VictorJuiz/thesis huggingface dataset:
A laboratory investigation into the behaviour of sand at low confining stresses
Keywords: Hyperplasticity
Triaxial
NorSand
SANISAND
Cyclic
HySand
sand
Low stress
Leighton Buzzard sand
Stress path

The mechanical behaviour of sands at low confining stresses may have important implications for the design of offshore wind turbine (OWT) foundations. However, previous research investigating this behaviour is limited and conflicting, and cyclic testing campaigns have historically adopted load characteristics that may be unrepresentative of those sustained by OWT foundations. This thesis endeavours to fill the gap in the literature through creation of a new experimental database of soil element tests, that explores the constitutive response of sand at low stress levels subjected to monotonic and cyclic loading.
Results of the monotonic experimental campaign indicate that while the shear strength properties (ηmax and ϕ'max) tend to increase with decreasing effective confining stress, σ'c,0), this effect becomes increasingly minor for σ'c,0≤ 50 kN/m2. Furthermore, tests undertaken at lower confining stresses exhibit a comparatively stiffer response than those tests sheared at higher pressures. Results of the cyclic triaxial testing campaign exemplify the complexities of the response of sands subjected to cyclic loading. However, clear and systematic trends are found that can be robustly captured by the new cyclic modelling framework adopted in this study. Modern design methods for OWT foundations increasingly rely on finite element analysis (FEA); however, results depend critically on the constitutive models used, and the model parameters adopted in the numerical analyses.
This thesis reviews the state-of-the-art with regard to constitutive modelling frameworks developed for predicting sand behaviour. Evaluation of four sophisticated constitutive models found that it was not possible to determine a single set of calibrated model parameters that yield satisfactory model simulations for both drained and undrained load cases. Furthermore, only the general trends could be predicted when simulating sustained undrained cyclic loading. Further model development is therefore required if such models are to be relied upon for predicting the long-term behaviour of OWT foundations.
Probing the dynamics of nanoparticles at oil-water interfaces using high-speed total-internal-reflection dark-field microscopy
Keywords: liquid-liquid interfaces
size-dependence of particle diffusion at interfaces
surfactant
oil-water interfaces
dark-field microscopy
total-internal-reflection microscopy
nanoparticle dynamics
single-particle tracking
high-speed optical microscopy

Particles at fluid-fluid interfaces have a wide range of powerful uses in industry, technology and science. There is therefore a strong interest in exploring the dynamics of these systems to understand and gain more control in applications, as well as for fundamental investigations in condensed matter and statistical physics. Questions remain in particular about what governs adsorption dynamics and inter-particle interactions, and how mixtures of different-sized particles as well as particles and surfactants behave.
This thesis probes the dynamics of nanoparticles at oil-water interfaces using high-speed total-internal-reflection dark-field (TIR-DF) microscopy, comparing gold particles of diameters 20, 40 and 80 nm, and investigating the effect of an added surfactant (n-dodecyl-β-D-maltoside (DDM)). We built a TIR-DF microscope with a spatiotemporal resolution of up to 1 nm and 20 μs, and used home-written tracking and analysis software to characterise the particle motion. The diffusive motion within the interfacial plane is measured directly; out-of-plane motion is inferred from light scattering and in-plane motion.
The addition of DDM was found to qualitatively alter the interaction between the particles and the interface, with adsorptions becoming reversible and an inversion of the size trend in diffusivity (with larger particles diffusing faster than smaller ones, contrary to expectations). This, in combination with a paucity of adsorption events in larger particles, leads us to propose size-dependent barriers to adsorption to DDM interfaces. In addition, at DDM interfaces, many particles' diffusive behaviour changed over the course of a trajectory, indicating several different immersion states that are stable on the experimental timescale (~1 s).
This study shows that there remain qualitatively new dynamics of nanoparticles at oil-water interfaces to be explored. These dynamics can only be resolved at a high spatial resolution, and many of them only at high imaging speed, underlining the importance of novel imaging approaches probing the barriers of achievable spatiotemporal resolution.
Fluid flow through vegetation
Keywords: coastal engineering
hydrology
fluid mechanics
fluid-structure interaction

