684 research outputs found
Chemically Partly Delithiated Lithium Manganese Phospho Olivines: Investigations of Lattice and Atomic Structure and Electrochemistry
No full textCarbonyl sulfide (COS) as a tracer for canopy photosynthesis, transpiration and stomatal conductance: potential and limitations
No full textThe theoretical basis for the link between the leaf exchange of carbonyl sulfide (COS), carbon dioxide (CO2) and water vapour (H2O) and the assumptions that need to be made in order to use COS as a tracer for canopy net photosynthesis, transpiration and stomatal conductance, are reviewed. The ratios of COS to CO2 and H2O deposition velocities used to this end are shown to vary with the ratio of the internal to ambient CO2 and H2O mole fractions and the relative limitations by boundary layer, stomatal and internal conductance for COS. It is suggested that these deposition velocity ratios exhibit considerable variability, a finding that challenges current parameterizations, which treat these as vegetation-specific constants. COS is shown to represent a better tracer for CO2 than H2O. Using COS as a tracer for stomatal conductance is hampered by our present poor understanding of the leaf internal conductance to COS. Estimating canopy level CO2 and H2O fluxes requires disentangling leaf COS exchange from other ecosystem sources/sinks of COS. We conclude that future priorities for COS research should be to improve the quantitative understanding of the variability in the ratios of COS to CO2 and H2O deposition velocities and the controlling factors, and to develop operational methods for disentangling ecosystem COS exchange into contributions by leaves and other sources/sinks. To this end, integrated studies, which concurrently quantify the ecosystem-scale CO2, H2O and COS exchange and the corresponding component fluxes, are urgently needed
Influence of electrode preparation on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 composite electrodes for lithium-ion batteries
No full text
On the variability of the leaf relative uptake rate of carbonyl sulfide compared to carbon dioxide: Insights from a paired field study with two soybean varieties
No full textCarbonyl sulfide (COS) has been proposed as a promising tracer for the estimation of the gross primary productivity (GPP) from ecosystem to global scale in recent years. Despite substantial work at spatial scales from leaf to regions, the uncertainty of COS-based GPP estimates are poorly known compared to widely used GPP estimates derived from the net ecosystem CO2 exchange. One key uncertainty in this context is the leaf relative uptake (LRU) of the COS with respect to the GPP, which must be known a priori. To investigate the influence of environmental factors, like drought, on the variability of the LRU, we conducted an experiment using ecosystem flux measurements of COS, CO2 and H2O from two eddy covariance towers above a soybean field, growing a commercial cultivar and a chlorophyll deficient mutant variety, in two separate plots. Our findings suggest that the LRU does not only differ between plant varieties due to differences in the ratio of the internal to ambient CO2 mole fraction and the internal resistance to COS, but also changes in response to drought. We also found the internal resistance to COS uptake to be a significant factor in controlling the total COS flux for both varieties, but more so for the commercial cultivar. Our study indicates that species-specific differences in the LRU need to be investigated further, and that environmental stress might complicate the usage of COS as a tracer for predicting GPP at ecosystem and global scale
New spectral vegetation indices based on the near-infrared shoulder wavelengths for remote detection of grassland phytomass
No full textThis paper examines the possibility of exploiting ground reflectance in the near-infrared (NIR) for monitoring grassland phytomass on a temporal basis. Three new spectral vegetation indices (Infrared Slope Index, ISI; Near Infrared Difference Index, NIDI; and Normalized Difference Structural Index, NDSI), which are based on the reflectance values in the H25 (863-881 nm) and the H18 (745-751 nm) Chris Proba (mode 5) bands, are proposed. Ground measurements of hyperspectral reflectance and phytomass were made at six grassland sites in the Italian and Austrian mountains using a hand-held spectroradiometer. At full canopy cover, strong saturation was observed for many traditional vegetation indices (Normalised Difference Vegetation Index, Modified Simple Ratio, Enhanced Vegetation Index, Enhanced Vegetation Index 2, Renormalised Difference Vegetation Index, Wide Dynamic Range Vegetation Index). Conversely, ISI and NDSI were linearly related to grassland phytomass with negligible inter-annual variability. The relationships between both ISI and NDSI, and phytomass were however site-specific. The WinSail model indicated that this was mostly due to grassland species composition and background reflectance. Further studies are needed to confirm the usefulness of these indices (e.g. using multispectral specific sensors) for monitoring vegetation structural biophysical variables in other ecosystem types and to test these relationships with aircraft and satellite sensors data. For grassland ecosystems, we conclude that ISI and NDSI hold great promise for non destructively monitoring the temporal variability of grassland phytomas
