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It is well known that a reactor is stable if the core reactivity decreases with the core power. This is the case for many types of reactors, including the PWR. However, this was not the case for the RBMK (Reaktor Bolshoy Moshchnosti Kanalniy) which could be unstable at low power. What does it mean precisely? By using a 2 × 2 system of non-linear ordinary differential equations we show that naturally (i.e. without using the control rods), with the same reactivity injection, if the initial power is lowered, then the final power may be higher, which is a rather unusual behaviour.

The paper presents the findings of the study of the manifestation of state and trait anxiety and its features in adolescent athletes with different profiles of dispositional optimism. A total of 136 respondents (78 boys, 58 girls) aged 13-14 years were involved in the study. They were engaged in various sports, team and individual. It was found that adolescent athletes with optimistic expectations had a normal level of state and trait anxiety, their peers with pessimistic expectations had a higher level of state anxiety and had an increased level of trait anxiety. During the training sessions, the highest rates of state anxiety were found in adolescents of team sports with undifferentiated expectations, and the highest rates of trait anxiety were found in adolescents of individual sports with pessimistic expectations. Representatives of individual sports with undifferentiated expectations had the lowest rates of state and trait anxiety. [ABSTRACT FROM AUTHOR]

We studied the long-term population dynamic's (2005-2020) of six main insect pests of winter wheat (late wheat shoot fly, hessian fly, frit flies, cereal beetles, corn ground beetle and sun pest) in three climatic zones of Ukraine under conditions of increasing areas of application pesticides and global warming. The aim of the research was to investigate how these factors influence pest population dynamics. Comparison of sums of effective temperatures (SET) with standard values for different zones indicates significant climate warming over the past 15 years. Correlation analysis with two variables showed a general decrease in the numbers of most populations, especially in the steppe and forest-steppe zones. [ABSTRACT FROM AUTHOR]

There are a lot countries which use measures to prevent spread of coronavivus infection COVID 19 caused by SARS-CoV-2. But despite of this pandemic continues. Particularities of sports activities include systematic contact with significant numbers of people, regular visits to other countries and cities for participation in competitions. It means sportsmen are in group of increased risk of infection and spread of COVID 19. For safe participation it is important to know measures which are implemented by countries for epidemic control, to study dynamics of indicators, that characterize epidemic process, to investigate effectiveness used preventive measures and possibility to assess potential risks being sportsmen in particular country. Purpose of research. To assess risks of infection COVID 19 in process of sport activities and to study influence of economics and demographic indicators and level of vaccination spread on area and speed of COVID-19. Background. To overcome the epidemic of COVID-19, it is important to study the dynamics of indicators that characterize the epidemiological process. Material and methods. We analyzed the indicators of 100 countries of the world, which on 03/25/2020 topped the rating by the number of infected people in the country. There were analysis and synthesis of literature, Internet resources, statistical methods among research methods. Results. It was found that the economic and demographic indicators of the country do not affect the incidence of COVID-19 however effect on the proportion of population coverage with vaccinations. At the beginning of the study (03/25/2020), in countries with higher economic and demographic indicators, the spread of coronavirus occurred at a slower pace, but now (11/14/2021) the economic and demographic indicators do not affect the country's place in the ranking by the number of infected. The increase in the number of infected and the death rate from coronavirus in the world leads to an increase in the amount of vaccine used. Conclusions. It has been proven that an increase in the number of used vaccines leads to a decrease in the country's place in the ranking in terms of the number of infected. Vaccination is an effective measure to stop the spread of infection in the world. [ABSTRACT FROM AUTHOR]