Search Results (4,578)

The increasing scarcity of water and soil resources, combined with inefficient water and fertilizer management, poses significant challenges to agriculture in arid regions. This study aimed to determine an optimal water and nitrogen regulation model to alleviate water shortages and improve agricultural productivity and quality. In this study, a two-year experiment was conducted to investigate the effects of varying irrigation and nitrogen levels on the soil environment and crop growth in a Lycium barbarum||alfalfa system (LB||AS). The experiment involved four moisture gradients and four nitrogen application levels (using urea as the nitrogen source). The results indicated that soil moisture decreased during crop development, followed by a slow increase, with significant variation across soil depths. Soil temperature peaked during the fruiting stage of Lycium barbarum in July, decreasing significantly with soil depth. Higher temperatures were recorded in N0 under the same irrigation level and in W3 under the same nitrogen level. Soil organic carbon (SOC) levels increased by 16.24% in W3N0 and by 18.05% in W2N1, compared to W0N3. Easily oxidizable organic carbon (EOC) and soluble organic carbon (DOC) levels exhibited significant variations depending on irrigation and nitrogen treatments. Irrigation and nitrogen had a stronger individual impact on alfalfa height and stem thickness than their combined effects. Water and nitrogen regulation significantly influenced Lycium barbarum yield, its 100-fruit weight, and economic efficiency (p < 0.05). The W0N2 treatment produced the highest yield (3238 kg·ha⁻¹), exceeding other treatments by up to 29.52%. In conclusion, the optimal water–nitrogen regulation model for the LB||AS system is full irrigation (75–85% θ_fc) with a nitrogen application rate of 300 kg·ha⁻¹. These findings offer critical insights for improving water and nitrogen management strategies in arid regions. Full article

As the penetration of renewable energy increases, the distribution grid faces great challenges in integrating large amounts of distributed energy sources and dealing with their output uncertainty. To address this, a multi-time scale optimal dispatch method based on model predictive control is proposed, including a day-ahead stage and an intra-day rolling stage. In the day-ahead stage, to fully utilize the flexibility of variable speed pumped storage hydropower, the generating/pumping phase modulation condition is considered, not just generating or pumping. Day-ahead optimal dispatch is established with the objective of minimizing the operation economy and node voltage deviation of the distribution network. In the intra-day rolling stage, model predictive control with finite time domain rolling optimal dispatch is used to replace the traditional single-time section optimal dispatch, considering the forecast data of wind, photovoltaic (PV), and load within the finite time domain, so that can respond in advance to smooth the generator output. At the same time, the uncertainty problem of the distribution network is solved effectively by rolling optimization and feedback correction of model predictive control. In order to consider the daily operating capacity balance of energy storage in the intra-day stage, the capacity imbalance penalty is added to the intra-day rolling optimization objective function, so that the energy storage capacity tries to track the results of the day-ahead optimization, achieving the long-term development of energy storage. Simulation analysis proves the feasibility and effectiveness of the proposed method. The proposed method enhances the generation–load–storage coordinated dispatching ability, effectively improving the distribution network’s capability to respond to fluctuations of renewable energy. Full article

Delineating the mechanical characteristics of aeolian sand improved with silt under temperature action is of great significance for the construction and long-term operation of engineering materials in seasonal frozen areas. Against the backdrop of aeolian sand resource utilization in the western region, local obtainable wind turbine sand and silt were used as raw materials, and a series of triaxial compression tests were conducted on aeolian sand improved with silt through temperature-controlled triaxial testers. The experimental parameters were as follows: silt content of 0%, 5%, 10%, 15%, and 20%; confining pressures of 100 kPa, 200 kPa, and 300 kPa; and temperatures of room temperature, 0 °C, −5 °C, −10 °C, and −15 °C. The results of the experiment demonstrated that the interaction between silt dosage, confining pressure, and temperature effects significantly influenced the triaxial compression strength of aeolian sand improved with silt. As the dosage of silt increased from 0% to 15%, the peak strength of the samples rose by 7.72% to 18.03%. This maximum increase occurred at a silt dosage of 15%. With the increase in confining pressures, the stress–strain relationship curve for the sample exhibits strain softening characteristics. Under varying temperatures, the samples exhibited a consistent pattern of initial shrinkage followed by subsequent expansion. As temperatures decrease, cohesive forces exhibit a wavelike pattern in their variation, with an essentially constant internal friction angle. The research results can provide theoretical support for the selection of building materials in the northwest region, address the issue of regional material shortages, and improve the application of aeolian sand in seasonally frozen areas. Full article

