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  • 1
    Digitale Medien
    Digitale Medien
    Frequency domain design of FIR and IIR Laplacian of Gaussian filters for edge detection (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 555-572 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This work addresses the design of LoG filters in the frequency domain within a structure formed by the cascade of quasi-Gaussian and discrete Laplacian filters. The main feature of such a structure is that it requires half the number of convolutions of the classical structure in which the LoG transfer function is expressed as the sum of two separable transfer functions of 1-D Gaussian and LoG type. Such a perspective allows one to rephrase the design of IIR and FIR filters for edge detection as a frequency domain approximation problem solvable by standard digital filter design tools. The zero-phase IIR solutions have a good performance at low orders and approximation errors practically independent of the aperture parameter. The characteristics of the nearly linear-phase IIR filters solving the problem suggest the consideration of linear-phase FIR filters with zeros constrained on the unit circle. The use of such filters leads to remarkable computational savings with respect to the filters designed by impulse response sampling. The agreement between the edge values obtained by the filters designed according to the scheme proposed in this work and those obtained by standard techniques is very good.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188981
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  • 2
    Digitale Medien
    Digitale Medien
    On the connection between state-space representation and generalized Bezout identity of multivariable systems (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 505-514 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A novel and complete method is presented for constructing the generalized Bezout identity in polynomial form of the transfer matrix from its state-space representation of a reachable and observable system. As a result, one can easily apply well-developed synthesis and analysis theories to systems described in the frequency domain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183157
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  • 3
    Digitale Medien
    Digitale Medien
    Robustness analysis of polynomials with linearly correlated uncertain coefficients in lp-normed balls (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 543-554 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The aim of this paper is to obtain the uncertain value set in the complex plane for systems with real and complex parameters that are known to lie inside a ball in a weightedl p-norm. It generalizes previously available results and may be used to test the robust stability of polynomials whose coefficients lie in a weighted lp-ball.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183161
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  • 4
    Digitale Medien
    Digitale Medien
    Weighted mean squared error criterion with fixed-level modification for linear-phase fIR filter design (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 581-595 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper describes a new approach—a Fixed-Level Least Squares (FLLS) method for linear-phase FIR filter design. It is intended for rejection of the Gibbs phenomenon through the introduction of a set of equally spaced fixed levels in the transition band and subsequent redefinition of the approximated and weighted functions. Detailed mathematical solutions of the problem as well as many examples are given. The results in graphical form are shown as an output of the FLLS software model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188983
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  • 5
    Digitale Medien
    Digitale Medien
    Finite modeling of parabolic equations using Galerkin methods and inverse matrix approximations (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 631-648 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we examine order reduction of parabolic systems using modal truncation. The parabolic distributed system is first approximated using the Galerkin method. The system matrices have a special structure that allows us to find the approximate spectrum of the parabolic system. To do this we compute approximate inverses of tridiagonal, diagonally dominant symmetric matrices. The approximation leads to algorithms of orderO(n), as opposed to traditional algorithms of orderO(n), wheren is the order of the system. Finally, an example is presented to illustrate the proposed algorithm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188986
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  • 6
    Digitale Medien
    Digitale Medien
    Network approximation of input-output maps and functionals (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 711-725 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We give results concerning the problem of approximating the input-output maps of nonlinear discrete-time approximately finite-memory systems. Here the focus is on the linear dynamical parts of the approximating structures, and we give examples showing that these linear parts can be derived from asingle prespecified function that meets certain conditions. This is done in the context of an approximation theorem in which attention is focused on what we call “basic sets.” We also consider the related but very different problem of approximating nonlinear functionals using lattice operations or the usual linear ring operations. For this problem we give criteria, not just sufficient conditions, for approximation on compact subsets of reflexive Banach spaces (any Hilbert space is a reflexive Banach space).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190124
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  • 7
    Digitale Medien
    Digitale Medien
    Sensor location calibration for bearing estimation (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 763-770 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract New calibration methods are presented for bearing estimation with sensor location uncertainties, which are based on eigenvalue decomposition of the sample covariance matrix and three or more nondisjoint sources in known bearings. The methods can be applied to arbitrary arrays, including linear arrays, require fewer computations, and are suitable for low signal-to-noise ratio (SNR) cases. Computer simulations are given to illustrate the performance of the proposed methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190128
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  • 8
    Digitale Medien
    Digitale Medien
    A fast algorithm for FIR digital filtering with a sum-of-triangles weighting function (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 145-164 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A doubly recursive algorithm for time domain convolution with a piecewise linear weighting function is presented that combines the speed of a recursive (IIR) digital filter with the flexibility and ease of design of a nonrecursive (FIR) digital filter. The approach approximates the desired FIR weighting function by a sum-of-triangles weighting function. ForL triangles (or triangle pairs for a linear phase filter) the algorithm is of orderLN. The approximation improves with the number of triangles. A significant advantage of the algorithm compared to FFT filtering or direct convolution is that there is no necessity of a tradeoff between frequency response accuracy and computation time per output point as the data spacing decreases in the filtered signal. The computational complexity is dependent on the number of triangles chosen, not the width of the weighting function, so the algorithm is especially effective for filters with an inherently wide FIR weighting function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183775
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  • 9
    Digitale Medien
    Digitale Medien
    Correlation analysis of stochastic amplitude-angle modulated signals (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 335-342 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A solution of the problem of correlation analysis of stochastic amplitude-angle modulated signals is presented. The solution is obtained on the basis of the theory of linear stochastic processes for the general case of nonstationary correlated Gaussian noises in both modulation channels. These noises are regarded as the results of a linear filtration of Gaussian white noise processes. As an example of the analysis a case of band-pass modulation noises is considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182590
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  • 10
    Digitale Medien
    Digitale Medien
    Analysis of 2-D state-space periodically shift-variant discrete systems (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 395-413 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Two-dimensional (2-D) periodically shift-variant (PSV) digital filters are considered. These filters have applications in processing video signals with cyclostationary noise, scrambling digital images, and 2-D multirate signal processing. The filters are formulated in the form of a Givone-Roesser (GR) state-space model with periodic coefficients. This PSV model is then presented in block form as a shift-invariant system that also has the same GR state-space form. This block form has reduced computations and ease of analysis. An algorithm is developed that transforms any given 2-D PSV GR system to its equivalent shift-invariant model. Invertibility of this model is an important consideration, especially in image scrambling applications. A condition is established for the invertibility of the shift-invariant model of the 2-D PSV system. Also, the inverse system can be easily computed from the original. The established results are illustrated with an example.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182594
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  • 11
    Digitale Medien
    Digitale Medien
    A note on error bounds for approximation in inner product spaces (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 515-518 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In a recent paper a method is described for constructing certain approximations to a general element in the closure of the convex hull of a subset of an inner product space. This is of interest in connection with neural networks. Here we give an algorithm that generates simpler approximants with somewhat less computational cost.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183158
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  • 12
    Digitale Medien
    Digitale Medien
    Stability for composite singular systems of differential equations with a delay (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 573-580 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, we gave an exponential estimate for the solutions of singular systems of differential equations with a delay and establish a comparison inequality for the systems. Based on this we estabish the criteria for asymptotic stability for the composite singular systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188982
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  • 13
    Digitale Medien
    Digitale Medien
    New VLSI architectures for three-level correlators (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 685-693 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents the VLSI architectures for three-level correlator design based on 1-μm CMOS technology. The architecture performs very high speed, real-time, three-level cross-correlation of signals. Two architectures, one for serial incoming samples of signals (serial data) and the other for stored signal samples (parallel data), are described in the paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188989
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  • 14
    Digitale Medien
    Digitale Medien
    Infinite nonlinear resistive networks, after Minty (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 727-733 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper gives the existence of and bounds for the branch voltages and currents in a given infinite network, which on each branch are related by a maximal monotone resistance function. We give a simpler proof than that of Minty, with smaller bounds, in the finite network case.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190125
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  • 15
    Digitale Medien
    Digitale Medien
    Computation of the frequency response of interval systems (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 807-818 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract An efficient procedure is presented for computing the frequency-response templates of uncertain rational transfer functions depending on two independent interval polynomials. It consists of a modified Cohen-Sutherland algorithm for the intersection test of two rectangles and a pivoting algorithm. Because the proposed procedure traces out the boundary of a frequency-response template directly, it is, in general, more efficient than the previously proposed algorithms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190130
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  • 16
    Digitale Medien
    Digitale Medien
