High spatial resolution ion microprobe measurements refine chronology of carbonate formation in Orgueil     

Peter Hoppe  Doug MacDougall  Günter W. Lugmair 《Meteoritics & planetary science》2007,42(7-8):1309-1320

Abstract— Aqueous activity on meteorite parent bodies is indicated by the presence of carbonates. High spatial resolution ion microprobe analyses of nine individual carbonate grains (four dolomites, five breunnerites) from the Orgueil meteorite reveal linear correlations between ⁵³Cr excesses and Mn/Cr ratios in all grains, indicative of in situ decay of radioactive ⁵³Mn (half‐life 3.7 million years). The well‐defined isochrons appear to have chronological significance. If this is the case, then ⁵³Mn/⁵⁵Mn ratios between 2.1 and 4.7 × 10^?6 are inferred for the time of carbonate formation and absolute ages of between 4561 and 4565 Ma are calculated (systematic uncertainty of ±2 Ma). Dolomites tend to have formed slightly earlier than the breunnerites. Our data imply extensive aqueous activity on the Orgueil parent body over a period of several million years, starting ～3–4 Myr after formation of the solar system, that most likely was the result of impact heating and latent heat from the decay of radioactive ²⁶Al and ⁶⁰Fe.  相似文献   

Ages and metallicities of five intermediate-age star clusters projected towards the Small Magellanic Cloud     

Andrés E. Piatti  João F. C. SantosJr  Juan J. Clariá  Eduardo Bica  Ata Sarajedini  Doug Geisler 《Monthly notices of the Royal Astronomical Society》2001,325(2):792-802

Colour–magnitude diagrams are presented for the first time for L32, L38, K28 (L43), K44 (L68) and L116, which are clusters projected on to the outer parts of the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system C and T ₁ filters, allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turn-off, and metallicities from the red giant branch locus. The clusters have ages in the range 2–6 Gyr , and metallicities in the range −1.65<[Fe/H]<−1.10, increasing the sample of intermediate-age clusters in the SMC. L116, the outermost cluster projected on to the SMC, is a foreground cluster, and somewhat closer to us than the Large Magellanic Cloud. Our results, combined with those for other clusters in the literature, show epochs of sudden chemical enrichment in the age–metallicity plane, which favour a bursting star formation history as opposed to a continuous one for the SMC.  相似文献   

Seamless integration of spatial statistics and GIS: The S-PLUS for ArcView and the S+Grassland Links     

Shuming Bao  Luc Anselin  Doug Martin  Diana Stralberg 《Journal of Geographical Systems》2000,2(3):287-306

The extension of the functional capacity of geographic information systems (GIS) with tools for statistical analysis in general and exploratory spatial data analysis (ESDA) in particular has been an increasingly active area of research in recent years. In this paper, two operational implementations that combine the functionality of spatial data analysis software with a GIS are considered more closely. They consist of linkages between the S-PLUS software for data analysis and two different GIS implementations, the ArcView desktop system, which is mostly vector-oriented, and the primarily raster-based Grassland open GIS environment. We emphasize conceptual and technical issues related to the software implementation of these approaches and suggest future directions for linking spatial statistics and GIS. Received: 14 January 1999 / Accepted: 11 May 1999  相似文献   

Ages and metallicities of eight star clusters and their surrounding fields in the inner disc of the Large Magellanic Cloud     

Doug Geisler  rés E. Piatti  Eduardo Bica  Juan J. Clariá 《Monthly notices of the Royal Astronomical Society》2003,341(3):771-784

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Editorial     

Doug Robinson 《Journal of Metamorphic Geology》1990,8(3):249-249

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Cosmogenic radionuclide dating of glacial landforms in the Lahul Himalaya,northern India: defining the timing of Late Quaternary glaciation     

Lewis A. Owen  Lyn Gualtieri  Robert C. Finkel  Marc W. Caffee  Doug I. Benn  Milap C. Sharma 《第四纪科学杂志》2001,16(6):555-563

