121,078 research outputs found
Size Gap for Zero Temperature Black Holes in Semiclassical Gravity
We show that a gap exists in the allowed sizes of all zero temperature static
spherically symmetric black holes in semiclassical gravity when only
conformally invariant fields are present. The result holds for both charged and
uncharged black holes. By size we mean the proper area of the event horizon.
The range of sizes that do not occur depends on the numbers and types of
quantized fields that are present. We also derive some general properties that
both zero and nonzero temperature black holes have in all classical and
semiclassical metric theories of gravity.Comment: 4 pages, ReVTeX, no figure
Bose Fluids Above Tc: Incompressible Vortex Fluids and "Supersolidity"
This paper emphasizes that non-linear rotational or diamagnetic
susceptibility is characteristic of Bose fluids above their superfluid Tcs, and
for sufficiently slow rotation or weak B-fields amounts to an incompressible
response to vorticity. The cause is a missing term in the conventionally
accepted model Hamiltonian for quantized vortices in the Bose fluid. The
resulting susceptibility can account for recent observations of Chan et al on
solid He, and Ong et al on cuprate superconductors
Vacuum polarization of scalar fields near Reissner-Nordstr\"{o}m black holes and the resonance behavior in field-mass dependence
We study vacuum polarization of quantized massive scalar fields in
equilibrium at black-hole temperature in Reissner-Nordstr\"{o}m background. By
means of the Euclidean space Green's function we analytically derive the
renormalized expression at the event horizon with the area
. It is confirmed that the polarization amplitude
is free from any divergence due to the infinite red-shift
effect. Our main purpose is to clarify the dependence of on
field mass in relation to the excitation mechanism. It is shown for
small-mass fields with how the excitation of
caused by finite black-hole temperature is suppressed as increases, and it
is verified for very massive fields with that
decreases in proportion to with the amplitude equal to the
DeWitt-Schwinger approximation. In particular, we find a resonance behavior
with a peak amplitude at in the field-mass dependence of
vacuum polarization around nearly extreme (low-temperature) black holes. The
difference between Scwarzschild and nearly extreme black holes is discussed in
terms of the mass spectrum of quantum fields dominant near the event horizon.Comment: 24 pages, 1 figure Accepted in PR
Design, evaluation and recommedation effort relating to the modification of a residential 3-ton absorption cycle cooling unit for operation with solar energy
The possible use of solar energy powered absorption units to provide cooling and heating of residential buildings is studied. Both, the ammonia-water and the water-lithium bromide cycles, are considered. It is shown that the air cooled ammonia water unit does not meet the criteria for COP and pump power on the cooling cycle and the heat obtained from it acting as a heat pump is at too low a temperature. If the ammonia machine is water cooled it will meet the design criteria for cooling but can not supply the heating needs. The water cooled lithium bromide unit meets the specified performance for cooling with appreciably lower generator temperatures and without a mechanical solution pump. It is recommeded that in the demonstration project a direct expansion lithium bromide unit be used for cooling and an auxiliary duct coil using the solar heated water be employed for heating
Vacuum Polarisation and the Black Hole Singularity
In order to investigate the effects of vacuum polarisation on mass inflation
singularities, we study a simple toy model of a charged black hole with cross
flowing radial null dust which is homogeneous in the black hole interior. In
the region we find an approximate analytic solution to the
classical field equations. The renormalized stress-energy tensor is evaluated
on this background and we find the vacuum polarisation backreaction corrections
to the mass function . Asymptotic analysis of the semiclassical mass
function shows that the mass inflation singularity is much stronger in the
presence of vacuum polarisation than in the classical case.Comment: 12 pages, RevTe
Gravitational waveforms from the evaporating ACO cosmic string loop
The linearly polarized gravitational waveforms from a certain type of
rotating, evaporating cosmic string - the Allen-Casper-Ottewill loop - are
constructed and plotted over the lifetime of the loop. The formulas for the
waveforms are simple and exact, and describe waves which attenuate
self-similarly, with the amplitude and period of the waves falling off linearly
with time.Comment: 30 pages, 16 figure
On big rip singularities
In this comment we discuss big rip singularities occurring in typical phantom
models by violation of the weak energy condition. After that, we compare them
with future late-time singularities arising in models where the scale factor
ends in a constant value and there is no violation of the strong energy
condition. In phantom models the equation of state is well defined along the
whole evolution, even at the big rip. However, both the pressure and the energy
density of the phantom field diverge. In contrast, in the second kind of model
the equation of state is not defined at the big rip because the pressure bursts
at a finite value of the energy density.Comment: 8 page
Particle-hole symmetry breaking in the pseudogap state of Pb0.55Bi1.5Sr1.6La0.4CuO6+d: A quantum-chemical perspective
Two Bi2201 model systems are employed to demonstrate how, beside the Cu-O
\sigma-band, a second band of purely O2p\pi character can be made to cross the
Fermi level owing to its sensitivity to the local crystal field. This result is
employed to explain the particle-hole symmetry breaking across the pseudo-gap
recently reported by Shen and co-workers, see M. Hashimoto et al., Nature
Physics 6, (2010) 414. Support for a two-bands-on-a-checkerboard candidate
mechanism for High-Tc superconductivity is claimed.Comment: 25 pages, 8 figure
Transport of Sellafield-derived C-14 from the Irish Sea through the North Channel
Since the early 1950s, the Sellafield nuclear fuel reprocessing plant in Northwest England has released radio-carbon into the Irish Sea in a mainly inorganic form as part of its authorized liquid effluent discharge. In contrast to the trend in which the activities of most radionuclides in the Sellafield liquid effluent have decreased substantially, C-14 discharges have increased since 1994-95. This has largely been due to a policy change favoring marine discharges over atmospheric discharges. C-14 is radiologically important due to its long half life, mobility in the environment, and propensity for entering the food chain. Current models for radionuclide dispersal in the Irish Sea are based on a reversible equilibrium distribution coefficient (k(d)), an approach which has been shown to be inadequate for C-14. Development of predictive models for the fate of Sellafield-derived C-14 requires a thorough understanding of the biogeochemical fluxes between different carbon reservoirs and the processes controlling the net flux of C-14 out of the Irish Sea, through he North Channel. In this study., both an empirical and a halving time approach indicate that close to 100% of the C-14 that is discharged from Sellafield is dispersed beyond the Irish Sea on a time-scale of months in the form of DIC, with little transfer to the PIC, POC, and DOC fractions, indicating that the "dilute and disperse" mechanism is operating satisfactorily. This is consistent with previous research that indicated little transfer of C-14 to Irish Sea sediments, While significant C-14 enhancements have been observed in the biota of the Irish Sea, this observation is not necessarily in conflict with either of the above as the total biomass has to be taken into account in any calculations of C-14 retention within the Irish Sea
Research pressure instrumentation for NASA Space Shuttle main engine, modification no. 6
Research concerning the utilization of silicon piezoresistive strain sensing technology for space shuttle main engine applications is reported. The following specific topics were addressed: (1) transducer design and materials, (2) silicon piezoresistor characterization at cryogenic temperatures, (3) chip mounting characterization, and (4) frequency response optimization
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