Clap and Fling Interaction of Bristled Wings: Effects of Varying Reynolds Number and Bristle Spacing on Force Generation and Flow Structures

The smallest flying insects with body lengths under 1 mm, such as thrips and fairyflies, typically show the presence of long bristles on their wings. Thrips have been observed to use wing-wing interaction via 'clap and fling' for flapping flight at low Reynolds number (Re) on the order of 10, where a wing pair comes into close contact at the end of upstroke and fling apart at the beginning of downstroke. We examined the effects of varying the following parameters on force generation and flow structures formed during clap and fling: (1) Re ranging from 5 to 15 for a bristled wing pair (G/D=17) and a geometrically equivalent solid wing pair; and (2) ratio of spacing between bristles to bristle diameter (G/D) for Re=10. The G/D ratio in 70 thrips species were quantified from published forewing images. Scaled-up physical models of three bristled wing pairs of varying G/D (5, 11, 17) and a solid wing pair (G/D=0) were fabricated. A robotic model was used for this study, in which a wing pair was immersed in an aquarium tank filled with glycerin and driven by stepper motors to execute clap and fling kinematics. Dimensionless lift and drag coefficients were determined from strain gauge measurements. Phase-locked particle image velocimetry (PIV) measurements were used to examine flow through the bristles. Chordwise PIV was used to visualize the leading edge vortex (LEV) and trailing edge vortex (TEV) formed over the wings during clap and fling. With increasing G/D, larger reduction was observed in peak drag coefficients as compared to reduction in peak lift coefficients. Net circulation, defined as the difference in circulation (strength) of LEV and TEV, diminished with increasing G/D. Reduction in net circulation resulted in reducing lift generated by bristled wings as compared to solid wings. Leaky, recirculating flow through the bristles provided large drag reduction during fling of a bristled wing pair. If flight efficiency is defined as the ratio of lift to drag, largest peak lift to peak drag ratios were obtained in bristled wings as compared to the solid wings across the entire range of Re and G/D tested.Mechanical & Aerospace Engineerin

Aerodynamics of active and passive dispersal of miniature insects with bristled wings

Tiny insects with body lengths under 2 mm, such as thrips, use fringed/bristled wings for active flapping at Reynolds number (Re) on the order of 10. Even at such tiny scales these insects were found to fly effectively owing to significant variations in wing kinematics and bristled wing morphology. Very few data is available on these variations at such small scales. Morphological investigation on forewing images of bristled wings revealed large diversity in their wing design. This includes variations in gaping or spacing between pair of bristles (G), bristle diameter (D), number of bristles (n) and wing span (S). In the present study, we quantified these design parameters from forewing images of 59 species of thrips and fairyfly species from previously published data. Physical scaled-up bristled wing models were then fabricated based on these parameters and tested for aerodynamic force generation using a robotic model. Results revealed that tiny insects may experience less biological pressure to optimize n or G/D for a given wingspan. Thrips have been observed to use wing-wing interaction via the clap and fling mechanism to augment lift generation. However, drag was also found to significantly increase. We found that tiny insects use large rotation angle to reduce this drag and proposed that circulatory lift alone cannot explain lift force generation and other lift generating mechanisms such as pressure distribution in the flow field were discussed. Actively flying at such tiny scales demands lot of power and these miniature insects were found to employ two additional strategies that helps in overcoming large power demand. We found that pausing between upstroke and downstroke decrease power required during a cycle with small compromise in lift. In addition to active flight, these insects can intermittently parachute by spreading their bristled wings at a particular inter-wing angle (O). We found that a dense bristled wing maintains aerodynamic loading relative to leakiness through the bristles for O>/=100 degrees. Also, we developed a scaled up robotic flapping device that could mimic any flapping flight in a horizontal stroke plane and proposed that pitch rate significantly alters the aerodynamic force generation compared to wing revolution

