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Interannual Variation of Tropical Night Frequency in Beijing and Associated Large-Scale Circulation Background

Advances in Atmospheric Sciences 2012年第2期29卷 295-306页

作者： Jong-Kil PARK 陆日宇李超凡 eun byul kim Department of Atmospheric Environment Information Engineering Atmospheric Environment Information Research Center Inje University State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences

This study examined the variability in frequency of tropical night occurrence （i.e., minimum air tem- perature 25℃） in Beijing, using a homogenized daily temperature dataset during the period 1960–2008. Our results show that tropical nights occur most frequently in late July and early August, which is consis- tent with relatively high air humidity associated with the rainy season in Beijing. In addition, year-to-year variation of tropical night occurrence indicates that the tropical nights have appeared much more frequently since 1994, which can be illustrated by the yearly days of tropical nights averaged over two periods： 9.2 days of tropical nights per year during 1994–2008 versus 3.15 days during 1960–1993. These features of tropical night variations suggest a distinction between tropical nights and extreme heat in Beijing. We further investigated the large-scale circulations associated with the year-to-year variation of tropical night occurrence in July and August, when tropical nights appear most frequently and occupy 95% of the annual sum. After comparing the results in the two reanalysis datasets （NCEP/NCAR and ERA-40） and considering the possible effects of decadal change in the frequency of tropical nights that occurred around 1993/94, we conclude that on the interannual time scale, the cyclonic anomaly with a barotropic structure centered over Beijing is responsible for less frequent tropical nights, and the anticyclonic anomaly is responsible for more frequent occurrence of tropical nights over Beijing.

关键词： tropical night large-scale circulation interannual variability decadal change Beijing

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High-performance MoS_(2)/p^(+)-Si heterojunction field-effect transistors by interface modulation

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Nano Research 2022年第7期15卷 6500-6506页

作者： Yoonsok kim Taeyoung kim eun Kyu kim Department of Physics and Research Institute of Natural Science Hanyang UniversitySeoul 04763Republic of Korea

Molybdenum disulfide(MoS_(2)),one of transition metal dichalcogenides,is a promising semiconductor material for electronic or optoelectronic devices due to its favorably electronic ***,in metal-oxide semiconductor field-effect transistor(MOSFET)structures using MoS_(2),electrical performances such as mobility and subthreshold swing are suppressed by the interface trap density between the channel and dielectric ***,the electrical stability of such structures is compromised due to interface traps and that can be analyzed such as current hysteresis and transient ***,we demonstrate MoS_(2) heterojunction field-effect transistors(HFET)by applying MoS_(2)/p^(+)-Si heterojunctions and achieve high performance characteristics,including a mobility of 636.19 cm^(2)/(V∙s),a subthreshold swing of 67.4 mV/dec,minimal hysteresis of 0.05 V,and minimized transient ***,the HFET devices with varying the channel length demonstrated degradation of electrical performance with increasing the overlap area of the channel and dielectric *** results regarding MoS_(2)/p^(+)-Si HFETs resulted in the structural optimization of high-performance electronic devices for practical applications.

关键词： molybdenum disulfide(MoS_(2)) transition metal dichalcogenide junction field-effect transistor dielectric layer interface trap

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Lattice design for a hybrid multi-bend achromat light source

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Nuclear Science and Techniques 2020年第7期31卷 55-64页

作者： eun-San kim Department of Accelerator Science Korea University Sejong CampusSejong 30019Korea

We present a lattice design and beam dynamics analysis for a 4 GeV low-emittance,high-brilliance synchrotron light *** lattice consisted of 26 six-bend achromats with 26 long and 26 short straight *** present the design results for a hybrid multi-bend achromat(HMBA)lattice with a natural emittance of 168 pm and circumference of 729.3 *** cell had 4 longitudinal gradient bendings,2 combined bendings,14 quadrupoles,and 2 families of *** lattice was designed to beflexible to provide both nonzero and zero dispersion functions in the long straight *** two straight sections in each cell had lengths of 5.6 and 1.2 *** ensure sufficient injection,we optimized the design lattice and dynamic *** investigated the dynamic aperture in the lattice with machine errors,and the results showed that the lattice design provides sufficient dynamic aperture after COD correction for beam *** present the results of an injection scheme that demonstrates the space in the injection section and the particle motions of the injected *** also present the results of beam tracking after the beam injection to examine the characteristics of the beam *** designed HMBA lattice was well optimized in terms of the beam parameters and brilliance as an intermediate light source at 4 GeV and a circumference of 729.3 m.

