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Samuil Kaplan (1921-1978) was a productive and famous astrophysicist. He was affiliated with a number of scientific centers in different cities of the former Soviet Union. During the earliest 13 years of his career, namely in 1948-1961, he worked at the Lviv University in Ukraine. In the present paper, the Lviv period of his life and scientific activity is described on the basis of archival materials and his published studies. Kaplan arrived in Lviv in June 1948, the same month when he obtained the degree of the Candidate of Science. He was a head of the astrophysics sector at the Astronomical Observatory of the University, a professor of the department for theoretical physics, as well as the founder and head of a station for optical observations of artificial satellites of the Earth. He was active in the organization of an astronomical observatory outside the city. During the years in Lviv, Kaplan wrote more than 80 articles and 3 monographs in 9 areas. At that time, his focus was on the stability of circular orbits in the Schwarzschild field, on the white dwarf theory, on space gas dynamics, on cosmic plasma physics and turbulence, on the acceleration of cosmic rays, on the physics of interstellar medium, on the physics and evolution of stars, on cosmology and gravitation, and on the optical observations of the Earth's artificial satellites. Some of his findings are fundamental to the development of theory in those fields as well as of observational techniques. The paper presents a complete bibliography of Kaplan's works published during the Lviv period and reviews his respective scientific achievements in the light of the current state of research in those areas. [ABSTRACT FROM AUTHOR]

Precise analysis of complex gas mixtures is an urgent task today, since its accuracy and quality is important not only for human health, but also for the ecology of population centers or the planet as a whole. Traditional methods of gas environment analysis are imperfect, and those that have the necessary sensitivity and selectivity do not yield results in a particularly short time. Nowadays, the Fabry- Pérot interferometry is used for research in a significant number of industrial and scientific areas. The analysis of the works presented in this paper confirms the relevance of research in the field of multibeam interferometry and the prospects of developing modifications of the Fabry- Pérot interferometer. The article is devoted to classical optical correlation methods for the analysis of gas mixtures with a quasi-periodic structure of the spectrum. A modification of the analyzer was developed and it was shown that the use of the modified Fabry- Pérot interferometer as a correlation mask ensures the express realization of the selectivity of the measurement components. An experimental study was conducted to test the possibility of scanning the SO2 absorption spectrum in the 220 nm region. Laboratory tests of the described layout of the SO2 analyzer demonstrated its high metrological parameters. The main reported error was 1% on the 0 -10000 ppm scale and 10% on the 0 -1000 ppm scale. The length of the cuvette was 170 mm, the warm-up time of the model was 30 minutes, the minimum measured concentration was 25 ppm. We can state that the correlation masks based on the IFP can be widely used for the analysis of gas components with a quasi-periodic structure of the spectrum. Compared to other devices of a similar type, they have a much higher luminous intensity: U = ΩA, where Ω is the solid angle; A is the light diameter of the IFP with the same resolution. This is crucial for remote instruments [V. R. Kozubovskii, Yu. Yu. Bilak, Ukr. J. Phys. 66, 664 (2021)]. In addition, their small weight and dimensions allow one to create portable devices based on them. However, since the IFP is a multi-beam interferometer, the procedure for optimizing its parameters is rather complicated, although technical methods for solving this problem exist [V. R. Kozubovskii, V. L. Goldovskii, O. D. Kraysler, AS 1182345 USSR, MKI G01N 21/61]. The conducted analysis and research open up new opportunities for the optimization of interferometric devices and interferometric methods of gas analysis. [ABSTRACT FROM AUTHOR]