Certification with optimal control strategies

The optimal control methodology called concentration-of-measure optimal control (COMOC), seeks to minimise a concen- tration-of-measure upper bound on the probability of failure of an uncertain system. This bound is computed for a system characterised by a single performance measure depending on random inputs. This work considers controlled multibody dynamics taking place in an uncertain environment. The goal is to quantify uncertainty in a controlled robot manoeuvre and to minimise the probability of failure with regard to a performance measure. First, a deterministic optimal control problem is solved, yielding state and control trajectories that minimise an objective function. Boundary conditions for the optimal control problem are chosen such that the system performs ideally in the sense of the performance measure. Secondly, the obtained manoeuvre is reconsidered in the presence of uncertainty. Using a concentration-of-measure inequality, a rigorous upper bound for the probability of failure is derived. Finally, an optimisation is performed that searches for a control sequence (in the neighbourhood of the given one), that minimises the probability of failure. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-empirical CI potential curves for the ground and excited states of PH and its positive ion

A series of calculated potential curves is reported for the low lying valence and (selected) Rydberg states of the PH molecule by employing the multi-reference (single- and) double-excitation CI method. A large AO basis including f functions on phosphorous is chosen for this study and up to twenty main configurations are used to generate a given MRD-CI space in the accompanying theoretical treatment. Very good agreement is obtained between calculation and experiment for a variety of spectroscopic constants and a number of predictions for electronically excited states of PH are made for cases in which no comparable empirical data are yet available. The repulsive ⁵∑^- state is shown to be responsible for the predissociation of several states of the neutral system and is also thought to explain the failure to detect a number of low lying Rydberg states experimentally. Analogous calculations for the PH⁺ molecular ion have also been carried out and spectroscopic constants for this system are reported. In this case the ⁴Π state plays much the same role as the neutral ⁵∑^- species in bringing about predissociation in its electronic spectrum. Finally a comparison is made throughout between the results for PH and PH⁺ and a number of isovalent systems, especially NH and NH⁺ and also SiH.     

On frequency estimations in phase fitted variational integrators for the general N-body problem

In the present work, the advantages of high order variational integrator methods are combined with phase lag properties for the numerical integration of the general N-body problem. Expressing the action integral at any intermediate points along the curve segment using a discrete Lagrangian that depends only on the end points of the interval, high order integrators can be obtained by defining the discrete Lagrangian in any time segment as a weighted sum on intermediate points, whose expressions for positions and velocities use Galerkin interpolation techniques. When oscillatory behavior is taken into account, the methods derived use trigonometric interpolation functions that depend on a frequency, which needs to be estimated. For that, using phase lag analysis, a new way to derive methods has been developed, that uses frequency estimation for each body at every time step. Results on special cases of the N-body problem show more stable orbits and less energy error when compared with the linear interpolation scheme. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Benchmarking of Density Functionals for the Description of Optical Properties of Newly Synthesized π-Conjugated TADF Blue Emitters

Computational modeling of the optical characteristics of organic molecules with potential for thermally activated delayed fluorescence (TADF) may assist markedly the development of more efficient emitting materials for organic light-emitting diodes. Recent theoretical studies in this area employ mostly methods from density functional theory (DFT). In order to obtain accurate predictions within this approach, the choice of a proper functional is crucial. In the current study, we focus on testing the performance of a set of DFT functionals for estimation of the excitation and emission energy and the excited singlet-triplet energy gap of three newly synthesized compounds with capacity for TADF. The emitters are designed specifically to enable charge transfer by π-electron conjugation, at the same time possessing high-energy excited triplet states. The functionals chosen for testing are from various groups ranging from gradient-corrected through global hybrids to range-separated ones. The results show that the monitored optical properties are especially sensitive to how the long-range part of the exchange energy is treated within the functional. The accurate functional should also be able to provide well balanced distribution of the π-electrons among the molecular fragments. Global hybrids with moderate (less than 0.4) share of exact exchange (B3LYP, PBE0) and the meta-GGA HSE06 are outlined as the best performing methods for the systems under study. They can predict all important optical parameters correctly, both qualitatively and quantitatively.     

Effectiveness of teacher education

Teacher-education research lacks a common theoretical basis, which prevents a convincing development of instruments and makes it difficult to connect studies to each other. Our paper models how to measure effective teacher education in the context of the current state of knowledge in the field. First, we conceptualize the central criterion of effective teacher education: “professional competence of future teachers”. Second, individual, institutional, and systemic factors are modeled that may influence the acquisition of this competence during teacher education. In doing this, we turn round the perspective taken by Cochran-Smith and Zeichner (Studying teacher education. The report of the AERA panel on research and teacher education. Lawrence Erlbaum, Mahwah 2005), who mainly take an educational-sociological perspective by focusing on characteristics of teacher education and looking for their effects. In contrast, we take an educational-psychological perspective by focusing on professional competence of teachers and examining influences on this. Challenges connected to an assessment of teacher-education outcomes are discussed as well.     

Formation of trioctylamine from octylamine on Au(111)

The adsorption of octylamine on Au(111) under ultrahigh vacuum conditions is investigated. The molecules surprisingly undergo a thermally activated chemical reaction, resulting in formation of trioctylamine as confirmed both by X-ray photoelectron spectroscopy (XPS) and by comparison to the scanning tunneling microscopy (STM) signature of trioctylamine deposited directly onto the surface.