Pseudo-amenability of certain semigroup algebras

In this paper, we investigate the pseudo-amenability of semigroup algebra ? ¹(S), where S is an inverse semigroup with uniformly locally finite idempotent set. In particular, we show that for a Brandt semigroup \(S={\mathcal{M}}^{0}(G,I)\), the pseudo-amenability of ? ¹(S) is equivalent to the amenability of G.     

Left Orders in Special Completely 0-Simple Semigroups

A subsemigroup S of a semigroup Q is a left order in Q, and Q is a semigroup of left quotients of S, if every element of Q can be written as a ^?1 b for some ${a, b\in S}$ with a belonging to a group ${\mathcal{H}}$ -class of Q. Characterizations are provided for semigroups which are left orders in completely 0-simple semigroups in the following classes: without similar ${\mathcal{L}}$ -classes, without contractions, ${\mathcal{R}}$ -unipotent, Brandt semigroups and their generalization. Complete discussion of two examples and an idea for a new concept conclude the paper.     

The cardinality of β A (S J )

Let J be an infinite set and let $I=\mathcal{P}_{f}( J)$ . For i??I, define $\mathcal{B}_{J}( i) =\{ f\mid f:\mathcal{P}( i) \rightarrow \mathcal{P}( i) \} $ and let $$S_{J}=\{ ( i,f) \mid i\in I\text{ and } f\in \mathcal{B}_{J}( i) \}.$$ For (i,f), (k,g)??S _J , define $f\ast g:\mathcal{P}( i\cup k) \rightarrow \mathcal{P}( i\cup k) $ as follows. For $x\in \mathcal{P}( i\cup k) $ , let $$( f\ast g) ( x) =\left\{\begin{array}{l@{\quad }l}g( x) , & \text{if\ }x=\emptyset, \\g( x\cap k) , & \text{if\ }x\cap k\neq \emptyset, \\f( x) , & \text{if\ }x\in \mathcal{P}( i\backslash k)\text{ and }x\neq \emptyset.\end{array}\right.$$ Define (i,f)?(k,g)=(i??k,f?g). It is shown that (S _J ,?) is a semigroup. Let ??S _J denote the collection of all ultrafilters on the set S _J . We consider (??S _J ,?), the compact (Hausdorff) right topological semigroup that is the Stone?C?ech Compactification of the semigroup (S _J ,?) equipped with the discrete topology. Similar to the construction in Grainger (Semigroup Forum 73:234?C242, 2006), it is shown that there is an injective map A???? _A (S _J ) of $\mathcal{P}( J) $ into $\mathcal{P}( \beta S_{J}) $ such that each ?? _A (S _J ) is a closed subsemigroup of (??S _J ,?), the set ?? _J (S _J ) is the smallest ideal of (??S _J ,?) and the collection $\{ \beta_{A}( S_{J}) \mid A\in \mathcal{P}( J) \} $ is a partition of???S _J . The main result is establishing that the cardinality of??? _A (S _J ) is $2^{2^{\vert J\vert }}$ for any?A?J.     

Module amenability of the second dual and module topological center of semigroup algebras

In this paper we define the module topological center of the second dual $\mathcal{A}^{**}$ of a Banach algebra $\mathcal{A}$ which is a Banach $\mathfrak{A}$ -module with compatible actions on another Banach algebra $\mathfrak{A}$ . We calculate the module topological center of ? ¹(S)^**, as an ? ¹(E)-module, for an inverse semigroup S with an upward directed set of idempotents E. We also prove that ? ¹(S)^** is ? ¹(E)-module amenable if and only if an appropriate group homomorphic image of S is finite.     

On the Generality of Assuming that a Family of Continuous Functions Separates Points

