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Pump-jet holds a pivotal position in various marine applications, underscoring the need for comprehending their transient behavior for the purpose of design enhancement and performance refinement. This paper employs Reynolds-averaged Navier–Stokes equations method in conjunction with Detached Eddy Simulation model. The study delves into the ramifications of accelerating and decelerating ducts, distinguished by camber f and attack angles α, on transient hydrodynamic characteristics. The hydrodynamic characteristics are investigated numerically, after the validation of the numerical methodology by comparing simulation outcomes against experimental results. Subsequently, the study delves into propulsion characteristics, followed by an exploration of time-domain and frequency-domain data transformed through fast Fourier transform to analyze thrust fluctuations and pulsating pressures. Additionally, a detailed examination of pressure distribution and velocity field is provided, aiming to dissect the mechanisms through the variations in f and α influence the flow field. Findings suggest that the outlet velocity of accelerating ducts significantly surpasses the inlet velocity, a behavior contrasted by decelerating ducts. Notably, the patterns of accelerating and decelerating ducts resulting from alterations in f exhibit consistent characteristics with those brought about by changes in α. However, several opposite characteristics surface in transient flow field due to the distinct modifications in the duct profile. Furthermore, by considering vorticity magnitude distribution and vortices, a comparative analysis elucidates the effects of varying f and α on rotor and stator trailing vortices. This contributes to understanding the flow instability mechanism under differing duct configurations. It is evident that changes in f and α exert significant influence on both performance and flow field. [ABSTRACT FROM AUTHOR]

Non-point source pollution caused by rainfall runoff is an important pollution source for river water. To explore the impact of heavy rain on urban river water environments, this paper studied the changes in carbon, nitrogen, and phosphorus levels, composition, and structure in the river water of Kaifeng, China, during the heavy rain in July 2021. The results showed that the concentrations of different forms of carbon, nitrogen, and phosphorus all increased under the effect of the heavy rain. The increase of phosphorus in the river was the largest, and that of carbon was the smallest. The most significant pollution from carbon, nitrogen, and phosphorus occurred in the HJ River. Colored dissolved organic matter (CDOM) was present in the form of macromolecules after the rain, and the degree of humification was deeper compared with before the rain. But heavy rain did not affect the CDOM composition in urban rivers. The spectral slope (SR) and the absorption coefficient at 240 nm to 420 nm (E2/E4) values showed that the CDOM was dominated by exogenous input after the rain, with endogenous pollution again becoming the main factor one week after the rain. [ABSTRACT FROM AUTHOR]

Purpose: The objectives of this study were to (1) analyze heavy metals (Cr, As, Cu, Zn, Cd, and Pb) in the rhizosphere soil and roots, leaves, stems, and grains of maize and wheat crops using different methods; (2) evaluate the advantages of diffusive gradients in thin films technology (DGT) for predicting the bioavailability of heavy metals; and (3) compare the characteristics of DGT with other methods. Materials and Methods: In this study, we collected maize and wheat samples and their rhizosphere soil over a pollution gradient in Kaifeng City, China. Six heavy metal (Cr, As, Cu, Zn, Cd, and Pb) levels in rhizosphere soil were determined using DGT, EDTA, soil solution, and total amount methods, respectively. The heavy metal content in the roots, leaves, stems, and grains of maize and wheat was also analyzed. The relationships between six heavy metal soils concentrations detected by different methods, and their contents in the different parts of wheat and maize, were analyzed using statistical methods. The characteristics and application scope of the different methods were evaluated. Results and Discussion: The accumulation of heavy metals in maize and wheat was generally higher in the roots than in the above-ground parts (i.e., stems, leaves, and grains). For the soil solution method, only soil As levels showed a significantly positive correlation with its content in different parts of wheat and corn. For the EDTA method and the soil total amount method, only As, Zn, and Pb levels were significantly correlated with their contents in different parts of wheat and corn. Six heavy metal concentrations detected by DGT were all significantly positively correlated with their contents in the different parts of wheat and maize. Furthermore, DGT was less affected by the soil pH than EDTA. Conclusions: DGT was more accurate in simultaneously predicting plant-available Cr, As, Cu, Zn, Cd, and Pb. However, other methods, like EDTA, soil solution, and total amount methods, can also be considered when predicting the bioavailability of a single heavy metal (e.g., As or Zn) in rhizosphere soil. [ABSTRACT FROM AUTHOR]

We present a Chebyshev-Davidson method to compute a few smallest positive eigenvalues and corresponding eigenvectors of linear response eigenvalue problems. The method is applicable to more general linear response eigenvalue problems where some purely imaginary eigenvalues may exist. For the Chebyshev filter, a tight upper bound is obtained by a computable bound estimator that is provably correct under a reasonable condition. When the condition fails, the estimated upper bound may not be a true one. To overcome that, we develop an adaptive strategy for updating the estimated upper bound to guarantee the effectiveness of our new Chebyshev-Davidson method. We also obtain an estimate of the rate of convergence for the Ritz values by our algorithm. Finally, we present numerical results to demonstrate the performance of the proposed Chebyshev-Davidson method. [ABSTRACT FROM AUTHOR]