visualization of the space time impulse response of the subcritical wake of a cylinder the well known benard von karman cylinder wake is one of the most challenging phenomena of fluid mechanics as the reynolds number of the flow around a cylinder passes through a critical value alternating vortex shedding appears via a hopf bifurcation theoretical studies of the wake have described the appearance of this self sustained oscillation as the result of a convective to absolute transition resulting in the formation of a global mode we illustrate here the convective global regime of the subcritical wake by analyzing visualizations of its impulse response

a novel scheme for the solution of the time domain integral equations of electromagnetics a new method to numerically solve time domain integral equations pertinent to electromagnetic surface scattering phenomena is presented the method uses approximate prolate spheroidal wave functions and standard rao wilton glisson basis functions to effect the temporal and spatial discretization of the integral equations respectively because the temporal basis functions are noncausal an extrapolation scheme is used to construct a system of equations that can be solved by marching on in time numerical results show that the proposed method is stable and that its solutions converge exponentially fast with the time bandwidth product of the approximate prolate spheroidal wave functions to results from a frequency domain method of moments solver that uses spatial basis functions and integration rules identical to those in the time domain solver

fast analysis of transient acoustic wave scattering from rigid bodies using the multilevel plane wave time domain algorithm the analysis of transient wave scattering from rigid bodies using integral equation based techniques is computationally intensive if carried out using classical schemes the evaluation of the velocity potential on the surface of a three dimensional scatterer represented in terms of ns spatial basis functions for nt time steps requires o ntns2 operations the recently developed plane wave time domain pwtd algorithm permits the rapid evaluation of transient fields that are generated by bandlimited source distributions it has been shown that incorporation of the pwtd algorithm into integral equation based solvers in a two level setting reduces the computational complexity of a transient analysis to o ntns1 5 logns in this paper it is shown that casting the pwtd scheme into a multilevel framework permits the analysis of transient acoustic surface scattering phenomena in o ntnslog2ns operations using o ntns memory numerical examples that demonstrate the efficacy of the multilevel implementation are also presented

an accurate scheme for the solution of the time domain integral equations of electromagnetics using higher order vector bases and bandlimited extrapolation despite the numerous advances made in increasing the computational efficiency of time domain integral equation tdie based solvers the stability and accuracy of tdie solvers remain problematic this paper introduces a new numerical method for the accurate solution of tdies for scattering from arbitrary perfectly conducting surfaces the work described in this paper uses the higher order divergence conforming basis functions of graglia et al for spatial discretization and bandlimited interpolation functions for the temporal discretization of the relevant integral equations since the basis functions used for the temporal representation are noncausal an extrapolation scheme is employed to recover the ability to solve the problem by marching on in time numerical results demonstrate that the proposed method is stable and that it exhibits superlinear convergence with regard to the spatial discretization and exponential convergence with respect to the temporal discretization

polar integration for exact space time quadrature in time domain integral equations a space time polar quadrature technique for numerical integration of green s function interactions in time domain integral equations is presented the method transforms 2 d surface space time integrals associated with vector and scalar potentials to a 1 d integral that is performed using gauss legendre integration the advantage of the presented technique compared to standard 2 d gaussian quadrature is that time delays between each section of the source basis function and the observation point are accounted for exactly in an analytic manner this ensures highly accurate temporal behavior of the green s function interactions thereby contributing to the stability of the overall time domain integral equations

computational study of subcritical response in flow past a circular cylinder flow past a circular cylinder is investigated in the subcritical regime below the onset of benard von karman vortex shedding at reynolds number re c similar or equal to 47 the transient response of infinitesimal perturbations is computed the domain requirements for obtaining converged results is discussed at length it is shown that energy amplification occurs as low as re 2 2 throughout much of the subcritical regime the maximum energy amplification increases approximately exponentially in the square of re reaching 6800 at re c the spatiotemporal structure of the optimal transient dynamics is shown to be transitory benard von karman vortex streets at re similar or equal to 42 the long time structure switches from exponentially increasing downstream to exponentially decaying downstream three dimensional computations show that two dimensional structures dominate the energy growth except at short times

derivation and implementation of the boundary integral formula for the convective acoustic wave equation in time domain kirchhoff s formula for the convective wave equation is derived using the generalized function theory the generalized convective wave equation for a stationary surface is obtained and the integral formulation the convective kirchhoff s formula is derived the formula has a similar form to the classical kirchhoff s formula but an additional term appears due to a moving medium effect for convenience the additional term is manipulated to a final form as the classical kirchhoff s formula the frequency domain boundary integral can be obtained from the current time domain boundary integral form the derived formula is verified by comparison with the analytic solution of source in the uniform flow the formula is also utilized as a boundary integral equation time domain boundary element method bem analysis using the boundary integral equation is conducted and the results show good agreement with the analytical solution the formula derived here can be useful for sound radiation and scattering by arbitrary bodies in a moving medium in the time domain

