The electron temperature difference between the $o$ -point and the $x$ -point of a magnetic island is studied numerically by solving the two-dimensional energy transport equation. It is found that, even without a localized radio-frequency heating at the island's $o$ -point, there is usually a temperature difference between these two points. This difference depends on the radial profile of the heating power deposition, the ratio between the parallel and the perpendicular heat conductivity and the island width, and it takes a minimum when the island width is about twice the local heat diffusion layer width. The effect of the temperature difference on the island growth is further studied, and the peaked heating power density profile at magnetic axis is found be destabilizing.

Liquid spreading on a soluble substrate is known as dissolutive wetting, a common phenomenon in the medical and industrial fields. However, the dynamic process of dissolutive wetting is not fully understood due to the complex transport of mass and momentum. In this article, we present a hydrodynamic model that accounts for both Marangoni and buoyancy effects to analyze interface shape, flow, and solute transport in dissolutive wetting. Based on our theoretical analysis and experiments, we propose two dimensionless numbers, Ya and Pe′, to plot a phase diagram of dissolutive wetting. We investigate the evolution of the flow field, concentration field, and solid–liquid interface shape for different types of dissolutive wetting. Furthermore, we discovered a new type of dissolutive wetting resulting from the competition between Marangoni convection and buoyancy, using both experimental and theoretical approaches. Our study provides significant insight into dissolutive wetting, which may has applications in joining processes of materials, material synthesis, structural fabrication, and so on.

Polyurea spraying is a new temporary support technology that can significantly enhance the mechanical properties of coal. However, the mechanism of interactions between the polymer coating and coal is unclear. In this study, the No. 4 non-stick coal from Mengcun Coal Mine and polyurea material were used to conduct experiments and numerical simulations. The tests and simulations were used to examine the role of the sprayed coating in the formation of residual strength and the unloading and rebound mechanism after brittle failure of the coal. The results showed that the presence of the polyurea coating had a significant impact on the mechanical behavior of the coal. The specimens sprayed with polyurea were affected by the confining pressure applied by the coating and the internal friction of the coal; consequently, the specimens exhibited certain plastic characteristics and maintained their residual strength after experiencing brittle failure. The polyurea coating not only effectively prevents the loosening and slippage of the coal but also improves the stability of the coal by altering its mechanical behavior during the loading process. This study lays the foundation for popularizing and applying polyurea spraying technology in coal mine support while providing rich data to support further theoretical research.

The dynamic mechanism of reactive droplet impact is significantly different from that of inert droplets. The impact and spreading dynamics of reactive polyurea droplets on a smooth hydrophilic glass surface is investigated, focusing on the interplay between fluid mechanics and in situ curing reactions. Using high-speed imaging, we identify two distinct stages in the droplet dynamics: a pinning stage and a spreading stage. During the pinning stage, the droplet's contact line remains stationary while internal flow and surface tension drive tip retraction. We show that the tip retraction process provides a sensitive probe of evolving viscosity, which is modeled by using third-order mass-action kinetics. In this stage, crucially, we demonstrate that the variation in viscosity drives enhanced viscous dissipation and results in the prolonged pinning. In the spreading stage, the chemically induced viscosity increase dominates, leading to a contact line radius evolution that follows a R ∼ t1/8 scaling law. Unlike inert droplets, which dissipate energy primarily through rebounds, receding-height increase, and oscillations, reactive polyurea droplets exhibit time-dependent dissipation driven by in-flight and post-impact curing. This work reveals the critical role of reaction-driven viscosity enhancement in shaping droplet impact behavior and offers new insight into the design and control of reactive spraying processes.