• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.159-159
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• 2010

본 논문은 테라헤르츠 소스로 저온 InGaAs를 대체하기 위한 저온 $In_{0.64}Al_{0.36}Sb$의 실리콘(Si) 도핑 농도에 따른 광학적 특성 변화를 photoluminescence (PL)과 time-resolved PL (TRPL) 측정을 이용하여 분석하였다. $In_{0.64}Al_{0.36}Sb$ 시료는 분자선 엑피탁시 (molecular beam epitaxy)법으로 GaAs 기판 위에 약 $420^{\circ}C$에서 $3.7\;{\mu}m$ 두께 성장하였다. Si은 $In_{0.64}Al_{0.36}Sb$ 시료에서 도핑 농도가 낮을 때는 어셉터(acceptor)로 작용하다가 도핑 농도가 증가함에 따라 도너(donor)로 작용하였다. 본 연구에 사용한 $In_{0.64}Al_{0.36}Sb$ 시료의 Si 도핑 농도는 $4.5{\times}10^{16}\;cm^{-3}$ (n형), $4{\times}10^{16}\;cm^{-3}$ (n형), $8{\times}10^{15}\;cm^{-3}$ (n형), $1{\times}10^{15}\;cm^{-3}$ (p형), $4{\times}10^{14}\;cm^{-3}$ (p형)인 다섯 개의 시료를 사용하였다. Si 도핑한 시료의 PL 피크는 undoped 시료보다 약 100-200 nm 단파장에서 나타나고 PL 세기도 크게 증가하였다. 그러나 Si 도핑 농도가 가장 낮은 n형과 p형 시료의 PL 피크가 가장 짧은 파장 (높은 에너지)에 나타나고 도핑 농도가 증가함에 따라 장파장으로 이동함을 보였다. n형 시료의 도핑 농도가 $8{\times}10^{15}\;cm^{-3}$에서 $4.5{\times}10^{16}\;cm^{-3}$로 증가하였을 때 PL 피크는 1232 nm에서 1288 nm까지 장파장쪽으로 이동하였으며, p형 시료는 도핑 농도가 $4{\times}10^{14}\;cm^{-3}$에서 $1{\times}10^{15}\;cm^{-3}$로 증가하였을 때 PL 피크가 1248 nm에서 1314 nm로 이동함을 보였다. 또한 시료 온도에 따른 PL 결과는 온도가 증가함에 따라 PL 피크는 장파장으로 이동하면서 PL 세기는 급격하게 감소하고 약 100 - 150 K에서 소멸하였다. 그러나 ~1500 nm 이상 장파장 영역에 매우 넓은 새로운 피크가 나타났으며 온도가 증가함에 따라 PL 세기가 증가함을 확인하였다. Si 도핑 농도에 따른 운반자 수명시간 변화를 TRPL을 이용하여 측정하였다. 운반자 수명시간은 double exponential function을 이용하여 얻었다. Si 도핑 시료의 운반자 수명시간이 undoped 시료에 비해 매우 길게 나타났으며, Si 도핑 시료에서는 p형 시료들보다 n형 시료들의 운반자 수명시간이 길게 나타났다. PL 방출파장에 따른 운반자 수명시간은 Si 도핑 농도에 따라 다르게 나타났다. 이러한 PL과 TRPL 결과로부터 $In_{0.64}Al_{0.36}Sb$의 발광 특성 및 운반자 동역학은 Si 도핑에 크게 영향을 받는다는 것을 확인하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.80-90
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• 2001

The aim of this study is to develop the methodology which enables to identify the mechanical properties of element such as stress intensity factor by using the AE parameters. Considering the multivariate and nonlinear properties of AE parameters such as ringdown count, rise time, energy, event duration and peak amplitude from fatigue cracks of machine element the principal component regression(PCR) and artificial neural network(ANN) models for the estimation of stress intensity factor were developed and validated. The AE parameters were found to be very significant to estimate the stress intensity factor. Since the statistical values including correlation coefficients, standard mr of calibration, standard error of prediction and bias were stable, the PCR and ANN models for stress intensity factor were very robust. The performance of ANN model for unknown data of stress intensity factor was better than that of PCR model.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.220-225
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• 2020

