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In this paper, functionalized nanotube-reinforced cementitious composites were prepared, and the mechanical property test results showed that the 28d flexural strength of the composite was increased by 41.58% at a hydroxylated carbon nanotube mass fraction of 0.08 wt.% compared to the original cement mortar. Carboxylated carbon nanotubes with a mass fraction of 0.02%, on the other hand, increased the 28d compressive strength by 99.12%. Probing the effect of the presence of functional groups on carbon nanotubes on the CNT/C–S–H interface by first principles. The results showed that the shear strengths (11.392 MPa and 14.130 MPa) of hydroxylated carbon nanotubes and plain carbon nanotubes at the interface with cementitious (CNT-OH/CSH and CNT/CSH) were lower than the shear strengths (21.584 MPa) of carboxylated carbon nanotubes at the interface with cementitious (CNT-COOH/CSH). The adsorption of functional groups on carbon nanotubes changes the electron distribution on the surface of carbon nanotubes. The introduction of carboxyl groups exacerbates the charge transfer between carbon nanotubes and cementitious groups and promotes the generation of solid chemical bonds. This is the reason that carboxylated nanotubes added as reinforcement to cement mortar give better strength to the composite than hydroxylated nanotubes. [ABSTRACT FROM AUTHOR]

Extreme precipitation can lead to major flooding, impacting human health and safety. Thus, reliable projections of population and GDP exposure to future extreme precipitation are imperative. Here, we quantify future precipitation characteristics from robust emergent constraint relationships between historical and future monthly precipitation extremes (99th percentile) across 19 CMIP6 models (r2 > 0.7 in 74–84% of 0.5° global land grids), and narrow uncertainty by 37.0–39.5% (absolute reduction being 0.753–0.774 mm/day). The constrained grid‐averaged future 99th percentile extreme is 6.96 ± 0.0059, 7.03 ± 0.0061, 7.11 ± 0.0063, and 7.29 ± 0.0067 mm/day, under SSP126, SSP245, SSP370, and SSP585, respectively, which exceeds historical extremes substantially in terms of intensity (12.9–19.7%) and frequency (1.6–2.3 times more). Future population and GDP exposed to 99th percentile extreme precipitation grow quickly, and are projected to exceed 1 million people in 27–40 countries and 10 billion USD (2005 Purchasing‐Power Parity) in 48–77 countries. Growth of future population exposure is dominated by an increase in extreme precipitation frequency rather than a rise in population, especially in developed countries. GDP exposure is controlled by the coupled effects of rapid socio‐economic development and significant shifts in precipitation frequency. Using indices of socio‐economic vulnerability, government effectiveness and economic freedom, we identify the unequal situation that high‐risk countries with high exposure are commonly characterized by low GDP per capita and high sociopolitical instability. Plain Language Summary: Extremely heavy precipitation poses a substantial threat to human lives, wellbeing, and property, particularly in disadvantaged countries. To better understand the future risk due to exposure to extreme precipitation, we propose a new relationship, the "emergent constraint" between historical simulations and future projections from climate models. This relationship allows us to provide more accurate projections of extreme precipitation with 99th percentile. These improved estimates show that future extreme precipitation is expected to surpass historical levels in both intensity and frequency. Thus, more than 1 million people in 27–40 countries, notably in China and India, could be threatened, and over 10 billion USD of GDP (2005 Purchasing‐Power Parity) could be wiped out in 48–77 countries. The increase in population exposure to extreme precipitation is primarily driven by a rise in the frequency of the extreme events, while the rising exposure of GDP results from both socio‐economic development and shifts in extreme frequency. Notably, the high‐risk countries stand out due to their sociopolitical instability and typically low GDP per capita, which may lead to a self‐perpetuating situation due to the incapability to cope with the risk. Key Points: A new emergent constraint relationship is proposed which reduces uncertainty in extreme precipitation projections by CMIP6 modelsFuture population and GDP exposure to extreme precipitation is expected to increase, driven by climatic and coupled socio‐economic factorsMost high‐risk countries are socio‐economically vulnerable, politically unstable, with low‐income, and may be self‐perpetuating [ABSTRACT FROM AUTHOR]

A mathematical model based on advection-diffusion theory is established to study the non-equilibrium sediment transport process in vegetated channels. The effects of vegetation on velocity distribution and sediment diffusion coefficients were considered, respectively. Validation against experimental data from flume studies confirms the model's ability to accurately predict the longitudinal sediment deposition rate and the vertical distribution of suspended sediment concentration (SSC). A comparative analysis of three sediment diffusion coefficient formulations indicates that the linear-exponential formula provides a more precise estimate of ε s z , and the linear-exponential formula performs well in predicting the turbulent diffusion coefficients of both rigid and flexible vegetation when gently swaying. Moreover, the distance required for SSC to regain equilibrium is influenced by the submergence level of the vegetation canopy. At lower submergence levels, the canopy shear vortices significantly affect the vertical exchange of sediment, and the sediment diffusion coefficients exhibit pronounced stratification near the vegetation canopy. An increase in vegetation density at these lower submergence levels intensifies the shear vortices, thereby extending the distance needed for SSC to reach equilibrium. At higher submergence levels, the impact of canopy shear vortices is lessened, which reduces sediment diffusion coefficient stratification characteristics, and the flow is similar to rough boundary layer flow. An increase in vegetation density increases flow resistance, which shortens the distance required for SSC to attain equilibrium. However, further efforts are required to explore turbulent characteristics with highly flexible vegetation motion and the grain size distribution of non-uniform sediments in vegetated flows. [ABSTRACT FROM AUTHOR]

Drag coefficients (CD) are a key metric in quantifying the vegetation effect on riverine and coastal modeling. However, drag coefficients determined using various approaches under combined wave-current flows have not been comprehensively explored. In the paper, a three-dimensional (3D) numerical model was developed to study the wave dissipation induced by submerged canopies in both following and opposing currents. The results reveal the characteristics of variation of vegetation drag force under pure wave and combined wave-unidirectional flow, as well as the relationship between drag force and flow velocity. The calibration and direct measurement methods were applied to conduct the drag coefficients under various wave-current combinations. The temporal variation in horizontal velocity U, drag force F, and the drag coefficient within the aligned canopy and staggered canopy considering the combined effects of wave and current show different patterns. Moreover, the empirical relations between drag coefficients derived using different methods with Reynolds number (Re) and Keulegan-Carpenter number (KC) are proposed. Comparison of the CD-Re and CD-KC relations would provide insight into the understanding of wave dissipation by vegetation under combined wave-current flow conditions. [ABSTRACT FROM AUTHOR]