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Microstructural Evolution in Directionally Solidified Ni-Base Superalloy iN792+hf

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Journal of Materials Science & Technology 2008年第1期24卷 110-114页

作者： S.M.seo i.S.Kim J.h.Lee C.Y.Jo h.Miyahara K.Ogi high Temperature Materials Research Group KiMS Changwon641-010Korea Dept.of Metall.& Mater.Eng. Changwon Univ. Changwon641-773Korea Dept.of Mater.Sci.& Eng. Kyushu Univ. Fukuoka819-0395Japan Oita National College of Technology Oita 870-0152Japan

Microstructural evolution during directional solidification （DS） of Ni-base superalloy iN792＋hf has been investigated with an emphasis on theγ′precipitates and MC-type *** quantitative image analyses revealed that the increase in the solidification rate up to 100μm/s at constant thermal gradient of 178 K/cm resulted in a fine and uniform distribution ofγ′*** relationship between the as-castγ′size and cooling rate was also determined for DS iN792＋*** the mean time,the MC carbide size was found to be dependent both on the solidification rate and the S/L interface morphology while the area fraction of MC carbide was significantly influenced by the S/L interface morphology.

关键词： iN792 MC corbide Gamma prime Solidification rate

is quantum capacitance in graphene a potential hurdle for device scaling？

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Nano Research 2014年第4期7卷 453-461页

作者： Jaeho Lee hyun-Jong Chung David h. seo Jaehong Lee hyungcheol Shin Sunae seo seongjun Park Sungwoo hwang Kinam Kim Samsung Advanced institute of Technology Samsung Electronics Yongin-Si Gyeonggi-Do 446-712 Korea inter-University Semiconductor Research Center (iSRC) School of Electrical Engineering and Computer Science Seoul National University Seoul 151-742 Korea Division of Quantum Phases and Devices Department of Physics Konkuk University Seou1143-701 Korea Semiconductor R&D Center Somsung Electronics Hwasung-City Gyeonggi-Do 446-711 Korea Department of Physics Sejong University Seou1143-74 7 Korea Memory Division Samsung Electronics Hwasung-City Gyeonggi-Do 446-711 Korea

Transistor size is constantly being reduced to improve performance as well as power consumption. For the channel length to be reduced, the corresponding gate dielectric thickness should also be reduced. Unfortunately, graphene devices are more complicated due to an extra capacitance called quantum capacitance （CQ） which limits the effective gate dielectric reduction. in this work, we analyzed the effect of CQ on device-scaling issues by extracting it from scaling of the channel length of devices. in contrast to previous reports for metal-insulator- metal structures, a practical device structure was used in conjunction with direct radio-frequency field-effect transistor measurements to describe the graphene channels. in order to precisely extract device parameters, we reassessed the equivalent circuit, and concluded that the on-state model should in fact be used. By careful consideration of the underlap region, our device modeling was shown to be in good agreement with the experimental data. CQ contributions to equivalent oxide thickness were analyzed in detail for varying impurity concentrations in graphene. Finally, we were able to demonstrate that despite contributions from CQ, graphene＇s high mobility and low-voltage operation allows for ~raphene channels suitable for next generation transistors.

关键词： graphene equivalent circuit quantum capacitance intrinsic delay

Work function tuned, surface Cs intercalated BiVO_(4) for enhanced photoelectrochemical water splitting reactions

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Journal of Energy Chemistry 2022年第5期31卷 612-623页

作者： Shankara S.Kalanur hyungtak seo Department of Materials Science and Engineering Ajou UniversitySuwon 443-739Republic of Korea Department of Energy Systems Research Ajou UniversitySuwon 443-739Republic of Korea

Monoclinic BiVO_(4) is a widely researched semiconductor in solar water splitting owing to its suitable characteristics. however, BiVO_(4) faces limitations, such as the inefficient separation and transportation of photogenerated charges in the bulk and poor catalytic water oxidation reactions at the surface that affect the water-splitting efficiency. in this work, the Cs intercalation strategy at the surface of BiVO_(4) is proposed for the enhanced water splitting to h_(2) and O_(2) productions via the effective separation and transportation photogenerated charges and improved surface catalytic water oxidation reactions. The Cs ions are found to intercalate at the surface of BiVO_(4) and regulate the oxygen vacancies to provide active O_(2) production sites and stability. The surface intercalation of Cs boosts the photocurrent to 1.89 mA cm^(-2)at 1.23 V *** hydrogen electrode(RhE). A stoichiometric evolution of h_(2) and O_(2) is recorded with a faradaic efficiency of 92%. The open-circuit voltage measurements confirmed the increase in the carrier lifetime with the work function tuning upon Cs intercalation. The proposed Cs intercalation strategy suggests an effective route to suppress the charge recombination with an increase in carrier lifetime and charge separation in BiVO_(4) for the enhanced PEC application.

