• Phonetics and Speech Sciences
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• v.15 no.4
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• pp.61-69
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• 2023

Sulcus vocalis is characterized by incomplete closure of the vocal folds, with a high mean airflow rate (MFR) as a distinctive feature. The MFR is measured using two aerodynamic analysis methods [the maximum sustained phonation protocol (MXPH) and voicing efficiency protocol (VOEF)] of the phonatory aerodynamic system (PAS), and the results may vary depending on the method. This study compared the differences in MFR before and after treatment (microsurgery and voice therapy) according to the MXPH and VOEF of the PAS in 30 patients with sulcus vocalis. Additionally, we examined whether there were differences in the subjective voice evaluation (voice handicap index, VHI), perceptual voice evaluation (GRBS), and fundamental frequency (F0) before and after treatment. The results showed significant differences between the two methods, both before and after treatment, in patients with sulcus vocalis. However, there were no significant differences by methods in the changes before and after treatment. The VHI and GRBS scores significantly decreased after treatment; however, F0 showed no significant differences before and after treatment. This study indicates that when evaluating MFR changes in patients with sulcus vocalis, it is acceptable to use either aerodynamic analysis (MXPH or VOEF).

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.64.2-64.2
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• 2010

From 2009, CEOU of Seoul National University has been utilizing the United Kingdom Infrared Telescope (UKIRT) at Mauna Kea, Hawaii, as one of its research facilities. UKIRT is a telescope with 3.8m primary mirror, and it is currently the largest telescope specialized for infrared observations. We will summarize our research activities using UKIRT, which include Infrared Medium-deep Survey (IMS) of proto-clusters and high redshift quasars, NIR imaging programs of Gamma Ray Bursts (GRBs), Gamma Ray sources, and SNUQSO quasars. Our research programs include international collaboration with the UK GRB team, the NASA/Swift team, Pomona College, and National Central University of Taiwan. We will also touch on our future plan of using UKIRT.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.36.2-36.2
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• 2010

CQUEAN (Camera fo QUasars in EArly uNiverse) is a newly developed camera by CEOU for the 2.1m telescope at the McDonald Observatory, Texas, USA. We report the early science results from the commissioning run of CQUEAN which include the observations of the gamma-ray burst (GRB) afterglows and quasars at z ~ 5.5. Although the data were originally taken to test the instrument performance, the results are already very encouraging. We uncovered GRB afterglows at z = 0.8 - 1.4, with our data being used for the international collaboration research to understand the nature of GRBs. The unique filter sets we employed are providing the data which are effective for selecting quasars at z ~ 5.5. The special aspects of CQUEAN - high sensitivity at 0.8-1.1 ${\mu}m$ and fast readouts - will allow us to produce many interesting through surveys of high redshift quasars and fast follow-up of transient objects such as GRBs and exoplanets in future.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.49.3-50
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• 2015

Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that such fast-cooling electrons have a power-law distribution in energy with an index -2, and their synchrotron radiation has a photon spectral index -1.5. On the other hand, in a transient expanding astrophysical source, such as a gamma-ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast-cooling electrons can have a harder energy spectrum. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon spectral index has a typical value -1 could be due to synchrotron radiation in this moderately fast-cooling regime.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.67.1-67.1
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• 2012

Shocks are evolved when the relativistic jets in active galactic nuclei (AGNs), black hole binaries, supernova remnants (SNR) and gamma-ray bursts (GRBs) interact with the surrounding medium. The high energy particles are believed to be accelerated by the diffusive shock acceleration and the strong magnetic field is generated by Weibel instability in the shock. When ultrarelativistic electrons with strong magnetic field cool by the synchrotron emission, the radiation is observed in gamma-ray burst and the near-equipartitioned magnetic field in the external shock delays the afterglow emission. In this paper, we performed the 3D particle-in-cell (PIC) simulations to understand the characteristics of these relativistic shock and particle acceleration. Forward and reverse shocks are shaped while the unmagnetized injecting jet interacts with the unmagnetized ambient medium. Both upstream and downstream become thermalized and the particle accelerations are shown in each transition region of the shock structures.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.39.1-39.1
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• 2018

