generalized topological derivative for the navier equation and inverse scattering in the time domain abstract in this work the concept of generalized topological sensitivity developed recently to deal with inverse elastodynamic scattering by penetrable obstacles in the frequency domain is extended to permit non invasive defect reconstruction and material characterization by means of transient elastic waves this quantity which signifies the first order perturbation of a given cost functional due to nucleation of an infinitesimal elastic defect in the reference defect free solid is intended to be used as an obstacle indicator though an assembly of interior sampling points where it attains pronounced negative values from an asymptotic analysis of the transient scattered field emanating from a defect with vanishing size in the reference elastic solid the expression for topological sensitivity explicit in terms of i the green s function and ii the free i e incident field for the reference domain is obtained by employing the so called direct approach and a convolution based boundary integral representation of the featured elastodynamic wavefields for generality the proposed formula is recast in terms of its adjoint field counterpart that caters for general reference domains where the green s function may not be available through numerical simulations it is shown that the generalized topological sensitivity in the time domain provides an effective preliminary tool for the 3d reconstruction and material identification of discrete internal heterogeneities the results also demonstrate that the defect illumination by transient elastic waveforms results in a higher quality of reconstruction relative to its time harmonic monotonal counterpart

discussion of second order topological sensitivity analysis by j rocha de faria et al abstract the aim of this discussion is to expose incorrect results in a previous ijss article

development of a boundary element method for time dependent planar thermoelasticity abstract a new boundary element method is developed for two dimensional quasistatic thermoelasticity this time domain formulation involves only surface quantities consequently volume discretization is completely eliminated and the method becomes a viable alternative to the usual finite element approaches after presenting a brief overview of the governing equations boundary integral equations for coupled quasistatic thermoelasticity are derived by starting with existing fundamental solutions along with an appropriate reciprocal theorem details of a general purpose numerical implementation are then discussed next boundary element methods for the two more practical theories uncoupled quasistatic and steady state thermoelasticity are developed directly from limiting forms of the coupled formulation several numerical examples are provided to illustrate the validity and attractiveness of the boundary element approach for this entire class of problems

on the stress wave imaging of cavities in a semi infinite solid the problem of mapping underground cavities from surface seismic measurements is investigated within the framework of a regularized boundary integral equation bie method with the ground modeled as a uniform elastic half space the inverse analysis of elastic waves scattered by a three dimensional void is formulated as a task of minimizing the misfit between experimental observations and theoretical predictions for an assumed void geometry for an accurate treatment of the gradient search technique employed to solve the inverse problem sensitivities of the predictive bie model with respect to cavity parameters are evaluated semi analytically using an adjoint problem approach and a continuum kinematics description several key features of the formulation including the rigorous treatment of the radiation condition for semi infinite solids modeling of an illuminating seismic wave field and treatment of the prior information are highlighted a set of numerical examples with spherical and ellipsoidal cavity geometries is included to illustrate the performance of the method it is shown that the featured adjoint problem approach reduces the computational requirements by an order of magnitude relative to conventional finite difference estimates thus rendering the three dimensional elastic wave imaging of solids tractable for engineering applications

a chebyshev expansion method for solving nonlinear optimal control problems this paper presents a numerical technique for solving the controlled duffing oscillator the control and state variables are approximated by chebyshev series a technique is provided for approximating the system dynamics boundary conditions and performance index this technique is based on using an explicit formula for the chebyshev polynomials in terms of arbitrary order of their derivatives the system dynamics and the performance index are converted into some algebraic equations then the optimal control problem is reduced to constrained optimization problem results and comparisons are given at the end of this paper

inelastic transient dynamic analysis of three dimensional problems by bem a direct boundary element formulation and its numerical implementation for inelastic transient dynamic analysis of three dimensional solids is presented the formulation is based on an initial stress approach and is the first ever of its kind in the field of the boundary element method this formulation employs the navier cauchy equation of motion graffi s dynamic reciprocal theorem stokes fundamental solution and the divergence theorem together with kinematical and constitutive equations to obtain the pertinent integral equations of the problem in the time domain within the context of small displacement theory of elastoplasticity the boundary integral equations are cast in an incremental form in which elastoplastic relations of the incremental type are used for the material description these equations are then solved using a time stepping algorithm in conjunction with an iterative solution scheme to satisfy the constitutive relations higher order shape functions are used to approximate the field quantities in space as well as in time finally the applicability of this methodology is demonstrated by presenting a few example problems

