155,286 research outputs found
3D-electrical resistivity tomography monitoring of salt transport in homogeneous and layered soil samples
No full textMonitoring transport of dissolved substances in soil deposits is particularly relevant where safety is concerned, as in the case of geo-environmental barriers. Geophysical methods are very appealing, since they cover a wide domain, localising possible preferential flow paths and providing reliable links between geophysical quantities and hydrological variables. This paper describes a 3D laboratory application of Electrical Resistivity Tomography (ERT) used to monitor solute transport processes. Dissolution and transport tests on both homogeneous and heterogeneous samples were conducted in an instrumented oedometer cell. ERT was used to create maps of electrical conductivity of the monitored domain at different time intervals and to estimate concentration variations within the interstitial fluid. Comparisons with finite element simulations of the transport processes were performed to check the consistency of the results. Tests confirmed that the technique can monitor salt transport, infer the hydro-chemical behaviour of heterogeneous geomaterials and evaluate the performances of clay barrier
Phase separation in the 2D Hubbard model: a fixed-node quantum Monte Carlo study
No full textFixed-node Green's-function Monte Carlo calculations have been performed for very large 16x16 two-dimensional Hubbard lattices, large interaction strengths U=10,20, and 40, and many (15 similar to 20) densities between empty and half-filling. The nodes were fixed by a simple Slater-Gutzwiller trial wave function. For each value of U we obtained a sequence of ground-state energies which is consistent with the possibility of a phase separation close to half-filling, with a hole density in the hole-rich phase which is a decreasing function of U. The energies suffer, however, from a fixed-node bias: more accurate nodes are needed to confirm this picture. Our extensive numerical results and their test against size, shell, shape, and boundary-condition effects also suggest that phase separation is quite a delicate issue, on which simulations based on smaller lattices than considered here are unlikely to give reliable predictions. RI Capone, Massimo/A-7762-2008; Guidoni, Leonardo/G-3759-201
Evolving fabric and its impact on the shearing behaviour of a compacted clayey silt exposed to drying-wetting cycles
No full textThe fabric and the hydro-mechanical behaviour of compacted clayey silt samples were investigated before and after drying-wetting cycles. Drying-wetting cycles changed the soil fabric by increasing the macro-porosity, while the total void ratio remained almost constant. The cycled samples were more compressible than the original ones and experienced a smaller decrease of suction during shearing at constant water content. The higher compressibility is associated to a more evident reduction of macroporosity.
The smaller suction decrease is reproduced with a double structure water retention model accounting for changes in macro-porosity during shearing. Cycled samples mobilised higher strength and showed a higher dilatancy than original samples sheared at the same initial total stress and suction; furthermore, dilatancy increased with suction for both fabrics. The Li and Dafalias stress-dilatancy relationship, formulated in terms of a macro-structural Bishop stress and accounting for a suction dependency, allowed reproducing the experimental results accurately
Phase separation in the 2D Hubbard model: a fixed-node quantum Monte Carlo study
No full textFixed-node Green's-function Monte Carlo calculations have been performed for very large 16x16 two-dimensional Hubbard lattices, large interaction strengths U=10,20, and 40, and many (15 similar to 20) densities between empty and half-filling. The nodes were fixed by a simple Slater-Gutzwiller trial wave function. For each value of U we obtained a sequence of ground-state energies which is consistent with the possibility of a phase separation close to half-filling, with a hole density in the hole-rich phase which is a decreasing function of U. The energies suffer, however, from a fixed-node bias: more accurate nodes are needed to confirm this picture. Our extensive numerical results and their test against size, shell, shape, and boundary-condition effects also suggest that phase separation is quite a delicate issue, on which simulations based on smaller lattices than considered here are unlikely to give reliable predictions
Phase separation in the 2D Hubbard model: a challenging application of fixed-node QMC
No full textNATO-ASI serie
Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography
No full textIn situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi
Geodetic monitoring and geotechnical analyses of subsidence induced settlements of historic structures
No full textThis paper focuses on the integration of geodetic monitoring and geotechnical modeling for the analyses of subsidence induced settlements in historic structures. The aim is the assessment of the behavior over time of the monuments, with particular attention to differential settlements, in order to evaluate the potential risk scenarios in a preventive strategy. The methodology is applied to the UNESCO site of Modena where the Cathedral and the Ghirlandina Tower are characterized by strong visible deformations due to a complex construction history, the peculiar subsoil conditions and the effects of both natural and man induced subsidence. A 3D finite element numerical model has been developed taking into account the soil characteristics gained by laboratory and in situ tests. The model takes into account the influence of previously existing structures, as well as the subsidence phenomena and provides a settlements profile in agreement with the real dataset collected by high-precision leveling. The geodetic monitoring, carried out since 1984, allows to optimize and then to validate the numerical model giving the Conservation Authority a useful tool to manage the safety of the heritage
Progressive deficiencies in blood T cells associated with a 10p12-13 interstitial deletion
No full textWe report on a 8-year-old patient affected by a selective T-cell defect associated with mental retardation and dysmorphic signs. At birth thymic aplasia and hypoparathyroidism were noted, suggesting a DiGeorge-like anomaly. The immunological evaluation during the 8 years follow-up revealed a progressive decrease of CD3+CD4+ lymphocytes, which paralleled deficiencies of blood T cells. Chromosome analysis using GTL banding revealed an interstitial deletion of the short arm of chromosome 10. We next investigated whether the expression of IL-2R alpha chain and Nil-2-a genes, which are located on the short arm of chromosome 10, was affected by the deletion. Transcription of these two genes was normal, thus suggesting that the two regions were preserved. In situ hybridization studies with the painting libraries #G3A7 and #G9 confirmed that the two regions were preserved and allowed us to define the breakpoint as 10p12-10p13. Due to the similarities between DiGeorge and 10p syndromes, we suggest that the 10p13-10p12 region contains a gene(s) potentially related to gene products of the 22q11 region, frequently altered in patients with DiGeorge
Colonisation in Stable Patients with COPD: Results of an Italian Epidemiological Study (Prime Study)
No full textProgressive deficiencies in blood T cells associated with a 10p12-13 interstitial deletion
No full textWe report on a 8-year-old patient affected by a selective T-cell defect associated with mental retardation and dysmorphic signs. At birth thymic aplasia and hypoparathyroidism were noted, suggesting a DiGeorge-like anomaly. The immunological evaluation during the 8 years follow-up revealed a progressive decrease of CD3+CD4+ lymphocytes, which paralleled deficiencies of blood T cells. Chromosome analysis using GTL banding revealed an interstitial deletion of the short arm of chromosome 10. We next investigated whether the expression of IL-2R alpha chain and Nil-2-a genes, which are located on the short arm of chromosome 10, was affected by the deletion. Transcription of these two genes was normal, thus suggesting that the two regions were preserved. In situ hybridization studies with the painting libraries #G3A7 and #G9 confirmed that the two regions were preserved and allowed us to define the breakpoint as 10p12-10p13. Due to the similarities between DiGeorge and 10p syndromes, we suggest that the 10p13-10p12 region contains a gene(s) potentially related to gene products of the 22q11 region, frequently altered in patients with DiGeorg
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