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  • 1
    Digitale Medien
    Digitale Medien
    Modified Wigner bispectrum and its generalizations (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 27-40 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The Wigner bispectrum of multicomponent signals is studied, and its modified and reduced forms are introduced. A generalization of the presented forms to the Wigner higher-order spectra (WHOS), in the case of multicomponent signals, is provided. From our previous work it is known that cross terms removal (reduction) is possible for odd-order spectra with equal numbers of conjugated and nonconjugated terms. Here, we extend the analysis to even-order spectra. The theory is illustrated by examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183173
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  • 2
    Digitale Medien
    Digitale Medien
    On identifiability and information-regularity in parametrized normal distributions (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 83-89 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We describe methods to establish identifiability and information-regularity of parameters in normal distributions. Parameters are considered identifiable when they are determined uniquely by the probability distribution and they are information-regular when their Fisher information matrix is full rank. In normal distributions, information-regularity implies local identifiability, but the converse is not always true. Using the theory of holomorphic mappings, we show when the converse is true, allowing information-regularity to be established without having to explicitly compute the information matrix. Some examples are given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183177
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  • 3
    Digitale Medien
    Digitale Medien
    Two-dimensional model-based power spectrum estimation for nonextendible correlation bisequences (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 141-163 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The extendibility of estimated correlation bisequences from an available sampled data array is described in terms of the generating functions of associated block Toeplitz with Toeplitz block (BTTB) matrices. The periodogram-based correlation bisequences are shown to be extendible. It is shown that the method of resultants and subresultants is convenient for generating the nonlinear constraints in the optimization problem which is solved iteratively for power spectrum estimation. A nontrivial example illustrates the concepts developed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183272
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  • 4
    Digitale Medien
    Digitale Medien
    A multiresolutional approach to 3D object recognition (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 217-239 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A multiresolutional approach is presented for effectively recognizing three-dimensional (3D) objects. The approach is both pose and scale invariant. A multiresolutional model base is constructed, and multiscale edges of the object are detected using the wavelet transform. The minimum alignment between model base and object is realized by the linear mapping scheme.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183276
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  • 5
    Digitale Medien
    Digitale Medien
    Fractal interpolation functions and data compression for tracking (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 59-67 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The potential for data compression in using fractal interpolation functions (FIFs) is realized by the construction of a set of multirate filters. The filter tap weights are determined by optimizing the energy contents of a preselected set of frequency bands. This filter bank implementation of the FIF is successfully used to compress data simulated in a tracking environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183175
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  • 6
    Digitale Medien
    Digitale Medien
    On cyclically time-varying autoregressive digital filters (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 91-106 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A first-order autoregressive filter is altered by changing the constant gain to two or more gains that cyclically alternate in time. The advantages of this system are shown, and the relation to linear autoregressive moving average difference equations of higher order is derived.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183178
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  • 7
    Digitale Medien
    Digitale Medien
    Fast implementation of the forward positional acceleration of robots via the distributed arithmetic technique (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 165-195 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper refers to the fast implementation of the positional forward acceleration of the end effector of revolute robotic arms with spherical wrists, using the distributed arithmetic technique. The acceleration of the end effector is calculated by a cascade configuration of two pipelined arrays that calculate the Jacobian matrix and its time derivative, as well as the centrifugal-Coriolis and linear accelerations. These partial accelerations are then added in the adder tree. The building blocks of the arrays are the distributed arithmetic-based circuits that implement the matrix-vector multiplications involved in the calculations. The digit-serial configuration of the proposed implementation of the positional forward acceleration of the end effector is described. The serial and the parallel configurations may result as special cases of the digit-serial configuration. The proposed distributed arithmetic (DA) implementation of the positional forward acceleration may be applied, after appropriate modifications, to the general case of robots having either revolute or prismatic joints, with any type of wrist.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183273
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  • 8
    Digitale Medien
    Digitale Medien
    Locations and amplitudes of the extrema of the sinx/x function (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 241-245 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper addresses the calculation of the extrema of the sin x/x function. First the Newton-Raphson method is used, which allows us to obtain the extrema locations very fast through the use of a recursion formula. Then a second approach is proposed, which gives the extrema locations and the extrema amplitudes in the form of series expansions. Simple, accurate algebraic expressions are derived.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183277
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  • 9
    Digitale Medien
    Digitale Medien
    Unicursal resistive networks (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 307-324 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We give some existence results for a resistive network in which the components are neither voltage nor current controlled; that is, they are merely unicursal. In fact we allow coupling. Degree arguments give existence and bounds. We study several ways of avoiding the requirement of eventual passivity. No-gain and passive multiterminal elements are included. The results are extended to infinite networks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246715
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  • 10
    Digitale Medien
    Digitale Medien
    A new approach for estimating spectra from randomly sampled sequences (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 375-386 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Random sampling is one of the methods that can overcome the Nyquist limit when evaluating a frequency spectrum of a signal. However, the computational complexity becomesN 2 as the FFT cannot be used. A new approach, called hybrid additive random sampling, is proposed. This new scheme is devised by concatenating random sampling sequences in such a way that symmetry is created in the transform kernel for reducing the computational effort while the anti-alias property is maintained. A savings of the least 75% in computation is achieved. The sampling scheme is also found to be suitable for parallel implementation. In this paper, the algorithms for generating the sampling sequence and evaluating the spectrum are described in detail. The performances of the scheme in terms of noise, accuracy, etc., are compared with genuine random sampling and another approach proposed previously. The advantages and limitations are included.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246719
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  • 11
    Digitale Medien
    Digitale Medien
    A quick neural network for computer vision of gray images (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 41-58 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a comparison between the traditional image processing method and the area vector concept as well as the new technique of artificial neural networks. Freeman chain coding is considered in the study, and the principle of segmentation may be based and implemented for further investigations resulting from the proposed work. The pattern recognition concept is analyzed and defined through the sigmoid function and the determination of the threshold of a gray image for an object. The block schemes for the given protocols are summarized in a single scheme for illustration and comparison purposes. The synthetic pictures are generated and investigated regarding the dependence of computer vision on the contents of the artificial neural network. The normalization technique is included to eliminate noise and zooming problems. The minimum computational time for image processing with the generated pictures is also determined. The rate of deflection in the computational time is recommended for sensing the minimum computational time according to the variation of the number of hidden units in the hidden layer. A three-layer neural network has been used. The study of gray binary imaging for color pictures is illustrated to save computational time and effort.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183174
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  • 12
    Digitale Medien
    Digitale Medien
    Time-limited and band-limited environment: Signals and systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 247-270 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Of concern is an environment made up of signals and systems tightly confined both in time and frequency. Such an environment is often encountered in transmission line circuits, radar, sonar, and optical circuits, and when the principal signals are well-defined sharp pulses. It will be seen that once this environment is achieved, the signals and systems possess some attractive properties. A conventional system may preserve the symmetry of a propagating signal or change its symmetry from even to odd or from odd to even. Another system may be used to predict the arrival of an incoming pulse with a high degree of accuracy. Electrical networks may also be associated with these properties. Approximation problems, existence theorems, and realization schemes will be addressed and developed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183278
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  • 13
    Digitale Medien
    Digitale Medien
    Digitally redesigned PAM controller and ideal state reconstructor for input time-delay/nondelay systems with nonsynchronous sampling (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 325-347 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper develops a new digitally redesigned pulse-amplitude modulated (PAM) controller for a continuous-time input time-delay/nondelay system with nonsynchronous sampling. The concept of the law of the mean from the input integral calculus is utilized for the development of the equivalent digital predictor controllers from the available analog predictor controllers. As a result, the digitally controlled states closely match the original continuous-time states. To implement the developed discrete-time state-feedback PAM controller, this paper also develops an ideal discrete-time state using nonsynchronously sampled input-output data of the continuous-time input delay/nondelay system without establishing a dynamic observer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246716
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  • 14
    Digitale Medien
    Digitale Medien
    Model matching under external and input-output equivalence (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 429-438 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The model-matching problem for systems described by external models is considered in frameworks of both external and input-output equivalence. Necessary conditions for the solvability of the problem are produced, and it is shown that in certain cases these conditions are also sufficient. In the case where necessary and sufficient conditions exist, the solutions of the problem are obtained in a constructive way and a parametrization of solutions is given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198060
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  • 15
    Digitale Medien
    Digitale Medien
