Fluorescent Blue Materials for Efficient Organic Light-Emitting Diode with High Color Purity

Kyungsun Choi,Chanhyo Lee,Kwan Hee Lee,Su Jin Park,손성욱,정영근,홍종인 대한화학회 2006 Bulletin of the Korean Chemical Society Vol.27 No.10

We report a new series of blue dopants composed of both electron donating and electron accepting moieties in one molecule, based on nalidixic acid. The EL device derived from the dopant exhibits pure blue light emission (0.15, 0.14) The current efficiency is estimated to be 3.88 cd/A at 100 cd/m2, which shows remarkable enhancement, compared to that of the host itself (2.5 cd/A at 100 cd/m2) under the same conditions. These results demonstrate that the incorporation of a proper guest into the host in a guest-host doped system improves not only the purity of the fluorescent blue emission but also elevates its quantum efficiency, thus improving the OLED performance.

4P Model for Strategic Research Planning: Focusing on the Cases of Korea Research Institute of Chemical Technology

Choi, Kyungsun,Choe, Hochull,Ko, Youngjoo Asian Society for Innovation and Policy 2018 Asian Journal of Innovation and Policy Vol.7 No.2

The demand for efficient utilization of input resources and productive outcomes is increasing as the government's R&D investments in Government-funded research institutes (GRIs) expand. These changes call for improving research-planning activities, which are defined as a set of activities wherein objectives are established, strategies for acquisition and expenditures of research resources are devised, and utilizations of research outcomes are addressed. This study introduces the integrated 4P analysis model that identifies the relationships among patents, papers, products, and projects. It looks into 4P analysis structure and its efficiency as a research planning means through case studies of the Korea Research Institute of Chemical Technology. This study introduces 4P analysis applied to KRICT, which can be utilized for outcome-oriented research planning of GRIs. At the same time, it investigates into the benefits and implications of 4P analysis. It proffers policy suggestions on such aspects as how research planning of GRIs should go through changes in a strategic and systematic way.

Label-free optical activation of astrocyte in vivo.

Choi, Myunghwan,Yoon, Jonghee,Ku, Taeyun,Choi, Kyungsun,Choi, Chulhee SPIE--the International Society for Optical Engine 2011 Journal of biomedical optics Vol.16 No.7

<P>As the most abundant cell type in the central nervous system, astrocyte has been one of main research topics in neuroscience. Although various tools have been developed, at present, there is no tool that allows noninvasive activation of astrocyte in vivo without genetic or pharmacological perturbation. Here we report a noninvasive label-free optical method for physiological astrocyte activation in vivo using a femtosecond pulsed laser. We showed the laser stimulation robustly induced astrocytic calcium activation in vivo and further verified physiological relevance of the calcium increase by demonstrating astrocyte mediated vasodilation in the brain. This novel optical method will facilitate noninvasive physiological study on astrocyte function.</P>

Pirfenidone inhibits transforming growth factor-β1-induced fibrogenesis by blocking nuclear translocation of Smads in human retinal pigment epithelial cell line ARPE-19

Choi, Kyungsun,Lee, Kihwang,Ryu, Seung-Wook,Im, Minju,Kook, Koung Hoon,Choi, Chulhee Molecular Vision 2012 Molecular vision Vol.18 No.-

<P><B>Purpose</B></P><P>Transforming growth factor-β (TGF-β) plays a key role in transforming retinal pigment epithelial (RPE) cells into mesenchymal fibroblastic cells, which are implicated in proliferative vitreoretinopathy. Herein, we tested the effect of pirfenidone, a novel antifibrotic agent, on TGF-β1-mediated fibrogenesis in the human RPE cell line ARPE-19.</P><P><B>Methods</B></P><P>The effect of pirfenidone on the TGF-β1-induced phenotype in ARPE-19 cells was measured with immunocytochemistry as the change in F-actin. Fibronectin and collagen production was measured with enzyme-linked immunosorbent assay, and cell migration activity was investigated using a scratch assay. Immunoblot analyses of cofilin, sma and mad protein (smad) 2/3, p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, and extracellular signal-related kinase expression were conducted to elucidate the cell signaling networks that contribute to the antifibrotic effect of pirfenidone.</P><P><B>Results</B></P><P>Treatment with TGF-β1 induced typical phenotypic changes such as formation of stress fiber running parallel to the long axis of cells and enhanced migration and production of extracellular matrix components such as collagen type I and fibronectin. This fibroblast-like phenotype induced by TGF-β1 was significantly inhibited by pretreatment with pirfenidone in a dose-dependent manner. We also elucidated the TGF-β signaling pathways as the target of the inhibitory effect of pirfenidone. Pirfenidone inhibited TGF-β signaling by preventing nuclear accumulation of active Smad2/3 complexes rather than phosphorylation of Smad2/3.</P><P><B>Conclusions</B></P><P>These results collectively provide a rational background for future evaluation of pirfenidone as a potential antifibrotic agent for treating proliferative vitreoretinopathy and other fibrotic retinal disorders.</P>

