Displaying theses 3140 of 1078 total
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M.R. Wesseling 
Bachelor programme: Natuur en Sterrenkunde  July 25th, 2018  
Institute: ITFA  Research group: Edan Lerner  Graduation thesis  Supervisor: Edan Lerner 
Micromechanical framework of nonlinear excitations in glassy solids Many materials possess an ordered, crystallic atomic structure. However, there are also materials where the atoms are randomly jumbled together, called amorphous solids. These materials can possess interesting properties, however how these properties arise is not fully understood. This project researched a model that attempts to understand the properties of amorphous materials. The research was performed with computational simulations. We have found that the model is capable of identifying weak points in an amorphous material. The properties of these weak points do not depend on the amount of particles. As there is more material, more weak points exist. 

Scientific abstract (pdf 1K) Full text (pdf 1510K) 
J.N. van Haastere 
Bachelor programme: Natuur en Sterrenkunde  July 25th, 2018  
Institute: API  Research group: Planet formation group  Graduation thesis  Supervisor: prof. dr. J.M.L.B. Desert 
Transiting Exoplanet Atmosphere with James Webb Space Telescope In 2021 the highly anticipated James Webb Space Telescope will finally become operational. In my research I focused on its potential for researching exoplanet atmospheres. An exoplanet atmosphere contains information about the formation location of the exoplanet, and it can be used to look at signs of extraterrestrial life. We can probe exoplanet atmospheres with transit spectroscopy, which is measuring the flux dependency on wavelength during a transit. A transit is basically a solar eclipse but observed from very far away. The exoplanet passes in front (or behind) its hoststar from Earth’s pointofview which decreases the overall flux. However, we can only observe such a transit with one instrument at the time, which makes for a very important decision; which instrumental mode to use? I developed a tool which can determine by simulating such observations, which instrumental mode of the JWST gives the best constrains for measuring certain key atmospheric characteristics for a given planet and star. I also looked into a revolutionary mode of the MIRI instrument, where I explored its capabilities to follow individual spectral features with high resolution spectroscopy. 

Scientific abstract (pdf 75K) For more info or full text, mail to: desert@uva.nl 
M.P. Stoop 
Bachelor programme: Natuur en Sterrenkunde  July 22nd, 2018  
Institute: API  Research group: General Neutron Stars  Graduation thesis  Supervisor: Rudy Wijnands 
Investigating deep crustal heating in accreting neutron stars A neutron star is one of the most dense objects in the universe. If the neutron star exists in a binary system, it can accrete matter from the companion star. This accreted matter builds up and compresses the crust, releasing heat through exothermic reactions. This brings the crust out of thermal equilibrium with the core. When accretion stops, the crust of the neutron star cools down. This cooling can be observed and allows us to test theoretical models on accreting neutron stars. Currently, two heating mechanisms are used; deep crustal heating and shallow heating. However, the processes behind shallow heating are unknown. If shallow heating alone is enough to describe accreting neutron stars then deep crustal heating could be neglected. I tested this for six accreting neutron stars using the thermal evolution code NSCool by D. Page and L.S. Ootes. I found that models with only shallow heating were able to fit with similar accuracy as models with both deep and shallow crustal heating. This might indicate that deep crustal heating could be neglected in accreting neutron stars. Because of this, understanding shallow heating is of extra importance and requires further research. 

Scientific abstract (pdf 2K) For more info or full text, mail to: R.A.D.Wijnands@uva.nl 
L.M. van Manen 
Bachelor programme: Natuur en Sterrenkunde  July 19th, 2018  
Institute: ITFA  Research group: String theory  Graduation thesis  Supervisor: dhr. dr. B.W. Freivogel 

Holographic vs. nonholographic inequalities. In 1997, the antideSitter spacetime/conformal field theory (AdS/CFT) conjecture was proposed by Maldacena and became a big breakthrough in high energy physics. All of the sudden, quantum gravity theories could be related to quantum field theories. In 2006, Ryu and Takayanagi proposed an interesting idea in the context of AdS/CFT. Their proposition was to relate entanglement entropy of a quantum system A to the minimal surface in AdS, with the boundary of the minimal surface fixed to the boundary of A. This relation is also known as the holographic entropy. With the holographic entropy, another holographic relation between the logarithmic entanglement negativity and mutual information was proposed. In this project, inequalities as (strong) subadditivity, ArakiLieb, and mutual information, which are obeyed by entanglement entropy, are studied for holographic and nonholographic systems. After this, the relation between holographic logarithmic negativity and mutual information was evaluated with the Werner state and random Hamiltonians. The aim was to find a pattern in states for which this relation occurs, and such, to possibly learn about the physical interpretation of this relation and why the logarithmic negativity is always threequarters of the mutual information for holographic systems. 

