a locking free fem for cavitation computation in nearly incompressible nonlinear elasticity abstract a reduced selective integration finite element method coupled with a gradient flow method is introduced for the cavitation computation in nearly incompressible nonlinear elasticity numerical experiments show that for the iso parametric biquadratic finite element approximation of the displacement field the method is locking free and efficient for the nearly incompressible cavitation computation and has the same optimal convergence rates as in the compressible case for the elastic energy as well as the deformation and stress field if and only if the reduced integration is applied to the bulk energy term using no more than 2 gaussian quadrature nodes in each dimension

amenability properties of the centres of group algebras abstract let g be a locally compact group and zl 1 g be the centre of its group algebra we show that when g is compact zl 1 g is not amenable when g is either non abelian and connected or is a product of infinitely many finite non abelian groups we also study for some non compact groups g some conditions which imply amenability and hyper tauberian property for zl 1 g

a square root nyquist m filter design for digital communication systems designing matched transmit and receive filters whose combination satisfies the nyquist condition is a classical problem in digital communication systems in this correspondence we propose a novel method for designing such filters the proposed method is based on a cost function whose minimization leads to designs that can strike a balance between the stopband attenuation the residual intersymbol interference isi robust sensitivity to timing jitter and or reduced peak to average power ratio par an iterative algorithm for optimizing the proposed cost function is suggested and its excellent performance is shown by presenting a variety of design examples compared to the published works the proposed method offers the following unique advantages by introducing a symmetry in the filter coefficients filters with reduced computational complexity can be designed we also introduce a design parameter that allows one to strike a balance between the par and other features of the desired filter

weak amenability of banach algebras on locally compact groups abstract recent work by various authors has considered the implications of banach algebra amenability for various algebras defined over locally compact groups one of the basic tools being the fact that a continuous homomorphic image of an amenable algebra is again amenable in the present paper we look at the consequences of weak amenability here the homomorphism property fails in general however it remains true for suitable direct summands it is this technique that we make much use of here

rate dependent projection operators for frictional contact constraints we develop rate dependent regularization approaches for three dimensional frictional contact constraints based on the kelvin and maxwell viscoelastic constitutive models with the present regularization schemes we aim to provide a basis to better model friction and to stabilize the contact analysis while keeping the contact model as simple as possible the key feature of the regularization approaches implemented using an implicit time integrator is that one can recover in the limit the widely used rate independent elastoplastic regularization framework without encountering numerical difficulties intermediate contact tractions are defined in terms of the relative displacement the relative velocity and the regularization parameters the projection operators operate on the intermediate tractions and yield contact tractions that satisfy all the discretized contact constraints the use of projection operators allows a systematic implementation of the present regularization schemes through numerical simulations we observed that the maxwell type regularization effectively avoids convergence problems even for relatively large time step sizes while the kelvin type regularization does not copyright 2003 john wiley sons ltd

factorable fir nyquist filters with least stopband energy under sidelobe level constraints spectrally factorable nyquist filters are used in data communications to avoid intersymbol interference an approach is developed for obtaining a nyquist filter that is factorable having the smallest stopband energy for a given sidelobe level the resulting constrained minimization problem is solved efficiently and reliably using the goldfarb idnani 1983 algorithm some examples are presented comparing the present method with a previous approach from the literature

lipschitz algebras and derivations of von neumann algebras let m be an abelian von neumann algebra andean abelian operator m bimodule then the domain of any ultraweakly closed derivation from m intoeis a lipschitz algebra conversely every lipschitz algebra can be realized as such a domain we discuss the relevance of this result to the theory of noncommutative metric spaces

finite element analysis of anisotropic non linear incompressible elastic solids by a mixed model a mixed finite element method is presented for geometrically and materially non linear analysis of anisotropic incompressible hyperelastic materials an incremental iteractive total lagrangian formulation is adopted the nodal displacements and the hydrostatic pressure are independently interpolated leading to a mixed system of equations with characteristic zero diagonal terms computations are carried out using a three dimensional linear displacement constant pressure element a mixed penalty approximation is then employed to eliminate the pressure variables at the element level the anisotropic material handling capability of the formulation is tested through a number of transversely isotropic problems and the results compared to analytical solutions to demonstrate the applicability of this formulation to model complex anisotropic problems the inflation of a cut toroidal tube with helical fibre orientation is analysed