electromagnetic scattering from 3 d curved dielectric bodies using time domain integral equations a boundary integral equation bie approach is developed to calculate transient scattering from dielectric bodies the treatment is directly in terms of the e and h fields rather than magnetic and electric currents it employs curvilinear quadratic modeling which allows accurate representation of arbitrarily shaped curved bodies the treatment is isoparametric with the same quadratic representation of the spatial field variation and with the temporal variation modeled by similar quadratic elements integration employs high order gaussian quadrature with special treatment of the singular and hypersingular integrals that arise the treatment is implicit requiring the solution of a sparse matrix equation at each timestep this adds only trivially to the cost at each timestep and by freeing the timestep from the constraint that it be smaller than the smallest nodal spacing can greatly reduce the number of timesteps that must be employed additionally it produces stable results without resort to the averaging processes proposed elsewhere example calculations of scattering from a sphere a cube and an almond are presented and compared with earlier published transient results and with results from a frequency domain treatment good agreement and improved accuracy is found

a finite difference delay modeling approach to the discretization of the time domain integral equations of electromagnetics a new method for solving the time domain integral equations of electromagnetic scattering from conductors is introduced this method called finite difference delay modeling appears to be completely stable and accurate when applied to arbitrary structures the temporal discretization used is based on finite differences specifically based on a mapping from the laplace domain to the z transform domain first and second order unconditionally stable methods are derived spatial convergence is achieved using the higher order divergence conforming vector bases of graglia et al low frequency instability problems are avoided with the loop tree decomposition approach numerical results will illustrate the accuracy and stability of the technique

formulation of a galerkin spectral element fourier method for three dimensional incompressible flows in cylindrical geometries a primitive variable formulation for simulation of time dependent incompressible flows in cylindrical coordinates is developed spectral elements are used to discretise the meridional semi plane coupled with fourier expansions in azimuth unlike previous formulations where special distributions of nodal points have been used in the radial direction the current work adopts standard gauss lobatto legendre nodal based expansions in both the radial and axial directions using a galerkin projection of the symmetrised cylindrical navier stokes equations all geometric singularities are removed as a consequence of either the fourier mode dependence of axial boundary conditions or the shape of the weight function applied in the galerkin projection this observation implies that in a numerical implementation geometrically singular terms can be naively treated by explicitly zeroing their contributions on the axis in integral expressions without recourse to special treatments such as l hopital s rule exponential convergence of the method both in the meridional semi plane and in azimuth is demonstrated through application to a three dimensional analytical solution of the navier stokes equations in which flow crosses the axis

singular basis functions and curvilinear triangles in the solution of the electric field integral equation basis functions are formulated that account for singularities in the charge density near an edge on a conducting body the formulation is general and the basis functions are valid for planar as well curvilinear geometries in principle singularities of any order can be treated but best results are obtained for so called knife edge singularities results are compared with exact solutions or measurements where available for some simple problems

marching on in time solution of the time domain magnetic field integral equation using a predictor corrector scheme an explicit marching on in time mot scheme for solving the time domain magnetic field integral equation td mfie is presented the proposed mot td mfie solver uses rao wilton glisson basis functions for spatial discretization and a pe ce m type linear multistep method for time marching unlike previous explicit mot td mfie solvers the time step size can be chosen as large as that of the implicit mot td mfie solvers without adversely affecting accuracy or stability an algebraic stability analysis demonstrates the stability of the proposed explicit solver its accuracy and efficiency are established via numerical examples

a fast time domain integral equation based scheme for analyzing scattering from dispersive objects a fast integral equation based scheme for analyzing transient scattering from inhomogeneous dispersive bodies is presented a time domain integral equation in terms of the electric flux inside the body is constructed by invoking the volume equivalence principle i e by equating the sum of the incident electric field and that radiated by equivalent volume polarization currents to the total electric field the proposed algorithm for solving this time domain integral equation incorporates a recursive convolution scheme that updates the polarization current from knowledge of the electric flux to reduce the computational cost and memory requirement of the resulting marching on in time scheme it is augmented with the plane wave time domain algorithm numerical results that validate the proposed approach and demonstrate its accuracy are presented

stable electric field tdie solvers via quasi exact evaluation of mot matrix elements prior theoretical studies and experience confirm that the stability of marching on in time mot solvers pertinent to the analysis of scattering from free standing three dimensional perfect electrically conducting surfaces hinges on the accurate evaluation of mot matrix elements resulting from a galerkin discretization of the underlying time domain integral equation tdie unfortunately the accurate evaluation of the four dimensional spatial integrals involved in the expressions for these matrix elements is prohibitively expensive when performed by computational means here a method that permits the quasi exact evaluation of mot matrix elements is presented specifically the proposed method permits the analytical evaluation of three out of the four spatial integrations leaving only one integral to be evaluated numerically since the latter has finite range and a piecewise smooth integrand it can be evaluated to very high accuracy using standard quadrature rules as a result the proposed method permits the fast evaluation of mot matrix elements with arbitrary user specified accuracy extensive numerical experiments show that an mot solver for the electric field tdie that uses the proposed quasi exact method is stable for a very wide range of time step sizes and yields solutions that decay exponentially after the excitation vanishes

