• Publications of The Korean Astronomical Society
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• v.37 no.2
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• pp.13-31
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• 2022

We observed the symbiotic star AG Dra for a total of 61 nights between April 2004 and December 2021 using the 1.8-m telescope and the high-resolution Echelle spectrograph BOES at the Bohyunsan Optical Astronomy Observatory and obtained 355 frames of spectroscopic data to investigate the variations in its spectral lines. Overnight short-term and long-term changes in prominent emission lines are examined. No short-term changes are found in the line profiles. However, the peak intensity of the Hα emission line exhibits very small variation. In the long-term period, many emission lines including He I λ5875, λ6678, λ7065 and Fe II λ5018 are found to vary reflecting the symbiotic outburst activities. It is noted that He II λ4686 and Raman-scattered O VI λ6830, λ7088 are exceptions, where no significant variations are discernible. One of the noticeable lines is the λ5018 line. Its appearance and disappearance pattern are different from other emission lines, and the line is found to appear in outburst states. The Hα and Hβ lines remain very similar in our spectroscopic monitoring campaign.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2294-2296
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• 2005

Multilayer microstrip lines are an integral part of an MMIC. This paper presents an analysis of multilayer GaAs-MMIC microstrip line using a spectral domain method(SDM) taking into account the effect of the variation in the thickness of various layers of substrates on the characteristic impedance and the effective dielectric constant of the line. This work is expected to be useful in GaAs foundries for accurate CAD modelling of the microstrip lines up to 40GHz.

• Publications of The Korean Astronomical Society
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• v.20 no.1 s.24
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• pp.43-48
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• 2005

We present a high resolution spectrum of PU Vul observed at Bohyunsan Optical Astronomy Observatory (BOAO) on April 9, 2004. Permitted emission and nebular lines of PU Vul had been significantly changed compared to all spectra observed since its eruption in 1979. Therefore all new lines should be re-identified and were done so. We do-convoluted a $H{\beta}$ line into several emission components with Gaussian functions. Then we carefully discussed the geometrical feature of PU Vul in April 2004.

• Proceedings of the KOSOMBE Conference
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• v.1989 no.05
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• pp.27-28
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• 1989

In conventional line scan angiography, flow signal has been enhanced by the time_of_flight effect while the signal from stationary tissues has been suppressed by the saturation rf pulse followed by spoiling gradients. Due to the inhomogeneous rf field and the tissue dependent T1 relaxation time, however, stationary tissues can not be suppressed completely or uniformly, and the remnant stationary signal deteriorates the resultant angiogram. Here, the complete cancellation of stationary tissues is made possible by the spectral analysis of a series of repetitive line images of the same slice. The Fourier transformation of a set of line images results in the spectrum images, where stationary tissues are collected into the dc component while arteries are included in harmonic components because of the variation of the flow velocity and the resultant flow signal in arteries according to the cardiac cycle. The summation of harmonic components excluding the dc component results in the angiogram of arteries with the complete cancellation of stationary tissues.

• Bulletin of the Korean Chemical Society
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• v.26 no.1
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• pp.115-118
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• 2005

The miniaturized NIR (Near-infrared) spectrometer has been utilized for the determination of water content (1-19% range) in ethanol that is the most popular organic solvent in pharmaceutical industries. It has many potential capabilities that can replace the conventional analyzers especially for the on-line measurement since it is compact, versatile and cost-effective. By using two dimensional (2D) correlation spectroscopy, it was preliminarily investigated to find any unforeseen spectral distortion among the spectra collected from the miniaturized spectrometer. The 2D study revealed that the spectral variation clearly followed the variation of water concentration without any spectral distortion or abnormality. PLS (Partial Least Squares) was employed to build the calibration model and the resulting prediction performance was acceptable and stable over several days. Even though the miniaturized NIR system was evaluated to fairly simple chemical matrix, the overall study demonstrates the sufficient feasibility for diverse practical and industrial applications.

