In this research, we study the oxidation process of the Transition Metal Dichalcogenide (TMD) niobium diselenide, NbSe2. TMDs are a category of van der Waals materials, of which samples are...Show moreIn this research, we study the oxidation process of the Transition Metal Dichalcogenide (TMD) niobium diselenide, NbSe2. TMDs are a category of van der Waals materials, of which samples are obtained by exfoliation. The measurements are performed with the Low Energy Electron Microscope (LEEM), which measures reflectivity at different energy, resulting in the so-called IV curves. To analyze oxidation, we have developed a new method to obtain in situ exfoliated flakes in the LEEM set-up. First, we measure in situ cleaved NbSe2 flakes (bulk). The reflectivity upon adding (pure) oxygen is followed. Additionally, the reflectivity of ex situ cleaved NbSe2 flakes is assessed. Here, an intensity boundary between flake’s edge and center is recognized. The reflectivity measurements show that the electronic structure is different across the boundary: a V-shaped reflectivity minimum appears, which sharpens over time upon oxidation. The boundary is further researched with Atomic Force Microscopy and Energy Dispersive X-ray analysis. Additionally, we perform roughness analysis and Principal Component Analysis. The latter provides an alternative method to follow the change in electronic properties over time. We propose that already degraded NbSe2 flakes are more susceptible to oxidatin damage, compared to in situ exfoliated flakes. Upon further measurements, the in situ cleaved samples do not show any degradation signs, therefore we attribute the presence of an intensity contrast with the associated IV features, to oxidized NbSe2.Show less
Master thesis | Cultural Anthropology and Development Sociology (MSc)
open access
This thesis explores the relationship between humans and non-humans within a sea turtle conservation organization in Costa Rica’s Osa Peninsula. Through eleven weeks of in-depth visual ethnographic...Show moreThis thesis explores the relationship between humans and non-humans within a sea turtle conservation organization in Costa Rica’s Osa Peninsula. Through eleven weeks of in-depth visual ethnographic fieldwork, I investigate the influence these human/non-human relationships have on scientific knowledge production. The output of this research consists of an ethnographic film ‘The Turtle Team’ and this article. This research underscores the necessity of adopting transdisciplinary methodologies in which non-humans are integrated, which is crucial in the era of the Anthropocene. It provides a nuanced understanding of how human/non-human relationships shape the production of scientific knowledge in this team of conservationists and emphasizes the interwovenness of humans and non-humans. This research contributes to the existing literature on the Anthropocene and the nature-culture debate and I argue that the interwovenness of humans and non-humans should be discussed more within scientific research, especially in conservation biology.Show less
One of the greatest remaining puzzles in physics is what particle dark matter consists of. For this project, the theory of dark pions is considered, a Hidden Valley model that extends the Standard...Show moreOne of the greatest remaining puzzles in physics is what particle dark matter consists of. For this project, the theory of dark pions is considered, a Hidden Valley model that extends the Standard Model with new, dark particles and a new force, dark QCD. A sensitivity study is performed to determine how many dark pions are expected to be in acceptance of the LHCb detector for Run 2 conditions; the LHCb is well-suited to search for particles in the considered O(1) GeV mass and O(1) - O(100) ps lifetime range. Additionally, a framework has been developed to study the dependence of the sensitivity on a number of theoretical parameters of the dark QCD model, namely the probability to form a dark vector meson instead of a dark pion, the number of colours in dark QCD, the dark QCD scale, and the Higgs mass. It is found that O(100) dark pions are in LHCb acceptance for different track categories, and that the considered the- oretical parameters do not drastically change the number of expected particles (with some small caveats), staying within a difference of about 20%. This is acceptable given the expected experimental uncertainty, showing theory inde- pendent searches for dark pions are possible.Show less
The past decades have shown a rise in skin cancer. This creates the need for prevention and efficient treatment. The most common skin cancer (melanoma) can only be treated when detected early. In...Show moreThe past decades have shown a rise in skin cancer. This creates the need for prevention and efficient treatment. The most common skin cancer (melanoma) can only be treated when detected early. In this thesis we propose a method of increasing awareness for people with a high risk of skin cancer as well as allowing for early detection. Skin cancer is hard to detect, even for experiences healthcare professionals. One of the signals of potential harm full lesions is change over time. We propose to develop an application with which changes in skin lesions can be identified early. By allowing patients to film their body with a mobile phone camera we aim to track the development of lesions. If a patient films their body regularly changes can be detected and the application can urge the patient to consult a dermatologist. In this thesis we explore the possibility of combining the frames of these films into an overview displaying the patients complete back or arm. Combining frames is called stitching. Different stitching techniques found in literature are explored and tested for effectiveness. The optimizations performed are reported and the final result is presented. The location of the different lesions on an overview of the body is needed to show the patient and the healthcare professional where potential harmful lesions are located on the body. This allows for further inspection at the dermatology department.Show less
