3,733,541 research outputs found
On Schwarzschild's Topology in Brane-Worlds
The topological structure of Schwarzschild's space-time and its maximal
analytic extension are investigated in context of brane-worlds. Using the
embedding coordinates, these geometries are seen as different states of the
evolution of a single brane-world. Comparing the topologies and the embeddings
it is shown that this evolution must be followed by a signature change in the
bulk.Comment: 6 page
Functional integral over velocities for a spinning particle with and without anomalous magnetic moment in a constant electromagnetic field
The technique of functional integration over velocities is applied to the
calculation of the propagator of a spinning particle with and without anomalous
magnetic moment. A representation for the spin factor is obtained in this
context for the particle in a constant electromagnetic field. As a by-product,
we also obtain a Schwinger representation for the first case.Comment: latex, 19 page
The Infrared Jet In 3C66B
We present images of infrared emission from the radio jet in 3C66B. Data at
three wavelengths (4.5, 6.75 and 14.5 microns) were obtained using the Infrared
Space Observatory. The 6.75 micron image clearly shows an extension aligned
with the radio structure. The jet was also detected in the 14.5 micron image,
but not at 4.5 micron. The radio-infrared-optical spectrum of the jet can be
interpreted as synchrotron emission from a population of electrons with a
high-energy break of 4e11 eV. We place upper limits on the IR flux from the
radio counter-jet. A symmetrical, relativistically beamed twin-jet structure is
consistent with our results if the jets consist of multiple components.Comment: 7 pages, 4 figure
K-Rb Fermi-Bose mixtures: vortical states and sag
We study a confined mixture of bosons and fermions in the quantal degeneracy
regime with attractive boson-fermion interaction. We discuss the effect that
the presence of vortical states and the displacement of the trapping potentials
may have on mixtures near collapse, and investigate the phase stability diagram
of the K-Rb mixture in the mean field approximation supposing in one case that
the trapping potentials felt by bosons and fermions are shifted from each
other, as it happens in the presence of a gravitational sag, and in another
case, assuming that the Bose condensate sustains a vortex state. In both cases,
we have obtained an analytical expression for the fermion effective potential
when the Bose condensate is in the Thomas-Fermi regime, that can be used to
determine the maxima of the fermionic density. We have numerically checked that
the values one obtains for the location of these maxima using the analytical
formulas remain valid up to the critical boson and fermion numbers, above which
the mixture collapses.Comment: Submitted to Phys. Rev. A (on May 2004), 15 pages with 3 figure
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A database and challenge for acoustic scene classification and event detection
Composite sandwich lattice structure
A lattice type structural panel is described. The panel utilizes the unidirectional character of filamentary epoxy impregnated composites. The panels are stiff lightweight structures for use in constructing space satellites and the like
Analysis of electric-field-induced spin splitting in wide modulation-doped quantum wells
We analyze the proper inclusion of electric-field-induced spin splittings in
the framework of the envelope function approximation. We argue that the Rashba
effect should be included in the form of a macroscopic potential as diagonal
terms in a multiband approach rather than the commonly used Rashba term
dependent on k and electric field. It is pointed out that the expectation value
of the electric field in a subband is sometimes not unique because the
expectation values can even have opposite signs for the spin-split subband
components. Symmetric quantum wells with Dresselhaus terms and the influence of
the interfaces on the spin splitting are also discussed. We apply a well
established multiband approach to wide modulation-doped InGaSb quantum wells
with strong built-in electric fields in the interface regions. We demonstrate
an efficient mechanism for switching on and off the Rashba splitting with an
electric field being an order of magnitude smaller than the local built-in
field that determines the Rashba splitting. The implications of our findings
for spintronic devices, in particular the Datta-Das spin transistor and
proposed modifications of it, are discussed.Comment: Modified version, now published. 10 pages, 3 figures, 2 table
Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields
We investigate the decoupling of heavy Kaluza-Klein modes in
theory and scalar QED with space-time topology .
We calculate the effective action due to integrating out heavy KK modes. We
construct generalized RGE's for the couplings with respect to the
compactification scale . With the solutions to the RGE's we find the
-scale dependence of the effective theory due to higher dimensional quantum
effects. We find that the heavy modes decouple in theory, but do not
decouple in scalar QED. This is due to the zero mode of the 5-th component
of the 5-d gauge field. Because is a scalar under 4-d Lorentz
transformations, there is no gauge symmetry protecting it from getting mass and
interaction terms after loop corrections. In light of these
unpleasant features, we explore compactifications, which
eliminate , allowing for the heavy modes to decouple at low energies. We
also explore the possibility of decoupling by including higher dimensional
operators. It is found that this is possible, but a high degree of fine tuning
is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added
additional reference
Method of making a composite sandwich lattice structure
A lattice type structural panel is described, which utilizes the unidirectional character of filamentary epoxy impregnated composites to produce stiff lightweight structural panels for use in constructing large area panels for space satellites and the like
Sliding not sloshing in Abell 3744: the influence of radio galaxies NGC 7018 and 7016 on cluster gas
We present new X-ray (Chandra) and radio (JVLA) observations of the nearby
cluster Abell 3744. It hosts two prominent radio galaxies with powers in the
range critical for radio-mode feedback. The radio emission from these galaxies
terminates in buoyant tendrils reaching the cluster's outer edge, and the
radio-emitting plasma clearly influences the cluster's X-ray-emitting
atmosphere. The cluster's average gas temperature, of kT=3.5 keV, is high for
its bolometric luminosity of 3.2 \times 10^{43} ergs s^{-1}, but the 100
kpc-scale cavity carved out by radio-emitting plasma shows evidence of less
than 2 per cent of the excess enthalpy. We suggest instead that a high-velocity
encounter with a galaxy group is responsible for dispersing and increasing the
entropy of the gas in this non-cool-core cluster. We see no evidence for
shocks, or established isobaric gas motions (sloshing), but there is much
sub-structure associated with a dynamically active central region that
encompasses the brightest radio emission. Gas heating is evident in directions
perpendicular to the inferred line of encounter between the infalling group and
cluster. The radio-emitting tendrils run along boundaries between gas of
different temperature, apparently lubricating the gas flows and inhibiting heat
transfer. The first stages of the encounter may have helped trigger the radio
galaxies into their current phase of activity, where we see X-rays from the
nuclei, jets, and hotspots.Comment: Accepted for publication in ApJ (13 pages, 17 figures
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