bluuebunny/crossref_metadata_2025 huggingface dataset:
Isomorphisms of multiplier algebras
Authors: Tomiuk B. J.
Published: May 2009

Let A and B be semisimple Banach algebras, and let M1(A) (resp. M1(B)) be the algebra of left multipliers on A (resp. B). Suppose that A is an abstract Segal algebra in B. We find conditions on A and B which imply that M1(A) is topologically algebra isomorphic to M1(B). As a special case we obtain the result of [8] which states that if A is an A*-algebra that is a*-ideal in its B*-algebra completion B and A2 is dense in A then M1(A) is topologically algebra isomorphic to M1(B). We make an application of our main result to right complemented Banach algebras.
Products of idempotents in regular rings
Authors: O'Meara K. C.
Published: May 2009

The problem of describing the subsemigroup generated by the idempotents in various natural semigroups has received the attention of several semigroup theorists ([1], [2], [3], [5], [7]). However, in those cases where the parent semigroup is in fact the multiplicative semigroup of a natural ring, the known ring structure has not been exploited. When this ring structure is taken into account, proofs can often be streamlined and can lead to more general arguments (such as not requiring that the elements of the semigroup be already transformations of some known structure).
Clifford semigroups of left quotients
Authors: Gould Victoria
Published: May 2009

Several definitions of a semigroup of quotients have been proposed and studied by a number of authors. For a survey, the reader may consult Weinert's paper [8]. The motivation for many of these concepts comes from ring theory and the various notions of rings of quotients. We are concerned in this paper with an analogue of the classical ring of quotients, introduced by Fountain and Petrich in [3].
Congruences induced by transitive representations of inverse semigroups
Authors: Petrich Mario , Rankin Stuart
Published: May 2009

Transitive group representations have their analogue for inverse semigroups as discovered by Schein [7]. The right cosets in the group case find their counterpart in the right ω-cosets and the symmetric inverse semigroup plays the role of the symmetric group. The general theory developed by Schein admits a special case discovered independently by Ponizovskiǐ [4] and Reilly [5]. For a discussion of this topic, see [1, §7.3] and [2, Chapter IV].
On orders solely of abelian groups
Authors: Srinivasan S.
Published: May 2009

Let n = be the factorization of an integer n(>1) into prime powers, and set Φ(n):= . In particular, for squarefree n, Φ(n) = phi;(n). Consider the set

.

It is known (from [5]) that A consists precisely of those integers n for which there is no non-abelian group of order n. It is also known (from [7]) that the set

consists solely of integers n with the property that every group of order n is cyclic. We set C′ = A – C.
C*-algebras associated with amalgamated products of groups
Authors: Balogun Bola O.
Published: May 2009

Let V denote the class of discrete groups G which satisfy the following conditions (a), (b) and (c):

(a) G = (A * B; K = φ(H)) is the free product of two groups A and B with the subgroup H amalgamated.

(b) H does not contain the verbal subgroup A(X2) of A and K does not contain the verbal subgroup B(X2)of B.
Flows on hypermaps
Authors: Cori R. , Machi' A.
Published: May 2009

The combinatorial investigation of graphs embedded on surfaces leads one to consider a pair of permutations (σ, α) that generate a transitive group [7]. The permutation α is a fixed-point-free involution and the pair is called a map. When this condition on α is dropped the combinatorial object that arises is called a hypermap. Both maps and hypermaps have a topological description: for maps a classical reference is [13] and for hypermaps such a description can be found in [4] and [6]; a brief account of it will be given below. However, the relationship between maps and hypermaps is not simply that the latter generalize the former. Actually, with every hypermap there is associated a map, its bipartite map, and conversely every bipartite map arises in this way. We do not enter into the details of this question; we refer the reader to the work of Walsh [16]. In this sense hypermaps are, at the same time, a generalization and a special case of maps.
Basis properties for semigroups
Authors: Jones Peter R.
Published: May 2009

A universal algebra A is said to have the basis property (BP) if any two minimal generating sets (bases) for a subalgebra of A have the same cardinality. This property was studied by the author for inverse semigroups in [5, 6]. For instance free inverse semigroups have BP. When treated as universal algebras, a classical theorem of linear algebra states that vector spaces have BP. In this paper we study BP for semigroups.
The Stone-Čech compactification of the rational world
Authors: Stannett M. P.
Published: May 2009

In his paper [11], Peter Neumann considered in detail the cycle structures of elements of Aut(ℚ), the group of all homeomorphisms of the “rational world” ℚ onto itself, and further analyses of Aut(ℚ) and its subgroups have been given by Mekler [9], Bruyns [1], and Truss [13]. My interest in Aut(ℚ) stems from its utility in proving an at first sight rather startling (to a general topologist) result concerning β ℚ, the so-called Stone-Čech compactification of ℚ, namely that βℚ\ℚ is separable, and in fact contains a homogeneous countable dense subspace. (A space X is “homogeneous” provided whenever x, y ∈ X, there is some g ∈ Aut(X) with g(x) = y.) This is in sharp contrast to the spaces βℕ\ℕ and βℝ\ℝ, which are both inseparable.
QF-3 endomorphism rings of Σ-quasi-projective modules
Authors: Pardo José L. Gómez , González Nieves Rodríguez
Published: May 2009

