fast estimators of time delay and doppler stretch based on discrete time methods estimation of the time delay and the doppler stretch of a signal is required in several signal processing applications this paper is focused on the joint fine estimation of these two parameters by a fast interpolation of the estimated ambiguity function four discrete time methods viz multirate piecewise scaling linear scaling and indirect estimators based on an orthogonal model are introduced their mean square error is mathematically derived for random signals corrupted by additive random noises the obtained expressions have been evaluated for some typical parameter sets in the reference case of gaussian signals and noises the numerical results compared with the accuracy of a continuous time estimator show the near efficiency of the multirate estimator for a wide range of snrs in fact the adjustable multirate estimator can operate under near optimal conditions unlike the approximate i e piecewise and linear scaling and the indirect methods based on constant sampling rates

robust nonparametric cyclic correlation based spectrum sensing for cognitive radio cognitive radios sense the radio spectrum in order to find underutilized spectrum and then exploit it in an agile manner spectrum sensing has to be performed reliably in challenging propagation environments characterized by shadowing and fading effects as well as heavy tailed noise distributions in this paper a robust computationally efficient nonparametric cyclic correlation estimator based on the multivariate spatial sign function is proposed nonparametric statistics provide additional robustness against heavy tailed noise and when the noise statistics are not fully known asymptotic distribution of the spatial sign cyclic correlation estimator under the null hypothesis is established tests using constraint on false alarm rate are derived based on the estimated spatial sign cyclic correlation for single user and collaborative spectrum sensing by multiple secondary users theoretical justification for detecting cyclostationary signals using the spatial sign cyclic correlation is provided a sequential detection scheme for reducing the average detection time is proposed simulation experiments and theoretical results comparing the proposed method with cyclostationary spectrum sensing methods employing the conventional cyclic correlation estimator are presented simulations demonstrate the reliable and highly robust performance of the proposed nonparametric spectrum sensing method in both gaussian and non gaussian noise environments

performance analysis for channel estimation with 1 bit adc and unknown quantization threshold in this work the problem of signal parameter estimation from measurements acquired by a low complexity analog to digital converter adc with 1 bit output resolution and an unknown quantization threshold is considered single comparator adcs are energy efficient and can be operated at ultrahigh sampling rates for analysis of such systems a fixed and known quantization threshold is usually assumed in the symmetric case i e zero hard limiting offset it is known that in the low signal to noise ratio snr regime the signal processing performance degrades moderately by 2 pi text 1 96 db when comparing to an ideal infty bit converter due to hardware imperfections low complexity 1 bit adcs will in practice exhibit an unknown threshold different from zero therefore we study the accuracy that can be obtained with received data processed by a hard limiter with unknown quantization level by using asymptotically optimal channel estimation algorithms to characterize the estimation performance of these nonlinear algorithms we employ analytic error expressions for different setups while modeling the offset as a nuisance parameter in the low snr regime we establish the necessary condition for a vanishing loss due to missing offset knowledge at the receiver as an application we consider the estimation of single input single output wireless channels with intersymbol interference and validate our analysis by comparing the analytic and experimental performance of the studied estimation algorithms finally we comment on the extension to multiple input multiple output channel models

interaction integrals for fracture analysis of functionally graded piezoelectric materials this paper presents domain form of the interaction integrals based on three independent formulations for computation of the stress intensity factors and electric displacement intensity factor for cracks in functionally graded piezoelectric materials conservation integrals of j type are derived based on the governing equations for piezoelectric media and the crack tip asymptotic fields of homogeneous piezoelectric medium as auxiliary fields each of the formulation differs in the way auxiliary fields are imposed in the evaluation of interaction integral and each of them results in a consistent form of the interaction integral in the sense that extra terms naturally appears in their derivation to compensate for the difference in the chosen crack tip asymptotic fields of homogeneous and functionally graded piezoelectric medium the additional terms play an important role of ensuring domain independence of the presented interaction integrals comparison of the numerically evaluated intensity factors through the three consistent formulations with those obtained using displacement extrapolation method is presented by means of two examples

kinodynamic motion planning kinodynamic planning attempts to solve a robot motion problem subject to simultaneous kinematic and dynamics constraints in the general problem given a robot system we must find a minimal time trajectory that goes from a start position and velocity to a goal position and velocity while avoiding obstacles by a safety margin and respecting constraints on velocity and acceleration we consider the simplified case of a point mass under newtonian mechanics together with velocity and acceleration bounds the point must be flown from a start to a goal amidst polyhedral obstacles in 2d or 3d although exact solutions to this problem are not known we provide the first provably good approximation algorithm and show that it runs in polynomial time

