1,720,963 research outputs found
A theory of plasticity with generalized hardening for natural geomaterials under mechanical and environmental loading: Constitutive modeling and numerical implementation
No full textAn extended theory of plasticity with generalized hardening is proposed to describe the response of geomaterials under both mechanical and environmental processes. It is assumed that the coupling between mechanical and environmental processes takes place at two levels: a) as an additional direct contribution to the constitutive stress changes, taking place even for purely elastic processes; and, b) as a consequence of the evolution of the internal state variables of the material with the changes in the environmental process variables. This last effect is incorporated through a set of generalized hardening rules. The general formulation is then specialized to the case of calcarenite rocks under unsaturated conditions, which can experience significant degradation processes due to plastic deformations, changes in degree of saturation (short–term debonding) and chemical dissolution of the bond material and the solid grains (long–term debonding). The resulting model, implemented in a FE code through the GBE algorithm extended to incorporate the full formalism of plasticity with generalized hardening, demonstrate the practical relevance of environmental degradation effects in practical applications, over periods of time comparable with the life cycle of most geotechnical structures
Micromechanics of Pile Cyclic Response in Sand
Full text linkA 3D discrete element model is used to investigate the axial cyclic response of a small-scale displacement piles installed in Fontainebleau sand. Calibration chamber experimental results from literature are used to validate the pile penetration phase of the DEM model which is then employed to simulate stress controlled vertical cyclic loading. The crushable DEM particle model is calibrated using high pressure element test data for the same sand. The model predicts the experimental stress measurements surrounding the jacked pile in both penetrating and unloaded conditions. The DEM model is used to assess micromechanical features hard to detect using experimental and continuum numerical methods. Grain crushing within the soil is observed to occur only below the cone during pile penetration. The analysis of particle stresses and force chains highlight how arching develops around the shaft. These arching effects create a sort of shield around the shaft causing the radial stresses to be lower. After pile installation is completed, a numerical parametric study of stress controlled cyclic axial loading of the pile is performed. The results show that depending on the magnitude of the cyclic load stable or metastable pile cyclic response is attained. The cyclic load amplitude also influences in different ways both stress and density profiles around the pile. These results may serve as a step forward to the understanding of installation effects on axial cyclic performance of jacked piles in sand
On the installation effects of open ended piles in chalk
Full text linkChalk is a highly porous rock formed by cemented calcite grains. It covers areas of the UK and is widespread under the North Sea where offshore wind turbines (OWT) are currently being installed and where future offshore expansion will be sited (Figure 1(a)) [1]. Large piles are often driven in chalk to support OWT. The installation process causes the intact rock below the pile tip to crush into a putty characterised by a mechanical behaviour very different from the intact chalk. The difficulty to predict the final state of the putty and the stress around the pile after installation is the underlying reason for inadequate current design guidance for piles in chalk. Considering that for OWT, foundations account for 20-25% of the total development cost , pile design improvements in chalk, would be extremely beneficial from an economical and environmental perspective.Current guidelines for the design of piles in chalk (CIRIA C574) originate from the analysis of a limited number of pile tests [2]. These guidelines suggest crude average ultimate unit shaft friction (tsf) design values of between 20 and 120 kPa for low-medium density and high/very-high density chalk, respectively. tsf estimates are thought to be conservative hence introducing significant increases in cost and carbon footprint (Figure 1(b)). Reducing the level of conservatism (e.g. enabling more confident use of higher tsf) would reflect in significant savings of steel and consequent reduction of the cost and embodied carbon. Such design considerations are possible but require a better understanding of the long-term mechanical behaviour of the damage processes intact chalk experiences during dynamic installation in hydro-mechanical (HM) coupled conditions.In this work the coupled HM effects developing during pile installation in chalk are investigated numerically using a robust and mesh-independent implementation of an elasto-plastic constitutive model at large strains. The model, implemented into an open-source Geotechnical Particle Finite Element (G-PFEM) code [3], is shown to be able to capture the damage of the rock until the formation of a chalk putty layer around the shaft of a model piles jacked in chalk. In particular the complex flow processes occurring in the soil around both open and closed ended piles of variable shape jacked into saturated chalk are investigated. A fully coupled hydro-mechanical formulation, based on regularized, mixed low-order linear strain triangles is used [5]. To capture the relevant features of the mechanical response of chalk, a finite deformation, non-associative structured modified cam clay is used [6]. The model formulation is based on a multiplicative decomposition of the deformation gradient and on the adoption of an elastic response based on the existence of a suitable free energy function. Bonding-related internal variables, quantifying the effects of structure on the yield locus, are used to provide a macroscopic description of mechanical destructuration effects. To deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws [7]. The G-PFEM model is shown to be capable of capturing the destructuration associated with plastic deformations below and around the pile shoulder; the space and time evolution of pore water pressure as the pile advances; the effect of soil permeability on predicted excess pore water pressures, and the effect of chalk putty formation on predicted values of the load displacement curve. Installation effects are highlighted by comparing the axial performance between wished in place piles and piles which considered the full installation process
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
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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