349 research outputs found

    Yielding, Rigidity, and Tensile Stress in Sheared Columns of Hexapod Granules

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    Granular packings of non-convex or elongated particles can form free-standing structures like walls or arches. For some particle shapes, such as staples, the rigidity arises from interlocking of pairs of particles, but the origins of rigidity for non-interlocking particles remains unclear. We report on experiments and numerical simulations of sheared columns of "hexapods," particles consisting of three mutually orthogonal sphero-cylinders whose centers coincide. We vary the length-to-diameter aspect ratio, α\alpha, of the sphero-cylinders and subject the packings to quasistatic direct shear. For small α\alpha, we observe a finite yield stress. For large α\alpha, however, the column becomes rigid when sheared, supporting stresses that increase sharply with increasing strain. Analysis of X-ray micro-computed tomography (Micro-CT) data collected during the shear reveals that the stiffening is associated with a tilted, oblate cluster of hexapods near the nominal shear plane in which particle deformation and average contact number both increase. Simulation results show that the particles are collectively under tension along one direction even though they do not interlock pairwise. These tensions comes from contact forces carrying large torques, and they are perpendicular to the compressive stresses in the packing. They counteract the tendency to dilate, thus stabilize the particle cluster.Comment: 12 pages, 23 figure

    Exergy analysis of incremental sheet forming

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    Research in the last 15 years has led to die-less incremental forming processes that are close to realization in an industrial setup. Whereas many studies have been carried out with the intention of investigating technical abilities and economic consequences, the ecological impact of incremental sheet forming (ISF) has not been studied so far. Using the concept of exergy analysis, two ISF technologies, namely single sided and double sided incremental forming, are investigated and compared to conventional forming and hydroforming. A second exergy analysis is carried out with the purpose of examining the environmental impact of different forming technologies from a supply chain perspective. Therefore, related upstream activities (die set production, aluminum sheet production and energy conversion and supply) are included into the exergy analysis. The entire supply chain is modeled with Matlab/Simulink. The results of both analyses suggest that ISF is environmentally advantageous for prototyping and small production runs.United States. Dept. of Energy (Award DE-EE0003460

    Soluble proteins of chemical communication: an overview across arthropods

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    Detection of chemical signals both in insects and in vertebrates is mediated by soluble proteins, highly concentrated in olfactory organs, which bind semiochemicals and activate, with still largely unknown mechanisms, specific chemoreceptors. The same proteins are often found in structures where pheromones are synthesised and released, where they likely perform a second role in solubilising and delivering chemical messengers in the environment.A single class of soluble polypeptides, called Odorant-Binding Proteins (OBPs) is known in vertebrates, while two have been identified in insects, OBPs and CSPs (Chemosensory Proteins). Despite their common name, OBPs of vertebrates bear no structural similarity with those of insects. We observed that in arthropods OBPs are strictly limited to insects, while a few members of the CSP family have been found in crustacean and other arthropods, where however, based on their very limited numbers, a function in chemical communication seems unlikely.The question we address in this review is whether another class of soluble proteins may have been adopted by other arthropods to perform the role of OBPs and CSPs in insects. We propose that lipid-transporter proteins of the Niemann-Pick type C2 family could represent likely candidates and report the results of an analysis of their sequences in representative species of different arthropods

    Early Embryology of The Insect Oligotoma Saundersii (Embiidina) Using Targeted Genes as Developmental Landmarks

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    Embiidina, or webspinners , is a small, sexually dimorphic, polyneopterous insect order and is the only order to spin silk throughout their life cycle. Unique morphological features and the phylogenetic position of Embiidina make it an attractive subject for study of the evolution and development of the insect body plan and the origin of novel morphological features. Oligotoma saundersii is easily cultured and a viable laboratory organism. It has a fairly standard short-germ embryogenesis process requiring 453 hours at 28°C with progressive development beginning in the anterior region. Preliminary work on targeted developmental genes has yielded small portions of seven genes. ARACED-PCR is a novel, efficient method to amplify larger pieces of target genes using degenerate primers. This research represents the first detailed investigation of Embiidina embryology and one of few among the polyneopterous insects; therefore, it represents an important addition to our understanding of the evolution and development of insects

    The Genome of the Blind Soil-Dwelling and Ancestrally Wingless Dipluran Campodea augens: A Key Reference Hexapod for Studying the Emergence of Insect Innovations.

