Generalizing orthogonal arrays, a new class of arrays called quasiorthogonal arrays, are introduced and it is shown that fractional factorial plans represented by these arrays are universally optimal under a wide class of models. Some methods of construction of quasi-orthogonal arrays are also described.

We introduce quasi-cyclic codes of index 1 1 2 , construct such codes in terms of polynomials and matrices; and prove that the quasi-cyclic codes of index 1 1 2 are asymptotically good. MSC classes: 94B05, 94B65, 15B52.

Condition (C3) is called the 2–increasing property of C, and VC ([x1, x2]× [y1, y2]) is called the C–volume of the rectangle [x1, x2]× [y1, y2]. According to Sklar’s Theorem, copulas are functions that express the rankinvariant dependence between a pair of continuous random variables and, as such, they have been largely used in statistical applications . In particular, examples of copulas are g...

When the boundary of the curve complex is connected any quasi-isometry is bounded distance from a simplicial automorphism. As a consequence, when the boundary is connected the quasi-isometry type of the curve complex determines the homeomorphism type of the surface.

This paper considers the equivalence problem for quasi-cyclic codes over finite fields. The results obtained are used to construct isodual quasi-cyclic codes.

an ideal i of a ring r is called right baer-ideal if there exists an idempotent e 2 r such that r(i) = er. we know that r is quasi-baer if every ideal of r is a right baer-ideal, r is n-generalized right quasi-baer if for each i e r the ideal in is right baer-ideal, and r is right principaly quasi-baer if every principal right ideal of r is a right baer-ideal. therefore the concept of baer idea...

We present the package SADE (Symmetry Analysis of Differential Equations) for the determination of symmetries and related properties of systems of differential equations. The main methods implemented are: Lie, non classical, Lie-Bäcklund and potential symmetries, invariant solutions, first-integrals, Nöther theorem for both discrete and continuous systems, solution of ordinary differential equa...

We prove that whenever G is negatively curved and ? = G ZZ n acts geometrically on two CAT(0)-spaces X and X 0 , their visual boundaries are ?-equivariantly homeomorphic, answering aarmatively a question of Gromov in this special case. However, we give a simple example that shows that the natural ?-equivariant quasi-isometry from X to X 0 does not continuously extend to a homeomorphism of visua...

We consider quasi-perfect codes in Z over the `p metric, 2 ≤ p <∞. Through a computational approach, we determine all radii for which there are linear quasi-perfect codes for p = 2 and n = 2, 3. Moreover, we study codes with a certain degree of imperfection, a notion that generalizes the quasi-perfect codes. Numerical results concerning the codes with the smallest degree of imperfection are pre...