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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 27-40 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The Wigner bispectrum of multicomponent signals is studied, and its modified and reduced forms are introduced. A generalization of the presented forms to the Wigner higher-order spectra (WHOS), in the case of multicomponent signals, is provided. From our previous work it is known that cross terms removal (reduction) is possible for odd-order spectra with equal numbers of conjugated and nonconjugated terms. Here, we extend the analysis to even-order spectra. The theory is illustrated by examples.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 83-89 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We describe methods to establish identifiability and information-regularity of parameters in normal distributions. Parameters are considered identifiable when they are determined uniquely by the probability distribution and they are information-regular when their Fisher information matrix is full rank. In normal distributions, information-regularity implies local identifiability, but the converse is not always true. Using the theory of holomorphic mappings, we show when the converse is true, allowing information-regularity to be established without having to explicitly compute the information matrix. Some examples are given.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 141-163 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The extendibility of estimated correlation bisequences from an available sampled data array is described in terms of the generating functions of associated block Toeplitz with Toeplitz block (BTTB) matrices. The periodogram-based correlation bisequences are shown to be extendible. It is shown that the method of resultants and subresultants is convenient for generating the nonlinear constraints in the optimization problem which is solved iteratively for power spectrum estimation. A nontrivial example illustrates the concepts developed.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 217-239 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A multiresolutional approach is presented for effectively recognizing three-dimensional (3D) objects. The approach is both pose and scale invariant. A multiresolutional model base is constructed, and multiscale edges of the object are detected using the wavelet transform. The minimum alignment between model base and object is realized by the linear mapping scheme.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 59-67 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The potential for data compression in using fractal interpolation functions (FIFs) is realized by the construction of a set of multirate filters. The filter tap weights are determined by optimizing the energy contents of a preselected set of frequency bands. This filter bank implementation of the FIF is successfully used to compress data simulated in a tracking environment.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 91-106 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A first-order autoregressive filter is altered by changing the constant gain to two or more gains that cyclically alternate in time. The advantages of this system are shown, and the relation to linear autoregressive moving average difference equations of higher order is derived.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 165-195 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper refers to the fast implementation of the positional forward acceleration of the end effector of revolute robotic arms with spherical wrists, using the distributed arithmetic technique. The acceleration of the end effector is calculated by a cascade configuration of two pipelined arrays that calculate the Jacobian matrix and its time derivative, as well as the centrifugal-Coriolis and linear accelerations. These partial accelerations are then added in the adder tree. The building blocks of the arrays are the distributed arithmetic-based circuits that implement the matrix-vector multiplications involved in the calculations. The digit-serial configuration of the proposed implementation of the positional forward acceleration of the end effector is described. The serial and the parallel configurations may result as special cases of the digit-serial configuration. The proposed distributed arithmetic (DA) implementation of the positional forward acceleration may be applied, after appropriate modifications, to the general case of robots having either revolute or prismatic joints, with any type of wrist.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 241-245 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper addresses the calculation of the extrema of the sin x/x function. First the Newton-Raphson method is used, which allows us to obtain the extrema locations very fast through the use of a recursion formula. Then a second approach is proposed, which gives the extrema locations and the extrema amplitudes in the form of series expansions. Simple, accurate algebraic expressions are derived.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 307-324 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We give some existence results for a resistive network in which the components are neither voltage nor current controlled; that is, they are merely unicursal. In fact we allow coupling. Degree arguments give existence and bounds. We study several ways of avoiding the requirement of eventual passivity. No-gain and passive multiterminal elements are included. The results are extended to infinite networks.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 375-386 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Random sampling is one of the methods that can overcome the Nyquist limit when evaluating a frequency spectrum of a signal. However, the computational complexity becomesN 2 as the FFT cannot be used. A new approach, called hybrid additive random sampling, is proposed. This new scheme is devised by concatenating random sampling sequences in such a way that symmetry is created in the transform kernel for reducing the computational effort while the anti-alias property is maintained. A savings of the least 75% in computation is achieved. The sampling scheme is also found to be suitable for parallel implementation. In this paper, the algorithms for generating the sampling sequence and evaluating the spectrum are described in detail. The performances of the scheme in terms of noise, accuracy, etc., are compared with genuine random sampling and another approach proposed previously. The advantages and limitations are included.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 27-42 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Of concern is the propagation of distortionless surface waves in a medium that may be nonuniform relative to depth. Distortionless wave propagation in inhomogeneous media was discussed by V. Burke, R. J. Duffin and D. Hazony, inQuart. Appl. Math., 183–194 (1976). Accordingly, the media could be modeled by a distributed electrical ladder network, nonuniform along the axis. We give a two-dimensional development based on Hooke's law and Newton's law which leads to the well-known case of Rayleigh waves in homogeneous media. It will be seen that the available pool of propagation modes greatly increases when high-pass propagation is included. The emphasis is on media where the elastic coefficients track one another as a function of depth. Special cases are studied in detail showing that as a disturbance travels along the surface, it may assume a broadband phase change, which translates into a shape distortion in the time domain, which is periodic with distance. Applications may be found in acousto-optics, in situ monitoring of elongated bodies, high-frequency SAW filters, microstrips, and any situations where surface waves are used in an environment of high precision or relatively large distances.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 131-147 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This study presents a linear output-based controller for stabilizing a rigid-link flexible-joint electrically driven (RLFJED) robot manipulator. The proposed controller ensures local exponential stability under some uncertainty conditions. It is assumed that the velocity signals from the link side are not measurable. The controller is analyzed by using tools for pole placement by an output-feedback in the framework of the linear system theory. Some useful structural properties of the systems under consideration have been studied. Applications of the results to the set-point regulation control problem are considered.