This thesis is concerned with the mechanical aspects of fluid-vegetation interaction in coastal flows and their resultant instabilities. Specifically, we consider the evolution of periodic waves as they propagate through vegetated domains, and the emergence of monami – the progressive, synchronous oscillation of submerged vegetation under sufficiently strong flows. We divide our analysis between rigid and flexible vegetative canopies. These new predictions and physical insights will be applicable in the analysis of a diverse range of industrial and environmental applications involving fluid-vegetation interactions.
In the case of rigid vegetation, using the method of multiple scales, we derive the evolution of small-amplitude waves propagating over a varying substrate fully covered with vegetation. In particular, we give time-averaged predictions for both the amplitude and the wavelength of the waves as functions of the distance of propagation. We then extend this analysis to include the situations of (i) combined current-wave flows and (ii) shallow-water waves through vegetation. For the case of combined current-wave flows, we demonstrate the manner in which the surface waves vary as a function of the current, and also how the current remains unaffected by the evolving wave. For shallow-water waves, we explore how cnoidal waves, nonlinear periodic solutions of the Korteweg-de Vries equation, evolve on horizontal substrates. For all of the flows considered above on rigid vegetation, their evolutions are only drag-dependent and hence independent of added mass and virtual buoyancy.
In the case of flexible vegetation, we propose a model where the plants are described by elastic cantilever beams. Our first analysis concerns the propagation of small-amplitude waves. Compared to the case of rigid vegetation, the fluid will load and deform each vegetative structure. This deformation, in turn, must affect the flow. Although the flow and the beam dynamics have to be determined simultaneously, we show that when the wavelength is sufficiently small, such quantities are asymptotically decoupled -- this allows us to first determine the local beam dynamics before evaluating the momentum loss in the macroscopic flow. In contrast to rigid vegetation, we find that added mass and virtual buoyancy play a role.
Finally, we focus on understanding the mechanisms and critical conditions for triggering monami. We treat the current as unidirectional and solve for the steady configurations of the flow and the deflected canopy. Our stability analysis predicts that monami is induced by shear along the top of the canopy. Meanwhile, monami can be suppressed if the canopy is sufficiently sparse or if there is sufficient inertia in the system.
Quantum correlations in space-time: foundations and applications
Keywords: quantum correlations
space-time

The absolute/relative debate on the nature of space and time is ongoing for thousands of years. Here we attempt to investigate space and time from the information theoretic point of view to understand spatial and temporal correlations under the relative assumption. Correlations, as a measure of relationship between two quantities, do not distinguish space and time in classical probability theory; quantum correlations in space are well-studied but temporal correlations are not well understood. The thesis investigates quantum correlations in space-time, by treating temporal correlations equally in form as spatial correlations and unifying quantum correlations in space and time. In particular, we follow the pseudo-density matrix formalism in which quantum states in spacetime are properly defined by correlations from measurements.
We first review classical correlations, quantum correlations in space and time, to motivate the pseudo-density matrix formalism in finite dimensions. Next we generalise the pseudo-density matrix formulation to continuous variables and general measurements. Specifically, we define Gaussian spacetime states by the first two statistical moments, and for general continuous variables spacetime states are defined via the Wigner function representation. We also define spacetime quantum states in position measurements and weak measurements for general measurement processes. Then we compare the pseudo-density matrix formalism with other spacetime formulations: indefinite causal structures, consistent histories, generalised non-local games, out-of-time-order correlation functions, and path integrals. We argue that in non-relativistic quantum mechanics, different spacetime formulations are closely related and almost equivalent via quantum correlations, except path integrals. Finally, we apply the pseudo-density matrix formulation to time crystals. By defining time crystals as long-range order in time, we analyse continuous and discrete time translation symmetry as well as discuss the existence of time crystals from an algebraic point of view. Finally, we summarise our work and provide the outlook for future directions.
Nested multilevel Monte Carlo methods and a modified Euler-Maruyama scheme  utilising approximate Gaussian random variables suitable for vectorised hardware and low-precisions
Keywords: Approximations
Monte Carlo
Random Numbers
Computing
Analysis

We present a modified Euler-Maruyama scheme using approximate random variables, produced by the inverse transform method, using cheap approximations to the inverse Gaussian cumulative distribution function. We analyse the error for two approximations: a piecewise constant approximation on equally spaced intervals, and a piecewise linear approximation using geometric intervals dense at the singularities. High speed implementations faster than Intel's MKL are provided, suitable for modern vector hardware. The error between the approximations from the exact and modified Euler-Maruyama schemes is bounded by the error from the approximate random variables.
We incorporate this scheme into a multilevel Monte Carlo framework producing a nested scheme, and show that the discretisation error couples to the random variables' approximation error. The result directly extends to Lipschitz and differentiable payoff functions. For Lipschitz and non-differentiable payoff functions simulated using a time step delta, there is a transition from a variance decay of O(delta) to order(delta1/2) as the discretisation error becomes dominant. These variance bounds are demonstrated numerically for geometric Brownian motion and a variety of payoff functions of varying smoothness.
For approximate random variables computed in low-precision, a model for the accumulated rounding error is developed and assessed. Half-precision is viable for a range of coarse path simulations, and can be extended further by incorporating a Kahan compensated summation. We empirically demonstrate these ideas are transferable to the Milstein scheme, and the more difficult Cox-Ingersoll-Ross process and its non-central chi-squared distribution. We estimate that under the Black-Scholes model, options can be priced using path simulations with approximate Gaussian random variables, obtaining a five-times or more speed improvement without losing accuracy.
Continual learning for efficient machine learning
Keywords: Fast Adaptation
Catastrophic Forgetting
Machine Learning
Multitask Learning
Continual Learning
Lifelong Learning