    Concurrent computation of two-dimensional discrete cosine transform (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 597-607 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, a novel VLSI algorithm for the computation of a two-dimensional discrete cosine transform is proposed. The 2D-DCT equation can be expressed by the sum of high order cosine functions, and the algorithm can be realized by combining a highly efficient first order recursive structure with some simplified matrix multiplications, which results in highly regular hardware architecture and simple routing. The algorithm has temporal and spatial locality of connection and can be segmentized for pipeline operations, so the computation time is greatly reduced. Owing to the simplicity in hardware structure, it is especially good for VLSI implementation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188984
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  • 17
    Digitale Medien
    Digitale Medien
    Time-varying matched filters (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 609-630 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We examine a generalized matched-filter problem in which the interference is a nonstationary process generated by passing white noise through a general linear time-varying filter. First a matched filter is constructed by transforming the problem into an equivalent formulation involving stationary interference and a time-varying propagation channel. Whereas the response of a time-invariant matched filter is sampled at its peak, the response of this time-varying matched filter is normalized before sampling to account for variations in the signal power. Next a matched filter is constructed using a spectral characterization of the nonstationary interference. This construction is then used to formulate a simplified solution for the case where the rate of variation in the nonstationary interference is sufficiently small. The different solutions are illustrated by a numerical example.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188985
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  • 18
    Digitale Medien
    Digitale Medien
    Universal approximation capability of EBF neural networks with arbitrary activation functions (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 671-683 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The purpose of this paper is to investigate the approximation capability of elliptic basis function (EBF) neural networks. The main results are: (1) A necessary and sufficient condition for a functionS′ (R 1) to be qualified as an activation function in the hidden layer of an EBF neural network is given. (2) Every nonzero functionG ε L 2(R n ) is qualified to be an activation function in the elliptic neural network to approximate any function in L2(Rn). (3) As applications, we give new proofs of the theorems concerning the approximation capability of affine basis function (ABF) neural networks and generalized radial basis function (GRBF) neural networks (including radial basis function neural networks) with arbitrary activation functions. In particular, we solve the problem of the approximation capability of sigma-pi neural networks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188988
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  • 19
    Digitale Medien
    Digitale Medien
    Frequency response of PID-controlled linear interval systems (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 735-748 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The frequency response of linear interval systems under PID controllers is analyzed. A two-stage elimination algorithm is presented to describe the boundary of the response in the complex plane. Illustrative examples are included.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190126
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  • 20
    Digitale Medien
    Digitale Medien
    A formal language description and inference strategy for analog circuit design (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 771-805 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This article deals with a new intelligent analog circuit design system. Unlike previous design methods, this approach introduces a formal circuit representation for both the numerical and heuristic knowledge of the design system. The predicate logic circuit representation is proposed as a new formal analog circuit description language. The language's syntax and semantics provide a precise symbolic description of analog circuit functionality at higher levels of hierarchy and network component connectivities, together with CMOS transistor sizes as the lowest level of hierarchy. It is shown how sentence conversion rules of language grammer can be used to derive transistor level circuits from input performance specifications. Language sentences have the form of clauses. In addition to clause representation, a frame representation to reflect VLSI design hierarchy is also introduced. An original bidirectional inference mechanism with elements of hypothesis has been introduced to infer designs from the knowledge in clause and frame representations. The unique feature of this circuit knowledge representation is its ability to automate the analog CMOS circuit design process. The design methodology is described in detail. The proposed iterative closed loop design system adopts an expert system approach to provide topological synthesis, uses a SPICE circuit simulator to evaluate the circuit performance, and uses a new diagnostic expert system to provide advice on how to improve the design. The implementation of the methodology and associated experimental results for simple CMOS operational amplifier designs are also presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190129
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  • 21
    Digitale Medien
    Digitale Medien
    A closed-form identification of multichannel moving average processes by ESPRIT (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 343-359 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, a closed-form identification of possibly nonminimum phase multichannel moving average (MA) processes is derived by exploiting the eigenstructures of the observation cumulant matrices using the ESPRIT algorithm. The proposed approach allows the combination of statistics of different orders for better performance and offers reduced computation complexity when compared with existing iterative approaches. Simulations are also presented to demonstrate the performance of the proposed algorithm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182591
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  • 22
    Digitale Medien
    Digitale Medien
    Direction finding of coherent sources with nonlinear arrays (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 137-144 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents an approach to estimate the directions-of-arrival (DOAs) of narrowband coherent (completely corrected) signals by an arbitrary geometry sensor array. The concept of focussing matrices is introduced to estimate the outputs of a virtual uniform linear array from the outputs of the real array in order to use spatial smoothing techniques. Unlike the work presented in [5], the proposed approach avoids multiple singular value decomposition (SVD) computations in the various sectors because it is not necessary to divide the field of view of the array into sectors. Simulation results are given to support the approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187697
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  • 23
    Digitale Medien
    Digitale Medien
    Optimal deconvolution filter design under parameters perturbation in transmission channels (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 213-231 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract An optimal deconvolution filter design method is proposed in this paper for signal transmission systems with small perturbation of parameters. The perturbative parameters of the transmission channel and noise model are of probabilistic structures. A realizable filter is derived to minimize the mean square estimation error from the viewpoint of frequency domain. The calculus of variation technique and the spectral factorization method are used in the design procedure. The design method is suitable for the deconvolution of both minimum-phase and nonminimum-phase perturbative transmission systems. The minimum mean square error of the optimal deconvolution filter is also discussed. Finally, an example is given to illustrate the simulation results of the proposed optimal deconvolution filter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183777
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  • 24
    Digitale Medien
    Digitale Medien
    Kalman filter with hypothesis testing: A tool for estimating uncertain parameters (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 291-311 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we present a simple and practical algorithm for the estimation of uncertain parameters of linear systems. The uncertainty is twofold, involving random observation noise, and possible jumps in the parameter values. The jumps may occur at unknown points in time, and are of unknown magnitudes and directions. The algorithm is based on the Kalman filter, with a single-sample hypothesis test, which is used to employ a three-state decision rule (yes, no, maybe). The “maybe” choice invokes a fading memory Kalman filter. The overall algorithm contains the constant parameter filter, fading memory filter, and the set of tests and rules that enable it to switch back and forth between the two filters. Application examples are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182588
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  • 25
    Digitale Medien
    Digitale Medien
    Using ordered binary decision diagrams to factorize multi-level logic (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 361-376 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A novel approach that employs ordered binary decision diagrams (OBDDs) is contributed to factorize multi-level logic functions by requiring as few literals as possible. A logic function with PLA format is represented as an OBDD form first. A heuristic decision method of variable ordering, called theorder lookahead method, is derived for the construction of OBDDs. This method is based on the constant cofactor and the number of erasable logic terms for each input variable. The total execution time of the OBDD construction by the above ordering decisions is very fast for some MCNC benchmarks. With the above OBDDs, we introduce a simple yet effective graph manipulation, calledEXT, to obtain a minimal number of literals in the Boolean function. This greedyEXT algorithm consists mainly of two phases. The first phase, calledgraph analysis, identifies the similarities between nodes on the same level in the OBDD. The second phase, calledtree analysis, utilizes the above features to extract the common parts of the nodes. TheEXT procedure runs from the bottom level up to the top level of the OBDD. The computational complexity depends on the number of nodes in the OBDD. The results of simulations show thatEXT has a very fast CPU execution time and a competitive literal ratio with other methods for some MCNC benchmarks.EXT will produce the smallest literal number, especially for structured or symmetric circuits.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182592
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  • 26
    Digitale Medien
    Digitale Medien
    Neural network training enhancement (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 467-480 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this study we explore the use of nonlinear embedding maps to expand the dimension of the input space. The efficacy of such maps to speed training and to enhance performance is illustrated through several examples. A natural connection to nonlinear synaptic interconnects is also developed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183155
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  • 27
    Digitale Medien
    Digitale Medien
    Sensitivity and robust stability of nonlinear input-output systems consisting of finitely many blocks (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 313-333 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We construct a general model of a nonlinear input-output system consisting of finitely many blocks whose variables are in extended spaces. This model encompasses all configurations used in control which have several feedback and feedforward loops. We show that such a system is essentially the traditional MI-MO feedback system. Moreover, assuming that one block of the system is a plant affected by perturbations, we derive conditions guaranteeing linear insensitivity and/or robust stability of the whole system. In particular, we consider systems whose variables are continuous, vector-valued functions on [0, ∞), and whose blocks are described by nonlinear Volterra operators. The applications of the results are illustrated by several examples of feedback-feedforward systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182589
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  • 28
    Digitale Medien
    Digitale Medien