A ring R is called left QF-3 if it has a minimal faithful left R-module. The endomorphism ring of such a module has been recently studied in [7], where conditions are given for it to be a left PF ring or a QF ring. The object of the present paper is to study, more generally, when the endomorphism ring of a Σ-quasi-projective module over any ring R is left QF-3. Necessary and sufficient conditions for this to happen are given in Theorem 2. An useful concept in this investigation is that of a QF-3 module which has been introduced in [11]. If M is a finitely generated quasi-projective module and σ[M] denotes the category of all modules isomorphic to submodules of modules generated by M, then we show that End(RM) is a left QF-3 ring if and only if the quotient module of M modulo its torsion submodule (in the torsion theory of σ[M] canonically defined by M) is a QF-3 module (Corollary 4). Finally, we apply these results to the study of the endomorphism ring of a minimal faithful R-module over a left QF-3 ring, extending some of the results of [7].
Character degrees and derived length in p-groups
Authors: Slattery Michael C.
Published: May 2009

There are a number of theorems which bound d.l.(G), the derived length of a group G, in terms of the size of the set c.d.(G) of irreducible character degrees of G assuming that G is in some particular class of solvable groups ([1], [3], [4], [7]). For instance, Gluck [4] shows that d.l.(G)≤2 |c.d.(G)| for any solvable group, whereas Berger [1] shows that d.l.(G)≤|c.d.(G)| if G has odd order. One of the oldest (and smallest) such bounds is a theorem of Taketa [7] which says that d.l.(G)≤|c.d.(G)| if G is an M-group. Most of the existing theorems are an attempt to extend Taketa's bound to all solvable groups. However, it is not even known for M-groups whether or not this is the best possible bound. This suggests that given a class of solvable groups one might try to find the maximum derived length of a group with n character degrees (i.e. the best possible bound).
Automorphy factors for a Hilbert modular group
Authors: Tsuyumine Shigeaki
Published: May 2009

Let K be a totally real algebraic number field of degree n > 1, and let OK be the maximal order. We denote by гk, the Hilbert modular group SL2(OK) associated with K. On the extent of the weight of an automorphy factor for гK, some restrictions are imposed, not as in the elliptic modular case. Maass [5] showed that the weight is integral for K = ℚ(√5). It was shown by Christian [1] that for any Hilbert modular group it is a rational number with the bounded denominator depending on the group.
On prime divisors of large powers of elements in Noether lattices
Authors: Becerra Linda
Published: May 2009

In [4], R. P. Dilworth introduced the concept of a Noether lattice as an abstraction of the lattice of ideals of a Noetherian ring and he showed that many important properties of Noetherian rings, such as the Noether decomposition theorems, also hold for Noether lattices. It was later shown, in [1], that every Noether lattice is not the lattice of ideals of any Noetherian ring, yet many studies have successfully been undertaken to relate other concepts between Noetherian rings and Noether lattices as had been begun by Dilworth. (See [3], [5], and [6].) In this paper we undertake such a study and show that some results of M. Brodmann in [2] and L. Ratliff in [7] concerning prime divisors of large powers of a fixed element of a commutative Noetherian ring may be generalized and extended to the setting of a Noether lattice. It is shown (Theorem 2.8) that if A is an element of a Noether lattice then all large powers of A have the same prime divisors and (Corollary 3.8) included among this fixed set of primes are those primes that are prime divisors of the integral closure of Ak for some k≧l. We note that the ring proof of this latter result does not generalize directly since it uses the notion of transcendence degree which to our knowledge has no analogue in multiplicative lattices.
Monogenic endomorphisms of a free monoid
Authors: Petrich Mario
Published: May 2009

Free monoids play a central role in the theory of formal languages. Their endomorphisms appear naturally in the context of deterministic OL-schemes which trace their origin to biology. Closely related to such a scheme is a DOL-system which consists of a triple (X, φ, w) where X is a finite set, φ is an endomorphism of the free monoid X* and w ∈ X. The associated language is defined as the set {w, φw, φ2w,…} called a DOL-language. For a full discussion of this subject, we recommend the book [2] by Herman and Rozenberg.
Unique factorisation of normal elements in non-commutative rings
Authors: Jordan D. A.
Published: May 2009

In the literature there are several generalisations to non-commutative rings of the notion of a unique factorisation domain from commutative algebra. This paper follows in the spirit of [1, 3] and is set in the context of Noetherian rings. In [3], A. W. Chatters and the author denned a Noetherian UFR (unique factorisation ring) to be a prime Noetherian ring R in which every non-zero prime ideal contains a prime ideal generated by a non-zero normal element p, that is, by an element p such that pR = Rp. The class of Noetherian UFRs includes the Noetherian UFDs studied by Chatters in [1], while a commutative Noetherian ring is a UFR if and only if it is a UFD in the usual sense. For a Noetherian UFR R, the following are simple consequences of the definition:

(i) every non-zero ideal of R contains a non-zero normal element;

(ii) the set N(R) of non-zero normal elements of R is a unique factorisation monoid in the sense of [4, Chapter 3].
A note on the positive Schur property
Authors: Wnuk Witold
Published: May 2009

The purpose of this note is to characterize those Banach lattices (E, ∥·∥) which have the property:

an operator T: E → c0 is a Dunford-Pettis operator if and only if T is regular (*)

(i.e., T is the difference of two positive operators). Our characterization generalizes a theorem recently proved by Holub [6] and Gretsky and Ostroy [4], who have remarked that the space L1[0, 1] has the property (*). The main result presented here is the following theorem.
Groups whose lattices of normal subgroups are distributive
Authors: Brandl Rolf
Published: May 2009

Various authors deal with distributive sublattices of the lattice ℒ(G) of subgroups of a group G. Perhaps the most basic result in this direction is due to O. Ore [9]: ℒ(G) is distributive if and only if G is locally cyclic.

