Nonlinear Rheological Behaviors in Polymer Melts after Step Shear

Using molecular dynamics simulation, we investigate the evolution of chain conformation, stress relaxation, and fracture for a polymer melt between two walls after step shear. We find that the characteristic overlap time for the reduced relaxation moduli and the time that the stretched primitive chain retracts to its equilibrium length are both much longer than the Rouse time. Importantly, we observe significant fracture-like flow after shear cessation. While there is considerable randomness in the location of the fracture plane and the magnitude of displacement from sample to sample, our analysis suggests that the randomness is not due to thermal noise, but may reflect inherent structural and dynamic heterogeneity in the entangled polymer network

System metabolic tools reveal fucoxanthin metabolism in Nitzschia laevis for the improvement of fucoxanthin productivity

The production of fucoxanthin from microalgae is rapidly gaining popularity due to its exceptional productivity, lack of contamination, and straightforward extraction process. However, the optimal conditions for increasing biomass concentration and/or fucoxanthin content through the manipulation of light and carbon sources are context specific. This study explored fucoxanthin metabolism in Nitzschia laevis under heterotrophic and mixotrophic conditions using 13C tracer-based metabolic flux analysis, targeted metabolomics, and transcriptome analysis. Mixotrophic culture at 10 μmol m-2 s-1 improved fucoxanthin content by 27.54% but decreased biomass concentration by 15.65% compared to heterotrophic culture. At the molecular level, exposure to low light results in a reduction in carbon flux in the TCA cycle, leading to an increased flux toward carotenoid and fatty acid biosynthesis. The accumulation of high levels of citrate, isocitrate, and α-ketoglutaric acid is attributed to the reduced activity of the TCA cycle. Moreover, the metabolism of glyceraldehyde-3-phosphate and phosphoenolpyruvate was found to be more active under mixotrophic cultivation than heterotrophic ones, resulting in a substantial accumulation of fucoxanthin. The higher ATP and NADPH consumption provided sufficient energy for fucoxanthin and fatty acid biosynthesis. Furthermore, gene expression analysis revealed that low light upregulated the genes involved in fucoxanthin biosynthesis and promoted the violaxanthin cycle, especially after 12 h of cultivation. To improve fucoxanthin productivity, low light conditions were applied after a fed-batch culture, resulting in a 22.92% increase in fucoxanthin accumulation. The findings of this study offer valuable insights into the advantages of employing multi-stage cultivation techniques to improve microalgal production

Nonlinear Rheological Behaviors in Polymer Melts after Step Shear

Using molecular dynamics simulation, we investigate the evolution of chain conformation, stress relaxation, and fracture for a polymer melt between two walls after step shear. We find that the characteristic overlap time for the reduced relaxation moduli and the time that the stretched primitive chain retracts to its equilibrium length are both much longer than the Rouse time. Importantly, we observe significant fracture-like flow after shear cessation. While there is considerable randomness in the location of the fracture plane and the magnitude of displacement from sample to sample, our analysis suggests that the randomness is not due to thermal noise, but may reflect inherent structural and dynamic heterogeneity in the entangled polymer network

Variation of Tensor Force due to Nuclear Medium Effect

The enhancement of $J^{\pi}(T)$=3$^{+}$(0) state with isospin $T=0$ excited by the tensor force in the free $^{6}$Li nucleus has been observed, for the first time, relative to a shrinkable excitation in the $^{6}$Li cluster component inside its host nucleus. Comparatively, the excitation of $J^{\pi}(T)$=0$^{+}$(1) state with isospin $T=1$ for these two $^{6}$Li formations take on an approximately equal excitation strength. The mechanism of such tensor force effect was proposed due to the intensive nuclear medium role on isospin $T$=0 state.Comment: 6 pages, 4 figure