    An analytic method for the design of a constant resistance multiplexer (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 453-466 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The design of a constant resistance multiplexer composed of three reactance ladder networks connected either in series or in parallel is a very practical problem. In this paper, an improvement on Norton's method and a set of necessary and sufficient conditions on the realizability of a Butterworth or elliptic constant resistance multiplexer are presented. Two illustrative examples are given to show the design procedure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183154
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  • 29
    Digitale Medien
    Digitale Medien
    Model conversions of uncertain linear systems via the interval Pade approximation method (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 1-22 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a new interval Pade approximation method to convert a continuous-time (discrete-time) uncertain linear system to an equivalent discrete-time (continuous-time) uncertain model via interval arithmetic operations. Based on the inclusion theorem related to the interval arithmetic, the interval Pade's approximants and their associated interval error matrices with interval arguments are obtained via the Pade's approximants and their associated error matrices with degenerate (real) arguments, respectively. Tighter error bounds of various approximate uncertain models with respect to their exact uncertain models are determined and used to modify the obtained Pade's approximants, so that the resulting approximate uncertain models are able to tightly enclose the original uncertain systems. Thus, the analysis and design of the original uncertain systems can be indirectly carried out using the converted uncertain models in either the continuous-time or the discrete-time domain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187691
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  • 30
    Digitale Medien
    Digitale Medien
    Breakdown points, breakdown probabilities, midpoint sensitivity curves, and optimization of stack filters (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 165-211 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Three new concepts — breakdown points, breakdown probabilities, and midpoint sensitivity curves — for stack filter analysis are introduced and analyzed in this paper. Breakdown points and probabilities can be used as measures of the robustness of stack filters. Midpoint sensitivity curves in turn give information on how sensitive the output of a stack filter is to the changes of a single value in the input window. The second major contribution of this paper is the extension of the current optimality theory of stack filters. This theory combines noise attenuation and different constraints on the filter's behavior. New constraints are introduced in this paper. A new optimization approach based on breakdown probability as a noise attenuation measure is also derived. In certain special cases it is shown that the optimal stack filter that achieves the best noise attenuation subject to given constraints can be obtained in closed form. An algorithm for finding this form is given in this paper, and its modification for finding a stack filter having (approximately) a required rank selection vector is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183776
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  • 31
    Digitale Medien
    Digitale Medien
    System identification from noisy measurements by using instrumental variables and subspace fitting (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 275-290 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper considers the estimation of the parameters of a linear discrete-time system from noise-perturbed input and output measurements. The conditions imposed on the system are fairly general. In particular, the input and output noises are allowed to be auto-correlated and they may be cross-correlated as well. The proposed method makes use of an instrumental variable (IV)-vector to produce a covariance matrix that is pre- and postmultiplied by some prechosen weights. The singular vectors of the so-obtained matrix possess complete information on the system parameters. A weighted subspace fitting (WSF) method is then applied to the aforementioned singular vectors to consistently estimate the parameters of the system. The IV-WSF technique suggested herein is noniterative and easy to implement, and has a small computational burden. The asymptotic distribution of its estimation errors is derived and the result is used to motivate the choice of the weighting matrix in the WSF step and also to predict the estimation accuracy. Numerical examples are included to illustrate the performance achievable by the method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183780
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  • 32
    Digitale Medien
    Digitale Medien
    (J, J′)-Spectral factorization and conjugation for discrete-time descriptor system (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 649-669 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper considers a (J, J′)-spectral factorization of a signed spectral matrix associated with a discrete-time improper transfer matrix by using the descriptor system representation and the generalized algebraic Riccati equation (GARE). Under the assumption that the improper transfer matrix is stable, a numerical algorithm for (J, J′)-spectral factorization is developed based on solutions of the generalized eigenvalue problem (GEP) and a related matrix equation. For an unstable transfer matrix, aJ-unitary conjugation method is applied to obtain a stable transfer matrix generating the same signed spectral matrix. Then a Hankel norm model reduction problem is briefly discussed. A simple example is also included to illustrate the numerical procedure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188987
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  • 33
    Digitale Medien
    Digitale Medien
    On the estimation of eigenvalue regions for discrete time-delay systems with a class of highly structured perturbations (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 695-709 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract By means of norm,M-matrix, and matrix measure techniques, this paper estimates several restricted regions in the complex plane in which all eigenvalues of a class of discrete time-delay systems subjected to highly structured parametric perturbations are located. Both the stability and the instability conditions for these systems are also investigated via the proposed schemes. Two numerical examples are given to verify the correctness and demonstrate the applicability of the quantitative results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188990
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  • 34
    Digitale Medien
    Digitale Medien
    Simple unified algorithm for estimating and tracking location of desired talker by microphone arrays (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 749-762 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, we discuss a unified approach and its simple algorithm for estimating and tracking the location of the desired talker in the far field and the near field by microphone arrays. The approach is unified for the far field and the near field and can enhance the effective power of the talker's signal. The simple algorithm further avoids singular-value decomposition (SVD) computations and is suitable for real-time processing. Computer simulations and experiments using actual array data support the techniques.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190127
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  • 35
    Digitale Medien
    Digitale Medien
    Implementation of cascaded and recursive stack filters (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 93-110 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Systematic methods are developed for simplified implementations of cascaded stack and WOS filters. For recursive stack and WOS filters, corresponding nonrecursive implementations are given, with linear complexity with respect to the number of iterations. Dynamic domino logic is proposed for VLSI hardware implementation of positive Boolean functions, and a pipelined stack filter architecture is described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187695
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  • 36
    Digitale Medien
    Digitale Medien
    Auxilliary computations for perceptron networks (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 51-69 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this study we consider a multilayer perceptron network with sigmoidal activation and trained via the backpropagation algorithm. The output of all neurons is collected and a simple linear regression is performed. It is shown that untrained networks with randomly chosen coefficients perform comparably with fully trained networks. This result casts a new light on the role of activation functions, the impact of dimensionality, and the efficacy of training algorithms such as backpropagation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187693
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  • 37
    Digitale Medien
    Digitale Medien
    PNS modules for the synthesis of parallel self-organizing hierarchical neural networks (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 23-50 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The PNS module is discussed as the building block for the synthesis of parallel, self-organizing, hierarchical, neural networks (PSHNNs). The PNS module contains three submodules (units), the first two of which are created as simple neural network constructs and the last of which is a statistical unit. The first two units are fractile in nature, meaning that each such unit may itself consist of a number of parallel PNS modules in a fractile fashion. Through a mechanism of statistical acceptance or rejection of input vectors for classification, the sample space is divided into a number of regions. The input vectors belonging to each region are classified by a dedicated set of PNS modules. This strategy results in considerably higher accuracy of classification and better generalization as compared to previous neural network models. If the delta rule network is used to generate the first two units, each region approximates a linearly separable region. In this sense, the total system becomes similar to a piecewise linear model. The various regions are determined nonlinearly by the first and third units of the PNS modules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187692
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  • 38
    Digitale Medien
    Digitale Medien
    Reflections on Schur-Cohn matrices and Jury-Marden tables and classification of related unit circle zero location criteria (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 111-136 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We use the so-calledreflection coefficients (RCs) to examine, review, and classify the Schur-Cohn and Marden-Jury (SCMJ) class of tests for determining the zero location of a discrete-time system polynomial with respect to the unit circle. These parameters are taken as a platform to propose a partition of the SCMJ class into four useful types of schemes. The four types differ in the sequence of polynomials (the “table”) they associate with the tested polynomials by scaling factors: (A) a sequence of monic polynomials, (B) a sequence of least arithmetic operations, (C) a sequence that produces the principal minors of the Schur-Cohn matrix, and (D) a sequence that avoids division arithmetic. A direct derivation of a zero location rule in terms of the RCs is first provided and then used to track a proper zero location rule in terms of the leading coefficients of the polynomials of the B, C, and D scheme prototypes. We review many of the published stability tests in the SCMJ class and show that each can be sorted into one of these four types. This process is instrumental in extending some of the tests from stability conditions to zero location, from real to complex polynomial, in providing a proof of tests stated without a proof, or in correcting some inaccuracies. Another interesting outcome of the current approach is that a byproduct of developing a zero location rule for the Type C test is one more proof for the relation between the zero location of a polynomial and the inertia of its Schur-Cohn matrix.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187696
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  • 39
    Digitale Medien
    Digitale Medien
    Image recovery from exponential blurring (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 261-274 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We study the following type of filtering problem: consider an image on ℤ2, that is, a nonnegative function on the vertices of a grid, which represents the brightness at each of these points. We assume that there is, however, a “smudging” effect. That is, what ought to be a point of light becomes the point together with a halo about it, visualized by a distribution of light which is greatest at the point itself and decreases with the distance. So what we actually see is a blurry image. In this article we investigate methods for clearing up the image, i.e. reconstructing the original function from the blurry haloed image when the halo decays exponentially, and also for some haloes with small finite support. This task is usually performed by inverting the convolution operator induced by the halo (that is, by Fourier analysis). We introduce a different recovery procedure, based upon a family of filtering operators that change from point to point. For the finitely supported haloes, this procedure compares favorably with the Fourier methods. Moreover, in principle it is more general, because it does not require assumptions of invariance under translation. In full generality, however, we are able to recover images not on grids, but only on trees.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183779
