ALBERT

Description: McMurdo Station, Antarctica, is a US Federal research facility operated year-round by the National Science Foundation (NSF). Its primary mission is to support scientific research, but it also provides logistical air and ground support for South Pole Station, seasonal field sites and nearby stations operated by other countries. It is the largest station in Antarctica, supporting up to 1,200 people. While McMurdo Station has a long scientific legacy, the facility also has an interesting architectural and engineering history that spans 60 years and has its antecedents in the ‘heroic age’ of exploration (1898–1916) and the Little America expeditions (1929–1958). Here, I describe the history of the built environment of McMurdo Station to clarify how it evolved from a temporary air station in the late 1950s to its current role as the flagship research facility of the US Antarctic Research Program (USAP). This historical review may provide insights that are useful as the station continues to transform and evolve, allowing it to continue its scientific mission into the 21st century.

Description: A general constitutive model is constructed and validated for highly concentrated monodisperse emulsions of deformable drops with insoluble surfactant through long-time, large-scale and high-resolution multidrop simulations. There is the same amount of surfactant on each drop, and the linear model is assumed for the surface tension versus the surfactant concentration. The surfactant surface transport is coupled to multidrop hydrodynamics through the convective-diffusive equation and the interfacial stress balance. Only the limit of small surfactant diffusivities is addressed, when this parameter does not affect the rheology. An Oldroyd constitutive equation is postulated, with five variable coefficients depending on one instantaneous flow invariant (chosen as the drop-phase contribution to the dissipation rate). These coefficients are found by fitting the model to five precise rheological functions from two steady base flows at arbitrary deformation rates. One base flow is planar extension (PE) , the other one is planar mixed flow (PM) ( , , 0) with . A small but finite (a precise choice in the range is unimportant) provides a necessarily perturbation to exclude severe ergodic difficulties and abnormal, kinked behaviour inherent in simple shear for high drop volume fractions , especially at small capillary numbers and small drop-to-medium viscosity ratios . The database rheological functions are obtained for , and surfactant elasticities (based on the equilibrium surfactant concentration) from long-time simulations by a multipole-accelerated boundary-integral code with drops in a periodic cell and 2000-4000 boundary elements per drop. The code is an extension from Zinchenko & Davis (J. Fluid Mech., vol. 779, 2015, pp. 197-244) to account for surfactant transport and Marangoni stresses. Massive drop cusping or (sometimes) drop break-up limit the range of from above in the base flows, but there is no substantial lower limitation owing to the absence of phase transition difficulties. At small , even minimal surface contamination may have a strong effect on the rheology. The simulations remain accurate for quite strong drop interactions, when the PE emulsion viscosity is nine times that for the carrier fluid. The model validation against a steady PM flow with a different shows a very good agreement for various , and . In the three PE and PM time-dependent flow tests, the quasi-steady approximation is found to predict stresses poorly. In contrast, the combination of the steady-state results for PE and PM used in the present method to generate the Oldroyd parameters gives a model with much better predictions for these time-dependent flows. © 2017 Cambridge University Press.

Description: Rectilinear collisions of three wetted spheres are considered under conditions of high capillary numbers, for which viscous lubrication forces dominate over capillary forces. The viscous forces resist the relative motion, as characterized by the Stokes number (a dimensionless ratio of particle inertia and viscous forces). At high Stokes numbers, the particles penetrate the fluid layers between them with sufficient inertia that they collide and rebound. Both simultaneous and sequential collisions are simulated, and various outcomes are demonstrated: full agglomeration of the three spheres at low Stokes numbers, full separation or Newton's cradle at large Stokes numbers and even reverse Newton's cradle at intermediate Stokes numbers when there is a thicker combined fluid layer between the two target spheres than between the striker sphere and the first target sphere. When there is an initial air gap between the two target spheres, even more exotic outcomes are predicted, such as full separation after the initial collisions followed by full agglomeration or reverse Newton's cradle (intermediate Stokes numbers) or Newton's cradle (large Stokes numbers) after the subsequent collisions when the striker sphere catches back up to the target spheres. The approach and findings of this work are expected to provide input and guidance to future work on discrete-element modelling of collisions of many wet particles. © 2019 Cambridge University Press.

Description: The current paper presents an experimental study of the energy budget of a two-dimensional internal wave attractor in a trapezoidal domain filled with uniformly stratified fluid. The injected energy flux and the dissipation rate are simultaneously measured from a two-dimensional, two-component, experimental velocity field. The pressure perturbation field needed to quantify the injected energy is determined from the linear inviscid theory. The dissipation rate in the bulk of the domain is directly computed from the measurements, while the energy sink occurring in the boundary layers is estimated using the theoretical expression for the velocity field in the boundary layers, derived recently by Beckebanze et al. (J. Fluid Mech., vol. 841, 2018, pp. 614-635). In the linear regime, we show that the energy budget is closed, in the steady state and also in the transient regime, by taking into account the bulk dissipation and, more importantly, the dissipation in the boundary layers, without any adjustable parameters. The dependence of the different sources on the thickness of the experimental set-up is also discussed. In the nonlinear regime, the analysis is extended by estimating the dissipation due to the secondary waves generated by triadic resonant instabilities, showing the importance of the energy transfer from large scales to small scales. The method tested here on internal wave attractors can be generalized straightforwardly to any quasi-two-dimensional stratified flow. © 2019 Cambridge University Press.

