the topology on the primitive ideal space of transformation group c algebras and c c r transformation group c algebras if g 8 is a second countable transformation group and the stability groups are amenable then c g 8 is c c r if and only if the orbits are closed and the stability groups are c c r in addition partial results relating closed orbits to c c r algebras are obtained in the nonseparable case in several cases the topology of the primitive ideal space is calculated explicitly in particular if the stability groups are all contained in a fixed abelian subgroup h then the topology is computed in terms of h and the orbit structure provided c g 8 and c h 8 are eh regular these conditions are automatically met if g is abelian and g 8 is second countable

a theoretical and empirical study on unbiased boundary extended crossover for real valued representation we present a new crossover operator for real coded genetic algorithms employing a novel methodology to remove the inherent bias of pre existing crossover operators this is done by transforming the topology of the hyper rectangular real space by gluing opposite boundaries and designing a boundary extension method for making the fitness function smooth at the glued boundary we show the advantages of the proposed crossover by comparing its performance with those of existing ones on test functions that are commonly used in the literature and a nonlinear regression on a real world dataset

isomorphisms of algebras associated with directed graphs given countable directed graphs g and g we show that the associated tensor algebras open image in new window g and open image in new window g are isomorphic as banach algebras if and only if the graphs g are g are isomorphic for tensor algebras associated with graphs having no sinks or no sources the graph forms an invariant for algebraic isomorphisms we also show that given countable directed graphs g g the free semigroupoid algebras open image in new window and open image in new window are isomorphic as dual algebras if and only if the graphs g are g are isomorphic in particular spatially isomorphic free semigroupoid algebras are unitarily isomorphic for free semigroupoid algebras associated with locally finite directed graphs with no sinks the graph forms an invariant for algebraic isomorphisms as well

semi crossed products of c algebras abstract given a c algebra u and endomorphim there is an associated nonselfadjoint operator algebra z x u called the semi crossed product of u with if is an automorphim z x u can be identified with a subalgebra of the c crossed product z x u if u is commutative and is an automorphim satisfying certain conditions z x u is an operator algebra of the type studied by arveson and josephson suppose s is a locally compact hausdorff space s s is a continuous and proper map and is the endomorphim of u c0 s given by necessary and sufficient conditions on the map are given to insure that the semi crossed product z x c0 s is i semiprime ii semisimple ii strongly semisimple

tensor algebras overc correspondences representations dilations andc envelopes tensor algebras overc correspondences are noncommutative generalizations of the disk algebra they contain as special cases analytic crossed products semi crossed products and popescu s noncommutative disk algebras in this paper a dilation theorem and a commutant lifting theorem for representations of tensor algebras is proved these are used to show that for certainc correspondences thec envelopes in the sense of arveson of the tensor algebras are the cuntz pimsner algebras of the correspondences

invariant subspaces and hyper reflexivity for free semigroup algebras in this paper we obtain a complete description of the invariant subspace structure of an interesting new class of algebras which we call free semigroup algebras this enables us to prove that they are reflexive and moreover to obtain a quantitative measure of the distance to these algebras in terms of the invariant subspaces such algebras are called hyper reflexive this property is very strong but it has been established in only a very few cases moreover the prototypes of this class of algebras are the natural candidate for a non commutative analytic toeplitz algebra on n variables the case we make for this analogy is very compelling in particular in this paper the key to the invariant subspace analysis is a good analogue of the beurling theorem for invariant subspaces of the unilateral shift this leads to a notion of inner outer factorization in these algebras in a sequel to this paper 13 we add to this evidence by showing that there is a natural homomorphism of the automorphism group onto the group of conformal automorphisms of the ball in cn a free semigroup algebra is the weak operator topology closed algebra generated by a set s1 sn of isometries with pairwise orthogonal ranges these conditions are described algebraically by s i sj iji for 1 i j n f

model flames in the boussinesq limit the effects of feedback we have studied the fully nonlinear behavior of premixed flames in a gravitationally stratified medium subject to the boussinesq approximation the key results include the establishment of criteria for when such flames propagate as simple planar flames elucidation of scaling laws for the effective flame speed and a study of the stability properties of these flames the simplicity of some of our scaling results suggests that analytical work may further advance our understandings of buoyant flames

operator algebras and the conjugacy of transformations abstract a family of algebras is associated with each continuous map on a compact hausdorff space these algebras are called conjugacy algebras it is shown that two continuous maps are conjugate if and only if some conjugacy algebra of one is isomorphic to some conjugacy for the other numerous examples of conjugacy algebras are provided

propagation in a fisher kpp equation with non local advection abstract we investigate the influence of a general non local advection term of the form k u to propagation in the one dimensional fisher kpp equation this model is a generalization of the keller segel fisher system when k l 1 r we obtain explicit upper and lower bounds on the propagation speed which are asymptotically sharp and more precise than previous works when k l p r with p 1 and is non increasing in 0 and in 0 we show that the position of the front is of order o t p if p and o e t for some 0 if p and k 0 we use a wide range of techniques in our proofs

a note on the finite time behavior of simulated annealing simulated annealing has proven to be a very successful heuristic for various combinatorial optimization problems it is a randomized algorithm that attempts to find the global optimum with high probability by local exchanges in this paper we give a new proof of the convergence of simulated annealing by applying results about rapidly mixing markov chains with this proof technique it is possible to obtain better bounds for the finite time behavior of simulated annealing than previously known

