Influence of structure on the optical limiting properties of nanotubes

We investigate the role of carbon nanotubes structure on their optical limiting properties. Samples of different and well-characterized structural features are studied by optical limiting and pump-probe experiments. The influence of the diameter's size on the nano-object is demonstrated. Indeed, both nucleation and growth of gas bubbles are expected to be sensitive to diameter

Structurally stable Mg-doped P2-Na2/3Mn1-yMgyO2 sodium-ion battery cathodes with high rate performance : insights from electrochemical, NMR and diffraction studies

This work was partially supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program subcontract #7057154 (R.J.C). C.P.G. and R.J.C. thank the EU ERC for an Advanced Fellowship for CPG. This work was partially supported by the LINABATT project from the Ministerio de Economía Competitividad under Contract No. ENE2013-44330-R (G.S. and T.R.). P.G.B. is grateful to the EPSRC, including the SUPREGEN programme, for financial support.Sodium-ion batteries are a more sustainable alternative to the existing lithium-ion technology and could alleviate some of the stress on the global lithium market as a result of the growing electric car and portable electronics industries. Fundamental research focused on understanding the structural and electronic processes occurring on electrochemical cycling is key to devising rechargeable batteries with improved performance. We present an in-depth investigation of the effect of Mg doping on the electrochemical performance and structural stability of Na2/3MnO2 with a P2 layer stacking by comparing three compositions: Na2/3Mn1-yMgyO2 (y = 0.0, 0.05, 0.1). We show that Mg substitution leads to smoother electrochemistry, with fewer distinct electrochemical processes, improved rate performance and better capacity retention. These observations are attributed to the more gradual structural changes upon charge and discharge, as observed with synchrotron, powder X-ray, and neutron diffraction. Mg doping reduces the number of Mn3+ Jahn-Teller centers and delays the high voltage phase transition occurring in P2-Na2/3MnO2. The local structure is investigated using 23Na solid-state nuclear magnetic resonance (ssNMR) spectroscopy. The ssNMR data provide direct evidence for fewer oxygen layer shearing events, leading to a stabilized P2 phase, and an enhanced Na-ion mobility up to 3.8 V vs. Na+/Na upon Mg doping. The 5% Mg-doped phase exhibits one of the best rate performances reported to date for sodium-ion cathodes with a P2 structure, with a reversible capacity of 106 mAhg-1 at the very high discharge rate of 5000 mAg-1. In addition, its structure is highly reversible and stable cycling is obtained between 1.5 and 4.0 V vs. Na+/Na, with a capacity of approximately 140 mAhg-1 retained after 50 cycles at a rate of 1000 mAg-1.Publisher PDFPeer reviewe

A experiência social de risco ecológico como fundamento da relação com o meio ambiente.

Por constituir objetivo de desenvolvimento, o conceito de agricultura sustentavel supoe um engajamento por parte dos agricultores familiares. A compreensao da relacao dos produtores agricolas com a natureza, com as tecnicas e de, modo global, com o risco ao meio ambiente e uma das principais metas de acao das politicas de desenvolvimento sustentavel. Propoe-se, a partir de um estudo empirico na regiao de Guaira/SP, Brasil, uma abordagem teorica e metodologica que permita, do ponto de vista das ciencias sociais, uma analise das tecnicas e das representacoes dos agricultores sobre o meio ambiente, que se encontram em situacao de constante, em relacao ao plano tecnologico e em face de uma incerteza cientifica e tecnica. Esta analise e uma forma de interrogar sobre o papel da natureza nas sociedades modernas, o qual e dependente de um duplo processo do qual se trata de estudar a dinamica: como se articula, dentro de uma certa configuracao, a relacao entre os processos tecnicos e sociais e os dispositivos de gestao

Quantitative reconstruction of climatic variations during the Bronze and early Iron ages based on pollen and lake-level data in the NW Alps, France

International audienceVegetation and lake-level data from the archaeological site of Tresserve, on the eastern shore of Lake Le Bourget (Savoie, France), are used to provide quantitative estimates of climatic variables over the period 4000-2300 cal BP in the northern French Pre-Alps, and to examine the possible impact of climatic changes on societies of the Bronze and early Iron Ages. The results obtained indicate that phases of higher lake level at 3500-3100 and 2750-2350 cal BP coincided with major climate reversals in the North Atlantic area. In west-central Europe, they were marked by cooler and wetter conditions. These two successive events may have affected ancient agricultural communities in west-central Europe by provoking harvest failures, more particularly due to increasing precipitation during the growing season. However, archaeological data in the region of Franche-Comté (Jura Mountains, eastern France) show a general expansion of population density from the middle Bronze Age to the early Iron Age. This suggests a relative emancipation of proto-historic societies from climatic conditions, probably in relation to the spread of new modes of social and economic organisation

Between learning and schooling: the politics of human rights monitoring at the Universal Periodic Review

This paper explores the politics of monitoring at the Universal Periodic Review (UPR), a new United Nations human rights monitoring mechanism which aims to promote a universal approach and equal treatment when reviewing each country’s human rights situation. To what extent are these laudable aims realised, and realisable, given entrenched representations of the West and the Rest as well as geopolitical and economic inequalities both historically and in the present? Based on ethnographic fieldwork at the UN in 2010–11, the final year of the UPR’s first cycle, we explore how these aims were both pursued and subverted, paying attention to two distinct ways of talking about the UPR: first, as a learning culture in which UN member states ‘share best practice’ and engage in constructive criticism; and second, as an exam which UN member states face as students with vastly differing attitudes and competences. Accounts and experiences of diplomats from states that are not placed in the ‘good students’ category offer valuable insights into the inherent contradictions of de-historicised and de-contextualised approaches to human rights