Modelling railway bridge degradation based on historical maintenance data

As structures deteriorate with age and use, it is necessary to devise a maintenance plan to control their states in a cost effective way. In order to evaluate the effectiveness of alternative maintenance strategies their success must be measured by their ability to control the structure condition. The condition can be expressed for either the entire structure or for the components which make up the structure. A problem is how to express this condition. This is a particular problem for bridges where there can be several deterioration mechanisms taking place and there is no clear way of measuring the current state of either the structure or its elements. One approach to defining the condition of bridges is to use condition scores or condition indices, for the infrastructure owners, as it is desirable that they understand how their population of assets is changing over time. For bridges this has involved providing a condition rating for each structure based on observation and by tracking the changes in the distribution of structure condition for population over time. The current maintenance strategy can then be shown to be inadequate (leading to deteriorating population condition), adequate (producing a stable population condition) or effective and resulting in an improving population condition. There have been a variety of bridge condition scoring systems that have been devised by different infrastructure owners in both the highway and railway sectors. Whilst these scores are not devised to be used in detailed maintenance modelling, due to the lack of alternative data they have frequently been used in this manner. This paper addresses the problems of using this data for bridge degradation modelling and proposes an alternative method to model the degradation of bridge elements using historical work done data. The deterioration process is modelled by a Weibull distribution that governs the time a component deteriorates to a degraded condition state following a repair. The method is demonstrated on real historical maintenance data where the analyses of the deterioration processes of several main bridge components are presented

Non-minimality of corners in subriemannian geometry

We give a short solution to one of the main open problems in subriemannian geometry. Namely, we prove that length minimizers do not have corner-type singularities. With this result we solve Problem II of Agrachev's list, and provide the first general result toward the 30-year-old open problem of regularity of subriemannian geodesics.Comment: 11 pages, final versio

Petri net modelling of bridge asset management using maintenance-related state conditions

Bridge structures are an important part of the UK transportation network. They are also experiencing increasing rates of deterioration due to the increasing traffic volume and load intensity. Available bridge models have many restrictions due to the assumptions of the analytical method used and the means by which the model states are defined to represent the condition of the structure. These models also lack the complexity to allow detailed maintenance and renewal options to be explored. This paper presents a bridge model developed based on the Petri net (PN) approach. The method allows for detailed modelling of the individual components in the structure whilst maintaining the size of the analytical problem to a manageable size and resulting in an efficient analysis. The bridge model is formed from sub-models of each of the bridge components and takes into consideration the component deterioration process, the interaction and dependency between different component deterioration processes, along with the inspection and maintenance processes. The model states are defined based on actual degraded component conditions which they experience. It is therefore easy to relate these to the appropriate maintenance options. This gives a considerable advantage over those models based on the condition scores or ratings. The state residence times between changes in state resulting from deterioration and maintenance are governed by appropriate Weibull distributions. Thus, avoiding the restriction of constant failure rates used in Markov approaches which are rarely appropriate to model deteriorating asset conditions. The application of the model is demonstrated on a typical bridge structure where the PN model is solved using Monte Carlo simulation, the model results are also presented and discussed

