NUCLEAR MASSES AND THEIR IMPACT IN R-PROCESS NUCLEOSYNTHESIS

During the present Thesis, the role of the nuclear masses in r-process nucleosynthesis calculations have been explored. In order to accomplish this goal, we have computed neutron capture rates in the framework of the statistical model for all relevant nuclei in the r-process regime, to be more specific, nuclei ranging from Zn (Z=30) to Bi (Z=83) and contained inside the model dependent driplines. We have use the currently available mass models that best reproduce the known masses with a root mean square deviation smaller than RMSD<600 keV. This include the following set of mass models: Finite Range Droplet Model (FRDM), Weizsäcker-Skyrme model (WS3) and two variants of the Duflo-Zuker mass model, namely DZ10 and DZ31. The thermodynamical conditions were taken from hydrodynamical simulations corresponding to high entropy neutrino winds from core collapse supernovae (SNe) and Neutron star mergers(NSM)

Microscopic mass estimations

The quest to build a mass formula which have in it the most relevant microscopic contributions is analyzed. Inspired in the successful Duflo-Zuker mass description, the challenges to describe the shell closures in a more transparent but equally powerful formalism are discussed.Comment: 14 pages, 6 figures, submitted to Journal of Physics G, Focus issue on Open Problems in Nuclear Structure Theor

On the nuclear robustness of the r process in neutron-star mergers

We have performed r-process calculations for matter ejected dynamically in neutron star mergers based on a complete set of trajectories from a three-dimensional relativistic smoothed particle hydrodynamic simulation. Our calculations consider an extended nuclear network, including spontaneous, $\beta$- and neutron-induced fission and adopting fission yield distributions from the ABLA code. We have studied the sensitivity of the r-process abundances to nuclear masses by using different models. Most of the trajectories, corresponding to 90% of the ejected mass, follow a relatively slow expansion allowing for all neutrons to be captured. The resulting abundances are very similar to each other and reproduce the general features of the observed r-process abundance (the second and third peaks, the rare-earth peak and the lead peak) for all mass models as they are mainly determined by the fission yields. We find distinct differences in the abundance yields at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r-process nuclei around neutron number $N=130$. The remaining trajectories, which contribute 10% by mass to the total integrated abundances, follow such a fast expansion that the r process does not use all the neutrons. This also leads to a larger variation of abundances among trajectories as fission does not dominate the r-process dynamics. The total integrated abundances are dominated by contributions from the slow abundances and hence reproduce the general features of the observed r-process abundances. We find that at timescales of weeks relevant for kilonova light curve calculations, the abundance of actinides is larger than the one of lanthanides. Hence actinides can be even more important than lanthanides to determine the photon opacities under kilonova conditions. (Abridged)Comment: 17 pages, 7 figures, resubmitted to PRC addressing referee comment

Behavior of early warnings near the critical temperature in the two-dimensional Ising model

Among the properties that are common to complex systems, the presence of critical thresholds in the dynamics of the system is one of the most important. Recently, there has been interest in the universalities that occur in the behavior of systems near critical points. These universal properties make it possible to estimate how far a system is from a critical threshold. Several early-warning signals have been reported in time series representing systems near catastrophic shifts. The proper understanding of these early-warnings may allow the prediction and perhaps control of these dramatic shifts in a wide variety of systems. In this paper we analyze this universal behavior for a system that is a paradigm of phase transitions, the Ising model. We study the behavior of the early-warning signals and the way the temporal correlations of the system increase when the system is near the critical point.Comment: 20 pages, 8 figures, Submitted to PLOS ONE on Oct. 20th 2014. PONE-D-14-4718

The anatomy of the simplest Duflo-Zuker mass formula

The simplest version of the Duflo-Zuker mass model (due entirely to the late Jean Duflo) is described by following step by step the published computer code. The model contains six macroscopic monopole terms leading asymptotically to a Liquid Drop form, three microscopic terms supposed to mock configuration mixing (multipole) corrections to the monopole shell effects, and one term in charge of detecting deformed nuclei and calculating their masses. A careful analysis of the model suggests a program of future developments that includes a complementary approach to masses based on an independently determined monopole Hamiltonian, a better description of deformations and specific suggestions for the treatment of three body forces.Comment: 30 pages, 21 figures, extensives changes to improve presentation and clarity, with an ample discussion of the anomalous term. Accepted for publication in Nuclear Physics

