Misc: What does the abbreviation "i.o.u." Really stand for?

Questions

In 1918 USSR ---------- conversion. ?

In 1929 St. Valentine's Day ---------- in Chicago, 7 gangsters killed by rivals disguised as cops (The Night Chicago Died). ?

In 1934 Florence ---------- (in Indiana), actress (Alice in The Brady Bunch), born. ?

In 1946 Gregory---------- , actor, dancer, born. ?

In 1961 Element 103, ---------- , first produced in Berkeley, California lab. ?