Thèses : « Object characterization »

1

LaPointe, Jamie. « Adaptive estimation techniques for resident space object characterization ». Thesis, The University of Arizona, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10250698.

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This thesis investigates using adaptive estimation techniques to determine unknown model parameters such as size and surface material reflectivity, while estimating position, velocity, attitude, and attitude rates of a resident space object. This work focuses on the application of these methods to the space situational awareness problem.

This thesis proposes a unique method of implementing a top-level gating network in a dual-layer hierarchical mixture of experts. In addition it proposes a decaying learning parameter for use in both the single layer mixture of experts and the dual-layer hierarchical mixture of experts. Both a single layer mixture of experts and dual-layer hierarchical mixture of experts are compared to the multiple model adaptive estimation in estimating resident space object parameters such as size and reflectivity. The hierarchical mixture of experts consists of macromodes. Each macromode can estimate a different parameter in parallel. Each macromode is a single layer mixture of experts with unscented Kalman filters used as the experts. A gating network in each macromode determines a gating weight which is used as a hypothesis tester. Then the output of the macromode gating weights go to a top level gating weight to determine which macromode contains the most probable model. The measurements consist of astrometric and photometric data from non-resolved observations of the target gathered via a telescope with a charge coupled device camera. Each filter receives the same measurement sequence. The apparent magnitude measurement model consists of the Ashikhmin Shirley bidirectional reflectance distribution function. The measurements, process models, and the additional shape, mass, and inertia characteristics allow the algorithm to predict the state and select the most probable fit to the size and reflectance characteristics based on the statistics of the measurement residuals and innovation covariance. A simulation code is developed to test these adaptive estimation techniques. The feasibility of these methods will be demonstrated in this thesis.

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LaPointe, Jamie J., et Jamie J. LaPointe. « Adaptive Estimation Techniques for Resident Space Object Characterization ». Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/623263.

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This thesis investigates using adaptive estimation techniques to determine unknown model parameters such as size and surface material reflectivity, while estimating position, velocity, attitude, and attitude rates of a resident space object. This work focuses on the application of these methods to the space situational awareness problem. This thesis proposes a unique method of implementing a top-level gating network in a dual-layer hierarchical mixture of experts. In addition it proposes a decaying learning parameter for use in both the single layer mixture of experts and the dual-layer hierarchical mixture of experts. Both a single layer mixture of experts and dual-layer hierarchical mixture of experts are compared to the multiple model adaptive estimation in estimating resident space object parameters such as size and reflectivity. The hierarchical mixture of experts consists of macromodes. Each macromode can estimate a different parameter in parallel. Each macromode is a single layer mixture of experts with unscented Kalman filters used as the experts. A gating network in each macromode determines a gating weight which is used as a hypothesis tester. Then the output of the macromode gating weights go to a top level gating weight to determine which macromode contains the most probable model. The measurements consist of astrometric and photometric data from non-resolved observations of the target gathered via a telescope with a charge coupled device camera. Each filter receives the same measurement sequence. The apparent magnitude measurement model consists of the Ashikhmin Shirley bidirectional reflectance distribution function. The measurements, process models, and the additional shape, mass, and inertia characteristics allow the algorithm to predict the state and select the most probable fit to the size and reflectance characteristics based on the statistics of the measurement residuals and innovation covariance. A simulation code is developed to test these adaptive estimation techniques. The feasibility of these methods will be demonstrated in this thesis.

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Mandadi, Bharath Kumar Reddy. « Advanced Object Characterization and Monitoring Techniques Using Polarimetric Imaging ». University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1243780947.

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Biller, Beth A., Johanna Vos, Esther Buenzli, Katelyn Allers, Mickaël Bonnefoy, Benjamin Charnay, Bruno Bézard et al. « Simultaneous Multiwavelength Variability Characterization of the Free-floating Planetary-mass Object PSO J318.5−22 ». IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627034.

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We present simultaneous Hubble Space Telescope (HST) WFC3+Spitzer IRAC variability monitoring for the highly variable young (similar to 20 Myr) planetary-mass object PSO J318.5-22. Our simultaneous HST + Spitzer observations covered approximately two rotation periods with Spitzer and most of a rotation period with the HST. We derive a period of 8.6. +/-. 0.1 hr from the Spitzer light curve. Combining this period with the measuredvsinifor this object, we find an inclination of 56 degrees.2. +/-. 8 degrees.1. We measure peak-to-trough variability amplitudes of 3.4%. +/-. 0.1% for Spitzer Channel 2 and 4.4%-5.8% (typical 68% confidence errors of similar to 0.3%) in the near-IR bands (1.07-1.67 mu m) covered by the WFC3 G141 prism-the mid-IR variability amplitude for PSO J318.5-22 is one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary-mass object. Additionally, we detect phase offsets ranging from 200 degrees to 210 degrees (typical error of similar to 4 degrees) between synthesized near-IR light curves and the Spitzer mid-IR light curve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

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Flasseur, Olivier. « Object detection and characterization from faint signals in images : applications in astronomy and microscopy ». Thesis, Lyon, 2019. http://www.theses.fr/2019LYSES042.

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La détection et la caractérisation d’objets dans des images à faible rapport signal sur bruit est un problème courant dans de nombreux domaines tels que l’astronomie ou la microscopie. En astronomie, la détection des exoplanètes et leur caractérisation par imagerie directe depuis la Terre sont des sujets de recherche très actifs. Une étoile cible et son environnement proche (abritant potentiellement des exoplanètes) sont observés sur de courtes poses. En microscopie, l’holographie en ligne est une méthode de choix pour caractériser à faibles coûts les objets microscopiques. Basée sur l’enregistrement d’un hologramme, elle permet une mise au point numérique dans n’importe quel plan du volume 3-D imagé. Dans ces deux applications cibles, le problème est rendu difficile par le faible contraste entre les objets et le fond non stationnaire des images enregistrées.Dans cette thèse, nous proposons un algorithme non-supervisé dédié à la détection et à la caractérisation d’exoplanètes par une modélisation statistique des fluctuations du fond. Cette méthode est basée sur une modélisation de la distribution statistique des données à une échelle locale de patchs, capturant ainsi leur covariances spatiales. Testé sur plusieurs jeux de données de l’imageur haut-contraste SPHERE opérant au Très Grand Télescope Européen, cet algorithme atteint de meilleures performances que les méthodes de l’état de l’art. En particulier, les cartes de détection produites sont stationnaires et statistiquement fondées. La détection des exoplanètes peut ainsi être effectuée à probabilité de fausse alarme contrôlée. L’estimation de la distribution d’énergie spectrale des sources détectées est également non biaisée. L’utilisation d’un modèle statistique permet également de déduire des précisions photométriques et astrométriques fiables. Ce cadre méthodologique est ensuite adapté pour la détection de motifs spatialement étendus tels que les motifs de diffraction rencontrés en microscopie holographique qui sont également dominés par un fond non-stationnaire. Nous proposons aussi des approches robustes basées sur des stratégies de pondération afin de réduire l’influence des nombreuses valeurs aberrantes présentes sur les données réelles. Nous montrons sur des vidéos holographiques que les méthodes de pondération proposées permettent d’atteindre un compromis biais/variance. En astronomie, la robustesse améliore les performances de détection, en particulier à courtes séparations angulaires, où les fuites stellaires dominent. Les algorithmes développés sont également adaptés pour tirer parti de la diversité spectrale des données en plus de leur diversité temporelle, améliorant ainsi leurs performances de détection et de caractérisation. Tous les algorithmes développés sont totalement non-supervisés: les paramètres de pondération et/ou de régularisation sont estimés directement à partir des données. Au-delà des applications considérées en astronomie et en microscopie, les méthodes de traitement du signal introduites dans cette thèse sont générales et pourraient être appliquées à d’autres problèmes de détection et d’estimation
Detecting and characterizing objects in images in the low signal-to-noise ratio regime is a critical issue in many areas such as astronomy or microscopy. In astronomy, the detection of exoplanets and their characterization by direct imaging from the Earth is a hot topic. A target star and its close environment (hosting potential exoplanets) are observed on short exposures. In microscopy, in-line holography is a cost-effective method for characterizing microscopic objects. Based on the recording of a hologram, it allows a digital focusing in any plane of the imaged 3-D volume. In these two fields, the object detection problem is made difficult by the low contrast between the objects and the nonstationary background of the recorded images.In this thesis, we propose an unsupervised exoplanet detection and characterization algorithm based on the statistical modeling of background fluctuations. The method, based on a modeling of the statistical distribution of patches, captures their spatial covariances. It reaches a performance superior to state-of-the-art techniques on several datasets of the European high-contrast imager SPHERE operating at the Very Large Telescope. It produces statistically grounded and spatially-stationary detection maps in which detections can be performed at a constant probability of false alarm. It also produces photometrically unbiased spectral energy distributions of the detected sources. The use of a statistical model of the data leads to reliable photometric and astrometric accuracies. This methodological framework can be adapted to the detection of spatially-extended patterns in strong structured background, such as the diffraction patterns in holographic microscopy. We also propose robust approaches based on weighting strategies to reduce the influence of the numerous outliers present in real data. We show on holographic videos that the proposed weighting approach achieves a bias/variance tradeoff. In astronomy, the robustness improves the performance of our detection method in particular at close separations where the stellar residuals dominate. Our algorithms are adapted to benefit from the possible spectral diversity of the data, which improves the detection and characterization performance. All the algorithms developed are unsupervised: weighting and/or regularization parameters are estimated in a data-driven fashion. Beyond the applications in astronomy and microscopy, the signal processing methodologies introduced are general and could be applied to other detection and estimation problems

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Lopes, Alex Cerqueira. « Máscaras : transformações em “Doroteia” de Nelson Rodrigues ». Escola de Teatro, 2014. http://repositorio.ufba.br/ri/handle/ri/27042.

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RESUMO Este trabalho trata máscara-objeto e máscara-maquiagem como meiode transformação dos atores no espetáculo “Doroteia”, de Nelson Rodrigues. A dissertação é constituída a partir de experiências com máscaras, tanto objeto quanto maquiagem, apresentando no percurso das vivências a solidificação e base para a concepção e criação dos elementos cênicos em questão. Essainvestigação tem como objetivo abordar a caracterização visual dos personagens no referido espetáculo, com foco nas máscaras supracitadas, destacando sua importância fundamental para a construção do personagem teatral. Posteriormente, são analisadas as aplicabilidades das referidas máscaras nas cenas do espetáculo. As leituras a partir da percepção do espectador acontecem como consequência da consciência coerente com o todo que o portador estabelece.
ABSTRACT This thesis deals with mask-object and mask-make up asinstruments of transformation of the actors at Nelson Rodrigues’ play, “Doroteia”. The dissertation is built over experiences with mask-object and mask-make up, introducing during the process the solidification and basis for conception and creation of the scenic elements being studied. This investigation aims to broach the visual characterization of the characters in the play, focusing on the two previously mentioned masks, emphasizing their fundamental importance for the theatrical character’s construction. Subsequently, the applicability of the masks will be analyzed in the scenes of the play. The readings from the spectator’s perception happen as consequence of the conscience consistent with the whole established by the mask’s wearer.

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Al, Hayek Marianne. « Modélisation optique de signatures spectrales et polarimétriques d'objets pour augmenter les performances d'un système de reconnaissance ». Electronic Thesis or Diss., Brest, 2023. http://www.theses.fr/2023BRES0101.

