• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2007년도 제34회 시멘트 심포지엄
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• pp.129-137
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• 2007

This paper presents a numerical model which can predict degree of hydration of cement mineral component, such as $C_{3}S$, $C_{2}S$, $C_{3}A$, $C_{4}AF$ and microstructure of hydrating cement as a function of water to cement ratio, cement particle size distribution, cement mineral components and temperature. In this model cement particles are parked randomly in cell space and hydration process is described using a multi-component integrated kinetic model. The simulation result of degree of hydration of cement mineral component agrees well with experiment result. The content of cement hydration product, such as CSH and CH can be obtained as an accompanied result during hydration process. By introducing of equal-area projection method, water withdrawl mechanism and contact area among cement particles can be considered in detail. By using proposed method, pore size distribution of hydrating cement is predicted.

• 시멘트 심포지엄
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• 통권34호
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• pp.129-137
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• 2007

This paper presents a numerical model which can predict degree of cement mineral component, such as $C_3S$, $C_2S$, $C_3A$, $C_4AF$ and microstructure of hydrating cement as a function of water to cement ratio, cement particle size distribution, cement mineral components and temperature. In this model cement particles are parked randomly in cell space and hydration process is described using a multi-component intergrated kinetic model. The simulation result of degree of hydration of cement mineral component agrees well with experiment result. The content of cement hydration product, such as CSH and CH can be obtained as an accompanied result during hydration process. By introducing of equal-area projection method, water withdrawl mechanism and contact area among cement particles can be considered in detail. By using proposed method, pore size distribution of hydrating cement is predicted.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.245-250
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• 2004

The discharge current oscillation has been measured for various hollow anode widths and its axial positions using a 1㎾-class anode layer hall thruster. As a result, there were thresholds of magnetic flux density for stable discharge. The plasma structure inside the hollow anode was numerically analyzed using the fully kinetic 2D3V Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) methods. The results reproduced both stable and unstable operation modes. In the stable operation case, which corresponds to the case with low magnetic flux, the plasma penetrated into the hollow anode deeper than the case with higher magnetic flux density case. This suggests that comparably large substantial anode area should contribute to stable operation.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.22-27
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• 2009

Target design study to improve the quality of an accelerated proton beam from the interaction of a high-intensity short pulse laser with an overdense plasma slab has been accomplished by using a two-dimensional, fully electromagnetic and relativistic particle-in-cell (PIC) simulation. The target consists of a thin core part and a thick peripheral part of equivalent plasma densities, while the ratio of the radius of the core part to the laser spot size, and the position of the peripheral part relative to the fixed core part were varied. The positive effects of this core-peripheral target structure could be expected from the knowledge of the typical target normal sheath acceleration (TNSA) mechanism in a laser-plasma interaction, and were apparently evidenced from the comparison with the case of a conventional simple planar target and the case of the transversal size reduction of the simple planar target. Improvements of the beam qualities including the collimation, the forward directionality, and the beam divergence were verified by detailed analysis of relativistic momentum, angular directionality, and the spatial density map of the accelerated protons.

• 산업경영시스템학회지
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• 제39권2호
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• pp.46-53
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• 2016

In mobile communication systems, location management deals with the location determination of users in a network. One of the strategies used in location management is to partition the network into location areas. Each location area consists of a group of cells. The goal of location management is to partition the network into a number of location areas such that the total paging cost and handoff (or update) cost is a minimum. Finding the optimal number of location areas and the corresponding configuration of the partitioned network is a difficult combinatorial optimization problem. This cell grouping problem is to find a compromise between the location update and paging operations such that the cost of mobile terminal location tracking is a minimum in location area wireless network. In fact, this is shown to be an NP-complete problem in an earlier study. In this paper, artificial bee colony (ABC) is developed and proposed to obtain the best/optimal group of cells for location area planning for location management system. The performance of the artificial bee colony (ABC) is better than or similar to those of other population-based algorithms with the advantage of employing fewer control parameters. The important control parameter of ABC is only 'Limit' which is the number of trials after which a food source is assumed to be abandoned. Simulation results for 16, 36, and 64 cell grouping problems in wireless network show that the performance of our ABC is better than those alternatives such as ant colony optimization (ACO) and particle swarm optimization (PSO).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.312-312
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• 2011