In [11] and [12] finite groups with distributive lattices of subnormal subgroups were considered, while [3], [4], [7], [8], [10] and [13] deal with the case of groups G whose lattice N(G) of normal subgroups is distributive. Such groups were called DLN-groups in [10].
x4 + dx2y2 + y2= z2: Some cases with only trivial solutions—and a solution Euler missed
Authors: Brown Ezra
Published: May 2009

Mathematicians have studied the diophantine equation of the title ever since the days of Fermat, Leibniz and Euler. In this paper, we review the history of this problem, present several new classes of values of d for which the equation has only trivial solutions, and find a nontrivial solution for d = 85 (a case Euler missed). With these results, the question of whether

has nontrivial solutions is now answered for all d, 0≤d ≤100.
Multiple semidirect products of associative systems
Authors: Steiner Richard
Published: May 2009

Suppose that a groupGis the semidirect product of a subgroupNand a normal subgroupM. Then the elements ofGhave unique expressionsmn(m∈M,n∈N) and the commutator function

mapsNxMintoM. In fact there is an action (by automorphisms) ofNonMgiven by

Conversely, if one is given an action of a groupNon a groupMthen one can construct a semidirect product.
Isomorphic exponential Weyl algebras
Authors: Robinson P. L.
Published: May 2009

Canonically associated to a real symplectic vector space are several associative algebras. The Weyl algebra (generated by the Heisenberg commutation relations) has been the subject of much study; see [1] for example. The exponential Weyl algebra (generated by the canonical commutation relations in exponential form) has been less well studied; see [8].
Totally real surfaces of the six-dimensional sphere
Authors: Bashir M. A.
Published: May 2009

An almost Hermitian manifold (,J, g) with Riemannian connectionis callednearly Kaehlerianif (xJ)X= 0 for any. The typical example is the sphereS6. The nearly Kaehlerian structureJforS6is constructed in a natural way by making use of Cayley division algebra [3]. It is because of this nearly Kaehler, non-Kaehler, structure thatS6has attracted attention. Different classes of submanifolds ofS6have been considered by A. Gray [4], K. Sekigawa [5] and N. Ejiri [2]. In this paper we study 2-dimensional totally real submanifolds ofS6. These are submanifolds with the property that for everyx є M, J(TxM) belongs to the normal bundle v. For this class we have obtained the following result.
An Infinite Construction in Ring Theory
Authors: Whelan E. A.
Published: May 2009

1. Point (3) of the main theorem of our paper [3, Theorem 1.1] is incorrect: this note corrects the main and consequential errors, and shows that (after minor adjustments) almost all the other results of [3], including the remaining seven points of Theorem 1.1, remain correct.

2. The theme of [3] was a family of functors G,(–), defined on the category of rings
with unity for each cardinal t. For t = 0, 1, the results of [3] are unchanged, but, for 2≤t<∞, major, and, for t infinite, less major, corrections are necessary; we therefore assume 2≤t. Terminology and notation are standard or as in [3], and I would like to thank A. W. Chatters and an anonymous referee for comments which prompted this correction.
On approximating Lebesgue integrals by Riemann sums
Authors: Révész Szilárd GY. , Ruzsa Imre Z.
Published: May 2009

Iffis a real function, periodic with period 1, we define

In the whole paper we write ∫ for,mEfor the Lebesgue measure ofE∩ [0,1], whereE⊂ ℝ is any measurable set of period 1, and we also useXEfor the characteristic function of the setE. Consistent with this, the meaning of ℒpis ℒp[0, 1]. For all realxwe have

iffis Riemann-integrable on [0, 1]. However,∫fexists for allf∈ ℒ1and one would wish to extend the validity of (2). As easy examples show, (cf. [3], [7]), (2) does not hold forf∈ ℒpin general ifp< 2. Moreover, Rudin [4] showed that (2) may fail for allxeven for the characteristic function of an open set, and so, to get a reasonable extension, it is natural to weaken (2) to

whereS⊂ ℕ is some “good” increasing subsequence of ℕ. Naturally, for different function classes ℱ ⊂ ℒ1we get different meanings of being good. That is, we introduce the class of ℱ-good sequences as
Factorization and congruence in the arithmetics of Cayley's algebra
Authors: Lamont P. J. C.
Published: May 2009

This paper treats factorization and congruence in the arithmetics of Cayley's algebra C. Results, proved by Rankin [10], on the number of factorizations of a given element in the nonmaximal arithmetics Ho and Jo are reviewed. Further, new results on congruence are established and are used to find the number of factorizations of a prescribed element in the remaining arithmetics, including the maximal arithmetics Jw When computer factorizing a given element, the congruence results can be used as a heuristic device to prune the search tree.
Attainable sets and one-parameter semigroups of sets
Authors: Chon I. , Lawson J. D.
Published: May 2009

The methods of Lie theory have found widespread application in the study of the Lie algebras of vector fields on manifolds that arise naturally in geometric control theory (for some such applications, see [1]). Control systems on Lie groups themselves also have received considerable attention (see, for example, [9]). After reviewing basic facts about control systems on Lie groups, we derive the close relationship between attainable sets and Rådström's theory [12] of one-parameter semigroups of sets (Section 2). These ideas are then linked to the recently emerging Lie theory of semigroups [5]. The authors are indebted to the referee for pointing out some of the pertinent literature and analogous results from the area of geometric control.
Nuclear operators on spaces of continuous vector-valued functions
Authors: Saab Paulette , Smith Brenda
Published: May 2009

