Dissertations / Theses: 'Field'

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Rozario, Rebecca. "The Distribution of the Irreducibles in an Algebraic Number Field." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/RozarioR2003.pdf.

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Rakotoniaina, Tahina. "Explicit class field theory for rational function fields." Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/1993.

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Smith, John D. "Scalar fields in quantum field theory and black holes." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265489.

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Lewis-Nash, Robert J. "Old Fields and New Fields: Ceramics and the Expanded Field of Sculpture." Oberlin College Honors Theses / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin150695125608167.

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5

Endres, Michael G. "Topics in lattice field theory /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9713.

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Ganic, Djenan, and dga@rovsing dk. "Far-field and near-field optical trapping." Swinburne University of Technology. Centre for Micro-Photonics, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20051130.135436.

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Optical trapping techniques have become an important and irreplaceable tool in many research disciplines for reaching non-invasively into the microscopic world and to manipulate, cut, assemble and transform micro-objects with nanometer precision and sub-micrometer resolution. Further advances in optical trapping techniques promise to bridge the gap and bring together the macroscopic world and experimental techniques and applications of Microsystems in areas of physics, chemistry and biology. In order to understand the optical trapping process and to improve and tailor experimental techniques and applications in a variety of scientific disciplines, an accurate knowledge of trapping forces exerted on particles and their dependency on environmental and morphological factors is of crucial importance. Furthermore, the recent trend in novel laser trapping experiments sees the use of complex laser beams in trapping arrangements for achieving more controllable laser trapping techniques. Focusing of such beams with a high numerical aperture (NA) objective required for efficient trapping leads to a complicated amplitude, phase and polarisation distributions of an electromagnetic field in the focal region. Current optical trapping models based on ray optics theory and the Gaussian beam approximation are inadequate to deal with such a focal complexity. Novel applications of the laser trapping such as the particle-trapped scanning near field optical microscopy (SNOM) and optical-trap nanometry techniques are currently investigated largely in the experimental sense or with approximated theoretical models. These applications are implemented using the efficient laser trapping with high NA and evanescent wave illumination of the sample for high resolution sensing. The proper study of these novel laser trapping applications and the potential benefits of implementation of these applications with complex laser beams requires an exact physical model for the laser trapping process and a nanometric sensing model for detection of evanescent wave scattering. This thesis is concerned with comprehensive and rigorous modelling and characterisation of the trapping process of spherical dielectric particles implemented using far-field and near-field optical trapping modalities. Two types of incident illuminations are considered, the plane wave illumination and the doughnut beam illumination of various topological charges. The doughnut beams represent one class of complex laser beams. However, our optical trapping model presented in this thesis is in no way restricted to this type of incident illumination, but is equally applicable to other types of complex laser beam illuminations. Furthermore, the thesis is concerned with development of a physical model for nanometric sensing, which is of great importance for optical trapping systems that utilise evanescent field illumination for achieving high resolution position monitoring and imaging. The nanometric sensing model, describing the conversion of evanescent photons into propagating photons, is realised using an analytical approach to evanescent wave scattering by a microscopic particle. The effects of an interface at which the evanescent wave is generated are included by considering the scattered field reflection from the interface. Collection and imaging of the resultant scattered field by a high numerical aperture objective is described using vectorial diffraction theory. Using our sensing model, we have investigated the dependence of the scattering on the particle size and refractive index, the effects of the interface on the scattering cross-section, morphology dependent resonance effects associated with the scattering process, and the effects of the incident angle of a laser beam undergoing total internal reflection to generate an evanescent field. Furthermore, we have studied the detectability of the scattered signal using a wide area detector and a pinhole detector. A good agreement between our experimental measurements of the focal intensity distribution in the back focal region of the collecting objective and the theoretical predictions confirm the validity of our approach. The optical trapping model is implemented using a rigorous vectorial diffraction theory for characterisation of the electromagnetic field distribution in the focal region of a high NA objective. It is an exact model capable of considering arbitrary amplitude, phase and polarisation of the incident laser beam as well as apodisation functions of the focusing objective. The interaction of a particle with the complex focused field is described by an extension of the classical plane wave Lorentz-Mie theory with the expansion of the incident field requiring numerical integration of finite surface integrals only. The net force exerted on the particle is then determined using the Maxwell stress tensor approach. Using the optical trapping model one can consider the laser trapping process in the far-field of the focusing objective, also known as the far-field trapping, and the laser trapping achieved by focused evanescent field, i.e. near-field optical trapping. Investigations of far-field laser trapping show that spherical aberration plays a significant role in the trapping process if a refractive index mismatch exists between the objective immersion and particle suspension media. An optical trap efficiency is severely degraded under the presence of spherical aberration. However, our study shows that the spherical aberration effect can be successfully dealt with using our optical trapping model. Theoretical investigations of the trapping process achieved using an obstructed laser beam indicate that the transverse trapping efficiency decreases rapidly with increasing size of the obstruction, unlike the trend predicted using a ray optics model. These theoretical investigations are in a good agreement with our experimentally observed results. Far-field optical trapping with complex doughnut laser beams leads to reduced lifting force for small dielectric particles, compared with plane wave illumination, while for large particles it is relatively unchanged. A slight advantage of using a doughnut laser beam over plane wave illumination for far-field trapping of large dielectric particles manifests in a higher forward axial trapping efficiency, which increases for increasing doughnut beam topological charge. It is indicated that the maximal transverse trapping efficiency decreases for reducing particle size and that the rate of decrease is higher for doughnut beam illumination, compared with plane wave illumination, which has been confirmed by experimental measurements. A near-field trapping modality is investigated by considering a central obstruction placed before the focusing objective so that the obstruction size corresponds to the minimum convergence angle larger than the critical angle. This implies that the portion of the incident wave that is passed through the high numerical aperture objective satisfies the total internal reflection condition at the surface of the coverslip, so that only a focused evanescent field is present in the particle suspension medium. Interaction of this focused near-field with a dielectric micro-particle is described and investigated using our optical trapping model with a central obstruction. Our investigation shows that the maximal backward axial trapping efficiency or the lifting force is comparable to that achieved by the far-field trapping under similar conditions for either plane wave illumination or complex doughnut beam illumination. The dependence of the maximal axial trapping efficiency on the particle size is nearly linear for near-field trapping with focused evanescent wave illumination in the Mie size regime, unlike that achieved using the far-field trapping technique.

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Ganic, Djenan. "Far-field and near-field optical trapping." Australasian Digital Thesis Program, 2005. http://adt.lib.swin.edu.au/public/adt-VSWT20051130.135436.

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Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, Centre for Micro-Photonics, 2005.
A thesis submitted for the degree of Doctor of Philosophy, Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, 2005. Typescript. Includes bibliographical references (p. 164-177). Also available on cd-rom.

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YANG, BING. "Source and field reconstruction with field splitting." Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2503165.

