Wet Areas Research Articles

Turbulent Flow and Heat Transfer Enhancement for Turbine Blade Trailing Edge Cooling With Gyroid-Type Triply Periodic Minimal Surfaces

Abstract The Gyroid is a type of triply periodic minimal surface (TPMS) that has interconnected, perfectly curved topologies and excellent thermomechanical properties. Due to its topological feature to enhance heat transfer and self-support structure, this study presents numerical investigations of the flow, heat transfer, and pressure loss in various Gyroid architectures in a wedge-shaped channel, representing a trailing edge cooling for gas turbine blades. The Gyroid structures are partly arranged near the outlet of the wedged channel or are fully filled within the wedged channel. The local and overall flow and heat transfer mechanisms with different Gyroid configurations are compared to the baseline pin fins within the Reynolds number range of 10,000–30,000. The results show that for the case with partly infilled Gyroid structures, the overall heat transfer enhancement is higher by 39–102%, and the related pressure loss is higher by 93–154% than the baseline pin fins. For the case with fully infilled Gyroid structures, the total heat transfer is superiorly higher by 157–188%, and the related pressure loss is higher by 248–555% than the baseline pin fins. For all the Gyroid configurations, obviously improved cooling uniformity is achieved on the whole trailing edge wall. The significant heat transfer enhancement in the trailing edge channel with Gyroid structures is mainly due to a much increased wetted area, the generated helical and impingement flow through the curved interconnected channels and improved flow distribution within the wedged channel.

Remote Sensing with UAVs for Modeling Floods: An Exploratory Approach Based on Three Chilean Rivers

The use of unmanned aerial vehicles (UAVs) has been steadily increasing due to their ability to acquire high-precision ground elevation information at a low cost. However, these devices have limitations in estimating elevations of the water surface and submerged terrain (i.e., channel bathymetry). Therefore, the creation of a digital terrain model (DTM) using UAVs in low-water periods means a greater dry channel surface area and thus reduces the lack of information on the wet area not appropriately measured by the UAV. Under such scenarios, UAV-DTM-derived data present an opportunity for practical engineering in estimating floods; however, the accuracy of estimations against current methods of flood estimations and design needs to be measured. The objective of this study is therefore to develop an exploratory analysis for the creation of hydraulic models of river floods using only UAV-derived topographic information. Hydraulic models were constructed based on DTMs created in (i) the traditional manner, considering the bathymetry measured with RTK-GPS and topography, and via (ii) remote sensing, which involves topography measurement with a UAV and assumes a flat bed in the part of the channel covered by water. The 1D steady-state HEC-RAS model v.5.0.3 was used to simulate floods at different return periods. The applied methodology allows a slightly conservative, efficient, economical, and safe approach for the estimation of floods in rivers, with an RMSE of 6.1, 11.8 and 12.6 cm for the Nicodahue, Bellavista and Curanilahue rivers. The approach has important implications for flood studies, as larger areas can be surveyed, and cost- and time-efficient flood estimations can be performed using affordable UAVs. Further research on this topic is necessary to estimate the limitations and precision in rivers with different morphologies and under different geographical contexts.

Quantifying the water donation potential of commercial and corn starch hydrogels in a cementitious matrix

In this study, we introduce a new methodology to quantify the internal curing potential of hydrogels in a cementitious matrix. The swollen Super Absorbent Polymers (SAPs) and newly synthesized corn-starch hydrogels are investigated by embedding a capsule filled with swollen hydrogel in a cement mortar cube and monitoring the internal wetting area around the hydrogel capsule for 56 days. Our findings demonstrate that all of the investigated hydrogels serve as effective internal curing agents, releasing water in a cyclic pattern governed by the humidity gradient between the hydrogel and the surrounding matrix. Moreover, the regions around the hydrogel capsules display a denser accumulation of calcium silicate hydrate (CSH) gel, indicating improved hydration due to internal curing from the hydrogels. This research offers valuable understanding into the possibilities of utilizing bio-based materials and SAPs for internal curing and the creation of environmentally friendly cementitious materials. In summary, the proposed innovative approach serves as an effective way for measuring the internal curing capabilities of hydrogels within cementitious materials.