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  • 40
    Digitale Medien
    Digitale Medien
    Generalized maximum a posteriori processing of multichannel images and applications (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 233-260 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper considers several aspects of robust estimation in the restoration of mutichannel images. Robust functionals emerging from a generalized maximum a posteriori (MAP) approach are employed for the representation of both the noise and the signal statistics. Several linear multichannel techniques can be derived as special cases of the approach presented. In addition, the robust approach derives nonlinear algorithms that simultaneously account for the suppression of nominal noise and outliers, and for the efficient reconstruction of sharp detailed structure in the estimate. The robust multichannel approach is presented as a general approach for the regularization of the ill-posed restoration problem. From this perspective, we develop a method for the selection of the regularization parameter, which can be used in a wide variety of applications that may or may not involve noise outliers. We consider several issues associated with the application of robust algorithms to multichannel images, we discuss computational inefficiencies of such algorithms, and we propose approximations that are appropriate for their cost-efficient multichannel implementation. We demonstrate the robust approach in two examples from the rapidly developing fields of color image processing and multiresolution image processing in the wavelet domain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183778
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  • 41
    Digitale Medien
    Digitale Medien
    On the factorization of polynomials and direct sum properties in integer polyomial rings (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 415-435 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In our recent work, we solved the word sequence length constraint problem associated with number theoretic transforms defined in finite integer rings. This is based on the American-Indian-Chinese extension of the Chinese remainder theorem. This work builds further on the results by extending them to the domain of integer polynomial rings. The theory of polynomial factorization and the resulting direct sum property are studied in depth. The emphasis is on the theory of computational algorithms for processing sequences defined in finite integer and complex integer rings.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182595
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  • 42
    Digitale Medien
    Digitale Medien
    On algorithms for digital signal processing of sequences (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 437-452 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this work, we analyze the algebraic structure of fast algorithms for computing one- and two-dimensional convolutions of sequences defined over the fields of rational and complex rational numbers. The algorithms are based on factorization properties of polynomials and the direct sum property of modulo computation over such fields. Algorithms are described for cyclic as well as acyclic convolution. It is shown that under certain nonrestrictive conditions, all the previously defined algorithms over the fields of rational and complex rational numbers are also valid over the rings of finite integers. Examples are presented to illustrate the results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183153
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  • 43
    Digitale Medien
    Digitale Medien
    Computing potentials on a periodic bidimensional grid (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 519-527 
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    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 2-dimensional grid such that the conductances on the vertical and horizontal edges have period 2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183159
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  • 44
    Digitale Medien
    Digitale Medien
    A new FIR filterbank design algorithm using frequency scaling and modulation (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 529-542 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Digital filterbanks, an important signal processing tool, are used in a radar signal processor to measure target range and/or velocity [4]. The windowed FFT is the most common radar filterbank. The FFT is a special case of modulated filterbank. Modulated filterbanks subdivide the frequency region by modulating a prototype baseband filter. This baseband filter usually satisfies certain frequency response constraints. Filterbanks used in radar applications are not concerned with reconstruction as are wavelet-based approaches [2], but rather with how well the filters subdivide the frequency region into a prescribed number of equal frequency regions. Wavelets use time decimation or frequency scaling to form filterbanks. This paper focuses on using a wavelet-like scaling approach along with modulation to design a digital filterbank. However, we are not concerned with reconstruction but with the subdivision of the frequency region into a prescribed number of equal segments. It will be shown that this new design algorithm has a frequency response performance comparable to existing techniques but with less computational effort. The performance measures considered are rejection of out of bands signals, uniformity of inband signal gain, and transition width from inband to stopband.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183160
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  • 45
    Digitale Medien
    Digitale Medien
    Sequential speech segmentation based on the spectral ARMA transition measure (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 71-92 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Sequential segmentation algorithms based on the AR model tend to produce false alarms or to omit the change for sequences that corresponds to the ARMA model. In this paper a new sequential segmentation algorithm based on the ARMA model is presented. The ARMA model is estimated over the relatively short sequence, which has called for the implementation of the estimation algorithm with appropriately initialized starting values. The proposed algorithm adopts the MGLR concept of the sliding reference and test windows, which allow the process of decision making to be separated from the evaluation of the discrimination function. This has enabled the new triangular decision rule to be proposed; this is based on the expected shape of the discrimination function at the time of the model change. Two possible discrimination functions have been suggested. One of them is optimal in the statistical sense; the other has the better asymptotic behavior. Natural speech signal segmentation is also discussed, and an appropriate pitch-synchronous signal prearrangement has been suggested. This not only enhances the segmentation algorithm but also increases its speed, as the time can be increased by a step equal to the pitch period. The segmentation algorithm is verified on test signals as well as on the natural speech signal. The experimental results also include a comparison of the sequential AR and ARMA model-based segmentation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01187694
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  • 46
    Digitale Medien
    Digitale Medien
    Large-sample analysis of MUSIC and Min-Norm direction estimators in the presence of model errors (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 377-393 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We analyze the large-sample mean square error (MSE) of MUSIC and Min-Norm direction-of-arrival (DOA) estimators under fairly general conditions, including mismodelling of the array response and the noise covariance. We separate the contributions to the MSE into a bias part caused by modelling errors and a variance part caused by finite (yet large) sample effects. The bias is simply evaluated by comparing the limiting estimate (corresponding to an infinite number of snapshots) with the true DOAs (which are known to the analyzer). To simplify the variance derivation we assume that the snapshots are complex i.i.d. Gaussian vectors and that the largest eigenvalues of their covariance matrix are distinct, but,otherwise, make none of the assumptions commonly used in previous analyses; in particular we do not constrain the snapshots to satisfy any model equation. The theoretical results obtained are illustrated by means of numerical examples using various modelling errors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01182593
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  • 47
    Digitale Medien
    Digitale Medien
    A parallel algorithm for evaluating general linear recurrence equations (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. 481-504 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A block parallel partitioning method for evaluating general linearmth order recurrence equations is presented and applied to solve the eigenvalues of symmetric tridiagonal matrices. The algorithm is based on partitioning, in a way that ensures load balance during computation. This method is applicable to both shared memory and distributed memory MIMD systems. The algorithm achieves a speedup ofO(p) on a parallel computer withp-fold parallelism, which is linear and is greater than the existing results, and the data communication between processors is less than that required for other methods. For solving symmetric tridiagonal eigenvalue problems, our method is faster than the best previous results. The results were tested and evaluated on an MIMD machine, and were within 79% to 96% of the predicted performance for the second order linear recurrence problem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183156
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  • 48
    Digitale Medien
    Digitale Medien
    In memoriam (1996)
    Springer
    Circuits, systems and signal processing 15 (1996), S. I 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188980
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  • 49
    Digitale Medien
    Digitale Medien
    A study on the adsorption of some cationic dyes onto acrylamide/itaconic acid hydrogels (1996)
    Springer
    Polymer bulletin 36 (1996), S. 745-752 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Acrylamide/itaconic acid (AAm/IA) hydrogels prepared by irradiating with γ radiation were used in experiments on the adsorption of some cationic dyes such as basic red 9 (BR 9), basic green 4 (BG 4), cresyl violet (CV), and basic blue 20 (BB 20). Adsorption of the cationic dyes onto AAm/IA hydrogels is studied by batch adsorption technique. In the experiments of the adsorption, Langmiur type adsorption in the Giles classification system was found. Monolayer coverages for AAm/IA hydrogel-dye systems were calculated by using B point method. Adsorption studies indicated that monolayer coverages of AAm/IA hydrogel by these dyes were increased with following order; BB 20〉CV〉BR9〉BG 4.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00338639
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  • 50
    Digitale Medien
    Digitale Medien
    Polymerization of styrene by diphenylzinc-additive systems (1996)
    Springer
    Polymer bulletin 37 (1996), S. 13-19 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Styrene was polymerized using combined systems of diphenylzinc, Ph2Zn, and metallocene compounds activated by methylaluminoxane, MAO. From the various metallocenes employed bis (indenyl) zirconium dichloride, Ind2ZrCl2, [isopropyl (cyclopentadienyl) (1-fluorenyl)] zirconiumdichloride, i-Pr (Flu) (Cp) ZrCl2, and bis (cyclopentadienyl) titanium dichloride, Cp2TiCl2, produced the larger amounts of polymer. Ph2Zn-Cp2TiCl2-MAO system gave polystyrene, PSt, whose DSC analysis indicated a major endotherm peak at 256°C. A butanone insoluble fraction of the polymer was separated from the crude PSt. The proportion of insoluble polymer depends on the metallocene employed and on the conversion to polymer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00313813
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  • 51
    Digitale Medien
    Digitale Medien
    Isotactic polymerization of propylene with zirconocene catalysts in the presence of a lewis base (1996)
    Springer
    Polymer bulletin 37 (1996), S. 29-33 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Polymerization of propylene was carried out at 0°C in the presence of methyl methacrylate(MMA) or ethyl benzoate(EB) using rac-Et(Ind)2ZrMe2 or rac-Me2Si(Ind)2ZrMe2/Ph3CB(C6F5)4 as catalyst, which resulted in highly isotactic poly(propylene) with [mmmm]〉98%, Tm=160–161°C and very few 1,3- or 2,1 regioirregular units. With the use of an achiral zirconocene Cp2ZrMe2, a polymer with Tm=139°C was resulted as well. Base on these experimental fact that the zirconocene can form a C1-symmetrical complex with a Lewis base.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00313815
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  • 52
    Digitale Medien
    Digitale Medien
