a distinguisher for high rate mceliece cryptosystems the goppa code distinguishing gd problem consists in distinguishing the matrix of a goppa code from a random matrix the hardness of this problem is an assumption to prove the security of code based cryptographic primitives such as mceliece s cryptosystem up to now it is widely believed that the gd problem is a hard decision problem we present the first method allowing to distinguish alternant and goppa codes over any field our technique can solve the gd problem in polynomial time provided that the codes have sufficiently large rates the key ingredient is an algebraic characterization of the key recovery problem the idea is to consider the rank of a linear system which is obtained by linearizing a particular polynomial system describing a key recovery attack it appears that this dimension depends on the type of code considered explicit formulas derived from extensive experimentations for the rank are provided for generic random alternant and goppa codes over any field finally we give theoretical explanations of these formulas in the case of random codes alternant codes over any field of characteristic two and binary goppa codes

iterative solution of multiple radiation and scattering problems in structural acoustics using a block quasi minimal residual algorithm abstract finite element discretizations of time harmonic acoustic wave problems in exterior domains result in large sparse systems of linear equations with complex symmetric coefficient matrices in many situations these matrix problems need to be solved repeatedly for different right hand sides but with the same coefficient matrix recently freund and malhotra have proposed a block quasi minimal residual bl qmr algorithm 13 for the iterative solution of non hermitian linear systems with multiple right hand sides the bl qmr algorithm is a block krylov subspace iterative method that incorporates deflation to delete linearly and almost linearly dependent vectors in the underlying block krylov sequences in this paper we describe a j symmetric variant of the bl qmr algorithm that introduces important simplifications for the case when the coefficient matrix is symmetric with respect to a bilinear form induced by a certain matrix j in particular the j symmetric variant includes the complex symmetric form of bl qmr as a special case we identify suitable preconditioners for the bl qmr algorithm applied to multiple radiation and scattering problems our numerical tests with the preconditioned bl qmr algorithm for such multiple linear systems show that instead of solving each of the linear systems individually it is significantly more efficient to employ the block version of the iterative method moreover the numerical results clearly illustrate the importance of deflation and its effect on iterative convergence

a comparison of approximate boundary conditions and infinite element methods for exterior helmholtz problems we compare the accuracy of a variety of approximate boundary conditions abcs and two versions of an infinite element method iem for approximating solutions of exterior helmholtz problems the infinite elements are of variable order in the radial direction and differ only in whether the test functions in the weak formulation are conjugated or not we find that the accuracy of the abcs decreases with increasing frequency and that at higher frequencies their accuracy is several orders of magnitude lower than that obtained with the iems we show that the convergence rate of the conjugated element is slower than the rate for the unconjugated element and that the latter element fails to converge in the far field

acoustic design by topology optimization abstract to bring down noise levels in human surroundings is an important issue and a method to reduce noise by means of topology optimization is presented here the acoustic field is modeled by helmholtz equation and the topology optimization method is based on continuous material interpolation functions in the density and bulk modulus the objective function is the squared sound pressure amplitude first room acoustic problems are considered and it is shown that the sound level can be reduced in a certain part of the room by an optimized distribution of reflecting material in a design domain along the ceiling or by distribution of absorbing and reflecting material along the walls we obtain well defined optimized designs for a single frequency or a frequency interval for both 2d and 3d problems when considering low frequencies second it is shown that the method can be applied to design outdoor sound barriers in order to reduce the sound level in the shadow zone behind the barrier a reduction of up to 10 db for a single barrier and almost 30 db when using two barriers are achieved compared to utilizing conventional sound barriers

statistical analysis of digital images of periodic fibrous structures using generalized hurst exponent distributions abstract distinction of diverse two dimensional periodic structures can be based on a large number of methods and parameters while the quantitative description of differences between similar samples is usually difficult this article aims by the use of statistical random walk in a generalized q order dimensional space at introducing a methodology to qualify the networked structures on the basis of exemplary textile samples the presented results were obtained at 1 bit monochromatic maps obtained from optical microscopic pictures significant features of samples were represented by the obtained distributions of hurst exponents and shannon entropy calculations

a high level programming language implementation of topology optimization applied to steady state navier stokes flow we present a versatile high level programming language implementation of non linear topology optimization our implementation is based on the commercial software package femlab and it allows a wide range of optimization objectives to be dealt with easily we exemplify our method by studies of steady state navier stokes flow problems thus extending the work by borrvall and petersson on topology optimization of fluids in stokes flow int j num meth fluids 2003 41 77 107 we analyse the physical aspects of the solutions and how they are affected by different parameters of the optimization algorithm a complete example of our implementation is included as femlab code in an appendix copyright 2005 john wiley sons ltd