Let Ω: be a compact Hausdorff space, let E be a Banach space, and let C(Ω, E) stand for the Banach space of continuous E-valued functions on Ω under supnorm. It is well known [3, p. 182] that if F is a Banach space then any bounded linear operator T:C(Ω, E)→ F has a finitely additive vector measure G defined on the σ-field of Borel subsets of Ω with values in the space ℒ(E, F**) of bounded linear operators from E to the second dual F** of F. The measure G is said to represent T. The purpose of this note is to study the interplay between certain properties of the operator T and properties of the representing measure G. Precisely, one of our goals is to study when one can characterize nuclear operators in terms of their representing measures. This is of course motivated by a well-known theorem of L. Schwartz [5] (see also [3, p. 173]) concerning nuclear operators on spaces C(Ω) of continuous scalar-valued functions. The study of nuclear operators on spaces C(Ω, E) of continuous vector-valued functions was initiated in [1], where the author extended Schwartz's result in case E* has the Radon-Nikodym property. In this paper, we will show that the condition on E* to have the Radon-Nikodym property is necessary to have a Schwartz's type theorem. This leads to a new characterization of dual spaces E* with the Radon-Nikodym property. In [2], it was shown that if T:C(Ω, E)→ F is nuclear than its representing measure G takes its values in the space (E, F) of nuclear operators from E to F. One of the results of this paper is that if T:C(Ω, E)→ F is nuclear then its representing measure G is countably additive and of bounded variation as a vector measure taking its values in (E, F) equipped with the nuclear norm. Finally, we show by easy examples that the above mentioned conditions on the representing measure G do not characterize nuclear operators on C(Ω, E) spaces, and we also look at cases where nuclear operators are indeed characterized by the above two conditions. For all undefined notions and terminologies, we refer the reader to [3].
Topological invariants of weighted homogeneous polynomials
Authors: Szafraniec Zbigniew
Published: May 2009

Let ℝn → ℝ be a weighted homogeneous polynomial such that df(0) = 0, L = {x ∈ Sn−1|f(x) = 0}, and let χ(L) be the Euler characteristic of L. The problem is how to calculate χ(L) in terms of f.
On a periodic neutral logistic equation
Authors: Gopalsamy K. , He Xue-Zhong , Wen Lizhi
Published: May 2009

The oscillatory and asymptotic behaviour of the positive solutions of the autonomous neutral delay logistic equation

with r, c, T, K ∈ (0, ∞) has been recently investigated in [2]. More recently the dynamics of the periodic delay logistic equation

in which r, K are periodic functions of period τ and m is a positive integer is considered in [6]. The purpose of the following analysis is to obtain sufficient conditions for the existence and linear asymptotic stability of a positive periodic solution of a periodic neutral delay logistic equation

in which Ṅ denotes and r, K, c are positive continuous periodic functions of period τ at and m is a positive integer. For the origin and biological relevance of (1.3) we refer to [2].
On a Ramanujan's identity
Authors: Tamba Manvendra
Published: May 2009

In [4], Ramanujan stated the following beautiful identity which was later proved by Bailey [2] and [3];

We denote by S(n) the coefficient of qn on the right hand side of (1). The object of this paper is to prove the following two theorems.
The zeros of a certain family of trinomials
Authors: Dilcher Karl , Nulton James D. , Stolarsky Kenneth B.
Published: May 2009

Many of the classical inequalities of analysis can be written in the form P(x) ≥ 0 for x ∈ I or P(x) > 0 for x ∈ I′, where P(x) is a polynomial and I′ ⊂ I are certain intervals on the real line. This gives rise to the question of where the zeros of P(x) are located. For example, if f is a polynomial with real zeros, then an inequality of Laguerre [8, p. 171 f.] asserts that

for all x. A detailed study of the zeros of this particular P(x) has been made [5].
A structure theorem for SI-Modules
Authors: van Huynh Dinh , Wisbauer Robert
Published: May 2009

An associative ringRis called aleft SI-ringif every singular leftR-module is injective. In Goodearl [4] it is shown that these rings have a finite ring decomposition into a ringKwithK/SocKleft semisimple, and simple rings which are Morita equivalent to left SI-domains.
Somep-algebras and doublep-algebras having only principal congruences
Authors: Beazer R.
Published: May 2009

In [6], Blyth and Varlet characterize those algebras having only principal congruences in some well known classes of algebras having distributive lattice reducts. In particular, they characterize those Stone algebras having only principal congruences. In this paper we characterize those quasi-modularp-algebras having only principal congruences and show on specializing that distributivep-algebras having only principal congruences can be described in exactly the same way as Blyth and Varlet described Stone algebras having the same property. The same problem is addressed for some distributive doublep-algebras.
Quantum stochastic integrals as belated integrals
Authors: Barnett Chris , Lindsay J. M. , Wilde Ivan F.
Published: May 2009

Quantum stochastic integrals have been constructed in various contexts [2, 3, 4, 5, 9] by adapting the construction of the classical L2-Itô-integral with respect to Brownian motion. Thus, the integral is first defined for simple integrands as a finite sum, then one establishes certain isometry relations or suitable bounds to allow the extension, by continuity, to more general integrands. The integrator is typically operator-valued, the integrand is vector-valued or operator-valued and the quantum stochastic integral is then given as a vector in a Hilbert space, or as an operator on the Hilbert space determined by its action on suitable vectors.
Homotopy of compact symmetric spaces
Authors: Burns John M.
Published: May 2009

