This issue is the second in a series of direct submissions making the Journal of Mathematical Sciences an excellent new platform for the publication of high-quality papers submitted by scientists from all over the world.

This issue consists of ten research articles and one review article. Many thanks to the multinational team of contributors who submitted manuscripts to this issue, including authors from Portugal, Israel, Russia, Kazakhstan, Argentina, China, Turkey, Uzbekistan, and Algeria.

The issue is a thematic one dedicated to Professor Stefan Samko. I am happy to express appreciation to the excellent team of guest editors, A. Almeida (Portugal), Z. Kusraeva (Russia), and H. Rafeiro (UAE), who collected the articles and organized peer-review process for the issue.

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Professor Stefan Samko, born on March 28, 1941, is a Russian and Portuguese mathematician. He is a world-leading specialist in various areas of analysis and applications, including fractional integrodifferentiation, theory of functions and function spaces, operator theory, analysis of variable order, and many other areas of mathematics. He supervised and led the work of numerous science students who now work in various countries of the world. I am honored to be among his students and call him my teacher. I will not dwell on the biography and scientific achievements of Professor Samko, since this issue contains a review article on the recent achievements of the professor, written by the guest editors, A. Almeida, Z. Kusraeva, and H. Rafeiro. There is also a previously published article by V. Kokilashvili dedicated to the 70th anniversary of S. Samko in Operator Theory: Advances and Applications, Vol. 229, 1–48, 2013 Springer Basel, by S. Rogosin (same volume, pages 49–63) and Editorial by V. Kiryakova in FCAA–Vol 24–2–2021 (with my participation) to mark the 80th anniversary of Stefan Samko, which presents the biography of S. Samko and achievements from the very beginning of his career.

It should be noted that this thematic collection was preceded by the activities within the framework of the OTHA international conference in 2021 which was dedicated to the 80th anniversary of S. Samko. It is worth mentioning that a series of international conferences OTHA emerged as a result of a real interest in regular face-to-face communication between mathematicians from Russia and abroad, united by long-standing scientific contacts. This interest was clearly manifested during the first conference, which had been planned in 2011 as a seminar devoted to the 70th anniversary of S. Samko, which eventually grew into a large-scale conference. We rightly call S. Samko the scientific father of the OTHA conference series. The conference in 2021 was held in a mixed online and offline format, and among online plenary speakers were Hans Feichtinger (Austria), Virginia Kiryakova (Bulgaria), Carlo Sbordone (Italy), Eichi Nakai (Japan), and Yoshihiro Sawano (Japan). I will not list all the plenary lecturers as well as participants with session talks from Armenia, Belarus, Kazakhstan, Mexico, Portugal, Spain, Sweden, UAE, and USA, who took part in the conference in person, but this does not diminish their significant contribution.

This is not the only collection that has been prepared as a thematic issue related to research interests and achievements of S. Samko. An analogous thematic issue was prepared for publication under the editorship of A. Karapetyants, V. Kravchenko, and E. Liflyand in the Journal of Fourier Analysis and Applications (JFAA). We, the guest editors, are grateful to the EiC of JFAA, Professor Hans G. Feichtinger, for giving us this great opportunity.

I am convinced that this thematic issue and the one in the JFAA will form an excellent scientific information platform for supporting and developing areas of analysis related to the theory of functions and spaces, including those with variable parameters, the theory of non-standard growth spaces, Fourier analysis, and harmonic analysis in general.

Sincerely yours,

Alexey Karapetyants,

Editor-in-Chief Journal of Mathematical Sciences, Series A