VictorJuiz/thesis huggingface dataset:
Mixed-integer optimal control of fast dynamical systems
Keywords: Approximate dynamic programming
Integer programming
Optimal control
Hybrid systems

Many applications in engineering, computer science and economics involve mixed-integer optimal control problems. Solving these problems in real-time is a challenging task because of the explosion of integer combinations to evaluate. This thesis focuses on the development of new algorithms for mixed-integer programming with an emphasis on optimal control problems of fast dynamical systems with discrete controls.
The first part proposes two reformulations to reduce the computational complexity. The first reformulation avoids integer variables altogether. By considering a sequence of switched dynamics, we analyze the switching time optimization problem. Even though it is a continuous smooth problem, it is non-convex and the cost function and derivatives are hard to compute. We develop a new efficient method to compute the cost function and its derivatives. Our technique brings up to two orders of magnitude speedups with respect to state-of-the-art tools. The second approach reduces the number of integer decisions. In hybrid model predictive control (MPC) the computational complexity grows exponentially with the horizon length. Using approximate dynamic programming (ADP) we reduce the horizon length while maintaining good control performance by approximating the tail cost offline. This approach allows, for the first time, the application of such control techniques to fast dynamical systems with sampling times of only a few microseconds.
The second part investigates embedded branch-and-bound algorithms for mixed-integer quadratic programs (MIQPs). A core component of these methods is the solution of continuous quadratic programs (QPs). We develop OSQP, a new robust and efficient general-purpose QP solver based on the alternating direction method of multipliers (ADMM) and able, for the first time, to detect infeasible problems. We include OSQP into a custom branch-and-bound algorithm suitable for embedded systems. Our extension requires only a single matrix factorization and exploits warm-starting, thereby greatly reducing the number of ADMM iterations required. Numerical examples show that our algorithm solves small to medium scale MIQPs more quickly than commercial solvers.
Essays on the market for corporate bonds
Keywords: liquidity
price impact
correlation
credit ratings
corporate bonds

This thesis contains three empirical studies on the US corporate bond market; each chapter is self-contained and can be read independently. Chapter 1 studies the impact of credit rating changes on corporate bond returns. This study uses a large dataset of corporate bond transactions from the TRACE database for the US corporate bond market, combined with credit rating changes from Fitch, Moody's and Standard and Poor's (S&P), to analyse over 22,000 bonds, coupled with approximately 28,400 rating events over nearly six years. The results show that the bond market responds to news on credit quality asymmetrically: credit rating downgrades, representing bad news for bond holders, produce the strongest response in returns, whilst upgrades do not generate a statistically significant increase in returns. Chapter 2 analyses how order flow (investor "buy" and "sell" trades), impacts corporate bond prices. Order flow plays an important informational role, acting as a conduit through which private information about fundamental value is aggregated into prices. Using intraday transaction data from the TRACE database, I analyse over 1,000 of the most liquid corporate bonds, a total of 9.5 million trades. Drawing on similar studies of other markets, the relationship between returns and order flow is modelled using a vector autoregression, and the information content of a trade is measured as the long-run price impact of a shock to order flow. Price impacts are particularly strong and significant for order flow from institutional investors and for bonds with higher default risk, higher volatility and lower liquidity. Chapter 3 provides novel evidence on the importance of high frequency measures of volatility and correlation for the corporate bond market. Realized measures of volatility have been shown to be important in modelling and forecasting equity, exchange rate, and Treasury bill return volatility. We merge the NYSE's TAQ database of high frequency equity prices with the TRACE database, and show that the information contained in high frequency data is valuable in modelling the dynamics of the firm-level covariance matrix of bond and stock returns, for over 100 individual U.S. firms.
The role of technology in Pakistani private schools: the principals' perspective
Keywords: Computer
Tech
Ed-Tech
Principals' perspective
Internet
Education
Role of technology
Private schools
Pakistani Schools
Pedagogy
Technology
Schools

