1,721,016 research outputs found
Crystallization of calcium carbonate salts into beta-chitin scaffold
No full textComposites of β-chitin with calcium carbonate polymorphs were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The β-chitin was obtained from the pen of the Loligo sp. squid. The three main polymorphs of calcium carbonate: aragonite, calcite and vaterite, were observed. Their location within the matrix is a function of the polymorph. The supersaturation inside the compartmentalized space in the chitin governs the location and polymorphism of the crystals. © 2002 Elsevier Science Inc. All rights reserved
Oriented crystallization of octacalcium phosphate into beta-chitin scaffold
No full textComposites of β-chitin with octacalcium phosphate (OCP) or hydroxylapatite (HAP) were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The β-chitin was obtained from the pen of the Loligo sp. squid. Only oriented precipitation of OCP was observed. The OCP crystals with the usual form of (001) blades grow inside chitin layers preferentially oriented with the {100} faces parallel to the surface of the squid pen and were more stable to the hydrolysis to HAP with respect to that precipitated in solution. Reasons are given why mechanical factors are thought to be the predominant cause for the orientation of the OCP crystals with the a-axis almost normal to the chitin fibers. We conclude that in these in vitro experiments the compartmentalized space in the chitin governs the orientation of the crystals, even if epitaxial factors may play a role in the nucleation processes. © 2001 Elsevier Science B.V. All rights reserved
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
Oriented crystallization of vaterite in collagenous matrices
No full textThe influence of high supersaturation on kinetic control and the importance of the polypeptide structure in the crystallization of calcium carbonate polymorphs were studied in crosslinked gelatin films containing high concentrations of the polypeptides poly-L-aspartate and poly-L-glutamate. Oriented crystallization of vaterite occurs in uniaxially deformed gelatin films containing poly-L-aspartate at concentations greater than 100 mg per gram of gelatin. The fact that no orientation of the mineral phase was observed with entrapped poly-L-glutamate at the same concentrations suggests that the oriented crystallization is controlled by the beta sheet structure assumed by poly-L-aspartate in the presence of calcium ions. These results indicate that local supersaturation in the microenvironment in which nucleation and growth occur plays an important role in controlling the deposition of vaterite in cross-linked gelatin films. However, collagen bundles se and the ordered and oriented polypeptide chains of poly-L-aspartate can contribute to the control of polymorphism by inducing the formation of a specific phase by epitaxial crystallization, as suggested by the preferentially oriented deposition of vaterite and aragonite. This is of potential significance in biomineralization processes and in materials science
Polymorphism and architectural crystal assembly of calcium carbonate in biologically inspired polymeric matrices f
No full textThe control of the polymorphism and architectural crystal assembly of calcium carbonate minerals in gels formed by means of collagenous matrices with entrapped polypeptides is reported. It has been observed that the calcium carbonate polymorphic selectivity is related to the local supersaturation within the microenvironment where nucleation and growth occur. This crucial parameter is controlled in terms of the entrapped additive concentration and of the tailoring of the biopolymeric scaffold by mechanical deformation. Specific orientation effects and crystal aggregation of the mineral phases can be controlled either by the charged polypeptide with a beta structure or by the structural organization of the triple helical stretches in the collagenous matrix. This results in the growth and assembly of crystals into desired shapes and sizes by molecular recognition at a definite crystal face or by the control of the organic macromolecular microenvironment fit in the emerging area of biologically inspired approach to structured inorganic materials with appropriate physical and chemical properties. © The Royal Society of Chemistry 2000
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