a fast higher order time domain finite element boundary integral method for 3 d electromagnetic scattering analysis a novel hybrid time domain finite element boundary integral method for analyzing three dimensional 3 d electromagnetic scattering phenomena is presented the method couples finite element and boundary integral field representations in a way that results in a sparse system matrix and solutions that are devoid of spurious modes to accurately represent the unknown fields the scheme employs higher order vector basis functions defined on curvilinear tetrahedral elements to handle problems involving electrically large objects the multilevel plane wave time domain algorithm is used to accelerate the evaluation of the boundary integrals numerical results demonstrate the accuracy and versatility of the proposed scheme

analysis of transient electromagnetic scattering phenomena using a two level plane wave time domain algorithm a fast algorithm is presented for solving electric magnetic and combined field time domain integral equations pertinent to the analysis of surface scattering phenomena the proposed two level plane wave time domain pwtd algorithm permits a numerically rigorous reconstruction of transient near fields from their far field expansion and augments classical marching on in time mot based solvers the computational cost of analyzing surface scattering phenomena using pwtd enhanced mot schemes scales as o n sub i n sub s sup 2 3 log n sub s as opposed to spl oscr n sub t n sub s sup 2 for classical mot methods where n sub t and n sub s are the numbers of temporal and spatial basis functions discretizing the scatterer current numerical results that demonstrate the efficacy of the proposed solver in analyzing transient scattering from electrically large structures and that confirm the above complexity estimate are presented

application of stable fem fdtd hybrid to scattering problems a recently developed stable finite element method fem finite difference time domain fdtd hybrid that eliminates the staircase approximation of complex geometries is tested by convergence studies for radar cross sections for a conducting sphere 1 db accuracy in all directions is obtained with nine cells per wavelength whereas the nasa almond requires a higher resolution of about 15 cells per wavelength for scatterers with a smooth boundary the results converge quadratically with the mesh size but for a horizontally polarized wave incident on the nasa almond the order of convergence is lower because of singular fields at the tip

hierarchal vector boundary elements and p adaption for 3 d electromagnetic scattering this paper describes the development of new vector boundary elements for solving electromagnetic em scattering problems the new elements are suitable for the magnetic field integral equation mfie electrical field integral equation efie or the combination field integral equation cfie the basis functions are assigned to the edges of an element rather than to its nodes the new element guarantees the continuity of the normal component of the surface current across element edges furthermore the basis functions are hierarchical from linear to higher order which enables one to use the new elements in a p adaption scheme

shape invariant modeling of circadian rhythms with random effects and smoothing spline anova decompositions medical studies often collect physiological and or psychological measurements over time from multiple subjects to study dynamics such as circadian rhythms under the assumption that the expected response functions of all subjects are the same after shift and scale transformations shape invariant models have been applied to analyze this kind of data the shift and scale parameters provide efficient and interpretable data summaries while the common shape function is usually modeled nonparametrically to provide flexibility however due to the deterministic nature of the shift and scale parameters potential correlations within a subject are ignored furthermore the shape of the common function may depend on other factors such as disease in this article we propose shape invariant mixed effects models a second stage model with fixed and random effects is used to model individual shift and scale parameters a second stage smoothing spline anova model is used to study potential covariate effects on the common shape function we apply our methods to a real data set to investigate disease effects on circadian rhythms of cortisol a hormone that is affected by stress we find that patients with cushing s syndrome lost circadian rhythms and their 24 hour means were elevated to very high levels patients with major depression had the same circadian shape and phases as normal subjects however their 24 hour mean levels were elevated and amplitudes were dampened for some patients

regularized integral equations and curvilinear boundary elements for electromagnetic wave scattering in three dimensions the boundary integral equations bies in their original forms which govern the electromagnetic em wave scattering in three dimensional space contain at least a hypersingularity 1 r sup 3 or a cauchy singularity 1 r sup 2 usually both thus obtaining reliable numerical solutions using such equations requires considerable care especially when developing systematic numerical integration procedures for realistic problems regularized bies for the numerical computation of time harmonic em scattering fields due to arbitrarily shaped scatterers are introduced two regularization approaches utilizing an isolation method plus a mapping are presented to remove all singularities prior to numerical integration both approaches differ from all existing approaches to em scattering problems both work for integral equations initially containing either hypersingularities or cauchy singularities without the need to introduce surface divergences or other derivatives of the em fields on the boundary also neither approach is limited to flat surfaces nor flat element models of curved surfaces the muller linear combination of the electric and magnetic field integral equations efie and mfie is used to avoid the resonance difficulty that is usually associated with integral equation based formulations some preliminary numerical results for em scattering due to single and multiple dielectric spheres are presented and compared with analytical solutions

a hybrid time domain technique that combines the finite element finite difference and method of moment techniques to solve complex electromagnetic problems this paper describes a hybrid technique directly operating in time domain that combines the finite element time domain fetd the finite difference time domain fdtd and the integral equation based method of moments in the time domain momtd techniques to analyze complex electromagnetic problems involving thin wire antennas radiating in the presence of inhomogeneous dielectric bodies whose shape can be arbitrary the method brings together the ability of the fdtd scheme to deal with arbitrary material properties the versatility of the fetd to accurately model curved geometries and that of the mom to analyze thin wire structures working in the time domain provides wide band information from a single execution of the marching on in time procedure and simplifies the interfacing of the fe and mom methods with the fdtd an approach specifically designed for time domain analysis numerical results that validate the hybrid method and show its capabilities are presented in the paper