two dimensional elastodynamic displacement discontinuity method a time domain elastodynamic displacement discontinuity method is presented for analysing two dimensional problems in solid mechanics linear continuous in time and piecewise linear in space interpolation functions are assumed for the displacement discontinuities causal and analytical integrations are used throughout the resulting numerical algorithms are time marching and implicit the displacement discontinuity method can be used to model a class of traction boundary value problems where the unknowns are the transient shear and normal discontinuities in displacement across the surface of a mathematical crack in an infinite isotropic and homogeneous linear elastic medium

variable stepsize chebyshev type methods for the integration of second order i v p s panovsky and richardson a family of implicit chebyshev methods for the numerical integration of second order differential equations j comput appl math 23 1988 35 51 presented a method based on chebyshev approximations for numerically solving the problem y f x y being the steplength constant coleman and booth analysis of a family of chebyshev methods for y f x y j comput appl math 44 1992 95 114 made an analysis of the above method and suggested the convenience to design a variable steplength implementation as far as we know this goal has not been achieved until now later on we extended the above method this journal 2003 and obtained a scheme for numerically solving the equation y 2gy g 2 w 2 f x y the question of how to extend these formulas to variable stepsize procedures is the primary topic of this paper

computing zeros on a real interval through chebyshev expansion and polynomial rootfinding robust polynomial rootfinders can be exploited to compute the roots on a real interval of a nonpolynomial function f x by the following i expand f as a chebyshev polynomial series ii convert to a polynomial in ordinary series of powers form and iii apply the polynomial rootfinder complex valued roots and real roots outside the target interval are discarded the expansion is most efficiently done by adaptive chebyshev interpolation with n equal to a power of two where n is the degree of the truncated chebyshev series all previous evaluations of f can then be reused when n is increased adaption stops when n is sufficiently large so that further increases produce no significant change in the interpolant we describe two conversion strategies the convert to powers method uses multiplication by mildly ill conditioned matrices to create a polynomial of degree n the degree doubling strategy defines a polynomial of larger degree 2n but is very well conditioned the convert to powers method although faster restricts n to moderate values this can always be accomplished by subdividing the target interval both these strategies allow simultaneous approximation of many roots on an interval whether simple or multiple for nonpolynomial f x

dissipative chebyshev exponential fitted methods for numerical solution of second order differential equations a family of implicit methods based on intra step chebyshev interpolation has been developed to integrate oscillatory second order initial value problems of the form y t 2g y t g2 w2 y t f t y t the procedure integrates the homogeneous part exactly in the absence of round off errors the chebyshev approach uses stepsizes that are considerably larger than those typically used in runge kutta or multistep methods computational overheads are comparable to those incurred by high order conventional procedures chebyshev interpolation coupled with the exponential fitted nature of the method substantially reduces local errors global error propagation rates are also reduced making these procedures good candidates to be used in long term simulations of perturbed oscillatory systems with a dissipative term

bayesian adaptive estimation of the auditory filter a bayesian adaptive procedure for estimating the auditory filter shape was proposed and evaluated using young normal hearing listeners at moderate stimulus levels the resulting quick auditory filter qaf procedure assumed the power spectrum model of masking with the auditory filter shape being modeled using a spectrally symmetric two parameter rounded exponential roex function during data collection using the qaf procedure listeners detected the presence of a pure tone signal presented in the spectral notch of a noise masker dependent on the listener s response on each trial the posterior probability distributions of the model parameters were updated and the resulting parameter estimates were then used to optimize the choice of stimulus parameters for the subsequent trials results showed that the qaf procedure gave similar parameter estimates to the traditional threshold based procedure in many cases and was able to reasonably predict the masked signal thresholds additional measurements suggested that occasional failures of the qaf procedure to reliably converge could be a consequence of incorrect responses early in a qaf track the addition of a parameter describing lapses of attention reduced the likelihood of such failures

the topological asymptotic for pde systems the elasticity case the aim of the topological sensitivity analysis is to obtain an asymptotic expansion of a design functional with respect to the creation of a small hole in this paper such an expansion is obtained and analyzed in the context of linear elasticity for general functionals and arbitrary shaped holes by using an adaptation of the adjoint method and a domain truncation technique the method is general and can be easily adapted to other linear pdes and other types of boundary conditions

