Tight binding description of the electronic response of a molecular device to an applied voltage

We analyze the effect of an external electric field on the electronic structure of molecules which have been recently studied as molecular wires or diodes. We use a self-consistent tight binding technique which provides results in good agreement with ab initio calculations and which may be applied to a large number of molecules. The voltage dependence of the molecular levels is mainly linear with slopes intimately related to the electronic structure of the molecules. We emphasize that the response to the applied voltage is an important feature which governs the behavior of a molecular device

Forecasting environmental migration to the United Kingdom, 2010 - 2060: an exploration using Bayesian models

Over the next fifty years the potential impact on human livelihoods of environmental change could be considerable. One possible response may be increased levels of human mobility. This paper offers a first quantification of the levels of environmental migration to the United Kingdom that might be expected. The authors apply Bijak and Wi?niowski’s (2010) methodology for forecasting migration using Bayesian models. They seek to advance the conceptual understanding of forecasting in three ways. First, the paper is believed to be the first time that the Bayesian modelling approach has been attempted in relation to environmental mobility. Second, the paper examines the plausibility of Bayesian modelling of UK immigration by cross-checking expert responses to a Delphi survey with the expectations about environmental mobility evident in the recent research literature. Third, the values and assumptions of the expert evidence provided in the Delphi survey are interrogated to illustrate the limited set of conditions under which the forecasts of environmental mobility, as set out in this paper, are likely to hold

The Floor of the Arctic Ocean in Photographs

Over 2,000 usable bottom photographs have been taken in the western Arctic Ocean. The 87 stations cover the major geomorphic provinces of this part of the Arctic Basin, including the Alpha Cordillera, Mendeleyev Ridge, and Canada Abyssal Plain as well as smaller features. The ridge and plain provinces differ markedly in their bottom characteristics. Scattered rocks, living animals and indications of bottom current are most prevalent on the ridges. Trails are most abundant on the abyssal plains. The differences are attributed to bottom current distributions and turbidity currents. Bedrock outcrops were observed on the tops of two knolls on the Mendeleyev Ridge.Le fond de l'océan Arctique en photographies. Dans la partie occidentale de l'océan Arctique, on a pris plus de 2,000 clichés du fond sous-marin. Les 87 stations couvrent les principales provinces géomorphologiques de cette partie du bassin arctique et comprennent la cordillère Alpha, la dorsale de Mendéléev et la plaine abyssale canadienne, ainsi que des reliefs de moindre importance. Les dorsales et la plaine abyssale diffèrent beaucoup dans leurs caractéristiques de fond. Sur les dorsales, des roches éparpillées, des animaux vivants et des indices de courants de fond dominent. Dans la plaine abyssale, les pistes d'animaux mains sont abondantes. On attribue ces différences à la distribution des courants de fond et aux courants de turbidité. On a observé des affleurements du soubassement sur le sommet de deux monticules de la dorsale de Mendéléev

Roundtable discussion: what is the future role of the private sector in health?

Background: The role for the private sector in health remains subject to much debate, especially within the context of achieving universal health coverage. This roundtable discussion offers diverse perspectives from a range of stakeholders – a health funder, a representative from an implementing organization, a national-level policy-maker, and an expert working in a large multi-national company – on what the future may hold for the private sector in health. Discussion: The first perspective comes from a health funder, who argues that the discussion about the future role of the private sector has been bogged down in language. He argues for a ‘both/and’ approach rather than an ‘either/or’ when it comes to talking about health service provision in low- and middle-income countries. The second perspective is offered by an implementer of health insurance in sub-Saharan Africa. The piece examines the comparative roles of public sector actors, private sector actors and funding agencies, suggesting that they must work together to mobilize domestic resources to fund and deliver health services in the longer term. Thirdly, a special advisor working in the federal government of Nigeria considers the situation in that country. He notes that the private sector plays a significant role in funding and delivering health services there, and that the government must engage the private sector or forever be left behind. Finally, a representative from a multi-national pharmaceutical corporation gives an overview of global shifts that are creating opportunities for the private sector in health markets. Summary: Overall, the roundtable discussants agree that the private sector will play an important role in future health systems. But we must agree a common language, work together, and identify key issues and gaps that might be more effectively filled by the private sector.DFI

Molecular rectifying diodes from self-assembly on silicon

We demonstrate a molecular rectifying junction made from a sequential self-assembly on silicon. The device structure consists of only one conjugated (p) group and an alkyl spacer chain. We obtain rectification ratios up to 37 and threshold voltages for rectification between -0.3V and -0.9V. We show that rectification occurs from resonance through the highest occupied molecular orbital of the p-group in good agreement with our calculations and internal photoemission spectroscopy. This approach allows us to fabricate molecular rectifying diodes compatible with silicon nanotechnologies for future hybrid circuitries

Size-dependent optical properties of colloidal PbS quantum dots

We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots) by combining-the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases With the Not volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on E in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mu s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems

Quantum confinement effects in Pb Nanocrystals grown on InAs

In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by quantum confinement effects in the Pb nanocrystals. We identified three distinct regimes of quantum confinement. For the largest nanocrystals, quantum confinement effects appear through the formation of quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.Comment: Main 12 pages, Supp: 6 page