Ultra-fast spin dynamics in the 2s2p^2 configuration of C^+ studied by time-dependent R-matrix theory

We employ time-dependent R-matrix theory to study ultra-fast dynamics in the doublet 2s2p(2) configuration of C+ for a total magnetic quantum number M = 1. In contrast to the dynamics observed for M = 0, ultra-fast dynamics for M = 1 is governed by spin dynamics in which the 2s electron acts as a flag rather than a spectator electron. Under the assumption that m(S) = 1/2, m(2s) = 1/2 allows spin dynamics involving the two 2p electrons, whereas m(2s) = -1/2 prevents spin dynamics of the two 2p electrons. For a pump-probe pulse scheme with (h) over bar omega(pump) = 10.9 eV and (h) over bar omega(probe) = 16.3 eV and both pulses six cycles long, little sign of spin dynamics is observed in the total ionization probability. Signs of spin dynamics can be observed, however, in the ejected-electron momentum distributions. We demonstrate that the ejected-electron momentum distributions can be used for unaligned targets to separate the contributions of initial M = 0 and M = 1 levels. This would, in principle, allow unaligned target ions to be used to obtain information on the different dynamics in the 2s2p(2) configuration for the M = 0 and M = 1 levels from a single experime

Late glacial interhemispheric climate dynamics revealed in South African hyrax middens

Our ability to identify the timing and extent of past major climate fluctuations is central to understanding changes in the global climate system. Of the events that have occurred in recent geological time, the Younger Dryas (YD, 13-11.5 ka), an abrupt return to near-glacial conditions during the last glacial-interglacial transition (ca. 18-11.5 ka), is one of the most widely reported. While this event is apparent throughout the Northern Hemisphere (Peteet, 1995), evidence for its occurrence in the Southern Hemisphere remains equivocal due to a lack of well-dated terrestrial records. Here we report high-resolution stable carbon and nitrogen isotope records obtained from a rock hyrax midden, revealing the first unequivocal terrestrial manifestation of the YD from the southern African subtropics. These results provide key evidence for the relative influence of the YD, and suggest that a subtropical-temperate transition zone existed along the oceanic Subtropical Front (similar to 41 degrees S) across the Southern Hemisphere, with the Northern Hemisphere exerting a strong influence on all but the higher latitudes of the Southern Hemisphere after the Heinrich Stadial 1 (15 ka).

Focusing Dynamics of High-Energy Density, Laser-Driven Ion Beams

The dynamics of the focusing of laser-driven ion beams produced from concave solid targets was studied. Most of the ion beam energy is observed to converge at the center of the cylindrical targets with a spot diameter of 30 mu m, which can be very beneficial for applications requiring high beam energy densities. Also, unbalanced laser irradiation does not compromise the focusability of the beam. However, significant filamentation occurs during the focusing, potentially limiting the localization of the energy deposition region by these beams at focus. These effects could impact the applicability of such high-energy density beams for applications, e. g., in proton-driven fast ignition.