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Science in Progress

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Displaying theses 51-60 of 1078 total
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E.R. Olberts
Bachelor programme: Natuur- en Sterrenkunde July 7th, 2018
Institute: Other Research group: DopTrack Satellite Tracking Station (TU Delft) Graduation thesis Supervisor: prof. dr. L. Kaper
Set up of radio interferometry at the TU Delft DopTrack ground station for improvement of satellite orbit determination
Communication with the Delfi-C3 satellite has been realized in 2014 with the construction of the TU Delft DopTrack ground station. Since then, the range rate during a flyover is determined by measuring the Doppler shift of the communication signal. By using an additional radio interferometry (RI) tracking method, the satellite elevation can be determined as well. This research investigates, by computer simulations, whether the RI method can make reliable measurements using the current equipment at the DopTrack station. First, simulations were made using Python to test the accuracy of the cross correlation function of two signals for different frequencies, sampling rates and phase differences. Second, signals with a frequency equal to the satellite communication signal (145.87 MHz) were generated and downsampled to a frequency (100 Hz and 1 kHz), which were determined from the results of the simulations. Finally, required additional equipment was built to be able to use radio interferometry.
picture that illustrates the research done
Scientific abstract (pdf 2K)   For more info or full text, mail to: L.Kaper@uva.nl

A. van de Coevering
Bachelor programme: Natuur- en Sterrenkunde July 7th, 2018
Institute: AMC Research group: Biomedical Engineering and Physics Graduation thesis Supervisor: Ton van Leeuwen
Label-free differentiation of lipoproteins from extracellular vesicles by flow cytometry.
Extracellular vesicles (EVs) are particles that are excreted into the blood by cells to transport substances or messages between cells. EVs seem to change if a person is ill and are therefore useful to diagnose diseases. EVs are hard to detect, because other particles in the blood, like lipoproteins, share a lot of features with EVs. Flow cytometry is used to detect EVs, but flow cytometers display the particles in arbitrary units. This makes it impossible to distinguish EVs from lipoproteins in the data. Recently, a new method is invented to present this data based upon the refractive index and diameter of the particles. The aim of this article is to show which particles in the new data are the lipoproteins. To reach this goal, the EVs and lipoproteins in blood are separated according to density and molecular mass. In this article it is concluded that the particles with the highest refractive index in the new data are the lipoproteins. By concluding this, it is shown that the new method makes it possible to distinguish lipoproteins from EVs in the data of flow cytometry.
picture that illustrates the research done
Scientific abstract (docx 15K)   For more info or full text, mail to: t.g.vanleeuwen@amc.uva.nl

C.A. Bozon
Bachelor programme: Natuur- en Sterrenkunde July 7th, 2018
Institute: UvA / Other Research group: ASTRON Graduation thesis Supervisor: mw. dr. B.A. Rowlinson
Low frequency study of peaked-spectrum sources and quality assurance of the Multifrequency Snapshot Sky Survey
Astronomical radio surveys provide an indiscriminate view of our sky, which is essential for finding new stellar objects and conducting statistical reviews of entire stellar populations. This thesis has looked at one of the latest surveys, the Multifrequency Snapshot Sky Survey, which has observed all objects in the Northern sky at 8 unique radio frequencies. Both a final quality control and a specific population analysis of peaked-spectrum sources were conducted. The quality control has found that the luminosity brightness of the sources in the survey deviates from previous surveys and established theory, which indicates that the survey is not yet perfectly calibrated. The resulting sample size of peaked-spectrum sources, sources which show a peak in their spectrum, was around 2% of the entire survey, compared to 5% in previous surveys. This sample's spectral characteristics deviated slightly from previous surveys, which, together with the sample size difference, could be caused by a biased selection process.
picture that illustrates the research done
Scientific abstract (pdf 2K)   Full text (pdf 1724K)