empirical likelihood and general estimating equations for some time so called empirical likelihoods have been used heuristically for purposes of nonparametric estimation owen showed that empirical likelihood ratio statistics for various parameters theta f of an unknown distribution f have limiting chi square distributions and may be used to obtain tests or confidence intervals in a way that is completely analogous to that used with parametric likelihoods our objective in this paper is twofold first to link estimating functions or equations and empirical likelihood second to develop methods of combining information about parameters we do this by assuming that information about f and theta is available in the form of unbiased estimating functions empirical likelihoods for parameters are developed and shown to have properties similar to those for parametric likelihood efficiency results for estimates of both theta and f are obtained the methods are illustrated on several problems and areas for future investigation are noted

matrix pade approximation definitions and properties abstract some proposals are made to give a general definition of matrix pade approximants depending on the normalization of the denominator we define type i constant term is the unit matrix and type ii by conditions on the leading coefficient approximants existence and uniqueness are considered determinant expressions are given and relations among types i ii and left right approximants are considered

empirical likelihood ratio confidence intervals for a single functional summary the empirical distribution function based on a sample is well known to be the maximum likelihood estimate of the distribution from which the sample was taken in this paper the likelihood function for distributions is used to define a likelihood ratio function for distributions it is shown that this empirical likelihood ratio function can be used to construct confidence intervals for the sample mean for a class of m estimates that includes quantiles and for differentiable statistical functionals the results are nonparametric extensions of wilks s 1938 theorem for parametric likelihood ratios the intervals are illustrated on some real data and compared in a simulation to some bootstrap confidence intervals and to intervals based on student s t statistic a hybrid method that uses the bootstrap to determine critical values of the likelihood ratio is introduced

topology optimization of an acoustic horn we present a method for topology optimization of an acoustic horn with the aim of radiating sound as efficiently as possible using a strategy commonly employed for topology optimization of elastic structures we optimize over a scalar function indicating presence of material the helmholtz equation modeling the wave propagation is solved using the finite element method and the associated adjoint equation provides the required gradients numerical experiments validates that the result of the optimization provides horns with the desired acoustical properties the resulting horns are very efficient in the frequency span subject to optimization

boundary conditions for the numerical solution of elliptic equations in exterior regions elliptic equations in exterior regions frequently require a boundary condition at infinity to ensure the weill posedness of the problem examples of practical applications include the helmholtz equation and laplace s equation computational procedures based on a direct discretization of the elliptic problem require the replacement of the condition at infinity by a boundary condition on a finite artificial surface direct imposition of the condition at infinity along the finite boundary results in large errors a sequence of boundary conditions is developed which provides increasingly accurate approximations to the problem in the infinite domain estimates of the error due to the finite boundary are obtained for several cases computations are presented which demonstrate the increased accuracy that can be obtained by the use of the higher order boundary conditions the examples are based on a finite element formulation but finite difference methods can also be used

finding the permutation between equivalent linear codes the support splitting algorithm two linear codes are permutation equivalent if they are equal up to a fixed permutation on the codeword coordinates we present here an algorithm able to compute this permutation it operates by determining a set of properties invariant by permutation one for each coordinate called a signature if this signature is fully discriminant i e different for all coordinates the support of the code splits into singletons and the same signature computed for any permutation equivalent code will allow the reconstruction of the permutation a procedure is described to obtain a fully discriminant signature for most linear codes the total complexity of the support splitting algorithm is polynomial in the length of the code and exponential in the dimension of its hull i e the intersection of the code with its dual

topology optimization of bounded acoustic problems using the hybrid finite element wave based method abstract this paper presents an alternative topology optimization method for bounded acoustic problems that uses the hybrid finite element wave based method fe wbm the conventional method for the topology optimization of bounded acoustic problems is based on the finite element method fem which is limited to low frequency applications due to considerable computational efforts to this end we propose a gradient based topology optimization method that uses the hybrid fe wbm whereby the entire domain of a problem is partitioned into design and non design domains in this respect the fem is used as a design domain of topology optimization and the wbm is used as a non design domain to increase computational efficiency the adjoint variable method based on the hybrid fe wbm is also proposed as a means of computing design sensitivities numerical examples are presented to demonstrate the effectiveness of the proposed method we compare the optimized design obtained from the proposed method to that obtained from the conventional method in terms of objective function values optimized topologies and computational efficiency the optimization results show that the proposed method can perform more efficient topology optimization than conventional method and can thus be applied to much higher frequency applications that conventional method takes considerable computation time to manage

