761 research outputs found
Ink Drying in Inkjet Printers
The first problem put to the Study Group for Maths in Industry by Domino UK Ltd
concerns ink drying and blocking nozzles in a printer. The goals were as follows:
1. To propose mechanisms for the growth of a plug of dried ink in the open end of a Drop-on-Demand drop generator,
2. To suggest cures to this problem,
3. To consider why oscillating the meniscus appears to alleviate the problem
A non-destructive method for measuring the salinity and solid fraction of growing sea ice in situ
We describe an instrument developed to make in situ measurements of salinity and solid-fraction profiles in growing sea ice. The vertical resolution of the measurements is up to a few millimeters, with a temporal resolution of up to fractions of a second. The technique is based on impedance measurements between platinum wires around which sea ice grows. Data obtained using this instrument in laboratory experiments are in good agreement with theoretical predictions. In a field test in the Arctic, the bulk salinity of growing sea ice has been measured in situ throughout the whole depth of the ice layer. The data are compared with bulk salinities obtained from ice cores, and confirm the general understanding that the bulk salinity in ice-core studies is significantly underestimated in the lower parts of the cores. The approach can also be used in other glaciological applications and for general studies of two-phase, two-component porous media
Recommended from our members
Controls on microstructural features during solidification of colloidal suspensions
We present a mathematical model of the directional freezing of colloidal suspensions. Key ingredients of the model are the disjoining forces between the colloidal particles and the solidified suspending fluid, flow of the suspending fluid towards the solidification front through an accumulating layer of particles, and flow through microscopic films of unfrozen liquid separating particles from the freezing front. Our model predicts three dif- ferent modes of solidification leading to different microstructures: dendritic formations; laddered structures of ice spears and lenses; a frozen fringe, from which transverse ice lenses can form. It explains why different researchers have reported the existence of ice lensing with and without the pre-existence of frozen fringes. Our quantitative predictions are encapsulated within a universal, dimensionless phase diagram showing which mi- crostructure is to be expected under which operating conditions, and we show that these predictions are consistent with previous experimental studies as well as new experiments that we present here.Innovation Foundation for Doctor Dissertation in Northwestern Poltechnical University (CX201703)
National Natural Science Foundation of China (Grant No. 51701155)
British Council
China Scholarship Counci
Recommended from our members
Computerised speechreading training for deaf children: A randomised controlled trial
Purpose: We developed and evaluated in a randomised controlled triala computerised speechreading training programme to determine a) whether it is possible to train speechreading in deaf children and b) whether speechreading training results in improvements in phonological and reading skills.Previous studies indicate a relationship between speechreading and reading skill and further suggest this relationshipmay be mediated by improved phonological representations. This is important since many deaf children find learning to read to be very challenging.
Method: Sixty-six deaf 5-7 year olds were randomised into speechreading and maths training arms. Each training programme was comprised of10 minutesessionsa day, 4 days a week for 12 weeks. Children were assessed on a battery of language and literacy measures before training, immediately after training, 3 months and 10 months after training.
Results: We found no significant benefits for participants who completed the speechreading training, compared to those who completed the maths training, on the speechreading primary outcome measure. However, significantly greater gains were observed in the speechreading training group on one of the secondary measures of speechreading. There was also some evidence of beneficial effects of the speechreading training on phonological representations, however these effects were weaker. No benefits were seen toword reading.
Conclusions: Speechreading skill is trainable in deaf children. However, to support early reading, training may need to be longer or embedded in a broader literacy programme. Nevertheless, a training tool that can improve speechreading is likely to be of great interest to professionals working with deaf children
Ice-lens formation and geometrical supercooling in soils and other colloidal materials
We present a new, physically-intuitive model of ice-lens formation and growth
during the freezing of soils and other dense, particulate suspensions.
