• Korean Chemical Engineering Research
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• 제57권5호
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• pp.723-729
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• 2019

A theoretical analysis was conducted of convective instability driven by buoyancy forces under transient temperature fields in an annular porous medium bounded by coaxial vertical cylinders. Darcy's law and Boussinesq approximation are used to explain the characteristics of fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven motion. The linear stability equations are derived in a global domain, and then cast into in a self-similar domain. Using a spectral expansion method, the stability equations are reformed as a system of ordinary differential equations and solved analytically and numerically. The critical Darcy-Rayleigh number is founded as a function of the radius ratio. Also, the onset time and corresponding wavelength are obtained for the various cases. The critical time becomes smaller with increasing the Darcy-Rayleigh number and follows the asymptotic relation derived in the infinite horizontal porous layer.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1989년도 춘계학술대회
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• pp.29-34
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• 1989

300 MHz proton NMR spectra of human blood plasma were analyzed by deconvolution of spectrum, and we compared its results with Fossel's test in normal (15 cases), liver cancer (14 cases) , and other cancer (14 cases) groups. This analysis had enabled us to obtain dynamic characteristics of each individual lipoprotein. As a result of deconvolution method, the VLDL and chylomicron intensity level were found to be elevated in the patients with liver cancer. Moment ratio values of $CH_2$ resonance in the raw spectrum were found to be higher than the normal group for patients with, malignant tumors other than liver cancer. These differences between the three groups could not be found in the conventional Fossel's test. We could simulate plasma spectra by addition of spectra of individual lipoproteins through deconvolution method. Further clinical trials in larger populations and additional biochemical method may shed new light on many of clinical and biochemical interests for knowing characteristics about lipoprotein not separated from blood and the background of Fossel test.

• 한국전자파학회논문지
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• 제14권4호
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• pp.330-335
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• 2003

OFDM은 무선 환경에서 고속 data 전송에 적합한 방식이다. 그러나 높은 peak-to-average power ratio(PAPR)로 인하여 비선형 왜곡의 문제점이 있다. 여러가지 PAPR 저감 방법 중에 partial transmit sequences(PTS)는 매우 유연하고 스페트럼 왜형이 발생하지 않는 좋은 방식으로 평가된다. 이 방법의 문제점은 최적화된 phase factor를 side information으로서 수신기에 전송해야만 data를 정확히 복원할 수 있다. 본 논문에서는 기존 PTS 방식에서 feedback type으로 side information을 부가하는 기법을 새롭게 제안한다. Simulation 결과를 통해 제안 방식이 종전의 PTS와 동일한 PAPR 저감 성능을 가지면서 정확하게 data를 복원하여 요구 BER을 확보할 수 있다. 또한, 제안 방식은 전송 채널 특성 변화에 무관하며, 간단히 시스템을 구성할 수 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.344-348
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• 2004

The CdSe thin films wee grown on the Si(100) wafers by a hot wall epitaxy method(HWE). The source and substrate temperature are $600^{\circ}C\;and\;430^{\circ}C$ respectively. The crystalline structure of epilayers was investigated by double crystal X-ray diffraction(DCXD). Hall effect on the sample was measured by van der Pauw method and studied on the carrier density and mobility dependence on temperature. From Hall data, the mobility was increased in the timperature range 30K to 150K by impurity scatering and decreased in the temperature range 150K to 293K by the lattice scattering. In order to explore the applicability as a photoconductive cell, we measured the sensitivity($\gamma$), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation(MAPD), spectral response and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in Cu vapor compare with in Cd, Se, air and vacuum vapour. Then we obtained the sensitivity of 0.99, the value of pc/dc of $1.39{\times}10^7$, the MAPD of 335mV, and the rise and decay time of 10ms and 9.5ms, respectively

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.304-308
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• 2004

The $Cd_{1-x}Zn_xS$ thin films were grown on the Si(100) wafers by a hot wall epitaxy method(HWE). The source and substrate temperature are $600^{\circ}C\;and\;440^{\circ}C$ respectively. The crystalline structure of epilayers was investigated by double crystal X-ray diffraction(DCXD). Hall effect on the sample was measured by the van der Pauw method and studied on the carrier density and mobility dependence on temperature. In order to explore the applicability as a photoconductive cell, we measured the sensitivity($\gamma$), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation(MAPD), spectral response and response time. The results indicated that the photoconductive characteristic were the best for the $Cd_{0.53}Zn_{0.47}S$ samples annealed in Cu vapor compare with in Cd, Se, air and vacuum vapour. Then we obtained the sensitivity of 0.99, the value of pc/dc of $1.65{\times}10^7$, the MAPD of 338mW, and the rise and decay time of 9.7ms and 9.3ms, respectively

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3401-3408
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• 2023

In this study, we used the Monte Carlo N-Particle program to simulate the gamma-ray spectra obtained from plastic scintillators holes filled with bismuth nanoparticles. We confirmed that the incorporation of bismuth nanoparticles into a plastic scintillator enhances its performance for gamma-ray spectroscopy using the subtraction method. The subtracted energy spectra obtained from the bismuth-nanoparticle-incorporated and the original plastic scintillator exhibit a distinct energy peak that does not appear in the corresponding original spectra. We varied the diameter and depth of the bismuth-filled holes to determine the optimal hole design for gamma-ray spectroscopy using the subtraction method. We evaluated the energy resolutions of the energy peaks in the gamma-ray spectra to estimate the effects of the bismuth nanoparticles and determine their optimum volume in the plastic scintillator. In addition, we calculated the peak-to-total ratio of the energy spectrum to evaluate the energy measuring limit of the bismuth nanoparticle-containing plastic scintillator using the subtraction method.

