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- 저자 : ( Songhyun Lee ) (검색결과 47 건)
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Wavelength-Switchable Erbium-Doped Fiber Ring Laser Using Inline Fiber Bragg Grating Filter
Lee, Seul-Lee,Park, Kyongsoo,Jo, Songhyun,Choi, Sungwook,Jeong, Jun Hyeok,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Jihoon,Lee, Yong Wook American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.10
<P>Here, we propose a wavelength-switchable erbium-doped fiber (EDF) ring laser by harnessing the unique switching feature of an inline fiber Bragg grating (FBG) filter based on a polarization-diversified loop. The inline filter consists of a four-port polarization beam splitter, three quarter-wave plates (QWPs), and two FBGs with different Bragg wavelengths. By adjusting the orientation angles of the three QWPs, this inline filter can select one of the two different resonances of the two FBGs. The proposed laser is composed of EDF pumped by a 980 nm laser diode, a wavelength-division multiplexing coupler, an optical isolator, a 3 dB optical coupler, and the inline FBG filter. At a special combination of the orientation angles of the three QWPs, one of the two reflection spectra of two FBGs could be chosen and thus the lasing wavelength of the proposed laser, which corresponds to the Bragg wavelength of the selected FBG, could be switched by adjusting the QWP angles. The fabricated ring laser accomplished stable and uniform lasing at each Bragg wavelength or switching operation between two wavelengths at proper QWP angle sets.</P>
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Unveiling coke formation mechanism in MFI zeolites during methanol-to-hydrocarbons conversion
Lee, Songhyun,Choi, Minkee Elsevier 2019 Journal of catalysis Vol.375 No.-
<P><B>Abstract</B></P> <P>Coke formation over MFI zeolites of different crystallite sizes was rigorously investigated in methanol-to-hydrocarbon conversion (MTH). The key experimental idea was based on the fact that soft coke in the zeolite micropores (internal coke) could be selectively removed by thermal treatment under H<SUB>2</SUB>, while heavy coke at the zeolite external surface (external coke) remained intact. This enabled us to analyze the amount, composition, chemical nature, and deactivating effects of internal and external cokes, separately. As the mass transfer of hydrocarbons was retarded with increasing zeolite crystallite size, an aromatic-based catalytic cycle became dominant in MTH compared to an olefin-based cycle. Consequently, methylated benzene intermediates were accumulated within the zeolite micropores. These methylated benzenes could also act as coke precursors and polymerize to form internal coke within the micropores. Aromatic products that diffused out of zeolite micropores could also be condensed at the external surface of the zeolite crystallites. Once the carbon deposits were formed at the external zeolite surface, the external coke continued to grow even non-catalytically by the thermal reaction with the methylated benzenes. Different zeolite catalysts and reaction times affected only the relative amounts of internal and external cokes, but not their respective chemical natures. The internal coke appeared to have the H/C ratio of 1.26 and a density of 1.0 g cm<SUP>−3</SUP>, while the external coke had much lower H/C ratio (0.28) and higher density (1.5 g cm<SUP>−3</SUP>). We propose that internal coke is likely to have the polymeric structures of the methylated acenes (<I>i.e</I>., linearly fused aromatic rings such as benzene, naphthalene, and anthracene) connected via methylene bridges. On the other hand, the external coke is highly polyaromatic with many fused rings. In terms of catalyst deactivation, the internal coke proved to be much more detrimental than the external coke.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formation mechanism, location, and nature of coke species in MFI zeolites were studied in MTH. </LI> <LI> Methylated benzenes accumulated within the zeolite micropore polymerize to form internal coke. </LI> <LI> External coke grow non-catalytically by the thermal reaction with the methylated benzenes. </LI> <LI> Different zeolites and reaction times affected the amounts of internal/external cokes, not their natures. </LI> <LI> In terms of catalyst lifetime, internal coke is much more detrimental than external coke. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Lee, Kyungho,Lee, Songhyun,Jun, Youngsun,Choi, Minkee Academic Press 2017 Journal of catalysis Vol.347 No.-
