Trailing-edge fringes enable robust aerodynamic force production and noise suppression in an owl wing model.

As one of the unique owl-wing morphologies, trailing-edge (TE) fringes are believed to play a critical role in the silent flight of owls and have been widely investigated using idealized single/tandem airfoils. However, the effect of TE fringes and associated mechanisms on the aeroacoustics of owl wings, which feature curved leading edges, wavy TEs, and several feather slots at the wingtips, have not yet been addressed. In this study, we constructed two 3D owl wing models, one with and one without TE fringes, based on the geometric characteristics of a real owl wing. Large-eddy simulations and the Ffowcs Williams‒Hawkings analogy were combined to resolve the aeroacoustic characteristics of the wing models. Comparisons of the computed aerodynamic forces and far-field acoustic pressure levels demonstrate that the fringes on owl wings can robustly suppress aerodynamic noise while sustaining aerodynamic performance comparable to that of a clean wing. By visualizing the near-field flow dynamics in terms of flow and vortex structures as well as flow fluctuations, the mechanisms of TE fringes in owl wing models are revealed. First, the TE fringes on owl wings are reconfirmed to robustly suppress flow fluctuations near the TE by breaking up large TE vortices. Second, the fringes are observed to effectively suppress the shedding of wingtip vortices by mitigating the flow interaction between feathers (feather-slot interaction). These complementary mechanisms synergize to enhance the robustness and effectiveness of the TE fringe effects in owl wing models, in terms of aerodynamic force production and noise suppression. This study thus deepens our understanding of the role of TE fringes in real owl flight gliding and points to the validity and feasibility of employing owl-inspired TE fringes in practical applications of low-noise fluid machinery.

Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils.

Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.

Relation Between Prefrontal Cortex Activity and Respiratory Rate During Mental Stress Tasks: A Near-Infrared Spectroscopic Study.

In order to clarify the central mechanism controlling respiratory rate during mental stress, we examined the relation between prefrontal cortex (PFC) activity and respiratory rate during mental arithmetic (MA) tasks. Employing two-channel near-infrared spectroscopy (NIRS), we measured hemoglobin (Hb) concentration changes in the bilateral PFC during MA tasks in normal adults. To evaluate asymmetry of the PFC activity, we calculated the laterality index (LI); (R-L)/(R + L) of oxy-Hb concentration changes (R = right, L = left); positive LI scores indicate right-dominant activity, while negative scores indicate left-dominant activity. For measurements of respiratory rate, we employed a Kinect motion sensor (Microsoft). The MA tasks increased both oxy-Hb in the bilateral PFC and respiratory rate (p < 0.001). In addition, there was a significant correlation between LI and respiratory rate (r = 0.582, p < 0.02). These results indicate that the MA-induced activity in the right PFC was greater than that in the left PFC in subjects with large increases of respiratory rate, suggesting that the right PFC has a greater role in cerebral regulation of respiratory rate during mental stress.

Effects of Antioxidant Supplements (BioPQQ™) on Cerebral Blood Flow and Oxygen Metabolism in the Prefrontal Cortex.

Pyrroloquinoline quinone (PQQ) is a quinone compound originally identified in methanol-utilizing bacteria and is a cofactor for redox enzymes. At the Meeting of the International Society on Oxygen Transport to Tissue (ISOTT) 2014, we reported that PQQ disodium salt (BioPQQ™) improved cognitive function in humans, as assessed by the Stroop test. However, the physiological mechanism of PQQ remains unclear. In the present study, we measured regional cerebral blood flow (rCBF) and oxygen metabolism in prefrontal cortex (PFC), before and after administration of PQQ, using time-resolved near-infrared spectroscopy (tNIRS). A total of 20 healthy subjects between 50 and 70 years of age were administered BioPQQ™ (20 mg) or placebo orally once daily for 12 weeks. Hemoglobin (Hb) concentration and absolute tissue oxygen saturation (SO2) in the bilateral PFC were evaluated under resting conditions using tNIRS. We found that baseline concentrations of hemoglobin and total hemoglobin in the right PFC significantly increased after administration of PQQ (p < 0.05). In addition, decreases in SO2 level in the PFC were more pronounced in the PQQ group than in the placebo group (p < 0.05). These results suggest that PQQ causes increased activity in the right PFC associated with increases in rCBF and oxygen metabolism, resulting in enhanced cognitive function.