358 research outputs found
Ballistic Coalescence Model
We study statistical properties of a one dimensional infinite system of
coalescing particles. Each particle moves with constant velocity
towards its closest neighbor and merges with it upon collision. We propose a
mean-field theory that confirms a concentration decay obtained in
simulations and provides qualitative description for the densities of growing,
constant, and shrinking inter-particle gaps.Comment: 4 pages, 2 column Revtex, 5 figures include
Lattice Boltzmann method for viscoelastic fluids
Lattice Boltzmann model for viscoelastic flow simulation is proposed; elastic
effects are taken into account in the framework of Maxwell model. The following
three examples are studied using the proposed approach: a transverse velocity
autocorrelation function for free evolving system with random initial
velocities, a boundary-driven propagating shear waves, and a resonant
enhancement of oscillations in a periodically driven fluid in a capillary. The
measured shear wave dispersion relation is found to be in a good agreement with
the theoretical one derived for the Navier-Stokes equation with the Maxwell
viscoelastic term.Comment: 4 pages, 5 figure
A model for the self-organization of vesicular flux and protein distributions in the Golgi apparatus
The generation of two non-identical membrane compartments via exchange of
vesicles is considered to require two types of vesicles specified by distinct
cytosolic coats that selectively recruit cargo and two membrane-bound SNARE
pairs that specify fusion and differ in their affinities for each type of
vesicles. The mammalian Golgi complex is composed of 6-8 non-identical
cisternae that undergo gradual maturation and replacement yet features only two
SNARE pairs. We present a model that explains how the distinct composition of
Golgi cisternae can be generated with two and even a single SNARE pair and one
vesicle coat. A decay of active SNARE concentration in aging cisternae provides
the seed for a cis > trans SNARE gradient that generates the predominantly
retrograde vesicle flux which further enhances the gradient. This flux in turn
yields the observed inhomogeneous steady-state distribution of Golgi enzymes,
which compete with each other and with the SNAREs for incorporation into
transport vesicles. We show analytically that the steady state SNARE
concentration decays exponentially with the cisterna number. Numerical
solutions of rate equations reproduce the experimentally observed SNARE
gradients, overlapping enzyme peaks in cis, medial and trans and the reported
change in vesicle nature across Golgi: Vesicles originating from younger
cisternae mostly contain Golgi enzymes and SNAREs enriched in these cisternae
and extensively recycle through the Endoplasmic Reticulum (ER), while the other
subpopulation of vesicles contains Golgi proteins prevalent in older cisternae
and hardly reaches the ER.Comment: 15 pages, 6 figure
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