Scale Model Studies of a Transient Electromagnetic Prospecting System Using an Interactive Minicomputer
Scale models have been used for over thirty years in studying the electrical and electromagnetic techniques of geophysical prospecting, and are particularly useful when mathematical or numerical methods are unreasonably difficult. A model study facility has been set up at Macquarie University, Sydney, Australia, to study the transient electromagnetic method of geophysical prospecting. The basic unit in the facility consists of a 35Kword INTERDATA minicomputer which controls the timing and waveform of the transmitted pulse as well as subsequent data collection and processing. A wide-band amplifiler provides an interface between the computer and the small multiturn loops used for model studies. Input and output data are fed via the computer to a teletypewriter. The use of an interactive technique between the computer and operator enables optimum timing and amplifier settings to be easily determined for each model. A model of a uniformly conductive half-space was used to validate the experimental arrangement, and excellent agreement was found between theoretical and model results. A model study of an orebody enabled estimates of bulk conductivity to be made.
THE DERIVATION OF ABSOLUTE UNITS IN ELECTROMAGNETIC SCALE MODELING
Scaled model studies often are used to determine the structure of secondary magnetic fields when the numerical approach is unreasonably difficult. For most purposes, it is sufficient to model the geometric configurations or relative components of the magnetic field and, neglecting displacement currents, the general modeling relation σμfL2=constant is valid. However, in some applications such as transient electromagnetic (TEM) modeling, it is necessary to determine the power level of the full‐scale system. An expression relating the voltage levels of the model and the full‐scale situation is derived as Vm/V=LmT/LTm,where the subscript m represents the model system. This expression must be used in order to compensate for changes in the modeling parameters.
At the end of the rope: Geophilus hadesi sp. n. – the world’s deepest cave-dwelling centipede (Chilopoda, Geophilomorpha, Geophilidae)
Abstract A new geophilomorph centipede, Geophilus hadesi sp. n., is described from caves in the Velebit Mountain, central Croatia. Together with Geophilus persephones Foddai & Minelli, 1999, described from Pierre Saint-Martin cave in France, they are the only two remarkably troglomorphic geophilomorphs hitherto known. The new species apparently belongs to a group of Geophilus species inhabiting mainly Western and Southern Europe, with a uniquely modified pretarsus in the second maxillae. Geophilus hadesi sp. n. shows unusual traits, some of which commonly found in troglobitic arthropods, including exceptionally elongated antennae, trunk segments and leg claws. The species is described upon specimens found in two caves at a depth below -250 m. Another two specimens apparently belonging to the same species have been recorded in another deep vertical cave at -980 m and -1100 m. The latter represents the world’s deepest record of Chilopoda as a whole.