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Effect of CaO addition on ignition behavior in molten AZ31 and AZ91D Magnesium alloys

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Rare Metals 2006年第Z2期25卷 155-159页

作者： lee Jin-Kyu JO hyung-Ho KIM Shae K. Department of Advanced Material Engineering Sungkyunkwan University 300 Chunchun-dong Jangan-gu Suwon Gyunggi-do 440-746 KoreaAdvanced Material Center Korea Institute of Industrial Technology 7-47 Songdo-dong Yeonsu-gu Incheon 406-840 Korea dvanced Material Center Korea Institute of Industrial Technology 7-47 Songdo-dong Yeonsu-gu Incheon 406-840 Korea

Mg alloys have been widely used in automobile and electronic industries because of high specific strength, good castability, etc. However, molten Mg alloys will burn rapidly in air if not protected. To solve this problem, the molten metal should be protected from oxidation by blanketing the surface with flux or protective gases. SF6 gas is widely used for Mg alloys as a cover gas and has proved to be a successful inhibitor. However, the use of SF6 gas is limited because of its high cost and its significant impact on non-global warming potential. Therefore, SF6 gas is being replaced by alternative protection gases. Recent studies show that there has been another attempt by adding CaO into Mg alloys. The aim of this study is to evaluate the effect of CaO on the minimum amount of protective gas, which is necessary not to make ignition in the molten AZ31 and AZ91 Mg alloys.

关键词： AZ91 AZ31 CaO clean production ignition resistance

Numerical characterization of heat transfer in closed-loop vertical ground heat exchanger

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Science China(Technological Sciences) 2010年第1期53卷 111-116页

作者： Chulho lee Hujeong GIL Hangseok CHOI Shin-hyung KANG School of Civil Environmental and Architectural EngineeringKorea University5-GaAnam-DongSeongbuk-GuSeoul 136-713Republic of Korea Pyungsan SI Co. Ltd.1337-31 Seocho-DongSeocho-GuSeoul 137-860Republic of Korea Department of Mechanical Engineering Konyang University119Deahak-RoNonsanChungnam 320-711Republic of Korea

A series of numerical analyses has been performed on the characteristics of heat transfer in a closed-loop vertical ground heat exchanger(U-loop).A 2-D finite element analysis was conducted to evaluate the temperature distribution over the cross section of the U-loop system involving high-density polyethylene(HDPE) pipe/grout/soil to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system,which is equipped with a thermally insulating lattice in order to reduce thermal interference between the inlet and outlet *** addition,a 3-D finite volume analysis(FLUENT) was adopted to simulate the operation of the closed-loop vertical ground heat exchanger with the consideration of the effect of a distance between the inlet and outlet pipes,grout's thermal properties,the effectiveness of the latticed HDPE pipe system,and the rate of circulation *** was observed that the thermal interference between the two strands of U-loop is of importance in enhancing efficiency of the ground heat ***,it is recommended to modify the configuration of the conventional U-loop system by equipping the thermally insulating lattice between the two pipe strands.

关键词： ground heat exchanger HDPE pipe latticed pipe sectional efficiency

Callus proliferation-induced hypoxic microenvironment decreases shoot regeneration competence in Arabidopsis

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Molecular Plant 2024年第3期17卷 395-408页

作者： Dohee Koo Hong Gil lee Soon hyung Bae Kyounghee lee Pil Joon Seo Department of Chemistry Seoul National UniversitySeoul 08826Korea Plant Genomics and Breeding Institute Seoul National UniversitySeoul 08826Korea Research Institute of Basic Sciences Seoul National UniversitySeoul 08826Korea

Plants are aerobic organisms that rely on molecular oxygen for respiratory energy *** conditions,with oxygen levels ranging between 1%and 5%,usually limit aerobic respiration and affect plant growth and ***,we demonstrate that the hypoxic microenvironment induced by active cell proliferation during the two-step plant regeneration process intrinsically represses the regener-ation competence of the callus in Arabidopsis *** showed that hypoxia-repressed plant regener-ation is mediated by the RELATED TO APETALA2.12(RAP2.12)protein,a memberof the Ethylene Response Factor VIl(ERF-Vll)*** found that the hypoxia-activated RAP2.12 protein promotes salicylic acid(SA)biosynthesis and defense responses,thereby inhibiting pluripotency acquisition and de novo shoot regeneration in *** and genetic analyses revealed that RAP2.12 could bind directly to the SALICYLIC ACID INDUCTION DEFICIENT 2(SID2)gene promoter and activate SA biosynthesis,repressing plant regeneration possibly via a PLETHORA(PLT)-dependent ***,the rap2.12 mutant calli exhibits enhanced shoot regeneration,which is impaired by SA *** together,these find-ings uncover that the cell proliferation-dependent hypoxic microenvironment reduces cellular pluripotency and plant regeneration through the RAP2.12-SID2 module.

