Communities in university mathematics

This paper concerns communities of learners and teachers that are formed, develop and interact in university mathematics environments through the theoretical lens of Communities of Practice. From this perspective, learning is described as a process of participation and reification in a community in which individuals belong and form their identity through engagement, imagination and alignment. In addition, when inquiry is considered as a fundamental mode of participation, through critical alignment, the community becomes a Community of Inquiry. We discuss these theoretical underpinnings with examples of their application in research in university mathematics education and, in more detail, in two Research Cases which focus on mathematics students' and teachers' perspectives on proof and on engineering students' conceptual understanding of mathematics. The paper concludes with a critical reflection on the theorising of the role of communities in university level teaching and learning and a consideration of ways forward for future research

Travelling-wave thermoacoustic electricity generator using an ultra-compliant alternator for utilization of low-grade thermal energy

This paper proposes a novel concept of a travelling-wave thermoacoustic electricity generator, which employs a looped-tube travelling-wave thermoacoustic engine to convert thermal energy into acoustic power, an ultra-compliant alternator within the engine loop to extract and convert the engine acoustic power to electricity and an acoustic stub matching technique to match the alternator to the engine. In addition, a carefully designed cold heat exchanger acts as a phase shifting inertance to improve the performance. A simple model has been developed to capture and demonstrate the physics of this new concept, while the whole system has been investigated in detail numerically by using a specialized design tool DeltaEC. Based on the current concept, a prototype has been designed, constructed and tested. It uses atmospheric air as the working fluid, a commercially available audio loudspeaker as the electro-dynamic transducer, and inexpensive standard parts as the acoustic resonator. The experimental results have verified the simplified model and the numerical simulations of the practical build. The small-scale inexpensive prototype generator produced 11.6 W of electrical power, which shows the potential for developing cheap thermoacoustic electricity generators for energy recovery from waste heat sources. It is concluded that such concept could be very attractive provided that inexpensive ultra-compliant alternators based on the standard technology used in audio loudspeakers could be developed. Finally, some guidelines have been discussed and proposed for developing such alternators

Selection and experimental evaluation of low-cost porous materials for regenerator applications in thermoacoustic engines

This paper aims at evaluating three selected low-cost porous materials from the point of view of their suitability as regenerator materials in the design of thermoacoustic travelling wave engines. The materials tested include: a cellular ceramic substrate with regular square channels; steel “scourers”; and stainless steel “wool”. Comparisons are made against a widely used regenerator material: stainless steel woven wire mesh screen. For meaningful comparisons, the materials are selected to have similar hydraulic radii. One set of regenerators was designed around the hydraulic radius of 200 μm. This included the ceramic substrate, steel “scourers”, stainless steel “wool” and stacked wire screens (as a reference). This set was complemented by steel “scourers” and stacked wire screens (as a reference) with hydraulic radii of 120 μm. Therefore six regenerators were produced to carry out the testing. Initial tests were made in a steady air flow to estimate their relative pressure drop due to viscous dissipation. Subsequently, they were installed in a looped-tube travelling-wave thermoacoustic engine to test their relative performance. Testing included the onset temperature difference, the maximum pressure amplitude generated and the acoustic power output as a function of mean pressure between 0 and 10 bar above atmospheric. It appears that the performance of regenerators made out of “scourers” and steel “wool” is much worse than their mesh-screen counterparts of the same hydraulic radius. However cellular ceramics may offer an alternative to traditional regenerator materials to reduce the overall system costs. Detailed discussions are provided

Determining the Influence of the Built Environment on Pedestrian-Vehicle Crashes in Dekalb County, Georgia Using Geographic Information Systems

This study aimed to examine how the characteristics of the road network and the built environment influence the frequency of pedestrian-vehicle crashes. Pedestrian crashes (2000 – 2007) on major roads in DeKalb County of Georgia were obtained from Georgia Department of Transportation. Hotspot analysis was performed on locations with frequent pedestrian incidents to determine their built environment characteristics. Using Geographic Information Systems, the built environment was characterized using road grade, curvature, population density, the amount stores and restaurants, bars, and public transit stops nearby. A negative binomial regression model was used to examine the influence of the built environment characteristics on pedestrian crashes. The results showed that all the variables except for road grade were positively associated with increased number of pedestrian crashes. Findings provided insights into the influence of built environment characteristics which is important for injury prevention to improve pedestrian safety

Shopping and chatting: Reports of tourist-host interaction in the Gambia

As it becomes continually easier, at least technologically, for people to move around the world, so the growing numbers of global tourists, in their search for constantly novel experiences (Urry 2002), travel to destinations which are increasingly exotic and distant to them, not only geographically, but also in economic, social and cultural terms. This, in turn, brings them into contact with people from these very different cultures and societies. This paper examines interactions between tourists and hosts in The Gambia, a 'winter sun package holiday destination in West Africa. To investigate the nature of such interactions, 20 'communication diaries' were completed by a group of British tourism students during their week-long field trip to The Gambia and followed up by small group discussions with some of the participants. The students were asked to record as many individual interactions with Gambians as possible noting the following information: Time; Place; Situation; Interlocutor; Languages spoken; Topics; Result of interaction; Perceptions of interactions. 194 interactions were recorded. Many of the interactions were 'transactional' in that tourism workers treat them as potential sources of income. However, their tenor is predominantly 'personal as they were full of phatic communion and chatting. Central to the tourist experience in The Gambia is the role of the 'bumsters' due to their mediating function between the tourists and other Gambian people. The omnipresence of the 'bumsters' in all tourist areas and their constant 'pestering' of tourists is initially annoying to the latter but also acts as a catalyst in encouraging contact with other Gambians by familiarising tourists with local people. We conclude by discussing our findings in the context of the global economies of tourism. © Walter de Gruyter.published_or_final_versio

A low-cost electricity generator for rural areas using a travelling-wave looped-tube thermoacoustic engine

This article describes the construction and preliminary testing of a pre-prototype thermoacoustic electricity generator to test the concept of a low-cost device for application in remote or rural areas of developing countries. A travelling-wave thermoacoustic engine with a configuration of a looped-tube resonator is designed and constructed to convert heat to acoustic power. Air at atmospheric pressure is used as the working gas, PVC tubing is utilized for the feedback pipe, whereas an inexpensive commercially available loudspeaker is adopted to convert the acoustic power, produced by the engine, to electricity. Preliminary experimental results are presented and discussed in detail. The results show that the approach is feasible in principle and it is possible to produce the electrical power levels in the order of 4-5 W with overall heat-to-electric efficiencies in the order of 1 per cent. Further work towards optimizing the device from the performance, manufacturing, and cost points of view is outlined

Phonon driven spin distribution due to the spin-Seebeck effect

Here we report on measurements of the spin-Seebeck effect of GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.Comment: 12 pages, 3 figure