Stable carbon isotope ratios of carbon dioxide from EDC and Berkner Island ice cores for 40-50 ka BP

The stable carbon isotopic signature of carbon dioxide (d13CO2) measured in the air occlusions of polar ice provides important constraints on the carbon cycle in past climates. In order to exploit this information for previous glacial periods, one must use deep, clathrated ice, where the occluded air is preserved not in bubbles but in the form of air hydrates. Therefore, it must be established whether the original atmospheric d13CO2 signature can be reconstructed from clathrated ice. We present a comparative study using coeval bubbly ice from Berkner Island and ice from the bubble-clathrate transformation zone (BCTZ) of EPICA Dome C (EDC). In the EDC samples the gas is partitioned into clathrates and remaining bubbles as shown by erroneously low and scattered CO2 concentration values, presenting a worst-case test for d13CO2 reconstructions. Even so, the reconstructed atmospheric d13CO2 values show only slightly larger scatter. The difference to data from coeval bubbly ice is statistically significant. However, the 0.16 per mil magnitude of the offset is small for practical purposes, especially in light of uncertainty from non-uniform corrections for diffusion related fractionation that could contribute to the discrepancy. Our results are promising for palaeo-atmospheric studies of d13CO2 using a ball mill dry extraction technique below the BCTZ of ice cores, where gas is not subject to fractionation into microfractures and between clathrate and bubble reservoirs.

Methane fluxes and carbonate deposits at eastern Mediterranean cold seeps

High acoustic seafloor-backscatter signals characterize hundreds of patches of methane-derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the Nile Deep Sea Fan (NDSF) in the Eastern Mediterranean Sea. During a high-resolution ship-based multibeam survey covering a ~ 225 km**2 large seafloor area in the Central Province of the NDSF we identified 163 high-backscatter patches at water depths between 1500 and 1800 m, and investigated the source, composition, turnover, flux and fate of emitted hydrocarbons. Systematic Parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies (flares), indicative of gas bubble streams, above 8% of the high-backscatter patches. In echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution. Visual inspection of three high-backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter. Volume estimates, considering results from high-resolution autonomous underwater vehicle (AUV)-based multibeam mapping, were used to calculate the amount of carbonate-bound carbon stored in these slabs. Additionally, the flux of methane bubbles emitted at one high-backscatter patch was estimated (0.23 to 2.3 × 10**6 mol a**-1) by combined AUV flare mapping with visual observations by remotely operated vehicle (ROV). Another high-backscatter patch characterized by single carbonate pieces, which were widely distributed and interspaced with sediments inhabited by thiotrophic, chemosynthetic organisms, was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption (0.1 to 1 × 10**6 mol a**-1) and dissolved methane flux (2 to 48 × 10**6 mol a**-1). Our comparison of dissolved and gaseous methane fluxes as well as methane-derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo-, bio-, and hydrosphere at cold seeps.

Underway measurements of dissolved gases along POLARSTERN cruise track ANT-XXVII/2

We present measurements of pCO2, O2 concentration, biological oxygen saturation (Delta O2/Ar) and N2 saturation (Delta N2) in Southern Ocean surface waters during austral summer, 2010-2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chla) concentrations in regions of frontal mixing and sea-ice melt. pCO2 and Delta O2 /Ar exhibited large spatial gradients (range 90 to 450 µatm and -10 to 60%, respectively) and co-varied strongly with Chla. However, the ratio of biological O2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O2 and CO2 air-sea equilibration. We measured significant oceanic CO2 uptake, with a mean air-sea flux (~ -20 mmol m-2 d-1) that significantly exceeded regional climatological values. N2 was mostly supersaturated in surface waters (mean Delta N2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O2 (mean Delta O2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of Delta N2 and Delta O2phys along the cruise track, demonstrating significant effects of air-sea exchange processes (e.g. atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface Delta O2 /Ar data, ranged from ~ -40 to > 300 mmol O2 m-2 d-1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and regions of sea-ice melt with shallow mixed layer depths, reflecting the importance of mixing in controlling surface water light and nutrient availability.

