20,420 research outputs found

    The new and reinstated genera of agglutinated foraminifera published between 1986 and 1996

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    In the 10 years following the publication of "Foraminiferal Genera and their Classification" by Loeblich & Tappan (1987), some 91 new genera of agglutinated foraminifera have been proposed by various authors. Additionally, at least four of the genera listed by Loeblich & Tappan as junior synonyms have been resurrected by subsequent authors. This compilation is an attempt at bringing together the nomenclatorial changes to the agglutinated foraminiferal genera that have appeared in the accessible literature

    The utility of deep-water agglutinated Foraminiferal acmes for correlating Eocene to Oligocene abyssal sediments in the North Atlantic and Western Tethys

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    Quantitative analysis of Deep-water Agglutinated Foraminifera (DWAF) assemblages from key ODP sites in the North Atlantic reveal the presence of stratigraphically-significant abundance maxima, that may be useful for correlating sedimentary sequences deposited beneath the CCD. The DWAF record from ODP Hole 647A in the Labrador Sea was re-studied and abundances were recalculated by excluding calcareous benthic foraminifera. This hole is a key locality, as it provides direct calibration of the DWAF biostratigraphy to the standard chronostratigraphy. Eight DWAF acmes are recognised in the Eocene to lower Oligocene at Site 647 and at other North Atlantic and Norwegian Sea sites. These are: The Paleocene-Eocene Thermal Maximum (PETM) Glomospira Acme, a lower Eocene N. excelsa acme, an early/middle Eocene Glomospira Acme, a Karrerulina acme, a middle Eocene Reticulophragmium amplectens acme, a middle/late Eocene Spiroplecta- mmina acme, a latest Eocene-early Oligocene Ammodiscus latus acme, and an early Oligocene Spirosigmoilinella acme. Some of these acmes can be correlated with similar events occurring at onshore localities in the Western Tethys (northern Spain, Moroccan Rif, Italian Appenines, Western Carpathians). The occurrence of these DWAF acmes is caused by variations in the trophic continuum which is a consequence of the profound climatic and oceanographic changes that took place in the deep ocean during the Eocene and early Oligocene

    On massive dust clumps in the envelope of the red supergiant VY Canis Majoris

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    The envelope of the red supergiant VY CMa has long been considered an extreme example of episodic mass loss that is possibly taking place in other cool and massive evolved stars. Recent submm observations of the envelope revealed massive dusty clumps within 800 mas from the star which reinforce the picture of drastic mass-loss phenomena in VY CMa. We present new ALMA observations at an angular resolution of 0.1" and at an unprecedented sensitivity that reveal further details about the dusty clumps. We resolve more discrete features and identify a submm counterpart of a more distant Clump SW known from visual observations. The brightest clump, named C, is resolved in the observations. Gas seen against the resolved continuum emission of clump C produces a molecular spectrum in absorption. Except for SW Clump, no molecular emission is found to be associated with the dusty clumps and we propose that the dusty structures have an atypically low gas content. We attempt to reproduce the properties of the dusty clumps through three-dimensional radiative-transfer modeling. Although a clump configuration explaining the observations is found, it is not unique. A very high optical depth of all clumps to the stellar radiation make the modeling very challenging and requires unrealistically high dust masses. It is suggested that the dusty features have substructures, e.g. porosity, that allows deeper penetration of stellar photons within the clumps than in a homogeneous configuration. A comparison of the estimated clumps ages to variations in the stellar visual flux for over a century suggests that the mechanism responsible for their formation is not uniquely manifested by enhanced or strongly diminished visual light. The study demonstrates that the dusty mass-loss episodes of VY CMa are indeed unparalleled among all known non-explosive stars. The origin of these episodes remains an unsolved problem.Comment: accepted to A&

    Generalized backward induction: Justification for a folk algorithm

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    I introduce axiomatically infinite sequential games that extend Kuhn’s classical framework. Infinite games allow for (a) imperfect information, (b) an infinite horizon, and (c) infinite action sets. A generalized backward induction (GBI) procedure is defined for all such games over the roots of subgames. A strategy profile that survives backward pruning is called a backward induction solution (BIS). The main result of this paper finds that, similar to finite games of perfect information, the sets of BIS and subgame perfect equilibria (SPE) coincide for both pure strategies and for behavioral strategies that satisfy the conditions of finite support and finite crossing. Additionally, I discuss five examples of well-known games and political economy models that can be solved with GBI but not classic backward induction (BI). The contributions of this paper include (a) the axiomatization of a class of infinite games, (b) the extension of backward induction to infinite games, and (c) the proof that BIS and SPEs are identical for infinite games
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