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Bolt connection is commonly used to assemble shell structures in engineering fields. Prolonged external excitation can induce stick, slip, even separation states at the connection interface, leading to complex nonlinear dynamics in bolted shell structures. Understanding the dynamic mechanism of bolted joined shells under stick–slip-separation condition is crucial for the design and application of these structures. In this study, we aim to build the nonlinear dynamic model and reveal the vibration mechanism of bolted joined conical-cylindrical shells with stick–slip-separation behavior. During the development of the mechanical model of the bolt connection, the axial bilinear stiffness characteristics and interface friction behaviors are taken into account simultaneously, which could simulate the transition of the contact state at the connection interface. The rigid joint between the conical and cylindrical shells is realized via successive distributed artificial springs. Donnell's shell theory as well as the displacement assumption of Chebyshev polynomials are employed in theoretical modeling, and the governing equation is obtained by the Lagrange equation. In contrast with existing research and experimental data, the accuracy of the present theoretical model is validated. Both theoretical and experimental results indicate the frequency multiplication and dynamic softening phenomena as the excitation level increases. By the consideration of the stick-slip-separation behavior at the connection interface in the modeling, these nonlinear vibration behaviors can be effectively illustrated. Additionally, hysteresis characteristics are further investigated to explore frictional energy dissipation. The stick–slip-separation contact state at the connection interface under different excitation levels, bolt preloads and cone angles are also analyzed. The present investigation provides a basis for the design and health condition monitoring of bolted shell structures. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5) exposure is strongly associated with vascular endothelial senescence, a process implicated in cardiovascular diseases. While there is existing knowledge on the impact of Lycium barbarum polysaccharide (LBP) on vascular endothelial damage, the protective mechanism of LBP against PM 2.5 -induced vascular endothelial senescence remains unclear. In this study, we investigated the impact of PM 2.5 exposure on vascular endothelial senescence and explored the intervention effects of LBP in human umbilical vein endothelial cells (HUVECs). We found that PM 2.5 exposure dose-dependently reduced cell viability and proliferation in HUVECs while increasing the production of reactive oxygen species (ROS), malondialdehyde (MDA), and hydrogen peroxide (H 2 O 2). Additionally, PM 2.5 exposure inhibited the activity of superoxide dismutase (SOD). Notably, PM 2.5 exposure induced autophagy impairments and cellular senescence. However, LBP mitigated PM 2.5 -induced cell damage. Further studies demonstrated that correcting autophagy impairment in HUVECs reduced the expression of the senescence markers P16 and P21 induced by PM 2.5. This suggests the regulatory role of autophagy in cellular senescence and the potential of LBP in improving HUVECs senescence. These findings provide novel insights into the mechanisms underlying PM 2.5 -induced cardiovascular toxicity and highlight the potential of LBP as a therapeutic agent for improving vascular endothelial health. • Exposure to PM 2.5 leads to damage and senecence of HUVECs. • Senescence of HUVECs is associated with PM 2.5 -induced autophagy impairment. • Lycium barbarum polysaccharides inhibited cell senescence induced by PM 2.5. [ABSTRACT FROM AUTHOR]

• A new strategy is proposed for vibration control of flexible pendulums. • We introduce a flywheel to control flexible pendulum vibration. • The control method has robustness and is effective for nonlinear forced vibration. • An experiment platform is built to validate the proposed control strategy. Flexible inverted pendulums have found wide applications in mechanical systems, but their stability is susceptible to external disturbances. In this study, a new strategy that employs a flywheel to suppress vibration of flexible inverted pendulums is proposed. We develop the theoretical dynamic model of flexible pendulums with a flywheel by the Euler-Bernoulli beam theory, where the axial displacement of the pendulum and geometric nonlinearities are considered. An active control method based on the Bézier trajectory is proposed, where the acceleration of the flywheel is set as the input. Additionally, the equivalent damping ratio of the system including flywheel's motion is derived. The relationship between the parameters in the control equation and the suppression effect is obtained through the simulation of the equivalent damping ratio. Then, an experimental platform is built. The experimental results show that the present control strategy has good suppression effect on the vibration of the flexible inverted pendulums when selecting appropriate parameters. Meanwhile, the results of anti-disturbance test show that the present method has a certain robustness. Finally, the simulation results show that this strategy is also effective for nonlinear forced vibration under different excitation frequencies. [ABSTRACT FROM AUTHOR]