28,648 research outputs found
Application of the Asymptotic Iteration Method to a Perturbed Coulomb Model
We show that the asymptotic iteration method converges and yields accurate
energies for a perturbed Coulomb model. We also discuss alternative
perturbation approaches to that model.Comment: 9 pages, 2 figures, 1 tabl
Effect of higher orbital angular momenta in the baryon spectrum
We have performed a Faddeev calculation of the baryon spectrum for the chiral
constituent quark model including higher orbital angular momentum states. We
have found that the effect of these states is important, although a description
of the baryon spectrum of the same quality as the one given by including only
the lowest-order configurations can be obtained. We have studied the effect of
the pseudoscalar quark-quark interaction on the relative position of the
positive- and negative-parity excitations of the nucleon as well as the effect
of varying the strength of the color-magnetic interaction.Comment: 7 pages, 4 figures. To be published in Phys. Rev. C (November 2001
On the variational homotopy perturbation method for nonlinear oscillators
In this paper we discuss a recent application of a variational homotopy
perturbation method to rather simple nonlinear oscillators . We show that the
main equations are inconsistent and for that reason the results may be of
scarce utility
Quark Cluster Model Study of Isospin-Two Dibaryons
Based on a quark cluster model for the non-strange sector that reproduces
reasonably well the nucleon-nucleon system and the excitation of the
isobar, we generate a nucleon- interaction and present the predictions
for the several isospin two channels. The only attractive channels are
and , but not attractive enough to generate a resonance. If a resonance is
artificially generated and is required to have the observed experimental mass,
then our model predicts a width that agrees with the experimental result.Comment: 12 pages, 5 poscript figures available under request. To appear in
Phys. Rev.
and systems at threshold: II. The effect of D waves
Using the two-body interactions obtained from a chiral constituent quark
model we study all and states with I=0,1,2 and
J=1/2,3/2 at threshold, taking into account all three-body configurations with
S and D wave components. We constrain further the limits for the
spin-triplet scattering length a_{1/2,1}. Using the hypertriton binding energy
we find a narrow interval for the possible values of the
spin-singlet scattering length a_{1/2,0}. We found that the system
has a quasibound state in the (I,J) = (1,1/2) channel very near threshold with
a width of about 2.1 MeV.Comment: 19 pages, 4 tables, 6 figures. Accepted for publication in Phys. Rev.
The confined hydrogen atom with a moving nucleus
We study the hydrogen atom confined to a spherical box with impenetrable
walls but, unlike earlier pedagogical articles on the subject, we assume that
the nucleus also moves. We obtain the ground-state energy approximately by
means of first--order perturbation theory and by a more accurate variational
approach. We show that it is greater than the one for the case in which the
nucleus is clamped at the center of the box. Present approach resembles the
well-known treatment of the helium atom with clamped nucleus
Bulk viscosity and the conformal anomaly in the pion gas
We calculate the bulk viscosity of the massive pion gas within Unitarized
Chiral Perturbation Theory. We obtain a low temperature peak arising from
explicit conformal breaking due to the pion mass and another peak near the
critical temperature, dominated by the conformal anomaly through gluon
condensate terms. The correlation between bulk viscosity and conformal breaking
supports a recent QCD proposal. We discuss the role of resonances, heavier
states and large- counting.Comment: Revised version accepted in Phys.Rev.Lett. 4 pages, 3 figure
CCharPPI web server: computational characterization of protein–protein interactions from structure
The atomic structures of protein–protein interactions are central to understanding their role in biological systems, and a wide variety of biophysical functions and potentials have been developed for their characterization and the construction of predictive models. These tools are scattered across a multitude of stand-alone programs, and are often available only as model parameters requiring reimplementation. This acts as a significant barrier to their widespread adoption. CCharPPI integrates many of these tools into a single web server. It calculates up to 108 parameters, including models of electrostatics, desolvation and hydrogen bonding, as well as interface packing and complementarity scores, empirical potentials at various resolutions, docking potentials and composite scoring functions.The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Unions Seventh Framework Programme (FP7/2007-
2013) under REA grant agreement PIEF-GA-2012-327899 and grant BIO2013-48213-R from Spanish Ministry of Economy and
Competitiveness.Peer ReviewedPostprint (published version
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