"minor" Upanishads

[Howard Resnick]

     I would very much appreciate any bibliographic information about 
serious studies or articles done on two "minor" Upanishads: the 
Paramatika Upanishad and the Ekakshara Upanishad, both of which are found 
in the Mantra Prasna of the Vaikhanasas.  Both Upanishads are also found 
in the large compendium of Upanishads called the Upanisat-samgraha, 
edited by Professor J. L. Sastri.
      Thank you very much for any help in this regard.
Howard Resnick
Department of Sanskrit and Indian Studies
Harvard University