20,404 Works

Irreversibility and symmetry principles in quantum information

Cristina Cirstoiu
Symmetry principles have played a crucial role in the development of modern physics and underpin our most fundamental theories of nature. The present thesis is concerned with the analysis of symmetries in the context of quantum information theory. Whenever a quantum mechanical system interacts with its environment it is subjected to decoherence, a process that is typically irreversible and most generally treated abstractly using the concept of quantum operations. If there is an underlying symmetry...

Spectroscopic studies of the charge-transfer state and device performance of hybrid and organic solar cells

Flurin Eisner
The last few years have witnessed a remarkable explosion in advances in the field of photovoltaics (PV) based on organic semiconductors as the light absorbing material, both in terms of device efficiency and in terms of the physical understanding of the underlying processes. This thesis aims to contribute to this field by examining two different types of solar cells based on light-absorbing organic semiconductors. It consists of two main parts connected through their focus on...

Practical deep learning

Hao Dong
Deep learning is experiencing a revolution with tremendous progress because of the availability of large datasets and computing resources. The development of deeper and larger neural network models has made significant progress recently in boosting the accuracy of many applications, such as image classification, image captioning, object detection, and language translation. However, despite the opportunities they offer, existing deep learning approaches are impractical for many applications due to the following challenges. Many applications exist with...

Controlling the evolution of antibiotic resistance

Rafael Pena-Miller
Modelling antibiotic resistance evolution is inherently a multiscale problem: from the physical interactions between drug molecules and their targets to the epidemiology of drug resistance in clinical settings. Although predicting the evolution of resistance is a difficult and ongoing problem, it is known that pathogens are continually adapting to our drug prescription patterns. For this reason, as well as the continual downturn in the discovery of new drugs, the question of how to best deploy...

Sign inversions in optical rotation as a function of wavelength (ORD spectra)

Henry Rzepa
Gaussian 16 calculations

Genetic and cellular mechanisms of autoimmunity in lupus-prone B6.129-Sle16 mice

Norzawani Binti Buang
Genome sequencing and transcriptomic analyses are hypothesis-free approaches to identify genetic variants(s) and biological pathway(s) associated with a disease. T cells are paramount in the pathogenesis of systemic lupus erythematosus (SLE). Hyperactive CD4+ T cells can promote the production of auto-antibodies by offering excessive help to B cells. B6 congenic mice carrying the Sle16 locus (B6.129-Sle16) have increased auto-antibody levels, mild glomerulonephritis, and hyperactive T and B cells. These data indicate that intrinsic T cell...

Ethylene oligomerisation and polymerisation: catalyst synthesis, mechanisms and product analysis

Craig Scott Tere Young
Products from the oligomerisation and polymerisation of ethylene are ubiquitous in daily life. These products represent a major revenue stream for the commodity chemicals industry which, along with academia, has driven research and development into the control of polymer properties via manipulation at the molecular level. This research, conducted at Imperial College London and funded by INEOS, focuses on the synthesis, characterisation, and properties of non-Cp transition metal complexes, featuring terphenyl and aromatic ligands, and...

Effects of aging on ScSZ/LSCrF dual-phase oxygen transport membrane for syngas production

Chi Ho Wong
A dual-phase composite material comprised of scandia-stabilized zirconia (ScSZ) and doped lanthanum chromite (La,Sr)(Cr,Fe)O3-δ (LSCrF) was investigated in this work as a potential oxygen transport membrane material in the production of synthesis gas. The main focus of this work was to examine the effects of exposure to three aging environments (air, 4% H2-96% N2, 5% H2-95% CO2) for two durations (300 hours, 1000 hours) on the oxygen transport kinetics and surface chemistry of ScSZ/LSCrF. Determination...

Alternative theories in quantum foundations

Andre Ranchin
Abstraction is an important driving force in theoretical physics. New insights often accompany the creation of physical frameworks which are both comprehensive and parsimonious. In particular, the analysis of alternative sets of theories which exhibit similar structural features as quantum theory has yielded important new results and physical understanding. An important task is to undertake a thorough analysis and classification of quantum-like theories. In this thesis, we take a step in this direction, moving towards...

