• Journal of the Economic Geographical Society of Korea
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• v.5 no.1
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• pp.69-87
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• 2002

This study examines the spatial diffusion and locational charateristics of convenience stores in Daegu which had increased rapidly in the 1990s. The first convenience store (CVS) was introduced in the zone of transition of (Namgu district) adjacent to the city center or CBD in 1992. Thereafter they diffused into CBD and residential areas, but they have centered around places where their steady purchasing population was distributed. As a result, the spatial distribution of CVSs in Daegu shows a very uneven pattern concentrated in areas with many high school, in commercial and business areas, and apartment residential areas. It seems that this pattern is derived from two basic locational factors. Primarily, the location of CVSs in Daegu is very closely related with the spatial distribution of the demand population which will be clients for CVSs. Secondarily, it is also affected by the accessibility of streets which the demand population utilizes easily.

• Korean Journal of Ecology and Environment
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• v.53 no.2
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• pp.185-194
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• 2020

Pomacea canaliculate (channeled apple snail; CAS), which is one of the world's worst alien invasive species, is widely distributed in Korea, and raised ecological and economic problems. In this study, we surveyed the distribution and dispersal characteristics of CAS in Korea, and analyzed the effects of environmental and anthropogenic (or social) factors on their distribution and dispersal. We considered various events related to CAS such as changes of policy including promotion of agriculture using CAS and enactment of biological diversity conservation law. Our results showed that human activities strongly influenced to the distribution and dispersal of CAS in Korea. Distribution of CAS seemed to relate with environment-friendly agriculture considering environmental conditions of CAS habitats. And dispersal characteristics of CAS were significantly correlated with social factors such as cultivation area and rate of organic products, production CAS on inland fishery.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.992-998
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• 2017

For local advertising based on D2D communications, sources want advertisement messages to be diffused to unspecified users as many as possible. It is one of challenging issues to select target-areas for advertising if users are uniformly distributed. In this paper, we propose D2D based advertisement dissemination algorithm using user clustering with expectation-maximization. The user distribution of each cluster can be estimated by principal components (PCs) obtained from each cluster. That is, PCs enable the target-areas and routing paths to be properly determined according to the user distribution. Consequently, advertisement messages are able to be disseminated to many users. We evaluate performances of our proposed algorithm with respect to coverage probability and average reception number per user.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.145-154
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• 1996

Polymer-modified mortars have an excellent water proofness and water retentivity. Therefore, the study on the moisture diffusion behavior- is very important. The purpose of' this study is to investigate the effects of relative humidity and moisture content in mortars on the moisture diffusion, and the relationship between the shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H and 80% R.H. The pore size distribution of the polymer-modified mortars was also measured. From the test results, the relative humidity and moisture content in mortars influenced on the moisture diffusion of polymer-modified mortars. The shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H. was bigger than that cured at $20{\circ}C$ 80% R.H.. and decreased with increasing polymer-cement ratio regardless of polymer type.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.301-301
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• 2010

2010년경 2.5G APD 시장은 3, 000억원 규모로 증가하는데 이는 FTTH 망의 확산에 힘입은 바 크다. 이와 같이 중요한 APD 소자는 현재 광통신 부품시장을 석권해 가고 있는 대만, 중국 업체들은 제조기술을 갖고 있지 않고 주로 미국-일본 기술에 의존하고 있기 때문에 Niche market으로 중요한 부품이라 할 수 있다. APD의 증폭은 높은 전기장에 의해 얻어지는데, 이 때문에 메사형 구조로는 신뢰성을 확보하기 어렵게 되고 따라서 평면형(Planar) 구조로 설계-제작하게 된다. APD 소자는 증폭층의 너비에 의해 APD의 이득-대역폭이 정해지므로 증폭층 폭을 정확하게 조절하는 것은 매우 중요하다. 증폭층의 폭은 에피 성장과 같은 높은 정밀성을 갖는 장비에 의해 조절하는 것이 아니라, Planar 구조의 특성상 Zn-확산에 의해 조절하게 된다. 대부분의 경우 Zn-확산은 Zn 또는 $Zn_3P_2$를 증착하여 drive-in 시키는 방법을 사용하는데, 이 경우 Zn가 interstitial site를 치고 들어감으로 인해 캐리어 농도가 $2{\times}10^{17}\;cm^{-3}$ 정도로 낮게 형성된다. 따라서 높은 인가 바이어스에서 p-side로 공핍층이 전개되기 때문에 증폭층의 폭을 조절하기가 매우 어렵다. 이 현상은 APD 제작에 있어서 수율과 관련이 깊다. 따라서 APD의 증폭층 폭을 tight하게 조절하기 위해서는 p-type 캐리어 농도를 높일 수 있는 gas-phase 확산 방식의 개발이 필요하다. 이 방식에는 Ampoule과 같은 closed tube 방식과 확산로와 같이 Gas를 지속적으로 흘려주면서 확산시키는 open-tube 방식이 있다. Ampoule 방식은 캐리어 농도 측면에서는 가장 좋은 방식이나, Ampoule의 size 및 온도 균일성 등으로 인해 생산성에 문제가 있다. 따라서 open-tube 방식의 확산기술개발은 매우 중요하다 할 수 있다. 본 연구에는 rapid thermal annealing (RTA) 방법에 의한 $Zn_3P_2$ 고체의 확산 방식과 DEZn MO source에 의한 Gas 확산 방식을 바탕으로 InP로의 확산된 Zn원자와 doping의 분포를 비교하였다. 실험결과, Gas 확산방식의 경우 Zn원자가 더욱 더 깊게 확산이 되었으며, 확산된 원자의 대부분이 도펀트로 작용함을 확인할 수 있었다.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06c
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• pp.16-21
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• 2010

