no-arbitrage model

1. What is the difference between an equilibrium model and a no-arbitrage model?
2. Suppose that the short rate is currently 4% and its standard deviation is 1% per annum. What happens to the standard deviation when the short rate increases to 8% in (a) Vasicek’s model; (b) Rendleman and Bartter’s model; and (c) the Cox, Ingersoll, and Ross model?