Transparent metal electrodes from ordered nanosphere arrays

We show that perforated metal electrode arrays, fabricated using nanosphere lithography, provide a viable alternative to conductive metal oxides as transparent electrode materials. The inter-aperture spacing is tuned by varying etching times in an oxygen plasma, and the effect of inter-aperture “wire” thickness on the optical and electronic properties of perforated silver films is shown. Optical transmission is limited by reflection and surface plasmons, and for these results do not exceed 73%. Electrical sheet resistance is shown to be as low as 3 Ω ◻−1 for thermally evaporated silver films. The performance of organic photovoltaic devices comprised of a P3HT:PCBM bulk heterojunction deposited onto perforated metal arrays is shown to be limited by optical transmission, and a simple model is presented to overcome these limitations

A reconstruction of the past trend of atmospheric CO based on firn air samples from Berkner Island, Antarctica

International audienceAlthough for several atmospheric trace gases trends over the past 100 year have been reconstructed using firn air analyses, little is known about one of the chemically most significant trace gases, namely CO. Among the 3 Antarctic drilling expeditions reported, the one from Berkner Island appears to have given results of sufficient analytical quality to warrant a modelling with the aim to reconstruct past changes in atmospheric CO. Based on our reconstructions, CO in high latitudes of the Southern Hemisphere has been increasing since beginning of the 20th century from ~38 ppbv to a recent value of about 52.5 ppbv. The increase in CO is mainly explained by the known increase in CH4, with biomass burning output being most likely responsible for an additional increase. Which, if any, role changes in OH have played cannot be derived

Snow densification and recent accumulation along the iSTAR traverse, Pine Island Glacier, Antarctica

Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual-layer identification routine. A mean density profile which can be used to convert radar two-way-travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain-boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10–14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence

Real-time diagnostics of gas/water assisted injection moulding using integrated ultrasonic sensors

YesAn ultrasound sensor system has been applied to the mould of both the water and gas assisted injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid (gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or water) polymer boundary whilst the samples are still inside the mould and a good correlation with a physical measurement is observed

An examination of the precipitation delivery mechanisms for Dolleman Island, eastern Antarctic Peninsula

Copyright @ 2004 Wiley-BlackwellThe variability of size and source of significant precipitation events were studied at an Antarctic ice core drilling site: Dolleman Island (DI), located on the eastern coast of the Antarctic Peninsula. Significant precipitation events that occur at DI were temporally located in the European Centre for Medium-Range Weather Forecasting (ECMWF) reanalysis data set, ERA-40. The annual and summer precipitation totals from ERA-40 at DI both show significant increases over the reanalysis period. Three-dimensional backwards air parcel trajectories were then run for 5 d using the ECMWF ERA-15 wind fields. Cluster analyses were performed on two sets of these backwards trajectories: all days in the range 1979–1992 (the climatological time-scale) and a subset of days when a significant precipitation event occurred. The principal air mass sources and delivery mechanisms were found to be the Weddell Sea via lee cyclogenesis, the South Atlantic when there was a weak circumpolar trough (CPT) and the South Pacific when the CPT was deep. The occurrence of precipitation bearing air masses arriving via a strong CPT was found to have a significant correlation with the southern annular mode (SAM); however, the arrival of air masses from the same region over the climatological time-scale showed no such correlation. Despite the dominance in both groups of back trajectories of the westerly circulation around Antarctica, some other key patterns were identified. Most notably there was a higher frequency of lee cyclogenesis events in the significant precipitation trajectories compared to the climatological time-scale. There was also a tendency for precipitation trajectories to come from more northerly latitudes, mostly from 50–70°S. The El Niño Southern Oscillation (ENSO) was found to have a strong influence on the mechanism by which the precipitation was delivered; the frequency of occurrence of precipitation from the east (west) of DI increased during El Niño (La Niña) events