Hair is made of proteins containing various amino acids. Ultraviolet (UV) radiation is believed to be responsible for the most damaging effects of sunlight, and also plays an important role in hair aging. The purpose of this study was to investigate the changes in morphological and chemical structures after ultraviolet B (UVB) irradiation of human hair. The UVB-irradiated hair showed characteristic morphological and structural changes, compared to those of the normal hair. The result from a scanning electron microscope (SEM) equipped with an energy dispersive X-ray diffractometer (EDX) showed that the scale of UV-irradiated hair appeared to be rough and the amount of oxygen element was higher than that of the normal hair. Fluorescence and three dimensional (3D) topographical images were obtained by a confocal laser scanning microscope (CLSM). In 3D images, the green emission intensity of normal hair was much higher than that of fluorescing UVB-irradiated hair. The intensity of green emission reflects the intrinsic fluorescence of hair protein. Also, a fluorescent imaging method using fluorescamine reagent was used to identify the free amino groups resulting from a peptide bond breakage in UVB-irradiated hair. Strong blue fluorescence of UVB-irradiated hair, which indicates a very high level of amino groups, was observed by CLSM. Therefore, the fluorescamine as an extrinsic fluorescence could provide a useful tool to identify the peptide bond breakage in UVB-irradiated hair. Infrared image mapping was also employed to assess the cross-sections of normal and UVB-irradiated specimens to examine the oxidation of disulfide bonds. The degree of peak areas with strong absorbance for the disulfide mono-oxide was spread from the outside to the inside of hair. The spectroscopic techniques used alone, or in combination, launch new possibilities in the field of hair cosmetics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.80-85
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• 2019

Vanadium dioxide is a well-known metal-insulator phase transition material. Lots of researches of vanadium redox flow batteries have been researched as large scale energy storage system. In this study, vanadium oxide($VO_x$) thin films were applied to cathode for lithium ion battery. The $VO_x$ thin films were deposited on Si substrate($SiO_2$ layer of 300 nm thickness was formed on Si wafer via thermal oxidation process), quartz substrate by RF magnetron sputter system for 60 minutes at $500^{\circ}C$ with different RF powers. The surface morphology of as-deposited $VO_x$ thin films was characterized by field-emission scanning electron microscopy. The crystallographic property was confirmed by Raman spectroscopy. The optical properties were characterized by UV-visible spectrophotometer. The coin cell lithium-ion battery of CR2032 was fabricated with cathode material of $VO_x$ thin films on Cu foil. Electrochemical property of the coin cell was investigated by electrochemical analyzer. As the results, as increased of RF power, grain size of as-deposited $VO_x$ thin films was increased. As-deposited thin films exhibit $VO_2$ phase with RF power of 200 W above. The transmittance of as-deposited $VO_x$ films exhibits different values for different crystalline phase. The cyclic performance of $VO_x$ films exhibits higher values for large surface area and mixed crystalline phase.

• The Korean Journal of Nuclear Medicine Technology
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• v.23 no.1
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• pp.50-53
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• 2019

Purpose Yttrium-90 (Y-90) is high-energy beta emitters ($E{\beta}$, max = 2.28 MeV) with the mean penetration depth of 2.5 mm in tissue. Radioactive microspheres containing Y-90 is widely used for the transarterial radioembolization of hepatocellular carcinoma. However, bremsstrahlung radiation from Y-90 can cause the external radiation exposure to medical staff who handle the Y-90 microspheres. In this study, shielding device for Y-90 microspheres was developed to minimize the external radiation exposure. Materials and Methods Y-90 microsphere shielding device was made from 6 mm thicknesses of tungsten including the lead glass window. Radiation shielding ability of Y-90 microsphere shielding device was evaluated using 4 GBq of $SIR-Spheres^{(R)}$ Y-90 microspheres. The bremsstrahlung radiation was measured using radiation survey meter. Results The mean radiation dose of Y-90 microspheres in acrylic shield was $261.7{\pm}2.3{\mu}Sv/h$ (n=5) at 10 cm away from the shield. With the additional tungsten shielding device, it was $23.7{\pm}1.3{\mu}Sv/h$ (n=5). Thus, the bremsstrahlung radiation dose was decreased by 90.9%. At 50 cm away from the shield, bremsstrahlung radiation was reduced by 89.2% after using tungsten shielding device. Conclusion During the preparation and radioembolization of Y-90 microsphere, medical staff are exposed to external radiation. In this study, we demonstrated that the use of tungsten shielding device devices significantly reduced the amount of bremsstrahlung radiation. Y-90 microsphere tungsten shielding device can be highly effective in reducing the bremsstrahlung radiation.

• Journal of the Korean Society of Radiology
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• v.13 no.3
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• pp.333-338
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• 2019

In the field of radiotherapy, the Quality Assurance(QA) procedure to verify the safety of treatment is considered to be very important. However, due to various problems of the conventional dosimeters used for the QA, researches on these dosimeters have been actively carried out to replace them. In this study, to maximize the sensitivity by visible light(VL) emitted from phosphors, blended hybrid sensors were fabricated by blending various weight percent(wt%) of $Gd_2O_2S:Tb$ which is a phosphor with excellent fluorescence efficiency into $PbI_2$. Then, the electrical properties to high energy radiation from the blended sensors and the pure $PbI_2$ sensor were compared and evaluated. As a result of the sensitivity evaluation, the sensor of 3wt% showed the highest value with more than 40% difference from the other sensors, and gradual decreasing in sensitivity was observed with increasing wt% except for the sensor of 3wt%. Also, in the reproducibility evaluation, the pure $PbI_2$ sensor exhibited a large variation in coefficient of variation(CV)>0.015, while all the blended sensors showed CV<0.015.

