• Electronics and Telecommunications Trends
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• v.35 no.7
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• pp.13-22
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• 2020

There is no denying that computing power has been a crucial driving force behind the development of artificial intelligence today. In addition, artificial intelligence (AI) semiconductors and computing systems are perceived to have promising industrial value in the market along with rapid technological advances. Therefore, success in this field is also meaningful to the nation's growth and competitiveness. In this context, ETRI's AI strategy proposes implementation directions and tasks with the aim of strengthening the technological competitiveness of AI semiconductors and computing systems. The paper contains a brief background of ETRI's AI Strategy #2, research and development trends, and key tasks in four major areas: 1) AI processors, 2) AI computing systems, 3) neuromorphic computing, and 4) quantum computing.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.121-128
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• 1997

The Boundary Element Method(BEM) has many advantages. Nevertheless the applicability of BEM to structural analysis is seemed to be behind the other methods. This study presents the application of the BEM for analysis of assembled plate structures which is light weight and has a great loading capacity. Firstly, we formulate the boundary integral equation of the single plate, using the biharmonic fundamental solution for plate bending and internal force problems. Nextly, each plates are assembled on 3-dimensional space. In this process, the boundary conditions on assemble line are used. To verify the objectivity and universal validity of analysis by BEM, the results of BEM was compared to that of SAP90 by using FEM.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.314-324
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• 1996

Scanning probe microscopes (SPMs) such as the scanning tunneling microscope (STM) and the atomic force microscope (AFM) were used for surface modification tools at the nanometer scale. Material surfaces, i. e., titanium, hydrogen-terminated silicon and trimethylsilyl organosilane monolayer on silicon, were locally oxidized with the best lateral spatial resolution of 20nm. The principle behind this proximal probe oxidation method is scanning probe anodization, that is, the SPM tip-sample junction connected through a water column acting as a minute electrochemical cell. An SPM-nanolithogrphy process was demonstrated using the organosilane monolayer as a resist. Area-selective chemical modifications, i. e., etching, electroless plating with gold, monolayer deposition and immobilization of latex nanoparticles; were achieved in nano-scale resolution. The area-selectivity was based on the differences in chemical properties between the SPM-modified and unmodified regions.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.651-659
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• 2019

The IB-SEM numerical method combines the spectral/hp element method and the rigid immersed boundary method. This method avoids the problems of low computational efficiency and errors that are caused by the re-division of the grid when the solids move. Based on the Fourier transformation and the 3D immersed boundary method, the 3D IB-SEM system was established. Then, using the open MPI and the Hamilton HPC service, the computational efficiency was increased substantially. The flows around a cylinder and a sphere were simulated by the system. The surface of the cylinder generates vortices with alternating shedding, and these vortices result in a periodic force acting on the surface of the cylinder. When the shedding vortices enter the flow field behind the cylinder, a recirculation zone is formed. Finally, the three-dimensional pore flow was successfully investigated.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.27 no.4
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• pp.232-244
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• 2023

The unsteady dynamics of the starting flow of a flat plate is studied by using a vortex shedding model. The model describes the body and separated vortex from the trailing edge of the plate by vortex sheets, retaining a singularity at the leading edge. The model is applied to simulate the flow of an accelerated plate for small angles of attack. For numerical computations, we take two representative cases of the translational velocity of a plate: impulsive translation and uniform acceleration. The model successfully demonstrates the formation of wakes shed from the plate. The wake behind the plate is stronger for a larger angle of attack. Predictions for the lifting force from the model are in agreement with results of Navier-Stokes simulations.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.96-96
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• 2016

Nanotechnology mostly employs nano-materials and nano-structures with distinctive properties based on their size, structure, and composition. It is quite difficult to produce nano-materials and nano-structures with identical sizes, structures, and compositions in large quantities, because of spatiotemporal fluctuation of production processes. In other words, fluctuation is the bottleneck in nanotechnology. We propose three strategies to suppress such fluctuations: employing 1) difference between linear and nonlinear phenomena, 2) difference in time constants, and 3) nucleation as a bottleneck phenomenon. We are also developing nano- and micro-scale guided assembly using plasmas as a plasma nanofabrication.1-5) We manipulate nano- and micro-objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of an object in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. We conducted in-situ evaluation of local plasma potential fluctuation using tracking analysis of fine particles (=objects) in plasmas. Experiments were carried out with a radio frequency low-pressure plasma reactor, where we set two quartz windows at the top and bottom of the reactor. Ar plasmas were generated at 200 Pa by applying 13.56MHz, 450V peak-to-peak voltage. The injected fine particles were monodisperse methyl methacrylate-polymer spheres of $10{\mu}m$ in diameter. Fine particles were injected into the reactor and were suspended around the plasma/sheath boundary near the powered electrode. We observed binary collision of fine particles with a high-speed camera. The frame rate was 1000-10000 fps. Time evolution of their distance from the center of mass was measured by tracking analysis of the two particles. Kinetic energy during the collision was obtained from the result. Potential energy formed between the two particles was deduced by assuming the potential energy plus the kinetic energy is constant. The interaction potential is fluctuated during the collision. Maximum amplitude of the fluctuation is 25eV, and the average is 8eV. The fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one, because the fine particle has a large negative charge of -17000e and the corresponding electrostatic force is large compared to other forces.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.1
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• pp.26-34
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• 2015