numerical solution of time domain volume integral equations for transient electromagnetic scattering by dielectric objects electromagnetic em interaction with penetrable objects can be described by volume integral equations vies in integral equation approach and time domain vies tdvies are required for formulating transient em problems with such objects the tdvies are usually solved by combining the method of moments mom with well designed basis function in space domain and a march on in time mot scheme in time domain the space domain mom requires conforming meshes in geometric discretization and twofold numerical integrations in matrix generation while the mot in time domain suffers from a late time instability problem in this communication we propose an alternative approach that uses the nystrom method to discretize the vies in space domain while employing the mom with laguerre basis and testing functions to discretize the equations in time domain the proposed approach can simplify the numerical implementation and produce a march on in degree procedure similar to that in frequency domain approaches numerical examples are presented to illustrate the approach and good results have been observed

high order splitting methods for the incompressible navier stokes equations abstract a new pressure formulation for splitting methods is developed that results in high order time accurate schemes for the solution of the incompressible navier stokes equations in particular improved pressure boundary conditions of high order in time are introduced that minimize the effect of erroneous numerical boundary layers induced by splitting methods a new family of stiffly stable schemes is employed in mixed explicit implicit time intgration rules these schemes exhibit much broader stability regions as compared to adams family schemes typically used in splitting methods their stability properties remain almost constant as the accuracy of the integration increases so that robust third or higher order time accurate schemes can readily be constructed that remain stable at relatively large cfl number the new schemes are implemented within the framework of spectral element discretizations in space so that flexibility and accuracy is guaranteed in the numerical experimentation a model stokes problem is studied in detail and several examples of navier stokes solutions of flows in complex geometries are reported comparison is made with the previously used first order in time spectral element splitting and non splitting e g uzawa schemes high order splitting spectral element methods combine accuracy in space and time and flexibility in geometry and thus can be very efficient in direct simulations of turbulent flows in complex geometries

spatially large domain and temporally entire domain electric field integral equation method of moments for 3 d scattering analysis in time domain a novel spatially large domain and temporally entire domain method of moments mom is proposed for surface integral equation sie modeling of 3 d conducting scatterers in the time domain td the method uses higher order curved lagrange interpolation generalized quadrilateral geometrical elements higher order spatial current expansions based on hierarchical divergence conforming polynomial vector basis functions and temporal current modeling by means of orthogonal weighted associated laguerre basis functions it implements full temporal and spatial galerkin testing and marching on in degree mod scheme for an iterative solution of the final system of spatially and temporally discretized mom td equations numerical examples demonstrate excellent accuracy efficiency convergence and versatility of the new mom mod method the results also demonstrate very effective large domain mom td sie models of scatterers using flat and curved patches of electrical sizes of up to about 1 7 wavelengths at the maximum frequency in the frequency spectrum of the pulse excitation higher order current expansions of spatial orders from 2 to 8 in conjunction with entire domain laguerre temporal bases and minimal numbers of unknowns

a stabilized marching on in degree scheme for the transient solution of the electric field integral equation time domain electric integral equation methods td efie suffer from the numerical stability problem numerous schemes have been proposed over the years for the purpose of taking care of this instability among them the marching on in degree mod method is one of the newly proposed algorithms for calculating the various transient responses the mod solver employs a set of associated laguerre functions and incorporates exact temporal galerkin testing although the mod scheme is assumed to be more stable when compared with marching on in time mot there are few numerical or theoretical investigations on the stability of the various numerical recursive operations for the mod methodology it has been shown that the time domain magnetic field integral equation td mfie using the mod method can be stabilized by using a filon type quadrature formula to accurately integrate the highly oscillatory laguerre functions which has caused instability for the mod solvers using a higher degree of approximation on the other hand the analytical expression of temporal derivatives used in the mod scheme is strongly affected by an unbounded initial value of the transient current in this paper a novel filon type radial integration method and a sequential constraint term for td efie mod are proposed which make the stabilized mod solver accurate and stable for the arbitrary degree of the laguerre polynomials some numerical results are presented to illustrate the validity of the stabilized mod solution of td efie for transient scattering problems

implicit runge kutta methods for the discretization of time domain integral equations implicit runge kutta based schemes are proposed for solving the time domain integral equations of electromagnetic theory the proposed technique maps a laplace domain equation to a domain equation using the butcher tableau of the implicit runge kutta scheme a discrete time domain system is recovered by computing the inverse transform numerically the resulting technique is capable of third or fifth order accuracy in time and is stable independent of time step numerical results illustrate the accuracy and stability of the technique

bayesian confidence intervals for the cross validated smoothing spline summary we consider the model y t g ti ei i 17 2 n where g t t 0 1 is a smooth function and the ei are independent n 0 a2 errors with g2 unknown the cross validated smoothing spline can be used to estimate g non parametrically from

