1,721,141 research outputs found
Effects of geometric nonlinearities and uniform temperature fields on the detachment of patched beam-plates under pressure loading
No full textPatched structures have many engineering applications, ranging from aircraft repair to electronic devices and beyond. Delamination growth at the edge of the interface between the substructures may lead to catastrophic results. In the spirit of preventing this, edge delamination failure is studied such that behavior may be predicted as well as characterized for a patched beam-plate structure under different physical conditions. The loading scenario on such structures includes transverse pressure and an applied uniform temperature field. These conditions are intended to mimic possible conditions under which a patched beam-plate may be used. The patched beam-plate consists of two plates: the "patch," which is of shorter length, adhered to the longer "baseplate". This composite structure is examined under various support conditions on the endpoints: hinged-free, clamped-free, hinged-fixed, and clamped-fixed.
The problem is formulated analytically, from first principles, using linear and geometrically nonlinear models. Governing equations are derived using a local force balance on an element of the structure incorporating an appropriate geometrically nonlinear thin structure theory, and can be reduced accordingly to simplify to a corresponding linear model. A Griffith type criterion, is adopted to determine the onset of delamination growth. Exact analytical solutions are obtained for nonlinear as well as linear problems and numerical simulations based on these solutions are performed using MATLAB.
Results are presented in the form of delamination growth paths, which may be interpreted physically to describe the onset, extent, and stability of the delamination growth resulting from each scenario. The effect of various physical parameters on delamination behavior is explored. The results show that a temperature difference has a profound effect on the delamination behavior of the patched plates when subject to transverse pressure, as it significantly alters the delamination growth thresholds. There are scenarios where delamination propagation begins in the absence of transverse pressure, due solely to the applied temperature difference. Conclusions are drawn and physical explanations are given for the behavior of each patched plate system. The nonlinear model reveals different delamination growth thresholds and stabilities than the linear model. It observed that the linear model does not adequately describe the salient behavior in comparison to the nonlinear model.M.S.Includes bibliographical references (p. 144-146)
Employees no longer: on the federal government's proposals for contractors
No full textThe federal government is committed to removing laws restricting the use of independent contractor arrangements. Yet many independent contractors are really dependent workers. Changing the law, then, will produce a new class of workers who are effectively employees but no longer recognised and protected as such, according to Giuseppe Carabetta and Cynthia Coleman
CCS semantics via proved transition systems and rewriting logic
No full textWe consider a slight variant of the CCS calculus and we analyze two operational semantics defined in the literature: the first exploits Proved Transition Systems (PTSs) and the second Rewriting Logic (RL). We show that the interleaving interpretation of both semantics agree in that they dene the same transitions and exhibit the same nondeterministic structure. In addition we study causality in CCS computations.
We recall the treatment via PTSs that exhibits the notion of causality presented in the literature and we show how to recast it in the RL semantics via suitable axioms
On the interaction of thermal buckling and debonding of patched structures
No full textThe widespread use of patched assemblies in engineering structures creates the need for better fundamental understanding of the failure phenomena of such structures to ensure their safe and effective usage. A structure possessing two substructures, the
“patch” and “baseplate”, with mismatched coefficients of thermal expansion is studied under thermal loading for two extreme edge conditions. The composite structure is taken as initially flawed, such that partial separation exists at the edges of the patch between the
two substructures. Two relevant failure mechanisms are sling-shot buckling and edge debonding (separation). Sling-shot buckling, first observed for perfectly intact structures under thermal loads, occurs when the structure dynamically slings from one equilibrium configuration to another in an opposite sense of deflection at a critical load. It is desired
to be able to predict and characterize buckling of the structure, and its coupling with debonding. The geometrically nonlinear problem is formulated via a variational formulation, which allows the boundaries of the domains of the structure to vary in addition to the displacements. The vanishing of the first variation of the potential energy yields governing equilibrium equations, boundary/matching conditions, and transversality
conditions. The transversality condition yields a Griffith type delamination criterion. A closed-form solution is obtained after recasting the problem in a mixed formulation. A stability analysis is performed using the second variation of the potential energy functional. The partially debonded structure is seen to possess a “dual nature”, where it is structurally different depending on the deflection, due to the existence of the initial
flaw. It experiences sling-shot buckling, which, coupled with the structure’s duality leads to what we refer to as “Buckle Trapping.” It is suggested that, for certain critical
temperature fields, the structure oscillates dynamically between unstable equilibrium configurations. In addition, examination of the energy release rate against the bond size reveals a variety of possible behaviors, dependent on flaw size, temperature difference,
and bond strength. It is observed how and when separation leads to thermal buckling, and vice versa. Through this analysis, the onset, extent, and stability of debonding, as well as the relationship with buckling, are diagnosed and characterized.Ph.D.Includes bibliographical referencesIncludes vitaby Pamela Marie Carabett
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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