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Essays on the impact of peer-to-peer lending
No full textThis thesis investigates whether serial borrowing from the peer-to-peer platform and increased investors' reliance on the auto investing technology of the platform reduces the friction (credit cost) in the credit market, which arises due to information asymmetry and adverse selection. This study also examines how peer-to-peer entry policy affects traditional credit providers. Chapter 1 provides the general introduction of the thesis and highlights the research problems and contributions.
Chapter 2 investigates how serial borrowing on peer-to-peer platforms alleviates information asymmetry between borrowers and lenders. The results show that serial borrowing from the platform reduces interest rate by two percentage points, and the results are more pronounced in the case of higher information opacity. The study also finds that serial borrowing significantly reduces the probability of default. The chapter addresses endogeneity concerns, conduct a battery of robustness tests and finds consistent results. The findings of the study imply that serial borrowing could be beneficial for both borrowers in terms of access to finance at lower cost and lenders in terms of increased loan quality.
Chapter 3 turns up the investment technology dimension of the peer-to-peer platform and shows that the dominant role of the peer-to-peer platform in loan screening and allocation (auto investing) reduces the information production cost of investors. Later this cost advantage is reflected in the loan price. This chapter also finds that auto investing is associated with a lower default rate. This chapter addresses endogeneity concerns and applies multiple approaches to ensure the consistency of the results. The results highlight the importance of automated data-driven technology in the credit market to overcome imperfections in the consumer credit market.
Chapter 4 uses the removal of the staggered restrictions on lending by two major peer-to-peer platforms such as Lending Club and Prosper, in US, states; this chapter shows that banks' interest in consumer loans decreases following the exposure of peer-to-peer policy. This study uses a battery of robust tests and finds a consistent result. The chapter provides regulatory insights as it sheds light on the unintended consequences of peer-to-peer entry on the stability of consumer banking. Finally, chapter 5 concludes the thesis, provides policy implications, and opens future avenues of research
From synthesis to 3D printing: a journey into stereochemistry and its impact on polymer networks
Get PDFPhoto-active polymeric materials are valuable to a myriad of industries from paints and inks to binders in rocket propellers and even in healthcare and 3D printing. Changing the thermomechanical properties relies mostly on changing the functionality of monomer units, which limits the choice of possible candidate owing to restriction resulting from a need for biocompatibility or printability. For this reason, it is of high relevance to manipulate the mechanical properties without a change in the chemical functionality. An emerging technique in the field of thermoplastic polymers is now devoted to tuning the mechanical properties via the rational control of the backbone stereochemistry. More specifically, the thiol-ene step growth addition between a dithiol and a diacrylate proved to be a valuable advance for the implementation of cis/trans chemistry for high molecular weight thermoplastic. In addition to be mild enough to preclude the occurrence of unwanted crosslinking or isomerisation, the technique revealed itself to be versatile since the diacrylates are prepared from stereopure diols, enabling the preparation of cis or trans unsaturated or the isohexides ring-based units. In this thesis manuscript, efforts made towards the translation of this unique system to photo-active polymeric materials using 2 kinds of stereopure diacrylate monomers, namely cis and trans 1,4-but-2-ene diol and isohexides will be described. In parallel, the synthesis of a glucose-derived diacrylate and dithiol will be explored in the aim at synthesising a synthetic polysaccharide via nucleophile catalysed thiol-Michael addition. The first chapter will present the state of the art and impact of stereochemistry in polymers. The second chapter will present the synthesis and further functionalisation of the stereopure diols selected for this study with a commercially available isocyanate-acrylate and also the synthesis of a glucose derived dithiol. Chapter three will discuss the work made towards controlling the molecular weight and end groups of diacrylate telechelic oligomers via Michael step-growth polymerisation of the commercially available 1,6-hexanedithiol and the cis/trans unsaturated and isohexides-based diacrylate monomer. In addition, the attempt at producing a high molecular weight polysaccharide mimic using the same polymerisation technique will be presented. Finally, the fourth chapter will focus on the formulation of cis and trans unsaturated prepolymers into photo-active resins to produce films suitable for thermomechanical testing. It was found that for low curing time (< 1 min) the radical initiated crosslinking only occurred at the acrylate end groups and isomerisation of the internal double bonds was mitigated. Furthermore, for films prepared from prepolymers with low molecular weight (4.0 kDa) a significant difference in the thermomechanical properties between cis and trans films was observed as a consequence of the different degree of crystallinity between the two materials. However, at higher molecular weights (8-10 kDa), the cis polymer gains progressive crystallinity and its thermomechanical behaviour becomes comparable to the trans polymer network. Finally, the prepolymers were formulated into resins suitable for 3D printing which displayed both thermomechanical and degradation properties dependent on the backbone stereochemistry
Constraining in situ denitrification and its role as nitrous oxide sink in conventional and regenerative agriculture
Get PDFThe current food production system is responsible for 19 to 29% of the overall global emissions of greenhouse gases. In particular, it contributes about 75% of the global anthropogenic nitrous oxide (N2O) emissions, a greenhouse gas with 298 times greater radiative forcing than carbon dioxide (CO2). These emissions mostly result from the large quantities of synthetic nitrogen (N) fertilizer applied in arable agriculture. In the UK, intensive cultivation practices are the main contributors to the ~£1.2 billion annual costs of soil degradation, which represents 30% of the UK farm gate income. To ensure future food security whilst addressing these environmental and economic challenges, a transition to less intensive food production systems and a better understanding of the mechanisms and controls of N2O emissions are needed. However, this better understanding can only be complete by constraining the denitrification process.
