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  • Chemical Engineering  (8)
  • Engineering General  (5)
  • Atomic, Molecular and Optical Physics  (3)
  • organoiron  (2)
  • Wiley-Blackwell  (18)
  • American Chemical Society
  • Cell Press
  • 1990-1994  (18)
  • 1930-1934
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  • Wiley-Blackwell  (18)
  • American Chemical Society
  • Cell Press
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  • 1
    Electronic Resource
    Electronic Resource
    The effect of processing on rheological and molecular characteristics of a low density polyethylene (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 377-382 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330702
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  • 2
    Electronic Resource
    Electronic Resource
    Calculations on the electronic structure and spectroscopy of C60 and C70 cage structures (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 557-568 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the electronic structure and spectroscopy of models of C60 and C70 cage structures has been carried out using the intermediate neglect of differential overlap (INDO) model Hamiltonian. The geometry for these cages was obtained using gradient-driven methods, and at least in the case of C60, where information is available, is in good accord with the calculations of others. Using a small active space of only single excitations, both configuration interaction (CI) and random phase approximations (RPA) yield spectra in excellent agreement with that obtained from recent experiments. The oscillator strength of the band calculated at ∼47000 cm-1, however, dramatically diminishes as the active space is increased, even though the sum rule increases. We discuss this interesting observation as well as the calculated structure and spectrum of C70.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400849
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of 13C-NMR chemical shift using the intermediate neglect of differential overlap model (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 43 (1992), S. 327-342 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The local origin/local orbital (LORG) method of Hansen and Bouman has been implemented with the intermediate neglect of differential overlap Hamiltonian for spectroscopy (INDO/S). The method is shown capable of demonstrating the inductive effects associated with electron-withdrawing substituents through the diamagnetic shielding term. In addition, the method is capable of differentiating chemical shift in differing bond environments. The calculated paramagnetic contribution, however, is deficient for substituents that saturate the minimal basis such as oxygen and fluorine, which severely limits the general utility of the procedure. Through the utilization of reduced linear equations for the paramagnetic term, the method is amenable to any molecule for which a self-consistent field can be performed and therefore can potentially be used to study very large systems. At present, however, the LORG method when used with the rapid INDO/S model Hamiltonian does not reliably reproduce the paramagnetic contribution to the shielding.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560430304
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  • 4
    Electronic Resource
    Electronic Resource
    On the calculation of oscillator strength for electronic transitions using “effective core” methods (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 475-486 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the effect on calculated oscillator strengths for electronic transitions caused by reintroducing the nodes of valence orbitals in effective core methods through a simple Schmidt orthogonalization. This refinement is then tested within the Intermediate Neglect of Differential Overlap (INDO) model, a valence orbital only model, in both configuration interaction and Random-Phase Approximation (RPA) calculations. It is shown that the differences in oscillator strengths calculated using the dipole-length and dipole-velocity formulations are reduced somewhat for π → * transitions and significantly for n → π* transitions. The oscillator strengths calculated from the dipole-length formalism by the RPA model are in best accord with experiment. © 1992 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560440843
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  • 5
    Electronic Resource
    Electronic Resource
    Mathematical analysis of potentiometric oxygen sensors for combustion-gas streams (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1498-1514 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mathematical tools necessary to describe quantitatively the chemical processes that dictate the performance of exhaust oxygen sensors are developed. Such sensors are used commonly to monitor exhaust streams generated by internal-combustion processes. Calculated results compare well with available experimental results, although several open questions are idetified that require more experimental data. The mathematical formalism for describing the transport of gaseous species through the porous spinel structure protecting the platinum electrode on the exhaust side of the sensor is developed based on the Stefan-Maxwell equations. The kinetic processes occurring at the interface formed by the platinum electrode and the spinel structure, including the oxidation of hydrogen and carbon monoxide and various adsorption-desorption reactions, enter as boundary conditions for the transport equations. The analysis enables one to calculate the sensor's voltage response as a function of the air-to-fuel ratio λ and to investigate phenomena such as the magnitude of the voltage jump in going from rich to lean gas mixtures and the λ value at which this jump occurs.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400909
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  • 6
    Electronic Resource
    Electronic Resource
    A non-linearly stable implicit finite element algorithm for hypersonic aerodynamics (1992)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 34 (1992), S. 419-441 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A generalized curvilinear co-ordinate Taylor weak statement implicit finite element algorithm is developed for the two-dimensional and axisymmetric compressible Navier-Stokes equations for ideal and reacting gases. For accurate hypersonic simulation, air is modelled as a mixture of five perfect gases, i.e. molecular and atomic oxygen and nirogen as well as nitric oxide. The associated pressure is then determined via Newton solution of the classical chemical equilibrium equation system. The directional semi-discretization is achieved using an optimal metric data Galerkin finite element weak statement, on a developed ‘companion conservation law system’, permitting classical test and trial space definitions. Utilizing an implicit Runge-Kutta scheme, the terminal algorithm is then non-linearly stable, and second-order accurate in space and time on arbitrary curvilinear co-ordinates. Subsequently, a matrix tensor product factorization procedure permits an efficient numerical linear algebra handling for large Courant numbers. For ideal- and real-gas hypersonic flows, the algorithm generates essentially non-oscillatory numerical solutions in the presence of strong detached shocks and boundary layer inviscid flow interactions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620340203
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  • 7
    Electronic Resource
    Electronic Resource
    Accelerated bisection techniques for tri- and quindiagonal matrices (1992)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 35 (1992), S. 203-218 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper considers accelerated bisection methods for calculating the eigenvalues of symmetric tridiagonal and quindiagonal matrices using cubic polynomial interpolation, as well as first and second order Newton iteration. Recursive relations based on the Sturm sequences are presented for the Newton type methods. The relations use a convenient scaling which retains the relative magnitudes in the iterative schemes but which avoids numerical overflow. Numerical examples show a significant increase in convergence rate.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620350113
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of the length of the short chain branch on the impact properties of linear low density polyethylene (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 944-955 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The ability to evaluate various mechanical test parameters of polymers using an instrumented impact tester is reviewed. The nature of the short chain branching (SCB) in a series of linear low density polyethylenes (LLDPE) was characterized and related to several impact test parameters for these materials. The impact strength, ductility, and impact fatigue life were observed to increase with increasing branch length. This was attributed, in fact, to an increase in the number of interlamellar tie molecules as the SCB length increased. With an increase in the SCB length the SCB distribution became broader; the number of chains rich in short chain branches increased. This component acts somewhat like the rubber particles in a rubber-toughened blend which gives rise to the concept of a “one copolymer blend”.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321406
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  • 9
    Electronic Resource
    Electronic Resource
    The separate roles of phase structure and interfacial adhesion in toughening a brittle polymer (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1695-1702 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760322207
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  • 10
    Electronic Resource
    Electronic Resource
    The use of cryogenically ground rubber tires as a filler in polyolefin blends (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 166-174 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene-acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composites.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330307
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