Formation and reactions of alkyl adamantanes in sediments: Carbon surface reactions     

Lyndon BerwickRobert Alexander  Kieran Pierce 《Organic Geochemistry》2011,42(7):752-761

Diamondoids are hydrocarbons with a carbon skeleton that is superimposable on the diamond lattice. Adamantane is the cage-shaped primary unit of diamondoids and occurs widely in sediments and petroleum. The first report of adamantane isolated from petroleum extends back seven decades, but the precursors and reaction mechanisms for the formation of adamantane and related diamondoids in sediments has remained unclear. We report the formation of alkyl adamantanes by heating β-ionone with activated carbon in closed system pyrolysis experiments in the range 170-320 °C. In addition, hydrogen exchange, demethylation, methyl transfer and isomerisation reactions were observed when the model compounds adamantane and 1,3-dimethyladamantane were heated at moderate temperature with activated carbon. A reaction pathway for the formation and reactions of alkyl adamantanes is proposed on the basis of ring isomerisation of adamantane to protoadamantane on the activated carbon surface. The carbonaceous surface reactions described help account for the occurrence and distribution of alkyl adamantanes in petroleum basins, as evidenced by the strong linear relationships between compound pairs related by isomerisation and demethylation for a set of crude oils from the Carnarvon Basin, Western Australia.  相似文献   

First results from the Very Small Array – III. The cosmic microwave background power spectrum     

Paul F. Scott  Pedro Carreira  Kieran Cleary  Rod D. Davies  Richard J. Davis  Clive Dickinson  Keith Grainge  Carlos M. Gutiérrez  Michael P. Hobson  Michael E. Jones  Rüdiger Kneissl  Anthony Lasenby  Klaus Maisinger  Guy G. Pooley  Rafael Rebolo  José Alberto Rubiño-Martin †  Pedro J. Sosa Molina  Ben Rusholme ‡  Richard D. E. Saunders  Richard Savage  An&#;e Slosar  Angela C. Taylor  David Titterington  Elizabeth Waldram  Robert A. Watson §  Althea Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,341(4):1076-1083

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Source subtraction for the extended Very Small Array and 33-GHz source count estimates   总被引：1，自引：0，他引：1  

Kieran A. Cleary †  Angela C. Taylor ‡  Elizabeth Waldram  Richard A. Battye  Clive Dickinson §  Rod D. Davies  Richard J. Davis  Ricardo Genova-Santos  Keith Grainge  Michael E. Jones ¶  Rüdiger Kneissl  G. G. Pooley  Rafael Rebolo  José Alberto Rubiño-Martín  Richard D. E. Saunders  Paul F. Scott  An&#;e Slosar &#;  David Titterington  Robert A. Watson 《Monthly notices of the Royal Astronomical Society》2005,360(1):340-353

We describe the source subtraction strategy and observations for the extended Very Small Array (VSA), a cosmic microwave background interferometer operating at 33 GHz. A total of 453 sources were monitored at 33 GHz using a dedicated source subtraction baseline. 131 sources brighter than 20 mJy were directly subtracted from the VSA visibility data. Some characteristics of the subtracted sources, such as spectra and variability, are discussed. The 33-GHz source counts are estimated from a sample selected at 15 GHz. The selection of VSA fields in order to avoid bright sources introduces a bias into the observed counts. This bias is corrected and the resulting source count is estimated to be complete in the flux-density range 20–114 mJy. The 33-GHz source counts are used to calculate a correction to the VSA power spectrum for sources below the subtraction limit.  相似文献   

Cassiopeia A: dust factory revealed via submillimetre polarimetry     

L. Dunne  S. J. Maddox  R. J. Ivison  L. Rudnick  T. A. DeLaney  B. C. Matthews  C. M. Crowe  H. L. Gomez  S. A. Eales  S. Dye 《Monthly notices of the Royal Astronomical Society》2009,394(3):1307-1316

If Type II supernovae – the evolutionary end points of short-lived, massive stars – produce a significant quantity of dust  (>0.1 M_⊙)  then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre (submm) observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type II supernovae. In this paper, we present new data which show that the submm emission from Cas A is polarized at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarized submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarization in this way and so we attribute the excess polarized submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarized and unpolarized dust emission in the north of the remnant where there is no contamination from foreground molecular clouds. The inferred dust polarization fraction is unprecedented  ( f _pol∼ 30 per cent)  which, coupled with the brief time-scale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where   f _pol= 2−7  per cent) or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.  相似文献   

Driving environmental certification: its impact on the furniture and timber products value chain in South Africa     

Mike Morris  Nikki Dunne 《Geoforum》2004,35(2):251-266

In this new globalised era there is an increasing demand in the developed world for environmental certification (Forestry Stewardship Council) of furniture and timber products. The imposition of this requirement has major implications for producers in developing countries. This paper examines this issue from a value chain perspective, exploring how certification requirements are driven through the links of the global furniture value chain. It does so by focusing on the dynamic underlying the spread of FSC certification through the furniture and timber industry in South Africa, and investigates the role of the various organisational ‘drivers’ of the system. In doing so it explores how developing country firms relate to these opportunities and pressures, drawing out the logistical implications, the costs and benefits, as well as the future for FSC certification. It concludes with a discussion of the role of buyers, agents, certification agencies and manufacturers in driving FSC certification through the wood products value chain in South Africa.  相似文献   

