5,746 research outputs found
Fuel/engine/airframe tradeoff study, phase 1
The effects of broadening the specifications for JP-4 and JP-8 fueled on the performance and cost of all USAF aircraft presently using JP-4 as well as those expected to be introduced into the force structure by 1983 are investigated. Test results indicated that there was no impact on engine performance, turbine durability, and coking, however there was a small maintenance cost increase as a result of a small combustor life decrease. Using JP-4 as standard fuel will avoid the use of high demand middle distillate fuels and give producers flexibility. Extensive use of JP-8 in the United States will increase middle distillate demand and cause a slight increase in engine hot-section maintenance. It is also concluded that the maximum allowable freeze point of JP-4 or JP-8 cannot be increased without degrading system performance and safety as critical conditions are approached
Clarifying spherical collapse in coupled dark energy cosmologies
The spherical collapse model is often used to follow the evolution of
overdensities into the nonlinear regime. We describe the correct approach to be
used in coupled dark energy cosmologies, where a fifth force, different from
gravity and mediated by the dark energy scalar field, influences the collapse.
We reformulate the spherical collapse description by deriving it directly from
the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with
the corresponding relativistic equations, we show how the fifth force should be
taken into account within the spherical collapse picture and clarify the
problems arising when an inhomogeneous scalar field is considered within a
spherical collapse picture. We then apply our method to the case of coupled
quintessence, where the fifth force acts among cold dark matter particles, and
to growing neutrino quintessence, where the fifth force acts between neutrinos.
Furthermore, we review this method when applied to standard cosmologies and
apply our analysis to minimally coupled quintessence and check past results for
early dark energy parametrizations.Comment: 16 pages, 13 figures, published in Physical Review D, minor changes
and correction
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