    Invariance property of Gaussian signals: A new interpretation, extension and applications (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 523-536 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper addresses the invariance property of Gaussian signals, originally derived by Bussgang, which characterizes the input/output moment relation of a hybrid nonlinear moment (HNM) estimator based on a zero-memory nonlinearity (ZMN) g(y). Some re-derivations of this property are reviewed, and an original, direct, and simple proof is presented (Appendix 1). The paper then derives a new interpretation of this property (Theorem 1) that shows a moment-sense equivalence between g(y) and a linear mappingh 1(y) whose coefficients a0 and a1 are completely characterized in terms ofg(y) and are shown to be optimal in a mean square error (MSE) sense. A direct and very interesting byproduct of this interpretation is a simple linear relationship between the input and output of the HNM estimator involved. The property is then generalized (Theorem 2) to signals other than Gaussian, resulting in an infinite cumulant series expansion of the HNM estimator output, whose coefficients are all characterized in terms ofg(y). Applications of Theorem 1 to some ZMNs commonly used in signal processing and control theory are presented that clearly illustrate the power and elegance of the invariance property. Finally, some conclusions are given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185002
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  • 16
    Digitale Medien
    Digitale Medien
    The discrete Einstein relation (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 547-557 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper the connection between ‘mass’M, ‘resistance’ϱ and ‘commute time’θ for random walks on graphs is further explored, and the relationθ=2M ·ϱ is proved. An extension of the result is made to multigraphs, which are an extension of the graph concept where a black box is treated like an edge.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185004
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  • 17
    Digitale Medien
    Digitale Medien
    Input-output systems whose transmission operators furnish nearly best approximations to a given map (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 625-647 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Let {S(A):A ∈A}, whereA is a subset of an infinite-dimensional normed linear spaceL, be a class of general nonlinear input-output systems that are governed by operator equations relating the input, state, and output, all of which are in extended spaces. IfQ is a given operator from a specified set ¯D i, of inputs into the space of outputs ¯H 0, the problem we consider is to find, for a given ɛ〉0, a “parameter”A ε∈A such that the transmission operatorR(A ε) ofS(A ε) furnishes a nearly best (or ɛ-best) approximation toQ from allR(A),A ∈A. Here the “distance” betweenQ andR(A) is defined as the supremum of distances betweenQz andR(A)z taken over allz ∈ ¯D i. In Theorems 2 through 5 we show that ifS(A) is “normal” (Definition 2),A satisfies some mild requirement andL contains a fundamental sequence, then establishingA ε∈A reduces to minimizing a certain continuous functional on a compact subset ofR n, and thus can be carried out by conventional methods. The applications of results are illustrated by the example of a model-matching problem for a nonlinear system, and of optimal tracking.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01371569
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  • 18
    Digitale Medien
    Digitale Medien
    Notes on uniform approximation of shift-varying systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 649-654 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract It is shown that the elementsG of a large class of input-output maps can be uniformly approximated arbitrarily well using a certain structure if and only ifG is continuous. For the case considered the system inputs and outputs are defined on a discrete set {0, 1,...,a 1}×...{0, 1,...,a m }, in which a1,...,a m are positive integers. Our approximating structure involves certain functions that can be chosen in different ways. For the special case in which these functions are taken to be certain polynomial functions, the input-output map of our structure is a generalized discrete Volterra series. Our results provide an analytical basis for the use of such series.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01371570
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  • 19
    Digitale Medien
    Digitale Medien
    Guaranteed stability margins for discrete-time LQ optimal regulators for the performance index with cross-product terms (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 663-701 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper, the stability robustness of deterministic state feedback discretetime linear quadratic (LQ) optimal regulators for the performance index with cross-product terms is analyzed. Guaranteed stability margins for such a type of LQ optimal regulator are suggested for the first time. These stability margins are obtained on the basis of a modified return difference equality and are expressed directly in terms of the elementary cost and system matrices. Sufficient conditions to guarantee the required stability margins are presented. Finally, the connection between the suggested stability margins and the selection of weighting state, input, and cross-product matrices is investigated, and useful guidelines for choosing proper weighting matrices are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01371572
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  • 20
    Digitale Medien
    Digitale Medien
    Feedback design and precompensation for generalized systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 611-624 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Feedback control designs are useful for removing the impulses that disturb the behavior of generalized state space systems. The aim of this paper is to detail the design of dynamic precompensators for the implementation of such feedback control designs. Necessary and sufficient conditions are given so that the resulting regulators are biproper. It is pointed out that these conditions are restrictive and that feedback control designs can lead to nonproper precompensators. To overcome this difficulty, a class of proper precompensators is proposed. These regulators, which result from an adaptation of the Silverman structure algorithm, remove the impulse behaviors that occur after the initial time by smoothing out the input vector.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185008
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  • 21
    Digitale Medien
    Digitale Medien
    Analysis of the Chinese remainder theorem and cyclotomic polynomials-based algorithms for cyclic convolution—Part II: Complex rational number system (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 595-610 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper investigates the factorization properties of cyclotomic polynomials over the field of complex rational numbers. Based on this factorization and the Chinese remainder theorem, we analyze the mathematical structure of the associated algorithms for computing the cyclic convolution of data sequences. The relevant results pertaining to finite integer and complex integer rings are also summarized.Note: This work is being reported in two parts. In Part I, we analyze the structure of the cyclic convolution algorithms over the rational number system. In Part II, we describe complex cyclotomic polynomials and the structure of the resulting cyclic convolution algorithms over the complex rational number system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185007
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  • 22
    Digitale Medien
    Digitale Medien
    Analysis of the Chinese remainder theorem and cyclotomic polynomials-based algorithms for cyclic convolution—Part I: Rational number system (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 569-594 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The Chinese remainder theorem plays a central role in the design of fast algorithms for computing cyclic and acyclic convolution of data sequences. A mathematical analysis of the theorem and related aspects form the topic of this investigation. The focus is almost exclusively on cyclic convolution algorithms. The number system that is studied is the field of rational numbers. Several properties related to the mathematical structure of the algorithms are derived.Note: This work is being reported in two parts. In Part I, we analyze the structure of the cyclic convolution algorithms over the rational number system. In Part II, we describe complex cyclotomic polynomials and the structure of the resulting cyclic convolution algorithms over the complex rational number system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185006
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  • 23
    Digitale Medien
    Digitale Medien
    On a “central inequality” in the theory of input-output systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 655-661 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In the stability and sensitivity theory of general, nonlinear input-output systems we encounter a certain inequality concerning solely the nominal system that plays a central role in the whole theory. In particular, this “central inequality,” combined with other assumptions, implies (a) stability of the nominal system, (b) robustness, and (c) insensitivity of the input-output system. This paper presents conditions equivalent to this central inequality, and a further result on the stability-robustness problem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01371571
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  • 24
    Digitale Medien
    Digitale Medien
    On the zeros of discrete-time linear periodic systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 703-718 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Discrete-time linear periodic single-input/single-output (SISO) systems having uniform relative degree are considered. A closed-form expression of the blocking input is derived and exploited to obtain a computationally advantageous characterization of the structural zeros. Indeed, it suffices to compute the eigenvalues of a suitably defined (n × n) matrix, wheren is the system order. It is shown that, in contrast to the general case studied in previous papers, the number of zeros of linear periodic SISO systems with uniform relative degree is always time invariant and equal to the difference between the system order and the relative degree. The new characterization is also used to provide a simple expression for the zeros of linear periodic systems described by input-output difference equations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01371573
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  • 25
    Digitale Medien
    Digitale Medien
    Observability of nonlinear differential algebraic systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 271-285 
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    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We define the smooth observability of nonlinear DAE systems and give sufficient conditions for this property to hold locally in a neighborhood of a solution. The matrix rank conditions for observability are verifiable by a combination of symbolic and numerical linear algebra computations. These conditions generalize conditions that have appeared in the literature for observability of linear time-varying DAE systems. We indicate how the main result is potentially useful in studying a system's zero dynamics. Some relevant rank properties of Hessenberg DAE systems are established.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183279
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  • 26
    Digitale Medien
    Digitale Medien
    A new family of Routh approximants (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 1-25 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Based on the combinatorial Routhα-β andγ-δ expansions of a stable transfer function, a new energy decomposition tree for linear systems is developed. The pertinent properties to the energy decomposition tree are investigated, and an algorithm is derived for synthesizing transfer functions from the tree. The synthesis process naturally leads to a new family of Routh approximants to the system. It is indicated that the selection of Routh approximants based on the values of impulse-response energy is often inadequate because there may be a number of different Routh approximants with the same order and the same impulse-response energy. In such cases, an additional performance criterion, such as the integral of squared error of impulse response or unit-step response, has to be used to select a suitable Routh approximant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183172
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  • 27
    Digitale Medien
    Digitale Medien
    A genetic algorithm for the maximum likelihood estimation of the parameters of sinusoids in a noisy environment (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 69-81 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract An adaptive generic algorithm was developed to solve the optimization problem of the maximum likelihood estimation of the sum of sinusoids in a noisy environment. The algorithm is based on genetic concepts and is extended, with modifications, to this problem. Simulation results were performed to see the effect of different parameters such as permutation and crossover probabilities. The effects of the signal-to-noise ratio (SNR) were also studied. It was found that the key factor for accuracy is the probabilities of permutation and crossover. Thus, we developed an adaptive method to estimate these probabilities, on line, to reduce the error. This was accomplished by considering them as unknown parameters to be estimated with the signal parameters. The mean square error of the frequency estimates was compared favorably to the Cramér-Rao lower bound. Several simulations are shown for SNR values ranging between −7 dB and 20 dB.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183176
