Fysik // Physics

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https://odr.chalmers.se/handle/20.500.12380/13

Utforskar och använder fysik för att förstå världen och bidrar med tillämpningar, nya material och innovationer som möter dagens behov och framtidens utmaningar.
Stimulerade av vår tids behov och utmaningar är institutionens ambition att främja en kreativ miljö för forskning, lärande och samverkan. Vi tillför en konkurrensfördel genom att länka de bästa internationella forskarna i materialvetenskap, nanoteknologi och energiforskning med ledande industriella partners.

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Explores and uses physics to understand the world, and provide applications, new materials and innovations that meet today's needs, and the challenges of the future.
Stimulated by major needs and challenges in society and industry, our ambition is to foster a creative environment for academic research, learning, innovations and utilisation. We provide a competitive advantage by linking top-level international and interdisciplinary academic performance in the areas of material science, nanotechnology, life science engineering and energy research with world-leading industrial R&D&I projects.

Studying at the Department of Physics at Chalmers

For research and research output, please visit https://research.chalmers.se/en/organization/physics/

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3D Nanoplasmonic Sensors
(2012) Nugroho, Ferry A. A.; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
3D SLAM using Microsoft Kinect
(2011) Johansson, Elias; Johansson, Sebastian; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
In this thesis, the Microsoft Kinect sensor has been considered for the purpose of simultaneous localization and mapping. A simple system for 6D pose estimation and 3D mapping is presented. The system uses the Kinect sensor, feature detection and recognition based on the speeded up robust features algorithm, estimation of movement based on the iterative closest point and random sample consensus algorithms and mapping with RGB colored 3D point clouds. The results indicate that the Kinect, which provides both 3D depth and RGB color images, is a suitable sensor for simultaneous localization and mapping systems. The system shows robustness for frame-to-frame rotation angles of 5 or less.
A combined Li-ion & lead-acid battery system for start-stop application: potential & realization
(2011) Taha Mahmoud, Heza; Xu, Lishan; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
The aim of this master thesis is to investigate the possibility of using lithium-ion batteries as a second battery instead of lead-acid batteries for the start-stop application in vehicles. To achieve the specified target, the following steps are explored: investigation of the technology market, choice of relevant sizing of the battery, development of charge algorithms for the battery system, creation of an electric simulation model with Simulink, development of a prototype for installation in car and finally verification of the new battery model in a vehicle. The battery which is chosen is a Li-ion battery with a voltage of 16.6V and a capacity of 30Ah due to the test-rig requirements and availability. Before implementation in the vehicle, tests are performed on the battery pack and the combined system. The controller system for charging and discharging is created in Simulink. Through several experiments, the working voltage range of the Li-ion battery pack was defined from 14.8V to 14.2V. In addition, a verification of this solution has been done in a real vehicle. Moreover, comparing the experimental results with our literature study, a new type of lithium-ion battery chemistry, which matches the characteristics required in this work is investigated: a LiFePO4 cathode based battery.
A FRET based assay for the quantification of synthetic and native lipid vesicles
(2018) Thorsteinsson, Konrad; Chalmers tekniska högskola / Institutionen för fysik (Chalmers); Chalmers University of Technology / Department of Physics (Chalmers)
Lipid nanoparticles, both of artificial and biological origin, have attracted significant attention in recent years. Biological lipid nanoparticles in the form of extracellular vesicles are involved in intercellular communication and biological material transport. Synthetic liposomes have also been proposed as promising drug delivery systems. In view of this broad interest, methods capable of accurately quantifying the content of lipid nanoparticles in a sample are urgently needed. To date, quantification is most commonly achieved by counting the particles after visualization, or by quantifying the total protein content in the case of particles of biological origin. In this thesis we present an alternative method allowing for the quantification of the total lipid surface area of an unknown sample. Our approach is based on Förster Resonance Energy Transfer (FRET), where the unknown lipid nanoparticle sample is sonicated with vesicles containing a FRET-fluorophore pair, leading to membrane fusion. The change in FRET fluorescence can then be correlated to the total surface area of the unknown sample. We first calibrated the method using synthetic vesicles of known surface area. We then tested the method on synthetic vesicles containing cholesterol, herpes simplex virus type 2, and two species of outer membrane vesicles secreted from E. coli bacteria. Finally, we benchmarked our results against alternative established methods and discussed potential and limitation of each. Our results indicate that the FRET assay is suitable to quantify all the lipid nanoparticle samples tested here and serves as a viable measurement technique to quantify lipid surface areas.
