528 research outputs found

    Pre-Pennsylvanian Rocks of Aquidneck and Conanicut Islands, Rhode Island

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    Guidebook for field trips to the Boston area and vicinity : 68th annual meeting, New England Intercollegiate Geological Conference, October 8-10, 1976: Trip B-1

    An analysis of the variables in the decision to revert from a dual source to sole source acquisition method

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    This thesis examines the various methods the Navy has used to develop and foster competition. It also discusses the economic analysis of using more than one source of supply. Rising costs and budgetary pressures have forced the Navy to reexamine its acquisition process. With the impending force draw down, the Program Manager is faced with reduced quantity requirements. Since the enactment of the Competition in Contracting Act in 1984, the Navy has required the use of dual sources in major weapons systems. However, this method of acquisition may no longer be economically feasible. Faced with reduced requirements and limited resources, the Program Manager must reevaluate the costs and benefits of his acquisition method.http://archive.org/details/annalysisofvaria1094527676Lieutenant Commander, United States NavyApproved for public release; distribution is unlimited

    Effect of Equilibration Time on Bovine Spermatozoa Forzen in Straws

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    Animal Scienc

    Geochemical, Isotopic and Single Crystal 40Ar/39Ar Age Constraints on the Evolution of the Cerro Galan Ignimbrites

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    The giant ignimbrites that erupted from the Cerro Galan caldera complex in the southern Puna of the high Andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone. Major and trace element analyses of Cerro Galan ignimbrites (68-71% SiO2) that include 65 new analyses can be interpreted by evolution at three crustal levels. AFC modeling and new fractionation corrected d18O values from quartz (+7.63-8.85%o) are consistent with the ignimbrite magmas being near 50:50 mixtures of enriched mantle (87Sr/86Sr ~ 0.7055) and crustal melts (87Sr/86Sr near 0.715-0.735). Processes at lower crustal levels are predicated on steep heavy REE patterns (Sm/Yb = 4-7), high Sr contents (>250 ppm) and very low Nb/Ta (9-5) ratios, which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produces hybrid melt that rise leaving a gravitationally unstable garnet-bearing residue. Processes at mid crustal levels create large negative Eu anomalies (Eu/Eu* = 0.45-0.70) and variable trace element enrichment in a crystallizing mush zone with a temperature near 800-850ÂșC The mush zone was repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction. Crystallinity differences in the ignimbrites are attributed to biotite, zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near-eutectic crystallization occurs at temperature as low as 680ÂșC just preceding eruption. 40Ar/39Ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the Galan ignimbrite erupted in more than one batch including a ~ 2.13 Ma intracaldera flow and outflows to the west and north at near 2.09 and 2.06 Ma. Episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas whose changing chemistry reflects their evolution over a steepening subduction zone could trigger the eruptions of the Cerro Galan ignimbrites.Fil: Kay, Suzanne Mahlburg. Cornell University; Estados UnidosFil: Coira, Beatriz Lidia Luisa. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas; ArgentinaFil: Wörner, Gerhard. UniversitĂ€t Göttingen; AlemaniaFil: Kay, Robert W.. Cornell University; Estados UnidosFil: Singer, Bradley S.. University of Wisconsin; Estados Unido
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