XY checkerboard antiferromagnet in external field

Ordering by thermal fluctuations is studied for the classical XY antiferromagnet on a checkerboard lattice in zero and finite magnetic fields by means of analytical and Monte Carlo methods. The model exhibits a variety of novel broken symmetries including states with nematic ordering in zero field and with triatic order parameter at high fields.Comment: 6 page

Orexin-1 receptor-cannabinoid CB1 receptor heterodimerization results in both ligand-dependent and -independent coordinated alterations of receptor localization and function

Following inducible expression in HEK293 cells, the human orexin-1 receptor was targeted to the cell surface but became internalized following exposure to the peptide agonist orexin A. By contrast, constitutive expression of the human cannabinoid CB1 receptor resulted in a predominantly punctate, intracellular distribution pattern consistent with spontaneous, agonistindependent internalization. Expression of the orexin-1 receptor in the presence of the CB1 receptor resulted in both receptors displaying the spontaneous internalization phenotype. Single cell fluorescence resonance energy transfer imaging indicated the two receptors were present as heterodimers/oligomers in intracellular vesicles. Addition of the CB1 receptor antagonist SR-141716A to cells expressing only the CB1 receptor resulted in re-localization of the receptor to the cell surface. Although SR-141716A has no significant affinity for the orexin-1 receptor, in cells co-expressing the CB1 receptor, the orexin-1 receptor was also re-localized to the cell surface by treatment with SR-141716A. Treatment of cells co-expressing the orexin-1 and CB1 receptors with the orexin-1 receptor antagonist SB-674042 also resulted in re-localization of both receptors to the cell surface. Treatment with SR-141716A resulted in decreased potency of orexin A to activate the mitogen-activated protein kinases ERK1/2 only in cells co-expressing the two receptors. Treatment with SB-674042 also reduced the potency of a CB1 receptor agonist to phosphorylate ERK1/2 only when the two receptors were co-expressed. These studies introduce an entirely novel pharmacological paradigm, whereby ligands modulate the function of receptors for which they have no significant inherent affinity by acting as regulators of receptor heterodimers

Anomalous Hall Effect due to the spin chirality in the Kagom\'{e} lattice

We consider a model for a two dimensional electron gas moving on a kagom\'{e} lattice and locally coupled to a chiral magnetic texture. We show that the transverse conductivity $\sigma\_{xy}$ does not vanish even if spin-orbit coupling is not present and it may exhibit unusual behavior. Model parameters are the chirality, the number of conduction electrons and the amplitude of the local coupling. Upon varying these parameters, a topological transition characterized by change of the band Chern numbers occur. As a consequence, $\sigma\_{xy}$ can be quantized, proportional to the chirality or have a non monotonic behavior upon varying these parameters.Comment: 8 pages, 7 figure

Magnetic frustration in an iron based Cairo pentagonal lattice

The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per elemental brick, this lattice, subject to first neighbor antiferromagnetic interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic properties have been investigated by macroscopic magnetic measurements and neutron diffraction. The observed non-collinear magnetic arrangement is related to the one stabilized on a perfect tiling as obtained from a mean field analysis with direct space magnetic configurations calculations. The peculiarity of this structure arises from the complex connectivity of the pentagonal lattice, a novel feature compared to the well-known case of triangle-based lattices

Chiral nature of magnetic monopoles in artificial spin ice

Micromagnetic properties of monopoles in artificial kagome spin ice systems are investigated using numerical simulations. We show that micromagnetics brings additional complexity into the physics of these monopoles that is, by essence, absent in spin models: besides a fractionalized classical magnetic charge, monopoles in the artificial kagome ice are chiral at remanence. Our simulations predict that the chirality of these monopoles can be controlled without altering their charge state. This chirality breaks the vertex symmetry and triggers a directional motion of the monopole under an applied magnetic field. Our results also show that the choice of the geometrical features of the lattice can be used to turn on and off this chirality, thus allowing the investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure

Influence of parent's eating attitudes on eating disorders in school adolescents

Objective: To investigate the relationship between parents' cognitive and behavioural dimensions and the risk of eating disorders (ED) in non-clinical adolescents. Methods: From an initial sample of 1,336 boys and girls with a mean age of 11.37, a total of 258 subjects were selected either as being at risk of ED or as controls. These subjects and their parents comprised the sample at T1 and were followed-up 2 years later (T2). We examined disordered eating attitudes, body dissatisfaction (BD), body mass index (BMI) and ED diagnoses in the adolescents at two points in time. We also used the Eating Disorder Inventory-2 to examine the disordered eating attitudes of their parents at T1. Results: The mother's BD, drive for thinness (DT), ineffectiveness and interoceptive awareness, and the father's DT and perfectionism were related to long-term ED. Logistic regression showed that predictors of ED were being female, mother's DT and social insecurity, and adolescent's BD. The BMI was not a predictor in this model. Father's perfectionism was a risk factor of ED. Conclusion: Specific cognitive and behavioural dimensions of ED in both parents can influence the development of an ED in early adolescents. This should be taken into account in the prevention and family oriented treatment of ED

Hierarchical geometric frustration in La3Cu2VO9

The crystallographic structure and magnetic properties of the La3Cu2VO9 were investigated by powder neutron diffraction and magnetization measurements. The compound materializes geometric frustration at two spatial scales, within clusters and between clusters, and at different temperature scales. It is shown by exactly solving the hamiltonian spectrum that collective spins are formed on each clusters at low temperature before inter-clusters coupling operates.Comment: 6 pages, 4 figures. HFM2006 proceeding pape

Parity-broken ground state for the spin-1 pyrochlore antiferromagnet

The ground-state properties of the spin-1 pyrochlore antiferromagnet are studied by applying the VBS-like tetrahedron-unit decomposition to the original spin system. The symmetrization required on every vertex is taken into account by introducing a ferromagnetic coupling. The pairwise effective Hamiltonian between the adjacent tetrahedrons is obtained by considering the next nearest neighbor and the third neighbor exchange interactions. We find that the transverse component of the spin chirality exhibits a long-range order, breaking the parity symmetry of the tetrahedral group, while the chirality itself is not broken.Comment: 4 pages, 3 figures, REVTeX(ver.3.1

Caracterización geológica de la región de enlace entre la Cuenca de Bransfield y la Dorsal Sur de Scotia (Antártida)

In February 1992, a geological and geophysical survey was carried out in the NW Antarctic Peninsula region, between South Shetland, Elephant and Orkney Islands (Antarctica), during the "Scotia 92" cruise aboard BIO Hespérides. The multi-channel seismics, magnetics and gravity data show the different sedimentary characteristics between Scotia and Powell Basins. At the western end of the South Scotia Ridge (SSR), an area (50 x 100 km) covered by multibearn bathymetry reveals a maximum depth of more than 5,300 m corresponding to what we refer to as the Hespérides Deep. The SSR is a sinistral transform plate boundary between the Scotia and Antarctic plates (on the north and south respectively). The morphology of the SSR is constituted by two ridges separated by a deep and narrow valiey (10 to 30 km wide). Two main families of faults can be distinguished, one trending E-W and parallel to the plate boundary, and another one trending NW-SE. We iriterpret that the former accommodates the regional strike-slip motion, whereas the later has an extensional component which may be related to the main trend of Bransfield Basin. The rhomboid-shape of the Deep is the result of the interplay between both sets of faults. Assuming that the transform boundary runs between the two ridges we consider that the Hesperides Deep is a smaU puli-apart basin developed by the sinistral strike-slip motion along the SSR