Koichi Arai

Superconductivity and magnetic fluctuations in Cd(2))Re(2)O(7) via Cd nuclear magnetic resonance and re nuclear quadrupole resonance.

We report Cd NMR and Re NQR studies on Cd2Re2O7, the first superconductor among pyrochlore oxides Tc=1 K. Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below Tc exhibits a pronounced coherence peak and behaves within the weak-coupling BCS theory with nearly isotropic energy gap. Cd NMR results point to moderate ferromagnetic enhancement at high temperatures followed by rapid decrease of the density of states below the structural transition temperature of 200 K.

NMR observation of rattling phonons in the pyrochlore superconductor KOs2O6.

We report nuclear magnetic resonance studies on the beta-pyrochlore oxide superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused by fluctuations of the electric field gradient, which we ascribe to highly anharmonic low frequency oscillation (rattling) of K ions. A phenomenological analysis shows a crossover from overdamped to underdamped behavior of the rattling phonons with decreasing temperature and its sudden sharpening below the superconducting transition temperature T(c). Suppression of the Hebel-Slichter peak in the relaxation rate at the O sites below T(c) also indicates strong electron-phonon coupling.

A Novel Ordered Phase in SrCu2(BO3)2 under High Pressure

We report results of 11 B NMR and susceptibility measurements on the quasi two-dimensional frustrated dimer spin system SrCu 2 (BO 3 ) 2 under high pressure. At 2.4 GPa and in a magnetic field of 7...

Structural transition in the pyrochlore superconductor Cd2Re2O7 observed by Re nuclear quadrupole resonance

We report results of nuclear quadrupole resonance (NQR) experiments on the Re sites in the pyrochlore superconductor Cd2Re2O7. A discontinuous change of the NQR spectrum was observed near T s2 = 120 K, confirming the first-order structural transition in addition to the already known second-order transition at T s1 = 200 K. The spin?lattice relaxation rate at the Re sites shows a steep increase above T s2, in contrast to the reported results for the Cd sites, suggesting changes of orbital fluctuations.

Characterization of immunoreactive endothelin in human urine

We developed three antibodies, specific and sensitive to endothelin-1 (ET-1), and established two sandwich and three competitive enzyme immunoassays (EIAs). By using these EIAs, large immunoreactive ET (IR-ET) of molecular weight 10 k Da was identified as a main component of IR-ETs in human urine. This large IR-ET, which reacted with two antibodies specific for N-terminal region of ET-1 but not with the antibody against C-terminal peptide of ET-1, was partially purified by six-step procedure and examined by Western blotting after SDS polyacrylamide gel electrophoresis. The large IR-ET was detected as a single band at molecular weight of 10 k Da both in reduced and non-reduced conditions. From these results, the large IR-ET was thought to consist of a single polypeptide chain and possess the steric restricted N-terminal region of ET-1.

Pyrogenic action of endothelin in conscious rabbit

Injection of 0.3 nmol/kg endothelin(ET)-1 into the ear vein of conscious rabbits induced a significant increase in body temperature. ETB receptor specific agonist, namely 4-Ala-ET-1, also caused an elevation of the body temperature in a dose-dependent manner by injection into the ear vein of rabbit. These results suggest that ET play important roles in regulation of body temperature through selective stimulation of ETB receptor.

Magnetism, structure, and superconductivity of Cd2Re2O7 pyrochlore: Cd and Re NMR

Abstract We present Cd and Re NMR results on Cd2Re2O7, the first and as yet the only superconductor (T c ≃1 K ) among pyrochlore oxides. Re spin-lattice relaxation rate below Tc exhibits a pronounced coherence peak and follows the weak-coupling BCS with nearly isotropic energy gap. Cd NMR points to moderate ferromagnetic enhancement at high temperatures followed by rapid decrease of the density of states below 200 K , and to strong suppression of spin fluctuations below ∼75 K . Cd and Re NMR spectra reveal two structural phase transitions, one at 200 K and another at 120 K . Re NQR rules out any magnetic or charge order.