Scientific abstract (pdf 2K) Full text (pdf 1613K) 
M. Jaarsma 
Bachelor programme: Natuur en Sterrenkunde  July 17th, 2018  
Institute: NIKHEF  Research group: Theoretical Physics at NIKHEF  Graduation thesis  Supervisor: Marieke Postma 

Baryogenesis in a FirstOrder Electroweak Phase Transition A thesis on how the abundance of matter over antimatter could have arisen in the electroweak phase transition in the early universe 

Scientific abstract (pdf 6K) Full text (pdf 655K) 
T.M. Vonk 
Master programme: Physics  Theoretical Physics  July 17th, 2018  
Institute: ITFA  Research group: Condensed Matter Theory  Graduation thesis  Supervisor: Jasper van Wezel 

A new look at edge modes, in the context of the bulkboundary correspondence The bulkboundary correspondence is a major, but underrated, part of the topological classification of solids. In this thesis, bulk topology and an example of the correspondence are reviewed. A recent method for finding boundary modes is discussed and implemented to investigate the SSH chain and the chargedensitywave. This method reveals level repulsion between bulk and boundary modes. 

Scientific abstract (pdf 3731K) Full text (pdf 3731K) 
J.M. de Wit 
Master programme: Physics  Theoretical Physics  July 17th, 2018  
Institute: ITFA  Research group: Condensed Matter Theory  Graduation thesis  Supervisor: JeanSébastien Caux 
Spin chains with integrabilitypreserving impurities We will analyse the YangBaxter integrable spin1/2 XXX model. For this 2 model, the form of the monodromy matrix that returns the XXX model in the algebraic Bethe ansatz is known. Now we will evaluate the matrix away from the homogeneous limit that is used to generate the XXX model’s Hamiltonian. The resulting Hamiltonian mimics the XXX model with additional spin interactions terms including nextnearest neighbour interactions. We extend domain of the impurities from the real axis to the complex plane by imposing some restrictions, with substantiated arguments that would guar antee physical relevance, on how to move away from the homogeneous limit. We analyse the twoparticle sector and we show how the impurities lead to the disappearing of complex solutions and validate these predictions with numerical analysis of the newly obtained inhomogeneous XXX Bethe equations. 

Scientific abstract (pdf 1K) Full text (pdf 758K) 
T. Zwart 
Master programme: Physics  Theoretical Physics  July 17th, 2018  
Institute: ITFA  Research group: Statistical Physics and Condensed Matter Theory  Graduation thesis  Supervisor: JeanSébastien Caux 
Summing matrix elements of the LiebLiniger model with reinforcement learning Correlation functions play an important role in physics. Calculating these functions is impossible for many systems and has to be done with a computer. One way to do this is to transform the correlation function to a form in which we perform a summation of matrix elements. It turns out that only a small fraction of all states has to be considered to get a very good approximation of the correlation functions. The ABACUS algorithm can do this summation for a class of systems that are “Bethe ansatz solvable”. The subject of this thesis is the optimization of the summation such that only important matrix elements are summed, using reinforcement learning. Reinforcement learning is a form of machine learning in which an algorithm has an interaction with the environment and sees the results of this interaction in the form of a reward, after which the interaction is changed to optimize for higher rewards. We trained a reinforcement learning algorithm to select states with large matrix elements, given the current state the system is occupying. The algorithm was able to find large matrix elements, especially when compared to randomly selecting states. Compared with ABACUS however, ABACUS turned out to perform better. 

Scientific abstract (pdf 1K) Full text (pdf 6020K) 
T. Nikolakopoulou 
Master programme: Physics  Theoretical Physics  July 16th, 2018  
Institute: ITFA  Research group: String theory  Graduation thesis  Supervisor: Ben Freivogel 
Building traversable wormholes from Casimir energy and nonlocal couplings The main purpose of this project is finding ways to construct traversable wormholes and study various aspects of them, first by using Casimir energy and then by the use of nonlocal couplings. In the second case we perform explicit calculations in order to make sure that if we send a particle through this wormhole it will indeed reach the other side safely, and we calculate a bound on the number of particles we are allowed to send. 

Scientific abstract (pdf 2K) Full text (pdf 1367K) 
B.Y.W.K. Matthaei 
Bachelor programme: Natuur en Sterrenkunde  July 15th, 2018  
Institute: NIKHEF  Research group: VIRGO  Graduation thesis  Supervisor: prof. dr. Frank Linde 

Comparison of parameter estimates of a simulated spinning and nonspinning Binary Neutron Star Inspiral using TaylorF2 with 6PN, 7.5PN and NR Tidal approximants Gravitational waves are a physical phenomenom predicted by Einstein more than 100 years ago. Only recently have detectors reached a high enough sensitivity to detect the waves. The waves are emitted by the most compact objects in the universe: black holes and neutron stars. These objects have been observed before but the physics behind them puzzles scientists. Gravitational waves offer a new source of information. Deciphering the waves could play a key role in understanding these objects. Gravitational waves emitted by black holes and neutron stars share an equal base form, but the waves emitted by neutron stars have an additional tidal imprint. To make the most of the limited data available, many simulations of events which emit gravitational waves are made. By analysing the simulations and comparing them with the observed signals, the models can be refined. This thesis simulates gravitational waves emitted by a binary neutron star inspiral. To the created waveform simulated noise will be added and an algorithm will be applied in order to attempt to retrieve the parameters. The simulation will compare different tidal approximants to gauge the accuracy of the approximants. 

Scientific abstract (pdf 37K) Full text (pdf 1196K) 
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