bluuebunny/crossref_metadata_2025_split huggingface dataset:
A note on Riesz sets and lacunary sets
Authors: Brummelhuis R. G. M. 
Published: April 2009

AbstractW. Rudin has proved that the union of the Riesz set N ⊆ R with a Λ(l)-subset of Z is again a Riesz set. In this note we generalize his result to compact groups whose contains a circle group, thereby extending an earlier F. and M. Riesz theorem for such groups by the author. We also investigate the possibility of constructing Λ(p)-sets for these groups, departing from Λ(p)-sets for the circle group in center.
Fixed points of mappings satisfying semicontractivity conditions
Authors: Schu Jürgen 
Published: April 2009

AbstractLet A be a subset of a Banach space E. A mapping T: A →A is called asymptoically semicontractive if there exists a mapping S: A×A→A and a sequence (kn) in [1, ∞] such that Tx=S(x, x) for all x ∈A while for each fixed x ∈A, S(., x) is asymptotically nonexpansive with sequence (kn) and S(x,.) is strongly compact. Among other things, it is proved that each asymptotically semicontractive self-mpping T of a closed bounded and convex subset A of a uniformly convex Banach space E which satisfies Opial's condition has a fixed point in A, provided s has a certain asymptoticregurity property.
On prime one-sided ideals, bi-ideals and quasi-ideals of a gamma ring
Authors: Booth G. L. , Groenewald N. J. 
Published: April 2009

AbstractLet M be a Γ-ring with right operator ring R. We define one-sided ideals of M and show that there is a one-to-one correspondence between the prime left ideals of M and R and hence that the prime radical of M is the intersection of its prime left ideals. It is shown that if M has left and right unities, then M is left Noetherian if and only if every prime left ideal of M is finitely generated, thus extending a result of Michler for rings to Γ-rings.Bi-ideals and quasi-ideals of M are defined, and their relationships with corresponding structures in R are established. Analogies of various results for rings are obtained for Γ-rings. In particular we show that M is regular if and only if every bi-ideal of M is semi-prime.
Periodic groups with many permutable subgroups
Authors: Longobardi Patrizia , Maj Mercede , Rhemtulla Akbar , Smith Howard 
Published: April 2009

AbstractGroups in which every infinite set of subgroups contains a pair that permute were studied by M. Curzio, J. Lennox, A. Rhemtulla and J. Wiegold. The question whether periodic groups in this class were locally finite was left open. Here we show that if the generators of such a group G are periodic then G is locally finite. This enables us to get the following characterisation. A finitely generated group G is centre-by-finite if and only if every infinite set of subgroups of G contains a pair that permute.
On questions of B. J. Gardner and A. D. Sands
Authors: Beidar K. I. 
Published: April 2009

AbstractAn example of two disjoint special classes whose upper radicals coincide is presented. It is shown that the left hereditary subradical of the hereditary idempotent radical is right hereditary. An example of a hereditary and principally left hereditary radical which is not left hereditary is constructed.
Radicals and subdirect decompositions of Ω-groups
Authors: Mlitz R. , Veldsman S. 
Published: April 2009

AbstractStarting with a class ℳ of Ω-groups, necessary and sufficient conditions on ℳ are given to ensure that the corresponding Hoehnke radical ρ (determined by the subdirect closure of ℳ as semisimple class) is a radical in the sense of Kurosh and Amitsur; has a hereditary semisimple class; satisfies the ADS-property; has a hereditary radical class or satisfies ρN ∩ I ⊆ ρI and lastly, have both a hereditary radical and semisimple class or satisfies ρN ∩ I = ρI.
Pairwise complete regularity as a separation axiom
Authors: Aarts J. M. , Mršević M. 
Published: April 2009

AbstractFocussing on complete regularity, we discuss the separation properties of bitopological spaces. The unifying concept is that of separation by a pair of bases (B1, B2) for the closed sets of a bitopological space (S, J1, J2). For various separation properties a characterization is presented in terms of separation by a pair of closed bases. This is extended to results concerning pairs of subbases. Here the notion of screening by pairs of subbases plays a central role and the characterization of complete regularity in a natural way fits in between those of regularity and normality. In the key lemma the relation with quasi-proximities is exhibited.
Functional least squares estimators in an additive effects outliers model
Authors: Dhar Sunil K. 
Published: April 2009

