• 천문학회보
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• 제41권1호
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• pp.36.1-36.1
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• 2016

The physical scenario describing the origin of quasar winds remains largely unsettled due to our failure to account for X-ray weak BAL quasars. We approach this problem by studying the relation between the inner part of the outflow which is likely to be shielding the X-ray emission and thereby helping to drive the UV winds characterised by broad absorption lines (BALs). In particular, we aim to probe the wind-shield connection in the highly X-ray variable BAL quasar PG 2112+059, which has exhibited periods of X-ray weakness and X-ray normality in the past. A set of two 20 ks Chandra observations and two contemporaneous HST observations, separated by at least eight months, combined with a nearly simultaneous archival Chandra-HST observation from 2002, afford us a unique opportunity to study the connection between the shield (which is thought to be responsible for the X-ray absorption) and the ionisation state of the wind (observed as UV BAL features; e.g., C IV and O VI lines) over various timescales.

• 한국콘텐츠학회논문지
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• 제13권3호
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• pp.198-203
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• 2013

본 연구에서는 손, 머리, 복부 등에 대한 X선 촬영 시행 시 조사야 크기를 최적화할 경우와 최대화할 경우 검사목적부위로부터 30cm 거리에서의 X선 산란선량이 각각 어느 정도인지를 알아보았다. 그 결과 손, 머리, 복부 등에 대한 X선 산란선량은 첫째, 소인촬영의 경우 조사야 크기를 최적화하였을 때 각각 $0.08{\mu}Sv$, $4.39{\mu}Sv$, $5.56{\mu}Sv$로 나타났고, 조사야 크기를 최대화하였을 때 각각 $0.58{\mu}Sv$, $33.47{\mu}Sv$, $35.93{\mu}Sv$로 나타났으며, 둘째, 성인촬영의 경우 조사야 크기를 최적화하였을 때 각각 $0.40{\mu}Sv$, $14.51{\mu}Sv$, $18.86{\mu}Sv$로 나타났고, 조사야 크기를 최대화하였을 때 각각 $2.78{\mu}Sv$, $107.40{\mu}Sv$, $117.52{\mu}Sv$로 나타났다(P<0.001). 결론적으로, X선 촬영 시 조사야 크기를 필요한 만큼만으로 최대한 줄여주어 최적화시켰을 때에 최대화 시켰을 때보다 피사체 주변의 X선 산란선 발생량은 약 6~7배 정도 감소하였다.

• 천문학회지
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• 제29권spc1호
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• pp.291-294
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• 1996

The .Japanese sun observing satellite, Yohkoh, has been operational for five years and her scientific instruments are still in good condition. They have revealed ample of evidences that solar flares were triggered by magnetic reconnection, which was, for the first time, clearly indicated to take place in the solar corona. Cusp structures in soft X-rays and a new type of hard X-ray sources at the top of flaring loops have strongly supported the scenario originally proposed by C-S-H-KP. Nonthermal energy input in hard X-rays and thermal energy estimated from soft X-rays are fundamentally consistent with the interpretation of thick-target and chromospheric-evaporation models (Neupert effect). X-ray jets, another discovery of Yohkoh, were also associated with magnetic reconnection, as a result of the interaction of emerging fluxes with pre-existing coronal loops. Temperature structures of active regions, quiet sun, and coronal holes had very dynamic differential-emission-measure (DEM) distributions and high-temperature tails of DEM were considered to come from the contribution of flare-like activity.

• 천문학회지
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• 제38권3호
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• pp.339-344
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• 2005

We present analysis results of the energy spectra of MCG-2-58-22 associated with occasional flares which appear in a long-term X-ray light curve. We measure an intrinsic power-law slope of this object to be ${\Gamma}=1.74{\pm}0.02$ in the energy range of ${\sim}1-5keV$ and find that this slope is little affected by flares. We confirm that there exists a broad excess emission above 5 keV to the power-law continuum. The excess emission is less variable compared with a flux variation of flare and tends to be relatively weak during flares. A soft X-ray spectrum is also found to change, implying the presence of a variable soft component. We discuss the implications of these spectral variations.

