2,046 research outputs found
Energy density and pressure of long wavelength gravitational waves
Inflation leads us to expect a spectrum of gravitational waves (tensor
perturbations) extending to wavelengths much bigger than the present observable
horizon. Although these gravity waves are not directly observable, the energy
density that they contribute grows in importance during the radiation- and
dust-dominated ages of the universe. We show that the back reaction of tensor
perturbations during matter domination is limited from above, since
gravitational waves of wavelength have a share of the total energy
density during matter domination that is at most
equal to the share of the total energy density that they had when the mode
exited the Hubble radius during inflation. This work is to
be contrasted to that of Sahni, who analyzed the energy density of gravity
waves only insofar as their wavelengths are smaller than . Such a
cut-off in the spectral energy of gravity waves leads to the breakdown of
energy conservation, and we show that this anomaly is eliminated simply by
taking into account the energy density and pressure of long wavelength
gravitational waves as well as short wavelength ones.Comment: Updated one reference; 17 pages, no figure
Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
Kepler photometry of the hot Neptune host star HAT-P-11 suggests that its
spot latitude distribution is comparable to the Sun's near solar maximum. We
search for evidence of an activity cycle in the CaII H & K chromospheric
emission -index with archival Keck/HIRES spectra and observations from the
echelle spectrograph on the ARC 3.5 m Telescope at APO. The chromospheric
emission of HAT-P-11 is consistent with a year activity cycle,
which plateaued near maximum during the Kepler mission. In the cycle that we
observed, the star seemed to spend more time near active maximum than minimum.
We compare the normalized chromospheric emission index of
HAT-P-11 with other stars. HAT-P-11 has unusually strong chromospheric emission
compared to planet-hosting stars of similar effective temperature and rotation
period, perhaps due to tides raised by its planet.Comment: 16 pages, 8 figures; accepted to the Astrophysical Journa
Gravitational radiation from compact binary systems: gravitational waveforms and energy loss to second post-Newtonian order
We derive the gravitational waveform and gravitational-wave energy flux
generated by a binary star system of compact objects (neutron stars or black
holes), accurate through second post-Newtonian order () beyond the lowest-order quadrupole approximation. We cast the
Einstein equations into the form of a flat-spacetime wave equation together
with a harmonic gauge condition, and solve it formally as a retarded integral
over the past null cone of the chosen field point. The part of this integral
that involves the matter sources and the near-zone gravitational field is
evaluated in terms of multipole moments using standard techniques; the
remainder of the retarded integral, extending over the radiation zone, is
evaluated in a novel way. The result is a manifestly convergent and finite
procedure for calculating gravitational radiation to arbitrary orders in a
post-Newtonian expansion. Through second post-Newtonian order, the radiation is
also shown to propagate toward the observer along true null rays of the
asymptotically Schwarzschild spacetime, despite having been derived using flat
spacetime wave equations. The method cures defects that plagued previous
``brute- force'' slow-motion approaches to the generation of gravitational
radiation, and yields results that agree perfectly with those recently obtained
by a mixed post-Minkowskian post-Newtonian method. We display explicit formulae
for the gravitational waveform and the energy flux for two-body systems, both
in arbitrary orbits and in circular orbits. In an appendix, we extend the
formalism to bodies with finite spatial extent, and derive the spin corrections
to the waveform and energy loss.Comment: 59 pages ReVTeX; Physical Review D, in press; figures available on
request to [email protected]
The Quantum Gravitationally Induced Stress Tensor
We derive non-perturbative relations between the expectation value of the
invariant element in a homogeneous and isotropic state and the quantum
gravitationally induced pressure and energy density. By exploiting previously
obtained bounds for the maximum possible growth of perturbative corrections to
a locally de Sitter background we show that the two loop result dominates all
higher orders. We also show that the quantum gravitational slowing of inflation
becomes non-perturbatively strong earlier than previously expected.Comment: 13 pages, LaTeX 2 epsilo
Laboratory Evaluation of Dynamic Routing of Air Traffic in an En Route Arrival Metering Environment
Arrival air traffic operations in the presence of convective weather are subject to uncertainty in aircraft routing and subsequently in flight trajectory predictability. Current management of arrival operations in weather-impacted airspace results in significant flight delay and suspension of arrival metering operations. The Dynamic Routing for Arrivals in Weather (DRAW) concept provides flight route amendment advisories to Traffic Management Coordinators to mitigate the impacts of convective weather on arrival operations. DRAW provides both weather conflict and schedule information for proposed route amendments, allowing air traffic managers to simultaneously evaluate weather avoidance routing and potential schedule and delay impacts. Subject matter experts consisting of retired Traffic Management Coordinators and retired Sector Controllers with arrival metering experience participated in a simulation study of Fort Worth Air Route Traffic Control Center arrival operations. Data were collected for Traffic Management Coordinator and Sector Controller participants over three weeks of simulation activities in October, 2017. Traffic Management Coordinators reported acceptable workload levels, a positive impact on their ability to manage arrival traffic while using DRAW, and initiated weather mitigation reroutes earlier while using DRAW. Sector Controllers also reported acceptable workload levels while using DRAW
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Pipeline corridors through wetlands
This paper presents preliminary findings from six vegetational surveys of gas pipeline rights-of-way (ROW) through wetlands and quantifies the impacts of a 20-year-old pipeline ROW through a boreal forest wetland. Six sites of various ages were surveyed in ecosystems ranging from coastal marsh to forested wetland. At all sites except one, both the number and the percentage of wetland species on the Row approximated or exceeded those in the adjacent natural area. The boreal forest study showed that (1) adjacent natural wetland areas were not altered in type; (2) water sheet flow restriction had been reversed by nature; (3) no nonnative plant species invaded the natural area; (4) three-quarters of the ROW area was a wetland, and (5) the ROW increased diversity
Gravitational Optics: Self-phase modulation and harmonic cascades
Nonlinear wave interaction of low amplitude gravitational waves in flat
space-time is considered. Analogy with optics is established. It is shown that
the flat metric space-time is equivalent to a centro-symmetric optical medium,
with no second order susceptibility. The lowest order nonlinear effects are
those due to the third order nonlinearity and include self-phase modulation and
high harmonic generation. These processes lead to an efficient energy dilution
of the gravitational wave energy over an increasingly large spectral range.Comment: 12 pages, REVTEX
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