• 천문학회보
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• 제45권1호
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• pp.64.3-65
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• 2020

It has been studied that galaxies evolve following a typical trajectory on the phase space under the influence of deep gravitational potential of galaxy clusters. Similarly, the large-scale filaments could also affect the evolution of galaxies before falling into the clusters. In this study, using a dark matter-only cosmological simulation, N-Cluster Run, we explore the evolution of galaxies on the phase space drien by large-scale filaments. We find that galaxies around the filaments form a common trajectory on the phase space as well as cluster galaxies do. We also examine how these trajectories change depending on various physical parameters such as galaxy mass, initial distance of galaxies from large-scale filaments, and cluster mass.

• Interaction and multiscale mechanics
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• 제1권2호
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• pp.191-209
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• 2008

In this paper, we model grain boundary evolution based on a multiple level set method. Grain boundary migration under a curvature-induced driving force is considered and the level set method is employed to deal with the resulting topological changes of grain structures. The complexity of using a level set method for modeling grain structure evolution is due to its N-phase nature and the associated geometry compatibility constraint. We employ a multiple level set method with a predictor-multicorrectors approach to reduce the gaps in the triple junctions down to the grid resolution level. A ghost cell approach for imposing periodic boundary conditions is introduced without solving a constrained problem with a Lagrange multiplier method or a penalty method. Numerical results for both uniform and random grain structures evolution are presented and the results are compared with the solutions based on a front tracking approach (Chen and Kotta et al. 2004b).

• 한국유변학회:학술대회논문집
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• 한국유변학회 2001년도 춘계 학술발표회 논문집
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• pp.11-14
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• 2001

Our study have aimed to identify the deformation and breakup mechanism of minor phase in polymer blends under uniaxial enlongational flow. Experimentally, we measured the transient elongational viscosity of PS/HDPE blends using the uniaxial elongational rheometer at two temperatures. And we observed the evolution of blend morphology with elongation time. Morphological change was observed by quenching the specimen after deformation. If the viscosity variation of PS was compared with that of HDPE at each temperature, PS showed larger temperature dependence than HDPE. At 155$^{\circ}C$, the dispersed phase of larger size were easily affected by affine deformation. The initial spherical shape changed to flat ellipsoid at first, then flat ellipsoid to bulbous shape, and bulbous to thin thread and its satellites. But dispersed phase of smaller size showed the change from sphere to ellipsoid. At 175$^{\circ}C$, the dispersed phase were mostly deformed from spherical shape to ellipsoid. As a result, the morphological change of dispersed phase in elongational deformation is affected by chain flexibility and viscosity ratio. We need to further study to make sure the mechanism of elongation of viscoelastic polymer blends.

• 열처리공학회지
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• 제16권6호
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• pp.320-328
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• 2003

A specimen of Cu-35%Sn alloy has been subjected to the unidirectional heat treatment in an attempt to examine the evolution of microstructures under varying thermal conditions. The specimen was cast in the form of a cylinder 10 mm in diameter and 200 mm in length, which was then installed in the temperature gradient field established inside a vertical tube furnace. The furnace temperature was adjusted to make the upper part at $750^{\circ}C$ and bottom end part at $300^{\circ}C$ of the specimen. The experiment was terminated by dropping it into water after the 30 minutes holding at given temperature. By the rapid cooling, the high temperature phases, ${\gamma}$ and ${\zeta}$, were retained at ambient temperature with some of ${\gamma}$ phase transformed to ${\varepsilon}$ phase, especially at the grain boundaries of ${\gamma}$ phase. The presence of ${\varepsilon}$ phase was found to determine the nature of phase transformations of the ${\zeta}$ phase undergoes upon cooling. In the close area of the ${\varepsilon}$ phase, ${\varepsilon}$ phase grew separately out of ${\zeta}$, and adds to the preexisting ${\varepsilon}$ whereas in areas away from ${\varepsilon}$, both ${\delta}$ and ${\varepsilon}$ grew simultaneously out of ${\zeta}$, and formed a lamella eutectoid structure. The transformation to ${\delta}$ was found to occur only in slow cooling. The hardness on each phase showed that the retained phases, ${\gamma}$ and ${\zeta}$, could be plastically deformed without brittle fracture while the phases, ${\varepsilon}$ and ${\delta}$, were too brittle to be deformed.

