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Journal of Environmental Sciences 2014年第6期26卷 1340-1347页

作者： Hansaem lee Zuwhan yun Research Institute for Environmental Technology and Sustainable Development Korea University Department of Environmental Engineering Korea University

A successful enhanced biological phosphorus removal （EBPR） was observed in both anaerobic- aerobic sequencing batch reactor （An-Ox SBR） to induce growth of phosphorus accumulating organism （PAO） and anaerobic-anoxic （An-Ax） SBR to induce growth of denitrifying PAO （DPAO）. Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR （22.8 ± 3.5 mg P/（g ***）） and the An-Ox SBR （22.4 ± 4.8 mg P/（g ***）） were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/（g ***）（An-Ax SBR） and 25.6 ± 2.8 mg P/（g ***）（An-Ox SBR）, respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates （PHA） synthesized under anaerobic conditions with phosphorous release （Preleased/PHAsynthesized） and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake （Puptaked/PHAutilized） verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.

关键词： denitrifying EBPR poly-β-hydroxyalkanoates specific phosphorus release rate specific phosphorus uptake rate

Synergistically coupling of Ni–Fe LDH arrays with hollow Co–Mo sulfide nanotriangles for highly efficient overall water splitting

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Rare Metals 2024年第2期43卷 522-532页

作者： yun Jae lee Seung-Keun Park Department of Advanced Materials Engineering Chung-Ang UniversityAnseongGyeonggi-do17546Republic of Korea Department of Intelligent Energy and Industry Chung-Ang University84 Heukseok-ro Dongjak-guSeoul06974Republic of Korea Western Seoul Center Korea Basic Science Institute150 Bugahyeon-roSeodaemun-guSeoul03759Republic of Korea

Developing bifunctional catalysts that can catalyze both oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)is pivotal to commercializing large-scale water ***,a novel hollow nanotriangle composed of NiFe LDH-CoMoS_(x) heterojunction(H-CMSx@NiFe LDH)is proposed as a highly efficient bifunctional electrocatalyst for both OER and *** fabricate a heterojunction system,ultra-thin nickel–iron layered double hydroxide(NiFe LDH)nanosheets are uniformly electrodeposited onto a metal–organic framework-derived hollow CoMoS_(x) *** strong coupling of CoMoS_(x) and NiFe LDH catalysts forms the intimate heterojunction interfaces to facilitate interfacial charge transfer,which is favorable to enhance the bifunctional catalytic ***,the large void of CoMoS_(x) nanotriangles and interconnected ultra-thin NiFe LDH nanosheets result in good electrolyte penetration and gas ***,the as-prepared H-CMSx@NiFe LDH on nickel foam(NF)exhibits an impressive catalytic activity and durability for OER and HER activities,delivering a current density of 100 mA·cm^(−2) at the small overpotentials of 214 and 299 mV in OER and HER,***,H-CMSx@NiFe LDH/NF proves to be an effective electrode for an alkaline electrolyzer,as a voltage of only 1.99 V is enough to achieve a current density voltage of only 1.99 V is enough to achieve a current density of 400 mA·cm^(−2) with no degradation in performance over 50 h.

关键词： Overall water splitting Metal-organic framework Molybdenum sulfide Layered double hydroxide Heterojunction

Evidence of Specific MJO Phase Occurrence with Summertime California Central Valley Extreme Hot Weather

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Advances in Atmospheric Sciences 2019年第6期36卷 589-602页

作者： yun-Young lee Richard GROTJAHN Asia-Pacific Economic Cooperation Climate Center Department of Land Air and Water Resources University of California

