Managing urban socio-technical change? Comparing energy technology controversies in three European contexts

A {\em local graph partitioning algorithm} finds a set of vertices with small conductance (i.e. a sparse cut) by adaptively exploring part of a large graph $G$, starting from a specified vertex. For the algorithm to be local, its complexity must be bounded in terms of the size of the set that it outputs, with at most a weak dependence on the number $n$ of vertices in $G$. Previous local partitioning algorithms find sparse cuts using random walks and personalized PageRank. In this paper, we introduce a randomized local partitioning algorithm that finds a sparse cut by simulating the {\em volume-biased evolving set process}, which is a Markov chain on sets of vertices. We prove that for any set of vertices $A$ that has conductance at most $\phi$, for at least half of the starting vertices in $A$ our algorithm will output (with probability at least half), a set of conductance $O(\phi^{1/2} \log^{1/2} n)$. We prove that for a given run of the algorithm, the expected ratio between its computational complexity and the volume of the set that it outputs is $O(\phi^{-1/2} polylog(n))$. In comparison, the best previous local partitioning algorithm, due to Andersen, Chung, and Lang, has the same approximation guarantee, but a larger ratio of $O(\phi^{-1} polylog(n))$ between the complexity and output volume. Using our local partitioning algorithm as a subroutine, we construct a fast algorithm for finding balanced cuts. Given a fixed value of $\phi$, the resulting algorithm has complexity $O((m+n\phi^{-1/2}) polylog(n))$ and returns a cut with conductance $O(\phi^{1/2} \log^{1/2} n)$ and volume at least $v_{\phi}/2$, where $v_{\phi}$ is the largest volume of any set with conductance at most $\phi$.Comment: 20 pages, no figure

Magmatic and hydrothermal behavior of uranium in syntectonic leucogranites: The uranium mineralization associated with the Hercynian Guérande granite (Armorican Massif, France)

Most of the hydrothermal uranium (U) deposits from the European Hercynian belt (EHB) are spatially associated with Carboniferous peraluminous leucogranites. In the southern part of the Armorican Massif (French part of the EHB), the Guérande peraluminous leucogranite was emplaced in an extensional deformation zone at ca. 310 Ma and is spatially associated with several U deposits and occurrences. The apical zone of the intrusion is structurally located below the Pen Ar Ran U deposit, a perigranitic vein-type deposit where mineralization occurs at the contact between black shales and Ordovician acid metavolcanics. In the Métairie-Neuve intragranitic deposit, uranium oxide-quartz veins crosscut the granite and a metasedimentary enclave. Airborne radiometric data and published trace element analyses on the Guérande leucogranite suggest significant uranium leaching at the apical zone of the intrusion. The primary U enrichment in the apical zone of the granite likely occurred during both fractional crystallization and the interaction with magmatic fluids. The low Th/U values (18Owhole rock = 9.7–11.6‰ for deformed samples and δ18Owhole rock = 12.2–13.6‰ for other samples) indicate that the deformed facies of the apical zone underwent sub-solidus alteration at depth with oxidizing meteoric fluids. Fluid inclusion analyses on a quartz comb from a uranium oxide-quartz vein of the Pen Ar Ran deposit show evidence of low-salinity fluids (1–6 wt.% NaCl eq.), in good agreement with the contribution of meteoric fluids. Fluid trapping temperatures in the range of 250–350 °C suggest an elevated geothermal gradient, probably related to regional extension and the occurrence of magmatic activity in the environment close to the deposit at the time of its formation. U-Pb dating on uranium oxides from the Pen Ar Ran and Métairie-Neuve deposits reveals three different mineralizing events. The first event at 296.6 ± 2.6 Ma (Pen Ar Ran) is sub-synchronous with hydrothermal circulations and the emplacement of late leucogranitic dykes in the Guérande leucogranite. The two last mineralizing events occur at 286.6 ± 1.0 Ma (Métairie-Neuve) and 274.6 ± 0.9 Ma (Pen Ar Ran), respectively. Backscattered uranium oxide imaging combined with major elements and REE geochemistry suggest similar conditions of mineralization during the two Pen Ar Ran mineralizing events at ca. 300 Ma and ca. 275 Ma, arguing for different hydrothermal circulation phases in the granite and deposits. Apatite fission track dating reveals that the Guérande granite was still at depth and above 120 °C when these mineralizing events occurred, in agreement with the results obtained on fluid inclusions at Pen Ar Ran. Based on this comprehensive data set, we propose that the Guérande leucogranite is the main source for uranium in the Pen Ar Ran and Métairie-Neuve deposits. Sub-solidus alteration via surface-derived low-salinity oxidizing fluids likely promoted uranium leaching from magmatic uranium oxides within the leucogranite. The leached out uranium may then have been precipitated in the reducing environment represented by the surrounding black shales or graphitic quartzites. As similar mineralizing events occurred subsequently until ca. 275 Ma, meteoric oxidizing fluids likely percolated during the time when the Guérande leucogranite was still at depth. The age of the U mineralizing events in the Guérande region (300–275 Ma) is consistent with that obtained on other U deposits in the EHB and could suggest a similar mineralization condition, with long-term upper to middle crustal infiltration of meteoric fluids likely to have mobilized U from fertile peraluminous leucogranites during the Late Carboniferous to Permian crustal extension events

