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In this paper, the effect of ambient temperature, sliding speed and normal load on friction coefficient and wear mechanism were investigated through end-face testing to simulate the influence of process parameters during hot forming–quenching integrated process. With the increasing ambient temperature, the wear mechanism changes from abrasive wear to adhesive wear and oxidation wear. When the ambient temperature reaches 400 °C, the delamination wear characteristics occur due to the crack propagation caused by thermal stress. The friction coefficient and wear rate increase with the increase in the normal load. When the normal load is 1.8 and 3 kN, because of the generation of a large amount of heat and the increase in the contact area, the peeling morphology appears, and the adhesive wear and oxidation wear are further enhanced with the increase in the temperature. The enhancement of work hardening weakened the adhesion effect due to the high sliding speed. The friction coefficient decreases with the increase in the sliding speed. In addition, the wear rate at 10 r/min and 50 r/min sliding speed are 29.6 and 29.2 mm3/m, respectively. [ABSTRACT FROM AUTHOR]

The effects of alloying elements on the microstructure evolution and properties of GH2107 superalloy during long-term aging are investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The results indicate that the microstructure of the alloy becomes unstable with the prolongation of aging time. Cr element promotes the precipitation of M23C6 carbides at grain boundaries, and Fe element inhibits the precipitation and growth of M23C6 carbides at high temperature. At the same time, high Fe promotes the growth of γ' phase and the precipitation of TCP phase, which has a certain influence on the plasticity and strength of the alloy. The yield strength of alloy1 (15.41% Cr, 35.3% Fe) and alloy2 (15.08% Cr, 40.1% Fe) decreases with the increase in aging time. However, for alloy3 with high Fe content, the yield strength increases suddenly at 3000 h aging time due to the improving effect of solid solution strengthening. In addition, the dislocation movement mechanism of GH2107 alloy was studied, and Orowan bypass mechanism is more likely to occur in alloys with high Fe content. [ABSTRACT FROM AUTHOR]

Droughts or floods are usually attributed to precipitation deficits or surpluses, both of which may become more frequent and severe under continued global warming. Concurring large-scale droughts in the Southwest and flooding in the Southeast of China in recent decades have attracted considerable attention, but their causes and interrelations are not well understood. Here, we examine spatiotemporal changes in hydrometeorological variables and investigate the mechanism underlying contrasting soil dryness/wetness patterns over a 54-year period (1965–2018) across a representative mega-watershed in South China—the West River Basin. We demonstrate that increasing rainfall intensity leads to severe drying upstream with decreases in soil water storage, water yield, and baseflow, versus increases therein downstream. Our study highlights a simultaneous occurrence of increased drought and flooding risks due to contrasting interactions between rainfall intensification and topography across the river basin, implying increasingly vulnerable water and food security under continued climate change. Increasing rainfall intensity produces opposite hydrological effects across a large river basin in South China (drying in the uplands vs. wetting in the lowlands) due to spatially contrasting interactions between rainfall intensification and topography. [ABSTRACT FROM AUTHOR]

Industrial robots are widely used in various industrial fields, such as handling and welding, due to their good repeat positioning accuracy. The motion error determines the absolute accuracy. For robot design, dimensional parameter errors and drive parameter errors, a mathematical model of a kinematic exponential product with error screws was proposed. The influence of different rod lengths and transmission errors on the accuracy of the end motion was analysed. A composite analysis method based on screw theory and vector method is proposed for the spatial deflection error of robot rotating joints with clearance. By using screw theory, a mathematical error model of the axial movement and spatial deflection of the joint gap was established. A mathematical model of joint space radial movement was established by using the three-dimensional vector method. Through numerical simulation, the position distribution law of the random error of the robot terminal in the workspace and the distribution of the plane projection density were obtained. By solving the attitude matrix, the distribution of each Euler angle error was obtained. A simulation test was carried out to verify the model's correctness. The calculation showed that the method is simple and correct, and the obtained error distribution characteristics are of great significance to improving robotic kinematic calibration accuracy and optimising the spatial position error distribution. [ABSTRACT FROM AUTHOR]

Escalators are a widely used means of transportation. The escalator truss structure is subjected to random loads during working operation, and fatigue failure of escalator truss structure occurs from time to time. In this study, the pedestrian load time history of escalator in a subway station was counted by means of real measurements. The stability of the collected data was verified by the round-trip test method. By using rain-flow counting method to process the load time history, the random load spectrum of escalator structure was obtained. And the eight-level fatigue load spectrum of escalator truss was simplified. To study the probabilistic characteristics of the truss material, the P-S-N curve of the truss material was obtained based on the subsample method and modified to obtain the P-S-N curve of the truss structure. Finally, the fatigue life of the dangerous part of the escalator truss structure was predicted by using Miner liner fatigue accumulation damage theory. The probabilistic life of the truss structure was obtained. Based on the finite element simulation analysis, the fatigue life of the truss structure is verified, and the results show that the simulation results are basically consistent with the calculation results, which proves the effectiveness of the method of this paper. [ABSTRACT FROM AUTHOR]

