arXiv subjects

Fabio D. Lora-Clavijo

Publications and source records attributed to Fabio D. Lora-Clavijo.

8 recordsLinked to original sources

arXiv2026

Magnetic Reconnection Process in Partially Ionized Fluids: Insights from the Solar Chromosphere

Magnetic reconnection converts stored magnetic energy into kinetic energy, heat, and radiation. While extensively studied in fully ionized plasmas, observations show that ionization and recombination also play a role by modifying the local plasma resistivity and enabling additional heating channels. This study examines magnetic reconnection in the partially ionized solar chromosphere, analyzing its morphology and energy releases with attention to elastic collisions, ionization, and recombination. The MAGNUS code, originally built for ohmic resistivity and heat transfer, was modified to handle elastic and inelastic collisions. The simulations are 2.5D resistive MHD with two-fluid effects (charged + neutrals), adapted to handle interactions via these collision terms. A mixed explicit-implicit scheme was implemented to manage the stiffness of these terms. Simulations were carried out for three magnetic field strengths: 100~G, 110~G, and 120~G. These values correspond to the low- to mid-chromosphere under quiet-Sun conditions. We found that reconnection heats the plasma components by 18\% to 110\%. Although plasma beta rises only slightly, the energy release grows far more, indicating that charged--neutral collisions, not just beta or available magnetic energy, drive the enhanced reconnection. Furthermore, ionization and recombination become most significant in regions of peak temperature, particularly where particles are accelerated. Maximum reconnection rates from temporal analysis are 0.226, 0.253, and 0.279, respectively. Finally, in terms of energy, our results show that in a chromospheric volume of $0.4 \times 0.01 \times 0.4$~Mm$^{3}$, the energy released ranges from $10^{22}$ to $10^{23}$.

astro-ph.SR↗

arXiv2026

Relativistic Common-envelope Dynamics of a Stellar-mass Black Hole II: Kerr Black Hole

The common envelope phase plays a critical role in binary system evolution. In this study, we investigate the mass and momentum accretion rates during the interaction between a stellar mass black hole and the envelope of a red supergiant using simplified two dimensional simulations. We explore various Mach numbers and density gradients, finding that our simulations align with previous Bondi Hoyle Lyttleton accretion analyses. We observe the formation of a shock cone in the downstream flow, bow shocks in specific configurations, and subsonic regions within shocked flows. The shock cone is dragged when significant pressure gradients are present in the common envelope, with additional dragging near the black hole for highly rotating cases. We provide analytical fits for mass and momentum accretion rates, as well as bremsstrahlung luminosity, as functions of black hole spin, density gradients, and Mach number, offering first insights into general relativistic hydrodynamics modelling of the secular evolution of the common envelope phase.

astro-ph.HE↗

arXiv2024

Systematic 2.5 D resistive MHD simulations with ambipolar diffusion and Hall effect for fast magnetic reconnection

In this work, we explore the possibility of the Hall effect and ambipolar diffusion as a mechanism for fast reconnection. The reconnected flux of our resistive and resistive+Hall simulations replicates the GEM results. Furthermore, we investigate, for the first time, the effect of ambipolar diffusion in the GEM. The reconnected flux of the resistive+ambipolar and resistive+Hall+ambipolar simulations showed increases of up to 75\% and 143\%, respectively, compared to the resistive and resistive+Hall simulations, showing that ambipolar diffusion contributes significantly to the reconnected flux. Our second scenario has a magnetic Harris field without perturbations but with an out-of-plane component, known as a guide field. We found that the reconnection rate increased faster with ambipolar diffusion, reaching values close to 0.1 for the resistive+Hall+ambipolar simulation followed by the resistive+Hall. These two simulations achieved the highest kinetic energy, implying more efficient energy conversion during reconnection.

astro-ph.SR↗

arXiv2024

Magnetized tori with magnetic polarization around Kerr black holes: Variable angular momentum discs

Analytical models of magnetized, geometrically thick disks are relevant to understand the physical conditions of plasma around compact objects and to explore its emitting properties. This has become increasingly important in recent years in the light of the Event Horizon Telescope observations of Sgr A$^*$ and M87. Models of thick disks around black holes usually consider constant angular momentum distributions and do not take into account the magnetic response of the fluid to applied magnetic fields. We present a generalization of our previous work on stationary models of magnetized accretion disks with magnetic polarization (Pimentel et al. 2018). This extension is achieved by accounting for non-constant specific angular momentum profiles, done through a two-parameter ansatz for those distributions. We build a large number of new equilibrium solutions of thick disks with magnetic polarization around Kerr black holes, selecting suitable parameter values within the intrinsically substantial parameter space of the models. We study the morphology and the physical properties of those solutions, finding qualitative changes with respect to the constant angular momentum tori solutions (Pimentel et al. 2018). However, the dependences found on the angular momentum distribution or on the black hole spin do not seem to be strong. Some of the new solutions, however, exhibit a local maximum of the magnetization function, absent in standard magnetized tori. Due to the enhanced development of the magneto-rotational instability as a result of magnetic susceptibility, those models might be particularly well-suited to investigate jet formation through general-relativistic MHD simulations. The new equilibrium solutions reported here can be used as initial data in numerical codes to assess the impact of magnetic susceptibility in the dynamics and observational properties of black hole-thick disk systems.