Deep learning has enjoyed tremendous success over the last decade, but the training of practically useful deep models remains highly inefficient both in terms of the number of weight updates and training samples. To address one aspect of these issues, this thesis studies the continual learning setting whereby a model utilizes a sequence of tasks leveraging previous knowledge to learn new tasks quickly. The main challenge in continual learning is to keep the model from catastrophically forgetting the previous information when updating it for a new task.
Towards this, firstly this thesis proposes a continual learning algorithm that preserves previous knowledge by regularizing the KL-divergence between the conditional likelihoods of two successive tasks. It is shown that this regularization imposes a quadratic penalty on the network weights based on the curvature at the minimum of the previous task.
Second, this thesis presents a more efficient continual learning algorithm, utilizing an episodic memory of past tasks as a constraint such that the loss of episodic memory does not increase when a weight update is made for a new task. It is shown that using episodic memory to constrain the objective is more effective than regularizing the network parameters. Furthermore, to increase the speed of learning of new tasks, the use of compositional task descriptors using a joint embedding model is proposed that greatly improves the forward transfer.
The episodic memory-based continual learning objective is then simplified by directly using the memory in the loss function. Despite its tendency to memorize the data present in the tiny episodic memory, the resulting algorithm is shown to generalize better than the one where memory is used as a constraint. An analysis is proposed that attributes this sur- prising generalization to the regularization effect brought by the data of new tasks.
This algorithm is then used to learn continually from synthetic and real data. For this, a method is proposed that generates synthetic data points for each task by optimizing the forgetting loss in hindsight on the replay buffer. A nested optimization objective for continual learning is devised that effectively utilizes these synthetic points to reduce forgetting in memory-based continual learning methods.
Finally, this thesis presents a continual learning algorithm that learns different tasks in nonoverlapping feature subspaces. It is shown that minimizing the overlap by keeping the subspaces of different tasks orthogonal to each other reduces the interference between the representations of these tasks.
Out in Morocco: homosexuality and transnationalism in the writings of Rachid O. and Abdellah Taïa
Keywords: Rachid O.
Francophone Literature
Abdellah Taïa
Moroccan Literature
Queer Writings
Postcolonial Literature

This is the first comprehensive study of the work of Rachid O. and Abdellah Taïa, two contemporary Moroccan authors whose writings deal with same-sex desire. Offering a close reading of the work of Rachid O. and Taïa, this study assesses how same-sex desire is expressed in a discursive space which does not acknowledge homosexuality and to what extent these forms of desire need to be situated in the transnational space and amid the sexual-political context of Morocco and the West. One of the foci of this study is to compare and contrast queer contemporary Moroccan writing with western queer theory and to examine to what extent Rachid O.’s and Taïa’s writings challenge or inform queer western scholarship. I offer two principal arguments. First, I suggest that Rachid O. and Abdellah Taïa loosen rigid ideologies around masculinity, sexuality, and gender in Arab/Muslim culture and offer a new understanding of sexuality and sexual orientation in their culture. By re-appropriating a heritage around same-sex love rooted in Arab/Muslim culture, they proffer a more inclusive, visionary idea of Islam, affording space for the sexually different. Second, I demonstrate that the invention of different ways of experiencing masculinity, homosexuality, and Islam is also facilitated by the West – specifically France. It illustrates how both authors critically engage with western modes of homosexuality, the notion of being ‘out’, the idea of living in an equal relationship with a same-sex partner, sometimes adopting these models, sometimes creating hybrid forms, often, however, problematically distancing themselves from western concepts and assessing their racial bias. Drawing upon western queer theory, postcolonial studies and a wide range of sociological accounts of homoeroticism in the West and North African society, this study makes an empirical and theoretical contribution to queer theory, to transnational conceptualizations of gender and sexuality, and to new understandings of masculinity in Morocco today.
Atomic structure and dynamics of defects in transition metal dichalcogenide bilayers
Keywords: van der Waals interactions
Aberration-corrected transmission electron microscopy
bilayer structures
Transition metal dichalcogenides
annular dark field scanning transmission electron microscopy