multiple collinear cracks in a piezoelectric material abstract in this paper an exact solution of multiple collinear cracks in piezoelectric material is obtained the permittivity of air environment is considered two cases have been studied in the first case the permittivity of air is far less than that of piezoelectric material therefore the electric induction in the air is negligible in the second case the permittivity of air is comparable with that of piezoelectric material the problem is deduced into riemann hilbert problem and solved by the way the electric boundary conditions are discussed this result demonstrates that the consideration of air in crack gap reduces the stress intensity factor

the boundary contour method for magneto electro elastic media with quadratic boundary elements abstract this paper presents a development of the boundary contour method bcm for magneto electro elastic media first the divergence free of the integrand of the magneto electro elastic boundary element is proved second the boundary contour method formulations are obtained by introducing quadratic shape functions and green s functions ding h j jiang a m 2004 a boundary integral formulation and solution for 2d problems in magneto electro elastic media computers and structures 82 20 21 1599 1607 for magneto electro elastic media and using the rigid body motion solution to regularize the bcm and avoid computation of the corner tensor the bcm is applied to the problem of magneto electro elastic media finally numerical solutions for illustrative examples are compared with exact ones the numerical results of the bcm coincide very well with the exact solution and the feasibility and efficiency of the method are verified

spatial sign cyclic feature detection this paper studies the impact of the spatial sign function on the cyclic features of communication signals and thereby on the performance of cyclic feature detectors it extends the existing results obtained for gaussian signals and provides new insights into the interactions between the cyclic features of a cyclostationary signal sent through a spatial sign filter which lead to the modified cyclic features at the output we apply these results to analytically derive the performance of the spatial sign cyclic correlation sscc detector which filters a received signal by the spatial sign function prior to its processing using a cyclic feature detector these results are extended to variations of the spatial sign function and we further motivate their application to general zero memory non linear zmnl functions

consistency and recovery in electroelasticity part i standard finite elements developing finite elements for electroelastic analysis requires a special care as the coupling in the discrete equations depends on the matching between the approximations assumed for mechanical and electrical variables to provide a formal basis to this intuitive remark a notion of consistency is established and a rigorous consistency analysis is presented for the standard finite element model based on assumed displacement and electric potential in this way specific analytical requirements are obtained which serve as a guide to select the interpolation functions for primary variables moreover the analysis shows that violating consistency can be reflected as spurious outcomes upsetting the local distributions of secondary variables indeed this undesirable effect is shown to be typical of the standard approach if stress and electric flux density are computed via the constitutive equations to cure the trouble an alternative recovery procedure is devised based on the consistency analysis the procedure is variationally correct and reconstitutes in a consistent manner the distributions of stress and electric flux density

analysis of stress and electric fields in a rectangular piezoelectric body with a center crack under anti plane shear loading abstract the singular stress and electric fields in a rectangular piezoelectric ceramic body containing a griffith center crack under anti plane shear loading are obtained by the theory of linear piezoelectricity fourier transforms and fourier sine series are used to reduce the problem to a pair of dual integral equations which is expressed to a fredholm integral equation of the second kind numerical values on the stress intensity factor and the energy release rate are obtained to show the influence of the electric field

infinite sequence of parallel cracks in an anisotropic piezoelectric solid in this paper the problem of an infinite sequence of parallel cracks in an infinite extended piezoelectric solid is analyzed a system of singular integral equations is formulated for general anisotropic piezoelectric materials of which the kernel functions developed are in complex form for commonly used transversely isotropic piezoelectric materials the kernel functions are given in real forms furthermore the obtained real kernel functions may be reduced respectively to those kernel functions for purely elastic and purely electric problems when the coupled mechanical and electric effects disappear the system of singular integral equations is solved numerically and the coupling effects of the mechanical and electric phenomena are presented by the generalized stress intensity factors

constructing roadmaps of semi algebraic sets i completeness abstract this paper describes preliminary work on an algorithm for planning collision free motions for a robot manipulator in the presence of obstacles the physical obstacles lead to forbidden regions in the robots configuration space and for collision free motion we need paths through configuration space which avoid these regions our method is to construct a certain one dimensional subset or roadmap of the space of allowable configurations if s denotes the set of allowable configurations the roadmap has the property that any connected component of s contains a single connected component of the roadmap it is also possible starting from an arbitrary point p s to rapidly construct a path from p to a point on the roadmap thus given any two points in s we can rapidly determine whether they lie in the same connected component of s and if they do we can return a candidate path between them we do not give a complete description of the algorithm here but we define the roadmap geometrically and verify that it has the necessary connectivity

