Dissertations / Theses on the topic 'Coherence'

Abstract This thesis describes the application of Low Coherence Interferometry (LCI) and Optical Coherence Tomography (OCT) in paper measurements. The developed measurement system is a combination of a profilometer and a tomographic imaging device, which makes the construction versatile and applicable in several paper measurement applications. The developed system was first used to measure the surface structure of paper. Different grades of paper were selected to provide maximum variation in surface structure. The results show that the developed system is capable of measuring grades of paper from rough base paper to highly coated photo printing paper. To evaluate the developed system in surface characterization, the roughness parameters of five laboratory-made paper samples measured with the developed system and with a commercial optical profilometer were compared. A linear correlation was found with roughness parameters Ra and Rq. Next, the surface quality of paper was evaluated using LCI, a Diffractive Optical Element Based Glossmeter (DOG), and a commercial glossmeter. The results show linear correlation between Ra and gloss measured with the commercial glossmeter. The roughness Ra and averaged gloss measured with the DOG didn't give such a correlation, but a combination of these techniques provided local properties of gloss and surface structure, which can be used to evaluate the local surface properties of paper. In the next study, determination of the filler content of paper using OCT is discussed. The measurement results show clear correspondence of the slope of the averaged logarithmic fringe signal envelope and the filler content. The last studies focus on 2D and 3D imaging of paper using OCT and begin with imaging of a self-made wood fiber network. The visibility of the fibers was clear. Next, several refractive index matcing agents are studied by means of light transmittance and OCT measurements to find the best possible agent for enhancing the imaging depth of OCT in paper. Benzyl alcohol was found to have the best possible combination of optical, evaporation, and sorption characteristics, and it is applied in 2D and 3D visualizations of copy paper.

Coherence and entanglement are the two key concepts that distinguish quantum mechanics from classical mechanics. Many novel phenomena occuring in the quantum world are due to these two “physical quantities”. They also play essential roles in quantum computation and quantum information. For example, coherence, which says that a quantum mechanical system could be in a superposition state, makes the quantum parallel computing scheme possible; and entanglement, which says that two quantum systems separated in space could be in an intervened state, is the key factor in various quantum teleportation algorithms. We have studied entanglement generation in various systems. We found that with atomic coherence, entanglement could be generated between two thermal fields with arbitrarily high temperatures. We also found that temperature difference instead of the purity of state is essential for the entanglement generation between an atom and a thermal field. We discovered that correlated spontaneous emission lasers (CELs) could be used to generate bright entanglement laser beams. As a special case of CEL systems, we studied entanglement generation in Non-degenerate Optical Parametric Amplifiers (NOPAs). We performed the input-output calculations for a NOPA system and showed that the two output optical beams are still entangled. This justifies our idea that CEL (or NOPA) systems can be used as an ideal entanglement source for various quantum information schemes. From an experimental point of view, we considered the effects of pumping fluctuations on entanglement generation in CEL and NOPA systems. We found that these fluctuations, especially the phase diffusion processes, in the pump laser would greatly reduce the entanglement generated in such systems.

In this thesis, we introduce a novel model based on the idea of autoencoders. Different from a classic autoencoder which reconstructs its own inputs through a neural network, our model is closer to Kernel Canonical Correlation Analysis (KCCA) and reconstructs input data from another data set, where these two data sets should have some, perhaps non-linear, dependence. Our model extends traditional KCCA in a way that the non-linearity of the data is learned through optimizing a kernel function by a neural network. In one of the novelties of this thesis, we do not optimize our kernel based upon some prediction error metric, as is classical in autoencoders. Rather, we optimize our kernel to maximize the "coherence" of the underlying low-dimensional hidden layers. This idea makes our method faithful to the classic interpretation of linear Canonical Correlation Analysis (CCA). As far we are aware, our method, which we call a Kernel Coherence Encoder (KCE), is the only extent approach that uses the flexibility of a neural network while maintaining the theoretical properties of classic KCCA. In another one of the novelties of our approach, we leverage a modified version of classic coherence which is far more stable in the presence of high-dimensional data to address computational and robustness issues in the implementation of a coherence based deep learning KCCA.

Thesis (Ph.D.) - University of Glasgow, 2003.
Ph.D. thesis submitted to the Department of Cardiovascular and Medical Sciences, Faculty of Medicine, University of Glasgow, 2003. Includes bibliographical references. Print version also available.

Recent musicological output has viewed neither the aesthetic concept of organicism nor the methodology of formalistic music analysis in a favourable light. Both organicism and formalistic music analysis in the current age have been plagued by criticisms concerning its validity, purpose, and function. Thus there has been a decrease in the perceived value and usefulness of both organicism as means of rendering contemporary post-tonal compositions as cohesive entities and music analysis as a means of elucidating such organic musical construction. My aims for my thesis are, at its simplest, two-fold. Drawing upon the aesthetics of organicism and cohesion as seen in Schoenberg’s writings, I aim primarily to espouse both the purpose and effectiveness of organicism as well as music analysis in rendering art music of the twentieth and twenty-first centuries comprehensible. I also argue that organicism must be accompanied by contrast in order to maintain musical variety and interest, and I explain how I, as a composer, satisfy these two imperatives in my own compositional output. A comprehensive motivic analysis of selected works from the twentieth century in conjunction with analyses of my own compositions created as part of this degree will not only demonstrate the presence of organicism but will also argue its value in achieving coherence in post-tonal music. Investigating the intervallic properties inherent in the primary musical material of each work will demonstrate the multifaceted ways in which the composer in question takes advantage of these properties to create a work that is simultaneously diverse yet unified in its structure. A consideration of the work’s construction on both the micro and macro scale (that is, the ways in which musical cells both interact and develop on local and global levels) will demonstrate how the composer has generated an organic structural trajectory through the manipulation of a small musical cell; it will also demonstrate how such an organic structure can create meaningful and coherent listenings of the work. I aim to convey the ways in which I and the selected composers develop material to achieve variety whilst maintaining unifying musical elements. I hope to convince the reader of the value of employing a motivic-based approach when composing post-tonal works due to its possibilities of ensuring musical coherence.