The Eurozone crisis is an example of how democratic regimes can be threatened under emergencies, and it revealed two contributing phenomena – the state of exception and technocracy. This thesis...Show moreThe Eurozone crisis is an example of how democratic regimes can be threatened under emergencies, and it revealed two contributing phenomena – the state of exception and technocracy. This thesis aims to understand the link between the two in the context of emergency politics, through the paradox of politics. This paradox, which can be traced back to Rousseau, brings to light an aporia in democratic politics, where we need good citizens to make good laws and good laws to make good citizens. This thesis starts by analysing each phenomenon individually and the way they threaten democracy. It then interprets them through the paradox of politics as arrangements meant to resolve that paradox, but infringing upon the ideal of democracy it subscribes to (inspired by the analysis of political theorist Bonnie Honig). Finally, it analyses the link between them and the potentials for the democratization of emergency politics. The main conclusions are 1) in emergency politics, technocracy and exception display a link of mutual reinforcement that infringes upon democratic politics (empirically and conceptually), and 2) the democratization of emergency politics requires not only a deexceptionalization of emergency (as suggested by Honig), but also a process of detechnocratization of democracy.Show less
This thesis sought to investigate the relationships between treatment delays in bipolar disorder (BD) and cognitive impairments which characterize the disorder, measured both objectively and...Show moreThis thesis sought to investigate the relationships between treatment delays in bipolar disorder (BD) and cognitive impairments which characterize the disorder, measured both objectively and subjectively. Previous studies have established that a long delay occurs between the onset of mood symptoms in BD and the first form of treatment received, estimates ranging between 6 and 11 years. Cognitive impairments in the domains of executive functions, processing speed and memory were found to persist in BD patients even during euthymia. Such cognitive impairments burden BD patients, prevent them from regaining an appropriate level of general functioning and diminish their quality of life. Thus, in order to determine whether treatment delay impacts the cognitive impairments present in BD, 69 participants were followed over the course of one year, at three different time points. The participants took part in clinical interviews, and then were asked to complete multiple measures, such as the YMRS, the QIDS, four WAIS subscales (Block Design, Arithmetic, Information and Digit symbol), and the Cognition subscale of the WHODAS. The average treatment delay found in the current sample was 14.53 years. The results of the current study suggest that longer treatment delays did not significantly predict worse cognitive functioning in BD patients, either when measured subjectively, or when measured objectively.Show less
Competency-based intervention is an approach in youth services focusing on enhancing skills aligned with age-appropriate developmental tasks. It is employed across various contexts and for diverse...Show moreCompetency-based intervention is an approach in youth services focusing on enhancing skills aligned with age-appropriate developmental tasks. It is employed across various contexts and for diverse target populations. However, the extent of evidence supporting this method in literature is unclear. This thesis synthesizes multiple sources to provide a comprehensive overview of to which extend this topic has been researched: What is known about this methodology, its strengths and weaknesses, and the specific target groups under investigation? Through a narrative review, ten evidence-based and seven non-evidence-based sources have been integrated to present a holistic perspective on the field of competency-based intervention. Several sources have indicated that the application of this model is effective in improving behavior and psychosocial conditions, including youth residing in residential facilities, high-risk families, adolescents with severe psychiatric/behavioral issues, and elementary school children with antisocial behavior. Although indications have been found that this method brings many advantages in practice, it was concluded that there is not enough evidence for competence-based work in the literature due to limitations in the studies. There is a need for further research to assess the effectiveness of this widely used approach.Show less
In this thesis the relative spectral energy density of stochastic primordial gravitational waves is investigated. Decoupling of Standard Model particles and neutrino free-streaming affect the...Show moreIn this thesis the relative spectral energy density of stochastic primordial gravitational waves is investigated. Decoupling of Standard Model particles and neutrino free-streaming affect the expansion history of the universe and thus leave characteristic signatures on the amplitude of the gravitational wave spectrum. Adding extra light or heavy particles damps the spectrum at frequencies before the particle decouples. Including an extra neutrino species amplifies the spectrum at larger wave numbers, but damps it at shorter wave numbers. Measuring these primordial gravitational waves reveals the thermal history of the universe. One possible non-standard thermal history is early matter domination due to the inflaton. It is shown that, in this cosmology, the end of early matter domination and beginning of the radiation era depend linearly on the reheating temperature.Show less