A Global Optimization Scheme for Bimetallic Nanoparticles
(2011) Takahashi, Keisuke; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
The nature of atomic clusters has increasingly attracted the attention of researchers over the last few decades. One of the primary reasons for the rise in interest is that the physical and chemical properties of atomic metal clusters are different from their corresponding bulk metals. To understand cluster properties, knowledge of the relevant structures are needed. However, structural information is very difficult to acquire from experiments. In this thesis, a theoretical approach is used instead. In particular, a Basin-Hopping global optimization algorithm is implemented where the atomic interactions are calculated from first principles by use of the Density Functional Theory (DFT). The Basin-Hopping code is written with the Python programming language and the Siesta and Dmol softwares are used to run the DFT calculations. Structures of bimetallic structures are the primary focus, as they are known as highly-effective hydrogenation catalysts. In addition, the monometallic cluster structures of Sn and Ru are explored. Sn clusters in a range from 2 to 20 atoms with higher stability than previously reported structures were obtained. The optimized Ru clusters match with previous reported results. The electronic, magnetic, and chemical properties of ground state clusters are discussed. The new method was, furthermore, used to study structures of a range of bimetallic systems including Ru-Sn, Ru-Pd, Pd-Au, and other similar structures.
A GPU Polyhedral Discrete Element Method
(2020) Bilock, Adam; Chalmers tekniska högskola / Institutionen för fysik; Logg, Anders; Jareteg, Klas
This thesis presents a Discrete Element Method (DEM) to simulate irregular shaped particles by a non-convex polyhedron representation. By using novel GPU techniques and an efficient HPC implementation the presented method shows a level of throughput not previously attained with polyhedron particle representations in the open literature. Further, via such a representation the exact volumetric overlaps of the particles are resolved and, as a result, the method is robust and numerically stable with respect to geometric changes. The efficient and well-behaved method allows for significant progress in the study of granular materials, where previously mainly the inadequate particle representation of spherical or clumped spherical particles have been used. The exact volumetric overlaps are resolved by a simplex representation which allows for the use of non-convex particles without any decomposition, aiding both performance and the ease of use of the method. Further, care is given to attain efficient scaling of the method with respect to particle resolution. Such a property enables studies on higher resolution particles than previously shown in relatedwork, and is result of efficient filtering of polyhedron triangles in the narrow contact phase. In addition, other novel techniques, such as a GPU BVH implementation for the broad phase contact detection, also aids the performance and the flexibility of the proposed and implemented method. The method is shown to be convergent with respect to particle resolution, both for individual particle collisions and also for laboratory scale particle systems. The HPC implementation is proven to be highly efficient, where, for instance, a one second simulation of one million non-convex particles is simulated within an hour on a single GPU. By the effective filtering of triangles in the narrow contact phase, near linear scaling can be achieved with regards to particle resolution.