In recent years a new approach to the study of compact symmetric spaces has been taken by Nagano and Chen [10]. This approach assigned to each pair of antipodal points on a closed geodesic a pair of totally geodesic submanifolds. In this paper we will show how these totally geodesic submanifolds can be used in conjunction with a theorem of Bott to compute homotopy in compact symmetric spaces. Some of the results are already known (see [1], [5], [11] for example) but we include them here for completeness and to illustrate this unified approach. We also exhibit a connection between the second homotopy group of a compact symmetric space and the multiplicity of the highest root. Using this in conjunction with a theorem of J. H. Cheng [6] we obtain a topological characterization of quaternionic symmetric spaces with antiquaternionic involutive isometry. The author would like to thank Prof T. Nagano for all his help and his detailed descriptions of the totally geodesic submanifolds mentioned above.
Inner Bogoliubov automorphisms of the minimal C* Weyl algebra
Authors: Robinson P. L.
Published: May 2009

Within the context of orthogonal geometry, isometries of a real inner product space induce Bogoliubov automorphisms of its associated Clifford algebras. The question whether or not such automorphisms are inner is of considerable interest and importance. Inner Bogoliubov automorphisms were fully characterized for the C* Clifford algebra by Shale and Stinespring [14] and for the W* Clifford algebra by Blattner [2]: each case engenders a corresponding notion of spin group, constructed as a group of units inside the Clifford algebra [4].
An integral formula for compact hypersurfaces in a Euclidean space and its applications
Authors: Deshmukh Sharief
Published: May 2009

Let M be a compact hypersurface in a Euclidena space ℝn+1. The support function p of M is the component of the position vector field of Min ℝn+1 along the unit normal vector field to M, which is a smooth function defined on M. Let S be the scalar curvature of M. The object of the present paper is to prove the following theorems.
A remarkable identity found in Ramanujan's third notebook
Authors: Berndt Bruce C. , Bhargava S.
Published: May 2009

Ramanujan's short third notebook contains 33 pages of unorganized material. On page 386 of the third notebook, in the pagination of the Tata Institute's publication [3], Ramanujan offers the following remarkable identity.
On the Gauss map of ruled surfaces
Authors: Baikoussis Christos , Blair David E.
Published: May 2009

Let M2 be a (connected) surface in Euclidean 3-space E3, and let G:M2→S2(1) ⊂ E3 be its Gauss map. Then, according to a theorem of E. A. Ruh and J. Vilms [3], M2 is a surface of constant mean curvature if and only if, as a map from M2 to S2(1), G is harmonic, or equivalently, if and only if

where δ is the Laplace operator on M2 corresponding to the induced metric on M2 from E3 and where G is seen as a map from M2to E3. A special case of (1.1) is given by

i.e., the case where the Gauss map G:M2→E3 is an eigenfunction of the Laplacian δ on M2.
Relative Ockham lattices: their order-theoretic and algebraic characterisation
Authors: Bordalo G. , Priestley H. A.
Published: May 2009

Given a variety of lattice-ordered algebras, a lattice L is said to be a relative-lattice if every closed interval [a, b] of L may be given the structure of an algebra in (in other words, is the reduct of a member of —not necessarily unique). This paper discusses the characterisation in terms of forbidden substructures of finite relative.stf-lattices. We treat a large class of varieties of distributive-lattice-ordered algebras. For these varieties, the finite algebras can be described dually in terms of finite ordered sets, so that order-theoretic results and techniques prove valuable.
On some classes of weighted composition operators
Authors: Campbell James T. , Jamison James E.
Published: May 2009

Let (X, Σμ) denote a complete a-finite measure space and T: X → X a measurable (T-1A ε Σ each A ε Σ) point transformation from X into itself with the property that the measure μ°T-1 is absolutely continuous with respect to μ. Given any measurable, complex-valued function w(x) on X, and a function f in L2(μ), define WTf(x) via the equation
The modularity of the lattice of varieties of completely regular semigroups and related representations
Authors: Petrich Mario , Reilly Norman R.
Published: May 2009

A semigroup endowed with a unary operation satisfying the identities

is a completely regular semigroup. In several recent papers devoted to the study of the lattice of subvarieties of the variety of completely regular semigroups, various results have been obtained which decompose special intervals in into either direct products or subdirect products. Petrich [14], Hall and Jones [6] and Rasin [20] have shown that certain intervals of the form , where is the trivial variety and are subdirect products of and Pastijn and Trotter [13] show that certain intervals of the form are direct products of the intervals and The main objective of this paper is to develop an appropriate lattice theoretic framework for these representations.
Generalized fractions and Hughes' gradetheoretic analogue of the Cousin complex
Authors: Sharp R. Y. , Yassi M.
Published: May 2009

Let A be a commutative Noetherian ring (with non-zero identity). The Cousin complex C(A) for A is described in [19, Section 2]: it is a complex of A-modules and A-homomorphisms

with the property that, for each n ∈ N0 (we use N0 to denote the set of non-negative integers),

Cohen–Macaulay rings can be characterized in terms of the Cousin complex: A is a Cohen–Macaulay ring if and only if C(A) is exact [19, (4.7)]. Also, the Cousin complex provides a natural minimal injective resolution for a Gorenstein ring (see [19,(5.4)]).
Inverse semigroups with certain types of partial automorphism monoids
Authors: Goberstein Simon M.
Published: May 2009

For an inverse semigroupS, the set of all isomorphisms betweeninverse subsemigroups ofSis an inverse monoid under composition which is denoted by(S) and called the partial automorphism monoid ofS. Kirkwood [7] and Libih [8] determined which groups have Clifford partial automorphism monoids. Here we investigate the structure of inverse semigroups whose partial automorphism monoids belong to certain other important classes of inverse semigroups. First of all, we describe (modulo so called “exceptional” groups) all inverse semigroupsSsuch that(S) is completely semisimple. Secondly, for an inverse semigroupS, we find a convenient description of the greatest idempotent-separating congruence on(S), using a well-known general expression for this congruence due to Howie, and describe all those inverse semigroups whose partial automorphism monoids are fundamental.
Duals of Banach spaces of entire functions
Authors: Anderson J. M. , Duncan J.
Published: May 2009

Let w be a strictly positive function on ℂ and let , respectively denote the Banach spaces of those entire functions φ(z) with ∣φ(z)∣= O(w(z)) and ∣φ(z)∣ = o(w(z)). In this generality, these spaces may contain only constants, but for many functions w(z) these will be interesting Banach spaces with norm

.