Mapping Forage Biomass and Quality of the Inner Mongolia Grasslands by Combining Field Measurements and Sentinel-2 Observations

Grasslands provide essential forage sources for global livestock production. Remote sensing approaches have been widely used to estimate the biomass production of grasslands from regional to global scales, but simultaneously mapping the forage biomass and quality metrics (e.g., crude fiber and crude protein) is still relatively lacking despite an increasing need for better livestock management. We conducted novel gradient grass-cutting experiments and measured hyperspectral reflectance, forage biomass, crude fiber per area (CFarea), and crude protein per area (CParea) across 19 temperate grassland sites in the Xilingol region, Inner Mongolia, China. Based on these measurements, we identified sensitive spectral bands, calculated nine potential spectral indices (Normalized Difference Vegetation Index, Enhanced Vegetation Index, Red Edge Normalized Difference Vegetation Index, Red-Edge Inflection Point, Inverted Red-Edge Chlorophyll Index algorithm, Normalized Difference Red Edge Index, Nitrogen Reflectance Index, Normalized Greenness Index, Land Surface Water Index) and established Random Forest (RF) models that well predicted forage biomass (R2 = 0.67, NRMSE = 12%), CFarea (R2 = 0.59, NRMSE = 14%), and CParea (R2 = 0.77, NRMSE = 10%). Among these nine indices, Land Surface Water Index (LSWI, calculated by R785-900 and R2100-2280) was identified to be the most important predictor and was then used to establish empirical power law models, showing comparable prediction accuracies (forage biomass, R2 = 0.53; NRMSE = 14%; CFarea, R2 = 0.40, NRMSE = 17%; CParea, R2 = 0.72, NRMSE = 11%) in comparison to Random Forest models. Combining the empirical power law models with the LSWI calculated from Sentinel-2 observations, we further mapped the forage biomass and quality and estimated the livestock carrying capacity. The predicted forage biomass, CFarea, and CParea all showed a significant increase with higher mean annual precipitation, but showed no significant correlations with mean annual temperature. Compared with the estimates based on crude protein, the conventional approach solely based on forage biomass consistently overestimated livestock carrying capacity, especially in wetter areas. Our work provides an approach to simultaneously map the forage biomass and quality metrics and recommends a LSWI-based power law model for rapid and low-cost assessment of regional forage status to guide better livestock management.

Climate factors rather than human activities controlled NDVI trends across wet meadow areas in the Andes Centrales of Argentina

In the Andes of southern South America, wet meadows are much more productive than nearby arid areas. Human activities, along with climate variations may reduce the productivity of these ecosystems. However, we do not know what the relative effect of climate and human activities on their degradation status is. Here, we first quantified the degradation extent through the temporal trend of normalized difference vegetation index (NDVI), a proxy of productivity, from 1999 to 2017. We did it in 736 wet meadow areas inserted in three nearby zones with contrasting land management. Second, we analyzed the relationship between NDVI and a large-scale mode of climate variability (El Niño Southern Oscillation, ENSO) and regional climate variables (precipitation and temperature) through a structured climate model. Finally, we evaluated human activities’ effects through the temporal trends in the residuals of the climate model. Independently of land management, NDVI trends were mainly negative and affected 56% of the wet meadow areas. The climate model indicated that NDVI increased under La Niña, cool and wet years. Regarding land management, the degradation level was similar across the contrasted land management. Our results suggest that climate factors rather than human activities influenced the degradation process in these areas.

Spatial and Temporal Diversity Variation in the Anopheles Communities in Malaria-Endemic Regions of Colombia.

