Induction of auroral zone electric currents within the Alaska pipeline     

Wallace H. Campbell 《Pure and Applied Geophysics》1978,116(6):1143-1173

The Alaskar pipeline is a highly conducting anomaly extending 800 miles (1300 km) from about 62° to 69° geomagnetic latitude beneath the most active regions of the ionospheric electrojet current. The spectral behavior of the magnetic field from this current was analyzed using data from standard geomagnetic observatories to establish the predictable patterns of temporal and spatial changes for field pulsation periods between 5 min and 4 hr. Such behavior is presented in a series of tables, graphs and formulae. Using 2- and 3-layer models of the conducting earth, the induced electric fields associated with the geomagnetic changes were established. From the direct relationship of the current to the geomagnetic field variation patterns one can infer counterpart temporal and spatial characteristics of the pipeline current. The relationship of the field amplitudes to geomagnetic activity indices,A _p, and the established occurrence of various levels ofA _p over several solar cycles were employed to show that about half of the time the induced currents in the pipe would be under 1 A for the maximum response oscillatory periods near 1 hr. Such currents should be of minimal consequence in corrosion effects for even a section of the pipeline unprotected by sacrificial electrodes. Of greater interest was the result that the extreme surges of current should reach over one-hundred amperes in the pipeline during high activity.  相似文献   

The loading problem for a linear viscoelastic earth: I. Compressible,non-gravitating models     

Campbell  David L. 《Pure and Applied Geophysics》1974,112(6):997-1010

Summary A Legendre mode solution is given for deformation of a solid isotropic linear viscoelastic sphere under applied surface stresses. Under the simplifying assumptions that the sphere is elastic in compression and standard linear solid in shear two relaxation times appear; one the creep relaxation time of the material, the other depending on mode. It is shown formally how to reduce the case of a layered viscoelastic sphere to an equivalent unlayered one.  相似文献   

Magnetic polarity stratigraphy of the middle Pleistocene (Ensenadan) Tarija Formation of southern Bolivia     

Bruce J. MacFadden  Oscar Siles  Peter Zeitler  Noye M. Johnson  Kenneth E. Campbell 《Quaternary Research》1983,19(2):172-187

The Tarija Formation of southern Bolivia, which is well known for its classic vertebrate faunas, is of prime importance in understanding of the chronology of the Ensenadan Land Mammal Age. This formation consists of well-exposed and relatively fossiliferous sections of clays, clayey silts, sands, gravels, and tuffs which were deposited in a predominately fluviatile regime in a Pleistocene structural basin. Four stratigraphic sections, each measuring 110 m or less, were studied to establish a magnetic polarity stratigraphy. Paleomagnetic samples were collected from the finer-grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less. All paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds (oe). Some specimens were also thermally demagnetized at 200°C or more. Of the 100 sites, 77 were ultimately used to determine the magnetic polarity zonation. Based on the four sections sampled, the Tarija Formation spans a time interval from about 1 my to about 0.7 my B.P. or perhaps younger. The lower half of the composite section is of reversed polarity punctuated by a short normal event. This sequence probably represents the late Matuyama chron with the Jaramillo subchron. The upper part of the section is of normal polarity and represents early Brunhes time. A tuffaceous unit 43 m above the Brunhes-Matuyama boundary yielded a fission track (zircon) age of 0.7 ± 0.2 by B.P. These data indicate that the classic Tarija fauna is middle Pleistocene Ensendan in age.  相似文献   

Geochemical signature of orogenic hydrothermal activity in an active tectonic intersection zone,Alpine Fault,New Zealand   总被引：1，自引：0，他引：1  

J.?R.?Campbell  D.?CrawEmail author  R.?Frew  T.?Horton  C.?P.?Chamberlain 《Mineralium Deposita》2004,39(4):437-451

A highly faulted and fractured rock mass has developed at the intersection of the Alpine and Hope faults, two major active faults in the South Island, New Zealand. The Alpine Fault is an oblique dextral reverse fault at the late Cenozoic-Recent Pacific-Australian plate boundary. The Hope Fault is a strike-slip fault parallel to the plate convergence vector. Hydrothermal fluids driven by the active tectonic processes have passed through the fractured rock mass, causing localised rock alteration and vein formation. Mylonites in the Alpine Fault zone are crosscut by cm-scale veins of quartz and/or ankerite with minor sulphides, with cemented breccias in dilational jogs. Breccia clasts and immediate (cm-scale) host rocks have been variably impregnated with carbonates and quartz. This generation of veins, breccias and altered rocks is post-dated by cataclasite and fault gouge zones which have been cemented by calcite, illite, smectite and chamosite. Ankerite and calcite have ¹⁸O between +10 and +30, and ¹³C between 0 and –8. These minerals are inferred to have formed from water with variable components of both meteoric and crustally exchanged fluid. Rock alteration associated with ankerite–quartz veins has added arsenic (up to 200 ppm As), strontium, and some Y to the rocks. Host-rock mylonites (<2 ppm As) have been depleted in arsenic compared to their precursors (5–15 ppm As). This depletion of arsenic in the middle crust provides the source for arsenic in shallower-level vein systems.Editorial handling: N. White  相似文献   

