VictorJuiz/thesis huggingface dataset:
Non-price competition in college admissions

This study theoretically analyses college admission mechanisms where students’ applications have uncertain outcomes and the number of applications they can make are limited. I construct a model where two colleges engage in costly investment to compete for better students, and students apply to colleges facing admission uncertainty. I examine the equilibrium of this game when students are limited to a single application, and when they are not. I show, echoing previous research, that in some equilibria, the low-ranked college might benefit from an application limit and admission uncertainty by attracting cautious applicants desirable by its rival. I then offer the novel prediction that this generates a competitive effect to the benefit of the high-ranked college. By improving the students the low-ranked college enrols, these frictions mitigate the competition between colleges. Subsequently, the high-ranked college competes for the better students at a more favourable investment, increasing its payoff. I then embed this game to a larger model where colleges choose whether to impose an application limit to students. I find that when the equilibrium is as described, both colleges choose to impose an application limit to students, distorting the stable matching.

Keywords: decentralized two-sided matching
prematch investments
frictional matching
college admissions
Advisor: Jewitt, I
Antitrust and upstream platform power plays - a policy in bed with procrustes

Ubiquitous digital platforms are fundamentally altering our ways of life. Competition policy-makers, though, are on edge. Among the many issues they are considering, one matter has remained under-appreciated: “upstream” effects. Powerful platforms, consensus has it, are now (or inevitably will be) marshalling our digital markets. They have apparently also found new ways to decimate competition and harm our wallets, menu options, privacy and autonomy. But while antirust academics are furiously debating how best to address such consumer concerns, policy-makers are also reacting to worries expressed by another group of stakeholders, namely (allegedly) victimized suppliers – app developers, merchants, drivers, couriers (etc.), as well as dependent content providers (like Spotify or Yelp), without whom the powerful platforms would have little to attract consumers.
This thesis, then, is about antitrust and its application to such “upstream” concerns. Prosaically: are upstream platform power plays really relevant antitrust problems? The answer would certainly be quite obvious if contemporary (pre-platform) antitrust theory and practice were anything to go by. Supplier-side anxieties have indeed been all but written off the policy agenda for the brick-and-mortar economy. Moreover, academic consensus still has it that provider interests cannot be the touchstone of antitrust. Today, though, policy-maker attitudes seem to be shifting. Inasmuch as antitrust is the envisaged response, we need a policy introspection to make some sense of what is going on.
To this end, the analysis offered here is altogether normative, theoretical and practical. Normative because it engages in a supplier-mindful soul-searching exercise, which advances our understanding of antitrust’s foundations; theoretical as it sheds evidence-based insights on upstream effects and develops new frameworks for rationalizing them; practical since it takes a deep dive into the complex antitrust machinery and reveals how “looking up” exacerbates key difficulties that have long been the source of occasional seize ups.

Keywords: fairness
platforms
Antitrust
digital economy
consumer welfare
Competition law
Advisor: Ezrachi, A
Improving automated protocol verification: real world cryptography

Analysing the security of cryptographic protocols by hand is a challenging endeavour. It requires substantial expertise, weeks of intensive effort and the resulting proof of security often arrives long after the protocol design has been finalised and even deployed. However, automated protocol verification tools, such as Tamarin and ProVerif, offer a compelling alternative as they require less expertise, promise quicker results and have been used to successfully analyse complex real world protocols such as TLS, 5G and Signal.
These tools are built on a idealised model of cryptography, termed the symbolic model, which requires strong assumptions about the properties of cryptographic primitives. Consequently, automated protocol analyses may miss attacks which rely on properties of real primitives which are missing from the symbolic model. Furthermore, some protocols are not amenable to automated analysis as they use cryptographic primitives for which no suitable symbolic model currently exists.
This motivates natural research questions: How closely does the contemporary symbolic model approximate the real world behaviour of common cryptographic primitives? Can we improve the accuracy and breadth of the symbolic model by developing new approaches to underlying formalism? In this thesis, we set out to address these questions for two popular cryptographic primitives: digital signatures and Diffie-Hellman groups.
The symbolic model of digital signatures was first published nearly two decades ago and is widely used. We uncover a startling mismatch between the standard cryptographic definition of signature scheme security and the symbolic description. We repair this mismatch through the development of a novel symbolic model which we use to discover a number of new attacks on deployed protocols. We also document a number of previous analyses which missed these attacks due to their traditional symbolic model.
Next we consider Diffie-Hellman groups. Unlike digital signatures, symbolic Diffie-Hellman models have evolved considerably in recent years and we review the progress in this area, highlighting two key limitations. Firstly, that these models only describe prime order groups, despite the popularity of non-prime order groups in practice. We develop new symbolic models to remedy this and use them to discover new attacks on real world protocols. Secondly, that there is no effective procedure for analysing protocols which make use of the full field structure of Diffie-Hellman exponents. We develop a new formalism which can be used to mechanically analyse such protocols and demonstrate its effectiveness on hand-worked examples.
Finally, we conclude by examining the methodology behind our approach. We argue that the techniques behind our new symbolic models can be applied to many other cryptographic primitives to yield more accurate symbolic models. We go on to summarise our contributions and sketch several promising lines of future work.

