General :: Ways To Get In-depth Knowledge Of OS

I'm currently trying to find ways to get in-depth knowledge of the Linux OS. To give a brief overview of where I am at right now, I am a computational science graduate student who does all of his work on *nix scientific clusters.I also took a lot of computer engineering and computer science courses in college, as well as being the stereotypical standard computer nerd growing up, so I'm somewhat familiar with computer architecture, though more from the hardware side.So I'm familiar (though I wouldn't claim to be an expert quite yet, by any means) with using Linux and C programming, and I have a basic grasp of generic computer architecture, but what I feel I really lack knowledge in is the specific details of the Linux. All the details of the boot process, exactly what the kernel does, how Linux handles memory management, etc. I'm having difficulty finding any information on this;all I can find is generic information targeted towards people who are just starting out, and the stuff I've found that talks about the kernel seems more oriented towards "you change setting X and Y happens" rather than what the kernel is doing.