• 대한조선학회논문집
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• 제29권3호
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• pp.131-139
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• 1992

본 연구에서는 Dommermuth and Yue(1987)의 고차 스펙트럴법에 새로이 물체 포텐셜을 도입하여 물체와 자유표면과의 비선형 상호작용 문제를 다룰 수 있는 새로운 수치해법을 개발하였다. 또한, 이를 이용한 2차원 수치 파수조(numerical wave tank)에서 잠수 주상체의 조파저항문제와 규칙파군을 얻기 위한 조파 및 소파문제를 적용예로 다루었다. 계산예들을 통하여 초기의 물체운동이 급격히 시작되면 상당한 과도파를 유발하여 유용한 결과를 얻는데 실제적인 장애가 됨을 보였고, 초기의 점진적인 구동에 의해 이를 억제할 수 있음을 보였다. 본 수치해법은 자유표면의 분할요소수를 N이라 할때 계산량이 NlogN에 비례하여 증가하는 매우 효율적인 수치해법이며, 앞으로 그 활용이 기대 된다.

• 천문학회지
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• 제38권2호
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• pp.129-133
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• 2005

The temperature (T) and entropy (S) fields of baryonic gas, or intergalactic medium (IGM), in the ACDM cosmology are analyzed using simulation samples produced by a hybrid cosmological hydrodynamic/N-body code based on the weighted essentially non-oscillatory scheme. We demonstrate that, in the nonlinear regime, the dynamical similarity between the IGM and dark matter will be broken in the presence of strong shocks in the IGM. The heating and entropy production by the shocks breaks the IGM into multiple phases. The multiphase and non-Gaussianity of the IGM field would be helpful to account for the high-temperature and high-entropy gas observed in groups and clusters with low-temperature IGM observed by Ly$\alpha$ forest lines and the intermittency observed by the spikes of quasi-stellar object's absorption spectrum.

• 천문학회지
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• 제35권2호
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• pp.75-85
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• 2002

We present N-body simulations of globular clusters including gravitational field of the Galaxy, in order to study effects of tidal field systematically on the shape of outer parts of globular clusters using NBODY6. The Galaxy is assumed to be composed of central bulge and outer halo. We mvestigate the cluster of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, initial number of particles, different slopes of the IMF and different orbits of the cluster. We have examined the general evolution of the clusters, the shape of outer parts of the clusters, density profiles and the direction of tidal tails. The density profiles appear to become somewhat shallower just outside the tidal boundary consistent with some observed data. The position angle of the tidal tall depends on the location in the Galaxy as well as the direction of the motion of. clusters. We found that the clusters become more elongated at the apogalacticon than at the pengalacticon. The tidal tails may be used to trace the orbital paths of globular clusters.

• 천문학회보
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• 제40권2호
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• pp.29.2-29.2
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• 2015

Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. We used the Horizon Run 4 cosmological N-body simulations to study the aligments of spins and shapes of interacting haloes as a function of the halo mass and large-scale density. Interactions preferentially occur in the plane of rotation, and in the direction of the major axis of prolate haloes, and the trajectories are preferentially radial and prograde. We found a very strong alignment of the shapes already at redshift as high as 4. The spins are initially unaligned or even anti-aligned, and become more and more aligned as the redshift decreases. The alignment signals are stronger and evolve more at lower densities, and mass plays a secondary role.

• 천문학회보
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• 제40권2호
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• pp.35.3-35.3
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• 2015

The central molecular zone (CMZ) is a region of rich molecular gas located in the inner few hundred parsecs in barred spiral galaxies. We study the size and morphology evolution of the CMZ of Milky Way-like galaxies both in isolation and in interaction by using N-body/hydrodynamic simulations. Specifically, we examine the gas flows and star formation activities in the central region of the galaxies. We focus in particular on the effects of galaxy interactions, including flybys and minor mergers, on the evolution of the CMZ.