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L’imagerie conventionnelle, qui se limite aux formes et couleurs des objets, montre ses limites en matière de reconnaissance. Pour améliorer les performances des systèmes d’imagerie, l’imagerie hyperspectrale et polarimétrique apporte une richesse d’informations, notamment des grandeurs physiques difficiles à obtenir autrement. Cela permet d’améliorer la détection, la caractérisation quantitative et la classification des objets. Cependant, le traitement des données complexes de ces modalités reste un défi. L’objectif de ce travail est de proposer une méthodologie générique pour analyser les signaux optiques, en se concentrant sur l’imagerie hyperspectrale (HSI) en premier terme. Une classification originale des modèles hyperspectraux inversibles basés sur la physique est présentée, avec description des modèles variés les plus récents pour des applications diverses : MPBOM pour le biofilm d’algues et de bactéries, MARMIT pour le sol, PROSPECT pour les feuilles de plantes, Farrell pour les tissus biologiques turbides, Schmitt pour la peau humaine et Hapke pour les objets du système solaire. Une convergence entre les modèles PROSPECT et Farrell pour des objets intermédiaires (pomme verte et poireau) ouvrant la voie au développement d’une nouvelle modélisation générique et complète. Notamment dans le domaine de la biologie, par une collaboration avec le laboratoire de l’ANSES, nous avons procédé à une détection précoce suivie d’une quantification du biofilm qui se forme dans les bassins d’élevage de poissons en utilisant l’imagerie hyperspectrale et polarimétrique du fait que sa détection actuelle est visuelle et n’est pas assez efficace pour prévenir son accumulation et pour mettre en place des procédures de nettoyage et de désinfection. Ainsi une première version d’une modélisation physique propre nommée "DNA-HSI" a été mise en place
Conventional imaging, limited to object shapes and colors, faces limitations in object recognition. To enhance imaging system performance, hyperspectral and polarimetric imaging provides a wealth of information, includingchallenging-to-obtain physical parameters. This facilitates improved object detection, quantitative characterization, and classification. However, the processing of complex data from these modalities remains a challenge. The aim of this work is to propose a generic methodology for the analysis of optical signals, with a primary focus on hyperspectral imaging (HSI). An original classification of invertible physics-based hyperspectral models is presented, along with descriptions of recent diverse models for various applications: MPBOM for algae and bacteria biofilm, MARMIT for soil, PROSPECT for plant leaves, Farrell for turbid biological tissues, Schmitt for human skin, and Hapke for objects in the solar system. A convergence between the PROSPECT and Farrell models for intermediate objects (green apple and leek) paves the way for the development of a new generic and comprehensive modeling approach.Particularly in the field of biology, in collaboration with the ANSES laboratory, we conducted early detection ollowed by quantification of biofilms forming in fish farming basins using hyperspectral and polarimetric imaging. This is crucial as the current visual detection method is not efficient in preventing biofilm accumulation and implementingcleaning and disinfection procedures. Hence, an initial version of a dedicated physical modeling approach called "DNA-HSI" has been established

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Fernandes, Lénia Janete Oliveira. « Characterization and identification of printed objects ». Master's thesis, FCT - UNL, 2008. http://hdl.handle.net/10362/1763.

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A study about the physical appearance of pre-photographic, photomechanical, photographic and digital positive reflective prints was made, relating the obtained images with the history, materials and technology used to create them. The studied samples are from the Image Permanence Institute (IPI) study collection. The digital images were obtained using a digital SLR on a copystand and a compound light microscope, with different lighting angles (0º, 45ºand 90º) and magnifications from overall views on the copystand down to a 20x objective lens on the microscope. Most of these images were originally created by IPI for www.digitalsamplebook.org, a web tool for teaching print identification, and will be used on the www.graphicsatlas.org website, along with textual information on identification, technology and history information about these reproduction processes.

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Goh, Jinzhong Jeremy [Verfasser], Denise [Gutachter] Manahan-Vaughan et Klaus-Peter [Gutachter] Hoffmann. « Characterization of the effects of novel object-space information on synaptic plasticity in the hippocampal CA1 sub-region of freely behaving mice / Jinzhong Jeremy Goh ; Gutachter : Denise Manahan-Vaughan, Klaus-Peter Hoffmann ; International Graduate School of Neuroscience ». Bochum : Ruhr-Universität Bochum, 2013. http://d-nb.info/1212660749/34.

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bin, Ahmad Khairuddin Taufiq. « Characterization of objects by fitting the polarization tensor ». Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/characterization-of-objects-by-fitting-the-polarization-tensor(1ee0de67-fdd4-4fae-ba00-3f2e4f3987a8).html.

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This thesis focuses on some mathematical aspects and a few recent applications of the polarization tensor (PT). Here, the main concern of the study is to characterize objects presented in electrical or electromagnetic fields by only using the PT. This is possible since the PT contains significant information about the object such as shape, orientation and material properties. Two main applications are considered in the study and they are electrosensing fish and metal detection. In each application, we present a mathematical formulation of the PT and briefly discuss its properties. The PT in the electrosensing fish is actually based on the first order generalized polarization tensor (GPT) while the GPT itself generalizes the classical PT called as the P\'lya-Szeg\H PT. In order to investigate the role of the PT in electrosensing fish, we propose two numerical methods to compute the first order PT. The first method is directly based on the quadrature method of numerical integration while the second method is an adaptation of some terminologies of the boundary element method (BEM). A code to use the first method is developed in \textit while a script in \textit is written as an interface for using the new developed code for BEM called as \textit. When comparing the two methods, our numerical results show that the first order PT is more accurate with faster convergence when computed by \textit. During this study, we also give a strategy to determine an ellipsoid from a given first order PT. This is because we would like to propose an experiment to test whether electrosensing fish can discriminate a pair of different objects but with the same first order PT such that the pair could be an ellipsoid and some other object. In addition, the first order PT (or the P\'{o}lya-Szeg\H{o} PT) with complex conductivity (or complex permittivity) which is similar to the PT for Maxwell's equations is also investigated. On the other hand, following recent mathematical foundation of the PT from the eddy current model, we use the new proposed explicit formula to compute the rank 2 PT for a few metallic targets relevance in metal detection. We show that the PT for the targets computed from the explicit formula agree to some degree of accuracy with the PT obtained from metal detectors during experimental works and simulations conducted by the engineers. This suggests to alternatively use the explicit formula which depends only on the geometry and material properties of the target as well as offering lower computational efforts than performing measurements with metal detectors to obtain the PT. By using the explicit formula of the rank 2 PT, we also numerically investigate some properties of the rank 2 PT where, the information obtained could be useful to improve metal detection and also in other potential applications of the eddy current. In this case, if the target is magnetic but non-conducting, the rank 2 PT of the target can also be computed by using the explicit formula of the first order PT.

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Delgado, Hugo. « Characterization and surface reconstruction of objects in tomographic images of composite materials ». Master's thesis, Faculdade de Ciencias e Tecnologia, 2013. http://hdl.handle.net/10362/13141.

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Dissertação para obtenção do Grau de Mestre em Engenharia Informática
In the scope of the project Tomo-GPU supported by FCT / MCTES the aim is to build an interactive graphical environment that allows a Materials specialist to define their own programs for analysis of 3D tomographic images. This project aims to build a tool to characterize and investigate the identified objects, where the user can define search criteria such as size, orientation, bounding boxes, among others. All this processing will be done on a desktop computer equipped with a graphics card with some processing power. On the proposed solution the modules for characterizing objects, received from the identification phase, will be implemented using some existing software libraries, most notably the CGAL library. The characterization modules with bigger execution times will be implemented using OpenCL and GPUs. With this work the characterization and reconstruction of objects and their research can now be done on conventional machines, using GPUs to accelerate the most time-consuming computations. After the conclusion of this thesis, new tools that will help to improve the current development cycle of new materials will be available for Materials Science specialists.

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Toullier, Thibaud. « Simultaneous characterization of objects temperature and radiative properties through multispectral infrared thermography ». Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S038/document.

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L'utilisation de caméras infrarouges bas coûts pour la surveillance long-terme d'infrastructures est prometteuse grâce aux dernières avancées technologiques du domaine. Une mesure précise de la température des surfaces observées in-situ se heurte au manque de connaissance des propriétés radiatives de la scène. L'utilisation d'une instrumentation multi-capteurs permet d'affiner le modèle de mesure afin d'obtenir une estimation plus précise de la température. A contrario, il est montré qu'il est toujours possible d'exploiter des données climatiques en ligne pour pallier un manque de capteur. Des méthodes bayésiennes d'estimation conjointe d'émissivité et de température sont ensuite développées et comparées aux méthodes de la littérature. Un simulateur d'échanges radiatifs diffus de scènes 3D a été implémenté afin de tester ces différentes méthodes. Ce logiciel utilise l'accélération matérielle de la machine pour réduire les temps de calcul. Les résultats numériques obtenus mettent en perspective une utilisation avancée de la thermographie infrarouge multi-spectrale pour la surveillance de structures. Cette estimation conjointe permet alors d'obtenir un estimé de la température par thermographie infrarouge avec une incertitude connue
The latest technological improvements in low-cost infrared cameras have brought new opportunities for long-term infrastructures monitoring. The accurate measurement of surfaces' temperatures is facing the lack of knowledge of radiatives properties of the scene. By using multi-sensors instrumentation, the measurement model can be refined to get a better estimate of the temperature. To overcome a lack of sensors instrumentation, it is shown that online and free available climatic data can be used. Then, Bayesian methods to estimate simultaneously the emissivity and temperature have been developed and compared to literature's methods. A radiative exchange simulator of 3D scenes have been developed to compare those different methods on numerical data. This software uses the hardware acceleration as well as a GPGPU approach to reduce the computation time. As a consequence, obtained numerical results emphasized an advanced use of multi-spectral infrared thermography for the monitoring of structures. This simultaneous estimation enables to have an estimate of the temperature by infrared thermography with a known uncertainty

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Ley, Clemens. « Forward looking logics and automata ». Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d6eb0004-47b9-4e32-b6c9-7796afecabd5.

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This thesis is concerned with extending properties of regular word languages to richer structures. We consider intricate properties like the relationship between one-way and two-way temporal logics, minimization of automata, and the ability to effectively characterize logics. We investigate whether these properties can be extended to tree languages or word languages over an infinite alphabet. It is known that linear temporal logic (LTL) is as expressive as first-order logic over finite words [Kam68, GPSS80]. LTL is a unidirectional logic, that can only navigate forwards in a word, hence it is quite surprising that it can capture all of first-order logic. In fact, one of the main ideas of the proof of [GPSS80] is to show that the expressiveness of LTL is not increased if modalities for navigating backwards are added. It is also known that an extension of bidirectional LTL to ordered trees, called Conditional XPath, is first-order complete [Mar04]. We investigate whether the unidirectional fragment of Conditional XPath is also first-order complete. We show that this is not the case. In fact we show that there is a strict hierarchy of expressiveness consisting of languages that are all weaker than first-order logic. Unidirectional Conditional XPath is contained in the lowest level of this hierarchy. In the second part of the thesis we consider data word languages. That is, word languages over an infinite alphabet. We extend the theorem of Myhill and Nerode to a class of automata for data word languages, called deterministic finite memory automata (DMA). We give a characterization of the languages that are accepted by DMA, and also provide an algorithm for minimizing DMA. Finally we extend theorems of Büchi, Schützenberger, McNaughton, and Papert to data word languages. A theorem of Büchi states that a language is regular iff it can be defined in monadic second-order logic. Schützenberger, McNaughton, and Papert have provided an effective characterization of first-order logic, that is, an algorithm for deciding whether a regular language can be defined in first-order logic. We provide a counterpart of Büchi's theorem for data languages. More precisely we define a new logic and we show that it has the same expressiveness as non-deterministic finite memory automata. We then turn to a smaller class of data languages, those that are recognized by algebraic objects called orbit finite data monoids. We define a second new logic and show that it can define precisely the languages accepted by orbit finite data monoids. We provide an effective characterization of a first-order variant of this second logic, as well as of restrictions of first-order logic, such as its two variable fragment and local variants.

