91,104 research outputs found
Further Series Studies of the Spin-1/2 Heisenberg Antiferromagnet at T=0: Magnon Dispersion and Structure Factors
We have extended our previous series studies of quantum antiferromagnets at
zero temperature by computing the one-magnon dispersion curves and various
structure factors for the linear chain, square and simple cubic lattices. Many
of these results are new; others are a substantial extension of previous work.
These results are directly comparable with neutron scattering experiments and
we make such comparisons where possible.Comment: 15 pages, 12 figures, revised versio
Tables of X-coefficients and Lambda-factors for Triple Angular Correlation Analysis
Tables of x-coefficients and lambda-factors for triple angular correlation measurements in nuclear reaction studie
Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites
The prospects for high thermoelectric performance in phosphide skutterudites
are investigated based on first principles calculations. We find that
stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in
that it is metallic. As such the band structure must be modified if high
thermopowers are to be achieved. In analogy to the antimonides it is expected
that this may be done by filling with La. Calculations for LaFe_4P_12 show that
a gap can in fact be opened by La filling, but that the valence band is too
light to yield reasonable p-type thermopowers at appropriate carrier densities;
n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl
Knowlesi malaria in Vietnam
The simian malaria parasite Plasmodium knowlesi is transmitted in the forests of Southeast Asia. Symptomatic zoonotic knowlesi malaria in humans is widespread in the region and is associated with a history of spending time in the jungle. However, there are many settings where knowlesi transmission to humans would be expected but is not found. A recent report on the Ra-glai population of southern central Vietnam is taken as an example to help explain why this may be so
Spin-wave excitation spectra and spectral weights in square lattice antiferromagnets
Using a recently developed method for calculating series expansions of the
excitation spectra of quantum lattice models, we obtain the spin-wave spectra
for square lattice, Heisenberg-Ising antiferromagnets. The calculated
spin-wave spectrum for the Heisenberg model is close to but noticeably
different from a uniformly renormalized classical (large-) spectrum with the
renormalization for the spin-wave velocity of approximately . The
relative weights of the single-magnon and multi-magnon contributions to neutron
scattering spectra are obtained for wavevectors throughout the Brillouin zone.Comment: Two postscript figures, 4 two-column page
First Principles Study of Zn-Sb Thermoelectrics
We report first principles LDA calculations of the electronic structure and
thermoelectric properties of -ZnSb. The material is found
to be a low carrier density metal with a complex Fermi surface topology and
non-trivial dependence of Hall concentration on band filling. The band
structure is rather covalent, consistent with experimental observations of good
carrier mobility. Calculations of the variation with band filling are used to
extract the doping level (band filling) from the experimental Hall number. At
this band filling, which actually corresponds to 0.1 electrons per 22 atom unit
cell, the calculated thermopower and its temperature dependence are in good
agreement with experiment. The high Seebeck coefficient in a metallic material
is remarkable, and arises in part from the strong energy dependence of the
Fermiology near the experimental band filling. Improved thermoelectric
performance is predicted for lower doping levels which corresponds to higher Zn
concentrations.Comment: 5 pages, 6 figure
Bifurcation Analysis of Reaction Diffusion Systems on Arbitrary Surfaces
In this paper we present computational techniques to investigate the
solutions of two-component, nonlinear reaction-diffusion (RD) systems on
arbitrary surfaces. We build on standard techniques for linear and nonlinear
analysis of RD systems, and extend them to operate on large-scale meshes for
arbitrary surfaces. In particular, we use spectral techniques for a linear
stability analysis to characterize and directly compose patterns emerging from
homogeneities. We develop an implementation using surface finite element
methods and a numerical eigenanalysis of the Laplace-Beltrami operator on
surface meshes. In addition, we describe a technique to explore solutions of
the nonlinear RD equations using numerical continuation. Here, we present a
multiresolution approach that allows us to trace solution branches of the
nonlinear equations efficiently even for large-scale meshes. Finally, we
demonstrate the working of our framework for two RD systems with applications
in biological pattern formation: a Brusselator model that has been used to
model pattern development on growing plant tips, and a chemotactic model for
the formation of skin pigmentation patterns. While these models have been used
previously on simple geometries, our framework allows us to study the impact of
arbitrary geometries on emerging patterns.Comment: This paper was submitted at the Journal of Mathematical Biology,
Springer on 07th July 2015, in its current form (barring image references on
the last page and cosmetic changes owning to rebuild for arXiv). The complete
body of work presented here was included and defended as a part of my PhD
thesis in Nov 2015 at the University of Ber
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