Ce memoire est une contribution a l'etude des coherence optique et coherence de spin dans les puits quantiques a semiconducteur. Les manifestations de ces coherences sont observees sur la luminescence au cours d'experiences de spectroscopie optique ultra-rapide. La conservation de la coherence de spin de l'electron ou de l'exciton conduit a la mesure precise des facteurs de lande de l'electron, du trou, ou de l'exciton, a l'aide d'experiences de battements quantiques de spin. La conservation de la coherence optique de l'exciton permet le controle coherent de la phase de l'etat quantique d'un systeme excitonique. Nous mesurons ainsi le temps de dephasage optique en etudiant la perte de la coherence. A forte densite, nous etudions les effets de l'interaction d'echange interexcitons. Outre l'impact de cette interaction sur la coherence optique, nous rapportons de nouvelles manifestations touchant a la largeur des raies spectrales, a leur decalage, ainsi qu'un phenomene de saturation de l'absorption.

Thesis (PhD)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: This dissertation explores the utility of using Complexity studies to improve our understanding of peacebuilding and the coherence dilemma, which is regarded as one of the most significant problems facing peacebuilding interventions. Peacebuilding is said to be complex, and this study investigates what this implies, and asks whether Complexity could be of use in improving our understanding of the assumed causal link between coherence, effectiveness and sustainability. Peacebuilding refers to all actions undertaken by the international community and local actors to consolidate the peace – to prevent a (re)lapse into violent conflict – in a given conflict-prone system. The nexus between development, governance, politics and security has become a central focus of the international effort to manage transitions, and peacebuilding is increasingly seen as the collective framework within which these diverse dimensions of conflict management can be brought together in one common framework. The coherence dilemma refers to the persistent gap between policy-level assumptions about the value and causal role of coherence in the effectiveness of peacebuilding and empirical evidence to the contrary from peacebuilding practice. The dissertation argues that the peacebuilding process is challenged by enduring and deep-rooted tensions and contradictions, and that there are thus inherent limits and constraints regarding the degree to which coherence can be achieved in any particular peacebuilding context. On the basis of the application of the general characteristics of Complexity to peacebuilding, the following three recommendations reflect the core findings of the study: (1) Peacebuilders need to concede that they cannot, from the outside, definitively analyse complex conflicts and design ‘solutions’ on behalf of a local society. Instead, they should facilitate inductive processes that assist knowledge to emerge from the local context, and such knowledge needs to be understood as provisional and subject to a continuous process of refinement and adaptation. (2) Peacebuilders have to recognise that self-sustainable peace is directly linked to, and influenced by, the extent to which a society has the capacity, and space, to selforganise. For peace consolidation to be self-sustainable, it has to be the result of a home-grown, bottom-up and context-specific process. (3) Peacebuilders need to acknowledge that they cannot defend the choices they make on the basis of pre-determined models or lessons learned elsewhere. The ethical implications of their choices have to be considered in the local context, and the effects of their interventions - intended and unintended - need to be continuously assessed against the lived-experience of the societies they are assisting. Peacebuilding should be guided by the principle that those who will have to live with the consequences should have the agency to make decisions about their own future. The art of peacebuilding lies in pursuing the appropriate balance between international support and home-grown solutions. The dissertation argues that the international community has, to date, failed to find this balance. As a result, peacebuilding has often contributed to the very societal weaknesses and fragilities that it was meant to resolve. On the basis of these insights, the dissertation concludes with a call for a significant re-balancing of the relationship between international influence and local agency, where the role of the external peacebuilder is limited to assisting, facilitating and stimulating the capacity of the local society to self-organise. The dissertation thus argues for reframing peacebuilding as something that must be essentially local.
AFRIKAANSE OPSOMMING: Hierdie proefskrif ondersoek die toepaslikheid van Kompleksiteitstudies om ons begrip van vredesbou en die dilemma van koherensie te verbeter, wat as een van die gewigtigste probleme vir die toetrede tot vredesbou beskou kan word. Vredesbou word as kompleks beskou en die implikasies van hierdie siening word in hierdie proefskrif ondersoek. Dienooreenkomstig word die vraag na die nut van Kompleksiteitstudies vir die verbetering van ons begrip van die veronderstelde kousale verband tussen koherensie, doeltreffendheid en volhoubaarheid aangespreek. Vredesbou verwys na alle handelinge wat deur die internasionale gemeenskap en plaaslike belanghebbendes onderneem word om vrede binne ʼn gegewe sisteem, wat neig na konflik, te konsolideer om sodoende ’n (her)verval in gewelddadige konflik te voorkom. Die aanknopingspunt tussen ontwikkeling, staatsbestuur, staatkunde en sekuriteit is tans die sentrale fokus van die internasionale poging om sodanige oorgange te beheer, en vredesbou word toenemend as ’n kollektiewe raamwerk beskou, waarbinne hierdie onderskeie dimensies van konflikbestuur in een gemeenskaplike raamwerk saamgebring kan word. Die koherensiedilemma verwys na die voortdurende gaping tussen beleidsvlakaannames ten opsigte van die waarde en kousale rol van koherensie vir die doeltreffendheid van vredesboupogings en empiriese data vanuit die vredesboupraktyk wat hierdie aanvaarde kousale verband weerspreek. Die proefskrif toon dat vredesboupogings uitgedaag word deur voortdurende en diepgewortelde spanninge en teenstrydighede, en dat daar dus inherente beperkings en stremmings is ten opsigte van die mate waartoe koherensie binne enige spesifieke vredesboukonteks moontlik is. Op grond van die toepassing van die algemene kenmerke van Kompleksiteitstudies op die vredesbouproses, weerspieël die volgende drie aanbevelings die kernbevindings van die studie: (1) Vredesbouers moet toegee dat hulle nie daartoe in staat is om komplekse konflikte van buite af bepalend te analiseer en ‘oplossings’ namens ’n plaaslike gemeenskap te ontwerp nie. Hulle behoort eerder induktiewe prosesse te fasiliteer om ondersteuning te bied sodat kennis uit die plaaslike konteks na vore kom, en sodanige kennis moet as voorlopig en onderhewig aan ’n voortdurende proses tot verfyning en aanpassing, verstaan word. (2) Vredesbouers moet besef dat die selfvolhoubaarheid van vrede direk verband hou met, en beïnvloed word deur, die mate waartoe ’n gemeenskap oor die vermoë tot en ruimte vir selforganisering beskik. Vir vredeskonsolidering om selfvolhoubaar te wees, moet die proses wat daartoe aanleiding gee inheems, van ‘onder-na-bo’ en konteks-spesifiek wees. (3) Vredesbouers moet aanvaar dat hulle nie die besluite wat hulle neem op grond van voorafbestaande modelle of lesse wat elders geleer is kan regverdig nie. Die etiese implikasies van hulle besluite moet in terme van die plaaslike konteks beoordeel word, en die effekte van hulle ingrepe – bepland en onbepland – moet voortdurend opgeweeg word teen die daaglikse ervaring van die samelewings wat bygestaan word. Vredesbehoupogings behoort gelei te word deur die beginsel dat diegene wat met die gevolge van die proses sal moet saamleef, die agentskap behoort te hê om besluite oor hulle eie toekoms te neem. Die kuns van vredesbou lê in die vasstel van ’n toepaslike balans tussen internasionale ondersteuning en inheemse oplossings. Die proefskrif se argument is dat die internasionale gemeenskap tot dusver daarin gefaal het om hierdie balans te vind. As gevolg hiervan het pogings tot vredesbou dikwels bygedra tot die presiese swakhede en broosheid in die gemeenskap wat dit veronderstel was om aan te spreek. Op grond van hierdie insigte sluit die proefskrif af met ’n beroep tot ’n betekenisvolle herbalansering van die verhouding tussen internasionale invloed en plaaslike agentskap, waarin die rol van die eksterne vredesbouer beperk moet word tot die ondersteuning, fasilitering en stimulering van die plaaslike gemeenskap se vermoë tot selforganisering. Die proefskrif bepleit dus dat vredesbou herontwerp word binne ’n essensieel plaaslike raamwerk.

