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Science in Progress

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Displaying theses 41-50 of 1078 total
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F.A. Kummer
Bachelor programme: Natuur- en Sterrenkunde July 13th, 2018
Institute: API Research group: Planet formation group Graduation thesis Supervisor: Jayne Birkby
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Ranking stars based on the possibility to characterize a habitable Earth-like planet in orbit
Many astronomers are busy searching for Earth-like, habitable planets. To be able to sustain life on a planet, it has to satisfy certain conditions. The problem is that discovering and determining the habitability of Earth-like planets is very difficult. In this study, it is determined around which stars we have the best chance of characterizing an Earth-like planet in the shortest time possible. Every star has different properties. Some stars are hot and emit much light. Others stars are cold and emit little light. A duplicate of the Earth has been simulated around every star close to our solar system and calculated how long it would take to characterize this planet. A ranking has been made based on the shortest observation time needed to characterize the Earth-like planet. It appears that the M-type star ranks best. This type of star is fairly cold and thus emits little light. To support this outcome, planets orbiting hotter stars are harder to detect, because the signal of the planet is dominated by the stellar light. Also, planets orbiting colder stars are harder to detect, because the planet moves too close to the star in order to be distinguished from the stellar light.
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Scientific abstract (pdf 3K)   Full text (pdf 1919K)

B.P. Post
Bachelor programme: Natuur- en Sterrenkunde July 13th, 2018
Institute: ITFA Research group: String theory Graduation thesis Supervisor: dr. Diego Hofman
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Toric Geometry in the Gauged Linear Sigma Model
Mirror symmetry is one of the most fascinating interplays between geometry and physics from the last 30 years. Part of the mathematics behind mirror symmetry comes from toric geometry, which is concisely introduced and applied to a specific physical model. This model, the GLSM, has many interesting features such as supersymmetry, and it turns out that its supersymmetric ground states are toric varieties.
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Scientific abstract (pdf 245K)   For more info or full text, mail to:

W.J. van Soest
Bachelor programme: Natuur- en Sterrenkunde July 13th, 2018
Institute: Universiteit Utrecht Research group: Descartes Centre for the History and Philosophy of Graduation thesis Supervisor: Jeroen van Dongen
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Quantum teleportation understood though first-order pilot-wave theory
Pilot wave theory is an alternative interpretation of quantum mechanics that might solve the measurement problem. In this paper, the development of pilot wave theory by Louis de Broglie, David Bohm and John Stewart Bell will be discussed. De Broglie first presented the idea in 1927, but it was met with criticism and forgotten, I will argue that disappearance of pilot wave theory was not justified. In 1952, Bohm revived the theory by including the measuring device in the wave function when describing measurements. After reviewing this, I will develop the mathematics to describe the puzzling teleportation protocol in pilot wave terms. I will show that the expected result will arise by following the dynamics of the theory rather than by the collapse of the wave function. Also, I will argue that nothing is actually teleported and thus that teleportation is not the right term to describe the phenomenon, at least, not in the pilot wave interpretation. There is already one treatment in the literature, which uses Bohm's second-order formalism, but I will be using the simpler first-order formalism developed by de Broglie and Bell.
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Scientific abstract (pdf 1K)   Full text (pdf 432K)

N.A.C. van Sterkenburg
Bachelor programme: Natuur- en Sterrenkunde July 13th, 2018
Institute: AMC Research group: Biomedical Engineering and Physics Graduation thesis Supervisor: Dr. ir. D.J. Faber
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From reflectance as a function of absorption coefficient to path length distribution for photons in tissue using an inverse Laplace transform
When photons move through tissue, they are scattered in random directions until they leave the tissue or are absorbed. Photons are reflected when leaving the tissue on the same side they entered. We can research the properties of tissue by measuring how many photons are reflected. One thing we can measure is the reflectance as a function of absorption coefficient. This relation is interesting because it is connected to the path length distribution of the photons by an inverse Laplace transformation. But since the transformation is very hard to perform on experimental data, we looked at an algorithm created by Harald Stehfest which performs inverse Laplace transforms. It was tested how well this algorithm handles smooth signals and signals with added noise and how well the algorithm works on experimental data. This experimental data was created using a Monte Carlo simulation, that simulated photons moving through tissue. It turned out that the algorithm only works for smooth functions and returns useless results when there is noise in the signal. It is, however, possible to use the algorithm on a fit that was made to the experimental data. This was also tested in this project, but further research is necessary.
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Scientific abstract (pdf 1K)   Full text (pdf 630K)