This study examines associations between California Central Valley(CCV) heat waves and the Madden Julian Oscillation(MJO). These heat waves have major economic impact. Our prior work showed that CCV heat waves are frequently preceded by convection over the tropical Indian and eastern Pacific oceans, in patterns identifiable with MJO phases. The main analysis method is lagged composites(formed after each MJO phase pair) of CCV synoptic station temperature, outgoing longwave radiation(OLR), and velocity potential(VP). Over the CCV, positive temperature anomalies occur only after the Indian Ocean(phases 2-3) or eastern Pacific Ocean(phases 8-1) convection(implied by OLR and VP fields). The largest fractions of CCV hot days occur in the two weeks after onset of those two phase pairs. OLR and VP composites have significant subsidence and convergence above divergence over the CCV during heat waves, and these structures are each part of larger patterns having significant areas over the Indian and Pacific Oceans. Prior studies showed that CCV heat waves can be roughly grouped into two clusters: Cluster 2 is preceded by a heat wave over northwestern North America, while Cluster 1 is not. OLR and VP composite analyses are applied separately to these two clusters. However, for Cluster 2, the subsidence and VP over the CCV are not significant, and the large-scale VP pattern has low correlation with the MJO lagged composite field. Therefore, the association between the MJO convection and subsequent CCV heat wave is more evident in Cluster 1 than Cluster 2.

关键词： MJO heat wave large-scale meteorological pattern extratropical response tropical convection

Anoxic gas recirculation system for fouling control in anoxic membrane reactor

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Journal of Environmental Sciences 2014年第6期26卷 1289-1293页

作者： Hansaem lee Daeju lee Seongwan Hong Geum Hee yun Sungpyo Kim Jung Ki Hwang Woojae lee Zuwhan yun Research Institute for Environmental Technology and Sustainable Development Korea UniversitySeoul 136-713 Korea Department of Environmental Engineering Korea UniversitySejong 339-700 Korea Dongbu Corporation Seoul 135-523 Korea

Anoxic gas recirculation system was applied to control the membrane fouling in pilot-scale 4- stage anoxic membrane bioreactor （MBR）. In the anaerobic-anoxic-anoxic-aerobic flow scheme, hydrophilic polytetrafluoroethylene （PTFE） membrane （0.2 μm, 7.2 m2/module） was submerged in the second anoxic zone. During 8 months operation, the average flux of the membrane was 21.3 L/（***）. Chemical cleaning of the membrane was conducted only once with sodium hydroxide and sodium hypochlorite. Dissolved oxygen （DO） concentration in the second anoxic zone was maintained with an average of 0.19 ± 0.05 mg/L. Gas chromatography analysis showed that the headspace gas in the second anoxic reactor was mainly consisted of N2 （93.0% ± 2.5%）, O2 （3.8% ± 0.6%）, and CO2 （3.0% ± 0.5%）, where the saturation DO concentration in liquid phase was 1.57 mg/L. Atmospheric 02 content （20.5% ± 0.8%） was significantly reduced in the anoxic gas. The average pH in the reactor was 7.2 ± 0.4. As a result, the recirculation of the anoxic gas was successfully applied to control the membrane fouling in the anoxic MBR.

关键词： anoxic gas recirculation system anoxic membrane bioreactor fouling

Development of Precise Geoid Model for the Establishment of Consistent Height System in Geoga Grand Bridge Construction Area

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China Ocean Engineering 2009年第4期23卷 679-694页

作者： Dong-Ha lee Hong-Sic yun Department of Civil Architectural and Environmental System EngineeringSungkyunkwan University

