Search

In order to enhance the comprehensive performance of plasma nitrided heavy load components used in corrosive environments, post-oxidation was conducted under different conditions after plasma nitriding 42CrMo4 steel at 500 °C for 5 h. The results show that an oxide film composed of Fe3O4 and Fe2O3 was formed above the compound layer, resulting in a significant increase in corrosion resistance; the self-corrosion potential was greatly increased from −658.72 mV to −429.23 mV. Meanwhile, it needs to be emphasized that the characteristics of the plasma nitriding layer could be effectively adjusted as expected by post-oxidation. The compound layer thickness decreased from 9.41 μm to 3.62 μm by post-oxidation at 400 °C for 2 h, while the thickness of the effective hardening layer increased from 300 μm to 378 μm. Due to the expected change in the characteristics of the plasma nitriding layer, post-oxidation could simultaneously improve the toughness, hardness, and wear resistance of the samples; the brittleness level decreased from Grade 4 to Grade 1; the surface hardness increased from 765 HV0.05 to 825 HV0.05; and the wear rate decreased from 3 × 10−5 g·m−1·N−1 to 1.19 × 10−5 g·m−1·N−1, illustrating that the wear resistance was greatly improved. [ABSTRACT FROM AUTHOR]

Rolling treatments have been identified as a promising fabrication and deformation processing technique for graphene/metal composites with high performance. However, it is still a challenge to choose appropriate rolling parameters to achieve high strength, ductility and electrical conductivity of the composite simultaneously. In this study, graphene/Cu composites were prepared with an in situ growth method and rolling treatment. The effects of rolling deformation and temperature on the microstructural evolution of graphene and Cu grains, interface bonding between graphene and the matrix, mechanical and electrical properties were systemically investigated. The cold-rolled composite with 85% deformation displayed a maximum ultimate strength of 548 MPa, a high elongation of 8.8% and a good electrical conductivity of 86.2% IACS. This is attributed to oriented graphene arrangement and matrix grain refinement. Our research provides a comprehensive understanding for the rolling behavior of graphene/Cu composites, and can promote the development of graphene-based composites with high performance. [ABSTRACT FROM AUTHOR]

Three-dimensional porous network encapsulation strategy is an effective means to obtain composite phase-change materials (PCMs) with high heat storage capacity and enhanced thermal conductivity. Herein, macroporous reduced graphene oxide (rGO) aerogels with adjustable pore size are prepared by the emulsion template method and hydrothermal reduction process. Further, the shape-stabilized rGO-aerogel-based composite PCMs are constructed after the combination of 3D porous rGO supports and paraffin wax (PW) through vacuum melting infiltration. By regulating the pore structure of the rGO aerogel network, the rGO-based composite PCMs achieve excellent energy storage properties with a phase-change enthalpy of 179.94 J/g for the loading amount of 95.61 wt% and an obvious enhancement in thermal conductivity of 0.412 W/m−1·K−1, which is 54.89% higher than pristine PW and enduring thermal cycling stability. The obtained macroporous rGO-aerogel-based composite PCMs with high thermal storage and heat transfer performance effectively broaden the application of PCMs in the field of thermal energy storage. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the effect of charging conditions on hydrogen damage. The effects of electrochemical hydrogen charging current density and time on hydrogen-induced blistering (HIB), cracking behavior, and mechanical properties of Q690 steel are studied by electrochemical hydrogen charging, microstructure observation, and slow strain rate tensile (SSRT) tests. The results show that HIB and internal cracks occur when the Q690 steel is charged at different current densities. The charging conditions have a significant effect on the HIB characteristics of the material and the morphology, number, size, and location of internal cracks. The geometrical parameters of blisters on the surface of Q690 steel are quantitatively evaluated, and deeper cracks are found at higher hydrogen concentrations. At high hydrogen charging current density (50 mA/cm2), due to the accumulation of a large number of hydrogen atoms and the precipitation of hydrogen, the active sites on Q690 steel surface increase dramatically, leading to the initiation of a large number of blisters. At this time, high current density is responsible for the initiation of blisters. The relationship between hydrogen charging current density and mechanical properties of Q690 steel is studied, and the change in the fracture morphology is observed. The Q690 steel was damaged and failed due to an internal crack caused by excessive hydrogen pressure. On the other hand, electrochemical hydrogen charging leads to the degradation of mechanical properties and the transition from ductile fracture to brittle fracture. [ABSTRACT FROM AUTHOR]

