4,817 research outputs found
Finite-Width Bundle is Most Stable in a Solution with Salt
We applied the mean-field approach to a columnar bundle assembled by the
parallel arrangement of stiff polyelectrolyte rods in a salt bath. The
electrostatic potential can be divided into two regions: inside the bundle for
condensed counter-ions, and outside the bundle for free small ions. To
determine the distribution of condensed counter-ions inside the bundle, we use
a local self-consistent condition that depends on the charge density, the
electrostatic potential, and the net polarization. The results showed that,
upon bundle formation, the electric charge of polyelectrolytes, even those
inside the bundle, tend to survive in an inhomogeneous manner, and thus their
width remains finite under thermal equilibrium because of the long-range effect
of charge instability.Comment: 7 pages, 4 figure
The probability of double-strand breaks in giant DNA decreases markedly as the DNA concentration increases
DNA double-strand breaks (DSBs) represent a serious source of damage for all
living things and thus there have been many quantitative studies of DSBs both
in vivo and in vitro. Despite this fact, the processes that lead to their
production have not yet been clearly understood, and there is no established
theory that can account for the statistics of their production, in particular,
the number of DSBs per base pair per unit Gy, here denoted by P1, which is the
most important parameter for evaluating the degree of risk posed by DSBs. Here,
using the single-molecule observation method with giant DNA molecules (166
kbp), we evaluate the number of DSBs caused by gamma-ray irradiation. We find
that P1 is nearly inversely proportional to the DNA concentration above a
certain threshold DNA concentration. A simple model that accounts for the
marked decrease of P1 shows that it is necessary to consider the
characteristics of giant DNA molecules as semiflexible polymers to interpret
the intrinsic mechanism of DSBs
Why is the condensed phase of DNA preferred at higher temperature? DNA compaction in the presence of a multivalent cation
Upon the addition of multivalent cations, a giant DNA chain exhibits a large
discrete transition from an elongated coil into a folded compact state. We
performed single-chain observation of long DNAs in the presence of a
tetravalent cation (spermine), at various temperatures and monovalent salt
concentrations. We confirmed that the compact state is preferred at higher
temperatures and at lower monovalent salt concentrations. This result is
interpreted in terms of an increase in the net translational entropy of small
ions due to ionic exchange between higher and lower valence ions.Comment: 4pages,3figure
The effect of facial expression and gaze direction on memory for unfamiliar faces
We report data from an experiment that investigated the influence of gaze direction and facial expression on face memory. Participants were shown a set of unfamiliar faces with either happy or angry facial expressions, which were either gazing straight ahead or had their gaze averted to one side. Memory for faces that were initially shown with angry expressions was found to be poorer when these faces had averted as opposed to direct gaze, whereas memory for individuals shown with happy faces was unaffected by gaze direction. We suggest that memory for another individual's face partly depends on an evaluation of the behavioural intention of that individual
Two-Temperature Intracluster Medium in Merging Clusters of Galaxies
We investigate the evolution of intracluster medium during a cluster merger,
explicitly considering the relaxation process between the ions and electrons by
N-body and hydrodynamical simulations. When two subclusters collide each other,
a bow shock is formed between the centers of two substructures and propagate in
both directions along the collision axis. The shock primarily heats the ions
because the kinetic energy of an ion entering the shock is larger than that of
an electron by the ratio of masses. In the post-shock region the energy is
transported from the ions to electrons via Coulomb coupling. However, since the
energy exchange timescale depends both on the gas density and temperature,
distribution of electron temperature becomes more complex than that of the
plasma mean temperature, especially in the expanding phase. After the collision
of two subclusters, gas outflow occurs not only along the collision axis but
also in its perpendicular direction. The gas which is originally located in the
central part of the subclusters moves both in the parallel and perpendicular
directions. Since the equilibrium timescale of the gas along these directions
is relatively short, temperature difference between ions and electrons is
larger in the directions tilted by the angles of with respect to
the collision axis. The electron temperature could be significantly lower that
the plasma mean temperature by at most. The significance of our
results in the interpretation of X-ray observations is briefly discussed.Comment: 20 pages, 11 figures, Accepted for publication in Ap
Properties of the cosmological filament between two clusters: A possible detection of a large-scale accretion shock by
We report on the results of a observation of the plasma in the
filament located between the two massive clusters of galaxies Abell 399 and
Abell 401. Abell 399 (=0.0724) and Abell 401 (=0.0737) are expected to be
in the initial phase of a cluster merger. In the region between the two
clusters, we find a clear enhancement in the temperature of the filament plasma
from 4 keV (expected value from a typical cluster temperature profile) to
6.5 keV. Our analysis also shows that filament plasma is present out to
a radial distance of 15' (1.3 Mpc) from a line connecting the two clusters. The
temperature profile is characterized by an almost flat radial shape with
6-7 keV within 10' or 0.8 Mpc. Across =8'~from the axis, the
temperature of the filament plasma shows a drop from 6.3 keV to 5.1 keV,
indicating the presence of a shock front. The Mach number based on the
temperature drop is estimated to be 1.3. We also successfully
determined the abundance profile up to 15' (1.3 Mpc), showing an almost
constant value (=0.3 solar) at the cluster outskirt. We estimated the
Compton -parameter to be 14.5, which is in
agreement with 's results (14-17 on the filament). The
line of sight depth of the filament is 1.1 Mpc, indicating that the
geometry of filament is likely a pancake shape rather than cylindrical. The
total mass of the filamentary structure is 7.7. We discuss a possible interpretation of the drop of X-ray emission
at the rim of the filament, which was pushed out by the merging activity and
formed by the accretion flow induced by the gravitational force of the
filament.Comment: 8 pages, 8 figures, accepted for publication in A&
Discrete Klein-Gordon models with static kinks free of the Peierls-Nabarro potential
For the nonlinear Klein-Gordon type models, we describe a general method of
discretization in which the static kink can be placed anywhere with respect to
the lattice. These discrete models are therefore free of the {\it static}
Peierls-Nabarro potential. Previously reported models of this type are shown to
belong to a wider class of models derived by means of the proposed method. A
relevant physical consequence of our findings is the existence of a wide class
of discrete Klein-Gordon models where slow kinks {\it practically} do not
experience the action of the Peierls-Nabarro potential. Such kinks are not
trapped by the lattice and they can be accelerated by even weak external
fields.Comment: 6 pages, 2 figure
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