Magnetic-Field-Induced 4f-Octupole in CeB6 Probed by Resonant X-ray Diffraction

CeB6, a typical Gamma_8-quartet system, exhibits a mysterious antiferroquadrupolar ordered phase in magnetic fields, which is considered as originating from the T_{xyz}-type magnetic octupole moment induced by the field. By resonant x-ray diffraction in magnetic fields, we have verified that the T_{xyz}-type octupole is indeed induced in the 4f-orbital of Ce with a propagation vector (1/2, 1/2, 1/2), thereby supporting the theory. We observed an asymmetric field dependence of the intensity for an electric quadrupole (E2) resonance when the field was reversed, and extracted a field dependence of the octupole by utilizing the interference with an electric dipole (E1) resonance. The result is in good agreement with that of the NMR-line splitting, which reflects the transferred hyperfine field at the Boron nucleus from the anisotropic spin distribution of Ce with an O_{xy}-type quadrupole. The field-reversal method used in the present study opens up the possibility of being widely applied to other multipole ordering systems such as NpO2, Ce_{x}La_{1-x}B_{6}, SmRu_{4}P_{12}, and so on.Comment: 5 pages, 4 figures, submitte

Evidence for short-range antiferromagnetic fluctuations in Kondo-insulating YbB12

The spin dynamics of mixed-valence YbB12 has been studied by inelastic neutron scattering on a high-quality single crystal. In the Kondo-insulating regime realized at low temperature, the spectra exhibit a spin-gap structure with two sharp, dispersive, in-gap excitations at E = 14.5 and approximately 20 meV. The lower mode is shown to be associated with short-range correlations near the antiferromagnetic wave vector q0 = (1/2, 1/2, 1/2). Its properties are in overall agreement with those expected for a "spin exciton'' branch in an indirect hybridization gap semiconductor.Comment: 4 pages, 4 figures ; submitted to Physical Review Letter

Are pregnancy-associated plasma protein-A (PAPP-A) and CA 125 measurements after IVF-ET possible predictors of early pregnancy wastage?

Pregnancy-associated plasma protein-A (PAPP-A), a macromolecular glycoprotein of placental origin, was reported to be depressed in established ectopic pregnancies. CA 125 is a known marker for ovarian cancer found to be elevated during the first trimester of pregnancy and in women with pelvic inflammatory disease. The present study investigated the usefulness of these parameters to predict the outcome of pregnancy in asymptomatic patients with a positive pregnancy test after in-vitro fertilization and embryo transfer (IVF-ET). Blood samples (n = 159) were obtained at different periods of time post-ET from 39 women, 21 of whom experienced a normal pregnancy, 12 had an intrauterine abortion and six had an ectopic pregnancy. PAPP-A and CA 125 were measured by radioimmunoassays. From day 30 onwards in normal pregnancies, PAPP-A was significantly increased over non-pregnant controls. In the spontaneous abortion group, the levels of PAPP-A were significantly lower than in normal pregnancy but higher than in non-pregnant controls. In ectopic pregnancy, PAPP-A remained at the level of non-pregnant controls throughout the entire observation period. CA 125 was significantly increased in all types of pregancy. However, in two cases of hyperstimulation followed by a normal pregancy and in four cases of ectopic pregnancy with signs of peritoneal irritation (hydrosalpinx, ruptured ectopic or salpingitis) the levels of CA 125 were 15-50 times higher than in normal pregnancies. PAPP-A levels < 10th percentile, measured after 30 days post-ET, were an excellent diagnostic parameter for ectopic pregnancy or intrauterine abortion with a sensitivity of 87.5% and a predictive value of disease of 100%. In contrast, CA 125 determinations had no diagnostic value and were only indicative of peritoneal inflammation in either normal or pathological pregnancies. It is concluded that PAPP-A is a good parameter by which to monitor post-implantation viability of embryos in IVF-ET patient

On the porosity of barrier layers

Barrier layers are defined as the layer between the pycnocline and the thermocline when the latter are different as a result of salinity stratification. We present a revisited 2-degree resolution global climatology of monthly mean oceanic Barrier Layer (BL) thickness first proposed by de Boyer Montégut et al. (2007). In addition to using an extended data set, we present a modified computation method that addresses the observed porosity of BLs. We name porosity the fact that barrier layers distribution can, in some areas, be very uneven regarding the space and time scales that are considered. This implies an intermittent alteration of air-sea exchanges by the BL. Therefore, it may have important consequences for the climatic impact of BLs. Differences between the two computation methods are small for robust BLs that are formed by large-scale processes. However, the former approach can significantly underestimate the thickness of short and/or localized barrier layers. This is especially the case for barrier layers formed by mesoscale mechanisms (under the intertropical convergence zone for example and along western boundary currents) and equatorward of the sea surface salinity subtropical maxima. Complete characterisation of regional BL dynamics therefore requires a description of the robustness of BL distribution to assess the overall impact of BLs on the process of heat exchange between the ocean interior and the atmosphere

Spontaneous deformation of the Fermi surface due to strong correlation in the two-dimensional t-J model

Fermi surface of the two-dimensional t-J model is studied using the variational Monte Carlo method. We study the Gutzwiller projected d-wave superconducting state with an additional variational parameter t'_v corresponding to the next-nearest neighbor hopping term. It is found that the finite t'_v<0 gives the lowest variational energy in the wide range of hole-doping rates. The obtained momentum distribution function shows that the Fermi surface deforms spontaneously. It is also shown that the van Hove singularity is always located very close to the Fermi energy. Using the Gutzwiller approximation, we show that this spontaneous deformation is due to the Gutzwiller projection operator or the strong correlation.Comment: 4 pages, 3 eps figures, revte