THE ELECTRICAL CURRENT PATTERN INDUCED BY AN OSCILLATING MAGNETIC DIPOLE IN A SEMI INFINITE CONDUCTIVE THIN PLATE*     

O. KOEFOED  A. P. STRUYK 《Geophysical Prospecting》1969,17(2):182-195

In a paper by Koefoed and Kegge (1968), which was based on previous work of Wesley (1958), the electrical current pattern has been derived that is induced by an oscillating magnetic dipole in a semi-infinite thin plate of infinitesimal resistivity. In the present paper, the range of validity of the assumptions, on which the work of Wesley is based, is subjected to a theoretical analysis. It is found that the decisive factor for the validity of Wesley's derivation is the quotient of the square of the penetration depth of the electrical current over the product of the thickness of the plate and a distance that is indicative of the size of the current loops in the plate. Wesley's derivation is shown to be valid only when this factor is negligible. It is also shown that in this condition the imaginary component of the anomaly must be negligible. Model experiments are described in which the electrical current pattern is studied also in the range in which the derivation of Wesley is not valid. The procedure used in these model experiments was to measure the tangential component of the magnetic field strength very close to the metal plate that simulated the conductive dyke. In order to express the results of the measurements in terms of the imaginary to real ratio, these results are compared with an interpretation graph for field measurements that was published by Hedström and Parasnis (1958). It is found that the current pattern in the plate is essentially the same as that which follows from Wesley's derivation, provided that the imaginary to real ratio is less than one third. The measurements do not permit to draw conclusions regarding the current pattern in the plate in conditions that correspond to larger values of the imaginary to real ratio.  相似文献   

AERIAL SURVEY: COLONY OF HONG KONG     

H. G. Dawe 《The Photogrammetric Record》1969,6(34):335-347

This paper describes the planning and implementation of a very extensive aerial survey contract undertaken by Hunting Surveys on behalf of the Hong Kong Government. From photography carried out during January and February 1963, photogrammetric plotting at 1 : 600 and 1 : 1200 proceeded steadily over a period of 5 years to the point where all but the highest land in the Colony had been surveyed at one or other of these two large scales. The problems arising from the rather unique terrain conditions and the urban and industrial development of Hong Kong are dealt with mainly from the photographic and photogrammetric aspect but reference is made to the contribution of the Crown Lands and Survey Office of the Public Works Department of Hong Kong, who provided all ground control and undertook field verification.  相似文献   

THE LAUSANNE CONGRESS     

G. R. Cooper  G. Petrie  A. D. N. Smith  M. Sowton  K. B. Atkinson 《The Photogrammetric Record》1969,6(33):239-258

The International Society for Photogrammetry held the Xlth International Congress at Lausanne during July 1968. The authors review the activities of five of the seven I.S.P. Commissions.  相似文献   

THOUGHTS ON MAPPING BY PHOTOGRAMMETRY     

V. A. Williams 《The Photogrammetric Record》1968,6(31):18-23

Topics of immediate practical interest formed the basis of the Address. Particular emphasis was placed upon problems of point transfer, pre-marking of ground control points, aerial triangulation by observation of independent models, and the status of photogrammetric operators.  相似文献   

AN OPTICAL METHOD OF MEASURING GRAIN ORIENTATION IN SEDIMENTS     

A. M. WINKELMOLEN  W. VAN DER  KNAAP R. EIJPE 《Sedimentology》1968,11(3-4):183-196

  相似文献   

“SEA-CAMP” FOR TEACHERS AND BEGINNERS     

Roger H. Charlier  Patricia S. Charlier 《The Professional geographer》1968,20(3):209-210

  相似文献   

The Origin of Associated Basic and Acid Rocks in the Lebombo--Nuanetsi Igneous Province, Southern Africa, as implied by Strontium Isotopes     

MANTON  W. I. 《Journal of Petrology》1968,9(1):23-39

Whole rock Rb–Sr measurements were made on associatedbasic and acid intrusives and extrusives from the northern andsouthern ends of the Lebombo monocline with a view to determineif the acid rocks came from the mantle or from the crust. Inthe south, in Swaziland (now called Ngwame) and Zululand, rhyolitesand granophyres (age 202 14 m.y.) have an initial Si⁸⁷–Sr⁸⁶ratio of 0.7042 0.0005; in the north, in the Nuanetsi syncline,rhyolites (age 206 13 m.y.) and granites from ring complexes(age 177 7 m.y.) have initial ratios of 0.7081 0.0008 and0.7085 0.0007, respectively. The initial ratios of the basicrocks, basalts and gabbros, vary in both areas and have a rangefrom 0.7042 to 0.7125 which can be explained by crustal contamination.The low initial ratios and isotopic homogeneity of the acidmagmas over long distances (160 km) in Swaziland and Zululandare interpreted as implying that they were derived from themantle.  相似文献   

Microstructures of High-grade Metamorpbic Rocks at Broken Hill, Australia     

VERNON  R. H. 《Journal of Petrology》1968,9(1):1-22

Frequency distributions of true interfacial angles in high-grade,regional metamorphic rocks from Broken Hill indicate that interfacialtension varies with relative crystallographic orientation incommon minerals. In some single-phase aggregates (e.g. quartz,feldspar, garnet, and calcite) the grains are equant and polygonal,anisotropy of interfacial tension having only a small effecton the appearance of such aggregates. This is also true of two-phaseaggregates of these phases, but their appearance is complicatedby the presence of inclusions, the relative proportions of ihephases, and the characteristic dihedral angle formed by a grainof one phase in contact with two grains of the other. In phases for which interfacial tension is more orientation-dependent,crystal forms exert some control on the appearance of the microstructure.For example, in hornblende and pyroxene aggregates, some interfacesare parallel to planes of the form {110}, although most areirrational. In still more anisotropic phases, low-energy forms(e.g. {001} of biotite and {110} of sillimanite) are very stable,giving rise to a predominance of planar, rational boundariesover curved, adjustment boundaries. Anisotropy of interfacial tension is expressed in the shapesof inclusions. However, even where strongly anisotropic mineralsare involved, inclusions with partly planar boundaries occuralongside inclusions with completely curved boundaries.  相似文献   

MYTHICAL TOPOGRAPHIC FEATURES IN THE EARLY MAPPING OF OTAGO AND SOUTHLAND, 1823-1851     

Murray A. Bathgate 《New Zealand geographer》1968,24(2):206-213

  相似文献   

GEOGRAPHIC ACTIVITIES OF THE DIVISION OF EARTH SCIENCES,NATIONAL RESEARCH COUNCIL     

Walter H. Bailey 《The Professional geographer》1968,20(4):272-275

  相似文献