Thrifty swimming with shear-thinning

Microscale propulsion is integral to numerous biomedical systems, for example biofilm formation and human reproduction, where the surrounding fluids comprise suspensions of polymers. These polymers endow the fluid with non-Newtonian rheological properties, such as shear-thinning and viscoelasticity. Thus, the complex dynamics of non-Newtonian fluids presents numerous modelling challenges, strongly motivating experimental study. Here, we demonstrate that failing to account for "out-of-plane" effects when analysing experimental data of undulatory swimming through a shear-thinning fluid results in a significant overestimate of fluid viscosity around the model swimmer C. elegans. This miscalculation of viscosity corresponds with an overestimate of the power the swimmer expends, a key biophysical quantity important for understanding the internal mechanics of the swimmer. As experimental flow tracking techniques improve, accurate experimental estimates of power consumption using this technique will arise in similar undulatory systems, such as the planar beating of human sperm through cervical mucus, will be required to probe the interaction between internal power generation, fluid rheology, and the resulting waveform

Suppression of backscattered diffraction from sub-wavelength ‘moth-eye’ arrays

The eyes and wings of some species of moth are covered with arrays of nanoscale features that dramatically reduce reflection of light. There have been multiple examples where this approach has been adapted for use in antireflection and antiglare technologies with the fabrication of artificial moth-eye surfaces. In this work, the suppression of iridescence caused by the diffraction of light from such artificial regular moth-eye arrays at high angles of incidence is achieved with the use of a new tiled domain design, inspired by the arrangement of features on natural moth-eye surfaces. This bio-mimetic pillar architecture contains high optical rotational symmetry and can achieve high levels of diffraction order power reduction. For example, a tiled design fabricated in silicon and consisting of domains with 9 different orientations of the traditional hexagonal array exhibited a ~96% reduction in the intensity of the ?1 diffraction order. It is suggested natural moth-eye surfaces have evolved a tiled domain structure as it confers efficient antireflection whilst avoiding problems with high angle diffraction. This combination of antireflection and stealth properties increases chances of survival by reducing the risk of the insect being spotted by a predator. Furthermore, the tiled domain design could lead to more effective artificial moth-eye arrays for antiglare and stealth applications

Gaia DR2 Distances and Peculiar Velocities for Galactic Black Hole Transients

We report on a first census of Galactic black hole X-ray binary (BHXRB) properties with the second data release (DR2) of {\em Gaia}, focusing on dynamically confirmed and strong candidate black hole transients. DR2 provides five-parameter astrometric solutions including position, parallax and proper motion for 11 of a sample of 24 systems. Distance estimates are tested with parallax inversion as well as Bayesian inference. We derive an empirically motivated characteristic scale length of $L$=2.17$\pm$0.12 kpc for this BHXRB population to infer distances based upon an exponentially decreasing space density prior. Geometric DR2 parallaxes provide new, independent distance estimates, but the faintness of this population in quiescence results in relatively large fractional distance uncertainties. Despite this, DR2 estimates generally agree with literature distances. The most discrepant case is BW Cir, for which detailed studies of the donor star have suggested a distant location at >~25 kpc. A large DR2 measured parallax and relatively high proper motion instead prefer significantly smaller distances, suggesting that the source may instead be amongst the nearest of XRBs. However, both distances create problems for interpretation of the source, and follow-up data are required to resolve its true nature. DR2 also provides a first distance estimate to one source, MAXI J1820+070, and novel proper motion estimates for 7 sources. Peculiar velocities relative to Galactic rotation exceed $\sim$ 50 km s$^{-1}$ for the bulk of the sample, with a median system kinetic energy of peculiar motion of $\sim$ 5 $\times$ 10$^{47}$ erg. BW Cir could be a new high-velocity BHXRB if its astrometry is confirmed. A putative anti-correlation between peculiar velocity and black hole mass is found, as expected in mass-dependent BH kick formation channels, but this trend remains weak in the DR2 data.Comment: MNRAS in pres

Professional capacity and organizational change as measures of educational effectiveness: assessing the impact of postgraduate education in development policy and management

We tend to measure educational performance by students' attainment in coursework or examinations. In the case of professional education, the impact of the educational programme on the students' own capacities to enhance their work practices, and the wider organizational effects of the students' education and training, are also key 'products' of the educational process. This is particularly important with education for Development Policy and Management (DPAM), which is directly concerned with capacity-building. This article adopts a work-related approach to educational effectiveness and examines four professional programmes in DPAM--three in Southern Africa and one in the UK. Through the analysis of the results of surveys and case studies, the article demonstrates how a positive learning experience is related to the application of learning at work. However the conditions for applying learning also depend strongly on organizational context, as do the wider organizational impacts of learning. The article presents a broad approach to assessing educational effectiveness in professional programmes which incorporate these factors

Some Observations on Regeneration in Dileptus Anser

One of the most interesting capacities of protozoans is their ability to replace lost parts following injury. Although they are structurally the equivalent of cells they are functional organisms, and a study of their behavior makes it possible to bring together concepts usually applied in the cellular field with those applied in the analysis of whole organisms. The same factors that operate to evoke a particular form in the whole organism must act in a small regenerating piece of a protozoan. Whether these factors are nuclear genes or protoplasmic organization, they act rapidly in the regenerating animal, regulating the form of the piece. Unlike the metazoan material, the morphogenetic activities are not a matter of differential growth rates, but are rather redistribution and reorganization of materials present in the regenerating piece. In this sense the repair of injury inprotozoans more closely resembles cellular differentiation than organogeny