Modelling railway bridge asset management

The UK has a long history in the railway industry with a large number of railway assets. Railway bridges form one of the major asset groups with more than 35,000 bridges. The majority of the bridge population are old being constructed over 100 years ago. Many of the bridges were not designed to meet the current network demand. With an expected increasing rate of deterioration due to the increasing traffic loads and intensities, the management authorities are faced with the difficult task of keeping the bridge in an acceptable condition with the constraint budget and minimum service disruptions. Modelling tools with higher complexity are required to model the degradation of assets and the effects of different maintenance strategies, in order to support the management decision making process. This research aims to address the deficiencies of the current bridge condition systems and bridge models reported in the literature and to demonstrate a complete modelling approach to bridge asset management. The degradation process of a bridge element is studied using the historical maintenance data where previous maintenance actions were triggered by a certain type of defects. Two bridge models are then developed accounting for the degradation distributions, service and inspection frequency, repair delay time and different repair strategies. The models provide a mean of predicting the asset future condition as well as investigating the effects of different maintenance strategies will have on a particular asset. The first model is a continuous-time Markov bridge model and is considered more complex than other models in the literature, the model demonstrates the advantages of the Markov modelling technique as well as highlighting its limitations. The second bridge model presented a novel Petri-Net modelling approach to bridge asset modelling. This stochastic modelling technique allows much more detail modelling of bridge components, considering: non-constant deterioration rates; protective coating modelling; limits of the number of repairs can be carried out; and the flexibility of the model allows easily extension to the model or the number of components modelled. By applying the two models on the same asset, a comparison can be made and the results further confirm the validations and improvements of the presented Petri-Net approach. Finally, optimisation technique (Genetic Algorithm) is applied to the bridge models to find the optimum maintenance strategies in which the objectives are to minimise the whole life cycle cost whist maximising the asset average condition. A hybrid optimisation that takes advantage of both bridge models, resulting in a significant time saving, is also presented

Characterization of hexabundles: Initial results

New multi-core imaging fibre bundles -- hexabundles -- being developed at the University of Sydney will provide simultaneous integral field spectroscopy for hundreds of celestial sources across a wide angular field. These are a natural progression from the use of single fibres in existing galaxy surveys. Hexabundles will allow us to address fundamental questions in astronomy without the biases introduced by a fixed entrance aperture. We have begun to consider instrument concepts that exploit hundreds of hexabundles over the widest possible field of view. To this end, we have compared the performance of a 61-core fully-fused hexabundle and 5 lightly-fused bundles with 7 cores each. All fibres in the bundles have 100 micron cores. In the fully-fused bundle, the cores are distorted from a circular shape in order to achieve a higher fill fraction. The lightly-fused bundles have circular cores and five different cladding thicknesses which affect the fill fraction. We compare the optical performance of all 6 bundles and find that the advantage of smaller interstitial holes (higher fill fraction) is outweighed by the increase in modal coupling, cross-talk and the poor optical performance caused by the deformation of the fibre cores. Uniformly high throughput and low cross-talk are essential for imaging faint astronomical targets with sufficient resolution to disentangle the dynamical structure. Devices already under development will have between 100 and 200 lightly-fused cores, although larger formats are feasible. The light-weight packaging of hexabundles is sufficiently flexible to allow existing robotic positioners to make use of them.Comment: Accepted for publication in MNRAS. See also a complimentary paper on the development of hexabundles - Bland-Hawthorn et al. 2011, Optics Express, vol. 19, p. 2649 (http://www.opticsinfobase.org/abstract.cfm?URI=oe-19-3-2649

Modelling railway bridge asset management

The UK has a long history in the railway industry with a large number of railway assets. Railway bridges form one of the major asset groups with more than 35,000 bridges. The majority of the bridge population are old being constructed over 100 years ago. Many of the bridges were not designed to meet the current network demand. With an expected increasing rate of deterioration due to the increasing traffic loads and intensities, the management authorities are faced with the difficult task of keeping the bridge in an acceptable condition with the constraint budget and minimum service disruptions. Modelling tools with higher complexity are required to model the degradation of assets and the effects of different maintenance strategies, in order to support the management decision making process. This research aims to address the deficiencies of the current bridge condition systems and bridge models reported in the literature and to demonstrate a complete modelling approach to bridge asset management. The degradation process of a bridge element is studied using the historical maintenance data where previous maintenance actions were triggered by a certain type of defects. Two bridge models are then developed accounting for the degradation distributions, service and inspection frequency, repair delay time and different repair strategies. The models provide a mean of predicting the asset future condition as well as investigating the effects of different maintenance strategies will have on a particular asset. The first model is a continuous-time Markov bridge model and is considered more complex than other models in the literature, the model demonstrates the advantages of the Markov modelling technique as well as highlighting its limitations. The second bridge model presented a novel Petri-Net modelling approach to bridge asset modelling. This stochastic modelling technique allows much more detail modelling of bridge components, considering: non-constant deterioration rates; protective coating modelling; limits of the number of repairs can be carried out; and the flexibility of the model allows easily extension to the model or the number of components modelled. By applying the two models on the same asset, a comparison can be made and the results further confirm the validations and improvements of the presented Petri-Net approach. Finally, optimisation technique (Genetic Algorithm) is applied to the bridge models to find the optimum maintenance strategies in which the objectives are to minimise the whole life cycle cost whist maximising the asset average condition. A hybrid optimisation that takes advantage of both bridge models, resulting in a significant time saving, is also presented

