Revistas académicas de la Universidad Católica del Norte
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Perfect measures and the dunford-pettis property
No full textLet X be a completely regular Hausdorff space. We denote by Cb(X) the Banach space of all real-valued bounded continuous function's on X endowed with the supremum-norm. Mp(X) denotes the subspace of the (Cb(X), II II)' of all perfect measures on X and ?p denotes a topology on Cb(X) whose dual is Mp(X).In this paper we give a characterization of E-valued weakly compact operators which are ?-continuous on Cb(X), where E denotes a Banach space. We also prove that (Cb(X),( ?p) has strict Dunford-Pettis property and, if X contains a ?-compact dense subset, (Cb(X), ?p) has Dunford-Pettis property
An impulsive version of Perron's theorem
No full textWe prove the asymptolic stability of the null solution of the impulsive system x' = Ax+ f(t, x) under the influence of externa linear impulses defined by constant matrices {Dj }j. These matrices act at a given fixed and increasing unbonnded sequence of positive times {lj }j· The main idea is to apply a generalization of Bellman's inequality lo such impulsive system
On commutativity of rings with constraints involving a nil subset
No full textThe main theorem of this paper is that a ring R with unity is commutative if and only if there is a nil subset B of R such thatl. for each x ? R, either x ? Z(R) or there is a polynormial f over Z with x - x2 f (x) ? B;2. for each x, y x ? R, there are non-negative integers n > 1, m, r, s depending on a pair of ring elements x,y with x(xmy ± xrynxs) - (xm y ± xrynxs)x = 0.A related result for a nil commutative subset of R is given and the restrictions on the hypothesis of our result are justified by examples
Classes de steinitz et extensions quaternioniennes
No full textLet k be a number field. We prove that the set of Steinitz clases of quadratic extensions K/ k which can be embedded in quaternionic extensions of degree 8, tamely or wildly ramified over k, is the full class group Cl(k) of k. Moreover, we provide explicit formulas to construct these quaternionic extensions
Caractere elliptique et opérations cohomologiques
No full textTheorem 4-6 of [6] gives the expression of Todd character in terms of Landweber-Novikov cohomology operations. In this paper we generalise this result to any I -oriented cohomology theory, and express elliptic character by means of Landweber-Novikov operations
A note on an adaptive algorithm based on Chebyshev coefficients for two-point boundary value problems
No full textAn adaptive version of an algorithm, first described by Greengard and Rokhlin, for numerical solution of two-point boundary value problems is proposed. The algorithm transforms two-point BVPs into integral equations, which are then solved by the Nyström method using Chebyshev quadratures. The dense system of algebraic equations is solved in recursively in O(N) operations. The a posteriori node addition algorithm based on the size of Chebyshev coefficients of the solution approximations yields a robust method. The proposed approach combines the advantages of integral formulation and fast solution of dense linear systems with an automatic resolution of boundary and internal layers
Controllability of two-dimensional bilinear systems : restricted controls and discrete-time
No full textGiven a bilinear control system x = (X+ uY) x with restricted control range, necessary and sufficient conditions for controllability are given under the assumption that the group of the system is Sl (2). These conditions extend known conditions for systems with unrestricted controls and work also for the discrete-time version of the system
Amenidades
No full textProblemas.Presentamos en esta sección una lista de problemas que tienen como finalidad, fundamentalmente, entretener. Pensamos que cualquiera persona con conocimientos generales de matemáticas puede resolverlos
Algebraic probability spaces
No full textIn this chapter we recall some definitions of quantum probability theory in the general framework developed by Accardi and several co-workers. Several expository papers in the series Quantum Probability and Related Topics and two monographes [68], [74] are already available in the literature. We will only illustrate the definitions by two examples which are included only with the aim to give a flavour of the relation with classical probability
Riemann-Liouville fractional trapezium-like inequalities via generalized (m, h₁, h₂)-preinvexity
No full textIn this paper, we derive a fractional integral identity concerning three times differentiable generalized preinvex mappings defined on minvex set. By using of this identity, we obtain new estimates on generalization of trapezium-like inequalities for functions whose third order derivatives are generalized (m, h₁, h₂)-preinvex via Riemann-Liouville fractional integrals. Some interesting special cases of our main result are also considered and shown to be connected with certain known ones