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Carrizo, Carlos. « Hyperspectral and Polarimetric Imaging for Advanced Characterization of the Ocean Surface and Underwater Objects ». Thesis, The City College of New York, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13425979.

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Hyperspectral and polarimetric imaging of the ocean, both below and above the water surface, has increased the interest of the Ocean Color (OC) scientific community for decades in an attempt to answer questions related to climate change, monitoring of water quality, assessment of the impact of anthropogenic activities on marine life and underwater ecosystems, detection and characterization of underwater targets. These needs are recognized by worldwide efforts devoted to acquiring accurate time series measurements in open-ocean and coastal waters by OC satellite imagery to produce reliable high-quality data records, which can be used both in support of operations and in climate studies. The reliability of satellite observations of the open-ocean and coastal zones requires these remote instruments to be regularly assessed and validated against actual in-situ measurements along with related atmospheric corrections. However, despite improvements in satellite data and retrieval algorithms, accurate retrievals in coastal waters remain challenging.

Modern hyperspectral imagers usually carry out their measurements on moving platforms, aircrafts or orbiting satellites, using push-broom scanning techniques for the acquisition of 3-D data cubes (along-track, cross-track and spectral). These data, however, may not always reflect accurately the temporal variability of measurements in a very dynamic atmosphere-ocean environment, especially in coastal areas. In recent years, new technologies have made possible the exploration of snapshot hyperspectral and polarimetric imaging of the ocean in an attempt to improve the accuracy of existing methods and exploring the pixel-by-pixel variability of the signal measured, often neglected in standard approaches.

The work presented in this thesis investigates and discusses imaging of underwater polarimetric targets in various water types and the estimation of parameters of the veiling light and the attenuation coefficients responsible for image degradation and blurring as a function of the water properties. In above water observations the effects of atmospheric aerosols and wind speed on the surface reflectance coefficients are studied along with the pixel-by-pixel variability of water-leaving radiance (L_w) and its relationship to water constituents for different coastal waters and atmospheric conditions, the impact of this variability on the uncertainties in above water measurements and satellite retrievals. Validation of all results has been achieved by the comparison with the comprehensive Vector Radiative Transfer simulations of the Atmosphere-Ocean System, as well as measurements by a number of other collocated radiometric and polarimetric instruments.

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Mommert, M., D. E. Trilling, D. Borth, R. Jedicke, N. Butler, M. Reyes-Ruiz, B. Pichardo, E. Petersen, T. Axelrod et N. Moskovitz. « FIRST RESULTS FROM THE RAPID-RESPONSE SPECTROPHOTOMETRIC CHARACTERIZATION OF NEAR-EARTH OBJECTS USING UKIRT ». IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/614713.

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Using the Wide Field Camera for the United Kingdom Infrared Telescope (UKIRT), we measure the near-infrared colors of near-Earth objects (NEOs) in order to put constraints on their taxonomic classifications. The rapid-response character of our observations allows us to observe NEOs when they are close to the Earth and bright. Here we present near-infrared color measurements of 86 NEOs, most of which were observed within a few days of their discovery, allowing us to characterize NEOs with diameters of only a few meters. Using machine-learning methods, we compare our measurements to existing asteroid spectral data and provide probabilistic taxonomic classifications for our targets. Our observations allow us to distinguish between S-complex, C/X-complex, D-type, and V-type asteroids. Our results suggest that the fraction of S-complex asteroids in the whole NEO population is lower than the fraction of ordinary chondrites in the meteorite fall statistics. Future data obtained with UKIRT will be used to investigate the significance of this discrepancy.

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Casadei, Valerio. « Experimental characterization of backscattering properties of UWB antennas in the presence of close objects ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/4073/.

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RTLS and RFID systems are becoming more and more important in several fields. When these systems meet the UWB technology, they can take advantage of each other strengths. Since nowadays a strong importance is given to the "green" technology, we chose to adopt a passive solution. In this case the backscattering modulation can be used to carry data. Therefore it is necessary to analyze the behavior of the antennas used as tags, when they are closed to dierent material objects. In particular, the antenna mode part has been deeply observed, as it is the crucial part of the signal regarding the backscatter modulation.

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Afridi, Pirzada. « Syntheses & ; characterization of nanoZSM-5 & ; MOR zeolites, characterization of ZNS in the pore network of MOR ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:8117cf4f-0a27-4eff-a328-8558573fc3b8.

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This study was carried out on the synthesis of mordenite zeolite and ZSM-5 zeolite. In Chapter 3 reports the growth of ZnS nanoclusters in the pore channels of mordenite zeolite. ZnS as an important wide-band-gap (3.6 eV) semiconductor nanoclusters and have various technological applications such as photocatalysis, nonlinear optics, sensors, solar cells, injection lasers, flat panel displays, ultraviolet light emitting diodes (LED). Zeolites have several different applications in industries, such as in catalysis, ion exchange adsorption and gas separation. Zeolites are mostly used as a catalyst in the petrochemical industry. ZSM-5 zeolite is widely used a heterogeneous catalyst in the petrochemical industry due to its unique porous structure. Special attention has been made to synthesize nano-ZSM-5 in order to improve its catalytic activity. Catalysis depends on the characteristics length scale of the active sites, while the rate depends on the accessible active sites. In order to improve the performance of ZSM-5 zeolite used as a catalyst in the petrochemical industry, the researchers amid to produce nanocrystalline of the ZSM-5 zeolite. That will help to reduce the path length for the reaction and hence will increase the rate of a reaction. Comparative synthesis nano-particles of ZSM-5 zeolite using two different methods of treatment i.e. pre-treatment and interrupted treatment with ultrasound and without ultrasound was studied, its effect on aging and crystal growth during the hydrothermal treatment. In Chapter 4 the pre-treatment with ultrasound and without ultrasound (static) with an increasing time intervals have been reported. The resulting product the particle size is clearly decreased by using ultrasound pre-treatment. While in Chapter 5 using a different method of treatment called interrupted of the hydrothermal process. As in this method, we stopped the hydrothermal process for 20 minutes and treated the gel with ultrasound for 15 minutes. This treatment was repeated after every 2 hours of hydrothermal treatment. Similarly, the same method was applied to the experiment but without the use of ultrasound called a static method of aging. A 3rd method was also applied to investigate the effect of ultrasound on the particle size distribution of the synthesized crystalline powder. All the results showed that the ultrasound not only effects on the particle size but it also affects the crystallinity too i.e. increased the crystallinity and the reduced in the particle size.

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Seet, Li Fong. « Characterization of the biological properties of FGF-9 ». Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:a46cee92-c179-4d22-b27b-0e67c3c85a37.

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The fibroblast growth factor family of polypeptides currently consists of nine structurally-related members. Cloning of the mouse homologue of the latest reported member of the family, FGF-9, is described in this study. Mouse Fgf9 exhibits a high level of sequence conservation with the human, rat and Xenopus counterparts. Of note is the lack of a hydrophobic signal peptide at the N-terminus of the coding sequence. The protein, however, appeared to be secreted by producer cells since a significant quantity of the protein could be purified from the culture supernatant of transfected cells. Members of the FGF family are known to bind to cell surface tyrosine kinase receptors (FGFRs) to elicit a variety of physiological responses. These receptors themselves form a family of four structurally-related tyrosine kinases and each FGF member commonly has the ability to bind several members of the FGFR family. By using in vitro plate binding assays, FGF-9 is shown in this study to bind specifically to two FGFR members: FGFR2b and FGFR3c. To further study the potential functional role of FGF-9, its expression pattern in the mouse embryo was examined by both RNase protection and RNA in situ hybridization analyses. The transcript was detected in a variety of embryonic tissues: the germinal epithelium of the central nervous system, the mesonephric cords, the somites, the gut primordia and the developing eye and ear, suggesting that the gene may have multiple roles during development. In addition, the potential involvement of FGF-9 in mediating adult brain functions was examined by double RNA in situ hybridization analysis of the distribution of both Fgf9 and Fgfr3 transcripts in the adult mouse brain. Most apparent areas of co-localization are the olfactory bulb and cerebral cortex. The two transcripts are also shown to have distinct distribution patterns in the cerebellum.

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Wang, Shanshan. « Synthesis and characterization of monolayer molybdenum disulphide ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:182cdf51-c6e2-40bc-abf8-8057130bc2f5.

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Monolayer molybdenum disulphide (MoS₂) is a semiconductor with a direct bandgap of ∼1.9 eV. Much research attention has been attracted to its potential applications in nanoelectronics and optoelectronics recently, all of which are based upon a scalable production of high-quality monolayer MoS₂ and the in-depth comprehension of its fundamental properties. The PhD project focused on developing chemical vapour deposition (CVD) methods to grow monolayer MoS₂ and its related two-dimensional (2D) vertical heterostructures with an understanding of the growth mechanism. Subsequently, a range of characterizations were conducted to investigate the structural, vibrational, optical and mechanical properties of as-grown samples. An atmospheric-pressure CVD (APCVD) approach was first developed to grow monolayer MoS2 crystals on silicon substrates with a 300 nm oxide layer (SiO₂/Si) by using molybdenum trioxide (MoO₃) and sulphur (S) as precursors. A sharp gradient of MoO3 was intentionally created, which induced a location-dependent shape evolution of MoS₂ domains. A qualitative explanation was proposed, attributing this phenomenon to local changes in the Mo:S ratio of precursors and its influence on the kinetic growth dynamics of edges. Subsequently, the CVD setup was improved in both the precursor loading manner and the substrate orientation to achieve centimetre-scale monolayer MoS₂ films with large domain sizes of 10-20μm. Finally, 2D MoS₂/hexagonal boron nitride (h-BN) vertical heterostructures were fabricated via an all-CVD method. Raman and photoluminescence (PL) spectroscopy were applied to show its merits of smaller lattice strain, lower doping level and better interlayer contact compared with CVD-grown MoS₂ on SiO₂/Si substrates and mechanically stacked samples. Aberration-corrected transmission electron microscopy (AC-TEM) was carried out to study the defect structure and fracture mechanics of monolayer MoS₂ at a single atom level. Subtle lattice reconstructions of line defects in various lengths and widths were resolved. Density functional theory (DFT) predicted a reduction of the bandgap as the line defects broaden, which eventually makes them behave as metallic channels embedded in the semiconducting MoS₂. Another joint experimental and theoretical study was conducted to track the real-time crack propagation in monolayer MoS₂. The atomically sharp crack tip went through the preferential lattice direction with least energy release. Increasing defect density was found to induce an enhanced fracture toughness and a fracture mechanism transition from brittle to ductile.

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Xu, Diming. « Synthesis and characterization of mixed-metal germanates ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:8a6b4ca2-0824-4d9a-8907-b40537405c72.

