• Title, Summary, Keyword: Gravitational Field

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Dynamics and control of a large spacecraft with flexible appendages in gravitational field

  • Nohmi, Masahiro;Uchiyama, Masaru
    • 제어로봇시스템학회:학술대회논문집
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    • pp.368-371
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    • 1995
  • This paper describes dynamic analysis and attitude control of a large spacecraft with flexible appendages in gravitational field. The effect of attitude control and vibration control of flexible appendages in gravitational field has been clarified. We demonstrate some simulations in gravitational field for some cases, and suggest the effects of gravitational torque, parameters of flexible appendages, attitude control and vibration control of flexible appendages.

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ASTIGMATIC PROPERTY OF N-BODY GRAVITATIONAL LENS

  • Chang, Kyong-Ae
    • Journal of The Korean Astronomical Society
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    • v.19 no.1
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    • pp.11-14
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    • 1986
  • It is shown in this paper that the astigmatic property of single gravitational lens in static bounded gravitational field can be retained, if n-gravitating body as a whole acts simultaneously as gravitational lens.

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CAUSTIC AND IMAGE PROPERTIES OF GRAVITATIONALLY BENDING LIGHT RAYS

  • Chang, Kyong-Ae
    • Journal of The Korean Astronomical Society
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    • v.19 no.2
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    • pp.63-68
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    • 1986
  • In this paper we deal with the orientation and the deformation of the circular light bundle passing in a static bounded gravitational field. The properties of caustic of the gravitational lens are discussed.

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Gravitational Wave Emission from Pulsars with Glitches

  • Kim, Jin-Ho;Lee, Hyung-Mok
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.1
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    • pp.47.2-47.2
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    • 2011
  • Gravitational waves from the pulsar glitch can be detected by next generation gravitational wave observatories. We investigate characteristics of the modes that can emit the gravitational waves excited by three different types of perturbations satisfying conservation of total rest mass and angular momentum. These perturbations mimic the pulsar glitch theories i.e., change of moment of inertia due to the star quakes or angular momentum transfer by vortex unpinning at crust-core interface. We carry out numerical hydrodynamic simulations using the pseudo-Newtonian method which makes weak field approximation for the dynamics, but taking all forms of energies into account to compute the Newtonian potential. Unlike other works, we found that the first and second strongest modes that give gravitational waves are $^2p_1$ and $H_1$ rather than$^2f$. We also found that vortex unpinning model excites the inertial mode in quadrupole moment quite effectively. The inertial mode may evolve into the non-axisymmetric r-mode.

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UNVEILING THE PROPERTIES OF FLS 1718+59: A GALAXY-GALAXY GRAVITATIONAL LENS SYSTEM

  • TAAK, YOON CHAN;IM, MYUNGSHIN
    • Publications of The Korean Astronomical Society
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    • v.30 no.2
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    • pp.401-403
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    • 2015
  • We present the results of the analysis of FLS 1718+59, a galaxy-galaxy gravitational lens system in the Spitzer First Look Survey (FLS) field. A background galaxy ($z_s=0.245$) is severely distorted by a nearby elliptical galaxy ($z_l=0.08$), via gravitational lensing. The system is analysed by several methods, including surface brightness fitting, gravitational lens modeling, and spectral energy distribution fitting. From Galfit and Ellipse we measure basic parameters of the galaxy, such as the effective radius and the average surface brightness within it. gravlens yields the total mass inside the Einstein radius ($R_{Ein}$), and MAGPHYS gives us an estimate of the stellar mass inside $R_{Ein}$. By comparing these parameters, we confirm that the lens galaxy is an elliptical galaxy on the Fundamental Plane and calculate the stellar mass fraction inside $R_{Ein}$, and discuss the results with regards to the initial mass function.

Analysis of a New Gravitational Lens FLS 1718+59

  • Taak, Yoon Chan;Im, Myungshin
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.2
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    • pp.89.2-89.2
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    • 2012
  • We present our analysis of a newly discovered galaxy-galaxy gravitational lens system in the First Look Survey (FLS) field. This object shows a highly distorted background galaxy (z=0.245) image by a nearby elliptical galaxy (z=0.08), which can be interpreted as a result of gravitational lensing. We model the lens with elliptical isothermal sphere model, and present the mass and potential distribution of the system.

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Size Determination of Pollens Using Gravitational and Sedimentation Field-Flow Fractionation

  • Kang, Dong-Young;Son, Min-Seok;Eum, Chul-Hun;Kim, Won-Suk;Lee, Seung-Ho
    • Bulletin of the Korean Chemical Society
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    • v.28 no.4
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    • pp.613-618
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    • 2007
  • Pollens are known to be an allergen. They penetrate human respiratory system, triggering a type of seasonal allergic rhinitis called pollen allergy (hey fever). The purpose of this study is to test two field-flow fractionation (FFF) techniques, gravitational FFF (GrFFF) and sedimentation FFF (SdFFF), for their applicability to sizecharacterization of micron-sized pollens. Both GrFFF and SdFFF are elution techniques, providing sequential elution of particles based on size. They allow the size distribution as well as the mean size of the sample to be determined from the elution time. In this study, GrFFF and SdFFF were used to determine the size distribution of Paper Mulberry and Bermuda Grass pollens. For the Paper Mulberry pollen, the mean size obtained by GrFFF is 12.7 μm, and agrees rather well with the OM data with the relative error of 8.0%. For the Bermuda Grass pollen, the mean size obtained by GrFFF is 32.6 μm with the relative error of 12.3%. The mean sizes determined by SdFFF are 12.4 (relative error = 10.1%) and 27.1 μm (relative error = 5.2%) for the Paper Mulberry and the Bermuda Grass pollen, respectively. Although SdFFF tends to yield more accurate size distribution due to lower band broadening under the field strength higher than 1 G, the sizes determined by GrFFF were not significantly different from those by SdFFF.

Gravitational Microlensing Astrophysics

  • Han, Cheongho
    • The Bulletin of The Korean Astronomical Society
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    • v.41 no.2
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    • pp.29.1-29.1
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    • 2016
  • I introduce the field of gravitational microlensing that I have worked on for more than 2 decades. I describe how microlensing can be applied to various fields in astrophysics including dark matter, Galactic structure, binary objects, and extrasolar planets and present my scientific achievements in the individual fields. I start with a description of basic microlensing physics and state how microlensing can be applied to various fields. Finally, I briefly describe ongoing efforts and future projects in microlensing.

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