Análisis de preferencias del paisaje urbano entre barrios compactos y barrios postindustriales en Vitoria-Gasteiz. Implicaciones en la planificación urbana

Las características urbanísticas de las expansiones urbanas postindustriales desarrolladas en las últimas décadas en numerosas ciudades españolas presentan diferencias notables con las de barrios centrales y pericentrales más compactos preexistentes. Con el fin de estudiar cómo son percibidas por los ciudadanos de Vitoria-Gasteiz dichas diferencias urbanísticas, se realizaron 250 encuestas a residentes en los barrios compactos de la ciudad sobre sus preferencias entre el paisaje urbano de su barrio y el de los barrios postindustriales. Se observó que la gran mayoría de los encuestados prefirieron su compacto barrio en aspectos de sociabilidad, accesibilidad a servicios y bienestar global. Los resultados obtenidos se contrastaron con los de un estudio previo en el que una encuesta similar fue realizada a residentes en un barrio postindustrial. Se discuten las implicaciones de los resultados para desarrollar una práctica urbanística más sostenible y que integre la percepción de los usuarios de la ciudad.

A reconciliation of empirical and mechanistic models of the air-sea gas transfer velocity

Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the influence of bubble-mediated transfer, which can vary between gases, is not explicitly accounted for. Mechanistic models are hindered by an incomplete knowledge of the mechanisms of air-sea gas transfer. We describe a hybrid model that incorporates a simple mechanistic view—strictly enforcing a distinction between direct and bubble-mediated transfer—but also uses parameterizations based on data from eddy flux measurements of dimethyl sulphide (DMS) to calibrate the model together with dual tracer results to evaluate the model. This model underpins simple algorithms that can be easily applied within schemes to calculate local, regional, or global air-sea fluxes of gases.

A reconciliation of empirical and mechanistic models of the air-sea gas transfer velocity

Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the influence of bubble-mediated transfer, which can vary between gases, is not explicitly accounted for. Mechanistic models are hindered by an incomplete knowledge of the mechanisms of air-sea gas transfer. We describe a hybrid model that incorporates a simple mechanistic view—strictly enforcing a distinction between direct and bubble-mediated transfer—but also uses parameterizations based on data from eddy flux measurements of dimethyl sulphide (DMS) to calibrate the model together with dual tracer results to evaluate the model. This model underpins simple algorithms that can be easily applied within schemes to calculate local, regional, or global air-sea fluxes of gases.

Air-sea transfer of gas phase controlled compounds

Gases in the atmosphere/ocean have solubility that spans several orders of magnitude. Resistance in the molecular sublayer on the waterside limits the air-sea exchange of sparingly soluble gases such as SF6 and CO2. In contrast, both aerodynamic and molecular diffusive resistances on the airside limit the exchange of highly soluble gases (as well as heat). Here we present direct measurements of air-sea methanol and acetone transfer from two open cruises: the Atlantic Meridional Transect in 2012 and the High Wind Gas Exchange Study in 2013. The transfer of the highly soluble methanol is essentially completely airside controlled, while the less soluble acetone is subject to both airside and waterside resistances. Both compounds were measured concurrently using a proton-transfer-reaction mass spectrometer, with their fluxes quantified by the eddy covariance method. Up to a wind speed of 15 m s-1, observed air-sea transfer velocities of these two gases are largely consistent with the expected near linear wind speed dependence. Measured acetone transfer velocity is ~30% lower than that of methanol, which is primarily due to the lower solubility of acetone. From this difference we estimate the "zero bubble" waterside transfer velocity, which agrees fairly well with interfacial gas transfer velocities predicted by the COARE model. At wind speeds above 15 m s-1, the transfer velocities of both compounds are lower than expected in the mean. Air-sea transfer of sensible heat (also airside controlled) also appears to be reduced at wind speeds over 20 m s-1. During these conditions, large waves and abundant whitecaps generate large amounts of sea spray, which is predicted to alter heat transfer and could also affect the air-sea exchange of soluble trace gases. We make an order of magnitude estimate for the impacts of sea spray on air-sea methanol transfer.

