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1
Edwards, Peter Ivan Edwards Peter Ivan. „Two explorations in musical objects /“. Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3170275.
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Thesis (Ph. D.)--University of California, San Diego, 2005.Includes 2 compositions: Puer natus est nobis (zu irgendeiner Zeit) for full orchestra, and Annicha, for flute, clarinet, and piano. Vita. Includes audio reel tape of compositions (analog, stereo., 7 1/2 ips : 7 in.).
2
Duchi, Enrica. „ECO method and object grammars : two methods for the enumeration of combinatorial objects“. Nice, 2003. http://www.theses.fr/2003NICE4010.
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Cette thèse se situe dans le domaine de la combinatoire énumérative et bijective. La thèse commence par une introduction sur les structures et les méthodes qui sont ensuite utilisées. Puis elle se divise en deux parties. La première analyse des problèmes liés à ECO. En particulier, on analyse le problème de monter des règles de succession équivalentes. Plus précisément, on introduit des classes de règles équivalentes et on démontre l’équivalence en utilisant la méthode ECO. Dans le chapitre 3, on montre comment déterminer des règles de succession associées à une grande classe de récurrences littéraires positives croissantes. Puis on montre comment il est possible de décrire des récurrences linéaires au moyen de règles de succession négatives. Dans la seconde partie on étudie les relations entre les grammaires d’objets et la méthode ECO. En particulier, dans le chapitre 4, on montre comment on peut passer d’une grammaire d’objet à un ECO système associé selon un paramètre linéaire. Dans le chapitre 5 ce résultat est étendu au cas des paramètres q-linéaire pour les grammaires unidimensionnelles. Dans le chapitre 6 on obtient, d’une façon quasi-automatique, une grammaire pour la classe des polyominos convexes à partir d’un ECO système pour cette classeThis thesis is about enumerative and bijective combinatorics. We start by giving an introduction to the basic objects and methods we use (chapter 1). Then, the thesis divides in two parts. In the first part we address various questions about the expressiveness of the ECO method. In particular, in chapter 2 we talk about the problem of the equivalence of succession rules. More precisely, we introduce some classes of equivalent succession rules, by showing their equivalence using the ECO method and the generating functions. In chapter 3 we show how to represent a large class of positive linear recurrences by means of succession rules. Then, we show how any linear recurrence could be treated by means of signed succession rules. In the second part of the thesis, the relations between object grammars and ECO method are studied. In particular, in chapter 4 we show how it is possible to pass from an object grammar to an associated ECO-system according to a linear parameter. In chapter 5 we extend this result to natural q-parameters on unidimensional object grammars. In chapter 6 we provide, in a quasi-automatic way, a grammar for the class of convex polyominoes from an ECO-system for this class
3
Rastello, Sara. „Multifrequency VLBA observations of two compact symmetric objects“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8913/.
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In this thesis the results of the multifrequency VLBA observations of the GPS 1944+5448 and the HFP J0111+3906 are presented. They are compact objects smaller than about 100 pc, completely embedded in the host galaxy. The availability of multi-epoch VLBI observations spanning more than 10 years, allowed us to compute the hot spot advance speed in order to obtain the kinematic age of both sources. Both radio sources are young, in agreement with the idea that they are in an early evolutionary stage. The spectral analysis of each source component, such as the lobes, the hot spots, the core and the jets, making a comparison with the theoretical ones is described. In addition the physical parameters derived from VLBA images as the magnetic field, the luminosity, the energy and the ambient medium density of both sources are discussed.
4
Hann, Christopher Eric. „Recognising two planar objects under a projective transformation“. Thesis, University of Canterbury. Mathematics and Statistics, 2001. http://hdl.handle.net/10092/1785.
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This thesis involves solving problems associated with object recognition
for two dimensional images under a projective transformation.
In order to recognise an object under any viewing angle requires invariant
features to be identified. These invariant features can be used to match two
images arising from two different views of a single object.
One invariant is the projective curvature which characterises all curves
up to a projective transformation. However the projective curvature depends
on seventh order derivatives so is very sensitive to noise in the discretisation
of the images and is of little practical use.
Using links between the projective group and its subgroups, invariant
points are found which depend on much lower order derivatives so are less
sensitive to noise. They can be located on the images using a smoothing
process then used to match the curves. However the smoothing process introduces
error into the invariant points so that there will be error in the
matching. This will not cause a problem if the two images have significantly
different image features as then they can be detected within the wider tolerances
of error. But this will cause a problem in distinguishing two images
which are similar but different as it will not be known whether the error in
the matching is due to error in the identification of the invariant points or
not.
A method, called the canonical form method, is developed incorporating
an error analysis which corrects the error in the matchings of the images.
This enables two similar but different two dimensional objects to be distinguished.
It also provides the background knowledge to solve new problems
as they arise.
In addition to this practical method for two dimensional object recognition,
a new characterisation of curves under the projective group and two of
its subgroups is done using potentials and an alternative method for deriving
and representing the projective curvature is given.
5
McAndrew, Patrick. „Recognising and locating objects in two dimensional perspective views“. Thesis, Heriot-Watt University, 1990. http://hdl.handle.net/10399/853.
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6
Clemens, David T. „The recognition of two-dimensional modeled objects in images“. Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/27950.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: p. 108.
by David T. Clemens.
M.S.
7
Hunter, Jerry James 1964. „Planning stable in-hand reconfiguration of objects in two dimensions“. Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/278194.
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This thesis presents a method to reconfigure objects in an articulated robotic hand, where reconfiguration is defined as moving an object from one orientation in the hand to another orientation. Several methods using object configuration rely on a stationary work area. These methods assume that the object is stably grasped by the hand, and is moved around the work area in an assembly process. This thesis assumes that the hand is the primary obstacle. The object now reacts to the hand instead of the work area. Reconfiguration of the object within the hand is the goal. Models were developed that portrayed the mechanics and the contacts for frictionless manipulation in a plane. Contact formation trees used in conjunction with the simulated mechanics is a unique method for solving this problem; the solution we attain is an optimal reconfiguration plan. (Abstract shortened with permission of author.)
8
Klapez, Martin. „A study of two Languages for Active Objects with Futures“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5691/.
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In computer systems, specifically in multithread, parallel and distributed systems, a deadlock is both a very subtle problem - because difficult to pre- vent during the system coding - and a very dangerous one: a deadlocked system is easily completely stuck, with consequences ranging from simple annoyances to life-threatening circumstances, being also in between the not negligible scenario of economical losses.
Then, how to avoid this problem? A lot of possible solutions has been studied, proposed and implemented. In this thesis we focus on detection of deadlocks with a static program analysis technique, i.e. an analysis per- formed without actually executing the program.
To begin, we briefly present the static Deadlock Analysis Model devel- oped for coreABS−− in chapter 1, then we proceed by detailing the Class- based coreABS−− language in chapter 2.
Then, in Chapter 3 we lay the foundation for further discussions by ana- lyzing the differences between coreABS−− and ASP, an untyped Object-based calculi, so as to show how it can be possible to extend the Deadlock Analysis to Object-based languages in general.
In this regard, we explicit some hypotheses in chapter 4 first by present- ing a possible, unproven type system for ASP, modeled after the Deadlock Analysis Model developed for coreABS−−.
Then, we conclude our discussion by presenting a simpler hypothesis, which may allow to circumvent the difficulties that arises from the definition of the ”ad-hoc” type system discussed in the aforegoing chapter.
9
Nightingale, Trevor R. T. „Acoustic diffraction by two and three dimensional objects using integral techniques“. Thesis, Heriot-Watt University, 1990. http://hdl.handle.net/10399/2124.
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10
Welch, Thaddeus B. „Electromagnetic scattering from two dimensional objects using the Field Feedback Formulation“. Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25894.
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11
Davies, Ioan Tudur. „Sedimentation of circular and elliptical objects in a two-dimensional foam“. Thesis, Aberystwyth University, 2009. http://hdl.handle.net/2160/97552d65-3e01-4afc-a576-ef0bd11e0fff.
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The rheology of a two-dimensional dry foam is probed with quasi-static bubblescale simulations of the sedimentation of circular discs and elliptical objects. The sedimenting objects move in response to a combination of their weight and the forces exerted on them by the network of soap films and the pressures in the bubbles. Viewed macroscopically, the plasticity and elasticity of the foam combine to determine the rate of descent of a circular disc. A critical disc weight is found that determines whether the disc is supported by the foam or not. This critical weight increases linearly with disc diameter and decreases with the liquid fraction of the foam with a power-law relation. Similarly, the drag force exerted on a disc increases linearly with its diameter and decreases with the liquid fraction of the foam with a power-law relation. An attractive force between a disc and a nearby wall is seen when the disc is further than two bubble diameters from the wall. Such wall effects are minimal when the disc sediments from a central position in a channel of sufficient width. The interaction between two sedimenting discs is quantified by placing them in one of two configurations: one in which the discs are placed side by side and the other in which the discs are initially one above the other. The discs descend through the foam and move towards a stable orientation in which they are positioned directly above one another with a constant separation of one or two bubbles. Above a critical initial separation of the order of 5 bubble diameters, the discs do not interact. The existence of the critical separation is shown to be a result of the discrete nature of a dry foam. The descent and rotational motion of an ellipse of similar size and weight to one of the circular discs is then considered. An ellipse rotates towards a stable orientation in which its major axis becomes parallel to gravity, driven by the local structure of the foam. This rotational motion is much slower than the downward motion.
12
Zhen, Yi. „Numerical Simulation of Dropped Cylindrical Objects into Water in Two Dimensions (2D)“. ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2568.
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The dropped objects are identified as one of the top ten causes of fatalities and serious injuries in the oil and gas industry. It is of importance to understand dynamics of dropped objects under water in order to accurately predict the motion of dropped objects and protect the underwater structures and facilities from being damaged. In this thesis, we study nondimensionalization of dynamic equations of dropped cylindrical objects. Nondimensionalization helps to reduce the number of free parameters, identify the relative size of effects of parameters, and gain a deeper insight of the essential nature of dynamics of dropped cylindrical objects under water. The resulting simulations of dimensionless trajectory confirms that drop angle, trailing edge and drag coefficient have the significant effects on dynamics of trajectories and landing location of dropped cylindrical objects under water.
