• 천문학회보
• /
• 제46권1호
• /
• pp.29.3-29.3
• /
• 2021

Globular clusters (GCs) form at the very early stage of galaxy formation, and thus can be used as an important clue indicating the environment of the galaxy formation era. Although various GC formation scenarios have been suggested, they have not been examined in the cosmological context. Here we introduce the 'particle tagging method' in order to investigate the formation scenarios of GCs in a galaxy cluster. This method is able to trace the evolution of GCs that form in the dark matter halos which undergo the hierarchical merging events in galaxy cluster environments with an effective computational time. For this we use dark matter merger trees from the cosmological N-body simulation. Finally, we would like to find out the best GC formation scenario which can explain the observational properties of GCs in galaxy clusters.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
• /
• pp.9-11
• /
• 2003

A homogeneous flow field including more than 2000 spherical particles was directly simulated. Particles are settling by gravity with the Reynolds number ranging from 50 to 300, based on diameter and slip velocity. Particular attention was focused on the distribution of particles. The Reynolds-number dependence, influences of particle rotation and loading ratio, and the dynamics of particle clusters are discussed. In the higher Reynolds number case, the wake attraction causes particle clusters and the average drag coefficient decreases significantly. Non-rotating particles maintain cluster structure and rotating ones moves randomly in the horizontal direction. It is because of the difference in the direction of the lift force.

• 대한기계학회논문집B
• /
• 제24권7호
• /
• pp.984-993
• /
• 2000

Characteristics of carbon soot particles generated in diffusion flames were studied. Non-sooting and sooting normal diffusion flames using propane or ethylene as fuel were selected. In the flames, soot volume fraction was measured by a thermocouple, and primary particle diameter and cluster size were analyzed by TEM photographs. The characteristics of soot particles depended on flame(non-sooting or sooting) and fuel(propane or ethylene) type. Unlike the sooting diffusion flames, particle growth and oxidation processes were clearly observed in the non-sooting diffusion flames. In the sooting diffusion flames, soot particle size was slightly changed at the flame tip.

• 한국대기환경학회지
• /
• 제13권5호
• /
• pp.345-353
• /
• 1997

The purpose of the study was to stastically classify individual PM-10 measured by SEM/EDX (scanning electron microscopy/energy dispersive x-ray analyzer). The SEM/EDX provided various physical parameters like optical diameter, as well as major 18 chemical information (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Pb) for a particle-by-particle basis. The total of 1,419 particles were analyzed for the study. Thus density and mass of each particle can be estimated based on its chemical composition. Further the study developed 4 semisource profiles including highway, oil boiler, incinerator, and soil emissions, where each sample was collected near the source in the ambient air The profiles developed were consisted of mass fractions and their uncertainties based on a particle class concept. To obtain mass fraction of each particle class, an agglomerative hierarchical cluster analysis was initially applied to create particle classes for each sample. Then uncertainties were calculated for each class based on the jacknife method. The 1,258 particles out of 1,419 (88.7%) were assorted in newly generated particle classes. The study provides opportunities to identify particle's source quantitatively and to develope various receptor models.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 춘계 학술발표회
• /
• pp.136-145
• /
• 2009

Factors influencing shear behavior of granular material include particle size, shape, distribution, relative density, particle crushing, etc. In this study, these factors are characterized by viewpoint of shear behavior using numerical analysis based on DEM. Geometrical particle shape is represented by a combination of small circular particles and influence of particle shape on crushing is studied through relative comparisons between clump (uncrushable) and cluster (crushable) models which are modeled using DEM. Also, particle shape is quantified by the dimensionless parameters such as circularity and convexity. The results indicate that particle shape indexes have a negative association with internal friction angle. Also, internal friction angle becomes reduced and failure envelop curve becomes nonlinear due to the particle crushing. It is also found that numerical results are quite good agreement with the experimental test conducted in this study.

