Gelatinous zooplankton populations are well known for their ability to take over perturbed ecosystems. The ability of these animals to outcompete and functionally replace fish that exhibit an effective visual predatory mode is counterintuitive because jellyfish are described as inefficient swimmers that must rely on direct contact with prey to feed. We show that jellyfish exhibit a unique mechanism of passive energy recapture, which is exploited to allow them to travel 30% further each swimming cycle, thereby reducing metabolic energy demand by swimming muscles. By accounting for large interspecific differences in net metabolic rates, we demonstrate, contrary to prevailing views, that the jellyfish (Aurelia aurita) is one of the most energetically efficient propulsors on the planet, exhibiting a cost of transport (joules per kilogram per meter) lower than other metazoans. We estimate that reduced metabolic demand by passive energy recapture improves the cost of transport by 48%, allowing jellyfish to achieve the large sizes required for sufficient prey encounters. Pressure calculations, using both computational fluid dynamics and a newly developed method from empirical velocity field measurements, demonstrate that this extra thrust results from positive pressure created by a vortex ring underneath the bell during the refilling phase of swimming. These results demonstrate a physical basis for the ecological success of medusan swimmers despite their simple body plan. Results from this study also have implications for bioinspired design, where low-energy propulsion is required.swimming efficiency | animal-fluid interactions

High-performance, all-aromatic, insoluble, engineering thermoplastic polyimides, such as pyromellitic dianhydride and 4,4'-oxydianiline (PMDA-ODA) (Kapton), exhibit exceptional thermal stability (up to ≈600 °C) and mechanical properties (Young's modulus exceeding 2 GPa). However, their thermal resistance, which is a consequence of the all-aromatic molecular structure, prohibits processing using conventional techniques. Previous reports describe an energy-intensive sintering technique as an alternative technique for processing polyimides with limited resolution and part fidelity. This study demonstrates the unprecedented 3D printing of PMDA-ODA using mask-projection stereolithography, and the preparation of high-resolution 3D structures without sacrificing bulk material properties. Synthesis of a soluble precursor polymer containing photo-crosslinkable acrylate groups enables light-induced, chemical crosslinking for spatial control in the gel state. Postprinting thermal treatment transforms the crosslinked precursor polymer to PMDA-ODA. The dimensional shrinkage is isotropic, and postprocessing preserves geometric integrity. Furthermore, large-area mask-projection scanning stereolithography demonstrates the scalability of 3D structures. These unique high-performance 3D structures offer potential in fields ranging from water filtration and gas separation to automotive and aerospace technologies.

Many of the crystals in the pharmaceuticals, photographic, and other industries are multidimensional; that is, their growth is associated with the change of multiple internal coordinates. The main governing equation for such systems is a highly nonlinear multidimensional population balance equation that must be solved for a wide range of length scales. For population balance equations, it is well-known that the standard first-order schemes give diffusive solutions while the commonly used second-order schemes give spurious oscillations. This paper presents a highresolution simulation algorithm that provides short computation times and high accuracy. The high-resolution algorithm is compared to the upwind difference and Lax-Wendroff methods through simulations of potassium dihydrogen phosphate (KDP, KH 2 PO 4 ) crystal nucleation and growth. No spurious oscillations or numerical diffusion occurred, in contrast to the upwind method and Lax-Wendroff methods. The numerical stability of the algorithm is assessed using the Courant-Friedrichs-Lewy condition.

Three-dimensional numerical simulation of the unsteady flow over a blunt plate held normal to a uniform stream has been carried out to study the physics of unsteady separation and reattachment. A finite-difference procedure is used with 32 spanwise grid cells. In comparison with previous two-dimensional results, it is observed that the inclusion of spanwise variations significantly improves the calculations and provides superior comparisons with experimental data. Mean turbulent quantities are calculated and found to be in good agreement with experiments. Instantaneous as well as statistical quantities describing the characteristic length and time scales of the large-scale structures are also presented. The calculations have also been able to capture the experimentally observed low-frequency unsteadiness of the separation bubble. In addition, a selective high-frequency shedding from the separated shear layer was found to occur with a period equal to that of the low-frequency unsteadiness.

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