Results from Super-Kamiokande and K2K

Results from Super-Kamiokande-I’s entire 1496 live days of solar neutrino data are presented, including the absolute flux, energy spectrum, zenith angle (day/night) and seasonal variation. The possibility of MSW and vacuum oscillations is discussed in light of these results. Results from the first 1289 days of Super-K-I’s atmospheric neutrino analysis are also presented, including the evidence for ν_μ →ν _τ oscillations, against ν_μ → ν_sterile oscillations, and the current limits on proton decay. Finally, results based on 56 × 10¹⁹ protons on target are given for the K2K long-baseline neutrino oscillation experiment.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Neural stem cells from protein tyrosine phosphatase sigma knockout mice generate an altered neuronal phenotype in culture

Background  

The LAR family Protein Tyrosine Phosphatase sigma (PTPσ) has been implicated in neuroendocrine and neuronal development, and shows strong expression in specific regions within the CNS, including the subventricular zone (SVZ). We established neural stem cell cultures, grown as neurospheres, from the SVZ of PTPσ knockout mice and sibling controls to determine if PTPσ influences the generation and the phenotype of the neuronal, astrocyte and oligodendrocyte cell lineages.     

Double-spin-flip resonance of rhodium nuclei at positive and negative spin temperatures

Sensitive SQUID-NMR measurements were used to study the mutual interactions in the highly polarized nuclear-spin system of rhodium metal. The dipolar coupling gives rise to a weak double-spin-flip resonance. The observed frequency shifts allow deducing separately the dipolarlike contribution and the isotropic exchange term. For the first time, such measurements were extended to negative absolute temperatures as well. We find an effective dipolar moment 0. 10&mgr;(N) of which about 15% is attributed to a conduction electron mediated pseudodipolar interaction. The isotropic exchange is described by R = -0.9+/-0.1.     

Neutron thermometry on polarized silver nuclei at sub-microkelvin spin temperatures

We have utilized both neutron transmission and neutron diffraction to measure the spin polarization in a single crystal of ¹⁰⁹Ag, whereby the nuclear spin temperature could be obtained. Transmission of a polarized neutron beam provides an accurate and convenient primary thermometer. The feasibility of unpolarized neutron transmission was demonstrated as well. The diffraction measurements were strongly influenced by extinction, whence this method had to be calibrated against another thermometer. In this way we obtained information about extinction in the crystal.