ZDC SMD gain factor vs. time

1. Gain vs time for individual strips can be found at: https://drupal.star.bnl.gov/STAR/system/files/gain_1.pdf  
2. gain factor equal to zero is caused by very cold strip whose adc is below the slope fitting range. This can be fixed by re-running the calibration code. 
3. The axis is just sequence numbers, the corresponding time stamp and fill numbers can be found at one of the text files