Dynamics of liquid nano-threads : fluctuation-driven instability and rupture

The instability and rupture of nanoscale liquid threads is shown to strongly depend on thermal fluctuations. These fluctuations are naturally occurring within molecular dynamics (MD) simulations and can be incorporated via fluctuating hydrodynamics into a stochastic lubrication equation (SLE). A simple and robust numerical scheme is developed for the SLE that is validated against MD for both the initial (linear) instability and the nonlinear rupture process. Particular attention is paid to the rupture process and its statistics, where the `double-cone’ profile reported by Moseler & Landmann [Science, 2000, 289(5482): 1165-1169] is observed, as well as other distinct profile forms depending on the flow conditions. Comparison to the Eggers’ similarity solution [Physical Review Letters, 2002, 89(8): 084502], a power law of the minimum thread radius against time to rupture, shows agreement only at low surface tension; indicating that surface tension cannot generally be neglected when considering rupture dynamics

Bouncing off the walls : the influence of gas-kinetic and van der Waals effects in drop impact

A model is developed for liquid drop impact on a solid surface that captures the thin film gas flow beneath the drop, even when the film’s thickness is below the mean free path in the gas so that gas kinetic effects (GKE) are important. Simulation results agree with experiments, with the impact speed threshold between bouncing and wetting reproduced to within 5 least 50 mapped and provides experimentally verifiable predictions. There are two principal modes of contact leading to wetting and both are associated with a van der Waals driven instability of the film

Can fundamental movement skill mastery be increased via a six week physical activity intervention to have positive effects on physical activity and physical self-perception?

Previous research has suggested a positive relationship between fundamental movement skills (FMS) mastery and physical activity (PA) level. Research conducted on interventions to improve FMS mastery is equivocal and further research is needed.An intervention group of 82 children (35 boys and 47 girls) and a control group of 83 children (42 boys and 41 girls) were recruited from Years 4 and 5 (mean age ± SD = 8.3 ± 0.4 years) of two schools in Central England. The intervention included a combination of circuits and dancing to music. Pre and post intervention tests were conducted. Tests included: subjective assessment of eight FMS; objective measurement of two FMS; four day pedometer step count recording; height and mass for Body Mass Index (BMI); and the completion of Harter et al.'s (1982) self-perception questionnaire.Following a two (pre to post) by two (intervention and control group) mixed-model ANOVA it was highlighted that the intervention group improved mastery in all eight FMS, and increased both daily steps and physical self-perception.It can be concluded that focussing one Physical Education (PE) lesson per week on the development of FMS has had a positive benefit on FMS, PA level and physical self-perception for the children in this study

On board sampling of the rockfish and lingcod commerical passenger fishing vessel industry in northern and central California, May 1987 to December 1991

From May 1987 to June 1990 and from August to December 1991 Fishery Technicians sampled catches on board 690 Commercial Passenger Fishing Vessel (CPFV) trips targeting rockfish and lingcod from the general port areas of Fort Bragg, Bodega Bay, San Francisco, Monterey, and Morro Bay. Data are presented for species composition by port area, year, and month, for catch-per-unit-effort, mean length, and length frequency of lingcod and the 18 most frequently observed rockfish species, and for trends in fishing effort related to fishing time, depth, and distance from port. Total catch estimates are presented based on unadjusted logbook records, logbook records adjusted by sampling data and compliance rates, and effort data from a marine recreational fishing statistics survey. Average catch of kept fish per angler day was 11.8 and average catch of kept fish per angler hour was 3.7. A trend of an increasing frequency of trips to deep (>40 fm) locations was observed in the Bodega Bay, San Francisco, and Monterey areas from 1988 to 1990-91. No trend was evident relative to trip frequency and distance from port. A total of 74 species was observed caught during the study. Rockfishes comprised 88.5% to 97.9% by number of the observed catch by port area. The five most frequently observed species were chilipepper, blue, yellowtail, and widow rockfishes, and bocaccio, with lingcod ranking seventh. In general, mean length and catch-per-angler-hour of sport fishes caught by CPFV anglers varied considerably and did not show steady declines during the study period. However, port-specific areas of major concern were identified for chilipepper, lingcod, and black rockfish, and to a lesser extent brown, canary, vermilion, yelloweye, olive, and widow rockfish. These areas of concern included steadily declining catch rate, steadily declining mean length, and a high percentage of sexually immature fish in the sampled-catch. Recent sampling of the commercial hook-and-line fishery in northern and central California indicated that most species of rockfishes taken by CPFV anglers are also harvested commercially. (261pp.

