Ultrafast and reversible control of the exchange interaction in Mott insulators

The strongest interaction between microscopic spins in magnetic materials is the exchange interaction $J_\text{ex}$. Therefore, ultrafast control of $J_\text{ex}$ holds the promise to control spins on ultimately fast timescales. We demonstrate that time-periodic modulation of the electronic structure by electric fields can be used to reversibly control $J_\text{ex}$ on ultrafast timescales in extended antiferromagnetic Mott insulators. In the regime of weak driving strength, we find that $J_\text{ex}$ can be enhanced and reduced for frequencies below and above the Mott gap, respectively. Moreover, for strong driving strength, even the sign of $J_\text{ex}$ can be reversed and we show that this causes time reversal of the associated quantum spin dynamics. These results suggest wide applications, not only to control magnetism in condensed matter systems, for example, via the excitation of spin resonances, but also to assess fundamental questions concerning the reversibility of the quantum many-body dynamics in cold atom systems.Comment: 9 pages, 4 figure

Non-equilibrium Green's function approach to inhomogeneous quantum many-body systems using the Generalized Kadanoff Baym Ansatz

In non-equilibrium Green's function calculations the use of the Generalized Kadanoff-Baym Ansatz (GKBA) allows for a simple approximate reconstruction of the two-time Green's function from its time-diagonal value. With this a drastic reduction of the computational needs is achieved in time-dependent calculations, making longer time propagation possible and more complex systems accessible. This paper gives credit to the GKBA that was introduced 25 years ago. After a detailed derivation of the GKBA, we recall its application to homogeneous systems and show how to extend it to strongly correlated, inhomogeneous systems. As a proof of concept, we present results for a 2-electron quantum well, where the correct treatment of the correlated electron dynamics is crucial for the correct description of the equilibrium and dynamic properties

Percutaneous pulmonary valve implantation alters electrophysiologic substrate

BACKGROUND: Percutaneous pulmonary valve implantation (PPVI) is first‐line therapy for some congenital heart disease patients with right ventricular outflow tract dysfunction. The hemodynamics improvements after PPVI are well documented, but little is known about its effects on the electrophysiologic substrate. The objective of this study is to assess the short‐ and medium‐term electrophysiologic substrate changes and elucidate postprocedure arrhythmias. METHODS AND RESULTS: A retrospective chart review of patients undergoing PPVI from May 2010 to April 2015 was performed. A total of 106 patients underwent PPVI; most commonly these patients had tetralogy of Fallot (n=59, 55%) and pulmonary insufficiency (n=60, 57%). The median follow‐up time was 28 months (7‐63 months). Pre‐PPVI, 25 patients (24%) had documented arrhythmias: nonsustained ventricular tachycardia (NSVT) (n=9, 8%), frequent premature ventricular contractions (PVCs) (n=6, 6%), and atrial fibrillation/flutter (AF/AFL) (n=10, 9%). Post‐PPVI, arrhythmias resolved in 4 patients who had NSVT (44%) and 5 patients who had PVCs (83%). New arrhythmias were seen in 16 patients (15%): 7 NSVT, 8 PVCs, and 1 AF/AFL. There was resolution at medium‐term follow‐up in 6 (86%) patients with new‐onset NSVT and 7 (88%) patients with new‐onset PVCs. There was no difference in QRS duration pre‐PPVI, post‐PPVI, and at medium‐term follow‐up (P=0.6). The median corrected QT lengthened immediately post‐PPVI but shortened significantly at midterm follow‐up (P<0.01). CONCLUSIONS: PPVI reduced the prevalence of NSVT. The majority of postimplant arrhythmias resolve by 6 months of follow‐up

On the Coulomb-dipole transition in mesoscopic classical and quantum electron-hole bilayers

We study the Coulomb-to-dipole transition which occurs when the separation $d$ of an electron-hole bilayer system is varied with respect to the characteristic in-layer distances. An analysis of the classical ground state configurations for harmonically confined clusters with $N\leq30$ reveals that the energetically most favorable state can differ from that of two-dimensional pure dipole or Coulomb systems. Performing a normal mode analysis for the N=19 cluster it is found that the lowest mode frequencies exhibit drastic changes when $d$ is varied. Furthermore, we present quantum-mechanical ground states for N=6, 10 and 12 spin-polarized electrons and holes. We compute the single-particle energies and orbitals in self-consistent Hartree-Fock approximation over a broad range of layer separations and coupling strengths between the limits of the ideal Fermi gas and the Wigner crystal

