Physics Theses

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This collection is made up of doctoral and master theses by research, which have been received in accordance with university regulations.

For more information, please visit the UCD Library Theses Information guide.

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Now showing 1 - 5 of 28
  • Publication
    Observations of Circumstellar Interaction in Diverse CCSNe
    (University College Dublin. School of Physics, 2022) ;
    0000-0002-1178-2859
    In this thesis, I investigate the observational properties of two supernovae displaying strong signatures of interaction with circumstellar material, and how they contribute to furthering our understanding of their respective subtypes. The first part of this thesis concerns the photometric and spectroscopic analysis of SN 2018zd. I coordinated the follow-up campaign for this object on behalf of the NUTS collaboration, acquiring hours of observations in the UV through NIR bands. I determine that this transient event is the result of the Fe core collapse of a 8-10M¿ red supergiant. The high ionisation lines observed in the early epochs of spectra are the observational signature of delayed shock breakout through circumstellar material detached from the progenitor envelope. Finally, I compare SN 2018zd to the sample of objects known as LLEV’s, luminous low expansion velocity transients; these objects have an enhanced plateau magnitude relative to their expansion velocities due to the extra photon source provided by early time interaction with circumstellar material. This enhanced plateau luminosity affects the inclusion of these objects in samples used to derive correlations from “normal” Type II SN characteristics. One such relationship we investigate is the Standard Candle Method, which can be used to estimate distances to Type IIP SNe where spectra are lacking, and we show that SN 2018zd breaks this correlation. I propose that a caveat should be attached to the Standard Candle Method, and other similar photometric distance estimate methods for Type IIP SNe, that in the absence of early spectral observations to rule out interaction with circumstellar material, strict cuts should be applied to the light curves of these transients before they are included in such samples. The second half of this thesis concerns the analysis of an archival dataset for SN 2015G, comprising of one of the highest cadence and lengthy follow-up campaigns of a Type Ibn SNe to date. SN 2015G was one of the closest observed Type Ibn’s at a distance of ~20.9 Mpc, allowing for prolonged observations of the tail phase, up to approximately six and a half months after discovery. We observed undulations in the light curve, and determine that these are the result of prolonged interaction with circumstellar material ejected shortly prior to the SN explosion. This excludes production of the circumstellar material via smooth progenitor winds, and we conclude that the material was most likely stripped by a binary companion. The results presented in this thesis span nearly the full range of possible circumstellar interaction scenarios, from the very brief, early interaction of SN 2018zd, to the interaction observed in SN 2015G which endured for the entire follow-up campaign. Both studies further our understanding of how interaction affects the evolution of transients; they bolster the broad diversity possible even within well established subtypes of SNe, and act as an all important reminder that our understanding of these subtypes is still limited by the cadences, duration, and wavelength coverage of our observational follow-up capabilities.
      22
  • Publication
    Observational constraints on Supernovae and Supernova Impostors
    (University College Dublin. School of Physics, 2022) ;
    0000-0003-1325-6235
    This thesis focuses on the observational campaign for the interacting transient AT 2016jbu, and the development and workings of a novel automated photometry code, AutoPhOT. We provide an overview of the current stellar evolutionary theory and transient astronomy, including a brief section on photometry, in Chapter 1. Chapter 2 covers the Automated Photometry Of Transients (AutoPhOT) photometric pipeline. This software package was designed to provide a fast, precise, and accurate means for the modern astronomer to measure the magnitude of astronomical point sources. We demonstrate the modern photometric techniques implemented in the code, and its capabilities to produce publication ready data with little human interaction. Chapters 3 and 4 cover the observational campaign for the interacting transient, AT 2016jbu. This transient was observed almost a decade before it exploded, allowing for strong constraints on the progenitor. Comparing to the current stellar evolutionary theory, this star is not expected to explode as a core collapse supernova, and one must question whether we are observing the death of a star at all. We present the multi-chromatic dataset for AT 2016jbu in Chapter 3 and compare with similar transients. Chapter 4 focuses on modelling the progenitor for AT 2016jbu and using a high quality, high cadence dataset, we attempt to model the transient, producing a self-consistent explosion model, that may be applied to similar transients. In Chapter 5, we present observations from the Hubble Space Telescope almost 5 years after its apparent demise. The goal of these measurements was to address whether the progenitor may have survived the 2016 events, and is now enshrouded by massive amounts of dust formed in the ejecta of AT 2016jbu. We find a unrealistic amount of dust (for a non-terminal explosion) is needed to hide the progenitor. We conclude that AT 2016jbu is indeed a genuine, albeit strange, terminal explosion and further investigate a possible explosion scenario, focusing on massive stars within a binary system. Chapter 6 provides a general overview of the most salient findings found during this thesis and comments on future work.
      15
  • Publication
    PEAR: A super-resolution imaging technique throughactive plasmonics
    (University College Dublin. School of Physics, 2022) ;
    0000-0003-2877-4836
