176 research outputs found
In situ consolidation of thermoplastic prepreg tape using automated tape placement technology: Potential and possibilities
The key parameters of the in-situ consolidation of carbon fibre reinforced poly-ether-etherketone
(AS4-CF/PEEK) by automated tape placement (ATP) process were investigated by
manufacturing of continuous rings and by laying tape onto pre-consolidated laminates. In
order to establish and understand correlations between the process parameters and
mechanical properties, a number of parametric studies were performed by manufacturing and
testing the interlaminar shear strength, single lap shear strength and fracture toughness
samples. The main process parameters investigated were the compaction force, tape laying
speed and tool temperature. To achieve a uniform heat distribution across the thermoplastic
tape, a new nozzle was designed. Baseline samples were also manufactured using the
autoclave process to provide a comparison for the ATP composites produced. Optical
microscopy was used for investigating the microstructure of composites compared. It was
found that increasing the tool temperature reduced the temperature gradient between the
incoming tape and substrate, resulting in better lap-shear strength and fracture toughness
properties
Tooling materials compatible with carbon fibre composites in a microwave environment
Although metals are the most commonly used tooling materials to cure composites, they do not provide optimal results in a microwave environment. Following a selection process based on the properties of the materials, an alternative tooling material in carbon fibre reinforced plastic (CFRP) was successfully utilised to cure CFRP panels in laboratory and industrial microwaves. The conductive carbon fibres in the tool facilitated the fast heat transfer across the part. Other tooling materials including a glass fibre cyanate ester prepreg and tooling board were trialled, although the latter exhibited damage during cure. These advantages demonstrate that the CFRP tool is a compatible material that can be used when microwave curing composites
Damage detection and location in woven fabric CFRP laminate panels
The need for multifunctional carbon fibre composite laminates has emerged to improve the reliability and safety of carbon fibre composite components and decrease costs. The development of an electrical selfsensing system for woven fabric carbon fibre composite laminate panels which can detect and locate damage due to impact events is presented. The electrical sensing system uses a four probe electrical resistance method. Two different sensing mats are investigated, the main difference between them are the surface area of the electrodes and the distance between the electrodes. To investigate the damage sensitivity of the sensing system for woven fabric carbon fibre composite laminate panels, panels are produced with various thicknesses from 0.84 to 3.5 mm and are impacted at energies from 1 to 10 J to generate barely visible impact damage. Damage is detected using global electrical resistance changes, the changes in electrical resistance vary depending on carbon fibre volume fraction, spacing distance between the sensing electrodes in the sensing mats, the surface area of the electrodes, damage size, and damage type; it is found that the thicker the panel, the less sensitive the electrical resistance system is. The effect of the surface area of the sensing electrodes is high on the electrical resistance baseline, where the baseline increases by up to 55% when the surface area of the sensing electrodes increases from 100 mm2 to 400 mm2; while spacing distance between electrodes has a greater effect on damage sensitivity of the electrical resistance sensing system than the surface area of the sensing electrodes
On ordinal utility, cardinal utility, and random utility
Though the Random Utility Model (RUM) was conceived
entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties of
cardinal utility. The adoption of cardinal utility as a
working operation of ordinal is perfectly valid, provided
interpretations drawn from that operation remain faithful
to ordinal utility. The paper considers whether the latterrequirement holds true for several measurements commonly
derived from RUM. In particular it is found that
measurements of consumer surplus change may depart from
ordinal utility, and exploit the cardinality inherent in
the practical apparatus.
Rescaling quality of life values from discrete choice experiments for use as QALYs: a cautionary tale
Background: Researchers are increasingly investigating the potential for ordinal tasks such as ranking and discrete choice experiments to estimate QALY health state values. However, the assumptions of random utility theory, which underpin the statistical models used to provide these estimates, have received insufficient attention. In particular, the assumptions made about the decisions between living states and the death state are not satisfied, at least for some people. Estimated values are likely to be incorrectly anchored with respect to death (zero) in such circumstances.
Methods: Data from the Investigating Choice Experiments for the preferences of older people CAPability instrument (ICECAP) valuation exercise were analysed. The values (previously anchored to the worst possible state) were rescaled using an ordinal model proposed previously to estimate QALY-like values. Bootstrapping was conducted to vary artificially the proportion of people who conformed to the conventional random utility model underpinning the analyses.
Results: Only 26% of respondents conformed unequivocally to the assumptions of conventional random
utility theory. At least 14% of respondents unequivocally violated the assumptions. Varying the relative
proportions of conforming respondents in sensitivity analyses led to large changes in the estimated QALY
values, particularly for lower-valued states. As a result these values could be either positive (considered
to be better than death) or negative (considered to be worse than death).
Conclusion: Use of a statistical model such as conditional (multinomial) regression to anchor quality of life values from ordinal data to death is inappropriate in the presence of respondents who do not conform to the assumptions of conventional random utility theory. This is clearest when estimating values for that group of respondents observed in valuation samples who refuse to consider any living state to be worse than death: in such circumstances the model cannot be estimated. Only a valuation task requiring respondents to make choices in which both length and quality of life vary can produce estimates that properly reflect the preferences of all respondents
On Combining Stated Preferences and Revealed Preferences Approaches to Evaluate Environmental Resources Having a Recreational Use
This work aims at analysing the value of recreational water uses for the Idro Lake (Lombardy, Northern Italy), which has been experiencing dramatic fluctuations in its levels in recent years, due to excessive productive withdrawal that affected recreational uses. It estimates the economic benefits deriving from recreational uses, by considering the current recreational demand and the hypothetical one obtained by considering an “improved quality” scenario. Through an on-site survey, we built a panel dataset. Following Whitehead et al. (2000) and Hanley et al. (2003) we get welfare estimates by combining SP and RP responses. The present CS is estimated in €134 per individual, whilst the increase in CS is estimated in €173 per individual. These figures can be confronted with the economic value of competitive uses and with the clean up costs, respectively, to infer some policy indications
Sustainable Forest Management Preferences of Interest Groups in Three Regions with Different Levels of Industrial Forestry: An Exploratory Attribute-Based Choice Experiment
The challenge of sustainable forest management is to integrate diverse and sometimes conflicting management objectives. In order to achieve this goal, we need a better understanding of the aspects influencing the preferences of diverse groups and how these groups make trade-offs between different attributes of SFM. We compare the SFM preferences of interest groups in regions with different forest use histories based on the reasoning that the condition of the forest reflects the forest use history of the area. The condition of the forest also shapes an individual’s forest values and attitudes. These held values and attitudes are thought to influence SFM preferences. We tested whether the SFM preferences vary amongst the different interest groups within and across regions. We collected data from 252 persons using a choice experiment approach, where participants chose multiple times among different options described by a combination of attributes that are assigned different levels. The novelty of our approach was the use of choice experiments in the assessment of regional preference differences. Given the complexity of interregional comparison and the small sample size, this was an exploratory study based on a purposive rather than random sample. Nevertheless, our results suggest that the aggregation of preferences of all individuals within a region does not reveal all information necessary for forest management planning since opposing viewpoints could cancel each other out and lead to an interpretation that does not reflect possibly polarised views. Although based on a small\ud
sample size, the preferences of interest groups within a region are generally statistically significantly different from each other; however preferences of interest groups across regions are also significantly different. This illustrates the potential importance of assessing heterogeneity by region and by group
Preferences for Domestic Water Services in the Middle Olifants Sub-Basin of South Africa
Effects of local treatment with and without sensorimotor and balance exercise in individuals with neck pain: protocol for a randomized controlled trial
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