged ). The developed wireless accelerometric device was attached on the intervertebral space between L3 and L4 using a semi-elastic waist belt. A three-dimensional motion analysis system, synchronized with the accelerometry, was used for detecting gait phases. There was no significant correlation between the body weight and the acceleration. The first peak curve covered loading response phase. The second downward peak point was matched accurately with the opposite toe-off. In mid-stance and terminal stance, the acceleration curve highly resembled the vertical ground reaction force curve. There was no significant difference in timing between the final upward peak point and the initial contact. Therefore, the developed accelerometry system would be helpful in determining determine temporal gait pattems in patients with gait disorders.

The case for a massive black hole in the center of the Galaxy is reassessed using improved modeling techniques and observational data. A dark mass of ~2 ×10 6 M⊙ is present within 0.2 pc of the Galactic center. However, the available data can be modeled, without appealing to a massive black hole, using an extended distribution of dark stellar remnants (neutron stars and stellar mass black holes) provided that the stellar initial mass function in the central parsec is deficient in stars less massive than ~1 M⊙. Such a situation may be a natural consequence of repeated gas build-up followed by starbursts in the central region. A clear distinction between this and the massive central black hole model cannot be made using red giant tracers outside 0.2 pc due to uncertainties in the radial velocity dispersion distribution. The cluster of massive early-type emission-line stars in the central parcsec more effectively probe the mass distribution close to Sgr A *, but their small number and partial rotational support complicate mass determinations. Proper motion determinations for stars within 0.5' of Sgr A * may be the most effective means of unambiguously determining the mass distribution in the immediate vicinity of the Galactic center.

Generating motion of center of mass for biped robots is a challenging issue since biped robots can easily lose balance due to limited contact area between foot and ground. In this paper, we propose force control method to generate high-speed motion of the center of mass for horizontal direction without losing balancing condition. Contact consistent multi-body dynamics of the robot is used to calculate force for horizontal direction of the center of mass considering balance. The calculated force is applied for acceleration or deceleration of the center of mass to generate high speed motion. The linear inverted pendulum model is used to estimate motion of the center of mass and the estimated motion is used to select either maximum or minimum force to stop at goal position. The proposed method is verified by experiments using 12-DOF torque controlled human sized legged robot.

본 연구에서는 건물의 질량중심과 면진층의 강성중심 사이의 차이에 따른 면진효과에 대하여 살펴보았다. 면진기술은 면진층에 설치되는 면진장치의 성능에 크게 의존하는 기술이므로 면진장치 제작 후 전수검사를 통하여 면진장치의 수평강성을 검토하게 되어 있다. 하지만면진장치 성능실험 시 각각의 면진장치의 품질기준은 건축기준에는 정해져 있지 않으며, 이로 인해 설계 시 적용된 강성과 실제 강성의 차이가 발생하여 면진층 상부 부재에 큰 문제를 야기할 수 있다. 연구결과, 최대응답변위의 차이는 크게 나타나지 않았으나 편심이 증가할수록 최대응답가속도, 층전단력 및 상부구조의 부재력은 크게 증가하여 일부 부재에서는 과도한 손상이 예상된다. 따라서 면진층은 실제 장치제작 후 전수검사를 실시하여 반드시 설계된 의도대로 편심이 발생하지 않도록 장치를 재배치할 필요가 있으며, 가능하다면 건물의 질량중심과 강성중심의 차이는 동일하게 설계할 것을 추천한다.