• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.64-66
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• 1993

This paper presents an efficient method to calculate voltage collapse point and to improve static voltage stability. To evaluate static voltage stability in power systems. it is necessary to get critical loading points. For this purpose, we use linear programming to calculate efficiently voltage collapse point. And if index value becomes larger than given threshold value, vol tags stability is improved by compensation of reactive power at selected bus. This algorithm is verified by simulation on the sample system.

• Steel and Composite Structures
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• 제46권4호
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• pp.513-523
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• 2023

Buckling and post-buckling behaviors of geometrically perfect double-curvature shells made from smart composites have been investigated. The shell has been supposed to be exposed to transverse mechanical loading and magneto-electro-elastic (MEE) coupling. The composite shell has been made of two constituents which are piezoelectric and magnetic ingredients. Thus, the elastic properties might be variable based upon the percentages of the constituents. Incorporating small scale impacts in regard to nonlocal theory leads to the establishment of the governing equations for the double-curvature nanoshell. Such nanoshell stability will be shown to be affected by composite ingredients. More focus has been paid to the effects of small scale factor, electric voltage and magnetic intensity on stability curves of the nanoshell.

• 국제물리치료학회지
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• 제12권2호
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• pp.2370-2374
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• 2021

Background: Masticating is an activity that is free from temporal or spatial constraints, with an advantage that it can be combined easily with other treatment methods. While several studies have reported a positive effect of the intervention of chewing using the jaw on postural stability, only a few studies were conducted on stroke patients. Objectives: To investigated the effects of masticating chewing gum on the static and dynamic balancing of stroke patients. Design: Randomized cross-over study design. Methods: Nineteen stroke patients were randomly assigned to the chewing group or control group. BT4 was used to measure the static and dynamic balancing abilities. Pre-test measurements were taken before mastication of chewing gum, and post-test measurements were taken after 2 days. The stroke patients in the chewing group were guided to sit on a chair and chew gum for 3 min, and their balancing abilities were simultaneously measured. The balancing abilities of the control group patients were measured while they sat at rest without masticating chewing gum. Results: The chewing group showed significant increases in the measures of static balance (i.e., C90 area, trace length, X mean, and Y mean). In the between-group comparison, the measures of static balance were significantly higher in the chewing group than in the control group. Conclusion: These findings suggest that masticating chewing gum enhanced the static balancing ability of stroke patients. Thus, gum chewing should be considered a viable clinical intervention to control posture in stroke patients.

• 한국농공학회논문집
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• 제65권5호
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• pp.1-11
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• 2023

Due to climate change and aging of reservoirs, damage to embankment slopes is increasing. However, the safety diagnosis of the reservoir slope is mainly conducted by visual observation, and the time and economic cost are formidable to apply soil mechanical tests and slope stability analysis. Accordingly, this study presented a predicting method for the compaction and strength characteristics of the reservoir embankment soil using a portable static cone penetration test. The predicted items consisted of dry density, cohesion, and internal friction angle, which are the main factors of slope stability analysis. Portable static cone penetration tests were performed at 19 reservoir sites, and prediction equations were constructed from the correlation between penetration resistance data and test results of soil samples. The predicted dry density and strength parameters showed a correlation with test results between R² 0.40 and 0.93, and it was found to replace the test results well when used as input data for slope stability analysis (R² 0.8134 or more, RMSE 0.0320 or less). In addition, the prediction equations for the minimum safety factor of the slope were presented using the penetration resistance and gradient. As a result of comparing the predicted safety factor with the analysis results, R² 0.5125, RMSE 0.0382 in coarse-grained soil, R² 0.4182 and RMSE 0.0628 in fine-grained soil. The results of this study can be used as a way to improve the existing slope safety diagnosis method, and are expected to be used to predict the characteristics of various soils and inspect slopes.

• 한국항공우주학회지
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• 제34권4호
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• pp.25-32
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• 2006

현대의 고성능 전투기는 공력성능 및 조종성능의 향상을 위하여 대부분 세로축 방향으로 항공기를 불안정하게 설계하는 정안정성 완화(Relaxed Static Stability) 개념을 채택하고 있다. 비행제어법칙의 설계 작업은 불안정하게 설계된 항공기에 안정성(Stability)을 부여하고, 주어진 비행임무에 대하여 만족스런 조종성능(Controllability)을 발휘할 수 있도록 비행성능을 조작하는 일련의 과정이다. 항공기의 세로축 운동은 장주기 및 단주기 운동이라는 2개의 감쇠진동 모드가 중첩되어 있다고 간주한다. 전투기에서 세로축 제어법칙설계는 장주기 모드가 설계대상으로 고려되지 않으며, 미 군사규격인 MIL-F-8785C에 정의되어 있는 단주기 모드(Short Period Mode)의 요구조건을 이용하여 주파수와 감쇠비를 최적화한다. 이 때, 제어법칙이 포함된 고차시스템을 저차 등가시스템으로 등가 시켜 판별한다. 현재까지 항공기의 단주기 운동 특성에 관한 연구는 활발하게 진행되어 왔으나, 장주기 운동 특성에 관한 연구는 그렇지 못하였다. 본 논문에서는 T-50 훈련기의 장주기 모드 운동 특성을 분석하기 위해 선형 및 비선형해석을 수행하였으며, 받음각제한기 및 자동 피치자세각 트림 명령이 세로축 운동에 미치는 영향성을 분석하였다.

