A large volume magnetic field free space for thermal demagnetization and other experiments in palaeomagnetism     

M. W. McElhinny  G. R. Luck  D. Edwards 《Pure and Applied Geophysics》1971,90(1):126-130

Summary Three orthogonal coil systems have been constructed within a cube of side 2.5 m to cancel the geomagnetic field to less than 1 gamma over a large volume. The north-south and vertical components are cancelled by systems of four square coils whilst a square Helmholtz pair cancels the east-west component. Cancellation to 1 part in 10⁵ (0.5 gamma in Canberra) is achieved within a sphere of diameter 35 cm, more than 20 times the field-free volume which could be obtained using conventional Helmholtz coils within the available space. Three fluxgate detectors monitor the residual field and their output, taken through a feedback circuit, allows compensation for field variations. The residual field can be maintained to less than 0.5 gamma over the working volume of about 22,000 cm³ during the critical part of a laboratory experiment.  相似文献   

Artificial watershed acidification on the Fernow Experimental Forest, USA     

M. B. Adams  P. J. Edwards  F. Wood  J. N. Kochenderfer 《Journal of Hydrology》1993,150(2-4):505-519

A whole-watershed manipulation project was begun on the Fernow Experimental Forest in West Virginia, USA, in 1987, with the objective of increasing understanding of the effects of acidic deposition on forest ecosystems. Two treatment watersheds (WS9 and WS3) and one control watershed (WS4) were included. Treatments were twice-ambient N and S deposition, applied via NH₄SO₄ fertilizer, with three applications per year. Three years of pretreatment data were collected and used for calibration. Stream water chemistry data collected during 3 years of treatment were evaluated. Stream water pH and electrical conductivity were not significantly affected by the elevated N and S inputs on either treatment watershed. On WS9, there were no statistically significant treatment effects on stream water export of Ca, SO₄, or NO₃. On WS3, however, stream export of both NO₃ and Ca have increased as a result of acidification treatments. The implications of these results are discussed. Research is continuing so that the processes involved may be elucidated. In addition, effects on vegetation, aquatic invertebrates and amphibians also are being evaluated.  相似文献   

Conductivity anomalies: lower crust or asthenosphere?     

R.N. Edwards  R.C. Bailey  G.D. Garland 《Physics of the Earth and Planetary Interiors》1981,25(3):263-272

The indication from surface measurements of a zone of relatively high conductivity (resistivity<200 ohm-m) at depths between 20 and 50 km has become so general over the Earth that regions without this zone can be considered anomalous. However, the depths indicated often span the lower crust and the uppermost mantle, so that before any effect can be definitely attributed to one or the other, the depth resolution in the electromagnetic measurements must be carefully considered. This paper applies the eigenvector decomposition of generalized linear inverse theory to soundings by Schlumberger resistivity, by magnetotellurics, by man-made electromagnetic fields formed by controlled current flow in grounded electric transmission lines, and by natural magnetic field variation studies to improve the bounds on depth, thickness and conductivity of a conductive layer. It is shown that many of the methods are capable of giving the depth to the top of a conductor with remarkable accuracy. Joint inversion of two or more of them offers an advantage in the separation of thickness and conductivity of both conductive and resistive layers. Natural geomagnetic field transfer functions, while accurately mapping the position of the edge of a conductor, do not provide the resolution of the other techniques, largely because the frequencies that can be practically measured at present are much too low.  相似文献   

The effect of slime coatings of the serpentine minerals,chrysotile and lizardite,on pentlandite flotation     

C.R. Edwards  W.B. Kipkie  G.E. Agar 《International Journal of Mineral Processing》1980,7(1):33-42

