A study of the impact of dislocations on the thermoelectric properties of quantum wells in the Si/SiGe materials system

Thermoelectric materials generate electricity from thermal energy using the Seebeck effect to generate a voltage and an electronic current from a temperature difference across the semiconductor. High thermoelectric efficiency ZT requires a semiconductor with high electronic conductivity and low thermal conductivity. Here, we investigate the effect of scattering from threading dislocations of edge character on the thermoelectric performance of individual n and p-channel SiGe multiple quantum well structures. Our detailed physical simulations indicate that while the thermal and electrical conductivities decrease with increasing dislocation scattering/density, the Seebeck coefficient actually increases with increasing threading dislocation density above 10<sup>6</sup> cm<sup>-2</sup> at room temperature, due to an increase in the entropy associated with each carrier. The collective result of these individual effects, is that the present Si-based quantum well designs can tolerate scattering by a threading dislocation density up to ~10<sup>8</sup> cm<sup>-2</sup>, well within the capabilities of modern growth techniques, before significant reductions in ZT due to scattering from threading dislocations is observed

The Day-to-Day Dynamics of Route Choice

This paper reviews methods proposed for modelling the day-to-day dynamics of route choice, on an individual driver level. Extensions to within-day dynamics and choice of departure time are also discussed. A new variation on the approaches reviewed is also described. Simulation tests on a simple two-link network are used to illustrate the approach, and to investigate probabilistic counterparts of equilibrium uniqueness and stability. The long-term plan is for such a day-to-day varying demand-side model to be combined with a suitable microscopic supply-side model, thereby producing a new generation network model. The need for such a model - particularly in the context of assessing real-time transport strategies - has been identified in previous working papers

A Comparison of System Optimal and User Optimal Route Guidance.

The work described in this paper (carried out under the EC `DRIVE' programme) extends the simulations described in Working Paper 315, with the aim of studying the likely benefits to and reactions of drivers to system optimal (SO) route guidance - in particular, these effects are compared with those obtained under user optimal (UE) guidance. The model used is again one of a multiple user class equilibrium assignment, so that equipped drivers may be directed to more than one route per origin-destination movement. UE and SO guidance are compared, at different levels of equipped vehicles and demand levels, on the basis of the number of routes they recommend and the similarity of the flows on these routes, as well as link-based properties such as actual flows and queues resulting. These serve to demonstrate the extent to which the routes recommended under UE guidance serve as proxies to those under SO guidance. Secondly, a comparison is made of average (dis)benefits to guided drivers as well as the excess travel time incurred by individual equipped drivers in following SO, as opposed to UE guidance, in order to determine the extent of user sub-optimality of SO routing. Thirdly, input from a parallel DRIVE project, investigating user reactions to guidance information, is used to infer the extent to which drivers are likely to accept the sub-optimality of SO guidance, and the factors which are likely to influence their acceptance. Finally, some preliminary analysis is performed on combined strategies, which aim to strike a balance between the system benefits of SO guidance and the user benefits of UE routing

Student as producer and open educational resources: enhancing learning through digital scholarship

At the University of Lincoln, the student as producer agenda is seeking to disrupt consumer-based learning relationships by reinventing the undergraduate curriculum along the lines of research-engaged teaching. The open education movement, with its emphasis on creative commons and collaborative working practices, also disrupts traditional and formal campus-based education. This paper looks at the linkages between the Student as Producer project and the processes of embedding open educational practice at Lincoln. Both reinforce the need for digital scholarship and the prerequisite digital literacies that are essential for learning in a digital age