• Journal of Advanced Navigation Technology
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• v.7 no.1
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• pp.51-58
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• 2003

Generally, multi-path is viewed as an undesirable feature of wireless communications. Therefore, diversity reception and adaptive array schemes are proposed to mitigate its effects. Recently, to increase the spectrum efficiency and the link reliability, multiple-input multiple-output (MIMO) scheme is devised to exploit multi-path in a scattering wireless channel. In this paper, we have evaluated the channel capacity of MIMO Multi-Carrier CDMA system in path correlation fading channel. And, the channel capacity of MIMO system is compared with single-input single-output (SISO) system. From the results, the MIMO multi-carrier CDMA system with path correlation yields better performance with respect to channel capacity than a SISO system.

• Journal of the Korean institute of surface engineering
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• v.51 no.4
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• pp.237-242
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• 2018

We report on the fabrication and photoelectrochemical (PEC) properties of a ZnO nanorod array structure as an efficient photoelectrode for hydrogen production from sunlight-driven water splitting. Vertically aligned ZnO nanorods were grown on an indium-tin-oxide-coated glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which was formed by thermally oxidizing a sputtered Zn metal thin film. The structural and morphological properties of the synthesized ZnO nanorods were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated ZnO nanorod photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the vertically aligned ZnO nanorod photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., $0.65mA/cm^2$ at 0.8 V vs Ag/AgCl in a 1 mM $Na_2SO_4$ electrolyte. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs Ag/AgCl, which made the device self-powered.

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.51-56
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• 2019

LuAG:Ce(Lu₃Al₅O₁₂:Ce³⁺) nano phosphor were synthesized by applying the coprecipitation method. It is used to increase the color rendering of phosphor ceramic plate for high power LEDs and laser lighting. Internal quantum efficiency and absorption of LuAG:Ce nano phosphor are 51.5 % and 64.4 %, respectively, which is higher than the previously studied nano phosphors. The maximum absorption wavelength of this phosphor is 450 nm blue light, and the emission wavelength is 510 nm. The emission wavelength shifted to longer wavelength when the concentration of Ce increased in the heat treatment of the reducing atmosphere. Thermal quenching of LuAG nano phosphor was 70 % at 200 ℃, it was explained by their significant quenching of all raman scattering modes, implying the restriction of electron-phonon couplings caused by their defects.

• Clean Technology
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• v.26 no.4
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• pp.251-256
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• 2020

The biocompatibility and plasmonic properties of Au nanoparticles make them useful for photothermal therapy, drug delivery, imaging, and many other fields. This study demonstrated a novel, facile, economic, and green synthetic method to produce gold nanoparticles. Gold nanoparticles (AuNPs) with spherical and triangular shapes were effectively synthesized using only Schisandra chenesis fruit extract as the capping and reducing agent. The shape of the AuNPs could be engineered simply by adjusting the molar concentration of HAuCl4 in the reaction mixture. The as-synthesized AuNPs were characterized using UV-VIS spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), and energy dispersive X-ray analysis (EDXA). This study revealed that by using the HAuCl4 concentration in the AuNP synthesis, the shape and size of the AuNPs could be controlled by the concentration of HAuCl4 and Schisandra chinensis fruit extract as a surfactant. The as-synthesized AuNPs samples had sufficient colloidal stability without noticeable aggregation and showed the predominant growth of the (111) plane of face-centered cubic gold during the crystal growth. The catalytic efficiency of the AuNPs synthesized using Schisandra chenesis fruit extract was examined by monitoring the catalytic reduction of 4-nitrophenol to 4-aminophenol using Ultraviolet-visible spectroscopy (UV-Vis spectroscopy). The synthesized AuNPs showed good catalytic activity to reduce 4-nitrophenol to 4-aminophenol, revealing their practical usefulness.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3470-3477
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• 2022

