305,426 research outputs found
Mechanics of plant fruit hooks
No full textHook-like surface structures, observed in some plant species, play an important role in the process of plant growth and seed dispersal. In this study, we developed an elastic model and further used it to investigate the mechanical behaviour of fruit hooks in four plant species, previously measured in an experimental study. Based on Euler–Bernoulli beam theory, the force–displacement relationship is derived, and its Young's modulus is obtained. The result agrees well with the experimental data. The model aids in understanding the mechanics of hooks, and could be used in the development of new bioinspired Velcro-like materials
Kaolin nano-powder effect on insect attachment ability
No full textThe present study investigates under controlled conditions the effect of kaolin particle film on reduction of insect attachment ability. Two economically important polyphagous insect pests characterized by different attachment devices were tested, the Southern green stink bug Nezara viridula (Heteroptera: Pentatomidae) and the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae). We performed traction force experiments with females pulling on treated (covered with kaolin par- ticle film) and untreated (control) natural (leaf surfaces with different morphological traits) and artificial (hydrophilic and hydrophobic glass) surfaces. The data demonstrated that insect adhesion is heavily affected by kaolin particle film in both tested species. The degree of reduction of insect adhesion to the treated substrates compared with the untreated ones differed according to the kind of treated substrate owing to its initial wettability and morphology (presence of trichomes). To unravel the insect adhesion reduction mechanism of kaolin particle film, we evaluated the safety factor for females before and after walking on treated surfaces and analyzed under cryo-SEM the tarsal attachment devices of N. viridula and C. capitata after walking on treated surfaces. We observed contamination by the kaolin nanoflakes in both the smooth pads of the bug and the hairy pads of the fly. The present study can help to better understand the mechanism of action of kaolin particle film and can contribute to develop future physical control barriers against pest insects, particularly relevant owing to the need to reduce the negative impacts of pesticides on environment and human healt
Ruolo della variazione di larghezza e di spessore nelle spatole delle lucertole e degli insetti
No full textMolti dispositivi biologici di adesione degli insetti, dei ragni e dei gechi consistono di matrici di peli (setae) che terminano con elementi di contatto di diverse forme. Tuttavia, la forma più osservata è una spatola appiattita. Nonostante nei diversi animali le spatole esistano in una notevole varietà di dimensioni, la maggior parte di esse non sono uniformi ma posseggono un gradiente sia in spessore che in larghezza. In questo lavoro investighiamo perché le spatole dei gechi diventano gradualmente più sottili e più larghe avvicinandosi alla loro estremità. Il motivo di questa particolare geometria è studiato utilizzando un approccio numerico basato sul metodo degli elementi finiti. La modellazione numerica del peeling della singola spatola richiede l’introduzione delle forze di van der Waals tra spatole e substrato. I risultati numerici suggeriscono che la variazione di spessore e di larghezza delle spatole sono entrambe utili per migliorare la capacità dell’animale di camminare
Mechanical interaction of the egg parasitoid Anastatus bifasciatus (Hymenoptera: Eupelmidae) with artificial substrates and its host egg
No full textEgg parasitoids play an important role in biological control of pest species attacking and killing their hosts at an early stage of their development. During the antagonistic coevolution with their hosts, egg parasitoids have developed a great ability to locate their host using chemical cues. A considerable amount of literature is available on this topic, while nothing is known about a possible adaptation of egg parasitoids to topography and mechanical properties of egg surface features and its shape when attaching to the host egg for oviposition. In the present investigation, the attachment ability of adults of both sexes of the egg parasitoid Anastatus bifasciatus (Hymenoptera: Eupelmidae) to artificial (polishing paper, flat glass, glass beads as dummies of the host egg) and natural surfaces (eggs of Halyomorpha halys and Nezara viridula, both Heteroptera: Pentatomidae), with different roughness and wettability, was measured using centrifugal force tester and traction force experiments. The parasitoid attachment devices and the egg surfaces were examined under cryo scanning electron microscope, wettability and roughness of natural and artificial substrates were characterised. We detected differences in the attachment devices and attachment ability of the two sexes. The collected data revealed a special ability of the female to attach to the eggs of the host species, thus suggesting an adaptation of the A. bifasciatus female to the surface features of the eggs during oviposition
Attachment devices and the tarsal gland of the bug Coreus marginatus (Hemiptera: Coreidae)
No full textThe present ultrastructural investigation using scanning and transmission electron microscopy as well as light and fluorescence microscopy describes in detail the attachment devices and tarsal gland of the bug Coreus marginatus (L.) (Hemiptera: Coreidae). In particular, the fine structure of pulvilli reveals a ventral surface rich with pore channels, consistent with fluid emission, and a folded dorsal surface, which could be useful to enhance the pulvillus contact area during attachment to the substrate. The detailed description of the tarsal gland cells, whose structure is coherent with an active secretory function, allows us to consider the tarsal gland as the plausible candidate for the adhesive fluid production. Scolopidia strictly adhering to the gland cells are also described. On the basis of the fine structure of the tarsal gland, we hypothesise a fluid emission mechanism based on changes of the hydraulic pressure inside the gland, due to the unguitractor tendon movements. This mechanism could provide the fluid release based on compression of the pad and capillary suction, as demonstrated in other insects. The data here reported can contribute to understanding of insect adhesive fluid production, emission and control of its transport
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Origin of the superior adhesive performance of mushroom-shaped microstructured surfaces
No full textThe superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics and engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers, because experiments have proved their superiority compared to other micro- and nano-structures. In this article, we explain theoretically the physical mechanism behind the enhanced adhesion of such microstructures, and provide for the first time a useful tool to predict adhesive performance depending on the geometry, mechanical properties of the material, and energy of adhesion. Our theoretical predictions are strongly supported by the available experimental data. The present study can streamline the optimisation of adhesive microstructures for industrial applications
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Direct observation of microcavitation in underwater adhesion of mushroom-shaped adhesive microstructure
No full textIn this work we report on experiments aimed at testing the cavitation hypothesis [Varenberg, M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383–385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting conditions and simultaneously video recording the detachment behavior at very high temporal resolution (54,000–100,000 fps). Although microcavitation was observed during the detachment of individual MSAMSs, which was a consequence of water inclusions present at the glass–MSAMS contact interface subjected to negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L.; Gorb, S. N. Underwater adhesion of mushroom-shaped adhesive microstructure: An air-entrapment effect. In Biological and biomimetic adhesives: Challenges and opportunities; Santos, R.; Aldred, N.; Gorb, S. N.; Flammang, P., Eds.; The Royal Society of Chemistry: Cambridge, U.K., 2013; pp 65–71] rather than by cavitation. These results obtained due to the high-speed visualisation of the contact behavior at nanoscale-confined interfaces allow for a microscopic understanding of the underwater adhesion of MSAMSs and may aid in further development of artificial adhesive microstructures for applications in predominantly liquid environments
Adhesion Tilt-Tolerancy in Bio-Inspired Mushroom-Shaped Adhesive Microstructure
No full textWe studied experimentally and theoretically the effect of different tilt angles on the adhesion of mushroom-shaped adhesive microstructures. The marginal measured influence of tilting on pull-off forces is quantitatively well confirmed by numerical and theoretical calculations and was shown to be a direct consequence of an optimized stress distribution. In addition, the presence of a joint-like narrowing under the contact elements, as found in some biological attachment systems, was shown to further contribute to the tilt-tolerance. The results obtained allow us to explain the advantage of the widely observed mushroom-shaped contact geometry in nature for long-term and permanent adhesion
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