A Microcontroller Measuring Resistance Converter

A software method is considered for converting a resistance into binary code that makes it possible to control the current flowing through a transformable resistance. The resolving power of the microcontroller measuring converter (MMC) is set by programmatically in the range from 2 to 16 bits. The resistive sensors with different nominal resistance values not lower than 50 Ω can be used as a transformable resistance. A block diagram of an MMC with an explanation of its operation algorithm, an oscillogram of output signals of a double-channel pulse-width modulator (PWM) built into the microcontroller, and an example of MMC calculation are presented. It is found from the calculated and experimental data that the transforming characteristic of MMC is linear in the range of the most relevant resolution from 8 to 16 bits. The operation of two PWM channels at the same frequency when supplying the measuring and reference circuits with current of the same value makes it possible to exclude the negative influence of external factors: temperature, instability of supply voltage, electromagnetic fields, and changes of parameters of elements as a result of their aging.     

A study of graft polymerization of methacrylic acid to polycaproamide using a reversible redox system containing CU2+ ions

Graft polymerization of methacrylic acid to polycaproamide, initiated by the K₂S₂O₈? Na₂S₂O₃? Cu²⁺ reversible redox system, has been studied. Kinetic characteristics of graft polymerization have been investigated in a wide concentration range of every component of the initiating system. Cu²⁺ ions have been found to catalyze graft polymerization in the 1.0 · 10^?5?1.2 · 10^?4M concentration range, whereas at concentrations higher than 1.2 · 10^?4M, Cu²⁺ ions are involved in the kinetic chain termination. A mechanism of graft polymerization is proposed. © 1993 John Wiley & Sons, Inc.     

Peculiarities of phase and supermolecular structure of graft copolymers of polycaproamide with poly(methacrylic acid)

The structure of graft copolymers of PCA with PMAA obtained by the methods of chemically initiated liquid-phase grafting polymerization has been investigated with the use of electron microscopy, electron-probe microanalysis, and X-ray radiography. The concentration profiles of the graft copolymer distribution along the fiber cross section and diffusion coefficients of the monomer solutions correlated with the kinetics of the graft layer penetration inside the polymeric matrix have been determined. The concentration profile of the graft polymer distribution has been shown to have drops down to the zero level. Grafting proceeds both in the amorphous regions and on the surface of imperfect crystals. The structure of the graft layer, in which the segregated chains of graft PMAA constitutes the dispersed medium and the PCA inclusions represent the dispersed phase, has been found to be heterogeneous.     

The prospects of brewery waste application in biohydrogen production by photofermentation of Rhodobacter sphaeroides

Selection of the source for biohydrogen (H₂) production is essential, since it affects bacterial metabolism. Pure organic substrates give fast H₂ generation with high yields, but they increase the production cost. Using industrial wastes as a source provides inexpensive energy generation with simultaneous waste utilization. H₂ production by photofermentation of Rhodobacter sphaeroides is monitored during cultivation on brewery waste. Maximum specific growth rate is observed for 5–10% waste containing media. H₂ production by cells, grown on waste, is detected at 48–96 h of growth; it is comparable or higher than that of control medium with expensive carbon and nitrogen sources. N,N′-dicyclohexylcarbodiimide-sensitive ATPase activity of R. sphaeroides membrane vesicles from growth on waste containing media is 1.6–1.7-fold higher compared to control, correlating with enhanced H₂ production. Growth medium containing optimal amount of wastes may be a successful alternative to expensive media for high H₂ yield in R. sphaeroides during photofermentation.