texture synthesis by analysis with hard limited gaussian processes a twin stage texture synthesis by analysis method is presented it aims to approximate first and second order distributions of the texture accordingly to the julesz conjecture in the first stage the binary textural behavior of a given prototype is represented by means of a hard limited gaussian process in the second stage the texture is synthesized by passing the binary hard limited gaussian process through a linear filter followed by a zero memory histogram equalizer

decoupled formulation of piezoelectric elasticity under generalized plane deformation and its application to wedge problems abstract this paper presents the formulation of piezoelectric elasticity under generalized plane deformation derived from the three dimensional theory there are four decoupled classes in the generalized plane deformation formulation i e when l 3 l 2 0 l 3 l 3 0 l 3 l 2 0 or l 3 l 3 l 2 0 only the inplane fields of the first class and the antiplane field of the second class include the piezoelectric effect several examples of wedge problem often encountered in smart structures such as sensors or actuators are studied to examine the stress singularity near the apex of the structure the bonded materials to the pzt 4 wedge are pzt 5 graphite epoxy or aluminum conductor the influencing factors on the singular behavior of the electro elastic fields include the wedge angle material type poling direction and the boundary and interface conditions the numerical results of the first case are compared with xu s graphs and some comments are made in detail in addition some new results regarding the antiplane stress singularity of the second class are obtained via the case study the coupled singularity solutions under generalized plane deformation are also investigated to seek the conditions of the weakest or vanishing singular stress fields

reduced complexity modeling and reproduction of colored textures an unsupervised color texture synthesis by analysis method is described the texture is reproduced to appear perceptually similar to a given prototype by copying its statistical properties up to the second order the synthesized texture is obtained at the output of a single input three output nonlinear system driven by a realization of a white gaussian random field significant complexity reduction is gained by exploiting the rank deficiency of the cross power spectral density matrix of the color texture samples

collision detection for moving polyhedra we consider the collision detection problem for a three dimensional solid object moving among polyhedral obstacles the configuration space for this problem is six dimensional and the traditional representation of the space uses three translational parameters and three angles typically euler angles the constraints between the object and obstacles then involve trigonometric functions we show that a quaternion representation of rotation yields constraints which are purely algebraic in a seven dimensional space by simple manipulation the constraints may be projected down into a six dimensional space with no increase in complexity the algebraic form of the constraints greatly simplifies computation of collision points and allows us to derive an efficient exact intersection test for an object which is translating and rotating among obstacles

a vertex algorithm for collision detection abstract an algorithm for detecting the collision of moving objects is presented the algorithm applies to polyhedral objects that can be represented as convex hulls of finite number of vertices in two or three dimensional space this is then extended to a three or four dimensional space respectively to represent the objects and their motion nonlinear programming techniques are then employed to detect possible interference the algorithm detects in one step whether or not the objects will interfere during their motion which may involve pure translations or rotations or both a subalgorithm for computing the minimum distance between the objects is also presented this can be used to solve the interference detection problem or for more general applications

estimation of a quadrature cross correlation detector by analog polarity coincidence and relay methods corresp the variance of the output of a cross correlation detector which is called a quadrature cross correlation detector is estimated in this type of detector two zero mean gaussian quadrature processes alpha t and beta t of a complex process alpha t j beta t are cross correlated this cross correlation function r a tau is estimated when neither of the two processes is distorted the analog method when both processes are distorted by a signum function before being cross correlated the polarity coincidence method and when one of the two processes is distorted by either a signum function or by a comparator logic function the relay method these quadrature cross correlation detectors then are compared on the basis of output signal to noise ratio s n and the clipping and relay losses are computed for two test quadrature processes of an edgeworth expansion approximated power spectrum since r a 0 is zero the four corresponding differential estimators such as r a tau r a 0 are also estimated and are compared on the basis of s n for these differential estimators the clipping and relay losses are computed for the two test processes in all cases the exact expressions for the s n are derived as a function of tau some applications of these correlation detectors are outlined the mathematical techniques employed here are thought to have potential usefulness for related problems in statistical communication theory and signal processing

new robust estimators of correlation and weighted basis pursuit the autocorrelation function is a commonly used tool in statistical time series analysis in this paper we examine the robustness of two estimators of correlation based on memoryless nonlinear functions of the observations the median of ratios estimator mre and the phase phase correlator ppc which are applicable to complex valued gaussian random processes we show that they are robust to impulsive noise from a bias perspective at the expense of statistical efficiency at the gaussian distribution additionally we develop iterative versions of these estimators named the imre and ippc realizing an improved bias performance over their non iterative counterparts and the well known robust schweppe type generalized m estimator utilizing a huber cost function shgm we use robust mahalanobis distances generated by the imre and ippc to improve the performance of impulsive noise suppression through the use of weighted basis pursuit methods these estimation and data cleaning techniques are applied to both synthetic and actual collected data using an ettus research usrp to perform robust spectral estimation on signals from the digital television band in the presence of additive impulsive noise finally the analysis reveals that if the time series is highly correlated and the contamination rate is low the mre outperforms the ppc estimator from a variance and bias perspective however the ppc is the estimator of choice when the correlation is lower and is better suited to time critical applications due to lower computation costs