Investment in technology in the field of education has increased radically over the past 2 decades. The main reason for this is the notion that technology will restructure our schools and reform the system of education. Although this trend initially began in developed economies, it can now also be witnessed in various developing countries. Both policymakers and technology companies are supporting this trend, however, a number of researchers have repeatedly made calls for critically assessing the usefulness of integrating these technologies in schools.
The primary aim of our study is to explore the perceptions and experiences of private school principals in Pakistan regarding the implementation of digital technologies. In most developed countries, there was an evident push from the governments to integrate technology in schools. However, in the case of Pakistani private schools there is no government intervention for technology integration as the schools are owned and operated by individuals and private trusts. Many of these individual school owners also act as the principal at their schools as well. Based on the aforementioned information, the views of these school principals are invaluable to understand technology integration in Pakistani private schools.
The analysis from the interviews, which was the sole technique used to gather data, revealed that the majority of principals viewed technology integration positively. Abundance of information and enhancement of student learning were seen by them as the two key values of technology. The interviewees emphasized that overreliance on technology can have a negative impact. The school heads identified four major barriers to successful technology integration: teachers’ readiness; cost of technologies; school culture; and state infrastructure.
Applications of the gauge/gravity duality
Keywords: Gauge Field Theory
Kondo model
Hydrodynamics
AdS/CFT Correspondence
Quantum Field Theory
General Relativity

This thesis investigates applications of the gauge/gravity duality to strongly coupled quantum field theories. After a review of the duality and of correlators and transport in quantum systems, we present our results on second-order non-conformal hydrodynamics. We derive new Kubo formulae for five second-order transport coefficients in non-conformal relativistic fluids. We then apply these Kubo formulae to a class of non-conformal holographic fluids at infinite coupling. We find strong evidence that the Haack-Yarom identity, known to relate second-order coefficients in conformal holographic fluids at infinite coupling, continues to hold in holographic fluids without conformal symmetry: Within our class of models, we prove that it still holds when leading non-conformal corrections are taken into account, and we show numerically that it is also obeyed beyond leading order. This provides further evidence that the identity may be a universal feature of strongly coupled fluids. Next, we present our results on magnetic spin impurities in strongly correlated systems. We build a holographic two-impurity Kondo model, identifying the inter-impurity interaction as double-trace deformation. Our numerical results for the phase diagram suggest a quantum phase transition between a trivial phase with uncorrelated spins and no Kondo screening, and a non-trivial phase with anti-ferromagnetic correlations and simultaneous Kondo screening. Computing the spectrum in the single-impurity case, we observe Fano resonances, which at low temperatures we identify with the Kondo resonance.
Membrane filtration: fouling and cleaning in forward osmosis, reverse osmosis, and ultrafiltration membranes
Keywords: Fouling
Membrane Filtration
Ultrafiltration Membranes
Reverse Osmosis
Forward Osmosis

A comparison of fouling in osmotically driven processes with that in pressure driven processes is the main focus of the thesis. Forward osmosis (FO) and reverse osmosis (RO) have received considerable attention for water treatment and seawater desalination. This research compared the nature of fouling in FO mode with that in RO starting with the same initial flux in connection with cleaning effects and then comparing to those in ultrafiltration membranes. In all cases, with cleaning as an integral part, the extent of fouling reversibility, and the question whether a critical flux could be determined were examined.
The work during the first phase (undertaken at Oxford) quantified the removal of reversible fouling through rinsing by cold and hot water for a range of concentrations using the foulants dextran and carboxymethyl cellulose. The flux-TMP relationship was conventionally compared to that of the clean water flux.
The later phase (at Singapore) compared the fouling in FO and RO by alginate in terms of multiple parameters using cellulose tri acetate (CTA) and thin film composite (TFC) membranes. Silica and alginate were selected as model foulants. Whilst experimental water flux profiles in the present study did not exhibit significant differences in trend between FO and RO fouling, foulant resistance for FO was found to be increasingly greater than for RO with the progression of the fouling tests. This was further corroborated by membrane autopsies post fouling tests; both foulant mass deposition density and specific foulant resistance for FO were greater than for RO. The analysis clearly revealed that FO is essentially more prone to fouling than RO which was presumably due to less flux decline in FO (or greater average flux) as compared to that in RO in result of ICP-self compensation effect which is opposite to the prevailing claim in the literature. Additionally, the present study did not find evidence that hydraulic pressure in RO has a role in foulant layer compaction.
FO membrane fouling by real waters was the focus of the final phase of the research at SMTC. Pilot scale FO experiments were conducted on spiral wound CTA membrane with treated waste water obtained from a NEWater factory (Singapore) as the feed. In the second stage, experiments were repeated at bench scale with membrane coupons taken from the spiral wound membranes used earlier. The key finding was that the mass transfer coefficients in the Spiral-Wound module were around 50% lower than the corresponding values in the flat sheet unit and this severely limited the fluxes. The reason could be attributed to strong internal concentration polarisation in the former, where tightly wound spacers act to increase the structural parameter.
The formation of International Relations: ideas, practices, institutions, 1914-1940
Keywords: History of Social Sciences
Diplomacy
International Relations
Intellectual Cooperation
League of Nations

