34,579 research outputs found
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
Excitation spectrum and critical exponents of a one-dimensional integrable model of fermions with correlated hopping
We investigate the excitation spectrum of a model of colour fermions with
correlated hopping which can be solved by a nested Bethe ansatz. The gapless
excitations of particle-hole type are calculated as well as the spin-wave like
excitations which have a gap. Using general predictions of conformal field
theory the long distance behaviour of some groundstate correlation functions
are derived from a finite-size analysis of the gapless excitations. From the
algebraic decay we show that for increasing particle density the correlation of
so-called -multiplets of particles dominates over the density-density
correlation. This indicates the presence of bound complexes of these
-multiplets. This picture is also supported by the calculation of the
effective mass of charge carriers.Comment: 15 pages, 3 PostScript figures appende
Non-unique factorization of polynomials over residue class rings of the integers
We investigate non-unique factorization of polynomials in Z_{p^n}[x] into
irreducibles. As a Noetherian ring whose zero-divisors are contained in the
Jacobson radical, Z_{p^n}[x] is atomic. We reduce the question of factoring
arbitrary non-zero polynomials into irreducibles to the problem of factoring
monic polynomials into monic irreducibles. The multiplicative monoid of monic
polynomials of Z_{p^n}[x] is a direct sum of monoids corresponding to
irreducible polynomials in Z_p[x], and we show that each of these monoids has
infinite elasticity. Moreover, for every positive integer m, there exists in
each of these monoids a product of 2 irreducibles that can also be represented
as a product of m irreducibles.Comment: 11 page
Soybean harvest aids
"Soybean harvest can be filled with problems. Weeds, particularly green weeds, *can slow the speed of harvest, *cause combine problems, *result in excessive combining losses, *result in excessive combining losses, *results in docking for moisture and quality when sold, or *create problems if soybeans are stored."--First page.Z.R. Helsel and L.E. Anderson (Agronomy Department, College of Agriculture)New 9/84/7
Scale-invariance in gravity and implications for the cosmological constant
Recently a scale invariant theory of gravity was constructed by imposing a
conformal symmetry on general relativity. The imposition of this symmetry
changed the configuration space from superspace - the space of all Riemannian
3-metrics modulo diffeomorphisms - to conformal superspace - the space of all
Riemannian 3-metrics modulo diffeomorphisms and conformal transformations.
However, despite numerous attractive features, the theory suffers from at least
one major problem: the volume of the universe is no longer a dynamical
variable. In attempting to resolve this problem a new theory is found which has
several surprising and atractive features from both quantisation and
cosmological perspectives. Furthermore, it is an extremely restrictive theory
and thus may provide testable predictions quickly and easily. One particularly
interesting feature of the theory is the resolution of the cosmological
constant problem.Comment: Replaced with final version: minor changes to text; references adde
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