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  • 1990-1994  (1.445)
  • 1980-1984
  • 1992  (1.445)
  • Engineering  (757)
  • Chemical Engineering  (688)
  • Nuclear reactions
Materialart
Erscheinungszeitraum
  • 1990-1994  (1.445)
  • 1980-1984
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 275-288 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents the simulation of a class of MIMD systems using discrete-event simulation enhanced by graphics-oriented reporting. MIMD systems can be specified, modelled and simulated using the package and in turn provide estimates of certain performance indices. A multiserver queueing model is constructed to describe the flow of data and instructions through the various elements of the system. The model is composed of P processors sharing M memory modules through a user-defined interconnection network. Graphical outputs allow the user to view the state of every processor/memory module over the simulation time with performance estimates such as the relative speedup, throughput, and utilization factor. Moreover, system performance graphs as a function of various system parameters are obtained to indicate the expected system behaviour for various loads and system configurations. The results section shows a case study of the influence of the memory modules' access time on the system performance. The purpose of the results is to aid in the analysis, understanding, design, and performance prediction of a class of MIMD systems in a user-friendly environment.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 83-92 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The permeability tensor of the homogeneous bulk material externally equivalent to a laminated packet of non-linear, anisotropic, non-hysteretic sheets is derived by symbolic computation. The composite permeability bears a surprisingly simple algebraic relationship to the local permeabilities of its component materials even in the general case. Several special cases of common interest, where the tensor permeability assumes symmetric or diagonal form, are examined. Results are presented both as algebraic expressions and as brief optimized Fortran subroutines suitable for fitting into field analysis programs.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 111-120 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In this paper, the method of transmission-line modelling is used to determine the transient response of a lossy transmission line. Non-linearity and frequency-dependent parameters (R and G) can be included without undue difficulty. Several numerical examples are described and are compared with exact and/or experimental results. In all cases good agreements are obtained.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 139-139 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 121-127 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A random flight model of linear transport processes in two spatial dimensions is considered and solved exactly in closed algebraic form. Its one-dimensional version had been proposed by Taitel as a means to overcome the paradox of infinite speed of propagation within classical heat diffusion theory. The connection with hyperbolic diffusion theory is complemented here by deriving the discrete fluxes and their relaxation term. Moreover, such an approach circumvents the discretization of a continuum model for an intrinsically discrete process, when diffusion processes are to be solved numerically. Finite samples are treated by means of the reflection method. Some applications of these general results are mentioned.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 143-144 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 149-161 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Under wideband and especially ultrawideband (short pulse) excitation, the electromagnetic fields, after encounters with a propagation or scattering environment, reveal features which range from highly resolved spikes or dips to smooth oscillations at early and late observation times, respectively. Time-domain (TD) analytic modelling should be structured around wave objects which relate features (observables) in data to distinct features in the environment. A strategy to this end, named observable-based parametrization (OBP), is proposed here. The rules are learned from frequency- and time-domain asymptotics applies to spatial and spectral domain representations of tractable prototype problems. This leads to self-consistent hybrid combinations OBP-TD travelling (wavefront) and oscillatory (resonant) synthesizing basis fields; the latter include novel TD leaky modes for guiding wave channels and TD Bragg modes for periodic arrays. These concepts are illustrated by examples.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 183-201 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An approach for numerically integrating the partial differential equations describing passive physical systems consists in modelling the continuous-domain physical system by means of a passive discrete-domain system. As has recently been shown, this can be achieved, in particular also for Maxwell's equations, by means of the same principles as known from multidimensional wave digital filters, which offers a number of important advantages. The present paper deals specifically with the application of the approach to Maxwell's equations and supplements corresponding results previously published.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 203-218 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: There is an increasing interest in the numerical modelling of physical and biological processes using cellular automata or cellular systems. One of the main advantages in using the concept of cellular systems is the inherent high degree of parallelism. The purpose of the contribution is to formally relate two different areas: time-domain modelling of physical processes using cellular systems and massive parallel implementations. At first, an overview of applications of cellular systems in computation theory and in modelling of physical systems and an overview of implementations of cellular systems is given. The subsequent sections address the following two questions: (1) Which class of algorithms can be interpreted as cellular systems. (2) Can cellular systems be efficiently simulated on a given parallel architecture. Results concerning these issues are presented.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 163-182 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An overview is given on the application of finite difference time-domain analysis techniques to the simulation of electromagnetic wave phenomena and the design of planar microwave integrated circuits. In particular the application to the analysis of three-dimensional discontinuities in coplanar microwave circuits is described and numerical and experimental results are presented. Finally the design of planar microwave circuits containing non-linear active components using the finite difference time-domain method in combination with a harmonic balance technique is demonstrated using an example of a LUFET circuit.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992) 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. i 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 251-257 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper details general expressions for implementing timestep transformations in transmission-line matrix (TLM) modelling of diffusion processes. The expressions can be conveniently incorporated into any TLM routine which models multidimensional problems using a variable meshing technique.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 227-243 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Purpose of this work is to present a new macromodelling approach for the simulation at the device level of large MOS integrated circuits, requiring only marginal modifications to be implemented in the widely used circuit simulator SPICE. This method results in a substantial saving in computing time and guarantees the same accuracy of SPICE. A prototype simulator based on this method has been developed and used to analyse several significant circuits. In addition, since the method is particularly suitable to be implemented in parallel computers, some results obtained with the CRAY-YMP/432 computer are provided.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 23-39 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An efficient algorithm is presented for the self-consistent numerical solution of the single-band effective mass equation. This algorithm has a different form depending on whether the effective mass is modelled as continuous or piecewise continuous. Coupled with a Poisson solver, an established algorithm is applied for the attainment of self-consistency. The rate of convergence to a self-consistent solution is investigated, and the solvers are applied to three different structures to demonstrate its versatility and robustness. The first of these is a nominally undoped quantum well AlGaAs/GaAs heterostructure, the second a doubly δ-doped GaAs homostructure and lastly a quasi-square well modulation-doped field effect transistor. The algorithm is of sufficient efficiency so as to allow the software to run reasonably quickly on a modern microcomputer.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992) 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 17
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992) 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 18
