• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1608-1615
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• 1999

In this study, we investigate the inter cell interference of LMDS(Local multipoint Distribution Service) system cell in LMDS system design process. There are several interference sources in LMDS system but we consider co-channel adjacent interference, cross-polarization interference, tx/rx interworking interference as three major factors. As the summation of each interference, C/N is keep 19 dB in 2km range but decreased gradually over 2km. Based on theoretical results, we process the experimental test and get results that C/I=20 dB have to be maintained to transmit the data successfully under rain fall attenuation condition. This experiential results are similar to the theoretical analysis results we examined.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.8-23
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• 2004

정보화 시대로 접어들면서 빌딩은 전자화 가전기기나 전기설비들이 많이 설치되고 있다. 통신 시스템의 발달 및 보안, 방재 시스템의 발달로 빌딩들은 통신이나 신호 케이블들이 설치되어 있다. 이들 건축물과 외부의 통신회사들과도 동축케이블 등으로 연결되어 있다. 낙뢰나 과도서지가 전원 및 통신케이블을 타고 빌딩 내부로 유입되어 전자기기나 통신기기들을 파괴시키거나 오동작하는 사례가 많다. 독일의 경우 도심 빌딩에 낙뢰가 떨어진 경우 반경 3〔km〕 떨어진 건물에서 피해가 발생된 것으로 보고되고 있다. (중략)

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.547-552
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• 1996

확률론적 방법을 이용한 MCNP4A 전산코드를 이용하여 두꺼운 차폐체내에서 효과적인 분산감소기법에 대하여 가장 단순화된 모델을 이용하여 고찰하여 보았다. 등방점선원과 이를 둘러싼 반경 50cm의 납차폐체를 계산을 위한 모빌로 사용하여 차폐체 내부 각 영역과 외부에서의 평균선속을 계산하였다. 분산감소기법으로는 구역분할법과 Exponential transform을 적용하여 각 구역에서의 분산의 변화를 비교하였다. 계산결과 두꺼운 차폐체문제에서는 exponential transform이 가장 효과적인 분산감소기법으로 나타났고 이때 구역분할법을 통하여서는 상대오차의 크기를 더욱 줄일 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.10 no.5
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• pp.46-50
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• 1991

고체내부에 존재하는 결함의 에이지에서 회절되는 반사신호의 스페그럼을 해석하여 결함의 크기 를 결정하는 방법을 연구하였다. 실험을 위하여 순도 99.99%의 알루미늄 재료를 샘플로서선택하고 표면 에서 20mm 깊이에 반경 3500μm, 높이 1000μm 의 동전형 결함을 제작하였다. 결함의 탐상은 피치-캐 치법으로 하였으며, 스펙트럼분석에 의한 결함의 기존의 펄스 반사법에 의한 측정값과 비교하였다.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.5-12
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• 1994

고속절삭을 통해서 가공능률과 가공정밀도의 향상을 도모할 수 있기 때문에, 최근에는 공작기계용 고속주축계가 많은 주목을 받고 있다. 본 연구에서는 주축 선단부에 무거운 척과 공작물이 위치하는 선반용 고속주축계의 동특성을 해석하기 위해서 유한요소법을 도입하였다. 특히 세장비가 비교적 작은 주축은 Timoshenko 이론으로, 폭이 유한한 베어링은 반경방향 외에도 모멘트방향의 강성 및 감쇠특성을 가지고 있는 것으로 모델화하였다. 그리고 선반용 고속주축계의 고유진동수와 감쇠비에 대한 주축회전수, 베어링의 지지특성, 베어링의 간격, 주축재료의 내부감쇠율 등의 영향을 고찰하였다.

• Journal of Biomedical Engineering Research
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• v.23 no.5
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• pp.375-383
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• 2002

Aneurysm embolisation method using coils have been widely used. Micro coils are introduced via a small catheter, and are packed inside of aneurysm sac, which induces intraaneurysmal flow stagnation and thrombus formation. When partial blocking of an aneurysm is inevitable, the location of coils is important since it changes the flow patterns inside the aneurysm, which affect the embolisation process. We measured the flow field inside the partially blocked lateral aneurysm models in vitro, and tried to suggest the effective locations of coils for aneurysm embolisation. Velocity fields are measured using a particle image velocitimeter for different coil locations- proximal neck, distal neck, proximal dome and distal dome. Flow into the aneurysm sac was significantly reduced in the distally blocked models, and coils at distal neck blocked inflow more effectively comparing to those at distal dome. This study suggests that distal neck should be the most effective location for aneurysm embolisation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.32-36
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• 2008

In this paper, we investigate the capacity of CDMA/TDD in the inner zone of multimode scenario with dual-band operation where high frequency band is used for TDD in the inner zone and lower frequency band is utilized for FDD in the outer zone. The effects of various system parameters such as cell radius, date rate, and time slot allocation are analyzed.

• Nuclear Engineering and Technology
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• v.21 no.3
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• pp.216-222
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• 1989

The MC-50 cyclotron at Korea Canter Center Hospital is now operational for neutron therapy and medical radioisotope production. Design features, mechanical structures and operating characteristics of the MC-50 are described in this paper. Optimum operating condition for this cyclotron has been determined by the repetitive running, and the performances of the internal beam have been investigated through the measurements of intensity and spatial distribution of the internal beam as a function of the radius of the cyclotron. Routinely, the 40 $\mu$A of 50 MeV protons have been obtained at first Faraday cup with a extraction efficiency of 61%.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1043-1050
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• 2014

An air-core vortex is generated during draining after stirring a rotating cylindrical tank or after filling it with water. The formation of the air-core vortex and the time of its formation are dependent on drain conditions such as the dimensions of the tank, the initial rotation or stirring speed, and the shape of the drain port. In this study, a draining process using a two-stage drain port was numerically investigated. The length and radius of the first drain stage located in the lower part of the drain port were kept constant, whereas the radius of the second drain stage was varied for simulating the draining process. The simulation was conducted by considering an axisymmetric swirling flow for all cases. The declining water level was monitored by an interface capturing method. Further, the effects of the radius of the second drain stage on the time of formation of the air-core vortex and the internal flow structure were investigated.