Nous proposons dans ce travail un nouveau formalisme qui nous permet de decrire de facon homogene les principales definitions de coherences memoire uniformes. Nous etudions ensuite la coherence causale qui permet un plus grand parallelisme que la coherence sequentielle habituelle. Nous proposons une nouvelle solution algorithmique permettant de maintenir efficacement la coherence causale. Cette solution est basee sur l'evolution de numeros de version. Nous l'avons mise en oeuvre au-dessus du systeme d'exploitation chorus. Des extensions ont ete apportees a notre solution pour diminuer les tailles de message et pour gerer la coherence d'une meme donnee selon plusieurs politiques simultanees. Nous appelons cette nouvelle forme de partage la polycoherence.

This thesis introduces a skeletal representation of the "kind" of individual Doris Lessing promotes in her work. Organized around five semantic qualifiers, this analysis explores a number of Lessing's works belonging to several literary categories for evidence of the appearance of the daring, self-aware, public, engaged, and vocal individual. It argues that Lessing, as a humanist, is committed to individual personal actualization but that this is tempered with her personnally held views about what is valuable and enriching human experience. It concludes that as author of fictional tales, autobiographical texts as well as political essays, she designs the path of self-development she considers worthy of mention.

In Part I, we propose a new method for dynamic nuclear polarisation in a quasi one-dimensional quantum wire utilising the spin-orbit interaction, the hyperfine interaction, and a finite source-drain potential difference. In contrast with previous methods, our scheme does not rely on external magnetic or optical sources which makes local control much more feasible. Using this method, a significant polarisation of a few per cent is possible in currently available InAs wires which may be detected by conductance measurements. This may prove useful for nuclear magnetic resonance studies in nanoscale systems as well as in spin-based devices where external magnetic and optical sources will not be suitable. In Part II, we study an electron-hole gas within a microcavity, which is a system that exhibits spontaneous quantum coherence. We consider a model of electrons and holes interacting with each other via Coulombic forces and coupled to light in the cavity. We propose a variational mean-field ansatz for the ground state of zero temperature that consists of a coherent photonic part and bound electron-hole pairs. By minimising the free energy, variational equations are derived and their solutions presented in the low and high excitonic density regimes, corresponding to analytical results. In the dilute limit, atomic excitons (bound electron-hole pairs) are Bose condensed; and at high densities, there is pairing in momentum space to give an excitonic insulator. The intermediate regime is calculated numerically. Finally, we discuss the phase diagram and make correspondence with finite temperatures.

The phase coherent properties of electrons in low temperature graphene are measured and analyzed. I demonstrate that graphene is able to coherently transport spin-polarized electrons over micrometer distances, and prove that magnetic defects in the graphene sheet are responsible for limiting spin transport over longer distances. It is shown that these magnetic defects are also partly responsible for the high decoherence (phase loss) observed at low temperature, and that another (as yet unknown) non-magnetic mechanism is required to explain the remainder. Similar measurements are used to probe and characterize the size scales of the roughness of the graphene sheet. The effects of an in-plane magnetic field threading through the rough graphene sheet are analogous to the effects of the built-in strain; I argue that the observed large valley-dependent scattering rates are a consequence of this built-in strain. I also describe an original, robust technique for extracting coherence information from conductance fluctuations. The technique is demonstrated in experiments on graphene, used to efficiently detect the presence of magnetic defects. This new approach to studying phase coherence can be easily carried over to other mesoscopic semiconducting systems.

TELECOMUNICAÇÕES BRASILEIRAS S/A
Reflectometria óptica de baixa coerência tem se tornado uma importante ferramenta para a caracterização de componentes ópticos e optoeletrônicos integrados, cujas dimensões são micrométricos. Este trabalho inclui os princípios básicos de reflectometria, um estudo aprofundado de reflectometria óptica de baixa coerência, uma revisão das técnicas demonstradas na literatura cientifíca e suas resoluções e, principalmente, uma nova topologia na montagem experimental. Esta nova topologia permite que as mediadas sejam feitas de maneira mais simples e eficaz. A resolução obtida ficou tão boa que permitiu a visualização dos modos de propagação TE E TM na cavidade de um laser semicondutor.
Optical low Coherence Reflectometry has become an important tool for the characterization of optical and integrated optoeletronics components of dimensions on the micrometer scale. This work includes the basic principles of reflectometry, a detailed study of optical low coherence reflectometry, a review of the techniques reported in the literature and a new scheme for the experimental set-up. This new scheme has proved to be simpler and more efficient. In addition the high resolution achieved allowed the visual observation of the TE and TM propagation modes in the semiconductior cavity.

