Claudio Chiaruttini

Grade of fine composite mineral particles by dual-energy X-ray radiography

Abstract Standard X-ray radiographs of a composite particle made up by two mineralogical species with different linear attenuation coefficients produce 2D attenuation images that do not allow differentiating between a thin high stopping power and a thick low stopping power-mineralogical inclusion. Dual-energy (DE) imaging—i.e., a pair of radiographs taken at different incident X-ray energy—followed by digital image subtraction allows transforming the log processed energy images into two thickness images. This linear transformation permits the estimation of the particle volumetric content in the two phases and it is fast, as required for the development of an online ‘mineral liberation’ or a ‘washability’ sensor or a ‘valuable-phase-inclusion’ detector. In this paper, micro-CT was used to reconstruct fine particle slices so that the thickness of the two phases could be precisely calculated and compared with that one derived by DE. Preliminary experiments with monochromatic X-ray demonstrated the potential of the DE method to retrieve the particle grade. The tests were conducted with fine composite particles made up of two mineralogical species. Due to the nonhomogeneous composition and density variation within the two mineralogical phases segmented and also to partial volume effects in the tomographic reconstruction of particle slices, each of the two segmented phases have a Gaussian distribution of the linear attenuation coefficient μ (rather that one single value) and values of the σ ( μ ) such that the density distribution right tail of the species with the lower μ overlaps the left tail of the other species giving rise to a bimodal distribution of μ within the particle. This material feature adds further complexity to the problem.

Seismic signal understanding: a knowledge-based recognition system

The authors address the issue of automating routine signal analysis in the seismological domain and propose an approach that combines artificial intelligence and signal processing techniques. Distinctive features of the knowledge involved in the expert activity are investigated and used to design a knowledge-based system to support seismological interpretation. The architecture of the system, which is based on the blackboard scheme, is discussed. The implementation of a prototype (SNA2) is presented, and details are given on its hybrid problem-solving activity. Emphasis is given to the initial, selective inspection of data records, a critical aspect on the interpretive process; accurate parameter estimates are seen as subsequent, straightforward applications of well-known procedures. Several solutions are proposed to modeling the experts focus of attention, simple but effective tools are adopted to extract relevant signal features, and a method is proposed for approximate location of events. Results of the application of the system confirm the effectiveness of the approach. >

Focal mechanism of an earthquake of Baroque age in the “Regno delle Due Sicilie” (Southern Italy)

Abstract A new kinematic function (KF), which incorporates fault dimension, mean variation in velocity of rupture ( ΔV r ), radiation pattern, and mean depth from which the majority of the damaging energy is radiated, is able to model the shape of isoseismals of the 1694 earthquake. The focal mechanism of this earthquake is estimated to be a normal fault of Apenninic direction, dipping 60°–70° towards the NE, with a left-lateral strike-slip component. Due to the similarity with isoseismals of other earthquakes in the southern Apennines it is argued that similar mechanisms could be responsible for other earthquakes in the region.

Focus-of-attention techniques in the automatic interpretation of seismograms

The focus-of-attention techniques implemented in SNA2, a knowledge-based system for seismogram interpretation, are presented. They consist of data compression of the input digital records, scanning of the compressed traces to detect candidate seismograms and extraction of seismogram features. A criterion is given to rate the clarity of seismograms; the clarity defines the order in which the system will consider them to build up the interpretation. The proposed techniques are simple and fast; they allow quick rejection of noise and focussing the attention of the system on the portions of traces containing relevant information.

A stereologically posed mass balance for calculating the distributed efficiency of particle separation systems

Abstract Size and composition specific — i.e., distributed — efficiency of particle separation systems is calculated by exploiting measurements of particle composition in low dimension — i.e., areal grade. A stereologically based framework for the mass balance around the separator was set out and an original regularization criterium was used for its solution. It allows retrieving the distribution of volumetric grade of the streams entering and exiting the separator from the respective areal grade distributions, and makes possible the calculation of the distributed efficiency. Synthetic data are used to demonstrate the method proposed.

Modeling and reasoning techniques in geologic interpretation

A thorough investigation is reported on the qualitative modeling of geologic systems, focusing on the reconstruction of three-dimensional (3-D) profiles from image data by means of spatial and temporal reasoning techniques. A conceptual model of the relevant knowledge is proposed for both the domain elements and the inference processes. At the former level the authors describe the objects in terms of geometric primitives and relations among them; at the inference level, reconstruction is identified as a synthesis task, in which a 3-D model of underground bodies results from assembling simpler components. The process is incremental and nomnonotonic, according to a basic assemble-validate-and-debug cycle, underlying both low-level and high-level steps. A formal (logical) model of the latter is proposed and worked out in detail. Concepts from topology and graph theory provide effective tools to define representations and algorithms, and allow one to address the intertwining of spatial and temporal knowledge. Some relevant reasoning steps are also regarded as constraint satisfaction problems. The authors analyze the constraints, show that the related tasks can be solved with algorithms of polynomial complexity, and provide the appropriate procedures. The practical feasibility of the model has been tested, and results of the applications to realistic input data are discussed. The authors also discuss solutions for embedding the modules into a man-machine interface for the intelligent support to the interpretation of data.

Syntactic filtering and recognition of wide-band noise waveforms

Abstract A syntactic processing technique is presented and applied to the problem of wide-band noise filtering in seismic signals. The signal is scanned by means of three cooperating parsers, constructed on deterministic attribute grammars. Results of filtering real data from seismometric networks equipped with both broad-band and narrow-band sensors are given; the descriptive capabilities, inherent to the syntactic processing, are also shown. Finally, the performances of the filtering algorithm are discussed, and compared to those of a simple stochastic filter.

An assessment of the efficiency of a stereological correction for recovering the volumetric grade of particles from measures on polished sections

An application of the kernel-based inversion method for recovering the volumetric grade distribution of an assembly of particles from computer generated areal grade measures is presented. The application involves: 1. generation of a spatial mineral texture of a mineralized rock sample, Ž . 2. derivation of the volumetric liberation spectrum of the particulate resulting from the simulation of the sample fragmentation, 3. calculation of the inversion kernel based on measures of areal grade made on the intersection of random testing planes with the particles generated, 4. generation of areal measures on a virtual polished section, 5. solving the inversion problem for comparison of the recovered volumetric distribuŽ . tion with the original simulated liberation spectrum. The whole process allows to evaluate the efficiency of the inversion method achieved with an exact kernel and the suitability of the mathematical methods used for the Ž . inversion and their statistical significance; a plain by number of occurrences kernel and

Modelling of ground motion in the vicinity of massive structures

Abstract A two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturctures mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the ‘free-field’ ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings.

A knowledge-based system for geophysical interpretation

The issue of automating the interpretation of data in geophysical exploration by means of artificial intelligence and pattern recognition techniques is addressed. The main features of the knowledge adopted by a domain expert are outlined and used as the basis for the design of a knowledge-based system named Horizons that will support the stratigraphic interpretation of seismic data. The architecture of the system is presented, including generation, validation, consistency-maintenance, and control modules, all designed as cooperating intelligent units. A prototype version of Horizons is presented, and results are briefly discussed.<<ETX>>