amenable and weakly amenable banach algebras with compact multiplication abstract we investigate amenable and weakly amenable banach algebras with compact multiplication any amenable banach algebra with compact multiplication is biprojective as a consequence every semisimple such algebra which has the approximation property is a topological direct sum of full matrix algebras in the radical case no such structure theorem is at hand we also investigate banach algebras which have a bounded approximate identity consisting of normalized powers of an element x any such banach algebra is either unital or radical if the algebra is also generated by x it is weakly amenable we construct a radical example with compact multiplication which moreover is an integral domain this furnishes a new example of a commutative weakly amenable non amenable radical banach algebra

weak amenability of fourier algebras and local synthesis of the anti diagonal abstract we show that for a connected lie group g its fourier algebra a g is weakly amenable only if g is abelian our main new idea is to show that weak amenability of a g implies that the anti diagonal g g g 1 g g is a set of local synthesis for a g g we then show that this cannot happen if g is non abelian we conclude for a locally compact group g that a g can be weakly amenable only if it contains no closed connected non abelian lie subgroups in particular for a lie group g a g is weakly amenable if and only if its connected component of the identity g e is abelian

on the synthesis of digital transmit filters a simple method for calculating the coefficients of a digital transversal filter when cascaded with analog filters is proposed the optimization criterion takes into account both the spectral characteristics of the signal and the residual amount of intersymbol interference at the decision device input in contrast with standard methods no a priori constraints are applied to the filter in the time or in the frequency domain

optimal structural design considering flexibility a topology optimization method based on the homogenization method the homogenization design method has been successfully applied to a variety of optimization problems such as the stiffness maximization problem and the eigen frequency maximization problem in this study a methodology to obtain the optimal structure design considering flexibility is developed as a new extension of the homogenization design method first flexibility is formulated using the mutual energy concept second a new multi objective function is proposed to obtain optimal solutions incorporating flexibility and stiffness next the topology optimization procedure is constructed using the homogenization method and sequential linear programming slp finally some examples are presented to confirm that the methodology presented here can provide flexible structures satisfying the problem specifications

analysis of mixed finite elements methods for the stokes problem a unified approach we develop a method for the analysis of mixed finite element methods for the stokes problem in the velocity pressure formulation a technical macroelement condition which is sufficient for the classical babuska brezzi inequality to be valid is introduced using this condition we are able to verify the stability and optimal order of convergence of several known mixed finite element methods

weak amenability of module extensions of banach algebras we start by discussing general necessary and sufficient conditions for a module extension banach algebra to be n weakly amenable for n 0 1 2 then we investigate various special cases all these case studies finally provide us with a way to construct an example of a weakly amenable banach algebra which is not 3 weakly amenable this answers an open question raised by h g dales f ghahramani and n gronbaek

selective and reduced numerical integrations for nurbs based isogeometric analysis we propose a new approach to construct selective and reduced integration rules for isogeometric analysis based on nurbs elements the notion of an approximation space that approximates the target space is introduced we explore the use of various approximation spaces associated with optimal patch wise numerical quadratures that exactly integrate the polynomials in approximation spaces with the minimum number of quadrature points patch rules exploit the higher continuity of spline basis functions the tendency of smooth spline functions to exhibit numerical locking in nearly incompressible problems when using a full gauss legendre quadrature is alleviated with selective or reduced integration stability and accuracy of the schemes are examined analyzing the discrete spectrum in a generalized eigenvalue problem we propose a local algorithm which is robust and computationally efficient to compute element by element the quadrature points and weights in patch rules the performance of the methods is assessed on several numerical examples in two dimensional elasticity and reissner mindlin shell structures

the cyclic and simplicial cohomology of l 1 mathbf n let a l 1 z be the unital semigroup algebra of n we show that the cyclic cohomology groups hc n a a vanish when n is odd and are one dimensional when n is even n 2 using connes exact sequence these results are used to show that the simplicial cohomology groups h n a a vanish for n 2 the results obtained are extended to unital algebras l 1 s for some other semigroups of r