some new results for optimal ternary linear codes let d sub 3 n k be the maximum possible minimum hamming distance of a ternary n k d code for given values of n and k we describe a package for code extension and use this to prove some new exact values of d sub 3 n k moreover we classify the ternary n k d sub 3 n k codes for some values of n and k

on some fourier methods for inference abstract common statistical procedures such as maximum likelihood and m estimation admit generalized representations in the fourier domain the fourier domain provides fertile ground for approaching a number of difficult problems in inference in particular the empirical characteristic function and its extension for stationary time series are shown to be fundamental tools which support numerically simple inference procedures having arbitrarily high asymptotic efficiency and certain robustness features as well a numerical illustration involving the symmetric stable laws is given

is code equivalence easy to decide we study the computational difficulty of deciding whether two matrices generate equivalent linear codes i e codes that consist of the same codewords up to a fixed permutation on the codeword coordinates we call this problem code equivalence using techniques from the area of interactive proofs we show on the one hand that under the assumption that the polynomial time hierarchy does not collapse code equivalence is not np complete on the other hand we present a polynomial time reduction from the graph isomorphism problem to code equivalence thus if one could find an efficient i e polynomial time algorithm for code equivalence then one could settle the long standing problem of determining whether there is an efficient algorithm for solving graph isomorphism

estimation of affine asset pricing models using the empirical characteristic function abstract the known functional form of the conditional characteristic function ccf of discretely sampled observations from an affine diffusion is used to develop computationally tractable and asymptotically efficient estimators of the parameters of affine diffusions and of asset pricing models in which the state vectors follow affine diffusions both time domain estimators based on fourier inversion of the ccf and frequency domain estimators based directly on the ccf are constructed a method of moments estimator based on the ccf is shown to approximate the efficiency of maximum likelihood for affine diffusion and asset pricing models

efficient and stable model reduction scheme for the numerical simulation of broadband acoustic metamaterials this study proposes an efficient and stable model reduction scheme for the numerical simulation of broadband inhomogeneous and anisotropic acoustic systems unlike a conventional model reduction scheme the proposed model reduction scheme uses the adaptive quasi static ritz vector aqsrv as a basis vector the proposed aqsrv based model reduction scheme has the following two representative features 1 multiple frequency subintervals and 2 adaptive selection of the subinterval information i e the proper number and location of the center frequencies and basis vector at each subinterval using the error indicator multiple frequency subintervals means to divide the frequency band of interest into several frequency bands from the computational time viewpoint adaptive selection of the subinterval information and basis vector means to select a different number of subintervals and basis vectors for use according to the target system the proposed model reduction scheme is applied to the numerical simulation of the simple mass damping spring system and the acoustic metamaterial systems i e acoustic lens and acoustic cloaking device for the first time through these numerical examples the proposed model reduction scheme was verified from the efficiency and stability point of view the aqsrv scheme is developed for the efficient analysis of the acoustic systems the aqsrv scheme has always a guaranteed convergence of solution the aqsrv scheme automatically constructs the reduced model the heuristic algorithm automatically chooses the subintervals and basis vectors the aqsrv scheme is applied to the broadband acoustic metamaterial systems

a survey of finite element methods for time harmonic acoustics many of the current issues and methodologies related to finite element methods for time harmonic acoustics are reviewed the effective treatment of unbounded domains is a major challenge most prominent among the approaches that have been developed for this purpose are absorbing boundary conditions infinite elements and absorbing layers standard computational methods are unable to cope with wave phenomena at short wave lengths due to resolutions required to control dispersion and pollution errors leading to prohibitive computational demands since computation naturally separates the scales of a problem according to the mesh size multiscale considerations provide a useful framework for viewing these difficulties and developing methods to counter them other issues addressed are related to the efficient solution of systems of specialized algebraic equations and inverse problems of acoustics the tremendous progress that has been made in all of the above areas in recent years will surely continue leading to many more exciting developments

a pade based factorization free algorithm for identifying the eigenvalues missed by a generalized symmetric eigensolver when computing the solution of a generalized symmetric eigenvalue problem of the form ku mu the sturm sequence check also known as the inertia check is the most popular method for reporting the number of missed eigenvalues within a range l r this method requires the factorization of the matrices k l m and k r m when the size of the problem is reasonable and the matrices k and m are assembled these factorizations are possible when the eigensolver is equipped with an iterative solver which is nowadays the preferred choice for large scale problems the factorization of k m is not desired or feasible and therefore the inertia check cannot be performed to this effect the purpose of this paper is to present a factorization free algorithm for detecting and identifying the eigenvalues that were missed by an eigensolver equipped with an iterative linear equation solver within an interval of interest l r this algorithm constructs a scalar rational transfer function whose poles are exactly the eigenvalues of the symmetric pencil k m approximates it by a pade expansion and computes the poles of this approximation to detect and identify the missed eigenvalues the proposed algorithm is illustrated with an academic numerical example its potential for real engineering applications is also demonstrated with a large scale structural vibrations problem

