We introduce the notion of regularized quasi-semigroup of bounded linear operators on Banach spaces and its infinitesimal generator, as a generalization of regularized semigroups of operators.After some examples of such quasi-semigroups, the properties of this family of operators will be studied. Also some applications of regularized quasi-semigroups in the abstract evolution equations will be considered. Next some elementary perturbation results on regularized quasisemigroups will be discussed.4 R s, t ≤ M s t , for some continuous increasing mapping M : 0, ∞ → 0, ∞ .Also regularized semigroups and their connection with abstract Cauchy problems are introduced in 7 and have been studied in 8-12 and many other papers.
Abstract and Applied AnalysisWe mention that if C ∈ B X is an injective operator, then a one-parameter family {T t } ≥0 ⊆ B X is called a C-semigroup if for any s, t ≥ 0 it satisfies T s t C T s T t and T 0 C.In this paper we are going to introduce regularized quasi-semigroups of operators.In Section 2, some useful examples are discussed and elementary properties of regularized quasi-semigroups are studied.In Section 3 regularized quasi-semigroups are applied to find solutions of the abstract evolution equations. Also perturbations of the generator of regularized quasi-semigroups are also considered in this section. Our results are mainly based on the work of Barcenas and Leiva 1 .
Regularized Quasi-SemigroupsSuppose X is a Banach space and {K s, t } s,t≥0 is a two-parameter family of operators in B X . This family is called commutative if for any r, s, t, u ≥ 0,3 {K s, t } s,t≥0 is strongly continuous, that is, lim s,t → s 0 ,t 0 K s, t x − K s 0 , t 0 x 0, x ∈ X; 2.2 4 there exists a continuous and increasing function M : 0, ∞ → 0, ∞ , such that for any s, t > 0, K s, t ≤ M s t .For a C-quasi-semigroups {K s, t } s,t≥0 on Banach space X, let D be the set of all x ∈ X for which the following limits exist in the range of C:
2.3Now for x ∈ D and s ≥ 0, defineCx t . 2.4 {A s } s≥0 is called the infinitesimal generator of the regularized quasi-semigroup {K s, t } s,t≥0 . Somewhere we briefly apply generator instead of infinitesimal generator. Abstract and Applied Analysis 3 Here are some useful examples of regularized quasi-semigroups. Example 2.2. Let {T t } t≥0 be an exponentially bounded strongly continuous C-semigroup on Banach space X, with the generator A. Then K s, t : T t , s,t ≥ 0, 2.5 defines a C-quasi-semigroup with the generator A s A, s ≥ 0, and so D D A . Example 2.3. Let X BUC R , the space of all bounded uniformly continuous functions on R with the supremum-norm. Define C, K s, t ∈ B X , bySubmit your manuscripts at