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  • 28
    Digitale Medien
    Digitale Medien
    Fast algorithms for computing one- and two-dimensional convolution in integer polynomial rings (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 121-139 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In a recent work, the factorization properties of polynomials defined over finite integer polynomial rings were analyzed. These properties, along with other results pertaining to polymomial theory, led to the direct sum property and the American-Indian-Chinese extension of the Chinese remainder theorem over such integer rings. The objective of this paper is to describe algorithms for computing the one-and two-dimensional convolution of data sequences defined over finite integer rings. For one-dimensional convolution, algorithms for computing acyclic and cyclic convolution are described. For two-dimensional convolution, only the cyclic case is analyzed. Computational and other relevant aspects associated with the structure of these algorithms are also studied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183180
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  • 29
    Digitale Medien
    Digitale Medien
    Robust adaptive beamforming for broadband arrays (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 207-216 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract It is very important in many applications to preserve a desired signal without distortion. This paper presents a robust adaptive beamforming method to extract a desired signal from the signals received by broadband arrays. The proposed method relaxes the requirement of approximate knowledge of the desired direction and the sensor gains and delays (phases). Also the method enhances the desired signal based on a focusing transform for that signal, requires less computation than the taped-delay-line beamforming method, and provides good results even in a multipath environment. Computer simulations are given to support the proposed method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183275
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  • 30
    Digitale Medien
    Digitale Medien
    MODE-type algorithm for estimating damped, undamped, or explosive modes (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 349-362 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We propose a new algorithm for estimating the parameters of damped, undamped, or explosive sinusoidal signals. The algorithm resembles the MODE algorithm, which is commonly used for direction of arrival estimation in the array signal processing field. It is derived as a natural approximation to an asymptotically (high-SNR) optimal parameter estimator and has excellent statistical accuracy. Nevertheless, it is computationally simple and easy to implement. Numerical examples are included to illustrate the performance of the proposed method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246717
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  • 31
    Digitale Medien
    Digitale Medien
    Uniform Approximation of Discrete-Space Multidimensional Myopic Maps (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 387-403 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Our main result is a theorem that gives, in a certain setting, a necessary and sufficient condition under which discrete-space multidimensional shift-invariant input-output maps with vector-valued inputs drawn from a certain large set can be uniformly approximated arbitrarily well using a structure consisting of a linear preprocessing stage followed by a memoryless nonlinear network. Noncausal as well as causal maps are considered. Approximations for noncausal maps for which inputs and outputs are functions of more than one variable are of current interest in connection with, for example, image processing.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246720
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  • 32
    Digitale Medien
    Digitale Medien
    Computation of simple and group factors of multivariate polynomials (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 455-473 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper generalizes a recent result onsimple factorization of 2-variable (2-v) polynomials to simple andgroup factorization ofn-variate (n-v), (n≥3) polynomials. The emphasis is on developing a reliablenumerical technique for factorization. It is shown that simple as well as group factorization can be achieved by performing singular value decomposition (SVD) on certain matrices obtained from the coefficients of the givenn-v polynomial expressed in a Kronecker product form. For the polynomials that do not have “exact” simple and/or group factors, the concepts of approximate simple and group factorization are developed. The use of SVD leads to an elegant solution of an approximaten factorization problem. Several nontrivial examples are included to illustrate the results presented in this paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198062
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  • 33
    Digitale Medien
    Digitale Medien
    A sequentially operated periodic FIR filter for perfect reconstruction (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 475-486 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a sequentially operated periodic FIR filter to perform the functions of multirate filter banks for perfect reconstruction. This filter consists of an analysis filter and a synthesis filter. Each of these filters has a single-input/single-output FIR filter with periodically time-varying coefficients and a sequentially operated multichannel sampling scheme. As a result, the proposed filter can offer considerable improvements in computation and implementation. For the design of the filter, we provide a necessary and sufficient condition for perfect reconstruction in terms of the blocked transfer matrices and give a design procedure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198063
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  • 34
    Digitale Medien
    Digitale Medien
    Design of linear-phase, FIR integrators of degreer, r=1, 2, 3,..., for midband frequency range (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 537-545 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper a novel analytical technique for designing linear-phase, FIR integrators of first degree has been proposed by taking the optimality criteria of maximal flatness (in the Butterworth sense) of the amplitude response, at midband frequency:ω=π/2. Mathematical formulas to compute exact weights for the design of first-degree integrators (i.e., frequency response 1/(jω)) have been derived. Thereafter, the design has been extended to approximate linear-phase integrators for any generic degreer, r〉1. The performance characteristics of the first-, second- and third-degree integrators have been given to highlight the efficacy of the designs. The suggested designs are particularly suitable for the midband frequency range of operations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185003
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  • 35
    Digitale Medien
    Digitale Medien
    Design of IIR digital notch filters (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 415-427 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A method is presented for the design of notch filters with specified notch frequency Ω0 and 3-dB rejection bandwidthB t, using a first-order real all-pass filter, wherein the only coefficient is used to control the notch frequency. To control the bandwidth, use is made of a new amplitude change function (ACF), and it is shown that given notch filter specifications can be exactly met thereby. Also, using the ACF, it is shown that stability of the second-order notch filter designs can be improved along with the noise gain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198059
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  • 36
    Digitale Medien
    Digitale Medien
    When is the stability of a nonlinear input-output system robust? (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 487-505 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract We consider a general nonlinear input-output system governed by operator equations that relate the system's input, state, and output, all of which are in extended spaces. It is assumed that the system variables are separated. Our results give conditions under which the stability of the nominal system is robust; i.e., it is not destroyed by any sufficiently small admissible perturbation of the system. Theorem 1 deals with the case when by stability we mean theincremental stability. Theorem 3 concerns the*-stability; i.e., the case when the stability is essentially the boundedness of the transmission operator. Moreover, in Theorem 2 it is shown that, under certain conditions, the incremental stability of the nominal system implies insensitivity. Basically, our results show that if the operators describing the nominal system are well behaved, and the transition from the nominal system to the perturbed system is not abrupt, then the nominal system stability is robust. The applications of the results are illustrated by several examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198064
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  • 37
    Digitale Medien
    Digitale Medien
    A separation theorem for finite-precision digital systems (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 107-119 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract For models of zero-input direct-form digital filters implemented in fixed-point digital hardware it is known that if saturation arithmetic is used and stability holds when the quantization is ignored, then the amplitude of all limit cycles can be made arbitrarily small by making the bound on the magnitude of the quantization sufficiently small. In that sense the effects of quantization and overflow can be considered separately. Recently, this proposition was extended to the case in which the input need not be zero. Here we give a result to the effect that quantization and overflow can be considered separately for a much more general class of discrete-time systems, and we give as an example an application of this result to systems governed by state equations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183179
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  • 38
    Digitale Medien
    Digitale Medien
    Image restoration using a conjugate gradient-based adaptive filtering algorithm (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 197-206 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A new two-dimensional (2D) sample-based conjugate gradient (SCG) algorithm is developed for adaptive filtering. This algorithm is based on the conjugate gradient method of optimization and therefore has a fast convergence characteristic. The SCG is computationally simpler than the recursive least squares (RLS) algorithm. The SCG algorithm with the equation-error and output-error methods is investigated for application in image restoration. Simulation results show that the new algorithm significantly outperforms existing algorithms in the restoration of noisy images.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01183274
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  • 39
    Digitale Medien
    Digitale Medien
    Row Straightening via local interactions (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 287-305 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A number of agents can arrange themselves equidistantly in a row via a sequence of adjustments, based on a simple “local” interaction. The convergence of the configuration to the desired one is exponentially fast. A similarity is shown between this phenomenon and the dynamics of pulse propagation along a distributedRC line, and a conjecture is made concerning the evolution of a similar system with a probabilistic rule of behavior.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246714
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  • 40
    Digitale Medien
    Digitale Medien
    Orthogonal cycle transforms of stochastic matrices (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 363-374 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we investigate new Fourier series with respect to orthonormal families of directed cycles $$\gamma $$ , which occur in the graph of a recurrent stochastic matrixP. Specifically, it is proved thatP may be approximated in a suitable Hilbert space by the Fourier series $$\sum {w_\gamma } \underline \gamma $$ . This approach provides a proof in terms of Hilbert space of the cycle decomposition formula for finite stochastic matricesP.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246718
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  • 41
    Digitale Medien
    Digitale Medien
    Potentials on the hexagonal grid (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 405-414 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The aim of this paper is to give an explicit computation for the potential generated by a dipole on a hexagonal grid. Such a computation will be expressed as the Fourier transform of a distribution on the bidimensional torus $$\mathbb{T}^2 $$ .
