• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 추계 학술대회논문집
• /
• pp.26-27
• /
• 2006

Characteristics of spatial structure of particle clusters are investigated by using the flow field data obtained from three-dimensional numerical simulations. Eulerian/Lagrangian approach with two-way coupling is applied and individual particle-particle collisions are taken into account by using the hard-sphere model. More than 16 million particles are traced in the maximum case. The results show that the cluster is consisted from the multiple-spatial scale components while the low wave-number, hence the large-scale structure, is dominant. Three-dimensional structure reconstructed from the low-pass filtered data enables us to investigate the essential dynamics of particle clusters in detail.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2016년도 추계학술대회 논문집
• /
• pp.111-111
• /
• 2016

Two step PEO ceramic coatings were formed on AZ91 magnesium alloy in $ZrO_2$ nanoparticles and $K_2ZrF_6$ based colloidal electrolyte solution for various voltages. Surface and layers tructure of the coatings was analyzed using SEM (ScanningElectronMicroscope). Structure analysis revealed that surface of the coating was transferred from individual pancake or craters-based structure to cluster-based structure with increasing the voltage of the secondary step process. Further, it was confirmed that the cluster zone was richin Zr-based complexes and formed due to high intensives parks. Increase in the Zr contents as discovered from the EDS analysis confirmed the rise in amorphous form of the Zr-based species, which justified the results of XRD where no increase in the intensity of Zr-based species was observed with increase in voltage. Potentiodynamic polarizariotion and impedance spectroscopy techniques were used to evaluate the corrosion performance of the coatings. The highest corrosion resistance was found for coatings prepared at 240V. The same specimen was found having highest and uniform vickers hardness ~1070.5 HV. The superior mechanical and electrochemical properties of the said coating can be attributed to the defect-less microstructure and the optimal role of $ZrO_2$ nanoparticles in the secondary PEO process at 240V.

• Bulletin of the Korean Chemical Society
• /
• 제15권7호
• /
• pp.545-549
• /
• 1994

Using the extended Hackel molecular orbital method in connection with the tight binding model, we have studied electronic structure and related properties of the charged cluster models relating to superconducting $YBa_{2}Cu_{3}O_{7-x}$, crystals in which O-atoms in regular sites were selectively replaced with Se atoms. In analogy to the isomorphism problem with molecules, we discuss all possible combinations of Se-substitutions in O-sites with one, two, and four Se atoms. The calculations are carried out within charged cluster models for analogues of YBa-copper oxide. Our results suggest that the electronic structure of the symmetrically Se-substituted or Se-added compound is closer to that of the YBCO superconducting compound than that obtained from the unsymmetrical substitution. This applies in particular if O is replaced with Se around the Cu(1) site. Symmetrical substitutions in the $CuO_2$ layers give rise to large variations in the electronic structure of $YBa_{2}Cu_{3}O_{7}$. This is consistent with the fact that superconductivity is very sensitive to the electronic population of the $CuO_2$ layers.

• 대한금속재료학회지
• /
• 제47권8호
• /
• pp.461-465
• /
• 2009

We study the diffusion of Ag based bimetallic nanoclusters supported on graphite. Using a molecular dynamics simulation, we reveal that the Ag clusters show rapid diffusion because of their hexagonal bottom layer. In order to decrease the rate of diffusion, we added Pt and Ni to distort the structure of the alloy cluster (i.e., the alloying method). We expected Pt to provide a stronger force on Ag atoms, and Ni to shorten the bond length and thereby change the structure of Ag cluster. However, the attempt was unsuccessful, because Pt and Ni atoms formed cores inside the Ag clusters. We therefore designed a collision system where large Ag clusters collide with small Pt or Ni clusters. Upon collision with Pt clusters, the diffusion showed little change, because Pt atoms are substituted at the Ag atomic site and form a perfectly ordered structure. The collision with Ni, however, deforms the bottom layer as well as the overall cluster structure and decreases diffusion. This outcome appoints toward the possibility of further application to the manufacture of durable nanocatalysts.