A microscopy study of the atmospheric corrosion of aluminium
(2005) Ingemarsson, Linda; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
A model for the evolution of local adaptation of a subdivided population
(2014) emanuelsson, anna; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
The ecotypes of Littorina saxatalis are believed to be intermediate steps in an ongoing speciation process. L. saxatalis is therefore of scientific interest as a model organism for speciation by local adaptation. In order to understand the genetic patterns that arise from the local adaptation, temporal and spatial adaptation dynamics in a model with two partly isolated subpopulations are analysed. The model is implemented by means of individualbased stochastic simulations and deterministic approximations. We obtain qualitative understanding of the mechanisms underlying local adaptation by investigating how a mutant allele (beneficial in one sub-population) is accepted in a system already containing two alleles (each adapted to opposite sub-populations) with frequencies in steady state. The sizes of the original alleles describe the level of local adaptation before the mutation event. We find the parameter regions where the mutant allele replaces one original allele and investigate the dynamics further within this region. We investigate the replacement probability of the mutant allele. We show that the replacement probability increases with increasing mutation effect size, decreases with increasing degree of local adaptation and decreases with increasing value of the migration rate. We investigate the improvement in average phenotype that results from a replacement of one of the original alleles by the mutant allele, and we investigate the amount of deleterious alleles within each sub-population (the gene flow). We find that the gene flow between the sub populations decrease with increased level of adaptation. By allowing for recombination between two loci, we derive results that implies that a concentrated genetic architecture is preferred by the system in certain parameter regions.
A Neural Network Approach to Absolute State-of-Health Estimation in Electric Vehicles Battery Degradation Study Based on Fleet Data
(2018) Johansson, Herman; Chalmers tekniska högskola / Institutionen för fysik (Chalmers); Chalmers University of Technology / Department of Physics (Chalmers)
Electrification is a trend within the automotive industry. Many car manufacturers are launching electric vehicles, which are believed to be more sustainable and environmentally friendly. A major component in these cars is the battery, and its performance is crucial to the success of the electric vehicle. Therefor, the degradation of battery properties is interesting, especially the capacity decline. To understand and counter this degradation it must be measured with high precision in the cars, and be connected to car use. This project approaches this challenge by: using real fleet data, the aggregation of the data into events, and a neural network to estimate the state of the battery. The result is a proof of concept that gives an improved measure of the battery state and how different usage affects the capacity degradation. The result is, however, not validated at this point, shows unexplained properties, and should be further developed.
A non-Gaussian Approach to Heavy Particle Simulation in Turbulent Flow
(2024) Freygardsson, Thorsteinn; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Gustafsson, Kristian; Gustafsson, Kristian; Mehlig, Bernhard
The behaviour of heavy particles suspended in turbulence is of vital importance in many branches of science. It gives insight into droplet formation in clouds, plankton distribution in the oceans and pollen carried by the wind, among other things. Turbulent systems are highly dependent on the system parameters, making experimental observation and classical simulations difficult. However, statistical models of these systems can often give insight into the dynamics of suspended particles. In this thesis such a statistical model is constructed, and the dynamics of inertial particles in such a flow are analyzed. Our main focus is on how non-Gaussian flows affect preferential sampling, and we will also look into void formation and fractal clustering.
A question of aggregation A comparative study of objective function creation methods applied to missile defense for helicopters
(2014) djurfeldt, hanna; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
This report describes an investigation done about method one can use when creating a target function for optimization and the e ects of those choices. Three simple and four advanced target function creation methods are described in detail and the results from optimizing with these target functions are analyzed. Lastly suggestions into possible continuations of this investigation is made.
