3,110 research outputs found
Origins of Replication in Sorangium cellulosum and Microcystis aeruginosa
The genome of Sorangium cellulosum has recently been completely sequenced, and it is the largest bacterial genome sequenced so far. In their report, Schneiker et al. (in Complete genome sequence of the myxobacterium Sorangium cellulosum, Nat. Biotechnol., 2007, 25, 1281â1289) concluded that âIn the absence of the GC-skew inversion typically seen at the replication origin of bacterial chromosomes, it was not possible to discern the location of oriCâ. In addition, the complete genome of Microcystis aeruginosa NIES-843 has also been recently sequenced, and in this report, Kaneko et al. (in Complete genomic structure of the bloom-forming toxic cyanobacterium Microcystis aeruginosa NIES-843, DNA Res., 2007, 14, 247â256) concluded that âthere was no characteristic pattern, according to GC skew analysisâ. Therefore, oriC locations of the above genomes remain unsolved. Using Ori-Finder, a recently developed computer program, in both genomes, we have identified candidate oriC regions that have almost all sequence hallmarks of bacterial oriCs, such as asymmetrical nucleotide distributions, being adjacent to the dnaN gene, and containing DnaA boxes and repeat elements
Radiative pion capture by a nucleon
The differential cross sections for and are computed up to in heavy baryon chiral perturbation
theory (HBChPT). The expressions at and have no free
parameters. There are three unknown parameters at , low energy
constants of the HBChPT Lagrangian, which are determined by fitting to
experimental data. Two acceptable fits are obtained, which can be separated by
comparing with earlier dispersion relation calculations of the inverse process.
Expressions for the multipoles, with emphasis on the p-wave multipoles, are
obtained and evaluated at threshold. Generally the results obtained from the
best of the two fits are in good agreement with the dispersion relation
predictions.Comment: 24 pages, Latex, using RevTe
Properties of Regge Trajectories
Early Chew-Frautschi plots show that meson and baryon Regge trajectoies are
approximately linear and non-intersecting. In this paper, we reconstruct all
Regge trajectories from the most recent data. Our plots show that meson
trajectories are non-linear and intersecting. We also show that all current
meson Regge trajectories models are ruled out by data.Comment: 30 pages, latex, 18 figures, to be published in Physical Review
Analytic Confinement and Regge Trajectories
A simple relativistic quantum field model with the Yukawa-type interaction is
considered to demonstrate that the analytic confinement of the constituent
("quarks") and carrier ("gluons") particles explains qualitatively the basic
dynamical properties of the spectrum of mesons considered as two-particle
stable bound states of quarks and gluons: the quarks and gluons are confined,
the glueballs represent bound states of massless gluons, the masses of mesons
are larger than the sum of the constituent quark masses and the Regge
trajectories of mesonic orbital excitations are almost linear.Comment: RevTeX, 16 pages, 3 figures and 2 table
Unified Approach to High- and Low-Energy Strong Interactions on the Basis of the Mandelstam Representation
Balancing Minimum Spanning and Shortest Path Trees
This paper give a simple linear-time algorithm that, given a weighted
digraph, finds a spanning tree that simultaneously approximates a shortest-path
tree and a minimum spanning tree. The algorithm provides a continuous
trade-off: given the two trees and epsilon > 0, the algorithm returns a
spanning tree in which the distance between any vertex and the root of the
shortest-path tree is at most 1+epsilon times the shortest-path distance, and
yet the total weight of the tree is at most 1+2/epsilon times the weight of a
minimum spanning tree. This is the best tradeoff possible. The paper also
describes a fast parallel implementation.Comment: conference version: ACM-SIAM Symposium on Discrete Algorithms (1993
Extraction of the coupling constant from NN scattering data
We reexamine Chew's method for extracting the coupling constant from
np differential cross section measurements. Values for this coupling are
extracted below 350 MeV, in the potential model region, and up to 1 GeV. The
analyses to 1~GeV have utilized 55 data sets. We compare these results to those
obtained via mapping techniques. We find that these two methods give
consistent results which are in agreement with previous Nijmegen
determinations.Comment: 12 pages of text plus 2 figures. Revtex file and postscript figures
available via anonymous FTP at ftp://clsaid.phys.vt.edu/pub/n
Body-assisted van der Waals interaction between two atoms
Using fourth-order perturbation theory, a general formula for the van der
Waals potential of two neutral, unpolarized, ground-state atoms in the presence
of an arbitrary arrangement of dispersing and absorbing magnetodielectric
bodies is derived. The theory is applied to two atoms in bulk material and in
front of a planar multilayer system, with special emphasis on the cases of a
perfectly reflecting plate and a semi-infinite half space. It is demonstrated
that the enhancement and reduction of the two-atom interaction due to the
presence of a perfectly reflecting plate can be understood, at least in the
nonretarded limit, by using the method of image charges. For the semi-infinite
half space, both analytical and numerical results are presented.Comment: 17 pages, 9 figure
Hybrid viscosity and the magnetoviscous instability in hot, collisionless accretion disks
We aim to illustrate the role of hot protons in enhancing the
magnetorotational instability (MRI) via the ``hybrid'' viscosity, which is due
to the redirection of protons interacting with static magnetic field
perturbations, and to establish that it is the only relevant mechanism in this
situation. It has recently been shown by Balbus \cite{PBM1} and Islam & Balbus
\cite{PBM11} using a fluid approach that viscous momentum transport is key to
the development of the MRI in accretion disks for a wide range of parameters.
However, their results do not apply in hot, advection-dominated disks, which
are collisionless. We develop a fluid picture using the hybrid viscosity
mechanism, that applies in the collisionless limit. We demonstrate that viscous
effects arising from this mechanism can significantly enhance the growth of the
MRI as long as the plasma \beta \gapprox 80. Our results facilitate for the
first time a direct comparison between the MHD and quasi-kinetic treatments of
the magnetoviscous instability in hot, collisionless disks.Comment: To appear in the proceedings of the first Kodai-Trieste workshop on
Plasma Astrophysics (Aug 27-Sept 07 2007), Springer Astrophysics and Space
Science Proceedings serie
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