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Mixed-metal germanates with the general formula ABB'Ge₄O₁₂ have been synthesised using the ceramic method and their properties characterised by X-ray diffraction, neutron diffraction, dc and ac magnetometry, specific heat and Mossbauer spectroscopy. DFT calculations were conducted on two compounds ZrM₂Ge₄O₁₂ (M = Mn, Co). All compositions adopt a tetragonal structure (space group P4/nbm with the unit-cell parameters a = b ~ 2c). The cation A occupies the 2b site and is coordinated by eight oxide ions at the corners of a square antiprism whereas B and B' are disordered over the 4f site which is at the centre of a distorted octahedron of oxide ions. They can be considered to lie in layers perpendicular to the [001] axis. These layers are separated from each other by layers containing [Ge₄O₁₂]8- rings, each ring being comprised of four vertex-sharing GeO4 tetrahedra. CeMn_2âxCo_xGe₄O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) become anti-ferromagnetic (x = 0.0, 1.5, 2.0) or weakly ferromagnetic (x = 0.5, 1.0) at 4.2 ≤ T ≤ 7.6 K. The ordered moments lie along [001] when x = 0.0 and in the (001) plane otherwise. The unit cell doubles along [001] when x = 1.5 and 2.0, but the doubling is lost when a first-order metamagnetic transition occurs on the application of a 10 kOe magnetic field. The ordered moments at 1.6 K for x = 0.0 and 2.0 are 4.61(2) and 2.58(2) Î1⁄4_B, respectively; the corresponding effective moments in the paramagnetic phase are 5.91 and 5.36 Î1⁄4_B. CeM1.5M'0.5Ge₄O₁₂ (M = Mn, Co; M' = Zn, Ni, Cu) show similar magnetic properties as CeM₂Ge₄O₁₂ albeit with changes in the NÃ©el temperature and Weiss constant due to the differences between the cations used. ZrMn_2âxCo_xGe₄O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) show long-range magnetic order with transition temperatures, T_C, in the range 2 ≤ T_C/K ≤ 10. The underlying magnetic structure is the same in each case but the ordered spins lie along [001] when x = 0.0 and in the (001) plane for all other compositions. In all cases the magnetically-ordered phase is a weak ferromagnet although the magnitude of the spontaneous magnetisation and the strength of the coercive field are composition-dependent. The magnetic structure can be rationalized by considering the strengths of the interactions along the distinct MâOâGeâOâM superexchange pathways in the crystal and the observed magnetic structure is entirely consistent with the predictions of ab initio calculations. LnFeMGe₄O₁₂ (Ln = Y, Eu, Gd, Lu; M = Mn, Zn) show long-range antiferromagnetic order with transition temperatures 15 ≤ T_N/K &;e; 30. The magnetic structure is the same in each case and consists of an A-type ordering of (001) planes; the ordered spins lie in the (001) plane. Comparison with isostructural compounds leads to the conclusion that subtle structural changes play a greater role than the electronic configuration of the cation in determining the magnetic structure. Ln₂MGe₄O₁₂ (Ln = Gd-Yb; M = Ca, Mn, Co) and LnBCoGe₄O₁₂ (B = Sc or Lu) show various magnetic behaviours. The calcium-, holmium- and erbium-containing compositions remain paramagnetic down to 2 K; the other cases show a transition at the temperatures ~ 4 K. Dy₂CoGe₄O₁₂ and DyScCoGe₄O₁₂ behave as spin glasses and the terbium- and gadolinium-cobalt-containing compounds show long-range magnetic order. Tb2MnGe₄O₁₂ shows a weakly ferromagnetic phase and Gd₂MnGe₄O₁₂, Dy₂MnGe₄O₁₂ are antiferromagnets. The data can be rationalized qualitatively in terms of the interplay between magnetic anisotropy and crystal field effects.

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Van, Essen-Fishman Lucy. « Character through interaction : Sophocles and the delineation of the individual ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c23353ec-cc60-453e-8c58-b13d01840a19.

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In this thesis, I argue that Sophoclean characters take shape through a number of different kinds of interaction. On the most basic level, interaction occurs between characters; interactions between characters, however, provide a framework for interactions between those characters and a variety of more abstract concepts. These interactions, by allowing characters to situate themselves with respect to concepts such as, for example, the social roles which shape the society of the play, provide a more complex picture of the personalities depicted onstage; a fuller view of Antigone’s personality, for example, emerges both from her own interactions with the concept of sisterhood and from the differences between her interactions with that concept and Ismene’s. At the same time, these interactions involve the audience in both the construction and the interpretation of Sophoclean characters; as they watch figures interact with each other onstage, the audience, in turn, interact with their own prior knowledge of the concepts which drive the characters of a play. In my five chapters, I discuss five different areas of interaction. In my first chapter, I look at interactions between characters and myth, arguing that Sophoclean characters emerge out of a tension between novelty and familiarity. In my second chapter, I discuss the interactions between characters and their social roles, looking at the problem of appropriate role performance as it applies to Sophoclean characters. My third chapter deals with characters and their memories; I argue that Sophoclean characters shape and are shaped by their memories of past events depending on shifting present circumstances. In my fourth chapter, I discuss the interactions between characters and the passage of time and suggest that Sophoclean figures are characterized by the ways in which they move through time and respond to its passage. In my final chapter, I look at the use of general statements by Sophoclean characters, arguing that the ability of characters to generalize successfully provides a useful measure of their ability to function in the world of the play.

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Gelabert, Javier. « Investigation of ultra-wideband wireless communication inside electromagnetically ultra small confined environments ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:672f535d-431d-44be-88db-8dfbfd709247.

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Ultra-wideband (UWB) communication has been the subject of extensive research in recent years due to its unique capabilities and potential applications, particularly in short-range multiple access wireless communications. However, many important aspects of UWB-based communication systems have not yet been thoroughly investigated. The propagation of UWB signals inside very small enclosed environments is one of the important issues with significant impacts on the future direction, scope, and generally the extent of the success of UWB technology. The objective of this thesis is to obtain a more thorough and comprehensive understanding of ultra-small UWB channels for communication applications and design issues for enhancing the data rate of UWB systems. This works supports the postulation of a high capacity UWB wireless interconnect scheme for communicating devices within conducting enclosures – a wireless “backplane”. This thesis proposes the use of an Ultra-Wide Bandwidth (UWB) ultra-small scale wireless interconnect scheme for use within electrically small enclosures. Such ultra-small environments (size ≤ 10 wavelengths) are topologically much more complex, being more cluttered, than typical indoor environments (size ≥ 10 wavelengths). The concept is presented through two different scenarios. Firstly, a PC Tower case is presented as a model environment and the work seeks to present the optimum channel performance, where EMI issues are discussed and problem avoidance proposed. Secondly, in order to extrapolate the different results from the study inside the PC, an investigation is carried out using an Aluminium tower case as a more generic model environment. The analysis is based on the behaviour of box modes within a conducting resonator enclosure and the effective communications bandwidth for UWB systems for different sizes and components within. From these general considerations the research presents theoretical and experimental results from which are derived the communications metrics measured within enclosures. Simulations of the different scenarios are performed using different techniques such as ray tracing and a full wave model, based on CST Microstripes. Empirical data is recorded using a vector network analyser (VNA)-based wideband channel sounding system where channel measurements are carried out in every scenario regarding different aspects such as frequency response and time domain analysis, evaluation of the channel capacity, power delay study and the nature of the environment.

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Nelson, Geoffrey Winston. « Surface characterization and functional properties of carbon-based materials ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:f22b95ce-65f3-4d9e-ac3d-a88f6e142c1a.

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Carbon-based materials are poised to be an important class of 21st century materials, for bio-medical, bio-electronic, and bio-sensing applications. Diamond and polymers are two examples of carbon-based materials of high interest to the bio-materials community. Diamond, in its conductive form, can be used as an electrochemical bio-sensor, whilst its nanoparticle form is considered a non-inflammatory platform to deliver drugs or to grow neuronal cells. Polymers, especially when chemically modified, have been used extensively in biological environments, from anti-microbial use to drug delivery. The large-scale use of either material for biological use is limited by two factors: ease of chemical modification and the paucity of knowledge of their surface chemistry in aqueous media. This thesis addresses aspects of both these issues. The first study reported is an in situ study of the adsorption dynamics of an exemplar globular protein (bovine serum albumin, BSA) on nanodiamond using the relatively novel quartz crystal microbalance with dissipation (QCM-D) technique. For the first time, QCM-D enabled the detailed study of protein dynamics (i.e. kinetics, viscoelastic properties, overlayer structure, etc.) onto nanodiamond thin films having various surface chemistry and roughness. The dynamics of protein adsorption is found to be sensitive to surface chemistry at all stages of adsorption, but it is only sensitive to surface roughness during initial adsorption phases. Our understanding of the nanodiamond-biology interface is enhanced by this study, and it suggests that QCM-D is useful for the study of the surface chemistry of nanoparticle forms of inorganic materials. A second study concerns a novel surface functionalization scheme, based on carbene and azo-coupling chemistry, which has been recently introduced as a practical, facile method for modifying the surfaces of polymers. Using modern surface characterization techniques, it is demonstrated that a chemical linker can be attached to polystyrene surfaces using carbene-based chemistry, and that further chemical functionality can be added to this chemical linker via an azo-coupling reaction. In situ studies of protein dynamics at these interfaces were conducted using QCM-D, thus enabling a link between specific protein behaviour and the polymer surface chemical termination chemistry to be made. A third area of study of investigates the use of diamond electrodes as a bio-sensor for dopamine under physiological conditions. For these conditions, ascorbic acid interferes with the dopamine oxidation signal, in ways that render the two signals irresolvable. Various modifications are used in attempts to reduce this interference, including: small and large cathodic treatments, grafting of electro-active polymers, addition of carbon nanotubes, and hydrogen plasma treatment. Those modifications leading to the hydrogen-termination of diamond are shown to work the best. Notably, hydrogen plasma treatment effects the complete electrochemical separation of dopamine and ascorbic acid at a diamond electrode. This is the first time this has been accomplished without adding non-diamond materials to the diamond electrode surface.

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Kiappes, John Leon. « Synthesis and biological characterization of natural and designed sugars ». Thesis, University of Oxford, 2014. https://ora.ox.ac.uk/objects/uuid:ccc0e4dd-a8b4-445b-9fee-260c35b0040d.

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Carbohydrates represent a keystone among biological molecules. Well known as a source of energy, sugars also form the backbone of various biopolymers, act as markers and receptors for cellular communication and modulate lipid and protein functions. As such a powerful class, carbohydrates represent a useful pool from which both nature and man have drawn structures to produce biologically active compounds with a variety of modes of action. Beyond their importance to biology, sugars have represented attractive synthetic targets to chemists given their densely functionalized scaffolds. The work presented in this thesis aims to employ synthetic chemistry to provide both natural and designed carbohydrates in order to carry out biological studies to improve our understanding of these compounds' particular effects. In the first part, a synthesis is developed for the carboline disaccharide domain of the cytotoxic enediyne, shishijimicin A. The route employs a Reetz-Müller-Starke reaction to install the domain's quaternary center, with addition of a carboline dianion to complete the target. Iminosugars represent the focus of the second portion of the thesis. These polyhydroxylated alkaloids have long been investigated for their ability to mimic single sugars, inhibiting various glycosidases and glycosyltransferases. The endocyclic nitrogen atom of members of this class can act as a functional handle for alkylation, with increased chain length increasing both potency of enzyme inhibition and toxicity in cellula. Specific iminopyranose structures with D-gluco stereochemistry have broad-spectrum antiviral activity, while those with D-galacto stereochemistry are antiviral with respect to hepatitis C, but not other genetically related viruses. Reported herein are syntheses of classes of iminosugars to determine the influence of both N-alkylation chain length and iminopyranose stereochemistry on the spectrum of antiviral activity. Complementing antiviral activity with isolated enzyme inhibition assays, the work aims to identify new targets for next generation antivirals. Finally, the prototypical iminosugar, D-deoxynojirimycin, is conjugated to a second natural product, D-α-tocopherol. By replacing the more common normal alkyl group with a lipid, the goal was to reduce cellular toxicity, while also taking advantage of the natural active transport for the lipid to increase uptake of the drug. Surprisingly, this change provided a marked shift in selectivity of enzyme inhibition and antiviral ability. In order to fully characterize the mechanism, the mentioned enzymatic and antiviral studies were supplemented with lipidomic, STED-microscopy and pharmacokinetic investigations.

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Tan, Felicia. « Characterization of pilE antisense RNA in Neisseria meningitidis ». Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:23d8f4c4-b423-4638-986b-b6b8e3fe95ec.

