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An automatic audio-magnetotelluric equipment, controlled by microprocessor, for the telesurvellance of the volcano Momotombo (Nicaragua) (1984)

Clerc, G. ; Décriaud, J-P. ; Doyen, G. ; [weitere]

Springer

Surveys in geophysics 6 (1984), S. 291-304

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ISSN: 1573-0956

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract A campaign of audio-magnetotelluric soundings in the crater of Momotombo has shown that the structure of this volcano is suitable to a surveillance by this method; it has an only central activity, and the resistivity versus the depth decreases suddenly at least 100 times at about 270 m. So, this technical paper describes the equipment designed and built in order to measure every 2 hr the apparent resistivity in a given direction, at seven frequencies regularly spaced from 5 to 312 Hz. The data are preprocessed to fill only 32 bytes: they are - on the one hand, printed locally for the close surveillance; - on the other hand, transmitted by an ARGOS platform and received in Garchy via satellite for searching studies

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01465544

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Digitale Medien

Dielectric and piezoelectric properties of modified lead titanate zirconate ceramics from 4.2 to 300 K (1983)

Zhang, X. L. ; Chen, Z. X. ; Cross, L. E. ; [weitere]

Springer

Journal of materials science 18 (1983), S. 968-972

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ISSN: 1573-4803

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Notizen: Abstract The dielectric and piezoelectric properties (d-p properties) of four kinds of doped lead titanate zirconate piezoelectric ceramics (PZTs) have been measured from 4.2 to 300 K. The d-p properties of the materials converge with decreasing temperature down to liquid helium temperature, even though the properties have large differences at room temperatue. The values of mechanical and electrical quality factors,Q m,Q e, and of the frequency constant,N, of the materials increased at low temperature. It is evident from the freeze out inK′ and the associate temperature: frequency-dependent maxima in tan 5 that the relaxation processes including ferroelectric domain wall motion and thermal defect motion contribute to the d-p properties. The Navy type-III composition has a minimum temperature coefficient of d-p parameters and it is evident that PZT ceramics modified with Fe2O3 can provide good stability and also give the strongest piezoelectric response at liquid helium temperature.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00551962

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