Alexandra Bellow (née Ionescu; born 1935) is a distinguished Romanian-American mathematician specializing in functional analysis, ergodic theory, and probability theory. Her work has significantly contributed to the fields of lifting theorems, martingale theory, and vector measures.
Born in Bucharest, Romania, Bellow pursued her higher education in mathematics, earning her Ph.D. from the University of Bucharest. She later immigrated to the United States, where she established a prominent academic career.
Bellow served as a professor of mathematics at Northwestern University from 1968 until her retirement as professor emerita in 2000. Prior to her tenure at Northwestern, she held positions at institutions such as Yale University and the University of Illinois at Urbana-Champaign.
Her research is particularly known for its depth and impact in several areas. She made foundational contributions to lifting theory, a branch of functional analysis that deals with the existence of measurable selections for various types of mappings. Her work on martingales, a concept central to probability theory, has also been highly influential, exploring their convergence properties and applications in other mathematical domains. Additionally, Bellow has conducted extensive research on vector measures, which generalize the concept of a measure to take values in a Banach space. She is recognized for her joint work with her late husband, mathematician Alberto Pedro Calderón, including contributions to what is known as the Calderón-Bellow theorem in functional analysis.
In recognition of her significant contributions to mathematics, Alexandra Bellow was an invited speaker at the International Congress of Mathematicians (ICM) in Vancouver in 1974. She was also awarded the Humboldt Prize for Senior U.S. Scientists in 1990, an honor given to internationally recognized scientists and scholars.