Thin-sheet flow between coalescing bubbles

When two spherical bubbles touch, a hole is formed in the fluid sheet between them, and capillary pressure acting on its tightly curved edge drives an outward radial flow which widens the hole joining the bubbles. Recent images of the early stages of this process (Paulsen et al., Nat. Commun., vol. 5, 2014) show that the radius of the hole $r_{\!E}$ at time $t$ grows proportional to $t^{1/2}$, and that the rate is dependent on the fluid viscosity. Here, we explain this behaviour in terms of similarity solutions to a third-order system of radial extensional-flow equations for the thickness and velocity of the sheet of fluid between the bubbles, and determine the growth rate as a function of the Ohnesorge number $\mathit{Oh}$. The initially quadratic sheet profile allows the ratio of viscous and inertial effects to be independent of time. We show that the sheet is slender for $r_{\!E}\ll a$ if $\mathit{Oh}\gg 1$, where $a$ is the bubble radius, but only slender for $r_{\!E}\ll \mathit{Oh}^{2}a$ if $\mathit{Oh}\ll 1$ due to a compressional boundary layer of length $L\propto \mathit{Oh}\,r_{\!E}$, after which there is a change in the structure but not the speed of the retracting sheet. For $\mathit{Oh}\ll 1$, the detailed analysis justifies a simple momentum-balance argument, which gives the analytic prediction $r_{\!E}\sim (32a{\it\gamma}/3{\it\rho})^{1/4}t^{1/2}$, where ${\it\gamma}$ is the surface tension and ${\it\rho}$ is the density.J.P.M. acknowledges an Engineering and Physical Sciences Research Council studentship. C.R.A. and O.A.B. acknowledge the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. All data accompanying this publication are directly available within the publication.This is the accepted manuscript of a paper published in the Journal of Fluid Mechanics (Munro JP, Anthony CR, Basaran OA, Lister JR, Journal of Fluid Mechanics, 2015, 773, doi:10.1017/jfm.2015.253). The final version is available at http://dx.doi.org/10.1017/jfm.2015.25

Metal Insulator transition at B=0 in p-SiGe

Observations are reported of a metal-insulator transition in a 2D hole gas in asymmetrically doped strained SiGe quantum wells. The metallic phase, which appears at low temperatures in these high mobility samples, is characterised by a resistivity that decreases exponentially with decreasing temperature. This behaviour, and the duality between resistivity and conductivity on the two sides of the transition, are very similar to that recently reported for high mobility Si-MOSFETs.Comment: 4 pages, REVTEX with 3 ps figure

Effective mass and band nonparabolicity in remote doped Si/Si0.8Ge0.2 quantum wells

The effective masses in remote doped Si/Si0.8Ge0.2/Si quantum wells having sheet densities, Ns in the range 2 × 1011–1.1 × 1012 cm – 2 have been determined from the temperature dependencies of the Shubnikov–de Haas oscillations. The values obtained increase with magnetic field and Ns. This behavior is taken as evidence for the nonparabolicity of the valence band and accounts for the discrepancies in previously reported masses. Self-consistent band structure calculations for a triangular confinement of the carriers have also been carried out and provide confirmation of the increase in mass with Ns. Theory and experiment give extrapolated Gamma point effective masses of 0.21 and 0.20 of the free-electron mass, respectively

The European Registered Toxicologist (ERT) : Current status and prospects for advancement

Acknowledgements We would like to thank the participants of the five workshops in which the issues presented in this paper were discussed and the revised guidelines prepared, as well as the EUROTOX Executive Committee and the societies of toxicology of Sweden, the Netherlands, Switzerland, Austria and France for their support which allowed the workshops to take place.Peer reviewedPostprin

Antifungal Activity of a Wireless Electroceutical Dressing

Background:Fusarium and Mucor are two filamentous fungus strains that can cause infections in humans. Fusarium is known for causing corneal infections. Patients who have diabetes mellitus or are immunocompromised are at a higher risk of mucormycosis. Wireless electroceutical dressing (WED) contains embedded silver and zinc nanoparticles in a geometric pattern. Both zinc and silver have been known to be antimicrobial; yet the combination results in a weak electric field when exposed to an electrolyte-containing solution. WED has been found to have antifungal effects against Candida albicans and Aspergillus fumigatus. Methods:We investigated the antifungal effect of WED against Fusarium and Mucor growth and survival through daily radial growth and optic density readings. Results:Our results show that the WED weakly inhibits radial growth of Fusarium strains and strongly inhibits radial growth of Mucor strains, with greater inhibition near physiologic temperatures. Although zinc and silver-only fabric inhibited the radial growth of Mucor, no growth occurred on WED (Ag-Zn) plates for Mucor strains. Optic density readings had mixed results; Ag-Zn liquid cultures had reduced absorbance than control cultures for both strains. Zone of inhibition studies of Fusarium showed no growth on Ag-Zn fabrics with full coverage on all other control and metal containing plates. WED had a greater effect on reducing Mucor growth than Fusarium. Conclusions:WED utilizes a weak electrical field created by silver and zinc nanoparticles to create an antifungal effect. This leads to strong inhibition of Mucor, Candida, and Aspergillus growth and weak inhibition of Fusarium growth. Further studies are needed to determine the specific effect of WED on fungal viability, the mechanism, and in vivo efficacy. This work could increase patient treatment options for fungal wound infections

