On the Shelf Fierce Poise: Helen Frankethaler and 1950s New York By Alexander Nemerov Penguin Press: 288 pages, $28 If you buy books linked on our site, The Times may earn a commission from Bookshop.org, whose fees support independent bookstores. The cover of “Fierce Poise,” a new biography of the painter Helen Frankenthaler, features a famous photograph of the artist, …