Growth stoichiometry

An elemental material balance approach to growth stoichiometry requires an empirical formula for dry weight material ... 

A.F. Wright and U. Grossner, The effect of doping and growth stoichiometry on the core structure of a threading edge dislocation in GaN , Appl. Phys. Lett., 73, 2751-2753 (1998). 

A thermodynamic analysis obviously offers potential as a basis for predicting growth yields. Several correlations have been proposed comparing actual growth stoichiometries with the upper limit just described in terms of thermodynamic efficiencies [54,55]. 

For example, Okabe et al. (1992) [52] report the following growth stoichiometry for the sulfate reducing bacteria Desulfovibrio desulfur icons growing on lactic acid and sulfate, and producing biomass, acetic acid, CO2 and H2S. 

The requirements of thin-film ferroelectrics are stoichiometry, phase formation, crystallization, and microstmctural development for the various device appHcations. As of this writing multimagnetron sputtering (MMS) (56), multiion beam-reactive sputter (MIBERS) deposition (57), uv-excimer laser ablation (58), and electron cyclotron resonance (ECR) plasma-assisted growth (59) are the latest ferroelectric thin-film growth processes to satisfy the requirements. 

The stoichiometry of growth and metabolism can also be described by elemental material balances. This approach can provide an insight into the potential of the organism for biomass or product production, and thus the scope for process improvement. 

Now lets consider the elemental approach to stoichiometry for a relatively simple situation aerobic growth where the only products formed are cells, carbon dioxide and water. The following formulas can be used if we consider the four main elements ... 

Table 3.3 Experimental stoichiometries for cell growth and exopolysaccharide production from various carbon sources by Agrvbacterhim radlobacter under nitrogen-limiting conditions.

The respiratory quotient (RQ) is often used to estimate metabolic stoichiometry. Using quasi-steady-state and by definition of RQ, develop a system of two linear equations with two unknowns by solving a matrix under the following conditions the coefficient of the matrix with yeast growth (y = 4.14), ammonia (yN = 0) and glucose (ys = 4.0), where the evolution of C02 and biosynthesis are very small (o- = 0.095). Calculate the stoichiometric coefficient for RQ =1.0 for the above biological processes ... 

Linear step-growth polymerizations require exceptionally pure monomers in order to ensure 1 1 stoichiometry for mutually reactive functional groups. For example, the synthesis of high-molecular-weight polyamides requires a 1 1 molar ratio of a dicarboxylic acid and a diamine. In many commercial processes, the polymerization process is designed to ensure perfect functional group stoichiometry. For example, commercial polyesterification processes often utilize dimethyl terephthalate (DMT) in the presence of excess ethylene glycol (EG) to form the stoichiometric precursor bis(hydroxyethyl)terephthalate (BHET) in situ. 

Step-growth polymerization processes must be carefully designed in order to avoid reaction conditions that promote deleterious side reactions that may result in the loss of monomer functionality or the volatilization of monomers. For example, initial transesterification between DMT and EG is conducted in the presence of Lewis acid catalysts at temperatures (200°C) that do not result in the premature volatilization of EG (neat EG boiling point 197°C). In addition, polyurethane formation requires the absence of protic impurities such as water to avoid the premature formation of carbamic acids followed by decarboxylation and formation of the reactive amine.50 Thus, reaction conditions must be carefully chosen to avoid undesirable consumption of the functional groups, and 1 1 stoichiometry must be maintained throughout the polymerization process. 

Inasmuch as the RKR model is a generalization, specific exceptions should be expected. The most important exceptions relate to growth conditions that can affect the stoichiometry of nutrient incorporation into plankton biomass. During respiration, the... 

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