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198058
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  • 42
    Digitale Medien
    Digitale Medien
    Generalized inverses of two-variable polynomial matrices and applications (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 439-453 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The main contribution of this paper is to present (a) an algorithm for the computation of the generalized inverse of a not necessarily square two-variable polynomial matrix and (b) some applications of the proposed algorithm to the solution of Diophantine equations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198061
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  • 43
    Digitale Medien
    Digitale Medien
    H∞ approximation with point constraints applied to impedance estimation (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 507-522 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper offers a flexible new approach to interpolating impedance data by bounded analytic functions. This approach is motivated by the conviction that any scheme for interpolating data from a physical system must incorporate knowledge of the system into the procedure. The classical Nehari's method is extended to include physical constraints from the system and point constraints from the data. An algorithm is developed and applied to estimating the impedance function of an antenna from a minimal data set.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185001
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  • 44
    Digitale Medien
    Digitale Medien
    Comments on “reachability of polynomial matrix descriptions (PMDs)” by G. F. Fragulis and A. I. G. Vardulakis (1997)
    Springer
    Circuits, systems and signal processing 16 (1997), S. 559-568 
    Details
    ISSN: 1531-5878
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract The main purpose of these comments is to correct (a) the definitions of admissible initial conditions, (b) the exact solution of a polynomial matrix description (PMD), and (c) the proof of the controllability and reachability criteria, presented in the above-mentioned work. The results concerning the reachability and controllability subspaces and thus the reachability and controllability criteria remain the same.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01185005
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  • 45
    Digitale Medien
    Digitale Medien
    Effect of Ca doping on the structural and superconducting properties of EuBaSrCu3O7−δ (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 645-647 
    Details
    ISSN: 1557-1947
    Schlagwort(e): EuBaSrCu3O7−δ superconductor ; Ca doping ; orthorhombicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The effect of Ca doping in EuBaSrCu3O7−δ has been investigated by X-ray diffraction, ac susceptibility, and electrical resistivity measurements. X-Ray diffraction analyses of the samples showed that up to 30 at.% Ca can be substituted for Sr in EuBaSrCu3O7−δ, which has orthorhombic symmetry. The orthorhombicity decreases with increase inx, in EuBaSr1−xCax Cu3O7−δ, the material becoming tetragonal atx=0.2. Ac susceptibility and dc electrical resistivity measurements as function of temperature from 10 to 300 K showed that the superconducting transition temperatureT c decreases monotonically from 84 to 75K as the Ca concentrationx increases from 0.0 to 0.3 The decrease inT c can be attributed to the structural change taking place in EuBaSrCu3O7 as a consequence of replacement of Sr by Ca.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471926
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  • 46
    Digitale Medien
    Digitale Medien
    New research opportunities in superconductivity IV (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 583-621 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Superconductivity ; research opportunities ; state of the art
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471924
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  • 47
    Digitale Medien
    Digitale Medien
    High-resolution electron microscopy and low-temperature electron diffraction studies of a Bi2212 single crystal grown by the floating zone method (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 649-655 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Single crystal of Bi2Sr2CaCu2O8 ; high-resolution electron microscopy ; low-temperature electron diffraction ; lattice anomaly
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract High-resolution electron microscopy of a Bi2Sr2CaCu2O8 (Bi2212) single crystal prepared by the floating zone method shows that the single crystal is of high quality; there is no intergrowth faulting in the layered structure along thec-axis. Low-temperature selected area diffraction and convergent beam electron diffraction (CBED) studies of this high-quality single crystal show that there is no detectable change for both the point group symmetry of the basic structure and the modulated structure from room temperature to about 15 K. However, a lattice anomaly around 215 K was suggested by measuring the temperature dependence of the ratio between the cross-point distances of the HOLZ lines in high-index CBED patterns. The presence of the lattice anomaly was further confirmed by low-temperature X-ray diffraction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471927
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  • 48
    Digitale Medien
    Digitale Medien
    The crystal field in rare earth based high-temperature superconductors (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 623-643 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Superconductivity ; crystal field ; rare earth ; relaxation ; gap symmetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Neutron spectroscopy is a powerful tool to determine unambiguously the crystal-field (CF) potential in rare-earth (R) based high-T c superconducting materials. This technique provides detailed information on the electronic ground state of the R ions which is important to understand the thermodynamic magnetic properties as well as the observed coexistence between superconductivity and long-range magnetic ordering of the R ion sublattice at low temperatures. Moreover, the decay of the antiferromagnetic state of the parent compound as well as the evolution of the superconducting state upon doping can be directly and quantitatively monitored. It is found that the observed CF spectra separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for cluster formation. The onset of superconductivity can be shown to result from percolation which means that the superconductivity is an inhomogeneous materials property. Since the linewidths of CF transitions directly probe the static electronic susceptibility, we discuss temperature-dependent experiments of the relaxation rate of CF excitations in both optimally doped and underdoped regimes. It is shown that there is clear evidence for the opening of an electronic gap in the normal state of underdoped superconductors. Furthermore, the relaxation behavior appears to be extremely dependent upon the energy at which the static susceptibility is being probed. The main observed features can be reproduced by considering a strongly anisotropic gap function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471925
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  • 49
    Digitale Medien
    Digitale Medien
    The effects of cobalt substitution on the thermal diffusivity of YBa2Cu3O7−δ superconductor (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 663-668 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Thermal diffusivity ; acoustic plasmons ; cobalt substitution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The thermal diffusivity κ(T) of the cobalt-substituted sintered YBCO system, YBa2Cu3−x Co x O7∮δ (x=0.0, 0.1), has been measured to, investigate, effects of atomic substitution and charge carrier concentration on the thermal diffusion processes. The thermal diffusivity was measured in the temperature range 35–300 K, using the transient-plane-source technique. The results show that, belowT c , the κ(T) values of the doped (x=0.1), samples are lower than the corresponding values for the undoped (x=0.0) samples. This may be due to the difference in the free-charge carrier concentrations of the two samples. A decoupling between the conducting Cu−O planes as a result, of Co-doping in the chain sites may contribute to additional decrease in the thermal diffusivity of the doped sample. An attempt was made to explain the rise in the thermal diffusivity belowT c by adopting a recent theoretical model based on the existence of weakly damped collective electron excitations of Bose type, with acoustic dispersion relation, (acoustic plasmons) inside the superconducting gap.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471929
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  • 50
    Digitale Medien
    Digitale Medien
    Intrinsic surface depression of the order parameter under mixed (s+id)-wave pair symmetry and its effect on the critical current of high-T c SIS Josephson junctions (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 657-662 
    Details
    ISSN: 1557-1947
    Schlagwort(e): High-T c superconductors ; order parameter ; Josephson junctions ; Josephson critical current ; pair symmetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract An intrinsic gap depression at the superconductor-insulator interface due to the very short value of the coherence length in high-T c superconductors [HTS] is considered in the framework of a mixed (s+id)-wave pair symmetry for the order parameter ranging from pures to pured-wave. This gap depression acts as the main physical agent causing the relevant reduction ofI c (T)R n (T) values with respect to BCS expectations in HTS SIS Josephson junctions. Good agreement with various experimental data is obtained with both pures-wave and pured-wave symmetries of the order parameter, but with amounts of gap depression depending on the pair symmetry adopted. Regardless of the apir symmetry considered, these results prove the importance of the surface order-parameter depression in the correct interpretation of theI c (T)R n (T) data in HTS SIS junctions. In the case of a planar YBCO-based junction the use of the de Gennes condition allowed us to tentatively obtain an upper limit for the amount ofd-wave present in the gap of YBCO.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471928
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  • 51
    Digitale Medien
    Digitale Medien
    An equation of state of high-temperature superconductor (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 669-672 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Equation of state ; bulk modulus ; cohesive energy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-T c copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born-Landé inverse power form. The model, parameters of the Born-Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of pressure derivatives of bulk modulus atP=0 and the values of bulk modulus are found to be in very close agreement with experimental values for high-T c copper oxide and their nonsuperconducting parent compounds. It is also found that the quantity ΔU/U(V o) of these compounds increases with increasing hydrostistic pressure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471930
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  • 52
    Digitale Medien
    Digitale Medien
    Van hove singularity and “pseudo-gap” in HTSC (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 673-675 
    Details
    ISSN: 1557-1947
    Schlagwort(e): Cuprates ; van Hove singularity ; pseudo-gap
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Several experimental features in the normal state of cuprates have been interpreted using a “pseudogap”. We show that these results may be explained by the band structure of the CuO2 planes in the metallic region, which exhibits, saddle points (van Hove singularities).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02471931
