• Journal of Radiation Protection and Research
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• v.11 no.2
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• pp.130-138
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• 1986

A study on the measurement of alpha activity in ground air has been carried out using CA 80-15 and LR 115-1 cellulose nitrate nuclear track detectors. The detection efficiency of the detectors were determined by making use of an $^{241}Am$ alpha source of $0.1{\mu}Ci$ in activity under a known geometrical arrangement. For the field measurement of alpha activity of emanated radon and its progeny in ground air two different radon cups were installed for a certain period of time in two neighbouring ground holes of about 15 cm in diameter and 45 cm in depth. Of the two radon cups one kept closed space during the detecting period, while the other kept open space with a hole enabling the air to ventilate. The etched tracks were read out by a microscope and the results obtained through statistical analysis were evaluated in terms of alpha activity per unit volume of air.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.37-47
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• 2008

Design and construction of tunnels require understanding the influence of groundwater. Particularly, it is essential to know how the drainage conditions at the tunnel boundary affect flow behavior of ground adjacent to the tunnels. In this study flow behavior of a leaking tunnel was investigated using physical model tests for tunnel depths and various hydraulic boundary conditions. Particular concerns were given to flow lines toward tunnels. Test results showed that the boundary conditions hardly influence on flow patterns and time required to reach steady state conditions. It is revealed that with an increase in water depth, flow lines concentrated to the drain holes. The physical tests were numerically simulated. Numerical results showed that the flow behavior was represented appropriately by considering filter-drain hole drainage rather than boundary drainage all over the lining.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.132-140
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• 2016

In this paper, we propose boundary-preserving stereo matching method based on adaptive disparity adjustment using confidence region detection. To find the initial disparity map, we compute data cost using the color space (CIE Lab) combined with the gradient space and apply double cost aggregation. We perform left/right consistency checking to sort out the mismatched region. This consistency check typically fails for occluded and mismatched pixels. We mark a pixel in the left disparity map as "inconsistent", if the disparity value of its counterpart pixel differs by a value larger than one pixel. In order to distinguish errors caused by the disparity discontinuity, we first detect the confidence map using the Mean-shift segmentation in the initial disparity map. Using this confidence map, we then adjust the disparity map to reduce the errors in initial disparity map. Experimental results demonstrate that the proposed method produces higher quality disparity maps by successfully preserving disparity discontinuities compared to existing methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.109-117
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• 2002

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with $65^{\circ}$ sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of $4.4\times10^5$ based on the wing root chord. The angle of attack and sideslip angle range from $16^{\circ}\sim28^{\circ}$ and $0^{\circ}\sim-15^{\circ}$, respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.

• Journal of The Korean Astronomical Society
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• v.40 no.1
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• pp.1-7
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• 2007

About 10 percent of quasars are known to exhibit deep broad absorption troughs blueward of prominent permitted emission lines, which are usually attributed to the existence of outflows slightly above he accretion disk around the supermassive black hole. Typical widths up to 0.2c of these absorption roughs indicate the velocity scales in which special relativistic effects may not be negligible. Under he assumption of the ubiquity of the broad absorption line region in quasars, the broad emission line flux will exhibit Thomson scattered components from these fast outflows. In this paper, we provide our Monte Carlo calculation of linear polarization of singly Thomson scattered line radiation with the careful considerations of special relativistic effects. The scattering region is approximated by a collection of rings that are moving outward with speeds ${\upsilon}=c{\beta}<0.2c$ near the equatorial plane, and the scattered line photons are collected according to its direction and wavelength in the observer's rest frame. We find that the significantly extended red tail appears in the scattered radiation. We also find that the linear degree of polarization of singly Thomson scattered line radiation is wavelength-dependent and hat there are significant differences in the linear degree of polarization from that computed from classical physics in the far red tail. We propose that the semi-forbidden broad emission line C III]1909 may be significantly contributed from Thomson scattering because this line has small resonance scattering optical depth in the broad absorption line region, which leads to distinct and significant polarized flux in this broad emission line.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.32.5-33
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• 2009