Heat transfer and vortex shedding effects in single- and multi-scale grid-generated turbulence

Gianfrancesco Melina
In this thesis the potential of single- and multi-scale turbulence-generating grids in improving the heat transfer from a circular cylinder and from a flat plate is experimentally explored. Hot-wire and heat transfer measurements downstream of low-blockage grids with different geometries were performed in a wind tunnel. Particular emphasis is given to the impact of the vortex shedding from the bars of the grids both on the turbulent flow field and on the heat transfer. The...

Technologies for the conversion of external heat to power with reciprocating motion

Aly Taleb
Reciprocating energy-conversion devices, such as ORCs using reciprocating expanders or Thermofluidic Oscillators (TFOs), are promising technologies for the conversion of low- or medium-grade heat from waste heat, solar, or geothermal sources at power outputs below 100 kW. In this thesis, three topics associated with reciprocating machines are investigated. Firstly, a novel two-phase TFO engine concept, named ERPE, is modelled using a linear dynamic approach. Secondly, the use of working-fluid mixtures in ORCs is examined. Thirdly,...

Flow structure and coherence in the wake of a lifting wing with multiscale sinusoidal cut-in trailing edge serrations

Simon Prigent
This thesis presents an experimental investigation into the wake of a lifting wing with multiscale cut-in trailing edge serrations. More specifically, it looks into how the wake is affected by the serration patterns, both in terms of mean properties and dynamic and spectral information. The flow is investigated by means of particle image velocimetry and hot-wire anemometry to combine the dynamic and spatial strengths of the two experimental techniques. The response of a wing fitted...

On the validation of nonlinear dynamic models for structures with frictional joints

Luca Pesaresi
High cycle fatigue caused by dynamic stresses is one of the main threats for aeroengine components. Friction damping is regularly being used as a passive system to dissipate the vibrational energy of these components. Due to the presence of friction contacts, the dynamic behaviour of engine components becomes nonlinear, making an analysis much more challenging. Various modelling approaches have been proposed, however due to the complexity of the systems, a standard fully validated approach is...

The quantification of cardiac function

Graham David Cole
Quantification of cardiac function is a crucial part of diagnosis, prognosis and ongoing management for many patients with heart disease. Clinical examination is an insensitive marker of cardiac dysfunction, resulting in echocardiography being an in-demand gold-standard test. In recent years, there has been a revolution in point-of-care echocardiography, with the availability of affordable equipment with limited functionality capable of obtaining 2-dimensional pictures and limited measurements. This equipment is often used by non-specialists who make visual...

Crystallographic and ligand binding studies on human secretory Rab27a

Mostafa Jamshidiha
Rab27a is a member of Rab GTPase family of proteins, which plays a key role in cellular transport and docking of secretory vesicles at the plasma membrane. Rab27a is involved in transport/secretion of melanosomes and vesicles containing insulin, histamine, amylase, chemokines, metaloproteases and exosomes. Rab27a has been shown to promote the growth and invasion of multiple cancer types such as breast, lung, pancreatic and hepatocellular carcinoma. Evidence suggesting the significant role of Rab27a in multiple...

High-throughput recording, analysis and manipulation of sleep in drosophila

Quentin Geissmann
Sleep is a fascinating mystery that has bemused thinkers since the dawn of civilisations. Scientifically, the formalisation of sleep as an observable behaviour has been a conceptual milestone, which has enabled researchers to address the question of its ubiquity and ultimately led to the discovery of sleep-like states in most animal phyla. The fruit fly Drosophila melanogaster has long been at the vanguard of the discovery of many biological processes. In particular, it has been...

Simulating infinite vortex lattices in superfluids: a novel scheme and its applications

Luca Mingarelli
This thesis is mostly based on the research presented in [1, 2, 3]. We introduce a novel efficient framework to treat infinite periodic vortex lattices in rotating superfluids under a mean-field Gross-Pitaevskii description. In doing so, we introduce a generalisation of the Fourier transform which correctly diagonalises the kinetic energy terms while respecting the required twisted boundary conditions. We call this integral transform a Magnetic Fourier transform. Testing the method, we re-obtain known results in...

