373 research outputs found
Two-dimensional hydrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic fluid flow through porous media
The behaviour of two dimensional binary and ternary amphiphilic fluids under
flow conditions is investigated using a hydrodynamic lattice gas model. After
the validation of the model in simple cases (Poiseuille flow, Darcy's law for
single component fluids), attention is focussed on the properties of binary
immiscible fluids in porous media. An extension of Darcy's law which explicitly
admits a viscous coupling between the fluids is verified, and evidence of
capillary effects are described. The influence of a third component, namely
surfactant, is studied in the same context. Invasion simulations have also been
performed. The effect of the applied force on the invasion process is reported.
As the forcing level increases, the invasion process becomes faster and the
residual oil saturation decreases. The introduction of surfactant in the
invading phase during imbibition produces new phenomena, including
emulsification and micellisation. At very low fluid forcing levels, this leads
to the production of a low-resistance gel, which then slows down the progress
of the invading fluid. At long times (beyond the water percolation threshold),
the concentration of remaining oil within the porous medium is lowered by the
action of surfactant, thus enhancing oil recovery. On the other hand, the
introduction of surfactant in the invading phase during drainage simulations
slows down the invasion process -- the invading fluid takes a more tortuous
path to invade the porous medium -- and reduces the oil recovery (the residual
oil saturation increases).Comment: 48 pages, 26 figures. Phys. Rev. E (in press
Shear-Induced Isotropic-to-Lamellar Transition in a Lattice-Gas Model of Ternary Amphiphilic Fluids
Although shear-induced isotropic-to-lamellar transitions in ternary systems
of oil, water and surfactant have been observed experimentally and predicted
theoretically by simple models for some time now, their numerical simulation
has not been achieved so far. In this work we demonstrate that a recently
introduced hydrodynamic lattice-gas model of amphiphilic fluids is well suited
for this purpose: the two-dimensional version of this model does indeed exhibit
a shear-induced isotropic-to-lamellar phase transition.Comment: 17 pages, LaTeX with epsf and REVTeX, PostScript and EPS
illustrations included. To appear in J. Phys. Cond. Ma
Symmetry-breaking in chiral polymerisation
We propose a model for chiral polymerisation and investigate its symmetric
and asymmetric solutions. The model has a source species which decays into
left- and right-handed types of monomer, each of which can polymerise to form
homochiral chains; these chains are susceptible to `poisoning' by the opposite
handed monomer. Homochiral polymers are assumed to influence the proportion of
each type of monomer formed from the precursor. We show that for certain
parameter values a positive feedback mechanism makes the symmetric steady-state
solution unstable. The kinetics of polymer formation are then analysed in the
case where the system starts from zero concentrations of monomer and chains. We
show that following a long induction time, extremely large concentrations of
polymers are formed for a short time, during this time an asymmetry introduced
into the system by a random external perturbation may be massively amplified.
The system then approaches one of the steady-state solutions described above.Comment: 26pages, 6 Figure
Three dimensional hysdrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media
We report the results of a study of multiphase flow in porous media. A
Darcy's law for steady multiphase flow was investigated for both binary and
ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager
reciprocity were shown to be a good approximation of the simulation data. The
dependence of the relative permeability coefficients on water saturation was
investigated and showed good qualitative agreement with experimental data.
Non-steady state invasion flows were investigated, with particular interest in
the asymptotic residual oil saturation. The addition of surfactant to the
invasive fluid was shown to significantly reduce the residual oil saturation.Comment: To appear in Phys. Rev.
Spinodal decomposition of off-critical quenches with a viscous phase using dissipative particle dynamics in two and three spatial dimensions
We investigate the domain growth and phase separation of
hydrodynamically-correct binary immiscible fluids of differing viscosity as a
function of minority phase concentration in both two and three spatial
dimensions using dissipative particle dynamics. We also examine the behavior of
equal-viscosity fluids and compare our results to similar lattice-gas
simulations in two dimensions.Comment: 34 pages (11 figures); accepted for publication in Phys. Rev.
