arXiv subjects

F. S. Guzmán

Publications and source records attributed to F. S. Guzmán.

15 recordsLinked to original sources

arXiv2025

Plain Convolution Encryption as an Alternative to Overcoming the Limitations of Synchronization-Based Methods

This paper revisits the send/retrieve message process using synchronization of the Lorenz system with a monochromatic message. We analyze how the fidelity of the retrieved signal depends on the message frequency and demonstrate message hacking through Fourier spectrum analysis. Various parameters affecting fidelity and noise in the hacked signal are also examined. Additionally, we transmit text messages recovered through synchronization and investigate their vulnerability to hacking. As a countermeasure, we propose a method to send both types of messages using the convolution as the encryption function to hide the message in the chaotic signal. This approach enhances retrieval fidelity and significantly increases resistance to hacking compared to synchronization-based methods.

nlin.CD↗

arXiv2020

Spicule jets in the solar atmosphere modeled with resistive MHD and thermal conduction

Using numerical simulations, we study the effects of magnetic resistivity and thermal conductivity in the dynamics and properties of solar jets with characteristics of Type II spicules and cool coronal jets. The dynamic evolution of the jets is governed by the resistive MHD equations with thermal conduction along the magnetic field lines on a 2.5D slice. The magnetic field configuration consists of two symmetric neighboring loops with opposite polarity, used to support reconnection and followed by the plasma jet formation. In total 10 simulations were carried out with different values of resistivity and thermal conductivity, that produce jets with different morphological and thermal properties we quantify. We find that an increase in magnetic resistivity does not produce significant effects on the morphology, velocity and temperature of the jets. However, thermal conductivity affects both temperature and morphology of the jets. In particular, thermal conductivity causes jets to reach greater heights and increases the temperature of the jet-apex. Also, heat flux maps indicate the jet-apex and corona interchange energy more efficiently than the body of the jet. These results could potentially open a new avenue for plasma diagnostics in the Sun's atmosphere.

astro-ph.SR↗

arXiv2020

Gravitational atoms: general framework for the construction of multistate axially symmetric solutions of the Schrödinger-Poisson system

We present a general strategy to solve the stationary Schrödinger-Poisson (SP) system of equations for multistates with axial symmetry. The approach allows us to obtain the well known single and multistate solutions with spherical symmetry, Newtonian multistate $\ell-$boson stars and axially symmetric multistate configurations. For each case we construct particular examples that illustrate the method, whose stability properties are studied by numerically solving the time-dependent SP system. Among the stable configurations there are the mixed-two-state configurations including spherical and dipolar components, which might have an important value as potential anisotropic dark matter halos in the context of ultralight bosonic dark matter scenarios. This is the reason why we also present a possible process of formation of these mixed-two-state configurations that could open the door to the exploration of more general multistate structure formation scenarios.

astro-ph.GA↗

arXiv2019

Relaxation of structures resulting from head-on mergers of ultralight bosonic dark matter cores

In this work we study some features of head-on mergers of equilibrium solutions of the Gross-Pitaevskii-Poisson system that rules the dynamics of the ultralight bosonic dark matter model. The importance of equilibrium solutions is that they play the role of halo cores in structure formation simulations. We consider a given range of initial conditions in order to sample the parameter space in terms of mass ratio and head-on momentum. In each case we analyze the relaxation process induced by gravitational cooling in the high and low momentum regimes and estimate the relaxation time scales in each case. We detect a low frequency mode in the whole parameters space and it was found that the resulting configuration oscillates under this mode with amplitude that depends on the mass ratio and head-on momentum. In some cases the resulting configuration oscillates with changes in density of two orders of magnitude and with a matter distribution that is far from isotropic. These results could contribute to the collection of possible mass distributions considered in the reconstruction of mass profiles obtained in structure formation simulations.

astro-ph.CO↗

arXiv2019

CAFE-R a code that solves the special relativistic radiation hydrodynamics equations

We present a 3D special-relativistic radiation hydrodynamics code. It uses the radiative inversion scheme with the M1-closure relation for the radiation equations, which allows the treatment of a wide range of optical depth, temperature and opacity. The radiation field is treated in the grey-body approximation. We present the standard 1D and 2D tests that include both optically thin and thick scenarios, as well as hydrodynamical and radiation pressure dominated configurations. As an application in 3D, we show the evolution of a jet driven by radiation-hydrodynamics with a helical perturbation. The code is expected to allow the exploration of scenarios in high-energy astrophysics where the radiation is important, like sources of GRBs.

astro-ph.HE↗

arXiv2018

Analysis of 3D plasma motions in a chromospheric jet formed due to magnetic reconnection