A study of electrolytes for rechargeable zinc-metal batteries
(2022) Engblom, Alexander; Chalmers tekniska högskola / Institutionen för fysik; Matic, Aleksandar; Xiong, Shizhao
Today batteries can be found in a large variety of products and the use of batteries increases every year. However, current battery technologies are approaching their limit and will likely struggle to keep up with future demands. Due to this, battery technology must take a leap forward and explore new chemistries and concepts. One promising candidate for this is the zinc-metal battery, which is made out of more environmentally friendly and safer materials and could offer high energy density. However, the disadvantage of zinc-metal batteries is their short cycle life which is caused by the growth of zinc dendrites, inducing short circuiting. There have been several approaches to suppress the growth of zinc dendrites and electrolyte design is one of the most promising approaches. In this project electrolyte design, including salt concentration and exploration of additives, was studied with the aim to stabilize the zinc anode in a zinc-metal battery. The salt chosen was zinc sulfate heptahydrate, which was added at different concentration to water to create aqueous electrolytes. Their physical properties such as ion conductivity, viscosity, density, and their infrared and Raman spectrum were then measured. The effect of salt concentration on the stability and Coulombic efficiency of coin cells were also investigated. To explore the effects of additives sulfated cellulose nanocrystals (CNC) and sodium carboxymethyl cellulose (CMC) were added to the electrolyte and the characterization was performed once again on these new electrolytes. How the salt concentration and the additives affected the zinc deposition was studied through the use of scanning electron microscopy (SEM). The results of this project show that a molar ratio of water and zinc ions between 25:1-50:1 is the most suitable for the stability and Coulombic efficiency of coin cells. The additives did not affect the physical properties of the electrolyte notably, apart from the viscosity. However, they did affect the electrochemical performance, CNC improved the Coulombic efficiency and CMC improved the stability. The SEM images showed that the salt concentration and the additives do affect the morphology of the deposited zinc.
A study of periodic and quasi-periodicorientational motion of microrods in a shear flow using optical tweezers
(2014) Laas, Alexander; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
The orientational motions of single isolated inertialess microrods are studied in a reversible creeping shear ow. In previous work [12, 24, 30] it was observed that rodlike particles could experience both periodic and quasi-periodic behavior. This work studies how the orientational motion, including periodic and quasi-periodic motion, depends upon the orientational initial conditions, for a single microrod. For the purpose of changing the initial conditions, optical tweezers are installed in the experimental setup. In order to demonstrate that the microdrods and uid are inertialess the ow is reversed and the trajectories before and after the reversal are analyzed. If both the microrod and the ow are inertialess, the orientational motion of the rod is expected to retrace itself when the ow is reversed. The experimental results show that if the ow is reversed smoothly, particles can show this retraceibility. The experimental results also demonstrate that a single rod may exhibit either periodic or quasi-periodic motion, depending solely on its orientational initial condition. The observable dynamics show good agreement with Je ery's equations of motion for an inertialess ellipsoid in a creeping shear flow.
A taste of dark portals
(2021) Åstrand, Emil; Chalmers tekniska högskola / Institutionen för fysik; Martin Heinz, Andreas; Catena, Riccardo
Overwhelming evidence on all cosmological scales points to the inevitable existence of Dark Matter (DM), constituting approximately 85% of all matter in the Universe. The different evidence have one thing in common: they all depend on indirect, gravitational effects arising from the presence of DM. The particle nature of DM remains unknown. While the Weakly Interacting Massive Particle (WIMP) has been a promising candidate to DM, extensive direct detection searches has not yet found a conclusive signal. A possibility is that DM does not interact directly with the Standard Model (SM) but rather through an unstable mediator particle, scenarios commonly referred to as dark portals. A way to probe such models is through flavour changing rare decays of mesons, which are heavily suppressed in the SM, but receive contributions from dark portal models. In this work I consider a model where spin-1 DM is realised as a hidden U(1) symmetry, spontaneously broken by a singlet scalar that acts as the mediator and mixes with the SM Higgs field. This extension induces contributions to the branching fractions B0 s,d ! `+`− where the particular ones B0 s ! μ+μ− and B0 ! μ+μ− have been measured experimentally. The contributions were found to be primarily dependent on the mixing angle and the mediator mass MH1 . I find that while the most likely combination of fundamental parameters lies on the straight line sin2 /M2H 1 = 0.001 where sin 2 [10−3, 1] and MH1 2 [100.5, 101.5] GeV, a large region below this line possess a flat, intermediate likelihood. This is due to the effects of H1’s presence is heavily suppressed by its mass. At the moment the analysis of constraints on spin-1 DM by rare meson decays is largely
A Tensor Formalism for Exceptional Geometry
(2014) Edlund, Joakim; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental Physics
Toroidal compactification of M-theory and its low energy limit, eleven-dimensional supergravity, possess hidden symmetries giving fields additional degrees of freedom. By extending the space-time to accomodate these extra degrees of freedom and constructing a generalised geometry on this space, the U-duality symmetry can be made manifest. The local diffeomorphism invariance is replaced by the larger exceptional groups which also happens to include gauge transformations. In this thesis, a tensor calculus for the exceptional generalised geometry is constructed. The geometrical concepts of diffeomorphisms, torsion, curvature, reducibility, tensors and tensor fields are given a generalised, covariant construction in the toroidally compactified, enhanced space-directions.