Denitrification is the anaerobic microbial respiration process which transforms soil nitrate (NO3-) into gaseous dinitrogen (N2). When incomplete, it can be a predominant source of N2O in soil, while its full sequence of reaction is the only natural terrestrial sink for N2O emissions. The high sensitivity needed to distinguish small soil-N2 fluxes from the high N2 atmospheric background (~78%) unfortunately restricts its measurement to peak events. A new methodology is therefore needed to resolve the enigma of denitrification quantification in soil.
In contrast with conventional farming management, regenerative agriculture aims to restore degraded lands and maintain soil fertility using crop rotations, including 3– 4 year “ley” mixture comprising of grasses and nitrogen-fixing legumes such as clovers. These leys have the double benefit of increasing soil organic carbon and naturally fertilizing soil with nitrogen, reducing reliance on synthetic fertilizer. However, little is known about the impact of these leys on the soil nitrogen cycle and their potential contribution to greenhouse gas emission reduction.
The present work aims to investigate the importance of denitrification in conventional agriculture and long term ley rotations; in particular in response to N fertilizer application. To address the challenges of denitrification quantification, a new methodology combining 15N tracer and N2-depleted artificial atmosphere has been developed and subsequently used for a one-year field campaign. This successful campaign was the first UK attempt to characterize in situ denitrification rates under artificial atmosphere.
The newly developed method enabled the detection of soil-N2 fluxes 90% of the time, with an 8 fold greater sensitivity than conventional methods and allowing the simultaneous incubation of 24 soil cores; capturing spatial variability at farm scale. The field campaign spanned from March 2022 to May 2023 and was characterized by a large denitrification activity in the arable control following fertilizer application. Indeed, 15 kgN ha-1 were lost in this field (~8% of the 200 kgN ha-1 applied) through denitrification between April and October 2022. Our measurements indicated that 9 % of this flux occurred as N2O rather than N2. The application of fertilizer in leys also resulted in 3 times higher N2O emissions and an N2O sink efficiency dropping from 93% to 85%.
The present work improves the characterization and understanding of the denitrification process and highlights the high existing correlation between nitrous oxide sink efficiency and soil nitrate availability; calling for new strategies of fertilizer application in agricultural fields
Biomedical multi-materials bone scaffolds with tuneable properties using additive manufacturing
Get PDFBone tissue engineering is a promising field that focuses on developing new techniques and materials for repairing or replacing damaged bones with bone scaffolds. Recently, 3D printing technologies have emerged as a feasible alternative to conventional manufacturing techniques, enabling the customization of bone scaffolds to meet individual patient needs. This technology has the potential to overcome the shortcomings of traditional approaches and provide better solutions for bone injuries by allowing for customized geometries, materials, and pore structures.
The structural properties of bone scaffolds, such as pore size and porosity, play a crucial role in their functionality in both in vitro and in vivo environments. In general, interconnected porous bone scaffolds that promote cell migration and proliferation are highly desirable. Polylactic acid (PLA) is a widely used biodegradable polymer in tissue engineering applications due to its favourable biocompatibility and mechanical properties. Calcium peroxide (CPO), which can release oxygen upon contact with water, is a valuable component in bone tissue engineering as increased oxygen levels can aid in promoting bone growth and healing.
