• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.209-215
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• 2002

This study investigated the crystal growth, crystalline structure and the basic optical properties of $SnSe/BaF_2$ epilayers. The SnSe epilayer was grown on $BaF_2$(111) insulating substrates using a hot wall epitaxy(HWE) technique. It was found from the analysis of X-ray diffraction patterns that $SnSe/BaF_2$ epilayer was growing to single crystal with orthorhombic structure oriented [111] along the growth direction. Using Rutherford back scattering(RBS), the atomic ratios of the SnSe was found to be stoichiometric, almost 50 : 50. The best values for the full width at half maximum (FWHM) of the DCXRD was 163 arcsec for SnSe epilarer. The epilayer-thickness dependence of the FWHM of the DCXRD shows that the quality of the $SnSe/BaF_2$ is as expected. The dielectric function ${\varepsilon}$(E) of a semiconductor is closely related to its electronic energy band structure and such relation can be drawn from features around the critical points in the optical spectra. The real and imaginary parts(${\varepsilon}_1$ and ${\varepsilon}_2$) of the dielectric function ${\varepsilon}$ of SnSe were measured. These data are analyzed using a theoretical model known as the model dielectric function(MDF). The optical constants related to dielectric function such as the complex refractive index(n*-n+ik), absorption coefficient (${\alpha}$) and normal- incidence reflectivity (R) are also presented for $SnSe/BaF_2$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.3
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• pp.110-113
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• 2011

In this paper, we propose a new method for the fabrication of GaN microstructures formed only on the vertex of GaN pyramid by using of metal catalysts. GaN pyramidal structures were selectively grown on 3 ${\mu}m$ $SiO_2$ dot patterns followed by thin film deposition of Au and Cr only on the vertex area of the GaN pyramids with precisely controlled photolithography. After the metal deposition, the samples were loaded in the MOVPE reactor for the growth of GaN microstructures for 10 minutes. Temperature for the growth of the GaN microstructures was changed from $650^{\circ}C$ to $750^{\circ}C$. Rod type GaN microstructures were grown in the direction of vertical to the six {1-101} facets and the shape of the GaN microstructures was changed depend on the type of metal.

• Journal of Food Hygiene and Safety
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• v.26 no.2
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• pp.120-124
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• 2011

Predictive mathematical models were developed for predicting the kinetics of growth of Listeria monocytogenes in smoked salmon, which is the popular ready-to-eat foods in the world, as a function of temperature (4, 10, 20 and $30^{\circ}C$). At these storage temperature, the primary growth curve fit well ($r^2$=0.989~0.996) to a Gompertz equation to obtain specific growth rate (SGR) and lag time (LT). The Polynomial model for natural logarithm transformation of the SGR and LT as a function of temperature was obtained by nonlinear regression (Prism, version 4.0, GraphPad Software). Results indicate L. monocytogenes growth was affected by temperature mainly, and SGR model equation is $365.3-31.94^*Temperature+0.6661^*Temperature^{\wedge^2}$ and LT model equation is $0.1162-0.01674^*Temperature+0.0009303^*Temperature{\wedge^2}$. As storage temperature decreased $30^{\circ}C$ to $4^{\circ}C$, SGR decreased and LT increased respectively. Polynomial model was identified as appropriate secondary model for SGR and LT on the basis of most statistical indices such as bias factor (1.01 by SGR, 1.55 by LT) and accuracy factor (1.03 by SGR, 1.58 by LT).