Coherence ensures individual sentences work together to form a meaningful document. When properly translated, a coherent document in one language should result in a coherent document in another language. In Machine Translation, however, due to reasons of modeling and computational complexity, sentences are pieced together from words or phrases based on short context windows and with no access to extra-sentential context. In this thesis I propose ways to automatically assess the coherence of machine translation output. The work is structured around three dimensions: entity-based coherence, coherence as evidenced via syntactic patterns, and coherence as evidenced via discourse relations. For the first time, I evaluate existing monolingual coherence models on this new task, identifying issues and challenges that are specific to the machine translation setting. In order to address these issues, I adapted a state-of-the-art syntax model, which also resulted in improved performance for the monolingual task. The results clearly indicate how much more difficult the new task is than the task of detecting shuffled texts. I proposed a new coherence model, exploring the crosslingual transfer of discourse relations in machine translation. This model is novel in that it measures the correctness of the discourse relation by comparison to the source text rather than to a reference translation. I identified patterns of incoherence common across different language pairs, and created a corpus of machine translated output annotated with coherence errors for evaluation purposes. I then examined lexical coherence in a multilingual context, as a preliminary study for crosslingual transfer. Finally, I determine how the new and adapted models correlate with human judgements of translation quality and suggest that improvements in general evaluation within machine translation would benefit from having a coherence component that evaluated the translation output with respect to the source text.

In this work our aim is to study several aspects related to quantum coherence as understood to correspond with the non-classical behaviour that can be observed for certain particular states of a physical system. In particular we are interested in the possible mechanisms that result in dynamically induced transitions between quantum and classical regimes. The thesis is organized as follows: The first chapter dubs as an introduction and serves to set out the basic philosophy underlying the questions addressed in this thesis. It also presents some elementary properties of states and state spaces in Quantum Theory including what we have chosen to define as classical and quantum behaviour. In chapter 2 we study some of the aspects related to observing quantum behaviour and of the properties of our main definition of classicality (and quantumness). Here we also study some of the restrictions imposed on measurements by the existence of globally conserved quantities (Wigner-Araki-Yanase theorem) and their relationship to weak measurements coupled to postselection. In the following chapter we review some of the basic tools used in the description of open quantum system dynamics that will be applied in other chapters. In chapter 4 we review the basics of decoherence and analyse the importance of the choice of initial conditions when trying to study the dynamical emergence of classical behaviour within Quantum Theory. Next we study the other direction of the transition and focus on how to obtain pure quantum states from states that originally were classically mixed. Along the same lines, in chapter 6 we cover some topics related to the production of pure quantum states from measurements. We pay special attention to a model of the non-selective continuous monitoring of a system coupled to another unmonitored system. Lastly we explore some of the possible similarities between the theory of phase transitions and the quantum-classical transition. We must emphasize that all the work done in this thesis assumes that Quantum Theory is generally valid (at least within a broad enough range of energies). Thus, when we say that a state is "classical" we will mainly be referring to one of all the possible states contained in Quantum Theory, but that is susceptible to being interpreted as corresponding to "classical" behaviour. Similarly when we speak of creating a "quantum", or "quantum coherent", state we mean that the system has evolved to this state from one of the "classical" ones, but all of these still correspond to valid states within Quantum Theory. In the opinion of the author the main original contributions that can be found in this thesis are the following: - The recognition of the relationship between the Wigner-Araki-Yanase theorem and weak measurements coupled to postselection (sections 2.2 and 2.4); - A mathematical proof of the possible ambiguities arising when two observers try to decide if a state corresponds to quantum or classical behaviour (section 2.6); - The implications of initial correlations in decoherence models. In particular how the choice of certain (correlated) initial conditions can result in residual coherence and the production of pure quantum states in a model that otherwise results in ideal decoherence when (locally equivalent) uncorrelated initial conditions are used (section 4.2); - Various results related to the production of quantum states from initially classical states (sections 5.2 to 5.4); - The analysis of the inverse of a generalized depolarizing channel (section 5.7); - The study of a model of the non-selective continuous monitoring, in the quantum Zeno limit, of a subsystem A interacting with an unmonitored subsystem B. In particular the absence of the purification of B, which has been previously predicted in the selective case, but the possibility of coherent dynamics for B (section 6.4); - The identification of the loose equivalent of a broken symmetry and order parameter in the quantum-classical transition (section 7.2).

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 159-184).
Nanotechnology and optoelectronics have the potential to revolutionize the medicine, communications, and energy industries, with applications utilizing nanotechnology beginning to appear. However, there are still fundamental questions about optoelectronic devices incorporating nanotechnology. In particular, how do nanometer-scale materials affect potential functionality, and how can we take advantage of this scale to design nanomaterials for applications? Natural light harvesting systems in bacteria and plants provide exquisite examples of nanomaterial design, featuring remarkably efficient light harvesting antennas. Sunlight absorption first creates excitons. Complex antenna architectures control the excitons, directing them to reaction centers for conversion to chemical energy. Recently, studies found that excitonic interactions play a significant role in controlling antennas' light harvesting abilities, and that coherence may greatly affect energy transport efficiencies. While these studies have propelled our understanding of excitons in these systems, it is desirable to extend our expertise to artificial systems. In this thesis I describe experiments uncovering many fundamental properties of excitons in various nanostructured materials, relating physical structure to excitonic structure and perhaps to subsequent function in an excitonic device. Nonlinear spectroscopy offers distinct possibilities for detailed exploration of excitonic properties and processes in nanomaterials. Transient grating experiments are sensitive to population dynamics and energy transport, while multi-dimensional spectroscopy clearly reveals excitonic interactions, correlations, and coherence. In this thesis, these techniques are performed with a unique multi-dimensional spectrometer using femtosecond pulse shaping. I present results on two classes of artificial nanostructures: supramolecular J-aggregates and semiconductor quantum wells. In J-aggregate thin films I determined that coherence is controlled by thermal dephasing rather than film inhomogeneities, even at cryogenic temperatures. Tubular J-aggregates in solution undergo morphological rearrangement while maintaining a common sub-unit that remains relatively intact both structurally and excitonically. In semiconductor quantum wells, many-body correlations among excitons were shown to decay on the timescale picoseconds, depending on the exciton density and therefore revealing of high-order correlations. These insights into coherence and excitonic structure are important in determining the origin and strength of coherence in excitonic systems, potentially leading toward methods to alter or control exciton dynamics and toward possible novel application of coherence in optoelectronic devices.
by Dylan H. Arias.
Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1993.
Includes bibliographical references (leaves 33-34).
by Gabrielle M. Owen.
B.S.

