Self-tuning of threshold for a two-state system

A two-state system (TSS) under time-periodic perturbations (to be regarded as input signals) is studied in connection with self-tuning (ST) of threshold and stochastic resonance (SR). By ST, we observe the improvement of signal-to-noise ratio (SNR) in a weak noise region. Analytic approach to a tuning equation reveals that SNR improvement is possible also for a large noise region and this is demonstrated by Monte Carlo simulations of hopping processes in a TSS. ST and SR are discussed from a little more physical point of energy transfer (dissipation) rate, which behaves in a similar way as SNR. Finally ST is considered briefly for a double-well potential system (DWPS), which is closely related to the TSS

Incommensurate Mott Insulator in One-Dimensional Electron Systems close to Quarter Filling

A possibility of a metal-insulator transition in molecular conductors has been studied for systems composed of donor molecules and fully ionized anions with an incommensurate ratio close to 2:1 based on a one-dimensional extended Hubbard model, where the donor carriers are slightly deviated from quarter filling and under an incommensurate periodic potential from the anions. By use of the renormalization group method, interplay between commensurability energy on the donor lattice and that from the anion potential has been studied and it has been found that an "incommensurate Mott insulator" can be generated. This theoretical finding will explain the metal-insulator transition observed in (MDT-TS)(AuI$_2$)$_{0.441}$.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jpn. at December 24 200

First-Principles Study of Electronic Structure in α\alpha-(BEDT-TTF)2_2I3_3 at Ambient Pressure and with Uniaxial Strain

Within the framework of the density functional theory, we calculate the electronic structure of $\alpha$-(BEDT-TTF)$_2$I$_3$ at 8K and room temperature at ambient pressure and with uniaxial strain along the $a$- and $b$-axes. We confirm the existence of anisotropic Dirac cone dispersion near the chemical potential. We also extract the orthogonal tight-binding parameters to analyze physical properties. An investigation of the electronic structure near the chemical potential clarifies that effects of uniaxial strain along the a-axis is different from that along the b-axis. The carrier densities show $T^2$ dependence at low temperatures, which may explain the experimental findings not only qualitatively but also quantitatively.Comment: 10 pages, 7 figure

Non-thermal origin of nonlinear transport across magnetically induced superconductor-metal-insulator transition

We have studied the effect of perpendicular magnetic fields and temperatures on the nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the nonlinear transport in the superconducting and metallic phase is of non-thermal origin and accompanies an extraordinarily long voltage response time.Comment: 5 pages, 4 figure

Impacts of water pH on the toxicity of fluoxetine on Daphnia magna: a multi-generational study

Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), has been widely prescribed as anti-depressant. While FLX has been frequently detected in surface waters, sediments and biota, only limited information is available on its in vivo toxicity, particularly in invertebrates, under changing water pH. In the present study, the ecotoxicity of FLX (pKa = 9.8) was investigated in different pH levels (6.8, 8.3, and 9.2) using Daphnia magna. Daphnia neonates ( (F0) were exposed to 0, solvent control, 31.3, 62.5, 125, 250, 500, or 1000 μg/L for 48 hr and its effects on survivals (EC20, 50 and 75) were determined. Moreover, Daphnia neonates (The first brood daphnids from the chronic tests were discarded and the second brood daphnids (F1) were employed for the multigenerational acute test within 12 hours. F1 neonates were further exposed to 0, solvent control, 31.3, 62.5, 125, 250, or 500 μg/L for 48 hr and their survivals (EC20, 50 and 75) were determined. F0 juveniles exposed to 0 or 55.6 μg/L at 10 d were measured for MDA. After 48 hr of F0 and F1 exposure, the EC50 significantly decreased (p < 0.05) at 6.17 μg/L of FLX at all tested pHs. Moreover, after 21 d F0 exposure, the reproduction showed an increasing trend until 55.6 μg/L and significantly decreased at 166.7 μg/L at pH 9.2. F1 neonates showed significantly decreased body length after 21 d exposure to 2.06, 6.17, 18.5 and 55.6 μg/L at pH 9.2. Malformation of F1 daphnids development was also observed at 2.06 μg/L to 500 μg/L. MDA concentration was also demonstrated increasing trends in all pHs and significantly increased at 55.6 μg/L at pH 6.8 and 9.2. Our observation clearly indicates that survival, reproduction, and growth performance in aquatic invertebrate can be adversely affected by FLX and the toxicity increases as water pH increases. A greater amount of uncharged ions from FLX has increased Reactive Oxidative Stress (ROS), MDA, by the ionic speciation at higher pH. Increased MDA concentration affected the mortality of F0 daphnids. Increased F1 daphnids population demonstrated significantly greater toxicity. As a result, the toxicity of FLX has increased acutely, chronically, and multigenerational effects by increasing pH levels. Consequences of longer-term exposure over multigenerations warrant further investigation

Growth Dynamics of Photoinduced Domains in Two-Dimensional Charge-Ordered Conductors Depending on Stabilization Mechanisms

Photoinduced melting of horizontal-stripe charge orders in quasi-two-dimensional organic conductors \theta-(BEDT-TTF)2RbZn(SCN)4[BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] and \alpha-(BEDT-TTF)2I3 is investigated theoretically. By numerically solving the time-dependent Schr\"odinger equation, we study the photoinduced dynamics in extended Peierls-Hubbard models on anisotropic triangular lattices within the Hartree-Fock approximation. The melting of the charge order needs more energy for \theta-(BEDT-TTF)2RbZn(SCN)4 than for \alpha-(BEDT-TTF)2I3, which is a consequence of the larger stabilization energy in \theta-(BEDT-TTF)2RbZn(SCN)4. After local photoexcitation in the charge ordered states, the growth of a photoinduced domain shows anisotropy. In \theta-(BEDT-TTF)2RbZn(SCN)4, the domain hardly expands to the direction perpendicular to the horizontal-stripes. This is because all the molecules on the hole-rich stripe are rotated in one direction and those on the hole-poor stripe in the other direction. They modulate horizontally connected transfer integrals homogeneously, stabilizing the charge order stripe by stripe. In \alpha-(BEDT-TTF)2I3, lattice distortions locally stabilize the charge order so that it is easily weakened by local photoexcitation. The photoinduced domain indeed expands in the plane. These results are consistent with recent observation by femtosecond reflection spectroscopy.Comment: 9 pages, 8 figures, to appear in J. Phys. Soc. Jpn. Vol. 79 (2010) No.