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The research activity has concerned diagnostics for antennas and other intentional or un-intentional radiating structures (e.g. for EMI considerations). The diagnostics effort is based on measured field, and on information on the device under test (DUT) wrapping volume; the latter is used to reconstruct equivalent currents that radiate the same field as measured. Current reconstruction is based on a previous work. The activity has involved testing of the existing approach -not reported in this thesis document-, and its extension. The main emphasis has been on relating the polarization of the radiated field to the (equivalent) currents on the DUT, especially to allow the designer a clear view of what the origin could be of possible deviations from expected or desired performance. In this sense, the geometry of the current reconstruction surface plays a key role: one would like to do this reconstruction on a closely wrapping surface to maximize the information content. The basic idea is to split the measured field into two polarization components (co- and cross-polarization), and then observe the corresponding equivalent currents; for example, the sources of cross-polarization could be directly tracked this way. However, this approach cannot be applied in a straightforward manner for two different reasons. In the first place, it is well known that polarization (co-polarized and cross-polarized orthogonal components of the radiated field) is not defined uniquely, and the definition of co- and cross-polarization depends on utility for the specific use. This problem can be handled in a conventional way, but requires attention, and in view of the subsequent use, and in particular for the definition of the cross-polarized field. Second, and more important for the present purpose, there is no guarantee that a purely polarized field could be radiated by a set of currents having spatial support on the wrapping surface of the DUT (e.g., a purely polarized field might require a larger antenna). Also, one is normally interested in co- and cross-polarizations levels only in the main radiation lobe, or a portion thereof. This has prompted the definition of an “improved” field. This “improved” field has a given polarization purity only in a portion of the main beam, via a windowing process that sets the level of cross-polarization and the extent of the (angular) region where the improvement is enforced. The improvement is in any case a perturbation of the actual measured fields, that potentially worsens the current reconstruction process; therefore, trade-offs have been studied in several cases between the information conveyed by the current reconstruction via improved field, and the accuracy in reproducing the measured field. The concept is more general, though, and can indeed be used to “improve” a prototype DUT whose measured performances are below the level of expectation, e.g. by lowering the side lobes. This can be recognized as a linear synthesis (“field synthesis”) procedure, whose results is a useful indication for the designer on what parts of the DUT have to be modified and on how to get a better performance. Issues about the extent of the “improvement” (distance from actually measured pattern) and physical realizability in the volume occupied by the DUT are still to be considered. Conversely, and to some extent counter-intuitively, the polarization splitting is simpler when two polarizations are specified at the source level; this is what commonly happens for dual-polarized antennas. In this case it can be seen that the field splitting in polarization leads to a stable reconstructions of the related currents.

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9

Wang, Chun-yen. "Closed-time-path formalism for gauge field theory /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.

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Tarrús, Castellà Jaume. "Explicit Bound states and Resonance fields in Effective Field Theories." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/82144.

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The first three chapters of this thesis have been devoted to the theoretical background. We presented the novel work of this thesis in chapters 4 and 5. In chapter 4 we have constructed a Chiral effective field theory for the nucleon--nucleon system which contains dibaryon fields as fundamental degrees of freedom. The large scattering lengths in the 1S0 and the 3S1 channels force the dibaryon residual masses to be much smaller than the pion mass. Since no counterterm has to be enhanced like in the KSW approach, naïve dimensional analysis is sufficient to assess the size of the effective field theory low--energy constants, keeping the perturbative expansion under control. We organized the calculation in a series of effective theories, which are obtained by sequentially integrating out higher energy and momentum scales. We first integrate out energy scales of the order of the pion mass. This leads to an effective theory with dibaryon and nucleon fields, pNNEFT. For three momenta much smaller than the pion mass, it is convenient to further integrate out three momenta of the order of pion mass, which leads to the npNNEFT. We have calculated the nucleon--nucleon scattering amplitudes for energies smaller than the pion mass in the 1S0 and the 3S1-3D1 channels at NNLO. The numerical results for the phase shifts and mixing angle are also similar to the ones obtained in the KSW approach. A good description of the 1S0 channel is obtained, but for the 3S1-3D1 channel our results also fail to describe data. The reasons of this failure can be traced back to the iteration of the one potential pion exchange potential. We have calculated the matching of the dibaryon residual masses and dibaryon-nucleon couplings up to NLO. We have showed that, certain class of diagrams that contribute to the residual mass, involving n potential pion exchanges in loops with radiation a pion, have to be summed in the 3S1 channel. In the 3S1 channel the resummation can be carried out. However in the 1S0 channel the resummation is not possible, but it is very likely that loop contributions are still large. Using the results for the matching for residual masses and dibaryon--nucleon coupling for npNNEFT we have given Chiral extrapolation formulas for scattering lengths of the scalar channels up to corrections of order mq(3) We have fitted these expressions to lattice data and compared the results to previous studies of the quark mass dependence of the scattering lengths. In chapter 5 we have considered the possibility that the spectrum of QCD in the Chiral limit contains an isosinglet scalar with a mass much lower than the typical hadronic scale, and have constructed the corresponding effective theory that includes it together with the standard pseudo-Goldstone bosons, ChiPTs. In the purely scalar sector of the theory we argued that the scalar self interactions can be ignored. Demanding that the scalar does not mix with the vacuum together with Chiral symmetry imposes that two of the low--energy constants should be taken as zero. We have presented the calculation of pion mas and decay constant at NLO. The dynamical scalar field introduces new non-analyticities in the quark mass dependence of these observables. We have used lattice data from the ETM collaboration to fit the low--energy constants. The chi-squared per degree-of-freedom delivered by the ChiPTs fits are similar to ChiPT ones indicating that lattice data does not favor any of the theories over the other. The ChiPTs expressions for the S-wave pion-pion scattering lengths differ from those of ChiPT already at leading order. Furthermore ChiPTs allows for the calculation of the sigma decay width. Neither the value of the scattering lengths for the I=0 and I=2 channels are close to the experimental numbers. Although the value of I=0 is slightly closer to it than the one obtained in tree-level ChiPT, the value of the I=2 channel is much further away. We argue, using the decoupling limit that this is due to the sizable NLO corrections because of the large value of l1. We also show a different approach in which we fit the scattering length expressions with all parameters free to lattice data and use the results to provide predictions for the sigma mass and decay width.
En el marc de teories efectives per a Cromodinàmica Quàntica a baixes energies, una situació interessant es presenta quan els graus de llibertat de baixes energies poden formar estats lligats, estats virtuals o ressonàncies pròximes al llindar. Com que aquest estats estan a prop del llindar afecten a les amplituds de dispersió, però tan mateix no poden ser descrites utilitzant teoria de pertorbacions, ja que les series polinòmiques finites en el moment no poden generar un pol en l’amplitud. Aquest pols es poden obtenir resumant certes classes de diagrames, per exemple usant tècniques d’unitarització, que no són consistents amb el comptatge de la teoria efectiva, o alternativament assumint un augment de l’importància de certs acoblaments. En aquest últim cas s’han de calcular les equacions del grup de renormalització per a tots els acoblaments per tal de determinar-ne el tamany correcte, el que dificulta mantenir la sèrie pertorbativa sota control. És una vella observació de Weinberg que la inclusió explícita d’estats lligats i ressonàncies com a graus de llibertat de la teoria efectiva millora la convergència de la teoria de pertorbacions. Es pot entendre fàcilment aquesta millora de la convergencia ja que les amplituds de dispersió tindran la estructura analítica correcta. Un dels temes principals d’aquesta tesi ha sigut explorar aquest fet dins d'un marc modern de teories efectives. El treball original d’aquesta tesi és als capítols 4 i 5. Al capítol 4 hem construït una teoria efectiva Quiral pel sistema nucleó–nucleó que conté camps dibariònics com a graus de llibertat fonamentals. Les longituds de dispersió grans en els canals 1S0 i 3S1 poden ser representades de forma natual gràcies a les petites masses residuals dels dibarions. Em calculat les amplituds de dispersió per aquesta teoria fins a NNLO per als canals 1S0 i 3S1-3D1, i em donat fòrmules d'extrapolació quiral per a les longituds de dispersió d'ona S fins a NLO. Al capítol 5 hem considerat la possiblitat de que l’espectre de QCD en el limit Quiral contingui un isosinglet escalar amb massa molt mes petita que l’escala hadroníca típica, i hem construït una teoria efectiva que l’inclou conjuntament amb els pseudo–bosons de Goldstone. Hem calculat la massa i la constant de decaïment del pion fins a NLO i hem ajustat els resultats a dades en el reticle. També hem estudiat les longituds de dispersió de les col•lisions pió-pió per a ona S en isospin I=0 i I=2 i les hem comprat amb dades al reticle.