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Expression of Type four pili is important for colonization and virulence in Neisseria meningitidis, which is a major causative agent of bacterial meningitis and septicaemia. Pili mediate adhesion, twitching motility, DNA uptake, and can be subject to phase and antigenic variation (Av). Pilin expression and Av may be modulated in response to environmental cues; however, the mechanisms of regulation are still unclear. This work demonstrates the identification of a novel cis-encoded RNA on the antisense (AS) strand of pilE, which encodes the major pilin subunit. The AS promoter is conserved in different N. meningitidis isolates, suggesting that the AS RNA may play an important role N. meningitidis biology. By Northern blot and strand-specific qRT-PCR, the AS transcript was shown to be expressed during specific conditions, namely after overnight growth and in response to salt stress. The AS RNA was found to encompass sequences antisense to the entire pilE coding sequence and 5' untranslated region, and extends to a promoter upstream of pilE that drives expression of a G4 small RNA that is important for pilin Av. Noncoding RNAs are increasingly recognized as important regulators of gene expression in bacteria. AS RNAs often modulate expression of the sense mRNA, however in this study, overexpression or deletion of the AS RNA had no significant effect on pilE transcript or pilin levels despite its long stretch of complementarity to the pilE mRNA. Potential trans targets were also investigated by performing RNAseq analysis to identify differentially expressed genes in the absence of the AS RNA. Expression of the AS RNA was found to reduce the frequency of pilE variation. The possible influence of the AS RNA on G4 small RNA transcription was investigated by examining its effect on the levels of G4 small RNA and RNA:DNA hybrids. Although technical issues prevented us from obtaining definitive results, our findings suggest the AS RNA forms RNA:DNA hybrids, adding an additional layer of complexity of molecular processes in the pilE locus of N. meningitidis.

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Yeh, Shaoyang Anthony. « Three-dimensional aligned fibrillar scaffolds : fabrication and characterization ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:4e83606f-134f-4cb0-a4a5-78dfc8b33010.

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Aligned fibrillar scaffolds (AFSs) have been widely studied for their application in regenerative medicine, providing possible transplantable tissue replacements for nerve, spinal cord, tendon, ligament, muscle, etc. However, researches in AFSs are technically challenging mainly due to the complex fabrication and characterization processes, especially when the AFSs are made to be fully three-dimensional (3D). As the structure is linked to the quality and function of the engineered tissue product, there is an urgent need for novel techniques to characterize AFSs non-invasively and non-destructively and to link their characteristics to their functions and outcome. In this thesis AFS fabrication and characterization were explored. By combining second harmonic generation (SHG) imaging, multiphoton microscopy (MPM), and various image processing tools, the whole process of 3D tissue characterization could be achieved in a non-invasive, precise, and quantitative way. A proof-of-concept AFS with blended fibers made of polycaprolactone and porcine gelatin was used to demonstrate the feasibility of implementing such a strategy. The data indicated that, in terms of scaffold characterization, the proposed MPM method was capable of measuring the porosity of homogenous scaffolds precisely from deconvolved 3D images. Furthermore, the method could also be used to illustrate the orientation of the aligned nanofibers. Next, when SH-SY5Y neurons were cultured on the AFS, the MPM imaging was capable of evaluating the cell viability ratio, cell-localization in AFS, and neurite outgrowth. This provided guidance for selecting the alignment method for AFS functional recovery. Lastly, when employing this non-invasive imaging-based characterization method, it was possible to illustrate the relationship between the alignment of collagen arrays in decellularized corneal stroma and the transparency. In summary, the proposed strategy can provide some essential scaffold/tissue properties (such as alignment of fiber, porosity of scaffold, and cell viability ratio) quantitatively and non-invasively, which will help both scaffold processing design and characterization.

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Peng, Yung-Kang. « Surface mapping of faceted metal oxides by chemical probe-assisted NMR for catalytic applications ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:7b56021f-71fb-437b-8c6b-0569705ef68e.

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Semiconductive metal oxides are of great importance in environmental remediation and electronics because of their ability to generate charge carriers when excited with appropriate energy. The electronic structure, light absorption and charge transport properties have made the transition metal oxides an attractive material as photocatalyst. Recently, facet-engineering by morphology control has been intensively studied as an efficient approach to further enhance their photocatalytic performance. However, various processing steps and post-treatments used in the preparation of facet-engineered particles may generate different surface active sites which may affect their photocatalysis. Moreover, many traditional techniques (PL, EPR and XPS) used for materials characterization (oxygen vacancy, hydroxyl group, cation, etc.) are not truly surface specific but analyzing a range from surface few layers to bulk. Accordingly, they can only provide very limited information on chemical states of the surface active features and their distribution among facets, causing difficulties to unambiguously correlate facet-dependent results with activity. As a result, this often leads to different interpretations amongst researchers during the past decades. As the publications of titanium and zinc ranked top two among studies of first row of transition oxides in the past decades, this thesis will firstly review on the disagreements generated among researchers when they correlated the performance of ZnO and TiO₂ with their facet activities based on traditional techniques. As there are shortcomings of these techniques in producing truly facet-dependent features, some results can be misleading and with no cross-literature comparison. To address these issues, we have developed a new technique "probe-molecule-assisted NMR" which allows a genuine differentiation of surface active sites from various facets. This surface-fingerprint technique has been demonstrated to provide both qualitative (chemical shift) and quantitative (peak intensity) information on the concentration and distribution of truly surface features among facets. In light of the new technique, this thesis will revisit the facet-dependent photocatalytic properties and shed light on these issues.

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Cohen, Carla J. « Characterization of RNA aptamers that bind to HIV-1 gp120 ». Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:e218ac2d-7269-49b2-826e-15ab05b7c1a0.

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RNA aptamers with 2'-fluoro-pyrimidine chemistry were previously selected by in vitro evolution to bind to monomeric HIV-1 gp120 from the R5 strain BaL. A group of 36 novel aptamers were cloned and sequenced from the heterogeneous pool and were tested for their ability to bind to gp120. The diversity of the RNA secondary structure of these, and 27 aptamers isolated previously, was analysed using a bioinformatics approach. This showed that eight aptamers contain a common branched motif, and RNA mutagenesis indicated that this structure is probably required for gp120 binding. Chemically synthesised derivatives of one such aptamer, B40, were designed and tested for binding to gp120. Truncation was found to decrease their binding, but the introduction of point mutations to stabilise the branched conformation and 2'-O-dimethylallyl-modified residues to stabilise helices increased binding to levels greater than that of the parental aptamer. The aptamer epitope on gp120 was mapped by testing aptamer binding to alanine-scanning mutants and deletion mutants of gp120 using a novel plate-based assay. This study showed that the aptamer binding site overlaps with the CCR5 epitope and is confined to four key residues at the base of the V3 loop, one of which is highly conserved. This finding may account for the observation that a number of aptamers were shown previously to neutralise a range of HIV-1 R5 clinical isolates in PBMC cultures. Interestingly however, the aptamer was unable to neutralise HIV-1 pseudovirus in a cell line, which is most likely due to the increased levels of cell-surface CCR5 in cell lines compared to PBMC. Future work should focus on identifying the structure and epitopes of other anti-gp120 aptamers as well as testing neutralisation of HIV-1, HIV-2 and SIV by the B40-derived aptamers. These aptamers can be used as tools to investigate the HIV-1 entry pathway and also have the potential to be developed as anti-HIV-1 microbicides.

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Zhu, Danni. « Characterization of nicotinic acid adenine dinucleotide phosphate (NAADP) binding proteins ». Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:cb3309e7-ad14-4c0b-a24c-c42d95b52845.

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Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent intracellular second messenger capable of inducing calcium release from acidic organelles and is responsible for many important physiological activities. It has been recognized that an intermediate protein is required for NAADP to mediate its calcium-mobilizing effect through two-pore channels (TPCs). However, the identity of the intermediate NAADP binding protein remains unknown. This thesis aims to identify the elusive NAADP binding proteins to further elucidate the molecular mechanism of NAADP signalling pathway. The first part of this thesis describes the characterization of NAADP binding protein using a chemistry approach, which includes crosslinking study in mouse embryonic fibroblasts (MEFs) and affinity isolation of binding protein via a NAADP affinity column. Crosslinking introduced significant interference to NAADP binding in MEFs. Radioligand binding assays revealed that NAADP binding in MEFs were predominantly in the membrane fraction and no high affinity binding site was detected. Affinity isolation of binding proteins by NAADP affinity columns was carried out using mouse liver cytosol. However, no high-affinity binding protein was isolated through this approach. The second part of this thesis describes the identification of NAADP binding proteins via a combination of techniques including protein chromatography, photoaffinity labelling, mass spectrometry, virtual screen and label-free ligand binding assays. A sequential chromatography was conceived and optimized, which achieved a more than 2300-fold enrichment of high-affinity binding proteins. Photoaffinity labelling of the enriched fractions by [³²P]-5-azido-NAADP revealed a 27 kDa band in SDS-PAGE gel. Subsequent mass spectrometry analysis generated a list of 35 candidates. Virtual screening of candidates by AutoDock Vina and CLC Drug Discovery Workbench predicted Carbonyl Reductase 1 (CBR1), Thiopurine S-Methyltransferase (TPMT) and Cytochrome b5 Reductase 3 (CYB5R3) as promising NAADP binding protein candidates. Further experimental validation by bio-layer interferometry (BLI) and microscale thermophoresis (MST) confirmed that TPMT and CBR1 are NAADP binding proteins. CBR1 binds NAADP and NADP with similar affinities. On the other hand, TPMT showed higher affinity and high selectivity to NAADP as no binding of NADP was observed. The identification of NAADP binding protein suggests new possibility of NAADP functionality and may provide new insights into the mechanism of action of NAADP signalling pathways.

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Lam, Andy Ka Ming. « Electrophysiological characterization of the human two-pore channel 2 ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:3a16d16e-f692-40d7-87f7-920151896038.

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The Two-pore channel (TPC1-3) family represents a recently identified class of endolysosomal ion channels. TPCs were originally proposed to be promising candidate channels for NAADP-induced Ca²⁺ release. However, subsequent studies have emerged to propose an alternative view where TPCs may be Na+-selective channels regulated by the lysosome-specific phosphoinositide PI(3,5)P2 or voltage in an isoform-dependent manner. This thesis asks the question of whether pharmacological and ion permeation properties of TPCs, in particular the human TPC2, may satisfy or may be consistent with the requirement of a potential NAADP-sensitive Ca²⁺-release channel. These fundamental properties of hTPC2 were approached using patch-clamp electrophysiology and confocal fluorescence microscopy, and were analysed quantitatively to extract relevant physical parameters important to our understanding of their physiological and functional significance. Chapter 2 presents the basic electrophysiological characterisation of hTPC2. It follows a logical way by first determining the ion permeation properties, followed by the investigation of its physical relation with fractional Ca²⁺ current and Ca²⁺ nanodomains to rigorously prove that this Na⁺ selectivity is sufficient to ensure negligible Ca²⁺ leakage both experimentally and theoretically. This follows the logic that matter must not be created nor destroyed so that a Na+-selective channel that poses a physiologically significant energy barrier to Ca²⁺ permeation from one side would not lead to the creation of Ca²⁺ on the other side. Chapter 3 represents a natural progression from Chapter 2 and is aimed at investigating the underlying mechanisms responsible for the electrophysiological ion selectivity observed. This chapter also follows a logical way by first identifying spermine as a high valence intracellular blocker, its mutual antagonism with different external ionic species that allows the determination of ion-binding affinity, followed by the determination of the concentration dependence of ion conduction to identify possible lower affinity binding. By considering all the above qualities, the outcome is a coherent description and connection of ion binding selectivity, kinetic selectivity and ion binding configuration with the observed electrophysiological selectivity. Chapter 4 discusses the missing puzzles and how these questions might be addressed.

