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The paper presents a hybrid model of disc-type power transformer winding for frequency response analysis (FRA) based on traveling wave and multiconductor transmission line (MTL) theories. Each disc of a winding is described by traveling wave equations, which are connected to each other in a form of MTL matrix model. This significantly reduces the order of the model with respect to previously established MTL models of transformer winding. The model is applied to frequency response simulation of two single-phase transformers. The simulations are compared with the experimental data and calculated results using lumped parameter and MTL models reported in other publications. It is shown that the model can be used for FRA result interpretation in an extended range of frequencies up to several mega Hertz and resonance analysis under very fast transient overvoltages (VFTOs). Index Terms--Frequency response analysis, muiticonductor transmission lines, transfer functions, transformer windings.

The directed transfer function (DTF) and the partial directed coherence (PDC) are frequency-domain estimators that are able to describe interactions between cortical areas in terms of the concept of Granger causality. However, the classical estimation of these methods is based on the multivariate autoregressive modelling (MVAR) of time series, which requires the stationarity of the signals. In this way, transient pathways of information transfer remains hidden. The objective of this study is to test a time-varying multivariate method for the estimation of rapidly changing connectivity relationships between cortical areas of the human brain, based on DTF/PDC and on the use of adaptive MVAR modelling (AMVAR) and to apply it to a set of real high resolution EEG data. This approach will allow the observation of rapidly changing influences between the cortical areas during the execution of a task. The simulation results indicated that time-varying DTF and PDC are able to estimate correctly the imposed connectivity patterns under reasonable operative conditions of signal-to-noise ratio (SNR) ad number of trials. An SNR of five and a number of trials of at least 20 provide a good accuracy in the estimation. After testing the method by the simulation study, we provide an application to the cortical estimations obtained from high resolution EEG data recorded from a group of healthy subject during a combined foot-lips movement and present the time-varying connectivity patterns resulting from the application of both DTF and PDC. Two different cortical networks were detected with the proposed methods, one constant across the task and the other evolving during the preparation of the joint movement. Index Terms--Cortical connectivity, directed transfer function (DTF), high resolution electroencephalography (EEG), limb movement, partial directed coherence (PDC), recursive least squares (RLS).

The problem of [H.sub.2]-optimal sampled.data (SD) preview control is considered. It is assumed that a stochastic reference signal corrupted with additive colored noise acts upon the system so that future values of this input are known within a preview window [tau]. A rigorous frequency-domain solution of the problem is given for SISO SD systems on the basis of the parametric transfer function concept. Numerator and denominator degrees of the optimal controller are calculated explicitly on the basis of initial data. The dependence of the optimal cost function on r is investigated and the limiting value as [tau] [right arrow] [infinity] is found. Moreover, it is shown that this limit depends on the relation between [tau] and the sampling period. Index Terms--Delay systems, polynomial methods, sampled data systems, stochastic optimal control, transfer functions.

The block decoupling problem by admissible dynamic precompensation for LTI systems is considered. Admissibility refers to the preservation of the class of controlled output trajectories, i.e. functional output controllability is concerned, which is more demanding than just pointwise output controllability. This problem has been solved by Hautus and Heyman, within a transfer function matrix approach. Different new equivalent solvability conditions in terms of controllability subspaces, transfer function matrices or matrix pencils are given. One of these conditions (expressed in the input space) is at the origin of new necessary and sufficient conditions for block decoupling by general precompensation (possibly non admissible and nonsquare), in the wider sense of Basile and Marro. Index Terms--Block decoupling, controllability subspaces, linear time-invariant (LTI) systems, precompensation, transfer function matrices.

A genetic algorithm (GA)-based search method is used to design the sigma-delta modulators with arbitrary signal and noise transfer functions. The GA-based search engine is developed in order to determine the poles and zeros of the transfer functions for minimizing an objective function and the numerical results have shown the effectiveness of the proposed method.