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Yang, Nan. "Molecules in Sculpted Fields: Magnetic Field Effects and Multipole Transitions." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10684.

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This thesis describes work related to the theme of sculpted electromagnetic fields - engineered fields with particular spatial patterns - and their interactions with molecules. We are motivated by the following questions: what are ways of detecting spatial patterns in electromagnetic fields? What are possible applications of spatially engineered fields? Are there molecular transitions that are dark to plane waves but that can be probed by sculpted fields? The first part of this thesis is in the area of magnetic field effects in chemistry. We focus on magnetic field modulated fluorescence, which provides a convenient method for imaging magnetic field strength. We proposed and demonstrated a fluorescence technique that allows imaging through strongly scattering media. We achieve this by exploiting the fact that most materials do not scatter magnetic field. This allows us to project a magnetic field pattern beyond the scattering surface. The magnetic field dependent fluorescence then allows us to map out the object of interest. We constructed a setup that demonstrates 2D imaging using this technique. We synthesized new molecular systems to enhance the sensitivity to magnetic field. We characterized and compared these molecules with steady state fluorescence spectroscopy, transient fluorescence and transient absorption measurements. The results reveal patterns that point to directions for engineering chemical systems to further enhance their magnetic field sensing properties. The second portion of this thesis is a theoretical study of the molecular multipole transitions and their couplings to local electromagnetic quantities. Using a semiclassical approach, we performed a multipole expansion of molecular transitions driven by monochromatic radiation. We derived the local electromagnetic quantities that couple to different multipole transitions and observables such as circular dichroism and magnetic circular dichroism. It was observed that certain transitions are dark to plane waves, but could be probed by simple spatial arrangements such as superpositions of plane waves. Experiments for their detection are also proposed.
Engineering and Applied Sciences

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Haines, Ross. "Simultaneous reconstruction of spatial frequency fields and field sample locations." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:aa35073d-003b-4939-bf0e-8348243871b7.

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Classically, spatial smoothing methods such as kriging estimate smooth interpolating fields for features measured at well-located points. In this thesis, we make a simultaneous reconstruction of interpolating spatial fields and measurement locations. We give models, and sample-based Bayesian inference, for estimating locations of dialect samples on a map of England. The method exploits dialect-based spellings to locate these samples. The data are feature vectors extracted from written dialect samples. Just a fraction of the feature vectors ('anchors') have an associated spatial location. When coupled to a prior for the smoothly varying feature field, and the anchor texts, the unlocated feature vectors are jointly informative of their own location and the feature fields. The dataset is large, but sparse, since a given word has a large number of variant spellings which may appear in just a few documents. We report an analysis including Bayesian model fitting and validation on a large and representative subset of the data. The thesis has two main aims - to provide statistical tools for the linguists who collected the data, and to meet the computational and inferential challenge of simultaneously locating large numbers of feature vectors. The results presented in this thesis show that we have largely succeeded in meeting these challenges.

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Zhou, Sichao. "Complex Optical Fields Generation Using a Vectorial Optical Field Generator." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1461689435.

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Zhao, Xiang. "Aspects of conformal field theories and quantum fields in AdS." Electronic Thesis or Diss., Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX103.