Evaluation of modelling approaches for predicting the spatial distribution of soil organic carbon stocks at the national scale

Soil organic carbon (SOC) plays a major role in the global carbon budget. It can act as a source or a sink of atmospheric carbon, thereby possibly influencing the course of climate change. Improving the tools that model the spatial distributions of SOC stocks at national scales is a priority, both for monitoring changes in SOC and as an input for global carbon cycles studies. In this paper, we compare and evaluate two recent and promising modelling approaches. First, we considered several increasingly complex boosted regression trees (BRT), a convenient and efficient multiple regression model from the statistical learning field. Further, we considered a robust geostatistical approach coupled to the BRT models. Testing the different approaches was performed on the dataset from the French Soil Monitoring Network, with a consistent cross-validation procedure. We showed that when a limited number of predictors were included in the BRT model, the standalone BRT predictions were significantly improved by robust geostatistical modelling of the residuals. However, when data for several SOC drivers were included, the standalone BRT model predictions were not significantly improved by geostatistical modelling. Therefore, in this latter situation, the BRT predictions might be considered adequate without the need for geostatistical modelling, provided that i) care is exercised in model fitting and validating, and ii) the dataset does not allow for modelling of local spatial autocorrelations, as is the case for many national systematic sampling schemes

Description and validation of an AOT product over land at the 0.6 μm channel of the SEVIRI sensor onboard MSG