Keywords: term rewriting
formal verification
protocol
equational theory
cryptography
symbolic model
Advisor: Cremers, C
Simpson, A
Metrology, calibration, integration and testing of the WEAVE fibre positioner

This thesis is about a pick-and-place fibre positioner for WEAVE, a new fibre-fed multi-object spectrograph for the 4.2 m William Herschel Telescope with a multiplex of 960. First light is expected sometime in 2020. The research presented in this thesis has been a major step in ensuring that the fibre positioner will be able to perform to the design specifications, and meet WEAVE’s scientific requirements.
The first piece of work presented in this thesis concerns the full positioner build, and the errors that are propagated by stacking components of the positioner. The guide to building a positioner shows that these errors can be measured and tracked, and ultimately compensated for.
The tumbler assembly can be built to a high precision, but as long as the robot positioners do not move accurately, it is impossible to position fibres in the correct places on the field plate. One reason why this movement can be inaccurate, is that the coordinate systems of the targets, the robots, and the field plates are not expressed in each other correctly. Another is that the positioning structure itself changes under external influences such as temperature and gravity. A novel algorithm ensures that the positioning structure can be recalibrated periodically, removing these kinds of effects.
Lastly, if the robot gantries cannot make repeatable accurate movements, this is a show-stopping problem too. Test procedures developed during this DPhil have shown that the X- and Y-gantries perform as expected, but the Z-gantry introduces unwanted movements in the x,y-plane when moving in the vertical direction. Because of the test procedures this design flaw was discovered and rectified by a new Z-gantry with a different internal structure. With these changes, the positioner robots are found to be repeatable to within the design specifications.

Keywords: metrology
instrumentation
astronomy
calibration
fibre-fed spectroscopy
pick-and-place positioning
high multiplex spectroscopy
Advisor: Dalton, G
Lewis, I
An investigation of frequency scanning interferometry for the alignment of the ATLAS semiconductor tracker

The relative alignment of the silicon detector modules of the ATLAS semiconductor tracker will need remote monitoring during operation, within a high radiation environment. A geodetic grid of distance measurement fibre-coupled interferometers will monitor changes in the shape of the support structure. Eight hundred fibre-coupled grid line interferometers (GLIs) will be compared simultaneously to a stable, evacuated reference interferometer using Frequency Scanning Interferometry (FSI). The GLIs, (from 70 mm to 1400 mm long, with pW level return signals) must be measured to a precision of 1 micron, to reconstruct the grid shape, in three dimensions, to a precision of 10 microns.
In this work two important limitations were overcome :
1. Inflated errors due to relative interferometer drift were significantly reduced using two lasers scanned in opposite directions.
2. The fine tuning range was effectively extended by linking the phase information in two 30 GHz fine tuning subscans, separated by a 3.5 THz coarse tuning interval.
A demonstration system was built using tunable laser diodes operating at wavelengths close to 836 nm. Several different fibre coupled GLIs were built. Each was measured against an invar reference interferometer sharing the same laboratory air.
The 400 mm GLI was measured to a (one standard deviation) precision of 120 nm and a 1195 mm GLI to a precision of 215 nm. Decreasing the GLI signal was not found to significantly degrade the measurement precision. Spurious reflections and vibrations were separately introduced to degrade the measurements. The errors were found to increase, with errors larger than 4 parts per million, observed for vibrations of 400 nm peak to peak amplitude.
Suggestions are given for reducing remaining errors. Further investigations into the effects of vibrations and spurious reflections are recommended.

