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Science in Progress

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Displaying theses 1-10 of 1078 total
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S. Huseby
Master programme: Astronomy and Astrophysics February 19th, 2019
Institute: API Research group: X-ray Timing Group Graduation thesis Supervisor: Phil Uttley
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Searching for AGN accretion states with X-ray timing
The aim of this project is to investigate whether variability behaviour seen in AGN is consistent with the mass scaling from the same range of variability types seen in BHXRBs in their different scales. This thesis has developed a method to look at the power spectral shapes of AGN and compare these with the corresponding power spectra of BHXRBs using the power colour method. These power colours were then compared with corresponding power colours from BHXRBs. This comparison showed that AGN appear to experience the same range of power colours as seen in the different BHXRB variability states. However, there appeared to be a systematic difference between AGN and BHXRBs.
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Scientific abstract (pdf 1K)   Full text (pdf 6055K)

A. These
Master programme: Science for Energy and Sustainability - Physics / Chemistry December 14th, 2018
Institute: VU / Physics & Astr. Research group: Hybrid Solar Energy Conversion Graduation thesis Supervisor: Elizabeth von Hauff
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Developing a Surface Enhanced Raman Spectroscopy Substrate for Nanothermometry
Plasmonic metal Nanoparticles (NPs) are employed in various areas ranging from sensing to medical applications and photovoltaics. They have optical resonances that highly increase absorption and scattering for certain frequencies of light.This leads to localized areas around the NPs that have strongly enhanced electric fields and intense thermal heating. Surface-Enhanced Raman Spectroscopy (SERS) can determine the temperature around such nano systems non-invasively and without system perturbation.We developed SERS substrates suitable for Nanothermometry by Stokes to anti-Stokes intensity ratio evaluation. Physical Vapor deposited gold nanospheres are hereby compared to commercial Pelco® SERS substrates and nanodiscs created by electron beam lithography.
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Scientific abstract (pdf 1K)   For more info or full text, mail to:

E.B. Ippel
Master programme: Physics - Theoretical Physics November 15th, 2018
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: Bernard Nienhuis
Universality in one-dimensional models displaying self-organized criticality
The concept of self-organized criticality is considered to be one of the mechanisms by which self-similar fractal structures and complexity in nature arise. In this thesis, we first introduce the concept of self-organized criticality and give a brief overview of self-organized criticality in one dimension. We then proceed by analysing various models, all of which are governed by different stochastic toppling rules. These models quickly evolve towards a steady state which is characterized by the occurrence of avalanches of varying size, which do not necessarily have a characteristic scale, and possibly display power-law behaviour in the frequency of their occurrence. Indeed, we find that three of our models exhibit critical behaviour in the form of distributions of avalanches following a power-law, all of which are characterized by different scaling exponents. Furthermore, we find certain critical properties intrinsic to the steady state of two of our models. Lastly, we investigate whether the critical behaviour emerging through the dynamics of our models is universal. We indeed find that the critical behaviour emerging in the nonlocal-limited model is universal between a class of different models, where the universality class to which these models belong can be characterized by four critical exponents.
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Scientific abstract (pdf 2K)   Full text (pdf 952K)

S.L. ten Have
Master programme: Science for Energy and Sustainability - Physics / Chemistry November 9th, 2018
Institute: UvA / Other Research group: UvA / Other Graduation thesis Supervisor: Prof. Dr. T. Gregorkiewicz
Photoluminescence from cold all-inorganic perovskite nanocrystals
Perovskite is among the most promising materials for new solar cells. From perovskite one can make very thin and flexible cells at potentially much lower cost than the current cells from silicon. By using very small bits of the material, bits only a few nanometers long, one can tune the properties of the material even better. To get to a well-working solar cell, a display or other devices, quite some work needs to be done though. There are issues with the stability of the material and it is also not yet understood why the material actually performs so well. This research tries to get a better understanding of fundamental processes of all-inorganic perovskite nanocrystals by cooling them to very cold temperatures. All temperature related effects will then vanish, allowing us to distinguish fundamental processes. In order to explain those processes the the emission from the material is studied. Several models and explanations for the material's behaviour are presented to clarify the physical processses in a perovskite nanocrystal ensemble. Hopefully a better understanding will eventually lead to better perovskite devices.
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Scientific abstract (pdf 1K)   For more info or full text, mail to:

H.J.G. Pijpers
Bachelor programme: Natuur- en Sterrenkunde November 9th, 2018
Institute: AMC Research group: Biomedical Engineering and Physics Graduation thesis Supervisor: M.C.G. Aalders
Determining the exposure temperature of burnt bones using Raman microspectroscopy
In the forensic field, cases involving burnt bodies are difficult to solve. Due to the lack of forensic material to work with, there is a need for non-invasive methods which can provide critical forensic information out of the leftover remains. In this thesis Raman spectroscopy is explored as such a non-invasive method to determine the exposure temperature of burnt bones. For example, knowing the exposure temperature can tell you the circumstances in which the body was burned.
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Scientific abstract (pdf 40K)   For more info or full text, mail to:

