VictorJuiz/thesis huggingface dataset:
Special purpose quantum information processing with atoms in optical lattices
Keywords: Quantum simulations
Optical lattices
Quantum information theory
Ultracold atoms
Polarons
Bose-Einstein condensation

Atoms in optical lattices are promising candidates to implement quantum information processing. Their behaviour is well understood on a microscopic level, they exhibit excellent coherence properties, and they can be easily manipulated using external fields. In very deep optical lattices, each atom is restricted to a single lattice site and can be used as a qubit. If the lattice is shallow enough such that the atoms can move, their properties can be used to simulate certain condensed matter phenomena such as superconductivity. In this thesis, we show how technical problems of optical lattices such as restricted decoherence times, or fundamental shortcomings such as the lack of phonons or strong spin interactions, can be overcome by using current or near-future experimental techniques. We introduce a scheme that makes it possible to simulate model Hamiltonians known from high-temperature superconductivity. For this purpose, previous simulation schemes to realise the spin interaction terms are extended. We especially overcome the condition of a filling factor of exactly one, which otherwise would restrict the phase of the simulated system to a Mott-insulator. This scheme makes a large range of parameters accessible, which is difficult to cover with a condensed matter setup. We also investigate the properties of optical lattices submerged into a Bose-Einstein condensate (BEC). A weak-coupling expansion in the BEC-impurity interaction strength is used to derive a model that describes the lattice atoms in terms of polarons, i.e.~atoms dressed by Bogoliubov phonons. This is analogous to the description of electrons in solids, and we observe similar effects such as a crossover from coherent to incoherent transport for increasing temperatures. Moreover, the condensate mediates an attractive off-site interaction, which leads to macroscopic clusters at experimentally realistic parameters. Since the atoms in the lattice can also be used as a quantum register with the BEC mediating a two-qubit gate, we derive a quantum master equation to examine the coherence properties of the atomic qubits. We show that the system exhibits sub- and superdecoherence and that a fast implementation of the two-qubit gate competes with dephasing. Finally, we show how to realise the encoding of qubits in a decoherence-free subspace (DFS) using optical lattices. We develop methods for implementing robust gate operations on qubits encoded in a DFS exploiting collisional interactions between the atoms. We also give a detailed analysis of the performance and stability of the gate operations and show that a robust implementation of quantum repeaters can be achieved using our setup. We compare the robust repeater scheme to one that makes use of conventional qubits only, and show the conditions under which one outperforms the other.
Stability of magnetic remanence in multidomain magnetite
Keywords: Verwey transition
multi domain magnetite
thermoremanence
micro magnetic modelling

If a rock is to retain a geologically meaningful magnetic record of its history, it is essential that it contains magnetic minerals which are capable of carrying stable magnetic remanence. Of the natural occurring magnetic minerals, magnetite is the most important because of its abundance and strong magnetic signature. The stability, i.e., the resistance to demagnetisation or reorientation, of magnetic remanence is related to grain size; in smaller grains the magnetic moments align to have single domain (SD) structures, in larger grains complex magnetic patterns are formed (multidomain (MD)). “Classical” domain theory predicts that SD remanence is stable, whilst MD remanence is not. However experimental evidence has shown that both SD and MD grains can have stable remanences.
In this thesis the origin of stable MD remanence is examined. There are two opposing theories; one suggests that the stability is due to independent SD-like structures, the other postulates that the stability is due to metastable MD structure. A series of experiments were designed to examine the stability using a selection of characterised synthetic and natural samples. Low-stress hydrothermal recrystallised samples where grown for this study.
For the first time, the stability of thermoremanence induced in hydrothermal crystals to cooling was examined. The results agree with previous observations for crushed and natural magnetites, and support kinematic models.
The behaviour of SIRM and thermoremanences in MD magnetite to low-temperature cooling to below the crystallographic Verwey transition at 120-124 K (Tv) and the cubic magnetocrystalline anisotropy isotropic point (Tk) at 130 K was investigated. On cooling through Tv, SIRM was observed to decrease and demagnetise, however thermoremanence was found to display a large increase in the magnetisation at Tv, which was partially re- versible on warming. The size of the anomaly is shown to be dependent on the temperature at which the thermoremanence is acquired, internal stress and grain size. The anomaly is attributed to the large increase in the magnetocrystalline anisotropy which occurs on cooling through Tv . It is postulated that low-temperature cycling demagnetisation is due to kinematic processes which occur on cooling between room temperature and Tk. Characterisation of low-temperature treated remanence and partially alternating field demagnetised remanence, suggest that the stable remanence is multidomain.
Low-temperature cooling of remanence in single sub-micron crystals was simulated using micromagnetic models. The models predict the observed anomaly for thermoremanence on cooling through Tv, and also the relative behaviour of SIRM and thermoremanence. The single domain threshold was calculated for the low-temperature phase of magnetite, and was found to be 0.14 microns, compared to 0.07 microns at room temperature.
Personal identity and the police occupation in South Africa
Keywords: personal identity
Criminology
law and order
crime
security governance
police
South African Police Service
police officers

