Estimation of parameters where dependent observations are related by equality constraints

Pirt's model for microbial growth and product formation are reparameterized to obtain multiresponse models with common parameters. The dependent variables in the models are related through the available electron and carbon balance constraints. Covariance adjustment is used to reduce the growth model to a unit variate linear model with covariates. Therefore, standard multiple regression programs can be used to obtain combined point and interval estimates of true biomass energetic yield, true product yield and maintenance coefficient. This approach may yield “better” estimates than the maximum likelihood approach when an appropriately selected subset of covariates is used. Nonlinear estimation procedures are also considered; these procedures are efficient with few responses; however, as the number of responses per observation increase, they may require a lot of computing time. For illustration several data from the biochemical engineering literature are analyzed by the proposed methods.     

Strength Degradation of Thermally Tempered Glass Plates

An earlier theory of contact-induced strength degradation of brittle materials is extended to include plates in residual surface compression. The scale of the strength-controlling flaw is predicted by indentation fracture mechanics, with the modifying effect of the residual field incorporated into both indentation and strength equations. Experimental verification of the predictions is obtained from diamond-pyramid indentation tests on thermally tempered glass plates. As with untempered plates, the theory accounts for the load dependence of the strength loss; it also explains the insensitivity of the degradation characteristics to initial flaw distribution and identifies toughness as the controlling material parameter. Most significant, however, is the demonstration that surface strengthening can produce dramatic improvements in degradation resistance. The possibility of obtaining all parameters necessary for a complete degradation analysis of a given tempered inaterial entirely by routine indentation/strength testing is discussed.     

Hydrolytic degradation of ionically cross-linked polyphosphazene microspheres

The hydrolytic degradation of gel microspheres based on calcium cross-linked phosphazene polyelectrolytes, poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[(carboxylatophenoxy) (glycinato)phosphazene] (PCGPP), was investigated. These microspheres are of importance as carriers in protein and cell encapsulation. Both PCPP and PCGPP ionotropic polyphosphazene hydrogels are degradable in an aqueous environment (pH 7.4, 37°C). The degradation rates can be increased by incorporation of hydrolysis sensitive glycinato groups as the pendant structures in the polymer (PCGPP). Hydrolysis of these polymer hydrogels led to low molecular weight (<1,000 Da) products. The erosion and molecular weight profiles varied also according to the molecular weight of the polyphosphazene constituting the gel beads. Another approach to affect the degradation rates consists of coating microspheres with poly-L -lysine. Ionotropic polyphosphazene hydrogels have potential as biodegradable devices for controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Modeling of Filtration Combustion of Carbon

The kinetics of the overall reactions of carbon gasification at temperatures up to 1600 K is studied. The kinetic characteristics of the reactions are taken into account in a distributed mathematical model of filtration combustion of carbon. By computational experiment at different values of process control parameters (the gas flow rate, the fraction of the oxidant in the gas, and the mass ratio of carbon to the inert material in the combustible mixture), it is found that, in the wave of filtration combustion of carbon under superadiabatic conditions, carbon gasification can predominately yield either CO₂ or CO.     

Performance of hybrid reinforcements in PVC composites. II: Use of surface-modified mica and different cellulosic materials as reinforcements

The effect of the composition of various wood fibers and surface-treated mica as well as different surface treatments of cellulosic materials on the mechanical properties of PVC composites has been evaluated. Cellulosics were surface modified by prior coating with maleic andydride (MA), mixtures of MA and Na-silicate and isocyanate. The filler concentration was fixed at 25 wt%. Both tensile strength and modulus of composities filled solely with mica are superior to those of non-treated wood fiber-filled composities. while the reverse is true for impact strength (except for bagasse-filled composities), ultimate elongation, and tensile toughness. Moreover, the mechanical properties of composities, with the exception of modulus, filled only with mica and/or non-treated wood fibers are inferior to those of unfilled PVC. Compared to non-treated fiber-filled composites, properties improved when surface-modified wood fibers were used alone, or along with mica. Isocyanate-coated wood fibers ranked best with regard to the mechanical properties of the composities. Properties also changed with the change of wood species and compositions of mica and wood fibers. Experimental results indicate good compatibility between surface-treated wood fibers/mica and PVC composities.     

Diffusion-controlled adsorption processes

Numerical solutions of differential equations for diffusion-controlled adsorption processes in spherical particles are presented for slow diffusion of gaseous molecules followed by rapid adsorption according to the Langmuir isotherm. As the parameter in the denominator of the Langmuir equation is increased the rate increases and the generalized rate curves shift progressively from that for the linear isotherm, the Langmuir parameter = 0, to the curve of the parabolic law. Adsorption and desorption cycles are considered and parameters are provided for relating any of these processes to the generalized curves. A simple linear equation was shown to approximate the rate curves with moderate accuracy.     

Spontaneous combustion regimes

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 5, pp. 13–27, September–October, 1992