weak and cyclic amenability for fourier algebras of connected lie groups abstract using techniques of non abelian harmonic analysis we construct an explicit non zero cyclic derivation on the fourier algebra of the real a x b group in particular this provides the first proof that this algebra is not weakly amenable using the structure theory of lie groups we deduce that the fourier algebras of connected semisimple lie groups also support non zero cyclic derivations and are likewise not weakly amenable our results complement earlier work of johnson 1994 15 plymen 2001 18 and forrest samei and spronk 2009 9 as an additional illustration of our techniques we construct an explicit non zero cyclic derivation on the fourier algebra of the reduced heisenberg group providing the first example of a connected nilpotent group whose fourier algebra is not weakly amenable

finite element hourglassing control a new hourglassing control technique for quadrilateral and hexahedral elements used in dynamic finite element codes is presented based on expansion of the strees in a taylor series and retention of additional terms beyond the usual constant stress term this technique has the advantage that actual rather than artificial material properties are used simplifications that render this technique competitive with artificial viscosity and stiffness procedures in terms of additional storage and computation requirements are described

a locking free solver for linear elasticity on quadrilateral and hexahedral meshes based on enrichment of lagrangian elements abstract this paper presents a new finite element solver for linear elasticity on quadrilateral and hexahedral meshes based on enrichment of the classical bilinear or trilinear lagrangian elements it solves the primal variable displacement in the strain div formulation and can handle both displacement and traction boundary conditions it is a locking free solver based on conforming finite elements the solver has second order accuracy in displacement and first order accuracy in stress and dilation divergence of displacement as validated by theoretical analysis and illustrated by numerical experiments on benchmarks deal ii implementation is also discussed

locking spurious mechanisms and pressure divergence in penalty finite element methods for stokes flow problems abstract solution locking spurious mechanisms and pressure divergence exhibited in the stokes flow calculations by the penalty finite element methods are analyzed employing a fourier analysis technique comparison of the approximate discrete operator components with the corresponding continuum ones enables one to explicitly identify the conditions for avoiding locking spurious mechanisms and pressure divergence in terms of discrete operator components which are applicable to either the finite difference or finite element discretizations a synthesis approach is explored to eliminate the solution locking spurious mechanisms and pressure divergence in uniformly reduced integrated four noded elements extensions of the present analysis and synthesis approach to navier stokes equations appear to be straightforward if one deals with a set of consistently linearized operators

generalized notions of amenability ii this paper continues the investigation of the first two authors begun in part i it is shown that approximate amenability and approximate contractibility are the same properties as are uniform approximate amenability and amenability bounded approximate contractibility and bounded approximate amenability are characterized by the existence of suitable operator bounded approximate identities for the diagonal ideal results are given on banach sequence algebras lipschitz algebras and beurling algebras and on the crucial role of approximate identities a new proof is given for a result due to n gronbaek on characterizing of amenability for beurling algebras

realization of root raised cosine roll off filters using a recursive fir filter structure root raised cosine roll off rrc filter is one of the most fundamental elements in modern digital communications this paper proposes a new method to efficiently realize the rrc filter the method employs cubic hermite interpolation to obtain a piecewise polynomial approximation for the impulse response of the rrc filter then the approximated impulse response is efficiently realized by using a transversal filter with a very small number of taps followed by integrators with a simple recursive structure named cascaded recursive finite impulse response cr fir filter as an example an rrc filter with roll off factor 0 5 is constructed by using the cr fir filter with only nine multipliers performance of the rrc filter in matched filtering is examined by computer simulations then it is shown that the constructed rrc matched filter has nearly the same performance as the ideal filter

amenability properties of banach algebra valued continuous functions abstract let x be a compact hausdorff space and a a banach algebra we investigate amenability properties of the algebra c x a of all a valued continuous functions we show that c x a has a bounded approximate diagonal if and only if a has a bounded approximate diagonal if a has a compactly central approximate diagonal unbounded then c x a has a compactly approximate diagonal weak amenability of c x a for commutative a is also considered

large deformation triangular and tetrahedral element formulations for unstructured meshes abstract the increasing use of automatic mesh generators and remeshers has spurred the need for accurate and efficient triangular and tetrahedral elements in unstructured meshes in large deformation analysis of solids accuracy and efficiency require the treatment of volumetric locking and element distortions respectively in this paper a mixed formulations is proposed to treat these issues and applied to triangular and tetrahedral elements the formulations enforces in the weak sense the expression for the volumetric strain in terms of the deformation gradient the mixed formulation is combined with an irreducible formulation to provide a balance between the treatment of volumetric locking and the maintenance of an adequate critical timestep three techniques are proposed to determine such a balance at the local element level example computations in two and three dimensions of an iron cylinder impacting a rigid surface are used to demonstrate the formulations and to compare them to the irreducible displacement based formulation

