1,597 research outputs found
DNA Spools under Tension
DNA-spools, structures in which DNA is wrapped and helically coiled onto
itself or onto a protein core are ubiquitous in nature. We develop a general
theory describing the non-equilibrium behavior of DNA-spools under linear
tension. Two puzzling and seemingly unrelated recent experimental findings, the
sudden quantized unwrapping of nucleosomes and that of DNA toroidal condensates
under tension are theoretically explained and shown to be of the same origin.
The study provides new insights into nucleosome and chromatin fiber stability
and dynamics
Flexoelectricity and piezoelectricity - reason for rich variety of phases in antiferroelectric liquid crystals
The free energy of antiferroelectric liquid crystal which takes into account
polar order explicitly is presented. Steric, van der Waals, piezoelectric and
flexoelectric interactions to the nearest layers and dipolar electrostatic
interactions to the nearest and to the next nearest layers induce indirect tilt
interactions with chiral and achiral properties, which extend to the third and
to the fourth nearest layers. Chiral indirect interactions between tilts can be
large and induce helicoidal modulations even in systems with negligible chiral
van der Waals interactions. If indirect chiral interactions compete with chiral
van der Waals interactions, the helix unwinding is possible. Although strength
of microscopic interactions change monotonically with decreasing temperature,
effective interlayer interactions change nonmonotonically and give rise to
nonmonotouous change of modulation period through various phases. Increased
enatiomeric excess i.e. increased chirality changes the phase sequence.Comment: 4 pages, 1 figur
Screened and Unscreened Phases in Sedimenting Suspensions
A coarse-grained stochastic hydrodynamical description of velocity and
concentration fluctuations in steadily sedimenting suspensions is constructed,
and analyzed using self-consistent and renormalization group methods. We find
that there exists a dynamical, non-equilibrium phase transition from an
"unscreened" phase in which we recover the Caflisch-Luke (R.E. Caflisch and
J.H.C. Luke, Phys. Fluids 28, 759 (1985)) divergence of the velocity variance
to a "screened" phase where the velocity fluctuations have a finite correlation
length growing as where is the particle volume fraction,
in agreement with Segr\`e et. al. (Phys. Rev. Lett. 79, 2574 (1997)) and the
velocity variance is independent of system size. Detailed predictions are made
for the correlation function in both phases and at the transition.Comment: 4 pages, revtex 1 figur
Fluctuation-Facilitated Charge Migration along DNA
We propose a model Hamiltonian for charge transfer along the DNA double helix
with temperature driven fluctuations in the base pair positions acting as the
rate limiting factor for charge transfer between neighboring base pairs. We
compare the predictions of the model with the recent work of J.K. Barton and
A.H. Zewail (Proc.Natl.Acad.Sci.USA, {\bf 96}, 6014 (1999)) on the unusual
two-stage charge transfer of DNA.Comment: 4 pages, 2 figure
Vibrational Enhancement of the Effective Donor - Acceptor Coupling
The paper deals with a simple three sites model for charge transfer phenomena
in an one-dimensional donor (D) - bridge (B) - acceptor (A) system coupled with
vibrational dynamics of the B site. It is found that in a certain range of
parameters the vibrational coupling leads to an enhancement of the effective
donor - acceptor electronic coupling as a result of the formation of the
polaron on the B site. This enhancement of the charge transfer efficiency is
maximum at the resonance, where the effective energy of the fluctuating B site
coincides with the donor (acceptor) energy.Comment: 5 pages, 3 figure
Intermittency in Dynamics of Two-Dimensional Vortex-like Defects
We examine high-order dynamical correlations of defects (vortices,
disclinations etc) in thin films starting from the Langevin equation for the
defect motion. We demonstrate that dynamical correlation functions of
vorticity and disclinicity behave as where is the
characteristic scale and is the fugacity. As a consequence, below the
Berezinskii-Kosterlitz-Thouless transition temperature are
characterized by anomalous scaling exponents. The behavior strongly differs
from the normal law occurring for simultaneous correlation
functions, the non-simultaneous correlation functions appear to be much larger.
The phenomenon resembles intermittency in turbulence.Comment: 30 pages, 11 figure
Dynamic Scaling of Ion-Sputtered Surfaces
We derive a stochastic nonlinear equation to describe the evolution and
scaling properties of surfaces eroded by ion bombardment. The coefficients
appearing in the equation can be calculated explicitly in terms of the physical
parameters characterizing the sputtering process. We find that transitions may
take place between various scaling behaviors when experimental parameters such
as the angle of incidence of the incoming ions or their average penetration
depth, are varied.Comment: 13 pages, Revtex, 2 figure
Aggressive therapy in patients with early arthritis results in similar outcome compared with conventional care: the STREAM randomized trial
Objective. To compare the effects of aggressive tight control therapy and conventional care on radiographic progression and disease activity in patients with early mild inflammatory arthritis
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