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   

Evaluating Kinematic Controls on Planar Translational Slope Failure Mechanisms Using Three-Dimensional Distinct Element Modelling   总被引：1，自引：0，他引：1  

Marc-André Brideau  Doug Stead 《Geotechnical and Geological Engineering》2012,30(4):991-1011

This paper investigates the importance of kinematic release mechanisms on planar translational slope failure using three-dimensional distinct element codes. The importance of the dip and dip direction of the rear, basal and lateral release surfaces and their influence on failure mechanism, dilation, and the development of step-path failures is illustrated. The three-dimensional block shape and volume of the unstable rock masses simulated with the different discontinuity set geometries are characterized. Two assumed three-dimensional slope models are investigated in order to assess the importance of varying kinematic confinement/release mechanisms. These two assumed boundary conditions are shown to be critical in the development of asymmetrical rock mass deformation patterns. Scale effects due to the block size and discontinuity persistence are shown to control the calculated displacement and failure mechanisms. The numerical modelling results are also demonstrated to be sensitive to the assumed normal and shear stiffness of the discontinuities. The influence of the factors investigated on the failure of a single rock block versus a rock mass are compared and discussed.  相似文献   

Managing coastal vulnerability     

Doug Ramsay 《New Zealand geographer》2008,64(2):170-171

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Seven young star clusters in the inner region of the Small Magellanic Cloud     

Andrés E. Piatti  Doug Geisler  Ata Sarajedini  Carme Gallart  Marina Wischnjewsky † 《Monthly notices of the Royal Astronomical Society》2008,389(1):429-440

We present CCD photometry in the Washington system C and T ₁ passbands down to   T ₁∼ 22  in the fields of L35, L45, L49, L50, L62, L63 and L85, seven poorly studied star clusters in the inner region of the Small Magellanic Cloud (SMC). We measured T ₁ magnitudes and   C − T ₁  colours for a total of 114 826 stars distributed throughout cluster areas of 13.7 × 13.7 arcmin² each. Cluster radii were estimated from star counts distributed throughout the entire observed fields. The seven clusters are generally characterized by a relatively small angular size and by a high field star contamination. We performed an in-depth analysis of the field star contamination of the colour–magnitude diagrams (CMDs), and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the  ( T ₁,  C − T ₁)  CMDs, we derive ages for the sample, assuming Z = 0.004, finding ages between 25 Myr and 1.2 Gyr. We then examined different relationships between positions in the SMC, age and metallicity of a larger sample of clusters including our previous work whose ages and metallicities are on the same scale used in this paper. We confirm previous results in the sense that the further a cluster is from the centre of the galaxy, the older and more metal poor it is, with some dispersion; although clusters associated with the Magellanic Bridge clearly do not obey the general trend. The number of clusters within ∼ 2° of the SMC centre appears to have increased substantially after ∼2.5 Gyr ago, hinting at a burst.  相似文献   

Global Detection of Infrasonic Signals from Three Large Bolides     

Stephen J. Arrowsmith  Doug ReVelle  Wayne Edwards  Peter Brown 《Earth, Moon, and Planets》2008,102(1-4):357-363

We present the infrasonic observations of three large bolides that were observed at numerous International Monitoring System (IMS) infrasound arrays on a global scale. First, a simple procedure for the global association of infrasound detections from large infrasound events is outlined. Infrasound signals are associated with large events based on arrival time, backazimuth and uniqueness at a given IMS array. Next, we apply the algorithm to three bolides and investigate some of the factors affecting the detectability of infrasound from large events. Our findings suggest that site-noise effects significantly degrade the capability of the IMS infrasound network, suggesting that more effort is required to reduce ambient site noise. These results have implications for the use of infrasound measurements (in particular those from IMS stations) as a tool for evaluating the global flux of near-Earth objects.  相似文献