• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.69.1-69.1
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• 2009

• Bulletin of the Korean Space Science Society
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• 2009.04a
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• pp.38.3-38.3
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.76.2-76.2
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• 2012

We present the first simulations of cosmic reionization that include the first stars and their radiative feedback that limited their formation, in a volume large enough to capture the spatial variations that affected the process and its observability. We show hat these first stars made reionization begin much earlier than without, and was reatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the cosmic microwave background (CMB) significantly. Although within current WMAP uncertainties, this will enable Planck see he signature of the first stars at high redshift, currently undetectable by other probes.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.38.4-39
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• 2018

We analyze the Planck 2015 cosmic microwave background temperature fluctuation data to find any anomaly in the angular power spectra measured for partial regions on the sky. For disks with radius of $20^{\circ}$, $45^{\circ}$ and $90^{\circ}$, which are densely overlapping on the sky, we estimate the power excess and its statistical significance relative to the LambdaCDM expectation for some chosen ranges of angular scales. We also investigate the dipolar asymmetry using the power excess maps obtained for some chosen angular scales, and confirm the previously announced consistent dipole directions. The average dipole amplitude and the inner products of dipoles have been measured from the power excess maps at different angular scales. We conclude that although dipole directions are consistent the measured amplitudes are not statistically significant compared to the LambdaCDM model prediction.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.397-399
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• 2015

Recently, cosmic voids have been recognized as a powerful cosmological probe. A number of studies have focused on the effects of the gravitational lensing by voids on the temperature (and in some cases polarization) anisotropy of the Cosmic Microwave Background (CMB) background at relatively large to medium scales, l ~ 1000. Many of these studies attempt to explain the unusually large cold spot in CMB temperature maps and dynamical evidence of dark energy via detections of late-time integrated Sachs Wolfe (ISW) effect. Here, the effects of lensing by voids on the CMB temperature anisotropy at small scales, up to l = 3000, will be investigated. This work is carried out in the light of the benefits of adding large catalogues of cosmic voids, to be identified by future large galaxy surveys such as EUCLID and LSST, to the analysis of CMB data such as those from Planck mission. Our numerical simulation utilizes two methods, namely, the small-de ectionangle approximation and full ray-tracing analysis. Using the fitted void density profiles and radius (RV ) distribution available in the literature from N-body simulations, we simulated the secondary temperature anisotropy (lensing) of CMB photons induced by voids along a line of sight from redshift 0 to 2. Each line of sight contains approximately 1000 voids of effective radius $RV_{,eff}=35h^{-1}Mpc$ with randomly distributed radial and projected positions. Both methods are used to generate temperature maps. The two methods will be compared for their accuracy and effciency in the implementation of theoretical modeling.

• The Bulletin of The Korean Astronomical Society
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• v.25 no.2
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• pp.100-100
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• 2000

• The Bulletin of The Korean Astronomical Society
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• v.27 no.1
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• pp.59-59
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• 2002

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1817-1825
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• 2020

Background: Cosmic ray-induced particles can lead to failure of semiconductors packaged for export during air transport. This work performed MCNP 6.2 simulations to optimize shielding against neutrons and protons induced by cosmic radiation Methods and materials: The energy spectra of protons and neutrons by incident angle at the flight altitude were determined using atmospheric cuboid model. Various candidates for the shielding materials and the geometry of the Unit Load Device Container were evaluated to determine the conditions that allow optimal shielding at all sides of the container. Results: It was found that neutrons and protons, at the flight altitude, generally travel with a downward trajectory especially for the particles with high energy. This indicated that the largest number of particles struck the top of the container. Furthermore, the simulation results showed that, among the materials tested, borated polyethylene and stainless steel were the most optimal shielding materials. The optimal shielding structure was also determined with the weight limit of the container in consideration. Conclusions: Under the determined optimal shielding conditions, a significantly reduced number of neutrons and protons reach the contents inside the container, which ultimately reduces the possibility of semiconductor failure during air transport.

• Publications of The Korean Astronomical Society
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• v.22 no.4
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• pp.113-132
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• 2007

On the framework of stochastic gravitational wave background(SGWB) by compact binary systems, we studied the strain spectra of SGWB produced by cosmological cataclysmic variables(CV). For this we reviewed the empirical properties of CVs by using newly published CV catalogue and calculated the cosmological densities of CVs considering the galaxy luminosity function and cosmic stellar birth rate function. Assuming the secular evolution of CVs, we calculated the time scale of CV gravitational wave(GW) radiation and derived formulae for the strain spectra of SGWB by cosmological CVs.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.517-525
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• 2004

We present an update on our proposal that during the 'quasar era' (1.5 $\le$ z $\le$ 3), powerful radio galaxies could have played a major role in the enhanced global star-formation, and in the widespread magnetization and metal pollution of the universe. A key ingredient of this proposal is our estimate that the true cosmological evolution of the radio galaxy population is likely to be even steeper than what has been inferred from flux-limited samples of radio sources with redshift data, when an allowance is made for the inverse Compton losses on the cosmic microwave background which were much greater at higher redshifts. We thus estimate that a large fraction of the clumps of proto-galactic material within the cosmic web of filaments was probably impacted by the expanding lobes of radio galaxies during the quasar era. Some recently published observational evidence and simulations which provide support for this picture are pointed out. We also show that the inverse Compton x-ray emission from the population of radio galaxies during the quasar era, which we inferred to be largely missing from the derived radio luminosity function, is still only a small fraction of the observed soft x-ray background (XRB) and hence the limit imposed on this scenario by the XRB is not violated.