Biomedical subjects

B Utter

Publications and source records attributed to B Utter.

3 recordsLinked to original sources

PubMed2002

Dynamics of low anisotropy morphologies in directional solidification.

We report experimental results on quasi-two-dimensional diffusion limited growth in directionally solidified succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense branching morphology, is selected by growing grains close to the [111] plane, where the in-plane surface tension is nearly isotropic. The observed growth morphologies are very sensitive to small anisotropies in surface tension caused by misorientations from the [111] plane. Different seaweed morphologies are found, including the degenerate, the stabilized, and the strongly tilted seaweeds. The degenerate seaweeds show a limited fractal scaling range and, with increased undercooling, suggests a transition from "fractal" to "compact" seaweed. Strongly tilted seaweeds demonstrate a significant twofold anisotropy. In addition, seaweed-dendrite transitions are observed in low anisotropy growth.

Journal Article↗

PubMed2001

Alternating tip splitting in directional solidification.

We report experimental results on the tip splitting dynamics of seaweed growth in directional solidification of succinonitrile alloys. Despite the random appearance of the growth, a tip splitting morphology was observed in which the tip alternately splits to the left and to the right. The tip splitting frequency f was found to be related to the growth velocity V as a power law f~V1.5. This finding is consistent with the predictions of a tip splitting model that is also presented. Small anisotropies are shown to lead to different kinds of seaweed morphologies.

Journal Article↗

PubMed1996

Wave-induced forces on the giant kelp Macrocystis pyrifera (Agardh): field test of a computational model

We propose a hydro-mechanical numerical model that predicts the maximal tension to which stipes of the giant kelp Macrocystis pyrifera will be subjected when exposed to ocean waves. Predicted maximal tensions are close to those measured in the field. The strength of Macrocystis pyrifera stipes was measured, allowing our prediction of forces to be translated into a prediction of the fraction of stipes broken. Predicted breakage is low even for extreme storm waves, a testament to the mechanical design of individual kelp fronds. However, empirically measured rates of kelp mortality can be high, considerably higher than those predicted on the basis of hydrodynamic forces acting alone. This indicates that factors not taken into account in our model (such as holdfast dislodgment, entanglement of stipes, damage from herbivory and wave breaking) contribute substantially to mortality in Macrocystis pyrifera.

Journal Article↗