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Digitale Medien

Light Scattering by Clusters: the Al-Term Method (1995)

Okamoto, Hajime

Springer

Optical review 2 (1995), S. 407-412

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ISSN: 1349-9432

Schlagwort(e): scattering ; clusters ; the discrete dipole approximation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract This paper concerns the theoretical improvement of the discrete dipole approximation (DDA) to provide scattering properties of clusters of spherical monomers. The first scattering coefficient (al-term) in Mie theory is introduced to determine the dipole polarizability used in the DDA. In the al-term method, a spherical monomer in the cluster is replaced by a single dipole. The accuracy of this method is tested to calculate extinction and scattering cross sections by a single sphere, two-touching spheres and three collinear touching spheres. It is found that when each monomer is replaced by a dipole the al-term method is superior to the different types of DDA, e.g., the Lattice Dispersion Relation (LDR), at least for the target with the volume equivalent size parameter X, 0.2≦X≦2. This method also allows treatment of a relatively large sub-volume element which is replaced by a dipole, i.e. the size parameter of the monomer Xm∼1.5. Furthermore, a great reduction in memory requirement and computing time are achieved, e.g. for two touching spheres the al-term method requires only 6% of the total memory requirement and 0.008% of the total computing time for N=8448 with the LDR.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s10043-995-0407-1

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Digitale Medien

Isothermal pyrolysis of cellulose untreated and treated with some flame-retardants (1984)

Hirata, Toshimi ; Okamoto, Hajime

New York : Wiley-Blackwell

Journal of Polymer Science: Polymer Chemistry Edition 22 (1984), S. 3071-3089

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ISSN: 0360-6376

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Linter cellulose, untreated and treated with boric acid, ammonium sulfamate, and guanidine sulfamate, was heated iosthermally in an imaging furnace thermal balance under a flow of helium gas to obtain kinetic parameters of the weight loss and changes in the elemental content and infrared (IR) spectra during pyrolysis. The weight, carbon, hydrogen, and oxygen losses of the untreated cellulose obey a zeroth-order reaction at an early stage and a first-order reaction at a later stage. The Arrhenius parameters for the weight and elemental losses are in agreement for both reactions. The activation energy and preexponential factor of the first-order weight loss are 185 kJ/mol and 2.0 × 1013 s-1, respectively. The carbon, hydrogen, and oxygen losses of the samples treated with boric acid and guanidine sulfamate also obey a first-order reaction at a later stage of pyrolysis. The results of the elemental and IR spectral analyses suggest that the zeroth- and first-order reactions are caused mainly by the production of levoglucosan and that an initial rapid step, especially for the treated samples, is contributed by dehydration.

Zusätzliches Material: 21 Ill.