13
Poeschel, Friedrich Gerd. „Signals in two-sided search“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:c1decfbb-5fdf-4c13-805e-2cc7fe115641.
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We introduce signals to search models of two-sided matching markets and explore the implications for efficiency. In a labour market model in which firms can advertise wages and workers can choose effort, we find that advertisements can help overcome the Diamond paradox. Advertisements fix workers' beliefs, so that workers will react if firms renege on advertisements. Firms then prefer to advertise truthfully. Next, we consider a market with two-sided heterogeneity in which types are only privately observable. We identify a simple condition on the match output function for agents to signal their types truthfully and for the matching to exhibit positive assortative matching despite search frictions. While our theoretical work implies that the efficiency of matching increases as information technology spreads, empirical matching functions typically suggest that it declines. By estimating more general matching functions, we show that the result of declining efficiency can partly be attributed to omitted variable bias.
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Cox, Courtney Marie. „Two problems in dynamic ethics“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:aa01c397-0211-4c70-8938-3c4a443798ca.
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Time raises a host of difficult ethical questions. This doctoral project focuses on two: 1. How are "static" comparative principles (e.g. equality, desert) to be understood over time? (The Problem of Fairness & Time) 2. How might separation (in time) between agents, objects, and threats affect claims to the relevant resources? (The New Problem of Temporal Distance) My work begins with a simple observation: our prima facie intuitions about the value of simple distributions change depending on whether such cases are presented as static (occurring at one time) or dynamic (extended over time). Further examination of more complicated distributions leads to the proposal of a new theory, Weighted Progressive Egalitarianism. This theory has two features: only past-regarding complaints matter (a scope restriction), and a comparative complaint between persons located at a great temporal distance matters less than a complaint between contemporaries (a weighting restriction). This theory provides one plausible answer to the first question, the Problem of Fairness & Time. The evaluation of this theory relies on and reveals some non-standard answers to the second question, the New Problem of Temporal Distance. I conclude by arguing that the theory’s application to a few puzzles in population axiology merits further investigation.
15
JeongAhn, Youngmin, und Renu Malhotra. „Simplified Derivation of the Collision Probability of Two Objects in Independent Keplerian Orbits“. IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624717.
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Many topics in planetary studies demand an estimate of the collision probability of two objects moving on nearly Keplerian orbits. In the classic works of Opik and Wetherill, the collision probability was derived by linearizing the motion near the collision points, and there is now a vast amount of literature using their method. We present here a simpler and more physically motivated derivation for non-tangential collisions in Keplerian orbits, as well as for tangential collisions that were not previously considered. Our formulas have the added advantage of being manifestly symmetric in the parameters of the two colliding bodies. In common with the Opik-Wetherill treatments, we linearize the motion of the bodies in the vicinity of the point of orbit intersection (or near the points of minimum distance between the two orbits) and assume a uniform distribution of impact parameter within the collision radius. We point out that the linear approximation leads to singular results for the case of tangential encounters. We regularize this singularity by use of a parabolic approximation of the motion in the vicinity of a tangential encounter.
16
Bennett, Philip Mark. „Two-photon dyes for biological application“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:b8cb9ce4-35eb-433c-86fc-b5df53a2e566.
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Two photon absorption (TPA) is the near simultaneous absorption of two photons of light to achieve an electronically excited state. It has led to huge advances in microscopy and microfabrication due to its quadratic dependence on the local light intensity. This thesis describes the design, synthesis and application of dyes with strong TPA properties, and as such is divided into three chapters. The first introduces the theory and measurement of TPA as well as structure-property relationships known to maximise the efficiency of TPA. The subsequent chapters present explorations of the application of these dyes in biological applications; namely two-photon uncaging and two-photon photodynamic therapy. A recurring theme in my research is the discussion and evaluation of strategies for improving the compatibility of organic macromolecules with biological systems. Uncaging is the use of photolysis to achieve a rapid increase in the local concentration of a physiologically active species via a photoremovable protecting groups. Photoremovable protecting groups are covalently attached to the physiologically active species, thus rendering it inactive. At the desired time and location, a light dose releases the molecule in its active form. There are many compounds known to uncage following photoexcitation, but there are few examples of caging groups which exhibit both strong two-photon absorption properties and highly efficient uncaging. Chapter 2 discusses the rational design of such groups through the development of a new mechanism for uncaging, in which a photoinduced electron transfer (PeT) between a two-photon-excited electron donor and an electron acceptor/release group drives the uncaging event. Photodynamic therapy (PDT) is a treatment for neoplastic disorders such as cancer in which localised cell death is induced through photoexcitation of a sensitiser. Following light absorption, the photosensitiser enters a relatively long-lived excited state which reacts with cellular oxygen to produce its highly cytotoxic singlet form. The main challenges of the field are to achieve deep penetration of light into tissue and to reduce coincident damage to unaffected tissue by light scattering during irradiation. In 2008, the Anderson group reported the development of PDT photosensitisers with highly efficient two-photon absorption as well as high singlet oxygen quantum yields. Chapter 3 discusses strategies for improving the pharmacokinetics and defining the sub-cellular localisation of these photosensitisers.
17
Miller, Richard. „Two approaches to architecture-independent parallel computation“. Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:e40bd426-9660-468e-96e2-3281a9159909.
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Two approaches to architecture-independent parallel computation are investigated: a constructive functional notation for specifying implicitly parallel operations on multidimensional arrays, and an extension to imperative sequential programming languages for implementing bulk-synchronous parallel algorithms. An algebra of multidimensional rectangular arrays is defined constructively, by means of an injective singleton operator which maps each value from a base type into a one-element array, and a set of join operators which map a pair of arrays into their concatenation along one of a set of dimensions. A repertoire of array operations is defined in the context of the Bird-Meertens Formalism, using array versions of polymorphic higher-order functions such as map, reduce, zip and cross. This approach gives rise to a collection of algebraic laws which can be used to guide the transformation of array expressions into different equivalent forms. In particular, the promotion laws have a natural interpretation as descriptions of different parallel realisations of an array computation. The use of the array algebra is illustrated by the derivation of two example algorithms: the L-U decomposition of a matrix, and the numerical solution of an elliptic partial differential equation. The bulk-synchronous parallel model of an abstract general-purpose parallel computer is described, along with several variants of the BSP cost model. A refinement to the cost model is proposed, introducing a `half-bandwidth' parameter to quantify the effect of data granularity on communication cost. A simple BSP programming model is defined, with semantics specified in CSP. The programming model is realised by extending sequential programming languages with a small set of primitives for process creation and termination, bulk synchronisation, and inter-process data access. The author has created implementations of these primitives in the Oxford BSP library, with versions for a variety of parallel systems including networked workstations, shared-memory multiprocessors and massively-parallel distributed-memory machines, and has used them to produce an architecture-independent parallel version of the molecular dynamics module of the UCSF AMBER 4.0 package.
18
Townsend, Alex. „Computing with functions in two dimensions“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:02f92917-809e-477d-8413-417bb8106e56.
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New numerical methods are proposed for computing with smooth scalar and vector valued functions of two variables defined on rectangular domains. Functions are approximated to essentially machine precision by an iterative variant of Gaussian elimination that constructs near-optimal low rank approximations. Operations such as integration, differentiation, and function evaluation are particularly efficient. Explicit convergence rates are shown for the singular values of differentiable and separately analytic functions, and examples are given to demonstrate some paradoxical features of low rank approximation theory. Analogues of QR, LU, and Cholesky factorizations are introduced for matrices that are continuous in one or both directions, deriving a continuous linear algebra. New notions of triangular structures are proposed and the convergence of the infinite series associated with these factorizations is proved under certain smoothness assumptions. A robust numerical bivariate rootfinder is developed for computing the common zeros of two smooth functions via a resultant method. Using several specialized techniques the algorithm can accurately find the simple common zeros of two functions with polynomial approximants of high degree (≥ 1,000). Lastly, low rank ideas are extended to linear partial differential equations (PDEs) with variable coefficients defined on rectangles. When these ideas are used in conjunction with a new one-dimensional spectral method the resulting solver is spectrally accurate and efficient, requiring O(n2) operations for rank $1$ partial differential operators, O(n3) for rank 2, and O(n4) for rank &geq,3 to compute an n x n matrix of bivariate Chebyshev expansion coefficients for the PDE solution. The algorithms in this thesis are realized in a software package called Chebfun2, which is an integrated two-dimensional component of Chebfun.
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BONOME, YADIRA GARNICA. „PROPOSING TWO NEW HANDLING INTERACTION TECHNIQUES FOR 3D VIRTUAL OBJECTS USING THE MYO ARMBAND“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=30744@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Flexibilidade e liberdade são sempre desejados em ambientes de realidade virtual. Dispositivos de entrada tradicionais, como mouse ou teclado, dificultam as interações entre o usuário e o ambiente virtual. Para melhorar a interação em termos qualitativos em um ambiente virtual, a interação deve ser tão natural quanto possível, por isso, gestos com a mão se tornaram um meio popular para a interação humanocomputador. O desenvolvimento de dispositivos de imersão como os capacetes trouxeram a necessidade de uma nova forma de interação e um desafio para os desenvolvedores. O reconhecimento de gestos da mão usando sinais eletromiográficos (EMG) tem chamado a atenção devido ao surgimento de dispositivos mais baratos que conseguem gravar dados EMG precisos. Um dos dispositivos mais destacados nessa área é o bracelete Myo, equipado com oito sensores EMG e uma unidade de medição inercial (IMU). O objetivo deste trabalho é avaliar a usabilidade do bracelete Myo como um dispositivo de seleção e manipulação de objetos 3D em ambientes de realidade virtual, visando melhorar a experiência do usuário, aproveitando a possibilidade de medir a força aplicada a um gesto assim como de usar as vibrações do Myo como sistema de feedback. Este estudo pretende responder à seguinte pergunta: O bracelete Myo tem alto grau de usabilidade para a seleção/manipulação de objetos 3D em Ambientes de Realidade Virtual? Para atingir esse objetivo, foram propostas quatro subquestões para orientar essa pesquisa: I) Quais recursos do Myo podem ser usadas em Ambientes de Realidade Virtual (VRE)? II) Quais são as limitações do bracelete Myo? III) É possível realizar tarefas de seleção e manipulação usando o bracelete Myo? IV) Como o uso do bracelete Myo pode enriquecer as tarefas de seleção e manipulação? Para responder às duas primeiras subquestões foi realizada uma revisão da literatura que compreende a tecnologia do Myo, vantagens e limitações, e os trabalhos relacionados. Além disso, inclui conceitos básicos sobre Interações em VRE. Para responder às duas últimas subquestões foram propostas duas técnicas de seleção/manipulação usando o Myo e foram testadas com os usuários e os resultados foram comparados, avaliando sua usabilidade.
