30 research outputs found
Symmetry-projected cluster mean-field theory applied to spin systems
We introduce spin-projection based on cluster mean-field theory and
apply it to the ground state of strongly-correlated spin systems. In cluster
mean-field, the ground state wavefunction is written as a factorized tensor
product of optimized cluster states. In previous work, we have focused on
unrestricted cluster mean-field, where each cluster is symmetry adapted.
We here remove this restriction by introducing a generalized cluster mean-field
(GcMF) theory, where each cluster is allowed to access all sectors,
breaking symmetry. In addition, a projection scheme is used to restore
global , which gives rise to spin-projected generalized cluster
mean-field (SGcMF). Both of these extensions contribute to accounting for
inter-cluster correlations. We benchmark these methods on the 1D, quasi-2D, and
2D and Heisenberg models. Our results indicate that the new
methods (GcMF and SGcMF) provide a qualitative and semi-quantitative
description of the Heisenberg lattices in the regimes considered, suggesting
them as useful references for further inter-cluster correlations, which are
discussed in this work
A cluster-based mean-field, perturbative and coupled-cluster theory description of strongly correlated systems
We introduce cluster-based mean-field, perturbation and coupled-cluster
theories to describe the ground state of strongly-correlated spin systems. In
cluster mean-field, the ground state wavefunction is written as a simple tensor
product of optimized cluster states. The cluster-language and the mean-field
nature of the ansatz allows for a straightforward improvement based on
perturbation theory and coupled-cluster, to account for inter-cluster
correlations. We present benchmark calculations on the 2D square
Heisenberg model, using cluster mean-field, second-order perturbation theory
and coupled-cluster. We also present an extrapolation scheme that allows us to
compute thermodynamic limit energies very accurately. Our results indicate
that, even with relatively small clusters, the correlated methods can provide
an accurate description of the Heisenberg model in the regimes considered. Some
ways to improve the results presented in this work are discussed
Creativity in the era of social networking: A case study in Tertiary Education in the Greek context.
This paper investigates the utilization of a social network tool in order to promote creativity in higher education. Buddypress was selected as a social network tool and de Bono’s “6 thinking hats” as a creativity strategy. The participants were 17 undergraduate students from a case study in a Univer-sity in Greece in the field of social sciences. Creativity was defined by Tor-rance & Ball’s [25] factors and the results were analyzed using authentic assessment and a questionnaire. The findings show that the research pro-cess was beneficial to students’ creativity and that social network tools can be utilized successfully with such a focus. These findings should be treated carefully in terms of generalizing them, as they were derived from a case study. This research could be useful to educators and researchers as a pio-neering approach in all levels of education
Construction and analytical applications of liquid-membrane electrodes for atropine and novatropine
Liquid-membrane electrodes sensitive to atropinium and novatropinium cations are described. The atropinium electrode exhibits rapid and near-Nernstian response in the 10-2-3 × 10-5 M range over the pH range 2-8.5; the novatropinium electrode shows near-Nernstian response in the 10-2-3 × 10-6 M range at pH 2-10. Other alkaloids interfere. Direct potentiometry and potentiometric titrations are used to determine atropine and novatropine in pharmaceutical preparations with satisfactory results. © 1981
Construction and analytical applications of liquid-membrane electrodes for atropine and novatropine
Liquid-membrane electrodes sensitive to atropinium and novatropinium cations are described. The atropinium electrode exhibits rapid and near-Nernstian response in the 10-2-3 × 10-5 M range over the pH range 2-8.5; the novatropinium electrode shows near-Nernstian response in the 10-2-3 × 10-6 M range at pH 2-10. Other alkaloids interfere. Direct potentiometry and potentiometric titrations are used to determine atropine and novatropine in pharmaceutical preparations with satisfactory results. © 1981