In this manuscript, we prove the existence of strictly positive solutions for a class of p&q systems whose nonlinearities involved may exhibit semipositone behavior, which arise naturally in several applications that includes models of competing species and the dynamics of particle movement. Our approach combines variational methods, comparison principles and a novel regularity result for systems. This estimate, which may be of independent interest, is new even in the classical Laplacian case.
The petroleum and petrochemical industries operate in highly aggressive environments where corrosion can severely compromise the integrity of critical equipment. This work investigates how key high-velocity oxygen fuel (HVOF) spraying factors influence the coating integrity and corrosion performance of tungsten carbide layers deposited on AISI 4130 steel. The powder feed rate (ranging from 60 to 80 g/min) and spray pressure (ranging from 6.5 to 7.4 bar) were systematically varied for samples C1-C5, while an uncoated specimen served as the control. Microstructural characterization using scanning electron microscopy confirmed variations in coating density and thickness across the samples. Mechanical performance was evaluated through Vickers hardness measurements, indicating a significant increase (from 225 HV for the uncoated steel to 2060 HV and 2020 HV for samples C3 and C5, respectively). Corrosion performance was examined using Tafel polarization testing and EIS (electrochemical impedance spectroscopy). The HVOF-processed coatings significantly enhanced corrosion resistance compared with the bare substrate, with sample C3 demonstrating the lowest corrosion current density and a more noble corrosion potential. Nyquist analysis further indicated that C3 possessed the highest charge-transfer resistance due to its uniform WC distribution and reduced porosity. Overall, the optimal performance was achieved using a spray pressure of 7.2 bar and a powder feed rate of 72 g/min, identifying sample C3 as the most effective configuration for corrosion protection.
This study investigates the combined effects of silica fume addition and variable steam-curing durations on concrete mechanical properties. Unlike most prior research, which typically used fixed steam durations and focused mainly on compressive strength, this work directly compares multiple steam-curing intervals (4–48 h at 66 ± 2 °C) with conventional water curing (3–28 days), enabling clear one-to-one comparisons of compressive, splitting tensile, and flexural strength development. Four mixtures were tested: control mixes at w/c 0.6 and 0.35 (no silica fume), plus mixes with silica fume added at 10
Accurate flood and damage forecasting is essential for mitigating the severe impacts of floods, which affect millions of people worldwide and cause substantial economic losses each year. This study evaluates the efficacy of the Weather Research and Forecasting (WRF) model in simulating precipitation for flood forecasting and direct damage estimation in the Poldokhtar basin, Iran. By testing 87 WRF configurations, optimal schemes (e.g., WSM3, Kessler, Grell 3D, and YSU) were identified for accurate precipitation and flood simulation. The WRF outputs were coupled with the HEC-HMS and HEC-RAS models to simulate flood hydrographs and hydraulic characteristics. The integrated modeling framework achieved Nash-Sutcliffe efficiency values above 0.85 and peak discharge errors below 15
Abscission is a crucial biological process for organ detachment in plants. Flower bud abscission in the 'ON' year significantly contributed to pistachio alternate bearing, with carbohydrate levels involved in this phenomenon. The study aimed to investigate the role of foliar silicon (Si) as a nutrient in the expression pattern of genes involved in carbohydrate metabolism at concentrations of 0, 5, and 10 g L−1 in two commercial pistachio cultivars including “Fandoghi” and “Akbari”, 14 days after full bloom (DAFB) in the 'ON' year. The results indicated that the expression levels of all five genes including α and β-amylase, callose synthase (CalS), galactinol synthase (GolS), and Starch synthase, were different in leaf, fruit, and abscission zone (AZ) tissues. Additionally, these genes were upregulated with silicon treatment in the AZ. Overall, the sucrose content was higher in treated samples compared to the control. The highest level of soluble carbohydrates (0.58 mg g−1 FW) was observed in the “Akbari” cultivar at a concentration of 5 g L−1 of silica in the AZ. Glucose content increased in both cultivars, with a significant rise of 2.90 mM at 5 g L−1 of Si. The “Akbari” cultivar showed the highest fructose concentration at 5 and 10 g L−1 of Si, and the application of 10 g L−1 of Si in 14 DAFB reduced the bud abscission rate to 9.69. The simultaneous regulation of these genes and activation of the carbohydrate storage and consumption pathway during the critical flowering stage by silicon indicate its dual role in regulating the expression of carbohydrate pathway genes.