Transfer function analysis of blood pressure and cerebral blood flow in humans demonstrated that cerebrovascular autoregulation operates most effectively for slow fluctuations in perfusion pressure, not exceeding a frequency of -0.15 Hz. No information on the dynamic properties of cerebrovascular autoregulation is available in rats. Therefore, we tested the hypothesis that cerebrovascular autoregulation in rats is also most effective for slow fluctuations in perfusion pressure below 0.15 Hz. Normotensive Wistar-Kyoto rats (n = 10) were instrumented with catheters in the left common carotid artery and jugular vein and flow probes around the right internal carotid artery. During isoflurane anesthesia, fluctuations in cerebral perfusion pressure were elicited by periodically occluding the abdominal aorta at eight frequencies ranging from 0.008 Hz to 0.5 Hz. The protocol was repeated during inhibition of myogenic vascular function (nifedipine, 0.25 mg/kg body wt iv). Increases in cerebral perfusion pressure elicited initial increases in cerebrovascular conductance and decreases in resistance. At low occlusion frequencies ( myogenic vascular function; blood pressure variability; hemorrhagic stroke; nifedipine; transfer function analysis

The cyclically switching operation of a novel zero-voltage-zero-current-switching three-level converter is briefly presented. Based on a steady-state time-domain analysis of each equivalent switching topology, an average model is obtained. Small-signal open-loop ac line-to-output, control-to- output, and output-current-to-output-voltage transfer functions are deducted. The stability, gain margin, and phase margin of the open-loop transfer functions are studied. After designing the closed loop, the study of the audiosusceptibility and closed-loop output impedance allows for a dynamic analysis: the transient responses to changes in the input voltage and load current are obtained. The results got from the small-signal modeling are compared and confirmed by those obtained by PSPICE simulation and those measured in the laboratory, on an experimental converter of 4.5 kW. Index Terms--Converters, modeling, simulation, transfer-functions, transient-response.

Dynamic atomic force microscopy (AFM) offers many opportunities for the characterization and manipulation of matter on the nanometer scale with a high temporal resolution. For a quantitative investigation of surface properties by dynamic AFM an appropriate system identification procedure is required characterizing the force sensor beyond the usual parameters spring constant, quality factor and detection sensitivity.

The development of powerline communication (PLC) systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents an analytic model describing complex transfer functions of typical powerline networks using only a small set of parameters. The model is based on physical signal propagation effects in mains networks including numerous branches and impedance mismatching. Besides multipath propagation accompanied by frequency-selective fading, signal attenuation of typical power cables increasing with length and frequency is considered. A verification of the model at a test network, as well as its use for definition of attenuation profiles and reference channels, demonstrate the practical value of the proposed model. Index Terms--Channel model, multipath channel, powerline.

The dynamic behavior of position sensitive detectors is described. The position sensitive detector (PSD) response to a change of light spot position is investigated.

This paper extends the energy function to the analysis of the stability of neural networks with asymmetric interconnections and noninvertible transfer functions. Based on the new energy function, stability theorems and convergent criteria are derived which improve the available results in the literature. A simpler proof of a previous result for complete stability is given. Theorems on complete stability of neural networks with noninvertible output functions are presented. Index Terms: Energy function, Hopfield network, neural networks, stability.

In this paper we give simplified proofs of the stability and the margin of stability criteria of Zeheb and Walach for n-dimensional recursive digital filters. We base our proofs on the method of Lagrange multipliers. Both the stability and margin of stability questions are converted into the problem of locating the zeros of a system of polynomial equations. These systems can then be solved using Buchberger's algorithm for computing the Groebner basis of a polynomial ideal. Index Terms - Digital filter wordlength effects, multivariable systems, polynomials, recursive digital filters, signal processing, stability criteria.

