What do you think caused NO2 and CO2 levels to decrease between winter 2019 and winter 2020? (Particularly in high population areas such as China and the United States?) *

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.

Aball horizontally thrown from a cliff at 8m/s

Is the portion of the electromagnetic spectrum that has a frequency just above that of visible light.