The seasonality of floods is a key factor affecting riparian agriculture. Flood season staging is the main means of identifying the seasonality of floods. In the process of staging the flood season, set pair analysis is a widely used method. However, the set pair analysis method (SPAM) cannot take into account the differences in and volatility of the staging indicators, and at the same time, the SPAM cannot provide corresponding staging schemes according to different scenarios. To address these problems, the improved set pair analysis method (ISPAM) is proposed. Kernel density estimation (KDE) is used to calculate the interval of the staging indicators to express their volatility. Based on the interval theory, the deviation method is improved, and the weights of the staging indicators are calculated to reflect the differences in different staging indicators. The theoretical correlation coefficient can be calculated by combining the weights and interval indicators and fitting the empirical connection coefficient corresponding to each time period. Finally, the ISPAM is established under different confidence levels to derive staging schemes under different scenarios. Based on the daily average precipitation flow data from 1961 to 2022 in the Nandujiang middle basin and surrounding areas in tropical island regions, the staging effect of the ISPAM was verified and compared using the SPAM, Fisher optimal segmentation method, and improved set pair analysis method without considering differences in the indicator weights (ISPAM-WCDIIW), and the improved set pair analysis method without considering indicator fluctuations (ISPAM-WCIF). According to the evaluation results from the silhouette coefficient method, it can be concluded that compared with the SPAM and ISPAM-WCIF, the ISPAM provided the optimal staging scheme for 100% of the years in the test set (2011–2022). Compared with the Fisher optimal segmentation method, the optimal staging scheme for more than 83% of the years (2011, 2013–2015, and 2017–2022) in the test set was provided by the ISPAM. Although the ISPAM-WCDIIW, like the ISPAM, can provide optimal staging schemes, the ISPAM-WCDIIW could not provide an exact staging scheme for more than 55% of the scenarios (the ISPAM-WCDIIW could not provide an exact staging scheme in scenarios (0.7, 0.6), (0.8, 0.6), (0.8, 0.9), (0.95, 0.6), and (0.95, 0.8)). The results show that the ISPAM model is more reasonable and credible compared with the SPAM, Fisher optimal segmentation method, ISPAM-WCDIIW, and ISPAM-WCIF. The purpose of this study is to provide a reference for flood season staging research during flood seasons. Full article

Secondary flows in Francis turbines are induced by the presence of a gap between guide vanes and top–bottom covers and rotating–stationary geometries. The secondary flow developed in the clearance gap of guide vanes induces a leakage vortex that travels toward the turbine downstream, affecting the runner. Likewise, secondary flows from the gap between rotor–stator components enter the upper and lower labyrinth regions. When Francis turbines are operated with sediment-laden water, sediment-containing flows affect these gaps, increasing the size of the gap and increasing the leakage flow. This work examines the secondary flows developing at these locations in a Francis turbine and the consequent sediment erosion effects. A reference Francis turbine at Bhilangana III Hydropower Plant (HPP), India, with a specific speed (Ns = 85.4) severely affected by a sediment erosion problem, was selected for this study. All the components of the turbine were modeled, and a reference numerical model was developed. This numerical model was validated with numerical uncertainty measurement and experimental results. Different locations in the turbine with complex secondary flows and the consequent sediment erosion effects were examined separately. The erosion effects at the guide vanes were due to the development of leakage flow inside the guide vane clearance gaps. At the runner inlet, erosion was mainly due to a leakage vortex from the clearance gap and leakage flow from rotor–stator gaps. Toward the upper and bottom labyrinth regions, erosion was mainly due to the formation of secondary vortical rolls. The simultaneous effects of secondary flows and sediment erosion at all these locations were found to affect the overall performance of the turbine. Full article