Flexibility and freedom are always desired in virtual reality environments. Traditional inputs, like mouse or keyboard, hamper the interactions between the user and the virtual environment. To improve the interaction in qualitative terms in a virtual environment, the interaction must be as natural as possible, and because of that, hand gestures have become a popular means to the human-computer interaction. The development of immersion devices like head-mounted displays brought the need for a new way of interaction and a challenge to developers. Hand gestures recognition using electromyography signals (EMG) has increased the attention because the rise of cheaper wearable devices that can record accurate EMG data. One of the outstanding devices in this area is Myo armband, equipped with eight EMG sensors and a nineaxis inertial measurement unit (IMU). The objective of this work is to evaluate the usability of the Myo armband as a device for selection and manipulation of 3D objects in virtual reality environments, aiming to improve the user experience, taking advantage of the possibility to measure the force applied to a gesture and to use Myo vibrations as a feedback system. This study aims to answer the following question: Has Myo armband high grade of usability for selection/manipulation of 3D objects in Virtual Reality Environments? And to achieve that purpose, four sub-questions were proposed to guide this research: I) Which resources of Myo can be used in Virtual Reality Environments (VRE)? II) What are the limitations of the Myo armband? III) Can selection and manipulation tasks be performed using Myo armband? IV) How can Myo armband enrich the selection and manipulation tasks? To answer to the first two sub-questions, we conducted a literature review that covers Myo technology, its advantages and limitations, and related works. Also, it includes basic concepts about Interactions in VRE. To answer to the last two sub-questions, we proposed two selection/manipulation techniques using Myo, which were tested with users and the results were compared, evaluating their usability.
20
Clarke, Simon James. „An experimental study of some two-dimensional antiferromagnets“. Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:a559d173-edd3-4c9b-aa6e-a09a6d0fd37f.
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This thesis discusses the investigation of the two-dimensional S = œ Heisenberg antiferromagnet copper formate tetrahydrate (CFTH) and the layered triangular lattice material NaTi02 which was thought to be a candidate for the possession of a non-classical antiferromagnetic ground state due to the frustration inherent in a triangular antiferromagnet. Single crystals of CFTH are investigated using elastic, quasielastic and inelastic neutron scattering, electron spin resonance (ESR) spectroscopy and DC magnetometry. Using the appropriate theory, these measurements are used to determine values for the terms in the Hamiltonian which describes the interactions between the Cu2+ ions in this material. The Hamiltonian is compared with that of La2Cu04, and the two are determined to be quite similar. There does not appear to be any evidence for a non-classical ground state in either material. This was proposed to exist in La2Cu04 to account for the superconductivity of doped samples. The difficulties in preparing pure NaTi02 have been surmounted, and a technique is described for preparing powder samples with very reproducible structural and magnetic properties. The structural properties have been investigated using X-ray and neutron diffraction, the latter at temperatures between 100 K and room temperature. The magnetic properties have been probed using DC magnetometry and ESR spectroscopy. The sample dependence of the structural and magnetic properties of samples prepared in slightly different ways is discussed. The temperature dependence of the magnetic susceptibility and of the structural parameters is explained by comparison with other oxides and chlorides of trivalent Ti and V, many of which show similar behaviour. The magnetic and structural changes which occur between 200 and 250 K are assigned to changes in the Ti-Ti bonding within the layers, which leads to a transition between two metallic states with subtle differences in their band structures.
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Skinner, Thomas Olof Edwin. „Two-dimensional colloidal systems : grain boundaries and confinement“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:e5407868-7c67-4252-9867-6955d9b71825.
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The behaviour of colloidal particles in two-dimensional (2D) systems is addressed in real space and time using magnetic fields, optical tweezers and optical video microscopy. First, the fluctuations of a grain boundary in a 2D colloidal crystal are analysed. A real space analogue of the capillary fluctuation method is derived and successfully employed to extract the key parameters that characterise the grain boundary. Good agreement is also found with a fluctuation-dissipation based method recently suggested in simulation. Following on from analysis of the interface fluctuations, the properties of the individual grain boundary particles are analysed to investigate the long standing hypothesis that suggests that grain boundary particle dynamics are similar to those in supercooled liquids. The grain boundary particle dynamics display cage breaking at long times, highly heterogeneous particle dynamics and the formation of cooperatively moving regions along the interface, all typical behaviour of a supercooled liquid. Next, the frustration induced by confining colloidal particles inside a pentagonal environment is investigated. The state of the system is adjusted via two separate control parameters: the inter-particle interaction potential and the number density. A gradual crystalline to confined liquid-like transition is observed as the repulsive inter-particle interaction potential is decreased. In contrast, re-entrant orientational ordering and dynamical effects result as the number density of the confined colloidal particles is increased. Finally, the dynamics of colloidal particles distributed amongst a random array of fixed obstacle particles is probed as a function of both the mobile particle and fixed obstacle particle number densities. Increasing the mobile and the obstacle particle number density drives the system towards a glass transition. The dynamics of the free particles are shown to behave in a similar way to the normal glass transition at low obstacle density and more analogous to a localisation glass transition at high obstacle density.
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Funnell, Timothy. „Characterisation of the human two-pore channels“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:8c148321-5c6d-4942-ac31-3a4ca3791077.
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The Ca²⁺-mobilising messenger NAADP has been shown to play a key role in the regulation of mammalian physiology. Recently, the two-pore channels (TPCs) have been proposed as an NAADP-gated Ca²⁺ channel. Chapter 1 introduces the TPCs as the major candidates in governing NAADP-mediated Ca²⁺-release from acidic stores. Chapter 2 explains the methodologies developed and used. Chapter 3 demonstrates the successful immunopurification of HsTPC2 and its incorporation into an artificial lipid bilayer. K⁺ and Ca²⁺ currents were seen in reponse to nM - μM concentrations of NAADP; with the open probability (P₀) fitting a bell-shaped concentration-response curve. Ligand sensitivity was shown to be regulated by luminal [Ca²⁺], whereby a 20-fold increase in [Ca²⁺] lumen (10 μM to 200 μM) caused a 100-fold reduction in the EC50 from ≈ 500 nM to 5 nM. Furthermore, a reduction in luminal pH from 7.2 to 4.8 reduced the P₀ but 1 μM Ned-19 inhibiting all channel activity. Chapter 4 investigates the in situ properties of HsTPC2 by the purification and patch clamp of intact lysosomes from cells overexpressing HsTPC2. Three methods of purification were compared: differential centrifugation, whole lysosome immunoprecipitation and magnetic chromatography. Techniques involving lysosomal swelling and whole cell homogenisation were also optimised to ensure minimal contamination by non-lysosomal proteins. Whole lysosome patch clamping revealed NAADP-induced, Ca²⁺-specific currents in response to NAADP, but not cADPR, IP₃ or Ned-19. High concentrations of NAADP (mM) and Ned-19 (μM) showed prolonged ≈ 5 minutes) inhibition of channel activity. Chapter 5 explores the protein-protein interactions of the purified HsTPC2 and identifies a heterodimeric interaction between HsTPC1 and HsTPC2 was further dissected by coimmunoprecipitation, colocalisation and FRET studies. Despite clear evidence that both isoforms independently form homodimers, it is likely that heterodimerisation is a dynamic interaction only seen in a subset of the channel population. Chapter 6 discusses the results obtained in the wider context of cell physiology.
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Blades, Gareth. „Re-engineering bacterial two-component signalling systems“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:2865c02d-c208-45fa-8108-d8ced9486c19.
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Bacteria use Two Component Systems (TCS) to sense and respond to changes in their external environment. TCS are used to navigate to nutrients or away from toxins (chemotaxis) and to adapt to changes in osmolarity (osomosensing). TCS are composed of a histidine protein kinase (HPK) which trans-autophosphorylates in response to environmental change, transferring the phosphoryl group to a cognate response regulator (RR). Phosphorylated RRs modulate an output response such as protein-protein interaction for chemotaxis, and transcription for osmosensing. RRs are composed of a conserved amino terminal REC domain, and where present a variable effector domain. CheY, the chemotaxis RR, contains only a REC domain, whilst OmpR, the osmosensing RR, also contains a DNA binding effector domain. Recently, TCS have been used in synthetic biology applications due to their modularity and conserved signalling mechanism. This thesis aimed to investigate whether it was possible to design a synthetic TCS composed of fused chemotaxis and osmosensing components. Synthetic RRs were designed, fusing the highly conserved REC domains of CheY and OmpR upstream of the OmpR effector domain. REC domains were fused across the α4-β5-α5 region, a region which transmits REC domain phosphorylation into effector domain activation. Synthetic RRs were designed to undergo phosphotransfer to their fused REC domains from the chemotaxis HPK, CheA, activate the attached OmpR effector domain and bind promoter DNA. Four chimeric RRs were created, although only three were structurally viable; F2, F3 and F4. Each fusion bound CheA, and F3 and F4 bound CheA with a significantly higher affinity than CheY. The chimeric RRs could all be phosphorylated byCheA-P; F4 and F3 were phosphorylated to wild-type levels. DNA binding affinitywas investigated with fluorescence anisotropy, hosphorylated and unphosphorylated F3 could not bind promoter DNA. F2 bound promoter DNA regardless of phosphorylation state. These data indicate that phosphorylation of the F2 REC domain does not lead to activation of the effector domain. F2 is likely to be constitutively active suggesting a previously unknown role for OmpR α5 as a mediator of effector domain activation. Furthermore, using a simple fusion approach to design RRs is not a viable method to create a synthetic TCS with a controllable output.
