Verification of an optical metrology system (ARAMIS) by comparing experimental data with FE calculations and continuum approaches

Optical 3D field measuring systems, based on DIC (Digital Image Correlation) deliver kinematic quantities. They are appropriate devices helping to understand the material behavior especially at high strains. One problem of these systems is the missing information about material points located behind the observed surface of the specimen, which is needed to assign the full deformation gradient. Different ways of dealing with raw point coordinate data that is confidently given by the metrology system lead to different kinematic results. To ensure the correctness of strain-like results determined by the system, they are compared to analytical and finite element calculations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

New solid-shell and solid-beam finite elements with applications to medical technology

In this paper, new solid-shell and solid-beam finite element formulations for finite deformation problems are introduced. One application of interest, concerning these types of elements, can be found in the simulation of stent implementation in the treatment of stenosis. The beam-like structure of the stent and the shell-like structure of the blood vessel can be modelled easily by using these types of elements. Moreover, the modelling of the interaction of the different structural types between each other and with the surounding tissue becomes more simple. A high rate of convergence, by using only one element in thickness direction that is comparable to classical structural elements, can be named as a major requirement for the element formulations. In this regard, different locking effects are cured by a special combination of the assumed natural strain method (ANS) and the enhanced assumed strain method (EAS). In addition a variable number of quadrature points can be used in thickness direction in order to capture nonlinearites. This is combined with the concept of reduced integration for the sake of computational efficiency. An adaptive hourglass stabilization that also accounts for material nonlinearities is a crucial issue in this regard. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Constrained optimal discrimination designs for Fourier regression models

In this article, the problem of constructing efficient discrimination designs in a Fourier regression model is considered. We propose designs which maximize the power of the F-test, which discriminates between the two highest order models, subject to the constraints that the tests that discriminate between lower order models have at least some given relative power. A complete solution is presented in terms of the canonical moments of the optimal designs, and for the special case of equal constraints even more specific formulae are available.     

Self‐Assembly Made Durable: Water‐Repellent Materials Formed by Cross‐Linking Fullerene Derivatives

Fullerene flakes : A diacetylene‐functionalized fullerene derivative self‐organizes into flakelike microparticles (see picture). Both the diacetylene and C₆₀ moieties can be effectively cross‐linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross‐linked flakelike objects is highly durable and water‐repellent.

     

DCDHF Fluorophores for Single‐Molecule Imaging in Cells

There is a persistent need for small‐molecule fluorescent labels optimized for single‐molecule imaging in the cellular environment. Application of these labels comes with a set of strict requirements: strong absorption, efficient and stable emission, water solubility and membrane permeability, low background emission, and red‐shifted absorption to avoid cell autofluorescence. We have designed and characterized several fluorophores, termed “DCDHF” fluorophores, for use in live‐cell imaging based on the push–pull design: an amine donor group and a 2‐dicyanomethylene‐3‐cyano‐2,5‐dihydrofuran (DCDHF) acceptor group, separated by a π‐rich conjugated network. In general, the DCDHF fluorophores are comparatively photostable, sensitive to local environment, and their chemistries and photophysics are tunable to optimize absorption wavelength, membrane affinity, and solubility. Especially valuable are fluorophores with sophisticated photophysics for applications requiring additional facets of control, such as photoactivation. For example, we have reengineered a red‐emitting DCDHF fluorophore so that it is dark until photoactivated with a short burst of low‐intensity violet light. This molecule and its relatives provide a new class of bright photoactivatable small‐molecule fluorophores, which are needed for super‐resolution imaging schemes that require active control (here turning‐on) of single‐molecule emission.     

Single-Ion Kondo scaling of the coherent Fermi liquid regime in Ce(1-x)La(x)Ni2Ge2

Thermodynamic and transport properties of the La-diluted Kondo lattice CeNi(2)Ge(2) were studied in a wide temperature range. The Ce-rich alloys Ce(1-x)La(x)Ni(2)Ge(2) were found to exhibit distinct features of the coherent heavy Fermi liquid. At intermediate compositions (0.7≤x≤0.9), non-Fermi liquid properties have been observed, followed by the local Fermi liquid behavior in the dilute limit. The 4f-electron contribution to the specific heat was found to follow the predictions of the Kondo-impurity model in both the local as well as the coherent regimes, with the characteristic Kondo temperature decreasing rapidly from about 30 K for the parent compound CeNi(2)Ge(2) to about 1 K in the most dilute samples. The specific heat does not show any evidence for the emergence of a new characteristic energy scale related to the formation of the coherent Kondo lattice.     

A pseudo‐trigonal bipyramidally ­coordinated Pt atom in dicarbonyl­bis(octacarbonyl‐μ‐di­cyclo­hexyl­phosphidodirhenio)­platinum(II)

In the title compound, [PtRe₄(C₁₂H₂₂P)₂(CO)₁₈] or [(μ‐PCy₂)(CO)₈Re₂]₂Pt(CO)₂ (Cy is cyclohexyl), two phosphido‐bridged dirhenium groups are linked by a Pt(CO)₂ unit and show different bonding patterns for stereochemical reasons. The Re—Re distances are 3.2620 (15) and 3.0739 (15) Å, and the Pt—Re distances are 2.9165 (12), 2.9025 (15) and 2.8548 (13) Å.     

The chemistry of the highly reactive 2,6‐bis(bromomethyl)‐4‐pyrone

Under basic conditions 2,6‐bis(bromomethyl)‐4‐pyrone 8 reacts with tetraethylene glycol to yield the unexpected macrocycle 9 , which is related to the antibiotic Kjellmanianone 10 . We propose that this ring transformation proceeds via the cyclopropyl intermediate d (Scheme 2), which undergoes a ring opening reaction comparable to the Favorskii rearrangement. Also, 8 reacts with methanol/sodium methoxide to yield the 3(2H)‐furanone derivative 11 , the formation of which is suggested to proceed via the intermediate k with a carbenium‐oxonium‐ion subunit (Scheme 3). The structure of the 3(2H)‐furanone derivative was confirmed by X‐ray analysis.     

Creep of Single Crystals – Modelling and Numerical Aspects

A number of constitutive models, utilizing both microstructural and/or phenomenological considerations, have been developed for the simulation of the creep behaviour of nickel-base single crystal superalloys at elevated temperatures. In this work, emphasis is placed on the rate-dependent single crystal plasticity model [1]. A strategy for the identification of the material parameters of the model to fit the results from experiments has been implemented. The parameter fitting methodology rests upon a two-membered evolution strategy. In addition, a proposal is made for the extension of the Cailletaud model [1] by means of an evolution equation for a damage variable which enables the modelling of the tertiary creep stage. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)