rapid estimation of high parameter auditory filter shapes a bayesian adaptive procedure the quick auditory filter qaf procedure was used to estimate auditory filter shapes that were asymmetric about their peaks in three experiments listeners who were naive to psychoacoustic experiments detected a fixed level pure tone target presented with a spectrally notched noise masker the qaf procedure adaptively manipulated the masker spectrum level and the position of the masker notch which was optimized for the efficient estimation of the five parameters of an auditory filter model experiment i demonstrated that the qaf procedure provided a convergent estimate of the auditory filter shape at 2 khz within 150 to 200 trials approximately 15 min to complete and for a majority of listeners excellent test retest reliability in experiment ii asymmetric auditory filters were estimated for target frequencies of 1 and 4 khz and target levels of 30 and 50 db sound pressure level the estimated filter shapes were generally consistent with published norms especially at the low target level it is known that the auditory filter estimates are narrower for forward masking than simultaneous masking due to peripheral suppression a result replicated in experiment iii using fewer than 200 qaf trials

a fem based topological sensitivity approach for fast qualitative identification of buried cavities from elastodynamic overdetermined boundary data a time domain topological sensitivity ts approach is developed for elastic wave imaging of media of arbitrary geometry the ts which quantifies the sensitivity of the misfit cost functional to the creation at a specified location of an infinitesimal hole is expressed in terms of the time convolution of the free field and a supplementary adjoint field as a function of that specified location following previous studies performed under mostly static or time harmonic conditions the ts field is here considered as a natural and computationally efficient approach for defining a defect indicator function this study emphasizes the implementation and exploitation of ts fields using standard displacement based fem approaches a straightforward task once the correct sensitivity formulation is available a comprehensive set of numerical experiments on 3d and 2d elastodynamic and acoustic configurations is reported allowing to assess and highlight many features of the proposed ts based fast qualitative identification such as its ability to identify multiple defects and its robustness against data noise

a family of implicit chebyshev methods for the numerical integration of second order differential equations abstract a family of implicit methods based on intra step chebyshev interpolation is developed for the solution of initial value problems whose differential equations are of the special second order form y f y x x the general procedure allows stepsizes which are considerably larger than commonly used in conventional methods computation overhead is comparable to that required by high order single or multistep procedures in addition the iterative nature of the method substantially reduces local errors while maintaining a low rate of global error growth

zero dissipative semi implicit hybrid method for solving oscillatory or periodic problems in this paper a new semi implicit two step hybrid method with fifth algebraic order is derived for the integration of second order oscillatory initial value problems the new method possesses dispersion of order eight and dissipation of order infinity numerical experiment reveals the superiority of the new method for solving oscillatory or periodic problems over several methods of the same algebraic order in the literature

time dependent axisymmetric thermoelastic boundary element analysis a boundary element method is developed for problems of quasistatic axisymmetric thermoelasticity unlike previous approaches this new time domain formulation is written exclusively in terms of surface quantities thereby eliminating the need for volume discretization furthermore since the exact three dimensional infinite space fundamental solutions are employed very accurate solutions are obtainable including the determination of surface stresses in the integral formulation the fundamental solutions are separated into steady state and transient components the steady state portion which contains all of the singularities is integrated analytically in the circumferential direction yielding the familiar axisymmetric kernels the remaining non singular transient integrands are treated by a combination of analytical and numerical quadrature the method is implemented in a general purpose boundary element code which includes multiregion capability along with higher order conforming surface elements several numerical examples are provided to illustrate the validity of the formulation and the attractiveness of this approach for practical engineenring analysis

posterior mode estimation by extended kalman filtering for multivariate dynamic generalized linear models abstract a family of multivariate dynamic generalized linear models is introduced as a general framework for the analysis of time series with observations from the exponential family besides common conditionally gaussian models this article deals with univariate models for counted and binary data and as the most interesting multivariate case models for nonstationary multicategorical time series for univariate responses a related yet different class of models has been introduced in a bayesian setting by west harrison and migon assuming conjugate prior posterior distributions for the natural parameter of the exponential family they derive an approximate filter for estimation of time varying states or parameters however their method raises some problems in particular in extending it to the multivariate case a different approach to filtering and smoothing is chosen in this article to avoid a full bayesian analysis based on numerical integration which becomes computationally critical for higher