Persistence of memory in drop breakup: the breakdown of universality

A low-viscosity drop breaking apart inside a viscous fluid is encountered when air bubbles, entrained in thick syrup or honey, rise and break apart. Experiments, simulations, and theory show that the breakup under conditions in which the interior viscosity can be neglected produces an exceptional form of singularity. In contrast to previous studies of drop breakup, universality is violated so that the final shape at breakup retains an imprint of the initial and boundary conditions. A finite interior viscosity, no matter how small, cuts off this form of singularity and produces an unexpectedly long and slender thread. If exterior viscosity is large enough, however, the cutoff does not occur because the minimum drop radius reaches subatomic dimensions first

Wireless Electroceutical Dressing Inhibition of Azole sensitive and resistant strains of Aspergillus fumigatus

Background/Objective:The opportunistic fungus Aspergillus fumigatus is responsible for nosocomial infections, particularly in immunocompromised patients. Fungal infections are increasingly likely in burn victims, as the epidermis serves as the body’s first line of defense against microbial pathogens. In an effort to utilize complementary methods of control, an electroceutical dressing containing geometrically patterned silver and zinc nanoparticles embedded in fabric was used. The dressing utilizes generates a weak electric field when moist to produce antimicrobial effects. Preliminary research showed that the dressing effectively inhibited Candida albicans. This foundational research has led us to hypothesize that the electroceutical dressing could also be an effective option for inhibiting A. fumigatus. The objective of this project was to establish the inhibitory effects of the dressing across multiple strains of A. fumigatus. Methods:We used both radial growth on Aspergillus Minimal Media (AMM) agar plates and concentration in AMM liquid cultures to determine A. fumigatus growth rates. The plates were initially inoculated with 100 conidia of A. fumigatus. Liquid cultures were inoculated with 200,000 conidia/mL. The liquid cultures Radial growth was measured daily for 14 days, and concentration was measured every third day for 24 days. Results:Our results show that the Wireless Electroceutical Dressing (WED) effectively inhibits A. fumigatus growth. Summary:The data indicates that WED inhibits azole resistant and non-resistnat strains of A. fumigatus. By illustrating the effectiveness of the electroceutical dressing, it presents additional options for controlling A. fumigatus infection. Additional research should be conducted to determine if the dressing is fungistatic or fungicidal, along with assessing its effectiveness in inhibiting other fungal infections

Compressive Response of Polycrystalline NiCoMnGa High-Temperature Meta-magnetic Shape Memory Alloys

The effects of the addition of quaternary element, Co, to polycrystalline NiMnGa alloys on their magnetic and shape memory properties have been investigated. NiCoMnGa polycrystalline alloys have been found to demonstrate good shape memory and superelasticity behavior under compression at temperatures greater than 100 °C with about 3% transformation strain and low-temperature hysteresis. It is also possible to train the material to demonstrate a large two-way shape memory effect

Formation of beads-on-a-string structures during break-up of viscoelastic filaments

Break-up of viscoelastic filaments is pervasive in both nature and technology. If a filament is formed by placing a drop of saliva between a thumb and forefinger and is stretched, the filament’s morphology close to break-up corresponds to beads of several sizes interconnected by slender threads. Although there is general agreement that formation of such beads-on-a-string (BOAS) structures occurs only for viscoelastic fluids, the underlying physics remains unclear and controversial. The physics leading to the formation of BOAS structures is probed by numerical simulation. Computations reveal that viscoelasticity alone does not give rise to a small, satellite bead between two much larger main beads but that inertia is required for its formation. Viscoelasticity, however, enhances the growth of the bead and delays pinch-off, which leads to a relatively long-lived beaded structure. We also show for the first time theoretically that yet smaller, sub-satellite beads can also form as seen in experiments.National Science Foundation (U.S.). ERC-SOPS (EEC-0540855)Nanoscale Interdisciplinary Research Thrust on 'Directed Self-assembly of Suspended Polymer Fibers' (NSF-DMS0506941