Quantitative Description of Grain Contacts in a Locked Sand

Quantifying the fabric of intact soil is of great importance in both geomechanics and geology. A unique and interesting example of fabric can be found in “locked sands”. These geologically old sands are characterized by significant grain interlocking and a low cement content. They can be sampled with minimal fabric disturbance. This study analyzes images acquired by x-ray microtomography of resin impregnated samples of a natural sand, Reigate Silver Sand part of the Folkestone Bed formation from southeast England. 2D and 3D image analyses were carried out to identify the grain-grain contacts and quantify individual contact areas. In contrast to earlier studies that have focused on the coordination number, this work demonstrates that for non-punctual contacts a measure of fabric that considers the contact area may be more appropriate

The role of particle mineralogy in mixtures of sands

Several recent studies on mixtures of sands of different granulometries and/or mineralogies have focused on the key factors that might lead the behaviour to change from transitional to not transitional, where a transitional behaviour is characterised by non-convergent compression paths and critical state lines that might be non-unique. The authors present a review of mixtures of different soils showing a complex pattern of compression and shearing behaviour in which transitional behaviour can be caused by relatively small varia- tions to the proportion or nature of soil particles. Laboratory investigations, carried out by means of oedometer tests, have confirmed the role of the mineralogy of the matrix composed by larger grains. This determines the mode of behaviour so that, if there is a strong and stiff matrix made of quartz sand particles, which are either larger than or at least of similar size to the other component, then non-convergent compression paths are likely to occur, no matter whether particle breakage occurs or not

Experimental investigation into the primary fabric of stress transmitting particles

Understanding the stress distribution amongst the constituent grains is fundamental to predict the response of soil and advance science-based, rather than purely empirical, constitutive models. Photoelastic experiments and discrete element method simulations have provided evidence that, upon loading, discrete force chains form in granular materials. These force chains are made up of particles transmitting relatively large stresses and they are aligned in the direction of the major principal stress. A few qualitative studies have identified the presence of these force chains in sands but direct measurements of force chains have not been previously documented and tracking stress transmission in assemblies of real soil grains remains a challenging task. The present study makes use of three dimensional micro CT images to investigate the evolution of the internal topology of a sand subjected to triaxial compression loading. The analysis of the contact normal and branch vector orientations has shown the realignment of the contact normals in the direction of the major principal stress as a clear indication of the formation of force chains in the post-peak regime. Here the extent of the non-colinearity of the branch and contact normal vectors is explored. Using the micro CT data contact force networks within and outside of shear bands are compared

Image segmentation techniques for granular materials

To improve understanding of the mechanical behavior of granular materials it is important to be able to quantify the relative arrangement of the grains, i.e. the fabric. This can be done, for example, by measuring the orientations of the particles (e.g. the long axis orientation) or by considering the orientations of the vectors normal to each grain‐grain contact. In two dimensional (2D) analyses this information can be obtained by digital image analysis of images of thin sections obtained from an optical microscope. While such data is useful, granular materials of engineering interest are three dimensional (3D) materials and quantification of the 3D fabric is necessary. Micro Computed‐Tomography (μCT) together with 3D image analysis has emerged as a promising technique for obtaining the 3D data required. This paper aims to highlight the challenges associated with using image analysis to provide quantitative information on fabric. While automated image segmentation has proved to produce reasonable results in some cases, it is sometimes less successful when dealing with highly irregular and angular soil grains. This paper evaluates the effectiveness of 2D and 3D segmentation techniques that rely on the watershed segmentation algorithm. The primary material considered is Reigate Silver Sand, a natural quartzitic sand with grain diameters in the range of 150–300 μm. While the sand considered is primarily of interest to geotechnical engineers, the results of this study will be of interest to anyone seeking to quantify granular material fabric using either 2D microscopy data or μCT 3D data sets

Pseudorehearsal in value function approximation

Catastrophic forgetting is of special importance in reinforcement learning, as the data distribution is generally non-stationary over time. We study and compare several pseudorehearsal approaches for Q-learning with function approximation in a pole balancing task. We have found that pseudorehearsal seems to assist learning even in such very simple problems, given proper initialization of the rehearsal parameters

