• 천문학회보
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• 제46권2호
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• pp.71.1-71.1
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• 2021

We perform disk-halo decomposition of the Large Magellanic Cloud (LMC) using a novel HI velocity field extraction method, aimed at better deriving its HI kinematics and thus mass distribution in the galaxy including both baryons and dark matter. We decompose all the line-of-sight velocity profiles of the combined HI data cube of the LMC, taken from the Australia Telescope Compact Array (ATCA) and Parkes radio telescopes with an optimal number of Gaussian components. For this, we use a novel tool, the so-called BAYGAUD which performs profile decomposition based on Bayesian MCMC techniques. From this, we disentangle turbulent non-ordered HI gas motions from the decomposed gas components, and produce an HI bulk velocity field which better follows the global circular rotation of the galaxy. From a 2D tilted-ring analysis of the HI bulk velocity field, we derive the rotation curve of the LMC after correcting for its transverse, nutation and precession motions. The dynamical contributions of baryons like stars and gaseous components which are derived using the Spitzer 3.6 micron image and the HI data are then subtracted from the total kinematics of the LMC. Here, we present the bulk HI rotation curve, the mass models of stars and gaseous components, and the resulting dark matter density profile of the LMC.

• 천문학회보
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• 제46권1호
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• pp.28.1-28.1
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• 2021

We present a statistical analysis of dark matter halos with interacting neighbors using a set of cosmological simulations. We classify the neighbors into two groups based on the total energy (E₁₂) of the target-neighbor system; flybying neighbors (E₁₂ ≥ 0) and merging ones (E₁₂ < 0). First, we find a different trend between the flyby and merger fractions in terms of the halo mass and large-scale density. The flyby fraction highly depends on the halo mass and environment, while the merger fraction show little dependence. Second, we measure the spin-orbit alignment, which is the angular alignment between the spin of a target halo (${\vec{S}}$ ) and the orbital angular momentum of its neighbor (${\vec{L}}$). In the spin-orbit angle distribution, the flybying neighbors show a weaker prograde alignment with their target halos than the merging neighbors do. With respect to the nearest filament, the flybying neighbor has a behavior different from that of the merging neighbor. Finally, we discuss the physical origin of two interaction types.

• 천문학회보
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• 제46권2호
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• pp.43.5-44
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• 2021

In the local Universe, the gravitational effects of mass density fluctuations exert perturbations on galaxies' redshifts on top of Hubble's Law, called 'peculiar velocities'. These peculiar velocities provide an excellent way to test the cosmological model in the nearby Universe. In this talk, we present new cosmological constraints using peculiar velocities measured with the 2MASS Tully-Fisher survey (2MTF), 6dFGS peculiar-velocity survey (6dFGSv), the Cosmicflows-3 and Cosmicflows-4TF compilation. Firstly, the dipole and the quadrupole of the peculiar velocity field, commonly named 'bulk flow' and 'shear' respectively, enable us to test whether our cosmological model accurately describes the motion of galaxies in the nearby Universe. We develop and use a new estimators that accurately preserves the error distribution of the measurements to measure these moments. In all cases, our results are consistent with the predictions of the Λ cold dark matter model. Additionally, measurements of the growth rate of structure, fσ8 in the low-redshift Universe allow us to test different gravitational models. We developed a new estimator of the "momentum" (density weighted peculiar velocity) power spectrum and use joint measurements of the galaxy density and momentum power spectra to place new constraints on the growth rate of structure from the combined 2MTF and 6dFGSv data. We recover a constraint of fσ8=0.404+0.082-0.081 at an effective redshift zeff=0.03. This measurement is also fully consistent with the expectations of General Relativity and the Λ Cold Dark Matter cosmological model.

• Bulletin of the Korean Chemical Society
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• 제20권6호
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• pp.720-726
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• 1999

It has been proved by the semi-classical gauge invariant formulation (GIF) that the correct interaction operator for coupling the field-free material states with the radiation field must be the position form regardless of the gauge chosen for expressing the electromagnetic potentials, in accordance with the well-established principle of gauge invariance. The semi-classical GIF is now extended to the quantized radiation field interacting with matter by defining the energy operator for the quantized radiation field in the presence of matter. It will be shown in this paper that the use of the energy operator guarantees the position form of the interaction operator even in the Coulomb gauge, contrary to the conventional approach in which the dark material Hamiltonian is used to get the interaction operator of the momentum form. The multipolar Hamiltonian is examined in the context of the quantum mechanical gauge transformation.