La coherència quàntica, o la propietat dels sistemes que es troben en una superposició d’estats capaç de donar lloc a patrons d’interferència en els experiments adequats, és el segell distintiu de la mecànica quàntica. Més enllà de les seves fascinants implicacions epistemològiques, la coherència quàntica resulta també un recurs valuós a l’hora de dur a terme diferents tasques quàntic-informacionals i ha estat fins i tot emprada en la descripció de certs processos biològics. Per aquest motiu s’ha fet necessari el desenvolupament d’una teoria de recursos que formalitzi rigorosament la noció de coherència, i que permeti així quantificar la coherència present en els sistemes físics, així com estudiar la seva manipulació amb vista a un millor aprofitament d’aquest recurs. Aquesta tesi doctoral pretén contribuir a la teoria de la coherència de la següent manera. En primer lloc, demostrem que la coherència, tal com la teoria la formalitza, està sòlidament ancorada en la física dels interferòmetres ­—almenys en el context de les Operacions Estrictament Incoherents—, i encarna, per tant, el seu propi principi operacional. En segon lloc, després de fer notar que els estats poden ser entesos com a canals de “output” constant, emprenem la generalització de la teoria de la coherència dels estats a la teoria dels canals. En concret, proposem diverses maneres de mesurar el contingut en coherència d’un canal quàntic i el calculem considerant dues classes diferents d’operacions del tipus “free”: Operacions Incoherents i Operacions Màximament Incoherents. Finalment, investiguem si la coherència pot ser també testimoni d’alguna manifestació de no classicitat diferent dels propis efectes interferomètrics. En particular, analitzem la connexió de la coherència amb la no classicitat dels processos estocàstics quàntics, tant en el règim markovià com en el no markovià.
La coherencia cuántica, o la propiedad de los sistemas que se encuentran en una superposición de estados capaz de dar lugar a patrones de interferencia en los experimentos adecuados, es el sello distintivo de la mecánica cuántica. Más allá de sus fascinantes implicaciones epistemológicas, la coherencia cuántica resulta también un recurso valioso a la hora de llevar a cabo diferentes tareas cuántico-informacionales y ha sido incluso empleada en la descripción de ciertos procesos biológicos. Por este motivo se ha hecho necesario el desarrollo de una teoría de recursos que formalice rigurosamente la noción de coherencia, y que permita así cuantificar la coherencia presente en los sistemas físicos, así como estudiar su manipulación con vistas a un mejor aprovechamiento de este recurso. Esta tesis doctoral pretende contribuir a la teoría de la coherencia del siguiente modo. En primer lugar, demostramos que la coherencia, tal y como la teoría la formaliza, está sólidamente anclada en la física de los interferómetros —al menos en el contexto de las Operaciones Estrictamente Incoherentes—, con lo que encarna su propio principio operacional. En segundo lugar, tras hacer notar que los estados pueden ser entendidos como canales de “output” constante, emprendemos la generalización de la teoría de la coherencia de los estados a la teoría de los canales. En concreto, proponemos diversas maneras de medir el contenido en coherencia de un canal cuántico y lo calculamos considerando dos clases diferentes de opera- ciones de tipo “free”: Operaciones Incoherentes y Operaciones Máximamente Incoherentes. Finalmente, investigamos si la coherencia puede ser también testigo de alguna manifestación de no clasicidad distinta de los propios efectos inter- ferométricos. En particular, analizamos la conexión de la coherencia con la no clasicidad de los procesos estocásticos cuánticos, tanto en el régimen markoviano como en el no markoviano.
Quantum coherence, or the property of systems which are in a superpo- sition of states yielding interference patterns in suitable experiments, is the main hallmark of departure of quantum mechanics from classical physics. Besides its fascinating epistemological implications, quantum coherence also turns out to be a valuable resource for quantum information tasks, and has even been used in the description of fundamental biological processes. This calls for the development of a resource theory which rigorously formalizes the notion of coherence, that further allows both to quantify the coherence present in physical systems and to study its manipulation in order to better leverage it. This thesis intends to make a contribution to the recently built resource theory of coherence in a number of ways. First, we show that coherence, as formalized by its resource theory, is soundly grounded in the physics of interferometers—at least in the con- text of Strictly Incoherent Operations—and thus embodies its operational foundations. Second, we note that states can be thought of as constant-output channels, and start to generalize the coherence theory of states to that of channels. In particular, we propose several measures of the coherence content of a channel and further compute them when considering two different classes of free operations: Incoherent Operations and the largest set of Maximally Incoherent Operations. Finally, we investigate the question whether coherence can witness some other manifestations of non-classicality (we mean, beyond interference effects). In particular, we analyze the connection of coherence to the non-classicality of quantum stochastic processes both in the Markovian and in the non-Markovian regimes.

Many-core architectures provide an efficient way of harnessing the growing numbers of transistors available in modern fabrication processes; however, the parallel programs run on these platforms are increasingly limited by the energy and latency costs of communication. Existing designs provide a functional communication layer but do not necessarily implement the most efficient solution for chip-multiprocessors, placing limits on the performance of these complex systems. In an era of increasingly power limited silicon design, efficiency is now a primary concern that motivates designers to look again at the challenge of cache coherence. The first step in the design process is to analyse the communication behaviour of parallel benchmark suites such as Parsec and SPLASH-2. This thesis presents work detailing the sharing patterns observed when running the full benchmarks on a simulated 32-core x86 machine. The results reveal considerable locality of shared data accesses between threads with consecutive operating system assigned thread IDs. This pattern, although of little consequence in a multi-node system, corresponds to strong physical locality of shared data between adjacent cores on a chip-multiprocessor platform. Traditional cache coherence protocols, although often used in chip-multiprocessor designs, have been developed in the context of older multi-node systems. By redesign- ing coherence protocols to exploit new patterns such as the physical locality of shared data, improving the efficiency of communication, specifically in chip-multiprocessors, is possible. This thesis explores such a design - Proximity Coherence - a novel scheme in which L1 load misses are optimistically forwarded to nearby caches via new dedicated links rather than always being indirected via a directory structure.