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 205-223 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we consider an adaptive controller with vanishing gain and excitation of the reference signal. We use the burst recovery concept to show that all signals in the adaptive loop remain uniformly bounded. We also show that the mean-square performance converges so that the adaptive system is optimal in the sense that the parameter estimation error and the one-step ahead prediction error are uncorrelated in the mean despite the presence of the unmodeled dynamics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 191-204 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Finite homogeneous Markov chains ξ, which admit invariant probability distributions, can be defined by the cycloids { $$\bar C_k $$ } (closed polygonal lines whose consecutive edges have various orientations that do not necessarily determine a common direction for $$\bar C_k $$ ) occurring in their graphs. These Markov chains are called cycloid chains, and the corresponding finite-dimensional distributions are linear expressions on the cycloids { $$\bar C_k $$ } with the real coefficients αk. Then the collection {{ $$\bar C_k $$ }, {αk}}, called the cycloid decomposition of ξ, gives a minimal description of the finite-dimensional distributions that, except for a choice of the maximal tree, uniquely determines the chain ξ. Furthermore, the cycloid decompositions have an interpretation in terms of the transition probability functions expressing the same essence as the known Chapman-Kolmogorov equations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 241-267 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We study solutions of the “linear system in a saturated mode” $$\begin{array}{*{20}c} {(M)} & {x' \in Tx + c - \partial I_{D^n } x.} \\ \end{array} $$ We show that a trajectory is in a constant face of the cubeD n on some interval (0,d]. We answer a question about comparing the two systems: (M) and $$\begin{array}{*{20}c} {(H)} & {\begin{array}{*{20}c} {Cu' = T\upsilon + c - R^{ - 1} u,} & {\upsilon = G(\lambda } \\ \end{array} u)} \\ \end{array} $$ . As λ→∞, limits ofv corresponding to asymptotically stable equilibrium points of (H) are asymptotically stable equilibrium points of (M), and the converse is also true. We study the assumptions to see which are required and which may be weakened.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 291-314 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we introduce a new computational method for solving the diffusion equation. In particular, we construct a “generalized” state-space system and compute the impulse response of an equivalent truncated state-space system. In this effort, we use a 3D finite element method (FEM) to obtain the state-space system. We then use the Arnoldi iteration to approximate the state impulse response by projecting on the dominant controllable subspace. The idea exploited here is the approximation of the impulse response of the linear system. We study the homogeneous and heterogeneous cases and discuss the approximation error. Finally, we compare our computational results to our experimental setup.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 351-364 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A simple state-space approach for the four-block singular nonlinearH ∞ control problem is proposed in this paper. This approach combines a (J, J′)-lossless and a class of conjugate (J, J′)-expansive systems to yield a family of nonlinearH ∞ output feedback controllers. The singular nonlinearH ∞ control problem is thus transformed into a simple lossless network problem that is easy to deal with in a network-theory context.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 395-406 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The stability of time-varying autoregressive (TVAR) models is an important issue in many applications such as time-varying spectral estimation, EEG simulation and analysis, and time-varying linear prediction coding (TVLPC). For stationary AR models there are methods that guarantee stability, but the for nonadaptive time-varying approaches there are no such methods. On the other hand, in some situations, such as in EEG analysis, the models that temporarily exhibit roots with almost unit moduli are difficult to use. Thus we may need a tighter stability condition such as stability with margin 1−ϱ. In this paper we propose a method for the estimation of TVAR models that guarantees stability with margin 1−ϱ, that is, the moduli of the roots of the time-varying characteristic polynomial are less than or equal to some arbitrary positive number ϱ for every time instant. The model class is the Subba Rao-Liporace class, in which the time-varying coefficients are constrained to a subspace of the coefficient time evolutions. The method is based on sequential linearization of the associated nonlinear constraints and the subsequent use of a Gauss-Newton-type algorithm. The method is also applied to a simulated autoregressive process.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 443-443 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 41-58 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a comparison between the traditional image processing method and the area vector concept as well as the new technique of artificial neural networks. Freeman chain coding is considered in the study, and the principle of segmentation may be based and implemented for further investigations resulting from the proposed work. The pattern recognition concept is analyzed and defined through the sigmoid function and the determination of the threshold of a gray image for an object. The block schemes for the given protocols are summarized in a single scheme for illustration and comparison purposes. The synthetic pictures are generated and investigated regarding the dependence of computer vision on the contents of the artificial neural network. The normalization technique is included to eliminate noise and zooming problems. The minimum computational time for image processing with the generated pictures is also determined. The rate of deflection in the computational time is recommended for sensing the minimum computational time according to the variation of the number of hidden units in the hidden layer. A three-layer neural network has been used. The study of gray binary imaging for color pictures is illustrated to save computational time and effort.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 247-270 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Of concern is an environment made up of signals and systems tightly confined both in time and frequency. Such an environment is often encountered in transmission line circuits, radar, sonar, and optical circuits, and when the principal signals are well-defined sharp pulses. It will be seen that once this environment is achieved, the signals and systems possess some attractive properties. A conventional system may preserve the symmetry of a propagating signal or change its symmetry from even to odd or from odd to even. Another system may be used to predict the arrival of an incoming pulse with a high degree of accuracy. Electrical networks may also be associated with these properties. Approximation problems, existence theorems, and realization schemes will be addressed and developed.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 325-347 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper develops a new digitally redesigned pulse-amplitude modulated (PAM) controller for a continuous-time input time-delay/nondelay system with nonsynchronous sampling. The concept of the law of the mean from the input integral calculus is utilized for the development of the equivalent digital predictor controllers from the available analog predictor controllers. As a result, the digitally controlled states closely match the original continuous-time states. To implement the developed discrete-time state-feedback PAM controller, this paper also develops an ideal discrete-time state using nonsynchronously sampled input-output data of the continuous-time input delay/nondelay system without establishing a dynamic observer.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 429-438 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The model-matching problem for systems described by external models is considered in frameworks of both external and input-output equivalence. Necessary conditions for the solvability of the problem are produced, and it is shown that in certain cases these conditions are also sufficient. In the case where necessary and sufficient conditions exist, the solutions of the problem are obtained in a constructive way and a parametrization of solutions is given.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 523-536 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper addresses the invariance property of Gaussian signals, originally derived by Bussgang, which characterizes the input/output moment relation of a hybrid nonlinear moment (HNM) estimator based on a zero-memory nonlinearity (ZMN) g(y). Some re-derivations of this property are reviewed, and an original, direct, and simple proof is presented (Appendix 1). The paper then derives a new interpretation of this property (Theorem 1) that shows a moment-sense equivalence between g(y) and a linear mappingh 1(y) whose coefficients a0 and a1 are completely characterized in terms ofg(y) and are shown to be optimal in a mean square error (MSE) sense. A direct and very interesting byproduct of this interpretation is a simple linear relationship between the input and output of the HNM estimator involved. The property is then generalized (Theorem 2) to signals other than Gaussian, resulting in an infinite cumulant series expansion of the HNM estimator output, whose coefficients are all characterized in terms ofg(y). Applications of Theorem 1 to some ZMNs commonly used in signal processing and control theory are presented that clearly illustrate the power and elegance of the invariance property. Finally, some conclusions are given.