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.618-619
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• 2010

LED는 기존의 발광원에 비해 훨씬 높은 파워와 효율성으로 인해 최근 들어 각종 조명이나 교통신호 등에서 사용이 급증하고 있다. LED 재료를 위해 지금까지 여러가지가 연구되어 왔는데, 갈륨 질화물 (Gallium Nitride, GaN)에 기반한 시스템이 최근들어 가장 큰 관심을 받고 있다. GaN 방식은 열적으로 매우 안정성이 있고, 1.9 ~ 6.2 eV 범위의 넓은 밴드의 Gap, 그리고 인듐이나 알루미늄과 결합하여 청, 녹, 백색등의 다양한 빛을 발생할 수 있는 장점을 가지고 있다. 예를 들어 청색 LED는 광학 방식의 기록매체에, 백색 LED는 기존의 조명램프의 대체용으로 활용이 가능하다. 이러한 장점 덕분에 GaN기반 LED 시장은 1994년에 최초로 상용화 된 이래 최근 급격한 성장을 보여 왔다. 그러나 GaN은 다른 III~V 타입의 반도체 재료와는 달리 재료가 성장하기 위해 사파이어와 같은 별도의 기판을 필요로 하는 문제가 있다. 이것은 결국 전위발생과 같은 격자의 부조화 같은 문제를 야기하여 결국 LED의 성능을 떨어뜨리는 요인이 된다. 이러한 문제를 해결하기 위해 HVPE(Hydride Vapor Phase Epitaxy) 방법이 개발되었는데, 이 방법은 시간당 100 미크론의 매우 빠른 성장속도로 높은 두께의 레이어를 만드는 장점이 있다. 이렇게 성장된 GaN 레이어는 베이스 기판에서 쉽게 분리되어 활용이 가능하다. 그러나 HVPE 기술은 성장 공정에서 두께를 균일하게 만들도록 제어하는 것이 매우 어렵다는 문제가 있다. 따라서 HVPE 방식에서는 이러한 조건을 만족시키기 위해 반응현상에 대한 물리적 해석을 토대로 공정조건을 정밀하게 설계해야 한다. 이를 위해 최근에 실험 또는 시뮬레이션을 활용하여 이러한 공정조건을 향상시키기 위한 여러 연구가 진행되었다. 본 연구에서는 이러한 연구의 일환으로 반응로에 투입되는 여러 기체의 유량과 존별 주변온도 조건을 입력변수로 하고, 이들이 GaN 성장에 미치는 영향을 분석하였다. HVPE 시스템에서 가장 이상적인 목표는 반응기체가 층류유동을 유지하면서 대부분의 반응이 기판위에서 이뤄지며, 기판위에서 성장되는 재료의 두께가 균일하게 되는 것이다. 입력변수들이 이러한 결과에 어떠한 영향을 미치는 지 분석하기 위해 전산유체역학(CFD, Computational Fluid Dynamics)을 수행하는 상용코드 FLUENT를 사용하였다. 보다 실제에 가까운 해석을 위해서는 기체간의 화학반응을 포함해야 하나, 해석의 편의와 효율을 위해 본 연구에서는 열 및 유동해석만을 수행하였다. 한편 실제 반응로의 우수성은 성장속도와 두께분포의 균일도를 통해 평가된다. CFD 해석을 통해 이들을 분석하기 위해 기존에 수행한 실험조건을 해석하고 해석결과의 유동패턴/압력분포를 실험결과의 성장속도/두께분포와 비교하고, 이중에서 관련성이 높은 해석결과변수를 우수성 평가에 활용하였다. 기존의 실험결과를 토대로 이러한 중요 결과변수와 함께 이들에 대한 목표값이 도출되고 나면, 입력 공정조건 - 사용기체의 유량과 주변온도 조건 - 에 대해 실험계획(DOE,Design of Experiment)을 수립하고 목표성능을 구현하기 위한 최적설계를 수행할 수 있다. 일반적으로 CFD를 통해 최적의 설계나 공정조건을 탐색하는 작업은 1회의 CFD 계산시간이 매우 오래 소요되기 때문에 쉽지 않다. 그러나 본 연구에서는 CFD와 DOE의 적절한 조합을 통해 적은 수의 해석을 가지고도 원하는 결과를 효율적으로 얻는 것이 가능함을 입증하고자 한다. 본 발표에서는 아직 이러한 연구가 완성되지 않은 시점에서 제반 연구개요를 소개하고 현 시점까지의 연구 결과 및 향후 계획을 소개하고자 한다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.49-52
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• 2006

