757 research outputs found
Chaotic Mixing in Three Dimensional Porous Media
Under steady flow conditions, the topological complexity inherent to all
random 3D porous media imparts complicated flow and transport dynamics. It has
been established that this complexity generates persistent chaotic advection
via a three-dimensional (3D) fluid mechanical analogue of the baker's map which
rapidly accelerates scalar mixing in the presence of molecular diffusion. Hence
pore-scale fluid mixing is governed by the interplay between chaotic advection,
molecular diffusion and the broad (power-law) distribution of fluid particle
travel times which arise from the non-slip condition at pore walls. To
understand and quantify mixing in 3D porous media, we consider these processes
in a model 3D open porous network and develop a novel stretching continuous
time random walk (CTRW) which provides analytic estimates of pore-scale mixing
which compare well with direct numerical simulations. We find that chaotic
advection inherent to 3D porous media imparts scalar mixing which scales
exponentially with longitudinal advection, whereas the topological constraints
associated with 2D porous media limits mixing to scale algebraically. These
results decipher the role of wide transit time distributions and complex
topologies on porous media mixing dynamics, and provide the building blocks for
macroscopic models of dilution and mixing which resolve these mechanisms.Comment: 36 page
Localized shear generates three-dimensional transport
Understanding the mechanisms that control three-dimensional (3D) fluid
transport is central to many processes including mixing, chemical reaction and
biological activity. Here a novel mechanism for 3D transport is uncovered where
fluid particles are kicked between streamlines near a localized shear, which
occurs in many flows and materials. This results in 3D transport similar to
Resonance Induced Dispersion (RID); however, this new mechanism is more rapid
and mutually incompatible with RID. We explore its governing impact with both
an abstract 2-action flow and a model fluid flow. We show that transitions from
one-dimensional (1D) to two-dimensional (2D) and 2D to 3D transport occur based
on the relative magnitudes of streamline jumps in two transverse directions.Comment: Copyright 2017 AIP Publishing. This article may be downloaded for
personal use only. Any other use requires prior permission of the author and
AIP Publishin
Wall Adhesion and Constitutive Modelling of Strong Colloidal Gels
Wall adhesion effects during batch sedimentation of strongly flocculated
colloidal gels are commonly assumed to be negligible. In this study in-situ
measurements of colloidal gel rheology and solids volume fraction distribution
suggest the contrary, where significant wall adhesion effects are observed in a
110mm diameter settling column. We develop and validate a mathematical model
for the equilibrium stress state in the presence of wall adhesion under both
viscoplastic and viscoelastic constitutive models. These formulations highlight
fundamental issues regarding the constitutive modeling of colloidal gels,
specifically the relative utility and validity of viscoplastic and viscoelastic
rheological models under arbitrary tensorial loadings. The developed model is
validated against experimental data, which points toward a novel method to
estimate the shear and compressive yield strength of strongly flocculated
colloidal gels from a series of equilibrium solids volume fraction profiles
over various column widths.Comment: 37 pages, 12 figures, submitted to Journal of Rheolog
Rodent Aβ Modulates the Solubility and Distribution of Amyloid Deposits in Transgenic Mice
The amino acid sequence of amyloid precursor protein (APP) is highly conserved, and age-related Abeta aggregates have been described in a variety of vertebrate animals, with the notable exception of mice and rats. Three amino acid substitutions distinguish mouse and human Abeta that might contribute to their differing properties in vivo. To examine the amyloidogenic potential of mouse Abeta, we studied several lines of transgenic mice overexpressing wild-type mouse amyloid precursor protein (moAPP) either alone or in conjunction with mutant PS1 (PS1dE9). Neither overexpression of moAPP alone nor co-expression with PS1dE9 caused mice to develop Alzheimer-type amyloid pathology by 24 months of age. We further tested whether mouse Abeta could accelerate the deposition of human Abeta by crossing the moAPP transgenic mice to a bigenic line expressing human APPswe with PS1dE9. The triple transgenic animals (moAPP x APPswe/PS1dE9) produced 20% more Abeta but formed amyloid deposits no faster and to no greater extent than APPswe/PS1dE9 siblings. Instead, the additional mouse Abeta increased the detergent solubility of accumulated amyloid and exacerbated amyloid deposition in the vasculature. These findings suggest that, although mouse Abeta does not influence the rate of amyloid formation, the incorporation of Abeta peptides with differing sequences alters the solubility and localization of the resulting aggregates
Supersymmetric particle mass measurement with invariant mass correlations
The kinematic end-point technique for measuring the masses of supersymmetric
particles in R-Parity conserving models at hadron colliders is re-examined with
a focus on exploiting additional constraints arising from correlations in
invariant mass observables. The use of such correlations is shown to
potentially resolve the ambiguity in the interpretation of quark+lepton
end-points and enable discrimination between sequential two-body and three-body
lepton-producing decays. The use of these techniques is shown to improve the
SUSY particle mass measurement precision for the SPS1a benchmark model by at
least 20-30% compared to the conventional end-point technique.Comment: 29 pages, 23 .eps figures, JHEP3 style; v2 adds some references and
small clarifications to text; v3 adds some more clarifications to the tex
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