An integration to optimally constrain the thermal structure of oceanic lithosphere

[1] The evolution through time of the oceanic lithosphere is a substantial, incompletely resolved geodynamical problem. Consensus remains elusive regarding its thermal structure, physical properties, and the best model through which to unify observational constraints. We robustly reevaluate all three of these by (i) simultaneously fitting heat flow, bathymetry, and temperatures derived from a shear velocity model of the upper mantle, (ii) using the three main thermal models (half-space, plate, and Chablis), and (iii) analyzing five depth-age curves, wherein contrasting techniques were used to exclude anomalous features from seafloor depths. The thermal models are updated to all include a temperature-dependent heat capacity, a temperature- and pressure-dependent thermal conductivity, and an initial condition of adiabatic decompression including melting. The half-space model, which lets the lithosphere thicken indefinitely, cannot accurately fit the subsidence curves and requires mantle potential temperatures, Tm, that are too high. On the other hand, the models including a mechanism of basal heat supply are able to simultaneously explain all observations within two standard errors, with best-fitting parameters robust to the choice of the filtered bathymetry curve. For the plate model, which imposes a constant temperature at a fixed depth, Tm varies within 1380–1390°C, the equilibrium plate thickness a within 106–110 km, and the bulk thermal expansivity inline image within 2.95−3.20 ⋅ 10−5 K−1. For the Chablis model, which prescribes a fixed heat flow at the base of a thickening lithosphere, the best-fitting values are Tm = 1320−1380°C, a = 176−268 km, inline image K−1. Driven by more accurate ocean depths, the plate model provides better joint-fittings to the observations; however, it requires values of inline image lower than experimentally measured, which can be explained by a reduction of the apparent expansivity due to elastic rigidity of the upper lithosphere. The Chablis model better fits the data when inline image is set close to or above the experimental values. Although statistically consistent within two standard errors, a tendency toward incompatibility between observed depth-age curves and seismically derived temperatures is revealed with new clarity, because the latter do not exhibit a clear steady state whereas the former flatten; further work is needed to identify the origin of this apparent discrepancy.This work opens the way to investigations fully independent of particular solutions of the heat equation

Urban-rural air humidity differences in Szeged, Hungary

Measurements of vapour pressure, taken four times a day over a 3-year period, were used to investigate the urban influence on diurnal and annual patterns of vapour pressure differences. The examined settlement is a medium-sized city without significant relief in the Great Hungarian Plain. Its regional climate is continental with a long warm season. On the basis of the results, the air in the city centre is more humid than in the rural area both by day and at night for the duration of the whole year. The diurnal pattern shows that the urban excess has its minimum at 01:00 h and its maximum at 19:00 h in the summer months, but similar regular diurnal variation does not exist during the rest of the year. The annual patterns show that the excess increases from January–February to August and then decreases until November–December at each observation time. The differences and variations of urban humidity excess can be explained by different moisture sources and by different energy balances in the urban and rural environments. Unambiguous relationships exist between the variations of urban humidity excess and a regional aridity index, between the variations of humidity excess and the water temperature of the River Tisza crossing the city, as well as between the variations of humidity excess and maximum heat island intensity. The role of combustion processes is also significant, especially in the colder half of the year

Global heat flow trends resolved from multiple geological and geophysical proxies

