This paper analyzes a discrete-time $Geo/Geo/c$ queueing system with multiple working vacations and reneging in which customers arrive according to a geometric process. As soon as the system gets empty, the servers go to a working vacations all together. The service times during regular busy period, working vacation period and vacation times are assumed to be geometrically distributed. Customer...

We present sufficient conditions under which effective descent morphisms in a quasivariety of universal algebras are the same as regular epimorphisms and examples for which they are the same as regular epimorphisms satisfying projectivity. 1. Preliminaries A variety is a full subcategory of the category of structures for a first order (one sorted) language, closed under substructures, products ...

The (bounded) hairpin completion, the hairpin lengthening, and their iterated versions are operations on formal languages which have been inspired by the hairpin formation in DNA biochemistry. In this paper we discuss the hairpin formations from a language theoretic point of view. The hairpin completion of a formal language has been defined in 2006. In the first paper on this topic it has been ...

We consider here two formal operations on words inspired by the DNA biochemistry: hairpin lengthening introduced in [10] and its inverse called hairpin shortening. We study the closure of the class of regular languages under the non-iterated and iterated variants of the two operations. The main results are: although any finite number of applications of the hairpin lengthening to a regular langu...

— The opérations of homomorphic repHcation and substitution are strongly independent forfull semiAFLs in the sense that if ££ is afull semiAFL closed under neither homomorphic repHcation nor substitution, then the closure of ^ under homomorphic repHcation («&,(&)) is incomparable with the closure of <£ under substitution {Jta(<£)). The leastfull AFL containing afull semiAFL ££ and closed under ...

‎in this paper some properties of weak regular injectivity for $s$-posets‎, ‎where $s$ is a pomonoid‎, ‎are studied‎. ‎the behaviour‎ ‎of different kinds of weak regular injectivity with products‎, ‎coproducts and direct sums is considered‎. ‎also‎, ‎some‎ ‎characterizations of pomonoids over which all $s$-posets are of‎ ‎some kind of weakly regular injective are obtained‎. ‎further‎, ‎we‎ ‎giv...

Let N and P be smooth closed manifolds of dimensions n and p respectively. Given a Thom-Boardman symbol I, a smooth map f : N → P is called an Ω -regular map if and only if the Thom-Boardman symbol of each singular point of f is not greater than I in the lexicographic order. We will represent the group of all cobordism classes of Ω -regular maps of n-dimensional closed manifolds into P in terms...

We investigate (quantifier-free) spatial constraint languages with equality, contact and connectedness predicates, as well as Boolean operations on regions, interpreted over low-dimensional Euclidean spaces. We show that the complexity of reasoning varies dramatically depending on the dimension of the space and on the type of regions considered. For example, the logic with the interior-connecte...

We consider closure properties of classes of languages under the operation of iterated splicing. The main result is that full abstract families of languages are closed under splicing using a regular set of splicing rules. We have the same result for families of circular strings, with two extra assumptions: the languages in the abstract family must be closed under cyclic permutations and the spl...