Acoustic suppression of the coffee-ring effect

We study the influence of acoustic fields on the evaporative self-assembly of solute particles suspended inside sessile droplets of complex fluids. The self-assembly process often results in an undesirable ring-like heterogeneous residue, a phenomenon known as the coffee-ring effect. Here we show that this ring-like self-assembly can be controlled acoustically to form homogeneous disc-like or concentrated spot-like residues. The principle of our method lies in the formation of dynamic patterns of particles in acoustically excited droplets, which inhibits the evaporation-driven convective transport of particles towards the contact line. We elucidate the mechanisms of this pattern formation and also obtain conditions for the suppression of the coffee-ring effect. Our results provide a more general solution to suppress the coffee-ring effect without any physiochemical modification of the fluids, the particles or the surface, thus potentially useful in a broad range of industrial and analytical applications that require homogenous solute depositions

Simplicial gauge theory on spacetime

We define a discrete gauge-invariant Yang-Mills-Higgs action on spacetime simplicial meshes. The formulation is a generalization of classical lattice gauge theory, and we prove consistency of the action in the sense of approximation theory. In addition, we perform numerical tests of convergence towards exact continuum results for several choices of gauge fields in pure gauge theory.Comment: 18 pages, 2 figure

The role of reinvestment in performance of simulated laparoscopic surgery under time pressure

Free Communications: Verbal and Poster - Motor Learning and ControlOBJECTIVE: To examine the impact of ‘reinvestment’ on laparoscopic performance under a common intra-operative stressor, time pressure. Background Study of the breakdown of performance under stress has been gaining momentum in the motor skill learning domain as well as domains like aviation and anesthesia, but this has not been the case in the domain of surgery until recently. Research on intra-operative stressors has focused on external factors without considering individual differences in the ability to cope with stress. One individual difference that is implicated in adverse effects of stress on performance is ‘reinvestment’, the propensity for conscious monitoring and control of movements. METHODS: Thirty-one medical students were divided into high and low reinvestment groups based on their scores on the Movement Specific Reinvestment Scale. Participants were first trained to proficiency on a peg transfer task and then tested on the same task in a control and time pressure condition. In the control condition, participants were simply asked to do their best, as they had in training. In the time pressure condition, participants were informed that operating surgeons sometimes are required to perform under time constraints and they should try to complete the task faster than their best time in training (of which they were informed).Outcome measures included generic performance and process measures. Stress levels were assessed using heart rate and the State Trait Anxiety Inventory (STAI). RESULTS: High and low reinvesters demonstrated increased anxiety levels from control to time pressure conditions as indicated by their STAI scores, although no differences in heart rate were found. Low reinvesters performed significantly faster when under time pressure, whereas high reinvesters showed no change in performance times. Low reinvesters tended to display greater performance efficiency (shorter path lengths, fewer hand movements) than high reinvesters. Conclusion Trained medical students with a high individual propensity to consciously monitor and control their movements (high reinvesters) displayed less capability (than low reinvesters) to meet the demands imposed by time pressure during a laparoscopic task. The finding implies that the propensity for reinvestment may have a moderating effect on laparoscopic performance under time pressure.published_or_final_versionThe 2012 Conference of the North American Society for the Psychology of Sport and Physical Activity (NASPSPA 2012), Honolulu, HI., 7-9 June 2012. In Journal of Sport and Exercise Psychology, 2012, v. 34 suppl., p. S10

Examining Movement-Specific Reinvestment and Performance in Demanding Contexts.

Two experiments examined the roles of the dimensions of movement-specific reinvestment (movement self-consciousness and conscious motor processing) on performance under demanding conditions. In Experiment 1, novice golfers practiced a golf putting task and were tested under low- and high-anxiety conditions. Conscious motor processing was not associated with putting proficiency or movement variability; however, movement self-consciousness was positively associated with putting proficiency and appeared to be negatively associated with variability of impact velocity in low-anxiety conditions, but not in high-anxiety conditions. Increased anxiety and effort possibly left few attention resources for movement self-consciousness under high anxiety. In Experiment 2, participants performed a quiet standing task in single- and dual-task conditions. Movement self-consciousness was positively associated with performance when attention demands were low (single task) but not when attention demands were high (dual task). The findings provide insight into the differential influence of the two dimensions of movement-specific reinvestment under demanding conditions

Assimilation of healthy and indulgent impressions from labelling influences fullness but not intake or sensory experience

