A model for dispersion experiments

Summary A new model is proposed for the dispersion of animals and other organisms and its use is discussed for the analysis of the data from experiments on dispersion. The model is a generalisation of the random walk model, but because of its flexibility it should be much more widely applicable than the random walk model.The new model has been found to fit the results of many dispersion experiments and examples are given of its use with data for millipedes and Drosophila.     

Bacteriological studies on Iraqi milk products

F. ABBAR AND H. KH. KADDAR. 1991. Samples from different types of domestic milk products including cheese, kishfa and gaymer were assessed for bacteriological quality over a 4-month period. A total of 400 samples were randomly selected across Mosul city and tested for faecal coliform counts, enteropathogenic Escherichia coli (EPEC) and enterotoxigenic E. coli (ETEC). Faecal coliforms were present at levels greater than 10² cfu/g in 72.5% and less than 10² cfu/g in 27.5% of samples. Of the 430 E. coli strains isolated from the 400 samples of milk products, 138 were serotypes of EPEC. These were found in 81 (40.5%) samples of cheese, 35 (23.8%) of kishfa and 22 (29.7%) of gaymer. During this period, 26 strains of ETEC were also isolated, all of which demonstrated heat-labile or heat-stable toxins. The high proportion of strains of three groups of E. coli showing resistance to antibiotics is discussed in relation to widespread use of antibiotics and the possible public health implication.     

A dynamic model of angiotensin II infusion experiments

Applications of control theory in studies of biological system dynamics have come to be called compartmental modelling. A second order, nonlinear, compartmental model is developed which describes the dynamics of the hormone angiotensin II (AII) and arterial blood pressure (BP) during AII infusion experiments. The model is partially identified using dose response data for constant infusion rates between 0.01 and 0.10 μg/kg/min over a period of several minutes. This study represents a first step in understanding the dynamics of regulation of arterial blood pressure by the renin-angiotensin system. All is a vasoconstrictor and is known to participate in the natural regulation of BP. AII is also believed to be an agent in the development of hypertension and atherosclerosis. The model is used to identify causal mechanisms which are consistent both with the established correlation between plasma AII concentration and arterial BP and with current physiological knowledge. The study demonstrates how a simple state variable model can be used to provide guidance concerning the design of future infusion experiments.     

Optimal dynamic experiments for bioreactor model discrimination

 This paper describes a general approach fordynamic model discrimination for continuous cultures and presents dynamic models for pure cultures of E. coli and C. utilis obtained using the method. For each pure culture system, four candidate models representing various levels of structure were considered. All models reduce to Monod growth kinetics at steady state. An optimized set of multivariable step inputs in selected manipulative variables was used to discriminate between candidate models. The models that best predicted the dynamic behavior were selected by comparison of model predictions with experimental data. Two discrimination functions were compared in terms of their ability to determine the optimal set of multivariable step inputs to discriminate between candidate models. Results indicate that model discrimination based on maximizing the minimum absolute difference between any two models for a given set of inputs possessed good potential for discrimination between candidate models. Models selected for E. coli andC. utilis from the model discrimination work arepresented and compared with experimental data. Received: 24 May 1994/Received revision: 28 September 1994/Accepted: 5 December 1994