J.H. Bootsma
Master programme: Astronomy and Astrophysics October 29th, 2018
Institute: API Research group: Planet formation group Graduation thesis Supervisor: Carsten Dominik
Constraining starspot fraction and temperature in weak-lined T Tauri stars using spectroscopy
Whether the gas situated in the innermost regions of a protoplanetary disk (PPD) is optically thin or optically thick determines the radial distance upward of which rocky planets (or planetary cores) can form. Determining the opacity of this gas, however, is impeded by a number of phenomena. The presence of starspots on the surface of the stars that host these protoplanetary disks, is one of these. This, because the starspots and the inner gas are believed to have similar temperatures. In this work we present a method that constrains the starspot fraction and temperature on the surface of T Tauri stars using spectroscopy. We select starspot-sensitive absorption lines of which we compare the line profile with synthetic line profiles (derived from PHOENIX models).
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Scientific abstract (pdf 2K)   Full text (pdf 8307K)

A.R.R. Bosschaert
Master programme: Science for Energy and Sustainability - Physics / Chemistry October 26th, 2018
Institute: VU / Physics & Astr. Research group: Physics of Energy Graduation thesis Supervisor: Dr. I. Heller
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An electrical glucose sensor, the quest for true non-invasive detection
Diabetes is becoming a worldwide epidemic. Unmanaged or untreated diabetes can lead to several health problems. The first step in alleviating diabetes for patients is through the measurement of blood glucose levels. In this research project a viable novel measurement method was proposed along with a strategy of commercialization. This novel method could lower the burden of diabetes on patients. The novel method has been evaluated partially theoretically and partially emperically in technical, economical and social dimensions during this project. In each dimension the novel method showed promise to be able to add value for patients suffering from diabetes. Currently the finger prick method is the most used and known method of blood glucose measurement. For diabetics this method of measurement is uncomfortable and impractical. [A company] is developing the said novel blood glucose sensor for diabetes patients to overcome the problems with the fingerprick method and those of other measurement techniques. Some technical design additions were proposed during this project. Furthermore, strategies to increase chances of commercialization were proposed.
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Scientific abstract (pdf 3K)   For more info or full text, mail to:

S.A.S. de Wit
Master programme: Astronomy and Astrophysics September 28th, 2018
Institute: API Research group: Massive Star Group Graduation thesis Supervisor: Prof. Dr. A. de Koter
Characterizing the properties of the VFTS 176 binary in the 30 Dor. starburst region
In this work we present an analysis of the massive binary system VFTS 176. VFTS 176 is a close binary, with two massive main sequence components and a short orbital period (~0.1 AU). It is thus very likely that the stars have either interacted in the past or will interact while still on the main sequence. We investigate the possibility of a past phase of mass-transfer. However, since this system is a known spectroscopic binary, the observed spectra consists of features from both components. To tackle this problem, we use a spectral disentangling technique to separate both contributions. We then found a set of properties for both stars by means of quantitative spectroscopy, including their masses, stellar radii and effective temperature. By then fitting evolutionary models, we find the posterior age distributions. Based on the posterior age distributions, the absence of tidal synchronization and the absence of a stripped primary, we reject the possibility of a past phase of mass-transfer. We do however, predict that the primary will donate mass to its companion around an age of 4.20 Myr, drastically changing the final fate of this system.
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Scientific abstract (pdf 2K)   For more info or full text, mail to:

J.A.L. Seneca
Master programme: Physics - Particle and Astroparticle Physics September 26th, 2018
Institute: NIKHEF Research group: KM3NeT Graduation thesis Supervisor: Ronald Bruijn
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Models of Particle Signatures in KM3NeT ORCA
The neutrinos are elusive particles which are constantly produced in the Earth's atmosphere. Neutrinos are able to travel through the entire Earth barely affected, but the way they are affected can tell us about the particle's properties; their masses. Our detector, KM3NeT ORCA, is specialized in detecting these particles. When a neutrino eventually interacts in the detector, it produces a myriad of other particles which produce light. Based on the light we see from these particles, we can extract information about the neutrino which produced them. Understanding the light signature produced by these product particles is a challenge in itself which has been a matter of research for almost a century. This knowledge is also useful for KM3NeT, as lets us work backwards from the light signatures to the properties of the original particle, and thus, that of the neutrino. For the first time in KM3NeT, we create models of these light signatures for individual particles and present them in all their gory details. We then use these models to estimate neutrino information from simulations and to perform simulations of our own. The results are promising, but more work is needed for practical use of the models.
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Scientific abstract (pdf 89K)   Full text (pdf 11439K)

N. Petropoulos
Master programme: Physics - Theoretical Physics September 11th, 2018
Institute: ITFA Research group: String theory Graduation thesis Supervisor: Erik Verlinde
A Double-Headed Centaur in a Black de Sitter Universe
In my thesis we study black holes in the early and late phases of our Universe. Also, we probe to find the nature of these black holes and of the so-called cosmological horizon. This is a horizon which seems to surround us when we look at the Universe through our telescopes.
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Scientific abstract (pdf 1K)   Full text (pdf 3431K)

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