Revisiting the Rayleigh-Plateau instability for the nanoscale

The theoretical framework developed by Rayleigh and Plateau in the 19th century has been remarkably accurate in describing macroscale experiments of liquid cylinder instability. Here we re-evaluate and revise the Rayleigh-Plateau instability for the nanoscale, where molecular dynamics experiments demonstrate its inadequacy. A new framework based on the stochastic lubrication equation is developed that captures nanoscale flow features and highlights the critical role of thermal fluctuations at small scales. Remarkably, the model indicates that classically stable (i.e. ‘fat’) liquid cylinders can be broken at the nanoscale, and this is confirmed by molecular dynamics

Molecular simulation of thin liquid films : thermal fluctuations and instability

The instability of a thin liquid film on a solid surface is studied both by molecular dynamics simulations (MD) and a stochastic thin-film equation (STF), which models thermal fluctuations with white noise. A linear stability analysis of the STF allows us to derive a power spectrum for the surface fluctuations, which is quantitatively validated against the spectrum observed in MD. Thermal fluctuations are shown to be critical to the dynamics of nanoscale films. Compared to the classical instability mechanism, which is driven by disjoining pressure, fluctuations (a) can massively amplify the instability, (b) cause the fluctuation wavelength that is dominant to evolve in time (a single fastest-growing mode does not exist), and (c) decrease the critical wavelength so that classically stable films can be ruptured

Nanoscale thin-film flows with thermal fluctuations and slip

The combined effects of thermal fluctuations and liquid-solid slip on nanoscale thin-film flows are investigated using stochastic lubrication equations (SLEs). The previous no-slip SLE for films on plates is extended to consider slip effects and a new SLE for films on fibres is derived, using a long-wave approximation to fluctuating hydrodynamics. Analytically derived capillary spectra, which evolve in time, are found from the new SLEs and compared to molecular dynamics simulations. It is shown that thermal fluctuations lead to the generation and growth of surface waves, and slip accelerates this growth. SLEs developed here provide useful tools to study nanoscale film dewetting, nanofibre coating, and liquid transport using nanofibres

Lifetime of a nanodroplet : kinetic effects and regime transitions

A transition from a d2 to a d law is observed in molecular dynamics (MD) simulations when the diameter (d) of an evaporating droplet reduces to the order of the vapor’s mean free path; this cannot be explained by classical theory. This Letter shows that the d law can be predicted within the Navier-Stokes-Fourier (NSF) paradigm if a temperature-jump boundary condition derived from kinetic theory is utilized. The results from this model agree with those from MD in terms of the total lifetime, droplet radius, and temperature, while the classical d2 law underpredicts the lifetime of the droplet by a factor of 2. Theories beyond NSF are also employed in order to investigate vapor rarefaction effects within the Knudsen layer adjacent to the interface

Safety of guselkumab in hepatitis B virus infection

Reactivation of hepatitis B virus (HBV) following the use of TNF antagonists has been reported and is a contraindication to use of these medications. Although the risk of reactivation of HBV during use of ustekinumab and secukinumab is low in patients with only HBV core antibody positivity, the risk is substantial in patients with chronic HBV infection. Less information is available regarding the use of pure IL-23 antagonists. Herein we discuss the successful treatment with guselkumab of a patient with HBV core antibody positivity, without evidence of HBV reactivation or other liver complications