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AbstractAbstract
[en] Optical coherence tomography (OCT) is a non-invasive optical interferometric imaging technique that provides reflectivity profiles of the sample structures with high axial resolution. The high axial resolution is due to the use of low coherence (broad-band) light source. However, the lateral resolution in OCT depends on the numerical aperture (NA) of the focusing/imaging optics and it is affected by defocus and other higher order optical aberrations induced by the imperfect optics, or by the sample itself.Hardware based adaptive optics (AO) has been successfully combined with OCT to achieve high lateral resolution in combination with high axial resolution provided by OCT. AO, which conventionally uses Shack-Hartmann wavefront sensor (SH WFS) and deformable mirror for wavefront sensing and correction respectively, can compensate for optical aberration and can enable diffraction-limited resolution in OCT. Visualization of cone photoreceptors in 3-D has been successfully demonstrated using AO-OCT. However, OCT being an interferometric imaging technique can provide access to phase information.This phase information can be exploited by digital adaptive optics (DAO) techniques to correct optical aberration in the post-processing step to obtain diffraction-limited space invariant lateral resolution throughout the image volume. Thus, the need for hardware based AO can be eliminated, which in turn can reduce the system complexity and economical cost. In the first paper of this thesis, a novel DAO method based on sub-aperture correlation is presented which is the digital equivalent of SH WFS. The advantage of this method is that it is non-iterative in nature and it does not require a priori knowledge of any system parameters such wavelength, focal length, NA or detector pixel size. For experimental proof, a FF SS OCT system was used and the sample consisted of resolution test target and a plastic plate that introduced random optical aberration. Experimental results show that sub-aperture based DAO can recover near diffraction-limited images. The method was also used to show depth of focus (DOF) extension in a biological (grape) sample. Limitations of the sub-aperture based DAO method are also discussed in detail in this paper. In the second paper of the thesis, sub-aperture based DAO method for defocus correction is compared with the inverse scattering (IS) based image reconstruction, similar to interferometric synthetic aperture microscopy (ISAM), and a simple digital phase conjugation method based on a forward model (FM). It is demonstrated through experimental results that FM based defocus correction is the fastest in terms of computational speed and have the same performance in terms of DOF extension as IS or DAO when the sample with uniform refractive index in depth is imaged at NA of 0.1. However, it is shown that in the case of samples with non-uniform refractive index, DAO performs the best in terms of DOF extension. In the third and the final paper of the thesis, a region of interest (ROI) based DAO is presented that corrects anisotropic aberration across the lateral field of view (FOV). The proof of principle is shown using an iron (III) oxide nano-particle phantom sample imaged with a fiber-based point scanning spectral domain (SD) OCT setup at a high NA of 0.6 and a limited DOF of 7 . Sub-micron lateral resolution is obtained over a depth range of 218 , thus achieving DOF improvement by ⁓ 30x .The implementation of this method is also demonstrated in ex vivo mouse adipose tissue. The major limitations associated with sub-aperture based DAO and its future prospects in OCT are also discussed. (author)
[de]
Optische Kohärenztomographie (OCT) ist ein nichtinvasives bildgebendes Verfahren, welches auf optischer Interferometrie basiert und das Reflektivitätsprofil einer Probe mit hoher axialer Auflösung liefert. Die hohe axiale Auflösung ist auf die Nutzung einer breitbandigen Lichtquelle mit geringer zeitlicher Kohärenz zurückzuführen. Die laterale Auflösung hingegen ist bei OCT unabhängig von der spektralen Bandbreite der Lichtquelle. Sie hängt von der numerischen Apertur (NA) der fokussierenden oder abbildenden Optiken ab. Die laterale Auflösung ist dabei beeinflusst von Defokussierung und anderen optischen Aberrationen höherer Ordnung, verursacht durch die Optiken oder der Probe selbst. Um neben dem hohen axialen Bereich auch eine hohe laterale Auflösung zu erzielen wurde Hardware basierte adaptive Optik (AO) erfolgreich mit OCT kombiniert. AO, welche üblicherweise einen Shack-Hartmann Wellenfrontsensor in Kombination mit einem verformbaren Spiegel zur Berichtigung der Wellenfront benutzt, kann optische Aberrationen kompensieren und erlaubt eine beugungslimitierte Auflösung in OCT. OCT, als ein interferometrisches, bildgebendes Verfahren, kann außerdem Zugang zu Phaseninformation liefern. Diese Phaseninformation kann mit Techniken der digitalen adaptiven Optik (DAO) genutzt werden um optische Aberrationen im Nachbearbeitungsschritt zu korrigieren und eine beugungslimitierte, räumlich invariante laterale Auflösung im gesamten Bildvolumen zu erreichen. Dadurch kann auf Hardware basierte AO verzichtet werden und können in Folge dessen die Systemkomplexität und Kosten reduziert