No target class reveals compelling evidence for photon emitting sources in the EeV energy regime. (auger.org)
These limits connect, for the first time, measurements of sources in the TeV energy range to the highest energy regime, constrain the allowed parameter space for a flux continuation to EeV energies and place upper limits on the cutoff energy of sources. (auger.org)
But our current fossil fuel - based energy regime faces two serious challenges: depletion of the «low - hanging fruit» of global petroleum supplies, and the need to reduce carbon emissions to avert catastrophic climate change. (postcarbon.org)