25,294 research outputs found
High-temperature ''hydrostatic'' extrusion
Quasi-fluids permit hydrostatic extrusion of solid materials. The use of sodium chloride, calcium fluoride, or glasses as quasi-fluids reduces handling, corrosion, and sealing problems, these materials successfully extrude steel, molybdenum, ceramics, calcium carbonate, and calcium oxide. This technique also permits fluid-to-fluid extrusion
Algal Assemblage Distribution as Related to Seasonal Fluctuations of Selected Metal Concentrations
Seasonal variations of phytoplankton assemblages have been observed in a mildly eutrophic lake in northwestern Arkansas for six years. The data indicated that certain metal concentrations also varied seasonally. Sodium, potassium, calcium and magnesium ion concentrations, and phytoplankton composition and abundances were examined spatially and temporally. Four major algal blooms characterized the lake: a spring, a summer and an autumnal cyanophycean assemblage and a winter diatom-chrysophyte dominated population. Each metal concentration was inversely proportional to the abundance of the cyanophytes. The presence of the winter assemblage was accompanied by decreases in sodium, calcium and magnesium and increased levels of potassium. First and second order linear regression models were developed for each assemblage
Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume III. Big Cypress National Preserve
Amphibian declines and extinctions have been documented around the world, often in protected
natural areas. Concern for this trend has prompted the U.S. Geological Survey and the National Park
Service to document all species of amphibians that occur within U.S. National Parks and to search for any
signs that amphibians may be declining. This study, an inventory of amphibian species in Big Cypress
National Preserve, was conducted from 2002 to 2003. The goals of the project were to create a
georeferenced inventory of amphibian species, use new analytical techniques to estimate proportion of
sites occupied by each species, look for any signs of amphibian decline (missing species, disease, die-offs,
and so forth.), and to establish a protocol that could be used for future monitoring efforts.
Several sampling methods were used to accomplish these goals. Visual encounter surveys and
anuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportion
of sites or proportion of area occupied (PAO) by each amphibian species in each habitat. Opportunistic
collections, as well as limited drift fence data, were used to augment the visual encounter methods for
highly aquatic or cryptic species. A total of 545 visits to 104 sites were conducted for standard sampling
alone, and 2,358 individual amphibians and 374 reptiles were encountered. Data analysis was conducted
in program PRESENCE to provide PAO estimates for each of the anuran species.
All of the amphibian species historically found in Big Cypress National Preserve were detected
during this project. At least one individual of each of the four salamander species was captured during
sampling. Each of the anuran species in the preserve was adequately sampled using standard
herpetological sampling methods, and PAO estimates were produced for each species of anuran by habitat.
This information serves as an indicator of habitat associations of the species and relative abundance of
sites occupied, but it will also be useful as a comparative baseline for future monitoring efforts.
In addition to sampling for amphibians, all encounters with reptiles were documented. The
sampling methods used for detecting amphibians are also appropriate for many reptile species. These
reptile locations are included in this report, but the number of reptile observations was not sufficient to
estimate PAO for reptile species. We encountered 35 of the 46 species of reptiles believed to be present in
Big Cypress National Preserve during this study, and evidence exists of the presence of four other reptile
species in the Preserve.
This study found no evidence of amphibian decline in Big Cypress National Preserve. Although no
evidence of decline was observed, several threats to amphibians were identified. Introduced species,
especially the Cuban treefrog (Osteopilus septentrionalis), are predators and competitors with several
native frog species. The recreational use of off-road vehicles has the potential to affect some amphibian
populations, and a study on those potential impacts is currently underway. Also, interference by humans
with the natural hydrologic cycle of south Florida has the potential to alter the amphibian community.
Continued monitoring of the amphibian species in Big Cypress National Preserve is recommended.
The methods used in this study were adequate to produce reliable estimates of the proportion of sites
occupied by most anuran species, and are a cost-effective means of determining the status of their
populations
Effects of a traffic noise background on judgements of aircraft noise
A study was conducted in which subjects judged aircraft noises in the presence of road traffic background noise. Two different techniques for presenting the background noises were evaluated. For one technique, the background noise was continuous over the whole of a test session. For the other, the background noise was changed with each aircraft noise. A range of aircraft noise levels and traffic noise levels were presented to simulate typical indoor levels
Modular instrumentation system for real-time measurements and control on reciprocating engines
An instrumentation system was developed for reciprocating engines. Among the parameters measured are the indicated mean effective pressure, or theoretical work per cycle, and the mass fraction burn rate, a measure of the combustion rate in the cylinder. These computations are performed from measured cylinder pressure and crankshaft angle and are available in real time for the experimenter. A 100 or 200 consecutive-cycle sample is analyzed to reduce the effect of cyclic variations in the engine. Data are displayed in bargraph form, and the mean and standard deviation are computed. Other instruments are also described
Vortices in self-gravitating disks
Vortices are believed to greatly help the formation of km sized planetesimals
by collecting dust particles in their centers. However, vortex dynamics is
commonly studied in non-self-gravitating disks. The main goal here is to
examine the effects of disk self-gravity on the vortex dynamics via numerical
simulations. In the self-gravitating case, when quasi-steady gravitoturbulent
state is reached, vortices appear as transient structures undergoing recurring
phases of formation, growth to sizes comparable to a local Jeans scale, and
eventual shearing and destruction due to gravitational instability. Each phase
lasts over 2-3 orbital periods. Vortices and density waves appear to be coupled
implying that, in general, one should consider both vortex and density wave
modes for a proper understanding of self-gravitating disk dynamics. Our results
imply that given such an irregular and rapidly changing, transient character of
vortex evolution in self-gravitating disks it may be difficult for such
vortices to effectively trap dust particles in their centers that is a
necessary process towards planet formation.Comment: to appear in the proceedings of Cool Stars, Stellar Systems and The
Sun, 15th Cambridge Workshop, St. Andrews, Scotland, July 21-25, 200
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