As potential wave-transparent materials applied at high temperatures, 3D BNf/Si3N4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition (LPCVI/ CVD) process from SiCl4-NH3-H2-Ar gas precursor at 800 °C. The densification process, microstructure and dielectric properties of 3D BNf/Si3N4 composites were investigated. The results indicated that 3D BNf/ Si3N4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/ cm3. Densification kinetics of 3D BNf/Si3N4 is a typical exponential pattern. The Si3N4 matrix was uniformly infiltrated into porous BNf preform. The deposited Si3N4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si3N4 ceramic lowered the permittivity of Si3N4. The fabricated BNf/Si3N4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below 400 °C. Transmission coefficient of BNf/Si3N4 composite is 0.57 and keeps stable below 400 °C. BNf/Si3N4 can be fabricated at low temperature and may be candidates for the microwave transparent materials. [ABSTRACT FROM AUTHOR]

Random composites with negative permittivity or negative permeability have developed rapidly while few were accomplished using ceramic materials as the functional fillers. In this work, titanium nitride/polyphenylene sulfide (TiN/PPS) composites with different TiN content were prepared by hot-pressing method. The electrical percolation threshold phenomenon occurred and the conductive mechanism transferred from hopping conduction to metal-like conduction when TiN’s content increased. Negative permittivity in composite with high TiN content was derived from low frequency plasmonic state of free electrons and the plasm-like negative permittivity spectra was analyzed by Drude model. Besides, it’s indicated that the dielectric loss was dominated by conduction loss and polarization loss in composites with high TiN content. Equivalent circuit model was utilized to investigate the impedance properties and suggested that parallel inductances played critical role in achieving negative permittivity. [ABSTRACT FROM AUTHOR]

A novel model with low-high-low permittivity hierarchical architecture was designed for high-temperature electromagnetic wave (EM) absorption. SiN-SiC/SiO composite ceramic was fabricated to verify this model. Dielectric properties of SiN-SiC/SiO in X-band from 25 to 600 °C were investigated. Due to the special designed structure, the effective permittivity of SiN-SiC/SiO increases slightly with rising temperature. When the temperature increases from 25 to 600 °C, average $$ \varepsilon^{\prime} $$ in X-band increases from 5.6 to 6.1, and $$ \varepsilon^{\prime\prime} $$ increases from 3.0 to 3.8. Because of the weak temperature dependence of effective permittivity, SiN-SiC/SiO exhibits good coordination between room temperature EM absorption and high-temperature EM absorption. Minimum reflection coefficient (RC) of SiN-SiC/SiO at room temperature reaches −38.6 dB with the sample thickness of 3.2 mm. At 500 and 600 °C, minimum RC of SiN-SiC/SiO with certain sample thickness reaches −51.9 and −35.9 dB, respectively. Meanwhile, the effective bandwidth reaches 4.16 and 4.02 GHz, which indicates the promising prospect of SiN-SiC/SiO for high-temperature EM absorption. [ABSTRACT FROM AUTHOR]

With the aim to design broadband microwave absorbers with optically transparent, flexible and stable performances in 8-18 GHz, a sandwich structure is designed and fabricated by sandwiching the periodic arrayed ITO film into two transparent and flexible polyvinyl chloride layers. With the induced metamaterial structure to tailor the effective input impedance, the proposed sandwich absorber can realize more than 90% absorption in 8-18 GHz for both TE and TM polarization when the incident angle is less than 30°. Meanwhile, the optical transmittance of the designed absorber reaches more than 80% transmittance with the wavelength larger than 532 nm, and the average optical transmittance for the visible light (400-800 nm) is 80.2%. The proposed absorber shows broadband microwave absorption in both X and Ku band with simultaneously high transmittance in visible frequencies, indicating that the proposed sandwich metamaterial absorber has great potentials for developing optical transparent absorbing devices. [ABSTRACT FROM AUTHOR]

The increase in vegetation coverage resulting from the implementation of the Grain for Green Project (GFGP) on the Loess Plateau (LP) in China has sparked debates on how the GFGP affects the water cycle, due to the limited understanding of the interaction between land cover and the atmosphere. This study investigated spatiotemporal changes in atmospheric water vapor (WV) from 1979 to 2022 using ERA5 dataset and quantified the impacts of the GFGP on the WV budget on the LP through numerical simulations with the Community Earth System Model. The analysis of ERA5 data revealed an increase in WV content (WVC) after the implementation of the GFGP (2000–2022) compared to the pre-program period (1979–1999). This increase was primarily attributed to a greater reduction in WV outflow at the eastern boundary than the reduction in inflow at the western boundary, resulting in greater WV retention. Our sensitivity simulation experiments indicated that the GFGP had positive effects on WVC, with evident increases in the lower atmosphere (700–1000 hPa). The GFGP increased WV inflows at the southern and western boundaries by 3.84 × 104 kg·s-1·m-1, while WV outflows at the eastern and northern boundaries also increased by 1.40 × 104 kg·s-1·m-1, leading to a net WV input in the low atmospheric layer due to higher inflows than outflows. These findings suggested that although the GFGP positively impacted WV, the observed post-2000 WV increase cannot be solely attributed to the GFGP, indicating that changes in atmospheric circulation patterns under climate change also play an important role. [ABSTRACT FROM AUTHOR]