Dissertations / Theses on the topic 'X-ray structure'
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1
Marchesini, Stefano. "X ray fluorescence holography." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10012.
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Dans de nombreux cas la structure atomique des solides ne peut etre resolue par les techniques traditionnelles de la cristallographie. Cela peut etre le cas, par exemple, pour les etudes locales d'impuretes diluees, les interfaces enterrees et plus generalement les systemes non periodiques. En 1996 une nouvelle methode structurale, l'holographie x a resolution atomique est apparue. Elle a pour origine la technique d'imagerie holographique, inventee par gabor il y a 50 ans. Dans ce travail, nous presentons d'abord le principe et le cadre theorique de l'holographie par fluorescence, fondes sur le concept de source / detecteur interne. Puis nous decrivons les developpements techniques que nous avons progressivement obtenus, afin de transposer cette methode des rayons x de laboratoire vers la source synchrotron esrf ; ceci sous le double point vue du montage experimental et de l'analyse des donnees. Des resultats intermediaires interessants sont l'imagerie des configurations des lignes de kossel et des ondes stationnaires, a partir desquelles des informations structurales - parametre de reseau, symetrie et orientation cristallines - peuvent etre deduites. Puis l'hologramme et la reconstruction atomique de monocristaux modeles tels que coo(111) sont presentes, avec - pour la premiere fois, une resolution isotrope de 0,5 a et une qualite d'image qui n'avait pas ete obtenue jusqu'a present. Enfin, la premiere application de l'holographie par fluorescence aux films epitaxiques est donnee. Des differences significatives entre des films d'alliages fept chimiquement ordonne et desordonne ont ete obtenus, ouvrant la voie a l'etude de l'ordre a courte distance directionnel dans de tels systemes, au-dela des possibilites de la spectroscopie xafs. De nouvelles perspectives sont offertes en conclusion, concernant l'holographie atomique resolue en temps, ainsi que - sur la base d'une etude preliminaire d'holographie nucleaire - le potentiel de cette technique pour le magnetisme local et la selectivite en site.
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Lawson, David Mark. "X-ray structure determination of recombinant ferritins." Thesis, University of Sheffield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264615.
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Oblezov, Alexandr Evgenievich. "Crystal structure determination at the Center for X-ray Crystallography a practical guide /." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0002700.
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Stevenson, Clare E. M. "X-ray structure determination of small signalling proteins." Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439893.
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Poiarkova, Anna V. "X-ray absorption fine structure Debye-Waller factors /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9731.
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Tangouna, Liambo Bissa Marie-Louise. "Host-guest compounds : structure and thermal behaviour." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2442.
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Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2016.Inclusion compounds of two hydroxyl hosts with a variety of guests have been investigated. These host compounds are bulky molecules and have the ability to interact with smaller organic guests to form new compounds. The host 9-(1-naphthyl)-9H-xanthen-9-ol (H1), forms inclusion compounds with pyridine (PYR), N,N-dimethylacetamide (DMA), morpholine (MORP) and N-methyl-2-pyrrolidinone (NMP). The crystal structures of H1•NMP, H1•DMA and H1•MORP1 were successfully solved in the triclinic space group PĪ, whereas the inclusion compound H1•PYR crystallised in the monoclinic space group P21/c. A different inclusion compound involving morpholine, H1•MORP2 resulted from dissolution of H1 in a 1:1 molar ratio of MORP: DMA. H1•MORP2 crystallised in the space group PĪ. All of the abovementioned inclusion compounds demonstrated a host: guest ratio of 1:1 except for H1•MORP1 (host: guest ratio = 1: ). H1 interacts with pyridine and morpholine guests via (Host)O-H•••N(Guest) hydrogen bonds and via (Host)OH•••O(Guest) hydrogen bonds with N-methyl-2-pyrrolidinone and N,N-dimethylacetamide.
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Buchanan, Piers. "The structure of liquid semiconductors, superionic conductors and glasses by neutron scattering, X-ray diffraction and extended X-ray absorption fine structure." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392943.