AbstractConsider the additive effects outliers (A.O.) model where one observes , with The sequence of r.v.s is independent of and , are i.i.d. with d.f. , where the d.f.s Ln, n ≦ 0, are not necessarily known and εj's are i.i.d.. This paper discusses the asymptotic behavior of functional least squares estimators under the above model. Uniform consistency and uniform strong consistency of these estimators are proven. The weak convergence of these estimators to a Gaussian process and their asymptotic biases are also discussed under the above A.O. model.
Fonctions propres de l'opérateur de Laplace-Beltrami associé au bi-disque
Authors: Tahani Taoufiq 
Published: April 2009

AbstractSoit D I'opérateur de Laplace-Beltrami sur le bi-disque. On démontre que les fonctions ζ → Plgr; (ζ, u) provenant du noyau de Poisson associé au bi-disque sont les seules solutions réelles normalisées du système. qui satisfont une certaine hypothèse.
Characterization of two-distance sequences
Authors: Lunnon W. F. , Pleasants P. A. B. 
Published: April 2009

AbstractThree differently defined classes of two-symbol sequences, which we call the two-distance sequences, the linear sequences and the characteristic sequences, have been discussed by a number of authors and some equivalences between them are known. We present a self-contained proof that the three classes are the same (when ambiguous cases of linear sequences are suitably in terpreted). Associated with each sequence is a real invariant (having a different appropriate definition for each of the three classes). We give results on the relation between sequences with the same invariant and on the symmetry of the sequences. The sequences are closely related to Beatty sequences and occur as digitized straight lines and quasicrystals. They also provide examples of minimal word proliferation in formal languages.
Covering in the lattice of subuniverses of a finite distributive lattice
Authors: Lengvárszky Zsolt , McNulty George F. 
Published: April 2009

AbstractThe covering relation in the lattice of subuniverses of a finite distributive lattices is characterized in terms of how new elements in a covering sublattice fit with the sublattice covered. In general, although the lattice of subuniverses of a finite distributive lattice will not be modular, nevertheless we are able to show that certain instances of Dedekind's Transposition Principle still hold. Weakly independent maps play a key role in our arguments.
Lp-multipliers of mixed-norm type on locally compact Vilenkin groups
Authors: Onneweer C. W. , Quek T. S. 
Published: April 2009

AbstractLet G be a locally compact Vilenkin group with dual group Γ. We prove Littlewood-Paley type inequalities corresponding to arbitrary coset decompositions of Γ. These inequalities are then applied to obtain new Lp(G) multiplier theorems. The sharpness of some of these results is also discussed.
Testing modules for irreducibility
Authors: Holt Derek F. , Rees Sarah 
Published: April 2009

AbstractA practical method is described for deciding whether or not a finite-dimensional module for a group over a finite field is reducible or not. In the reducible case, an explicit submodule is found. The method is a generalistaion of the Parker-Norton ‘Meataxe’ algorithm, but it does not depend for its efficiency on the field being small. The principal tools involved are the calculation of the nullspace and the characteristic polynomial of a matrix over a finite field, and the factorisation of the latter. Related algorithms to determine absolute irreducibility and module isomorphism for irreducibles are also described. Details of an implementation in the GAP system, together with some performance analyses are included.
Kronecker classes of fields and covering subgroups of finite groups
Authors: Praeger Cheryl E. 
Published: April 2009

AbstractKronecker classes of algebraci number fields were introduced by W. Jehne in an attempt to understand the extent to which the structure of an extension K: k of algebraic number fields was influenced by the decomposition of primes of k over K. He found an important link between Kronecker equivalent field extensions and a certain covering property of their Galois groups. This surveys recent contributions of Group Theory to the understanding of Kronecker equivalence of algebraic number fields. In particular some group theoretic conjectures related to the Kronecker class of an extension of bounded degree are explored.
The nuclear length of a character
Authors: Wheeler Wayne W. 
Published: April 2009

AbstractIf G is a π-separable group and χ is an irreducible character of G, then Issacs gas defined an associated pair (W, γ), called a nucleus of χ. The nucleus is the last term in a certain chain of pairs (I, Ω), where I is a subgroup of G and Ω is an irreducible character of I. The length of this chain is an invariant of χ that we call the nuclear length. In this paper we study bounds on the nuclear length of χ as a function of the π-length of G and as a function of the character degree χ(1).
A Class of Limit Algebras Associated with Directed Graphs
Authors: Kribs David W. , Solel Baruch 
Published: April 2009

