• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.119-134
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• 2004

The purpose of this study was to analyze the angular momentum characteristics of the Fosbury Flop high jump and the role of the body segments for the production of 3 angular momentum components. The subjects were three male jumpers who were former Korean national team players. Their jumping motions were analyzed using the DLT method of three-dimensional cinematography. The conclusions were as follows. 1. All the forward angular momentum needed to clear the bar was created in the take-off phase. Take-off leg was the great contributor of the forward angular momentum. On the other hand, free leg produced large opposite angular momentum. 2. All subject had some lateral angular momentum before the take-off phase. Head and free leg had major contribution to the lateral angular momentum production. Take-off leg produced opposite angular momentum. 3. All subject had some twisting angular momentum, which make the back of the athlete him to the bar, before the take-off phase. Free leg was the major contributor of the twisting angular momentum. Head and trunk was the second contributor of the twisting angular momentum. 4. Total angular momentum needed to clear the bar had no significant correlation to the jumping height. 5. Subject who made excessive angular momentum showed different pattern of angular momentum production and had a poor record compared to other subject.

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.1
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• pp.1-17
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• 1998

두개의 임플랜트로 지지되는 overdenture를 이용한 하악무치악환자의 치료법은 경제적이면서, 실용적인 치료로 인정을 받고 있다. 하지만 해부학적인 조건으로 임플랜트를 설측 혹은 후방에 식립해야 되는 경우에는 일반적인 bar설계는 bar가 구강저 상방을 지나게 되어 혀운동, 발음, 위생관리 등에 많은 문제점을 부여한다. 이에 대한 해결방법으로 전방부 치조제 상에 보철물의 회전을 허용하는 angular bar를 설계할 수 있다. 하지만 이 설계는 임플랜트에 불리한 moment를 유발한다. 그럼에도 불구하고 뛰어난 유지력과 지지능력, 경제적인 면 때문에 angular bar는 임상에서 많이 사용되고 있다. 이에 본 연구는 angular bar의 전방 cantilever양을 달리하여 임플랜트 및 주변조직에 미치는 영향을 삼차원 유한요소분석법을 통해서 알아보고자 하였다. 이공사이의 하악골을 단순화시킨 준하악골모형에 직경 3.75mm인 브로네마르크 임플랜트 2개를 길이가 13,15mm인 경우로 설정하여 제 1소구치 부위에 식립하였다. 두 임플랜트를 연결하는 bar는 전방부 cantilever양을 0-5mm, 1mm씩 하여 6가지 경우를 가정하고 제작하였다. 각각 bar 중앙부에 수직압 (90도) 35N, 경사압(120도) 70N, 수평압(0도) 10N을 가하였으며 이때 나타나는 응력 분산형태와 임플랜트의 골유착에 불리하게 작용하는 최대주응력(인장력)과 변위량을 살펴보았다. 연구결과 다음과 같은 결론을 얻었다. 1. Cantilever양이 증가할수록 주변피질골과 임플랜트로 응력이 집중되었으며 상부 보철물의 변위량도 커졌다. 2. Cantilever양에 대한 수평압의 영향은 크지 않았으며 임플랜트 길이가 긴 것이 변위량과 응력이 작았다. 3. 경사압에 대한 응력의 변화는 cantilever양의 증가에 따라 급격히 증가하는 양상을 띠었으며 임플랜트길이가 응력 및 변위의 양에 미치는 영향은 없었다. 4. 수직압에 대한 응력의 변화는 초기에는 완만한 증가를 보이다가 일정 시점 지난 후에는 증가율이 커지는 경향을 띠었다. 증가현상이 두드러지기 전에는 길이의 증가가 응력의 분산효과는 가져왔으나 이후에는 길이의 응력분산 효과는 없었다. 5. 응력분포양상은 cantilever양이 증가할수록 골조직을 통한 분산정도는 작아지고 특정부위의 피질골과 임플랜트, 상부보철물에 집중되는 경향을 보였다. 6. 임플랜트와 주변 골조직으로의 응력분산능력이 예후를 좌우한다는 점에서 angular bar는 적합치 못하며 부득이한 경우는 임플랜트 길이를 길게 하고 최대한 3mm이내로 cantilever양을 제한하는 것이 추천된다.

• Korean Journal of Applied Biomechanics
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• v.33 no.4
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• pp.137-146
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• 2023

Objective: The horizontal bar of gymnastics is fundamentally based on rotational movements. This study aimed to determine the effect of kinematics variables and sequence during horizontal bar performance (Kovacs, Tkatchev Stretched & Kolman) in gymnastic. Method: Four gymnastics athletes of the national team were participated in this study. All subjects were asked to perform the three types of horizontal bar skill. Simi marker-less cameras were used to collect the raw data (120 Hz). Kinematic variables (total time, interval, center of mass, height, angular velocity etc.) and sequence variables were calculated to examine the differences. Results: As a result, horizontal bar performance in gymnastic has special sequence that making the peak angular velocity from distal joint to proximal joint (knee-hip-shoulder). It is rare sequence that typical sport does not have. Conclusion: In field, gymnastic coaches and players should know the result that there is special sequence in horizontal bar performance. It could be very useful to teach and enhance their performance.