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Benach-Andreu, Jordi. "X-ray structure analysis of short-chain dehydrogenases/reductases /." Stockholm, 1999. http://diss.kib.ki.se/1999/91-628-3498-3/.
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Bean, R. J. "Domain structure imaging by Bragg geometry X-ray ptychography." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1418466/.
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Domain structure in materials is important for their physical properties, technological uses and response to external perturbations. Domains are small regions within a material with a consistent atomic structure that may have different ordering origins or different orientations. Domain structure is present in any material which exhibits super-structure ordering with correlation lengths shorter than the extent of the sample. The domain size is controlled by the strength of the ordering interactions and growth conditions. Domains are present in a huge range of materials from con¬densed matter to biological samples with a structure unique to the individual sample. For domains in crystalline samples with sizes of Angstroms to nanometres X-rays are an ideal probe. Many domain systems exhibit no X-ray amplitude contrast, i.e. all domains attenuate the X-ray beam uniformly, the domain structure is apparent only in the deviation of the phase of the incident X-ray beam. An imaging method is required which is sensitive to these phase differences. Coherent X-ray Diffraction Imaging (CXDI) is a method which exploits the Fourier transform relationship between the sample and its far field diffraction pattern collected at a pixellated detector to iteratively solve the phase problem and reconstruct an amplitude and phase image of the sample. Support based coherent X-ray diffraction methods have been successfully applied to the three dimensional imaging of crystalline structures by collecting the scattering around the sample Bragg peaks in reflection geometry. In general, phase retrieval algorithm constraints require that the sample is isolated within the X-ray beam and as a result these methods have not been successful at imaging extended domain systems. Ptychography is a combined experimental and analysis procedure that can overcome the requirement for the sample to be isolated by collecting a series of diffraction patterns from overlapping regions of the sample. This thesis develops the ptychography algorithms and experimental methods for use in Bragg geometry with the goal of imaging phase domain structures in extended crystalline samples. Bragg coherent diffraction imaging and ptychography methods are reviewed before the adaptations of the experimental method and algorithm for the application of ptychography in Bragg geometry are discussed and detailed. Simulations of ptychography on phase domain structures and a Bragg geometry ptychography X-ray experiment with a specifically designed phase domain test sample confirm that the method is capable of providing accurate quantitative phase information on the domain structure of extended samples. A coherent diffraction experimental setup for ptychography is developed at Diamond beamline I16. Bragg ptychography is applied to the investigation of domain structure in a niobium thin film and anti-phase domain structure in the binary alloy Fe65Al35 and the results of the reconstructions are presented.
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Al-Khuzaee, Jafar Hameed. "X-ray absorption edge structure in hot dense plasmas." Thesis, University of Essex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424128.
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Louca, P. "From X-ray structure factors to electron-density distributions." Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374638.
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Walker, Andrew W. "Synthesis and X-ray structure analysis of novel calixarene receptors." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318740.
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Jeffrey, Philip D. "The structure and specificity of immunoglobulins." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:79bcae45-289d-4401-9916-d719bc2751a4.
