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MIG welding and ER5356 welding wire were used for butt welding of 7075 aluminum alloy with a thickness of 3 mm. The joint was subjected to T6 heat treatment after welding. The microstructure, mechanical properties and corrosion resistance of the joints were analyzed by optical microscope, X-ray diffraction, scanning electron microscope and energy spectrometer combined with room temperature stretching, microhardness and electrochemical corrosion. The results show that the molten pool flow brings Zn, Cu and other alloying elements in the molten part of the base metal into the weld, and precipitates MgZn2 and AlCuMg phases during the welding process, which become the basis for the heat treatment and strengthening of the weld. After heat treatment, most of the precipitated phase melts into the matrix to form solid solution+aging strengthening, the joint tensile strength increases by 20%, and the weld hardness increases by 18.4%, the corrosion resistance improves. However, due to the limited alloying element content flowing into the weld from the base metal, the difference in mechanical properties between the welding wire and the base metal and the heat-affected zone softening phenomenon cannot be eliminated.

BackgroundPassive safety system reliability is generally evaluated through best estimation plus uncertainty (BEPU) analysis. An important step in the evaluation process is sensitivity analysis of parameters, which is used to identify key system parameters to reduce the complexity of the model. However, local sensitivity analysis methods based on linear or monotonic assumptions may yield incorrect sensitivity results for complex nuclear power systems. Meanwhile, applying the global sensitivity method is difficult in practical engineering because of its high calculation cost.PurposeThis study aims to develop an efficient and low-cost global sensitivity analysis method for passive systems under ocean conditions.MethodsFirstly, the low-rank approximation (LRA) method was employed to improve the Sobol method based on Monte Carlo simulation. The number of unknown coefficients was significantly reduced by using the multivariate-based tensor product. Then, the LRA coefficients were used to calculate the sensitivity index, and the validity of the proposed method was verified by addressing several sensitivity analysis benchmark questions. Finally, taking an integrated pressurized water reactor including the passive residual heat removal system as the object, a simulation program for thermal-hydraulics analysis under ocean conditions was developed. And its sensitivity analysis was conducted using the proposed method.ResultsThe results show that the proposed method can accurately identify system key parameters after only 200 simulation calculations taking about 55 min, and the sensitivity ranking results are consistent with those obtained by Sobol method after 1.0×105 simulation calculations taking about 19 d.ConclusionsThe efficient global sensitivity analysis method established in this study can provide effective guidance for reliability analysis and design optimization of passive systems.

Lithium-ion battery is an ideal power source for portable electronic products, electric vehicles and smart grid. At present, there are still some problems, such as safety and short service life, in lithium-ion batteries using organic liquid electrolyte, however, solid-state batteries (SSB) with non-combustible solid-state electrolyte (SSE) are expected to solve these problems. In principle, nonflammable solid electrolyte can fundamentally prevent the battery from combustion and explosion and only allow lithium ions to flow in the solid electrolyte, which can reduce the occurrence of side reactions. In recent years, with the emergence of several solid electrolytes with high ionic conductivity, the transport of lithium ion in solid electrolytes is no longer a bottleneck. However, the various components in solid-state batteries have different chemical, physical and mechanical properties, as a result, there are many types of interfaces in solid-state batteries, including loose physical contact, grain boundary, chemical and electrochemical reaction interfaces, which may impede the ion transport at the interface. The interface reaction between the cathode and electrolyte is especially complex. It is necessary to understand these complex interfaces and the reaction characteristics. Therefore, the work of exploring and understanding the cathode/electrolyte interface in recent years was reviewed in this paper, and the typical cathode side interface and their unique reaction characteristics in solid-state batteries were summarized.