Given an algebraic theory which can be described by a (possibly symmetric) operad P, we propose a definition of the weakening (or categorification) of the theory, in which equations that hold strictly for P -algebras hold only up to coherent isomorphism. This generalizes the theories of monoidal categories and symmetric monoidal categories, and several related notions defined in the literature. Using this definition, we generalize the result that every monoidal category is monoidally equivalent to a strict monoidal category, and show that the “strictification” functor has an interesting universal property, being left adjoint to the forgetful functor from the category of strict P -categories to the category of weak P -categories. We further show that the categorification obtained is independent of our choice of presentation for P , and extend some of our results to many-sorted theories, using multicategories.

Time domain Optical Coherence Tomography (TD-OCT), first reported in 1991, makes use of the low temporal coherence properties of a NIR broadband laser to create depth sectioning of up to 2mm under the surface using optical interferometry and point to point scanning. Prior and ongoing work in OCT in the research community has concentrated on improving axial resolution through the development of broadband sources and speed of image acquisition through new techniques such as Spectral domain OCT (SD-OCT). In SD-OCT, an entire depth scan is acquired at once with a low numerical aperture (NA) objective lens focused at a fixed point within the sample. In this imaging geometry, a longer depth of focus is achieved at the expense of lateral resolution, which is typically limited to 10 to 20 [micro]m. Optical Coherence Microscopy (OCM), introduced in 1994, combined the advantages of high axial resolution obtained in OCT with high lateral resolution obtained by increasing the NA of the microscope placed in the sample arm. However, OCM presented trade-offs caused by the inverse quadratic relationship between the NA and the DOF of the optics used. For applications requiring high lateral resolution, such as cancer diagnostics, several solutions have been proposed including the periodic manual re-focusing of the objective lens in the time domain as well as the spectral domain C-mode configuration in order to overcome the loss in lateral resolution outside the DOF. In this research, we report for the first time, high speed, sub-cellular imaging (lateral resolution of 2 [micro]m) in OCM using a Gabor domain image processing algorithm with a custom designed and fabricated dynamic focus microscope interfaced to a Ti:Sa femtosecond laser centered at 800 nm within an SD-OCM configuration. It is envisioned that this technology will provide a non-invasive replacement for the current practice of multiple biopsies for skin cancer diagnosis. The research reported here presents three important advances to this technology all of which have been demonstrated in full functional hardware conceived and built during the course of this research. First, it has been demonstrated that the coherence gate created by the femtosecond laser can be coupled into a scanning optical microscope using optical design methods to include liquid lens technology that enables scanning below the surface of skin with no moving parts and at high resolution throughout a 2x2x2 mm imaging cube. Second, the integration the variable-focus liquid lens technology within a fixed-optics microscope custom optical design helped increase the working NA by an order of magnitude over the limitation imposed by the liquid lens alone. Thus, this design has enabled homogenous axial and lateral resolution at the micron-level (i.e., 2 [micro]m) while imaging in the spectral domain, and still maintaining in vivo speeds. The latest images in biological specimens clearly demonstrate sub-cellular resolution in all dimensions throughout the imaging volume. Third, this new modality for data collection has been integrated with an automated Gabor domain image registration and fusion algorithm to provide full resolution images across the data cube in real-time. We refer to this overall OCM method as Gabor domain OCM (GD-OCM). These advantages place GD-OCM in a unique position with respect to the diagnosis of cancer, because when fully developed, it promises to enable fast and accurate screening for early symptoms that could lead to prevention. The next step for this technology is to apply it directly, in a clinical environment. This step is underway and is expected to be reported by the next generation of researchers within this group.
Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.
Includes bibliographical references (p. 118-119).
by Aaron Dominic Aguirre.
S.M.

The principle of superposition is one of the main building blocks of quantum physics and has tremendous consequences both for our fundamental understanding of nature and for technological applications. In particular, the existence of coherent superposition leads to the concept of unavoidable quantum uncertainty. The role played by this "coherent" uncertainty within thermodynamics, as well as its relationship to classical lack of knowledge, is the main subject of this thesis. In Part I we study thermodynamic limitations of processing quantum coherence within a resource-theoretic framework. Using the time-translation symmetry that arises from the first law of thermodynamics, we find constraints on possible manipulations of coherence and prove their irreversibility due to the second law. We also generalise to the quantum domain Szilard's concept of converting information into work. Namely, we show how, in the presence of a heat bath, coherence of a system can be exploited to perform mechanical work. Finally, we analyse the effect that coherence has on the structure of the thermodynamic arrow of time, i.e., on the set of states into which a given state can freely evolve under thermodynamic constraints. In Part II we focus on the interplay between quantum and classical uncertainty manifested in uncertainty relations. We show that separating the total uncertainty into these two distinct components leads to a new type of "fixed-entropy" uncertainty relation. We also analyse how classical ignorance affects the structure of states that minimise the unavoidable uncertainty arising from the noncommutativity of two observables. Finally, we study error-disturbance trade-off relations and, by proving that quantum uncertainty can be simultaneously maximised for any two observables, we clarify the unphysical nature of state-dependent relations.

A fully extended framed topological field theory with target in a symmetric monoidal n-catgeory C is a symmetric monoidal functor Z from Bord(n) to C, where Bord(n) is the symmetric monoidal n-category of n-framed bordisms. The cobordism hypothesis says that such field theories are classified by fully dualizable objects in C. Given a fully dualizable object X in C, we are interested in computing the values of the corresponding field theory on specific framed bordisms. This leads to the question of finding a presentation for Bord(n). In view of the cobordism hypothesis, this can be rephrased in terms of finding coherence data for fully dualizable objects in a symmetric monoidal n-category. We prove a characterization of full dualizability of an object X in terms of existence of a dual of X and existence of adjoints for a finite number of higher morphisms. This reduces the problem of finding coherence data for fully dualizable objects to that of finding coherence data for duals and adjoints. For n=3, and in the setting of strict symmetric monoidal 3-categories, we find this coherence data, and we prove the corresponding coherence theorems. The proofs rely on extensive use of a graphical calculus for strict monoidal 3-categories.