Let H(z) = [summation of] [H.sub.k] [z.sup.-k] where k = 0 to [infinity] be a q x p rational causal minimum phase transfer function, and let [([R.sub.n]).sub.n[element of]Z] be the autocovariance sequence associated to the spectral density H(z)[H.sup.T]([z.sup.-1]). In this paper, the authors address the identification problem of H(z) from the truncated autocovariance sequence [([R.sub.n]).sub.n[not equal to]0] for the case q > p. Index Terms - MIMO systems, rational transfer function matrices, stochastic realization theory.

The recently developed Generalized Mapping Theorem provides a means to synthesize convex-hull generator points for uncertain polynomials and transfer functions. However, its application requires maximizing a projection onto a unit ray over a uniform grid of angles, which is inefficient and ignores the errors associated with a finite grid. The algorithm developed in this paper addresses both of these issues by characterizing errors and synthesizing generator points only when needed to meet a given convergence tolerance. Index Terms - Convex hull, parametric uncertaainty, uncertain transfer function, value set.

Dynamic systems of an arbitrary real order (fractional-order systems) are considered. A concept of a fractional-order [PI.sup.[Lambda]] [D.sup.[Mu]]-controller, involving fractional-order integrator and fractional-order differentiator, is proposed. The Laplace transform formula for a new function of the Mittag-Leffler-type made it possible to obtain explicit analytical expressions for the unit-step and unit-impulse response of a linear fractional-order system with fractional-order controller both for the open and closed loop. An example demonstrating the use of the obtained formulas and the advantages of the proposed [PI.sup.[Lambda]] [D.sup.[Mu]]-controllers is given. Index Terms - Fractional-order controllers, fractional-order systems, fractional differential equations, Laplace transforms, transfer functions.

Estimation of a parametric input-output (I/O) infinite impulse response transfer function given time-domain I/O data is considered. Some of the desirable properties of any approach to this problem are: unimodality of the performance surface (cost function), consistent identification in the sufficient-order case, and stability of the fitted model under undermodeling. Some of the well-known approaches fail to satisfy one or more of these properties. The time-domain equation error method (also called least squares equation error) yields a unimodal performance surface, biased estimates in colored noise and the sufficient-order case, and stable fitted models under undermodeling if the input is autoregressive. In this paper we first consider a frequency-domain solution to the least squares equation error identification problem using the power spectrum and the cross-spectrum of the I/O data to estimate the I/O parametric transfer function. The proposed approach is shown to yield a unimodal performance surface, consistent identification in colored noise and sufficient-order case, and stable fitted models under undermodeling for arbitrary stationary inputs so long as they are persistently exciting of sufficiently high order. Asymptotic performance analysis is carried out for both sufficient-order and reduced-order cases. These asymptotic results are then used to derive statistics on the corresponding estimated transfer function. We also investigate an iterative pseudomaximum likelihood approach and analyze its performance under sufficient-order modeling. Finally, computer simulation examples are provided to illustrate the two approaches. Index Terms - Maximum likelihood, model approximation, spectral analysis, stability, system identification.

The parametric multiple-input multiple-output (MIMO) infinite impulse response transfer function given time-domain input-output (IO) data was estimated. A frequency-domain solution to the least-squares equation error multivariable system identification problem was used by employing the power spectrum and the cross-spectrum of the IO data to estimate the IO parametric transfer function. This provided a unimodal performance surface and consistent identification in colored noise and the sufficient-order case. An iterative- pseudo-maximum likelihood method was examined including its consistency under sufficient-order modeling.

An asymptotic distributed transfer function method (TFM) was developed for conical shell analyses. Formulations of the TFM involved the use of partial differential equations, the analysis of eigenvalue problems and Fourier expansions as well as perturbation techniques. The static responses of different types of conical shells were determined using numerical analyses procedures. Results pointed to the convenience of asymptotic TFM for use in computer coding and numerical simulations.

An equation for the error variance of transfer function of a two-dimensional system was derived. The optimal realization problem was then formulated by minimizing this variance with respect to all possible realizations of the system. This problem was found to be similar to the minimization of a pure L2 norm based sensitivity measure. The problem can be solved through any standard minimization algorithm.