Aerodynamics of revolving bristled wings at low Reynolds Number

Thrips are one among the wide variety of tiny insects (body length under 2 mm) that are capable of flight at Reynolds number on the order of 10. Unlike larger insects like dragonflies and fruit flies, the wing structure of thrips is composed of a thin membrane with long bristles at the fringes. Previous studies have shown that bristled wings produce less drag when compared to equivalent non-bristled (solid) wings during the start of downstroke. However, it still remains unclear as to how the smallest flying insects with bristled wings are capable of sustained flight during rest of the downstroke, suggesting a need for further research. In this study, we examined the aerodynamic force generation on a revolving bristled wing model as a function of varying angle of attack. A robotic platform was used to revolve physical models of non-bristled and bristled wing models and strain gauges were used to acquire lift and drag forces. We hypothesize that bristles would show diffuse vorticity patterns in the leading and trailing edge vortices when compared to an equivalent solid wing, which in turn can help in maintaining lift generation across the cycle. Particle image velocimetry (PIV) will be used to visualize the flow along chordwise planes.Lew Wentz FoundationMechanical and Aerospace Engineerin

A nearest level control technique for an asymmetric source configuration of multi-level inverter topology

In this paper, an asymmetric source configuration of Multilevel Inverter (MLI) topology has been proposed. It consists of eight unidirectional switches, two bidirectional switches and four isolated DC sources. By considering 1:5 and 1:4 source configurations, the inverter produces 25-level and 21-level outputs respectively with the same switching action. For producing negative voltage levels, there is no requirement of separate backend H-bridge and inherently produces both positive and negative voltage levels. The main advantage of this topology is that in every state, only four switches are in ON mode and else are in OFF state. It also gives less per unit Total Standing Voltage (TSV) and thereby cost requirement of semiconductor devices can become decreases. For generating gate pulses, the simple Nearest Level Control (NLC) has been used by considering the round function. This technique is basically a fundamental switching frequency technique thereby switching losses are greatly reduces as compared with high switching frequency Pulse Width Modulation (PWM) techniques and it is particularly suitable for large number of levels. With this control technique, there is no inrush current has been developed at the input of DC sources. Finally, with step change in Modulation Index (MI) values the proposed topology with two different source configurations have been validated through MATLAB/Simulink platform

Antioxidant, antibacterial, cytotoxic, and apoptotic activity of stem bark extracts of Cephalotaxus griffithii Hook. f

<p>Abstract</p> <p>Background</p> <p><it>Cephalotaxus </it>spp. are known to possess various therapeutic potentials. <it>Cephalotaxus griffithii</it>, however, has not been evaluated for its biological potential. The reason may be the remoteness and inaccessibility of the habitat where it is distributed. The main aim of this study was to: (1) evaluate multiple biological potentials of stem bark of <it>C. griffithii</it>, and (2) identify solvent extract of stem bark of <it>C. griffithii </it>to find the one with the highest specific biological activity.</p> <p>Methods</p> <p>Dried powder of stem bark of <it>C. griffithii </it>was exhaustively extracted serially by soaking in petroleum ether, acetone and methanol to fractionate the chemical constituents into individual fractions or extracts. The extracts were tested for total phenolic and flavonoid content, antioxidant (DPPH radical scavenging, superoxide radical scavenging, and reducing power models), antibacterial (disc diffusion assay on six bacterial strains), cytotoxic (MTT assay on HeLa cells), and apoptotic activity (fluorescence microscopy, DNA fragmentation assay, and flow cytometry on HeLa cells).</p> <p>Results</p> <p>Among the three extracts of stem bark of <it>C. griffithii</it>, the acetone extract contained the highest amount of total phenolics and flavonoids and showed maximum antioxidant, antibacterial, cytotoxic (IC₅₀of 35.5 ± 0.6 μg/ml; P < 0.05), and apoptotic (46.3 ± 3.6% sub-G0/G1 population; P < 0.05) activity, followed by the methanol and petroleum ether extracts. However, there was no significant difference observed in IC₅₀values (DPPH scavenging assay) of the acetone and methanol extracts and the positive control (ascorbic acid). In contrast, superoxide radical scavenging assay-based antioxidant activity (IC₅₀) of the acetone and methanol extracts was significantly lower than the positive control (P < 0.05). Correlation analysis suggested that phenolic and flavonoid content present in stem bark of <it>C. griffithii </it>extracts was responsible for the high antioxidant, cytotoxic, and apoptotic activity (P < 0.05).</p> <p>Conclusions</p> <p>Stem bark of <it>C. griffithii </it>has multiple biological effects. These results call for further chemical characterization of acetone extract of stem bark of <it>C. griffithii </it>for specific bioactivity.</p

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed