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S.-J. Lee,Suguru Sato,Tomohiko Niizeki,Hideto Yanagihara,Eiji Kita,Chiharu Mitsumata 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
A numerical simulation of magnetic materials with random magnetic anisotropy was performed. The magnetization of an assembly of magnetically-interacting grains with randomly-oriented uniaxialanisotropy was calculated using the Landau-Lifshitz-Gilbert equation. For simplicity in thesimulation, the magnetizations in a grain were assumed to be aligned in the same direction; thisassumption is known as the single spin model. The interaction at the interface of the grains wastaken into account by including an interaction energy between the unit vectors that represent themagnetization directions of the grains. Calculations were carried out for an N × N × N system,where the grain sizes D ranged from 5 to 40 nm and N ranged from 10 to 80. The relation betweenthe coercive forces HC and the grain size is represented by HC ~ Dk. For the case of N = 10,k = 5.7, which corresponds to the primitive theory of the random anisotropy model (RAM) wherek = 6. As N increased, k decreased slightly from 5.7 to 4.2. The gradient of the log-log plot of thecoercive force versus the grain size (d logHC/d logD) was deduced by smoothing the data and wasfound to have a peak value of approximately 6. This result suggests that the RAM is supported bythe simulation within the range of grain sizes where the peak was observed.
Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU<sub>2</sub>
Kuroda, Daisuke,Ishiguro, Masateru,Watanabe, Makoto,Hasegawa, Sunao,Sekiguchi, Tomohiko,Naito, Hiroyuki,Usui, Fumihiko,Imai, Masataka,Sato, Mitsuteru,Kuramoto, Kiyoshi EDP Sciences 2018 Astronomy and astrophysics Vol.611 No.-
<P>We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the <I>R</I>C band and 44.0 ± 0.6% in the <I>V</I> band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (<0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.</P>