analysis of a family of chebyshev methods for y f x y abstract methods proposed by panovsky and richardson this journal 1988 are interpreted as a family of symmetric two step hybrid methods each method is based on a polynomial interpolant of degree n for y for which the nodes are determined by the extrema of the chebyshev polynomial of degree n it is shown that the order of accuracy is n 1 for odd n and n 2 for even n and expressions for the local error constants are given the stability properties of each method are determined by the roots of a quadratic equation 2 2 n 1 0 where n 2 is a rational approximation for cos the intervals of periodicity which are also intervals of absolute stability are tabulated for n 10 numerical examples provide comparisons with other methods

topological sensitivity for 3d elastodynamic and acoustic inverse scattering in the time domain building on previous work for 3d inverse scattering in the frequency domain this article develops the concept of topological derivative for 3d elastic and acoustic wave imaging of media of arbitrary geometry using data in the time domain the topological derivative which quantifies the sensitivity of the cost functional associated with the inverse scattering problem due to the creation at a specified location of an infinitesimal hole for the elastodynamic case or rigid inclusion for the acoustic case is found to be expressed in terms of the time convolution of the free field and a supplementary adjoint field the derivation of the topological derivative follows the generic pattern proposed in previous studies which is transposable to a variety of other physical problems a numerical example where the featured cost function is defined in terms of synthetic data arising from the scattering of plane acoustic waves by a rigid spherical inclusion illustrates the utility of the topological derivative concept for defect identification using time varying data

using mesh adaption for the identification of a spatial field of material properties it is well known that the solution of an inverse problem is ill posed and not unique to avoid difficulties caused by this when solving such a problem tikhonov s regularization terms are usually added to the norm quantifying the discrepancy between the model s predictions and experimental data this regularization term however is often inadequate to perform the identification of a field of material properties that varies spatially this is all the more difficult when dealing with the numerical solution of this inverse problem for the sought field is spatially discretized and this discretization can influence the result of the identification we will here examine an overall strategy using classical adaptive meshing methods used to circumvent these drawbacks the first step consists of using two distinct meshes one associated with the discretization of the sought spatial field and the other associated with the solution of the mechanical problems forward and adjoint states in the second step we will introduce local error estimators that allow an oriented refinement of the mesh associated with the sought parameters this general strategy is applied to a practical case study the detection of underground cavities using experimental data obtained by an interferometric device on a satellite we will then address the question of how the regularization terms and the error estimator driving the mesh refinement were selected copyright 2011 john wiley sons ltd

boundary element methods in three dimensional thermoelasticity abstract a boundary element method is developed for the solution of time dependent problems in three dimensional thermoelasticity the time domain boundary only formulation represents the first of its kind for quasistatic analysis which by definition considers transient heat conduction but ignores the effects of inertia by eliminating the need for volume discretization the method becomes an attractive alternative to finite element analysis for this class of problems additionally because an exact green s function is used in the interior steep thermal gradients can be captured much more readily than with standard domain based methods the presentation includes details of the fundamental solution a derivation of the boundary integral equations and an overview of a general purpose numerical implementation this implementation permits the solution of large multiregion problems with arbitrary geometry and boundary conditions several examples are included to validate the proposed method as well as to highlight its usefulness

numerical methods for ordinary differential equations in the 20th century abstract numerical methods for the solution of initial value problems in ordinary differential equations made enormous progress during the 20th century for several reasons the first reasons lie in the impetus that was given to the subject in the concluding years of the previous century by the seminal papers of bashforth and adams for linear multistep methods and runge for runge kutta methods other reasons which of course apply to numerical analysis in general are in the invention of electronic computers half way through the century and the needs in mathematical modelling of efficient numerical algorithms as an alternative to classical methods of applied mathematics this survey paper follows many of the main strands in the developments of these methods both for general problems stiff systems and for many of the special problem types that have been gaining in significance as the century draws to an end

