33,480 research outputs found
NASP X-30 Propulsion technology status
The performance goals of the NASP program require an aero-propulsion system with a high effective specific impulse. In order to achieve these goals, the high potential performance of air-breathing engines must be achieved over a very wide Mach number operating range. This, in turn, demands high component performance and involves many important technical issues which must be resolved. Scramjet Propulsion Technology is divided into five major areas: (1) inlets, (2) combustors, (3) nozzles, (4) component integration, and (5) test facilities. A status report covering the five areas is presented
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Leiocephalus semilineatus
Number of Pages: 2Integrative BiologyGeological Science
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Leiocephalus lunatus
Number of Pages: 5Integrative BiologyGeological Science
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Anolis longitibialis
Number of Pages: 4Integrative BiologyGeological Science
Geometrical frustration in the spin liquid beta'-Me3EtSb[Pd(dmit)2]2 and the valence bond solid Me3EtP[Pd(dmit)2]2
We show that the electronic structures of the title compounds predicted by
density functional theory (DFT) are well described by tight binding models. We
determine the frustration ratio, J'/J, of the Heisenberg model on the
anisotropic triangular lattice, which describes the spin degrees of freedom in
the Mott insulating phase for a range of Pd(dmit)2 salts. All of the
antiferromagnetic materials studied have J'/J 0.9, consistent
with predictions for the Heisenberg model. All salts with 0.5 < J'/J < 0.9,
where many-body theories find a number of competing ground states, are known,
experimentally, to be charge ordered, valence bond solids or spin liquids.Comment: Accepted for publication in Phys. Rev. Lett. 4+11 pages, 3+15
figures, major rewrite, added calculations of Hubbard
Ichthyoplankton Adjacent to Live-Bottom Habitats in Onslow Bay, North Carolina
The abundance and distribution of ichthyoplankton adjacent to live-bottom habitats (rock outcroppings containing rich, sessile invertebrate communities and many species of
tropical and subtropical fishes) in open-shelf waters « 55-m isobath) in Onslow Bay, North Carolina, were investigated. Larvae of reef-associated genera, especially the economically important subtropical and tropical members of the families Haemulidae (Haemulon), Lutjanidae (Lutjanus and Rltomboplites), Serranidae (Mycteroperca and Epinephelus), and Sparidae (Calamus and Pagrus) were targeted. Larvae representing 40 families were collected in neuston tows. Commonly collected reef-associated families were Balistidae, Blenniidae (dominated by the reef-associated Parablennius marmoreus) , Mullidae, and Gobiidae. Larvae representing 70 families were
collected in subsurface tows. Reef-associated families commonly collected included Apogonidae, Balistidae, Gobiidae, Haemulidae, LutJanidae, Scaridae, and Serranidae. Larval Haemulon sp (p)., Lutjanus sp(p)., and Rltomboplites aurorubens were commonly collected and thus it is likely that these taxa spawn in Onslow Bay and recruit to live-bottom sites within the area. Other families of fishes commonly collected but generally not considered reef-associated included Bothidae, Callionymidae, Carangidae, Clupeidae, Engraulidae, and Ophidiidae. Estuarine-dependent species (e.g. the clupeid Brevoortia tyrannus and the sciaenids Leiostomus xanthurus and Micropogonias undulatus) were an important component of the ichthyoplankton during late fall and winter. The frequent occurrence of larvae from
oceanic species (e.g. gonostomatids and myctophids) indicated that Gulf Stream waters had intruded onto the shelf, transporting these larvae to open-shelf waters off North Carolina.(PDF file containes 36 pages.
Signalling mechanisms of long term facilitation of breathing with intermittent hypoxia.
Intermittent hypoxia causes long-term facilitation (LTF) of respiratory motor nerve activity and ventilation, which manifests as a persistent increase over the normoxic baseline for an hour or more after the acute hypoxic ventilatory response. LTF is likely involved in sleep apnea, but its exact role is uncertain. Previously, LTF was defined as a serotonergic mechanism, but new evidence shows that multiple signaling pathways can elicit LTF. This raises new questions about the interactions between signaling pathways in different time domains of the hypoxic ventilatory response, which can no longer be defined simply in terms of neurochemical mechanisms
Accurate metasurface synthesis incorporating near-field coupling effects
One of the most promising metasurface architectures for the microwave and
terahertz frequency ranges consists of three patterned metallic layers
separated by dielectrics. Such metasurfaces are well suited to planar
fabrication techniques and their synthesis is facilitated by modelling them as
impedance sheets separated by transmission lines. We show that this model can
be significantly inaccurate in some cases, due to near-field coupling between
metallic layers. This problem is particularly severe for higher frequency
designs, where fabrication tolerances prevent the patterns from being
highly-subwavelength in size. Since the near-field coupling is difficult to
describe analytically, correcting for it in a design typically requires
numerical optimization. We propose an extension of the widely used
equivalent-circuit model to incorporate near-field coupling and show that the
extended model can predict the scattering parameters of a metasurface
accurately. Based on our extended model, we introduce an improved metasurface
synthesis algorithm that gives physical insight to the problem and efficiently
compensates for the perturbations induced by near-field coupling. Using the
proposed algorithm, a Huygens metasurface for beam refraction is synthesized
showing a performance close to the theoretical efficiency limit despite the
presence of strong near-field coupling
The design of a numerically controlled drilling system using fluidic elements 1966/7
This report outlines the aims of the
project and procedures used to bring
it to a successful conclusion. It
also summarises the results of an
investigation into the parameters
which govern the specification of a
numerically controlled point to point
drilling machine
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