关键词： callus cell proliferation-induced hypoxia SID2 plant regeneration salicylic acid RAP2.12

Bidirectional transfer of quantum information for unknown photons via cross-Kerr nonlinearity and photon-number-resolving measurement

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Chinese Physics B 2016年第2期25卷 82-92页

作者： Jino Heo Chang-Ho Hong Dong-Hoon lee hyung-Jin Yang Graduate School of Information Security (GSIS) Korea University Center for Information Security Technologies (CIST) Korea University Department of Physics Korea University

We propose an arbitrary controlled-unitary （CU） gate and a bidirectional transfer scheme of quantum information （BTQI） for unknown photons. The proposed CU gate utilizes quantum non-demolition photon-number-resolving measure- ment based on the weak cross-Kerr nonlinearities （XKNLs） and two quantum bus beams; the proposed CU gate consists of consecutive operations of a controlled-path gate and a gathering-path gate. It is almost deterministic and is feasible with current technology when a strong amplitude of the coherent state and weak XKNLs are employed. Compared with the existing optical multi-qubit or controlled gates, which utilize XKNLs and homodyne detectors, the proposed CU gate can increase experimental realization feasibility and enhance robustness against decoherence. According to the CU gate, we present a BTQI scheme in which the two unknown states of photons between two parties （Alice and Bob） are mutually swapped by transferring only a single photon. Consequently, by using the proposed CU gate, it is possible to experimentally implement the BTQI scheme with a certain probability of success.

关键词： cross-Kerr nonlinearity quantum non-demolition photon-number-resolving measurement bidirec-tional transfer of quantum information

Germline-competent stem cell in avian species and its application

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Asian Journal of Andrology 2015年第3期17卷 421-426页

作者： Jae Yong Han hyung Chul lee Tae Sub Park Department of Agricultural Biotechnology College of Agriculture and Life Sciences and Research Institute of Agriculture and Life Sciences Seoul National University Seoul 151-921 Korea Graduate School of International Agricultural Technology and Institute of Green-Bio Science and Technology Seoul National University Pyeongchang-gun Gangwon-do 232-916 Korea

Germ cells are the only cell type in the body that can transfer genetic information to the next generation. Germline-competent stem cells can self-renew and contribute to the germ cell lineage giving rise to pluripotent stem cells under specific conditions. Hence far, studies on germline-competent stem cells have contributed to,the generation of avian model systems and the conservation of avian genetic resources. In this review, we focus on previous studies on germline-competent stem cells from avian species, mainly chicken germline-competent stem cells, which have been well established and characterized. We discuss different sources of germline-competent stem cells and recent advances for the future applications in birds.

关键词： birds germline-competent stem cells primordial germ cells spermatogonial stem cells

Observation and Numerical Simulations with Radar and Surface Data Assimilation for Heavy Rainfall over Central Korea

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Advances in Atmospheric Sciences 2011年第3期28卷 573-590页

作者： Ji-Hyun HA hyung-Woo KIM Dong-Kyou lee Atmospheric Sciences Program School of Earth and Environmental SciencesSeoul National UniversitySeoul 151-747Korea

This study investigated the impact of multiple-Doppler radar data and surface data assimilation on forecasts of heavy rainfall over the central Korean Peninsula;the Weather Research and Forecasting(WRF) model and its three-dimensional variational data assimilation system(3DVAR) were used for this purpose. During data assimilation,the WRF 3DVAR cycling mode with incremental analysis updates(IAU) was used. A maximum rainfall of 335.0 mm occurred during a 12-h period from 2100 UTC 11 July 2006 to 0900 UTC 12 July *** radar data showed that the heavy rainfall was due to the back-building formation of mesoscale convective systems(MCSs).New convective cells were continuously formed in the upstream region,which was characterized by a strong southwesterly low-level jet(LLJ).The LLJ also facilitated strong convergence due to horizontal wind shear,which resulted in maintenance of the *** assimilation of both multiple-Doppler radar and surface data improved the accuracy of precipitation forecasts and had a more positive impact on quantitative forecasting(QPF) than the assimilation of either radar data or surface data *** back-building characteristic was successfully forecasted when the multiple-Doppler radar data and surface data were *** data assimilation experiments,the radar data helped forecast the development of convective storms responsible for heavy rainfall,and the surface data contributed to the occurrence of intensified low-level *** surface data played a significant role in enhancing the thermal gradient and modulating the planetary boundary layer of the model,which resulted in favorable conditions for convection.