This study aimed to evaluate at a temporospatial scale, the influence of anthropogenic land cover changes in the Anopheles species community composition and diversity in two Colombian malaria-endemic regions, Bajo Cauca and Pacific. To determine variations over time, mosquitoes were collected in two time periods; land cover types were characterized on orthorectified aerial photographs, and landscape metrics were estimated for each locality and period. A temporal dissimilarity analysis to evaluated species replacement and the nestedness species loss/gain showed the influence of the species loss or gain component on Anopheles species assemblage (23%). The relationship between land cover variation and Anopheles beta diversity, evaluated by regression analysis, showed the effect of forest variation in the Anopheles community (βsim and forest r2 = 0.9323; βsne and forest r2 = 0.9425). Furthermore, a canonical correspondence analysis showed that the land cover types associated with Anopheles species presence were bare soil, shrub, wet areas, and forest. Results demonstrated the impact of land cover changes attributed to human activities on Anopheles population dynamics, over time; this was evidenced as species loss or gain, which was specific to each locality. Notably, the main malaria vectors were dominant in most localities over time, suggesting their tolerance to anthropogenic transformations; alternatively, the environmental changes are providing adequate ecological conditions for their persistence. Finally, the data generated are relevant for understanding the impact that environmental change may have on the dynamics of the neotropical malaria vectors. Thus, this research has potential implications for vector control interventions.

Climatic conditions affect shoot flammability by influencing flammability-related functional traits in non-fire-prone habitats.

Plant flammability is an important driver of wildfires, and flammability itself is determined by several plant functional traits. While many plant traits are influenced by climatic conditions, the interaction between climatic conditions and plant flammability has rarely been investigated. Here, we explored the relationships among climatic conditions, shoot-level flammability components, and flammability-related functional traits for 186 plant species from fire-prone and non-fire-prone habitats. For species originating from non-fire-prone habitats, those from warmer areas tended to have lower shoot moisture content and larger leaves, and had higher shoot flammability with higher ignitibility, combustibility, and sustainability. Plants in wetter areas tended to have lower shoot flammability with lower combustibility and sustainability due to higher shoot moisture contents. In fire-prone habitats, shoot flammability was not significantly related to any climatic factor. Our study suggests that for species originating in non-fire-prone habitats, climatic conditions have influenced plant flammability by shifting flammability-related functional traits, including leaf size and shoot moisture content. Climate does not predict shoot flammability in species from fire-prone habitats; here, fire regimes may have an important role in shaping plant flammability. Understanding these nuances in the determinants of plant flammability is important in an increasingly fire-prone world.

The effects of soil type and moisture on the survival of Pseudophilothrips ichini (Hood)

ABSTRACT Pseudophilothrips ichini (Hood) (Thysanoptera: Phlaeothripidae) is a classical biological control agent used to control Brazilian peppertree, Schinus terebinthifolia Raddi, in Florida, USA. Brazilian peppertree is an invasive weed that threatens natural and agricultural environments, including sensitive habitats such as mangrove swamps. As P. ichini generally pupates in the soil and its host plant can occur in wet areas, it is important to investigate the effects of soil type, moisture, salinity, and immersion survival time on adult emergence. Five moisture contents (0%, 25%, 50%, 75%, and 100%) were used in factorial combination with three soil types (fine sand, sand, and muck) using fresh or brackish water. To simulate sporadic flooding, we also assessed larval and pupal survival after being immersed in fresh and brackish water for 0, 1, 2, 3, 5, 8, 16, and 32 h. A generalised mixed model logistic regression was used to analyse the data in both experiments. As soil moisture content increased, the proportion of P. ichini emerging as adults decreased across all soil types and water types. The survival of larvae and pupae immersed in either brackish or fresh water declined over time, with no survival at 32 h. There was a significant difference between water types for the survival of pupae and adult emergence of pupae and larvae, with higher survival in brackish water. The outcome of this study contributes to our understanding of P. ichini ecology and the estimation of thrips establishment success in a variety of habitats infested by Brazilian peppertree.

Role of coffee plantation in reducing erosion under coarse textured soil in wet tropical region

