• Transactions on Electrical and Electronic Materials
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• 제12권2호
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• pp.51-55
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• 2011

We investigated the etching characteristics of zinc oxide (ZnO) thin films deposited by the atomic layer deposition method. The gases of the inductively coupled plasma chemistry consisted of $Cl_2$, Ar, and $O_2$. The maximum etch rate was 40.3 nm/min at a gas flow ratio of $Cl_2$/Ar=15:5 sccm, radio-frequency power of 600 W, bias power of 200 W, and process pressure of 2 Pa. We also investigated the plasma induced damage in the etched ZnO thin films using X-ray diffraction (XRD), atomic force microscopy and photoluminescence (PL). A highly oriented (100) peak was present in the XRD spectroscopy of the ZnO samples. The full width at half maximum value of the ZnO sample etched using the $O_2/Cl_2$/Ar chemistry was higher than that of the as-deposited sample. The roughness of the ZnO thin films increased from 1.91 nm to 2.45 nm after etching in the $O_2/Cl_2$/Ar plasma chemistry. Also, we obtained a strong band edge emission at 380 nm. The intensities of the peaks in the PL spectra from the samples etched in all of the chemistries were increased. However, there was no deep level emission.

• 한국대기환경학회지
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• 제28권2호
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• pp.142-158
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• 2012

This paper investigates the physical and chemical characteristics of long-range transport (LRT) process of air pollutants by employing the MM5-CMAQ and its comparison with local emission dominant (LED) case over northeast Asia. We first classified high air pollution days into LRT and LED cases based on the synoptic meteorological variables of vorticity and geostrophic wind speed/direction at a geopotential level of over 850hPa. LRT cases are further categorized into three types of transport patterns (LRT-I-III) according to the air mass pathways from source regions. LRT-I-III are originated from northern, central, and southern China, respectively, identified by back trajectory analysis. Three LRT-I-III groups have different and unique locations of high pressure and transport pathways. The chemical characteristics showed that the simulated spatial distributions varied in terms of locations of maximum concentrations and the temporal variation of surface concentrations. The primary air pollutants such as $NO_x$, $PM_{10}$ and $SO_2$ of all of three LRT cases are well transported into Korea peninsula with different concentration levels. Of LRT cases, LRT-II has the greatest effect on air quality of Korea peninsula, followed by LRT-I and LRT-III. In comparison with LRT, the LED case shows relatively higher air pollution concentrations in general, but showed a variety of different air quality levels following the emission strength pattern. These widely varying patterns are impling the case dependent multi-directional approach for the development of indicators of long-range transport process over northeast Asia.

• 한국결정성장학회지
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• 제21권4호
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• pp.137-146
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• 2011

Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on GaN/sapphire and Si substrate from Zn vapor deposition without catalysts. Experimental results showed that the number density, diameter, crystallinity and degree of the alignment of ZnO NWs depended strongly on both the substrate position and kind of the substrates used for the growth. The photoluminescence (PL) characteristics of the grown ZnO NW arrays exhibit a strong and sharp ultraviolet (UV) emission at 379 nm and a broad weak emission in the visible range, indicating that the obtained ZnO NWs have a high crystal quality with excellent optical properties. The as-grown ZnO NWs were characterized by using scanning electron microscopy (SEM), high resolution transmission electronic microscopy (HR-TEM), and X-ray diffraction (XRD).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.78-78
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• 2011

수열합성법을 이용하여 Si(111) 기판에 ZnO 박막을 성장하였다. ZnO 박막의 성장을 위한 씨앗층은 plasma-assisted molecular beam epitaxy (PA-MBE)를 이용하였다. 씨앗층의 표면 거칠기(root-mean-square roughness)는 2.5 nm이고, 씨앗층 위에 성장된 ZnO 박막은 다양한 크기의 입자들로 이루어져 있었으며 두께는 약 $1.8{\mu}m$로 매우 일정하였다. 배향성을 알아보기 위하여 texture coefficient (TC)를 계산해 보았다. TC(100)과 TC(200)은 a-축 배향성을, TC(002)는 c-축 배향성을 나타내는데, c-축으로 더 우세한 배향성(99.5%)을 보였다. TC 비율(TCa-axis/TCc-axis)은 열처리 온도를 $700^{\circ}C$까지 올렸을 때, 점차적으로 증가하였고, 그 이상의 열처리 온도(< $900^{\circ}C$)에서는 급격히 감소하였다. 잔류응력과 Zn와 O의 bond length도 유사한 경향을 보였다. $700^{\circ}C$까지 열처리 온도가 증가함에 따라, 잔류응력은 증가하였고 bond length는 감소하였다. Near-band-edge emission (NBE)의 피크 강도는 열처리 온도가 $700^{\circ}C$까지 증가함에 따라 점차적으로 증가하였다. 열처리 온도가 $800^{\circ}C$ 이상 증가함에 따라 deep-level emission (DLE)가 적색편이(red-shift)하였다. $700^{\circ}C$로 열처리를 한 ZnO 박막이 가장 우세한 (002)방향의 배향성을 보였을 뿐만 아니라 가장 큰 발광효율 증가를 보였다.

