• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권9호
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• pp.4357-4378
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• 2017

In cooperative multi-relay networks, the relay nodes which are selected are very important to the system performance. How to choose the best cooperative relay nodes is an optimization problem. In this paper, multi-relay selection schemes which consider either single objective or multi-objective are proposed based on evolutionary algorithms. Firstly, the single objective optimization problems of multi-relay selection considering signal to noise ratio (SNR) or power efficiency maximization are solved based on the quantum bee colony optimization (QBCO). Then the multi-objective optimization problems of multi-relay selection considering SNR maximization and power consumption minimization (two contradictive objectives) or SNR maximization and power efficiency maximization (also two contradictive objectives) are solved based on non-dominated sorting quantum bee colony optimization (NSQBCO), which can obtain the Pareto front solutions considering two contradictive objectives simultaneously. Simulation results show that QBCO based multi-relay selection schemes have the ability to search global optimal solution compared with other multi-relay selection schemes in literature, while NSQBCO based multi-relay selection schemes can obtain the same Pareto front solutions as exhaustive search when the number of relays is not very large. When the number of relays is very large, exhaustive search cannot be used due to complexity but NSQBCO based multi-relay selection schemes can still be used to solve the problems. All simulation results demonstrate the effectiveness of the proposed schemes.

• Journal of Radiation Protection and Research
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• 제41권4호
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• pp.344-349
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• 2016

Background: Carbon ion therapy has achieved satisfactory results. However, patients have a risk to get a secondary cancer. In order to estimate the risk, it is essential to understand particle transportation and nuclear reactions in the patient's body. The particle transport Monte Carlo simulation code is a useful tool to understand them. Since the code validation for heavy ion incident reactions is not enough, the experimental data of the elementary reaction processes are needed. Materials and Methods: We measured neutron production double-differential cross-sections (DDXs) on a carbon bombarded with 430 MeV/nucleon carbon beam at PH2 beam line of HIMAC facility in NIRS. Neutrons produced in the target were measured with NE213 liquid organic scintillators located at six angles of 15, 30, 45, 60, 75, and $90^{\circ}$. Results and Discussion: Neutron production double-differential cross-sections for carbon bombarded with 430 MeV/nucleon carbon ions were measured by the time-of-flight method with NE213 liquid organic scintillators at six angles of 15, 30, 45, 60, 75, and $90^{\circ}$. The cross sections were obtained from 1 MeV to several hundred MeV. The experimental data were compared with calculated results obtained by Monte Carlo simulation codes PHITS, Geant4, and FLUKA. Conclusion: PHITS was able to reproduce neutron production for elementary processes of carbon-carbon reaction precisely the best of three codes.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1091-1097
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• 2019

After the Fukushima accident in 2011, there has been increased public concern about radioactive contamination of water resources through fallout in neighboring countries. However, there is still no available initial response system that can promptly detect radionuclides. The purpose of this research is to develop the most efficient gamma spectrometer to monitor radionuclides in an aquatic environment. We chose a thallium-doped sodium iodide (NaI(Tl)) scintillator readout with a silicon photo multiplier (SiPM) due to its compactness and low operating voltage. Three types of a scintillation detector were tested. One was composed of a scintillator and a photomultiplier tube (PMT) as a reference; another system consisted of a scintillator and an array of SiPMs with a light guide; and the other was a scintillator directly coupled with an array of SiPMs. Among the SiPM-based detectors, the direct coupling system showed the best energy resolution at all energy peaks. It achieved 9.76% energy resolution for a 662 keV gamma ray. Through additional experiments and a simulation, we proved that the light guide degraded energy resolution with increasing statistical uncertainty. The results indicated that the SiPM-based scintillation detector with no light guide is the most efficient design for monitoring radionuclides in an aquatic environment.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.238-241
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• 1999

Analog-to-digital converter has attracted a lot of interests as one of the most prospective area of an application of Josephson Junction technology. Recently, the development of a digital-to-analog converter has been pursued to achieved the high performance. One of the main advantage in using single flux quantum logic in a digital-to-analog converter is the low voltage drop in a single Josephson Junction and hence the resolution of the output voltage of this digital-to-analog converter can be very high. In this work, we have used a software, called WRspice, to study a voltage multiplier circuit which is the basic block in building a digital-to-analog circuit. In simulation, we operated a voltage multiplier with .4 Josephson Junctions per stage and studied the dependence on the circuit bias currents and the circuit inductors of the voltage multiplier. Our simulation results showed a fast operation and reasonable circuit margins.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.93-93
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• 2010

In this talk, I will introduce a reactive force field (ReaxFF) molecular dynamics (MD) simulation. In contrast to common MD simulations with empirical FFs, we can predict chemical reactions (bond breaking and formation) in large scale systems with the ReaxFF simulation where all of the ReaxFF parameters are from quantum mechanical calculations such as density functional theory to provide high accuracy. Accordingly, the ReaxFF simulation provides both accuracy of quantum mechanical calculations and description of large scale systems of atomistic simulations at the same time. Here, I will first discuss a theory in the ReaxFF including the differences from other empirical FFs, and then show several applications for studying chemical reactions of SiHx radicals on Si surfaces, which is an important issue in Si process.

