53,144 research outputs found
Development of an analytical technique for the optimization of jet engine and duct acoustic liners
A special integral representation of the external solutions of the Helmholtz equation is described. The analytical technique developed for the generation of the optimum acoustic admittance for an arbitrary axisymmetric body is also presented along with some numerical procedures and some preliminary results for a straight duct
Development of an analytical technique for the optimization of jet engine and duct acoustic liners
A new method was developed for the calculation of optimum constant admittance solutions for the minimization of the sound radiated from an arbitrary axisymmetric body. This method utilizes both the integral equation technique used in the calculation of the optimum non-constant admittance liners and the independent solution generated as a by product of these calculations. The results generated by both these methods are presented for three duct geometries: (1) a straight duct; (2) the QCSEE inlet; and (3) the QCSEE inlet less its centerbody
Development of advanced fuel cell system, phase 3
A multiple task research and development program was performed to improve the weight, life, and performance characteristics of hydrogen-oxygen alkaline fuel cells for advanced power systems. Gradual wetting of the anode structure and subsequent long-term performance loss was determined to be caused by deposition of a silicon-containing material on the anode. This deposit was attributed to degradation of the asbestos matrix, and attention was therefore placed on development of a substitute matrix of potassium titanate. An 80 percent gold 20 percent platinum catalyst cathode was developed which has the same performance and stability as the standard 90 percent gold - 10 percent platinum cathode but at half the loading. A hybrid polysulfone/epoxy-glass fiber frame was developed which combines the resistance to the cell environment of pure polysulfone with the fabricating ease of epoxy-glass fiber laminate. These cell components were evaluated in various configurations of full-size cells. The ways in which the baseline engineering model system would be modified to accommodate the requirements of the space tug application are identified
Development of advanced fuel cell system, phase 2
A multiple task research and development program was performed to improve the weight, life, and performance characteristics of hydrogen-oxygen alkaline fuel cells for advanced power systems. Development and characterization of a very stable gold alloy catalyst was continued from Phase I of the program. A polymer material for fabrication of cell structural components was identified and its long term compatibility with the fuel cell environment was demonstrated in cell tests. Full scale partial cell stacks, with advanced design closed cycle evaporative coolers, were tested. The characteristics demonstrated in these tests verified the feasibility of developing the engineering model system concept into an advanced lightweight long life powerplant
A Reanalysis of the Carbon Abundance in the Translucent Cloud toward HD 24534
We have reanalyzed the Goddard High Resolution Spectrograph data set
presented by Snow et al. which contains the interstellar intersystem C II]
2325A line through the translucent cloud toward HD 24534 (X Persei). In
contrast to the results of Snow et al., we clearly detect the C II] feature at
the 3-sigma confidence level and measure a C^+ column density of 2.7 +/- 0.8 x
10^17 cm^-2. Accounting for the C I column density along the line of sight, we
find 10^6 C/H = 106 +/- 38 in the interstellar gas toward this star. This
gas-phase carbon-to-hydrogen ratio suggests that slightly more carbon depletion
may be occurring in translucent as compared to diffuse clouds. The average
diffuse-cloud C/H, however, is within the 1-sigma uncertainty of the
measurement toward HD 24534. We therefore cannot rule out the possibility that
the two cloud types have comparable gas-phase C/H, and therefore comparable
depletions of carbon.Comment: 9 pages, 3 figures, to appear in the Astrophysical Journal Letter
Effects of live-bait shrimp trawling on seagrass beds and fish bycatch in Tampa Bay, Florida
The use of live shrimp for bait in
recreational fishing has resulted in
a controversial fishery for shrimp in
Florida. In this fishery, night collections
are conducted over seagrass
beds with roller beam trawls to capture
live shrimp, primarily pink
shrimp, Penaeus duorarum. These
shrimp are culled from the catch on
sorting tables and placed in onboard
aerated “live” wells. Beds of
turtlegrass, Thalassia testudinum,
a species that has highest growth
rates and biomass during summer
and lowest during the winter (Fonseca
et al., 1996) are predominant
areas for live-bait shrimp trawling
(Tabb and Kenny, 1969).
Our study objectives were 1) to
determine effects of a roller beam
trawl on turtlegrass biomass and
morphometrics during intensive
(up to 18 trawls over a turtlegrass
bed), short-term (3-hour duration)
use and 2) to examine the mortality
of bycatch finfish following capture
by a trawl
Pair-factorized steady states on arbitrary graphs
Stochastic mass transport models are usually described by specifying hopping
rates of particles between sites of a given lattice, and the goal is to predict
the existence and properties of the steady state. Here we ask the reverse
question: given a stationary state that factorizes over links (pairs of sites)
of an arbitrary connected graph, what are possible hopping rates that converge
to this state? We define a class of hopping functions which lead to the same
steady state and guarantee current conservation but may differ by the induced
current strength. For the special case of anisotropic hopping in two dimensions
we discuss some aspects of the phase structure. We also show how this case can
be traced back to an effective zero-range process in one dimension which is
solvable for a large class of hopping functions.Comment: IOP style, 9 pages, 1 figur
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