VictorJuiz/thesis huggingface dataset:
Neutron scattering from low-dimensional quantum magnets

Neutron scattering measurements were used to investigate the magnetic and crystal structure and magnetic excitations of three compounds characterized as low-dimensional quantum magnets. The materials are frustrated systems with low spin quantum number. The first was a powder sample of AgNiO2. The Ni ions form a triangular lattice antiferromagnet in which, according to the published crystal structure, both the orbital order and magnetic couplings are frustrated. However, it is shown here that there was a small distortion of the crystal structure at 365 K, which is proposed to result from charge disproportionation and this relieves the orbital frustration. The magnetic structure was investigated and, below 20 K, the triangular lattice of electron-rich Ni sites was observed to order into antiferromagnetic stripes. Investigations of the magnetic excitations showed that the main dispersions were within the triangular plane, indicating a strong two-dimensionality. The dispersion was larger along the stripes than between the stripes of collinear spins. The second material investigated was CoNb2O6, a quasi Ising-like ferromagnet. It was studied with a magnetic field applied transverse to the Ising direction. The magnetic field introduced quantum fluctuations which drove a phase transition at a field comparable to the main exchange interaction. The phase diagram of the magnetic order was mapped outs and a transition from an ordered phase to a paramagnetic phase was identified at high field. This low-temperature high-field phase transition was further investigated by inelastic neutron scattering measurements to observe the change in the energy gap and magnetic excitation spectrum on either side of the transition. The spectrum had two components in the ordered phase and had sharp magnon modes in the paramagnetic phase. The third material was the spin-half layered antiferromagnet CuSb2O6. It has a square lattice of Cu2+ ions in which the main interaction is across only one diagonal of the square. The magnetic structure was studied by neutron scattering with a field applied along the direction of the zero-field ordered moment. A spin-flop was observed at low field and there was evidence for a high-field transition. The magnetic excitation spectrum was unusual in that it had an intense resonance at 13 meV at the magnetic Brillouin zone boundary.

Keywords: strongly correlated electron systems
transition metal oxides
neutron scattering
magnetism
Advisor: Boothroyd, AT
Coldea, R
Enderle, M
Scepticism at sea: Herman Melville and philosophical doubt

This thesis explores Herman Melville’s relationship to sceptical philosophy. By reading Melville’s fictions of the 1840s and 1850s alongside the writings of Descartes, Berkeley, Hume, and Kant, I seek to show that they manifest by turns expression, rebuttal, and mitigated acceptance of philosophical doubt.
Melville was an attentive reader of philosophical texts, and he refers specifically to concepts such as Berkeleyan immaterialism and the Kantian “noumenon”. But Melville does not simply dramatise pre-existing theories; rather, in works such as Mardi, Moby-Dick, and Pierre he enacts sceptical and anti-sceptical ideas through his literary strategies, demonstrating their relevance in particular regions of human experience. In so doing he makes a substantive contribution to a philosophical discourse that has often been criticised – by commentators including Samuel Johnson and Jonathan Swift – for its tendency to abstraction.
Melville’s interest in scepticism might be read as part of a wider cultural response to a period of unprecedented social and political change in antebellum America, and with this in mind I compare and contrast his work with that of Dickinson, Douglass, Emerson, and Thoreau. But in many respects Melville’s distinctive and original treatment of scepticism sets him apart from his contemporaries, and in order to fully make sense of it one must range more widely through the canons of philosophy and literature. His exploration of the ethical consequences of doubt in The Piazza Tales, for example, can be seen to anticipate with remarkable precision the theories of twentieth-century thinkers such as Emmanuel Levinas and Stanley Cavell.
I work chronologically though selected prose from the period 1849-1857, paying close attention to the textual effects and philosophical allusions in each work. In so doing I hope to offer fresh ways of looking at Melville’s handling of literary form and the wider shape of his career. I conclude with reflections on how Melville’s normative emphasis on the acknowledgement of epistemological limitation might inform the practice of literary criticism.

Keywords: The Piazza Tales
American literature
Mardi
scepticism
epistemology
Stanley Cavell
Herman Melville
doubt
Moby-Dick
Pierre
philosophy
Advisor: Marcus, L
Truth, deflationism and the ontology of expressions: an axiomatic study.

