1,720,991 research outputs found
An Experimental Approach to Study Drainage in Relation to Geometrical Features of Artificial Adhesives
No full textWith growing interest in wet adhesion, animals such as tree frogs are often used as paradigm for creating grippers in wet environments. Tree frogs are capable of attaching to surfaces under several conditions (smooth, rough, dry, wet, and flooded) due to the microstructure of their toe pads. This microstructure consists of pillar-shaped hexagonal cells separated by thin and deep channels. Drainage is an important phenomenon to consider, since too much liquid between the toe pad and surface results in a low adhesive force. Therefore, understanding the relationship between pillar-shaped microstructures and drainage can lead to the creation of adhesive pads that are functional in wet conditions and to other drainage related applications. Adhesives with a pillar-shaped microstructure were fabricated and their drainage speed was experimentally studied against a glass substrate. Gathering experimental data was accomplished by using Particle Image Velocimetry, and by using fluid velocity as a proxy for drainage. A custom-made set-up was built to accurately control the speed at which the adhesive and the substrate approached each other. Adhesives with various pillar diameters, pillar spacings, and pillar alignments were tested with fluids of various viscosities. It was found that the pillar diameter most likely has a significant effect on drainage, whereas the effect of pillar spacing and the effect of fluid type could not be determined. Pillar alignment did not have a significant effect on drainage. In future work, it is recommended to complement the findings of this thesis with adhesion and friction measurements to understand how drainage associates to adhesive force
Grip on wet interfaces: an experimental study on the role of drainage
No full textDrainage of fluid from wet adhesive-substrate interfaces is often mentioned to be an important mechanism in obtaining strong grip. It has been hypothesized that micropatterned adhesives – that contain features (e.g., pillars) separated by channels on their surface – have a better drainage capability compared to unpatterned adhesives. Nevertheless, the fluid flow behavior on micropatterned interfaces has not been analyzed before. In this work, the fluid flow on wet adhesive-substrate interfaces was captured on three focal planes and analyzed in terms of flow direction, flow trajectory and flow velocity. The aspect ratio and spacing ratio of the features on the micropatterned adhesives as well as the stiffness of the substrates were varied. Ultimately, the fluid flow velocity was related to the pull-off and friction forces of the adhesives on the substrates. From the results it appeared that the initiation of drainage through the channels of micropatterned adhesives is likely not the direct cause of changes in flow direction. A straight flow path and a semi-wave flow path are distinguished as the two main flow trajectories of the fluid flow. The flow velocity depends on the flow path width and the separation distance between the adhesive and the substrate: the flow velocity increases with a smaller flow path width, and is higher before than after adhesive-substrate contact was established. The flow velocity did not differ among the substrates, which could be the result of the effects of the stiffness and the wetting capability of the substrates cancelling each other out. Moreover, our results suggest that shear forces increase with a larger channel area and a smaller fluid volume, whereas this is not necessarily the case for pull-off forces. The outcomes of this study can be used to develop surfaces for the generation of strong grip under wet conditions.Mechanical Engineerin
3D printed bio-inspired adhesives, friction force generation by modulating stiffness
No full textFor over a decade the use of bio inspired adhesives have been explored to achieve high reversable attachment on a wide range of surfaces. Based on the fibrillar adhesive toepads of geckos, many patterned adhesives have been produced that are able to form and preserve contact with rigid and smooth substrates. But on other types of surfaces, such as soft and deformable substrates, the performance of these micro patterned adhesives diminishes. Alternative methods have to be investigated to create adhesives that optimize the ability to form and preserve contact on these types of substrates. In this study, 3D printing is used to produce a series of adhesives with internal cylindrical porous structures of various geometry. The internal structure modulates the adhesives stiffness in the normal and shearing direction, designed to affect the friction force. Friction forces are measured on glass, soft elastomeric substrates and cloth. On glass, the highest friction forces are generated by the adhesive with the lowest normal stiffness, unaffected by their shear stiffness. On soft substrates, the highest friction forces are achieved with adhesives that combine a low normal stiffness, promoting contact formation, with a high sear stiffness, enhancing contact preservation. The effect of this anisotropic stiffness becomes more pronounced when the stiffness of the substrate decreases, contributing to contact formation. On cloth, generation of friction forces remains challenging, more research is required to create adhesives that excel on these kinds of substrates.Applied Physic
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Development of a high resolution topography and colour scannner: Applied to the craquelure pattern of paintings
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