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X-ray absorption spectra at the Ti K-edge of a SrTiO

X-ray absorption spectra under uniaxial pressure were measured at the Ti K-edge of a SrTiO3 single crystal in order to obtain direct evidence for the ferroelectric transition that is expected on the basis of second harmonic generation studies. A uniaxial pressure was applied perpendicular to the ab-plane. The pre-edge peak, which corresponds to Ti 3d e g -O 2pσ bonding, shows little change across the transition temperature of 40 K at 1 GPa. This indicates that a local electric dipole moment is not induced under uniaxial pressure, as opposed to the macroscopic ferroelectric moments that are predicted to be induced along the ab-plane.

X-ray absorption spectra at the Ti K-edge of a SrTiO3 single crystal under uniaxial pressure were measured to obtain evidence of uniaxial pressure-induced polarization predicted in SrTiO3 from the electronic viewpoint. The pre-edge 3d-e g peak decreases in intensity with increasing uniaxial pressure, together with an energy shift to higher energy side. Contrary to uniaxial deformation, these changes were independent of incident x-ray polarization. This implies the presence of a mechanism that maintains the isotropic coordination environment around a Ti atom, i.e. a tilt and rotation of the TiO6 octahedron accompanied by its isotropic shrinkage, hence the local polarization essential to the ferroelectric order cannot be observed.

We measure the Ti Kβ resonant X-ray emission spectra of SrTiO3 in the quantum paraelectric phase. We find that charge transfer (CT) excitation is affected by temperature decrease and UV irradiation, which provides direct evidence of the fact that the induced electric dipole moment is derived from the Ti off-center displacement. The UV-assisted dipole moments are aligned parallel to the applied DC electric field, as inferred from the additional change in the CT peak. We conclude that the local polar region formed by UV irradiation evolves under DC field application at low temperature.

The GPR119 was recently shown to be activated by oleoylethanolamide (OEA), a naturally occurring bioactive lipid with hypophagic and anti-obesity effects. In this study, we have cloned and characterized its murine counterpart, Gpr119. The full-length cDNA contained an open reading frame of 1008 bp encoding a 335-amino acid protein. The genomic organization of Gpr119 was unique, having a 3′-untranslated second exon that was also involved in an alternative splicing event. Gene expression analyses confirmed its specific expressions in pancreatic islets and two endocrine cell-lines, MIN6 and αTC1. Immunohistochemistry and double-immunofluorescence studies using a specific antibody revealed the predominant Gpr119 localization in pancreatic polypeptide (PP)-cells of islets. No definitive evidence of Gpr119-immunoreactivity in adult β- or α-cells was obtained. The Gpr119 mRNA levels were elevated in islets of obese hyperglycemic db/db mice as compared to control islets, suggesting a possible involvement of this receptor in the development of obesity and diabetes.