• Journal of the Korean Magnetics Society
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• v.9 no.5
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• pp.239-244
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• 1999

Bi-doped lanthanum magnetics $(La_{0.67-x}Bi_xCa_{0.33}MnO_3(x\;=\;0,\; 0.04,\; 0.1,\; 0.2))$ samples have been prepared by standard ceramic process. The crystallinity and microstructures of the samples have been investigated by x-ray diffractometry and optical microscopy, respectively. The magnetic and magnetoresistive properties of the samples have been measured by vibrating sample magnetometery and van der Pauw method, respectively, at the temperatures ranging of 100 K~300 K with applied magnetic field of 0.4~0.5 T. Good crystallinity and high Curie temperature (275 K) have been obtained for the Bi-doped samples with small dosage (x = 0.04, 0.1) even they were sintered at 120$0^{\circ}C$, which is about 20$0^{\circ}C$ lower than normal sintering temperature of 140$0^{\circ}C$. The Bi-doped samples with the small dosage showed lower relative electrical resistivity and higher magneto-resistive ratio compared to the undoped sample in the most temperatures measured. The Bi-doped samples also exhibited large magnetoresisitve ratio (maximum of 15% for x = 0.1) at room temperature even under a weak magnetic field of 0.4 T.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1071-1075
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• 2003

In a closed square cavity filled with a liquid, a cooled the upper horizontal wail and a heated the lower horizontal wall, the flow isn't generated under the ground-based condition when Rayleigh number is lower than 1700. In such case the flow phenomena near an air bubble under a cooled horizontal wall were investigated. The temperature and the flow fields were studied by using the Thermo-sensitive Liquid-Crystal and the image processing. The qualitative analysis for the temperature and the flow fields were carried out by applying the image processing technique to the original data. Injecting bubble at the center point of upper cooled wall, the symmetry shape of two vortexes near an air bubble was observed. The bubble size increased, the size of velocity and the magnitude of velocity increased. In spite of elapsed time, a pair of two vortexes was the unique and steady-state flow in a square cavity and wasn't induce to the other flow in the surround region.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.879-888
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• 2009

Unsteady three-dimensional reacting flowfield generated by transverse hydrogen injection into a supersonic mainstream is numerically investigated using DES and finite-rate chemistry model. Comparisons are made with experimental results to investigate the turbulent reacting flow physics. The numerical OH distribution describes well the experimental OH-PLIF result, while the numerical ignition delay time shows some disparity due to the restricted available experimental data. The intermittency phenomena are identified by the comparative analysis between RANS and DES. Those effects are also quantified by the temperature distributions along streamlines and superimposed OH mass fraction along with time.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.352-358
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• 1995

Measurements of the Faraday rotation and magnetization of terbium-doped Hoya FR5 glass and cerium-doped Hoya FR4 glass have been made as a function of temperature T in the range 4.2 K -10 K and of magnetic field H of up to 80 kG at the $Ar^+$ laser wavelength of 514.5nm. The saturations of magnetization and Faraday rotation above H/T> $5kG.K^{-1}$ can be analyzed by the quantum theory of paramagnetism. Calculated parameters show that the large Verdet constant of $Ce^{3+}$ glass is due to the effective $4f\rightarrow5d$ electric dipole transition effect and that of $Tb^{3+}$ glass is due to the magnetization effect.effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.426-426
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• 2012

본 연구에서는 GaAs p-i-n 접합 구조에 InAs 양자점을 삽입한 양자점 태양전지(Quantum Dot Solar Cell; QDSC)의 내부 전기장(internal electric field)을 조사하기 위하여 Photoreflectance (PR) 방법을 이용하였다. QDSC 구조는 GaAs p-i-n 구조의 공핍층 내에 8주기의 InAs 양자점 층을 삽입하였으며 각 양자점 층은 40 nm 두께의 i-GaAs로 분리하였다. InAs/GaAs QDSC는 분자선박막 성장장치(molecular beam epitaxy; MBE)를 이용하여 성장하였다. 이 때 양자점의 형성은 InAs 2.0 ML(monolayer)를 기판온도 $470^{\circ}C$에서 증착하였다. QDSC 구조에서 여기광원의 세기에 따른 전기장의 변화를 조사하였다. 아울러 양자점 층 사이의 i-GaAs 층 내에 6.0 nm의 AlGaAs 퍼텐셜 장벽(potential barrier)을 삽입하여 퍼텐셜 장벽 유무에 따른 전기장 변화를 조사하였다. PR 측정에서 여기광원으로는 633 nm의 He-Ne 레이저를 이용하였으며 여기광의 세기는 $2mW/cm^2$에서 $90mW/cm^2$까지 변화를 주어 여기광세기 의존성실험을 수행하였다. 여기광의 세기가 증가할수록 photovoltaic effect에 의한 내부 전기장의 변화를 관측할 수 있었다. PR 결과로부터 p-i-n 구조의 p-i 영역과 i-n 접합 계면의 junction field를 검출하였다. p-i-n의 i-영역에 양자점을 삽입한 경우 PR 신호에서 Franz-Keldysh oscillation (FKO)의 주파수가 p-i-n 구조와 비교하여 변조됨을 관측하였다. 이러한 FKO 주파수성분은 fast Fourier transform (FFT)을 이용하여 검출하였다. FKO의 주파수 성분들은 고전기장하에서 electron-heavyhole (e-hh)과 electron-lighthole (e-lh) 전이에 의해 나타나는 성분으로 확인되었다.