For an algebra ${\mathcal{A}}$ of complex-valued, continuous functions on a compact Hausdorff space (X, τ), it is standard practice to assume that ${\mathcal{A}}$ separates points in the sense that for each distinct pair ${x, y \in X}$ , there exists an ${f \in \mathcal{A}}$ such that ${f(x) \neq f(y)}$ . If ${\mathcal{A}}$ does not separate points, it is known that there exists an algebra ${\widehat{\mathcal{A}}}$ on a compact Hausdorff space ${(\widehat{X}, \widehat{\tau})}$ that does separate points such that the map ${\mathcal{A} \mapsto \widehat{\mathcal{A}}}$ is a uniform norm isometric algebra isomorphism. So it is, to a degree, without loss of generality that we assume ${\mathcal{A}}$ separates points. The construction of ${{\widehat{\mathcal{A}}}}$ and ${(\widehat{X}, \widehat{\tau})}$ does not require that ${\mathcal{A}}$ has any algebraic structure nor that ${(X, \tau)}$ has any properties, other than being a topological space. In this work we develop a framework for determining the degree to which separation of points may be assumed without loss of generality for any family ${\mathcal{A}}$ of bounded, complex-valued, continuous functions on any topological space ${(X, \tau)}$ . We also demonstrate that further structures may be preserved by the mapping ${\mathcal{A} \mapsto \widehat{\mathcal{A}}}$ , such as boundaries of weak peak points, the Lipschitz constant when the functions are Lipschitz on a compact metric space, and the involutive structure of real function algebras on compact Hausdorff spaces.     

Topological Aspects of Differential Chains

In this paper we investigate the topological properties of the space of differential chains $\,^{\prime}\mathcal{B}(U)$ defined on an open subset U of a Riemannian manifold M. We show that $\,^{\prime}\mathcal {B}(U)$ is not generally reflexive, identifying a fundamental difference between currents and differential chains. We also give several new brief (though non-constructive) definitions of the space $\,^{\prime}\mathcal{B}(U) $ , and prove that it is a separable ultrabornological (DF)-space. Differential chains are closed under dual versions of the fundamental operators of the Cartan calculus on differential forms (Harrison in Geometric Poincare lemma, Jan 2011, submitted; Operator calculus??the exterior differential complex, Jan 2011, submitted). The space has good properties, some of which are not exhibited by currents $\mathcal{B}'(U)$ or? $\mathcal{D}'(U)$ . For example, chains supported in finitely many points are dense in $\,^{\prime}\mathcal{B}(U)$ for all open U?M, but not generally in the strong dual topology of? $\mathcal{B}'(U)$ .     

A note on κ-uniform points of G^{\mathcal{LUC}}

Let G be a Hausdorff, non-compact, locally compact topological group. We show that, for every infinite cardinal number κ with κ≤κ(G), the set of all κ-uniform points of $G^{\mathcal{LUC}}$ is a closed, two-sided ideal of $G^{\mathcal{LUC}}$ .     

An extension of Mercer’s theory to L p

Let X be a topological space, either locally compact or first countable, endowed with a strictly positive measure ?? and ${\mathcal{K}:L^2(X,\nu)\to L^2(X,\nu)}$ an integral operator generated by a Mercer like kernel K. In this paper we extend Mercer??s theory for K and ${\mathcal{K}}$ under the assumption that the function ${x\in X\to K(x,x)}$ belongs to some L ^p/2(X, ??), p??? 1. In particular, we obtain series representations for K and some powers of ${\mathcal{K}}$ , with convergence in the p-mean, and show that the range of certain powers of ${\mathcal{K}}$ contains continuous functions only. These results are used to estimate the approximation numbers of a modified version of ${\mathcal{K}}$ acting on L ^p (X, ??).     

Jordan τ-Derivations of Locally Matrix Rings

Let R be a prime, locally matrix ring of characteristic not 2 and let Q _ms (R) be the maximal symmetric ring of quotients of R. Suppose that ${\delta}\colon R\to Q_{ms}(R)$ is a Jordan τ-derivation, where τ is an anti-automorphism of R. Then there exists a?∈?Q _ms (R) such that δ(x)?=?xa???aτ(x) for all x?∈?R. Let X be a Banach space over the field ${\mathbb F}$ of real or complex numbers and let ${\mathcal B}(X)$ be the algebra of all bounded linear operators on X. We prove that $Q_{ms}({\mathcal B}(X))={\mathcal B}(X)$ , which provides the viewpoint of ring theory for some results concerning derivations on the algebra ${\mathcal B}(X)$ . In particular, all Jordan τ-derivations of ${\mathcal B}(X)$ are inner if $\text{dim}_{\mathbb F}X>1$ .     

Completely continuous and weakly completely continuous abstract Segal algebras

Let $\mathcal{A}$ be a Banach algebra. It is obtained a necessary and sufficient condition for the complete continuity and also weak complete continuity of symmetric abstract Segal algebras with respect to $\mathcal{A}$ , under the condition of the existence of an approximate identity for $\mathcal{B}$ , bounded in $\mathcal{A}$ . In addition, a necessary condition for the weak complete continuity of $\mathcal{A}$ is given. Moreover, the applications of these results about some group algebras on locally compact groups are obtained.     

