Focusing on soil-foundation heterogeneity through high-resolution electrical and seismic tomography

The reconstruction of the current status of a historic building is essential for seismic safety assessment and for designing the retrofitting interventions since different safety and confidence factors have to be assumed, depending on the level of information about the subsoil structure. In this work, we present an investigation of the shallow subsurface below and around a historic building affected by differential settlements in order to define its geometry and to characterise its stiffness at low strain. To this end, we employed high-resolution electrical resistivity and seismic (both P-wave and S-wave) tomographies. A three-dimensional electrical resistivity tomography survey was performed to obtain more information about the type and the maximum depth of the building foundation. Electrical resistivity and seismic tomographies were carried out alongside the building, aimed at imaging the top soils and the near-surface geometry. The corresponding inverted models pointed out a remarkable heterogeneity of the shallow subsoil below the building, which is partly founded on a weathered layer and partly on a more rigid lithotype. This heterogeneity is probably a concurrent cause of the building's instability under both static and seismic loading. Our results demonstrate that the man-made fillings and the top soils have to be thoroughly investigated to fully understand the soil-structure behaviour. In this light, the integration of non-invasive high-resolution geophysical techniques, especially tomographic methods, has been proved to properly address the problem of imaging the shallow subsoil

Tomographic inversion of time-domain resistivity and chargeability data for the investigation of landfills using a priori information

In this paper, we present a new code for the modelling and inversion of resistivity and chargeability data using a priori information to improve the accuracy of the reconstructed model for landfill. When a priori information is available in the study area, we can insert them by means of inequality constraints on the whole model or on a single layer or assigning weighting factors for enhancing anomalies elongated in the horizontal or vertical directions. However, when we have to face a multilayered scenario with numerous resistive to conductive transitions (the case of controlled landfills), the effective thickness of the layers can be biased. The presented code includes a model-tuning scheme, which is applied after the inversion of field data, where the inversion of the synthetic data is performed based on an initial guess, and the absolute difference between the field and synthetic inverted models is minimized. The reliability of the proposed approach has been supported in two real-world examples; we were able to identify an unauthorized landfill and to reconstruct the geometrical and physical layout of an old waste dump. The combined analysis of the resistivity and chargeability (normalised) models help us to remove ambiguity due to the presence of the waste mass. Nevertheless, the presence of certain layers can remain hidden without using a priori information, as demonstrated by a comparison of the constrained inversion with a standard inversion. The robustness of the above-cited method (using a priori information in combination with model tuning) has been validated with the cross-section from the construction plans, where the reconstructed model is in agreement with the original design

Time-lapse monitoring of an electrokinetic soil remediation process through frequency-domain electrical measurements

The electrokinetic (EK) method is an emerging technique for soil remediation, even though a monitoring system of the contaminant removal through geophysical methods has not been developed yet. In this paper, frequency-domain time-lapse measurements are used on heavy-metal contaminated sediments for monitoring an EK remediation process in a small-scale measuring cell. Our goal is to monitor the development of the electrokinetic process within the sediment and to evaluate the total time needed for the treatment. In fact, frequency-domain electrical monitoring provides complex resistivity spectra at different time steps that can be correlated to changes in the physical properties of the sediments. We perform laboratory spectral induced polarization (SIP) measurements on different samples before, during and after the EK treatment, using different electrolyte solutions (acids and tap water), commonly employed in EK remediation. Direct-current measurements (resistivity and chargeability) were also acquired on one sample for testing the reliability of the system by a comparison with a widespread commercial instrumentation for field measurements. Results indicate that resistivity is a diagnostic parameter as long as it is linked to changes in water saturation, pH and ionic concentration and not to the percentage of metal extraction. The resistivity exhibited well-defined signatures as a function of time that changes depending on the conditioning agent and the grain size distribution. These peculiarities were used to understand the physical processes occurring within the cell and consequently to assess the effectiveness of the electrokinetic treatment. Conversely, the polarization effect was negligible using acids as conditioning agents at the electrolyte chambers. Therefore, the SIP method is not effective under these conditions, being the polarization effect significant only when tap water was used at both ends of the measuring cell. In this case, we were able to correlate changes in water saturation with the time-shift observed on relaxation time distributions (RTDs) after inversion of SIP data and to observe, using normalized chargeability, that polarization is stronger at high pH values. On these basis, resistivity is suitable to monitor the development of the remediation, to optimise the energy levels required for treatment and to assess the end time of the EK process (time when metal mobilization ends). In fact, the end time of treatment can be associated with the time at which resistivity becomes stable. This time is highly dependent on the particular working conditions and sediment grain size as demonstrated by our experiments

