Understanding the microplastic pollution impact on Chironomus sancticaroli larvae development and emergence

Plastic materials are increasingly present in our lives. It is estimated that more than 360 million tonnes of plastics are produced annually worldwide. Particularly, single-use plastics represent an important segment in plastic production. In this context, plastic contamination, and consequently microplastic release, has become a growing concern for aquatic ecosystems. In this study, we investigated the effects of exposure to polyethylene terephthalate (PET) microplastics (<32 μm) on Chironomus sancticaroli larvae. The larvae were exposed to different concentrations of PET particles (0 (control group), 500, and 5,000 particles.kg−1 of dry sediment) for 10 days. Our results demonstrated that C. sancticaroli larvae displayed PET microplastics in their digestive tracts, and the ingestion increased with increasing PET concentrations. Plastic particles in the digestive tract can reduce the energy obtained by larvae feeding and, consequently, impair their development. The adult emergence rate displayed a significant decrease observed at the highest PET concentration compared with the control group. These findings reinforce existing concerns that microplastics, at concentrations currently found in the natural freshwater environments, can impact the development of benthic macroinvertebrates and, consequently, result in an unbalance in the freshwater ecosystems

On the effect of Lüders bands on the bending of steel tubes

textIn several practical applications, hot-finished steel pipe that exhibits Lüders bands is bent to strains of 2-3%. Lüders banding is a material instability that leads to inhomogeneous plastic deformation in the range of 1-4%. This work investigates the influence of Lüders banding on the inelastic response and stability of tubes under rotation controlled pure bending. It starts with the results of an experimental study involving tubes of several diameter-to-thickness ratios in the range of 33.2 to 14.7 and Lüders strains of 1.8% to 2.7%. In all cases, the initial elastic regime terminates at a local moment maximum and the local nucleation of narrow angled Lüders bands of higher strain on the tension and compression sides of the tube. As the rotation continues, the bands multiply and spread axially causing the affected zone to bend to a higher curvature while the rest of the tube is still at the curvature corresponding to the initial moment maximum. With further rotation of the ends, the higher curvature zone(s) gradually spreads while the moment remains essentially unchanged. For relatively low D/t tubes and/or short Lüders strains, the whole tube eventually is deformed to the higher curvature entering the usual hardening regime. Subsequently it continues to deform uniformly until the usual limit moment instability is reached. For high D/t tubes and/or materials with longer Lüders strains, the propagation of the larger curvature is interrupted by collapse when a critical length is Lüders deformed leaving behind part of the structure essentially undeformed. The higher the D/t and/or the longer the Lüders strain is, the shorter the critical length. This class of problems is analyzed using 3D finite elements while the material is modeled as an elastic-plastic solid with an “up-down-up” response over the extent of the Lüders strain, followed by hardening. The analysis reproduces the main features of the mechanical behavior provided the unstable part of the response is suitably calibrated. The uniform curvature elastic regime terminates with the nucleation of localized banded deformation. The bands appear in pockets on the most deformed sites of the tube and propagate into the hitherto intact part of the structure while the moment remains essentially unchanged. The Lüders-deformed section has a higher curvature, ovalizes more than the rest of the tube, and develops wrinkles with a characteristic wavelength. For every tube D/t there exists a threshold of Lüders strain separating the two types of behavior. This bounding value of Lüders strain was studied parametrically.Engineering Mechanic

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O amortecimento em linhas de ancoragem é uma parcela importante quanto à dissipação de energia em sistemas flutuantes ancorados. Até cerca de 15 anos atrás, ele era desprezado, mas hoje é considerado fundamental para determinar o comportamento dinâmico em baixa freqüência de sistemas flutuantes ancorados, pois os movimentos em baixa freqüência são ressonantes. Além disso, o acréscimo dos movimentos em freqüência de onda incrementa abruptamente a dissipação de energia e devem ser considerados no cálculo desta. Os primeiros métodos para o cálculo do amortecimento nas linhas impõem que a linha se movimente de forma quase-estática e, muitas vezes, desprezam o efeito da correnteza e dos movimentos em freqüência de onda. Métodos no domínio do tempo são capazes de análises não-lineares complexas, mas demandam muito tempo computacional, freqüentemente indisponível. Portanto, métodos simplificados que considerem todas as nuances presentes neste fenômeno são necessários, principalmente nas etapas iniciais de projeto. A proposta deste trabalho é apresentar o desenvolvimento de um modelo linearizado do amortecimento para que sejam possíveis análises no domínio da freqüência. Para não eliminar totalmente a não-linearidade apresentada pelo fenômeno, opta-se pelo cálculo iterativo. Ao eliminar a hipótese quase-estática, é possível calcular a dinâmica da linha em 1a ordem. São propostas correções no cálculo da dissipação de energia nas linhas ao incluirmovimentos em freqüência de onda e a presença de correnteza. Os resultados do modelo assim desenvolvido são comparados com resultados de cálculos no domínio do tempo e no domínio da freqüência.Among the several contributions to the damping of moored floating structures, the mooring line damping is a very important part of the energy dissipation during the motions of these structures. It was usually neglected until the mid 80s, but nowadays its calculation is essential in order to determine the low frequency resonant motions of moored floating structures. Furthermore, the superposed wave frequency motions dramatically increase the energy dissipation, so they should be properly taken into account. Although the quasi-static approach is much faster than the more accurate time domain simulations, it rests upon the assumption that the line is always described by the catenary equations. These simple analytic methods usually neglect the effects of current and wave frequency motions superposed on the low frequency motions. Therefore, simplified methods that consider these effects are desired and useful for conceptual designing. This text presents a frequency domain method based on a linear, but iterative, damping model. The method takes into account the effects of current and wave frequency motions on the dissipation of energy during the mooring line motions and does not require the quasi-static behavior of the lines. The results are compared to results obtained by frequency domain methods and time domain methods

On the effect of Lüders bands on the bending of steel tubes. Part II: Analysis

AbstractPart II of this study presents a modeling framework that is shown to successfully simulate all aspects of the inhomogeneous bending of tubes associated with Lüders banding reported in Part I. The structure is discretized with solid finite elements using a mesh that is fine enough for Lüders bands to develop and evolve. The material is modeled as a finitely deforming, J2 type, elastic–plastic solid with an “up–down–up” response over the extent of the Lüders strain, followed by hardening. Regularization of the solution was accomplished by introducing a mild rate dependence of the material. Simulation of the rotation controlled bending experiments confirmed most of the experimental observations and revealed additional details of the localization. Thus, the initial uniform-curvature elastic regime terminates with the nucleation of localized banded deformation on the tensioned and compressed sides of the tube. The bands appear in pockets that propagate into the hitherto intact part of the structure while the moment remains essentially unchanged. The tube develops two curvature regimes; a relatively high curvature in the Lüders deformed section and a low curvature in the unaffected one. Simultaneously, the plasticized zone develops higher ovalization and wrinkles with a wavelength that corresponds to the periodicity of the banded pockets. For tubes with lower D/t and/or shorter Lüders strain the higher curvature eventually spreads to the whole structure at which point homogenous bending resumes. For tubes with higher D/t and/or longer Lüders strain the localized curvature, ovalization, and wrinkle amplitude are larger and cannot be sustained; the tube collapses prematurely leaving behind part of its length essentially undeformed. For every tube D/t there exists a threshold of Lüders strain separating the two types of behavior. This bounding value of Lüders strain was studied parametrically