• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.108.1-108.1
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• 2012

Previously we introduced ray-tracing based 3D optical earth system model for specular and scattering properties of all components of the system (i.e. clear-sky atmosphere, land surfaces and an ocean surface). In this study, we enhanced 3-dimensional atmospheric structure with vertical atmospheric profiles for multiple layer and cloud layers using Lambertian and Mie theory. Then the phase dependent disk averaged spectra are calculated. The main results, simulated phase dependent disk averaged spectra and light curves, are compared with the 7 bands(300~1000nm) light curves data of the Earth obtained from High Resolution Instrument(HRI) in Deep Impact spacecraft during Earth flyby in 2008. We note that the results are comparable with the observation.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.19 no.39
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• pp.255-264
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• 1996

This Paper presents a heuristic algorithm for machine-part group formation considering part production information (Production volume, roution sequence, unit operation time, facility size) in cellular manufacturing logistics system. In general, factory space is restricted within limited size when cells are located. A twofold heuristic algorithm is developed for considering factory space restrictions of located cells. The first phase is a aggregation procedure to minimize inter cell movement for satisfactoring space restriction. The second phase is a rearrangement procedure to maximize line balancing efficiency between machines within the cell and non assigned machine during first phase. Numerical example is presented to verify the efficiency of proposed algorithm.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.121-129
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• 2019

The present study investigates the propagation of shear waves in a composite structure comprised of imperfectly bonded piezoelectric layer with a micropolar half space. Piezoelectric layer is considered to be initially stressed. Micropolar theory of elasticity has been employed which is most suitable to explain the size effects on small length scale. The general dispersion equations for the existence of waves in the coupled structure are obtained analytically in the closed form. Some particular cases have been discussed and in one particular case the dispersion relation is in well agreement to the classical-Love wave equation. The effects of various parameters viz. initial stress, interfacial imperfection and micropolarity on the phase velocity are obtained for electrically open and mechanically free system. Numerical computations are carried out and results are depicted graphically to illustrate the utility of the problem. The phase velocity of the shear waves is found to be influenced by initial stress, interface imperfection and the presence of micropolarity in the elastic half space. The theoretical results obtained are useful for the design of high performance surface acoustic devices.

• Proceedings of the KSMRM Conference
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• 2006.11a
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• pp.76-76
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• 2006

• Journal of Astronomy and Space Sciences
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• v.41 no.1
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• pp.43-60
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• 2024

Korea Pathfinder Lunar Orbiter (KPLO) is South Korea's first space exploration mission, developed by the Korea Aerospace Research Institute. It aims to develop technologies for lunar exploration, explore lunar science, and test new technologies. KPLO was launched on August 5, 2022, by a Falcon-9 launch vehicle from cape canaveral space force station (CCSFS) in the United States and placed on a ballistic lunar transfer (BLT) trajectory. A total of four trajectory correction maneuvers were performed during the approximately 4.5-month trans-lunar cruise phase to reach the Moon. Starting with the first lunar orbit insertion (LOI) maneuver on December 16, the spacecraft performed a total of three maneuvers before arriving at the lunar mission orbit, at an altitude of 100 kilometers, on December 27, 2022. After entering lunar orbit, the commissioning phase validated the operation of the mission mode, in which the payload is oriented toward the center of the Moon. After completing about one month of commissioning, normal mission operations began, and each payload successfully performed its planned mission. All of the spacecraft operations that KPLO performs from launch to normal operations were designed through the system operations design process. This includes operations that are automatically initiated post-separation from the launch vehicle, as well as those in lunar transfer orbit and lunar mission orbit. Key operational procedures such as the spacecraft's initial checkout, trajectory correction maneuvers, LOI, and commissioning were developed during the early operation preparation phase. These procedures were executed effectively during both the early and normal operation phases. The successful execution of these operations confirms the robust verification of the system operation.

• Journal of Astronomy and Space Sciences
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• v.31 no.4
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• pp.295-301
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• 2014

Whistler mode chorus wave is considered to play a critical role in accelerating and precipitating the electrons in the outer radiation belt. In this paper we test a conventional scenario of triggering chorus using THEMIS satellite observations of waves and particles. Specifically, we test if the chorus onset is consistent with development of anisotropy in the electron phase space density (PSD). After analyzing electron PSD for 73 chorus events, we find that, for ~80 % of them, their onsets are indeed associated with development of the positive anisotropy in PSD where the pitch angle distribution of electron velocity peaks at 90 degrees. This PSD anisotropy is prominent mainly at the electron energy range of ${\leq}$ ~20 keV. Interestingly, we further find that there is sometimes a time delay among energies in the increases of the anisotropy: A development of the positive anisotropy occurs earlier by several minutes for lower energy than for an adjacent higher energy.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.6
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• pp.299-305
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• 2006

In this paper, we suggest a new space vector PWM modulation method with very short processing time which does not need identification of nearest three vectors(NTV) and duty ratio for each vector. The suggested PWM method makes mean value of phase voltage to be same as reference during every modulation period by use of a triangle in small hexagon on multi-level vector space. This paper described the suggested modulation method can be successfully applied to the space vector modulation use of multi-level inverter by computer simulations and experiments.

• Journal of Astronomy and Space Sciences
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• v.24 no.2
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• pp.111-118
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• 2007

We have studied energetic neutral atom (ENA) disturbances during the magnetic storm main phase that occurred on October 3,2001, using the ENA data from the HENA instrument onboard the IMAGE spacecraft. We find that the main phase is characterized by five ENA enhancement events that occurred quasi-periodically. The repetitive ENA enhancements are most significant in the highest energy (138-222 keV) oxygen channel and become less significant for hydrogen and in lower energies. Also they are separated by ${\sim}1.2$ to ${\sim}1.7$ hrs, which is well below an average period usually seen for other repetitive injection events.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.80.2-80.2
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• 2014

We present the results of high resolution (R>35,000) optical spectroscopic monitoring observations of a new FU Orionis-like young stellar object, HBC 722. We observed HBC 722 with the Bohyunsan Optical Echelle Spectrograph (BOES) and Hobby-Eberly Telescope (HET) since November 26, 2010. HBC 722 is the FU Orionis-like object best characterized for the pre-outburst phase, and it provides the first opportunity to profile the burst phase of accretion across all wavelengths. We detected a number of lines such as $H{\alpha}$, $H{\beta}$, Fe II ${\lambda}$ 5018, Mg I ${\lambda}$ 5183, Na I D doublets, and metallic photospheric lines. In this work, we focus on the time variations of those spectral lines to understand the accretion process of HBC 722.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.7
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• pp.742-752
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• 1992

In this paper, a space vector concept is generalized for PWM(pulse-width modulated) inverters and PWM rectifiers with current link and voltage link respectively. Through representing three-phase variables as a space vector, we propose space vector modulations for PWM voltage and current source inverters, and PWM rectifiers with current link and voltage link. For these types, switching states of the switches are systematically analyzed from tables. It is shown in three-phase PWM rectifiers that power factor of the line current and output dc voltage can be controlled arbitrarily. The PWM rectifier with current link is also given as an example system.