Multiplex Analysis of Cytokines in the Serum and Cerebrospinal Fluid of Patients With Alzheimer's Disease by Color-Coded Bead Technology

Choi, Chulhee,Jeong, Jee-Hyang,Jang, Joong Sik,Choi, Kyungsun,Lee, Jungsul,Kwon, Jongbum,Choi, Kyoung-Gyu,Lee, Jong-Seo,Kang, Sang Won 대한신경과학회 2008 Journal of Clinical Neurology Vol.4 No.2

<P><B>Background and purpose</B></P><P>The availability and promise of effective treatments for neurodegenerative disorders are increasing the importance of early diagnosis. Having molecular and biochemical markers of Alzheimer's disease (AD) would complement clinical approaches, and further the goals of early and accurate diagnosis. Combining multiple biomarkers in evaluations significantly increases the sensitivity and specificity of the biochemical tests.</P><P><B>Methods</B></P><P>In this study, we used color-coded bead-based Luminex technology to test the potential of using chemokines and cytokines as biochemical markers of AD. We measured the levels of 22 chemokines and cytokines in the serum and cerebrospinal fluid (CSF) of 32 <I>de novo</I> patients (13 controls, 11 AD, and 8 Parkinson's disease [PD]).</P><P><B>Results</B></P><P>MCP-1 was the only cytokine detectable in CSF, and its levels did not differ between control and disease groups. However, the serum concentration of eotaxin was significantly higher in AD patients than in the control group.</P><P><B>Conclusions</B></P><P>The analysis of multiple inflammatory mediators revealed marginal differences in their CSF and serum concentrations for the differential diagnosis of AD and PD. These results provide evidence that immunological responses are not major contributors to the pathogenesis of AD and PD.</P>

개인적·사회적 요인을 고려한 가상 공동체에서의 지식 공유 모형

최경선 ( Choi Kyungsun ),안현철 ( Ahn Hyunchul ) 한국정보시스템학회 2019 情報시스템硏究 Vol.28 No.1

Purpose Virtual communities (VCs) are becoming ever more important in these days, sometimes more than offline communities. Notably, they have become significant sources of knowledge sharing. Therefore, in order to foster a VC, it is very important to understand why people share their knowledge in the VC. Under this background, this paper aims at proposing the behavioral model best explains knowledge sharing activities in VCs. Design/methodology/approach We basically design our behavioral model for knowledge sharing in VCs based on theory of reasoned action (TRA). However, to understand knowledge sharing in VCs better, we specify knowledge sharing by dividing it into knowledge contribution and knowledge use. Also, instead of ‘subjective norm’, we adopt ‘sense of virtual community (SOVC)’ as a main social factor, which has been found to be important in the literature. We also include the antecedents such as ‘quality of the shared knowledge’, ‘trust in community members’, ‘passion of the community leader’, ‘reciprocity’, and ‘self efficacy’, which affect VC users’attitude towards knowledge sharing and SOVC. To test the hypotheses in our proposed model, we collected 253 valid surveys from the VC users. Structural equation modeling (SEM) using AMOS 23 is employed to assess the relationships proposed as the hypotheses. Findings Major findings are as follows. SOVC positively affects both intention to contribute knowledge and intention to use knowledge. And, trust in community members positively affects the attitude towards knowledge use and SOVC. The attitude towards knowledge use is also affected by the quality of the shared knowledge. Reciprocity is found to strongly positively affect the attitude towards knowledge contribution. However, passion of the community leader and self efficacy are found to have insignificant effect on SOVC and the attitude towards knowledge contribution respectively. Our study sheds a light on how to foster VCs from the perspective of knowledge management.

Smartphone Use at Night Affects Melatonin Secretion, Body Temperature, and Heart Rate

Na, Nooree,Choi, Hojun,Jeong, Kyeong Ah,Choi, Kyungah,Choi, Kyungsun,Choi, Chulhee,Suk, Hyeon-Jeong Korean Society for Emotion and Sensibility 2017 감성과학 Vol.20 No.4

In the present study, we investigated the physiological effects of smartphone use at night when the display luminance and white balance were differently manipulated. Two levels of luminance and two types of white balance were combined to form four types of displays. Subjects were instructed to use smartphones between 23:00 to 01:00 twice a week for two weeks, and for each trial, subjects were given one of the four display types. Melatonin concentration in the saliva, body temperature and heart rate were measured before and after each experiment. The experimental result showed that the low luminance display supported melatonin secretion and thermoregulation compared to the high luminance display. With regard to the white balance, higher melatonin level was observed when using the display that filtered blue light. The low luminance display together with yellowish tint best supported restful sleep at night in terms of every physiological response. This study collectively demonstrates that bright and blue light emitted from smartphone displays adversely affect melatonin secretion, body temperature, and heart rate, and therefore, suggests the use of a display with low luminance or a display that filters blue light for a restful sleep at night.

