Searcharxiv⌕ Search

arXiv subjects

C. O. Dorso

Publications and source records attributed to C. O. Dorso.

At least 37 records · Page 2Linked to original sources

Coulomb forces in neutron star crusts

We study the role the proton-electron gas interaction has on the formation of nuclear structures in neutron star crusts. Using a classical molecular dynamics model we study isospin symmetric and asymmetric matter at subsaturation densities and low temperatures varying the Coulomb interaction strength. The effect of such variation is quantified on the fragment size multiplicity, the inter-particle distance, the isospin content of the clusters, the nucleon mobility and cluster persistence, and on the nuclear structure shapes. We find that the proton-electron Coulomb interaction distributes matter more evenly, disrupts the formation of larger objects, reduces the isospin content, modifies the nucleon average displacement, but does not affect the inter-nucleon distance in clusters . The nuclear structures are also found to change shapes by different degrees depending on their isospin content, temperature and density.

nucl-th↗

Topological characterization of neutron star crusts

Neutron star crusts are studied using a classical molecular dynamics model developed for heavy ion reactions. After the model is shown to produce a plethora of the so-called "pasta" shapes, a series of techniques borrowed from nuclear physics, condensed matter physics and topology are used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

nucl-th↗

Diseases spreading through individual based models with realistic mobility patterns

The individual-based models constitute a set of widely implemented tools to analyze the incidence of individuals heterogeneities in the spread of an infectious disease. In this work we focus our attention on human contacts heterogeneities through two of the main individual-based models: mobile agents and complex networks models. We introduce a novel mobile agents model in which individuals make displacements with sizes according to a truncated power-law distribution based on empirical evidence about human mobility. Besides, we present a procedure to obtain an equivalent weighted contact network from the previous mobile agents model, where the weights of the links are interpreted as contact probabilities. From the topological analysis of the equivalent contact networks we show that small world characteristics are related with truncated power-law distribution for agent displacements. Finally, we show the equivalence between both approaches through some numerical experiments for the spread of an infectious disease.

q-bio.PE↗

Alternative approach to community detection in networks

The problem of community detection is relevant in many disciplines of science and modularity optimization is the widely accepted method for this purpose. It has recently been shown that this approach presents a resolution limit by which it is not possible to detect communities with sizes smaller than a threshold which depends on the network size. Moreover, it might happen that the communities resulting from such an approach do not satisfy the usual qualitative definition of commune, i.e., nodes in a commune are more connected among themselves than to nodes outside the commune. In this article we introduce a new method for community detection in complex networks. We define new merit factors based on the weak and strong community definitions formulated by Radicchi et al (Proc. Nat. Acad. Sci. USA 101, 2658-2663 (2004)) and we show that this local definitions avoid the resolution limit problem found in the modularity optimization approach.

physics.soc-ph↗

Isoscaling and the high Temperature limit

This study shows that isoscaling, usually studied in nuclear reactions, is a phenomenon common to all cases of fair sampling. Exact expressions for the yield ratio $R_{21}$ and approximate expressions for the isoscaling parameters $α$ and $β$ are obtained and compared to experimental results. It is concluded that nuclear isoscaling is bound to contain a component due to sampling and, thus, a words of caution is issued to those interested in extracting information about the nuclear equation of state from isoscaling.

nucl-th↗

Dynamical aspects of fragmentation

In this short communication we address the problem of reducibility in a highly excited Lennard-Jones system. We show that the probability of emitting $n$ fragments can be described in terms of a single probability through the binomial expression. However, the Arrhenius law does not hold and the process can be viewed as a mixture of sequential and simultaneous fragmentation events.

nucl-th↗

Information theory of open fragmenting systems

An information theory description of finite systems explicitly evolving in time is presented. We impose a MaxEnt variational principle on the Shannon entropy at a given time while the constraints are set at a former time. The resulting density matrix contains explicit time odd components in the form of collective flows. As a specific application we consider the dynamics of the expansion in connection with heavy ion experiments. Lattice gas and classical molecular dynamics simulations are shown.

