• Journal of the Korean Magnetics Society
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• v.20 no.6
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• pp.212-215
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• 2010

Spin polarized tunneling studies were carried out with Al-Ga bilayer as a spin detector, by Meservey-Tedrow technique. The superconductor (SC)/Insulator (I)/Ferromagnet (FM) tunnel junctions were provided by ultra high vacuum molecular beam epitaxy (UHV-MBE) technique. The analysis of interfacial properties in the Al-Ga bilayer was also carried out by Auger electron spectroscopy. It was observed that the superconducting transition temperature and energy gap were raised in comparison with that of bulk Ga and pure ultrathin Al films. Current studies clearly show how one can modify the material properties at the interface just with a few monolayers.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.275-280
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• 2004

Augmentation of heat transfer by ultrasonic vibration in pipes are investigated. Measurements of convective heat transfer coefficients on circular pipe walls are made with and without ultrasonic vibration applied to water. These data are compared with each other to quantify the effects of ultrasonic vibration on heat transfer enhancement. Numerical analysis has been also performed in order to extend the ranges of examined temperature and flow rate. FLUENT Ver.6.1 is used to simulate velocity and temperature fields and evaluate heat transfer coefficient with and without ultrasonic vibration. The results show that the ultra- sonic vibration enhances the Nusselt number of forced convection flow and the increase rate strongly depends on flow rate.

• Journal of the Korean Magnetics Society
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• v.4 no.1
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• pp.44-47
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• 1994

High $T_{c}$ superconducting $Y_{1}Ba_{2}Cu_{3}O_{7-\delta}$ thin film was grown up for c-axis orientation by epitaxial growth method on $LaAlO_{3}$ single crystal substrate. The crystal structures of this thin film were found to be c-axis orientation by X-ray diffraction patterns. Hall effect and resistivity measurements were made by van der Pauw method. Hall resistivity was calculated from the magnetoresistivity by considering thermomagnetic effect. The relation was $pH=p_{s}tan{\alpha}_{n}-QBT\frac{S_s}{K_s}$ The measured Hall resistivity and the calculated one are in good agreement each other.

• Journal of the Korean Society of Visualization
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• v.20 no.2
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• pp.86-92
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• 2022

Pipe failure due to thermal fatigue and environmental regulations are increasing the importance of pipe monitoring systems in industrial plants. Since most pipe monitoring systems are focus on external crack inspected, it is necessary to temperature and concentration measuring monitoring system inside the pipe. These systems have spatial uncertainty due to sample inspection by one-point measurement. In addition, real-time measurement is not possible due to the limitation of time delay due to contact measurement. In this study, CT-TDLAS (Computed tomography-Tunable diode laser absorption spectroscopy) apply to overcome the limitations of existing methods. Lasers exhibiting an absorption response at a wavelength of 1395 nm were arranged in a lattice pattern on measuring cell. It showed that the inside of the pipe changed to an unstable combustion state over time.

• Journal of the Korean Society of Visualization
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• v.22 no.3
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• pp.70-77
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• 2024

The objective of this study is to experimentally measure condensation heat transfer at the vapor-liquid interface of boiling bubbles generated in subcooled water. Rainbow Schlieren Deflectometry (RSD) is an optical technique that allows for the non-intrusive visualization of the temperature gradient field in liquid. It is known that the refractive index of a liquid changes as a function of temperature. When light passes through a liquid medium, the degree of deflection is proportional to the spatial gradient of the temperature field. The deflected light passes through a rainbow filter with a continuous variation in color from the center to the outer boundary. As a result, the temperature gradient field in the liquid can be visualized as a color contour. Boiling experiments in a pool of subcooled water were conducted to visualize the temperature gradient field near the vapor-liquid interface of a vapor bubble. A set of RSD images was obtained for the entire life cycle of a boiling bubble, from nucleation through growth to departure from the heating wall. The temperature gradient field near the vapor-liquid interface around the bubble was carefully analyzed. The condensation heat transfer coefficient was calculated and compared to existing prediction models.

• Fire Science and Engineering
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• v.28 no.5
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• pp.23-29
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• 2014

The present study has been conducted to investigate the validity of the computational fire model and the results predicted by BRANZFIRE zone model and FDS field model are compared with a real scale fire test with spray fire in a multi-compartment. The liquid spray fires fueled with toluene and methanol are used as the fire source and the quantitative measurement of heat release rate is performed in an isolated ISO-9705 compartment with a standard door opening. The temperature field predicted by FDS model showed good agreement with the measurement in the fire room and the corridor, and BRANZFIRE model also gave acceptable result in spite of its simplicity and roughness. The mean temperature predicted by FDS model corresponds with measurement within maximum discrepancy range of 25% and the overall mean value of FDS model matched well with experimental data less than 10%. This study can contribute to establish the limitation and application scope of computational fire model and provide reference data for applying to reliable fire risk assessment.

