Quantum Phase Transitions to Charge Order and Wigner Crystal Under Interplay of Lattice Commensurability and Long-Range Coulomb Interaction

Relationship among Wigner crystal, charge order and Mott insulator is studied by the path-integral renormalization group method for two-dimensional lattices with long-range Coulomb interaction. In contrast to Hartree-Fock results, the solid stability drastically increases with lattice commensurability. The transition to liquid occurs at the electron gas parameter $r_s \sim 2$ for the filling $n=1/2$ showing large reduction from $r_s \sim 35$ in the continuum limit. Correct account of quantum fluctuations are crucial to understand charge-order stability generally observed only at simple fractional fillings and nature of quantum liquids away from them.Comment: 4 pages including 7 figure

Effects of Neonatal Treatment With 6-Hydroxydopamine and Endocrine Disruptors on Motor Activity and Gene Expression in Rats

To investigate the mechanisms underlying motor hyperactivity, we performed intracisternal injection of 6-hydroxydopamine or endocrine disruptors in rats on postnatal day 5. 6-Hydroxydopamine (100 μg, 488 nmol) caused a significant increase in spontaneous motor activities at 4 weeks of age. Gene-expression profiling using a cDNA membrane array revealed alterations in several classes of gene at 8 weeks of age. In the midbrain, gene expression was enhanced in dopamine transporter 1; a platelet-derived growth factor receptor; dopamine receptor D4; galanin receptor 2; arginine vasopressin receptor 2; neuropeptide Y; tachykinin 2; and fibroblast growth factor 10. Expression was also enhanced in the glutamate/aspartate transporter gene in the striatum. Rats received an endocrine disruptor (87 nmol), such as bisphenol A, nonylphenol, p-octylphenol, or diethylhexylphthalate, which also caused motor hyperactivity at 4 weeks. The effects of bisphenol A on motor activity were dose-dependent from 0.87 to 87 nmol. The phenols caused a deficit in dopamine neurons, similarly to the deficit caused by 6-hydroxydopamine. Gene-expression profiles after treatment with endocrine disruptors showed variation and differed from those of 6- hydroxydopamine. The results suggest that neonatal treatment with environmental chemicals can generate an animal model of attention-deficit hyperactivity disorder, in which clinical symptoms are pervasive

Quantum-number projection in the path-integral renormalization group method

We present a quantum-number projection technique which enables us to exactly treat spin, momentum and other symmetries embedded in the Hubbard model. By combining this projection technique, we extend the path-integral renormalization group method to improve the efficiency of numerical computations. By taking numerical calculations for the standard Hubbard model and the Hubbard model with next nearest neighbor transfer, we show that the present extended method can extremely enhance numerical accuracy and that it can handle excited states, in addition to the ground state.Comment: 11 pages, 7 figures, submitted to Phys. Rev.