Philosophical enquiry on the notion of truth has traditionally involved the identification of a class of objects to which truth is ascribed. At the same time, formal investigations are often required when the notion of truth is at issue: semantic paradoxes force in fact philosophers to shape their arguments in a precise way. Objects of truth, in formal context, are always reduced to other, more manageable objects that mimic their structural properties such as numbers or sets. This form of reduction renders the distinction between linguistic or syntactic objects, to which truth is usually applied, and their mathematical counterparts opaque, at least from the point of view of the theory of truth. In informal metatheoretic discussion, in fact, they are clearly different entities.
In this thesis we focus on an alternative way of constructing axiomatic theories of truth in which syntactic objects and mathematical objects belong to different universes. A brief introduction tries to situate the proposed theories in the context of different investigations on axiomatic truth. Chapter 2 is devoted to the discussion of historical and more theoretical motivations behind the proposed alternative. Chapter 3 will present the syntactic koinè spoken by our theories. Morphological categories of the object language and logical concepts concerning the object theory will be formalised in a recent axiomatisation of hereditarily finite sets. In Chapter 4 we finally introduce theories of truth with a built-in syntactic theory and examine some of their consequences. We briefly focus on disquotational truth, then consider compositional axioms for truth. Chapter 5 investigates a possible application of the setting just introduced: a realisation of the all-present interaction, in metamathematical practice, between informal metatheoretic claims and their (suitably chosen) coded counterparts. In the final chapter, after a brief characterisation of the key doctrines of the delflationary conception of truth, we evaluate the impact that the theories of truth studied in this work can have on the debate on the so-called conservativeness argument, which tries to match the alleged insubstantiality of the notion of truth, advocated by deflationists, with the deductive power of deflationary acceptable theories of truth.

Keywords: axiomatic truth
bearers of truth
deflationism
Advisor: Halbach, V
A corporate geography of Canada: governance and networks

Understanding corporate governance from an academic, practical, legislative, and social perspective has never been more important given the increasingly internationalized and financialized global economy. The global financial crisis of 2008 and resultant recession painfully evidence what many scholars have argued throughout the last century: in market-based economies, the economic and the social spheres remain inseparable. Today, such economies rest on the backs of publicly-traded corporations and understanding how such corporations are governed is the goal of this research effort. I argue that corporate governance is not a set of characteristics to be measured, modelled, and packaged as prescriptive principles but rather it is a series of exercises in decision-making across space and time rife with idiosyncrasies. As such, I present a novel corporate governance research agenda which focuses on the two pillars of decision-making, namely the environmental contexts within which the decision-making processes are embedded and the networks of agents involved in such processes. In a globalized economic setting, both the environmental contexts and the networks of agents readily transcend multiple social, cultural, and geo-political boundaries—resultantly, the research agenda I present is one predicated on the geography of governance. I apply my research agenda to the Canadian setting in efforts to demonstrate the utility of this research agenda while providing a better understanding of the Canadian model of corporate governance. This research is the first to systematically investigate the Canadian model of corporate governance and concludes that, contrary to predominant assumptions, there is no single harmonious national model but rather a mosaic of thirteen distinct provincial and territorial models which are asymmetrically linked by means of market actors and interactions and which exists in a temporary balance of parochial and cosmopolitan forces.

Keywords: corporate geography
networks
corporate governance
Canada
Advisor: Clark, G
Multiscale modelling of sintering in thermal barrier coatings

