Influence of preparation method on the performance of vanadia-niobia catalysts for the oxidative dehydrogenation of propane

The influence of various preparation methods on the performance of V-Nb-0 catalysts has been investigated. It was found that the activity and selectivity of a vanadium site depend on the nature of the neighbouring atoms. Vanadium neighbours provide activity, while niobium neighbours provide selectivity. Careful preparation of these catalysts ensures a homogeneous distribution and good mixing of the vanadium and niobium. It was also found that the vanadium becomes mobile upon reduction and this results in better distribution of vanadium in used catalysts

Framing Egypt : Roman literary perceptions of Egypt from Cicero to Juvenal

This is a comprehensive study of Roman literary references to Egypt without preference for one particular period, author or subject, in contrast to most previous scholarship. In doing so, it shows that these references vary greatly, are context-dependent, and cannot be rightly understood when interpreted only within the normative and fixated frameworks of negative perceptions of contemporary Egypt or positive perceptions of Egypt’s antiquity. Moreover, this study suggests that approaching Roman literary references from the notion of Roman self-representationis useful for understanding and explaining their multifarious and sometimes contradictory messages. This observation does not imply that every reference to Egypt is therefore ‘Roman’. On the contrary, Egypt was occasionally framed as the Other. Yet the omnipresence of Egypt in Roman literature is of major importance when the Roman identity is at stake. Egypt, then, is neither only the Other, nor only the Self, but always a polyvalent notion in terms of identity-making.Classical & Mediterranean Archaeolog

Lattice distortions in coccolith calcite crystals originate from occlusion of biomacromolecules

During biomineralization, organisms control the formation and morphology of a mineral using biomacromolecules. The biomacromolecules that most strongly interact with the growing crystals frequently get occluded within. Such an observation has been recently obtained for the calcium carbonate producing coccolithophore species Pleurochrysis carterae. Coccolithophores are unicellular algae that produce calcified scales built from complex-shaped calcite crystals, termed coccoliths. It is unclear how widespread the phenomenon of biomacromolecular occlusion within calcite crystals is in calcifying haptophytes such as coccolithophores. Here, the coccoliths of biological replicates of the bloom forming Emiliania huxleyi are compared with that of Pleurochrysis carterae, two species with different coccolith morphologies and crystal growth mechanisms. From high-resolution synchrotron X-ray diffraction, changes in the lattice parameters of coccolith calcite, after heating to 450 °C, are observed and associated with macrostrain originating from occluded biomacromolecules. We propose a mechanism governing the biomacromolecules’ interaction with the growing coccolith crystals and their likely origin

Mapping of individual dislocations with dark-field X-ray microscopy

This article presents an X-ray microscopy approach for mapping deeply embedded dislocations in three dimensions using a monochromatic beam with a low divergence. Magnified images are acquired by inserting an X-ray objective lens in the diffracted beam. The strain fields close to the core of dislocations give rise to scattering at angles where weak beam conditions are obtained. Analytical expressions are derived for the image contrast. While the use of the objective implies an integration over two directions in reciprocal space, scanning an aperture in the back focal plane of the microscope allows a reciprocal-space resolution of DQ/Q < 5 x10^-5 in all directions, ultimately enabling highprecision mapping of lattice strain and tilt. The approach is demonstrated on three types of samples: a multi-scale study of a large diamond crystal in transmission, magnified section topography on a 140 mm-thick SrTiO3 sample and a reflection study of misfit dislocations in a 120 nm-thick BiFeO3 film epitaxially grown on a thick substrate. With optimal contrast, the half-widths at half-maximum of the dislocation lines are 200 nm