18,914 research outputs found
Morphology, structure, optical, and electrical properties of AgSbO₃
The morphology of defect pyrochlore-type, AgSbO₃ microparticle/nanoparticles obtained via solid state reaction evolve from irregular to Fullerene-like polyhedra before finally decomposing into metal-organic framework-5 like particles with increase in sintering temperature. The defect pyrochlore-type AgSbO₃ particles are slightly Ag deficient while the valence of the antimony ion is shown to be +5 giving rise to a probable stoichiometry of Ag₁ˍₓ SbVO₃ˍₓ/₂, with x∼0.01–0.04. A highly structured diffuse intensity distribution observed via electron diffraction is interpreted in terms of correlated displacements of one-dimensional (1D) silver ion chains along ⟨110⟩ directions. A redshifting in the absorption edges in UV-visible absorption spectra is observed for samples prepared at sintering temperatures higher than 1000 °C and attributed to the surface plasma resonance effect associated with small amounts of excess metallic Ag on the Ag₁ˍₓ SbVO₃ˍₓ/₂ particles. An electrical properties investigation of the silver antimonate samples via dielectric, conductivity, and electric modulus spectroscopy shows a prominent dielectric relaxation associated with grain boundaries. The silver ion conductivity is associated with correlated displacements of 1D silver ion chains along ⟨110⟩ directions.Z.G.Y., Y.L., and R.L.W. acknowledge financial support
from the Australian Research Council ARC in the form of
ARC Discovery Grants
Dynamical properties of a trapped dipolar Fermi gas at finite temperature
We investigate the dynamical properties of a trapped finite-temperature
normal Fermi gas with dipole-dipole interaction. For the free expansion
dynamics, we show that the expanded gas always becomes stretched along the
direction of the dipole moment. In addition, we present the temperature and
interaction dependences of the asymptotical aspect ratio. We further study the
collapse dynamics of the system by suddenly increasing the dipolar interaction
strength. We show that, in contrast to the anisotropic collapse of a dipolar
Bose-Einstein condensate, a dipolar Fermi gas always collapses isotropically
when the system becomes globally unstable. We also explore the interaction and
temperature dependences for the frequencies of the low-lying collective
excitations.Comment: 11 pages, 7 figure
The effects of strong temperature anisotropy on the kinetic structure of collisionless slow shocks and reconnection exhausts. Part II: Theory
Simulations of collisionless oblique propagating slow shocks have revealed
the existence of a transition associated with a critical temperature anisotropy
epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 = 0.25 (Liu, Drake and Swisdak
(2011)). An explanation for this phenomenon is proposed here based on
anisotropic fluid theory, in particular the Anisotropic Derivative
Nonlinear-Schrodinger-Burgers equation, with an intuitive model of the energy
closure for the downstream counter-streaming ions. The anisotropy value of 0.25
is significant because it is closely related to the degeneracy point of the
slow and intermediate modes, and corresponds to the lower bound of the coplanar
to non-coplanar transition that occurs inside a compound slow shock
(SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of
compound SS/RD waves that bound the outflows in magnetic reconnection, instead
of a pair of switch-off slow shocks as in Petschek's model. This fact might
explain the rareness of in-situ observations of
Petschek-reconnection-associated switch-off slow shocks.Comment: 18 pages, 10 figure
Model anisotropic quantum Hall states
Model quantum Hall states including Laughlin, Moore-Read and Read-Rezayi
states are generalized into appropriate anisotropic form. The generalized
states are exact zero-energy eigenstates of corresponding anisotropic two- or
multi-body Hamiltonians, and explicitly illustrate the existence of geometric
degrees of in the fractional quantum Hall effect. These generalized model
quantum Hall states can provide a good description of the quantum Hall system
with anisotropic interactions. Some numeric results of these anisotropic
quantum Hall states are also presented.Comment: 10 pages, 5 figure
Factors affecting the sticking of insects on modified aircraft wings
Past studies have shown that the surface energy of a polymer coating has an important effect on the sticking of insects to the surface. However, mechanical properties of polymer coatings such as elasticity may also be important. A further study is suggested using polymer coatings of known surface energy and modulus so that a better understanding of the mechanism of the sticking of insects to surfaces can be achieved. As the first step for the study, surface analysis and road tests were performed using elastomers having different energies and different moduli. The number of insects sticking to each elastomer was counted and compared from sample to sample and with a control (aluminum). An average height moment was also calculated and comparisons made between samples
Factors affecting the sticking of insects on modified aircraft wings
Previous work showed that the total number of insects sticking to an aluminum surface was reduced by coating the aluminum surface with elastomers. Due to a large number of possible experimental errors, no correlation between the modulus of elasticity, the elastomer, and the total number of insects sticking to a given elastomer was obtained. One of the errors assumed to be introduced during the road test is a variable insect flux so the number of insects striking one surface might be different from that striking another sample. To eliminate this source of error, the road test used to collect insects was simulated in a laboratory by development of an insect impacting technique using a pipe and high pressure compressed air. The insects are accelerated by a compressed air gun to high velocities and are then impacted with a stationary target on which the sample is mounted. The velocity of an object exiting from the pipe was determined and further improvement of the technique was achieved to obtain a uniform air velocity distribution
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
Structural phase transitions of vortex matter in an optical lattice
We consider the vortex structure of a rapidly rotating trapped atomic
Bose-Einstein condensate in the presence of a co-rotating periodic optical
lattice potential. We observe a rich variety of structural phases which reflect
the interplay of the vortex-vortex and vortex-lattice interactions. The lattice
structure is very sensitive to the ratio of vortices to pinning sites and we
observe structural phase transitions and domain formation as this ratio is
varied.Comment: 4 pages, 3 figure
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