a directed genetic algorithm for global optimization within the framework of real coded genetic algorithms this paper proposes a directed genetic algorithm dga that introduces a directed crossover operator and a directed mutation operator the operation schemes of these operators borrow from the reflection and the expansion search mode of the nelder mead s simplex method first the taguchi method is employed to study the influence analysis of the parameters in the dga the results show that the parameters in the dga have strong robustness for solving the global optimal solution then several strategies are proposed to enhance the solution accuracy capability of the dga all of the strategies are applied to a set of 30 100 dimensional benchmark functions to prove their superiority over several genetic algorithms finally a cantilevered beam design problem with constrained conditions is used as a practical structural optimization example for demonstrating the very good performance of the proposed method

order preservation in limit algebras abstract the matrix units of a digraph algebra a induce a relation known as the diagonal order on the projections in a masa in the algebra normalizing partial isometries in a act on these projections by conjugation they are said to be order preserving when they respect the diagonal order order preserving embeddings in turn are those embeddings which carry order preserving normalizers to order preserving normalizers this papers studies operator algebras which are direct limits of finite dimensional algebras with order preserving embeddings we give a complete classification of direct limits of full triangular matrix algebras with order preserving embeddings we also investigate the problem of characterizing algebras with order preserving embeddings

meet irreducible ideals and representations of limit algebras in this paper we give criteria for an ideal j of a taf algebra a to be meet irreducible we show that j is meet irreducible if and only if the c envelope of a j is primitive in that case a j admits a faithful nest representation which extends to a representation of the c envelope for a j we also characterize the meet irreducible ideals as the kernels of bounded nest representations this settles the question of whether the n primitive and meet irreducible ideals coincide

existence of traveling waves in the stokes boussinesq system for reactive flows abstract we consider the stokes boussinesq equations in a slanted that is not aligned with gravity s direction cylinder of any dimension and with an arbitrary rayleigh number we prove the existence of a non planar traveling wave solution propagating at a constant speed and satisfying the dirichlet boundary condition in the velocity and the neumann condition in the temperature

the algebraic structure of non commutative analytic toeplitz algebras the non commutative analytic toeplitz algebra is the wot closed algebra generated by the left regular representation of the free semigroup on n generators we develop a detailed picture of the algebraic structure of this algebra in particular we show that there is a canonical homomorphism of the automorphism group onto the group of conformal automorphisms of the complex n ball the k dimensional representations form a generalized maximal ideal space with a canonical surjection onto the ball of k kn matrices which is a homeomorphism over the open ball analogous to the fibration of the maximal ideal space of h over the unit disk in 6 17 18 20 a good case is made that the appropriate analogue for the analytic toeplitz algebra in n non commuting variables is the wotclosed algebra generated by the left regular representation of the free semigroup on n generators the papers cited obtain a compelling analogue of beurling s theorem and inner outer factorization in this paper we add further evidence the main result is a short exact sequence determined by a canonical homomorphism of the automorphism group onto this algebra onto the group of conformal automorphisms of the unit ball of cn the kernel is the subgroup of quasi inner automorphisms which are trivial modulo the wot closed commutator ideal additional evidence of analytic properties comes from the structure of k dimensional completely contractive representations which have a structure very similar to the fibration of the maximal ideal space of h over the unit disk an important tool in our analysis is a detailed structure theory for wot closed right ideals curiously left ideals remain more obscure the non commutative analytic toeplitz algebra ln is determined by the left regular representation of the free semigroup fn on n generators z1 zn which acts on 2 fn by w v wv for v w in fn in particular the algebra ln is the unital wot closed algebra generated by the isometries li zi for 1 i n this algebra and its norm closed version the noncommutative disk algebra were introduced by popescu 19 in an abstract sense in connection with a non commutative von neumann inequality and 1991 mathematics subject classification 47d25 march 9 1997 october 9 1997 final draft first author partially supported by an nserc grant and a killam research fellowship second author partially supported by an nsf grant

a new crossover operator for real coded genetic algorithms abstract in this paper a new real coded crossover operator called the laplace crossover lx is proposed lx is used in conjunction with two well known mutation operators namely the makinen periaux and toivanen mutation mptm and non uniform mutation num to define two new generational genetic algorithms lx mptm and lx num respectively these two genetic algorithms are compared with two existing genetic algorithms hx mptm and hx num which comprise of heuristic crossover operator and same two mutation operators a set of 20 test problems available in the global optimization literature is used to test the performance of these four genetic algorithms to judge the performance of the lx operator two kinds of analysis is performed firstly a pair wise comparison is performed between lx mptm and hx mptm and then between lx num and hx num secondly the overall comparison of performances of all the four genetic algorithms is carried out based on a performance index pi the comparative study shows that laplace crossover lx performs quite well and one of the genetic algorithms defined lx mptm outperforms other genetic algorithms

semicrossed products of operator algebras and their c envelopes abstract let a be a unital operator algebra and let be an automorphism of a that extends to a automorphism of its c envelope c env a we introduce the isometric semicrossed product a is z and we show that c env a is z c env a z in contrast the c envelope of the familiar contractive semicrossed product a z may not equal c env a z our main tool for calculating c envelopes for semicrossed products is a new concept the relative semicrossed product of an operator algebra by an endomorphism as an application of our theory we show that if t x is the tensor algebra of a c correspondence x a and is a extendible automorphism of t x that fixes the diagonal elementwise then the contractive semicrossed product satisfies c env t x z o x z where o x denotes the cuntz pimsner algebra of x a this extends the main result of davidson and katsoulis 2010 6