The food–energy–water (FEW) nexus has emerged as an alternative for managing resources in the food, energy, and water systems. However, there are limited case studies applying this approach in the Latin American and Caribbean region. This region stands to benefit significantly from the FEW nexus approach due to its heavy reliance on hydropower for electricity generation and unevenly distributed and poorly managed water resources. In this study, an urban FEW nexus framework was used in the Otun River Watershed (ORW) to evaluate changes in food, energy, and water demand for four scenarios. Additionally, regional climate models (RCMs) were used to forecast water availability in the ORW from 2030–2039. The results show that water demand could increase by 16% and energy demand will increase by roughly 15% for scenario 2, while water demand in scenario 3 will likely remain unchanged in relation to the current conditions (base scenario). Enhancing water resources management in the ORW will involve a variety of measures, including: implementing practices to reduce water losses in distribution systems, developing green infrastructure and decentralized wastewater systems, and embracing urban and peri-urban farming. Successful application of urban FEW nexus solutions requires involvement from stakeholders across the food, energy, and water systems. Full article

The highly hazardous chemical ammonia has been proven to be absorbed by nanoparticles, thereby exerting highly toxic effects on aquatic organisms. As a ubiquitous pollutant in aquatic environments, polystyrene nanomicroplastics (PSNPs) have shown strong adsorption capacity due to their large surface area. Therefore, the potential joint effects of ammonia and PSNPs need to be clarified. In this study, zebrafish embryos were exposed to a water solution with ammonia concentrations (0, 0.1, 1, and 10 mg/L) with or without PSNP (100 μg/L) treatment up to 120 hpf. The results showed that combined exposure increased the accumulation of ammonia and obviously reduced the locomotor speed of zebrafish larvae compared with exposure to ammonia alone. Further studies indicated that PSNPs can aggravate ammonia-induced neurotoxicity by altering the cholinergic system, dopaminergic neurons, and the retinal structure in zebrafish larvae. In addition, our results revealed that ammonia caused significant alterations in the expression of genes related to neurodevelopment and retinal development, and PSNPs exacerbated this adverse effect. In conclusion, PSNPs can aggravate ammonia-induced neurotoxicity in the early stage of zebrafish and their associated health risk to aquatic animals should not be underestimated. The main contribution of this article lies in revealing the synergistic neurotoxicity of ammonia and PSNPs in the early stage of zebrafish. Moreover; it emphasizes that the associated health risks to aquatic animals should not be underestimated. Full article

Design floods are traditionally estimated based on the at-site annual maximum flood series, including historical information of hydraulic structures. Nevertheless, the construction and operation of upstream reservoirs undermine the assumption of stationarity in the downstream flood data series. This paper investigates non-stationary design flood estimation considering historical information from the Three Gorges Reservoir (TGR) in the Yangtze River. Based on the property that the distribution function of a continuous random variable increases monotonically, we proposed a novel time-varying P-III distribution coupled with the curve fitting method (referred to as the Tv-P3/CF model) to estimate design floods in the TGR operation period, and we comparatively studied the reservoir indices and parameter estimation methods. The results indicate that: (1) The modified reservoir index used as a covariate can effectively capture the non-stationary characteristics of the flood series; (2) The Tv-P3/CF model emphasizes the fitness of historical information, yielding superior results compared to time-varying P-III distribution estimated by the maximum likelihood method; (3) Compared to the original design values, the 1000-year design peak discharge Q_m and 3-day and 7-day flood volumes in the TGR operation period are reduced by approximately 20%, while the 15-day and 30-day flood volumes are reduced by about 16%; (4) The flood-limited water level of the TGR can be raised from 145 m to 154 m, which can annually generate 0.32 billion kW h more hydropower (or increase by 6.8%) during flood season without increasing flood prevention risks. Full article

Due to their exceptional operational versatility, doubly fed induction machines (DFIM) are widely employed in power systems comprising variable renewable energy-based electrical generation sources, such as wind farms and pumped-storage hydropower plants. However, their starting and grid synchronization methods require numerous maneuvers or additional components, making the process challenging. In this paper, a soft start method for DFIM, inspired by the traditional synchronization method of synchronous machines, is proposed. This method involves matching the frequencies, voltages, and phase angles on both sides of the main circuit breaker, by adjusting the excitation through the controlled power converter at standstill conditions. Once synchronization is achieved, the frequency is gradually reduced to the rated operational levels. This straightforward starting method effectively suppresses large inrush currents and voltage sags. The proposed method has been validated through computer simulations and experimental tests, yielding satisfactory results. Full article