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Reza, Hasnain. „Detection, location, and trajectory tracing of moving objects in the real world two-dimensional images“. Ohio : Ohio University, 1988. http://www.ohiolink.edu/etd/view.cgi?ohiou1182869492.
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Beer, Ann. „The use of two languages in Samuel Beckett's art“. Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:fe430cb4-ec07-4f18-9d4a-6860b0d85fbb.
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This study argues that Samuel Beckett's works in English and French reveal the organising energy of a "bilingual consciousness". Bilingualism is no personal eccentricity but the foundation for Beckett's mature art, without which it could not have developed. He has never been a unilingual writer; at every stage of his career his two languages have enriched, challenged and opposed each other. Bilingual art has allowed Beckett to move between linguistic circles, claiming as his own a transitional space that has protected his need for imaginative solitude. Gradually abandoning the cultural specificity of his early works in favour of archetypal settings that "translate" successfully to other contexts, he has focussed directly on what unites rather than divides human communities. Yet his writing retains an evident alertness to, and love of, the linguistic and cultural resources of English and French. His alternations between languages and his frequent activities as translator and self- translator contribute to a detachment from generic conventions that encourages innovation. Thus the often-criticised marginality of the bilingual has become for Beckett a source of strength. This analysis draws on a close reading of certain key texts, crossing languages freely to follow Beckett's own development. The prose has central place, because it spans his entire career, and because his most radical innovations have occurred in prose to be, subsequently, transferred in new forms to the drama. Chapter I presents Beckett's dual language-use in a wider context, exploring the early exposure afcd later suppression of "bilingual awareness, the implications of bilingualism for his artistic outlook, and the bilingual aesthetic he has developed. The remaining chapters draw on a new chronology of his writing and translating activities to show the development of his dual language-use and how it has interacted distinctively at each period with his artistic goals and practice.
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Melia, Tom. „NLO QCD And two weak bosons at the LHC“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:e55bde16-1aa0-4a6f-a19a-5437b6b901f2.
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We present original calculations of standard model processes involving two weak bosons at NLO in QCD, and study related phenomenology with reference to Higgs boson and new physics searches at the LHC. We employ a new theoretical technique, D-dimensional generalised unitarity, to obtain the multi-particle, one-loop scattering amplitudes for the processes pp → W+W- + 1j, pp → W+W- + 2j, pp → W+W+ + 2j, and gg → W+W-g. We consider the LHC phenomenology of: the W+W- + n jets background to Higgs searches, for n = 0,1,2; the effects of anomalous tri-linear gauge couplings in WW and WZ production; the background W+W+ + 2j to new physics searches involving like-sign leptons; and a method of spin determination of new states in a scenario where conventional methods fail.
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Sorgiovanni, Ben. „Reconciling content-externalism and self-knowledge : two frameworks considered“. Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:dde7b307-da02-412a-9022-289fefc7dd6d.
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In this thesis, I assess the prospects for reconciling content-externalism and crucial guiding intuitions about self-knowledge within two different frameworks, respectively. The first framework belongs to the prominent contemporary externalist, Tyler Burge. The second framework is built from central strands of thought in Ludwig Wittgenstein's later work. I argue that a tension between the basic externalist intuition and crucial guiding intuitions about self-knowledge arises within a Burgean framework which does not arise within a Wittgensteinian framework. I show that given Burge's views about the individuation of mental content, switching a subject slowly between two relevantly dissimilar contexts can undermine knowledgeability of her epistemic reasons. I argue that this is a troubling result, given Burge's views about the sorts of things that epistemic reasons are. On Burge's view, epistemic reasons are rational relations between mental states. If slow-switching can undermine knowledgeability of one's epistemic reasons, then it can undermine knowledgeability of the rational relations between mental states. But the thought that the knowledgeability of the rational relations between mental states might be sensitive to changes in one's context in this way seems at odds with our intuitive picture of self-knowledge. I argue that this tension does not arise within a Wittgensteinian framework because there is evidence that Wittgenstein rejects certain of the claims about the individuation of mental content which generate the tension in Burge's case. The thesis examines the substantive similarities and differences between the Burgean and Wittgensteinian frameworks more generally. In doing so, it maps two contrasting ways in which the basic content-externalist intuition might be elaborated.
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Gola, Paweł. „Essays on two-sector matching, status rewards and liability“. Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:d2476ffb-3853-4e5b-bdc2-4105db6036c3.
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This thesis consists of three self-contained chapters. Chapter 1 develops a two-sector, bivariate matching model, in which each sector uses a different dimension of skill in the production process. I show there exists a unique assignment of agents to sectors and derive comparative statics. The main result is that if jobs are scarce, both an increase in sector one skills' spread and a technological improvement increase the supply of talent in sector one, but decrease it in sector two. In sector two, this raises wages and wage inequality. In sector one, the effects are ambiguous in general, but wages increase for the most and decrease for the least talented agents. Chapter 2 studies the impact of social status on occupational sorting in a two-sector matching framework. Talent is two-dimensional and thus status is not a zero-sum game; it depends both on occupational prestige and within-sector rank (local status). I show that the weights with which these two components enter - the structure of status - crucially influence the way in which agents self-select into sectors and argue that it is likely that these weights differ across occupations. The more important are the individual components of status in a sector, or the less important the collective component, the better the agents who join that industry, which has important implications for total payoffs, wage levels and inequality, and profits. I also show that the stable assignment is typically inefficient, which is driven by the distortion of relative status rewards, not status concerns per se. Chapter 3 investigates whether directors of companies should have limited liability. I develop a three-player model in which: (a) debtholders and equityholders are defined by their control rights and (b) the project is run by the directors. The main result is that increased liability for directors forces them to internalise more of the downside risk of the project and hence reduces their risk-taking. This is optimal if over-investment was a problem initially. I show that the extent to which over-investment is a problem depends on how well debtholders are protected compared to equityholders. If debtholders are strong, increased liability can cause under-investment.
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Thorneywork, Alice L. „Structure and dynamics of two-dimensional colloidal hard spheres“. Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:c0929b42-c819-4782-a555-083513e396ea.
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The structural and dynamic behaviour of quasi-two-dimensional monodisperse and bidisperse colloidal hard spheres are studied by optical microscopy. Firstly, a full characterisation of the equilibrium structure is presented through a consideration of structural correlation functions and number fluctuations. Comparison to fundamental measure theory and Monte Carlo simulations confirms both the behaviour of the system as a model for hard disks and the equation of state. The differing structural behaviour of binary systems at different size ratios is also discussed in relation to the nonadditivity. Next, the short- and long-time self-diffusion of particles is considered. Results for the long-time diffusion coefficient are again compared to Monte Carlo simulations, which demonstrates that at long times the dynamic behaviour is effectively not affected by hydrodynamic interactions. Additionally, simple theoretical expressions for the area fraction dependence of the short- and long-time diffusion coefficients are discussed. The selfdynamic properties of particles are probed further using the self-intermediate scattering function and the self-van Hove correlation function. In particular, the extent to which these quantities may be described by the Gaussian approximation is considered in relation to the relevant hydrodynamic limits for colloidal systems. A scaling relation to describe the crossover between these limits at short and long times is also developed. The consideration of dynamic behaviour is then extended to collective phenomena and, in particular, to the process of interdiffusion. Here, the thermodynamic and kinetic drives for this process are explored for binary systems at two different size ratios. The differing interdiffusive effects seen in the two systems are considered in light of the predictions of the Darken equation. Finally, the melting of quasi-two-dimensional colloidal hard spheres is studied by considering a monolayer of particles in sedimentation-diffusion equilibrium. Density profiles and the equation of state are used to characterise the system. These quantities display a discontinuity, indicating a coexistence gap and hence an interface. This interface is located and analysed using capillary wave theory, from which both the size of the coexistence gap and the anisotropic stiffness of the interface are determined.
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Mitchell, Andrew Keith. „Two-channel Kondo phases in coupled quantum dots“. Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:3d4e9d86-794c-441c-9d4b-20e6f1bd1de1.
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We investigate systems comprising chains and rings of quantum dots, coupled to two metallic leads. Such systems allow to study the competition between orbital and spin degrees of freedom in a nanodevice, and the effect this subtle interplay has on two-channel Kondo (2CK) physics. We demonstrate that a rich range of strongly correlated electron behaviour results, with non-Fermi liquid 2CK phases and non-trivial phase transitions accessible. We employ physical arguments and the numerical renormalization group (NRG) technique to analyse these systems in detail, examining in particular both thermodynamic and dynamical properties. When leads are coupled to either end of a chain of dots, we show that the resulting behaviour on low temperature/energy scales can be understood in terms of simpler paradigmatic quantum `impurity' models. An effective low-energy single-spin 2CK model is derived for all odd-length chains, while the behaviour of even-length chains is related fundamentally to that of the classic `two-impurity Kondo' model. In particular, for small interdot coupling, we show that an effective coupling mediated though incipient single-channel Kondo states drives all odd chains to the 2CK fixed point (FP) on the lowest temperature/energy scales. A theory is also developed to describe a phase transition in even chains. We derive an effective channel-anisotropic 2CK model, which indicates that the critical FP of such models must be the 2CK FP. This physical picture is confirmed using NRG for various chain systems. We also examine the effect of local frustration on 2CK physics in mirror-symmetric ring systems. The importance of geometry and symmetry is demonstrated clearly in the markedly different physical behaviour that arises in systems where two leads are either connected to the same dot, or to neighbouring dots. In the latter case, we show for all odd-membered rings that two distinct 2CK phases, with different ground state parities, arise on tuning the interdot couplings. A frustration-induced phase transition thus occurs, the 2CK phases being separated by a novel critical point for which an effective low-energy model is derived. Precisely at the transition, parity mixing of the quasidegenerate local trimer states acts to destabilise the 2CK FPs, and the critical FP is shown to consist of a free pseudospin together with effective single-channel spin quenching. While connecting both leads to the same dot again results in two parity-distinct phases, a simple level-crossing transition now results due to the symmetry of the setup. The proposed geometry also allows access to a novel ferromagnetically-coupled two-channel local moment phase. Driven by varying the interdot couplings and occurring at the point of inherent magnetic frustration, such transitions in ring structures provide a striking example of the subtle interplay between internal spin and orbital degrees of freedom in coupled quantum dot systems, and the resulting effect on Kondo physics.