Serpentine minerals in the gangue often interfere with the concentration of nickel sulfide ores. The influence of slime coatings of the serpentine minerals chrysotile and lizardite on the flotation of unoxidized pentlandite has been studied. In addition to microflotation testing at pH 9 with potassium amyl xanthate collector, electrophoresis and scanning electron microscopy have been used. The formation of a slime coating was found to be directly related to the surface charges on the slime and the sulfide mineral. Chemical additives which modified the slime surface charge, such as carboxy methyl cellulose, dextrin, sodium pyrophosphate and sodium silicate, were shown to be effective in reducing the adverse influence of the slime on the flotation of pentlandite.  相似文献   

Toxic Metals in Ground Water of the Front Range, Colorado     

Ronald W. Klusman  Kenneth W. Edwards 《Ground water》1977,15(2):160-169

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Weathering processes in baked sediments and their effects on archaeomagnetic field-intensity measurements     

M.F. Barbetti  M.W. McElhinny  D.J. Edwards  P.W. Schmidt 《Physics of the Earth and Planetary Interiors》1977,13(4):346-354

Thellier-type measurements of ancient field intensity on specimens of clay and other sediments, which were apparently well-baked and oxidised in ancient times, often fail to give consistent results over part or even most of the blocking-temperature spectrum. It is suggested that post-baking chemical alteration, or weathering, leading to the presence of hydrated Fe minerals, is a major cause of non-ideal behaviour in such material. The behaviour of hypothetical specimens containing either goethite or lepidocrocite can be predicted using simple models, and actual examples are given from two sites in southern Australia which show some similarities with the predicted model behaviour. The results of the Thellier measurements, after interpretations, agree closely with previously published results from the northern hemisphere for the period 4700-4200 yr. B.P. The presence of hydrated minerals may not be readily detected by methods other than the Thellier technique and, if so, would result in estimates of the ancient geomagnetic field strength that are systematically too low.  相似文献   

Oceanography and marine biology,annual review: Volume 20. Margaret Barnes (ed.). Aberdeen University Press. 777 pp, 19 plates. Price £45.00. ISBN 0 08 028460 4     

A.J. Edwards  S. Howard 《Marine pollution bulletin》1983,14(8):315-316

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Week-end field meeting: The Upper Eocene—Lower Oligocene beds of the Isle of Wight: 6–8 October 1972     

B. Daley  N. Edwards 《Proceedings of the Geologists' Association. Geologists' Association》1974,85(2):281-292

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Oolitic iron formations in Northern Australia     

A. B. Edwards 《International Journal of Earth Sciences》1959,47(2):668-682

Summary Recent exploration in northern Australia has discovered three shallow water oolitic iron formations, one of Permian age, and two of Upper Proterozoic age. The Permian formation resembles the oxidized oolitic chamositic formations of south-eastern England, but contains more detrital quartz and felspar.The two Precambrian iron formations, consist, below the zone of weathering, of oolites of hematite and of a chamosite-like substance, in a siderite cement, together with well-rounded quartz grains, and are interlayered with sandstones with a chamosite-like cement. Within the zone of weathering the siderite and chamosite are more or less completely replaced by quartz, but with preservation in detail of original textures.Published by permission of the Commonwealth Scientific and Industrial Research Organization (CSIRO).  相似文献   

A late Wisconsin and Holocene vegetation history from the central brooks range: Implications for Alaskan palaeoecology     

Linda B. Brubaker  Harriet L. Garfinkee  Mary E. Edwards 《Quaternary Research》1983,20(2):194-214

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glauca and P. mariana pollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betula zone with increased total pollen influx and very high percentages of Betula pollen, predominantly in the size range of B. nana and B. glandulosa; and (3) and Alnus zone dominated by Alnus pollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Picea pollen in the Alnus zone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamifera pollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glauca pollen reached 10–15%, indicating the arrival of P. glauca in or near the study area. P. glauca populations evidently decreased ca. 8000 yr ago, when Picea pollen percentages and influx fell to low values. About 7000 yr B.P., Alnus pollen percentages and influx rose sharply as alder shrubs became established widely. Picea once more expanded ca. 5000 yr ago, but these populations were dominated by P. mariana rather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situ vegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.  相似文献