The timing of glaciation in the Lahul Himalaya of northern India was ascertained using the concentrations of cosmogenic ¹⁰Be and ²⁶Al from boulders on moraines and drumlins, and from glacially polished bedrock surfaces. Five glacial stages were identified: Sonapani I and II, Kulti, Batal and Chandra. Of these, cosmogenic exposure ages were obtained on samples representative of the Batal and Kulti glacial cycles. Stratigraphical relationships indicate that the Sonapani I and II are younger. No age was obtained for the Chandra glacial advance. Batal Glacial Stage deposits are found throughout the valley, indicating the presence of an extensive valley glacial system. During the Kulti Stage, glaciers advanced ca. 10 km beyond their current positions. Moraines produced during the Batal Stage, ca. 12–15.5 ka, are coeval with the Northern Hemisphere Late‐glacial Interstadial (Bølling/Allerød). Deglaciation of the Batal Glacial Stage was completed by ca. 12 ka and was followed by the Kulti Glacial Stage during the early Holocene, at ca. 10–11.4 ka. On millennial time‐scales, glacier oscillations in the Lahul Himalaya apparently reflect periods of positive mass‐balance coincident with times of increased insolation. During these periods the South Asian summer monsoon strengthened and/or extended its influence further north and west, thereby enhancing high‐altitude summer snowfall. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Constraining the LMC cluster age gap: Washington photometry of NGC 2155 and SL 896 (LW 480)     

Andrés E. Piatti  Ata Sarajedini  Doug Geisler  Eduardo Bica  Juan J. Clariá 《Monthly notices of the Royal Astronomical Society》2002,329(3):556-566

We carried out Washington system photometry of the intermediate-age Large Magellanic Cloud (LMC) star clusters NGC 2155 and SL 896 (LW 480). We derive ages and metallicities from the T ₁ versus     colour–magnitude diagrams (CMDs). For the first time an age has been obtained for SL 896,     . For NGC 2155 we derive     . The two clusters basically define the lower age limit of the LMC age gap. In particular, NGC 2155 is confirmed as the oldest intermediate-age LMC cluster so far studied. The derived metallicities are     and     for NGC 2155 and SL 896, respectively. We also studied the CMDs of the surrounding fields, which have a dominant turn-off comparable to that of the clusters themselves, and similar metallicity, showing that one is dealing with an intermediate-age disc where clusters and field stars have the same origin. We inserted the present clusters in the LMC and Small Magellanic Cloud (SMC) age–metallicity relations, using a set of homogeneous determinations with the same method as in our previous studies, now totalling 15 LMC clusters and four SMC clusters, together with some additional values from the literature. The LMC and SMC age–metallicity relations appear to be remarkably complementary, since the SMC was actively star-forming during the LMC quiescent age gap epoch.  相似文献   

Editorial     

Doug Robinson 《Journal of Metamorphic Geology》2006,24(1):1-1

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Lithologically controlled invisible gold,Yukon, Canada   总被引：1，自引：0，他引：1  

Doug MacKenzie  Dave Craw  Craig Finnigan 《Mineralium Deposita》2015,50(2):141-157

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A Spherical Lens For The Ska     

John S. Kot  Richard Donelson  Nasiha Nikolic  Doug Hayman  Mike O’Shea  Gary Peeters 《Experimental Astronomy》2004,17(1-3):141-148

Spherical refracting lenses based upon the Luneburg lens offer unique capabilities for radioastronomy, but the large diameter of lens required for the Square Kilometre Array (SKA) means that traditional lens materials are either too dense or too lossy. We are investigating a composite dielectric that theoretically offers extremely low loss and low density, and is suitable for low-cost mass production. We describe our progress towards realising this material and demonstrating the manufacturing concept, via the manufacture and testing of a small (0.9 m) spherical lens.  相似文献