In this brief, the margin of stability of two-dimensional (2D) discrete systems is considered. A new method to compute the stability margin of 2-D continuous systems is provided. Illustrative examples are also included. Index Terms - Multidimensional systems, stability, stability margin, 2-D filters, 2-D systems.

A numerical approach is proposed for computing the frequency-response templates of a class of rational transfer functions whose coefficients are affine functions of some interval parameters. This approach is based on characterizing the template as the set of points in the complex plane that make the value set of a certain polytope of polynomials to include the origin. With this characterization, the proposed approach traces out the boundary of the frequency-response template corresponding to a single frequency by using a simple pivoting procedure along with an efficient zero-inclusion test algorithm. Index Terms - Frequency response, robust stability, uncertain linear system, value set.

In this paper, the basic transfer functions and time-response functions of linear phenomenological models are revisited. The relation between the analyticity of a transfer function and the causality of the corresponding time-response function is extended for the case of generalized transfer functions. By using the properties of the Hilbert transform and the associated Kramers-Kroning relations it is shown that transfer functions that have a singularity at [Omega] = 0 in their imaginary part should be corrected by adding a delta function in their real part. This operation ensures that the resulting time-response function is causal and is consistent with the theory of generalized functions. Accordingly, the transfer functions of classical viscoelastic models presented in standard vibration handbooks are revised. Finally, the addition of a delta function in the impedance of the noncausal ideal hysteretic dashpot that has been proposed in the literature is discussed.

An important property of cellular neural networks (CNN's) is the binary output property, that, when the self-feedback is greater than one, the final activations are [+ or -]1. This brief considers the generalization of this property to networks with sigmoidal output functions. It is shown that in this case the property cannot be stated without reference to the cross feedback, and conditions are found under which the property remains valid.

Consider the problem of identifying a scalar bounded-input/bounded-output stable transfer function from pointwise measurements at frequencies within a bandwidth. We propose an algorithm which consists of building a sequence of maps from data to models converging uniformly to the transfer function on the bandwidth when the number of measurements goes to infinity, the noise level to zero, and asymptotically meeting some gauge constraint outside. Error bounds are derived, and the procedure is illustrated by numerical experiments. Index Terms - Approximate modeling, linear systems, Nehari extension, robust identification.

This paper presents an alternative formulation for the transfer function of the absolute acceleration response of a single-degree-of-freedom (SDOF) secondary system supported on an earthquake-excited, classically damped primary system. This formulation is based on the use of fixed-base mode shapes of the primary system and thus does not require the computation of the modal properties of the combined system. This formulation requires the knowledge of the power-spectral-density function of the earthquake motion to obtain the desired floor response spectra. This has been illustrated in the case of an example building and a band-limited white noise excitation.

In this contribution, the problem of blind identification of p-inputs/q-outputs FIR transfer functions is addressed. Existing subspace identification methods derived for p = i are first reformulated. In particular, the links between the noise subspace of a certain covariance matrix of the output signals (on which subspace methods build on) and certain rational subspaces associated with the transfer function to be identified are elucidated. Based on these relations, we study the behavior of the subspace method in the case where the order of the transfer function is overestimated. Next, an asymptotic performance analysis of this estimation method is carried out. Consistency and asymptotical normality of the estimates is established. Closed-form expression for the asymptotic covariance of the estimates is given. Numerical simulations and investigations are presented to demonstrate the potential of the subspace method. Finally, we take advantage of our new reformulation to discuss the extension of the subspace method to the case p >1. We show where the difficulties lie, and we briefly indicate how to solve the corresponding problems. The possible connections with classical approaches for MA model estimations are also outlined. Index Terms - System identification, subspace methods, rational subspaces, polynomial matrices, statistical performance analysis.

