19,086 research outputs found
Theory of DNA translocation through narrow ion channels and nanopores with charged walls
Translocation of a single stranded DNA through genetically engineered
-hemolysin channels with positively charged walls is studied. It is
predicted that transport properties of such channels are dramatically different
from neutral wild type -hemolysin channel. We assume that the wall
charges compensate the fraction of the bare charge of the DNA piece
residing in the channel. Our prediction are as follows (i) At small
concentration of salt the blocked ion current decreases with . (ii) The
effective charge of DNA piece, which is very small at (neutral
channel) grows with and at reaches . (iii) The rate of DNA
capture by the channel exponentially grows with . Our theory is also
applicable to translocation of a double stranded DNA in narrow solid state
nanopores with positively charged walls.Comment: 3 pages, 1 figur
Hopping conductivity of a suspension of nanowires in an insulator
We study the hopping conduction in a composite made of straight metallic
nanowires randomly and isotropically suspended in an insulator. Uncontrolled
donors and acceptors in the insulator lead to random charging of wires and
hence finite bare density of states at the Fermi level. Then the Coulomb
interactions between electrons of distant wires result in the soft Coulomb gap.
At low temperatures the conductivity is due to variable range hopping of
electrons between wires and obeys the Efros-Shklovskii (ES) law . We show that , where
is the concentration of wires and is the wire length. Due to enhanced
screening of Coulomb potentials, at large enough , the ES law is replaced
by the Mott law.Comment: 5 pages, 5 figure
How a protein searches for its specific site on DNA: the role of intersegment transfer
Proteins are known to locate their specific targets on DNA up to two orders
of magnitude faster than predicted by the Smoluchowski three-dimensional
diffusion rate. One of the mechanisms proposed to resolve this discrepancy is
termed "intersegment transfer". Many proteins have two DNA binding sites and
can transfer from one DNA segment to another without dissociation to water. We
calculate the target search rate for such proteins in a dense globular DNA,
taking into account intersegment transfer working in conjunction with DNA
motion and protein sliding along DNA. We show that intersegment transfer plays
a very important role in cases where the protein spends most of its time
adsorbed on DNA.Comment: 9 pages, 7 figure
Improved transfer matrix method without numerical instability
A new improved transfer matrix method (TMM) is presented. It is shown that
the method not only overcomes the numerical instability found in the original
TMM, but also greatly improves the scalability of computation. The new improved
TMM has no extra cost of computing time as the length of homogeneous scattering
region becomes large. The comparison between the scattering matrix method(SMM)
and our new TMM is given. It clearly shows that our new method is much faster
than SMM.Comment: 5 pages,3 figure
Approximation in LQG control of a thermoelastic rod
Control and estimator gains are computed for linear-quadratic-Gaussian (LQG) optimal control of the axial vibrations of a thermoelastic rod. The computations are based on a modal approximation of the partial differential equations representing the rod, and convergence of the approximations to control and estimator gains is the main issue
Simple Recurrent Units for Highly Parallelizable Recurrence
Common recurrent neural architectures scale poorly due to the intrinsic
difficulty in parallelizing their state computations. In this work, we propose
the Simple Recurrent Unit (SRU), a light recurrent unit that balances model
capacity and scalability. SRU is designed to provide expressive recurrence,
enable highly parallelized implementation, and comes with careful
initialization to facilitate training of deep models. We demonstrate the
effectiveness of SRU on multiple NLP tasks. SRU achieves 5--9x speed-up over
cuDNN-optimized LSTM on classification and question answering datasets, and
delivers stronger results than LSTM and convolutional models. We also obtain an
average of 0.7 BLEU improvement over the Transformer model on translation by
incorporating SRU into the architecture.Comment: EMNL
How does a protein search for the specific site on DNA: the role of disorder
Proteins can locate their specific targets on DNA up to two orders of
magnitude faster than the Smoluchowski three-dimensional diffusion rate. This
happens due to non-specific adsorption of proteins to DNA and subsequent
one-dimensional sliding along DNA. We call such one-dimensional route towards
the target "antenna". We studied the role of the dispersion of nonspecific
binding energies within the antenna due to quasi random sequence of natural
DNA. Random energy profile for sliding proteins slows the searching rate for
the target. We show that this slowdown is different for the macroscopic and
mesoscopic antennas.Comment: 4 pages, 4 figure
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