Three-dimensional shape of natural riblets in the white shark: relationship between the denticle morphology and swimming speed of sharks.

The ridges of the dermal denticles of migratory sharks have inspired riblets to reduce the frictional drag of a fluid. In particular, the dermal denticles of white sharks (Carcharodon carcharias) are characterized by a high middle ridge and low side ridges. The detailed morphology of their denticles and their variation along the body, however, have never been investigated. Moreover, the hydrodynamic function of high-low combinations of ridges is unknown. In this article, the ridge spacings and heights of the white shark denticles were three-dimensionally quantified using microfocus X-ray computed tomography. Then, the swimming speed at which the ridges would reduce drag was hydrodynamically calculated with a flat plate body model and previous riblet data. High ridges with a large spacing were found to effectively reduce drag at a migration speed of 2.3 m s-1, while adjacent high and low ridges with a small spacing reduced drag at a burst hunting speed of 5.1 m s-1. Moreover, the above hydrodynamic calculation method was also applied to the shortfin mako shark and an extinct giant shark (called megalodon) with known ridge spacings, resulting in the estimated hunting speeds of 10.5 m s-1and 5.9 m s-1, respectively.

Deterioration of modern concrete structures and asphalt pavements by respiratory action and trace quantities of organic matter.

In concrete structures (concrete), damage from cracks, deterioration, amorphization, and delamination occur in some structures, causing disaggregation (concrete changed to very fine particles) and hollowing out of the concrete. In concrete pavements, damage from large amounts of pop-out of aggregate occurs from the surface of the concrete pavement 4-5 hours after spraying of snow melting agent on the surface of the pavement. The damage from disaggregation, blistering, cracks, and peeling-off of a surface course have also been observed in asphalt runways and highways. The damage from disaggregation, cracks and pop-out of aggregate in asphalt pavements and concrete structures have long been seen as strange and unexpected and have defied explanation. As a result of examinations in various experiments, it was concluded that all of the unexplained kinds of damage of both asphalt pavements and concrete structures were caused by Trace Quantities of Organic Matter (TQOM), Air Entrained (AE) water reducing agent in air and/or cement, and surfactant in snow melting agent. The emission sources of TQOM and these organic substances were also identified by chemical analysis for these unexpected and unexplained phenomena. The TQOM includes phthalate compounds (phthalates in the following), amine compounds, phosphate compounds, snow melting agent and Sodium Polyoxyethylene Nonyl phenyl Ether Sulfate (SPNES). SPNES is a surfactant in windshield washer fluid for automobiles. We found that the water content and content of organic matter in damaged asphalt pavements and concrete structures are also important indicators for the damage. Further, a new evaluation method for amorphization was proposed in this study and it appears suitable for evaluating the safety of concrete structures along roads which were exposed to TQOM in severely air-polluted environments.