The Spinning Enhanced Visible and InfraRed Imager (SEVIRI) aboard Meteosat Second Generation (MSG) launched in 2003 by EUMETSAT is dedicated to the Nowcasting applications and Numerical Weather Prediction and to the provision of observations for climate monitoring and research. We use the data in visible and near infrared (NIR) channels to derive the aerosol optical thickness (AOT) over land. The algorithm is based on the assumption that the top of the atmosphere (TOA) reflectance increases with the aerosol load. This is a reasonable assumption except in case of absorbing aerosols above bright surfaces. We assume that the minimum in a 14-days time series of the TOA reflectance is, once corrected from gaseous scattering and absorption, representative of the surface reflectance. The AOT and the aerosol model (a set of 5 models is used), are retrieved by matching the simulated TOA reflectance with the TOA reflectances measured by SEVIRI in its visible and NIR spectral bands. <br><br> The high temporal resolution of the data acquisition by SEVIRI allows to retrieve the AOT every 15 min with a spatial resolution of 3 km at sub-satellite point, over the entire SEVIRI disk covering Europe, Africa and part of South America. The resulting AOT, a level 2 product at the native temporal and spatial SEVIRI resolutions, is presented and evaluated in this paper. <br><br> The AOT has been validated using ground based measurements from AErosol RObotic NETwork (AERONET), a sun-photometer network, focusing over Europe for 3 months in 2006. The SEVIRI estimates correlate well with the AERONET measurements, <i>r</i> = 0.64, with a slight overestimate, bias = −0.017. The sources of errors are mainly the cloud contamination and the bad estimation of the surface reflectance. The temporal evolutions exhibited by both datasets show very good agreement which allows to conclude that the AOT Level 2 product from SEVIRI can be used to quantify the aerosol content and to monitor its daily evolution with a high temporal frequency. The comparison with daily maps of Moderate Resolution Imaging Spectroradiometer (MODIS) AOT level 3 product shows qualitative good agreement in the retrieved geographic patterns of AOT. <br><br> Given the high spatial and temporal resolutions obtained with this approach, our results have clear potential for applications ranging from air quality monitoring to climate studies. This paper presents a first evaluation and validation of the derived AOT over Europe in order to document the overall quality of a product that will be made publicly available to the users of the aforementioned research communities

Spatial distribution of soil organic carbon stocks in France

Soil organic carbon plays a major role in the global carbon budget, and can act as a source or a sink of atmospheric carbon, thereby possibly influencing the course of climate change. Changes in soil organic carbon (SOC) stocks are now taken into account in international negotiations regarding climate change. Consequently, developing sampling schemes and models for estimating the spatial distribution of SOC stocks is a priority. The French soil monitoring network has been established on a 16 km × 16 km grid and the first sampling campaign has recently been completed, providing around 2200 measurements of stocks of soil organic carbon, obtained through an in situ composite sampling, uniformly distributed over the French territory. <br><br> We calibrated a boosted regression tree model on the observed stocks, modelling SOC stocks as a function of other variables such as climatic parameters, vegetation net primary productivity, soil properties and land use. The calibrated model was evaluated through cross-validation and eventually used for estimating SOC stocks for mainland France. Two other models were calibrated on forest and agricultural soils separately, in order to assess more precisely the influence of pedo-climatic variables on SOC for such soils. <br><br> The boosted regression tree model showed good predictive ability, and enabled quantification of relationships between SOC stocks and pedo-climatic variables (plus their interactions) over the French territory. These relationships strongly depended on the land use, and more specifically, differed between forest soils and cultivated soil. The total estimate of SOC stocks in France was 3.260 ± 0.872 PgC for the first 30 cm. It was compared to another estimate, based on the previously published European soil organic carbon and bulk density maps, of 5.303 PgC. We demonstrate that the present estimate might better represent the actual SOC stock distributions of France, and consequently that the previously published approach at the European level greatly overestimates SOC stocks

Large magnetic anisotropy in Ferrihydrite nanoparticles synthesized from reverse micelles

Six-line ferrihydrite(FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes $$ $\approx$ 2 to 4 nm. The blocking temperatures $T_B^m$ extracted from magnetization data increased from $\approx 10$ to 20 K for increasing particle size. Low-temperature \MOS measurements allowed to observe the onset of differentiated contributions from particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the \FH phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility \chi_{ac}(\emph{f},T) measurements showed the dependence of the effective magnetic anisotropy energies $E_{a}$ with particle volume, and yielded an effective anisotropy value of $K_{eff} = 312\pm10$ kJ/m$^3$.Comment: 8 pages, 10 figures. Nanotechnology, v17 (Nov. 2006) In pres

Elucidating the crystal-chemistry of Jbel Rhassoul stevensite (Morocco) by advanced analytical techniques

The composition of Rhassoul clay is controversial regarding the nature of the puremineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20 (Mg5.04Al0.37Fe0.20&0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral

Structural insights into Clostridium perfringens delta toxin pore formation

Clostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins