486 research outputs found
Dynamics of Molecular Motors and Polymer Translocation with Sequence Heterogeneity
The effect of sequence heterogeneity on polynucleotide translocation across a
pore and on simple models of molecular motors such as helicases, DNA
polymerase/exonuclease and RNA polymerase is studied in detail. Pore
translocation of RNA or DNA is biased due to the different chemical
environments on the two sides of the membrane, while the molecular motor motion
is biased through a coupling to chemical energy. An externally applied force
can oppose these biases. For both systems we solve lattice models exactly both
with and without disorder. The models incorporate explicitly the coupling to
the different chemical environments for polymer translocation and the coupling
to the chemical energy (as well as nucleotide pairing energies) for molecular
motors. Using the exact solutions and general arguments we show that the
heterogeneity leads to anomalous dynamics. Most notably, over a range of forces
around the stall force (or stall tension for DNA polymerase/exonuclease
systems) the displacement grows sublinearly as t^\mu with \mu<1. The range over
which this behavior can be observed experimentally is estimated for several
systems and argued to be detectable for appropriate forces and buffers. Similar
sequence heterogeneity effects may arise in the packing of viral DNA.Comment: 42 pages, 12 figure
Unzipping flux lines from extended defects in type-II superconductors
With magnetic force microscopy in mind, we study the unbinding transition of
individual flux lines from extended defects like columnar pins and twin planes
in type II superconductors. In the presence of point disorder, the transition
is universal with an exponent which depends only on the dimensionality of the
extended defect. We also consider the unbinding transition of a single vortex
line from a twin plane occupied by other vortices. We show that the critical
properties of this transition depend strongly on the Luttinger liquid parameter
which describes the long distance physics of the two-dimensional flux line
array.Comment: 5 pages, 4 figure
Slow Coarsening in a Class of Driven Systems
The coarsening process in a class of driven systems is studied. These systems
have previously been shown to exhibit phase separation and slow coarsening in
one dimension. We consider generalizations of this class of models to higher
dimensions. In particular we study a system of three types of particles that
diffuse under local conserving dynamics in two dimensions. Arguments and
numerical studies are presented indicating that the coarsening process in any
number of dimensions is logarithmically slow in time. A key feature of this
behavior is that the interfaces separating the various growing domains are
smooth (well approximated by a Fermi function). This implies that the
coarsening mechanism in one dimension is readily extendible to higher
dimensions.Comment: submitted to EPJB, 13 page
Phase transition in a non-conserving driven diffusive system
An asymmetric exclusion process comprising positive particles, negative
particles and vacancies is introduced. The model is defined on a ring and the
dynamics does not conserve the number of particles. We solve the steady state
exactly and show that it can exhibit a continuous phase transition in which the
density of vacancies decreases to zero. The model has no absorbing state and
furnishes an example of a one-dimensional phase transition in a homogeneous
non-conserving system which does not belong to the absorbing state universality
classes
Quantum interface between an electrical circuit and a single atom
We show how to bridge the divide between atomic systems and electronic
devices by engineering a coupling between the motion of a single ion and the
quantized electric field of a resonant circuit. Our method can be used to
couple the internal state of an ion to the quantized circuit with the same
speed as the internal-state coupling between two ions. All the well-known
quantum information protocols linking ion internal and motional states can be
converted to protocols between circuit photons and ion internal states. Our
results enable quantum interfaces between solid state qubits, atomic qubits,
and light, and lay the groundwork for a direct quantum connection between
electrical and atomic metrology standards.Comment: Supplemental material available on reques
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