Lattice-Gas Simulations of Minority-Phase Domain Growth in Binary Immiscible and Ternary Amphiphilic Fluid
We investigate the growth kinetics of binary immiscible fluids and emulsions
in two dimensions using a hydrodynamic lattice-gas model. We perform
off-critical quenches in the binary fluid case and find that the domain size
within the minority phase grows algebraically with time in accordance with
theoretical predictions. In the late time regime we find a growth exponent n =
0.45 over a wide range of concentrations, in good agreement with other
simluations. In the early time regime we find no universal growth exponent but
a strong dependence on the concentration of the minority phase. In the ternary
amphiphilic fluid case the kinetics of self assembly of the droplet phase are
studied for the first time. At low surfactant concentrations, we find that,
after an early algebraic growth, a nucleation regime dominates the late-time
kinetics, which is enhanced by an increasing concentration of surfactant. With
a further increase in the concentration of surfactant, we see a crossover to
logarithmically slow growth, and finally saturation of the oil droplets, which
we fit phenomenologically to a stretched exponential function. Finally, the
transition between the droplet and the sponge phase is studied.Comment: 22 pages, 13 figures, submitted to PR
Lattice-gas simulations of Domain Growth, Saturation and Self-Assembly in Immiscible Fluids and Microemulsions
We investigate the dynamical behavior of both binary fluid and ternary
microemulsion systems in two dimensions using a recently introduced
hydrodynamic lattice-gas model of microemulsions. We find that the presence of
amphiphile in our simulations reduces the usual oil-water interfacial tension
in accord with experiment and consequently affects the non-equilibrium growth
of oil and water domains. As the density of surfactant is increased we observe
a crossover from the usual two-dimensional binary fluid scaling laws to a
growth that is {\it slow}, and we find that this slow growth can be
characterized by a logarithmic time scale. With sufficient surfactant in the
system we observe that the domains cease to grow beyond a certain point and we
find that this final characteristic domain size is inversely proportional to
the interfacial surfactant concentration in the system.Comment: 28 pages, latex, embedded .eps figures, one figure is in colour, all
in one uuencoded gzip compressed tar file, submitted to Physical Review
Stress transfer quantification in gelatin-matrix natural composites with tunable optical properties
© 2015 American Chemical Society.This work reports on the preparation and characterization of natural composite materials prepared from bacterial cellulose (BC) incorporated into a gelatin matrix. Composite morphology was studied using scanning electron microscopy and 2D Raman imaging revealing an inhomogeneous dispersion of BC within the gelatin matrix. The composite materials showed controllable degrees of transparency to visible light and opacity to UV light depending on BC weight fraction. By adding a 10 wt % fraction of BC in gelatin, visible (= 550 nm) and UV (= 350 nm) transmittances were found to decrease by ∼35 and 40%, respectively. Additionally, stress transfer occurring between the gelatin and BC fibrils was quantified using Raman spectroscopy. This is the first report for a gelatin-matrix composite containing cellulose. As a function of strain, two distinct domains, both showing linear relationships, were observed for which an average initial shift rate with respect to strain of -0.63 ± 0.2 cm-1%-1 was observed, followed by an average shift rate of -0.25 ± 0.03 cm-1%-1. The average initial Raman band shift rate value corresponds to an average effective Youngs modulus of 39 ± 13 GPa and 73 ± 25 GPa, respectively, for either a 2D and 3D network of BC fibrils embedded in the gelatin matrix. As a function of stress, a linear relationship was observed with a Raman band shift rate of -27 ± 3 cm-1GPa-1. The potential use of these composite materials as a UV blocking food coating is discussed
Forecasting in the light of Big Data
Predicting the future state of a system has always been a natural motivation
for science and practical applications. Such a topic, beyond its obvious
technical and societal relevance, is also interesting from a conceptual point
of view. This owes to the fact that forecasting lends itself to two equally
radical, yet opposite methodologies. A reductionist one, based on the first
principles, and the naive inductivist one, based only on data. This latter view
has recently gained some attention in response to the availability of
unprecedented amounts of data and increasingly sophisticated algorithmic
analytic techniques. The purpose of this note is to assess critically the role
of big data in reshaping the key aspects of forecasting and in particular the
claim that bigger data leads to better predictions. Drawing on the
representative example of weather forecasts we argue that this is not generally
the case. We conclude by suggesting that a clever and context-dependent
compromise between modelling and quantitative analysis stands out as the best
forecasting strategy, as anticipated nearly a century ago by Richardson and von
Neumann
Hungry for change: the Sydney Food Fairness Alliance
The Sydney Food Fairness Alliance is one of a growing number of nascent food movements in Australia to have emerged out of concern for the country’s food future, as well as the deleterious effect the present food system is having on its citizens’ health and the continent’s fragile environment. The Alliance’s structure and activities clearly position it as a new social movement (NSM) engaged in collective action on a specific issue, in this instance, food security/justice, and operating outside the political sphere while aiming to influence and affect societal change. Food security as a human right lies at the heart of the Alliance’s philosophy, and equitable, sustainable food policies for New South Wales are a core focus of its advocacy work. The authors argue that the Alliance is a distinctive food movement in that it positions itself as an \u27umbrella\u27 organization representing a wide range of stakeholders in the food system. This chapter reflects on the values, achievements, issues of concern, strengths and weaknesses, and future of the Sydney Food Fairness Alliance.
This resource is Chapter 8 in \u27Food Security in Australia: Challenges and Prospects for the Future\u27 published by Springer in 2013
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