2,350 research outputs found
Rotating saddle trap as Foucault's pendulum
One of the many surprising results found in the mechanics of rotating systems
is the stabilization of a particle in a rapidly rotating planar saddle
potential. Besides the counterintuitive stabilization, an unexpected
precessional motion is observed. In this note we show that this precession is
due to a Coriolis-like force caused by the rotation of the potential. To our
knowledge this is the first example where such force arises in an inertial
reference frame. We also propose an idea of a simple mechanical demonstration
of this effect.Comment: 13 pages, 9 figure
The effects of Chern-Simons gravity on bodies orbiting the Earth
One of the possible low-energy consequences of string theory is the addition
of a Chern-Simons term to the standard Einstein-Hilbert action of general
relativity. It can be argued that the quintessence field should couple to this
Chern-Simons term, and if so, it drives in the linearized theory a
parity-violating interaction between the gravito-electric and gravitomagnetic
fields. In this paper, the linearized spacetime for Chern-Simons gravity around
a massive spinning body is found to include new modifications to the
gravitomagnetic field that have not appeared in previous work. The orbits of
test bodies and the precession of gyroscopes in this spacetime are calculated,
leading to new constraints on the Chern-Simons parameter space due to current
satellite experiments.Comment: 9 pages, 2 figures; minor corrections made; to appear in PR
Nonequilibrium theory of Coulomb blockade in open quantum dots
We develop a non-equilibrium theory to describe weak Coulomb blockade effects
in open quantum dots. Working within the bosonized description of electrons in
the point contacts, we expose deficiencies in earlier applications of this
method, and address them using a 1/N expansion in the inverse number of
channels. At leading order this yields the self-consistent potential for the
charging interaction. Coulomb blockade effects arise as quantum corrections to
transport at the next order. Our approach unifies the phase functional and
bosonization approaches to the problem, as well as providing a simple picture
for the conductance corrections in terms of renormalization of the dot's
elastic scattering matrix, which is obtained also by elementary perturbation
theory. For the case of ideal contacts, a symmetry argument immediately allows
us to conclude that interactions give no signature in the averaged conductance.
Non-equilibrium applications to the pumped current in a quantum pump are worked
out in detail.Comment: Published versio
Weak localization and conductance fluctuations of a chaotic quantum dot with tunable spin-orbit coupling
In a two-dimensional quantum dot in a GaAs heterostructure, the spin-orbit
scattering rate is substantially reduced below the rate in a bulk
two-dimensional electron gas [B.I. Halperin et al, Phys. Rev. Lett. 86, 2106
(2001)]. Such a reduction can be undone if the spin-orbit coupling parameters
acquire a spatial dependence, which can be achieved, e.g., by a metal gate
covering only a part of the quantum dot. We calculate the effect of such
spatially non-uniform spin-orbit scattering on the weak localization correction
and the universal conductance fluctuations of a chaotic quantum dot coupled to
electron reservoirs by ballistic point contacts, in the presence of a magnetic
field parallel to the plane of the quantum dot.Comment: 4 pages, RevTeX; 2 figures. Substantial revision
Semiclassical theory of a quantum pump
In a quantum charge pump, the periodic variation of two parameters that
affect the phase of the electronic wavefunction causes the flow of a direct
current. The operating mechanism of a quantum pump is based on quantum
interference, the phases of interfering amplitudes being modulated by the
external parameters. In a ballistic quantum dot, there is a minimum time before
which quantum interference can not occur: the Ehrenfest time. Here we calculate
the current pumped through a ballistic quantum dot when the Ehrenfest time is
comparable to the mean dwell time. Remarkably, we find that the pumped current
has a component that is not suppressed if the Ehrenfest time is much larger
than the mean dwell time.Comment: 14 pages, 8 figures. Revised version, minor change
A nearly closed ballistic billiard with random boundary transmission
A variety of mesoscopic systems can be represented as a billiard with a
random coupling to the exterior at the boundary. Examples include quantum dots
with multiple leads, quantum corrals with different kinds of atoms forming the
boundary, and optical cavities with random surface refractive index. The
specific example we study is a circular (integrable) billiard with no internal
impurities weakly coupled to the exterior by a large number of leads with one
channel open in each lead. We construct a supersymmetric nonlinear
-model by averaging over the random coupling strengths between bound
states and channels. The resulting theory can be used to evaluate the
statistical properties of any physically measurable quantity in a billiard. As
an illustration, we present results for the local density of states.Comment: 5 pages, 1 figur
Third post-Newtonian accurate generalized quasi-Keplerian parametrization for compact binaries in eccentric orbits
We present Keplerian-type parametrization for the solution of third
post-Newtonian (3PN) accurate equations of motion for two non-spinning compact
objects moving in an eccentric orbit. The orbital elements of the
parametrization are explicitly given in terms of the 3PN accurate conserved
orbital energy and angular momentum in both Arnowitt, Deser, and Misner-type
and harmonic coordinates. Our representation will be required to construct
post-Newtonian accurate `ready to use' search templates for the detection of
gravitational waves from compact binaries in inspiralling eccentric orbits. Due
to the presence of certain 3PN accurate gauge invariant orbital elements, the
parametrization should be useful to analyze the compatibility of general
relativistic numerical simulations involving compact binaries with the
corresponding post-Newtonian descriptions. If required, the present
parametrization will also be needed to compute post-Newtonian corrections to
the currently employed `timing formula' for the radio observations of
relativistic binary pulsars.Comment: 33 pages, 1 figur
Sensory diversity of fonio landraces from West Africa
This study aims to establish if there is some sensory variability among fonio landraces. Fonio, the oldest indigenous and very tasty cereal growing in West Africa, is usually consumed as a couscous. Group interviews of consumers were conducted in Bamako, Mali to identify the main quality criteria of a cooked grain. Fonio grain must be swollen, not sticky with a soft consistency, pale and containing low impurities. Sensory properties of 20 fonio landraces from Mali, Guinea and Burkina Faso were established using a descriptive sensory analysis. Five sensory descriptors were chosen among the quality criteria. Each landrace was tasted and scored in triplicate by a group of 18 trained panellists. Principal component analysis and hierarchical cluster analysis were used. The 20 landraces clustered into four sensory classes. Sensory criteria of variability were first visual characteristics (colour and impurities) and then the consistency of cooked grains. Landraces from Guinea and Mali were variable for both visual and textural characteristics; those from Burkina Faso appeared to be more homo-genous. The sensory variability of fonio offers to processors, who intend to promote this tiny cereal both in the sub-region and beyond, the possibility to choose adapted landraces to develop new products.Keywords: Digitaria exilis, fonio, landraces, cooked grain, sensory variability, MaliAfrican Journal of Biotechnology Vol. 12(15), pp. 1836-184
Diagonally Neighbour Transitive Codes and Frequency Permutation Arrays
Constant composition codes have been proposed as suitable coding schemes to
solve the narrow band and impulse noise problems associated with powerline
communication. In particular, a certain class of constant composition codes
called frequency permutation arrays have been suggested as ideal, in some
sense, for these purposes. In this paper we characterise a family of neighbour
transitive codes in Hamming graphs in which frequency permutation arrays play a
central rode. We also classify all the permutation codes generated by groups in
this family
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