    Highly active rare earth catalysts for the solution polymerization of ε-caprolactone (1996)
    Springer
    Polymer bulletin 37 (1996), S. 21-28 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary By using γ-butyrolactone (γ-BL) as the reaction media, highly active catalysts--light rare earth chloride-epoxidy-γ--BL-for the solution polymerization of ε-caprolactone, have been obtained for the first time. With these catalyst, PCL with molecular weight as his as 40x104(Mv) can be prepared at 60°C for 1.5 hr. The amount of epoxide in catalyst solution, catalyst aging temperature and time affect the catalyst activity significantly. The mechanism study shows that in γ-BL, the weakening of Ln-Cl bonds by the donation of coordinated γ-BL with Ln3+ and the homogenous effect promote the reaction between light rare earth chloride and epoxide. The produced rare earth alkoxide initiates CL polymerization via a ‘coordination-insertion’ mechanism with Acyl-oxygen bond cleavage.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00313814
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  • 53
    Digitale Medien
    Digitale Medien
    Surface modification of ethylene-vinyl alcohol (EVOH) copolymer films by the attachment of triethoxysilane functionality (1996)
    Springer
    Polymer bulletin 37 (1996), S. 51-57 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Triethoxysilane groups were covalently attached onto the surface of ethylene-vinyl alcohol (EVOH) copolymer film via a urethane linkage through reaction between the hydroxyl groups in EVOH and 3-isocyanatopropyltriethoxysilane in the presence of dibutyltin dilaurate as catalyst. This reaction was confirmed by ATR-IR and XPS analysis. XPS results also indicated that this reaction was not surface sensitive and the modified layer was at least 40 Å in depth. The modified film samples were further reacted with tetramethoxysilane (TMOS) for partial hydrolysis and condensation and XPS results showed a significant increase in the contents of oxygen and silicone on the surface which confirmed the above reaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00313818
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  • 54
    Digitale Medien
    Digitale Medien
    An analysis of the 1H- and 13C-NMR spectra of poly(6-vinyl-1,4-benzodioxane) (1996)
    Springer
    Polymer bulletin 37 (1996), S. 59-65 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The title monomer was synthesized from the corresponding aldehyde via a Wittig reaction. The monomer was polymerized using free radical initiation and its high field 1H- and 13C-NMR spectra were recorded. When analyzed in terms of stereochemistry the spectra showed poly(6-vinyl-1,4-benzodioxane) is an atactic polymer when synthesized via free radical initiation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00313819
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  • 55
    Digitale Medien
    Digitale Medien
    Dual sorption of metal-ions on a crosslinked resin of 2-acrylamidoglycolic acid and 4-vinylpyridine (1996)
    Springer
    Polymer bulletin 37 (1996), S. 191-198 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary A resin containing 4-vinylpyridine and 2-acrylamidoglycolic acid was synthesized by radical polymerization with subsequent crosslinking by N,N′-methylene-bis-acrylamide. The resin was characterized by elemental analyses and FT-IR spectroscopy. The ability of this resin as well as both crosslinked homopolymers to bind Cu(II), Fe(II), Fe(III) and U(VI) was studied at different pHs depending on the metal ion. From pH=2 U(VI) was sorbed above 96% from an aqueous solution of 1.0 g/L. A dual sorption mechanism to U(VI) depending on the pH is suggested. The elution of the metal ions from the loaded resins was assayed with H2SO4 and Na2CO3.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294121
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  • 56
    Digitale Medien
    Digitale Medien
    Effect of the sulfide group on photopolymerization kinetics of di(meth)acrylates (1996)
    Springer
    Polymer bulletin 37 (1996), S. 199-206 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The photopolymerization of four analogous monomers: 2,2′-thiobisethanol diacrylate and its dimethacrylate plus 2,2′-oxybisethanol diacrylate and its dimethacrylate has been studied by isothermal differential scanning calorimetry (DSC) over a range of incident light intensities. The results obtained prove that the sulfide group accelerates polymerization both in the presence and absence of oxygen and enhances the conversion. The light intensity exponents for each monomer were determined and the mechanism of termination was discussed. The intensity exponents of sulfur-containing monomers are lower than their corresponding oxygen analogues, pointing to a greater participation of the bimolecular termination during their polymerization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294122
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  • 57
    Digitale Medien
    Digitale Medien
    Size distribution of polymers during the photoinitiated free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (1996)
    Springer
    Polymer bulletin 37 (1996), S. 207-213 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Photoinitiated methyl methacrylate-ethylene glycol dimethacrylate (MMA/EGDM) copolymerization has been investigated in toluene at a monomer concentration of 35 w/v %. Diphenyl-2,4,6-trimethylbenzoylphosphine oxide (DPTPO) was used as a photoinitiator at 0.3 wt% concentration. Monomer conversions and the size distribution of the polymer molecules were measured as a function of the reaction time up to the onset of macrogelation. Compared to the photoinitiators benzoin or benzoin derivatives, gelation process proceeds at much higher rates in the presence of DPTPO. The size distribution curves obtained by size-exclusion chromatography (SEC) change from monomodal to bimodal distributions as the polymerization proceeds. Strongly bimodal SEC curves were obtained in the close vicinity of the gel point. This finding confirms the coagulation type gelation mechanism of compact primary particles. It also indicates that the present gelation theories cannot describe the structure dependent kinetics of free-radical crosslinking copolymerization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294123
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  • 58
    Digitale Medien
    Digitale Medien
    FT-Raman analysis of the effects of γ-radiation on nylon 6–12 filaments (1996)
    Springer
    Polymer bulletin 37 (1996), S. 221-228 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary FT-Raman spectroscopy of commercial amorphous and crystalline nylon 6–12 filaments subjected to various γ-radiation doses are presented. The results show that a difference exists in the interaction of γ-radiation with these polyamides, depending on the crystallinity which can be evaluated by measuring the CH-stretching/CH-bending Raman band intensity ratio as a function of applied γ-dose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294125
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  • 59
    Digitale Medien
    Digitale Medien
    Solid-state NMR study of natural rubber blended with EVA and EVA modified with mercaptoacetic acid (1996)
    Springer
    Polymer bulletin 37 (1996), S. 215-220 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract Solid-state 13C NMR spectroscopy involving magic angle spinning (MAS) techniques with and without cross-polarization was employed for interaction studies in natural rubber (NR)/EVA and NR/mercapto-modified EVA (EVASH) blends. From arrayed of variable contact time spectra, the proton T1ϱ values were determined at short contact times to analyze the EVA or EVASH domains and longer contact times to investigate the interactions in the NR domains. Substantial changes have been observed when dicumyl peroxide was employed as curing agent in NR/EVASH and NR/EVA/EVASH blends.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294124
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  • 60
    Digitale Medien
    Digitale Medien
    Thermogravimetric analysis of starch-based biodegradable blends (1996)
    Springer
    Polymer bulletin 37 (1996), S. 229-235 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Thermogravimetric analysis (TGA) has been shown to be a useful technique to determine the content of starch and other components that are usually present in blends of starch with synthetic polymers. However, some of these blends are composed of elements with an important superposition in their temperature degradation range. In these cases interpretation of the TGA results becomes quite difficult and usually important errors are committed in the determination of blend composition. We present here a method to improve the accuracy of the interpretation of TGA data. The analysis was developed to study blends containing starch, an ethylene-vinyl alcohol copolymer, and water plus glycerin as plasticizers. Using this procedure it is possible to predict blend composition with an error less than 3%, even when there is an appreciable superposition between the temperature degradation range of starch and poly(ethylene-co-vinyl alcohol). As the proposed method of analysis is quite general it may be extended to be used with other types of blends that give thermograms with similar characteristics to those described in this paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00294126
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  • 61
    Digitale Medien
    Digitale Medien
    Synthesis of polysulfone block copolymers containing polydimethylsiloxane (1996)
    Springer
    Polymer bulletin 37 (1996), S. 329-336 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract The synthesis of polysulfone-polydimethylsiloxane (PSU-PDMS)linear block copolymers has been carried out in solution by condensation of chloro-terminated bisphenol A, diphenylsulfone and α, ω-di (hydrogensilyl)-polydimethylsiloxane with Si−C bond. 1H-NMR spectra of the block copolymers allow the estimation of siloxane and polysulfone ratio. The molecular weight of the polysulfone and polysiloxane oligomers and the block copolymers was determined by GPC. Thermogravimetric analysis indicates a thermal stability of block copolymers up to 400°C and allows estimation of the process activation energy. Microphase separation of the block copolymers was observed by differential scanning calorimetry (DSC).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318065
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  • 62
    Digitale Medien
    Digitale Medien
    Compatibilization of PP/PBT and PP/PA6 blends with a new oxazoline-functionalized polypropylene (1996)
    Springer
    Polymer bulletin 37 (1996), S. 353-359 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Aim of this work was to study the effectiveness of a novel oxazoline-functionalized polypropylene as a compatibilizer for PP/PBT and PP/PA6 blends. This polypropylene-based compatibilizer mixes well with the polypropylene and is capable of reacting with the carboxylic and amine end groups of PBT and PA6. Significant improvements in blend toughness were achieved without reduction in strength and stiffness. These effects were related to stabilized morphology of finely dispersed minor phase well attached to the matrix. The enhanced interfacial interactions between the two phases, in particular at high PBT content were evidenced by increased melt viscosity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318068
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  • 63
    Digitale Medien
    Digitale Medien
    Miscibility of polyamide-6,6 with aromatic polyamides (1996)
    Springer
    Polymer bulletin 37 (1996), S. 361-367 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The polyamides with aromatic rings in the main chain were synthesized by the solution polymerization of 4,4′-diphenylmethane diisocyanate and aliphatic dicarboxylic acid in the presence of catalyst. The thermal properties and the miscibility behaviours with polyamide-6,6 of these aromatic polyamides were studied. The aromatic polyamides synthesized with one kind of dicarboxylic acid had typical thermal properties of crystalline polymers, whereas those synthesized with the mixtures of dicarboxylic acids were not easily crystallized. The observed miscibility behaviours showed some differences from those predicted by binary interaction model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318069
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  • 64
    Digitale Medien
    Digitale Medien
    Miscibility and mechanical properties of aryl-aliphatic polyamides/nylon 6 molecular composites (1996)
    Springer
    Polymer bulletin 37 (1996), S. 369-376 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary A series of aryl-aliphatic polyamides, copoly(4,4′-diaminobenzanilide-adipamide/2,6-naphthalamide)s, with feed mole ratios of adipic acid/2,6-naphthalene dicarboxylic acid of 1/9, 3/7, and 5/5 were synthesized. A new family of molecular composites based on the synthesized aryl-aliphatic polyamides and nylon 6 has been discovered. The molecular composites were found to have at least partial miscibility between aryl-aliphatic polyamides and nylon 6. Well-defined aryl-aliphatic polyamide microfibrils a few nanometers in diameter were observed in the molecular composites. 10 wt% aryl-aliphatic polyamide clearly promoted the toughness of nylon 6.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318070
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  • 65
    Digitale Medien
    Digitale Medien