The study of International Relations (IR) emerged in the context of transnational networks of scholars, politicians, and philanthropists who sought to devise a peaceful world order in the face of international conflict. Prompted by the Great War, the pioneers of IR argued that international politics should be subject to public and academic investigation. In order to generate the required expertise, they established a range of university-based as well as policy-oriented institutions during the 1910s and 20s. Rather than studying political theory or advancing scientific methodology, however, early IR scholars focused on current affairs and became involved in foreign politics themselves. Throughout the formative period of IR, from 1914 to 1940, its protagonists oscillated between understanding and making international politics.
This dissertation examines the formation of IR from about 1914 to the Second World War, with particular emphasis on the range of international actors and institutions that shaped the discipline. Based on multi-archival research in Austria, Britain, France, Germany, Switzerland, and the United States, it explores the key venues for the study of IR. In particular, the dissertation reflects how IR scholars used transnational forms of exchange, such as the organs of intellectual cooperation at the League of Nations. It also incorporates women and feminist approaches to IR.
Contrary to conventional historiography, the dissertation argues that IR was neither founded in 1919, nor dominated by coherent schools of thought during the inter-war period. Instead, it demonstrates how the discipline was formed by an eclectic group of scholars and practitioners, men and women, English-speaking and international. By building on recent revisionist literature and by re- integrating neglected actors, the dissertation reveals the complex and sometimes inconsistent ways in which issues of international politics became the subject of academic study.
Structural studies of defects in two-dimensional materials with atomic resolution
Keywords: HRTEM
Graphene
Structural defects
2D materials

Defective structures in two-dimensional (2D) materials have been proved to have significant influences on the materials’ properties. Understanding structural defects in 2D materials at atomic scale is therefore required. With the use of advanced imaging techniques, one of the main approaches applied in this project was aberration-corrected transmission electron microscopy (AC-TEM), the structures are able to be resolved with single-atom sensitivity with the reduction of both spherical aberration and the influence of chromatic aberration. This laid the foundation for the first two experiments, which involve the bond length measurement of each C-C bond within three types of divacancies and Si-C bonds at graphene edges. The former explains the tendency of bond rotations within the divacancies from the perspective of strain inside the defective areas and surrounding lattice; the latter revels the interactions between isolated Si atoms and zigzag/armchair graphene edges.
The use of in-situ heating holder in the AC-TEM makes the direct visualization of structures and their dynamics at elevated temperatures possible. The Si-graphene edge interactions, as well as the following two experiments are all designed to study the high-temperature performances for different systems. Gold nanoclusters are introduced to monolayer graphene by thermal evaporation to study the interaction between gold and graphene at elevated temperature. Due to the strong interaction between gold and graphene, gold crystals are able to adapt to planar configurations with two different crystalline forms, and an epitaxial relationship was found for planar gold crystals and graphene. Atomically flat and long line defects and zigzag edges in monolayer molybdenum disulfide (MoS2) are successfully created by in-situ thermal annealing. The relationship between S vacancy mobility and defect forms are revealed based on the experiment. High-temperature atomic configurations of line defects and edge terminations are resolved in the first time. Their electronic properties are also explored with the support of density functional theory calculations.
All that glitters is not gold: the re-use of securities collateral as a source of systemic risk
Keywords: Financial Collateral
Contagion
Re-use
Securities financing
Systemic risk
Repos
Re-hypothecation
Derivatives