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.250-252
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• 1999

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.57.1-57.1
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• 2011

Using high-resolution numerical simulations, we investigate the formation of gaseous substructures and mass inflow rates in barred spiral galaxies in the presence of both bar and spiral potentials. The gaseous medium is assumed to be infinitesimally-thin, isothermal, unmagnetized, and non-self-gravitating. To consider various galactic situations, we vary the pattern speed and strength of spiral arms as well as the black hole mass. We find that spiral arms with pattern speed smaller than that of the bar remove angular momentum from the gas outside corotation which transports to the bar region, making the dust lanes strong and live long. When the arm pattern speed is identical to that of the bar, on the other hand, the gas outside corotation gains angular momentum and thus moves outward, without affecting the bar region. Overall gaseous morphologies in simulations match well with observed IR images of barred spiral galaxies such as NGC 1097, when the arms and bar are in phase at the corotation radius. The presence of spiral arms increases the mass inflow rate as well, making it larger than $0.01M_{\odot}/yr$ when MBH is $4{\times}10^7M_{\odot}$, possibly explaining AGN activities in Seyfert galaxies.

• Korean Journal of Applied Biomechanics
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• v.13 no.3
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• pp.15-26
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• 2003

This study was conducted to investigate the performance times, CM position and CM speed, pole chord length and pole chord angle, whole body angular momentum(X axis), and grip width in pole vault event according to the event and phase; touch down, pole plant, take-off, maximum pole bending pole straight, pole release, peak height, and foot contact, pole contact, free flight. The pole vaulting of four male elite vaulters including six trial were filmed using two video digital cameras at 60 Hz at 56th national athletic match, and data were collected through the DLT method of three dimensional cinematography. In general the better jumper is, the longer the performance time is. And the greater CM speed is, and the better his transformation ability of CM horizontal speed into vertical speed is. As he uses a longer pole, his grip is higher, and it is a enough for him to rock back his body, so that he pulls and pushes the pole well keeping his hips close to. An greater maximum angular momentum and early positioning of the hips parallel to the bar makes his body far side of the bar and his bar clearance easier. Specially our national jumper needs to have more powerful braking force during foot contact phase, and take his body on the pole after maximum pole bending, and pull and push the pole strongly keeping his hips close to. Also he needs to have stronger muscular strength in order to control the longer pole and use the pole of proper tension more efficiently.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.101-104
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• 2004

This paper addresses uncertainty issues encountered recently in measuring head vibration using the conventional 6-axis or 9-axis bite-bar Those conventional bite-bars are shown to present insufficient information to measure a complete 6 degree-of-freedom motion of head vibration. In order to overcome such limit, a theoretical measurement model that consists of four 3-axis linear accelerometers is suggested (Theoretical backgrounds presented in this paper shall have been addressed in the international congress of ICA 2004 in this April). It is shown to enable the direct measurement of three angular acceleration components and six angular velocity-dependent nonlinear terms. In audition to the three linear acceleration terms, those nine angular motion-dependent ones are found to make it possible to evaluate the general head vibration for a given position. To examine the feasibility of the proposed method, a newly designed 12-axis bite-bar was developed. Detailed experimental results obtained using the developed 12-axis bite-bar are illustrated in the presentation of this paper, which illustrates what amount of measurement accuracy provides. But, this paper provides more detailed experimental data and extended uncertainty factors.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.131-132
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• 2010

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.20-28
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• 2005

This paper addresses uncertainty issues encountered recently in measuring head vibration using the conventional 6-axis or 9-axis bite-bar model. Those conventional bite-bar models are shown to present insufficient information to evaluate a generalized motion of head vibration. In order to overcome such limit, a new theoretical measurement model that consists of four 3-axis linear accelerometers is suggested. It is shown to enable the measurement of three angular acceleration components and six second-order angular velocity-dependent terms. Those nine angular motion-related ones, in addition to the three linear acceleration terms at the origin, are found to make it possible to evaluate the generalized head vibration for a given position. To examine the feasibility of the proposed method, a newly designed 12-axis bite-bar was developed. Detailed experimental results obtained from the developed 12-axis bite-bar are demonstrated in this paper. They illustrate that the popular 6-axis bite-bar model yield about $4.0\%$ relative measurement uncertainty for the pitch component of head vibration, $14\%$ and $10\%$ relative measurement uncertainty for the roll and yaw components of head vibration, respectively. Furthermore, this paper proposes other uncertainty factors to be considered in the future.

• The Journal of the Acoustical Society of Korea
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• v.24 no.1E
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• pp.7-15
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• 2005

This paper addresses issues encountered in measuring the general, 6-degree-of-freedom motion of a human head, A complete mathematical description for measuring the head motion using the six-accelerometer configured bite-bar is suggested, The description shows that the six-axis vibration cannot be completely obtained without the roll, pitch and yaw angular velocity components, A new method of estimating the three orthogonal (roll, pitch and yaw) angular velocities from the six acceleration measurements is introduced. The estimated angular velocities are shown to enable further quantitative error analysis in measuring the translational and angular accelerations at the head. To make this point clear, experimental results are also illustrated in this paper. They show that when the effects of angular velocities are neglected in the head vibration measurement the maximum percentage errors were observed to be more than $3 \%$ for the angular acceleration of the head and to be close to $5 \%$ for its translational acceleration, respectively. It means that the inclusion of all the angular velocity dependent acceleration components gives more accurate measurement of the head vibration.