3,253 research outputs found

    Waterborne GPR survey for estimating bottom-sediment variability: A survey on the Po River, Turin, Italy

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    We conducted an integrated geophysical survey on a stretch of the river Po in order to check the GPR ability to discriminate the variability of riverbed sediments through an analysis of the bottom reflection amplitudes. We conducted continuous profiles with a 200-MHzGPR system and a handheld broadband EM sensor.Aconductivity meter and a TDR provided punctual measurements of water conductivity, permittivity, and temperature. The processing and interpretation of the GEM-2 and GPR data were enhanced by reciprocal results and by integration with the punctual measurements of the EM properties of the water. We used a processing flow that improved the radargram images and preserved the amplitude ratios among the different profiles and the frequency content at the bottom reflection signal.We derived the water attenuation coefficient both from the punctual measurements using the Maxwell formulas and from the interpretation of the GPR data, finding an optimal matching between the two values. The GPR measurements provided maps of the bathymetry and of the bottom reflection amplitude. The high reflectivity of the riverbed, derived from the GPR interpretation, agreed with the results of the direct sampling campaign that followed the geophysical survey. The variability of the bottom-reflection-amplitudes map, which was not confirmed by the direct sampling, could also have been caused by scattering phenomena due to the riverbed clasts which are dimensionally comparable to the wavelength of the radar pulse

    CED Update on Money & Politics: Party Fundraising in the 2006 Election

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    Just ahead of the 2006 mid-term elections, CED issued a Update on Money & Politics that addresses party fundraising in the 2006 election. Prepared by prominent campaign finance expert Anthony Corrado of Colby College, the brief makes a compelling case that the political parties have remained financially viable by courting small donors. The parties have not been crippled by the "soft money" ban imposed by the Bipartisan Campaign Reform Act of 2002 (BCRA), as many critics of BCRA suggested would happen

    Fracture of solar-grade anisotropic polycrystalline Silicon: A combined phase field–cohesive zone model approach

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    Artículo Open Access en el sitio web del editor. Pago por publicar en abierto. This work presents a novel computational framework to simulate fracture events in brittle anisotropic polycrystalline materials at the microscopical level, with application to solar-grade polycrystalline Silicon. Quasi-static failure is modeled by combining the phase field approach of brittle fracture (for transgranular fracture) with the cohesive zone model for the grain boundaries (for intergranular fracture) through the generalization of the recent FE-based technique published in [M. Paggi, J. Reinoso, Comput. Methods Appl. Mech. Engrg., 31 (2017) 145–172] to deal with anisotropic polycrystalline microstructures. The proposed model, which accounts for any anisotropic constitutive tensor for the grains depending on their preferential orientation, as well as an orientation-dependent fracture toughness, allows to simulate intergranular and transgranular crack growths in an efficient manner, with or without initial defects. One of the advantages of the current variational method is the fact that complex crack patterns in such materials are triggered without any user-intervention, being possible to account for the competition between both dissipative phenomena. In addition, further aspects with regard to the model parameters identification are discussed in reference to solar cells images obtained from transmitted light source. A series of representative numerical simulations is carried out to highlight the interplay between the different types of fracture occurring in solar-grade polycrystalline Silicon, and to assess the role of anisotropy on the crack path and on the apparent tensile strength of the material. Unión Europea FP/2007–2013/ERC 306622 Ministerio de Economía y Competitividad MAT2015–71036-P y MAT2015–71309-P Junta de Andalucía P11-TEP-7093 y P12-TEP- 105

    Long-term behaviour of a dam affected by alkali–silica reaction studied by a multi-scale model

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    This paper aims to employ a 2D thermo-mechanical multi-scale ASR model for the analysis of a concrete gravity dam in Western Switzerland. Simulation results are compared to the field measurements and observations. Analysis of the results reveals negligible effect of temperature variation on the ASR advancement. The difference in length between the upstream and the downstream faces is identified as the main source for the upstream drift at the level of the crest. Study of the structural effects reveals ASR-related expansion anisotropy and cracks alignment being more pronounced along the upstream part and the foundation. If the former is explained by the transmission of the self-weight, the latter is attributed to the constraining effect of the underlying rock

    Wave reflection on dissipative quay walls: an experimental study

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