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Huang, Nathaniel Jian. „Magnetotransport in graphene and related two-dimensional systems“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:4944f2d4-83e5-44ee-90f5-faa35acac80f.
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This thesis describes studies on two-dimensional electron gases (2DEG) in graphene and related 2D systems. Magnetotransport investigations specifically in graphene and its bilayer system are demonstrated in detail, while the experimental techniques presented in this thesis are widely applicable to a large variety of other 2D materials. Chapter 1 gives an introduction and motivation for the principal topic presented in this thesis, with a general introduction to carbon nano-materials and an overview of the current state of graphene-related research and technological development (RTD). Chapter 2 establishes a basic theoretical framework which is essential for interpreting the results presented in this thesis, starting with the crystal and electronic band structures of graphene and its bilayer, followed by high magnetic fields effects on transport properties in these 2D systems. Chapter 3 details the experimental methods directly related to the presented work. The next three chapters report experimental results of three specific magnetotransport studies. Chapter 4 reports the disorder effects on epitaxial graphene in the vicinity of the Dirac point. Quadratic increases of carrier densities with temperature are found to be due to intrinsic thermal excitation combined with electron-hole puddles induced by charged impurities. It is also shown that the minimum conductivity increases with increasing disorder strength, in good agreement with quantum-mechanical numerical calculations. Chapter 5 reports measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to a magnetic field dependent charge transfer process from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels this process is modelled in excellent agreement with experimental results. In Chapter 6, energy relaxation of hot carriers in graphene bilayer systems is investigated from measurements on Shubnikovde Haas oscillations and weak localisation. The hot-electron energy loss rate follows the predicted T4 power-law at carrier temperatures from 1.4 up to about 100 K, due to electron-acoustic phonon interactions. Comparisons are made between graphene monolayer and bilayer systems and a much stronger carrier density dependence of the energy loss rate is found in the bilayer system. This thesis concludes with a summary of the most important findings of the topics that have been discussed. The significance and limitations of the present research are listed. Some suggestions and outlook are given for possible improvements and interesting areas of future research and development.
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Korzycka, Karolina Anna. „Two-photon sensitive protecting groups for biological application“. Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:7e895ed2-04a5-4c0b-9105-74461eae8796.
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Caged compounds are a class of photosensitive reagents used to stimulate cells with spatial control down to a sub-cellular level, and millisecond temporal control. They comprise of biologically important molecule which is modified with a photolabile protecting group. In the absence of light, caged compounds are physiologically silent but irradiation with light induces the release of biologically active species. Illumination under two-photon conditions is particularly advantageous as it enables restriction of the photolysis volume to ~1 fL and it provides deeper penetration into scattering samples. This thesis reports the development of new protecting groups for two-photon uncaging in neuroscience. Mechanistically, the deprotection in these novel groups is designed to operate via an intramolecular photoinduced electron transfer (PeT) between the absorbing unit (electron-donor) and the release module (electron-acceptor). The modular design of these cages ensures separation of absorption and release steps, and allows each process to be tuned and optimized independently. Chapter 1 provides an introduction to the two-photon absorption phenomenon and a historic overview of the uncaging technique. It also discusses recent advances in the development of two-photon sensitive probes used in neuroscience. Chapter 2 describes the exploration of molecular designs for novel protecting groups. A two-photon absorbing dye (electron-donor; fluorene dye) and three different release units (electron-acceptors; nitrobenzyl, pyridinium and phenacyl) were identified as suitable building blocks for the current project. Efficiency of the intramolecular electron transfer between chosen units was evaluated using model dyads which constitute covalently linked electron-donor and acceptor species. Chapter 3 is devoted to the synthesis and photophysical evaluation of nitrobenzyl-based protecting group. Chapter 4 describes the preparation of pyridinium-derived protecting group and demonstrates PeT-mediated release of tryptophan and GABA under one- and two-photon excitation. Hydrolytic instability of pyridinium esters is highlighted. Chapter 5 reports the synthesis, hydrolytic stability and one-photon uncaging efficiency of phenacyl-based derivatives. Chapter 6 discusses properties of developed caged compounds and compares them with other compounds reported in literature. It contains overall conclusions and outlook for the current project. Chapter 7 details the experimental procedures and the characterization of compounds synthesized during this work.
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Kimpton, Laura Saranne. „On two-phase flow models for cell motility“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:93c3cc12-4aac-424d-83bf-3e695efb49fe.
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The ability of cells to move through their environment and spread on surfaces is fundamental to a host of biological processes; including wound healing, growth and immune surveillance. Controlling cell motion has wide-ranging potential for medical applications; including prevention of cancer metastasis and improved colonisation of clinical implants. The relevance of the topic coupled with the naturally arising interplay of biomechanical and biochemical mechanisms that control cell motility make it an exciting problem for mathematical modellers. Two-phase flow models have been widely used in the literature to model cell motility; however, little is known about the mathematical properties of this framework. The majority of this thesis is dedicated to improving our understanding of the two-phase flow framework. We first present the simplest biologically plausible two-phase model for a cell crawling on a flat surface. Stability analyses and a numerical study reveal a number of features relevant to modelling cell motility. That these features are present in such a stripped-down two-phase flow model is notable. We then proceed to investigate how these features are altered in a series of generalisations to the minimal model. We consider the effect of membrane-regulated polymerization of the cell's actin network, the effect of describing the network as viscoelastic, and the effect of explicitly modelling myosin, which drives contraction of the actin network. Validation of hydrodynamical models for cell crawling and spreading requires data on cell shape. The latter part of the thesis develops an image processing routine for extracting the three-dimensional shape of cells settling on a flat surface from confocal microscopy data. Models for cell and droplet settling available in the literature are reviewed and we demonstrate how these could be compared to our cell data. Finally, we summarise the key results and highlight directions for future work.
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He, Zhengyu. „Tuning the electrical and optical properties of two dimensional materials“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d794f6ee-8ea8-4c28-b199-6dbe28992e52.
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The emergence of 2D materials inspires the pursuit of all-2D materials based devices which are predicted to outperform those with conventional architectures and materials. To achieve this goal, thorough understanding of the fundamental electrical and optical properties of 2D materials separately and the ability to manipulate these properties via external modulation methods are essential. Graphene can perform as transparent electrodes, yet suffering from its high sheet resistance. It was demonstrated that it can be greatly reduced via doping iron (III) chloride solution onto graphene film with high optical transmission at visible range if an optimal dopant solution concentration was employed. Doping with nanoscale spatial resolution was then achieved with the help of aberration-corrected transmission electron micro- scope, allowing in-situ observation of the atomic structures of doped regions, which possess unique properties predicted by DFT calculations. Transition metal dichalcogenides (TMDCs) can perform as active materials due to their sizeable bandgap. Therefore, the focus of this thesis then shifted to the investigation of WS2 . Three different methods were employed to alter the optical properties of WS2 . Firstly, the photoluminescence (PL) of WS2 presents layer dependent response towards lateral electric field, with PL quenching in monolayer and PL enhancement in bilayer. The results of temperature dependent PL measurement ruled out the joule heating effect. A possible mechanism based on the inter-valley electron transfer induced recombination pathways modification was then proposed.
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Tinti, Paola. „Between two civilisations : history and self representation of Bangladeshi Buddhism“. Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:fe2861b7-4ec2-4830-810d-a6f60a3e4246.
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Buddhism is believed to have all but died out in India following the thirteenth century Muslim invasion. However, in Bengal groups of non-Bengali people have continued to practice Therāvada Buddhism, which they are said to have imported from nearby Burma, or which they were converted to from other forms of Buddhism after migrating to Bengal. Their practices were "reformed" in 1856 by Burmese monks. An analysis of the historical material reveals a tendency by non-Buddhist Bengalis to downplay any relationship between the Buddhist traditions of Burma and Bangladesh, and to represent Buddhism as a phenomenon of the past. This reinterpretation of historical data is part of the formation process of a Bangladeshi national identity. That this process is in progress is confirmed by the existence in Bangladesh of a centralised and standardised educational system, having among its aims the integration of the national population. Religious education, in Bangladesh as elsewhere, plays within this system an important role in national integration. On the other hand, certain institutions of Bangladeshi Buddhism, such as temporary ordination, and features like the importance attributed to the Mahāmuni temple (which houses a replica of a very sacred Buddha image from Burma) confirm the historical connection between the Bangladeshi and the Southeast Asian Buddhist traditions. Any remaining doubts about the nature of Bangladeshi Buddhism are dispelled by the reading of a devotional song belonging to the genre known as Bauddha pālā kīrtana. The kīrtana, a ballad originating within the Hindu devotional movements, is very popular among all Bengalis, with no distinction of faith. The subject of this text, deriving from an apocryphal birth-story of the Buddha of Southeast Asian origin, reveals once again a link between the Buddhist traditions of Southeast Asia and Bangladesh, its Indian style just indicating regional taste.
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Noonan-Ganley, Joseph. „The contagion of desire : two case studies of appropriation art“. Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:d86430f7-41dd-4b85-b094-2e256b899d9c.
