автор: Dorian Popa

​Janusz Brzdek has published numerous papers on Ulam type stability (e.g., of functional, difference, differential and integral equations), its applications and connections to other areas of mathematics. He has been editor of several books and special volumes focused on such subjects. He was the chairman of the organizing and/or scientific committees of several conferences on Ulam type stability and on functional equations and inequalities. Dorian Popa is the author of numerous papers on Ulam type stability of functional equations, differential equations, linear differential operators, and positive linear operators in approximation theory. Other papers deal with the connections of Ulam type stability with some topics of multivalued analysis (e.g., the existence of a selection of a multivalued operator satisfying a functional inclusion associated to a functional equation). Themistocles M. Rassias published more than 300 papers, 10 research books and 45 edited volumes in research Mathematics as well as 4 textbooks in Mathematics (in Greek) for university students. His research work has received more than 15, 000 citations according to Google Scholar and more than 4, 900 citations according to Math Sci Net. His h-index is 44. He serves as a member of the Editorial Board of several international mathematical journals. His publications have strongly influenced the development of the theory of Ulam stability.