*Editors*: H. Amann (Zürich), G. Auchmuty (Houston), D. Bao
(Houston), H. Brezis (Paris), J. Damon (Chapel Hill), K. Davidson (Waterloo), C.
Hagopian (Sacramento), R. M. Hardt (Rice), J. Hausen (Houston), J. A. Johnson
(Houston), J. Nagata (Osaka), V. I. Paulsen (Houston), G. Pisier (College
Station and Paris), S. W. Semmes (Rice)
*Managing Editor*: K. Kaiser (Houston)

Houston Journal of Mathematics

*Contents*

**D.F. Anderson, ** Department of Mathematics, The University of
Tennessee, Knoxville, Tennessee 37996 (anderson@math.utk.edu), **G. Chang, **
Department of Mathematics, University of Incheon, Incheon 402-749
(whan@incheon.ac.kr) and **J. Park, **Department of Mathematics, Inha
University, Incheon 402-751, Korea (jnpark@math.inha.ac.kr).

Generalized Weakly Factorial
Domain,
pp. 1-13.

ABSTRACT.
In this paper, we study integral domains in which each nonzero prime ideal
contains a primary element. We show that if R is an integrally closed domain,
then each nonzero prime ideal of R[X] contains a primary element if and only if
R[X] is an almost weakly factorial domain, if and only if R is an almost weakly
factorial and almost GCD-domain. We also prove that if R is an almost weakly
factorial Noetherian domain, then the integral closure of R is an almost
factorial domain.

**John Dauns, ** Tulane University, New Orleans, Louisiana 70118-5698
(dauns@tulane.edu) and **Yiqiang Zhou, ** Memorial University of
Newfoundland, St.John's, Newfoundland A1C 5S7, Canada (zhou@math.mun.ca)

Type dimension of modules and
chain conditions, pp. 15-23.

ABSTRACT.
For submodules *A,B* of a module *M*, a formula relating the type
dimensions of *M, A* and *M/A* is derived and a formula for the type
dimension of *A+B* is obtained. Modules satisfying both type descending
and ascending chain conditions are characterized.

**Emil Daniel Schwab, **Department of Mathematical Sciences, University of
Oradea, 3700 Oradea, Romania and Department of Mathematical Sciences, University
of Texas at El Paso, El Paso, Texas, 79968 (sehwab@math.utep.edu).

On Triangular Categories,
pp. 25-40.

ABSTRACT.
The triangular categories defined and studied by P. Leroux [1] are particular
Möbius categories. In this paper, considering a lattice-triangular category C,
we study the basic properties of the "category of fractions" I(C) associated to
C (the universal property and the representation theorem for I(C) are also
presented). These properties are determined by the lattices of "C-morphisms
having the same codomain", the lattices that also essentially determine the
incidence algebra of the category C.
*Reference*

[1] Catégories triangulaires. Exemples, applications et problémes, Rapport
de recherche, Univ. du Québec a Montréal (1980), 72 pp.

**Augusto Nobile, **Louisiana State University, Department of Mathematics,
Baton Rouge, LA 70803, USA (nobile@math.lsu.edu).

Singularities of Reflexive
Sheaves,
pp. 41-57.

ABSTRACT.
Singularities of rank-two reflexive sheaves on smooth three-folds are studied.
They must be isolated, and several numerical invariants are attached to them. It
is shown that it is possible to eliminate the singularities by taking quadratic
transformations and suitable transforms of the sheaf.

** Y. Nikolayevsky, **
Department of Mathematics, Melbourne University, Parkville, 3052, Victoria,
Australia
(Y.Nikolayevsky@latrobe.edu.au)

Osserman Manifolds and
Clifford structures , pp. 59-75.

ABSTRACT.
A Riemannian manifold is called Osserman if the eigenvalues of its Jacobi
operator are constant on the unit tangent bundle. R. Osserman conjectured that
every such manifold is two-point homogeneous. A Riemannian manifold has a
Clifford structure, if its curvature tensor can be expressed quadratically in
terms of anticommuting almost Hermitian structures. We study the connection
between the Osserman property and the existence of a Clifford structure and
show, in particular, that a Riemannian manifold with a Clifford structure is
two-point homogeneous, with few exceptions.

**Duran, Carlos E., ** IVIC, matematicas, Aptdo 21827, Caracas 1020A,
Venezuela
(cduran@cauchy.ivic.ve).

Finsler Almost Blaschke
manifolds, pp. 72-92.

