1,721,108 research outputs found
Fingertip scanning on a surface: friction coefficients and induced vibrations
No full textTactile perception happens when scanning the fingertip on object surfaces (haptic sensing), by activating the receptors that are located in the skin. The skin deformation due to the contact stresses and the vibrations induced by the sliding contact activate the mechanoreceptors which generate electric impulses and allow the brain to identify objects and perceive information about their surfaces.
In this paper, the friction coefficient between a real human finger and both rigid surfaces and fabrics is recovered, as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the characteristics of the induced vibrations, measured on the fingernail, as a function of surface features and contact parameters.
Different behaviour of the friction coefficient is recovered scanning rigid surfaces or textiles, with respect to the contact parameters.
Results show that frequency spectrum distribution when touching a rigid surface is mainly determinate by the relative geometry of the two contact surfaces, while, when scanning a fabric, the structure and the deformation of the textile itself affect largely the spectrum of the induced vibration. Some main characteristics of the measured vibrations are found to be representative of tactile perception, by comparison with psychophysical and neurophysiologic works in literature
Competition between 3rd body flows and local contact dynamics
No full textWhen contact occurs between two bodies in relative
motion, instability state – i.e. stick-slip or
stick-slip-separation up so several kHz – often occur in
the contact . Such phenomenon has been
numerically highlighted and studied by Baillet and
Massi using dynamic finite element modelling
(FEM) with constant Coulomb’s friction coefficient.
Nevertheless, such model doesn’t take account for the
3rd body flow inside the contact and its interactions
with contact dynamics. Recently, Renouf has
coupled finite element method with discrete element
method (DEM) to compensate for this lack.
The purpose of the present work is so to validate
experimentally the numerical results obtained from
both contact dynamics and 3rd body flows . An
experimental set-up, called “PhotoTrib”, has so been
developed to reproduce the birth conditions of both
instability state and 3rd body particles
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon: the case of the spring-brake system
Full text linkThe main objective of the PhD thesis is the analysis of stick-slip phenomena in lubricated contacts, by merging the physical, experimental and numerical points of view and proposing a novel methodological approach, applied here to an industrial case. Nowadays, in the field of applied mechanics and tribology, one of the most important challenges is the ability to predict and reduce surface damages, failure of machine components and undesirable frictional and dynamic characteristics. In particular, the appearance of friction-induced vibrations at the contact is hardly controllable and can result in high local contact pressure, elevated stresses, system oscillations, discontinuous motion and premature failure]. Understanding the conditions for which the system is more predisposed to the stick-slip phenomenon may allow preventing the appearance of such instabilities, and the related vibrations and noise emission. Friction-Induced Vibrations are a phenomenon that engages multiple scientific challenges, due to the complexity of their physics. Focusing the attention on stick-slip phenomena, these are generally characterized by a saw-tooth displacement-time evolution. Each change in the contact parameters influences directly the dynamic and frictional response of the system, due to the mutual influence of the local scale (contact) and the system scale (macroscopic frictional and vibrational response). Moreover, the presence of a lubricant, and in particular of grease, at the contact interface, increases the complexity of the phenomenon, from both a tribological and dynamic point of view. Lubricated systems are supposed to reduce the frictional losses and wear, but they can also collaborate in the appearance of dynamic contact instabilities, due to the friction-velocity characteristics when passing from boundary to mixed contact regimes. The complex rheology of a grease, function of both the matrix, additive and oil responses, becomes then a key point for the occurrence and evolution of stick-slip. Despite the great importance of this phenomenon, from both scientific and industrial points of view, a lack emerges into the literature about stick-slip of lubricated interfaces. The few works are manly focused on molecular dynamics simulations and numerical modelling of the dynamical response of the system. The different role of the grease components, during the sliding, is nowadays still not clear. Nevertheless, the complex rheology of a grease, function of both the thickener, the base oil and the additives, is a key point for understanding and controlling the occurrence and evolution of stick-slip. Moreover, a general approach is needed to account for the coupling between the local phenomena (e.g. lubricated contact response) and the system dynamic response. Aiming to improve the understanding of stick-slip in lubricated contacts, the present Ph.D. work proposes a novel methodological approach to the stick-slip problem of a lubricated contact, referring to a real industrial case, in order to deploy the obtained results in a more realistic and detailed manner. The subject of the investigation is a mechanical brake used in tubular electric actuators, which can present frictional instabilities originated at the lubricated contact between the two main brake components. The methodology used is twofold: i) on one hand, experimental tests are carried out to understand the local frictional response of the lubricated contact; ii) on the other hand, a lumped model is created in order to simulate and analyse the system dynamic response. Introducing the information about the local lubricated contact behaviour (friction law), achieved experimentally, into the numerical model, it is possible to investigate the parameters for which the system is more predisposed to the stick-slip phenomenon and recreate a representative scenario of its appearance. Particular attention has been placed on the analysis of the lubricant rheology, dealing with different types of lubricants and regimes of lubrication, with both oils and greases. The frictional response has been thus related to the different contributions of the grease components (i.e. thickener, base oil and additives) on the rheology at the interface. The obtained local information has been then integrated in the lumped model to evaluate the unstable dynamic response of the entire system (i.e. the stick-slip phenomena) and identify the lubrication parameters that most influence its appearance. The numerical analysis had the dual objective of understanding the role of the local contact response in the system instability and investigating the stick-slip occurrence as a function of the key system parameters. The obtained results allowed to identify the lubrication components, and the respective friction-velocity curves, more favourable for the stick-slip occurrence. Combining the grease rheology evolutions with the stick-slip dynamic response represents a further challenge in both the domains of research. The Ph.D. thesis has been developed in collaboration between the Sapienza University of Rome, Department of Mechanical and Aerospace Engineering (Rome, Italy), the Institut National des Sciences Appliquées (INSA) of Lyon, laboratory LaMCoS (Lyon, France), and the company SOMFY S.A. (Cluses, France)
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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