Group Connectivity in 3-Edge-Connected Graphs

Let A be an abelian group with |A|?≥ 4. For integers k and l with k?>?0 and l?≥ 0, let ${{\mathcal C}(k, l)}$ denote the family of 2-edge-connected graphs G such that for each edge cut ${S\subseteq E(G)}$ with two or three edges, each component of G ? S has at least (|V(G)| ? l)/k vertices. In this paper, we show that if G is 3-edge-connected and ${G\in {\mathcal C}(6,5)}$ , then G is not A-connected if and only if G can be A-reduced to the Petersen graph.     

On the Intersection of the Normalizers of the \boldsymbol{\cal{F}}-Residuals of Subgroups of a Finite Group

In this paper we give criteria for a finite group to belong to a formation. As applications, recent theorems of Li, Shen, Shi and Qian are generalized. Let G  be a finite group, $\cal F$ a formation and p  a prime. Let $D_{\mathcal {F}}(G)$ be the intersection of the normalizers of the $\cal F$ -residuals of all subgroups of G, and let $D_{\mathcal {F}}^{p}(G)$ be the intersection of the normalizers of $(H^{\cal F}O_{p'}(G))$ for all subgroups H of G. We then define $D_{\mathcal F}^{0}(G)=D_{\mathcal F, p}^{~0}(G)=1$ and $D_{\mathcal F}^{i+1}(G)/D_{\mathcal F}^{i}(G)=D_{\mathcal F}(G/D_{\mathcal F}^{i}(G))$ , $D_{\mathcal F, p}^{i+1}(G)/D_{\mathcal F, p}^{~i}(G)=D_{\mathcal F, p}(G/D_{\mathcal F, p}^{~i}(G))$ . Let $D_{\mathcal {F}}^{\infty}(G)$ and $D_{\mathcal {F}, p}^{~\infty}(G)$ denote the terminal member of the ascending series of $D_{\mathcal F}^{i}(G)$ and $D_{\mathcal F, p}^{~i}(G)$ respectively. In this paper we prove that under certain hypotheses, the the $\cal F$ -residual $G^{\cal F}$ is nilpotent (respectively,p-nilpotent) if and only if $G=D_{\mathcal {F}}^{\infty}(G)$ (respectively, $G=D_{\mathcal {F}, p}^{~\infty}(G)$ ). Further more, if the formation $\cal F$ is either the class of all nilpotent groups or the class of all abelian groups, then $G^{\cal F}$ is p-nilpotent if and only if and only if every cyclic subgroup of G order p and 4 (if p?=?2) is contained in $D_{\mathcal {F}, p}^{~\infty}(G)$ .     

Almost periodic events generated by random flows

Under suitable conditions, a measurable action of a semigroup S on a probability space $(\varOmega,\mathcal {F},\mu )$ generates various σ-fields reflecting the dynamical properties of the associated representation of S and containing the information provided by certain subspaces of $\mathcal {L}^{1}(\mu )$ determined by the representation. For example, the functions in $\mathcal {L}^{1}(\mu )$ with norm relatively compact orbits under S are precisely the $\mathcal {L}^{1}$ functions that are measurable with respect to the σ-field of almost periodic events. In the special case of a measure-preserving action, the minimal projection operator associated with the action is a conditional expectation with respect to this σ-field, leading to a result on transformation of martingales. The unifying construct throughout the paper is the weakly almost periodic compactification of S, a powerful tool that provides a convenient platform to study operator semigroups associated with the action.     

A Characterization of Some Mixed Volumes via the Brunn–Minkowski Inequality

We consider a functional $\mathcal{F}$ on the space of convex bodies in ? ⁿ of the form $$ {\mathcal{F}}(K)=\int_{\mathbb{S}^{n-1}} f(u) \mathrm{S}_{n-1}(K,du), $$ where $f\in C(\mathbb{S}^{n-1})$ is a given continuous function on the unit sphere of ? ⁿ , K is a convex body in ? ⁿ , n≥3, and S _n?1(K,?) is the area measure of K. We prove that $\mathcal{F}$ satisfies an inequality of Brunn–Minkowski type if and only if f is the support function of a convex body, i.e., $\mathcal{F}$ is a mixed volume. As a consequence, we obtain a characterization of translation invariant, continuous valuations which are homogeneous of degree n?1 and satisfy a Brunn–Minkowski type inequality.     

