On the origin of fluorine in the Milky Way     

Agostino Renda  Yeshe Fenner  Brad K. Gibson  Amanda I. Karakas  John C. Lattanzio  Simon Campbell  Alessandro Chieffi  Katia Cunha  Verne V. Smith 《Monthly notices of the Royal Astronomical Society》2004,354(2):575-580

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The 6dF Galaxy Survey: samples, observational techniques and the first data release     

D. Heath Jones  Will Saunders  Matthew Colless  Mike A. Read  Quentin A. Parker  Fred G. Watson  Lachlan A. Campbell  Daniel Burkey  Thomas Mauch  Lesa Moore  Malcolm Hartley  Paul Cass  Dionne James  Ken Russell  Kristin Fiegert  John Dawe  John Huchra  Tom Jarrett  Ofer Lahav  John Lucey  Gary A. Mamon  Dominique Proust  Elaine M. Sadler  Ken-ichi Wakamatsu 《Monthly notices of the Royal Astronomical Society》2004,355(3):747-763

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Using time‐domain reflectometry to characterize shallow solute transport in an oak woodland hillslope in northern California,USA     

Chris G. Campbell  Masoud Ghodrati  Fernando Garrido 《水文研究》2002,16(15):2921-2940

The natural heterogeneity of water and solute movement in hillslope soils makes it difficult to accurately characterize the transport of surface‐applied pollutants without first gathering spatially distributed hydrological data. This study examined the application of time‐domain reflectometry (TDR) to measure solute transport in hillslopes. Three different plot designs were used to examine the transport of a conservative tracer in the first 50 cm of a moderately sloping soil. In the first plot, which was designed to examine spatial variability in vertical transport in a 1·2 m² plot, a single probe per meter was found to adequately characterize vertical solute travel times. In addition, a dye and excavation study in this plot revealed lateral preferential flow in small macropores and a transport pattern where solute is focused vertically into preferential flow pathways. The bypass flow delivers solute deeper in the soil, where lateral flow occurs. The second plot, designed to capture both vertical and lateral flow, provided additional evidence confirming the flow patterns identified in the excavation of the first plot. The third plot was designed to examine lateral flow and once again preferential flow of the tracer was observed. In one instance rapid solute transport in this plot was estimated to occur in as little as 3% of the available pore space. Finally, it was demonstrated that the soil anisotropy, although partially responsible for lateral subsurface transport, may also homogenize the transport response across the hillslope by decreasing vertical solute spreading. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The RHESSI Spectrometer   总被引：2，自引：0，他引：2  

Smith  D.M.  Lin  R.P.  Turin  P.  Curtis  D.W.  Primbsch  J.H.  Campbell  R.D.  Abiad  R.  Schroeder  P.  Cork  C.P.  Hull  E.L.  Landis  D.A.  Madden  N.W.  Malone  D.  Pehl  R.H.  Raudorf  T.  Sangsingkeow  P.  Boyle  R.  Banks  I.S.  Shirey  K.  Schwartz  Richard 《Solar physics》2002,210(1-2):33-60

RHESSI observes solar photons over three orders of magnitude in energy (3 keV to 17 MeV) with a single instrument: a set of nine cryogenically cooled coaxial germanium detectors. With their extremely high energy resolution, RHESSI can resolve the line shape of every known solar gamma-ray line except the neutron capture line at 2.223 MeV. High resolution also allows clean separation of thermal and non-thermal hard X-rays and the accurate measurement of even extremely steep power-law spectra. Detector segmentation, fast signal processing, and two sets of movable attenuators allow RHESSI to make high-quality spectra and images of flares across seven orders of magnitude in intensity. Here we describe the configuration and operation of the RHESSI spectrometer, show early results on in-flight performance, and discuss the principles of spectroscopic data analysis used by the RHESSI software.  相似文献   

Development of an In Situ Ion-Exchange Technique for the Determination of Free Cd,Co, Ni,and Zn Concentrations in Freshwaters     

A. Crémazy  S. Leclair  K. K. Mueller  B. Vigneault  P. G. C. Campbell  C. Fortin 《Aquatic Geochemistry》2015,21(2-4):259-279

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Severity, duration and frequency of drought in SE England from 1697 to 2011     

B. Todd  N. Macdonald  R. C. Chiverrell  C. Caminade  J. M. Hooke 《Climatic change》2013,121(4):673-687

Severe droughts have affected much of Europe over the last 40 years. A limitation to current understanding of droughts is based around drought characteristics (e.g. frequency, severity and duration) as there are limited long series (>100 years) with well documented severe droughts. This is further complicated with future climate projections, and the potential implications that these will have on drought characteristics. This paper presents reconstructed drought series from 1697, 1726 and 1767 to 2011 for three sites in southeast England. Precipitation and temperature series are reconstructed to generate long drought series using the self-calibrated Palmer Drought Severity Index, enabling determination of drought characteristics. The reconstructions identify multiple drought-rich periods, 1730–1760 and 1890-present, with an increasing tendency towards more severe droughts during the latter period. Prolonged rainfall deficiencies are found to be the primary cause of severe droughts, with rising temperatures increasing soil moisture deficit, therefore intensifying drought conditions. Cycles at the 6–10 year period identify a sub-decadal to decadal signal during drought-rich periods. Analysis of the spatial variability of droughts finds that whilst severe events are predominantly regionally coherent, there are notable variations in severity and duration between sites, which are attributed to localised rainfall variability. This study extends the temporal range of previous drought studies and places recent drought events in a longer context improving upon existing ‘benchmark’ drought analyses in southeast England; with far-reaching implications for local, national and continental scale reduction of drought vulnerability and risk.  相似文献   

