The heat generated by yeast cultures with a mixed metabolism in the transition between respiration and fermentation

The heat generated by both batch and continuous cultures of the yeast Kluyveromycs fragilis was studied using a modified bench scale calorimeter. Batch cultures were used to measure the heat dissipation rates and the heat yields during fully aerobic and completely anaerobic growth, whereas continuous cultures also allowed a quant. study of heat dissipation rates during growth on mixed metab. The extent of fermn. vs. respiration could be specified and controlled by O2 limitation. The heat dissipated per unit biomass formed was highest for fully respirative catabolism and fell continuously to a much lower value typical of anaerobic cultures as the catabolism was shifted increasingly to the fermentative mode. The heat generated/mol O2 taken up stayed quite close to the fully aerobic value of 50 kJ/mol even when a sizable fraction of the substrate available to catabolism was fermented. If the fraction of respiration in the metab. is lowered beyond a certain threshold, the ratio of the heat generation to O2 consumption starts to increase dramatically and finally tends to infinity for fully anaerobic growth. All exptl. results were quant. analyzed and explained on the basis of a simple model which formally describes the cultures in terms of 2 parallel chem. reactions. In simple cases, the model enables calcn. of the whole stoichiometry of the culture from a single measured heat yield. [on SciFinder (R)

Use of a novel heat-flux calorimeter for the measurement of heat generated during growth of K. fragilis on lactose

A novel bench-scale calorimeter, which is based on a heat-flux principle and modified to accommodate biol. reactions, was evaluated for detg. the heat evolution rate of an aerobic culture of the yeast Kluyveromyces fragilis grown on lactose. The instantaneous heat evolution rate was an accurate indicator for the instantaneous overall metabolic activity. On the other hand, the integrated heat prodn. increased in parallel to the accumulated cell dry wt. The ratios of heat generated per g biomass produced and of heat generated per mol of consumed O were const. throughout the expt. despite changing growth rates and metab. [on SciFinder (R)

A calorimetric study of microbial growth energetics

Isothermal reaction calorimetry was employed on the bench scale to measure the enthalpy efficiency and O2 efficiency of growth of several microbial strains cultured on a range of substrates with varying degrees of redn. The obsd. values of these energetic efficiency factors agreed well with simple theor. predictions based solely on the degree of redn. of the substrates as independent variable. Calorimetry is thus shown to be a useful tool for investigations of microbial growth energetics. Measuring heat dissipation in large scale bioreactors provides online information on the energetics of growth and should therefore be useful for process control purposes. [on SciFinder (R)

Optimal Fuzzy Controller Tuned by TV-PSO for Induction Motor Speed Control

This paper reports an automated procedure for the design of an optimal fuzzy logic controller to be used as an induction motor speed controller. The procedure consists of selection of a suitable well known fuzzy logic controller and tuning via particle swarm optimization optimal for the selected criteria. In this way the time required for tuning of the controller is significantly reduced in comparison with trial and error methods. As a benchmark a proportional-integral (PI) controller is used. The PI controller is tuned via the symmetrical optimum procedure, the standard procedure for tuning a speed controller of an induction motor. Simulation results are obtained via a mathematical model developed in Matlab/Simulink. Experimental verification is carried out with a laboratory model based on the DS1104 digital control card. To minimize iron losses and to provide better motor performance for low loads, flux is reduced from nominal and speed is kept below nominal. Results are presented in tables and graphics. The optimal fuzzy logic controller provides a slight practical advantage