Electric polarization memory effect in a magnetoelectric multiferroic CuFe1−xGaxO2

Magnetic oxide CuFeO₂ is a magnetoelectric multiferroic with new type of spin–polarization coupling different from that in the spin-current mechanism, where magnetic field-induced or nonmagnetic impurity-induced proper helical magnetic ordering generates a spontaneous electric polarization parallel to the helical axis. Using a CuFe_1−xGa_xO₂ sample with x=0.035, in which the single ferroelectric phase is realized below T_N8 K in zero magnetic field unlike CuFe_1−xAl_xO₂, we have performed pyroelectric current, thermally stimulated current (TSC) and polarized neutron diffraction measurements to study a memory effect that the electric polarization is partially preserved even for 2nd-cooling from above T_N without poling electric field. It was found that the charge trapped during 1st-cooling with poling electric field, which is released as TSC on heating, plays an important role in the memory effect.     

Supramolecular Light‐Harvesting Antennas of Metal‐Coordinated Bis(8‐Hydroxyquinoline)‐Substituted Porphyrin Networks

Artificial antenna complexes of metal‐coordinated bis(8‐hydroxyquinoline)‐substituted porphyrin networks that mimic antenna chromophores in plants were organized on titanium dioxide electrodes in photoelectrochemical cells. The generated photocurrents can be optimized according to the two ways of porphyrin self‐assembly due to the “antenna effect”: changing the number of assembled porphyrin monolayers and the number of generations of the metal‐coordinated porphyrin networks.     

Sidelobe reduction of tightly focused radially higher-order Laguerre-Gaussian beams using annular masks

We report the reduction of sidelobes in tight focusing patterns of radially higher-order Laguerre-Gaussian (LG) beams with nonhelical phase structures. Numerical calculations based on the vectorial Debye theory reveal that a class of annular masks reduces sidelobes in the tight focusing patterns only for radially even-order LG beams. The present scheme produces small focal spots beyond the diffraction limit suitable for application to scanning microscopy, laser fine processing, etc.     

Iridium-catalyzed α-selective deuteration of alcohols

The development of chemoselective C(sp³)-H deuteration is of particular interest in synthetic chemistry. We herein report the α-selective, iridium(iii)-bipyridonate-catalyzed hydrogen(H)/deuterium(D) isotope exchange of alcohols using deuterium oxide (D₂O) as the primary deuterium source. This method enables the direct, chemoselective deuteration of primary and secondary alcohols under basic or neutral conditions without being affected by coordinative functional groups such as imidazole and tetrazole. Successful substrates for deuterium labelling include the pharmaceuticals losartan potassium, rapidosept, guaifenesin, and diprophylline. The deuterated losartan potassium shows higher stability towards the metabolism by CYP2C9 than the protiated analogue. Kinetic and DFT studies indicate that the direct deuteration proceeds through dehydrogenation of alcohol to the carbonyl intermediate, conversion of [Ir^III–H] to [Ir^III−D] with D₂O, and deuteration of the carbonyl intermediate to give the α-deuterated product.

An α-selective, iridium(iii)-bipyridonate-catalyzed hydrogen isotope exchange of alcohols using D₂O has been developed for the direct, chemoselective deuteration of primary and secondary alcohols, thereby providing deuterated bioactive molecules.     

Euler Products Beyond the Boundary

We investigate the behavior of the Euler products of the Riemann zeta function and Dirichlet L-functions on the critical line. A refined version of the Riemann hypothesis, which is named “the Deep Riemann Hypothesis”, is examined. We also study various analogs for global function fields. We give an interpretation for the nontrivial zeros from the viewpoint of statistical mechanics.     

Degeneration of weight spectral sequences

 A notion of morphism of semi-stable type is a higher dimensional analogue of semi-stable degeneration over the unit disc. For a proper surjective morphism of semi-stable type, the author constructed a cohomological mixed Hodge complex which gives a candidate of the limit of Hodge structures. In this article we define finite increasing filtrations on the cohomological mixed Hodge complex above and prove the E ₂ -degeneracy of the spectral sequences obtained from these filtrations. Received: 5 December 2000 / Revised version: 29 January 2002     

Transitive ensembles of random matrices related to orthogonal polynomials

Transitive correlations of eigenvalues for random matrix ensembles intermediate between real symmetric and hermitian, self-dual quaternion and hermitian, and antisymmetric and hermitian are studied. Expressions for exact n-point correlation functions are obtained for random matrix ensembles related to general orthogonal polynomials. The asymptotic formulas in the limit of large matrix dimension are evaluated at the spectrum edges for the ensembles related to the Legendre polynomials. The results interpolate known asymptotic formulas for random matrix eigenvalues.