1,721,543 research outputs found
The treewidth of 2-section of hypergraphs
No full textLet be a simple hypergraph without loops. is called linear if
for any with . The -section of ,
denoted by , is a graph with and for any , if and only if there is such that . The treewidth of a graph is an important invariant in structural and
algorithmic graph theory. In this paper, we consider the treewidth of the
-section of a linear hypergraph. We will use the minimum degree, maximum
degree, anti-rank and average rank of a linear hypergraph to determine the
upper and lower bounds of the treewidth of its -section. Since for any graph
, there is a linear hypergraph such that , we provide a
method to estimate the bound of treewidth of graph by the parameters of the
hypergraph
Electrochemical copolymerization of pyrrole and thiophene nanofibrils using template-synthesis method
No full textCopolymer nanofibrils composed of pyrrole and thiophene were prepared by synthesizing the desired polymer within the pores of microporous anodic aluminum oxide (AAO) template membranes. The copolymer nanofibrils were photographed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for microstructure analyses. The results of the SEM and TEM revealed that the copolymer nanofibrils obtained had uniform and well-aligned arrays and their diameter and length could be controlled by changing the aspect ratios of the AAO membrane. The results of cyclic voltammetry and IR spectrometry indicated that polypyrrole and polythiophene were both involved in the copolymer. The nanofibrils that were obtained were identified as copolymers rather than composites. The influence of the applied polymerization potential on the synthesis of copolymer nanofibrils was investigated. The higher potential favored the incorporation of thiophene units into the copolymer nanofibrils
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
Spectral properties of the eccentricity matrix of graphs
No full textThe eccentricity matrix E(G) of a graph G is derived from the distance matrix by keeping for each row and each column only the largest distances and leaving zeros in the remaining ones. The E-eigenvalues of a graph G are those of its eccentricity matrix E(G). The E-spectrum of G is the multiset of its E-eigenvalues, where the largest one is the E-spectral radius. In this paper, we proceed to study the algebraic properties of the E-spectrum. In particular, we give a condition to connected graphs with cut vertices so that their eccentricity matrices are irreducible. The latter partially answers the problem given in Wang et al. (2018). We determine the lower and upper bounds for the E-spectral radius of graphs, and we identify the corresponding extremal graphs. Finally, we investigate the least E-eigenvalue of graphs, and list the E-eigenvalues of trees with order 8. © 2019 Elsevier B.V
The anti-adjacency matrix of a graph: Eccentricity matrix
No full textIn this paper we introduce a new graph matrix, named the anti-adjacency matrix or eccentricity matrix, which is constructed from the distance matrix of a graph by keeping for each row and each column only the largest distances. This matrix can be interpreted as the opposite of the adjacency matrix, which is instead constructed from the distance matrix of a graph by keeping for each row and each column only the distances equal to 1. We show that the eccentricity matrix of trees is irreducible, and we investigate the relations between the eigenvalues of the adjacency and eccentricity matrices. Finally, we give some applications of this new matrix in terms of molecular descriptors, and we conclude by proposing some further research problems
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
Synthesis and characterization of conducting copolymer nanofibrils of pyrrole and 3-methylthiophene using the template-synthesis method
No full textCopolymer nanofibrils composed of pyrrole and 3-methylthiophene had been prepared by synthesizing the desired polymer within the pores of microporous anodic aluminum oxide (AAO) template membrane. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the obtained copolymer nanofibrils had uniform and well-aligned array and its diameter and length can be controlled by changing the aspect ratios of the AAO membrane. The results of infrared (IR) spectra, X-ray photoelectron spectroscopy (XPS) and elemental analysis indicated that both pyrrole and 3-methylthiophene were involved in the copolymer and pyrrle is the major component of the prepared copolymer nanofibrils. Finally, the uses of conductivity and thermogravimetric analysis (TGA) proved that the electric conductivity and the thermal stability of copolymer nanofibrils are higher than individual homopolymers
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
- …