Air-sea transfer of gas phase controlled compounds

Gases in the atmosphere/ocean have solubility that spans several orders of magnitude. Resistance in the molecular sublayer on the waterside limits the air-sea exchange of sparingly soluble gases such as SF6 and CO2. In contrast, both aerodynamic and molecular diffusive resistances on the airside limit the exchange of highly soluble gases (as well as heat). Here we present direct measurements of air-sea methanol and acetone transfer from two open cruises: the Atlantic Meridional Transect in 2012 and the High Wind Gas Exchange Study in 2013. The transfer of the highly soluble methanol is essentially completely airside controlled, while the less soluble acetone is subject to both airside and waterside resistances. Both compounds were measured concurrently using a proton-transfer-reaction mass spectrometer, with their fluxes quantified by the eddy covariance method. Up to a wind speed of 15 m s-1, observed air-sea transfer velocities of these two gases are largely consistent with the expected near linear wind speed dependence. Measured acetone transfer velocity is ~30% lower than that of methanol, which is primarily due to the lower solubility of acetone. From this difference we estimate the "zero bubble" waterside transfer velocity, which agrees fairly well with interfacial gas transfer velocities predicted by the COARE model. At wind speeds above 15 m s-1, the transfer velocities of both compounds are lower than expected in the mean. Air-sea transfer of sensible heat (also airside controlled) also appears to be reduced at wind speeds over 20 m s-1. During these conditions, large waves and abundant whitecaps generate large amounts of sea spray, which is predicted to alter heat transfer and could also affect the air-sea exchange of soluble trace gases. We make an order of magnitude estimate for the impacts of sea spray on air-sea methanol transfer.

La situación de los museos españoles ante la crisis. El patrimonio implicado

La crisis como coyuntura y tránsito a una nueva situación, y el cambio social que parece conllevar, lejos de ser un fenómeno exclusivamente actual, viene acompañando a los museos españoles desde décadas atrás, debido a indecisiones, faltas de planificación, cambios políticos y de estrategias de funcionamiento. Pero será a partir de la Transición democrática, y la década de 1980, en que comenzará a fraguarse la llamada “burbuja” de los museos, que estalla bajo el “efecto Guggenheim” a finales del siglo XX, seguida de la merma de presupuestos oficiales para el sostenimiento del sistema museístico que trae como consecuencia la tan mencionada “crisis” económica desde aproximadamente 2008. El artículo examina esta situación y advierte de que el momento delicado que viven los museos en la actualidad es ocasión para replantearse su futuro y adaptarse a una nueva realidad cambiante. El Museo Etnológico de Navarra “Julio Caro Baroja” constituye un caso de adaptación a tales circunstancias.

Three-dimensional simulations of gravitationally confined detonations compared to observations of SN 1991T

The gravitationally confined detonation (GCD) model has been proposed as a possible explosion mechanism for Type Ia supernovae in the single-degenerate evolution channel. It starts with ignition of a deflagration in a single off-centre bubble in a near-Chandrasekhar-mass white dwarf. Driven by buoyancy, the deflagration flame rises in a narrow cone towards the surface. For the most part, the main component of the flow of the expanding ashes remains radial, but upon reaching the outer, low-pressure layers of the white dwarf, an additional lateral component develops. This causes the deflagration ashes to converge again at the opposite side, where the compression heats fuel and a detonation may be launched. We first performed five three-dimensional hydrodynamic simulations of the deflagration phase in 1.4 M⊙ carbon/oxygen white dwarfs at intermediate-resolution (2563computational zones). We confirm that the closer the initial deflagration is ignited to the centre, the slower the buoyant rise and the longer the deflagration ashes takes to break out and close in on the opposite pole to collide. To test the GCD explosion model, we then performed a high-resolution (5123 computational zones) simulation for a model with an ignition spot offset near the upper limit of what is still justifiable, 200 km. This high-resolution simulation met our deliberately optimistic detonation criteria, and we initiated a detonation. The detonation burned through the white dwarf and led to its complete disruption. For this model, we determined detailed nucleosynthetic yields by post-processing 106 tracer particles with a 384 nuclide reaction network, and we present multi-band light curves and time-dependent optical spectra. We find that our synthetic observables show a prominent viewing-angle sensitivity in ultraviolet and blue wavelength bands, which contradicts observed SNe Ia. The strong dependence on the viewing angle is caused by the asymmetric distribution of the deflagration ashes in the outer ejecta layers. Finally, we compared our model to SN 1991T. The overall flux level of the model is slightly too low, and the model predicts pre-maximum light spectral features due to Ca, S, and Si that are too strong. Furthermore, the model chemical abundance stratification qualitatively disagrees with recent abundance tomography results in two key areas: our model lacks low-velocity stable Fe and instead has copious amounts of high-velocity 56Ni and stable Fe. We therefore do not find good agreement of the model with SN 1991T.

