6,082 research outputs found
Order parameters in the Verwey phase transition
The Verwey phase transition in magnetite is analyzed on the basis of the
Landau theory. The free energy functional is expanded in a series of components
belonging to the primary and secondary order parameters. A low-temperature
phase with the monoclinic P2/c symmetry is a result of condensation of two
order parameters X_3 and \Delta_5 . The temperature dependence of the shear
elastic constant C_44 is derived and the mechanism of its softening is
discussed.Comment: 4 pages, 1 figur
Acoustic waves: should they be propagated forward in time, or forward in space?
The evolution of acoustic waves can be evaluated in two ways: either as a
temporal, or a spatial propagation. Propagating in space provides the
considerable advantage of being able to handle dispersion and propagation
across interfaces with remarkable efficiency; but propagating in time is more
physical and gives correctly behaved reflections and scattering without effort.
Which should be chosen in a given situation, and what compromises might have to
be made? Here the natural behaviors of each choice of propagation are compared
and contrasted for an ordinary second order wave equation, the time-dependent
diffusion wave equation, an elastic rod wave equation, and the Stokes'/ van
Wijngaarden's equations, each case illuminating a characteristic feature of the
technique. Either choice of propagation axis enables a partitioning the wave
equation that gives rise to a directional factorization based on a natural
"reference" dispersion relation. The resulting exact coupled bidirectional
equations then reduce to a single unidirectional first-order wave equation
using a simple "slow evolution" assumption that minimizes effect of subsequent
approximations, while allowing a direct term-to-term comparison between exact
and approximate theories.Comment: 12 pages, v2 correcte
The effect of dairy manure on summer annual broadleaves grown as alternative silages in the Cross Timbers
Last updated: 10/19/201
The influence of harvest timing on forage sorghum silage yield and quality
Last updated: 10/19/201
Corn variety performance at Stephenville under irrigation as affected by manure application
Last updated: 10/19/201
The effect of dairy manure on summer annual grasses grown as alternative silages in the Cross Timbers
Last updated: 10/19/201
Noncovariant gauge fixing in the quantum Dirac field theory of atoms and molecules
Starting from the Weyl gauge formulation of quantum electrodynamics (QED),
the formalism of quantum-mechanical gauge fixing is extended using techniques
from nonrelativistic QED. This involves expressing the redundant gauge degrees
of freedom through an arbitrary functional of the gauge-invariant transverse
degrees of freedom. Particular choices of functional can be made to yield the
Coulomb gauge and Poincar\'{e} gauge representations. The Hamiltonian we derive
therefore serves as a good starting point for the description of atoms and
molecules by means of a relativistic Dirac field. We discuss important
implications for the ontology of noncovariant canonical QED due to the gauge
freedom that remains present in our formulation.Comment: 8 pages, 0 figure
The declining representativeness of the British party system, and why it matters
In a recent article, Michael Laver has explained âWhy Vote-Seeking Parties May Make Voters Miserableâ. His model shows that, while ideological convergence may boost congruence between governments and the median voter, it can reduce congruence between the party system and the electorate as a whole. Specifically, convergence can increase the mean distance between voters and their nearest party. In this article we show that this captures the reality of todayâs British party system. Policy scale placements in British Election Studies from 1987 to 2010 confirm that the pronounced convergence during the past decade has left the Conservatives and Labour closer together than would be optimal in terms of minimising the policy distance between the average voter and the nearest major party. We go on to demonstrate that this comes at a cost. Respondents who perceive themselves as further away from one of the major parties in the system tend to score lower on satisfaction with democracy. In short, vote-seeking parties have left the British party system less representative of the ideological diversity in the electorate, and thus made at least some British voters miserable
Consequences of asteroid fragmentation during impact hazard mitigation
The consequences of the fragmentation of an Earth-threatening asteroid due to an attempted deflection are examined in this paper. The minimum required energy for a successful impulsive deflection of a threatening object is computed and compared to the energy required to break up a small size asteroid. The results show that the fragmentation of an asteroid that underwent an impulsive deflection, such as a kinetic impact or a nuclear explosion, is a very plausible event.Astatistical model is used to approximate the number and size of the fragments as well as the distribution of velocities at the instant after the deflection attempt takes place. This distribution of velocities is a function of the energy provided by the deflection attempt, whereas the number and size of the asteroidal fragments is a function of the size of the largest fragment. The model also takes into account the gravity forces that could lead to a reaggregation of the asteroid after fragmentation. The probability distribution of the pieces after the deflection is then propagated forward in time until the encounter with Earth. A probability damage factor (i.e., expected damage caused by a given size fragment multiplied by its impact probability) is then computed and analyzed for different plausible scenarios, characterized by different levels of deflection energies and lead times
Alfalfa variety performance in central Texas
Last updated: 10/19/201
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