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 547-557 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper the connection between ‘mass’M, ‘resistance’ϱ and ‘commute time’θ for random walks on graphs is further explored, and the relationθ=2M ·ϱ is proved. An extension of the result is made to multigraphs, which are an extension of the graph concept where a black box is treated like an edge.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 625-647 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Let {S(A):A ∈A}, whereA is a subset of an infinite-dimensional normed linear spaceL, be a class of general nonlinear input-output systems that are governed by operator equations relating the input, state, and output, all of which are in extended spaces. IfQ is a given operator from a specified set ¯D i, of inputs into the space of outputs ¯H 0, the problem we consider is to find, for a given ɛ〉0, a “parameter”A ε∈A such that the transmission operatorR(A ε) ofS(A ε) furnishes a nearly best (or ɛ-best) approximation toQ from allR(A),A ∈A. Here the “distance” betweenQ andR(A) is defined as the supremum of distances betweenQz andR(A)z taken over allz ∈ ¯D i. In Theorems 2 through 5 we show that ifS(A) is “normal” (Definition 2),A satisfies some mild requirement andL contains a fundamental sequence, then establishingA ε∈A reduces to minimizing a certain continuous functional on a compact subset ofR n, and thus can be carried out by conventional methods. The applications of results are illustrated by the example of a model-matching problem for a nonlinear system, and of optimal tracking.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 649-654 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract It is shown that the elementsG of a large class of input-output maps can be uniformly approximated arbitrarily well using a certain structure if and only ifG is continuous. For the case considered the system inputs and outputs are defined on a discrete set {0, 1,...,a 1}×...{0, 1,...,a m }, in which a1,...,a m are positive integers. Our approximating structure involves certain functions that can be chosen in different ways. For the special case in which these functions are taken to be certain polynomial functions, the input-output map of our structure is a generalized discrete Volterra series. Our results provide an analytical basis for the use of such series.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 663-701 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, the stability robustness of deterministic state feedback discretetime linear quadratic (LQ) optimal regulators for the performance index with cross-product terms is analyzed. Guaranteed stability margins for such a type of LQ optimal regulator are suggested for the first time. These stability margins are obtained on the basis of a modified return difference equality and are expressed directly in terms of the elementary cost and system matrices. Sufficient conditions to guarantee the required stability margins are presented. Finally, the connection between the suggested stability margins and the selection of weighting state, input, and cross-product matrices is investigated, and useful guidelines for choosing proper weighting matrices are presented.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 17-25 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A complete analytic characterization and solution construction (done either explicitly or by recursion) for the minimax control problem using optimal rate feedback is given for the case when the plant consists of a known fixed set of coupled oscillators of cardinality not exceeding three. When this is not the case, the problem appears to be analytically intractable, and suboptimal solutions based on numerical techniques are currently the only recourse.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 1-16 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The task of constructing an energy function is essential for direct stability analysis of electric power systems. This paper presents a general procedure for constructing analytical energy functions for detailed lossless network-reduction power system stability models. This paper primarily (i) develops canonical representations for lossless networkreduction power system models and shows that such canonical representations cover existing stability models, (ii) derives theoretical results regarding the existence of analytical energy functions for the canonical representations, and (iii) presents a systematic procedure to construct corresponding energy functions.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 89-110 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The problem of finding all the DC solutions of a certain class of piecewise-linear electronic circuits containing locally passive and locally active one-ports is considered in this paper. An effective method enabling us to locate the solutions is developed. The method constitutes the crucial point of an algorithm based on the idea of successive contraction, division, and elimination that is capable of determining all the solutions. Several numerical examples are given, and some comparison analyses are performed confirming the usefulness of the proposed approach.
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 269-290 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The controllability and observability properties of a singular system are extensively studied. The definitions of controllability,R-controllability, and impulse controllability are introduced via characteristics of the original state vector. Analogous definitions are presented for the case of observability. The criteria established for controllability and observability are simple rank criteria related to the Markov parameters from the inputs to the states and from the initial conditions to the outputs, respectively. The present results can be considered as the direct extension of Kalman's controllability and observability criteria to the case of singular systems. Finally, the controllability and observability subspaces are derived from the image and the kernel of the controllability and the observability matrices, respectively.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 431-442 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Given a stationary time seriesX and another stationary time seriesY (with a different power spectral density), we describe an algorithm for constructing a stationary time series Z that contains exactly the same values asX permuted in an order such that the power spectral density ofZ closely resembles that ofY. We call this methodspectral mimicry. We prove (under certain restrictions) that, if the univariate cumulative distribution function (CDF) ofX is identical to the CDF ofY, then the power spectral density ofZ equals the power spectral density ofY. We also show, for a class of examples, that when the CDFs ofX andY differ modestly, the power spectral density ofZ closely approximates the power spectral density ofY. The algorithm, developed to design an experiment in microbial population dynamics, has a variety of other applications.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 479-487 
    ISSN: 1531-5878
    Schlagwort(e): Cramér-Rao bounds ; direction-of-arrival estimation ; unknown noise
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The deterministic and stochastic direction estimation Cramér-Rao bounds (CRBs) are studied in the presence of one signal and spatially uncorrelated sensor noise with unknown nonequal variances in array sensors. The explicit CRB expressions are obtained, and their relationship is studied showing some typical properties inherent in the nonidentical noise case.
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 457-477 
    ISSN: 1531-5878
    Schlagwort(e): Nonlinear circuit theory ; co-content ; functional minimization ; image processing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The solutions of many physical-mathematical problems can be obtained by minimizing proper functionals. In the literature, some methods for the synthesis of analog circuits (mainly cellular neural networks) are presented that find the solution of some of these problems by implementing the discretized Euler-Lagrange equations associated with the pertinent functionals. In this paper, we propose a method for defining analog circuits that directly minimize (in a parallel way) a class of discretized functionals in the frequently occurring case where the solution depends on two spatial variables. The method is a generalization of the one presented in Parodi et al.,Internat. J. Circuit Theory Appl., 26, 477–498, 1998. The analog circuits consist of both a (nonlinear) resistive part and a set of linear capacitors, whose steady-state voltages represent the discrete solution to the problem. The method is based on the potential (co-content) functions associated with voltage-controlled resistive elements. es an example, we describe an application in the field of image processing: the restoration of color images corrupted by additive noise.