T.J.N. Reus
Bachelor programme: Natuur- en Sterrenkunde July 6th, 2018
Institute: VU / Physics & Astr. Research group: VU Physics of living systems Graduation thesis Supervisor: Iddo Heller
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Exploring the accuracy of Fluorescence Correlation Spectroscopy and Fluorescence Polarization Anisotropy on local temperature measurements inside a confocal setup
Temperature is an important parameter in many processes in physics, chemistry and biology. When research is done on these temperature-dependent processes, it is useful to be able to check the temperature. This makes temperature specific studies possible, which can give interesting results. For many processes, especially in larger environments, this check is already available. This is not yet available for processes in biology, such as in small-scale research in the micrometer scale. In this study, two candidate methods: Fluorescence correlation spectroscopy (FCS) and Fluorescence polarization spectroscopy (FPA), were tested for their capability to measure accurate temperature patterns in small environments (micrometer scale). Both methods use a form of diffusion of fluorescent particles to calculate the temperature with the help of mathematical relations. This study concludes that with FCS and FPA it is possible to measure temperature patterns and relations in systems on a micrometer scale. The particular deviation in the measurements of about two degrees, however, does not make it possible to do this for small temperature changes. It is recommended for further research to continue with FPA, and thereby increase the concentration of fluorescent particles.
picture that illustrates the research done
Scientific abstract (pdf 2K)   For more info or full text, mail to: i.heller@vu.nl

T.W.H.L. Dodds
Bachelor programme: Natuur- en Sterrenkunde July 6th, 2018
Institute: API Research group: BinCosmos Graduation thesis Supervisor: S.E. de Mink
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Estimating the Physical Properties of Stripped-Envelope Supernovae
Thanks to transient-surveys, ever more supernovae are being observed. The shape of their light curves can be used to deduce the physical properties of the supernova explosions: the explosion-energy, the amount of nickel-56 produced, the progenitor's structure, etc. Observers typically use analytical scaling-relations, like those derived by Arnett (1982), to infer these properties. In this study, we investigate how accurate such methods are for stripped-envelope supernovae. We use the one-dimensional hydrocode SNEC to simulate a grid of supernova events of varying explosion-energy and nickel-56 abundance. The light curves are then analyzed by means of several different commonly-used methods to estimate the physical properties of the events. Comparing the recovered values to those used as input for the simulations, we find that both the nickel-56 mass and explosion-energy are systematically underestimated with these methods. The possible causes are discussed, and a comparison is made to observations. We also show that the use of expansion-velocities from literature yields highly discrepant estimates. Observers are therefore encouraged to measure velocities spectroscopically whenever possible, and reminded to treat properties inferred on the basis of literature values cautiously. Finally, we suggest future steps to improve the accuracy with which the physical properties of supernovae are estimated.
picture that illustrates the research done
Scientific abstract (pdf 2K)   For more info or full text, mail to: S.E.deMink@uva.nl

M.P. Snelders
Bachelor programme: Natuur- en Sterrenkunde July 6th, 2018
Institute: API Research group: Massive Star Group Graduation thesis Supervisor: Prof. dr. L. Kaper
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On the Kinematical Properties of High-mass X-ray Binaries using Gaia DR2
In this project the recent data release of the Gaia spacecraft is used to determine the kinematical properties of High-mass X-ray binaries (HMXB). HMXBs are binary systems which consist of a compact object (neutron star or black hole) and a massive O-type or B-type star. The research of HMXBs is important because they represent an important phase in the evolution of massive binaries. Using the parallaxes and proper motions, measured by Gaia, it is possible to estimate the distance to these HMXBs and to calculate the peculiar velocities of these systems. This project has two main goals. First, to determine if there is a systematic difference between the peculiar velocities between OB-Supergiant systems and Be/X-ray binaries. Second, to find a correlation between the spin period and the peculiar velocities of Be/X-ray binaries.
picture that illustrates the research done
Scientific abstract (pdf 2K)   For more info or full text, mail to: L.Kaper@uva.nl