Constraining dark matter with renormalisation and global fits

James McKay
I present precision two-loop corrections of O(MeV) mass splittings in electroweak multiplets. These are relevant for both collider phenomenology and dark matter and can affect particle lifetimes by up to 40%. I then show that a commonly used iterative procedure to compute radiatively-corrected pole masses can lead to very different mass splittings than a non-iterative calculation at the same loop order. I show that this has significant phenomenological impact, leading to the conclusion that the...

Barium titanate: photophysics, photocatalysis & the influence of the ferroelectric effect

Madeleine Rachel Morris
Photocatalytic and photoelectrochemical water splitting processes remain hindered by fast recombination of photogenerated electrons and holes. Ferroelectric materials are increasingly being considered to address this issue; their internal electric fields have been shown to spatially separate electrons and holes, and thus should greatly reduce recombination rates. A kinetic understanding of the extent to which electron–hole recombination can be slowed in ferroelectric materials is essential to ascertain if they can play a significant role in achieving...

Robotic manipulators for single access surgery

Piyamate Wisanuvej
This thesis explores the development of cooperative robotic manipulators for enhancing surgical precision and patient outcomes in single-access surgery and, specifically, Transanal Endoscopic Microsurgery (TEM). During these procedures, surgeons manipulate a heavy set of instruments via a mechanical clamp inserted in the patient’s body through a surgical port, resulting in imprecise movements, increased patient risks, and increased operating time. Therefore, an articulated robotic manipulator with passive joints is initially introduced, featuring built-in position and force...

Characterisation of the MICE experiment

Sophie Charlotte Middleton
Muon beams of low emittance would deliver intense, well-characterised neutrino beams necessary to explicate the physics of flavour at a Neutrino Factory and for high-luminosity lepton-antilepton collisions at a multi- TeV muon collider. The International Muon Ionisation Cooling Experiment (MICE), based at the Rutherford Appleton Laboratory, aims to demonstrate ionisation cooling, the technique proposed to reduce the emittance of muon beams at such facilities. An ionisation cooling channel has been constructed. The muon beam traverses...

The impacts of habitat loss and fragmentation upon the maintenance of biodiversity in tropical ecosystems

Jack Henry Hatfield
Habitat loss and fragmentation are major threats to biodiversity on a global scale. Human modified landscapes now comprise large areas of the globe, heavily contributing to the observed decline in biodiversity. By understanding the processes governing species communities in these fragmented landscapes we may be better able to manage them in a way that provides conservation benefits. The first part of this thesis focuses on dispersal in complex landscapes with Chapter 2 taking a regional...

Topological insulator nanoparticles and their photonic analogues

Gleb Siroki
The exploration of topological insulators has been a remarkable success of band theory. Topological insulators are distinguished from ordinary ones by the boundary states which exist at the edge of those materials and are robust against disorder. Moreover, for these states the propagation direction depends on the spin in the absence of time-reversal breaking. This makes topological insulators promising candidates for spintronics as well as some optical applications. Because the their unique properties from single-particle...

Optimisation and applications of a Raman quantum memory for temporal modes of light

Joseph Munns
Within any practical proposal for utilising quantum mechanics for information processing whether for the efficient computation of problems intractable by classical methods, or for secure communication; at some stage one must have the means to transfer quantum information between remote nodes of a network. For this, light is the obvious choice. To realise this vision one requires the means to overcome the ``scaling problem'' intrinsic to many photonic-based quantum technologies due to probabilistic operations. It...

Generation of finite simple groups

Carlisle King
Let G be a finite simple group. Well-known results of Miller, Steinberg and Aschbacher-Guralnick prove that G can be generated by a pair of elements - we say that G is 2-generated. In this thesis, we consider some variations of this result. A natural refinement of the 2-generation result is to ask, for a pair of integers (a,b), whether a finite simple group G is generated by an element of order a and an element...

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