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  • 53
    Digitale Medien
    Digitale Medien
    Dehydrogenative polycondensation of telechelically bis(dimethylsilyl)functionalized oligo(dimethylsiloxane)s or aromatics and 1,3,3,5,5,7,7,7-octamethyltetrasiloxane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 1-5 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Telechelically bis(hydrodimethylsilyl)-functionalized oligo(dimethylsiloxane)s or aromatics were found to give polymers constituting of alternating disilylene and oligodimethylsiloxane or 4,4′-diylaromatics as repeating units by dehydrogenative coupling reaction in the presence of palladium dibenzylideneacetone complex. The same catalyst gave polysilylenes with trisiloxane pendant from 1,1-dihydro-1,3,3,5,5,7,7,7-octamethyltetrasiloxane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050011
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  • 54
    Digitale Medien
    Digitale Medien
    Synthesis of polyorganosiloxane particles (1997)
    Springer
    Polymer bulletin 38 (1997), S. 23-25 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Hybrid particles have been synthesized from methyltriethoxysilane (MTEOS) by the sol-gel process. The particle size, size distribution, particle surface morphology conductivity and pH of the reaction solution at different reaction times were determined. Compared with tetraethyl orthosilicate (TEOS) and p-(chloromethyl)phenyl-trimethoxysilane (CMPTOS), MTEOS has a slower hydrolysis rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050014
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  • 55
    Digitale Medien
    Digitale Medien
    Polymerization of 4-n-alkylstyrenes with typical Ziegler-Natta and metallocene catalysts (1997)
    Springer
    Polymer bulletin 38 (1997), S. 43-48 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Polymerization of 4-n-alkylstyrenes (alkyl side group; methyl, ethyl, propyl and buthyl) was carried out with the η-C5(CH3)5TiCl3-methylaluminoxane (MAO) and TiCl3-triethylaluminum (TEA) catalyst systems. When the η-C5(CH3)5TiCl3-MAO catalyst was used, the stereoregularity of resulting polymers markedly depended on the length of substituted alkyl groups, i.e., the catalyst gave highly syndiotactic poly(4-methylstyrene), but produced atactic polymers for the monomers with ethyl, propyl and buthyl substituents. On the other hand, all the poly(4-n-alkylstyrene)s obtained with the TiCl3-TEA catalyst were highly isotactic. As a result, a large difference was observed in the thermal properties of polymers obtained between the two catalyst systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050017
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  • 56
    Digitale Medien
    Digitale Medien
    Enzyme-catalyzed peptide syntheses in aqueous polymer two-phase systems (1997)
    Springer
    Polymer bulletin 38 (1997), S. 49-53 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Peptide synthesis in the aqueous polymer two-phase system was examined. Water soluble polymers adopted were dextran and polyethyleneglycol (PEG). By the modification of a proteolytic enzyme, trypsin, with dextran carrying a very small number of carboxyl groups, a separation of the enzyme from its peptide product, N-benzoyl-L-arginine glycinamide, which is relatively more soluble in a PEG phase could be realized. This separation drastically reduced a so-called "mass-law" effect, and increased the yield of the reaction product. The aqueous polymer two-phase system would be useful to enhance the usefulness of biocatalysts in organic syntheses.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050018
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  • 57
    Digitale Medien
    Digitale Medien
    Effect of the crosslinking with 1,1,1-trimethylolpropane trimethacrylate on 5-fluorouracil release from poly(2-hydroxyethyl methacrylate) hydrogels (1997)
    Springer
    Polymer bulletin 38 (1997), S. 55-62 
    Details
    ISSN: 1436-2449
    Schlagwort(e): Key words: Poly(2-hydroxyethyl methacrylate) (PHEMA) – 5-fluorouracil (5-FU) – 1,1,1-trimethylolpropane trimethacrylate (TPT) – hydrogel – controlled release – diffusion coefficient
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The aim of this study is to examine the influence of crosslinking density on 5-Fluorouracil release from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels crosslinked with 1,1,1-trimethylolpropane trimethacrylate (TPT). PHEMA hydrogels were synthesized by bulk polymerization with different proportions of TPT (1 – 10 wt%) as crosslinker agent and ammonium persulphate as initiator, enabling polymerization in the feed mixture in the presence of water. As a result, 5-FU could be trapped by including it as a sodium salt in the feed mixture of polymerization. Discs with 5-FU loads between 1 – 16 mg/disc were obtained. Swelling and 5-FU release kinetics studies were carried out in saline solution at 310 K. The diffusion studies were in accordance with Fick's second law during the initial stages, enabling the diffusion coefficients of the process to be determined. The time required for discs to reach total 5-FU release was between 35 h and 160 h and was a function of crosslinking density of the gels and 5-FU load of the discs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050019
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  • 58
    Digitale Medien
    Digitale Medien
    Effect of surfactant concentration, pH, and shear rate on the rheological properties of aqueous systems of a hydrophobically modified chitosan and its unmodified analogue (1997)
    Springer
    Polymer bulletin 38 (1997), S. 71-79 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Oscillatory shear, shear relaxation and viscosity experiments have been carried out on semidilute solutions of chitosan and on a hydrophobically modified analogue (HM-chitosan) in 1% acetic acid. This was done in the presence of various amounts of cetyltrimethylammonium bromide (CTAB) and at different pH values. All the rheological measurements on the HM-chitosan solutions revealed significant polymer-surfactant interaction and pH effects. The observed rheological effects were least pronounced at pH ≈ 4, while a strong viscoelastic response was found at pH values of 1 and 5 in HM-chitosan solutions of low surfactant concentration. At these conditions, significant shear-thinning effects were observed. In semidilute solutions of unmodified chitosan, the influence of pH, surfactant concentration and shear rate on the rheological properties was moderate or insignificant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050021
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  • 59
    Digitale Medien
    Digitale Medien
    Electrical conductivity of polystyrene/styrene-butadiene block copolymer blends containing carbon black (1997)
    Springer
    Polymer bulletin 38 (1997), S. 95-100 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The electrical resistivity and mechanical properties of carbon black (CB)-filled polystyrene (PS)/styrene-butadiene block copolymer (SB) blends have been studied. Good electrical performance was achieved with pure SB and PS/SB blends indicating an inhomogeneity of these materials and the heterogeneous micro-dispersion of the CB particles. The percolation threshold of the filler inside SB or PS/SB blends is around 3.6 wt%, which is lower than that expected for incompatible PS/PBD blend. The addition of small amount CB decreases the elongation at break of PS/SB blends indicating some disturbance at the interface of these compatible material.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050024
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  • 60
    Digitale Medien
    Digitale Medien
    Homo-, co- and terpolymerization of 1,5-hexadiene using a methylalumoxane activated mono-Cp-amido-complex (1997)
    Springer
    Polymer bulletin 38 (1997), S. 141-148 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Homo- and copolymerizations of 1,5-hexadiene with ethene and styrene using halfsandwich metallocene catalyst Me2Si(Me4Cp)(N-tert.-butyl)TiCl2/MAO (Cp = cyclopentadienyl, Me = methyl, MAO = methylalumoxane) were investigated. According to 13C-NMR spectroscopic microstructure analysis, cyclopolymerization of 1,5-hexadiene afforded randomly distributed cis- and trans-cyclopentane rings in the homo- and copolymer backbone. 1,5-hexadiene incorporation reached 52 mol-%. The ratio of vinyl side chains to cyclopentane rings was controlled by 1,5-hexadiene concentration, where low 1,5-hexadiene concentration promoted cyclopolymerization. Copolymer glass transition temperatures increased with increasing content of cyclic units in the backbone. Styrene was used successfully as termonomer in ethene/1,5-hexadiene polymerization, resulting in a semicrystalline terpolymer with cyclic and styrenic units in the polymer backbone.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050030
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  • 61
    Digitale Medien
    Digitale Medien
    Synthesis and properties of polyurethanes containing phosphatidylcholine analogues in the main chains and long-chain alkyl groups in the side chains (1997)
    Springer
    Polymer bulletin 38 (1997), S. 133-140 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. New phospholipid polyurethanes containing phosphatidylcholine analogues in the main chains and octyl or oleyl groups in the side chains were synthesized by the addition polymerization of diols, bis[2-(2-hydroxyethyldimethylammonio)ethyl]2-octyl-1,3-propanediphosphate or bis[2-(2-hydroxyethyldimethylammonio)ethyl]2-oleyl-1,3-propanediphosphate, with diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and 2,4-tolylene diisocyanate (TDI). The new phospholipid diols and polyurethanes were characterized by their IR and 1H-NMR spectral data and elemental analysis. The new phospholipid polyurethanes exhibit common polyelectrolyte viscosity behaviours revealed by viscosity measurements. Moreover, π-A isotherms for these polyurethanes were also prepared.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050029
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  • 62
    Digitale Medien
    Digitale Medien
    Photoinitiated cationic ring-opening polymerization of a cyclosiloxane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 165-168 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Hexamethylcyclotrisiloxane was found to undergo photoinitiated cationic ring-opening polymerization in solution and bulk, upon exposure to UV radiation, in the presence of either sulfonium or iodonium salts or an iminosulfonate derivative. Glass transition temperatures were below − 100 °C. Molecular weights, determined by size exclusion chromatography relative to polystyrene standards, increased with photolysis lamp intensity. Use of an iodonium photoinitiator afforded poly(dimethylsiloxane) with Mn = 172,000. Polymerization of hexamethylcyclotrisiloxane was accompanied by a small increase in volume (3 – 4%).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050033
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  • 63
    Digitale Medien
    Digitale Medien
    An alternating copolymer for a blue light-emitting diode (1997)
    Springer
    Polymer bulletin 38 (1997), S. 169-176 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. An alternating copolymer composed of 9,9′-dihexylfluorene and N-2-ethylhexyl carbazole was synthesized to use as an emissive polymer in a light-emitting diode (LED). The copolymer is soluble in organic solvents and spin-cast to make a fine film. An LED fabricated by sandwiching the alternating copolymer between indium-tin oxide and aluminum emits a white color with the full width at half maximum of 150 nm. The electroluminescence spectrum becomes simplified to have an emission peak at 460 nm for fine blue color when the copolymer is blended with poly(vinylcarbazole) with a ratio of 1 to 4 before the use as an emissive layer. The forward bias turn-on voltage for the LED is 13, and quantum efficiency is 0.002%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050034