compact operators and nest representations of limit algebras in this paper we study the nest representations p a alg n of a strongly maximal taf algebra a whose ranges contain non zero compact operators we introduce a particular class of such representations the essential nest representations and we show that their kernels coincide with the completely meet irreducible ideals from this we deduce that there exist enough contractive nest representations with non zero compact operators in their range to separate the points in a using nest representation theory we also give a coordinate free description of the fundamental groupoid for strongly maximal taf algebras for an arbitrary nest representation p a alg n we show that the presence of non zero compact operators in the range of p implies that n is similar to a completely atomic nest if in addition p a is closed then every compact operator in p a can be approximated by sums of rank one operators p a in the case of n ordered nest representations we show that p a contains finite rank operators iff ker fails to be a prime ideal

nest representations and dynamical systems abstract a nest representation is a generalized irreducible representation of a banach algebra on hubert space for a free discrete dynamical system every ideal in the semicrossed product algebra is equal to an intersection of kernels of nest representations a proper subset of all such kernels is a topological space homeomorphic to the space of all discrete finite arcs in the dynamical system with the subarc topology for certain continuous dynamical systems the corresponding set of kernels is isomorphic to the topological space of continuous finite arcs a banach algebra isomorphism of semicrossed products implies orbit order conjugacy of the underlying dynamical systems nest algebras and a non free action are also considered

primitive limit algebras and c envelopes in this paper we study irreducible representations of regular limit subalgebras of af algebras the main result is twofold every closed prime ideal of a limit of direct sums of nest algebras nsaf is primitive and every prime regular limit algebra is primitive a key step is that the quotient of an nsaf algebra by any closed ideal has an af c envelope and this algebra is exhibited as a quotient of a concretely represented af algebra when the ideal is prime the c envelope is primitive the gns construction is used to produce algebraically irreducible in fact n transitive for all n 1 representations for quotients of nsaf algebras by closed prime ideals thus the closed prime ideals of nsaf algebras coincide with the primitive ideals moreover these representations extend to representations of the c envelope of the quotient so that a fortiori these algebras are also operator primitive the same holds true for arbitrary limit algebras and the 0 ideal

automorphisms of some banach algebras of analytic functions abstract in this paper we factorize an arbitrary automorphism of the algebra considered by peters in j peters j functional anal 59 1984 498 534 and its weak version and use it to identify an isomorphism invariant which is the quotient group of the full automorphism group over the maximal ideal fixing automorphisms subgroup

some point derivations for semicrossed products abstract we consider point derivations of semicrossed product algebras in particular we focus on point derivations into the upper triangular n n matrices and show that such point derivations are inner finally we consider point derivations corresponding to periodic points where the range is a standard semicrossed product considered in previous work on point derivations for graph algebras again we conclude that all such point derivations are inner

c envelopes of semicrossed products by lattice ordered abelian semigroups abstract a semicrossed product is a non selfadjoint operator algebra encoding the action of a semigroup on an operator or c algebra we prove that when the positive cone of a discrete lattice ordered abelian group acts on a c algebra the c envelope of the associated semicrossed product is a full corner of a crossed product by the whole group by constructing a c cover that itself is a full corner of a crossed product and computing the shilov ideal we obtain an explicit description of the c envelope this generalizes a result of davidson fuller and kakariadis from z n to the class of all discrete lattice ordered abelian groups

semisimple triangular af algebras abstract we give several necessary and sufficient conditions for a triangular af algebra to be semisimple in particular a triangular af algebra which can be written using the standard embedding infinitely often is semisimple we also give a semisimple triangular af algebra which does not have a presentation of this form if two triangular af algebras have the same peters poon wagner diagonal invariant then either both are semisimple or both are not however we give two algebras with the same diagonal invariant where one has the jacobson radical equal to the strong radical and the other does not semisimplicity can be characterized in terms of power s fundamental relation we give generalizations of these results to triangular subalgebras of groupoid c algebras it is shown that there is a unique maximal bimodule over the diagonal which does not intersect the radical using this we show that the wedderburn principal theorem does not hold for all triangular af algebras a necessary condition for the theorem to hold is that the above mentioned unique bimodule is a subalgebra

triangular uhf algebras in this paper we classify triangular uhf algebras the generic triangular uhf algebra is constructed as follows let pn be any sequence of positive integers such that pm pn whenever m n for each n let tpn be the algebra of all pn pn upper triangular complex matrices and for m n let pn pm tpm tpn be the mapping x 1d x where d pnpm a triangular uhf algebra tuhf of rank pn is any banach algebra that is isometrically isomorphic to the banach algebra inductive limit t limn tpn pm the principal result of the paper is that if j and t are arbitrary tuhf algebras then j is isometrically isomorphic to t if and only if j and t have the same supernatural number

tensor algebras of c correspondences and their c envelopes abstract we show that the c envelope of the tensor algebra of an arbitrary c correspondence x coincides with the cuntz pimsner algebra o x as defined by katsura t katsura on c algebras associated with c correspondences j funct anal 217 2004 366 401 this improves earlier results of muhly and solel p s muhly b solel tensor algebras over c correspondences representations dilations and c envelopes j funct anal 158 1998 389 457 and fowler muhly and raeburn n fowler p muhly i raeburn representations of cuntz pimsner algebras indiana univ math j 52 2003 569 605 who came to the same conclusion under the additional hypothesis that x is strict and faithful

