Estimating the altitude of aerosol plumes over the ocean from reflectance ratio measurements in the O2 A-band

A methodology is proposed to infer the altitude of aerosol plumes over the ocean from reflectance ratio measurements in the O₂ absorption A-band (759 to 770 nm). The reflectance ratio is defined as the ratio of the reflectance in a first spectral band, strongly attenuated by O₂ absorption, and the reflectance in a second spectral band, minimally attenuated. For a given surface reflectance, simple relations are established between the reflectance ratio and the altitude of an aerosol layer, as a function of atmospheric conditions and the geometry of observation. The expected accuracy for various aerosol loadings and models is first quantified using an accurate, high spectral resolution, radiative transfer model that fully accounts for interactions between scattering and absorption. The method is developed for POLDER and MERIS, satellite sensors with adequate spectral characteristics. The simulations show that the method is only accurate over dark surfaces when aerosol optical thickness at 765 nm is relatively large (> 0.3). In this case, the expected accuracy is on the order of ± 0.5 km or ± 0.2 km for POLDER or MERIS respectively. More accurate estimates are obtained with MERIS, since in this case the spectral reflectance ratio is more sensitive to aerosol altitude. However, a precise spectral calibration is needed for MERIS. The methodology is applied to MERIS and POLDER imagery acquired over marine surfaces. The estimated aerosol altitude is compared with in situ lidar profiles of backscattering coefficient measured during the AOPEX-2004 experiment for MERIS, or obtained with the space-borne lidar CALIOP for POLDER. The retrieved altitudes agree with lidar measurements in a manner consistent with theory. These comparisons demonstrate the potential of the differential absorption methodology for obtaining information on aerosol altitude over dark surfaces.     

Full Film, Boundary Lubrication and Tribochemistry in Steel Circular Contacts Lubricated with Glycerol

In this article, the lubricating properties of pure glycerol are investigated under both mild and severe EHL regimes. Amazingly low friction coefficients (about 0.01) are reported by experiments in thick film regimes compared to traditional base oils. EHL calculations of film thickness and friction (including thermal effects) predict friction coefficients that are twice those actually found for glycerol. Chemical analysis of glycerol before and after the friction tests were performed by NMR and Karl Fischer methods, and they reveal that water is produced by tribochemical reaction as well as other species like aldehydes. This finding is in agreement with a corrosion pattern observed inside the wear scars of the steel samples. This study provides an explanation to the anomalously low friction observed in the thick film regime. In fact, water produced in the lubricant decreases traction forces due to the drastic decrease of the viscosity of glycerol with water addition.     

Friction Properties of Carbon Nano-Onions from Experiment and Computer Simulations

The carbon nano-onion can be considered as a new kind of interesting lubricating nanoparticle. Used as lubricant additives, carbon nano-onions lead to a strong reduction of both friction and wear, even at low temperature. To better elucidate the mechanisms by which these processes occur, coupled experimental and computational investigations are carried out. In addition, it is found that lubricious iron oxide nanoparticles are generated in the core of the steel contact through mechanisms that are not yet known. The molecular dynamics simulations of carbon onions placed between sliding diamond-like carbon surfaces at high contact pressure indicate that the lubrication mechanism of the onions is based on a coupled process of rolling and sliding inside the contact area. We conclude that most of carbon onions seem to remain intact under friction processes and do not generate graphitic planes, which is in contrast to the previously determined behavior of MoS₂ fullerenes that are mainly exfoliated inside the contact area and liberate lubricating lamellar sheets of h-MoS₂.     

Aryl Bis‐Sulfonamide Inhibitors of IspF from Arabidopsis thaliana and Plasmodium falciparum

2‐Methylerythritol 2,4‐cyclodiphosphate synthase (IspF) is an essential enzyme for the biosynthesis of isoprenoid precursors in plants and many human pathogens. The protein is an attractive target for the development of anti‐infectives and herbicides. Using a photometric assay, a screen of 40 000 compounds on IspF from Arabidopsis thaliana afforded symmetrical aryl bis‐sulfonamides that inhibit IspF from A. thaliana (AtIspF) and Plasmodium falciparum (PfIspF) with IC₅₀ values in the micromolar range. The ortho‐bis‐sulfonamide structural motif is essential for inhibitory activity. The best derivatives obtained by parallel synthesis showed IC₅₀ values of 1.4 μm against PfIspF and 240 nm against AtIspF. Substantial herbicidal activity was observed at a dose of 2 kg ha^?1. Molecular modeling studies served as the basis for an in silico search targeted at the discovery of novel, non‐symmetrical sulfonamide IspF inhibitors. The designed compounds were found to exhibit inhibitory activities in the double‐digit micromolar IC₅₀ range.     

