Transition from variable delay of reinforcement schedules to variable-time (VT) schedules of reinforcement. A systematic investigation.

Six experiments are reported in which rats were trained under response- dependent reinforcement schedules prior to being transferred to variable-time (VT) schedules which were matched in terms of both the overall rate and temporal distribution of reinforcement to the prior response-dependent reinforcement schedule. The response-dependent reinforcement baseline schedules varied according to whether they permitted reinforcement delays or only allowed the designated response to be contiguous with the reinforcer. In addition, some of the baseline schedules required either 'other behaviour'-response or response- 'other behaviour' sequences for reinforcement. The results indicated that delay of reinforcement schedules generally were associated with stronger resistance to response-independent reinforcement relative to immediate reinforcement schedules. Further, immediate reinforcement . schedules which demanded 'other behaviour'-response sequences for reinforcement tended to produce stronger resistance to response-independent reinforcement than those which permitted more than one response class to occur, but only required the emission of the designated operant for reinforcement. Rate of responding, level of efficiency of responding and postreinforcement pause duration during the baseline were poor predictors of response persistence during VT schedules. Response rate during the VT schedules was inversely related to mean delay of reinforcement (experiments IV and VI), while response decrement was related to the proportion of interreinforcement intervals without a response (experiments I, II,III, iv, v and VI). Reinforced and overall interresponse time (IRT) distributions during the VT condition were significantly correlated; further, changes in response rate were r e f l e c t e d in changes in the IRT distributions. It was concluded that an analysis of response maintenance under VT schedules which is framed in terms of the discrimination of response-reinforcer correlations was not supported. It was proposed that a molecular theory in which IRT-reinforcer contiguities are emphasized probably holds more promise

Tribological and mechanical properties of compliant bearings for total joint replacements.

The tribology of a wide range of designs of compliant layer acetabular cups has been evaluated using a simulator. The simulator applied a dynamic load of 2 kN and a sinusoidal motion of ±25 , and measured the frictional resistance directly. In general the friction developed in these joints was extremely low, with friction factors typically below 0.01. When the experimental results were compared with theoretical estimates of friction a poor correlation was found. Further analysis suggested that the design of compliant layer acetabular cups was insensitive to many of the parameters suggested by theory. In particular, the radial clearance and femoral head size were not found to be critical. In addition, methods were proposed and their effectiveness demonstrated to measure friction at the on-set of motion (start-up friction), and the steady state friction in realistic compliant layer knees. The adhesion between compliant layers and a rigid backing have been investigated, with the aim of developing a good bond between them. The peel test was used to demonstrate an excellent diffusion bond between a low modulus medical grade polyurethane, and a similar high modulus grade of polyurethane. The processing conditions used to manufacture the test piece were optimised to maximise the bond strength. The bond was found to be stable after immersion in Ringers solution at 37 C for 52 weeks, and after acetabular cups were subjected to 14 million 4 kN loading cycles. A six station knee wear simulator was designed and commissioned. The simulator applied a dynamic load and an anterior-posterior translation individually to each station, as well as a flexion-extension motion common to all six stations. The simulator was computer controlled entirely using servo hydraulics. Wear rates were obtained from tests lasting up to 8 million cycles conducted on UHMWPE joints

PREFACE

Preface to Proceedings of the International Conference in Dubrovnik, 15-16 October, 2015

Developing a multi-pollutant conceptual framework for the selection and targeting of interventions in water industry catchment management schemes

In recent years water companies have started to adopt catchment management to reduce diffuse pollution in drinking water supply areas. The heterogeneity of catchments and the range of pollutants that must be removed to meet the EU Drinking Water Directive (98/83/EC) limits make it difficult to prioritise areas of a catchment for intervention. Thus conceptual frameworks are required that can disaggregate the components of pollutant risk and help water companies make decisions about where to target interventions in their catchments to maximum effect. This paper demonstrates the concept of generalising pollutants in the same framework by reviewing key pollutant processes within a source-mobilisation-delivery context. From this, criteria are developed (with input from water industry professionals involved in catchment management) which highlights the need for a new water industry specific conceptual framework. The new CaRPoW (Catchment Risk to Potable Water) framework uses the Source-Mobilisation-Delivery concept as modular components of risk that work at two scales, source and mobilisation at the field scale and delivery at the catchment scale. Disaggregating pollutant processes permits the main components of risk to be ascertained so that appropriate interventions can be selected. The generic structure also allows for the outputs from different pollutants to be compared so that potential multiple benefits can be identified. CaRPow provides a transferable framework that can be used by water companies to cost-effectively target interventions under current conditions or under scenarios of land use or climate change

Can head louse repellents really work? Field studies of piperonal 2% spray

Background. Many families find regular checking of children’s heads for head louse infestation too onerous and would prefer to be able to prevent infestation by use of a topical application that deters lice from infesting the head. Identification in the laboratory of a repellent activity for piperonal provided the basis for developing a spray product to repel lice.Methods. A proof of principle field study in Dhaka, Bangladesh, compared the effect of using 2% piperonal spray with that of a placebo in 105 children and adults from three communities with infestation levels close to 100%. All participants were treated for infestation and subsequent incidence of reinfestation monitored daily by investigators. A second randomised, controlled, double blind, study in North London, UK, evaluated the effect of the product in normal use. One hundred and sixty-three children from schools with a high level (20–25%) of infestation were treated and confirmed louse free and randomly divided between 2% piperonal, a placebo spray, and a control group for up to 22 weeks. Parents applied the spray and monitored for infestation. Regular investigator visits confirmed the parental monitoring and replenished supplies of spray.Results. In Dhaka, over 18 days there were only 4 infestations in the piperonal group and 8 in the placebo group. This difference was not significant (p = 0.312). In North London, there were 41 cases of infestation over the course of the study. Although there were fewer infestations in the piperonal group, analysis of time to first infestation showed a no significant (p = 0.4368) difference between groups.Conclusion. Routine use of 2% piperonal spray in communities with a high prevalence of head louse infestation may provide some protection from infestation. However, the difference between use of the product and no active intervention was sufficiently small that regular checking for presence of lice is likely to be a more practical and cost effective approach to prevention of infestation