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Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for their use in separation, gas adsorption, catalysis, and biotechnology. Their practical applications, however, can be hampered by their structural instability in humid acidic conditions. Here, guided by density functional theory calculations, we demonstrate that the acidic stability of two polymorphic ZIFs (i.e., ZIF-8 and ZIF-L) can be enhanced by the incorporation of functional groups on polypeptides or DNA. A range of complementary synchrotron investigations into the local chemical structure and bonding environment suggest that the enhanced acidic stability arises from the newly established coordinative interactions between the Zn centers and the inserted carboxylate (for polypeptides) or phosphate (for DNA) groups, both of which have lower pKas than the imidazolate ligand. With functional biomolecular homologs (i.e., enzymes), we demonstrate a symbiotic stability reinforcement effect, i.e., the encapsulated biomolecules stabilize the ZIF matrix while the ZIF exoskeleton protects the enzyme from denaturation.
The inter-instrument, inter-laboratory, and long-term comparability of fluorescence data requires the correction of the measured emission and excitation spectra for the wavelength- and polarization-dependent spectral irradiance of the excitation channel at the sample position and the spectral responsivity of the emission channel employing procedures that guarantee traceability to the respective primary standards. In this respect the traceability chain of fluorometry is discussed from a radiometrists point of view. This involves, in a first step, the realization of the spectral radiance scale, based on the blackbody radiator and electron storage ring, and the spectral responsivity scale, based on the cryogenic radiometer and their control via key comparisons of the national metrology institutes. In a second step, the characterization including state-of-the art uncertainties of the respective source and detector transfer standards such as tungsten strip lamps, integrating sphere radiators, and trap detectors used to disseminate these radiometric quantities to users of spectroscopic techniques is presented.
An assessment of the elastic-plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design.
This paper reports on an international ‘round-robin’ exercise conducted in 2022 aiming to take stock of the computational shell buckling expertise around the world which attracted 29 submissions. Participants were asked to perform analyses of increasing complexity on a standardised benchmark of an 8-MW multi-strake steel wind turbine support tower segment, from a linear elastic stress analysis to a linear bifurcation analysis to a geometrically and materially nonlinear buckling analysis with imperfections. The results are a showcase of the significant shell buckling expertise now available in both industry and academia.
This paper is the first of a pair. The second paper presents a detailed reference solution to the benchmark, including an illustration of the Eurocode-compliant calibration of two important imperfection forms.
Für die Installation von Offshore-Windenergie-Anlagen der 5-Megawattklasse vor der Küste Deutschlands in der Nordsee ist es erforderlich, Gründungsstrukturen in hoher Stückzahl wirtschaftlich herstellen zu können. Für den Wassertiefenbereich der Nordsee wird im Rahmen dieses Aufsatzes der Konstruktions-typ Jacket hinsichtlich dynamischer Eigenschaften untersucht.
Darüber hinaus wird über Stahlgussbauteile berichtet, die in den hochbelasteten Knotenpunkten des Jackets verbaut werden. Derzeit ist es üblich, Jackets aus handelsüblichen Stahlhohlprofilen zu fertigen, die an den Enden zu einer Knotenverbindung miteinander verschweißt werden. Diese Lösung besitzt jedoch eine Vielzahl von Nachteilen, über die nachfolgend berichtet wird.
Bauteile aus Stahlguss hingegen weisen unter anderem die Vorteile auf, universell einsetzbar und in Form bzw. Gestaltung völlig frei wählbar zu sein. Um das komplexe Tragverhalten dieser Stahlgussbauteile bewerten zu können, wurden neben Simulationsrechnungen auch Laborversuche durchgeführt. Es wurde das Tragverhalten unter statischer Belastung am Stahlgussbauteil im 1:1-Modell und das Ermüdungsverhalten an Stahlgussproben getestet.
Load bearing behaviour of cast steel components in offshore wind turbines under fatigue and static loads.
The installation of offshore wind turbines of the 5-megawatt class in deep water of the North Sea makes it economically necessary to build foundations in high quantities.
Constructions of this kind are a major technical challenge in terms of design, manufacturing and operation. In this paper the dynamic behaviour of jacket constructions in the North Sea are investigated. Currently jacket structures are constructed with steel pipes that are welded at the connecting nodes. This procedure implies several disadvantages.
In contrast cast steel elements are universally applicable and designable. To verify the load bearing behaviour numerical simulations and laboratory tests are done. Laboratory tests include the testing of the ultimate load bearing capacity. In a large scale setup and fatigue tests at small cast steel specimen.