Sodium Insertion into Fe[Fe(CN)6] Framework Prepared by Microwave-Assisted Co-Precipitation
No full textPrussian blue analogues (PBAs) are interesting materials for Na electrochemical insertion, owing to their ease of synthesis, rigid open framework and large interstitial space. In this work, iron hexacyanoferrate nanoparticles, FeIII[FeIII(CN)6], also known as Berlin green (BG), where both Fe centers are in the Fe(III) configuration, have been synthesized by an easy microwave assisted co-precipitation method, with an average particle size of around 44 nm. The BG nanoparticles exhibited a 120 mAh g−1 specific capacity with a capacity retention of 84.8 % over 100 cycles at 20 mA g−1 current and up to 80 mAh g−1 at 10 C rate. The initial charge and discharge processes were fully investigated by ex-situ X-ray absorption spectroscopy (XAS). The XAS results reveal that there is some irreversibility in the initial electrochemical processes and the Fe−C and Fe−N bond lengths change during the first charge/discharge cycle. This effect was attributed to BG electrode activation processes, and partly explained the observed capacity fading
Qualitative and Quantitative Characterization of Volatile Organic Compound Emissions from Cut Grass
No full textMechanical wounding of plants triggers the release of a blend of reactive biogenic volatile organic compounds (BVOCs). During and after mowing and harvesting of managed grasslands, significant BVOC emissions have the potential to alter the physical and chemical properties of the atmosphere and lead to ozone and aerosol formation with consequences for regional air quality. We show that the amount and composition of BVOCs emitted per unit dry weight of plant material is comparable between laboratory enclosure measurements of artificially severed grassland plant species and in situ ecosystem-scale flux measurements above a temperate mountain grassland during and after periodic mowing and harvesting. The investigated grassland ecosystem emitted annually up to 130 mg carbon m(-2) in response to cutting and drying, the largest part being consistently represented by methanol and a blend of green leaf volatiles (GLV). In addition, we report the plant species-specific emission of furfural, terpenoid-like compounds (e.g., camphor), and sesquiterpenes from cut plant material, which may be used as tracers for the presence of given plant species in the ecosystem
A safe, low-cost, and sustainable lithium-ion polymer battery
No full textA polymer lithium-ion battery, formed by a Li4/3Ti5/3O4- LiFePO4 electrode combination and a poly(vinylidene fluoride) (PVdF)-based gel electrolyte, is presented and discussed. The electrochemical characterization demonstrates that this battery is capable of delivering appreciable capacity values at rates ranging from C/32 (160 mAh g(-1)) to 0.75C (130 mAh g(-1)), this being accompanied by a remarkable cycle life. In addition, because the two electrodes are based on common and nontoxic materials and operate within the stability window of the electrolyte, the battery is expected to be safe, inexpensive, and compatible with the environment. All these properties make the battery of prospective interest for application in the hybrid and electric vehicle field. (C) 2004 The Electrochemical Society
On the relationship between ecosystem-scale hyperspectral reflectance and CO<sub>2</sub> exchange in European mountain grasslands
No full textIn this paper we explore the skill of hyperspectral reflectance measurements
and vegetation indices (VIs) derived from these in estimating carbon dioxide
(CO2) fluxes of grasslands. Hyperspectral reflectance data, CO2
fluxes and biophysical parameters were measured at three grassland sites
located in European mountain regions using standardized protocols. The
relationships between CO2 fluxes, ecophysiological variables,
traditional VIs and VIs derived using all two-band combinations of
wavelengths available from the whole hyperspectral data space were analysed.
We found that VIs derived from hyperspectral data generally explained a large
fraction of the variability in the investigated dependent variables but
differed in their ability to estimate midday and daily average CO2
fluxes and various derived ecophysiological parameters. Relationships between
VIs and CO2 fluxes and ecophysiological parameters were site-specific,
likely due to differences in soils, vegetation parameters and environmental
conditions. Chlorophyll and water-content-related VIs explained the largest
fraction of variability in most of the dependent variables. Band selection
based on a combination of a genetic algorithm with random forests (GA–rF)
confirmed that it is difficult to select a universal band region suitable
across the investigated ecosystems. Our findings have major implications for
upscaling terrestrial CO2 fluxes to larger regions and for remote- and
proximal-sensing sampling and analysis strategies and call for more
cross-site synthesis studies linking ground-based spectral reflectance with
ecosystem-scale CO2 fluxes
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