Water erosion is one phenomenon causing land degradation in a wet area. The research was aimed to evaluate the total of soil erosion under coffee plantations having coarse textured soil in wet tropical regions. This research was taken out on a coffee plantation in Sibarasok, Maninjau having rather to very steep slope and high annual rainfall, with Inceptisol soil order. Soil samples were taken from 6 land units (Coffee-86 y having 0-8%, 25-45%, and >45%, Coffee 5 y-15-25%, Coffee 8 y-25-45%, and forest >45% as control). The samples of soil were prepared and analyzed in the Laboratory of Soil, Department of Soil Science and Land Resource, Andalas University. The actual amount of soil eroded was predicted using the USLE formula. Then, it was compared to the tolerated (Etol) soil erosion. The result showed that the predicted amount of soil eroded was quite low (<10 T/Ha/y), except under coffee having >45% slope. The highest soil eroded in the very steep slope was due to its low SOM content and permeability, with an erosion hazard level of 1.2. Compared to tolerated erosion (Etol), the actual soil erosion predicted was lower than the Etol. The fiber roots of the coffee dominating the top 5 cm of soil surface as well as high SOM content and hydraulic conductivity rate caused the soil on the top to become tightly held avoiding erosion.

Farmers’ perception and management of water scarcity in irrigated rice-based systems in dry climatic zones of West Africa

Water scarcity threatens irrigated agriculture in sub-Saharan Africa (SSA). Knowledge of farmers’ perceptions and drivers for decision-making in view of coping with water scarcity is so far lacking but needed to improve local technologies and frame policies fostering their adoption. Here, for the first time, we investigated farmers’ perception of water scarcity, key adaptation strategies, and the determinants of their adoption in irrigated rice schemes in dry climatic zones of West Africa. We surveyed 572 farming households and conducted expert interviews with key informants in four contrasting irrigated rice schemes in Burkina Faso between April 2018 and August 2019. Information was gathered on biophysical field characteristics, grain yields, agronomic and water management practices, farmers’ perception of water scarcity, their adaptive responses, and social-economic attributes of adopting households. Nearly 80% of the respondents reported having experienced water scarcity during the past 5 years. To cope with the adverse effect of water scarcity, farmers implemented seventeen different adaptation strategies that could be categorized into seven groups. Most popular among those were “water and soil conservation practices” (consisting mainly of field bunding and leveling), “no rice cultivation,” and “crop rotation.” Farmers in drier areas (Sudano-Sahelian zone) were less likely to adopt and implement several adaptation strategies to water scarcity compared to farmers in wetter areas (Sudanian zone). Belonging to farming associations increased the probability of implementing several strategies to alleviate water scarcity, while female-headed households tended to have a lower propensity to adopt and implement concomitantly several adaptation strategies in comparison with their male counterpart. The dissemination of scheme- and household-specific technology options could contribute to mitigating water scarcity in irrigated rice-based systems in the dry climatic zones of West Africa, thus contributing to rural livelihood and food security.

Investigation of the leak tightness of structural adhesive joints for use in battery housings considering mechanical and corrosive loads

ABSTRACT Due to increasing legal requirements to reduce emissions from vehicle fleets, vehicle manufacturers are focusing on the electrification of the powertrain. In entirely electrically driven vehicles, the energy is stored in traction batteries integrated below the passenger cell between the axles and thus located in the vehicle’s wet area. Therefore, high requirements apply to the protection of the sensitive cells against mechanical stress as well as against moisture penetration. In addition, one of the main requirements for the connections of the battery housing is to ensure gas tightness over the entire service life. Adhesive bonding technology as a planar joining process offers the potential to produce functionally tight connections. However, there is a lack of reliable test methods for validating the long-term tightness of structural adhesive joints under mechanical and corrosive loads. For this reason, the paper deals with developing a test concept with laboratory-scale test specimens for leak testing under mechanical loading. Various leakage test methods investigate the leakage rate of structurally bonded joints. An analysis of the leakage rate under superimposed cyclic mechanical shear tensile loading follows this. The test method is validated on a specially developed sample battery housing on a laboratory scale.

Understanding Responses of Summer Continental Daily Temperature Variance to Perturbations in the Land Surface Evaporative Resistance