nucl-th↗

Geometrical aspects of isoscaling

The property of isoscaling in nuclear fragmentation is studied using a simple bond percolation model with ``isospin'' added as an extra degree of freedom. It is shown analytically, first, that isoscaling is expected to exist in such a simple model with the only assumption of fair sampling with homogeneous probabilities. Second, numerical percolations of hundreds of thousands of grids of different sizes and with different $N$ to $Z$ ratios confirm this prediction with remarkable agreement. It is thus concluded that isoscaling emerges from the simple assumption of fair sampling with homogeneous probabilities, a requirement which, if put in the nomenclature of the minimum information theory, translates simply into the existence of equiprobable configurations in maximum entropy states.

nucl-th↗

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↗

Dynamics and thermodynamics of fragment emission from excited sources

In this paper we study the process of fragmentation of highly excited Lennard-Jones drops by introducing the concept of emitted fragments (clusters recognizable in configuration space which live more than a minimum lifetime). We focus on the dynamics and thermodynamics of the emitted sources, and show, among other things, that this kind of process can not be cast into a sequential or simultaneous one, and how a local equilibrium scenario comes up, allowing us to define and explore a local temperature, which turns out to be a strongly time-dependent quantity.

nucl-th↗

Enhancement of kinetic energy fluctuations due to expansion

Global equilibrium fragmentation inside a freeze out constraining volume is a working hypothesis widely used in nuclear fragmentation statistical models. In the framework of classical Lennard Jones molecular dynamics, we study how the relaxation of the fixed volume constraint affects the posterior evolution of microscopic correlations, and how a non-confined fragmentation scenario is established. A study of the dynamical evolution of the relative kinetic energy fluctuations was also performed. We found that asymptotic measurements of such observable can be related to the number of decaying channels available to the system at fragmentation time.

nucl-th↗

Caloric Curves in two and three-dimensional Lennard-Jones-like systems including Long-range forces

We present a systematic study of the thermodynamics of two and three-dimensional generalized Lennard-Jones ($LJ$) systems focusing on the relationship between the range of the potential, the system density and its dimension. We found that the existence of negative specific heats depends on these three factors and not only on the potential range and the density of the system as stated in recent contributions.

cond-mat.stat-mech↗

The role of Coulomb interaction in fragmentation

We examine the impact of adding a Coulomb term to a constrained system of 147 particles interacting via a Lennard-Jones (LJ) potential, finding that the inclusion of the coulombic interaction produces a shift, but no qualitative changes in the thermodynamical properties of the system. We also performed the systems characterization from a morphological point of view.

nucl-th↗

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↗

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↗

Time dependence of critical behavior in multifragmentation

We study signatures of critical behavior in microscopic simulations of small, highly excited Lennard-Jones drops. We focus our attention on the behavior of the system at the time of fragment formation (which takes place in phase space) and compare the results with the corresponding ones obtained at asymptotic times (experimentally accessible). The four critical exponents ($τ$,$β$, $σ$ and $γ$) found at fragmentation time have shown to be stable against time evolution, indicating that the asymptotic stage reflects accurately the physics at fragmentation time. Even though evidence of critical behavior arises from the calculations, we can not affirm that the system is performing a second order like phase transition.

nucl-th↗

A Quasi-Classical Model of Intermediate Velocity Particle Production in Asymmetric Heavy Ion Reactions

The particle emission at intermediate velocities in mass asymmetric reactions is studied within the framework of classical molecular dynamics. Two reactions in the Fermi energy domain were modelized, $^{58}$Ni+C and $^{58}$Ni+Au at 34.5 MeV/nucleon. The availability of microscopic correlations at all times allowed a detailed study of the fragment formation process. Special attention was paid to the physical origin of fragments and emission timescales, which allowed us to disentangle the different processes involved in the mid-rapidity particle production. Consequently, a clear distinction between a prompt pre- equilibrium emission and a delayed aligned asymmetric breakup of the heavier partner of the reaction was achieved.

nucl-th↗

Dynamical properties of constrained drops

In this communication we analyze the behavior of excited drops contained in spherical volumes. We study different properties of the dynamical systems i.e. the maximum Lyapunov exponent MLE, the asymptotic distance in momentum space $d_{\infty}$ andthe normalized variance of the maximum fragment NVM. It is shown that the constrained systems behaves as undergoing a first order phase transition at low densities while as a second order one at high densities. The transition from liquid-like to vapor-like behavior is signaled both by the caloric curves, thermal response functions and the MLE. The relationship between $MLE,d_{\infty}$, and the CC is explored.

nucl-th↗