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- Konstantinos Drakakis, Rod Gow, Liam O'Carroll
- 2006 40th Annual Conference on Information…
- 2006

We prove that Welch-constructed Costas arrays are in general not symmetric and that the Golomb-constructed ones are symmetric in two cases only, namely the Lem-pel one and a (rare) second one leading to the construction of dense Golomb rulers. Finally, we look into the (hard) problem of the number of fixed points of a Welch-constructed Costas array and… (More)

- Konstantinos Drakakis, Rod Gow, Liam O'Carroll
- Discrete Mathematics
- 2009

We prove that Welch Costas arrays are in general not symmetric and that there exist two special families of symmetric Golomb Costas arrays: one is the well-known Lempel family, while the other, although less well known, leads actually to the construction of dense Golomb rulers. © 2008 Elsevier B.V. All rights reserved.

- Liam O'Carroll, Francesc Planas-Vilanova, Rafael H. Villarreal
- SIAM J. Discrete Math.
- 2014

We study the degree of nonhomogeneous lattice ideals over arbitrary fields, and give formulas to compute the degree in terms of the torsion of certain factor groups of Zs and in terms of relative volumes of lattice polytopes. We also study primary decompositions of lattice ideals over an arbitrary field using the Eisenbud–Sturmfels theory of binomial ideals… (More)

The main part of the theory of residuated groupoids has been technical and the results apparently diverse in nature. However P. Dubreil and R. Croisot [5], using the concepts of residuated and residual maps, were able to present the basic properties of residuals in a simple unified manner. R. Croisot [3] carried on this study. In this paper we build a… (More)

- Liam O'Carroll
- 2010

A semilattice decomposition of an inverse semigroup has good internal mapping properties. These are used to give natural proofs of some embedding theorems, which were originally proved in a rather artificial way. The reader is referred to [1] for the basic theory of inverse semigroups. In an earlier paper [3] we proved the following embedding result: (1) An… (More)

- Liam O'Carroll
- 2010

In contrast to the semilattice of groups case, an inverse semigroup S which is the union of strongly ^-reflexive inverse subsemigroups need not be strongly £-reflexive. If, however, the union is saturated with respect to the Green's relation <3), and in particular if the union is a disjoint one, then 5 is indeed strongly £-reflexive. This is established by… (More)

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