Motivated by experimental evidence, we consider the growth of an ice-filled
crack in a freezing soil. At low temperatures, ice in the crack exerts large
pressures on the crack walls that will eventually cause the crack to split
open. We show that the crack will then propagate across the soil to form a new
lens. The process is controlled by two factors: the cohesion of the soil, and
the geometrical supercooling of the water in the soil; a new concept introduced
to measure the energy available to form a new ice lens. When the supercooling
exceeds a critical amount (proportional to the cohesive strength of the soil) a
new ice lens forms. This condition for ice-lens formation and growth does not
appeal to any ad hoc, empirical assumptions, and explains how periodic ice
lenses can form with or without the presence of a frozen fringe. The proposed
mechanism is in good agreement with experiments, in particular explaining
ice-lens pattern formation, and surges in heave rate associated with the growth
of new lenses. Importantly for systems with no frozen fringe, ice-lens
formation and frost heave can be predicted given only the unfrozen properties
of the soil. We use our theory to estimate ice-lens growth temperatures
obtaining quantitative agreement with the limited experimental data that is
currently available. Finally we suggest experiments that might be performed in
order to verify this theory in more detail. The theory is generalizable to
complex natural-soil scenarios, and should therefore be useful in the
prediction of macroscopic frost heave rates.Comment: Submitted to PR
Natural versus forced convection in laminar starting plumes
A starting plume or jet has a well-defined, evolving head that is driven
through the surrounding quiescent fluid by a localized flux of either buoyancy
or momentum, or both. We studied the scaling and morphology of starting plumes
produced by a constant flux of buoyant fluid from a small, submerged outlet.
The plumes were laminar and spanned a wide range of plume Richardson numbers
Ri. Ri is the dimensionless ratio of the buoyancy forces to inertial effects,
and is thus our measurements crossed over the transition between
buoyancy-driven plumes and momentum-driven jets. We found that the ascent
velocity of the plume, nondimensionalized by Ri, exhibits a power law
relationship with Re, the Reynolds number of the injected fluid in the outlet
pipe. We also found that as the threshold between buoyancy-driven and
momentum-driven flow was crossed, two distinct types of plume head mophologies
existed: confined heads, produced in the Ri > 1 regime, and dispersed heads,
which are found in the Ri < 1 regime. Head dispersal is caused by a breakdown
of overturning motion in the head, and a local Kelvin-Helmholtz instability on
the exterior of the plume.Comment: 8 pages, 8 figures, accepted for publication in Physics of Fluids
(final version with corrections
Axisymmetric viscous gravity currents flowing over a porous medium
We study the axisymmetric propagation of a viscous gravity current over a
deep porous medium into which it also drains. A model for the propagation and
drainage of the current is developed and solved numerically in the case of
constant input from a point source. In this case, a steady state is possible in
which drainage balances the input, and we present analytical expressions for
the resulting steady profile and radial extent. We demonstrate good agreement
between our experiments, which use a bed of vertically aligned tubes as the
porous medium, and the theoretically predicted evolution and steady state.
However, analogous experiments using glass beads as the porous medium exhibit a
variety of unexpected behaviours, including overshoot of the steady-state
radius and subsequent retreat, thus highlighting the importance of the porous
medium geometry and permeability structure in these systems.Comment: 11 pages, 6 figures, 1 tabl
Nonlinear mushy-layer convection with chimneys: stability and optimal solute fluxes
We model buoyancy-driven convection with chimneys -- channels of zero solid
fraction -- in a mushy layer formed during directional solidification of a
binary alloy in two-dimensions. A large suite of numerical simulations is
combined with scaling analysis in order to study the parametric dependence of
the flow. Stability boundaries are calculated for states of finite-amplitude
convection with chimneys, which for a narrow domain can be interpreted in terms
of a modified Rayleigh number criterion based on the domain width and
mushy-layer permeability. For solidification in a wide domain with multiple
chimneys, it has previously been hypothesised that the chimney spacing will
adjust to optimise the rate of removal of potential energy from the system. For
a wide variety of initial liquid concentration conditions, we consider the
detailed flow structure in this optimal state and derive scaling laws for how
the flow evolves as the strength of convection increases. For moderate
mushy-layer Rayleigh numbers these flow properties support a solute flux that
increases linearly with Rayleigh number. This behaviour does not persist
indefinitely, however, with porosity-dependent flow saturation resulting in
sub-linear growth of the solute flux for sufficiently large Rayleigh numbers.
Finally, we consider the influence of the porosity dependence of permeability,
with a cubic function and a Carmen-Kozeny permeability yielding qualitatively
similar system dynamics and flow profiles for the optimal states.Comment: 20 pages, 10 figures. Changes from previous version correct typos,
expand on discussion of the method including new appendix A, and minor
changes to the discussion. A modified final version has been accepted for
publication in the Journal of Fluid Mechanic
- …