A Theoretical Study of Doping and the Hydration Process of Barium Zirconate
(2013) Pór Benediktsson, Magnús; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
In this thesis we give a brief review of Kohn-Sham density functional theory and different exchange-correlation functionals. The BaZrO3 lattice constant is obtained and the ground state considered. We examine the electronic structure using PBE and PBE0. PBE0 provides a greatly improved density of states. We consider the use of H2O as a reference molecule for O which reduces error due to PBE’s description of O2 binding energy by 40%. We compare the local environment around an oxygen vacancy in BaZrO3 to that in SrTiO3 and examine the expansion due to dopant atoms and hydration in BaZrO3. Then follows a comparative study between the PBE and PBE0 description of oxidation and hydration in BaZrO3. We calculate the reaction enthalpies, equilibrium rate constants and defect concentration profiles most relevant for the reactions. The PBE0 and PBE oxidation enthalpy are positive and negative respectively which leads to very different rate constants and concentration profiles. However, neither one of the enthalpies seem to contradict experimental evidence of increased electrical conductivity at elevated temperature.
A top-down model for layered holographic strange metals
(2021) Lexell, Olle; Chalmers tekniska högskola / Institutionen för fysik; Gran, Ulf; Gran, Ulf
The AdS/CFT correspondence is a potentially powerful tool in describing condensed matter systems for which our current theoretical understanding is lacking. This is because it can be used to map a strongly coupled field theory to a weakly coupled gravitational theory. In this thesis I describe some aspects of the AdS/CFT correspondence and look at a top-down model. This model is built upon a large number of D3 and D5 branes with a D7 probe brane. The goal is to see whether this model can be used to describe aspects of the strange metal phase that is found in layered high-temperature superconductors. Starting from a weakly coupled string theory setting I derive the temperaturedependence of a DC current in different regimes, as well as dispersion relations for electromagnetic fluctuations. There is a possibility of obtaining resistivity that matches the linear in T dependence for the resistivity in strange metals. This is done by adjusting the number of D5 branes depending on the temperature and the charge density, which is obtained holographically. With a particular choice of boundary conditions, plasmonic dispersion relations are found, as required. This is the first layered top-down model with this behaviour for the current available in its parameter-space. While it has not produced correct predictions without an adjustment of the parameter-space, the freedoms granted from the said parameter-space makes it possible that this model could describe other layered systems that lacks quasi-particles, and not just strange metals.
Ab Initio Modelling of Zirconium Hydrides
(2013) OLOFSSON, JOHAN; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
Zirconium alloys are very suitable as fuel claddings and structural components in nuclear reactors due to their low cross section for ab- sorption of thermal neutrons and high resistance to corrosion and irra- diation damage. Zirconium alloys are however susceptible to hydrogen embrittlement. Precipitation of zirconium hydrides is attributed to the embrittlement effect in zirconium alloys. In this project ab-initio simulations of Zr and the three different zirconium hydrides -ZrH, -ZrH1:5 and -ZrH2 are performed to calculate structural, elastic and thermal properties of these different compounds. The goal with the project was to calculate the equilibrium structures of the H-Zr system using ab-initio methods. The results from the calculations of thermal and mechanical properties were found to be in good agreement with previous results and experiments where these were available. Calcula- tions of the phonon band structure for the different hydrides show that the band structure of the hydrides has two characteristic bands, one corresponding to vibrations in the zirconium sublattice and one cor- responding to vibrations in the hydrogen sublattice. The calculated heat capacity of the different compounds was found to be described very well by the Einstein model for the heat capacity of a solid. By calculating the free energy of formation for the different compounds it was found that at high hydrogen concentrations -hydride is the equi- librium structure. At intermediate hydrogen levels the equilibrium structure can't be determined.
