Alexandra Bellow

Alexandra Bellow (1935 to 2025) was a Romanian-American mathematician who worked in ergodic theory, probability and analysis. Born Alexandra Bagdasar in Bucharest to physician parents, she took her degree at the University of Bucharest in 1957 and her doctorate at Yale in 1959 under Shizuo Kakutani, with a thesis on the ergodic theory of random series. After posts at Yale, Pennsylvania and Illinois she joined Northwestern University in 1967 and retired in 1996. With her first husband Cassius Ionescu-Tulcea she wrote a standard monograph on lifting theory and early work on Banach space valued martingales, and she later introduced uniform amarts. From the early 1980s her papers on pointwise convergence along sequences such as the squares and the primes revived limit theorems in ergodic theory, and she showed that lacunary sequences are bad universal sequences in L1. She later married Alberto Calderon and died in Chicago in 2025.