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Advanced operation of heated fluidic resonators via mechanical and thermal loss reduction in vacuum

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Microsystems & Nanoengineering 2023年第5期9卷 255-262页

作者： Juhee Ko Bong Jae lee Jungchul lee Department of Mechanical Engineering Center for Extreme Thermal Physics and ManufacturingKorea Advanced Institute of Science and Technology(KAIST)34141 DaejeonKorea

For simultaneous and quantitative thermophysical measurements of ultrasmall liquid volumes,we have recently developed and reported heated fluidic resonators(HFRs).In this paper,we improve the precision of HFRs in a vacuum by significantly reducing the thermal loss around the sensing element.A vacuum chamber with optical,electrical,and microfluidic access is custom-built to decrease the convection loss by two orders of magnitude under 10-4 mbar *** a result,the measurement sensitivities for thermal conductivity and specific heat capacity are increased by 4.1 and 1.6 times,*** differentiating between deionized water(H2O)and heavy water(D2O)with similar thermophysical properties and~10%different mass densities,the signal-to-noise ratio(property differences over standard error)for H2O and D2O is increased by 9 and 5 times for thermal conductivity and specific heat capacity,respectively.

关键词： fluid operation vacuum

New lumped-mass-stick model based on modal characteristics of structures: development and application to a nuclear containment building

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Earthquake Engineering and Engineering Vibration 2013年第2期12卷 307-317页

作者： Hwasung Roh Huseok lee Jong Seh lee Department of Civil Engineering Chonbuk National University Department of Civil and Environmental Engineering Hanyang University

In this study, a new lumped-mass-stick model （LMSM） is developed based on the modal characteristics of a structure such as eigenvalues and eigenvectors. The simplified model, named the ＂frequency adaptive lumped-massstick model,＂ hasonly a small number of stick elements and nodes to provide the same natural frequencies of the structure and is applied to a nuclear containment building. To investigate the numerical performance of the LMSM, a time history analysis is carried out on both the LMSM and the finite element model （FEM） for a nuclear containment building. A comparison of the results shows that the dynamic responses of the LMSM in terms of displacement and acceleration are almost identical to those of the FEM. In addition, the results in terms of floor response spectra at certain elevations are also in good agreement.

关键词： new lumped-mass-stick model frequency adaptive nuclear containment buildings seismic response floor response spectrum

Dynamic Behavior and Deformation Analysis of the Fish Cage System Using Mass-Spring Model

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China Ocean Engineering 2015年第3期29卷 311-324页

作者： Chun Woo lee Jihoon lee Subong PARK Division of Marine Production System Management Pukyong National University Division of Marine Technology Chonnam National University Department of Fisheries Physics Pukyong National University

Fish cage systems are influenced by various oceanic conditions, and the movements and deformation of the system by the external forces can affect the safety of the system itself, as well as the species of fish being cultivated. Structural durability of the system against environmental factors has been major concern for the marine aquaculture system. In this research, a mathematical model and a simulation method were presented for analyzing the performance of the large-scale fish cage system influenced by current and waves. The cage system consisted of netting, mooring ropes, floats, sinkers and floating collar. All the elements were modeled by use of the mass-spring model. The structures were divided into finite elements and mass points were placed at the mid-point of each element, and mass points were connected by springs without mass. Each mass point was applied to external and internal forces, and total force was calculated in every integration step. The computation method was applied to the dynamic simulation of the actual fish cage systems rigged with synthetic fiber and copper wire simultaneously influenced by current and waves. Here, we also tried to find a relevant ratio between buoyancy and sinking force of the fish cages. The simulation results provide improved understanding of the behavior of the structure and valuable information concerning optimum ratio of the buoyancy to sinking force according to current speeds.

