19,733 research outputs found
Charles M. Breder, Jr.: Atlantis Expedition, 1934
Dr. Charles M. Breder participated on the 1934 expedition of the Atlantis from Woods Hole, Massachusetts to Panama and back and kept a field diary of daily activities. The Atlantis expedition of 1934, led by Prof. A. E. Parr, was a milestone in the history of scientific discovery in the Sargasso Sea and the West Indies. Although naturalists had visited the Sargasso Sea for many years, the Atlantis voyage was the first attempt to investigate in detailed quantitative manner biological problems about this varying, intermittent ‘false’ bottom of living, floating plants and associated fauna. In addition to Dr. Breder, the party also consisted of Dr. Alexander Forbes, Harvard University and Trustee of the Woods Hole Oceanographic Institution (WHOI); T. S. Greenwood, WHOI hydrographer; M. D. Burkenroad, Yale University’s Bingham Laboratory, carcinology and Sargasso epizoa; M. Bishop, Peabody Museum of Natural History, Zoology Dept., collections and preparations and H. Sears, WHOI ichthyologist. The itinerary included the following waypoints: Woods Hole, the Bermudas, Turks Islands, Kingston, Colon, along the Mosquito Bank off of Nicaragua, off the north coast of Jamaica, along the south coast of Cuba, Bartlett Deep, to off the Isle of Pines, through the Yucatan Channel, off Havana, off Key West, to Miami, to New York City, and then the return to Woods Hole. During the expedition, Breder collected rare and little-known flying fish species and developed a method for hatching and growing flying fish larvae. (PDF contains 48 pages
Equation of motion of an interstellar Bussard ramjet with radiation and mass losses
An interstellar Bussard ramjet is a spaceship using the protons of the
interstellar medium in a fusion engine to produce thrust. In recent papers, it
was shown that the relativistic equation of motion of an ideal ramjet and of a
ramjet with radiation loss are analytical. When a mass loss appears, the limit
speed of the ramjet is more strongly reduced. But, the parametric equations, in
terms of the ramjet's speed, for the position of the ramjet in the inertial
frame of the interstellar medium, the time in this frame, and the proper time
indicated by the clocks on board the spaceship, can still be obtained in an
analytical form. The non-relativistic motion and the motion near the limit
speed are studied.Comment: 4 figure
Radiative falloff in black-hole spacetimes
This two-part contribution to the Proceedings of the Eighth Canadian
Conference on General Relativity and Relativistic Astrophysics is devoted to
the evolution of a massless scalar field in two black-hole spacetimes which are
not asymptotically flat.
In Part I (authored by Eric Poisson) we consider the evolution of a scalar
field propagating in Schwarzschild-de Sitter spacetime. The spacetime possesses
a cosmological horizon in addition to the usual event horizon. The presence of
this new horizon affects the late-time evolution of the scalar field.
In part II (authored by William G. Laarakkers) we consider the evolution of a
scalar field propagating in Schwarzschild-Einstein-de Sitter spacetime. The
spacetime has two distinct regions: an inner black-hole region and an outer
cosmological region. Early on in the evolution, the field behaves as if it were
in pure Schwarzschild spacetime. Later, the field learns of the existence of
the cosmological region and alters its behaviour.Comment: 5 pages, 7 figures, ReVTe
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Soil domestication by rice cultivation results in plant-soil feedback through shifts in soil microbiota.
BackgroundSoils are a key component of agricultural productivity, and soil microbiota determine the availability of many essential plant nutrients. Agricultural domestication of soils, that is, the conversion of previously uncultivated soils to a cultivated state, is frequently accompanied by intensive monoculture, especially in the developing world. However, there is limited understanding of how continuous cultivation alters the structure of prokaryotic soil microbiota after soil domestication, including to what extent crop plants impact soil microbiota composition, and how changes in microbiota composition arising from cultivation affect crop performance.ResultsWe show here that continuous monoculture (> 8 growing seasons) of the major food crop rice under flooded conditions is associated with a pronounced shift in soil bacterial and archaeal microbiota structure towards a more consistent composition, thereby domesticating microbiota of previously uncultivated sites. Aside from the potential effects of agricultural cultivation practices, we provide evidence that rice plants themselves are important drivers of the domestication process, acting through selective enrichment of specific taxa, including methanogenic archaea, in their rhizosphere that differ from those of native plants growing in the same environment. Furthermore, we find that microbiota from soils domesticated by rice cultivation contribute to plant-soil feedback, by imparting a negative effect on rice seedling vigor.ConclusionsSoil domestication through continuous monoculture cultivation of rice results in compositional changes in the soil microbiota, which are in part driven by the rice plants. The consequences include a negative impact on plant performance and increases in greenhouse gas emitting microbes
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