Inertial Imaging with Nanomechanical Systems

Mass sensing with nanoelectromechanical systems has advanced significantly during the last decade. With nanoelectromechanical systems sensors it is now possible to carry out ultrasensitive detection of gaseous analytes, to achieve atomic-scale mass resolution and to perform mass spectrometry on single proteins. Here, we demonstrate that the spatial distribution of mass within an individual analyte can be imaged—in real time and at the molecular scale—when it adsorbs onto a nanomechanical resonator. Each single-molecule adsorption event induces discrete, time-correlated perturbations to all modal frequencies of the device. We show that by continuously monitoring a multiplicity of vibrational modes, the spatial moments of mass distribution can be deduced for individual analytes, one-by-one, as they adsorb. We validate this method for inertial imaging, using both experimental measurements of multimode frequency shifts and numerical simulations, to analyse the inertial mass, position of adsorption and the size and shape of individual analytes. Unlike conventional imaging, the minimum analyte size detectable through nanomechanical inertial imaging is not limited by wavelength-dependent diffraction phenomena. Instead, frequency fluctuation processes determine the ultimate attainable resolution. Advanced nanoelectromechanical devices appear capable of resolving molecular-scale analytes

Abordagem contextual nos capítulos de estequiometria e de soluções dos livros didáticos de Química aprovados pelo PNLD (Programa Nacional do Livro Didático - Brasil) /2012

A contextualização tem sido proposta no currículo escolar com o propósito de promover mudanças de comportamentos, atitudes e valores. Nessa abordagem, entende-se que o ensino de química deve se desenvolver de forma ampla, envolvendo também aspectos sociais, políticos, econômicos,ambientais e culturais, e não somente aspectos científicos. Tendo em vista a grande importância dada ao livro didático (LD) na prática docente, buscamos analisar a abordagem contextual nos capítulos de estequiometria e soluções nos LD de química aprovados pelo PNLD/2012. Os resultados mostraram que os autores dos LD analisados reconhecem a contextualização como elemento central para a formação da cidadania, porém a abordagem é diferente em cada obra. As leituras dos LD possibilitaram a identificação de alguns "níveis" de contextualização que percorreram quatro categorias de análise

Aerosol chemical composition and distribution during the Pacific Exploratory Mission (PEM) Tropics

Distributions of aerosol-associated soluble ions over much of the South Pacific were determined by sampling from the NASA DC-8 as part of the Pacific Exploratory Mission (PEM) Tropics campaign. The mixing ratios of all ionic species were surprisingly low throughout the free troposphere (2-12 km), despite the pervasive influence from biomass burning plumes advecting over the South Pacific from the west during PEM-Tropics. At the same time, the specific activity of 7Be frequently exceeded 1000 fCi m-3 through much of the depth of the troposphere. These distributions indicate that the plumes must have been efficiently scavenged by precipitation (removing the soluble ions), but that the scavenging must have occurred far upwind of the DC-8 sampling regions (otherwise 7Be activities would also have been low). This inference is supported by large enhancements of HNO3 and carboxylic acids in many of the plumes, as these soluble acidic gases would also be readily scavenged in any precipitation events. Decreasing mixing ratios of NH4 + with altitude in all South Pacific regions sampled provide support for recent suggestions that oceanic emissions of NH3 constitute a significant source far from continents. Our sampling below 2 km reaffirms the latitudinal pattern in the methylsulfonate/non-sea-salt sulfate (MSA/nss SO4 =) molar ratio established through surface-based and shipboard sampling, with values increasing from \u3c0.05 in the tropics to nearly 0.6 at 70°S. However, we also found very high values of this ratio (0.2-0.5) at 10 km altitude above the intertropical convergence zone near 10°N. It appears that wet convective pumping of dimethylsulfide from the tropical marine boundary layer is responsible for the high values of the MSA/nss SO4 = ratio in the tropical upper troposphere. This finding complicates use of this ratio to infer the zonal origin of biogenic S transported long distances. Copyright 1999 by the American Geophysical Union