werden. In der ersten Veröffentlichung dieser Doktorarbeit wird eine neuartige DAO Methode basierend auf einer sub-Apertur Korrelation präsentiert. Der Vorteil dieser Methode ist ihr Verzicht auf Iterativität und dass sie kein a priori Wissen jeglicher Systemparameter wie Wellenlänge, Brennweite, NA oder Detektorpixelgröße erfordert. In den Experimenten wurde ein FF SS OCT System benutzt, wobei ein Auflösungstestbild in Kombination mit einem deformieren Plastikplättchen, das zufällige optisch Aberrationen einführt, herangezogen wurde. Die experimentellen Ergebnisse zeigen, dass sub-Apertur basierte DAO die Strukturen des Auflösungstesttargets nahezu beugungsbegrenzt wiederherstellen kann. Die Methode wurde außerdem benutzt um die Ausweitung der Schärfentiefe (DOF) in einer biologischen Probe zu zeigen. In der zweiten Veröffentlichung dieser Arbeit wird die sub-Apertur basierte DAO Methode zur Fokuskorrektur mit einer auf inversen Streuung (IS) basierten Bildrekonstruktion und einer einfachen digitalen Phasenkonjugationsmethode, basierend auf einem Vorwärtsmodel (FM), verglichen. Es wird durch experimentelle Ergebnisse gezeigt, dass die FM basierte Fokuskorrektur in Bezug auf die Rechengeschwindigkeit am schnellsten ist. Bezüglich einer DOF Ausweitung erzielt sie dasselbe Ergebnis wie IS und DAO, solange die Probe mit homogenen Brechungsindex und einer geringen NA von 0.1 abgebildet wird. Allerdings zeigt sich bei einer Probe mit nicht-homogenen Brechungsindex, dass DAO das beste Ergebnis bezüglich einer DOF Ausweitung erzielt. Im dritten und letzten Paper dieser Arbeit wird eine region-of-interest basierte DAO Methode präsentiert, die anisotropische Aberrationen quer über den sichtbaren Bildbereich korrigiert. Das Prinzip wird an einem Eisen(III) Oxid Nanopartikel Phantom gezeigt, welches mit einem faserbasierten, punktscannenden Spektralbereich OCT Aufbau mit einer NA von 0.6 und einem limitierten DOF von 7µm abgebildet wird. Es wird eine sub-Mikrometer laterale Auflösung über einen Tiefenbereich von 218µm erreicht, wodurch eine ungefähr 30-fache DOF Ausweitung erzielt werden kann. Die Umsetzung dieser Methode wird außerdem in Mausfettgewebe ex vivo gezeigt. Die wesentlichen Limitationen der sub-Apertur basierten DOA und deren Aussichten für die Zukunft von OCT werden ebenfalls in diesem Paper diskutiert. (author)Primary Subject
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2015; 90 p; Thesis (Ph.D.)
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Thesis/Dissertation
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ANIMAL TISSUES, ANIMALS, BODY, CHALCOGENIDES, COHERENT SCATTERING, CONNECTIVE TISSUE, DIAGNOSTIC TECHNIQUES, IRON COMPOUNDS, MAMMALS, MEDICINE, NUCLEAR MEDICINE, OPTICAL PROPERTIES, OXIDES, OXYGEN COMPOUNDS, PHYSICAL PROPERTIES, RADIOLOGY, RODENTS, SCATTERING, TRANSITION ELEMENT COMPOUNDS, VERTEBRATES
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AbstractAbstract
[en] Lyapunov direct method is applied to study the stability of charged solitons (including pulsons), described by the complex scalar field. It is shown that the direct consequence of Lyapunov theorem of stability is their instability. Some necessary and sufficient conditions for the Q-stability (stability with the additional condition of charge fixation) of nonnodal charged scalar solitons are established
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1981; 15 p; 24 refs.
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AbstractAbstract
No abstract available
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1974; 128 p; University Microfilms Order No. 74-24,594.; Thesis (Ph. D.).
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Report
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AbstractAbstract
[en] A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6keV to 1.332MeV and a Ni-63 beta source of maximum energy of 66keV. A simulation was also carried out in MCNP4a to verify the number of H-3 beta particles with max energy 18.6keV that would reach the plastic scintillator in a vacuum setting as well as in an air medium. Scintillator thicknesses ranged from 10μm to 2500μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. The results of these measurements showed the expected positive linear correlation between scintillator thicknesses and integrated counts for all the gamma sources while the slopes of the correlations of each gamma source was a function of the source energy. The beta particle response showed an initial increase of counts with scintillator thickness followed by a slight decrease. The MCNP simulation confirmed an analytical calculation of the fraction of H-3 beta particles for a given air concentration that would reach the scintillator. These results in conjunction with the experimental findings were used to assess the potential of a plastic scintillator system forming the basis of a tritium monitor for the detection of tritium in high-energy gamma backgrounds for Canadian nuclear power workers. (author)
Primary Subject
Source
2011; 101 p; ISBN 9780494811573; 
; Available from https://central.bac-lac.gc.ca/.item?id=MR81157& op=pdf& app=Library. Also available from ProQuest Dissertation Express, Ann Arbor, Michigan (United States), under document no. MR81157; 41 refs., 16 tabs., 21 figs.; Thesis (M.A.Sc.)
