ASSESSMENT OF CHANGES IN HEART RATE VARIABILITY INDICES OF STUDENTS AFTER COVID-19 LOCKDOWN: A COHORT STUDY.

Introduction: The objective of this study was to investigate the heart rate variability indicators of students who had contracted COVID-19 after performing physical activity. The aim was to uncover the potential cardiac complications and dysregulations of the autonomic nervous system.

Material And Method: We explored about 11 heart rate variability indicators and their changes immediately after a 5-minute physical activity performed by using Proteus pes 3320 bicycle odometer.

Peculiarities of the Phase Formation during Electroconsolidation of AlO-SiO-ZrO Powders Mixtures.

This paper is devoted to the sintering process of AlO-SiO-ZrO ceramics. The studied method was electroconsolidation with directly applied electric current. This method provides substantial improvements to the mechanical properties of the sintered samples compared to the traditional sintering in the air.

Activated Sintering of CrO-Based Composites by Hot Pressing.

The paper presents and discusses questions on structure formation during the sintering process of CrO-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because CrO decomposes when sintered at temperatures above 1300 °C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter.

Analysis of the Electroconsolidation Process of Fine-Dispersed Structures Out of Hot Pressed AlO-WC Nanopowders.

Fabrication of alumina-tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after a temperature of 1000 °C was reached.

Wear Resistance of the Glass-Fiber Reinforced Polymer Composite with the Addition of Quartz Filler.

The paper presents the results of investigations on the glass fiber reinforced composite for the floor panels with quartz powder additions of different percentages in terms of wear resistance, friction coefficient, hardness, and strength. The wear resistance was assessed using the specific wear work parameter determined by the novel tribotester with friction band. It was found that an increase in quartz powder addition to the tested polymer composite does not enhance its mechanical increasingly properties.

Feasibility of Cobalt-Free Nanostructured WC Cutting Inserts for Machining of a TiC/Fe Composite.

The paper presents results of investigations on the binderless nanostructured tungsten carbide (WC) cutting tools fabrication and performance. The scientific novelty includes the description of some regularities of the powder consolidation under electric current and the subsequent possibility to utilize them for practical use in the fabrication of cutting tools. The sintering process of WC nanopowder was performed with the electroconsolidation method, which is a modification of spark plasma sintering (SPS).

Novel Microwave-Assisted Method of Y2Ti2O7 Powder Synthesis.

In the paper, a novel technique for highly dispersed pyrochlore YTiO is proposed. The experimental results proved that the application of microwave irradiation at a certain stage of calcination allowed synthesizing of YTiO in much shorter time, which ensured substantial energy savings. An increase up to 98 wt.

Effect of SiC Addition to AlO Ceramics Used in Cutting Tools.

In this study, the effect of the addition of silicon carbide to alumina ceramics commonly used in cutting tool applications is addressed. Performance of AlO-SiC composite cutting inserts during the machining of hardened steels and ductile iron was compared to the results obtained for a cutting tool made out of 99 wt.% AlO, AlO-TiC, AlO-TiC-ZrO, and AlO-TiN.

Effect of Yttrium and Rhenium Ion Implantation on the Performance of Nitride Ceramic Cutting Tools.

In the paper, the results of experimental investigations of ion implanted cutting tools performance are presented. The tools, made out of SiN with additives typically used for turning of Ti-6Al-4V alloy, underwent implantation with ions of yttrium (Y) and rhenium (Re) using the metal vapor vacuum arc method. Distribution of ions on the tool surface was measured.

[Sedative effect of lavender during physical loads].

There was investigated the dynamics of the functional state of the cardiovascular system of students after bicycle exercise load, followed by cold inhalation of lavender oil. Examinations were performed in the first half of the day at the same time, three times: 1) before exercise load (the state ofphysiological norm); 2) immediately after the load for 15minutes on the bike training apparatus «Proteus Pec 3320» in the third position, followed by aromatherapy; 3) at the 15 minute of the post-exercise load recovery period. Aromacorrection was executed by the method of cold inhalation.

[The levels of electrolytes and nitric oxide in saliva of students under mental-emotional exertion].

The influence of examination-induced psycho-emotional stress on students' hemodynamic parameters, nitric oxide (NO) level and electrolyte composition of saliva was investigated. Before examinations, the examinees with a sympathotonic response (75.0%) showed the increase of heart rate levels and blood pressure indices, the decline of salivary NO excretion that was retained within 24-hours after an exam.

[Effect of stevia on the picture of peripheral blood under exposure to vibration].

There were investigated changes in the peripheral blood of rabbits under prolonged exposure to vibration (5, 10, 20, 30 days). In a separate series of experiments, the nature of changes in the peripheral blood was investigated under the combined action of vibration and stevia leaves. Contained in stevia biologically active substances were found to accelerate metabolism in bone marrow stem cells, promote the compensatory ability of the organism, thereby providing the resistance of the body to the vibration factor.

The obtaining of high-density specimens and analysis of mechanical strength characteristics of a composite based on ZrO2-WC nanopowders.

The structures, processes of shrinkage, and phase composition of the compact system ZrO2-WC, obtained by hot pressing with the transmission of high current, are considered in the article. We found that as a result of compaction, the ZrO2-WC-ceramics have uniform density distribution, with the following optimal mode consolidation values T = 1,350°C, P = 30 MPa and t = 2 min. These conditions allow us to achieve the best combination of ceramic properties by criteria density and strength.

Effect of licorice root on peripheral blood indexes upon vibration exposure.

We studied the effect of continuous vibration and treatment with licorice root (Glycyrrhiza glabra L.) on peripheral blood red cells in rabbits. Active substances of licorice root accelerated metabolism in cells of the bone marrow erythroid stem, enhanced compensatory reserve of the organism, and increased animal's resistance to stress.

Responses of hypothalamic neurons to stimulation of the vestibular nerve and lateral vestibular nucleus in the rabbit.

Acute experiments were performed on rabbits to study the responses of neurons in the anterior, ventromedial, and posterior nuclei of the hypothalamus to single, paired, and rhythmic stimulation of the vestibular nerve and lateral vestibular nucleus of Deiters. The data obtained showed that neurons of the posterior nucleus of the hypothalamus were the most sensitive. Three types of response were seen from hypothalamic neurons, with short, long, and intermediate latent periods.