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Displaying theses 81-90 of 1078 total
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O. Pavlou
Master programme: Physics - Particle and Astroparticle Physics April 11th, 2018
Institute: API Research group: CTA Group Graduation thesis Supervisor: dr. Jacco Vink
Fermi-LAT Gamma-Ray data analysis of the Supernova Remnant Cassiopeia A
In this work, we perform data analysis of Gamma-Ray observational data of the Supernova Remnant Cassiopeia A, taken from the Fermi-LAT satellite mission between August 2008 and March 2016, in the energy ranges between 100 MeV - 300 GeV. The analysis was done using the latest Fermi Science Tools with the Pass 8 Fermi library to extract the Spectral Energy Distribution of Cas A. A comparison is made with the most recent official releases of data for this SNR by the Fermi Science team (in 2013), which used a previous version of the tools (Pass 7) to showcase the improvement in statistics. Model fi tting was done using a Python fi tting package called "Naima", to compare between the leptonic and hadronic emission models for the Cosmic- Rays. We used values for parameters provided by the 2013 Fermi paper, as well as estimating different values for these parameters that best t the emission models in question. We also performed a deeper theoretical and analytical examination on the enhancement factor used by the Fermi Science team and present the effect a different nuclear composition of the Remnant and the surrounding environment would have on the total estimated explosion kinetic energy.
picture that illustrates the research done
Scientific abstract (pdf 1K)   Full text (pdf 11221K)

E.G.M. Elias
Master programme: Science for Energy and Sustainability - Physics / Chemistry March 9th, 2018
Institute: Other Research group: Universit`a di Roma La Sapienza, Department of Phy Graduation thesis Supervisor: Roberta Croce
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In Silico Investigation of the Spectral Properties of P700
In the field of photosynthesis the P700 complex lies at the hart of the photosystem I reaction center and plays a vital role in the process. Not suprisingly therefore in the past a lot of spectroscopic studies have been conducted aimed at elucidating its electronic structure, because it is this electronic structure that gives the P700 complex its amazing properties. However, these studies are not always completely understood. With the help of quantum mechanical computer simulations we have therefore calculated the infrared- , absorption - and resonance Raman spectra of the P700 complex. We have shown that coupled vibrations and furthermore all C=O groups in the P700 complex are important in its infrared spectrum. Furthermore we confirm the hypothesis that exciton-, charge-transfer- and pigment-protein-interactions redshift the bandgap in the P700 complex. Finally, we provide a starting point for assigning the bands in the resonance Raman spectrum of the positively charged form of P700. All in all, our research gives valuable information about how charge transfer could proceed within the PSI reaction center and we suggest to perform QM/MM simulations in the future in order to clarify our results.
picture that illustrates the research done
Scientific abstract (pdf 25K)   For more info or full text, mail to: r.croce@vu.nl

K.D. Temmink
Master programme: Physics - Theoretical Physics February 28th, 2018
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: dr. Philippe R. Corboz
On Tensor Network Methods for One-Dimensional Open Quantum Systems
Many quantum systems of interest cannot be described with detailed mathematical expressions, or even numerically exactly. This is because the number of parameters necessary to describe a quantum system grows exponentially with the system size. Tensor Networks (TN) are powerful numerical methods that allow one to efficiently represent or approximate quantum states and operators. Presently, a wide range of TN methods are available for Isolated Quantum Systems (IQS) that do not have any interaction with their environments. Less has been accomplished for Open Quantum Systems (OQS), systems that do interact with their environments. These interactions typically result in complicated mathematical expressions for the behaviour of a system, if they can be obtained at all. Numerically, these systems are notoriously difficult, because extensions of IQS methods are generally unable to represent these systems in a physically valid manner. In this thesis, we study and compare the most general methods for OQS: a naïve extension of an IQS method, a variational method, and the ‘local purification’ method, which was designed to explicitly ensure the physical validity of simulated systems. We find that this last method performs the best in terms of the combination of accuracy, reliability and computational cost.
picture that illustrates the research done
Scientific abstract (pdf 56K)   Full text (pdf 6652K)

I.R. van Voorst
Bachelor programme: Natuur- en Sterrenkunde January 15th, 2018
Institute: VU / Physics & Astr. Research group: Hybrid Solar Energy Conversion Graduation thesis Supervisor: Elizabeth von Hauff
Non-invasive glucose detection on an artificial sweat dropletwith Raman spectroscopy
At the moment, the glocose level of diabetes patients is measured with blood through finger pricking. This is often painful for the skin. The goal of this project is to design a glucose meter which is non-invasive by measuring the glucose level with Raman spectroscopy. This means that a laser is focused on the sweat, which will make the molecules vibrate. When the molecules stop vibrating, a photon is send back and that will be measured. The photon send back will have a different energy than the incoming light. All molecular bonds will send a photon back with an unique energy, which means that this can be used to identify the molecules. Our measurements counted all photons. When the concentration of glucose is increase, the counts will increase. For this theses we used a liquid sample which contained glucose sodiumchloride, urea and lactic acid. We show that there is a linear relation between the concentration of the glucose and the intensity of the Raman peaks of glucose in the Raman spectrum. This linearity can be used to detect glucose concentrations. We also measured samples for 16.5 minutes long and have shown that the measurements are stable during this period.
picture that illustrates the research done
Scientific abstract (pdf 1K)   For more info or full text, mail to: e.l.von.hauff@vu.nl