ABSTRACT.
A Riemannian (or Finslerian) manifold is said to be a
* Blaschke manifold * if the injectivity radius and the diameter coincide.
The Blaschke conjecture asserts that any Riemannian Blaschke manifold is
isometric to a compact, rank one symmetric space. A manifold is said to be an *
almost-Blaschke manifold * if the injectivity radius and the diameter are
`almost equal' in a scale-independent sense. Given the Blaschke conjecture, it
is natural to expect that a Riemannian almost Blaschke manifold is at least
homeomorphic to a compact, rank one symmetric space. It has been shown by
Duromeric (1984) that this is indeed the case under certain additional
restrictions. The main result of this paper is the construction of examples of
almost-Blaschke Finsler metrics on any product of real of complex Grassmann
manifolds, thus showing that the rigidity related to the Blaschke condition goes
beyond simple calculus of variations techniques which typically apply in a
similar fashion in the Riemannian and Finslerian case. Several related problems
are considered.

**Caldas, Miguel, ** Departamento de Matemática Aplicada, Universidade
Federal Fluminense, Niterói, Rio de Janeiro, CEP 24220-140, Brasil (gmamccs@vm.uff.br) and **Jafari, Saeid,
** Department of Mathematics and Physics, Roskilde University, 4000
Roskilde, Denmark (sjafari@ruc.dk).

On Some Low Separation Axioms
in Topological Spaces pp. 93-104.

ABSTRACT.
We say that a subset A of a topological space X is D Lambda_{delta}-set
if there are two (Lambda,delta)-open subsets (in the sense of Georgiou, Jafari
and Noiri (2001)) U and V, such that A is the diference of U and V with U
as a proper subset of X. If we replace open sets in the usual definition of T_{i}
(i=0,1,2) with D Lambda_{delta}-set (resp. (Lambda,delta)-open ) we
obtain new weak separation axioms. In this paper we study some of the
characterizations and properties of these separation axioms. The implications of
these axioms among themselves are also investigated. Moreover, the notions of
Lambda_{delta}-R_{i} spaces (i=0,1) analogous to R_{i}
spaces (i=0,1) are presented and the necessary and sufficient conditions for a
space to be Lambda_{delta}-R_{0} are given.

**E.E. Grace, ** Department of Mathematics, Arizona State University,
Tempe, Arizona 85287-1804 (egrace@asu.edu) and
**E.J. Vought, **Department of Mathematics and Statistics, California State
University, Chico; Chico, California 95929-0525 (eeevought@worldnet.att.net).

Preservation of Properties of
Continua by Refinable Maps pp. 105-112.

ABSTRACT.
If *f* is a refinable map from a continuum *X* onto *Y* that is
(1) an acyclic curve or (2) not an n-od, then *Y* is (1) an acyclic curve
or (2) not an n-od, respectively. An example is given where *X* is
hereditarily divisible by points and
*Y* is not. A survey of research results concerning preservation of
properties of continua by refinable maps and by the inverses of refinable maps
is included.

**R. Lowen ** and ** D. Vaughan** Department of Mathematics and
Computer Science, University of Antwerp, Antwerp, Belgium (rlow@ruca.ua.ac.be)
and **M. Sioen, ** Department of Mathematics, Vrije Universiteit Brussel,
Brussels, Belgium (msioen@vub.ac.be).

Completing Quasi-metric Spaces --
an Alternative Approach , pp. 113--113.

ABSTRACT.
We define a completion theory for approach spaces which satisfy only a very mild
separation property. The completion agrees with the usual metric completion
theory for metric spaces. We can complete any quasi-metric space, but
remarkably the completion of a quasi-metric space need not be quasi-metric
and can be a genuine approach space. The theory corresponds well with the
strict completion of nearness spaces.

** Amine Fawaz, ** The University of Texas of the Permian Basin,
Department of Mathematics, 4901 East University, Odessa, TX 79762
(fawaz_a@utpb.edu).

A Note on Riemannian Flows on
3-Manifolds , pp. 137-147.

ABSTRACT.
Let L be a Riemannian flow on a closed 3-dimensional manifold M and g a holonomy
invariant metric on M. We give a geometric interpretation of the first Chern
class of the normal bundle to L. We consider a projectable vector field X on M
perpendicular to L and we define the residue of X at a singular point. We give
an expression of the sum of the residues of X which in particular reduces to a
curvature integral over M.

**Salvador Hernandez, ** Universitat Jaume I, Departamento de
Matematicas, 12071-Castellon, Spain (hernande@mat.uji.es)

Uniformly continuous
mappings defined by isometries of spaces of bounded uniformly continuous
functions , pp. 149-155.

ABSTRACT.
Let μ X be a complete metrizable uniform space and let C*(μ X) denote its
algebra of bounded uniformly continuous real-valued functions. In this paper we
show that the metric structure of C*(μ X)determine the structure of μ X up to an
isomorphism of uniform spaces. This result is applied to prove that if (G,R) is
a topological group equipped with its associate right uniformity such that for
every neighbourhood U of the neutral element there is a closed subgroup H
contained in U with the space of left cosets (G/H,R/H) being metrizable, then G
is a SIN group if and only if every left uniformly continuous real-valued
function on G is right uniformly continuous.