The reasonable and efficient prediction of dam failure events is of great significance to the emergency rescue operations and the reduction in dam failure losses. This work presents a model that is based on the physical mechanism. It is coupled with a multi-architecture (multi-CPU and GPU) open-source two-dimensional flood model, which is based on high-precision terrain and land use data. The aim is to enhance the accuracy of dam break flood process simulations. The model uses DEM data as a computational grid and updates it at each time step to reflect breach evolution. Simultaneously, the breach evolution model incorporates an analysis of stress on sediment particles, establishing the initial erosion state and lateral expansion model while accounting for seepage. The determination of the overflow of the breach is resolved through the application of a two-dimensional hydrodynamic model. This approach achieves a robust connection between the upstream reservoir, the dam structure, and the downstream inundation area. The coupled model is utilized to calculate the failure of earth-rock dams and landslide dams, and a sensitivity analysis is conducted. Taum Sauk Dam and Tangjiashan landslide dam were selected to represent earth dam break and barrier lake break, respectively, which are the main types of dam breaks. The obtained results demonstrate strong concurrence with the measured data, the relative errors of the four important parameters of the application case, the peak discharge of the breach, the top width of the final breach, the depth of the breach and the arrival time of the maximum peak discharge are all within ±10%. Although the relative error of the completion time of the final breach is greater than 10%, it is about 30% less than the relative error of the physical model. Full article

The increasing integration of renewable energy sources (RESs) into the Italian electricity market has heightened inter-zonal congestion challenges as power flows vary across importing and exporting zones. Utilizing a Multinomial Logistic Regression model as an empirical approach, this study investigates the key factors driving inter-zonal congestion between zonal pairs from 2021 to 2023, focusing on how local and neighboring zones’ RES generation (wind, solar, and hydropower) and demand dynamics impact congestion probabilities. The findings reveal that increased local RES generation generally reduces the likelihood of congestion for importing regions but increases it for exporting zones. Specifically, higher wind and solar production in importing zones like CNOR and CSUD alleviates congestion by reducing the need for imports, while in exporting zones, such as NORD and CALA, increased RES generation can exacerbate congestion due to higher export volumes. Hydropower production shows similar trends, with local production mitigating congestion in importing zones but increasing it in exporting zones. In addition to the effects of local generation and demand within each zonal pair, the generation and demand from neighboring zones also have a notable and statistically significant impact. Although their marginal effects tend to be smaller, the contributions from neighboring zones are essential for comprehending the overall congestion dynamics. These insights underscore the need for strategic RES placement to enhance market efficiency and minimize congestion risks across the Italian zonal electricity market. Full article

The study of the co-transport of Cr(VI) and microplastics (MPs) in porous media is important for predicting migration behavior and for achieving pollution removal in natural soils and groundwater. In this work, the effect of MPs on Cr(VI) migration in saturated porous media was investigated at different ionic strengths (ISs) and pHs. The results showed that pH 7 and low IS (5 mM), respectively, promoted the movement of Cr(VI), which was further promoted by the presence of MPs. The Derjaguin–Landau–Verwey–Overbeek (DLVO) results showed that the repulsive energy barrier between MPs and quartz sand decreased with increasing IS and decreasing pH, respectively, which promoted the retention of MPs in quartz sand and constrained the competition of Cr(VI) for adsorption sites on the surface of the quartz sand, thus facilitating the enhanced migration of Cr(VI), while Cr(VI) behaved conversely. Sodium alginate/nano zero-valent iron-reduced graphene oxide (SA/NZVI-rGO) gel beads could achieve the removal of MPs through a π-π interaction, hydrogen bonding, and electrostatic attraction, but the MPs removal would be reduced by 40% due to the competitive adsorption of Cr(VI). Notably, 97% Cr(VI) removal could still be achieved by the gel beads in the presence of MPs. Therefore, the gel beads can be used as a permeation reaction barrier to inhibit the MP-induced high migration of Cr(VI). The Cr(VI) breakthrough curves in reactive migration were well-fitted with the two-site chemical nonequilibrium model. Overall, the findings of this work contribute to the understanding of the migration behavior of Cr(VI) and MPs in saturated porous media and provide a theoretical basis for the remediation of soils and groundwater contaminated with Cr(VI) and MPs. Full article