euclidean and hermitian hulls of mds codes and their applications to eaqeccs in this paper we construct several classes of maximum distance separable mds codes via generalized reed solomon grs codes and extended grs codes where we can determine the dimensions of their euclidean hulls or hermitian hulls it turns out that the dimensions of euclidean hulls or hermitian hulls of the codes in our constructions can take all or almost all possible values as a consequence we can apply our results to entanglement assisted quantum error correcting codes eaqeccs and obtain several new families of mds eaqeccs with flexible parameters the required number of maximally entangled states of these mds eaqeccs can take all or almost all possible values moreover several new classes of q ary mds eaqeccs of length n q 1 are also obtained

topology optimization for three phase materials distribution in a dissipative expansion chamber by unified multiphase modeling approach the sound attenuation performance of a dissipative expansion chamber is a combinational result of reflective and dissipative effects although it is well known that the performance can be substantially improved by altering the distribution of constituent materials the process of finding an optimal distribution of the materials still remains a challenge this work proposes a new design method for interior space of a dissipative expansion chamber by using topology optimization method different from the existing topology optimizations for expansion chamber designs based on simplified material modeling the present design deals with fully modeled multiphase constituent materials such as acoustic poroelastic and elastic one difficulties in the optimization formulation for the multiphase material distribution arise from extremely different acoustic behavior of the materials and the use of various governing equations for different phase materials to systematically vary the attributes of the chamber interior space a unified multiphase modeling approach that allows continuous variations between the three phase materials within the same implementation is employed with an elaborately derived penalty parameters of material interpolation functions various design examples are successfully solved for wide frequency bands and the optimal configurations clearly demonstrate the importance of using specific configurations tuned to different target frequencies

computing automorphism groups of error correcting codes an algorithm is described for computing the automorphism group of an error correcting code the algorithm determines the order of the automorphism group and produces a set of monomial permutations which generate the group it has been implemented on a computer and has been used successfully on a great number of codes of moderate length

a krylov subspace projection method for simultaneous solution of helmholtz problems at multiple frequencies abstract a krylov subspace projection method which provides simultaneous solutions of the helmholtz equation at multiple frequencies in one solution step is presented the projector is obtained with an unsymmetric block lanczos algorithm applied to a transfer function derived from a finite element discretization this approach is equivalent to a matrix valued pade approximation of the transfer function the proposed method is an extension of the formulation presented in j comput acoust 8 2000 223 to unsymmetric systems and allows the treatment of a much wider range of practical problems including near field and fluid structure interaction computations

a test for normality based on the empirical characteristic function summary an omnibus test of normality is proposed which has high power against many alternative hypotheses the test uses a weighted integral of the squared modulus of the difference between the characteristic functions of the sample and of the normal distribution together with the one to one correspondence between t and f x suggest utilizing kn t in statistical inference here we use n t to test the composite hypothesis that f x is normal let 00 t exp it1 1t2 a2 be the characteristic function under the null hypothesis with 1u and u2 the unspecified mean and variance the test introduced here is based on a weighted integral over t of the squared modulus of kn t o t where 0 t depends on sample estimates of ju and a2 we compare the power of the test with that of prominent tests based on order statistics and on sample moments heathcote 1972 and feigin heathcote 1977 have previously considered using either the real or imaginary part alone of 4n t in tests of simple hypotheses their tests relied on the fact that for given t either component of 4n t is asymptotically normal with mean given by its population counterpart if the alternative hypothesis is also simple it may be possible to find a value of t that maximizes the power of the test in large samples epps singleton pulley 1982 showed how the sample moment generating function may be employed to test composite hypotheses that the data come from one or the other of two separate families of distributions murota takeuchi 1981 have recently proposed a location and scale invariant test based on the statistic an t i n t s 12 where s is the sample standard deviation applied to the problem of testing normality an t was found to have high power in the vicinity of t 10 against members of six families of symmetric alternatives but its

constructions of linear codes with one dimensional hull the hull of a linear code is defined to be the intersection of the code and its dual and was originally introduced to classify finite projective planes the hull plays an important role in determining the complexity of algorithms for checking permutation equivalence of two linear codes and computing the automorphism group of a linear code it has been shown that these algorithms are very effective in general if the size of the hull is small the objective of this paper is to present some sufficient and necessary conditions that linear codes and cyclic codes have one dimensional hull it is shown that there are no such binary or ternary cyclic codes based on these characterizations some constructions of linear codes with one dimensional hull were given by employing quadratic number fields partial difference sets and difference sets we also construct cyclic codes with one dimensional hull some optimal codes with one dimensional hull are obtained

