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Yağlanmış temaslarda kavitasyon varlığında viskoelastik etkiler
No full textCataloged from PDF version of article.Includes bibliographical references (leaves 86-91).A model is proposed to study the influence of fluid viscoelasticity on the performance of lubricated contacts in the presence of cavitation. Previous studies on viscoelastic lubricants did not consider the presence of cavitation, rather reported
negative pressures in regions where cavitation was expected to occur. The proposed model uses the Oldroyd-B constitutive model to describe the presence of cavitation and assumes that the Deborah number (De), the ratio between polymer relaxation time and flow time scale, is small. In doing so, the viscoelastic thin film equations can be linearised in a similar approach to what was pioneered by
”Tichy, J., 1996, Non-Newtonian lubrication with the convected Maxwell model.”
The zeroth order solution in De corresponds to the Reynolds equation and has
been modified to describe also the film cavitation through the mass-conserving
Elrod-Adams model. We model several bearing configurations for the flow of
viscoelastic lubricants using (i) a cosine/parabolic profile representing a journal
bearing unwrapped geometry, and (ii) a pocketed profile to model a textured
surface in lubricated contacts. Introducing viscoelasticity to the cavitating journal bearing decreases the length of the non-active (cavitation) region due to an increasing pressure distribution in the lubricant film. This results in an increase
to the load carrying capacity with increasing De corroborating the beneficial influence of the polymers in fluid film bearings. The pocket profile is shown to
either increase or decrease the load carrying capacity with increasing viscoelastic
effects, depending on the location of surface texturing at the contact. An oscillating squeeze flow problem is modeled for viscoelastic lubricants between two flat plates with motion only at the top surface. A reduction in the load carrying capacity at larger values of De is observed as film reformation is seen to be retarded with increasing viscoelastic effects. As viscoelastic effects become stronger, the
nonactive region is grows continuously until reaching a value of De beyond which
a full film reformation does not occur upon the inception of cavitation. The study is extended to a direct numerical simulations using the openFoam toolbox.
A model that couples a solver for incompressible, isothermal, two phase flow with
interaction between the phases and a solver for viscoelastic fluids is proposed.
However, DNS are only valid for lower values of De as instabilities occur as a result of the non-linear coupling.by Samuel Shari Gamanie
Tribo-mechanical stability of mucous boundary layers in biofidelic contacts
Get PDFIn everyday life, stable mucous boundary layers on wet epithelial tissues play a vital role in providing lubrication, reducing friction and preventing tissue damage. Understanding the stability of these layers under tribo-mechanical and tribo-chemical stresses, as well as the extent of damage to the exposed surfaces following mucous film rupture, is crucial for informing the development of food ingredients, consumer products and biomedical devices. In this thesis, biofidelic experimental platforms were employed to systematically evaluate the stability and functionality of mucous boundary layers under controlled conditions. The main aim of the current work is to investigate and understand the mechanisms governing friction, lubrication and the protective function of mucous layers by assessing their stability during tribological interactions of biological tissues. Following a systematic approach, lab-scale systems that replicate the bio-tribological and tribo-mechanical behaviour of wet epithelial tissues were used to simulate the contact of biological tissues. A novel methodology was introduced to evaluate the mechanical stability of mucous protein films adsorbed on PDMS surfaces, distinguishing between stable and unstable mucous boundary layers. This enabled the study of molecular mechanisms driving lubrication loss and film rupture, particularly during tribological interactions in the presence of mucins and plant-derived compounds. Studies explored the effects of fava bean protein isolate (FBPI), tannic acid (TA), and microcrystalline cellulose (MCC) particles on bovine submaxillary mucin (BSM) layers. To link experimental observations with theoretical modelling, a mechanical contact framework was developed for a sphere-on-flat geometry. The model incorporated the boundary lubrication model of Bowden and Tabor using a binary and Gaussian-smoothed boundary layer coverage fraction (BLCF) approach, coupled with the JKR contact model, to predict contact pressures, and shear stresses. Comparison with experimental data confirmed the capability of the BLCF model to capture lubrication behaviour under varying surface coverage conditions.Building on this foundation, a biofidelic platform consisting of protein boundary layers on epithelial cell monolayers adhered to PDMS substrates was introduced to study the influence of mucous layers on stresses transmitted to the underlying surfaces. This system enabled simultaneous evaluation of friction and tissue damage, revealing mechanisms by which mucous layers protect underlying cells. Further investigations into the interactions between the interfacial layer and the cell monolayer examined particle-mediated (de)lubrication and stress-induced cell responses. The study revealed a clear distinction in the friction levels and the amount of damage to the cell monolayer resulting from the absence of mucous coverage, strong adhesive interactions and the presence of particles within the contact.The findings from this work highlight the mechanical stability of mucous layers during tribological interactions, revealing the role of stable mucous layers in providing lubrication and protective coverage that prevents damage to underlying tissues. The methodology and test platforms introduced in the current work offer practical applications in biomedical testing, development of sustainable food formulations, and biomedical device–tissue interaction studies. <br/
Design of a tongue equivalent for astringency assessment of plant based proteins
Get PDFConsumption of food products containing polyphenols has resulted in a feeling of dryness, roughness and puckering of the oral epithelium which is known as astringency. At high concentrations, astringent food compounds are perceived by consumers as unpleasant and has led food scientist to initiate multiple studies with the aim of reducing the unwanted effects of astringency. This project proposes a tongue equivalent design that closely mimics the properties of oral surfaces which are relevant for assessing changes to oral lubrication resulting from astringency. The nature of interactions occurring at oral interfaces containing astringents point towards a system dependence of astringency and shows the importance of adopting a tribosystems approach. By adopting a systems engineering approach, this project has been able to identify the main stakeholders and the influence they possess on the system under design. This was followed by the identification of needs from the main stakeholders which were translated into system requirements. Design concepts with the aim of satisfying the system’s requirements were proposed alongside some planned evaluation methods, performance indicators and expectations from the project main stakeholders. A final design concept was chosen based on the conceptual designs proposed to the stakeholders. The final design considers the topography, mechanical properties and operating conditions of the human tongue during oral assessment. Experiments have been used to verify the properties of several aspects of the design including Direct Mechanical Analysis, Dynamic Light Scattering and Tribological work. This thesis concludes by making recommendations on possible applications and future developments to the proposed design. Based on the investigation into the mechanism of astringency, it is recommended that current test protocols must undergo further development, making them capable of investigating the tribochemical basis of astringency
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
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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