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Cette thèse concerne la structure et l'espace des théories conformes des champs (CFT), et plus généralement de propriétés diverses des fonctions de corrélation conformes. Elle s'étend dans de multiples directions, à la fois perturbatives et non perturbatives, locales et non locales, avec et sans supersymétrie.Le premier aspect concerne les fonctions de corrélation conformes dans l'espace-temps de dimension d et leur relation avec les S-matrices de l'espace plat dans l'espace-temps de (d+1) dimensions. La connexion est établie en considérant une théorie quantique des champs (QFT) dans un espace-temps Anti-de Sitter (AdS) de dimension fixe (d+1) et en envoyant le rayon de la courbure de l'AdS vers l'infini. C'est-à-dire que l'objet central à étudier est la limite d'espace plat de QFT dans AdS. L'analyse commence en prenant la limite de l'espace plat des blocs de construction des diagrammes de Witten, à savoir les propagateurs diverses. Cette analyse conduit à des prescriptions génériques conjecturales pour extraire la physique des espaces plats à partir de corrélateurs conformes. L'idée qu'un diagramme de Witten réduit simplement au diagramme de Feynman correspondant ne tient pas toujours et l'origine de cet écart réside dans ces propagateurs: ils pourraient avoir deux limites d'espace plat différentes. L'une des limites existe toujours et se réduit au propagateur Feynman, tandis que l'autre, lorsqu'elle est présente, diverge dans la limite de l'espace plat. Cette observation est testée par des exemples explicites, y compris les diagrammes de Witten de contact scalaire à quatre points, d'échange et de triangle et les conjectures devraient fonctionner chaque fois que l'énergie de diffusion est suffisamment grande.Le deuxième aspect étudie le problème de classification des défauts CFT. Le but est de répondre en partie à la question: étant donné une CFT du volume et des conditions de cohérence telles que la symétrie de croisement et l'unitarité, quels sont les défauts de conformité autorisés avec un couplage non trivial au volume? Des techniques de bootstrap analytiques sont appliquées pour étudier une version simplifiée de ce problème où, dans l'ensemble, un seul champ scalaire libre est considéré. L'analyse de diverses fonctions à trois points parmi conduit à la conclusion que presque toutes les fonctions de corrélation à n points des champs de défauts sont complètement fixées jusqu'à une fonction à un point potentiellement non fixée. Cette analyse conduit également à un résultat intermédiaire dans lequel il est prouvé que les fonctions de corrélation à n points d'une théorie conforme à spectre libre généralisé doivent être celles de la théorie du champ libre généralisée.Le troisième aspect concerne l'interaction entre l'analyticité en spin dans les CFT et la supersymétrie. Le spectre des opérateurs dans une CFT unitaire générale devrait être capturé par une analyse de fonction pour le spin L > 1, et les opérateurs sont organisés en diverses trajectoires de Regge. La présence de supersymétrie étend en général la région d'analyticité en spin. Les 6d N = (2,0) théories des champs superconformes (SCFT) sont considérées comme un exemple concret, dans lequel l'analyticité en spin devrait se maintenir à L > - 3. Une analyse détaillée de la fonction à quatre points du supermultiplet du tenseur des contraintes révèle une interaction inattendue entre les multiplets non protégés et protégé s: le multiplet du tenseur des contraintes peut être trouvé sur une longue trajectoire de Regge (non protégée) lorsqu'il continue analytiquement de tourner L = 2. Dans cette étude, un programme général de bootstrap itératif est également établi, qui s'applique à tous les SCFT qui ont un sous-secteur d'algèbre chirale
This thesis studies the structure and the space of conformal field theories (CFTs), and more generally various properties of conformal correlation functions. It extends into multiple directions, both perturbative and non-perturbative, local and non-local, with and without supersymmetry.The first aspect concerns the conformal correlation functions in d-dimensional spacetime and their relation to flat-space S-matrices in (d + 1)-dimensional spacetime. The connection is built up by considering a quantum field theory (QFT) in a fixed (d + 1)-dimensional Anti-de Sitter (AdS) background and sending the radius of the AdS curvature to infinity. That is, the central object to study is the flat-space limit of QFT in AdS. The analysis starts from taking the flat-space limit of the building blocks of Witten diagrams, namely the bulk-boundary and bulk-bulk propagators. This analysis leads to conjectural generic prescriptions to extracting flat-space physics from conformal correlators. Interestingly, the intuitional picture that a Witten diagram simply reduces to the corresponding Feynman diagram does not always hold and the origin of this discrepancy lies in the bulk-bulk propagators: they could have two different flat-space limits. One of the limits always exists and reduces to Feynman propagator, while the other, when present, diverges in the flat-space limit. This observation is tested by explicit examples, including four-point scalar contact, exchange and triangle Witten diagrams and the conjectures are expected to work whenever the scattering energy is large enough.The second aspect studies the classification problem of defect CFTs. The goal is to partially answer the question: given a bulk CFT and consistency conditions such as crossing symmetry and unitarity, what are the allowed conformal defects with a non-trivial coupling to the bulk? Analytic bootstrap techniques are applied to study a simplified version of this problem where in the bulk only a single free scalar field is considered. Analysis of various three-point functions among bulk and defect fields leads to the conclusion that almost all the n-point correlation functions of defect fields are completely fixed up to a potentially unfixed one-point function. This analysis also leads to an intermediate result in which it is proven that the n-point correlation functions of a conformal theory with a generalized free spectrum must be those of the generalized free field theory.The third aspect studies the interplay between analyticity in spin in CFTs and supersymmetry. Operator spectrum in a general unitary CFT is expected to be captured by a function analytic for spin L > 1, and the operators are organised into various Regge trajectories. The presence of supersymmetry in general extends the region of analyticity in spin. The 6d N = (2, 0) superconformal field theories (SCFTs) is considered as a concrete example, in which analyticity in spin is expected to hold down to L > -3. Detailed analysis of the four-point function of the the stress tensor supermultiplet uncovers an unexpected interplay between unprotected and protected multiplets: the stress tensor multiplet can be found on a long (unprotected) Regge trajectory when analytically continued to spin L = -2. In this study a general iterative bootstrap program is also established, which applies to all SCFTs that have a chiral algebra subsector

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Bougourzi, A. Hamid. "Free field realization of extended conformal field theories." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70279.

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I investigate the free field realization (FFR) of various extended conformal field theories (ECFT's). More specifically, I first present a systematic method that allows the construction of the exponential type screening currents in terms of free fields in the case of the ECFT's with Kac-Moody algebras. This method is explicitly illustrated through the $su(n) sb{k}$ and $sp(4) sb{k}$ Kac-Moody algebras. Then, I use the FFR to unravel the embedding structure of the Verma modules of the ECFT with a $W sb3$ algebra. This embedding structure is expressed through a set of intertwining diagrams, which in turn, is used to compute the irreducible characters of the $W sb3$ algebra. Next, I construct two FFR's for the ECFT with the $su(n) sb{k}$ parafermion algebra. Finally, I sketch the FFR of the coset model $su(n) sb{k} times su(n) sb ell/su(n) sb{k+ ell},$ which is given in terms of the fields realizing the $su(n) sb{k}$ parafermion model and an extra free field with a background charge.

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Kawai, S. "Boundary conformal field theory in free-field representation." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249280.

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Darah, Alhashmi A. "Magnetic field generation within an ambient magnetic field." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505835.

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Davis, Brian. "The Field." Digital Commons at Loyola Marymount University and Loyola Law School, 2017. https://digitalcommons.lmu.edu/etd/307.

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Helland, Madeline. "Field Guide." Scholarship @ Claremont, 2018. http://scholarship.claremont.edu/scripps_theses/1182.

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Field Guide is a mixed-media artist book detailing the exploration of a fictitious culture through cartography, narrative, and illustration. It is presented through the lens of an amateur archaeologist, navigating a chain of islands to search for ruins and artifacts. In part, the project is focused on the fantasy of an imagined world. The island chain is a place entirely of my own creation. By creating the viewpoint of an outside explorer, it was possible to navigate through this world. Although I, as the artist, can know everything about this fictitious world, adopting the perspective of someone distanced by time and place allowed for discrepancies, misinterpretation, and the sense of mystery that typically colors interpretations of foreign, ancient cultures. This character is forced to fill in the context for what she is viewing based upon her conjectures, which may or may not reveal the full truth. Overall, perspective on cultures is often shaped by the observations of a few individuals. In the same way, viewers are forced to consider this culture through the lens of one character, without being entirely certain if they are consuming objective truths.

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Cedlind, Michael. "Field Recordings." Thesis, Konstfack, Institutionen för Konst (K), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:konstfack:diva-6780.

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Castilho, C. M. C. de. "Theory of field ionization in the field ion microscope." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373668.

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Huang, Tao. "Holographic techniques for antenna near-field/far-field measurements." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301549.

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CIORBA, LORENZO. "UAV-based Far-Field and Near-Field Antenna Measurements." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2972561.

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Simsir, Muazzez Fatma. "Conformal Vector Fields With Respect To The Sasaki Metric Tensor Field." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605857/index.pdf.