• 천문학회보
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• 제44권2호
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• pp.53.4-53.4
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• 2019

We reconstruct the underlying dark matter (DM) density distribution of the local universe within 20Mpc/h cubic box by using the galaxy position and peculiar velocity. About 1,000 subboxes in the Illustris-TNG cosmological simulation are used to train the relation between DM density distribution and galaxy properties by using UNet-like convolutional neural network (CNN). The estimated DM density distributions have a good agreement with their truth values in terms of pixel-to-pixel correlation, the probability distribution of DM density, and matter power spectrum. We apply the trained CNN architecture to the galaxy properties from the Cosmicflows-3 catalogue to reconstruct the DM density distribution of the local universe. The reconstructed DM density distribution can be used to understand the evolution and fate of our local environment.

• 천문학회보
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• 제44권2호
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• pp.55.3-55.3
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• 2019

We present a pipeline to estimate baryonic properties of a galaxy inside a dark matter (DM) halo in DM-only simulations using a machine trained on high-resolution hydrodynamic simulations. As an example, we use the IllustrisTNG hydrodynamic simulation of a (75 h^-1 Mpc)³ volume to train our machine to predict e.g., stellar mass and star formation rate in a galaxy-sized halo based purely on its DM content. An extremely randomized tree (ERT) algorithm is used together with multiple novel improvements we introduce here such as a refined error function in machine training and two-stage learning. Aided by these improvements, our model demonstrates a significantly increased accuracy in predicting baryonic properties compared to prior attempts --- in other words, the machine better mimics IllustrisTNG's galaxy-halo correlation. By applying our machine to the MultiDark-Planck DM-only simulation of a large (1 h^-1 Gpc)³ volume, we then validate the pipeline that rapidly generates a galaxy catalogue from a DM halo catalogue using the correlations the machine found in IllustrisTNG. We also compare our galaxy catalogue with the ones produced by popular semi-analytic models (SAMs). Our so-called machine-assisted semi-simulation model (MSSM) is shown to be largely compatible with SAMs, and may become a promising method to transplant the baryon physics of galaxy-scale hydrodynamic calculations onto a larger-volume DM-only run. We discuss the benefits that machine-based approaches like this entail, as well as suggestions to raise the scientific potential of such approaches.

• 한국토양비료학회지
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• 제8권3호
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• pp.121-133
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• 1975

1. 제주도(濟州道) 전토양(田土壤)은 육지(陸地)에 비(比)하여 PH 가 높고 유기물(有機物)과 염기(鹽基)의 함량(含量)이 높으나 유효인산(有效燐酸)의 함량(含量)만은 현저(顯著)히 낮다. 한편 남제주(南濟州) 전토양(田土壤) (91점(點))의 pH 및 유기물(有機物)과 유효인산(有效燐酸)의 함량(含量)은 각각(各各) 6.1, 13%, 23ppm이고 북제주(北濟州) 전토양(田土壤)은 각각(各各) 6.4, 3.7%, 76ppm이다. 2. 제주도(濟州道) 전토양(田土壤)은 토양비옥도(土壤肥沃度)의 면(面)에서 볼때 흑색토(黑色土), 농암갈색토(濃暗褐色土) 그리고 암갈색토(暗褐色土) 및 적황색토(赤黃色土)로 분류(分類)될 수 있다. 3. 토양유기물(土壤有機物)의 함량(含量)은 흑색토(黑色土)(15%)>농암갈색토(濃暗褐色土)(7%)>암갈색(暗褐色) (3%)의 순(順)이며 유기물함량(有機物含量)이 높은 토양(土壤)일수록 인산흡수계수(燐酸吸收係數)가 높고 유효인산함량(有效燐酸含量)이 낮다. 한편 유기물함량(有機物含量)이 높은 토양(土壤)은 염기치환용량(鹽基置換容量)이 크나 염기(鹽基)의 함량(含量)이 적어서 염기포화도(鹽基飽和度)는 낮다. 4. 대맥(大麥)의 지역별(地域別) 수량(收量)을 보면 북제주(北濟州)가 남제주(南濟州)보다 높고 서부(西部)가 동부지역(東部地域)보다 높으며 토양종류별(土壤種類別)로는 암갈색토(暗褐色土)>농암갈색토(濃暗褐色土)>흑색토(黑色土)의 순(順)이다. 5. 감자와 고구마의 생산력(生産力)은 육지(陸地)보다도 제주도(濟州道)에서 높은데 이들은 반토성(礬土性)에 강(强)한 작물(作物)이라고 생각된다. 화산회토양(火山灰土壤)에서는 내(耐)알루미늄성(性)의 작물(作物)이나 품종(品種)의 선택(選擇)이 중요(重要)하다. 6. 제주도(濟州道)에서의 3요소(要素)의 비효(肥效)를 보면 육지토양(陸地土壤)에 비(比)하여 고구마는 3요소(要素)의 비효(肥效)가 모두 낮으나 동작물(冬作物)인 대맥(大麥)과 유채(油菜)는 질소(窒素)와 인산(燐酸)의 비효(肥效)가 높으며 특(特)히 질소(窒素)의 비효(肥效)가 높다. 한편 남제주(南濟州) 토양(土壤)이 북제주(北濟州)에 비(比)하여 3요소(要素)의 비효(比效)가 높다. 7. 생산력(生産力)이 낮은 화산회토양(火山灰土壤)의 개량(改良)을 위(爲)하여는 매우 많은 양(量)의 석회(石灰)를 요구(要求)하나 석회(石灰)를 일시에 다량시용(多量施用)하는 것은 양분(養分)의 균형(均衡)을 악화(惡化)시킬 우려가 있으므로 석회적량(石灰適量)을 수작기(數作期)에 걸쳐 나누어주거나 고토(苦土) 및 가리(加里)의 증시(增施) 및 퇴비(堆肥)와 함께 주는 것이 바람직하다. 8. 화산회토양(火山灰土壤)에서는 시용인산(施用燐酸)의 대부분(大部分)이 불가급태(不可給態)로 되여 유효화비율(有效化比率)이 낮으므로 인산(燐酸) 30~40kg/10a 정도(程渡)의 시용량(施用量)으로는 그 비효(肥效)가 극(極)히 적으며 최대수량(最大收量)을 얻기 위(爲)한 인산시용량(燐酸施用量)은 300~400kg/10a 달(達)하는 것으로 추정(推定)된다. 한편 인산(燐酸)의 효과(效果)도 유기질비료(有機質肥料)를 병용(倂用)하는 조건(條件)에서 더욱 크다.

