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The friction of a solid contact typically shows a positive dependence on normal load according to classic friction laws. A few exceptions were recently observed for nanoscale single-asperity contacts. Here, we report the experimental observation of negative friction coefficient in microscale monocrystalline heterojunctions at different temperatures. The results for the interface between graphite and muscovite mica heterojunction demonstrate a robust negative friction coefficient both in loading and unloading processes. Molecular dynamics simulations reveal that the underlying mechanism is a synergetic and nontrivial redistribution of water molecules at the interface, leading to larger density and more ordered structure of the confined subnanometer-thick water film. Our results are expected to be applicable to other hydrophilic van der Waals heterojunctions.
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http://dx.doi.org/10.1126/sciadv.aaz6787 | DOI Listing |
Front Bioeng Biotechnol
August 2025
Solventum, St. Paul, MN, United States.
Introduction: Not all wound patients are candidates for surgical debridement. A felted, reticulated open cell foam with an array of 10 mm holes (VFCC) for use with instillation therapy has been used to eliminate non-viable tissue from patient wound beds. The mechanisms for this have not been fully elucidated.
View Article and Find Full Text PDFSmall
September 2025
Department of Materials Science, Key Laboratory of Automobile Materials, MOE and State Key Laboratory of High Pressure and Superhard Materials, International Center of Future Science, Jilin University, Changchun, 130012, China.
Molybdenum disulfide (MoS) exhibits excellent lubrication capacity rooted in its layered structure, but it suffers significant structural and functional deterioration due to oxidation in ambient environments, limiting its applications. Concerted efforts are focused on enhancing the antioxidation ability of MoS, but challenges remain. This work conceptualizes and demonstrates a contrarian design of MoS-based film via metal incorporation and oxidation based on consideration of key fundamental principles of thermodynamics, chemistry, and physical mechanics.
View Article and Find Full Text PDFFront Bioeng Biotechnol
August 2025
Sport Biomechanics Center, Institute of Artificial Intelligence in Sports, Capital University of Physical Education and Sports, Beijing, China.
Introduction: Cross-country sit-skiers are often individuals with spinal cord injuries, cerebral palsy, or lower limb disabilities, relying heavily on upper limb strength to generate propulsion during skiing. However, frequent shoulder joint movements significantly increase the incidence of shoulder joint disorders. Therefore, quantifying muscle forces during movement is crucial for understanding upper limb force generation patterns.
View Article and Find Full Text PDFNat Commun
September 2025
Department of Artificial Intelligence, Donders Center for Cognition, Radboud University, Nijmegen, The Netherlands.
Cooperative transport is a striking phenomenon where multiple agents join forces to transit a payload too heavy for the individual. While social animals such as ants are routinely observed to coordinate transport at scale, reproducing the effect in artificial swarms remains challenging, as it requires synchronization in a noisy many-body system. Here we show that cooperative transport spontaneously emerges in swarms of stochastic self-propelled robots.
View Article and Find Full Text PDFMaterials (Basel)
August 2025
School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221000, China.
Green and low-carbon filling materials, primarily composed of dredged waste fills, are commonly used in the foundation of coastal highways. These materials possess high water content and under-consolidation characteristics, which can lead to differential settlement between piles and the surrounding environment. However, mechanical models of negative friction in piles within recycled dredged waste fills are insufficiently developed and presented.
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