III-V Solar Cells

III-V materials show a wide range of gaps making them ideal for the design of high efficiency solar cells. This chapter reviews relevant growth methods and material properties of these materials and discusses methods of combining heterogeneous materials, demonstrating the flexibility of design possible with these materials. The fundamental loss mechanisms of solar cells are analysed and quantified as a prelude to analysing high efficiency cell designs in single, tandem, and triple junction solar cells. The detailed analysis of loss mechanisms is used to obtain understanding of the limiting behaviour of these designs, and show that bulk cells remain dominated by non-radiative losses despite unity ideality factors. To conclude, this is contrasted with the operating regime of nanostructured solar cells which can be shown to operate in a radiatively dominated mode, and which therefore approach ideal solar cell efficiency limits.Comment: Draft of chapter in Materials Challenges: Inorganic Photovoltaic Solar Energy - RSC Energy and Environment Series v. 1

Variance component score test for time-course gene set analysis of longitudinal RNA-seq data

As gene expression measurement technology is shifting from microarrays to sequencing, the statistical tools available for their analysis must be adapted since RNA-seq data are measured as counts. Recently, it has been proposed to tackle the count nature of these data by modeling log-count reads per million as continuous variables, using nonparametric regression to account for their inherent heteroscedasticity. Adopting such a framework, we propose tcgsaseq, a principled, model-free and efficient top-down method for detecting longitudinal changes in RNA-seq gene sets. Considering gene sets defined a priori, tcgsaseq identifies those whose expression vary over time, based on an original variance component score test accounting for both covariates and heteroscedasticity without assuming any specific parametric distribution for the transformed counts. We demonstrate that despite the presence of a nonparametric component, our test statistic has a simple form and limiting distribution, and both may be computed quickly. A permutation version of the test is additionally proposed for very small sample sizes. Applied to both simulated data and two real datasets, the proposed method is shown to exhibit very good statistical properties, with an increase in stability and power when compared to state of the art methods ROAST, edgeR and DESeq2, which can fail to control the type I error under certain realistic settings. We have made the method available for the community in the R package tcgsaseq.Comment: 23 pages, 6 figures, typo corrections & acceptance acknowledgemen

Strengthening America's Best Idea: An Independent Review of the National Park Service's Natural Resource Stewardship and Science Directorate

NRSS requested that an independent panel of the National Academy conduct a review of its effectiveness in five core functions, its relationships with key internal stakeholders, and its performance measurement system. Among other things, the National Park Service's Natural Resource Stewardship and Science Directorate (NRSS) is responsible for providing usable natural and social science information throughout the National Park Service (NPS). NRSS leadership requested this review of the directorate's performance on five core functions, its relationships with key internal NPS stakeholders, and its performance measurement system.Main FindingsThe panel determined that NRSS is a highly regarded organization that provides independent, credible scientific expertise and technical information. The panel also found that NRSS and NPS have additional opportunities to advance natural resource stewardship throughout the Service. If implemented, the panel's eight major recommendations will: (1) help the Service respond to the parks' environmental challenges while raising public awareness about the condition of these special places; (2) strengthen NRSS as an organization; (3) promote scientifically based decision-making at the national, regional, and park levels; and (4) improve the existing performance measurement system

High-fidelity entanglement purification using chains of atoms and optical cavities

In our previous paper [Phys. Rev. A 84, 042303 (2011)], we proposed an efficient scheme to purify dynamically a bipartite entangled state using short chains of atoms coupled to high-finesse optical cavities. In contrast to conventional entanglement purification protocols, we avoid controlled-NOT gates and thus reduce complicated pulse sequences and superfluous qubit operations. In this paper, we significantly improve the output fidelity of remotely entangled atoms by introducing one additional entanglement protocol in each of the repeater nodes and by optimizing the laser beams required to control the entire scheme. Our improved distillation scheme yields an almost unit output fidelity that, together with the entanglement distribution and swapping, opens an attractive route towards an efficient and experimentally feasible quantum repeater for long-distance quantum communication.Comment: 13 pages, 4 figures, revised version accepted in PRA. arXiv admin note: text overlap with arXiv:1106.353

The time course of routine action

Previous studies of action selection in routinized tasks have used error rates as their sole dependent measure (e.g. Reason, 1979; Schwartz et al., 1998). Consequently, conclusions about the underlying mechanisms of correct behavior are necessarily indirect. The present experiment examines the performance of normal subjects in the prototypical coffee task (Botvinick & Plaut, 2004) when carried out in a virtual environment on screen. This has the advantage of (a) constraining the possible errors more tightly than a real world environment, and (b) giving access to latencies as an additional, finer grained measure of performance. We report error data and timing of action selection at the crucial branching points for the production of routinized task sequences both with and without a secondary task. Processing branching points leads to increased latencies. The presence of the secondary task has a greater effect on latencies at branching points than at equivalent non-branching points. Furthermore, error data and latencies dissociate, suggesting that the exact timing is a valid and valuable source of information when trying to understand the processes that govern routine tasks. The results of the experiment are discussed in relation to their implication for computational accounts of routine action selection