Quantifying the evolution of soil fabric during shearing using directional parameters

Over the past 50 years, experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric, that is, the arrangement of the grains. Up until now there have been relatively few attempts to describe this fabric quantitatively. Much of our understanding of the link between the particle movements and interactions and the macro-scale response of granular materials, including sand, comes from discrete-element modelling and experiments on ‘analogue’ sands with simple, idealised shapes. This paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading. Statistical analyses of the distribution of fabric directional data in terms of particle, contact normal, branch vector and void orientations were carried out at different stages of shearing deformation. The data show that the initial particle orientation fabric that develops during the deposition of the material tends to persist during shearing, while in the post-peak regime the contact normals seem to be reoriented along the direction of the major principal stress. Different patterns were observed within the shear band, as both the particles and the contact normal vectors appeared to rotate along the shear plane

Negotiating growth of online education in higher education

Universities are facing growing internal and external pressures to generate income, educate a widening continuum of learners, and make effective use of digital technologies. One response has been growth of online education, catalysed by Massive Open Online Courses, availability of digital devices and technologies, and notions of borderless global education. In growing online education, learning and teaching provision has become increasingly disaggregated, and universities are partnering with a range of private companies to reach new learners, and commercialise educational provision. In this paper, we explore the competing drivers which impact decision making within English universities and their strategies to grow online education provision, through interviews with senior managers, and interrogation of their views through the lens of a range of internal, external and organisational drivers. We show that pressures facing universities may be alleviated by growth of online education provision, but that negotiating an appropriate route to realise this ambition involves attempts to resolve these underlying tensions deriving from competing drivers. We use a modified form of the PEST model to demonstrate the complexities, inter-dependencies and processes associated with these drivers when negotiating delivery of unbundled online education through use of private company services, or in partnership with private companies

Development and Evaluation of a Trapping System for Anoplophora glabripennis (Coleoptera: Cerambycidae) in the United States

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), commonly known as the Asian longhorned beetle, is an invasive wood-boring pest that infests a number of hardwood species and causes considerable economic losses in North America, several countries in Europe, and in its native range in Asia. The success of eradication efforts may depend on early detection of introduced populations; however, detection has been limited to identification of tree damage (oviposition pits and exit holes), and the serendipitous collection of adults, often by members of the public. Here we describe the development, deployment, and evaluation of semiochemical-baited traps in the greater Worcester area in Massachusetts. Over 4 yr of trap evaluation (2009-2012), 1013 intercept panel traps were deployed, 876 of which were baited with three different families of lures. The families included lures exhibiting different rates of release of the male-produced A. glabripennis pheromone, lures with various combinations of plant volatiles, and lures with both the pheromone and plant volatiles combined. Overall, 45 individual beetles were captured in 40 different traps. Beetles were found only in traps with lures. In several cases, trap catches led to the more rapid discovery and management of previously unknown areas of infestation in the Worcester county regulated area. Analysis of the spatial distribution of traps and the known infested trees within the regulated area provides an estimate of the relationship between trap catch and beetle pressure exerted on the traps. Studies continue to optimize lure composition and trap placemen

Political brand image: an investigation into the operationalisation of the external orientation of David Cameron’s Conservative brand

This paper seeks to address the limited understanding of how to operationalise the external brand image of a political brand. More specifically, this research critically assesses the transfer potential of the six variables of brand image by Bosch, Venter, Han and Boshoff to deconstruct the UK Conservative Party brand from the perspective of young people aged 18–24 years during the 2010 UK General Election campaign. This research demonstrates the applicability of the six variables otherwise known as the ‘brand image framework’ to the political environment. However, the application of the brand image framework in its original conceptualisation proved problematic. Many of the brand image variables were clarified, rearticulated and simplified to address the political context. This refined conceptualisation provided an in-depth understanding of how to investigate the political brand image of David Cameron’s Conservative Party. This study addresses the paucity of research that operationalises external brand image and provides practitioners and academics within and beyond the context of political branding a mechanism to understand the external orientation of brands. This research may also be used by political and non-political brands as a basis to explore external brand image and compare its consistency with internal brand identity