97,254 research outputs found
Temperature, chemical potential and the rho meson
We describe some applications of the Dyson-Schwinger equations at
nonzero-(T,mu). Employing a simple model dressed-gluon propagator we determine
the boundary of the deconfinement phase transition and the medium dependence of
rho-meson properties. We introduce an extension to describe the time-evolution
of scalar and vector self energies.Comment: 6 pages, LaTeX with 3 EPS figures; Contribution to the 'International
Workshop XXVIII on Gross Properties of Nuclei and Nuclear Excitations',
Hirschegg, Austria, 16-22.01.200
Dynamical critical exponent of the Jaynes-Cummings-Hubbard model
An array of high-Q electromagnetic resonators coupled to qubits gives rise to
the Jaynes-Cummings-Hubbard model describing a superfluid to Mott insulator
transition of lattice polaritons. From mean-field and strong coupling
expansions, the critical properties of the model are expected to be identical
to the scalar Bose-Hubbard model. A recent Monte Carlo study of the superfluid
density on the square lattice suggested that this does not hold for the
fixed-density transition through the Mott lobe tip. Instead, mean-field
behavior with a dynamical critical exponent z=2 was found. We perform
large-scale quantum Monte Carlo simulations to investigate the critical
behavior of the superfluid density and the compressibility. We find z=1 at the
tip of the insulating lobe. Hence the transition falls in the 3D XY
universality class, analogous to the Bose-Hubbard model.Comment: 4 pages, 4 figures. To appear as a Rapid Communication in Phys. Rev.
A generalized spatiotemporal covariance model for stationary background in analysis of MEG data
Using a noise covariance model based on a single Kronecker product of spatial
and temporal covariance in the spatiotemporal analysis of MEG data was
demonstrated to provide improvement in the results over that of the commonly
used diagonal noise covariance model. In this paper we present a model that is
a generalization of all of the above models. It describes models based on a
single Kronecker product of spatial and temporal covariance as well as more
complicated multi-pair models together with any intermediate form expressed as
a sum of Kronecker products of spatial component matrices of reduced rank and
their corresponding temporal covariance matrices. The model provides a
framework for controlling the tradeoff between the described complexity of the
background and computational demand for the analysis using this model. Ways to
estimate the value of the parameter controlling this tradeoff are also
discussedComment: 4 pages, EMBS 2006 conferenc
On Superalgebras of Matrices with Symmetry Properties
It is known that semi-magic square matrices form a 2-graded algebra or
superalgebra with the even and odd subspaces under centre-point reflection
symmetry as the two components. We show that other symmetries which have been
studied for square matrices give rise to similar superalgebra structures,
pointing to novel symmetry types in their complementary parts. In particular,
this provides a unifying framework for the composite `most perfect square'
symmetry and the related class of `reversible squares'; moreover, the
semi-magic square algebra is identified as part of a 2-gradation of the general
square matrix algebra. We derive explicit representation formulae for matrices
of all symmetry types considered, which can be used to construct all such
matrices.Comment: 25 page
- …