• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.4
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• pp.237-240
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• 2016

The improvement of irradiation intensity and irradiation uniformity is essential for large area and high power UVA light source application. In this study, large number of chips bonded by micro soldering technique were driven by low current, and current limiting diodes were configured to supply constant current to parallel circuits consisting of large number of series strings. The dimension of light source module circuit board was $350{\times}90mm^2$ and 16,650 numbers of 385 nm flip chip LEDs were used with a configuration of 90 parallel and 185 series strings. The space between LEDs in parallel and series strings were maintained at 1.9 mm and 1.0 mm distance, respectively. The size of the flip chip was $750{\times}750{\mu}m^2$ were used with contact pads of $260{\times}669{\mu}m^2$ size, and SAC (96.5 Sn/3.0 Ag/0.5 Cu) solder was used for flip chip bonding. The fabricated light source module with 7.5 m A supply current showed temperature rise of $66^{\circ}C$, whereas irradiation was measured to be $300mW/cm^2$. Inaddition, 0.23% variation of the constant current in each series string was demonstrated.

• Journal of Radiation Protection and Research
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• v.43 no.4
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• pp.160-169
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• 2018

Background: This study aims to develop an integrated optical system that can simultaneously or selectively measure the signals obtained from radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL), which are luminescence phenomena of materials stimulated by radioactivity, heat, and light, respectively. The luminescence mechanism of various materials could be investigated using the glow curves of the luminescence materials. Materials and Methods: RL/TL/OSL integrated measuring system was equipped with a X-ray tube (50 kV, $200{\mu}A$) as an ionizing radiation source to irradiate the sample. The sample substrate was used as a heating source and was also designed to optically stimulate the sample material using various light sources, such as high luminous blue light emitting diode (LED) or laser. The system measured the luminescence intensity versus the amount of irradiation/stimulation on the sample for the purpose of measuring RL, TL and OSL sequentially or by selectively combining them. Optical filters were combined to minimize the interference of the stimulation light in the OSL signal. A long-pass filter (420 nm) was used for 470 nm LED, an ultraviolet-pass filter (260-390 nm) was used for detecting the luminescence of the sample by PM tube. Results and Discussion: The reliability of the system was evaluated using the RL/OSL characteristics of $Al_2O_3:C$ and the RL/TL characteristics of LiF:Mg,Cu,Si, which were used as dosimetry materials. The RL/OSL characteristics of $Al_2O_3:C$ showed relatively linear dose-response characteristics. The glow curve of LiF:Mg,Cu,Si also showed typical RL/OSL characteristics. Conclusion: The reliability of the proposed system was verified by sequentially measuring the RL characteristics of radiation as well as the TL and OSL characteristics by concurrent thermal and optical stimulations. In this study, we developed an integrated measurement system that measures the glow curves of RL/TL/OSL using universal USB-DAQs and the control program.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.20.2-20.2
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• 2011

III-nitrides have attracted much attention for optoelectronic device applications whose emission wavelengths ranging from green to ultraviolet due to their wide band gap. However, due to the strong polarization properties of conventional c-plane III-nitrides, the built-in polarization-induced electric field limits the performance of optical devices. Therefore, there has been a renewed interest in the growth of nonpolar III-nitride semiconductors for polarization free heterostructure optoelectronic and electronic devices. However, the crystal and the optical quality of nonpolar/semipolar GaN have been poorer than those of conventional c-plane GaN, resulting in the relative poor optical and electrical properties of light emitting diodes (LEDs). In this presentation, I will discuss the growth and characterization of high quality nonpolar a-plane and semipolar (11-22) GaN and InGaN multiple quantum wells (MQWs) grown on r- and m-plane sapphire substrates, respectively, by using metalorganic chemical vapor deposition (MOCVD) without a low temperature GaN buffer layer. Especially, the epitaxial lateral overgrowth (ELO) technique will be also discussed to reduce the dislocation density and enhance the performance of nonpolar and semipolar GaN-based LEDs.