semicrossed products generated by two commuting automorphisms abstract in this paper we study the semicrossed product of a finite dimensional c algebra for two types of z 2 actions and identify them with matrix algebras of analytic functions in two variables we look at the connections with semicrossed by z actions

approximately finitely acting operator algebras let e be an operator algebra on a hilbert space with finite dimensional c algebra c e a classification is given of the locally finite algebras a0 formula ak k and the operator algebras a formula ak k obtained as limits of direct sums of matrix algebras over e with respect to star extendible homomorphisms the invariants in the algebraic case consist of an additive semigroup with scale which is a right module for the semiring ve homu e e of unitary equivalence classes of star extendible homomorphisms this semigroup is referred to as the dimension module invariant in the operator algebra case the invariants consist of a metrized additive semigroup with scale and a contractive right module ve action subcategories of algebras determined by restricted classes of embeddings such as 1 decomposable embeddings between digraph algebras are also classified in terms of simplified dimension modules

ensemble strategies with adaptive evolutionary programming mutation operators such as gaussian levy and cauchy have been used with evolutionary programming ep according to the no free lunch theorem it is impossible for ep with a single mutation operator to outperform always for example classical ep cep with gaussian mutation is better at searching in a local neighborhood while the fast ep fep with the cauchy mutation performs better over a larger neighborhood motivated by these observations we propose an ensemble approach where each mutation operator has its associated population and every population benefits from every function call this approach enables us to benefit from different mutation operators with different parameter values whenever they are effective during different stages of the search process in addition the recently proposed adaptive ep aep using gaussian acep and cauchy afep mutations is also evaluated in the aep the strategy parameter values are adapted based on the search performance in the previous few generations the performance of ensemble is compared with a mixed mutation strategy which integrates several mutation operators into a single algorithm as well as against the aep with a single mutation operator improved performance of the ensemble over the single mutation based algorithms and mixed mutation algorithm is verified using statistical tests

operator algebras and subproduct systems arising from stochastic matrices we study subproduct systems in the sense of shalit and solel arising from stochastic matrices on countable state spaces and their associated operator algebras we focus on the non self adjoint tensor algebra and viselter s generalization of the cuntz pimsner c algebra to the context of subproduct systems suppose that x and y are arveson stinespring subproduct systems associated to two stochastic matrices over a countable set and let t x and t y be their tensor algebras we show that every algebraic isomorphism from t x onto t y is automatically bounded furthermore t x and t y are isometrically isomorphic if and only if x and y are unitarily isomorphic up to a automorphism of l when is finite we prove that t x and t y are algebraically isomorphic if and only if there exists a similarity between x and y up to a automorphism of l moreover we provide an explicit description of the cuntz pimsner algebra o x in the case where is finite and the stochastic matrix is essential

comments on theoretical analysis of evolutionary algorithms with an infinite population size in continuous space i basic properties of selection and mutation with reply this paper aims at establishing fundamental theoretical properties for a class of genetic algorithms in continuous space gacs the algorithms employ operators such as selection crossover and mutation in the framework of a multidimensional euclidean space the paper is divided into two parts the first part concentrates on the basic properties associated with the selection and mutation operators recursive formulae for the gacs in the general infinite population case are derived and their validity is rigorously proven a convergence analysis is presented for the classical case of a quadratic cost function it is shown how the increment of the population mean is driven by its own diversity and follows a modified newton s search sufficient conditions for monotonic increase of the population mean fitness are derived for a more general class of fitness functions satisfying a lipschitz condition the diversification role of the crossover operator is analyzed in part ii the treatment adds much light to the understanding of the underlying mechanism of evolution like algorithms

algebraic isomorphisms of limit algebras we prove that algebraic isomorphisms between limit algebras are automatically continuous and consider the consequences of this result in particular we give partial solutions to a conjecture and an open problem by power as a further consequence we describe epimorphisms between various classes of limit algebras in this paper we study automatic continuity for limit algebras automatic continuity involves algebraic conditions on a linear operator from one banach algebra into another that guarantee the norm continuity of the operator this is a generalization via the open mapping theorem of the uniqueness of norms problem recall that a banach algebra a is said to have a unique banach algebra topology if any two complete algebra norms on a are equivalent so that the norm topology determined by a banach algebra is unique uniqueness of norms automatic continuity and related questions have played an important and long standing role in the theory of banach algebras 6 29 28 10 11 2 limit algebras whose theory has grown rapidly in recent years are the nonselfadjoint analogues of uhf and af c algebras we first prove that algebraic isomorphisms between limit algebras are automatically continuous theorem 1 4 this proof uses the ideal theory of limit algebras as well as key results from the theory of automatic continuity for banach algebras combining this with 23 theorem 8 3 verifies power s conjecture that the c envelope of a limit algebra is an invariant for purely algebraic isomorphisms for limits of finite dimensional nest algebras and in particular for all triangular limit algebras corollary 1 6 in 5 the first two authors studied triangular limit algebras in terms of their lattices of ideals by combining automatic continuity with this work we show that within the class of algebras generated by their order preserving normalizers see below for definitions algebraically isomorphic algebras are isometrically isomorphic theorem 2 5 this shows that the spectrum or fundamental relation 20 a topological binary relation which provides coordinates for limit algebras and is a useful tool in classifications is a complete algebraic isomorphism invariant for this class corollary 2 6 in recent work the second two authors studied primitivity for limit algebras 9 showing that a variety of limit algebras are primitive these results together with automatic continuity give descriptions of epimorphisms between various classes of limit algebras namely lexicographic algebras theorem 3 2 and z analytic algebras theorem 3 3 received by the editors april 6 1998 and in revised form october 7 1999 2000 mathematics subject classification primary 47d25 46k50 46h40 research partially supported by an nsf grant 2000 american mathematical society