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An investigation into the structures of the antigen-binding fragments (Fab) of mouse monoclonal immunoglobulins by X-ray crystallography, is presented. The family of immunoglobulins studied, Gloops 1-5, possess the ability to bind to both the peptide antigen and the parent protein: Hen Egg-white Lysozyme. The Gloop1 and Gloop4 Fabs were generated by proteolytic cleavage of the antibody, and crystallisation trials yielded crystals of uncomplexed Fabs of both species. Attempts to grow Fab:antigen complex crystals proved unsuccessful. Partial purification of the heterogeneous Gloop4 Fab was found to be essential for the success of the crystallisations. Data were collected on crystal forms of Gloop1, Gloop2 and Gloop4 on an area detector. The structures of three Gloop2 crystal forms were solved by the molecular replacement technique, using models consisting of Fab domain pairs. Two of the crystal forms were refined by molecular dynamics methods at maximum resolutions of 3.3Å and 2.8Å, and the third by rigid body methods alone at 3.5Å resolution. Analysis of the Gloop2 structures between the crystal forms and with other Fabs indicated no atypical features in the domains. The elbow bend of the Gloop2 Fabs differed by up to 7°. The relative association of variable and constant domain pairs was also seen to vary between the Fabs. The changes in domain pairing caused significant differences in the relative disposition of the complementarity determining regions (CDRs), although there was no evidence for conformational change within individual CDRs. The Gloop2 combining site is dominated by a groove of approximate dimensions 12Åx9Åx7Å, containing many aromatic side-chains and a pair of glutamic acid residues in analogous positions to a those found in a FabrHen egg-white Lysozyme complex.
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Swift, Helen Juliet. "X-ray studies of Taka alpha-amylase and penicillin acylase." Thesis, University of York, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258543.
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Magnuson, Martin. "Electronic structure studies using resonant X-ray and photoemission spectroscopy." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-973.
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This thesis addresses the electronic structure of molecules and solids using resonant X-ray emission and photoemission spectroscopy. The use of monochromatic synchrotron radiation and the improved performance of the instrumentation have opened up the possibility of detailed analyses of the response of the electronic systems under interaction with X-rays. The experimental studies are accompanied by numerical ab initio calculations in the formalism of resonant inelastic scattering. The energy selectivity has made it possible for the first time to study how the chemical bonds in a molecule break up during resonant inelastic X-ray scattering. In the conjugated polymer systems, the element selectivity of the X-ray emission process made it possible to probe the different atomic elements separately. The X-ray emission technique proved to be useful for extracting isomeric information, and for measuring the change in the valence levels at different degrees of doping. In this thesis, spectral satellite features in transition metals were thoroughly investigated for various excitation energies around a core-level threshold. By measuring the relative spectral intensity of the satellites it was possible to extract information on the partial core-level widths. Using the nickel metal system as an example, it was shown that it is possible to probe the different core-excited states close toshake-up thresholds by measuring the relative spectral intensity variation of the Auger emission.Resonant photoemission measurements showed unambiguous evidence of interference effects. Theseeffects were also thoroughly probed using angle-dependent measurements. The combination of X-rayemission and absorption were useful for studying buried layers and interfaces due to the appreciable penetration depth of soft X-rays. X-ray scattering was further found to be useful for studying low-energy excited states of rare earth metallic compounds and transition metal oxides.
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Magnuson, Martin. "Electronic Structure Studies Using Resonant X-ray and Photemission Spectroscopy." Doctoral thesis, Uppsala University, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56480.
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This thesis addresses the electronic structure of molecules and solids using resonant X-ray emission and photoemission spectroscopy. The use of monochromatic synchrotron radiation and the improved performance of the instrumentation have opened up the possibility of detailed analyses of the response of the electronic systems under interaction with X-rays. The experimental studies are accompanied by numerical ab initio calculations in the formalism of resonant inelastic scattering. The energy selectivity has made it possible for the first time to study how the chemical bonds in a molecule break up during resonant inelastic X-ray scattering. In the conjugated polymer systems, the element selectivity of the X-ray emission process made it possible to probe the different atomic elements separately. The X-ray emission technique proved to be useful for extracting isomeric information, and for measuring the change in the valence levels at different degrees of doping. In this thesis, spectral satellite features in transition metals were thoroughly investigated for various excitation energies around a core-level threshold. By measuring the relative spectral intensity of the satellites it was possible to extract information on the partial core-level widths. Using the nickel metal system as an example, it was shown that it is possible to probe the different core-excited states close toshake-up thresholds by measuring the relative spectral intensity variation of the Auger emission.Resonant photoemission measurements showed unambiguous evidence of interference effects. Theseeffects were also thoroughly probed using angle-dependent measurements. The combination of X-rayemission and absorption were useful for studying buried layers and interfaces due to the appreciable penetration depth of soft X-rays. X-ray scattering was further found to be useful for studying low-energy excited states of rare earth metallic compounds and transition metal oxides.
