• Proceedings of the Korea Water Resources Association Conference
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• 1988.07a
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• pp.148-157
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• 1988

A generalized hydrograph equation was derived by using the well known concepts of superimposition and nonlinear multiple recessions. Application of the equation showed that characteristics of delay and attenuation of the runoff process were effectively accounted for.

• The Korean Journal of Nuclear Medicine
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• v.32 no.4
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• pp.382-390
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• 1998

Purpose: The purpose of this study was to evaluate the accuracy of radioactivity quantitation in Tc-99m SPECT by using combined scatter and attenuation correction. Materials and Methods: A cylindrical phantom which simulates tumors (T) and normal tissue (B) was filled with varying activity ratios of Tc-99m. We acquired emission scans of the phantom using a three-headed SPECT system (Trionix, Inc.) with two energy windows (photopeak window: $126{\sim}154keV$ and scatter window: $101{\sim}123keV$). We performed the scatter correction with dual-energy window subtraction method (k=0.4) and Chang attenuation correction. Three sets of SPECT images were reconstructed using combined scatter and attenuation correction (SC+AC), attenuation correction (AC) and without any correction (NONE). We compared T/B ratio, image contrast [(T-B)/(T+B)] and absolute radioactivity with true values. Results: SC+AC images had the highest mean values of T/B ratios. Image contrast was 0.92 in SC+AC, which was close to the true value of 1, and higher than AC (0.77) or NONE (0.80). Errors of true activity by SPECT images ranged from 1 to 11% for SC+AC, $22{\sim}47%$ for AC, and $2{\sim}16%$ for NONE in a phantom which was located 2.4cm from the phantom surface. In a phantom located 10.0cm from the surface, SC+AC underestimated by 24%, NONE 40%. However, AC overestimated by 10%. Conclusion: We conclude that accurate SPECT activity quantitation of Tc-99m distribution can be achieved by dual window scatter correction combind with attenuation correction.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.4
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• pp.28-36
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• 1995

The use of image planes can reduce effectively the radiated emissions from a printed circuit board. This work deals with the influence of image planes on radiation from current trace. The configu- rations of one and two layers of image planes on both sides of current trace are proposed. The radiated emissions of those configurations have been calculated by solving a set of electric field integral equations by the method of moments. The induced current distributions on image planes and the radiation patterns are analyzed for different configurations of image planes, the distance between current trace and image planes, and the frequency of signal current.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2315-2325
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• 1996

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.407-410
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• 2005

Acoustic coupling between combustion chamber and gas-liquid scheme injectors are studied numerically in liquid rocket engine adopting linear acoustic analysis. The injectors can play a role as half-wave resonators. The combustion chamber with numerous injectors shows peculiar acoustic coupling with the injectors. As the injector length approaches a half wavelength or the original tuning length, new injector-coupled acoustic modes show up in the chamber and thereby, the acoustic-damping effect of the tuned injectors is appreciably degraded.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.97-104
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• 2015

Compared with a strong axial rigidity due to large intial tension, cable has a weak laterally flexural rigidity. A variety of dynamic loads such as traffic loads and wind loads etc. cause the cables to vibrate significantly and affect the mechanical properties and the performance of cables. Therefore, vibration reduction design is an urgent task to control the vibration of cable-supported bridges. Because a various kind of dampers have shown to reduce the amplitude and duration time of vibration of cable from measured date in field test, damper can be considered that it is effective device significantly to reduce the amplitude and duration time in vibration of cable. Vibration characteristics of cable can change according to manufacturing method and type of established form, and damper has been designed according to distribution of natural frequencies and vibration modes. In this study, numerical analysis is used to show the reduction effects of vibrations and present the design of damper for vibration reduction of cable.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.678-678
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• 2009