structure of free semigroupoid algebras abstract a free semigroupoid algebra is the wot closure of the algebra generated by a tck family of a graph we obtain a structure theory for these algebras analogous to that of free semigroup algebra we clarify the role of absolute continuity and wandering vectors these results are applied to obtain a lebesgue von neumann wold decomposition of tck families along with reflexivity a kaplansky density theorem and classification for free semigroupoid algebras several classes of examples are discussed and developed including self adjoint examples and a classification of atomic free semigroupoid algebras up to unitary equivalence

the lattice of ideals of a triangular af algebra we study triangular af taf algebras in terms of their lattices of closed two sided ideals not isometrically isomorphic taf algebras can have isomorphic lattices of ideals indeed there is an uncountable family of pairwise non isomorphic algebras all with isomorphic lattices of ideals in the positive direction if a and b are strongly maximal taf algebras with isomorphic lattices of ideals then there is a bijective isometry between the subalgebras of a and b generated by their order preserving normalizers this bijective isometry is the sum of an algebra isomorphism and an anti isomorphism using this we show that if the taf algebras are generated by their order preserving normalizers and are triangular subalgebras of primitive c algebras then the lattices of ideals are isomorphic if and only if the algebras are either isometrically isomorphic or anti isomorphic finally we use complete distributivity to show that there are taf algebras whose 0 lattices of ideals can not arise from taf algebras generated by their order preserving 8 normalizers our techniques rely on constructing a topological binary relation based on the lattice of ideals this relation is closely connected to the spectrum or fundamental relation also a topological binary relation of the taf algebra

new bounds for binary covering arrays using simulated annealing covering arrays cas are combinatorial structures specified as a matrix of n rows and k columns over an alphabet on v symbols such that for each set of t columns called the strength of the array every t tuple of symbols is covered recently they have been used to represent interaction test suites for software testing given that they provide economical sized test cases while still preserving important fault detection capabilities this paper introduces an improved implementation of a simulated annealing algorithm called isa for constructing cas of strengths three through six over a binary alphabet i e binary cas extensive experimentation is carried out using 127 well known benchmark instances for assessing its performance with respect to an existing simulated annealing implementation a greedy method and five state of the art algorithms the results show that our algorithm attains 104 new bounds and equals the best known solutions for the other 23 instances consuming reasonable computational time furthermore the implications of using these results as ingredients to recursive constructions are also analyzed

invariant subspaces for algebras of analytic operators associated with a periodic flow on a finite von neumann algebra soit m une algebre de von neumann avec un etat et t t est une representation faiblement continue du cercle unite des automorphismes de m tel que t t soit h l ensemble de tous les x m tels que sp x n z n 0 on etudie les sous espaces invariants de h

uniform design theory and application a uniform design ud seeks design points that are uniformly scattered on the domain it has been popular since 1980 a survey of ud is given in the first portion the fundamental idea and construction method are presented and discussed and examples are given for illustration it is shown that ud s have many desirable properties for a wide variety of applications furthermore we use the global optimization algorithm threshold accepting to generate ud s with low discrepancy the relationship between uniformity and orthogonality is investigated it turns out that most ud s obtained here are indeed orthogonal

operator algebras of monomial ideals in noncommuting variables abstract we study operator algebras arising from monomial ideals in the ring of polynomials in noncommuting variables through the apparatus of subproduct systems and c correspondences we provide a full comparison amongst the related operator algebras for our analysis we isolate a partially defined dynamical system to which we refer as the quantised dynamics of the monomial ideal in addition we revisit several previously considered constructions these include matsumoto s subshift c algebras as well as the tensor and the pimsner algebras associated with dynamical systems or graphs we sort out the various relations by giving concrete conditions and counterexamples that orientate the operator algebras of our context it appears that the boundary c algebras do not arise as the quotient with the compact operators unconditionally we establish a dichotomy to this effect by examining the resulting tensor algebras we identify their boundary representations we analyse their c envelopes and we give criteria for hyperrigidity moreover we completely classify them in terms of the data provided by the monomial ideals for tensor algebras of c correspondences and bounded isomorphisms this is achieved up to the level of local conjugacy in the sense of davidson and roydor for the quantised dynamics for tensor algebras of subproduct systems and algebraic isomorphisms this is achieved up to the level of equality of monomial ideals modulo permutations of the variables in the process we accomplish more in different directions most notably we show that tensor algebras form a complete invariant for isomorphic resp similar subproduct systems of homogeneous ideals up to isometric resp bounded isomorphisms the results on local conjugacy are obtained via an alternative proof of the breakthrough result of davidson and katsoulis on piecewise conjugate systems for our purposes we use appropriate compressions of the fock representation we then apply this alternative proof locally for the partially defined quantised dynamics in this way we avoid the topological graphs machinery and pave the way for further applications these include operator algebras of dynamical systems over commuting contractions or over row commuting contractions

