MULTISCALE MODELING OF RADIATION EFFECTS ON MATERIALS: PRESSURE VESSEL EMBRITTLEMENT

JUNHYUN KWON,이경근,신찬선 한국원자력학회 2009 Nuclear Engineering and Technology Vol.41 No.1

Radiation effects on materials are inherently multiscale phenomena in view of the fact that various processes spanning a broad range of time and length scales are involved. A multiscale modeling approach to embrittlement of pressure vessel steels is presented here. The approach includes an investigation of the mechanisms of defect accumulation, microstructure evolution and the corresponding effects on mechanical properties. An understanding of these phenomena is required to predict the behavior of structural materials under irradiation. We used molecular dynamics (MD) simulations at an atomic scale to study the evolution of high-energy displacement cascade reactions. The MD simulations yield quantitative information on primary damage. Using a database of displacement cascades generated by the MD simulations, we can estimate the accumulation of defects over diffusional length and time scales by applying kinetic Monte Carlo simulations. The evolution of the local microstructure under irradiation is responsible for changes in the physical and mechanical properties of materials. Mechanical property changes in irradiated materials are modeled by dislocation dynamics simulations, which simulate a collective motion of dislocations that interact with the defects. In this paper, we present a multiscale modeling methodology that describes reactor pressure vessel embrittlement in a light water reactor environment.

Effect of Neutron Energy Spectra on the Formation of the Displacement Cascade in ${\alpha}-Iron$

Kwon Junhyun,Seo Chul Gyo,Kwon Sang Chul,Hong Jun-Hwa Korean Nuclear Society 2003 Nuclear Engineering and Technology Vol.35 No.5

This paper describes a computational approach to the quantification of primary damage under irradiation and demonstrates the effect of neutron energy spectra on the formation of the displacement cascade. The development of displacement cascades in ${\alpha}-Iron$ has been simulated using the MOLDY code - a molecular dynamics code for simulating radiation damage. The primary knock-on atom energy, key input to the MOLDY code, was determined from the SPECTER code calculation on two neutron spectra. The two neutron spectra include; (i) neutron spectrum in the instrumented irradiation capsule of the high-flux advanced neutron application reactor (HANARO), and (ii) neutron spectrum at the inner surface of the reactor pressure vessel steel for the Younggwang nuclear power plant No.5 (YG 5). Minor differences in the normalized neutron spectra between the two spectra produce similar values of PKA energy, which are 4.7 keV for HANARO and 5.3 keV for YG 5. This similarity implies that primary damage to the components of the commercial nuclear reactors should be well simulated by irradiation in the HANARO. Moreover, the application of the MD calculations corroborates this statement by comparing cascades simulation results.

Multiscale Modeling of Radiation Damage: Radiation Hardening of Pressure Vessel Steel

Kwon Junhyun,Kwon Sang Chul,Hong Jun-Hwa Korean Nuclear Society 2004 Nuclear Engineering and Technology Vol.36 No.3

Radiation hardening is a multiscale phenomenon involving various processes over a wide range of time and length. We present a multiscale model for estimating the amount of radiation hardening in pressure vessel steel in the environment of a light water reactor. The model comprises two main parts: molecular dynamics (MD) simulation and a point defect cluster (PDC) model. The MD simulation was used to investigate the primary damage caused by displacement cascades. The PDC model mathematically formulates interactions between point defects and their clusters, which explains the evolution of microstructures. We then used a dislocation barrier model to calculate the hardening due to the PDCs. The key input for this multiscale model is a neutron spectrum at the inner surface of reactor pressure vessel steel of the Younggwang Nuclear Power Plant No.5. A combined calculation from the MD simulation and the PDC model provides a convenient tool for estimating the amount of radiation hardening.

한중 50대와 20대의 소비가치 비교연구를 통한 제품 및 서비스 콘텐츠 개발 방향 탐색

권준현(Junhyun Kwon),한세미(Semi Han),김숙응(Sook-Eung Kim),김은혜(Eunhye Kim) 한국콘텐츠학회 2018 한국콘텐츠학회논문지 Vol.18 No.12

