Modelling the redshift-space distortion of galaxy clustering     

Steve Hatton  & Shaun Cole 《Monthly notices of the Royal Astronomical Society》1998,296(1):10-20

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Mock 2dF and SDSS galaxy redshift surveys   总被引：1，自引：0，他引：1  

Shaun Cole  Steve Hatton  David H. Weinberg  & Carlos S. Frenk 《Monthly notices of the Royal Astronomical Society》1998,300(4):945-966

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The radio properties of radio-quiet quasars     

Marek J. Kukula  James S. Dunlop  David H. Hughes  & Steve Rawlings 《Monthly notices of the Royal Astronomical Society》1998,297(2):366-382

Although radio-quiet quasars (RQQs) constitute ≳ 90 per cent of optically identified quasar samples, their radio properties are only poorly understood. In this paper we present the results of a multi-frequency VLA study of 27 low-redshift RQQs. We detect radio emission from 20 objects, half of which are unresolved (≤ 0.24 arcsec). In cases where significant structure can be resolved, double, triple and linear radio sources on scales of a few kpc are found. The radio emission (typically) has a steep spectrum (α ∼ 0.7, where S  ∝ ν^−α), and high brightness temperatures ( T _B ≥ 10⁵ K) are measured in some of the radio components. The RQQs form a natural extension to the radio luminosity–absolute magnitude distribution of nearby Seyfert 1s. We conclude that a significant fraction of the radio emission in RQQs originates in a compact nuclear source directly associated with the quasar. There are no significant differences between the radio properties of RQQs with elliptical hosts and those in disc galaxies within the current sample.  相似文献   

Melanoidins—kerogen precursors and geochemical lipid sinks: a study using pyrolysis gas chromatography (PGC)     

S.R. Larter  A.G. Douglas 《Geochimica et cosmochimica acta》1980,44(12):2087-2095

Melanoidins, acidic polymeric products of amino acid/sugar condensation reactions, are shown to be capable of reacting with and binding functionalized lipid molecules. Pyrolysis gas chromatography is used to monitor the inclusion of lipids (alcohols and acids) into, and to monitor the changes in composition caused by artificial diagenesis of, the melanoidins. Artificial diagenesis of the lipidcontaining melanoidins produces a material resembling kerogen. The possible role of melanoidins in the formation of kerogens is discussed as are internal transformations within kerogens during diagenesis.  相似文献   

Organic carbon isotope ratios of recent sediments from coastal lagoons of the Gulf of Mexico,Mexico     

Alfonso V. Botello  Enrique F. Mandelli  Steve Macko  Patrick L. Parker 《Geochimica et cosmochimica acta》1980,44(3):557-559

The stable carbon isotope composition sedimentary organic carbon was determined in the sediments of seven coastal lagoons of the Gulf of Mexico, Mexico. For most of the lagoons the δ¹³C values for sediments ranged from ?20.1 to ?23.9%. Anomalously low values, ?26.8 to 29.3%. were determined in sediments of two of the studied lagoons, probably due to the presence of organic carbon from anthropogenic sources, naturally absent in these environments. The δ¹³C values determined in the tissues of oysters collected at the same time in the different lagoons were very similar to those recorded in the sediments.  相似文献   

Saturn's auroral/polar H₃ infrared emission: I. General morphology and ion velocity structure     

Tom Stallard  Steve Miller  Makenzie Lystrup  Nicholas Achilleos 《Icarus》2007,189(1):1-13

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Efficacy of a multi-metric fish index as an analysis tool for the transitional fish component of the Water Framework Directive     

Coates S  Waugh A  Anwar A  Robson M 《Marine pollution bulletin》2007,55(1-6):225-240

The WFD has introduced an international commitment to assess the ecological status of transitional waters (TWs), within which fish communities are a key biological monitoring component. The Transitional Fish Classification Index (TFCI) outlined in this paper uses 10 ecological measures to analyse fish populations caught from various ecological niches using a variety of gear types within the Thames estuary. These reach and method-specific communities are then compared to a reference population created from a 'healthy' population from TWs of a similar type. The results indicate a progressive downstream increase the quality of fish communities, consistent with previous work; variation between methods can be accounted for by gear selectivity. Overall, the TFCI is an effective communication tool for converting ecological information into an easily understood format for managers, policy makers and the general public.  相似文献   

Benthic meiofauna community composition at polluted and non-polluted sites in New Zealand intertidal environments   总被引：1，自引：0，他引：1  

Hack LA  Tremblay LA  Wratten SD  Lister A  Keesing V 《Marine pollution bulletin》2007,54(11):1801-1812

Meiofauna composition was investigated for six field sites, including polluted and non-polluted sites, within two regions (Auckland and Bay of Plenty) during winter (July-August 2004) in the North Island of New Zealand. Physico-chemical parameters were measured during the sampling period and meiofauna distribution and abundance were compared with these measured parameters. Analysis of meiofauna abundance indicated that foraminiferans, nematodes and ostracods were the taxa that contributed to the variability between field sites within the Auckland region. However, no clear taxa dominance was seen in the Bay of Plenty region. Comparison of meiofauna abundance and physico-chemical parameters was done using multivariate analysis (PRIMER). However, no clear relationships between the parameters were observed in any field site in either region. The Shannon-Weiner index of diversity did not show any clear differentiation between polluted and non-polluted field sites. Therefore, from the present study, the taxa or physico-chemical parameters used could not effectively characterise pollution at the investigated field sites.  相似文献   

