Question: A drug is injected into a patient's blood vessel. The function c = f(x, t) represents the concentration of the drug at a distance x mm in the direction of the blood flow measured from the point of injection and at time t seconds since the injection. What are the units of the following partial derivatives? What are their practical interpretations? What do you expect their signs to be?
(a) ∂c/∂x
(b) ∂c/∂t