http://hdl.handle.net/2122/149 2013-05-23T20:09:08Z http://hdl.handle.net/2122/8029 Title: Low pressure experiments in piston cylinder apparatus: calibration of newly designed 25 mm furnace assemblies to P = 150 MPa Authors: Masotta, M.; Sapienza Università Roma; Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Paul, T. A.; Depths of the Earth co; Moore, G.; Arizona State University; Gaeta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Troll, V. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: We present new pressure calibration experiments demons trating that the piston cylinder apparatus is suit-able for experiments at pressure as low as 150 MPa. Two newly designed 25 mm furnace assembly have been developed and calibrated using two differe nt calibration methods: the NaC l melting curve and the sol-ubility of H2 O in albitic and rhyolitic melts. The NaCl calibration experiments performed in the pressure range 150 –500 MPa yield the pressure correction that has to be applied to the nominal pressure in order to have the equivalent (real) pressure on the sample. This correction varies as a function of the experime ntal pressure as follows: Pcorrection MPaðÞ¼ −0 :115xP nominal MPaðÞþ 78 : 23 The H 2O solubility experiments in albitic and rhyolitic melts con firm the corrections determined using the NaCl calibration method. Moreover, because these experiments are performed at temperatures higher than those used for NaCl calibration, they demonstrate that the pressure correction is not affected by temperature in the range 800– 1000 °C. The accuracy of the pressure estimate associated wi th the calibration methods is ± 25 MPa. The major advantage of using the new assemblies is that low pressure experiments, which require rapid heating and quenching rates (e.g. volcanic and hydrothermal systems), can be performed with the same ease and precision as standard high pressure experiments for which piston cylinder is routinel y used. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/3573 Title: On the shape of reflecting surfaces investigated by a 60 MHz radar Authors: Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tabacco, I. E.; Universita` di Milano — Sezione Geofisica, Milan, Italy; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Radio echo sounding (RES) systems for ice thickness measurements are practically the only suitable equipment for large-scale radar flight surveys in polar regions. The length of the radio wave carrier does not allow the employment of sophisticated antennas, so folded dipoles are used, arranged beneath the wings. As a consequence, the transmitted radio wave beam illuminates a relatively large area, making the power of the echo signal related in a significant way to the shape of the reflecting surfaces. An electromagnetic analysis shows that the amplitude variations detected by the system, under certain conditions, are mainly due to focusing or defocusing effects determined by the shape of the reflectors. 2002-12-31T23:00:00Z http://hdl.handle.net/2122/1448 Title: A geoelectrical survey above an Antarctic ice shelf Authors: Merlanti, F.; Dipartimento di Scienze della Terra, Universitá di Genova, Italy; Pavan, M.; Dipartimento di Scienze della Terra, Universitá di Genova, Italy Abstract: A geoelectrical survey was performed on the Hells Gate ice shelf (Victoria Land-Antarctic) within the framework of an integrated geophysical and glaciological research program. The resistivity profiles show a similar trend, with resistivity values ranging from about 25000 W · m to 500000 W · m. These results have been interpreted as the effect of a sharp transition from "marine ice" to "continental" ice an interpretation that is consistent with the results of surface mapping. Interpreting the Vertical Electrical Soundings (VES) is a complex process. In fact, the alternating layers of ice with different compositions and salt content generate great uncertainty relative to the corresponding electric stratigraphies. To solve these problems of equivalency, all the available constraints were used including the drilling thickness, seismic reflection profiles as well as radar profiles. The results were used to provide what is mainly a qualitative overview that is coherent with the glaciological hypotheses relative to the evolution and structure proposed by some researchers for this ice shelf. 1998-07-31T22:00:00Z