This thesis explores the question, 'Who do South African police officers think they are and how does this shape police practice?' Based on eight months of ethnographic fieldwork in Cape Town and the Eastern Cape province of South Africa in 2012/13, it is an exploration of the deep-seated perceptions, stories and imaginings that South African Police Service (SAPS) officers have of themselves, their occupation and their country, in the early twenty-first century. It unpacks how officers’ individual narratives shape, and are shaped by organisational narratives and forces, and how this interplay influences police practice in an unequal and violent young democracy.
The thesis suggests that a job in the SAPS is primarily just that, a job. It is a means to strive and survive in a country saturated in vulnerability and risk. Most officers join the organisation after other dreams have slipped out of reach. Once recruited they re-write their self-narratives to accommodate their new circumstances. Recruited from lineages long-oppressed, the meaning and income the job brings to their lives is usually more important to them than the work they carry out. As a result, they seek first to please their institutional overseers and ease the pressure of the job. This is achieved by enacting institutional performances that promote the idea that the SAPS is a rational, effective, evidence-based and rule-bound organisation made of up well trained officers performing common-sense crime prevention tasks, while hiding the darker side of police work. Using carefully choreographed performances, the SAPS and its officers present a strategically crafted façade behind which individual officers strive to secure their sense of self. When the façade is challenged, some resort to violence in an attempt to garner the respect they seek.
Britain and Albion in the mythical histories of medieval England
Keywords: Anglo-Norman literature
manuscript studies
Middle English literature
genealogy
Latin literature
mythical history

This dissertation examines the ideological role and adaptation of the mythical British past (derived from Geoffrey of Monmouth’s Historia regum Britanniae) in chronicles of England written in Anglo-Norman, Latin, and English from the twelfth to the fifteenth century, in terms of the shaping of English history during this time. I argue that the past is an important lens through which we can read the imagined geographies (Albion, Britain and England) and ‘imagined communities’ (the British and English), to use Benedict Anderson’s term, constructed by historical texts. I consider how British history was carefully re-shaped and combined with chronologically conflicting accounts of early English history (derived from Bede) to create a continuous view of the English past, one in which the British kings are made English or ‘of England’. Specifically, I examine the connections between geography and genealogy, which I argue become inextricably linked in relation to mythical British history from the thirteenth century onwards. From that point on, British kings are increasingly shown to be the founders and builders of England, rather than Britain, and are integrated into genealogies of England’s contemporary kings.
I argue that short chronicles written in Latin and Anglo-Norman during the thirteenth century evidence a confidence that the ancient Britons were perceived as English, and equally a strong sense of Englishness. These texts, I contend, anticipate the combination of British and English histories that scholars find in the lengthier and better-known Brut histories written in the early fourteenth century.
For the fourteenth and fifteenth centuries, my study takes account of the Albina myth, the story of the mothers of Albion’s giants (their arrival in Albion before Brutus’s legendary conquest of the land). There has been a surge of scholarship about the Albina myth in recent years. My analysis of hitherto unknown accounts of the tale, which appear in some fifteenth-century genealogical rolls, leads me to challenge current interpretations of the story as a myth of foundation and as apparently problematic for British and English history.
My discussion culminates with an analysis of some copies of the prose Brut chronicle (c. 1300) – the most popular secular, vernacular text in later medieval England, but it is seldom studied – and of some fifteenth-century genealogies of England’s kings. In both cases, I am concerned with presentations of the passage of dominion from British to English rulership in the texts and manuscripts in question. My preliminary investigation of the genealogies aims to draw attention to this very under-explored genre.
In all, my study shows that the mythical British past was a site of adaptation and change in historical and genealogical texts written in England throughout the high and later Middle Ages. It also reveals short chronicles, prose Brut texts and manuscripts, and royal genealogies to have great potential future research.
Vector host choice and the environmental context of mosquito-borne virus transmission
Keywords: ethology
virus
mosquitoes
learning

