Examensarbeten för masterexamen

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    Detecting and Tracking Regions of Interest for Remote Measurement of Vital Parameters
    (2022) Müller, Madeleine; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Forssen, Christian; Garcia Lozano, Marianela
    The initial assessment of a mass casualty incident is essential to effectively conduct a rescue operation. The survival rate is affected by the complexity of the incident, and it is therefore imperative to enhance the operational capacities of emergency medical services and civil protection agencies in mass casualty incidents. This thesis investigates the possibilities for an unmanned aerial vehicle (UAV) to detect and track regions of interest for remote measurement of vital parameters in visual and thermal footage for first response triage purposes. The regions of interest are the nose, mouth, and chest, and the UAV characteristic taken under consideration in this thesis is image blur due to random camera motion. In this thesis, we take an object detection approach and implement the keypoint estimation framework KAPAO and the tracking algorithm SORT in several different experimental setups. Using KAPAO and SORT, we achieve a good result. For the detection in the thermal domain, the model created by transferring knowledge from the visual to the thermal domain achieves the highest performance. We also consider adversarial training on random motion blur, however the result shows a minimal impact on the model performance in the presence of characteristic low-altitude UAV motion blur. Regarding the tracking of the regions of interest, the result concludes that the SORT algorithm improves the performance compared to assigning tracking identification numbers based on frame-to-frame differences. The result shows that the distance to the subjects and the image quality impacts the performance. Compared with previous work on remote measurement of vital parameters, the algorithms of this thesis achieve a nearly perfect score on corresponding distances. If the distances are realizable in a UAV triage application is however unknown and has to be investigated further. Moreover, the work of this thesis problematizes the low-altitude UAV motion blur which poses a potential limitation in a potential UAV triage application. An alternative could hence be to use optical stabilization measurement for blur reduction.
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    High energy lithium-ion battery characterisation and overcharge abuse test
    (2022) PATIL, AKHILESH SATISH; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Mellander, Bengt-Erik; Furlani, Maurizio
    Batteries are finding extensive applications in different domains. Lithium-ion batteries are one of the most interesting kinds. They are used in most of the portable electronic equip ment, small and large appliances, electrical energy storage system and electric vehicles due to their high power and high energy densities. Nevertheless lithium-ion technology has its own dangers due to presence of highly volatile and flammable materials. These properties can lead to emissions of gas from the cell package, further leading to thermal runaway and toxic gas emissions. Many researches have reported that gas emissions in clude highly detrimental gases like hydrogen fluoride (HF), carbon monoxide (CO) as well as phosphoryl fluoride (POF3). The lithium-ion cell construction involves graphite based anode metal oxide cathode and a liquid electrolyte with high lithium ion mobility. Due to high electrochemical reactivity and mechanical degradation under different operative conditions, the battery will eventu ally lead to decreased performance. Cathodic materials limit the energy density and are the primary reason for the battery cost. Those materials being Nickel (Ni), Manganese (Mn) and Cobalt (Co) with lithium intercalating oxides. The different proportion of these metals can influence the performance levels in the batteries. In this thesis, a number of methods have been used to characterize prismatic lithium-ion battery cells. The investigation has included analysis of the disassembled cell components using: thermal analysis for the separator material, X-ray diffraction (XRD) for electrode materials and Fourier transform infrared spectroscopy (FTIR) for liquid electrolyte anal ysis, gas analysis, as well as electrical measurements such as impedance, charge and dis charge tests on the complete cell. Overcharge abuse tests have been performed to further investigate cell safety by analysing gas emissions using gas sensors, FTIR and physical parameters such as temperature across the thermal runaway in a cell fault scenario.