• 호남수학학술지
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• 제36권1호
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• pp.11-27
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• 2014

In this paper, we propose closures for multi-phase flow models, which satisfy boundary conditions and conservation constraints. The models governing the evolution of the fluid mixing are derived by applying an ensemble averaging procedure to the microphysical equations characterized by distinct phases. We consider compressible multi species multi-phase flow with surface tension and transport.

• Advances in nano research
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• 제5권3호
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• pp.203-214
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• 2017

In this study we present the reaction mechanism of $Cu_2ZnSnSe_4$ (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

• 한국결정성장학회지
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• 제8권2호
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• pp.324-331
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• 1998

2, 5, 10 mol% YAG(yttrium aluminum garnet) 분말을 액상 소결조제로 $\alpha$상 탄화규소 분말에 첨가한 후 $1850^{\circ}C$에서 소결시간을 달리하여 소결체를 제조한 다음, 소결시 일어나는 미세구조 변화를 첨가된 액상량과 소결시간의 변화에 대하여 고찰하였다. 각 조성중 2시간 소결한 시편에서 가장 높은 밀도를 나타냈으며, 소결시간이 길수록 액상의 기화로 인하여 중량감소량이 점차 증가하였다. 또한 첨가된 YAG 액상량이 증가할 수록 상대밀도(apparent density)와 중량감소량은 증가하였으나 입성장속도는 감소하였다. 액상량이 적은 시편에서는 소결시간이 길수록 일부 6H상의 탄화규소 입자가 4H상 탄화규소 입자로 상전이 되었으며, 이로 인하여 막대상 입자들이 일부 존재하였다.

• Progress in Superconductivity
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• 제3권1호
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• pp.5-12
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• 2001

Our experimental research focuses on manipulating pinning deflects to alter the phase diagram of vortex matter, creating new vortex phases. Vortex matter offers a unique opportunity for creating and studying these novel phase transitions through precise control of thermal, pinning and elastic energies. The vortex melting transition in untwinned YB $a_2$C $u_3$ $O_{7-}$ $\delta$/ crystals is investigated in the presence of disorder induced by particle irradiation. We focus on the low disorder regime, where a glassy state and a lattice state can be realized in the same phase diagram. We follow the evolution of the first order vortex melting transition line into a continuous transition line as disorder is increased by irradiation. The transformation is marked by an upward shift in the lower critical point on the melting line. With columnar deflects induced by heavy ion irradiation, we find a second order Bose glass transition line separating the vortex liquid from a Bose glass below the lower critical point. Furthermore, we find an upper threshold of columnar defect concentration beyond which the lower critical point and the first order melting line disappear together. With point deflect clusters induced by proton irradiation, we find evidence for a continuous thermodynamic transition below the lower critical point..

• 열처리공학회지
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• 제19권2호
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• pp.103-108
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• 2006

Microstructural evolution of Pt-aluminide coated Ni-based superalloy has been investigated with ductilization heat treatment. The Pt coat was prepared on the superalloy and then aluminide coating was conducted using a pack cementation process. Samples were heat-treated at $1050^{\circ}C$ for 2 hrs and the microstructure and element analysis were preformed. A various precipitated compounds were observed within the coating layer and the diffusion region in the Pt-aluminide coating and heat treatment, indicating that the bi-phase compounds of $PtAl_2$ and NiAl were performed during the Pt-aluminide coating, whereas $M_{23}C_6$, MC, $Ni_3Al$ and ${\sigma}$ phases were precipitated in the inter-diffusion region. The bi-phase compounds of $PtAl_2$ and NiAl were transformed into the single phase compound of $PtAl_2$ with the heat treatment, increasing the amount of carbide and ${\sigma}$ phase.

• 한국전기전자재료학회논문지
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• 제34권5호
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• pp.337-341
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• 2021

Phase evolution, thermal and microwave dielectric properties of cordierite-Al₂O₃ composite were investigated. As the content of Al₂O₃ increased, mullite, sapphirine, and spinel were formed as secondary phases, implying that cordierite may be decomposed by the reaction with Al₂O₃. All sintered specimens exhibited dense microstructures. The densification occurred through liquid phase sintering. As the content of Al₂O₃ increased, the thermal expansion coefficient and the dielectric constant increased, whereas the quality factor decreased. The thermal expansion coefficient, the dielectric constant, and the quality factor of the 90 wt% cordierite 10 wt% Al₂O₃ composite sintered at 1,425℃ were 2.9×10^-6 K^-1, 5.1, and 34,844 GHz, respectively.