The direct field boundary impedance of two-dimensional periodic structures with application to high frequency vibration prediction.

Large sections of many types of engineering construction can be considered to constitute a two-dimensional periodic structure, with examples ranging from an orthogonally stiffened shell to a honeycomb sandwich panel. In this paper, a method is presented for computing the boundary (or edge) impedance of a semi-infinite two-dimensional periodic structure, a quantity which is referred to as the direct field boundary impedance matrix. This terminology arises from the fact that none of the waves generated at the boundary (the direct field) are reflected back to the boundary in a semi-infinite system. The direct field impedance matrix can be used to calculate elastic wave transmission coefficients, and also to calculate the coupling loss factors (CLFs), which are required by the statistical energy analysis (SEA) approach to predicting high frequency vibration levels in built-up systems. The calculation of the relevant CLFs enables a two-dimensional periodic region of a structure to be modeled very efficiently as a single subsystem within SEA, and also within related methods, such as a recently developed hybrid approach, which couples the finite element method with SEA. The analysis is illustrated by various numerical examples involving stiffened plate structures.

The generation of wear surfaces

Abrasive wear is likely to occur whenever a hard asperity or a trapped hard particle is dragged across a softer surface, and it has been estimated that this form of wear contributes to as many as half of the wear problems that are met in industry. Such damaging hard particles may be external contaminants, products of corrosion or even the debris from previous wear events. During the life of a component, damage caused by individual asperity or particle interactions builds up and, at each stage of its life, the worn surface is the result of many such superimposed wear events. The practical, quantitative prediction of wear rates depends on having both a satisfactory understanding of individual interactions and a suitable procedure for combining these when subsequent contacts are made on a surface whose topography and material properties may have been much changed Irom their initial states. The paper includes some details of an analytical model for the interaction of a representative asperity and the worn surface which can both predict the frictional force and the balance between ploughing, when material is displaced but not lost from the surface, and micromachining or cutting, when actual detachment occurs. Experiments tö !rvvéSuQ8Î8 the validity of the model have been carried out on a novel wear rig which provides very precise control over the position of the asperity and the counterface. This facility, together with that of on-board profilometry, means that it is possible to carry out wear experiments on areas of the surface whose previous deformation history is well known; in this way it is possible to follow the development of a worn surface in a controlled manner as the damage from individual wear events accumulates. Experimental data on the development of such a surface, produced by repeated parallel abrasion, are compared with the predictions of the model. © 1992 IOP Publishing Ltd.

The value of cooperatives in rural electrification

The electricity sectors of many developing countries underwent substantial reforms during the 1980s and 1990s, driven by global agendas of privatization and liberalization. However, rural electrification offered little by way of market incentives for profit-seeking private companies and was often neglected. As a consequence, delivery models for rural electrification need to change. This paper will review the experiences of various rural electrification delivery models that have been established in developing countries, including concessionary models, dealership approaches and the strengthening of small and medium-sized energy businesses. It will use examples from the USA, Bangladesh and Nepal, together with a detailed case study of a Nepali rural electric cooperative, to explore the role that local cooperatives can play in extending electricity access. It is shown that although there is no magic bullet solution to deliver rural electrification, if offered appropriate financial and institutional support, socially orientated cooperative businesses can be a willing, efficient and effective means of extending and managing rural electricity services. It is expected that this paper will be of particular value to policy-makers, donors, project planners and implementers currently working in the field of rural electrification. © 2010 Elsevier Ltd.

Advanced applications of a computational design synthesis method

From modelling to manufacturing, computers have increasingly become partners in the design process, helping automate many phases once carried out by hand. In the creative phase, computational synthesis methods aim at facilitating designers' task through the automated generation of optimally directed design alternatives. Nevertheless, applications of these techniques are mainly academic and industrial design practice is still far from applying them routinely. This is due to the complex nature of many design tasks and to the difficulty of developing synthesis methods that can be easily adapted to multiple case studies and automated simulation. This work stems from the analysis of implementation issues and obstacles to the widespread use of these tools. The research investigates the possibility to remove these obstacles through the application of a novel technique to complex design tasks. The ability of this technique to scale-up without sacrificing accuracy is demonstrated. The successful results confirm the possibility to use synthesis methods in complex design tasks and spread their commercial and industrial application.

