VGT turbochargers

Hello, I'm struggling with report for my studies about difference between VGTs turbochargers with adjustable nozzle and VGTs with sliding ring. As the 1st one is quite common, all the schemes, descriptions, performance graphs and comparissons to FGTs are quite easy to find. The 2nd type is usually applied to some heavy duty engines and rarely mentioned anywhere. Do you have any links/ publications that might help me to understand its idea and all differences between those 2?