Absorption characteristics of a quantum dot array induced intermediate band: implications for solar cell design

We present a theoretical study of the electronic and absorption properties of the intermediate band (IB) formed by a three dimensional structure of InAs/GaAs quantum dots (QDs) arranged in a periodic array. Analysis of the electronic and absorption structures suggests that the most promising design for an IB solar cell material, which will exhibit its own quasi-Fermi level, is to employ small QDs (~6–12 nm QD lateral size). The use of larger QDs leads to extension of the absorption spectra into a longer wavelength region but does not provide a separate IB in the forbidden energy gap

The effect of cycling on cognitive function and well-being in older adults

It has been demonstrated that, on their own, both exercise and stimulation from the environment can improve cognitive function and well-being in older adults. The combined effect of exercising in the outdoor environment on psychological function is less well studied. The aim of the current study was to investigate the effect of an outdoor cycling intervention on cognitive function and mental health and well-being in older adults. A total of 100 older adults took part in the study (aged 50–83), 26 of which were non-cycling controls, 36 were conventional pedal cyclists and 38 were participants using an e-bike (a bike fitted with an electric motor to provide assistance with pedaling), as part of a larger project (www.cycleboom.org). Participants took part in the study for an eight-week period, with cycling participants required to cycle at least three times a week for thirty minutes in duration for each cycle ride. Cognitive function and well-being were measured before and after the intervention period. For executive function, namely inhibition (the Stroop task) and updating (Letter Updating Task), both cycling groups improved in accuracy after the intervention compared to non-cycling control participants. E-bike participants also improved in processing speed (reaction times in go trials of the Stop-It task) after the intervention compared to non-cycling control participants. Finally, e-bike participants improved in their mental health score after the intervention compared to non-cycling controls as measured by the SF-36. This suggests that there may be an impact of exercising in the environment on executive function and mental health. Importantly, we showed a similar (sometimes larger) effect for the e-bike group compared to the pedal cyclists. This suggests that it is not just the physical activity component of cycling that is having an influence. Both pedal cycles and e-bikes can enable increased physical activity and engagement with the outdoor environment with e-bikes potentially providing greater benefits

Socio‐economic impact classification of alien taxa (SEICAT)

1 Many alien taxa are known to cause socio‐economic impacts by affecting the different constituents of human well‐being (security; material and non‐material assets; health; social, spiritual and cultural relations; freedom of choice and action). Attempts to quantify socio‐economic impacts in monetary terms are unlikely to provide a useful basis for evaluating and comparing impacts of alien taxa because they are notoriously difficult to measure and important aspects of human well‐being are ignored. 2 Here, we propose a novel standardised method for classifying alien taxa in terms of the magnitude of their impacts on human well‐being, based on the capability approach from welfare economics. The core characteristic of this approach is that it uses changes in peoples' activities as a common metric for evaluating impacts on well‐being. 2 Impacts are assigned to one of five levels, from Minimal Concern to Massive, according to semi‐quantitative scenarios that describe the severity of the impacts. Taxa are then classified according to the highest level of deleterious impact that they have been recorded to cause on any constituent of human well‐being. The scheme also includes categories for taxa that are not evaluated, have no alien population, or are data deficient, and a method for assigning uncertainty to all the classifications. To demonstrate the utility of the system, we classified impacts of amphibians globally. These showed a variety of impacts on human well‐being, with the cane toad (Rhinella marina) scoring Major impacts. For most species, however, no studies reporting impacts on human well‐being were found, i.e. these species were data deficient. 2 The classification provides a consistent procedure for translating the broad range of measures and types of impact into ranked levels of socio‐economic impact, assigns alien taxa on the basis of the best available evidence of their documented deleterious impacts, and is applicable across taxa and at a range of spatial scales. The system was designed to align closely with the Environmental Impact Classification for Alien Taxa (EICAT) and the Red List, both of which have been adopted by the International Union of Nature Conservation (IUCN), and could therefore be readily integrated into international practices and policies

Characterizing the variation of propagation constants in multicore fibre

We demonstrate a numerical technique that can evaluate the core-to-core variations in propagation constant in multicore fibre. Using a Markov Chain Monte Carlo process, we replicate the interference patterns of light that has coupled between the cores during propagation. We describe the algorithm and verify its operation by successfully reconstructing target propagation constants in a fictional fibre. Then we carry out a reconstruction of the propagation constants in a real fibre containing 37 single-mode cores. We find that the range of fractional propagation constant variation across the cores is approximately $\pm2 \times 10^{-5}$.Comment: 17 pages; preprint format; 5 figures. Submitted to Optics Expres

