The Hall conductance σ xy of two-dimensional lattice electrons with random potential is investigated. The change of σ xy due to randomness is focused on. It is a quantum phase transition where the sum rule of σ xy plays an important role. By the string (anyon) gauge, numerical study becomes possible in sufficiently weak magnetic field regime which is essential to discuss the floating scenario in the continuum model. Topological objects in the Bloch wavefunctions, charged vortices, are obtained explicitly. The anomalous plateau transitions ( ∆σ xy = 2, 3, • • • > 1) and the trajectory of delocalized states are discussed.

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Magneto-optical Kerr effects have been investigated for perovskite-type hole-doped oxides La 1Ϫx Sr x MnO 3 (0рxр0.3) and La 1Ϫx Sr x CoO 3 (0рxр0.3) in the photon energy range between 0.9 and 5.3 eV at room temperature. In La 1Ϫx Sr x MnO 3 , charge-transfer-type Kerr spectra are observed for the lowest (ϳ1.2 eV) and the second-lowest (ϳ3.5 eV) optical transitions that are likely to arise from electron excitations from the O 2 p to the majority-spin e g band and to the minority-spin t 2g band, respectively. In La 1Ϫx Sr x CoO 3 , a crystal-field-transition-type Kerr spectrum is observed that is assigned to the electron excitation from the bonding t 2g state to the antibonding e g state allowed by the strong hybridization effect between Co 3d and O 2p states. Different characters in the Hund's-rule coupling and covalency seem to cause such a difference in magneto-optical properties between ferromagnetic Mn and Co oxides. ͓S0163-1829͑98͒05336-3͔

To investigate the cognitive processes underlying creative inspiration, we tested the extent to which viewing or copying prior examples impacted creative output in art. In Experiment 1, undergraduates made drawings under three conditions: (a) copying an artist's drawing, then producing an original drawing; (b) producing an original drawing without having seen another's work; and (c) copying another artist's work, then reproducing that artist's style independently. We discovered that through copying unfamiliar abstract drawings, participants were able to produce creative drawings qualitatively different from the model drawings. Process analyses suggested that participants' cognitive constraints became relaxed, and new perspectives were formed from copying another's artwork. Experiment 2 showed that exposure to styles of artwork considered unfamiliar facilitated creativity in drawing, while styles considered familiar did not do so. Experiment 3 showed that both copying and thoroughly viewing artwork executed using an unfamiliar style facilitated creativity in drawing, whereas merely thinking about alternative styles of artistic representation did not do so. These experiments revealed that deep encounters with unfamiliar artworks-whether through copying or prolonged observation-change people's cognitive representations of the act of drawing to produce novel artwork.

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