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On the tangent bundle of a Riemannian manifold the most natural choice of metric tensor field is the Sasaki metric. This immediately brings up the question of infinitesimal symmetries associated with the inherent geometry of the tangent bundle arising from the Sasaki metric. The elucidation of the form and the classification of the Killing vector fields have already been effected by the Japanese school of Riemannian geometry in the sixties. In this thesis we shall take up the conformal vector fields of the Sasaki metric with the help of relatively advanced techniques.

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Moreno, Almeida Javier. "Time evolution of inflaton fields in non-equilibrium quantum field theory." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439566.

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Schritt, Dimitri. "Symmetries in quantum and classical field theories." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8032.

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The initial chapter of the thesis provides a review of Weinberg’s formalism for the derivation of quantum fields. The formalism is extended to allow for the derivation of quantum fields with more than one spin degree of freedom. It is conjectured that it may be possible to construct massive bosonic quantum field theories of any desired spin j that are consistent and unitary at all energies without the need for regulator terms by including j + 1 spin degrees of freedom: j, j - 1, down to j - j. The concept is then demonstrated in two subsequent chapters by the derivation of a quantum field with spin one and spin zero degrees of freedom followed the derivation of a quantum field with spin two, spin one, and spin zero degrees of freedom. Both field theories are found to be consistent and unitary at all energies without the need for regulator terms. The final two chapters are on unrelated topics. The penultimate chapter provides an explicit derivation of quantum fields for massless particles of spin one-half. In the final chapter, a derivation of the free-space Proca and Maxwell equations is provided via a consistent identification of the linear combinations of the classical fields of the (1,0) and (0,1) representations of the orthochronous Lorentz group.

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Spanner, Michael. "Field-Free Alignment and Strong Field Control of Molecular Rotors." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/1256.

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Methods of controlling molecular rotations using linearly polarized femtosecond and picosecond pulses are considered and analyzed theoretically. These laser pulses, typically in the infrared, are highly non-resonant with respect to the electronic degrees of freedom of the molecules and have intensities of ∼ 10^13 to 10^14 W/cm². It is shown how these laser pulses can force small linear molecules to align with the direction of the electric field vector of the laser both in the presence of the laser field as well as after the application of a short laser pulse. Recent experiments on laser-induced molecular alignment are modeled and excellent agreement between experiment and theory is found. Additional methods of controlling molecular rotational dynamics are outlined. The first method considers the forced rotational acceleration of diatomic molecules, called the optical centrifuge. Here, the direction of polarization of a linearly polarized laser field is made to smoothly rotate faster and faster. The molecules, which tend to align with the polarization vector of the laser field, follow the rotation of the laser polarization and are accelerated to high angular momentum. The second method considers the control of field-free rotational dynamics by applying phase shifts to the molecular wave function at select times called fractional revivals. At these select moments, an initially localized wave function splits into several copies of the initial state. Adding phase shifts to the copies then induces interference effects which can be used to control the subsequent evolution of the rotational wave function. This same control scheme has a close link to quantum information and this connection is outlined. Finally, a recently proposed method of controlling the quantum dynamics of the classically chaotic kicked rotor system [J. Gong and P. Brumer, Phys. Rev. Lett. 86, 1741 (2001)] is analyzed from a phase space perspective. It is shown that the proposed quantum control can be linked to small islands of stability in the classical phase space. An experimentally feasible variant of this control scenario using wave packets of molecular alignment is proposed. Two applications of molecular alignment are discussed. The first application uses field-free aligned molecules as a non-linear medium for compression of a laser pulse to the 1 fs regime at optical wavelengths. At such durations, these laser pulses contain nearly a single oscillation of the electric field and represent the shortest laser pulses physically achievable for such frequencies. The second application uses molecular alignment to create a sort of gas phase "molecular crystal" which forms a basis for laser-induced electron diffraction and imaging of the aligned molecules. Here, a first laser pulse aligns the molecules in space. A second laser pulse is then used to ionize outer-shell electrons, accelerate them in the laser field, and steer them back to collide with the parent ion creating a diffraction image with sub-femtosecond and sub-Angstrom resolution.

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Daniel, Michael J. "Modular forms on a function field over a finite field." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3273712.

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Kildén, Smith Martin. "Chaotic Field Exploration : Exploring systemic field dynamics in bilateral negotiations." Thesis, Linköpings universitet, Pedagogik och sociologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-114770.

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The purpose of this paper is to explore the nature of the social field as described by Pierre Bourdieu as well as to explore the possibility of creating a more focused and tailored set of conditions in the form of a model to repurpose the field theory to more clearly be applicable to bilateral negotiations. The methodological approach is conceptual analysis based on the epistemology of critical realism. The supporting theories for the approach are a combination of systemic, chaos and complexity theory while the fundaments for the implementation of the methodological approach are the four main concepts in Bourdieu’s theory of the social field: the field, habitus, illusio and symbolic capital. One of the main points of repurposing this specific dynamic is to explicitly allow for deliberate human agency within the field. Analytical data consists purely of the secondary type. This essay is not empirically based but rather theoretical and abstract. The paper is founded on the basic principles of macrosociology and presumes social agency where appropriate. This paper focuses on creating a tentative framework model based on repurposed concepts derived from Bourdieu. The results are arguably interesting but are mostly limited to affecting further development of this tentative model and prefacing application of it through attempting to implement it in an analytical manner on empirical data.

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陶福臻 and Fook-tsun To. "Soliton solutions to gravitational field and Yang-Mills gauge field." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31233910.

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Watterson, P. A. "Force-free magnetic field evolution in the reversed-field pinch." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355048.

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Карнаушенко, В. П., and А. В. Бородин. "Field Programmable Counter Arrays Integration with Field Programmable Gates Arrays." Thesis, NURE, MC&FPGA, 2019. https://mcfpga.nure.ua/conf/2019-mcfpga/10-35598-mcfpga-2019-004.

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Field Programmable Counter Arrays (FPCAs) have been recently introduced to close the gap between Field Programmable Gates Arrays (FPGA) and Application Specified Integrated Circuits (ASICs) for arithmetic dominated applications. FPCAs are reconfigurable lattices that can be embedded into FPGAs to efficiently compute the result of multi-operand additions.

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To, Fook-tsun. "Soliton solutions to gravitational field and Yang-Mills gauge field /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13671728.

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Vaidya, Manushka. "Steering Electromagnetic Fields in MRI| Investigating Radiofrequency Field Interactions with Endogenous and External Dielectric Materials for Improved Coil Performance at High Field." Thesis, New York University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261392.

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Although 1.5 and 3 Tesla (T) magnetic resonance (MR) systems remain the clinical standard, the number of 7 T MR systems has increased over the past decade because of the promise of higher signal-to-noise ratio (SNR), which can translate to images with higher resolution, improved image quality and faster acquisition times. However, there are a number of technical challenges that have prevented exploiting the full potential of ultra-high field (≥ 7 T) MR imaging (MRI), such as the inhomogeneous distribution of the radiofrequency (RF) electromagnetic field and specific energy absorption rate (SAR), which can compromise image quality and patient safety.

