113,776 research outputs found
Radiated noise from an externally blown flap
The far field noise from subsonic jet impingement on a wing-flap with a 45 deg bend was experimentally investigated. The test parameters are jet Mach number and flap length. For long flaps, the primary source mechanisms are found to be turbulent mixing and flow impingement. For short flaps, the interaction of turbulent flow with the flap trailing edge appears to strongly influence the radiated noise
Excitation properties of galaxies with the highest [OIII]/[OII] ratios: No evidence for massive escape of ionizing photons
The possibility that star-forming galaxies may leak ionizing photons is at
the heart of many present-day studies that investigate the reionization of the
Universe. We test this hypothesis on local blue compact dwarf galaxies of very
high excitation. We assembled a sample of such galaxies by examining the
spectra from Data Releases 7 and 10 of the Sloan Digital Sky Survey. We argue
that reliable conclusions cannot be based on strong lines alone, and adopt a
strategy that includes important weak lines such as [OI] and the
high-excitation HeII and [ArIV] lines. Our analysis is based on purely
observational diagrams and on a comparison of photoionization models with
well-chosen emission-line ratio diagrams. We show that spectral energy
distributions from current stellar population synthesis models cannot account
for all the observational constraints, which led us to mimick several scenarios
that could explain the data. These include the additional presence of hard
X-rays or of shocks. We find that only ionization-bounded models (or models
with an escape fraction of ionizing photons lower than 10%) are able to
simultaneously explain all the observational constraints.Comment: accepted in Astronomy & Astrophysic
Interactions between a massless tensor field with the mixed symmetry of the Riemann tensor and a massless vector field
Consistent couplings between a massless tensor field with the mixed symmetry
of the Riemann tensor and a massless vector field are analyzed in the framework
of Lagrangian BRST cohomology. Under the assumptions on smoothness, locality,
Lorentz covariance, and Poincare invariance of the deformations, combined with
the requirement that the interacting Lagrangian is at most second-order
derivative, it is proved that there are no consistent cross-interactions
between a single massless tensor field with the mixed symmetry of the Riemann
tensor and one massless vector field.Comment: LaTeX, 24 page
Application of The Method of Elastic Maps In Analysis of Genetic Texts
Abstract - Method of elastic maps ( http://cogprints.ecs.soton.ac.uk/archive/00003088/ and
http://cogprints.ecs.soton.ac.uk/archive/00003919/ )
allows us to construct efficiently 1D, 2D and 3D non-linear approximations to the principal manifolds with different topology (piece of plane, sphere, torus etc.) and to project data onto it. We describe the idea of the method and demonstrate its applications in analysis of genetic sequences. The animated 3D-scatters are available on our web-site: http://www.ihes.fr/~zinovyev/7clusters/
We found the universal cluster structure of genetic sequences, and demonstrated the thin structure of these clusters for coding regions. This thin structure is related to different translational efficiency
On the nature of QPO in the tail of SGR giant flares
A model is presented for the quasiperiodic component of magnetar emission
during the tail phase of giant flares. The model invokes modulation of the
particle number density in the magnetosphere. The magnetospheric currents are
modulated by torsional motion of the surface and we calculate that the
amplitude of neutron star surface oscillation should be ~1% of the NS radius in
order to produce the observed features in the power spectrum. Using an
axisymmetric analytical model for structure of the magnetosphere of an
oscillating NS, we calculate the angular distribution of the optical depth to
the resonant Compton scattering. The anisotropy of the optical depth may be why
QPO are observed only at particular rotational phases.Comment: 7 pages, 4 figures, emulateapj styl
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