• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.6
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• pp.939-946
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• 2018

In this work, we present simple schematics for a three-terminal graphene-based nanoelectromechanical switch with the vertical electrode, and we investigated their operational dynamics via classical molecular dynamics simulations. The main structure is both the vertical pin electrode grown in the center of the square hole and the graphene covering on the hole. The potential difference between the bottom gate of the hole and the graphene of the top cover is applied to deflect the graphene. By performing classical molecular dynamic simulations, we investigate the nanoelectromechanical properties of a three-terminal graphene-based nanoelectromechanical switch with vertical pin electrode, which can be switched by the externally applied force. The elastostatic energy of the deflected graphene is also very important factor to analyze the three-terminal graphene-based nanoelectromechanical switch. This simulation work explicitly demonstrated that such devices are applicable to nanoscale sensors and quantum computing, as well as ultra-fast-response switching devices.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2018-2025
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• 2023

In our previous study, we proposed an integrated PG-PET-based imaging method to increase the prediction accuracy for patient dose distributions. The purpose of the present study is to experimentally validate the feasibility of the PG-PET system. Based on the detector geometry optimized in the previous study, we constructed a dual-head PG-PET system consisting of a 16 × 16 GAGG scintillator and KETEK SiPM arrays, BaSO₄ reflectors, and an 8 × 8 parallel-hole tungsten collimator. The performance of this system as equipped with a proof of principle, we measured the PG and positron emission (PE) distributions from a 3 × 6 × 10 cm³ PMMA phantom for a 45 MeV proton beam. The measured depth was about 17 mm and the expected depth was 16 mm in the computation simulation under the same conditions as the measurements. In the comparison result, we can find a 1 mm difference between computation simulation and measurement. In this study, our results show the feasibility of the PG-PET system for in-vivo range verification. However, further study should be followed with the consideration of the typical measurement conditions in the clinic application.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.328-328
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• 2007

Large area matrix-addressed image detectors are a recent technology for x-ray imaging with medical diagnostic and other applications. The imaging properties of x-ray pixel detectors depend on the quantum efficiency of x-rays, the generated signal of each x-ray photon and the distribution of the generated signal between pixels. In a phosphor coated detector the light signal is generated by electrons captured in the phosphor screen. In our study we simulated the lateral spread distributions for phosphor coupled detector by Monte Carlo simulations. Most simulations of such detectors simplify the setup by only taking the conversion layer into account neglecting behind. The Monte Carlo code MCNPX has been used to simulate the complete interaction and subsequent charge transport of x-ray radiation. This has allowed the analysis of charge sharing between pixel elements as an important limited factor of digital x-ray imaging system. The parameters are determined by lateral distribution of x-ray photons and x-ray induced electrons. The primary purpose of this study was to develop a design tool for the evaluation of geometry factor in the phosphor coupled optical imaging detector. In order to evaluate the spatial resolution for different phosphor material, phosphor geometry we have developed a simulation code. The developed code calculates the energy absorption and spatial distribution based on both the signal from the scintillating layer and the signal from direct detection of x-ray in the detector. We show that internal scattering contributes to the so-called spatial resolution drop of the image detector. Results from the simulation of spatial distribution in a phosphor pixel detector are presented. The spatial resolution can be increased by optimizing pixel size and phosphor thickness.

• Korean Chemical Engineering Research
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• v.48 no.2
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• pp.224-231
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• 2010

In GvdW EOS, a recently presented paper, shows that the characteristic status for spherical non-linear particle, of which the mutual behavior is known to be vdWf(van der Waals force) only, could be described well enough in the critical region. However, in current papers, analysis has not been done on GvdW about whether it is accurate or not, even for the particles in the linear form or those with the additional mutual behavior such as static-electricity, so there's some argument about the wide use of that. Therefore, in this paper, for the simulation in the critical region of Normal-alkane group(R=methane, ethane, propane, butane) which are the particles that has a linear charateristic and Normal-amine group($RNH_2$, R=methyl-, ethyl-, propyl-amine) where static-electricity is extremely shown, GvdW parameter values about these particles are defined, and based on this simulation, we compared results to the current EOS presented recently, and analyzed them. Through the simulation, it was shown that in case of Normal-alkane group and Normal-amine group molecules, GvdW presents an accurate critical region characteristic which is far more close to the measurement compared to current EOSs. Especially for butane with big amount in molecules, we found out that only GvdW EOS can reach close enough to the critical point.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.103-112
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• 2005

In this paper, in order to derive the current-voltage characteristics of n-AlGaN/GaN HEMTs with the piezoelectric and spontaneous polarizations, we suggested analytical solutions for the two-dimensional Poisson equation in the AlGaN and GaN regions by taking into account the longitudinal field variation, field-dependent mobility, and the continuity condition of the channel current flowing in the quantum well. Obtained expressions for long and short channel devices would be applicable to the entire operating regions in a unified manner. Simulation results show that the drain saturation current increases and the cutoff voltage decreases as drain voltage increases. Compared with the conventional models, the present model seems to provide more reasonable explanation for the drain-induced threshold voltage roll-off and the channel length modulation effect.

