New relations between the Schur-Cohn-Fujiwara and Nour Eldinstability criteria

The authors demonstrate relationships between two different stability criteria, including reduced-order versions of these criteria. Modifications of the criteria can also be used for root counting. The various matrices whose signatures are the key to obtaining root distributions are related by congruency transformations with triangular structure, implying that the sign patterns of the leading principal minors are identical     

Iterative simplex-finite difference method for the characterizationof optical waveguides

A new method is presented for reconstructing smooth refractive index profiles of optical waveguides from measured effective indexes. It is based on the semivectorial finite difference method to solve the polarized wave equation for a given refractive index profile. An iterative simplex algorithm is used to find the best refractive index parameters that give, as a solution, effective indexes close to the measured ones. The method is applied successfully to Ag⁺-Na ⁺ ion-exchanged glass slab waveguides and to diffused Mg/Ti:LiNbO₃ slab waveguides. Dopant concentration profiles are obtained by using secondary ion mass spectrometry. The relationship between the refractive index change and the dopant concentration is determined for both cases. The iterative simplex algorithm-finite difference method (ISA-FDM) is compared to other index profile reconstruction methods, and the advantages with respect to WKB-based methods are pointed out     

Lignocellulose–polymer composite. I

Bagasse grinded to different mesh sizes was used for the production of lignocellulose polymer composites. Samples of different polymer loads were prepared from crude-grafted bagasse with polymethyl methacrylate. A sodium bisulfite–soda lime glass system was used as an initiator for the grafting reaction. The properties of the resulting composites have been found to be affected by both the polymer load and the mesh size of the ground bagase. Grafting in the absence of soda lime glass from the initiator system was successful, and the properties of the composite produced from the prepared samples differed greatly from those containing glass. Other oxides, namely, copper (cupric) oxide and iron (ferric) oxide, were used in replacing glass in the initiator system. Some of the properties of the composite containing the latter were deteriorated. A composite from the true-grafted sample (homopolymer free) showed improvement in some of the properties, while the others deteriorated. Composites prepared from impregnated bagasse with polymer or homopolymer behaved differently in their properties and from those from crude-grafted samples, depending on the mesh size of the ground bagasse they are made from.     

Dielectric investigation of the molecular dynamics of blends (II): polymers with dissimilar molecular architecture (PS/TMPC blend)

The molecular dynamics of polystyrene/tetramethyl polycarbonate (PS/TMPC) blends were investigated using dielectric spectroscopy in the frequency and temperature ranges 10^?2?10⁷ Hz and 50–220°C, respectively. Blends with different compositions, namely 12.5, 25, 50, 75 and 87.5 wt% PS/TMPC were found to be compatible over the entire composition range and showed one glass relaxation process corresponding with the transition observed by calorimetric measurements. It was found that neither the kinetics or the distribution of relaxation times of the local process observed in pure TMPC were affected by blending. This fact implies that the local environment of the segments is not changed upon blending. Furthermore, these blends showed that the blending of TMPC with weakly polar polystyrene does not cause any change in the dipolar interaction of the TMPC segments, so that the relaxation strength varies linearly with composition. It is concluded that the polymeric chains of the TMPC and PS are not mixed at a segmental level, but at a higher structural level lying somewhere between segmental and molecular. This conclusion is in good agreement with that obtained in the case of blends composed of polymers with similar molecular architecture.     

Determination of the effective mass for highly degenerate copper selenide from reflectivity measurements

An investigation was made of the plasma reflection of light and the results were used to find the effective mass of highly degenerate copper selenide,p>10²⁰ cm^–3, as a function of carrier concentrationp. The study of the temperature dependence of effective mass, electrical conductivity, thermoelectric power and Hall mobility carried out in the present work gives an idea of the nature of the valence bands in these materials.     

Lignocellulose–polymer composite. III

A linear relationship was achieved between the polymer load and the monomer concentration up to 200% when china clay or talc replaced the glass in the initiating system, sodium bisulfite–soda lime glass, for the free-radical graft polymerization reactions using semichemical pulp of bagasse as substrate. The results showed that china clay is better than talc, which may be contributed to the difference in their network structure. The properties of the composites prepared from the cografted semichemical pulp–polymethyl methacrylate revealed that the china clay leads to composites with high compression strength and hardness. Deformation percent increased with increasing polymer load. However, decreasing or increasing the polymer load affects the properties of the composites up to a limit, where there is a maximum or minimum for both compression strength and hardness at china clay ratio of 2 or 3. Composites were also prepared from poly(methyl methacrylate)-cografted-pith of bagasse using the initiating system sodium bisulfite in the absence or presence of soda lime glass. Compression strength, deformation percent, and hardness increased on decreasing the glass ratio from 1 to 0, at nearly the same polymer load. The presence of waxes and resins decreased the compression strength of the composites prepared by impregnation of the lignocellulose in polymer solution. The hardness of these composites increased on removing waxes and resins. Removal of part of hemicellulose by alkali treatment of the lignocellulose has increased the effect on hardness. Alkali treatments of the substrates lead to a high deformation percentage. The compression strength of alkali-treated lignocellulose are lower than the untreated ones. The change of compression strength to deformation percent and the compressibility due to complete removal of waxes and resins by the extraction with methanol–benzene or partial removal of the waxes, resins, and hemicellulose through alkali treatment followed the change of both the compression strength and percent of deformation. Water uptake of the composites prepared in this work was ranged between 6.8 and 7%. After 48 h the water uptake increased to the range 8.5–14.1%. Impregnation of the composites in water for 72 h increased the water uptake to the range 10.2–18.1%. © 1993 John Wiley & Sons, Inc.