Multiscale (analytical and computational) models have been developed based on a thermodynamic variational principle (TVP) to model sintering and eventual mudcracking in thermal barrier coatings (TBCs) made using the electron beam physical vapour deposition (EB-PVD) process. It is assumed that the sintering occurs by interfacial diffusion at local contacts between columns and driven by changes in interface free energy and elastic stored energy of the coating. The models link diffusional processes at the scale of contacting feathery columns with the macroscopic deformation and sintering response. In service, the columns can come into contact and sinter together. As sintering progresses there is a build up of strain energy in the system which reduces the driving force for sintering and leads to either complete or incomplete sintering of the TBC depending on the magnitude of effective modulus (E) of the coating. By seeding the coating with initial imperfections, different types of behaviour are observed depending on the value of E and the spacing between imperfections. For compliant coatings, the response is insensitive to the presence of imperfections and the coating fully sinters. At higher values of E, strain energy is released by the development of intercolumnar cracks in the coating, which can propagate to the interface with the TGO (thermally grown oxide), deflect into the interface and propagate, leading to spallation of regions of the coating and loss of thermal protection. It is observed that cracks develop at initial imperfections in the structure. The greater the spacing between imperfections the faster the development of cracks at these locations. If a TBC contains a distribution of imperfections there is progressive formation of cracks, with the average spacing decreasing with time, after an initial incubation period. The crack density eventually saturates to a constant value, which depends on the mechanical properties of the TBC.
Initially, a crack spacing, CS, in the range 1.5H ≤ CS ≤ 3H has been predicted based on trapezoidal contact models. Here H is the thickness of the coating. Crack spacing predicted using this model is consistent in the lower range of experimentally observed crack spacing. However, axisymmetric contact models predict a crack spacing, CS, in the range 4H ≤ CS ≤ 8H, which is in good agreement with experimentally observed crack spacing range 3H ≤ CS ≤ 10H reported in the literature. Compared to the trapezoidal contact models, axisymmetric contact models more accurately predict the sintering response.

Keywords: multiscale modelling
thermal barrier coatings
mud-craking
sintering
Advisor: Cocks, A
The monastic thought and culture of Pope Gregory the Great in their Western context, c.400-604

Gregory was the first monk to be pope; proverbially, he would have preferred to have remained a monk; the audience he addressed was almost always made up of monks. However, no sustained attempt has been made to establish the contexts for Gregory as a monastic writer. The thesis represents an initial attempt to do so, and in particular, to question the image of Gregory as a monk unable to cope with the assumption of episcopal power.
The sources principally chosen for study are as follows: Augustine's Praeceptum; Cassian's Institutes and Conferences; the writings of the early Lerins circle; the Sermons and Rules of Caesarius of Aries; the Rule of St. Benedict, together with the Rules of the Master and Eugippius of Lucullanum. The thesis has been structured as a series of comparisons between these texts, and the situations in which they were produced, with Gregory's writings and his situation in late sixth century Rome.
Gregory's ecclesial and eschatalogical perspectives, to which he adhered before papal election, are seen to set him apart from earlier monastic writers, and into confrontation with contemporary ascetics and clerics, the Roman clerical establishment in particular.
These aspects of Gregory's thought are related to his rhetorical performance, and the voice he develops is compared to those of earlier ascetics. It is argued that the central concern of the texts considered is that of language: western ascetic projects are seen to focus on holiness of rhetoric, especially in the sixth century. In choosing to speak and write primarily as an exegete, Gregory signalled that he did not wish to contribute to the Gaulish or Italian monastic cultures developing around written Rules. He was concerned instead to articulate a personal holy authority.
Graph colourings and games

Graph colourings and combinatorial games are two very widely studied topics in discrete mathematics. This thesis addresses the computational complexity of a range of problems falling within one or both of these subjects.
Much of the thesis is concerned with the computational complexity of problems related to the combinatorial game (Free-)Flood-It, in which players aim to make a coloured graph monochromatic ("flood" the graph) with the minimum possible number of flooding operations; such problems are known to be computationally hard in many cases. We begin by proving some general structural results about the behaviour of the game, including a powerful characterisation of the number of moves required to flood a graph in terms of the number of moves required to flood its spanning trees; these structural results are then applied to prove tractability results about a number of flood-filling problems. We also consider the computational complexity of flood-filling problems when the game is played on a rectangular grid of fixed height (focussing in particular on 3xn and 2xn grids), answering an open question of Clifford, Jalsenius, Montanaro and Sach.
The final chapter concerns the parameterised complexity of list problems on graphs of bounded treewidth. We prove structural results determining the list edge chromatic number and list total chromatic number of graphs with bounded treewidth and large maximum degree, which are special cases of the List (Edge) Colouring Conjecture and Total Colouring Conjecture respectively. Using these results, we show that the problem of determining either of these quantities is fixed parameter tractable, parameterised by the treewidth of the input graph. Finally, we analyse a list version of the Hamilton Path problem, and prove it to be W[1]-hard when parameterised by the pathwidth of the input graph. These results answer two open questions of Fellows, Fomin, Lokshtanov, Rosamond, Saurabh, Szeider and Thomassen.

