• 천문학회보
• /
• 제35권2호
• /
• pp.39.2-39.2
• /
• 2010

We have investigated the evolution of the galaxy morphology in the hierarchical universe taking advantage of Semi-Analytic Model (SAM). It is well known that the galaxy morphology is related to the dynamical and the chemical evolution. This implies that we need to understand overall physical processes in the galaxy to reproduce its morphology. Thus we implemented gradual hot gas stripping of satellite galaxies in a galaxy cluster and recycling of stellar mass losses into our model in order to describe star formation rate of galaxies accurately. To morphologically classify galaxies, the evolution of disc and bulge components is traced carefully. We compute our models based on the dark matter halo merger trees generated by N-body simulations as well as the Extended Press-Schechter (EPS) formalism. We present morphological differences caused by the use of different merger trees.

• 천문학회보
• /
• 제41권1호
• /
• pp.68.1-68.1
• /
• 2016

Binary black hole mergers are one of the important candidate of gravitational wave (GW) emission. Recently a successful GW observation was done by LIGO team, but it is still uncertain how many GW signals will be observable. In this research, we perform simplified N-body simulations containing three mass components, ordinary stars with two kind of stellar mass black holes. Various BH compositions are tested to investigate the effect of BH mass function on binary formation rate. As a result, we find the binary formation rate is not much affected by BH mass function and always around 30 %, but the detectable merging binaries are largely depend on higher mass BH population.

• 천문학회보
• /
• 제39권1호
• /
• pp.80-80
• /
• 2014

Dynamics of a globular cluster (GC) is dominated by behaviors of high-mass components such as neutron stars or black holes (BHs). Massive components in a cluster are segregated into the cluster core and some of them are ejected by dynamical interactions. In this study, we perform N-body simulations of GCs adapting two BH mass components, $10M_{\odot}$ and $20M_{\odot}$. Previous studies which mostly assume single-mass BHs suggested a rapid collapsing and escaping of BHs. A cluster with a two-component BH mass spectrum, however, retains a large fraction of $10M_{\odot}$ BHs longer. In addition to their roles in cluster dynamics, massive components in binaries are one of important sources of gravitational waves (GWs). We investigate properties of BH binaries escaped from the cluster and discuss their implications for GW detection.

• 천문학논총
• /
• 제30권2호
• /
• pp.345-347
• /
• 2015

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of an initial axi-symmetry due to rotation. Central black hole seeds are included in our models, and black hole growth due to the consumption of stellar matter is simulated until the central potential dominates the kinematics of the core. Our goal is to study the long-term evolution (Gyr) of relaxed dense stellar systems which deviate from spherical symmetry, and their morphology and final kinematics. With this purpose in mind, we developed a 2D Fokker-Planck analytical code, and confirmed its results using detailed N-Body simulations, applying a high performance code developed for GPU machines. We conclude that the initial rotation significantly modifies the shape and lifetime of these systems, and cannot be neglected in the study of the evolution of globular clusters, and the galaxy itself. Our models give a constraint for the final intermediate black hole masses expected to be present in globular clusters.

• 천문학회보
• /
• 제44권1호
• /
• pp.55.5-55.5
• /
• 2019

We present our first attempt at understanding the dual impact of the large-scale density and velocity environment on the formation of very first astrophysical objects in the Universe. Following the recently developed quasi-linear perturbation theory on this effect, we introduce the publicly available initial condition generator of ours, BCCOMICS (Baryon Cold dark matter COsMological Inital Condition generator for Small scales), which provides so far the most self-consistent treatment of this physics beyond the usual linear perturbation theory. From a suite of uniform-grid simulations of N-body+hydro+BCCOMICS, we find that the formation of first astrophysical objects is strongly affected by both the density and velocity environment. Overdensity and streming-velocity (of baryon against cold dark matter) are found to give positive and negative impact on the formation of astrophysical objects, which we quantify in terms of various physical variables.

• 천문학회보
• /
• 제44권2호
• /
• pp.52.3-52.3
• /
• 2019

We present our first attempt at understanding the dual impact of the large-scale density and velocity environment on the formation of very first astrophysical objects in the Universe. Following the recently developed quasi-linear perturbation theory on this effect, we introduce the publicly available initial condition generator of ours, BCCOMICS (Baryon Cold dark matter COsMological Inital Condition generator for Small scales), which provides so far the most self-consistent treatment of this physics beyond the usual linear perturbation theory. From a suite of uniform-grid simulations of N-body+hydro+BCCOMICS, we find that the formation of first astrophysical objects is strongly affected by both the density and velocity environment. Overdensity and streming-velocity (of baryon against cold dark matter) are found to give positive and negative impact on the formation of astrophysical objects, which we quantify in terms of various physical variables.

• 천문학회보
• /
• 제44권2호
• /
• pp.73.1-73.1
• /
• 2019

We investigate the evolution of the galactic spin of spiral galaxies in various dynamical situations using the N-body/SPH simulations. To do this we first construct a Milky Way-like galaxy model. Then we perform both prograde and retrograde encounters between the spiral galaxy pair. We also conduct a simulation with our galaxy model in isolation for comparison. We find that the circular motion of the disk stars in the inner region of the galaxy decrease clearly when the galaxy experiences strong prograde interactions. Such decrease has not found when the galaxy experiences weak or no interactions. We compare our simulation results with recent observational studies on the galactic spins.