전세계적인 고령화 현상 및 베이비붐세대의 고령층 진입에 따라 시니어 대상 비즈니스에 대한 관심과 기대가 증가하고 있다. 그럼에도 불구하고 수요층에 대한 이해 부족 및 한정적인 내수시장 규모 등 때문에 국내 관련 산업의 성장이 더디게 이루어지고 있다. 이의 활성화를 위해서는 국내 및 해외 시니어에 대한 이해 제고와 이를 기반으로 한 제품 및 서비스 콘텐츠 전략 제시가 필요하다. 이에 따라 본 연구는 소비가치 개념을 적용하여 연령대(20대 vs. 50대) 및 국가간(한국 vs. 중국) 행동을 탐색함으로써, 각 집단이 중요하게 인식하는 소비가치를 베이비붐세대이자 예비시니어층인 50대 소비자를 중점으로 비교분석하고 이들을 위한 제품 및 서비스 콘텐츠 개발 방향을 제안하였다. 연령 및 국가간 소비가치 비교분석을 위하여 설문을 진행하였으며, 설문문항은 12개 소비가치의 하위차원인 총 40개의 문항으로 구성되었다. 분석결과를 통해 예비시니어층인 50대에 대한 이해 제고가 가능하며 이는 타겟에 적절한 콘텐츠 기획, 개발, 유통, 홍보등의 전략 구축에 활용될 수 있다. Senior business has been paid attention due to rapid global aging and baby boomers turning 60. However, senior business is not successful as expected because of a lack of understanding of consumers and small size of Korean domestic market. Understanding of senior consumers and overseas markets and providing attractive product and service contents needs to overcome the current challenges. Therefore, this study explores and compares consumers of different generation and different countries. We employ consumption value theory and analyze which consumption values are perceived strongly by each four group(Korean consumers in their 20s, Korean their consumers in 50s, Chinese consumers in their 20s, and Chinese consumers in their 50s). We conducted online survey to compare consumption values among samples of consumers in two countries: Korea and China. There are forty survey instruments in twelve consumption values. The results can be used to develop a strategy for planning, developing, distributing, and promoting product and service contents which consumers, in particular baby boomers, have a strong intention to purchase it.

Role of the Histone Acetyltransferase Rtt109 in Development and Pathogenicity of the Rice Blast Fungus

Kwon, Seomun,Lee, Jaejoon,Jeon, Jongbum,Kim, Seongbeom,Park, Sook-Young,Jeon, Junhyun,Lee, Yong-Hwan Scientific Societies 2018 Molecular plant-microbe interactions Vol.31 No.11

High-mobility-group A2 overexpression provokes a poor prognosis of gastric cancer through the epithelial-mesenchymal transition

LEE, JUNHYUN,HA, SHINJUNG,JUNG, CHAN-KWON,LEE, HAN HONG Spandidos Publications 2015 International journal of oncology Vol.46 No.6

<P>Tumor metastases are the ultimate target in cancer therapy. In epithelial malignancies, the expression of high-mobility-group A2 (HMGA2) is associated with disease progression and the epithelial-mesenchymal transition (EMT), which is involved in the metastatic process. The present study assessed the clinical and molecular effects of HMGA2 with the malignant tissues of 170 patients with gastric cancer and gastric cancer cells expressing HMGA2. HMGA2 expression was determined using immunohistochemistry and analyzed with respect to the clinicopathological data of patients with this tumor. In the gastric cancer cell line MKN28, in which HMGA2 was knocked down by two different short-hairpin RNAs, Transwell migration and invasion assays were conducted and western blotting was used to detect the altered expression of EMT markers. In patients with gastric cancer, HMGA2 overexpression correlated with tumor progression and was indicative of a significantly worse overall survival. Migration and invasion assays using HMGA2-knocked down MKN28 cells showed a reduction in cell migration and invasion. The upregulation of E-cadherin, an epithelial marker, and the downregulation of N-cadherin, a mesenchymal marker were observed in HMGA2-knocked down cells. In addition, expression of the transcriptional factors Snail and Zeb1 and of the EMT-pathway molecule β-catenin were decreased. HMGA2 overexpression, through its relationship to EMT, thus seems to aggravate invasion and metastasis in gastric cancer. It may therefore serve as a predictive marker in determining the clinical outcome of patients with gastric cancer and offer a promising therapeutic target.</P>

Experimental Study on the Element-Specific Positron Annihilation Spectroscopy

김용민,Junhyun Kwon,HamdyF. Mohamed,MoonJoo Hyun,Changsun Kang 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6

