2,013 research outputs found
Coupled-channels density-matrix approach to low-energy nuclear reaction dynamics
Atomic nuclei are complex, quantum many-body systems whose structure
manifests itself through intrinsic quantum states associated with different
excitation modes or degrees of freedom. Collective modes (vibration and/or
rotation) dominate at low energy (near the ground-state). The associated states
are usually employed, within a truncated model space, as a basis in (coherent)
coupled channels approaches to low-energy reaction dynamics. However, excluded
states can be essential, and their effects on the open (nuclear) system
dynamics are usually treated through complex potentials. Is this a complete
description of open system dynamics? Does it include effects of quantum
decoherence? Can decoherence be manifested in reaction observables? In this
contribution, I discuss these issues and the main ideas of a coupled-channels
density-matrix approach that makes it possible to quantify the role and
importance of quantum decoherence in low-energy nuclear reaction dynamics.
Topical applications, which refer to understanding the astrophysically
important collision C + C and achieving a unified quantum
dynamical description of relevant reaction processes of weakly-bound nuclei,
are highlighted.Comment: Invited Talk at FINUSTAR3, August 23-27, 2010, Rhodes, Greece. To be
published in AIP Conference Proceeding
Dynamical collective potential energy landscape: its impact on the competition between fusion and quasi-fission in a heavy fusing system
A realistic microscopically-based quantum approach to the competition between
fusion and quasi-fission in a heavy fusing system is applied to several
reactions leading to No. Fusion and quasi-fission are described in
terms of a diffusion process of nuclear shapes through a dynamical collective
potential energy landscape which is initially diabatic and gradually becomes
adiabatic. The microscopic ingredients of the theory are obtained with a
realistic two-center shell model based on Woods-Saxon potentials. The results
indicate that (i) the diabatic effects play a very important role in the onset
of fusion hindrance for heavy systems, and (ii) very asymmetric reactions
induced by closed shell nuclei seem to be the best suited to synthesize the
heaviest compound nuclei.Comment: 6 pages, 5 figures, To be published in the AIP Proceedings of
FUSION06, International Conference on Reaction Mechanisms and Nuclear
Structure at the Coulomb barrier, March 19-23, 2006, San Servolo (Venice),
Ital
Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies
The classical dynamical model for reactions induced by weakly-bound nuclei at
near-barrier energies is developed further. It allows a quantitative study of
the role and importance of incomplete fusion dynamics in asymptotic
observables, such as the population of high-spin states in reaction products as
well as the angular distribution of direct alpha-production. Model calculations
indicate that incomplete fusion is an effective mechanism for populating
high-spin states, and its contribution to the direct alpha production yield
diminishes with decreasing energy towards the Coulomb barrier. It also becomes
notably separated in angles from the contribution of no-capture breakup events.
This should facilitate the experimental disentanglement of these competing
reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the
author), Accepted in Journal of Physics
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Marmots do not consistently use their left eye to respond to an approaching threat but those that did fled sooner.
In many vertebrates, the brain's right hemisphere which is connected to the left visual field specializes in the processing of information about threats while the left hemisphere which is connected to the right visual field specializes in the processing of information about conspecifics. This is referred to as hemispheric lateralization. But individuals that are too predictable in their response to predators could have reduced survival and we may expect selection for somewhat unpredictable responses. We studied hemispheric lateralization in yellow-bellied marmots Marmota flaviventer, a social rodent that falls prey to a variety of terrestrial and aerial predators. We first asked if they have lateralized responses to a predatory threat. We then asked if the eye that they used to assess risk influenced their perceptions of risk. We recorded the direction marmots were initially looking and then walked toward them until they fled. We recorded the distance that they responded to our experimental approach by looking, the eye with which they looked at us, and the distance at which they fled (i.e., flight initiation distance; FID). We found that marmots had no eye preference with which they looked at an approaching threat. Furthermore, the population was not comprised of individuals that responded in consistent ways. However, we found that marmots that looked at the approaching person with their left eye had larger FIDs suggesting that risk assessment was influenced by the eye used to monitor the threat. These findings are consistent with selection to make prey less predictable for their predators, despite underlying lateralization
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