Biology and Physiology

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Biology and Physiology


Chaos in Physiological Systems 0.01truecm

Experimental investigations performed of The Department of Medicine, University of Chicago, have shown the existence of internally generated pulsations in human insulin production and release with a typical period of 100-120 min.

To understand the mechanisms underlying these pulses, we have developed a model of the glucose-insulin regulatory system in collaboration with K. Polonsky and J. Sturis, University of Chicago. By adding to the standard picture of this regulation mechanisms which allow for the distribution of insulin between the plasma and the intercellular spaces and for the delayed release of glucose from the liver, the model becomes unstable and generates self-sustained oscillations with a typical period of 2h.

By forcing the insulin release by means of a periodically varying intravenous glucose infusion, frequency-locking and other highly nonlinear dynamic phenomena have been experimentally observed. -0.1truecm R. Feldberg, E. Mosekilde, C. Knudsen, (J. Sturis), and J.S. Thomsen 0.3truecm

Hyperchaos in Microbiological Population Dynamics 0.01truecm

We have simulated a variety of different growth, competition and selection processes that may arise in interacting populations of bacteria and phages. Our model considers a culture containing several variants of the same bacterium, each sensitive to attacks from a specific phage. The culture grows in a chemostat with continuous supply of nutrients. Surplus bacteria and phages are removed through dilution. Depending of the rate of dilution, the model exhibits stable equilibrium, self-sustained oscillations, quasiperiodic behavior, deterministic chaos or hyperchaos. This last form of dynamics is characterized by two or more positive Lyapunov exponents. It is likely that this type of behavior can arise in many biological systems when more than a few species are involved. -0.1truecm (G. Baier), (J. Engelbrecht), E. Mosekilde, and J.S. Thomsen 0.3truecm

Chaos and hyperchaos in ecological models 0.01truecm

We have studied the dynamics of a simple model of an aquatic ecosystem with four different species (bacteria, algae, zooplankton and fish) and three different dead pools (detritus and accessible nutrients in the water column and nutrients bound to the sediment). Depending on the characteristics of the species and on the inlet concentration of nutrients, various types of solutions from simple periodic oscillations to hyperchaos were found. -0.1truecm M. Barfred, M. Liberoth, and E. Mosekilde 0.3truecm

Bifurcations in a Vocal Fold Model 0.01truecm

An autonomous fourth-order model of vibrations of the vocal folds has been proposed. Each of the vocal folds is modeled by an upper and a lower mass. The aerodynamic forces are derived from a modified Bernoulli equation. In a wide parameter region the dynamics of the model exhibits many features of normal phonation. Near the borders of this parameter region coexistence of limit cycles, bifurcations, and chaos are observed. The implications for an understanding of pathological voices are addressed. -0.1truecm (H. Herzel) and C. Knudsen 0.3truecm

Enhancement/Inhibition of HIV Infection 0.01truecm

Antibodies specific for epitopes on HIV glycoprotein gp120 or gp41 can inhibit or enhance HIV infection of human cells in vito. These effects may have significant implications both for the pathogenesis of chronic HIV infection and for vaccine development. A particular puzzling finding in vito is antibody dependent enhancement at low concentrations of antibodies while high concentrations of the same antibody inhibit infection. Antibodies can inhibit infection by several mechanisms. However, by binding to receptors on target cells, virus bound antibodies can also enhance adhesion to these cells and thereby facilitate infection. We have developed a mathematical model which can account for these phenomena in detail. -0.1truecm (J. Hansen), (J.-E.S. Hansen), O. Lund, E. Mosekilde, and (J.O. Nielsen) 0.3truecm

Glycosylation and Protein Conformation 0.01truecm

Peptide linked carbohydrate affect such physical properties of glycoproteins as solubility, stability and conformation. Biologically, glycosylation modulates immunogenecity, tissue distribution and life time of glycoproteins. Increasing evidence indicates that surface carbohydrates play a major role in recognition, development, oncogenesis and viral infection. It is therefore of interest to investigate the relation between O- or N-linked oligosaccharides and glycoprotein conformation. We have applied artificial neural networks to stochastically analyse the local amino acid distribution and conformation at glycosylation sites in glycoproteins as inferred from the data bases. -0.1truecm (H. Clausen), (J.E. Hansen), (J.-E.S. Hansen), O. Lund, E. Mosekilde, (J.O. Nielsen), and (K. Rapacki) 0.3truecm

Computerized Image Comparison 0.01truecm

In the calculation of bone connectivity a comparison between two closely made cuts in bone tissue is performed. This comparison is normally carried out by copying the two cuts on two transparencies, and the alignment of the two sections is made by hand. However, inaccuracies in the copy process and distortion from the cutting of the bone samples often imply that the images will not match well over their whole area. We have developed a method of applying techniques from non-linear dynamics to computerize the processes of alignment and comparing two bone sections. -0.1truecm E. Mosekilde, (Li. Mosekilde), and J.S. Thomsen 0.3truecm

Simulation of Multiple Remodeling Events in Human Cancellons Bone 0.01truecm

Imbalances in the remodeling process have significant influence on the rate and severity of the microstructural alterations in the trabecular network and consequently on the strength of bone at the organ level. These alterations include changes in the remodeling frequency and changes in bone balance at the level of the remodeling unit due to altered resorption cell or osteoblastic cell activity. We have developed a model with published remodeling data from different treatment regimens and applied it to simulate multiple remodeling events and to predict the long time effects of various treatments on bone mass, trabecular thickness, and perforations. -0.1truecm E. Mosekilde, (Li. Mosekilde), and J.S. Thomsen

next up previous contents
Next: Chemical Reaction-Diffusion Systems Up: RESEARCH PROJECTS Previous: Fractalscritical phenomena

Nikolaj Berntsen
Mon Feb 6 10:24:27 MET 1995
14. Feb. 1995
Nikolaj Berntsen,