The present thesis explored ethological and geographical approaches for the investigation of vector-borne parasites. In the first part, the role of associative learning on vector preferences for hosts was investigated through a comprehensive series of behavioural experiments using the vector of dengue and yellow fever diseases, the mosquito Aedes aegypti. To this end, the possibility that the mosquitoes were able to associate unconditional stimuli with particular odours and visual patterns to which they were responsive was explored, but no evidence supporting the hypothesis that associative learning abilities are present in adults of this species was found. A critical review of the literature on learning in mosquitoes conducted afterward allowed the reinterpretation of findings in the field, narrowing the scope of evidence suggesting the existence of these cognitive abilities in some species.
In the second part of the thesis, the distribution and evolution of mosquito-borne viruses was investigated with the use of geo-coded environmental data and spatial statistics. Initially, the eco-climates associated with the distribution of Japanese encephalitis virus were described and modelled, allowing the production of a worldwide predictive map defining the probability of each region to develop this disease in the future. Predominating amongst those areas shown to be under high risk were the equatorial regions of South America and Africa. The methodology used to infer such patterns – non-linear discriminant analysis – was subsequently explored with a number of simulations. Overall, differences in the choice of parameters required for the analysis were shown to lead to differences in the final outputs produced, basically in those cases where the environmental range for which predictions are generated is not rigorously limited. Finally, eco-climate surrogates for the evolution of the Japanese encephalitis serocomplex were investigated, but the current environmental distances between the viruses did not seem to be associated with the events leading to their speciation.
Properties of tests for mis-specification in non-stationary autoregressions
Keywords: specification testing
autoregressions

We are interested in the stochastic properties, individual and joint, of mis- specification testing when the data are generated by an autoregressive process. Good mis-specification tests are invariant to the dynamic properties of the pro- cess summarized by its characteristic roots, and to irrelevant misspecifications. Invariance in parameter space obviates inference prior to mis-specification test- ing. This is important as the latter is used to validate the former. Mutual independence of the tests allows calibration of the overall significance level. Es- tablishing such results requires work on individual tests and on their stochastic interactions.
In Chapter 2, we derive the asymptotic distribution of two types of CUSUM of squares test, one implemented with standardized one-step-ahead OLS pre- diction errors and another implemented with OLS residuals. The latter is found to be valid in all but singular explosive cases, but the former only in purely non-explosive, or regular explosive cases with all roots in the explosive region of the parameter space; in Chapter 3, we show that a nuisance term arises in the mixed case. In Chapter 4, we derive numerically a finite sam- ple correction to render the tests implementable into software, and Chapter 1 contains two examples of applications.
In Chapter 5, we consider inference on the parameters associated with the stationary part of the process, together with tests for a unit root, lag length, variance constancy, and normality of the regression innovations. In character- izing the joint distribution of these tests, we rely on asymptotic theory, and show independence in the limit. A simulation experiment suggests that finite sample correlations between some of the tests are statistically significant but small. Asymptotically, then, control of the overall significance level of the test procedure is feasible, and there is no reason to discount inference for the use of these mis-specification tests in model selection.
An analysis of the morality of intention in nuclear deterrence, with special reference to final retaliation
Keywords: morality
nuclear deterrence
final retaliation

Quite apart from its apparent political obsolescence, the policy of nuclear deterrence is vulnerable to attack for its seemingly obvious immorality. Nuclear war is blatantly immoral, and nuclear deterrenec requires a genuine intention to resort to the nuclear retaliation which would precipitate such a war. Therefore, since it is wrong to intend that which is wrong to do, deterrence is immoral.
This thesis seeks to examine the nature of the deterrent intention as a means of verifying the soundness of the above deontological argument. This examination is carried out by first suggesting an acceptable notion of intention in general and then, after analysing the views of deterrent intention by other writers, proceeding to demonstrate the uniqueness of that intention. Having done this, and having explored the possibility that deterrence need not contain a genuine intention to retaliate, the thesis moves on to suggest and defend a moral principle which states that endeavours requiring the formation of an immoral intention may nevertheless be moral. Called the Principle of Double Intention (and based on the Principle of Double Effect), it offers a method for the moral assessment of agents who form immoral intentions within larger contexts. By applying this principle to nuclear deterrence, it is demonstrated that agents who undertake such a policy may be morally justified in doing so, provided certain conditions are met.
The thesis closes with a refutation of the objection that an agent cannot rationally form an intention (such as that required in deterrence) which he has no reason to carry out. By highlighting the objection's reliance on a claimed isomorphism between intention and belief, it is shown that the objection, while generally sound, does not apply to the special case of nuclear deterrence. The conclusion suggests a framework for disarmament which results in a deterrent force structure which is both strategically effective and morally acceptable.
Molecular characterisation of functionally important regions of Drosophila melanogaster Notch and Serrate
Keywords: Abruptex
calcium
EGF-domain
Notch
Serrate
MNNL