weak amenability for fourier algebras of 1 connected nilpotent lie groups a special case of a conjecture raised by forrest and runde 2005 10 asserts that the fourier algebra of every non abelian connected lie group fails to be weakly amenable this was already known to hold in the non abelian compact cases by earlier work of johnson 1994 13 and plymen unpublished note in recent work choi and ghandehari 2014 4 the authors verified this conjecture for the real ax b group and hence by structure theory for any semisimple lie group in this paper we verify the conjecture for all 1 connected non abelian nilpotent lie groups by reducing the problem to the case of the heisenberg group as in our previous paper an explicit non zero derivation is constructed on a dense subalgebra and then shown to be bounded using harmonic analysis en route we use the known fusion rules for schrodinger representations to give a concrete realization of the dual convolution for this group as a kind of twisted operator valued convolution we also give some partial results for solvable groups which give further evidence to support the general conjecture

an integration scheme for prandtl reuss elastoplastic constitutive equations we investigate the generalized midpoint rule for the time integration of elastoplastic constitutive equations for pressure independent yield criteria the incremental equations are divided into one scalar hydrostatic pressure dilation rate equation and a stress deviator strain rate deviator tensorial equation this formulation is applied to two classical problems bulging of a tube under internal pressure and tension test on a notched specimen

on the convergence of the bilinear velocity constant pressure finite element method in viscous flow abstract in this paper we show that the standard isoparametric q 1 q 0 velocity pressure finite element method for solving viscous flow problems leads to a fully and optimally convergent sequence of approximations if an appropriate quadrangulation of the domain is used

treatment of internal constraints by mixed finite element methods unification of concepts a general method to generate assumed stress and strain fields within the context of mixed finite element methods is presented the assumed fields are constructed in such a way that internal constraints are satisfied a priori consequently the locking behaviour commonly observed in finite element solutions of problems with internal constraints is avoided to this end the assumed stress and strain fields are constructed to satisfy a priori the homogeneous part of the equilibrium equations thus avoiding fraeijs de veubeke s limitation principle results obtained using the proposed methodology on a nearly incompressible plane strain problem and thin plate application using a shear deformable theory are indicated

optimum fir transmitter and receiver filters for data transmission over band limited channels the paper deals with the design of digital transmitter and receiver filters with finite impulse response fir for data transmission over band limited channels the filters are matched and satisfy a zero intersymbol interference constraint when cascaded for baseband transmission the filters achieve optimum spectral concentration in the frequency range 1 beta 2t 1 beta 2t mathematically the filter design leads to a generalized eigenvalue problem which is solved numerically by a projected gradient procedure for transmission over bandpass channels by combined amplitude and phase modulation the design technique is modified so that filters with complex valued impulse response and optimum spectral concentration in the range of positive bandpass frequencies f c 1 beta 2t f c 1 beta 2t are obtained in addition the complex formulation allows the design of impulse responses with enhanced spectral attenuation in the corresponding range of negative frequencies in order to minimize imageband interference results are shown in terms of filter coefficients signal spectra and spectral concentrations obtained for example filters designed for a voiceband data modem operating at a symbol rate of 2400 baud achieve a spectral concentration of 98 5 percent with 24 coefficients and beta 0 1 and with only 0 001 percent of the total energy in the imageband region

disjointness preserving operators between little lipschitz algebras abstract given a real number 0 1 and a metric space x d let lip x be the algebra of all scalar valued bounded functions f on x such that p f sup f x f y d x y x y x x y endowed with any one of the norms f max p f f or f p f f the little lipschitz algebra lip x is the closed subalgebra of lip x formed by all those functions f such that f x f y d x y 0 as d x y 0 a linear mapping t lip x lip y is called disjointness preserving if f g 0 in lip x implies t f t g 0 in lip y in this paper we study the representation and the automatic continuity of such maps t in the case in which x and y are compact we prove that t is essentially a weighted composition operator t f h f for some nonvanishing little lipschitz function h and some continuous map if in addition t is bijective we deduce that h is a nonvanishing function in lip y and is a lipschitz homeomorphism from y onto x and in particular we obtain that t is automatically continuous and t 1 is disjointness preserving moreover we show that there exists always a discontinuous disjointness preserving linear functional on lip x provided x is an infinite compact metric space

