cyclic homology of totally disconnected groups acting on buildings abstract we prove a homological counterpart of a conjecture of p baum and a connes concerning k theory for convolution c algebras of p adic groups by calculating the periodic cyclic homology for the convolution algebra of a totally disconnected group acting properly on a building

parametrization of the cumulant lattice boltzmann method for fourth order accurate diffusion part ii the optimized cumulant lattice boltzmann method with fourth order accurate diffusion is used to simulate the flow around a sphere up to reynolds number 106 the drag crisis is well captured by the method we demonstrate with our results that the drag crisis corresponds to an almost discrete jump in the flow conditions the intermediate values of drag in a small range of reynolds numbers around the drag crisis observed in averaged data sets are found to originate from the flow switching between the high and the low drag conditions around the critical reynolds number the time spent in the low drag condition increases with the reynolds number such that the average drag curve has a finite steepness we demonstrate that the cumulant lattice boltzmann model with optimized parameters captures the drag crisis for flows over a sphere no sub grid model and no wall function is required and the boundary layer is only marginally resolved it is observed that in the transition regime between the high and the low drag configuration the flow switches from one state to the other state

a central moments based lattice boltzmann scheme for shallow water equations abstract in this paper we explore the possibility to derive an original lattice boltzmann scheme for solving shallow water equations specifically it is proposed to decompose the collision operator by means of a non orthogonal basis of central moments which relax independently to a discrete equilibrium our method is strictly consistent with the bgk operator as the latter is recovered exactly if all the moments relax with a common frequency the methodology is validated against five well consolidated established benchmark problems showing very good agreement moreover it possesses very high properties in terms of stability

cyclic cohomology of crossed products with z soit a une c etoile algebre unitale 7b a est une sous algebre lisse de a contenant l unite et un automorphisme de a appliquant 7b a sur 7b a et tels que 7b a et 1 7b a soient continus par rapport a chacune des semi normes definissant la topologie de 7b a on donne une construction du produit croise lisse de 7b a par on etudie la cohomologie cyclique du produit croise lisse

some remarks on kasparov theory on considere une autre preuve de l invariance d homotopie du bifoncteur ext on etudie l associativite du produit de kasparov a travers la motion de connextion

group cohomology and the cyclic cohomology of crossed products definite results are obtained in the conditions the group g is torsion free and the class h of the extension 0 zh g h n h 0 in h2 nh k is niipotent here gh for h g stands for the centralizer of h the cyclic homology groups hc a g decompose naturally as a direct sum of two subgroups called the homogeneous and the inhomogeneous parts ofhc a g the homogeneous part can be obtained from a spectral sequence converging to it with e2 q hp g hcq a the inhomogeneous part vanishes after inverting s for g z and in the topological situation we thus reobtain the result of nest 17 for general g but a k and trivial action thus for group rings k g we reobtain results of burghelea 4 the free groups satisfy our conditions see 10 for other classes of groups satisfying these conditions in this case our results are compatible with the results of pimsner and voiculescu 18 19 and suggest that for a large class of groups the part of ktor a r d g is obtained from a convergent spectral sequence with e q hp g k here r176 denotes the topological k theory functors see 2 a is a c algebra and a d g the reduced crossed product c algebra is a suitable completion of a g kasparov 13 succeeded to prove this for groups having a special manifold as classifying space we expect that our spectral sequence will give more insight in kasparov s spectral sequence we also mention

