Pulsar reflections within the Crab Nebula     

A. G. Lyne  R. S. Pritchard  F. Graham-Smith 《Monthly notices of the Royal Astronomical Society》2001,321(1):67-70

Between 1997 August and October, the radio pulses from the Crab pulsar were followed by discrete moving echoes, which appear to be reflections from part of an ionized shell in the outer part of the Crab Nebula, crossing the line of sight to pulsar. Similar events have now been recognized in recordings from the past 30 yr, and it seems that the Nebula must contain a large number of ionized shell-like surfaces on a much finer scale than recognized hitherto.  相似文献   

Suspended sediment transport along an idealised tidal embayment: settling lag, residual transport and the interpretation of tidal signals     

David Pritchard 《Ocean Dynamics》2005,55(2):124-136

We present semi-analytical solutions for suspended sediment concentration (SSC) and residual sediment transport in a simple mathematical model of a short tidal embayment. These solutions allow us to investigate in some detail the characteristic tidal and semi-tidal variation of SSC and the processes leading to residual sediment transport, including settling and scour lags, the roles of ‘local’ and ‘advective’ contributions, and the presence of internally or externally generated overtides. By interpreting the transport mechanisms in terms of the classic conceptual models of settling lag we clarify how these models may be expressed in mathematical terms. Our results suggest that settling lag is usually a more important process than scour lag, and that a local model which neglects advection may predict the direction of net sediment transport incorrectly. Finally, we discuss our results in the context of other transport processes and morphodynamic feedback.  相似文献   

Nitrogen and carbon dioxide occurrence in UK coal seams     

D. P. Creedy  F. W. Pritchard 《Geotechnical and Geological Engineering》1983,1(1):71-77

Conclusions Some bituminous coals, mostly of high volatile rank, sampled from various coalfields contained on average 0.5 m³ t^–1 nitrogen and 0.13 m³ t^–1.Nitrogen is released more readily than methane during coal winning but the volumes of nitrogen released are small compared with ventilation quantities and are only likely to be of significance for detailed oxygen deficiency studies.  相似文献   

Seismic tomography shows that upwelling beneath Iceland is confined to the upper mantle   总被引：3，自引：0，他引：3  

G. R. Foulger  M. J. Pritchard  B. R. Julian  J. R. Evans  R. M. Allen  G. Nolet  W. J. Morgan  B. H. Bergsson  P. Erlendsson  S. Jakobsdottir  S. Ragnarsson  R. Stefansson  K. Vogfjörd 《Geophysical Journal International》2001,146(2):504-530

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How do long-term patterns affect time-limited environmental monitoring programmes?     

R. S. Lee  T. R. Pritchard 《Marine pollution bulletin》1996,33(7-12):260-268

A five year Environmental Monitoring Programme (EMP) was set up in east-Australian coastal waters to determine the environmental effects of diverting most of Sydney's primary treated sewage from cliff face outfalls to diffuser outfall systems some 3 km offshore in 60–80 m of water. Many component EMP studies adopted Before and After Control Impact (BACI and ‘beyond BACI’) designs, to isolate outfall impacts on the marine ecosystem from background variability. Although seasonal patterns dominated ambient conditions in coastal waters, long-term climatic signals, such as the El Nino Southern Oscillation (ENSO), were apparent during the EMP. The Southern Oscillation Index (SOI) indicated the two year post-commissioning study period of 1991–1993 was dominated by an El Nino episode, while the 1989–1990 pre-commissioning period experienced a La Nina episode. Anomalous rainfall conditions and ocean temperature structure were associated with these episodes with respect to long-term records. Rainfall patterns suggested that the pre-commissioning period experienced high rainfall causing an increased incidence of stormwater pollution in coastal waters. Effects of the lower rain levels during post-commissioning phase were, however, outweighed by the dramatic improvements due to the commissioning of the deepwater outfalls. Decreased thermal stratification was experienced during the winter months of the 1992–1993 El Nino episode, and promoted increased dilutions associated with a greater frequency in sewage plume surfacing. There was, however, no apparent short-term effect of this change in plume behaviour on the marine environment as measured by EMP indicators.  相似文献   

The prevention of oil pollution: edited by J. Wardley-Smith Graham & Trotman,London, 1979, 309pp, £15.00     

S.Z. Pritchard 《Marine Policy》1980,4(1):83-84

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Sea waves near the coasts of South Africa     

Mollie Darbyshire  Eileen Pritchard 《Ocean Dynamics》1966,19(5):218-225

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Cosmological and astrophysical neutrino mass measurements     

K.N. AbazajianE. Calabrese  A. CoorayF. De Bernardis  S. Dodelson  A. FriedlandG.M. Fuller  S. HannestadB.G. Keating  E.V. Linder  C. LunardiniA. Melchiorri  R. Miquel  E. PierpaoliJ. Pritchard  P. SerraM. Takada  Y.Y.Y. Wong 《Astroparticle Physics》2011,35(4):177-184

Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.  相似文献   

HD 9770, a southern active-chromosphere system     

L.C. Watson  J.D. Pritchard  J.B. Hearnshaw  P.M. Kilmartin  A.C. Gilmore 《Monthly notices of the Royal Astronomical Society》2001,325(1):143-150

The visual triple system HD 9770 (BB Scl) has been the subject of a four-year programme of UVB ( RI )_C photometry and H α échelle spectroscopy. Analysis of the data obtained over that period shows that star B, and probably also star A, of HD 9770 is a binary. The A system comprises a K1V star, which may be in a binary system with another K dwarf. The B system is an eclipsing binary of the BY Dra type in which both stars are chromospherically active. An orbital period of 0.476 525±0.000 013 d has been derived from the light curve in V . Physical parameters derived from analysis of the light curves in UBV ( RI )_C are presented.  相似文献   

EROS-II Variable Stars: Eclipsing Binaries in the EROS Microlensing Surveys     

J. Pritchard  J. B. Marquette  Patrick Tisserand  J. P. Beaulieu  E. Lesquoy  A. Milsztajn 《Astrophysics and Space Science》2006,304(1-4):227-229

More than 10 years of microlensing survey observations by the EROS Collaboration have monitored several million stars, amongst them several thousand eclipsing binary stars. In this poster we present some of the difficulties and rewards of the study of this immense database.Based on observations made at ESO by the EROS collaboration  相似文献