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 611-624 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Feedback control designs are useful for removing the impulses that disturb the behavior of generalized state space systems. The aim of this paper is to detail the design of dynamic precompensators for the implementation of such feedback control designs. Necessary and sufficient conditions are given so that the resulting regulators are biproper. It is pointed out that these conditions are restrictive and that feedback control designs can lead to nonproper precompensators. To overcome this difficulty, a class of proper precompensators is proposed. These regulators, which result from an adaptation of the Silverman structure algorithm, remove the impulse behaviors that occur after the initial time by smoothing out the input vector.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 595-610 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper investigates the factorization properties of cyclotomic polynomials over the field of complex rational numbers. Based on this factorization and the Chinese remainder theorem, we analyze the mathematical structure of the associated algorithms for computing the cyclic convolution of data sequences. The relevant results pertaining to finite integer and complex integer rings are also summarized.Note: This work is being reported in two parts. In Part I, we analyze the structure of the cyclic convolution algorithms over the rational number system. In Part II, we describe complex cyclotomic polynomials and the structure of the resulting cyclic convolution algorithms over the complex rational number system.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 569-594 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The Chinese remainder theorem plays a central role in the design of fast algorithms for computing cyclic and acyclic convolution of data sequences. A mathematical analysis of the theorem and related aspects form the topic of this investigation. The focus is almost exclusively on cyclic convolution algorithms. The number system that is studied is the field of rational numbers. Several properties related to the mathematical structure of the algorithms are derived.Note: This work is being reported in two parts. In Part I, we analyze the structure of the cyclic convolution algorithms over the rational number system. In Part II, we describe complex cyclotomic polynomials and the structure of the resulting cyclic convolution algorithms over the complex rational number system.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. i 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 111-130 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The cumulants defined in terms of moments are basic to the study of higher-order statistics (HOS) of a stationary stochastic process. This paper presents a concurrent systolic array system for the computation of higher-order moments. The system allows for the simultaneous computation of the second-, third-, and fourth-order moments. The architecture achieves good speedup through its excellent exploitation of parallelism, pipelining, and reusability of some intermediate results. The computational complexity and system performance issues related to the architecture are discussed. The concurrent system is designed with the CMOS VLSI technology and is capable of operating at 3.9 MHz.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 183-187 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Necessary and sufficient conditions for the invertibility of a (not necessarily linear) operatorN between normed linear spaces are given. It is shown thatN is invertible precisely if a certain operator associated withN is a contraction.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 655-661 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In the stability and sensitivity theory of general, nonlinear input-output systems we encounter a certain inequality concerning solely the nominal system that plays a central role in the whole theory. In particular, this “central inequality,” combined with other assumptions, implies (a) stability of the nominal system, (b) robustness, and (c) insensitivity of the input-output system. This paper presents conditions equivalent to this central inequality, and a further result on the stability-robustness problem.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 703-718 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Discrete-time linear periodic single-input/single-output (SISO) systems having uniform relative degree are considered. A closed-form expression of the blocking input is derived and exploited to obtain a computationally advantageous characterization of the structural zeros. Indeed, it suffices to compute the eigenvalues of a suitably defined (n × n) matrix, wheren is the system order. It is shown that, in contrast to the general case studied in previous papers, the number of zeros of linear periodic SISO systems with uniform relative degree is always time invariant and equal to the difference between the system order and the relative degree. The new characterization is also used to provide a simple expression for the zeros of linear periodic systems described by input-output difference equations.
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  • 44
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 271-285 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We define the smooth observability of nonlinear DAE systems and give sufficient conditions for this property to hold locally in a neighborhood of a solution. The matrix rank conditions for observability are verifiable by a combination of symbolic and numerical linear algebra computations. These conditions generalize conditions that have appeared in the literature for observability of linear time-varying DAE systems. We indicate how the main result is potentially useful in studying a system's zero dynamics. Some relevant rank properties of Hessenberg DAE systems are established.
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 1-25 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Based on the combinatorial Routhα-β andγ-δ expansions of a stable transfer function, a new energy decomposition tree for linear systems is developed. The pertinent properties to the energy decomposition tree are investigated, and an algorithm is derived for synthesizing transfer functions from the tree. The synthesis process naturally leads to a new family of Routh approximants to the system. It is indicated that the selection of Routh approximants based on the values of impulse-response energy is often inadequate because there may be a number of different Routh approximants with the same order and the same impulse-response energy. In such cases, an additional performance criterion, such as the integral of squared error of impulse response or unit-step response, has to be used to select a suitable Routh approximant.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 69-81 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract An adaptive generic algorithm was developed to solve the optimization problem of the maximum likelihood estimation of the sum of sinusoids in a noisy environment. The algorithm is based on genetic concepts and is extended, with modifications, to this problem. Simulation results were performed to see the effect of different parameters such as permutation and crossover probabilities. The effects of the signal-to-noise ratio (SNR) were also studied. It was found that the key factor for accuracy is the probabilities of permutation and crossover. Thus, we developed an adaptive method to estimate these probabilities, on line, to reduce the error. This was accomplished by considering them as unknown parameters to be estimated with the signal parameters. The mean square error of the frequency estimates was compared favorably to the Cramér-Rao lower bound. Several simulations are shown for SNR values ranging between −7 dB and 20 dB.
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  • 47
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 121-139 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In a recent work, the factorization properties of polynomials defined over finite integer polynomial rings were analyzed. These properties, along with other results pertaining to polymomial theory, led to the direct sum property and the American-Indian-Chinese extension of the Chinese remainder theorem over such integer rings. The objective of this paper is to describe algorithms for computing the one-and two-dimensional convolution of data sequences defined over finite integer rings. For one-dimensional convolution, algorithms for computing acyclic and cyclic convolution are described. For two-dimensional convolution, only the cyclic case is analyzed. Computational and other relevant aspects associated with the structure of these algorithms are also studied.
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 207-216 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract It is very important in many applications to preserve a desired signal without distortion. This paper presents a robust adaptive beamforming method to extract a desired signal from the signals received by broadband arrays. The proposed method relaxes the requirement of approximate knowledge of the desired direction and the sensor gains and delays (phases). Also the method enhances the desired signal based on a focusing transform for that signal, requires less computation than the taped-delay-line beamforming method, and provides good results even in a multipath environment. Computer simulations are given to support the proposed method.
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 349-362 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We propose a new algorithm for estimating the parameters of damped, undamped, or explosive sinusoidal signals. The algorithm resembles the MODE algorithm, which is commonly used for direction of arrival estimation in the array signal processing field. It is derived as a natural approximation to an asymptotically (high-SNR) optimal parameter estimator and has excellent statistical accuracy. Nevertheless, it is computationally simple and easy to implement. Numerical examples are included to illustrate the performance of the proposed method.
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  • 50
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 387-403 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Our main result is a theorem that gives, in a certain setting, a necessary and sufficient condition under which discrete-space multidimensional shift-invariant input-output maps with vector-valued inputs drawn from a certain large set can be uniformly approximated arbitrarily well using a structure consisting of a linear preprocessing stage followed by a memoryless nonlinear network. Noncausal as well as causal maps are considered. Approximations for noncausal maps for which inputs and outputs are functions of more than one variable are of current interest in connection with, for example, image processing.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 455-473 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper generalizes a recent result onsimple factorization of 2-variable (2-v) polynomials to simple andgroup factorization ofn-variate (n-v), (n≥3) polynomials. The emphasis is on developing a reliablenumerical technique for factorization. It is shown that simple as well as group factorization can be achieved by performing singular value decomposition (SVD) on certain matrices obtained from the coefficients of the givenn-v polynomial expressed in a Kronecker product form. For the polynomials that do not have “exact” simple and/or group factors, the concepts of approximate simple and group factorization are developed. The use of SVD leads to an elegant solution of an approximaten factorization problem. Several nontrivial examples are included to illustrate the results presented in this paper.
