33,689 research outputs found
Polar Molecules with Three-Body Interactions on the Honeycomb Lattice
We study the phase diagram of ultra-cold bosonic polar molecules loaded on a
two-dimensional optical lattice of hexagonal symmetry controlled by external
electric and microwave fields. Following a recent proposal in Nature Physics
\textbf{3}, 726 (2007), such a system is described by an extended Bose-Hubbard
model of hard-core bosons, that includes both extended two- and three-body
repulsions. Using quantum Monte-Carlo simulations, exact finite cluster
calculations and the tensor network renormalization group, we explore the rich
phase diagram of this system, resulting from the strongly competing nature of
the three-body repulsions on the honeycomb lattice. Already in the classical
limit, they induce complex solid states with large unit cells and macroscopic
ground state degeneracies at different fractional lattice fillings. For the
quantum regime, we obtain effective descriptions of the various phases in terms
of emerging valence bond crystal states and quantum dimer models. Furthermore,
we access the experimentally relevant parameter regime, and determine the
stability of the crystalline phases towards strong two-body interactions
Influence Of Oxygen Activity On The Sintering Of MgCr2O4
The sintering behavior of MgCr2O4 powder compacts was investigated as a function of temperature, time, and oxygen activity. The results show that MgCr2O4 cannot be densified to \u3e70% of theoretical density at temperatures up to 1700°C if the oxygen activity exceeds 10−6 atm. The oxygen activity must be decreased to \u3c10−10 atm before densities exceeding 90% of theoretical can be achieved. Weight loss and X‐ray data indicated that maximum density occurred at an oxygen activity just above that where MgCr2O4 becomes unstable. Copyright © 1974, Wiley Blackwell. All rights reserve
Review Of P-type Doped Perovskite Materials For SOFC And Other Applications
p-type perovskite-type oxides are candidates for use as components of high temperature fuel cells and as oxygen separation membranes. The particular properties that these applications require are reviewed. The characteristics that these oxides have which allow them to satisfy many of these requirements are discussed and a defect model presented. The status of the utilization of these oxides and of the areas which need to be addressed such as thermal expansion and sintering characteristics are reviewed. © 1992
An analysis of the relationships between selected variables and the adoption and diffusion of computers for instructional purposes among community college faculty
The adoption of computers by faculty for instructional purposes depends on a universe of variables which either facilitate or hinder the change process. This study surveyed 305 community college faculty in order to examine the relationships between the intensity of adoption and perceived faculty barriers to the adoption of computers. The perceived barriers examined were (1) administrative support for educational computing, (2) the institution\u27s economic climate, (3) the complexity of computers, and (4) the attitudes of faculty towards the use of computers. The variables of age and sex (gender) were also examined for relationships to the areas of adoption and perceived barriers;It was concluded that no significant relationships existed between the degree of computer adoption for instructional purposes and the perceived barriers. No significant relationships were found between age and the degree of adoption or the perceived barriers. Significant differences did exist between sex and the degree of computer adoption. However, no significant relationships were found between sex (gender) and the perceived adoption barriers
Superantenna made of transformation media
We show how transformation media can make a superantenna that is either
completely invisible or focuses incoming light into a needle-sharp beam. Our
idea is based on representating three-dimensional space as a foliage of sheets
and performing two-dimensional conformal maps on each shee
Collective charge fluctuations and Casimir interactions for quasi one-dimensional metals
We investigate the Casimir interaction between two parallel metallic
cylinders and between a metallic cylinder and plate. The material properties of
the metallic objects are implemented by the plasma, Drude and perfect metal
model dielectric functions. We calculate the Casimir interaction numerically at
all separation distances and analytically at large separations. The
large-distance asymptotic interaction between one plasma cylinder parallel to
another plasma cylinder or plate does not depend on the material properties,
but for a Drude cylinder it depends on the dc conductivity . At
intermediate separations, for plasma cylinders the asymptotic interaction
depends on the plasma wave length while for Drude cylinders
the Casimir interaction can become independent of the material properties. We
confirm the analytical results by the numerics and show that at short
separations, the numerical results approach the proximity force approximation
Tuning the interactions of spin-polarized fermions using quasi-one-dimensional confinement
The behavior of ultracold atomic gases depends crucially on the two-body
scattering properties of these systems. We develop a multichannel scattering
theory for atom-atom collisions in quasi-one-dimensional (quasi-1D) geometries
such as atomic waveguides or highly elongated traps. We apply our general
framework to the low energy scattering of two spin-polarized fermions and show
that tightly-confined fermions have infinitely strong interactions at a
particular value of the 3D, free-space p-wave scattering volume. Moreover, we
describe a mapping of this strongly interacting system of two quasi-1D fermions
to a weakly interacting system of two 1D bosons.Comment: Submitted to Phys. Rev. Let
Model For Evaporation Of A Grain‐Boundary Phase
The surface profile which develops in the vicinity of a grain boundary precipitate in the course of evaporation is calculated. It is shown that the presence of the grain boundary precipitate affects the profile significantly if the product of the width of the grain boundary precipitate and the ratio of the evaporation rates of the unperturbed surface and the grain boundary precipitate is larger than one. Copyright © 1981, Wiley Blackwell. All rights reserve
- …