ABSTRACT
Poly (vinylidene fluoride) membranes were prepared by freeze-casting. The effects of PVDF concentration, and freezing temperature on the morphology, crystallization, and performance of prepared membranes were examined. Polymer concentration was varied from 10 to 25 wt%. The freezing temperature was varied from -5 to -25 °C. Dimethyl sulfoxide (DMSO) and distilled water were used as solvents and non-solvents, respectively. The first step of this study was devoted to estimating the optimal concentration of PVDF solution in DMSO. Membranes prepared at different ratios were characterized using physical and mechanical characteristics and porosity. The second step was to optimize the time required for the production of the membranes. In the third step, it was shown that the freezing temperature had a remarkable effect on the morphology of the membranes: as the temperature decreases, there is a transition from spherulite structures to interconnected pores. It was shown that the diversity in the pore pattern for PVDF affects remarkably the water permeability through the polymer membrane. During the monitoring of the spread of crystallized areas during the formation of the membrane, it was found that the crystallization of the solvent begins at localized points of the microscale, further crystallized areas spread radially or unevenly along the surface of the solution, forming contact borders, which can lead to changes in the properties of the membrane in its area.
ABSTRACT
The article presents the results of neuropsychological remote and face-to-face testing of 25 children aged 12 to 17 years in the nearest (during and 1-2 weeks after the treatment) and later period (2-12 months) after COVID-19 infection with predominant respiratory tract infection, organized in Ekaterinburg in the State Autonomous Institution "Children's Hospital â 8". Indication of family contact with patients with a new coronavirus infection was found in all patients, a positive nasopharyngeal swab for SARS-CoV-2 RNA by PCR was found in 58%, non-focal neurological complaints were found in 54% of children. The control group consisted of 25 pupils of Moscow comprehensive schools (14 girls and 11 boys) aged between 12 and 16 years who were examined before the pandemic. The methods included: investigation of the kinesthetic, spatial, dynamic, graphic praxis; auditory-motor coordination; visual, object-constructive gnosis; auditory-speech, visual memory; voluntary attention; thinking. Significant differences with the results of neuropsychological tests performed in children in the control group were found, allowing us to assert impairment of memory, attention, visual gnosis, visual-spatial function, kinesthetic and dynamic praxis, verbal and non-verbal component of thinking. According to A.R. Luria's theory, the topic of the disorders involves the temporo-parieto-occipital, mediobasal, frontotemporal parts of the brain, the reticular formation and limbic structures. This necessitates the development of corrective educational programs and an in-depth diagnostic algorithm that determines the morphological substrate of cognitive disorders in children, who have undergone COVID-19.
