• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.462-462
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• 2013

Gallium Oxide (Ga2O3) has been widely investigated for the optoelectronic applications due to its wide bandgap and the optical transparency. Recently, with the development of fabrication techniques in nanometer scale semiconductor materials, there have been an increasing number of extensive reports on the synthesis and characterization of Ga2O3 nano-structures such as nano-wires, nanobelts, and nano-dots. In contrast to typical vaporliquid-solid growth mode with metal catalysts to synthesis 1-dimensional nano-wires, there are several difficulties in fabricating the nanostructures by using sputtering techniques. This is attributed to the fact that relatively low growth temperatures and higher growth rate compared with chemical vapor deposition method. In this study, Ga2O3 chestnut burr were synthesized by using radio-frequency magnetron sputtering method. In contrast to typical sputtering method with sintered ceramic target, a Ga2O3 powder (99.99% purity) was used as a sputtering target. Several samples were prepared with varying the growth parameters, especially he growth time and the growth temperature to investigate the growth mechanism. Samples were characterized by using XRD, SEM, and PL measurements. In this presentation, the details of fabrication process and physical properties of Ga2O3 nano chestnut burr will be reported.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.139-152
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• 1999

These days we broadly apply drilled shafts for deep foundations to build infrastructures. The defects of the deep foundations cause the decrease of their support load capacity and the increase of settlement, and the subsequent damage of the super-structures. In consequence, non-destructive testings techniques of concrete piles are important for their integrity evaluation. To improve understanding and reliable application of the impact echo method for the integrity evaluation of the drilled concrete piles, numerical studies of the impact response of concrete piles by using axi-symmetric three-dimensional finite element method are peformed for (a) sound piles: (b) piles containing necks, voids and layers of low-quality concrete: and (c) piles in soil and/or above rock. The results of these studies show that the finite element method is effective for evaluating the impact response of drilled concrete piles.

• Wind and Structures
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• v.22 no.5
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• pp.595-616
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• 2016

Providing high starting torque and efficiency simultaneously is a significant challenge for vertical axis wind turbines (VAWTs). In this paper, a new approach is studied in order to modify VAWTs performance and cogging torque. In this approach, J-shaped profiles are exploited in the structure of blades by means of eliminating the pressure side of airfoil from the maximum thickness toward the trailing edge. This new profile is a new type of VAWT airfoil using the lift and drag forces, thereby yielding a better performance at low TSRs. To simulate the fluid flow of the VAWT along with J-shaped profiles originated from NACA0018 and NACA0030, a two-dimensional computational analysis is conducted. The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the two-equation Shear Stress Transport (SST) turbulence model. The main objective of the study is to investigate the effects of J-shaped straight blade thickness on the performance characteristics of VAWT. The results obtained indicate that opting for the higher thickness in J-shaped profiles for the blade sections leads the performance and cogging torque of VAWT to enhance dramatically.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.15-22
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• 2018

A compressible multiphase flow was investigated using a DIM consisting of seven equations, including the fifth-order MLP and a modified HLLC Riemann solver to achieve a precise interface structure of liquid and gas. The numerical methods were verified by comparing the flow structures of the high-pressure water and low-pressure air in the shock tube. A 2D air-helium shock-bubble interaction at the incident shock wave condition (Mach number 1.22) was numerically solved and verified using the experimental results.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.48-52
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• 2009

Micro-hole targets are studied to generate energetic protons from laser-thin foil targets by using 2-dimensional particle-in-cell simulations. By using a small hole, the maximum energy of the accelerated proton is increased to 4 times higher than that from a simple planar target. The main proton acceleration mechanism of the hole-targets is the electrostatic field created between the fast electrons accelerated by the laser pulse ponderomotive force combined with the vacuum heating and the target rear surface. But in this case, the proton angular distribution shows double-peak shape, which means poor collimation and low current density. By using a small cone-shaped hole, the maximum proton energy is increased 3 times higher than that from a simple planar target. Furthermore, the angular distribution of the accelerated protons shows good collimation.

