5,244 research outputs found
Directional motion of forced polymer chains with hydrodynamic interaction
We study the propulsion of a one-dimensional (1D) polymer chain under
sinusoidal external forces in the overdamped (low Reynolds number) regime. We
show that, when hydrodynamical interactions are included, the polymer presents
directional motion which depends on the phase differences of the external force
applied along the chain. Moreover, the velocity shows a maximum as a function
of the frequency. We discuss the relevance of all these results in light of
recent nanotechnology experiments.Comment: 5 pages, 6 figure
Two Langevin equations in the Doi-Peliti formalism
A system-size expansion method is incorporated into the Doi-Peliti formalism
for stochastic chemical kinetics. The basic idea of the incorporation is to
introduce a new decomposition of unity associated with a so-called Cole-Hopf
transformation. This approach elucidates a relationship between two different
Langevin equations; one is associated with a coherent-state path-integral
expression and the other describes density fluctuations. A simple reaction
scheme is investigated as an illustrative example.Comment: 14page
Proper motions with Subaru II. A sample in the Subaru/XMM-Newton Deep Survey field
We search for stars with proper motions in a set of deep Subaru images,
covering about 0.48 square degrees to a depth of , taken over a
span of five and a half years. We follow the methods described in
\citet{Richmond2009} to reduce and analyze this dataset. We present a sample of
69 stars with motions of high significance, and discuss briefly the populations
from which they are likely drawn. Based on photometry and motions alone, we
expect that 14 of the candidates may be white dwarfs. Our candidate with the
largest proper motion is surprisingly faint and likely to prove interesting:
its colors and motions suggest that it might be an M dwarf moving at over 500
km/sec or an L dwarf in the halo.Comment: 10 pages, 5 figures. Accepted by Publications of the Astronomical
Society of Japan, to appear in volume 62, February 2010. Revised version:
removed PASJ LaTeX tutorial which was mistakenly appended to pape
Bounds on effective Majorana neutrino masses at HERA
The lepton-number violating process e p \to nu_e l l' X mediated by Majorana
neutrinos is studied for the HERA collider for (l l') = (e tau), (mu tau), (mu
mu) and (tau tau). Only the muonic decay of the tau is considered. The direct
limit on the effective muon Majorana mass, is improved
significantly to 4.0 times 10^3 GeV and for the first time direct limits on the
analogous effective masses connected with the tau sector are given, namely 4.2
times 10^3 GeV for , 4.4 times 10^3 GeV for and 2.0
times 10^4 GeV for . We find that a more general analysis for an
upgraded HERA could improve this values by a factor of up to 40, yet still
being orders of magnitude worse than indirect limits.Comment: 9 pages, 4 figures, revised versio
Dynamics of a Rigid Rod in a Glassy Medium
We present simulations of the motion of a single rigid rod in a disordered
static 2d-array of disk-like obstacles. The rotational, , and
center-of-mass translational, , diffusion constants are calculated
for a wide range of rod length and density of obstacles . It is found
that follows the behavior predicted by kinetic theory for a hard
disk with an effective radius . A dynamic crossover is observed in
for comparable to the typical distance between neighboring
obstacles . Using arguments from kinetic theory and reptation, we
rationalize the scaling laws, dynamic exponents, and prefactors observed for
. In analogy with the enhanced translational diffusion observed in
deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for
.Comment: 8 pages, 4 figures. Major changes. To be published in Europhysics
Letter
A field theoretic approach to master equations and a variational method beyond the Poisson ansatz
We develop a variational scheme in a field theoretic approach to a stochastic
process. While various stochastic processes can be expressed using master
equations, in general it is difficult to solve the master equations exactly,
and it is also hard to solve the master equations numerically because of the
curse of dimensionality. The field theoretic approach has been used in order to
study such complicated master equations, and the variational scheme achieves
tremendous reduction in the dimensionality of master equations. For the
variational method, only the Poisson ansatz has been used, in which one
restricts the variational function to a Poisson distribution. Hence, one has
dealt with only restricted fluctuation effects. We develop the variational
method further, which enables us to treat an arbitrary variational function. It
is shown that the variational scheme developed gives a quantitatively good
approximation for master equations which describe a stochastic gene regulatory
network.Comment: 13 pages, 2 figure
A multi-wavelength view of galaxy evolution with AKARI
AKARI's all-sky survey resolves the far-infrared emission in many thousands
of nearby galaxies, providing essential local benchmarks against which the
evolution of high-redshift populations can be measured. This review presents
some recent results in the resolved galaxy populations, covering some
well-known nearby targets, as well as samples from major legacy surveys such as
the Herschel Reference Survey and the JCMT Nearby Galaxies Survey. This review
also discusses the prospects for higher redshifts surveys, including strong
gravitational lens clusters and the AKARI NEP field.Comment: Accepted for Publications of the Korean Astronomical Society
(September 30, 2012 issue, volume 27, No. 3), Proceedings of the Second AKARI
conference, Legacy of AKARI: A Panoramic View of the Dusty Universe. 6 page
Competition of the connectivity with the local and the global order in polymer melts and crystals
The competition between the connectivity and the local or global order in
model fully-flexible chain molecules is investigated by molecular-dynamics
simulations. States with both missing (melts) and high (crystal) global order
are considered. Local order is characterized within the first coordination
shell (FCS) of a tagged monomer and found to be lower than in atomic systems in
both melt and crystal. The role played by the bonds linking the tagged monomer
to FCS monomers (radial bonds), and the bonds linking two FCS monomers (shell
bonds) is investigated. The detailed analysis in terms of Steinhardt's
orientation order parameters Q_l (l = 2 - 10) reveals that increasing the
number of shell bonds decreases the FCS order in both melt and crystal.
Differently, the FCS arrangements organize the radial bonds. Even if the
molecular chains are fully flexible, the distribution of the angle formed by
adjacent radial bonds exhibits sharp contributions at the characteristic angles
{\theta} = 70{\deg}, 122{\deg}, 180{\deg}. The fractions of adjacent radial
bonds with {\theta} = 122{\deg}, 180{\deg} are enhanced by the global order of
the crystal, whereas the fraction with 70{\deg} < {\theta} < 110{\deg} is
nearly unaffected by the crystallization. Kink defects, i.e. large lateral
displacements of the chains, are evidenced in the crystalline state.Comment: J. Chem. Phys. in pres
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