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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

Nanotribological properties and scratch resistance of MoS_(2)bilayerona SiO_(2)/Si substrate

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Friction 2023年第1期11卷 154-164页

作者： Si-hwan kim Hyo-sok AHN Department of Transdisciplinary Studies Seoul National UniversitySeoul 08826Republic of Korea Department of Manufacturing Systems and Design Engineering Seoul National University of Science and TechnologySeoul 08826 Republic of Korea

The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are *** force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 *** resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 *** probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom *** analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred *** FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)*** the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.

关键词： chemical vapor deposition(CVD)-grown MoS,bilayer friction force microscopy(FFM) nanoscratch test Kelvin probe force microscopy(KPFM) scratch resistance

A modeling method for vibration analysis of cracked beam with arbitrary boundary condition

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Journal of Ocean Engineering and Science 2018年第4期3卷 367-381页

作者： Kwanghun kim sok kim Kyongjin sok Chanil Pak Kwangbok Han Department of Engineering Machine Pyongyang University of Mechanical EngineeringPyongyang 999093Democratic People’s Republic of Korea Department of Information Engineering Chongjin Mine&Metal UniversityChongjin 999091Democratic People’s Republic of Korea Institute of Information Technology University of SciencesPyongyang 999093Democratic People’s Republic of Korea Information Center Kim Chaek University of TechnologyPyongyang 950003Democratic People’s Republic of Korea Department of Resource Development Machinery Engineering Pyongyang University of Mechanical EngineeringPyongyang 999093Democratic People’s Republic of Korea

This paper establishes a cracked Timoshenko beams model to investigate the vibration behavior based on the ultraspherical *** beam theory is applied to model the free vibration analysis of the cracked beam and the numerical results are obtained by using ultraspherical orthogonal *** boundary conditions of both ends of the cracked beam are modeled as the elastic spring and the beam is divided into two parts by the crack section,and continuous conditions at the connecting face are modeled by the inverse of the flexibility coefficients of fracture mechanics *** the influence of boundary conditions,displacements admissible functions of cracked Timoshenko beam can be set up as ultraspherical orthogonal *** accuracy and robustness of the present method are evidenced through comparison with previous literature and the results achieved by the finite element method(FEM).In addition,the effects of flexibility coefficient on the natural frequencies are also investigated by using the proposed *** examples are given for free vibration analysis of cracked beams with various boundary conditions,which may be provided as reference data for future study.

关键词： Cracked beam Free vibration Ultraspherical polynomials Arbitrary boundary conditions

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

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

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

A semi-analytical method for forced vibration analysis of cracked laminated composite beam with general boundary condition

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Journal of Ocean Engineering and Science 2021年第1期6卷 40-53页

作者： sok kim Kwanghun kim Myongchol Ri Yongsong Paek Choljun kim Department of Information Engineering Chongjin Mine&Metal UniversityChongjin 999091Democratic People’s Republic of Korea Department of Engineering Machine Pyongyang University of Mechanical EngineeringPyongyang 999093Democratic People’s Republic of Korea Institute of Science Pyongyang University of Mechanical EngineeringPyongyang 999093Democratic People’s Republic of Korea Department of Resources Development Mechanical Engineering Pyongyang University of Mechanical EngineeringPyongyang 999093Democratic People’s Republic of Korea

In this paper,a semi-analytical method for the forced vibration analysis of cracked laminated composite beam(CLCB)is *** computational model is formulated by Timoshenko beam theory and its dynamic solution is solved using the Jacobi-Ritz *** boundary conditions(BCs)at both ends of the CLCB are generalized by the application of artificial elastic springs,the CLCB is separated into two elements along the crack,the flexibility coefficient of fracture theory is used to model the essential continuous condition of the connective *** the allowable displacement functions used to analyze dynamic characteristics of CLCB are expressed by classical Jacobi orthogonal polynomials in a more general *** accuracy of the proposed method is verified through the compare with results of the finite element method(software ABAQUS is used in this paper).On this basis,the parametric study for dynamic analysis characteristics of CLCB is performed to provide reference datum for engineers.

关键词： Semi-analytical method Cracked laminated composite beam(CLCB) Dynamic analysis General boundary condition Numerical analysis

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

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

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