2,539 research outputs found
Electro-Reflectance Spectra of Blue Bronze
We show that the infrared reflectance of the quasi-one dimensional
charge-density-wave (CDW) conductor K0.3MoO3 (blue bronze) varies with position
when a voltage greater than the CDW depinning threshold is applied. The spatial
dependence and spectra associated with these changes are generally as expected
from the electro-transmission [B.M. Emerling, et al, Eur. Phys. J. B 16, 295
(2000)], but there are some differences which might be associated with changes
in the CDW properties on the surface. We have examined the electro-reflectance
spectrum associated with CDW current investigation for light polarized parallel
to the conducting chains for signs of expected current-induced intragap states,
and conclude that the density of any such states is at least an order of
magnitude lower than expected.Comment: 1)submitted to Eur. Phys. J B 2) revised (July 24) to a) better
emphasize results and b) with new figure insets to make paper more
self-containe
The isolation of gravitational instantons: Flat tori V flat R^4
The role of topology in the perturbative solution of the Euclidean Einstein
equations about flat instantons is examined.Comment: 15 pages, ICN-UNAM 94-1
Evaluation of the synoptic and mesoscale predictive capabilities of a mesoscale atmospheric simulation system
The overall performance characteristics of a limited area, hydrostatic, fine (52 km) mesh, primitive equation, numerical weather prediction model are determined in anticipation of satellite data assimilations with the model. The synoptic and mesoscale predictive capabilities of version 2.0 of this model, the Mesoscale Atmospheric Simulation System (MASS 2.0), were evaluated. The two part study is based on a sample of approximately thirty 12h and 24h forecasts of atmospheric flow patterns during spring and early summer. The synoptic scale evaluation results benchmark the performance of MASS 2.0 against that of an operational, synoptic scale weather prediction model, the Limited area Fine Mesh (LFM). The large sample allows for the calculation of statistically significant measures of forecast accuracy and the determination of systematic model errors. The synoptic scale benchmark is required before unsmoothed mesoscale forecast fields can be seriously considered
Initial Data for General Relativity with Toroidal Conformal Symmetry
A new class of time-symmetric solutions to the initial value constraints of
vacuum General Relativity is introduced. These data are globally regular,
asymptotically flat (with possibly several asymptotic ends) and in general have
no isometries, but a group of conformal isometries. After
decomposing the Lichnerowicz conformal factor in a double Fourier series on the
group orbits, the solutions are given in terms of a countable family of
uncoupled ODEs on the orbit space.Comment: REVTEX, 9 pages, ESI Preprint 12
Asymptotic Behaviour of the Proper Length and Volume of the Schwarzschild Singularity
Though popular presentations give the Schwarzschild singularity as a point it
is known that it is spacelike and not timelike. Thus it has a "length" and is
not a "point". In fact, its length must necessarily be infinite. It has been
proved that the proper length of the Qadir-Wheeler suture model goes to
infinity [1], while its proper volume shrinks to zero, and the asymptotic
behaviour of the length and volume have been calculated. That model consists of
two Friedmann sections connected by a Schwarzschild "suture". The question
arises whether a similar analysis could provide the asymptotic behaviour of the
Schwarzschild black hole near the singularity. It is proved here that, unlike
the behaviour for the suture model, for the Schwarzschild essential singularity
and , where
is the mean extrinsic curvature, or the York time.Comment: 13 pages, 1 figur
Dynamics of the hysteretic voltage-induced torsional strain in tantalum trisulfide
We have studied how the hysteretic voltage-induced torsional strain,
associated with charge-density-wave depinning, in orthorhombic tantalum
trisulfide depends on square-wave and triangle-wave voltages of different
frequencies and amplitudes. The strains are measured by placing the sample,
with a wire glued to the center as a transducer, in a radio frequency cavity
and measuring the modulated response of the cavity. From the triangle waves, we
map out the time dependence of the hysteresis loops, and find that the
hysteresis loops broaden for waves with periods less than 30 seconds. The
square-wave response shows that the dynamic response to positive and negative
voltages can be quite different. The overall frequency dependence is
relaxational, but with multiple relaxation times which typically decrease with
increasing voltage. The detailed dynamic response is very sample dependent,
suggesting that it depends in detail on interactions of the CDW with sample
defects.Comment: 13 pages, 6 figures, to be published in Journal of Physics: Cond.
Mat
Collision of spinning black holes in the close limit
In this paper we consider the collision of spinning holes using first order
perturbation theory of black holes (Teukolsky formalism). With these results
(along with ones, we published in the past) one can predict the properties of
the gravitational waves radiated from the late stage inspiral of two spinning,
equal mass black holes. Also we note that the energy radiated by the head-on
collision of two spinning holes with spins (that are equal and opposite)
aligned along the common axis is more than the case in which the spins are
perpendicular to the axis of the collision.Comment: 6 pages, 3 figures, submitted to PR
Uniqueness of the asymptotic AdS3 geometry
We explicitly show that in (2+1) dimensions the general solution of the
Einstein equations with negative cosmological constant on a neigbourhood of
timelike spatial infinity can be obtained from BTZ metrics by coordinate
transformations corresponding geometrically to deformations of their spatial
infinity surface. Thus, whatever the topology and geometry of the bulk, the
metric on the timelike extremities is BTZ.Comment: LaTeX, 8 pages, no figures, version that will appear in Class. Quant.
Gra
The metaphysics of Machian frame-dragging
The paper investigates the kind of dependence relation that best portrays Machian frame-dragging in general relativity. The question is tricky because frame-dragging relates local inertial frames to distant distributions of matter in a time-independent way, thus establishing some sort of non-local link between the two. For this reason, a plain causal interpretation of frame-dragging faces huge challenges. The paper will shed light on the issue by using a generalized structural equation model analysis in terms of manipulationist counterfactuals recently applied in the context of metaphysical enquiry by Schaffer (2016) and Wilson (2017). The verdict of the analysis will be that frame-dragging is best understood in terms of a novel type of dependence relation that is half-way between causation and grounding
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