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Road condition classification from CCTV images using machine learning
(2023) Askbom, Ludvig; Chalmers tekniska högskola / Institutionen för matematiska vetenskaper; Persson, Daniel; Persson, Daniel
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.
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Static solutions of the Einstein-Dirac system for an increasing number of particles behave as solutions of the Einstein- Vlasov system
(2023) Blomqvist, Joakim; Chalmers tekniska högskola / Institutionen för matematiska vetenskaper; Andréasson, Håkan; Andréasson, Håkan
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. [10] 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 [14]. 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.
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Evaluation of Novel Wingsail Concepts in Terms of Aerodynamic Efficiency
(2023) Ljungberg, Erik; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Yao, Hua-Dong; Zhu, Heng; Ramne, Bengt; Lee, Henry; Marimon Giovannetti, Laura
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.
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The influence of viscoelastic properties of bioinks on 3D bioprinted tissue models - A study of cell behaviour and printability
(2023) Ekström, Sofie; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Gold, Julie; Pernevik, Elin
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.
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Sfäriska polynom och deras nollställen på sfären
(2023) Hjelström, August; Sundkvist, Levi; Bilén, Pontus; Flodén, Quentin; Chalmers tekniska högskola / Institutionen för matematiska vetenskaper; Chalmers University of Technology / Department of Mathematical Sciences; Dinger, Ulla; Zhang, Genkai
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.