• Bulletin of the Korean Chemical Society
• /
• 제24권6호
• /
• pp.771-776
• /
• 2003

The structural and dynamic properties of small n-alkane clusters embedded in a mesoscopic solvent are investigated. The solvent interactions are taken into account through a multi-particle collision operator that conserves mass, momentum and energy and the solvent dynamics is updated at discrete time intervals. The cluster molecules interact among themselves and with the solvent molecules through intermolecular forces. The properties of n-heptane and n-decane clusters interacting with the mesoscopic solvent molecules through repulsive Lennard-Jones interactions are studied as a function of the number of the mesoscopic solvent molecules. Modifications of both the cluster and solvent structure as a result of cluster-solvent interactions are considered. The cluster-solvent interactions also affect the dynamics of the small n-alkane clusters.

• 천문학회보
• /
• 제43권2호
• /
• pp.38.1-38.1
• /
• 2018

A merging galaxy cluster is a useful laboratory to study many interesting astrophysical processes such as intracluster medium heating, particle acceleration, and possibly dark matter self-interaction. However, without understanding the merger scenario of the system, interpretation of the observational data is severely limited. In this work, we focus on the off-axis binary cluster merger Abell 115, which possesses many remarkable features. The cluster has two cool cores in X-ray with disturbed morphologies and a single giant radio relic just north of the northern X-ray peak. In addition, there is a large discrepancy (almost a factor of 10) in mass estimate between weak lensing and dynamical analyses. To constrain the merger scenario, we perform a hydrodynamical simulation with the adaptive mesh refinement code RAMSES. We use the multi-wavelength observational data including X-ray, weak-lensing, radio, and optical spectroscopy to constrain the merger scenario. We present detailed comparisons between the simulation results and these multi-wavelength observations.

• 한국지반신소재학회논문집
• /
• 제10권2호
• /
• pp.1-12
• /
• 2011

조립재료의 입자 결합 및 파쇄 형태가 전단거동 특히 잔류 전단거동 특성에 미치는 영향을 분석하기 위하여, 개별요소법(DEM, discrete element method)에 기초를 둔 프로그램인 PFC(Particle Flow Code)를 이용하여 링 전단시험을 수치해석적으로 모델링하였다. 본 연구에서는 PFC내의 clump 모델 및 cluster 모델을 이용하여 두 개의 비파쇄모델 그리고 두 개의 파쇄모델을 포함한 총 네 개의 모델을 제시하였다. Lobo-Guerrero and Vallejo(2005)가 제안한 Lobo-crushing 모델의 적합성을 검토하였다. 또한 링 전단시험 모델링의 결과 분석을 통하여 직접전단시험 모델링 결과와 비교하였다. 연구 결과, 잔류 전단거동 분석을 위해서는 링 전단시험의 모델링이 필수적임을 알 수 있었다. 또한 잔류 전단강도 분석을 위해서는 Lobo-crushing 모델이 부적합함을 알 수 있었다. 따라서 본 연구에서 제시한 수치해석 모델은 향후 입자 파쇄를 포함한 조립재료의 잔류 전단강도 특성 연구에 다양하게 적용될 수 있다고 판단된다.

• 반도체디스플레이기술학회지
• /
• 제20권2호
• /
• pp.34-42
• /
• 2021

Recent cleaning technologies of mask in extremely ultraviolet semiconductor processes were reviewed, focused on newly developed issues such as particle size determination or hydrocarbon and tin contaminations. In detail, critical particle size was defined and proposed for mask cleaning where nanosized particles and its various shapes would result in surface atomic ratio increase vigorously. A new cleaning model also was proposed with amphoteric behavior of electrolytically ionized water which had already shown excellent particle removing efficiency. Having its non-equilibrium and amphoteric properties, electrolyzed ion water seemed to oxidize contaminant surface selectively in nano-scale and then to lift up oxidized ones from mask surface very effectively. This assumption should be further investigated in future in junction with hydrogen bonding and cluster of water molecules.

• 한국정밀공학회지
• /
• 제12권7호
• /
• pp.92-98
• /
• 1995

In the cluster tool, it is necessary to precisely control the vacuum pressure for the wafer transportation between transport module and cassette or process modules with the range of 1*10$^{-4}$ to 5*10$^{-5}$ torr. So we have designed the pressure control system for the transport module of the cluster tool and have evaluated its performance. Digital PID is utilized with the weighted sum of both three previous errors and one current error. The feedback signal is put into the nitrogen mass flow controller using the transport module controller. This pressure control system can prevent the transport module from the particle generation and backstreaming of hazardous process gases of the process chamber.