Background: Recent evidence suggests that products believed to be healthy may be over-consumed relative to believed indulgent or highly caloric products. The extent to which these effects relate to expectations from labelling, oral experience or assimilation of expectations is unclear. Over two experiments, we tested the hypotheses that healthy and indulgent information could be assimilated by oral experience of beverages and influence sensory evaluation, expected satiety, satiation and subsequent appetite. Additionally, we explored how expectation-experience congruency influenced these factors. Results: Results supported some assimilation of healthiness and indulgent ratings—study 1 showed that indulgent ratings enhanced by the indulgent label persisted post-tasting, and this resulted in increased fullness ratings. In study 2, congruency of healthy labels and oral experience promoted enhanced healthiness ratings. These healthiness and indulgent beliefs did not influence sensory analysis or intake—these were dictated by the products themselves. Healthy labels, but not experience, were associated with decreased expected satiety. Conclusions: Overall labels generated expectations, and some assimilation where there were congruencies between expectation and experience, but oral experience tended to override initial expectations to determine ultimate sensory evaluations and intake. Familiarity with the sensory properties of the test beverages may have resulted in the use of prior knowledge, rather than the label information, to guide evaluations and behaviour

Measuring intestinal fluid transport in vitro: Gravimetric method versus non-absorbable marker

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The gut sac is a long-standing, widely used in vitro preparation for studying solute and water transport, and calculation of these fluxes requires an accurate assessment of volume. This is commonly determined gravimetrically by measuring the change in mass over time. While convenient this likely under-estimates actual net water flux (Jv) due to tissue edema. We evaluated whether the popular in vivo volume marker [(14)C]-PEG 4000, offers a more representative measure of Jvin vitro. We directly compared these two methods in five teleost species (toadfish, flounder, rainbow trout, killifish and tilapia). Net fluid absorption by the toadfish intestine based on PEG was significantly higher, by almost 4-fold, compared to gravimetric measurements, compatible with the latter under-estimating Jv. Despite this, PEG proved inconsistent for all of the other species frequently resulting in calculation of net secretion, in contrast to absorption seen gravimetrically. Such poor parallelism could not be explained by the absorption of [(14)C]-PEG (typically <1%). We identified a number of factors impacting the effectiveness of PEG. One was adsorption to the surface of sample tubes. While it was possible to circumvent this using unlabelled PEG 4000, this had a deleterious effect on PEG-based Jv. We also found sequestration of PEG within the intestinal mucus. In conclusion, the short-comings associated with the accurate representation of Jv by gut sac preparations are not overcome by [(14)C]-PEG. The gravimetric method therefore remains the most reliable measure of Jv and we urge caution in the use of PEG as a volume marker.We are grateful to Ian and Tony McClure, the local fishermen of Flookburgh, Cumbria (U.K.) for collecting the flounder used in this study, and to Jan Shears for assistance with fish husbandry at Exeter (U.K.). We thank Ray Hurley and Debbie Fretz in Miami (U.S.A.) for supplying the toadfish. This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) grants BBS/S/A/2004/11078 and BB/F009364/1 to R.W.W., and National Science Foundation (NSF) grants IAB0743903 and 1146695 to M.G

Accounting for female space sharing in St. Kilda Soay sheep (Ovis aries) results in little change in heritability estimates

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.When estimating heritability in free-living populations, it is common practice to account for common environment effects, because of their potential to generate phenotypic covariance among relatives thereby biasing heritability estimates. In quantitative genetic studies of natural populations, however, philopatry, which results in relatives being clustered in space, is rarely accounted for. The two studies to have done so suggest absolute declines in heritability estimates of up to 43% when accounting for space sharing by relatives. However, due to methodological limitations these estimates may not be representative. We used data from the St. Kilda Soay sheep population to estimate heritabilities with and without accounting for space sharing for five traits for which there is evidence for additive genetic variance (birth weight, birth date, lamb August weight, and female post mortem jaw and metacarpal length). We accounted for space sharing by related females by separately incorporating spatial autocorrelation, and a home range similarity matrix. Although these terms accounted for up to 17% of the variance in these traits, heritability estimates were only reduced by up to 7%. Our results suggest that the bias caused by not accounting for space sharing may be lower than previously thought. This suggests that philopatry does not inevitably lead to a large bias if space sharing by relatives is not accounted for. We hope our work stimulates researchers to model shared space when relatives in their study population share space, as doing so will enable us to better understand when bias may be of particular concern.The Soay Sheep Project is supported by grants from the UK Natural Environment Research Council, whilst CER is supported by a BBSRC PhD studentship

Similarity solutions for unsteady shear-stress-driven flow of Newtonian and power-law fluids : slender rivulets and dry patches

Unsteady flow of a thin film of a Newtonian fluid or a non-Newtonian power-law fluid with power-law index N driven by a constant shear stress applied at the free surface, on a plane inclined at an angle α to the horizontal, is considered. Unsteady similarity solutions representing flow of slender rivulets and flow around slender dry patches are obtained. Specifically, solutions are obtained for converging sessile rivulets (0 < α < π/2) and converging dry patches in a pendent film (π/2 < α < π), as well as for diverging pendent rivulets and diverging dry patches in a sessile film. These solutions predict that at any time t, the rivulet and dry patch widen or narrow according to |x|3/2, and the film thickens or thins according to |x|, where x denotes distance down the plane, and that at any station x, the rivulet and dry patch widen or narrow like |t|−1, and the film thickens or thins like |t|−1, independent of N