• Journal of The Korean Astronomical Society
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• v.50 no.3
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• pp.61-70
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• 2017

We study the angular correlation function of bright ($K_s{\leq}19.5$) Extremely Red Objects (EROs) selected in the Subaru GTO 2$deg^2$ field. By applying the color selection criteria of $R-K_s$ > 5.0, 5.5, and 6.0, we identify 9055, 4270, and 1777 EROs, respectively. The number density is consistent with similar studies on the optical - NIR color selected red galaxies. The angular correlation functions are derived for EROs with different limiting magnitude and different $R-K_s$ color cut. When we assume that the angular correlation function $w({\theta})$ follows a form of a power-law (i.e., $w({\theta})=A{\theta}^{-{\delta}}$), the value of the amplitude A was larger for brighter EROs compared to the fainter EROs. The result suggests that the brighter, thus more massive high-redshift galaxies, are clustered more strongly compared to the less massive galaxies. Assuming that EROs have redshift distribution centered at ~ 1.1 with ${\sigma}_z=0.15$, the spatial correlation length $r_0$ of the EROs estimated from the observed angular correlation function ranges ${\sim}6-10h^{-1}Mpc$. A comparison with the clustering of dark matter halos in numerical simulation suggests that the EROs are located in most massive dark matter halos and could be progenitors of $L_{\ast}$ elliptical galaxies.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.615-624
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• 2014

In this paper, we explore the electrical properties and high-frequency performance of carbon nanotube field-effect transistors (CNTFETs), based on the non-equilibrium Green's functions (NEGF) solved self - consistently with Poisson's equations. The calculated results show that CNTFETs exhibit superior performance compared with graphene nanoribbon field-effect transistors (GNRFETs), such as better control ability of the gate on the channel, higher drive current with lower subthreshold leakage current, and lower subthreshold-swing (SS). Due to larger band-structure-limited velocity in CNTFETs, ballistic CNTFETs present better high-frequency performance limit than that of Si MOSFETs. The parameter effects of CNTFETs are also investigated. In addition, to enhance the immunity against short - channel effects (SCE), hetero - material - gate CNTFETs (HMG-CNTFETs) have been proposed, and we present a detailed numerical simulation to analyze the performances of scaling down, and conclude that HMG-CNTFETs can meet the ITRS'10 requirements better than CNTs.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.86-92
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• 1999

A SiGe p-channel MESFET using $\delta$-doped layers is designed and the considerabel enhancement of the current driving capability of the device is observed from the result of simulation. The channel consists of double $\delta$-doped layers separated by a low-doped spacer which consists of Si and SiGe. A quantum well is formed in the valence band of the Si/SiGe heterojunction and much more holes are accumulated in the SiGe spacer than those in the Si spacer. The saturation current is enhanced by the contribution of the holes in the spacer. Among the design parameters that affect the performance of the device, the thickness of the SiGe layer and the Ge composition are studied. The thickness of 0~300$\AA$ and the Ge composition of 0~30% are investigated, and saturation current is observed to be increased by 45% compared with a double $\delta$-doped Si p-channel MESFET.

• Journal of the Korean Chemical Society
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• v.47 no.6
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• pp.541-546
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• 2003

Experimental vapor pressure measurements available in the literature for the inert gases have been rigorously analyzed and used to evaluate the constants A, B, C, D, and exponent of the following equation in the form of reduced vapor pressure and reduced temperature : $InP_r=A+{\frac{B}{T_r}+CInT_r+DT_n^r}$ According to varying exponent n all four constants have been obtained for the inert gases by the error analysis. This has provided us the best n and four constants for each of the inert gases ; Argon, krypton, xenon, helium, and neon. In order to obtain the calculated vapor pressure by the above equation, only the normal boiling point and the critical pressure and critical temperature are necessary to get the vapor pressure for an overall average deviation of 0.31 % for 406 experimental vapor pressure points consisting of five gases available in the literature. The average deviation for argon, krypton, and xenon is 0.24%, 0.09%, and 0.22%, respectively, for neon 1.31% and for helium 0.61%. These results are not unexpected in view of the significant quantum effects associated with helium and to a lesser degree with neon.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.77-77
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• 2008

금(Au)이나 은(Ag)과 같은 귀금속 물질로 형성된 금속 나노 구조체는 표면 플라즈몬 공진(Surface Plasmon Resonance, SPR) 현상과 이의 국부 환경(local environment) 변화에 대해 민감한 의존성으로 인하여 생화학적 센서로의 응용이 주목 받고 있다. 표면 플라즈몬 공진은 광 흡수와 광 산란을 수반하는데, 두 가지 특성 모두 분광학적 신호검출방식으로 센서에 응용가능하다. 이 중 광 산란을 이용하는 방식은 광원의 배경잡음 효과가 배제되기 때문에 단일 입자 검출에 유리하다. 광 흡수와 광 산란 특성은 금속 나노 구조체는 크기, 형상, 주변 매질, 물질의 선택에 따라서 영향을 받는다. 본 연구에서는 금 나노 디스크(nanodisc)의 형상에 따라서 여기 되는 표면 플라즈몬이 광 흡수와 광 산란 특성에 미치는 영향을 가시광과 근적외선 영역에 대해서 불연속 쌍극자 근사법(Discrete Dipole Approximation, DDA)을 이용하여 전사모사(simulation) 하였다. 금 나노 디스크의 형상과 플라즈몬 특성 간의 관계는 공명 파장과 산란 양자 거둠율(scattering quantum yield, $\eta$)을 이용하여 분석하였고, 센서로서의 응용을 가늠하기 위해 주변 매질의 굴절률을 조절하여 그에 따른 민감도(sensitivity )를 비교하였다. 나노 디스크의 모양이 판상에 가까워질수록 공명 파장은 적색 편이하였고 광 산란 효율과 민감도는 증가하는 현상이 나타났다. 또한, 산란 양자 거둠율은 증가하다가 완만하게 감소하는 경향이 나타났다.