This thesis aims to explore how narrative films that are marked by crucial obscurities and explanatory gaps in their development manage to become coherent. More specifically, the thesis is interested in examining how these obscurities and explanatory gaps can be understood as meaningful aspects of the films' organisation. Since the function of coherence in film has rarely been examined directly, the thesis first attempts to illuminate it by drawing on the work of two aestheticians who have examined it more systematically. Thus, the first part of the thesis discusses the work of Victor F. Perkins and George Wilson, while attempting to explore aspects of the work of these two aestheticians through the analysis of specific films. The writings of Perkins and Wilson provide a good starting point for the thesis because they raise crucial questions regarding the ways through which narrative films manage to deal with significant tensions in their organisation and intelligibility. The main body of the thesis (the second part of the thesis) then examines four narrative films, each of which is marked by a significant aspect of apparent incoherence. In each case, the thesis attempts to show that this aspect of apparent incoherence - rather than merely obstructing the film's intelligibility - essentially contributes to the creation of the film's idiosyncratic internal logic. In order to understand how this becomes possible, the thesis pays close attention to the ways in which the various components of each examined film relate to each other, observing and analysing the aesthetic strategies which enable each examined film ultimately to come together.

Redes de computadores estão sob constante ameaça, ainda mais quando conectadas à Internet. Para reduzir o risco, dispositivos de segurança como o filtro de pacotes são usados. Uma primeira camada de segurança, o filtro de pacotes é responsável pelo bloqueio do tráfego indesejado em posições chave da rede. Os pacotes que devem ser permitidos ou bloqueados pelo filtro são definidos através de um conjunto de regras programadas pelo administrador da rede. Essas regras tem duas partes: a seleção e a ação. Conforme cresce a rede e o número de serviços, a quantidade de regras tende a aumentar. Passado certo limite, a complexidade de manter uma quantidade grande de regras se torna um fardo para o administrador. Isso aumenta a probabilidade de enganos que podem prejudicar a segurança da rede. Este trabalho desenvolve o conceito de “anomalia”, cada qual representa um problema em potencial, uma contradição ou uma regra supérflua dentro do conjunto de regras; ou seja, cada anomalia alerta o administrador da rede para determinada situação. Há 7 tipos de anomalias, que podem ser divididos em dois grupos: anomalias de filtro único e anomalias em rede. As anomalias de filtro único alertam o administrador sobre regras que se contradizem (“bloqueio”) ou que não possuem efeito no filtro (“invisibilidade” e “redundância”). As anomalias em rede, por sua vez, alertam o administrador sobre filtros que se contradizem (“discordância”), filtros que bloqueiam tráfego desejado (“bloqueio”), regras que não se aplicam a nenhum pacote que passe pelo filtro onde estão (“irrelevância”) e roteadores que permitem a passagem de tráfego indesejado (“vazamento”). Cada um desses tipos de anomalia é definido formalmente e apresentado junto com um algoritmo que a encontra. As anomalias e seus algoritmos foram usados para implementar uma ferramenta, o Packet Filter Checker (PFC), que lê as regras e a descrição da topologia da rede e cria um relatório com todas as anomalias presentes. Este trabalho apresenta um caso de uso fictício que é analisado e corrigido com base nos resultados apresentados pela ferramenta. O caso de uso é apresentado em diversas iterações, cada uma representando alterações nos requisitos da rede. Este caso mostra a ferramenta e os conceitos no contexto-alvo: na ajuda ao administrador da rede.
Computer networks are under constant threat, even more when connected to the Internet. To decrease the risk of invasions and downtime, security devices such as the packet filter are deployed. As a first layer of security, the packet filter is responsible for blocking out unwanted traffic at key network locations. The packets dropped or forwarded by the filter are defined by a set of rules programmed by the network administrator. These rules are in the form of guarded commands, each with a condition and a decision section. As the number of services and networks grow, the number of rules tend to grow as well. Beyond a certain threshold, the complexity of maintaining such a large and distributed set of rules becomes a burden for the network administrator. Mistakes can be easily made, compromising security. This work develops the concept of “anomaly”, each representing a potential problem, a contradiction or a superfluous rule in the rule set; i.e. a warning to the system administrator. There are 7 types of anomalies divided in two groups: single filter anomalies and networked anomalies. The single-filter anomalies warns the administrator about rules that contradict one another (the “conflict” anomaly) or have no effect (“invisibility” and “redundancy”) in the analysed filter. The networked anomalies, on the other hand, analyse the filters in the context of the network topology and warn the administrator about filters that contradict one another (“disagreement”), filters that block desired traffic (“blocking”), rules that have no effect on the given network topology (“irrelevancy”) and routers that are enabling unwanted traffic (“leaking”). Each type of anomaly is formally defined along with its algorithm. The developed concepts were used to implement a tool — the Packet Filter Checker (PFC) — that reads a description of the rules and network topology in a simple custom language and reports all anomalies present. This tool is used to analyse and fix a fictional user case in several iterations of changing requirements. This shows the tool and the anomalies in the target context: where they help the network administrator.

Cette these s'inscrit dans un courant de recherches en theorie de la demonstration qui a commence en 1987 avec la mise au point par jean-yves girard de la logique lineaire (ll) avec 1) sa syntaxe : les reseaux de demonstration 2) sa notion de calcul : la normalisation des reseaux 3) sa notion d'equivalence de preuves fournie par la semantique coherente et 4) sa fameuse decomposition de la logique minimale. La these s'articule en 3 parties : i) une etude syntaxique des reseaux de demonstration : chapitres 1-5 et annexe a ii) une etude semantique des reseaux de demonstration : chapitres 6-14 iii) une etude syntaxique et semantique des preuves de la logique classique : chapitre 15 et annexe b. Les deux premiers chapitres rassemblent les elements epars dans la litterature sur les reseaux, pour en donner la premiere presentation rigoureuse et complete a ce jour. Les deux chapitres suivants sont consacres au theoreme de confluence de la normalisation de ces reseaux. Le chapitre qui suit examine une variation de la syntaxe des additifs en introduisant les multiboites qui materialisent le theoreme de confluence acquis au chapitre precedent. Dans la seconde partie, excluant additifs et quantificateurs, on se propose de comparer la notion d'equivalence de preuves decrite par la normalisation, et les equivalences induites par les semantiques de trames (en particulier la semantique coherente) : c'est ce que nous appelons la question de l'injectivite, que nous posons au chapitre 7. Apres avoir repris la definition d'experience, nous introduisons la notion-clef de experience obsessionnelle : celle-ci permet de decrire entierement les reseaux de certains fragments de ll, et de construire des contre-exemples dans le cas general. Dans la troisieme partie, nous presentons un systeme classique (lk-eta-rho-pol), clos par normalisation, et nous donnons une decomposition de la conjonction multiplicative a l'aide de la conjonction additive, a isomorphisme pres.