efficient evaluation of double surface integrals in time domain integral equation formulations a new integration approach is presented for accurately calculating time domain efie mfie and cfie matrix elements over triangular domains it mainly consists of a radial integration scheme for handling weakly singular and near hypersingular inner integrals and some new smoothing techniques for treating outer two dimensional 2 d integrals the proposed approach has sufficient generality and efficiency for solving time domain integral equations tdie with arbitrary types of temporal basis functions and temporal discretization schemes such as marching on in time mot marching on in degree mod and finite difference delay modeling convolution quadrature fddm cq etc the numerical results for calculating some typical integrals are given to demonstrate its capability with high accuracy and rapid convergence rate achieved

stabilization of time domain acoustic boundary element method for the interior problem with impedance boundary conditions the time domain boundary element method bem is associated with numerical instability that typically stems from the time marching scheme in this work a formulation of time domain bem is derived to deal with all types of boundary conditions adopting a multi input multi output infinite impulse response structure the fitted frequency domain impedance data are converted into a time domain expression as a form of an infinite impulse response filter which can also invoke a modeling error in the calculation the response at each time step is projected onto the wave vector space of natural radiation modes which can be obtained from the eigensolutions of the single iterative matrix to stabilize the computation unstable oscillatory modes are nullified and the same decay rate is used for two nonoscillatory modes as a test example a transient sound field within a partially lined parallelepiped box is used within which a point source is excited by an octave band impulse in comparison with the results

on the stability of time domain magnetic field integral equation using laguerre functions the marching on in degree mod method has been proposed for solving time domain integral equations tdies and it uses the associated laguerre functions as temporal basis and testing functions although the mod scheme is assumed to be stable and accurate there exists little investigation into the accuracy of the integral operations involving the associated laguerre functions of high degree it is shown in this paper that the numerical quadrature for integrating the highly oscillatory laguerre functions may not be accurate and this may result in instability for the mod solvers in this paper the highly oscillatory nature of the high degree associated laguerre functions is investigated first based on that the numerical procedures are described which result in the inaccuracy of the numerical quadrature associated with the highly oscillatory nature for the higher order laguerre functions this can produce instability for the mod solvers when a solution requires a high degree of the laguerre functions hence a novel filon type quadrature method and a stabilized mod technique for time domain magnetic field integral equations td mfie smod are presented in this paper some numerical results are presented to illustrate the validity of the proposed filon type quadrature rule resulting in stable solution of the td mfie for transient scattering problems

stability and convergence of collocation schemes for retarded potential integral equations time domain boundary integral formulations of transient scattering problems involve retarded potential integral equations solving such equations numerically is both complicated and computationally intensive and numerical methods often prove to be unstable collocation schemes are easier to implement than full finite element formulations but little appears to be known about their stability and convergence here we derive and analyze some new stable collocation schemes for the single layer equation for transient acoustic scattering and use spatial fourier and temporal laplace transform techniques to demonstrate that such stable schemes are second order convergent

using a radial ultrasound probe s virtual origin to compute midsagittal smoothing splines in polar coordinates tongue surface measurements from midsagittal ultrasound scans are effectively arcs with deviations representing tongue shape but smoothing spline analysis of variances ssanovas assume variance around a horizontal line therefore calculating ssanova average curves of tongue traces in cartesian coordinates davidson j acoust soc am 120 1 407 415 2006 creates errors that are compounded at tongue tip and root where average tongue shape deviates most from a horizontal line this paper introduces a method for transforming data into polar coordinates similar to the technique by mielke j acoust soc am 137 5 2858 2869 2015 but using the virtual origin of a radial ultrasound transducer as the polar origin allowing data conversion in a manner that is robust against between subject and between session variability

smoothing spline anova for time dependent spectral analysis in this article we propose a smoothing spline anova model ss anova to estimate and to make inference on the time varying log spectrum of a locally stationary process the time varying spectrum is assumed to be smooth in both time and frequency this assumption essentially turns a time frequency spectral estimation problem into a 2 dimensional surface estimation problem a smooth localized complex exponential slex basis is used to calculate the initial periodograms and a ss anova is fitted to the log periodograms this approach allows the time and frequency domains to be modeled in a unified approach and jointly estimated inference procedures such as confidence intervals and hypothesis tests proposed for the ss anova can be adopted for the time varying spectrum because of the smoothness assumption of the underlying spectrum once we have the estimates on a time frequency grid we can calculate the estimate at any given time and frequency this leads to a high computational efficiency because for

higher order frequency domain computational electromagnetics a review of the higher order computational electromagnetics cem for antenna wireless and microwave engineering applications is presented higher order cem techniques use current field basis functions of higher orders defined on large e g on the order of a wavelength in each dimension curvilinear geometrical elements which greatly reduces the number of unknowns for a given problem the paper reviews all major surface volume integral and differential equation electromagnetic formulations within a higher order computational framework focusing on frequency domain solutions with a systematic and unified review of generalized curved parametric quadrilateral triangular hexahedral and tetrahedral elements and various types of higher order hierarchical and interpolatory vector basis functions in both divergence and curl conforming arrangements a large number of actual higher order techniques representing various combinations of formulations elements bases and solution procedures are identified and discussed the examples demonstrate the accuracy efficiency and versatility of higher order techniques and their advantages over low order discretizations the most important one being a much faster higher order convergence of the solution it is demonstrated that both components of the higher order modeling namely higher order geometrical modeling and higher order current field modeling are essential for accurate and efficient cem analysis of general antenna scattering and microwave structures