• Journal of the Korean earth science society
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• v.38 no.1
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• pp.1-10
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• 2017

The symbiotic star AG Peg is a nebulous binary system that consists of giant star (GS) and white dwarf (WD). We investigated the HI Balmer emission lines of the symbiotic nova AG Peg, observed in 1998, 2001, and 2002 at Lick Observatory. The $H{\alpha}$ and $H{\beta}$ line profiles consist of blue-shifted, red-shifted, and broad components of which intensities and width showed notable changes. The HI emission line profiles that represent the kinematics of the gaseous nebula appear to be mainly from an accretion disk in relatively large radius from the WD. Considering the line of an observer's sight, both GS and WD are located at the sky plane side by side during the 1998 observation, while the WD is in front of GS during 2002 but the WD in rear during 2001. Such a relative position and the spectral line intensity variation imply that a fairly constant outflow occurs into WD from GS which caused to maintain the rotating thick accretion disk structure responsible for the observed spectral lines.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.719-726
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• 2004

In this paper, compensation characteristics of distorted WDM channel due to both chromatic dispersion and self phase modulation (SPM) is numerically investigated under the assumptions of non-uniformly distributed fiber dispersion, in order to inspect the application of mid-span spectral inversion (MSSI) to any exact transmission links. The MSSI is compensation method used in this approach. This method has an optical phase conjugator (OPC) placed in mid-way of total transmission length to compensate distorted WDM channels. It is confirmed that MSSI will become applicable to long-haul WDM systems by controlling input light power of transmission channels, when the averaged dispersion of both fiber sections with respect OPC was varied and distributed unequally each other. Applying MSSI to long-haul WDM system, it is possible to remove all in-line compensator, consequently it will be expected to reducing system cost.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.265-277
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• 2019

Using the measured data of waves and shore-line, we reviewed the grand circulation process and seasonal variation of beach cusp at the Mang-Bang beach from the perspective of trapped mode Edge waves known as the driving mechanism of beach cusp. In order to track the temporal and spatial variation trends of beach cusp, we quantify the beach cusp in terms of its wave length and amplitude detected by threshold crossing method. In doing so, we also utilize the spectral analysis method and its associated spectral mean sand wave number. From repeated period of convergence and ensuing splitting of sand waves detected from the yearly time series of spectral mean sand wave number of beach cusp, it is shown that the grand circulation process of beach cusp at Mang-Bang beach are occurring twice from 2017. 4. 26 to 2018. 4. 20. For the case of beach area, it increased by $14,142m^2$ during this period, and the shore-line advanced by 18 m at the northen and southern parts of the Mang-Bang beach whereas the shore-line advanced by 2.4 m at the central parts of Mang-Bang beach. It is also worthy of note that the beach area rapidly increased by $30,345m^2$ from 2017.11.26. to 2017.12.22. which can be attributed to the nature of coming waves. During this period, mild swells of long period were prevailing, and their angle of attack were next to zero. These characteristics of waves imply that the main transport mode of sediment would be the cross-shore. Considering the facts that self-healing capacity of natural beaches is realized via the cross-shore sediment once temporarily eroded. it can be easily deduced that the sediment carried by the boundary layer streaming toward the shore under mild swells which normally incident toward the Mang-Bang beach makes the beach area rapidly increase from 2017.11.26. to 2017.12.22.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.269-270
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• 2015

We carried out near-IR photometric and optical spectroscopic observations of V582 Aur, which is a FU Orionis type object, to investigate any periodic and/or aperiodic variations. We obtained light curves on the scale of a night and a year, in J, H and Ks bands with KASINICS (KASI Near Infrared Camera System) attached to the BOAO (Bohyun-san Optical Astronomy Observatory) 1.8-m reflector in Youngcheon, South Korea and examined photometric variations on the two time scales. So far we have not found any periodic brightness variations on the scale of a night. On the other hand, we have found that there seems to be a periodic brightness variation with a period of approximately 45 days. In addition, high-resolution optical spectroscopic observations of V582 Aur were performed from February 2013 to May 2014 with the high-resolution echelle spectrograph BOES attached to the BOAO 1.8-m reflector. We analyzed several spectral lines to understand the physical state of V582 Aur. The P Cyg profiles are clearly shown in the $H{\alpha}$ line and Na I D line.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.51.2-51.2
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• 2020

Luminous blue variables (LBVs) are massive evolved stars that show unpredictable photometric and spectral variation. It is generally assumed that they undergo one or more of large eruptions. We have obtained high dispersion NIR spectra of several LBVs with Immersion GRating INfrared Spectrometer (IGRINS). One notable feature in their IGRINS spectra is the existence of broad lines (~ a few hundred km/s) with unusual boxy profile. They are fluorescent lines of Fe II by Lyman α photons in the stellar wind. However, modeling of these lines with radiative transfer code CMFGEN predicts much weaker line strength. We propose that incorporating broadening of Lyman α line by scattering processes in dense wind can enhance the Fe II fluorescent lines. We further discuss how these Fe II fluorescent lines can be used to characterize massive LBV wind.