With the development of electric vehicles, higher requirements for battery energy density are put forward. High nickel/SiOx-C batteries with high energy density have become the first choice for long-range electric vehicles. However, high nickel/SiOx-C batteries have the problem of rapid capacity decay in practical use. Non-destructive electrochemical analysis and post-mortem analysis were used to detect the changes in battery capacity and internal resistance during the cycle. The changes in the structure, material morphology and surface composition of positive and negative electrodes before and after the battery cycle were compared, revealing the mechanism of cycling failure of high nickel/SiOx-C batteries. The results show that the capacity decay of the battery presents three stages: the stationary period, the rapid decay period and the extreme decay period. After cycling, the polarization of the battery is more serious, and the polarization internal resistance of the battery, the surface film resistance of the negative electrode and the charge transfer resistance increase significantly. Through differential curve analysis combined with disassembly analysis, it is found that the high nickel cathode material has less attenuation, and the silica carbon anode material has more attenuation and active lithium-ion loss. The expansion and cracking of silicon oxide particles, the loss of negative electrode active material, and the continuous growth of solid electrolyte interface film on the negative electrode surface consuming too much active lithium are the main reasons for the rapid decline of battery capacity.

In order to solve the problems of hydraulic fracturing fractures easy to close, uneven fracturing, poor fracturing effect and difficult gas drainage in broken soft coal seam, combinning with the current mature drilling technology, self-developed directional sand blasting perforation equipment and process technology, hydraulic sand fracturing equipment and process technology, the idea of “directional sand blasting perforation + staged sand fracturing” for directional long drilling of coal seam roof to increase coal seam permeability was proposed, and the engineering test has been carried out in Xinjing Coal Mine 3# coal seam roof in Yangquan Mining Area. The hydraulic sand fracturing technology of long directional drilling in coal seam roof is formed. The test results show that the long drilling hole in the roof of 609 m coal seam is divided into 6 sections for sand fracturing, the construction displacement is more than 1 m3/min, the single section liquid injection is more than 150 m3, and the cumulative liquid injection is 967 m3; the fracture pressure from the hole bottom to the orifice decreases gradually, and the maximum fracture pressure is 29.6 MPa. The highest proportion of walnut shell sand injected is 3%, the maximum injection of walnut shell sand in a single section is 2.41 t, and the cumulative addition is 13.11 t. Statistical analysis of 60 d gas drainage data shows that the average gas drainage concentration is 60.6%; the maximum net amount of gas drainage in a single day reaches 1 381.5 m3. The gas drainage concentration is 8.81 times and 3.96 times higher than that of bedding hole and kilometer hole respectively; the net extraction volume of 100 m borehole was increased by 21.4 times and 7.28 times respectively, and a good antireflection effect was obtained.

With the increasing demand for lithium-ion batteries, lithium-ion batteries with high energy density and high power density have become one of the research hotspots. Material modification and new material development can effectively increase the energy density of lithium-ion batteries. In addition, the microstructure parameters of the electrode such as porosity, pore size and distribution, tortuosity and electrode composition distribution are also factors that determine the performance of the electrode and battery. Improving the performance of high specific energy batteries by optimizing the electrode structure design has gradually become the focus of attention. The research progress of porous electrode structure design optimization for lithium ion batteries was reviewed in this article, the design factors and preparation methods of porous electrode structure were summarized. Then the future development of electrode structure design optimization and the promotion of novel preparation technologies for large-scale application in the field of high specific energy lithium ion batteries were prospected in the field of high specific energy lithium ion batteries.

To explore the effect of Baduanjin exercise on the self-rated health of some special college students in China, and to provide theoretical reference and practical basis for popularizing Baduanjin and making it "enter the campus and be included in PE curriculum". By using the method of experiment and mathematical statistics, this paper takes 69 special college students who take Sports Health Care Course as the experimental objects in two universities, and adopts Self-rated Health Scale (SRHMSV110) to measure and analyze the physical health, mental health, social adaptation and the overall health level of the special college students before and after the experiment. Results: 1) Before the experiment, the experimental group and the control group in physical health, mental health, social adaptation and overall health scores were not statistically significant (P > 0.05). After the experiment, there were significant differences between the experimental group and the control group in physical health, mental health, social health and overall health (P<0.01), indicating that Baduanjin exercise improved the self-rated health level of the special college students in the experimental group; 2) After Baduanjin exercise, the scores of general health level and other dimensions of the students in the experimental group were higher than those before the experiment, and the difference test results were all P < 0.01. The control group before and after Baduanjin exercise overall health and its various dimensions score difference test results were P > 0.05, which further shows that Baduanjin exercise can improve the health level of special college students. Research conclusion: The mean self-rating scores of physical health, mental health, social adaptation and general health level of the special college students are significantly lower than that of the general college students, whose self-rated health status is general, especially the problems in the mental health self-rating are prominent. 8-week Baduanjin exercise of moderate intensity, 3 times per week, 40-60 minutes each time can significantly improve the level of special college students' health. It is suggested that Baduanjin should be included in the curriculum of sports health care or as a means of health intervention for special college students. [ABSTRACT FROM AUTHOR]