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 53-66 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper reviews the state of the art in hydrodynamic simulation of hot-carrier transport in semiconductor devices with application to MOSFET substrate current calculation. Hydrodynamic equations for semiconductors and derived and discretized expressions of these equations for device simulation are presented. Special attention has been given to the discretization of the input power term that appears in the energy conservation equation. A new discretization method for the input power term, based on power generation consideration, is proposed. Energy-based physical models for mobility and impact ionization are described for use in hydrodynamic simulation. Simulation results for both conventional and lightly-doped-drain MOSFETs are presented.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 67-81 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A novel spectral procedure for the numerical solution of non-linear boundary value problems is presented. The discrete spectral equations are solved by an iterative algorithm using space-domain preconditioning. The preconditioning operator is obtained by spatial weighting (or windowing) of the exact differential operator.Convergence behaviour of the iterative solution is investigated using an eigenvalue analysis. Theoretical estimates for the convergence rate and accuracy are compared with that achieved in a numerical application - a non-linear boundary value problem from semiconductor device modelling.The method combines the infinite-order exponential accuracy of spectral discretizations with the sparse structure of finite difference equations. This offers numerical advantages in comparison to previously developed Fourier-Galerkin algorithms, particularly important for physically ill-conditioned and strongly non-linear problems. The tradeoff of achievable accuracy versus computer time is easily controlled, thus making essential speed-ups possible for moderate accuracy requirements.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 93-110 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In this paper the application of the TLM method to electromagnetic scattering problems is investigated. To achieve the full computational benefits of using a time-domain numerical method, pulse excitation can be applied together with Fourier transformation of an output impulse response to yield frequency-domain results over a wide bandwidth. The configuration of the mesh is the same as that used in FD-TD scattering simulations (i.e., separation of the simulation space into total and scattered field regions). To terminate the exterior boundaries of the mesh, absorbing boundary conditions are applied to absorb the outward travelling waves. The effect of the absorbing boundaries on both time- and frequency-domain results is investigated. Frequency-domain scattered far-field patterns are presented for perfectly conducting square and circular cylinders illuminated by an incident plane wave (TM case). Forward and back scattering cross-section results obtained from a single TLM simulation indicate both the accuracy and efficiency of the method for calculating frequency-domain results over a wide bandwidth.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 129-137 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper reports the results of a study of an error parameter, m, which has been proposed as a measure for determining the effects on accuracy of the basic assumptions upon which TLM modelling of diffusion and heat flow has been founded. The nature of the m parameter is studied in detail by using a two-dimensional thermal diffusion problem. The use of m in the implementation of automatic timestepping is discussed in a practical three-dimensional engineering problem.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992) 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 141-141 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 145-147 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 219-225 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The paper provides an extension to the one-dimensional TLM diffusion model. The extended diffusion node presented here models the exact transport equation with diffusion drift and recombination of charge carriers in semiconductors. A general algorithm for providing a numerical solution to the transport phenomena is also presented here. The analytical solution for infinitely long semiconductors is compared with the TLM numerical results.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 245-250 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In order to efficiently store the information of a special class of matrices, a very useful algorithm has been derived and applied to the subsectional basis function approach to the method of moments. The algorithm represents a simple law of mapping and allows a reduction in the required computational storage by several orders of magnitude.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 259-274 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Three numerical methods are applied to the analysis of a rectangular waveguide-fed aperture radiating into a lossy media. A novel approach, the finite element method with an impedance boundary condition, and two established methods, the moment method and the mode-matching method, are presented. The methods are compared with respect to accuracy, execution time, memory requirement, and versatility. Four aperture geometries are chosen for detailed study: the full aperture of the rectangular waveguide, and three reduced apertures. The reflection coefficient of the aperture in contact with five known dielectrics is calculated in the frequency range 8·5-11·5 GHz. The theoretical results are validated by measurements performed on an HP8510 network analyser.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 289-295 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper describes an application of transmission-line modelling (TLM) for the solution of heat diffusion in a three-dimensional metallic structure, surrounded by a dielectric material. The example of heat propagation along an electric fuse embedded in granular silica is presented. Heat is generated by the flow of an electric current through the metallic element and results are shown for the variation of temperature with time and temperature distribution along the fuse element.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 11-21 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A novel algorithm has been implemented within our new semiconductor device simulation program TESSA that allows large signal periodic time-domain simulation to be performed by integrating over just one period of the excitation. Conventionally the need to integrate out initial transients, over many cycles, had effectively made such simulations impracticable. The algorithm can also be implemented in the field of circuit simulation so a combined large signal circuit/device simulation package is now a practical possibility.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 41-52 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A numerical time-domain modelling of non-linear microwave circuits is presented. It is based on a numerical procedure allowing the solution of the integro-differential equation driving the instantaneous electrical behaviour of a lumped-element circuit while accounting for the semiconductor device by means of an accurate numerical macroscopic model. This modelling is firstly validated by studying the DC turn-on and DC forward-reverse commutation of a PIN diode. The diode voltage and current waveform are qualitatively consistent with experimental ones, Moreover, the predicted recovery time values are found to be in good agreement with those issued from the classical analytical theory. Secondly, in order to illustrate the present capabilities of the model, the whole transient response of a back-to-back silicon PIN diode passive power limiter to a high-input-RF-power pulse is described. It is demonstrated that in the present case of a 2 μm-long PIN diode, the high-input-power steady-state operation only relies on one diode. To our knowledge, it is the first time this kind of simulation is applied to a two-diode circuit.
    Zusätzliches Material: 8 Ill.
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  • 31
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 1-1 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 32
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 3-9 
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A detailed one-dimensional energy transport model for unipolar GaAs/AlGaAs heterojunction structures is implemented, by extending the basic transport equations to include the energy balance equation for electrons. A non-uniform grid-mesh is used to obtain short simulation times, while the grid-distance at the N-n++ interface is small, which is essential to obtain a low reverse current.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1605-1609 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Au patterns are formed by photographical patterning of polymeric Au mercaptoterpenes (Au resinate), followed by bakeout of the Au resinate patterns to remove carbonaceous materials. Since commercially available Au resinate is not sensitive to 436 nm (g-line) light and cannot be photographically patterned, we mixed azide (photocrosslinker) with Au resinate to give photosensitivity to the g-line. The mixture of Au resinate and azide was spun on an Si substrate, and then exposed with 436 nm (g-line) light by a standard contact printing technique. Upon exposure, Au resinate was crosslinked by the reaction with azide, and became insoluble. Au resinate patterns were generated by development with monochlorobenzene. On baking out the Au resinate patterns to remove carbonaceous materials, we obtained 2 μm line and space Au patterns. The conductivity of the Au patterns obtained was 1/4 that of bulk Au. For a mask repair application, we mixed Cr resinate with a mixture of Au resinate and azide to improve the adhesion of the resulting metal patterns onto the quartz plate. The transmittance and the adhesion were found to depend on the bakeout condition and the mixing ratios of the Cr resinate. Bakeout in vacuum with 0.1 torr oxygen gave far better adhesion and opaqueness than bakeout in air, because of residual carbon in the resultant metal. Mask repair was carried out at the optimized condition by using a spot exposure system. The clear defect was repaired with the transmittance 〈 1% and good adhesion.