The nature of Trojan asteroid 624 Hektor     

William K. Hartmann  Dale P. Cruikshank 《Icarus》1978,36(3):353-366

We report new visual and 20-μm photometry obtained when Hektor was seen nearly along its rotation axis. The visual amplitude was near its minimum, only 0.06 mag, confirming the Dunlap-Gehrels (1969) rotation model. The new observations confirm and refine the large size and low albedo assigned by Cruikshank (1977) from observations of the opposite rotation pole. The albedo of this pole is found to be pv = 0.022 ± 0.003, overlapping the uncertainty of Cruikshank's 0.03 value for the opposite pole. The low albedo makes Hektor roughly three times bigger than estimates of a few years ago. The light variations are interpreted as due to elongated shape. If this is correct, Hektor is both the largest and most elongated known Trojan, as well as being the most elongated known asteroid of its size. From considerations of Trojans' peculiar properties, we propose that Hektor is a somewhat dumbbell shaped object roughly 150 × 300 km in size, resulting from partial coalescence of two primitive spheroidal planetesimals during a relatively low-speed collision in the Trojan Lagrangian cloud, with energy too low for complete disruption. Calculations supporting this model indicate that Trojans may be less altered by collisions than belt asteroids. Observations in 1979 and 1980 can help test this model. A note added on July 17, 1978 relates our result to recent evidence of possible binary asteroid pairs, which may also arise from early low-velocity asteroid-asteroid interactions.  相似文献   

Regional Sources of Methyl Chloride, Chloroform and Dichloromethane Identified from AGAGE Observations at Cape Grim, Tasmania, 1998–2000     

M. L. Cox  G. A. Sturrock  P. J. Fraser  S. T. Siems  P. B. Krummel  S. O'Doherty 《Journal of Atmospheric Chemistry》2003,45(1):79-99

There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH₃Cl), chloroform (CHCl₃) and dichloromethane (CH₂Cl₂), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH₃Cl, CHCl₃ and CH₂Cl₂ during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 10¹²) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH₃Cl and CHCl₃ records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH₃Cl and CHCl₃ that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH₂Cl₂ (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences  相似文献   

Long-term changes in salt marsh extent affected by channel deepening in a modified estuary   总被引：2，自引：0，他引：2  

Ruth Cox  R. A. Wadsworth  A. G. Thomson 《Continental Shelf Research》2003,23(17-19):1833

The aim of this study is to quantify the long-term (54 years) rates of marsh extension and retreat at two sites in the Westerschelde Estuary, SW Netherlands. Nine sets of aerial photographs were obtained for each of the two salt marsh sites, Zuidgors and Waarde, taken at various times between 1944 and 1998. The seaward edges of the marshes were digitised from rectified images after the photographs had been scanned and georegistered to the Dutch National Grid. Comparison of the extents of the marshes at these nine time points revealed that the areas of both marshes had fluctuated during these 54 years with periods of both extension and retreat of the seaward marsh edges. These periods of extension and retreat appeared to be approximately synchronised until the 1990s, with mean changes in position of marsh front ranging from −7.92 to 6.04 m a⁻¹.The rate of landward retreat and seaward extension of the marsh front is shown to be related to an increase in the tidal prism brought about by dredging operations to maintain or increase the depth of the main navigable channel of the estuary. The consequent greater frequency with which the high tides reach the edge of the fringing marshes increases the risk of erosion. Strong westerly winds may also be a factor in increasing erosion. No relationship between the volume of shipping traffic using the estuary and marsh erosion was found.  相似文献   

Terrane accretion and dispersal in the northern Gondwana margin. An Early Paleozoic analogue of a long-lived active margin     

G. Gutirrez-Alonso  J. Fernndez-Surez  T.E. Jeffries  G.A. Jenner  M.N. Tubrett  R. Cox  S.E. Jackson 《Tectonophysics》2003,365(1-4):221

If reconstruction of major events in ancient orogenic belts is achieved in sufficient detail, the tectonic evolution of these belts can offer valuable information to widen our perspective of processes currently at work in modern orogens. Here, we illustrate this possibility taking the western European Cadomian–Avalonian belt as an example. This research is based mainly on the study and interpretation of U–Pb ages of more than 300 detrital zircons from Neoproterozoic and Early Paleozoic sedimentary rocks from Iberia and Brittany. Analyses have been performed using the laser ablation–ICP–MS technique. The U–Pb data record contrasting detrital zircon age spectra for various terranes of western Europe. The differences provide information on the processes involved in the genesis of the western European Precambrian terranes along the northern margin of Neoproterozoic Gondwana during arc construction and subduction, and their dispersal and re-amalgamation along the margin to form the Avalonia and Armorica microcontinents. The U–Pb ages reported here also support the alleged change from subduction to transform activity that led to the final break-up of the margin, the birth of the Rheic Ocean and the drift of Avalonia. We contend that the active northern margin of Gondwana evolved through several stages that match the different types of active margins recognised in modern settings.  相似文献   

