620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Process-induced changes in thermo-mechanical viscoelastic properties and the corresponding morphology of biodegradable polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) blown film blends modified with four multifunctional chain-extending cross-linkers (CECL) were investigated. The introduction of CECL modified the properties of the reference PBAT/PLA blend significantly. The thermal analysis showed that the chemical reactions were incomplete after compounding, and that film blowing extended them. SEM investigations of the fracture surfaces of blown extrusion films reveal the significant effect of CECL on the morphology formed during the processing. The anisotropic morphology introduced during film blowing proved to affect the degradation processes as well. Furthermore, the reactions of CECL with PBAT/PLA induced by the processing depend on the deformation directions. The blow-up ratio parameter was altered to investigate further process-induced changes proving synergy with mechanical and morphological features. Using blown film extrusion, the elongational behavior represents a very important characteristic. However, its evaluation may be quite often problematic, but with the SER Universal Testing Platform it was possible to determine changes in the duration of time intervals corresponding to the rupture of elongated samples.
Force field (FF) based molecular modeling is an often used method to investigate and study structural and dynamic properties of (bio-)chemical substances and systems. When such a system is modeled or refined, the force field parameters need to be adjusted. This force field parameter optimization can be a tedious task and is always a trade-off in terms of errors regarding the targeted properties. To better control the balance of various properties’ errors, in this study we introduce weighting factors for the optimization objectives. Different weighting strategies are compared to fine-tune the balance between bulk-phase density and relative conformational energies (RCE), using n-octane as a representative system. Additionally, a non-linear projection of the individual property-specific parts of the optimized loss function is deployed to further improve the balance between them. The results show that the overall error is reduced. One interesting outcome is a large variety in the resulting optimized force field parameters (FFParams) and corresponding errors, suggesting that the optimization landscape is multi-modal and very dependent on the weighting factor setup. We conclude that adjusting the weighting factors can be a very important feature to lower the overall error in the FF optimization procedure, giving researchers the possibility to fine-tune their FFs.
The lattice Boltzmann method (LBM) stands apart from conventional macroscopic approaches due to its low numerical dissipation and reduced computational cost, attributed to a simple streaming and local collision step. While this property makes the method particularly attractive for applications such as direct noise computation, it also renders the method highly susceptible to instabilities. A vast body of literature exists on stability-enhancing techniques, which can be categorized into selective filtering, regularized LBM, and multi-relaxation time (MRT) models. Although each technique bolsters stability by adding numerical dissipation, they act on different modes. Consequently, there is not a universal scheme optimally suited for a wide range of different flows. The reason for this lies in the static nature of these methods; they cannot adapt to local or global flow features. Still, adaptive filtering using a shear sensor constitutes an exception to this. For this reason, we developed a novel collision operator that uses space- and time-variant collision rates associated with the bulk viscosity. These rates are optimized by a physically informed neural net. In this study, the training data consists of a time series of different instances of a 2D barotropic vortex solution, obtained from a high-order Navier–Stokes solver that embodies desirable numerical features. For this specific text case our results demonstrate that the relaxation times adapt to the local flow and show a dependence on the velocity field. Furthermore, the novel collision operator demonstrates a better stability-to-precision ratio and outperforms conventional techniques that use an empirical constant for the bulk viscosity.