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  • 64
    Digitale Medien
    Digitale Medien
    IR study of hydrogen bonding in novel liquid crystalline epoxy/DGEBA blends (1997)
    Springer
    Polymer bulletin 38 (1997), S. 439-445 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The hydrogen bonding of LCE/DGEBA blend was studied using FT-IR. IR spectra of hydroxyl region and carbonyl region were investigated according to the content of LCE. IR spectra of LCE/DGEBA blend before and after curing were compared. Most hydroxyl group in DGEBA rich blends formed intermolecular or intramolecular hydrogen bonding after curing, while free hydroxyl group was present in LCE rich blends. Intramolecular hydrogen bonding was popular in DGEBA rich blends due to the conformational reason. Most carbonyl group was hydrogen bonded with hydroxyl or amine group after curing and the fraction of hydrogen bonded carbonyl was high in DGEBA rich blends.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050071
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  • 65
    Digitale Medien
    Digitale Medien
    A route to polysiloxanes with pendant imidazole groups Hydrosilylation of N-allylimidazole hydrochloride with methyldichlorosilane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 371-378 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Hydrosilylation of N-allylimidazole hydrochloride by methyldichlorosilane (MeCl2SiH) under mild conditions leads to a high yield of N-[γ-(methyldichlorosilyl)propyl]imidazole hydrochloride – highly reactive monomer for synthesis of imidazole modified polysiloxanes. This compound was used as the substrate for the generation of new cyclooligosiloxanes with the imidazole group attached through the trimethylene bridge to a siloxane ring. The anionic ring-opening polymerization of these cyclics permits the controlled synthesis of polysiloxanes with imidazole groups pendant to the polymer chain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050062
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  • 66
    Digitale Medien
    Digitale Medien
    Novel aprotic polar polymers 1. Synthesis of aliphatic polysulfoxides (1997)
    Springer
    Polymer bulletin 38 (1997), S. 379-386 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Aliphatic polysulfoxides having sulfoxide groups in the main chain were prepared by the selective oxidation of aliphatic polysulfides using aqueous hydrogen peroxide in chloroform. Degree of oxidation to sulfoxides was calculated from the integral ratios of methylene protons adjacent to sulfur atoms in 1H-NMR spectra. Poly(hexamethylene sulfoxide) was subjected to Swern oxidation of primary or secondary alcohols, in which 1-octanol and 6-undecanol were oxidized to give octanal and 6-undecanone, respectively, in quantitative yields.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050063
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  • 67
    Digitale Medien
    Digitale Medien
    Electrical conductivity in iodine-doped nonconjugated polyanilinefurfural (1997)
    Springer
    Polymer bulletin 38 (1997), S. 573-577 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Polyanilinefurfural (PAF) has been prepared. Its chain contains aromatic and furan rings, but the backbone is nonconjugated. However, when treatment with iodine, the color of PAF turns metallic black, and PAF becomes electrically conductive. The electrical conductivity of I2-doped PAF can reach 10−3 S ⋅ cm−1 which is more than 10 orders of magnitude higher than what was observed at the pristine state. The effects of iodine content on the conductivity of PAF and the conductivity stability were investigated. FTIR spectra, U.v./vis absorption spectra, E.s.r. measurement and X.p.s. measurement of the undoped and doped PAF were studied. This paper will demonstrate that: if given appropriate substituents and dopants, significant charge transfer may be expected even for nonconjugated polymers and it may display electronic conductivity to a certain level.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050090
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  • 68
    Digitale Medien
    Digitale Medien
    Factor analysis in the NMR characterization of multicomponent polymers (1997)
    Springer
    Polymer bulletin 38 (1997), S. 555-562 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Factor analysis has been found to be suitable for the analysis NMR data of polymers which contain multiple components. Two series of ethylene/propylene copolymers have been studied by this technique. In general, the number of components that can be resolved from NMR data depends on both the quality and the quantity of available experimental data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050087
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  • 69
    Digitale Medien
    Digitale Medien
    The role of complex formation in the anionic polymerization of l-lactide (1997)
    Springer
    Polymer bulletin 38 (1997), S. 609-612 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The rate lowering effect of crown ethers in the anionic polymerization of l-lactide is interpreted by the formation of activated monomer-cation complex. This interpretation is supported by molecular mechanics calculations. The formation of a 1 : 1 complex between lithium ion and l-lactide in THF was proved by 1H NMR and the formation constant was measured to be 3.8 M−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050095
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  • 70
    Digitale Medien
    Digitale Medien
    Application of a statistical method to study the spherulitic growth of polymer blends (1997)
    Springer
    Polymer bulletin 38 (1997), S. 601-608 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. This paper has two objectives. Firstly, to plan experimental blends (based on PVDF, PMMA and PVA) according to a statistical method proposed by Scheffé and subsequently to apply the model to the study of the spherulitic growth of PVDF with the aim of assess its suitability. In case it proved adequate, a simple method would become for the design of new materials from the polymer under study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050094
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  • 71
    Digitale Medien
    Digitale Medien
    An investigation into the synthesis of polycarbazole squaraine derivatives (1997)
    Springer
    Polymer bulletin 38 (1997), S. 493-499 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The polycondensation of squaric acid with 1,2-(9-Ethylcarbazol-3-yl)ethene and N-ethyliminostilbene in polyphosphoric acid yielded insoluble polymers which included substituted phosphate groups on the phenyl rings. The presence of phosphorus in these polymers was identified using solid-state 31P NMR and EDAX techniques. Furthermore the phosphate groups were not ionic, hence no charge-balancing anions were present. Both polymers did not electrically conduct but exhibited dielectric breakdown values of 0.1 and 0.06 MV cm−1 respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050078
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  • 72
    Digitale Medien
    Digitale Medien
    Comparative study on the lamellar crystal structure of high and low density polyethylenes (1997)
    Springer
    Polymer bulletin 38 (1997), S. 707-714 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. A comparative study was undertaken on well characterized HDPE and LDPE samples in order to obtain a better understanding of the morphology of the crystalline phase. Thickness of the lamellae was determined by WAXS. The melting points were calculated by empirical and Gibbs-Thomson equations, considering either folded or extended chains, and compared to DSC data. The results confirm that in HDPE the chains are folded, the segment between folds containing about 100 carbon atoms, while in LDPE, the chains are extended, with segments of about 73 carbon atoms in the crystalline core, linked to the paracrystalline layer and amorphous zones, which contain long folds and chain ends, as proposed in the 3-phase model by Vile et al.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050109
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  • 73
    Digitale Medien
    Digitale Medien
    The synthesis and thermotropic liquid crystalline behavior of the novel poly(aryl ether ketone)s containing chloro-side group (1997)
    Springer
    Polymer bulletin 38 (1997), S. 621-625 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The novel poly(aryl ether ketone)s containing chloro-side group were synthesized by nucleophilic substitution reactions of 4,4′-biphenol and chlorohydroquinone with either 4,4′-difluorobenzophenone (BP/CH/DF) or 1,4-bis(p-fluorobenzoyl)benzene (BP/CH/BF) and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. The thermotropic liquid crystalline behavior was observed in the copolymers containing 50 and 70% biphenol. Melting transition (Tm) and isotropization transition (Ti) both appeared in the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline state. The novel poly(aryl ether ketone)s had relatively higher glass transition temperature (Tg) in the range of 168 ∼ 200 °C and lower melting temperature (Tm) in the range of 290 ∼ 340 °C. The thermal stability (Td) was in the range of 430 ∼ 490 °C.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050097
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  • 74
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of wholly aromatic polyamides containing pendent amino and cyano groups (1997)
    Springer
    Polymer bulletin 38 (1997), S. 635-642 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The new pyrazole-ring containing diamine monomer with amino and cyano groups, 1,3-di-p-aminophenyl-4-cyano-5-aminopyrazole (PYA), was prepared from 4-nitrobenzoyl chloride and 4-nitrophenyl hydrazine with 4 steps. The monomer was converted to polyamides with terephthaloyl chloride and isophthaloyl chloride. The amino and cyano groups on the pyrazole-ring were not affected during polymerization. The synthesized polyamides having intrinsic viscosities of 0.92 – 1.18 dL/g were amorphous, and soluble in polar aprotic solvents and boiling acetone and THF. The polymers had high glass transition temperatures and high thermal stability. 5% weight loss temperatures in nitrogen occurred around 490 °C, but these polymers are partially degraded at 300 °C in air due to the amino group on the pyrazole-ring.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050099
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  • 75
    Digitale Medien
    Digitale Medien
    On-line HPLC 1H NMR coupling for the analysis of fatty alcohol ethoxylates (1997)
    Springer
    Polymer bulletin 38 (1997), S. 673-679 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The characterisation of fatty alcohol ethoxylate based surfactants by on-line LC-NMR coupling is described. Different surfactant mixtures were separated by a mixed exclusion-adsorption method of liquid chromatography and simultaneously characterised by 1H-NMR spectroscopy. Information about the degree of oligomerisation of the ethylene oxide chain and the chemical structure of the endgroups can be obtained in a one-step experiment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050104
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  • 76
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of polyamides based on cubane-1,4-dicarboxylic acid (1997)
    Springer
    Polymer bulletin 38 (1997), S. 651-655 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The direct polycondensations of cubane-1,4-dicarboxylic acid with 1,4-phenylenediamine (2 a), 4,4′-oxydianiline (2 b), 4,4′-sulfonyldianiline (2 c), and 9,9′-bis(4-aminophenyl)florene (2 d) were carried out in N-methyl-2-pyrrolidone/pyridine containing triphenylphosphite and lithium chloride at 110 °C for 9 h. Polyamide 3 a obtained from 2 a was scarcely soluble in organic solvent even during heating, and was soluble only in conc-H2SO4, whereas 3 c and 3 d derived from 2 c and 2 d, respectively, were readily soluble in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. After treating polyamide 3 d with the rhodium complex catalyst in NMP, cubane units were quantitatively converted into cyclooctatetraenes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050101
