Observations on the crystal structures of lueshite     

Roger H. Mitchell  Peter C. Burns  Kevin S. Knight  Christopher J. Howard  Anton R. Chakhmouradian 《Physics and Chemistry of Minerals》2014,41(6):393-401

Laboratory powder XRD patterns of the perovskite-group mineral lueshite from the type locality (Lueshe, Kivu, DRC) and pure NaNbO₃ demonstrate that lueshite does not adopt the same space group (Pbma; #57) as the synthetic compound. The crystal structures of lueshite (2 samples) from Lueshe, Mont Saint-Hilaire (Quebec, Canada) and Sallanlatvi (Kola, Russia) have been determined by single-crystal CCD X-ray diffraction. These room temperature X-ray data for all single-crystal samples can be satisfactorily refined in the orthorhombic space group Pbnm (#62). Cell dimensions, atomic coordinates of the atoms, bond lengths and octahedron tilt angles are given for four crystals. Conventional neutron diffraction patterns for Lueshe lueshite recorded over the temperature range 11–1,000 K confirm that lueshite does not adopt space group Pbma within these temperatures. Neutron diffraction indicates no phase changes on cooling from room temperature to 11 K. None of these neutron diffraction data give satisfactorily refinements but suggest that this is the space group Pbnm. Time-of-flight neutron diffraction patterns for Lueshe lueshite recorded from room temperature to 700 °C demonstrate phase transitions above 550 °C from Cmcm through P4/mbm to \(Pm\overline{3} m\) above 650 °C. Cell dimensions and atomic coordinates of the atoms are given for the three high-temperature phases. The room temperature to 400 °C structures cannot be satisfactorily resolved, and it is suggested that the lueshite at room temperature consists of domains of pinned metastable phases with orthorhombic and/or monoclinic structures. However, the sequence of high-temperature phase transitions observed is similar to those determined for synthetic NaTaO₃, suggesting that the equilibrated room temperature structure of lueshite is orthorhombic Pbnm.  相似文献   

Geoarchaeology,Climate Change,and Sustainability. Antony G. Brown,Laura S. Basell,and Karl W. Butzer (Eds.). 2011. Special Paper 476. Geological Society of America,Boulder, CO. 194 pp., ISBN: 978‐0‐8137‐2476‐8, $80 (paperback).     

Christopher L. Hill 《Geoarchaeology》2014,29(2):175-177

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A Comprehensive Framework for Intrinsic OpenStreetMap Quality Analysis   总被引：5，自引：2，他引：3  

Christopher Barron  Pascal Neis  Alexander Zipf 《Transactions in GIS》2014,18(6):877-895

OpenStreetMap (OSM) is one of the most popular examples of a Volunteered Geographic Information (VGI) project. In the past years it has become a serious alternative source for geodata. Since the quality of OSM data can vary strongly, different aspects have been investigated in several scientific studies. In most cases the data is compared with commercial or administrative datasets which, however, are not always accessible due to the lack of availability, contradictory licensing restrictions or high procurement costs. In this investigation a framework containing more than 25 methods and indicators is presented, allowing OSM quality assessments based solely on the data's history. Without the usage of a reference data set, approximate statements on OSM data quality are possible. For this purpose existing methods are taken up, developed further, and integrated into an extensible open source framework. This enables arbitrarily repeatable intrinsic OSM quality analyses for any part of the world.  相似文献   

Fragmentation of massive protostellar discs     

Kaitlin M. Kratter  Christopher D. Matzner 《Monthly notices of the Royal Astronomical Society》2006,373(4):1563-1576

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The frequency of explosive volcanic eruptions in Southeast Asia     

Patrick L. Whelley  Christopher G. Newhall  Kyle E. Bradley 《Bulletin of Volcanology》2015,77(1):1-11

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A 24 h investigation of the hydrogeochemistry of baseflow and stormwater in an urban area impacted by mining: Butte,Montana     

Christopher H. Gammons  Christopher L. Shope  Terence E. Duaime 《水文研究》2005,19(14):2737-2753

Changes in water quality during a storm event were continuously monitored over a 24 h period at a single location along an urban stormwater drain in Butte, Montana. The Butte Metro Storm Drain (MSD) collects groundwater baseflow and stormwater draining Butte Hill, a densely populated site that has been severely impacted by 130 years of mining, milling, and smelting of copper‐rich, polymetallic mineral deposits. On the afternoon of 26 June 2002, a heavy thunderstorm caused streamflow in the MSD to increase 100‐fold, from 0·2 ft³ s⁻¹ to more than 20 ft³ s⁻¹. Hourly discharge and water quality data were collected before, during, and following the storm. The most significant finding was that the calculated loads (grams per hour) of both dissolved and particulate copper passing down the MSD increased more than 100‐fold in the first hour following the storm, and remained elevated over baseline conditions for the remainder of the study period. Other metals, such as zinc, cadmium, and manganese, showed a decrease in load from pre‐storm to post‐storm conditions. In addition to the large flush of copper, loads of soluble phosphorus increased during the storm, whereas dissolved oxygen dropped to low levels (<2 mg l⁻¹). These results show that infrequent storm events in Butte have the potential to generate large volumes of runoff that exceed Montana water quality standards for acute exposure of aquatic life to copper, as well as depressed levels of dissolved oxygen. This study has important implications to ongoing reclamation activities in the upper Clark Fork Superfund site, particularly with respect to management of storm flow, and may be applicable to other watersheds impacted by mining activities. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Mid-infrared polarisation and inferred magnetic field direction toward YSOs with outflow     

Christopher M. Wright 《Astrophysics and Space Science》2007,311(1-3):47-55

The position angle of mid-infrared polarisation can be directly related to the magnetic field direction projected onto the plane of the sky. Such observations, from both ground and space-based platforms, have been used to investigate the relation between the magnetic field and other “symmetry axes” associated with embedded young stars, such as the interstellar magnetic field, bipolar outflow and disk/toroid axes. Interpretation of the results in terms of hydromagnetic driving mechanisms of bipolar outflow is discussed.  相似文献   

Density profiles of galaxy groups and clusters from SDSS galaxy–galaxy weak lensing     

Rachel Mandelbaum  Uro&#; Seljak  Richard J. Cool  Michael Blanton  Christopher M. Hirata  Jonathan Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,372(2):758-776

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The fundamental properties of galaxies and a new galaxy classification system     

Christopher J. Conselice 《Monthly notices of the Royal Astronomical Society》2006,373(4):1389-1408

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Mid-infrared, spatially resolved spectroscopy of the nucleus of the Circinus galaxy     

Patrick F. Roche  Christopher Packham  Charles M. Telesco  James T. Radomski  Almudena Alonso-Herrero  David K. Aitken  Luis Colina  Eric Perlman 《Monthly notices of the Royal Astronomical Society》2006,367(4):1689-1698

High spatial resolution spectroscopy at 8–13 μm with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy (hereafter Circinus) on subarcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of   A_V ∼ 25 mag  . Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disc-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disc found from observations of water masers by Greenhill et al..  相似文献