Valence-band electronic structure of YbInCu 4 has been investigated by means of high-resolution photoemission spectroscopy with an excitation energy of hϭ800 eV. With decreasing temperature from 50 to 40 K, the intensity of the Yb 2ϩ 4 f peak increases remarkably, while that of the Yb 3ϩ 4 f multiplet structures decreases due to the valence transition at 42 K. The Yb valence directly derived from the photoemission spectra is z ϳ2.81 at 100 K, decreases continuously to 50 K and changes sharply to zϳ2.68 at 40 K. The larger valence compared with the other photoemission experiments with smaller probing depth suggests that there is a subsurface region in YbInCu 4 . We have also found that the Yb 3ϩ 4 f multiplet structures shift toward the deeper binding-energy side by ϳ50 meV with decreasing temperature from 50 to 40 K. This energy shift is assumed to reflect that the energy to add the bare Yb 4 f hole increases for the low-temperature region in accordance with the valence transition.
The serum antibody titers against oral streptococci were studied by enzyme-linked immunosorbent assay (ELISA) both in patients with Behcet's disease (BD) and control groups. The patients with BD showed significantly higher antibody titers to S. sanguis strains 113-20, 114-23, and 118-1 which were isolated from patients with BD, in comparison with control groups. Also, the reactions of hightitered sera to the crude cell wall and soluble (or membrane) fractions of the 113-20 strain were observed by western blot test. The sera of the patients with BD demonstrated strong bands of approximately 36 kDa, 82 kDa, and 87 kDa in the crude cell wall fractions, and many bands of 80 kDa to 150 kDa in the membrane fractions, indicating that these proteins are the ones leading the high antibody titers to this bacterium in the sera of patients with BD.
The DNA homology and cell wall sugar constituents of eight Streptococcus sanguis(-like) strains, three isolated from the patients with Behcet's disease (BD114-23, BD113-20, BD118-1), two from patients with Kawasaki disease (MCLS-1, MCLS-2), and three type and reference strains of ATCC (ATCC10556T: S. sanguis, ATCC10557: S. oralis, and ATCC10558T: S. gordonii) were analyzed. Strains BD114-23 and BD118-1 showed high DNA homology to ATCC10556T, and their cell wall constituents were identical. Conversely, BD113-20, MCLS-1, MCLS-2, and ATCC10557 showed little DNA homology to ATCC105561. and ATCC10558T, but showed approximately 50 to 60% homology to each other. The cell wall constituents of BD113-20, MCLS-1, MCLS-2, and ATCC10557, however, were somewhat different, indicating that some of the clinical isolates have different characters from those of the three ATCC strains.
Yb 3d and valence-band photoemission spectra of the first-order valence-transition compound YbInCu4 have been measured with hard x ray at an excitation energy of 5.95 keV. Abrupt changes are clearly observed in both spectra around the transition temperature T(V)=42 K, in comparison with ultraviolet and soft x-ray photoemission (VUV-PES and SX-PES) spectra. From the Yb 3d spectra, the Yb valence has been estimated to be approximately 2.90 from 220 down to 50 K and approximately 2.74 at 30-10 K. We propose that Yb 3d hard x-ray photoemission spectroscopy is a very powerful method to estimate the valence of Yb with high accuracy. On the other hand, the Yb2+ 4f-derived peaks in the valence-band spectra exhibit a remarkable enhancement below T(V). The shape of the valence-band spectra is different from those of the VUV-PES and SX-PES spectra above T(V), reflecting the In 5s and 5p contributions.
We have studied the unoccupied electronic structure of the band insulator CaTiO 3 , the Mott insulator YTiO 3 , and Y 0.61 Ca 0.39 TiO 3 with a metal-insulator transition ͑MIT͒ around 150 K by means of Ti 3p-3d resonant inverse photoemission spectroscopy ͑RIPES͒. The Ti 3d partial density of states of CaTiO 3 deduced from the on-and off-resonance RIPES spectra is in good agreement with results of a band-structure calculation, while that of YTiO 3 is explained based on a calculation with the dynamical mean-field theory taking into account an electron correlation. In the case of Y 0.61 Ca 0.39 TiO 3 , we have successfully observed the temperature dependence of RIPES spectra across MIT; the intensity of the incoherent part ͑a remnant of the upper Hubbard bands͒ relative to the coherent part ͑quasiparticle bands͒ is reduced with decreasing temperature from the insulator to metal phases.
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