• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.560-567
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• 2006

Although various conjectures have been proposed to explain abnormal increase in thermal conductivity of nanofluids, the detailed mechanism could not be understood and explained yet. The main reason is primarily due to the lack of knowledge on the most fundamental factor governing the mechanisms such as Brownian motion, liquid layering, phonon transport, surface chemical effects and agglomeration. By applying surface complexation model for the measurement data of hydrodynamic size, zeta potential, and thermal conductivity, we have shown that sulfate charge state is mainly responsible for the increase in the present condition and may be the factor incorporating all the mechanisms as well. Moreover, we propose a new model including concepts of fractal and interfacial layer. The properties such as thickness and thermal conductivity of the layer are estimated from the surface charge states and the concept of electrical double layer. With this, we could demonstrate the pH dependences of the layer properties and eventually of the effective thermal conductivity of the nanofluid.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1999.11a
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• pp.157-161
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• 1999

본 연구에서 직물의 열, 수분 전달특성과 KES-FB의 역학적 특성치, 직물표면의 fractal dimension을 측정하여 주관적 의복 착용 쾌적감을 예측하고자 하였다. 실험의복에 사용된 직물은 면 100% 평직물, 면/PET 혼방직물, 피치가공된 면/PET 혼방직물, PET 100% 평직물, 알칼리 감량가공된 PET 100% 크레이프 직물이었으며, 실험의복의 형태는 긴 소매 셔츠로 하였다. 착용실험은 온도 29$\pm$0.5$^{\circ}C$, 상대습도 75$\pm$2%RH, 기류 0.15m/s를 유지하는 항온항습실에서 실시하였고 36명의 여성 피험자(20-23세)들이 참여하였다. 의복 착용감의 하위 구성차원을 파악하기 위해 실험결과를 요인분석한 결과 5 개의 요인으로 추출되었다. 제 1 요인은 체온상승, 수분특성과 관련이 있는 온열.발한감이었으며, 제 2 요인은 무게ㆍ두께감, 제 3 요인은 회복특성감, 제 4 요인은 표면접촉감, 제 5 요인은 온냉감으로 구성되었다. 직물의 표면특성을 정량화하는 방법으로 도입한 fractal dimension 의 분석값들과 종래의 가장 보편적으로 이용되어 온 KES_FB 의 표면 특성치들이 주관적 착용쾌적감 예측에 얼마나 기여하는지 비교해 본 결과, 표면접촉감은 fractal dimension, 접촉점들의 총면적, 접촉점들의 평균 axis ratio, MMD, SMD와 높은 상관을 나타내었다. 또한 종합적 착용쾌적감에 대해서는 SMD 를 제외한 척도들이 유의한 상관을 보였으며, 그 중에서도 fractal dimension 과 접촉점들의 총면적은 0.8 이상의 높은 상관을 나타내었다. 착용쾌적감을 예측하기 위한 회귀분석결과에서는 fractal dimension 만으로 쾌적감의 74%가 설명되었으며 공기 투과도를 첨가하면 두 변수로 $R^2$=.792가 되었다. 설명되는 누적분산값은 67.18%였다.주관적 평가의 결과와 객관적 평가 결과를 이용해 마직물의 태를 평가하는 산출식을 제시하였다. 태 평가치의 경우 16가지 특성치를 모두 넣는 방법과 stepwise 방법, 또 Kawabatark 사용한 순차적 군 회귀법의 세가지 방법의 회귀식 중 16가지 특성치를 모두 넣는 방법의 결정계수가 가장 높았다.tosterone농도는 107.7$\pm$12.0 pmol／l이었고, 남성의 타액내 농도는 274.2$\pm$22.1 pmol／l이었다. 이상의 결과로 보아 본 연구에서 정립된 EIA 방법은 RIA를 대신하여 소규모의 실험실에서도 활용할 수 있을 것으로 사려된다.또한 상실기 이후 배아에서 합성되며, 발생시기에 따라 그 영향이 다르고 팽창과 부화에 관여하는 것으로 사료된다. 더욱이, 조선의 ${\ulcorner}$구성교육${\lrcorner}$이 조선총독부의 관리하에서 실행되었다는 것을, 당시의 사범학교를 중심으로 한 교육조직을 기술한 문헌에 의해 규명시켰다.nd of letter design which represents -natural objects and was popular at the time of Yukjo Dynasty, and there are some documents of that period left both in Japan and Korea. "Hyojedo" in Korea is supposed to have been influenced by the letter design. Asite- is also considered to have been "Japanese Letter Jobcheso." Therefore, the purpose of this study is to look into the origin of the letter designs in t

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.400-405
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• 2018

This paper presents a compact ultra-wideband (UWB) flexible monopole antenna design on a paper substrate. The proposed antenna is made of iterations of a circular slot inside an octagonal metallic patch. This fractal-based geometry has been deployed to achieve compactness along with improved bandwidth, measured reflection coefficient -10 dB bandwidth ranging from 2.7 to 15.8 GHz. The overall size of the antenna is $26mm{\times}19mm{\times}0.5mm$, which makes it a compact one. The substrate used is paper and the main features like environment friendly, flexibility, green electronics applications and low cost of fabrication are the key factors for the proposed antenna. The aforementioned UWB prototype is suitable for many wireless communication systems such as WiMAX, WiFi, RFID and WSN applications. Antenna has been tested for the effect of bending by placing it over a curved surface of a very small radius of 10 mm.

