Acase-control study was conducted to assess whether occupational radiation exposure among men was associated with down syndrome in their children. the investigators matched cases and controls on age of the mother at childbirth by 5-year categories. why was this done?

(a) to minimize recall bias of exposure
(b) to minimize detection bias for cases
(c) to minimize differential misclassification of exposure
(d) to remove selection bias of non-radiation exposed fathers
(e) to provide dose-response information

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite

Water at 55c flows across a flat plate whose surface temperature is held constant at 95c. if the temperature gradient at the plate's surface for a given value of x is 18 c/mm, find a) local heat transfer coefficient. b) heat flux

A2-m rigid tank initially contains saturated water vapor at 100 kpa. the tank is connected to a supply line through a valve. steam is flowing in the supply line at 600 kpa and 300 c. the valve is opened, and steam is allowed to enter the tank until the pressure in the tank reaches the line pressure, at which point the valve is closed. a thermometer placed in the tank indicates that the temperature at the final state is 200°c. determine (a) the mass of steam that has entered the tank (b) the amount of heat transfer.