The aerodynamic effects of wing rotation and a revised quasi-steady model of flapping flight

We used a dynamically scaled model insect to measure the rotational forces produced by a flapping insect wing. A steadily translating wing was rotated at a range of constant angular velocities, and the resulting aerodynamic forces were measured using a sensor attached to the base of the wing. These instantaneous forces were compared with quasi-steady estimates based on translational force coefficients. Because translational and rotational velocities were constant, the wing inertia was negligible, and any difference between measured forces and estimates based on translational force coefficients could be attributed to the aerodynamic effects of wing rotation. By factoring out the geometry and kinematics of the wings from the rotational forces, we determined rotational force coefficients for a range of angular velocities and different axes of rotation. The measured coefficients were compared with a mathematical model developed for two-dimensional motions in inviscid fluids, which we adapted to the three-dimensional case using blade element theory. As predicted by theory, the rotational coefficient varied linearly with the position of the rotational axis for all angular velocities measured. The coefficient also, however, varied with angular velocity, in contrast to theoretical predictions. Using the measured rotational coefficients, we modified a standard quasi-steady model of insect flight to include rotational forces, translational forces and the added mass inertia. The revised model predicts the time course of force generation for several different patterns of flapping kinematics more accurately than a model based solely on translational force coefficients. By subtracting the improved quasi-steady estimates from the measured forces, we isolated the aerodynamic forces due to wake capture

Mitochondrial ATP synthase genes may be implicated in cytoplasmic male sterility in Sorghum bicolor

Incompatible nuclear-cytoplasmic interactions are responsible for the phenomenon of cytoplasmic male sterility in plants. We have analysed male sterile (2077A, 296A), maintainer fertile (2077B, 296B) and fertility restored (2077R, 296R) lines of sorghum for the restriction fragment locations of various mitochondrial genes and their transcripts. We report here a polymorphism in genes related to the ATP synthase complex between two different cytoplasms from the A and B set of lines of 2077 and 296. There is also a difference in the transcript size of theatpA gene between the A and B cytoplasms. We propose that incompatibility in nuclear cytoplasmic interactions may be explained in terms of incompatible subunits being synthesized by the mitochondria and nucleus for a multisubunit complex of the mitochondrial membrane such as ATPase

The aerodynamic effects of wing–wing interaction in flapping insect wings

We employed a dynamically scaled mechanical model of the small fruit fly Drosophila melanogaster (Reynolds number 100–200) to investigate force enhancement due to contralateral wing interactions during stroke reversal (the 'clap-and-fling'). The results suggest that lift enhancement during clap-and-fling requires an angular separation between the two wings of no more than 10–12°. Within the limitations of the robotic apparatus, the clap-and-fling augmented total lift production by up to 17%, but depended strongly on stroke kinematics. The time course of the interaction between the wings was quite complex. For example, wing interaction attenuated total force during the initial part of the wing clap, but slightly enhanced force at the end of the clap phase. We measured two temporally transient peaks of both lift and drag enhancement during the fling phase: a prominent peak during the initial phase of the fling motion, which accounts for most of the benefit in lift production, and a smaller peak of force enhancement at the end fling when the wings started to move apart. A detailed digital particle image velocimetry (DPIV) analysis during clap-and-fling showed that the most obvious effect of the bilateral 'image' wing on flow occurs during the early phase of the fling, due to a strong fluid influx between the wings as they separate. The DPIV analysis revealed, moreover, that circulation induced by a leading edge vortex (LEV) during the early fling phase was smaller than predicted by inviscid two-dimensional analytical models, whereas circulation of LEV nearly matched the predictions of Weis-Fogh's inviscid model at late fling phase. In addition, the presence of the image wing presumably causes subtle modifications in both the wake capture and viscous forces. Collectively, these effects explain some of the changes in total force and lift production during the fling. Quite surprisingly, the effect of clap-and-fling is not restricted to the dorsal part of the stroke cycle but extends to the beginning of upstroke, suggesting that the presence of the image wing distorts the gross wake structure throughout the stroke cycle

The aerodynamics of insect flight

Summary: The flight of insects has fascinated physicists and biologists for more than a century. Yet, until recently, researchers were unable to rigorously quantify the complex wing motions of flapping insects or measure the forces and flows around their wings. However, recent developments in high-speed videography and tools for computational and mechanical modeling have allowed researchers to make rapid progress in advancing our understanding of insect flight. These mechanical and computational fluid dynamic models, combined with modern flow visualization techniques, have revealed that the fluid dynamic phenomena underlying flapping flight are different from those of non-flapping, 2-D wings on which most previous models were based. In particular, even at high angles of attack, a prominent leading edge vortex remains stably attached on the insect wing and does not shed into an unsteady wake, as would be expected from non-flapping 2-D wings. Its presence greatly enhances the forces generated by the wing, thus enabling insects to hover or maneuver. In addition, flight forces are further enhanced by other mechanisms acting during changes in angle of attack, especially at stroke reversal, the mutual interaction of the two wings at dorsal stroke reversal or wing–wake interactions following stroke reversal. This progress has enabled the development of simple analytical and empirical models that allow us to calculate the instantaneous forces on flapping insect wings more accurately than was previously possible. It also promises to foster new and exciting multi-disciplinary collaborations between physicists who seek to explain the phenomenology, biologists who seek to understand its relevance to insect physiology and evolution, and engineers who are inspired to build micro-robotic insects using these principles. This review covers the basic physical principles underlying flapping flight in insects, results of recent experiments concerning the aerodynamics of insect flight, as well as the different approaches used to model these phenomena

Steady or unsteady? Uncovering the aerodynamic mechanisms of insect flight

This article does not have an abstract

Trions in a periodic potential

The group-theoretical classification of trion states is presented. It is based on considerations of products of irreducible representations of the 2D translation group. For a given BvK period N degeneracy of obtained states is N^2. Trions consist of two identical particles so the symmetrization of states with respect to particles transposition is considered. Completely antisymmetric states can be constructed by introducing antisymmetric spin functions. Two symmetry adapted bases are considered. The third possibility is postponed for the further investigations.Comment: revtex, 5 p., sub. to Physica

Stimulation of macromolecular synthesis by ascorbate in Neurospora

Stimulation of macromolecular synthesis by ascorbat

Water Movement in Vascular Plants: A Primer

The origin of land plants was one of the most important events in evolutionary history of earth in terms of its broad impact on metazoan life and the biotic environment. Because vascular tissues enabled land plants to meet the challenges of terrestrial life, it is important to understand the mechanistic basis of water transport through these tissues from soil to the canopy of trees, in some cases almost 100 meters high. The answers to these questions involve not only the biology of plant vasculature, but also the physical properties of water that enable such transport. Although early researchers proposed the hypothesis of cohesion-tension of water as the likely mechanism for sap ascent, the exact mechanism of transport continues to be a hotly debated topic in the field of plant physiology. This debate continues to be enriched with several sophisticated studies on plants of various morphologies growing in diverse habitats. Although a wealth of evidence has upheld the cohesion-tension theory as being fundamentally correct, several important details about how plants deal with vascular stress remain unknown. Here, we review the recent literature on this topic with the aim of highlighting how a multi-disciplinary perspective has contributed to our understanding of the cohesion-tension theory of sap ascent in plants.Comment: 10 pages, 5 figure