AbstractEvery directed graph defines a Hilbert space and a family of weighted shifts that act on the space. We identify a natural notion of periodicity for such shifts and study their C* -algebras. We prove the algebras generated by all shifts of a fixed period are of Cuntz-Krieger and Toeplitz-Cuntz-Krieger type. The limit C* -algebras determined by an increasing sequence of positive integers, each dividing the next, are proved to be isomorphic to Cuntz-Pimsner algebras and the linking maps are shown to arise as factor maps. We derive a characterization of simplicity and compute the K-groups for these algebras. We prove a classification theorem for the class of algebras generated by simple loop graphs.
Generalized hypergroups and orthogonal polynomials
Authors: Lasser Rupert , Obermaier Josef , Rauhut Holger 
Published: April 2009

AbstractThe concept of semi-bounded generalized hypergroups (SBG hypergroups) is developed. These hypergroups are more special than generalized hypergroups introduced by Obata and Wildberger and more general than discrete hypergroups or even discrete signed hypergroups. The convolution of measures and functions is studied. In the case of commutativity we define the dual objects and prove some basic theorems of Fourier analysis. Furthermore, we investigate the relationship between orthogonal polynomials and generalized hypergroups. We discuss the Jacobi polynomials as an example.
Moduli space of branched superminimal immersions of a compact Riemann surface into S4
Authors: Loo Bonaventure 
Published: April 2009

AbstractIn this paper we describe the moduli spaces of degree d branched superminimal immersions of a compact Riemann surface of genus g into S4. We prove that when d ≥ max {2g, g + 2}, such spaces have the structure of projectivzed fibre products and are path-connected quasi projective varieties of dimension 2d − g + 4. This generalizes known results for spaces of harmonic 2-spheres in S4.
Maximal convergence groups and rank one symmetric spaces
Authors: Basmajian Ara , Zeinalian Mahmoud 
Published: April 2009

abstractWe show that the group of conformal homeomorphisms of the boundary of a rank one symmetric space (except the hyperbolic plane) of noncompact type acts as a maximal convergence group. Moreover, we show that any family of uniformly quasiconformal homeomorphisms has the convergence property. Our theorems generalize results of Gehring and Martin in the real hyperbolic case for Möbius groups. As a consequence, this shows that the maximal convergence subgroups of the group of self homeomorphisms of the d–sphere are not unique up to conjugacy. Finally, we discuss some implications of maximality.
The Monge-Ampère equation and warped products of higher rank
Authors: Bechtluft-Sachs Stefan , Samiou Evangelia 
Published: April 2009

abstractWe show that a warped product Mf = nf has higher rank and nonpositive curvature if and only if f is a convex solution of the Monge-Ampère equation. In this case we show that M contains a Euclidean factor.
Elastica in SO(3)
Authors: Popiel Tomasz , Noakes Lyle 
Published: April 2009

AbstractIn a Riemannian manifold M, elastica are solutions of the Euler-Lagrange equation of the following second order constrained variational problem: find a unit-speed curve in M, interpolating two given points with given initial and final (unit) velocities, of minimal average squared geodesic curvature. We study elastica in Lie groups G equipped with bi-invariant Riemannian metrics, focusing, with a view to applications in engineering and computer graphics, on the group SO(3) of rotations of Euclidean 3-space. For compact G, we show that elastica extend to the whole real line. For G = SO(3), we solve the Euler-Lagrange equation by quadratures.
Local Homomorphisms of Topological Groups
Authors: Zelenyuk Yevhen 
Published: April 2009

AbstractA mapping f : G → s from a left topological group G into a semigroup S is a local homomorphism if for every x є G \ {e}, there is a neighborhood Ux of e such that f (xy) = f (x)f (y) for all y є Ux \ {e}. A local homomorphism f : G → S is onto if for every neighborhood U of e, f(U \ {e}) = S. We show that(1) every countable regular left topological group containing a discrete subset with exactly one accumulation point admits a local homomorphism onto N,(2) it is consistent that every countable topological group containing a discrete subset with exactly one accumulation point admits a local homomorphism onto any countable semigroup,(3) it is consistent that every countable nondiscrete maximally almost periodic topological group admits a local homomorphism onto the countably infinite right zero semigroup.
Strongly zero-dimensional bispaces
Authors: Künzi Hans-Peter A. 
Published: April 2009