• Journal of Biosystems Engineering
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• 제42권3호
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• pp.127-135
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• 2017

Purpose: Purpose: The usability of a mathematical model modified for analysis of the static stability of an asymmetric tractor-harvester system was investigated. Method: The modified asynchronous mathematical model was validated through empirical experiments, and the effects of movements of the center of gravity (CG) coordinates on the stability against lateral overturning were analyzed through simulations. Results: Changes in the lateral overturning angle of the system were investigated when the coordinates of the CG of the system were moved within the variable range. The errors between simulation results and empirical experiments were compared, and the results were -4.7% at the left side overturning and -0.1% at the right side overturning. The asymmetric system was characterized in such a way that the right side overturning had an increase in overturning angle in the (+) variable range, while it had a decrease in overturning angle in the (-) variable range. In addition, the left side overturning showed an opposite result to that of the right side. At the declination angle (296<${\gamma}$<76), the right side overturning had an increase in the maximum overturning angle of 3.6%, in the minimum overturning angle of 20.3%, and in the mean overturning angle of 15.9%. Furthermore, at the declination angle (284<${\gamma}$<64), the left side overturning had a decrease in the maximum overturning angle of 29.2%, in the minimum overturning angle of 44%, and in a mean overturning angle of 39.7%. Conclusion: The modified mathematical model was useful for predicting the overturning angle of the asymmetric tractor-harvester system, and verified that a movement of the CG coordinates had a critical effect on its stability. In particular, the left side overturning was the most vulnerable to stability, regardless of the direction of declination angle.

• Physical Therapy Rehabilitation Science
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• 제8권1호
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• pp.40-44
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• 2019

Objective: The purpose of this study was to examine the changes in postural stability according to ankle fixation in healthy university students. Design: Cross-sectional study. Methods: Thirty healthy subjects (15 males and 15 females, 20.13 years, 167.49 cm, 65.87 kg) were recruited on a voluntary basis. The BT4 system (HUR Laps Oy, Tampere, Finland) was used to measure the static (standing posture with eyes open and eyes closed) and dynamic (external perturbation and limits of stability (LOS) in the forward, backward, left, and right side) balance abilities. External perturbation was measured by the subject's postural sway velocity and area for 20 seconds after being impacted by a gym ball. Static and dynamic stabilities were measured with ankle joint fixation and non-fixation conditions. Ankle fixation was provided using Mueller tape on both ankle joints. Results: For static stability under the standing posture, there was no significant difference between standing with ankle joint fixation and non-fixation conditions. However, dynamic stability (external perturbation and LOS in the forward, backward, left, and right side) was significantly higher in the standing with the non-fixation condition compared to the standing with ankle joint fixation condition (p<0.05). Conclusions: Our results reveal that ankle joint fixation can influence dynamic stability during standing. Thus, we believe that this result provides basic information for making improvements in postural control and may be useful in balance training for fall prevention.

• The Journal of Korean Physical Therapy
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• 제33권6호
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• pp.272-277
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• 2021

Purpose: The purpose of this study is to confirm the effect of static stretching of the plantar flexor for 5 minutes on balance and ankle muscle activity when walking in young adults. Methods: This study experimented on 20 healthy college students without vestibular and musculoskeletal diseases. Subjects performed static stretching intervention of plantar flexor for 5 minutes on a stretch board set at 15° to 25° Balance was measured four times before intervention (pre), after intervention (post), 5 minutes after intervention (post 5 min), 10 minutes after intervention (post 10 min), and ankle muscle activity was measured during walking. For the analysis and post hoc analysis, one-way Repeated Measure ANOVA and Fisher's LSD (Last Significant Difference) was performed to find out the change in balance and the activity of ankle muscles before static stretching, pre, post, post 5 minutes rest, post 10 minutes rest. Results: There was no significant difference in weight distribution index (WDI) in balance, but stability index (ST) showed a significant difference, and there was also a significant difference in correlation pre, post, post 5min rest, post 10 minutes rest (p<0.05). There was no significant difference in ankle muscle activity during walking in Tibialis anterior (TA), Medial gastrocnemius (GM), and Lateral gastrocnemius (GL) (p>0.05). Conclusion: The stability index (ST) increased significantly immediately after static stretching and decreased after 5 minutes. After static stretching, at least 5 minutes of rest are required to restore balance.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1997년도 전력전자학술대회 논문집
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• pp.204-210
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• 1997

The paper deals with the design and evaluation of a new static-exciter for generator excitation systems to improve the steady-state and transient stabilities. It increases or maintains the generator field current by boosting the field voltage in the case of an input AC line voltage drop during and immediately after a fault. The validity of the proposed excitation system is verified with computer simulation. The simulation results of the stability analysis on the generator with the proposed exciter is better than that of a conventional static exciter and a conventional AC exciter. Also, this proposed exciter can be simply implemented and controlled by modern power electronics technology.

• 한국정밀공학회지
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• 제17권3호
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• pp.83-91
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• 2000

During static walking of a quadruped walking robot, stability of the robot depends on whether the projection of the mass center is located within the supporting area that is varying with leg motion and formed by standing legs. In this paper, force margin instead of the mass center was used to determine stability and body-tilting method was used to enhance it. On-line control of body tilting was realized with simple reaction feedback based on force margin of the static walking model of the robot instead of complicated calculation. Model reference on-line control where the model searches stable pose for predefined force margin also gave good walking performance.