doubts in output of ps

[Sreeramkr <Sreeramkr@xxxxxxxx>]

Hi,
	I am reposting this mail again. 

well I have a small doubt.

when i do ps -al ti shows this. 

F	S	UID	PID	PPID	C	PRI	NI	ADDR	SZ
WCHAN		TTY	TIME		CMD
00	A	501	286	274	0	75	0	-	443
wait4		tty1	00:00:00	bash
00	S	501	729	601	0	69	0	-	266
nanos1	tty1	00:00:00	a.out
44	Z	501	730	729	0	69	0	-	0
do_exit	tty1	00:00:00	a.out<defunc>

I have the following doubts

Actually I have forked a.out and the child returned while parent is doing
something. 

what is F, C, NI, WCHAN

also y are some of these values 0. and what is time here? and why is it
zero?

what does sz refer to? is it the size of the file? and y is it 0 incase of
child which is defunc

after the parent exited I did ps again
I saw the priority for bash being changed to something else. how is this
possible? y is it changing? arent the priorities fixed? or does teh kernel
keeps changing the priorities dynamically? Please throw some light on this.
I mean why it has to do this? 


I hope I can get teh answer

TIA

Regards
sreeram