Fourier neural operator approach to large eddy simulation of three-dimensional turbulence

Fourier neural operator (FNO) model is developed for large eddy simulation (LES) of three-dimensional (3D) turbulence. Velocity fields of isotropic turbulence generated by direct numerical simulation (DNS) are used for training the FNO model to predict the filtered velocity field at a given time. The input of the FNO model is the filtered velocity fields at the previous several time-nodes with large time lag. In the a posteriori study of LES, the FNO model performs better than the dynamic Smagorinsky model (DSM) and the dynamic mixed model (DMM) in the prediction of the velocity spectrum, probability density functions (PDFs) of vorticity and velocity increments, and the instantaneous flow structures. Moreover, the proposed model can significantly reduce the computational cost, and can be well generalized to LES of turbulence at higher Taylor-Reynolds numbers.     

In-situ constructing visible light CdS/Cd-MOF photocatalyst with enhanced photodegradation of methylene blue

Based on high specific surface area, high porosity of metal-organic frameworks (MOFs) and excellent visible light response of CdS, the CdS/Cd-MOF nanocomposites were constructed by in-situ sulfurization to form CdS using Cd-MOF as precursor and the CdS loading was controlled by the dose of thioacetamide. Under the irradiation of simulated sunlight, the degradation rate of methylene blue (MB) by 10 mg MOF/CdS-6 (mass ratio of MOF to thioacetamide is 6:1) was 91.9% in 100 min, which was higher than that of pure Cd-MOF (62.3%) and pure CdS (67.5%). This is attributed to the larger specific surface area of the composite catalysts, which provides more active sites. Meanwhile, the loading of CdS obviously broadens the light response range of Cd-MOF and improves the utilization of visible light. The Mott-Schottky model experiment shows that the formed type-II heterojunction between Cd-MOF and CdS can effectively inhibit the recombination of photogenerated electrons and holes. Meanwhile, the photocurrent intensity of MOF/CdS-6 is 8 times and 2.5 times of that of pure Cd-MOF and CdS. In addition, MOF/CdS-6 showed good photocatalytic performance after five cycles, showing excellent stability and reusability.     

Artificial Water Channels: Towards Biomimetic Membranes for Desalination

Natural Aquaporin (AQP) channels are efficient water translocating proteins, rejecting ions. Inspired by this masterpiece of nature, Artificial Water Channels (AWCs) with controlled functional structures, can be potentially used to mimic the AQPs to a certain extent, offering flexible avenues toward biomimetic membranes for water purification. The objective of this paper is to trace the historical development and significant advancements of current reported AWCs. Meanwhile, we attempt to reveal important structural insights and supramolecular self-assembly principles governing the selective water transport mechanisms, toward innovative AWC-based biomimetic membranes for desalination.     

Novel redox-active ionic thermotropic liquid crystalline complexes of polyelectrolyte and ferrocenyl surfactants

Redox-active polyelectrolyte-surfactant complexes(PSC) were prepared via the ionic self-assembly of sodium poly(styrenesulfonate) (PSS) and ferrocenyl surfactant,(11-ferrocenylundecyl)trimethylammonium bromide(FTMA) in aqueous solution. The PSS-FTMA complex exhibited an ordered interdigitated monolayer mesomorphous structure with the long period of d = 3.13 nm,and was in the ionic thermotropic liquid crystal SmA state at room temperature.Interestingly,in the solid complex, the ferrocenyl moieties formed H-aggregation showing an increase in theπ-π~* energy transfer of cyclopentadienes in the ferrocene moieties as known from the blue-shift in the UV spectrum.The complexes showed higher thermal stability compared with their components due to the ionic interaction.The PSS-FTMA film had a good redox reversibility,which promised to be used in electrochemical sensors.     

Fabrication and characterization of micro-encapsulated sodium phosphate dodecahydrate with different crosslinked polymer shells

Microencapsulations of sodium phosphate dodecahydrate with different crosslinked polymer as shells were carried out by in situ polymerization and solvent evaporation method. Methyl methacrylate (MMA), urea were employed to crosslink with ethyl acrylate (EA) and formaldehyde, respectively. The influences of the type of crosslinking agent on the performance of as-prepared microencapsulated phase change materials (microPCMs) have been studied. The microPCMs were investigated using Fourier transformed infrared spectroscopy, scanning electron microscopy, and transmission electron microscope. Thermal properties and thermal stability of microPCMs were characterized by differential scanning calorimetry and thermalgravimetric analysis. Conclusion points out that thermal properties and thermal resistant temperatures of microPCMs vary from the type of crosslinkable functional moieties of the crosslinking agents. The temperature range of melting enlarged and the melting temperature increased according to the prepared microPCMs, which is suitable for thermal energy storage.     

多振子声子晶体的低频特性研究

本文设计了一种由硅橡胶包覆层包裹4个钨振子的新型声子晶体结构,通过有限元法计算该结构的色散曲线、振动模态和传输损失谱。结果表明,该结构的带隙范围为18.85~225.28 Hz,与传输损失谱频率衰减范围相吻合,能够有效抑制20~200 Hz的弹性波在声子晶体中传播。通过分析色散曲线上点的振动模态,说明带隙产生的原因。本文讨论了声子晶体板的缺口角度和振子之间的纵向和横向间距对带隙的影响,结果表明:当缺口角度减小时,带隙下边界几乎保持不变,带隙上边界升高从而增加了带隙的宽度;振子之间横向或纵向间距增大时,带隙下边界和上边界均上升,带隙变宽,进而优化了声子晶体模型的带隙。同时声子晶体板的缺口设计能够节省材料,从而减轻结构的质量。     

Development and validation of a novel rheological test device and measurement system for determining the influence of humidity on viscosity

Although a strong impact of humidity on polymers and the formation of their molecular network is known, the complex interactions between humidity, temperature, diffusion, reaction kinetics, rheological behaviour and mechanical properties are not fully understood yet. Most current approaches solely analyse the relationships between environmental conditions in a solidified or crosslinked state and the mechanical properties. In contrast, this work focusses on measuring changes in rheological properties depending on relative humidity in the liquid state. A custom designed novel measuring geometry is introduced and validated. It enables for the first time to rheometrically investigate the influence of relative humidity on reactive systems during their cross-linking process. Our results significantly depict the influence of humidity on the cross-linking process and the gel time. The potential of the introduced measuring geometry for improving reactive systems, adapting these precisely to environmental boundary conditions or assuring product performance is hereby demonstrated. This is especially important for industrial manufacturing processes running at different production sites around the world in different climatic zones or repair processes being performed outdoor, e.g. for wind energy plants.