The experimental oceanographic satellite Seasat-A     

James A. Dunne 《Boundary-Layer Meteorology》1978,13(1-4):393-404

A Seasat-A Project was conceived and is being implemented to establish the utility of an array of microwave instruments in space for oceanic research and marine technology. The instruments include: a short-pulse radar altimeter, a wind-field scatterometer, an experimental synthetic-aperture imaging radar, a scanning multifrequency microwave radiometer, and a supporting visual and infrared radiometer. All weather, day-night measurements of sea-surface temperature, surface wind speed and direction, sea state and directional wave spectra will be made, the latter over limited areas and times because of operational limitations on the synthetic-aperture-radar instrument. Highly precise (&<0.1 m) range information from the radar altimeter, in combination with an accurate satellite emphemeris, will be used to infer dynamic departures of sea level from the marine geoid produced by tides, currents, and storm surges. Sea ice will be observed by the synthetic-aperture radar, radar altimeter and the scanning multifrequency microwave radiometer, with particular emphasis on demonstrating their capability to determine polar ice coverage, dynamics and navigability.The satellite will be launched into a high-inclination (108 °), non-sun-synchronous, nearly-circular 800 km orbit in May of 1978. The orbit is such that a dense network traced out by the subsatellite point (18.5-km equatorial separation of ascending orbits) will be obtained in 152 days for geodesy. The satellite is designed for a minimum lifetime of one year; with expendables, including orbit adjust capability, for three.All data, except those obtained from the synthetic-aperture radar, will be collected globally, and returned, as measured, first by a 25 kbps data stream, and then after playback at a rate of 800 kbps from the on-board tape recorder. Synthetic-aperture radar data will be returned in real time only, over a 20-MHz analog telemetry link. We expect that satellite data will be distributed through the National Oceanic and Atmospheric Administrations Environmental Data Service. Processed data are expected to be generally available through this agency within a very few months of launch, following preliminary assessment of instrument operation and evaluation of performance.  相似文献   

Geosynthesis of dibenzothiophene and alkyl dibenzothiophenes in crude oils and sediments by carbon catalysis     

Muhammad Asif  Robert Alexander  Tahira Fazeelat  Kieran Pierce 《Organic Geochemistry》2009,40(8):895-901

Sediment extracts and crude oils have been shown to contain methyl substituted biphenyls and dibenzothiophenes, with isomer distributions suggesting a geochemical relationship between the two compound classes. Laboratory simulation experiments have shown that carbon catalyses the reaction between surface adsorbed sulfur and biphenyl to form dibenzothiophene. Similarly, the methyl substituted biphenyls reacted to yield corresponding methyl dibenzothiophenes. We suggest that the widespread distribution of dibenzothiophene and alkylated dibenzothiophenes in sediments and crude oils is the result of a catalytic reaction of biphenyl ring systems and surface-adsorbed sulfur on the surface of carbonaceous material.  相似文献   

The SCUBA Local Universe Galaxy Survey – I. First measurements of the submillimetre luminosity and dust mass functions     

Loretta Dunne  Stephen Eales  Michael Edmunds  Rob Ivison  Paul Alexander  David L. Clements 《Monthly notices of the Royal Astronomical Society》2000,315(1):115-139

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Spitzer Space Telescope Infrared Spectrograph mapping of the central kpc of Centaurus A     

Alice C. Quillen  Joss Bland-Hawthorn  Joel D. Green  J. D. Smith  D. Amelia Prasad  Almudena Alonso-Herrero  Kieran Cleary  Mairi H. Brookes  Charles R. Lawrence 《Monthly notices of the Royal Astronomical Society》2008,384(4):1469-1482

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The SCUBA HAlf Degree Extragalactic Survey (SHADES) – VII. Optical/IR photometry and stellar masses of submillimetre galaxies     

S. Dye  S. A. Eales  I. Aretxaga  S. Serjeant  J. S. Dunlop  T. S. R. Babbedge  S. C. Chapman  M. Cirasuolo  D. L. Clements  K. E. K. Coppin  L. Dunne  E. Egami  D. Farrah  R. J. Ivison  E. van Kampen  A. Pope  R. Priddey  G. H. Rieke  A. M. Schael  D. Scott  C. Simpson  T. Takagi  T. Takata  M. Vaccari 《Monthly notices of the Royal Astronomical Society》2008,386(2):1107-1130

We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the Submillimetre Common-User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ∼320 arcmin². Using photometry spanning the B band to 8 μm, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of spectral energy distribution types, only two out of the 51 sources we have obtained photometric redshifts for are best fitted by a quasar-like spectrum, with approximately 80 per cent of the sources being best fitted with late-type spectra (Sc, Im and starburst). By including photometry at 850 μm, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15–65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright  ( L _*+ 2 < L _optical < L _*− 1 mag)  galaxies in the field over the interval  0 < z < 3  will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around   z ∼ 2  .  相似文献