W. Stolp
Master programme: Physics - Theoretical Physics July 12th, 2018
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: Bernard Nienhuis
Convolutional Neural Network Assisted Limited Angle Tomography by FBP, SIRT and TV-MIN Approximation
CT-scanners, such as used in medical and biological research, are able to produce detailed cross-sectional images of objects without opening them up. These images are calculated from projection data, collected by by emitting and recording penetrating radiation through the object at a number of different angles. As this radiation is generally harmful the number of angles and also the energy of the radiation source should be minimized, but minimizing them also lowers reconstruction quality. The methods to convert this measured projection data into a human friendly reconstruction image are diverse and numerous, and all have their advantages and disadvantages in terms of reconstruction quality and computation time. I have explored the possibilities of approximating reconstructions made by some traditional methods using a newly popularized computational tool that mimics some principles of the biological brain called an artificial neural network. Using this approach it is possible to create higher quality reconstructions when only lower quality projection data is available, and also to save significant computation time.
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Scientific abstract (pdf 1K)   Full text (pdf 4962K)

T.P.E. Blankenstein
Bachelor programme: Natuur- en Sterrenkunde July 12th, 2018
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: dhr. prof. dr. E.L.M.P. Laenen
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Renormalization, Regularization and the Renormalization Group in Quantum Field Theory
In physics, there are three main theories describing the physical world: general relativity (Einsteins theory of gravity), quantum mechanics (the theory of particles) and the 19th century theory of electricity and magnetism (electromagnetism). While unifying these theories has proved a difficult task, physicists have done a step in right direction with quantum electrodynamics, a theory that merges quantum mechanics and electromagnetism not with general relativity, but special relativity, the theory concerned with motion without gravity, using it together with the theory of fields (of particles, charges, etc.). Quantum electrodynamics is one of many so-called quantum field theories: a set of theories that all combine the same theories as quantum electrodynamics, minus the theory of electromagnetism. While these theories turned out to be extremely accurate, they did face a major problem: when physicists tried to calculate corrections on their predictions, their answers always diverged. To remedy this, they devised a set of techniques called renormalization to remove these divergences. To make the divergences manageable, so-called regularization methods were invented. After renormalization, physicists also found out that a related mathematical apparatus called the renormalization group enabled them to find the limitations of the predictive ability of the various quantum field theories.
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Scientific abstract (pdf 1K)   Full text (pdf 693K)

B.T.H. Verdonschot
Bachelor programme: Natuur- en Sterrenkunde July 10th, 2018
Institute: WZI Research group: Soft matter Graduation thesis Supervisor: prof. dr. P. Schall
FET mobility measurements of CsPbBr3 Perovskite Quantum Dot Films
The last few decades, there is a lot of research being done on improving the efficiency of solar panels, either by improving existing materials or applying new ones. One such new material are ‘Quantum Dots’, which are nanometer sized particles known for their outstanding ability to absorb, and emit, specific wavelengths of light. There are many materials exhibiting this behaviour, one of them being CsPbBr3. When this material is suspended in a solution, there are several methods to deposit this solution onto a surface which in this case affects how well it conducts. Therefore, three deposition methods – ‘drop-casting’, ‘spin-coating’ and ‘layered spin-coating’ – were compared to see which one gave the best conductance which turned out to be the last of the three. Next to this, three other effects that affected the conductance of the material were investigated: the increase of conductance over time, the difference in conductance when going further away from the center when spin-coating and the effect light intensity has on the conductance. Furthermore, it is noticed that the crystals of CsPbBr3 merge to small round shapes when the material is heated instead of the cubic shape they are normally found in.
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Scientific abstract (pdf 64K)   For more info or full text, mail to:

S.H. Vergouwen
Bachelor programme: Natuur- en Sterrenkunde July 10th, 2018
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: J. Rojo
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Constraining the Standard Model Effective Field Theory with top quark measurements
Although the standard model has made a large number of predictions, there are phenomena such as dark matter that it leaves unexplained. A beyond the standard model theory might provide more insight on these topics. This thesis focuses on the standard model as an effective field theory as a description of beyond the standard model physics. In this theory, operators with a mass dimension higher than four are included in the Lagrangian and suppressed by the energy scale. These operators describe new physics that have a small contribution at low energies, but have larger contribution at higher energies. The goal of this bachelor project was to put constraints on the Standard Model Effective Field Theory coefficient of the OtW operator, that influences the Wtb-coupling. Contributions of the operator to LO single top quark production processes are analyzed by computing the differential cross-sections for varied values of the operator coefficient and comparing them with measured cross-sections. The coefficient of the operator is calculated to be -6.49. This non-zero value hints that this operator represents a new physical particle.
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Scientific abstract (pdf 1K)   Full text (pdf 546K)

R.A.P. van den Ende
Bachelor programme: Natuur- en Sterrenkunde July 9th, 2018
Institute: NIKHEF Research group: KM3NeT Graduation thesis Supervisor: Ivo van Vulpen
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Eavesdropping on whales; the acoustic detection of ultra high energy neutrinos in the Mediterranean Sea
Neutrinos are elementary particles with an energy between 10^-6 and 10^19 eV. Only interacting via the weak force, neutrinos can provide valuable information but are hard to detect. KM3NeT is an international collaboration with a neutrino telescope of about a cubic kilometer that focuses on the detection of neutrinos via Cherenkov radiation. However, because ultra-high energy neutrinos have a low flux, a larger detection volume is required. As sound waves have a long attenuation length in water, KM3NeT aims to develop an experiment to detect the neutrino by its acoustic signal: when a neutrino interacts with a nucleon, the energy transfer that thereafter arises results in an increase in temperature, leading to a propagating expansion: a sound wave! A preparation for this large experiment is the deployment of two hydrophones in the Mediterranean Sea. In this thesis, data from these hydrophones has been analysed to eventually distinguish the neutrino signal from the background noise. Two algorithms have been tested, respectively based on amplitude or shape. It is found that both of these methods are not sensitive enough to detect the neutrino signal and further investigation as well as the deployment of more hydrophones are required.
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Scientific abstract (pdf 1K)   Full text (pdf 9371K)

P.J.N. Braat
Bachelor programme: Natuur- en Sterrenkunde July 8th, 2018
Institute: NIKHEF Research group: KM3NeT Graduation thesis Supervisor: dr. Paul de Jong
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Investigating possible biases in the efficiency determination of the KM3NeT detectors
In modern day physics there still exist a lot of unknowns of the neutrino particle, such as its exact mass or the proposed existence of sterile neutrinos. KM3NeT is an international research collaboration that focuses on neutrino physics by detecting these particles in the Mediterranean Sea using Photo-Multipliertubes (PMTs). To do this type of research it is necessary to accurately reconstruct the energy of the detected neutrino, and this is only possible if the efficiencies of the PMTs are accurately known as well. Luckily one of the background sources in the sea water can be used to determine the relative efficiencies of the PMTs, using the so called K40 calibration. My research focused on determining the inaccuracy of these relative efficiencies by investigating possible biases in this calibration. An overall inaccuracy of 5% on the determined efficiencies was found, and a suggestion was made in this report to improve the accuracy of the determination.
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Scientific abstract (pdf 57K)   Full text (pdf 3805K)

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