Characteristics Analysis and Technical Prospect of Low-Frequency Main Transformer for Offshore Wind Power

[Introduction] Low-frequency alternating current power transmission technology has attracted wide attention. Although its theoretical research continues to go deeper, there are still many problems to be solved before its engineering implementation in large-capacity long-distance offshore wind power transmission scenarios. The development and selection of offshore low-frequency main transformer is one of such problems. [Method] Based on the detailed description of the structure and working principle of the low-frequency alternating current transmission system for offshore wind power, the low-frequency operation characteristics of the offshore main transformer were analyzed. [Result] If the transformer is transformed by increasing the core section and winding turns, the weight, volume and total loss of the low-frequency transformer will be increased greatly, which will have a great impact on the economy of the overall transmission scheme of offshore wind power and the load and layout of offshore step-up station. It is necessary to study the miniaturization, light weight and low loss design of offshore low-frequency transformer. [Conclusion] The key transformation technologies of offshore low-frequency transformer are discussed in detail. In the aspect of transformer core, the research and development of high-performance oriented silicon steel sheet with high magnetic density or low loss is the most concerned low-frequency transformer transformation technology. With the offshore advantages, the design of water cooling mode and intelligently monitored transformer cooling mode can also optimize the overall quality and volume of transformer. Ester high ignition point insulated oil transformer has the advantages of biodegradability, inflammability and high reliability of oil, which means that it is more suitable for offshore low-frequency transformer compared with the conventional mineral oil transformer. The future development of the above key technologies is expected to provide reference for the development and application of large-capacity and high-voltage class offshore low-frequency transformer, so as to promote the engineering practice of low-frequency technology in the field of large-capacity long-range offshore wind power transmission

Extraction, structural characterization, and antioxidant activity of polysaccharides derived from Arctium lappa L.

IntroductionArctium lappa L. root has high nutritional and medicinal values and has been identified as a healthy food raw material by the Ministry of Health of the People's Republic of China.MethodsIn the present study, an aqueous two-phase system (ATPS) of polyethylene glycol (PEG)-(NH4)2SO4 was used to extract Arctium lappa L. polysaccharides (ALPs) from the Arctium lappa L. roots, the optimal extraction conditions of crude ALPs were optimized by using the single-factor experiment and response surface methodology. The structure and composition of ALPs were determined by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and high-performance liquid chromatography (HPLC). At the same time, the antioxidant activity of ALPs was investigated by in vitro antioxidant experiment.ResultsThe optimized extraction parameters for extraction ALPs were as follows: the PEG relative molecular weight of 6,000, a quality fraction of PEG 25%, a quality fraction of (NH4)2SO4 18%, and an extraction temperature of 80°C. Under these conditions, the extraction rate of ALPs could reach 28.83%. FTIR, SEM and HPLC results showed that ALPs were typical acidic heteropolysaccharides and had uneven particle size distribution, an irregular shape, and a rough surface. The ALPs were chiefly composed of glucose, rhamnose, arabinose, and galactose with a molar ratio of 70.19:10.95:11.16:6.90. In addition, the ALPs had intense antioxidant activity in vitro with IC50 values in the ·OH radical (1.732 mg/ml), DPPH radical (0.29 mg/ml), and superoxide anion (0.15 mg/ml) scavenging abilities.DiscussionThe results showed that ATPS was an efficient method to extract polysaccharides and could be used for the extraction of other polysaccharides. These results indicated that ALPs had great prospects as a functional food and could be exploited in multiple fields

Protective Effect of Antioxidant Peptides Derived from Yak Milk Casein on Oxidative Stress Injury in HEK293 Cells