• Journal of the Korean Association of Geographic Information Studies
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• v.9 no.3
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• pp.123-135
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• 2006

In this study, in order to maximize the accuracy and efficiency of the existing interpolation method fractal methods are applied. Developed FEDISA model revives the irregularity of the real topography with only a few information about base topography, which can produce almost complete geographic information. Moreover, as a tool for examining the adaptability and efficiency of the model, index of slope range $I_{SR}$, index of surface $I_{SA}$, and index of volume $I_V$ were developed. The model area is respectively set to $75m{\times}75m$, $150m{\times}150m$, $300m{\times}300m$, $600m{\times}600m$, and $1,200m{\times}1,200m$, and then the data obtained by combining the existing interpolation methods and FEDISA model were compared with real measurements. The result of the study showed the adaptability and efficiency of FEDISA model in topography restoration.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.335-336
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• 2012

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.9 s.100
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• pp.949-956
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• 2005

In this paper, a new CPW-fed cross shape fractal antenna having a self-affinity is presented. This novel configuration, which has anisotropic scaling symmetry, makes smaller profile characteristic compared to the fractal antenna using a self-similarity. Increase of the iteration coefficient, which leads to decrease of the fundamental resonant frequency, shows a good impedance matching condition and multi-band characteristics due to new surface current paths. The radiation patterns are similar to those of monopole antennas. In the K3 stage of iteration, the proposed antenna shows a measured maximum gain 2.27 dBi at 940 MHz. A commercially available software based on the FDTD algorithm has been used to obtain the predicted results. In addition, an RT/Duroid 5880 substrate has been employed for the experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.20-26
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• 2003

This study proposes the construction of attractor quadrant method for high-precision cutting characteristics evaluation of non-ferrous metals. Also this paper aims to find the optimal cutting conditions of diamond turning machine by measuring surface form and roughness to perform the cutting experiment of non-ferrous metals, which are aluminum, with diamond tool. As well, according to change cutting conditions such as feed rate, using diamond turning machine to Perform cutting Processing, by measuring cutting force and surface roughness and according to cutting conditions the aluminum about cutting properties. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics and attractor quadrant characteristics. In quantitative quadrant feature extraction, 1,309 point in the case of A17075 (one quadrant) and 1,406 point (one quadrant) in the case of brass were proposed on the basis of attractor reconstruction. Proposed attractor quadrant method can be used for high-precision cutting characteristics evaluation of non-ferrous metals.

• Korean Journal of Optics and Photonics
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• v.9 no.2
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• pp.63-69
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• 1998

For detailed characterization of scattering losses occurring in VCSEL's distributed Bragg reflectors, we performed scattering experiment and obtained the information about surface roughness through the analysis of a modified transmission matrix method. The various wafers grown for VCSELs were used for the scattering experiment. The fractal surface assumption and extrapolation is used to estimate the scattered intensity near specular angle. The modified transmission matrix method employed in the analysis considers the scattering loss at each interface and calculates the reflectivity efficiently and easily. As a result, the surface roughness ranges from $4{\AA}$ to $10{\AA}$ The reduction of reflectivity due to the scattering amounts to 0.26% in case of $10{\AA}$ roughness.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.101-107
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• 2017

This study aimed to conduct the basic analysis on the fractal characteristics of cementitious materials. The pore structure of cement paste incorporating ground granulated blast furnace slag (GGBFS) was measured using mercury intrusion porosimetry (MIP) and the fractal characteristics were investigated using different models. Because the pore structure of GGBFS-blended cement paste is an irregular system in the various range from nanometer to millimeter, the characteristics of pore region in the different scale may not be adequately described when the fractal dimension was calculated over the whole scale range. While Zhang and Li model enabled analyzing the fraction dimension of pore structure over the three divided scale ranges of micro, small capillary and macro regions, Ji el al. model refined analysis on the fractal characteristics of micro pore region consisting of micro I region corresponding to gel pores and micro II region corresponding to small capillary pores. As the pore size decreased, both models suggested that the pore surface of micro region became more irregular than macro region and the complexity of pores increased.

• Korean Journal of Remote Sensing
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• v.24 no.2
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• pp.125-131
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• 2008

Hyperspectral imaging is used in a wide variety of research since the image is obtained with a wider wavelength range and more bands than multispectral imaging. However, there are limitations, namely that each band has a shorter wavelength range, the computation cost is increased in the case of numerous bands, and a high correlation between each band and noise bands exists. The previous analysis method does not produce ideal results due to these limitations. Therefore, in the case of using the hyperspectral image, image analysis after eliminating noise bands is more accurate and efficient. In this study, noise band elimination of the hyperspectral image preprocessing is highlighted, and we use fractal dimension for noise band elimination. The Triangular Prism Method is used, being the typical fractal dimension method of the curved surface. The fractal dimension of each band is calculated. We then apply the Continuum Removal method to normalize. A total of 35 bands are estimated by noise band with a threshold value that is obtained empirically. The hyperion hyperstpectral image collected on the EO-1 satellite is used in this study. The result delineates that noise bands of the hyperion image are able to be eliminated with the fractal dimension and Continuum Removal method.