Performance analysis of a stand-alone high-sensitivity receiver     

G. MacGougan  G. Lachapelle  R. Klukas  K. Siu  L. Garin  J. Shewfelt  G. Cox 《GPS Solutions》2002,6(3):179-195

The use of GPS for personal location using wireless devices requires satellite signal measurements both outdoors and indoors. In the outdoor environment propagation paths may range from line-of-sight to shaded or blocked. The indoor environment may range from single-floor wooden constructions to high-rise buildings and underground facilities. In this paper, a high-sensitivity receiver which operates in unaided stand-alone mode is tested under a range of shaded and blocked signal environments, ranging from residential outdoor areas to urban canyons and residential houses. The measurement analysis is performed in both the observation and position domains. The results show that the receiver tested is able to yield measurements with C/N₀ degradations in excess of 20 dB-Hz, as compared to line-of-sight measurements. Position results are a function of the geometry of the remaining satellites, which in turn is a function of the environment. Electronic Publication  相似文献   

Handbook for the field assessment of land degradation by Michael A. Stocking and Niamh Murnaghan,Earthscan, London, 2001. No. of pages: 169. Price: £25.00. ISBN 1 85383 831 4.     

Nicholas J. Cox 《地球表面变化过程与地形》2002,27(7):790-791

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Environmental physics by Clare Smith,Routledge, London, 2001. No. of pages: 304. Price: £17.99 (paperback), £60 (hardback). ISBN 0 415 20191 8 (paperback), 0 415 20190 X (hardback).     

Nicholas J. Cox 《地球表面变化过程与地形》2002,27(9):1028-1029

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Répartition de l'uranium et du thorium dans les apatites : implications pour la thermochronologie UTh/He     

Marc Jolivet  Tim Dempster  Richard Cox 《Comptes Rendus Geoscience》2003,335(12):899-906

The UTh/He thermochronology technique assumes a homogeneous distribution of U and Th within the analysed crystals. Cathodoluminescence imaging reveals a strong chemical heterogeneity within apatite a mineral widely used for UTh/He dating. This heterogeneity is then susceptible to induce large errors when calculating the UTh/He age. Chemical analysis using laser ablation ICP–MS of the various zones shown by cathodoluminescence display a link between the Ce, U and Th concentration and the luminescence intensity allowing the UTh/He age to be corrected for zonation. To cite this article: M. Jolivet et al., C. R. Geoscience 335 (2003).  相似文献   

Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project     

Sebastiano Foti  Fabrice Hollender  Flora Garofalo  Dario Albarello  Michael Asten  Pierre-Yves Bard  Cesare Comina  Cécile Cornou  Brady Cox  Giuseppe Di Giulio  Thomas Forbriger  Koichi Hayashi  Enrico Lunedei  Antony Martin  Diego Mercerat  Matthias Ohrnberger  Valerio Poggi  Florence Renalier  Deborah Sicilia  Valentina Socco 《Bulletin of Earthquake Engineering》2018,16(6):2367-2420

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V_S,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic principles and specific suggestions related to the most common situations. They are primarily targeted to non-expert users approaching surface wave testing, but can be useful to specialists in the field as a general reference. The guidelines are based on the experience gained within the InterPACIFIC project and on the expertise of the participants in acquisition and analysis of surface wave data.  相似文献   

DTSGUI: A Python Program to Process and Visualize Fiber-Optic Distributed Temperature Sensing Data     

Marian Domanski  Daven Quinn  Frederick D. Day-Lewis  Martin A. Briggs  Dale Werkema  John W. Lane Jr. 《Ground water》2020,58(5):799-804

Fiber-optic distributed temperature sensing (FO-DTS) has proven to be a transformative technology for the hydrologic sciences, with application to diverse problems including hyporheic exchange, groundwater/surface-water interaction, fractured-rock characterization, and cold regions hydrology. FO-DTS produces large, complex, and information-rich datasets. Despite the potential of FO-DTS, adoption of the technology has been impeded by lack of tools for data processing, analysis, and visualization. New tools are needed to efficiently and fully capitalize on the information content of FO-DTS datasets. To this end, we present DTSGUI, a public-domain Python-based software package for editing, parsing, processing, statistical analysis, georeferencing, and visualization of FO-DTS data.  相似文献