nest representations of directed graph algebras this paper is a comprehensive study of the nest representations for the free semigroupoid algebra mathfrak l g of a countable directed graph g as well as its norm closed counterpart the tensor algebra mathcal t g we prove that the finite dimensional nest representations separate the points in mathfrak l g and a fortiori in mathcal t g the irreducible finite dimensional representations separate the points in mathfrak l g if and only if g is transitive in components which is equivalent to being semisimple also the upper triangular nest representations separate points if and only if for every vertex x in mathcal t g supporting a cycle x also supports at least one loop edge we also study faithful nest representations we prove that mathfrak l g or mathcal t g admits a faithful irreducible representation if and only if g is strongly transitive as a directed graph more generally we obtain a condition on g which is equivalent to the existence of a faithful nest representation we also give a condition that determines the existence of a faithful nest representation for a maximal type mathbb n nest

weak crossed products and a generalisation of a result of sarason abstract in this paper the weak semicrossed products of finite dimensional w algebras by z are identified with algebras of matrices of functions of h t and then they are classified up to algebraic isomorphism in the second part of the paper the weak operator density of matrices of polynomials in the unit ball of our main algebra is shown moreover a generalisation of a result due to d sarason trans amer math soc 127 1967 179 203 about the closure of h t c t in l t is obtained

crossed products of operator algebras applications of takai duality abstract let g be a partially ordered abelian group with haar measure let a g be a dynamical system and let a be the associated semicrossed product using takai duality we establish a stable isomorphism a s a k g ad g where k g denotes the compact operators in the csl algebra alg l g and denotes the right regular representation of g we also show that there exists a complete lattice isomorphism between the invariant ideals of a and the ad invariant ideals of a k g using takai duality we also continue our study of the radical for the crossed product of an operator algebra and we solve open problems stemming from the earlier work of the authors among others we show that the crossed product of a radical operator algebra by a compact abelian group is a radical operator algebra we also show that the permanence of semisimplicity fails for crossed products by r a final section of the paper is devoted to the study of radically tight dynamical systems i e dynamical systems a g for which the identity rad a g rad a g persists a broad class of such dynamical systems is identified

algebraically irreducible representations and structure space of the banach algebra associated with a topological dynamical system abstract if x is a compact hausdorff space and is a homeomorphism of x then a banach algebra l 1 of crossed product type is naturally associated with this topological dynamical system x if x consists of one point then l 1 is the group algebra of the integers we study the algebraically irreducible representations of l 1 on complex vector spaces its primitive ideals and its structure space the finite dimensional algebraically irreducible representations are determined up to algebraic equivalence and a sufficiently rich family of infinite dimensional algebraically irreducible representations is constructed to be able to conclude that l 1 is semisimple all primitive ideals of l 1 are selfadjoint and l 1 is hermitian if there are only periodic points in x if x is metrizable or all points are periodic then all primitive ideals arise as in our construction a part of the structure space of l 1 is conditionally shown to be homeomorphic to the product of a space of finite orbits and t if x is a finite set then the structure space is the topological disjoint union of a number of tori one for each orbit in x if all points of x have the same finite period then it is the product of the orbit space x z and t for rational rotations of t this implies that the structure space is homeomorphic to t 2

primitive triangular uhf algebras abstract we prove that a large class of triangular uhf algebras are primitive we use two avenues to obtain our results a direct approach in which we explicitly construct a faithful algebraically irreducible representation of the algebra on a separable hilbert space as well as an indirect algebraic approach which utilizes the prime ideal structure of the algebra using these results we completely characterize the primitive ideal spaces of all lexicographic algebras an ideal there is primitive if and only if it is closed prime specializing on the algebras a q we obtain a complete classification of their algebraic isomorphisms and epimorphisms through the use of a new invariant involving the primitive ideal space finally we characterize the primitive ideal spaces of z analytic and order preserving algebras and obtain information about their epimorphisms

hardy algebras w correspondences and interpolation theory given a von neumann algebra m and a w correspondence e over m we construct an algebra h e that we call the hardy algebra of e when m open image in new window e h e is the classical hardy space h open image in new window of bounded analytic functions on the unit disc when m open image in new window and e open image in new window h e is the free semigroup algebra studied by popescu davidson and pitts and many others we show that given any faithful normal representation of m on a hilbert space h there is a natural correspondence e over the commutant m called the dual of e and that h e can be realized in terms of b h valued functions on the open unit ball open image in new window e in the space of adjoints of elements in e we prove analogues of the nevanlinna pick theorem in this setting and discover other aspects of the value distribution theory for elements in h e we also analyze the boundary behavior of elements in h e and obtain generalizations of the sz nagy foias functional calculus and the functional calculus of popescu for c n c row contractions the correspondence e has a dual that is naturally isomorphic to e and the commutants of certain so called induced representations of h e can be viewed as induced representations of h e for these induced representations a double commutant theorem is proved