关键词： fish cage mathematical model aquaculture computer simulation mass-spring model

Femtosecond Tm-Ho co-doped fiber laser using a bulk-structured Bi2Se3 topological insulator

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Chinese Physics B 2018年第9期27卷 137-143页

作者： Jinho lee Ju Han lee School of Electrical and Computer Engineering University of SeoulSeoul 02504Republic of Kore

We experimentally demonstrate a femtosecond mode-locked thulium-holmium（Tm-Ho） co-doped fiber laser incorporating a saturable absorber（SA） based on a bulk-structured bismuth selenide（Bi2Se3） topological insulator（TI）. The SA was prepared by depositing a mechanically exfoliated Bi2Se3 TI layer onto a side-polished optical fiber platform. Unlike high-quality nano-structured Bi2Se3 TI-based SA, bulk-structured Bi2Se3 with non-negligible oxidation was used as a saturable absorption material for this experimental demonstration due to its easy fabrication process. The saturation power and modulation depth of the prepared SA were measured to be -28.6 W and -13.4%, respectively. By incorporating the prepared SA into a Tm-Ho co-doped fiber ring cavity, stable soliton pulses with a temporal width of - 853 fs could be generated at 1912.12 nm. The 3-dB bandwidth of the mode-locked pulse was measured to be -4.87 nm. This experimental demonstration reaffirms that Bi2Se3 is a superb base material for mid-infrared passive mode-locking even under oxidation.

关键词： topological insulator mode-locked lasers femtosecond pulse fiber lasers

Velocity Profiles between Two Baffles in a Shell and Tube Heat Exchanger

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Journal of Thermal Science 2015年第4期24卷 356-363页

作者： Tae-Hyun Chang Chang-Hoan lee Hae-Soo lee Kwon-Soo lee Senior Research Fellow of RESEAT Korea Institute of Science and Technology Information Korea Institute of Science and Technology Information Postdoctoral Research Fellow School of Mechanical Engineering of Kyungnam University International University of Korea

Heat exchangers are extensively utilized for waste heat recovery,oil refining,chemical processing,and steam *** this study,velocity profiles are measured using a 3D particle image velocimetry(PIV)system between two baffles in a shell and tube heat exchanger for parallel and counter *** PIV and computational fluid dynamics results show the occurrence of some strong vectors near the *** vectors are assumed due to the clearance between the inner tubes and the front ***,the major parts of the vectors are moved out through the bottom opening of the rear baffle,and other vectors produce a large circle between the two *** simulations are conducted to investigate the effects of the baffle on the heat exchanger using the Fluent *** k-εturbulence model is employed to calculate the flows along the heat exchanger.

关键词： Baffle P1V Shell and tube heat exchanger Cut off ratio CFD

Effects of elastic-plastic properties of materials on residual indentation impressions in nano-indentation using sharp indenter

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中国有色金属学会会刊：英文版 2012年第S3期22卷 585-595页

作者： Jung-Min lee Chan-Joo lee Kyung-Hun lee Byung-Min KIM Dongnam Regional Division Korea Institute of Industrial Technology Precision Manufacturing Systems Division Pusan National University School of Mechanical Engineering Pusan National University

One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the ***,this indirect measurement occasionally leads to inaccurate properties of the indented *** objective of this study is to investigate the effects of E/σr and the strain hardening exponents n of materials on the behaviors of pile-up and sink-in in nano-indentation and to predict n values of materials from the residual indentation *** relations between the residual indentation profile and n value of the indented material were identified by dimensional ***,they were numerically formulated using FE analysis of nano-indentation for 140 different combinations of elastic-plastic parameters such as E,σy and *** parameters of hrp/hm,herp/hm,Rr/hm and HO&P/Hreal were introduced as various dimensionless parameters to represent and quantify the residual indentation profile after *** were subsequently characterized as dimensionless functions using n and E/σr ***,the validity of these functions was verified through 3D FE analysis of nano-indentation for Al 6061-T6 and AISI 1010 materials.

关键词： nano-indentation pile-up sink-in strain hardening exponent FE simulation

The effect of the dopant's reactivity for high-performance 2D MoS2 thin-film transistor

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Nano Research 2021年第1期14卷 198-204页

作者： Hanleem lee Sora Bak Joosung Kim Hyoyoung lee Center for Integrated Nanostructure Physics(CINAP) Institute for Basic Science(IBS)Suwon 16419Republic of Korea Department ofChem istryy Sungkyunkwan University Suwon 16419Republic of Korea Department of Energy Science Sungkyunkwan UniversitySuwon 16419Republic of Korea Department of Biophysics Sungkyunkwan UniversitySuwon 16419Republic of Korea

