15,008 Works

Ecosystem emergence : an investigation of the emergence processes of six digital service ecosystems

Llewellyn Thomas
This thesis investigates processes of ecosystem emergence. Ecosystem research has thus far focused on understanding the structure and dynamics of already existing ecosystems. However much less attention has been devoted to the emergence of ecosystems. I first theoretically develop an institutional approach to ecosystems, arguing that the ecosystem is an organisational field which has value co-creation as its recognised area of institutional life. Synthesising the theories of dominant design, social movements, and institutional entrepreneurship, I...

A magnetic resonance imaging (MRI) investigation into the effects of ageing on the functional and structural connectivity of the brain

Emer Hughes
Ageing in the absence of disease is associated with reduced cognitive function. Cognitive function depends on the integrated operation of large-scale distributed brain networks. In this thesis I use structural and functional magnetic resonance imaging to test the hypothesis that age related cognitive decline arises from disruption to the integrated operation of large-scale networks, and the disrupted operation of these networks is associated with structural disconnection to white matter tracts. There are five studies presented...

A search for supersymmetry using the alphaT variable with the CMS detector and the impact of experimental searches for supersymmetry on supersymmetric parameter space

Samuel Rogerson
A search for supersymmetry in final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of sqrt(s)=7TeV. The data sample corresponds to 4.98fb^-1 collected by the CMS experiment at the LHC in 2011. A dimensionless kinematic variable is used as the main discriminant between genuine and misreconstructed signal events. The search is performed in a signal region binned according to the scalar sum of the transverse energy of...

Uniform Linear Poly(ethylenimine) via Poly(oxazoline)s - Synthesis, Mechanism of Toxicity and the Role of the Free Polymer during Transfection

Bryn Monnery
Linear poly(ethylenimine) is the current “gold standard” gene transfection agent. It is synthesised via the cationic ring opening polymerisation of 2-ethyl-2-oxazoline followed by the acid catalysed hydrolysis to the hydrochloride salt. However the synthesis of the parent polymer produces a broad distribution of molecular weights. Ideally the polymer should have a narrow molecular weight distribution - it should be “uniform”. By exploring the possible side reactions it is possible to minimise them and optimise the...

Quadtree Structured Approximation Algorithms

Adam Scholefield
The success of many image restoration algorithms is often due to their ability to sparsely describe the original signal. Many sparse promoting transforms exist, including wavelets, the so called ‘lets’ family of transforms and more recent non-local learned transforms. The first part of this thesis reviews sparse approximation theory, particularly in relation to 2-D piecewise polynomial signals. We also show the connection between this theory and current state of the art algorithms that cover the...

Development and application of atomistic force fields for ionic materials

Joanne Sarsam
In the field of molecular dynamics (MD), the time evolution of a set of interacting atoms is determined by integrating their equations of motion using Newton’s Second Law. By using efficient potentials that capture the essential physics of a material, the properties of systems containing tens of thousands of atoms can be accurately modelled. This thesis describes three substantial developments in the science and simulation of ionic materials. In the opening chapters, we provide an...

Synthetic approaches to improving perylene diimide-based organic electronics

Stuart John Oram
This thesis deals with the family of small molecules known as perylene diimides, their synthesis, properties, and use in organic electronics. In particular it is focussed on the use of perylene diimides as small molecular organic semiconductors in organic photovoltaics and organic field-effect transistors. Here is reported the synthesis, characterisation, properties and device testing of a range of new perylene diimide materials, designed to have properties amenable to use as acceptors in organic photovoltaics. Also...

Charge separation, triplets and photochemical stability in polymer / fullerene solar cells

Ying Soon
Charge generation and stability are key issues that have great impact upon the commercial viability of organic solar cells. In this thesis, a range of donor polymers, mainly of donor-acceptor class, were employed. Various materials characterisation, photophysical and photostability studies were performed on neat polymer films and polymer/fullerene blend films with the aim of establishing relationships between material structure and device function/stability. Transient absorption spectroscopy (TAS) was employed for the photophysical studies on neat films....

Investigating inhomogeneous FM at SC/FM interfaces using point-contact Andreev spectroscopy

Irham Tri Muharram Usman
The unconventional long range (m=1) spin triplet proximity effect is theorised to be created at a Superconductor/Ferromagnet (SC/FM) interface that is magnetically inhomogeneous and provides the conditions for spin mixing. Many experimental and theoretical works have identified the existence of the m=1 spin triplet state using Josephson junctions to show how the critical current does not diminish significantly in a thick FM layer, (thickness being relative to the decay length of a Cooper pair in...