Within the framework of resistive MHD, implementing the C7 equilibrium atmosphere model and a 3D potential magnetic field realistic configuration, we simulate the formation of a plasm jet with the morphology, upward velocity up to 130 km/s and timescale formation between 60 and 90 s after beginning of simulation, similar to those expected for Type II spicules. Initial results of this simulation were published in Paper (e.g., González-Avilés et al. 2018) and present paper is devoted to the analysis of transverse displacements and rotational type motion of the jet. Our results suggest that 3D magnetic reconnection may be responsible for the formation of the jet in Paper (González-Avilés et al. 2018). In this paper, by calculating times series of the velocity components $v_x$ and $v_y$ in different points near to the jet for various heights we find transverse oscillations in agreement with spicule observations. We also obtain a time-distance plot of the temperature in a cross-cut at the plane $x=$0.1 Mm and find significant transverse displacements of the jet. By analyzing temperature isosurfaces of $10^{4}$ K with the distribution of $v_x$, we find that if the line-of-sight (LOS) is approximately perpendicular to the jet axis then there is both motion towards and away from the observer across the width of the jet. This red-blue shift pattern of the jet is caused by rotational motion, initially clockwise and anti-clockwise afterwards, which could be interpreted as torsional motion. From a nearly vertical perspective of the jet the LOS velocity component shows a central blue-shift region surrounded by red-shifted plasma.

astro-ph.SR↗

arXiv2018

Flows and magnetic field structures in reconnection regions of simulations of the solar atmosphere: do flux pile-up models work?

We study the process of magnetic field annihilation and reconnection in simulations of magnetised solar photosphere and chromosphere with magnetic fields of opposite polarities and constant numerical resistivity. Exact analytical solutions for reconnective annihilations are used to interpret the features of magnetic reconnection in simulations of flux cancellation in the solar atmosphere. We use MURaM high-resolution photospheric radiative magneto-convection simulations to demonstrate the presence of magnetic field reconnection consistent with the magnetic flux pile-up models. Also, a simulated data-driven chromospheric magneto-hydrodynamic simulation is used to demonstrate magnetic field and flow structures, which are similar to the ones theoretically predicted. Both simulations demonstrate flow and magnetic field structures roughly consistent with accelerated reconnection with magnetic flux pile-up. The presence of standard Sweet-Parker type reconnection is also demonstrated in stronger photospheric magnetic fields.

astro-ph.SR↗

arXiv2018

Evolution of jets driven by relativistic radiation hydrodynamics as Long and Low Luminosity GRBs

We present the three-dimensional numerical simulation of jets modeled with Relativistic Radiation Hydrodynamics (RRH), that evolve across two environments: i) a stratified surrounding medium and ii) a 16TI progenitor model. We consider opacities consistent with various processes of interaction between the fluid and radiation, specifically, free-free, bound-free, bound-bound and electron scattering. We explore various initial conditions, with different radiation energy densities of the beam in hydrodynamical and radiation pressure dominated scenarios, considering only ultra-relativistic jets. In order to investigate the impact of the radiation field on the evolution of the jets, we compare our results with purely hydrodynamical jets. Comparing among jets driven by RRH, we find that radiation pressure dominated jets propagate slightly faster than gas pressure dominated ones. Finally, we construct the luminosity Light Curves (LCs) associated with all these cases. The construction of LCs uses the fluxes of the radiation field which is fully coupled to the hydrodynamics equations during the evolution. The main properties of the jets propagating on the stratified surrounding medium are that the LCs show the same order of magnitude as the gamma-ray luminosity of typical Long Gamma-Ray Bursts $10^{50}-10^{54}$erg/s and the difference between the radiation and gas temperatures is of nearly one order of magnitude. The properties of jets breaking out from the progenitor star model are that the LCs are of the order of magnitude of low-luminosity GRBs $10^{46}-10^{49}$ erg/s, and in this scenario the difference between the gas and radiation temperature is of four orders of magnitude, which is a case far from thermal equilibrium.

astro-ph.HE↗

arXiv2018

I. Jet Formation and Evolution due to 3D Magnetic Reconnection

Using simulated data-driven three-dimensional resistive MHD simulations of the solar atmosphere, we show that magnetic reconnection can be responsible of the formation of jets with characteristic of Type II spicules. For this, we numerically model the photosphere-corona region using the C7 equilibrium atmosphere model. The initial magnetic configuration is a 3D potential magnetic field, extrapolated up to the solar corona region from a dynamic realistic simulation of solar photospheric magnetoconvection model which is mimicking quiet-Sun. In this case we consider a uniform and constant value of the magnetic resistivity of $12.56 ~Ω~{\rm m}$. We have found that formation of the jets depends on the Lorentz force, which helps to accelerate the plasma upwards. Analyzing various properties of the jet dynamics, we found that the jet structure shows Doppler shift near to regions with high vorticity. The morphology, upward velocity, covering a range up to 100 $\rm km$ $\rm s^{-1}$, and life-time of the estructure, bigger than 100 ${\rm s}$, are similar to those expected for Type II spicules.

