1,720,983 research outputs found
Tight globally simple nonzero sum Heffter arrays and biembeddings
Full text linkSquare relative nonzero sum Heffter arrays, denoted by N H t ( n ; k ) , have been introduced as a variant of the classical concept of Heffter array. An N H t ( n ; k ) is an n x n partially filled array with elements in Z v , where v = 2 n k + t , whose rows and whose columns contain k filled cells, such that the sum of the elements in every row and column is different from 0 (modulo v ) and, for every x is an element of Z v not belonging to the subgroup of order t , either x or - x appears in the array. In this paper we give direct constructions of square nonzero sum Heffter arrays with no empty cells, N H t ( n ; n ) , for every n odd, when t is a divisor of n and when t is an element of { 2 , 2 n , n 2 , 2 n 2 } . The constructed arrays have also the very restrictive property of being "globally simple"; this allows us to get new orthogonal path decompositions and new biembeddings of complete multipartite graphs
A class of highly symmetric Archdeacon embeddings
No full textArchdeacon, in his seminal paper in Electron. J. Combin. (2015), defined the concept of Heffter array to provide explicit constructions of biembeddings of the complete graph Kv into orientable surfaces, the so-called Archdeacon embeddings, and proved that these embeddings are Zv-regular. In this paper, we show that an Archdeacon embedding may admit an automorphism group that is strictly larger than Zv . Indeed, as an application of the interesting class of arrays recently introduced by Buratti in https://arxiv.org/abs/2210.16672, we exhibit, for infinitely many values of v, an embedding of this type having full automorphism group of size (Formula Presented) that is the largest possible one
Constructing generalized Heffter arrays via near alternating sign matrices
No full textLet S be a subset of a group G (not necessarily abelian) such that S∩−S is empty or contains only elements of order 2, and let h=(h1,...,hm)∈Nm and k=(k1,...,kn)∈Nn. A generalized Heffter array GHASλ(m,n;h,k) over G is an m×n matrix A=(aij) such that: the i-th row (resp. j-th column) of A contains exactly hi (resp. kj) nonzero elements, and the list {aij,−aij|aij≠0} equals λ times the set S∪−S. We speak of a zero sum (resp. nonzero sum) GHA if each row and each column of A sums to zero (resp. a nonzero element), with respect to some ordering. In this paper, we use near alternating sign matrices to build both zero and nonzero sum GHAs, over cyclic groups, having the further strong property of being simple. In particular, we construct zero sum and simple GHAs whose row and column weights are congruent to 0 modulo 4. This result also provides the first infinite family of simple (classic) Heffter arrays to be rectangular (m≠n) and with less than n nonzero entries in each row. Furthermore, we build nonzero sum GHASλ(m,n;h,k) over an arbitrary group G whenever S contains enough noninvolutions, thus extending previous nonconstructive results where ±S=G∖H for some subgroup H of G. Finally, we describe how GHAs can be used to build orthogonal decompositions and biembeddings of Cayley graphs (over groups not necessarily abelian) onto orientable surfaces
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
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