In this experiment, HEK293 cells were induced by H2O2 to establish a cell model of oxidative damage, and the optimal H2O2 concentration and treatment time were determined. The effects of five antioxidant peptides (AFK, IEQI, FPFF, LPVPQ and RELEEL) derived from yak milk casein on the survival rate, malondialdehyde (MDA) content, antioxidant enzyme activities, reduced glutathione and oxidized glutathione contents of the damaged cells were studied, and the mechanism of action of the antioxidant peptides was explored to provide a theoretical basis for their development and application in high value-added biological products and functional foods. The results showed that these antioxidant peptides had different scavenging effects on different radical species, but they all showed a dose-effect relationship. After being treated with a final concentration of 400 μmol/L H2O2 for 12 h, the inhibitory rate of HEK293 cells was (46.21 ± 0.40)%. Cytotoxicity test showed that the five antioxidant peptides had no toxic or side effects on HEK-293 cells, and did not promote cell proliferation either. These antioxidant peptides could significantly reduce the contents of malondialdehyde (except LPVPQ) and oxidized glutathione in HEK293 cells damaged by oxidation, and enhance the activity of antioxidant enzymes. RELEEL at a concentration of 200 μg/mL significantly reduced MDA content to (0.062 ± 0.000) nmol/104 cells and increased glutathione content to (61.17 ± 2.48) μg/106 cells while maintaining high GSH/GSSG ratio of 64.93 ± 0.95. The antioxidant peptide LPVPQ at 200 μg/mL significantly reduced the content of oxidized glutathione to (0.74 ± 0.26) μg/106 cells and increased the activity of superoxide dismutase (SOD) to (1.17 ± 0.02) U/104 cells; the antioxidant peptide AFK at 200 μg/mL significantly enhanced catalase (CAT) activity to (0.60 ± 0.09) U/104 cells. These results indicate that the antioxidant peptides derived from yak milk casein have positive effects on cells damaged by oxidation, which can provide a reference for further development of relevant products

Protein and mRNA expression of estradiol receptors during estrus in yaks (Bos grunniens)

ABSTRACTThe objective of this study was to investigate mRNA by real-time PCR and protein expression by immunofluorescence of the estradiol receptors (ER) in the pineal gland, hypothalamus, pituitary gland, and gonads of yaks (Bos grunniens). The analysis showed that the level of expression of ER mRNA was greater in the pituitary gland tissue than in other glands during estrus. Immunofluorescence analyses showed that ER proteins were located in the pineal cells, synaptic ribbon, and synaptic spherules of the pineal gland. In the hypothalamus, ER proteins were located in the magnocellular and parvocellular neurons. The ER proteins were located in acidophilic cells and basophilic cells in the pituitary gland. In the ovary, ER proteins were present in the ovarian follicle, corpus luteum and Leydig cells. Estradiol exerts its main effects on the pituitary gland during estrus in yak

Response surface methodology for the mixed fungal fermentation of Codonopsis pilosula straw using Trichoderma reesei and Coprinus comatus

The objective of this study was to investigate the cellulose degradation rate (CDR) and lignin degradation rate (LDR) of Codonopsis pilosula straw (CPS) and the optimal fermentation parameters for mixed fungal fermentation. Single-factor tests were used to study the effects of the fungal ratio (Trichoderma reesei: Coprinus comatus), fungal inoculum, corn flour content, and fermentation time on the degradation rate of cellulose and lignin. Based on the results of this experiment, the optimal fermentation factors were identified, and the effects of various factors and their interactions on the degradation rates of cellulose and lignin were further evaluated using the response surface method. The quadratic polynomial mathematical model of degradation rates of the cellulose and lignin in CPS by mixed fungus fermentation was established using Design Expert software v8.0.6. Under the optimal parameters for fungal fermentation of CPS straw (fungal ratio 4:6, fungal inoculum 8%, corn flour content 10%, fermentation time of 15 d), the CDR and LDR reached 13.65% and 10.73%, respectively. Collectively, the mixed fungal fermentation of CPS resulted in decreased lignin and cellulose content, better retention of nutrients, and enhanced fermentation quality. The results of this study indicate that fermentation using Trichoderma reesei and Coprinus comatus is a productive method for straw degradation, providing a theoretical basis for the development of CPS as feed