a consistent nonparametric test of symmetry in linear regression models abstract this article proposes a consistent nonparametric test of the hypothesis that the disturbance in a linear regression model is distributed symmetrically around zero simulation results show that the test has good size and power properties for sample sizes as small as 50 we illustrate the use of the test in a cross country model of inflation and monetary growth

fast frequency sweep computations using a multi point pade based reconstruction method and an efficient iterative solver problems of the form z u f where z is a given matrix f is a given vector and is a circular frequency or circular frequency related parameter arise in many applications including computational structural and fluid dynamics and computational acoustics and electromagnetics the straightforward solution of such problems for fine increments of is computationally prohibitive particularly when z is a large scale matrix this paper discusses an alternative solution approach based on the efficient computation of u and its successive derivatives with respect to at a few sample values of this parameter and the reconstruction of the solution u in the frequency band of interest using multi point pade approximants this computational methodology is illustrated with applications from structural dynamics and underwater acoustic scattering in each case it is shown to reduce the cpu time required by the straightforward approach to frequency sweep computations by two orders of magnitude copyright 2006 john wiley sons ltd

a new multi frequency approach based on pade approximants for the treatment of transient dynamics problems with the variational theory of complex rays abstract frequency based methods were set up in order to circumvent the limits of classical finite element methods in fast dynamic simulations due to discretizations in this approach the dynamic loading was shifted in the frequency domain by fft then treated by the variational theory of complex rays and then the time response was reconstructed through an ifft this strategy proved to be very efficient due to the cpu vtcr very low cost however in the case of a large loading spectrum this frequency by frequency approach could seriously degrade the computational performances of the strategy this paper addresses this point by proposing the use of pade approximants in order to limit the number of frequencies at which the response should be calculated pade approximation is applied to the overall vtcr system based on its frequency dependency finally as simulations on a simple academic case and on a civil engineering structure show this method is found to be very efficient for interpolating the frequency response functions of a complex structure this is a key point to preserve the efficiency of the complete vtcr strategy for transient dynamic problems

empirical likelihood methods based on characteristic functions with applications to levy processes levy processes have been receiving increasing attention in financial modeling one distinctive feature of such models is that their characteristic functions are readily available inference based on characteristic functions is very useful for studying levy processes by incorporating the recent advances in nonparametric approaches empirical likelihood methods based on characteristic functions are developed in this paper for parameter estimation testing a particular parametric class including the presence of a jump component in the levy process and testing for symmetry of a distribution simulation and case studies confirm the effectiveness of the proposed method

acoustical topology optimization of zwicker s loudness with pade approximation abstract zwicker s loudness is a conventional standard index for measuring human hearing annoyance and has been widely considered in many industrial fields for noise evaluations the calculation of zwicker s loudness which is needed for a wide range of frequency responses with a fine frequency resolution using the finite element procedure usually requires significant computation time since a numerical solution must be obtained for each considered frequency furthermore if the analysis is the basis for an iterative optimization procedure such as a gradient based acoustical topology optimization this approach imposes prohibitively high computational costs in this research we propose a computationally efficient approach to resolve the computational issue in the computation and optimization of zwicker s loudness we present an efficient approach which combines the finite element method fem with the pade approximation pa procedure for obtaining zwicker s loudness and for applying it in a gradient based acoustical topology optimization procedure applied to the design of acoustic devices to minimize zwicker s loudness in this respect the calculation of zwicker s loudness is represented by the pa the main specific loudness considered as an objective function is evaluated using the pa procedure with a sufficient number of subintervals and expansion terms an adjoint variable formulation for the design sensitivities that uses the advantages of the pa is used we compare the performance of the proposed algorithm with the standard fem in terms of accuracy and the cpu time required for the calculation of zwicker s loudness in addition we also compare the optimized designs obtained by the proposed method to optimized designs obtained by the standard method in terms of objective values optimized topology and iterations or cpu times needed for the optimization through several examples including 2 d and 3 d acoustics the efficiency and reliability of using pa for computation and acoustical topology optimization of zwicker s loudness are compared and validated

