Abstract Although the classical steady and quasi-steady friction term often overestimates hydraulic head, it remains widely used in water hammer equations to simulate hydraulic transients in piping systems. Its popularity stems from its simple mathematical form and ease of implementation compared to unsteady friction models, particularly in complex networks. Within the method of characteristics (MOC) framework, this classical friction term for turbulent flows is typically integrated using explicit numerical schemes, producing linear finite difference equations that are straightforward and computationally efficient to solve. In contrast, more accurate implicit methods are often avoided due to the perceived need for nonlinear iterative schemes to resolve the resulting equations. This work introduces a unique closed-form analytical solution to the nonlinear algebraic recurrence equation governing discharge in the water hammer problem derived using the Crank–Nicolson approximation of classical turbulent friction. The proposed approach not only delivers second-order accuracy, which is unattainable with conventional explicit approximations, but also remains computationally efficient and robust, offering a superior alternative to existing methods. By evaluating a global normalized absolute error as a function of step size across multiple methods and a representative dimensionless governing parameter, we demonstrate that the improved accuracy offsets the modest increase in central processing unit (CPU) time. Specifically, the proposed methodology consistently reduces global mean errors by up to an order of magnitude compared with other second-order explicit methods, with only approximately a 60% increase in computational cost.
Urban coastal lagoons are heavily impacted by untreated sewage, industrial effluents and diffuse pollution, heightening ecotoxicological risks. Herein, Nile tilapia (Oreochromis niloticus) was employed as a sentinel species concerning metal exposure at the Jacarepaguá Lagoon Complex (JLC), a critical case of ecological degradation under intense anthropogenic pressure in Rio de Janeiro, Southeastern Brazil. Samplings were conducted between 2022 and 2023 during the dry (autumn–winter) and rainy (spring–summer) seasons. Organosomatic indices and total (muscle) and subcellular (liver and muscle) metal levels were determined. Antioxidant system alterations were evaluated through superoxide dismutase (SOD), glutathione-S-transferase (GST), reduced glutathione (GSH), total antioxidant capacity (TAC) and metallothionein (MT) assessments. Lipid peroxidation (LPO) and protein carbonylation (PTC) levels were also determined as oxidative effect markers, while vitellogenin (VTG) was used as an estrogenic effect indicator. Arsenic (0.018–0.033 mg L⁻¹), Mn (0.041–0.050 mg L⁻¹), Rb (0.019–0.023 mg L⁻¹), and V (0.008–0.010 mg L⁻¹) were detected in water samples in both sampling seasons; while Fe was detected only in the dry season (0.023 ± 0.03 mg L⁻¹). Subcellular As, Co, Cu, Fe, Mn, Ni, Pb, Rb, Ti, V, and Zn were quantified in both liver and muscle, albeit with no significant differences between seasons or sexes. Seasonal variations were noted for male VTG, although not statistically significant, with attenuation of sexual VTG differences from the dry (M/F = 0.67) to the rainy season (M/F = 1.20). The multibiomarker approach applied to wild tilapia under diffuse urban pollution indicates mild sublethal effects while highlighting the need for expanded, integrated monitoring of additional endocrine and oxidative biomarkers. Although centered on a specific lagoon complex system, these mechanisms recur in urban lagoons worldwide, indicating the need for consumption-risk evaluations and actionable remediation/management frameworks.
Microplastics (MPs) are a pervasive environmental threat due to their persistence, bioavailability, and toxicity. In marine environments, MPs are widely distributed and ingested by fish, posing risks to human consumers. This study examined how ecological and anthropogenic factors—body size, water column position, seasonality, and human impact—influence MP concentrations in the muscle and digestive tissues of coastal fish from southeastern Brazil. We hypothesized that fish from more impacted environments would contain higher MP levels; that pelagic species would ingest more MPs due to particle buoyancy; and that ingestion would be higher in summer and in larger fish due to seasonal and size-related factors. Additionally, we hypothesized that MP loads would be higher in digestive tissues than in muscle, given limited translocation capacity. Four commercially important species (Caranx crysos, Sardinella aurita, Menticirrhus americanus, and Micropogonias furnieri) were collected from two bays with contrasting anthropogenic influences—Sepetiba (more impacted) and Ilha Grande (less impacted)—during summer and winter. Digestive tracts and muscle tissues were digested, vacuum-filtered, and analyzed using microscopy and micro-FTIR. MPs were detected in all species and in 83.1
Shape memory alloys present remarkable thermomechanical behaviors due to solid phase transformations. The complexity of the involved phenomena makes the constitutive modeling of this class of smart material a challenging subject. Considering the different approaches presented in the literature, the constitutive models with assumed phase transformation kinetics are popular, achieving reasonable results. This paper deals with one-dimensional constitutive models that employs a novel strategy to describe phase transformation kinetics using polynomial functions. Three different polynomial functions are treated: linear, quadratic, and cubic. Besides, the novel approach defines the phase transformation surfaces in such a way that allows the description of new phenomena including tension-compression behaviors and two-way shape memory effect. Experimental data compiled from the literature guides the investigation treating temperature-induced phase transformation; pseudoelasticity; one-way and two-way shape memory effects; internal subloops due to incomplete phase transformations. Numerical simulations are carried out comparing the novel functions with the classical cosine function. Results indicate that the model with polynomial phase transformation kinetics is able to capture the main features of SMA thermomechanical behavior. The investigation shows that the cubic polynomial is equivalent to the cosine function and the linear polynomial presents good estimations, being related to low computational cost since it avoids iterative approaches for strain-driven cases.
Microplastic (MP) pollution is ubiquitous in aquatic ecosystems, but comparative analyses across wetland types and fish life histories are still rare. This study compares microplastic contamination in killifishes (Cyprinodontiformes: Rivulidae) with contrasting life histories: annual (Notholebias minimus, Leptopanchax opalescens) vs. perennial (Kryptolebias ocellatus; Kryptolebias hermaphroditus), across two wetland types (temporary ponds vs. mangroves) on the coastal plain of Rio de Janeiro (Brazil). The tested hypothesis is that small annual fishes in temporary wetlands exhibit lower microplastic contamination than perennial mangrove species, due to lower hydrological connectivity and shorter exposure time. Fishes were digested (KOH solution), vacuum filtered, and analysed using microscopy and µ-FTIR. Microplastics were detected in all species and 60.5