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    The dipluran two-pronged bristletail Campodea augens is a blind ancestrally wingless hexapod with the remarkable capacity to regenerate lost body appendages such as its long antennae. As sister group to Insecta (sensu stricto), Diplura are key to understanding the early evolution of hexapods and the origin and evolution of insects. Here we report the 1.2-Gb draft genome of C. augens and results from comparative genomic analyses with other arthropods. In C. augens, we uncovered the largest chemosensory gene repertoire of ionotropic receptors in the animal kingdom, a massive expansion that might compensate for the loss of vision. We found a paucity of photoreceptor genes mirroring at the genomic level the secondary loss of an ancestral external photoreceptor organ. Expansions of detoxification and carbohydrate metabolism gene families might reflect adaptations for foraging behavior, and duplicated apoptotic genes might underlie its high regenerative potential. The C. augens genome represents one of the key references for studying the emergence of genomic innovations in insects, the most diverse animal group, and opens up novel opportunities to study the under-explored biology of diplurans

    Subdivision of the neotropical Prisopodinae Brunner von Wattenwyl, 1893 based on features of tarsal attachment pads (Insecta, Phasmatodea)

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    The euplantulae of species from all five genera of the Prisopodinae Brunner von Wattenwyl, 1893 were examined using scanning electron microscopy with the aim to reveal the significance of attachment pads regarding their phylogenetic relationships. The split into the conventional two sister groups is supported by the two-lobed structure of the euplantulae with a smooth surface in the Prisopodini and a nubby surface microstructure in the Paraprisopodini. The two lineages are well distinguishable by this feature, as well as by the shape of the euplantulae themselves. The functional importance of the attachment pad surface features is discussed

    Extensive collection of femtoliter pad secretion droplets in beetle Leptinotarsa decemlineata allows nanoliter microrheology

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    Pads of beetles are covered with long, deformable setae, each ending in a micrometric terminal plate coated with secretory fluid. It was recently shown that the layer of the pad secretion covering the terminal plates is responsible for the generation of strong attractive forces. However, less is known about the fluid itself because it is produced in extremely small quantity. We here present a first experimental investigation of the rheological properties of the pad secretion in the Colorado potato beetle {\it Leptinotarsa decemlineata}. Because the secretion is produced in an extremely small amount at the level of the terminal plate, we first develop a procedure based on capillary effects to collect the secretion. We then manage to incorporate micrometric beads, initially in the form of a dry powder, and record their thermal motion to determine the mechanical properties of the surrounding medium. We achieve such a quantitative measurement within the collected volume, much smaller than the 1μ1 {\rm \mu}l sample volume usually required for this technique. Surprisingly, the beetle secretion was found to behave as a purely viscous liquid, of high viscosity. This suggests that no specific complex fluid behaviour is needed during beetle locomotion. We build a scenario for the contact formation between the spatula at the setal tip and a substrate, during the insect walk. We show that the attachment dynamics of the insect pad computed from the high measured viscosity is in good agreement with observed insect pace. We finally discuss the consequences of the secretion viscosity on the insect adhesion

    Design and Production of a 3-D Printed Wireless Hexapod

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    The purpose of this MQP was to research, analyze, and construct a working prototype of a low-cost, wirelessly-controlled hexapod. The goal of the prototype was to achieve the capability of forward, backward, and turning motions while using additive manufacturing methods for open source technology. The prototype was completed and tested by an interdisciplinary team of electrical and mechanical engineering students and required collaborative design across two engineering disciplines. 3-D printing was used as the central additive manufacturing method, including technologies such as FDM and Photopolymerization. Printed parts ranged in complexity from simple gears to intricate joint assemblies. The key focus of the project was designing for manufacturability in real-time applications

    HydroDog: A Quadruped Robot Actuated by Soft Fluidic Muscles

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    This report presents the very first effort aimed to develop a legged terrestrial robot actuated by Hydro Muscles, which are elastic tubes actuated by fluid, constrained by fabric that extend and contract emulating life-like performance of biological muscles. The team designed and manufactured a 30-pound quadruped “dog” using versatile aluminum extrusions and minimally machined components. The team tested and observed a variety of bounding gaits that resulted from different skeletal/muscular geometries and actuation times. These tests yielded varying jump heights and robot forward velocities. Future projects should extensively research optimal leg kinematics to maximize the mechanical power the muscles apply on the robot

    HydroDog: A Quadruped Robot Actuated by Soft, Fluidic Muscles

    Get PDF
    This report presents the very first effort aimed to develop a legged terrestrial robot actuated by Hydro Muscles, which are elastic tubes actuated by fluid, constrained by fabric that extend and contract emulating life-like performance of biological muscles. The team designed and manufactured a 30-pound quadruped “dog” using versatile aluminum extrusions and minimally machined components. The team tested and observed a variety of bounding gaits that resulted from different skeletal/muscular geometries and actuation times. These tests yielded varying jump heights and robot forward velocities. Future projects should extensively research optimal leg kinematics to maximize the mechanical power the muscles apply on the robot
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