10,691 research outputs found
Numerical analysis of corrugated tube flow using RBFNs
This paper reports the application of neural networks for the numerical analysis of steady-state axisymmetric flow through an indefinitely long corrugated tube. Meshless global radial basis function networks (RBFNs) are employed to represent all dependent variables in the governing differential equations. For a better quality of approximation, the networks used here are constructed based on the integration process rather than the usual differentiation process. Multiple spaces of network weights for each variable are converted into the single space of nodal variable values, resulting in the square system of
equations with usual size. The governing equations are discretized in the strong form by point collocation and the resultant nonlinear system is solved with trust-region methods. The corrugated tube flow of a Newtonian fluid, power-law fluid and Oldroyd-B fluid are considered. With relatively low numbers of data points, flow resistance predictions obtained are in good agreement with the benchmark solutions
Microscopic 8-quark study of the antikaon nucleon nucleon systems
We study the possibility to bind eight quarks in a molecular hadronic system
composed of two nucleons and an antikaon, with the quantum numbers of a
hexaquark flavour, in particular with strangeness -1, isospin 1/2, parity -,
baryonic number 2 and two possible spins, 0 or 1. These exotic hadrons are
motivated by the deuteron, a proton-neutron boundstate, and by the model of the
Lambda(1405) as an antikaon proton boundstate. We discuss the possible
production of this hadron in the experiments which are presently investigating
hot topics like the Theta+ pentaquark or the K- deeply bound in nuclei. The K-
N interactions and the coupling to other channels are computed microscopically
from a confining and chiral invariant quark model resulting in local plus
separable Gaussian potentials. The N N interactions used here are the state of
the art Nijmegen potentials. The binding energy and the decay rate of the K- N
and K- N N systems are computed with configuration space variational methods.
The only systems that bind with our microscopic interaction are the K- N in the
I=0 channel and the K- N N in the S=0 channel.Comment: 5 pages, 5 figures (1 new and 2 updated), more detailed study of
binding with a small parameter increase, and an algebraic correction,
submitted to Physical Review
Production of the pentaquark in scattering
We study and processes
for both of the positive and negative parities of the . Employing
the effective chiral Lagrangians for the and interactions, we
calculate differential cross sections as well as total cross sections for the
and reactions. The total
cross sections for the positive-parity turn out to be approximately
ten times larger than those for the negative parity in the range of
the CM energy . The results are
rather sensitive to the mechanism of exchanges in the -- channel.Comment: 9 pages and 11 figure
Evidence for the two pole structure of the Lambda(1405) resonance
The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary
model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows,
in agreement with a recent experiment, a peak at 1420 MeV and a relatively
narrow width of Gamma = 38 MeV. The mechanism for the reaction is largely
dominated by the emission of a pi^0 prior to the K^- p interaction leading to
the Lambda(1405). This ensures the coupling of the Lambda(1405) to the K^- p
channel, thus maximizing the contribution of the second state found in chiral
unitary theories, which is narrow and of higher energy than the nominal
Lambda(1405). This is unlike the pi^- p --> K^0 \pi Sigma reaction, which gives
more weight to the pole at lower energy and with a larger width. The data of
these two experiments, together with the present theoretical analysis, provides
a firm evidence of the two pole structure of the Lambda(1405).Comment: 4 pages, 6 figure
Automatic Dimension Selection for a Non-negative Factorization Approach to Clustering Multiple Random Graphs
We consider a problem of grouping multiple graphs into several clusters using
singular value thesholding and non-negative factorization. We derive a model
selection information criterion to estimate the number of clusters. We
demonstrate our approach using "Swimmer data set" as well as simulated data
set, and compare its performance with two standard clustering algorithms.Comment: This paper has been withdrawn by the author due to a newer version
with overlapping content
K*-couplings for the antidecuplet excitation
We estimate the coupling of the K* vector meson to the N-->Theta+ transition
employing unitary symmetry, vector meson dominance, and results from the GRAAL
Collaboration for eta photoproduction off the neutron. Our small numerical
value for the coupling constant is consistent with the non-observation of the
Theta+ in recent CLAS searches for its photoproduction. We also estimate the
K*-coupling for the N-->Sigma* excitation, with Sigma* being the Sigma-like
antidecuplet partner of the Theta+-baryon.Comment: 9 pages, 1 figure. Minor changes in text and abstract, references
added; version to appear in Phys. Rev.
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