• Tunnel and Underground Space
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• v.23 no.5
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• pp.372-382
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• 2013

Thermal-hydro-mechanical (THM) modeling is a critical R&D issue in the performance and safety assessment of a high-level waste repository. With an $\ddot{A}$sp$\ddot{o}$ prototype repository, its thermal behavior was analyzed and then compared with in-situ experimental data for its validation. A model simulation was used to calculate the temperature distributions in the deposition holes, deposition tunnel, and surrounding host rock. A comparison of the simulation results with the experimental data was made for deposition hole DH-6, which showed that there was a temperature difference of $2{\sim}5^{\circ}C$ depending on the location of the measuring points, but there was a similar trend in the evolution curves of temperature as a function of time. It was expected that the coupled modeling of the thermal behavior with the hydro-mechanical behavior in the buffer and backfill of the $\ddot{A}$sp$\ddot{o}$ prototype repository would give a better agreement between the experimental and model calculation results.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.7
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• pp.944-954
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• 2007

The Purpose of this study was to investigate overall sanitation levels of restaurants in Korea by examining sanitation management. Sanitation inspections were carried out in 200 large Korean, Western, Chinese, and Japanese restaurants and in buffet-style restaurants of over 100 pyeong in size located in Daegu and Gyeongbuk province. This survey of sanitation management practices found that in large restaurants employing many workers, sanitation management was good in the areas of the kitchen environment, equipment and utensils, food handling, and worker's personal hygiene. Restaurants having relatively large kitchens showed significantly high scores in these sanitation areas. Furthermore, open-kitchen-type restaurants showed significantly higher scores in kitchen sanitation compared with closed-kitchen-type restaurants. Survey results of sanitation management show that, in all restaurants surveyed, sanitation management was good in dining hall sanitation and in providing a safe drinking water supply, but poor in food handling sanitation. Kitchen environment sanitation was poor in Korean, Chinese, and Japanese restaurants. Equipment and utensils sanitation was unsatisfactory in Western and buffet-style restaurants. In the food handling area, especially food sanitation and temperature, checks were rarely made, and pasteurization and temperature records were not kept. Therefore, it is recommended that, in planning a kitchen facility in the future, the floor area should be as large as Possible and open. In terms of management, more attention should be paid to food pasteurization, sanitation of cooking equipment and utensils, and checking of food temperature.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.55.2-55.2
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• 2010

최근 태양전지에 대한 연구가 본격적으로 진행 중인 가운데 Local back contact 태양전지에 대한 연구가 새로운 이슈로 떠오르고 있다. LBC 구조의 태양전지는 후면 passivation에 대한 최적화 공정이 가장 중요하다. 후면 passivation으로 사용되는 물질로는 $SiO_2$, SiNx, $Al_2O_3$ 등의 산화막이 대표적이다. 본 연구에서는 LBC 구조 태양전지의 후면 passivation 박막으로 사용되는 $SiO_2$ 산화막의 공정가변에 따른 박막의 특성을 비교 분석하였다. $SiO_2$ 성장은 RTP를 사용하였다. 성장 온도 $850^{\circ}C$의 온도에서 진행하였으며, 4L/min의 $O_2$분위기에서 진행하였다. 공정 시간 5분 일 때 12.5nm, 15분 일 때 21.7nm의 두께의 박막을 성장 시킬 수 있었다. Carrier lifetime 확인 결과 박막의 두께가 얇을수록 lifetime이 향상함을 확인 할 수 있었고, C-V 측정을 통한 charge 비교를 통해 두께가 얇은 박막 일수록 더 적은 positive charge를 갖고있는 것을 확인 할 수 있었으며 이를 통해 passivation 효과가 우수함을 확인 할 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.123.2-123.2
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• 2011

$ALU^+$ 태양전지는 PN접합을 후면에서 즉, Al을 소성하여 형성시키기 때문에 얼마나 균일하고 두껍게 형성하는 것이 가장 중요하다. 소성(Firing)은 태양전지 제조 과정에서 후면의 접촉을 위한 중요한 공정이다. 본 연구에서는 상업화가 가능한 n-type $ALU^+$ Emitter 태양전지에서 소성 횟수에 따른 특성을 연구 하였다. $ALU^+$ emitter 형성의 최적화를 위해 소성온도를 가변하고, 최적화된 온도에서 소성 횟수에 따른 DIV 측정을 통해 셀을 분석 하였다. 소성 횟수는 1~3회로 하였고, 그 결과 단락전류 밀도(Jsc)가 33.57mA/$cm^2$로 처음보다 15.1%증가 하였고, 곡선인자(Fill Factor)는 3회에서 66.04%로 218%증가 하였다. Al을 짧은 시간 안에 소성을 시키므로 해서 후면의 $P^+$ Emitter가 균일하게 형성되었기 때문에 개방전압(Voc)의 증가를 확인하였다. 본 연구를 통해 $ALU^+$ 태양전지의 후면 Aluminium 소성 조건의 최적화를 통하여 $ALU^+$ emitter가 충분히 형성되지 못하면 누설전류가 발생되고 직렬저항(Rs)이 크게 증가하여 개방전압(Voc) 및 단락전류밀도(Jsc)의 감소가 발생하게 되고, 직렬저항(Rs)의 증가와 병렬저항(Rsh)의 감소는 Fill Factor의 급격한 감소를 초래하게 됨을 알 수 있다. 이를 개선하면 태양전지 효율을 상승시키는 결과를 얻을 수 있음을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.927-933
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• 2007

Heat transfer characteristic near a sharp fin was studied in a supersonic flow. Mach number and the Reynolds number were 3 and $5{\times}10^7$ respectively. Infra-red thermography was used to obtain the variation of surface heat transfer coefficient distribution. The angles of attack were ranged from $12.5^{\circ}$ to $20^{\circ}$ and the numerical analysis and the oil flow method were conducted to understand flow fields near a sharp fin.