• 한국지구과학회지
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• 제28권5호
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• pp.572-584
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• 2007

The quantification of ammonia concentrations has received a lot of scientific attention. Numerous devices for the quantification of $NH_3$ in the ambient air have been developed to provide more technical possibilities for research in abating $NH_3$ emission from various source processes. For the proper quantification of $NH_3$, a number of sampling methods have been discussed by grouping them into different categories based on the principle of functioning. In general, active samplers employ pumps to draw air in, while passive samplers are exposed to air over a certain period of time to obtain integrated signature of $NH_3$. In case of the former, impingers and absorption flasks can be employed simultaneously with suitable absorbents to capture $NH_3$ passing through them. The methods of analysis include both in-situ and laboratory determination. In the laboratory, colorimetric or ion chromatographic methods are generally used for its quantification. In the field, a number of real time analyzers have been proven to be useful. These real time analyzers can be grouped according to their principle of operation. These analyzers may use the principle of spectroscopy (e.g. DOAS), photoacousticics (e.g. photoacoustic monitor) or Chemiluminescence ($NO_x$ analyzer). The automated annular denuder sampling system with on-line analyzer is also suitable for continuous monitoring of ammonia in air.

• 청정기술
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• 제15권1호
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• pp.1-8
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• 2009

전 세계적으로 급성장하고 있는 자동차연료로 압축천연가스(CNG)의 사용이 일반화되고 있다. 1996년도에 100만 대이던 CNG자동차가 2006년도에는 5배가 증가하였으며, 지금도 계속 증가하고 있는 추세이다. CNG연료는 가솔린 및 디젤연료에 비하여 효율적이고 완전연소에 가까워 청정연료로서 적합하다. 또한 배출 가스로서 일산화탄소, 탄화수소 및 질소산화물 등이 다른 연료에 비하여 유리하며, 경제적인 면에서도 투자가치가 있다. 본 연구에서는 천연가스자동차의 환경적인 특성화 효율적이고 경제적인 면에서 고찰하고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권4호
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• pp.575-594
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• 2010

In this study, we propose a space search algorithm (SSA) and then introduce a hybrid optimization of fuzzy inference systems based on SSA and information granulation (IG). In comparison with "conventional" evolutionary algorithms (such as PSO), SSA leads no.t only to better search performance to find global optimization but is also more computationally effective when dealing with the optimization of the fuzzy models. In the hybrid optimization of fuzzy inference system, SSA is exploited to carry out the parametric optimization of the fuzzy model as well as to realize its structural optimization. IG realized with the aid of C-Means clustering helps determine the initial values of the apex parameters of the membership function of fuzzy model. The overall hybrid identification of fuzzy inference systems comes in the form of two optimization mechanisms: structure identification (such as the number of input variables to be used, a specific subset of input variables, the number of membership functions, and polyno.mial type) and parameter identification (viz. the apexes of membership function). The structure identification is developed by SSA and C-Means while the parameter estimation is realized via SSA and a standard least square method. The evaluation of the performance of the proposed model was carried out by using four representative numerical examples such as No.n-linear function, gas furnace, NO.x emission process data, and Mackey-Glass time series. A comparative study of SSA and PSO demonstrates that SSA leads to improved performance both in terms of the quality of the model and the computing time required. The proposed model is also contrasted with the quality of some "conventional" fuzzy models already encountered in the literature.