There are many studies on the solution-processed thin-film transistor(TFT)using transition metal dichalcogenide(TMD)***,it is hard to control the electrical property of chemically exfoliated TMD materials compared to the chemical vapor deposition *** investigation into the electrical modulation behavior of exfoliated two-dimensional(2D)material is important tofabricate weH-modulated electronic devices via solution ***,we report the effects of reactivity of organic dopants on MoS2 and investigate how the chemical doping behavior influences the electrical properties of *** band state of dopants,which is related to the electron-withdrawing and donating behavior of chemical dopant,provides a proportional shift in the threshold voltages(Vth)of their field-effect transistors(FETs).However,on/off current ratio(Ion/Ioff)and mobility(μ)are strongly influenced by the defect density depending on the reactivity of doping reaction,rather than the band state of organic *** the in-depth study on the doping reaction,we fabricate a FET and a TFT,having high mobility and a relatively high on/off ratio(10^(4))using a solution process.

关键词： 2D materials functionalization thin-film transistor doping defect

Catalysts for electrochemical ammonia oxidation:Trend,challenge,and promise

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Science China Materials 2022年第12期65卷 3334-3352页

作者： Sol A lee Mi Gyoung lee Ho Won Jang Department of Materials Science and Engineering Seoul National UniversitySeoul 08826Republic of Korea Department of Electrical and Computer Engineering University of TorontoToronto M5S 3G4OntarioCanada Advanced Institute of Convergence Technology Seoul National UniversitySuwon 16229Republic of Korea

Developing sustainable and clean energy technology is critial to address the current energy and environmental *** an energy carrier,hydrogen has been getting attention due to its abundance,high energy density,and zero carbon *** to the difficulty of hydrogen storage and transport,the electro-oxidation of ammonia shows great potential for renewable energy since it satisfies both energy supply and environmental protection as a carbon-free fuel with high hydrogen ***,ammonia electro-oxidation is a sluggish reaction and shows low *** the complicated mechanism and intermediates is conducive to developing efficient electrocatalysts with high catalytic activity and *** review begins with the ammonia oxidation technologies and their *** two typical mechanisms for ammonia electro-oxidation,Oswin-Salomon mechanism and Gerischer-Mauerer mechanism,are discussed,and attention to the poisoning species is ***,the electrocatalysts for ammonia reaction are classified into Pt-based catalysts and non-noble metal-based catalysts,and their performances are reviewed with various *** on the progress on the electrochemical ammonia oxidation catalysts,the challenges and future insight on ammonia oxidation reaction are discussed and proposed.

关键词： NH3 oxidation reaction electrocatalysts green hydrogen

Cu^+-incorporated TiO_2 overlayer on Cu_2O nanowire photocathodes for enhanced photoelectrochemical conversion of CO_2 to methanol

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Journal of Energy Chemistry 2018年第1期27卷 264-270页

作者： Kangha lee Seokwon lee Hyunjin Cho Sunil Jeong Whi Dong Kim Sooho lee Doh C.lee Department of Chemical and Biomolecular Engineering(BK21+program) KAIST Institute for the NanocenturyKorea Advanced Institute of Science and Technology(KAIST)

In this paper, we report photoelectrochemical（PEC） conversion of carbon dioxide（CO_2） using photocathodes based on Cu_2O nanowires（NWs） overcoated with Cu~＋-incorporated crystalline TiO_2（TiO_2–Cu~＋）shell. Cu_2O NW photocathodes show remanent photocurrent of 5.3% after 30 min of PEC reduction of CO_*** coating Cu_2O with TiO_2–Cu~＋ overlayer, the remanent photocurrent is 27.6%, which is an increase by5.2 fold. The charge transfer resistance of Cu_2O/TiO_2–Cu~＋ is 0.423 k/cm2, whereas Cu_2O photocathode shows resistivity of 0.781 k/cm2 under irradiation. Mott–Schottky analysis reveals that Cu~＋ species embedded in TiO_2 layer is responsible for enhanced adsorption of CO_2 on TiO_2 surface, as evidenced by the decrease of capacitance in the Helmholtz layer. On account of these electrochemical and electronic effects by the Cu~＋ species, the Faradaic efficiency（FE） of photocathodes reaches as high as 56.5% when TiO_2–Cu~＋ is added to Cu_2O, showing drastic increase from 23.6% by bare Cu_2O photocathodes.

关键词： Photoelectrochemical CO2 reductionMethanol generation Copper oxide Titanium dioxide Cu+ catalyst