关键词： Cesium BiVO_(4) Annona structure Surface intercalation Photoelectrochemical water splitting

Fabrication of ultrafine Nd-Fe-B powder by a modified reduction-diffusion process

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Rare Metals 2006年第z2期25卷 223-226页

作者： JANG T.S. LEE D.h. Ch.i.C.J. seo W.S. LEE Y.h. Department of Electronic Materials Engineering Sunmoon University Korea Powder Materials Research Center Korea Institute of Machinery and Materials Korea Advanced Materials Analysis & Evaluation Center Korea Institute of Ceramic Engineering and Technology Korea

in order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was icles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were ihc=～5.9 kOe, Br=～5.5 kG, and (Bh)max=～6 MGOe.

关键词： NdFeB powder spray drying reduction-diffusion process Nd2Fe14B magnetic powder

Diel vertical migration of the copepod Calanus sinicus before and during formation of the Yellow Sea Cold Bottom Water in the Yellow Sea

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Acta Oceanologica Sinica 2013年第9期32卷 99-106页

作者： KANG Jung-hoon seo Minho KWON Oh Youn KiM Woong-seo South Sea Environment Research Division Korea Institute of Ocean Science&Technology (KIOST) Deep-sea and Seabed Resources Research Division

To understand the effects of the Yellow Sea Cold Bottom Water （YSCBW） on the diel vertical migration （D- VM） of the copepod Calanus sinicus, we surveyed vertical distribution of C. sinicus at a fixed station in the Yellow Sea before （spring） and during （summer） formation of the YSCBW. Cold water （〈10℃） was observed in the bottom layer when the water column was thermally stratified in summer, but the water column was thermally well-mixed in spring 2010. Samples were collected from five different layers at 3-h.i.tervals using an opening-closing net. Adult females （1-155 ind./m3） showed a clear normal DVM pattern throughout the entire water column in spring, whereas adult males did not migrate. DVM of copepodite V （CV） individuals was not clear, but the maximum abundance of Ci-CiV occurred consistently in the upper 10-20 m layer, where there was a high concentration of chlorophyll-a （Chl-a）（0.49-1.19μg/L）. in summer, weak DVM was limited to cold waters beneath the thermocline for adult females （〈30 ind./m3）, but not for adult males. The maximum abundance of Ci-CiV also occurred consistently in the subsurface layer （20-40 m） together with high concentrations of Chl-a （0.81-2.36 μg/L）. CV individuals （1-272 ind./m3） moved slightly upward noc- turnally to the near-surface layer （10-20 m）, where the average temperature was 25.74℃, but they were not found in the surface layer （0-10 m; 28.31℃）. These results indicate that the existence of the YSBCW affected food availability at depth and the vertical temperature distribution, leading to variation in the amplitude and shape of stage-specific vertical distributions （Ci to adults） in C. sinicus before and during the formation of cold waters in the Yellow Sea during the study period.

关键词： Yellow Sea Cold Bottom Water (YSCBW) copepod Calanus sinicus developmental stages,diel vertical migration (DVM)

Brazilin and Caesalpinia sappan L. extract protect epidermal keratinocytes from oxidative stress by inducing the expression of GPX7

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Chinese Journal of Natural Medicines 2018年第3期16卷 203-209页

作者： hyung seo hwang Joong hyun Shim Department of Oriental Cosmetic Science Semyung University

Caesalpinia sappan L., belonging to the family Leguminosae, is a medicinal plant that is distributed in Southeast Asia. The dried heartwood of this plant is used as a traditional ingredient of food, red dyes, and folk medicines in the treatment of diarrhea, dysentery, tuberculosis, skin infections, and inflammation. Brazilin is the major active compound, which has exhibited various phar- macological effects, including anti-platelet activity, anti-hepatotoxicity, induction of immunological tolerance, and anti-inflammatory and antioxidant activities. The present study aimed to evaluate the antioxidant activity and expression of antioxidant enzymes of C. sappan L. extract and its major compound, brazilin, in human epidermal keratinocytes exposed to UVA irradiation. Our results indi- cated that C. sappan L. extract reduced UVA-induced h202 production via GPX7 activation. Moreover, brazilin exhibited anfioxidant effects that were similar to those of C. sappan L. via glutathione peroxidase 7 （GPX7）, suggesting that C. sappan L. extract and its natural compound represent potential treatments for oxidative stress-induced photoaging of skin.

