0000000000210325
AUTHOR
J. F. Mahlmann
showing 7 related works from this author
Chemotherapy and Hepatic Steatosis: Impact on Postoperative Morbidity and Survival after Liver Resection for Colorectal Liver Metastases
2020
<b><i>Background:</i></b> Hepatic steatosis and chemotherapy in the treatment of colorectal liver metastases (CLM) are often linked to increased mortality and morbidity after liver resection. This study evaluates the influence of macrovesicular hepatic steatosis and chemotherapeutic regimes on graded morbidity and mortality after liver resection for CLM. <b><i>Methods:</i></b> A total of 323 cases of liver resection for CLM were retrospectively analysed using univariable and multivariable linear, ordinal and Cox regression analyses. The resected liver tissue was re-evaluated by a single observer to determine the grade and type of hepatic steat…
Striped Blandford/Znajek jets from advection of small-scale magnetic field
2020
Black hole - accretion disc systems are the central engines of relativistic jets from stellar to galactic scales. We numerically quantify the unsteady outgoing Poynting flux through the horizon of a rapidly spinning black hole endowed with a rotating accretion disc. The disc supports small-scale, concentric, flux tubes with zero net magnetic flux. Our General Relativistic force-free electrodynamics simulations follow the accretion onto the black hole over several hundred dynamical timescales in 3D. For the case of counter-rotating accretion discs, the average process efficiency reaches up to $\left\langle\epsilon\right\rangle\approx 0.43$, compared to a stationary energy extraction by the B…
Computational general relativistic force-free electrodynamics
2020
General relativistic force-free electrodynamics is one possible plasma-limit employed to analyze energetic outflows in which strong magnetic fields are dominant over all inertial phenomena. The amazing images of black hole shadows from the galactic center and the M87 galaxy provide a first direct glimpse into the physics of accretion flows in the most extreme environments of the universe. The efficient extraction of energy in the form of collimated outflows or jets from a rotating BH is directly linked to the topology of the surrounding magnetic field. We aim at providing a tool to numerically model the dynamics of such fields in magnetospheres around compact objects, such as black holes an…
Computational general relativistic force-free electrodynamics
2021
Scientific codes are an indispensable link between theory and experiment; in (astro-)plasma physics, such numerical tools are one window into the universe's most extreme flows of energy. The discretization of Maxwell's equations - needed to make highly magnetized (astro)physical plasma amenable to its numerical modeling - introduces numerical diffusion. It acts as a source of dissipation independent of the system's physical constituents. Understanding the numerical diffusion of scientific codes is the key to classify their reliability. It gives specific limits in which the results of numerical experiments are physical. We aim at quantifying and characterizing the numerical diffusion propert…
Instability of twisted magnetar magnetospheres
2019
We present three-dimensional force-free electrodynamics simulations of magnetar magnetospheres that demonstrate the instability of certain degenerate, high energy equilibrium solutions of the Grad-Shafranov equation. This result indicates the existence of an unstable branch of twisted magnetospheric solutions and allows to formulate an instability criterion. The rearrangement of magnetic field lines as a consequence of this instability triggers the dissipation of up to 30% of the magnetospheric energy on a thin layer above the magnetar surface. During this process, we predict an increase of the mechanical stresses onto the stellar crust, which can potentially result in a global mechanical f…
Diffusivity in force-free simulations of global magnetospheres
2021
Abstract: Assuming that the numerical diffusivity triggered by violations of the force-free electrodynamics constraints is a proxy for the physical resistivity, we examine its impact on the overall dynamics of force-free aligned pulsar magnetospheres endowed with an equatorial current sheet. We assess the constraint violations as a diffusivity source. The effects of modifications on electric fields used to restore force-free conditions are not confined to the equatorial current sheet, but modify the magnetospheric dynamics on timescales shorter than the pulsar rotational period. These corrections propagate especially via a channel that was unexplored, namely, changes induced to the electric…
Numerically solving the relativistic Grad–Shafranov equation in Kerr spacetimes: numerical techniques
2018
The study of the electrodynamics of static, axisymmetric and force-free Kerr magnetospheres relies vastly on solutions of the so called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced in the literature, but none of them has been fully assessed from the numerical point of view in terms of efficiency and quality of the solutions found. We present a generalization of these algorithms and give detailed background on the algorithmic implementation. We assess the numerical stability of the implemented algorithms and quantify the convergence of the presented methodology for the most established setups (split-monopole, parab…