2,529 research outputs found
Dynamics of double emulsion break-up in three phase glass capillary microfluidic devices
Pinch-off of a compound jet in 3D glass capillary microfluidic device, which combines co-flowing and countercurrent flow focusing geometries, was investigated using an incompressible three-phase axisymmetric Volume of Fluid–Continuum Surface Force (VOF–CSF) numerical model. The model showed good agreement with the experimental drop generation and was capable of predicting formation of core/shell droplets in dripping, narrowing jetting and widening jetting regimes. In dripping and widening jetting regimes, the presence of a vortex flow around the upstream end of the necking thread facilitates the jet break-up. No vortex flow was observed in narrowing jetting regime and pinch-off occurred due to higher velocity at the downstream end of the coaxial thread compared to that at the upstream end. In all regimes, the inner jet ruptured before the outer jet, preventing a leakage of the inner drop into the outer fluid. The necking region moves at the maximum speed in the narrowing jetting regime, due to the highest level of shear at the outer surface of the thread. However, in widening jetting regime, the neck travels the longest distance downstream before it breaks
Continuum Theory for Piezoelectricity in Nanotubes and Nanowires
We develop and solve a continuum theory for the piezoelectric response of one
dimensional nanotubes and nanowires, and apply the theory to study
electromechanical effects in BN nanotubes. We find that the polarization of a
nanotube depends on its aspect ratio, and a dimensionless constant specifying
the ratio of the strengths of the elastic and electrostatic interactions. The
solutions of the model as these two parameters are varied are discussed. The
theory is applied to estimate the electric potential induced along the length
of a BN nanotube in response to a uniaxial stress.Comment: 4 pages in RevTex4, 2 epsf figure
Double emulsion production in glass capillary microfluidic device: Parametric investigation of droplet generation behaviour
A three-phase axisymmetric numerical model based on Volume of Fluid–Continuum Surface Force (VOF–CSF) model was developed to perform parametric analysis of compound droplet production in three-phase glass capillary devices that combine co-flow and countercurrent flow focusing. The model predicted successfully generation of core–shell and multi-cored double emulsion droplets in dripping and jetting (narrowing and widening) regime and was used to investigate the effects of phase flow rates, fluid properties, and geometry on the size, morphology, and production rate of droplets. As the outer fluid flow rate increased, the size of compound droplets was reduced until a dripping-to-jetting transition occurred. By increasing the middle fluid flow rate, the size of compound droplets increased, which led to a widening jetting regime. The jetting was supressed by increasing the orifice size in the collection capillary or increasing the interfacial tension at the outer interface up to 0.06 N/m. The experimental and simulation results can be used to encapsulate CO2 solvents within gas-permeable microcapsules
Ferroelectricity in ultra-thin perovskite films
We report studies of ferroelectricity in ultra-thin perovskite films with
realistic electrodes. The results reveal stable ferroelectric states in thin
films less than 10 \AA thick with polarization normal to the surface. Under
short-circuit boundary conditions, the screening effect of realistic electrodes
and the influence of real metal/oxide interfaces on thin film polarization are
investigated. Our studies indicate that metallic screening from the electrodes
is affected by the difference in work functions at oxide surfaces. We
demonstrate this effect in ferroelectric PbTiO and BaTiO films.Comment: 4 pages in REVTEX4, 4 epsf figure
Emerging applications of integrated optical microcombs for analogue RF and microwave photonic signal processing
We review new applications of integrated microcombs in RF and microwave
photonic systems. We demonstrate a wide range of powerful functions including a
photonic intensity high order and fractional differentiators, optical true time
delays, advanced filters, RF channelizer and other functions, based on a Kerr
optical comb generated by a compact integrated microring resonator, or
microcomb. The microcomb is CMOS compatible and contains a large number of comb
lines, which can serve as a high performance multiwavelength source for the
transversal filter, thus greatly reduce the cost, size, and complexity of the
system. The operation principle of these functions is theoretically analyzed,
and experimental demonstrations are presented.Comment: 16 pages, 8 figures, 136 References. Photonics West 2018 invited
paper, expanded version. arXiv admin note: substantial text overlap with
arXiv:1710.00678, arXiv:1710.0861
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