Detecting changes in high frequency data streams, with applications

Gordon J. Ross
In recent years, problems relating to the analysis of data streams have become widespread. A data stream is a collection of time ordered observations x1, x2, ... generated from the random variables X1, X2, .... It is assumed that the observations are univariate and independent, and that they arrive in discrete time. Unlike traditional sequential analysis problems considered by statisticians, the size of a data stream is not assumed to be fixed, and new observations...

Glasses for energy applications : atomic scale network structure and properties

Thorsten Roland Stechert
Glass is used for the vitrification of high level waste that results from the reprocessing of spent nuclear fuel. A better understanding of the structure of vitrified wastes may lead to insights into the observed compositional flexibility. It is also the starting point for studies of the self-irradiation behaviour of glasses under long-term repository conditions. Appropriate models need to be employed for the study of glasses when using molecular dynamics. The nature of nuclear waste...

Synthesis and evaluation of receptors for phosphatidylinositol phosphates

Gillian Whyte
Phosphatidylinositol phosphates (PIPs) are signalling phospholipids with a diverse set of cellular functions. The most important of these PIPs are phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2) and phosphatidylinositol (3,4,5) trisphosphate (PI(3,4,5)P3). These two are responsible for a number of cellular events which regulate cell growth, proliferation and apoptosis. Deregulation of PIP levels disrupts these pathways and can therefore lead to uncontrolled cell growth and which can lead to tumourigenesis. Control of PIP levels has been identified as...

Density functional theory study of LaMnO3 and its competing oxides: an insight into a prospective alkaline fuel cell cathode

Ehsan Aleem Ahmad
LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum) as a catalyst for the oxygen reduction reaction (ORR) in alkaline fuel cells (AFCs). In fact, recent studies have shown that among a range of non-noble metal catalysts, LaMnO3 provides the highest catalytic activity. However, further development of this catalyst is limited by the fact that very little is known about LaMnO3 in the AFC environment. While it has been established that the bulk phase...

A study of MHC class I binding viral and host derived peptides and natural killer cell function

Kuldeep Cheent
Natural killer (NK) cells are a key component of innate immunity and have been implicated in determining the outcome of HCV infection in both genetic and functional studies. The last two decades have seen significant advances in the understanding of NK cell regulation with the discovery of a multitude of activating and inhibitory receptors. CD94:NKG2A operates in tandem with the polymorphic killer cell immunoglobulin-like receptors (KIR) and Ly49 systems to inhibit NK cells, however it...

The feature-based computational geometry and secondary air system modelling for virtual gas turbines

Davendu Yashwant Kulkarni
This dissertation presents a novel method for generating the computational geometry of three spool aero engine for the Virtual Engine (VE) design environment, which is capable of carrying out full integration of preliminary and detailed design and analysis activities. The multi-fidelity and multi-disciplinary analysis of complex gas-turbine assemblies is the prime requirement of industrial design. The present challenges for gas-turbine industry, namely excessive design times, lack of decisive information till the late design stages, mismatching...

Russian governance and investment

Anna Grosman
Research on firm’s investment behaviour is central to corporate finance. Investment policy can be explained by many corporate finance theories involving the choice of financing (debt vs. equity vs. internal funds), agency costs (management vs. monitoring blockholders), asymmetric information (between management and providers of external finance) and moral hazard (the choice of level of risk of an investment project). Research on governance focuses on whether internal and external governance mechanisms improve firm value and profitability,...

Orthogonal polynomials, perturbed Hankel determinants and random matrix models

Nazmus Saqeeb Haq
In this thesis, for a given weight function w(x), supported on [A,B]\subseteq\mathbb{R}, we consider the sequence of monic polynomials orthogonal with respect to w(x), and the Hankel determinant D_n=\det(\mu_{j+k})_{j,k=0}^{n-1}, generated from the moments \mu_j of w(x). A motivating factor for studying such objects is that by observing the Andreief-Heine identity, these determinants represent the partition function of a Hermitian random matrix ensemble. It is well known that the Hankel determinant can be computed via the...