잠재 의미를 색인하는 것은 문서 색인에 있어서 그 색인 품질에 주요한 요인을 차지한다. 본 논문에서 살펴보는 의미 확산 방법은 문서 집합에 나타나는 단어들의 의미적 연관성을 바탕으로 활성화 작용 모델(spreading activation model)을 구축하고 색인 대상 문서의 단어 분포를 출발점으로 삼아, 그 모델 안에서 의미적으로 수렴할 수 있도록 랜덤 워크 방법(random walk method)1)을 수정한 변형 방법을 이용해 확률을 확산시킨다. 이 방법은 단어 사이의 연관성을 따라 탐색하며 동의어와 다의어 등 단순 단어 일치로는 알 수 없는 의미적 유사 단어들이 의미 있는 확률 분포를 갖게 한다. 이는 단어들의 의미 분포를 가중치 그래프를 통해 보다 합리적으로 다루게 된다. 실험에서는 문서 분류를 시행하여 평균 정확도 및 정확도-재현율 곡선을 산출하였고, 비교 실험을 통해서 전반적인 우수성을 관찰할 수 있었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.2
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• pp.105-112
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• 2007

Sediment transport model based on the Lagrangian concept considering the grain size distribution(GSD) was setup and the change of the sediment diffusion range was analysed in the condition of considering and not considering the GSD. The GSD curve is assumed as the Log-normal distribution function in order to consider the GSD with respect to the Lagrangian concept and the random numbers, i.e. sediment particles, are generated based on the distribution function. The sediment particles is assumed as the spherical type and the random numbers based on the sediment weight is converted to the sediment diameters. Sediment transport patterns are analysed by the settling simulation, in which the settling velocity is computed by the van Rijn formulae and the horizontal diffusion coefficient is used as the constant parameter. The diffusion patterns are very similar to the patterns with GSD condition. The diffusion range defined as the range including 90%, 99% sediment weight of the total sediment weight, however, is larger than without considering GSD condition in 90%-option and shorter than with considering GSD condition in 99-option, respectively. The diffusion range is defined as tile p-percentage of the cumulative sediment weight region with reference to the 50% region, 90%- option, 99%-option, respectively.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.499-509
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• 2001

2-D transport model based on a discrete probability distribution for a particle displacement was developed too solve advection-diffusion problems in natural stream. In this proposed model, the probabilities expressed as an average and variance function were used to predict the mass transfer between cells in one time step. The proposed model produces solutions without numerical dispersion for constant velocity, diffusion coefficient, and cross-sectional area. When the stability and positivity restrictions were satisfied, the model produced excellent results compared to analytical solutions and other finite difference methods. The proposed model is tested against the dispersion data collected in the Grand River, Canada. The simulation results show that the proposed model can properly describe the two-dimensional mixing phenomena in the natural stream.

• 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.

• Journal of Korea Multimedia Society
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• v.12 no.3
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• pp.362-371
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• 2009

The key technology for developing high quality LCDs is about manufacturing BLUs with homogeneous dot distributions. Commonly, homogeneous dot distributions are obtained by the halftoning methods which convert a gray-scale image to a binary image. Among many halftoning algorithms, the error-diffusion technique based on the principle distance is known to show homogeneous dot distributions. However, this technique has a drawback; the extent of the principle distance at each pixel with respect to those of the neighboring pixels can be too small or big creating a gap or overlap. In this paper, we propose a new error diffusion algorithm based on the variable principle distance which improves the existing error diffusion technique based on the principle distance. The variable principle distance at a given pixel is calculated with gray-scale values of the pixel and its neighbors and thus the principle distance value is variable depending on the direction from that pixel. This variable principle distance technique helps BLUs obtain homogeneous dot distributions.