In SiH4/H2 discharge for growth process of hydrogenated amorphous silicon (a-Si:H), silane polymers, produced by SiH2 + Sin-1H2n ${\rightarrow}$ SinH2n+2, have no reactivity on the film-growing surface. However, under the SiH2 rich condition, high silane reactive species (HSRS) can be produced by electron collision to silane polymers. HSRS, having relatively strong reactivity on the surface, can react with dangling bond and form Si-H2 networks which have a close correlation with photo-induced degradation of a-Si:H thin film solar cell [1]. To find contributions of suggested several external plasma conditions (pressure, frequency and ratio of mixture gas) [2,3] to suppressing productions of HSRS, some plasma characteristics are studied by numerical methods. For this study, a zero-dimensional global model for SiH4/H2 discharge and a one-dimensional particle-in-cell Monte-Carlo-collision model (PIC-MCC) for pure SiH4 discharge have been developed. Densities of important reactive species of SiH4/H2 discharge are observed by means of the global model, dealing 30 species and 136 reactions, and electron energy probability functions (EEPFs) of pure SiH4 discharge are obtained from the PIC-MCC model, containing 5 charged species and 15 reactions. Using global model, SiH2/SiH3 values were calculated when pressure and driving frequency vary from 0.1 Torr to 10 Torr, from 13.56 MHz to 60 MHz respectively and when the portion of hydrogen changes. Due to the limitation of global model, frequency effects can be explained by PIC-MCC model. Through PIC-MCC model for pure SiH4, EEPFs are obtained in the specific range responsible for forming SiH2 and SiH3: from 8.75 eV to 9.47 eV [4]. Through densities of reactive species and EEPFs, polymerization reactions and production of HSRS are discussed.

• 한국추진공학회지
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• 제25권4호
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• pp.1-11
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• 2021

2000년 대에 들어 가파르게 성장하고 있는 우주비행체용 전기추진시스템의 안정적인 운영기술 개발을 위해, PIC-DSMC를 이용하여 전기추력기의 배기플룸의 거동을 해석하였다. 해석 방법에서 Boltzmann 관계식을 이용한 Simple Electron Fluid Model을 적용하였고, 원자-이온 간 충돌에 의해 발생하는 전하 교환 및 운동량 교환을 함께 고려하였다. 본 연구의 해석결과는 실험에서 계측한 플라즈마 전위값을 비교적 잘 예측하였다. 추력기 출구 근처에서는 활발한 입자 간 충돌 및 원자-이온 간 전하 교환으로 인해, 느린 이온 및 빠른 원자가 생성되었으며, 추력기 배기플룸의 궤적 및 속도에 중요한 영향을 미칠 것으로 예측되었다.

• 천문학회보
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• 제46권1호
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• pp.36.2-36.2
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• 2021

In the outskirts of galaxy clusters, weak shocks with M_s < ~3 appear as radio relics where the synchrotron radiation is emitted from cosmic-ray (CR) electrons. To understand the production of CR electrons through the so-called diffusive shock acceleration (DSA), the electron injection into the DSA process at shocks in the hot intracluster medium (ICM) has to be described. However, the injection remains as an unsolved, outstanding problem. To explore this problem, 2D Particle-in-Cell (PIC) simulations were performed. In this talk, we present the electron preacceleration mechanism mediated by multi-scale plasma waves in the shock transition zone. In particular, we find that the electron preacceleration is effective only in the supercritical shocks, which have the sonic Mach number M_s > M_crit ≈ 2.3 in the high-beta (β~100) plasma of the ICM, because the Alfven ion cyclotron instability operates and hence multi-scale plasma waves are induced only in such supercritical shocks. Our findings will help to understand the nature of radio relics in galaxy clusters.

• 한국연소학회지
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• 제11권4호
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• pp.9-13
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• 2006

Recent advances in energetic materials modeling and high-resolution hydrocode simulation enable enhanced computational analysis of bio-medical treatments that utilize high-pressure shock waves. Of particular interest is in designing devices that use such technology in medical treatments. For example, the generated micro shock waves with peak pressure on orders of 10 GPa can be used for treatments such as kidney stone removal, transdermal micro-particle delivery, and cancer cell removal. In this work, we present a new computational methodology for applying the high explosive dynamics to bio-medical treatments by making use of high pressure shock physics and multi-material wave interactions. The preliminary calculations conducted by the in-house code, GIBBS2D, captures various features that are observed from the actual experiments under the similar test conditions. We expect to gain novel insights in applying explosive shock wave physics to the bio-medical science involving drug injection. Our forthcoming papers will illustrate the quantitative comparison of the modeled results against the experimental data.

• 천문학회보
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• 제37권1호
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• pp.93.1-93.1
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• 2012

In this study, we investigated the generation of consecutive electrostatic solitary waves (ESWs) using by one-dimensional electrostatic particle-in-cell (PIC) simulation. For a given Gaussian perturbation, it is found that electron two-stream instability occurs in local grids region. Thus because of this instability, the electrostatic potential grows rapidly so as to be separated into electron and ion in perturbation region, and then electrons are trapped with heating during growing instability. It is found that these heated and trapped electrons are caused the generation of ESW, and ions are reflected backward and forward at the boundary of the initial perturbation, then form cold ion beam whereas electrons are confined to inside of the potential. Furthermore backward reflected ion beam forms ion holes by ion two-stream instability. On the other hand, as the confined electrons are released, and then released electrons also form hot electron beam, which play an important role in the generation of consecutive ESWs such as broadband electrostatic noise (BEN) observed frequently in space environment. Therefore the reason of the generation of consecutive ESWs is the existence of heated electrons which can sufficiently support energy to produce ESWs.