• 자원환경지질
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• 제38권6호
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• pp.707-716
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• 2005

ODP Leg 127 Site 794A에서 채취한 제4기 퇴적물의 유기지화학적 특성을 규명하고 고해양학적 의의를 이해하기 위하여 Rock-Eval 열분석, 원소 분석 및 유기물의 탄소동위원소 분석 등의 유기지화학적 분석을 실시하였다. 총유기탄소 함량, 총유기탄소에 대한 총질소 함량비, 총유기탄소에 대한 총황 함량비, 수소지수와 산소지수의 관계 및 유기물의 탄소동위원소 비를 기초로 유기물 특성 및 퇴적 당시의 고해양환경 해석을 시도하였다. 유기지화학적 분석결과 암색층은 상당량의 육상기원 유기물을 함유하고 빈산소/무산소환경에서 퇴적된 것으로 나타났다. 반면 담식층은 해양기원 유기물이 우세하게 포함되어 있으며 산소환경에서 퇴적된 것으로 나타났다. 이와 같은 결과는 해수면이 상승했던 간빙기동안 주변 대륙으로부터 다량의 육상기원 유기물의 유입으로 동해 표층생산성이 높아짐으로써 암색층이 퇴적된 것으로 해석된다. 반면에 해수면이 하강했던 빙기동안에는 육상기원 유기물 유입이 급감하였으며, 주로 해양의 일차생산과 중국사막지역으로부터 유입된 Kosa에 의한 퇴적물 희석작용에 의해 담색층이 퇴적된 것으로 해석된다.

• 천문학회보
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• 제42권2호
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• pp.73.3-73.3
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• 2017

Environment has a significant impact on the evolution of dark halo profiles. We used a cosmological N-body simulation based on WMAP5 cosmology to study environmental effects on halo profiles. Host haloes located in sparse regions are highly concentrated, and more massive haloes have higher concentration index. This is because mass accretion affects only the outer part of the halo and consequently increase the virial radius having no effect on the scale radius. Conversely, host haloes located in dense regions have low concentration index. This is because frequent mergers affect even the inner part of the halo. So, scale radius increases with the growth of virial radius. Evolutions of subhalo profiles are essentially different from those of host haloes because subhaloes undergo tidal stripping. The stripping begins once a subhalo approaches closer than ~3 virial radii of the host halo. During the stripping, the inner part of the subhalo keep following NFW profile, but the mass of the outer part gradually decreases. As a result, when the subhalo reaches the pericenter of its host, only about inner 30% of the subhalo follows the NFW profile.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.130-131
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• 2000

One of the more promising proposals for guiding and focusing neutral atoms involves dark hollow laser beams. When the frequency of the laser is detuned to the blue of resonance, the dipole force the atoms feel in the light confines them to the dark core where the atoms can be transported with minimal interaction with the light. The ability of the all-light atom guides to transport large number of ultracold atoms for long distances without physical walls leads to the possibility of a versatile tool for atom lithography, atom interferometry, atomic spectroscopy as well as for transporting and manipulating Bose-Einstein condensates. Furthermore since the atoms transported in all-light atom guides do not come into contact with matter, they can in principle be used to transport antimatter as well. The ability to vary the core size of the hollow beam makes the all-light atom guide potentially useful for focusing neutral atoms. The atoms could be focused as tight as the core size of the hollow beam at its waist. This new focusing scheme, called the atom funnel, would not show spherical and chromatic aberrations that conventional harmonic focusing suffers from. (omitted)