Today I held a presentation (pps, 803 kB) based on Aghion and Howitt's seminal article A Model of Growth Through Creative Destruction (Econometrica, 1992). The presentation was optimized for an online audience, i.e. you'll understand the whole model by just going through the slides. During the presentation I also mentioned Aghion's speech "Growth and Education: Gerschenkron meets Schumpeter". I blogged about it here.

PS: There is one important derivation you find neither in their 1992 article nor in their textbook Endogenous Growth Theory. Since I have written it on the blackboard during the presentation I'll replicate it here:

Expected welfare is

Given that the innovation process is Poisson with parameter λφ(n) and the stock of technology A_t grows geometrically we have

"Factoring out" multiplicative constants yields

Since

and ∫e^-axdx = 1/a we get