In this thesis, a novel Fused Deposition Modelling (FDM) PLA/CPO composite filament was created through wet solution mixing and hot melt extrusion. The filaments were produced with different CPO ratios ranging from 1.5% to 24% and subjected to various physical analyses, including X-ray diffraction, surface morphology assessment, evaluation of filament extrudability and printability, microstructural analysis, and examination of rheological and mechanical properties.
The findings of the study indicated that increasing the CPO content resulted in changes in viscosity and microstructure, thereby influencing the mechanical strength and ductility of the composite filaments. However, it was found that the filament with 6% CPO content exhibited promising properties, including acceptable surface morphology and strength, making it suitable for 3D printing applications.
Additionally, the release of oxygen and calcium ions, generated porosity, antibacterial activities and cell culturing of the PLA/CPO composite filaments were assessed. The results revealed that among all the CPO ratios investigated, the 6% CPO content exhibited optimal outcomes, including higher oxygen and calcium ions release, effective bacterial inhibition and exhibited differentiation to bone. These findings suggest that the PLA/CPO composite filament with 6% CPO content holds significant potential for enhancing bone generation by improving oxygenation of bone cells and providing resistance against bacterial infections
Investigating the production and secretion of PEPITEM, a regulator of leukocyte trafficking
Get PDFLeukocyte trafficking is an essential part of the inflammatory response. Immune cells need to migrate to areas of inflammation to initiate pathogen clearance and mediate tissue repair. It is vital that this process is tightly regulated, as aberrant lymphocyte recruitment contributes to immune-mediated inflammatory diseases (IMIDs). PEPITEM (PEPtide Inhibitor of TransEndothelial Migration) is an immuno-regulatory peptide secreted by adiponectin-stimulated B-cells and acts to suppress T-cell transendothelial migration. It is known that PEPITEM is derived from the parent protein 14-3-3ζ, however the mechanisms behind PEPITEM production and secretion are currently unknown. In this thesis, we explored proteases involved in PEPITEM production. Using genetic silencing and blockade with inhibitors, we identified the matrix metalloproteinases MMP-2 and MMP-9 are both required for cleavage of 14-3-3ζ into functional peptide. We also found inflamed endothelial cells upregulate MMP-9 expression and MMP-2 activity in parallel, with a concomitant downregulation of expression of their endogenous inhibitors, TIMP1 and TIMP2. This represents a novel mechanism of regulation of the PEPITEM pathway in inflammatory conditions.
We explored mechanisms of PEPITEM secretion and identified B-cells secrete whole 14-3-3ζ protein in response to adiponectin, which is then proteolytically cleaved once in the extracellular environment. We investigated extracellular vesicle release from B-cells and observed constitutive release of vesicles that was not regulated by adiponectin. Importantly, these vesicles did not contain 14-3-3ζ and therefore do not represent the mechanism of 14-3-3ζ release from B-cells. Despite 14-3-3ζ lacking the signal recognition particle required for trafficking to the endoplasmic reticulum, we identified inhibition of the classical secretory pathway suppressed 14-3-3ζ secretion. Therefore, it is likely 14-3-3ζ is transported out of the cell coupled with a classically secreted protein.
Thus, we report that 14-3-3ζ is secreted via the classical secretory pathway and subsequently cleaved by MMP-2 and MMP-9 to yield PEPITEM once in the extracellular milieu. Data from this thesis offer a novel understanding of the mechanisms and regulation of PEPITEM production, which will support the development of PEPITEM as a therapeutic agent
Prolonging release in high-risk, complex, violent, male offenders.