The angle of attack of a cambered otter board in a bottom trawl was estimated using a three-dimensional semi-analytic treatment of a towing cable (warp) system that was applied to the field experiments of a bottom trawl obtained by the Scanmar system. The equilibrium condition of the horizontal component and vertical component of forces was used to the three forces acting on the otter board in the horizontal plane. Those forces were the force on the warp at the bracket, hydrodynamic lift and drag forces on the otter board and the force on the hand rope attached just behind the otter board. Also the equilibrium of moment about the front edge of the otter board was used to find out the angle of attack of the cambered otter board. When the warp length was 120m and 180m long and the towing speed was between 1.23 and 1.90 m/s, the estimated angle of attack of the cambered otter board was ranged between $26.1^{\circ}$ and $29.6^{\circ}$, respectively, though the maximum lift force was at the angle of attack $22.6^{\circ}$. The angle of attack of the otter board was tended to increase weakly with the longer length of warp (180 m) at the same towing speed in the experiment.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.133-138
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• 2002

The technique of high speed machining is widely studied in machining fields, because the high efficiency and accuracy in machining can be obtained in high speed machining. Unfortunately the development of tool fur high speed machining in not close behind that of machine tool. In this study, 10 types flat endmill is prepared for obtaining data according to tool shape. Especially, we concentrated in helix angle, number of cutting edge and rake angle. Cutting condition is selected for several experiments and measuring cutting farce, tool life, tool wear and chip shape according to cutting length. 3-axis cutting farces are acquired from the tool dynamometer with high natural frequency, as the conventional tool dynamometer (9257B, Kistler) has cannot measure the state of high frequency force. Particularly, we found out that the axial cutting force waveform has a good relation with tool wear features. And flow is interrupted at the beginning of cutting by the decrease of rake angle. By above results. it is suggested the endmill tool with 45$^{\circ}$helix angle, 6 cutting edge and -15$^{\circ}$rake angle is suitable for high speed machining.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.586-591
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• 2013

The printing of nanomaterials onto certain substrates is one of the key technologies behind high-speed interconnection and high-performance electronic devices. For the printing of next-generation electronic devices, a printing process which can be applied to a flexible substrate is needed. A printing process on a flexible substrate requires a lowtemperature, non-vacuum process due to the physical properties of the substrate. In this study, we obtained well-ordered Ag nanowires using modified gravure printing techniques. Ag nanowires are synthesized by a silver nitrate ($AgNO_3$) reduction process in an ethylene glycol solution. Ag nanowires were well aligned by hydrodynamic force on a micro-engraved Si substrate. With the three-dimensional structure of polydimethylsiloxane (PDMS), which has an inverse morphology relative to the micro-engraved Si substrate, the sub-micron alignment of Ag nanowires is possible. This technique can solve the performance problems associated with conventional organic materials. Also, given that this technique enables large-area printing, it has great applicability not only as a next-generation printing technology but also in a range of other fields.

• Wind and Structures
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• v.26 no.5
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• pp.267-277
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• 2018

Numerical simulations are performed of a long flexible cylinder undergoing vortex-induced vibration at a Reynolds number of 500. The cylinder is pinned at both ends, having an aspect ratio of 100 (cylinder length to cylinder diameter) and a mass ratio of 4.2 (structural mass to displaced fluid mass). Temporal and spatial information on the cross-flow (CF) and in-line (IL) vibrations is extracted. High modal vibrations up to the $6^{th}$ in the CF direction and the $11^{th}$ in the IL direction are observed. Both the CF and IL vibrations feature a multi-mode mixed pattern. Mode competition is observed. The $2^{nd}$ mode with a low frequency dominates the IL vibration and its existence is attributed to a wave group propagating back and forth along the span. Distributions of fluid force coefficients are correlated to those of the CF and IL vibrations along the span. Histograms of the x'-y motion phase difference are evaluated from the total simulation time and a complete vibration cycle representing the standing or travelling wave pattern. Correlations between the phase difference and the vibrations are discussed. Vortex structures behind the cylinder show an interwoven near-wake pattern when the standing wave pattern dominates, but an oblique near-wake pattern when the travelling wave pattern prevails.