• Journal of the Korean Society of Radiology
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• v.9 no.4
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• pp.239-247
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• 2015

It should be accurate dose calculation to increase the efficiency of radiation therapy, and it is priority to figure out the beam characteristics for this purpose. The target and primary collimator in head components of the linear accelerator have the greatest influence on determining the beam characteristics which is caused by backscatter and it is the factor to consider the shielding structures and equipment management. In this study, we made modeling of the linear accelerator through the Geant4 Monte Carlo simulation and investigated backscatter according to the change of the size and shape in head components. For the scattered electrons, it showed the greatest number of distributions inside of the inner radius at primary collimator. But, for the scattered photons which have the high energy, it was mostly located outside of the inner radius at primary collimator. Scattered positrons showed a small occurrence in about 0.03%. According to the change of the inner radius at primary collimator, it was great changes in the inside of inner radius for all three scattered particles. According to the change of the outer radius at primary collimator, it was shown some considerable effects from more than 60 mm outer radius. It was no significant effect according to the change of target thickness. In this study, we found that backscatter should be considered, and figured out that geometric size and shape of the peripheral components are the factors that influences the backscatter effect.

• Journal of Korean Elementary Science Education
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• v.24 no.4
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• pp.417-425
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• 2005

Although there are some challenges to a view of science teaming as conceptual change, the view still occupies an important position in science teaming and teaching. Conceptual change theory implies that students' conceptions need to be exchanged for the new science conceptions. This was at the heart of conceptual change theory of Posner et al. (1982). According to this theory, cognitive conflict is known as an important factor in conceptual change even though there is still a controversial on effects on science teaming. This study is intended to interpret the cognitive conflict from cybernetics' perspective and explain difficulties of conceptual change which students have in teaming science and the conditions of conceptual change.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.45-50
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of a 0.2 % aqueous solution of sodium carbomethyl cellulose (CMC) at a inner cylinder rotational speed of $0{\sim}600$ rpm. The transitional flow has been examined by the measurement of pressure losses, to reveal the relation of the Reynolds numbers with the skin-friction coefficients, in the laminar and transitional flow regimes. The occurrence of transition has been checked by the gradient change of pressure losses and skin-friction coefficient with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• Journal of Mechanical Science and Technology
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• v.17 no.4
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• pp.562-570
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• 2003

This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0～600 rpm. Also, the visualization of vortex flows has been performed to observe the unstable waves. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. 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. Consequently, the critical (bulk flow) Reynolds number Re$\_$c/ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.8-15
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• 2005

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 coefficient is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. This study shows the change of skin friction coefficient and wall shear stress corresponding to the variation of rotating speed of the inner cylinder, radius ratio, eccentricity, and working fluids.

• Transactions of Materials Processing
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• v.15 no.4 s.85
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• pp.326-332
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• 2006

Sandwich structures, which are composed of a thick core between two faces, are commonly used in many engineering applications because they combine high stiffness and strength with low weight. Depending on the sheets by a rolling process, which is a more efficient and economical approach compared to other types of processes, has become an increasingly important subject of study. In this paper, we made a roll forming machine which progressive forming possible and force measurement for a roll forming of the sheet metal forming. And we designed a roll molding that arrayed of embossing size 3mm in diameter fabricate micro dimple inner structure plate. We carried out forming experiment such as array change and thickness to sts304 sheet. Ultimately, this research developed inner structure plate of high stiffness.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.1-8
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• 1998

The purpose of this study is to determine the distribution of the suspended matter caused by dredging at the northeastern part of Kwangyang Bay and to determine the effect of the single silt protector for it. According to the direction of the tidal current, six sampling stations were chosen from the dredging site to the southeast. At the high tide, the high concentration of the suspended matter was observed below the mid-depth near the dredging site. As the tidal currents were stronger. its concentrations below the mid-depth at the inner stations of the single silt protector were rapidly increased, but those of the outer stations did not show any significant change. The concentrations at the inner stations of the silt protector at that time were from 20~140mg/l and those of the outer stations, which was only about 30 m apart from the inner station, were from 20~30mg/l. It suggests that the large amount of suspended matter caused by dredging were moved to the inner stations near the silt protector at the ebb tide and that the silt protector is very effective for the suspended matter.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.264-267
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• 2008

Dual-cooled fuel with inner and outer flow channel was proposed for high burup, next generation nuclear fuel design. The annular cylinder of dual cooled fuel has higher structural strength compared to the conventional one, but also have concerns about flow induced vibration due to an additional flow of inner channel and the difference of flow velocity in between inner and outer channel. In this study, the dynamic stability of flexible, annular cylinder was evaluated according to the flow variation and compared to the that of the conventional PWR fuel rod. Centrifugal and Coriolis force by the additional flow in the inner channel were added in the dynamic equation of flexible beam in uniform, external, and axial flow. Complex eigenfrequency was calculated by the finite element method. Stability margin of annular cylinder compared to the solid cylinder and change of the dynamic characteristic are presented and discussed as a analysis results.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.3
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• pp.213-221
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• 2005

In order to get more accurate GPS position with the changes of the inner configuration setting of GPS receiver, the authors carried out measurements of the position at known it with one antenna and two GPS receivers manufactured by same company. We have investigated the accuracies of positions according to the change of the maskangle and receiving mode of output data in inner configuration of GPS receivers, and analyzed the relationships between numbers of satellites visibility and maskangles, and values of HDOP and maskangles. When the maskangles in inner configuration were set below 20 degree, the accuracies of positions were high. But if they were became bigger than 25 degree, standard deviations ot position errors and HDOPS of positions were became bigger. Numbers of satellites visibility(y) and maskangles(x) have relations with a formula, y = -0.1662x+9.9225, and values of HDOP(y) and maskangles(x) have relations with a formula, y = 0.6035 $e^{0.0517x}$. The results of position accuracies observed by two GPS receivers to the known position at same time were that average errors of position fixs by GPS receiver configured with NMEA0183 mode were 6.7m and standard deviations were 1.5m, and them by GPS receiver configured with binary mode were 5.0m and standard deviations were 1.1m respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.6
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• pp.15-24
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• 2005

The normalization on the characteristics of water level change at the upstream gauging station was attempted according to the operation of drainage sluice gate of the Geumgang estuary dam. The characteristics were normalized by the analysis of water level change and by the linear-regression of the water level data measured at the inner station of Geumgang estuary dam and upstream gauging station. The results of normalization may be referred to the management of Geumgang estuary lake, the operation of pumping and drainage stations in the shore of the lake. The mean response time of water level change on Ibpo, Ganggyeong and Gyuam water level station were 39,81 and 160 minutes, when sluice gate was opened respectively. The mean velocity of surface wave, the mean displacement of water level change, the mean time of water level change and the mean rate of water level change varied largely depending on the location of gauging station and the characteristics of stream section of the water level gauging station.