The intergalactic medium (IGM) contains most of the baryonic matter of the Universe and serves as a suitable environment for probing the thermal history of the Universe. The crucial moment in IGM...Show moreThe intergalactic medium (IGM) contains most of the baryonic matter of the Universe and serves as a suitable environment for probing the thermal history of the Universe. The crucial moment in IGM evolution is the Epoch of Reionization, corresponding to the transition from neutral to ionized IGM. However, due to the observational limitations, this period is still not well understood. In this thesis, we focus on constraining IGM thermal history by using Lyman-alpha forests data. This method is applicable in a wide range of temperatures, densities, and ionization fractions of cosmic gas at z about 2 − 5. Observations show that the longitudinal flux power spectrum of the Lyman-α forest exhibits a cut-off at small scales. This phenomenon is caused by thermal Doppler broadening, peculiar velocities along the line of sight (LOS), Hydrogen pressure smoothing, and warm dark matter. The first two effects act only along LOS, while the last two affect all spatial directions. To separate the one-dimensional and three-dimensional effects, we used the method of close quasar pairs, which is based on studying the correlations between Lyman-alpha forests of close quasar pairs. We used the Kolmogorov-Smirnov test to analyze the differences between distributions of phase difference, which characterizes correlations between Lyman-alpha forests. The calculations were performed for various thermal histories, parameters characterizing IGM, LOS separations, and wavenumbers, and accounting for different effects (Doppler broadening and peculiar velocities). Our results indicate that this method can distinguish various thermal histories regardless of the IGM thermal state and one-dimensional effects. Moreover, at separations of the order of pressure broadening, there is a prominent feature caused by different influences of pressure smoothing at large and small scales. In addition, this simple and powerful approach has the potential to distinguish scenarios with warm dark matter.Show less
In this thesis we present an experimental realisation of a double loop type Magnetic Paul Trap. We show that a microgram heavy NdFeB permanent magnet can stably be levitated for hours at room...Show moreIn this thesis we present an experimental realisation of a double loop type Magnetic Paul Trap. We show that a microgram heavy NdFeB permanent magnet can stably be levitated for hours at room temperature in this trap. Magnetic levitation of a magnetized particle is theoretically possible with this trap by generating opposed alternating magnetic fields. We show the fabrication of a printed circuit structure capable of producing these fields, as well as the engineering behind the realisation of the trap. Both by optical and magnetic readout we characterize the motion of the trapped magnet and show that its center of mass motion frequencies $\omega_z = 2\omega_{x,y} \approx 20Hz$. We characterize the damping on these modes and find that at low pressure the quality factor is strongly limited (to $Q \approx 90$) by coupling to the environment through generation of Eddy currents.Show less
This project employs reinforcement learning techniques to explore novel decoding strategies for quantum error correction, particularly focusing on the toric code, to address the challenge of...Show moreThis project employs reinforcement learning techniques to explore novel decoding strategies for quantum error correction, particularly focusing on the toric code, to address the challenge of maintaining stable quantum states for fault-tolerant quantum computing. Two game frameworks are established, including a novel dynamic game framework applicable to the training and measuring of RL agents and potential application in multiagent scenarios. The RL agents use Stable Baselines 3’s Proximal Policy Optimization and show to achieve Minimum Weight Perfect Matching performance on 3 × 3 toric code lattices in both the static and dynamic game frameworks.Show less
This study aims to investigate relative age within primary school grades as a potential influential factor of perceived ADHD symptoms. It examines whether relatively younger pupils show more ADHD...Show moreThis study aims to investigate relative age within primary school grades as a potential influential factor of perceived ADHD symptoms. It examines whether relatively younger pupils show more ADHD symptoms than their classmates. The study is of cross-sectional design, using data of primary school children throughout the Netherlands. Participating children are in the age range of four to twelve years old, N = 168. To measure ADHD symptoms, the SNAP-IV (18) has been filled out by parents of the participating children. Relative age serves as the main predictor of this study. Simple linear regressions have been run on relative age (predictor) and ADHD symptoms (dependent). Analyses showed that relative age is no predictor of ADHD symptoms, implying that relative age is no influential factor in perceived ADHD symptoms. However, data screening pointed out that the sample of the current study might not be representative for the general population. Furthermore, the current research design worked with parental observations of ADHD symptoms, and not official ADHD diagnoses. Whether a child has had an ADHD diagnosis was unknown during this study. Incorporating this information in future research could potentially lead to a better understanding of the topic. All in all, the results of this study must be interpreted with care and future research is needed to (dis)prove the relation between relative age and ADHD symptoms.Show less
Understanding the early formation of attitudes towards emerging technologies, such as quantum science & technology (QS&T), is essential for aligning the effect of science communication in...Show moreUnderstanding the early formation of attitudes towards emerging technologies, such as quantum science & technology (QS&T), is essential for aligning the effect of science communication in practice with its intentions. This study explores the application of natural language processing (NLP) techniques to investigate the influence of news articles on social media comments regarding QS&T. We curated a dataset of 217 articles and 14, 391 top-level comments from Reddit. Employing GPT-4, a semi-automated annotation method was developed to label comments for sentiment and engagement towards QS&T, achieving a Cohen’s kappa of 0.82 when pooling over multiple labelling repetitions and comparing with human annotations. We then used support-vector regression to determine if news article embeddings could be used to predict comment sentiment and engagement. After experimenting with various embedding strategies, including Sentence-BERT and RoBERTa models, no significant correlations were found between article content and comment sentiment or engagement towards QS&T. Further interdisciplinary work in empirical communication research and NLP is suggested to explore alternative representations for news articles and their ability to predict perceptions in news comments.Show less
