1,720,997 research outputs found
Linear Elastic Fracture Mechanics Pullout Analyses of Headed Anchors in Stressed Concrete
No full textThe results of research initiated in the early 1980s led to the replacement of plasticity-based design guidelines for the load-carrying capacity of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions are
available in the design codes that account for the presence of tensile fields causing concrete cracking, no provisions are available for anchors embedded in prestressed concrete. This paper presents the results of linear elastic fracture mechanics (LEFM) analyses and of a preliminary experimental investigation of the progressive failure of headed anchors embedded in a concrete matrix under compressive or tensile prestress. The model predicts an increase (decrease) in load-carrying capacity and ductility with increasing compressive tensile prestress. It is shown that despite neglecting the dependence on size of concrete fracture toughness, LEFM predicts with remarkable accuracy the functional dependence of the ultimate capacity on prestress
Modeling and measuring visco-elastic properties: From collagen molecules to collagen fibrils
No full textCollagen is the main structural protein in vertebrate biology, determining the mechanical behavior of
connective tissues such as tendon, bone and skin. Although extensive efforts in the study of the origin of
collagen exceptional mechanical properties, a deep knowledge of the relationship between molecular
structure and mechanical properties remains elusive, hindered by the complex hierarchical structure of
collagen-based tissues. Understanding the viscoelastic behavior of collagenous tissues requires knowledge
of the properties at each structural level. Whole tissues have been studied extensively, but less is
known about the mechanical behavior at the submicron, fibrillar and molecular level. Hence, we
investigate the viscoelastic properties at the molecular level by using an atomistic modeling approach,
performing in silico creep tests of a collagen-like peptide. The results are compared with creep and
relaxation tests at the level of isolated collagen fibrils performed previously using a micro-electromechanical
systems platform. Individual collagen molecules present a non-linear viscoelastic behavior,
with a Young's modulus increasing from 6 to 16 GPa (for strains up to 20%), a viscosity of 3.8470.38 Pa s,
and a relaxation time in the range of 0.24–0.64 ns. At the fibrils level, stress–strain–time data indicate
that isolated fibrils exhibit viscoelastic behavior that could be fitted using the Maxwell–Weichert model.
The fibrils showed an elastic modulus of 123746 MPa. The time-dependent behavior was well fit using
the two-time-constant Maxwell–Weichert model with a fast time response of 772 s and a slow time
response of 10275 s
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
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
- …