Soils are porous materials with high shielding capability to attenuate gamma and X-rays. The disposal of radionuclides throughout the soil profile can expose the living organisms to ionizing radiation. Thus, studies aiming to analyze the shielding properties of the soils are of particular interest for radiation shielding. Investigations on evaluating the shielding capabilities of highly weathered soils are still scarce, meaning that additional research is necessary to check their efficiency to attenuate radiation. In this study, the radiation shielding properties of contrasting soils were evaluated. The radiation interaction parameters assessed were attenuation coefficients, mean free path, and half- and tenth-value layers. At low photon energies, the photoelectric absorption contribution to the attenuation coefficient predominated, while at intermediate and high photon energies, the incoherent scattering and pair production were the dominant effects. Soils with the highest densities presented the best shielding properties, regardless of their chemical compositions. Increases in the attenuation coefficient and decreases in shielding parameters of the soils were associated with increases in clay, Fe₂O₃, Al₂O₃, and TiO₂ amounts. In addition, this paper provides a comprehensive description of the shielding properties of weathered soils showing the importance of their granulometric fractions and oxides to the attenuation of the radiation.

• Journal of ILASS-Korea
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• v.28 no.1
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• pp.32-42
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• 2023

In this study, spray characteristics of n-heptane and propane were investigated under different injection pressure using various imaging techniques such as Mie-scattering, DBI (diffuse back-illumination), and Schlieren imaging techniques. NI compact RIO system was used to control a test injector. Spray penetration length, length-to-width ratio and number of black pixels were calculated by using MATLAB software to compare spray characteristics of each fuel. Longer spray penetration length and higher length-to-width ratio were observed in propane spray because of flash boiling caused by high saturated vapor pressure. Spray collapse occurred in propane spray due to the high plume-to-plume interaction. Moreover, rapid evaporation occurred in propane spray, so that nozzle tip wetting could not be observed. Rapid evaporation of propane also caused fewer residual droplets compared to n-heptane spray. Therefore, propane is advantageous in reducing the generation of soot emission from large droplets that are not atomized. However, additional evaluation should be conducted considering combustion efficiency and the possibility of deposits by nozzle tip icing during fuel injection.

• Journal of Ceramic Processing Research
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• v.18 no.11
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• pp.810-814
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• 2017

Proton exchange membrane fuel cells (PEMFCs) are some of the most efficient electrochemical energy sources for transportation applications because of their clean, green, and high efficiency characteristics. The optimization of catalyst layer morphology is considered a feasible approach to achieve high performance of PEMFC membrane electrode assembly (MEA). In this work, we studied the effect of the solvent on the catalyst layer of PEMFC MEAs fabricated using the electrostatic spray deposition method. The catalyst ink comprised of Pt/C, a Nafion ionomer, and a solvent. Two types of solvent were used: isopropyl alcohol (IPA) and dimethylformamide (DMF). Compared with the catalyst layer prepared using IPA-based ink, the catalyst layer prepared with DMF-based ink had a dense structure because the DMF dispersed the Pt/C-Nafion agglomerates smaller and more homogeneously. The size distribution of the agglomerates in catalyst ink was confirmed through Dynamic Light Scattering (DLS) and the microstructure of the catalyst layer was compared using field emission scanning electron microscopy (FE-SEM). In addition, the electrochemical investigation was performed to evaluate the solvent effect on the fuel cell performance. The catalyst layer prepared with DMF-based ink significantly enhanced the cell performance (1.2 A cm-2 at 0.5 V) compared with that fabricated using IPA-based ink (0.5 A cm-2 at 0.5 V) due to the better dispersion and uniform agglomeration on the catalyst layer.

• Analytical Science and Technology
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• v.18 no.1
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• pp.59-65
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• 2005

When the low level radioactivity sample is measured, it is required to have many samples. For increase of the sample volume, a scattering and absorbing probability of the emitted gamma-ray in the sample are to be increased. In order to correct the self-absorption effect, the counting efficiency must be calibrated according to a geometrical condition and sample density. But, it is impossible to determine efficiency for counting sample using standard source with the same geometrical condition and density. In this study, the measuring efficiencies were determined with various counting containers and densities. In order to compare the self-absorption effect with the sample density in the various sample container, the variation of the counting efficiency with the densities was investigated by adding NaI, which has high solubility and density. Also, they were compared with Monte Carlo simulation. The self-absorption effect was found to be significant in the low energy region below 0.5 MeV.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.1
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• pp.109-113
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• 1998