<P><B>Abstract</B></P> <P>The cooperative effects of secondary mesoporosity and defects on the coke formation and deactivation of zeolite were investigated in <I>n</I>-pentane aromatization using model Ga/ZSM-5 catalysts. Mesoporosity was introduced to a commercial ZSM-5 by alkaline desilication, while the defects sites (<I>i.e.</I>, internal silanols) in zeolites were annealed by the treatment with ammoniumhexafluorosilicate. Aromatization after supporting Ga showed that the mesopore generation retarded catalyst deactivation via the suppression of internal coke formation while facilitating the external coke formation due to the enhanced diffusion of coke precursors <I>(e.g</I>., alkylaromatics) out of zeolite micropores. Internal coke can cause a more severe deactivation than external coke because the acid sites are mainly located in the zeolite micropores. However, the mesopore generation alone could not efficiently reduce the total amount of coke deposition (it mainly changed the location of coke). In contrast, the annealing of internal silanols could suppress the overall coke formation. This phenomenon could be explained by the fact that coke precursors are initially generated at the zeolite internal defects, and then deposited as coke at either the internal or the external surfaces of the zeolite depending on the relative kinetics of coke precursor diffusion and its polymerization. Consequently, the catalyst with mesoporosity and annealed internal silanols exhibited the slowest catalyst deactivation due to the suppression of both internal and external coke depositions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of zeolite mesopore and internal defects on coke formation were studied. </LI> <LI> Mesopore mainly changes the location of coke deposition, not its overall quantity. </LI> <LI> Mesopore induces external coke deposition which is less harmful than internal coke. </LI> <LI> Annealing defects suppress coke formation by inhibiting coke precursor formation. </LI> <LI> Generating mesopore while minimizing defect is effective for retarding deactivation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Lee, Songhyun,Lee, Kyungho,Im, Juhwan,Kim, Hyungjun,Choi, Minkee Elsevier 2015 Journal of catalysis Vol.325 No.-
<P><B>Abstract</B></P> <P>Historically, Pt/LTA (<I>e.g</I>., Pt/NaA) has often been used as a model catalyst for studying the catalytic functions of hydrogen spillover (H spillover). Notably, none of the works reported appreciable catalytic activities for Pt/LTA alone, while markedly enhanced activities were reported after physical dilution with some acidic oxides. It was often speculated without experimental evidence that activated hydrogen generated from Pt/LTA can migrate to the diluents surface (“inter-particular” H spillover) where organic reactants can react with spilt-over hydrogen. In this work, we carefully studied benzene hydrogenation activities of Pt/NaA and its decationized form (Pt/HA), before and after the physical dilution with various metal oxides possessing different Lewis and Brønsted acidity. The originally negligible activity of Pt/NaA increased significantly after mixing with various acidic oxides. The physical dilutions, however, resulted in a significant alteration of Pt/NaA structure due to solid-state H<SUP>+</SUP> exchange, which made the catalytic interpretation vague. In contrast, Pt/HA structure did not change after the dilutions, and thus could be used as an ideal catalytic model system for studying inter-particular H spillover. The catalytic results showed that Al-rich metal oxides with abundant Lewis acid sites are effective for enhancing the catalytic activity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Catalytic effects of physically diluting Pt/NaA and Pt/HA with various acidic metal oxides were studied. </LI> <LI> Physical dilution altered the original structure of Pt/NaA due to solid-state H<SUP>+</SUP>-exchange. </LI> <LI> Physical dilution did not change the structure of decationized form of Pt/NaA (Pt/HA). </LI> <LI> Dilution with Al-rich metal oxides can markedly enhance the catalytic activity of Pt/HA. </LI> <LI> Lewis acid sites may play a significant role in the catalytic use of hydrogen spillover. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Songhyun Lee,Hyeryun Jeong,Eloise Anguluan,Jae Gwan Kim 한국광학회 2018 Current Optics and Photonics Vol.2 No.1
Our previous study showed that switching the inhaled gas from hypoxic gas to hyperoxic gas for 10 minutes increased tumor oxygenation and that the magnitude of oxyhemoglobin increase responded earlier than tumor volume change after chemotherapy. During 10 minutes of inhaled-oxygen modulation, oxyhemoglobin concentration first shows a rapid increase and then a slow but gradual increase, which has been fitted with a double-exponential equation in this study. Two amplitude values, amplitudes 1 and 2, respectively represent the magnitudes of rapid and slow increase of oxyhemoglobin. The trends of changes in amplitudes 1 and 2 were different, depending on tumor volume when chemotherapy started. However, both amplitudes 1 and 2 changed earlier than tumor volume, regardless of when chemotherapy was initiated. These results imply that by observing amplitude 1 changes post chemotherapy, we can reduce the time of a respiratory challenge from 10 minutes to less than 2 minutes, to see the chemotherapy response. We believe that by reducing the time of the respiratory challenge, we have taken a step forward to translating our previous study into clinical application.