energy optimization of band limited nyquist signals in the time domain this paper presents a theoretical consideration of the optimal design of band limited nyquist type signal shapes for data transmission which maximizes its energy in a given time interval and which generates no intersymbol interference at the periodic sampling instants a method based on a completely analytical approach is given for design of such signals the optimal signal is a solution of an inhomogeneous linear integral equation of fredholm type a technique for solving this equation is given the computation is straightforward and involves the determination of eigenvalues and eigenfunctions of a positive definite and symmetric kernel in terms of prolate spheroidal wave functions the constraint for intersymbol interference is shown to be easily included into the problem finally some numerical examples are given and the performance of the optimal signal shapes is compared to that resulting from the use of the raised cosine type of signals it is also concluded that especially for small values of rolloff factor the optimal signals thus obtained are almost maximally immune to small timing offsets at the sampling instants

optimized signaling waveforms to reduce the effects of intersymbol interference and timing jitter the mainlobe energy of a member from the class of symbol waveforms with null derivatives at zero crossings is maximized thus a bandlimited pulse shape without intersymbol interference robust against jitter and timing errors is obtained comparisons to known pulses show advantages for these signals at the expense of bandwidth which linearly increases with the number of null derivatives

banach algebra structure and amenability of a class of matrix algebras with applications abstract we introduce a new category of banach algebras l 1 munn algebras which we use as a tool in the study of semigroup algebras then we characterize amenable l 1 munn algebras and also semisimple ones in this category applying these results to the semigroup algebras provides some characterizations of amenable semigroup algebras we also provide a counter example to a conjecture of duncan and paterson

convergence of mixed finite element approximations for the shallow arch problem the stability and convergence of mixed finite element methods are investigated for an equilibrium problem for thin shallow elastic arches the problem in its standard form contains two terms corresponding to the contributions from the shear and axial strains with a small parameter lagrange multipliers are introduced to formulate the problem in an alternative mixed form questions of existence and uniqueness of solutions to the standard and mixed problems are addressed it is shown that finite element approximations of the mixed problem are stable and convergent reduced integration formulations are equivalent to a mixed formulation which in general is distinct from the formulation shown to be stable and convergent except when the order of polynomial interpolationt of the arch shape satisfies 1 t min 2 r wherer is the order of polynomial approximation of the unknown variables

multiple quadrature underintegrated finite elements new multiple quadrature point underintegrated finite elements with hourglass control are developed the elements are selectively underintegrated to avoid volumetric and shear locking and save computational time an approach for hourglass control is proposed such that the stabilization operators are obtained simply by taking the partial derivatives of the generalized strain rate vector with respect to the natural co ordinates so that the elements require no stabilization parameter to improve accuracy over the traditional one point quadrature elements several quadrature points are used to integrate the internal forces especially for tracing the plastic fronts in the mesh during loading and unloading in elastic plastic analysis two and four point quadrature elements are proposed for use in the two and three dimensional elements respectively other multiple quadrature points can also be employed several numerical examples such as thin beam plate and shell problems are presented to demonstrate the applicability of the proposed elements

finite element analysis of linear and non linear planar deformations of elastic initially curved beams reference epfl article 102719view record in web of science record created on 2007 04 23 modified on 2016 08 08

behaviour of isoparametric quadrilateral family of lagrangian fluid finite elements this paper presents the formulation of both the consistent and inconsistent four eight and nine noded isoparametric quadrilateral fluid finite elements that are based on lagrangian frame of reference the mesh locking phenomenon due to simultaneous enforcement of twin constraints namely the incompressibility and irrotationality constraints is studied in detail the study shows that the characteristic of the locked fluid elements is that it always generates numerous spurious acoustic volume change modes upon the enforcement of rotational constraints that is the rotational constraints change the character of certain volume change modes the study further reinforces the necessity of rotational constraints in not only identifying the spurious pressure modes but also in reducing the computational effort for determining the eigenvalues and eigenvectors it is found that all fully integrated inconsistent models exhibit locking behaviour however the inconsistent eight and nine noded elements integrated with full integration of volumetric stiffness and one point integration of the rotational stiffness matrices gives excellent performance although they do not pass the inf sup test the four and nine noded consistent models are found to give locking free performance while their eight noded counterpart exhibited locking behaviour the study shows that only consistent nine noded element models pass the inf sup test the utility of these elements in coupled fluid structure interaction problem is also demonstrated

