Natural organisms contain rich elements and naturally optimized smart structures,both of which have inspired various innovative concepts and desig ns in human society.In particular,several natural organisms have been ...Natural organisms contain rich elements and naturally optimized smart structures,both of which have inspired various innovative concepts and desig ns in human society.In particular,several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction(ORR)in fuel cells and metal-air batteries,which are clean energy devices.However,to date,no naturally optimized smart structures have been employed in the synthesis of ORR catalysts,including graphene-based materials.Here,we demonstrate a novel strategy to synthesize graphene-graphite films(GGFs)by heating butterfly wings coated with FeCI3 in N2,in which the full power of natural organisms is utilized.The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping,two-dimensional spreading,and double-face exposure of the GGFs.These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of<0.07%for ORR electrocatalysis;these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media.This two-in-one strategy is also successful with cicada and dragonfly wings,indicating that it is a universal,green,and cost-effective method for developing high-performance graphene-based materials.展开更多
Small Unmanned Aerial Vehicles have been receiving an increasingly interest in the last decades, fostered by the need of vehicles able to perform surveillance, communications relay links, ship decoys, and detection of...Small Unmanned Aerial Vehicles have been receiving an increasingly interest in the last decades, fostered by the need of vehicles able to perform surveillance, communications relay links, ship decoys, and detection of biological, chemical, or nuclear materials. Smaller and handy vehicles Micro Air vehicles (MAVs) become even more challenging when DARPA launched in 1997 a pilot study into the design of portable (150 mm) flying vehicles to operate in D3—dull, dirty and dangerous—environments. More recently DARPA launched a Nano Air Vehicle (NAV) program with the objective of developing and demonstrating small (<100 mm;<10 g) lightweight air vehicles with the potential to perform indoor and outdoor missions. The current investigation is focused on the mechanisms involved with natural locomotion (propulsion and lift should not be considered independently). Biological systems with interesting applications to MAVs are generally inspired on flying insects or birds;however, similarly to the aerodynamics of flight, powered swimming requires animals to overcome drag by producing thrust. Commonalities between natural flying and swimming are analyzed together with flow control issues as a purpose of improvement on biology-inspired or biomimetic concepts for Micro Air Vehicles implementation.展开更多
In this study,the aerodynamic performance of flapping wings using a parallel motion was investigated and compared with the insect-like‘‘fan-sweep’’motion,and the effect of adding a slit to the wings was analyzed.F...In this study,the aerodynamic performance of flapping wings using a parallel motion was investigated and compared with the insect-like‘‘fan-sweep’’motion,and the effect of adding a slit to the wings was analyzed.First,numerical simulations were performed to analyze the wing aerodynamics of two flapping motions with equivalent stroke amplitudes over a range of pitching angles based on computational fluid dynamics(CFD).The simulation results indicated that flapping wings with a rapid and short parallel motion achieved better lift and efficiency than those of the fan-sweep motion while maintaining the same aerodynamic characteristics regarding stall delay and leading-edge vortices.For a parallel motion with a pitching angle of 25◦and 100 mm stroke amplitude,the wings generated an average lift of 8.4 gf with a lift-to-drag ratio of 1.06,respectively,which were 1.8%and 26%greater than those of the fan-sweep motion with a corresponding 96◦stroke amplitude.This situation was reversed when the pitching angle and stroke amplitude were increased to 45◦and 144◦for the fan-sweep motion,which was equivalent to the parallel motion with a 150 mm stroke amplitude.The slit effect in the parallel motion was also evaluated,and the CFD results indicated that a slit width of 1 mm(1/50 wing chord)increased the lift of the wing by approximately 27%in the case of the 150 mm stroke amplitude.Further,the slit width slightly influenced the lift and aerodynamic efficiency.展开更多
Jamin–Lebedeff polarizing interference microscopy is a classical method for determining the refractive index and thickness of transparent tissues.Here,we extend the application of this method to pigmented,absorbing b...Jamin–Lebedeff polarizing interference microscopy is a classical method for determining the refractive index and thickness of transparent tissues.Here,we extend the application of this method to pigmented,absorbing biological tissues,based on a theoretical derivation using Jones calculus.This novel method is applied to the wings of the American Rubyspot damselfly,Hetaerina americana.The membranes in the red-colored parts of the damselfly’s wings,with a thickness of 2.5 μm,contain a pigment with maximal absorption at 490 nm and a peak absorbance coefficient of 0.7 μm^(-1).The high pigment density causes a considerable and anomalous dispersion of the refractive index.This result can be quantitatively understood from the pigment absorbance spectrum by applying the Kramers–Kronig dispersion relations.Measurements of the spectral dependence of the refractive index and the absorption are valuable for gaining quantitative insight into how the material properties of animal tissues influence coloration.展开更多
基金the National Key R&D Program of China(No.2017YFA0700104)the National Natural Science Foundation of China(Nos.21601136 and 11404016)+1 种基金the National Program for Thousand Young Talents of China,Tianjin Municipal Education Commission,Tianjin Municipal Science and Technology Commission(No.15JCYBJC52600)the Fundamental Research Fund of Tianjin University of Technology.