In order to study the effect of freezing and thawing of liquid nitrogen on the mechanical and seepage characteristics of coal rock with different water content values, conventional triaxial loading tests on freeze–thawed coal samples with different water content values were carried out using non-contact digital image processing technology. The research results showed that with the same water content, the peak strength of a liquid nitrogen freeze–thawed coal sample was smaller than that of a non-freeze–thawed coal sample, and the Poisson's ratio was larger than that of the non-freeze–thawed coal sample; compared with the non-freeze–thawed coal sample, the strain fluctuation and concentration in the stages of compression density, elasticity, yield, and damage were weakened after freeze–thawing by liquid nitrogen, but the local stress concentration was more obvious; the non-freeze–thawed coal sample mainly showed single shear damage, and the damage fissures were inclined fissures with small openings. The higher the water content, the more obvious the tensile damage; with the increase in water content, the permeability of non-freeze–thawed coal samples showed a linear decreasing trend, and the permeability of coal samples was 0.03 × 10–3 μm2 when the water content reached 9%. The permeability of freeze–thawed coal samples showed a non-linear increasing trend, and the higher the water content under the effect of expansion, the faster the permeability growth rate; the permeability of coal samples could reach 6.30 × 10–3 μm2 when the water content was 9%. The results of the study can provide a theoretical guidance for gas permeation enhancement in deep low-permeability coal seams. [ABSTRACT FROM AUTHOR]

With the increasing mining depth, the dynamic disaster of coal and gas outbursts in coal mines has become increasingly prominent, and the bursting liability of coal and rock mass in deep coal seam mining is a necessary condition for the occurrence of rock burst and an important index to measure the failure of coal and rock mass. Thermal damage leads to rock instability and failure, which seriously influences the safe and efficient operation of coal mines. To investigate the effect of thermal damage on the bursting liability of deep coals, the burst tendency index of standard coal was measured after subjecting it to thermal damage at different temperatures. The effects of different thermal damage temperatures on the uniaxial compressive strength index, dynamic failure duration, stiffness ratio index, effective impact energy index, residual energy index change rate, and impact energy velocity of the coal and the influence of the post-peak failure mode of the coal were evaluated. The results revealed that the uniaxial compressive strength of the coal generally decreased with increasing thermal damage temperature. At temperatures above 200 °C, the strength significantly decreased. The comprehensive impact property index indicated that, with increasing thermal impact temperature, the burst tendency first increased up to the peak value at 200 °C and then gradually decreased. With the increase in the thermal damage temperature, the burst tendency decreased and disappeared in the temperature range of 250–300 °C, and the failure mode of the coal changed from brittle failure to brittle plastic failure, and finally ductile failure. The influence of thermal damage on coal bursting liability is studied, which provides a theoretical basis for preventing and controlling coal impact ground pressure hazards. [ABSTRACT FROM AUTHOR]

In view of the low accuracy of the motion parameters generated by the typical ship trajectory generator, and the fact that the problem of wind, current and wave interference is not considered, this paper establishes a new ship trajectory generator by analyzing the changes in the ship's attitude and speed under different motion states. Through simulation, the accuracy of the main motion parameters is significantly improved compared with the typical trajectory generator; the time-varying non-uniform wind, current and wave fields are constructed, and the interference effect of wind, current and waves on ship motion is analyzed by combining the empirical formulas of force and moment; an adaptive neuro fuzzy inference system (ANFIS) based on wind, current and wave interference is designed, and the fuzzy rules of the fuzzy system are determined by training and testing the measured data; the motion parameters of superimposed wind, current and wave interference are compared with the measured data, and the accuracy is further improved after superimposing wind, current and wave interference. [ABSTRACT FROM AUTHOR]

For solving the problem of polar performance of the inertial navigation system (INS) at mid-low latitudes, the simulation test system constructed by the "attitude and velocity invariant method of trajectory transfer rule based on the transverse coordinate system (T-AVIM)" of the Earth sphere model is used. The test system structure, especially the IMU conversion formula from mid-low latitudes to polar region simulation test, is introduced, and it is proved that the IMU conversion error can be equivalently superimposed on the bias error of the polar simulated IMU. According to the marine estimation formula for the effect of the reference error on the IMU conversion error, the specific influence of the constant error component and the random error component of the reference system on the simulated IMU is analyzed. The calculation method of the simulated IMU error is given with examples and intuitively explained, and the correctness of the theory is verified through simulation experiments. [ABSTRACT FROM AUTHOR]

