A highly oriented cubic phase formed by lipids under shear

We demonstrate the formation of a macroscopically oriented inverse bicontinuous cubic (QII) lipid phase from a sponge (L3) phase by controlled hydration during shear flow. The L3 phase was the monoolein/ butanediol/water system; the addition of water reduces the butanediol concentration, inducing the formation of a diamond (QIID) cubic phase, which is oriented by the shear flow. The phenomenon was reproduced in both capillary and Couette geometries, indicating that this represents a robust general route for the production of highly aligned bulkQII samples, with applications in nanomaterial templating and protein research

A Predictive Model for Waste Package Terminal Velocity in Deep Borehole Disposal

Summary The aim of this work is to provide insight into the sinking rate of waste packages in Deep Borehole Disposal (DBD). An investigation was performed using simplified, scaled down experiments, analytical modelling and molecular modelling. The experiments systematically varied a range of cylinder parameters to understand their influences upon the sinking rate of the cylinder. Results showed that this sinking velocity varied as a function of cylinder diameter, length and density, with diameter being the predominant factor in dictating the sinking rate. An analytical model was subsequently developed using the experiment data as validation. The model was developed by solving the Navier-Stokes equations for the flow within the annular gap, in addition to characterising pressures applied at the front of the cylinder. Results showed good levels of accuracy for low values of clearance, although velocity was increasingly over predicted as clearance increased. Molecular dynamics simulations were used as a method of gaining pseudoexperiment data and further insight into the fluid flow. Sinking disc simulations provided several correlating results with experiments; confirming that sinking velocity decreases linearly with diameter at sinker-container ratios greater than 0.6, and that density appears to increase sinking velocity towards a plateau. Stationary disc simulations illustrated that highly turbulent flow regimes occurred at the wake of objects in confined boundary systems. Several of these flow regimes occurred at significantly lesser streaming velocity for finite boundary systems as opposed to infinite boundary systems. This shows the importance of accounting for turbulence in finite boundary systems, and provides a logical path for the future development of a predictive sinking velocity model

Assessing final-year practical work through group projects

The final year project is a valuable research experience for undergraduates and can be one of the most rewarding aspects of their degree course. With increasing student numbers it is becoming more difficult to supervise students effectively, as truly independent enquiry-based working requires significant supervision, time and resource. To address this, the Department of Chemistry at the University of Reading has recently explored the use of group projects for final year practical work. Students work in teams of 3 to 5 and are presented with a research problem to investigate. These are genuine problems where the answer is unknown and the work open-ended. The students must work together to investigate the problem, dividing the work and sharing results in a manner that more closely resembles project working outside of academia. The students’ output is assessed through a variety of means including a group presentation and report. The projects were successful, with all students completing the work to a satisfactory level and developing strong team-working skills. This paper will outline some of the issues faced in the first year of delivery, and the steps taken to alleviate them

Kinetics and mechanism of the interconversion of inverse bicontinuous cubic mesophases

This paper describes time-resolved x-ray diffraction data monitoring the transformation of one inverse bicontinuous cubic mesophase into another, in a hydrated lipid system. The first section of the paper describes a mechanism for the transformation that conserves the topology of the bilayer, based on the work of Charvolin and Sadoc, Fogden and Hyde, and Benedicto and O'Brien in this area. We show a pictorial representation of this mechanism, in terms of both the water channels and the lipid bilayer. The second section describes the experimental results obtained. The system under investigation was 2:1 lauric acid: dilauroylphosphatidylcholine at a hydration of 50% water by weight. A pressure-jump was used to induce a phase transition from the gyroid (Q(II)(G)) to the diamond (Q(II)(D)) bicontinuous cubic mesophase, which was monitored by time-resolved x-ray diffraction. The lattice parameter of both mesophases was found to decrease slightly throughout the transformation, but at the stage where the Q(II)(D) phase first appeared, the ratio of lattice parameters of the two phases was found to be approximately constant for all pressure-jump experiments. The value is consistent with a topology-preserving mechanism. However, the polydomain nature of our sample prevents us from confirming that the specific pathway is that described in the first section of the paper. Our data also reveal signals from two different intermediate structures, one of which we have identified as the inverse hexagonal (H-II) mesophase. We suggest that it plays a role in the transfer of water during the transformation. The rate of the phase transition was found to increase with both temperature and pressure-jump amplitude, and its time scale varied from the order of seconds to minutes, depending on the conditions employed

The global spatial distribution of economic activity:nature, history and the role of trade

We study the distribution of economic activity, as proxied by lights at night, across 250,000 grid cells of average area 560 square kilometres. We first document that nearly half of the variation can be explained by a parsimonious set of physical geography attributes. A full set of country indicators only explains a further 10%. When we divide geographic characteristics into two groups, those primarily important for agriculture and those primarily important for trade, we find that the agriculture variables have relatively more explanatory power in countries that developed early and the trade variables have relatively more in countries that developed late, despite the fact that the latter group of countries are far more dependent on agriculture today. We explain this apparent puzzle in a model in which two technological shocks occur, one increasing agricultural productivity and the other decreasing transportation costs, and in which agglomeration economies lead to persistence in urban locations. In countries that developed early, structural transformation due to rising agricultural productivity began at a time when transport costs were still relatively high, so urban agglomerations were localized in agricultural regions. When transport costs fell, these local agglomerations persisted. In late developing countries, transport costs fell well before structural transformation. To exploit urban scale economies, manufacturing agglomerated in relatively few, often coastal, locations. With structural transformation, these initial coastal locations grew, without formation of more cities in the agricultural interior

Determination of orientations of aromatic groups in self-assembled peptide fibrils by polarised Raman spectroscopy

In this paper we describe a novel combination of Raman spectroscopy, isotope editing and X-ray scattering as a powerful approach to give detailed structural information on aromatic side chains in peptide fibrils. The orientation of the tyrosine residues in fibrils of the peptide YTIAALLSPYS with respect to the fibril axis has been determined from a combination of polarised Raman spectroscopy and X-ray diffraction measurements. The Raman intensity of selected tyrosine bands collected at different polarisation geometries is related to the values and orientation of the Raman tensor for those specific vibrations. Using published Raman tensor values we solved the relevant expressions for both of the two tyrosine residues present in this peptide. Ring deuteration in one of the two tyrosine side chains allowed for the calculation to be performed individually for both, by virtue of the isotopic shift that eliminates band overlapping. Sample disorder was taken into account by obtaining the distribution of orientations of the samples from X-ray diffraction experiments. The results provide previously unavailable details about the molecular conformation of this peptide, and demonstrate the value of this approach for the study of amyloid fibrils