11,087 research outputs found
Nonlinear input-normal realizations based on the differential eigenstructure of hankel operators
This paper investigates the differential eigenstructure of Hankel operators for nonlinear systems. First, it is proven that the variational system and the Hamiltonian extension with extended input and output spaces can be interpreted as the GĂÂąteaux differential and its adjoint of a dynamical input-output system, respectively. Second, the GĂÂąteaux differential is utilized to clarify the main result the differential eigenstructure of the nonlinear Hankel operator which is closely related to the Hankel norm of the original system. Third, a new characterization of the nonlinear extension of Hankel singular values are given based on the differential eigenstructure. Finally, a balancing procedure to obtain a new input-normal/output-diagonal realization is derived. The results in this paper thus provide new insights to the realization and balancing theory for nonlinear systems.
Environmental dependence of star formation induced by cloud collisions in a barred galaxy
Cloud collision have been proposed as a way to link the small-scale star
formation process with the observed global relation between the surface star
formation rate and gas surface density. We suggest that this model can be
improved further by allowing the productivity of such collisions to depend on
the relative velocity of the two clouds. Our adjustment implements a simple
step function that results in the most successful collisions being at the
observed velocities for triggered star formation. By applying this to a high
resolution simulation of a barred galaxy, we successfully reproduce the
observational result that the star formation efficiency (SFE) in the bar is
lower than that in the spiral arms. This is not possible when we use an
efficiency dependent on the internal turbulence properties of the clouds. Our
results suggest that high velocity collisions driven by the gravitational pull
of the clouds are responsible for the low bar SFE.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS Letter
Test of QEDPS: A Monte Carlo for the hard photon distributions in e+ e- annihilation proecss
The validity of a photon shower generator QEDPS has been examined in detail.
This is formulated based on the leading-logarithmic renormalization equation
for the electron structure function and it provides a photon shower along the
initial e+-. The main interest in the present work is to test the reliability
of the generator to describe a process accompanying hard photons which are
detected. For this purpose, by taking the HZ production as the basic reaction,
the total cross section and some distributions of the hard photons are compared
between two cases that these photons come from either those generated by QEDPS
or the hard process e+e- -> H Z gamma gamma. The comparison performed for the
single and the double hard photon has shown a satisfactory agreement which
demonstrated that the model is self-consistent.Comment: 22 pages, 4 Postscript figures, LaTeX, uses epsf.te
The X-ray Line Emission from the Supernova Remnant W49B
The Galactic supernova remnant W49B has one of the most impressive X-ray
emission line spectra obtained with the Advanced Satellite for Cosmology and
Astronomy (ASCA). We use both plasma line diagnostics and broadband model fits
to show that the Si and S emission lines require multiple spectral components.
The spectral data do not necessarily require individual elements to be
spatially stratified, as suggested by earlier work, although when ASCA line
images are considered, it is possible that Fe is stratified with respect to Si
and S. Most of the X-ray emitting gas is from ejecta, based on the element
abundances required, but is surprisingly close to being in collisional
ionization equilibrium. A high ionization age implies a high internal density
in a young remnant. The fitted emission measure for W49B indicates a minimum
density of 2 cm^-3, with the true density likely to be significantly higher.
W49B probably had a Type Ia progenitor, based on the relative element
abundances, although a low-mass Type II progenitor is still possible. We find
persuasive evidence for Cr and possibly Mn emission in the ASCA spectrum--the
first detection of these elements in X-rays from a cosmic source.Comment: 22 pages incl 8 postscript figures, to appear in Ap
A QED Shower Including the Next-to-leading Logarithm Correction in e+e- Annihilation
We develop an event generator, NLL-QEDPS, based on the QED shower including
the next-to-leading logarithm correction in the e^+e^- annihilation. The shower
model is the Monte Carlo technique to solve the renormalization group equation
so that they can calculate contributions of alpha^m log^n(S/m_e^2) for any m
and n systematically. Here alpha is the QED coupling, m_e is the mass of
electron and S is the square of the total energy in the e^+e^- system. While
the previous QEDPS is limited to the leading logarithm approximation which
includes only contributions of (alpha log(S/m_e^2))^n, the model developed here
contains terms of alpha(alpha log(S/m_e^2))^n, the the next-to-leading
logarithm correction.
The shower model is formulated for the initial radiation in the e^+e^-
annihilation. The generator based on it gives us events with q^2, which is a
virtual mass squared of the virtual photon and/or Z-boson, in accuracy of
0.04%, except for small q^2/S.Comment: 35 pages, 1 figure(eps-file
Comment on `Equilibrium crystal shape of the Potts model at the first-order transition point'
We comment on the article by Fujimoto (1997 J. Phys. A: Math. Gen., Vol. 30,
3779), where the exact equilibrium crystal shape (ECS) in the critical Q-state
Potts model on the square lattice was calculated, and its equivalence with ECS
in the Ising model was established. We confirm these results, giving their
alternative derivation applying the transformation properties of the
one-particle dispersion relation in the six-vertex model. It is shown, that
this dispersion relation is identical with that in the Ising model on the
square lattice.Comment: 4 pages, 1 figure, LaTeX2
Do Giant Molecular Clouds Care About the Galactic Structure?
We investigate the impact of galactic environment on the properties of
simulated giant molecular clouds formed in a M83-type barred spiral galaxy. Our
simulation uses a rotating stellar potential to create the grand design
features and resolves down to 1.5 pc. From the comparison of clouds found in
the bar, spiral and disc regions, we find that the typical GMC is environment
independent, with a mass of 5e+5 Msun and radius 11 pc. However, the fraction
of clouds in the property distribution tails varies between regions, with
larger, more massive clouds with a higher velocity dispersion being found in
greatest proportions in the bar, spiral and then disc. The bar clouds also show
a bimodality that is not reflected in the spiral and disc clouds except in the
surface density, where all three regions show two distinct peaks. We identify
these features as being due to the relative proportion of three cloud types,
classified via the mass-radius scaling relation, which we label A, B and C.
Type A clouds have the typical values listed above and form the largest
fraction in each region. Type B clouds are massive giant molecular associations
while Type C clouds are unbound, transient clouds that form in dense filaments
and tidal tails. The fraction of each clouds type depends on the cloud-cloud
interactions, which cause mergers to build up the GMA Type Bs and tidal
features in which the Type C clouds are formed. The number of cloud
interactions is greatest in the bar, followed by the spiral, causing a higher
fraction of both cloud types compared to the disc. While the cloud types also
exist in lower resolution simulations, their identification becomes more
challenging as they are not well separated populations on the mass-radius
relation or distribution plots. Finally, we compare the results for three star
formation models to estimate the star formation rate and efficiency in each
region.Comment: 21 pages, 14 figures. Accepted for publication in MNRA
Chain breaks and the susceptibility of Sr_2Cu_{1-x}Pd_xO_{3+\delta} and other doped quasi one-dimensional antiferromagnets
We study the magnetic susceptibility of one-dimensional S=1/2
antiferromagnets containing non-magnetic impurities which cut the chain into
finite segments. For the susceptibility of long anisotropic Heisenberg
chain-segments with open boundaries we derive a parameter-free result at low
temperatures using field theory methods and the Bethe Ansatz. The analytical
result is verified by comparing with Quantum-Monte-Carlo calculations. We then
show that the partitioning of the chain into finite segments can explain the
Curie-like contribution observed in recent experiments on
Sr_2Cu_{1-x}Pd_xO_{3+\delta}. Possible additional paramagnetic impurities seem
to play only a minor role.Comment: 4 pages, 3 figures, final versio
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