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In order to address the issues of energy depletion, more resources are being searched for in the deep sea. Therefore, research into how the deep-sea environment affects cement-based materials for underwater infrastructure is required. This paper examines the impact of ocean depth (0, 500, 1000, and 1500 m) on the ion interaction processes in concrete nanopores using molecular dynamics simulations. At the portlandite interface, the local structural and kinetic characteristics of ions and water molecules are examined. The findings show that the portlandite surface hydrophilicity is unaffected by increasing depth. The density profile and coordination number of ions alter as depth increases, and the diffusion speed noticeably decreases. The main cause of the ions' reduced diffusion velocity is expected to be the low temperature. This work offers a thorough understanding of the cement hydration products' microstructure in deep sea, which may help explain why cement-based underwater infrastructure deteriorates over time. [ABSTRACT FROM AUTHOR]

To promote the safe use of MgO expansive agent (MEA) in mass concrete, the influence of fineness and sintering temperature of MEA on the expansion, mechanical properties, and microstructure of fly ash-Portland cement pastes was studied. The results indicate that the agent prepared at 950 °C does not adversely affect the compressive strength of the pastes. Whereas the agent prepared at 1150 °C (MII) has a marked negative impact on the volume stability and strength of the pastes. Furthermore, incorporating MII with coarser particle size results in a larger expansion, greater strength loss, and coarser pore structure. The presence of fly ash delays the hydration of MgO, making more MgO available for the formation of Mg(OH)2 at the late age. Meanwhile, the pozzolanic reaction leads to decreased total porosity, leaving less space available for the accommodation of Mg(OH)2. Consequently, fly ash cement pastes suffer greater strength loss than plain cement pastes when the destructive expansion occurs due to the delayed hydration of MgO. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems have taken up about 32% of the total anthropogenic CO2 emissions in the past six decades1. Large uncertainties in terrestrial carbon–climate feedbacks, however, make it difficult to predict how the land carbon sink will respond to future climate change2. Interannual variations in the atmospheric CO2 growth rate (CGR) are dominated by land–atmosphere carbon fluxes in the tropics, providing an opportunity to explore land carbon–climate interactions3–6. It is thought that variations in CGR are largely controlled by temperature7–10 but there is also evidence for a tight coupling between water availability and CGR11. Here, we use a record of global atmospheric CO2, terrestrial water storage and precipitation data to investigate changes in the interannual relationship between tropical land climate conditions and CGR under a changing climate. We find that the interannual relationship between tropical water availability and CGR became increasingly negative during 1989–2018 compared to 1960–1989. This could be related to spatiotemporal changes in tropical water availability anomalies driven by shifts in El Niño/Southern Oscillation teleconnections, including declining spatial compensatory water effects9. We also demonstrate that most state-of-the-art coupled Earth System and Land Surface models do not reproduce the intensifying water–carbon coupling. Our results indicate that tropical water availability is increasingly controlling the interannual variability of the terrestrial carbon cycle and modulating tropical terrestrial carbon–climate feedbacks.Records show that tropical water availability rather than temperature appears to have been increasingly controlling the interannual variability of the terrestrial carbon cycle over the past 59 years. [ABSTRACT FROM AUTHOR]

Desert expansion can cause tremendous damage to human wellbeing. However, the process of shifting from the non‐desert state to the desert state, a representation of a system regime shift, remains unclear on a global scale. Clarifying the underpinning patterns, predictors and signals of this process is of great value in advancing our understanding of both ecosystem resilience and sustainable development. Here, we combine the climate classification map and long‐term observational land cover data to assess the global desert distribution and its changes from 2000 to 2019. The identified desert areas covered approximately 7.53% of the global land in the past two decades. Only approximately 16.03% of these deserts showed expanding trends, especially in countries such as Tunisia, Tajikistan, and Peru. After assessing 26 climatic, ecological, and socioeconomic factors that could potentially influence desert expansion rates, vegetation cover diversity was identified as the strongest predictor in both hot and cold deserts, followed by cattle density in hot deserts and desert size in cold deserts. In addition, we also found that pronouncedly high fluctuations in vegetation productivity could serve as a possible signal for desert conversion. Our results provide not only a long‐term overview of current global desert changing patterns but also possible guidance for constraining desert expansion. [ABSTRACT FROM AUTHOR]

Benefiting from its excellent sustainable plastic carrying capacity, rubberized concrete (RuC) has received extensive attention. In this study, the dependency of rubber aggregate (RA) particle size influencing factor on content is investigated through quasi-static compression tests. The results demonstrate that the influence of RA particle size on stress–strain behavior of RuC shows a content-dependent effect. The postpeak stress-buffering area and strain-softening area of RuC reduce significantly with the increase of RA particle size at higher RA contents. Moreover, the corresponding rubber aggregate influencing factor (RIF) model is established. The constitutive model of RuC is proposed by introducing the RIF model into the characteristic parameters. Finally, the stress–strain relationship of RuC is predicted by using the proposed constitutive model. It is concluded that the proposed constitutive model can be further applied to the structural design optimization of RuC. [ABSTRACT FROM AUTHOR]

The dominance of vapor pressure deficit (VPD) and soil water content (SWC) for plant water stress is still under debate. These two variables are strongly coupled and influenced by climatic drivers. The impacts of climatic drivers on the relationships between gross primary production (GPP) and water stress from VPD/SWC and the interaction between VPD and SWC are not fully understood. Here, applying statistical methods and extreme gradient boosting models—Shapley additive explanations framework to eddy‐covariance observations from the global FLUXNET2015 data set, we found that the VPD‐GPP relationship was strongly influenced by climatic interactions and that VPD was more important for plant water stress than SWC across most plant functional types when we removed the effect of main climatic drivers, e.g. air temperature, incoming shortwave radiation and wind speed. However, we found no evidence for a significant influence of elevated CO2 on stress alleviation, possibly because of the short duration of the records (approximately one decade). Additionally, the interactive effect between VPD and SWC differed from their individual effect. When SWC was high, the SHAP interaction value of SWC and VPD on GPP was decreased with increasing VPD, but when SWC was low, the trend was the opposite. Additionally, we revealed a threshold effect for VPD stress on GPP loss; above the threshold value, the stress on GPP was flattened off. Our results have important implications for independently identifying VPD and SWC limitations on plant productivity, which is meaningful for capturing the magnitude of ecosystem responses to water stress in dynamic global vegetation models. [ABSTRACT FROM AUTHOR]