on the problem of multiple mobile robots cluttering a workspace we consider the problem of multiple mobile robots navigating in a common workspace initially based on the premise that the costs of operation of the robots can be ignored results regarding the probability of collision of two point robots in the workspace are derived obviously these results depend on the geometry of the workspace and hence they are derived for workspaces with various geometries the results are then extended for two robots of finite dimensions the question are k 1 robots better than k is then considered based on two modes of operation namely the batch scheduled mode and the list scheduled mode various theoretical results are derived if the costs of operation of the robots can be ignored based on various computational results obtained we conjecture that the answer to the question is in the affirmative in both modes of operation finally by using the model of computation which includes the costs of operation of the robots the problem is revisited we have shown that for various geometries and revenue to cost ratios there are optimal finite values for the number of robots that can operate within the workspace expressions for these optimal values have been derived

a coupled electromechanical analysis of a piezoelectric layer bonded to an elastic substrate part ii numerical solution and applications this two part contribution presents a novel and efficient method to analyze the two dimensional 2 d electromechanical fields of a piezoelectric layer bonded to an elastic substrate which takes into account the fully coupled electric and mechanical behaviors in part i we have obtained a system of governing integro differential equations for the structure via a variational principle this part presents a numerical solution algorithm of the integro differential equations and the numerical results of some applications a numerical algorithm for solving the system of four integro differential equations with strongly singular kernels is developed the convergence of the numerical algorithm is discussed the numerical results suggest that the fully coupled electromechanical analysis is helpful for a better understanding of the performance of the piezoelectric sensor and actuator the interfacial normal stress is much higher than the interfacial shear stress suggesting that the interfacial normal stress causes a delamination initiation

penny shaped crack in a piezoelectric cylinder surrounded by an elastic medium subjected to combined in plane mechanical and electrical loads the fracture problem of a penny shaped crack in a piezoelectric ceramic cylinder surrounded by an infinite elastic medium under in plane normal mechanical and electrical loads is considered with the electric continuous boundary conditions on the crack surface by using the potential theory and hankel transform a system of dual integral equations is obtained and expressed to a fredholm integral equation of the second kind the mechanical and electrical field equations and all sorts of field intensity factors of mode i are obtained and the numerical values of various field intensity factors for pzt 6b piezoelectric ceramic surrounded by several different elastic media are graphically shown for a uniform load and a ring shaped load respectively and the effects of the size of the piezoelectric cylinder and the elastic material properties on various field intensity factors are obtained

a boundary integral formulation and 2d fundamental solutions for piezoelectric media abstract first based on the basic equations of piezoelectricity the boundary integral formulation is derived by utilizing the reciprocal work theorem second for the plane problem of piezoelectric media one general solution in terms of harmonic functions is derived and the fundamental solutions are therefore obtained numerical calculations by boundary element method bem are performed to give the stress concentration coefficient of an infinite piezoelectric plane with a circular hole as well as the stress and electric intensity factors of a central crack locating on an infinite plate results are found to agree well with the exact solutions

piezoelectric solid with an elliptic inclusion or hole the two dimensional problem of an elliptic hole in a solid of anisotropic piezoelectric material is studied the stroh formalism is adopted here real form solutions are obtained along the hole boundary in the case of an arbitrarily prescribed vector field on the hole surface for an elliptic rigid inclusion of electric conductor subjected to a line force a torque and a line charge a real form solution at the interface is obtained finally general solutions for an elliptic piezoelectric inclusion with uniform loading at infinity are investigated

smb collision detection based on temporal coherence the paper presents a novel collision detection algorithm termed the sort moving boxes smb for large number of moving 2d 3d objects which are represented by their axis aligned bounding boxes aabbs the main feature of the algorithm is the full exploitation of the temporal coherence of the objects exhibited in a dynamic environment in the algorithm the aabbs are first projected to each cartesian axis the projected intervals on the axes are separately sorted by the diminishing increment sort dis and further divided into subsections by processing all the intervals within the subsections to check if they overlap a complete contact list can be built the smb is a fast and robust collision detection algorithm particularly for systems involving a large number of moving aabbs and also supports for the dynamic insertion and deletion of objects its performance in terms of both expected total detection time and memory requirements is proportional to the total number of aabbs n and is not influenced by size differences of aabbs the space size and packing density over a large range up to ten times difference the only assumption made is that the sorted list at one time step will remain an almost sorted list at the next time step which is valid for most applications whose movement and deformation of each aabb and the dynamic change of the total number n are approximately continuous

