60 research outputs found
Classical and Quantum Gravity in 1+1 Dimensions, Part III: Solutions of Arbitrary Topology
All global solutions of arbitrary topology of the most general 1+1
dimensional dilaton gravity models are obtained. We show that for a generic
model there are globally smooth solutions on any non-compact 2-surface. The
solution space is parametrized explicitly and the geometrical significance of
continuous and discrete labels is elucidated. As a corollary we gain insight
into the (in general non-trivial) topology of the reduced phase space.
The classification covers basically all 2D metrics of Lorentzian signature
with a (local) Killing symmetry.Comment: 39 pages, 22 figures, uses AMSTeX, extended version of former chapter
7 (Gravitational Kinks) now available as gr-qc/9707053, problem with figure 6
fixe
Geochemical response of the mid-depth Northeast Atlantic Ocean to freshwater input during Heinrich events 1 to 4
PublishedArticleHeinrich events are intervals of rapid iceberg-sourced freshwater release to the high latitude North Atlantic Ocean that punctuate late Pleistocene glacials. Delivery of fresh water to the main North Atlantic sites of deep water formation during Heinrich events may result in major disruption to the Atlantic Meridional Overturning Circulation (AMOC), however, the simple concept of an AMOC shutdown in response to each freshwater input has recently been shown to be overly simplistic. Here we present a new multi-proxy dataset spanning the last 41,000 years that resolves four Heinrich events at a classic mid-depth North Atlantic drill site, employing four independent geochemical tracers of water mass properties: boron/calcium, carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates. We also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast North Atlantic. Our data reveal distinct geochemical signatures for each Heinrich event, suggesting that the sites of fresh water delivery and/or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released. At no time during the last 41 kyr was the mid-depth northeast North Atlantic dominantly ventilated by southern-sourced water. Instead, we document persistent ventilation by Glacial North Atlantic Intermediate Water (GNAIW), albeit with variable properties signifying changes in supply from multiple contributing northern sources.This research used samples provided by the Integrated Ocean Drilling (Discovery) Program IODP, which is sponsored by the US National Science Foundation and participating countries under management of Joint Oceanographic Institutions, Inc. We thank Walter Hale and Alex WĂŒlbers for help with sampling, Kirsty Crocket for providing additional samples and Matt Cooper, Andy Milton, Mike Bolshaw and Dave Spanner for analytical support. Heiko PĂ€like, David Thornalley and Rachel Mills are thanked for productive discussions and comments on earlier versions of this work. We also thank three anonymous reviewers for their constructive feedback, which greatly improved the manuscript. Funding for this project was provided by NERC studentships to A.J.C. (grant NE/D005728/2) and T.B.C. (NE/I528626/1), with additional funding support from a Royal Society Wolfson Research Merit Award and NERC grants NE/F00141X/1 and NE/I006168/1 to P.A.W. and NE/D00876X/2 to G.L.F
Characterizations of C(X) among Its Subalgebras
VII, 159 tr.; 25 cm
N° 137. â Ătudes quantitatives des spectres excitoniques des halogĂ©nures de Cu, Pb et Hg aux basses tempĂ©ratures
DĂ©termination des intensitĂ©s dâoscillateur de raies excitoniques dâhalogĂ©nures de Cu, Pb et Hg. Deux mĂ©thodes sont utilisĂ©es. La premiĂšre fait correspondre une courbe de dispersion thĂ©orique Ă la courbe de dispersion trouvĂ©e expĂ©rimentalement, tandis que la deuxiĂšme consiste Ă mesurer lâabsorption intĂ©grale de lâĂ©chantillon. Les Ă©chantillons sont soit dĂšs couches sublimĂ©es, soit des monocristaux. Les valeurs trouvĂ©es sont en accord avec la thĂ©orie dâElliott pour les spectres de premiĂšre classe. Les discordances observĂ©es pour CuI font lâobjet de quelques remarques
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