astro-ph.SR↗

arXiv2017

Classifying initial conditions of long GRBs modeled with relativistic radiation hydrodynamics

We present a method to classify initial conditions of a long gamma ray bursts model sourced by a single relativistic shock. It is based on the use of artificial neural networks (ANNs) that are trained with light curves (LC) generated with radiation relativistic hydrodynamics simulations. The model we use consists in a single shock with a highly relativistic injected beam into a stratified surrounding medium with profile $1/r^2$. In the process we only consider the bremsstrahlung radiation and Thomson scattering process. The initial conditions we use to train the ANN are three: the rest mass density, Lorentz factor and radiation energy density of the beam that produces the relativistic shock, together with the LC generated during the process. The classification selects the location of a box in the 3d parameter space that better fits a given LC, and in order to decrease the uncertainty of the parameters this box is refined and the classification selects a new box of smaller size.

astro-ph.IM↗

arXiv2016

Accretion of a Phantom Scalar Field by a Black Hole: restrictions on the field distribution

Using numerical simulations we study the accretion of a phantom scalar field into a black hole and track the black hole horizon shrinking process. We integrate the amount of field left outside the black hole during the process in terms of the properties of the wave packet sent toward the black hole. Our results indicate that the accretion of thick wave packets with small wave number is inefficient and a portion of the scalar field remains outside the black hole.

gr-qc↗

arXiv2016

Jet formation in solar atmosphere due to magnetic reconnection

Using numerical simulations, we show that jets with features of type II spicules and cold coronal jets corresponding to temperatures $10^{4}$ K can be formed due to magnetic reconnection in a scenario in presence of magnetic resistivity. For this we model the low chromosphere-corona region using the C7 equilibrium solar atmosphere model and assuming Resistive MHD rules the dynamics of the plasma. The magnetic filed configurations we analyze correspond to two neighboring loops with opposite polarity. The separation of the loops' feet determines the thickness of a current sheet that triggers a magnetic reconnection process, and the further formation of a high speed and sharp structure. We analyze the cases where the magnetic filed strength of the two loops is equal and different. In the first case, with a symmetric configuration the spicules raise vertically whereas in an asymmetric configuration the structure shows an inclination. With a number of simulations carried out under a 2.5D approach, we explore various properties of excited jets, namely, the morphology, inclination and velocity. The parameter space involves magnetic field strength between 20 and 40 G, and the resistivity is assumed to be uniform with a constant value of the order $10^{-2}Ω\cdot m$

astro-ph.SR↗

arXiv2016

Parameter estimates in binary black hole collisions using neural networks

We present an algorithm based on artificial neural networks (ANNs), that estimates the mass ratio in a binary black hole collision out of given Gravitational Wave (GW) strains. In this analysis, the ANN is trained with a sample of GW signals generated with numerical simulations. The effectiveness of the algorithm is evaluated with GWs generated also with simulations for given mass ratios unknown to the ANN. We measure the accuracy of the algorithm in the interpolation and extrapolation regimes. We present the results for noise free signals and signals contaminated with Gaussian noise, in order to foresee the dependence of the method accuracy in terms of the signal to noise ratio.

astro-ph.IM↗

arXiv2010

Evolution of a mass-less test scalar field on Boson Stars space-times

We numerically solve the mass-less test scalar field equation on the space-time background of boson stars and black holes. In order to do so, we use a numerical domain that contains future null infinity. We achieve this construction using a scri-fixing conformal compactification technique based on hyperboloidal constant mean curvature foliations of the space-time and solve the conformally invariant wave equation. We present two results: the scalar field shows oscillations of the quasi- normal-mode type found for black holes only for boson star configurations that are compact, and no signs of tail decay is found in the parameter space we explored. Even though our results do not correspond to the master equation of perturbations of boson star solutions, they indicate that the parameter space of boson stars as black hole mimickers is restricted to compact configurations.

gr-qc↗

arXiv2008

Constraining a bulk viscous matter-dominated cosmological model using SNe Ia, CMB and LSS

We present and constrain a cosmological model which component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a constant bulk viscosity coefficient ζ_m. The possible values of ζ_m are constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB shift parameter R from the three-year WMAP observations, the Baryon Acoustic Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is submitted to the three cosmological tests together (SNe+CMB+BAO) the results are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data with a χ^2_{min} \approx 400 (χ^2_{d.o.f.} \approx 2.2). These results indicate that this model is ruled out by the observations.

gr-qc↗