on a systematic development of trilinear three dimensional solid elements based on simo s enhanced strain formulation a systematic development of eight node trilinear three dimensional solid elements based on simo s theoretical framework for the enhanced assumed strain formulation is presented for linear elasticity the starting point is a regular brick followed by parallelepipeds and then arbitrarily distorted elements the advantages and deficits of various enhanced strain formulations are extensively discussed using the regular brick for arbitrarily distorted elements a simple modification of the element stiffness matrix is proposed to achieve a more reliable and very efficient element on some numerical examples the advantages and limits of the family of enhanced strain elements and the improved elements are discussed

a general methodology for deriving shear constrained reissner mindlin plate elements in this paper the necessary requirements for the good behaviour of shear constrained reissner mindlin plate elements for thick and thin plate situations are re interpreted and a simple explicit form of the substitute shear strain matrix is obtained this extends the previous work of the authors presented in references 18 and 31 the general methodology is applied to the re formulation of some well known quadrilateral plate elements and some new triangular and quadrilateral plate elements which show promising features some examples of the good behaviour of these elements are given

on character amenability of banach algebras abstract we continue our work e kaniuth a t lau j pym on amenability of banach algebras math proc cambridge philos soc 144 2008 85 96 in the study of amenability of a banach algebra a defined with respect to a character of a various necessary and sufficient conditions of a global and a pointwise nature are found for a banach algebra to possess a mean of norm 1 we also completely determine the size of the set of means for a separable weakly sequentially complete banach algebra a with no mean in a itself a number of illustrative examples are discussed

approximate and pseudo amenability of various classes of banach algebras we continue the investigation of notions of approximate amenability that were introduced in work of the second and third authors together with r j loy it is shown that every boundedly approximately contractible banach algebra has a bounded approximate identity and that the fourier algebra of the free group on two generators is not operator approximately amenable further examples are obtained of l1 semigroup algebras which are approximately amenable but not amenable using these we show that bounded approximate contractibility need not imply sequential approximate amenability results are also given for segal algebras on locally compact groups and algebras of p pseudo functions on discrete groups

the b bar method and the limitation principles abstract the generalized elastic material provides a reference model to cast in a unitary framework many structural models which are based on nonlinear monotone multivalued relations such as viscoelasticity plasticity and unilateral models the modified forms of the hu washizu and hellinger reissner principles and the displacement based variational formulation are recovered for the generalized elastic material starting from a functional in the complete set of state variables the related limitation principles are derived and their specialization to elasticity and elastoplasticity with mixed hardening are provided it is shown that the interpolating fields for the pressure and the volumetric strain usually adopted in the b bar method lead to a limitation principle accordingly the same elastic and elastoplastic solutions can be obtained by means of an approximate mixed displacement pressure variational principle a second application is concerned with the conditions ensuring the coincidence of the solutions between an approximate two field mixed formulation and the displacement based method numerical examples are provided to show the coincidence of the solutions obtained from different mixed finite element formulations in elasticity or elastoplasticity under the validity of the limitation principles

enhanced linear triangle for plasticity problems in j 2 solids due to their economy and capability to reproduce high gradient zones low order elements are of great interest in the calculations involving localized failure however the performance of the simplest element the three nodes triangle under incompressible and bending dominated situations is very poor and the computed results unreliable this paper presents an inexpensive three fields u p formulation solving these issues as shown in the examples of application

a theory of friction a rather general theory of friction inspired from the classical theory of plasticity is proposed it includes the contact impenetrability condition as a by product

finite element solution of the unsteady navier stokes equations by a fractional step method abstract a finite element method is presented for the numerical simulation of time dependent incompressible viscous flows the method is based on a fractional step approach to the time integration of the navier stokes equations in which only the incompressibility condition is treated implicitly this leads to a computational scheme of extremely simple algorithmic structure that is particularly attractive for cost effective solutions of large scale problems numerical results indicate the versatility and effectiveness of the proposed method

