• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.1
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• pp.84-92
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• 1989

The purpose of this paper is to demonstrate the effect of a FH spread spectrum communication interference in TV channels and frequency compatibility in 30-88 MHz frequency band. To calculate this interferece, the strength of electric field of TV signals is derived as a function of distance between TV transmitter and receiver. An interference model is established based upon thefield strength by using the relation between the transmitted power of FH spread spectrum communications and the distance between the TV image signals, which makes TV screen a cceptble, Simultaneous transmission of FH sprea spectrum signals and TV signals is shown to be feasible, as far as the interference level is lower than the TV image signal level by 23.5dBm. As a result of frequency analysis and experiment, the FH spread spectrum communication can be used together with TV channels.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.1
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• pp.42-48
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• 2010

In this paper, we proposed analysis performance improvement technique for T-DMB watermarking based on MBOK spread spectrum. By applying the proposed scheme to T-DMB system, it allows additional data transmission and improves spectral efficiency of data transmission through watermarking spreading code. Using MBOK spread spectrum technique, data rate improved 2m-times existing direct sequence spread spectrum. However, since hardware complexity increase as the value of m becomes large, the method should be used with optimal situation. We analyze T-DMB watermarking techniques performance with MBOK spread spectrum and averaging. As a result, we confirm DER performance of MBOK spread spectrum scheme and it is shown system performance is improved as the number of averaging increases. The results of the paper can be applied to wireless multimedia digital broadcasting system.

• Journal of the Korean earth science society
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• v.32 no.4
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• pp.360-372
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• 2011

In order to clarify the advection and dispersion characteristics of volcanic tephra to be emitted from the Mt. Baekdu, several numerical experiments were carried out using three-dimensional atmospheric dynamic model, Weather and Research Forecast (WRF) and Laglangian particles dispersion model FLEXPART. Four different temporally averaged meteorological values including wind speed and direction were used, and their averaged intervals of meteorological values are 1 month, 10 days, and 3days, respectively. Real time simulation without temporal averaging is also established in this study. As averaging time of meteorological elements is longer, wind along the principle direction is stronger. On the other hands, the tangential direction wind tends to be clearer when the time become shorten. Similar tendency was shown in the distribution of volcanic tephra because the dispersion of particles floating in the atmosphere is strongly associated with wind pattern. Wind transporting the volcanic tephra is divided clearly into upper and lower region and almost ash arriving the Korean Peninsula is released under 2 km high above the ground. Since setting up the temporal averaging of meteorological values is one of the critical factors to determine the density of tephra in the air and their surface deposition, reasonable time for averaging meteorological values should be established before the numerical dispersion assessment of volcanic tephra.

• Fire Science and Engineering
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• v.34 no.1
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• pp.55-65
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• 2020

In this study, the ISO 5660 and ISO 5659 combustion tests were conducted with synthetic resin conduits (CD, VE) and metal conduit (ST) used for wiring work in electrical facilities, which can be installed in ceiling concealed places. Then, fire spreading and evacuation risks were analyzed based on the measured data. In the ISO 5660 test, CD of 120.5 MJ/㎡, VE of 81.9 MJ/㎡, and ST of 4.9 MJ/㎡ were measured. In the ISO 5659 test, the CD 1320, VE 731, and ST 102 were measured, and then the maximum smoke densities were measured for CD 605 s, VE 740 s, and ST 1,200 s. In terms of fire spreading and evacuation risk, the CD conduit, VE conduit, and ST conduit were in order. In the fire spreading risk analysis, total heat emission was calculated as 4,820 MJ/㎡, 4,267 MJ/㎡, and 196 MJ/㎡ for CD, VE, and ST, respectively. Evacuation risk analysis shows at transmittance of 89%, CD is 127 s, VE is 35 s, and ST is 969 s. At transmittance of 79%, representing almost invisible concentration, CD is 157 s and VE is 50 s. The CD and VE conduits had a high fire spreading and evacuation risks, while the ST conduit had little effect on fire spreading and evacuation risk.