the general solution of three dimensional problems in piezoelectric media abstract the governing equations of three dimensional problems in transversely isotropic piezo electric material are composed of four second order partial differential equations in which the displacement components and electric potential functions are the essential unknowns in this paper the so called general solutions of these equations are obtained with the aid of a set of new potential functions which are used to express the components of displacements and the electric potential functions as an application of the general solution the problem of a half space piezoelectrics acted by a concentrated lateral shear force is solved

investigation of the dynamic behavior of two parallel symmetric cracks in piezoelectric materials use of non local theory in this paper the dynamic behavior of two parallel symmetric cracks in piezoelectric materials under harmonic anti plane shear waves is investigated by use of the non local theory for permeable crack surface conditions to overcome the mathematical difficulties a one dimensional non local kernel is used instead of a two dimensional one for the problem to obtain the stress occurs near the crack tips by means of the fourier transform the problem can be solved with the help of two pairs of dual integral equations that the unknown variables are the jumps of the displacement along the crack surfaces these equations are solved using the schmidt method numerical examples are provided contrary to the previous results it is found that no stress and electric displacement singularity is present near the crack tip the non local elastic solutions yield a finite hoop stress near the crack tip thus allowing for a fracture criterion based on the maximum stress hypothesis the finite hoop stress at the crack tip depends on the crack length the frequency of the incident wave the distance between two cracks and the lattice parameter of the materials respectively contrary to the impermeable crack surface condition solution it is found that the dynamic electric displacement for the permeable crack surface conditions is much smaller than the results for the impermeable crack surface conditions the results show that the dynamic field will impede or enhance crack propagation in the piezoelectric materials at different stages of the dynamic load

scaled largest eigenvalue detection for stationary time series this paper studies the performance of the scaled largest eigenvalue sle detector used for the detection of stationary time series we focus on a single antenna setup and a blind detection scenario neither the signal covariance nor the noise variance are known the sle detector has received much attention in the context of cognitive radios cr due to its simplicity good performance and robustness to noise level uncertainties specifically our goal is to analyze the detector based on the statistic gamma lambda 1 over sum i 1 p lambda i where lambda 1 geq lambda 2 geq ldots geq lambda p represent the ordered eigenvalues of the sample covariance matrix we derive a large sample size closed form approximation for the test statistic which allows us to derive its statistical distribution and set up the detector to achieve the required probability of false alarm p fa and probability of detection p d we also study the robustness of the detector in the presence of noise uncertainty and impulsive noise and investigate the benefits of the spatial sign filter for such scenarios

plane problems in piezoelectric media with defects abstract a two dimensional electroelastic analysis is performed on a transversely isotropic piezoelectric material containing defects a general solution is provided in terms of complex potentials with emphasis being placed on stress concentrations that arise in the vicinity of circular and elliptical holes it is shown that for this genre of problem both mechanical and electrical variables are responsible for the peak stresses

collision computation of moving bodies abstract in this paper an explicit mathematical representation of n dimensional bodies moving in translation along general trajectories is derived this representation is used to find out if two moving bodies are going to collide an optimization problem is developed for finding the time and location of collision we consider the special cases of linear and piece wise linear trajectories the collision in this case can be obtained by solving a linear program or a sequence of linear programs respectively the problem of finding the collision time and location of several moving bodies is cast as an integer programming problem a comprehensive simulation study shows that this approach requires much lesser computation time when compared with the current approach of finding the collision between all pairs of bodies

the two dimensional electroelasticity problems for multiconnected bodies situated under electric potential difference action abstract solutions of the two dimensional electroelasticity problems for infinitely long piezoelectric cylinders with cavities and cracks under electrical potential difference action are obtained using the lekhnitskii s generalized complex potentials herewith piezoelectric bodies under consideration are free from mechanical loads some or all openings and maybe the exterior boundary of the cylinders are fully covered by thin electrodes voltage differences are supplied on the electroded surfaces the rest boundary surfaces are charge free in this case the complex potentials are investigated boundary conditions are satisfied by the least squares method there are carried out numerical investigations of behaviour of some basic electroelastic characteristics in a circular hollow cylinder and in an infinite body with two longitudinal cavities and a charge free plane crack new electromechanical regularities of influence of material properties geometrical characteristics of considered regions on values of electroelastic state characteristics and the stress electric displacements and tensions intensity factor k 1 are determined