• 센서학회지
• /
• 제30권2호
• /
• pp.114-118
• /
• 2021

In this study, the sensitivity of an active pixel sensor (APS) was adjusted by employing a gate/body-tied (GBT) p-channel metal-oxide semiconductor field-effect transistor (PMOSFET)-type photodetector with a transfer gate. A GBT PMOSFET-type photodetector can amplify the photocurrent generated by light. Consequently, APSs that incorporate GBT PMOSFET-type photodetectors are more sensitive than those APSs that are based on p-n junctions. In this study, a transfer gate was added to the conventional GBT PMOSFET-type photodetector. Such a photodetector can adjust the sensitivity of the APS by controlling the amount of charge transmitted from the drain to the floating diffusion node according to the voltage of the transfer gate. The results obtained from conducted simulations and measurements corroborate that, the sensitivity of an APS, which incorporates a GBT PMOSFET-type photodetector with a built-in transfer gate, can be adjusted according to the voltage of the transfer gate. Furthermore, the chip was fabricated by employing the standard 0.35 ㎛ complementary metal-oxide semiconductor (CMOS) technology, and the variable sensitivity of the APS was thereby experimentally verified.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제8권2호
• /
• pp.156-163
• /
• 2008

We proposed a new $p^+/n^+$ gate locally-separated-channel (LSC) bulk FinFET which has vertically formed oxide region in the center of fin body, and device characteristics were optimized and compared with that of normal channel (NC) FinFET. Key device characteristics were investigated by changing length of $n^+$ poly-Si gate ($L_s$), the material filling the trench, and the width and length of the trench at a given gate length ($L_g$). Using 3-dimensional simulations, we confirmed that short-channel effects were properly suppressed although the fin width was the same as that of NC device. The LSC device having the trench non-overlapped with the source/drain diffusion region showed excellent $I_{off}$ suitable for sub-50 nm DRAM cell transistors. Design of the LSC devices were performed to get reasonable $L_s/L_g$ and channel fin width ($W_{cfin}$) at given $L_gs$ of 30 nm, 40 nm, and 50 nm.

• 한국물환경학회지
• /
• 제35권3호
• /
• pp.224-233
• /
• 2019

액비(분뇨)에 포함된 질소성분은 환경의 질을 악화시키고 안정성을 감소시킬 수 있다. 액비로 인한 환경적 위해성을 최소화하기 위해서는 환경 매체 내에서의 액비의 거동을 이해할 필요가 있다. 액비에 포함된 암모니아성 질소($NH_3-N$)의 환경 내 거동과 이송을 분석하고, 액비시스템에서 질소(N)관리의 개선을 위한 기반을 제공하며 질소의 환경에 미치는 악영향을 최소화하기 위해서, 본 연구는 단순화된 Level III fugacity 모델의 적용 가능성을 조사하는 것을 목적으로 하였다. 벼 재배 기간 중 4개의 환경구획(공기, 물, 토양 및 벼)에서 암모니아성 질소($NH_3-N$) 성분을 축적하기 위해 정상상태의 fugacity 개념을 이용한 모델의 모의 실험을 실시하였으며 그 결과 Level III fugacity 모델의 적용 가능성을 검증하였다. 모델 결과, 대부분의 암모니아성 질소($NH_3-N$)는 논물(수체)과 벼(식물)에 분포하였으며 공기와 논물 그리고 토양에 대한 로그-로그 그래프선상에서 fugacity와 농도는 시간에 따라 선형적으로 감소한 반면에 벼(식물)에서의 변화는 비선형적으로 나타났다. 제거과정의 민감성을 살펴본 결과 제거과정(침적과 유출)이 고려된 경우 대부분의 암모니아성 질소는 논물에 분포하였으며 제거과정이 무시된 경우에는 벼(식물)가 암모니아성 질소를 흡수하는 것으로 나타났다. 또한 질소의 물질수지에 따라 각 구획별로 질소가 분포됨을 알 수 있었다. 본 연구는 실제 관측 자료에 의한 모델 보정을 수행하지 않고 토양층에 의한 잔류량 및 질소 형태의 변화를 기술하지 않았으며 모델 시뮬레이션은 간헐적인 실제 배출량 입력과 달리 연속 배출량으로 간주하였다. 그러므로 수질에 대한 비점 오염원으로서의 액비의 영향을 정량화하기 위해서는 보다 구체적이고 지속적인 모델링 및 모니터링 연구가 필요하다. 향후 연구의 Level III fugacity 모델에서는 더 정확한 제거 과정을 기술하고, 입력 변수의 적절한 값을 적용하여 다양한 N 형 비료에 대한 모델 시뮬레이션을 실시하고, 액비와 다양한 N 형 비료를 사용하여 얻은 N 성분의 관측 자료를 이용하여 모델을 평가할 것이다.