J.L. de Kuijper
Bachelor programme: Natuur- en Sterrenkunde July 6th, 2018
Institute: API Research group: X-ray Timing Group Graduation thesis Supervisor: dr. Anna Watts
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Constraining the Coupling Constants in the Equation of State Describing the Nucleonic and Hyperonic Core of Neutron Stars
The equation of state for the core of a neutron star can be described using several models such as the piecewise polytropic equation of state. This model is thermodynamic and does not accurately represent the particles and nuclear physics within the star. Improvements to the equation of state are the FSU2R and FSU2H models, the first describing the presence of nucleons and the other including exotic particles such as hyperons. It is unclear how many free parameters there are in these models and in what range they can vary, which is necessary in order to be able to infer them from observational and experimental data. In this manner, the equation of state of neutron stars and their parameters can be used to provide information on cold, highly dense matter at high densities. The nuclear properties are derived to determine whether the coupling constants can be varied within a range in which the nuclear properties are still within their experimental and observational limits. The possible free parameters are now known, however the range in which they can be varied has to be researched further.
picture that illustrates the research done
Scientific abstract (pdf 54K)   For more info or full text, mail to: A.L.Watts@uva.nl

N.T. Lam
Bachelor programme: Natuur- en Sterrenkunde July 4th, 2018
Institute: VU / Physics & Astr. Research group: VU Physics of living systems Graduation thesis Supervisor: Greg Stephens
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Determining suitable models for C. elegans locomotion by evaluating Lyapunov exponents
One of the most extensively studied organisms in biology is the worm C. elegans. Its nervous system has been entirely mapped. However, what remains not well understood is how the structure of the brain of C. elegans gives rise to its varying (movement) behavior. The dynamics of this behavior can be characterised by numbers known as the Lyapunov exponents (LEs), which for C. elegans have 6 different values that altogether are symmetric around a certain number. Based on these quantities, two model systems that might have similarly symmetric LEs are researched. The first is a pair of coupled Nosé-Hoover oscillators: two pendulum-like systems that pull on each other. The second is a pendulum driven by a periodic force, which is generated by another pendulum-like system. It is tested what the effect of coupling systems has on the LEs, and whether the same symmetry in the LEs can be obtained in these configurations. The results show that the driven pendulum cannot generate such a set of LEs, while the results for the Nosé-Hoover oscillators are inconclusive.
picture that illustrates the research done
Scientific abstract (pdf 1K)   Full text (pdf 3778K)

K. de Mos
Bachelor programme: Natuur- en Sterrenkunde July 4th, 2018
Institute: WZI Research group: Soft matter Graduation thesis Supervisor: Rudolf Sprik
Seismic Imaging
In this thesis Seismic Imaging is studied. Often people are interested in creating an image of the subsurface. This is done by sending seismic waves into the subsurface and then measuring the reflections at the surface. Sending in the waves can be done by vibrating trucks, explosions or so-called airguns. Translating the data into an image is called imaging. The waves are mathematically described by the wave equation. This thesis describes the mathematics behind commonly used methods to translate the data into images.
picture that illustrates the research done
Scientific abstract (pdf 1K)   Full text (pdf 808K)

E.M.H. Verheijden
Master programme: Physics - Theoretical Physics July 4th, 2018
Institute: ITFA Research group: String theory Graduation thesis Supervisor: dr. Diego Hofman
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Traversable Wormholes, Shock Waves and de Sitter Space
Black holes are fascinating objects: we cannot see them, because the gravitational attraction is so strong that even light cannot escape. Arguably even more exciting are wormholes: connections between two black holes. These might allow us to travel to the other side of the Universe. However, this would require the presence of matter with negative energy. This poses a problem, since theoretical physicists generally assume energy to be positive. In 2016, Gao, Jafferis and Wall showed that connecting the black holes makes it possible for a signal to traverse through the wormhole. In my thesis, I review this set-up, and in particular focus on the effect of the coupling, which results in shock waves. I then discuss a possible application of this idea to a so-called de Sitter space, which is a toy model for our Universe. It shows striking similarities with a black hole: black holes are surrounded by an ‘event horizon’, beyond which nothing can escape; an observer in de Sitter space is surrounded by a ‘cosmological horizon’, beyond which she cannot see. I present a shock wave solution that could allow observers separated by such cosmological horizons to communicate, and study perturbations of this solution.
picture that illustrates the research done
Scientific abstract (pdf 60K)   For more info or full text, mail to: D.M.Hofman@uva.nl

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