New algorithms for the derivation of the transfer-function matrices of two-dimensional (2-D) discrete systems from the Roesser and Fornasini-Marchesini state-space models are presented. Two key steps in developing the algorithms are as follows. First, the transfer-function matrix is reformulated in terms of the characteristic polynomials of the matrices involved. Second, an efficient algorithm for the determination of 1-D polynomial coefficients is developed and is, in turn, used to determine the coefficient matrices of the 2-D transfer-function matrix. The proposed algorithms are computationally efficient and reliable. The efficiency of the algorithms is illustrated by comparing the proposed method with two existing methods through examples. Index Terms - 2-D transfer-function matrix, 2-D discrete systems.

In this paper, the method for obtaining of various state-space realizations of the Roesser type for an assigned two-variable transfer function is developed. Two-variable elementary polynomial operations are employed. A new version of the general, state-space model is constructed too. One also throw some new fight on the problem of the mutual connections among the different 2-D state-space models as the Roesser, the Fornasini-Marchesini, and the general one. Singular as well as the standard (nonsingular) models are considered. Index Terms - Multivariable (nD) systems, systems theory.

The generalized Weyl symbol (GWL) formalizes the freedom in the definition of a time-varying transfer function. The GWL can only be applied to underspread linear time-varying (LTV) channel systems. The application of the GWL in underspread LTV channel systems is similar to its application in the linear time-invariant (LTI) systems. The GWL fails to possess the essential features of the time-invariant transfer-function of LTI systems, in case of overspread systems, which makes it inapplicable to these systems. Proof for the validity of the transfer function calculus for underspread systems is presented.

Localization of sound sources by human listeners has been widely studied and theories and various models of the localization and hearing mechanism have been constructed. In the classical 'duplex' theory, sound localization in azimuth is explained by interaural time or equivalently, phase differences at low frequencies, and by interaural amplitude differences at higher frequencies. Head related transfer functions (HRTF's) present a linear system approach to modeling localization by representing the direction-dependent transformation the sound undergoes at each ear. Localization in elevation is explained by directional differences in the HRTF's, which also explains monaural localization. We conjecture that the HRTF's evolved during the course of nature (due to the evolution of the shape and structure of the ear etc.) are optimal with respect to several physically realizable criteria. In this paper, we investigate the problem of defining the design constraints which when optimized yield a set of HRTF's for hearing and monaural vertical localization in an attempt to better understand, and if possible, duplicate nature's design. We pursue an engineer's design perspective and formulate a constrained optimization problem, where the desired set of HRTF's is optimized according to a cost function based on several criteria for localization, hearing and smoothness, and also by imposing physically realizable constraints on the HRTF's such as nonnegativity, energy etc. The value of the cost function for a candidate set of HRTF's is an indication of the similarity of that set of HRTF's with respect to the ideal solution (measured HRTF data). The final optimization results we present are similar to the actual HRTF's measured in human subjects, and the associated cost function values are found to be almost equal. This points to the fact that the optimization criteria defined are quite relevant. The significant outcome of this research is the identification of a relevant set of mathematical criteria that could be optimized in the human auditory system to facilitate good hearing and localization. These criteria along with the associated constraints represent the desirable characteristics of the HRTF's in an HRTF-based localization system, and could lead to a better understanding and modeling of the auditory system.

A modification of the cross-spectral method that utilizes the nonstationary properties of the data to evade bias effects caused by correlated stationary noise efficiently identifies the transfer function of a linear system. Moreover, the method is extendable to multidimensional signals, multichannel signal enhancement, and noise cancellation techniques. Simulation results of the method are presented and compared to the conventional method results for a speech signal.

A new approach based on the calculation of a flowmeter factor as a function of the position of the transducers for the noninvasive measurement of flow in pipes is described. The acoustic transfer function's description in the spatial frequency domain, corresponding to the decomposition of the sonic beam into an angular spectrum of plane waves, enables accurate measurement of flow, using the known methods for plane waves. This approach renders the unavoidable mispositioning of transducers insignificant and the need for large impractical transducer sizes superfluous.

