FEM–BEM coupling for the large-body limit in micromagnetics

AbstractWe present and analyze a coupled finite element–boundary element method for a model in stationary micromagnetics. The finite element part is based on mixed conforming elements. For two- and three-dimensional settings, we show well-posedness of the discrete problem and present an a priori error analysis for the case of lowest order elements

The saturation assumption yields optimal convergence of two-level adaptive BEM

We consider the convergence of adaptive BEM for weakly-singular and hypersingular integral equations associated with the Laplacian and the Helmholtz operator in 2D and 3D. The local mesh-refinement is driven by some two-level error estimator. We show that the adaptive algorithm drives the underlying error estimates to zero. Moreover, we prove that the saturation assumption already implies linear convergence of the error with optimal algebraic rates

Coupling of dynamical micromagnetism and a stationary spin drift-diffusion equation: A step towards a fully self-consistent spintronics framework

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.We consider the coupling of the Landau-Lifshitz-Gilbert equation with a quasilinear diffusion equation to describe the interplay of magnetization and spin accumulation in magnetic-nonmagnetic multilayer structures. For this problem, we propose and analyze a convergent finite element integrator, where, in contrast to prior work, we consider the stationary limit for the spin diffusion. Numerical experiments underline that the new approach is more effective, since it leads to the same experimental results as for the model with time-dependent spin diffusion, but allows for larger time-steps of the numerical integrator.The authors acknowledge support from the Vienna Science and Technology Fund (WWTF) under grant MA14-44 (GH, DP, DS), from the Austrian Science Fund (FWF) under grant W1245 (DP, MR), from TU Wien through the innovative projects initiative (DP, MR), from the Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development (CA, DS), through the EPSRC grant EP/K008412/1 (GH), from the Royal Society under grant UF080837 (GH)

The Mass-Lumped Midpoint Scheme for Computational Micromagnetics: Newton Linearization and Application to Magnetic Skyrmion Dynamics

We discuss a mass-lumped midpoint scheme for the numerical approximation of the Landau-Lifshitz-Gilbert equation, which models the dynamics of the magnetization in ferromagnetic materials. In addition to the classical micromagnetic field contributions, our setting covers the non-standard Dzyaloshinskii-Moriya interaction, which is the essential ingredient for the enucleation and stabilization of magnetic skyrmions. Our analysis also includes the inexact solution of the arising nonlinear systems, for which we discuss both a constraint-preserving fixed-point solver from the literature and a novel approach based on the Newton method. We numerically compare the two linearization techniques and show that the Newton solver leads to a considerably lower number of nonlinear iterations. Moreover, in a numerical study on magnetic skyrmions, we demonstrate that, for magnetization dynamics that are very sensitive to energy perturbations, the midpoint scheme, due to its conservation properties, is superior to the dissipative tangent plane schemes from the literature

Verbal reports in psychological investigations: a logical and psychological analysis

Since the era of Wundtian introspectionism the status and usefulness of verbal reports from subjects in psychological investigations have been a recurring topic of heated debate and controversy in the international psychological literature. In order to untangle and clearify some of the uncertainties and confusions in this debate, an analysis is attempted of some of the logical and psychological conditions for research involving verbal reports. In the course of this analysis we argue first that any psychological investigation logically presupposes, that communication takes place in a shared language in which both the investigator and the subject know correct statements and descriptions and their correct uses. It is argued, more over, that different areas of psychological research differ distinctively with regard to the opportunities of observation and description - for the investigator and the subject - and,consequently, in the amount of control exercised over events and variables by the investigator and the subject. Examples are given of different psychological conditions and problems encountered in different areas of research and their implications for the development of different research methodes and programmes.Since the era of Wundtian introspectionism the status and usefulness of verbal reports from subjects in psychological investigations have been a recurring topic of heated debate and controversy in the international psychological literature. In order to untangle and clearify some of the uncertainties and confusions in this debate, an analysis is attempted of some of the logical and psychological conditions for research involving verbal reports. In the course of this analysis we argue first that any psychological investigation logically presupposes, that communication takes place in a shared language in which both the investigator and the subject know correct statements and descriptions and their correct uses. It is argued, more over, that different areas of psychological research differ distinctively with regard to the opportunities of observation and description - for the investigator and the subject - and,consequently, in the amount of control exercised over events and variables by the investigator and the subject. Examples are given of different psychological conditions and problems encountered in different areas of research and their implications for the development of different research methodes and programmes

Functional Association Between Three Archaeal Aminoacyl-tRNA Synthetases

Aminoacyl-tRNA synthetases (aaRSs) are responsible for attaching amino acids to their cognate tRNAs during protein synthesis. In eukaryotes aaRSs are commonly found in multi-enzyme complexes, although the role of these complexes is still not completely clear. Associations between aaRSs have also been reported in archaea, including a complex between prolyl-(ProRS) and leucyl-tRNA synthetases (LeuRS) in Methanothermobacter thermautotrophicus that enhances tRNAPro aminoacylation. Yeast two-hybrid screens suggested that lysyl-tRNA synthetase (LysRS) also associates with LeuRS in M. thermautotrophicus. Co-purification experiments confirmed that LeuRS, LysRS, and ProRS associate in cell-free extracts. LeuRS bound LysRS and ProRS with a comparable KD of about 0.3–0.9 μm, further supporting the formation of a stable multi-synthetase complex. The steady-state kinetics of aminoacylation by LysRS indicated that LeuRS specifically reduced the Km for tRNALys over 3-fold, with no additional change seen upon the addition of ProRS. No significant changes in aminoacylation by LeuRS or ProRS were observed upon the addition of LysRS. These findings, together with earlier data, indicate the existence of a functional complex of three aminoacyl-tRNA synthetases in archaea in which LeuRS improves the catalytic efficiency of tRNA aminoacylation by both LysRS and ProRS

Mechanical oscillations of magnetic strips under the influence of external field

This is the final version of the article. Available from EDP Sciences via the DOI in this record.JEMS 2012 – Joint European Magnetic SymposiaBy application of a magnetic field on an amorphous metallic strip, the orientation of magnetization of Weiss domains can be changed. When the strip changes its length, this effect is called magnetostriction. We simulate this effect using a finite element method. In particular we calculate the change of the mechanical resonance frequency of a magnetic platelet as a function of the applied field. This gives a quantitative model of the influence of the applied magnetic field on the effective Young's Modulus of the material. © 2013 Owned by the authors, published by EDP Sciences

Residual-based a posteriori error estimate for hypersingular equation on surfaces

The hypersingular integral equation of the first kind equivalently describes screen and Neumann problems on an open surface piece. The paper establishes a computable upper error bound for its Galerkin approximation and so motivates adaptive mesh refining algorithms. Numerical experiments for triangular elements on a screen provide empirical evidence of the superiority of adapted over uniform mesh-refining. The numerical realisation requires the evaluation of the hypersingular integral operator at a source point; this and other details on the algorithm are included