• 천문학회보
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• 제38권2호
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• pp.56.2-56.2
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• 2013

We study the three-dimensional genus topology of large-scale structure using the CMASS Data Release 11 sample of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). The CMASS sample yields a genus curve that is characteristic of one produced by Gaussian random-phase initial conditions. The data thus supports the standard model of inflation where random quantum fluctuations in the early universe produced Gaussian random-phase initial conditions. Modest deviations in the observed genus from random phase are as expected from the nonlinear evolution of structure. We construct mock SDSS CMASS surveys along the past light cone from the Horizon Run 3 (HR3) N-body simulations, where gravitationally bound dark matter subhalos are identified as the sites of galaxy formation. We study the genus topology of the HR3 mock surveys with the same geometry and sampling density as the observational sample, and the observed genus topology to be consistent with LCDM as simulated by the HR3 mock samples.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1993년도 추계학술대회 논문집
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• pp.29-34
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• 1993

In this paper, we used one-dimensional process simulator, SUPREM-II, and two-dimensional device simulator, MINIMOS 4.0 to extract optimal process parameter that can minimize degradation of device characteristics caused by process parameter variation in the case of short channel nMOSFET and pMOSFET device. From this simulation, we have derieved the relationship between process parameter and device characteristics. Here we have presented a method to extract process parameters from design trend curve(DTC) obtained by process and device simulations. We parameters to verify the validity of the DTC method. The experimental result of 0.8 $\mu\textrm{m}$ channel length devices that have been fabricated with optimal that reduces short channel effects, that is, good drain current-voltage characteristics, low body effects and threshold voltage of 1.0 V, high punchthrough and breakdown voltage of 12 V, low subthreshold swing(S.S) values of 105 mV/decade.

• 천문학회보
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• 제39권2호
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• pp.41.1-41.1
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• 2014

Clusters of galaxies provide unique laboratories to study astrophysical processes on large scales, and are also important probes for cosmology. X-ray observations are still the best way to find and characterise clusters. The extended ROSAT-ESO flux-limited X-ray (REFLEX II) galaxy clusters form currently the largest well-defined and tested X-ray galaxy cluster sample, providing a census of the large-scale structure of the Universe out to redshifts of z-0.4. I will describe the properties of the survey and the X-ray luminosity function, which led to our recent cosmological constraints on omegaM-sigma8. They tighten the previous constraints from other X-ray experiments, showing good agreements with those from the Planck clusters, but some tension exists with the Planck CMB constraints. The second part of my talk will concern the structure of the local Universe, and the study of the first X-ray superclusters. The density of the clusters reveals an under-dense region in the nearby Universe, which has an interesting implication for the cosmological parameters. Using the X-ray superclusters, that are constructed with a physically motivated procedure, I will show environmental aspects that X-ray superclusters provide, and compare to cosmological N-body simulations.

• 천문학회보
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• 제41권2호
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• pp.35.2-35.2
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• 2016

Lyman alpha photons emitted from the early generation galaxies are scattered through the intergalactic medium, and can be observed as Lyman alpha emitting sources. We examine the Lyman alpha line transfer mechanism by tracing the random scattering histories of Lyman alpha photons in the intergalactic medium of the early universe. The density and ionization fields are based on the 3D map by N-body + radiation transfer simulations of the epoch of reionization. The calculation is compared with analytical models, too. The emergent line profile and the size of the Lyman alpha blob are strongly tied to the density and ionization environment, likely to give constraints when high-z Lyman alpha blobs are observed.

• 천문학회보
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• 제41권2호
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• pp.40.3-41
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• 2016

Previous HI survey data have shown that the central HI gas in the Milky Way that resides within ~1.5 kpc of the Galactic Centre (GC) is tilted by ${\sim}15^{\circ}$ with respect to the Galactic plane. Although several models, such as a tilted disk model, have been suggested to interpret the observed morphology of the HI layer, it is still unknown what causes and how it preserves its tilted structure. We study the behavior of a gas disk near the GC using an N-body / SPH code. Our galaxy model includes four components; nuclear bulge, bulge, disk and halo. We construct a HI model whose radius is 1.3 kpc, scale height is 100 pc and mass is $3.6{\times}10^6M_{\odot}$. We also assume that the gas disk is initially tilted $30^{\circ}$ with respect to the Galactic plane. Here we report our simulation results and discuss the evolution of the tilted gas disk.