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1623-1629 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An overview is given on auto-photosensitive polyimides as introduced for the first time in 1985. It is shown how development proceeded and how the chemical basis of auto-photosensitive polyimides was extended beyond BTDA. Novel “photosensitizer tetracarboxylic dianhydrides” like 2,3,6,7-thioxanthonetetracarboxylic dianhydride (TXDA) were synthesized and copolymerized into preimidized nonphotoactive polyimides containing tetracarboxylic acids like 6FDA or ODPA. Novel photosensitive polyimides were obtained that carry all essential features of BTDA based systems plus higher photospeed. They provide the ability to better tailor material properties to specific applications.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1695-1702 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of rubber particle size and rubber/matrix adhesion on the impact properties of a brittle polymer have been separated using polystyrene (PS)/acrylonitrile-butadiene rubber (NBR) as a model system in which interfacial chemical reaction could be controlled. It has been proven that the interfacial adhesion between the rubber phase and the PS matrix not only greatly aids in reducing the rubber particle size but also plays a further role in improving the impact properties of the matrix polymer. The impact energies of PS/NBR blends with interfacial chemical bonding are four to ten times as high as those without interfacial bonding for the same average rubber particle size. However, at temperatures below the glass transition temperature of the rubber, there is no difference in impact energies with or without interfacial chemical bonding. It has been found that the optimum rubber particle size for toughening PS is influenced by interfacial adhesion. Smaller optimum rubber particle size is observed for blends with greater amounts of interfacial chemical bonding.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1703-1710 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An increasing number of polymer alloys made by reactive processing of a compatibilizer precursor (CP) to form the compatibilizer in situ have appeared in recent years. Literature reports on compatibilization studies have focused on interactions of chemistry-morphology, processing-morphology, morphology-rheology, morphology-properties, etc. In commercial alloys, the interaction of chemistry and processing results in a material that has a balance of physical properties and rheological behavior. To maximize the contribution of each phase, it is of interest to be near the phase inversion region. In this work, maleic anhydride functionalized polyethylene is used as an effective CP for polyamide/polyethylene blends. In blends containing 50% nylon 6, the melt viscosity of the alloy increases exponentially as the ratio of CP to polyethylene increases though the morphology remains dispersed polyamide 6. High ratios of CP/PE are desired for toughness, alloys containing lesser amounts of CP exhibit better processability. The balance of toughness and processability is shown to be affected by the molecular weight of the CP.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1750-1754 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: For two high density polyethylene resins, the isothermal time dependency of extrudate swell has been measured. Very minor differences in the large molecular weight part of the molecular weight distribution, hardly detectable with gel permeation chromatography and low angle laser light scattering techniques, dramatically influence the time dependency of extrudate swell as well as the maximum swell attainable. The presence of larger molecules in sample 802 than in 801 is reflected in a lower short time (after seconds) and a larger long time (after minutes) or maximum extrudate swell value. Extruding the polymers through a capillary die L:D = 30:2 mm into air at ambient temperature allows only the short time swelling behavior to be observed, because cooling and sagging of the strand.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1824-1833 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ≥ 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, φd ≥ 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin-screw extruder. Their value is limited to serving as general guides to the process modeling.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1834-1845 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In Part II of the work, the intermeshing twin-screw extruder is briefly described and the theoretical procedures used to model its operation are summarized. Based on the microrheological considerations discussed in Part I, a predictive procedure of the morphology evolution during compounding of two immiscible polymers is proposed. In this first generation model, only the shear flow effects are considered. Furthermore, to avoid complications due to coalescence a low concentration of the dispersed phase was assumed. In the procedure, two drop breakup mechanisms are discussed. The first assumes that the drops do not break under flow while the second postulates that breakup occurs under flow. Two dispersion mechanisms are considered, the first postulating continuously increasing polydispersity of drop size and the second postulating that drop polydispersity is inversely proportional to deformation strain. The influence of the screw configuration and operating conditions on blend morphology evolution is studied. It is expected that the computed drop size distribution provides limiting values for the experimental data. Dependency of predicted morphology on operating conditions is also investigated. Increasing screw rotating speed (resulting in increasing energy consumption) and decreasing throughput (resulting in decreasing productivity) lead to prediction of finer drop size. In practice, therefore, a compromise would be required. The proposed procedure is limited to melt flow (excluding the die region) within the region of large capillary parameter values, k 〉 4kcrit.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1857-1862 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress-strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the system.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 41
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 383-391 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effect of short-length carbon and Kevlar fibers on the crystallization of isotactic polypropylene (iPP) in composites prepared by compression molding has been investigated. The tendency of carbon and Kevlar fibers to nucleate the iPP during isothermal and nonisothermal crystallization has been evaluated by differential scanning calorimetry. The influence of different thermal histories used to prepare the unreinforced and reinforced samples on the crystallization parameters of iPP was examined. In addition, the tensile behavior was related to the resulting morphologies of the samples. It was observed that the crystallinity content, obtained by using different thermal treatments (slowly cooling or quenching), gives rise to different morphologies by influencing the mechanical behavior of materials as well. Moreover, the composites obtained by slow cooling seem to present a better fibber/matrix adhesion then that found in quenched samples. Possible underlying microstructures, which can explain the properties and the morphological characteristics, are also discussed.
    Zusätzliches Material: 21 Ill.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 409-414 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A series of bismaleimide resin systems has been examined in order to identify the molecular features responsible for the mechanical response of these materials. A range of network structures was produced both by formulation of resins with different ratios of N,N′-bismaleimido-4,4′-diphenylmethane (BMI) and methylene dianiline (MDA), and by the use of different thermal processing cycles. Spectrographic and chromatographic techniques were used to study the reactions that occurred during the cure. Two principal reactions were confirmed: a Michael addition reaction which provides linear chain growth, and an addition reaction which produces crosslinking through the double bonds of the maleimide group. In general, curing at a lower temperature or increasing the MDA content served to favor chain extension over crosslinking, which might be expected to increase molecular mobility in the resin.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 400-408 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Thermotropic LCP/LCP fiber blends were prepared by a combination of meltblending and hot-drawing, using a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman). Morphological evidence, including scanning electron (SEM) and transmission electron microscopy (TEM), showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 μm diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic LCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. The fiber blends were characterized using dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), gas chromotography/mass spectroscopy (GC/MS), and rheological measurements. It appears that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two LCP components during the melt blending process. Differential scanning calorimetry (DSC) thermograms as well as nuclear magnetic resonance (NMR) spectra of the extracted fraction from the mixture of 30 wt% K161/70 wt% PET(PHB60) confirmed the chemical interaction between the two thermotropic liquid crystalline polymers.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 426-430 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A foam rheometer has been developed based on the impulse theory of linear viscoelasticity. The rheometer is a large-volume parallel-plate device which operates under gap-loaded conditions, and is designed as an add-on fixture for the Materials Testing System Model 312. The rheometer provides characterization data of the pre-gel (via the zero-shear viscosity) or the post-gel (via the equilibrium modulus) properties of a foaming cellular polymer with a precision of better than ± 15%.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 443-447 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The usefulness of waste (mainly cellulosic) materials as a reinforcement for acrylonitrile-butadiene rubber (NBR) compounds is shown in this work. The materials tested are: henequen, pine, coconut, sugarcane husks, lignin, and wood sawdust. Their performance is compared with that of commercial reinforcement materials (santocel and solka), using the same copolymer composition without reinforcement as a reference compound. Uniform particle size is achieved by milling and screening. For some of the materials, 6 mm fibers and polymerfiber coupling agent are also tested. Reinforced copolymer formulations are prepared by milling. Optimum curing times are determined with a torsion rheometer. Mechanical and rheological tests (stress-strain behavior, tear resistance, hardness, interfacial strength, storage modulus, and loss tangent), show promising results for some materials, especially when looking for a reinforced product with low dissipation energy.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 46