Everywhere and nowhere: nearshore software development in the context of globalisation

Offshore software development has been identified as one of the most striking manifestations of contemporary globalisation and as evidence of placelessness, the idea that information and communication technologies have rendered location irrelevant. Research in the International Business and Information Systems fields, in contrast, has suggested that all locations are not equal and has identified a number of characteristics that may influence the attractiveness of a location for multinational investment and offshoring, respectively. These literatures, however, focus almost exclusively on quantitative, economic characteristics that are seen as fixed and applying uniformly throughout a whole country. They therefore offer little guidance on the suitability of particular locations as offshoring destinations, especially in countries without a track record in offshore software development. Drawing on two cases of nearshore software development centres set up by offshore service providers in the Caribbean, this paper illustrates that, while the initial decision to establish the ventures reflected a logic of placelessness, characteristics of these particular locations affected their subsequent success. Through the findings, we therefore develop a typology of espoused, unanticipated and remediable locational characteristics, which illustrates that locational attractiveness may vary significantly within countries and that offshore service providers and government agencies can modify locational characteristics to their advantage.

Development of teaching resources for physical modelling community

Physical modelling of interesting geotechnical problems has helped clarify behaviours and failure mechanisms of many civil engineering systems. Interesting visual information from physical modelling can also be used in teaching to foster interest in geotechnical engineering and recruit young researchers to our field. With this intention, the Teaching Committee of TC2 developed a web-based teaching resources centre. In this paper, the development and organisation of the resource centre using Wordpress. Wordpress is an open-source content management system which allows user content to be edited and site administration to be controlled remotely via a built-in interface. Example data from a centrifuge test on shallow foundations which could be used for undergraduate or graduate level courses is presented and its use illustrated. A discussion on the development of wiki-style addition to the resource centre for commonly used physical model terms is also presented. © 2010 Taylor & Francis Group, London.

Growth and shape control of disks by bending and extension

Differential growth of thin elastic bodies furnishes a surprisingly simple explanation of the complex and intriguing shapes of many biological systems, such as plant leaves and organs. Similarly, inelastic strains induced by thermal effects or active materials in layered plates are extensively used to control the curvature of thin engineering structures. Such behaviour inspires us to distinguish and to compare two possible modes of differential growth not normally compared to each other, in order to reveal the full range of out-of-plane shapes of an initially flat disk. The first growth mode, frequently employed by engineers, is characterised by direct bending strains through the thickness, and the second mode, mainly apparent in biological systems, is driven by extensional strains of the middle surface. When each mode is considered separately, it is shown that buckling is common to both modes, leading to bistable shapes: growth from bending strains results in a double-curvature limit at buckling, followed by almost developable deformation in which the Gaussian curvature at buckling is conserved; during extensional growth, out-of-plane distortions occur only when the buckling condition is reached, and the Gaussian curvature continues to increase. When both growth modes are present, it is shown that, generally, larger displacements are obtained under in-plane growth when the disk is relatively thick and growth strains are small, and vice versa. It is also shown that shapes can be mono-, bi-, tri- or neutrally stable, depending on the growth strain levels and the material properties: furthermore, it is shown that certain combinations of growth modes result in a free, or natural, response in which the doubly curved shape of disk exactly matches the imposed strains. Such diverse behaviour, in general, may help to realise more effective actuation schemes for engineering structures. © 2012 Elsevier Ltd. All rights reserved.

