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This volume brings together a number of previously unpublished essays that will advance the reader's philosophical understanding of specific aspects of causation, agency and moral responsibility. These are deeply intertwined notions, and a large proportion of the volume is taken up by papers that shed light on their mutual connections or defend certain claims concerning them. The volume investigates several important questions, including: Can causation be perceived? If it can, can it be perc.

Causation --- Causality --- Cause and effect --- Effect and cause --- Final cause --- Beginning --- God --- Metaphysics --- Philosophy --- Necessity (Philosophy) --- Teleology --- Research. --- Psychological aspects.

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Astrophysical environments such as black holes and neutron stars are among the most interesting test-grounds for our understanding of high-energy phenomena. There, the competing effect of gravity, electromagnetic forces, radiation, and kinetic dynamics govern the behaviour of a magnetised, low-density gas called plasma. The colorful interaction of such diverse physical processes originates extremely energetic events such as flares and jets, that we measure as distant observers at Earth. Astrophysical plasmas do not exist solely in black hole environments, but rather consitute 99% of the observable matter in the universe; it is the case for our own Sun, where the same (although less energetic) plasma processes take place, without however the effect of strong gravity. The study of the dynamics of plasmas, from stars to black holes, is the very foundation of modern astrophysics, and an ever-growing active research field.The theoretical investigation of such phenomena is commonly carried out with numerical methods, implemented in computer codes, that produce simulations of the systems of interest. Among the large variety of numerical methods, particle-based methods shine for their versatility and physical accuracy. These methods can be applied to the study of plasmas in multiple fashions, from the description of the microscopic scales of single-particle motion, to the macroscopic scales of solar eruptions. Implemented in appropriate models, their use is necessary for describing phenomena that less fundamental approaches cannot capture, allowing foe matching current and future observations with our theoretical predictions.The research on accurate, inexpensive particle-based methods for plasmas is essential for improving our understanding of high-energy astrophysical phenoma. My research is dedicated to the construction and application of new, advanced particle methods for simulations of plasmas both in the weak and strong gravity regimes. The ultimate goal is to unlock the mysteries of unexplored astrophysical processes at previously unreachable time, length, and energy scales.

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In 2019, the Event Horizon Telescope captured the very first image of a supermassive black hole in center of galaxy Messier 87 (M87*). In the image you observe a black disk in the center, which contains the black hole, and an orange ring surrounding it, which represents an accretion disk. An accretion disk is a flattened structure composed of matter (e.g. gas, dust plasma) found in orbital motion around a massive, gravitating object. Due to gravity, friction, and possibly other forces, it leads to matter gradually spiraling inwards towards the object. This infalling of matter onto the central object is called accretion. In astronomy, we typically observe these accretion disks around compact objects, which are very dense objects formed from the remains of a dying star. A neutron star is one known example of such a compact object. In this thesis, we investigated how the accretion of matter onto the surface of neutron stars affects their spin parameter, which is a dimensionless parameter that depends on their angular momentum and mass, and is a value between 0 and 1. Static neutron stars have a spin parameter equal to zero, while rapidly rotating neutron star have a spin parameter closer to one. Depending on how matter accretes onto the surface of the neutron star, we expect the neutron star to speed up or slow down, which results in the spin parameter to evolve in time. By changing the initial conditions of both the neutron star and the matter orbiting around it, we expect the evolution of the spin parameter to vary between different scenarios. The way how we investigated the evolution of the spin parameter during the accretion process is by simulating an accretion disk around a neutron star. This can be achieved using the recently developed accretion code GMUNU, which is specially designed to numerically solve both Einstein’s equations in General Relativity and the hydrodynamic equations. This code is different from most existing accretion codes because they use a specific approach that involves only solving the latter equations. However, if want more realistic results, we should solve them both simultaneously. We concluded that non-rotating accretion disk models had the biggest impact on slowing down both slow and fast rotating neutron stars. Additionally, when a disk rotates uniformly in the opposite direction to a fast spinning neutron star, it results in a greater increase of the spin parameter compared to the other rotating disk models considered in the simulations.