• 천문학회보
• /
• 제46권2호
• /
• pp.81.1-81.1
• /
• 2021

Stellar kinematics is a useful tool to understand the formation and evolution of young stellar systems. Here, we present a kinematic study of the HII region, NGC 821, using the Gaia Early Data Release 3. NGC 281 contains the open cluster IC 1590. This cluster has a core and a low-stellar density halo. We detect a pattern of cluster expansion from the Gaia proper motion vectors. Most stars radially escaping from the cluster are distributed in the halo. We measure the 1-dimensional velocity dispersion of stars in the core. The velocity dispersion (1 km/s) is comparable to the expected virial velocity dispersion of this cluster, and therefore the core is at a virial state. The core has an initial mass function shallower than that of the halo, which is indicative of mass segregation. However, there is no significant correlation between stellar masses and tangential velocities. This result suggests that the mass segregation has a primordial origin. On the other hand, it has been believed that the formation of young stars in NGC 281 West was triggered by feedback from massive stars in IC 1590. We investigate the ages of stars in the two regions, but the age difference between the two regions is not comparable to the timescale of the passage of an ionization front. Also, the proper motion vectors of the NGC 281 West stars relative to IC 1590 do not show any systematic receding motion from the cluster. Our results suggest that stars in NGC 281 West might have been formed spontaneously. In conclusion, the formation of NGC 281 can be understood in the context of hierarchical star formation model.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.950-955
• /
• 2003

The fluid propulsion mechanism of two oscillating flat plates is studied numerically using a discrete vortex method. Presently, the flat plates are assumed to be rigid. To analyze the closely coupled aerodynamic interference between the flat plates, a core addition scheme and a vortex core model are combined together. A calculated wake pattern for a flat plate in heaving oscillation motion is compared with the flow visualization. The effect of wake shapes on the aerodynamic characteristics of the flat plate in pitching oscillation is investigated. The velocity profiles behind the flat plates in pitching oscillations are plotted to investigate the possible thrust generation mechanism.

• 대한통합의학회지
• /
• 제6권4호
• /
• pp.39-45
• /
• 2018

Purpose : The purpose of this study is to investigate the effect of core motion pattern on abdominal muscle thickness on unstable support surface using sling suspension system and to provide an effective exercise program for therapeutic rehabilitation in clinical practice. Methods : In this study, we used the flank exercise using a sling. It was intended for 21 healthy men and 9 healthy women. Before and after the exercise of the subjects, abdominal muscles (EO, IO, TrA the thickness of the muscle) was determined using a diagnostic ultrasonic apparatus. The period of exercise was 3 times a week for 6 weeks. The exercise for each group started with 3 sets per week and 1 set per week was added. A description of the method and attitude of each exercise is as follows. First, the push-up flank 's exercise position is to put both feet on the sling and hold the floor with both hands. Second, the side flank's exercise postures take the side flanks, while the two legs hang on the sling and one arm supports the body with an articulated bend (about $90^{\circ}$). Third, the elbow flank's exercise position is to put the two legs on the sling, and take a flank posture with the arms bent and joint bending (about $90^{\circ}$). Results : There was a significant difference in the thickness of the muscle in the three flank movements after the exercise (p<.05). The most significant difference was in the change of the muscle thickness in the abdominal muscle, the outer muscle, and the stomach in the elbow flank exercise after exercise. There was a significant difference between the mean thickness of the abdominal muscles according to the flank type after exercise (p<.05). Conclusion : In flank exercise for core stabilization using sling, it is considered effective to strengthen the abdominal muscles by considering the support surface, difficulty level, change of movement pattern.

• Earthquakes and Structures
• /
• 제20권2호
• /
• pp.175-185
• /
• 2021

This study strives to highlight the importance of considering the vertical ground motions (VGM) in the seismic evaluation of RC buildings. To this aim, IDA (Incremental Dynamic Analysis) is conducted on three code-based designed high-rise RC frame-core wall buildings using a suite of earthquake records comprising of significant VGMs. To unravel the significance of the VGM inclusion on the performance of the buildings, IDAs are conducted in two states (with and without the vertical component), and subsequently based on each analysis, fragility curves are developed. Non-simulated collapse criteria are used to determine the collapse state drift ratio and the area under the velocity spectrum (SIm) is taken into account as the intensity measure. The outcome of this study delineates that the inclusion of VGM leads to the increase in the collapse vulnerability of the structures as well as to the change in the pattern of inter-story drifts and failure mode of the buildings. The results suggested that it would be more conservative if the VGM is included in the seismic assessment and the fragility analysis of RC buildings.

• 한국수산과학회지
• /
• 제22권6호
• /
• pp.415-423
• /
• 1990

In a laboratory model the response of the boundary layer flow over topography is studied in a rotating sliced cylinder by employing the source-sink analogy with Ekman layer dynamics. The boundary layer flow is produced by two different fluid. In the first experiment homogeneous fluid is used both for the source and the working fluid of the container. In the second experiment a denser fluid is used for the source with the same working fluid. For the homogeneous western boundary layer flow both the northward and the southward flow were affected by the topography(ridge) to produce a cyclonic motion near the ridge. When woughward moving heavy boundary flow of slower speed and the northward moving faster flow were present at the same time, the splitting of southward flow and the separating of the northward flow were observed with a cyclonic motion at the ridge. The most important factor that influence production of the cyclonic motion has been turned out to be the presence of the topography in the western boundary layer. In particular the role of the southward moving heavy flow over the interior flow pattern was found to be very significant.

