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RISS 인기검색어
- 검색키워드
- 저자 : Changsoo Jung (검색결과 115 건)
- 무료
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Enhancement of ultraviolet-beam generation through a double walk-off compensation
Jung, Changsoo,Kim, Kun-Kook,Yu, Bong-Ahn,Lee, Yeung Lak,Shin, Woojin,Kang, Hoonsoo,Noh, Young-Chul The Optical Society 2015 Applied Optics Vol.54 No.27
<P>We propose a novel walk-off-compensation method for ultraviolet-light-source development. A walk-off occurring in the frequency mixing of infrared and green beams is doubly compensated for using an external walk-off compensator and a nonlinear-material set with internal walk-off-compensation arrangement. We theoretically and experimentally verified that our method can improve the power and beam shape of the output ultraviolet beam.</P>
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Smartphone based Indoor Localization Technology using 1D CNN -BLSTM
Changsoo Yu,Beomju Shin,Chung G. Kang,Jung Ho Lee,Hankyeol Kyung,Taehun Kim,Taikjin Lee 제어로봇시스템학회 2022 제어로봇시스템학회 국제학술대회 논문집 Vol.2022 No.11
The study of indoor localization technology using smart phone has been continuously studied. Fingerprinting is a representative indoor positioning technology. This technology estimates the location by comparing Radio Signal Strength (RSS) information received in one-shot at a specific location with the previously constructed Radio Map. Since the RSS received in one-shot is used, the ability to discriminate signals according to space is low. To solve this problem, the use of RSS spatial patterns based on Pedestrian Dead Reckoning (PDR) improves signal discrimination according to space and increases accuracy. However, since PDR is used, there is a problem that it is difficult to use a spatial pattern if PDR distortion occurs due to a heading drift error and a change motion. We propose an indoor positioning technology using 1D Convolutional Neural Network (CNN) and Bi-directional Long Short Term Memory (BLSTM). We estimated the position by learning the 1D RSS pattern. In order to generate a large amount of data, we used the pre-built Radio Map. We use a model that combines 1D CNN and BLSTM. 1D CNN is used to extract RSS patterns, and BLSTM is used to learn the relationship of sequential data in both directions. Through this, it is possible to estimate the position using only the RSS. To verify the proposed technology, we compared it with the previous technology. As a result, the previous technology showed 2.19m error and the proposed technology showed 4.663m error. However, the calculation speed is 30 times faster than the proposed technology. It was confirmed that indoor positioning technology using deep learning technology can provide position information with only 1D RSS pattern.
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Jung, Chanwon,Lee, Changsoo,Bang, Kihoon,Lim, JeongHoon,Lee, Hoin,Ryu, Ho Jin,Cho, EunAe,Lee, Hyuck Mo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>Recently, Pt3M (M = Fe, Ni, Co, Cu, etc.) intermetallic compounds have been highlighted as promising candidates for oxygen reduction reaction (ORR) catalysts. In general, to form those intermetallic compounds, alloy phase nanoparticles are synthesized and then heat-treated at a high temperature. However, nanoparticles easily agglomerate during the heat treatment, resulting in a decrease in electrochemical surface area (ECSA). In this study, we synthesized Pt-Fe alloy nano particles and employed carbon coating to protect the nanoparticles from agglomeration during heat treatment. As a result, Pt3Fe L1(2) structure was obtained without agglomeration of the nanoparticles; the ECSA of Pt-Fe alloy and intermetallic Pt3Fe/C was 37.6 and 33.3 m(2) g(pt)(-1), respectively. Pt3Fe/C exhibited excellent mass activity (0.454 A mg(pt)(-1)) and stability with superior resistances to nanoparticle agglomeration and iron leaching. Density functional theory (DFT) calculation revealed that, owing to the higher dissolution potential of Fe atoms on the Pt3Fe surface than those on the Pt-Fe alloy, Pt3Fe/C had better stability than Pt-Fe/C. A single cell fabricated with Pt3Fe/C showed higher initial performance and superior durability, compared to that with commercial Pt/C. We suggest that Pt3M chemically ordered electrocatalysts are excellent candidates that may become the most active and durable ORR catalysts available.</P>
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Unstructured Data Quantification Scheme Based on Text Mining for User Feedback Extraction
Jung-Heum Jo,Yong-Taek Chung,Seong-Wook Choi,Changsoo Ok 한국산업경영시스템학회 2018 한국산업경영시스템학회지 Vol.41 No.4
People write reviews of numerous products or services on the Internet, in their blogs or community bulletin boards. These unstructured data contain important emotions and opinions about the author's product or service, which can provide important information for future product design or marketing. However, this text-based information cannot be evaluated quantitatively, and thus they are difficult to apply to mathematical models or optimization problems for product design and improvement. Therefore, this study proposes a method to quantitatively extract user’s opinion or preference about a specific product or service by utilizing a lot of text-based information existing on the Internet or online. The extracted unstructured text information is decomposed into basic unit words, and positive rate is evaluated by using existing emotional dictionaries and additional lists proposed in this study. This can be a way to effectively utilize unstructured text data, which is being generated and stored in vast quantities, in product or service design. Finally, to verify the effectiveness of the proposed method, a case study was conducted using movie review data retrieved from a portal website. By comparing the positive rates calculated by the proposed framework with user ratings for movies, a guideline on text mining based evaluation of unstructured data is provided.