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My doctoral thesis is comprised of two bodies of research: two artworks taking the form of installations (videos, audio recordings, textiles, texts), which will be exhibited for viva. Femme Fabrications, 2016, is made from research into the American artist Joseph Cornell's (1903-1972) source materials held in the Smithsonian American Art Museum alongside research on Jean Wilkinson's 1977 book Flower Fabrications. A series of textile works encased in silk lined boxes trace my step-by-step construction of a rose from organdie. The floral emblem of the white rose (dried), 'death is preferable to a loss of innocence' , becomes an editing device, which I use to consider a number of possible recipients for the rose, such as Cornell himself. Spoken word audio recordings, which ruminate on how his sexuality pertain to the criteria of the rose are edited together with home-camcorder video footage of the house that Cornell lived in for most of his life - the house he made the entirety of his artworks within. Central to The Cesspool of Rapture, 2017, are moving-image studies of zippers, stains, rips, abrasions, openings, and closings in a series of dresses made by the American couturier Charles James (1906-1978). These videos register and move through the material research, the garments, at alternating speeds. The changing speed is registered in sound by clicks synced to each individual frame. It is at times violent and at other times tentative and gentle as the uncovering of the damage to the dresses unfolds. Audio recordings of James explicating his interests in eroticism and sexuality persistently interject the footage. This work includes the installation of a series of reconstructions of James's 1932 Taxi dress. Its black linen body is reconfigured and abstracted as the splayed design makes unfinished seams and unzipped zippers visible. In each artwork I configure viewing and consuming as a mode of authorship. I show how these diverse processes of identification become authored acts. When drawn into intimate relation with the leftover material of these historical authors, my contamination proves deviant: I gain possession of the capacity to speak for them, to expose, idolise, misrepresent, and fictionalise them. My thesis is composed of this group of methodologies, which were found and developed within the production of the artworks.
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Moon, Bill. „Employment of Crystallographic Image Processing Techniques to Scanning Probe Microscopy Images of Two-Dimensional Periodic Objects“. PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/699.
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Thin film arrays of molecules or supramolecules are active subjects of investigation because of their potential value in electronics, chemical sensing, catalysis, and other areas. Scanning probe microscopes (SPMs), including scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are commonly used for the characterization and metrology of thin film arrays. As opposed to transmission electron microscopy (TEM), SPMs have the advantage that they can often make observations of thin films in air or liquid, while TEM requires highly specialized techniques if the sample is to be in anything but vacuum. SPM is a surface imaging technique, while TEM typically images a 2D projection of a thin 3D sample. Additionally, variants of SPM can make observations of more than just topography; for instance, magnetic force microscopy measures nanoscale magnetic properties. Thin film arrays are typically two-dimensionally periodic. A perfect, infinite two-dimensionally periodic array is mathematically constrained to belong to one of only 17 possible 2D plane symmetry groups. Any real image is both finite and imperfect. Crystallographic Image Processing (CIP) is an algorithm that Fourier transforms a real image into a 2D array of complex numbers, the Fourier coefficients of the image intensity, and then uses the relationship between those coefficients to first ascertain the 2D plane symmetry group that the imperfect, finite image is most likely to possess, and then adjust those coefficients that are symmetry-related so as to perfect the symmetry. A Fourier synthesis of the symmetrized coefficients leads to a perfectly symmetric image in direct space (when accumulated rounding and calculation errors are ignored). The technique is, thus, an averaging technique over the direct space experimental data that were selected from the thin film array. The image must have periodicity in two dimensions in order for this technique to be applicable. CIP has been developed over the past 40 years by the electron crystallography community, which works with 2D projections from 3D samples. Any periodic sample, whether it is 2D or 3D has an "ideal structure" which is the structure absent any crystal defects. The ideal structure can be considered one average unit cell, propagated by translation into the whole sample. The "real structure" is an actual sample containing vacancies, dislocations, and other defects. Typically the goal of electron and other types of microscopy is examination of the real structure, as the ideal structure of a crystal is already known from X-ray crystallography. High resolution transmission electron microscope image based electron crystallography, on the other hand, reveals the ideal crystal structure by crystallographic averaging. The ideal structure of a 2D thin film cannot be easily in a spatially selective fashion examined by grazing incidence X-ray or low energy electron diffraction based crystallography. SPMs straightforwardly observe thin films in direct space, but SPM accuracy is hampered by blunt or multiple tips and other unavoidable instrument errors. Especially since the film is often of a supramolecular system whose molecules are weakly bonded (via pi bonds, hydrogen bonds, etc.) both to the substrate and to each other, it is relatively easy for a molecule from the film to adhere to the scanning tip during the scan and become part of the tip during subsequent observation. If the thin film array has two-dimensional periodicity, CIP is a unique and effective tool both for image enhancement (determination of ideal structure) and for the quantification of overall instrument error. In addition, if a sample of known 2D periodicity is scanned, CIP can return information about the contribution of the instrument itself to the image. In this thesis we show how the technique is applied to images of two dimensionally periodic samples taken by SPMs. To the best of our knowledge, this has never been done before. Since 2D periodic thin film arrays have an ideal structure that is mathematically constrained to belong to one of the 17 plane symmetry groups, we can use CIP to determine that group and use it for a particularly effective averaging algorithm. We demonstrate that the use of this averaging algorithm removes noise and random error from images more effectively than translational averaging, also known as "lattice averaging" or "Fourier filtering". We also demonstrate the ability to correct systematic errors caused by hysteresis in the scanning process. These results have the effect of obtaining the ideal structure of the sample, averaging out the defects crystallographically, by providing an average unit cell which, when translated, represents the ideal structure. In addition, if one has recorded a scanning probe image of a 2D periodic sample of known symmetry, we demonstrate that it is possible to use the Fourier coefficients of the image transform to solve the inverse problem and calculate the point spread function (PSF) of the instrument. Any real scanning probe instrument departs from the ideal PSF of a Dirac delta function, and CIP allows us to quantify this departure as far as point symmetries are concerned. The result is a deconvolution of the "effective tip", which includes any blunt or multiple tip effects, as well as the effects caused by adhesion of a sample molecule to the scanning tip, or scanning irregularities unrelated to the physical tip. We also demonstrate that the PSF, once known, can be used on a second image taken by the same instrument under approximately the same experimental conditions to remove errors introduced during that second imaging process. The preponderance of two-dimensionally periodic samples as subjects of SPM observation makes the application of CIP to SPM images a valuable technique to extract a maximum amount of information from these images. The improved resolution of current SPMs creates images with more higher-order Fourier coefficients than earlier, "softer" images; these higher-order coefficients are especially amenable to CIP, which can then effectively magnify the resolution improvement created by better hardware. The improved resolution combined with the current interest in supramolecular structures (which although 3D usually start building on a 2D periodic surface) appears to provide an opportunity for CIP to significantly contribute to SPM image processing.
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Lam, Andy Ka Ming. „Electrophysiological characterization of the human two-pore channel 2“. Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:3a16d16e-f692-40d7-87f7-920151896038.
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The Two-pore channel (TPC1-3) family represents a recently identified class of endolysosomal ion channels. TPCs were originally proposed to be promising candidate channels for NAADP-induced Ca2+ release. However, subsequent studies have emerged to propose an alternative view where TPCs may be Na+-selective channels regulated by the lysosome-specific phosphoinositide PI(3,5)P2 or voltage in an isoform-dependent manner. This thesis asks the question of whether pharmacological and ion permeation properties of TPCs, in particular the human TPC2, may satisfy or may be consistent with the requirement of a potential NAADP-sensitive Ca2+-release channel. These fundamental properties of hTPC2 were approached using patch-clamp electrophysiology and confocal fluorescence microscopy, and were analysed quantitatively to extract relevant physical parameters important to our understanding of their physiological and functional significance. Chapter 2 presents the basic electrophysiological characterisation of hTPC2. It follows a logical way by first determining the ion permeation properties, followed by the investigation of its physical relation with fractional Ca2+ current and Ca2+ nanodomains to rigorously prove that this Na+ selectivity is sufficient to ensure negligible Ca2+ leakage both experimentally and theoretically. This follows the logic that matter must not be created nor destroyed so that a Na+-selective channel that poses a physiologically significant energy barrier to Ca2+ permeation from one side would not lead to the creation of Ca2+ on the other side. Chapter 3 represents a natural progression from Chapter 2 and is aimed at investigating the underlying mechanisms responsible for the electrophysiological ion selectivity observed. This chapter also follows a logical way by first identifying spermine as a high valence intracellular blocker, its mutual antagonism with different external ionic species that allows the determination of ion-binding affinity, followed by the determination of the concentration dependence of ion conduction to identify possible lower affinity binding. By considering all the above qualities, the outcome is a coherent description and connection of ion binding selectivity, kinetic selectivity and ion binding configuration with the observed electrophysiological selectivity. Chapter 4 discusses the missing puzzles and how these questions might be addressed.
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Docherty, Callum James. „Terahertz spectroscopy of graphene and other two-dimensional materials“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:98c03952-dc3f-442b-bbc0-d8397645cc1b.
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In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.
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Lavergne, François Alexandre. „Dynamics of grain boundaries in two-dimensional colloidal crystals“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:257cdd07-1f0d-46b4-9d8f-8530711dafb4.
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The dynamics of grain boundaries in two-dimensional colloidal crystals is studied using optical microscopy and holographic optical tweezing. First, grain growth in a polycrystalline monolayer is investigated. The bond-orientational correlation function is found to satisfy scaling features predicted for systems containing random domain walls. The time-evolution of the correlation length indicates abnormal grain growth, which is shown to be due to the preferential coarsening of the large angle grain boundaries. Next, the segregation of impurities to grain boundaries is studied by embedding large spherical impurities in a polycrystalline monolayer of small colloidal spheres. The segregation behaviour is found to be in very good agreement with equilibrium grain boundary segregation, which enables the direct measurement of the free energy of adsorption. Near saturation, the formation of clusters of impurities in the boundary region is found to strongly depend on the size ratio between the impurities and the small particles, due to non-additivity effects and geometrical constraints imposed by the lattice. In order to characterise the geometry of grain boundaries, a new method to extract their geometrical features directly from microscopy images is developed. This method is used to determine the local normal direction, tangent direction and curvature of a grain boundary in a two-dimensional colloidal polycrystalline material. Further insight between the geometry and dynamics of grain boundaries is gained by analysing the shrinking kinetics of circular grain boundaries created using optical vortices. Upon increasing misorientation, these strongly curved boundaries exhibit a geometrically determined transition between pure sliding and shrinkage. In addition, the shrinking rate is found to decrease when increasing the misorientation. Dislocation reactions, which cause the reduction of the grain boundary length, are directly visualised and correlated to the kinetics of shrinkage. Finally, the dynamics of the particles during the migration of circular grain boundaries is analysed. The presence of dynamical heterogeneities is shown to be strongly determined by geometry, especially in the case of coincident site lattice boundaries where coincident particles exhibit no motion during grain boundary migration. The particle displacements involved in the motion of dislocations, which constitute the elementary mechanism of grain boundary migration, are revealed.