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COVID-19 감염병 확산에 따른 일회용 마스크의 적정 관리 방안 연구
이송현 ( Songhyun Lee ),김병환 ( Byeonghwan Kim ),지승민 ( Seungmin Ji ),장용철 ( Yong-chul Jang ),이어진 ( Eojin Lee ),박미솔 ( Misol Park ),김선용 ( Sunyong Kim ),심유나 ( Yuna Sim ),김동현 ( Donghyeon Kim ),한소영 ( Soyeong Han 한국폐기물자원순환학회 2021 한국폐기물자원순환학회지 Vol.38 No.4
This study examined the current management and problems of discarded single-use masks in Korea during COVID- 19. Field visits have been made to identify potential problems associated with the disposal of single-use face masks. We analyzed a total of 32 discarded single-use face masks and newly made singe-use face masks for material composition and characteristics. Based on this study, there were more than 6.7 billion single-use masks manufactured in 2020, indicating that more than six times higher than the production of the masks in 2019 due to COVID-19 pandemic. The average use of single-use face masks per person was found to be 130 masks/yr, which is equivalent to 6.7 billion masks/yr in 2020 in Korea. After the collection of the used masks, the large fraction of discarded masks was incinerated (14,961 ton or 3.8 billion masks) and landfilled (8,056 ton or 2.1 billion masks). Only approximately 1% of the discarded masks from households was improperly disposed on streets, parks, roads, shopping carts, rivers and streams, and other environment. Improper disposal of such masks may pose a threat to humans, animals, and other ecological receptors because of potential spread of virus, the occurrence of microplastics and their non-biodegradable characteristics. Technical development of biodegradable face masks has been made from scientific community to reduce plastic pollution from single-use face masks. However, more research is still needed to warrant the safety, biodegradability, waste management, and economic factors of the eco-friendly face masks. Waste minimization and prevention of single-use face masks is a challenging task due to the preference of the mask to consumers over the COVID-19 pandemic.
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공유피드백 유로를 갖는 초음속 유체진동기의 진동특성에 관한 연구
이승헌(SeungHeon Lee),박상훈(SangHoon Park),고희창(HeeChang Ko),서송현(SongHyun Seo),이열(Yeol Lee) 한국항공우주학회 2020 韓國航空宇宙學會誌 Vol.48 No.3
내부에 공유피드백 유로를 갖는 공유형 초음속 유체진동기에서 나타나는 유동특성에 관한 연구가 수행되었다. 비정상 전산유체역학적 해석이 수행되었고 수치해석 결과는 동일한 운용조건에서 수행된 실험결과와 비교 검증되었다. 수치해석 결과, 공유피드백 유로가 해당 유체진동기의 진동 메커니즘에 큰 영향을 주어 진동기 출구 각 제트유동의 동조화에 큰 역할을 하고 있음이 확인되었다. 공유형 유체진동기는 동일 형상의 단일형 유체진동기와 비교하여 진동수가 증가하나 압력손실 또한 커짐이 확인되었다. A study of flow characteristics of supersonic fluidic oscillators with shared feedback channel inside was carried out. Unsteady CFD analysis were performed and the numerical results were validated by comparison with the experimental ones observed for the same operation conditions. It was found that the mass flow between individual oscillators through the shared feedback channel directly influenced on the oscillating flow mechanism inside the oscillator, and finally on the synchronization of the jet oscillations. It was also observed that the oscillator with shared feedback channel provided higher pressure loss as well as higher oscillation frequency as compared to the single oscillator of the same geometric shape.
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