To better understand the origin of these issues, we first investigated the dependence of the spatial distribution of the magnetic field associated with a surface RF coil on the operating frequency and electrical properties of the sample. Our results demonstrated that the asymmetries between the transmit (B₁⁺) and receive (B₁^–) circularly polarized components of the magnetic field, which are in part responsible for RF inhomogeneity, depend on the electric conductivity of the sample. On the other hand, when sample conductivity is low, a high relative permittivity can result in an inhomogeneous RF field distribution, due to significant constructive and destructive interference patterns between forward and reflected propagating magnetic field within the sample.

We then investigated the use of high permittivity materials (HPMs) as a method to alter the field distribution and improve transmit and receive coil performance in MRI. We showed that HPM placed at a distance from an RF loop coil can passively shape the field within the sample. Our results showed improvement in transmit and receive sensitivity overlap, extension of coil field-of-view, and enhancement in transmit/receive efficiency. We demonstrated the utility of this concept by employing HPM to improve performance of an existing commercial head coil for the inferior regions of the brain, where the specific coil’s imaging efficiency was inherently poor. Results showed a gain in SNR, while the maximum local and head SAR values remained below the prescribed limits. We showed that increasing coil performance with HPM could improve detection of functional MR activation during a motor-based task for whole brain fMRI.

Finally, to gain an intuitive understanding of how HPM improves coil performance, we investigated how HPM separately affects signal and noise sensitivity to improve SNR. For this purpose, we employed a theoretical model based on dyadic Green’s functions to compare the characteristics of current patterns, i.e. the optimal spatial distribution of coil conductors, that would either maximize SNR (ideal current patterns), maximize signal reception (signal-only optimal current patterns), or minimize sample noise (dark mode current patterns). Our results demonstrated that the presence of a lossless HPM changed the relative balance of signal-only optimal and dark mode current patterns. For a given relative permittivity, increasing the thickness of the HPM altered the magnitude of the currents required to optimize signal sensitivity at the voxel of interest as well as decreased the net electric field in the sample, which is associated, via reciprocity, to the noise received from the sample. Our results also suggested that signal-only current patterns could be used to identify HPM configurations that lead to high SNR gain for RF coil arrays. We anticipate that physical insights from this work could be utilized to build the next generation of high performing RF coils integrated with HPM.

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Webber, Matthew. "Stochastic neural field models of binocular rivalry waves." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c444a73e-20e3-454d-85ae-bbc8831fdf1f.

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Binocular rivalry is an interesting phenomenon where perception oscillates between different images presented to the two eyes. This thesis is primarily concerned with modelling travelling waves of visual perception during transitions between these perceptual states. In order to model this effect in such a way that we retain as much analytical insight into the mechanisms as possible we employed neural field theory. That is, rather than modelling individual neurons in a neural network we treat the cortical surface as a continuous medium and establish integro-differential equations for the activity of a neural population. Our basic model which has been used by many previous authors both within and outside of neural field theory is to consider a one dimensional network of neurons for each eye. It is assumed that each network responds maximally to a particular feature of the underlying image, such as orientation. Recurrent connections within each network are taken to be excitatory and connections between the networks are taken to be inhibitory. In order for such a topology to exhibit the oscillations found in binocular rivalry there needs to be some form of slow adaptation which weakens the cross-connections under continued firing. By first considering a deterministic version of this model, we will show that, in fact, this slow adaptation also serves as a necessary "symmetry breaking" mechanism. Using this knowledge to make some mild assumptions we are then able to derive an expression for the shape of a travelling wave and its wave speed. We then go on to show that these predictions of our model are consistent not only with numerical simulations but also experimental evidence. It will turn out that it is not acceptable to completely ignore noise as it is a fundamental part of the underlying biology. Since methods for analyzing stochastic neural fields did not exist before our work, we first adapt methods originally intended for reaction-diffusion PDE systems to a stochastic version of a simple neural field equation. By regarding the motion of a stochastic travelling wave as being made up of two distinct components, firstly, the drift-diffusion of its overall position, secondly, fast fluctuations in its shape around some average front shape, we are able to derive a stochastic differential equation for the front position with respect to time. It is found that the front position undergoes a drift-diffusion process with constant coefficients. We then go on to show that our analysis agrees with numerical simulation. The original problem of stochastic binocular rivalry is then re-visited with this new toolkit and we are able to predict that the first passage time of a perceptual wave hitting a fixed barrier should be an inverse Gaussian distribution, a result which could potentially be experimentally tested. We also consider the implications of our stochastic work on different types of neural field equation to those used for modelling binocular rivalry. In particular, for neural fields which support pulled fronts propagating into an unstable state, the stochastic version of such an equation has wave fronts which undergo subdiffusive motion as opposed to the standard diffusion in the binocular rivalry case.

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Nazarian, Bamshad. "Integrated Field Modeling." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-84.

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This research project studies the feasibility of developing and applying an integrated field simulator to simulate the production performance of an entire oil or gas field. It integrates the performance of the reservoir, the wells, the chokes, the gathering system, the surface processing facilities and, whenever applicable, gas and water injection systems.

The approach adopted for developing the integrated simulator is to couple existing commercial reservoir and process simulators using available linking technologies. The simulators are dynamically linked and customized into a single hybrid application that benefits from the concept of open software architecture. The integrated field simulator is linked to an optimization routine developed based on the genetic algorithm search strategies. This enables optimization of the system at field level, from the reservoir to the process. Modeling the wells and the gathering network is achieved by customizing the process simulator.

This study demonstrates that the integrated simulation improves currentcapabilities to simulate the performance of an entire field and optimize its design. This is achieved by evaluating design options including spread and layout of the wells and gathering system, processing alternatives, reservoir development schemes, and production strategies.

Effectiveness of the integrated simulator is demonstrated and tested through several field-level case studies that discuss and investigate technical problems relevant to offshore field development. The case studies cover topics such as process optimization, optimum tie-in of satellite wells into existing process facilities, optimal well location, and field layout assessment of a high pressure high temperature deepwater oil field.

Case study results confirm the viability of the total field simulator by demonstrating that the field performance simulation and optimal design were obtained in an automated process with reasonable computation time. No significant simplifying assumptions were required to solve the system and tedious manual data transfer between simulators, as conventionally practiced, was avoided.

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Muenster, Korbinian. "String field theory." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-160964.