a cascaded phase field lattice boltzmann model for the simulation of incompressible immiscible fluids with high density contrast abstract in this work a conservative phase field model for the simulation of immiscible multiphase flows is developed using an incompressible velocity based cascaded lattice boltzmann method clbm extensions are made to the lattice boltzmann lb equations for interface tracking and incompressible hydrodynamics proposed by fakhari et al 1 by performing relaxation operations in central moment space this was motivated by the work of fei et al 2 3 where promising results from such a transformation were observed the relaxation of central moments is defined in a reference frame moving with the fluid while the existing multiple relaxation time 4 5 scheme performs collision in a fixed frame of reference moreover the derivations make use of continuous maxwellian distribution functions as a result the clbm enhances the galilean invariance and stability of the method when high lattice mach numbers are evident the cascaded scheme has been previously used in the literature to simulate multiphase flows based on the pseudo potential model where it allowed for high density and viscosity contrasts to be captured 6 7 here the clbm is implemented within the phase field framework and is verified through the analysis of a layered poiseuille flow the performance of the clbm is then investigated in terms of spurious currents galilean invariance and computational efficiency finally the work of fakhari et al 1 is extended by validating the model s ability to capture the relation between surface tension and the rise velocity of a planar taylor bubble in both stagnant and flowing fluids new counter current results indicate that the rise velocity model of ha ngoc and fabre 8 also applies in this regime

linear stability and isotropy properties of athermal regularized lattice boltzmann methods the present work proposes a general methodology to study stability and isotropy properties of lattice boltzmann lb schemes as a first investigation such a methodology is applied to better understand these properties in the context of regularized approaches to this extent linear stability analyses of two dimensional models are proposed the standard bhatnagar gross krook collision model the original precollision regularization and the recursive regularized model where off equilibrium distributions are partially computed thanks to a recursive formula a systematic identification of the physical content carried by each lb mode is done by analyzing the eigenvectors of the linear systems stability results are then numerically confirmed by performing simulations of shear and acoustic waves this work allows drawing fair conclusions on the stability properties of each model in particular among the aforementioned models recursive regularization turns out to be the most stable one for the d2q9 lattice especially in the zero viscosity limit two major properties shared by every regularized model are highlighted 1 a mode filtering property and 2 an incorrect and broadly anisotropic dissipation rate of the modes carrying physical waves in under resolved conditions the first property is the main source of increased stability especially for the recursive regularization it is a direct consequence of the reconstruction of off equilibrium populations before each collision process decreasing the rank of the system of discrete equations the second property seems to be related to numerical errors directly induced by the equilibration of high order moments in such a case this property is likely to occur with any collision model that follows such a stabilization methodology

homomorphisms of convolution algebras abstract we establish an explicit algebraic one to one correspondence between the homomorphisms l 1 f m g of group and measure algebras over locally compact groups f and g and group homomorphisms f m where m is a semi topological subgroup of m g w we show how to extend any such homomorphism to a larger convolution algebra to obtain nicer continuity properties we augment greenleaf s characterization of the contractive subgroups of m g greenleaf 1965 17 by completing the description of their topological structures we show that not every contractive homomorphism has the dual form of cohen s factorization in the abelian case thus answering a question posed by kerlin and pepe 1975 in 27 we obtain an alternative factorization of any contractive homomorphism l 1 f m g into four homomorphisms where each of the four factors is one of the natural types appearing in the cohen factorization

twisted orbifold k theory we use equivariant methods to define and study the orbifold k theory of an orbifold x adapting techniques from equivariant k theory we construct a chern character and exhibit a multiplicative decomposition for k orb x in particular showing that it is additively isomorphic to the orbifold cohomology of x a number of examples are provided we then use the theory of projective representations to define the notion of twisted orbifold k theory in the presence of discrete torsion an explicit expression for this is obtained in the case of a global quotient

isometric isomorphisms of beurling algebras abstract let g and h be locally compact groups with continuous weights 1 and 2 respectively such that i e i 1 i 1 2 in this article we show that if m g 1 the weighted measure algebra on g is isometrically algebra isomorphic to m h 2 then the underlying weighted groups are isomorphic i e there exists an isomorphism of topological groups g h such that 1 2 is multiplicative similarly we show that any weighted locally compact group g is completely determined by its beurling group algebra l 1 g luc g 1 and l 1 g when the two last algebras are equipped with an arens product