    Preparation of ultrafine metal particles/polyurethane composites (1996)
    Springer
    Polymer bulletin 37 (1996), S. 377-383 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary A new type of coordination polyurethane was prepared by incorporating the transition metal ions into the pyridine containing thermoplastic polyurethane films. Then the metal ions dispersed in the polyurethane matrix were reduced by controlling the exposure of the metal sites to NaBH4 under mild condition. The reduction of the polyurethane metal complex films resulted in the production of amorphous ultrafine metal powders. The size of these powders was controlled by the content of the metal ions and the polarity of the polymer matrix. A polar polymer backbone and lower metal ion concentration favored to achieve a smaller particle. It was also found that the polymer chains prohibited the excessive aggregation of the metal atoms and have protective effect on the final metal powders.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318071
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  • 66
    Digitale Medien
    Digitale Medien
    Toughening mechanisms in modified epoxy resins with different crosslink densities (1996)
    Springer
    Polymer bulletin 37 (1996), S. 399-406 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Crack-tip deformation has been investigated in pre-cracked samples of core-shell rubber particle modified epoxy resins with different degrees of crosslinking. Light cross linking resulted in cavitation of the modifier, the formation of croids and extensive crack-tip yielding, whereas these deformation mechanisms were suppressed at room T in highly crosslinked specimens. A zone of particle debonding was observed in these latter at high T, but this appeared detrimental to the toughness. Indeed it was possible to increase the toughness in this case by oxygen plasma treatment of the modifier particles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318074
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  • 67
    Digitale Medien
    Digitale Medien
    Synthesis and properties of 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine, an initiator for living free radical styrene polymerization (1996)
    Springer
    Polymer bulletin 37 (1996), S. 451-456 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary An initiator for living free radical polymerization may be prepared by trapping the benzylic ethylbenzene radical with the stable 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical. The adduct, 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine (TMPEP), smoothly undergoes thermal fragmentation at temperatures approaching 140° C to afford an active carbon radical capable of initiating polymerization and a passive mediating nitroxyl radical to reversibly cap and preserve the propagating polymer chain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556804
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  • 68
    Digitale Medien
    Digitale Medien
    Kinetics of association processes of d-fructose dehydrogenase onto liposome surfaces (1996)
    Springer
    Polymer bulletin 37 (1996), S. 407-414 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Association processes of D-fructose dehydrogenase (FDH) onto surfaces of liposomes which were composed of N-(5-dimethylamino-1-naphthalenesulfonyl)-L-α-dimyristoylphosphatidylethanolamide and L-α-dimyristoylphosphatidylcholine or L-α-dimyristoylphosphatidylglycerol (1:9) were investigated by the fluorescence stopped-flow technique. The association processes were divided into two relaxation processes: the faster process whose apparent rate constant monotonously increased with the concentration of FDH, and the slower process whose rate constant showed a saturation behavior. Taking the number of binding sites on the liposome surface into consideration, the corrected association rate constant of the faster process was 4.4% of the theoretical value for a binary collision, probably due to a disadvantageous surface-searching and dehydration processes on the liposome and protein surfaces. The Arrhenius plots of the rate constants both for the faster and slower steps showed a discontinuous change around the gel to liquid-crystal phase transition temperature of the liposomes. Strong influences of deformability of liposomes, and state of hydrating water molecules around polar heads, on the rate of association processes were suggested.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318075
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  • 69
    Digitale Medien
    Digitale Medien
    Ruthenium catalyzed copolymerization of 2-acetylphenanthrene and α,ω-dienes (1996)
    Springer
    Polymer bulletin 37 (1996), S. 423-428 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Copolymers with 2-aceto-1,3-phenanthrenylene units in the chain have been directly prepared by Ru catalyzed step-growth copolymerization of 2-acetyl phenanthrene and α,ω-dienes such as 1,3-divinyltetramethyldisiloxane. Copolymers which incorporate 2-aceto-1,3-phenanthrenylene units possess higher TgS and increased thermal stability compared to analogous copolymers which have 2-aceto-5-phenyl-1,3-phenylene(biphenyl) or 2-aceto-1,3-phenylene units. Fluorescence spectra of these copolymers have been obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556800
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  • 70
    Digitale Medien
    Digitale Medien
    Synthesis and regeneration of reactive polymers bearing triphenylphosphine dichloride functional groups using triphosgene (1996)
    Springer
    Polymer bulletin 37 (1996), S. 415-421 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary A new methodology is described for the synthesis of reactive polymers bearing triphenylphosphine dichloride groups by the use of triphosgene. These materials show high reactivity for the room temperature conversion of benzyl alcohol to benzyl chloride. In one hour, yields higher than 90% were achieved using reactive copolymers with up to 25 w% divinylbenzene (DVB). The functional groups can be easily and efficiently regenerated using 1.0 mol of triphosgene for every 2.6 moles of phosphine in the polymer. Preliminary results showed up to 40% conversion of benzyl alcohol in column reactions using regenerated polymers at 5 to 10 min contact times.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556799
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  • 71
    Digitale Medien
    Digitale Medien
    Biosynthesis and characterization of poly(β-hydroxybutyrate) produced byBacillus circulans (1996)
    Springer
    Polymer bulletin 37 (1996), S. 429-435 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The biosynthesis of poly (β-hydroxybutyrate) (PHB) byBacillus circulans was carried out through cultivation in nutrient broth in a single step. $$\overline {\text{M}} {\text{v}}$$ of polymer fractions soluble in chloroform were close to 2 x 105. IR,1H and13C NMR spectra of the isolated PHB were in agreement with the assumed structure of this poly-β-hydroxyester. NMR spectroscopy pointed out a high percentage of isotactic polymer, while differential scanning calorimetry showed that the PHB was crystalline.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556801
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  • 72
    Digitale Medien
    Digitale Medien
    Polyacrylonitrile-graft-poly(ethylene oxide) (1996)
    Springer
    Polymer bulletin 37 (1996), S. 437-442 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Graft copolymers of polyacrylonitrile (PAN) and poly(ethylene oxide) (PEO) were synthesized by radical copolymerization of acrylonitrile and methacrylate-headed poly(ethylene oxide) macromonomer. The macromonomer was prepared by reaction of methacryloyl chloride with PEO. The effects of solution concentration, initiator concentration and acrylonitrile/macromonomer molar ratio on the conversion, molecular weight and PEO branch content in the graft copolymer were studied. The graft copolymers were characterized by GPC, FTIR,13C-NMR and Kjeldhal method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556802
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  • 73
    Digitale Medien
    Digitale Medien
    Copolymerization of 2,5-dimethyl-3-vinylthiophene with methyl methacrylate, styrene and isobutyl methacrylate (1996)
    Springer
    Polymer bulletin 37 (1996), S. 457-462 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The title vinyl thiophene monomer was synthesized by dehydration of the corresponding secondary alcohol. Free radical initiated copolymerizations with methyl methacrylate, styrene or isobutyl methacrylate were performed and the copolymer compositions were used in the calculation of reactivity ratios. The data was analyzed via a nonlinear least squares error-in-variables method. The 2,5-dimethyl-3-vinylthiophene was shown to have equal or slightly less reactivity than each of the monomers chosen as comonomers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556805
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  • 74
    Digitale Medien
    Digitale Medien
    Synthesis and radical polymerization of novel vinyl monomers having the imidazoline and pyrimidine moiety (1996)
    Springer
    Polymer bulletin 37 (1996), S. 443-450 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Alkylation of the methylene bridged tetrahydropyrimidine derivatives by chloromethylstyrene produces the bridged bis(4-vinylbenzyl)-1,4,5,6,-tetrahydropyrimidinium salts in high yields. Similar procedures are used to prepare 2-imidazolinium derivatives. The quaternary salts which support functional side groups of potential biomedical interest are characterized by means of spectroscopic methods. These monomers are readily polymerized free radically in solution of dimethyl formamide at moderate temperatures. The soluble and insoluble polymers containing 2-imidazolinium and 1,4,5,6-tetrahydropyrimidinium salts were found to exhibit antibacterial activites againstEscherichia coli.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556803
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  • 75
    Digitale Medien
    Digitale Medien
    Synthesis, characterization of poly(allylamine)chelates with Cu(II), Co(II) and Ni(II) (1996)
    Springer
    Polymer bulletin 37 (1996), S. 463-468 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The parent polymer, poly(allylamine) as ligand polymer was employed to synthesize polychelates of heavy metal ions. The functional poly(allylamine) and its Ni(II), Co(II) and Cu(II) metal chelates were characterized by elemental analysis, FT-IR spectroscopy, TGA, and SEM. For the polychelates magnetic and conductivimetry studies were also carried out.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556806
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  • 76
    Digitale Medien
    Digitale Medien
    Novel chemically amplified imaging materials containing malonate pendant groups (1996)
    Springer
    Polymer bulletin 37 (1996), S. 475-482 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary A new chemically amplified polymeric imaging system based on polymers containingt-butylmalonate pendant groups has been demonstrated. Both the homopolymer of di-t-butyl (vinylbenzyl)benzylmalonate and its copolymer with styrene have been tested in coatings containing a photoacid generator. Imaging experiments confirm that the materials have very high sensitivities when exposed to UV radiation near 250nm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556808
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  • 77
    Digitale Medien
    Digitale Medien
    Preparation of new gels derived from poly(sucrose acrylate) with immobilized Cibacron Blue and their application in affinity chromatography (1996)
    Springer
    Polymer bulletin 37 (1996), S. 483-488 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary New pseudoaffinity chromatography supports were prepared and characterized from poly(sucrose acrylate) crosslinked with MDI or TDI and Cibacron Blue dye as ligand. Blue gels were useful in the retention of albumin and the results are reported.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556809
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  • 78
    Digitale Medien
    Digitale Medien
    The effect of the ethylene pressure on its reaction with 1-hexene, 1-octene and 4-methyl-1-pentene (1996)
    Springer
    Polymer bulletin 37 (1996), S. 469-474 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Copolymers of ethylene and 1-hexexe, 1-octene and 4-methyl-1-pentene were obtained using Et[In]2ZrCl2/MAO catalyst at various pressures. The increase of 1-hexene and 1-octene concentration in the feed increases catalyst activity(g/nZr.h.bar) and productivity(g/nZr.h). For 4-methyl-1-pentene the activity is independent on comonomer concentration. Increasing the ethylene pressure the productivity of the copolymerization increases and the activity shows a weak decay. Characterization of the copolymer shows that at higher pressure the cristallinity of the copolymers is higher due to lower comonomer incorporation. There is a good linear correlation of cristallinity with comonomer concentration in the feed for 1-hexene and 1-octene at a fixed pressure, but not for 4-methyl-1-pentene.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00556807
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  • 79
    Digitale Medien
    Digitale Medien