• Horticultural Science & Technology
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• v.34 no.4
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• pp.596-606
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• 2016

The growth and contents of anthocyanins and ascorbic acid in lettuce(Lactuca sativa L., 'Jeokchima') as affected by supplemental UV-A LED irradiation under different light quality and photoperiod conditions were analyzed in this study. Five light qualities, namely B (blue LED), R (red LED), BUV (blue LED+UV-A LED), RUV (red LED+UV-A LED) and Control (white fluorescent lamps) with photoperiods of 12/12 hours (day/night), 16/8 hours, or 20/4 hours were provided to investigate the effects of light quality and photoperiod on the growth and accumulation of anthocyanins and ascorbic acid in lettuce leaves. As measured 28 days after transplanting, the number of leaves, leaf length, leaf width, leaf area, shoot fresh weight and dry weight of lettuce were significantly affected by light quality and photoperiod. The number of leaves, leaf length, leaf width, leaf area, shoot fresh weight and dry weight of lettuce grown under R treatment increased with increasing light period. By contrast, leaf development was inhibited, but chlorophyll content increased, under B treatment. Supplemental UV-A irradiation significantly decreased leaf length, leaf width, leaf area and shoot fresh weight. Anthocyanins in lettuce increased significantly with decreasing dark period under B treatment. A synergistic effect of supplemental UV-A LED irradiation on anthocyanins accumulation was found for lettuce leaves grown under R treatment but not B treatment. Ascorbic acid in lettuce was greatly affected by photoperiod. Ascorbic acid content at BUV and RUV treatments increased by 20-30% compared to without UV-A LED irradiation. From these results, it was concluded that growth and contents of anthocyanins and ascorbic acid in lettuce are significantly affected by supplemental UV-A LED irradiation. The results obtained in this study will be informative for efforts to improve the nutritional value of leafy vegetables grown in plant factories.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.17 no.1
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• pp.16-33
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• 2004

In Oriental medicine, aging is just a natural process like change of seasons. Ancient Oriental people accepted it as a natural thing to be growing older and to die at last. The science of aging has advanced dramatically. In the last 2 decades, advances in genetics and molecular biology have led to extraordinary new understandings in how cells age, how apoptosis programs cells to die, and how neuroendocrinology plays a role in the lifespan of organisms. Today, the matter of primary concern about aging is a cellular and mitochondrial damage of human body induced by reactive oxygen species(ROS). The skin aging can be divided into two areas, intrinsic(chronologic)-aging and photo-aging. There are lots of photo damage about skin aging. The skin is increasingly exposed to ultraviolet(UV) irradiation in life. Therefore, the risk of photo-oxidative damage of the skin induced by reactive oxygen species(ROS) has increased substantially. Nowadays, many people believe that they can stop or at least delay the process of aging. There are lots of treatments that promise to slow the process of aging and the associated ailments. Many of these treatments, for example, exercise, Vit E, Vit C therapy, hormone therapy, restrict diet, are gradually being subjected to clinical trials. But in spite of all efforts, researches and investigations, there is no single method or treatment which is revealed to be truly effective for delaying progress of aging. Every methods insisted on effect for delaying aging process, has its dark side. All we can do is just keeping ourself healthy until the time of death.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.811-814
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• 2002

$(Ba,Sr)_2SiO_4:Eu^{2+}$ phosphor particles with high brightness were prepared by spray pyrolysis. The changes in the photoluminescence intensity and morphology of $(Ba,Sr)_2SiO_4:Eu^{2+}$ were investigated by changing the posttreatment temperature and the concentration of dopant. The prepared $(Ba,Sr)_2SiO_4:Eu^{2+}$ particles has a dense structure, but irregular shape after the posttreatment. When they were excited by the ultraviolet light of 410 nm, a broad emission band with a peak at 508 nm was observed. The photoluminescence intensity of the prepared $(Ba,Sr)_2SiO_4:Eu^{2+}$ particles was enhanced by increasing the posttreatment temperature up to 1300 $^{\circ}C$ and further improved by adding several rear-earth codopants. The $(Ba,Sr)_2SiO_4:Eu^{2+}$ particles prepared by spray pyrolysis had a good excitation spectrum in the wavelength longer than 350 nm. Therefore, it was concluded that the $(Ba,Sr)_2SiO_4:Eu^{2+}$ prepared by spray pyrolysis is a good green-emitting phosphor for LED application.

• Journal of Life Science
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• v.28 no.8
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• pp.892-899
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• 2018

Portulaca oleracea L. is an edible plant widely consumed in daily diet throughout Europe, Asia and America. In this study, protective effects of P. oleracea L. extracts against oxidative stress and matrix metalloproteinase (MMP) activity induced by ultraviolet B (UVB) radiation were investigated using HaCaT immortal human keratinocytes. In this context, the mRNA and protein productions of MMPs (MMP-1, -2, and -9) and type I procollagen, which are major markers of photoaging induced by UVB radiation in HaCaT keratinocytes, were evaluated. Furthermore, UVB-induced reactive oxygen species (ROS) generation and mRNA and protein expression levels of superoxide dismutase-1 (SOD-1), oxygenase-1 (OH-1), and nuclear factor-erythroid 2-related factor-2 (Nrf-2), all of which are associated with the antioxidant balance, were investigated. As shown by the results, UVB radiation induced ROS formation and led to increased production of MMPs and decreased collagen production in human keratinocytes, which resulted in skin photoaging or photodamage. The treatment with P. oleracea L. extracts downregulated MMP (MMP-1, -2, and -9) production and upregulated type I procollagen expression in UVB-induced HaCaT cells. Furthermore, treatment with the extracts decreased UVB-induced ROS generation and increased the expression of antioxidant enzymes, such as SOD-1 and OH-1, through the Nrf-2 pathway. Taken together, these results suggest that P. oleracea L. extracts could be a potential cosmeceutical agent for the prevention of skin photoaging or photodamage.

