27,120 research outputs found
f(R) as a dark energy fluid
We study the equations for the evolution of cosmological perturbations in
and conclude that this modified gravity model can
be expressed as a dark energy fluid at background and linearised perturbation
order. By eliminating the extra scalar degree of freedom known to be present in
such theories, we are able to characterise the evolution of the perturbations
in the scalar sector in terms of equations of state for the entropy
perturbation and anisotropic stress which are written in terms of the density
and velocity perturbations of the dark energy fluid and those in the matter, or
the metric perturbations. We also do the same in the much simpler vector and
tensor sectors. In order to illustrate the simplicity of this formulation, we
numerically evolve perturbations in a small number of cases.Comment: 12 pages, 5 figure
Coal feed component testing for CDIF
Investigations conducted during the conceptual design of the Montana MHD Component Development and Integration Facility (CDIF) identified commercially available processing and feeding equipment potentially suitable for use in a reference design. Tests on sub-scale units of this equipment indicated that they would perform as intended
Results from the National Aeronautics and Space Administration remote sensing experiments in the New York Bight, 7-17 April 1975
A cooperative operation was conducted in the New York Bight to evaluate the role of remote sensing technology to monitor ocean dumping. Six NASA remote sensing experiments were flown on the C-54, U-2, and C-130 NASA aircraft, while NOAA obtained concurrent sea truth information using helicopters and surface platforms. The experiments included: (1) a Radiometer/Scatterometer (RADSCAT), (2) an Ocean Color Scanner (OCS), (3) a Multichannel Ocean Color Sensor (MOCS), (4) four Hasselblad cameras, (5) an Ebert spectrometer; and (6) a Reconafax IV infrared scanner and a Precision Radiation Thermometer (PRT-5). The results of these experiments relative to the use of remote sensors to detect, quantify, and determine the dispersion of pollutants dumped into the New York Bight are presented
Fishes of the Ohio River
Author Institution: Water Resources Laboratory, University of Louisville and Biology Department, Spalding UniversityTo date, 159 species of fishes (14 of them introduced by humans) have been reported from the Ohio River. Three native fishes {Acipenser fulvescens, Alosa alabamae, and Ammocrypta asprella) have apparently been eliminated from the river. The Ohio River fish community was severely affected by the siltation of clean gravel substrates, and the inundation of those substrates by the canalization of the river before 1927. In the past 20-30 years, populations of many species have increased, particularly in the upper third of the river. Some pollution-intolerant species which had disappeared from the upper reaches of the river between 1900 and 1950 have been returning since 1970 (e.g. Polyodon spathula, Hiodon tergisus, and Carpiodes velifer). A few pollution-tolerant species have declined in abundance since 1970 (e.g. bullheads and Ictalurus catus). The most abundant fishes in the lock chamber samples of 1957-87 were Notropis atherinoides, Dorosoma cepedianum, Aplodinotus grunniens, Notropis volucellus, and Ictalurus punctatus. The ongoing recovery of the Ohio River fish community should encourage us to take additional steps to protect the river from catastrophic spills of toxic materials and to reintroduce eliminated native fishes
Whisking with robots from rat vibrissae to biomimetic technology for active touch
This article summarizes some of the key features of the rat vibrissal system, including the actively controlled sweeping movements of the vibrissae known as whisking, and reviews the past and ongoing research aimed at replicating some of this functionality in biomimetic robots
Are Local Filters Blind to Provenance? Ant Seed Predation Suppresses Exotic Plants More than Natives
The question of whether species’ origins influence invasion outcomes has been a point of substantial debate in invasion ecology. Theoretically, colonization outcomes can be predicted based on how species’ traits interact with community filters, a process presumably blind to species’ origins. Yet, exotic plant introductions commonly result in monospecific plant densities not commonly seen in native assemblages, suggesting that exotic species may respond to community filters differently than natives. Here, we tested whether exotic and native species differed in their responses to a local community filter by examining how ant seed predation affected recruitment of eighteen native and exotic plant species in central Argentina. Ant seed predation proved to be an important local filter that strongly suppressed plant recruitment, but ants suppressed exotic recruitment far more than natives (89% of exotic species vs. 22% of natives). Seed size predicted ant impacts on recruitment independent of origins, with ant preference for smaller seeds resulting in smaller seeded plant species being heavily suppressed. The disproportionate effects of provenance arose because exotics had generally smaller seeds than natives. Exotics also exhibited greater emergence and earlier peak emergence than natives in the absence of ants. However, when ants had access to seeds, these potential advantages of exotics were negated due to the filtering bias against exotics. The differences in traits we observed between exotics and natives suggest that higher-order introduction filters or regional processes preselected for certain exotic traits that then interacted with the local seed predation filter. Our results suggest that the interactions between local filters and species traits can predict invasion outcomes, but understanding the role of provenance will require quantifying filtering processes at multiple hierarchical scales and evaluating interactions between filters.Fil: Pearson, Dean. University of Montana; Estados Unidos. United States Department of Agriculture; Estados UnidosFil: Icasatti, Nadia Soledad. United States Department of Agriculture; Estados Unidos. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Hierro, Jose Luis. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Bird, Benjamin B.. United States Department of Agriculture; Estados Unido
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