Solar Cell Light Trapping beyond the Ray Optic Limit

In 1982, Yablonovitch proposed a thermodynamic limit on light trapping within homogeneous semiconductor slabs, which implied a minimum thickness needed to fully absorb the solar spectrum. However, this limit is valid for geometrical optics but not for a new generation of subwavelength solar absorbers such as ultrathin or inhomogeneously structured cells, wire-based cells, photonic crystal-based cells, and plasmonic cells. Here we show that the key to exceeding the conventional ray optic or so-called ergodic light trapping limit is in designing an elevated local density of optical states (LDOS) for the absorber. Moreover, for any semiconductor we show that it is always possible to exceed the ray optic light trapping limit and use these principles to design a number of new solar absorbers with the key feature of having an elevated LDOS within the absorbing region of the device, opening new avenues for solar cell design and cost reduction

Light trapping beyond the 4n^2 limit in thin waveguides

We describe a method for determining the maximum absorption enhancement in thin film waveguides based on optical dispersion relations. For thin film structures that support one, well-confined guided mode, we find that the absorption enhancement can surpass the traditional limit of 4n^2 when the propagation constant is large and/or the modal group velocity is small compared to the bulk value. We use this relationship as a guide to predicting structures that can exceed the 4n^2 light trapping limit, such as plasmonic and slot waveguides. Finally, we calculate the overall absorption for both single and multimode waveguides, and show examples of absorption enhancements in excess of 4n^2 for both cases

Low cost carriers and the changing fortunes of airports in the UK

This paper investigates how low cost carrier (LCC) developments have affected the traffic and financial performance of UK airports from 2002 to 2014. Considerable growth in traffic was experienced from 2002 to 2007, especially at regional airports as a result of LCC expansion. This was replaced with a more volatile period from 2008 to 2014 where many of the regional airports that experienced the greatest increases in traffic during the early years, then experienced the largest reductions. This has clearly had an impact on their financial well-being, resulting in reduced profits for many airports. It has also meant that many regional airports that seemed like attractive investments as a result of LCC expansion are now less financially appealing, especially given that the LCC sector in the UK appears to be shifting capacity to larger regional airports, and in some cases, London airports

Gamma-soft Analog of the Confined Beta-soft Rotor Model

A gamma-soft analog of the confined beta-soft (CBS) rotor model is developed, by using a gamma-independent displaced infinite well beta-potential in the Bohr Hamiltonian, for which exact separation of variables is possible. Level schemes interpolating between the E(5) critical point symmetry (with R(4/2)=E(4)/E(2)= 2.20) and the O(5) gamma-soft rotor (with R(4/2)=2.50) are obtained, exhibiting a crossover of excited 0+ bandheads which leads to agreement with the general trends of first excited 0+ states in this region and is observed experimentally in 128-Xe and 130-Xe.Comment: 10 pages, LaTeX, including 7 eps figure

UK Regional Connectivity on the North Atlantic: Hub-Bypassing or just changing hubs?

London Heathrow Airport (LHR) has maintained its position as the main gateway for UK passengers for international services, but has no services to many UK regional airports. This research examines whether UK regional airports have increased direct services to North Atlantic destinations or to other European hub airports in response to the lack of air services to the London area. The study analysed the changing dynamics of the UK aviation network from 1997 to 2017 as it pertains to hub connectivity and North Atlantic services. Both the number of connections from regional airports and the quality of those connections, measured in terms of the frequency of direct air services, have been examined. As most LCC passengers do not connect to other flights, only flights by full service carriers to both London and selected European hubs were considered. The data indicate that regional airport connectivity development has been heterogeneous. Whilst the number of UK regional airports with service to LHR has remained stable, the frequency of service has decreased noticeably. The larger and more geographically distant regional airports of Edinburgh, Glasgow, and Manchester have been able to develop more connections to both European hub airports and to North American cities, and in many cases have seen an increase in frequencies as well. Birmingham Airport, although of similar size to the above-mentioned airports, has on the contrast experienced a reduction in its connections to North American airports and of frequency to the European hub airports examined. Smaller UK regional airports have also seen a reduction in frequencies to European airports

Connecting the X(5)-β2\beta^2, X(5)-β4\beta^4, and X(3) models to the shape/phase transition region of the interacting boson model

The parameter independent (up to overall scale factors) predictions of the X(5)-$\beta^2$, X(5)-$\beta^4$, and X(3) models, which are variants of the X(5) critical point symmetry developed within the framework of the geometric collective model, are compared to two-parameter calculations in the framework of the interacting boson approximation (IBA) model. The results show that these geometric models coincide with IBA parameters consistent with the phase/shape transition region of the IBA for boson numbers of physical interest (close to 10). Nuclei within the rare-earth region and select Os and Pt isotopes are identified as good examples of X(3), X(5)-$\beta^2$, and X(5)-$\beta^4$ behavior

Towards A Short to Medium Term Mitigation Strategy to Address the External Air and Sea Connectivity Challenges posed by the COVID-19 Pandemic for Northern Ireland

The overall aim of the research is the preparation of a short to medium term Access Mitigation Strategy to respond to the challenges posed for the business, travel, leisure and tourism sectors by the physical and psychological impacts on travel access to/from Northern Ireland during/post the COVID-19 Pandemic. The research programme reflects the need to understand the implications of the COVID-19 crisis on accessibility to/from Northern Ireland given the region’s heavy reliance on air and sea access for trade, Foreign Direct Investment (FDI) and tourism. This includes the fall-out from COVID-19 (and additional factors including Flybe, Brexit) on the capacity of air and sea routes, how demand has and will be impacted in the future because of changing behaviours and what actions need to be taken to minimise these effects and keep Northern Ireland open for business. The project objectives are as follows: To establish the current position and near to medium term prospects for air and sea connectivity to Northern Ireland (including Irish Sea ports and airports); review the contribution of air and sea links to the performance of the Northern Ireland Economy and Wider Society; assess the factors shaping this position and their impact on demand for external travel before, during and post the Coronavirus Pandemic; develop a range of future scenarios around passenger transport by air and sea to inform the development of a range of mitigation policy interventions to maximise the accessibility of the region; table recommendations for a mitigation policy to maximise accessibility of the region; and assess the potential for funding and financing a Short to Medium Term Access Mitigation Strategy for the region. The research findings and its recommendations are informed by robust empirical evidence bases and include proven public policy interventions to maximise the region’s access and openness to business and tourism related travel going forward

Observation of Leggett's collective mode in a multi-band MgB2 superconductor

We report observation of Leggett's collective mode in a multi-band MgB2 superconductor with T_c=39K arising from the fluctuations in the relative phase between two superconducting condensates. The novel mode is observed by Raman spectroscopy at 9.4 meV in the fully symmetric scattering channel. The observed mode frequency is consistent with theoretical considerations based on the first principle computations.Comment: Accepted for PR

The diffuse X-ray spectrum from 14-200 keV as measured on OSO-5

The measurement of energy spectrum of the diffuse component of cosmic X-ray flux made on the OSO-5 spacecraft is described. The contributions to the total counting rate of the actively shielded X-ray detector are considered in some detail and the techniques used to eliminate the non-cosmic components are described. Positive values for the cosmic flux are obtained in seven energy channels between 14 and 200 keV and two upper limits are obtained between 200 and 254 keV. The results can be fitted by a power law spectrum. A critical comparison is made with the OSO-3 results. Conclusions show that the reported break in the energy spectrum at 40 keV is probably produced by an erroneous correction for the radioactivity induced in the detector on each passage through the intense charged particle fluxes in the South Atlantic anomaly