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  • Chemical Engineering  (6)
  • Computational Chemistry and Molecular Modeling  (3)
  • Wiley-Blackwell  (9)
  • Public Library of Science (PLoS)
  • Springer Nature
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  • Wiley-Blackwell  (9)
  • Public Library of Science (PLoS)
  • Springer Nature
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  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 188-191 
    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: Rheological and processing parameters have been measured for a commercial polystyrene at temperatures from 155°C to 210°C resulting in no clear evidence for the existence of liquidliquid transition. Zero shear viscosities obtained from dynamic measurements and ends corrections and extrudate swell from capillary rheometry are analyzed, with the conclusion that the mechanism of flow is the same throughout the range of temperatures considered.
    Additional Material: 4 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 389-401 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An asymptotic analysis based on Taylor series expansions is used for first-order correction terms to the Henry's law approximation to describe solvation phenomena in multiple solute-multiple solvent systems. The magnitude of these correction terms in solvent systems very near their critical points is of particular concern, as shown in model fluid calculations with the aid of integral equation theory. The results clearly demonstrate that close proximity to the critical point in pure and mixed solvent systems causes the Henry's law approximation to show large errors in predicting solubilities, especially near the critical azeotrope of a mixed solvent system. Theoretical results also show that cross solubility enhancements in a two solutesupercritical solvent system cause cooperative synergism (both solute solubilities are increased relative to the corresponding single solute situations) or reverse synergism (both depressed relative to the single solute situation). It appears to be consistent with the available data. In computer simulations, the solute's infinitely dilute reference state is often used as a basis for describing solute thermodynamic behavior. These simulations are best achieved in the canonical ensemble because of the weak composition dependence of free energies in terms of characteristic variables of this ensemble.
    Additional Material: 9 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2300-2305 
    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 relative merits of various approaches using computer simulation methods for estimating first-order correction terms to Henry's law in dilute supercritical mixtures are investigated. Three thermodynamic formulations are provided for the calculation of these properties. One method, termed the fluctuation integral approach, requires the explicit calculation of solute-solvent pair correlation functions at the infinite dilution limit, which is a difficult task for simulations given the conflicting demands of both small numbers of solute species (for approximating the infinite dilution limit) as well as the need for large numbers of solute species to improve simulation statistics. A second approach, called the pressure gradient method, does not require the explicit, determination of these solute-solute functions and, as a result, is not as sensitive to the choice of system size and other difficulties associated with establishing an adequate ensemble size and/or number of solute species to be used in the simulations. The third approach uses the exact formulation for the property of interest using Kirkwood-Buff theory. This approach, however, requires all the solute pair correlation functions to be established, making it the most sensitive to issues concerning number of solute species used in the simulations, and so on. An examples is given showing simulation results for these approaches, illustrating their respective strengths and drawbacks.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1985-1994 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Computer simulation results are presented for the residual chemical potential μ1r, local solvent density enhancement Δρloc, and average solute potential energy u1 of a solute molecule immersed in afluid very close to its critical point. The simulation algorithm involves the Monte Carlo method in conjunction with free energy perturbation ideas. A number of ideas related to the feasibility of computer simulations in near-critical solvents are investigated. Due to long-range correlations near the critical point, it is not clear that simulations in this regime can be expected to yield accurate results using ensemble sizes of the magnitude typically used in simulations. Examination of system size and number of sampling steps on the simulations shows that the accuracy of the results depend to a large extent on the nature of the thermodynamic property being investigated. The solute chemical potential is suited particularly to simulation since it depends primarily on short-range structure in the system. A comparison of the simulation results with integral equation theory calculations shows both approaches agree well with each other.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 359-370 
    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 general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.
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  • 6
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 43-48 
    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: A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280°C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range 10-1 s-1 to 102s-1. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of liquid crystal, is more pronounced at high shear rates.
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 681-692 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Semiempirical AM1, MINDO/3, and MNDO methods have been used in the study of the alkaline hydrolysis of β-lactam antibiotics through a base-catalyzed, acyl-cleavage, bimolecular mechanism. In this work, the hydroxyl ion has been chosen as nucleophilic agent and the azetidin-2-one ring like a model of β-lactam antibiotic. The MINDO/3 method does not predict correctly the energies of small rings. This, together with the fact that, like MNDO, it cannot detect the occurrence of hydrogen bonds, gives rise to uncertain estimates of energy barriers. The AM1 method can be considered the most suitable for studying the hydrolysis of β-lactam compounds.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 7 (1985), S. 22-25 
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The viscosty and the recoverable shear compliance of poly(viny chloride)/dioctyl phthalate systems are studied at different temperatures and concentrations. The recoverable shear compliance is determined by the method of the stress relaxation after cessation of flow in a Couette flow viscosimeter. The results show the existence of a concentration dependent critical temperature Tc which separates two different flow regions.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 1545-1552 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A comprehensive study on the gas-phase alkaline hydrolysis of cephalosporins by using the semiempirical AM1 method was carried out. Cephalothin was the model compound used on account of the presence of a good leaving group at C(3′). According to the results obtained, the hydrolysis process takes place via a twostep reaction mechanism that involves the formation of an intermediate with a fully open β-lactam ring that still preserves the acetate group. Likewise, the exo methylene end product is chiefly formed by nucleophilic attack on the β-lactam carbonyl group of cephalosporins containing a good leaving group at C(3′). On the other hand, the alternative mechanism involving hydrolysis of the ester function in the side chain at 3′ and subsequent hydrolysis of the resulting β-lactam yieds essentially the corresponding enamine. The presence of a first solvation layer consisting of five water molecules showed that, even though some potential barriers are slightly increased, the mechanism involved is identical to that of the gas-phase hydrolysis of this antibiotic. © John Wiley & Sons, Inc.
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