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        검색결과 4

        1.
        2015.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The galactic magnetic field (GMF) and the intergalactic magnetic field (IGMF) affect the propagation of ultra-high energy cosmic rays (UHECRs) from the source to us. Here we examine the in uences of the GMF/IGFM and the dependence of their sky distribution on galactic latitude, b. We analyze the correlation between the arrival direction (AD) of UHECRs observed by the Pierre Auger Observatory and the large-scale structure of the universe in regions of sky divided by b. Specifically, we compare the AD distribution of observed UHECRs to that of mock UHECRs generated from a source model constructed with active galactic nuclei. Our source model has the smearing angle as a free parameter that re ects the de ection angle of UHECRs from the source. The results show that larger smearing angles are required for the observed distribution of UHECRs in lower galactic latitude regions. We obtain, for instance, a 1σ credible interval for smearing angle of 0° ≤ θs ≤ 72° at high galactic latitudes, 60° < b ≤ 90°, and of 75° ≤ θs ≤ 180°, -30° ≤ b ≤ 30°, at low galactic latitudes, respectively. The results show that the in uence of the GMF is stronger than that of the IGMF. In addition, we can estimate the strength of GMFs by these values; if we assume that UHECRs would have heavier nuclei, the estimated strengths of GMF are consistent with the observational value of a few μG. More data from the future experiments may make UHECR astronomy possible.
        3,000원
        2.
        2010.10 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Magnetars are neutron stars possessing a magnetic field of about 1014-1015 G at the surface. Thermodynamic properties of neutron star matter, approximated by pure neutron matter, are considered at finite temperature in strong magnetic fields up to 1018 G which could be relevant for the inner regions of magnetars. In the model with the Skyrme effective interaction, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter corresponds to the case when the majority of neutron spins are oriented opposite to the direction of the magnetic field (i.e. negative spin polarization). Moreover, starting from some threshold density, the self-consistent equations have also two other branches of solutions, corresponding to positive spin polarization. The influence of finite temperatures on spin polarization remains moderate in the Skyrme model up to temperatures relevant for protoneutron stars. In particular, the scenario with the metastable state characterized by positive spin polarization, considered at zero temperature in Phys. Rev. C 80, 065801 (2009), is preserved at finite temperatures as well. It is shown that, above certain density, the entropy for various branches of spin polarization in neutron matter with the Skyrme interaction in a strong magnetic field shows the unusual behavior, being larger than that of the nonpolarized state. By providing the corresponding low-temperature analysis, we prove that this unexpected behavior should be related to the dependence of the entropy of a spin polarized state on the effective masses of neutrons with spin up and spin down, and to a certain constraint on them which is violated in the respective density range.
        4,000원
        3.
        2006.09 구독 인증기관·개인회원 무료
        The mechanical properties of ceramics materials can be tailored by designing their microstructures. We have reported that development of texture can be controlled by slip casting in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina. A strong magnetic field of 12T was applied to the suspension indcuding alumina powder to rotate each particle during slip casting. The sintering was conducted at the desired temperature in air without a magnetic field. C-axis of alumina was parallel to the magnetic field. Bending strength of textured alumina depended on the direction of oriented microstructure.
        4.
        2006.09 구독 인증기관·개인회원 무료
        This work will report a highly textured β-Si3N4 ceramic by aqueous slip casting in a magnetic field and subsequent pressureless sintering, Effects of the sintering aids, polymer dispersant, pH and stirring time on the stability of the Si3N4 slurries were studied. The textured β-Si3N4 with 97 % relative density could be obtained by slip casting in a magnetic field of 12 T and subsequent sintering at 1800 oC for 1 h. The textured microstructure is featured by the alignment of c-axis of β-Si3N4 crystals perpendicular to the magnetic field, and the Lotgering orientation factor, f, is determined to be 0.8.