Chalmers Open Digital Repository
Välkommen till Chalmers öppna digitala arkiv!
Här hittar du:
- Studentarbeten utgivna på lärosätet, såväl kandidatarbeten som examensarbeten på grund- och masternivå
- Digitala specialsamlingar, som t ex Chalmers modellkammare
- Utvalda projektrapporter
Enheter i Chalmers ODR
Välj en enhet för att se alla samlingar.
Road condition classification from CCTV images using machine learning
Understanding and categorizing road conditions is crucial for driver safety and road maintenance. This research explores practical approaches to classify road conditions using images from CCTV stations. Two classification challenges are addressed: distinguishing between snowy and non-snowy conditions and between snowy, wet, and dry conditions. The thesis evaluates various machine learning methods for road condition classification on multiple CCTV stations, including established and novel approaches. Established methods involve feature extraction through texture analysis and finetuning convolutional neural networks and vision transformers. Novel contributions include training an image segmentation model for road segmentation and utilizing persistent homology for feature extraction. Notably, this thesis sets itself apart by separating data into training and test sets based on CCTV stations. This is important to evaluate the methods’ and models’ abilities to generalize to new CCTV stations. The best-performing model, a fine-tuned vision transformer, achieved accuracies of 87.9% and 75.3% for classifying snow/no snow and snow/wet/dry, respectively. These results underscore the complexity of the classification problem and highlight the effectiveness of deep learning models for large-scale road condition classification based on images.
Static solutions of the Einstein-Dirac system for an increasing number of particles behave as solutions of the Einstein- Vlasov system
In this thesis we will study static solutions to the spherically symmetric Einstein- Dirac system. This system couples Einstein’s theory of general relativity to Dirac’s relativistic description of quantum mechanics. The goal was to study the transition from a quantum mechanical description to a classical description by comparing properties of the solutions to the Einstein-Dirac system to solutions of the Einstein- Vlasov system as the number of particles of the former system increases. In 1999 Finster et al.  found for the first-time static solutions to the Einstein-Dirac system in the case of two fermions with opposite spins. Recently this study has been extended to a larger number of particles by Leith et al . In particular, they construct highly relativistic solutions. The structure of the solutions is strikingly similar to the structure of highly relativistic solutions of the Einstein-Vlasov system. In both cases multi-peak solutions are obtained, and moreover, the maximum compactness of the solutions is very similar. The compactness is measured by the quantity m/r, where m is the mass and r the areal radius, and in both cases the maximum value appears to be 4/9. Furthermore, in quantum mechanics the pressure may be negative whereas classically it is non-negative. We find that already for 16 particles the pressure is non-negative and thus behaves classically. In order to compare the solutions, I need to construct solutions numerically to the Einstein- Dirac system in the case of a large number of particles. This requires a delicate procedure with significant numerical precision when the number of particles in the system grows.
Evaluation of Novel Wingsail Concepts in Terms of Aerodynamic Efficiency
In this project the evaluation and comparison of five different designs for rigid wingsails were made by performing simulations in the CFD software STAR-CCM+ and two parameters, gap distance between foils and camber angle for three of the wingsails were varied to understand its effects. The wingsails in question were the crescent-shaped profile, two-element foil sails and three element foil sails. Three different designs were created for the two element foil sails with the following ratios of the total chord length between the front and aft foils; 70/30, 80/20, 90/10, and only one design for the three element foil sail with ratio 15/70/15. The parameters of gap distance and camber angle were only altered for the two element foil wingsails, while only the camber was altered for the three element foil wingsail. The comparisons that were made between the different designs were between the propulsive performances as well as stall angles. This study has found that, regarding the two element foil designs, the absence of a gap between the front and aft foils yield superior propulsive performance and that the difference in performance between different non-zero gap sizes is not very significant. The crescent-shaped profile performs significantly better than the non-cambered multi-element foil sails, but appeared to be a less favourable design when compared with the no-gap, cambered multi-element foil sails. However 3D simulation results revealed that the performance of the best multi-element foil design, the two element foil sail with ratio 70/30, no gap and 25° camber had been severely overestimated, and performed worse through all apparent wind angles when compared to the crescent-shaped profile. If we were to assume that the relation between the multi-element foil designs remained the same, in terms of performance over all apparent wind angles, when performing 3D simulations, then they would be ranked as follows. The best designs in terms of overall propulsion, in order of greatest to worst, are the crescent-shaped profile followed by the two element foil sails with ratio 70/30 and 80/20 with no gap and 25° camber and lastly ratio 90/10 (also no gap and 25° camber) and the three element foil profile with ratio 15/70/15 and 15° camber. It was discovered that the crescent-shaped profile began to experience stall, often much later than the multi-element foil designs, and reached its critical angle of attack earlier as well.