• 천문학논총
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• 제30권2호
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• pp.417-421
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• 2015

We analyzed 0.5-45 keV data of NGC 3227 observed by Suzaku six times between 2008 October 28 and December 2. The count-count plot between the 0.5-3 keV and 3-10 keV bands exhibits a clear break, separating the data into bright and faint phases. Applying the difference spectrum method and time-averaged spectral fits to the phase data, we found the presence of two kinds of variable primary X-rays, (1) a hard primary component with ${\Gamma}{\sim}1.7$ dominating in the faint phase and (2) a soft primary continuum with ${\Gamma}{\sim}2.4$ appearing in the bright phase, both affected by partial absorption. Considering their timing and spectral characteristics, component (1) is presumably identical to a Compton continuum in the low/hard state, while component (2) may correspond to the hard tail emission in the high/soft state, or compact-jet emission. In that case, an accretion ow onto the central super massive black hole in NGC 3227 can be interpreted to include the two different states.

• 천문학회지
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• 제37권5호
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• pp.433-438
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• 2004

Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. The basic properties of cluster mergers and their effects are discussed. Mergers drive shocks into the intracluster gas, and these shocks heat the intracluster gas. As a result of the impulsive heating and compression associated with mergers, there is a large transient increase in the X-ray luminosities and temperatures of merging clusters. These merger boost can affect X-ray surveys of clusters and their cosmological interpretation. Similar boosts occur in the strong lensing cross-sections and Sunyaev-Zeldovich effect in merging clusters. Merger shock and turbulence associated with mergers should also (re)accelerate nonthermal relativistic particles. As a result of particle acceleration in shocks and turbulent acceleration following mergers, clusters of galaxies should contain very large populations of relativistic electrons and ions. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these shocks will also be described. Gamma-ray observations with GLAST seem particularly promising.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1845-1850
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• 2012

Layered metal hydroxides (LMHs) containing calcium were synthesized by coprecipitation in solution having two different trivalent metal ions, iron and aluminum. Two mixed metal solutions ($Ca^{2+}/Al^{3+}$ and $Ca^{2+}/Fe^{3+}$ = 2/1) were added to sodium hydroxide solution and the final pH was adjusted to ~11.5 and ~13 for CaAl-and CaFe-LMHs. Powder X-ray diffraction (XRD) for the two LMH samples showed well developed ($00l$) diffractions indicating 2-dimensional crystal structure of the synthesized LMHs. Rietveld refinement of the X-ray diffraction pattern, the local structure analysis through X-ray absorption spectroscopy, and thermal analysis also confirmed that the synthesized precipitates show typical structure of LMHs. The chemical formulae, $Ca_{2.04}Al_1(OH)_6(NO_3){\cdot}5.25H_2O$ and $Ca_{2.01}Fe_1(OH)_6(NO_3){\cdot}4.75H_2O$ were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Particle morphology and thermal behavior for the synthesized LMHs were examined by field emission scanning electron microscopy and thermogravimetricdifferential scanning calorimetry.

• 한국진공학회지
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• 제20권6호
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• pp.403-408
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• 2011

MFX tube를 개발하기 위하여, MFX tube 내에서 전계방출음극으로부터 방출된 전자의 궤적을 SIMION 프로그램을 이용하여 전산모사하였다. 전자의 출발위치와 상관없이 emitter에서 방출된 전자빔을 한곳에 집중시킬 수 있는 optimum extractor voltage Ve가 존재한다는 것을 알아내었다. Extractor voltage Ve는 source voltage Vs에 따라 변하지만, 두 전압의 비율(Ve/Vs)는 항상 일정하고, 그 값은 99.4%였다. Source와 extractor에 인가된 전압의 비율(Ve/Vs)이 99.4%일 때, 교차점에서의 빔 직경은 $1.2{\mu}m$였다. MFXG의 초점 크기는 교차점에서의 beam diameter보다 작을 수 없기 때문에, 교차점에서의 beam diameter을 작게 할 수 있는 조건을 찾는 것은 중요하다. 따라서 위의 두 결과는 MFX tube의 개발에 있어서 매우 중요한 결과로 판단된다.

• 천문학회보
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• 제24권2호
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• pp.76-76
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• 1999

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1977년도 제9회 학술발표회 초록
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• pp.111.1-111
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• 1977