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance     

J. Todd Hoeksema  Yang Liu  Keiji Hayashi  Xudong Sun  Jesper Schou  Sebastien Couvidat  Aimee Norton  Monica Bobra  Rebecca Centeno  K. D. Leka  Graham Barnes  Michael Turmon 《Solar physics》2014,289(9):3483-3530

The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An automated processing pipeline keeps pace with observations to produce observable quantities, including the photospheric vector magnetic field, from sequences of filtergrams. The basic vector-field frame list cadence is 135 seconds, but to reduce noise the filtergrams are combined to derive data products every 720 seconds. The primary 720 s observables were released in mid-2010, including Stokes polarization parameters measured at six wavelengths, as well as intensity, Doppler velocity, and the line-of-sight magnetic field. More advanced products, including the full vector magnetic field, are now available. Automatically identified HMI Active Region Patches (HARPs) track the location and shape of magnetic regions throughout their lifetime. The vector field is computed using the Very Fast Inversion of the Stokes Vector (VFISV) code optimized for the HMI pipeline; the remaining 180^° azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The Milne–Eddington inversion is performed on all full-disk HMI observations. The disambiguation, until recently run only on HARP regions, is now implemented for the full disk. Vector and scalar quantities in the patches are used to derive active region indices potentially useful for forecasting; the data maps and indices are collected in the SHARP data series, hmi.sharp_720s. Definitive SHARP processing is completed only after the region rotates off the visible disk; quick-look products are produced in near real time. Patches are provided in both CCD and heliographic coordinates. HMI provides continuous coverage of the vector field, but has modest spatial, spectral, and temporal resolution. Coupled with limitations of the analysis and interpretation techniques, effects of the orbital velocity, and instrument performance, the resulting measurements have a certain dynamic range and sensitivity and are subject to systematic errors and uncertainties that are characterized in this report.  相似文献   

Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes     

Douglas A. Simons  Paola Amico  Dietrich Baade  Sam Barden  Randall Campbell  Gert Finger  Kirk Gilmore  Roland Gredel  Paul Hickson  Steve Howell  Norbert Hubin  Andreas Kaufer  Ralf Kohley  Philip MacQueen  Sergej Markelov  Mike Merrill  Satoshi Miyazaki  Hidehiko Nakaya  Darragh O'Donoghue  Tino Oliva  Andrea Richichi  Derrick Salmon  Ricardo Schmidt  Hongjun Su  Simon Tulloch  Maria Luisa García Vargas  R. Mark Wagner  Olivier Wiecha  Binxun Ye 《Experimental Astronomy》2005,19(1-3):15-44

Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 10⁹ pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.  相似文献   

Refined conceptualization of TOPMODEL for shallow subsurface flows     

M. Todd Walter  Tammo S. Steenhuis  Vishal K. Mehta  Dominique Thongs  Mark Zion  Elliot Schneiderman 《水文研究》2002,16(10):2041-2046

The TOPMODEL framework was used to derive expressions that account for saturated and unsaturated flow through shallow soil on a hillslope. The resulting equations were the basis for a shallow‐soil TOPMODEL (STOPMODEL). The common TOPMODEL theory implicitly assumes a water table below the entire watershed and this does not conceptually apply to systems hydrologically controlled by shallow interflow of perched groundwater. STOPMODEL provides an approach for extending TOPMODEL's conceptualization to apply to shallow, interflow‐driven watersheds by using soil moisture deficit instead of water table depth as the state variable. Deriving STOPMODEL by using a hydraulic conductivity function that changes exponentially with soil moisture content results in equations that look very similar to those commonly associated with TOPMODEL. This alternative way of conceptualizing TOPMODEL makes the modelling approach available to researchers, planners, and engineers who work in areas where TOPMODEL was previously believed to be unsuited, such as the New York City Watershed in the Catskills region of New York State. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Mixture models and atypical values     

N. A. Campbell 《Mathematical Geology》1984,16(5):465-477

The resolution of a mixture of two or more populations into its component distributions may be markedly influenced by one or a few atypical values. The maximum likelihood solution effectively assigns (part of) each observation to one or another of the components via the posterior probabilities, even though the observation may be widely discrepant from all components. This paper presents a modification of the mixture problem, in which the typicality of each observation is considered, as well as the posterior probabilities, with the contribution of atypical observations being downweighted. The extension to the multivariate case is discussed.  相似文献