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Eric Yee 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.2
Seismic probabilistic safety assessments are used to help understand the impact potentialseismic events can have on the operation of a nuclear power plant. An importantcomponent to seismic probabilistic safety assessment is the seismic hazard curve whichshows the frequency of seismic events. However, these hazard curves are estimatedassuming a normal distribution of the seismic events. This may not be a strong assumptiongiven the number of recorded events at each source-to-site distance. The use of a normaldistribution makes the calculations significantly easier but may underestimate or overestimatethe more rare events, which is of concern to nuclear power plants. This papershows a preliminary exploration into the effect of using a distribution that perhaps morerepresents the distribution of events, such as the t-distribution to describe data. Theintegration of a probability distribution with potentially larger tails basically pushes thehazard curves outward, suggesting a different range of frequencies for use in seismicprobabilistic safety assessments. Therefore the use of a more realistic distribution resultsin an increase in the frequency calculations suggesting rare events are less rare thanthought in terms of seismic probabilistic safety assessment. However, the opposite wasobserved with the ground motion prediction equation considered.
Koh, Yee Kan,Lyons, Austin S.,Bae, Myung-Ho,Huang, Bin,Dorgan, Vincent E.,Cahill, David G.,Pop, Eric American Chemical Society 2016 NANO LETTERS Vol.16 No.10
<P>heat transfer across interfaces of graphene and polar dielectrics (e.g.; SiO2) could be Mediated by direct: phonon coupling, as well as electronic coupling with remote interfacial phonons (RIPs). To understand-the relative contribution of each component, we develop a new pump probe technique called voltage-modulated thermorefleetance (VMTR) to accurately measure the change-of interfacial: thermal conductance under an electrostatic field. We employed VMTR on top gates of graphene field-,effect-transistors. and find that the thermal conductance of SiO2/graphene/SiO2 interfaces increases by up to Delta G approximate to 0.8 MW M-2 K-1 under electrostatic fields of <0.2 V nm(-1). We propose two possible explanations for-the small observed Delta G. First, because the applied electrostatic field induces charge carriers in graphene, out VMTR measurements could originate from heat transfer-between the charge carriers in graphene and RIPs in SiO2. Second, the increase in heat conduction could be caused by better conformity of graphene interfaces under electrostatic pressure exerted by the induced charge carriers. Regardless of the origins of the observed Delta G, our VMTR measurements eStablish, an upper limit for heat transfer from unbiased graphene to SiO2 substrates via RIP scattering; for example, only <2% of the interfacial heat transport is facilitated' y RIP scattering even at a carrier concentration of similar to 4 X 10(12) cm(-2).</P>
Estimating a Maximum Magnitude
Minyoung Kang,Eric Yee,Ekaputra Rhajendra,Changkyu Lee,Soojin Jung,Euihyun Jung 대한토목학회 2023 대한토목학회 학술대회 Vol.2023 No.10
This research discusses maximum magnitude for each seismic source in Korea, and to compare the maximum magnitude before and after the 2016 Gyeongju and 2017 Pohang earthquakes. Based on the Wells and Coppersmith(1994), the largest possible earthquake is estimated to have a magnitude of 7.9 from Tsushima faults. The application of the measured fault length as the surface rupture length introduces a potential for overestimating the values of high-magnitude.
Koh, Renwei Eric,Sun, Cha Chee,Yap, Yee Ling,Cheang, Pei Ling,You, Ah Heng The Korean Electrochemical Society 2021 Journal of electrochemical science and technology Vol.12 No.2
In this study, Monte Carlo (MC) simulation is conducted with recurrence relation to study the effect of SiO<sub>2</sub> with different particle size and their roles in enhancing the ionic conductivity and lithium transference number of PMMA composite polymer electrolytes (CPEs). The MC simulated ionic conductivity is verified with the measurements from Electrochemical Impedance Spectroscopy (EIS). Then, the lithium transference number of CPEs is calculated using recurrence relation with the MC simulated current density and the reference transference number obtained. Incorporation of micron-size SiO<sub>2</sub> (≤10 ㎛) fillers into the mixture improves the ionic conductivity from 8.60×10<sup>-5</sup> S/cm to 2.35×10<sup>-4</sup> S/cm. The improvement is also observed on the lithium transference number, where it increases from 0.088 to 0.3757. Furthermore, the addition of nano-sized SiO<sub>2</sub> (≤12 nm) fillers further increases the ionic conductivity up towards 3.79×10<sup>-4</sup> S/cm and lithium transference number of 0.4105. The large effective surface area of SiO<sub>2</sub> fillers is responsible for the improvement in ionic conductivity and the transference number in PMMA composite polymer electrolytes.
