Which option identifies the type of study described in the following scenario? A group of 50 men are being studied. Of those men, 25 have heart disease and 25 do not. The groups of men are as similar as possible in every other way: race, diet, socioeconomic status, marital status, etc. The researchers are trying to determine what caused the 25 men to develop heart disease when 25 other men did not. They ask the men a lot of questions about their life and experiences to try to determine what could have caused these differences. Prospective cohort study Randomized controlled trial Historical cohort study Case study

As part of an industrial process, air as an ideal gas at 10 bar, 400k expands at steady state through a valve to a pressure of 4 bar. the mass flow rate of air is 0.5 kg/s. the air then passes through a heat exchanger where it is cooled to a temperature of 295k with negligible change in pressure. the valve can be modeled as a throttling process, and kinetic and potential energy effects can be neglected. (a) for a control volume enclosing the valve and heat exchanger and enough of the local surroundings that the heat transfer occurs at the ambient temperature of 295 k, determine the rate of entropy production, in kw/k. (b) if the expansion valve were replaced by an adiabatic turbine operating isentropically, what would be the entropy production? compare the results of parts (a) and (b) and discuss.