Subphonemic variation in Russian

[K -Romaine]

I am looking for reliable information on subphonemic variations in standard
Russian and would be very grateful to anyone who could point me toward work
(particularly instrumental and quantitative studies) on:

1. The diphthongal nature of vowels (particularly /a/ & /i/) under stress
   in CV* syllables;

2. Place-based differences in the velarization of non-palatalized consonants.
   (Is /b/ "harder" than /d/?)

3. Consonant-induced differences in pronunciation of stressed vowels (e.g. how
   does the /a/ in /ba/ compare to the /a/ in /da/?);

4. Details on the formation of the palatalized/plain (hard/soft) distinction
   as a function of stress, especially differences in the consonants themselves
   or in their transitions to following vowels (e.g. how does the /b/ in
   stressed /ba/ compare to the /b/ in unstressed /ba/?);

5. Any information of vowel-to-vowel coarticulation.

Articles need not be in English.

Many thanks in advance!  -- K