Alright, I've actually looked into this myself since I was deciding on whether to take 20c and 10c (Bio major).
Alright so here's basically all I know...
Popescu, won't say much look for yourself though!
Link:
Christian Popescu - University of California San Diego - RateMyProfessors.com
From what I know, Zhang taught at Rutgers University at the math department, no real ratings exist for her though, so taking her is a bet.
Kadison taught at UPenn in the mathematics department, though he has no ratings available through RMP or any other known site. So enrolling in his class is a bet too...
Try looking through the UCSD Mathematics Department site.
This link,
http://math.ucsd.edu/people/index.ph...sitors_by_type, looks kind of interesting, tells you where their office hours are (but not when), their position, and basic contact information if it's available.
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