isomorphisms between topological conjugacy algebras a family of algebras which we call topological conjugacy algebras is associated with each proper continuous map on a locally compact hausdorff space assume that i xi xi is a continuous proper map on a locally compact hausdorff space xi for i 1 2 we show that the dynamical systems x1 1 and x2 2 are conjugate if and only if some topological conjugacy algebra of x1 1 is isomorphic as an algebra to some topological conjugacy algebra of x2 2 this implies as a corollary the complete classification of the semicrossed products c0 x z which was previously considered by arveson and josephson 3 peters 19 hadwin and hoover 8 and power 21 we also obtain a complete classification of all semicrossed products of the form a d z where a d denotes the disc algebra and d d a continuous map which is analytic on the interior in this case a surprising dichotomy appears in the classification scheme which depends on the fixed point set of we also classify more general semicrossed products of uniform algebras

the ideal structure of certain nonselfadjoint operator algebras soit x un systeme dynamique localement compact et z x co x la sous algebre close en norme du produit croise zx co x engendre par les puissances non negatives de dans le cas homeomorphisme on determine la structure ideale de ces algebres dans le cas ou agit librement

on the existence of traveling waves in the 3d boussinesq system we extend earlier work on traveling waves in premixed flames in a gravitationally stratified medium subject to the boussinesq approximation for three dimensional channels not aligned with the gravity direction and under the dirichlet boundary conditions in the fluid velocity it is shown that a non planar traveling wave corresponding to a non zero reaction exists under an explicit condition relating the geometry of the crossection of the channel to the magnitude of the prandtl and rayleigh numbers or when the advection term in the flow equations is neglected

operator algebras associated with unitary commutation relations abstract we define nonselfadjoint operator algebras with generators l e 1 l e n l f 1 l f m subject to the unitary commutation relations of the form l e i l f j k l u i j k l l f l l e k where u u i j k l is an n m n m unitary matrix these algebras which generalise the analytic toeplitz algebras of rank 2 graphs with a single vertex are classified up to isometric isomorphism in terms of the matrix u

ensemble of niching algorithms although niching algorithms have been investigated for almost four decades as effective procedures to obtain several good and diverse solutions of an optimization problem no effort has been reported on combining different niching algorithms to form an effective ensemble of niching algorithms in this paper we propose an ensemble of niching algorithms ena and illustrate the concept by an instantiation which is realized using four different parallel populations the offspring of each population is considered by all parallel populations the instantiation is tested on a set of 16 real and binary problems and compared against the single niching methods with respect to searching ability and computation time results confirm that ena method is as good as or better than the best single method in it on every test problem moreover comparison with other state of the art niching algorithms demonstrates the competitiveness of our proposed ena

the jacobson radical for analytic crossed products we characterise the jacobson radical of an analytic crossed product c0 x z answering a question first raised by arveson and josephson in 1969 in fact we characterise the jacobson radical of analytic crossed products c0 x zd this consists of all elements whose fourier coefficients vanish on the recurrent points of the dynamical system and the first one is zero the multidimensional version requires a variation of the notion of recurrence taking into account the various degrees of freedom

applications of the wold decomposition to the study of row contractions associated with directed graphs based on a wold decomposition for families of partial isometries and projections of cuntz krieger toeplitz type we extend several fundamental theorems from the case of single vertex graphs to the general case of countable directed graphs with no sinks we prove a szego type factorization theorem for ckt families which leads to information on the structure of the unit ball in free semigroupoid algebras and show that joint similarity implies joint unitary equivalence for such families for each graph we prove a generalization of von neumann s inequality which applies to row contractions of operators on hilbert space which are related to the graph in a natural way this yields a functional calculus determined by quiver algebras and free semigroupoid algebras we establish a generalization of coburn s theorem for the c algebra of a ckt family and prove a universality theorem for c algebras generated by these families in both cases the c algebras generated by quiver algebras play the universal role

an equivariant brauer group and actions of groups onc algebras suppose that g t is a second countable locally compact trans formation group given by a homomorphism l g homeo t and that a is a separable continuous trace c algebra with spectrum t an action g aut a is said to cover l if the induced action of g on t coincides with the original one we prove that the set brg t of morita equivalence classes of such systems forms a group with multiplication given by the balanced tensor product a b a c0 t b and we refer to brg t as the equivariant brauer group we give a detailed analysis of the structure of brg t in terms of the moore cohomology of the group g and the integral cohomology of the space t using this we can characterize the stable continuous trace c algebras with spectrum t which admit actions covering l in particular we prove that if g r then every stable continuous trace c algebra admits an essentially unique action covering l thereby substantially improving results of raeburn and rosenberg

traveling fronts in a reactive boussinesq system bounds and stability this paper considers a simplified model of active combustion in a fluid flow with the reaction influencing the flow the model consists of a reaction diffusion advection equation coupled with an incompressible navier stokes system under the boussinesq approximation in an infinite vertical strip we prove that for certain ignition nonlinearities including all that are c2 and for any domain width planar traveling front solutions are nonlinearly and exponentially stable within certain weighted h2 spaces provided that the rayleigh number is small enough the same result holds for bistable nonlinearities in unweighted h2 spaces we also obtain uniform bounds on the nusselt number the bulk burning rate and the average maximum vertical velocity for chemistries that include bistable and ignition nonlinearities

on c algebras associated with c correspondences abstract we study c algebras arising from c correspondences which were introduced by the author we prove the gauge invariant uniqueness theorem and obtain conditions for our c algebras to be nuclear exact or satisfy the universal coefficient theorem we also obtain a 6 term exact sequence of k groups involving the k groups of our c algebras