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Szilágyi, Anna Tünde. « Structural characterization of liver fibrosis in magnetic resonance images ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1860b1d9-2b10-409f-9220-e12b002a9e32.

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The overall clinical motivation of this thesis is to differentiate between the different stages of liver disease stratifying into: no disease, mild disease, and severe fibrosis using Magnetic Resonance Imaging (MRI). As a related aim, we seek to differentiate as much as possible pericellular and nonpericellular fibrosis. This latter is clinically important, but currently no method exists that is able to perform this. Quickly, we realised that these aims push low level image analysis beyond their current bounds and so a great deal of the thesis is dedicated to extending such techniques before they can be applied. To work on the most fundamental low level image analysis concepts and algorithms we choose one of the most recent developments, namely continuous intrinsic dimensionality (ciD), which allows the continuous classification of homogeneous patches from 1D structures to intrinsically 2D structures. We show that the current formalism has several fundamental limitations and we propose a number of developments to improve on these. We re-evaluated feature energy statistics that were originally proposed in ciD, and additionally we examined the confidence one may have in stateof- the-art methods to estimate the orientation of features. We show that new statistical methods are required for feature energy, and that orientation predictability is more important than correctness of the estimation. This evaluation led us to the monogenic signal local orientation. Analysis of feature or texture energy is also a main contribution of this thesis. Within this framework we propose the Riesz-weighted phase congruency model. This is able to detect internal texture structures but it is not capable of delineating boundaries. Nevertheless, it proves an appropriate basis for texture quantification. Finally, we show that in contrast to using the standard established Kovesi approach, the developed texture measure leads to good results on the suboptimal T1w MRI liver image staging images. We show that we are able to differentiate automatically between the separate disease scores and between pericellular and non-pericellular fibrosis.

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Albanna, Sarmad. « Design, Characterization, and Implementation of Optical Systems for Remote Sensing of the Atmosphere and Astrophysical Objects ». Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/594951.

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This dissertation investigates the optical design and characterization for two distinct remote sensing applications. The first application is focused on the high precision optical phase correction for the photonic Local Oscillator (LO) designed for the Atacama Large Millimeter Array (ALMA). The phase instability in the original fiber optics design scheme is characterized and a novel, singlemode fiber-based interferometric approach to measure and actively zero out the unwanted Photonic LO phase drift is introduced. The proposed technique is implemented and characterized by using a 16 km baseline with a two element array. In the second application, the first iteration of the quasioptics design used in the ATOMMS instrument is characterized. (ATOMMS-Active Temperature, Ozone and Moisture Microwave Spectrometer-is the pathfinding implementation of an Earth and Space Atmosphere Global Remote Sensing Instrument).The diffraction problems in this design which were limiting the instrument performance were analyzed. Then different design concepts to mitigate these limitations and optimize system performance are presented.

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Menad, Samia. « Assemblage permanent de micro-objets par diélectrophorèse associée à une méthode de couplage covalent ». Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0037/document.

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La réalisation de micro et nanomatériaux avec des propriétés contrôlées nécessite le développement de nouvelles voies d’élaboration dites ascendantes « ou Bottom-up ». Les travaux présentés dans ce manuscrit visent à maîtriser la formation d’agrégats de particules colloïdales et de cellules, avec des applications potentielles dans les domaines des biocapteurs, de la microélectronique, de l’optique et de l’ingénierie tissulaire. L’approche proposée pour assembler les particules en structures organisées se base sur l’emploi de la diélectrophorèse, reposant sur l’application d’un champ électrique non- uniforme. L’un des inconvénients de cette technique tient au caractère réversible des assemblages ainsi formés, l’annulation du champ électrique entrainant la redispersion des colloïdes. Afin d’apporter une solution à ce problème, il est possible de recourir à un couplage chimique pour maintenir la cohésion des structures formées dans le milieu liquide. Afin de mieux maîtriser le comportement diélectrophorétique et les réactions chimiques exploitées, des travaux de caractérisation électrique et chimique des particules manipulées ont été réalisés. D’autre part, différents types de microélectrodes ont été étudiées pour la génération du champ électrique nécessaire à l’assemblage. Une nouvelle filière technologique a été développée pour la réalisation de microélectrodes transparentes en ITO et leur intégration en système microfluidique, basée sur l’exploitation du pouvoir isolant d’une fine couche de PDMS micro-structurée. La méthode a été appliquée à la fabrication de microélectrodes « verticales » puis à la réalisation de matrices d’électrodes quadripolaires. Ces dernières ont permis d’obtenir des assemblages permanents de particules de polystyrène fluorescentes présentant des groupements carboxyliques en surface, en combinant l’emploi de la diélectrophorèse négative et l’utilisation d’un agent de couplage chimique (Jeffamine). Des agrégats de cellules HEK 293 ont également été réalisés par diélectrophorèse négative. Nous avons démontré qu’il était possible, sous certaines conditions, de préserver le caractère permanent des agrégats cellulaires après coupure du champ
The design of micro and nanomaterials with controlled properties requires the development of new bottom- up assembly approaches. The work presented in this manuscript aims to control the formation of aggregates of colloidal particles and cells, with potential applications in the fields of biosensors, microelectronics, optics and tissue engineering. The proposed approach for assembling colloids into organized structures is based on the use of dielectrophoresis, a phenomenon observed when polarizable particles are placed in a non-uniform electric field. One of the drawbacks of this technique is the reversibility of the assemblies thus formed, the cancellation of the electric field causing the redispersion of the colloids. As a solution to this problem, we proposed to use a coupling agent to maintain the cohesion of the structures formed in the liquid medium. In order to better control the dielectrophoretic behavior and the chemical reactions exploited, electrical and chemical characterizations of the manipulated particles were carried out. Moreover, different types of microelectrodes have been studied for the generation of the electric field required for the assembly. A new approach has been developed for the fabrication of transparent micro patterned ITO microelectrodes and their integration in microfluidic systems, based on the exploitation of a thin micro-structured PDMS membrane used as an insulating layer. The method has been applied to the fabrication of "vertical" microelectrodes and of quadrupolar electrode arrays. The latter were used to obtain permanent assemblies of carboxylic acid functionalized, fluorescent, polystyrene particles, by combining negative dielectrophoresis with the use of a chemical coupling agent (Jeffamine). HEK 293 cell aggregates were also produced by negative dielectrophoresis. We have demonstrated that it was possible, under certain conditions, to preserve the permanent character of the cell aggregates after field removal

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Jafri, Syed Hassan Mujtaba. « Building Systems for Electronic Probing of Single Low Dimensional Nano-objects : Application to Molecular Electronics and Defect Induced Graphene ». Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160630.

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Nano-objects have unique properties due to their sizes, shapes and structure. When electronic properties of such nano-objects are used to build devices, the control of interfaces at atomic level is required. In this thesis, systems were built that can not only electrically characterize nano-objects, but also allow to analyze a large number of individual nano-objects statistically at the example of graphene and nanoparticle-molecule-nanoelectrode junctions. An in-situ electrical characterization system was developed for the analysis of free standing graphene sheets containing defects created by an acid treatment. The electrical characterization of several hundred sheets revealed that the resistance in acid treated graphene sheets decreased by 50 times as compared to pristine graphene and is explained by the presence of di-vacancy defects. However, the mechanism of defect insertion into graphene is different when graphene is bombarded with a focused ion beam and in this case, the resistance of graphene increases upon defect insertion. The defect insertion becomes even stronger at liquid N2 temperature. A molecular electronics platform with excellent junction properties was fabricated where nanoparticle-molecule chains bridge 15-30nm nanoelectrodes. This approach enabled a systematic evaluation of junctions that were assembled by functionalizing electrode surfaces with alkanethiols and biphenyldithiol. The variations in the molecular device resistance were several orders of magnitude and explained by variations in attachment geometries of molecules. The spread of resistance values of different devices was drastically reduced by using a new functionalization technique that relies on coating of gold nanoparticles with trityl protected alkanedithiols, where the trityl group was removed after trapping of nanoparticles in the electrode gap. This establishment of a reproducible molecular electronics platform enabled the observation of vibrations of a few molecules by inelastic tunneling spectroscopy. Thus this system can be used extensively to characterize molecules as well as build devices based on molecules and nanoparticles.

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Seong, Tae-Yeon. « Microstructural characterization of heteroepitaxial layers of III-V compound semiconductors ». Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:77ce3d0d-dc9b-45ab-af6b-eeb66785b2e5.

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This work describes results obtained from TEM, TED and HREM studies of MBE and MOCVD InAS_ySb₁_-_y, MOCVD In_xGa₁_-_xAs, MOCVD InP_ySb₁_-_y and MOCVD GaP_ySb₁_-_y layers which were grown over a wide range of conditions. These semiconductor layers are of considerable importance for a variety of applications in optoelectronic and high-speed devices. TEM/TED investigations showed that phase separation occurs in MBE InAsSb layers, resulting in two phases with platelet structures ~5 to ~200nm thick approximately parallel to the layer surface. Phase separation was dependent on growth temperature and layer composition. Anisotropic geometry of the platelets was observed when viewed in the [110] and [110] directions. The compositions of the two phases were derived by TED and EDX analyses. A model for the phase-separated layers was proposed based on the presence of a miscibility gap and using the lateral and island growth mechanisms. TEM results of InGaAs, InPSb and GaPSb layers showed a fine scale modulated contrast (8-20nm in scale) which is a characteristic of alloy clustering occurring by spinodal decomposition, and a fine scale speckle contrast (4-5nm in scale). TEM/TED studies showed that [110] diffuse intensity lines in [001] TED patterns of InGaAs are not related to the fine scale modulated contrast but to the fine scale speckle contrast. It was concluded that a fine scale modulated contrast due to alloy clustering coexists with a fine scale speckle contrast associated with static atomic displacements from the average lattice in InGaAs. For InPSb and GaPSb, a fine needle-like contrast was also observed, which corresponds to diffuse streaks in the [110] patterns. This fine needle-like contrast was attributed to segregation of atoms at missing rows of atoms in the reconstructed growing surface. TED investigations revealed CuPt-type ordering in some of the InGaAs, InAsSb and InPSb layers. Regardless of alloy systems and growth conditions, the ordering occurred on only two of the four possible {111} variants. The degree of ordering was strongly dependent on growth conditions. Two variants of the ordered regions in InGaAs nucleated separately. TED/HREM studies of the ordered structure in InGaAs revealed a direct relationship between the inclination and elongation of superlattice spots and the morphology of anti-phase boundaries present within the domains. Two competing processes of surface-induced ordering, and bulk-induced disordering within a transition region, were considered to interpret the growth condition dependence of the ordering in InGaAs. A model for the ordering observed was proposed based on the surface reconstruction mechanism. MBE InAsSb strained layer superlattices (SLSs) were examined by TEM and HREM techniques. Defect configuration and the atomic structure of tetragonal distortion of the SLSs were directly imaged. Defect behaviour was dependent on the geometry of the SLSs. Possible relaxation mechanisms for the SLSs were proposed.

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Zhang, Chi. « The characterization and engineering of human antigen-specific cytotoxic T cells ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:38718489-9fa3-4fa5-b50d-547ccc9adeed.