Absorption av mörk materia i dielektriska material
(2024) Chan, Emma; Hermansson, Johan; Hoogervorst, Carl; Syvänen, Isak; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Swenson, Jan; Catena, Riccardo
Syftet med denna studie var att undersöka absorption av mörk materia i form av mörka fotoner för de åtta materialen Al2O3, GaN, Al, ZnS, GaAs, SiO2, Si och Ge. För att göra detta undersöktes absorptionshastigheten Γ samt absorptionshastighetens händelsefrekvens N hos de mörka fotonerna. Detta gjordes med numeriska och analytiska metoder. Det centrala för båda analyserna var att Γ och N delades upp i en longitudinell del samt en transversell del som undersöktes separat. Den numeriska analysen utfördes med hjälp av Python-paketet DarkELF som innehöll färdig data för den dielektriska funktionen εr(q,ω). Resultaten för Γ presenterades med grafer i massintervallet 1-10 eV och för N redovisades respektive materials händelsefrekvens för massan 1 eV i en tabell. Från tabellen kunde slutsatsen dras att Al var mest benägen att absorbera mörka fotoner medan SiO2 var minst benägen. För den analytiska delen användes Kramers-Kronig relationerna för att härleda ett uttryck för en övre gräns av N. För den longitudinella delen presenteras en graf som visar hur materialen förhåller sig till den övre gränsen. Resultatet visar att aluminium är nära att mätta den övre gränsen. Den transversella händelsefrekvensen kunde däremot inte evalueras då uttrycket blev materialberoende.
Accelerating computations for dark matter direct detection experiments via neural networks and GPUs
(2023) OLVHAMMAR, HANNA; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Catena, Riccardo; Catena, Riccardo
There is indisputable evidence for the existence of dark matter (DM). Examples are the rotation curves of galaxies, the velocity dispersions of galaxy clusters and dark matter density measurements. One of the biggest questions in physics today con cerns the nature of dark matter, and the most promising theory is that dark matter consists of one or more new particle species. To discover the nature of dark matter particles, they need to be inferred from collider experiments or found via indirect or direct detection. Since none of these alternatives has led to conclusive results within the current theoretical frameworks, new approaches should be investigated. In this thesis, sub-GeV dark matter particles are studied through interactions in direct de tection experiments described with an effective field theory (EFT). More specifically, dark matter-induced electronic transition rates in crystal detectors are studied. The rate of electronic transitions is described with EFT scattering amplitudes, which introduce many model-independent coupling strengths. By computing transition rates corresponding to different sets of EFT parameters, direct detection data can be used for inferring properties of dark matter particles without relying on any specific theoretical framework. Since the computation of the electronic transition rates is very expensive, the aim of this thesis is to implement a deep neural network for fast predictions of transition rates. Furthermore, since the neural network re quires a large data set for training, the generation of training data was accelerated using computations on graphics processing units (GPUs). I developed two neural networks, one with the DM mass as input and one with the DM mass and two EFT coupling strengths as inputs, that are about 600 times faster than the original computations and capture the overall behaviour of the transition rates. However, the relative error of the predictions has a standard deviation of about 30% with a mean of around 0%. On the other hand, the GPU computations are about 16 times faster than the original computations and have negligible error while being able to compute transition rates corresponding to all 28 coupling strengths. I conclude that there is great potential for using both neural networks and GPUs for dark matter research, and suggest further improvements.

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