The influence of viscoelastic properties of bioinks on 3D bioprinted tissue models - A study of cell behaviour and printability
The recent advancement within the field of 3D bioprinting has enabled its appli cation in areas such as the pharmaceutical industry, tissue engineering and many types of cell-based research. The principle is to utilize 3D printing technology to print a variety of biomaterials together with viable cells, to produce accurate tissue models by mimicking the in vivo cell environment. Bioinks used for 3D bioprint ing are commonly composed of hydrogels based on naturally derived polymers like gelatin, collagen, alginate and nanofibrillated cellulose (NFC). Bioinks are viscoelas tic materials which can be crosslinked after being printed to keep their structure and shape. The crosslinking method and conditions determine the stiffness of the result ing tissue construct, which can in turn also affect the behaviour of incorporated cells. This study aims to investigate the influence of the bioink’s viscoelastic properties on both cell behaviour and printability of the bionink. The studied bioinks include CELLINK Bioink, GelMA, GelMA C, GelXA and Photogel95, which are crosslinked either ionically using a CaCl2 solution or using photo-crosslinking, or a combination of the two. The bioinks’ viscoelastic properties, as well as stiffness after crosslinking at two different conditions for each bioink were investigated using rheological measure ments, showing that different stiffnesses could be achieved. 3D bioprinting of the bioinks with mesenchymal stem cells (MSC) was used to produce samples which were crosslinked at the same two conditions, cultured over 14 days and analyzed at several time points. The cell viability was evaluated by fluorescent staining using Calcein-AM and propidium iodide (PI), and the cell morphology by using Actin Green and DAPI, followed by fluorescent microscopy imaging. The stiffness of the cell samples over time was also evaluated by measurements at the same time points. The stiffness of the cell samples over time showed some unexpected results and high variation between samples, which can to some extent be explained by the method not being fully suitable and well-adapted for these samples. The cell viability was relatively high at day 1 for all bioinks and crosslinking conditions, above 90 % for most samples but around 80 % for a few. A decrease in cell viability was then observed for all samples at day 7 and day 14. The cell morphology analysis showed cells spreading in all gelMA-based bioinks at day 7 and day 14, except for Photogel95. However, no distinct correlations between the stiffnesses achieved at the different crosslinking conditions and the cell behaviour could be determined.
Sfäriska polynom och deras nollställen på sfären
Bérard och Helffer visar i artikeln A. Stern’s analysis of the nodal sets of some families of spherical harmonics revisited [BH] på existensen av sfäriska polynom med en känd mängd nodaldomäner, områden som omsluts av nodalkurvor. Mer specifikt är ett av deras resultat att för udda gradtal har deras polynom exakt 2 nodaldomäner och för jämna gradtal ℓ exakt ℓ + 1 nodaldomäner. En modern artikel i matematik kan vara svår att ta till sig för studenter på kandidatnivå, även de inom matematik. Mycket bakgrund ligger i varje mening för att det forskarna vill presentera skall komma fram effektivt för andra forskare. Detta arbete syntetiserar deras studie med bakgrund om de sfäriska polynomen. Dessutom förklaras och förenklas deras artikel mer ingående och kräver mindre förkunskap. Slutligen simuleras och visualiseras några utvalda polynom och deras nodalkurvor och nodaldomäner.