Comprehensive quantum Monte Carlo study of the quantum critical points in planar dimerized/quadrumerized Heisenberg models

We study two planar square lattice Heisenberg models with explicit dimerization or quadrumerization of the couplings in the form of ladder and plaquette arrangements. We investigate the quantum critical points of those models by means of (stochastic series expansion) quantum Monte Carlo simulations as a function of the coupling ratio $\alpha = J^\prime/J$. The critical point of the order-disorder quantum phase transition in the ladder model is determined as $\alpha_\mathrm{c} = 1.9096(2)$ improving on previous studies. For the plaquette model we obtain $\alpha_\mathrm{c} = 1.8230(2)$ establishing a first benchmark for this model from quantum Monte Carlo simulations. Based on those values we give further convincing evidence that the models are in the three-dimensional (3D) classical Heisenberg universality class. The results of this contribution shall be useful as references for future investigations on planar Heisenberg models such as concerning the influence of non-magnetic impurities at the quantum critical point.Comment: 10+ pages, 7 figures, 4 table

Models for implementing sustainable development into the university

Published ArticleAny effort to build up an educational framework needs an adequate structure and a formal basis. This is especially true whenever complex multifaceted issues like Sustainable Development, ethics, or project management have to be integrated in the existing setting of a university and its educational system. In this paper, we present models for integrating Sustainable Development and Education for Sustainable Development into the university agenda. Based on the experience of the authors gained in Germany and South Africa we derive various representations for the sustainability activities and models for implementing Sustainable Development that can be used for planning, implementation and communication purposes

Zusammensetzung rezyklierter (Th, U) O2_{2}-Brennelemente mit mitterem U-Anreicherungsgrad und ihre Auswirkung auf den Kernbrennstoffkreislauf

The MEU-HTR fuel element is proposed in order to use lower enriched U and to preserve the potential of the HTR as converter and as process heat source. If the final storage of nuclear fuel is not licensed in the Federal Republic of Germany, a complete fuel cycle must be available for the spent nuclear fuel management of this type of fuel. Therefore, the composition of spent mixed oxide MEU-HTR fuel was calculated in this study, considering various recycling strategies. The following conclusions may be drawn from the resulting data. [...

Testing for Markovian Character and Modeling of Intermittency in Solar Wind Turbulence

We present results of statistical analysis of solar wind turbulence using an approach based on the theory of Markov processes. It is shown that the Chapman-Kolmogorov equation is approximately satisfied for the turbulent cascade. We evaluate the first two Kramers-Moyal coefficients from experimental data and show that the solution of the resulting Fokker-Planck equation agrees well with experimental probability distributions. Our results suggest the presence of a local transfer mechanism for magnetic field fluctuations in solar wind turbulence