Simulation of thermo-mechanical loading processes on amorphous thermoplastic polymers

A constitutive model for the thermo-mechanical behavior of amorphous thermoplastic polymers is presented that accounts for the dependence of the macromolecular network and entropic hardening on large temperature changes. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Minimum Stiffness Criteria for Edge Reinforcements of Elastically Clamped Plates

In many structural situations, e.g. in aerospace engineering, composite plates with edge reinforcements are used, for example as stiffeners of a fuselage section of an airplane. Based on an explicit analysis of the buckling behavior of the laminate plate, a minimum stiffness criterion is presented in this contribution. A transformation of the governing equations into a dimensionless system is used, that proved to be very advantageous. Besides a minimum stiffness criterion that can be used for generation of minimum stiffness diagrams, an absolute minimum stiffness is found that enables the reinforcement to act like a simple support for arbitrarily slender plates. The relevance of the criteria for stiffener design is discussed. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Approximation order of interpolatory nonlinear subdivision schemes

Linear interpolatory subdivision schemes of C^r smoothness have approximation order at least r+1. The present paper extends this result to nonlinear univariate schemes which are in proximity with linear schemes in a certain specific sense. The results apply to nonlinear subdivision schemes in Lie groups and in surfaces which are obtained from linear subdivision schemes. We indicate how to extend the results to the multivariate case.     

From Luminescent Complexes to Framework Formation from Ln‐trichlorides and Pyrazine

The three‐dimensional framework ³_∞[LaCl₃(pyz)] and the dimeric complexes [Ln₂Cl₆(pyz)(py)₆] · 2pyz (Ln = Sm, Er) were obtained from solvothermal reaction of the respective chlorides LnCl₃ with pyrazine (pyz) in pyridine (py) at 200 °C. In the compounds, pyrazine ligands interlink Ln‐cations: in the complexes to a dimer, in the framework structure to 2D sheets, which are further connected via chloride bridges. This results in an uninodal 6‐c net with the point symbol (4⁸.6⁷) and a variant of the sxa topology. The dimeric complexes exhibit 4f‐based emission in the visible for samarium and in the NIR for erbium, both sensitized by the pyrazine ligands, as mechanistic insights show.     

Pulsed EPR Dipolar Spectroscopy on Spin Pairs with one Highly Anisotropic Spin Center: The Low-Spin FeIII Case

Pulsed electron paramagnetic resonance (EPR) dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling constants and thus the distance between electron spin centers. Up to now, PDS measurements have been mostly applied to spin centers whose g-anisotropies are moderate and therefore have a negligible effect on the dipolar coupling constants. In contrast, spin centers with large g-anisotropy yield dipolar coupling constants that depend on the g-values. In this case, the usual methods of extracting distances from the raw PDS data cannot be applied. Here, the effect of the g-anisotropy on PDS data is studied in detail on the example of the low-spin Fe³⁺ ion. First, this effect is described theoretically, using the work of Bedilo and Maryasov (Appl. Magn. Reson. 2006 , 30, 683–702) as a basis. Then, two known Fe³⁺/nitroxide compounds and one new Fe³⁺/trityl compound were synthesized and PDS measurements were carried out on them using a method called relaxation induced dipolar modulation enhancement (RIDME). Based on the theoretical results, a RIDME data analysis procedure was developed, which facilitated the extraction of the inter-spin distance and the orientation of the inter-spin vector relative to the Fe³⁺ g-tensor frame from the RIDME data. The accuracy of the determined distances and orientations was confirmed by comparison with MD simulations. This method can thus be applied to the highly relevant class of metalloproteins with, for example, low-spin Fe³⁺ ions.     

Second‐Sphere Biomimetic Multipoint Hydrogen‐Bonding Patterns to Boost CO2 Reduction of Iron Porphyrins

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO₂, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO₂) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO₂ reduction in this family of molecular catalysts and importantly increased the CO₂ binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO₂ reduction.     

Reducing backaction when measuring temporal correlations in quantum systems

Dynamic correlations of quantum observables are challenging to measure due to measurement backaction incurred at early times. Recent work [P. Uhrich et al., Phys. Rev. A 96, 022127 (2017)] has shown that ancilla-based noninvasive measurements are able to reduce this backaction, allowing for dynamic correlations of single-site spin observables to be measured. We generalise this result to correlations of arbitrary spin observables and extend the measurement protocol to simultaneous noninvasive measurements which allow for real and imaginary parts of correlations to be extracted from a single set of measurements. We use positive operator-valued measures to analyse the dynamics generated by the ancilla-based measurements. Using this framework we prove that special observables exist for which measurement backaction is of no concern, so that dynamic correlations of these can be obtained without making use of ancillas.     

Blending Dual Time Stepping and Newton-Krylov Methods for Unsteady Flows

We explore the idea of using nonlinear schemes as preconditioners in Newton-Krylov schemes for unsteady flow computations. Analysis shows that left preconditioning changes the Newton scheme in a non equivalent way, leading to a stall in Newton convergence, whereas right preconditioning leads to a sound method. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Definitizability of a Class of J-Selfadjoint Operators with Applications

We formulate an abstract result concerning the definitizability of J-selfadjoint operators which, roughly speaking, differ by at most finitely many dimensions from the orthogonal sum of a J-selfadjoint operator with finitely many negative squares and a semibounded selfadjoint operator in a Hilbert space. The general perturbation result is applied to a class of singular Sturm–Liouville operators with indefinite weight functions. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)