• 한국통신학회논문지
• /
• 제34권4C호
• /
• pp.349-354
• /
• 2009

H.264/AVC 디코더의 하드웨어 구현 시 실시간 동작을 위한 가장 큰 장애 요소 중 하나인 외부 메모리 엑세스량을 크게 줄인 움직임 보상 기법을 제안한다. H.264/AVC 디코더의 움직임 보상용 참조 영상은 큰 용량 때문에 대게 외부 메모리에 보관되며, 참조 영역은 수시로 디코더 코어 내부로 읽혀지게 되는데, 단순히 참조 영역 단위별 순차적 메모리 접근을 할 경우 그 데이터 엑세스 량은 디코더의 실시간 동작이 불가능할 정도로 막대할 수가 있다. 본 논문에서는 참조 영역을 매크로블럭 단위로 분석하여 가급적 적은 메모리 엑세스로 필요한 참조 영역을 읽어 들이는 방식을 제안하고 있으며, 실험 결과 제안된 움직임 보상 기법은 단순한 순차적 참조 블록별 데이터 접근 방식 대비 외부 메모리 사용 대역폭을 약 30% 감소시킴을 확인할 수 있었다.

• Structural Engineering and Mechanics
• /
• 제60권1호
• /
• pp.1-19
• /
• 2016

In this study, the supersonic panel flutter of doubly curved composite sandwich panels with variable thickness is considered under aerothermoelastic loading. Considering different radii of curvatures of the face sheets in this paper, the thickness of the core is a function of plane coordinates (x,y), which is unique. For the first time in the current model, the continuity conditions of the transverse shear stress, transverse normal stress and transverse normal stress gradient at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are satisfied. The formulation is based on an enhanced higher order sandwich panel theory and the vertical displacement component of the face sheets is assumed as a quadratic one, while a cubic pattern is used for the in-plane displacement components of the face sheets and the all displacement components of the core. The formulation is based on the von $K{\acute{a}}rm{\acute{a}}n$ nonlinear approximation, the one-dimensional Fourier equation of the heat conduction along the thickness direction, and the first-order piston theory. The equations of motion and boundary conditions are derived using the Hamilton principle and the results are validated by the latest results published in the literature.

• 설비공학논문집
• /
• 제7권4호
• /
• pp.577-588
• /
• 1995

A numerical study is made on the melting process of an unconstrained ice inside an isothermal ice-ball capsule. The unmelted ice core is continuously ascending on account of buoyancy forces. Such a buoyancy-assisted melting is commonly characterized by the existence of a thin liquid film above the ice core. The present study is motivated to present a full-equation-based analysis of the influences of the initial subcooling and the natural convection on the fluid flow associated with the buoyancy-assisted melting. In the light of the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the melted and unmelted regions are resolved in one domain. Numerical results are obtained by varying the wall temperature and initial temperature. The present results reported the transition of the flow pattern in a spherical capsule, as the wall temperature was increased over the density inversion point. In addition, time wise variation of the shapes for the liquid film and the lower ice surface, the time rate of change in the melt volume fraction and the melting distance at symmetric line is analyzed and is presented.

• Journal of Mechanical Science and Technology
• /
• 제18권2호
• /
• pp.313-324
• /
• 2004

A rich phenomenon in the dynamics of azimuthal vortices in a circular cylinder caused by the inertial oscillation is investigated numerically at high Reynolds numbers and moderate Rossby numbers. In the actual spin-up flow where both the Ekman circulation and the bottom friction effects are included, the first appearance of a seed vortex is generated by the Ekman boundary-layer on the bottom wall and the subsequent roll-up near the corner bounded by the side wall. The existence of the small vortex then rapidly propagates toward the inviscid region and induces a complicated pattern in the distribution of azimuthal vorticity, i.e. inertial oscillation. The inertial oscillation however does not deteriorate the classical Ekman-pumping model in the time scale larger than that of the oscillatory motion. Motions of single vortex and a pair of vortices are further investigated under a slip boundary-condition on the solid walls. For the case of single vortex, repeated change of the vorticity sign is observed together with typical propagation of inertial waves. For the case of a pair of vortices with a two-step profile in the initial azimuthal velocity, the vortices' movement toward the outer region is resisted by the crescent-shape vortices surrounding the pair. After touching the border between the core and outer regions, the pair vortices weaken very fast.

• 한국지구과학회지
• /
• 제26권6호
• /
• pp.560-572
• /
• 2005

이 연구에서는 1979년부터 1999년까지 21년 동안에 한반도 겨울철 한파와 관련된 대기 순환 및 열원$(Q_1)$의 분포 특성을 조사하였다. 한파 발생 빈도는 1년간 약 1개로 나타났으며, 1989년을 중심으로 전반기에 전체의 $60\%$가 발생하였다. 한파 발생 동안 하층의 대기 순환 패턴은 평년에 비해 서고동저형의 기압 패턴이 더 뚜렷하며, 상층에서도 한반도에 기압골의 영향이 더 강하게 나타난다. 한파가 발생하는 동안에 한반도 부근의 기온 하강 패턴은 바이칼호 부근의 기온 패턴과 반대로 나타나며, 기온의 연직 구조에서도 400 hPa을 기준으로 하층과 상층의 기온 편차는 반대로 나타난다. 열원에 대한 분석은 한파 발생 시 한랭 이류에 의한 냉각은 하강 운동에 의한 단열 승온에 의해 균형을 이룬다는 것을 보여주는데, 이것은 한랭 핵의 이동이 열흡수원의 이동 경로와 연관되어 있음을 나타낸다. 따라서 한파의 유지 기작을 이해하고 한파를 예측하기 위해서는 열원 그리고 열흡수원의 이동 기작이 밝혀져야 할 것이다.