We study two specific problems.
Subnormality and generalized commutation relations of families of operators
Authors: Stochel Jerzy Bartłomiej
Published: May 2009

1. Every family of subnormal operators in a Hilbert space fulfils the Halmos-Bram condition on a suitable dense subset of its domain [2], [3]. In [2] and [4] it is shown that the generalized commutation relation implies the Halmos-Bram condition for one operator. In this paper it is proved that the generalized commutation relation implies the Halmos-Bram condition for infinite families of operators (in a special case Jorgensen proved it in a different way for finite families of operators, see [2]) and as an example of the application of this property it is shown that every family of generalized creation operators in the Bargmann space of an infinite order, indexed by mutually orthogonal vectors from I2 is subnormal. See [1] for the definitions.
Union results for thin sets
Authors: Hare Kathryn E.
Published: May 2009

Let G be a compact abelian group and let Γ be its (discrete) dual group. Denote by M(G) the space of complex regular Borel measures on G.

Let E be a subset of Γ. Then:

(i) E is called a Rajchman set if, for all μ ∈M(G) implies

(ii) E is called a set of continuity if given ε > 0 there exists δ > 0 such that if and

(iii) E is called a parallelepiped of dimension N if |E| = 2N and there are two-element sets . (The multiplication indicated here is the group operation.)
Homological stability for On,n over semi-local rings
Authors: Betley Stanislaw
Published: May 2009

Let R be a commutative, semi-local ring. Let On,n be the group of linear automorphisms of R2n which preserve the bilinear form . The main result of this paper is the following theorem.

Theorem A. The natural inclusion of Onn into On,n into On+1,n+1induces an isomorphism on the ith homology group if only n is large enough with respect to i.
Semi-normal operators on uniformly smooth Banach spaces
Authors: Chō Muneo
Published: May 2009

In this paper we shall examine the relationship between the numerical ranges and the spectra for semi-normal operators on uniformly smooth spaces.

Let X be a complex Banach space. We denote by X* the dual space of X and by B(X) the space of all bounded linear operators on X. A linear functional F on B(X) is called state if ∥F∥ = F(I) = 1. When x ε X with ∥x∥ = 1, we denote

D(x) = {f ε X*:∥f∥ = f(x) = l}.
Levels of division algebras
Authors: Leep David B.
Published: May 2009

In [7] the level, sublevel, and product level of finite dimensional central division algebras D over a field F were calculated when F is a local or global field. In Theorem 1.4 of this paper we calculate the same quantities if all finite extensions K of F satisfy ū(K) ≤2, where ū is the Hasse number of a field as defined in [2]. This occurs, for example, if F is an algebraic extension of the function field R(x) where R is a real closed field or hereditarily Euclidean field (see [4]).
The range of a continuous linear functional over a class of functions defined by subordination
Authors: Fournier Richard
Published: May 2009

Let Δ = {z ∈ ℂ ⃒ ⃓z⃓ <1) and H(Δ) the set of analytic functions on Δ. We recall the definition of subordination between two functions, say ƒ and g, analytic on Δ: this means that f(0)= g(0) and there is a function ρ ∈ H (Δ) such that ρ(0) = 0, ⃒ ρ(z)⃒<1 if z ∈ Δ, and f(z) ≡ g(ρ(z)). Subordination between f and g will be denoted by

f<g. The Hadamard product (or convolution) of two functions and in H(Δ)is the function f * g ∈ H(Δ)definedas f * g (z)= .
On ternary quadratic forms that represent zero
Authors: Hooley C.
Published: May 2009

Serre [6] has recently created a theory of some generality in response to a query from Manin about the size of the number N(x) of (indefinite) ternary quadratic forms AX2 + BY2 + CZ2 that represent zero and have coefficients of magnitudes not exceeding x.
The congruence lattice of an ideal extension of semigroups
Authors: Petrich Mario
Published: May 2009

Let S be an ideal of a semigroup V. In such a case, V is an (ideal) extension of S by T = V/S. The problem considered in [2] is the construction of all congruences on V in terms of congruences on S and T. This did not succeed for all congruences but it did for those congruences whose restriction to S is weakly reductive. If the extension is strict, more precise constructions are also given there. With some relatively weak restrictions on S, we are able to obtain in this way all congruences on V in the form indicated above.
A note on the characterisation of eigencurves for certain two parameter eigenvalue problems in ordinary differential equations
Authors: Browne Patrick J. , Sleeman B. D.
Published: May 2009

We are interested in two parameter eigenvalue problems of the form

subject to Dirichlet boundary conditions

The weight function 5 and the potential q will both be assumed to lie in L2[0,1]. The problem (1.1), (1.2) generates eigencurves

in the sense that for any fixed λ, ν(λ) is the nth eigenvalue ν, (according to oscillation indexing) of (1.1), (1.2). These curves are in fact analytic functions of λ and have been the object of considerable study in recent years. The survey paper [1] provides background in this area and itemises properties of eigencurves.
Positive solutions of integrodifferential and difference equations with unbounded delay
Authors: Kiventidis Thomas
Published: May 2009

We establish a necessary and sufficient condition for the existence of a positive solution of the integrodifferential equation

where nis an increasing real-valued function on the interval [0, α); that is, if and only if the characteristic equation

admits a positive root.