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 457-466 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: To understand the performance of multicomponent reactions in twin screw extruders the mixing mechanism in the extruder had to be understood. Therefore, two new relevant mixing parameters are defined; the mixing efficiency, which is the average number of passages of material through a high shear region; and the mixing deficiency, which is the fraction of material that does not pass through a high shear region. With these parameters an analysis can be made of the mixing circumstances in the extruder. The new model was applied to the polymerization of urethanes in a counter-rotating twin screw extruder. The results agreed very well with the theoretical expectations.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 47
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 467-474 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The grafting of maleic anhydride (MAH) on high density polyethylene in a counter-rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non-linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 48
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 582-585 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Deep penetration welding of polymers can be carried out at high speed with relatively low laser power. This results from an efficient coupling CO2 laser radiation to polymers that leads to volume heating. A brief review of energy coupling and heat transfer effects in polymers under CO2 laser welding conditions is given. Some examples of low power (10 to 100 watt) CO2 welding of polypropylene and polyethylene at depths of up to 1.5 cm are discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 593-599 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Fatigue data are presented for the strengths of 120-Hz vibration-welded butt joints of four resins: the three amorphous polymers polycarbonate (PC), polyetherimide (PEI), and modified polyphenylene oxide; and the semicrystalline polymer poly(butylene terephthalate). Data are also presented for the fatigue strength of 250-Hz vibration welds of the high-temperature polymer PEI. For all the welds, fatigue strength was evaluated through 10-Hz, tension-tension, load-controlled tests at an R value (ratio of minimum stress) of 0.1. Surprisingly, for all the stress levels studied, none of the PC test specimens failed at the welds, indicating that the fatigue strength of PC welds equals that of the base resin. This is not true of the other three resins, except at relatively low stress levels. For each of the four resins, macrographs are used to highlight the differences between the failure surfaces of monolithic specimens and specimens that failed at the welds.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 50
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 612-619 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The influence of tie-layer Melt Flow Index on the lap-shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie-layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap-shear strength properties were obtained using tie-layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie-layers, hot spot formation and concomitant changes in fusion zone and heat-affected-zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie-layers were used, the mode of failure during lap-shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie-layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo-oxidative processes.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 51
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 620-631 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A study to investigate fusion bonding (welding) of AS4 graphite/polyetheretherketone (PEEK) thermoplastic composites is presented. Processing studies are conducted for resistance welding preconsolidated AS4/PEEK laminates in both unidirectional and quasi-isotropic configurations using PEEK and polyetherimide (PEI) film at the joint interface. All bonding was done under a constant displacement process. The influence of processing time, initially applied consolidation pressure, and the rate of heat generation on weld performance is examined through lap shear and Mode I interlaminar fracture toughness testing. A rapid increase in strength with processing time that asymptotically approaches the compression molded baseline is measured. Weld times for quasi-isotropic lap shear coupons are significantly shorter than those with a unidirectional lay-up. Variation of the initially applied consolidation pressure is shown to have little influence on the lap shear strength of PEEK film welded lap joints. A discussion of the mechanisms allowing void formation during the welding process is given. Bond strength test results are correlated with ultrasonic C-scans of the weld regions.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 221-230 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A critical part of any master model used to simulate or control a composite material manufacturing process is the description of resin flow through the fiber bed. We present here a review of both theoretical and experimental studies of fluid flow through porous media, including fiber beds. For the practical porosity range of interest in continuous fiber composites processing (0.3〈 ∊ 〈 0.6), the permeability cannot be accurately described using the Blake-Kozeny-Carman equation, even though the flow is Newtonian at very low Reynold's number. For aligned fiber situations, the Kozeny constant, k, deviates radically from theory, depends on bed nonuniformities, and is only constant over very narrow porosity ranges. Thus, one cannot experimentally determine k at high porosities and use this value to describe low porosity situations. Theoretical attempts, based on perfectly spaced and aligned arrays of cylinders, adequately describe the transverse permeability of ideal fiber beds in the high porosity range, but do not succeed at porosities below 0.6. For axial flow through aligned fiber beds, the theory yields permeabilities much lower than are experimentally observed throughout the entire porosity range. For randomly arranged fibers, random cylinder theory also predicts permeabilities that are significantly lower than are measured.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 53
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 267-272 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of thermal modification on the structural properties were studied for a poly(ethylene terephthalate-co-p-hydroxybenzoic acid) liquid crystal bended with phenoxy resin. Poor miscibility and phase separation between the blend components are observed by the temperature dependence of dynamic mechanical properties of sample molded at 260°C, over the composition range studied. The miscibility of the blends is increased by molding at 280°C, and the blends molded by increasing the processing time show a dynamic mechanical transition to a homogeneous blend. These changes are the result of an interchange reaction between the blend components. A rubbery modulus has been observed for such blends. This implies the formation of cross-linked structures that accompany the interchange reactions.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 54
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 231-239 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Proper description of the resin flow through fibrous media is an important input to the modeling of composite manufacturing processes. Based on our conclusions in a recent review of pertinent literature (see Part I, this issue), Newtonian flow through ideal cylinder arrangements has been analyzed and measured. The analytical and numerical solutions agreed well with both our own experimental observation and those of others. Experiments with actual carbon fiber beds revealed significant deviations from ideal bed behavior. These deviations include dependence of the permeability on the nature of the permeant and the applied pressure difference, both of which make questionable the use of the Blake-Kozeny-Carman (BKC) equation to describe flow in real carbon fiber beds. Experiments that simulate the autoclave process by featuring combined permeation and consolidation of fiber beds have yielded additional dependencies of the permeability on process characteristics, such as the consolidation load and the original resin-rich areas within the fiber beds.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 55