auditory filter nonlinearity across frequency using simultaneous notched noise masking psychoacoustic masking experiments have been widely used to investigate cochlear function in human listeners here we use simultaneous notched noise masking experiments in normal hearing listeners to characterize the changes in auditory filter shape with stimulus level over the frequency range 0 25 6khz at each frequency a range of fixed signal levels 30 70db spl and fixed masker levels 20 50db spl spectrum level are used in order to obtain accurate descriptions of the filter shapes in individual listeners the notched noise data for individual listeners are fitted with two filter shape models a rounded exponential roex shape in which the filter skirt changes as a linear function of probe tone level and the other in which the gain of the tip filter relative to the filter tail changes as a function of signal level glasberg and moore j acoust soc am 108 2318 2328 2000 the parameters for these fitted models are then described with a simple set of equations that quantify the changes in aud

a time dependent incompressible viscous bem for moderate reynolds numbers the boundary element method is applied to transient viscous incompressible flow the time domain formulation allows a boundary only solution for linear stokes flow for higher speed flows in which the non linear convective effects cannot be ignored a volume integral must be retained however the introduction of reference velocities often limits the non linear region to the vicinity of obstacles or bounding surfaces additionally the volume terms are rewritten to eliminate the need for the calculation of velocity gradients a general purpose numerical implementation of this new formulation then produces a very attractive tool for engineering analysis this implementation includes a newton raphson algorithm permitting accurate solutions up to the moderate reynolds number range several numerical examples are provided to validate the present approach

the deterioration of hearing with age frequency selectivity the critical ratio the audiogram and speech threshold the frequency selectivity of the auditory system was measured by masking a sinusoidal signal 0 5 2 0 or 4 0 khz or a filtered speech signal with a wideband noise having a notch or stopband centered on the signal as the notch was widened performance improved for both types of signal but the rate of improvement decreased as the age of the 16 listeners increased from 23 to 75 years indicating a loss in frequency selectivity with age auditory filter shapes derived from the tone in noise data show a that the passband of the filter broadens progressively with age and b that the dynamic range of the filter ages like the audiogram that is the range changes little with age before 55 but beyond this point there is an accelerating rate of loss the speech experiment shows comparable but smaller effects the filter width measurements show that the critical ratio is a poor estimator of frequency selectivity because it confounds the tuning of the system with the efficiency of the signal detection and speech processing mechanisms that follow the filter an alternative one point measure of frequency selectivity which is both sensitive and reliable is developed via the filter shape model of masking

trigonometrically fitted multi step rkn methods for second order oscillatory initial value problems abstract trigonometrically fitted multi step runge kutta nystrom tfmsrkn methods for solving numerically oscillatory special second order initial value problems are introduced tfmsrkn methods integrate exactly the differential system whose solutions can be expressed as the linear combinations of functions from the set exp i w t exp i w t or equivalently the set cos wt sin wt where w represents an approximation of the main frequency of the problem the corresponding order conditions are given and two explicit four stage tfmsrkn methods with order five are constructed stability of the new methods is examined and the regions of stability are depicted numerical results show that our new methods are more efficient in comparison with other well known high quality methods proposed in the scientific literature

individualized estimation of the speech intelligibility index for short sentences test retest reliability the speech intelligibility index sii model was modified to allow individualized parameters these parameters included the relative weights of speech cues in five octave frequency bands ranging from 0 25 to 4 khz i e the band importance function and the transfer function that allows the sii to generate predictions on speech recognition scores a bayesian adaptive procedure the quick band importance function qbif procedure was utilized to enable efficient estimation of the sii parameters from individual listeners in two experiments the sii parameters were estimated for 30 normal hearing adults using institute of electrical and electronics engineers ieee sentences at speech levels of 55 65 and 75 db sound pressure level in experiment i and for 15 hearing impaired hi adult listeners using amplified ieee or azbio sentences in experiment ii in both experiments even without prior training the estimated model parameters showed satisfactory reliability between two runs of the qbif procedure at least one week apart for the hi listeners inter listener variability in most estimated sii parameters was larger than intra listener variability of the qbif procedure

qualitative identification of cracks using 3d transient elastodynamic topological derivative formulation and fe implementation a time domain topological derivative td approach is developed for transient elastic wave imaging of buried cracks the td which quantifies the sensitivity of the misfit cost functional to the creation at a specified location of an infinitesimal trial crack is expressed in terms of the time convolution of the free field and an adjoint field as a function of that specified location and of the trial crack shape following previous studies on cavity identification in similar conditions the td field is here considered as a natural and computationally efficient approach for defining a crack location indicator function this study emphasizes the implementation and exploitation of td fields using the standard displacement based fem a straightforward exploitation of the relevant sensitivity formulation established here results on several numerical experiments on 3d elastodynamic and acoustic configurations are reported and discussed allowing to assess and highlight many features of the proposed td based fast qualitative crack identification including its ability to identify multiple cracks and its robustness against data noise