The clay and yellow loess have capability to adsorb and precipitate particles. The removal efficiencyes of those flocculents on the dinoflagellate, Cochlodinium polykrikoides, have been studied in laboratory and in field near Tongyong fish farm in September, 1996. The removal efficiencyes in the laboratory experiment was $43\%$ for $2\;g/{\ell}$, $64\%$ for $6g/{\ell}$ and $88\%$ for $10\;g/{\ell}$ in one hour after dispersion. No big difference of removal efficiency was found between the raw and the acid-activated loess. In the field survey, the removal rates ranged from 72 to $80\%$ in 30 min after the dispersion. The effect of loess scattering on water quality was estimated. The concentrations of dissolved inorganic nitrogen (DIN), chemical of gen demand (COD) and chlorophyll a decreased more or less after dispersion, while the concentration of suspended solid (SS) increased. The concentrations of dissolved oxygen (DO) and dissolved inorganic phosphorous (DIP) were kept constant. These results indicated that the dispersion concentration of more than $10g/{\ell}$ has a good removal efficiency of above $80\%$ without big variation of water quality after dispersion of yellow loess.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.97.1-97.1
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• 2010

유연금속기판위에 DC 마그네트론 스퍼터링을 이용하여 Ag/ZnO 이중구조의 후면반사막을 증착하고 Ag 표면조도 변화에 따른 후면반사막의 반사특성 변화와 플렉서블 비정질 실리콘 박막 태양전지의 셀 특성에 미치는 영향을 조사하였다. Substrate구조를 갖는 플렉서블 실리콘 박막 태양전지에서는 실리콘 박막 광흡수층의 상대적으로 낮은 광 흡수율로 인하여 입사광에 대한 태양전지 내에서의 광 산란 및 포획이 태양전지 효율을 증대시키는데 매우 중요한 역할을 하는 것으로 알려져 있다. 플렉서블 실리콘 박막 태양전지에서의 후면반사막은 광 흡수층에서 흡수되지 않는 입사광을 다시 반사시켜 광 흡수를 증대시키며 이때 후면반사막 표면에서 반사 빛을 효율적으로 산란시켜 이동경로를 증대시킴으로써 광 흡수율을 더욱 향상시킬 수 있다. 본 연구에서는 유연금속 기판위에 Ag와 ZnO:Al($Al_2O_3$ 2.5wt%) 타겟을 사용한 DC 마그네트론 스퍼터링법으로 Ag/AZO 이중구조의 후면반사막을 제조하고, Ag 박막의 표면형상 변화와 이에 따른 후면반사막의 반사도 변화를 비교, 분석하였다. 증착 조건 변화에 따른 표면 형상 및 반사 특성은 Atomic Force Mircroscope(AFM), Scanning electron miroscopy(SEM), UV-visible-nIR spectrometry를 통하여 분석하였다. 서로 다른 표면 거칠기를 갖는 후면반사막 위에 n-i-p구조의 a-Si:H 실리콘 박막 태양전지를 제조한 후 태양전지 동작 특성에 미치는 영향을 조사하였다. n,p층은 13.56MHz PECVD, i층은 60MHz VHF CVD를 사용하여 각각 제조 하였으며, Photo I-V, External Quantum Efficiency(EQE) 분석을 통하여 태양전지 특성을 조사 하였다. SEM 분석결과 공정 온도가 증가 할수록 Ag 박막의 표면 결정립 크기도 증가하였으며, AFM분석을 통한 Root-mean-square(Rms)값은 상온에서 $500^{\circ}C$로 증착온도가 증가함에 따라 6.62nm에서 46.64nm까지 증가하였다. Ag 박막의 표면 거칠기 증가에 따라 후면반 사막의 확산 반사도도 함께 증가하였다. 공정온도 $500^{\circ}C$에서 증착된 후면반사막을 사용하여 a-Si:H 태양전지를 제조하였을 때 상온에서 제조한 후면반사막에 비하여 단락전류밀도 (Jsc)값은 9.94mA/$cm^2$에서 13.36mA/$cm^2$로 증가하였으며, 7.6%의 가장 높은 태양전지 효율을 나타내었다.