Consider the difference equation , where is a sequence of non-negative numbers. We prove this has positive solution if and only if the characteristic equation admits a root in (0, 1). For general results on integrodifferential equations we refer to the book by Burton [1] and the survey article by Corduneanu and Lakshmikantham [2]. Existence of a positive solution and oscillations in integrodifferential equations or in systems of integrodifferential equations recently have been investigated by Ladas, Philos and Sficas [5], Györi and Ladas [4], Philos and Sficas [12], Philos [9], [10], [11].

Recently, there has been some interest in the existence or the non-existence of positive solutions or the oscillation behavior of some difference equations. See Ladas, Philos and Sficas [6], [7].

The purpose of this paper is to investigate the positive solutions of integrodifferential equations (Section 1) and difference equations (Section 2) with unbounded delay. We obtain also some results for integrodifferential and difference inequalities.
Double MSn-algebras and double Kn.m-algebras
Authors: Sequeira M.
Published: May 2009

The variety O2 of all algebras (L; ∧, ∨, f, g, 0, 1) of type (2, 2, 1, 1, 0, 0) such that (L; ∧, ∨, f, 0, 1) and (L; ∧, ∨, g, 0, 1) are Ockham algebras is introduced, and, for n, m εℕ, its subvarieties DMSn, of double MSn-algebras, and DKn,m, of double Kn,m-algebras, are considered. It is shown that DKn,m has equationally definable principal congruences: a description of principal congruences on double Kn,m-algebras is given and simplified for double MSn-algebras. A topological duality for O2-algebras is developed and used to determine the subdirectly irreducible algebras in DKn,m and in DMSn. Finally, MSn-algebras which are reduct of a (unique) double MSn-algebra are characterized.
Some remarks on pramarts and mils
Authors: Wang Zhen-Peng , Xue Xing-Hong
Published: May 2009

Let F be a Banach space, (ω, ℱ, P) a fixed probability space, D a directed set filtering to the right with the order ≤, and (ℱt, D) a stochastic basis of ℱ, i.e. (ℱt, D) is an increasing family of sub-σ-algebras of ℱ:ℱs ⊂ for any s,t ε D and s≤t. Throughout this paper, (Xt) is an F-valued, (ℱt)-adapted sequence, i.e. Xt, is ℱt-measurable, t ε D. We also assume that Xt, ∈ L1, i.e. ∫ ∥Xt∥ <∞. We use I(H) to denote the indicator function of an event H. Let ∞ be a such element: t <∞, t ∈ D, = D ∪ ∞, and ℱ∞ = σ. A stopping time is a map τ:Ω→ such that (τ<t) ∈ ℱt, t ∈ D. A stopping time τ is called simple (countable) if it takes finitely (countably) many values in D(). Let T and Tc be the sets of simple and countable stopping times respectively and Tf = {τ ∈ Tc: τ<∞ a.s.}. Clearly, (T, <) and (Tf, <) are directed sets filtering to the right. For τ ∈ Tc, let

and

= {(Xt): there is σ∈ Tf such that ∫(ι<∞) ∥Xι∥ < ∞, σ ≤ τ ∈ Tc},

= {(Xt):(Xι, ι ∈ T) converges stochastically (i.e. in probability) in the norm topology},

ℰ = {(Xt):(Xι, ι ∈ T) converges essentially in the norm topology}.
A converse of an inequality of G. Bennett
Authors: Alzer Horst
Published: May 2009

We prove that if n>0 is an integer and r>0 is a real number, then

The upper bound is best possible. Inequality (*) is a converse of a result of G. Bennett who proved that Qn(r)>l.
Interpolation and inequalities for functions of exponential type: the Arens irregularity of an extremal algebra
Authors: Crabb M. J. , McGregor C. M.
Published: May 2009

For any compact convex set K ⊂ ℂ there is a unital Banach algebra Ea(K) generated by an element h in which every polynomial in h attains its maximum norm over all Banach algebras subject to the numerical range V(h) being contained in K, [1]. In the case of K a line segment in ℝ, we show here that Ea(K) does not have Arens regular multiplication. We also show that ideas about Ea(K) give simple proofs of, and extend, two inequalities of C. Frappier [4].
Some characterizations of the hereditary pretorsion class of semigroup automata
Authors: Lam Clement S.
Published: May 2009

Let S be a semigroup. A class of S-automata is called a hereditary pretorsion class (HPC) if it is closed under quotients, subautomata, coproducts (disjoint unions) and finite products. In this paper we present two characterizations of HPC. Specifically, we show that there is a bijective correspondence between the HPCs of S-automata, the right linear topologies on S′ and the idempotent preradicals r on the category of S-automata such that the set of automata {M|r(M) = M} is closed under subautomata and finite products.
Embeddings of nonorientable surfaces with totally reducible focal set
Authors: Carter Sheila , Ezentas Ridvan
Published: May 2009

In an earlier paper [5] we introduced the idea of an immersion f: Mm-ℝn with totally reducible focal set. Such an immersion has the property that, for all p ∈ M, the focal set with base p is a union of hyperplanes in the normal plane to f(M) at f(p). Trivially, this always holds if n = m + 1 so we only consider n > m + 1.
Some results on stable p-harmonic maps
Authors: Cheung Leung-Fu , Leung Pui-Fai
Published: May 2009

