We present57 Fe-NMR measurements of the novel normal and superconducting-state characteristics of the iron-arsenide superconductor Ba 0:6 K 0:4 Fe 2 As 2 (T c ¼ 38 K). In the normal state, the measured Knight shift and nuclear spin-lattice relaxation rate (1=T 1 ) demonstrate the development of wave-number (q)-dependent spin fluctuations, except at q ¼ 0, which may originate from the nesting across the disconnected Fermi surfaces. In the superconducting state, the spin component in the 57 Fe-Knight shift decreases to almost zero at low temperatures, evidencing a spin-singlet superconducting state. The 57 Fe-1=T 1 results are totally consistent with a s AE -wave model with multiple full gaps in the strong coupling regime. We demonstrate that the respective 1=T 1 data for Ba 0:6 K 0:4 Fe 2 As 2 and LaFeAsO 0:7 , which seemingly follow a T 5 -and a T 3 -like behaviors below T c , are consistently explained in terms of this model only by changing the size of the superconducting gap. The recent discovery of superconductivity in the iron (Fe)-based oxypnictide LaFeAsO 1Àx F x at the superconducting (SC) transition temperature T c ¼ 26 K has provided a new route toward the realization of high-T c superconductivity.1) The mother material, LaFeAsO, exhibits a structural phase transition from tetragonal (P4=nmm) to orthorhombic (Cmma) form at T $ 155 K and then exhibits a striped antiferromagnetic (AFM) order with Q ¼ ð0; Þ or ð; 0Þ and T N $ 140 K.2) The calculated Fermi surfaces (FSs) for undoped LaFeAsO consist of two small electron cylinders around the tetragonal M point and two hole cylinders, plus a heavy 3D hole pocket, around the À point.3) Measurements of the nuclear spin-lattice relaxation rate (1=T 1 ) for the LaFeAsO system in the SC state revealed the lack of a coherence peak below T c and the presence of T 3 -like behavior, suggesting an unconventional SC nature. [4][5][6]

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We discuss the novel superconducting characteristics and unusual normal-state properties of iron (Fe)-based pnictide superconductors REFeAsO 1−y (RE=La,Pr,Nd) and Ba 0.6 K 0.4 Fe 2 As 2 (T c = 38 K) by means of 57 Fe-NMR and 75 As-NQR/NMR. In the superconducting state of LaFeAsO 0.7 (T c = 28 K), the spin component of the 57 Fe-Knight shift decreases to almost zero at low temperatures, which provide firm evidence of the superconducting state formed by spin-singlet Cooper pairing. The nuclear spin-lattice relaxation rates (1/T 1 ) in LaFeAsO 0.7 and Ba 0.6 K 0.4 Fe 2 As 2 exhibit a T 3 -like dependence without a coherence peak just below T c , indicating that an unconventional superconducting state is commonly realized in these Fe-based pnictide compounds. All these events below T c are consistently argued in terms of an extended s ± -wave pairing with a sign reversal of the order parameter among Fermi surfaces. In the normal state, 1/T 1 T decreases remarkably upon cooling for both the Fe and As sites of LaFeAsO 0.7 . In contrast, it gradually increases upon cooling in Ba 0.6 K 0.4 Fe 2 As 2 . Despite the similarity between the superconducting properties of these compounds, a crucial difference was observed in their normal-state properties depending on whether electrons or holes are doped into the FeAs layers. These results may provide some hint to address a possible mechanism of Fe-based pnictide superconductors.

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In seismic isolation system for lightweight structures, sufficient effect is not acquired when laminated rubber bearings are used. It is because that the pressure on the surface is small. Since sliding base isolators expect the performance even when the pressure on the surface is small, sliding base isolators are used for lightweight structures. Generally, the frictional coefficients of sliding base isolators are assigned in the range 0.01-0.10. However, it is examined by three-dimensional finite element method that it is effective in the case of a big earthquake even if the frictional coefficients are 0.20. The purpose of this study is to examine the effect of base-isolated structures using sliding bearings by experimental and analytical methods. The experiment by horizontal earthquake excitation (modified JMA KOBE 1995) was conducted, and the frictional coefficient was identified. As a result, the values are identified around 0.20. By using the identified frictional coefficients, the response reduction effect of multi-degree-of-freedom system model is investigated by a simulation. The responses are reduced by in the range 50-80%.