Although it is agreed that the gamma-ray bursts (GRBs) invoke highly relativistic jets with bulk Lorentz factors of a few hundreds, the exact physical mechanism producing such powerful gamma-rays still remains debated. Three outstanding and important questions in the field concern (1) the composition of GRB jets (i.e., matter-dominated vs Poynting-flux-dominated), (2) the involved radiative process responsible for the observed gamma-rays (i.e., synchrotron mechanism vs photospheric radiation), and (3) the distance of the emitting region from the central engine where the prompt gamma-rays are released (i.e., ~10^12 cm vs 10^14 cm vs 10^16 cm). I will present recent important breakthroughs that we have made, which answer these three questions.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.38.1-38.1
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• 2016

Gamma ray burst, the most brightest explosion phenomena in the current universe is well suited for study of high redshift universe. We report the afterglow multi-wavelength observation and GTC spectroscopy follow up of GRB 140304A which was exploded at z=5.283. The spectrum was shown damped Lyman alpha features and a series of absorption lines S, Si, SiII*, Oi, CII, CII*, SiIV are clearly detected at common redshift. Clear optical flares are detected when X-ray flare happened and a possible gamma-ray excess also. At this conference, we report on implications for the GRB host and environments using its absorption features which place the results in context to other well studied high redshift GRBs and studies about the ejecta using its observed flaring activities.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.79.1-79.1
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• 2015

We describe our ongoing project, Intensive Monitoring Survey of Nearby Galaxies. This survey is designed to study transients such as Supernovae (SNe) in nearby galaxies. Our targets are UV-bright (MUV < -18.4) and nearby (d < 50 Mpc) 50 galaxies selected from a GALEX catalog, whose star formation rates are larger than normal galaxies. High star formation in these galaxies ensures that core-collapse supernova explosions occur more frequently in them than normal galaxies. By monitoring them with a short cadence of a few hours, we expect to discover 5 SNe/yr events. Most importantly, we hope to construct very early light curves in rising phase for some of them, which enables us to understand better the physical properties of progenitor star and the explosion mechanism. To enable such a high cadence observation, we constructed a world wide telescope network covering northern, southern hemisphere distributed over a wide range of longitudes (Korea, US, Australia, Uzbekistan and Spain). Data reduction pipe line, detection and classification algorithms are being developed for an efficient processing of the data. Using the network of telescopes, we expect to reach observe not only SNe but also other transients like GRBs, Asteroid, variable AGNs and gravitaional wave optical counter part.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.57.2-57.2
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• 2013

Based on N-body simulations, we find out that significant fraction of dynamically formed BH-BH (10 $M_{\odot}$ and NS-NS (1.4 $M_{\odot$ ecah) binaries are ejected from globular clusters. About 30 percent of compact stars are ejected in the form of binary. The merging time of ejected binary depends on the velocity dispersion of globular cluster. Some of ejected binaries have merging time-scales shorter than Hubble time and are expected to produce gravitational waves that can be detectable by the advanced ground-based interferometers. The merger rates of ejected BH-BH and NS-NS binaries per globular cluster are estimated to be 3.5 and 17 per Gyr, respectively. Assuming the spatial density of globular clusters as 8.4 $h^3$ clusters $Mpc^{-3}$ and extrapolating to the horizon distance of the advanced LIGO-Virgo network, we expect the detection rates solely attributed to BH-BH and NS-NS with cluster origin are to be 42 and 1.7 $yr^{-1}$, respectively. Besides, we find out that BH-NS binary ejection hardly occurs in globular clusters and dynamically formed compact binaries may possibly be the source of short GRBs whose locations are far from host galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.39.3-40
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• 2020

For the space weather research, KASI (Korea Astronomy and Space Science Institute) is developing the SNIPE (Small-scale magNetospheric and Ionospheric Plasma Experiment) mission, which consists of four 6U CubeSats of ~10 kg. Besides of space weather research, the SNIPE mission has another astrophysical objective, detecting Gamma-Ray Bursts(GRB). By cross-correlating the light curves of the detected GRBs, the fleet shall be able to determine the time difference of the arriving signal between the satellites and thus determine the position of bright short bursts with an accuracy ~100'. To demonstrate the technology of the GRB observation, CSI gamma-ray detectors combined with GPS and IRIDIUM communication modules are placed on each SNIPE CubeSat. The time of each spacecraft is synchronized and when the GRB is detected, the light curve will be transferred to the Mission Operation Center (MOC) by IRIDIUM communication module. By measuring time difference of each GRB signals, the technology for localization of GRB will be proved. If the results show some possibilities, we can challenge the new astrophysical mission for investigating the origin of GRB.