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 254-266 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: We develop a numerical method for calculating fiber orientation in the midsurface of a molded part of small thickness. Two-dimensional fiber orientation is predicted on the basis of either Jeffery's equation or a constitutive equation for the orientation tensor. The calculation is fully transient; it is performed on a time-dependent flow domain. The method is based on finite elements. Updated finite element meshes are generated at every instant of filling and allow one to perform an accurate calculation of the orientation even along the boundary of the flow domain. The method is applied to several examples in plane and three-dimensional geometries.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 240-253 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A method is presented for measuring three-dimensional fiber orientation in fiber-reinforced polymers and placing confidence limits on the results. The orientations of individual fibers are determined from the elliptical intersections between the cylindrical fibers and a polished section. This can be done using either manual digitization or automated image analysis. Volume averages for the sample are computed using an orientation-dependent weighting function that corrects for the bias of an area-based sample. Equations are developed for nonuniform fiber lengths, using both number-average and weight-average measures of orientation. Sources of systematic, measurement, and sampling error are discussed and equations for sampling error and the propagation of measurement error are derived. The results use a second-rank tensor to characterize fiber orientation, but the error analysis can be applied to any type of orientation parameter. We implement the technique using manual digitization of optical micrographs. Our implementation accurately measures samples with known orientation, and produces identical results from two perpendicular sections of a glass fiber/nylon injection-molded sample.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 57
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 273-279 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: We have studied the impact strength, by Charpy and Izod tests, of blends of polyamide 6 with different rubbers, 10 wt% of each, or rubbers and glass fibers (8.5 wt% and 15 wt% respectively). The rubbers are from three different families: (i) a nonreactive cross-linked terpolymer, methyl methacrylate/butadiene/styrene (17/64.5/18.5); (ii) two block copolymers compatible with the matrix, poly(tetramethylene glycol)/polamide 12 (70/30 or 34/66); and (iii) two polymers containing reactive functionality, a terpolymer ethylene/ethyl acrylate/maleic anhydride (68/30.5/1.5) and a copolymer ethylene/acrylic acid (90/10). The classification of additives in regard to improved impact depends on the procedure used for the impact strength measurement, particularly on whether the samples are notched or unnotched. The results are discussed in relation to the dimensions and the adhesion of the rubber particles. The level of adhesion has been estimated from observations in scanning electron microscopy of cavities due to pullout nodules and of nonextracted rubber after treatment in boiling xylene. Strong variations in the morphologies are found, depending on the chemical nature of the rubber. The crystalline state of the polyamide in the blends has also been evaluated from differential scanning calorimetry.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 287-297 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Sheet composites of polypropylene and poly(ethylene terephthalate) were produced by melt consolidation of alternating layers of polymer films and random glass fiber mats. The composites had a nominal glass content of 50 wt% (∼30 vol%). The sheets were stamped into a complex part from which test specimens were machined, and mechanical properties determined. Flexural strengths as high as 159 MPa were recorded for polypropylene composites and 313 MPa for poly(ethylene terephthalate) composites. The flexural modulus of the polypropylene composites reached 9.1 MPa, whereas the modulus of the stiffest poly(ethylene terephthalate) composite was 15 GPa. The impact properties of the composites were equally high. Polypropylene composites absorbed up to 257 J/cm during an instrumented falling dart impact test. Poly(ethylene terephthalate) composites absorbed as much as 116 J/cm in the same test.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 60
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 298-304 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The fiber straightening pre-tension applied during the sample preparation of single fiber composites is suggested here to significantly affect the number of fragments as well as the value of the Kelly-Tyson interface shear strength obtained from single filament composite tests. This implies that fragmentation tests performed under seemingly identical conditions, but in which the fiber pre-tension is not accurately controlled during sample preparation, might yield widely differing experimental results. We present and discuss a new set of experimental results dealing with fiber pre-tension effects in carbon/epoxy single fiber composites.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 61
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Surface-induced transcrystallization in fibers has been reported in some advanced polymer composites. It is believed that transcrystalline interphase may affect stress transfer efficiency between the reinforcing fiber and the matrix. In this study, attempts were made to examine the effects of transcrystallinity on composite performance, particularly on fiber-matrix interfacial bond strength, and to investigate possible attributes of transcrystallization. Three polymer resins, poly(etherketoneketone) (PEKK), poly(etheretherketone) (PEEK), and poly(phenylenesulfide) (PPS), and four types of fiber, polyacrylonitrile (PAN)-based AU-4 (untreated AS-4) carbon, pitch-based carbon, poly (p-phenylene terephthalamide) (PPDT) aramid, and E-glass were used. It was found that PPDT aramid and pitch-based carbon fibers induce a transcrystalline interphase in all three polymers because of an epitaxial effect. Under certain conditions, transcrystallization was also observed in PAN-based carbon and E-glass fibers, which may be partially attributed to the thermal conductivity mismatch between the fiber and the matrix. Plasma treatment on fiber surface showed a negligible effect on inducing transcrystallization, whereas solution-coating of PPDT on the fiber surface showed a positive effect. The Microdebonding test, which measures the interfacial bond strength between the fiber and the matrix, consistently showed more than 40% increments for various single filament systems with transcrystalline interphase versus without. However, the effects of transcrystallinity on the interfacial bond strength appeared to decrease as the fiber content increased in composites.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 305-309 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Superconductor/polymer composites were prepared by mixing powders representing the Y-Ba-Cu-O and Bi(Pb)-Sr-Ca-Cu-O systems with high-density polyethylene. Their electrical resistivities were measured as a function of temperature. By controlling the powder preparation techniques, it was possible to fabricate composites with superconductive transition to zero resistivity in the Bi(Pb)-Sr-Ca-Cu-O system. These composites can be fabricated in certain desired shapes.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 335-343 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effect of surface treatment of particulates on the curing kinetics of unsaturated polyester resin has been investigated using a differential scanning calorimeter. Two coupling agents, γ-methacryloxy propyltrimethoxy silane (γ-MPS) and phenyltriethoxy silane (PTS), were employed. The former reacted with the resin; the latter did not. A kinetic model of free radical addition polymerization was used. A correction factor was used to represent the effective free radical concentration in order to account for the formation of charge transfer complex between the glass beads and the free radicals in the resin. The results indicate that (1) the resin with treated particulates showed generally faster reaction rate and conversion than the resin with untreated particulates; (2) no obvious difference on the curing kinetics was observed between these two coupling agents; the primary role of coupling agent is to inhibit the influence of particulates on the curing kinetics of the resin by effective surface coverage; and (3) a minimum aqueous concentration of 0.05 wt% was suggested for surface treatment of particulates; the reaction rate of the resin was slightly improved when the concentration of the coupling agent was 0.01 wt%; this might possibly be due to insufficient coverage of the particulate surface.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 327-334 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Magnesium hydroxide and magnesium carbonates have attracted attention as endothermic flame retardants that are sufficiently stable to be incorporated into thermoplastics without decomposition. In this survey, a basic form of magnesium carbonate, magnesium carbonate hydroxide pentahydrate [(MgCO3)4 · Mg(OH)2 · 5H2O] was evaluated as a flame retardant for polypropylene. This filler (MCHP) has a thermal stability intermediate between that of alumina trihydrate (ATH) and magnesium hydroxide, which is sufficient to allow incorporation into polypropylene without decomposition. The MCHP is most effective at high filler concentrations near 60% where it was found to impart a Limiting Oxygen Index of 28.2 with a V-O rating (no dripping). This is slightly more effective than the flammability ratings for ATH and Mg(OH)2 under the same conditions. The effectiveness of MCHP was attributed to the large endothermic loss of water of hydration, which also dilutes the combustion gases. This action was further aided by the formation of an intumescent char on the burning surface, which eventually extinguished the flame. Various combinations of magnesium oxide, magnesium hydroxide, magnesium carbonate, and MCHP were evaluated in order to clarify the mechanism of the flame retardant and improve the efficiency of the protective action. However, no synergism was evident, and the flame retardant results were found to be additive. The mechanical properties and processabilities of these highly filled compounds are very sensitive to the type of surface treatment. The method of Savides was employed to compare the burning temperature of the test specimens and to measure the rates of combustion.