Intake Ground Vortex Prediction Methods

For an aircraft turbofan engine in ground operations or during the take-off run a ground vortex can occur which is ingested and could potentially adversely affect the engine performance and operation. The vortex characteristics depend on the ground clearance, intake flow capture ratio and the relative wind vector. It is a complex flow for which there is currently very little appropriate quantitative preliminary design information. These aspects are addressed in this work where a range of models are developed to provide a method for estimating the key metrics such as the formation boundary and the ground vortex size and strength. Three techniques are presented which utilize empirical, analytical and semi-empirical approaches. The empirical methods are primarily based on a large dataset of model-scale experiments which quantitatively measured the ground vortex characteristics for a wide range of configurations. These include the effects of intake ground clearance, approaching boundary layer thickness, intake Mach number and capture velocity ratio. Overall the models are able to predict some of the key measured behaviours such as the velocity ratio for maximum vortex strength. With increasing empiricism for key sub-elements of the model construction, an increasing level of agreement is found with the experimental results. Overall the three techniques provide a relatively quick and easy method in establishing the important vortex characteristics for a given headwind configuration which is of significant use from a practical engineering perspective

Intake ground vortex characteristics

The development of ground vortices when an intake operates in close proximity to the ground has been studied computationally for several configurations including front and rear quarter approaching flows as well as tailwind arrangements. The investigations have been conducted at model scale using a generic intake geometry. Reynolds Averaged Navier–Stokes calculations have been used and an initial validation of the computational model has been carried out against experimental data. The computational method has subsequently been applied to configurations that are difficult to test experimentally by including tailwind and rear quarter flows. The results, along with those from a previous compatible study of headwind and pure cross-wind configurations, have been used to assess the ground vortex behaviour under a broad range of velocity ratios and approaching wind angles. The characteristics provide insights on the influence of the size and strength of ground vortices on the overall quality of the flow ingested by the intake

Prosomal-width-to-weight relationships in American horseshoe crabs (Limulus polyphemus): examining conversion factors used to estimate landings

Horseshoe crabs (Limulus polyphemus) are valued by many stakeholders, including the commercial fishing industry, biomedical companies, and environmental interest groups. We designed a study to test the accuracy of the conversion factors that were used by NOAA Fisheries and state agencies to estimate horseshoe crab landings before mandatory reporting that began in 1998. Our results indicate that the NOAA Fisheries conversion factor consistently overestimates the weight of male horseshoe crabs, particularly those from New England populations. Because of the inaccuracy of this and other conversion factors, states are now mandated to report the number (not biomass) and sex of landed horseshoe crabs. However, accurate estimates of biomass are still necessary for use in prediction models that are being developed to better manage the horseshoe crab fishery. We recommend that managers use the conversion factors presented in this study to convert current landing data from numbers to biomass of harvested horseshoe crabs for future assessments

The problem of maintaining compliance within stable coalitions: experimental evidence

This study examines the performance of stable cooperative coalitions that form to provide a public good when coalition members have the opportunity to violate their commitments. A stable coalition is one in which no member wishes to leave and no non-member wishes to join. To counteract the incentive to violate their commitments, coalition members fund a third-party enforcer. This leads to the theoretical conclusion that stable coalitions are larger, and provide more of a public good, when their members are responsible for financing enforcement. However, our experiments reveal that member-financed enforcement of compliance reduces the provision of the public good. The decrease is attributed to an increase in the participation threshold for a stable coalition to form and to significant levels of noncompliance. Provision of the public good increases significantly when we abandon the strict stability conditions and require all subjects to join a coalition for it to form.lab experiments

Revisiting core issues in dynamic assessment

Dynamic assessment is currently poised at a juncture at which theoretical and practical assessment resolutions are necessitated. Such issues concern theoretical approaches towards  psycho-educational assessment.  In order to partially explore these basic assessment approaches, a questionnaire was delivered via electronic mail to one hundred internationally, currently active dynamic assessment researchers and practitioners. The findings from the responses formed the basis for an informal content analysis, which was conducted utilising themes as primary meaning unit and word counts as secondary meaning unit of analyses. The one common and uniting feature about the current research in this area is the broad range of theoretical approaches towards assessment and the current lack of unanimity across types of approaches. Responses showed that varied theoretical frameworks are employed in dynamic assessments which do not necessarily cohere with other traditional approaches. It is contended that an exploratory revisiting of core assessment approaches would assist in positioning practitioners’ and researchers’ theoretical approaches in future assessments

The Problem of Maintaining Compliance within Stable Coalitions: Experimental Evidence

This study examines the performance of stable cooperative coalitions that form to provide a public good when coalition members have the opportunity to not comply with their commitments. A stable coalition is one in which no member wishes to leave and no non-member wishes to join. To counteract the incentive to violate their commitments, coalition members fund a third-party enforcer. This leads to the theoretical conclusion that stable coalitions are larger (and provide more of a public good) when their members must finance enforcement relative to when compliance is ensured without the need for costly enforcement. However, our experiments reveal that giving coalition members the opportunity to violate their commitments while requiring them to finance enforcement to maintain compliance reduces the overall provision of the public good. The decrease in the provision of the public good is attributed to an increase in the participation threshold for a theoretically stable coalition to form and to significant levels of noncompliance. When we abandon the strict stability conditions and require all subjects to join a coalition for it to form, the average provision of the public good increases significantly. Key Words: stable coalitions, self-enforcing agreements, compliance, enforcement, public goods

Five year prognosis in patients with angina identified in primary care : incident cohort study

Peer reviewedPublisher PD

A review of South African research in the field of dynamic assessment

Dynamic assessment, which is often characterised by the learning potential approach across the world and in South Africa, is receiving more attention from educators and research practitioners alike. When compared to the status of international research, local dynamic assessment research can still be regarded as being in its infancy. A selection of studies conducted within this domain was analysed and the results carefully assessed in terms of positive and negative findings to serve as an indication of the trends that this discipline may face in South Africa. The main findings indicate that although the field is still being researched today, there has been a decrease in the number of studies as well as a concomitant decrease in the implementation of dynamic research efforts. The reasons cited are a lack of time, costs, inefficiencies and also confusion as to what dynamic assessment entails. There is, as yet, no consistent definition of dynamic assessment in South Africa, which makes it all the harder to entrench dynamic assessment as a methodology and implement it on as wide a scale as possible