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Displaying theses 471-480 of 1078 total
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R.M. van Westen
Bachelor programme: Natuur- en Sterrenkunde July 3rd, 2014
Institute: API Research group: Anton Pannekoek Observatory (APO) Graduation thesis Supervisor: Rudy Wijnands
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Swifts X-ray observations of the Be/X-ray transient KS 1947+300; analysis of the source in the propeller regime
During a recent outburst of the Be/X-ray transient KS 1947+300 we observed with the XRT on board of the satellite Swift this outburst. We wanted to investigate if the object was observed in the propeller regime where accreting matter is blown away. This causes a sudden drop in luminosity which is observed during the decrease of the outburst. Simultaneously we see a jump in the photon index and the spin frequency of KS 1947+300 reached a maximum as well because angular momentum is transferred into outflow of matter. All of this lead to the conclusion that KS 1947+300 was observed while entering the propeller regime.
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Scientific abstract (pdf 46K)   For more info or full text, mail to: r.a.d.wijnands@uva.nl

M.W. Moeijs
Bachelor programme: Natuur- en Sterrenkunde July 3rd, 2014
Institute: WZI Research group: Soft matter Graduation thesis Supervisor: Daniel Bonn
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On the effect of dimensionality and plasticity on the crumpling of a thin sheet
Crumpling is an everyday phenomenon, yet it’s physics is poorly understood. Describing a power-law relation between force and compaction, with an exponent β depending on the dimensionality of the folding, it is claimed that a theory for hierarchical folding captures the main features of the crumpling of a thin sheet. The validity of this model is examined by investigating the effect of plasticity and by elaborating on it’s dimensional arguments. Although β is found to deviate from the theoretical predictions, it is argued the theory needs not to be rejected. The effect of plasticity on β is quantified by analyzing the amount of layers of a crumpled structure, described by the layer exponent γ. This exponent is found to deviate from the models prediction, hence a redefinition of β is proposed.
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Scientific abstract (pdf 95K)   Full text (pdf 5498K)

J.S. Sinninghe Damsté
Bachelor programme: Natuur- en Sterrenkunde July 3rd, 2014
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: Eric Laenen
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The Higgs Boson as a Composite Pseudo-Goldstone Boson From a Dynamically Broken Symmetry
In this thesis the possibility of a composite Higgs boson that is a Goldstone mode of an approximate symmetry (hence a pseudo-Goldstone boson) is illustrated using the analogy with pion physics, after the Standard Model Higgs mechanism has been explained. A Higgs structure like this is interesting, as a pseudo-Goldstone boson is naturally light and hence the hierarchy problem is avoided. The thesis is continued with the introduction of two specific Higgs models and concluded with the discussion of an effective model in which different types of Higgs models could be tested.
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Scientific abstract (pdf 30K)   For more info or full text, mail to: e.l.m.p.laenen@uva.nl

O. Tzuk
Master programme: Astronomy and Astrophysics July 2nd, 2014
Institute: API Research group: Anton Pannekoek Observatory (APO) Graduation thesis Supervisor: Dr. Shin'ichiro Ando
Distortion of CMB spectrum due to dark matter annihilation
The Cosmic Microwave Background (CMB) is a probe to the early Universe. The energy spectrum of the CMB holds the information of energy release episodes from redshift of about two million to the epoch of recombination. Analysis of the energy spectrum of the CMB allows us to test various hypothesis about physical processes during this time span. In this thesis we give forecast for the spectral distortion arising from supersymmetric dark matter annihilation. If such spectral distortion will be detected in the CMB in future experiments, and if this distortion will be associated with dark matter annihilation, we will have another method of constraining dark matter properties and shed some light on the nature of dark matter.
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Scientific abstract (pdf 18K)   Full text (pdf 2119K)

R. Albers
Bachelor programme: Natuur- en Sterrenkunde July 2nd, 2014
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: Kareljan Schoutens
Quantum world on a sphere
To get the energy levels for spin-1/2 particles in antiferromagnetic materials, it is necessary to find the energy eigenvalues of the Hamiltonian. The dimensions of this Hamiltonian are proportional to 2^N (N is the amount of particles), so for larger problems it is necessary to reduce the dimensionality. Using symmetry, this can be achieved for systems of up to about 10 particles. For larger systems it is necessary to find other methods to reduce dimensionality even further.
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Scientific abstract (pdf 44K)   Full text (pdf 10494K)

