• 대한기계학회논문집B
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• 제24권9호
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• pp.1210-1218
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• 2000

Thermal convection in a horizontal annulus is considered, and the bifurcation phenomena of flows from time-periodic to chaotic convection are numerically investigated. The unsteady two-dimensional streamfunction-vorticity equation is solved with finite difference method. As Rayleigh number is increased, the steady flow bifurcates to a time-periodic flow with a fundamental frequency, and afterwards a period-tripling bifurcation occurs with further increase of the Rayleigh number. Chaotic convection is established after a period-doubling bifurcation. A periodic convection with period 4 appears after the first chaotic convection. At still higher Rayleigh numbers, chaotic flows reappear.

• 대한기계학회논문집B
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• 제24권2호
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• pp.169-176
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• 2000

Natural convection in a wide-gap horizontal annulus is considered, and the transition of flows and the bifurcation phenomenon are investigated for the fluids with Pr=0.2 and 0.3. At Pr=0.2, a bicellular flow pattern is observed at high Rayleigh number, and the solution is unique. At Pr=0.3, both the steady unicellular and bicellular flows exist above a certain critical Rayleigh number. For the fluids of Pr=0.2, the bicellular flow can be obtained by the impulsive heating of the inner cylinder, but it is not obtained from the zero initial condition for Pr=0.3. Hysteresis phenomena have not been observed. A transition from a bicellular flow to a unicellular flow occurs for Pr=0.3.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권1호
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• pp.1-9
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• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2003년도 추계 학술발표회 논문집
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• pp.153-158
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• 2003

This study concerns the characteristics of helical flow in a concentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2％ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of 0∼500rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• 대한정형도수물리치료학회지
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• 제1권1호
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• pp.99-104
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• 1995

Markolf and Morris suggests that the deranged disk and torn annulus have an exellent recovery ability from the position of spine extension, where the posterior annulus is not under stress and the gel can move anterioly. McKenzie explains side gliding as a combination of rotation and side bending, his clinical studies indicate that side-gliding can gel laterally. In conclusion, the prone unilateral traction on the opposite side from the patient's pain along with the other treatment appered to have helped reduce those patient's pain. The method of treatment described in this report is suggested for Korean physical therapists who treat patients suspected of posterolateral herniated nucleus pulposus.

• Nuclear Engineering and Technology
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• 제28권4호
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• pp.423-430
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• 1996

The improved and advanced Annulus Gas System(AGS) has been developed for Wolsong 2 to satisfy the requirements of the regulatory body. The Atomic Energy Control Board(AECB) required a shorter detection time following a small leak from a pressure tube and/or calandria tube. This paper describes licensing requirements, functional requirements and detail design description for the AGS. The Wolsong unit No. 1 AGS was designed to operate as a stagnant system normally requiring only pressure regulation and having provisions for purging. no improved AGS involves the adoption of gas recirculation in AGS, duplication of dew point indicators with additional instrumentation and sampling provisions to prompt operator action. The improved system operates in the recirculation mode with continuous dew point measurement for leak detection. An AGS with improved detection instrumentation is provided.

• 대한수학회지
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• 제48권6호
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• pp.1285-1325
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• 2011

We solve the isoperimetric problem, the least-perimeter way to enclose a given area, on various Euclidean, spherical, and hyperbolic surfaces, sometimes with cusps or free boundary. On hyperbolic genus-two surfaces, Adams and Morgan characterized the four possible types of isoperimetric regions. We prove that all four types actually occur and that on every hyperbolic genus-two surface, one of the isoperimetric regions must be an annulus. In a planar annulus bounded by two circles, we show that the leastperimeter way to enclose a given area is an arc against the outer boundary or a pair of spokes. We generalize this result to spherical and hyperbolic surfaces bounded by circles, horocycles, and other constant-curvature curves. In one case the solution alternates back and forth between two types, a phenomenon we have yet to see in the literature. We also examine non-orientable surfaces such as spherical M$\ddot{o}$obius bands and hyperbolic twisted chimney spaces.

• Journal of Chest Surgery
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• 제20권4호
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• pp.655-658
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• 1987

Aortic annulus size was measured by two-dimensional echocardiography [2DE] in 29 patients undergoing aortic valve replacement or double valve replacement in order to predict prosthetic aortic valve size. Fifteen patients had aortic stenoinsufficiency, eleven had aortic insufficiency, and three had aortic stenosis. 2DE measurements of aortic annulus diameter, as determined from the parasternal long-axis view, demonstrated a high correlation with actual prosthetic valve size implanted at surgery [r=0.85, p<0.05]. 2DE exactly predicted actual prosthetic valve size in 8 of 29 patients [27.6%], was within 1mm of prosthetic valve size in 11 of 29 patients [37.9%], was within 2mm of prosthetic valve size in 8 of 29 patients, and was within 3mm of prosthetic valve size in 2 patients.

• 대한물리치료과학회지
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• 제2권2호
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• pp.481-486
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• 1995

Markolf and Morris suggests that the deranged disk and torn annulus have an exellent recovery ability from the position of spine extension, where the posterior annulus is not under stress and the gel can move anterioly. McKenzie explains side gliding as a combination of rotation and side bending, his clinical studies indicate that side-gliding can gel laterally. In conclusion, the prone unilateral traction on the opposite side from the patient's pain along with the other treatment appered to have helped reduce those patient's pain. The method of treatment described in this report is suggested for Korean physical therapists who treat patients suspected of posterolateral herniated nucleus pulposus.

• Journal of Chest Surgery
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• 제23권6호
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• pp.1128-1138
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• 1990

The mitral valve is not a simple but a complex structure, mitral valve complex. This complex is composed of mitral orifice, annulus, valve leaflet, chordae tendineae and papillary muscles. There were many controversies about this structures. We studied mitral valve complex in 63 cases of normal Korean adults, such as the circumference of mitral annulus, the intercommissural diameter, height and breadth of the cusps, including commissure, the ratio of rough to clear zone, breadth of the achordal zone, the number of scallops of posterior cusp, the number, length and the pattern of arrangement of the several types of chordae, the number and morphological characteristics of papillary muscles.