the extension of time domain integral equation analysis to scattering from imperfectly conducting bodies an extension of integral equation time domain analysis to treat electromagnetic scattering from imperfect conductors embedded in a dielectric is presented it employs isoparametric curvilinear representations and an implicit time stepping approach is used to achieve stability the principal difficulties arise from the diffusive wake term which the finite conductivity introduces into the green s function the consequent computational complexity and costs both significantly greater than for perfectly conducting scatterers are discussed examples of the application of the methods are presented

time domain analysis of electromagnetic scattering problems by using integral equation method with space delayed temporal basis functions this communication presents a new numerical method for the efficient solution of marching on in time mot based time domain integral equations tdie for electromagnetic scattering from perfect electrically conducting pec object with large smooth surfaces a set of space delayed temporal basis functions is proposed for the temporal discretization and the curvilinear rao wilson glisson crwg basis functions for the spatial discretization the space delayed temporal basis functions are firstly extended to the time domain electric field integral equations tdefie then easily to the time domain combined field integral equations tdcfie numerical results demonstrate that the new method is stable and effective for the transient scattering problems from pec objects with large smooth surfaces and a single plane wave incidence a significant reduction of the number of spatial unknowns is achieved by using the space delayed temporal basis functions

potential integrals for uniform and linear source distributions on polygonal and polyhedral domains formulas for the potentials due to uniform and linearly varying source distributions defined on simply shaped domains are systematically developed and presented domains considered are infinite planar strips infinite cylinders of polygonal cross sections planar surfaces with polygonal boundaries and volumetric regions with polyhedral boundaries the expressions obtained are compact in form and their application in the numerical solution of electromagnetics problems by the method of moments is illustrated

regular article an accurate cartesian grid method for viscous incompressible flows with complex immersed boundaries a cartesian grid method has been developed for simulating two dimensional unsteady viscous incompressible flows with complex immersed boundaries a finite volume method based on a second order accurate central difference scheme is used in conjunction with a two step fractional step procedure the key aspects that need to be considered in developing such a solver are imposition of boundary conditions on the immersed boundaries and accurate discretization of the governing equation in cells that are cut by these boundaries a new interpolation procedure is presented which allows systematic development of a spatial discretization scheme that preserves the second order spatial accuracy of the underlying solver the presence of immersed boundaries alters the conditioning of the linear operators and this can slow down the iterative solution of these equations the convergence is accelerated by using a preconditioned conjugate gradient method where the preconditioner takes advantage of the structured nature of the underlying mesh the accuracy and fidelity of the solver is validated by simulating a number of canonical flows and the ability of the solver to simulate flows with very complicated immersed boundaries is demonstrated

robust solution of time domain integral equations using loop tree decomposition and bandlimited extrapolation a stabilization method that eradicates low frequency instabilities in the solution of the time domain integral equations of electromagnetic scattering is presented the method uses the loop tree decomposition originally suggested for the solution of low frequency scattering problems via the method of moments specifically a temporally differentiated form of the pertinent integral equation is tested using tree basis functions and the undifferentiated form is tested using solenoidal basis functions the underlying solution method uses bandlimited interpolation functions blifs and the higher order divergence conforming vector bases of graglia et al for the temporal and spatial discretization of the integral equations respectively an extrapolation technique has been implemented to overcome the noncausality introduced into the system by the blifs numerical results will demonstrate the stability and accuracy of the proposed technique

time domain bie analysis of large three dimensional electromagnetic scattering problems a time domain boundary integral equation bie solution of the magnetic field integral equation mfie for large electromagnetic scattering problems is presented it employs isoparametric curvilinear quadratic elements to model fields geometry and time dependence eliminating staircasing problems the approach is implicit which seems to provide both stability and permits arbitrary local mesh refinement to model geometrically difficult regions without the significant cost penalty explicit methods suffer error dependence on discretization is investigated accurate results are obtained with as few as five nodes per wavelength the performance both on large scatterers and on low radar cross section rcs scatterers is demonstrated including the six wavelength nasa almond two spheres a thirteen wavelength missile and a high q cavity

on the lingual organization of the german vowel system a hybrid parafac and principal component model of tongue configuration in vowel production is presented using a corpus of german vowels in multiple consonant contexts fleshpoint data for seven speakers at two speech rates from electromagnetic articulography the parafac approach is attractive for explicitly separating speaker independent and speaker dependent effects within a parsimonious linear model however it proved impossible to derive a parafac solution of the complete dataset estimated to require three factors due to complexities introduced by the consonant contexts accordingly the final model was derived in two stages first a two factor parafac model was extracted this succeeded the result was treated as the basic vowel model second the parafac model error was subjected to a separate principal component analysis for each subject this revealed a further articulatory component mainly involving tongue blade activity associated with the flanking consonants however the subject specific details of the mapping from raw fleshpoint coordinates to this component were too complex to be consistent with the parafac framework the final model explained over 90 of the variance and gave a succinct and physiologically plausible articulatory representation of the german vowel space