关键词： Caesalpinia sappan L. Brazilin Ultraviolet GPX7 Antioxidative

Spin coherence in two-dimensional materials

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npj Computational Materials 2019年第1期5卷 760-765页

作者： Meng Ye hosung seo Giulia Galli institute for Molecular Engineering The University of ChicagoChicagoILUSA Materials Science Division Argonne National LaboratoryLemontILUSA Department of Physics Ajou UniversitySuwonRepublic of Korea Department of Energy Systems Research Ajou UniversitySuwonRepublic of Korea Department of Chemistry University of ChicagoChicagoILUSA institute for Molecular Engineering Argonne National LaboratoryLemontILUSA

Spin defects in semiconducting solids are promising platforms for the realization of quantum *** low temperature and in the presence of a large magnetic field,the central spin decoherence is mainly due to the fluctuating magnetic field induced by nuclear spin flip-flop *** spin hamiltonians and a cluster expansion method,we investigate the electron spin coherence of defects in two-dimensional(2D)materials,including delta-doped diamond layers,thin Si films,MoS_(2),and *** show that isotopic purification is much more effective in 2D than in three-dimensional materials,leading to an exceptionally long spin coherence time of more than 30 ms in an isotopically pure monolayer of MoS_(2).

关键词： exceptional realization solids

A Cu-Pd alloy catalyst with partial phase separation for the electrochemical CO_(2) reduction reaction

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Journal of Energy Chemistry 2024年第6期93卷 8-15,I0001页

作者： Gyeong ho han Jung Yong seo Minji Kang Myung-gi seo Youngheon Ch.i.Soo Young Kim Sang hyun Ahn School of Chemical Engineering and Material Science Chung-Ang UniversitySeoul 06974Republic of Korea Lotte Chemical institute of Technology Daejeon 34110Republic of Korea Department of Materials Science and Engineering Korea UniversitySeoul 02841Republic of Korea

Cu catalysts can convert CO_(2) through an electrochemical reduction reaction into a variety of useful carbon-based ***,this capability provides an obstacle to increasing the selectivity for a single ***,we report a simple fabrication method for a Cu-Pd alloy catalyst for use in a membrane electrode assembly(MEA)-based CO_(2) electrolyzer for the electrochemical CO_(2) reduction reaction(ECRR)with high selectivity for CO *** the composition of the Cu-Pd alloy catalyst was fabricated at 6:4,the selectivity for CO increased and the production of multi-carbon compounds and hydrogen is *** a Cu-Pd alloy catalyst with 6:4 ratio as the cathode of the MEAbased CO_(2) electrolyzer showed a CO faradaic efficiency of 92.8%at 2.4 V_(cell).We assumed that these results contributed from the crystal planes on the surface of the Cu-Pd *** phases of the Cu-Pd alloy catalyst were partially separated through annealing to fabricate a catalyst with high selectivity for CO at low voltage and C_(2)h_4 at high *** results of CO-stripping testing confirmed that when Cu partially separates from the lattice of the Cu-Pd alloy,the desorption of~*CO is suppressed,suggesting that C-C coupling reaction is favored.

关键词： Cu-Pd catalyst Electrodeposition Electrochemical carbon dioxide reduction Partial phase separation Membrane electrode assembly-based electrolyzer

Effect of friction on the contact stress of a coated polymer gear

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Friction 2020年第6期8卷 1169-1177页

作者： Su-Min BAE Kuk-Jin seo Dae-Eun KiM Department of Mechanical Engineering Yonsei UniversitySeoul 03722Republic of Korea

Polymer gears are used extensively in various ***,durability issues have been emerging because of friction at gear tooth contact *** extend the lifetime of polymer gears,a low-frictional coating has been considered as a possible *** this study,a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer *** simulation included various friction coefficients(COFs)for studying the effects of friction during the *** results revealed that the friction causes the contact stress to shift over the roll angle,which.i. attributed to the direction of the sliding friction based on a free-body *** also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the ***,the stress distribution in the coating at the pitch point was investigated as the COF *** zero friction,three notable stress regions were observed:1)the center of the surface,2)the end of the contact,and 3)the overall contact *** COF was increased in the micro-slip region of the contact interface,both tensile and compressive stresses in the coating *** study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.

关键词： coating contact stress finite element method(FEM) friction polymer gear