1,720,985 research outputs found
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
What good is Linear Elastic Fracture Mechanics in Hydraulic Fracturing
No full textFluid-driven fracture presents an interesting case of crack elasticity and fracture propagation nonlinearly coupled to fluid flow. With the exceptions of a few numerical studies, previous hydraulic fracture modeling efforts have been based on the premise of Linear Elastic Fracture Mechanics (LEFM): specifically, that the damage (aka cohesive) zone associated with the rock breakage near the advancing fracture front is lumped into a singular point, under the tacit assumption that the extent of the cohesive zone is small compared to lengthscales of other physical processes relevant in the HF propagation. The latter include the dissipation in the viscous fluid flow in the fracture channel, of which the fluid lag - a region adjacent to the fracture tip filled with fracturing fluid volatiles and/or infiltrated formation pore fluid - is the extreme manifestation. In this work, we address the validity of the LEFM approach in hydraulic fracturing by considering the solution in the near tip region of a cohesive fracture driven by Newtonian fluid in an impermeable linearelastic rock. First, we show that the solution in general possesses an intricate structure supported by a number of nested lengthscales (a general sentiment for HF), on which different dissipation processes are realized (or are dominant). The latter processes can be cataloged as (1) dissipation in the fracture cohesive zone, â câ , parameterized by the fracture energy Gc (cohesive energy release per unit fracture advance), the peak cohesive stress destroyed by fracturing, and corresponding fracture aperture scale ; (2) the LEFM â reductionâ of the cohesive zone process, â â , quantified by , but with the cohesive zone replaced by a singularity ( and ); (3) viscous fluid dissipation associated with the fluid lag region, â oâ , parametrized by an equivalent fracture energy ,
where is the confining stress (signifying the fracturing fluid pressure drop in the lag region from value to near zero) and is the corresponding fracture aperture scale given previously by Garagash and Detournay (2000); and (4) the viscous dissipation along the rest of the fracture (away from the fluid lag), â mâ (Desroches et al, 1994). Furthermore, each of the above limiting processes corresponds to distinct solution asymptotes. The HF tip solution structure is bookended by the â câ or â oâ (solid or fluid process zones) asymptotes near the tip and by the â mâ asymptote away from
the tip, while the LEFM â kâ asymptote may emerge within the transitional region, as an intermediate asymptote, depending on values of the two governing parameters: the cohesive-to-lag fracture energy ratio and the cohesive-to-in-situ stress ratio . For typical sets of parameters representative of both field hydraulic fractures and their lab siblings, is either (low-viscosity frac. fluid) or is shown to be required for appearance of the LEFM intermediate asymptote near the HF tip. Since MPa for most rocks, it can be easily recognized that the latter condition for the relevance of the LEFM to hydraulic fracturing is mostly realized in laboratory experiments conducted under reduced levels of confining stress, and would almost never occur in the field (with the exception of very-near-surface fracturing and/or highly overpressured permeable formations).Non UBCUnreviewedAuthor affiliation: Dalhousie UniversityFacult
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Gravity driven hydraulic fracture with finite breadth
Get PDFThis study outlines a new method for disposing of hazardous (e.g., nuclear) waste. The technique is called Abyssal Sequestration, and it involves placing the waste at extreme depths in Earth’s crust where it could achieve the geologically long period of isolation. Abyssal Sequestration involves storing the waste in hydraulic fractures driven by gravity, a process we term as gravity fracturing. In short, we suggest creating a dense fluid (slurry) containing waste, introducing the fluid into a fracture, and extending the fracture downward until it becomes long enough to propagate independently. The fracture will continue to propagate downward to great depth, permanently isolating the waste. Storing solid wastes by mixing them with fluids and injecting them into hydraulic fractures is a well-known technology. The essence of our idea differs from conventional hydraulic fracturing techniques only slightly in that it uses fracturing fluid heavier than the surrounding rock. This difference is fundamental, however, because it allows hydraulic fractures to propagate downward and carry wastes by gravity instead of or in addition to being injected by pumping. An example of similar gravity-driven fractures with positive buoyancy is given by magmatic dikes that may serve as an analog of Abyssal Sequestration occurring in nature. Mechanics of fracture propagation in conditions of positive (diking) and negative (heavy waste slurry) buoyancy is similar and considered in this work for both cases. Analog experiments in gelatin show that fracture breadth (horizontal dimension) remains nearly stationary when fracturing process in the fracture “head” (where breadth is “created”) is dominated by solid toughness, as opposed to the viscous fluid dissipation dominant in the fracture tail. We model propagation of the resulting “buoyant” or “sinking” finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response of the crack to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins–Kern–Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to unit crack extension and the rock fracture toughness. It allows to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, which breadth is known a priori, the final breadth of a finger-like fracture is a result of the fracturing process in the fracture head. To resolve the breadth, we relax the local elasticity assumption in the fracture head by neglecting viscous pressure drop there. We then combine the finger crack solution for the viscous tail with the 3D pulse solution for the fracture head
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