Abstract Understanding the roles of land surface conditions and atmospheric circulation on continental daily temperature variance is key to improving predictions of temperature extremes. Evaporative resistance (rs, hereafter), a function of the land cover type, reflects the ease with which water can be evaporated or transpired and is a strong control on land–atmosphere interactions. This study explores the effects of rs perturbations on summer daily temperature variance using the Simple Land Interface Model (SLIM) by mimicking, for rs only, a global land cover conversion from forest to crop/grassland. Decreasing rs causes a global cooling. The cooling is larger in wetter areas and weaker in drier areas, and primarily results from perturbations in shortwave radiation (SW) and latent heat flux (LH). Decreasing rs enhances cloud cover due to greater land surface evaporation and thus reduces incoming SW over most land areas. When rs decreases, wetter areas experience strong evaporative cooling, while drier areas become more moisture-limited and thus experience less cooling. Thermal advection further shapes the temperature response by damping the combined impacts of SW and LH. Temperature variance increases in drier areas and decreases in wetter areas as rs decreases. The temperature variance changes can be largely explained from changes in the combined variance of SW and LH, including an important contribution of changes in the covariance of SW and LH. In contrast, the effects of changes in thermal advection variance mainly affect the Northern Hemisphere midlatitudes. Significance Statement This study aims to better understand processes governing daily near-surface air temperature variance over land. We use an idealized modeling framework to explore the effects of land surface evaporative resistance (a parameter that controls how hard it is to evaporate water from the surface) on summer daily temperature variance. We find that a uniform decrease of evaporative resistance across the global land surface causes changes in the temperature variance that can be predicted from changes in the combined variance of shortwave radiation and latent heat flux. The variance of horizontal advection is important in altering the temperature variance in the Northern Hemisphere midlatitudes. Our findings shed light on predicting the characteristics of temperature variability as a function of surface conditions.

Implementation of Retention Ponds in Flood Management in Sorong Regency – Southwest Papua

Mariat Subdistrict is one of the villages affected by the floods in Klasuluk Village, with an area of 0.7995 km2, and Klamalu Village, with an area of 1.0479 km2. This research uses experimental, descriptive, qualitative, and quantitative analysis methods. The results of the analysis and simulation, after being run at intervals of 10 years in the future, there are three flood points in the Klamalu village canal, where the most significant total flood volume is at JN64 146,687 m3/s, the smallest is at JN15 21,232 m3/s, and there are 56 flood points in the Klasuluk village canal, where the largest total flood volume was at JN91 1,863 m3/s and the smallest at JN9 and JN37 0.008 m3/s. The volume of wastewater discharge that enters the drainage is only 1%, so it has no effect. From the data on the dimensions of the retention pond, it is obtained that the wet cross-sectional area is about 145.05 m2, the wet perimeter of the retention pond is 101.69 meters, the hydraulic radius is 1.43 m, the flow velocity is 3.168 m/s, the guard height is 1.22 meters, the water discharge that comes out is 459.51 m3/second.

Parameterization of soil evaporation and coupled transport of moisture and heat for arid and semiarid regions

Soil moisture is an important parameter in numerical weather forecasting and climate projection studies, and it is extremely important for arid and semiarid areas. Different from those in relatively wet areas, for arid and semiarid areas, mechanisms associated with the transportation, condensation, and evaporation of water vapor in soil interior cannot be neglected. In this paper, schemes associated with soil evaporation and coupled transport of soil moisture and heat were developed for the integrated urban land model (IUM) to improve the simulation of soil moisture in arid and semiarid areas. The whole layer soil evaporation (WSE) scheme was developed to improve the simulation of soil evaporation. The soil’s inner layer water vapor transport is considered a part of WSE. The transport of water and heat in the inner soil was linked to the phase change of water. The NASA Soil Moisture Active Passive (SMAP) mission Level-4 Soil Moisture product and 10-cm volumetric soil moisture observations in 358 autonomic soil moisture observation sites were used for validating the simulation results. The results indicate that after using the WSE scheme and considering the coupled transport of moisture and heat in the soil interior, the simulation of soil moisture was improved definitely. For June, July, and August, the biases of soil moisture simulation decreased by approximately 22.5, 34.4, and 27.5%, respectively, while the RMSEs decrease by approximately 7.0, 8.7, and 9.6%, respectively. The improvement of soil moisture simulation indicates that in arid and semiarid areas soil water vapor transport is important and cannot be neglected.

Combining local, landscape, and regional geographies to assess plant community vulnerability to invasion impact.

