[Life expectancy for the regions of the Northwestern Federal District. Part 2: Dynamics of old age threshold.].

The paper continues the study of the population ageing in the regions of the Northwestern Federal District. It characterized population ageing based on prospective ageing indicators that take into account remaining life expectancy. The dynamics of life expectancy (LE) at birth was analyzed.

[Life expectancy for the regions of the Northwestern Federal District. Part 1: Dynamics of life expectancy at older ages.].

When studying the process of population ageing, much attention is invariably paid to mortality and its generalizing characteristic, life expectancy (LE). The dynamics of LE of men and women at older ages in the regions of the North-Western Federal District has been analyzed. It is shown that in all the regions considered, in all considered older ages, life expectancy decreased at the beginning of the reform period, then from the beginning of the 2000s it grew until 2019, after which it decreased.

[Effects of socio-economic factors on old-age mortality in Russia.].

Studies of old-age mortality are an important part of demography, especially the demography of ageing. Demographic development of Russia is characterized by heterogeneity including regional differences in mortality. The aim of the paper is to analyze the dependence of mortality at old-age groups on socio-economic indicators.

[On the use of mathematical statistics methods in clinical and experimental studies.].

In the paper a number of issues, including conceptual ones, related to the specific features of making statistical decisions, choosing tests and computing characteristics that will strengthen the evidence base of the conclusions obtained when analyzing data using methods of mathematical statistics, are considered. The paper aims not to describe the methods of mathematical statistics themselves, but to analyze the conditions and the need to apply the most common tests. In particular, the magnitude of the indicator of the statistical significance of the observed effects - p-value - and the sample size to obtain a significant effect are discussed, the effect of multiple comparisons, the application of the Bayesian approach, and others are considered.

Influence of self- and cross-phase modulations on an optical frequency doubling process for metamaterials.

In the process of doubling the frequency of high-power laser radiation in metamaterials, the self- and cross-phase modulations associated with the cubic nonlinearity of the medium are studied in the constant-intensity approximation. It is assumed that the pump wave propagates in a region with negative refraction. It is shown that in the case of a nonlinear-optical process of frequency doubling of an intense light wave in a metamaterial, it is important to take into account the self-action and cross-interaction effects that directly affect the optimal phase relationship between the interacting waves.