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Amonton's law of friction states that the friction force is proportional to the normal force in magnitude, and the slope gives a constant friction coefficient. In this work, with molecular dynamics simulation, we study how the kinetic friction at the nanoscale deviates qualitatively from the relation. Our simulation demonstrates that the friction behavior between a nanoscale AFM tip and an elastic graphene surface is regulated by the coupling of the applied normal force and the substrate deformability. First, it is found that the normal load-induced substrate deformation could lower friction at low load while increasing it at high load. In addition, when the applied force exceeds a certain threshold another abrupt change in friction behavior is observed, , the stick-slip friction changes to the paired stick-slip friction. The unexpected change in friction behavior is then ascribed to the change of the microscopic contact states between the two surfaces: the increase in normal force and the substrate deformability together lead to a change in the energy landscape experienced by the tip. Finally, the Prandtl-Tomlinson model also validates that the change in friction behavior can be interpreted in terms of the energy landscape.
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http://dx.doi.org/10.1039/d4na00252k | DOI Listing |
Am J Vet Res
September 2025
Division of Surgery, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen, Thailand.
Objective: To evaluate the impact of postoperative swimming therapy on hind limb functional recovery in dogs following femoral head and neck excision (FHNE) using the symmetry index (SI) of peak vertical force (PVF) data from ground reaction force measurements and orthopedic evaluations.
Methods: From February 18, 2021, through February 18, 2023, dogs undergoing FHNE were randomized to swimming and nonswimming therapy groups. Hind limb PVF and an orthopedic assessment score were recorded at 1, 2, 3, 4, 5, 6, 9, and 12 months postoperatively.
J Hazard Mater
September 2025
College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004, China.
Room-temperature crystallization of a cobalt-aminoterephthalate framework (CoBDC-NH) directly on 3D-printed polylactic acid (PLA) yields a super-wetting membrane that reconciles permeability and selectivity in oil-water separation. The ambient-pressure route dispenses with conventional hydrothermal steps and preserves the PLA architecture. Molecular dynamics (MD) combined with density-functional (DFT) calculations reveal that NaOH activation exposes carboxylate sites, while trace polyvinylpyrrolidone amplifies van der Waals forces, uniformly dispersing Co nuclei and anchoring the metal-organic framework (MOF) layer.
View Article and Find Full Text PDFWater Res
September 2025
State Key Laboratory of Geomicrobiology and Environmental Changes, Hubei Key Laboratory of Critical Zone Evolution, China University of Geosciences (Wuhan), Wuhan 430078, China; Hubei Key Laboratory of Marine Geological Resource, China University of Geosciences, Wuhan 430074, China. Electronic addre
Anthropogenic climate warming and coastal eutrophication have restructured phytoplankton communities in the East China Sea; however, the centennial-scale dynamics of phytoplankton remain poorly understood. By systematically integrating 33 sediment cores, we reconcile the variations of primary productivity during the last century. The results revealed increased primary productivity during the past century, while the phytoplankton groups showed divergent eco-regional responses: river-dominated estuaries have partially mitigated the dominance of dinoflagellates (1980s) via Changjiang nitrate loading, while potential hypoxic regions shifted earlier (1960s) under thermal forcing and silicate concentration.
View Article and Find Full Text PDFPLOS Glob Public Health
September 2025
Department of Pediatrics, University of Colorado, Aurora, Colorado, United States of America.
Children affected by armed conflict suffer devastating physical, emotional, and social harm. War uproots families, forcing many to flee as refugees or internally displaced persons, while others remain trapped in dangerous environments. In these crises, children face disproportionate risks-violence, exploitation, disrupted education, and collapsed healthcare systems.
View Article and Find Full Text PDFAdv Mater
September 2025
School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, P. R. China.
Liquid crystal elastomers (LCEs) are important soft actuators that show strong promise in many fields where traditional rigid actuators or robotics are impractical. However, their real-world applications are lacking primarily due to inadequate actuation performance and complicated fabrication processes. Here, a novel design is reported that significantly enhances actuation performance while simplifying the fabrication process.
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