Get PDFThe treatment and management of high-risk, violent, complex men released from custody to the community has gained much attention in recent years. This group are disproportionately affected by traits of personality disorder, making the processes of risk management and treatment both complex and slow. This thesis provides a detailed exploration of who services should target for intensive community interventions, what types of intervention appear to work with this complex group, and how best to measure the efficacy of such interventions. A general introduction to this area of research is presented, followed by a systematic review of the literature on how this group have typically been managed in the community. The findings are mixed, with some studies showing no effect of community interventions using recidivism outcome measures, but several high-quality studies finding strong intervention effects when contact begins in custody and continues into the community, thus representing a transitional service. Original research is then presented examining the efficacy of existing Intensive Intervention and Risk Management Services (IIRMS) and the Intensive Response Intensive Service (IRiS) project. Both cohorts are compared with large control groups matched using key variables. Whilst findings did not establish an overall intervention effect on survival time, for all participants, higher risk and personality complexity scores were predictive of shorter survival times in the community. The problems of defining and measuring ‘success in the community’ are discussed and a detailed examination of the Clinical Outcomes in Routine Evaluation – Outcome Measure (CORE-OM) is presented. Discussions about the strengths and weaknesses of using recidivism measures, and the need to incorporate more nuanced measures of progress, including self-report well-being measures, are presented. Finally, a general discussion brings together the findings from this thesis, making recommendations for practice, so that those most in need are offered high-quality services that can be effectively measured
Breaking the ceiling of capacity limit via anion redox reactions
Get PDFAnion redox reactions (ARRs) in lithium rich cathode materials (LRCMs) have attracted great attention due to their potential for delivering extra capacities beyond traditional cation redox activities. This thesis presents a study to stabilize the ARRs in LRCMs via developing the understanding of the nature of the oxygen redox activities and tailoring rational local structures to suppress the ARR-induced structural degradations (i.e., oxygen loss and transition metal (TM) migration).
Chapter 1 introduces a background to the field, including basic knowledge about lithium-ion batteries (LIBs), previous understanding of ARRs, and challenges for their future success in practical utilizations. The characterization techniques and experimental details are described in Chapter 2.
Monitoring the local coordination evolutions induced by ARRs and Ru redox reactions was carried out on the archetypal Li2RuO3 by using in-situ Raman spectroscopy. As detailed in Chapter 3, both the Raman-active Ru-Ru motions and the emergence of the O-O dimers were tracked and interpreted in combination with multimodal characterization techniques.
A F-doping study was conducted on Li2RuO3, as described in Chapter 4. Although F-dopants did not stabilize the ARRs, trace amount of F-doping improved the cycling stability of the Ru redox reactions. Such a performance enhancement was attributed to the effects of F-dopants on relaxing the interlayer repulsions and altering the preferential orientations.
In Chapter 5, a metastable O6-phase was reported to demonstrate stable cation and anion redox reactions under long-term operation. The hidden mechanisms underneath its structural stability were investigated by using a plenty of techniques including ex-situ/ in-situ X-ray diffraction (XRD), ex-situ X-ray absorption spectroscopy (XAS), ex-situ/ in-situ Raman spectroscopy, ex-situ electromagnetic resonance spectroscopy (EPR), ex-situ X-ray photoelectron spectroscopy (XPS), and electrochemical analyses. Unlike the edge-sharing local structures in the traditional O3-phase, the O6-phase presented the face-sharing geometry between the TMO2 and LiO2 slabs, in which the interlayer TM migration was suppressed.
An interferometric scattering microscopy (iSCAT) setup was introduced in Appendix C, which was built to track the ARR-induced evolutions at the single particle level via using nondestructive visible light as the probe
‘The Incarnate Now’: D.H. Lawrence, the New York School, and the Poetry of the Present and 'Things to Come'
Get PDFThis thesis consists of a critical study, “The Incarnate Now’: D. H. Lawrence, the New York School, and the Poetry of the Present’, followed by a collection of poetry, Things to Come. The critical study explores the legacy of D. H. Lawrence’s thinking about American poetry and the poetics of the present moment on the writing of the postwar period. Chapter I places Lawrence’s interest in America in context, introducing connections between his writing and the work of Walter Pater, Walt Whitman and Ralph Waldo Emerson; the chapter examines Lawrence’s own poetry in detail, drawing particularly on an important essay, ‘The Poetry of the Present’. Chapter II explores the significance of spontaneity and the present moment in postwar American poetry, outlining the emergence of a new set of cultural and aesthetic priorities and offering detailed readings (chiefly) of the poetry of Frank O’Hara and James Schuyler. Chapter III turns to the writing of John Ashbery, presenting a detailed examination of his poetry and its fulfillment of the ideas outlined in the previous chapters, focusing in particular on the poet’s temporal experiments and their impacts on the poem/reader. Overall, this study aims to emphasise the value of D. H. Lawrence to the poets of the New York School, offering his thinking as a new way to appreciate their various accomplishments
Tail risk and uncertainty in financial markets
Get PDFThis thesis explores the intricacies of managing and modelling tail risk and uncertainty in financial markets. Tail risks arise from infrequent but potentially significant events, while uncertainty refers to the unpredictable aspects of market dynamics that cannot be accounted for by standard probabilistic models. Traditional models often struggle to account for these elements, leading to inadequate investment strategies which underestimate risk. This thesis proposes a new investment framework centred around three objectives: (1) to develop forecasting methods that provide more accurate and robust predictions of asset prices and volatility, accounting for the inherent uncertainty in financial markets (2) to devise new methodologies which better predict the probability and impact of tail events (3) to create portfolio allocation algorithms which eliminate unrealistic assumptions and better reflect the complex dynamics of modern financial markets.
