1,736 research outputs found
Protein-Mediated DNA Loops: Effects of Protein Bridge Size and Kinks
This paper focuses on the probability that a portion of DNA closes on itself
through thermal fluctuations. We investigate the dependence of this probability
upon the size r of a protein bridge and/or the presence of a kink at half DNA
length. The DNA is modeled by the Worm-Like Chain model, and the probability of
loop formation is calculated in two ways: exact numerical evaluation of the
constrained path integral and the extension of the Shimada and Yamakawa saddle
point approximation. For example, we find that the looping free energy of a 100
base pairs DNA decreases from 24 kT to 13 kT when the loop is closed by a
protein of r = 10 nm length. It further decreases to 5 kT when the loop has a
kink of 120 degrees at half-length.Comment: corrected typos and figures, references updated; 13 pages, 7 figures,
accepted for publication in Phys. Rev.
Characterization of Acylated Anthocyanins in Callus Induced From Storage Root of Purple-Fleshed Sweet Potato, Ipomoea batatas L
Four anthocyanins were isolated from a highly pigmented callus induced from the storage root of purple-fleshed sweet potato (Ipomoea batatas L) cultivar Ayamurasaki. The anthocyanins were respectively identified as cyanidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D-glucopyranosyl)-β-D-glucopyranoside) -5-O-β-D-glucopyranoside, cyanidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-caffeoyl-β-D-glucopyranoside)-5-O-β-D-glucopyranoside, cyanidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-p-coumaroyl-β-D-glucopyranoside)- 5-O-β-D-glucopyranoside, and peonidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-p-coumaroyl-β-D-glucopyranoside)-5-O-β-D-glucopyranoside by chemical and spectroscopic analyses. These anthocyanins were examined with respect to the stability in neutral aqueous solution as well as the radical scavenging activity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. These acylated anthocyanins exhibited both higher stability and higher DPPH radical scavenging activity than corresponding nonacylated cyanidin and peonidin 3-O-sophoroside-5-O-glucosides
Radial distribution function of semiflexible polymers
We calculate the distribution function of the end--to--end distance of a
semiflexible polymer with large bending rigidity. This quantity is directly
observable in experiments on single semiflexible polymers (e.g., DNA, actin)
and relevant to their interpretation. It is also an important starting point
for analyzing the behavior of more complex systems such as networks and
solutions of semiflexible polymers. To estimate the validity of the obtained
analytical expressions, we also determine the distribution function numerically
using Monte Carlo simulation and find good quantitative agreement.Comment: RevTeX, 4 pages, 1 figure. Also available at
http://www.cip.physik.tu-muenchen.de/tumphy/d/T34/Mitarbeiter/frey.htm
Elasticity of Stiff Biopolymers
We present a statistical mechanical study of stiff polymers, motivated by
experiments on actin filaments and the considerable current interest in polymer
networks. We obtain simple, approximate analytical forms for the
force-extension relations and compare these with numerical treatments. We note
the important role of boundary conditions in determining force-extension
relations. The theoretical predictions presented here can be tested against
single molecule experiments on neurofilaments and cytoskeletal filaments like
actin and microtubules. Our work is motivated by the buckling of the
cytoskeleton of a cell under compression, a phenomenon of interest to biology.Comment: Submitted for publication, five pages, three figure
Quadrupole Susceptibility and Elastic Softening due to a Vacancy in Silicon Crystal
We investigate the electronic states around a single vacancy in silicon
crystal by using the Green's function approach. The triply degenerate vacancy
states within the band gap are found to be extended over a large distance
from the vacancy site and contribute to the reciprocal
temperature dependence of the quadrupole susceptibility resulting in the
elastic softening at low temperture. The Curie constant of the quadrupole
susceptibility for the trigonal mode () is largely
enhanced as compared to that for the tetragonal mode ().
