242 research outputs found
Finite element modeling of ground deformation and gravity field at Mt. Etna
An elastic 3-D axi-symmetric model based on Finite Element Method (FEM) is proposed to compute ground deformation
and gravity changes caused by overpressure sources in volcanic areas. The numerical computations
are focused on the modeling of a complex description of Mt Etna in order to evaluate the effect of topography,
medium heterogeneities and source geometries. Both ground deformation and gravity changes are investigated
by solving a coupled numerical problem considering a simplified ground surface profile and a multi-layered
crustal structure inferred from seismic tomography. The role of the source geometry is also explored taking into
account spherical and ellipsoidal volumetric sources. The comparison between numerical results and those
predicted by analytical solutions disclosed significant discrepancies. These differences constrain the applicability
of simple spherical source and homogeneous half-space hypotheses, which are usually implicitly assumed
when analytical solutions are applied
An Improved Solver for the M/EEG Forward Problem
Noninvasive investigation of the brain activity via
electroencephalography (EEG) and magnetoencephalography
(MEG) involves a typical inverse problem whose solution process
requires an accurate and fast forward solver. We propose the
Method of Fundamental Solutions (MFS) as a truly meshfree
alternative to the Boundary Element Method (BEM) for solving
the M/EEG forward problem. The solution of the forward
problem is obtained, via the Method of Particular Solutions
(MPS), by numerically solving a set of coupled boundary value
problems for the 3D Laplace equation. Numerical accuracy and
computational load are investigated for spherical geometries and
comparisons with a state-of-the-art BEM solver shows that the
proposed method is competitive
IL METODO DELLE SOLUZIONI FONDAMENTALI PER LA SOLUZIONE DEL PROBLEMA DIRETTO M/EEG
The research already started on the mesh-free solution of the M / EEG direct problem has led to the development of a solver based on the method of fundamental solutions (MFS, method of fundamental solutions) able to manage the physical-geometric complexity of realistic models of the head more efficiently than traditional
Integrated inversion of ground deformation and magnetic data at Etna volcano using a genetic algorithm technique
Geodetic and magnetic investigations have been playing an increasingly important role in studies on Mt. Etna
eruptive processes. During ascent, magma interacts with surrounding rocks and fluids, and inevitably crustal deformation
and disturbances in the local magnetic field are produced. These effects are generally interpreted separately
from each other and consistency of interpretations obtained from different methods is qualitatively
checked only a posteriori. In order to make the estimation of source parameters more robust we propose an integrated
inversion from deformation and magnetic data that leads to the best possible understanding of the underlying
geophysical process. The inversion problem was formulated following a global optimization approach based
on the use of genetic algorithms. The proposed modeling inversion technique was applied on field data sets
recorded during the onset of the 2002-2003 Etna flank eruption. The deformation pattern and the magnetic anomalies
were consistent with a piezomagnetic effect caused by a dyke intrusion propagating along the NE direction
The HOTSAT volcano monitoring system based on combined use of SEVIRI and MODIS multispectral data
Spaceborne remote sensing of high-temperature volcanic features offers an
excellent opportunity to monitor the onset and development of new eruptive activity. To provide a basis for real-time response during eruptive events, we designed and developed the volcano monitoring system that we call HOTSAT. This multiplatform system can elaborate both Moderate Resolution Imaging Spectroradiometer (MODIS) and Spinning Enhanced Visible and Infrared Imager (SEVIRI) data, and it is here applied to the monitoring of the Etna volcano. The main advantage of this approach is that the different features of both of these sensors can be used. It can be refreshed every 15 min due to the high frequency of the SEVIRI acquisition, and it can detect smaller and/or less intense thermal anomalies through the MODIS data. The system consists of data preprocessing, detection of volcano hotspots, and radiative power estimation. To locate thermal anomalies, a new contextual algorithm is introduced that takes advantage of both the spectral and spatial comparison methods. The derivation of the radiative power is carried out at all ‘hot’ pixels using the middle infrared radiance technique. The whole processing chain was tested during the 2008 Etna eruption. The results show the robustness of the system after it detected the lava fountain that occurred on May 10 through the SEVIRI data, and the very beginning of the eruption on May 13 through the MODIS data analysis
STIMA DEL POTENZIALE ELETTRICO IN tDCS CON APPROCCIO MESHLESS INNOVATIVO
Transcranial DC stimulation (transcranial Direct Current Stimulation,
tDCS) is a non-invasive technique aimed at modifying neuronal activity for the purpose
therapeutic and / or for the improvement of mental performance. A continuous current of entity
modest (below the threshold of perception) is injected into the brain via electrodes placed on the
scalp surface to produce changes in long-term cortical activity.
Despite the increasing use of this and other similar techniques, and the relevant ones
applications - for example in the field of neuropsychological rehabilitation - their impact
on neuronal activity is not yet fully known, mainly due to the difficulty of
predict the spatial distribution of the current within the brain, and to determine the
optimal position and size of the electrodes
Inverse modeling in geophysical applications
The interpretation of the potential ¯eld data is an useful tool that allows for
both investigating the subsurface structures and providing a quantitative evalu-
ation of the geophysical process preceding and accompanying period of volcanic
unrest. Potential ¯eld inversion problem are required to combine forward mod-
els with appropriate optimization algorithms and automatically ¯nd the best
set of parameters that well matches the available observations. Indeed, investi-
gations on the mathematical equations to be inverted, have revealed that these
models are ill-posed and highly non-linear. Numerical methods for modeling
potential ¯eld observations are proposed and applied on real dataset
ADVANCED BIO-ELECTROMAGNETIC NUMERICAL MODELLING AND ICT FOR HUMAN BRAIN RESEARCH
Functional imaging is used in the research area
neurological, neurophysiology and cognitive psychology, for the diagnosis of diseases
metabolic and for the detection of thin / squamous lesions (eg Alzheimer's disease) and for
the development of neural interfaces (brain-computer interfaces - BCI)
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