Showing papers by "Peter Davies published in 2006"

Benthic metabolism as an indicator of stream ecosystem health

Abstract: We tested direct and indirect measures of benthic metabolism as indicators of stream ecosystem health across a known agricultural land-use disturbance gradient in southeast Queensland, Australia. Gross primary production (GPP) and respiration (R-24) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophyll a) from cobbles and sediment cores, algal biomass accrual on artificial substrates and stable carbon isotope ratios of aquatic plants and benthic sediments were measured at 53 stream sites, ranging from undisturbed subtropical rainforest to catchments where improved pasture and intensive cropping are major land-uses. Rates of benthic GPP and R-24 varied by more than two orders of magnitude across the study gradient. Generalised linear regression modelling explained 80% or more of the variation in these two indicators when sediment and cobble substrate dominated sites were considered separately, and both catchment and reach scale descriptors of the disturbance gradient were important in explaining this variation. Model fits were poor for net daily benthic metabolism (NDM) and production to respiration ratio (P/R). Algal biomass accrual on artificial substrate and stable carbon isotope ratios of aquatic plants and benthic sediment were the best of the indirect indicators, with regression model R-2 values of 50% or greater. Model fits were poor for algal biomass on natural substrates for cobble sites and all sites. None of these indirect measures of benthic metabolism was a good surrogate for measured GPP. Direct measures of benthic metabolism, GPP and R-24, and several indirect measures were good indicators of stream ecosystem health and are recommended in assessing process-related responses to riparian and catchment land use change and the success of ecosystem rehabilitation actions.

Benthic metabolism as an indicator of stream ecosystem health

Abstract: We tested direct and indirect measures of benthic metabolism as indicators of stream ecosystem health across a known agricultural land-use disturbance gradient in southeast Queensland, Australia. Gross primary production (GPP) and respiration (R24) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophyll a) from cobbles and sediment cores, algal biomass accrual on artificial substrates and stable carbon isotope ratios of aquatic plants and benthic sediments were measured at 53 stream sites, ranging from undisturbed subtropical rainforest to catchments where improved pasture and intensive cropping are major land-uses. Rates of benthic GPP and R24 varied by more than two orders of magnitude across the study gradient. Generalised linear regression modelling explained 80% or more of the variation in these two indicators when sediment and cobble substrate dominated sites were considered separately, and both catchment and reach scale descriptors of the disturbance gradient were important in explaining this variation. Model fits were poor for net daily benthic metabolism (NDM) and production to respiration ratio (P/R). Algal biomass accrual on artificial substrate and stable carbon isotope ratios of aquatic plants and benthic sediment were the best of the indirect indicators, with regression model R2 values of 50% or greater. Model fits were poor for algal biomass on natural substrates for cobble sites and all sites. None of these indirect measures of benthic metabolism was a good surrogate for measured GPP. Direct measures of benthic metabolism, GPP and R24, and several indirect measures were good indicators of stream ecosystem health and are recommended in assessing process-related responses to riparian and catchment land use change and the success of ecosystem rehabilitation actions.

Threshold Concepts: how can we recognise them?

Abstract: A threshold concept is defined by Meyer and Land (2003) as possessing the following qualities: transformative, integrative, bounded, and probably irreversible. This concept provides a promising way of interpreting the learning demand presented by subjects and Meyer and Land have begun to apply the idea in analysing learning economics. It redefines the familiar idea of a ‘powerful concept’ in a social constructivist context, providing a penetrating tool for the analysis of the development of discipline specific learning. This paper examines some difficulties to be faced in the operationalisation of the idea of ‘threshold concepts’ in economics and, in so doing, begins to identify ways in which these problems might be overcome.

Mechanical behaviour of polyethylene terephthalate & polyethylene naphthalate fibres under cyclic loading

Abstract: Polyethylene naphthalate (PEN) fibres possess a higher initial stiffness than that of polyethylene terephthalate (PET) fibres and this makes them an attractive competitor for use in mooring ropes and other applications for which a low compliance would be an advantage. The two types of fibres have been characterised and compared in tension, creep and fatigue and found to behave in very similar ways. Failure of both fibres results in similar fracture morphologies although under high cyclic loading a new failure process has been observed for the PEN fibres which combines step by step crack propagation and final failure normal to the fibre axis. In the light of this observation, similar fracture behaviour has also been identified in PET fibres and which, until now had been overlooked. The loading criteria for fatigue failure are similar for both fibres and it has been shown that, for a given maximum cyclic load, lifetime is raised if the minimum cyclic load is increased.

Deep brain stimulation for neuropathic cephalalgia.

Abstract: The aim of this study was to determine the efficacy of deep brain stimulation (DBS) in the treatment of various types of intractable head and facial pains. Seven patients underwent the insertion of DBS electrodes into the periventricular/periaqueductal grey region and/or the ventroposteromedial nucleus of the thalamus. We have shown statistically significant improvement in pain scores (visual analogue and McGill's) as well as health-related quality of life (SF-36v2) following surgery. There is wide variability in patient outcomes but, overall, DBS can be an effective treatment. Our results are compared with the published literature and electrode position for effective analgesia is discussed.

