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Structural superlubricity, one of the most important concepts in modern tribology, has attracted lots of interest in both fundamental research and practical applications. However, despite promising theoretical models, such as the Prandtl-Tomlinson and Frenkel-Kontorova models, and great success in structural lubricant experiments with two-dimensional materials and colloids, these models have not been directly tested. Here, with the cholesteric liquid crystals confined under the Surface Force Balance, we measure the surface torque during rotational friction, and the molecular rotation from the commensurate to incommensurate configuration, at the onset of structural lubricity. Furthermore, by changing the surface potential, the Aubry transition is confirmed. The results agree well with the description by a modified three-dimensional version of the above models and provide molecular evidence for rupture nucleation during static friction. Our study bridges the gap between theories and experiments, and reinforces the connection between friction and fracture.

Permeative flows, known for the explanation of the anomalous viscosity (10^5 Poise) in cholesterics at low shear rates, are still under debate due to the difficulty of experiments. Here we use the Surface Force Balance, in which uniform domains with regular circular defects are formed, to probe the forces generated by compression in the direction of the helical axis. At the quasi-static speed of the surface approach, the measured forces are shown to be elastic (not dissipative), arising from the twist elastic deformation when the planar anchoring at the walls is strong. A mechanism involving frictional surface torque under strong planar surface anchoring will be proposed. The results indicate that the strong resistance to flow observed, previously interpreted as an enormous apparent viscosity, may in fact originate from the intrinsic non-linear increase of elasticity when the molecules are rotated away from equilibrium. The system is found to store energy (the force is reversible), without dissipation, as long as the applied stress is below the threshold for nucleating new defects. Our study underpins the importance of boundary conditions that may dramatically change the rheology of other viscoelastic materials and sheds light on the rational design of strain-stiffening materials, nanomotors, and artificial muscles involving helical architectures.

The stick-slip phenomenon widely exists in contact mechanics, from the macroscale to the nanoscale. During cholesteric-nematic unwinding by external fields, there is controversy regarding the role of planar surface anchoring, which may induce discontinuous stick-slip behaviors despite the well-known continuous transitions observed in past experiments. Here, we observe three regimes, namely constrained, stick-slip, and sliding-slip, under mechanical winding with different anchoring conditions, and measure the responded forces by the Surface Force Balance. These behaviors result from a balance of cholesteric elastic torque and surface torque, reminiscent of the slip morphology on frictional substrates [T. G. Sano et al., Phys. Rev. Lett. 118, 178001 (2017)], and provide evidence of dynamics in static rotational friction.

Air contaminants emitted from animal buildings may harm the environment and public health. A windbreak wall with slightly acidic electrolyzed water (SAEW) sprayed downwind of the exhaust fans offers a potential approach for the removal of some of these air contaminants, including ammonia and airborne culturable bacteria (CB). This study was conducted to investigate the removal efficiency of ammonia and airborne CB by a proof-of-concept windbreak wall with SAEW spray for a layer breeding house. A windbreak wall with spraying system was placed downwind of an exhaust fan. Tap water and SAEW, a novel environment-friendly disinfectant, were used in the spraying system. Separate sampling manifolds for ammonia and airborne CB were placed at the inlet and the outlet of the windbreak wall, respectively, for ammonia and CB sampling. The windbreak wall with water spray and 70 mg L -1 (available chlorine concentration) SAEW spray both significantly reduced ammonia emissions from the house though the removal was small. The 70 mg L -1 SAEW spray showed a numerically higher ammonia removal efficiency (13.2%) than water spray (8.8%), but no significant difference was found (p = 0.13). The windbreak wall with 70 mg L -1 and 100 mg L -1 SAEW spray both significantly and moderately reduced airborne CB emission from the layer breeding house (p

The FAO Livestock Environmental Assessment and Performance (LEAP) Partnership organised a Technical Advisory Group (TAG) to develop reference guidelines on water footprinting for livestock production systems and supply chains. The mandate of the TAG was to i) provide recommendations to monitor the environmental performance of feed and livestock supply chains over time so that progress towards improvement targets can be measured, ii) be applicable for feed and water demand of small ruminants, poultry, large ruminants and pig supply chains, iii) build on, and go beyond, the existing FAO LEAP guidelines and iv) pursue alignment with relevant international standards, specifically ISO 14040 (2006)/ISO 14044 (2006), and ISO 14046 (2014). The recommended guidelines on livestock water use address both impact assessment (water scarcity footprint as defined by ISO 14046, 2014) and water productivity (water use efficiency). While most aspects of livestock water use assessment have been proposed or discussed independently elsewhere, the TAG reviewed and connected these concepts and information in relation with each other and made recommendations towards comprehensive assessment of water use in livestock production systems and supply chains. The approaches to assess the quantity of water used for livestock systems are addressed and the specific assessment methods for water productivity and water scarcity are recommended. Water productivity assessment is further advanced by its quantification and reporting with fractions of green and blue water consumed. This allows the assessment of the environmental performance related to water use of a livestock-related system by assessing potential environmental impacts of anthropogenic water consumption (only “blue water”); as well as the assessment of overall water productivity of the system (including “green” and “blue water” consumption). A consistent combination of water productivity and water scarcity footprint metrics provides a complete picture both in terms of potential productivity improvements of the water consumption as well as minimizing potential environmental impacts related to water scarcity. This process resulted for the first time in an international consensus on water use assessment, including both the life-cycle assessment community with the water scarcity footprint and the water management community with water productivity metrics. Despite the main focus on feed and livestock production systems, the outcomes of this LEAP TAG are also applicable to many other agriculture sectors., Ecological Indicators, 124, ISSN:1470-160X, ISSN:1872-7034