two dimensional piezoelectricity part ii general solution green s function and interface cracks abstract the complete solution space of a piezoelectric material is the direct sum of several orthogonal eigenspaces one for each distinct eigenvalue each one of the 14 different classes of piezoelectric materials has a distinct form of the general solution expressed in terms of the eigenvectors of the zeroth and higher orders and a kernel matrix containing analytic functions when these functions are chosen to be logarithmic one obtains in a unified way green s function of the infinite space as a single 8 8 matrix function g for the various load cases of concentrated line forces dislocations and a line charge this expression of green s function is valid for all classes of nondegenerate and degenerate materials with an appropriate choice of the parameters it reduces to the solution of a half space with concentrated line forces at a boundary point and with dislocations in the displacements as another application eigenvalues and eigensolutions are obtained for the bimaterial interface crack problem

an exact correspondence between plane piezoelectricity and generalized plane strain in elasticity we consider an anisotropic body bounded by a cylindrical surface which is infinitely long in the axial direction suppose the body is loaded in such a way that the field variables do not vary along the generators an exact correspondence is established between the plane piezoelectric equations and those of generalized plane strain in elasticity in particular we show that by setting a linkage between the two sets of material constants any problem of a plane deformation in piezoelectricity may be solved as a generalized plane strain in elasticity and vice versa the assertation is true for rectilinearly as well as for cylindrically anisotropic solids the equivalence is found for the most general anisotropic case which links the fields between a monoclinic piezoelectric body of class m and a fully anisotropic triclinic elastic solid a few degenerate systems are also identified in addition these correspondences can be extended to inhomogeneous media applied to composite materials or polycrystalline aggregates they imply that results for effective elastic tensors immediately give the formulae for the effective electroelastic tensors and vice versa we also demonstrate that the connection can be used to extend the scope of the invariant stress theorem proved by cherkaev lurie and milton in illustration we present solutions for the plane problem of an elliptical inhomogeneity in an unbounded piezoelectric medium subjected to a uniform loading at infinity lekhnitskii9s complex potential approach together with the conformal mapping technique are employed general solutions of the fields inside the inhomogeneity and the matrix are obtained the results are analytically proven to be identical with the existing solutions of the corresponding purely elastic boundary value problem

on using lp to collision detection between a manipulator arm and surrounding obstacles abstract this paper is concerned with two linear programming lp models for the detection of a collision between a manipulator arm and its surrounding obstacles on the basis of a real case study in particular the first model finds the intersections between two convex polyhedra while the second one finds the intersections between suitable representations of the objects a comparison between the two approaches is presented on the basis of experimental data 9200 test cases have been analyzed

robustness analysis of the phase phase correlator to white impulsive noise with applications to autoregressive modeling using only the phase information and a relationship based on the gaussian hypergeometric function the phase phase correlator can be utilized to estimate the normalized cross correlation coefficient between two zero mean complex gaussian processes this estimator naturally introduces a certain robustness to white impulsive observation noise over the gaussian maximum likelihood estimator this correspondence examines the robustness of the phase phase correlator in the presence of uncorrelated impulsive noise we show that its asymptotic bias compares favorably to the robust schweppe type gm estimator with the huber function termed shgm at a cost of efficiency application of the ppc to autoregressive time series analysis is illustrated with a parametric spectral estimation example

a search algorithm for motion planning with six degrees of freedom abstract the motion planning problem is of central importance to the fields of robotics spatial planning and automated design in robotics we are interested in the automatic synthesis of robot motions given high level specifications of tasks and geometric models of the robot and obstacles the movers problem is to find a continuous collision free path for a moving object through an environment containing obstacles we present an implemented algorithm for the classical formulation of the three dimensional movers problem given an arbitrary rigid polyhedral moving object p with three translational and three rotational degrees of freedom find a continuous collision free path taking p from some initial configuration to a desired goal configuration this paper describes an implementation of a complete algorithm at a given resolution for the full six degree of freedom movers problem the algorithm transforms the six degree of freedom planning problem into a point navigation problem in a six dimensional configuration space called c space the c space obstacles which characterize the physically unachievable configurations are directly represented by six dimensional manifolds whose boundaries are five dimensional c surfaces by characterizing these surfaces and their intersections collision free paths may be found by the closure of three operators which i slide along five dimensional level c surfaces parallel to c space obstacles ii slide along one to four dimensional intersections of level c surfaces and iii jump between six dimensional obstacles these operators are employed by a best first search algorithm in c space we will discuss theoretical properties of the algorithm including completeness at a resolution this paper describes the heuristic search with particular emphasis on the heuristic strategies that evaluate local geometric information at the heart of this paper lie the design and implementation of these strategies for planning paths along level c surfaces and their intersection manifolds and for reasoning about motions with three degrees of rotational freedom the problems of controlling the interaction of these strategies and of integrating diverse local experts for geometric reasoning provide an interesting application of search to a difficult domain with significant practical implications the representations and algorithms we develop impact many geometric planning problems and extend to cartesian manipulators with six degrees of freedom

