@article{10054,
  author = {Ludwig Oster},
  title = {The Relation between Emission and Absorption Coefficients for Arbitrary Radiation Processes},
  year = {1974},
  journal = {Astronomy and Astrophysics},
  volume = {33},
  pages = {151},
  url = {http://adsabs.harvard.edu/full/1974A\%26A....33..151O},
  note = {JILA Pub. 1156},
}