The comparative hydrodynamics of rapid rotation by predatory appendages.

Countless aquatic animals rotate appendages through the water, yet fluid forces are typically modeled with translational motion. To elucidate the hydrodynamics of rotation, we analyzed the raptorial appendages of mantis shrimp (Stomatopoda) using a combination of flume experiments, mathematical modeling and phylogenetic comparative analyses. We found that computationally efficient blade-element models offered an accurate first-order approximation of drag, when compared with a more elaborate computational fluid-dynamic model. Taking advantage of this efficiency, we compared the hydrodynamics of the raptorial appendage in different species, including a newly measured spearing species, Coronis scolopendra The ultrafast appendages of a smasher species (Odontodactylus scyllarus) were an order of magnitude smaller, yet experienced values of drag-induced torque similar to those of a spearing species (Lysiosquillina maculata). The dactyl, a stabbing segment that can be opened at the distal end of the appendage, generated substantial additional drag in the smasher, but not in the spearer, which uses the segment to capture evasive prey. Phylogenetic comparative analyses revealed that larger mantis shrimp species strike more slowly, regardless of whether they smash or spear their prey. In summary, drag was minimally affected by shape, whereas size, speed and dactyl orientation dominated and differentiated the hydrodynamic forces across species and sizes. This study demonstrates the utility of simple mathematical modeling for comparative analyses and illustrates the multi-faceted consequences of drag during the evolutionary diversification of rotating appendages.

Blue microchip laser fabricated from Nd:YAG and KNbO(3).

A Nd:YAG/KNbO(3) composite-material microchip laser has generated blue radiation at 473 nm with output powers of 1 mW when diode laser pumped and 9 mW when Ti:sapphire laser pumped. The fundamental radiation generated by the quasi-three-level (4)F(3/2)-(4)I(9/2) transition in Nd:YAG at 946 nm was frequency doubled in KNbO(3) angle cut to be type I critically phase matched at 45 degrees C. Despite the normally isotropic nature of Nd:YAG, the fundamental is emitted linearly polarized and orthogonal to the linearly polarized blue radiation.