We examine when a matrix whose elements are differentiable functions in one variable commutes with its derivative. This problem was discussed in a letter from Issai Schur to Helmut Wielandt written in 1934, which we found in Wielandt’s Nachlass. We present this letter and its translation into English. The topic was rediscovered later and partial results were proved. However, there are many subt...

Let A and B be n × n matrices, let C = ABA−1B−1 be the multiplicative commutator of A and B, and assume AC = CA. Olga Taussky (1961) examined the structure of A and B for the case where A and B are unitary. Marcus and Thompson (1966) generalized her results to the case where A and C are assumed normal. We look at this problem for general A, with particular attention to the cases where A is diag...

Three species of the sea stars are reported from the waters of the northwestern Pacific. These species were referred by earlier authors as Henricia spiculifera or H. leviuscula spiculifera. Two of them, H. lineata and H. uluudax, were recently described from the Aleutian Islands. These species are reported for the first time from the western Pacific (southeastern Kamchatka shore, Commander Isla...

Alexander Fradkov*. Olga Tomchina** Viktoria Galitskaya***. Dmitry Gorlatov****  * Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, Saint Petersburg, Russia (Tel: 812-321-4410; e-mail: [email protected]) ** Saint Petersburg State Polytechnical University, Saint Petersburg, Russia (e-mail: [email protected]) *** Saint Petersburg State Polytechnical University, Saint P...

The paper describes the professional activities and merits of pediatric surgeon Olga G. Mokrushina in celebration her anniversary.