Methodological implications of critical realism for mixed-methods research

Building on recent developments in mixed methods, we discuss the methodological implications of critical realism and explore how these can guide dynamic mixed-methods research design in information systems. Specifically, we examine the core ontological assumptions of CR in order to gain some perspective on key epistemological issues such as causation and validity, and illustrate how these shape our logic of inference in the research process through what is known as retroduction. We demonstrate the value of a CR-led mixed-methods research approach by drawing on a study that examines the impact of ICT adoption in the financial services sector. In doing so, we provide insight into the interplay between qualitative and quantitative methods and the particular value of applying mixed methods guided by CR methodological principles. Our positioning of demi-regularities within the process of retroduction contributes a distinctive development in this regard. We argue that such a research design enables us to better address issues of validity and the development of more robust meta-inferences.

Active learning of model evidence using Bayesian quadrature

Numerical integration is a key component of many problems in scientific computing, statistical modelling, and machine learning. Bayesian Quadrature is a modelbased method for numerical integration which, relative to standard Monte Carlo methods, offers increased sample efficiency and a more robust estimate of the uncertainty in the estimated integral. We propose a novel Bayesian Quadrature approach for numerical integration when the integrand is non-negative, such as the case of computing the marginal likelihood, predictive distribution, or normalising constant of a probabilistic model. Our approach approximately marginalises the quadrature model's hyperparameters in closed form, and introduces an active learning scheme to optimally select function evaluations, as opposed to using Monte Carlo samples. We demonstrate our method on both a number of synthetic benchmarks and a real scientific problem from astronomy.

Seismic triggering of submarine slides in soft cohesive soil deposits

The geological profile of many submerged slopes on the continental shelf consists of normally to lightly overconsolidated clays with depths ranging from a few meters to hundreds of meters. For these soils, earthquake loading can generate significant excess pore water pressures at depth, which can bring the slope to a state of instability during the event or at a later time as a result of pore pressure redistribution within the soil profile. Seismic triggering mechanisms of landslide initiation for these soils are analyzed with the use of a new simplified model for clays which predicts realistic variations of the stress-strain-strength relationships as well as pore pressure generation during dynamic loading in simple shear. The proposed model is implemented in a finite element program to analyze the seismic response of submarine slopes. These analyses provide an assessment of the critical depth and estimated displacements of the mobilized materials and thus are important components for the estimation of submarine landslide-induced tsunamis. © 2003 Elsevier B.V. All rights reserved.

Global analysis of dynamical decision-making models through local computation around the hidden saddle

Bistable dynamical switches are frequently encountered in mathematical modeling of biological systems because binary decisions are at the core of many cellular processes. Bistable switches present two stable steady-states, each of them corresponding to a distinct decision. In response to a transient signal, the system can flip back and forth between these two stable steady-states, switching between both decisions. Understanding which parameters and states affect this switch between stable states may shed light on the mechanisms underlying the decision-making process. Yet, answering such a question involves analyzing the global dynamical (i.e., transient) behavior of a nonlinear, possibly high dimensional model. In this paper, we show how a local analysis at a particular equilibrium point of bistable systems is highly relevant to understand the global properties of the switching system. The local analysis is performed at the saddle point, an often disregarded equilibrium point of bistable models but which is shown to be a key ruler of the decision-making process. Results are illustrated on three previously published models of biological switches: two models of apoptosis, the programmed cell death and one model of long-term potentiation, a phenomenon underlying synaptic plasticity. © 2012 Trotta et al.

The process of making the business case for technology: A sales and marketing perspective for technologists

Technological investment is a key driver of innovation and the evaluation of technology potential is becoming increasingly important in this context. There is a range of approaches and tools for developing an understanding of the value of technology. However the process of communicating this potential to possible customers is not well documented in terms of theory and practice and falls outside the skill set of many technologists. This paper seeks to integrate the concepts of marketing and consultative selling into making business cases for new technologies. It describes an exploratory study which results in an outline process activity model for technologists wishing to build an effective business case for securing investment internally or when selling a technology externally. Following a review of literature, we suggest that there is potential to learn from market research and consultative sales techniques, and propose a five step process. The work has been industrially validated and forms a novel foundation for further development. © 2012 Elsevier Inc.