关键词： radar and surface data data assimilation mesoscale convective system heavy rainfall

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

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Journal of Materials Science & Technology 2018年第8期34卷 1397-1404页

作者： Junho lee Dongju lee Myung Hoon Song Wonhyuk Rhee Ho Jin Ryu Soon hyung Hong Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology291 Daehak-roYuseong-guDaejeon305-701Republic of Korea Department of Nuclear and Quantum Engineering Korea Advanced Institute of Science and Technology291 Daehak-roYuseong-guDaejeon305-701Republic of Korea Nuclear Materials Development Division Korea Atomic Energy Research Institute111 Daedeok-daero 989 Beon-gilYuseong-guDaejeon305-353Republic of Korea Daewha Alloytech Corporation 17-60Sanupdanji-gilMyeoncheon-myeonDangjin-siChungcheongnam-doRepublic of Korea

Fe alloy composites reinforced with in-situ titanium carbide （TIC） particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties ofin-situ TiC/Fe alloy composites. The microstructure showed that the in-situ syn- thesized TiC particles were spherical with a size of 1-3 }~m, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiCx at the common sintering temperature. The in-situ TiC/Fe alloy composite with C[Ti ~ 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon （C/Ti = 1 and 1.1） resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon （C/Ti = 0.8） caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC par- ticles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.

关键词： Metal matrix composites Sintering Mechanical properties Microstructures

Cell architecture designs towards high-energy-density microscale energy storage devices

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Nano Research Energy 2024年第2期3卷 69-82页

作者： Kwon-hyung lee Sang-Young lee Ulsan Advanced Energy Technology R&D Center Korea Institute of Energy Research(KIER)Ulsan44776Republic of Korea Department of Chemical and Biomolecular Engineering Yonsei UniversitySeoul03722Republic of Korea

The rapid growth of miniaturized electronics has led to an urgent demand for microscale energy storage devices(MESDs)to sustainably power the micro electronic ***,most MESDs reported to date have suffered from the limited energy densities and shape versatility compared to conventional large-scale counterparts because of the architectural constraints inherent in microfabrication-based cell manufacturing and cell dimension/*** review addresses the cell architecture design for MESDs that can achieve both miniaturization and high energy *** provide a comprehensive overview of five types of cell architectures of MESDs and their fabrication *** addition,to enable practical applications of MESDs,several cell design approaches are presented with the aim of minimizing the inactive parts of the cell and maximizing the performance metrics of ***,we discuss development direction and outlook of MESDs with a focus on materials chemistry,energy-dense electrochemical systems,and cell performance normalization,which will help to expand their applications and manufacturing scalability.

关键词： microscale energy storage device cell architecture microfabrication miniaturization high-energy-density

First-Order System Least-Squares Methods for a Flux Control Problem by the Stokes Flow

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Communications in Computational Physics 2010年第4期7卷 738-758页

作者： Soorok Ryu Sang Dong Kim hyung-Chun lee Department of Industrial and Applied Mathematics Kyungpook National UniversityDaegu 702-701Korea Department of Mathematics Kyungpook National UniversityDaegu 702-701Korea Department of Mathematics Ajou UniversitySuwon 443-749Korea

This article deals with a first-order least-squares approach to the solution of an optimal control problem governed by Stokes *** with our earlier work on a velocity control by the Stokes flow in[***,H.-*** and ***,SIAM ***.,47(2009),pp.1524-1545],we recast the objective functional as a H1 seminorm in the velocity control *** introducing a velocity-flux variable and using the Lagrange multiplier rule,a first-order optimality system is *** show that the least-squares principle based on L2 norms applied to this system yields the optimal discretization error estimates for each variable in H1 norm,including the velocity *** numerical tests,multigrid method is employed to the discrete algebraic system,so that the velocity and flux controls are obtained.

关键词： Optimal control optimization least-squares finite element methods Lagrange multiplier Stokes equations.