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Recent theoretical and experimental results have revealed the existence of magnetic monopoles, in the form of quasi particles, in both condensed matter known as spin ice, as well as in two-dimensional artificial versions of the same material. In this report a two-dimensional Ising model is first examined, then an artificial square spin ice model using a dipole approximation, only taking into account nearest and next nearest neighbors. The Metropolis algorithm is used to obtain the internal energy, specific heat capacity and entropy as functions of temperature. In the latter model the magnetic monopole concentration and monopole current is also simulated. The two models show similar quantitative behavior in the above mentioned physical quantities, and in comparison to previously published results. In the artificial square spin ice model, under the influence of a magnetic field, a rapidly decreasing monopole current is observed, which decreases faster for higher temperatures. The magnitude of the magnetic field plays a significant role in the generation of the monopole current, and no direct effect of the phase transitionis observed. / Nya teoretiska och experimentella resultat har uppvisat förekomsten av magnetiska monopoler, i form av kvasi-partiklar, både i kondenserade material kallade spinn-is, och i tvådimensionella artificiella versioner av samma material. I den här rapporten undersöks först en tvådimensionell Isingmodell, därefter en artificiell kvadratisk spinn-is-modell med hjälpav en dipolapproximation, där hänsyn endast tas till närmaste och näst närmaste grannar. Metropolis-algoritmen används för beräkna energi, specifika värmekapaciteten och entropinsom funktioner av temperatur. I den senare modellen simuleras även monopolskoncentrationen och monopolsströmmen. De två modellerna uppvisar snarlikt kvantitativt beteende med avseende på ovan nämnda fysikaliska storheter, jämfört med varandra och tidigare publicerade resultat. Under inverkan av ett magnetfält observeras en snabbt avtagande monopolsström, i den artificiella kvadratiska spinn-is-modellen, som avtar snabbare med högre temperaturer. Storleken på det pålagda magnetfältet har markant betydelse för alstrande av monopolsströmmen, och ingen direkt effekt av fasövergången observeras.

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PoGOLite (Polarised Gamma-Ray Observer Lite) is a balloon borne experiment meant to measure the polarisation of the electromagnetic radiation from specic astrophysical objects. The main target of interest for PoGOLite is the Crab pulsar. A considerable particle background was recorded during the short flight of PoGOLite in July 2011. In order to further study the particle background before the relaunch of PoGOLite, a smaller experiment named PoGOLino was initiated. For both experiments, methods to increase the signal to noise ratio in the data collected are important. The aim of this project has been to propose new methods for increasing the signal to noise ratio in collected data, and quantitatively compare them with the previous methods. On a data sample where the original ratio of signal to noise was 0.1, the prior methods were able to increase the ratio to 1.13. A signal to noise ratio of 1.98 was achieved on the same data sample, when executing two algorithms developed during the course of this project in sequence.

The interest in high-energy astrophysics and to venture beyond the standard model has driven theoretical and experimental physicists around the world to collaborate and buildthe necessary instrumentation to test out all the different theories in particle physics. Energies up to 14 TeV have been thoroughly investigated so far by colliding protons in the Large Hadron Collider (LHC). Cosmic ray maps showed us the existence of even higher energies coming from outer space. What is the nature of such particles, and why do they accelerate to as much as 1020 eV? The study of Ultra High-Energy Cosmic Rays (UHECR) is a new and active research area where physicists hope to find the sources of such high-energy particles and confirm already existing theories. This thesis discusses the detections of UHECR, and more specifically the space approach. The ongoing project JEM-EUSO is planned to be launched in 2018 by the Japanese heavy liftrocket H2B, and conveyed to the International Space Station (ISS), where it is thought to gather more data than what already have been obtained all the previous years from the earth’s surface. The detection of UHECR occurs through the "atmospheric detector", where an incoming particle makes a shower of secondary particles in the atmosphere called Extensive Air Shower (EAS) upon contact. This shower of particles yields both flourenscence light and Cherenkov light. The problem at hand is to figure out the amount and distribution of the photons created, and how many of these photons actually will reach the detectors of the JEM-EUSO up on the ISS.

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