**Jack T. Goodykoontz, Jr., **Department of Mathematics, West Virginia
University, Morgantown, West Virginia 26506-6310} (jgoody@math.wvu.edu) and **
Choon Jai Rhee**Department of Mathematics, Wayne State University, Detroit, MI
48202} (rhee@math.wayne.edu).

The Hyperspace of Closed
Connected Subsets of a Euclidean Space, pp. 157-162.

ABSTRACT.
Let R^{n }denote the n-dimensional Euclidean space and C(R^{n })
denote the hyperspace of closed connected subsets of R^{n }, with the
Vietoris topology. The following results are obtained: (1) C(R^{1}) is
homeomorphic to R^{1}×[0,1] and hence is locally compact; (2) If n≥2 and
A∈ C(R^{n }), then C(R^{n }) is locally compact at A if and only
if A is compact; (3) If n≥ 2, then C(R^{n }) is not metrizable; (4) C(R^{n }
) is separable.

**S. R. Foguel**, Institute of Mathematics, The Hebrew University of
Jerusalem, Jerusalem 91904, Israel (foguel@math.huji.ac.il).

On disjoint Markov operators ,
pp. 163-171.

ABSTRACT.
Let (X, Σ, λ) be a probability space, let P_{1}, P_{2 } be two
Markov operators defined on L_{∞} (X, Σ, λ) and assume that P_{1}
and P_{2 } are induced by transition probabilities denoted again by P_{1}
and P_{2 } respectively. For every subset β ⊂ X × X measurable with
respect to the product σ-algebra Σ × Σ, put β' =( X × X)\ β and β_{x} =
{ y ∈ X: (x, y) ∈ β}. Our main result is that the Markov operators P_{1}
and P_{2 } are disjoint iff there exists a Σ × Σ-measurable subset α of
X × X such that P_{1}(x, α_{x}) = P_{2}(x, α'_{x})
= 0 λ-a.e.

**P. Bandyopadhyay, **Stat--Math Division, Indian Statistical Institute,
203, B. T. Road, Kolkata 700 108, India (pradipta@isical.ac.in), **V. P. Fonf, **
Department of Mathematics, Ben-Gurion University of the Negev, P.O. Box 653,
Beer-Sheva 84105, Israel (fonf@cs.bgu.ac.il), **B.-L. Lin**, Department of
Mathematics, The University of Iowa, Iowa City, IA 52242 USA
(bllin@math.uiowa.edu) and **M. Martin, ** Departamento de Analisis
Matematico, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
(mmartins@ugr.es).

Structure of nested
sequences of balls in Banach spaces , pp. 173-193.

ABSTRACT.
In this paper, we study the structure of the union of unbounded nested sequences
of balls, and use them to characterize some geometric properties of X^{*.}
We show that the union of an unbounded nested sequence of balls is a cone if the
centers of the balls lie in a finite dimensional subspace. However, in general,
such a union need not be a cone. In fact, examples can be constructed, up to
renorming, in any infinite dimensional Banach space. We also study when such an
union is the intersection of at most *k* half-spaces, and relate it with
the number of extreme points of any face of the dual ball.

**Juan Bes ** and ** Kit C. Chan, **
Department of Mathematics and Statistics, Bowling Green State University,
Bowling Green, Ohio 43403 (jbes@bgnet.bgsu.edu), (kchan@math.bgsu.edu).

Denseness of Hypercyclic Operators
on a Frechet Space, pp. 195-206.

ABSTRACT.
In 1969 Rolewicz raised the question whether every separable infinite
dimensional Banach space admits a hypercyclic operator. This question was
answered recently in the positive, and the result was generalized to the Frechet
space case, in papers of Ansari, Bernal-Gonzalez, and Bonet and Peris. In the
present paper, we further show that the hypercyclic operators on a separable
infinite dimensional Frechet space form a dense subset of the algebra of
continuous linear operators in the strong operator topology.

**Aïssaoui, Noureddine**, Ecole Normale Supérieure, B.P. 5206 Ben Souda,
Fès, Maroc,
(n.aissaoui@caramail.com)

Weighted strongly Nonlinear
Potential theory pp. 207-230.

ABSTRACT.
Let **A **be an N-function such that the Orlicz space **L _{A} **
becomes reflexive. Let W(m,

**Gang Li, **Department of Mathematics,Yangzhou University, Yangzhou
225002, P. R. China (ligang@cimsl.yzu.edu.cn) and **Jong Kyu Kim, **
Department of Mathematics, Kyungnam University, Masan 631-701, Korea,
(jongkyuk@kyungnam.ac.kr).

Nonlinear Ergodic Theorems for
Commutative Semigroups of Non-Lipschitzian Mappings in Banach Spaces, pp.
231-246.

ABSTRACT.
In this paper, we study the ergodic theorems for commutative semigroups of
asymptotically nonexpansive type mappings in a uniformly convex Banach space
which satisfies Opial's condition.