18 research outputs found
Instabilities and waves in thin films of living fluids
We formulate the thin-film hydrodynamics of a suspension of polar self-driven
particles and show that it is prone to several instabilities through the
interplay of activity, polarity and the existence of a free surface. Our
approach extends, to self-propelling systems, the work of Ben Amar and Cummings
[Phys Fluids 13 (2001) 1160] on thin-film nematics. Based on our estimates the
instabilities should be seen in bacterial suspensions and the lamellipodium,
and are potentially relevant to the morphology of biofilms. We suggest several
experimental tests of our theory.Comment: 4 pages, pdflatex, accepted for publication in Phys Rev Let
Self-organized Pattern Formation in Motor-Microtubule Mixtures
We propose and study a hydrodynamic model for pattern formation in mixtures
of molecular motors and microtubules. The steady state patterns we obtain in
different regimes of parameter space include arrangements of vortices and
asters separately as well as aster-vortex mixtures and fully disordered states.
Such stable steady states are observed in experiments in vitro. The sequence of
patterns obtained in the experiments can be associated with smooth trajectories
in a non-equilibrium phase diagram for our model.Comment: 11 pages Latex file, 2 figures include
Two-Component Fluid Membranes Near Repulsive Walls: Linearized Hydrodynamics of Equilibrium and Non-equilibrium States
We study the linearized hydrodynamics of a two-component fluid membrane near
a repulsive wall, via a model which incorporates curvature- concentration
coupling as well as hydrodynamic interactions. This model is a simplified
version of a recently proposed one [J.-B. Manneville et al. Phys. Rev. E, 64,
021908 (2001)] for non-equilibrium force-centres embedded in fluid membranes,
such as light-activated bacteriorhodopsin pumps incorporated in phospholipid
(EPC) bilayers. The pump/membrane system is modeled as an impermeable,
two-component bilayer fluid membrane in the presence of an ambient solvent, in
which one component, representing active pumps, is described in terms of force
dipoles displaced with respect to the bilayer midpoint. We first discuss the
case in which such pumps are rendered inactive, computing the mode structure in
the bulk as well as the modification of hydrodynamic properties by the presence
of a nearby wall. We then discuss the fluctuations and mode structure in steady
state of active two-component membranes near a repulsive wall. We find that
proximity to the wall smoothens membrane height fluctuations in the stable
regime, resulting in a logarithmic scaling of the roughness even for initially
tensionless membranes. This explicitly non-equilibrium result, a consequence of
the incorporation of curvature-concentration coupling in our treatment, also
indicates that earlier scaling arguments which obtained an increase in the
roughness of active membranes near repulsive walls may need to be reevaluated.Comment: 39 page Latex file, 3 encapsulated Postscript figure
Integrated analysis of genomic and transcriptomic data for the discovery of splice-associated variants in cancer
Somatic mutations within non-coding regions and even exons may have unidentified regulatory consequences that are often overlooked in analysis workflows. Here we present RegTools ( www.regtools.org ), a computationally efficient, free, and open-source software package designed to integrate somatic variants from genomic data with splice junctions from bulk or single cell transcriptomic data to identify variants that may cause aberrant splicing. We apply RegTools to over 9000 tumor samples with both tumor DNA and RNA sequence data. RegTools discovers 235,778 events where a splice-associated variant significantly increases the splicing of a particular junction, across 158,200 unique variants and 131,212 unique junctions. To characterize these somatic variants and their associated splice isoforms, we annotate them with the Variant Effect Predictor, SpliceAI, and Genotype-Tissue Expression junction counts and compare our results to other tools that integrate genomic and transcriptomic data. While many events are corroborated by the aforementioned tools, the flexibility of RegTools also allows us to identify splice-associated variants in known cancer drivers, such as TP53, CDKN2A, and B2M, and other genes
Quantum Hall Skyrmion Lattices at
We investigate the classical ground state configurations of a collection of
skyrmions in the limit of vanishing L\'ande factor. We show that in this
limit, the skyrmions which are large and overlapping, behave qualitatively
differently from small skyrmions. We investigate the system in various regimes
of spin stiffness. We find that in all regimes, at , the ground state
configuration is a rectangular skyrmion lattice with N\'eel orientational
ordering. The charge distribution has a higher symmetry of a face-centered
rectangular lattice and the -component of the spin polarization is zero. We
also present general argument for the vanishing of spin polarization at
at finite temperature and in the presence of disorder and discuss some
experimental consequences of our results.Comment: Latex file, 15 figures, To appear in Physical Review