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vol. 24 num. 1 lang. es<![CDATA[SciELO Logo]]>http://www.scielo.cl/img/en/fbpelogp.gif
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<![CDATA[<B>SEQUENTIAL S*-COMPACTNESS IN L-TOPOLOGICAL SPACES</B><A HREF="#tit"><B>*</B></A>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100001&lng=es&nrm=iso&tlng=es
In this paper, a new notion of sequential compactness is introduced in L-topological spaces, which is called sequentially S*-compactness. If L = [0, 1], sequential ultra-compactness, sequential N-compactness and sequential strong compactness imply sequential S*-compactness, and sequential S*-compactness implies sequential F-compactness. The intersection of a sequentially S*-compact L-set and a closed L-set is sequentially S*-compact. The continuous image of an sequentially S*-compact L-set is sequentially S*-compact. A weakly induced L-space (X, T ) is sequentially S*-compact if and only if (X, [T ]) is sequential compact. The countable product of sequential S*-compact L-sets is sequentially S*-compact<![CDATA[<B>A NOTE ON POLYNOMIAL CHARACTERIZATIONS OF ASPLUND SPACES</B>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100002&lng=es&nrm=iso&tlng=es
In this note we obtain several characterizations of Asplund spaces by means of ideals of Pietsch integral and nuclear polynomials, extending previous results of R. Alencar and R. Cilia-J. Gutierrez<![CDATA[<B>REVERSIBILITY FOR SEMIGROUP ACTIONS</B><A HREF="#tit"><B><I>*</B></I></A><B> </B>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100003&lng=es&nrm=iso&tlng=es
Let Q be a topological space and S a semigroup of local homeomorphisms of Q. The purpose of this paper is to generalize the notion of reversibility and to introduce the reversible sets. And furthermore, it is established a relation between these sets and the control sets for S and it is studied reversibility of semigroup actions on fiber bundles<![CDATA[<B>GENERALIZATIONS OF THE ORLICZ-PETTIS THEOREM</B>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100004&lng=es&nrm=iso&tlng=es
The Orlicz-Pettis Theorem for locally convex spaces asserts that a series in the space which is subseries convergent in the weak topology is actually subseries convergent in the original topology of the space. A subseries convergent series can be viewed as a multiplier convergent series where the terms of the series are multiplied by elements of the scalar sequence space m0 of sequences with finite range. In this paper we show that the conclusion of the Orlicz-Pettis Theorem holds (and can be strengthened) if the multiplier space m0 is replaced by a sequence space with the signed weak gliding hump property<![CDATA[<B>SPECTRAL PROPERTIES OF A NON SELFADJOINT SYSTEM OF DIFFERENTIAL EQUATIONS WITH A SPECTRAL PARAMETER IN THE BOUNDARY CONDITION</B>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100005&lng=es&nrm=iso&tlng=es
<IMG SRC="http:/fbpe/img/proy/v24n1/fig1.jpg" WIDTH=550 HEIGHT=346><![CDATA[<B>REALIZABILITY BY SYMMETRIC NONNEGATIVE MATRICES</B><A HREF="#tit"><B>*</B></A>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100006&lng=es&nrm=iso&tlng=es
Let Λ= {λ1, λ2, . . . , λn} be a set of complex numbers. The nonnegative inverse eigenvalue problem (NIEP) is the problem of determining necessary and su.cient conditions in order that Λmay be the spectrum of an entrywise nonnegative n Χ n matrix. If there exists a nonnegative matrix A with spectrum Λ we say that Λ is realized by A.If the matrix A must be symmetric we have the symmetric nonnegative inverse eigenvalue problem (SNIEP). This paper presents a simple realizability criterion by symmetric nonnegative matrices. The proof is constructive in the sense that one can explicitly construct symmetric nonnegative matrices realizing Λ<![CDATA[<B>A NOTE ON THE FUNDAMENTAL GROUP OF A ONE-POINT EXTENSION</B>]]>
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172005000100007&lng=es&nrm=iso&tlng=es
In this note, we consider an algebra A which is a one-point extension of another algebra B and we study the morphism of fundamental groups induced by the inclusion of (the bound quiver of ) B into (that of ) A. Our main result says that the cokernel of this morphism is a free group and we prove some consequences from this fact