12,142 research outputs found
Calculations, and comparison with an ideal minimum, of trimmed drag for conventional and canard configurations having various levels of static stability
Classical drag equations were used to calculate total and induced drag and ratios of stabilizer lift to wing lift for a variety of conventional and canard configurations. The Flight efficiencies of such configurations that are trimmed in pitch and have various values of static margin are evaluated. Classical calculation methods are compared with more modern lifting surface theory
A bright millisecond radio burst of extragalactic origin
Pulsar surveys offer one of the few opportunities to monitor even a small
fraction (~0.00001) of the radio sky for impulsive burst-like events with
millisecond durations. In analysis of archival survey data, we have discovered
a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small
Magellanic Cloud. The burst properties argue against a physical association
with our Galaxy or the Small Magellanic Cloud. Current models for the free
electron content in the Universe imply a distance to the burst of <1 Gpc No
further bursts are seen in 90-hr of additional observations, implying that it
was a singular event such as a supernova or coalescence of relativistic
objects. Hundreds of similar events could occur every day and act as insightful
cosmological probes.Comment: 18 pages, 4 figures. Accepted by Science. Published electronically
via Science Express on September 27, 200
Analytical Model for the Optical Functions of Indium Gallium Nitride with Application to Thin Film Solar Photovoltaic Cells
This paper presents the preliminary results of optical characterization using
spectroscopic ellipsometry of wurtzite indium gallium nitride (InxGa1-xN) thin
films with medium indium content (0.38<x<0.68) that were deposited on silicon
dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent
parametric analytical model using Gaussian oscillators to describe the
absorption spectra has been developed to extract the real and imaginary
components of the dielectric function ({\epsilon}1, {\epsilon}2) of InxGa1-xN
films. Scanning electron microscope (SEM) images are presented to examine film
microstructure and verify film thicknesses determined from ellipsometry
modelling. This fitting procedure, model, and parameters can be employed in the
future to extract physical parameters from ellipsometric data from other
InxGa1-xN films
Simulation studies of STOL airplane operations in metropolitan downtown and airport air traffic control environments
The operating problems and equipment requirements for STOL airplanes in terminal area operations in simulated air traffic control (ATC) environments were studied. These studies consisted of Instrument Flight Rules (IFR) arrivals and departures in the New York area to and from a downtown STOL port, STOL runways at John F. Kennedy International Airport, or STOL runways at a hypothetical international airport. The studies were accomplished in real time by using a STOL airplane flight simulator. An experimental powered lift STOL airplane and two in-service airplanes having high aerodynamic lift (i.e., STOL) capability were used in the simulations
Terminal-area flight procedures and route design for supersonic transport New York-transatlantic operations
The results of an analytical investigation of two departure and arrival transition procedures between John F. Kennedy International Airport and projected North Atlantic track systems for supersonic transport (SST) operations are presented. The procedures studied were: (1) separated departure and arrival transition routes with departures made at supersonic speeds, and (2) superimposed departure and arrival routes with departures restricted to subsonic speed until the airplane is on the track system. For both procedures, transition routes with intercept angles of 30 deg to 90 deg to both six-and four-track systems were investigated. Track spacings of 30 and 60 nautical miles were studied
Asymptotics of the partition function for random matrices via Riemann-Hilbert techniques, and applications to graphical enumeration
We study the partition function from random matrix theory using a well known
connection to orthogonal polynomials, and a recently developed Riemann-Hilbert
approach to the computation of detailed asymptotics for these orthogonal
polynomials. We obtain the first proof of a complete large N expansion for the
partition function, for a general class of probability measures on matrices,
originally conjectured by Bessis, Itzykson, and Zuber. We prove that the
coefficients in the asymptotic expansion are analytic functions of parameters
in the original probability measure, and that they are generating functions for
the enumeration of labelled maps according to genus and valence. Central to the
analysis is a large N expansion for the mean density of eigenvalues, uniformly
valid on the entire real axis.Comment: 44 pages, 4 figures. To appear, International Mathematics Research
Notice
Timing of pulsars found in a deep Parkes multibeam survey
We have carried out a sensitive radio pulsar survey along the northern
Galactic plane ( and |b| \lapp 2^{\circ}) using
the Parkes 20-cm multibeam system. We observed each position for 70-min on two
separate epochs. Our analyses to date have so far resulted in the detection of
32 pulsars, of which 17 were previously unknown. Here we summarize the
observations and analysis and present the timing observations of 11 pulsars and
discovery parameters for a further 6 pulsars. We also present a timing solution
for the 166-ms bursting pulsar, PSR~J1938+2213, previously discovered during an
Arecibo drift-scan survey. Our survey data for this pulsar show that the
emission can be described by a steady pulse component with bursting emission,
which lasts for typically 20--25 pulse periods, superposed. Other new
discoveries are the young 80.1-ms pulsar PSR~J1935+2025 which exhibits a
significant amount of unmodeled low-frequency noise in its timing residuals,
and the 4.2-ms pulsar PSR~J1935+1726 which is in a low-mass binary system with
a 90.7-day circular orbit.Comment: 6 pages, 2 figures, accepted for publication in MNRA
A modified Newton-Raphson analysis of flight measurements of the trailing vortices of a heavy jet transport
A modified Newton-Raphson method has been used to determine the parameters in equations describing the vortex flow to obtain a best match with flight measurements of the flow behind the C-5A airplane. The flight measurements were made using a specially instrumented T-33 airplane which passed as closely as possible to the centers of the trailing vortices at several distances behind the C-5A airplane. The flight measurements were transformed to flow velocity relative to an inertial frame of reference. The assumed form of the flow consisted of the superposition of two counterrotating, finite core vortices. The positions of the vortex centers, their total circulation, the effective eddy viscosity and measurement bias were the parameters adjusted. The assumed form of vortex flow fit well the measured velocities for the numerous sets of data, both flaps up and down for the C-5A airplane. The resulting values of total circulation, however, were about two-thirds that expected of a wing with an elliptical loading. A partial explanation of the less than expected circulation is a dip in the spanwise lift distribution at the airplane's center line. The distance between the trailing vortices at the smallest times encountered is somewhat less than that expected for an elliptical wing loading
Lutz-Kelker bias in pulsar parallax measurements
Lutz & Kelker showed that parallax measurements are systematically
overestimated because they do not properly account for the larger volume of
space that is sampled at smaller parallax values. We apply their analysis to
neutron stars, incorporating the bias introduced by the intrinsic radio
luminosity function and a realistic Galactic population model for neutron
stars. We estimate the bias for all published neutron star parallax
measurements and find that measurements with less than ~95% certainty, are
likely to be significantly biased. Through inspection of historic parallax
measurements, we confirm the described effects in optical and radio
measurements, as well as in distance estimates based on interstellar dispersion
measures. The potential impact on future tests of relativistic gravity through
pulsar timing and on X-ray--based estimates of neutron star radii is briefly
discussed.Comment: 9 pages, 3 tables, 1 figure. Accepted for publication in MNRA
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