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de, Beyer Jennifer Anne. „Roles of the two chemotaxis clusters in Rhodobacter sphaeroides“. Thesis, University of Oxford, 2013. https://ora.ox.ac.uk/objects/uuid:51a1c753-25d6-4e4f-b09e-eb48bce9e4cb.
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Bacteria swim towards improving conditions by controlling flagellar activity via signals (CheY) sent from chemosensory protein clusters, which respond to changing stimuli. The best studied chemotactic bacterium, E. coli, has one transmembrane chemosensory protein cluster controlling flagellar behaviour. R. sphaeroides has two clusters, one transmembrane and one cytoplasmic. The roles of the two clusters in regulating swimming and chemosensory behaviour are explored here. Newly-developed software was used to measure the effect of deleting or mutating each chemotaxis protein on unstimulated swimming and on the chemosensory response to dynamic change. New behaviours were identified by using much larger sample sizes than previous studies. R. sphaeroides chemotaxis mutants were classified as (i) stoppy unresponsive; (ii) smooth unresponsive or (iii) stoppy inhibited compared to wildtype swimming and chemosensory behaviour. The data showed that the ability to stop during free-swimming is not necessarily connected to the ability to respond to a chemotaxis challenge. The data suggested a new model of connectivity between the two chemosensory pathways. CheY3 and CheY4 are phosphorylated by the transmembrane polar cluster in response to external chemoeffector concentrations. CheY6-P produced by the cytoplasmic cluster is a requirement for chemotaxis, whether or not the polar cluster is able to produce CheY6-P. CheY6-P stops the motor, whereas CheY3,4-P allow smooth swimming. When chemoeffector levels fall, the signals through CheY3,4 fall, allowing CheY6-P to bind and stop the motor. As the polar cluster adapts to the fall by the action of the adaptation proteins CheB1 and CheR2, the concentration of CheY3,4-P increases again, to compete with CheY6-P and allow periods of smooth swimming. Under aerobic conditions, the cytoplasmic cluster controls the basal stopping frequency and does not appear to respond to external chemoeffector changes. The role of the adaptation proteins in resetting the signalling state in R. sphaeroides is unclear, particularly the roles of the proteins associated with the cytoplasmic cluster, CheB2 and CheR3. Tandem mass spectrometry was used to identify glutamate and glutamine (EQ) sites on the cytoplasmic R. sphaeroides chemoreceptor TlpT that are deamidated and methylated by the R. sphaeroides adaptation homologues. In E. coli, adaptation sites are usually EQ/EQ pairs. However the sites reported in TlpT vary at the first residue in the pair. Mutation of the putative EQ adaptation sites caused changes in adaptation, suggesting that CheY6-P levels are controlled and reset by CheB2 and CheR3 controlling the adaptation state of TlpT.
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Chang, Fu-Sheng. „Analysis of two pore channel proteins in Dictyostelium development“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:982eb7bf-900b-4971-9cf5-203125e6557e.
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Calcium is a ubiquitous intracellular signal responsible for controlling numerous cellular responses including development and proliferation. Calcium (Ca2+) is stored in both neutral and acidic stores and its release through gated channels has been implicated in regulating development in Dictyostelium discoideum. This thesis aims to understand the roles of the calcium channel proteins, in particular the two-pore channel proteins (TPCs), found on acidic stores in Ca2+ signalling during Dictyostelium development. Bioinformatic analysis indicates conservation of a gene encoding an orthologue of TPC2 in Dictyostelia and, similar to plant TPCs, a Ca2+ sensing domain is predicted along with a novel potential calmodulin binding site. To investigate the role of intracellular Ca2+ channels, a series of strains was generated, disrupted in one or more of genes encoding the channels TPC2 and mucolipin (TRP-ML), predicted to be located on acidic stores, and IplA, located on neutral stores. All disrupted strains, including one lacking all three channels, are able to complete development. However, strains lacking TPC2 show a pronounced delay in early development, correlating with reduced expression of some early developmental genes. Vesicles derived from tpc2-null cells show normal Ca2+ release compared to parental cells but an increased rate of Ca2+ uptake. During early development, the pH of acidic vesicles is increased in the absence of TPC2. However development of tpc2-null cells showed increased sensitivity to weak bases in producing fewer aggregates but resistance to sodium chloride and weak bases in later development suggesting a complex role for TPC during development. In vivo cytosolic Ca2+ responses were analysed in strains expressing an ultra-sensitive Ca2+ indicator YC-Nano 15. Growing tpc2- and iplA- cells have lower basal cytosolic Ca2+ than parental Ax2 cells. Intercellular Ca2+ waves were observed in aggregates from Ax2, mcln- and tpc2- cells but were greatly reduced in iplA- aggregates, as was the increase in cytosolic Ca2+ in response to extracellular cAMP. In tpc2- aggregates, wave frequencies were reduced and the response to cAMP addition abolished after treatment with caffeine, a known adenylyl cyclase inhibitor in Dictyostelium. This work demonstrates that TPC2 plays a role in the early stages of Dictyostelium development. TPC2 is important for pH regulation in acidic vesicles and cytosolic Ca2+ levels, either or both of which could influence development either directly or via changes in early developmental gene expression.
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Eser, Sophie. „The responsible man : a study in two private prisons“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8274c151-0121-4804-8965-89d48d7d8d25.
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With the expansion of the use of private prisons and detention centres worldwide and the increasing involvement of private actors in the provision of custodial services, this doctoral thesis considers life inside two private prisons in England. Using theoretically informed ethnography it evaluates the effect of responsibility on men imprisoned in two private prisons in England. Firstly, it briefly reviews the background and development of prison privatisation in England and Wales and considers the role and place of private prisons as part of a wider neo-liberal shift. Secondly, using qualitative data gathered inside two private prisons, it evaluates if these prisons, through their regimes, are trying to create responsible self-governing prisoners. The thesis reviews both, how regimes and practices in place in these two prisons attempt to forge responsible prisoners, and how individual men and groups of prisoners experience, feel about, cope with and assimilate penal messages of self-governance and responsibility. Finally, it questions both the impact of responsible prisoners for prisons and the impact of responsibility on prisoners and argues that, whilst there is a benefit to fostering environments in which prisoners are enabled to become responsible and self-governing, a careful balance must be maintained, as for some men the responsibility itself becomes characteristic of the "pain of imprisonment".
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Greenstein, Daniel I. „Urban politics and the urban process : two case studies of Philadelphia“. Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:ed50068a-eeb2-433a-b2ab-279c7296b95f.
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Both academics and the makers of public policy have for a long time been interested in the study of urban politics, but the subject needs to be integrated with the process of urban growth and development. Too frequently, the urban polity is analyzed as an arena which passively reflects or mechanically responds to more fundamental changes in the urban social structure. In this work, case studies of political reform in Philadelphia at two periods, 1800 to 1854 and 1890 to 1915, develop a number of hypotheses about how the urban polity plays an influential role in shaping the process of urban growth and change. Both case studies begin with computer-assisted analyses of changes in the socio-economic and spatial structures of urban society. Such changes are often considered to be fundamental causes of urban political reform either because they altered political elites' interests in municipal government or because they created enormous new demands on existing municipal works and services. The studies show, however, that social structural changes cannot by themselves explain the course of urban political development in the city of Philadelphia. Concentrating primarily on the formulation and implementation of municipal public works, the studies show that in both periods, the course of political reform was often shaped by two things: the 'private' or selfish interests of political actors, and the fragmented financial, administrative and party structures of the urban polity. More important, the studies show how self-interested political activities, in a polity in which authority was highly fragmented, often had consequences which were far reaching in their impact on the structure and experience of urban life. Indeed, the first case study shows how urban politics shaped the process of social group formation in the industrializing city. The second case study shows how the structure and conduct of urban politics determined social groups' political power in the city. The conclusion then demonstrates how the case studies support a number of hypotheses about the relationship between urban politics and urban society which may be applied generally to analyses of the process of urban growth and change.
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De, Angelis Franco. „The evolution of two archaic Sicilian poleis : Megara Hyblaia and Selinous“. Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:f2347179-5efc-4cbe-881b-8bd5579c5849.
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This study attempts to revive T.J. Dunbabin's multi-dimensional approach to the history of Early Iron Age Sicily in The Western Greeks (Oxford 1948). Dunbabin recognised that archaic Sicily had no real history, and that any historical account involved combining the very scant documentary record with the fuller and ever-growing body of archaeological evidence to produce a framework for writing social and economic history. These innovative methods ended with Dunbabin, however: today the field is dominated by scholars impeded artificially by disciplinary boundaries, which discourage the productive combination of historical and archaeological sources, leaving a number of important questions in a sort of academic no man's land. In the introduction an overview of the study of Sicily since Dunbabin is given, and Dunbabin's own weaknesses are explored: Dunbabin modelled Greek colonisation in Sicily on modern British colonisation; such a decision strait-jacketed his image of the past, causing him to draw conclusions unacceptable today. The increase in the quantity of archaeological evidence since Dunbabin means that it is no longer possible to make an in-depth study of the whole of Sicily in a single volume. Consequently, the focus has to be considerably more restricted than Dunbabin's; specific questions need to be selected. Megara Hyblaia and Selinous offer two particular advantages for studying the evolution of Greek settlement in Sicily: besides being Megarian, both are sufficiently well explored archaeologically to make historical investigation profitable, but they were founded a century apart on different sides of the island, in different environmental and socio-political contexts. The study itself is divided into two main parts, the first focusing on Megara Hyblaia and the second on Selinous; each of these two parts consists of five chapters, in which the same questions are asked of the evidence from the two sites, for comparative purposes. Chapters I and VI explore the background to settlement, with such subjects as the native world encountered by the settlers at the time of colonisation, pre- and proto-colonial activity, and the respective foundations of the colonies examined. Settlement development is the subject of chapters II and VII; the emphasis here is to monitor the successive stages of the physical growth of the colonies, and also to study the size and nature of the settlement itself. Chapters III and VIII deal with demography (particularly population size). The following chapters (IV and IX) use archaeological and written evidence to reconstruct socio-political history. Chapters V and X investigate environment and economy. In the closing chapter, after a review of the conclusions reached, the question of why Selinous evolved so differently from it mother-city is addressed. The thesis ends with brief consideration of the (Megarian) Sicilian contribution to the study of the polis.