    The research conducted here firstly develops an active plasmonic element capable of local electric near-field modulation at a known frequency. The element is then used as a core part of PEAR, Plasmonically Electronically Addressable super-Resolution, a new diffraction-limit-breaking imaging technology. PEAR has been proven to work as an imaging technology with proof-of-concept images within this thesis. Key advantages of PEAR are that it is a completely deterministic method, has strong multi-channel capabilities, and its resolution is tied to the physical size of the active plasmonic emitter. Active plasmonic elements can allow external control of a Surface Plasmon Polariton (SPP), which is a highly spatially confined electric field formed on a metal dielectric interface. Confinement, in this case, is perpendicular to the interface and the SPP propagates along it. The active plasmonic element can modulate the intensity of this local electric field in a spatially confined area in the vicinity of this element. The modulation is caused by an electric current heating a metal constriction causing changes in the electrical permittivity. The active plasmonic element is investigated through fully featured simulations using Finite-Difference Time-Domain (FDTD) and Finite Element method (FEM) techniques. These characterise and optimise the modulation that the element uses. In this body of work Atomic Force Microscope (AFM) lithography was used to shape arbitrary nanostructures. Simulations were hence validated through experiments. Super-resolution techniques are an integral part of modern science especially the bio-medical field. Improvements to these imaging technologies are hugely impactful towards understanding key biological processes which leads to advances in medicine. The imaging technology developed here uses the active plasmonic element described, to out-couple near-field information into the far-field since information beyond the diffraction-limit cannot be resolved in the far-field. Hence, lock-in amplification is used with the frequency modulation on the plasmonic element, as a reference, to spatially map the source of the sub-diffraction limited data. Due to the evanescent character of SPPs (approximately 100 nm) the sample must be close to the active plasmonic element. The ability to modulate a particular emitter with a unique frequency means multiple elements can be used simultaneously, even within the same sub-wavelength area. Building a large array of the active plasmonic elements makes this imaging method truly groundbreaking because it is completely deterministic, while still having vast multi-channel capabilities. A dual element 'array' is demonstrated experimentally. A scalable mass fabrication design is shown along with intermediate designs for arrays of less than 100 elements. Proof of concept images for this method are demonstrated and compared to a complimentary imaging method.
      6
  • Publication
    Hydrophobicity and Electrostatic Properties in Models of Protein Aggregates
    (University College Dublin. School of Physics, 2022) ;
    0000-0001-6199-7551
    A nanoparticle entering the human body results in the formation of a nano-bio interface. This results in a dynamic interaction that takes place amongst the nanoparticle surface and a variety of biomolecules, especially proteins, forming a protein corona (PC). Recently, studies of the nanoparticle protein corona (NP-PC) biophysical properties have become a significant area of research. It is important to understand, characterize and model the biophysical properties and the molecular interactions related to the NP-PC. Protein-nanoparticle interactions are driven largely by corresponding physio-chemical changes. Here, we perform atomistic molecular dynamic (MD) conformational studies of five important proteins that are known to participate in the protein corona around the nanoparticle in the human body: Human Serum Albumin, Apolipoprotein, Human Surfactant Protein D, Alpha-1 antitrypsin, and Mucin 2 D3 domain. Using their structures from the RCSB protein data bank, we perform a statistical analysis of their MD trajectories to determine their representative, average equilibrium structures and their possible outlier structures (i.e., most different from the representative ones). Using these structures in conjunction with docking simulations, we generate both homo-oligomers and hetero-oligomers and analyze their surface biophysical properties such as their hydrophobic fraction of the solvent accessible surface area (SASAH) and surface charges. We also use atomistic models of TiO2 and SiO2 nanoparticles to generate and study the NP-PC interface around these nanoparticles, describe specific residues found in the NP-PC interfaces, and show that accurate SASAH, SASA+, SASA- values, and PC surface charges can be estimated for atomistic models of NP-PCs. The efficient yet accurate characterization of NP-PC biophysical properties should be useful in future studies of NP-NP and NP-biomolecular interactions and their possible effects (e.g., toxicity) in specific biological systems.
      18
  • Publication
    Quantum transport in interacting nanodevices: From quantum dots to single-molecule transistors
    (University College Dublin. School of Physics, 2022) ;
    0000-0002-0334-930X
    The enormous interest in industrial application of semiconductor components has led to the development of unprecedented control over the manufacture of electronic devices on the nanometer scale. This allows to perform highly controllable and fine-tuned experiments in the quantum regime where exotic effects can nowadays be measured. Among those, breakthrough measurements of electrical conductance experimentally confirmed the Kondo effect - a many-body quantum effect involving macroscopic entanglement. In quantum dot devices, enhanced conductance below a characteristic energy scale is the signature of Kondo singlet formation. Precise predictions of quantum transport properties in similar nanoelectronics devices is therefore desired to design optimal functionality and control. Standard mesoscopic transport methods suffer from limitations in nanostructure specifics, set-up design, energy, temperature and voltage regime of applicability. To overcome these issues, such that we obtain modelling flexibility and accurate conductance predictions, in this thesis we analytically derive alternative and improved quantum transport formulations having as their starting point scattering theory in the Landauer-Buettiker formula, linear response theory in the Kubo formula, nonequilibrium Keldysh theory in the Meir-Wingreen formula and Fermi liquid theory in the Oguri formula. We perform a systematic benchmark of our exact expressions, comparing with the standard approaches using a state-of-the-art numerical renormalization group techniques (NRG). The new formulations not only reproduce literature results, but also show higher accuracy and computational efficiency, as well as a wider applicability under regimes and conditions out of reach by existing methods. We also derive generalized effective models for multi-orbital two-lead interacting nanostructures in both Coulomb blockade and mixed-valence regime, which yield reusable conductance predictions directly in terms of the effective model parameters. We conclude by applying our novel formulations to complex nanoelectronics systems, including a single-molecule benzene transistor, a charge-Kondo quantum dot made from graphene and a semiconductor triple quantum dot.
      140