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The development of smart lubricating materials with lasting lubrication and outstanding wear resistance while achieving speed response is of great significance in the field of bearing cage applications but has proven to be challenging. Herein, polyimide (PI) molding powder containing two kinds of PI with different rigidities is synthesized in situ to fabricate a two‐scale porous polyimide (PPI) by (cold and hot) isostatic pressing. The unique two‐scale porous structure originates from the bimodal particle size distribution of the PI molding powder. The oil stored in the two‐scale PPI is gradually thrown out as the rotation speed increases, which makes the two‐scale PPI suitable for bearing cages with a wider rotation speed range and realize persistent and stable oil supply under different speeds. The porosity of PPI decreases with increasing pressure during hot isostatic pressing, but the effect of temperature on the porosity is not obvious. Moreover, the two‐scale PPI maintains good mechanical properties, and its ring tension is as high as 22.3 MPa. Due to the high oil content (>15%) and excellent oil retention rate (93.3%, at 3000 rpm for 180 min), the two‐scale oil‐containing PPI exhibits a stable low friction coefficient (≈0.096) and ultralow wear rate (≈0.68×10−6mm3 (Nm)−1). [ABSTRACT FROM AUTHOR]

China is a broad territory country. There are significant differences in the terrain, climate, and other environmental factors between different provinces, which affect wind power generation. In order to better analyze the situation of wind power generation in Chinese provinces, this paper uses the functional clustering analysis to classify the monthly data of wind power generation in 30 Chinese provinces from March 2013 to October 2019. The empirical results of this paper show that the wind energy generation in Chinese provinces can be divided into three categories, and the results are consistent with the actual situation. In this paper, functional clustering analysis is used to analyze monthly data, compared with the traditional clustering analysis to analyze annual data which are obtained by accumulated monthly data. Higher-dimensional data can be used for analysis to reduce information loss. Moreover, data can be viewed as functions, and more information can be mined by analyzing derivative functions, and so on. The analysis of wind energy generation has certain guiding significance for the development and utilization of renewable energy. [ABSTRACT FROM AUTHOR]

It is of great significance to forecast the intraday returns of stock index futures. As the data sampling frequency increases, the functional characteristics of data become more obvious. Based on the functional principal component analysis, the functional principal component score was predicted by BM, OLS, RR, PLS, and other methods, and the dynamic forecasting curve was reconstructed by the predicted value. The traditional forecasting methods mainly focus on "point" prediction, while the functional time series forecasting method can avoid the point forecasting limitation, and realize "line" prediction and dynamic forecasting, which is superior to the traditional analysis method. In this paper, the empirical analysis uses the 5-minute closing price data of the stock index futures contract (IF1812). The results show that the BM prediction method performed the best. In this paper, data are considered as a functional time series analysis object, and the interference caused by overnight information is removed so that it can better explore the intraday volatility law, which is conducive to further understanding of market microstructure. [ABSTRACT FROM AUTHOR]

Blends of entirely biosourced polymers, namely polylactide (PLA) and polyamide11 (PA11), have been prepared by a melt-blending process. Several kinds of PLA/PA11 blends (with different ratio of 0/100, 10/90, 30/70, 50/50, 70/30, 90/10, 100/0) were examined. DMA, XRD, SEM, mechanical Properties testing, FTIR analysis and molecular dynamics (MD) simulations were used to characterize the properties of the PLA/PA11 blends. The DMA analysis and MD simulation results showed that immiscibility prevails in all PLA/PA11 blends. XRD analysis indicated that in the 70/30 PLA/PA11 blends, the PLA component has been crystalized. SEM analysis indicated that there is a distinct interface between the PLA and PA11 in 70/30 PLA/PA11 blend, whose mechanical properties decrease significantly. The binding energy, radial distribution function g(r) obtained from MD simulations results revealed the existence of hydrogen-bonding between PLA and PA11, but the compatibility of PLA/PA11 blends can not be improved by the weak hydrogen bonding. [ABSTRACT FROM AUTHOR]

