39,976 research outputs found
A comparative analysis of XV-15 tiltrotor hover test data and WOPWOP predictions incorporating the fountain effect
Acoustic measurements from a hovering full scale XV-15 tilt rotor with the advanced technology blades are presented which show the directionality of fountain effect noise. Predicted acoustic directivity results are also presented which show agreement with the measured data. The aeroacoustic code, WOPWOP, was used in conjunction with a mathematical model which simulated the fountain recirculation aerodynamic effect on the rotor blade surface pressures. The predictions were used to identify the spike character in the measured data as fountain effect associated noise. The directivity of the fountain effect noise was observed to be dominant at the rear of the aircraft with increased intensities 45 degrees below the rotor disk planes
TRADE FLOWS AND MARKETING PRACTICES IN THE TEXAS NURSERY INDUSTRY
International Relations/Trade, Marketing,
Analytic Solutions to the Constraint Equation for a Force-Free Magnetosphere around a Kerr Black Hole
The Blandford-Znajek constraint equation for a stationary, axisymmetric
black-hole force-free magnetosphere is cast in a 3+1 absolute space and time
formulation, following Komissarov (2004). We derive an analytic solution for
fields and currents to the constraint equation in the far-field limit that
satisfies the Znajek condition at the event horizon. This solution generalizes
the Blandford-Znajek monopole solution for a slowly rotating black hole to
black holes with arbitrary angular momentum. Energy and angular momentum
extraction through this solution occurs mostly along the equatorial plane. We
also present a nonphysical, reverse jet-like solution.Comment: 6 pages, accepted for publication in Ap
A Bound on Mixing Efficiency for the Advection-Diffusion Equation
An upper bound on the mixing efficiency is derived for a passive scalar under
the influence of advection and diffusion with a body source. For a given
stirring velocity field, the mixing efficiency is measured in terms of an
equivalent diffusivity, which is the molecular diffusivity that would be
required to achieve the same level of fluctuations in the scalar concentration
in the absence of stirring, for the same source distribution. The bound on the
equivalent diffusivity depends only on the functional "shape" of both the
source and the advecting field. Direct numerical simulations performed for a
simple advecting flow to test the bounds are reported.Comment: 10 pages, 2 figures, JFM format (included
Opportunistic use of a wool-like artificial material as lining of Tit (Paridae) nests
The lining material is a key element of bird nests primarily serving as insulation for the adult, eggs and/or chicks but collection of such material will have an energetic cost. This study investigated the nest building effort of four species of tit (Paridae) in an English wood by determining the use of colored, wool-like artificial nest lining material over the period 2000-2010. The distances that birds carried the material from source to nest was recorded for each nest as an indirect measure of the energetic cost of collection of nest material by individual birds. Birds did not always use nest material from the nearest source to their nest and some birds collected material from 2, 3 or 4 well-separated sources. There was no detectable color preference in choice of material and few birds would travel more than 200 m to gather the material. Use of the material appeared to depend on the species. Within defined areas around material dispensers not all individual Great Tits (Parus major) used the artificial material and, for all species examined, the proportion of birds using the material declined with increasing distance between source and nest. Use of artificial material suggested that selection of nest materials was probably opportunistic but also reflected the preference of these species for a wool-like nest-lining
Robust CNOT gates from almost any interaction
There are many cases where the interaction between two qubits is not
precisely known, but single qubit operations are available. In this paper we
show how, regardless of an incomplete knowledge of the strength or form of the
interaction between two qubits, it is often possible to construct a CNOT gate
which has arbitrarily high fidelity. In particular, we show that oscillations
in the strength of the exchange interaction in solid state Si and Ge structures
are correctable.Comment: 5 pages, 2 figure
- …