For each p ∈ [2, ∞)a p-harmonic map f:Mm→Nn is a critical point of the p-energy functional

where Mm is a compact and Nn a complete Riemannian manifold of dimensions m and n respectively. In a recent paper [3], Takeuchi has proved that for a certain class of simply-connected δ-pinched Nn and certain type of hypersurface Nn in ℝn+1, the only stable p-harmonic maps for any compact Mm are the constant maps. Our purpose in this note is to establish the following theorem which complements Takeuchi's results.
Minimal Cockcroft subgroups
Authors: Harlander Jens
Published: May 2009

Consider any groupG. A [G, 2]-complexis a connected 2-dimensional CW-complex with fundamental groupG. IfXis a [G, 2]-complex andLis a subgroup ofG, letXLdenote the covering complex ofXcorresponding to the subgroupL. We say that a [G, 2]-complex isL-Cockcroftif the Hurewicz maphL:π2(X)→;H2(XL)is trivial. In caseL=Gwe callX Cockcroft. There are interesting classes of 2-complexes that have the Cockcroft property. A [G, 2]-complexXisasphericalif π2(X) = 0. It was observed in [4] that a subcomplex of an aspherical 2-complex is Cockcroft. The Cockcroft property is of interest to group theorists as well. LetXbe a [G, 2]-complex modelled on a presentation (〈S; R〉 of the groupG. If it can be shown thatXis Cockcroft, then it follows from Hopf's theorem (see [2, p. 31]) thatH2(G)is isomorphic toH2(X). In particularH2(G)is free abelian. For a survey on the Cockcroft property see Dyer [5]. A collection {Gα: α ∈ Ώ} of subgroups of a groupGthat is totally ordered by inclusion is called achain of subgroups of G. Denning β ≤ α if and only ifGα≤Gβmakes Ώ into a totally ordered set. The main result of this paper is the following theorem.
On the normal cores of certain subgroups of nilpotent groups
Authors: Smith Howard
Published: May 2009

Let G be a group and H a subgroup of finite index in G. Then of course H contains a G-invariant subgroup C such that G/C is finite. In attempting to establish results of a similar nature, where “finite” is replaced by, for example, “finitely generated”, one notices immediately that a quite differently stated hypothesis is required. One reasonable approach would be to consider subgroups H which are “f.g. embedded” in G—indeed, the notion of a polycyclic embedding was utilised by P. Hall in [1].
On the vanishing viscosity in the Cauchy problem for the equations of a nonhomogeneous incompressible fluid
Authors: Itoh Shigeharu
Published: May 2009

Let us consider the Cauchy problem

in QT= ℝ3 × [0, T], where f(x, t), ρ0(x) and v0(x) are given, while the density ρ(x, t), the velocity vector v(x, t)= (υ1(x, t), υ2(x, t), υ3(x, t)) and the pressure p(x, t) are unknowns. The viscosity coefficient μ is assumed to be nonnegative. In these equations, the pressure p is automatically determined (up to a function of t) by ρ and v, namely, by solving the equation

Thus we mention (ρ, v) when we talk about the solution of (1.1:μ).
The kernel and trace operators for ideal extensions of regular semigroups
Authors: Petrich Mario
Published: May 2009

Let V be a regular semigroup and an ideal extension of a semigroup S by a semigroup Q Congruences on V can be represented by triples of the form (σ, P, τ), here called admissible, where a is a congruence on S, P is an ideal of Q and τ is a O-restricted congruence on Q/P satisfying certain conditions. We characterize the trace relation T on V in terms of admissible triples. When the extension V of S is strict, for a congruence v on V given in terms of an admissible triple, we characterize vK, vK, vT and vT again in terms of admissible triples.
Wilson spaces and stable splittings of BTr
Authors: McGibbon C. A.
Published: May 2009

Let Q(X) denote and let BTr denote the classifying space of the r-torus. In [8], Segal showed that Q(BT1) is homotopy equivalent to a product BU × F where BU denotes the classifying space for stable complex vector bundles and F a space with finite homotopy groups. This result has been a very useful one. For example, in [5] it was used to show that up to a stable homotopy equivalence there is only one loop structure on the 3-sphere at each odd prime p. (The subsequent work of Dwyer, Miller, and Wilkerson shows this result is even true unstably, at every prime p.) In [6] it was used to classify, up to homology, the stable self maps of the projective spaces ℂPn and ℍPn. In [5] I asked if a splitting similar to Segal's might exist for Q(BTr) when r≥2. In particular, since the homotopy and homology groups of BU are torsion free it seemed natural to ask if Q(BTr), when r>, could likewise contain a retract with torsion free homology and homotopy groups and whose complement is rationally trivial. The purpose of this note is to show that the answer is no.
Properties (V) and (u) are not three-space properties
Authors: Castillo Jesús M. F. , González Manuel
Published: May 2009

In his fundamental papers [7,8], Pelczynski introduced properties (u), (V), and (V*) as tools as study the structure of Banach spaces. Let X be a Banach space. It is said that X has property (u) if, for every weak Cauchy sequence (xn) in X, there exists a weakly unconditionally Cauchy (wuC) series in X such that the sequence is weakly null. It is said that X has property (V) if, for every Banach space Z, every unconditionally converging operator from X into Z is weakly compact; equivalently, whenever K is a bounded subset of X* such that for every wuC series in X, then K is relatively weakly compact. A Banach space X is said to have property (V*) if whenever K is a bounded subset of X such that 0 for every wuC series in X*, then K is relatively weakly compact. Some well-known results which shall be needed later are contained in the following.
Semigroup varieties closed for the Bruck extension
Authors: Pastijn Francis , Yan Xiaoying
Published: May 2009

We shall show that there exists a chain, order isomorphic to the chain of real numbers, of semigroup varieties closed for the Bruck extension. The least semigroup variety closed for the Bruck extension will be obtained as the union of varieties in an infinite chain of semigroup varieties.