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  • 77
    Digitale Medien
    Digitale Medien
    Separation of block copolymers from parent homopolymers by means of liquid chromatography at the critical adsorption point (1997)
    Springer
    Polymer bulletin 38 (1997), S. 681-688 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The characterization of a block copolymer consisting of blocks of tetrahydrofuran, THF, and methyl methacrylate, MMA, was attempted with the aid of liquid chromatography, LC, at the critical adsorption point, CAP. The conditions applying to the CAP at 30 °C for the homopolymers are: PTHF: eluent composition: THF : acetonitrile = 50 : 50, w/w; column: Nucleosil C18. PMMA: eluent composition: THF : n-hexane = 81.8 : 18.2, w/w; column: bare silica gel. The presence of homo PTHF and of homo PMMA in the crude block copolymer was evidenced. Moreover, chromatography at the CAP for PMMA showed that the block copolymer contains multiblock (triblock) fractions. The formation of triblock copolymer is expected when the polymerization of MMA is terminated (partially) by combination. In conclusion, LC at the CAP is a powerful tool to characterize block copolymers regarding the presence of homopolymer and multiblock (triblock) fractions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050105
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  • 78
    Digitale Medien
    Digitale Medien
    New thermoplastic polyolefin elastomers from the novel Multicatalysts Reactor Granule Technology: their relevant physical-mechanical properties after crosslinking (1997)
    Springer
    Polymer bulletin 38 (1997), S. 701-705 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. A new process for the sequential copolymerization of olefins has been devised (Multicatalysts Reactor Granule Technology); it allows the synthesis of thermoplastic polyolefin elastomers having polypropylene from Ti-based catalysts and ethylene-propylene rubbers from metallocenes. Such new materials have been cured with peroxides and the relevant mechanical properties measured in comparison with those of heterophasic copolymers synthesized with traditional catalysts. It resulted that the new materials present an improved balance between strength and elasticity, especially at high temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050108
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  • 79
    Digitale Medien
    Digitale Medien
    Synthesis of graft copolymers by ring-opening polymerization of 2-nonyl- and 2-phenyl-2-oxazoline initiated by macroinitiators containing benzylchloride functions (1997)
    Springer
    Polymer bulletin 38 (1997), S. 657-664 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Graft copolymers with poly(2-nonyl-2-oxazoline) and poly(2-phenyl-2-oxazoline) graft arms have been synthesized using the "grafting from" method. Slightly branched statistical copolymers of isobutene and (m,p)-chloromethylstyrene, synthesized cationically, as well as linear homo-poly((m,p)-chloromethylstyrene) have been used as macroinitiators for the ring-opening polymerization of the substituted oxazolines. The graft copolymerizations were carried out in bulk and in benzonitrile solutions with and without addition of potassium iodide. The influence of the reaction conditions on the rate of polymerization and the different reactivities of 2-nonyl-2-oxazoline and 2-phenyl-2-oxazoline were discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050102
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  • 80
    Digitale Medien
    Digitale Medien
    The effect of stereoregularity on the thermal behavior of poly(methacrylic acid)s I. Thermal analysis studies (1997)
    Springer
    Polymer bulletin 39 (1997), S. 85-91 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The thermal degradation of a series of poly(methacrylic acid)s (PMADs) with different tacticities has been investigated under inert atmosphere. All the samples showed two main degradation stages. The first decomposition process of isotactic PMAD consisted of the formation of anhydride groups, almost quantitatively, by dehydration. In the case of PMADs with lower isotactic content, the elimination of water between neighboring carboxylic groups is less favored and the anhydridization shifts at higher temperatures where other degradation reactions may take place at the same time. The temperatures of maximum volatilization rates at the second step of decomposition increased in the order isotactic 〉 atactic 〉 syndiotactic.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050124
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  • 81
    Digitale Medien
    Digitale Medien
    Rheometrical behavior and equilibrium swelling in NR/BR/CEL II composites (1997)
    Springer
    Polymer bulletin 39 (1997), S. 117-124 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Natural rubber/butadiene rubber/cellulose II blends (NR/BR/CEL II) have been obtained by coprecipitation of the rubber latex-cellulose xanthate mixtures through acidulation. The elastomer ratio NR/BR has been varied from 100/0 to 25/75 and the cellulose content from 0 to 25 phr. The cure behavior of the compositions has been investigated by a Monsanto Oscillating Disk Rheometer. The results are a function of cellulose filler, NR, and BR contents. Some compositions were also analysed by equilibrium swelling in order to investigate polymer-filler interaction. The results show that composites with higher BR contents exhibit higher elastomer-filler attachment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050128
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  • 82
    Digitale Medien
    Digitale Medien
    Polymerization by phase transfer catalysis 22. Synthesis of poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from diphenols with the amide group in the side chain (1997)
    Springer
    Polymer bulletin 39 (1997), S. 9-14 
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    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from the diphenol-amides N-(2,6-dichloro-4-nitrophenyl)-2,2-bis(hydroxyphenyl)-propylamide (I), N-(2,6-dichloro-4-nitrophenyl)-3,3-bis(hydroxyphenyl)-butylamide (II), and N-(2,6-dichloro-4-nitrophenyl)-4,4-bis(hydroxyphenyl)-pentylamide (III), and phosgene or thiophosgene, have been synthesized under phase transfer conditions using several quaternary ammonium salts as phase transfer catalysts. Benzyltriethylammonium chloride (BTEAC) was effective in practically all cases due the hydrophilicity of this catalysts.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050113
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  • 83
    Digitale Medien
    Digitale Medien
    Interpolymer complex formation between form I helical and form II helical poly(l-proline) and poly(carboxylic acids) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 45-52 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Interpolymer complex formations between Form II helical poly(l-proline) [PLP(II)] and Form I helical poly(l-proline) [PLP(I)] and poly(carboxylic acids) such as polyacrylic acid (PAA), atatic polymethacrylic acid (at-PMAA), and syndiotatic polymethacrylic acid (st-PMAA) have been studied by FT-IR, X-ray diffraction, and light scattering measurements. It was found that the interpolymer complexes were formed via hydrogen bonding. The helical PLP(II) formed polymer complex more favorably with PAA and at-PMAA having a disordered structure than with st-PMAA having a ordered structure. In contrast, the helical PLP(I) formed polymer complex more favorably with st-PMAA than with PAA and at-PMAA. In addition, PLP(II) helix was destroyed on the complexation with PAA and at-PMAA, but the PLP(II) helix was perserved on the complexation with st-PMAA. However, the PLP(I) helix was all perserved on the complexation with poly(carboxylic acids). These findings could be explained in terms of molecular conformation of the complementary polymers associated with the complex formation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050118
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  • 84
    Digitale Medien
    Digitale Medien
    Local motion of crosslinks for poly(methyl methacrylate) gels by the fluorescence depolarization method (1997)
    Springer
    Polymer bulletin 39 (1997), S. 109-116 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Poly(methyl methacrylate) (PMMA) gels labeled at crosslinks with anthracene were prepared. Anthracene fluorescence depolarization was monitored to probe the local motion of crosslinks for PMMA gels at different equilibrium swelling states. The relaxation times and the activation energies of local motion were measured for PMMA gels at the swollen states in various solvents through fluorescence anisotropy decays. The local motion of PMMA gel at crosslinks became faster with the increase of swelling ratio. When the swelling ratios were almost the same, the mobility of crosslinks was the same irrespective of the molecular weights between crosslinks. These results indicate that the local motion of crosslinks for PMMA gel is mainly governed by the segment density of network chains in the vicinity of crosslinks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050127
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  • 85
    Digitale Medien
    Digitale Medien
    Influence of the structure and composition on surface tension of aqueous solution of graft copolymers of polyacrylamide backbone and polyalkyleneoxide branches (1997)
    Springer
    Polymer bulletin 39 (1997), S. 73-78 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Polyacrylamide homopolymers and graft copolymers of poly(acrylamide-g-ethylene oxide) and poly(acrylamide-g-propylene oxide) were synthesized, characterized by SEC, FTIR and 13C-NMR and the behavior of their aqueous solutions was evaluated by surface tension measurements. By using the macromonomer technique, it is more difficult to incorporate poly(propylene oxide) branches than poly(ethylene oxide) branches. Graft copolymers of polyacrylamide and poly(propylene oxide) showed higher reduction of surface tension than poly(acrylamide-g-ethylene oxide) since they present a structure made up of hydrophilic and hydrophobic segments. Poly(acrylamide-g-propylene oxide) exhibits surfactant behavior, and the surface tension of its aqueous solution depends on the poly(propylene oxide) graft chain length and amount.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050122
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  • 86
    Digitale Medien
    Digitale Medien
    Transition temperature control of liquid crystalline poly(heptene sulphone)s (1997)
    Springer
    Polymer bulletin 39 (1997), S. 179-184 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Liquid crystalline poly(heptene sulphone)s containing cholesteryl undecylenic ester and cholestanyl undecylenic ester were synthesized. The polymers displayed cholesteric mesophases during thermal transition. The clearing temperatures were from 114 to 172 °C depending on the molar ratio of mesogenic esters in the polymers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050136
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  • 87
    Digitale Medien
    Digitale Medien
    Molecular dimensions of poly(ethylene isophthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 257-263 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The rotational isomeric state (RIS) model was used to calculate the molecular dimensions of poly(ethylene isophthalate) (PEI) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) by introducing new description for aromatic segments and by adopting the statistical weight parameters of PET. The mean square dimension ratios ((〈r2〉0/M)∞) of PEN and PEI were 0.653 and 1.167, respectively, and the entanglement molecular weight (Me) of PEI and PEN were 1850 and 1810, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050146
