26,815 research outputs found
Coherent State Path Integrals in the Weyl Representation
We construct a representation of the coherent state path integral using the
Weyl symbol of the Hamiltonian operator. This representation is very different
from the usual path integral forms suggested by Klauder and Skagerstan in
\cite{Klau85}, which involve the normal or the antinormal ordering of the
Hamiltonian. These different representations, although equivalent quantum
mechanically, lead to different semiclassical limits. We show that the
semiclassical limit of the coherent state propagator in Weyl representation is
involves classical trajectories that are independent on the coherent states
width. This propagator is also free from the phase corrections found in
\cite{Bar01} for the two Klauder forms and provides an explicit connection
between the Wigner and the Husimi representations of the evolution operator.Comment: 23 page
Extreme thermopower anisotropy and interchain transport in the quasi-one-dimensional metal Li(0.9)Mo(6)O(17)
Thermopower and electrical resistivity measurements transverse to the
conducting chains of the quasi-one-dimensional metal Li(0.9)Mo(6)O(17) are
reported in the temperature range 5 K = 400 K the
interchain transport is determined by thermal excitation of charge carriers
from a valence band ~ 0.14 eV below the Fermi level, giving rise to a large,
p-type thermopower that coincides with a small, n-type thermopower along the
chains. This dichotomy -- semiconductor-like in one direction and metallic in a
mutually perpendicular direction -- gives rise to substantial transverse
thermoelectric (TE) effects and a transverse TE figure of merit among the
largest known for a single compound.Comment: PRL in press, manuscript (5pp, 4 Fig.'s) and Supplementary Material
(3pp, 3 Fig.'s
Analytical study of tunneling times in flat histogram Monte Carlo
We present a model for the dynamics in energy space of multicanonical
simulation methods that lends itself to a rather complete analytic
characterization. The dynamics is completely determined by the density of
states. In the \pm J 2D spin glass the transitions between the ground state
level and the first excited one control the long time dynamics. We are able to
calculate the distribution of tunneling times and relate it to the
equilibration time of a starting probability distribution. In this model, and
possibly in any model in which entering and exiting regions with low density of
states are the slowest processes in the simulations, tunneling time can be much
larger (by a factor of O(N)) than the equilibration time of the probability
distribution. We find that these features also hold for the energy projection
of single spin flip dynamics.Comment: 7 pages, 4 figures, published in Europhysics Letters (2005
Tecnologia para produção orgância de cenoura consorciada com alface em Sergipe.
bitstream/CPATC/19935/1/ct-50.pd
Straight spinning cosmic strings in Brans-Dicke gravity
It is presented an exact solution of straight spinning cosmic strings in
Brans-Dicke theory of gravitation. The possibility of the existence of closed
timelike curves around these cosmic strings is analyzed. Furthermore, the
stability about the formation of the topological defect discussed here is
checked. It is shown the existence of a suitable choice for the integration
constants in which closed timelike curves are not allowed. We also verify if it
is possible that the obtained spacetime can be the source that describes the
observed rotational curves in some galaxies.Comment: 13 pages, 1 figur
- …