Keywords: interferometer
frequency scanning interferometry
tunable laser
LHC, Large Hadron Collider
ATLAS
phase unwrapping
temporal phase extraction
phase step
absolute distance measurement
Advisor: Howell, D
Symplectic geometry of conical symplectic resolutions

Ever since Kronheimer's celebrated hyperkähler construction of gravitational instantons thirty years ago, many similar constructions have appeared in the mathematical literature, eventually producing a vast class of holomorphic symplectic manifolds nowadays called Conical Symplectic Resolutions (CSRs). So far, they have been considered in representation theory, algebraic and differential geometry, and also in theoretical physics as they arise from certain supersymmetric gauge theories. However, much of their symplectic geometry is unexplored. This thesis aims to make the first steps in this direction. There are two essentially different natural real symplectic structures on CSRs; for this reason, this thesis splits into two major parts.
The first part views CSRs as Liouville real symplectic manifolds (the symplectic form is exact). We investigate the presence of smooth closed exact Lagrangian submanifolds. The main theorem is that for any CSR there is a non-empty collection of non-isotopic such Lagrangians which arise from contracting C*-actions that act on the holomorphic symplectic structure by weight one. Lagrangians obtained from this method will be called minimal components. In particular, we use these to obtain (non-zero) lower bounds for the rank of symplectic cohomology. We will investigate two large subfamilies of CSRs where we are able to count minimal components and describe them. The family of Nakajima Quiver Varieties, in particular, we study in detail those of Dynkin type A; and the family of resolutions of Slodowy varieties that arise from the representation theory of semisimple Lie algebras and involve Springer theory. In the latter, we also obtain some further families of Lagrangians using Springer theoretic methods and certain crystal operators.
The second part studies CSRs with respect to non-exact symplectic structures arising from S1-invariant Kähler structures on CSRs. We construct a family of symplectic cohomologies for them, labelled by different contracting C*-actions. Although we prove that these vanish, this vanishing result allows us to obtain an action-dependent filtration by ideals on the ordinary cohomology of a CSR. Using Morse-Bott-Floer spectral sequences, we give many examples that explicitly describe these filtrations, in particular, we show an example where distinct filtrations arise from different C*-actions.

Keywords: symplectic resolutions
symplectic cohomology
C*-actions
lagrangian submanifolds
Advisor: Ritter, A
McGerty, K
Extending probabilistic programming systems and applying them to real-world simulators

Probabilistic programming is a paradigm that enables us to efficiently write probabilistic models as program code that we can sample, infer underlying parameters and predict outcomes based on complete or incomplete observations. Naturally, stochastic simulators, a special sub-class of simulators containing random variables, internal inference procedures, and the simulation of observations, are structurally rich probabilistic models. However, most simulators are not written in the probabilistic programming paradigm, as they are written in arbitrary programming code. This means that it is challenging to automatically update the variables in these simulators to account for observations from conducted experiments, which limits the simulators' use.
Furthermore, there are two components to a probabilistic programming system i) the language and compilation procedure, ii) the inference procedures. These components can limit our ability to compile particular classes of probabilistic models, such as models that contain mixtures of parameter types, due to restrictions in the expressiveness of the language. Restrictions in the expressivity of the language can also inhibit our ability to generate efficient inferences, as this naturally influences the design of the probabilistic programming system and the set of available inference backends. Creating probabilistic programming systems that are expressive enough for different probabilistic models leads to the creation of many different probabilistic programming systems, which is inefficient - it would be more efficient if we could repurpose existing probabilistic programming systems.
In this thesis, we develop three pieces of original work through four papers. The first piece of work describes how to extend differentiable first-order probabilistic programming systems to perform statistically correct and computationally efficient inference on models with mixtures of continuous and non-continuous parameters, without having to modify the underlying language, or develop an entirely new probabilistic programming system. The second describes how to translate real-world stochastic simulators written in arbitrary program languages to probabilistic programming systems. And finally, in the third piece of work, we develop two new Bayesian inference schemes to make inference more computationally and statistically efficient in nested models, models that contain probabilistic programs, within probabilistic programs, which arise in many real-world stochastic simulators.