During the long-term operation of hydraulic structures under the action of complex loads and impacts, non-design changes occur, which lead to a decrease in the bearing capacity and safety and, accordingly, to the need for structural reinforcements. Experiments were conducted to study the strengthening of reinforced concrete models of hydraulic structures with interblock construction joints (located in two directions) and with the low longitudinal reinforcement coefficients typical of hydraulic structures (μ_s = 0.0039 and μ_s = 0.0083), using the low concrete classes B15 and B25. These structures were strengthened using external reinforcement with carbon ribbons of the FibArm 530/300 type. The results revealed an increase in the bearing capacity (by 1.355- and 1.66-fold); accordingly, the high efficiency of this strengthening method for reinforced concrete hydraulic structures was proven. Using the results of these experiments, including the obtained special characteristic of the cracking of reinforced concrete structures and the results of studies by other authors, recommendations for calculations involving reinforced concrete hydraulic engineering structures strengthened with an external reinforcement system of carbon-fibre-based composite materials were developed and proposed. Carbon-fibre-based composite materials are used as elements of external reinforcement for building structures (unidirectional—tapes, bidirectional—meshes and fabrics). The calculation recommendations proposed by the authors can be taken into account for the creation of a regulatory framework for hydropower facilities, including hydroelectric power plants and pumped-storage power plants. They justify the use of an external reinforcement system made with carbon-fibre-based composite materials to strengthen hydraulic structures in operation and provide an increased level of safety for reinforced concrete structures and constructions. Full article

A suitable range of paste and mortar margins (α and β) to enhance compressive strength in Rich-Mix cemented sand gravel and rock (CSGR) material for application in CSGRD construction is critical. SL 678-2014 recommends margins > 1, which are specifically designed to fill the voids within the fine and coarse aggregates with paste and mortar, respectively, while allowing some excess for workability. However, the optimum ranges of values after 1 are inadequately determined, often leading to high efforts and time-consuming trial mixes that are not economical. This study evaluates two datasets to identify the optimal ranges of α and β margins for compressive strength development in Rich-Mix CSGR, aiming to achieve the compressive strength class C₁₈₀20, intended for use as cushion, protective, and seepage control layers in CSGRD. Using Pearson correlations, t-statistics, and p-values, the first dataset (7, 28, 90, and 180 days) showed weak correlations between paste margins and compressive strengths (coefficients 0.172 to 0.418, p-values > 0.05) and negligible relationships for mortar margins (coefficients −0.269 to 0.204, p-values > 0.05), affirming the contribution of other factors in the compressive strength development in CSGR. The second dataset (14, 28, 90, and 180 days) revealed significant positive correlations between paste margins and strengths at 14, 90, and 180 days (coefficients up to 0.850, p-values < 0.05). Mortar margins, however, negatively impacted strength (coefficients −0.544 to −0.628, p-values < 0.05), revealing the need to control the sand ratio. The optimal range of values was 1.05 ≤ α ≤ 1.09 and 1.15 ≤ β ≤ 1.25, with a water–binder ratio of 0.7~1.3, vibrating–compacted value (VC) of 2~8 s, and sand ratio of 18~35%. These findings highlight the significance of precise paste and mortar margin ranges in the compressive strength development of Rich-Mix CSGR. Full article

Caragana tibetica is a common species in the shrub-encroached desert grasslands of Inner Mongolia, China. Studying its distribution and factors can improve our grasp of shrub-encroached grassland dynamics and aid in regional biodiversity conservation. This study examined eight C. tibetica communities using point pattern analysis to assess the spatial distribution pattern (SDP) and the influencing factors of C. tibetica scrubs. We also propose a new index, i.e., the degree of deviation index (DoDI), to quantify the SDP of scrubs. The results revealed the following: (1) The shrubland of C. tibetica in the study area showed aggregated distribution on the scale of 0–30 m. On the scale of 30–50 m, the degree of aggregation gradually weakened and random distribution appeared. (2) There was not a significant correlation between SDP and environmental factors; however, DoDI showed that habitat heterogeneity had a certain impact on C. tibetica in the study area. Our research indicates that spatial heterogeneity contributes to the SDP of shrub plants in the shrub-encroached grasslands of the Inner Mongolia Plateau, and the use of DoDI enhances the ability to quantify and isolate the role of spatial heterogeneity. This study helps to deepen the understanding of the mechanisms of shrub encroachment formation in grasslands. Full article