5,377 research outputs found
Advanced aerodynamics and active controls technology
The results, status, and plans of NASA sponsored advanced aerodynamics and active controls technology activities are reported. Development of subsonic, energy efficient transport aircraft technologies is emphasized
Improving the staggered quark action to reduce flavour symmetry violations
We investigate a class of actions for lattice QCD with staggered quarks aimed
at reducing the flavour symmetry violations associated with using staggered
fermions. These actions replace the gauge field link fields in the quark action
with covariantly smeared fields. As such they are an extension of actions
considered by the MILC collaboration. We show that such actions systematically
reduce flavour symmetry violations in the weak coupling limit. Using the mass
splitting between Goldstone and non-Goldstone pions as a measure of flavour
symmetry violations we find that these actions have considerably less flavour
symmetry violations than the standard staggered action, and represent an
improvement on what can be achieved with the MILC action, on quenched
configurations with .Comment: 3 pages, Latex using espcrc2.sty. 1 coloured postscript figure
included with epsffile. Talk presented by D.K.Sinclair at LATTICE'97,
Edinburgh, Scotlan
Viscous damping of r-modes: Large amplitude saturation
We analyze the viscous damping of r-mode oscillations of compact stars,
taking into account non-linear viscous effects in the large-amplitude regime.
The qualitatively different cases of hadronic stars, strange quark stars, and
hybrid stars are studied. We calculate the viscous damping times of r-modes,
obtaining numerical results and also general approximate analytic expressions
that explicitly exhibit the dependence on the parameters that are relevant for
a future spindown evolution calculation. The strongly enhanced damping of large
amplitude oscillations leads to damping times that are considerably lower than
those obtained when the amplitude dependence of the viscosity is neglected.
Consequently, large-amplitude viscous damping competes with the gravitational
instability at all physical frequencies and could stop the r-mode growth in
case this is not done before by non-linear hydrodynamic mechanisms.Comment: 18 pages, 17 figures, changed convention for the r-mode amplitude,
version to be published in PR
Errors in hybrid computers
Method is described for reduction of error components in numerical integration, sampling with zero hold order, and execution time delay
Self-consistent parametrization of the two-flavor isotropic color-superconducting ground state
Lack of Lorentz invariance of QCD at finite quark chemical potential in
general implies the need of Lorentz non-invariant condensates for the
self-consistent description of the color-superconducting ground state.
Moreover, the spontaneous breakdown of color SU(3) in this state naturally
leads to the existence of SU(3) non-invariant non-superconducting expectation
values. We illustrate these observations by analyzing the properties of an
effective 2-flavor Nambu-Jona-Lasinio type Lagrangian and discuss the
possibility of color-superconducting states with effectively gapless fermionic
excitations. It turns out that the effect of condensates so far neglected can
yield new interesting phenomena.Comment: 16 pages, 3 figure
Variable sweep wing configuration Patent
Variable sweep wing configuration for supersonic aircraf
Aerodynamic-center considerations of wings and wing-body combinations
Aerodynamic center shifts of rigid wing-body combinations at increased Mach number
Dense quark matter in compact stars
The densest predicted state of matter is colour-superconducting quark matter,
in which quarks near the Fermi surface form a condensate of Cooper pairs. This
form of matter may well exist in the core of compact stars, and the search for
signatures of its presence is an ongoing enterprise. Using a bag model of quark
matter, I discuss the effects of colour superconductivity on the mass-radius
relationship of compact stars, showing that colour superconducting quark matter
can occur in compact stars at values of the bag constant where ordinary quark
matter would not be allowed. The resultant ``hybrid'' stars with colour
superconducting quark matter interior and nuclear matter surface have masses in
the range 1.3-1.6 Msolar and radii 8-11 km. Once perturbative corrections are
included, quark matter can show a mass-radius relationship very similar to that
of nuclear matter, and the mass of a hybrid star can reach 1.8 \Msolar.Comment: 11 pages, for proceedings of SQM 2003 conference; references added,
abstract reworde
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