28 research outputs found
Instrumentation of the Säntis Tower in Switzerland for lightning current measurements
No full textLRESCI-STI-FRDES
Measurement of lightning currents using a combination of Rogowski coils and B-Dot sensors
No full textSCI-STI-FRLREDES
Catalysis in the synthesis of hyperbranched polyesters
No full textAn AB2 monomer, dimethyl 5-(2-hydroxyethoxy)isophthalate was prepared on a scale of 3kg. It was successfully polymerised in the melt and the influence of reaction conditions and catalysts was studied. Structural and physical characterisation of these materials was performed using variety of analytical techniques, including SEC and MALDI-TOF MS. The polymerisations yielded high molecular weight materials with a broad polydispersity. All polymers were cyclised, the proportion of cyclised species increased with time, generally until complete cyclisation was achieved. The polymerisation process conditions were varied and a reaction protocol establishing a degree of reproducibility was achieved. Catalysts were found to promote polycondensation, cyclisation and transesterification reactions. The trends of increase in molecular weights were similar to those observed in uncatalysed reactions. Catalysts based on divalent metals showed a higher activity compared to those based on tri- and tetravalent metals. Qualitatively alcoholysis and cyclisation occurred at about the same rate whether catalysed or uncatalysed and ester-ester interchange was significantly slower under all circumstances. There were only relatively small differences between the effects of the catalysts investigated, apart from Vertec 400AC, which caused very fast reaction and yielded an insoluble product of unidentified structure. A new route to the synthesis of an A(_2)B monomer, methyl 3,5-bis(2-hydroxyethoxy)benzoate, was also reported. The monomer was synthesised on a 10g scale and successfully polymerised. The polymer samples were functionalised with acetoxy groups and characterised by SEC and MALDI-TOF MS. Evidences for the presence of polycondensation, cyclisation and ester-ester interchange reactions were observed. Growth in molecular weights and in cyclisation for poly(methyl 3,5-bis(2-hydroxyethoxy)benzoate)s was faster than that for poly(dimethyl 5-(2-hydroxyethoxy)isophthalate)s prepared under same conditions
Interseismic and postseismic shallow creep of the North Qaidam Thrust faults detected with a multitemporal InSAR analysis
No full textUnderstanding the mechanisms by which earthquake cycles produce folding and accommodate shortening is essential to quantify the seismic potential of active faults and integrate aseismic slip within our understanding of the physical mechanisms of the long-term deformation. However, measuring such small deformation signals in mountainous areas is challenging with current space-geodesy techniques, due to the low rates of motion relative to the amplitude of the noise. Here we successfully carry out a multitemporal Interferometric Synthetic Aperture Radar analysis over the North Qaidam fold-thrust system in NE Tibet, where eight Mw> 5.2 earthquakes occurred between 2003 and 2009. We report various cases of aseismic slip uplifting the thickened crust at short wavelengths. We provide a rare example of a steep, shallow, 13-km-long and 6-km-wide afterslip signal that coincides spatially with an anticline and that continues into 2011 in response to a Mw 6.3 event in 2003. We suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an-elastic folding and aseismic slip on the shallow thrusts. We produce a first-order two-dimensional model of the postseismic surface displacements due to the 2003 earthquake and highlight a segmented slip on three fault patches that steepen approaching the surface. This study emphasizes the fundamental role of shallow aseismic slip in the long-term and permanent deformation of thrusts and folds and the potential of Interferometric Synthetic Aperture Radar for detecting and characterizing the spatiotemporal behavior of aseismic slip over large mountainous regions
Measurement of lightning currents using a combination of Rogowski coils and B-Dot sensors
No full textThe paper presents laboratory tests and a characterization of commercial Rogowski coils and a specially designed B-dot sensor for the measurement of lightning currents on the Säntis telecommunications tower in Switzerland. In order to overcome the limited high frequency response of the Rogowski coils, we propose to use magnetic loops located very close to the tower. We introduce the design of a B-dot sensor based on improvements proposed by C. E. Baum, the inductance of which is lowered by extending the vertical dimension of the loop, with the overall effect of extending the operating frequency range. To overcome the integrating behavior of the loop when connected to low-impedance loads (such as 50 Ohm), an arrangement of 100-Ohm-impedance cables connected across conical-transmission-line gaps is used. The designed sensor is characterized by an upper frequency cutoff of 20 MHz and a 50 Ohm matched termination. Laboratory tests carried out in the high voltage laboratory of the EPFL show the effectiveness of the simultaneous use of Rogowski coils and B-dot sensors for the measurement of lightning currents
Critical review of the ECSS-E-ST-20-07C ESD test set-up for testing spacecraft equipment
No full text