The Notch signalling pathway is conserved in all metazoan species and plays a crucial role in development and tissue maintenance. Canonical Notch signalling requires cell-cell contact to allow the interaction between Drosophila Notch receptor and its ligands, Serrate and Delta. The Notch Abruptex (Ax) region comprises 24-29 of the 36 epidermal growth factor-like (EGF) repeats in the Notch extracellular domain. Mutations in the Ax region give rise to three distinct phenotypes in Drosophila. Notch EGF repeats 11-12 form the ligand binding region (LBR). The recently solved structure of the module at the N-terminal of Notch ligands (MNNL) of a human Notch ligand, Jagged1, revealed that the domain was a calcium-binding C2 domain with Ca2+-dependent lipid binding. This study aimed to investigate the intra- and intermolecular properties of Drosophila Notch Ax region, LBR, and the MNNL of Notch ligand Serrate.
In WT Drosophila Notch EGF23-25, all three EGF domains were found to be Ca2+-binding, and a previously unknown Ca2+ binding consensus sequence was identified. AxN-suppressor mutations D948V and N986I were shown to impair the Ca2+-binding properties of the mutant EGF domain without affecting the neighbouring domains, suggesting a mechanism to explain the signalling phenotype associated with this mutation type.
Notch EGF11-13 showed Ca2+-binding in each EGF domain and binding to ligand-expressing cells. Its C-terminal tag was found to influence the Ca2+-dependent fold of EGF13, suggesting a future strategy for protein expression.
A Serrate fragment MNNL-EGF3 showed Ca2+-dependent lipid binding, which was not observed in a construct lacking MNNL. The lipid binding could be reduced by a substitution D197A in MNNL, suggesting this mutant could be used to probe functional importance of MNNL in model organism studies.
Binding between Serrate and Notch was assessed with a new cell aggregation assay method using flow cytometry, and agreed with previously published studies. Binding to Delta was subsequently measured, which suggested ligand specific differences although Notch residue L504 was important for both Serrate- and Delta-binding.
Collectively these studies establish that Drosophila Notch and its ligand Serrate has similar properties to mammalian homologues, which will facilitate future structural and functional studies.
Experimentally simulating high rate deformation of polymers and composites
Keywords: experimental simulation
composites
modeling
deformation
strain rate
thermodynamics
high rate
polymers

The research presented in this dissertation presents a methodology to experimentally predict and simulate the mechanical behavior of polymers under high strain rate deformation. Specifically, the interplay between the effects of temperature and strain rate on polymer behavior is examined and then used as a tool to help recreate the high rate mechanical response of several different polymers: ranging from rubbers to amorphous polymers to composites. Multiple literature reviews are conducted and presented in this thesis, e.g. experimental mechanics test methods, high rate behavior, time-temperature equivalence, constitutive modeling, and temperature measurement methods.
In accordance with mechanical theory, an experimental and analytical protocol in rate- and temperature- dependence was applied to a range of PVC materials ranging in plasticizer contents. Further to this, these PVC materials were modeled with a rubbery model describing the network stress seen in polymer behavior, and an amorphous polymer model to describe PVC low to high rate responses to deformation. This modeling develops insights in the adiabatic nature of high rate response.
Time-temperature equivalence, and the temperature rise during adiabatic deformation, are studied and exploited in order to implement a proposed experimental method which simulates the high rate deformation of polymeric materials.
The development of an experimental methodology to simulate and predict high rate behavior is presented, applied, and expanded to a range of materials: amorphous polymers (e.g. PVC 20wt% plasticizer, PMMA, PC) and composites (e.g. polymer bonded explosive simulant). The work also presents and highlights the fact that micro to nano-scale imaging may be used in parallel with the simulation method in order to better understand high rate behavior.
Furthermore, in result of the studies conducted in this body of work, several novel techniques were developed, or improved upon, and applied to the current research (e.g. additions to time-temperature equivalence, temperature measurement methods at high, moderate, and low strain rates, and a method for measuring the high rate behavior of soft materials).