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  • Barrett's oesophagus  (1)
  • Electrical resistivity tomography  (1)
  • Springer  (2)
  • 2000-2004  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Reliability of dipole-dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes (2000)
    Springer
    Environmental geology 39 (2000), S. 760-766 
    Details
    ISSN: 1432-0495
    Keywords: Key words Karst terranes ; Electrical resistivity tomography ; Sinkholes ; Pinnacles and cutters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Because of the irregular distribution of pinnacles and cutters on the bedrock surface, uncertainties arise when "hit-or-miss" borehole drilling is used to locate potential collapse sites. A high-resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding the drilling program. Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a site in southern Indiana where limestone is covered by about 9 m of clayey soils. Forty-nine transects were conducted over an area of approximately 42,037 m2. The electrode spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were interpreted with the aid of soil borings. The repeatability of ERT was evaluated by comparing the rock surface elevations interpreted from pairs of transects where they crossed each other. The average difference was 2.4 m, with a maximum of 10 m. The discrepancy between interpreted bedrock-surface elevations for a transect intersection may be caused by variations in the subsurface geology normal to the transect. Averaging the elevation data interpreted from different transects improved the ERT results. A bedrock surface map was generated using only the averaged elevation data at the transect junctions. The accuracy of the map was further evaluated using data from four exploratory boreholes. The average difference between interpreted and actual bedrock surface-elevations was less than 0.4 m. The map shows two large troughs in the limestone surface: one coinciding with an existing sinkhole basin, while the other is in alignment with a small topographic valley. Because sinkholes were observed at the same elevation interval in similar valleys in the vicinity, the delineated trough may have implications for future land use at the site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002540050491
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  • 2
    Electronic Resource
    Electronic Resource
    Assessing the conditions forin vivo electrical virtual biopsies in Barrett's oesophagus (2000)
    Springer
    Medical & biological engineering & computing 38 (2000), S. 373-376 
    Details
    ISSN: 1741-0444
    Keywords: Virtual biopsies ; Barrett's oesophagus ; Bio-electrical impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract It has previously been shown that it is possible to differentiate between squamous and columnar epithelia in rat and resected human tissues using an impedance probe to makein vitro measurements. This probe can be passed down an endoscope allowing measurements to be made in patients. However, the probe emerges parallel to the oesophageal wall, with little room to manoeuvre. The conditions of control required to give reliable readings have been investigated. The importance of pressure applied and the angle of approach to the oesophagus was assessed. Pressures in the range 26.6 Pa to 46.3 kPa and angles in the range 15–90 degrees were considered. Inin vitro studies it was observed that it was possible to obtain consistent readings with pressures greater than 2.9 kPa and with angles greater than 15 degrees between the probe and the oesophagus. These conditions can be achievedin vivo, and readings obtained from twelve patients are shown (45 readings on normal squamous, 34 on Barrett's oesophagus and 22 on stomach). At low frequencies (9.6–153.2 kHz), a Mann-Whitney test shows a significant difference (p〈0.001) when comparing the means from squamous and columnar, and also when readings from Barrett's and normal gastric epithelia are compared (p〈0.001).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02345004
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    Paper (German National Licenses)
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