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This D.Phil. thesis focuses on human antigen-specific cytotoxic T lymphocytes (CTLs). In the first part of the thesis, the impact of antigen stimulation strength on CTL activation was investigated by evaluating the global transcriptomes of a wellcharacterized CTL clone and some of its surface protein expressions, with particular focus on immune checkpoint receptors. Based on the gene differentiations, an 'EGR2-CCL1-4-1BB' pathway, which is sensitive to very low-strength antigen stimulation, was identified. We proposed to block CCL1/CCR8 for future cancer therapeutic treatment as this could be a key mechanism for attracting immune-suppressive cells to local tumour-specific CTLs. Further, an âinverse correlation of inhibitory signal and expression levelâ model was developed to explain the expression patterns of five inhibitory immune checkpoint receptors (CTLA-4, PD-1, LAG-3, TIM-3 and TIGIT). These findings throw lights on the understanding of CTL functions and the future design of T cell-based cancer immunotherapy. In the second half the thesis, the potential use of CRISPR/Cas9 technology was explored in manipulating antigen-specific CTLs and the antigen-specific CTL clone gene delivery method was optimised. Successful disruption of PD-1 gene by CRISPR/Cas9 via lentivirus has been achieved on several antigen-specific CTL lines and clones. After disrupting PD-1 gene, CTLs function better when the target cells express high level of PD-1 ligand. This part of work is the first study to knock out PD-1 gene on human antigenspecific primary CD8+ T cells and has the potential for clinical applications such as the treatment of infection, autoimmunity and cancer.

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Lee, Yi Xin Fiona. « Purification and characterization of extracellular vesicles released from pluripotent stem cells ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:224c718f-cc91-4286-8d6b-a50107fc1f04.

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Extracellular vesicles (EVs) are nano-sized particles constitutively released from cells into biological fluids such as blood, plasma, saliva and urine. Interestingly, these vesicles contain genetic cargoes including proteins, RNA and bioactive lipids that can be functionally delivered and affect recipient cells. Hence, EVs are postulated to be an alternative source of cell-cell communication in both normal physiological systems and pathological situations. Recently, EVs from mesenchymal stem cells have been shown to promote regeneration of injured cells. Induced pluripotent stem cells (iPSCs) are a relative newer type of stem cells that is emerging as useful tools for re-modeling diseases. However, knowledge about EVs from iPSCs is relatively sparse. In initial experiments, we successfully purified EVs from mouse iPSCs using the differential ultracentrifugation (UC) method. However, we noticed a discrepancy between total particle counts and expression of EV markers, across different EV batches. One crucial prerequisite for EV research is the availability of a standardized workflow for collection and purification of EVs from biological sources. Increasing evidence from recent studies has suggested that the original UC method is limited by several shortcomings such as low EV yield, purity and altered biophysical properties. Hence, this has led to a new wave in the development of alternative EV purification strategies. In this thesis, we start with a systematic comparison study between UC and an alternative purification protocol, size-exclusion liquid chromatography (LC) of EVs from serum-free conditions. We found that LC is better than UC in terms of overall EV yields, purity and vesicle integrity. Subsequently, we demonstrate that LC allowed for the derivation of pure EVs from complex media sources used for growing stem cells like iPSCs, which was previously impossible with UC. Lastly, we describe novel data on the characterization of EVs from pluripotent stem cell sources and discuss the possible roles of these EVs in stem cell biology.

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Chuang, Kai-Ting. « Characterization of mouse two-pore channels (TPCs) in NAADP-mediated Ca(2+) signalling ». Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:dbf87d55-4266-4fa9-9eef-5214e7f4cd01.

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Recent studies have identified Two-Pore Channels (TPCs) as the channels activated by NAADP. To date, most studies that characterized these channels have employed heterologous expression or overexpression systems. The research reported here has focused principally on endogenous TPC activity by using single and dual gene knockout (KO) in a mouse system and has yielded insights into TPC expression levels, subcellular localisation, NAADP binding, and channel function. Mouse models that had been generated by both the “gene-trapping” and the “genetargeting” techniques were obtained and validated. These included a knock-down strain (“hypomorph”). Surprisingly, all TPC mutant mice showed no gross phenotypes. In addition to the two known isoforms in mouse, TPC1 and TPC2, the expression of a shorter variant of TPC1 was discovered; this has an alternative (truncated) N-terminus, and has been termed (DELTA)N-TPC1. All TPC variants/isoforms were widely expressed in all mouse tissue types tested. Overexpression of mouse TPCs in mouse embryonic fibroblasts showed that (DELTA)N-TPC1 and TPC2 were expressed primarily in late endosomes/lysosomes while TPC1 was expressed in both endosomes and lysosomes. Dileucine sorting motifs target TPCs to late endosomes/lysosomes; it was shown that truncation or mutation of dileucine motifs significantly reduced localization in late endosomes/lysosomes. Furthermore, TPCs were shown not to be the direct binding target of NAADP, as the high affinity NAADP binding was retained in hepatic membranes from TPC double KO (DKO) mice. It is concluded that NAADP binds to an (as yet, unidentified) accessory protein. The functional role of TPCs was studied in depth using mouse pancreatic acinar cells. NAADP is known to release Ca²⁺ from the acidic stores in response to the stimulation by the hormone cholecystokinin (CCK). In all TPC mutant mice, CCK was still able to evoke Ca²⁺ oscillations, but with slower and attenuated oscillations in the TPC1 hypomorph, and with slower oscillations in TPC DKO. In all TPC KOs, oscillations were disrupted by known inhibitors of the NAADP-signalling pathway (Ned-19, GPN and bafilomycin A1), indistinguishable from the responses with wild-type cells. This suggests that TPCs are not involved in CCK signalling, although it is possible that functional compensation masked the phenotype arising from the impaired signalling.

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Serrano, Medina Sac Nicte Xiomara [Verfasser]. « Radio emission from massive Young Stellar Objects and their surroundings : Characterization and feedback / Sac Nicte Xiomara Serrano Medina ». Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1221668978/34.

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Berger, Karsten. « Discovery and Characterization of the first Low-Peaked and Intermediate-Peaked BL Lacertae Objects in the Very High Energy Gamma-Ray Regime ». kostenfrei, 2009. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3743/.

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Teixeira, Ribeiro Rui Agostinho Fernandes. « Spectral analysis of breast ultrasound data with application to mass sizing and characterization ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8768959f-cc5a-476d-b924-5a5d7df31b8d.

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Ultrasound is a commonly used imaging modality in diagnosis and pre-operative assessment of breast masses. However, radiologists often find it very difficult to correctly size masses using conventional ultrasound images. Consequently, there exists a strong need for more accurate sizing tools to avoid either the removal of an over-estimated amount of tissue or a second surgical procedure to remove margins involved by tumour not removed in the primary operation. In this thesis, we propose a new method of processing the backscattered ultrasound signals from breast tissue (based on the Fourier spectral analysis) to better estimate the degree of echogenicity and generate parametric images where the visibility of breast mass boundaries is improved (SPV parametric image). Moreover, an algorithm is proposed to recover some anatomical structures (particularly, Cooper’s ligaments) which are shadowed during the image acquisition process (LWSPV parametric image). The information from both algorithms is combined to generate a final SPV+LWSPV parametric image. A 20-case pilot study was conducted on clinical data, which showed that the SPV+LWSPV parametric image added useful information to the B-mode image for clinical assessment in 85% of the cases (increase in diagnostic confidence in at least one boundary). Moreover, in 35% of the cases, the SPV+LWSPV parametric image provided a better definition of the entire boundary. Note that the radiologist knew the final diagnosis from histopathology. In addition, the SPV+LWSPV method has the advantage that it uses the I/Q data from a standard ultrasound equipment without the need for additional hardware. On the basis of these facts, we believe there to be a case for further investigation of the SPV+LWSPV imaging as a useful clinical tool in the pre-operative assessment of breast mass boundaries.

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König, Dennis [Verfasser], Alfred [Gutachter] Ludwig et Gunther [Gutachter] Eggeler. « Fabrication and characterization of nanoscale shape memory alloy objects / Dennis König ; Gutachter : Alfred Ludwig, Gunther Eggeler ; Fakultät für Maschinenbau ». Bochum : Ruhr-Universität Bochum, 2014. http://d-nb.info/1229692681/34.

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Mousavi, Tayebeh. « Fabrication, microstructure and properties of new chalcogenide thin films and characterization of functional compounds ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:738fb9cd-220c-434b-9a67-472e8ae9f230.

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Fe-chalcogenides are of great interest because they have the simplest structure in the Fe-based superconductors, and show low anisotropies, high critical fields and high current densities all of which make these compounds useful for understanding Fe-based superconductors, a new class of superconductors with unusual properties, both for fundamental physics and potential high-field applications. The main part of this thesis concentrates on the fabrication and characterization of FeySe1-xTex (Fe-11) thin films in order to link superconductivity and microstructure in this system. Since sputtering has been rarely used for the deposition of Fe(Se,Te) films, we used sputtering to study the feasibility of this technique for this purpose and to optimize the processing conditions. Phase evolution and texture development as a function of processing conditions are studied, and the optimum conditions for the best quality film are found. Crystallization temperature of the 11-phase was found to be 250°C, and texture is shown to be dependent on substrate, substrate temperature and film thickness which strongly control in-plane alignment. The best texture is obtained at 315°C for films thinner than 50nm on the MgO. Texture of the films becomes poorer on the substrates in the order MgO > LAO > STO > CaF2 > LiF > LSAT, and the relationship between texture and substrate is shown to be more related to the growth mechanism rather than lattice misfit. 2D layer-by-layer growth is found for the LSAT, while the films on the LAO and MgO show 3D island growth, and a combination of both growths is found for the film on the STO. The films grown by in-situ sputtering are shown to have better quality than those grown by the ex-situ. A sharp TC of about 10.2K is obtained for a single crystal Fe1.01Se0.56Te0.44.film with a thickness of 58nm. Most of the deposited films are Fe-rich (y > 1) due to compositional variation in the target and the volatility of Se and Te. Extra Fe is the main detrimental parameter for the suppression of superconductivity in these films showing the necessity of using multiple sources in sputtering. Nano-scale inhomogeneities are also observed in the majority of the films possibly as a result of different Se/Te ratios and Fe3O4 impurity. Substitution of 2% Mn for Fe in the FeySe1-xTex structure leads to the stabilization of tetragonal 11 phase and improvement of crystallographic texture. Mn atoms are shown to occupy interstitial Fe sites in the tetragonal unit cell. I also applied TEM technique to functional materials from external collaborators including Bi2Te3 and CaFe2As2. Studies of Mn-doped Bi2Te3 single crystals reveal that at doping concentrations, Mn incorporates with the Bi2Te3 structure differently. At low doping concentrations (9%Mn), Mn atoms are randomly substituted onto the Bi sites resulting in the variation in both composition and lattice parameter. At high doping concentrations (15%Mn), supersaturation occurs and the extra Mn atoms occupy the interstitial sites in addition to forming nano-scale Mn-rich precipitates. CaFe2As2 single crystals grown by the FeAs-flux method are unstable FeAs-supersaturated crystals containing a high concentration of stacking faults. Annealing at high temperature (700°C) causes the extra FeAs to form needle-shaped precipitates perpendicular to the c-axis by Ca diffusion, and the matrix develops dislocations. Annealing at lower temperature (400°C) results in a number of stacking faults and similar precipitates with low Ca. As a result, the microstructure of the CaFe2As2 single crystals, especially the amount of strain, can be controlled by the annealing temperature resulting in similar effects to applying external pressure.

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Blagrove, Marcus S. C. « Generation and characterization of Wolbachia transinfections and development of female-specific RIDL technology in Aedes albopictus ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:f70a1ce7-de90-4a40-8760-58db88e7a823.

