A structural Markov property for decomposable graph laws that allows control of clique intersections

We present a new kind of structural Markov property for probabilistic laws on decomposable graphs, which allows the explicit control of interactions between cliques, so is capable of encoding some interesting structure. We prove the equivalence of this property to an exponential family assumption, and discuss identifiability, modelling, inferential and computational implications.Comment: 10 pages, 3 figures; updated from V1 following journal review, new more explicit title and added section on inferenc

Sampling decomposable graphs using a Markov chain on junction trees

Full Bayesian computational inference for model determination in undirected graphical models is currently restricted to decomposable graphs, except for problems of very small scale. In this paper we develop new, more efficient methodology for such inference, by making two contributions to the computational geometry of decomposable graphs. The first of these provides sufficient conditions under which it is possible to completely connect two disconnected complete subsets of vertices, or perform the reverse procedure, yet maintain decomposability of the graph. The second is a new Markov chain Monte Carlo sampler for arbitrary positive distributions on decomposable graphs, taking a junction tree representing the graph as its state variable. The resulting methodology is illustrated with numerical experiments on three specific models.Comment: 22 pages, 7 figures, 1 table. V2 as V1 except that Fig 1 was corrected. V3 has significant edits, dropping some figures and including additional examples and a discussion of the non-decomposable case. V4 is further edited following review, and includes additional reference

A Study into the Wealth of Successful Technology Entrepreneurs in the UK

This paper describes an academic study into the wealth of successful technology entrepreneurs in the United Kingdom. Here we are concerned with the dimensions of wealth in terms of its measurement. The methodology used involved three stages to determine the nature of the wealth involved. Initial sources (predominantly literature) and further sources (mainly business information) were considered in stage one to understand the measurement of the wealth of successful technology entrepreneurs. Analysis and synthesis of data undertaken in stage two determined the net wealth for technology entrepreneurs in different areas of activity. The nature and importance of the measurement of the wealth of technology entrepreneurs were examined in stage three to formulate conclusions. The research question investigated “what is the average net wealth of successful technology entrepreneurs in the United Kingdom?” The contribution of the study is to bring together findings of the research in terms of the measurement of the wealth of successful technology entrepreneurs

'Chief creator of Modern Wales'. The neglected legacy of Percy Thomas

The architecture of Percy Thomas, and the practice he founded (Percy Thomas Partnership), are neglected aspects of the development of twentieth century Wales. Twice president of the Royal Institute of British Architects, and awarded its Gold Medal, the architect’s work remains largely undocumented and unanalysed. This paper begins to address that deficiency. It argues that by virtue of its breadth and nature the practice’s work both responded to and helped shape perceptions of Wales as a modernising nation-state. In so doing, it identified itself with, and benefited from, a political project which assumed hegemonic status in Wales in the inter-war period and beyond. Yet the practice was not simply responding to clients’ requirements, as is illustrated by the process of designing the administrative block for the National Folk Museum at St Fagan’s in the 1960s. This reveals the contribution the architects made to reinterpreting modernity, amidst competing conceptions of Welsh identity and futures for the nation

Use of strain typing data to estimate bacterial transmission rates in healthcare settings

Journal ArticleOBJECTIVE: To create an affordable and accurate method for continuously monitoring bacterial transmission rates in healthcare settings. DESIGN: We present a discrete simulation model that relies on the relationship between in-hospital transmission rates and strain diversity. We also present a proof of concept application of this model to a prospective molecular epidemiology data set to estimate transmission rates for Pseudomonas aeruginosa and Staphylococcus aureus. SETTING: Inpatient units of an academic referral center. PATIENTS: All inpatients with nosocomial infections. INTERVENTION: Mathematical model to estimate transmission rates. RESULTS: Maximum likelihood estimates for transmission rates of these two species on different hospital units ranged from 0 to 0.36 transmission event per colonized patient per day. CONCLUSIONS: This approach is feasible, although estimates of transmission rates based solely on strain typed clinical cultures may be too imprecise for routine use in infection control. A modest level of surveillance sampling substantially improves the estimation accuracy (Infect Control Hosp Epidemiol 2005;26:638-645)

On the dielectric performance of modified epoxy networks

Epoxy resins represent a commonly used basis for insulation materials and have been used in many different electrical applications. The formation of these systems involves reactions between a hardener, such as an amine-curing system, and an epoxy terminated resin. Recent studies have reported that epoxy resin systems can exhibit enhanced physical properties when the stoichiometry of the resin is varied using reactive diluent. This has been attributed to the increased free volume within the molecular structures within the epoxy resin network. The work described here set out to investigate this hypothesis concerning the potential benefits of varying the network structure of epoxy resin through the inclusion of monofunctional reactive diluents within the epoxy formulation. This research is of potential significance because any modification of the epoxy resin network results in modified thermal, mechanical and electrical properties and, consequently, represents a potential mean of tailoring overall performance to suit particular applications

The effect of resin/hardener stoichiometry on the electrical properties of silicon nitride/epoxy nanocomposites

The effect of resin/hardener stoichiometry was investigated for both unfilled epoxy and nanocomposite samples. The results indicate that incorporating silicon nitride nanofiller, which contains amine groups on its surface, has a significant influence on the resin/hardener reaction. At 2 wt.% of nanofiller, it was estimated that the powder contains amine groups equivalent to around 5 wt.% of the hardener mass, which results in the displacement of the optimum resin/hardener mass ratio by the same amount (~5 wt.%). The dielectric spectra showed that the B relaxation is directly related to the hydroxyether groups that are generated by the reaction between the epoxy and the amine groups. Therefore, the relaxation strength is proportional to the crosslinking density and consequently related to the glass transition temperature. The DC conductivity increases considerably as a result of incorporating silicon nitride nanofiller when not compensating for its impact on the resin/hardener stoichiometry. This might be related to the increase in the amine content of the material caused by the amine groups existing on the surface of the nanoparticles. When the stoichiometry effect is taken into account, the DC conductivity decreased to a value that is comparable to that of the unfilled polymer

Evaluation of innovative sprayed-concrete-lined tunnelling

The front-shunt tunnel was the first tunnel of the Terminal 5 project at Heathrow to be constructed, and was the first section of sprayed-concrete-lined (SCL) tunnel to be constructed using the method known as LaserShell. This innovation represented a significant deviation from the methods previously used in SCL construction. Therefore it was subjected to a careful examination before and during construction using sophisticated 3D numerical modelling and monitoring during construction. The paper presents typical results from surface settlement levelling, inclinometers and extensometers, pressure cells and tunnel lining displacement measurements, and comments on the performance of the methods and instruments used. The paper then presents the methodology and typical results of the numerical modelling, and shows that the predictions of displacements and stresses compared well with the field measurements. In terms of the control of ground deformations and structural safety the tunnel performed well