• Journal of Biosystems Engineering
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• 제38권3호
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• pp.208-214
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• 2013

Purpose: Performances of a tractor diesel engine fueled by three different animal fats biodiesels were evaluated comparing with light oil tractor in terms of power, fuel consumption rate, exhaust gases, particulate matter amount and field work capacity. Methods: Animal fats based on pig biodiesel were manufactured manually and tested for its engine performance in the tractor diesel engine and fuel adoptability in the field works. Four different fuels, three different content of biodiesel (BD20, BD50, BD100) and light oil, were prepared and tested in the four strokes diesel engine. Power output, fuel consumption rate and exhaust gases of the four fuels in the diesel engine were compared and discussed. Results: Power output of light oil engine was the greatest showing 5.3% difference between light oil and BD100, but 0.37% better power than BD20 engine power. Less exhaust gases of $CO_2$, CO, $NO_X$ and THC were produced from animal fats biodiesel than light oil, which confirmed that biodiesel is environmental friendly fuel. For fuel adoptability in the tractor, biodiesel engine tractor showed its fuel competitiveness comparing with light oil for tractor works in the faddy field. Conclusions: With four different fuel types of animal-fats biodiesel, performances of a four cylinder diesel engine for tractor were evaluated in terms of power, exhaust gases, particulate matters (PM) and field work capacity. No significant differences observed in the engine performances including power output and exhaust gases emission rate. No significant power difference observed between the various fuels including light oil on the engine running, however, amounts of noxious exhaust gases including $CO_2$ and $NO_X$ decreased as biodiesel content increased in the fuels. Field performances of animal-fats biodiesel tractor were investigated by conducting plowing and rotary operation in the field. Tilling and rotary performance of light oil tractor and BD20 tractor in the field were compared, in which about 10% travelling speed difference on both operations were monitored that showed light oil tractor was superior to BD20 tractor by 10%. Animal-fats can be an alternative fuel source replacing light oil for agricultural machinery and an environmental friendly fuel to nature.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.386-386
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• 2012

For white light emitting diode (LED) applications, it has been reported that Y3Al5O12:Ce3+ (YAG:Ce) in nano-sized phosphor performs better than it does in micro-sized particles. This is because nano-sized YAG:Ce can reduce internal light scattering when coated onto a blue LED surface. Recently, there have been many reports on the synthesis of nano-sized YAG particles using bottom-up method, such as co-precipitation method, sol-gel process, hydrothermal method, solvothermal method, and glycothermal method. However, there has been no report using top-down method. Top-down method has advantages than bottom-up method, such as large scale production and easy control of doping concentration and particle size. Therefore, in this study, nano-sized YAG:Ce phosphors were synthesized by a high energy beads milling process with varying beads size, milling time and milling steps. The beads milling process was performed by Laboratory Mill MINICER with ZrO2 beads. The phase identity and morphology of nano-sized YAG:Ce were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. By controlling beads size, milling time and milling steps, we synthesized a size-tunable and uniform nano-sized YAG:Ce phosphors which average diameters were 100, 85 and 40 nm, respectively. After milling, there was no impurity and all of the peaks were in good agreement with YAG (JCPDS No. 33-0040). Luminescence and quantum efficiency (QE) of nano-sized YAG:Ce phosphors were measured by fluorescence spectrometer and QE measuring instrument, respectively. The synthesized YAG:Ce absorbed light efficiently in the visible region of 400-500 nm, and showed single broadband emission peaked at 550 nm with 50% of QE. As a result, by considering above results, high energy beads milling process could be a facile and reproducible synthesis method for nano-sized YAG:Ce phosphors.

• 전기학회논문지
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• 제67권10호
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• pp.1317-1321
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• 2018

PVDF as a semicrystal polymer, having a structure with C-F dipole moments, has been widely investigated because of its excellent chemical stability, mechanical strength, and ferroelectricity. In this study, ferroelectic ${\beta}$ type - PVDF layer was prepared by using an electrostatic spray deposition method and the effects of the addition of Ni-nitrate in precursor solution on the properties of PVDF layer were evaluated. Crystallinity and chemical structure of the PVDF layer were analyzed by a X-ray diffraction and Fourier Transform Infrared Spectrophotometer. Surface structure and fractured cross section of the layer were examined by a field emission-scanning electron microscope. LCR meter was used to obtain the dielectric properties of the layer. As the addition of an inorganic metal salt in PVDF sol, ${\beta}$ type - PVDF crystals were appeared in the hydrated metal salts doped-layer since the strong hydrogen bondings $(O-H{\cdots}F-C)_n$ due to high polarity of OH- were formed.