Transition metal dichalcogenides (TMDs), such as MoS2 and WS2, are direct band gap semiconductors in their monolayer form and indirect band gap semiconductors in bulk. They offer band gaps in the red visible spectrum and semiconducting properties that expand the application of the two-dimensional (2D) materials beyond what graphene alone can achieve. These layered materials are stacked through weak interlayer van der Waals interactions. Their bilayer structures offer an extra layer degree of freedom, which introduces performance enhancements compared to their monolayer counterpart. Interaction between MoS2 or WS2 layers as well as the specific stacking arrangement can significantly modify their electrical, optical and vibrational properties. The presence of defective structures has been proved to exert significant influences on TMD monolayers. Understanding the atomic structures and the dynamics of these defects in layered materials and their differences from those in monolayers is important for revealing their impact on TMD bilayers, leading approaches for their future device application.
Aberration-corrected transmission electron microscopy (AC-TEM) is one of the leading approaches to study the atomic structure of defects on 2D materials, laying the foundation for the first experiment, which involves the production and aggregation as well as observation of vacancies and line defects in differently stacked MoS2 bilayers at atomic-level resolution. DFT calculated models prove the main discrepancy between defective monolayer and bilayer systems, which is assigned to the interlayer van der Waals force in the bilayer system. In the next experiment, we move forward to probe the atomic structure of a more complex defective structure, the anti-phase grain boundary in MoS2 bilayers using annular dark field scanning transmission electron microscopy (ADF-STEM). Our results show the anti-phase GB in thebottom layer leads to the coexistence of both 2H and 3R stacking in the same bilayer domain, which is attributed to the lattice compression in the dislocation core due to the interlayer van der Waals force in the bilayer system. In the next experiment, the use of in-situ heating holder in the ADF-STEM makes the direct visualization of atomic structures and dynamics at elevated temperatures possible. Surface ripples, which are also denoted as stacking boundaries due to their morphologies in bilayer systems are analyzed at both micrometer and nanometer levels. These surface ripples introduce two perfect stacking orders with nanometer-wide transition regions, the morphology of which is decided by the interlayer van der Waals forces. The reversibility of these structures under temperature perturbation and beam irradiation is also studied.
A critical edition of the poems of Hildebert of Le Mans
Keywords: poems
edition
Hildebert
critical

This edition consists of three chapters of general introduction, followed by introduction, text and notes on each of the four divisions of Hildebert’s poetry, namely the Shorter Poems, Biblical Epigrams, De Mysterio Missae and Life of St. Mary the Egyptian.
Hildebert was born at Laverdin around 1056. After a period as scholasticus at Le Mans he became archdeacon in 1091. In 1096, on the death of Hoel, he was elected bishop, though not without a contest. Hildebert's first test as bishop came in 1099 with the attack on Le Mans by Helias, count of Maine, which was then held by William Rufus. Rufus, having succeeded in dislodging Helias, suspected Hildebert of complicity in the attempt, and took him with him back to England, His threat to demolish the towers of the cathedral of S. Julien were however left unfulfilled at his death. When peace returned Hildebert journeyed to Rome and the Norman lands of S. Italy (1100). This peace was broken by the fighting between Henry I of England and Louis VI, and it was at this period that Hildebert was imprisoned at Nogent-le-Rotrou. A different kind of trouble faced Hildebert some years later in the shape of the heretic Henry of Lausanne, who by his preaching succeeded in turning the people completely against their clergy. Even after his ignorance in religious matters had been shown up by Hildebert it was a long time before his influence was eradicated from the diocese. In 1125 Hildebert, now an old man, was elected archbishop of Tours. Here his refusal to install as dean and archdeacon the nominees of Louis VI, to whom Tours belonged led to the King cutting off the archiepiscopal revenues, and these were not entirely freed until 1150. Hildebert died in 1135.
Continued in thesis ...
Students’ experience of using primary sources at A-level and in an honours degree in history: an exploratory case-study
Keywords: primary sources
A-Level
historians' methodology
honours degree in history

The use of primary sources plays a significant role in history teaching in England. With the development of the School Council History Project (1976), the establishment of the GCSE (1985) and the National Curriculum (1991), students’ work on primary sources became fully integrated within history teaching, with assessment objectives specifically devoted to it.
Scholars in history education have investigated how students make sense of primary sources and develop historical thinking, by emphasising the importance of understanding sources in their context. Much less attention has been paid, however, to the ways in which students themselves think about the process and purpose of using sources within their study of history. In seeking to address this gap, my research uses a cross-sectional case-study design to examine the ways in which students approach the use of sources within history courses at A-Level and when within a single-honours history for an honours degree. Therefore, this dissertation aims to explore students’ perspectives of the journey towards becoming historians, examining the process of transition from working with sources at school, within a tightly structured programme tailored to A-Level examinations, to looking at primary materials when studying at university, with a more independent approach to the subject.
Data were gathered through semi-structured interviews, in which both A-Level students and third year undergraduates were involved. The analysis of the data collected revealed how A-Level students perceived a certain disconnect between historians’ methodology and the work done with primary sources during their course. Instead, undergraduates viewed more positively the tasks with sources carried out during an honours degree in history, highlighting how this work was often similar to historians’ way of thinking.