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Spiral ribs are among the most common morphological features in mollusk shells and previous studies have shown them to have functional significance with expected evolutionary consequences. Many previous studies, however, have treated these features as potentially analogous across taxa, without examining whether they may have important constructional dissimilarities. Mollusk shells are made of multiple layers of calcite or aragonite which may exhibit different microstructure or microstructure orientations which may in turn impact their mechanical properties. In this study, five specimens of marine mollusks with spiral ribs, including three turritellid gastropods and two bivalves, were examined under SEM to examine microstructure of ribbed region in comparison of non-ribbed region. SEM imaging revealed differences in the number and thickness of distinct microstructural layers of each shell and allowed comparisons to be made between the ribbed and non-ribbed region of each specimen, providing a greater understanding of how these ribs were constructed during shell deposition. Ribs in all specimens are formed through the thickening of single or multiple crossed-lamellar layers, but differences in rib ultrastructures were found among species and different ribs of same species, showing great diversity and complexity of constructional mechanisms. This diversity in rib construction might indicate heterology in the development of shell sculpture, especially mechanisms for differences in concurrently deposited rib strength. This is especially notable for turritellids where the pattern of onset of spiral ornamentation is phylogenetically informative, suggesting homology of rib identity. Further study will be conducted on turritellid gastropods in different lineages to explore the taxonomic meaning of different rib constructional mechanisms.
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Effect of Surface Topography on Particle Deposition from Liquid Suspensions in Channel Flow
A Eulerian—Lagrangian model has been developed to simulate particle attachment to surfaces with arc-shaped ribs in a two-dimensional channel flow at low Reynolds numbers. Numerical simulation has been performed to improve the quantitative understanding of how rib geometries enhance shear rates and particle-surface interact for various particle sizes and flow velocities. The enhanced shear rate is attributed to the wavy flows that develop over the ribbed surface and the weak vortices that form between adjacent ribs. Varying pitch-to-height ratio can alter the amplitude of the wavy flow and the angle of attack of the fluid on the ribs. In the presence of these two competing factors, the rib geometry with a pitch-to-height ratio of two demonstrates the greatest shear rate and the lowest fraction of particle attachment. However, the ribbed surfaces have negligible effects on small particles at low velocities. A force analysis identifies a threshold shear rate to reduce particle attachment. The simulated particle distributions over the ribbed surfaces are highly non-uniform for larger particles at higher velocities. The understanding of the effect of surface topography on particle attachment will benefit the design of surface textures for mitigating particulate fouling in a wide range of applications.
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- Award ID(s):
- 1705538
- PAR ID:
- 10319164
- Date Published:
- Journal Name:
- Fluids
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2311-5521
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/fluids5010008
