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Modeling the effect of guanidinium in hybrid halide perovskites
(2025) Dahlgren Blumenau, Rickard
advancing
solar cell technologies. However, they face many issues especially related
to stability, since in general they easily degrade into photo-inactive phases due to
environmental factors like temperature, humidity and light. It is thus of interest
to understand the phase behaviors of these systems to be able to engineer stable
perovskite solar cells with favorable optoelectronic properties. Two of the most
promising organic halide perovskites for solar cells are MAPbI3 (MAPI) and FAPbI3
(FAPI). By mixing these it is possible to tune the optoelectronic properties and
phase behavior. In recent studies it has been shown that incorporating GUAPbI3
(GUAPI) could further improve the optoelectronic properties by for instance increasing
the charge carrier lifetime. However, the exact phase behaviors of these
systems have not been investigated extensively. Thus, in this thesis the temperature
dependence of the phase behaviors of mixed (MA,FA,GUA)PbI3 as well as each
pure systems were investigated by training a neuro evolution potential (NEP) model
on structural properties calculated through density functional theory (DFT). The
model predicted the previously known phase behaviors of FAPI and MAPI. Additionally,
the morphotropic phase boundary (MPB) between MAPI and FAPI was
found around 21% of FAPI, which is in agreement with previous studies. GUAPI
was found to adopt the a−a−a− phase at temperatures below 280K. Furthermore,
it was found that adding GUAPI to (MA,FA)PbI3 the MPB shifted towards higher
FAPI concentrations.
Optimizing Night Driving Simulations: A Comparative Study of Light Simulation Software
(2025) Liang, Lanyu
Night driving simulations are essential tools for the development and validation of advanced automotive lighting systems. These simulations require not only photometrically accurate representations of light-material interactions but also real-time performance suitable for iterative design and driver-in-the-loop evaluations. This thesis presents a comparative study of three rendering platforms: Ansys AVxcelerate Headlamp, Synopsys LucidDrive, and Unity, to assess their capabilities in simulating nighttime driving environments with high visual fidelity.
The study benchmarks these tools across several dimensions, including rendering performance, photometric accuracy, and perceptual similarity, using standardized test scenes and real-world photometric profiles. A particular focus is placed on evaluating Unitys real-time ray tracing capabilities, enhanced by ReSTIR, against the more static and proprietary pipelines of AVxcelerate and LucidDrive. Experiments utilize standardized test scenes and automotive-grade models under controlled nighttime conditions, profiling performance via structural similarity of rendering results, GPU utilization, frame rate, and memory consumption.
The results underscore the limitations of commercial tools in handling dynamic lighting scenarios and complex BRDFs, while highlighting the flexibility and performance of open rendering frameworks. This work provides a reproducible benchmarking methodology and lays the foundation for future research on hybrid rendering strategies, perceptual validation models, and real-time simulation of intelligent headlight systems.
Bridging Trust and Design of a Multi-Agent LLM-Based HR Chatbot: For the Times They Are A-Changin’
(2025) Axetorn, Jonatan; Edholm, Felix
Introduction: The integration of Large Language Models (LLMs) into workplace systems presents significant opportunities, particularly in the domain of human resources (HR), where repetitive tasks—such as providing information that employees could retrieve themselves—are common and could potentially be replaced by an LLM-based solution. However, a lack of user trust remains a major barrier to the adoption of LLM-based systems.
Objective: This thesis investigates what trust factors exist in LLM-based systems and how they can be addressed by system design, with a specific focus on a multiagent HR chatbot.
Method: Using a Design Science Research methodology, the study was conducted in two iterative cycles. Cycle I identified trust factors through literature review and interviews with six employees at a multinational company. It also included a workshop with five AI experts to discuss and validate design choices. Cycle II involved implementing, and evaluating an artifact, a multi-agent chatbot tailored to HR queries.
Findings: Thematic analysis revealed external trust factors: transparency, organisational measures, and external security and internal trust factors: internal security, model differences, risk of bias and reliability, which emerged as the most critical trust factor. The artifact was evaluated through interviews and metrics such as answer relevancy, faithfulness, and robustness, showing consistently strong performance and broad user acceptance.
Conclusion: The multi-agent HR chatbot effectively addressed key trust concerns and was positively received by most interviewees, demonstrating its potential for real-world application. These findings suggest that trust factors can be meaningfully addressed through thoughtful design and should be treated as a core consideration throughout the development process of LLM-based systems.