optimal spectral approximation of 2n order differential operators by mixed isogeometric analysis abstract we approximate the spectra of a class of 2 n order differential operators using isogeometric analysis in mixed formulations this class includes a wide range of differential operators such as those arising in elliptic biharmonic cahn hilliard swift hohenberg and phase field crystal equations the spectra of the differential operators are approximated by solving differential eigenvalue problems in mixed formulations which require auxiliary parameters the mixed isogeometric formulation when applying classical quadrature rules leads to an eigenvalue error convergence of order 2 p where p is the order of the underlying b spline space we improve this order to be 2 p 2 by applying optimally blended quadrature rules developed in puzyrev et al 2017 caloet al 0000 and this order is an optimum in the view of dispersion error we also compare these results with the mixed finite elements and show numerically that the mixed isogeometric analysis leads to significantly better spectral approximations

finite element methods for constrained problems in elasticity several different variational formulations of boundary value problems with constraints are discussed with particular reference to constrained problems in elasticity special attention is given to exterior penalty methods a discussion of the conditions necessary for penalty methods to provide a basis for stable and convergent finite element methods is given in particular the use of reduced integration is discussed and criteria on the order of reduced integration rules sufficient to produce stable and convergent schemes are described applications of reduced integration penalty methods to incompressible elasticity problems and contact problems are described

on the weak amenability of a x and its relation with the approximation property abstract we investigate the weak amenability of the algebra a x of approximable operators on a banach space x and its relation with the bounded approximation property in particular it will be shown that the bounded approximation property is neither necessary nor sufficient for the weak amenability of a x

design of orthogonal pulse shapes for communications via semidefinite programming in digital communications orthogonal pulse shapes are often used to represent message symbols for transmission through a channel in this paper the design of such pulse shapes is formulated as a convex semidefinite programming problem from which a globally optimal pulse shape can be efficiently found the formulation is used to design filters that achieve a the minimal bandwidth for a given filter length b the minimal filter length for a given bandwidth c the maximal robustness to timing error for a given bandwidth and filter length bandwidth is measured either in spectral energy concentration terms or with respect to a spectral mask the effectiveness of the method is demonstrated by the design of waveforms with substantially improved performance over the chip waveforms specified in standards for digital mobile telecommunications

lipschitz algebras and derivations ii exterior differentiation abstract basic aspects of differential geometry can be extended to various non classical settings lipschitz manifolds rectifiable sets sub riemannian manifolds banach manifolds wiener space etc although the constructions differ in each of these cases one can define a module of measurable 1 forms and a first order exterior derivative we give a general construction which applies to any metric space equipped with a finite measure and produces the desired result in all of the above cases it agrees with cheeger s construction when the latter is defined it also applies to an important class of dirichlet spaces where however the known first order differential calculus in general differs from ours although the two are related

hybrid hexahedral element for solids plates shells and beams by selective scaling a robust two field hexahedral element capable of handling plate shell beam and nearly incompressible material analyses without locking are presented starting with the assumed stress element of pian and tong 7 parasitic strain components leading to locking in plate shell and beam analyses are first identified locking can be alleviated by scaling down selectively the parasitic strain components in the leverage matrix unfortunately the element then fails the patch test however patch test correction and reduction in computation can be achieved by the recently proposed admissible matrix formulation the resulting element is lock free and very efficient all matrices involved in constructing the stiffness matrix can be derived explicitly the accuracy of the element is tested by popular bench mark problems

accuracy of some finite element models for arch problems abstract this paper presents a theoretical accuracy study of some finite element models for thin arches as is well known the selection of finite elements for curved members is quite a delicate problem we obtain order estimates of errors of finite element solutions by means of the perturbation theory of mixed models and the technique of asymptotic expansion in particular we theoretically show that certain finite element models may suffer from the so called locking phenomenon numerical results are also given to be compared with the theoretical error estimates

solution of contact problem using the hp version of the finite element method abstract this paper is concerned with the numerical treatment of mechanical contact problems in two dimensions using the p version of the finite element method coupled with minor iterative modification of the mesh the method of solution is based on the augmented lagrangian technique examples are presented 1999 elsevier science ltd all rights reserved

mixed finite element methods reduced and selective integration techniques a unification of concepts the equivalence of certain classes of mixed finite element methods with displacement methods which employ reduced and selective integration techniques is established this enables one to obtain the accuracy of the mixed formulation without incurring the additional computational expense engendered by the auxiliary field of the mixed method applications and numerical examples are presented for problems with constraints which can be difficult to enforce in finite element approximations and have often dictated the use of mixed principles these include thin beams and plates and linear and nonlinear incompressible and nearly incompressible continuum problems in solid and fluid mechanics