文摘Natural organisms contain rich elements and naturally optimized smart structures,both of which have inspired various innovative concepts and desig ns in human society.In particular,several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction(ORR)in fuel cells and metal-air batteries,which are clean energy devices.However,to date,no naturally optimized smart structures have been employed in the synthesis of ORR catalysts,including graphene-based materials.Here,we demonstrate a novel strategy to synthesize graphene-graphite films(GGFs)by heating butterfly wings coated with FeCI3 in N2,in which the full power of natural organisms is utilized.The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping,two-dimensional spreading,and double-face exposure of the GGFs.These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of<0.07%for ORR electrocatalysis;these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media.This two-in-one strategy is also successful with cicada and dragonfly wings,indicating that it is a universal,green,and cost-effective method for developing high-performance graphene-based materials.
文摘Small Unmanned Aerial Vehicles have been receiving an increasingly interest in the last decades, fostered by the need of vehicles able to perform surveillance, communications relay links, ship decoys, and detection of biological, chemical, or nuclear materials. Smaller and handy vehicles Micro Air vehicles (MAVs) become even more challenging when DARPA launched in 1997 a pilot study into the design of portable (150 mm) flying vehicles to operate in D3—dull, dirty and dangerous—environments. More recently DARPA launched a Nano Air Vehicle (NAV) program with the objective of developing and demonstrating small (<100 mm;<10 g) lightweight air vehicles with the potential to perform indoor and outdoor missions. The current investigation is focused on the mechanisms involved with natural locomotion (propulsion and lift should not be considered independently). Biological systems with interesting applications to MAVs are generally inspired on flying insects or birds;however, similarly to the aerodynamics of flight, powered swimming requires animals to overcome drag by producing thrust. Commonalities between natural flying and swimming are analyzed together with flow control issues as a purpose of improvement on biology-inspired or biomimetic concepts for Micro Air Vehicles implementation.
基金funding organizations in China:the National Key Research and Development Program of China(Grant No.2018YFB1305400)the National Natural Science Foundation of China(Grant Nos.62173212 and 11972079).
文摘In this study,the aerodynamic performance of flapping wings using a parallel motion was investigated and compared with the insect-like‘‘fan-sweep’’motion,and the effect of adding a slit to the wings was analyzed.First,numerical simulations were performed to analyze the wing aerodynamics of two flapping motions with equivalent stroke amplitudes over a range of pitching angles based on computational fluid dynamics(CFD).The simulation results indicated that flapping wings with a rapid and short parallel motion achieved better lift and efficiency than those of the fan-sweep motion while maintaining the same aerodynamic characteristics regarding stall delay and leading-edge vortices.For a parallel motion with a pitching angle of 25◦and 100 mm stroke amplitude,the wings generated an average lift of 8.4 gf with a lift-to-drag ratio of 1.06,respectively,which were 1.8%and 26%greater than those of the fan-sweep motion with a corresponding 96◦stroke amplitude.This situation was reversed when the pitching angle and stroke amplitude were increased to 45◦and 144◦for the fan-sweep motion,which was equivalent to the parallel motion with a 150 mm stroke amplitude.The slit effect in the parallel motion was also evaluated,and the CFD results indicated that a slit width of 1 mm(1/50 wing chord)increased the lift of the wing by approximately 27%in the case of the 150 mm stroke amplitude.Further,the slit width slightly influenced the lift and aerodynamic efficiency.
基金This study was financially supported by the Air Force Office of Scientific Research/European Office of Aerospace Research and Development AFOSR/EOARD(grant FA8655-08-1-3012).
文摘Jamin–Lebedeff polarizing interference microscopy is a classical method for determining the refractive index and thickness of transparent tissues.Here,we extend the application of this method to pigmented,absorbing biological tissues,based on a theoretical derivation using Jones calculus.This novel method is applied to the wings of the American Rubyspot damselfly,Hetaerina americana.The membranes in the red-colored parts of the damselfly’s wings,with a thickness of 2.5 μm,contain a pigment with maximal absorption at 490 nm and a peak absorbance coefficient of 0.7 μm^(-1).The high pigment density causes a considerable and anomalous dispersion of the refractive index.This result can be quantitatively understood from the pigment absorbance spectrum by applying the Kramers–Kronig dispersion relations.Measurements of the spectral dependence of the refractive index and the absorption are valuable for gaining quantitative insight into how the material properties of animal tissues influence coloration.