关键词： injection beam lattice

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Computational approaches for fast generation of digital 3D video holograms(Invited Paper)

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Chinese Optics Letters 2009年第12期7卷 1083-1091页

作者： Seung-Cheol kim eun-Soo kim 3D Display Research Center Department of Electronic Engineering Kwangwoon University

Several approaches for fast generation of digital holograms of a three-dimensional （3D） object have been discussed. Among them, the novel look-up table （N-LUT） method is analyzed to dramatically reduce the number of pre-calculated fringe patterns required for computation of digital holograms of a 3D object by employing a new concept of principal fringe patterns, so that problems of computational complexity and huge memory size of the conventional ray-tracing and look-up table methods have been considerably alleviated. Meanwhile, as the 3D video images have a lot of temporally or spatially redundant data in their inter- and intra-frames, computation time of the 3D video holograms could be also reduced just by removing these redundant data. Thus, a couple of computational methods for generation of 3D video holograms by combined use of the N-LUT method and data compression algorithms are also presented and discussed. Some experimental results finally reveal that by using this approach a great reduction of computation time of 3D video holograms could be achieved.

关键词： LUT Computational approaches for fast generation of digital 3D video holograms CGH

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Simple sacrificial-layer-free microfabrication processes for air-cavity Fresnel acoustic lenses(ACFALs)with improved focusing performance

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Microsystems & Nanoengineering 2022年第4期8卷 233-249页

作者： Yongkui Tang eun Sok kim Department of Electrical and Computer Engineering University of Southern CaliforniaLos AngelesCA90089-0271USA

Focused ultrasound(FUs)is a powerful tool widely used in biomedical therapy and imaging as well as in sensors and *** focusing techniques based on curved surfaces,metamaterial structures,and multielement phased arrays either present diffculties in massively parallel manufacturing with high precision or require complex drive electronics to *** difficulties have been addressed by microfabricated self-focusing acoustic transducers(SFATs)with Parylene air-cavity Fresnel acoustic lenses(ACFALs),which require a time-demanding step in removing the sacrificial *** paper presents three new and improved types of ACFALs based on polydimethylsiloxane(PDMS),an SU-8/PDMS bilayer,and SU-8,which are manufactured through simple sacrificiallayer-free microfabrication processes that are two to four times faster than that for the Parylene ***,by studying the effect of the lens thickness on the acoustic transmittance through the lens,the performance of the transducers has been optimized with improved thickness control techniques developed for PDMS and *** a result,the measured power transfer effciency(PTE)and peak output acoustic pressure are up to 2.0 and 1.8 times higher than those of the Parylene ACFALs,*** simple microfabrication techniques described in this paper are useful for manufacturing not only high-performance ACFALs but also other miniaturized devices with hollow or suspended structures formicrofluidicand optical applications.

关键词： Parylene Fresnel cavity

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Mechanical strength and corrosion resistance of Al-additive friction stir welded AZ31B joints

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Journal of Magnesium and Alloys 2023年第5期11卷 1519-1535页

作者： Jae-Yeon kim eun-Woo kim Dong-O kim eun-Kyo Ju Ji-eun Lee Jaeheon Lee Jai-Won Byeon Mining Engineering Department Colorado School of MinesGoldenCO 80401USA Department of Materials Science and Engineering Seoul National University of Science and TechnologySeoul 01811Republic of Korea

Compared to other structural alloys,magnesium alloys have a relatively poor corrosion resistance and low mechanical strength,which can be further deteriorated when these alloys are subjected to joining processes using the existing joining ***,we propose for the first time an additive friction stir-welding(AFSW)using fine Al powder as an additive to improve the mechanical strength as well as corrosion resistance of AZ31B weld *** is a solid-state welding method of forming a high-Al AZ31B joint via an in-situ reaction between pure Al powders filled in a machined groove and the AZ31B *** optimize the process parameters,AFSW was performed under different rotational and transverse speeds,and number of passes,using tools with a square or screw *** particular,to fabricate a weld zone,where the Al was homogenously dispersed,the effects of the groove shape were investigated using three types of grooves:surface one-line groove,surface-symmetric grooves,and inserted symmetric *** homogenous and defect-less AFS-welded AZ31B joint was successfully fabricated with the following optimal parameters:1400 rpm,25 mm/min,four passes,inserted symmetric grooves,and the tool with a square *** AFSW fully dissolved the additive Al intoα-Mg and in-situ precipitated Mg_(17)Al_(12)particles,which was confirmed via scanning electron microscopy,transmission electron microscope,and X-ray diffraction *** microhardness,joint efficiency,and elongation at the fracture point of the AFS-welded AZ31B joint were 80 HV,101%,and 8.9%,*** values are higher than those obtained for the FS-welded AZ31 joint in previous *** corrosion resistance of the AFS-welded AZ31B joint,evaluated via hydrogen evolution measurements and potentiodynamic polarization tests,was enhanced to 55%relative to the FS-welded AZ31B joint.

关键词： AZ31B magnesium alloy Additive friction stir-welding In-situ reaction Mg_(17)Al_(12)particles Joint efficiency Corrosion resistance

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Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

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Friction 2023年第7期11卷 1292-1306页

作者： Kuk-Jin SEO Hyun-Joon kim Dae-eun kim Department of Mechanical Engineering Yonsei UniversitySeoul 03722Republic of Korea Department of Precision Mechanical Engineering Kyungpook National UniversitySangju 37224Republic of Korea Department of Advanced Science and Technology Convergence Kyungpook National UniversitySangju 37224Republic of Korea

This work shows that a soft,thin film comprising randomly aligned carbon nanotubes(CNTs)can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh *** investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film,multi-walled CNTs(MWCNTs)and diamond-like carbon(DLC)thin films were prepared to conduct nanoscale tribological experiments using the atomic force microscopy(AFM).The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal *** demonstrate the wear reduction mechanism of the MWCNT thin film,its indentation and frictional behaviors were *** indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin *** permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load *** results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures.