Security-Aware Scheduling of Real-Time Tasks on Multi-core Processors
(2025) Cotton, Liam
Modern real-time systems are increasingly exposed to timing-based security threats due to their predictable task scheduling. When scheduling tasks for real-time execution, a predictable execution pattern is needed to ensure all tasks will meet their deadlines. A common practice is to employ a fixed-priority scheduler, a deterministic scheduling algorithm always choosing the same task to execute every time it’s given the same conditions. Schedule-based attacks exploit this determinism, enabling adversaries to manipulate or extract sensitive information by aligning their execution with critical tasks. To counter this, schedule randomization has emerged as a potential solution, introducing controlled unpredictability into task execution.
This thesis investigates the application of schedule randomization in multi-core realtime systems, particularly when tasks are pre-allocated to specific cores. The study builds upon TaskShuffler, an already existing algorithm that introduces randomness into the previously deterministic fixed priority scheduler. This algorithm, designed for single-core systems, is now extended for multi-core use. Further, we examine techniques to mitigate or circumvent schedule-based attacks targeting multi-core systems. We also extend the concept of schedule entropy, a “randomness” metric, to better suit multi-core systems, as well as introduce new security-aware metric to capture the risk of common types of targeted attacks. We evaluate the security and performance impact of our methods by by simulating tasks execution on multi-core processors under different task sets and configurations. This provides insights into how core assignment and priority relations affect the system’s exposure to schedulebased attacks. Such insights may help the system designer to strengthen the security of the systems by allocating or not allocating certain tasks to certain cores at design time.
Synthesis and Characterization of Barium Titanate and Barium Indate-Zirconate Perovskite Oxyhydrides
(2025) Johansson, Isac
The global imperative to reduce CO2 emissions has driven interest in catalytic conversion technologies, particularly CO2 hydrogenation, which transforms CO2 into valuable chemicals. This reaction often relies on metallic nanoparticles supported
on catalyst substrates, commonly metal oxides like Al2O3 or ZrO2. Perovskite oxides have emerged as promising alternatives due to their adjustable surface chemistry, thermal stability, and ability to host redox-active defect sites. Recent attention has turned to anion-adjusted perovskite materials, amongst them oxyhydrides, where oxygen anions are partially replaced by hydride ions. These modifications can enhance catalytic performance and introduce properties such as hydride ion conductivity and interesting electronic and magnetic properties. This project focused on the synthesis and structural analysis of reduced perovskite oxides of synthesised barium titanate (BaTiO3), nano-crystalline barium titanate and barium indate-zirconate (BaZr1−xInxO3− x2 ). For BaTiO3, synthesis routes mainly investigated reduction with CaH2 enclosed in stainless steel capsules, filled with high purity argon. For BaZr1−xInxO3− x2 , reduction by H2 gas annealing was investigated. Characterization heavily relied on powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) measurements. Inelastic neutron scatterin (INS) was performed for a reduced 50% indium substituted BaZr0.5In0.5O2.75. The study primarily investigated how synthesis parameters such as molar ratio of CaH2, temperature, and heating time affect reduction extent, anion composition, phase formation, impurity formation and crystallinity. The CaH2 reduction of synthesized tetragonal BaTiO3 at 600◦C for 48 hours yields reduced products with a cubic phase, accompanied by a colour change from white to dark blue or black. An increased molar ratio of CaH2 leads to a greater degree of reduction. Rietveld refinements indicate formation of a single phase in these reduced samples. In contrast, samples of nano-BaTiO3 subjected to the same reduction conditions exhibit a lower degree of reduction and show more pronounced two-phase indications. Higher molar CaH2 ratios result in the formation of Ba2TiO4 impurities. These impurity phases can be reduced by decreasing the CaH2 ratio. For the nano-BaTiO3, a temperature decrease to 580◦ C doesn’t impact Ba2TiO4 amounts. Shortening the heating time to 24 hours leads to decreased amounts, at the expense of a lower reduction extent in the nano-BaTiO3 perovskite phase. Hydrogen annealing of BaZr1−xInxO3− x2 with 50% indium substitution at 800◦ C for 24 hours and 70% substitution at 650◦ C for 20 hours give reduced perovskite oxides of barium indate-zirconate. The extent of reduction is comparable between the two compositions. Inelastic neutron scattering (INS) measurements on the 50% BaZr1−xInxO3−x/2 sample indicate minimal hydride incorporation.