• Progress in Medical Physics
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• v.4 no.1
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• pp.29-39
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• 1993

Electron beams have found unique and complementary used in the treatment of cancer, but it's very difficult to delineate dose distribution, because of multi-collisions. Numerical solution is more usefull to describe electron distributed in tissue. A semi-empirical eqution is given for the dose at any point at various depths in water. This equation is a modificated model which was based on solutions of a general age diffusion equation. Parameters have been calulated from electron beams data with energies 6～18MeV form a LINAC for use in computerised dosimetry calculations. The depth doses and isodose curves are predicted as a function of the practical range, source skin distance and field size. Depth dose accuracy have been achieved 2% above 50% depth dose and 5% at lower doses, relative to maximum dose. Also, the shape of the isodose curves with the constrictions at higher dose and bulging ot lower values are accurately predicted. Computer calculated beams have been used to generate ever isodose distribution for certain clinical situations.

• Membrane Journal
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• v.12 no.2
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• pp.90-96
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• 2002

A novel methodology on the calculations of osmotic pressure and gradient diffusion coefficient has been provided ill the present study, by applying a succinct numerical analysis on the experimental results. Although both the osmotic pressure and the gradient diffusion coefficient represent a fundamental characteristic in related membrane filtrations such as microfiltration and ultrafiltration, neither theoretical analysis nor experiments can readily determine them. The osmotic pressure of colloidal suspension has been successfully determined from a relationship between the data of the time-dependent permeate flux, their numerical accumulations, and their numerical derivatives. It is obvious that the osmotic pressure is gradually increased, as the particle concentration increases. The thermodynamic coefficient was calculated from the numerical differentiation of the correlation equation of osmotic pressure, and the hydrodynamic coefficient was evaluated from the previously developed relation for an ordered system. Finally, the estimated gradient diffusion coefficient, which entirely depends on the particle concentration, was compared to the previous results obtained from the statistical mechanical simulations.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.501-504
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• 2008

A concrete carbonation model has been constructed that takes account of the diffusion of carbon dioxide through a coating and reaction with calcium hydroxide, and this model has been validated by an accelerated carbonation experiment. (1) By using values for the coatings calculated on the basis of a diffusion.permeation theory as input data for the analysis of diffusion.reaction carbonation in an unsteady state, the effect of the coatings in reducing carbonation can be represented with high accuracy. (2) Through a sensitivity analysis of the diffusion.reaction carbonation model and the experimental results, we found that the diffusion coefficient of calcium hydroxide shows a high interrelationship at 1e-12($m^2/s$). The reaction rate constant for carbonation shows a high interrelationship at 5e-5($m^3/mol/s$).

• Proceedings of the Korean Information Science Society Conference
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• 2004.10b
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• pp.769-771
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• 2004

영상을 유사한 특성을 갖는 영역 단위로 분할하는 작업은 다양한 영상 처리를 위한 전처리 과정으로 사용되고 있다. 본 논문에서는 모폴로지(Morphology)와 비선형 확산(Non-Linear Diffusion)을 이용한 영상분할 방법을 제안한다. 초기에 LUV 색상공간에 모폴로지를 응용한 재구성(Reconstruction)에 의한 닫힘(Closing) 연산과 비선형 확산(Non-Linear Diffusion)을 통해 실형 영상을 획득한다 이 영상에서 칼라 영상의 기울기(Gradient) 정보를 획득하고, 마커(Marker) 정보를 이용한 워터쉐드(Watershed) 알고리즘을 적용하여 영상을 효과적으로 분할한다. 그레이 영상과 칼라 영상을 대상으로 한 실험에서 제안 방법이 영상을 효과적으로 분할함을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.250-258
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• 1985

비균열 접선속도장에 기인한 화염스트레치 인자와 확산선호도가 예혼합화염의 전파속도에 미치는 영향을 연소가스와 예혼합기의 대향류 유동장을 모델로 하여 접합 전개 방법을 이용하여 일반 인 Lewis수 및 기체팽창을 고려하여 해석하였다. 이 결과 스트레치가 작은 경우에는 확산선호 도에 따라 화염특성이 급격히 변화하는데 이는 곡률을 가진 자유전파화염의 특성과 동일하며 스트레치가 큰 경우에는 확산선호도에 관계없이 화염전파속도는 감소하는 특성을 보여주었다. 또한, 화염스트레치의 실험적 측정 및 이론적 해석에 있어서의 정의 및 화염스트레치의 영향에 관한 현상적 설명에 대하여 재검토하였다.

• Investigative Magnetic Resonance Imaging
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• v.6 no.2
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• pp.107-113
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• 2002