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 878-885 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Melt blends of nylon-6/modified ABS (acrylonitrile-butadiene-styrene terpolymer) have been prepared using a single screw extruder. Electron microscopic observations revealed that the rubber particles are as finely dispersed as in ABS. Both the heat of fusion and the dynamic storage modulus of the blends were linear functions of the blend composition. The melting point of nylon crystallites and glass transition temperatures of poly(acrylonitrile-co-styrene) (AS) and the rubber phase in ABS and the amorphous phase in nylon were almost independent of the composition. Very high Izod impact strength was achieved over a broad compositional range. These facts suggest that the nylon and the modified ABS are not mixed on a molecular level although there must be sufficient interaction between them. The melt viscosities were increased with an increase in the ABS component. In the region of less than 65% ABS, the viscosities bend off to the zero-shear viscosity at low shear rates. Above 65% ABS, the viscosity curves were expressed by a power law fluid. The power law index decreased with an increase in the ABS content. The activation energy of flow vs. composition curve indicated a discontinuous point between 60% and 70% ABS. The phase inversion takes place at about 65% ABS, judging from the rheological point of view.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 370-375 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Ethyl α-hydroxymethyl acrylate (EHMA) was synthesized and evaluated as a candidate for wood impregnation and in-situ polymerization. Southern Pine softwood was impregnated under a variety of conditions with EHMA alone and with various comonomers plus free radical initiator. Following thermal polymerization, the wood-polymer composites were tested for increased dimensional stability (water soaking swell resistance) and mechanical properties over untreated wood. The greatest increase in dimensional stability was attained using EHMA alone, while the maximum compression modulus was achieved by impregnating with 1:1 EHMA-styrene and styrene alone. The composites were further characterized by 13C CP/MAS solid state NMR and scanning electron microscopy.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 376-382 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The isothermal crystallization from the melt of isotactic polypropylene in the presence of Kevlar 49 fibers has been investigated. The nucleating ability of the fibers was demonstrated, and the presence of extensive transcrystalline regions was related to crystallization parameters, such as crystallization temperature, melt precrystallization temperature, and residence time at precrystallization temperature. The results are discussed in terms of the presence of heterogeneities in the bulk and preformed self-seeded nuclei located in the anfractuosities of fiber surfaces.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 494-505 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert-butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 517-523 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Improved compatibility of blends of polystyrene and an amorphous polyamide was achieved by lightly sulfonating the polystyrene. Hydrogen bonding between amide groups and either sulfonic acid or metal sulfonate groups lowered the interfacial tension between the two polymers, which led to a much finer dispersed phase size in blends involving the sulfonated polystyrene. At relatively high sulfonate to amide ratios, the two polymers formed a miscible blend. Improved mixing of the phases was verified by shifts in the glass transitions, and the specific interactions that occurred were characterized by Fourier transform infrared spectroscopy.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 70
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 931-938 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Steady-shear-viscosity data sets for commercial-grade acrylonitrile-butadiene-styrene terpolymer, nylon, polycarbonate, poly(methylmethacrylate), and polystyrence are fitted in terms of a generalized Cross/Carreau modeling for the shear-rate dependence. Based upon extensive data sets from the open literature as well as in-house measurements, it is shown that the shear-rate dependence can be more accurately described in terms of the Cross rather than Carreau model. Although the resulting viscosity fits based upon these two models might differ by 20% or more for the same well-characterized data set, the resulting effect upon simulating the injection-molding process is found to be much smaller since such predictions reflect a range of shear stresses (varying linearly from centerline to wall of cavity) over which the two models alternate in relative magnitude. This is demonstrated by detailed representative numerical predictions which are presented for both the filling and post-filling stages.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 924-930 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The structure and properties of a preimidized photosensitive polyimide (Probimide PSPI, a copolyimide of benzophenonetetracarboxylic dianhydride with alkyl groups substituted aromatic diamines) were studied with variations of UV exposure energy and bake temperature by means of wide angle X-ray diffraction, dynamic mechanical thermal analysis, stress-strain analysis, and residual stress analysis. The X-ray diffraction patterns patterns indicate that the PSPI is amorphous in the solid state. The Tg was 378°C ∼ 410°C, depending upon the thermal history over the range of 350°C ∼ 400°C. At the glass transition region, the dynamic storage modulus E′ was very sensitive to both i-line exposure energy and thermal history. However, the mechanical stress-strain behavior at room temperature was primarily dependent on the thermal history. The mechanical properties were 2.6 GPa ∼ 2.9 GPa Young's modulus, 131 MPa ∼ 168 MPa tensile strength, 10% ∼ 12% yield strain, and 16% ∼ 74% elongation at break, depending upon the baking or annealing. These dynamic and static mechanical properties indicate that on the PSPI backbone, crosslinks are formed thermally as well as photochemically. The thermal crosslinks might be formed through thermal liberation of the labile alkyl groups of aromatic diamine moieties and subsequent coupling of the radicals. The thermal degradation was also evidenced in the mechanical properties degraded by baking above 375°C or annealing above 350°C. In addition, during baking and cooling, the residual stress was dynamically measured on Si wafers as a function of temperature. The stress at room temperature was 48 MPa ∼ 52 MPa for the PSPI films baked at 350°C or 400°C, regardless of i-line exposure.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1028-1036 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The mechanical properties of squeezed flow films were measured on blends of a chlorinated poly(vinyl chloride) (CPVC) compound and a thermotropic liquid crystalline copolyester of p-hydroxybenzoic acid/poly(ethylene terephthalate) (60/40), hereafter referred to as LCC. CPVC is immiscible with LCC. The most serious and unique problem of liquid crystalline polymers is their tendency to fibrillate when fabricated into films and injection molded parts, primarily because of a high degree of mechanical anisotropy. It has been found that the mechanical anisotropy of LCC and blends could be lessened using nonisothermal squeezing equibiaxial extension flow. The maximum tensile properties of LCC are achieved when processed in the vicinity of 260°C. For blends of CPVC containing LCC, the mechanical properties are dependent on the processing temperature and compositions. Blends with no more than 20 wt% of LCC exhibit significant increases in tensile properties. This is due to the possibility of frozen-in macroscopic biaxial orientation of LCC in the blends during the nonisothermal squeezing flow. Within the range of processable temperatures, the reinforcement of CPVC due to the incorporation of LCC can be achieved at a temperature below the optimum processing temperature of LCC, although the thermal history of blends never reaches that temperature.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1037-1046 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A kinetic model based on reaction mechanisms was proposed for the description of the curing behavior of a TGDDM/DDS resin system. The characteristic of this model is the separation of the non-autocatalytic part from the autocatalytic part of the reaction, so the model can match the well-established pseudo second order reaction mechanism, as proposed by many other studies about the epoxide/amine reaction. The present model was compared with two other widely used models for the autocatalytic curing behavior of epoxide/amine system, i.e., an equation based on a single rate constant and another based on pure phenomenological analysis, by using DSC data. It was found that the reaction rate calculated from this new model can fit the DSC empirical result much better than those calculated from the other two models. Parallel studies on some other resins, such as the DGEBA/m-PDA system, also proved the superiority of this kinetic model. Results have revealed that the new model was valid for most of the epoxide/1o-amine systems studied. A discrepancy did appear as the epoxide/amine molar ratio and/or the isothermal curing temperature reached certain limits, owing to the occurrence of side reactions.