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Buades, Bárbara. "Attosecond X-ray absorption fine-structure spectroscopy in condensed matter." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663092.
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Attoscience aims to study electron dynamics in matter with unprecedented temporal resolution by using the shortest pulses generated on Earth. Currently, such resolution is only provided by sources that deliver attosecond pulses based on the high-harmonic generation (HHG) process. In this thesis we make use of the demonstration of the generation of isolated attosecond pulses in the soft X-ray (SXR) regime covering the entire water window (284 eV to 543 eV) with pulse durations shorter than 300 as. Such a source is used to explore its own development, the spectroscopic capabilities of the pulses as well as the spectroscopic differences from existing X-ray sources, and finally to exploit the potential of the provided extraordinary temporal resolution.
We report on the ability to spectrally tune our source 150 eV across the water window by controlling the pressure during the HHG process and the HHG target position with respect to the focal plane of the driving laser pulse. We associate the changes in pressure and target position to a phase matching change between the driving laser pulse of the HHG process and the generated SXR radiation that is mainly caused by a change in the ionisation fraction. These phase matching changes are also compared to a carrier-to-envelope phase changes of the driving laser field.
The attosecond SXR source is used for X-ray absorption fine structure (XAFS) spectroscopy. Our XAFS studies enable the simultaneous probing of extended XAFS (EXFAS) and near edge XAFS (NEXAFS) in graphite, providing element specificity and orbital sensitivity with identification of the sigma* and pi* orbitals in synchronicity with the material’s four characteristic bonding distances. This illustrates the potential capability of correlating electron dynamics with structural dynamics with attosecond resolution being able to resolve charge migration, electron-phonon coupling and structural transitions. Our XAFS investigations also reveal spectral changes in graphite and TiS2 as a consequence of the shorter attosecond pulse compared to the longer picosecond pulse that are typically used in synchrotron facilities. An extended theory is still required to link Auger electron spectroscopy, total electron yield and XAFS using synchrotron radiation with attoXAFS to decouple the different electron dynamics involved on each of the measurements.
Finally, the attosecond pulses are employed to interrogate charge dynamics with unprecedented temporal resolution inside a compound quasi-2D material, TiS2. By synchronising a 1.85 µm pump pulse with the probing attosecond SXR pulse, we observe that the shape of the X-ray absorption line changes from a Lorentzian distribution to a Fano-type distribution oscillating with twice the pump electric field frequency. The absorption changes appear due to an acquired dipole phase response of the photo-excited core-level electron induced by the consecutive arrival of the infrared pump pulse. This demonstrates that field-driven intra-band dynamics dominate over inter-band dynamics. SXR radiation also provides element specificity of attoXAFS which permits, in combination with theory, the visualisation of the flow of charge amongst the atoms inside the unit cell in real time. The combined spatio-temporal capabilities of attosecond transient XAFS may prove decisive to investigate the correlated motion of carriers in quantum materials such as phase-transitions and superconductors.La Attociencia tiene como objetivo estudiar la dinámica de electrones en la materia con una resolución temporal sin precedentes mediante el uso de los pulsos más cortos generados en la Tierra. Actualmente, dicha resolución