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Choi, Jaehyun,Hwang, Woonbong,You, Chisang,Jung, Byungwoon,Hong, Wonbin Institute of Electrical and Electronics Engineers 2019 IEEE transactions on antennas and propagation Vol.67 No.1
<P>This paper describes a low-profile <TEX>$2\times 2$</TEX> multi-input multi-output (MIMO) antenna system that is fully functional over the entire long-term evolution (LTE) spectrum 699–960 MHz (lower frequency spectrum) and 1710–2690 MHz (higher frequency spectrum) that is applicable to real-life metallic smartphone platforms. The presented methodology entails utilizing the longitudinal edges of the ground plane amid an extremely narrow ground clearance of 2 mm. The metallic frame of the smartphone is utilized along with a stub network to devise a reconfigurable coupled loop antenna topology. The proposed <TEX>$2\times 2$</TEX> MIMO antenna configuration is measured and confirmed to exhibit efficient envelope correlation coefficient (<0.5) and one of the highest radiation efficiencies to be reported in the literature across the entire LTE spectrum.</P>
Genomic Analysis of Monkeypox Virus During the 2023 Epidemic in Korea
Choi Chi-Hwan,Lee Minji,Lee Sang Eun,Kim Jin-Won,Shin Hwachul,Choi Myung-Min,Yi Hwajung,Kim Min-Kyung,Jeon Jaehyun,Park Jun-Sun,Kim Yeonjae,Lim So Yun,Chin BumSik,Chung Yoon-Seok 대한의학회 2024 Journal of Korean medical science Vol.39 No.18
We aimed to characterize the genomes of monkeypox virus isolates from the Far East, providing insights into viral transmission and evolution. Genomic analysis was conducted on 8 isolates obtained from patients with monkeypox virus disease in the Republic of Korea between May 2022 and early 2023. These isolates were classified into Clade IIb. Distinct lineages, including B.1.1, A.2.1, and B.1.3, were observed in 2022 and 2023 isolates, with only the B.1.3 lineage detected in six isolates of 2023. These genetic features were specific to Far East isolates (the Republic of Korea, Japan, and Taiwan), distinguishing them from the diverse lineages found in the Americas, Europe, Africa, and Oceania. In early 2023, the prevalence of the B.1.3 lineage of monkeypox virus identified in six patients with no overseas travel history is considered as an indicator of the potential initiation of local transmission in the Republic of Korea.
High-Efficiency Crossed-Loop 4G LTE Antenna for All Display Metal-Rimmed Smartphones
Choi, Jaehyun,Hwang, Woonbong,You, Chisang,Jung, Byungwoon,Hong, Wonbin Hindawi Limited 2018 International journal of antennas and propagation Vol.2018 No.-
<P>A symmetrically crossed-loop antenna featuring very high radiation efficiency across the entire LTE frequency bands for metal-rimmed smartphones with only 2 mm ground clearance is proposed, analyzed, and verified. The employment of even and odd modes is utilized to achieve wide bandwidth across 698-960 MHz (low-frequency spectrum), 1710-2170 MHz (middle-frequency spectrum), and 2300-2690 MHz (high-frequency spectrum). Empirical analysis confirms the crossed-loop topology results in a 180° phase shift of the electric current distribution on the ground plane, resulting in enhancement of the radiation resistance. As a result, the devised LTE antenna exhibits more than 48% to 75% total system efficiency across the entire band of interest, which is the highest efficiency reported in literature for metal-rimmed smartphones with extremely small ground clearance.</P>
Efficient Analysis of IT Facility Security Vulnerability Topics by Utilizing R Programming
Jaehyun Choi,Hoojin Lee 대한전자공학회 2019 IEIE Transactions on Smart Processing & Computing Vol.8 No.3
The recent development of domestic information and communications technologies (ICT) has made it possible to use the Internet anywhere in society, consequently exposing various security threats. Specifically, there is frequent leakage of personal information as well as system infringements, which are mainly caused by either internal or external security weaknesses. Besides, there is no exception for private companies or public corporations that have well-equipped security systems. In order to adequately prepare countermeasures against infringement incidents, security officers have been concerned every year. Hence, the government has designated information and communications infrastructures for major national facilities as a measure against the security threats and, since 2001, has enacted and promulgated the Information and Communication Infrastructure Protection Act. In this paper, we attempt to analyze the trends associated with the vulnerability status of information technology (IT) facilities, and to evaluate the weak points in IT facilities. And finally, we derive the most-mentioned vulnerabilities by effectively utilizing the R program to obtain statistical calculation and visualization, and thus, a common denominator for IT environments.