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 475-486 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a sequentially operated periodic FIR filter to perform the functions of multirate filter banks for perfect reconstruction. This filter consists of an analysis filter and a synthesis filter. Each of these filters has a single-input/single-output FIR filter with periodically time-varying coefficients and a sequentially operated multichannel sampling scheme. As a result, the proposed filter can offer considerable improvements in computation and implementation. For the design of the filter, we provide a necessary and sufficient condition for perfect reconstruction in terms of the blocked transfer matrices and give a design procedure.
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 537-545 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper a novel analytical technique for designing linear-phase, FIR integrators of first degree has been proposed by taking the optimality criteria of maximal flatness (in the Butterworth sense) of the amplitude response, at midband frequency:ω=π/2. Mathematical formulas to compute exact weights for the design of first-degree integrators (i.e., frequency response 1/(jω)) have been derived. Thereafter, the design has been extended to approximate linear-phase integrators for any generic degreer, r〉1. The performance characteristics of the first-, second- and third-degree integrators have been given to highlight the efficacy of the designs. The suggested designs are particularly suitable for the midband frequency range of operations.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 415-427 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A method is presented for the design of notch filters with specified notch frequency Ω0 and 3-dB rejection bandwidthB t, using a first-order real all-pass filter, wherein the only coefficient is used to control the notch frequency. To control the bandwidth, use is made of a new amplitude change function (ACF), and it is shown that given notch filter specifications can be exactly met thereby. Also, using the ACF, it is shown that stability of the second-order notch filter designs can be improved along with the noise gain.
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  • 55
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 16 (1997), S. 487-505 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We consider a general nonlinear input-output system governed by operator equations that relate the system's input, state, and output, all of which are in extended spaces. It is assumed that the system variables are separated. Our results give conditions under which the stability of the nominal system is robust; i.e., it is not destroyed by any sufficiently small admissible perturbation of the system. Theorem 1 deals with the case when by stability we mean theincremental stability. Theorem 3 concerns the*-stability; i.e., the case when the stability is essentially the boundedness of the transmission operator. Moreover, in Theorem 2 it is shown that, under certain conditions, the incremental stability of the nominal system implies insensitivity. Basically, our results show that if the operators describing the nominal system are well behaved, and the transition from the nominal system to the perturbed system is not abrupt, then the nominal system stability is robust. The applications of the results are illustrated by several examples.
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  • 56
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 315-329 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In earlier studies a multiclass vector quantization (MVQ)-based neural network design was explored for pattern classification. We reconsider that design here in the context of function emulation. With proper adjustment, the MVQ design demonstrates excellent performance. Moreover, the design algorithms sense discontinuities in the data and replicate them in the network.
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  • 57
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 365-376 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In earlier studies the concept of a fast form was generalized to a format that unified such discrete transform examples as the FFT, the FCT, the FST, and the FHT. In this study we consider the approximation of arbitrary linear maps by fast forms. Using simulation we evaluate the approximation capabilities of the generalized fast form.
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  • 58
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 377-393 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract On-line running spectral analysis is of considerable interest in many electrophysiological signals, such as the EEG (electroencephalograph). This paper presents a new method of implementing the fast Fourier transform (FFT) algorithm. Our “real-time FFT algorithm” efficiently utilizes computer time to perform the FFT computation while data acquisition proceeds so that local butterfly modules are built using the data points that are already available. The real-time FFT algorithm is developed using the decimation-in-time split-radix FFT (DIT sr-FFT) butterfly structure. In order to demonstate the synchronization ability of the proposed algorithm, the authors develop a method of evaluating the number of arithmetic operations that it requires. Both the derivation and the experimental result show that the real-time FFT algorithm is superior to the conventional whole-block FFT algorithm in synchronizing with the data acquisition process. Given that the FFT sizeN=2 r , real-time implementation of the FFT algorithm requires only 2/r the computational time required by the whole-block FFT algorithm.
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  • 59
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 523-523 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Circuits, systems and signal processing 18 (1999), S. 539-551 
    ISSN: 1531-5878
    Schlagwort(e): H 2 deconvolution filter ; envelope-constrained filter ; finite impulse response filter ; linear matrix inequality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, we consider an envelope-constrained (EC)H 2 optimal finite impulse response (FIR) filtering problem. Our aim is to design a filter such that theH 2 norm of the filtering error transfer function is minimized subject to the constraint that the filter output with a given input to the signal system is contained or bounded by a prescribed envelope. The filter design problem is formulated as a standard optimization problem with linear matrix inequality (LMI) constraints. Furthermore, by relaxing theH 2 norm constraint, we propose a robust ECFIR filter design algorithm based on the LMI approach.
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  • 61
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 565-585 
    ISSN: 1531-5878
    Schlagwort(e): Two-dimensional system ; model conversion ; Roesser's model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a geometric-series method for finding two-dimensional (2D) discrete-time (continuous-time) state-space models from 2D continuous-time (discretetime) systems. This method allows the use of well-developed theorems and algorithms in the 2D discrete-time (continuous-time) domain to indirectly carry out analysis and design of hybrid 2D composite systems.
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  • 62
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 505-521 
    ISSN: 1531-5878
    Schlagwort(e): Multirate systems ; multirate signal processing ; filter banks ; optimal design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The design of general nonuniform filter banks is studied. Contrary to uniform filter banks, in nonuniform filter banks, it may not be possible to achieve perfect reconstruction, but in some cases by using optimization techniques, we can design acceptable filter banks. Here, the initial finite impulse response (FIR) analysis filters are designed according to the characteristics of the input. By the design procedure, the FIR synthesis filters are found so that theH-norm of an error system is minimized over all synthesis filters that have a prespecified order. Then, the synthesis filters obtained in the previous step are fixed, and the analysis filters are found similarly. By iteration, theH-norm of the error system decreases until it converges to its final value. At each iteration, the coefficients of the analysis or synthesis filters are obtained by finding the least squares solution of a system of linear equations. If necessary, the frequency characteristics of the filters can be altered by adding penalty terms to the objective function.
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  • 63
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 617-617 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 107-119 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract For models of zero-input direct-form digital filters implemented in fixed-point digital hardware it is known that if saturation arithmetic is used and stability holds when the quantization is ignored, then the amplitude of all limit cycles can be made arbitrarily small by making the bound on the magnitude of the quantization sufficiently small. In that sense the effects of quantization and overflow can be considered separately. Recently, this proposition was extended to the case in which the input need not be zero. Here we give a result to the effect that quantization and overflow can be considered separately for a much more general class of discrete-time systems, and we give as an example an application of this result to systems governed by state equations.
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  • 65
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 197-206 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A new two-dimensional (2D) sample-based conjugate gradient (SCG) algorithm is developed for adaptive filtering. This algorithm is based on the conjugate gradient method of optimization and therefore has a fast convergence characteristic. The SCG is computationally simpler than the recursive least squares (RLS) algorithm. The SCG algorithm with the equation-error and output-error methods is investigated for application in image restoration. Simulation results show that the new algorithm significantly outperforms existing algorithms in the restoration of noisy images.