solo se puede lograr con fuentes de pulsos de attosegundos basados ¿¿en el proceso de generación de armónicos altos (HHG). En esta tesis hacemos uso de la demostración de la generación de pulsos aislados de attosegundos en el régimen de rayos X blandos (SXR) que cubre toda la ventana de agua (284 eV a 543 eV) con duraciones de pulso más cortos que 300 as. Dicha fuente se utiliza para explorar su propio desarrollo, las capacidades espectroscópicas de los pulsos, así como las diferencias espectroscópicas con las fuentes de rayos X existentes, y finalmente explotar el potencial de la resolución temporal extraordinaria proporcionada. Presentamos primero la capacidad de ajustar espectralmente nuestra fuente 150 eV a lo largo de la ventana de agua mediante el control de la presión del gas atómico involucrado en el proceso de HHG y de la posición del proceso de HHG con respecto al plano focal del láser impulsor de activación del proceso. Asociamos los cambios en la presión y en la posición a un cambio de coincidencia de fase entre el láser impulsor y la radiación SXR generada que es causada principalmente por un cambio en la fracción de ionización. Estos cambios de fase también se comparan con los cambios de fase entre la envolvente del campo y el campo (CEP). La fuente de SXR de attosegundo se utiliza para la espectroscopía de estructura fina de absorción de rayos X (XAFS). Nuestros estudios XAFS permiten el sondeo simultáneo de XAFS extendido (EXFAS) y XAFS cercano al borde (NEXAFS) en grafito, proporcionando especificidad de elemento y sensibilidad orbital con identificación de los orbitales sigma* y pi* en sincronicidad con las cuatro distancias de enlace características del material. Esto ilustra la capacidad potencial de correlacionar la dinámica de electrones con la dinámica estructural con resolución de attosegundos, pudiendo resolver la migración de carga, el acoplamiento electrón-fonón y las transiciones estructurales. Nuestras investigaciones XAFS también revelan cambios espectrales en grafito y TiS2 como consecuencia del pulso de atosegundo más corto en comparación con el pulso de picosegundo más largo que se utilizan normalmente en las instalaciones de sincrotrón. Todavía se requiere una teoría extendida para vincular la espectroscopia electrónica de Auger, el campo total de electrones (TEY) y XAFS utilizando radiación sincrotrón con attoXAFS para desacoplar las diferentes dinámicas electrónicas involucradas en cada una de las mediciones. Finalmente, los pulsos de attosegundo se emplean para analizar la dinámica de carga con una resolución temporal sin precedentes dentro de un material compuesto de cuasi-2D, TiS2. Al sincronizar un pulso de luz de bombeo de 1.85 µm con el pulso SXR de attosegundo, observamos que la línea de absorción de rayos X cambia de una distribución de Lorentzian a una distribución de tipo Fano que oscila con el doble de la frecuencia del campo eléctrico de bombeo. Los cambios de absorción aparecen debido a una respuesta de fase dipolar adquirida del electrón excitado por fotoionicaición por la llegada consecutiva del pulso de bombeo infrarrojo. Con esto se demuestra que las dinámicas dentro de la banda impulsadas por el campo dominan sobre la dinámica entre bandas. La radiación SXR también proporciona especificidad de elemento de attoXAFS que permite, en combinación con la teoría, la visualización del flujo de carga entre los átomos dentro de la celda unitaria en tiempo real. Las capacidades espaciotemporales combinadas del XAFS transitorio de attosegundo pueden ser decisivas para investigar el movimiento correlacionado de portadores en materiales cuánticos, como transiciones de fase y superconductores.
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Flood, Kelly-Jayne. "Comparative X-ray Structure Analyses of Multidentate Transition Metal Complexes." Thesis, University of Canterbury. Chemistry, 2006. http://hdl.handle.net/10092/1390.