환경 소음,진동 개선의 측면에서 철도 레일 하부로 전달되는 진동 및 구조소음을 효과적으로 차단하기 위하여 국내에서도 탄성지지 구조의 플로팅 슬라브를 적용하는 경우가 증가하고 있다. 플로팅 슬라브 구조설계에 있어 주안점은 슬라브 자체 중량에 비하여 열차 중량과 열차 주행간에 발생하는 동하중이 2$\sim$3배 이상 높아 열차 주행 안정성을 고려해야 하는 점이며 열차의 고속화 경향에 따라 동하중의 증가는 더욱 커지고 있다. 특히, 열차의 구조 동특성과 동하중의 주파수 특성을 고려할 경우 슬라브 구조의 동적 설계변수(고유진동수, 감쇠비 등) 결정이 매우 제한되고 있음을 고려하면 탄성지지부의 감쇠 및 강성의 가변 특성의 부여는 매우 중요하다 할 수 있다. 본 연구에서는 MR 댐퍼와 MR 방진고무 등의 반능동 소재를 사용하여 열차 주행간에 발생하는 탄성지지 슬라브의 진동을 제어하는 시뮬레이션을 수행함으로써 적용 가능성을 확인하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.403-409
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• 2000

In this paper, we measured and analyzed cross polarization discrimination(XPD), signal correlation coefficient($\rho$) and received signal level decrease, for the application of polarization diversity scheme in the up-link of microcell environments. We experimented in a dense building area, a dense residence area, a market area, a school area and etc at 1.9 GHz. Cross polarization discrimination (XPD) is about 6~11 dB, signal correlation coefficient($\rho$) is below 0.7 and received signal level decrease is smaller than 3 dB. The results of comparing polarization diversity with space diversity show that polarization diversity gain is about 2~5 dB higher in the various area. As a results, polarization diversity scheme is more effective than space diversity scheme in microcell environments.

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2006.06a
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• pp.107-115
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• 2006

본 논문은 유비쿼터스 환경하에서 수신된 RF 신호의 수신 강도를 이용하여 위치를 추정하고 이를 기반으로 각종 서비스를 제공하는 시스템이다. 이는 크게 무선 송신 단말기, 정보처리 기지국 위치인식 서버 및 시스템 호스트의 네 부분으로 구성되었으며, 30층 규모의 건물에 5000여 개의 단말기가 운영 중에 있다. 실내에서의 이동 객체 위치를 추정하기 위하여 자체 개발, 제작된 송/수신기의 RF 감쇠 특성을 살펴보고, 이를 이용하여 책상, 파티션 등 사무 기기로 이루어진 사무실에서의 위치추정 방법을 소개한다. 실내 환경의 변화와 주변 시설물 등의 영향으로 RF 신호는 감쇠, 흡수, 반사, 회절 등 많은 영향을 받으며, 특히 복층의 경우 층간 효과도 존재한다. 이러 한 실내 상황에서 위치추정 결과를 제시하며, BAS등 회부 시스템과의 연계를 통한 지능적인 서비스를 제공한다. 제고하는 서비스에는 사용자 위치에 근거한 자동 조명/공조 연동 및 주차장 Gate 연동 서비스 등 기본적인 공공 서비스부터 개인별 시강/wellness 이용 현황 등을 자동 체크하여 이에 근거한 요금 부과 및 Schedule 관리 등을 할 수 있게 하는 개인 서비스가 있다. 또한 본 시스템을 실제로 설치, 운영하고 있는 적용 사이트에 관한 사례를 통해 앞으로의 개선 방향 및 서비스 효율성 등에 관해 논의한다.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.480-493
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• 2011

Dynamic rock property is one of most important parameters in design of earthquake-resistant structures. In this study, free-free resonant column test has been conducted to obtain dynamic Young's modulus, dynamic shear modulus, and damping ratio among dynamic properties with granite specimen of Chungnam Yeongi area. The dynamic properties obtained from this test were compared with the physical properties from static rock tests, and their relationship has been analyzed. From our study, it has been concluded that the dynamic Young's modulus and the dynamic shear modulus are linearly proportional to the elastic wave velocity. And also the damping ratio has been identified to be in non-linear inverse proportion to the elastic wave velocity.