    Zusätzliches Material: 14 Ill.
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  • 74
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 75
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1047-1051 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Poly(benzimidazole) (PBI) was solution-blended with a low molecular weight ether-imide analog to Ultem 1000. The as-cast blends were found to form one-phase structures over the whole of the composition range. By the use of optical microscopy and differential scanning calorimetry, the blends were found to phase separate on heating above the blend glass transition temperature (Tg) but did not remix on cooling. It was concluded that the blends formed on room temperature casting were nonequilibrium and remained one-phase simply because they were well below Tg.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1053-1054 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 77
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1209-1212 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The study of single-molecule single-crystals of isotactic polystyrene was carried out by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). It was shown that STM provided more information than TEM. By means of STM, the single-molecule single-crystals were found even in the case of aggregation. Regular strips were also found on the top surface of single-molecule single-crystals. This seems to imply regular adjacent folding.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 78
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1188-1203 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The mesophase structures of some flexible chain polymers, which do not contain mesogenic groups, but are able to form thermodynamically equilibrium mesomorphic states, were studied by means of the X-ray analysis, the differential scanning calorimetry, and other methods. The mesophase polyethylene in bicomponent polymer blends, mesomorphic ultra-high molecular weight polyphosphazenes, and membrane polyvinylorganosilanes were investigated. The scheme of polymer phase transitions is discussed. Besides conformational disordering, the step-by-step loss of different levels of the positional order (i.e. the multiple-step character of melting) of flexible, semiflexible, and stiff chain polymers is deduced and illustrated by examples from the authors' experience and from the literature.
    Zusätzliches Material: 29 Ill.
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  • 79
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1213-1216 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: With specially shaped samples it is possible to study the stress-strain relation σ(γ) in simple shear up to large shear deformation γ. Measurements of σ(γ) on synthetic polyisoprene, IR 305, differently crosslinked with dicumylperoxide, are reported and compared with those for uniaxial extension on the same materials. Using the simple deformation geometry including shearbands proposed in the meander model (1), both stress-strain relations can be converted into each other. These results favor the applied superstructural model and moreover show that the deformation behavior of rubbers is governed by one material law, σ(γ).
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1217-1227 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Chalk-filled isotactic polypropylene (iPP) toughened by modifying the interfaces with liquid oligomer of ethylene oxide was subjected to high deformation at elevated temperature. Oriented chalk-filled material exhibits interesting properties: high concentration of open interconnected pores, high elastic modulus, high tensile strength, ability to absorb large quantities of liquids, white color and roughness of the surface. A continuous process for the production of oriented, toughened, chalk-filled isotactic polypropylene is described. The stretching ratios which can be achieved range from 4 to 8 for modified chalk concentrations with compositions of 60 and 40 wt%, respectively. Solid state extruded, toughened, chalk-filled iPP prepared for comparison exhibits similar morphology and properties as drawn toughened chalk-filled iPP although it contains much less voids.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1228-1235 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Isotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point, Tm°, is 405°C (678 K). The heat of fusion, Δ Hƒ° was found to be 50.82 J/g (5.60 kJ/mol) and Δ Cp at Tg, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature, Tg, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples, Tg increases up to 165°C (438 K) for crystallinities 〉 40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystalline polymer.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1236-1241 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo-oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000™ and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be derived.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1242-1254 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A large collection of data on Young's modulus and density of unfilled polyethylenes at ambient conditions has been compared with various competing theoretical mixing rules developed for composite micromechanics. The objective was to see if such theories usefully predict the dependence of stiffness on crystalline content in an archetypal isotropic semicrystalline thermoplastic polymer above its glass trnsition temperature. It was found that the self-consistent scheme derived by Hill and Budiansky from continuum micromechanics appears to have valid application to this system. The scheme naturally and coherently incorporates information on bulk and shear moduli and Poisson's ratios, while giving a good account of the main trend in the Young's modulus data. Conversely, other theoretical models frequently invoked in the polymer literature were explicitly found to be unsuitable for representing principal features of modulus-density relationships dectated by the data.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1255-1260 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Available literature data, augmented with a few mild and plausible assumptions, have been used to derive an estimated empirical compliance matrix for orthorhombic crystalline polyethylene at ambient conditions. Compared with this representation of experimental observations, reported theoretical compliance surfaces, derived from molecular mechanics, are shown to be in quantitative disagreement, although qualitatively their shapes are not dissimilar.It is further shown that if an accurate theoretical determination were to be available, it would yield an ability to translate (in surprisingly few, and rather simple, theoretical steps) directly from interatomic forces, acting over nanometer lengths, into realistic, crystallinity-dependent, estimates of macroscopic moduli of isotropic semicrystalline polyethylenes.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1261-1263 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The temperatures and kinetics of phase separation have been studied as a function of filler concentration in a polymer mixture of poly(vinyl acetate)-poly(methyl methacrylate). The filler was shown to have a marked effect on the cloud point position and the phase separation kinetics at various temperatures. The effects observed are dependent upon the component ratio.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1264-1269 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Thermal properties of Fortron®®Registered trademark of Hoechst Celanese Corporation. poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, Tg, has been calculated to be 28.1 J°C-1 mole-1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman-Weeks method. The Tg of PPS increases with molecular weight. The Tg of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at -92°C. Only the highest molecular weight could be quenched to a completely amorphous state.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 87
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Using a realistic model for polyethylene (PE), the molecular dynamics technique is used to simulate atomic motion in a crystal. The calculations reveal conformational disorder above a critical temperature. The rate of isomerization computed from molecular dynamics is compared to transition-state theory and leads to an activation energy under stress of ∼ 30 kJ/mol, 15 kJ/mol above the single-bond rotation value. In the unstressed case, the activation energy for the process is less.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1270-1277 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The non-isothermal crystallization of Fortron poly(phenylene sulfide), PPS, was examined to better understand its behavior during injection molding. The nonisothermal Avrami formalism was applied to this system, but this method was found to be questionable because of the sometimes severe curvature that appears in the plots of the transformed data. A method of ranking crystallization rates at low cooling rates by plotting the peak in the crystallization exotherm versus the cube root of cooling rate has been considered and shown to have limitations at the higher cooling rates of interest. The growth rate expression developed by J. D. Hoffman for polymer crystallization of chain folded lamella in three dimensions has been used to simulate crystallization exotherms. It was found that this could only fit the data at low cooling rates. At high cooling rates it was necessary to use a growth rate expression developed by Calvert and Ulhmann for polymer crystallization without chain folding. When this is used to describe a two dimensional growth geometry, close agreement in the positions of high cooling rate exotherms could be obtained. The implication is that a change in crystallization mechanism is possible as the conditions go from low to high cooling rates.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1286-1289 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polymer thick films are screenable polymer pastes which vary from electrically non-conducting to electrically conducting. These materials typically contain significant amounts of high boiling solvents, and cure therefore involves removal of solvent in addition to crosslinking of the polymer matrix. In this study thermogravimetric analysis and dynamic mechanical analysis were utilized to characterize the residual solvent and glass transition behavior, respectively, with cure of the polymer thick films. Thickness was maintained constant at approximately 25μ and 100μ by using stainless steel mesh substrates. Results showed that IR curing, although able to heat more rapidly, did not accelerate the cure beyond that expected from time at temperature. Time-temperature superposition kinetics were employed to measure activation energy of cure, generate master cure curves, and to quantify IR cure time-temperature profiles. Cure models describing Tg and residual cure as a function of time, temperature, and film thickness were developed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1366-1371 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: For relatively soft polymer coatings on soda-lime glass substrates the indentation load increases substantially when the indenter penetrates into the glass substrate since the glass can now directly support some of the indenter load. A model for the indentation load-depth behavior is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile-up of coating material underneath the indenter. The model predicts the indentation behavior as a function of coating and substrate hardnesses and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda-lime glass substrates shows good agreement.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 91
