Developing living information systems through systems tailorability: Deferred systems design

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.An interpretivist investigation of computer-based business information systems was conducted in two commercial companies and two higher education institutes, by using both quantitative questionnaire survey and qualitative interview research methods. The investigation focused on the social and organisational context of information systems development and usage in these organisations. The utility of structured methodologies is now being questioned by some researchers who are calling for alternative approaches, and this investigation draws on that alternative strand of thinking. The collected data primarily reveals that the development and usage of information systems happens in changing organisations, which suggests that the design and usage of information systems must cater for such a changing or dynamic environment. Therefore the data is interpreted using a philosophical outlook encompassing the notion of "living" information systems and Critical Theory, and this philosophical stance regards information technology as liberating human endeavour in organisations. Five sub-concepts and the concept of deferred system's design are derived from the data, which have been formulated to account and cater for change in information systems environments. The concept of deferred system's design encourages the design of information systems which allow for organisational human behaviour, consisting of organisational change, uncertainty, and learning, to be mediated by information technology. A systems design principle called `deferred system's design decisions' is derived to enable designs of tailorable information systems, which may be regarded as one form of living information systems to facilitate such organisational behaviour. An intersubjective theoretical model called the spiral of change model of tailorable information systems is proposed to explain and understand better the changing organisational environment in which information systems must be developed and in which they must function. To inform practice a computer tool is proposed which enables conceptions of " tailorable information systems that employ the principle of deferred system's design decisions and enables modelling changing or dynamic information systems

Coherent coupling between radio frequency, optical, and acoustic waves in piezo-optomechanical circuits

The interaction of optical and mechanical modes in nanoscale optomechanical systems has been widely studied for applications ranging from sensing to quantum information science. Here, we develop a platform for cavity optomechanical circuits in which localized and interacting 1550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides. Working in GaAs facilitates manipulation of the localized mechanical mode either with a radio frequency field through the piezo-electric effect, or optically through the strong photoelastic effect. We use this to demonstrate a novel acoustic wave interference effect, analogous to coherent population trapping in atomic systems, in which the coherent mechanical motion induced by the electrical drive can be completely cancelled out by the optically-driven motion. The ability to manipulate cavity optomechanical systems with equal facility through either photonic or phononic channels enables new device and system architectures for signal transduction between the optical, electrical, and mechanical domains

Recent Developments in the Dynamic Stability of Elastic Structures

Dynamic instability in the mechanics of elastic structures is a fascinating topic, with many issues still unsettled. Accordingly, there is a wealth of literature examining the problems from different perspectives (analytical, numerical, experimental etc.), and coverings a wide variety of topics (bifurcations, chaos, strange attractors, imperfection sensitivity, tailor-ability, parametric resonance, conservative or non-conservative systems, linear or nonlinear systems, fluid-solid interaction, follower forces etc.). This paper provides a survey of selected topics of current research interest. It aims to collate the key recent developments and international trends, as well as describe any possible future challenges. A paradigmatic example of Ziegler's paradox on the destabilizing effect of small damping is also included

The Mechanics and Multiphysics of Biomimetic Discrete Exoskeleton Substrates

Biological structures have inspired synthetic materials with unparalleled performances such as ultra-lightweight design, tunable elasticity, camouflaging, and antifouling. Among biological structures, exoskeletal scales that cover the exterior surfaces of fishes, fur, and many reptiles. These exoskeletal scales had appeared in the earliest stages of evolution of complex multicellular life and continued their existence in spite of millions of years of evolutionary pressures. This makes them an attractive candidate for biomimicry to produce high performance multifunctional materials with applications to soft robotics, wearables, energy efficient smart skins, antifouling surfaces and on-demand tunable materials. Canonically speaking, biomimetic samples can be fabricated by partially embedding stiffer plate-like segments on softer substrates to create a bi-material system, with overlapping scales. The bending behavior of this system has been carried out using assumption of periodic engagement even after scales contact. This is true only under the most ideal loading conditions or if the scales are extremely dense akin to a continuum assumption on the scales. Here, we develop a rigorous theory with computational validation of key parameters which relaxes these restrictions. We also present an analytical study to demonstrate a bioinspired mechanical pathway to tailor the elasticity of cantilevered beams as an alternative to traditional functional gradation. In addition, we explore for the first time the dynamic behavior of these scales during oscillatory motion using analytical models, supported by finite element (FE) computations. Finally, inspired by the hypothesis that fur surfaces, which consist of plate-like topography, significantly change the initial stages of biofouling, we shed light on the fundamentals of this process by reducing the fur to a scale-covered elastica under flow with biomass suspensions. A FE coupled nonlinear deposition-large deflection model of the system is developed

Optimization of spider web-inspired phononic crystals to achieve tailored dispersion for diverse objectives

International audienceSpider orb webs are versatile multifunctional structures with optimized mechanical properties for prey capture, but also for transmitting vibrations. The versatility of such a system mainly derives from its variable geometry, which can be effectively used to design phononic crystals, thus inhibiting wave propagation in wide frequency ranges. In this work, the design of spider web-inspired singlephase phononic crystals through selective variation of thread radii and the addition of point masses is proposed, determined through the use of optimization techniques. The obtained results show that spider web geometry displays a rich vibration spectrum, which by varying its the geometric characteristics and adding localized masses can be tailored to manipulate wave modes, and the resulting two-dimensional phononic crystals present wide complete band gaps generated by Bragg scattering and local resonances