• Journal of Naturopathy
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• v.9 no.1
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• pp.27-32
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• 2020

Purpose: The purpose of this study was to investigate the changes in the autonomic nervous system of the human body after the use of ocher bedding radiating far-infrared rays to 15 insomnia subjects. Methods: Changes of autonomous nerve in the subjects after using loess bedding estimated by heart rate variability. Results: The mean HF before the use of ocher bedding was 220.8 msec², and the mean after use decreased to 5.1 msec². The average value of LF before use was 418.1 msec², and the mean after use decreased to 5.2 msec². The average before use of the VLF was 1463.3 msec², and the average after use dropped to 6.8 msec². The average value of TP before use was 977.3 msec², and the average after use dropped to 6.7 msec². The decrease in postoperative values of all four items was statistically significant, and the high value of the subjects before use inferred to be the reason that all of the subjects had high stress and anxiety due to their long-term sleep disorder. There was no significant difference in the pulses of the subjects before the use of the bedding. SDNN and RMSSD were not significantly different before and after use. Conclusions: Autonomic nerves HF, LF, VLF, TP frequency is evaluated to be affected by the investigation of far-infrared radiation that occurs ocher. This research data regarded as high value as primary data in this field.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.2
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• pp.157-162
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• 2023

Among the failures of photovoltaic power generation facilities, failures caused by surges account for 20% of the total failure rate, and energy emissions of tens to hundreds [A] during power generation and electrical damage to inverters and connection boards lead to electrical safety accidents. In particular, in the case of lightning, an abnormal voltage is induced in an electric circuit to destroy insulation, and the current flowing at this time causes a fire and acts as a factor that accelerates the deterioration of parts. Due to this action, the problem of electrical safety of solar power generation devices spreading from outside the city center to the inside of the city center such as houses, apartments, and government offices is emerging. Since lightning strikes cause both field-based and conducted electrical interference, this effect increases with increasing cable length or conductor loops. In addition, surge damages not only solar modules, inverters and monitoring devices, but also building facilities, which can eventually cause operational shutdown due to fire of the photovoltaic power generation system and consequent financial loss. Therefore, in this paper, a lightning protection system for solar power generation devices is studied for the purpose of reducing property damage and human casualties due to the increase in fire and electrical safety accidents caused by lightning strikes in photovoltaic power generation systems.

• Clean Technology
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• v.29 no.3
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• pp.163-171
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• 2023

Hydrogen has been gaining a lot of attention as a possible clean energy source that can aid in reaching carbon neutrality. Currently, hydrogen production has relied on the steam reforming of fossil fuels. However, due to the carbon dioxide emissions caused by this process, hydrogen production based on the steam reforming of bio-oil derived from biomass has been proposed as an alternative approach. In order to use this alternative approach efficiently, one of the key issues that must be overcome is that the complexity of bio-oil, which has a large molecular weight and diverse functional groups of hydrocarbons, promotes the catalytic deactivation of nickel-based catalysts. In this review, research efforts to improve nickel-based catalysts for the steam reforming of bio-oil have been discussed in terms of the active phase, support, and promoters. The active phases are involved in activating C-C and C-H bonds of high-molecular-weight hydrocarbons, and noble and transition metals can be utilized. In terms of the support and promoters, the catalytic deactivation of Ni-based catalysts can be inhibited by utilizing reactive lattice oxygen for support or by suppressing the acidity. The development of active and stable Ni-based reforming catalysts plays a critical role in clean hydrogen production based on bio-oils.

• Journal of the Korean Geotechnical Society
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• v.39 no.7
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• pp.69-76
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• 2023

Cavity causes settlement and its remediation after an accident results in significant time and economic losses. This study aims to experimentally evaluate the prospect of using infrared camera to detect and measure underground subsidence. Emissivity is necessary to detect the energy emitted from an object and accurately assess temperature using an infrared camera. The emissivity in laboratory tests is fixed to evaluate a reasonable distance between the infrared camera and the object, and temperature values are assessed at various distances. In field experiments, the cavity of the field experiment is simulated using a PVC pipe with a diameter of 5 cm, artificially buried at depths of 5 and 25 cm from the surface. The infrared camera measurements are taken from 4 PM to 3 PM of the next day (a total of 23 h). The analysis included the time-series temperature distribution and the cooling rate index assessment, which represents the temperature change rate per unit of time. The results showed that various temperature trends are observed depending on the location of the subsidence. This study demonstrates that the infrared camera can be used to assess the condition of the subsurface.