; Available from https://central.bac-lac.gc.ca/.item?id=MR81157& op=pdf& app=Library. Also available from ProQuest Dissertation Express, Ann Arbor, Michigan (United States), under document no. MR81157; 41 refs., 16 tabs., 21 figs.; Thesis (M.A.Sc.)
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AbstractAbstract
[en] This thesis is devoted to the study of various aspects of the 2-dimensional conformal field theory and its applications to strings. We make a short review of the conformal field theory and its supersymmetric extension, called superconformal field theory. We present an elegant superspace formulation of these theories and solve the condition for the closure of the superconformal algebra. The we go on to classify the superconformal field theories according to these solutions. We prove that N ≥ 5 superconformal algebra, with N being the number of supersymmetries, does not have central charge. We find the primary representations of all the interesting superconformal algebra. We study the quantization of the superconformal theories and derive the constraints on the central charge of the algebra that has to be satisfied for a consistent quantum theory. This quantization process also determines the ground state energy of the system and the spectrum of the model. We study the global aspects of the conformal symmetry and its role in the construction of consistent heterotic string theories. We prove the uniqueness of heterotic superstring theories in 10 dimensions in the fermionic constructions. We show how the vertex operators are closely associated with the primary field representation of the conformal algebra. We utilize these vertex operator constructions to obtain tree amplitudes in the 10-dimensional heterotic string theory. We show by explicit calculation at the 3-point level that the scattering amplitudes derived from the heterotic superstring are same as the ones obtained from 10-dimensional supergravity theories
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1987; 115 p; Univ. of Maryland; College Park, MD (USA); University Microfilms, PO Box 1764, Ann Arbor, MI 48106, Order No.88-08,575; Thesis (Ph. D.).
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[en] With the help of Lyapunov direct method the Q-stability (stability with the additional condition of charge fixation) of particle-like solutions in quantum electrodynamics is studied. By the common methods of variational calculation making allowance of geometrical properties of Lyapunov's functional the Q-theorem is proved and the necessary and sufficient conditions for their Q-stability are established
[ru]
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1981; 8 p; 9 refs.
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Report
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AbstractAbstract
[en] The presence of a collimator in the neutron field alters the source spectrum due to the scattered neutrons and the secondary radiation contributed by the collimator. From a neutron therapy point of view, it is essential to investigate the resulting changes in the absorbed dose to the patient in the primary beam as well as in the penumbra region. The contribution by the collimator depends on various factors such as the shape and the composition of the collimator and its position with respect to the source. A Monte Carlo program has been applied to mathematically simulate and analyze the collimated neutron therapy system. Collimated DT neutron therapy beams have been investigated using the MORSE code, which is a three-dimensional Monte Carlo computer code, capable of handling combined neutron and gamma-ray transport with the given multigroup cross sections. The combinatorial geometry option of the code has been used to mock-up a typical neutron therapy configuration in three-dimensional geometry. The effects of the collimator parameters on the energy spectra and the absorbed dose were determined along the central axis of the beam and in the penumbra region, in air as well as in a tissue equivalent phantom. As compared to the absorbed dose at the phantom surface due to an uncollimated beam, there is approximately a 7% increase with a 5 x 5 cm field size collimator, a 22% increase with a12 x 8 cm field size collimator, and a 44% increase with a 20 x 20 cm field size collimator. For a 12 x 8 cm field size collimator, the gamma ray contribution to the total dose is approximately 3% in air, 5% at the phantom surface and 12% at 10 cm depth in the phantom. The contribution to the total dose by neutrons above 11 MeV for the same field size is approximately 87% in air, 78% at phantom surface and 83% at 10 cm depth in the phantom
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1978; 126 p; University Microfilms Order No. 78-21,577; Thesis (Ph. D.).
