• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.607-609
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• 2009

We present a Brownian molecular dynamics computer simulation method for calculating the rotational viscosity of the liquid crystal mixture comprising pentylcyanobiphenol (5CB) and decylcyanobiphenol (10CB). Mean director of the ensemble has been used as a nematic director. Results show a good agreement with experimental ones [Sudeshna DasGupta et al., Physics Letters A 306(2003)235-242].

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.473-474
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• 2015

Halo merger trees are the essential backbone of semi-analytic models for galaxy formation and evolution. Srisawat et al. (2013) show that different tree building algorithms can build different halo merger histories from a numerical simulation for structure formation. In order to understand the differences induced by various tree building algorithms, we investigate the impact of halo merger trees on a semi-analytic model. We find that galaxy properties in our models show differences between trees when using a common parameter set. The models independently calibrated for each tree can reduce the discrepancies between global galaxy properties at z=0. Conversely, with regard to the evolutionary features of galaxies, the calibration slightly increases the differences between trees. Therefore, halo merger trees extracted from a common numerical simulation using different, but reliable, algorithms can result in different galaxy properties in the semi-analytic model. Considering the uncertainties in baryonic physics governing galaxy formation and evolution, however, these differences may not necessarily be significant.

• Journal of Power Electronics
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• v.11 no.3
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• pp.381-388
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• 2011

This article presents the development of a model for SiC power diodes based on the physics of the semiconductor. The model is able to simulate the behavior of the dynamics of the charges in the N- region based on the stored charge inside the SiC power diode, depending on the working regime of the device (turn-on, on-state, and turn-off). The optimal individual calculation of the ambipolar diffusion length for every phase of commutation allows for solving the ambipolar diffusion equation (ADE) using a very simple approach. By means of this methodology development a set of differential equations that models the main physical phenomena associated with the semiconductor power device are obtained. The model is developed in Pspice with acceptable simulation times and without convergence problems during its implementation.

• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1346-1353
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• 2017

The FISPACT-II inventory simulation platform is a modern computational tool with advanced and unique capabilities. It is sufficiently flexible and efficient to make it an ideal basis around which to perform extensive simulation studies to scope a variety of responses of many materials (elements) to several different neutron irradiation scenarios. This paper briefly presents the typical outputs from these scoping studies, which have been used to compile a suite of nuclear physics materials handbooks, providing a useful and vital resource for material selection and design studies. Several different global responses are extracted from these reports, allowing for comparisons between materials and between different irradiation conditions. A new graphical output format has been developed for the FISPACT-II platform to display these "global summaries"; results for different elements are shown in a periodic table layout, allowing side-by-side comparisons. Several examples of such plots are presented and discussed.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1289-1294
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• 2018

The present study aims to investigate experimentally and theoretically thermal ablation in soft tissues by using high intensity focused ultrasound (HIFU) to assess tissue damage during HIFU thermotherapy. The HIFU field was calculated by solving the axisymmetric Khokhlov-Zabolotskaya-Kuznetsov equation from the frequency-domain perspective. The temperature field was calculated by solving Pennes' bioheat transfer equation, and the thermal dose required to create a thermal lesion was calculated by using the thermal dose formula based on the thermal dose of a 240-min exposure at $43^{\circ}C$. In order to validate the simulation results, we performed thermal ablation experiments in a tissue-mimicking phantom and ex-vivo porcine liver for two different HIFU source conditions by using a 1.1-MHz, single-element, spherically focused HIFU transducer. The small difference between the measured and the predicted lesion sizes suggests that the implementation of the numerical model used here should be modified to iteratively allow for temperature-dependent changes in the physical properties of tissues.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1750-1759
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• 2018

A complete code-package for gyrotron simulation to analyze its performance is under development in UNIST, Korea. We first time report the present status of the code-package named as UNIST Gyrotron Design Tool (UGDT). It can perform design simulations for gyrotron's interaction cavity, RF window, and the essential mode calculations including the study of mode competition. We will discuss about its salient features, theory, numerical implementation, and its calculation result for 95 GHz UNIST Gyrotron. Moreover, we will validate its capability to perform the mode competition calculation for fundamental and second harmonic modes.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.506-512
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• 2013

Recently, the color separation issue of wide-spreading white LEDs has attracted attention due to their wide applicability as light sources in direct-lit LCD backlights. These wide-spreading LED packages usually consist of LED chips, a color-conversion phosphor layer, and a light-shaping lens. The technical aspect of this color issue was related to a method for balancing the yellow spectral component emitting from phosphors with respect to the blue one from the LED chip as a function of viewing angle. In this study, we suggested an approach for carrying out quantitative analysis for the color separation problem occurring in wide-spreading LED packages by optical simulation. In addition, the effect of an internal scattering layer on the color uniformity was investigated, which may be considered as a potential solution for this problem.

• International Journal of Contents
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• v.17 no.3
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• pp.67-73
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• 2021

Dark matter is barely known because it cannot be explained using the Standard Model. In addition, dark matter has not been detected yet. It is currently being explored through various ways. In this paper, we studied dark matter in an electron-positron collider using MadGraph5. The signal channel is e⁺e^- → 𝜇⁺𝜇^-A' where A' decays to dimuon. We studied the cross-section by increasing the center-of-mass energy. Central processing unit (CPU) time of simulation was compared with that using a local Linux machine and a KISTI-5 supercomputer (Knight Landing and Skylake). Furthermore, one or more cores were used for comparing CPU time among machines. Results of this study will enable the exploration of dark matter in electron-positron experiments. This study also serves as a reference for optimizing high-energy physics simulation toolkits.

• Current Optics and Photonics
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• v.2 no.6
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• pp.623-628
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• 2018

Clotting properties of human blood are important clinical information to monitor for patients with platelet and coagulation disorders. Most devices used to diagnose these disorders utilize blood plasma together with tissue factors and $Ca^{{+}{+}}$ additives. In some instruments, magnetic particles were mixed with blood samples and a rotating magnetic field was applied, resulting in the rotation of magnetic particles, which was probed by impinging light. The working principle seems obvious yet had not been investigated in depth. We modeled the collective behavior of light propagating through magnetic needles, aligned in the direction of the rotating external magnetic field, with scattering light analysis software. Simulation results indicated that the scattering pattern undergoes periodic undulations with respect to the slant angle of the magnetic needles. Also provided is a means of extracting meaningful information from the scattering measurement.

• Current Optics and Photonics
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• v.5 no.4
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• pp.375-383
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• 2021

We present a simulation method to design antireflection coating (ARCs) for fiber-coupled superconducting nanowire single-photon detectors. Using a finite-element method, the absorptance of the nanowire is calculated for a defined unit-cell structure consisting of a fiber, ARC layer, nanowire absorber, distributed Bragg reflector (DBR) mirror, and air gap. We develop a method to evaluate the uncertainty in absorptance due to the uncontrollable parameter of air-gap distance. The validity of the simulation method is tested by comparison to an experimental realization for a case of single-layer ARC, which results in good agreement. We show finally a double-layer ARC design optimized for a system detection efficiency of higher than 95%, with a reduced uncertainty due to the air-gap distance.