• Fire Science and Engineering
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• v.33 no.5
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• pp.37-47
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• 2019

In the present study, the influences of the fire curtain and natural vent in a theater fire were investigated through the numerical simulation of a reduced-scale model of a theater fire using the Fire Dynamics Simulator (FDS). Based on a previous experimental study using the reduced-scale model, the 1/14 reduced-scale model and its conditions were constructed according to the law of similarity with a real-scale theater. Through a series of numerical simulations, the smoke movements were visualized, and the temperatures in the stage and auditorium, mass flow rate of the outflow through natural vent, and time at which smoke started moving toward the auditorium were measured and analyzed. The general trends on the effects of the fire curtain and natural vent during the theater fire predicted by the present numerical simulation were similar to the previous experimental results. For quantitative comparison of the present numerical simulation and previous experimental results, the mean percentage errors of temperatures in the stage and auditorium, and the mass flow rate of outflow through the natural vent were calculated. The present numerical simulation results showed good agreement with previous experimental results with reasonable accuracy.

• Food Engineering Progress
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• v.15 no.3
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• pp.230-234
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• 2011

The objective of this study was to optimize the thermal condition and determine the shelf life of heated Chunbokjang product. The optimum thermal condition of heated Chunbok-jang product was determined by sensory test, and heat penetration curve was obtained by Thermal Microprocessor. Sterilization time was a 21~23 min until $F_0$ value reached 9 min, depending upon the number of abalone. As solid content was reduced and temperature of sterilization was increased, the thermal death time was decreased. The score of sensory test indicated that there was no significant difference in flavor of heated Chunbok-jang product made at different sterilization temperatures (110, 121.1, 125, and $130^{\circ}C$). Heated Chunbok-jang product, however, sterilized at $125^{\circ}C$ showed the highest score in texture and taste values. Salinity and pH were not changed during seven month storages, but texture became firmer, and any microorganism had not been detected from the heated chunbok-jang product during these periods. As a result of storage experiment, the shelf-life of heated Chunbok-jang product was 3-month at room temperature.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.968-974
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• 2000

Nb$_2$O$_{5}$와 MnO 첨가에 따른 Pb$_{0.6}$Sr$_{0.4}$TiO$_3$반도체 세라믹의 미세구조와 전기적 특성은 유전특성, I(current)-V(voltage) 측정, 그리고 복소 임피던스 측정 등을 이용하여 고찰하였다. Nb 도핑량이 0.4 mol% 이하인 경우 Nb 도핑량에 따라 전도성과 입성장은 증가되었으나 그 이상의 도핑량에서는 Sr이나 Pb 공공의 생성으로 인하여 전도성이 감소되고 입성장도 억제되는 것을 관찰할 수 있었다. 0.4 mol% Nb-doped Pb$_{0.6}$Sr$_{0.4}$TiO$_3$에 0.01 mol% MnO를 첨가한 경우 비저항비($ho$$_{max}$/$\rho$/min/)가 $10^2$에서 $10^4$으로 크게 향상되었다. 그리고 전이 온도 주변에서 여러 개의 변곡점을 지니는 비옴성 거동이 발견되었다. 이와 같은 현상은 입계에 존재하는 Mn 이온이 부분적으로 편석되어 표면 전하의 보상 효과에 영향을 미치는 것이라고 사료된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.142-152
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• 1992

This paper presentes a new method to measure high electric field (or high voltage) by using crystalline SiO2 which has very high half wave voltage. There are many difficulties in measuring high electric field using other crystals which have generally low half wave voltage.By applying Stokes parameter and Mueller matrix. We derive optical modulation equation in the sensor which is composed of a polarizer, and Mueller matrix, we derive optical modulation equation in the sensor which is composed of a polarizer, a Pokels material, and an analyzer, We theoretically analyzed electro-optic effect, and calculated the phase retardation and half wave volt age of the birefringent material. The designed optical valtage sensor has very excellent linearity up to 20KV without divided volt-age. The maximum error was measured within 3%. Before annealing of Sio2 crystal, the maximum variation of the output voltage is 7.5% with varying temperature from \ulcorner20˚c to 60˚c. But, after annealing of SiO2 crystal, the output voltage variation is improved within 1%error.