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  • 66
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 287-305 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A number of agents can arrange themselves equidistantly in a row via a sequence of adjustments, based on a simple “local” interaction. The convergence of the configuration to the desired one is exponentially fast. A similarity is shown between this phenomenon and the dynamics of pulse propagation along a distributedRC line, and a conjecture is made concerning the evolution of a similar system with a probabilistic rule of behavior.
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  • 67
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 43-57 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We consider multirate digital control systems that consist of an interconnection of a continuous-time nonlinear plant (described by ordinary differential equations) and a digital lifted controller (described by ordinary difference equations). The input to the digital controller consists of the multirate sampled output of the plant, and the input to the continuous-time plant consists of the multirate hold output of the digital controller. In this paper we show that when quantizer nonlinearities are neglected, then under reasonable conditions (which exclude the critical cases), the stability properties (in the Lyapunov sense) of the trivial solution of the nonlinear multirate digital control system can be deduced from the stability properties of the trivial solution of its linearization. We also point out that certain results involving quantization effects and stabilizing controllers can be established which are in the spirit of some existing results.
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  • 68
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 59-73 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Chaotic systems provide a simple means of generating deterministic signals that resemble white noise. It is this noise-like property that provides the potential for applying chaotic systems in communications. In this work, we report a detailed study of the logistic map for use as direct-sequence spread-spectrum (DS/SS) codes. The advantages of the chaotic DS/SS codes are the almost unlimited number of distinct sequences of arbitrary lengths, the ease of generating these sequences, and the increased privacy afforded by the noise-like appearance of these sequences. Some design criteria are provided from the correlation properties of these sequences, and bit-error rate (BER) results are generated by Monte Carlo simulations.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 75-84 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The asymptotic behavior of block floating-point and floating-point digital filters is analyzed. As a result, mantissa wordlength conditions are derived guaranteeing the absence of limit cycles in the regular dynamic range. Explicitly, the requirements are given for block floating-point state space filters with different quantization formats. Although these conditions are only sufficient, examples are given in which they are also necessary. In most cases the conditions are easily satisfied.
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  • 70
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 85-85 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 87-88 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 72
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 189-190 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 73
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 169-181 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper the Cramér-Rao bound (CRB) for a general nonparametric spectral estimation problem is derived under a local smoothness condition (more exactly, the spectrum is assumed to be well approximated by a piecewise constant function). Further-more, it is shown that under the aforementioned condition the Thomson method (TM) and Daniell method (DM) for power spectral density (PSD) estimation can be interpreted as approximations of the maximum likelihood PSD estimator. Finally the statistical efficiency of the TM and DM as nonparametric PSD estimators is examined and also compared to the CRB for autoregressive moving-average (ARMA)-based PSD estimation. In particular for broadband signals, the TM and DM almost achieve the derived nonparametric performance bound and can therefore be considered to be nearly optimal.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 149-168 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The issue of stability of higher-order, single-stage Sigma-Delta (ΣΔ) modulators is addressed using a method from nonlinear system theory. As a result, theoretical bounds for the quantizer input of the modulators are derived. A new method for stabilizing the ΣΔ modulators is then presented. It uses the quantizer input bound for possible instability detection. Upon detection of such a state, the highest-order integrator is cut off, effectively reducing the order of the modulator, and thus resulting in a stable system. The method is easily implemented and results in a very good signal-to-noise ratio (SNR) and fast return to normal operation compared to other stabilization methods.
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  • 75
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 225-239 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The uncorrelated component analysis (UCA) of a stationary random vector process consists of searching for a linear transformation that minimizes the temporal correlation between its components. Through a general analysis we show that under practically reasonable and mild conditions UCA is a solution for blind source separation. The theorems proposed in this paper for UCA provide useful insights for developing practical algorithms. UCA explores the temporal information of the signals, whereas independent component analysis (ICA) explores the spatial information; thus UCA can be applied for source separation in some cases where ICA cannot. For blind source separation, combining ICA and UCA may give improved performance because more information can be utilized. The concept of single UCA (SUCA) is also proposed, which leads to sequential source separation.
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  • 76
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. i 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 77
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 331-350 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper analyzes the nonlinear phenomenon of rotating stall via the methods of projection [Elementary Stability and Bifurcation Theory, G. Iooss and D. D. Joseph, Springer-Verlag, 1980] and Lyapunov [J.-H. Fu,Math. Control Signal Systems, 7, 255–278, 1994]. A compressor model of Moore and Greitzer is adopted in which rotating stall dynamics are associated with Hopf bifurcations. Local stability for each pair of the critical modes is studied and characterized. It is shown that local stability of individual pairs of the critical modes determines collectively local stability of the compressor model. Explicit conditions are obtained for local stability of rotating stall which offer new insight into the design, and active control of axial flow compressors.
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  • 78
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 407-429 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We describe herein a new means of training dynamic multilayer nonlinear adaptive filters, orneural networks. We restrict our discussion to multilayer dynamic Volterra networks, which are structured so as to restrict their degrees of computational freedom, based on a priori knowledge about the dynamic operation to be emulated. The networks consist of linear dynamic filters together with nonlinear generalized single-layer subnets. We describe how a Newton-like optimization strategy can be applied to these dynamic architectures and detail a newmodified Gauss-Newton optimization technique. The new training algorithm converges faster and to a smaller value of cost than backpropagation-through-time for a wide range of adaptive filtering applications. We apply the algorithm to modeling the inverse of a nonlinear dynamic tracking system. The superior performance of the algorithm over standard techniques is demonstrated.
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  • 79
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    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 445-455 
    ISSN: 1531-5878
    Schlagwort(e): Linear-phase digital filters ; FIR integrators
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In many signal processing situations, the desired (ideal) magnitude response of the filter is a rational function: $$\tilde H(\omega ) = |1/\omega |$$ (a digital integrator). The requirements of a linear phase response and guaranteed stable performance limit the design to a finite impulse response (FIR) structure. In many applications we require the FIR filter to yield a highly accurate magnitude response for a narrow band of frequencies with maximal flatness at an arbitrary frequencyω 0 in the spectrum (0, π). No techniques for meeting such requirements with respect to approximation of $$\tilde H(\omega )$$ are known in the literature. This paper suggests a design by which the linear phase magnitude response $$|\tilde H(\omega )|$$ can be approximated by an FIR configuration giving a maximally flat (in the Butterworth sense) response at an arbitrary frequency ω0, 0〈ω0〈π*. A technique to compute exact weights for the design has also been given.
