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RISS 인기검색어
- 검색키워드
- 저자 : Kojima T. (검색결과 28 건)
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고재현,T.H. Kim,S. Kojima,K. Roleder,D. Rytz,C.J. Won,허남정,정종훈,구태영,S.B. Kim,박기복 한국물리학회 2012 Current Applied Physics Vol.12 No.4
The temperature variations of the elastic constant C11 and the corresponding acoustic attenuation coefficient of barium titanate single crystals grown by two different methods in the paraelectric phase were obtained in a wide temperature by means of Brillouin light scattering. Two phenomenological approaches were adopted to attempt to explain the anomalous change in C11 (denoted as DC11) in the paraelectric phase. ΔC11 exhibited a logarithmic variation as log[(T-T0)/T0] in a certain temperature range from Tc to about Tc+ 80 ℃ instead of the other variation of (T-T0) predicted by the mean-field approach. This temperature range was almost the same as the range where precursor dynamics were theoretically predicted to set in. The fact that the logarithmic variation was proposed for uniaxial systems might indicate that the correlated deformation of precursor polar clusters is tetragonal, as was suggested from nuclear magnetic resonance study [7].
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Ko, J.-H.,Kim, T.H.,Kojima, S.,Roleder, K.,Rytz, D.,Won, C.J.,Hur, N.J.,Jung, J.H.,Koo, T.-Y.,Kim, S.B.,Park, K. Elsevier 2012 Current Applied Physics Vol.12 No.4
<P><B>Abstract</B></P><P>The temperature variations of the elastic constant <I>C</I><SUB>11</SUB> and the corresponding acoustic attenuation coefficient of barium titanate single crystals grown by two different methods in the paraelectric phase were obtained in a wide temperature by means of Brillouin light scattering. Two phenomenological approaches were adopted to attempt to explain the anomalous change in <I>C</I><SUB>11</SUB> (denoted as Δ<I>C</I><SUB>11</SUB>) in the paraelectric phase. Δ<I>C</I><SUB>11</SUB> exhibited a logarithmic variation as log[(<I>T</I>−<I>T</I><SUB>0</SUB>)/<I>T</I><SUB>0</SUB>] in a certain temperature range from <I>T</I><SUB>c</SUB> to about <I>T</I><SUB>c</SUB>+80°C instead of the other variation of (<I>T</I>−<I>T</I><SUB>0</SUB>)<SUP><I>ζ</I></SUP> predicted by the mean-field approach. This temperature range was almost the same as the range where precursor dynamics were theoretically predicted to set in. The fact that the logarithmic variation was proposed for uniaxial systems might indicate that the correlated deformation of precursor polar clusters is tetragonal, as was suggested from nuclear magnetic resonance study <ce:cross-ref refid='bib7'>[7]</ce:cross-ref>.</P> <P><B>Highlights</B></P><P>► We measure the temperature variation of the elastic constant of barium titanate. ► The elastic constant shows logarithmic temperature variation in the paraelectric phase. ► The anomalous change of the elastic constant is related to the precursor dynamics.</P>
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atsushi Kojima,A. Itakura,H. Kakiuchi,H. Higaki,K. Ishii,M. Ichimura,M. Yoshikawa,N. Kaidou,S. Fujimoto,T. Cho,T. Yamaguchi,Y. Miyata 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
The radial particle flux induced by drift-type fluctuations is observed by use of a gold neutral beam probe in the tandem mirror GAMMA 10. When the drift waves are excited in the plasma, the measured phase difference between the density and potential fluctuations is not zero; the radial profile of the phase difference is not constant. This showed that the radial particle flux had some profile and then the density profile would be varied due to the radial particle transport induced by the fluctuations through the radial particle flux. Experimental results showed the density reduction due to the transport induced by the drift-type fluctuations. The phase difference is an important parameter to decide the radial particle flux. The profiles of the phase difference are measured to understand the decision mechanism of the phase difference. The radial profile of the phase difference is varied by the ion heating power, the density and the potential profiles. As a result, the phase difference had a correlation with the difference between the local drift frequency (the electron diamagnetic drift frequency and the E×B drift frequency) and the observed frequency.
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Kim, T.H.,Shibata, T.,Kojima, S.,Shin, D.M.,Hwang, Y.H.,Ko, J.H. Elsevier 2014 Current Applied Physics Vol.14 No.7
The vitrification process of racemic RS- and enantiomorphic S-ibuprofen was studied by using Brillouin light scattering and modulated differential scanning calorimetry (DSC). The sound velocity and the attenuation coefficient of both compounds were determined for the first time in the glassy, supercooled liquid and liquid states. The sound velocity and the hypersonic damping were similar between the two ibuprofen pharmaceuticals over the whole investigated temperature range including glassy, supercooled liquid and liquid states. The thermal expansion coefficient of the RS-ibuprofen was smaller than that of the S-ibuprofen, which suggests that the intermolecular force of the former is slightly stronger than the latter. The thermal relaxation times derived from the modulated DSC were consistent with the dielectric relaxation times in both RS- and S-ibuprofens. The fragility index of S-ibuprofen just above the glass transition was determined to be 73, which was smaller compared to the value of RS-ibuprofen, 89. This difference in the fragility indicates that the decrease in the fragility of S-ibuprofen compared to the racemic one may improve its stability of the amorphous state below the glass transition temperature against crystallization.
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X-ray and Neutron Structure Analysis of MeHPLN in the Low Temperature Phase
R. Kiyanagi,A. Kojima,H. Kimura,M. Watanabe,S. Kumazawa,T. Sugawara,T. Hayashide,T. Mochida,Y. Noda 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Structure analyses of 5-Methyl-9-hydroxyphenalenon(C14H10O2, MeHPLN) in the low temperature phase were performed by X-ray and neutron scattering experiments. It is found that the space group is P21/c with a super cell (a 2b c) and there are two types of molecules in the unit cell. In one of the independent molecules, hydrogen atoms in hydrogen-bond region occupy two sites as same as in the room temperature phase. On the other hand, in another independent molecules, hydrogen atoms in hydrogen-bond region clearly show ordering feature. In these ordered hydrogen atoms, there are obvious discrepancy beween electron and nuclear distribution, and hence static electrical dipolemoments exist in hydorgen-bond region with an antiferroelectric ordering.
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