8,055 research outputs found
Comparison of wind tunnel and flight test afterbody and nozzle pressures for a twin-jet fighter aircraft at transonic speeds
Afterbody and nozzle pressures measured on a 1/12-scale model and in flight on a twin-jet fighter aircraft were compared as Mach number varied from 0.6 to 1.2, Reynolds number from 17.5 million to 302.5 million, and angle of attack from 1 to 7 deg. At Mach 0.6 and 0.8, nozzle pressure coefficient distributions and nozzle axial force coefficients agreed and showed good recompression. At Mach 0.9 and 1.2, flow complexity caused a loss in recompression for both flight and wind tunnel nozzle data. The flight data exhibited less negative values of pressure coefficient and lower axial force coefficients than did the wind tunnel data. Reynolds number effects were noted only at these Mach numbers. Jet temperature and mass flux ratio did not affect the comparisons of nozzle axial flow coefficient. At subsonic speeds, the levels of pressure coefficient distributions on the upper fuselage and lower nacelle surfaces for flight were less negative than those for the model. The model boundary layer thickness at the aft rake station exceeded that for the forward rake station and increased with increasing angle of attack. The flight boundary layer thickness at the aft rake station was less than that for the forward rake station and decreased with increasing angle of attack
The volumetric rate of calcium-rich transients in the local universe
We present a measurement of the volumetric rate of `calcium-rich' optical
transients in the local universe, using a sample of three events from the
Palomar Transient Factory (PTF). This measurement builds on a detailed study of
the PTF transient detection efficiencies, and uses a Monte Carlo simulation of
the PTF survey. We measure the volumetric rate of calcium-rich transients to be
higher than previous estimates: events
yr Mpc. This is equivalent to 33-94% of the local volumetric type
Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce
the observed calcium abundances in galaxy clusters, assuming an asymptotic
calcium yield per calcium-rich event of ~0.05. We also
study the PTF detection efficiency of these transients as a function of
position within their candidate host galaxies. We confirm as a real physical
effect previous results that suggest calcium-rich transients prefer large
physical offsets from their host galaxies.Comment: Accepted for publication in ApJ. 9 pages, 5 figure
Could There Be A Hole In Type Ia Supernovae?
In the favored progenitor scenario, Type Ia supernovae arise from a white
dwarf accreting material from a non-degenerate companion star. Soon after the
white dwarf explodes, the ejected supernova material engulfs the companion
star; two-dimensional hydrodynamical simulations by Marietta et. al. show that,
in the interaction, the companion star carves out a conical hole of opening
angle 30-40 degrees in the supernova ejecta. In this paper we use
multi-dimensional Monte Carlo radiative transfer calculations to explore the
observable consequences of an ejecta-hole asymmetry. We calculate the variation
of the spectrum, luminosity, and polarization with viewing angle for the
aspherical supernova near maximum light. We find that the supernova looks
normal from almost all viewing angles except when one looks almost directly
down the hole. In the latter case, one sees into the deeper, hotter layers of
ejecta. The supernova is relatively brighter and has a peculiar spectrum
characterized by more highly ionized species, weaker absorption features, and
lower absorption velocities. The spectrum viewed down the hole is comparable to
the class of SN 1991T-like supernovae. We consider how the ejecta-hole
asymmetry may explain the current spectropolarimetric observations of SNe Ia,
and suggest a few observational signatures of the geometry. Finally, we discuss
the variety currently seen in observed SNe Ia and how an ejecta-hole asymmetry
may fit in as one of several possible sources of diversity.Comment: 11 pages, 9 figures, submitted to Ap
Riverbank Erosion: A Model For The Zambezi
A GAZ Proceedings article on river bank erosion on the Zambezi river
Developing knowledge confidence and perceptions of primary science teaching skills
In the English speaking world, elementary school teachers confidence in their ability to teach science is a major area of research (Murphy 2009). This paper will present data from a cohort of approximately 200 student primary teachers, all of whom have to take modules on teaching science in the primary school. Data will be presented on students’ science knowledge, their perceived confidence with which they hold that knowledge, and how that relates to their perceptions of their confidence to teach both science content and processes. The implications for teaching and learning science and for teacher education will be presented
Judicial Bias
This article examines how bias and prejudice may impact the decision making process of our judiciary. It begins in Part II from the premise that all judges, as a part of basic human functioning, bring to each decision a package of personal biases and beliefs that may unconsciously and unintentionally affect the decision making process. To the extent that we, as judges, recognize the potential for bias to enter into our deliberations, we combat the potential harm and unfairness that bias can produce if unchecked. Moreover, attorneys and other participants in the justice system should also be conscious of the operations of bias, both in the judges before whom they practice and in their own representation as counselors
The Euphrosyne family's contribution to the low albedo near-Earth asteroids
The Euphrosyne asteroid family is uniquely situated at high inclination in
the outer Main Belt, bisected by the nu_6 secular resonance. This large, low
albedo family may thus be an important contributor to specific subpopulations
of the near-Earth objects. We present simulations of the orbital evolution of
Euphrosyne family members from the time of breakup to the present day, focusing
on those members that move into near-Earth orbits. We find that family members
typically evolve into a specific region of orbital element-space, with
semimajor axes near ~3 AU, high inclinations, very large eccentricities, and
Tisserand parameters similar to Jupiter family comets. Filtering all known NEOs
with our derived orbital element limits, we find that the population of
candidate objects is significantly lower in albedo than the overall NEO
population, although many of our candidates are also darker than the Euphrosyne
family, and may have properties more similar to comet nuclei. Followup
characterization of these candidates will enable us to compare them to known
family properties, and confirm which ones originated with the breakup of (31)
Euphrosyne.Comment: Accepted for publication in Ap
The Yarkovsky Drift's Influence on NEAs: Trends and Predictions with NEOWISE Measurements
We used WISE-derived geometric albedos (p_V) and diameters, as well as
geometric albedos and diameters from the literature, to produce more accurate
diurnal Yarkovsky drift predictions for 540 near-Earth asteroids (NEAs) out of
the current sample of \sim 8,800 known objects. As ten of the twelve objects
with the fastest predicted rates have observed arcs of less than a decade, we
list upcoming apparitions of these NEAs to facilitate observations.Comment: Accepted for publication by The Astronomical Journal. 41 pages, 3
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