The impact of small-scale wood harvesting on neem Azadirachta indica A. Juss stands in the coastal savanna of Ghana     

Michael O'Neal Campbell 《Area》2005,37(1):8-16

Although the introduced neem tree Azadirachta indica A. Juss is a very important energy source in the coastal savanna of Ghana, the sustainability of small-scale wood harvesting (SSWH) has not been investigated with regard to this species. This paper assesses the sustainability of SSWH on neem stands in the coastal savanna, using a socio-economic and ecological survey. The results show that SSWH, incorporating coppicing, stand tolerance, balanced with total bole cutting and root removal, and based on socio-cultural supports, has created a modified yet sustainable system of SSWH. It is concluded that these systems may contribute to tree stand conservation.  相似文献   

Actor networking, technological planning and conceptions of space: The dynamics of irrigation farming in the coastal savanna of Ghana   总被引：1，自引：0，他引：1  

Michael O'Neal Campbell   《Applied geography (Sevenoaks, England)》2005,25(4):367-381

The sustainability of introduced technology in rural contexts is based on the socioenvironmental networking of local stakeholders, a point generally ignored in Ghana. A case study is given of an irrigation project from the coastal savanna of Ghana, a region appraised by contested assessments of drought and social conflict. Using a methodology based on a strand of actor network theory (ANT), including social surveys, meteorological and field data, it is concluded that such analyses of spatial linkages, serve as an effective methodology for assessing technological developments and socio-cultural contexts of various scales, and has applied relevance for environmental and development planning.  相似文献   

Gondwana 11: Correlations and Connections - Introduction     

Bryan C. Storey  N. Hiller  N. Mortimer  H.J. Campbell  T.A. Moore 《Gondwana Research》2004,7(1):3-5

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Holocene Alluvial Chronology of One Tree Creek, Southern Alberta, Canada   总被引：1，自引：0，他引：1  

David J.A. Evans  Ian A. Campbell  Donald S. Lemmen 《Geografiska Annaler: Series A, Physical Geography》2004,86(2):117-130

An alluvial chronology for the One Tree Creek basin, a southern tributary of the Red Deer River in southern Alberta, is reconstructed using terrace and palaeochannel remnants and associated radiocarbon dated bones. Prior to the development of One Tree Creek as a northeastward flowing tributary, the prairie surface was scoured by proglacial floodwaters decanting from Glacial Lake Bassano/Patricia in the west. Radiocarbon dates on bones from the bedload gravels in palaeochannels provide a morphochronology of Holocene stream incision. Tentative average incision rates for the middle and upper reaches are calculated at 0.34–0.38 cm a^‐1 since 2.8 ka BP and 0.80 – 1.60 cm and 0.81 – 0.96 cm a^‐1 for the two periods of 1870 to 1230 BP and 1230 BP to modern respectively. Terraces and palaeochannels dating to the period of highest incision (1870 BP to modern) include numerous reworked bones dating to earlier periods, indicating that fluvial downcutting triggered slope instability and terrace reworking. Although the lower bedrock reaches of the creek may have incised down to the present level of the Red Deer River during early postglacial time, the middle and upper reaches were rapidly incised into Quaternary sediments during the late Holocene when climatic conditions were more humid.  相似文献   

Absolute calibration of GPS antennas: laboratory results and comparison with field and robot techniques   总被引：5，自引：2，他引：5  

B. Görres  J. Campbell  M. Becker  M. Siemes 《GPS Solutions》2006,10(2):136-145

A critical assessment of the accuracy of GPS antenna calibration is most effectively done by comparison between different calibration methods. We present new chamber calibrations of five different GPS receiver antenna types in an anechoic chamber and a comparison of an individual antenna calibrated by the absolute field calibration technique with robot mount of IfE/GEO++. The accuracy is described using standard error parameters which allow the characterization of the quality of different antennas. The results validate the absolute calibration methods at the 1-mm level and confirm the presence of significant variations in quality between antennas of different design. For the antenna pattern we directly use the measured phase variations and do not have to fit any functions for the chamber calibrations. We include the results of an earlier test made with a set of identical antennas calibrated at five different institutions: two using the absolute field technique with robot mount and three others applying the standard field calibration with reference antenna.  相似文献   

Comments on “carbon cycling in a shallow turbid estuary of Southeast Texas: The use of plant pigment biomarkers and water quality parameters” by Bianchi, Baskaran, DeLord and Ravichandran,Estuaries 20:404–415     

Michael H. Flinn  Elizabeth Harris  Robert Cady  Christopher S. Johnson  Erla Björk Örnólfsdóttir  Lisa Campbell  Douglas C. Biggs 《Estuaries and Coasts》1998,21(4):837-838

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