D.W. Gardenier
Bachelor programme: Natuur- en Sterrenkunde July 1st, 2014
Institute: API Research group: Anton Pannekoek Observatory (APO) Graduation thesis Supervisor: Adam Ingram
The Rapid Variability of the Black Hole Binary Cygnus X-1
Black hole binary systems consist of a black hole and a companion star. Matter from the companion star can be accreted onto the black hole, whilst emitting radiation. Observations of such systems have revealed rapid variability in the observed light, believed to be linked to variations in the mass accretion rate. In this paper, a proposed model to explain the rapid variability of Cygnus X-1 - a black hole binary system - is tested, and found to only be selectively applicable.
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Scientific abstract (pdf 268K)   For more info or full text, mail to: a.r.ingram@uva.nl

B. Barendse
Bachelor programme: Natuur- en Sterrenkunde July 1st, 2014
Institute: API Research group: Anton Pannekoek Observatory (APO) Graduation thesis Supervisor: Dr. R.A.D. Wijnands
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Indications for the propeller regime in Be/X-ray transient GX304-1
Recently the Swift X-ray satellite was used to monitor GX304-1, a neutron star orbiting a Be star. GX304-1 is known to show periodical type one X-ray outbursts occurring when the neutron star is in transient. These outburst where used to search for evidence of the source entering the propeller regime. A fast drop in luminosity and a change in the spin frequency of the neutron star at the same time strongly suggest that GX304-1 is indeed observed during the transition towards the propeller regime. Studying the propeller regime gives new information about how strongly magnetized neutron star accrete matter.
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Scientific abstract (doc 23K)   For more info or full text, mail to: R.A.D.Wijnands@uva.nl

Y.D. van Nieuwkerk
Bachelor programme: Natuur- en Sterrenkunde July 1st, 2014
Institute: ITFA Research group: Statistical Physics and Condensed Matter Theory Graduation thesis Supervisor: prof. J.S. Caux
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Exact time evolution in the one-dimensional attractive Bose gas
In a very recent article, Kaminishi, Sato and Deguchi have described the equilibration of localized density distributions in the repulsive one-dimensional Bose gas. Starting from a narrow spatial notch in the expectation value of the density operator, the authors have used numerical methods to describe the ensuing time-evolution of the system, producing a number of snapshots of its evolving density profile. The present paper extends this work to the attractive one-dimensional Bose gas, focusing on density peaks, instead of notches. Analytical results, rather than numerical ones, have been obtained for so-called N -strings, describing the density operator’s expectation values at all times and positions, leading to similar snapshots that show the evolution of a density profile. To cover more complicated strings, several techniques have been explored, possibly leading to further extensions to the work of Kaminishi, Sato and Deguchi in the near future.
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Scientific abstract (pdf 87K)   Full text (pdf 1600K)

T.B. Bakker
Bachelor programme: Natuur- en Sterrenkunde July 1st, 2014
Institute: ITFA Research group: Instituut voor Theoretische Fysica Graduation thesis Supervisor: Dr. J.P. van der Schaar
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Area dependence of scalar field entanglement entropy
Since the seventies it has been known that a black hole's entropy - a measure of its disorder, or equivalently our lack of knowledge about what happens inside - is proportional the area of its event horizon. Interestingly, the entropy associated with entanglement between systems just inside and outside of the horizon, also satisfies this proportionality. We have attempted to reproduce this feature for non-black-hole configurations. We show the difficulties of such calculations, and discuss mathematical and physical reasons for expecting area proportional entropies.
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Scientific abstract (pdf 26K)   Full text (pdf 2410K)

D. van der Wende
Master programme: Physics - Particle and Astroparticle Physics June 30th, 2014
Institute: NIKHEF Research group: ATLAS Graduation thesis Supervisor: Stan Bentvelsen
A Multivariate analysis of Higgs to hadronic taus for Vector Boson Fusion production
At Juli 2012 the announcement has been made that the Higgs particle has been found in several channels. For exploration of unknown properties of the Higgs, the fermionic channel can be considered. In this thesis research is done to the Higgs decaying into two hadronic taus. Multi Variate Analysis and efficiency curves are used to optimize the separation between the Vector Boson Fusion signal and the background processes. Various sets of variables are considered. This method gives a 0.92 sigma result for the existence of a 125 GeV Higgs in the VBF production mode. Further optimization of the methods and increase of statistics both can decrease the error-bars, thereby increasing the significance.
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Scientific abstract (pdf 28K)   Full text (pdf 6157K)

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