4,674 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
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.
Diet, nutrition, obesity and their role in arthritis
Obesity and poor nutrition, individually and together, have created costly musculoskeletal disease epidemic in the United States. Processed food, with abundant empty calories, has contributed greatly to our dietary woes. Much of the food consumed today is packed with calories but refined to the point that essential nutrients are lacking. Even worse, processed food may have ingredients added that are detrimental to good health. Abundant research has documented a close relationship between obesity, poor diet and orthopaedic problems. Dietary supplements have been proven to provide both disease prevention and therapeutic benefits. Unfortunately, many weight loss programs and methods are ineffective and possibly dangerous. Additionally, the FDA does not regulate the nutritional supplement industry and product quality is high variable. It is imperative that physicians treating patients with musculoskeletal complaints understand these disease producing relationships and have a network in place to refer patients to reputable weight loss entities and for high quality nutritional supplements
A Two-Threshold Model for Scaling Laws of Non-Interacting Snow Avalanches
The sizes of snow slab failure that trigger snow avalanches are power-law
distributed. Such a power-law probability distribution function has also been
proposed to characterize different landslide types. In order to understand this
scaling for gravity driven systems, we introduce a two-threshold 2-d cellular
automaton, in which failure occurs irreversibly. Taking snow slab avalanches as
a model system, we find that the sizes of the largest avalanches just
preceeding the lattice system breakdown are power law distributed. By tuning
the maximum value of the ratio of the two failure thresholds our model
reproduces the range of power law exponents observed for land-, rock- or snow
avalanches. We suggest this control parameter represents the material cohesion
anisotropy.Comment: accepted PR
Responses of phosphorus limited Lake Michigan phytoplankton to factorial enrichments with nitrogen and phosphorus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109907/1/lno19741930409.pd
Phase separation in an homogeneous shear flow: Morphology, growth laws and dynamic scaling
We investigate numerically the influence of an homogeneous shear flow on the
spinodal decomposition of a binary mixture by solving the Cahn-Hilliard
equation in a two-dimensional geometry. Several aspects of this much studied
problem are clarified. Our numerical data show unambiguously that, in the shear
flow, the domains have on average an elliptic shape. The time evolution of the
three parameters describing this ellipse are obtained for a wide range of shear
rates. For the lowest shear rates investigated, we find the growth laws for the
two principal axis , , while
the mean orientation of the domains with respect to the flow is inversely
proportional to the strain. This implies that when hydrodynamics is neglected a
shear flow does not stop the domain growth process. We investigate also the
possibility of dynamic scaling, and show that only a non trivial form of
scaling holds, as predicted by a recent analytical approach to the case of a
non-conserved order parameter. We show that a simple physical argument may
account for these results.Comment: Version accepted for publication - Physical Review
Synaptotagmin 1 oligomers clamp and regulate different modes of neurotransmitter release
Release of neurotransmitters relies on submillisecond coupling of synaptic vesicle fusion to the triggering signal: AP-evoked presynaptic Ca2+ influx. The key player that controls exocytosis of the synaptic vesicle is the Ca2+ sensor synaptotagmin 1 (Syt1). While the Ca2+ activation of Syt1 has been extensively characterized, how Syt1 reversibly clamps vesicular fusion remains enigmatic. Here, using a targeted mutation combined with fluorescence imaging and electrophysiology, we show that the structural feature of Syt1 to self-oligomerize provides the molecular basis for clamping of spontaneous and asynchronous release but is not required for triggering of synchronous release. Our findings propose a mechanistic model that explains how Syt1 oligomers regulate different modes of transmitter release in neuronal synapses
Computer simulations of domain growth and phase separation in two-dimensional binary immiscible fluids using dissipative particle dynamics
We investigate the dynamical behavior of binary fluid systems in two
dimensions using dissipative particle dynamics. We find that following a
symmetric quench the domain size R(t) grows with time t according to two
distinct algebraic laws R(t) = t^n: at early times n = 1/2, while for later
times n = 2/3. Following an asymmetric quench we observe only n = 1/2, and if
momentum conservation is violated we see n = 1/3 at early times. Bubble
simulations confirm the existence of a finite surface tension and the validity
of Laplace's law. Our results are compared with similar simulations which have
been performed previously using molecular dynamics, lattice-gas and
lattice-Boltzmann automata, and Langevin dynamics. We conclude that dissipative
particle dynamics is a promising method for simulating fluid properties in such
systems.Comment: RevTeX; 22 pages, 5 low-resolution figures. For full-resolution
figures, connect to http://www.tcm.phy.cam.ac.uk/~ken21/tension/tension.htm
Spurious diffusion in particle simulations of the Kolmogorov flow
Particle simulations of the Kolmogorov flow are analyzed by the
Landau-Lifshitz fluctuating hydrodynamics. It is shown that a spurious
diffusion of the center of mass corrupts the statistical properties of the
flow. The analytical expression for the corresponding diffusion coefficient is
derived.Comment: 10 pages, no figure
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