23,525 research outputs found
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
Isospin breaking and - mixing in the reaction
We make a theoretical study of the and
reactions with an aim to determine the
isospin violation and the mixing of the and resonances.
We make use of the chiral unitary approach where these two resonances appear as
composite states of two mesons, dynamically generated by the meson-meson
interaction provided by chiral Lagrangians. We obtain a very narrow shape for
the production in agreement with a BES experiment. As to the amount
of isospin violation, or and mixing, assuming constant
vertices for the primary and
production, we find results which
are much smaller than found in the recent experimental BES paper, but
consistent with results found in two other related BES experiments. We have
tried to understand this anomaly by assuming an I=1 mixture in the
wave function, but this leads to a much bigger width of the mass
distribution than observed experimentally. The problem is solved by using the
primary production driven by followed by , which induces an extra singularity in the loop functions needed to
produce the and resonances. Improving upon earlier work
along the same lines, and using the chiral unitary approach, we can now predict
absolute values for the ratio which are in fair agreement with experiment. We also show that the same
results hold if we had the resonance or a mixture of these two
states, as seems to be the case in the BES experiment
Electronic States and Magnetism of Mn Impurities and Dimers in Narrow-Gap and Wide-Gap III-V Semiconductors
Electronic states and magnetic properties of single impurity and dimer
doped in narrow-gap and wide-gap - semiconductors have been studied
systematically. It has been found that in the ground state for single
impurity, - complex is antiferromagnetic (AFM) coupling when -
hybridization is large and both the hole level and the
impurity level are close to the midgap; or very weak ferromagnetic (FM)
when is small and both and are deep in the valence band.
In dimer situation, the spins are AFM coupling for half-filled or
full-filled orbits; on the contrast, the Mn spins are double-exchange-like
FM coupling for any -orbits away from half-filling. We propose the strong
{\it p-d} hybridized double exchange mechanism is responsible for the FM order
in diluted - semiconductors
Comparative study of CXC chemokines modulation in brown trout (Salmo trutta) following infection with a bacterial or viral pathogen
Acknowledgements We would like to acknowledge Richard Paley, Tom Hill and Georgina Rimmer for their collaboration during brown trout infection challenges in CEFAS-Weymouth biosecurity facilities. Bartolomeo Gorgoglione, Stephen W. Feist and Nick G. H. Taylor were supported by a DEFRA grant (F1198).Peer reviewedPostprin
Dynamic response of an embedded railway track subjected to a moving load
A dynamic computational model for the embedded railway track subjected to a moving load is developed in this paper. The model consists of two-layer Euler-Bernoulli beams and continuous viscoelastic elements. The lower beam, the upper beam are employed to model the concrete slab and the rail, respectively, whilst the continuous viscoelastic elements model the soil reaction and the fill material. The problem is solved by employing Newmark-β numerical integration method. The effects of the speed of the moving loads, the rail type, and the spring stiffness of rail supports are studied. Results indicate that the dynamic response of rail and slab increases with the larger moving load speeds, whilst the response of rail and slab decreases with the increase of spring stiffness and heavier rail used
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