• 기술혁신학회지
• /
• 제21권4호
• /
• pp.1207-1236
• /
• 2018

본 논문은 혁신클러스터의 수명주기에 관한 논의를 심화하는 연구이다. 이를 위해 국내 대표적인 혁신클러스터인 대덕연구개발특구의 성장과 발전 과정의 사례를 연구대상으로 한다. 본 연구는 선행연구를 통해 혁신클러스터 정책의 특징을 살펴보고 혁신클러스터 수명주기 이론에 기반하여 특정한 혁신클러스터가 성장 단계별로 어떠한 정책을 통해 구축되고 활성화되었는지의 현상과 각 주기별 유형적 특성을 진화론적 관점에서 고찰한다. 특히 대덕연구개발특구의 성장단계를 구분하고 각 단계와 발전과정에서 제도 및 정책의 변화를 실증적으로 분석한다. 본 연구결과, 첫째, 본 연구에서 대덕연구개발클러스터는 진화적 관점에서 잠재기, 출현기, 성장기, 성숙기의 단계(dimensions)적 특성을 가진다. 둘째, 대덕연구개발특구는 기본적으로 정부주도적 하향식 구조를 가지고 있어, 상당히 포괄적이며 유연한 우산정책적 특성을 가진 혁신클러스터 정책 구조(governance), 조치(measurements), 도구(tools)가 적용되고 있다. 셋째, 이와 같은 수명주기의 각 분면과 단계에서 혁신장애로 인식되는 점을 대상으로 정책적 기조를 재조정하면서 적응적 발전하는 것이 포착된다. 이성에서 혁신클러스터의 성장측면에서 구조적 접근보다 미세하게 정책이 적용되어야 하고 발전과정에서 변형(transformation)되어야 한다. 본 연구 결과를 통해 혁신클러스터의 진화론적 관점에서 각 단계별 유형적 특징 및 진화의 방향을 고찰하여 정부의 혁신클러스터 정책개입의 효과제고를 위한 시사점을 제안할 수 있다.

• Bulletin of the Korean Chemical Society
• /
• 제27권5호
• /
• pp.635-636
• /
• 2006

• 천문학회보
• /
• 제43권1호
• /
• pp.60.3-61
• /
• 2018

Abell 115 is a renowned cluster merger at z=0.197. It exhibits an asymmetric X-ray distribution with cometary tails and a megaparsec-sized radio relic stretching in the northeastern direction from the core of the northern cluster. Many observations have concluded that this cluster merger has a large impact parameter, but there has been no numerical analysis on the structure of Abell 115. In this study, we simulate Abell 115 with Gadget2 N-body/SPH code to reproduce the X-ray and weak lensing features of Abell 115. We find a new plausible merger scenario of Abell 115, wherein the northern cluster is currently in an outgoing phase. The predicted X-ray emission has a similar morphology to the observed tail of the northern cluster. However, in order to reproduce the observed line-of-sight velocity and projected distance while maintaining the two systems gravitationally bound, the system should possess a large projection angle, which makes the shock look considerably more diffused than the observed radio relic.

• 천문학회보
• /
• 제45권1호
• /
• pp.29.4-29.4
• /
• 2020

Structure in the universe forms hierarchically with the small scales forming first and merging into larger scales. Galaxy clusters are at the pinnacle of the formation process. Peering far into the universe, we can observe galaxy clusters early in their evolution. SpARCSJ1049+56 is a galaxy cluster located at a redshift of 1.71. It has been shown to be rich in cluster galaxies, to have intense star formation, and to have a significant amount of molecular gas. Through careful control of systematics, we detected the weak-lensing signal from this distant galaxy cluster. I will present our HST infrared weak-lensing detection of the cluster with a focus on the method. Our lensing analysis found that the cluster is massive and is rare in a LambdaCDM universe. I will also present the Chandra X-ray discovery of cold gas coincident with the intense star formation and discuss the implications of the detection.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1788-1793
• /
• 2008

Classical molecular dynamics simulations (MDS) were conducted to simulate nano-sized cluster collisions with a weakly attractive static surface. Energy exchanges associated with the cluster collision and the adhesion probability are discussed. Routes of the energy exchanges and the kinetic energy loss are vastly altered in their mode according to the cluster incident velocity. In the elastic collision regime ($V_0$<0.1), most incident kinetic energy is recovered into the rebounding kinetic energy, but a little loss in the incident kinetic energy causes the cluster adhesion. Dissipated kinetic energy is converted into the rotational energy. In the weakly plastic collision regime (0.1<$V_0$<0.3), the transition from elastic to plastic collision occurs, and a large part of the released potential energy is converted into rebounding translational energy. For strongly plastic collisions ($V_0$>0.3), permanent cluster deformation occurs with extensive collapse of the lattice structure inducing a solid-to-solid phase transition; moreover, most of the cluster kinetic energy is converted into cluster potential and thermal energy.

• 천문학회보
• /
• 제43권2호
• /
• pp.33.2-33.2
• /
• 2018

Fossil galaxy cluster has a dominant central elliptical galaxy (${\Delta}M12$ >2 in 0.5Rvir) embedded in highly relaxed X-ray halo, which indicates dynamically stable and passively evolved system. These features are expected as a final stage of the cluster evolution in the hierarchical structure formation paradigm. It is known that Abell 2261(A2261 hereafter) is classified as a fossil cluster, but has unusual features such as a high central X-ray entropy (i.e., non-cool core system), which is not expected in normal fossil clusters. We perform a kinematic study with a spectroscopic data of 589 galaxies in the A2261 field. We define cluster member galaxies using the caustic method and discover a new second bright galaxy at ~1.5 Rvir (nearly the splash-back region). It implies the current fossil state of the cluster can break in the near future. In addition, with three independent substructure finding methods, we find that A2261 has many substructures within 3 Mpc from the center of the cluster. These findings support that A2261 is not in a dynamically stable state. We argue that A2261 is in a transitional phase of dynamical evolution of the galaxy cluster and maybe previously defined fossil cluster does not mean the final stage of the evolution of galaxy clusters.