Macroseismic and Microseismic Events Declustering for Korea Peninsula
Ekaputra Rhajendra,Eric Yee,Minyoung Kang,Changkyu Lee,Soojin Jung,Euihyun Jung 대한토목학회 2023 대한토목학회 학술대회 Vol.2023 No.10
This research focuses on declustering the earthquake catalog by removing non-independent events, such as foreshocks and aftershocks. The Gardner and Knopoff (GK) method, known for its simplicity and efficiency, is used for declustering. However, the GK method may inadvertently remove more events than necessary and cannot handle complex cascading event sequences. The results showed that approximately 71% of the earthquake catalog consisted of independent events. Nonetheless, there were limitations in the data distribution and gaps in information for events outside a specific magnitude range. Further analysis is required to assess the usability of macroseismic events and analyze ground motion prediction equations using a refined catalog. This project emphasizes the significance of declustering and considering event independence in seismic hazard analysis for the Korean Peninsula.
유기산 재료를 이용한 사질토의 안정화 메커니즘에 관한 연구
기정서(Jungsu Ki),Eric Yee,이종휘(Jonghwi Lee),천병식(Byungsik Chun) 한국지반환경공학회 2013 한국지반환경공학회논문집 Vol.14 No.6
지반개량분야에서는 수많은 공법들이 지금까지 발전을 거듭하여 개발되어왔다. 그러나 대부분의 공법들은 지반의 강도 증진에만 중점을 두었으며 환경문제 발생에 대한 구체적인 해결방안을 제시하지 못하고 있다. 이에 최근에 들어 친환경적으로 지반의 강도를 증대시키는 방법으로 유기산 재료를 이용한 지반개량이 개발되어왔으나 아직 근본적인 안정화 메커니즘에 대해서는 잘 알려지지 않았다. 따라서 본 연구에서는 친환경 개량재인 유기산 재료를 활용한 일축압축강도시험 및 pH시험을 통해 안정화 메커니즘에 대해 규명하였다. 그 결과, 유기산 처리가 된 샘플이 유기산 처리가 되지 않은 샘플보다 시간에 따른 더 큰 일축압축강도를 보였다. 또한, 유기산 재료에 의해 미생물들의 증식이 촉진되며, 토양의 공극 감소를 통해 토양이 개량된다는 것을 규명할 수 있었다. 향후 유기산 재료를 활용한 지반개량 공법의 지속적인 연구가 필요하다고 사료된다. The field of ground amelioration, many construction methods have been developed more prosperously up to now, but even now, the majority focuses on the improvement of ground strength. And they could not suggest concrete solutions to the occurrence of environmental issues. To address this problem, soil improvement methods employing organic acid materials have recently been developed as eco-friendly technologies for increasing the soil strength, but details regarding the basic stabilization mechanism are not known yet. Against this background, this research was conducted to examine the soil stabilization mechanism; for this purpose, unconfined compressive strength and pH tests were conducted by using an improved eco-friendly organic acid material. The test results revealed that the samples processed with the organic acid showed a considerable increase in the unconfined compressive strength over time as compared to the strength of the samples that were processed without the organic acid. It was also confirmed that the organic acid material promoted microbial breeding and improved the soil structure by reducing the volume of the voids in the soil. Therefore, the sustainable development of this method needs to be analysed more in the future.