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  • 1
    Electronic Resource
    Electronic Resource
    Microwave thawing of cylinders (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1789-1800 
    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 finite element method was used to model microwave thawing of pure-water and 0.1-M NaCl cylinders. The electromagnetic field was described by Maxwell's equations with temperature-dependent dielectric properties, while the heat equation, coupled with the Stefan and Robin conditions, was used to describe the thawing process. An additional equation for the frozen volume fraction was used, when necessary, to account for the presence of a mushy region. Two microwave frequencies, 915 MHz and 2,450 MHz, were examined and the microwave radiation was assumed to be radially isotropic and normal to the surface of the cylinder. Results show that a two-phase mushy region may exist, and an additional thawing front may appear at the center of the cylinder. Salt cylinders have a higher dielectric loss than pure-water cylinders and therefore thaw more quickly. Internal resonance occurs when the wavelength of the radiation is a harmonic of the cylinder radius. Resonance increases power deposition and expedites the thawing process. The onset of resonance alters thawing times and complicates the development of heuristic rules for microwave thawing.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690371204
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of sample size on the microwave heating rate: Oil vs. water (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1433-1439 
    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: It is generally believed that oil samples heat faster in a microwave oven than do water samples of the same mass. For sufficiently large and thich samples this conventional wisdom is indeed correct, but this trend can be far from true in smaller samples. In a commercially-made home microwave oven, we observed that with decreasing sample size the heating rate of a water sample increases much faster than that of an oil sample. At 50 g the heating rate of a water sample is several times greater than that of an oil sample. Additionally, in studies of cylindrical samples in a customized oven having a unidirectional microwave source, the heating rate of water samples smaller than 2.4 cm in radius is greater than that of oil samples and is a strongly oscillatory increasing function of decreasing sample radius. Combining Maxwell's theory of microwave penetration and the heat conduction equation, we show that this previously unreported oscillatory heating behavior results from the added power absorbed by samples due to resonant absorption of microwaves. The added power arises from standing waves produced by internally reflected microwaves. This effect is small for oil because only 3% of the microwave power is reflected at an oil-air interface. On the other hand, 64% is reflected at a water-air interface, which causes strong resonant heating. Our findings might prove to be useful for future consumer food product development or oven design.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400902
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of microwave heating of materials with temperature-dependent properties (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 313-322 
    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: Transient temperature profiles in multilayer slabs are predicted, by simultaneously solving Maxwell's equations with the heat conduction equation, using Galerkin finite elements. It is assumed that the medium is homogeneous and has temperature-dependent dielectric and thermal properties. The method is illustrated with applications involving the heating of food and polymers with microwaves. The temperature dependence of dielectric properties affects the heating appreciably, as is shown by comparison with a constant property model.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370302
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  • 4
    Electronic Resource
    Electronic Resource
    Two-dimensional finite element analysis of microwave heating (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1577-1592 
    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: Transient temperature profiles for long rods of lossy dielectric materials with thermally-dependent dielectric properties exposed to uniform plane waves are obtained. Maxwell's equation and the heat equation are simultaneously solved using the finite element method to predict the power absorbed and the resulting temperature rise in samples of square and circular cross-section. Following the method introduced recently, we derive an exact radiation boundary condition which is independent of the rod cross-section. For a cylindrical sample, the boundary condition is imposed on the cylinder itself. For a square rod, the boundary condition is imposed on a cylinder containing the rod. The temperature dependence of dielectric properties and sample dimensions appreciably influence heating patterns. For square samples, the edges focus radiation, causing preferential heating at the edges. This effect is pronounced for larger samples. In addition, the incident wave polarization influences the heating of the rod. For waves where the electric field is polarized along the long axis of the sample (TMz polarization) the power absorbed is higher than when the electric field is perpendicular to the axis (TEz polarization). A case involving runaway heating is also investigated.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690381009
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave driven convection in a square cavity (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1268-1272 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400718
