4,715 research outputs found
Electromagnetic Casimir piston in higher dimensional spacetimes
We consider the Casimir effect of the electromagnetic field in a higher
dimensional spacetime of the form , where is the
4-dimensional Minkowski spacetime and is an -dimensional
compact manifold. The Casimir force acting on a planar piston that can move
freely inside a closed cylinder with the same cross section is investigated.
Different combinations of perfectly conducting boundary conditions and
infinitely permeable boundary conditions are imposed on the cylinder and the
piston. It is verified that if the piston and the cylinder have the same
boundary conditions, the piston is always going to be pulled towards the closer
end of the cylinder. However, if the piston and the cylinder have different
boundary conditions, the piston is always going to be pushed to the middle of
the cylinder. By taking the limit where one end of the cylinder tends to
infinity, one obtains the Casimir force acting between two parallel plates
inside an infinitely long cylinder. The asymptotic behavior of this Casimir
force in the high temperature regime and the low temperature regime are
investigated for the case where the cross section of the cylinder in is
large. It is found that if the separation between the plates is much smaller
than the size of , the leading term of the Casimir force is the
same as the Casimir force on a pair of large parallel plates in the
-dimensional Minkowski spacetime. However, if the size of
is much smaller than the separation between the plates, the leading term of the
Casimir force is times the Casimir force on a pair of large parallel
plates in the 4-dimensional Minkowski spacetime, where is the first Betti
number of . In the limit the manifold vanishes, one
does not obtain the Casimir force in the 4-dimensional Minkowski spacetime if
is nonzero.Comment: 22 pages, 4 figure
Finite Temperature Casimir Effect in Randall-Sundrum Models
The finite temperature Casimir effect for a scalar field in the bulk region
of the two Randall-Sundrum models, RSI and RSII, is studied. We calculate the
Casimir energy and the Casimir force for two parallel plates with separation
on the visible brane in the RSI model. High-temperature and low-temperature
cases are covered. Attractiveness versus repulsiveness of the temperature
correction to the force is discussed in the typical special cases of
Dirichlet-Dirichlet, Neumann-Neumann, and Dirichlet-Neumann boundary conditions
at low temperature. The Abel-Plana summation formula is made use of, as this
turns out to be most convenient. Some comments are made on the related
contemporary literature.Comment: 33 pages latex, 2 figures. Some changes in the discussion. To appear
in New J. Phy
STRENGTH AND CONDITIONING PROGRAMMES FOR IMPROVING BACK MUSCLE FATIGABILITY IN FIREFIGHTERS
Back pain and back-related injuries are common in firefighters. The purpose of this study was to compare the effectiveness of two different types of strength and conditioning programmes in improving back muscle fatigability in firefighters. A total of 12 male firefighters completed 16 weeks on supervised exercise intervention programme. The Functional Group was prescribed unilateral movements that mimicked the asymmetrical nature of firefighting tasks. The Conventional Group performed more bilaterally loaded, symmetrical exercise training. The lumbar extensor muscles’ resistance to fatigue was assessed using the Modified Sorensen test with electromyography (EMG). The EMG median frequency slope was less steep (p = 0.023, η²p =0.420) after training, indicating improvement in fatigability. There was no difference between the groups (p = .605, η²p = 0.028) and no interaction effect (p = 0.245, η²p =0.132). In conclusion, a well-rounded strength and conditioning programme is promising in improving back muscle fatigability in firefighters
Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies
The combined local structure techniques, extended x-ray absorption fine
structure (EXAFS) and neutron pair distribution function analysis, have been
used for temperatures 4 <= T <= 330 K to rule out a large Jahn-Teller (JT)
distortion of the Co-O bond in La1-xSrxCoO3 for a significant fraction of Co
sites (x <= 0.35), indicating few, if any, JT-active, singly occupied e_g Co
sites exist.Comment: 5 page
Viral quasispecies inference from 454 pyrosequencing
10.1186/1471-2105-14-355BMC Bioinformatics141-BBMI
Multi-black hole solutions in five dimensions
Using a recently developed generalized Weyl formalism, we construct an
asymptotically flat, static vacuum Einstein solution that describes a
superposition of multiple five-dimensional Schwarzschild black holes. The
spacetime exhibits a U(1)\times U(1) rotational symmetry. It is argued that for
certain choices of parameters, the black holes are collinear and so may be
regarded as a five-dimensional generalization of the Israel-Khan solution. The
black holes are kept in equilibrium by membrane-like conical singularities
along the two rotational axes; however, they still distort one another by their
mutual gravitational attraction. We also generalize this solution to one
describing multiple charged black holes, with fixed mass-to-charge ratio, in
Einstein-Maxwell-dilaton theory.Comment: 23 pages, 6 figure
A Storage Ring for Neutral Atoms
We have demonstrated a storage ring for ultra-cold neutral atoms. Atoms with
mean velocities of 1 m/s corresponding to kinetic energies of ~100 neV are
confined to a 2 cm diameter ring by magnetic forces produced by two
current-carrying wires. Up to 10^6 atoms are loaded at a time in the ring, and
7 revolutions are clearly observed. Additionally, we have demonstrated multiple
loading of the ring and deterministic manipulation of the longitudinal velocity
distribution of the atoms using applied laser pulses. Applications of this ring
include large area atom interferometers and cw monochromatic atomic beam
generation.Comment: 4 pages, 5 figure
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