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  • 80
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 524-524 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 81
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 525-537 
    ISSN: 1531-5878
    Schlagwort(e): Random sampling, digital signal processing ; spectral estimation ; computational algorithm
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Random sampling is one of the methods used to achieve sub-Nyquist sampling. This paper proposes a novel algorithm to evaluate the circular autocorrelation of a randomly sampled sequence, from which its power density spectrum can be obtained. With uniform sampling, the size of each lag (the step size) for computing an autocorrelation of a sequence is the same as the sampling period. When random sampling is adopted, the step size should be chosen such that the highest-frequency component of interest contained in a sequence can be accommodated. To find overlaps between a time sequence and its shifted version, an appropriate window is opened in one of the time sequences. To speed up the process, a marker is set to limit the range of searching for overlaps. The proposed method of estimating the power spectrum via autocorrelation is comparable in terms of accuracy and signal-to-noise ratio (SNR) to the conventional point rule. The techniques introduced can also apply to other operations for randomly sampled sequences.
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  • 82
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 587-609 
    ISSN: 1531-5878
    Schlagwort(e): Transfinite graphs ; infinite electrical networks ; current flows through infinity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Transfinite electrical networks of ranks larger than 1 have previously been defined by arbitrarily joining together various infinite extremities through transfinite nodes that are independent of the networks' resistance values. Thus, some or all of those transfinite nodes may remain ineffective in transmitting current “through infinity.” In this paper, transfinite nodes are defined in terms of the paths that permit currents to ”reach infinity.” This is accomplished by defining a suitable metricd v on the node setN S v of eachv-sectionS v, av-section being a maximal subnetwork whose nodes are connected by two-ended paths of ranks no larger thanv. Upon taking the completion ofN S v under that metricd v, we identify those extremities (now calledv-terminals) that are accessible to current flows. These are used to define transfinite nodes that combine such extremities. The construction is recursive and is carried out through all the natural number ranks, and then through the first arrow rank ω and the first limit-ordinal rank ω. The recursion can be carried still further. All this provides a more natural development of transfinite networks and indeed simplifies the theory of electrical behavior for such networks.
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  • 83
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 363-374 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we investigate new Fourier series with respect to orthonormal families of directed cycles $$\gamma $$ , which occur in the graph of a recurrent stochastic matrixP. Specifically, it is proved thatP may be approximated in a suitable Hilbert space by the Fourier series $$\sum {w_\gamma } \underline \gamma $$ . This approach provides a proof in terms of Hilbert space of the cycle decomposition formula for finite stochastic matricesP.
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  • 84
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 405-414 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The aim of this paper is to give an explicit computation for the potential generated by a dipole on a hexagonal grid. Such a computation will be expressed as the Fourier transform of a distribution on the bidimensional torus $$\mathbb{T}^2 $$ .
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  • 85
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 439-453 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The main contribution of this paper is to present (a) an algorithm for the computation of the generalized inverse of a not necessarily square two-variable polynomial matrix and (b) some applications of the proposed algorithm to the solution of Diophantine equations.
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  • 86
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 507-522 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper offers a flexible new approach to interpolating impedance data by bounded analytic functions. This approach is motivated by the conviction that any scheme for interpolating data from a physical system must incorporate knowledge of the system into the procedure. The classical Nehari's method is extended to include physical constraints from the system and point constraints from the data. An algorithm is developed and applied to estimating the impedance function of an antenna from a minimal data set.
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  • 87
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 16 (1997), S. 559-568 
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The main purpose of these comments is to correct (a) the definitions of admissible initial conditions, (b) the exact solution of a polynomial matrix description (PMD), and (c) the proof of the controllability and reachability criteria, presented in the above-mentioned work. The results concerning the reachability and controllability subspaces and thus the reachability and controllability criteria remain the same.
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  • 88
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 489-504 
    ISSN: 1531-5878
    Schlagwort(e): Source separation ; system identification ; pseudo-white noise ; FIR equation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In many voice-related applications, the presence of echoes and overlapping speech signals can degrade the quality or intelligibility of a desired speech signal to be processed. It is, therefore, important to cancel the echoes and to separate overlapping speech signals from a mixture of these components, so that a specific function of the system, for instance, transmission, speech identification, or recognition, can be accomplished with better performance. However, in many cases we do not know the properties of the communication channel, and sometimes even the number of speech sources is unknown. In this paper, we propose to use a reference signal to determine the channel characteristics. When the estimated channel parameter matrices are obtained, a recurrence formula can then be used to separate various speech signals including their reverberant counterparts. As a finite impulse response (FIR) model is used to describe the observation model of the sources in the reverberant environment, it is not necessary for the processing speech signals to be uncorrelated. Because it involves only simple computation, our approach can be used in online applications. In this paper, we will investigate the validity of our algorithm and compare it with extended fourth-order blind identification (EFOBI). It is found that our method preserves both signal waveforms and their amplitudes even in a noisy environment, whereas EFOBI has not been able to achieve similar performance.
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  • 89
    Digitale Medien
    Digitale Medien
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    Circuits, systems and signal processing 18 (1999), S. 553-564 
    ISSN: 1531-5878
    Schlagwort(e): Canonical forms ; discrete-time systems ; nonlinear systems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract It is shown that for each memberG of a large class of causal time invariant nonlinear input-output maps, with inputs and outputs defined on the nonnegative integers, there is a functionalA on the input set such that (Gs)(k) has the representationA(F k s) for allk and each inputs, in whichF k is a simple linear map that does not depend onG. More specifically, this holds—with anA that is unique in a certain important sense—for anyG that has approximately finite memory and meets a certain often-satisfied additional condition. Similar results are given for a corresponding continuous-time case in which inputs and outputs are defined on ℝ+. An example shows that the members of a large family of feedback systems have these “A-map” representations.
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  • 90
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    Digitale Medien
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    Journal of superconductivity and novel magnetism 10 (1997), S. 645-647 
    ISSN: 1557-1947
    Schlagwort(e): EuBaSrCu3O7−δ superconductor ; Ca doping ; orthorhombicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The effect of Ca doping in EuBaSrCu3O7−δ has been investigated by X-ray diffraction, ac susceptibility, and electrical resistivity measurements. X-Ray diffraction analyses of the samples showed that up to 30 at.% Ca can be substituted for Sr in EuBaSrCu3O7−δ, which has orthorhombic symmetry. The orthorhombicity decreases with increase inx, in EuBaSr1−xCax Cu3O7−δ, the material becoming tetragonal atx=0.2. Ac susceptibility and dc electrical resistivity measurements as function of temperature from 10 to 300 K showed that the superconducting transition temperatureT c decreases monotonically from 84 to 75K as the Ca concentrationx increases from 0.0 to 0.3 The decrease inT c can be attributed to the structural change taking place in EuBaSrCu3O7 as a consequence of replacement of Sr by Ca.
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  • 91
    ISSN: 1557-1947
    Schlagwort(e): Superconductivity ; research opportunities ; state of the art
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined.
