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Copper, permalloy, cobalt, and silicon are the materials that have been widely utilised in magnetic devices. When the size of interest is down to the nanoscale, the inter-diffusion between certain materials becomes influential. This paper studies the nanoscale friction characteristics between frictional pairs with and without inter-diffusion properties through the atomic force microscope. The distinct evolution features of nanoscale friction force when inter-diffusion is involved are discovered experimentally, which is also confirmed through theoretical analysis. Firstly, through the thin film deposition method, four pairs of contact materials (Cu–Ni81Fe19, Si–Ni81Fe19, Cu–Co, Cu–Si) are designed for friction tests, in which diffusion occurs at the interface of Cu–Ni81Fe19 pair. Then, the effects of sliding velocity and loading force on the nano friction of each pair are measured. It is found that regardless of the diffusion phenomenon: (1) the adhesion force values exhibit a notable correlation to the values of the friction force; (2) the friction force in all four material pairs consistently increases with the growth of the normal loading force, although the growth rate may differ. In terms of the sliding velocity effect, the friction forces of immiscible materials (Si–Ni81Fe19, Cu–Co, and Cu–Si) are found to increase with the increasing sliding velocity. However, the friction force of Cu–Ni81Fe19, decreases with the increasing sliding velocity. Furthermore, a compositive friction model considering both the velocity and the normal force effect was proposed, which shows good agreement with the experimental results and explains the nano friction behaviour of both miscible and immiscible metals. [ABSTRACT FROM AUTHOR]

Due to the broadband response and high sensitivity to low excitation levels, bistable energy harvesters (BEHs) have been viewed as an efficient method to overcome the shortcomings of linear energy harvesters only performing well near the resonant frequency. Previously, most strategies for performance enhancement of BEHs have been extensively discussed for systems with perfectly symmetric potentials. However, it is difficult to achieve a BEH with a perfectly symmetric potential due to practical constraints and previous investigations indicated that asymmetric potentials have a negative effect on the performance of BEH. Therefore, an adjustable unilateral stopper is introduced and positioned at the side with deeper potential well to broaden the response frequency band. Numerical simulations of bifurcation diagrams and maps of 0–1 test and output power indicate that the introduction of the stopper could enable the asymmetric BEH to realize interwell oscillation in a wider frequency range, and the performance are closely related to the collision gap, collision position, excitation frequency, as well as excitation levels. Regarding the basins of attraction, it is demonstrated that the stopper leads the system to achieve interwell oscillation with a high probability under certain excited conditions. Overall, this study provides a possible strategy for improving the performance of the asymmetric BEHs. [ABSTRACT FROM AUTHOR]

Friction-induced vibration is very common in engineering areas, such as aerospace, high-speed railways, robotics, and human/artificial joints. Analysing the dynamic behaviour of systems containing a multiple-contact point frictional interface is an important topic. However, accurately simulating nonsmooth/discontinuous dynamic behaviour due to friction is challenging. This paper presents a new physics-informed neural network approach for solving nonsmooth dynamic problems involved in the friction-induced vibration or friction-involved vibration. Compared with schemes of the conventional time-stepping methodology, this novel computational framework integrates the theoretical formulations of nonsmooth multibody dynamics into the training process of the neural network. We found that this new framework can not only more accurately simulate nonsmooth dynamic behaviours, but also could be a promising method to improve the efficiency as it eliminates the need for extremely small time steps typically associated with the conventional time-stepping methodology for multibody systems. Specifically, four kinds of high-accuracy Physics-informed-neural network (PINN) strategies were proposed: (1) single PINN; (2) dual PINN; (3) advanced single PINN; and (4) advanced dual PINN. Two typical dynamics problems with nonsmooth contact were simulated, including a 1-dimensional contact problem with stick–slip and a 2-dimensional contact problem considering separation–reattachment and stick–slip. Both single and dual PINN methods showed their advantages in dealing with the 1-dimensional stick–slip problem, which outperformed conventional methods across friction models that are difficult to simulate with the conventional time-stepping method. In contrast, the advanced single and advanced dual PINN methods provided better accuracy in simulating the 2-dimensional problem, even in the cases where conventional methods failed to simulate. [ABSTRACT FROM AUTHOR]

Carbonate rock chemical weathering carbon sinks reduce the rate of increase of the atmospheric CO2 concentration and global warming. However, uncertainty still exists in the estimation results of carbonate rock chemical weathering carbon sink fluxes (CCSF), and the contributions of climate change and ecological restoration to the CCSF are not clear. To this end, we compiled published site data on ion concentrations in different watersheds in China and used a classical thermodynamic dissolution model to reassess the potential and spatial and temporal patterns of the CCSF in China from 1991 to 2020. We quantified the contributions of temperature (MAT), precipitation (MAP), evapotranspiration (ET), soil water (SM), and the normalized difference vegetation index (NDVI) to the CCSF. The results revealed that (1) China's CCSF was 22.76 t CO2 km−2 yr−1, which was higher than the global average (15.771CO2 km−2 yr−1). The total carbonate rock chemical weathering carbon sink (CCS) was 4772.67×104 t CO2, contributing 14.91% of the global CCS through a carbonate rock area of 252.98×104 km−2. (2) China's CCSF decreased gradually from southeast to northwest, with values of 33.14, 12.93, and 7.27 t CO2 km−2 yr−1 in the southern karst, Qinghai-Tibetan karst, and northern karst regions, respectively. (3) The overall CCSF in China exhibited an increasing trend from 1991 to 2020, with a rate of increase of 0.16 t CO2 km−2 yr−1. (4) The contributions of the MAP, MAT, ET, SM, and NDVI to the CCSF were 63.3%, 3.02%, 27.5%, 3.1%, and 3.05%, respectively. Among them, the increase in precipitation was the main contributor to the increase in the CCSF in China over the last 30 years, while the enhancement of ET offset part of the positive contribution of the increase in precipitation to the CCSF. In conclusion, the results of this study provide a systematic quantification of the magnitude, the patterns, and the influencing factors of CCS over a long time series in China. The results are of great significance and provide a reference for the diagnosis and gap analysis of the national and global carbon neutrality capacities. [ABSTRACT FROM AUTHOR]