Climate of a school class

The theoretical part of the thesis deals predominantly with the climate of a school class, with the class being viewed as a social group. The focus is on the pupil as a member of both formal as well as informal groups and on his/her social behaviour

Regional variations in the nonlinearity and anisotropy of bovine aortic elastin

Arterial walls have a regular and lamellar organization of elastin present as concentric fenestrated networks in the media. In contrast, elastin networks are longitudinally oriented in layers adjacent to the media. In a previous model exploring the biomechanics of arterial elastin, we had proposed a microstructurally motivated strain energy function modeled using orthotropic material symmetry. Using mechanical experiments, we showed that the neo-Hookean term had a dominant contribution to the overall form of the strain energy function. In contrast, invariants corresponding to the two fiber families had smaller contributions. To extend these investigations, we use biaxial force-controlled experiments to quantify regional variations in the anisotropy and nonlinearity of elastin isolated from bovine aortic tissues proximal and distal to the heart. Results from this study show that tissue nonlinearity significantly increases distal to the heart as compared to proximally located regions (). Distally located samples also have a trend for increased anisotropy (), with the circumferential direction stiffer than the longitudinal, as compared to an isotropic and relatively linear response for proximally located elastin samples. These results are consistent with the underlying tissue histology from proximally located samples that had higher optical density (), fiber thickness (), and trend for lower tortuosity () in elastin fibers as compared to the thinner and highly undulating elastin fibers isolated from distally located samples. Our studies suggest that it is important to consider elastin fiber orientations in investigations that use microstructure-based models to describe the contributions of elastin and collagen to arterial mechanics

MCF7 cells at the time of release from circle (A), square (B) and cross (C) shaped constraints are shown.

<p>A representation of the regions chosen as the vertices (red), sides (blue) and intersections (green) in the three shapes are indicated in the boxes. Scale bar = 500 μm.</p

Velocity fields and vorticity maps for MDCK cells are shown at 2 hours (A, D), 8 hours (B, E) and 16 hours (C, F) after removal of constraint.

<p>The cluster border is also shown at 0 hours for reference. Cells in the vertices show minimal movement as compared to those in the sides and intersections (D, E, F). We see the development of vortices, in both clockwise (blue) and counter clockwise (yellow-red) directions at intersections by 16 hours. Scale bar = 250 μm.</p

Migrations of MCF7 cells located on the advancing edges of the circle (A), square (B) and cross shapes (C) were obtained using individual cell tracking and are illustrated on a windrose plot to show the cell migration trajectories from the cluster edge.

<p>We see differences in motility that depend on the cell spatial positions which are labelled corresponding to sides, vertices and intersections.</p

Cluster speeds show temporal differences in the different regions of the circle (A), square (B) and cross (C) shapes respectively.

<p>Speeds from the sides increase (I), plateau (II) and finally decrease (III) over time. These results show clear differences in cluster edge speeds which depend on spatial location in the geometry. Significant differences (p<0.05) in speeds are indicated in each figure.</p

Fluorescence images show actin (red) and the nucleus (blue) for MCF7 clusters at 0 hours (A), 24 hours (B), and 48 hours (C) after release from constraints.

<p>There is no clear cable-like structure bounding the cluster. Scale bar = 100 μm.</p

Velocity and vorticity fields in MCF7 cell monolayers in the circle (A), square (B), cross vertex (C) and intersections (D) at 30 hours summed every hour.

<p>The solid black line is the cluster border at the start of migration. Scale bar = 250 μm.</p

Velocity and vorticity plots are shown for cell clusters treated with 50 μM blebbistatin to inhibit myosin2 and alter cytoskeletal tension.

<p>A. MCF7 at 30 hours and B. MDCK at 16 hours. Scale bar = 200 μm.</p