Field-induced staggered magnetic moment in the quasi-two-dimensional organic Mott insulator κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2_{2}]Cl

We investigated the magnetism under a magnetic field in the quasi-two-dimensional organic Mott insulator $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl through magnetization and $^{13}$C-NMR measurements. We found that in the nominally paramagnetic phase (i.e., above N\'eel temperature) the field-induced local moments have a staggered component perpendicular to the applied field. As a result, the antiferromagnetic transition well defined at a zero field becomes crossover under a finite field. This unconventional behavior is qualitatively reproduced by the molecular-field calculation for Hamiltonian including the exchange, Dzyaloshinsky-Moriya (DM), and Zeeman interactions. This calculation also explains other unconventional magnetic features in $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl reported in the literature. The present results highlight the importance of the DM interaction in field-induced magnetism in a nominally paramagnetic phase, especially in low-dimensional spin systems.Comment: 11 pages, 12 figures, selected for Editors' Suggestion

NMR evidence for very slow carrier density fluctuations in the organic metal (TMTSF)2_2ClO4_4

We have investigated the origin of the large increase in spin-echo decay rates for the $^{77}$Se nuclear spins at temperatures near to $T=30K$ in the organic superconductor (TMTSF)$_2$ClO$_4$. The measured angular dependence of $T_2^{-1}$ demonstrates that the source of the spin-echo decays lies with carrier density fluctuations rather than fluctuations in TMTSF molecular orientation. The very long time scales are directly associated with the dynamics of the anion ordering occurring at $T=25K$, and the inhomogeneously broadened spectra at lower temperatures result from finite domain sizes. Our results are similar to observations of line-broadening effects associated with charge-ordering transitions in quasi-two dimensional organic conductors.Comment: 5 pages, 4 figure

Mott Transition from a Spin Liquid to a Fermi Liquid in the Spin-Frustrated Organic Conductor kappa-(ET)2Cu2(CN)3

Pressure-temperature phase diagram of the organic Mott insulator $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, a model system of the spin liquid on triangular lattice, has been investigated by $^1$H NMR and resistivity measurements. The spin-liquid phase is persistent before the Mott transition to the metal or superconducting phase under pressure. At the Mott transition, the spin fluctuations are rapidly suppressed and the Fermi-liquid features are observed in the temperature dependence of the spin-lattice relaxation rate and resistivity. The characteristic curvature of Mott boundary in the phase diagram highlights a crucial effect of the spin frustration on the Mott transition.Comment: 4 pages, 5 figure

Telerobotics test bed for space structure assembly

A cooperative research on super long distance space telerobotics is now in progress both in Japan and USA. In this program. several key features will be tested, which can be applicable to the control of space robots as well as to terrestrial robots. Local (control) and remote (work) sites will be shared between Electrotechnical Lab (ETL) of MITI in Japan and Jet Propulsion Lab (JPL) in USA. The details of a test bed for this international program are discussed in this report

Exact diagonalization study of Mott transition in the Hubbard model on an anisotropic triangular lattice

We study Mott transition in the two-dimensional Hubbard model on an anisotropic triangular lattice. We use the Lanczos exact diagonalization of finite-size clusters up to eighteen sites, and calculate Drude weight, charge gap, double occupancy and spin structure factor. We average these physical quantities over twisted boundary conditions in order to reduce finite-size effects. We find a signature of the Mott transition in the dependence of the Drude weight and/or charge gap on the system size. We also examine the possibility of antiferromagnetic order from the spin structure factor. Combining these information, we propose a ground-state phase diagram which has a nonmagnetic insulating phase between a metallic phase and an insulating phase with antiferromagnetic order. Finally, we compare our results with those reported in the previous theoretical studies, and discuss the possibility of an unconventional insulating state.Comment: 10 pages, 11 figure

Adenyl cyclases and cAMP in plant signaling - past and present

In lower eukaryotes and animals 3'-5'-cyclic adenosine monophosphate (cAMP) and adenyl cyclases (ACs), enzymes that catalyse the formation of cAMP from ATP, have long been established as key components and second messengers in many signaling pathways. In contrast, in plants, both the presence and biological role of cAMP have been a matter of ongoing debate and some controversy. Here we shall focus firstly on the discovery of cellular cAMP in plants and evidence for a role of this second messenger in plant signal transduction. Secondly, we shall review current evidence of plant ACs, analyse aspects of their domain organisations and the biological roles of candidate molecules. In addition, we shall assess different approaches based on search motifs consisting of functionally assigned amino acids in the catalytic centre of annotated and/or experimentally tested nucleotide cyclases that can contribute to the identification of novel candidate molecules with AC activity such as F-box and TIR proteins

Superconductivity and a Mott Transition in a Hubbard Model on an Anisotropic Triangular Lattice

A half-filled-band Hubbard model on an anisotropic triangular lattice (t in two bond directions and t' in the other) is studied using an optimization variational Monte Carlo method, to consider the Mott transition and superconductivity arising in \kappa-BEDT-TTF_2X. Adopting wave functions with doublon-holon binding factors, we reveal that a first-order Mott (conductor-to-nonmagnetic insulator) transition takes place at U=U_c approximately of the band width, for a wide range of t'/t. This transition is not directly connected to magnetism. Robust d-wave superconductivity appears in a restricted parameter range: immediately below U_c and moderate strength of frustration (0.4\lsim t'/t\lsim 0.7), where short-range antiferromagnetic correlation sufficiently develops but does not come to a long-range order. The relevance to experiments is also discussed.Comment: 15 pages, 17 figures, submitted to J. Phys. Soc. Jp

The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005

The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was R = 12.0, which represents the most luminous quasar state thus far observed (M_B ~ -31.4). In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm theComment: 7 pages, 4 figures, to be published in A&

Diversification and agrarian change under environmental constraints in rural China: Evidence from a poor township of Beijing municipality

Working paper du GATE 2007-11This article illustrates the impact of changes related to market reforms and environmental policies on the economic structure in rural China by providing a comparative analysis of several villages in a poor township in Beijing municipality. Two main concomitant phenomena are affecting agricultural and non-agricultural choices in the studied area. First, the introduction of market mechanisms is encouraging local population to engage in new activities that are closer to local comparative advantages. Second, rural households are facing new constraints in the form of environmental protection measures, which have weakened traditional insurance channels provided by forest resources and cattle stock. Drawing on household-level survey data and interviews with village heads conducted in ten villages of Labagoumen township in December 2003, this article analyzes households decisions in response to market reforms and environmental constraints. We find large disparities both between villages and households in the diversification process and discuss the reasons of observed inertia in the region, most households still heavily relying on corn production