The solubility parameters of polyacrylonitrile (PAN) and of three different solvents, N, N-dimethylformamide (DMF), N, N-dimethylacetamide, and N-methyl-2-pyrrolidone, as also Flory–Huggins parameters between PAN and these solvents were first calculated, using molecular dynamics simulation. From the simulation results, DMF was chosen as the solvent for PAN in magnetic-field-assisted electrospinning (MFAES). Then, a systematic investigation of the processing parameters, including their interaction and modeling of the degree of fiber alignment, was conducted using a three factor, three-level Box–Behnken design, combined with response surface methodology and quadratic programming. Three independent variables (solution concentration [X1], ranging from 12% to 14%; voltage [X2], ranging from 12 to 16 kV; and the distance between two magnets [X3], ranging from 2 to 3 cm) were consecutively coded as x1, x2 and x3 at three levels (−1, 0, and 1). The degree of PAN fiber alignment (Y) was maximized, based on 17 different MFAES experimental data, and a second-order polynomial regression equation was obtained to predict the corresponding results. The significance of independent variables and their interactions was tested by the analysis of variance with 95% confidence limits (a = 0.05). The standard effects of the independent variables and their interactions on the response were also investigated by preparing a Pie chart. The optimum values of the selected variables were obtained by solving the quadratic regression model and analyzing the response surface contour plots. The optimum coded values of the three test variables were computed as x1 = 0.35, x2 = −0.52, and x3 = 0.15. The experimental conditions at this global point were determined to be X1 = 13.35%, X2 = 13.03 kV, and X3 = 2.58 cm, and the corresponding Y was found to be about 96%. [ABSTRACT FROM AUTHOR]

The miscibility of polyethylene terephthalate (PET)/polylactide (PLA) blends is studied through atomistic molecular dynamics (MD) and mesoscale dissipative particle dynamics (DPD) simulation. Five PET/PLA blends (with the weight ratio at 90/10, 70/30, 50/50, 30/70 and 10/90) as well as pure PET and PLA are examined. The solubility parameter values obtained by using the MD simulation are in good agreement with the reference data. The Flory–Huggins parameters, χ, which are computed for different blends and determined from the cohesive energy densities, with the radial distribution functionsg(r) of the inter-molecular atoms, suggest that PET is completely miscible with PLA over the entire composition range. This is further proved by the mesoscopic morphologies of PET/PLA blends. All the simulation results are qualitatively consistent with the experimental results, and demonstrate that the modelling strategies in this study may serve as a powerful tool for predicting miscibility and mesoscopic morphology of polymer blends. [ABSTRACT FROM AUTHOR]

The structural properties, elastic anisotropy, electronic structures and work function of D022-type Al3TM (TM = Sc, Ti, V, Y, Zr, Nb, La, Hf, Ta) are studied using the first-principles calculations. The results indicate that the obtained formation enthalpy and cohesive energy of these compounds are in accordance with the other calculated values. It is found that the Al3Zr is the most thermodynamic stable compound. The mechanical property indexes, such as elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Vickers hardness are systematically explored. Moreover, the calculated universal anisotropic index, percent anisotropy and shear anisotropic factors of D022-type Al3TM are analyzed carefully. It demonstrates that the shear modulus anisotropy of Al3La is the strongest, while that of Al3Ta is the weakest. In particular, the density of states at Fermi level is not zero, suggesting that these phases have metal properties and electrical conductivity. More importantly, the mechanisms of correlation between hardness and Young's modulus are further explained by the work function. Finally, the experimental design proves that D022-Al3Ta has an excellent strengthening effect. [ABSTRACT FROM AUTHOR]

In this study, the cohesive energy, interfacial energy, electronic structure, and bonding of Mg 2 Si (111)/Mg 3 Sb 2 (0001) were investigated by using the first-principles method based on density functional theory. Meanwhile, the mechanism of the Mg 3 Sb 2 heterogeneous nucleation potency on Mg 2 Si grains was revealed. The results indicated that the Mg 3 Sb 2 (0001) slab and the Mg 2 Si (111) slab achieved bulk-like characteristics when the atomic layers N ≥ 11, and the work of adhesion of the hollow-site (HCP) stacking structure (the interfacial Sb atom located on top of the Si atom in the second layer of Mg 2 Si) was larger than that of the other stacking structures. For the four HCP stacking structures, the Sb-terminated Mg 3 Sb 2 /Si-terminated Mg 2 Si interface with a hollow site showed the largest work of adhesion and the smallest interfacial energy, which implied the strongest stability among 12 different interface models. In addition, the difference in the charge density and the partial density of states indicated that the electronic structure of the Si-HCP-Sb interface presented a strong covalent, and the bonding of the Si-HCP-Mg interface and the Mg-HCP-Sb interface was a mixture of a covalent bond and a metallic bond, while the Mg-HCP-Mg interfacial bonding corresponded to metallicity. As a result, the Mg 2 Si was conducive to form a nucleus on the Sb-terminated-hollow-site Mg 3 Sb 2 (0001) surface, and the Mg 3 Sb 2 particles promoted the Mg 2 Si heterogeneous nucleation, which was consistent with the experimental expectations.