49 research outputs found
Extended bodies with quadrupole moment interacting with gravitational monopoles: reciprocity relations
An exact solution of Einstein's equations representing the static
gravitational field of a quasi-spherical source endowed with both mass and mass
quadrupole moment is considered. It belongs to the Weyl class of solutions and
reduces to the Schwarzschild solution when the quadrupole moment vanishes. The
geometric properties of timelike circular orbits (including geodesics) in this
spacetime are investigated. Moreover, a comparison between geodesic motion in
the spacetime of a quasi-spherical source and non-geodesic motion of an
extended body also endowed with both mass and mass quadrupole moment as
described by Dixon's model in the gravitational field of a Schwarzschild black
hole is discussed. Certain "reciprocity relations" between the source and the
particle parameters are obtained, providing a further argument in favor of the
acceptability of Dixon's model for extended bodies in general relativity.Comment: 14 pages, Latex svjour2.cls article class, 7 eps figure files. To
appear on General Relativity and Gravitation, 200
A note on stress-driven anisotropic diffusion and its role in active deformable media
We propose a new model to describe diffusion processes within active
deformable media. Our general theoretical framework is based on physical and
mathematical considerations, and it suggests to use diffusion tensors directly
coupled to mechanical stress. A proof-of-concept experiment and the proposed
generalised reaction-diffusion-mechanics model reveal that initially isotropic
and homogeneous diffusion tensors turn into inhomogeneous and anisotropic
quantities due to the intrinsic structure of the nonlinear coupling. We study
the physical properties leading to these effects, and investigate mathematical
conditions for its occurrence. Together, the experiment, the model, and the
numerical results obtained using a mixed-primal finite element method, clearly
support relevant consequences of stress-assisted diffusion into anisotropy
patterns, drifting, and conduction velocity of the resulting excitation waves.
Our findings also indicate the applicability of this novel approach in the
description of mechano-electrical feedback in actively deforming bio-materials
such as the heart
Role of temperature on nonlinear cardiac dynamics.
Thermal effects affecting spatiotemporal behavior of cardiac tissue are discussed by relating temperature variations to proarrhythmic dynamics in the heart. By introducing a thermoelectric coupling in a minimal model of cardiac tissue, we are able to reproduce experimentally measured dynamics obtained simultaneously from epicardial and endocardial canine right ventricles at different temperatures. A quantitative description of emergent proarrhythmic properties of restitution, conduction velocity, and alternans regimes as a function of temperature is presented. Complex discordant alternans patterns that enhance tissue dispersion consisting of one wave front and three wave backs are described in both simulations and experiments. Possible implications for model generalization are finally discussed
NLP-based Metadata Extraction for Legal Text Consolidation
The paper describes a system for the automatic consolidation of Italian legislative texts to be used as a support of an editorial consolidating activity and dealing with the following typology of textual amendments: repeal, substitution and integration. The focus of the paper is on the semantic analysis of the textual amendment provisions and the formalized representation of the amendments in terms of metadata. The proposed approach to consolidation is metadata- oriented and based on Natural Language Processing (NLP) techniques: we use XML-based standards for metadata annotation of legislative acts and a flexible NLP architecture for extracting metadata from parsed texts. An evaluation of achieved results is also provided