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This thesis discusses several aspects of string field theory. The first issue is bosonic open-closed string field theory and its associated algebraic structure -- the quantum open-closed homotopy algebra. We describe the quantum open-closed homotopy algebra in the framework of homotopy involutive Lie bialgebras, as a morphism from the loop homotopy Lie algebra of closed string to the involutive Lie bialgebra on the Hochschild complex of open strings. The formulation of the classical/quantum open-closed homotopy algebra in terms of a morphism from the closed string algebra to the open string Hochschild complex reveals deformation properties of closed strings on open string field theory. In particular, we show that inequivalent classical open string field theories are parametrized by closed string backgrounds up to gauge transformations. At the quantum level the correspondence is obstructed, but for other realizations such as the topological string, a non-trivial correspondence persists. Furthermore, we proof the decomposition theorem for the loop homotopy Lie algebra of closed string field theory, which implies uniqueness of closed string field theory on a fixed conformal background. Second, the construction of string field theory can be rephrased in terms of operads. In particular, we show that the formulation of string field theory splits into two parts: The first part is based solely on the moduli space of world sheets and ensures that the perturbative string amplitudes are recovered via Feynman rules. The second part requires a choice of background and determines the real string field theory vertices. Each of these parts can be described equivalently as a morphism between appropriate cyclic and modular operads, at the classical and quantum level respectively. The algebraic structure of string field theory is then encoded in the composition of these two morphisms. Finally, we outline the construction of type II superstring field theory. Specific features of the superstring are the appearance of Ramond punctures and the picture changing operators. The sewing in the Ramond sector requires an additional constraint on the state space of the world sheet conformal field theory, such that the associated symplectic structure is non-degenerate, at least on-shell. Moreover, we formulate an appropriate minimal area metric problem for type II world sheets, which can be utilized to sketch the construction of a consistent set of geometric vertices. The algebraic structure of type II superstring field theory is that of a $\mathcal{N}=1$ loop homotopy Lie algebra at the quantum level, and that of a $\mathcal{N}=1$ homotopy Lie algebra at the classical level.

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Hutcheson, Kenneth Andrew. "Geomagnetic field modelling." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385503.

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Yfantouda, Renata Pires. "Field : smoking cessation." Thesis, City University London, 2007. http://openaccess.city.ac.uk/8555/.

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The UK government white paper on tobacco "Smoking Kills" set targets to reduce rates of smoking among adults from 28% to 24% by 2010. The success of behavioural smoking cessation programmes varies according to the type of intervention delivered (Viswesvaran & Schimidt, 1992). Group support programmes are the most commonly delivered smoking cessation interventions in the NHS, although in order to understand which methods are most effective, it is necessary to identify which psychosocial baseline factors predict successful outcomes. This study analysed the role of psychosocial predictors of decision to quit and 4-week abstinence in a community smoking cessation programme.

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林君煌 and Kwan-wong Alan Lam. "The lost field." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B3198521X.

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Smith, Joshua Reynolds. "Electric field imaging." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/29144.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts & Sciences, 1999.
Includes bibliographical references (p. 213-216).
The physical user interface is an increasingly significant factor limiting the effectiveness of our interactions with and through technology. This thesis introduces Electric Field Imaging, a new physical channel and inference framework for machine perception of human action. Though electric field sensing is an important sensory modality for several species of fish, it has not been seriously explored as a channel for machine perception. Technological applications of field sensing, from the Theremin to the capacitive elevator button, have been limited to simple proximity detection tasks. This thesis presents a solution to the inverse problem of inferring geometrical information about the configuration and motion of the human body from electric field measurements. It also presents simple, inexpensive hardware and signal processing techniques for making the field measurements, and several new applications of electric field sensing. The signal processing contribution includes synchronous undersampling, a narrowband, phase sensitive detection technique that is well matched to the capabilities of contemporary microcontrollers. In hardware, the primary contributions are the School of Fish, a scalable network of microcontroller-based transceive electrodes, and the LazyFish, a small footprint integrated sensing board. Connecting n School of Fish electrodes results in an array capable of making heterodyne measurements of any or all n(n - 1) off-diagonal entries in the capacitance matrix. The LazyFish uses synchronous undersampling to provide up to 8 high signal-to-noise homodyne measurements in a very small package. The inverse electrostatics portion of the thesis presents a fast, general method for extracting geometrical information about the configuration and motion of the human body from field measurements. The method is based on the Sphere Expansion, a novel fast method for generating approximate solutions to the Laplace equation. Finally, the thesis describes a variety of applications of electric field sensing, many enabled by the small footprint of the LazyFish. To demonstrate the School of Fish hardware and the Sphere Expansion inversion method, the thesis presents 3 dimensional position and orientation tracking of two hands.
by Joshua Reynolds Smith.
Ph.D.

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Gray, Michael D. "Convergent field elastography." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53464.

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A new approach to soft tissue elastography is presented. The work was motivated by the need to understand and mitigate the effects of anthropogenic sound on marine mammals. These efforts have been hampered by a lack of knowledge of in vivo tissue viscoelastic moduli. To address this problem, a measurement system concept was developed to non-invasively determine shear viscoelastic properties at tissue depths of over 12 cm – well beyond the capabilities of existing systems. The central design feature of the measurement system is a focused, sectored, annular ultrasonic source that generates a ring-like pressure field. This in turn produces a ring-like radiation force distribution in soft tissue, the response of which is primarily observable as a shear wave field that converges to the center of the force pattern. A second confocal transducer nested inside the shear wave generation source is used to measure the component of the shear wave motion along the beam axis. Propagation speed is estimated from displacement phase changes resulting from drive frequency induced dilation of the forcing radius. Forcing beams are modulated in order to establish shear speed frequency dependence, allowing quantification of shear speed dispersion. This concept for convergent field elastography (CFE) is intended to significantly improve the overall ability to estimate soft tissue shear speeds in thick, complex tissues while keeping within FDA-mandated ultrasound exposure limits. A prototype system was developed and tested in tissue mimicking materials for which properties were independently determined. Experiments were first carried out in a homogeneous material, and subsequently in a material containing elastic contrast inclusions. Transmission experiments with re-hydrated samples of bottlenose dolphin skull and mandibular bone samples were conducted to quantify ultrasonic beam attenuation and distortion effects, and their cumulative impact on CFE shear estimation performance. In addition to supporting marine mammal studies, the techniques developed in this thesis may enable or extend a wide range of human medical diagnostics.

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Fazi, Filippo Maria. "Sound field reproduction." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/158639/.

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This thesis is concerned with the problem of reproducing a desired sound field with an array of loudspeakers. A theory based on functional analysis and the theory of integral equations is developed for the study of this problem. An attempt is made to develop a mathematical framework that can be adopted as a generalized theory of sound field reproduction. The reproduction problem is formulated as an acoustical inverse problem, in which the target sound field is given on the boundary of a control volume located in the interior of the loudspeaker array, while the loudspeaker signals required for the reproduction of the desired field are to be determined. The loudspeaker array is initially modeled as a continuous distribution of secondary sources, mathematically represented by a single layer potential, whose density is to be determined. The singular value decomposition of the integral operator involved is proposed as a method for solving the inverse problem. Closed form expressions are derived for the singular system for the cases of secondary sources arranged on a sphere and on a circle. An attempt is also made to extend the calculation to unbounded geometries, such as an infinite line and a plane. The inverse problem under consideration is in general ill-posed, and the existence and uniqueness of its solution are studied in relation to sound fields of practical interest. It is shown that an exact and unique solution exists for a large family of sound fields. Strategies are proposed for overcoming the problem of nonexistence and nonuniqueness of the solution, arising in cases such as the reproduction of focused sources or when the operating frequency corresponds to one of the Dirichlet eigenvalues of the control region. An important analogy is also drawn between the problem of sound field reproduction and the theory of acoustic scattering. In a later part of this work, the assumptions of a continuous layer of secondary sources and of a single operating frequency are removed, and the resulting consequences are analyzed. The experimental validation of some of the theoretical results is described in the final part of the thesis. A large spherical loudspeaker array is used in an attempt to reproduce the sound field generated by a single virtual source, located in the exterior of the array. Experimental results are in good agreement with the theoretical results over a wide range of frequencies.