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  • 88
    Digitale Medien
    Digitale Medien
    Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels (1997)
    Springer
    Polymer bulletin 39 (1997), S. 233-239 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050143
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  • 89
    Digitale Medien
    Digitale Medien
    Highly flexible heterophasic copolymers through the novel multicatalysts reactor granule technology (1997)
    Springer
    Polymer bulletin 39 (1997), S. 241-247 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. New heterophasic copolymers with high rubber content have been synthesized by combining heterogeneous Ti-based catalysts with metallocenes. The molecular, morphological and mechanical features of these materials were evaluated: it was pointed out that the new copolymers, having more than 60 Wt.% of rubber, perform as reinforced elastomers whereas traditional ones show a more plastomeric behaviour. This suggests that new polyolefin materials can augment rather than compete with the traditional ones.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050144
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  • 90
    Digitale Medien
    Digitale Medien
    Ethylene-propylene copolymers by a supported Ziegler-Natta catalyst based on TiCl4/MgCl2 (1997)
    Springer
    Polymer bulletin 39 (1997), S. 133-140 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. Ethylene-propylene copolymers have been prepared by using Ziegler-Natta catalysts based on TiCl4, MgCl2, PCl3 and (n-Bu)3PO4. The catalysts TiCl4/MgCl2/PCl3 and TiCl4/MgCl2/(n-Bu)3PO4 were prepared by reacting TiCl4 with pretreated MgCl2. The support was prepared by ball milling of MgCl2 with varied amounts of PCl3 or (n-Bu)3PO4. The addition of PCl3 has remarkably increased the MgCl2 surface area in comparison with (n-Bu)3PO4. The effects of PCl3 and (n-Bu)3PO4 on ethylene homopolymerization, ethylene-propylene copolymerization and on copolymer properties were evaluated. The catalyst system containing PCl3 permitted to synthesize propylene-ethylene copolymers with up to 75% (w/w) of propylene and provided control of copolymer crystallinity. The reduction of the copolymer molecular weight distribution suggested that PCl3 acted as an internal donor, poisoning some active catalytic sites.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050130
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  • 91
    Digitale Medien
    Digitale Medien
    Grafting of side chain liquid crystal monomers onto polyethylene film (1997)
    Springer
    Polymer bulletin 39 (1997), S. 489-494 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. In order to obtain films of liquid crystalline polymers, a commercial polyethylene film was grafted with acryloyl chloride using γ-irradiation, and two tolane-containing alcohols were reacted with the chloride to obtain the corresponding acrylates. The morphology changes were studied by DSC, X-ray diffractometry and optical microscopy. The crystallinity of polyethylene films decreased by grafting, and mesophase with spherulites was observed over a wide temperature range.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050177
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  • 92
    Digitale Medien
    Digitale Medien
    Polymer-polymer interaction and modeling (1997)
    Springer
    Polymer bulletin 39 (1997), S. 519-526 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The nature of intermolecular interaction in PVC/EVA system was investigated. Bathochromic shifts in infrared region revealed that not only EVA carbonyl but the ester group participates on interaction with PVC chain. These shifts were proportional to acetate content in the copolymer and the composition of EVA in the blend. The PVC group that effectively participates on interaction was not elucidated by infrared spectrometry, but molecular modeling of low molecular weight analogues indicated that hydrogen bonding is the most probable kind of intermolecular interaction present in this system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050181
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  • 93
    Digitale Medien
    Digitale Medien
    Application of an association model to the PVC/EVA system (1997)
    Springer
    Polymer bulletin 39 (1997), S. 527-534 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. A thermodynamic association model was applied to the PVC/EVA system. In this model the enthalpy component is related quantitatively to intermolecular interaction forces. Molecular modeling was applied to obtain the parameters related with interaction forces. The phase diagrams showed lower critical solution temperature (LCST) behavior and also biphasic regions in PVC rich compositions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050182
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  • 94
    Digitale Medien
    Digitale Medien
    Synthesis, characterization, and properties of an efficient and selective adsorbent to mercury(II) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 445-452 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The synthesis of a water-insoluble adsorbent resin was carried out by radical polymerization of [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride by using ammonium peroxydisulfate as initiator and N,N′-methylene-bis-acrylamide (MBA) as crosslinking reagent. The adsorbent was characterized by elemental analyses, and FT-IR spectroscopy. The thermal stability was studied in the presence of Hg(II). The ability to bind Hg(II), Cd(II), Zn(II), Pb(II), Cu(II), Cr(III), and U(VI) as well as the maximum adsorption capacity, and elution of the Hg(II) from the loaded resin was studied. At pH 2 the adsorbent retained 95% of Hg(II) from an aqueous solution containing 1 g/L in Hg(II). The retention of other metal ions was lower than 15%. Sorption selectivity from the binary mixtures Hg(II)-Cd(II), Hg(II)-Zn(II), Hg(II)-Pb(II), and Hg(II)-Cr(III) was studied at the optimum sorption pH value.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050171
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  • 95
    Digitale Medien
    Digitale Medien
    Dendrite polymers from vinyl ether (1997)
    Springer
    Polymer bulletin 39 (1997), S. 399-406 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. 1-[(2-Vinyloxy)ethoxy]ethyl acetate (1) was prepared by the addition reaction between ethylene glycol divinyl ether and acetic acid. 1 contains both a cationically polymerizable C=C double bond and a dormant initiating moiety for cationic polymerization. It can, therefore, undergo self condensing cationic polymerization in the presence of a Lewis acid activator, such as zinc chloride. Using this procedure, a novel dendritic polymer consisting of vinyl ether was prepared and its hyperbranched molecular structure confirmed by FT-IR and 1H NMR spectra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050165
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  • 96
    Digitale Medien
    Digitale Medien
    On a novel molecular microstructure based approach to the extrinsic space charges releasing in polypropylene (PP) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 639-646 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The release of the extrinsic charges produced when applying an electric stress has been studied for four polypropylene samples of distinct well controlled molecular microstructure by Thermal Stimulated Discharge Current (TSDC), with the aim of stating the correlation between the ρ relaxation (intensity and temperature) and the tacticity induced polymer microstructure, and of, demonstrating that the traps of space charges are not chain defects as usually proposed but that they relate to some normal local chain configurations. The results are discussed in the light of the space charge distributions as measured in earlier recent work.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050197
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  • 97
    Digitale Medien
    Digitale Medien
    Regioselective introduction of β-galactoside branches into chitosan and chitin (1997)
    Springer
    Polymer bulletin 39 (1997), S. 543-549 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. β-d-Galactoside branches have been introduced into chitosan and chitin regioselectively through a series of controlled modification reactions based on N-phthaloyl-chitosan. The glycosylation reaction between a chitosan derivative having a reactive group only at C-6 and an orthoester of d-galactose proceeded efficiently to give a protected product with a degree of substitution up to about 0.5. Deprotection gave a branched chitosan, and the subsequent N-acetylation afforded a branched chitin. Unlike chitosan and chitin, the resulting nonnatural branched polysaccharides were characterized by high affinity for solvents and readily soluble in neutral water. Furthermore, branched chitin was easily degraded by lysozyme.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050184
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  • 98
    Digitale Medien
    Digitale Medien
    Effective catalysts for polymerization of cyclohexene oxide: Preparation of novel Martin-type pentacoordinate silicates (1997)
    Springer
    Polymer bulletin 39 (1997), S. 573-579 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The novel dialkylanilinium salts of pentacoordinate Martin-type silicates were prepared. They were found to be air stable catalysts for polymerization of cyclohexene oxide. The preparation of those silicates bearing a bulky substituent such as mesityl group was not successful.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050188
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  • 99
    Digitale Medien
    Digitale Medien
    Molecular packing of poly(azomethine)s having flexible (n-alkyloxy)methyl side chains in films (1997)
    Springer
    Polymer bulletin 39 (1997), S. 701-705 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. The molecular packing of poly(azomethine)s having (n-alkyloxy)methyl side chains in films was studied by wide-angle X-ray scattering. Solution-cast films on silicon wafer and melt-sheared films show the same type of molecular packing, i.e. the main chain layers are aligned parallel to the film surface but the main chains are macroscopically isotropic in the film surface plane. In the melt-sheared films, the shear does not orient the main chains but the main chain layers, which can be easily understood by their geometric shapes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050205
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  • 100
    Digitale Medien
    Digitale Medien
    Characteristics of permeation and separation of dimethyl acrylamidemethyl methacrylate random and graft copolymer membranes for a benzene/cyclohexane mixture (1997)
    Springer
    Polymer bulletin 39 (1997), S. 733-740 
    Details
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract. When a benzene/cyclohexane mixture was permeated through poly(dimethyl acrylamide-random-methyl methacrylate) (DMAA-r-MMA) and poly(dimethyl acrylamide)-graft-poly(methyl methacrylate) (DMAA-g-MMA) membranes by pervaporation, the benzene-permselectivity of the DMAA-r-MMA membrane changed from the diffusivity selectivity to the solubility selectivity with increasing DMAA content but DMAA-g-MMA membranes with a high DMAA content had the higher apparent diffusivity selectivity than the apparent solubility selectivity. Furthermore, the apparent solubility selectivity for a benzene/cyclohexane mixture between the DMAA-r-MMA membrane and the DMAA-g-MMA membrane with a high DMAA content was remarkably different. These results were attributed to the difference of structure between the copolymers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002890050210
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