AbstractLet Cb be the admissible functorial quasi-uniformity on the completely regular bispaces which is spanned by the upper quasi-uniformity on the real line. Answering a question posed by B. Banaschewski and G. C. L. Brümmer in the affirmative we show that CbX is transitive for every strongly zero-dimensional bispace X.
Maximal subgroups of infinite dimensional general linear groups
Authors: Macpherson Dugald 
Published: April 2009

AbstractLet k be an infinite cardinal, F a field, and let GL(k, F) be the group of all non-singular linear transformations on a ki-dimensional vector space V over F. Various examples are given of maximal subgroups of GL(k, F). These include (i) stabilizers of families of subspaces of V which are like filters or ideals on a set, (ii) almost stabilizers of certain subspaces of V, (iii) almost stabilizers of a direct decomposition of V into two k-dimensional subspaces.It is also noted that GL(k, F) is not the union of any chain of length k of proper subgroups.
Finite one-relator products of two cyclic groups with the relator of arbitrary length
Authors: Campbell C. M. , Heggie P. M. , Robertson E. F. , Thomas R. M. 
Published: April 2009

AbstractIn this paper we consider the groupsG = G(α, n)defined by the presentations. We derive a formula for [G′:″] and determine the order ofGwhenevern≦ 7. We show thatGis a finite soluble group ifnis odd, but thatGcan be infinite whennis even,n≧ 8. We also show thatG(6, 10) is a finite insoluble group involvingPSU(3, 4), and that the groupHwith presentationis a finite group of deficiency zero of order at least 114,967,210,176,000.
Generalised harmonic analysis of a class of nonstationary random fields
Authors: Anh V. V. , Lunney K. E. 
Published: April 2009

AbstractThe paper gives a spectral representation for a class of random fields which are bounded in mean square almost surely. A characterisation of the corresponding spectral measure in the representation is obtained based on Beurling's duality theory and generalised Fourier transforms. A representation for the covariance function of asymptotically stationary random fields is also derived.
Finite group actions on 4-manifolds
Authors: Cho Yong Seung 
Published: April 2009

AbstractLet X be a closed, oriented, smooth 4-manifold with a finite fundamental group and with a non-vanishing Seiberg-Witten invariant. Let G be a finite group. If G acts smoothly and freely on X, then the quotient X/G cannot be decomposed as X1#X2 with (Xi) > 0, i = 1, 2. In addition let X be symplectic and c1(X)2 > 0 and b+2(X) > 3. If σ is a free anti-symplectic involution on X then the Seiberg-Witten invariants on X/σ vanish for all spinc structures on X/σ, and if η is a free symplectic involution on X then the quotients X/σ and X/η are not diffeomorphic to each other.
Moore-Penrose inversion in complex contracted inverse semigroup algebras
Authors: Munn W. D. 
Published: April 2009

AbstractIt is shown that every element of the complex contracted semigroup algebra of an inverse semigroup S = S0 has a Moore-Penrose inverse, with respect to the natural involution, if and only if S is locally finite. In particular, every element of a complex group algebra has such an inverse if and only if the group is locally finite.
The Möbius boundedness of the space Qp
Authors: Pengyan Hu , Jihuai Shi , Wenjun Zhang 
Published: April 2009

AbstractIn this note, a characterization of the Möbius invariant space Qp for the range 1 - 1/n lt; p ≤ 1 is given. As a special case p = 1, we get the Möbius boundedness of BMOA in the space H2. This extends the corresponding result for 1-dimension.
β-transformation, invariant measure and uniform distribution
Authors: Brown Gavin , Yin Qinghe 
Published: April 2009

AbstractLet Tβ be the β-transformation on [0, 1). When β is an integer Tβ is ergodic with respect to Lebesgue measure and almost all orbits {} are uniformly distributed. Here we consider the non-integer case, determine when Tα, Tβ have the same invariant measure and when (appropriately normalised) orbits are uniformly distributed.
The module structure of Solomon's descent algebra
Authors: Blessenohl Dieter , Laue Hartmut 
Published: April 2009

AbstractA close connection is uncovered between the lower central series of the free associative algebra of countable rank and the descending Loewy series of the direct sum of all Solomon descent algebras Δn, n ∈ ℕ0. Each irreducible Δn-module is shown to occur in at most one Loewy section of any principal indecomposable Δn-module.A precise condition for his occurence and formulae for the Cartan numbers are obtained.
Strongly omnipresent operators: general conditions and applications to composition operators
Authors: Bernal-González L. , Calderón-Moreno M. C. , Grosse-Erdmann K.-G. 
Published: April 2009