pade approximants and the modal connection towards increased robustness for fast parametric sweeps summary in order to increase the robustness of a pade based approximation of parametric solutions to finite element problems an a priori estimate of the poles is proposed the resulting original approach is shown to allow for a straightforward efficient subsequent pade based expansion of the solution vector components overcoming some of the current convergence and robustness limitations in particular this enables for the intervals of approximation to be chosen a priori in direct connection with a given choice of pade approximants the choice of these approximants as shown in the present work is theoretically supported by the montessus de ballore theorem concerning the convergence of a series of approximants with fixed denominator degrees key features and originality of the proposed approach are i a component wise expansion which allows to specifically target subsets of the solution field and ii the a priori simultaneous choice of the pade approximants and their associated interval of convergence for an effective and more robust approximation an academic acoustic case study a structural acoustic application and a larger acoustic problem are presented in order to demonstrate the potential of the approach proposed this article is protected by copyright all rights reserved

adaptive frequency windowing for multifrequency solutions in structural acoustics based on the matrix pade via lanczos algorithm for many problems in structural acoustics it is desired to obtain solutions at many frequencies over a large range in the frequency domain a reduced order multifrequency algorithm based on matrix pade approximation using the matrix pade via lanczos mpvl connection has been previously used to solve both exterior and interior acoustic problems however the method is not guaranteed to give the correct solution across the entire frequency region of interest but only locally around a reference frequency an adaptive frequency windowing scheme is introduced to address this shortcoming for practical application of this method the application of this algorithm to tightly coupled problems in interior structural acoustics is presented

a fast method for solving acoustic scattering problems in frequency bands abstract we present a methodology for computing efficiently scattered fields in a frequency band the main feature of this methodology is the construction of a series of discrete problems that differ only by their right hand sides rather than by both their left and right hand sides its key steps are a the reformulation of the acoustic scattering problem in a bounded domain using any preferred absorbing boundary condition b the characterization of the repeated derivatives with respect to the frequency of the scattered field as solutions of scattering type problems with different source terms and boundary conditions and c the reconstruction of a scattered field by either the pade approximants or wynn s algorithm we report on several multifrequency acoustic scattering examples that illustrate the accuracy and computational efficiency of the proposed solution methodology

prolate and oblate spheroidal acoustic infinite elements in a previous paper the first author presented a new 3 d time harmonic prolate spheroidal acoustic infinite element for modeling acoustic fields in exterior domains here we present the development of the logical companion to that element viz an oblate spheroidal infinite element both elements are based on multipole expansions for the acoustic field in spheroidal coordinates developed by the second author in a separate paper recently submitted for publication for completeness an outline of the proofs of convergence of these expansions is included here also essential equations for the previously published prolate spheroidal infinite element are reproduced here in order that this paper can stand as an independent explication of the spheroidal family of infinite elements it is shown that a choice of prolate or oblate spheroidal infinite elements provides a capability for very efficiently modeling acoustic fields surrounding structures with a wide variety of practical shapes

a goodness of fit test based on the empirical characteristic function when parameters must be estimated summary the goodness of fit test using the empirical characteristic function proposed by koutrouvelis 1980 is extended to the case where parameters must be estimated the proposed test statistic is shown to have an asymptotic chi squared distribution with degrees of freedom reduced by the number of parameters estimated

a parallel hp fem infrastructure for three dimensional structural acoustics this paper describes a parallel three dimensional numerical infrastructure for the solution of a wide range of time harmonic problems in structural acoustics and vibration high accuracy and rate of error convergence in the mid frequency regime is achieved by the use of hp finite and infinite element approximations the infrastructure supports parallel computation in both single and multi frequency settings multi frequency solves utilize concurrent factoring of the frequency dependent linear algebraic systems and are naturally scalable scalability of large scale single frequency problems is realized by using feti dp an iterative domain decomposition scheme numerical examples are presented to cover applications in vibratory response of fluid filled elastic structures as well as radiation and scattering from elastic structures submerged in an infinite acoustic medium we demonstrate both the numerical accuracy as well as parallel scalability of the infrastructure in terms of problem parameters that include wavenumber and number of frequencies polynomial degree of finite infinite element approximations as well as the number of processors scalability and accuracy is evaluated for both single and multiple frequency sweeps on four high performance parallel computing platforms sgi altix sgi origin ibm p690 sp and linux cluster results show good performance on shared as well as distributed memory architecture copyright 2006 john wiley sons ltd

the second generation feti methods and their application to the parallel solution of large scale linear and geometrically non linear structural analysis problems the feti algorithms are a family of numerically scalable domain decomposition methods they have been designed in the early 1990s for solving iteratively and on parallel machines large scale systems of equations arising from the finite element discretization of solid mechanics structural engineering structural dynamics and acoustic scattering problems and for analyzing complex structures obtained from the assembly of substructures with incompatible discrete interfaces in this paper we present the second generation of these methods that operate more efficiently on large numbers of subdomains offer greater robustness better performance and more flexibility for implementation on a wider variety of computational platforms we also report on the application and performance of these methods for the solution of geometrically non linear structural analysis problems we discuss key aspects of their implementation on shared and distributed memory parallel processors benchmark them against optimized direct sparse solvers and highlight their potential with the solution of large scale structural mechanics problems with several million degrees of freedom

