Semi-conductors are made by adding impurities to silicon wafers. The silicon wafer is 0.1 cm thick and originally contains one phosphorus (P) atom for every 10 million Si atoms. After the diffusion process, there are 379 phosphorus atoms for every 10 million Si atoms at the top surface and the concentration at the bottom surface did not change. Calculate the concentration gradient in atomic percent/cm Note: The lattice constant of diamond cubic silicon is 5.4307 angstroms with 8 atoms per cell. The answer should have 3 decimals of accuracy.

Ashielded metal arc-welding operation is accomplished in a work cell by a fitter and a welder. the fitter takes 5.5 min to load components into the welding fixture at the beginning of the work cycle, and 1.5 min to unload the completed weldment at the end of the cycle. the total ength of the weld seams 1200 mm, and the travel speed used by the welder averages 300 mm/min. every 600 mm of seam length, the welding stick must be changed, which takes 0.8 min. while the fitter is working, the welder is idle (resting): and while the welder is working the fitter is idle. (a) determine the average arc-on time as a fraction of the work cycle time. (b) how much improvement in arc-on time would result if the welder used flux-cored arc welding (manually operated), given that the spool of weld wire must be changed every 10 weldments, and it takes the welder 5.0 min to accomplish the change? (c) what are the production rates for these two cases (weldments completed per hour)? attach your work and solutions.