Educating citizens for changing economies

Abstract: While economic factors play a crucial role in determining election outcomes, the place of economic understanding in educating citizens is neither widely recognized nor substantially articulated in the literature Although economic educators have frequently asserted that economic understanding is important to citizens’ education, they have not set out their case by engaging with the wider literature on citizenship education This paper identifies two dimensions of an economic education that enable it to contribute to a ‘maximalist’ citizenship education

Mechanical Properties of Composites Based on Low Styrene Emission Polyester Resins for Marine Applications

Abstract: Glass fibre reinforced polyester composites are used extensively for hulls and decks of pleasure boats. Boat-builders must optimise manufacturing technology, not only with respect to mechanical properties but also limiting volatile organic compounds (VOC) emissions. One way to achieve this is through modified polyester resin formulations such as low styrene content, low styrene emission or combinations of these. The resin matrix selection procedure is based on design specification (mechanical behaviour) but also manufacturing requirements and cost considerations. For this application post-cure is rarely used so it is important to optimise curing conditions. In this study the influence of the curing cycle on mechanical properties was examined first for two polyester resins. Then for one cycle (16 h at 40°C) the properties of eight resins have been determined. Significant differences in failure strain are observed, from 0.9% to 3.3%. The resins with improved VOC performance are the most brittle. The transverse tensile behaviour of these resins in composites with unidirectional glass fibre reinforcement and the limit of linearity for composites with glass mat both depend on these failure strains. These results are discussed in terms of admissible composite strains for boat design.

The influence of hydrostatic pressure on the interlaminar fracture toughness of carbon/epoxy composites

Abstract: The use of composites for deep sea applications requires a thorough understanding of the behaviour of these materials. While several studies have examined the influence of pressure on in-plane properties few data are available for the interlaminar fracture behaviour. This paper presents results from such tests performed in a specially designed pressure vessel mounted on a standard test machine, which allows pressures up to 1000 bars (100 MPa) to be applied during mechanical testing. Mode I and Mode II tests have been performed on a unidirectional IM7/977-2 carbon/epoxy composite. No effect of pressure was noted on Mode I fracture toughness. A data reduction scheme has been developed for Mode II loading and an increase in GIIC with increasing pressure was noted.

Characterization of residual stresses in wound composite tubes

Abstract: This paper presents a method for the characterization of residual stresses in thick filament wound tubes. The three materials considered in the study are wet wound epoxy composite tubes based on E glass, R glass and T700 carbon fibres with three winding angles, [+/- 35], [+/- 55] and [+/- 851 with respect to the longitudinal axis. The aim of the present work is to measure internal stresses, based on strains liberated by cutting composite tubes, and to compare results with predictions from a residual stress model based on the classical equations of solid mechanics. This leads to a simple technique which allows the quick identification of the effects of manufacturing and moisture on the internal multi-axial stress level.

The influence of schooling on the aspirations of young people with special educational needs

Abstract: The authors investigate the effect of schooling on the aspirations of young people designated as having mild learning difficulties (MLD) or emotional and behavioural difficulties (EBD) in the first large-scale study of its kind in England. Data were collected from parents and their 15/16 year-old children in the final year of their compulsory schooling in schools. The results indicate on average a positive effect of mainstream schooling on the aspirations of these pupils with the caveat that these benefits are more likely to accrue to pupils whose parents are in higher status occupations. In their conclusions the authors discuss the implications of these results for education policy in the context of local management of schools.

Should we have faith in not‐for‐profit providers of schooling?

Abstract: Western governments appear increasingly dissatisfied with the rising costs and apparent static performance of their education systems. This dissatisfaction has been manifested in a critical re‐examination of the near‐monopoly of publicly provided schooling. Elsewhere in the public sector, privatization and competitive tendering have been frequently used to reduce costs and raise productivity. However, in education the inability to fully specify contracts with private providers has led to renewed interest in increasing the role of not‐for‐profit providers. In this paper we utilize economic analysis to critically examine the strengths and weaknesses of not‐for‐profit providers of schooling. We explore the nature of the specific context in which they may prove to be effective providers, using successful faith schools as a case study. We conclude that there are prima facie grounds for governments to prefer contracting not‐for‐profit rather than for‐profit organizations for the provision of state funded educat...

Disciplines, Outcomes and Purpose in Social Science Education

Abstract: The gap between school knowledge and academic knowledge has long been acknowledged. The division of the curriculum into separate academic subjects has sometimes been blamed for this problem. On this reading it would make sense to re-model the curriculum so that teaching is multidisciplinary. However, efforts to achieve this ideal have a poor record in England. In this paper we suggest that the answer to the problem is more likely to lie in the way that the curriculum is built from a careful analysis of the actual outcomes of learning. We briefly outline three projects that are based on this supposition, describing the theoretical underpinnings and the main features of the projects.

Étude du comportement non-linéaire d'une colle dans un assemblage

Abstract: L'objectif de cette etude est de definir a terme un outil fiable de dimensionnement d'assemblages colles pour favoriser l'utilisation de cette technique d'assemblage, en particulier, dans le domaine des structures marines et sous-marines. Un dispositif de type "Arcan", adapte pour l'etude du comportement d'un assemblage "metal-metal", a ete developpe pour se concentrer sur l'analyse du comportement de la colle en films minces. Pour analyser la cinematique de la deformation du joint de colle nous avons utilise un systeme de mesure sans contact par correlation d'images. Ainsi differentes caracteristiques du comportement non-lineaire de la colle ont ete observees. Les premiers resultats obtenus pour les collages mixtes (acier, aluminium, composite) montrent des comportements similaires de la colle pour la procedure proposee. De plus, des controles de qualite par DSC, et des etudes de cuisson par DMA sont realisees pour verifier la conformite de la procedure de collage.