• 한국통신학회논문지
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• 제28권5A호
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• pp.333-340
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• 2003

본 논문에서는 주파수 선택적 페이딩 환경에서도 터보부호화된 모든 정보심벌들이 수신단에서 동일한 신뢰도를 갖도록 전송함으로써, 터보부호화된 OFDM (orthogonal frequency division multiplexing) 시스템의 성능을 크게 향상시키는 새로운 전송 방식을 제안한다. 모든 정보심벌들이 동일한 신뢰도를 갖는다는 것은 페이딩의 영향을 동일하게 받는다는 것을 의미한다. 이를 위하여 각 정보심벌에 서로 다른 직교코드를 할당하여 다중화하고, 이를 전송 가능한 모든 부채널들로 확산시켜 전송한다 (이후, 이 과정은 직교코드 다중화 (orthogonal code multiplexing: OCM) 라고 한다.). 다중화를 위한 직교코드로는 코드의 길이에 상관없이 코드들 상호간의 직교성을 유지하며 코드간 동일한 에너지를 갖는 DFT (discrete Fourier transform) 기본 시퀀스 (basis sequence)를 사용한다. 모의실험을 통하여 제안된 시스템의 성능분석이 이루어지며, 반복 복호를 위해서는 Log-MAP(Log-maximum a posteriori) 알고리즘을 사용한다.

• 대한전자공학회논문지TC
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• 제45권1호
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• pp.85-90
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• 2008

본 논문에서는 모노펄스 안테나 시스템에 적용되는 2중 반사경에 관하여 연구하였다. 연구 결과 주반사판의 효율이 70% 이상인 경우 반사경의 크기가 설계에 사용되는 최저 주파수(11.7GHz)의 30파장(약77cm)이면 최저주파수의 이득은 37.9dBi, 최대 주파수(12.7GHz)에서는 38.6dBi의 이득을 얻을 수 있다. 또한 부반사판의 성능 개선을 위한 방안으로 반지름 D이고 초점거리 $F_e$인 경우 초점거리 대 지름의 비가 더 클수록 원거리 장에서의 교차편파가 개선되며 반사판의 테두리에서의 구면 확산손실이 감소한다. 또한, 급전 안테나의 측면 변위($x_sy_s$평면에서)에 따른 방사패턴의 약화 정도가 더 작아지기 때문에 주빔의 주사 성능이 개선됨을 확인하였다.

• 한국정보과학회논문지:시스템및이론
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• 제27권6호
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• pp.567-582
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• 2000

본 논문은 로그파일시스템의 원리를 바탕으로 플래시메모리 저장시스템에 적합한 플래시메모리 공간 관리 방법을 제안한다. 플래시메모리는 비휘발성, 빠른 입출력 속도 등의 장점을 지니고 있지만, 제자리 덮어쓰기(in-place update)가 불가능하고 메모리 셀에 대한 쓰기(write) 횟수가 제한되는 단점이 있다. 이러한 특성은 플래시메모리를 저장 매체로 사용할 때 기존의 저장 매체 관리 방법과는 다른 방법을 요구하게 된다. 본 논문은 자유 공간유지를 위해 필요한 클리닝 메커니즘의 연산 비용을 낮추면서 동시에 저장공간이 전체적으로 균등하게 사용될 수 있도록 하는 사이클 평준화 기법을 제안한다. 제안된 방법은 특히 메모리 활용도와 로컬리티가 높을 때 좋은 성능을 보인다. 클리닝 메커니즘은 자주 접근되지 않는 COLD데이타를 그렇지 않은 데이타와 격리시킴으로써 그 효율이 향상되었으며, 사이클 평준화는 사용 횟수간의 최대 차이가 하드웨어적인 오차를 벗어나지 않는 수준까지 이루었다. 실험을 통해 제안된 방법은 비교 기준으로 삼은 직관적 방법(greedy policy)에 비해 사이클 평준화가 잘 이루어진 상태에서 최대 35%정도의 클리닝 비용 절감 효과를 보였다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.799-802
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• 2008

General behaviors based on hydraulic characteristics of natural streams and channels have been recently analyzed and developed via various numerical models. However in the states of natural hydraulics, an experimental research must be performed simultaneously with the mathematical analysis due to effects of hydraulic properties such as meander, sediment, and so on. In this study based on 2-D advection-dispersion equation, flow and tracer experiments were performed in the S-curved meandering laboratory channel with a rectangular cross-section. The channel was equipped with instrument carriages which was equipped with an auto-traversing system to be used with velocity measuring sensors throughout the depth and breadth of the flow field. To measure concentration distribution of the salt solution was adjusted to that of the flume water by adding methanol and a red dye (KMnO4) was added to aid the visualization of the tracer cloud, the tracer was instantaneously injected into the flow as a full-depth vertical line source by the instantaneous injector and the initial concentration of the tracer was 100,000 mg/l. The secondary current as well as the primary flow pattern was analyzed to investigate the flow distribution in the meandering channels. The velocity distribution of the primary flow for all cases skewed toward the inner bank at the first bend, and was almost symmetric at the crossovers, and then shifted toward the inner bank again at the next alternating bend. Thus, one can clearly notice that the maximum velocity occurs taking the shortest course along the channel, irrespective of the flow conditions. The result of the tracer tests shows that pollutant clouds are spreading following the maximum velocity lines in each cases with various mixing patterns like superposition, separation, and stagnation of pollutant clouds. Flow characteristics in each cases performed in this study can be compared with tracer dispersion characteristics with using evaluation of longitudinal and transverse dispersion coefficients(LDC, TDC). As expected, LDC and TDC in meandering parts have been evaluated with increasing distribution and straight parts have effected to evaluate minimum of LDC and TDC due to symmetric flow patterns and attenuations of secondary flow.