numerical solution of time domain integral equations for arbitrarily shaped conductor dielectric composite bodies in this work we present a numerical solution of the coupled time domain integral equations to obtain induced currents and scattered far fields on a three dimensional arbitrary shaped conducting dielectric composite body illuminated by a gaussian electromagnetic plane wave pulse the coupled integral equations are derived utilizing the equivalence principle the solution method is based on the method of moments and involves the triangular patch modeling of the composite body in conjunction with the patch basis functions detailed mathematical steps along with several numerical results are presented to illustrate the efficacy of this approach

an evaluation of several methods for computing lingual coarticulatory resistance using ultrasound the paper evaluates the efficiency of six computation methods in distinguishing lingual coarticulatory resistance among consonants and vowels using ultrasound data this research goal is tested on a corpus of symmetrical vowel consonant vowel sequences composed of 10 consonants and five vowels produced by five catalan speakers results show that while the coarticulatory resistance hierarchies obtained by all methods conform largely to the predictions of the degree of articulatory constraint model of coarticulation some i e area of the articulatory zone mean point by point coefficient of variation and mean nearest neighbour distance are somewhat more highly predictive than others i e locus equation mutual information and highest point of the tongue dorsum methods differ mostly regarding the classification of consonants exhibiting intermediate degrees of coarticulatory resistance due to the way the methods have been designed the implications of these findings for research on dialectal variation are discussed

comparing tongue shapes from ultrasound imaging using smoothing spline analysis of variance ultrasound imaging of the tongue is increasingly common in speech production research however there has been little standardization regarding the quantification and statistical analysis of ultrasound data in linguistic studies researchers may want to determine whether the tongue shape for an articulation under two different conditions e g consonants in word final versus word medial position is the same or different this paper demonstrates how the smoothing spline anova ss anova can be applied to the comparison of tongue curves gu smoothing spline anova models springer new york 2002 the ss anova is a technique for determining whether or not there are significant differences between the smoothing splines that are the best fits for two data sets being compared if the interaction term of the ss anova model is statistically significant then the groups have different shapes since the interaction may be significant even if only a small section of the curves are different i e the tongue root is the same but the tip of one group is raised bayesian confidence intervals are used to determine which sections of the curves are statistically different ss anovas are illustrated with some data comparing obstruents produced in word final and word medial coda position

smoothing spline anova for exponential families with application to the wisconsin epidemiological study of diabetic retinopathy the 1994 neyman memorial lecture let y i i 1 n be independent observations with the density of y i of the form h y i f i exp y i f i b f i c y i where b and c are given functions and b is twice continuously differentiable and bounded away from 0 let i t f t i where t t 1 t d t 1 t d t the t are measurable spaces of rather general form and f is an unknown function on t with some assumed smoothness properties given y i t i i 1 n it is desired to estimate f t for t in some region of interest contained in t we develop the fitting of smoothing spline anova models to this data of the form f t c f t f t t the components of the decomposition satisfy side conditions which generalize the usual side conditions for parametric anova the estimate of f is obtained as the minimizer in an appropriate function space of l y f j f j f where l y f is the negative log likelihood of y y 1 y n given f the j j are quadratic penalty functionals and the anova decomposition is terminated in some manner there are five major parts required to turn this program into a practical data analysis tool 1 methods for deciding which terms in the anova decomposition to include model selection 2 methods for choosing good values of the smoothing parameters 3 methods for making confidence statements concerning the estimate 4 numerical algorithms for the calculations and finally 5 public software in this paper we carry out this program relying on earlier work and filling in important gaps the overall scheme is applied to bernoulli data from the wisconsin epidemiologic study of diabetic retinopathy to model the risk of progression of diabetic retinopathy as a function of glycosylated hemoglobin duration of diabetes and body mass index it is believed that the results have wide practical application to the analysis of data from large epidemiologic studies

a stable marching on in time scheme for solving the time domain electric field volume integral equation on high contrast scatterers a time domain electric field volume integral equation td efvie solver is proposed for characterizing transient electromagnetic wave interactions on high contrast dielectric scatterers the td efvie is discretized using the schaubert wilton glisson swg and approximate prolate spherical wave apsw functions in space and time respectively the resulting system of equations cannot be solved by a straightforward application of the marching on in time mot scheme since the two sided apsw interpolation functions require the knowledge of unknown future field samples during time marching causality of the mot scheme is restored using an extrapolation technique that predicts the future samples from known past ones unlike the extrapolation techniques developed for mot schemes that are used in solving time domain surface integral equations this scheme trains the extrapolation coefficients using samples of exponentials with exponents on the complex frequency plane this increases the stability of the mot td efvie solver significantly since the temporal behavior of decaying and oscillating electromagnetic modes induced inside the scatterers is very accurately taken into account by this new extrapolation scheme numerical results demonstrate that the proposed mot solver maintains its stability even when applied to analyzing wave interactions on high contrast scatterers