The national benchmarks on islands were mostly established by trigonometric leveling in Korea. This method results in inaccuracy, which is a serious problem in Geoga Grand Bridge construction work that tried to link the mainland and the islands. The Geoga Grand Bridge （Pusan-Geoje fixed link project） was selected as the study area, a huge construction work in Korea that will connect the mainland （Pnsan） and an island （Gecje island）. However, the orthometric heights issued at benchmarks （JINH and GOFJ） were not consistent, because they did not refer to the same zero point, which would make the linking of the sections problematic. This paper introduces the precise local geoidas a vertical datum for the construction area in order to establish a consistent height system. To determine the precise local geoid for the construction area, we firstly developed a precise gravimetric geoid for Korea and its adjoining seas as a whole. This gravimetric geoid was developed by use of all available gravity data, including surface and satellite data on land and on the ocean. The gravimetrie gecid was computed by spherical fast fourier transform with modified Stokes＇ kernels. The remove-restore technique was used to eliminate the terrain effects by use of the RTM reduction and to determine the residual geoid by combining the GGM02S/EGM96 geopotential model, free-air gravity anomalies and high-resolutinn DEM data. Finally, the gravimetric model was fitted to the geoid heights obtained from GPS and tide observations （Ncps/Tiae） by least square couocatian, to provide the final GPS-consistent local precise geoid model. The post-fit error （std. dev. ） of the final geoid to the NetS/Tide derived from GPS and tide observations was ± 2.2 cm for the construction area. We solved the height inconsistency problem by calculating the orthometric height of the benchmarks and the cnntrol points using the final geoid model. Also, the highly accurate orthometric height was estimated through the GPS/lev

关键词： precise local geoid consistent height system gravity observations GPS! Tide observations least squares fitting

Prediction of Melt Pool Dimension and Residual Stress Evolution with Thermodynamically-Consistent Phase Field and Consolidation Models during Re-Melting Process of SLM

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Computers, Materials & Continua 2021年第1期66卷 87-112页

作者： Kang-Hyun lee Gun Jin yun Department of Aerospace Engineering Seoul National UniversitySeoul08826South Korea Institute of Advanced Aerospace Technology Seoul National UniversitySeoul08826South Korea

Re-melting process has been utilized to mitigate the residual stress level in the selective laser melting(SLM)process in recent ***,the complex consolidation mechanism of powder and the different material behavior after the first laser melting hinder the direct implementation of the re-melting *** this work,the effects of re-melting on the temperature and residual stress evolution in the SLM process are investigated using a thermo-mechanically coupled finite element *** degree of consolidation is incorporated in the energy balance equation based on the thermodynamically-consistent phase-field *** drastic change of material properties due to the variation of temperature and material state is also *** the proposed simulation framework,the single-track scanning is simulated first to predict the melt pool dimension and validate the proposed model with the existing experimental *** obtained thermal histories reveal that the highest cooling rate is observed at the end of the local solidification time which acts as an important indicator for the alleviation of temperature ***,the scanning of a whole single layer that consists of multiple tracks is simulated to observe the stress evolution with several re-melting *** the full melting of powder material in the first scanning process,the increase of residual stress level is observed with one remelting ***,the predicted stress level with the re-melting process shows the variation trend attributable to the accumulated heat in the *** numerical issues and the detailed implementation process are also introduced in this paper.

关键词： Selective laser melting thermo-mechanical analysis Ti-6Al-4V additive manufacturing re-melting residual stress

An integrated approach to improve the performance of lean–electrolyte lithium–sulfur batteries

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Journal of Energy Chemistry 2022年第4期31卷 585-592页

作者： Hualin Ye Jianguo Sun yun Zhao Jim Yang lee Department of Chemical and Biomolecular Engineering National University of Singapore119260Singapore Department of Mechanical Engineering National University of Singapore117575Singapore

While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle,electrode passivation and the loss of electrolyte due to side reactions,are *** challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur ***,the gel cathode reduces the polysulfide mobility and hence the polysulfide shuttle and the passivation of the lithium anode by the crossover *** redox mediator restrains the deposition of inactive sulfur species in the cathode thereby enabling the Fe–N and Co–N co–doped carbon catalyst to prolong its catalytic ***,the integrated catalytic system is able to increase the discharge capacity of high–loading (6.8 mg cm^(-2)) lean–electrolyte (4.0μL mg^(-1)) Li–S batteries from~630 to~1316 m Ah g^(-1),concurrently with an improvement of the cycle life (600 cycles with 46%capacity retention at 1.0 m A cm^(-2)).Redox mediator assisted catalysis in a gel cathode is therefore an effective strategy to extend the application of the sulfur conversion catalyst in lean electrolyte Li–S batteries.