• Steel and Composite Structures
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• v.10 no.4
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• pp.297-315
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• 2010

This paper is concerned with free vibration characteristics and natural frequency of horizontally curved composite plate girder bridges. Three-dimensional finite element models are developed for the girders using the software package LUSAS and analyses carried out on the models. The validity of the finite element models is first established through comparison with the corresponding results published by other researchers. Studies are then carried out to investigate the effects of total number of girders, number of cross-frames and curvature on the free vibration response of horizontally curved composite plate girder bridges. The results confirm the fact that bending modes are always coupled with torsional modes for horizontally curved bridge girder systems. The results show that the first bending mode is influenced by composite action between the concrete deck and steel beam at low subtended angle but, on the girders with larger subtended angle at the centre of curvature such influence is non-existence. The increase in the number of girders results in higher natural frequency but at a decreasing rate. The in-plane modes viz. longitudinal and arching modes are significantly influenced by composite action and number of girders. If no composite action is taken into account the number of girders has no significant effect for the in-plane modes.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.54.1-54.1
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• 2011

Formation of self-gravitating gas clouds and hence stars in galaxies is a consequence of both thermal and dynamical evolution of a gaseous medium. Using hydrodynamics simulations including cooling and heating explicitly, we follow simultaneously thermal and dynamical evolution of galactic gas disks to study dynamics and structures of galactic spiral shocks with thermal instability and regulation of the star formation rates (SFRs). We first perform one-dimensional simulations in direction perpendicular to spiral arms. The multiphase gas flows across the arm soon achieve a quasi-steady state characterized by transitions from warm to cold phases at the shock and from cold to warm phases in the postshock expansion zone, producing a substantial fraction of intermediate-temperature gas. Next, we allow a vertical degree of freedom to model vertically stratified disks. The shock front experiences unsteady flapping motions, driving a significant amount of random gas motions, and self-gravity promotes formation of bound clouds inside spiral arms. Finally, we include the star formation feedback in both mechanical (due to supernova explosion) and radiative (due to FUV heating by young stars) forms in the absence of spiral arms. At saturation, gravitationally bound clouds form via thermal and gravitational instabilities, which are compensated by disruption via supernova explosions. We find that the FUV heating regulates the SFRs when gas surface density is low, confirming the prediction of the thermal and dynamical equilibrium model of Ostriker et al. (2010) for star formation regulation.

• Journal of Information Display
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• v.12 no.1
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• pp.5-10
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• 2011

A novel architecture and proprietary electronic inks were developed to provide disruptive digital-media solutions based on an electrokinetic technology platform. The flexible reflective electronic media (eMedia) was fabricated by imprinting three-dimensional microscale structures with a roll-to-roll manufacturing platform. The HP technologies enable the required attributes for eMedia, such as low power, transparency, print-quality color, continuous levels of gray, and lowcost scalability. Pixelation was also demonstrated by integrating with the prototype oxide thin-film transistor backplane, and the system architecture was further developed by stacking primary-colorant layers for color reflective-display application. The innovations described in this paper are currently being developed further for the eSkins, eSignage, and ePaper applications.

• Journal of the Korean Society of Safety
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• v.13 no.3
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• pp.11-23
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• 1998

In this study, collapse test of thin-walled structure is performed under axially quasi-static and impact load in collapse characteristic to develop the optimum structural member for a light-oriented automobile. Furthermore, the energy-absorbing capacity is observed according to the variety of configuration(circular, square), aspect ratio in aluminum specimen to obtain basic data for the improved member of vehicle. In both quasi-static and impact collapse test, Al circular specimens collapse, in general, with axisymmetric mode in case of thin thickness while collapse with non-axisynmetric mode according to the thickness increase. For Al rectangular specimens, they collapse with axisymmetric mode in case of thin thickness, with mixed collapse mode according to the increase of thickness. In terms of initial max. load, Al square specimen turns out the best member among specimens, and then Al square, circular and circular with large scaling ratio, respectively. In case of quasi-static compression test, the absorbed energy per unit volume and mass shows higher in Al circular specimen, and then Al square, circular with large scaling ratio, respectively, according to shape ratio the absorbed energy per unit volume and mass in case of max. impact compression load is higher than that of static load. But the absorbed energy per unit volume and mass shows that Al circular specimen is the best member. Especially, unlike max. compression loan, the absorbed energy per unit volume and mass in impact test turns out the low value.

• Transactions on Electrical and Electronic Materials
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• v.5 no.1
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• pp.19-23
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• 2004

A novel method of high speed, accurate circuit simulation in 3-dimensional (3-D) parallel-plate capacitors is investigated. The basic concept of the circuit simulation methods is partial element equivalent circuit model. The three test structures of 3-D parallel-plate capacitors are fabricated by using multi-layer low-temperature co-fired ceramic (LTCC) process and their S-parameters are measured between 50 MHz and 5 GHz. S-parameters are converted to Y-parameters, for comparing measured data with simulated data. The circuit model parameters of the each building block are optimized and extracted using HSPICE circuit simulator. This method is convenient and accurate so that circuit design applications can be easily manipulated.