    Maximum product of spacings estimators for the generalized pareto and log-logistic distributions (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 1-15 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Spacings ; quantiles ; generalized Pareto distribution ; log-logistic distribution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The maximum product of spacings (MPS) method is discussed from the standpoint of information theory. MPS parameter and quantile estimates for the generalized Pareto distribution and the two parameter log-logistic distribution are compared with the maximum likelihood(ML) and probability weighted moment (PWM) estimates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581791
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  • 80
    Digitale Medien
    Digitale Medien
    A diffusion approximation for a network of reservoirs with power law release rule (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 17-37 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Diffusion ; network ; reservoir ; power law
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A diffusion approximation for a network of continuous time reservoirs with power law release rules is examined. Under a mild assumption on the inflow processes, we show that for physically reasonable values of the power law constants, the system of processes converges to a multi-dimensional Gaussian diffusion process. We also illustrate how the limiting Gaussian process may be used to compute approximations to the original system of reservoirs. In addition, we study the quality of our approximations by comparing them to results obtained by simulations of the original watershed model. The simulations offer support for the use of the approximation developed here.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581792
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  • 81
    Digitale Medien
    Digitale Medien
    Spatial and temporal analysis of groundwater recharge with application to sampling design (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 39-63 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Saturated flow ; rainfall ; groundwater monitoring
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A numerical experiment of flow in variably saturated porous media was performed in order to evaluate the spatial and temporal distribution of the groundwater recharge at the phreatic surface for a shallow aquifer as a function of the input rainfall process and soil heterogeneity. The study focused on the groundwater recharge which resulted from the percolation of the excess rainfall for a 90-days period of an actual precipitation record. Groundwater recharge was defined as the water flux across the moving phreatic surface. The observed spatial non-uniformity of the groundwater recharge was caused by soil heterogeneity and is particularly pronounced during the stage of recharge peak (substantial percolation stage). During that stage the recharge is associated with preferential flow paths defined as soil zones of locally higher hydraulic conductivity. For the periods of low percolation intensity the groundwater recharge was exhibiting more uniform spatial characteristics. The temporal distribution of the recharge was found to be a function of the frequency and intensity of the rainfall events. Application of sampling design demonstrates the joint influence of the spatial and temporal recharge variability on the cost-effective monitoring of groundwater potentiometric surfaces.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581793
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  • 82
    Digitale Medien
    Digitale Medien
    Stochastic renewal model of low-flow streamflow sequences (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 65-85 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Streamflow ; drought ; tree-ring data ; renewal model ; geometric variables
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract It is shown that runs of low-flow annual streamflow in a coastal semiarid basin of Central California can be adequately modelled by renewal theory. For example, runs of below-median annual streamflows are shown to follow a geometric distribution. The elapsed time between runs of below-median streamflow are geometrically distributed also. The sum of these two independently distributed geometric time variables defines the renewal time elapsing between the initiation of a low-flow run and the next one. The probability distribution of the renewal time is then derived from first principles, ultimately leading to the distribution of the number of low-flow runs in a specified time period, the expected number of low-flow runs, the risk of drought, and other important probabilistic indicators of low-flow. The authors argue that if one identifies drought threat with the occurrence of multiyear low-flow runs, as it is done by water supply managers in the study area, then our renewal model provides a number of interesting results concerning drought threat in areas historically subject to inclement, dry, climate. A 430-year long annual streamflow time series reconstructed by tree-ring analysis serves as the basis for testing our renewal model of low-flow sequences.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581794
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  • 83
    Digitale Medien
    Digitale Medien
    Regression model for generating time series of daily precipitation amounts for climate change impact studies (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 87-106 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Climate change ; daily precipitation modelling ; generalized linear models ; iteratively reweighted least squares ; spline functions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The precipitation amounts on wet days at De Bilt (the Netherlands) are linked to temperature and surface air pressure through advanced regression techniques. Temperature is chosen as a covariate to use the model for generating synthetic time series of daily precipitation in a CO2 induced warmer climate. The precipitation-temperature dependence can partly be ascribed to the phenomenon that warmer air can contain more moisture. Spline functions are introduced to reproduce the non-monotonous change of the mean daily precipitation amount with temperature. Because the model is non-linear and the variance of the errors depends on the expected response, an iteratively reweighted least-squares technique is needed to estimate the regression coefficients. A representative rainfall sequence for the situation of a systematic temperature rise is obtained by multiplying the precipitation amounts in the observed record with a temperature dependent factor based on a fitted regression model. For a temperature change of 3°C (reasonable guess for a doubled CO2 climate according to the present-day general circulation models) this results in an increase in the annual average amount of 9% (20% in winter and 4% in summer). An extended model with both temperature and surface air pressure is presented which makes it possible to study the additional effects of a potential systematic change in surface air pressure on precipitation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581761
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  • 84
    Digitale Medien
    Digitale Medien
    A spectral approach to estimation and smoothing of continuous spatial processes (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 107-126 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Gaussian process ; spatial correlation ; anisotropy ; Fourier transform ; Gauss-Newton ; ECM ; measurement error ; signal extraction ; irregular data
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract This paper is concerned with developing computational methods and approximations for maximum likelihood estimation and minimum mean square error smoothing of irregularly observed two-dimensional stationary spatial processes. The approximations are based on various Fourier expansions of the covariance function of the spatial process, expressed in terms of the inverse discrete Fourier transform of the spectral density function of the underlying spatial process. We assume that the underlying spatial process is governed by elliptic stochastic partial differential equations (SPDE's) driven by a Gaussian white noise process. SPDE's have often been used to model the underlying physical phenomenon and the elliptic SPDE's are generally associated with steady-state problems. A central problem in estimation of underlying model parameters is to identify the covariance function of the process. The cumbersome exact analytical calculation of the covariance function by inverting the spectral density function of the process, has commonly been used in the literature. The present work develops various Fourier approximations for the covariance function of the underlying process which are in easily computable form and allow easy application of Newton-type algorithms for maximum likelihood estimation of the model parameters. This work also develops an iterative search algorithm which combines the Gauss-Newton algorithm and a type of generalized expectation-maximization (EM) algorithm, namely expectation-conditional maximization (ECM) algorithm, for maximum likelihood estimation of the parameters. We analyze the accuracy of the covariance function approximations for the spatial autoregressive-moving average (ARMA) models analyzed in Vecchia (1988) and illustrate the performance of our iterative search algorithm in obtaining the maximum likelihood estimation of the model parameters on simulated and actual data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581762
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  • 85
    Digitale Medien
    Digitale Medien
    Nonlinear estimation of spatial distribution of rainfall — An indicator cokriging approach (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 127-150 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Rainfall estimation ; indicator cokriging ; rain gage measurements
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract Indicator cokriging (Journel 1983) is examined as a tool for real-time estimation of rainfall from rain gage measurements. The approach proposed in this work obviates real-time estimation of real-time statistics of rainfall by using ensemble or climatological statistics exclusively, and reduces computational requirements attendant to indicator cokriging by employing only a few auxiliary cutoffs in estimation of conditional probabilities. Due to unavailability of suitable rain gage measurements, hourly radar rain fall data were used for both indicator covariance estimation and a comparative evaluation. Preliminary results suggest that the indicator cokriging approach is clearly superior to its ordinary kriging counterpart, whereas the indicator kriging approach is not. The improvement is most significant in estimation of light rainfall, but drops off significantly for heavy rainfall. The lack of predictability in spatial estimation of heavy rainfall is borne out in the integral scale of indicator correlation: peaking to its maximum for cutoffs near the median, indicator correlation scale becomes increasingly smaller for larger cutoffs of rainfall depth. A derived-distribution analysis, based on the assumption that radar rainfall is a linear sum of ground-truth and a random error, suggests that, at low cutoffs, indicator correlation scale of ground-truth can significantly differ from that of radar rainfall, and points toward inclusion of rainfall intermittency, for example, within the framework proposed in this work.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581763
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  • 86
    Digitale Medien
    Digitale Medien
    Comment on “Operator and integro-differential representations of conditional and unconditional stochastic subsurface flow” (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 151-161 
    Details
    ISSN: 1436-3259
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581764
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  • 87
    Digitale Medien
    Digitale Medien
    Reply to comments by S.E. Serrano on “Operator and integro-differential representations of conditional and unconditional stochastic subsurface flow” (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 163-166 
    Details
    ISSN: 1436-3259
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581765
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  • 88
    Digitale Medien
    Digitale Medien
    Estimation of quantiles and confidence intervals for the log-Gumbel distribution (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 187-207 
    Details
    ISSN: 1436-3259
    Schlagwort(e): log-Gumbel distribution ; flood frequency analysis ; quantile estimation ; confidence intervals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The log-Gumbel distribution is one of the extreme value distributions which has been widely used in flood frequency analysis. This distribution has been examined in this paper regarding quantile estimation and confidence intervals of quantiles. Specific estimation algorithms based on the methods of moments (MOM), probability weighted moments (PWM) and maximum likelihood (ML) are presented. The applicability of the estimation procedures and comparison among the methods have been illustrated based on an application example considering the flood data of the St. Mary's River.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581463
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  • 89
    Digitale Medien
    Digitale Medien
