Graduate Thesis Or Dissertation


The dynamic shear moduli of blubber for selected large whale species Public Deposited

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  • Whale blubber is the insular tissue layer located between the dermis and the superficial fascia layer which sheathes the whale's musculature. It is made up of a lipid matrix ramified with strong, structural collagen and elastic fiber bundles, but little is known of its mechanical properties. Knowing these properties adds to the general knowledge of blubber and research that focuses on its physical response. Specifically, two current fields of research would gain from measurements of the complex dynamic shear modulus (G*=G'+iG"), a viscoelastic mechanical property, of blubber. The dynamic shear moduli G' and G" represent the elastic energy storage and the viscous energy dissipation, respectively. The first is drag reducing, compliant coatings, which seek to minimize the sonar signature and energy loss of submersibles. The second is subdermally attached satellite tracking tags that are remotely deployed into the dorsal region of large whales near the dorsal fin. The tags are used for defining whale migration patterns and behaviors to help reduce potentially harmful human interactions. In this study, the dynamic shear moduli were measured at different depths and oscillating frequencies (0.31-25Hz, rotational rheometer) for blubber samples taken from a humpback whale, sperm whale, and two gray whales. A semi-quantitative staining assay was also performed to determine relative changes in normalized collagen and normalized non-collagen proteins with depth. For all four whales, G' and G" were plotted for each sample against a log scale of oscillating frequency. In all cases G' and G" were fit with a linear and 3rd order polynomial trend line, respectively. For the vast majority, R² was higher than 0.960. In some cases it dropped as low as 0.870. The G', G", and G"/G' data points for 0.31Hz, 3.1Hz, and 25Hz were plotted against sample coin depth in the blubber. Polynomials were traced through these data sets to characterize the depth profiles of these properties at these three separate oscillating frequencies. Depth profiles were also created for the measured collagen and non-collagen protein content. In conclusion, the results showed that different whale species may have distinctly different depth profiles of G', G", collagen protein, and non-collagen protein, but also show a similarity in the orders of magnitude of these metrics. A potential correlation exists between the ratios of non-collagen/collagen protein and G"/G'. However, an obvious direct relation could not be found between the moduli or the protein types.
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