Dispersion of graphite nanoplates in polypropylene by melt mixing: the effects of hydrodynamic stresses and residence time

This work combines experimental and numerical (computational fluid dynamics) data to better understand the kinetics of the dispersion of graphite nanoplates in a polypropylene melt, using a mixing device that consists of a series of stacked rings with an equal outer diameter and alternating larger and smaller inner diameters, thereby creating a series of converging/diverging flows. Numerical simulation of the flow assuming both inelastic and viscoelastic responses predicted the velocity, streamlines, flow type and shear and normal stress fields for the mixer. Experimental and computed data were combined to determine the trade-off between the local degree of dispersion of the PP/GnP nanocomposite, measured as area ratio, and the absolute average value of the hydrodynamic stresses multiplied by the local cumulative residence time. A strong quasi-linear relationship between the evolution of dispersion measured experimentally and the computational data was obtained. Theory was used to interpret experimental data, and the results obtained confirmed the hypotheses previously put forward by various authors that the dispersion of solid agglomerates requires not only sufficiently high hydrodynamic stresses, but also that these act during sufficient time. Based on these considerations, it was estimated that the cohesive strength of the GnP agglomerates is in the range of 5-50 kPa.This research was funded by FCT (Portuguese Foundation for Science and Technology) through scholarship SFRH/BPD/100353/2014 and projects UIDB/00013/2020 and UIDP/00013/2020. This work was also funded by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the projects UID-B/05256/2020 and UID-P/05256/2020

Improving effectiveness of scoliotic posture prevention and correction in primary school children

For several decades the problem of prevention and correction of posture disorders in primary school children has not lost its relevance. Statistics show that 68-94 % of primary school students have posture disorders. A special place in the classification of posture disorders is occupied by a scoliotic posture. Such a statement indicates that health improving physical education does not fully solve the tasks assigned to it. Analysis of literature sources allowed us to establish two main reasons for the low effectiveness of prevention and correction of scoliotic posture in primary school children. The first reason relates to the low effectiveness of early diagnosis scoliotic posture, and the second reason is low overage of the aspects of the problem, revealing the model of periodization of fitness training with the children in the theory and practice of physical culture. The results of previous studies have allowed us to suggest ways to improve the effectiveness of prevention and correction of scoliotic posture in primary school children, namely: to expand the range of traditional methods of early diagnosis of scoliotic posture through motor and postural diagnostics; to use a nonlinear model of periodization of physical activity to create optimal conditions for leveling muscle imbalance and the formation of rational motor automatisms and patterns in the context of health training

The Role of Acidosis in the Pathogenesis of Severe Forms of COVID-19

COVID-19 has specific characteristics that distinguish this disease from many other infections. We suggest that the pathogenesis of severe forms of COVID-19 can be associated with acidosis. This review article discusses several mechanisms potentially linking the damaging effects of COVID-19 with acidosis and shows the existence of a vicious cycle between the development of hypoxia and acidosis in COVID-19 patients. At the early stages of the disease, inflammation, difficulty in gas exchange in the lungs and thrombosis collectively contribute to the onset of acidosis. In accordance with the Verigo-Bohr effect, a decrease in blood pH leads to a decrease in oxygen saturation, which contributes to the exacerbation of acidosis and results in a deterioration of the patient’s condition. A decrease in pH can also cause conformational changes in the S-protein of the virus and thus lead to a decrease in the affinity and avidity of protective antibodies. Hypoxia and acidosis lead to dysregulation of the immune system and multidirectional pro- and anti-inflammatory reactions, resulting in the development of a “cytokine storm”. In this review, we highlight the potential importance of supporting normal blood pH as an approach to COVID-19 therapy