On rank 3 projective designs

The finite projective designs with rank 3 collineation groupsG such thatG _p =G _l for some point-block pair (P, l) are divided into 4 classes. 2 of these classes are formed by the Paley designs and the designs complementary to the Paley designs. For the other 2 classes restrictions on the parameters are obtained. In particular it is shown that the only such design having =1 is the projective plane of order 2.With 2 Figures     

Constructions for resolvable and related designs

Methods are given for constructing block designs, using resolvable designs. These constructions yield methods for generating resolvable and affine designs and also affine designs with affine duals. The latter are transversal designs or semi-regular group divisible designs with ₁=0 whose duals are also designs of the same type and parameters. The paper is a survey of some old and some recent constructions.     

A note on square divisible designs

We consider square divisible designs with parameters n, m, k=r, 0 and . We show that being disjoint induces an equivalence relation on the block set of such a design and that any two disjoint blocks meet precisely the same point classes. Also, the intersection number of two blocks depends only on their equivalence classes. The number of blocks disjoint with a given block is at most n–1; equality holds for all blocks iff the dual of the given design is also divisible with the same parameters. We then give a few applications.The author gratefully acknowledges the support of the Deutsche Forschungsgemeinschaft via a Heisenberg grant during the time of this research.     

D‐optimal designs and group divisible designs

We obtain new conditions on the existence of a square matrix whose Gram matrix has a block structure with certain properties, including D‐optimal designs of order , and investigate relations to group divisible designs. We also find a matrix with large determinant for n = 39. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 451–462, 2006     

Some Triple Block Intersection Numbers of Paley 2-Designs of QN-type

We determine here some possible values for thecardinality of the intersection of three blocks from Paley2-(2q+1, q, (q-1)/2) designs where qis a prime power such that (mod 4).     

On an assertion of Dembowski

In his Finite Geometries, Dembowski asserted that the class of uniform projective Hjelmslev planes of order q and a certain class of symmetric divisible partial designs coincide. We give a counterexample for q=2 and prove the validitiy of Dembowski's assertion for all q3.     

Abelian and non-abelian Paley type group schemes

In this paper, we present a construction of abelian Paley type group schemes which are inequivalent to Paley group schemes. We then determine the equivalence amongst their configurations, the Hadamard designs or the Paley type strongly regular graphs obtained from these group schemes, up to isomorphism. We also give constructions of several families of non-abelian Paley type group schemes using strong multiplier groups of the abelian Paley type group schemes, and present the first family of p-groups of non-square order and of non-prime exponent that contain Paley type group schemes for all odd primes p.     

Orbit matrices of Hadamard matrices and related codes

In this paper we introduce the notion of orbit matrices of Hadamard matrices with respect to their permutation automorphism groups and show that under certain conditions these orbit matrices yield self-orthogonal codes. As a case study, we construct codes from orbit matrices of some Paley type I and Paley type II Hadamard matrices. In addition, we construct four new symmetric (100,45,20) designs which correspond to regular Hadamard matrices, and construct codes from their orbit matrices. The codes constructed include optimal, near-optimal self-orthogonal and self-dual codes, over finite fields and over ${\mathbb{Z}}_4$.     

Group divisible designs with block size four and two groups

We give some constructions of new infinite families of group divisible designs, GDD(n,2,4;λ₁,λ₂), including one which uses the existence of Bhaskar Rao designs. We show the necessary conditions are sufficient for 3?n?8. For n=10 there is one missing critical design. If λ₁>λ₂, then the necessary conditions are sufficient for . For each of n=10,15,16,17,18,19, and 20 we indicate a small minimal set of critical designs which, if they exist, would allow construction of all possible designs for that n. The indices of each of these designs are also among those critical indices for every n in the same congruence class mod 12.     

On the non-existence of a class of symmetric group divisible partial designs

Many non-existence theorems are known for symmetric group divisible partial designs. In the case that these partial designs are auto-dual with ₁=0, an ideal incidence structure can be defined whose elements are the equivalence-classes of non-collinear points and parallel blocks. Except for some trivial cases this incidence structure turns out to be a symmetric design, and by studying its existence we can prove much more powerful non-existence theorems.     

Efficiency of connected binary block designs when a single observation is unavailable

In this paper the problem of finding the design efficiency is considered when a single observation is unavailable in a connected binary block design. The explicit expression of efficiency is found for the resulting design when the original design is a balanced incomplete block design or a group divisible, singular or semiregular or regular with ₁>0, design. The efficiency does not depend on the position of the unavailable observation. For a regular group divisible design with ₁>0, the efficiency depends on the position of the unavailable observation. The bounds, both lower and upper, on the efficiency are given in this situation. The efficiencies of designs resulting from a balanced incomplete block design and a group divisible design are in fact high when a single observation is unavailable.The work of the first author is sponsored by the Air Force Office of Scientific Research under Grant AFOSR-90-0092.On leave from Indian Statistical Institute, Calcutta, India. The work of the third author was supported by a grant from the CMDS, Indian Institute of Management, Calcutta.     