In addressing the first objective, this thesis critiques existing forecasting models and introduces a Bayesian approach to ARMA-GARCH modelling. This new approach incorporates prior knowledge and directly accounts for the uncertainty in financial data, offering a more robust prediction framework.
Regarding the second objective, this thesis introduces existing quantitative tools to measure financial risk and then proposes a new algorithm called the Multicanonical Sequential Monte Carlo Sampler (MSMCS), which efficiently reconstructs probability distributions to capture tail risk.
For the final objective, this thesis proposes a series of Bayesian Optimisation algorithms that address optimal portfolio allocation. These algorithms are tailored to reduce the computational intensity often associated with such tasks and to take advantage of specific characteristics of portfolio optimisation problems.
This thesis culminates in the combined application of the Bayesian ARMAGARCH models to forecast asset returns, MSMCS to assess tail risk, and Bayesian Optimisation to find an optimal portfolio allocation. The combined framework is applied to historic market data and shown to outperform various existing strategies and market indices.
This work contributes to financial mathematics by challenging conventional approaches and introducing new Bayesian-based models that more accurately reflect the complexity and inherent uncertainties of financial markets. It provides a foundation for further research and practical applications in financial forecasting models, risk assessment, and portfolio management
Harmony in early visual cortex: uncovering the complementary roles of gamma & alpha oscillations in local & global processing
Get PDFUpon opening our eyes, we immediately perceive the world around us. Our remarkably seamless visual perception is a major source of information when interacting with our surroundings. Indeed, the dominance of vision over other senses is so significant that the brain allocates more resources to it than to any other sensory modality (Colavita, 1974; Van Essen et al., 1992). Yet, our seemingly effortless visual experience relies on a complex network of intricately interconnected cortical and sub-cortical structures performing real-time computations.
A central question in neuroscience is how the visual system optimally processes and routes incoming information. Popular ideas posit that neuronal oscillations, specifically gamma (> 30 Hz) and alpha oscillations (8 - 12 Hz), coordinate visual processing and attention (Fries, 2005, 2015; Jensen, 2023; Jensen & Mazaheri, 2010; Klimesch, 2012; Klimesch et al., 2007).
In this thesis, I will present findings based on empirical and computational work showing how gamma and alpha oscillations modulate visual inputs. The empirical part of my thesis consists of two studies using Magnetoencephalography (MEG) in combination with a high-frequency (subliminal) visual flicker. I will reveal that gamma oscillations in early visual regions are robust against this external, high-frequency stimulation and do not synchronise to the visual flicker. As I will discuss, this finding challenges the prevalent notion that gamma oscillations are critical for inter-areal communication in the visual system (also see Schneider et al., 2021, 2023; Vinck et al., 2023).
Following my experience with high-frequency stimulation gained in the first empirical chapter, I will use Rapid Invisible Frequency Tagging (RIFT) in the third chapter to investigate the neural correlates of feature-guided visual search. RIFT is a novel, subliminal stimulation technique used to probe cortical excitability to visual inputs (Zhigalov et al., 2019). I will demonstrate that alpha oscillations globally modulate the cortical excitability to the visual search display, which was further linked to improved search performance. This suggests that gain modulation by alpha oscillations can support performance in visual attention tasks with a high number of distracting stimuli. However, I will also discuss a set of analyses suggesting that the response time modulation by the alpha rhythm may be linked to task duration. I will offer different perspectives on these multi-faceted results, as well as future research directions to understand the relationship between inhibition by alpha oscillations and visual search performance.
Inspired by these empirical results, I will finally present a dynamical artificial neural network — a computer vision algorithm embracing the rhythmic dynamics of the visual cortex. I will demonstrate that this network, despite not being explicitly trained for the task, can handle multiple concurrent visual inputs by segregating them in time.
In summary, my thesis combines empirical and computational methods to explore how gamma and alpha oscillations contribute to computational processes in the visual system. I will conclude that while gamma oscillations reflect localised neural processes, alpha oscillations operate at a more global scale
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