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  • W Alt
  • Journal of mathematical biology
  • 1980
Stochastic models of biased random walk are discussed, which describe the behavior of chemosensitive cells like bacteria or leukocytes in the gradient of a chemotactic factor. In particular the turning frequency and turn angle distribution are derived from certain biological hypotheses on the background of related experimental observations. Under suitable(More)
In order to provide a general framework within which the dispersal of cells or organisms can be studied, we introduce two stochastic processes that model the major modes of dispersal that are observed in nature. In the first type of movement, which we call the position jump or kangaroo process, the process comprises a sequence of alternating pauses and(More)
Formation of lamellipodia and the retraction of ruffles are essential activities during motility and migration of eukaryotic cells. We have developed a computer-assisted stroboscopic method for the continuous observation of cell dynamics (stroboscopic analysis of cell dynamics, SACED) that allows one to analyze changes in lamellipodia protrusion and ruffle(More)
Most of the knowledge on falls of older persons has been obtained from oral reports that might be biased in many ways. Fall simulations are widely used to gain insight into circumstances of falls, but the results, at least concerning fall detection, are not convincing. Variation of acceleration and maximum jerk of 5 real-world backward falls of 4 older(More)
The motion of amoeboid cells is characterized by cytoplasmic streaming and by membrane protrusions and retractions which occur even in the absence of interactions with a substratum. Cell translocation requires, in addition, a transmission mechanism wherein the power produced by the cytoplasmic engine is applied to the substratum in a highly controlled(More)
Many molecular details of the ecophysiology of halophilic bacteria that use compatible solutes to maintain osmotic equilibrium have been examined. We ask whether the details are consistent and complete enough to predict growth and osmoregulation in these bacteria by integrating this information in a mathematical model. Parameterized for the halophilic(More)
Path integration enables desert arthropods to find back to their nest on the shortest track from any position. To perform path integration successfully, speeds and turning angles along the preceding outbound path have to be measured continuously and combined to determine an internal global vector leading back home at any time. A number of experiments have(More)
We report the realization of a deterministic source of single atoms. A standing-wave dipole trap is loaded with one or any desired number of cold cesium atoms from a magneto-optical trap. By controlling the motion of the standing wave, we adiabatically transport the atom with submicrometer precision over macroscopic distances on the order of a centimeter.(More)
Because of its regular shape, fission yeast is becoming an increasingly important organism in the study of cellular morphogenesis. Genetic experiments with mutants and drug treatment studies with wild-type cells have revealed the importance of microtubules in controlling new growth zone formation. It is believed that microtubules exert this role by(More)
The motility of cells crawling on a substratum has its origin in a thin cell organ called lamella. We present a 2-dimensional continuum model for the lamella dynamics of a slowly migrating cell, such as a human keratinocyte. The central components of the model are the dynamics of a viscous cytoskeleton capable to produce contractile and swelling stresses,(More)