astro-ph.HE↗

arXiv2024

Novel second-order model for tumor evolution: description of cytostatic and cytotoxic effects

Cancer is a disease that takes millions of lives every year. Then, to propose treatments, avoid recurrence, and improve the patient's life quality, we need to analyze this disease from a biophysical perspective with a solid mathematical formulation. In this paper we introduce a novel deterministic model for the evolution of tumors under several conditions (untreated tumors and treated tumors using chemotherapy). Our model is characterized by a second-order differential equation, whose origin and interpretation are presented by exploiting our understanding of fluid mechanics (via continuity equations) and the theory of differential equations. Additionally, we show that our model can fit various experimental data sets. Thus, we prove that our nuanced and general model can describe accelerated growth, as well as cytostatic and cytotoxic effects. All in all, our model opens up a new window in the understanding of tumor evolution and represents a promising connection between the macroscopic and microscopic descriptions of cancer.

q-bio.QM↗

arXiv2022

Synchrotron emitting Komissarov torus with magnetic polarization around Kerr black holes

Magnetic fields in black hole accretion disks are associated with processes of mass accretion and energy amplification. The contribution of the magnetic field due to the magnetic polarization of the material induces effects on the physical properties of the medium that have repercussions on the radiation coming from the accretion disks. Hence, from observations, it could be possible to infer the "fingerprint" left by the magnetic polarization of the material and establish the properties of the spacetime itself. As the first step in this purpose, we use numerical simulations to systematically analyze the possible observable effects produced by the magnetic properties of an accretion disk around a Kerr black hole. We found that under the synchrotron radiation power-law model the effects of the magnetic polarization are negligible when the plasma is gas pressure-dominated. Nevertheless, as beta-plasma decreases, the emission becomes more intense for magnetic pressure-dominated disks. In particular, we found that paramagnetic disks emit the highest intensity value independent of the beta-plasma parameter in this regime. By contrast, the emitted flux decreases with the increase of beta-plasma due to the dependence of the magnetic field on the emission and absorption coefficients. Moreover, the disk morphology changes with the magnetic susceptibility: paramagnetic disks are more compact than diamagnetic ones. This fact leads to diamagnetic disks emitting a greater flux because each photon has a more optical path to travel inside the disk.

gr-qc↗

arXiv2021

First steps on modelling wave propagation in isotropic-heterogeneous media: Numerical simulation of P-SV waves

In geophysics, wave propagation in elastic media is a crucial subject. In this context, seismology has made significant progress as a result of numerous advances, among these stands out the advancement of numerical methods such as the finite-difference one. Usually, seismic wave propagation in elastic media results in complex systems of partial differential equations, whose solutions cannot be obtained in an analytical way, especially when dealing with heterogeneous media. In consequence, there exists a necessity to implement numerical methods. However, the available information about the construction of a numerical solution of these equations is not as explicit as it should be. Our main goal is to provide pedagogical instructions for undergraduate students who want to improve their computational skills as well as their knowledge of the subject. The last through current teaching methods involving challenging problems and transversal tools. Particularly, we provide a brief description of the equations and a detailed description of the numerical solution of the seismic wave equation. Furthermore, we model two different seismic explosive sources in both homogeneous and heterogeneous media as an illustrative example. In the results, we include velocity maps showing wave propagation in the x-z plane, and the z-velocity as a function of time measured in a series of detectors distributed in the numerical domain.

physics.ed-ph↗

arXiv2021

GW190521 formation scenarios via relativistic accretion

The recent gravitational wave transient GW190521 has been interpreted by the LIGO-Virgo collaboration (LVC) as sourced by a binary black hole (BH) merger. According to the LVC parameter estimation, at least one of these progenitors falls into the so-called pair-instability supernova mass gap. This raises the important question of how and when these progenitors formed. In this paper we use an accretion model with super-Eddington mass accretion rate obtained from General Relativity hydrodynamics simulations to analyse the scenario wherein the GW190521 original progenitors (OPs) formed at lower masses (and spins) and grew to their estimated LVC parameters by relativistic accretion. We consider that the environment wherein the binary is immersed has density gradients as well as a dependence on the Mach number of the gas. Taking the LVC parameter estimation at $z=0.82$ as the endpoint of the accretion evolution, we estimate the initial masses and spins of the OPs at three different red-shifts $z=100, \ 50$, and $20$. We found three distinct possible types of OPs: $(i)$ $10^{-4} M_{\odot} - 3 M_{\odot}$ almost non-rotating (with Kerr spin parameter $a_{\star}< 10^{-2}$) primordial BHs; $(ii)$ $3 M_{\odot} - 40M_{\odot}$ slowly rotating ($ 10^{-2} < a_{\star} < 0.5$) stellar mass BHs; $(iii)$ $40M_{\odot} - 70M_{\odot}$ BHs with a moderate spin parameter $a_{\star}\sim 0.5$, which could originate from the collapse of high mass Pop III stars. The mass spread is due to varying the density gradient and the relativistic Mach number of the cosmic plasma; the variation of the masses due to the origin at different red-shifts, on the other hand, is negligible, $\sim 2\%$ ...

astro-ph.HE↗