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Report
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AbstractAbstract
[en] This work is dedicated to the investigation of specimens exhibiting anisotropic microstructures (and thus macroscopic elastic anisotropy) and/or inhomogeneous microstructures, as met near surfaces and in textured materials. The following aspects are covered: (i) Analysis of specimens with direction-dependent (anisotropic) elastic grain-interaction. Elastic grain-interaction determines the distribution of stresses and strains over the (crystallographically) differently oriented grains of a mechanically stressed polycrystal and the mechanical and diffraction (X-ray) elastic constants (relating (diffraction) lattice strains to mechanical stresses). Grain interaction models that allow for anisotropic, direction-dependent grain interaction have been developed very recently. The notion 'direction-dependent' grain-interaction signifies that different grain-interaction constraints prevail along different directions in a specimen. Practical examples of direction-dependent grain interaction are the occurrence of surface anisotropy in thin films and the surface regions of bulk polycrystals and the occurrence of grain-shape (morphological) texture. In this work, for the first time, stress analyses of thin films have been performed on the basis of these newly developed grain-interaction models. It has also been demonstrated that the identification of the (dominant) source of direction-dependent grain interaction is possible. The results for the grain interaction have been discussed in the light of microstructural investigations of the specimens by microscopic techniques. (ii) Analysis of specimens with depth gradients: Diffraction stress analysis can be hindered if gradients of the stress state, the composition or the microstructure occur in the specimen under investigation, as the so-called information depth varies in the course of a traditional stress measurement: Ambiguous results are thus generally obtained. In this work, a strategy for stress measurements at fixed information depths has been developed and from such stress measurements at fixed information depths employing a laboratory diffractometer and a diffractometer at a synchrotron source, the stress gradients and gradients in the elastic grain-interaction constraints of Nickel layers (layer thicknesses 2 micron and 4 micron) have been successfully deduced. Thereby the first evidence ever for the depth-dependence of the so-called surface anisotropy has been obtained. (Orig.)
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Dec 2005; 163 p; Available from: http://elib.uni-stuttgart.de/opus/volltexte/2005/2480/; Diss. (Dr.rer.nat.)
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AbstractAbstract
[en] India is generally described as an outlier in the non-proliferation regime, owing to its existence outside the NPT. However, India played a key role in the regime’s early evolution, especially the establishment of the IAEA. India ended up in its governing body and sustained this as its umbilical cord with the regime even after its isolation since the 1974 PNE and restrictions placed by NSG. Even after expanding its civilian nuclear program into a strategic one, it continued to subscribe to the INFCIRC-66 type safeguards for select facilities. India rejected calls to adopt the Comprehensive safeguards Agreement as it did not want to be designated as a non-nuclear weapon state, and also saw it as a discriminatory order of nuclear ‘haves’ and ‘have-nots’. India was always been apprehensive of the Agency transforming its role from that of a promoter of nuclear energy to a regulator. However, after the Indo-US nuclear deal, India renewed its safeguards arrangement with IAEA in 2008 and subsequently gained an NSG waiver. The agreement, along with the Additional Protocol deal, created a new template for a state that is neither a NWS nor among the NNWS, but is recognized as a “state with advanced nuclear technology.” The paper explains the India-IAEA relationship and its co-relation with the regime since the early interactions, and seeks to address the integration question by examining whether the new safeguards agreement implicitly endorses India as a nuclear capable state – both in terms of nuclear energy and nuclear weapons. (author)
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Rathkolb, O.; Roehrlich, E.; University of Vienna (Austria); [vp.]; 2012; [vp.]; International Conference: United Atoms in a Divided World: The early history of the IAEA; Vienna (Austria); 16-18 Sep 2012; Available in abstract form only, full text entered in this record; Conference program available from http://www.univie.ac.at/zeitgeschichte/cms/uploads/17-18-09-2012IAEA.pdf; Available in abstract form only, full text entered in this record; Conference program available from http://www.univie.ac.at/zeitgeschichte/cms/uploads/17-18-09-2012IAEA.pdf
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AbstractAbstract
[en] In the present work a comparative study of track registration response of 40Ar ions in different types of Makrofol polycarbonates viz. Makrofol-KG, KL and N have been done. The etched track parameters viz. bulk etch rate, track etch rate, etch rate ratio, cone angle and etching efficiency were calculated. The variation of etching rates with temperature were found to be exponential and follow the Arrhenius equation. The values of activation energy for bulk and track etching were also calculated. Maximum etchable track length/range were also obtained and compared with the theoretical values obtained from computer program RANGE. From the results it is found that the polycarbonates having same chemical composition manufactured by different chemical processes have slightly different behavior
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S1350448799001043; Copyright (c) 1999 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
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Journal Article
Journal
Country of publication
ARGON ISOTOPES, CARBON COMPOUNDS, CARBONATES, CHARGED PARTICLES, COMPUTER CODES, ENERGY, EQUATIONS, EVALUATION, EVEN-EVEN NUCLEI, IONS, ISOTOPES, LIGHT NUCLEI, MEASURING INSTRUMENTS, NUCLEI, ORGANIC COMPOUNDS, ORGANIC POLYMERS, OXYGEN COMPOUNDS, POLYMERS, RADIATION DETECTORS, STABLE ISOTOPES, SURFACE FINISHING
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