Separability of drag and thrust in undulatory animals and machines

For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal- istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation framework helps to predict the observed height of the ribbon fin of electric knifefish, a diverse group of neotropical fishes which are an important model system in sensory neurobiology. We also show how drag-thrust separation leads to models that can predict the swimming velocity of an organism or a robotic vehicle.Comment: 41 pages, 13 figures, 4 table

Photocatalytic, sonocatalytic and sonophotocatalytic degradation of Rhodamine B using ZnO/CNTs composites photocatalysts

A series of ZnO nanoparticles decorated on multi-walled carbon nanotubes (ZnO/CNTs composites) was synthesized using a facile sol method. The intrinsic characteristics of as-prepared nanocomposites were studied using a variety of techniques including powder X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM), transmission electron microscope (TEM), scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), Brunauer Emmett Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS). Optical properties studied using UV–Vis diffuse reflectance spectroscopy confirmed that the absorbance of ZnO increased in the visible-light region with the incorporation of CNTs. In this study, degradation of Rhodamine B (RhB) as a dye pollutant was investigated in the presence of pristine ZnO nanoparticles and ZnO/CNTs composites using photocatalysis and sonocatalysis systems separately and simultaneously. The adsorption was found to be an essential factor in the degradation of the dye. The linear transform of the Langmuir isotherm curve was further used to determine the characteristic parameters for ZnO and ZCC-5 samples which were: maximum absorbable dye quantity and adsorption equilibrium constant. The natural sunlight and low power ultrasound were used as an irradiation source. The experimental kinetic data followed the pseudo-first order model in photocatalytic, sonocatalytic and sonophotocatalytic processes but the rate constant of sonophotocatalysis is higher than the sum of it at photocatalysis and sonocatalysis process. The sonophotocatalysis was always faster than the respective individual processes due to the more formation of reactive radicals as well as the increase of the active surface area of ZnO/CNTs photocatalyst. Chemical oxygen demand (COD) of textile wastewater was measured at regular intervals to evaluate the mineralization of wastewater

Comparable Ages for the Independent Origins of Electrogenesis in African and South American Weakly Electric Fishes

One of the most remarkable examples of convergent evolution among vertebrates is illustrated by the independent origins of an active electric sense in South American and African weakly electric fishes, the Gymnotiformes and Mormyroidea, respectively. These groups independently evolved similar complex systems for object localization and communication via the generation and reception of weak electric fields. While good estimates of divergence times are critical to understanding the temporal context for the evolution and diversification of these two groups, their respective ages have been difficult to estimate due to the absence of an informative fossil record, use of strict molecular clock models in previous studies, and/or incomplete taxonomic sampling. Here, we examine the timing of the origins of the Gymnotiformes and the Mormyroidea using complete mitogenome sequences and a parametric Bayesian method for divergence time reconstruction. Under two different fossil-based calibration methods, we estimated similar ages for the independent origins of the Mormyroidea and Gymnotiformes. Our absolute estimates for the origins of these groups either slightly postdate, or just predate, the final separation of Africa and South America by continental drift. The most recent common ancestor of the Mormyroidea and Gymnotiformes was found to be a non-electrogenic basal teleost living more than 85 millions years earlier. For both electric fish lineages, we also estimated similar intervals (16–19 or 22–26 million years, depending on calibration method) between the appearance of electroreception and the origin of myogenic electric organs, providing rough upper estimates for the time periods during which these complex electric organs evolved de novo from skeletal muscle precursors. The fact that the Gymnotiformes and Mormyroidea are of similar age enhances the comparative value of the weakly electric fish system for investigating pathways to evolutionary novelty, as well as the influences of key innovations in communication on the process of species radiation

The time evolution of vortical structures in the swimming of weakly electric fish

The gymnotiform mode of aquatic locomotion is characterized by the use of an elongated anal fin, generically referred to as a ribbon fin. The extraordinarily maneuverable weakly electric black ghost knifefish (Apteronotus albifrons) uses this mode of locomotion. These animals also have an unusual sensory adaptation: the use of a self-generated electric field to detect surrounding objects. This allows them to hunt at night in the murky waters of Amazon Basin rivers, where they are indigenous. Electric fish are a leading model system within neurobiology for the study of the neural control of sensing and movement. These animals also offer a unique opportunity to develop novel sensing and propulsion technologies for use in systems such as underwater vehicles. The knifefish sends continuous sinusoidal traveling waves along the fin. By altering the direction of the traveling wave, it swims backward as gracefully as it swims forward, and frequently reverses the direction of swimming during natural behaviors such as prey capture. In order to better understand how the fish controls its movement, we are studying the hydrodynamics of ribbon fin propulsion. We investigated the mechanism of propulsive force generation by a non-translating, non-rotating ribbon fin - the situation relevant to the low-speed, rapid forward-backward maneuvers of the knifefish. Using flow visualizations of numerical simulation data [1], we found that the fin generates both surge force (equivalently, thrust, i.e. the propulsive force in the swimming direction), and heave force (force in the perpendicular direction). The thrust generation mechanism involves the generation of a longitudinal, central jet running along the lower end of the fin, and an associated series of vortex rings attached to the lower edge of the fin. Smaller secondary vortex rings were observed to be emitted at an angle to the swimming direction on both sides of the fin surfaces. This indicates that the peculiar combination of the morphology and the actuation pattern of the fin (traveling waves) of the knifefish may be utilized by the animal to generate significant sideways forces for rapid maneuvers. The mechanism of heave generation consists of longitudinally oriented vortex rolls shedding at the lower edge of the ribbon-fin [1]. The central jet becomes further evident from the velocity blobs that are advected down the length of the fin. This ``bucket effect?? gives rise to fluid carried by successive crests and troughs of the fin-wave and expelled into the surrounding fluid at the trailing edge of the fin. This results in an undulatory propulsive force. [1.] A. A. Shirgaonkar, O. M. Curet, N. A. Patankar, M. A. MacIver, The hydronamics of ribbon-fin propulsion during impulsive motion, Journal of Experimental Biolog

Measured and computed drag on the fish body at different body pitch angles.

<p>––, ––; ; ––; . Dashed lines indicate experimentally measured drag, while solid lines show the drag estimated with computational fluid dynamics. Insets show orientation of fish cast while being towed at these angles.</p

How the projected sensorium area and the energy needed to encounter one prey vary with body pitch angle and elongation factor.

<p>In each case, the number on the curve indicates the ratio of the length of the sensorium to its height. The natural case is that the sensorium is 2.2 times longer than its height. (A) Projected sensorium area in the direction of travel. (B) Energy needed to move to a single prey.</p

Effect of sonication on crystal properties

Ultrasonic irradiation resulting in acoustic cavitation was employed during the partial crystallization of diphenyl oxide and dimethyl phenyl carbinol from their respective crude melts. The crystals obtained showed improved purity and better olefactory values for both compounds. This was confirmed by melting point measurements and image analysis of the crystals thus obtained. The beneficial effect of ultrasonic irradiation on the resultant properties is explained on the basis of the theory of acoustic cavitation

Computed wakes of a model of the black ghost at different pitch angles, at a velocity of 15 cm/s.

<p>The body is shown colored by the surface pressure deviation with respect to the hydrostatic pressure. Vorticity contours are shown in gray scale in the mid-sagittal plane of the fish. Wakes of the body at pitch angles of (A) ; (B) ; (C) ; (D) .</p