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Biology and physiology


Study of the Folding - Unfolding Transition in Globular Proteins truecm

Proteins, unlike simple polymers, fold to a unique spatial conformation through a process which is little understood. Here we want to measure directly a good parameter to describe the transition, and we choose the average size of the molecule. Schematically, the experimental setup consists in confining a monolayer of protein molecules between two flat plates which are free to move, and monitor the distance between the plates, the swelling of the molecules pushing them apart as one crosses the transition. We measure variations of the plates' separation interferometrically, with 1 Angstrom resolution. At present the apparatus is essentially ready and we are about to start the measurements. truecm

G. Zocchi, M.H. Jensen and K. Sneppen truecm

Morphology in Growth of Interfaces truecm

We are performing an experimental study of the interface formed when a fungus colony grows on a two-dimensional surface. The characteristic length scales are studied by means of an analysis of the curvature of the interface. A macroscopic length scale characterising the interplay between diffusion and an inhibitory instability has been identified and is now being studied in detail. truecm

T. Sams, C. Ellegaard, V. Putkaradze, (B. E. Christensen) and (U. Thrane) truecm

Modeling Interactions between HIV and the Imune System truecm

Antibodies specific for epitopes of HIV glycoprotein gp 120 or gp 41 can inhibit or enhance HIV infection of human cells in vitro. These effects may have significant implications both for the pathogenesis of chronic HIV infection and for vaccine development. A particular puzzling finding in vitro is antibody dependent enhancement at low antibody concentrations while high concentrations of the same antibody inhibit infection.We have proposed a mathematical model that describes how these two processes interact and hereby provide an explanation of the observed enhancement. Simulation results were validated against empirical data from HIV infection of monocytoid (U937) cells in vitro. truecm

(J. Hansen), (J.-E. S. Hansen), O. Lund, E. Mosekilde and (J.O. Nielsen) truecm

Modeling Bone Remodeling truecm

Bone remodeling changes bones mass, architecture, and strength during aging. These changes seem to be accelerated during menopause.We have developed a stochastic simulation model of vertebral trabecular bone remodeling. The model can assist in evaluating the long-term effects of changes in the remodeling process. The results show that a menopause-related doubling of the activation frequency causes a transient, mainly reversible bone loss. If the menopause is accompanied by an increase in both activation frequency and resorption depth, then the resulting bone loss will be more pronounced and with a larger part being related with irreversible perforations. As part of the same study we have designed a computer program for direct measurement of 3D connectivity density in iliac crest bone sections as used for conventional histomorphometry. truecm

(R. Boyce), E. Mosekilde, (Li. Mosekilde) and J.S. Thomsen truecm

Modeling Pulsatile Insulin Secretion truecm

The relationship between the in vivo insulin secretory responsiveness of the pancreatic -cell to glucose and the flux of glucose through the enzyme glucokinase has been investigated in six subjects with heterozygous glucokinase mutations and in six matched control subjects. In two subjects with glucokinase mutations, which resulted in only a small reduction in enzyme activity, the decrease in insulin secretion was directly proportional to the reduction in the flux of glucose through glucokinase. In four subjects with severe reductions in enzymatic activity, insulin was reduced compared with control subjects, but less than predicted.We have suggested a simple model which can explain the compensatory change in the b-cells for the latter subjects. truecm

(P. Froguel), E. Mosekilde, (K. Polonsky) and (J. Sturis) truecm

Hyperchaos in Micro- and Macrobiological Population Dynamics truecm

We have simulated a variety of 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. 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. We have also 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). truecm

M. Barfred, M. Liberoth and E. Mosekilde

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Next: Nonlinear Chemical Dynamics Up: RESEARCH PROJECTS Previous: Fractalscritical phenomena

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