3,627 research outputs found
Casimir repulsion between metallic objects in vacuum
We give an example of a geometry in which two metallic objects in vacuum
experience a repulsive Casimir force. The geometry consists of an elongated
metal particle centered above a metal plate with a hole. We prove that this
geometry has a repulsive regime using a symmetry argument and confirm it with
numerical calculations for both perfect and realistic metals. The system does
not support stable levitation, as the particle is unstable to displacements
away from the symmetry axis.Comment: 4 pages, 4 figures; added references, replaced Fig.
Using {\sc top-c} for Commodity Parallel Computing in Cosmic Ray Physics Simulations
{\sc top-c} (Task Oriented Parallel C) is a freely available package for
parallel computing. It is designed to be easy to learn and to have good
tolerance for the high latencies that are common in commodity networks of
computers. It has been successfully used in a wide range of examples, providing
linear speedup with the number of computers. A brief overview of {\sc top-c} is
provided, along with recent experience with cosmic ray physics simulations.Comment: Talk to be presented at the XI International Symposium on Very High
Energy Cosmic Ray Interaction
Modeling near-field radiative heat transfer from sharp objects using a general 3d numerical scattering technique
We examine the non-equilibrium radiative heat transfer between a plate and
finite cylinders and cones, making the first accurate theoretical predictions
for the total heat transfer and the spatial heat flux profile for
three-dimensional compact objects including corners or tips. We find
qualitatively different scaling laws for conical shapes at small separations,
and in contrast to a flat/slightly-curved object, a sharp cone exhibits a local
\emph{minimum} in the spatially resolved heat flux directly below the tip. The
method we develop, in which a scattering-theory formulation of thermal transfer
is combined with a boundary-element method for computing scattering matrices,
can be applied to three-dimensional objects of arbitrary shape.Comment: 5 pages, 4 figures. Corrected background information in the
introduction, results and discussion unchange
Calculation of nonzero-temperature Casimir forces in the time domain
We show how to compute Casimir forces at nonzero temperatures with
time-domain electromagnetic simulations, for example using a finite-difference
time-domain (FDTD) method. Compared to our previous zero-temperature
time-domain method, only a small modification is required, but we explain that
some care is required to properly capture the zero-frequency contribution. We
validate the method against analytical and numerical frequency-domain
calculations, and show a surprising high-temperature disappearance of a
non-monotonic behavior previously demonstrated in a piston-like geometry.Comment: 5 pages, 2 figures, submitted to Physical Review A Rapid
Communicatio
Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders
The most general Lorentz-invariant decay-density-matrix for , or for , is expressed in terms
of eight helicity parameters. The parameters are physically defined in terms of
partial-width-intensities for polarized-final-states in decay.
The parameters are the partial width, the quark's chirality parameter
, the polarimetry parameter , a "pre-SSB" test parameter
, and four - interference parameters , ,
, which test for violation. They can be
used to test for non-CKM-type CP violation, anomalous 's, top
weak magnetism, weak electricity, and second-class currents. By stage-two
spin-correlation techniques, percent level statistical uncertainites are
typical for measurements at the Tevatron, and several mill level uncertainites
are typical at the LHC.Comment: Minor clarifications. Expression for r_{+-} corrected. 19 pages LaTex
+ Tables + 1 Figur
Geomagnetically Induced Currents in the Irish Power Network during Geomagnetic Storms
Geomagnetically induced currents (GICs) are a well-known terrestrial space
weather hazard. They occur in power transmission networks and are known to have
adverse effects in both high and mid-latitude countries. Here, we study GICs in
the Irish power transmission network (geomagnetic latitude 54.7--58.5
N) during five geomagnetic storms (06-07 March 2016, 20-21 December 2015, 17-18
March 2015, 29-31 October 2003 and 13-14 March 1989). We simulate electric
fields using a plane wave method together with two ground resistivity models,
one of which is derived from magnetotelluric measurements (MT model). We then
calculate GICs in the 220, 275 and 400~kV transmission network. During the
largest of the storm periods studied, the peak electric field was calculated to
be as large as 3.8~V~km\textsuperscript{-1}, with associated GICs of up to 23~A
using our MT model. Using our homogenous resistivity model, those peak values
were 1.46~V~km\textsuperscript{-1} and 25.8~A. We find that three 400 and
275~kV substations are the most likely locations for the Irish transformers to
experience large GICs.Comment: 14 pages, 11 Figures, 4 Table
Microstructure Effects for Casimir Forces in Chiral Metamaterials
We examine a recent prediction for the chirality-dependence of the Casimir
force in chiral metamaterials by numerical computation of the forces between
the exact microstructures, rather than homogeneous approximations. We compute
the exact force for a chiral bent-cross pattern, as well as forces for an
idealized "omega"-particle medium in the dilute approximation and identify the
effects of structural inhomogeneity (i.e. proximity forces and anisotropy). We
find that these microstructure effects dominate the force for separations where
chirality was predicted to have a strong influence. To get observations of
chirality free from microstructure effects, one must go to large separations
where the effect of chirality is at most of the total force.Comment: 5 pages, 4 figure
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