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Belote, Justin. "Cloud & Field." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3753.

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Cloud & field is an exploration into the role the past has in the formation of a personal language and the subsequent role that language has on a personal belief system. It investigates the subjective interchangeability of the external and internal landscape. Having abandoned my childhood faith four or five years ago, the writing of this manuscript was an attempt to develop a new moral/belief system I could carry with me into the future. It is, therefore, also the beginning of an investigation into if and why a belief system is necessary.

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Lam, Kwan-wong Alan. "The lost field." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25953047.

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Perlina, Anna. "Shaping the field." Doctoral thesis, Humboldt-Universität zu Berlin, Philosophische Fakultät I, 2016. http://dx.doi.org/10.18452/17672.

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Die vorliegende wissenschaftliche Arbeit rekonstruiert die Entwicklung der deutschen Psychologie zwischen der Eröffnung des ersten psychologischen Labors in 1879 und der Gleichschaltung durch das Nazi-Regime in den 1930er Jahren. Die Dissertation stellt den konzeptuellen und methodologischen Rahmen der psychologischen Disziplin anhand von drei Generationen von Pionierforschung dar. Hierbei wird herausgearbeitet, wie sich die frühe experimentelle Psychologie einen eigenen Platz zwischen den Natur- und Geisteswissenschaften kreiert. Die gestaltpsychologische Schule spielt darin eine entscheidende Rolle. Der zentrale Fokus der Arbeit liegt in der historischen Periode zwischen 1922 und 1936, über welche sich Kurt Lewins Untersuchungen zur Handlungs- und Affektpsychologie erstrecken. In dieser deutschen Schaffensperiode wurden der theoretische und methodologische Rahmen, sowie praktische experimentelle Designs erschaffen, welche die amerikanische Arbeit Lewins entscheidend prägten. Der Aufbau von Lewins berühmter Feldtheorie wird im Detail rekonstruiert. Die Dissertation zeigt auf, wie Lewin originelle psychologische Konzepte aus interdisziplinärer Erfahrung formte, und wie experimentelle Praktiken der Zeit die Entstehung eines immer komplexer werdenden Konzeptgerüstes herbeiführten. Anschließend wird die Bedeutung des Gestalt-Lewin-Falles für die Psychologiegeschichte erörtert. In die langfristige Wissenschaftsgeschichte ist Lewins Arbeit nicht etwa als gebündeltes Forschungsgebiet eingegangen. Stattdessen ist sie in so unterschiedliche Bereiche wie Entwicklungs- und Persönlichkeitspsychologie, Soziologie und Wirtschaftsmanagement eingeflossen und hat diese geprägt.
This dissertation represents a historical reconstruction of the development and transformation of German experimental psychology between the emergence of the first experimental laboratory in 1879 and its Gleichschaltung by the Nazi regime in the 1930s. It traces the evolution of the conceptual as well as the experimental framework of psychology over the course of these years following three generations of experimental research. Hereby, the work attempts to grasp how early experimental psychology negotiated its place between the humanities and the natural sciences. The project’s major focus lies in the period between 1922 and 1936, in which Kurt Lewin’s Berlin Experimental Program on Action and Emotions took place. The work specifically investigates the process of constitution of Lewin’s field theory, a system of concepts coined by Lewin in order to study psychological processes underlying human conduct. The dissertation shows how Lewin’s concepts emerged out of interdisciplinary sources, and how experimental practices in psychology triggered the emergence of new knowledge. Eventually, it is shown how the investigated historical case of Gestalt psychology in Berlin fits into and plays a decisive role in the long-term development of experimental psychology.

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Sarala, J. (Jouni). "Low field NMR." Bachelor's thesis, University of Oulu, 2019. http://jultika.oulu.fi/Record/nbnfioulu-201907252707.

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Abstract. The subject of this thesis is NMR in low magnetic field. Traditionally NMR instruments utilize a superconducting high field magnet, but recently, compact instruments are getting more common with the use of lower magnetic fields. In this thesis, the basic theory of NMR is explained and the instrumentation and different ways of producing homogeneous magnetic fields are described. An experimental set-up was constructed and tested. The theory of relaxation and dependence of resonance frequency on the magnetic field were demonstrated.

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Drummer, Emily. "Field of repose." Thesis, University of Iowa, 2018. https://ir.uiowa.edu/etd/6410.

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This essay documents the investigative and theoretical underpinnings of my thesis film, Field of Repose. Field of Repose is a speculative essay film that uses elements of science fiction and documentary to investigate hidden ecological networks of communication in the American Midwest. In this speculative world, the relationship between nature, technology, and society is radically restructured; it imagines a future in which the changing climate and environmental conditions are recast as an active resistance to nature’s own devastation. Using environmental realities already at play in the state of Iowa and beyond, the film defamiliarizes scenes of the present and charges them with dystopian elements. In so doing, Field of Repose dismantles imperialistic and anthropocentric motifs in science fiction and invites viewers to enter an anarchic web of feedback and response in which the essay film’s omniscient narrator is replaced by a cacophony of orphaned radio signals that pollute the air. Plants, earth’s first communicators, are now its last. Humanity is but a blip.

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49

Kilic, Delalcan. "The diffeomorphism field." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6156.

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The diffeomorphism field is introduced to the physics literature in [1] where it arises as a background field coupled to Polyakov’s quantum gravity in two dimensions, where Einstein’s gravity is trivial. Moreover, it is seen in many ways as the gravitational analog of the Yang-Mills field. This raises the question of whether the diffeomorphism field exists in higher dimensions, playing an essential role in gravity either by supplementing Einstein’s theory or by modifying it. With this motivation, several distinct theories governing the dynamics of the diffeomorphism field have been constructed and developed by mimicking the construction of the Yang-Mills theory from the Kac-Moody algebra. This analogy, however, is not perfect and there are many subtleties and difficulties encountered. This thesis constitutes a further development. The previously proposed theories are carefully examined; certain subtleties and problems in them have been discovered and made apparent. Some of these problems have been solved, and for others possible routes to follow have been laid down. Finally, other geometric approaches than the ones followed before are investigated.

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Mohamed, Adam. "Local Class Field Theory via Lubin-Tate Theory /." Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/1936.

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Dissertations / Theses on the topic 'Field'

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