Using fMRI and Behavioural Measures to Investigate Rehabilitation in Post-Stroke Aphasic Deficits

Sonia Brownsett
In this thesis I investigated whether an intensive computerised, home-based therapy programme could improve phonological discrimination ability in 19 patients with chronic post-stroke aphasia. One skill specifically targeted by the treatment demonstrated an improvement due to the therapy. However, this improvement did not generalise to untreated items, and was only effective for participants without a lesion involving the frontal lobe, indicating a potentially important role for this region in determining outcome of aphasia therapy. Complementary...

Fourier spectral/hp element method: investigation of time-stepping and parallelisation strategies

Alessandro Bolis
As computer hardware has evolved, the time required to perform numerical simulations has reduced, allowing investigations of a wide range of new problems. This thesis focuses on algorithm optimization, to minimize run-time, when solving the incompressible Navier-Stokes equations. Aspects affecting performance related to the discretisation and algorithm parallelization are investigated in the context of high-order methods. The roles played by numerical approximations and computational strategies are highlighted and it is recognized that a versatile implementation...

Viscosity and density of aqueous fluids with dissolved CO2

Mark McBride-Wright
Carbon Capture and Storage (CCS) is considered a technology which can help ease the emissions associated with the use of fossil fuels for energy and industrial processes. In Qatar, rapid industrial expansion has established a need for CCS. Here, saline aquifers represent a potential sink for geologically storing the associated CO2 emissions. CCS is an important component of meeting carbon emission targets; CO2 storage in the carbonate reservoirs of the Middle East and elsewhere will...

Feature extraction in classification

Raymond Liu
Feature extraction, or dimensionality reduction, is an essential part of many machine learning applications. The necessity for feature extraction stems from the curse of dimensionality and the high computational cost of manipulating high-dimensional data. In this thesis we focus on feature extraction for classification. There are several approaches, and we will focus on two such: the increasingly popular information-theoretic approach, and the classical distance-based, or variance-based approach. Current algorithms for information-theoretic feature extraction are usually...

Applications of scattering-type scanning near-field optical microscopy in the infrared

Edward Yoxall
This thesis is split into two broad sections. These are defined by the various applications of scattering-type near-field optical microscopy (s-SNOM) in different parts of the electromagnetic spectrum; the near-infrared (700 - 1000nm) and the mid-infrared (6 - 10um). S-SNOM is a means of imaging surfaces at resolutions well below the diffraction limit - the level of recorded detail does not depend on the wavelength of light (as it does with traditional optical microscopy), but...

The Fatigue and Fracture Properties of Nano-modified Epoxy Polymers

Seung Hwan Lee
The present Thesis investigates the quasi-static and cyclic-fatigue properties of nano-modified epoxy polymers. A diglycidyl ether of bisphenol-A was used as the base epoxy and polymer-based materials, block copolymers and core-shell rubber particles were used as the toughening agents. The morphologies formed by the tougheners were determined and the associated fracture and fatigue properties, including the toughening mechanisms, were investigated. The modified epoxy polymers with some of the best properties are described below. The unmodified...

The magnetocaloric effect at a first order phase transition

Milan Bratko
The magnetocaloric effect (MCE) can be defined as the isothermal entropy change (or adiabatic temperature change) of a material upon application/removal of an external magnetic field and is the key physics for a magnetic cooling device. A discontinuity of entropy at a first order phase transition (FOPT) allows for a large entropy change to be induced by a relatively small field. However, a hysteresis is necessarily associated with a FOPT. The effects of hysteresis, as...

Defects in topologically ordered lattice models

Benjamin James Brown
Developing quantum systems which are robust against noise are of prime importance to the realisation of quantum technologies. Without fault tolerance, we will never be able to preserve delicate quantum states for macroscopic time scales, a necessary requirement in the construction of scalable quantum computer. Topologically ordered models offer very beautiful mechanisms for preserving quantum states. In such models, quantum information is encoded globally over a degenerate topological Hilbert space which offers a natural robustness...

Registration Year

  • 2021
    135
  • 2020
    2,187
  • 2019
    7,966
  • 2018
    1,443
  • 2017
    1,502
  • 2016
    1,650
  • 2015
    79
  • 2014
    22
  • 2013
    11
  • 2012
    7

Resource Types

  • Text
    8,452
  • Dataset
    6,108
  • Collection
    447
  • Image
    1

Affiliations

  • Imperial College London
    15,008
  • University of Oxford
    36
  • University College London
    11
  • University of Cambridge
    10
  • University of Exeter
    10
  • University of Manchester
    8
  • Natural History Museum
    7
  • University of London
    7
  • University of Edinburgh
    6
  • University of Birmingham
    6