• Journal of Food Hygiene and Safety
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• v.36 no.5
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• pp.447-453
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• 2021

In this study, the effectiveness of physical control technology, a combined light sterilization (LED, UV) and hot water treatment in reducing Aspergillus ochraceus for food production environment was investigated. In brief, 1 mL aliquot of A. ochraceus spore suspension (10^7-8 spore/mL) was inoculated onto stainless steel chips, which was then dried at 37℃, and each was subjected to different physical treatment. Treatments were performed for 0.5, 1, 2, 5, 8, and 11 hours to reduce the strains using a light-emitting diode, but no significant difference was confirmed among the treatments. However, a significant reduction was observed on the chips treated with UV-C exposure and hot water immersion. After being treated solely with 360 kJ/m² of UV-C on stainless steel chip, the fungi were significantly reduced to 1.27 log CFU/cm². Concerning the hot water treatment, the initial inoculum amount of 6.49 log CFU/cm² was entirely killed by immersion in 83℃ water for 5 minutes. Maintaining a high temperature for 5 minutes at the site is difficult. Thus, considering economic feasibility and usability, we attempted to confirm the appropriate A. ochraceus reduction conditions by combining a relatively low temperature of 60℃ and UV rays. With the combined treatments, even in lukewarm water, A. ochraceus decreased significantly through the increases in the immersion time and the amount of UV-C irradiation, and the yield was below the detection limit. Based on these results, if work tools are immersed in 60℃ lukewarm water for 3 minutes and then placed in a UV sterilization device for more than 10 minutes, the possibility of A. ochraceus cross-contamination during work is expected to be reduced.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.414-414
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• 2008

Vertically well-aligned Ga-doped ZnO nanorods with different Ga contents were grown by thermal evaporation on a ZnO template. The Ga-doped ZnO nanorods synthesized with 50 wt % Ga with respect to the Zn content showed maximum compressive stress relative to the ZnO template, which led to a rapid growth rate along the c-axis due to the rapid release of stored strain energy. A further increase in the Ga content improved the conductivity of the nanorods due to the substitutional incorporation of Ga atoms in the Zn sites based on a decrease in lattice spacing. The p-n diode structure with Ga-doped ZnO nanorods, as a n-type, displayed a distinct white light luminescence from the side-view of the device, showing weak ultraviolet and various deep-level emissions.

• Journal of Physiology & Pathology in Korean Medicine
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• v.23 no.3
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• pp.574-580
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• 2009

Melanogenesis is induced mainly by ultraviolet radiation of sunlight and ${\alpha}$-Melanocyte stimulation hormone (${\alpha}$-MSH) which binds to a specific G protein coupled receptor. ${\alpha}$-MSH and cAMP-elevating agents are known to melanin syntheisis and dendrite outgrowth. The purpose of this study was to investigate the mechanism of melanogenesis inhibition in B16/F10 cells by ethanol extract of Artemisiae Capillaris Herba. In the present study, ${\alpha}$-MSH led to a stimulation of melanin synthesis that appeared to result from an increased tyrosinase activity and melanin content. However, the ethanol extract of Artemisiae Capillaris Herba inhibited the ${\alpha}$-MSH-induced tyrosinase activity and melanin content. In control conditions, B16/F10 cells displayed a fibroblastic appearance while ${\alpha}$-MSH treatment promoted the emergence of small and numerous dendrites from the plasma membrane. The ethanol extract of Artemisiae Capillaris Herba abolished the ${\alpha}$-MSH-induced dendricity. Regarding protein levels of the melanogenic enzymes, the amounts of tyrosinase were increased after incubation with ${\alpha}$-MSH. The treatment of Artemisiae Capillaris Herba ethanol extract decreased the ${\alpha}$-MSH expression levels of tyrosinase. Based on these findings, it is likely that the ethanol extract of Artemisiae Capillaris Herba exerts its depigmenting effects in B16/F10 cells through the suppression of tyrosinase expression, which are key enzymes for melanogenesis.