Exceptional-point-based optical amplifiers

The gain-bandwidth product is a fundamental figure of merit that restricts the operation of optical amplifiers. Here, we introduce a design paradigm based on exceptional points, which relaxes this limitation and allows for the building of a new generation of optical amplifiers that exhibits a better gain-bandwidth scaling. Additionally, our results can be extended to other physical systems such as acoustics and microwaves

Market Forces and Price Ceilings: A Classroom Experiment

The effect of price controls on competitive equilibrium is a standard topic in many undergraduate economics courses. This classroom experiment demonstrates the effect of rent control (price ceilings) on the market for apartments. As participants in the experiment, students experience the effect of a price ceiling as buyers (renters) and sellers (landlords). The classroom-posted offer market exhibits a shortage under a binding price ceiling. Further, we explore a secondary response to rent control. When given the opportunity, landlords lower the quality of the apartments by reducing maintenance expenditures under the price ceiling, thus moving the market back to equilibrium. Since many students are themselves renters, they should relate to changes in quality due to lower maintenance by landlords. This experiment will stimulate discussion on market forces and on public policy aimed at restricting prices.

BME children in London: educational needs and the role of community organisations. (An evaluation of the education services of Day-Mer, Turkish and Kurdish Community Centre)

London’s diversity is reflected in its school population: almost 65% of pupils in primary and secondary schools are of ‘ethnic minority’ background. Over the years, research has shown that migrant and BME children and families face a number of obstacles, including limited English language, lack of knowledge of the British education system, racism and social exclusion. One of the consequences is the significant difference in terms of school achievement among pupils of certain backgrounds. Groups long considered underachievers include in particular Pakistani, Bangladeshi and Black Caribbean, although more recent studies have also identified similar educational problems among Somali and Turkish-speaking pupils. In this respect, the role played by community organisations - including supplementary classes, schools support and parental engagement programmes - is highly valued by both families and teachers. Despite limited systematic evidence, research suggests the impact of these organisations is highly significant and more should be done to encourage partnership work between mainstream schools and community groups. In the last few years, however, community organisations have faced a number of new challenges, including a dramatic reduction of public funding available and major changes in educational policy, such as the closure of the ‘Ethnic Minority Achievement Grant’ programme and the introduction of new models of schools increasingly independent from local authority control. In this new scenario it is more important than ever to learn from the experiences of these organisations in order to identify good practices and address issues of sustainability. This can inform policy makers and practitioners in ensuring that children from all ethnic backgrounds receive the educational support they need. In Spring 2011 - building on previous research conducted at Middlesex University - Day-Mer and the Social Policy Research Centre (SPRC) came together to work on a research project on the educational needs of Turkish and Kurdish families in North London. The project focuses on Day-Mer’s experience to evaluate the effectiveness of its services, but is also builds on this case study to discuss more broadly the role of community organisations in providing educational support

Boiling instabilities in microtubes

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Microprocessor and microchip speeds are continuously increasing with their shrinking sizes. For this reason, the size of subject related heat sinks are continuously decreasing from mini size to micro size. Among many microscale heat transfer cooling applications, the most practical and extensively used micro heat sinks are plain microchannels. This study addresses the lack of information about microchannel boiling instability phenomena and includes a parametric investigation in microtubes. Experimental data were obtained from a microtube having a 250~μm inner diameter, which was tested at low mass fluxes (78.9-276.3 kg/m2s) to reveal potential boiling instabilities. De-ionized water was used as a coolant, while the microtube was heated by Joule heating. Configurations prone to boiling instabilities (low system pressures, low mass velocities) were imposed to observe boiling instabilities in microtubes. After the experiments without any inlet restriction, experiments were conducted with the configuration with inlet restriction where pressure drop over inlet restriction element was 4 times as much as pressure drop over the microtube. Temperature and pressure drop fluctuation signals were recorded and processed once boiling instabilities were observed