Description: We have recently discovered that the implicit assumption that N2 D0 for a monolayer suspension in the paper by Wilson & Davis (2002) was an error: the repercussions of this error are corrected below. For dilute systems, we neglected to calculate the second normal stress difference, which is negative. In concentrated systems, the viscosity is rather larger than reported (although the trends remain the same), and the second normal stress difference is negative; but the first normal stress difference N1 is now observed to change sign and become positive for concentrated systems. The behaviour of the viscosity and of N1 are of particular interest in the light of developments in the field since the publication of the original paper. There has been a growth of interest in the influence of roughness on suspension rheology via solid contact and friction, and its role in strong shear thickening. Since our original paper, experiments by Lootens et al. (2005) were able to make the first quantitative measurements of normal stress differences in a jamming suspension by using artificially roughened particles. They found negative N1 at low shear rates far from the jamming transition, but large positive fluctuations of N1 during jamming. Much more recently, Royer, Blair & Hudson (2016) carried out experiments on continuously shear-thickening suspensions; they also found a transition in N1 from negative to positive with increasing volume fraction and shear rate, but in this case without any associated sharp change in the viscosity. This behaviour has also been replicated in simulations by Mari et al. (2015), using a model which needs to incorporate both frictional contact and hydrodynamic forces, but also Brownian motion and a short-range colloidal repulsive force. Equation and figure numbers preceded by the letter C denote corrected versions of the original items; additional equations are numbered with a following letter. In addition to the material changes already mentioned, there was a small typographical error in equation (2.8): (Formula Presented). (Figure Presented). Concentrated systems For concentrated suspensions, there was a coding error corresponding to the assumption of zero second normal stress difference. When corrected, this makes only minor quantitative changes to the viscosity; however, the first normal stress difference N1, which was reported as negative, is now found to be positive for denser suspensions (shown in figure C5). In addition, we report that the second normal stress difference N2 is negative, shown in new figure C5A. © 2017 Cambridge University Press.

Description: The interfacial behaviour of surfactant-laden drops squeezing through tight constrictions in a uniform far-field flow is modelled with respect to capillary number, drop-to-medium viscosity ratio and surfactant contamination. The surfactant is treated as insoluble and non-diffusive, and drop surface tension is related to surfactant concentration by a linear equation of state. The constriction is formed by three solid spheres held rigidly in space. A characteristic aspect of this confined and contaminated multiphase system is the rapid development of steep surfactant-concentration gradients during the onset of drop squeezing. The interplay between two physical effects of surfactant, namely the greater interface deformability due to decreased surface tension and interface immobilization due to Marangoni stresses, results in particularly rich drop-squeezing dynamics. A three-dimensional boundary-integral algorithm is used to describe drop hydrodynamics, and accurate treatment of close squeezing and trapped states is enabled by advanced singularity subtraction techniques. Surfactant transport and hydrodynamics are coupled via the surface convection equation (or convection-diffusion equation, if artificial diffusion is included), the interfacial stress balance and a solid-particle contribution based on the Hebeker representation. For extreme conditions, such as drop-to-medium viscosity ratios significantly less than unity, it is found that upwind-biased methods are the only stable approaches for modelling surfactant transport. Two distinct schemes, upwind finite volume and flow-biased least squares, are found to provide results in close agreement, indicating negligible numerical diffusion. Surfactant transport is enhanced by low drop-to-medium viscosity ratios, at which extremely sharp concentration gradients form during various stages of the squeezing process. The presence of surfactant, even at low degrees of contamination, significantly decreases the critical capillary number for droplet trapping, due to the accumulation of surfactant at the downwind pole of the drop and its subsequent elongation. Increasing the degree of contamination significantly affects surface mobility and further decreases the critical capillary number as well as drop squeezing times, up to a threshold above which the addition of surfactant negligibly affects squeezing dynamics. © 2019 Cambridge University Press.

Description: Paleosols occur in the Driftless Area of southwestern Wisconsin because this area escaped direct Pleistocene glaciation, allowing long-term loess and colluvium accumulation in selected settings. The most complete known depositional sequence at Oil City, Wisconsin, contains eight lithologic units with five paleosols, all with normal remanent magnetism (i.e.,

Description: A small fauna of vertebrates is recorded from the Insect Limestone, Bembridge Marls Member, Bouldnor Formation, late Priabonian, latest Eocene, of the Isle of Wight, UK. The taxa represented are unidentified teleost fishes, lizards including a scincoid, unidentified birds and the theridomyid rodent Isoptychus. The scincoid represents the youngest record of the group in the UK. Of particular note is the taphonomic interpretation based on the preservation of anatomical parts of land-based tetrapods that would have been most likely transported to the site of deposition by wind, namely bird feathers and pieces of shed lizard skin. These comprise the majority of the specimens and suggest that the dominant transport mechanism was wind.

Description: We examine the environmental impacts of a cash transfer program in rural Zambia and investigate whether variation in market access is associated with heterogeneous impacts on natural resource use. We consider households’ use of firewood, charcoal, bushmeat and land for farming, as well as their ownership of non-farm businesses. We find that cash transfers increase the likelihood of charcoal consumption as well as the amount consumed for those living close to paved roads. The transfers also enable households to increase the size of their farms and establish non-farm businesses. These impacts are most pronounced for those living far from paved roads. While remoteness is associated with farm expansion in response to the cash transfer, more education causes those receiving the transfer to decrease the size of their farms. This impact heterogeneity has important implications for sustainable development.