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1.
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
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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
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Meredith T. Niles Hannah Waterhouse Robert Parkhurst Eileen L. McLellan Sara Kroopf 《Climate Policy》2019,19(7):893-907
The majority of emissions of nitrous oxide – a potent greenhouse gas (GHG) – are from agricultural sources, particularly nitrogen fertilizer applications. A growing focus on these emission sources has led to the development in the United States of GHG offset protocols that could enable payment to farmers for reducing fertilizer use or implementing other nitrogen management strategies. Despite the development of several protocols, the current regional scope is narrow, adoption by farmers is low, and policy implementation of protocols has a significant time lag. Here we utilize existing research and policy structures to propose an ‘umbrella’ approach for nitrogen management GHG emissions protocols that has the potential to streamline the policy implementation and acceptance of such protocols. We suggest that the umbrella protocol could set forth standard definitions common across multiple protocol options, and then modules could be further developed as scientific evidence advances. Modules could be developed for specific crops, regions, and practices. We identify a policy process that could facilitate this development in concert with emerging scientific research and conclude by acknowledging potential benefits and limitations of the approach.
Key policy insights
Agricultural greenhouse gas market options are growing, but are still underutilized
Streamlining protocol development through an umbrella process could enable quicker development of protocols across new crops, regions, and practices
Effective protocol development must not compromise best available science and should follow a rigorous pathway to ensure appropriate implementation
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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
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Seismic tomography shows that upwelling beneath Iceland is confined to the upper mantle 总被引:3,自引:0,他引:3
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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
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