Question 1: Assume you are required to design a logic circuit enclosed in a black box to detect a password, which can be changed by an authorized administrator any time. The password is composed
of a squence of a 4-bit decimal number, i. e., each bit is in the range 'O' to '9' and sent in BCD format.
As stated above, the password should be suitable to change any time, i. e., while the initial password
can be "0120", it can also be replaced by "3456" any time by the administrator. In this design, you are
allowed to use only 4-bit parallel output shift-registers with a single-serial input data line and 4-bit
magnitude comparators. The password to detect is "1234".

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?