polynomial time attack on wild mceliece over quadratic extensions we present a polynomial time structural attack against the mceliece system based on wild goppa codes defined over a quadratic finite field extension we show that such codes can be efficiently distinguished from random codes the attack uses this property to compute a filtration that is to say a family of nested subcodes which will reveal their secret algebraic description

proper generalized decomposition applied to linear acoustic a new tool for broad band calculation the calculation of the acoustic response of systems in frequency bands is becoming increasingly important in simulation based engineering design this is particularly true in medium frequency bands where the response is very sensitive to the frequency some standard techniques for addressing these problems present a frequency dependent formulation and may involve fixed frequency calculations at many different frequencies in this paper we propose a new technique which combines the variational theory of complex rays vtcr with proper generalized decomposition pgd and does not require the resolution of acoustic problems at many frequencies in this approach the vtcr is used to find an approximate solution of a medium frequency acoustic problem using only a few degrees of freedom dofs then pgd is used to find a representation of the approximate solution which is separated between two variables the wave propagation direction and the frequency a relevant numerical example is used to present the strategy and illustrate its applicability for frequency band calculations

chebyshev polynomial approximations and characteristic function estimation on developpe une nouvelle procedure pour estimer les fonctions caracteristiques basee sur un developpement en polynomes de chebyshev pour la densite du cosinus des resultats de simulation confirment l utilite de la methode

a cca2 secure variant of the mceliece cryptosystem the mceliece public key encryption scheme has become an interesting alternative to cryptosystems based on number theoretical problems different from rsa and elgamal mceliece pkc is not known to be broken by a quantum computer moreover even though mceliece pkc has a relatively big key size encryption and decryption operations are rather efficient in spite of all the recent results in coding theory based cryptosystems to the date there are no constructions secure against chosen ciphertext attacks in the standard model the de facto security notion for public key cryptosystems in this paper we show the first construction of a mceliece based public key cryptosystem secure against chosen ciphertext attacks in the standard model our construction is inspired by a recently proposed technique by rosen and segev

bayliss turkel like radiation conditions on surfaces of arbitrary shape this paper addresses the extension of the bayliss turkel second order radiation condition to an arbitrarily shaped surface the derivation is based mainly on the pseudo differential calculus as well as on the introduction of a criterion providing a precise handling of the approximation process involved in the derivation of the radiation condition the radiation condition then ranges among the most accurate of those of order two as a by product of the derivation almost all known radiation conditions of order less than or equal to two are recovered and their respective accuracies are compared

a two level domain decomposition method for the iterative solution of high frequency exterior helmholtz problems summary we present a lagrange multiplier based two level domain decomposition method for solving iteratively large scale systems of equations arising from the finite element discretization of high frequency exterior helmholtz problems the proposed method is essentially an extension of the regularized feti finite element tearing and interconnecting method to indefinite problems its two key ingredients are the regularization of each subdomain matrix by a complex interface lumped mass matrix and the preconditioning of the interface problem by an auxiliary coarse problem constructed to enforce at each iteration the orthogonality of the residual to a set of carefully chosen planar waves we show numerically that the proposed method is scalable with respect to the mesh size the subdomain size and the wavenumber we report performance results for a submarine application that highlight the efficiency of the proposed method for the solution of high frequency acoustic scattering problems discretized by finite elements

weak keys in the mceliece public key cryptosystem we show that it is possible to know whether the secret goppa code of an instance of the mceliece public key cryptosystem was chosen with a binary generator polynomial furthermore whenever such a weak key is used we present an attack which can be completed for codes of length 1024 and dimension 524 with a large but feasible amount of computation

an adaptive scheme for a class of interpolatory model reduction methods for frequency response problems frequency sweep problems arise in many structural dynamic acoustic and structural acoustic applications in each case they incur the evaluation of a frequency response function for a typically large number of frequencies because each function evaluation requires the solution of an often large scale system of equations frequency sweep problems are computationally intensive interpolatory model order reduction is a powerful tool for reducing their cost however the performance of this tool depends on the location and number of the interpolation frequency points it also depends on the number of consecutive frequency derivatives of the response function that are matched at each frequency point so far these two choices have been made in the literature in a heuristic manner in contrast this paper proposes an automatic adaptive strategy based on monitoring the euclidean norm of the relative residual associated with the function to be evaluated over the frequency band of interest more specifically the number of interpolation points and the number of matched frequency derivatives are adaptively increased until the global euclidean norm of the relative residual is reduced below a user specified tolerance the robustness accuracy and computational efficiency of this adaptive strategy are highlighted with the solution of several frequency sweep problems associated with large scale structural dynamic acoustic and structural acoustic finite element models copyright 2012 john wiley sons ltd