The Quaternary history of the Wash fluvial network, UK     

Steve Boreham  Tom S. White  Andy J. Howard 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(4):393-449

This paper appraises and compares the Middle-Upper Pleistocene sedimentary sequences preserved in the fluvial systems draining into the Fenland Basin and the Wash estuary. Of the main Fenland rivers the longest records, which extend back to the initial Anglian (glacial) formation of the basin, are found in the Great Ouse and its tributaries, particularly the Cam and the Nar. These sequences preserve sediments representing all four post-Anglian interglacials. The Nene also has an extensive post-Anglian history, with evidence for a Hoxnian estuary that is presumed to have been the precursor of the Wash. North of the Nene, however, the Welland and Witham (proto-Trent) have relatively short sequences, which are thought to commence with a later (post-Anglian-pre-Devensian) glaciation that affected Lincolnshire and fed the previously-recognized Tottenhill outwash delta south of Kings Lynn. Prior to Devensian deglaciation the Witham valley was occupied by the Trent, which was the trunk river of the late Middle Pleistocene Wash system. During periods of low sea level the river would have extended north-eastwards across what is now the floor of the North Sea, possibly via the Inner Silver Pit. Several of the central Fenland sequences show evidence of infrequent terrace formation during the late Quaternary, although this might in part be due to poor vertical separation between terraces, so that differentiating them has been difficult; this has been exacerbated by mixed biostratigraphical signals due to the preservation of sediments representing more than one interglacial beneath a single terrace surface. In several of the systems there is evidence for valley rejuvenation to the lowest terrace or valley-floor level during the MIS 4-3 transition. The observed differences within what, during the predominant periods of lower sea level, would have been a single Wash river system are difficult to explain.  相似文献   

Towards a volcanic–structural balance: relative importance of volcanism, folding, and remobilisation of nickel sulphides at the Perseverance Ni–Cu–(PGE) deposit, Western Australia     

Paul Duuring  Wouter Bleeker  Steve W. Beresford  Nicholas Hayward 《Mineralium Deposita》2010,45(3):281-311

Perseverance is a world-class, komatiite-hosted nickel sulphide deposit situated in the well-endowed Leinster nickel camp of the Agnew–Wiluna greenstone belt, Western Australia. The mine stratigraphy at Perseverance trends north-northwest (NNW), dips steeply to the west, and is overturned. Stratigraphic footwall units lie along the western margin of the Perseverance Ultramafic Complex (PUC). The PUC comprises a basal nickel sulphide-bearing orthocumulate- to mesocumulate-textured komatiite that is overlain by a thicker, nickel sulphide-poor, dunite lens. Hanging wall rocks include rhyodacite that is texturally and compositionally similar to footwall volcanic rocks. These rocks separate the PUC from a second sequence of nickeliferous, E-facing, spinifex-textured komatiite units (i.e. the East Perseverance komatiite). Past workers argue for a conformable stratigraphic contact between the PUC and the East Perseverance komatiite and conclude that the PUC is extrusive. This study, however, clearly demonstrates that these komatiite sequences are discordant, implying that the PUC may have intruded rhyodacite country rock as a sill with subsequent structural juxtaposition against the East Perseverance komatiite. Early N–S shortening associated with the regional D_I deformation event (corresponding to the local D_P1 to D_P3 events at Perseverance) resulted in the heterogeneous partitioning of strain along the margins of the competent dunite. A mylonite developed in the more ductile footwall rocks along the footwall margin of the PUC, while isoclinal F₃ folds, such as the Hanging wall limb and Felsic Nose folds, formed in low-mean stress domains along the fringes of the elongated dunite lens. Strata-bound massive and disseminated nickel sulphides were passively fold thickened in hinge areas of isoclinal folds, whereas basal massive sulphides lubricated fold limbs and promoted thrust movement along shallowly dipping lithological contacts. Massive sulphides were physically remobilised up to 20 m from their primary footwall position into deposit-scale fold hinges to form the 1A and Felsic Nose orebodies. First-order controls on the geometry of the Perseverance deposit include the thermomechanical erosion of footwall rocks and the channelling of the mineralised komatiitic magma. Second- or third-order controls are several postvolcanic deformation events, which resulted in the progressive folding and shearing of the footwall contact, as well as the passive fold thickening of massive and disseminated sulphide orebodies. Massive sulphides were physically remobilised into multiple generations of fold hinges and shear zones. Important implications for near-mine exploration in the Leinster camp include identifying nickeliferous komatiite units, defining their three-dimensional geometry, and targeting fold hinge areas. Fold plunge directions and stretching lineations are indicators of potential plunge directions of massive sulphide orebodies.  相似文献