trefftz indirect methods for plane piezoelectricity in this paper a unified theory for the general solutions of three dimensional elasticity is employed to transform the governing equations of plane piezoelectricity into three generalized laplace equations the latter equations are uncoupled and can be pursued separately by introducing three generalized complex variables the complete solution sets for plane piezoelectricity are constructed by adopting the constituents in the solution sets as the trial functions the trefftz collocation and the trefftz galerkin methods are formulated both methods fall into the category of trefftz indirect methods as the coefficients of their trial functions are non physical numerical examples are presented to illustrate the efficacy of the formulations copyright 2005 john wiley sons ltd

price s theorem for complex variates price s 1958 theorem is derived for complex valued variates the derivation differs from the existing derivation in two respects first the normal variates are not assumed to be circularly complex thus the result is more general second the characteristic function of the complex variates is not used

integral representation and green s functions for 3d time dependent thermo piezoelectricity abstract a boundary integral method is developed for 3d time dependent quasistatic thermo piezoelectricity this time domain formulation involves only surface quantities as a result volume discretization is completely avoided green s functions are derived by resorting to radon transform and presented in integral form reductions to the case of isotropic dielectric solid have been worked out in detail and its corresponding solutions expressed in explicit form are consistent with the existing solutions

fast collision detection in four dimensional space abstract in this paper we consider the collision detection problem for general objects a four dimensional approach is proposed for this problem which detects exactly and in one step when and where the earliest collison will occur between the objects this is done by using four dimensional sets to represent the objects in both space and time the problem is then posed as a nonlinear programming problem the algorithm can handle the case of a rigid body moving on a general path in r 2 or r 3 with simultaneous translation and rotation simulation results on some example problems are given and show that the algorithm is superior to those available in the literature

estimation of the autocorrelation function of complex gaussian stationary processes by amplitude clipped signals the normalized autocorrelation function of a gaussian process may be recovered from second order moments of their polarity through the arcsin law by analogy it is possible to calculate the normalized autocorrelation function of a circularly complex gaussian process from the knowledge of moments of its instantaneous phase in the present paper two estimators of the normalized autocorrelation function based on the phase only are presented their theoretical accuracy is evaluated and compared to the accuracy of the direct estimate

performance of normalized correlation estimators for complex processes direct and fast techniques for estimating normalized second order moments of complex processes are discussed first the accuracy of the direct estimate is explicitly given in terms of bias and covariance for the gaussian processes then a class of estimators based on the complex invariance property is considered their theoretical accuracy is given for some cases of paramount interest from a computational point of view in the gaussian case in particular applications in the areas of autoregressive spectrum analysis and spectral centroid estimation are presented general analytic results and simple expression for immediate evaluation are provided

methods for estimating the autocorrelation function of complex gaussian stationary processes new methods for estimating the autocorrelation function acf of a complex gaussian stationary process are presented these methods are based on a general invariance property for the autocorrelation of a common class of the above processes this property suggests estimation procedures based on magnitude hard limiting and phase quantization the procedures are an extension of the relay estimator currently employed for real processes the computational cost and the general properties of the methods are discussed in particular some estimators especially suited for very simple implementations are considered the performance of the complex hybrid sign estimator is evaluated and compared to that of the classical direct estimator the proposed methods are attractive for many applications in the field of digital signal processing

three dimensional eigenfunction analysis of a crack in a piezoelectric material abstract a three dimensional analysis of a semi infinite crack embedded in a transversely isotropic piezoelectric material was performed by means of the eigenfunction expansions method the results show the characteristic 1 r singular behavior of the stress tensor in the vicinity of the crack a similar behavior is also revealed for the electric field in addition the study demonstrates that coupling or decoupling of the mechanical and electrical variables is a function of the distance to the crack tip as well as of the crack orientation

spatial planning a configuration space approach this paper presents algorithms for computing constraints on the position of an object due to the presence of ther objects this problem arises in applications that require choosing how to arrange or how to move objects without collisions the approach presented here is based on characterizing the position and orientation of an object as a single point in a configuration space in which each coordinate represents a degree of freedom in the position or orientation of the object the configurations forbidden to this object due to the presence of other objects can then be characterized as regions in the configuration space called configuration space obstacles the paper presents algorithms for computing these configuration space obstacles when the objects are polygons or polyhedra

