9,538 research outputs found
Preen Gland-Secreted Alkanols Enhance Male Attractiveness in Parrots
The skin glands are widely used in pheromone production throughout the vertebrate worlds. Growing evidences show that birds also have chemical communication, but the uropygial (also called preen or oil) glands, serving as only specialized skin glands of birds, have no sex pheromones characterized. Here, by combining GC-MS analysis and bioassay, we show with the budgerigar, Melopsittacus undulatus, that birds can used the preen gland-secreted volatiles (a blend of octadecanol, nonadecanol and eicosanol for male budgerigars) spread over body plumage when preening to convey sex information. Here, we first report the avian pheromones derived from the uropyginal gland and suggests that the gland has broader implications than previously known (e.g. plumage waterproofing and reflectance in sexual behaviour of birds
Flat band electrons and interactions in rhombohedral trilayer graphene
Multilayer graphene systems with a rhombohedral stacking order harbor nearly
flat bands in their single-particle spectrum. We propose ansatz states to
describe the surface-localized states of flat band electrons. The absence of
kinetic dispersion near the fermi level leaves the interaction as a dominate
mechanism to govern the low energy physics of a low density electron system. We
build up an effective lattice model in two interacting low-energy bands, where
the full terms of the Coulomb interaction, including those long-range and
off-diagonal parts, have been considered. The interaction matrix coefficients
in the many-body Hamiltonian model are directly calculated for a trilayer
system using orthonormal Wannier basis. We then present a flat-band projection
to yield an interaction-only lattice model for flat band electrons. We find
that this limited model might energetically favor a ferromagnetic quantum
crystal under certain conditions.Comment: 8 pages, 3 figures, 3 tables. add journal reference and some
discussions in the context. arXiv admin note: text overlap with
arXiv:1108.008
The kHz QPOs as a probe of the X-ray color-color diagram and accretion-disk structure for the atoll source 4U 1728-34
We have taken the kHz QPOs as a tool to probe the correlation between the
tracks of X-ray color-color diagram (CCD) and magnetosphere-disk positions for
the atoll source 4U 1728-34, based on the assumptions that the upper kHz QPO is
ascribed to the Keplerian orbital motion and the neutron star (NS)
magnetosphere is defined by the dipole magnetic field. We find that from the
island to the banana state, the inner accretion disk gradually approaches the
NS surface with the radius decreasing from r ~33.0km to ~15.9 km, corresponding
to the magnetic field from B(r) ~4.8*10^6 G to ~4.3*10^7 G. In addition, we
note the characteristics of some particular radii of magnetosphere-disk -r are:
firstly, the whole atoll shape of the CCD links the disk radius range of ~15.9
- 33.0 km, which is just located inside the corotation radius of 4U 1728-34
-r_co ( ~34.4 km), implying that the CCD shape is involved in the NS spin-up
state. Secondly, the island and banana states of CCD correspond to the two
particular boundaries: (I)-near the corotation radius at r ~27.2 - 33.0 km,
where the source lies in the island state; (II)-near the NS surface at r ~15.9
- 22.3 km, where the source lies in both the island and banana states. Thirdly,
the vertex of the atoll shape in CCD, where the radiation transition from the
hard to soft photons occurs, is found to be near the NS surface at r ~16.4 km.
The above results suggest that both the magnetic field and accretion
environment are related to the CCD structure of atoll track, where the
corotation radius and NS hard surface play the significant roles in the
radiation distribution of atoll source.Comment: 6 pages, 3 figures, 1 table, accepted by Astronomy & Astrophysic
Aquaporin-4-dependent K(+) and water transport modeled in brain extracellular space following neuroexcitation.
Potassium (K(+)) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K(+)] accumulation and slowing K(+) reuptake. These effects could involve AQP4-dependent: (a) K(+) permeability, (b) resting ECS volume, (c) ECS contraction during K(+) reuptake, and (d) diffusion-limited water/K(+) transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K(+) and water uptake into astrocytes after neuronal release of K(+) into the ECS. The model computed the kinetics of ECS [K(+)] and volume, with input parameters including initial ECS volume, astrocyte K(+) conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte-ECS interface. The modeling showed that mechanisms b-d, together, can predict experimentally observed impairment in K(+) reuptake from the ECS in AQP4 deficiency, as well as altered K(+) accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K(+)/water coupling in the ECS without requiring AQP4-dependent astrocyte K(+) permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency
Layer Antiferromagnetic State in Bilayer Graphene : A First-Principle Investigation
The ground state of bilayer graphene is investigated by the density
functional calculations with local spin density approximation. We find a ground
state with layer antiferromagnetic ordering, which has been suggested by former
studies based on simplified model. The calculations prove that the layer
antiferromagnetic state (LAF) is stable even if the remote hopping and nonlocal
Coulomb interaction are included. The gap of the LAF state is about 1.8 meV,
comparable to the experimental value. The surface magnetism in BLG is of the
order of
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