Since the 1980s, regulators in the U.S. and the U.K. have protected the collateral taker’s right to re-use securities collateral in securities financing and OTC derivatives markets on the understanding that it would promote liquidity and credit growth, and reduce systemic risk. However, this rationale was incomplete: it failed to acknowledge the full implications of collateral re-use for systemic risk. In this dissertation, I aim to complete that understanding by illustrating how the re-use of securities collateral in those markets can aggravate systemic risk. In particular, I describe two effects. First, re-using securities collateral multiplies the number of market participants that will be exposed to changes in the price of the collateral asset and can thus amplify the role of asset prices as channels of contagion. Second, by conferring a right to re-use, the collateral provider will effectively waive its proprietary interests in the collateral assets and retain a mere contractual claim against the collateral taker for the return of equivalent securities. This transformation will accentuate the incentive of the collateral provider to run from an over-collateralised collateral taker if the latter were to experience financial difficulty. Information asymmetries and a lack of coordination among collateral providers could push the collateral taker over the brink of insolvency. These risks pose an obvious question for regulators: what should we do about collateral re-use? At a time when international bodies are drawing their attention to this widespread market practice, the question is an invitation to a very timely reflection. The final chapter of the dissertation offers an answer to this question and assesses the potential efficacy of the most recent regulatory initiatives in relation to collateral re-use.
The power of business and the power of people: understanding remedy and business accountability for human rights violations - Colombia 1970-2014
Keywords: access to justice
Transitional justice
Corporate complicity
business and human rights
Colombia

The questions of business involvement in human rights violations in countries facing civil conflict, as well as access to remedy and accountability for these violations have generated a considerable amount of attention from academia and practitioners. While most theoretical efforts on access to remedy and accountability have focused on identifying the obstacles to access to justice, these do not explain the unlikely case of Colombia, where despite all structural obstacles being present (e.g. armed conflict, corruption), the country has positioned itself as a leader in the region in terms of judicialisation and convictions of economic actors for their complicity with grave human rights violations committed in the course of the 50 year internal armed conflict. This thesis is a theory building and theory-testing project that looks for alternative explanations to the outcomes registered in Colombia, focusing on the agents involved in these cases and how the variation in the power of the people (claimants) and the power of businesses (defendants) explains access to justice.
This thesis uses the most comprehensive datasets in existence of business involvement in human rights violations (the Corporations and Human Rights Database and the Corporate Accountability and Transitional Justice Database) to present a novel and much needed systematic analysis to identify the factors explaining why and when remedy and accountability is possible. The results of the study suggest that the variations in the power of people and the power of business do offer a plausible alternative explanation to the unlikely case of Colombia. The Colombia data analyzed in this thesis suggests that while an increase in the power of the people (through the support of global actors and political opportunities) is necessary to secure judicialisation and remedy, these results are only possible when they face an economic actor with reduced veto power.
Kähler groups and Geometric Group Theory
Keywords: Geometry and Topology
Complex geometry
Geometric Group Theory
Kähler groups

In this thesis we study Kähler groups and their connections to Geometric Group Theory. This work presents substantial progress on three central questions in the field:
Which subgroups of direct products of surface groups are Kähler?
Which Kähler groups admit a classifying space with finite (n-1)-skeleton but no classifying space with finitely many n-cells?
Is it possible to give explicit finite presentations for any of the groups constructed in response to Question 2?
Question 1 was raised by Delzant and Gromov.
Question 2 is intimately related to Question 1: the non-trivial examples of Kähler subgroups of direct products of surface groups never admit a classifying space with finite skeleton.
The only known source of non-trivial examples for Questions 1 and 2 are fundamental groups of fibres of holomorphic maps from a direct product of closed surfaces onto an elliptic curve; the first such construction is due to Dimca, Papadima and Suciu.
Question 3 was posed by Suciu in the context of these examples.
In this thesis we:
provide the first constraints on Kähler subdirect products of surface groups (Theorem 7.3.1);
develop new construction methods for Kähler groups from maps onto higher-dimensional complex tori (Section 6.1);
apply these methods to obtain irreducible examples of Kähler subgroups of direct products of surface groups which arise from maps onto higher-dimensional tori and use them to show that our conditions in Theorem 7.3.1 are minimal (Theorem A);
apply our construction methods to produce irreducible examples of Kähler groups that (i) have a classifying space with finite (n-1)-skeleton but no classifying space with finite n-skeleton and (ii) do not have a subgroup of finite index which embeds in a direct product of surface groups (Theorem 8.3.1);
provide a new proof of Biswas, Mj and Pancholi's generalisation of Dimca, Papadima and Suciu's construction to more general maps onto elliptic curves (Theorem 4.3.2) and introduce invariants that distinguish many of the groups obtained from this construction (Theorem 4.6.2); and
construct explicit finite presentations for Dimca, Papadima and Suciu's groups thereby answering Question 3 (Theorem 5.4.4)).