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Lee, Wei-Koon. „Chaotic mixing in wavy-type channels and two-layer shallow flows“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:f5fcbe34-babb-4fae-9204-28de8774eb98.
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This thesis examines chaotic mixing in wavy-type channels and two-layer shallow water flow. For wavy-type channels, the equations of motion for vortices and fluid particles are derived assuming two-dimensional irrotational, incompressible flow. Instantaneous positions of the vortices and particles are determined using Lagrangian tracking, and are conformally mapped to the physical domain. Unsteady vortex motion is analysed, and vortex-induced chaotic mixing in the channels studied. The dynamics of mixing associated with the evolution of the separation bubble, and the invariant manifolds are examined. Mixing efficiencies of the different channel configurations are compared statistically. Fractal enhancement of productivity is identified in the study of auto-catalytic reaction in the wavy channel. For the two-layer shallow water model, an entropy-correction free Roe type two-layer shallow water solver is developed for a hyperbolic system with non-conservative products and source terms. The scheme is well balanced and satisfies the C-property such that smooth steady solutions are second order accurate. Numerical treatment of the wet-dry front of both layers and the loss of hyperbolicity are incorporated. The solver is tested rigorously on a number of 1D and 2D benchmark test cases. For 2D implementation, a dynamically adaptive quadtree grid generation system is adopted, giving results which are in excellent agreement with those on regular grids at a much lower cost. It is also shown that algebraic balancing cannot be applied directly to a two-layer shallow water flow due to the lack of simultaneous referencing for the still water position for both layers. The adaptive two-layer shallow water solver is applied successfully to flow in an idealised tidal channel and to tidal-driven flow in Tampa Bay, Florida. Finally, chaotic advection and particle mixing is studied for wind-induced recirculation in two-layer shallow water basins, as well as Tampa Bay, Florida.
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Walter, Sarah E. „One for you, two for me : quantitative sharing by young children“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:bdf38c29-1fda-41ab-b1c1-c675bc1d39c4.
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The current research aimed to examine children’s understanding of cardinality by looking at their ability to use several quantitative concepts that underpin this understanding: correspondence, counting and equivalence in the context of sharing. Understanding cardinality requires children to develop knowledge about the relations between these quantitative concepts which is important for the development of mathematical reasoning. The first study aimed to investigate how flexibly children can use correspondence to build equivalent sets in different types of sharing scenarios: equal sharing, reciprocity and equity. In some situations two characters each received one object at a time, and in others one character received double units while the other character received single units. After children shared blocks between the two characters, they were asked to make a number inference about the cardinal of one set after counting a second, equivalent set. Children had more difficulty sharing in the reciprocity and equity conditions than the equal sharing condition. The majority of children were able to make number inferences in the equal sharing and reciprocity conditions where both characters received equivalent shares in the end. A second study with new groups of four and five- year-olds investigated whether children were using visual cues about the relation between double and single blocks to help build equivalent sets and make number inferences. It was predicted that the use of coins would be difficult and would increase the difference between the equal sharing and reciprocity conditions. In half of the trials children shared Canadian $2 and $1 coins and in half they shared blocks. There are no visual cues about the relation between $2 and $1 coins because they are the same size. Children were allowed to use counting or correspondence to build equivalent sets to compare their use of both strategies. Contrary to the first study, the reciprocity and equal sharing conditions were not significantly different. This may be due to the appearance of a new sharing strategy in the reciprocity condition termed “equalizing” where children first counted each set, dealt singles to make the two sets equal and then shared blocks or coins on a one-to-one basis. There was also no significant difference between the trials using coins and trials using blocks. The majority of children were able to answer the number inference questions correctly, however 25% of children made the number inference after sharing all singles but not after sharing doubles and singles, suggesting that using different units did impact their understanding of the equivalence of the two sets. A third study aimed to investigate children’s ability to coordinate cardinal and ordinal information to determine the cardinal of a single set, and their ability to coordinate counting principles with knowledge of equivalence to determine the cardinal of an equivalent set. Children in this study were asked to make a numerical inference about a set of blocks after watching a puppet correctly or incorrectly count an equivalent set of blocks. Many children were able to identify that the puppet did not count correctly, but struggled to correct the mistake. This indicates a gap in their knowledge about ordinality and cardinality in the context of a single set. The miscount also impacted their ability to make a correct number inference. Children performed significantly better on trials where the puppet counted correctly than trials where he made a counting error. This suggests that while children have good knowledge of counting principles in isolation, they are still developing an understanding of how to coordinate these principles with ordinal information and knowledge of equivalence to establish the cardinal of one set and to infer the cardinal of an equivalent set.
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Lenhardt, Rastislav. „Two variable and linear temporal logic in model checking and games“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:b4de8937-4a4a-4281-92e7-aa4e93283250.
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Model checking linear-time properties expressed in first-order logic has non-elementary complexity, and thus various restricted logical languages are employed. In the first part of this dissertation we consider two such restricted specification logics on words: linear temporal logic (LTL) and two-variable first-order logic (FO2). LTL is more expressive but FO2 can be more succinct, and hence it is not clear which should be easier to verify. We take a comprehensive look at the issue, giving a comparison of verification problems for FO2, LTL, and various sublogics thereof across a wide range of models. In particular, we look at unary temporal logic (UTL), a subset of LTL that is expressively equivalent to FO2. We give three logic-to-automata translations which can be used to give upper bounds for FO2 and UTL and various sublogics. We apply these to get new bounds for model checking both non-deterministic systems (hierarchical and recursive state machines, games) and for probabilistic systems (Markov chains, recursive Markov chains, and Markov decision processes). Our results give a unified approach to understanding the behaviour of FO2, LTL, and their sublogics. We further consider the problem of computing maximal probabilities for interval Markov chains (and recursive interval Markov chains, stochastic context-free grammars) to satisfy LTL specifications. Using again our automata constructions we describe an expectation-maximisation algorithm to solve this problem in practice. Our algorithm can be seen as a variant of the classical Baum-Welch algorithm on hidden Markov models. We also introduce a publicly available on-line tool Tulip to perform such analysis. Finally, we investigate the extension of our techniques from words to trees. We show that the parallel between the complexity of FO2 satisfiability on general and on restricted structures breaks down as we move from words to trees, since trees allow one to encode alternating exponential time computation.
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Al-Assam, Sarah. „Quantum simulation using ultracold atoms in two-dimensional optical lattices“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:9a7ade78-561d-4d8d-87e4-1781c6b8454c.
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Ultracold atoms in optical lattices can be used to model condensed matter systems. They provide a clean, tuneable system which can be engineered to reach parameter regimes that are not accessible in condensed matter systems. Furthermore, they provide different techniques for probing the properties of these systems. This thesis presents an experimental and theoretical study of ultracold atoms in optical lattices for quantum simulation of two-dimensional systems.The first part of this thesis describes an experiment with a Bose-Einstein condensate of 87Rb loaded into a two-dimensional optical lattice. The beams that generate the optical lattice are controlled by acousto-optic deflection to provide a flexible optical lattice potential. The use of a dynamic ‘accordion’ lattice with ultracold atoms, where the spacing of the lattice is increased in both directions from 2.2 to 5.5 μm, is described. This technique allows an experiment such as quantum simulations to be performed with a lattice spacing smaller than the resolution limit of the imaging system, while allowing imaging of the atoms at individual lattice sites by subsequent expansion of the optical lattice. The optical lattice can also be rotated, generating an artificial magnetic field. Previous experiments with the rotating optical lattice are summarised, and steps to reaching the strongly correlated regime are discussed. The second part of this thesis details numerical techniques that can be used to describe strongly correlated two-dimensional systems. These systems are challenging to simulate numerically, as the exponential growth in the size of the Hilbert space with the number of particles means that they can only be solved exactly for very small systems. Recently proposed correlator product states [Phys. Rev. B 80, 245116 (2009)] provide a numerically efficient description which can be used to simulate large two-dimensional systems. In this thesis we apply this method to the two-dimensional quantum Ising model, and the Bose-Hubbard model subject to an artificial magnetic field in the regime where fractional quantum Hall states are predicted to occur.
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Helmers, Michael. „Kinks in a model for two-phase lipid bilayer membranes“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:15343985-1b1c-4123-838d-8e157e837db1.
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In the spontaneous curvature model for two-phase lipid bilayer membranes the shape of vesicles is governed by a combination of an elastic bending energy and an interface energy that penalises the size of phase boundaries. Each lipid phase induces a preferred curvature to the membrane surface, and these curvatures as well as phase boundaries may lead to the development of kinks. In a rotationally symmetric setting we introduce a family of energies for smooth surfaces and phase fields for the lipid components and study convergence to a sharp-interface limit, which depends on the choice of the bending parameters of the phase field model. We prove that, if kinks are excluded, our energies $Gamma$-converge to the commonly used sharp-interface spontaneous curvature energy with the additional assumption of $C^1$-regularity across interfaces. For a choice of parameters such that kinks may appear, we obtain a limit that coincides with the $Gamma$-limit on all reasonable membranes and extends the classical model by assigning a bending energy also to kinks. We illustrate the theoretical result by some numerical examples.