Combinatorial auctions for exchanging resources over a grid network

In grid systems, users compete for different types of resources such that they may execute their applications. Traditional grid systems are formed of organisations that join together for the purpose of collaborative projects. Resources of each of the participating organisation are pooled such that members of individual organisations may access the shared infrastructure. In general, each participant is both a provider and a consumer of resources. Whilst such systems address large organisations, in this paper we address democratic grid systems to satisfy needs of small organisations and even individuals, where on-demand grids may be formed by drawing idling resources available on the Internet. Whilst traditional grid systems resort to allocations that satisfy system specific objectives such as maximization of the resource utilisation, market mechanisms try to obtain allocations that are efficient economically. Economic mechanisms permit to achieve equilibrium between supply and demand and furthermore provide incentives for providers. Combinatorial auction has been argued as an effective mechanism to address the problem of resource allocation within grid systems. Auctions within which multiple types of resources in varying quantities may be traded eliminate the exposure problem by addressing co-allocation. In this paper, we describe a combinatorial exchange where multiple providers and multiple consumers may participate. We describe the winner determination problem that incorporates the time dimension, i.e. resource bundles may be requested for different time ranges, and describe a set of heuristics that have been designed to be fast. We show that these achieve a high level of efficiency as compared to exact solutions. The second part focusses on the pricing problem. The objective is to compute prices that represent the state of the market and bring trustworthy feedback to participants. Drawing on the approach taken by Kwasnica et al. (Manage Sci 51(3):419–434, 2005), we propose a pricing model that computes per-item pricing. Per-item pricing allows users to deduce the price of bundles that they require by linear summation. Furthermore, we propose a model that computes prices as a function of time, thus permitting users, in particular consumers to adjust their demand trading off price and time of execution.     

Transparent polycrystalline alumina obtained by SPS: Green bodies processing effect

Starting from a commercial slurry of high purity α-Al₂O₃, freeze-dried powders, cast, filter-pressed or cold isostatically pressed samples were produced. Resulting powders or green bodies showing different particles packing were densified by spark plasma sintering (SPS) to obtain transparent polycrystalline α-Al₂O₃. Microstructure and real in-line transmittance (RIT) after SPS were dependent on the particles packing quality. Avoiding large agglomerates, narrowing the pore size distribution, reducing the most-frequent pore size (D_mode) and avoiding macroscopic heterogeneities within the green bodies enabled high RIT values to be achieved in the visible and near-infrared spectrum. However, a limit was achieved in the preparation of green bodies for which reducing the D_mode had no more influence on the optical behaviour of samples sintered by SPS. Finally, pure α-Al₂O₃ samples presenting a high RIT_640 nm value of 53% were produced from all the green bodies obtained by the following techniques: filter-pressing, slip casting and cold isostatic pressing.     

Improvements for imaging ceramics sintering in situ in ESEM

Sintering of green samples of alumina produced by ice‐templating was followed in situ in an environmental scanning electron microscope (ESEM) up to temperatures as high as 1375°C. These alumina samples with well‐defined architectures are of great interest in the field of materials science due to their high specific strength (especially in compression), low density and adaptable porosity. For the present study, they also have the advantage to exhibit an important topography, inducing interesting contrast when imaged in an ESEM. Improvements of the imaging conditions in the ESEM were essential to really follow the sintering process involving formation of necks between grains or shift of the centre of grains. This paper describes the improvements made and the results observed on the sintering process of alumina green samples processed by ice‐templating.     

Contact formation dynamics: Mapping chemical bond formation between a molecule and a metallic probe

We present a study that maps out chemical bond formation between a Pt-inked probe and a single 1,3-cyclohexadiene (1,3-CHD) molecule on Si(100). By separating the mechanical and electronic contributions to the current during the approach to contact, we show that there are significant forces between the probe and the C=C of the molecule and we track the relaxation of the molecule, the emergence of a chemical bond feature in the LDOS, and the quenching of specific molecular vibrations during bond formation.     

Prion degradation in soil: possible role of microbial enzymes stimulated by the decomposition of buried carcasses

This study is part of a European project focused on understanding the biotic and abiotic mechanisms involved in the retention and dissemination of transmissible spongiform encephalopathies (TSE) infectivity in soil in order to propose practical recommendations to limit environmental contamination. A 1-year field experiment was conducted with lamb carcasses buried in a pasture soil at three depths (25, 45, and 105 cm). Microbial community response to carcasses was monitored through the potential proteolytic activity and substrate induced respiration (SIR). Soil above carcasses and control soil exhibited low proteolytic capacity, whatever the depth of burial. Contrastingly, in soil beneath the carcasses, proteolysis was stimulated. Decomposing carcasses also stimulated SIR, i.e., microbial biomass, suggesting that proteolytic populations specifically developed on lixiviates from animal tissues. Decomposition of soft tissues occurred within 2 months at subsurface while it lasted at least 1 year at deeper depth where proteolytic activities were season-dependent. The ability of soil proteases to degrade the beta form of prion protein was shown in vitro and conditions of burial relevant to minimize the risk of prion protein dissemination are discussed.