k theoretic amenability for sl2 qp and the action on the associated tree abstract it is proved that if a locally compact group g acts simplicially on a tree in such a way that the stabilizers of the vertices are amenable then g is k amenable in particular the canonical map from the full c algebra onto the reduced c algebra of g induces isomorphisms in k theory the main corollary of our result is that sl 2 q p and some other groups over local fields are k amenable

cyclic homology and the selberg principle abstract an abstract selberg principle is proved for a smooth compactly supported function f on a connected reductive p adic group which is the trace of some idempotent n n matrix this selberg principle states that the orbital integral of f relative to a non compact element vanishes this generalizes the work of julg and valette who treated the rank one case versions of the abstract selberg principle are proved also for finite groups and for discrete groups computations of the hochschild and cyclic homology of the convolution algebra of compactly supported functions are given

cyclic cohomology of crossed products by algebraic groups 4 reduction to the maximal compact subgroup 19 4 1 the ring c inv g 19 4 2 localization at x and at gx 20 4 3 definition of x j and 22 4 4 the definition of 23 4 5 the definition of and the equation 23 4 6 the condition of the main lemma are satisfied 25 4 7 the main theorem 27 4 8 some nonalgebraic groups 28

nonorthogonal central moments based lattice boltzmann scheme in three dimensions we present an alternative three dimensional lattice boltzmann collision operator consisting of a nonorthogonal basis of central moments our formulation is characterized by an intelligible derivation with a relatively simple and quite general implementation it is successfully validated against several established well consolidated well defined benchmark problems showing excellent properties in terms of accuracy and convergence if compared to the adoption of the classical bhatnagar gross krook operator our model possesses superior stability

isometric isomorphisms between banach algebras related to locally compact groups let g1 g2 be locally compact groups we prove in this paper that if t is an isometric isomorphism from the banach algebra luc g1 the continuous dual of the banach space of left uniformly continuous functions on g1 equipped with arens multiplication onto luc g2 i then t maps m g1 onto m g2 and li g onto l g2 we also prove that any isometric isomorphism from li g second conjugate algebra of l gi onto ll g2 maps l g1 onto l g2 0 introduction and preliminaries let g1 g2 be locally compact groups let m gi i 1 2 be the banach algebra of regular borel measures on gi a well known result of b e johnson 10 asserts that if t is an isometric isomorphism from m g1 onto m g2 then t maps ll g onto l g2 and hence g1 and g2 must be isomorphic by wendel s theorem 21 in this paper we prove theorem 3 1 c among other things that if t is an isometric isomorphism from ll g1 onto l1 g2 then t maps l1 g1 onto ll g2 this answers affirmatively a question raised in 4 theorem 3 1 c was proved for abelian locally compact groups by lau and losert in 13 and for compact and discrete groups by ghahramani and lau in 4 let g be a locally compact group let c g denote the space of bounded continuous complex valued functions on g with the sup norm topology and luc g denote the closed subspace of bounded left uniformly continuous functions on g i e all f e c g such that the map x lxf from g into c g is continuous where lxf y f xy x y e g then luc g is a banach algebra with the arens multiplication defined by nm f n m1f n m e luc g f e luc g where mlf x m lxf x e g furthermore m g may be identified with a closed subspace of luc g by the natural embedding u f f f x du x f e luc g u e m g it was received by the editors november 1 1988 1980 mathematics subject classification 1985 revision primary 43a20

an analogue of the thom isomorphism for crossed products of a c algebra by an action of r abstract in this paper we show the existence and uniqueness of a natural isomorphism oj of kj a with kj 1 a r j z 2 where a r is a c dynamical r system k is the functor of topological k theory and a r is the crossed product of a by the action of r the pimsner voiculescu exact sequence is obtained as a corollary we show that given an invariant trace on a with dual trace gt one has gto 1 u 1 2 i u u for any unitary u in the domain of the derivation of a associated to the action finally we show that the crossed product of c s3 continuous functions on the 3 sphere by a minimal diffeomorphism is a simple c algebra with no nontrivial idempotent