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Senast publicerade
- Modellering av utspädningskylare: Simulering och analys av 3He/4He-utspädningskylare i subkelvinområde(2026) Bornecrantz, Martin; Skog Brönnestam, Axel; Engh, Hugo; Hansson, Magdalena; Mohlin Lindgren, Oscar; Ottosson, MelvinInstitutionen för mekanik och maritima vetenskaper vill tillsammans med Wallenberg Center for Quantum Technology och Atlas Copco utveckla en skalbar modell av en utspädningskylare. Alla större kvantdatorer kyls idag med hjälp av 3He/4Heutspädningskylare. Dessa system är väl beprövade och pålitliga, men problem uppstår när man vill utöka antalet kvantbitar i kvantdatorn. Detta beror på att kraven på kyleffekt ökar för att kunna hålla kvantbitarna vid tillräckligt låga temperaturer. Målet med projektet var att utveckla en modell som kan användas som grund för framtida forskning med syftet att modellera och öka kylsystemets totala kyleffekt. Projektet inleddes med att skapa en förståelse för de individuella delsystemen i utspädningskylaren och modellera dem separat. Delsystemen implementerades därefter som klasser i en Pythonfil och integrerades sedan i en Jupyter Notebook för att sammanställa den kompletta modellen av utspädningskylaren. Resultatet är en välfungerande modell vars värden överensstämmer med litteraturen, och inga tydliga ofysikaliska beteenden har observerats. Eftersom inga liknade modeller finns öppet tillgängliga utgör modellen en god grund för framtida forskning inom området.
- Deposition of Graphene-based Nanoflakes on Polymer Substrates for Scalable Production of Antibacterial Medical Devices(2026) Al-Yousifi, PetraCatheter-associated urinary tract infections are a worldwide problem that is usually solved with antibiotics, leading to an increased risk of antibiotic resistance which is a global threat. A way of decreasing the prescription of antibiotics is reducing the risk of infections by mechanically killing the bacteria or inhibiting its ability to attach and create a biofilm on the surface of a catheter. This may be achieved with sharp vertically aligned graphene-based nanoflakes on the polymeric surface. The aim of the study was to identify a robust and effective method for a homogeneous deposition of graphene-based nanoflakes onto a polymeric surface for scalable production. To explore materials and methods a screening process was done before creating the final samples. The samples were made using plasma and flame treatments in combination with drop casting and dip coating methods. Surface characterization of the samples was performed with scanning electron microscopy and atomic force microscopy. The results showed that a homogeneous coating in combination with laser treatment can achieve vertically aligned nanoflakes structure with different densities depending on the amount of deposited graphene-based nanoflakes.
- Design, Simulation and Implementation of an Active Common Mode EMI Filter for a DC/DC Application(2026) Nilsson, Edvin; Karlsson, EdvinThis thesis implements an active common mode EMI filter in a DC/DC converter. Different topologies and strategies were analyzed and a voltage sense current injection type active filter was designed. The stability and performance were analyzed with analytical models, simulations and physical measurements. A stable active EMI filter was designed on a prototype PCB and was proven to attenuate common mode noise with up to 18 dB μV up to 700 kHz at 20 kW converter load. The inductance of the common mode chokes was then reduced, and it was verified theoretically and with low voltage measurements. An active filter with common mode chokes with 64% lower inductance has a similar performance to a passive filter. This could however not be confirmed with 20 kW tests due to voltage limitations in the Op-amp of the active filter. An off the shelf IC from Texas Instruments was also evaluated, with good low voltage performance but saturated for high noise voltages when the converter was loaded with 20 kW.
- Solar-fed Portable Charging Module for Camping/ Solcellsdriven Portabel Laddningsmodul för FriluftsaktiviteterSandström, Oliver; Moberg, Gabriel; Hasselgren, Anton; Karlsson, SimonWith an increasing interest in outdoor recreational activities such as hiking and camping and an increasing reliance on portable gadgets, the demand for portable power solutions is expanding. This project aims to design and prototype a solar fed portable charging module to address such a demand. The aim of the project is to efficiently extract solar energy and support charging of a power bank. The system architecture consist of an input from a solar panel, the designed DC-DC converter and a power bank as energy storage source. To efficiently extract solar energy, a Perturb & Observe based Maximum Power Point Tracking algorithm, along with the suitable charging control logic is implemented. The DC-DC converter and the control algorithm is verified using MATLAB Simulink. Following the simulation, a hardware prototype PCB is designed using KiCad with the control logic implemented on the Arduino platform. While the basic functionality of hardware is tested, further testing of the DC-DC converter with the implemented control logic needs to be performed in the future
- Dynamic Dependence Among Economic Sectors in Equity Markets(2026) Möller, MarcusThis study investigates the dynamic dependence structure between equity market sectors using a Markov regime-switching copula framework. The analysis focuses on return distributions across economic sectors and their lower-tail dependence, particularly across different market regimes. The proposed model builds on empirical evidence that market drawdowns can be contagious and that pairwise dependence between assets tends to increase during periods of market stress. Modeling dynamic dependence can provide a more robust risk framework for portfolio evaluation and asset allocation. In this setting, dependence is allowed to vary over time through regime shifts and is linked to market sentiment. This thesis extends Bubbles and dependence between international equity markets by Wuyi Ye, Lingbo Gao and Xiaoquan Liu (2024) by applying a similar framework to a different data sample. Specifically, the model is applied to equity market sectors (S&P 500 sub-indices: Industrials, Materials, Energy, Healthcare, Financials, Information Technology, and Consumer Non-Cyclical) rather than a geographic cross section, using daily returns over the period 1989-2026. Empirically, the conditional regime-switching copula provides a better fit for many index pairs than an unconditional regime-switching copula and a static copula benchmark. However, in an out-of-sample asset allocation exercise, we are unable to replicate the economic gains reported in Wuyi Ye, Lingbo Gao and Xiaoquan Liu (2024): portfolios based on the conditional model do not consistently achieve higher riskadjusted returns, evaluated by their Sharpe ratio, than equally weighted portfolios or portfolios constructed using a static copula model. Nonetheless, the model-based portfolios often exhibit lower maximum drawdowns, indicating that the framework can capture and mitigate some tail risk.