In Silico Analysis of the Small Molecule Content of Outer Membrane Vesicles Produced by Bacteroides thetaiotaomicron Indicates an Extensive Metabolic Link between Microbe and Host

The interactions between the gut microbiota and its host are of central importance to the health of the host. Outer membrane vesicles (OMVs) are produced ubiquitously by Gram-negative bacteria including the gut commensal Bacteroides thetaiotaomicron. These vesicles can interact with the host in various ways but until now their complement of small molecules has not been investigated in this context. Using an untargeted high-coverage metabolomic approach we have measured the small molecule content of these vesicles in contrasting in vitro conditions to establish what role these metabolites could perform when packed into these vesicles. B. thetaiotaomicron packs OMVs with a highly conserved core set of small molecules which are strikingly enriched with mouse-digestible metabolites and with metabolites previously shown to be associated with colonization of the murine GIT. By use of an expanded genome-scale metabolic model of B. thetaiotaomicron and a potential host (the mouse) we have established many possible metabolic pathways between the two organisms that were previously unknown, and have found several putative novel metabolic functions for mouse that are supported by gene annotations, but that do not currently appear in existing mouse metabolic networks. The lipidome of these OMVs bears no relation to the mouse lipidome, so the purpose of this particular composition of lipids remains unclear. We conclude from this analysis that through intimate symbiotic evolution OMVs produced by B. thetaiotaomicron are likely to have been adopted as a conduit for small molecules bound for the mammalian host in vivo

Analytic Metaphysics versus Naturalized Metaphysics: The Relevance of Applied Ontology

The relevance of analytic metaphysics has come under criticism: Ladyman & Ross, for instance, have suggested do discontinue the field. French & McKenzie have argued in defense of analytic metaphysics that it develops tools that could turn out to be useful for philosophy of physics. In this article, we show first that this heuristic defense of metaphysics can be extended to the scientific field of applied ontology, which uses constructs from analytic metaphysics. Second, we elaborate on a parallel by French & McKenzie between mathematics and metaphysics to show that the whole field of analytic metaphysics, being useful not only for philosophy but also for science, should continue to exist as a largely autonomous field

PARP-3 and APLF function together to accelerate nonhomologous end joining

PARP-3 is a member of the ADP-ribosyl transferase superfamily of unknown function. We show that PARP-3 is stimulated by DNA double-strand breaks (DSBs) in vitro and functions in the same pathway as the poly (ADP-ribose)-binding protein APLF to accelerate chromosomal DNA DSB repair. We implicate PARP-3 in the accumulation of APLF at DSBs and demonstrate that APLF promotes the retention of XRCC4/DNA ligase IV complex in chromatin, suggesting that PARP-3 and APLF accelerate DNA ligation during nonhomologous end-joining (NHEJ). Consistent with this, we show that class switch recombination in Aplf−/− B cells is biased toward microhomology-mediated end-joining, a pathway that operates in the absence of XRCC4/DNA ligase IV, and that the requirement for PARP-3 and APLF for NHEJ is circumvented by overexpression of XRCC4/DNA ligase IV. These data identify molecular roles for PARP-3 and APLF in chromosomal DNA double-strand break repair reactions