E. Malami
Master programme: Physics - Particle and Astroparticle Physics November 30th, 2017
Institute: NIKHEF Research group: Theoretical Physics at NIKHEF Graduation thesis Supervisor: Robert Fleischer
CP Violation in B0d → π0KS. Are there any Hints of New Physics?
We study Charge Conjugation and Parity (CP) Violation in B0→π0KS decay and we search for hints of New Physics. We perform a state-of-the-art analysis of the Standard Model picture with predictions, which will be very valuable for B-meson experiments. The B0d→π0KS decay is dominated by QCD loop diagrams (penguins) but electroweak penguins, where New Physics may enter, also have a significant impact on the decay amplitude. Our aim is to propose a new strategy for the optimal determination of the parameters which describe electroweak penguin effects, and apply it to the current data, utilising both neutral and charged B→πK decays. This new method can be fully exploited at the future Belle II experiment, which will hopefully answer the question: Do these decays imply New physics?
picture that illustrates the research done
Scientific abstract (pdf 2K)   For more info or full text, mail to: robert.fleischer@nikhef.nl

L.J.T. Verhoeven
Master programme: Physics - Theoretical Physics October 9th, 2017
Institute: NIKHEF Research group: Theoretical Physics at NIKHEF Graduation thesis Supervisor: Prof. dr. Robert Fleischer
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Lepton Flavor Violating Higgs
In the Standard Model, the flavor of charged leptons is almost completely conserved. In most beyond the Standard Model theories, however, lepton flavor changing interactions come forward naturally. This makes lepton flavor violation a very promising probe for new physics. So far, no signal of lepton flavor violation has been seen, but measurements on lepton flavor violating tauons give only weak bounds. This makes it interesting to look at many different interactions that involve tauons that change flavor and find out if we can detect a non-zero signal. Many models predict that Higgs interactions can change lepton flavor, so decays in which Higgs bosons play a role are a prime candidate for study. Of these, the Z -> tau mu gamma decay is experimentally very interesting, as it has the potential to be measured very accurately. We discuss whether this decay can be useful to find lepton flavor violation.
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Scientific abstract (pdf 140K)   Full text (pdf 1372K)

A.K. Frick
Master programme: Science for Energy and Sustainability - Physics / Chemistry October 6th, 2017
Institute: VU / Physics & Astr. Research group: Physics of Energy Graduation thesis Supervisor: Elizabeth von Hauff
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Elimination of Strong Background auto-fluorescence on Raman Spectroscopy in mouse brains tissue with low voltage inputs
Near-Infrared (NIR) Raman spectroscopy is a technique that has re-emerged as a potential tool for imaging and analysing biological materials due to new advancements in the field. One of the main areas that has received renewed attention is the reduction of auto-fluorescence, which has been one of the most troublesome issues within the community. In my Thesis I describe a new, minimally invasive technique for significantly reducing the Raman spectroscopy background fluorescence in mouse brains by electrically contacting them during the measurement. This finding opens up the possibility for a plethora of further investigations on the inner workings of living tissue when connected to a circuit and to what extent this quenching effect can be utilised in practice. The outlook for this new technology is that after some further development of this technique’s extensiveness, with regards to applicable materials and Raman excitation wavelength, biological tissue will be able to be measured with a reduced fluorescence, thus increasing the readability of all hard-to-read data.
picture that illustrates the research done
Scientific abstract (pdf 81K)   For more info or full text, mail to: e.l.von.hauff@vu.nl

J.A. Wildeboer
Master programme: Gravitation and Astroparticle Physics Amsterdam (GRAPPA), track offered by both Physics / Astronomy September 30th, 2017
Institute: NIKHEF Research group: Dark Matter Graduation thesis Supervisor: Prof. Dr. Patrick Decowski
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Threshold optimization and Bayesian inference on the XENON1T experiment
Dark matter is one of the basic constituents of the Universe, five times more abundant than ordinary matter. Several astronomical measurements have corroborated the existence of dark matter, leading to a worldwide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence. The XENON Collaboration now operates the XENON1T experiment. The result from a first science run shows that this detector has a new record low radioactivity level. With a total mass of about 3200kg, XENON1T is at the same time the largest detector of this type ever built. This thesis reports on the optimization of the thresholds inside XENON1T's data processor and examines Bayesian inference as an alternative statistical method to set upper limits on the WIMP-nucleon cross section.
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Scientific abstract (pdf 1K)   Full text (pdf 7155K)

J.C. Veenstra
Master programme: Physics - Theoretical Physics September 30th, 2017
Institute: ITFA Research group: Condensed Matter Theory Graduation thesis Supervisor: J. van Wezel
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Spontaneous Unitarity Breaking in Macroscopic Quantum Systems
A system's Hilbert space grows exponentially with the number of particles it contains due to the linearity of quantum mechanics. Classical state space, however, only scales linearly with system size. Naively, this would lead one to conclude that classical states become increasingly rare in the thermodynamic limit. Evidently, the opposite is true and it would seem that a symmetry of the macroscopic Hilbert space is implicitly broken. The macro-objectification problem, as this mismatch between theory and reality is known, has been the subject of debate for over a century. In this thesis we review some existing solutions and develop a dynamical description in terms of spontaneous symmetry breaking.
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Scientific abstract (pdf 2K)   Full text (pdf 2910K)

V.R. Stalman
Master programme: Physics - Theoretical Physics September 27th, 2017
Institute: ITFA Research group: String theory Graduation thesis Supervisor: Dr. Diego Hofman
Non-Relativistic String Theory in Newton-Cartan & Carroll Spacetimes
In this work we evaluate the properties of world sheet theories in spacetimes that have non-relativistic global symmetries supplemented by an infinite dimensional extension of the worldsheet symmetry algebra to possibly find an alternative holography.
picture that illustrates the research done
Scientific abstract (pdf 20K)   For more info or full text, mail to: D.M.Hofman@uva.nl

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