Invasive species science has focused heavily on the invasive agent. However, management to protect native species also requires a proactive approach focused on resident communities and the features affecting their vulnerability to invasion impacts. Vulnerability is likely the result of factors acting across spatial scales, from local to regional, and it is the combined effects of these factors that will determine the magnitude of vulnerability. Here, we introduce an analytical framework that quantifies the scale-dependent impact of biological invasions on native richness from the shape of the native species-area relationship (SAR). We leveraged newly available, biogeographically extensive vegetation data from the U.S. National Ecological Observatory Network to assess plant community vulnerability to invasion impact as a function of factors acting across scales. We analyzed more than 1000 SARs widely distributed across the USA along environmental gradients and under different levels of non-native plant cover. Decreases in native richness were consistently associated with non-native species cover, but native richness was compromised only at relatively high levels of non-native cover. After accounting for variation in baseline ecosystem diversity, net primary productivity, and human modification, ecoregions that were colder and wetter were most vulnerable to losses of native plant species at the local level, while warmer and wetter areas were most susceptible at the landscape level. We also document how the combined effects of cross-scale factors result in a heterogeneous spatial pattern of vulnerability. This pattern could not be predicted by analyses at any single scale, underscoring the importance of accounting for factors acting across scales. Simultaneously assessing differences in vulnerability between distinct plant communities at local, landscape, and regional scales provided outputs that can be used to inform policy and management aimed at reducing vulnerability to the impact of plant invasions.

Spatially prioritizing mitigation for amphibian roadkills based on fatality estimation and landscape conversion

Roads cause biodiversity loss and the effects of wildlife-vehicle collisions may ripple from individuals and populations to ecosystem functioning. Amphibians are threatened worldwide and, despite being particularly prone to roadkill impacts, they are often neglected in assessments. Here, we develop a sampling and analytical framework for spatially prioritizing mitigation actions for anuran amphibian roadkills based on fatality estimation and landscape conversion. The framework is composed of the six following steps: (1) pre-selection of segments to survey using the wetland coverage in the surroundings and the presence of roadkills of aquatic reptiles as a proxy for wet areas; (2) spatiotemporally replicated counts with a dependent double-observer protocol, that is, each segment is sampled multiple times by two pairs of people on foot; (3) extraction of covariates hypothesized to affect spatial and temporal variation in roadkill rates and persistence; (4) hierarchical open-population N-mixture modelling to estimate population dynamics parameters, which accounts for imperfect detection and spatiotemporal heterogeneity in removal, detection, and roadkill rates, and explicitly estimates carcass entries per time interval. (5) Assessment of land cover transition to infer landscape stability; and (6) prioritization of segments based on higher fatality rates and lower landscape conversion rates. We estimated a mean of 136 (95%CrI = 130–142) anurans roadkill per km per day in the 50 sample sites selected. The initial number of carcasses had a positive relationship with the percentage occupied by wetlands and a negative association with the percentage occupied by urban areas. The number of entrant carcass per interval was higher in the presence of rainfall and had a positive association with the wetlands cover. Carcass persistence probability was higher at night and lower in sites with high traffic volume. Ten segments (~1% of road extension) were prioritized using the median as threshold for fatality estimates and landscape conversion. It is urgent to appropriately evaluate the number of amphibians roadkilled aiming to plan and implement mitigation measures specifically designed for these small animals. Our approach accounts for feasibility (focused on sites with greater relevance), robustness (considering imperfect detection), and steadiness (less prone to loss of effectiveness due to landscape dynamics).

Numerical study on calculation model of airflow temperature and humidity prediction in humid airway

AbstractIn deep coal mining, the high temperature and humidity environment are one of the main disasters threatening workers and equipment. To predict the temperature and humidity of airflow in the airway accurately, this study establishes a numerical calculation model of the surrounding rock temperature, airflow temperature, and humidity under the conditions of considering the moisture evaporation and heat absorption of the airway wall, the condensation and heat release of supersaturated water vapor in the airflow, and the influence of air compression or expansion. Combined with the two‐dimensional (2D) heat conduction model (considering the influence of the axial surrounding rock heat conduction of the airway), the axial strip partial moisture calculation model of the airway is proposed, and then the uniform moist wall model and the axial strip partial moist wall model are established. The influence of different parameters on the temperature and humidity of airflow is discussed by analyzing the results of numerical simulation of the uniform wet surface model (UWSM) and partly wet surface model (PWSM) of the airway wall. The results show that the surrounding rock temperature, especially the temperature distribution of the airway wall, calculated by using the 2D heat conduction model under the local humid airway conditions, is more realistic. The increment of airflow temperature decreases with the increase of wet area ratio, airflow temperature at the entrance and airway radius, and increases with relative humidity at the entrance. The calculation accuracy of temperature and humidity prediction for large ventilation networks can be further improved by using the equivalent humidity of the UWSM to replace the correction coefficient of the wet area ratio of the PWSM.