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  • 92
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    Journal of superconductivity and novel magnetism 10 (1997), S. 649-655 
    ISSN: 1557-1947
    Schlagwort(e): Single crystal of Bi2Sr2CaCu2O8 ; high-resolution electron microscopy ; low-temperature electron diffraction ; lattice anomaly
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract High-resolution electron microscopy of a Bi2Sr2CaCu2O8 (Bi2212) single crystal prepared by the floating zone method shows that the single crystal is of high quality; there is no intergrowth faulting in the layered structure along thec-axis. Low-temperature selected area diffraction and convergent beam electron diffraction (CBED) studies of this high-quality single crystal show that there is no detectable change for both the point group symmetry of the basic structure and the modulated structure from room temperature to about 15 K. However, a lattice anomaly around 215 K was suggested by measuring the temperature dependence of the ratio between the cross-point distances of the HOLZ lines in high-index CBED patterns. The presence of the lattice anomaly was further confirmed by low-temperature X-ray diffraction.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 623-643 
    ISSN: 1557-1947
    Schlagwort(e): Superconductivity ; crystal field ; rare earth ; relaxation ; gap symmetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Neutron spectroscopy is a powerful tool to determine unambiguously the crystal-field (CF) potential in rare-earth (R) based high-T c superconducting materials. This technique provides detailed information on the electronic ground state of the R ions which is important to understand the thermodynamic magnetic properties as well as the observed coexistence between superconductivity and long-range magnetic ordering of the R ion sublattice at low temperatures. Moreover, the decay of the antiferromagnetic state of the parent compound as well as the evolution of the superconducting state upon doping can be directly and quantitatively monitored. It is found that the observed CF spectra separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for cluster formation. The onset of superconductivity can be shown to result from percolation which means that the superconductivity is an inhomogeneous materials property. Since the linewidths of CF transitions directly probe the static electronic susceptibility, we discuss temperature-dependent experiments of the relaxation rate of CF excitations in both optimally doped and underdoped regimes. It is shown that there is clear evidence for the opening of an electronic gap in the normal state of underdoped superconductors. Furthermore, the relaxation behavior appears to be extremely dependent upon the energy at which the static susceptibility is being probed. The main observed features can be reproduced by considering a strongly anisotropic gap function.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 663-668 
    ISSN: 1557-1947
    Schlagwort(e): Thermal diffusivity ; acoustic plasmons ; cobalt substitution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The thermal diffusivity κ(T) of the cobalt-substituted sintered YBCO system, YBa2Cu3−x Co x O7∮δ (x=0.0, 0.1), has been measured to, investigate, effects of atomic substitution and charge carrier concentration on the thermal diffusion processes. The thermal diffusivity was measured in the temperature range 35–300 K, using the transient-plane-source technique. The results show that, belowT c , the κ(T) values of the doped (x=0.1), samples are lower than the corresponding values for the undoped (x=0.0) samples. This may be due to the difference in the free-charge carrier concentrations of the two samples. A decoupling between the conducting Cu−O planes as a result, of Co-doping in the chain sites may contribute to additional decrease in the thermal diffusivity of the doped sample. An attempt was made to explain the rise in the thermal diffusivity belowT c by adopting a recent theoretical model based on the existence of weakly damped collective electron excitations of Bose type, with acoustic dispersion relation, (acoustic plasmons) inside the superconducting gap.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    ISSN: 1557-1947
    Schlagwort(e): High-T c superconductors ; order parameter ; Josephson junctions ; Josephson critical current ; pair symmetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract An intrinsic gap depression at the superconductor-insulator interface due to the very short value of the coherence length in high-T c superconductors [HTS] is considered in the framework of a mixed (s+id)-wave pair symmetry for the order parameter ranging from pures to pured-wave. This gap depression acts as the main physical agent causing the relevant reduction ofI c (T)R n (T) values with respect to BCS expectations in HTS SIS Josephson junctions. Good agreement with various experimental data is obtained with both pures-wave and pured-wave symmetries of the order parameter, but with amounts of gap depression depending on the pair symmetry adopted. Regardless of the apir symmetry considered, these results prove the importance of the surface order-parameter depression in the correct interpretation of theI c (T)R n (T) data in HTS SIS junctions. In the case of a planar YBCO-based junction the use of the de Gennes condition allowed us to tentatively obtain an upper limit for the amount ofd-wave present in the gap of YBCO.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 669-672 
    ISSN: 1557-1947
    Schlagwort(e): Equation of state ; bulk modulus ; cohesive energy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-T c copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born-Landé inverse power form. The model, parameters of the Born-Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of pressure derivatives of bulk modulus atP=0 and the values of bulk modulus are found to be in very close agreement with experimental values for high-T c copper oxide and their nonsuperconducting parent compounds. It is also found that the quantity ΔU/U(V o) of these compounds increases with increasing hydrostistic pressure.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 673-675 
    ISSN: 1557-1947
    Schlagwort(e): Cuprates ; van Hove singularity ; pseudo-gap
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Several experimental features in the normal state of cuprates have been interpreted using a “pseudogap”. We show that these results may be explained by the band structure of the CuO2 planes in the metallic region, which exhibits, saddle points (van Hove singularities).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Telechelically bis(hydrodimethylsilyl)-functionalized oligo(dimethylsiloxane)s or aromatics were found to give polymers constituting of alternating disilylene and oligodimethylsiloxane or 4,4′-diylaromatics as repeating units by dehydrogenative coupling reaction in the presence of palladium dibenzylideneacetone complex. The same catalyst gave polysilylenes with trisiloxane pendant from 1,1-dihydro-1,3,3,5,5,7,7,7-octamethyltetrasiloxane.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Polymer bulletin 38 (1997), S. 23-25 
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Hybrid particles have been synthesized from methyltriethoxysilane (MTEOS) by the sol-gel process. The particle size, size distribution, particle surface morphology conductivity and pH of the reaction solution at different reaction times were determined. Compared with tetraethyl orthosilicate (TEOS) and p-(chloromethyl)phenyl-trimethoxysilane (CMPTOS), MTEOS has a slower hydrolysis rate.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Polymerization of 4-n-alkylstyrenes (alkyl side group; methyl, ethyl, propyl and buthyl) was carried out with the η-C5(CH3)5TiCl3-methylaluminoxane (MAO) and TiCl3-triethylaluminum (TEA) catalyst systems. When the η-C5(CH3)5TiCl3-MAO catalyst was used, the stereoregularity of resulting polymers markedly depended on the length of substituted alkyl groups, i.e., the catalyst gave highly syndiotactic poly(4-methylstyrene), but produced atactic polymers for the monomers with ethyl, propyl and buthyl substituents. On the other hand, all the poly(4-n-alkylstyrene)s obtained with the TiCl3-TEA catalyst were highly isotactic. As a result, a large difference was observed in the thermal properties of polymers obtained between the two catalyst systems.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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