SIXTEENTH NOTES!?!?!
You've gotta be kidding, buddy. Ok, here are a few tips.
Please bear in mind that the highest note realistically achievable on a double bass is G, the open string.
If you write notes faster than 60 bpm, we'll run into some serious problems. This is due to the limitations of the double bass bow. It just doesn't respond well to anything faster than that.
Slower that 40? No. The bass bow is quite short, and the strings are really long. This means long notes are very challenging, and should be avoided.
Preferred notes are E, A, D and G. Please try to avoid accidentals when writing for bass, as this usually involves the use of the left hand, which is notoriously tricky.
Because the bass is so big, the realistic dynamics options available are: (a) Loud.
Also bear in mind that due to the size and register of the bass, it usually takes about 3 to 4 seconds for notes to actually sound, so, traditionally the cellos play the start of the note, and we kind of sneak in underneath at some vague point. Just make sure you don't write any separate lines for us. This is a terrible mistake.
Also, when writing exposed pizzicati, DON'T give it to the basses: it's physically impossible to get multiple basses playing a pizz at the same time. This is because of the length of the string, it makes it really really hard, unlike violins, which are tiny, and a breeze to play. Give it to them instead.
Also, if you HAVE to writing something loud and just for basses and celli (of course with celli NEVER solo basses), best add in some brass to 'smooth out' the intonation. Basses, when played loud, are really, really hard to get to sound in tune. Especially if there are more than about 1 of us, but even with 1.... This is because of the length of the fingerboard. In order to play 'in tune' as, say, a fiddle does, we'd need fingers the size of a small child's arms.
When trying to write quiet stuff for basses, it's best to write it 'sul pont', and 'forte'. Playing quiet on a bass is not possible. This is due to the size of the f-holes. Loads of sound comes out of there, not matter what you do, because they're really big. I once lost a watch in there. Never saw it again.
Hope this was some help.