We propose that stress can decrease the internal friction of amorphous
solids, either by increasing the potential barriers of defects, thus reducing
their tunneling and thermal activation that produce loss, or by decreasing the
coupling between defects and phonons. This stress can be from impurities,
atomic bonding constraints, or externally applied stress. Externally applied
stress also reduces mechanical loss through dissipation dilution. Our results
are consistent with the experiments, and predict that stress could
substantially reduce dielectric loss and increase the thermal conductivity.Comment: 9 pages, 7 figure