Comparing a simulation model with various analytic models of the international diffusion of consumer technology

In this paper we propose and evaluate a method for studying technology adoption at the national level using hybrid simulation. A hybrid simulation model is developed which combines elements of system dynamics and agent-based modelling, and treats nations as adopting agents. International diffusion is modelled as a social system where the adoption of an innovation, or even just growing pressure to adopt an innovation, in one nation can then influence its adoption in others. The model is used to investigate nine different technological innovations for which sufficient international data are available. Using the available empirical data, the method of differential evolution is used to configure the model which allows the parameter space to be explored in an efficient manner, without bias or subjective disagreement. Good agreement is found between the parameters derived in this way and those reported to configure analytic models. For each of the nine innovations, we report the rank order correlation between the actual order of adoption of the innovations by nations and the order predicted by the simulation model. We also report the rank order correlations between the actual order and the order predicted by a much simpler statistical model. Improvements in the rank order correlation are shown when some form of social influence between nations is included, although there is no significant difference in results between the four different types of social influence considered by the simulation. The nine technologies investigated also appear to fall into two groups with significantly different uptake speeds. Advantages and limitations of the approach are discussed along with suggested implications for practice

Simulating the diffusion of technological innovation with an integrated hybrid agent-based system dynamics model

The potential of hybrid models to enhance simulations of the real world is explored. While the scope for design of such models is large, the focus here brings together agent-based (AB) and system dynamics (SD) modelling within a defined architectural framework. Comprising a number of modules, each of which is implemented in a single modelling paradigm, the design of hybrid models looks to exploit the potential from a range of approaches and tools. Coded within a single programming environment, the international diffusion of technological innovation is used as a case study to highlight hybrid simulation model design and implementation. An integrated hybrid simulation design that incorporates feedback between modules in a continuous, fluid, process is employed to develop a model comprising two SD modules and one AB module. The predictions from the hybrid model are compared to known outcomes regarding the national adoption of mobile telephony, fixed internet and fixed broadband. We conclude with some thoughts on the design of hybrid simulation models

The Theory of High Frequency Gravitational Radiation, and its Application to Cosmology

In Chapter 1 a brief introduction to the theory of gravitational radiation in general relativity is presented, and an outline of the variety of different methods that have been used to study it is given. In the second chapter, a single theoretical approach, upon which to base the subsequent treatment, is chosen. This approach, developed by R. A. Isaacson (1968a,b), involves obtaining approximate gravitational wave solutions to the vacuum Einstein equations by supposing that the radiation is of high frequency. The work of Isaacson is reviewed to show how the high frequency approximation leads to a tensor representation of the gravitational field energy. In Chapter 3, the Isaacson theory is extended, by the present writer, so that it may be applied to situations in which gravitational radiation is present in a matter filled manifold. The work of J. Madore, who has also considered gravitational radiation in a material fluid, is discussed to show that his results may be found, as are Isaacson’s, as special cases within the proposed general formalism. Provided that certain assumptions are made, the wave energy in matter is shown to be of the same form as that found in vacuum. It is in Chapter 4 that the cosmological applications of the general formalism of Chapter 3 are first considered. Radiation travelling through a cosmological 'background' space-time is examined, with the intention of discovering how this background geometry interacts with the radiation. A Friedmann line element, with the space curvature constant K = 0, is used to represent the cosmological background upon which the radiation propagates. Employing this example I am able to show that test particles, located in a plane perpendicular to the direction of propagation of a monodirectional gravitational wave, experience acceler­ations due to the wave superimposed upon the effects of the model's cosmological expansion. Further, the theory, for constructing an isotropic gravitational radiation field is developed. It is shown that the energy tensor of such a field may be represented by a perfect fluid energy tensor, with an equation of state in which the radiation pressure is one-third of the energy density. In Chapter 5, the manner in which the radiation modifies the cosmological background is considered. The work is motivated by a model of the Universe, containing matter and gravitational radiation, proposed by Isaacson and Winicour (1972, 1973). They assumed that matter was converted into an isotropic field of gravitational radiation. However, as is shown in Chapter 5, the model can lead to a negative mass density. This difficulty is overcome by bringing the conversion to an end at some pre-assigned instant in cosmic time. This ensures that the energy distribution in the model remains physically acceptable throughout the model's development. The cosmological equations for the model are solved, by numerical methods where necessary, and a number of examples of the resulting universes are given in diagrammatic and tabular form. Finally, in an appendix, the possibility that gravit­ational radiation is generated during the ’fireball' era of the Universe is briefly considered

