• 대한기계학회논문집B
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• 제23권8호
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• pp.978-986
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• 1999

In this study, the general thermal and flow characteristics of flat tube with micro-channels has been studied and the correlation of Nusselt number and friction factor is proposed. The optimal flat tube geometry is determined by optimal design process. It is assumed to be a three dimensional laminar flow in the analysis of thermal and flow characteristics. The periodic boundary condition is applied since the geometry of flat tube with micro-channels shows uniform cross-section in primary flow direction. Local Nusselt number is examined for thermal characteristics of each membrane, and module average Nusselt number and friction factor are calculated to determine the characteristics of the heat transfer and pressure drop in overall flat tube with microchannels. The correlations between Nusselt number and friction factor are given by Reynolds number, aspect ratio of membranes, and the width of flat tube. ALM (Augmented Lagrangian Multiplier) method is applied to the correlations to determine an optimal shape of flat tube. It is shown that the optimal aspect ratio of flat tube is approximately 1.0, irrespective of the width of flat tube and Reynolds number.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.373-377
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• 2002

The Measurement of Pollution in the Troposphere (MOPITT) instrument is an eight-channel gas correlation radiometer launched on the Earth Observing System (EOS) Terra spacecraft in 1999. Its main objectives are to measure carbon monoxide (CO) and methane (CH4) concentrations in the troposphere. This work analyzes tropospheric carbon monoxide distributions using MOPITT data in East Asia and compared ozone distributions. In general, seasonal CO variations are characterized by a spring peak and decreased in the summer. Also, this work revealed that the seasonal cycles of CO are spring maximum and summer minimum with averaged concentrations ranging from 118ppbv to 170ppbv. The CO monthly means show a similar profiles to those of O3. This fact clearly indicates that the high concentration of CO in spring is caused by two possible causes: the photochemical CO production in the troposphere, transport of the CO in the northeast Asia. The CO and O3 seasonal cycles in northeast Asia are influenced extensively by the seasonal exchange of the different types of air mass due to the Asian monsoon. The continental air masses contain high concentrations of O3 and CO due to higher continental background concentrations and sometimes due to the contribution of regional pollution. In summer the transport pattern is reversed. The Pacific marine air masses prevail over Korea, so that the marine air masses bring low concentrations of CO and O3, which tend to give the apparent minimum in summer.

• 설비공학논문집
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• 제23권1호
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• pp.87-94
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• 2011

Characteristics of two-phase pressure drop in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having $205\;{\mu}m$ of bottom width, $800\;{\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Pressure drops in convective boiling of Refrigerant 113 were measured in the range of inlet pressure 105~195 kPa, mass velocity $150{\sim}920\;kg/m^2s$, and heat flux $10{\sim}100\;kW/m^2$. The total pressure drop generally increased with increasing mass velocity and/or heat flux. Two-phase frictional pressure drop across the microchannels increased rapidly with exit quality and showed bigger gradient at higher mass velocity. A critical review of correlations in the literature suggested that existing correlations were not able to match the experimental results obtained for two-phase pressure drop associated with convective boiling in microchannels. A new correlation suitable for predicting two-phase friction multiplier was developed based on the separated flow model and showed good agreement with the experimental data.

• 조명전기설비학회논문지
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• 제18권4호
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• pp.149-154
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• 2004

본 논문에서는, 구내용 저간섭 무선통신설비용 시스템으로서 이진 2m(zero-correlation duration) 확산코드를 이용한 저간섭 CDMA(code division multiple access)시스템을 제시하였다. 이진 ZCD확산코드는 확산코드의 주기가 N인 경우 그 값이 4부터 2의 배수로 계속 확장이 가능하기 때문에 코드발생기의 구현이 용이함과 동시에 ZCD 특성을 가짐으로 인해서, CDMA무선통신 시스템을 구내용 무선설비로 사용할 경우에 발생되는 다중접속 및 다중 경로로 인한 간섭문제를 확산코딩기법을 이용하여 근원적으로 해결해주는 역할을 한다. 본 논문에서는 제안한 이진 ZCD확산코드기반의 구내용 저간섭 CDMA시스템의 간섭완화 성능을 확인하기 위하여, AWGN(additive white gaussian noise) 및 MAI(multiple access interference), MPI(multi path interference)와 같은 잡음 및 다양한 간섭 환경 하에서의 BER(bit error rate)특성을 정량적으로 분석하고, 모의실험을 통해 제안시스템의 간섭완화 능력을 입증하였다.

• 한국공작기계학회논문집
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• 제15권5호
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• pp.1-6
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• 2006

The purpose of this study is to develop to portable near infrared analyzer measuring the sugar content of the fruits on a tree before harvesting ones. The portable near infrared system consists of a tungsten lamp, a coaxial optical fiber bundle and a multi-channel detector, which has 256 pixels and a concave transmission grating. Reflectance NIR spectra of orange were recorded by using a coaxial optical fiber bundle. The spectra were collected over the spectral range $400{\sim}1100nm$. Partial least squares regression(PLSR) was applied for a calibration and validation for determination of sugar contents. The multiple correlation coefficient was 0.99 and standard errors of calibration(SEC) was 0.069 brix. The calibration model predicted the sugar content for validation set with standard errors of prediction(SEP) of 0.092 brix. The sugar content in fruits was successfully quantified using the portable near infrared analyzer.

