• Journal of Astronomy and Space Sciences
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• v.3 no.2
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• pp.71-79
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• 1986

According to recent satellite observations, strong ion transverse acceleration to the magnetic field(ion conics) has been known. The ion conics may be a result of electrostatic waves frequently observed on the auroral zone. Both linear and nonlinear theory of electrostatic instability driven by an electron current based on 1-dimensional particle simulation experiment have been considered. From the results of simulation strong ion transverse acceleration has been shown.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.5
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• pp.297-304
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• 2015

A multilayer gaseous detector has been developed for fast dose-verification measurements of raster-scan-mode therapeutic beams in particle therapy. The detector, which was constructed with eight thin parallel-plate ionization chambers (PPICs) and polymethyl methacrylate (PMMA) absorber plates, is closely tissue-equivalent in a beam's eye view. The gas-electron signals, collected on the strips and pad arrays of each PPIC, were amplified and processed with a continuous charge.integration mode. The detector was tested with 190-MeV raster-scan-mode beams that were provided by the Proton Therapy Facility at Samsung Medical Center, Seoul, South Korea. The detector responses of the PPICs for a 190-MeV raster-scan-mode proton beam agreed well with the dose data, measured using a 2D ionization chamber array (Octavius model, PTW). Furthermore, in this study it was confirmed that the detector simultaneously tracked the doses induced at the PPICs by the fast-oscillating beam, with a scanning speed of 2 m s-1. Thus, it is anticipated that the present detector, composed of thin PPICs and operating in charge.integration mode, will allow medical scientists to perform reliable fast dose-verification measurements for typical dynamic mode therapeutic beams.

• Progress in Medical Physics
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• v.1 no.1
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• pp.97-107
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• 1990

A method of detecting charged particles in an allyl diglycol carbonate material (PN-3) which is available, amorphous, optically clear and thermoset plastic in which nuclear particle tracks could be revealed by etching in hot NaOH solutions, has been investigated. It has been applied to the study of alpha particle tracks over an energy range of 3.17～5.49 MeV which has been obtained after having passed through several sheets of polycarbonate. The dose equivalent rate of the alpha source was calculated and the spark chamber was used in order to measure the range of alpha particles after having passed through different number of absorbers. The etching characteristics and the detection response of PN-3 have been studied as a funcion of lengths of etched tracks against the parameters of energies and of the track etching rate(V$_{T}$). The investigation of the etching process for alpha particles in the PN-3 provided the most interesting results.s.

• Transactions on Electrical and Electronic Materials
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• v.15 no.2
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• pp.66-68
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• 2014

Most commercial white LED lamps use blue chip coated with yellow emitting phosphor. The use of blue excitable red and green phosphors is expected to improve the CRI. Several phosphors, such as $SrGa_2S_4:Eu^{2+}$ and $(Sr,Ba)SiO_4:Eu^{2+}$, have been suggested in the past as green components. However, there are issues of the sensitivity and stability of such phosphors. Here, we describe gallium substituted $YAG:Ce^{3+}$ phosphor, as a green emitter. YAG structures are already accepted by the industry, for their stability and efficiency. LEDs with improved CRI could be fabricated by choosing $Y_3Al_4GaO_{12}:Ce^{3+}$ (green and yellow), and $SrS:Eu^{2+}$ (red) phosphors, along with blue chip. Also, the effect of a slight change in chip wavelength is studied, for two phosphor-coated w-LEDs. The reduction in particle size of the coated phosphors also gives improved w-LED characteristics.

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.8-13
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• 2016

Superconducting properties of thin film MgB2 superconductors irradiated with 45 MeV ${\alpha}$-particle beam were studied. After the irradiation, enhancement of the critical current density and pinning force was observed, scaling close to strong pinning formula. Double logarithmic plots of the maximum pinning force density with irreversible magnetic field show a power law behavior close to carbon-doped MgB2 film or polycrystals. Variation of normalized pinning force density in the reduced magnetic field suggests scaling formulas for strong pinning mechanism like planar defects. We also observed a rapid decay of critical current density as the vortex lattice constant decreases, due to the strong interaction between vortices and increasing magnetic field.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.4142-4149
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• 2021

In the radiation protection application, the metal-polymer composites have been developed for their radiation shielding properties. In this research, the elastomer composites doped by 10 ㎛ and 100nm size of lead, bismuth and tungsten particles as filler with 30 and 60 wt percentages were prepared. To survey the shielding properties of the polymer composites using gamma-ray emitted from 152Eu and 137Cs sources, the gamma flux was measured by using NaI(Tl) detector, then the linear attenuation coefficient was calculated. Also, the Monte Carlo simulation (MCs) method was used. The results showed a direct relationship between the linear attenuation coefficients of the absorbent and filler ratio. Also, the decrease in the particle size of the shielding material in each weight percentage improved the radiation shielding features. When the dimension of the particles was in the order of nano-size, more attenuation was achieved. At low energies used for medical diagnostic X-ray applications due to the predominance of the photoelectric effect, bismuth and lead were suitable selection as filler.

• Journal of the Korea Computer Graphics Society
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• v.14 no.4
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• pp.27-33
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• 2008

Physics-based graphic techniques are used when simulating and rendering natural phenomena such as smoke, water and flame with computational physics. We propose novel methods which render simulated particle data fast onto 3D using tetrahedron splat. We calculate the position and the normal vector of splat by SPH(smoothed particle hydrodynamics) method then we reconstruct splat into quadrangular pyramid to reduce seam. We implement this technique for SPH fluid simulation, and animate natural flow of water successfully.

• Journal of Radiation Protection and Research
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• v.9 no.2
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• pp.61-66
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• 1984

A study on the characteristics of ${\alpha}$-particle track on cellulose nitrate film was carried out with a particular emphasis on the dependence of track diameter upon chemical etching condition. The track diameters etched in KOH solution appeared to be, on average, three times larger than those etched in NaOH under the same etching condition. The relationship between the track diameters and both etching time and the energy of incident ${\alpha}$-particles was also investigated. It is shown that the particle fluence rate is fairly independent of etching time as far as the condition of irradiation remains unchanged.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.49.1-49.1
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• 2019

Giant radio relics in the outskirts of galaxy clusters have been observed and they are interpreted as synchrotron emission from relativistic electrons accelerated via diffusive shock acceleration (DSA) in weak shocks of Ms < 3.0. In the DSA theory, the particle momentum should be greater than a few times the momentum of thermal protons to cross the shock transition and participate in the Fermi acceleration process. In the equilibrium, the momentum of thermal electrons is much smaller than the momentum of thermal protons, so electrons need to be pre-accelerated before they can go through DSA. To investigate such electron injection process, we study the electron pre-acceleration in weak quasi-perpendicular shocks (Ms = 2.0 - 3.0) in an ICM plasma (kT = 8.6 keV, beta = 100) through 2D particle-in-cell simulations. It is known that in quasi-perpendicular shocks, a substantial fraction of electrons could be reflected upstream, gain energy via shock drift acceleration (SDA), and generate oblique waves via the electron firehose instability (EFI), leading the energization of electrons through wave-particle interactions. We find that such kinetic processes are effective only in supercritical shocks above a critical Mach number, $Ms{\ast}{\sim}2.3$. In addition, even in shocks with Ms > 2.3, energized electrons may not reach high energies to be injected to DSA, because the oblique EFI alone fails to generate long-wavelength waves. Our results should have implications for the origin and nature of radio relics.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2002.11a
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• pp.112-114
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• 2002