8 research outputs found
Multi-sample SPIM image acquisition, processing and analysis of vascular growth in zebrafish
To quantitatively understand biological processes that occur over many hours or days, it is desirable to image multiple samples simultaneously, and automatically process and analyse the resulting datasets. Here, we present a complete multi-sample preparation, imaging, processing and analysis workflow to determine the development of the vascular volume in zebrafish. Up to five live embryos were mounted and imaged simultaneously over several days using selective plane illumination microscopy (SPIM). The resulting large imagery dataset of several terabytes was processed in an automated manner on a high-performance computer cluster and segmented using a novel segmentation approach that uses images of red blood cells as training data. This analysis yielded a precise quantification of growth characteristics of the whole vascular network, head vasculature and tail vasculature over development. Our multi-sample platform demonstrates effective upgrades to conventional single-sample imaging platforms and paves the way for diverse quantitative long-term imaging studies
Theory of liquid crystal elastomers and polymer networks
In liquid crystal elastomers, the orientational order of liquid crystals is
coupled with elastic distortions of crosslinked polymer networks. Previous
theoretical research has described these materials through two different
approaches: a neoclassical theory based on the liquid crystal director and the
deformation tensor, and a geometric elasticity theory based on the difference
between the actual metric tensor and a reference metric. Here, we connect those
two approaches using a formalism based on differential geometry. Through this
connection, we determine how both the director and the geometry respond to a
change of temperature
Angular deficits in flat space: remotely controllable apertures in nematic solid sheets
Recent attention has been given to the realization of angular deficits and surpluses in the local ground-state geometry of thin sheets of nematic solids as out-of-plane deformations. Such systems exhibit conical or anti-conical curvature sites, or possibly arrays of such polyhedral corners, in order to satisfy the material's spontaneous strain-generated metric requirements. Here, we turn the angular deficit requirement on its head, and show theoretically and experimentally that by appropriately altering the topology of the initially flat sheet-for example, by cutting it in carefully chosen regions-the same angular deficits and surpluses may manifest simply in-plane by changing the geometry of the cut region. Such amechanism offers a route to apertures or arrays of apertures that may be reversibly opened and closed by applying spontaneous strain with heat, light or chemical potential
Mechanical frustration and spontaneous polygonal folding in active nematic sheets
We analyze the bending response to light or heat of a solid nematic disk with a director twisted from being radial on the upper surface to be azimuthal on the lower. We find a number of curl lobes determined purely by the geometry of the mechanical frustration that arises during the response
Mechanical frustration and spontaneous polygonal folding in active nematic sheets
We analyze the bending response to light or heat of a solid nematic disk with a director twisted from being radial on the upper surface to be azimuthal on the lower. We find a number of curl lobes determined purely by the geometry of the mechanical frustration that arises during the response
Reshaping nemato-elastic sheets
We consider three-dimensional reshaping of thin nemato-elastic sheets
containing half-charged defects upon nematic-isotropic transition. Gaussian
curvature, that can be evaluated analytically when the nematic texture is
known, differs from zero in the entire domain and has a dipole or hexapole
singularity, respectively, at defects of positive or negative sign. The latter
kind of defects appears in not simply connected domains. Three-dimensional
shapes dependent on boundary anchoring are obtained with the help of finite
element computations.Comment: 4 pages, 4 figure
Phase separation and disorder in doped nematic elastomers
We formulate and analyse a model describing the combined effect of mechanical deformation, dynamics of the nematic order parameter, and concentration inhomogeneities in an elastomeric mixture of a mesogenic and an isotropic component. The uniform nematic state may exhibit a long-wave instability corresponding to nematic-isotropic demixing. Numerical simulations starting from either a perfectly ordered nematic state or a quenched isotropic state show that coupling between the mesogen concentration and the nematic order parameter influences the shape and orientation of the domains formed during the demixing process