Keywords: machine learning
simulators
probabilistic programming
statistics
Bayesian inference
AI
Advisor: Torr, PHS
Teh, YW
Günes Baydin, A
Rainforth, T
Electrification & renewable energy integration: a case study of methanol production

The electrification of the chemical industry is of paramount importance in meeting reduction targets in greenhouse gas emissions. However, it is tenable only if the electricity is generated from renewable sources. This project aims to investigate electrification schemes using methanol production processes as a case study, and to explore strategies for how to power such an electrified process with renewable energy. Taking a methanol production basis of 400,000 tonnes per annum, the energy and material flows are obtained from process simulations while renewable energy systems dedicated to the production are optimised through a modelling approach. In this work, direct (via heat pumps) and indirect electrification strategies (via sourcing alternative feedstocks) are compared, with results showing that the indirect electrification scheme has a more significant impact on the process energy structure. Based on the fully electrified methanol process, renewable power systems with an optional dispatchable power backup are modelled to fulfil the energy requirement aiming at the economic optimality. A two-regime behaviour of renewable penetration against dispatchable energy price has been found, which increases dramatically at the onset and slowly approaches 100% when the dispatchable energy price is above a critical point. The optimal operation of the renewable energy systems results in voluntary curtailment of renewable power, of which the cost analysis shows modest economic potential for its further utilisation. The benefits of a flexible process are shown to be significant, which can reduce the levelised methanol cost by up to 35%. Two geographical locations with distinct meteorological data are selected to investigate the impact of renewable source characteristics on the performance of methanol production and its renewable energy system. In particular, the diurnal and seasonal fluctuations of renewable sources and their impact on energy storage need are compared. The lessons of this project not only provide numerical results in terms of energy needs and production costs but also implications to policymaking, both of which will facilitate the energy transition from the current fossil fuels-based chemical industry to greener production.

Keywords: methanol
model-based optimisation
renewables
electrification
Advisor: Banares-Alcantara, R
Yang, A
Theories of cosmic time in the Mahābhārata

This thesis presents an examination of the Indian theories of cosmic time as they are found in the Mahabharata. It looks at the theories in detail and analyses their essential characteristics and structures of its three main elements: the divisions of time; the cycle of creation and destruction; and the characteristics of the four yugas. Special attention is paid to aspects of the theory that have been little explored, such as the nature of the cyclical repetition; the relationship between the yugas and the avataras of Visnu; the characteristics of the junctures between the yugas, etc. In the few areas where the theories of cosmic time found in the Mahabharata differ from those of the Purad nas, the differences are indicated. Ideas of cosmic time in literature preceding the Mahabharata are examined, and it is argued that the fundamental structures and concerns of the later theories can be seen to have clear antecedents in the cosmogony of the Vedas and the cosmogonic implications of certain sacrifices found in the Brahmad nas: Vedic cosmogonies show that the primary creative act is the imposition of order on chaos, in the spatial, temporal and ethical spheres, and the sacrifices show the existence of a cycle of creation and destruction, where creation must be periodically re-established by the sacrifice and the sacrificer. These principles are seen to still inform the later theories, and often help to throw light on obscure areas within them.

Keywords: cosmic time
Mahābhārata
Hinduism
Religious aspects
Advisor: Allen, N
Benson, J
Modelling the collective migration of neural crest cells

Collective neural crest cell migration contributes to the formation of several spatially and biologically diverse tissues during vertebrate development. If neural crest cells fail to reach a target or populate an incorrect location, then those cells may undergo improper cell differentiation or uncontrolled cell proliferation, leading to developmental defects. A wide range of mechanisms that drive collective cell migration are displayed by distinct types of neural crest cells that emerge at different axial levels of the neural tube and are affected by different local signals. For example, chick cranial neural crest cells are understood to be guided by a cell-induced chemotactic gradient and their migration occurs within a growing tissue, whilst in Xenopus, cranial neural crest cells are understood to be guided by co-attractive and co-repulsive intercellular interactions in the absence of growth. However, there are still many open questions as to how neural crest cells interact with each other and their microenvironment to undergo successful migration. Answers to these questions would not only help us understand embryonic development, but also provide insights into other less experimentally tractable collective migration phenomena, such as wound healing and tumour formation.
In this thesis we investigate the migration of chick cranial neural crest cells using a hybrid computational model, which consists of a discrete, off-lattice model for the motile behaviour of neural crest cells coupled with a continuum, reaction-diffusion model for the chemoattractant concentration. We work in parallel with our experimental colleagues who perform imaging of chick embryos under certain perturbations. In particular, we use our model to explore the role of the water-specific aquaporin 1 channel and spatial confinement on the migration of neural crest cells. We also investigate how domain growth affects collective cell migration. In the final part of the thesis, we develop a unified individual-based stochastic model to include the different cell-cell interaction mechanisms observed in Xenopus and chick. The model is used to compare and contrast the behaviour of neural crest cells in different organisms and to further investigate the cell-cell interaction mechanisms in chick.

Keywords: neural crest
collective cell migration
domain growth
hybrid model
Advisor: Baker, RE
Maini, PK