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571.
572.
David Hughes 《Marine pollution bulletin》1974,5(3):35-38
Many British estuaries are important wintering areas for large numbers of northern European wildfowl, and some of the biggest concentrations of the birds feed off large sewer outfalls. The Scottish Ornithologists' Club is organizing a survey to locate the major outfalls along the Scottish coast and the large concentrations of wildfowl which may be dependent upon them. Detailed studies are being made of the flocks feeding off the outfalls in the Tay which serve the city of Dundee and the following report summarizes the main findings to date in the Tay. 相似文献
573.
574.
Matthew Colless Gavin Dalton Steve Maddox Will Sutherland Peder Norberg Shaun Cole Joss Bland-Hawthorn Terry Bridges Russell Cannon Chris Collins Warrick Couch Nicholas Cross Kathryn Deeley Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Darren Madgwick John A. Peacock Bruce A. Peterson Ian Price Mark Seaborne Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,328(4):1039-1063
575.
Celestial Mechanics and Dynamical Astronomy - Closed-form expressions are derived for the density of the atmosphere as a function of altitude and exospheric temperature. The numerical model used as... 相似文献
576.
Summary. Magnetic variations at high latitudes represent the combination of magnetic perturbations from several different current systems. The relative effects of each of the contributory current systems vary from event to event, resulting in changes in magnetic perturbation patterns in a given local time sector which are a function of several variables, e.g. level of magnetospheric activity, spectrum of precipitating particles responsible for ionospheric conductivity, configuration of interplanetary magnetic field, etc. In this paper we extend the work of Hughes & Rostoker in which the steady state perturbation pattern in each local time sector was established from ground-based meridian line magnetometer data. We shall define the various current systems which contribute to the high-latitude magnetic perturbation pattern and we shall construct the model composite current system which best explains the high-latitude observations in the winter months. We shall discuss changes in this pattern as a function of season and as a function of the configuration of the interplanetary magnetic field. Finally, we shall relate the geometrical configuration of the ionosphere—magnetosphere current flow to the convection of plasma in the magnetosphere. 相似文献
577.
J. L. Hughes 《Astrophysics and Space Science》1977,46(2):L15-L18
It is now possible to test Dirac's Large Numbers hypothesis in the Earth-Mars system using microwave ranging techniques such as those associated with the Viking lander. The consequences of such a test are discussed. 相似文献
578.
Characterisation of mine waste rock with respect to acid generation potential is a necessary part of routine mine operations,
so that environmentally benign waste rock stacks can be constructed for permanent storage. Standard static characterisation
techniques, such as acid neutralisation capacity (ANC), maximum potential acidity, and associated acid–base accounting, require
laboratory tests that can be difficult to obtain rapidly at remote mine sites. We show that a combination of paste pH and
a simple portable carbonate dissolution test, both techniques that can be done in the field in a 15 min time-frame, is useful
for distinguishing rocks that are potentially acid-forming from those that are acid-neutralising. Use of these techniques
could allow characterisation of mine wastes at the metre scale during mine excavation operations. Our application of these
techniques to pyrite-bearing (total S = 1–4 wt%) but variably calcareous coal mine overburden shows that there is a strong
correlation between the portable carbonate dissolution technique and laboratory-determined ANC measurements (range of 0–10 wt%
calcite equivalent). Paste pH measurements on the same rocks are bimodal, with high-sulphur, low-calcite rocks yielding pH
near 3 after 10 min, whereas high-ANC rocks yield paste pH of 7–8. In our coal mine example, the field tests were most effective
when used in conjunction with stratigraphy. However, the same field tests have potential for routine use in any mine in which
distinction of acid-generating rocks from acid-neutralising rocks is required. Calibration of field-based acid–base accounting
characteristics of the rocks with laboratory-based static and/or kinetic tests is still necessary. 相似文献
579.
Recent experiments in macrophyte dominated communities on the relationship between biological diversity and ecosystem functioning
suggest that effects and mechanisms of genetic-genotypic and species diversity are analogous. As previously shown for species
diversity, genotypic diversity enhances ecosystem productivity and recovery from disturbance. These findings generalize ecological
theory, and provide an empirical basis for explicitly considering the maintenance of genetic or genotypic diversity for conservation
strategies. Macrophyte systems such as seagrasses or salt-marshes may be excellent systems to test the interaction between
diversity across several (genetic versus species) levels of biological organization because they are relatively species poor
while simultaneously allowing the manipulation of genotypic diversity by taking advantage of clonal propagation in many species. 相似文献
580.
This study documents two different modes of berm development: (1) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode 1 sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth. 相似文献