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  • 6
    Electronic Resource
    Electronic Resource
    Calculations of the circular dichroism of double-helical nucleic acids. I. Effects involving π → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1377-1389 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry using the theory of Tinoco and Johnson. This theory does not include contributions of near ultraviolet transitions that are not π → π* in nature. The calculated circular dichroism shows a strong dependence on the distance of base pairs from the helix axis and the tilt of the base pair. Smaller dependences are predicted for the propeller-like twist of a base pair and for variation of the angular increment per base pair. Moderately good agreement between calculated and many experimentally observed spectra could be generated.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130709
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  • 7
    Electronic Resource
    Electronic Resource
    Circular dichroism of DNA: Temperature and salt dependence (1972)
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 761-779 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the circular dichroism and ultraviolet absorbance of calf thymus DNA and poly dAT were measured in aqueous solutions of various 1-1 electrolytes. Although there was very little change in absorbance, the circular dichroism changed dramatically as a function of both temperature and solvent. There is a correlation of the heat of hydration of the cation and the magnitude of the temperature dependence of the circular dichroism. Our results are interpreted in terms of a large number (possibly a continuum) of intermediate secondary structures.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1972.360110404
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  • 8
    Electronic Resource
    Electronic Resource
    Calculations of the circular dichroism of double-helical nucleic acids. II. Effects involving n → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1391-1403 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry, including terms involving n → π* transitions. The “nonbonding” n or σ orbitals were of the azine type, delocalized, but concentrated at the nitrogen atoms of the purines and pyrimidines. Dynamic coupling of the magnetic moments of the n → π* transitions with the electric moments of π → π* transitions generated important terms. Mixing of electric dipole character into n → π* transitions by the static electric field perturbation of the molecule is of lesser importance. The largest contributions of n → π* transitions to the circular dichroism of double-helical nucleic acids are comparable in magnitude to the sum of π → π* terms only for geometries where the circular dichroism is weak. Using both n → π* and π → π* contributions one is able to match experimental and calculated circular dichroism spectra for DNA's over a much wider range of conditions than was possible previously.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130710
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  • 9
    Electronic Resource
    Electronic Resource
    Photolysis of poly(methyl acrylate) in solution (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 2657-2667 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Lösungen von Poly(methylacrylat) in Methylacetat, Chloroform, Methylendichlorid und Benzol wurden mit Strahlung der Wellenlänge 2 537 Å behandelt und die Änderungen des Zahlenmittels des Molekulargewichts gemessen. Der Einfluß der Bestrahlungszeit des Lösungsmittels, der Konzentration des Polymeren und der Anwesenheit des radikalischen Initiators wurden untersucht. Es wird der Schluß gezogen, daß die Kettenspaltung durch statistisch erfolgende Absorption der Strahlung durch das Polymere erfolgt und daß das Lösungsmittel dabei nicht direkt beteiligt und nur als ein optischer Filter wirksam ist.
    Notes: Solutions of poly(methyl acrylate) in methyl acetate, chloroform, methylene dichloride and benzene have been irradiated by 2 537 Å radiation and changes in number average molecular weight measured. The effect of time of irradiation, solvent, polymer concentration and the presence of radical initiator have been investigated and it is concluded that the scission results from random absorption of radiation directly by the polymer without direct participation by the solvent which acts only as an optical filter.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1974.021750912
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of crosslinker on properties of copolymeric N-vinyl-2-pyrrolidone/methyl methacrylate hydrogels and organogels (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 331-343 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The γ-ray initiated copolymerisation of N-vinyl-2-pyrrolidone with methyl methacrylate in the presence of crosslinker has been effected to high conversion. At two fixed compositions of the principal monomers, the inclusion of different concentrations of the tetrafunctional crosslinkers ethylene dimethacrylate and a low molar mass poly(ethylene glycol) dimethacrylate produced crosslinked xerogels, which were subsequently swollen in water and 1,4-dioxane to yield hydrogels and organogels, respectively. These gels were characterised by determinations of sol fraction, equilibrium solvent content and uniaxial compression stress/strain measurements. Differences among the swelling and mechanical properties according to the nature and concentration of crosslinking agent and according to the nature of the swelling medium are noted and discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1990.021910207
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