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J. A. López

Publications and source records attributed to J. A. López.

46 records · Page 3Linked to original sources
arXiv2005

Dynamical aspects of isoscaling

The origin and dynamical evolution of isoscaling was studied using classical molecular dynamics simulations of ${}^{40}$Ca + ${}^{40}$Ca, ${}^{48}$Ca + ${}^{48}$Ca, and ${}^{52}$Ca + ${}^{52}$Ca, at beam energies ranging from $20 \ MeV/A$ to $85 MeV/A$. The analysis included a study of the time evolution of this effect. Isoscaling was observed to exist in these reactions from the very early primary isotope distributions (produced by highly {\it non-equilibrated} systems) all the way to asymptotic times. This indicates that isoscaling is independent of quantum effects and thermodynamical equilibrium. In summary, collision-produced isoscaling appears to be due more to the mere partitioning of the proton-neutron content of the participant nuclei, than to specific details of the reaction dynamics.

nucl-th↗
arXiv2005

Entropy and Size in HIC

Distinct entropy definitions have been used to obtain an inverse correlation between the residual size and entropy for Heavy Ion Collisions. This explains the existence of several temperatures for different residual size bins, as reported elsewhere (Natowitz et. al., 2002). HIC collisions were simulated using binary interaction LATINO model where Pandharipande potential replicates internucleonic interaction. System temperature is defined as the temperature obtained when Kinetic Gas Theory is applied to the nucleons in the participant region. Fragments are detected with an Early Cluster Recognition Algorithm that optimizes the partitions in energy space.

nucl-th↗
arXiv2005

A HIC Primitive Spinodal Decomposition Signature

Evidence of a primitive spinodal decomposition has been obtained for central Ni+Ni Heavy Ion Collision, since higher order charge correlations show a peak when four fragments of size equal to 6 are produced with an excitation of 4.75 MeV. This can be considered as a signature of a primitive breakup in equal sized fragments with a privileged fragment size. This computational result confirms other experimental and theoretical evidences about spinodal decompostion in HIC.

nucl-th↗
arXiv2004

Relaxation, Emission Modes and Limit Temperatures in Ni+Ni HIC

A dynamical stability analysis is performed for Ni+Ni central collision at intermediate energies, showing that in chemical, thermal and dynamical equilibriums are reached at an early stage of system evolution. This is obtained by computing the relaxation times of the quadrupole momentum, speed of sound and electric charge density of the system. This way, fragment emission modes at low and high energies as well as the qualitative behavior of the limit temperatures are determined.

nucl-th↗
arXiv2003

Genetic Algorithms and Critical Phenomena

Genetic algorithms based on natural selection and minimal fluctuations have been applied to model physical and biological systems. Critical exponents have been extracted via computational simulations of nucleation for colossal magnetoresistance, heavy ions liquid-gas phase transitions and HIV to AIDS transition.

math-ph↗
arXiv2003

Critical Nucleation in Colossal Magnetoresistance

Critical exponents have been obtained for a 3D spin particle system. Clusters are formed and system reaches a critical behavior when fragment size distribution follows a power law, as predicted by Fisher Liquid Droplet Model. Also, spontaneous magnetization critical temperature is in agreement with other theoretical studies. System evolution is reproduced via a genetic algorithm that performs minimal genetic fluctuations until a stationary state is attained. Critical exponents are in the range of those belonging to Heavy Ion collisions previously reported, and therefore belong to the same universality class.

cond-mat↗
arXiv2003

Size Effects in Heavy Ions Fragmentation

Rise-Plateau Caloric curves for different Heavy Ion collisions have been obtained, in the range of experimental observations. Limit temperature decreases when the residual size is increased, in agreement with recent theoretical analysis of experimental results reported by other Collaborations. Besides, promptly emitted particles influence on temperature plateau is shown. LATINO binary interaction semiclassical model is used to reproduce the inter-nucleonic forces via Pandharipande Potential and fragments are detected with an Early Cluster Recognition Algorithm.

nucl-th↗
arXiv2001

Morphology and Galactic Distribution of PNs: a New Scenario

We review recent studies on the morphology and distribution with respect to the galactic plane of planetary nebulae (PNs), as well as recent advances in MHD modeling of PNs. We discuss a tentative explanation for the connection between morphological classes and their galactic distribution

astro-ph↗
arXiv2000

Three Dimensional Magneto-Hydrodynamical Modeling of Planetary Nebuale ~ II: The Formation of Bipolar and Elliptical Nebulae with Point-Symmetric Structures and Collimated Outflows

This work presents three dimensional, magneto-hydrodynamical simulations of the formation and early evolution of a subgroup of planetary nebulae that exhibit a variety of point-symmetric structures. For bipolar nebulae, the formation of point-symmetric nebular shapes along the inner borders of their opposing lobes and/or collimated outflows or jets internal or external to their cavities, is reproduced by considering a steady misalignment of the magnetic collimation axis with respect to the symmetry axis of the bipolar wind outflow, defined perpendicular to the equatorial density enhancement. Elliptical planetary nebulae with ansae displaced from the symmetry axis in point-symmetric fashion are reproduced through the same process by reducing the equatorial density enhancement. This mechanism represents an alternative explanation to some cases where morphological appearances give the impression of the action of a symmetric, rotating or precessing jet from the central source. The computational survey reveals that jet formation is detected only for dense enough winds with mass loss rates $\gtrsim 10^{-7}$ \Moy. For lower mass loss rates the jets tend to vanish leaving behind only ansae-like structures at the tips of the lobes, as observed in some cases. The results are rather independent of the wind terminal velocity, since magnetized bubbles behave adiabatically for low wind velocities ($\simeq$ $100 \kms$), which in the absence of a magnetic field would behave as momentum driven.

astro-ph↗