A theory of stochastic integration for bond markets

We introduce a theory of stochastic integration with respect to a family of semimartingales depending on a continuous parameter, as a mathematical background to the theory of bond markets. We apply our results to the problem of super-replication and utility maximization from terminal wealth in a bond market. Finally, we compare our approach to those already existing in literature.Comment: Published at http://dx.doi.org/10.1214/105051605000000548 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Focusing on Soil Foundation Heterogeneity through High-resolution Tomography

An historical building affected by differential settlements, which were triggered by an earthquake, is investigated by means of high-resolution tomography, both electrical and seismic. The objective is to image the geometric structure of the shallow soil below the building and to characterize its stiffness at low strain. A preliminary reconstruction of the geological units has been recovered through the combined use of electrical and seismic data, where the depth of the travertine bedrock varies significantly within the study site. The range of variation of the main geophysical parameters (resistivity, P- and S-wave velocities) inferred from these models has been set as reference point for tuning the results obtained from the geophysical survey performed near the building. The inverted tomographic models obtained from data acquired alongside the building exhibit heterogeneity of the shallow subsoil, which is partly founded on a weathered layer and partly on a more rigid lithotype, probably a fractured travertine or a gravel layer. Therefore the fill anthropic soils can play a relevant role for the structural stability in case of shallow foundations built on a heterogeneous subsoil

Hypergeometric Series and Harmonic Number Identities

The classical hypergeometric summation theorems are exploited to derive several striking identities on harmonic numbers including those discovered recently by Paule and Schneider (2003).Comment: 10 page

Hypoellipticity of Anisotropic Partial Differential Equations

2002 Mathematics Subject Classification: 35S05We propose an approach based on methods from microlocal analysis, for characterizing the hypoellipticity in C°° and Gevrey classes of semilinear anisotropic partial differential operators with multiple characteristics, in dimension n > 3

Three-dimensional reconstruction of a masonry building through electrical and seismic tomography validated by biological analyses

In this paper, we present an integrated approach, for assessing the condition of an ancient Roman building, affected by rising damp and cracking phenomena. The combination of high-resolution geophysical methods, such as seismic and electrical tomography, with biological information, allowed a more detailed evaluation of the state of conservation of the masonry building. A preliminary three-dimensional electrical survey was conducted to detect the existing building foundations and to determine the variation of the resistivity in the ground. Then, electrical and seismic tomography investigations were carried out on an inner wall of opus caementicium, subjected to rising damp effects and cracks. This approach was adopted to obtain a high-resolution image of the wall, which allowed to identify the inner mortar and the outer brick component from resistivity and velocity contrasts. Furthermore, the geophysical results revealed evidence of wall fractures (indicated by low velocity and high resistivity values) and a significant volume where rising of damp was taking place (resulting in a low resistivity zone). Biological analyses validated the geophysical model: in fact, the biological proliferation occurred up to a height of 0.75 m, where the interface between high and low resistivity values was recovered. This approach can be employed to reconstruct a three-dimensional model of masonry structures in order to plan recovery actions

AntibIoTic: Protecting IoT Devices Against DDoS Attacks

The 2016 is remembered as the year that showed to the world how dangerous Distributed Denial of Service attacks can be. Gauge of the disruptiveness of DDoS attacks is the number of bots involved: the bigger the botnet, the more powerful the attack. This character, along with the increasing availability of connected and insecure IoT devices, makes DDoS and IoT the perfect pair for the malware industry. In this paper we present the main idea behind AntibIoTic, a palliative solution to prevent DDoS attacks perpetrated through IoT devices

DDoS-Capable IoT Malwares: comparative analysis and Mirai Investigation

The Internet of Things (IoT) revolution has not only carried the astonishing promise to interconnect a whole generation of traditionally “dumb” devices, but also brought to the Internet the menace of billions of badly protected and easily hackable objects. Not surprisingly, this sudden flooding of fresh and insecure devices fueled older threats, such as Distributed Denial of Service (DDoS) attacks. In this paper, we first propose an updated and comprehensive taxonomy of DDoS attacks, together with a number of examples on how this classification maps to real-world attacks. Then, we outline the current situation of DDoS-enabled malwares in IoT networks, highlighting how recent data support our concerns about the growing in popularity of these malwares. Finally, we give a detailed analysis of the general framework and the operating principles of Mirai, the most disruptive DDoS-capable IoT malware seen so far