• 한국전자파학회논문지
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• 제15권4호
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• pp.414-420
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• 2004

Orthogonal frequency-division multiplexing(OFDM)은 무선 환경에서 고속 데이터 전송에 적합한 방식이다. 그러나 높은 peak-to-average power ratio(PAPR)로 인하여 비선형 왜곡의 문제점이 있다. 여러 PAPR 저감 방법 중에서 partial transmit sequences(PTS)는 매우 유연하고 스펙트럼 왜곡이 발생하지 않는 좋은 방법으로 평가된다. 이 방법의 문제점은 최적화된 rotation factor에 대한 부가 정보를 수신기에 전송해야만 데이터를 정확히 복원할 수 있다는 점이다. 본 논문에서는 기존 PTS 방식에서 기준 심볼을 이용하여 부가 정보를 전송하는 기법을 새롭게 제안한다. 이 기법은 rotation factors의 정보를 기준 심볼의 위상으로 표현하는 방법이다. 시뮬레이션 결과를 통해 제안 방식이 종전의 PTS와 동일한 PAPR 저감 성능을 가지면서 정확하게 데이터를 복원하여 요구 BER이 만족됨을 확인하였다. 또한, 제안 방식은 변조 방식에 무관하며, 간단하게 시스템을 구현할 수 있다.

• 한국지구과학회지
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• 제37권1호
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• pp.40-51
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• 2016

실제 국내에서 관측된 가속도를 이용한 스펙트럼 값이 내진설계기준보다 상대적으로 크게 나타나는 경향을 보이며, 특히 고진동수 구간에서 국내 내진설계 기준이 국내 고유의 지반증폭 특성을 제대로 반영하지 못하고 있어 문제점이 많다고 지적되어 왔다. 지반증폭 특성을 분석할 때 여러 가지 방법이 제시되어 왔으며 본 연구는 현장에서 자주 적용되고 있는 지반진동의 수평/수직 스펙트럼 비율을 이용하는 방법을 적용하였다. 이 방법은 S파 및 레일리파를 이용하는 것으로부터 출발하였으나, 최근 Coda파 및 배경잡음 등에 확대 적용되어 지반의 동적인 증폭특성 연구에 많이 이용되고 있다. 제한된 연구 기간 동안 4개 변전소시설 관측소 각각 2개 지점(노두 및 시추공)에서 운영되었고 본 연구는 4개 관측소의 노두에서 동시에 관측된 3개 중규모 지진의 가속도 지반진동(S파, Coda파 및 배경잡음)을 이용하여 지반증폭을 분석하였다. 분석결과는 4개 관측소 각각에 대해 기존 연구결과인 시추공 지반증폭 특성과 상호 비교하였다. 또한 각각 관측소 및 지점에서 지반의 우월진동수를 이용하여 각각 지반에 대한 등급분류도 시도하였다. 각각의 지진관측소마다 저진동수 및 고진동수 특성, 관측소 고유의 우월진동수가 서로 상이하여 관측소 고유의 증폭특성을 보여주었다. 대다수 관측소는 S파, Coda파 및 배경잡음 에너지를 분석한 결과와 많은 부분이 유사함을 보여 주었다. 물론 본 연구로부터 도출된 결과를 다른 방법에 적용하여 얻어진 결과와 비교한다면 지반의 동적 특성 및 지반분류 연구에 많은 정보를 제시할 수 있다고 판단된다.

• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2069-2074
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• 2007

The 27Al multiple quantum magic angle spinning (MQMAS) nuclear magnetic resonance (NMR) spectra of mordenite zeolites were simulated using the point charge model (PCM). The spectra simulated by the PCM considering nearest neighbor atoms only (PCM-n) or including atoms up to the 3rd layer (PCM-m) were not different from those generated by the Hartree-Fock (HF) molecular orbital calculation method. In contrast to the HF and density functional theory methods, the PCM method is simple and convenient to use and does not require sophisticated and expensive computer programs along with specialists to run them. Thus, our results indicate that the spectral simulation of the 27Al MQMAS NMR spectra obtained with the PCM-n is useful, despite its simplicity, especially for porous samples like zeolites with large unit cells and a high volume density of pores. However, it should be pointed out that this conclusion might apply only for the atomic sites with small quadrupole coupling constants.

• International Journal of Automotive Technology
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• 제6권2호
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• pp.141-148
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• 2005

In order to reduce the time and costs of improving the performance of vehicle suspensions, the techniques for optimizing damping and air spring characteristic were proposed. A full vehicle model for a bus is constructed with a car body, front and rear suspension linkages, air springs, dampers, tires, and a steering system. An air spring and a damper are modeled with nonlinear characteristics using experimental data and a curve fitting technique. The objective function for ride quality is WRMS (Weighted RMS) of the power spectral density of the vertical acceleration at the driver's seat, middle seat and rear seat. The objective function for handling performance is the RMS (Root Mean Squares) of the roll angle, roll rate, yaw rate, and lateral acceleration at the center of gravity of a body during a lane change. The design variables are determined by damping coefficients, damping exponents and curve fitting parameters of air spring characteristic curves. The Taguchi method is used in order to investigate sensitivity of design variables. Since ride and handling performances are mutually conflicting characteristics, the validity of the developed optimum design procedure is demonstrated by comparing the trends of ride and handling performance indices with respect to the ratio of weighting factors. The global criterion method is proposed to obtain the solution of multi-objective optimization problem.