    A new formulation for the stochastic control of systems with bounded state variables: An application to a single reservoir system (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 167-186 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Reservoir stochastic theory ; reliability ; mean ; variance ; indicator function ; storage bounds ; nonlinear programming ; simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A new formulation is presented for the analysis of reservoir systems synthesizing concepts from the traditional stochastic theory of reservoir storage, moments analysis and reliability programming. The analysis is based on the development of the first and second moments for the stochastic storage state variable. These expressions include terms for the failure probabilities (probabilities of spill or deficit) and consider the storage bounds explicitly. Using this analysis, expected values of the storage state, variances of storage, optimal release policies and failure probabilities — useful information in the context of reservoir operations and design, can be obtained from a nonlinear programming solution. The solutions developed from studies of single reservoir operations on both an annual and monthly basis, compare favorably with those obtained from simulation. The presentation herein is directed to both traditional reservoir storage theorists who are interested in the design of a reservoir and modern reservoir analysts who are interested in the long term operation of reservoirs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581462
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  • 90
    Digitale Medien
    Digitale Medien
    Stochastic sketching of infiltration-advance isochrones (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 209-229 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Infiltration-advance equation ; water spreading ; cellular automata ; irrigation ; surface hydrology ; hydrodynamics ; stochastic processes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A technique has been developed for predicting the irregular advance pattern often observed as water spreads on the surface of the ground. The technique is a combination of stochastic sketching, potential theory, probability theory, and a mass balance equation in the form of an advance equation. The technique can be used on flat as well as sloping terrain and addresses any form of obstructions or constraints to the flow of the water. The stochastic sketching portion of the technique uses cellular automata with transition probability movement rules to sketch the dynamics of small volume water elements in the defined environment. Randomly selected small volume flow path segments are computed and plotted. The envelope of these segments defines the wetted area and the advance front. Several examples are presented showing the patterns produced for various situations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581464
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  • 91
    Digitale Medien
    Digitale Medien
    Stochastic analysis of multiphase flow in porous media: II. Numerical simulations (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 231-251 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Stochastic ; multiphase ; three phase ; heterogeneity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The first paper (Chang et al., 1995b) of this two-part series described the stochastic analysis using spectral/perturbation approach to analyze steady state two-phase (water and oil) flow in a, liquid-unsaturated, three fluid-phase porous medium. In this paper, the results between the numerical simulations and closed-form expressions obtained using the perturbation approach are compared. We present the solution to the one-dimensional, steady-state oil and water flow equations. The stochastic input processes are the spatially correlated logk where k is the intrinsic permeability and the soil retention parameter, α. These solutions are subsequently used in the numerical simulations to estimate the statistical properties of the key output processes. The comparison between the results of the perturbation analysis and numerical simulations showed a good agreement between the two methods over a wide range of logk variability with three different combinations of input stochastic processes of logk and soil parameter α. The results clearly demonstrated the importance of considering the spatial variability of key subsurface properties under a variety of physical scenarios. The variability of both capillary pressure and saturation is affected by the type of input stochastic process used to represent the spatial variability. The results also demonstrated the applicability of perturbation theory in predicting the system variability and defining effective fluid properties through the ergodic assumption.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581465
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  • 92
    Digitale Medien
    Digitale Medien
    Investigation of changes in characteristics of hydrological time series by Bayesian methods (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 295-317 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Bayesion methods ; time series ; hydrology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A review of literature reveals the inadequacy of Intervention analysis and spectrum based methods to adequately quantify changes in hydrologic times series. A Bayesian method is used to investigate the statistical significance of observed changes in hydrologic times series and the results are reported herein. The Bayesian method is superior to the previous methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581871
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  • 93
    Digitale Medien
    Digitale Medien
    HYDRO_GEN: A spatially distributed random field generator for correlated properties (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 253-278 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Random fields ; stochastic processes ; fractals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract This paper describes a new method for generating spatially-correlated random fields. Such fields are often encountered in hydrology and hydrogeology and in the earth sciences. The method is based on two observations: (i) spatially distributed attributes usually display a stationary correlation structure, and (ii) the screening effect of measurements leads to the sufficiency of a small search neighborhood when it comes to projecting measurements and data in space. The algorithm which was developed based on these principles is called HYDRO_GEN, and its features and properties are discussed in depth. HYDRO_GEN is found to be accurate and extremely fast. It is also versatile: it can simulate fields of different nature, starting from weakly stationary fields with a prescribed covariance and ending with fractal fields. The simulated fields can display statistical isotropy or anisotropy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581869
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  • 94
    Digitale Medien
    Digitale Medien
    Analytical expressions of conditional mean, covariance, and sample functions in geostatistics (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 279-294 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Linear estimation ; interpolation ; kriging ; splines ; conditional
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract This work presents analytical expressions for the best estimate, conditional covariance function, and conditional realizations of a function from sparse observations. In contrast to the prevalent approach in kriging where the best estimates at every point are determined from the solution of a system of linear equations, the best-estimate function can be represented analytically in terms of basis functions, whose number depends on the observations. This approach is computationally superior when graphing a function estimate and is also valuable in understanding what the solution should look like. For example, one can immediately see that all “singularities” in the best-estimate function are at observation points.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581870
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  • 95
    Digitale Medien
    Digitale Medien
    A second look at the method of random walks (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 319-329 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Particle tracking ; numerical methods ; random walks ; advection-dispersion equation ; stochastic processes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A formal statistical discussion of the origins of the random walk and its relation to the classic advection-dispersion equation is given. At issue is the common use of Gaussian distributed steps in producing the desired dispersive effects. Shown are alternative solutions to the basic Langevin equation describing mass displacements based on non-Gaussian, white increments. In particular, the results reveal that uniform or symmetric-triangular steps can be employed without loss of generality in accuracy of the solution (over all Peclet numbers) and may yield significant savings in the computational generation of the random deviates required in the Monte Carlo procedures of the random walk method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581872
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  • 96
    Digitale Medien
    Digitale Medien
    Operator and integro-differential representations of conditional and unconditional stochastic subsurface flow (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 330-330 
    Details
    ISSN: 1436-3259
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01581873
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  • 97
    Digitale Medien
    Digitale Medien
    Block copolymerization of tetrahydrofuran with δ-valerolactone by the samarium iodide-induced transformation (1996)
    Springer
    Polymer bulletin 37 (1996), S. 597-601 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Polymerization behavior of δ-valerolactone (VL) with alkylsamarium (RSmI2) was studied, and its application to the block copolymerization of tetrahydrofuran (THF) with VL was examined. Polymerization of VL by butylsamarium gave the corresponding poly(VL) in good yield. The yield increased with increasing the concentration of VL and decreasing the polymerization temperature, resulting from the equilibrium between VL and poly(VL). The decrease in the molecular weight of poly(VL) by prolonging the polymerization time indicated the existence of back-biting reaction to form cyclic oligomers. The polymerization of VL with poly(THF)-macroanion obtained by the two-electron reduction of the propagation center of living poly(THF) with SmI2 led to the block copolymer of THF with VL. The initiation efficiency of VL-polymerization was almost quantitative, and the unit ratio of THF and VL-segments could be controlled by both the polymerization time of THF and the amounts of VL.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00296604
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  • 98
    Digitale Medien
    Digitale Medien
    Syndiotactic polymerization of styrene with CpTiCl2(OPri)/methylaluminoxane (1996)
    Springer
    Polymer bulletin 37 (1996), S. 719-721 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary CpTiCl2(OPri) was a very active catalyst for syndiotactic polymerization of styrene when activated with methyl aluminoxane (MAO). The catalyst activity and syndiospecificity of CpTiCl2(OPri)/MAO were about 107 g PS / mol Ti·mol S·h and about 95% respectively, both higher than those of CpTiCl3 / MAO.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00295768
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  • 99
    Digitale Medien
    Digitale Medien
    Cationic polymerization of styrene and indene in iodine/liquid sulfur dioxide system (1996)
    Springer
    Polymer bulletin 37 (1996), S. 729-735 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract The cationic polymerizations of indene (Ind) and styrene (Sty) initiated by iodine (I2) in liquid sulfur dioxide (SO2) were investigated. Reactions involving Ind were characterized by termination by neutralization between the growing carbocationic species and the nucleophilic counteranion, at low temperature. Sty polymerization is also termination-dominated and gives low conversion at -20°C. High resolution gas chromatography coupled with mass spectrometry (HGC-MS) analysis of non polymeric material in the Sty polymerization suggested that initiation of Sty polymerization involves the formation of 1,2 diiodide adduct prior to initiation with HI.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00295770
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  • 100
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of the novel cellulose derivative dansyl cellulose (1996)
    Springer
    Polymer bulletin 37 (1996), S. 743-749 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary Novel, soluble 5-dimethylamino-1-naphthalenesulfonyl esters of cellulose (2) with a degree of substitution from 0.67 to 1.59 were prepared by esterification of cellulose dissolved in N,N-dimethylacetamide/LiCl solvent system and characterized by means of FTIR-as well as 1H and 13C NMR-spectroscopy. The remaining OH groups of 2 can be fully acetylated in pyridine using N,N-dimethylaminopyridine as a catalyst. The polymers show typical fluorescence and absorption spectra with absorptions at 217, 250 and 317 nm which are in good agreement with quantum chemical calculations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00295772
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