An infinite family of (simple) 6-designs

A simple 6-(22,8,60) designs is exhibited. It is then shown using Qui-rong Wu's generalization of a result of Luc Teirlinck that this design together with our 6-(14,7,4) design implies the existence of simple 6-(23 + 16m,8,4(m + 1)(16m + 17)) designs for all positive integers m. All the above mentioned designs are halvings of the complete design. © 1993 John Wiley & Sons, Inc.     

An infinite family of symmetric designs

In this paper, using the construction method of [3], we show that if q>2 is a prime power such that there exists an affine plane of order q?1, then there exists a strongly divisible 2?(q?1)(q^h?1), q^h?1(q?1), q^h?1) design for every h?2. We show that these quasi-residual designs are embeddable, and hence establish the existence of an infinite family of symmetric 2?(q^h+1?q+1,q^h, q^h?1) designs. This construction may be regarded as a generalisation of the construction of [1, Chapter 4, Section 1] and [4].     

An infinite family of summation identities

Theta functions have historically played a prominent role in number theory. One such role is the construction of modular forms. In this work, a generalized theta function is used to construct an infinite family of summation identities. Our results grew out of some observations noted during a presentation given by the author at the 1992 AMS-MAA-SIAM Joint Meetings in Baltimore.

     

Unifying some known infinite families of combinatorial 3-designs

In this paper we present a construction of 3-designs by using a 3-design with resolvability. The basic construction generalizes a well-known construction of simple 3-(v,4,3) designs by Jungnickel and Vanstone (1986). We investigate the conditions under which the designs obtained by the basic construction are simple. Many infinite families of simple 3-designs are presented, which are closely related to some known families by Iwasaki and Meixner (1995), Laue (2004) and van Tran (2000, 2001). On the other hand, the designs obtained by the basic construction possess various properties: A theory of constructing simple cyclic 3-(v,4,3) designs by Köhler (1981) can be readily rebuilt from the context of this paper. Moreover many infinite families of simple resolvable 3-designs are presented in comparison with some known families. We also show that for any prime power q and any odd integer n there exists a resolvable 3-(qn+1,q+1,1) design. As far as the authors know, this is the first and the only known infinite family of resolvable t-(v,k,1) designs with t?3 and k?5. Those resolvable designs can again be used to obtain more infinite families of simple 3-designs through the basic construction.     

A new family of 4-designs

We construct a family of simple 4-designs with parameters 4 – (2 ^f + 1, 6, 10),f odd.     

An infinite family of biprimitive semisymmetric graphs

A regular and edge-transitive graph that is not vertex-transitive is said to be semisymmetric. Every semisymmetric graph is necessarily bipartite, with the two parts having equal size and the automorphism group acting transitively on each of these two parts. A semisymmetric graph is called biprimitive, if its automorphism group acts primitively on each part. In this article, a classification of biprimitive semisymmetric graphs arising from the action of the group PSL(2, p), p ≡ ±1 (mod 8) a prime, acting on cosets of S₄ is given, resulting in several new infinite families of biprimitive semisymmetric graphs. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 217–228, 1999     

An infinite family of tetravalent half-arc-transitive graphs

A graph is half-arc-transitive if its automorphism group acts transitively on vertices and edges, but not on arcs. In this paper, a new infinite family of tetravalent half-arc-transitive graphs with girth 4 is constructed, each of which has order 16m such that m>1 is a divisor of 2t²+2t+1 for a positive integer t and is tightly attached with attachment number 4m. The smallest graph in the family has order 80.     

An infinite family of octahedral crossing numbers

This paper calculates some crossing numbers for certain octahedral graphs. Precisely, if the number p is a prime power congruent to 1 modulo 4, then the crossing number of the p-dimensional octahedral graph in the orientable surface of genus (p–1)(p-4)/4 is (p²–p)/2. The key step is the construction of a self-dual imbedding of the complete graph on p vertices such that no face boundary contains a repeated vertex.     

Simple 7-designs with small parameters

We describe a computer search for the construction of simple designs with prescribed automorphism groups. Using our program package DISCRETA this search yields designs with parameter sets 7-(33, 8, 10), 7-(27, 9, 60), 7-(26, 9, λ) for λ = 54, 63, 81, 7-(26, 8, 6), 7-(25, 9, λ) for λ = 45, 54, 72, 7-(24, 9, λ) for λ = 40, 48, 64, 7-(24, 8, λ) for λ = 4, 5, 6, 7, 8, 6-(25, 8, λ) for λ = 36, 45, 54, 63, 72, 81, 6-(24, 8, λ) for λ = 36, 45, 54, 63, 72, 5-(19, 6, 4), and 5-(19, 6, 6). In several of these cases we are able to determine the exact number of isomorphism types of designs with that prescribed automorphism group. © 1999 John Wiley & Sons, Inc. J Combin Designs 7: 79–94, 1999     

An infinite family of sharply two-arc transitive digraphs

We disclaim Conjecture 1 posed by Seifter in [N. Seifter, Transitive digraphs with more than one end, Discrete Math., to appear], that stated that a connected locally finite digraph with more than one end is either 0-, 1- or highly arc transitive. We describe in this work an infinite family of 2-arc transitive two-ended digraphs, that are not 3-arc transitive.     

An infinite family of Hadamard matrices of Williamson type

In this paper a new proof is given of the following theorem of Turyn: Let q = 2n ? 1 be a prime power ≡1 (mod 4); then there exists an Hadamard matrix of order 4n that is of the Williamson type.     

An infinite family of homogeneous polynomial self-maps of spheres

We provide an infinite family of homogeneous polynomial self-maps of spheres. Furthermore, we identify the gradient map of the Cartan–Münzner polynomial as a member of this infinite family and thus supply it with a geometric meaning.     

An infinite family of Petersen geometries with nonlinear diagram

We construct new Petersen geometries. Starting with an inductively minimal geometry, we remove the elements of some well-chosen types and replace them with new objects. This yields an infinite family of Petersen geometries containing a family given bybuekenhout in [2]. We find a large amount of new Petersen geometries whose diagram is not linear.     

An infinite family of simply connected flag-transitive tilde geometries

We consider tilde-geometries (orT-geometries), which are geometries belonging to diagrams of the following shape: Here the rightmost edge stands for the famous triple cover of the classical generalized quadrangle related to the group Sp₄(2). The automorphism group of the cover is the nonsplit extension 3·Sp₄(2) – 3 ·S ₆. Five examples of flag-transitiveT-geometries were known. These are rank 3 geometries related to the groupsM ₂₄ (the Mathieu group),He (the Held group) and and 3⁷·Sp₆(2) (a nonsplit extension); a rank 4 geometry related to the Conway groupCo ₁ and a rank 5 geometry related to the Fischer-Griess Monster groupF ₁. In the present paper we construct an infinite family of flag-transitiveT-geometries and prove that all the new geometries are simply connected. The automorphism group of the rankn geometry in the family is a nonsplit extension of a 3-group by the symplectic group Sp_2n (2). The rank of the 3-group is equal to the number of 2-dimensional subspaces in ann-dimensional vector space over GF(2).