Rapid variability in quasars indicates that the region in which the energy is generated must be small. you can show why this is true. suppose, for example, that the region in which the energy is generated is a transparent sphere 1 light-year in diameter. suppose that in 1 s this region brightens by a factor of 10 and remains bright for two years, after which it returns to its original luminosity. draw its light curve (a graph of its brightness over time) as viewed from earth.

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.

Alfred pushes on a heavy box, but cannot move it. the box has a lot of inertia motion friction gravity

Much of the information taught in earth-space science would not be available if it weren’t for our remote sensing abilities. explain two ways our remote sensing strategies contribute to our knowledge of these topics.