7,578 research outputs found
Assessment of methods of acquiring analyzing, and reporting crop production statistics, volume 4
There are no author-identified significant results in this report
Charge ordering in charge-compensated by oxonium ions
Charge ordering behavior is observed in the crystal prepared through the
immersion of the crystal in distilled water. Discovery of the
charge ordering in the crystal with Na content less than 0.5 indicates that the
immersion in water brings about the reduction of the
. The formal valence of Co changes from +3.59 estimated from
the
Na content to +3.5, the same as that in . The charge
compensation is confirmed to arise from the intercalation of the oxonium ions
as occurred in the superconducting sodium cobalt oxide
bilayer-hydrate.\cite{takada1}
The charge ordering is the same as that observed in . It
suggests that the Co valence of +3.5 is necessary for the charge ordering.Comment: 5 pages, 4 figure
Zeta potentials of the rare earth element fluorcarbonate minerals focusing on bastnäsite and parisite
Rare earth elements (REE) are critical to a wide range of technologies ranging from mobile phones to wind turbines. Processing and extraction of REE minerals from ore bodies is, however, both challenging and relatively poorly understood, as the majority of deposits contain only limited enrichment of REEs. An improved understanding of the surface properties of the minerals is important in informing and optimising their processing, in particular for separation by froth flotation. The measurement of zeta potential can be used to extract information regarding the electrical double layer, and hence surface properties of these minerals. There are over 34 REE fluorcarbonate minerals currently identified, however bastnäsite, synchysite and parisite are of most economic importance. Bastnäsite-(Ce), the most common REE fluorcarbonate, supplies over 50% of the world's REE. Previous studies of bastnäsite have showed a wide range of surface behaviour, with the iso-electric point (IEP), being measured between pH values of 4.6 and 9.3. In contrast, no values of IEP have been reported for parisite or synchysite. In this work, we review previous studies of the zeta potentials of bastnäsite to investigate the effects of different methodologies and sample preparation. In addition, measurements of zeta potentials of parisite under water, collector and supernatant conditions were conducted, the first to be reported. These results showed an iso-electric point for parisite of 5.6 under water, with a shift to a more negative zeta potential with both collector (hydroxamic and fatty acids) and supernatant conditions. The IEP with collectors and supernatant was <3.5. As zeta potential measurements in the presence of reagents and supernatants are the most rigorous way of determining the efficiency of a flotation reagent, the agreement between parisite zeta potentials obtained here and previous work on bastnäsite suggests that parisite may be processed using similar reagent schemes to bastnäsite. This is important for future processing of REE deposits, comprising of more complex REE mineralogy
Multi-particle Correlations in Quaternionic Quantum Systems
We investigate the outcomes of measurements on correlated, few-body quantum
systems described by a quaternionic quantum mechanics that allows for regions
of quaternionic curvature. We find that a multi-particle interferometry
experiment using a correlated system of four nonrelativistic, spin-half
particles has the potential to detect the presence of quaternionic curvature.
Two-body systems, however, are shown to give predictions identical to those of
standard quantum mechanics when relative angles are used in the construction of
the operators corresponding to measurements of particle spin components.Comment: REVTeX 3.0, 16 pages, no figures, UM-P-94/54, RCHEP-94/1
A condition on the chiral symmetry breaking solution of the Dyson-Schwinger equation in three-dimensional QED
In three-dimensional QED, which is analyzed in the 1/ expansion, we obtain
a sufficient and necessary condition for a nontrivial solution of the
Dyson-Schwinger equation to be chiral symmetry breaking solution. In the
derivation, a normalization condition of the Goldstone bound state is used. It
is showed that the existent analytical solutions satisfy this condition.Comment: 11 pages, Latex, no figures, accepted by Phys.Lett.
The influence of void size on the micropolar constitutive properties of model heterogeneous materials
In this paper the mechanical behaviour of model heterogeneous materials consisting of regular periodic arrays of circular voids within a polymeric matrix is investigated. Circular ring samples of the materials were fabricated by machining the voids into commercially available polymer sheet. Ring samples of differing sizes but similar geometries were loaded using mechanical testing equipment. Sample stiffness was found to depend on sample size with stiffness increasing as size reduced. The periodic nature of the void arrays also facilitated detailed finite element analysis of each sample. The results obtained by analysis substantiate the observed dependence of stiffness on size. Classical elasticity theory does not acknowledge this size effect but more generalized elasticity theories do predict it. Micropolar elasticity theory has therefore been used to interpret the sample stiffness data and identify constitutive properties. Modulus values for the model materials have been quantified. Values of two additional constitutive properties, the characteristic length and the coupling number, which are present within micropolar elasticity but absent from its classic counterpart have also been determined. The dependence of these additional properties on void size has been investigated and characteristic length values compared to the length scales inherent within the structure of the model materials
Enhancing structure relaxations for first-principles codes: an approximate Hessian approach
We present a method for improving the speed of geometry relaxation by using a
harmonic approximation for the interaction potential between nearest neighbor
atoms to construct an initial Hessian estimate. The model is quite robust, and
yields approximately a 30% or better reduction in the number of calculations
compared to an optimized diagonal initialization. Convergence with this
initializer approaches the speed of a converged BFGS Hessian, therefore it is
close to the best that can be achieved. Hessian preconditioning is discussed,
and it is found that a compromise between an average condition number and a
narrow distribution in eigenvalues produces the best optimization.Comment: 9 pages, 3 figures, added references, expanded optimization sectio
Ground state solution of Bose-Einstein condensate by directly minimizing the energy functional
In this paper, we propose a new numerical method to compute the ground state
solution of trapped interacting Bose-Einstein condensation (BEC) at zero or
very low temperature by directly minimizing the energy functional via finite
element approximation. As preparatory steps we begin with the 3d
Gross-Pitaevskii equation (GPE), scale it to get a three-parameter model and
show how to reduce it to 2d and 1d GPEs. The ground state solution is
formulated by minimizing the energy functional under a constraint, which is
discretized by the finite element method. The finite element approximation for
1d, 2d with radial symmetry and 3d with spherical symmetry and cylindrical
symmetry are presented in detail and approximate ground state solutions, which
are used as initial guess in our practical numerical computation of the
minimization problem, of the GPE in two extreme regimes: very weak interactions
and strong repulsive interactions are provided. Numerical results in 1d, 2d
with radial symmetry and 3d with spherical symmetry and cylindrical symmetry
for atoms ranging up to millions in the condensation are reported to
demonstrate the novel numerical method. Furthermore, comparisons between the
ground state solutions and their Thomas-Fermi approximations are also reported.
Extension of the numerical method to compute the excited states of GPE is also
presented.Comment: 33 pages, 22 figure
Generalized Sums over Histories for Quantum Gravity I. Smooth Conifolds
This paper proposes to generalize the histories included in Euclidean
functional integrals from manifolds to a more general set of compact
topological spaces. This new set of spaces, called conifolds, includes
nonmanifold stationary points that arise naturally in a semiclasssical
evaluation of such integrals; additionally, it can be proven that sequences of
approximately Einstein manifolds and sequences of approximately Einstein
conifolds both converge to Einstein conifolds. Consequently, generalized
Euclidean functional integrals based on these conifold histories yield
semiclassical amplitudes for sequences of both manifold and conifold histories
that approach a stationary point of the Einstein action. Therefore sums over
conifold histories provide a useful and self-consistent starting point for
further study of topological effects in quantum gravity. Postscript figures
available via anonymous ftp at black-hole.physics.ubc.ca (137.82.43.40) in file
gen1.ps.Comment: 81pp., plain TeX, To appear in Nucl. Phys.
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