Analysis of three-dimensional ciliary beating by means of high-speed stereomicroscopy.

Results are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional data were obtained by using the anaxial illumination method for simultaneous recording of stereoscopic video images. Data processing involved the following steps: determination of a reference coordinate system based solely on features present in each stereo-pair; tracing of cirral axes in digitized images, conversion to parameter curves by means of least-squares polynomial approximation, conversion of pairs of two-dimensional data to a series of three-dimensional data; correction for distortion due to projective shortening and conversion to a series of polynomial triplets, and analysis of the periodical components of the motion pattern in the frequency domain. Reconstructed beating cycles show typical differences between hyperpolarization-induced ciliary activity and depolarization-induced ciliary activity. Reconstructions of the motion of the basal segment of a cirrus are in agreement with existing data. Analysis of the curvature and torsion of a cirral axis during beating does not reveal any simple pattern of propagated activity within the axoneme. The return stroke may be subdivided into two phases. First, a curvature peak develops proximally. Secondly, a region with increased torsion arises more distally and spreads out in proximal direction. Both curvature and torsion return to minimal values by the beginning of the power stroke.     

Further results on the survival of a gene represented in a founder population

This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982).     

FEM-based oxygen consumption and cell viability models for avascular pancreatic islets

Background  

The function and viability of cultured, transplanted, or encapsulated pancreatic islets is often limited by hypoxia because these islets have lost their vasculature during the isolation process and have to rely on gradient-driven passive diffusion, which cannot provide adequate oxygen transport. Pancreatic islets (islets of Langerhans) are particularly susceptible due to their relatively large size, large metabolic demand, and increased sensitivity to hypoxia. Here, finite element method (FEM) based multiphysics models are explored to describe oxygen transport and cell viability in avascular islets both in static and in moving culture media.