Interregional synaptic maps among engram cells underlie memory formation
Choi, Jun-Hyeok,Sim, Su-Eon,Kim, Ji-il,Choi, Dong Il,Oh, Jihae,Ye, Sanghyun,Lee, Jaehyun,Kim, TaeHyun,Ko, Hyoung-Gon,Lim, Chae-Seok,Kaang, Bong-Kiun American Association for the Advancement of Scienc 2018 Science Vol.360 No.6387
<P>Memory resides in engram cells distributed across the brain. However, the site-specific substrate within these engram cells remains theoretical, even though it is generally accepted that synaptic plasticity encodes memories. We developed the dual-eGRASP (green fluorescent protein reconstitution across synaptic partners) technique to examine synapses between engram cells to identify the specific neuronal site for memory storage. We found an increased number and size of spines on CA1 engram cells receiving input from CA3 engram cells. In contextual fear conditioning, this enhanced connectivity between engram cells encoded memory strength. CA3 engram to CA1 engram projections strongly occluded long-term potentiation. These results indicate that enhanced structural and functional connectivity between engram cells across two directly connected brain regions forms the synaptic correlate for memory formation.</P>
Global Grain Price Transmission to Korean Agricultural and Food Prices
( Jaehyun Choi ),( Doo Bong Han ) 한국농업경제학회 2017 農業經濟硏究 Vol.58 No.3
This study examines the price transmission of global grain prices on Korean agricultural and food markets. Furthermore, it tests the structural break points of global grain prices and analyzes whether their impact changes before and after the global financial crisis and agflation. The results are as follows. First, the structural break of global grain prices was found in May 2007. Second, causal relationships between global grain prices and domestic agricultural and food prices were also changed after the global financial crisis and agflation. Third, a significant price transmission from global soybeans price to domestic soybean price was observed only after 2007. Meanwhile, domestic wheat prices show significant price transmissions following the changes in global wheat prices in both periods. Fourth, the price transmission of global grain prices on domestic processed food prices was significant both before and after 2007. Lastly, an asymmetric price transmission between global and domestic prices was found only before 2007.
최재현(Jaehyun Choi) 한국지능시스템학회 2018 한국지능시스템학회논문지 Vol.28 No.4
최근 창업기업을 지원하기 위한 다양한 정책들이 실시되고 있다. 정책에 의해 지원을 받는 기업은 미래 성장가능성이 높아야 한다. 즉, 이러한 정책들은 지속적인 성장이 가능한 기업들에게 지원되어야 한다. 지속 성장이 가능한 창업기업을 찾기 위해서는, 창업기업과 비슷한 구조를 가지고 있는 중소기업의 정보를 이용할 수 있다. 본 논문에서는 대전창조경제혁신센터에서 기술기반의 창업 및 중소기업 지원 프로그램을 제공받은 창업기업과 중소기업들에 대해 k-means 군집분석과 t-SNE를 이용하여 기업 군집화를 실시한다. k-means 군집분석을 이용하여 기업들의 군집화를 실시하고 t-SNE로 기업 정보를 학습하여 2차원 공간에 투영하여 군집별 기업 특성을 확인한다. 실험으로 창업기업과 중소기업 169개에 대해 적용한 결과, 성장 가능성이 높은 창업기업에 대한 군집을 찾을 수 있었다. Recently, various policies have been implemented to support start-up enterprises. Enterprises that are supported by policies should have a high potential for future growth. That is, these policies should be supported by enterprises that are capable of sustainable growth. In order to find a start-up enterprise capable of sustainable growth, information of SMEs having a structure similar to a start-up enterprise can be used. In this paper, we conduct enterprise clustering using k-means cluster analysis and t-SNE for start-up enterprises and SMEs that have been provided with technology-based start-up enterprises and SMEs support programs at Daejeon Center for Creative Economy & Innovation in South Korea. The clustering of companies using k-means cluster analysis is performed, and the enterprise information is learned by t-SNE and projected in a two-dimensional space to confirm the characteristics of each cluster. As a result of applying the experiment to 169 start-up enterprises and SMEs, we found clusters of start-up enterprises with high growth potential.
최재현 ( Jaehyun Choi ),장혜선 ( Hyesun Jang ),임양원 ( Yangwon Lim ),임한규 ( Hankyu Lim ) 한국정보처리학회 2012 한국정보처리학회 학술대회논문집 Vol.19 No.2
최근 우리 사회에는 여성과 아동을 대상으로 하는 강력범죄들이 많이 발생하고 있어 개인 위치확인 및 안전에 대한 서비스들이 최근 재조명을 받고 있다. 하지만 서비스가 시작된 기간에 비해 아직도 높은 단말기 가격대와 월 사용료, 그리고 위험상황에서의 사용성은 상대적으로 미약한 발전을 이루었다. 그나마 스마트폰이 많이 보급되어 해당 서비스들의 가격이 조금씩 인하되고, GPS를 활용한 위치정보의 정확도를 개선하는 등 많은 노력을 기울이고 있지만 그 효과는 미비하다. 따라서 본 논문에서는 스마트폰의 다양한 센서를 이용하여, 스마트폰을 꺼낼 수 없는 위험상황에서 사용자가 위험상황에서 특정 이벤트를 발생시켜, 인지된 상태정보를 전송하는 방식을 분석하고, 이를 기반으로 앞으로 개인 안전에 대한 서비스가 발전할 방향을 제시하고자 한다.
Technical issues in graphene anode organic light emitting diodes
Moon, Jaehyun,Shin, Jin-Wook,Cho, Hyunsu,Han, Jun-Han,Cho, Nam Sung,Lim, Jong Tae,Park, Seung Koo,Choi, Hong Kyw,Choi, Sung-Yool,Kim, Ji-Hoon,Maeng, Min-Jae,Seo, Jaewon,Park, Yongsup,Lee, Jeong-Ik Elsevier 2015 Diamond and related materials Vol.57 No.-