International audienceBecause global coverage of heat flow measurements is still poor in many areas, empirical estimators based on the geology, the thermotectonic age or the velocity structure of the upper mantle have often been used to affect an estimate to regions where such measurements are absent. On the basis of the assumption that heat flow is strongly related to its geodynamic environment, one may integrate multiple proxies derived from a large body of global geo- logical and geophysical data sets assembled during the past decades; these should help to better capture the variety of present-day settings. This idea is illustrated through two simple empirical methods: both of them are based on a set of examples, where heat flow measure- ments are associated with relevant terrestrial observables such as surface heat production, upper-mantle velocity structure, tectono-thermal age, on a 1◦ × 1◦ grid. To a given target point owning a number of observables, the methods associate a heat flow distribution rather than a deterministic value to account for intrinsic variability and uncertainty within a defined geodynamic environment. The 'best combination method' seeks the particular combination of observables that minimizes the dispersion of the heat flow distribution generated from the set of examples. The 'similarity method' attributes a weight to each example depending on its degree of similarity with the target point. The methods are transparent and are able to handle sets of observables that are not available over the whole Earth (e.g. heat production). The resulting trends of the mean heat flow deduced from the two methods do not differ strongly, but the similarity method shows a better accuracy in cross-validation tests. These tests suggest that the selected proxies have the potential to recover at least partly medium- to large-scale features of surface heat flow. The methods depict the main global trends of low heat flow in stable and ancient regions, and thermal high in active orogens and rift zones. Broad thermal anomalies are outlined in the Sahara and in the tectonically active eastern part of Antarctica. The similarity method estimates a continental heat loss of 13.6 ± 0.8 TW (2σ uncertainty), which is consistent with previous estimates

Caractérisation par microscopie à force atomique des arrangements protéine/sucre impliquant la lectine PA-IL de la bactérie pseudomonas aeruginosa

La bactérie Pseudomonas aeruginosa est un pathogène opportuniste responsable de graves infections chez les personnes affaiblies immunitairement. Présentant des souches résistantes aux antibiotiques, une nouvelle approche thérapeutique est en cours de développement avec pour objectif l inhibition des facteurs de virulence de la bactérie. Lors de son processus d infection, le pathogène utilise les lectines pour reconnaître et se lier de manière spécifique aux glycoconjugués des cellules-hôtes en formant une interaction lectine/glycoconjugué. Plus particulièrement, la lectine PA-IL, spécifique du galactose, a été étudiée. A l aide de glycomimétique, il semble possible de bloquer l action de la lectine en créant une interaction lectine/glycomimétique. Pour développer cette approche, de nombreux glycocluster sont donc été élaborés et leur affinité avec la lectine PA-IL a été évaluée par plusieurs méthodes de caractérisation (SPR, HIA, ELLA, puce à sucre, ).Dans ce projet de thèse, nous avons cherché à visualiser par microscopie à force atomique (AFM) l arrangement des complexes lectine PA-IL/glycocluster formés pour trois glycoclusters différents. Nous avons ainsi pu montrer l influence du cœur du glycocluster et des bras-espaceurs sur l arrangement des complexes. Suivant le glycocluster, l arrangement prend la forme de filaments 1D,de structures dentelées avec des bras sinueux ou encore de larges structures compactes. Dans le cas des filaments, la résolution de nos images AFM nous a permis d identifier les lectines à l intérieur même de la structure filaire. Nous avons aussi démontré, en observant les lectines seules, l existence d une interaction lectine/lectine. De plus, des expériences ont été menées pour déterminer les conditions expérimentales appropriées à leur observation à l air et en milieu liquide.The bacterium P. aeruginosa is an opportunistic pathogen responsible for serious infections in immunocompromised patients. It also develops some strains resistant to antibiotics. A new approach is developed to inhibit virulence factors of the bacterium. During the process of infection, the pathogen uses lectins to recognize and bind specifically to glycoconjugates of the host cells forming alectin/glycoconjugate complex. Particularly, the lectin PA-IL, specific to galactose, was studied. Using glycomimetics, it seems possible to block the action of the lectin by creating lectin/glycomimetic interaction. To develop this approach, many glycoclusters were designed and their affinity with lectin PA-IL was evaluated by various characterization techniques (SPR, HIA, ELLA, microarrays, ).In this thesis project, we have tried to visualize by Atomic Force Microscopy (AFM) the arrangement of lectin PA-IL/glycocluster complexes with three different glycoclusters. Our results show the influence of the glycocluster core and the linker on the arrangement of complexes. Depending on glycocluster, the arrangement takes the form of 1D filaments, 2D "pinked" structures with sinuous branches or large compact structures. In the case of filaments, the resolution of AFM images allows us to identify lectins along the filament. We also demonstrated the existence of lectin/lectin interactions at high concentration of lectin. In addition, some experiments were performed to determine sample preparation techniques to observe lectins in air and in liquid.LYON-Ecole Centrale (690812301) / SudocSudocFranceF