Average Inhomogeneities in Milky Way SNII and The PAMELA Anomaly
  A model is presented to estimate the fraction of Supernova Type-II events
(SNII) occurring inside vs. outside a spiral arm for a given star formation
episode. The probability distribution function (PDF) for this fraction is given
for use in models similar to those of Shaviv et al. [13][11]. The calculated
PDF for the SNII fraction, SNII_{in/total}, defined as the number of SNII
inside a spiral arm divided by the total number of SNII from a star formation
event, provides a constraint on the magnitude of supernova remnant (SNR)
concentrations used in cosmic ray propagation models attempting to explain the
PAMELA anomaly. Despite the concentration of star formation within spiral arms,
this model predicts the majority of SNII events actually occur in inter-arm
regions and calls into question the SNR concentration assumption of Shaviv et
al.