  • Post
    The Path To Relaxation - Understanding thermal conduction in twisted stacks with non-equilibrium phonon dynamics
    (2022) Wallin Hybelius, Patrik; Chalmers tekniska högskola / Institutionen för fysik; Erhart, Paul
    In this work, the details of thermal transport in graphite is studied. The aim is to un derstand a striking anisotropy observed in the thermal conductivity of twisted stacks of van-der-Waals thin sheets, as well as to explore the limitations of the relaxation time approximation of the Boltzmann transport equation. To this end, classical molecular dynamics simulations were performed, and analyzed using projection onto phonon modes. Atomic forces were modeled using neuroevolution potentials previ ously trained on results from density functional theory, and gpumd was used to run simulations on graphical processing units. Phonon modes were defined from Second order force constants extracted from the neuroevolution potential using hiphive. The simulations were done both in equilibrium and in variations of non-equilibrium. The equilibrium phonons were modeled using Langevin dynamics to extract their lifetimes and finite-temperature renormalized frequencies. Non-equilibrium states were studied by exciting individual out-of-plane modes to extreme amplitudes be fore running the simulations, and then following the energy as it was distributed from the pumped modes to the rest of the system. Contrary to the exponential decay predicted by the relaxation time approximation, energy was observed to os cillate back and forth between modes when initially excited to a sufficient degree. Furthermore, the system was observed to reach a long-lived quasi-equilibrium state, where a set of coupled modes collectively retained an above-equilibrium energy for an extended period of time. The quasi-equilibrium lifetime was found to depend negatively on the size of the simulated system, but the limit at large sizes remains unknown.
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    Optimizing the Design of Nanofluidic Chips with Graph Reinforcement Learning A General Graph Attentional Framework Applied on Nanoscale Catalytic Reactor Systems
    (2022) Ulmestrand, Mattias; Chalmers tekniska högskola / Institutionen för fysik; Langhammer, Christoph
    Nanofluidic chips are devices where fluids are controlled at nanoscale. Langhammer Lab at Chalmers University of Technology researches nanofluidic chips for cataly sis reactions. On these nanoscale reactors, catalysts are placed to maximize some property such as the reactant conversion rate to product. However, to this point, no framework exists for optimizing the design of the group’s nanofludic chips. Chips are currently designed through laborious trial and error. In this master’s thesis, a framework based on reinforcement learning with graph attentional neural networks is presented and applied for optimizing the design of nanofludic chips. A reinforcement learning agent is trained on a reward system based on computational fluid dynam ics (CFD) and consistently outperforms simulated manual designs. Additionally, a considerably lighter reward system based on ant colony optimization (ACO) is developed for placing catalysts and forming channels. The ACO reward system is shown to be highly correlated with the CFD reward system, but requires some fur ther developement in order to achieve the same performance as the CFD reward system.
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    Potassium nucleation and growth on substrates of disparate potassiophilicity
    (2022) Chrobak, Wojciech; Chalmers tekniska högskola / Institutionen för fysik; Matic, Aleksandar; Rizell, Josef
    The increasing demand for batteries in combination with the limited lithium (Li) reserves has motivated the search for alternatives to the conventional Li-ion battery chemistry. Batteries based on potassium (K) have been proposed due to its greater abundance compared to Li in the Earth’s crust. However, the larger weight of K compared to Li necessitates the use of K metal anodes to attain competitive energy densities in K batteries. Metallic anodes are problematic pertaining to rechargeability, as a result of their tendency to form dendritic morphology during cycling. The dendrites are detrimental to the coulombic efficiency of the cells and even hazardous, as they can grow through the separator to the other electrode, causing a short circuit. To control the morphology of K metal, it is imperative to build a fundamental understanding of the electrochemical deposition of K. This work focuses on studying electrochemical deposition of K metal onto various substrates by method of constant current cycling. With this technique, the voltage response is recorded and the peaks during deposition correspond to the nucleation process. The substrate onto which the metal is deposited affects the nucleation and ostensibly the emerging morphology as a consequence. A surprising result is the similarity in depth of the nucleation peaks for the substrates tungsten (W), previously predicted to be superpotassiophobic and gold (Au), expected to be potassiophilic. Another is the both deeper and wider peak for copper (Cu) as compared to W, even though Cu was theoretically estimated to be over 4 times less potassiophobic.