7,456 research outputs found
Simulator model specification for the augmentor wing jet STOL research aircraft
The configuration and simulation studies of a C-8A (De Havilland Buffalo) aircraft are described. The modifications to STOL configuration consisted of augmentor-wing jet flaps, blown and drooped ailerons, and leading edge slats. The total simulator model includes a number of component parts for producing realistic visual, aural, tactile, vestibular, and kinesthetic cues for the pilot to assess the predicted behavior of the real airplane
Protecting unparticles from the MSSM Higgs sector
We construct a model of an unparticle sector consisting of a supersymmetric
SU(N) gauge theory with the number of flavors in the Seiberg conformal window.
We couple this sector to the MSSM via heavy messengers. The resulting low
energy theory has a Higgs coupling to unparticles. The Higgs vev drives the
hidden Seiberg sector to a new conformal fixed point. The coupling to the Higgs
mediates supersymmetry breaking to the Seiberg sector, and breaks conformal
invariance at a lower scale. The low energy theory contains light stable and
metastable mesons. Higgs decay into this sector gives signatures which are
similar to those of "hidden valley" models. Decays of the lightest superpartner
of standard model particles into the hidden sector reveal potentially
observable unparticle kinematics.Comment: References added. 11 pages, 4 figure
Optimal Occulter Design for Finding Extrasolar Planets
One proposed method for finding terrestrial planets around nearby stars is to
use two spacecraft--a telescope and a specially shaped occulter that is
specifically designed to prevent all but a tiny fraction of the starlight from
diffracting into the telescope. As the cost and observing cadence for such a
mission will be driven largely by the separation between the two spacecraft, it
is critically important to design an occulter that can meet the observing goals
while flying as close to the telescope as possible. In this paper, we explore
this tradeoff between separation and occulter diameter. More specifically, we
present a method for designing the shape of the outer edge of an occulter that
is as small as possible and gives a shadow that is deep enough and large enough
for a 4m telescope to survey the habitable zones of many stars for Earth-like
planets. In particular, we show that in order for a 4m telescope to detect in
broadband visible light a planet 0.06 arcseconds from a star shining
times brighter than the planet requires a specially-shaped occulter 50m in
diameter positioned about km in front of the telescope.Comment: 14 pages, 4 figures, 15 subfigure
InP shallow-homojunction solar cells
Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metalorganic chemical vapor deposition. Air mass zero efficiencies as high as 18.8 percent (NASA measurement) have been achieved. Although calculations show that, as is the case with GaAs, a heterostructure is expected to be required for the highest efficiencies attainable, the material properties of InP give the shallow-homojunction structure a greater potential than in the case of GaAs. The best cells, which were those made by ion implantation, show open-circuit voltage (V sub oc) of 873 mV, short-circuit current of 357 A/sq m (35.7 mA/sq cm), and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90 percent in the red end of the spectrum, but drops to 54 percent in the blue end. Other cells have achieved 74 percent in the blue end. Detailed modeling of the data indicates that a high front surface recombination velocity is responsible for the low blue response, that the carrier lifetime is high enough to allow good carrier collection from both the base and the emitter, and that the voltage is base-limited
The jungle of methods for evaluating phenotypic and phylogenetic structure of communities
13 páginas, 4 figuras, 4 tablas.The way communities are assembled is an old ecological question currently experiencing renewed interest thanks to the recent advances in molecular biology and phylogenetics. The generality of these new methods has allowed us to understand the structure of communities of organisms from different kingdoms and at different scales. Concomitant with this growing interest, new methods, metrics, terms, and software have appeared that independently solve similar questions, but with different approaches. Here we provide a unifying framework on methods for community structure based on the relationships between four key concepts: phylogeny, phenotype, environment, and co-occurrence. The different approaches are based on different community representations of traits, the phylogenetic relationships of species in the community, or species occurrence along the environmental gradients. We finally provide insights on future directions of this emerging discipline.We thank MarĂa Clara Castellanos, Steve Kembel, Evan Weiher, and three anonymous referees for helpful comments and suggestions. This work has been developed under the framework of the Spanish projects VIRRA (CGL2009-12048/BOS) and VAMPIRO(CGL2008-05289-C02-01).Peer reviewe
Gradient expansion, curvature perturbations and magnetized plasmas
The properties of magnetized plasmas are always investigated under the
hypothesis that the relativistic inhomogeneities stemming from the fluid
sources and from the geometry itself are sufficiently small to allow for a
perturbative description prior to photon decoupling. The latter assumption is
hereby relaxed and pre-decoupling plasmas are described within a suitable
expansion where the inhomogeneities are treated to a given order in the spatial
gradients. It is argued that the (general relativistic) gradient expansion
shares the same features of the drift approximation, customarily employed in
the description of cold plasmas, so that the two schemes are physically
complementary in the large-scale limit and for the low-frequency branch of the
spectrum of plasma modes. The two-fluid description, as well as the
magnetohydrodynamical reduction, are derived and studied in the presence of the
spatial gradients of the geometry. Various solutions of the coupled system of
evolution equations in the anti-Newtonian regime and in the quasi-isotropic
approximation are presented. The relation of this analysis to the so-called
separate Universe paradigm is outlined. The evolution of the magnetized
curvature perturbations in the nonlinear regime is addressed for the magnetized
adiabatic mode in the plasma frame.Comment: 40 pages, no figure
Environmental Principles in U.S. and Canadian Law
Published as Chapter 29 in Principles of Environmental Law, Ludwig Krämer & Emanuela Orlando, eds.https://digitalcommons.law.buffalo.edu/book_sections/1369/thumbnail.jp
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