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Yujin Byun,Chanyoung Seo,Ho Young Jo,Young Jae Lee,Ji-Hun Ryu,Hye-Yoon Chong,Seong-Wan Park 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2
Deep geological disposal is generally accepted to be the most practical approach to handling radioactive wastes. Bentonite has been considered as a buffer material in deep geological disposal repositories (DGR) for high-level radioactive wastes. Evaluating the effect of short-term bentonite alteration on EBS performance has limitations in safety assessment over thousands of years. Information on bentonite characteristics under various conditions obtained from natural systems can be used to evaluate long-term safety of bentonite buffer. The purpose of this study was to investigate mineralogical and physicochemical characteristics of bentonite in the Naah mine located in Yangnam-myeon, Gyeongju-si for a natural analogue of the bentonite barrier in DGR. A total of 15 samples were collected at regular intervals from the bentonite layer and andesitic lapilli tuff (i.e., parent rock) at the boundary with the bentonite layer. The bentonite layer is located at a depth of about 1 m below the ground surface. Each sample was separated into particles < < 75 μm and particles < 2 μm through grinding and sedimentation processes. The separated subsamples were characterized mineralogically and physiochemically using various analytic techniques. Bentonite samples have a similar SiO2/Al2O3 ratio to the parent rock and a lower (Na+K)/Si ratio than the parent rock, indicating depletion of alkali components during bentonitization. The parent rock and bentonite samples have similar mineral composition (i.e., quartz, feldspars, opal-cristobalite-tridymite and montmorillonite). Results of XRD analysis on the randomly distributed particles < 2 μm indicate that bentonite is mostly composed of Ca-montmorillonite, which is a typical dioctahedral smectite. Results of FTIR and VNIR analysis indicate that montmorillonite contained in bentonite is Al-dioctahedral montmorillonite, and Al is substituted with Mg in some octahedron units. The mineralogical and physicochemical characteristics are similar regardless of sampling location. These results suggest that bentonite potentially exposed to weathering, located near the ground surface, has hardly altered.
MinSoo Byun,Dahyun Yi,JunHo Lee,YoungMin Choe,BoKyung Sohn,JunYoung Lee,HyoJung Choi,Hyewon Baek,YuKyeong Kim,YunSang Lee,ChulHo Sohn,Inhee MookJung,Murim Choi,YuJin Lee,DongWoo Lee,SeungHo Ryu,ShinGy 대한신경정신의학회 2017 PSYCHIATRY INVESTIGATION Vol.14 No.6
Objective-The Korean Brain Aging Study for the Early Diagnosis and Prediction of Alzheimer’s disease (KBASE) aimed to recruit 650 individuals, aged from 20 to 90 years, to search for new biomarkers of Alzheimer’s disease (AD) and to investigate how multi-faceted lifetime experiences and bodily changes contribute to the brain changes or brain pathologies related to the AD process. Methods-All participants received comprehensive clinical and neuropsychological evaluations, multi-modal brain imaging, including magnetic resonance imaging, magnetic resonance angiography, [11C]Pittsburgh compound B-positron emission tomography (PET), and [18F]fluorodeoxyglucose-PET, blood and genetic marker analyses at baseline, and a subset of participants underwent actigraph monitoring and completed a sleep diary. Participants are to be followed annually with clinical and neuropsychological assessments, and biannually with the full KBASE assessment, including neuroimaging and laboratory tests. Results-As of March 2017, in total, 758 individuals had volunteered for this study. Among them, in total, 591 participants-291 cognitively normal (CN) old-aged individuals, 74 CN young- and middle-aged individuals, 139 individuals with mild cognitive impairment (MCI), and 87 individuals with AD dementia (ADD)-were enrolled at baseline, after excluding 162 individuals. A subset of participants (n=275) underwent actigraph monitoring. Conclusion-The KBASE cohort is a prospective, longitudinal cohort study that recruited participants with a wide age range and a wide distribution of cognitive status (CN, MCI, and ADD) and it has several strengths in its design and methodologies. Details of the recruitment, study methodology, and baseline sample characteristics are described in this paper.