The scientific and reasonable measurement of agricultural green total factor productivity is helpful to grasp the direction of rural-factor-market reform. This study constructs a Malmquist productivity index based on a non-radial and non-angular SBM directional distance function. This study calculates the agricultural green total factor productivity of 28 provinces (cities and autonomous regions) in China from 1997 to 2020 by considering unexpected outputs such as carbon emissions and agricultural non-point-source pollution. Finally, this study uses the spatial Dobbin model to explore the spatial impact of agricultural green total factor productivity under the distortion of the factor market. The results show that the agricultural green total factor productivity, considering the unexpected outputs, is more in line with the level of high-quality green development in China's agriculture. Regardless of whether the unexpected output is included, the increase in China's agricultural total factor productivity is primarily due to progress in agricultural technology, and the double boost is little in agricultural technology progress and technical efficiency. Agricultural green total factor productivity shows an increasing trend, but the growth rate is slow, and differences in different regions are significant. Factor market distortion negatively impacts agricultural green total factor productivity, and other factors improve the agricultural total green factor productivity. However, factor market distortion has a particular spatial spillover effect, which hinders the synchronous growth of agricultural green total factor productivity in different regions. Therefore, the government should promote the reform of the agricultural mode of production and agricultural green production, eliminate the blocking effect of factor market distortion on the improvement in agricultural green total factor productivity, narrow the regional gap of agricultural total factor productivity, and establish a policy system for high-quality green development of modern agriculture. [ABSTRACT FROM AUTHOR]

To solve the problem of high-precision and fast initial alignment for the Strapdown Inertial Navigation System (SINS) under both dynamic and static conditions, the high-precision attitude measured by the celestial navigation system (CNS) is used as the reference information for the initial alignment. The alignment algorithm is derived in the Earth-centered inertial (ECI) frame. Compared with the alignment algorithm in the navigation frame, it is independent of position parameters and avoids the influence of the approximate error caused by the dynamic deflection angle. In addition, hull deformation is considered in attitude optimal estimation, which can realize initial the alignment of the SINS installed in various parts of the carrier. On this basis, the velocity measurement information is added to the alignment process, which further improves the accuracy and speed of the initial alignment under static conditions. The experimental results show that the algorithms proposed in this paper have better performance in alignment accuracy, speed, and stability. The attitude and velocity matching algorithm in the ECI frame can achieve alignment accuracy better than 0.6′. The attitude matching algorithm in the ECI frame has better robustness and can be used for both dynamic and static conditions, which can achieve alignment accuracy better than 1.3′. [ABSTRACT FROM AUTHOR]

The spatial function division of urbanization (SFDU) based on the value chain has an important impact on optimizing the industrial layouts of these areas and promoting regional coordinated development. Based on urban panel data from the Yangtze River Economic Belt (YREB) from 2007 to 2016, this paper uses the SYS-GMM, fixed-effects, and quantile regression methods to test the impact of the SFDU on regional coordinated development and further reveals its mechanism of impact. The results show the following: (1) the SFDU significantly improves the level of regional coordinated development, and the introduction of the SYS-GMM method enables us to overcome the endogenous problem of regression; (2) the improvement of capital allocation efficiency is an important way for the SFDU to promote regional coordinated development, whereas labor allocation efficiency is related to "process distortion"; (3) the impact of the SFDU on coordinated regional development in the middle and lower reaches of the YREB is stronger than that in the upper reaches; and (4) the promoting effect of the SFDU on coordinated regional development is significantly higher in the "economic coordination dimension" than in the "people's livelihoods" and "ecological coordination" dimensions. This paper provides a valuable reference for the government to formulate regional coordinated development policies in basin economies around the world from the perspective of sustainable development. [ABSTRACT FROM AUTHOR]

Growing evidence now suggests that circulating tumour DNA (ctDNA) has great potential as a non-invasive biomarker for disease monitoring, since ctDNA carries tumour-specific modifications. In particular, monitoring ctDNA has important implications for identifying patients with haematological malignancies at clinical risk of disease progression. We hereby describe three patients with B-cell non-Hodgkin lymphoma and investigate the clinical value of sequential ctDNA profiling for the early detection of tumour relapse. Somatic mutations in diagnostic tumour biopsy samples of these three patients were identified by applying high-throughput next-generation sequencing. Droplet digital PCR probes and primers were designed and tested for each hotspot mutation. Serial ctDNA analysis was subsequently conducted among these three patients. We found that the longitudinal monitoring of plasma ctDNA could predict for at least one month in advance compared with flow cytometry, cytology and conventional imaging modalities. Therefore, our results support liquid biopsy based on ctDNA as a non-invasive complementary modality to other detection methods for detecting early relapse and contribute to more precise management for non-Hodgkin lymphoma patients. [ABSTRACT FROM AUTHOR]