Smartphone Use at Night Affects Melatonin Secretion, Body Temperature, and Heart Rate

( Nooree Na ),( Hojun Choi ),( Kyeong Ah Jeong ),( Kyungah Choi ),( Kyungsun Choi ),( Chulhee Choi ),( Hyeon-jeong Suk ) 한국감성과학회 2017 감성과학 Vol.20 No.4

In the present study, we investigated the physiological effects of smartphone use at night when the display luminance and white balance were differently manipulated. Two levels of luminance and two types of white balance were combined to form four types of displays. Subjects were instructed to use smartphones between 23:00 to 01:00 twice a week for two weeks, and for each trial, subjects were given one of the four display types. Melatonin concentration in the saliva, body temperature and heart rate were measured before and after each experiment. The experimental result showed that the low luminance display supported melatonin secretion and thermoregulation compared to the high luminance display. With regard to the white balance, higher melatonin level was observed when using the display that filtered blue light. The low luminance display together with yellowish tint best supported restful sleep at night in terms of every physiological response. This study collectively demonstrates that bright and blue light emitted from smartphone displays adversely affect melatonin secretion, body temperature, and heart rate, and therefore, suggests the use of a display with low luminance or a display that filters blue light for a restful sleep at night.

MCP-1 and MIP-3α Secreted from Necrotic Cell-Treated Glioblastoma Cells Promote Migration/Infiltration of Microglia

Jung, Yieun,Ahn, So-Hee,Park, Hyunju,Park, Sang Hui,Choi, Kyungsun,Choi, Chulhee,Kang, Jihee Lee,Choi, Youn-Hee S. Karger AG 2018 CELLULAR PHYSIOLOGY AND BIOCHEMISTRY Vol.48 No.3

<P><B><I>Background/Aims:</I></B> Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. The defining characteristics of GBM are diffuse infiltration of tumor cells into normal brain parenchyma, rapid growth, a high degree of infiltration of microglia and macrophages, and the presence of necrosis. Microglia/macrophages are frequently found in gliomas and they extensively infiltrate GBM tissue, up to 30% of total tumor mass. However, little is known about the effect of necrotic cells (NCs) on microglia infiltration in GBM and the tumor-infiltrating microglia-induced factors in GBMs. <B><I>Methods:</I></B> In this study, to address whether necrosis or necrosis-exposed GBM cells affect the degree of microglia/macrophage infiltration, migration and invasion/infiltration assays were performed. Culture supernatants and nuclear extracts of CRT-MG cells treated or untreated with necrotic cells were analyzed using a chemokine array and electrophoretic mobility shift assay, respectively. <B><I>Results:</I></B> The presence of NCs promoted the migration/infiltration of microglia, and GBM cell line CRT-MG cells exposed to NCs further enhanced the migration and infiltration of HMO6 microglial cells. Treatment with NCs induced mRNA and protein expression of chemokines such as <unterline>M</unterline>onocyte <unterline>C</unterline>hemoattractant <unterline>P</unterline>rotein-1 (CCL2/MCP-1) and <unterline>M</unterline>acrophage <unterline>I</unterline>nflammatory <unterline>P</unterline>rotein-3α (CCL20/MIP-3α) in CRT-MG cells. In particular, CCL2/MCP-1 and CCL20/MIP-3α were significantly increased in NC-treated CRT-MG cells. NCs induced DNA binding of the transcription factors <unterline>N</unterline>uclear <unterline>F</unterline>actor (NF)-κB and <unterline>A</unterline>ctivator <unterline>P</unterline>rotein 1 (AP-1) to the CCL2/MCP-1 and CCL20/MIP-3α promoters, leading to increased CCL2/MCP-1 and CCL20/MIP-3α mRNA and protein expression in CRT-MG cells. <B><I>Conclusion:</I></B> These results provide evidence that NCs induce the expression of CCL2/MCP-1 and CCL20/MIP-3α in glioblastoma cells through activation of NF-κB and AP-1 and facilitate the infiltration of microglia into tumor tissues.</P>

Study of degradation in bulk lifetime of n-type silicon wafer due to oxidation of boron-rich layer

Kyungsun Ryu,Chel-Jong Choi,Ajeet Rohatgi,Young-Woo Ok 한국물리학회 2016 Current Applied Physics Vol.16 No.5

Various boron (B) diffusion techniques are being investigated to fabricate n-type Si solar cells. Thermal oxidation is often used to remove boron-rich layer (BRL) formed as a byproduct of B diffusion because BRL interferes with surface passivation of boron emitter. However, oxidizing the BRL can cause significant degradation in bulk lifetime. In this paper, high resolution electron microscopy (HREM) was performed to detect the presence of BRL after B diffusion and its removal after subsequent oxidation. In addition, bulk lifetime of n-type Si with BRL was measured after various oxidation conditions to systematically investigate the mechanism of oxidation-induced lifetime degradation in n-type Si. Detailed analysis of the oxidized samples revealed that iron (Fe) is primary metal impurity responsible for the bulk lifetime degradation after oxidation. This happens because Fe is gettered in BRL after B diffusion and during the oxidation, when the BRL is consumed, Fe is released into the bulk to degrade lifetime.