• 멤브레인
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• 제30권4호
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• pp.242-251
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• 2020

고분자 소재 및 이를 이용하여 제조된 분리막에 주로 활용되는 전산모사 도구들은 모사대상의 크기 및 모사하고자 하는 시간에 따라 여러 가지 분야로 나뉘어진다. 본 총설에 소개되는 전산모사는 그 중에서 전산재료화학에 주로 사용되는 양자역학(quantum mechanics; QM), 분자동역학(molecular dynamics; MD), 메조스케일 전산모사(mesoscale modelling), 이렇게 3가지로 분류된다. 고분자 연구에서 사용되는 전산모사는 각각의 전산모사의 종류마다 연구내용이 달라지는데, 양자역학은 분자, 원자, 전자 등 미시적인 계의 현상을 다루어 작은 크기의 현상을 연구하고, 분자동역학은 원자들 사이의 퍼텐셜 또는 힘이 주어졌을 때 뉴턴의 운동방정식에 따른 원지 및 분자의 움직임을 수치적으로 풀어내고, 메조스케일 모델링은 원자들을 묶어서 그룹형태로 만들어 비드를 형성해 비교적 큰 분자량에서 계산시간을 줄여 거시적으로 판단하는 연구가 된다. 본 총설에서는 고분자 및 고분자 분리막에 주로 활용되는 다양한 전산모사 프로그램을 위에서 분류한 3가지 종류로 나누어 각각의 특징과 사용분야 등을 소개하고자 한다.

• 한국전기전자재료학회논문지
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• 제22권9호
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• pp.728-731
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• 2009

We report numerical simulations to investigate of the dependendce of the on/off current ratio and channel charge distributions in silicon nanowire (SiNW) field-effect transistors (FETs) on the channel width and thicknesses. In order to investigate the transport behavior in devices with different channel geometries, we have performed detailed two-dimensional simulations of SiNWFETs and control FETs with a fixed channel length L of $10\;{\mu}m$, but varying the channel width W from 5 nm to $5\;{\mu}m$, and thickness t from 10 nm to 30 nm. We have show that $Q_{ON}/Q_{OFF}$ drastically decreases (from $^{\sim}2.9{\times}10^4$ to $^{\sim}9.8{\times}10^3$) as the channel thickness increases (from 10 nm to 30 nm). As a result of the simulation using a quantum model, even higher charge density in the bottom of SiNW channel was observed then in the bottom of control channel.

• 정보보호학회논문지
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• 제28권3호
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• pp.551-561
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• 2018

최근 양자 컴퓨팅을 활용한 연산 기술이 발달함에 따라 기존 암호 시스템들에 대한 안전성이 위협받고 있다. 이에 따라 양자 컴퓨터를 이용한 분석 공격에도 견딜 수 있는 새로운 포스트 양자 암호시스템(post-quantum cryptosystem)에 대한 연구가 활발하다. 그럼에도 불구하고 NTRU와 같은 격자 기반의 포스트 양자 암호시스템도 구현상에서 발생하는 취약점을 이용하는 오류 주입 공격에 의해 비밀 키가 노출될 수 있음이 밝혀졌다. 본 논문에서는 NTRU 서명 시스템에 대한 기존의 오류 주입 공격 대응 기법을 분석하고 효율성과 안전성이 개선된 새로운 대응 기법을 제안한다. 제안된 대응 기법에 대해 시뮬레이션을 수행한 결과, 오류 주입 검출율이 우수하며 구현이 효율적임을 확인하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제11권4호
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• pp.278-286
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• 2011

In this paper, we present a compact model of gate-voltage-dependent quantum effects in short-channel surrounding-gate (SG) metal-oxide-semiconductor field-effect transistors (MOSFETs). We based the model on a two-dimensional (2-D) analytical solution of Poisson's equation using cylindrical coordinates. We used the model to investigate the electrostatic potential and current sensitivities of various gate lengths ($L_g$) and radii (R). Schr$\ddot{o}$dinger's equation was solved analytically for a one-dimensional (1-D) quantum well to include quantum effects in the model. The model takes into account quantum effects in the inversion region of the SG MOSFET using a triangular well. We show that the new model is in excellent agreement with the device simulation results in all regions of operation.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 동계학술발표회 논문집
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• pp.509-510
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• 2009

The optical gain of InGaN/GaN multi quantum well (MQW) resonant-cavity light-emitting diode (RC-LED) with different Indium composition and well width in the multi-quantum well was investigated. The optimized optical gain was obtained by simulating active region InGaN/GaN with some test values of well width and Indium composition. By simulation tool, we could simulate on several cases, and then we got exact well width and Indium composition that makes optical gain maximum due to the short wavelength of 470 nm for blue light emission.