Coincidence Doppler-broadening (CDB) and positron annihilation lifetime (PAL) techniques have been applied to study 12 pure elements. The existence of open-type defects was investigated in the elements. The characteristic features of the high-momentum part of the CDB spectra for elemental metals with/without defects were investigated. By normalizing the CDB spectra to the CDB spectrum of well-annealed Ti, ratio-curves are presented. The moment region range (12×10-3 moc < PL < 20 × 10-3 moc) was elucidated and provided important information on the elemental specificity. An empirical relation that linked the positron anities and the atomic number to the shape of the high-momentum part of the CDB spectra for 3-d elements was derived. The results imply that elements (closely located in the periodic table) can be identified from an analysis of the CDB spectra. Coincidence Doppler-broadening (CDB) and positron annihilation lifetime (PAL) techniques have been applied to study 12 pure elements. The existence of open-type defects was investigated in the elements. The characteristic features of the high-momentum part of the CDB spectra for elemental metals with/without defects were investigated. By normalizing the CDB spectra to the CDB spectrum of well-annealed Ti, ratio-curves are presented. The moment region range (12×10-3 moc < PL < 20 × 10-3 moc) was elucidated and provided important information on the elemental specificity. An empirical relation that linked the positron anities and the atomic number to the shape of the high-momentum part of the CDB spectra for 3-d elements was derived. The results imply that elements (closely located in the periodic table) can be identified from an analysis of the CDB spectra.

CNN과 주파수 대역 특성을 활용한 신호 세기 기반 Wi-Fi 채널 탐지 방법 연구 및 그 활용

박준현(Junhyun Park),변형호(Hyungho Byun),김종권(Chong-Kwon Kim) 한국정보과학회 2020 정보과학회논문지 Vol.47 No.3

모바일 기기에 있어 Wi-Fi 채널 스캔은 인터넷 접속을 개시하여 원활한 서비스 이용을 가능케하고, 연결 수립 이후에도 주기적으로 발생하여 안정적인 링크 유지를 지원하는 필수적인 작업이다. 하지만 불필요한 채널까지 탐색하는 비효율적인 동작은 자원의 낭비와 성능 저하를 초래한다. 본 논문에서는 저전력 안테나로 수집한 주파수 대역 신호 세기의 특성을 CNN을 통해 학습하고, 이에 기반하여 빠르고 정확한 Wi-Fi 채널 탐지 방법을 제안한다. 실험을 통해 다양하게 분포한 AP에 대해 높은 채널 탐지 정확도를 보였고, 이를 기존 Wi-Fi의 스캔 동작 보조에 활용할 시 기대되는 성능 향상을 분석하였다. For mobile devices, Wi-Fi channel scanning is essential to initiating an internet connection, which enables access to a variety of services, and maintaining a stable link quality by periodic monitoring. However, inefficient Wi-Fi operation, where all channels are scanned regardless of whether or not an access point (AP) exists, wastes resources and leads to performance degradation. In this paper, we present a fast and accurate Wi-Fi channel detection method that learns the dynamic frequency band characteristics of signal strengths collected via a low power antenna using a convolution neural network (CNN). Experiments were conducted to demonstrate the channel detection accuracy for different AP combination scenarios. Furthermore, we analyzed the expected performance gain if the suggested method were to assist the scanning operation of the legacy Wi-Fi.

Histone Acetylation in Fungal Pathogens of Plants

Jeon, Junhyun,Kwon, Seomun,Lee, Yong-Hwan The Korean Society of Plant Pathology 2014 Plant Pathology Journal Vol.30 No.1

Acetylation of histone lysine residues occurs in different organisms ranging from yeast to plants and mammals for the regulation of diverse cellular processes. With the identification of enzymes that create or reverse this modification, our understanding on histone acetylation has expanded at an amazing pace during the last two decades. In fungal pathogens of plants, however, the importance of such modification has only just begun to be appreciated in the recent years and there is a dearth of information on how histone acetylation is implicated in fungal pathogenesis. This review covers the current status of research related to histone acetylation in plant pathogenic fungi and considers relevant findings in the interaction between fungal pathogens and host plants. We first describe the families of histone acetyltransferases and deacetylases. Then we provide the cases where histone acetylation was investigated in the context of fungal pathogenesis. Finally, future directions and perspectives in epigenetics of fungal pathogenesis are discussed.

BLE 기반 메쉬 네트워크 연구 동향

박준현(Junhyun Park),김종권(Chong-kwon Kim) 한국정보과학회 2017 한국정보과학회 학술발표논문집 Vol.2017 No.12