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Science in Progress

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Displaying theses 71-80 of 1078 total
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F. Faura Iglesias
Bachelor programme: Natuur- en Sterrenkunde June 29th, 2018
Institute: NIKHEF Research group: ATLAS Graduation thesis Supervisor: Hella Snoek
Method to determine the width of the Higgs Boson of simulations of gg -> H -> ZZ and gg -> ZZ decay modes
The Standard Model of particle physics predicts the lifetime to be 1.56 · 10−22s, however the ATLAS and CMS detectors are not able to measure the lifetime due to their resolution. It is therefore necessary to find an alternative method to determine the lifetime of the Higgs boson. This report describes the test of a method to determine the lifetime. The method consists of the analysis on five simulations of processes that create an Higgs boson. Every simulation has a predetermined lifetime. The result of the analysis is a parameter that is a function of the lifetime. This function could then be used on a dataset that contained an unknown lifetime. This dataset also contained the above mentioned parameter, therefore creating the possibility to find the unknown lifetime in the data set. There are however uncertainties in determining the lifetime that suggest that the used method is not complete. It is therefore a necessitiy to conduct more research and clear the uncertainties.
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Scientific abstract (pdf 1K)   Full text (pdf 1776K)

E. Tourou
Master programme: Physics - Physics of Life and Health June 29th, 2018
Institute: VU / Other Research group: VUmc Department of Radiation Oncology Graduation thesis Supervisor: G.J. Streekstra
Knowledge-based radiotherapy treatment planning for stage III lung cancer patients
Radiotherapy treatment for lung cancer requires the creation of a treatment plan that provides a homogeneous dose to target volumes whilst optimally sparing the organs-at-risk (OAR). The treatment of large-volume lung cancer is carried out mostly using two techniques, the full-RapidArc (f-RA) or the hybrid-RapidArc (h-RA). The choice between the two methods is critical and depends on the individual characteristics of the patient, while it often happens that the treatment planners have to make both plans in order to choose for the optimal treatment technique for the patient. However, manual treatment planning is a labor-intensive and time-consuming process which, in many cases, does not yield consistent or optimal plans. Knowledge-based planning is a promising technique which utilizes a large number of prior treatment plans to construct a model that can predict the possible dosimetry and create treatment plans for future patients based on their own anatomical characteristics. The present study investigates the possibility of utilizing RapidPlan (Varian Medical Systems, Palo Alto, USA), a knowledge-based treatment solution, as a tool for selecting f-RA or h-RA technique for individual lung cancer patients, without the requirement of creating actual treatment plans.
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Scientific abstract (pdf 2K)   Full text (pdf 2478K)

S.L.E. Runderkamp
Master programme: Gravitation and Astroparticle Physics Amsterdam (GRAPPA), track offered by both Physics / Astronomy June 22nd, 2018
Institute: NIKHEF Research group: HiSPARC Graduation thesis Supervisor: Patrick Decowski
Investigating post-LHC hadronic interaction models and their predictions of cosmic ray shower observables
There are large systematic uncertainties in the interpretation of the data of cosmic ray experiments due to the unreliability of hadronic interaction models in MC simulations at high cosmic ray energies. In this work the predicted values of properties of the produced particles after the first hadronic interaction are compared for the three post-LHC models EPOS LHC, SIBYLL 2.3c and QGSJET-II-04. This study focuses on proton-nitrogen, alpha-nitrogen and iron-nitrogen collisions with primary energies up to $10^{20}$eV. Large shower-to-shower fluctuations are found, but also significant differences in the predicted values between the three models. Also, the position of shower maximum, the number of ground-level particles (for both photons, electrons, muons and hadrons) and the energy, arrival time and lateral distance to the shower core at ground level are compared for the three post-LHC models. Vertical proton, alpha and iron initiated showers with primary energies up to $10^{16.5}$eV are considered. Significant differences between the predictions of the models are already found at primary energies far below LHC energies. Could a cosmic ray experiment constrain the models by observing these properties?
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Scientific abstract (pdf 2K)   Full text (pdf 3215K)

R.G.J. Schoenmaker
Master programme: Science for Energy and Sustainability - Physics / Chemistry June 22nd, 2018
Institute: Other Research group: none Graduation thesis Supervisor: Marie Louise Blankesteijn
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In transition to electric trucks
To mitigate climate change and reduce air pollution in the freight sector, a transition to zero-emission vehicles is required with electric trucks being a serious option. The aim of this case study research is to generate insight in this transition by investigating which transition pathway towards electrification the transition will presumably follow. The lens through which the research was conducted is grounded in theories on socio-technical system transitions. The multi-level perspective on socio-technical transitions as described by Geels and Schot (2007) forms the basis to the analyses. These analyses include 1. the stakeholders and institutions in the current freight transport system; 2. the external developments that put pressure on that system; 3. the readiness of the battery-electric and fuel cell-electric options to meet the demands of regional transport, and 4. barriers and opportunities towards adoption. The case analysed in this research is the regional freight transport system in the Netherlands concerning heavy-duty trucks driving medium-hauls (of 300 km on average). The data for the analyses were collected through a comprehensive desk research (i.a. policy reports, consultancy reports, and expert blogs), ten qualitative expert interviews and one focus group.
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Scientific abstract (pdf 3K)   Full text (pdf 2652K)

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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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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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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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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