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Jung, Heejung,Kim, Jaai,Lee, Changsoo Elsevier 2017 Algal research Vol.28 No.-
<P><B>Abstract</B></P> <P>This study investigated the anaerobic digestion of <I>Ulva</I> biomass as an approach to diversifying energy sources and managing seaweed waste in a cost-effective manner. <I>Ulva</I> species are often identified as the main culprit of serious macroalgal blooms around the world, and their sulfur-rich nature causes difficulties in handling the biomass. Two reactors in continuous (Rc) and sequencing batch (Rs) modes were operated with decreasing hydraulic retention time in a stepwise manner from 20 to 6days. Rs allowed significantly higher methane productivity (0.19–0.22L/g chemical oxygen demand [COD] fed) and biomass retention capacity than Rc (0–0.16L/g COD fed) throughout the experiment. Interestingly, sulfide production was also higher in Rs than in Rc. These findings, together with microbial quantification results, suggested that Rs operation enhanced biomass retention and the activity of both methanogens and sulfate-reducing bacteria. The Rc microbial community was less diverse and more variable than the Rs community. Accordingly, the performance of Rc was more significantly affected by changes in hydraulic and thus organic loads. Aceticlastic <I>Methanosaetaceae</I> dominated the methanogen community in both reactors, with the abundance of methanogens being significantly higher in Rs than in Rc. This may explain the more efficient and stable methane production despite the greater sulfidogenic activity in Rs, particularly at high hydraulic loads. Together, the results suggest that sequencing batch operation is advantageous over conventional continuous flow operation for the biomethanation of <I>Ulva</I> biomass and potentially other sulfur-rich feedstocks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>Ulva</I> biomethanation was examined in continuous versus sequencing batch operations. </LI> <LI> Both sulfate-reducing and methanogenic activities were higher in sequencing batch. </LI> <LI> Aceticlastic <I>Methanosaetaceae</I> dominated the methanogen community in both reactors. </LI> <LI> Sequencing batch is advantageous for stable <I>Ulva</I> digestion at high organic loads. </LI> <LI> Sequencing batch is more suitable for the biomethanation of sulfur-rich feedstocks. </LI> </UL> </P>
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Jung-Tae Kim,Changsoo Lee,Jin-Seop Kim,Sinhang Kang 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
The International Atomic Energy Agency recommends the deep geological disposal system as one of the disposal methods for high-level radioactive waste (HLW), such as spent nuclear fuel. The deep geological disposal system disposes of HLW in a deep and stable geological formation to isolate the HLW from the human biosphere and restrict the inflow of radionuclides into the ecosystem. It mainly consists of an engineered barrier and a natural barrier. Safety evaluation using a numerical model has been performed primarily to evaluate the buffer’s long-term stability. However, although the gas generation rate input for long-term stability evaluation is the critical factor that has the most significant influence on the long-term hydraulic-mechanical behavior of the buffer, in-depth research and experimental data are lacking. In this study, the gas generation rate on the interface between the disposal canister and the buffer material, a component of the engineered barrier, was mainly studied. Gas can be generated between the disposal canister and the buffer material due to various causes such as anaerobic corrosion of the disposal canister metal, organic matter decomposition, radiation decomposition, and steam generation due to high temperature. The generation of gas in such a disposal environment increases the pore gas pressure in the buffer and causes internal cracks. The occurred cracks increase the intrinsic permeability of the buffer, which leads to a decrease in the primary performance of the buffer. For this reason, it is essential to apply the appropriate gas generation rate according to the disposal condition and buffer material for accurate long-term stability analysis. Therefore, the theoretical models regarding the estimation of gas generation were summarized through a literature study. The amount of gas generated was estimated according to the disposal environment and material of the disposal canister. It is expected that estimated values might be used to estimate the long-term stability analysis of buffer performance according to the disposal condition.
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Integrated Fluid-Structure-Burning Simulation for Axisymmetric Solid Rocket Motor
Changsoo Lee,Hyunjoo Cho,Chongam Kim,Jeeho Lee,Gyoodong Jung,Bangeop Lee,Jongyun Oh 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.10
This paper deals with fully integrated computational simulations to examine the non-linear feedback interaction between fluid, structure, and burning modules inside a solid rocket motor. Various methods are used for simulating the interior of the solid rocket motor. The Arbitrary Lagrangian-Eulerian (ALE) description and mesh moving method are employed to efficiently track the burning process along a grain surface. An automatic remeshing algorithm is added to the fluid, structure, and burning process to accurately analyze unsteady fluid-structure-burning coupling phenomena with deforming propellant grain during the simulation. The common-refinement method is implemented to obtain numerically accurate and physically conservative data transfers across the interface meshes between fluid and structure domain. Conventional serial-staggered scheme is adopted to efficiently integrate each module. The developed solver is then applied to the full-burning simulation of the axisymmetric solid rocket motor, Attitude Control Motor (ACM). The computed pressure-history inside the rocket motor shows the same tendency with experimental data in overall burning process.
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