Researchers in microelectronics have found that a slight scratch on the surface of 5 pts. gallium arsenide causes a zinc dopant to diffuse into the arsenide. When these devices are baked at 850°C the dopant spreads. Its diffusion coefficient at this temperature is 10−11cm^2/s. If it spreads enough to increase the zinc concentrationto 10% of the maximum concentrationat 4×10^−4 cm away from the scratch the device is ruined. How long can we safely bake the device?

For the closed feedwater heater below, feedwater enters state 3 at a pressure of 2000 psia and temperature of 420 °f at a rate of ix10 ibhr. the feedwat extracted steam enters state 1 at a pressure of 1000 psia and enthalpy of 1500 btu/lbm. the extracted er leaves at an enthalpy of 528.7 btu/lbm steam leaves as a saturated liquid. (16) a) determine the mass flow rate of the extraction steam used to heat the feedwater (10) b) determine the terminal temperature difference of the closed feedwater heater