1,721,048 research outputs found
Tensorial piezomagnetic coefficients for single-domain titanomagnetite crystals at saturation magnetization
No full textThe piezomagnetic and magnetostrictive behaviour of titanomagnetite single-domain crystals is described in a general tensorial formalism with respect to a reference initial configuration in which crystals possess a saturation remanence magnetization and are subjected to a prestress field. The equivalence between the present linearized theory and previous semi-empirical formulae is proved. Numerical values are given for the piezomagnetic coefficients in terms of the magnetostrictive constants Δ100 and Δ111 which have been experimentally determined for titanomagnetite single crystals
A thermomagnetoelastic model of the earthquake source mechanism
No full textAn explicit expression is derived for the body force, magnetic moment and heat source to be applied in the absence of a dislocation to produce a radiation pattern identical to that of a dislocation. These quantities depend only on the fault mechanism and the material properties of the medium in the immediate vicinity of the fault. The theory is developed for dislocations in an anisotropic inhomogeneous thermo-elastic medium that exhibits pyromagnetic and piezomagnetic properties. The magnetic moment equivalent, that completely describes the magnetical effects of the dislocation, is found to be dependent on the discontinuities of the disllacement prescribed across the fault, through the piezomagnetic coefficients. Discontinuities in the thermal field and its derivatives do not contribute to the magnetic moment equivalent, thus leading to the conclusion that pyromagnetism cannot produce magnetic effects
Some effects of elastic pre-stress within the Earth
No full textA dynamical theory, regarding the superposition of small deformations upon large ones, is applied to the study of the prestress effects in an isotropic medium. The primary configuration is in a dynamic state and no assumption is made regarding the smallness of time derivatives of the displacement field. In this framework, a reciprocity theorem is derived and the representation theorem for the displacement field is obtained in terms of the Green's function. Body force equivalents are derived in terms of the discontinuity of the displacement across the fault surface. The ray theory is briefly reviewed and applied to the study of seismic-wave propagation in homogeneous isotropic media. The prestressed configuration in proximity of the fault surface is treated as a perturbation on seismic waves and its effects are found to be of first order in the perturbation at the origin. The wave front equation and the nodal-surface equation for compressional waves are derived and both are found to suffer significant changes due to the perturbation
The hot topic of Thermo-Poro-Elastic deformation sources in volcanic and geothermal fields
No full textStress redistribution following unwelding of near-surface layers in strike-slip fault zones
No full textMajor strike-slip earthquakes are often associated with a complex pattern of surface fractures, organized in hierarchic order (en-echelon shear fracture arrays, open tensile fractures and hillocks), which are oriented differently from the strike of the main fault and often extend laterally 1 or 2 km. In the attempt to understand why
the main fault remains conned at depth, we have considered the possibility that, during the earthquake, a soft shallow sedimentary layer unwelds from the lower basement rock along a horizontal interface. The stress redistribution provided by the unwelding process in the shallow layer is studied in terms of a dislocation model employing the boundary-element method. We show that a nearly uniform Coulomb failure function develops above the main fault, over a km-wide strip along the fault strike (explaining shear fracture arrays) and positive tensile stresses appear near the surface over a similarly wide strip (explaining open fractures). A parametric study is performed to show when the unwelding process can take place and how the resulting stress redistribution in the shallow layer depends on the depth of the unwelded layer and on the coefficient of friction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Global post-seismic deformation
No full textWe quantify the effects of post-seismic deformation on the radial and horizontal components of the displacement, in the near- and far-field of strike- and dip-slip point dislocations; these sources are embedded in the elastic top layer of a spherical, self-gravitating, stratified viscoelastic earth. Within the scheme of the normal mode technique, we derive the explicit analytical expression of the fundamental matrix for the toroidal component of the field equations; this component is propagated, together with its spheroidal counterpart, from the core-mantle boundary to the earth's surface. Viscosity stratification at 670km depth influences the radial and horizontal deformation accompanying viscoelastic relaxation in the mantle over time-scales of 103-104 yr, both in the near-field, ranging from 100 to 500 km and in the far-field, from 103 to 5 X 103 km. If the upper mantle is differentiated into a low-viscosity zone beneath the lithosphere and a normal upper mantle, faster relaxation is obtained. For an asthenospheric viscosity of 1020 Pa s we obtain, for a strike-slip dislocation and a seismic moment of 1022 N m characteristic of an average large earthquake, horizontal rates of 1-4 mm yr-1 in the near-field and 0.05-0.4 mm yr-1 in the far-field; these values are maintained over time-scales of 10-103 yr. Larger rates, with shorter duration, are obtained if the viscosity is reduced in the low-viscosity channel. As expected, strike-slip dislocations are the most effective in driving horizontal deformation in the far-field in comparison with dip-slip ones. It is noteworthy that horizontal velocities are maintained longer in the far-field in comparison with radial ones, which is not surprising since momentum is propagated in far regions essentially in the horizontal direction; radial deformation is generally lower in the far-field. VLBI techniques, with a precision of a few parts per billion over distances of 103 km, can detect global post-seismic deformation induced by large earthquakes. Our results affect the interpretation of the transfer of stress and seismic activity among different plate boundaries
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