Periodic electric field assisted poling low loss (${\sim}0.1dB/cm$) single-mode Ti-diffused waveguides in $LiNbO_3$ has been achieved using a periodically patterned electrode on the +Z surface of Ti : $LiNbO_3$ crystal and homogeneous LiCl solution. Using selective chemical etching, we confirmed the periodic (${\sim}16{\mu}m$) domain inverted structure and measured SH (second harmonic) properties of fabricated periodically poled Ti : $LiNbO_3$ waveguides.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.477-480
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• 2009

최근 북한지역에 발생한 홍수와 가뭄 등 심각한 자연재해의 원인이 악화된 식량난으로 인한 과도한 산림의 훼손으로 추정되고 있어 북한 지역의 산림 생태계에 대한 연구의 필요성을 더욱 확인하는 계기가 되고 있다. 위성자료로부터 얻을 수 있는 식생지수(NDVI)는 농작물, 초목, 산림등과 같은 중요한 식생자원을 모니터링 하기 위해 설계된 도구로 식생의 활력도를 정량적으로 표현할 수 있다. 또한, 식생지수는 개략적인 식생을 파악하는데 주로 사용되기 때문에 초기조사에 많이 이용되고 있다. 따라서, 본 연구에서는 개마고원지대를 포함하는 표고 1000m 이상의 한대림지대의 산림식생에 대해 9년(2000~2008)간의 시계열 MODIS영상에서 나타나는 식생지수의 생물계절 특징을 분석하였다. 식생이 성장하기 시작하는 시기(the beginning of the growing season)는 5월 9일 이후부터 5월 25일 사이의 기간으로 나타났고, 식생의 휴면 시기(the end of growing season)는 9월 14일부터 9월 30일 사이 기간으로 관측되었다. 이는 4월 초에 시작하고 10월에 사라지는 한반도의 일반적이 식생패턴보다 성장은 한달 늦게, 휴면은 한달 이르게 한다는 것이 확인되었다. 또한, 8월 초순의 NDVI 값이 9년 동안 계속적으로 가장 높은 값을 보여주고 있다. 이것은 개마고원지역 및 주변 한대림 지대는 7월 말에서 8월 초순에 식생이 가장 활발한 것을 의미한다. 9년 동안 전반적인 식생지수는 0.2~0.9 값을 보였고, 특이할 점은 9년 동안의 평균적인 NDVI 값에 비해 2002년의 식생의 활동이 봄에 빨리 개화하고 가을에 일찍 지는 패턴을 보였다.

• Journal of Information Management
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• v.39 no.4
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• pp.241-257
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• 2008

This study describes the growth, contribution and impact of research carried out by University of Mysore scientists in science and technology. It indicates the patterns of communications of university scientists and studies the extent of concentration and scattering of their research output in different journals. It also analyses the strong and weak areas of university research, their growth rate and impact in terms of average citations received. It also studies the output and impact of research under different existing subject departments of the university and analyses the international collaborative share of research output at the overall level as well as across various subjects, indicating also the major countries involved in international collaboration. It describes the share and characteristics of select high cited papers and the top productive authors.

• Fire Science and Engineering
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• v.33 no.6
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• pp.126-131
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• 2019

Real-scale fire tests were performed on animal-origin foods using a gas stove with no overheating prevention device. When the animal-origin foods were ignited, a large quantity of white smoke and steam was generated from them; however, when they became dry and began to carbonize, a dark smoke was generated. Even after the gas stove was overheated for more than 5400 s, mackerel, pollack, chicken, etc., did not ignite. However, pork, beef, and tuna caught fire after 2643 s, 2819 s, and 6492 s of heating, respectively. The flame patterns of animal-origin foods were in the forms of a mixed laminar flow and a turbulent flow, and a halo pattern was produced. A sand glass form of the flame pattern was generated when a kitchen hood was operated, but a triangular flame pattern was produced when the kitchen hood was not operated. When the tuna in the pot was overheated, it spontaneously ignited after 6492 s, with the surface temperature of the kitchen hood rapidly rising to 464.5 ℃. Moreover, the temperature at the back of the pot, which was 6 cm away from the outer surface of the upper part of the pot, was 869 ℃ after 6660 s because of the radiant heat. The flame formed a sand glass pattern on the kitchen wall. When the kitchen hood was not operated, or when the flame grew lower than the height of the ceiling, a triangular pattern was formed.