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Aedes albopictus is an important vector of dengue and chikungunya viruses, and, over recent decades, has resisted traditional control strategies allowing it to spread from its native Southeast Asia throughout the world. In this thesis, two alternative control methods are assessed and developed: transinfection with the inherited bacteria Wolbachia, for population replacement with a refractory strain; and a genetic equivalent to the sterile insect technique, RIDL (Release of Insects carrying a Dominant Lethal), for population suppression. Wolbachia is a genus comprising maternally inherited intracellular α-proteobacteria which primarily infect arthropods. Certain strains of Wolbachia both have the ability to manipulate host reproduction through cytoplasmic incompatibility (CI) which allows Wolbachia to invade host populations by conferring a reproductive advantage on infected females, and have been shown to confer broad-spectrum pathogen resistance on their hosts. Here, a transinfection of wMel in Aedes albopictus (Uju.wMel) was generated which shows complete bidirectional CI with the natural Wolbachia infection of Ae. albopictus, in the absence of any major fitness costs and (as shown by collaborators) completely abolishes dengue and chikungunya virus transmission. It was also shown that the pathogen inhibition in Uju.wMel occurs in the absence of immune stimulation. Evidence supporting cholesterol sequestration by wMel as a mechanism for the pathogen inhibition observed in Uju.wMel was found. Previous attempts to produce a conditionally inviable genetic sexing Ae. albopictus RIDL line have resulted in a sub-optimal strain in which the construct was not sufficiently specific or repressible, resulting in a high proportion of off-target inviable mosquitoes. Here, the mating competitiveness of RIDL males was shown to be not significantly different from wild-type, confirming the potential utility of the system. Multiple truncations of the promoter were made in an attempt to reduce the off-target expression.

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Buehler, Tabitha Christi. « A Search for and Characterization of Young Stellar Objects in N206, An H II Complex in the Large Magellanic Cloud ». BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3178.

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I have identified 51 young stellar object candidates in N206, an H II complex in the nearby Large Magellanic Cloud galaxy. Using archival images from the Spitzer Space Telescope, supplemented with other infrared and optical images, I located point sources in this region. I distinguished possible young stellar objects based on their spectral energy distributions, morphologies, and locations in color-magnitude space. I classified the young stellar object candidates based on their likelihood of being young stellar objects and based on their apparent evolutionary stages. The spatial distribution of these candidates in N206 indicates that star formation is being triggered in a giant molecular cloud in the region.

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Karia, Dimple. « Characterization of the interactions between the H3K4 demethylase JARID1A and the SCL-nucleated oncogenic DNA binding complex ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:e2b330da-28ab-462f-a7bf-c78a85dd6696.

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Transcriptional regulation is of key importance to cellular processes such as development and differentiation, and it is dependent on the accessibility of DNA in the chromatin. Methylation and demethylation of histones alter properties of nucleosomes, thereby changing the accessibility of DNA. For many years, histone tail methylation was considered to be irreversible but in the last decade two families of histone demethylases were discovered, lysine specific demethylase 1 (LSD1) and Jumonji C (JMJC) demethylases. The work presented in this thesis focuses on the chromatin remodeling protein JARID1A, belonging to the JARID1 family of JMJC demethylases that demethylates lysine 4 (K4) on the tail of histone H3. Double and triple methylation of K4 on histone H3 are marks traditionally linked to transcriptionally active regions of DNA. Recently, a translocation fusing the third PHD domain (PHD3) of JARID1A to NUP98 (a common leukaemia fusion partner with transactivation activity) was identified in acute myeloid leukaemia patients (AML). Also, PHD3 was previously shown to mediate interactions between JARID1A and the second LIM domain of LMO2. LMO2 operates within the multiprotein DNA binding complex named "SCL complex" (including proteins SCL/TAL1, LDB1, E47, GATA1) that regulates gene expression at different stages of erythropoiesis. This thesis presents findings of an investigation into relations between JARID1A and the oncogenic multiprotein complex SCL-E47-LMO2-LDB1-GATA1. The study of the endogenous proteins from erythroid cells using techniques such as Co-immunoprecipitation, GST pull-down and Size-exclusion chromatography showed that JARID1A interacts with SCL and GATA1. These interactions were further characterized biochemically using analytical ultracentrifugation which revealed that the second PHD domain of JARID1A is involved in direct interaction with GATA1. Hence, JARID1A could play a role in regulation of erythropoiesis by modulating activities of transcription factors SCL and GATA1.

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Motnenko, Anna. « Characterization of UHRF2 (RNF107) as a novel sensor for DNA ICLs in the Fanconi Anemia pathway ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:019dffd3-cb3f-42dd-85b9-38eba5c554a9.

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The Fanconi Anemia (FA) pathway is important for repairing interstrand crosslinks (ICLs) between the Watson-Crick strands of the DNA helix. An initial and essential stage in the repair process is the detection of the ICL. In a previous study, UHRF1 was identified as an ICL sensor in humans, it was shown that downstream repair factors were not recruited normally to the ICL in the absence of UHRF1. However, the mechanism underlying this process was unknown. Here, we report the identification of UHRF2, a paralogue of UHRF1, as an ICL sensor protein. We show that UHRF2 cooperates with UHRF1, to ensure recruitment of FANCD2 to the ICL. We show that a direct protein-protein interaction with FANCD2 is formed via the SRA domain of UHRF1, and a direct interaction is formed between UHRF2 and UHRF1. Moreover, we demonstrate that the essential monoubiquitination of FANCD2 is stimulated by UHRF1/UHRF2, by mediating its retention on chromatin. Taken together, we uncover the mechanism of FANCD2 activation by monoubiquitination via recruitment and retention at ICLs dependent on an interaction with UHRF1/UHRF2.

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Fu, Josephine K. Y. « Functional characterization of the teleost multiple tissue (tmt) opsin family and their role in light detection ». Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:39bc18bb-16cb-4549-94cd-5f872daafe7e.

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In addition to a central circadian clock in the suprachiasmatic nucleus (SCN), zebrafish (Danio rerio) have local clock systems in their peripheral tissues. These peripheral tissues express a complement of clock genes that can be synchronized with the 24 h light/dark cycle and thus may be entrained by light. To date, teleost multiple tissue (tmt) opsin identified from Fugu rubripes and Danio rerio is the only opsin that has been proposed as a candidate to mediate this cellular photoentrainment (Moutsaki et al., 2003). Here we report the discovery of a multigene family of tmt opsins found not only in the teleost fishes, but in vertebrates,including amphibians, birds, reptiles, and some mammals. Phylogenetic analysis demonstrated that this gene family consists of three main classes, tmtI, tmtII and tmtIII, with each duplicating further to give two paralogues in the zebrafish genome. Their predicted amino acid sequences contain most of the characteristic features for the function of a photopigment opsin, as well as seven transmembrane segments indicative of a G protein coupled receptor (GPCR) superfamily. Significantly, reverse transcription polymerase chain reaction (RT-PCR) reveals that the tmt opsin genes in zebrafish are both temporally and spatially regulated. To investigate if these tmt photopigments mediate light-activated currents in cells, each opsin was expressed in vitro and the responses characterised by calcium imaging, whole-cell patch clamp electrophysiology, UV-Vis spectrophotometric analysis, and bioluminescence reporter assay. Collectively, these data suggest that some of the opsin photoproteins signal via Gi-type G protein pathway. Interestingly, the spectral analysis obtained shows that most tmt opsins tested are UV-sensitive when reconstituted in vitro with 11-cis and all-trans retinal, indicating an intrinsic bistable dynamics. Using site directed mutagenesis on one of the tmt opsins, tmt10, the potential spectral tuning sites involved in UV detection were tested. As part of this study, tmt opsin cDNAs were isolated from three populations of Mexican tetra (Astyanax mexicanus): surface, Pachon and Steinhardt. This allowed for a direct comparison between the tmt opsins present in the dark adapted species (cavefish) versus those of the light adapted species (zebrafish). It is hoped that the findings from this project will contribute to our understanding of non-visual light detection in fish and the evolution of their non-image forming photoreception.

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Walker, Paul Andreas. « Laser wakefield acceleration of electrons to GeV energies and temporal laser pulse compression characterization in a capillary discharge waveguide ». Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:e347422e-b097-4128-8733-f3686cc452fe.

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This thesis presents results from three strands of experimental work aimed towards establishing more reproducible, higher energy, and more accurately measured electron beams generated by a laser-driven plasma accelerator. The first experiment calibrated two types of detector frequently used to measure the bunch charge in laser wakefield accelerator experiments, namely scintillating screens and image plates. The experiments undertaken at the DAFNE beam test facility in Frascati, Italy, confirmed that the fluorescence signal from Kodak Lanex Regular screens varies linearly with the charge density for a nanosecond elec- tron bunch for charge densities in the range between ρ = 2 × 10⁻⁷ ^C/_m² to ρ = 10−5 ^C/_m². A sensitivity measurement of FUJIFILM BAS-IP MS image plates resulted in a sensitivity of SMS = (0.0487 ± 0.0028 ) PSL, which is 2.4 times higher than had been assumed prior to this work. The second strand aimed at improving the operation of the capillary discharge waveguide by re-designing the discharge circuit and the waveguide housing. The experiment showed that combining a glow discharge circuit with the pulsed discharge circuit of the capillary discharge waveguide reduced electrical noise, the timing jitter between the trigger pulse and the discharge, and the voltage required to initially break down the capillary gas for pressures below 10 mbar and above 150 mbar. The size of the housing of the capillary discharge waveguide was reduced in all three dimensions by an average of 60 %, enabling the device to be used in future staging experiments, and an open design of the housing eliminated the possibility of unwanted discharges. The new capillary design performed without flaw in the Astra-Gemini experiment and no disadvantages compared with the old housing were found. The third strand of work describes an experiment undertaken with the Astra-Gemini laser at the Central Laser Facility of the Rutherford Appleton Laboratory, United Kingdom. The improved capillary discharge waveguide was used to generate GeV-scale electron beams with good reproducibility. Beams of electrons with energies above 900 MeV, and with root- mean-square divergence of 3.5 mrad, were observed for a plasma density of 2.2 × 10¹⁸ cm⁻³ and a peak input laser power of 55 TW. The variation of the maximum electron energy with the plasma density was measured and found to agree well with simple models. The energy spectra of the generated electron beams exhibited good shot-to-shot reproducibility, with the observed variations attributable to the measured shot-to-shot jitter of the laser parameters. Two methods for correcting the effect of beam pointing variations on the measured energy spectrum were tested and it was found that using a thin Lanex screen in front of the electron spectrometer was easy to implement and did not degrade the recorded energy spectrum. The first observation of temporal compression of a laser pulse within a plasma channel with simultaneous electron acceleration to energies higher than 500 MeV is also presented. This measurement suggests that the pulse compresses linearly from the back as predicted by theory.

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Baranovic, Jelena. « Structural and functional characterization of reconstituted alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors ». Thesis, University of Oxford, 2011. https://ora.ox.ac.uk/objects/uuid:008f579f-828a-4792-8a2c-d2beffda458d.

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This thesis describes a novel reconstitution of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) for the purposes of structural characterization by atomic force microscopy (AFM) and functional characterization by electrical recordings of lipid bilayers. AMPARs are glutamate gated ion channels, ubiquitous in the vertebrate central nervous system where they mediate fast excitatory neurotransmission. In a healthy brain, AMPARs are involved in memory formation and learning and their dysfunction has been related to numerous neurological disorders such as Alzheimer's disease, epilepsy, schizophrenia and many others. AMPARs were reconstituted at high and low densities. Densely reconstituted samples contained >100 receptors per μm2, a value comparable to the AMPAR density at synapses. This allowed, for the first time, the imaging of full length tetrameric AMPARs in native-like conditions and with clearly assigned domains: the extracellular domains extended 14 nm above the membrane in agreement with electron microscopy (EM) and X-ray crystallography data. Lipid-protein interactions were studied in samples with low protein density with the receptors showing preference for lipids in the liquid crystalline phase. The activity of the reconstituted receptors was confirmed through single-channel recordings. This is the first case in which an AMPAR has been reconstituted and given (a) single-channel recordings with (b) physiologically plausible conductance levels and (c) pharmacological and no-protein controls and (d) structure. As a result, previously reported biochemistry and EM are now for the first time available in concert with AFM and single-channel recordings for a purified AMPAR of known composition.

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