The first is more a circle packing (there are also lot of example) and the last is just concentric circle.
Come on you can surely do the last 
if there is n concentric circles, separated by a distance dx, what is the number of circular dot on each circle. Knowing that image sampler default output is within a square with a corner at (0,0) and the other at (1,1). Where is the center on the image ? What is the radius of the greater circle ? Basic math ?
I used mesh instead of dot. I have always big problem with dots display !!!