weak amenability and 2 weak amenability of beurling algebras abstract let l 1 g be a beurling algebra on a locally compact abelian group g we look for general conditions on the weight which allows the vanishing of continuous derivations of l 1 g this leads us to introducing vector valued beurling algebras and considering the translation of operators on them this is then used to connect the augmentation ideal to the behavior of the derivation space we apply these results to give examples of various classes of beurling algebras which are weakly amenable 2 weakly amenable or fail to be even 2 weakly amenable

a smoothing technique for reduced integration penalty methods in contact problems the paper presents a smoothing technique to the oscillated contact pressure obtained by penalty methods for a class of unilateral contact problems in linear elasticity the main result is to show that the smoothed contact pressure satisfies the so called babuska brezzi condition which dominates the convergence of the penalty method one numerical example is described

b and f projection methods for nearly incompressible linear and non linear elasticity and plasticity using higher order nurbs elements abstract this paper presents projection methods to treat the incompressibility constraint in small and large deformation elasticity and plasticity within the framework of isogeometric analysis after reviewing some fundamentals of isogeometric analysis we investigate the use of higher order non uniform rational b splines nurbs within the b projection method the higher continuity property of such functions is explored in nearly incompressible applications and shown to produce accurate and robust results a new non linear f projection method based on a modified minimum potential energy principle and inspired by the b method is proposed for the large deformation case it leads to a symmetric formulation for which the consistent linearized operator for fully non linear elasticity is derived and used in a newton raphson iterative procedure the performance of the methods is assessed on several numerical examples and results obtained are shown to compare favorably with other published techniques

mixed finite element with drilling rotations for plane problems in finite elasticity abstract in this work we apply the mixed finite element method to construct a two dimensional membrane element with drilling rotations for geometrically nonlinear elasticity only the 4 node element interpolation is discussed but the formulation is plausible for higher order elements as well numerical examples for both linear and nonlinear analyses demonstrate that the element yields rather stiff but indeed convergent results

design and hybrid realization of fir nyquist filters with quantized coefficients and low sensitivity to timing jitter a design of finite impulse response fir nyquist filters with zero intersymbol interference isi and low sensitivity to timing jitter is presented using an affine scaling linear programming algorithm a near optimum quantized coefficient set can be obtained in a feasible computational time by varying a parameter the design provides a tradeoff between the tail energy of the impulse response in the time domain and the stopband of the magnitude response in the frequency domain we also present a pipelined multiplier free fir filter realization with periodically time varying ptv coefficients based on a hybrid form the realizations exploit the coefficient symmetry to reduce the hardware by about one half by placing most of the shifts followed by addition toward the back end of the structure hardware is reduced due to the shorter wordlength of the adders the proposed structure has a provision to increase the speed by adjusting a design parameter but at the expense of more hardware

stiffness matrix integration rules for contact friction finite elements abstract penalty contact finite elements are effective for modeling discontinuities in finite element analyses a key ingredient in the evaluation of contact element matrices is numerical integration computational experience has shown that use of full integration sometimes gives rise to spurious annoying oscillations in contact stresses while some reduced integration rules do not in this paper we thoroughly investigate the effects of numerical integration on element behavior by comparison to an equivalent mixed method conclusions are drawn regarding desirable characteristics that an integration rule should have and an effective local stress averaging scheme for use at contact interelement boundaries is developed

amenability and weak amenability of the fourier algebra let g be a locally compact group we show that its fourier algebra a g is amenable if and only if g has an abelian subgroup of finite index and that its fourier stieltjes algebra b g is amenable if and only if g has a compact abelian subgroup of finite index we then show that a g is weakly amenable if the component of the identity of g is abelian and we prove some partial results towards the converse

weak amenability of triangular banach algebras let a and b be unital banach algebras and let m be a banach a b module then t a m 0 b becomes a triangular banach algebra when equipped with the banach space norm a m 0 b a a m m b b a banach algebra t is said to be n weakly amenable if all derivations from t into its n th dual space t n are inner in this paper we investigate arens regularity and n weak amenability of a triangular banach algebra t in relation to that of the algebras a b and their action on the module m

discontinuous maps from lipschitz algebras for an infinite compact metric space x d 0 1 andf c x letp f sup f t f s d t s t s x t s the set lip x d f c x p f