This thesis addresses some theoretical issues generated by the results of recent analysis of EEG time series proving the brain dynamics are driven by abrupt changes making them depart from the ordinary Poisson condition. These changes are renewal, unpredictable and non-ergodic. We refer to them as crucial events. How is it possible that this form of randomness be compatible with the generation of waves, for instance alpha waves, whose observation seems to suggest the opposite view the brain is characterized by surprisingly extended coherence? To shed light into this apparently irretrievable contradiction we propose a model based on a generalized form of Langevin equation under the influence of a periodic stimulus. We assume that there exist two different forms of time, a subjective form compatible with Poisson statistical physical and an objective form that is accessible to experimental observation. The transition from the former to the latter form is determined by the brain dynamics interpreted as emerging from the cooperative interaction among many units that, in the absence of cooperation would generate Poisson fluctuations. We call natural time the brain internal time and we make the assumption that in the natural time representation the time evolution of the EEG variable y(t) is determined by a Langevin equation perturbed by a periodic process that in this time representation is hardly distinguishable from an erratic process. We show that the representation of this random process in the experimental time scale is characterized by a surprisingly extended coherence. We show that this model generates a sequence of damped oscillations with a time behavior that is remarkably similar to that derived from the analysis of real EEG's. The main result of this research work is that the existence of crucial events is not incompatible with the alpha wave coherence. In addition to this important result, we find another result that may help our group, or any other research group working on the analysis of brain's dynamics, to prove or to disprove the existence of crucial events. We study the diffusion process generated by fluctuations emerging from the same model after filtering out the alpha coherence, and we study the recursion to the origin. We study the survival probability of this process, namely the probability that up to a given time no re-crossing of the origin occurs. We find that this is an inverse power law with a power that depends on whether or not crucial events exist.

Thesis (Ph.D.) - University of Glasgow, 2008.
Ph.D. thesis submitted to the Faculty of Information and Mathematical Sciences, Department of Mathematics, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

Thesis (Ph. D.)--Worcester Polytechnic Institute.
Keywords: singularity; vortex; phase; diffraction; interference; nulling; singularities; coherence; dislocation; optical vortex. Includes bibliographical references (p. 123-146).

A plausible theory of human freedom must give some account of both alternate possibilities and self-determination. Debate over the correct interpretation of the first feature gives rise to the metaphysical problem of whether or not freedom is compatible with the thesis of determinism, according to which, given the actual past and the actual laws of nature, there is at any time only one physically possible future. It is my view that persons act freely only if the thesis of determinism is false. But since a distinction must be made between a free act and a random event, the incompatibilist who affirms the existence of freedom must say more about a free act than that it is indeterministically caused. A free act is one's own: it is authorized by the self. In this dissertation, I propose a conception of the self and a coherence theory of autonomous or self-determined action, modeled after Keith Lehrer's coherence theory of knowledge. I defend the consequence argument for incompatibilism and argue that the compatibilist understanding of freedom is unsatisfactory. Hence, drawing on the coherence account of autonomy, I develop a coherentist libertarian theory of freedom. I respond to challenges to that account and consider, finally, reasons for thinking that we sometimes act and will freely.

This doctoral dissertation investigates the corporeal basis of global and local coherence. As far as global coherence is concerned, the main argument of this thesis is that the search for global coherence is often guided by means of metaphorical mappings, particularly those having to do with the conceptual metaphor DISCOURSE IS A FORM OF MOTION ALONG A PATH INFLUENCED BY FORCE DYNAMICS. In the case of local coherence, the analysis presented focuses only on a subset of interclausal connections: cause-effect and cause-concession relations, when explicitly marked by means of discourse markers. This thesis successfully assesses the hypothesis that Talmy’s force-dynamic model, along with conceptual metaphor, may account for the semantic content and the type of inferences that said subset of connectives generate during language processing. More broadly, this thesis provides evidence to support the premise that not only the general structure of discourse, but also the coherence relations on which it relies, emerge from our embodied interaction with the world.
Esta tesis estudia la posible influencia que la metáfora conceptual, entendida como un proceso cognitivo, puede ejercer en la producción y comprensión del discurso, en particular en el modo en que las relaciones de coherencia global y local emergen y se sustentan. Mediante un análisis cualitativo, esta tesis muestra que la metáfora conceptual UN DISCURSO ES UNA FORMA DE MOVIMIENTO INFLUENCIADA POR DINÁMICAS DE FUERZA y sus esquemas de imagen subyacentes son recursos estructurales básicos. Dichos elementos dan forma a la organización del discurso, contribuyen a realzar las relaciones de coherencia del texto y facilitan la comprensión lectora al activar inferencias o expectativas que pueden ayudar a predecir el comportamiento del discurso. En el caso de a coherencia local, cuatro estudios experimentales proporciona evidencias empíricas, a través de una análisis comparativo del inglés y del castellano, que apoyan la tesis de que las relaciones de coherencia causales y concesivas tienen una naturaleza corpórea ya que parecen estar basadas en conceptos más concretos: interacciones de fuerza. Además este trabajo también ofrece datos que permiten afirmar que dichos patrones de fuerza no sólo son codificados en términos lingüísticos mediante verbos sino también mediante marcadores del discurso causales y concesivos. Todos estos datos llevan a pensar que los esquemas de imagen y la metáfora conceptual son cruciales en conceptualización de las nociones de causalidad y concesión ya que comprimen nuestra experiencia y la extienden a nociones mucho más abstractas tales como la causalidad y la concesión para hacer estas nociones comprensibles. En definitiva esta tesis proporciona evidencias de que apoyan la premisa de que no sólo la estructura general del texto sino también las relaciones de coherencia local emergen de nuestra interacción corpórea con el mundo que nos rodea.