Su Ho Her,Jaehoon Byun,Dongjun Lee,Jina Ryu,Yujin Kim,Hyeonjin Eun,Jong-Il Yun 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2
The ultimate objective of deep geological repositories is to achieve complete segregation of hazardous radioactive waste from the biosphere. Thus, given the possibility of leaks in the distant future, it is crucial to evaluate the capability of clay minerals to fulfill their promising role as both engineered and natural barriers. Selenium-79, a long-lived fission product originating from uranium- 235, holds significant importance due to its high mobility resulting from the predominant anionic form of selenium. To investigate the retardation behaviors of Se(IV) in clay media by sorption, a series of batch sorption experiments were conducted. The batch samples consisted of Se(IV) ions dissolved in 0.1 M NaCl solutions, along with clay minerals including kaolinite, montmorillonite, and illite-smectite mixed layers. The pH of the samples was also varied, reflecting the shift in the predominant selenium species from selenious acid to selenite ion as the environment can shift from slightly acidic to alkaline conditions. This alteration in pH concurrently promotes the competition of hydroxide ions for Se(IV) sorption on the mineral surface as the pH increases and impedes the selective attachment of selenium. The acquired experimental data were fitted through Langmuir and Freundlich sorption isotherms. From the Freundlich fit data, the distribution coefficient values of Se(IV) for kaolinite, montmorillonite, and illite-smectite mixed layer were derived, which exhibited a clear decrease from 91, 110, 62 L/kg at a pH of 3.2 to 16, 6.3, 12 L/kg at a pH of 7.5, respectively. These values derived over the pH range provide quantitative guidance essential for the safety assessment of clay mineral barriers, contributing to a more informed site selection process for deep geological repositories.
SIMULATIONS OF TORUS REVERBERATION MAPPING EXPERIMENTS WITH SPHEREX
Kim, Minjin,Jeong, Woong-Seob,Yang, Yujin,Son, Jiwon,Ho, Luis C.,Woo, Jong-Hak,Im, Myungshin,Byun, Woowon The Korean Astronomical Society 2021 Journal of The Korean Astronomical Society Vol.54 No.2
Reverberation mapping (RM) is an efficient method to investigate the physical sizes of the broad line region (BLR) and dusty torus in an active galactic nucleus (AGN). The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission will provide multi-epoch spectroscopic data at optical and near-infrared wavelengths. These data can be used for RM experiments with bright AGNs. We present results of a feasibility test using SPHEREx data in the SPHEREx deep regions for torus RM measurements. We investigate the physical properties of bright AGNs in the SPHEREx deep field. Based on this information, we compute the efficiency of detecting torus time lags in simulated light curves. We demonstrate that, in combination with complementary optical data with a depth of ~ 20 mag in B-band, lags of ≤ 750 days for tori can be measured for more than ~ 200 bright AGNs. If high signal-to-noise ratio photometric data with a depth of ~ 21-22 mag are available, RM measurements are possible for up to ~ 900 objects. When complemented by well-designed early optical observations, SPHEREx can provide a unique dataset for studies of the physical properties of dusty tori in bright AGNs.
( Bomin Kim ),( Yoonsik Gong ),( Yeowon Yoon ),( Jihoon Lee ),( Yujin Byun ),( Ho Young Jo ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
The contaminant transport in the unsaturated zone can be governed by soil heterogeneity. The characterization of soil heterogeneity is crucial for understanding the contaminant transport. In this study, the spatial distribution of soil physical properties was assessed using geostatistical methods. For the data acquisition, soil sampling with 20 m grid interval and depth of 2 m (i.e., sampling area: 0.6 ㎢) was conducted in the test bed located in Namyangju, South Korea. Soil physical and hydraulic properties (i.e., bulk density, dry density, water content, porosity, soil texture, and hydraulic conductivity) were measured for soil samples via laboratory tests. Three-dimensional distribution maps of soil physical and hydraulic properties were constructed using the SKUA-GOCAD software developed by Paradigm. The spatial correlation and its continuity of the variables were identified by variogram modeling. The quantification and visualization of each property were performed using different interpolation methods. All the values of each soil property were compared to assess the heterogeneity of the soil properties. By comparing the property distributions, the links between each parameter were explained. The validity of each model was verified by a comparison of the measured and estimated values.