There haven't been any live public performances at America's biggest arts center since mid-March. But New York's Lincoln Center has been hosting some free mini concerts for healthcare providers, teachers and other essential workers, featuring just one or two volunteer musicians and audiences of five, max. The musicians are volunteers from the New York Philharmonic, one of Lincoln Center's constituent organizations. One of the performers is Kuan Cheng Lu, a Taiwanese first violinist who joined the orchestra 16 years ago. On a recent Friday evening, he chose to play some solo Bach.