64,849 research outputs found
Phase 2 and 3 wind tunnel tests of the J-97 powered, external augmentor V/STOL model
Static and forward speed tests were made in a 40 multiplied by 80 foot wind tunnel of a large-scale, ejector-powered V/STOL aircraft model. Modifications were made to the model following earlier tests primarily to improve longitudinal acceleration capability during transition from hovering to wingborne flight. A rearward deflection of the fuselage augmentor thrust vector was shown to be beneficial in this regard. Other augmentor modifications were tested, notably the removal of both endplates, which improved acceleration performance at the higher transition speeds. The model tests again demonstrated minimal interference of the fuselage augmentor on aerodynamic lift. A flapped canard surface also showed negligible influence on the performance of the wing and of the fuselage augmentor
Understanding Floristic Diversity Though a Database of Greene County Specimens
We present a floristic list of Greene County, Arkansas, based on accessioned collections from the Arkansas State University Herbarium (STAR). Currently, there are 1569 specimens representing 540 taxa from Greene County in STAR. Using the USDA Plants Database, plant species were analyzed according to whether or not they are native to the state as well as whether or not they have been previously documented as species occurring in the county. Having analyzed all the Greene County collections from STAR, we found 225 previously undocumented species. The data suggest that most of the specimens in the STAR collection were found in wooded areas and/or near water. This may be a reflection of sampling bias as two of the primary collectors of these specimens were primarily interested in bog habitats. For this reason, the Greene County collections may not fully represent all habitats in the county, but it is likely that they are a good representation of the county’s seeps and bogs. The STAR Herbarium is emerging as a critical resource for understanding botanical diversity in the eastern counties of Arkansas, but it is clear that additional collections are necessary to fully represent all habitats in these areas
Level structures on the Weierstrass family of cubics
Let W -> A^2 be the universal Weierstrass family of cubic curves over C. For
each N >= 2, we construct surfaces parametrizing the three standard kinds of
level N structures on the smooth fibers of W. We then complete these surfaces
to finite covers of A^2. Since W -> A^2 is the versal deformation space of a
cusp singularity, these surfaces convey information about the level structure
on any family of curves of genus g degenerating to a cuspidal curve. Our goal
in this note is to determine for which values of N these surfaces are smooth
over (0,0). From a topological perspective, the results determine the
homeomorphism type of certain branched covers of S^3 with monodromy in
SL_2(Z/N).Comment: LaTeX, 12 pages; added section giving a topological interpretation of
the result
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Parton distributions
I discuss our current understanding of parton distributions. I begin with the underlying theoretical framework, and the way in which different data sets constrain different partons, highlighting recent developments. The methods of examining the uncertainties on the distributions and those physical quantities dependent on them is analyzed. Finally I look at the evidence that additional theoretical corrections beyond NLO perturbative QCD may be necessary, what type of corrections are indicated and the impact these may have on the uncertainties.</jats:p
Chirality in Liquid Crystals: from Microscopic Origins to Macroscopic Structure
Molecular chirality leads to a wonderful variety of equilibrium structures,
from the simple cholesteric phase to the twist-grain-boundary phases, and it is
responsible for interesting and technologically important materials like
ferroelectric liquid crystals. This paper will review some recent advances in
our understanding of the connection between the chiral geometry of individual
molecules and the important phenomenological parameters that determine
macroscopic chiral structure. It will then consider chiral structure in
columnar systems and propose a new equilibrium phase consisting of a regular
lattice of twisted ropes.Comment: 20 pages with 6 epsf figure
Cold water aquifer storage
A working prototype system is described in which water is pumped from an aquifer at 70 F in the winter time, chilled to a temperature of less than 50 F, injected into a ground-water aquifer, stored for a period of several months, pumped back to the surface in the summer time. A total of 8.1 million gallons of chilled water at an average temperature of 48 F were injected. This was followed by a storage period of 100 days. The recovery cycle was completed a year later with a total of 8.1 million gallons recovered. Approximately 20 percent of the chill energy was recovered
Control of supersonic wind-tunnel noise by laminarization of nozzle-wall boundary layer
One of the principal design requirements for a quiet supersonic or hypersonic wind tunnel is to maintain laminar boundary layers on the nozzle walls and thereby reduce disturbance levels in the test flow. The conditions and apparent reasons for laminar boundary layers which have been observed during previous investigations on the walls of several nozzles for exit Mach numbers from 2 to 20 are reviewed. Based on these results, an analysis and an assessment of nozzle design requirements for laminar boundary layers including low Reynolds numbers, high acceleration, suction slots, wall temperature control, wall roughness, and area suction are presented
Current fluctuations in stochastic systems with long-range memory
We propose a method to calculate the large deviations of current fluctuations
in a class of stochastic particle systems with history-dependent rates.
Long-range temporal correlations are seen to alter the speed of the large
deviation function in analogy with long-range spatial correlations in
equilibrium systems. We give some illuminating examples and discuss the
applicability of the Gallavotti-Cohen fluctuation theorem.Comment: 10 pages, 1 figure. v2: Minor alterations. v3: Very minor alterations
for consistency with published version appearing at
http://stacks.iop.org/1751-8121/42/34200
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