Physics and Astronomy in Progress

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Displaying theses 1-10 of 1000 total
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J.P.J. Manshanden
Master programme: Physics - Particle and Astroparticle Physics June 17th, 2018
Institute: ITFA Research group: GRAPPA Graduation thesis Supervisor: Gianfranco Bertone
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Black Hole Dark Matter: Constraining Primordial Black Holes as Dark Matter using Radio and X-ray Observations
One of the biggest mysteries in modern physics is the nature of dark matter. From cosmological observations it is known that we do not understand more than 80% of the matter in the universe. Despite our lack of understanding, there are many ingenious theories attempting to solve this mystery. One of these theories is that many black holes were formed in the early universe, shortly after the big bang. Fast-forwarding to the present universe, these 'primordial' black holes should still be among us today. Recent clues from gravitational waves indicated that such objects might exist with masses of a few ten times the mass of our sun. If this is indeed the case we would expect to see signifying radiation from the center of our galaxy. Recently, this scenario has been tested by simulating the expected emission and making comparisons with observations. In this thesis, several improvements are made to simulating this emission, making the results more reliable as well as this scenario much less likely. It will be interesting to see if upcoming radio telescopes will completely rule out this scenario, or perhaps be able to detect a population of black holes in the center of the Milky Way.
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Scientific abstract (pdf 82K)   For more info or full text, mail to: g.bertone@uva.nl

M.D. Moerkamp
Master programme: Physics - Theoretical Physics May 29th, 2018
Institute: UvA / Other Research group: UvA / Other Graduation thesis Supervisor: Jean-Sébastien Caux
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On the dynamics of point particles
Based on the corpuscular theory of light and matter, one may speculate that the universe consists of point particles, beyond which no further constitution can be found, and that the dynamical variables of the complete fundamental theory are the positions and velocities of these point particles. The goal of this thesis is to explore the point particle hypothesis anew and to determine if some of the characteristics of classical electrodynamics and general relativity theory (GRT) can be captured in the dynamics of point particles. It is argued that the experiments do not rule out the existence of instantaneous action at a distance (IAAD) and some additional reasons for reconsidering IAAD theories are pointed out. A Lorentzian field-free electrodynamics is presented based on an extension of the Darwin Lagrangian, which incorporates some of the basic features of classical electrodynamics. In a little-known article entitled from 1925, Erwin Schrödinger attempts to incorporate Mach's principle into a relational theory of gravity. We discuss this relational approach in connection with some crucial tests of GRT: the perihelion precession of the planets, the gravitational deflection of light and the expansion of the universe.
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Scientific abstract (pdf 31K)   For more info or full text, mail to: J.S.Caux@uva.nl

M.T. Doornhein
Master programme: Gravitation and Astroparticle Physics Amsterdam (GRAPPA), track offered by both Physics / Astronomy May 24th, 2018
Institute: ITFA Research group: GRAPPA Graduation thesis Supervisor: Dr. Christoph Weniger
Uses and Limitations of Fisher Forecasting in Setting Upper Limits on the Interaction Strength of Dark Matter
In the field of statistical analysis, we attempt to estimate the values of parameters determining the underlying pdf of the data we consider. Hereby we gain insight in what physical models can viably describe the source of that data. We are thus interested in the sensitivity of our experiment, since it determines how accurately we can estimate those parameters. This can be analyzed by calculating expected upper limits by means of Monte Carlo simulation, but this is computationally expensive. An alternative method is available in the form of a Fisher forecast, using the statistical concept of Fisher information. This determines the maximum amount of information that can be extracted from a parameter given some data set, creating the possibility of calculating upper limits in an independent, much faster way. It is equally accurate given that the distribution of maximum likelihood estimators is normal distributed, which is always the case if the sample size approaches infinity. We investigate the accuracy of a Fisher forecast considering a Poisson pdf subject to one free parameter when the sample size is small. In addition we look into the effects of finite angular resolution and modification of the energy spectrum of a dark matter signal.
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Scientific abstract (pdf 1K)   Full text (pdf 2110K)

J.F. van Velzen
Master programme: Physics - Advanced Matter and Energy Physics May 14th, 2018
Institute: WZI Research group: Opto-electronic materials group Graduation thesis Supervisor: Antonio Capretti
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Nanophotonics in the chloroplast
In this work we investigate the nanophotonic regime of light propagation in the chloroplast, and identify novel mechanisms in the optical response of the thylakoid membrane. Our results indicate that the relative contributions of light scattering and absorption to the overall optical response of grana strongly depend on the concentration of light-harvesting complexes. Furthermore, our calculations indicate that collective modes in ensembles of grana significantly increase light absorption at selected wavelengths, even in the presence of moderate biological disorder. We conclude that the morphological separation of the thylakoid membrane supports strong nanophotonic effects, which may be used by the chloroplast to regulate light absorption. This adaptive self-organization capability is of great interest as a model for novel bio-inspired optical materials, for applications in artificial photosynthesis, imaging and sensing.
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Scientific abstract (pdf 2K)   For more info or full text, mail to: A.Capretti@uva.nl

S. Tsiopelas
Master programme: Astronomy and Astrophysics May 3rd, 2018
Institute: API Research group: General Astronomy Group Graduation thesis Supervisor: Nanda Rea
Thermal evolution of neutron stars containing a quark core
Neutron stars (NSs) are compact remnants of massive stars which form in supernova explosions. The violent birth process, renders these objects extremely dense, rapidly spinning, hot and highly magnetized. Understanding NS structure and evolution requires a multilateral approach including several branches of physics in parameter regimes impossible to probe terrestrially. In particular, when it comes to describing the behavior of the highly-condensed matter in their interior, statistical, particle and nuclear physics must be summoned for establishing an appropriate Equation of State (EoS). Depending on the power source driving their emission, observed NSs are divided into accretion-powered, pulsars, magnetars, central compact objects and isolated thermally-emitting ones. Despite the significant level of understanding regarding the latter's thermal evolution, their cooling scenario remains strongly dependent on the assumed EoS. In this work, i developed EoSs suitable for describing the transition from hadronic to quark matter through a mixed phase and proceeded into using them for constructing hybrid stars (HSs). Considering both the hadronic and the quark contributions for compiling their thermodynamical profile, the constructed HSs were then subject to numerical simulations, focused on outlining the temporal evolution of their temperature and luminosity.
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Scientific abstract (pdf 1K)   Full text (pdf 1628K)

S. Juarez Rodriguez
Bachelor programme: Natuur- en Sterrenkunde April 13th, 2018
Institute: VU / Physics & Astr. Research group: VU Physics of living systems Graduation thesis Supervisor: Gijs Wuite
Analysis of intercalator-induced plectonemes in DNA using optical tweezers and single molecule fluorescence microscopy
DNA encodes all the information of an organism so any faults in this molecule or missteps in the replication process can have large consequences. An example of this is the creation of plectonemes or supercoils in the double helix structure of DNA when it is under the constraint of a closed topology. It is possible to use a combination of optical tweezers and a fluorescent molecule that intercalates between base pairs to induce and analyze supercoils as well as to manipulate the DNA molecule in vitro. Here we describe a short summary of the history of DNA research, the advantages of this technique, the method, the performed time analysis of the fluorescent image and suggestions for this particular experiment, part of a growing and exciting field.
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Scientific abstract (pdf 1K)   For more info or full text, mail to: g.j.l.wuite@vu.nl

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.
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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.
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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.
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Scientific abstract (pdf 56K)   Full text (pdf 6652K)

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?
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Scientific abstract (pdf 2K)   For more info or full text, mail to: robert.fleischer@nikhef.nl

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