Partitioning of electric and magnetic energy in SU(2) gauge theory
  This article provides some estimates for the relative sizes of the electric and magnetic contributions to the energy functional for the minimum energy configuration of an SU(2) gauge field on R^3 in the presence of an source in a fixed ball. The surprising fact is that the contribution to both energies from the free field region increases at worst linearly with the coupling, rather than quadratically. Moreover, the external electric field is severly surpressed outside the source at large coupling while the magnetic field is concentrated in a shell surrounding the source suggesting a classical mechanism for the formation of the 'MIT bag'. 
Clifford H. Taubes