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1350-1357 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dynamic creep behavior of a filled poly(dimethylsiloxane) elastomer was studied under cyclic stress. The stress level was chosen such that the increase in the internal temperature was small and that microcracks were not observed. This work has demonstrated that cyclic stress in combination with high temperature accelerates the degradation of the elastomer. The results suggest that because of the applied force, breaks in the load-bearing chains of the network occur. These breaks, while relieving the mechanical stress, create highly reactive ionic fragments. It is believed that because of the subsequent reactions of the ionic fragments, changes in the specific gravity, storage modulus, effective crosslink density, and length of the sample (creep) are observed. The observed decrease in the storage modulus is thought to occur because of the reaction of the ionic fragments with moisture, which results in the formation of silanol chain ends that reduce the effective crosslink density. The results also show that contrary to the prediction of the Boltzmann's Superposition Principle, the rate of creep is greatly enhanced when the sample is subjected to a sinusoidally varying dynamic load as compared to a comparable static load. The polymer weight loss was found to be linear with time and strongly dependent on the level of applied dynamic and static force. In addition, the weight loss and rate of creep were also found to be strongly dependent upon temperature.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1372-1378 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polymer coatings are widely used to protect glass from indentation damage. A model for the strength degradation that occurs when a sharp indenter penetrates through the coating is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile-up of coating material underneath the indenter. The model predicts the strength degradation as a function of indentation load, coating and substrate hardnesses, and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda-lime glass substrates shows good agreement.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 94
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polymer motion in solution and in model printing inks (as measured by NMR spectroscopy) was compared to the “tack” or tensile stress developed in the splitting of thin fluid films. For model inks based on polyisobutene, at constant pigment content, increasing the polymer content caused polymer motion to slow down, and caused the tack to increase. At constant polymer content, increasing the pigment level had much less effect on polymer motion. At 20% pigment content, tack values were little different from those of the corresponding polymer solutions. This suggests that the tensile stress developed in an ink film as it splits is related to the motion of its polymeric ingredients, but is much less dependent on the concentration of dispersed solid pigment.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 95
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This paper presents procedures to monitor oxidation degradation of two commonly used cable insulations, crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR). Since the techniques described require only micro specimens, deterioration of cable insulation can be monitored without destroying the function of the cable. The techniques described are melting point, crystallinity, infrared carbonyl absorbance, gel content, relative hardness, and differential scanning calorimetry (DSC) oxidation induction time. The techniques were applied following accelerated aging over a period in excess of two years. The results from the micro specimens were directly related to embrittlement and the decrease in ultimate elongation. The previous thermal history of XLPE was determined using DSC melting peak analysis.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1394-1399 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES). When there is perfect adhesion between constituents, an upper bound for tensile yield strength is found to be 1.33 times the matrix yield strength above a critical volume of particulate concentration. Utilizing Sjoerdsma's model for interacting stress concentration fields, one can determine the concentration dependence of the yield strength below the critical filler volume fraction. When there is no adhesion between constituents, a modified version of an equation by Nicolais and Narkis adequately describes a lower bound for the tensile yield strength. The particulate concentration and the matrix ductility are the prime factors in controlling the brittle failure of the composite. Upper and lower bounds for brittle failure strength are characterized using a strength-of-materials approach and stress concentration factors for both “perfect” and “zero” adhesion. The properties of calcium carbonate filled PP homopolymer were measured over a wide range of filler volume fractions. CaCO3 was either treated with stearic acid to prevent adhesion between constituents or used as received. Maleic anhydride grafted PP (MPP) was used to promote adhesion. For filler volume fractions below 0.2, yielding of the composite by combined microcavitation and shear deformation was the principal failure mechanism. At vf above 0.35, a brittle failure mechanism dominated. In the range between 0.2 and 0.35, both failure modes were observed in the populations tested. Good agreement was found between the experimental results and the proposed model.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1418-1425 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The rheological properties of polystyrene (PS) and poly(methyl methacrylate) (PMMA) composites filled with monodisperse sized crosslinked polymeric particles are sensitive to processing history and chemical composition. Particles compatible with the matrix, such as PMMA or copolystyrene-vinylphenol in a PMMA matrix, are randomly dispersed on mixing, yielding (almost) Newtonian fluids. Particles incompatible with the matrix, such as PS or copolystyrene-acetoxystyrene in PMMA, produce composites whose steady shear viscosities depend on shear rate and whose dynamic moduli are elevated at low frequency. Particles in incompatible composites tend to cluster, producing a structure that is destroyed at high shear rates and that reforms on aging at elevated temperatures.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1411-1417 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Co-rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co-rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time-dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package - FIDAP - using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-30 co-rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristics was analyzed.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1401-1410 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Optimization of final part thickness distributions is crucial in the extrusion blow molding process in order to minimize resin usage. Prediction of part thickness distributions from basic process and material parameters would be ideal. However, attempts to do so have been unsuccessful, largely because of the inability to predict parison thickness profiles. One must therefore resort to measurement of the parison thickness profile and estimation of the final part thickness distribution by computational methods. This paper describes a new technique for the noncontact estimation of parison thickness profiles in continuous extrusion blow molding. The method accounts for sag and requires no previous knowledge of rheological data. It can be employed on-line for the purposes of process monitoring and control. The approach is based on the measurement of the parison length evolution with time during extrusion, the parison diameter profile, the flow rate, and the melt temperature gradient along the length of the parison. These parameters are utilized in conjunction with a theoretical approach that describes the extrusion of a parison under the effects of swell, sag, and extrusion into ambient conditions. Results are presented for three resins of various molecular weight distributions. The degree of sag is minimal at the top and bottom of the parison, and reaches a maximum near the center of the parison. Results are also presented to demonstrate the versatility of the method under other process conditions, such as varying flow rate, die temperature, and die gap.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1426-1432 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The development of surface texture in biaxially deformed polypropylene is examined. Two polypropylenes formed into bottles under similar conditions by the injection stretch-blow molding process exhibit different levels of clarity. Vertical cracks of light scattering dimensions are found by optical microscopy to be the source of haze. Rheological measurements indicate the resin that develops surface cracking has a much higher extensional viscosity and exhibits a significant increase above the linear case of its extensional stress growth function. Possible mechanisms for the formation of surface texture are discussed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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