• Journal of the Korean Geographical Society
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• v.43 no.4
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• pp.561-579
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• 2008

The population concentration in Seoul has caused the chronic housing shortage. Accordingly the new towns in the Capital region were developed to alleviate overcrowding conditions in Seoul. The purpose of this study is to analyze changes of migration and commuting patterns according to new town development in the Capital region for the period of $1995{\sim}2005$. Further this study examines the changes of self-sufficiency level for new towns using jobs to housing ratio. During the last 10 years, the migration pattern in the Capital region has been pretty much followed the new town development. Such a migration pattern has influenced the commuting patterns, expanding the Seoul Metropolitan Area into northeastern par of the Capital region. The result reveals that self-sufficiency levels of new towns have become higher over the period of $1995{\sim}2005$, indicating that new towns are gradually strengthening their economic functions and have potential to become new business centers in the future. Therefore, the policy focusing on the increase of the job-housing balance ratio and self-sufficient level in new towns will be a desirable policy alternative to solve the transportation problems in the Capital region.

• Journal of Intelligence and Information Systems
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• v.17 no.2
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• pp.77-96
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• 2011

An exhibition is defined as market events for specific duration to present exhibitors' main products to business or private visitors, and it plays a key role as effective marketing channels. As the importance of exhibition is getting more and more, domestic exhibition industry has achieved such a great quantitative growth. But, In contrast to the quantitative growth of domestic exhibition industry, the qualitative growth of Exhibition has not achieved competent growth. In order to improve the quality of exhibition, we need to understand the preference or behavior characteristics of visitors and to increase the level of visitors' attention and satisfaction through the understanding of visitors. So, in this paper, we used the observation survey method which is a kind of field research to understand visitors and collect the real data for the analysis of behavior pattern. And this research proposed the following methodology framework consisting of three steps. First step is to select a suitable exhibition to apply for our method. Second step is to implement the observation survey method. And we collect the real data for further analysis. In this paper, we conducted the observation survey method to obtain the real data of the KIDS & EDU EXPO for Children in SETEC. Our methodology was conducted on 160 visitors and 78 booths from November 4th to 6th in 2010. And, the last step is to analyze the record data through observation. In this step, we analyze the feature of exhibition using Demographic Characteristics collected by observation survey method at first. And then we analyze the individual booth features by the records of visited booth. Through the analysis of individual booth features, we can figure out what kind of events attract the attention of visitors and what kind of marketing activities affect the behavior pattern of visitors. But, since previous research considered only individual features influenced by exhibition, the research about the correlation among features is not performed much. So, in this research, additional analysis is carried out to supplement the existing research with data mining techniques. And we analyze the relation among booths using data mining techniques to know behavior patterns of visitors. Among data mining techniques, we make use of two data mining techniques, such as clustering analysis and ARM(Association Rule Mining) analysis. In clustering analysis, we use K-means algorithm to figure out the correlation among booths. Through data mining techniques, we figure out that there are two important features to affect visitors' behavior patterns in exhibition. One is the geographical features of booths. The other is the exhibit contents of booths. Those features are considered when the organizer of exhibition plans next exhibition. Therefore, the results of our analysis are expected to provide guideline to understanding visitors and some valuable insights for the exhibition from the earlier phases of exhibition planning. Also, this research would be a good way to increase the quality of visitor satisfaction. Visitors' movement paths, booth location, and distances between each booth are considered to plan next exhibition in advance. This research was conducted at the KIDS & EDU EXPO for Children in SETEC(Seoul Trade Exhibition & Convention), but it has some constraints to be applied directly to other exhibitions. Also, the results were derived from a limited number of data samples. In order to obtain more accurate and reliable results, it is necessary to conduct more experiments based on larger data samples and exhibitions on a variety of genres.