sounding of finite solid bodies by way of topological derivative this paper is concerned with an application of the concept of topological derivative to elastic wave imaging of finite solid bodies containing cavities building on the approach originally proposed in the elastostatic theory of shape optimization the topological derivative which quantifies the sensitivity of a featured cost functional due to the creation of an infinitesimal hole in the cavity free reference body is used as a void indicator through an assembly of sampling points where it attains negative values the computation of topological derivative is shown to involve an elastodynamic solution to a set of supplementary boundary value problems for the reference body which are here formulated as boundary integral equations for a comprehensive treatment of the subject formulas for topological sensitivity are obtained using three alternative methodologies namely i direct differentiation approach ii adjoint field method and iii limiting form of the shape sensitivity analysis the competing techniques are further shown to lead to distinct computational procedures methodologies i and ii are implemented within a bem based platform and validated against an analytical solution a set of numerical results is included to illustrate the utility of topological derivative for 3d elastic wave sounding of solid bodies an approach that may perform best when used as a pre conditioning tool for more accurate gradient based imaging algorithms despite the fact that the formulation and results presented in this investigation are established on the basis of a boundary integral solution the proposed methodology is readily applicable to other computational platforms such as the finite element and finite difference techniques

on the topological derivative in shape optimization in this paper the topological derivative for an arbitrary shape functional is defined examples are provided for elliptic equations and the elasticity system in the plane the topological derivative can be used for solving shape optimization problems in structural mechanics

time domain transient elastodynamic analysis of 3 d solids by bem the numerical implementation of the direct boundary element formulation for time domain transient analysis of three dimensional solids is presented in a most general and complete manner the present formulation employs the space and time dependent fundamental solution stokes solution and graffi s dynamic reciprocal theorem to derive the boundary integral equations in the time domain a time stepping scheme is then used to solve the boundary initial value problem by marching forward in time higher order shape functions are used to approximate the field quantities in space as well as in time and a combination of analytical time integration and numerical spatial integration integration is carried out to form a system of linear equations at the end of each time step these equations are solved to obtain the unknown field quantities at that time finally the accuracy and reliability of this algorithm is demonstrated by solving a number of example problems and comparing the results against the available analytical and numerical solution

the role of orthogonal polynomials in numerical ordinary differential equations abstract orthogonal polynomials have many applications to numerical ordinary differential equations some of these especially those connected with the quadrature formulae on which many differential equation methods are based are to be expected on the other hand there are many surprising applications quite unlike traditional uses of orthogonal polynomials this paper surveys many of these applications especially those related to accuracy and implementability of runge kutta methods

new explicit adapted numerov methods for second order oscillatory differential equations this paper is concerned with a novel class of explicit adapted numerov an methods for solving initial value problems of second order oscillatory differential equations of the form y email protected 2y f x y the scheme of the methods incorporate the special structure of the problem carried by the term w 2y so that they can integrate the linear equation y email protected 2y 0 without truncation error a new type of simplifying assumption is proposed on the linear operators related to the quadratures that lead to the an scheme a practical an method of order five and three an methods of order six are derived the phase and stability properties of the new methods are analyzed the results of numerical experiments show the robustness and competence of the new methods compared with some highly efficient codes in the recent literature

analysis of symmetric domains in advanced applications with the boundary element method the strategy in the boundary element method for the analysis of symmetric domains that does not require the modelling of contours corresponding to the axes of symmetry is investigated for a number of advanced applications these applications include treatment of domain loadings two dimensional time domain transient elastodynamics and the analysis of probabilistic problems in elastostatics with a random geometric configuration both symmetric as well as arbitrary loadings acting on the symmetric objects are considered a number of case studies are presented to provide comparisons of computer memory and cpu time requirements for the analyses of the entire object versus the analyses of only the symmetric portion of the object the numerical data presented clearly demonstrates the advantages of developing efficient symmetric formulations for advanced applications