A Modified Weber Number Capturing the Bouncing–Wetting Transition of Droplet Impact on Rough Surfaces

AbstractIn this work, the effects of surface properties on bouncing–wetting transition of water droplet impacting rough surfaces in the Weber number (We) range from 18 to 221 are experimentally investigated. The correlation between impact outcomes and We is examined with an empirical function, and an impact outcome transition from bouncing to no bouncing is identified with the increase of We. The results suggest that a higher surface area ratio promotes the bouncing to no bouncing transition on sample surfaces used in this study. To quantify the effects of surface wetting area on the transitions of droplet impact regimes, a modified Weber number, We*, is proposed by taking the actual surface area into account. Results show that the regime transitions of droplet impact on samples of different surface area ratios can be unified by the We*. This study reveals the significance of actual surface area and the resultant adhesion force on the droplet impact dynamics on random rough surfaces.

Spatiotemporal variability and driving factors of the shallow soil moisture in North China during the past 31 years

To fully understand the dynamic change characteristics of soil moisture in North China, the spatiotemporal patterns of soil moisture anomalies (SMA) in the four active soil layers from January 1990 to December 2020 are analyzed based on the Global Land Data Assimilation System (GLDAS) model, then the driving factors and corresponding contribution rates (CRs) for SMA change are determined together with the meteorological, socioeconomic and land cover data. The results show that the SMA in the last three layers present decreasing trends, and the trend magnitudes increase in multiples with the increase of soil depth. The area with the most severe soil dry is clustered in the east-central plain, while the relatively wet areas are scattered in western Shanxi and northern Hebei. The annual, intra- and inter-annual cycles (1.0, 0.5, 4.3 and 7.3 yr) are the dominant frequency of the SMA time series, which are driven jointly by 6 natural-type factors and 6 human-type factors, especially the intensified evaporation and dramatically expanding urbanization. By combining principal component analysis (PCA) and grey absolute correlation degree, the reintegrated human and natural factors respectively account for 49.46% and 50.54% of mean CRs to SMA in the four layers, but the human factor dominates the change of the bottom SMA. On the other hand, the determined mean CRs by combining exploratory factor analysis (EFA) and grey absolute correlation degree are 53.46% and 46.44% for reintegrated positive and negative factors, but the negative factor has a greater effect on the bottom SMA. The results provide a clear clarification of the soil moisture dynamic change, which is conducive to shedding new light on water resources management, agricultural security and ecological sustainability.

Investigation of Adhesion Property between Asphalt Binder and Aggregate Using Modified Boiling Methods for Hot and Wet Area

For long-term hot and rainy climate areas, the moisture susceptibility of asphalt pavement is the most serious issue during the service of pavement, which primarily depends on the adhesion between asphalt binder and aggregate. To explore the adhesion between different asphalt binders and aggregates, two types of asphalt binders and three kinds of aggregates were selected in this study. The water boiling test was modified by increasing the boiling time, quantifying the stripping rate and increasing the sample weight. The contact angle test and the energy dispersive spectrometer test were also conducted. The results showed that longer boiling time, longer aging time for asphalt binder, and higher Si content in aggregates will increase the stripping rate between the asphalt binder and the aggregate. For base asphalt, the stripping rate of sandstone is about 35.76% at long-term aging. The stripping rate calculated by boiling loose mixture for 30 min has the good correlation with the silicon content in the aggregates, with R-square about 98.77%, which indicates a good indicator to evaluate the asphalt-aggregate adhesion.