1,720,963 research outputs found
On optimal (v,5,2,1) optical orthogonal codes
No full textThe size of a (v,5,2,1) optical orthogonal code (OOC) is shown to be at most equal to ⌈v/12⌉ when v ≡ 11 (mod 132) or v ≡ 154 (mod 924), and at most equal to ⌊v/12⌋ in all the other cases. Thus a (v,5,2,1)-OOC is naturally said to be optimal when its size reaches the above bound. Many direct and recursive constructions for infinite classes of optimal (v,5,2,1)-OOCs are presented giving, in particular, a very strong indication about the existence of an optimal (p,5,2,1)-OOC for every prime p ≡ 1 (mod 12)
Combinatorial designs and the Theorem of Weil on multiplicative character sums
No full textAbstractIn the last years, the theorem of Weil on multiplicative character sums has been very frequently used for getting existence results on combinatorial designs of various kinds. Case by case, the theorem has been applied directly and sometimes this required long and tedious calculations that could be avoided using a result that is a purely algebraic consequence of it.Here this result will be used, in particular, for giving a quick proof of the existence of a (q,k,λ) difference family for any admissible prime power q>(k2)2k/g2k−2 where g=gcd((k2),λ), improving in this way the original bound q>(k2)k2−k given by R.M. Wilson [R.M. Wilson, Cyclotomic and difference families in elementary abelian groups, J. Number Theory 4 (1972) 17–47].More generally, given any simple graph Γ, we prove that there exists an elementary abelian Γ-decomposition of the complete graph Kq for any prime power q≡1 (mod 2e) with q>d2e2d where d and e are the max–min degree and the number of edges of Γ, respectively. This improves, in some cases enormously, Wilson's bound q>ek2−k where k is the number of vertices of Γ (see [R.M. Wilson, Decompositions of complete graphs into subgraphs isomorphic to a given graph, in: C.St.J.A. Nash-Williams, J.H. van Lint (Eds.), Proc. Fifth British Combinatorial Conference. in: Congr. Numer., vol. XV, 1975, pp. 647–659]).The algebraic consequence of the theorem of Weil will be also applied for getting significative existence results on Γ-decompositions of a complete g-partite graph Kg×q with q a prime power
Further progress on difference families with block size 4 or 5
No full textA strong indication about the existence of a (7 p, 4, 1) difference family with p ≡ 7 (mod 12) a prime has been given in [1]. Here, developing some ideas of that paper, we give, much more generally, a strong indication about the existence of a cyclic (pq,4,1) difference family whenever p and q are primes congruent to 7 (mod 12) and of a cyclic (pq,5,1) difference family whenever p and q are primes congruent to 11 (mod 20). Indeed we give an algorithm for their construction that seems to be always successful and we have checked it works whenever both primes p and q do not exceed 1,000. All our (pq,4,1) and (pq,5,1) difference families have the nice property of admitting a multiplier of order 3 or 5, respectively, that fixes almost all base blocks. As an intermediate result we also find an optimal (p, 5, 1) optical orthogonal code for every prime p ≡ 11 (mod 20) not exceeding 10,000
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
On perfect -decompositions of the complete graph
No full textGeneralizing the well-known concept of an i-perfect cycle system, Pasotti [Pasotti, in press, Australas J Combin] defined a -decomposition (-factorization) of a complete graph to be i-perfect if for every edge [x, y] of there is exactly one block of the decomposition (factor of the factorization) in which x and y have distance i. In particular, a -decomposition (-factorization) of that is i-perfect for any i not exceeding the diameter of a connected graph will be said a Steiner (Kirkman) -system of order v. In this article we first observe that as a consequence of the deep theory on decompositions of edge-colored graphs developed by Lamken and Wilson [Lamken and Wilson, 2000, J Combin Theory Ser A 89, 149–200], there are infinitely many values of v for which there exists an i-perfect -decomposition of provided that is an i-equidistance graph, namely a graph such that the number of pairs of vertices at distance i is equal to the number of its edges. Then we give some concrete direct constructions for elementary abelian Steiner -systems with the wheel on 8 vertices or a circulant graph, and for elementary abelian 2-perfect cube-factorizations. We also present some recursive constructions and some results on 2-transitive Kirkman -systems
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