关键词： Redox mediators Gel electrolytes Polysulfide catalysis Lean electrolyte Lithium–sulfur batteries

Carbon-Coated Three-Dimensional MXene/Iron Selenide Ball with Core–Shell Structure for High-Performance Potassium-Ion Batteries

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Nano-Micro Letters 2022年第1期14卷 278-294页

作者： Su Hyun Yang yun Jae lee Heemin Kang Seung-Keun Park yun Chan Kang Department of Materials Science and Engineering Korea UniversityAnam-DongSeongbuk-GuSeoul 136-713Republic of Korea Department of Advanced Materials Engineering Chung-Ang University4726 Seodong-daeroDaedeok-myeonAnseong-siGyeonggi-do 17546Republic of Korea

Two-dimensional(2D)MXenes are promising as electrode materials for energy storage,owing to their high electronic conductivity and low diffusion ***,similar to most 2D materials,MXene nanosheets easily restack during the electrode preparation,which degrades the electrochemical performance of MXene-based materials.A novel synthetic strategy is proposed for converting MXene into restacking-inhibited three-dimensional(3D)balls coated with iron selenides and *** strategy involves the preparation of Fe_(2)O_(3)@carbon/MXene microspheres via a facile ultrasonic spray pyrolysis and subsequent selenization *** 3D structuring effectively prevents interlayer restacking,increases the surface area,and accelerates ion transport,while maintaining the attractive properties of ***,combining iron selenides and carbon with 3D MXene balls offers many more sites for ion storage and enhances the structural robustness of the composite *** resultant 3D structured microspheres exhibit a high reversible capacity of 410 mAh g^(−1) after 200 cycles at 0.1 A g^(−1) in potassium-ion batteries,corresponding to the capacity retention of 97% as calculated based on 100 *** at a high current density of 5.0 A g^(−1),the composite exhibits a discharge capacity of 169 mAh g^(−1).

关键词： MXene Spray pyrolysis Iron selenide Potassium-ion batteries 3D structures

Alleviating Interfacial Recombination of Heterojunction Electron Transport Layer via Oxygen Vacancy Engineering for Efficient Perovskite Solar Cells Over 23%

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Energy & Environmental Materials 2023年第2期6卷 311-322页

作者： Yohan Ko Taemin Kim Chanyong lee Changhyun lee Yong Ju yun Yongseok Jun Graduate School of Energy and Environment(Ku-KIST Green School) Korea UniversitySeoul 02841Korea

Electron transport layer(ETL)is pivotal to charge carrier transport for PSCs to reach the Shockley-Queisser *** study provides a fundamental understanding of heterojunction electron transport layers(ETLs)at the atomic level for stable and efficient perovskite solar cells(PSCs).The bilayer structure of an ETL composed of SnO_(2) on TiO_(2) was examined,revealing a critical factor limiting its potential to obtain efficient *** of oxygen vacancies in the TiO_(2) underlayer via an annealing process is found to induce manipulated band offsets at the interface between the TiO_(2) and SnO_(2) ***-depth electronic investigations of the bilayer structure elucidate the importance of the electronic properties at the interface between the TiO_(2) and SnO_(2) *** apparent correlation in hysteresis phenomena,including current density-voltage(J-V)curves,appears as a function of the type of band *** functional theory calculations reveal the intimate relationship between oxygen vacancies,deep trap states,and charge transport efficiency at the interface between the TiO_(2) and SnO_(2) *** formation of cascade band alignment via control over the TiO_(2) underlayer enhances device performance and suppresses *** performance exhibits a power conversion efficiency(PCE)of 23.45%with an open-circuit voltage(V_(oc))of 1.184 V,showing better device stability under maximum power point tracking compared with a staggered bilayer under one-sun continuous illumination.

关键词： electron transport bilayer heterojunction bilayers interfacial defect oxygen vacancy engineering perovskite solar cells