• Bulletin of the Korean Space Science Society
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• 1993.04a
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• pp.13-13
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• 1993

The space and ground based infrared spectra of red supergiants are modeled and arranged in order of their evolutionary status with their theoretical model Parameters. Because of their large amplitude pulsation, the observational data taken at different phases show wide discrepancies. The chemical compositions of the dust shells around red supergiants are affected by the nuclearreactions and dredge-up processes of the cental stars. Those processes aresensitiTelr dependent on the initial ma:ss, the initial chemical coMposition,and the evolutionarr status. Miras, infrared carbon stars, and OHAR starshaTe a close link in their evolution iii many aspects, i.e. the chemicalcomposition, the optical depths and the mass loss rates. The evolutionarytracks for the three classes of red super91iants on infrared Huo-color diagamhave been constructed.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.29.2-29.2
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• 2010

We present elemental abundances of 412 blue compact dwarf galaxies (BCDs) at z=0.2~0.5 using the Sloan Digital Sky Survey (SDSS) DR7. The gas-phase nitrogen to oxygen abundance ratios (N/O) of sample galaxies increase as the oxygen to hydrogen abundance ratios (O/H) decrease. This indicates that the nitrogen is more enriched than the oxygen. We found that there is a noticeable distinction between the merger candidates and the isolated galaxies. Merging candidates show more enrichment of nitrogen abundance compared to isolated galaxies. On the other hand, neon and oxygen abundances for merging candidates are slightly lower than the isolated systems. We discuss the main cause of these trends with internal mixing and mass loss by fast rotation of young massive stars. We also discuss the environmental effect to the relation between specific star formation rate and galaxy mass.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.49.4-49.4
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• 2018

We present measurement results of the fabricated ultra wideband corrugated horn for the planned ASTE band7+8 receiver. Return loss and vector beam pattern measurements were carried out over 275-500 GHz frequency range. Hardware set-ups for these measurements are described as well as beam measurement data are compared with such design criteria as beam width, phase curvature and cross-polarization. We discuss the impact of these beam measurement results to the aperture efficiency of the proposed 2-mirror receiver optics for the ASTE telescope.

• Journal of Power Electronics
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• v.13 no.4
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• pp.647-655
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• 2013

In this paper, an approach to reduce the common-mode voltage and to eliminate narrow pulse for implemented AC-DC matrix converters is presented. An improved space vector modulation (SVM) strategy is developed by replacing the zero space vectors with suitable pairs of active ones. Further, while considering the commutation time, the probability of narrow pulse in the conventional and proposed SVM methods are derived and compared. The advantages of the proposed scheme include: a 50% reduction in the peak value of the common-mode voltage; improved input and output performances; a reduction in the switching loss by a reduced number of switching commutations and a simplified implementation via software. Experimental results are presented to demonstrate the correctness of the theoretical analysis, as well as the feasibility of the proposed strategy.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.337-341
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• 1994

This paper describes an effort to develop a simulator of Active Power Filter (APF) by three dimentional(3-D) space current co-ordinate. System current is represented by 3-D vector composed of three current components - active, reactive and distorted. %THD (%Total Harmonics Distortion) can be converted to height-angle of system current vector and power factor can be defined on 3-D space current co-ordinate without loss of generality. Current of APF and power system can be analyzed by 3-D visualization of current vector trajectory. So, the computer simulation results show that the proposed method by 3-D space current co-ordinate make up for disadvantages of performance evaluation on time / frequency domain.

• Journal of Chest Surgery
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• v.3 no.2
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• pp.113-120
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• 1970

Since the turn of the century there has been a constant search for a satisfactory method of controlling a large intrathoracic space following lobectomy. Primarily these methods consist of thoracoplasty, plombage, and phrenic nerve paralysis which are not completely satisfactory for they may result in loss of chest wall motility or diaphragmatic function. Incising the diaphragm at its periphery and resuturing to the chest wall at a level several rib spaces higher is an effective method of reducing intrathoracic space with minimal interference with pulmonary function. It is of particular value when the anticipated space problem is in the lower part of the thoracic cavity. Five cases are presented in which the diaphragm was peripherally detached and advanced to higher levels. Two cases were following lower lobectomy and three cases were following decortication for chronic empyema in which expansion was not good enough to adequately fill the space. Results in these cases were satisfactory.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.76.2-76.2
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• 2021

We present the characterization of the performance of the next-generation controller (SDSU Gen III) for BOAO Echelle Spectrograph CCD (BOES CCD) at the Bohyunsan Optical Astronomy Observatory. The current controller (SDSU Gen II) of the BOES CCD will be upgraded to SDSU Gen III to provide a more stabilized operation. To assess the performance of the new controller (e.g., conversion gain, full well capacity, S/N), we obtain various types of calibration images (e.g., bias, flat, science images of standard stars). Based on those datasets, we find that the overall performance of the new controller is somewhat comparable to that of the old controller if the slow mode is adopted for the readout. This may demonstrate that the new controller can be successfully substituted for the old controller without a substantial loss of performance. However, further analysis with a large dataset obtained in various observational conditions is necessary to confirm our results.

• Journal of Astronomy and Space Sciences
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• v.40 no.4
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• pp.237-245
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• 2023

Laser communication has been considered as a novel method for earth observation satellites with generation of high data volume. It offers faster data transmission speeds compared to conventional radio frequency (RF) communication due to the short wavelength and narrow beam divergence. However, laser beams are refracted due to atmospheric turbulence between the ground and the satellite. Refracted laser beams, upon reaching the receiver, result in angle-of-arrival (AoA) fluctuation, inducing image dancing and wavefront distortion. These phenomena hinder signal acquisition and lead to signal loss in the course of laser communication. So, precise alignment between the transmitter and receiver is essential to guarantee effective and reliable laser communication, which is achieved by pointing, acquisition, and tracking (PAT) system. In this study, we simulate the effectiveness of tip/tilt compensation for more efficient laser communication in the satellite-ground downlink. By compensating for low-order terms using tip/tilt mirror, we verify the alleviation of AoA fluctuations under both weak and strong atmospheric turbulence conditions. And the performance of tip/tilt correction is analyzed in terms of the AoA fluctuation and collected power on the detector.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.2
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• pp.167-172
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• 2015

In this paper, we have compared some radio propagation models in order to verify the performance of W.C.Y LEE propagation model in mountain area. The four propagation models, which are Okumura-Hata, ITU-R P.525, Egli and W.C.Y. LEE, are analyzed by comparing the differences between measured values and propagation loss estimation values. And a correction method for W.C.Y LEE model is suggested to improve the performance of W.C.Y. LEE model with measured data in mountain area. Simulation results show that the estimation error using W.C.Y LEE model is the lowest among four propagation models. Also, the results show that the corrected W.C.Y LEE model with suggested method improves the performance of propagation loss estimation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.701-705
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• 2007

The equipment noise of machine room that generates at the building where human-being is living, is becoming to an object of strong civil appeal, and because it influences to the residential space through the floor or wall, its damage is very serious level. Accordingly, while an efficient forming of the sound insulating measures is earnest, as most of the transmission loss data was the material measured in laboratory, in case when it was applied to the job site, due to the precision difference of constructing work and the influence of detoured transmitting sound, the case of disaccord is the most. Therefore, this thesis has intended to present a fundamental data for an efficient establishment of sound insulation measure, by means of comparison analysis with the existing transmission loss data, after measurement of the transmission loss on the object of various walls, at the construction equipment machinery room.