RESUMO
Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes in the accretion flow lead to stochastic variability of this emission on a wide range of time scales. We measured the optical continuum variability observed in 67 active galactic nuclei and the characteristic time scale at which the variability power spectrum flattens. We found a correlation between this time scale and the black hole mass extending over the entire mass range of supermassive black holes. This time scale is consistent with the expected thermal time scale at the ultraviolet-emitting radius in standard accretion disk theory. Accreting white dwarfs lie close to this correlation, suggesting a common process for all accretion disks.
RESUMO
This work compares the photoinduced unimolecular electron transfer rate constants for two different solute molecules (D-SSS-A and D-SRR-A) in water and DMSO solvents. The D-SSS-A solute has a cleft between the electron donor and acceptor units, which is able to contain a water molecule but is too small for DMSO. The rate constant for D-SSS-A in water is significantly higher than that for D-SRR-A, which lacks a cleft, and significantly higher for either solute in DMSO. The enhancement of the rate constant is explained by an electron tunneling pathway that involves water molecule(s).