Given a scientific question, generate a correct answer to it.

Input: Consider Input: Solar cells create voltages directly from light, while thermoelectric devices create voltage from differences in what?

Output: temperature

Input: Consider Input: What did darwin call the evolutionary concept of change in populations over generations?

Output: descent with modifications

Input: Consider Input: Named after the dutch physicist, the van de graaff is a type of what device used for nuclear research?
Output: accelerator