NUCLEAR MASSES AND THEIR IMPACT IN R-PROCESS NUCLEOSYNTHESIS

During the present Thesis, the role of the nuclear masses in r-process nucleosynthesis calculations have been explored. In order to accomplish this goal, we have computed neutron capture rates in the framework of the statistical model for all relevant nuclei in the r-process regime, to be more specific, nuclei ranging from Zn (Z=30) to Bi (Z=83) and contained inside the model dependent driplines. We have use the currently available mass models that best reproduce the known masses with a root mean square deviation smaller than RMSD<600 keV. This include the following set of mass models: Finite Range Droplet Model (FRDM), Weizsäcker-Skyrme model (WS3) and two variants of the Duflo-Zuker mass model, namely DZ10 and DZ31. The thermodynamical conditions were taken from hydrodynamical simulations corresponding to high entropy neutrino winds from core collapse supernovae (SNe) and Neutron star mergers(NSM)

Enhancement of early warning properties in the Kuramoto model and in an atrial fibrillation model due to an external perturbation of the system

"When a complex dynamical system is externally disturbed, the statistical moments of signals associated to it can be affected in ways that depend on the nature and amplitude of the perturbation. In systems that exhibit phase transitions, the statistical moments can be used as Early Warnings (EW) of the transition. A natural question is thus to wonder what effect external disturbances have on the EWs of system. In this work we study the impact of external noise added to the system on the EWs, with particular focus on understanding the importance of the amplitude and complexity of the noise. We do this by analyzing the EWs of two computational models related to biology: the Kuramoto model, which is a paradigm of synchronization for biological systems, and a cellular automaton model of cardiac dynamics which has been used as a model for atrial fibrillation. For each model we first characterize the EWs. Then, we introduce external noise of varying intensity and nature to observe what effect this has on the EWs. In both cases we find that the introduction of noise amplified the EWs, with more complex noise having a greater effect"

Spatial configurations in the Ising model.

<p>Typical spatial configurations for a 2-dimensional Ising model. Three regimes are shown: a) <i>T</i> < <i>T</i>_<i>c</i>, b) <i>T</i> ≈ <i>T</i>_<i>c</i> and c) <i>T</i> > <i>T</i>_<i>c</i>. Black squares represent spins with <i>σ</i> = +1 and white one correspond to <i>σ</i> = −1.</p

Enhancement of early warning properties in the Kuramoto model and in an atrial fibrillation model due to an external perturbation of the system

<div><p>When a complex dynamical system is externally disturbed, the statistical moments of signals associated to it can be affected in ways that depend on the nature and amplitude of the perturbation. In systems that exhibit phase transitions, the statistical moments can be used as Early Warnings (EW) of the transition. A natural question is thus to wonder what effect external disturbances have on the EWs of system. In this work we study the impact of external noise added to the system on the EWs, with particular focus on understanding the importance of the amplitude and complexity of the noise. We do this by analyzing the EWs of two computational models related to biology: the Kuramoto model, which is a paradigm of synchronization for biological systems, and a cellular automaton model of cardiac dynamics which has been used as a model for atrial fibrillation. For each model we first characterize the EWs. Then, we introduce external noise of varying intensity and nature to observe what effect this has on the EWs. In both cases we find that the introduction of noise amplified the EWs, with more complex noise having a greater effect. This both offers a way to improve the chance of detection of EWs in real systems and suggests that natural variability in the real world does not have a detrimental effect on EWs, but the opposite.</p></div

Total magnetization as a function of time in the Ising model.

<p>Typical behavior of the total magnetization time series in a 2-dimensional Ising model. Three regimes are shown: a) <i>T</i> < <i>T</i>_<i>c</i>, b) <i>T</i> ≈ <i>T</i>_<i>c</i> and c) <i>T</i> > <i>T</i>_<i>c</i>. It is important to notice the change of scale between plots.</p