Planetary Gears Feature Extraction and Fault Diagnosis Method Based on VMD and CNN

Given local weak feature information, a novel feature extraction and fault diagnosis method for planetary gears based on variational mode decomposition (VMD), singular value decomposition (SVD), and convolutional neural network (CNN) is proposed. VMD was used to decompose the original vibration signal to mode components. The mode matrix was partitioned into a number of submatrices and local feature information contained in each submatrix was extracted as a singular value vector using SVD. The singular value vector matrix corresponding to the current fault state was constructed according to the location of each submatrix. Finally, by training a CNN using singular value vector matrices as inputs, planetary gear fault state identification and classification was achieved. The experimental results confirm that the proposed method can successfully extract local weak feature information and accurately identify different faults. The singular value vector matrices of different fault states have a distinct difference in element size and waveform. The VMD-based partition extraction method is better than ensemble empirical mode decomposition (EEMD), resulting in a higher CNN total recognition rate of 100% with fewer training times (14 times). Further analysis demonstrated that the method can also be applied to the degradation recognition of planetary gears. Thus, the proposed method is an effective feature extraction and fault diagnosis technique for planetary gears

Effects of the Cooling Equipment Based on Cooled Atomization Air on Environmental Physicochemical Indexes and Sedimental Microbial Community Structure of Sea Cucumber Culture Ponds in Summer

In recent years, continuous high temperature and marine heat waves in summer have become major limitations for the sustainable development of sea cucumber aquaculture. In 2019, our team invented a cooling equipment based on cooled atomization air, which can reduce the water temperature of the culture pond in summer. Previous tests showed that the survival rates of the sea cucumbers in the equipped ponds were higher than the unequipped ponds during the high temperature. In this study, five equipped ponds were selected as experimental groups (groups E1 and E2 were labeled according to their geographic location) and three unequipped ponds were selected as control groups (labeled group C), then the water quality, sedimental quality, and the sedimental microbial community structure of the eight ponds were analyzed in order to reveal the mechanism of the higher survival rate using the cooling equipment. The results showed that the temperature of the bottom water of the two experimental groups was significantly lower than that of the control group (P < 0.05). The dissolved oxygen (DO) level in the bottom water of the experimental groups was significantly higher than that of the control group (P < 0.05). Both the ammonia nitrogen concentration in the bottom water and the concentrations of nitrite nitrogen, and chemical oxygen demand (COD) and ammonia nitrogen in pond sediments of the two experimental groups were significantly lower than that of the control group (P < 0.05). The sedimental microbial community structure of all the ponds was also investigated, and the OTUs (optical transform units) were numbered from 707 to 808. Alpha diversity analysis showed that the abundance and diversity of the experimental group were higher than those of the control group. PCoA (principal coordinates analysis) showed that the bacterial composition and community structure among the two experimental groups were more similar, while there were significant differences between the experimental and the control groups. The species distribution analysis on the order level showed that the similarity between the two experimental groups is higher than that between the experimental and control groups. The relative abundance of Rhizobiales, Lactobacillales, and Micrococcineae in the experimental groups were significantly higher than that in the control groups. Thirteen OTUs with significant differences among three groups were selected using LEfSe (LDA effect size) analysis. The correlation analysis between microbial community structure and environmental factors showed that the abundance of microbial species involved in the nitrogen cycle was significantly higher in the experimental groups than that of the control groups. Then OTU7, OTU29 and OTU108 were screened and significant correlation was found with ammonia nitrogen concentration in all of the tested ponds, and they are classified as Ochrobactrum, Escherichia-Shigella and Bacillus, respectively. In the 25 predicted COG (clusters of orthologous groups of proteins) metabolic pathways in prokaryotes, 18 metabolic pathways exhibited significant differences (P < 0.05) between the experimental groups and the control groups. All the results indicated that the use of the equipment could significantly improve the pond water quality and sediment environment, and positively affect the sedimental microbial community structure of the bottom water. The results of this study would provide scientific support for the popularization and application of the equipment

Ultrathin NiCo2S4@graphene with a core-shell structure as a high performance positive electrode for hybrid supercapacitors

NiCo2S4 is a promising material for supercapacitors owing to its merits of high conductivity and activity in redox reactions. However it suffers poor cycling stability due to structural degradation of the electrode through the redox process. Herein we demonstrate a facile method for the synthesis of a NiCo2S4/graphene composite where NiCo2S4 is encapsulated with an ultrathin graphene layer to form a core/shell structure (NiCo2S4@G). Transmission electron microscopy (TEM) indicates that the shell is only 3–5 layers of graphene and the NiCo2S4 particle core has a uniform size of around 5–7 nm. The NiCo2S4@G composite exhibits excellent electrochemical performance with a specific capacitance of 1432 F g−1 at a current density of 1 A g−1. A hybrid supercapacitor assembled using the synthesized NiCo2S4@G as a positive electrode and porous carbon as a negative electrode demonstrates a high energy density of 43.4 W h kg−1 at a power density of 254.3 W kg−1 in the voltage range 0–1.35 V. After 5000 charge/discharge cycles, the device still retains 83.4% of its initial capacitance

Aqueous Rechargeable Zinc/Aluminum Ion Battery with Good Cycling Performance

Developing rechargeable batteries with low cost is critically needed for the application in large-scale stationary energy storage systems. Here, an aqueous rechargeable zinc//aluminum ion battery is reported on the basis of zinc as the negative electrode and ultrathin graphite nanosheets as the positive electrode in an aqueous Al₂(SO₄)₃/Zn­(CHCOO)₂ electrolyte. The positive electrode material was prepared through a simple electrochemically expanded method in aqueous solution. The cost for the aqueous electrolyte together with the Zn negative electrode is low, and their raw materials are abundant. The average working voltage of this aqueous rechargeable battery is 1.0 V, which is higher than those of most rechargeable Al ion batteries in an ionic liquid electrolyte. It could also be rapidly charged within 2 min while maintaining a high capacity. Moreover, its cycling behavior is also very good, with capacity retention of nearly 94% after 200 cycles

Highly efficient Co3O4/Co@NCs bifunctional oxygen electrocatalysts for long life rechargeable Zn-air batteries

© 2020 Elsevier Ltd Rational design and synthesis of high-performance bifunctional oxygen electrocatalysts are in high demand for metal air batteries. Herein, Co3O4/Co nano-heterojunctions tailored in nitrogen-doped porous graphitized carbon frameworks (Co3O4/Co@NCs) are synthesized via annealing Co-based metal-organic-frameworks (Co-based MOFs). This structure for electrocatalysts with a combination of mixed metallic Co species and encapsulating porous graphitized carbon offers an efficient charge/mass transport environment. In addition, the Co3O4/Co nano-heterostructured interfaces serve as efficient reactive sites to enhance oxygen electrocatalysis. Furthermore, the strong binding forces between nanoparticles and carbon frameworks through Co–N covalent bonds prevent the loss of nanoparticles from the electrocatalysts, providing outstanding durability. Consequently, Co3O4/Co@NCs surpasses the performance of noble-metal catalysts with a positive half-wave potential of 0.92 V (vs. reversible hydrogen electrode, RHE) for the oxygen reduction reaction and a low potential of 1.55 V at 10 mA cm−2 for the oxygen evolution reaction. Impressively, our assembled zinc–air batteries using Co3O4/Co@NCs as the rechargeable air electrode exhibit superior charge-discharge performance and ultra-stable cyclability with almost no increase in polarization even after 600 h (10 mA cm−2), possessing great potential for practical application in next-generation rechargeable batteries