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In this work, we apply the Particle Finite Element Method (PFEM) and Smoothed Particle Hydrodynamics (SPH) to simulate the orthogonal cutting chip formation of two workpiece materials, i.e., AISI 1045 steel and Ti6Al4V titanium alloy. A modified Johnson-Cook constitutive model is used to model the plastic behavior of the two workpiece materials. No damage or strain softening is included in the model. The friction between the workpiece and the tool is modeled following Coulomb's law with a temperature-dependent coefficient. The accuracy of PFEM and SPH in predicting thermomechanical loads at various cutting speeds and depths against the experimental data are compared. The results show that both numerical methods can predict the rake face temperature of AISI 1045 with errors less than 34%. For Ti6Al4V, however, the temperature prediction errors are significantly higher than those of the steel alloy. Errors in force prediction were in the range of 10% to 76% for both methods, which compare very well with those reported in the literature. This investigation infers that the Ti6Al4V behavior under machining conditions is difficult to model on the cutting scale irrespective of the choice of numerical method.
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Negative impacts are caused by oil spills on coastal ecosystems. In the phenomenon of oil spreading, the knowledge of the physical properties of the pollutant, such as velocities and positions, is of fundamental importance for the adoption of timely contingency measures to protect the environment (Fraga Filho, Smoothed Particle Hydrodynamics: Fundamentals and Basic Applications in Continuum Mechanics, 2019). This paper presents a Lagrangian particle modelling for the prediction of the oil slick diameter in the first stage of the oil spreading on a calm sea. At the first studies on the oil spreading (Fay, The Spread of Oil Slicks on a Calm Sea, 1969; Fay, Physical Processes in the Spread of Oil on a Water Surface, 1971), curves were adjusted to laboratory experimental data. The modelling employed in this work is based on the continuum Navier-Stokes equations, and the Smoothed Particle Hydrodynamics (SPH) method has been used to obtain the solution for the conservation equations of mass and momentum. The oil-water interface was treated using a reflective treatment. The solution achieved was compared to the oil slick diameter predicted by Fay's equation, and an error lower than 1% was found.
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Ecosistema , Contaminación por Petróleo , Gravitación , Modelos Teóricos , Contaminación por Petróleo/análisis , AguaRESUMEN
Recent seroprevalence studies in animals detected Rocio virus in regions of Brazil, indicating risk for re-emergence of this pathogen. We identified Rocio virus RNA in samples from 2 human patients for whom dengue fever was clinically suspected but ruled out by laboratory findings. Testing for infrequent flavivirus infections should expedite diagnoses.
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Dengue , Epidemias , Flavivirus , Animales , Brasil/epidemiología , Dengue/diagnóstico , Dengue/epidemiología , Flavivirus/genética , Humanos , Estudios SeroepidemiológicosRESUMEN
Iron accumulation and oxidative stress are hallmarks of retinas from patients with age-related macular degeneration (AMD). We have previously demonstrated that iron-overloaded retinas are a good in vitro model for the study of retinal degeneration during iron-induced oxidative stress. In this model we have previously characterized the role of cytosolic phospholipase A2 (cPLA2) and calcium-independent isoform (iPLA2). The aim of the present study was to analyze the implications of Group V secretory PLA2 (sPLA2), another member of PLA2 family, in cyclooxygenase (COX)-2 and nuclear factor kappa B (NF-κB) regulation. We found that sPLA2 is localized in cytosolic fraction in an iron concentration-dependent manner. By immunoprecipitation (IP) assays we also demonstrated an increased association between Group V sPLA2 and COX-2 in retinas exposed to iron overload. However, COX-2 activity in IP assays was observed to decrease in spite of the increased protein levels observed. p65 (RelA) NF-κB levels were increased in nuclear fractions from retinas exposed to iron. In the presence of ATK (cPLA2 inhibitor) and YM 26734 (sPLA2 inhibitor), the nuclear localization of both p65 and p50 NF-κB subunits was restored to control levels in retinas exposed to iron-induced oxidative stress. Membrane repair mechanisms were also analyzed by studying the participation of acyltransferases in phospholipid remodeling during retinal oxidation stress. Acidic phospholipids, such as phosphatidylinositol (PI) and phosphatidylserine (PS), were observed to show an inhibited acylation profile in retinas exposed to iron while phosphatidylethanolamine (PE) showed the opposite. The use of PLA2 inhibitors demonstrated that PS is actively deacylated during iron-induced oxidative stress. Results from the present study suggest that Group V sPLA2 has multiple intracellular targets during iron-induced retinal degeneration and that the specific role of sPLA2 could be related to inflammatory responses by its participation in NF-κB and COX-2 regulation.