The molecular forms of BMP15 in a range of mammalian species

BMP15 is an oocyte-secreted growth factor that is critical for ovarian follicular development and fertility in mammals. To improve our understanding of the species-specific effects of BMP15 on fertility, the aim of this study was to elucidate the molecular forms of BMP15 in mammals with high (rat and pigs) and low (sheep and deer) litter sizes. Western blotting experiments were undertaken using a monoclonal antibody directed against a semi-conserved area on the mature region of E.coli-expressed ovine BMP15. Within the oocyte lysate of all species tested, the predominant form was promature BMP15, although mature BMP15 was also present. Within oocyte-conditioned media of sheep, pigs and deer, the promature:mature BMP15 ratio dropped significantly from what was seen inside the oocyte, with promature BMP15 only slightly predominant in deer, and relatively equal amounts of each protein were present in pigs and sheep. No BMP15 was detected in the oocyte-conditioned media of rats. Cross-linking studies did not provide any evidence of BMP15/BMP15 homodimers or BMP15/GDF9 heterodimers in any species tested. Intra-oocyte levels of both promature and mature BMP15, from highest to lowest, were detected in deer, followed by sheep and pigs (similar), and then rats (significantly lower). In the oocyte-conditioned media, with the exception of the rat where BMP15 was absent, there was a similar pattern of promature BMP15 levels observed between species, whereas mature BMP15 levels showed no inter-species variation. In summary, the molecular forms and relative amounts of BMP15 protein differ across species. Generally, high BMP15 levels were associated with low litter size; however the pig is an exception. Furthermore, the molecular forms observed in this study differed from those reported in studies using recombinant BMP15 suggesting that recombinantly-expressed protein may not provide a fair representation of native BMP15

An innovation diffusion model of a local electricity network that is influenced by internal and external factors

Haynes et al. (1977) derived a nonlinear differential equation to determine the spread of innovations within a social network across space and time. This model depends upon the imitators and the innovators within the social system, where the imitators respond to internal influences, whilst the innovators react to external factors. Here, this differential equation is applied to simulate the uptake of a low-carbon technology (LCT) within a real local electricity network that is situated in the UK. This network comprises of many households that are assigned to certain feeders. Firstly, travelling wave solutions of Haynes’ model are used to predict adoption times as a function of the imitation and innovation influences. Then, the grid that represents the electricity network is created so that the finite element method (FEM) can be implemented. Next, innovation diffusion is modelled with Haynes’ equation and the FEM, where varying magnitudes of the internal and external pressures are imposed. Consequently, the impact of these model parameters is investigated. Moreover, LCT adoption trajectories at fixed feeder locations are calculated, which give a macroscopic understanding of the uptake behaviour at specific network sites. Lastly, the adoption of LCTs at a household level is examined, where microscopic and macroscopic approaches are combined

A new analysis of debris mitigation and removal using networks

Modelling studies have shown that the implementation of mitigation guidelines, which aim to reduce the amount of new debris generated on-orbit, is an important requirement of future space activities but may be insufficient to stabilise the near-Earth debris environment. The role of a variety of mitigation practices in stabilising the environment has been investigated over the last decade, as has the potential of active debris removal (ADR) methods in recent work. We present a theoretical approach to the analysis of the debris environment that is based on the study of networks, composed of vertices and edges, which describe the dynamic relationships between Earth satellites in the debris system. Future projections of the 10 cm and larger satellite population in a non-mitigation scenario, conducted with the DAMAGE model, are used to illustrate key aspects of this approach. Information from the DAMAGE projections are used to reconstruct a network in which vertices represent satellites and edges encapsulate conjunctions between collision pairs. The network structure is then quantified using statistical measures, providing a numerical baseline for this future projection scenario. Finally, the impact of mitigation strategies and active debris removal, which can be mapped onto the network by altering or removing edges and vertices, can be assessed in terms of the changes from this baseline. The paper introduces the network methodology, highlights the ways in which this approach can be used to formalise criteria for debris mitigation and removal. It then summarises changes to the adopted network that correspond to an increasing stability and changes that represent a decreasing stability of the future debris environment

Towards a framework for sustainable development planning in the Indonesian natural rubber industry supply network

Supply networks for natural resources such as rubber present significant opportunities to deliver global sustainability goals by reducing environmental, social and economic impacts of industrial activities. This research is using the Indonesian natural rubber industry as a case study. Early discussions with stakeholders highlighted a need for decision support tools to facilitate sustainability-related trade-offs in industry-wide and firm-level planning processes. The example used in this paper relates to rubber plantation replanting programmes and a three-way trade-off between customers’ needs for a steady flow of rubber, an industry need to improve its environmental sustainability and rubber plantation owners’ needs to maintain their financial sustainability which, in turn, influences social sustainability. An initial framework for sustainable development planning based on the case study and literature is proposed, and its use in the design of a computational simulation experiment using hybrid simulation models to predict the sustainability impacts of alternative replanting scenarios is reported

Instructive conductive 3D silk foam-based bone tissue scaffolds enable electrical stimulation of stem cells for enhanced osteogenic differentiation

Stimuli-responsive materials enabling the behaviour of the cells that reside within them to be controlled are vital for the development of instructive tissue scaffolds for tissue engineering. Herein we describe the preparation of conductive silk foam-based bone tissue scaffolds that enable the electrical stimulation of human mesenchymal stem cells to enhance their differentiation towards osteogenic outcomes