Dynamic measurements and simulations of airborne picolitre-droplet coalescence in holographic optical tweezers

We report studies of the coalescence of pairs of picolitre aerosol droplets manipulated with holographic optical tweezers, probing the shape relaxation dynamics following coalescence by simultaneously monitoring the intensity of elastic backscattered light (EBL) from the trapping laser beam (time resolution on the order of 100 ns) while recording high frame rate camera images (time resolution <10 µs). The goals of this work are to: resolve the dynamics of droplet coalescence in holographic optical traps; assign the origin of key features in the time-dependent EBL intensity; and validate the use of the EBL alone to precisely determine droplet surface tension and viscosity. For low viscosity droplets, two sequential processes are evident: binary coalescence first results from overlap of the optical traps on the timescale of microseconds followed by recapture of the composite droplet in an optical trap on the timescale of milliseconds. As droplet viscosity increases, the relaxation in droplet shape eventually occurs on the same timescale as recapture, resulting in a convoluted evolution of the EBL intensity that inhibits quantitative determination of the relaxation timescale. Droplet coalescence was simulated using a computational framework to validate both experimental approaches. The results indicate that time-dependent monitoring of droplet shape from the EBL potential of high frame rate imaging to examine the coalescence of dissimilar viscosity droplets is discussed

Witness: The Modern Writer as Witness

Editor\u27s Note [Excerpt] Magic can mean many different things, especially for writers. Magic can be an illusion, a sleight of hand designed to trick onlookers into believing the impossible. Or magic can be a supernatural force in a world of harsh reality, a set of beliefs that sits just outside the realms of organized religion and advanced technology. Wizards and demons, Las Vegas entertainers and houngans --they all practice a kind of sorcery. For poets and prose writers, though, magic affords an opportunity for us to stretch the limitations of the physical world in search of new themes, settings, and characters. Magic is a door we eagerly walk through to reach new lands. We at Witness have thoroughly enjoyed the process of selecting the themed works we have collected here, mainly because the idea of enchantment is inspiring. There is the possibility of positive charms; there is a chance for dark witchery. And sometimes the spell cast by a character is nebulous, difficult to categorize. It’s arguable that we cherish these incantations the most, since they leave us in a state of wonderment bordering on disorientation. Yes, magic can also leave us bewildered and thankful for the bewilderment.https://digitalscholarship.unlv.edu/witness/1001/thumbnail.jp

The nature of culture : an eight-grade model for the evolution and expansion of cultural capacities in hominins and other animals

Tracing the evolution of human culture through time is arguably one of the most controversial and complex scholarly endeavors, and a broad evolutionary analysis of how symbolic, linguistic, and cultural capacities emerged and developed in our species is lacking. Here we present a model that, in broad terms, aims to explain the evolution and portray the expansion of human cultural capacities (the EECC model), that can be used as a point of departure for further multidisciplinary discussion and more detailed investigation. The EECC model is designed to be flexible, and can be refined to accommodate future archaeological

Oxygen Vacancy Formation and Water Adsorption on Reduced AnO2 {111}, {110} and {100} Surfaces (An = U, Pu); A Computational Study

The substoichiometric {111}, {110} and {100} surfaces of UO2 and PuO2 are studied computationally using two distinct yet related approaches based on density functional theory; the periodic electrostatic embedded cluster method (PEECM) and Hubbard-corrected periodic boundary condition DFT. First and second layer oxygen vacancy formation energies and geometries are presented and discussed; the energies are found to be substantially larger for UO2 vs PuO2, a result traced to the substantially more positive An(IV)/An(III) reduction potential for Pu, and hence relative ease of Pu(III) formation. For {110} and {100}, the significantly more stable dissociative water adsorption seen previously for stoichiometric surfaces [J. Nucl. Mater. 2016, 482, 124–134; J. Phys. Chem. C 2017, 121, 1675-1682] is also found for the defect surfaces. By contrast, vacancy creation substantially changes the most stable mode of water adsorption on the {111} surface, such that the almost degenerate molecular and dissociative adsorptions on the pristine surface are replaced by a strong preference for dissociative adsorption on the substoichiometric surface. The implications of this result for the formation of H2 are discussed. The generally very good agreement between the data from the embedded cluster and periodic DFT approaches provides additional confidence in the reliability of the results and conclusions

Centre-level variation in dental treatment and oral health and individual- and area-level predictors of oral health in 5-year-old children with non-syndromic unilateral cleft lip and palate:The Cleft Care UK study. Part 3

Objectives: To explore centre-level variation in fluoride treatment and oral health outcomes and to examine the association of individual- and area-level risk factors with dental decay in Cleft Care UK (CCUK). Setting: Two hundred and sixty-eight 5-year-old British children with non-syndromic unilateral cleft lip and palate (UCLP). Materials and Methods: Data on caries and developmental defects of enamel (DDE) were collected. The child's history of fluoride ingestion and postcode was used to assess exposure to fluoridated water. Centre-level variation in fluoride exposure and caries was examined using hierarchical regression. Poisson regression was used to estimate the association between individual- and area-level fluoride exposures and outcome. Results: Children had high levels of caries, rampant caries and DDE. There was no evidence of variation between centres in the number of children with caries or rampant decay. There was evidence of variation in prescription of fluoride tablets and varnish and the type of toothpaste used. Area level of deprivation was associated with a higher risk of dental caries—risk ratio (RR) in the lowest quartile versus the rest was 1.43 (95% CI 1.13 to 1.81). Use of fluoride tablets and varnish was associated with higher risk of caries—RR 1.73 (95% CI 1.29 to 2.32) and RR 1.33 (95% CI 1.04 to 1.70), respectively, adjusted for age, sex and deprivation. Conclusion: The association with use of fluoride tablets and varnish probably reflects reverse causality but indicates the need for early preventative interventions in children with UCLP

Body Segment Differences in Surface Area, Skin Temperature and 3D Displacement and the Estimation of Heat Balance during Locomotion in Hominins

The conventional method of estimating heat balance during locomotion in humans and other hominins treats the body as an undifferentiated mass. This is problematic because the segments of the body differ with respect to several variables that can affect thermoregulation. Here, we report a study that investigated the impact on heat balance during locomotion of inter-segment differences in three of these variables: surface area, skin temperature and rate of movement. The approach adopted in the study was to generate heat balance estimates with the conventional method and then compare them with heat balance estimates generated with a method that takes into account inter-segment differences in surface area, skin temperature and rate of movement. We reasoned that, if the hypothesis that inter-segment differences in surface area, skin temperature and rate of movement affect heat balance during locomotion is correct, the estimates yielded by the two methods should be statistically significantly different. Anthropometric data were collected on seven adult male volunteers. The volunteers then walked on a treadmill at 1.2 m/s while 3D motion capture cameras recorded their movements. Next, the conventional and segmented methods were used to estimate the volunteers' heat balance while walking in four ambient temperatures. Lastly, the estimates produced with the two methods were compared with the paired t-test. The estimates of heat balance during locomotion yielded by the two methods are significantly different. Those yielded by the segmented method are significantly lower than those produced by the conventional method. Accordingly, the study supports the hypothesis that inter-segment differences in surface area, skin temperature and rate of movement impact heat balance during locomotion. This has important implications not only for current understanding of heat balance during locomotion in hominins but also for how future research on this topic should be approached