• 신재생에너지
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• 제1권1호
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• pp.44-53
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• 2005

To understand general status of the national wind environment and to distinguish potential areas to be developed as a largescale wind farm, a synoptic wind map of the Korean Peninsula is established by processing remote sensing data of the satellite, NASA QuikSCAT which Is deployed for the SeaWinds Project since 1999. According to the validation results obtained by comparing with the measurement data of marine buoys of KMA(Korea Meteorological Administration), the cross-correlation factor Is greatly Improved up to 0.87 by blending the sea-surface dat3 of QuikSCAT with NCEP/NCAR CDAS data. It is found from the established synoptic wind map that the wind speed in winter is prominent temporally and the South Sea shows high energy density up to the wind class 6 spatially. The reason is deduced that the northwest winds through the yellow Sea and the northeast winds through the East Sea derived by the low-pressure developed in Japan are accelerated passing through the Korea Channel and formed high wind energy region in the South Sea; the same trends are confirmed by the statistical analysis of meteorological observation data of KMA.

• Journal of Pharmaceutical Investigation
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• 제27권4호
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• pp.295-301
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• 1997

Nitrendipine, a slightly soluble calcium channel blocking agent forms a solid dispersion system with $hydroxypropyl-{\beta}-cyclodextrin$, which exhibits better dissolution characteristics than the uncomplexed drug. The dissolution rate of nitrendipine was markedly increased in solid dispersion system in pharmacopeial disintegration media at pH 1.2 and pH 6.8. Four different dosage forms of nitrendipine were administered to rats: (a) nitrendipine in the solution of PEG 400; (b) nitrendipine solid dispersion system with $hydroxypropyl-{\beta}-cyclodextrin$ in a molar ratio of 1:2 by solvent evaporation method and administered in capsule form; (c) physical mixture of nitrendipine with $hydroxypropyl-{\beta}-cyclodextrin$ in a molar ratio of 1:2 and administered in capsule form; (d) nitrendipine alone administered in capsule form. Relative bioavailability after the oral administration of various dosage forms to rats with a dose of 10 mg/kg equivalent to nitrendipine was compared with that of nitrendipine in the solution of PEG 400. The AUC of solid dispersion was significantly bigger than that of nitrendipine powder. $T_{max}$ of solid dispersion was significantly shorter and $C_{max}$ was higher than that of nitrendipine powder. These results indicate that the bioavailability of nitrendipine could be improved markedly by inclusion complexation. An interesting correlation also appears to exist between the in vitro dissolution data and the area under the plasma concentration-time curves.

• 한국항공우주학회지
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• 제32권4호
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• pp.67-72
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• 2004

경험식을 이용한 1차원 해석에 의하여 30톤급 재생냉각 연소기의 냉각 유로 설계를 수행하였다. 1차원 해석에 의한 벽온도는 3차원 CFD 해석과 비교하여 약 100 K의 온도차이를 보였다. 동일한 냉각성능을 유지하면서 냉각 채널의 최대 폭이 4mm 와 2mm인 두 가지 설계안을 제시하였다. 냉각유체의 압력강하는 20% 증가할 것으로 예측되었다. 열차 폐 코팅과 탄소 침착물의 열저항을 고려한 경우, 최대 벽온도는 700K로 예측되었다. 본 연구에서 제시한 냉각 방법은 용량이 부족한 것으로 판단되는 바 막냉각이 추가적으로 적용되어야 할 것으로 판단된다.

• 한국위성정보통신학회논문지
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• 제11권1호
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• pp.32-36
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• 2016

본 논문에서는 LED(Light Emitting Diode)의 White 조명을 이용한 VLC(Visible Light Communication) 송 수신기를 구현하였다. 가시광 통신과 다양한 환경에서 고속 데이터 전송을 위한 무선 통신 방식의 차이점을 분석하였고 QAM 전송 기법을 이용하여 실제채널을 통과한 심벌의 수신을 확인하였다. 그리고 가시광 통신의 높은 데이터 속도를 얻기 위해 실험을 통해서 고려해야 되는 변수를 찾았다. 또한 주파수 대역을 정하고 거리에 따른 송수신간의 최적의 게인을 찾았다. 효율적인 가시광 통신의 신호 전송 및 검출을 위하여 직교 시퀀스를 이용한 효율적인 신호 검출 기법의 성능을 랩뷰를 이용하여 보였다.

• 한국위성정보통신학회논문지
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• 제8권3호
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• pp.25-31
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• 2013

본 논문에서는 위성/지상 통합 시스템에서 효율적으로 동작할 수 있는 공간 다중화 다중 안테나 방식을 위한 효율적인 인터리빙 기법을 제안한다. 제안된 인터리빙 방식에서는 위성 경로로 전송되는 비트들에 대하여 효과적으로 인터리빙을 적용함으로써, 수신 부호어에서 이웃하는 매 비트마다 서로 다른 채널 이득을 가질 수 있도록 한다. 이와 같은 인터리빙 방식을 적용하면 위성 경로에서의 긴 상관시간으로 인한 성능 저하를 효과적으로 보상할 수 있다. 또한, 제안된 인터리빙 방식은 하드웨어 복잡도 측면에서 효율적으로 구현이 가능하며, 시간 지연도 최소화 할 수 있다.