48,612 research outputs found
Curvature-controlled defect dynamics in active systems
We have studied the collective motion of polar active particles confined to
ellipsoidal surfaces. The geometric constraints lead to the formation of
vortices that encircle surface points of constant curvature (umbilics). We have
found that collective motion patterns are particularly rich on ellipsoids, with
four umbilics where vortices tend to be located near pairs of umbilical points
to minimize their interaction energy. Our results provide a new perspective on
the migration of living cells, which most likely use the information provided
from the curved substrate geometry to guide their collective motion.Comment: Accepted manuscript. 8 pages, 7 Figures. Movies of the motion
patterns can be found at
https://www.youtube.com/playlist?list=PLEsE7_tnqXZ_U258VwxES8KAJTV_eO43
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Lipid and Protein Transfer between Nanolipoprotein Particles and Supported Lipid Bilayers.
A nanolipoprotein particle (NLP) is a lipid bilayer disc stabilized by two amphipathic "scaffold" apolipoproteins. It has been most notably utilized as a tool for solubilizing a variety of membrane proteins while preserving structural and functional properties. Transfer of functional proteins from NLPs into model membrane systems such as supported lipid bilayers (SLBs) would enable new opportunities, for example, two-dimensional protein crystallization and studies on protein-protein interactions. This work used fluorescence microscopy and atomic force microscopy to investigate the interaction between NLPs and SLBs. When incubated with SLBs, NLPs were found to spontaneously deliver lipid and protein cargo. The impact of membrane composition on lipid exchange was explored, revealing a positive correlation between the magnitude of lipid transfer and concentration of defects in the target SLB. Incorporation of lipids capable of binding specifically to polyhistidine tags encoded into the apolipoproteins also boosted transfer of NLP cargo. Optimal conditions for lipid and protein delivery from NLPs to SLBs are proposed based on interaction mechanisms
Theory, Simulation and Nanotechnological Applications of Adsorption on a Surface with Defects
Theory of adsorption on a surface with nanolocal defects is proposed. Two
efficacy parameters of surface modification for nanotechnological purposes are
introduced, where the modification is a creation of nanolocal artificial
defects. The first parameter corresponds to applications where it is necessary
to increase the concentration of certain particles on the modified surface. And
the second one corresponds to the pattern transfer with the help of particle
self-organization on the modified surface. The analytical expressions for both
parameters are derived with the help of the thermodynamic and the kinetic
approaches for two cases: jump diffusion and free motion of adsorbed particles
over the surface. The possibility of selective adsorption of molecules is shown
with the help of simulation of the adsorption of acetylene and benzene
molecules in the pits on the graphite surface. The process of particle
adsorption from the surface into the pit is theoretically studied by molecular
dynamic technique. Some possible nanotechnological applications of adsorption
on the surface with artificial defects are considered: fabrication of sensors
for trace molecule detection, separation of isomers, and pattern transfer.Comment: 12 pages, 2 Postscript figures. Submitted to Surface Science (1998
Dynamics and evaporation of defects in Mott-insulating clusters of boson pairs
Repulsively bound pairs of particles in a lattice governed by the
Bose-Hubbard model can form stable incompressible clusters of dimers
corresponding to finite-size n=2 Mott insulators. Here we study the dynamics of
hole defects in such clusters corresponding to unpaired particles which can
resonantly tunnel out of the cluster into the lattice vacuum. Due to bosonic
statistics, the unpaired particles have different effective mass inside and
outside the cluster, and "evaporation" of hole defects from the cluster
boundaries is possible only when their quasi-momenta are within a certain
transmission range. We show that quasi-thermalization of hole defects occurs in
the presence of catalyzing particle defects which thereby purify the Mott
insulating clusters. We study the dynamics of one-dimensional system using
analytical techniques and numerically exact t-DMRG simulations. We derive an
effective strong-interaction model that enables simulations of the system
dynamics for much longer times. We also discuss a more general case of two
bosonic species which reduces to the fermionic Hubbard model in the strong
interaction limit.Comment: 12 pages, 10 figures, minor update
Braiding Statistics and Congruent Invariance of Twist Defects in Bosonic Bilayer Fractional Quantum Hall States
We describe the braiding statistics of topological twist defects in abelian
bosonic bilayer (mmn) fractional quantum Hall (FQH) states, which reduce to the
Z_n toric code when m=0. Twist defects carry non-abelian fractional
Majorana-like characteristics. We propose local statistical measurements that
distinguish the fractional charge, or species, of a defect-quasiparticle
composite. Degenerate ground states and basis transformations of a multi-defect
system are characterized by a consistent set of fusion properties. Non-abelian
unitary exchange operations are determined using half braids between defects,
and projectively represent the sphere braid group in a closed system. Defect
spin statistics are modified by equating exchange with 4\pi rotation. The
braiding S matrix is identified with a Dehn twist (instead of a \pi/2 rotation)
on a torus decorated with a non-trivial twofold branch cut, and represents the
congruent subgroup \Gamma_0(2) of modular transformations.Comment: 6 pages, 3 figure
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