convex hull representations of models for computing collisions between multiple bodies abstract in this paper we consider a collision detection problem that frequently arises in the field of robotics given a set of bodies with their initial positions and trajectories we wish to identify the first collision that occurs between any two bodies or to determine that none exists for the case of bodies having linear trajectories we construct a convex hull representation of the integer programming model of s z selim and h a almohamad european journal of operational research 119 1 1999 121 129 and compare the relative effectiveness in solving this problem via the resultant linear program we also extend this analysis to model a situation in which bodies move along piecewise linear trajectories possibly rotating at the end of each linear segment for this case we again compare an integer programming approach with its linear programming convex hull representation and exhibit the effectiveness of solving a sequence of mathematical programs for each time segment over a global programming scheme which considers all segments at once we provide computational results to illustrate the effect of various numbers of bodies present in the collision scenarios as well as the times at which the first collision occurs

electroelastic analysis of an anti plane shear crack in a piezoelectric ceramic strip the electroelastic analysis of a piezoelectric strip with an anti plane shear crack whose surfaces are parallel to the strip boundaries is made four cases of combined electromechanical loadings applied at the strip boundaries are considered for the case of a crack lying at the center of a strip the electroelastic field field intensity factors and energy release rate can be determined in explicit form via solving a resulting singular integral equation for other cases they can be given in terms of an auxiliary function which is obtained as a power series of via solving a resulting fredholm integral equation using the iterative method 2 being the ratio of the crack length over the strip width some numerical results are presented graphically to show the influence of crack length and crack position on the normalized energy release rate

the boundary contour method for piezoelectric media with linear boundary elements this paper presents a development of the boundary contour method bcm for piezoelectric media first the divergence free property of the integrand of the piezoelectric boundary element is proved secondly the boundary contour method formulation is derived and potential functions are obtained by introducing linear shape functions and green s functions computer methods in applied mechanics and engineering 1998 158 65 for piezoelectric media the bcm is applied to the problem of piezoelectric media finally numerical solutions for illustrative examples are compared with exact ones and those of the conventional boundary element method bem the numerical results of the bcm coincide very well with the exact solution and the feasibility and efficiency of the method are verified copyright 2003 john wiley sons ltd

new developments concerning piezoelectric materials with defects abstract the problem of a piezoelectric body with an elliptic cavity is revisited within the frame work of two dimensional electro elasticity in contrast to our previous formulation the present analysis is based on the use of exact electric boundary conditions at the rim of the hole thus avoiding the common assumption of electric impermeability expressions for the elastic and electric variables induced inside and outside the cavity are derived in closed form in terms of complex potentials comparisons between present exact and previous approximate models are effected to establish the limitations associated with the assumption of the impermeable hole in particular when it becomes a slit crack

collision detection of a moving polygon in the presence of polygonal obstacles in the plane this paper presents a new approach for the following collision detection problem in the plane let a simple polygon p rotate at a center spl ogr with constant angular velocity spl omega and translate towards a set of polygonal obstacles s with constant velocity spl nu given p and s as well as their initial positions and given also the velocities of p determine whether or not p will collide with any element of s and report the collided elements of s if collisions occurred an o mn worst case optimal algorithm is proposed to solve this problem where n is the number of vertices of p and m is the number of vertices of the obstacles in s

distance estimation and collision prediction for on line robotic motion planning abstract an efficient method for computing the minimum distance and predicting collisions between moving objects is presented this problem has been incorporated in the framework of an in line motion planning algorithm to satisfy collision avoidance between a robot and moving objects modelled as convex polyhedra in the beginning the deterministic problem where the information about the objects is assumed to be certain is examined if instead of the euclidean norm l 1 or l norms are used to represent distance the problem becomes a linear programming problem the stochastic problem is formulated where the uncertainty is induced by sensing and the unknown dynamics of the moving obstacles two problems are considered first filtering of the distance between the robot and the moving object at the present time second prediction of the minimum distance in the future in order to predict the collision time

analysis of a central crack normal to a piezoelectric orthotropic interface this study is concerned with the general solution of the field intensity factors and energy release rate for a griffith crack normal to the interface between a rectangular piezoelectric ceramic and two same rectangular orthotropic materials of finite length under combined in plane electrical and anti plane mechanical loading both electrically continuous and impermeable crack surface conditions are considered employing fourier transforms and fourier series the problem is reduced to dual integral forms the solution to the resulting expressions is expressed in terms of fredholm integral equation of the second kind analytical solutions are provided for a number of cases to study the influence of material combinations geometry crack surface boundary and loading conditions the work also examines the influence of the crack boundary conditions on the results of the stress intensity factors and the energy release rate