At present, rotary tillage is a conventional farming method in wheat-maize rotation system in North China Plain, however, under the rotary tillage year after year, plough pan tends to become shallow and harden, which results in poor ventilation and drainage, and also is hard to increase grain production, especially in the farmland of lime concretion black soil. Using 'Zhoumai27' as the test material, the field experiment was conducted to research the effects of 3 tillage practices (no tillage, rotary tillage and deep tillage) on grain yield of winter wheat, soil bulk density, soil organic carbon and soil inorganic nitrogen, in order to select the appropriate tillage practices and further improve the potential of grain production in the farmland of lime concretion black soil. The results showed: 1) In terms of soil bulk density, there were no significant differences among 3 tillage treatments in 0-10 cm soil layer during wheat growth period, and also no differences at maturity period of wheat in >30-40 cm soil layer, but deep tillage practice could significantly decrease (P<0.05) soil bulk density in >10-30 cm soil layer compared with no tillage. 2) There were no significant differences among 3 tillage practices in 0-20 cm soil layer, but deep tillage could increase (P<0.05) the content of soil organic carbon in >20-40 cm soil layer compared with no tillage. 3) In 0-20 cm soil layer, compared with no tillage or deep tillage, rotary tillage significantly increased (P<0.05) the contents of nitrate nitrogen in the seedling, wintering and anthesis period of winter wheat. However, the content of nitrate nitrogen at jointing stage did not reach significant difference among 3 treatments, and was significantly higher (P<0.05) under no tillage than under rotary tillage and deep tillage at maturity of wheat. In >20-40 cm soil layer, the higher content of nitrate nitrogen was detected in rotary tillage in seedling and anthesis period, and no tillage was higher at other growth stages of winter wheat. 4) In terms of the content of ammonium nitrogen in soil, in 0-20 cm soil layer, during the seedling, wintering and anthesis period of winter wheat there were no significant differences between rotary tillage and deep tillage, but no tillage showed higher values. At jointing stage, the order of the content of ammonium nitrogen was rotary tillage > deep tillage > no tillage, and also there was significant differences among 3 tillage treatments (P<0.05), but at maturity stage, the content of ammonium nitrogen in 3 treatments did not reach significant differences. In >20-40 cm soil layer, the order of the content of ammonium nitrogen was deep tillage > rotary tillage > no tillage during the whole growth period of winter wheat. 5) Compared with no tillage, deep tillage could significantly increase (P<0.05) grain yield of winter wheat mainly, for deep tillage increased 1000-grain weight and grain number. To sum up, under the condition of our field experiment, deep tillage could decrease soil bulk density in >10-30 cm soil layer, improve the content of organic carbon and ammonium nitrogen in >20-40 cm soil layers, and also increase grain yield of winter wheat in the end. Therefore, deep tillage practice should be selected as an appropriate tillage practice in the farmland of lime concretion black soil. [ABSTRACT FROM AUTHOR]

Six cultivars including strong, middle and weak gluten wheat varieties were cultivated at five latitudes(from 32 degrees N to 36 degrees N) in Henan Province, and the variations of their qualitative characters were analyzed in relation to the different environments. The result indicated that latitudes had great effects on the protein content, wet gluten content, softening degree, evaluation value, and extensibility of the cultivars. The rheological parameters measured by farinogram and the extensogram were significantly different among different among different cultivars, and the coefficients of variation were quite large. The variations in qualitative characters among cultivars and among latitudes were different. With the rising latitude, the protein content, wet gluten content, development time, evaluation value, extensibility, resistance, and maximum resistance showed an increase tendency, with a few exceptions for certain latitude. For most qualitative characters, there was a clear boundary between Xinyan(32 degrees N) and Zhumadian(33 degrees N). According to these results, suggestions in the latitude layout of the hi-quality wheat cultivars and in improving their cultuvation practices were made.