7,266 research outputs found
The Paths of Quintessence
The structure of the dark energy equation of state phase plane holds
important information on the nature of the physics. We explain the bounds of
the freezing and thawing models of scalar field dark energy in terms of the
tension between the steepness of the potential vs. the Hubble drag.
Additionally, we extend the phase plane structure to modified gravity theories,
examine trajectories of models with certain properties, and categorize regions
in terms of scalar field hierarchical parameters, showing that dark energy is
generically not a slow roll phenomenon.Comment: 12 pages, 7 figures; matches PRD versio
Slicing the Vacuum: New Accelerating Mirror Solutions of the Dynamical Casimir Effect
Radiation from accelerating mirrors in a Minkowski spacetime provides
insights into the nature of horizons, black holes, and entanglement entropy. We
introduce new, simple, symmetric and analytic moving mirror solutions and study
their particle, energy, and entropy production. This includes an asymptotically
static case with finite emission that is the black hole analog of complete
evaporation. The total energy, total entropy, total particles, and spectrum are
the same on both sides of the mirror. We also study its asymptotically
inertial, drifting analog (which gives a black hole remnant) to explore
differences in finite and infinite production.Comment: 8 pages, 10 figure
Eternal and Evanescent Black Holes: It's All Done With Mirrors
The analogy between black hole radiation and accelerating mirror radiation
(the dynamical Casimir effect) is particularly strong for mirror trajectories
giving rise to a constant thermal flux of particles. We present new ways to
achieve such thermal plateaus, and customize their finite, semi-infinite, and
eternal presence, corresponding to forming/collapsing,
complete-evaporation/remnants, and eternal black holes. We find simple
expressions for the energy flux in terms of the mirror rapidity as a function
of proper time and null time.Comment: 13 pages, 11 figure
Finite Energy but Infinite Entropy Production from Moving Mirrors
Accelerating mirrors provide a simple conceptual laboratory for studying
particle production and the relation between trajectory and particle, energy,
and entropy fluxes. We focus on the relation between energy and entropy,
studying some special cases with finite total energy but infinite integrated
entropy (though the entropy flux may be finite at any particular moment). We
present a new asymptotically static moving mirror trajectory with solvable beta
Bogolyubov coefficients, total energy and fully relativistic particle count.
The integrated entropy diverges despite finite global radiative particle and
energy emission. Another class of models includes exponentially accelerated
mirrors in proper time; one of its unexpected behaviors is finite energy
emission but divergent entropy. We compare mirrors exponentially accelerated in
other coordinates as well, showing their close relation and an interesting
duality property.Comment: 10 pages, 8 figures, 2 table
Development of phase-change coatings for use as variable thermal control surfaces Final report
Phase change coatings for use as variable thermal control surface
Development of phase-change coatings for use as variable thermal control surfaces Final report, 8 Mar. 1967 - 8 Mar. 1968
Development of phase-change coatings for thermal control of spacecraft surface
The mirror at the edge of the universe: Reflections on an accelerated boundary correspondence with de Sitter cosmology
An accelerated boundary correspondence (ABC) is solved for the de Sitter
moving mirror cosmology. The beta Bogoliubov coefficients reveal the particle
spectrum is a Planck distribution with temperature inversely proportional to
horizon radius. The quantum stress-tensor indicates a constant emission of
energy flux consistent with eternal equilibrium, while the total energy carried
by the particles remains finite. The curved spacetime transformation to flat
spacetime with an accelerated boundary is illustrated, and also shown for
Anti-de Sitter (AdS) spacetime.Comment: 4 pages, 5 figure
The Effect of Repetitive Feedings on the Acceptability of Selected Metabolic Diets
Effect of repetitive feeding over extended periods of time on acceptability of selected metabolic diet
Measured space environmental effects to LDEF during retrieval
On the STS-32 shuttle mission, a space flight experiment provided an understanding of the effects of the space environment on the Long Duration Exposure Facility (LDEF) from rendezvous with the shuttle until removal from the payload bay at the Orbiter Processing Facility (OPF) at KSC. The Interim Operational Contamination Monitor (IOCM) is an attached shuttle payload that has been used on two earlier flights (STS 51C and STS 28) to quantify the contamination deposited during the course of the mission. The IOCM can characterize by direct measurement, the deposition of molecular and particulate contamination during any phase of flight. In addition to these principal measurements, the IOCM actively measures the thermophysical properties of thermal control surfaces by calorimetry, the flux of the ambient atomic oxygen environment, the incident solar flux, and the absolute ambient pressure in the payload bay. The IOCM also provides a structure and sample holders for the exposure of passive material samples to the space environment, e.g. thermal cycling, atomic oxygen, and micrometeoroids and/or orbital debris, etc. One of the more salient results from the STS-32 flight suggests that the LDEF emitted a large number of particulates after berthing into the shuttle. The mission atomic oxygen fluence was also calculated. Although the fluence was low by normal standards, the Kapton passive samples exhibited the onset of erosion. Orbital debris and micrometeoroid impacts also occurred during the retrieval mission. The average perforation diameter was approximately 12.5 microns. The largest perforation diameter was measured at 65 microns
Dark Energy Scaling from Dark Matter to Acceleration
The dark sector of the Universe need not be completely separable into
distinct dark matter and dark energy components. We consider a model of early
dark energy in which the dark energy mimics a dark matter component in both
evolution and perturbations at early times. Barotropic aether dark energy
scales as a fixed fraction, possibly greater than one, of the dark matter
density and has vanishing sound speed at early times before undergoing a
transition. This gives signatures not only in cosmic expansion but in sound
speed and inhomogeneities, and in number of effective neutrino species. Model
parameters describe the timing, sharpness of the transition, and the relative
abundance at early times. Upon comparison with current data, we find viable
regimes in which the dark energy behaves like dark matter at early times: for
transitions well before recombination the dark energy to dark matter fraction
can equal or exceed unity, while for transitions near recombination the ratio
can only be a few percent. After the transition, dark energy goes its separate
way, ultimately driving cosmic acceleration and approaching a cosmological
constant in this scenario.Comment: 10 pages, 8 figure
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