A Buffer Stocks Model for Stabilizing Price of Staple Food with Considering the Expectation of Non Speculative Wholesaler

This paper is a study of price stabilization in the staple food distribution system. All stakeholders experience market risks due to some possibility causes of price volatility. Many models of price stabilization had been developed by employing several approaches such as floor-ceiling prices, buffer funds, export or import taxes, and subsidies. In the previous researches, the models were expanded to increase the purchasing price for producer and decrease the selling price for consumer. Therefore, the policy can influence the losses for non-speculative wholesaler that is reflected by the descending of selling quantity and ascending of the stocks. The objective of this model is not only to keep the expectation of both producer and consumer, but also to protect non-speculative wholesaler from the undesirable result of the stabilization policy. A nonlinear programming model was addressed to determine the instruments of intervention program. Moreover, the result shows that the wholesaler behavior affects the intervention costs. Index Terms Buffer stocks, Price stabilization, Nonlinear programming, Wholesaler behavior

How effective are MPAs in conserving crab stocks? A comparison of fisheries and conservation objectives in three coastal MPAs in Thailand

Mangrove forest ecosystems support aquatic species important to tropical fishing communities, but habitat degradation and over-fishing have caused coastal fishery stocks to decline. Marine Protected Areas (MPAs) are widely promoted as a management option to reverse this situation. Using swimming crabs as indicator species, this paper explores the ecological effectiveness of two community-led MPAs and one co-managed MPA in Ranong and Phang-nga Provinces in southern Thailand. Comparisons were made of two fisheries objectives: catch per unit effort (CPUE); and size frequency distribution of Portunus spp. and Scylla olivacea; and one conservation objective: catch composition on benthic aquatic species, between each managed area and an associated control site to look for effects of management. Eight replicates of each survey were undertaken in each site: four in the wet season, from May to July 2011; and four in the dry season, from February to March 2012. Two of the MPAs, one a no-take zone and one a gear limitation zone, and both managed by local communities, showed a significant increase in CPUE of target species compared with their controls to the benefit of local fishers. There was little evidence of management impact on the composition of benthic aquatic species so community management is not achieving wider conservation in terms of increased biodiversity. The third MPA, a seasonal no-take zone, co-managed by local communities and local government, showed no significant effect on either CPUE of target species, or composition of benthic aquatic species when compared to its control. For size frequency distribution, a higher abundance of all size classes of Portunus pelagicus was observed in all MPAs compared to their control sites. The size distribution of animals suggests that the community-managed MPAs are supporting recruits and contributing to the fisheries by reducing the rates of growth overfishing. To conclude, the two community-led MPAs benefitted fishers but had no effect on marine biodiversity, while the co-managed MPA did not benefit fishers or marine biodiversity. However, all three MPAs showed increase crab abundance in each size class

Quota discarding and distributive justice: The case of the under-10m fishing fleet in Sussex, England

Marine fish discarding has become a contentious environmental issue, but little attention has been paid to the moral grievances that sometimes underlie discarding practices. This article explores such a moral grievance through a case study of the under-10. m fishery in Sussex, England, where discarding of cod (Gadus morhua) has become a highly charged issue, skippers blaming it on unjust quota allocations. The moral claim to a greater quota allocation is analysed using two conceptions of distributive justice, entitlement and desert. The conclusion reached is that the under-10. m fleet's entitlement arguments for a higher quota are weaker than their desert arguments, but that entitlement arguments weigh more heavily than desert arguments with government when it allocates quota

The formation of high number density InSb quantum dots, resulting from direct InSb/GaSb (001) heteroepitaxy

We report the direct deposition of indium antimonide, by molecular beam epitaxy (MBE) on gallium antimonide, resulting in the formation of quantum dots (QDs) with a maximum density of ~5.3×1010 cm−2. Using reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) for the analysis of samples with InSb depositions of 1–6 ML equivalent thickness, we observe an apparent value for the critical thickness for InSb/GaSb (001) deposition of 2.3±0.3 ML, for the growth temperatures of 275 °C and 320 °C

The c(4×4)–a(1×3) surface reconstruction transition on InSb(001) : static versus dynamic conditions

The transition between the a(1 × 3) and c(4 × 4) surface reconstructions of InSb(0 0 1) has been carefully monitored by reflection high energy electron diffraction as a function of temperature and Sb2 flux, without incident In flux. Arrhenius-like behaviour is observed across the whole range of Sb2 fluxes and temperatures, allowing accurate internal calibration of substrate temperature. This behaviour is in contrast to aggregated data obtained under dynamic molecular beam epitaxy conditions, which show two regimes rather than a single Arrhenius-like phase boundary. The results are explained qualitatively by the atomistic kinetics in static versus dynamic conditions