Keywords: graph colouring
games on graphs
computational complexity
algorithms
graph theory
parameterised complexity
Advisor: Scott, A
A theoretical investigation of gas source growth of the Si(001) surface

The growth of the Si(001) surface from gas sources such as disilane is technologically important, as well as scientifically interesting. The aspects of growth covered are: the clean surface, its defects and steps; the action of bismuth, a surfactant; the diffusion behaviour of hydrogen in different environments; and the entire pathway for formation of a new layer of silicon from adsorption of fragments of disilane to nucleation of dimer strings. The theoretical methods used, density functional theory and tight binding, are described. Four linear scaling tight binding methods are compared. The construction of the tight binding parameterisations used is also explained.
The structure of the most common defect on the Si(001) surface is identified by comparison of the electronic structure with scanning tunneling microscopy (STM) images. The energy and structure of steps is calculated, and their kinking behaviour is modelled, achieving good agreement with experimental results.
Two unusual features which form when bismuth is placed on the surface and annealed are investigated. The first has possible applications as a quantum wire, and its structure and growth are described. The second relates to a controversial area in the field; a structure is proposed which fits all available experimental evidence.
The behaviour of hydrogen is vital to understanding growth, as large amounts are deposited during disilane growth. After validating the tight binding parameterisation against DFT and experiment for the system of a single hydrogen diffusing on the clean Si(001) surface, the barriers for diffusion on the saturated surface, down a step and away from a defect are found, and prove to be in good agreement with available experimental data.
The pathway for the formation of a new layer of silicon from disilane is described step by step, giving barriers and structures for all events. The interaction with experiment is highlighted, and demonstrates that great benefit accrues from such close work, and that the atomistic modelling techniques used in the thesis produce results in close agreement with reality.

Keywords: Si(001)
tight binding
density functional theory
Advisor: Briggs, G
Pettifor, D
Incremental sheet forming process : control and modelling

Incremental Sheet Forming (ISF) is a progressive metal forming process, where the deformation occurs locally around the point of contact between a tool and the metal sheet. The final work-piece is formed cumulatively by the movements of the tool, which is usually attached to a CNC milling machine. The ISF process is dieless in nature and capable of producing different parts of geometries with a universal tool. The tooling cost of ISF can be as low as 5–10% compared to the conventional sheet metal forming processes. On the laboratory scale, the accuracy of the parts created by ISF is between ±1.5 mm and ±3mm. However, in order for ISF to be competitive with a stamping process, an accuracy of below ±1.0 mm and more realistically below ±0.2 mm would be needed. In this work, we first studied the ISF deformation process by a simplified phenomenal linear model and employed a predictive controller to obtain an optimised tool trajectory in the sense of minimising the geometrical deviations between the targeted shape and the shape made by the ISF process. The algorithm is implemented at a rig in Cambridge University and the experimental results demonstrate the ability of the model predictive controller (MPC) strategy. We can achieve the deviation errors around ±0.2 mm for a number of simple geometrical shapes with our controller. The limitations of the underlying linear model for a highly nonlinear problem lead us to study the ISF process by a physics based model. We use the elastoplastic constitutive relation to model the material law and the contact mechanics with Signorini’s type of boundary conditions to model the process, resulting in an infinite dimensional system described by a partial differential equation. We further developed the computational method to solve the proposed mathematical model by using an augmented Lagrangian method in function space and discretising by finite element method. The preliminary results demonstrate the possibility of using this model for optimal controller design.

Keywords: Incremental sheet forming
variational inequalities
finite element method
model predictive control
computational mechanics
Advisor: Duncan, S
The algebraic construction of invariant differential operators

Let G be a complex semisimple Lie Group with parabolic subgroup P, so that G/P is a generalized flag manifold. An algebraic construction of invariant differential operators between sections of homogeneous bundles over such spaces is given and it is shown how this leads to the classification of all such operators. As an example of a process which naturally generates such operators, the algebraic Penrose transform between generalized flag manifolds is given and computed for several cases, extending standard results in Twistor Theory to higher dimensions. It is then shown how to adapt the homogeneous construction to manifolds with a certain class of tangent bundle structure, including conformal manifolds. This leads to a natural definition of invariant differential operators on such manifolds, and an algebraic method for their construction. A curved analogue of the Penrose transform is given.

Advisor: Penrose, R
Eastwood, M