1,720,958 research outputs found
Particulate random composites homogenized as micropolar materials
No full textMany composite materials, widely used in different engineering fields, are characterized by random distributions of the constituents. Examples range from polycrystals to concrete and masonry-like materials. In this work we propose a statistically-based scale-dependent multiscale procedure aimed at the simulation of the mechanical behavior of a two-phase particle random medium and at the estimation of the elastic moduli of the energy-equivalent homogeneous micropolar continuum. The key idea of the procedure is to approach the so-called Representative Volume Element (RVE) using finite-size scaling of Statistical Volume Elements (SVEs). To this end properly defined Dirichlet, Neumann, and periodic-type non-classical boundary value problems are numerically solved on the SVEs defining hierarchies of constitutive bounds. The results of the performed numerical simulations point out the importance of accounting for spatial randomness as well as the additional degrees of freedom of the continuum with rigid local structure
Random masonry as homogenized micropolar continua.
No full textA scale-dependent homogenization approach for describing the mechanical behavior of composite materials with random microstructures, paying attention to materials employed in historical constructions, like roman concrete, rubble filled masonry or magmatic rocks, is proposed. To this aim, a statistical procedure for estimating the constitutive moduli of an equivalent micropolar continuum is performed. This procedure uses finite-size scaling of Statistical Volume Elements (SVEs) and approaches the so-called Representative Volume Element (RVE) through two hierarchies of constitutive bounds, respectively stemming from the numerical solution of Dirichlet and Neumann non-classical boundary value problems, set up on mesoscale material cells. The results of the performed numerical simulations point out the worthiness of accounting spatial randomness as well as the additional degrees of freedom of the Cosserat continuum
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
Homogenization for random micropolar composites. The case of masonry-like materials.
No full textThe worldwide concern for the stewardship of old structures and gems of ancient architecture calls for mechanics models of walls built of stones with random properties and shapes. Among different typologies according to the common constructive technologies, we focus our attention on two revealing random patterns: concrete masonry, in which aggregates of small size are surrounded by a mortar matrix, and “rubble” masonry where randomly distributed stones are held together by small amounts of mortar. The aim of this work is to study the constitutive behavior of such materials adopting homogenization techniques in order to obtain the overall constitutive coefficients directly related to the actual structure. Unlike the periodic homogenization in which the size of the Representative Volume Element(RVE) is a datum of the problem, in this case the
minimal size of RVE is a-priori unknown. We adopt a statistical homogenization procedure, well established for standard continua, in order to obtain information to detect the minimal size of RVE and to estimate the effective constitutive properties of such materials. Under the assumption that microstructure’s statistics is spatially homogeneous and ergodic, a so-called Statistical Volume Element(SVE) can be set up on a mesoscale, i.e. any finite scale relative to the microstructural length scale, and, on that basis, by solving Dirichlet and Neumann boundary value problems, two scale dependent hierarchies of mesoscale bounds for the effective material properties can been obtained. The convergence trend, as the SVE increases, allow one to
approximate the RVE size to adopt for performing the homogenization process. We here propose an extension of the aforementioned statistical homogenization procedure for composites perceived as Cosserat continua, both at the micro and macro level. The choice of micropolar continua modeling is related to the possibility of taking into account effects of material internal lengths and the non-symmetries of strain and stress tensors. This procedure exploits the macrohomogenity
condition generalized to micropolar continua, which holds also in the case of spatial nonperiodicity. The linear-elastic case is taken into account, providing a computational estimate of the
bounds for the classical and micropolar elastic coefficients for the two kind of random media considered. The numerical results, holds for several kind of composite materials, among which
masonry is just one example
Size of RVE in random micropolar composites
No full textThe worldwide concern for the stewardship of old structures and gems of ancient architecture calls for multiscale mechanics models of walls built of stones with random properties and shapes. While the walls of periodically structured masonry have already successfully been modeled by Cosserat (micropolar)
continua, the presence of disorder requires development of random micropolar continua, where one has to determine the finite-size scaling from a Statistical Volume Element (SVE) to a Representative Volume Element (RVE). To this end, we use the recently established macrohomogeneity (Hill-Mandel
type) condition accounting for couple-stress and curvature-torsion tensors besides the conventional Cauchy stressses and strains. Overall, the RVE is approached in terms of two hierarchies of bounds stemming, respectively, from Dirichlet and Neumann boundary value problems set up on the SVE. In
particular, we focus on composite materials with a random, non-periodic internal structure of Cosserat
type. Various combinations of matrix (mortar) and inclusion phases (stones) are examined and a stochastic study is carried out in order to extract the "averaged" homogenized constitutive properties for a fixed control window (mesoscale). Once the RVE size is determined as a function of the internal length of
the material, the converged homogenized constitutive parameters are obtained and are used for large scale
numerical simulations on 2D masonry panels. Since the micropolar model is richer than a corresponding one for a local medium, it is characterized by a higher number of constitutive parameters. This
methodology then forms a rational basis for setting up of mesoscale continuum random fields and stochastic finite element methods
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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