Mott transition in one dimension: Benchmarking dynamical cluster approaches

The variational cluster approach (VCA) is applied to the one-dimensional Hubbard model at zero temperature using clusters (chains) of up to ten sites with full diagonalization and the Lanczos method as cluster solver. Within the framework of the self-energy-functional theory (SFT), different cluster reference systems with and without bath degrees of freedom, in different topologies and with different sets of variational parameters are considered. Static and one-particle dynamical quantities are calculated for half-filling as a function of U as well as for fixed U as a function of the chemical potential to study the interaction- and filling-dependent metal-insulator (Mott) transition. The recently developed Q-matrix technique is used to compute the SFT grand potential. For benchmarking purposes we compare the VCA results with exact results available from the Bethe ansatz, with essentially exact dynamical DMRG data, with (cellular) dynamical mean-field theory and full diagonalization of isolated Hubbard chains. Several issues are discussed including convergence of the results with cluster size, the ability of cluster approaches to access the critical regime of the Mott transition, efficiency in the optimization of correlated-site vs. bath-site parameters and of multi-dimensional parameter optimization. We also study the role of bath sites for the description of excitation properties and as charge reservoirs for the description of filling dependencies. The VCA turns out to be a computationally cheap method which is competitive with established cluster approaches.Comment: 19 pages, 19 figures, v3 with minor corrections, extended discussio

Teologiese opleiding tydens die Reformasie

Theological training during the Reformation The profound changes in theological education during and after the Reformation are interpreted in the light of the new soteriology of Martin Luther, Philipp Melanchthon, and their followers. A comparison with the humanistic movement reveals the specifically theological character of education in that time. Salvation was no longer directly administered by the church, but communicated thrgugh the study of the Bible as witness. Finally, the article points to the importance of the heritage of this movement for theological education in today’s cultural and religious situation

God met ons! Die aanspraak op Goddelike steun in ’n konfliksituasie volgens die Ou Testament

God with us! The claim of divine support in a situation of conflict, seen from an Old Testament perspective Political discussions referring to Old Testament texts in order to claim divine support for one’s views, and disqualify opposing opinions as being in conflict with the God of the Bible, are hermeneutically based on analogies between a revealed God, His representatives or laws, and ethical or political principles. A synchronic investigation of relevant Old Testament passages fully denies and opposes this hermeneutic approach, which is based on an isolation of principles or norms - with no reg ard to the only relevant actual relation to God himself. Any political identification with God or associated function must therefore be rejected as blasphemous from an Old Tes-tament perspective

Exploring Millions of 6-State FSSP Solutions: the Formal Notion of Local CA Simulation

In this paper, we come back on the notion of local simulation allowing to transform a cellular automaton into a closely related one with different local encoding of information. This notion is used to explore solutions of the Firing Squad Synchronization Problem that are minimal both in time (2n -- 2 for n cells) and, up to current knowledge, also in states (6 states). While only one such solution was proposed by Mazoyer since 1987, 718 new solutions have been generated by Clergue, Verel and Formenti in 2018 with a cluster of machines. We show here that, starting from existing solutions, it is possible to generate millions of such solutions using local simulations using a single common personal computer

The common data acquisition platform in the Helmholtz Association

Various centres of the German Helmholtz Association (HGF) started in 2012 to developa modular data acquisition (DAQ) platform, covering the entire range from detector readout todata transfer into parallel computing environments. This platform integrates generic hardwarecomponents like the multi-purpose HGF-Advanced Mezzanine Card or a smart scientific cameraframework, adding user value with Linux drivers and board support packages. Technically the scopecomprises the DAQ-chain from FPGA-modules to computing servers, notably frontend-electronicsinterfaces, microcontrollers and GPUs with their software plus high-performance data transmissionlinks. The core idea is a generic and component-based approach, enabling the implementationof specific experiment requirements with low effort. This so called DTS-platform will supportstandards like MTCA.4 in hard- and software to ensure compatibility with commercial components.Its capability to deploy on other crate standards or FPGA-boards with PCI express or Ethernetinterfaces remains an essential feature.Competences of the participating centres are coordinated in order to provide a solid technological basis for both research topics in the Helmholtz Programme “Matter and Technology”:“Detector Technology and Systems” and “Accelerator Research and Development”. The DTSplatform aims at reducing costs and development time and will ensure access to latest technologiesfor the collaboration. Due to its flexible approach, it has the potential to be applied in other scientificprograms