14,941 research outputs found

    Biological, Technological, and Economic Relationships between Predator and Prey

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    Environmental Economics and Policy,

    Impurity crystal in a Bose-Einstein condensate

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    We investigate the behavior of impurity fields immersed in a larger condensate field in 1, 2, and 3 dimensions. We discuss the localization of a single impurity field within a condensate and note the effects of surface energy. We derive the functional form of the attractive interaction between two impurities due to mediation from the condensate. Generalizing the analysis to NN impurity fields, we show that within various parameter regimes a crystal of impurity fields can form spontaneously in the condensate. Finally, the system of condensate and crystallized impurity structure is shown to have nonclassical rotational inertia, which is characteristic of superfluidity, i.e. the system can be seen to exhibit supersolid behavior.Comment: 5 pages, 3 color figures; Accepted to Phys. Rev. Let

    When All the World\u27s a Stage: The Impact of Events on News Coverage of South Africa, 1979-1985

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    A time series analysis was used to investigate: (1) whether a significant increase in news coverage of South Africa occurred during the critical years of 1979-1985 ; (2) whether the geographic origin and/or sociopolitical impact of events, rather than deaths per se, caused the increase; and (3) the manner in which the increase occurred. Results indicated that two symbolic events (i.e., a series of riots in twenty-one South African townships, internal to South Africa; and the awarding of the Nobel Prize to Bishop Desmond Tutu, external to South Africa) cumulatively were responsible for a significant rise in news coverage of South Africa. The relationship of these symbolic sociopolitical events to the forces that shape short-term news headlines and long-term social change in general, including the imminent demise of apartheid in particular is discussed

    The permocarboniferous flora of north central Texas.

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    Thesis (M.A.)--Boston UniversityThe Permocarboniferous flora of north central Texas has not been studied as a whole, to my knowledge, although a few papers have been written about the plants in the area. Therefore, this thesis has been written, to describe the flora as a whole, and to indicate its spatial and temporal relationships and significance. The area from which the fossil flora comes comprises portions of Archer, Baylor, Clay, Throckmorton, Wichita, and Young Counties. Stratigraphically, it contains one formation from the Pennsylvanian Period, and six from the Lower Permian; the former is the Harpersville, and the latter are the Pueblo, Moran, Putnam, .Admiral, . Belle Plains, and Clyde. Up to the top of the Harpersville formation, the deposits are mostly marine, broken here and there by lenses of coal, which represent short recessions of the epicontinental sea which was present at the time. At the top of the Harpersville formation is a conglomerate layer which create a disconformity, and above it, the deposits are predominately fluviatile. Thus, the sea had moved to the west, but occasional limestones mark short reinvasions of the area. The disconformity at the top of the Harpersville is the boundary between the Pennsylvanian and Permian periods in north central Texas. [TRUNCATED