189,791 research outputs found
The q-component static model : modeling social networks
We generalize the static model by assigning a q-component weight on each
vertex. We first choose a component among the q components at random
and a pair of vertices is linked with a color according to their weights
of the component as in the static model. A (1-f) fraction of the entire
edges is connected following this way. The remaining fraction f is added with
(q+1)-th color as in the static model but using the maximum weights among the q
components each individual has. This model is motivated by social networks. It
exhibits similar topological features to real social networks in that: (i) the
degree distribution has a highly skewed form, (ii) the diameter is as small as
and (iii) the assortativity coefficient r is as positive and large as those in
real social networks with r reaching a maximum around .Comment: 5 pages, 6 figure
Quantum-disordered slave-boson theory of underdoped cuprates
We study the stability of the spin gap phase in the U(1) slave-boson theory
of the t-J model in connection to the underdoped cuprates. We approach the spin
gap phase from the superconducting state and consider the quantum phase
transition of the slave-bosons at zero temperature by introducing vortices in
the boson superfluid. At finite temperatures, the properties of the bosons are
different from those of the strange metal phase and lead to modified gauge
field fluctuations. As a result, the spin gap phase can be stabilized in the
quantum critical and quantum disordered regime of the boson system. We also
show that the regime of quantum disordered bosons with the paired fermions can
be regarded as the strong coupling version of the recently proposed nodal
liquid theory.Comment: 5 pages, Replaced by the published versio
Electronic structures of ZnCoO using photoemission and x-ray absorption spectroscopy
Electronic structures of ZnCoO have been investigated using
photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The
Co 3d states are found to lie near the top of the O valence band, with a
peak around eV binding energy. The Co XAS spectrum provides
evidence that the Co ions in ZnCoO are in the divalent Co
() states under the tetrahedral symmetry. Our finding indicates that the
properly substituted Co ions for Zn sites will not produce the diluted
ferromagnetic semiconductor property.Comment: 3 pages, 2 figure
Pentaquark in nuclear matter and hypernuclei
We study the properties of the in nuclear matter and
hypernuclei within the quark mean-field (QMF) model, which has been
successfully used for the description of ordinary nuclei and
hypernuclei. With the assumption that the non-strange mesons couple only to the
and quarks inside baryons, a sizable attractive potential of the
in nuclear matter is achieved as a consequence of the cancellation
between the attractive scalar potential and the repulsive vector potential. We
investigate the single-particle energies in light, medium, and heavy
nuclei. More bound states are obtained in hypernuclei in comparison
with those in hypernuclei.Comment: 16 pages, 5 figure
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