1,721,011 research outputs found
A soft effective segment representation of semidilute polymer solutions
No full textA coarse-grained effective segment description of polymer solutions is presented, based on soft, transferable effective interactions between bonded and nonbonded effective segments. The number of segments is chosen such that the segment density does not exceed their overlap threshold, allowing polymer concentrations to be explored deep into the semidilute regime. This quantitative effective segment description is shown to preserve known scaling laws of polymer solutions and provides accurate estimates of amplitudes, while leading to a orders-of-magnitude increase in the simulation efficiency and allowing analytic calculations of structural and thermodynamic properties. © 2007 American Institute of Physics
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
Entropic self-assembly of diblock copolymers into disordered and ordered micellar phases
No full textWe investigate the self-assembly of an athermal model of AB diblock copolymers into disordered and ordered micellar microphases. The original microscopic lattice model with ideal A strands and self-avoiding B strands is mapped onto a system of ultrasoft dumbbells, with monomer-averaged effective interactions between the centers of mass (CMs) of the two blocks. Extensive Monte Carlo simulations of this coarse-grained model are reported for several length ratios f ) L A/( L A + L B) of the two strands of lengths L A and L B. Clear-cut evidence is found for clustering and self-assembly into micelles with a mean aggregation number of n ≃ 100 beyond a critical micellar concentration (cmc) in the semidilute regime. The cmc is found to decrease with increasing f , as predicted by an analytic calculation based on the random phase approximation. The initially disordered dispersion of polydisperse spherical micelles undergoes a disorder-order transition to a micellar crystal phase at higher copolymer concentrations. The effective pair potential between the micellar CMs is determined by inverting the measured CM-CM pair distribution function and is found to become steeper with increasing density. © 2009 American Chemical Society
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
Multi-blob coarse graining for ring polymer solutions
No full textWe present a multi-scale molecular modeling of concentrated solutions of unknotted and non-concatenated ring polymers under good solvent conditions. The approach is based on a multi-blob representation of each ring polymer, which is capable of overcoming the shortcomings of single-blob approaches that lose their validity at concentrations exceeding the overlap density of the solution [A. Narros, A. J. Moreno, and C. N. Likos, Soft Matter, 2010, 6, 2435]. By means of a first principles coarse-graining strategy based on analytically determined effective pair potentials between the blobs, computed at zero density, we quantitatively reproduce the single molecule and solution properties of a system with well-defined topological constraints. Detailed comparisons with the underlying, monomer-resolved model demonstrate the validity of our approach, which employs fully transferable pair potentials between connected and unconnected blobs. We demonstrate that the pair structure between the centers of mass of the rings is accurately reproduced by the multi-blob approach, thus opening the way for simulation of arbitrarily long polymers. Finally, we show the importance of the topological constraint of non-concatenation on the structure of the concentrated solution and in particular on the size of the correlation hole and the shrinkage of the rings as melt concentrations are approached
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