1,042 research outputs found
Collapse Transition of Two-Dimensional Flexible and Semiflexible Polymers
The nature of the globule-coil transition of surface-confined polymers has
been an issue of debate. Here this 2D collapse transition is studied through a
partially directed lattice model. In the general case of polymers with positive
bending stiffness (), the collapse transition is {\em first-order};
it becomes {\em second-order} only in the limiting case of zero bending
stiffness (). These analytical results are confirmed by Monte
Carlo simulations. We also suggest some possible future experiments.Comment: 4 pages, 3 figure
Better synchronizability predicted by a new coupling method
In this paper, inspired by the idea that the hub nodes of a highly
heterogeneous network are not only the bottlenecks, but also effective
controllers in the network synchronizing process, we bring forward an
asymmetrical coupling method where the coupling strength of each node depends
on its neighbors' degrees. Compared with the uniform coupled method and the
recently proposed Motter-Zhou-Kurth method, the synchronizability of scale-free
networks can be remarkably enhanced by using the present coupled method.Comment: 6 pages, 6 figures; to be published in EPJ
Temperature dependence of circular DNA topological states
Circular double stranded DNA has different topological states which are
defined by their linking numbers. Equilibrium distribution of linking numbers
can be obtained by closing a linear DNA into a circle by ligase. Using Monte
Carlo simulation, we predict the temperature dependence of the linking number
distribution of small circular DNAs. Our predictions are based on flexible
defect excitations resulted from local melting or unstacking of DNA base pairs.
We found that the reduced bending rigidity alone can lead to measurable changes
of the variance of linking number distribution of short circular DNAs. If the
defect is accompanied by local unwinding, the effect becomes much more
prominent. The predictions can be easily investigated in experiments, providing
a new method to study the micromechanics of sharply bent DNAs and the thermal
stability of specific DNA sequences. Furthermore, the predictions are directly
applicable to the studies of binding of DNA distorting proteins that can
locally reduce DNA rigidity, form DNA kinks, or introduce local unwinding.Comment: 15 pages in preprint format, 4 figure
A Stochastic Second-Order Proximal Method for Distributed Optimization
In this paper, we propose a distributed stochastic second-order proximal
method that enables agents in a network to cooperatively minimize the sum of
their local loss functions without any centralized coordination. The proposed
algorithm, referred to as St-SoPro, incorporates a decentralized second-order
approximation into an augmented Lagrangian function, and then randomly samples
the local gradients and Hessian matrices of the agents, so that it is
computationally and memory-wise efficient, particularly for large-scale
optimization problems. We show that for globally restricted strongly convex
problems, the expected optimality error of St-SoPro asymptotically drops below
an explicit error bound at a linear rate, and the error bound can be
arbitrarily small with proper parameter settings. Simulations over real machine
learning datasets demonstrate that St-SoPro outperforms several
state-of-the-art distributed stochastic first-order methods in terms of
convergence speed as well as computation and communication costs.Comment: 6 pages, 8 figure
Instability and Periodic Deformation in Bilayer Membranes Induced by Freezing
The instability and periodic deformation of bilayer membranes during freezing
processes are studied as a function of the difference of the shape energy
between the high and the low temperature membrane states. It is shown that
there exists a threshold stability condition, bellow which a planar
configuration will be deformed. Among the deformed shapes, the periodic curved
square textures are shown being one kind of the solutions of the associated
shape equation. In consistency with recent expe rimental observations, the
optimal ratio of period and amplitude for such a texture is found to be
approximately equal to (2)^{1/2}\pi.Comment: 8 pages in Latex form, 1 Postscript figure. To be appear in Mod.
Phys. Lett. B. 199
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