Sharing Set and Normal Families of Entire Functions

Let ${\mathcal{F}}$ be a family of holomorphic functions defined in a domain ${\mathcal{D}}$ , let k( ≥ 2) be a positive integer, and let S = {a, b}, where a and b are two distinct finite complex numbers. If for each ${f \in \mathcal{F}}$ , all zeros of f(z) are of multiplicity at least k, and f and f ^(k) share the set S in ${\mathcal{D}}$ , then ${\mathcal{F}}$ is normal in ${\mathcal{D}}$ . As an application, we prove a uniqueness theorem.     

A class of {\Sigma _{3}^{0}} modular lattices embeddable as principal filters in {\mathcal{L}^{\ast }(V_{\infty })}

Let I ₀ be a a computable basis of the fully effective vector space V _∞ over the computable field F. Let I be a quasimaximal subset of I ₀ that is the intersection of n maximal subsets of the same 1-degree up to *. We prove that the principal filter ${\mathcal{L}^{\ast}(V,\uparrow )}$ of V = cl(I) is isomorphic to the lattice ${\mathcal{L}(n, \overline{F})}$ of subspaces of an n-dimensional space over ${\overline{F}}$ , a ${\Sigma _{3}^{0}}$ extension of F. As a corollary of this and the main result of Dimitrov (Math Log 43:415–424, 2004) we prove that any finite product of the lattices ${(\mathcal{L}(n_{i}, \overline{F }_{i}))_{i=1}^{k}}$ is isomorphic to a principal filter of ${\mathcal{ L}^{\ast}(V_{\infty})}$ . We thus answer Question 5.3 “What are the principal filters of ${\mathcal{L}^{\ast}(V_{\infty}) ?}$ ” posed by Downey and Remmel (Computable algebras and closure systems: coding properties, handbook of recursive mathematics, vol 2, pp 977–1039, Stud Log Found Math, vol 139, North-Holland, Amsterdam, 1998) for spaces that are closures of quasimaximal sets.     

Strict topology on locally compact semigroups

Let S be a locally compact Hausdorff semigroup, and \(\mathfrak {A}\) a solid subalgebra of measure algebra M(S). In this paper, among other results, we find necessary and sufficient conditions on S that implies \(\mathfrak {A}\) is a semi-topological or a topological algebra with respect to the strict topology on M(S). Applications to discrete semigroups, Brandt semigroups and Clifford semigroups are given. An example establishes negatively the open question of Maghsoudi (Semigroup Forum 86:133–139, 2012). Also, we give a correct proof of Proposition 2.1 of Maghsoudi (2012).     

Implicit definition of the quaternary discriminator

Let A be an algebra. A function f: A ⁿ → A is implicitly definable by a system of term equations ${\bigwedge t_{i}(x_{1}, . . . , x_{n}, z) = s_{i}(x_{1}, . . . ,x_{n}, z)}$ if f is the only n-ary operation on A making the identities ${t_{i}(\overrightarrow{x}, f(\overrightarrow{x})) \approx s_{i}(\overrightarrow{x}, f(\overrightarrow{x}))}$ hold in A. Let ${\mathcal{K}}$ be a class of non-trivial algebras. We prove that the quaternary discriminator is implicitly definable on every member of ${\mathcal{K}}$ (via the same system) iff ${\mathcal{K}}$ is contained in the class of relatively simple members of some relatively semisimple quasivariety with equationally definable relative principal congruences. As an application, we obtain a characterization of the relatively permutable members of such type of quasivarieties. Furthermore, we prove that every algebra in such a quasivariety has a unique relatively permutable extension.     

Maximal Regularity for Non-Autonomous Second Order Cauchy Problems

We consider non-autonomous wave equations $$\left\{\begin{array}{ll}\ddot{u}(t) + \mathcal{B}(t) \dot{u}(t) + \mathcal{A}(t)u(t) = f(t) \quad t{\text -}{\rm a.e.}\\ u(0) = u_{0},\, \dot{u}(0) = u_{1}.\\\end{array}\right.$$ where the operators ${\mathcal{A}(t)}$ and ${\mathcal{B}(t)}$ are associated with time-dependent sesquilinear forms ${\mathfrak{a}(t, ., .)}$ and ${\mathfrak{b}}$ defined on a Hilbert space H with the same domain V. The initial values satisfy ${u_0 \in V}$ and ${u_1 \in H}$ . We prove well-posedness and maximal regularity for the solution both in the spaces V′ and H. We apply the results to non-autonomous Robin-boundary conditions and also use maximal regularity to solve a quasilinear problem.