• 대한조선학회논문집
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• 제60권4호
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• pp.266-277
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• 2023

In this study, fundamental research is conducted for the generation technique and analysis of multi-directional irregular waves in the Deep Ocean Engineering Basin (DOEB). A three-dimensional boundary element method-based numerical tank is implemented to perform wave generation simulations, and directional spectrum estimation is carried out using the results of simulations. The wave generation technique of the Snake type wave maker, generating multi-directional irregular waves, is implemented using the Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) algorithms. The wave generation technique is validated by comparing the wave spectrum from simulations and experiments. A Maximum Likelihood Method (MLM) based estimation code is developed for estimating the directional wave spectra. The multi-directional irregular waves are tested in the DOEB and the numerical tank, and directional wave spectra obtained from two methodologies are estimated and compared. A correction procedure for the directional distribution of multi-directional waves is established, and the possibility of correcting the directional spreading function using the numerical tank is validated.

• 농업과학연구
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• 제38권1호
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• pp.153-162
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• 2011

This study analyzed the spatio-temporal change detection of land-use and urbanization in Yongin and Anseong regions, Kyunggi Province, using three Landsat-5 TM images for 1990, 1996, and 2000. Remote sensing (RS) and geographic information system (GIS) techniques were used for image classification and result analysis. Six land-use types were classified using supervised maximum likelihood classification. In the two study areas, the land-use changed significantly, especially the decrease of arable land and forest and increase of built-up area. Spatially, the urban expansion of Yongin region showed a spreading trend mainly along the national road and expressways. But in Anseong region the expansion showed 'urban sprawl phenomenon' with irregular shape like starfish. Temporally, the urban expansion showed disparity - the growth rates of urbanized area rose from the period 1990-1996 to 1996-2000 in both study areas. The increased built-up areas were converted mainly from paddy, dry vegetation, and forest.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권3호
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• pp.11-22
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• 2013

SEAWAT, a linked modeling program of Visual MODFLOW was used to analyze the change in groundwater levels and salinity related groundwater dam construction in Cheongsan island, Wando-Gun, Jeollanam-Do. The steady-state model results show the groundwater flow and salinity distribution of the studied area. The groundwater flows from north-west and south-east highlands into the river, located in the middle part of the basin, and is eventually discharged to the ocean. Part of the sea water infiltrates into the river; and through the estuary's alluvium aquifer, the sea water intrusion takes place spreading to about 830 m from the ocean. The transient model results show that after the groundwater dam construction, groundwater levels will rise to a maximum of 2.0 m upstream, and the groundwater storage will increase 21,000 after 10 years. Meanwhile 31% of the total area affected by sea water intrusion will decrease. To conclude, the groundwater dam is a very useful method for a secure water resource in preparation for drought and water shortages in the island regions.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권1호
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• pp.24-29
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• 2000

We propose a simple method to control the crystallization depth of amorphous silicon (a-Si) deposited by PECVD or LPCVD during the excimer laser annealing (ELA). Employing the new method, we have formed poly-Si/a-Si double film and fabricated a new poly-Si TFT with vertical a-Si offsets between the poly-Si channel and the source/drain of TFT without any additional photo-lithography process. The maximum leakage current of the new poly-Si TFT decreased about 80% due to the highly resistive vertical a-Si offsets which reduce the peak electric field in drain depletion region and suppress electron-hole pair generation. In ON state, current flows spreading down through broad a-Si cross-section in the vertical a-Si offsets and the current density in the drain depletion region where large electric field is applied is reduced. The stability of poly-Si TFT has been improved noticeably by suppressing trap state generation in drain region which is caused by high current density and large electric field. For example, ON current of the new TFT decreased only 7% at a stress condition where ON current of conventional TFT decreased 89%.

• 한국기계가공학회지
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• 제14권1호
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• pp.29-35
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• 2015

In this study, a FEM analysis is undertaken of a rubber sleeve which is mounted onto a spreading mandrel so as to avoid marking the first wrappings of coils (known as the 'end-mark'), as occasionally occurs when a concentrated load is placed on the edge of a steel sheet, significantly reducing its quality. A commercial numerical package, ANSYS, was utilized to analyze the structural behavior of the rubber sleeve. In general, the strain of the sleeve increases as the thickness of the rubber layer (H) covering the tubes increases, thus also increasing the surface of the sleeve for a constant boundary condition, and decreasing the pitch (P) between each tube, resulting in an increase in the strain on the surface of the sleeve for all rubber thickness conditions tested here. In a comparison of two different materials, rubber and urethane, when H=3 mm and P=1.1D, the maximum total deformations in these cases are 0.12669 mm and 0.086623 mm, respectively.

• 대한전자공학회논문지TE
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• 제37권5호
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• pp.85-92
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• 2000

본 논문에서는 옥내 채널환경에서 고속으로 데이터를 전송할 수 있는 무선 LAN의 전송방식으로 직렬과 병렬구조를 가진 다중부호 CDMA 방식을 모델링하여 모의실험을 수행함으로써 무선 LAN 모뎀시스템의 구현에 필요한 여러 파라미터의 최적값을 도출하고자 하였다. 전송대역폭과 최대 데이터 전송율이 주어졌을 때, 시스템 성능은 확산이득과 병렬채널의 수를 늘리거나 각 채널의 데이터율을 낮추면 개선된다는 것을 확인하였다. 특히 병렬구조는 직렬구조보다 시스템 성능이 크게 개선될 뿐만 아니라 같은 조건에서는 유효 칩속도가 줄어들게 되어 하드웨어 구현을 쉽게 하였다.