On the existence of self-complementary and non-self-complementary strongly regular graphs with Paley parameters

For p an odd prime, let \({{\mathcal A}_{p}}\) be the complete classical affine association scheme whose associate classes correspond to parallel classes of lines in the classical affine plane AG(2, p). It is known that \({{\mathcal A}_{p}}\) is an amorphic association scheme. We investigate rank 3 fusion schemes of \({{\mathcal A}_{p}}\) whose basis graphs have the same parameters as the Paley graphs \({P(p^{2})}\). In contrast to the Paley graphs, the great majority of graphs we detect are non-self-complementary and non-Schurian. In particular, existence of non-self-complementary graphs with Paley parameters is established for \({p \ge 17}\), with an analogous existence result for non-Schurian such graphs when \({p \ge 11}\). We demonstrate that the number of self-complementary and non-self-complementary strongly regular graphs with Paley parameters grows rapidly as \({p \to \infty}\).     

Determination of Sizes of Optimal Three‐Dimensional Optical Orthogonal Codes of Weight Three with the AM‐OPP Restriction

In this paper, we further investigate the constructions on three‐dimensional optical orthogonal codes with the at most one optical pulse per wavelength/time plane restriction (briefly AM‐OPP 3D ‐OOCs) by way of the corresponding designs. Several new auxiliary designs such as incomplete holey group divisible designs and incomplete group divisible packings are introduced and therefore new constructions are presented. As a consequence, the exact number of codewords of an optimal AM‐OPP 3D ‐OOC is finally determined for any positive integers and .     

Quotient divisible abelian groups

An abelian group is called quotient divisible if is of finite torsion-free rank and there exists a free subgroup such that is divisible. The class of quotient divisible groups contains the torsion-free finite rank quotient divisible groups introduced by Beaumont and Pierce and essentially contains the class of self-small mixed groups which has recently been investigated by several authors. We construct a duality from the category of quotient divisible groups and quasi-homomorphisms to the category of torsion-free finite rank groups and quasi-homomorphisms. Our duality when restricted to torsion-free quotient divisible groups coincides with the duality of Arnold and when restricted to coincides with the duality previously constructed by the authors.

     

Strongly divisible 1-designs

If a 1-design, D, admits a tactical decomposition such that the number of blocks through two distinct points depends only on their point classes and further that the number of blocks through any two distinct points of the same point class is a constant, then the decomposition is called a tactical division. In the case of D being a 2-design the terms tactical division and tactical decomposition are synonymous. If the division has c block classes and d point classes then b+dv+c where b is the number of blocks of D and v is the number of points of D. Tactical divisions for which b+d=v+c are of special interest and are called strong. A 1-design admitting a strong tactical division is called strongly divisible.All symmetric and affine 2-designs are strongly divisible and I shall indicate some of the properties of strongly divisible designs that are similar to those of symmetric and affine designs.     

Minimality and (weighted) interpolation in Paley–Wiener spaces

We investigate links between minimality, Carleson condition, and (weighted) interpolation in Paley–Wiener spaces. In particular, we show that the Carleson condition on a sequence Λ together with minimality in Paley–Wiener spaces ${PW_{\tau}^{p}}$ implies the interpolation property of Λ in ${PW_{\tau+\epsilon}^{p}}$ , for every ${\epsilon > 0}$ . This result does not, surprisingly, require uniform minimality.     

Some Comments on Deviation Inequalities for Infinitely Divisible Random Vectors

In this paper, we consider deviation inequalities for infinitely divisible random vectors in R ^k and infinite-dimensional spaces l _p, 1 p We compare the results obtained using the covariance representation for infinitely divisible random vectors with the well-known Talagrand's result on measure concentration phenomenon.     

A family of relative difference sets associated with Hjelmslev structures over finite projective spaces

In this note, we construct a new family of relative difference sets, with parameters n=q^d, m=q^d+...+q+1, k=q^d-1(q^d-1), ₁ =q^d-1(q^d-q^d-1-1) and ₂ =q^d-2(q-1)(q^d-1-1) where q is a prime power and d 2 an integer. The associated symmetric divisible designs admit natural epimorphisms onto the symmetric designs formed by points and hyperplanes in the corresponding projective spaces PG(d,q). As in the theory of Hjelmslev planes, points with the same image can be recognized from having the larger of the two possible joining numbers, and dually. More formally, these symmetric divisible designs are balanced c-H-structures (in the sense of Drake and Jungnickel [2]) with parameters c=q^d-2 (q-1)² and t=q^d-1 (q-1) over PG_d-1(d,q). These are the first examples of balanced non-uniform c-H-structures of type 2; they can be used in known constructions to obtain new balanced c-H-structures (for suitable c) of arbitrary type. In fact, all these results are special cases of a more general construction involving arbitrary difference sets.The author gratefully acknowledges the hospitality of the University of Waterloo and the financial support of NSERC under grant IS-0367.     

New Z-cyclic triplewhist frames and triplewhist tournament designs

Triplewhist tournaments are a specialization of whist tournament designs. The spectrum for triplewhist tournaments on v players is nearly complete. It is now known that triplewhist designs do not exist for v=5,9,12,13 and do exist for all other except, possibly, v=17. Much less is known concerning the existence of Z-cyclic triplewhist tournaments. Indeed, there are many open questions related to the existence of Z-cyclic whist designs. A (triple)whist design is said to be Z-cyclic if the players are elements in Z_m∪A where m=v, A=∅ when and m=v-1, A={∞} when and it is further required that the rounds also be cyclic in the sense that the rounds can be labelled, say, R₁,R₂,… in such a way that R_j+1 is obtained by adding to every element in R_j. The production of Z-cyclic triplewhist designs is particularly challenging when m is divisible by any of 5,9,11,13,17. Here we introduce several new triplewhist frames and use them to construct new infinite families of triplewhist designs, many for the case of m being divisible by at least one of 5,9,11,13,17.