关键词： carbon nanotube(CNT) thin film wear friction elastic recovery

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Detecting IoT Botnet in 5G Core Network Using Machine Learning

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Computers, Materials & Continua 2022年第9期72卷 4467-4488页

作者： Ye-eun kim Min-Gyu kim Hwankuk kim Department of Electronics Information and System Engineering Sangmyung UniversityCheonan-siKorea Department of Information Security Engineering Sangmyung UniversityCheonan-siKorea

As Internet of Things(IoT)devices with security issues are connected to 5G mobile networks,the importance of IoT Botnet detection research in mobile network environments is ***,the existing research focused on AI-based IoT Botnet detection research in wired network *** addition,the existing research related to IoT Botnet detection in ML-based mobile network environments have been conducted up to ***,this paper conducts a study on ML-based IoT Botnet traffic detection in the 5G core *** binary and multiclass classification was performed to compare simple normal/malicious detection and normal/threetype IoT Botnet malware *** both classification methods,the IoT Botnet detection performance using only 5GC’s GTP-U packets decreased by at least 22.99%of accuracy compared to detection in wired network *** addition,by conducting a feature importance experiment,the importance of feature study for IoT Botnet detection considering 5GC network characteristics was *** this paper analyzed IoT botnet traffic passing through the 5GC network using ML and presented detection results,think it will be meaningful as a reference for research to link AI-based security to the 5GC network.

关键词： IoT botnet 5G B5G malware machine learning

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Simultaneous acceleration of two kinds of ion beams in the RISP

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Nuclear Science and Techniques 2019年第6期30卷 70-77页

作者： Siwon Jang eun-San kim Department of Accelerator Science Korea University Sejong Campus

The Rare Isotope Science Project (RISP) is a research complex consisting of a heavy-ion accelerator, which contains a front-end system, a super-conducting linear accelerator, an isotope separator online (ISOL) system, and an in-flight system. The original purpose of the post-linear-accelerator (post-linac) section was to accelerate either a stable driver beam derived from an electron cyclotron resonance ion source, or an unstable rare-isotope beam from an ISOL system. The post-linac lattice has now been redesigned using a novel and improved acceleration concept that allows the simultaneous acceleration of both a stable driver beam and a radioisotope beam. To achieve this, the post-linac lattice is set for a mass-to-charge ratio (A/q) that is the average of the two beams. The performance of this simultaneous two-beam acceleration is here assessed using two ion beams: 58Ni^8+ and 132Sn^20+. A beam dynamics simulation was performed using the TRACK and TraceWin codes. The resultant beam dynamics for the new RISP post-linac lattice design are examined. We also estimate the effects of machine errors and their correction on the post-linac lattice.

关键词： Linear accelerator Simultaneous two-beam acceleration Heavy-ion accelerator Beam dynamics

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Electrophoretic deposition of a supercapacitor electrode of activated carbon onto an indium-tin-oxide substrate using ethyl cellulose as a binder

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Journal of Materials Science & Technology 2020年第23期58卷 188-196页

作者： Taeuk kim Seong-Hoon Yi Sang-eun Chun School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

A transparent energy storage device is an essential component for transparent *** increasing demand for high-power devices stimulates the development of transparent supercapacitors with high power density.A transparent electrode for such supercapacitors can be assembled via the electrophoretic deposition of an active material powder with a binder onto a transparent *** properties of the binder critically influence the electrochemical behavior and performance of the resulting *** cellulose(EC)is known as an eco-friendly,transparent,flexible,and inexpensive ***,we fabricated an electrode film with EC binder via electrophoretic deposition on an indium tin oxide(ITO)substrate instead of using the conventional polytetrafluoroethylene(PTFE)*** assembled electrodes with EC and PTFE were compared to investigate the feasibility of EC as a binder from different perspectives,including homogeneity,wettability,electrochemical behavior,and mechanical *** EC enabled the formation of a homogeneous film composed of smaller particles and with a higher specific capacitance compared with films prepared with *** annealing improved the adhesion strength of the EC because of its glass transition;however,its hydrophobic nature limited utilization of the active material for charge *** electrochemical activation improved the wettability of the electrode,resulting in an increased capacitance of 60 F g^(-1).Furthermore,even with the lower wettability of EC compared with that of PTFE,better rate performance was possible with the EC *** increased mechanical stability after the annealing process ensured an excellent cycle life of 95%capacitance retention for 15,000 cycles.

关键词： Electrophoretic deposition Transparent electrode Activated carbon Ethyl cellulose Indium tin oxide

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