psychometric function estimation by probabilistic classification conventional psychometric function pf estimation involves fitting a parametric unidimensional sigmoid to binary subject responses which is not readily extendible to higher order pfs this study presents a nonparametric bayesian multidimensional pf estimator that also relies upon traditional binary subject responses this technique is built upon probabilistic classification pc which attempts to ascertain the subdomains corresponding to each subject response as a function of multiple independent variables increased uncertainty in the location of class boundaries results in a greater spread in the pf estimate which is similar to a parametric pf estimate with a lower slope pc was evaluated on both one dimensional 1d and two dimensional 2d simulated auditory pfs across a variety of function shapes and sample numbers in the 1d case pc demonstrated equivalent performance to conventional maximum likelihood regression for the same number of simulated responses in the 2d case where the responses

advanced development of time domain bem for two dimensional scalar wave propagation an improved formulation for solving 2d transient scalar wave propagation problems by the boundary element method bem is presented the kernels presented are simpler and better behaved than those that have appeared in the published literature an appropriate set of temporal shape functions for linear variation is used for spatial variations isoparametric quadratic elements are used all of these represent significant improvements over the present level of sophistication in the analysis of 2d transient scalar problems the algorithm is implemented in a general purpose boundary element code known as gpbest

auditory filter characteristics and consonant recognition for hearing impaired listeners to examine the association between frequency resolution and speech recognition auditory filter parameters and stop consonant recognition were determined for 9 normal hearing and 24 hearing impaired subjects in an earlier investigation the relationship between stop consonant recognition and the articulation index ai had been established on normal hearing listeners based on ai predictions speech presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores this strategy provides a method of interpreting speech recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance it was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing impaired listeners performance was measured under conditions that assured equivalent audibility of the speech stimuli derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold stop consonant recognition scores for most hearing impaired listeners were not significantly poorer than predicted by the ai model furthermore differences between observed recognition scores and those predicted by the ai were not associated with auditory filter characteristics suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation

new quadrature formulas based on the zeros of the chebyshev polynomials of the second kind abstract the aim of this work is to construct a new quadrature formula based on the divided differences of the integrand at points 1 1 and the zeros of the nth chebyshev polynomial of the second kind the interesting thing is that this quadrature rule is closely related to the well known gauss turan quadrature formula and includes a recent result obtained by a k varma and e landau as a special case

modification of the richardson panovsky methods for precise integration of satellite orbits abstract a family of implicit methods based on intrastep chebyshev interpolation has been developed to integrate initial value problems of the second order harmonic oscillator form d 2 y dt 2 y f y t t the procedure integrates the homogeneous part exactly in the absence of roundoff errors the chebyshev approach uses stepsizes that are considerably larger than those typically used in runge kutta or multistep methods computational overhead is comparable to that incurred by high order conventional procedures chebyshev interpolation coupled with the iterative nature of the method substantially reduces local errors global error propagation rates are also reduced making these procedures good candidates for use in long term simulations of perturbed oscillator systems the procedure is applied to integrations of the ks transformed equations for the oblateness perturbed orbital motion of an artificial satellite

elastodynamic boundary element method for piecewise homogeneous media a general higher order formulation for the time domain elastodynamic direct boundary element method is presented for computing the transient displacements and stresses in multiply connected two dimensional solids the displacement and traction interpolation functions are linear in time and quadratic in space all integrations are analytical and are expressed in terms of twelve basic recurring integrals causality is ensured by integrating only over the dynamically active parts of each element and the algorithm presented is time marching and implicit the use of analytical integrations allows both unbounded and bounded domain problems to be solved without having to introduce special enclosing elements all of these improved features allow for a formulation that is very efficient and accurate the stability and accuracy of the elastodynamic boundary element algorithm is demonstrated by solving several example problems and comparing the results with available analytical and numerical solutions 1998 john wiley sons ltd

axisymmetric transient elastodynamic analysis by boundary element method abstract the first formulation of an axisymmetric transient elastod namic analysis by time domain boundary element method is presented and is implemented in a general purpose system gpbest for the evaluation of boundary convolution integrals both constant and linear variations in the time domain of displacement and traction fields are given transformation of 3 d dynamic kernels into cylindrical coordinates and the integration of kernels along circumferential direction leads directly to an axisymmetric analysis with only 2 d boundary discretization the numerical integration of these kernels has been done carefully by preserving the causality so that very good accuracy and reliability of the present analysis have been achieved as can be seen in the examples presented