The obtained results are consistent with the recent ultrasonic experiments in
silicon crystal down to 20 mK. We also calculate the dipole and octupole
susceptibilities and find that the octupole susceptibilities are extremely
enhannced for a specific mode.Comment: 6 pages, with 5 figure
Проблема конкуренції криінально-правових норм (кримінальних законів) у науці пострадянського (радянського) кримінального права та в науці кримінального права держав, які відносяться до романо-германської правової сім'ї
У статті проаналізовано наукові погляди на конкуренцію кримінально-правових норм (кримінальних законів) у теорії пострадянського (радянського) кримінального права та в теорії кримінального права держав, які відносяться до романо-германської правової сім'ї. Ключові слова: конкуренція кримінально-правових норм, конкуренція законів.В статье анализируются научные взгляды на конкуренцию уголовно-правовых норм (уголовных законов) в теории постсоветского (советского) уголовного права и в теории уголовного права государств, которые относятся к романо-германской правовой семье. Ключевые слова: конкуренция уголовно-правовых норм, конкуренция законов.In the article scientific looks are analyzed to the competition of criminal law norm’s (criminal laws) in the theory of post-soviet (soviet) criminal law and in the theory of criminal law of the states which behave to the legal system of civil law. Key words: competition of criminal law norm’s, competition of laws
Projectile Fragmentation of the Extremely Neutron-Rich Nucleus ^<11>Li at o.79 GeV/nucleon
Projectile fragmentations of ^Li, ^He, and ^He have been measured at 0.79 GeV/nucleon. Production cross sections and momentum distributions of the produced isotopes (Z≥2) are measured inclusively. Transverse-momentum distributions of ^Li from the fragmentation of ^Li show two Gaussian components of different widths. The width of the wide component is consistent with the values observed in the fragmentation of stable nuclei, whereas the other component shows an extremely narrow width reflecting the weak binding of the two outer neutrons in the ^Li nucleus
Bimodal distribution function of a 3d wormlike chain with a fixed orientation of one end
We study the distribution function of the three dimensional wormlike chain
with a fixed orientation of one chain end using the exact representation of the
distribution function in terms of the Green's function of the quantum rigid
rotator in a homogeneous external field. The transverse 1d distribution
function of the free chain end displays a bimodal shape in the intermediate
range of the chain lengths (). We present also
analytical results for short and long chains, which are in complete agreement
with the results of previous studies obtained using different methods.Comment: 6 pages, 3 figure
Exact theory of kinkable elastic polymers
The importance of nonlinearities in material constitutive relations has long
been appreciated in the continuum mechanics of macroscopic rods. Although the
moment (torque) response to bending is almost universally linear for small
deflection angles, many rod systems exhibit a high-curvature softening. The
signature behavior of these rod systems is a kinking transition in which the
bending is localized. Recent DNA cyclization experiments by Cloutier and Widom
have offered evidence that the linear-elastic bending theory fails to describe
the high-curvature mechanics of DNA. Motivated by this recent experimental
work, we develop a simple and exact theory of the statistical mechanics of
linear-elastic polymer chains that can undergo a kinking transition. We
characterize the kinking behavior with a single parameter and show that the
resulting theory reproduces both the low-curvature linear-elastic behavior
which is already well described by the Wormlike Chain model, as well as the
high-curvature softening observed in recent cyclization experiments.Comment: Revised for PRE. 40 pages, 12 figure
The distribution function of a semiflexible polymer and random walks with constraints
In studying the end-to-end distribution function of a worm like
chain by using the propagator method we have established that the combinatorial
problem of counting the paths contributing to can be mapped onto the
problem of random walks with constraints, which is closely related to the
representation theory of the Temperley-Lieb algebra. By using this mapping we
derive an exact expression of the Fourier-Laplace transform of the distribution
function, , as a matrix element of an inverse of an infinite rank
matrix. Using this result we also derived a recursion relation permitting to
compute directly. We present the results of the computation of
and its moments. The moments of can be
calculated \emph{exactly} by calculating the (1,1) matrix element of -th
power of a truncated matrix of rank .Comment: 6 pages, 2 figures, added a referenc
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