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Effective reference and current integration for large displacement interface
Full text linkThe most common interface formulations proposed in literature are generally based on the restrictive
hypothesis of small strains and small displacements and, even though their application to
geometrically nonlinear problems is of paramount interest, only few contributions are available in literature.
Motivations are probably due to the difficulties encountered on such formulation, as already
mentioned by several authors.
A pioneering formulation is the finite displacement three-dimensional interface developed by Ortiz
and Pandolfi in [1], where normal and tangential traction components are evaluated with respect
to the middle surface in the current configuration, producing a non-symmetric geometric stiffness
matrix.
More recently, an interface element formulation for geometrical non-linearity and material nonlinearity,
which is developed in the reference configuration, has been proposed by Reinoso and
Paggi in [2]. The constitutive model is formulated on the local reference, defined by normal axis
and tangential axis with respect to the middle surface in the current configuration. The interface
formulation generates a non symmetric geometric stiffness matrix, which is simplified by neglecting
the non symmetric contribution, in order to reduces computational cost by the use of symmetric
solver.
The state of the art of cohesive models for the material separation is presented by Mosler and
Scheider in [3], focusing the attention on the thermodynamics and variational consistency. In [3]
the authors state that many proposed models do not verify fundamental requirements such as thermodynamic
principles, frame invariance, equilibrium conditions. Such problems are magnified for
anisotropic models in geometrically nonlinear context. Attention is also focused on the unphysical
dissipation produced in elastic paths due to unsymmetrical stiffness matrix.
Some existing cohesive-zone models are analyzed under conditions of large displacement and
large strain by Ottosen et al in [4], and CZMs are also evaluated with respect to thermodynamic
consistency and the fundamental laws such as balance of angular momentum and frame invariance.
It is shown that in elastic regime only isotropic models, with traction vector aligned to separation
displacement vector, fulfill the physical principles, as already shown in [5].
In [6] some cohesive-zone models are compared at finite strain condition, by a wedge test and
by a peel test. The paper [6] shows that some models available in literature, or implemented in
commercial finite element codes, which integrate the weak form equilibrium condition over the
current configuration, produce significant error in terms of fracture energy. On the contrary, models
integrated over the reference configuration produce negligible numerical error.
The present paper investigates reasons of the different results between current and reference integration
schemes. It is shown that interface formulations integrated over current configuration violate
energy conservation principle, due to the elastic energy generated by the finite interface elongation
with constant elastic stiffness parameters. Moreover, an original mechanical interpretation of the
elastic stiffness parameters, defined as a density of elastic springs between the two interface edges,
can be considered an effective solution for interface integrated over the current configuration. In fact,
the interface elongation modify the density of springs, as well as volume change modifies the mass
density, and integration over current configuration and integration over the reference one produce
two identical solutions.
In the present paper the interface formulation is rigorously developed under large displacement
conditions, assuming as local reference for the constitutive model, normal and tangential axes to the
middle surface, as already proposed in [1]. The geometric operators in the current configuration,
such as the normal and tangential axes to the middle surface and elongation of the middle surface,
are defined as functions of nodal displacements, and first order and second order derivatives, with
respect to nodal displacements, are developed. Finally, nodal force vector and consistent stiffness
matrix are developed for a two-dimensional interface element, showing the symmetry condition of
the geometric stiffness matrix, if the second order derivative are not neglected.
The proposed interface formulation is implemented in the FEAP finite element code [7] and the
cohesive formulation proposed in [8] is considered as constitutive model. Results of numerical some
simulations are proposed with times of convergence obtained with a symmetric solver
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
Antenatal diagnosis and obstetric management of cystic hygroma occurring in twin pregnancies. A case report
No full text. Plasma calcitonin variations in normal women and in women with family history of diabetes during pregnancy.
No full text
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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