an application of the boundary element method to the magnetic field integral equation a boundary element method bem for the solution of electromagnetic scattering problems using the magnetic field integral equation mfie is discussed the discretized form of the mfie is written in indicial notation with no limitations placed on the order of either the geometric or functional approximation by considering several different types of boundary elements it is determined that geometric errors can be significant and degrade the accuracy of the numerical solution it is shown that a higher order approximation for the current could significantly improve the accuracy of the numerical solution the superparametric boundary element in which the geometry was given quadratic approximation and the current was given linear approximation was more efficient than elements using lower order approximations the bem results are compared to the results obtained using the dielectric bodies of revolution dbr code

semiparametric analysis of variance with tensor product thin plate splines we consider fitting multivariate models to response data based on analysis of variance anova like decompositions of functions of several variables f t 1 t d c f t f t t a theory for fitting some components of these models with polynomial smoothing splines exists when each t is in a subset of the real line in this case the various estimated components turn out to be certain tensor sums and products of polynomial splines this approach may not be natural when one or more of the variables are geographic in particular where nature does not know north from east

fast transient analysis of acoustic wave scattering from rigid bodies using a two level plane wave time domain algorithm it is well known that the computational cost associated with the application of classical time domain integral equation methods to the analysis of scattering from acoustical targets scales unfavorably with problem size indeed performing a three dimensional scattering analysis using these methods requires o ntns2 operations where ns denotes the number of basis functions that model the spatial field distribution over the surface of the scatterer and nt is the number of time steps in the analysis recently novel plane wave time domain algorithms that augment these classical methods and thereby reduce their high computational cost have been introduced this paper describes such a plane wave time domain algorithm within the context of the analysis of acoustic scattering from rigid bodies and outlines its incorporation into a time domain integral equation solver in a two level setting it is shown that the resulting scheme has a computational complexity of o ntns1 5 log ns examples comparing the accuracy

an accurate method for the calculation of singular integrals arising in time domain integral equation analysis of electromagnetic scattering an accurate method for the evaluation of the cauchy principal value integrals arising in time domain electromagnetic wave scattering is presented this is applied to a boundary integral equation bie method employing quadratic curvilinear surface elements where such singularities do not vanish as they generally do when simpler but less accurate discretizations are employed the technique involves weakening the singularity in the original kernel to a degree where conventional integration methods may be employed and transforming the strong singularity to a line integral in a form which allows cancellation of its singular components the effectiveness of the method is demonstrated by scattering calculations on a variety of targets and the computational cost of the approach is trivial

a hybrid scheme with nystrom discretization for solving transient electromagnetic scattering by conducting objects the interaction of transient electromagnetic em waves with objects can be formulated by the integral equation approach in time domain for conducting objects or homogeneous penetrable objects the time domain surface integral equations tdsies can be applied traditionally the tdsies are solved by combining the method of moments mom in spatial domain and a march on in time mot scheme in temporal domain the mom usually requires conforming meshes with a well designed basis function and the mot may suffer from a stability problem in this work we propose a hybrid scheme in which the nystrom method is used in spatial domain while the mom with laguerre function as basis and testing functions is employed with a march on in degree mod manner in the temporal domain the nystrom method does not require any basis and testing functions and can use nonconforming meshes in spatial domain whereas the mom with laguerre function as basis and testing functions can fully eliminate the stability problem in temporal domain numerical examples for em scattering by typical conducting objects are presented to demonstrate the scheme and its merits have been verified

an ultrasound study of canadian french rhotic vowels with polar smoothing spline comparisons this is an acoustic and articulatory study of canadian french rhotic vowels i e mid front rounded vowels o produced with a rhotic perceptual quality much like english or leading heureux commun and docteur to sound like k m and d kta ultrasound video and acoustic data from 23 canadian french speakers are analyzed using several measures of mid sagittal tongue contours showing that the low f3 of rhotic vowels is achieved using bunched and retroflex tongue postures and that the articulatory acoustic mapping of f1 and f2 are rearranged in systems with rhotic vowels a subset of speakers french vowels are compared with their english revealing that the french vowels are consistently less extreme in low f3 and its articulatory correlates even for the most rhotic speakers polar coordinates are proposed as a replacement for cartesian coordinates in calculating smoothing spline comparisons of mid sagittal tongue shapes because they enable comparisons to be roughly perpendicular to the tongue surface which is critical for comparisons involving tongue root position but appropriate for all comparisons involving mid sagittal tongue contours

electromagnetic scattering from dispersive dielectric scatterers using the finite difference delay modeling method a new method for solving the time domain integral equations of electromagnetic scattering from dispersive dielectric bodies is proposed the method is based on the finite difference delay modeling scheme which accomplishes the temporal discretization by substituting a z domain finite difference approximation for the continuous time laplace domain s parameter the inverse z transform used for computing the temporal kernels is calculated numerically using the trapezoidal rule and inverse discrete fourier transform arbitrary dispersive models can be simulated without extraneous convolution using the new technique the normal field equations are augmented to the standard tangential equations to solve the low frequency instability problem