mds codes with hulls of arbitrary dimensions and their quantum error correction the hull of linear codes has promising utilization in coding theory and quantum coding theory in this paper we study the hull of generalized reed solomon codes and extended generalized reed solomon codes over finite fields with respect to the euclidean inner product several infinite families of mds codes with hulls of arbitrary dimensions are presented as an application using these mds codes with hulls of arbitrary dimensions we construct several new infinite families of entanglement assisted quantum error correcting codes with flexible parameters

empirical likelihood methods with weakly dependent processes this paper studies the method of empirical likelihood in models with weakly dependent processes in such cases if the likelihood function is formulated as if the data process were independent obviously empirical likelihood fails we propose to use empirical likelihood of blocks of observations to solve this problem in a nonparametric manner this method of blockwise empirical likelihood preserves the dependence of data and the resulting likelihood ratios can be used to construct asymptotically valid confidence intervals we consider general estimating equations for which an efficient estimator is derived by maximizing blockwise empirical likelihood we also introduce blocks of blocks empirical likelihood to conduct inference for parameters of the infinite dimensional joint distribution of data the smooth function model is used for such cases we show that blockwise empirical likelihood of the smooth function model with weakly dependent processes is bartlett correctable a wide variety of problems such as time series regressions and spectral densities can be treated using our methodology

on the efficiency of empirical characteristic function procedures summary the asymptotic normality and arbitrarily high efficiency of some new statistical procedures based on the empirical characteristic function is established under general conditions

finite element solution of electromagnetic problems over a wide frequency range via the pade approximation in electromagnetic wave propagation problems it is usually necessary to calculate the field quantities over a wide band of frequencies in this paper we develop a computationally efficient scheme which combines the finite element method fem with the pade approximation procedure to derive the power series expansion of the unknown solution vector in terms of the frequency explicit power series expressions of the matrix operator are obtained for boundary value problems that are defined not only over bounded spatial domains but also over unbounded domains truncated either by an absorbing boundary condition abc or by a perfectly matched layer pml it is shown that the fem matrix is always a polynomial function of the frequency variable even with the abc or pml mesh truncations the coefficients of the power series expansion are obtained iteratively and certain a priori estimates are derived for the radius of convergence of this series expansion finally pade approximants are utilized to extend the region of convergence of the power series enabling us to cover the frequency band with a minimum number of lu decompositions

calculation of medium frequency vibrations over a wide frequency range abstract an enhancement of the variational theory of complex rays vtcr is being developed in order to calculate the vibrations of slightly damped elastic structures in the medium frequency range here the emphasis is put on the extension of this theory to the analysis over a wide frequency range the solution is sought in the form of an original decomposition the mean value and its complementary part over the frequency range numerical examples show the capability of the vtcr to predict the vibrational response of a structure in a frequency range

the method of moving asymptotes a new method for structural optimization a new method for non linear programming in general and structural optimization in particular is presented in each step of the iterative process a strictly convex approximating subproblem is generated and solved the generation of these subproblems is controlled by so called moving asymptotes which may both stabilize and speed up the convergence of the general process

topology optimization of dynamics problems with pade approximants an efficient procedure for topology optimization of dynamics problems is proposed the method is based on frequency responses represented by pade approximants and analytical sensitivity analysis derived using the adjoint method this gives an accurate approximation of the frequency response over wide frequency ranges and a formulation that allows for design sensitivities to be computed at low computational cost also for a large number of design variables two examples that deal with optimization of forced vibrations are included copyright 2007 john wiley sons ltd

iterative solution of large scale acoustic scattering problems with multiple right hand sides by a domain decomposition method with lagrange multipliers an extension of the feti h method is designed for the solution of acoustic scattering problems with multiple right hand sides a new local pre conditioning of this domain decomposition method is also presented the potential of the resulting iterative solver is demonstrated by numerical experiments for two dimensional problems with high wavenumbers as many as 2 5 million complex degrees of freedom and a sweep on the angle of the incident wave preliminary results for a three dimensional submarine problem are also included the feti h method whose numerical scalability with respect to the mesh and subdomain sizes was previously established is shown here to be also numerically scalable with respect to the wavenumber copyright 2001 john wiley sons ltd