In this paper several applications on the use of symbolic computation to control system design are discussed. These applications are of educational value to control engineering courses. The routines developed here provide a quick way to formulate control design problems, ranging from calculating elementary transfer functions to automating the construction of state space realization. This paper also gives detailed discussion on the symbolic computational process of the programs being developed. Examples of symbolic calculation of generalized plant state space realization for use in [H.sub.[infinity]]/[H.sub.2] optimal control are presented.

An efficient algorithm for computing the frequency response of discrete-time systems described by rational transfer functions is presented. The algorithm is simple, fast, recursive, and can be used for equally or unequally spaced frequencies. Based on an initial expansion of the system transfer functions to a novel Jacobi-type trigonometric continued fraction, the algorithm proposed permits all operations to be performed by real arithmetic, guarantees real results, saves a number of operations, and produces accurate results. The algorithm is easily programmable and needs only 2nN real multiplications/divisions for evaluating the frequency response of an nth-order system at N different frequencies.

It is shown that for a singularly perturbed system, the [H.sub.[infinity]] norm of the transfer matrix function tends to the largest of the [H.sub.[infinity]] norms for the boundary layer system and for the reduced slow model. As an application complementing the results of Pan and Basar, it is proven that fast transients cannot always be neglected when designing a stabilizing controller with disturbance attenuation.

This paper describes the first algorithm to efficiently compute the dominant poles of any specified high order transfer function. As the method is closely related to Rayleigh iterations (generalized Rayleigh quotient), it retains the numerical properties of global and ultimately cubic convergence. The results presented are limited to the study of low frequency oscillations in electrical power systems, but the algorithm is completely general. Keywords - Small-signal stability, poorly damped oscillations, transfer function, dominant poles, transfer function residues, participation factors, large scale systems, sparse eigenanalysis.

Let H(z) be a rational transfer function, with associated nonnegative impulse response sequence. The paper considers the question: When does there exist a triple A [element of] [R.sup.NxN], b [element of] [R.sup.N], c [element of] [R.sup.N] with all nonnegative entries and H(z) = c[prime][(zI - A).sup.-1]b? An essentially complete characterization is given of the H(z) allowing such a realization, in terms of the location of the pole or poles of H(z) with maximum modulus.

Cholesteryl ester transfer activity (CETA) is found in cultured hamster and rat adipose tissue that are released into the conditioned medium associated with a reciprocal decrease in adipose tissue CETA. This upholds the view that in hamsters, adipose CETA exhibits in situ and intravascular functions and in rats, its role is restricted to tissue-specific functions. The hamster cholesteryl ester transfer protein differs from rat adipose-associated CETA in the active site structure and secretion regulatory mechanisms.

A new expression for the coupled interconnect system transfer function has been derived under general linear generator and uncoupled load conditions, i.e., without any restrictions in circuit load impedance. High-speed signals on coupled interconnects have been simulated using this transfer function. The simulation uses generalized interconnect circuit model parameters in which all line parameters are frequency dependent. The validity of the interconnect circuit parameters was confirmed previously using s-parameter measurements. High-speed signal simulation using this novel interconnect transfer function has been verified with time-domain measurements using an HP54121T high-speed sampling oscilloscope. This work accurately predicts coupled interconnect circuit responses. With this transfer function, signal integrity problems of high-performance VLSI circuits can be predicted in the design stage.

In this paper, we propose to define the transfer function of a system in a new way, namely as a semi-cancellable fraction (SCF), i.e., a fraction in which unstable pole-zero cancellations are not allowed. Within this new framework, it is possible to be rigorous and coherent in dealing with the stabilizability of a system from an input-output viewpoint, as opposed to recent papers focusing on the stabilizability of infinite dimensional input-output systems.

In this paper we study the problem of synthesizing an internally stabilizing linear time-invariant controller for a linear time-invariant plant such that a given closed-loop transfer function is extended strictly positive real. Necessary and sufficiency conditions for the existence of a controller are obtained. State-space formulas for the controller design are given in terms of solutions to algebraic Riccati equations (or inequalities). The order of the constructed controller does not exceed that of the plant.