A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study ...techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.
The layering of ionic liquids close to flat, charged interfaces has been identified previously through theoretical and some experimental measurements. Here we present evidence for oscillations in ion ...density ('layering') in a long chain ionic liquid (1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) near the interface with mica using two complementary approaches. Neutron reflection at the ionic liquid-mica interface is used to detect structure at a single interface, and surface force balance (SFB) measurements carried out with the same ionic liquid reveal oscillatory density in the liquid confined between two mica sheets. Our findings imply the interfacial structure is not induced by confinement alone. Structural forces between two mica surfaces extend to approximately twice the distance of the density oscillations measured at a single interface and have similar period in both cases.
Lower Cretaceous (Aptian‐Albian) sandstones of the Ghaggar‐Hakra Formation in the Barmer Basin of northwest Rajasthan, India, have a complex depositional history which is confusing given they are ...quartzose arenites. The heavy mineral grains are very well‐rounded, and the assemblage is dominated by zircon and rutile grains suggesting that the sediments have been recycled multiple times, whilst the presence of staurolite indicates a metapelite provenance component. Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar‐Hakra sandstones are multi‐cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.
Palaeogeographical reconstruction displaying the provenance terrains exposed across the northern Indian Plate in the Lower Cretaceous Epoch able to provide sediment detritus delivered to the Barmer and Cambay basins. Variations in detrital mineralogy across the WIRS and LMIB result from fluvial transport systems sourced from multiple highs and controlled by the rift palaeogeographies. It’s like the failed rifts of the Barmer and Cambay basins form a natural transport barrier that precluded the transport of detritus from the Aravalli Mountain Range across these deep rifts into the more westerly rift basins of the Kachchh and South Indus basins.
The self-assembly and adsorption of the surfactants cetyltrimethylammonium bromide (CTAB) and didodecyldimethylammonium bromide (DDAB) at the muscovite mica-water interface are studied using ...molecular-dynamics simulations. Adsorption takes place by an ion-exchange mechanism, in which K
+
ions are replaced by the organic alkylammonium cations from the solution. Simulations are performed with and without the surface K
+
ions, with pure water, and with the surfactants in aqueous solution. CTAB and DDAB form micellar structures in bulk solution, and in the absence of the surface K
+
ions, they quickly adsorb and form bilayer structures. The bilayer ordering of CTAB is not perfect, and there is a competition with the formation of cylindrical micelles. DDAB, on the other hand, forms a well-ordered bilayer structure, with the innermost layer showing strong orientational ordering, and the outermost layer being more disordered. The simulations with pure water highlight the molecular ordering and strong electrostatic interactions with the mica-surface atoms. Using simulated scattering length density profiles, the results are compared directly and critically with existing neutron reflectivity measurements. The simulation results are generally consistent with experiments, and yield new insights on the molecular-scale ordering at the mica-water interface.
Molecular-dynamics simulations are used to explore bilayers formed by simple ionic surfactants at the mica-water interface, and to shed light on experimental observations.
Ancient dryland terminal fluvial systems are often recognized within the rock record for having a progressive downstream decrease in the size and amalgamation of channel elements and systematic ...downstream increase in sheet and overbank elements, alongside the downstream decrease in grain size that is displayed by most fluvial systems. The spatial distribution and downstream trends displayed by the fluvial sediments of the Lower Jurassic Kayenta Formation of south‐western USA, have been examined quantitatively. The results indicate many trends that are similar to those of a dryland terminal fluvial system, including; a lack of confinement of the fluvial system, a downstream decrease in channel and sheet element amalgamation and width‐to‐thickness ratios, a downstream decrease in grain size, albeit very small, and an increase in the percentage of overbank elements downstream. However, the study highlights several downstream relationships that are atypical. While some of these relationships may be the result of external factors inherent in this study, others, including the thicknesses of channel‐fill and sheet elements that display no significant relationships to distance downstream, and channel‐fill elements that display no significant variation in average grain size with distance downstream, may be a consequence of fluvial interaction with a competing and coeval aeolian system. This work demonstrates the inherent complexity in arid dryland fluvial systems and the downstream architectural and compositional relationships that they depict. Consequently, models for fluvial style may provide only a first‐order approximation for downstream trends in dryland systems, because the controlling factors upon these systems are inherently difficult to unravel, and the sedimentary detail is strongly dependent upon external setting and internal complexity. Consequently, a generalized model may not always be applicable to these systems.
Background. In 1999, meningococcal serogroup C conjugate (MCC) vaccines were introduced in the United Kingdom for those under 19 years of age. The impact of this intervention on asymptomatic carriage ...of meningococci was investigated to establish whether serogroup replacement or protection by herd immunity occurred. Methods. Multicenter surveys of carriage were conducted during vaccine introduction and on 2 successive years, resulting in a total of 48,309 samples, from which 8599 meningococci were isolated and characterized by genotyping and phenotyping. Results. A reduction in serogroup C carriage (rate ratio, 0.19) was observed that lasted at least 2 years with no evidence of serogroup replacement. Vaccine efficacy against carriage was 75%, and vaccination had a disproportionate impact on the carriage of sequence type (ST)-11 complex serogroup C meningococci that (rate ratio, 0.06); these meningococci also exhibited high rates of capsule expression. Conclusions. The impact of vaccination with MCC vaccine on the prevalence of carriage of group C meningococci was consistent with herd immunity. The high impact on the carriage of ST-11 complex serogroup C could be attributed to high levels of capsule expression. High vaccine efficacy against disease in young children, who were not protected long-term by the schedule initially used, is attributed to the high vaccine efficacy against carriage in older age groups.
The corrosive breakdown of thin iron films supported on silicon substrates under a number of conditions is presentedin particular to understand better how iron, and hence ferritic steel, behaves in ...a salty water environment. A combination of X-ray and neutron reflectometry was used to monitor the structures of both metal and oxide surface layers and also organic corrosion inhibitors adsorbed at the iron/aqueous interface. A range of behavior in seawater was observed, including complete dissolution and void formation under the metal surface. Importantly, two simple treatmentsUV/ozone or soaking in ultrapure waterwere found to significantly protect the iron surface for considerable lengths of time, although evidence of pitting corrosion began after around 10 days. The underlying causes of the efficacies of these treatments were further investigated using X-ray photoelectron spectroscopy. In addition, three potential corrosion inhibitors were investigated: (i) dodecyltrimethylammonium bromide (DTAB) demonstrated no ability to protect the surface; (ii) sodium dodecyl sulfate (SDS) appeared to accelerate corrosion; and (iii) bis(2-ethylhexyl)phosphate showed an impressive level of protection (the neutron reflectometry results indicated a thick diffuse layer of surfactant of 23% surface coverage). These findings have been interpreted in terms of preferential inhibitor adsorption at cathodic and anodic surface sites (depending on the nature of the inhibitor).
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