카네기 천문대에서 주도하여 개발 중인 구경 25.4m GMT 망원경 사업에 한국도 공식적으로 참여하였다. 현재 한국천문연구원은 GMT(Giant Magellan Telescope)부경부를 국내에서 개발하고자 이와 관련된 연구를 진행하고 있다. GMT 부경은 직경 1.06m 오목거울 7장이 모여 전체 직경 3.2m인 타원면을 형성하고 초점비는 F/0.7이다. GMT 부경개발 선행 연구과제로 카네기 천문대에서 개발되어 현재 운용중인 구경 6.5m 마젤란 망원경의 부경을 선택하였는데, 이는 마젤란 부경의 형상과 직경, 부경시스템 운영방식이 GMT 와 유사하기 때문이다. 천체관측 망원경에서 거울면의 변형에 가장 큰 영향을 미치는 인자는 거울의 자중이다. 거울의 직경이 커지면 자중이 증가하게 되어 거울면의 처짐이 커지게 된다. 이를 극복하고자 다양한 거울 support들이 개발되었다. 그중에서 counterweight lever 시스템 같은 부양(float) 시스템은 자중의 영향을 보상해 줌으로써 그것에 의한 거울의 변형을 최소화하는 역할을 하는데, GMT 부경 개발에 근간이 되는 마젤란 부경 또한 부양 시스템을 도입하였다. 마젤란 부경의 부양시스템은 counterweight lever 시스템과 유사한 진공 시스템을 도입하였다. 마젤란 부경의 support는 axial 방향으로 거울을 지지하는 axial support와 lateral 방향으로 거울을 지지하는 lateral support가 있는데, 이중에서 axial support가 진공시스템으로 구성된다. Lateral 방향의 지지는 경량화된 거울의 hole 안에 3개의 판스프링을 삽입하여 단지 거울과 판스링의 강성에 의해서만 이루어진다. 이 논문에서는 망원경이 작동을 할때 즉, 천정각(zenith angle)이 변할 때 axial support와 lateral support의 조합(combination)에 의해 지지되는 마젤란 부경의 표면 정밀도 RMS 값을 비교하였다.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.8 no.2
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• pp.36-47
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• 2012

Time-series variation of groundwater temperature in Mongolia shows that maximum temperature is occured from end of October to the first of February(winter time) and minimum temperature is observed from end of April to the first of May(summer time). Therefore ground temperature is s a good source for space heating in winter and cooling in summer. Groundwater temperatures monitored from 3 alluvial wells in Ulaabaatar at depth between 20 and 24 m are $(4.43{\pm}0.8)^{\circ}C$ with average of $4.21^{\circ}C$ but mean annual ground temperature(MAGT) at the depth of 100 m in Ulaanbaatar was about $3.5{\sim}6.0^{\circ}C$. Bore hole length required to extract 1 RT's heat energy from ground in heating time and to reject 1 RT's heat energy to ground in summer time are estimated about 130 m and 98 m respectively. But in case that thermally enhanced backfill and U tube pipe placement along the wall are used, the length can be reduced about 25%. Due to low MAGT of Ulaabaatar such as $6^{\circ}C$, the required length of GHX in summer cooling time is less than the one of winter heating time. Mongolia has enough available property, therefore the most cost effective option for supplying a heating energy in winter will be horizontal GHX which absorbs solar energy during summer time. It can supply 1 RT's ground heat energy by 570 m long horizontally installed GHX.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.2
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• pp.81-89
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• 2019

In this study, wind tunnel test on Quad-Tilt Propeller which has tandem wings is carried out to analyze the aerodynamic interference effect of front wing and propeller on rear wing during forward flight. Using 6-axis balance system, forces and moments of whole aircraft were measured and using strain gauge at wing root, bending moments were measured to observe change of aerodynamic force of each wings. A 12-hole probe was used to measure the flow field in the wing and propeller wake. Flow characteristics were observed qualitatively through flow visualization experiment using tuft and smoke. To measure the aerodynamic interference by elements, the influence of front wing and propeller on rear wing was analyzed by changing the wings and propellers mount combination.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.309-316
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• 2022

This paper presents nonlinear numerical analysis results which were compared with the tested tensile strengths of CFRP(Carbon Fiber Reinforced Plastic) laminates with 14 different stacking sequences. The composite laminate coupons were cured under an autoclave pressure using resin-impregnated unidirectional tapes. The nonlinearity of the matrix was considered for the analysis, which was obtained from lamina tests. The Hashin failure criteria and progressive failure analysis were used for the nonlinear finite element analysis. The comparison results show that the current approach is acceptable to predict the tensile strengths of the CFRP laminate coupons with various stacking sequences and no damage. However, it is not acceptable to predict the tensile strengths of the laminate specimens with a center hole.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.243-254
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• 2009

Tunnel problems relate to pore water pressure generally occur due to the restriction of groundwater flow into the tunnel which is generally caused by the deterioration of drainage systems. Previous studies have identified the problem as combined mechanical and hydraulic interaction occasions. In this study, detrimental effects of pore water pressure on the lining were investigated using the finite element method considering deterioration of the drainage system. Particularly, double-lined linings with drain-holes are considered. Deterioration of drainage system is represented as blockages of drain-holes. It is identified that the secondary lining ran be influenced by the deterioration of drainage system. It is shown that a tunnel with all drain-holes blocked moved upward, and unbalanced drain-hole blocking may result in torsional behavior of the tunnel which causes significant damages to the secondary linings.