1,720,957 research outputs found
A micromechanical investigation of soil-structure interface behaviour
Get PDFA limiting factor in the drive to deliver performance-based design is the lack of knowledge regarding the constitutive behaviour of soil-structure interfaces, particularly in the case of cyclic loading. Attempts to model the behaviour of these interfaces have failed to consider the long-term effects of cyclic loading, in particular how both the soil and structure may degrade over the course of thousands of cycles. To address this shortfall in understanding, consideration must be given to not only the geotechnical aspects of the interface, but also the structural aspects, and how these two components interact over the course of a structure's lifetime. This thesis presents a micromechanical investigation of the behaviour of soil-structure interfaces, with a particular focus on these cyclic effects by carrying out novel experimental testing at the macro-scale and single-particle scale.
At the macro-scale, a series of direct shear tests were carried out on a smooth stainless steel interface under a constant normal load. After continued shearing, the interface experiences a rapid elevation in the shear force transferred, accompanied by an increase in roughness of the surface and crushing of the Leighton Buzzard Sand grains. These observations are found to corroborate similar behaviour witnessed in literature. However, the initial trigger of this rapid increase in shear force cannot be explained by existing models, or verified by macro-scale observations. Therefore it was necessary to investigate the behaviour of the interface at the single-particle scale. A novel testing apparatus was developed to carry out single-particle direct shear tests on a smooth stainless steel interface. Testing revealed that the steep elevation in shear force also occurs at the single-particle scale and is caused by abrasive wear at the interface.
To investigate the abrasive wear at the single-particle scale further, a method was developed to accurately model the contact geometry of the particle. A particle virtualisation methodology was implemented to capture high resolution 3D meshes of the \SI{1.5}{\milli\metre} particles, with a provision to directly compare the grain meshes prior to and after testing. Using this methodology, it was found that the particle undergoes a significant change in shape during testing, with the particle becoming flattened and the nominal contact area increasing. This insight, of abrasive wear to the equivalently harder abrasive particle, has not been readily considered by tribological studies due to the difficulty of modelling and monitoring the contact geometry of irregular particles.
The frictional response of irregular particles during abrasive shearing therefore required further investigation, to establish a method for characterising local 3D angularity. Using the particle virtualisation methodology, a novel method was developed to characterise the local 3D angularity of the particle, and the evolution of this angularity during shearing. A new parameter, 3D attack angle, has been established, which characterises the angle an irregular abrasive grain makes with a planar surface. This new parameter is found to have a strong correlation with the rapid increase in shear force transmitted at the interface, whereby at the point of sudden shear load increase, there is a corresponding sudden change in 3D attack angle. It is therefore concluded that the rise in shear force is caused by an initial decrease in the 3D attack angle of the particle, which causes cutting abrasive wear to the surface.
With a better understanding of the micromechanical processes occurring at the interface, the macroscopic mechanisms that govern global response can be viewed in a new light. As such, more informed engineering decisions can be made regarding the design of soil-structure interfaces, which will ultimately lead to more efficient and sustainable infrastructure
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
A micromechanical investigation of soil-structure interface behaviour
Get PDFA limiting factor in the drive to deliver performance-based design is the lack of knowledge regarding the constitutive behaviour of soil-structure interfaces, particularly in the case of cyclic loading. Attempts to model the behaviour of these interfaces have failed to consider the long-term effects of cyclic loading, in particular how both the soil and structure may degrade over the course of thousands of cycles. To address this shortfall in understanding, consideration must be given to not only the geotechnical aspects of the interface, but also the structural aspects, and how these two components interact over the course of a structure's lifetime. This thesis presents a micromechanical investigation of the behaviour of soil-structure interfaces, with a particular focus on these cyclic effects by carrying out novel experimental testing at the macro-scale and single-particle scale.
At the macro-scale, a series of direct shear tests were carried out on a smooth stainless steel interface under a constant normal load. After continued shearing, the interface experiences a rapid elevation in the shear force transferred, accompanied by an increase in roughness of the surface and crushing of the Leighton Buzzard Sand grains. These observations are found to corroborate similar behaviour witnessed in literature. However, the initial trigger of this rapid increase in shear force cannot be explained by existing models, or verified by macro-scale observations. Therefore it was necessary to investigate the behaviour of the interface at the single-particle scale. A novel testing apparatus was developed to carry out single-particle direct shear tests on a smooth stainless steel interface. Testing revealed that the steep elevation in shear force also occurs at the single-particle scale and is caused by abrasive wear at the interface.
To investigate the abrasive wear at the single-particle scale further, a method was developed to accurately model the contact geometry of the particle. A particle virtualisation methodology was implemented to capture high resolution 3D meshes of the \SI{1.5}{\milli\metre} particles, with a provision to directly compare the grain meshes prior to and after testing. Using this methodology, it was found that the particle undergoes a significant change in shape during testing, with the particle becoming flattened and the nominal contact area increasing. This insight, of abrasive wear to the equivalently harder abrasive particle, has not been readily considered by tribological studies due to the difficulty of modelling and monitoring the contact geometry of irregular particles.
The frictional response of irregular particles during abrasive shearing therefore required further investigation, to establish a method for characterising local 3D angularity. Using the particle virtualisation methodology, a novel method was developed to characterise the local 3D angularity of the particle, and the evolution of this angularity during shearing. A new parameter, 3D attack angle, has been established, which characterises the angle an irregular abrasive grain makes with a planar surface. This new parameter is found to have a strong correlation with the rapid increase in shear force transmitted at the interface, whereby at the point of sudden shear load increase, there is a corresponding sudden change in 3D attack angle. It is therefore concluded that the rise in shear force is caused by an initial decrease in the 3D attack angle of the particle, which causes cutting abrasive wear to the surface.
With a better understanding of the micromechanical processes occurring at the interface, the macroscopic mechanisms that govern global response can be viewed in a new light. As such, more informed engineering decisions can be made regarding the design of soil-structure interfaces, which will ultimately lead to more efficient and sustainable infrastructure
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
The role of changing grain shape in abrasive wear and frictional resistance
Get PDFIn a range of applications — such as powder processing and geotechnical engineering — irregularly shaped grains interact with structural surfaces, resulting in abrasion. Traditional tribological analysis would imply that, when harder grains (e.g. sands) abrade against softer surfaces (e.g. metal), abrasive wear of the surface dominates the interaction mechanisms. However, this new research shows that this is not necessarily the case and wear of the harder grains themselves may dominate changes in shear behaviour. Studying this interaction is made more complicated by the irregular geometry of natural grains and the fact that their shapes evolve continuously during abrasion. Previous studies have substituted real grains with regularly shaped artificial abrasives (e.g. cones) to simplify the analysis. In contrast, this research creates high-resolution three-dimensional digital models of real grains, enabling direct measurement of shape characteristics as they change over time. From these digital reconstructions, a new ‘three-dimensional attack angle’ parameter has been defined, extending concepts previously restricted to simplified two-dimensional cases. This parameter can be updated in real-time as grains abrade, capturing the evolution of geometry in ‘real time’. Importantly, the three-dimensional attack angle correlates strongly with observed changes in frictional shear behaviour between irregular sand grains and stainless steel surfaces. This is the first study to establish a direct link between a measurable shape parameter of irregular grains and their evolving frictional characteristics. The framework developed here provides a basis for deeper understanding of grain-surface interactions and can be applied broadly across tribology and granular mechanics
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