AbstractThis paper studies the concept of strongly omnipresent operators that was recently introduced by the first two authors. An operator T on the space H(G) of holomorphic functions on a complex domain G is called strongly omnipresent whenever the set of T-monsters is residual in H(G), and a T-monster is a function f such that Tf exhibits an extremely ‘wild’ behaviour near the boundary. We obtain sufficient conditions under which an operator is strongly omnipresent, in particular, we show that every onto linear operator is strongly omnipresent. Using these criteria we completely characterize strongly omnipresent composition and multiplication operators.
Compact semilattices with open principal filters
Authors: Gutik Oleg V. , Rajagopalan M. , Sundaresan K. 
Published: April 2009

AbstractA locally compact semilattice with open principal filters is a zero-dimensional scattered space. Cardinal invariants of locally compact and compact semilattices with open principal filters are investigated. Structure of topological semilattices on the one-point Alexandroff compactification of an uncountable discrete space and linearly ordered compact semilattices with open principal filters are researched.
Vector valued mean-periodic functions on groups
Authors: Devaraj P. , Rana Inder K. 
Published: April 2009

AbstractLetGbe a locally compact Hausdorif abelian group andXbe a complex Banach space. LetC(G, X)denote the space of all continuous functionsf: G → X, with the topology of uniform convergence on compact sets. LetX′ denote the dual ofXwith the weak* topology. LetMc(G, X′)denote the space of allX′-valued compactly supported regular measures of finite variation onG. For a functionf ∈ C(G, X)and μ ∈Mc(G, X′), we define the notion of convolutionf* μ. A functionf ∈ C(G, X)is called mean-periodic if there exists a non-trivial measure μ ∈Mc(G, X′)such thatf* μ = 0. For μ ∈Mc(G, X′), letM P(μ) = {f ∈ C(G, X): f * μ = 0}and letM P(G, X) = ∪μM P(μ). In this paper we analyse the following questions: IsM P(G, X)≠ 0? IsM P(G, X) ≠ C(G, X)? IsM P(G, X)dense inC(G, X)? IsM P(μ) generated by ‘exponential monomials’ in it? We answer these questions for the groupsG= ℝ, the real line, andG= T, the circle group. Problems of spectral analysis and spectral synthesis forC(ℝ,X) andC(T,X) are also analysed.
Discrete series of fusion algebras
Authors: Srinivasan R. , Sunder V. S. , Wildberger N. J. 
Published: April 2009

AbstractWe show that the left regular representation of a countably infinite (discrete) group admits no finite-dimensional invariant subspaces. We also discuss a consequence of this fact, and the reason for our interest in this statement.We then formally state, as a ‘conjecture’, a possible generalisation of the above statement to the context of fusion algebras. We prove the validity of this conjecture in the case of the fusion algebra arising from the dual of a compact Lie group.We finally show, by example, that our conjecture is false as stated, and raise the question of whether there is a ‘good’ class of fusion algebras, which contains (a) the two ‘good classes’ discussed above, namely, discrete groups and compact group duals, and (b) only contains fusion algebras for which the conjecture is valid.
The block structure of complete lattice ordered effect algebras
Authors: Jenča Gejza 
Published: April 2009

AbstractWe prove that every for every complete lattice-ordered effect algebra E there exists an orthomodular lattice O(E) and a surjective full morphism øE: O(E) → E which preserves blocks in both directions: the (pre)imageofa block is always a block. Moreover, there is a 0, 1-lattice embedding : E → O(E).
On the asymptotic behaviour of associated primes of generalized local cohomology modules
Authors: Khashyarmaneshs Kazem , Abbasi Ahmad 
Published: April 2009

AbstractLetMandNbe finitely generated and graded modules over a standard positive graded commutative Noetherian ringR, with irrelevant idealR+. Letbe thenth component of the graded generalized local cohomology module. In this paper we study the asymptotic behavior of AssfR+() as n → –∞ wheneverkis the least integerjfor which the ordinary local cohomology moduleis not finitely generated.
Stable perturbation in Banach algebras
Authors: Xue Yifeng 
Published: April 2009

AbstractLet be a unital Banach algebra. Assume that a has a generalized inverse a+. Then is said to be a stable perturbation of a if . In this paper we give various conditions for stable perturbation of a generalized invertible element and show that the equation is closely related to the gap function . These results will be applied to error estimates for perturbations of the Moore-Penrose inverse in C*–algebras and the Drazin inverse in Banach algebras.