Characterisation of polyethylene powders for rotational moulding and effect of powder size and shape on densification behaviour

The particle size, shape and distribution of a range of rotational moulding polyethylenes (PEs) ground to powder was investigated using a novel visual data acquisition and analysis system (TP Picture®), developed by Total Petrochemicals. Differences in the individual particle shape factors of the powder samples were observed and correlations with the grinding conditions were determined. When heated, the bubble dissolution behaviour of the same powders was investigated and the shape factor correlated with densification rate, bubble size and bubble distribution.

Study into the densification behaviour of polyethylenes for rotational moulding

The melting and densification behaviour of a range of Polyethylenes (PEs) produced from 2 different catalysts, Ziegler-Natta and Metallocene types, were investigated using a novel visual data acquisition and analysis system (TP Picture®), developed by Total Petrochemicals Research Feluy [1]. Differences in the dissolution behaviour of the bubbles were observed and correlations with the material density, densification rate, bubble size / distribution and MFI were determined.

Efficient and Selectable Production of Reactive Species Using a Nanosecond Pulsed Discharge in Gas Bubbles in Liquid

A plasma gas bubble-in-liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point-to-plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas-plasma and water through bubbles, give higher productivity. H₂O₂ was the predominant species produced using Ar plasma, while predominantly  and NO₂ were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H₂O₂, with seven times higher production, and 92% selectivity for , with nearly twice the production, compared with a plasma above the water.

Levantamento do Tamanho Médio de Bolhas em Escoamento Bifásico Vertical por Técnica Fotográfica

Para confirmar e validar códigos computacionais de escoamento de fluidos, importantes na segurança de reatores nucleares, é preciso que sejam realizadas medidas experimentais. Como a geração de vapor no fluido refrigerante diminui a eficiência de troca térmica a fração de vazio passa a ser um dos parâmetros mais importantes a ser obtido, e que, num escoamento vertical, pode ser conhecido através da quantidade de bolha e seu diâmetro médio.

Copper-cobalt foams as active and stable catalysts for hydrogen release by hydrolysis of sodium borohydride

The progress of hydrogen generation by sodium borohydride hydrolysis depends highly on the development of efficient catalysts based on non-noble metals such as cobalt. However, such catalysts undergo extensive deactivation which has a detrimental effect on their stability. Herein, highly porous copper and cobalt-based bimetallic foams, CuxCo100-x (x = 0-100 at%), produced by electrodeposition using the dynamic hydrogen bubble template are reported. The chemical composition of the foams was optimized in order to enhance specific surface area and improve their catalytic activity and stability as heterogeneous catalysts for sodium borohydride hydrolysis. Among the tested catalysts, copper-rich samples like Cu85Co15 are slightly more active than Co-100 and above all, they are less sensitive to deactivation by borates adsorption. Porous copper-rich foams were found to be an alternative to cobalt as low-cost, active and stable heterogeneous catalysts for hydrogen generation by hydrolysis of sodium borohydride. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.