You have two features x_1x 1 = vibration intensity, and x_2x 2 = heat generated. both x_1x 1 and x_2x 2 take on values between 0 and 1 (and are strictly greater than 0), and for most "normal" engines you expect that x_1 \approx x_2x 1 ≈x 2 . one of the suspected anomalies is that a flawed engine may vibrate very intensely even without generating much heat (large x_1x 1 , small x_2x 2 ), even though the particular values of x_1x 1 and x_2x 2 may not fall outside their typical ranges of values. what additional feature x_3x 3 should you create to capture these types of anomalies:

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?