on some subalgebras of von neumann algebras with analyticity let m g be a covariant system on a locally compact abelian group g with the totally ordered dual group g which admits the positive semigroup g let h be the associated analytic subalgebra of m i e h x m sp x g let n g be the analytic crossed product determined by a covariant system n g we give the necessary and sufficient condition that an analytic subalgebra h is isomorphic to an analytic crossed product n g related to landstad s theorem we also investigate the structure of weakly closed subalgebra of a continuous crossed product n r which contains n r we show that there exists a proper weakly closed subalgebra of n r which contains n r and is not an analytic crossed product moreover we give an example that an analytic subalgebra is not a continuous analytic crossed product using the continuous decomposition of a factor of type iii 0 1

a hybrid genetic algorithm with the baldwin effect here we present a new hybrid genetic algorithm hga with the baldwin effect in the hga a local search is employed to change the fitness of individuals but the acquired improvements do not change the individual itself this local search step exploits the baldwin effect some numerical applications show that this algorithm can yield the global optimum more efficiently than commonly used hgas a theorem is presented that guarantees the convergence in probability of the new hga

semicrossed products of simple c algebras let mathcal a alpha and mathcal b beta be c dynamical systems and assume that mathcal a is a separable simple c algebra and that and are automorphisms then the semicrossed products mathcal a times alpha mathbb z and mathcal b times beta mathbb z are isometrically isomorphic if and only if the dynamical systems mathcal a alpha and mathcal b beta are outer conjugate

search space boundary extension method in real coded genetic algorithms abstract in real coded genetic algorithms gas some crossover operators do not work well on functions which have their optimum at the corner of the search space to cope with this problem we have proposed a boundary extension method which allows individuals to be located within a limited space beyond the boundary of the search space in this paper we give an analysis of the boundary extension methods from the viewpoint of sampling bias and perform a comparative study on the effect of applying two boundary extension methods namely the boundary extension by mirroring bem and the boundary extension with extended selection bes we were able to confirm that to use sampling methods which have smaller sampling bias had good performance on both functions which have their optimum at or near the boundaries of the search space and functions which have their optimum at the center of the search space the bes sd a bes by shortest distance selection with aging had good performance on functions which have their optimum at or near the boundaries of the search space we also confirmed that applying the bes sd a did not cause any performance degradation on functions which have their optimum at the center of the search space

derivations for a class of matrix function algebras abstract we study a class of matrix function algebras here denoted t c n we introduce a notion of point derivations and classify the point derivations for certain finite dimensional representations of t c n we use point derivations and information about n n matrices to show that every t c n valued derivation on t c n is inner

fronts in reactive convection bounds stability and instability this paper examines a simplified active combustion model in which the reaction influences the flow we consider front propagation in a reactive boussinesq system in an infinite vertical strip nonlinear stability of planar fronts is established for narrow domains when the rayleigh number is not too large planar fronts are shown to be linearly unstable with respect to long wavelength perturbations if the rayleigh number is sufficiently large we also prove uniform bounds on the bulk burning rate and the nusselt number in the kpp reaction case 2003 wiley periodicals inc

fronts from two dimensional dispersal kernels beyond the nonoverlapping generations model most integrodifference models of biological invasions are based on the nonoverlapping generations approximation however the effect of multiple reproduction events overlapping generations on the front speed can be very important especially for species with a long life spam only in one dimensional space has this approximation been relaxed previously although almost all biological invasions take place in two dimensions here we present a model that takes into account the overlapping generations effect or more generally the stage structure of the population and we analyze the main differences with the corresponding nonoverlapping generations results

a real coded genetic algorithm with a direction based crossover operator in this paper we develop a parallel structured real coded genetic algorithm rcga named the rga rdd for numerical optimization technically the proposed rga rdd integrates three specially designed evolutionary operators the ranking selection rs direction based crossover dbx and the dynamic random mutation drm as a whole to mimic a specific evolutionary process unlike the conventional rcgas that perform evolutionary operators in a series framework the rga rdd embeds a coordinator in the inner parallel loop to organize the operations of the dbx and drm so that a higher possibility of locating the global optimum is ensured besides based on the results of a systematic parametric analysis we provide a parameter selection guideline for the settings of the proposed rga rdd furthermore a data driven optimization scheme which incorporates the uniform design for design of experiments and a shape tunable neural network for auxiliary decision support is applied to search for an optimal set of the algorithm parameters the effectiveness and applicability of the proposed rga rdd are demonstrated through a variety of benchmarked optimization problems followed by comprehensive comparisons with some existing state of the art evolutionary algorithms extensive simulation results reveal that the performance of the proposed rga rdd is superior to comparative methods in locating the global optimum for real parameter optimization problems especially for unsolved multimodal and high dimensional hybrid functions

ideals in some continuous nonselfadjoint crossed product algebras abstract let y t be a locally compact dynamical system where the t denotes a continuous one parameter semigroup of maps on y when each t is a homeomorphism a nonselfadjoint crossed product algebra is defined as the subalgebra of the c crossed product c 0 y r supported on t 0 when each t is only continuous the crossed product c 0 y r can still be defined the ideal structure of such an algebra is determined in the case where the semigroup action is the suspension of a discrete free action on a smaller space x a generalization of effros hahn is given whereby one may find a meet irreducible ideal over any arc closure in y the meet irreducible ideals form a topological space in the hull kernel topology and there is a one to one correspondence between closed sets in this space and closed ideals in the algebra a subset of this space is homeomorphic to the space of finite arcs in the subarc topology the irrational flow algebra is considered as a special case