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The biological significance of macrocyclic complexes has been recognized since they were first synthesized by Neil Curtis. They have the potential to play a critical role in mimicking metalloprotein active sites. Nine Curtis macrocyclic complexes have been studied using X-ray crystallographic techniques. Their structures have been solved and comparisons of the results have been made. Biological importance is also true of the macrocyclic counterpart; side-off and end-off compartmental ligands. In some circumstances these types of ligands are more appropriate because they have extra flexibility due to their pendant arms not being fixed in place by another head-unit, like a traditional macrocycle. The synthesis of a proposed compartmental ligand; 2,2-(N,Nʼ-bis(benzimidazole-2-ylmethyl)methylamine-5,5ʼ-di-tert-butyl-3,3ʼmethanediyl-dibenzyl alcohol (Ligand 1(L1)), has been proposed and outlined. The pendant arms: bis(benzimidazole-2-ylmethyl)amine (BBIM), were successfully synthesized and characterized with 1H NMR, IR and X-ray crystallography. The head-unit: 5,5ʼ-Di-tert-butyl-2,2ʼ-dihydroxy-3,3ʼ-methanediyl-dibenzene methanol (DHTMBA), of L1 was synthesized and characterized using 1H NMR, IR and mass spectrometry. A similar head-unit; 5,5ʼ-Di-methyl-2,2ʼ-dihydroxy-3,3ʼ-methanediyl-dibenzene methanol (DHMMBA), was synthesized in an effort to shorten the synthetic time of the head-unit. This was consequently converted to the chlorine analogue; 3,3ʼ-Bis(chloromethyl)-5,5ʼ-dimethyl-2,2ʼ-methane-diyldiphenol (Cl-DHMMB), and characterized with 1H NMR, IR and X-ray crystallography. Efforts were made to synthesize Ligand 1, but due to synthetic difficulties and time restraints this proved unsuccessful. Suggestions have been made to develop this synthesis.
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Jürgensen, Astrid. "Probing electronic structure and chemical bonding with x-ray spectroscopy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0034/NQ46862.pdf.
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Tremayne, Maryjane. "Ab initio structure determination from X-ray powder diffraction data." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/6503.
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Many important crystalline solids cannot be prepared in the form of single crystals of sufficient size and quality for single crystal X-ray diffraction studies, and in such cases it is essential that structural information can be extracted from powder diffraction data. In this thesis, a number of crystal structures have been determined directly from X-ray powder diffraction data recorded on a conventional laboratory instrument, and the limitations of this technique explored using both conventional and new more sophisticated methods of structure solution. This work has focussed mainly on the more complex problem of molecular systems. The Patterson method has been applied to the determination of a simple unknown inorganic structure, lithium perchlorate, whereas conventional direct methods have been used in the determination of a number of organic structures, including the previously unknown crystal structure of 1,3,4,6-tetrathiopentalene-2,5-dione and formylurea - the first previously unknown organic structure containing only light atoms to be solved by this technique. The combined maximum entropy and likelihood method has been applied to determinate two crystal structures, lithium triflate and p-toluenesulphonhydrazide. Further developments of this technique are also discussed and illustrated in the structure solution of a previously known system. A Monte Carlo algorithm for ab initio crystal structure determination from powder diffraction data has also been developed, and the success of this method demonstrated by its application to the determination of several known structures, and the previously unknown crystal structure of p-bromophenylacetic acid. The effect of data range on the quality of structure solution obtained from both direct methods and the maximum entropy and likelihood method is also discussed.
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Kolodzig, Alexander. "Large-scale structure studies using AGN in X-ray surveys." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-182285.
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Large X-ray surveys are a powerful tool to study the large-scale structure (LSS) of the Universe. The scientific impact of LSS studies using active galactic nuclei (AGN)
in X-ray surveys can be significantly increased by conducting wider and deeper X-ray surveys and studying the surface brightness fluctuations of the unresolved cosmic X-ray background (CXB).
In the first part of this Thesis, we have investigated the prospects of using the AGN sample to be detected by the upcoming eROSITA all-sky survey (eRASS) for LSS studies. We show that eRASS will detect about 3 million AGN in the 0.5-2.0 keV band. This will result in a ~30 times larger number of sources and a ~30 times better sensitivity than its 25 year old predecessor, the ROSAT all-sky survey (RASS). We show that this unprecedented AGN sample will have a median luminosity of ~10^44 erg/s, which is typical for the entire AGN population in this energy band. It will have a median redshift of z ~ 1 and approximately 40% of the objects will be in the redshift range of z = 1-2, where the bulk of the X-ray emission of AGN is produced. About 10^4 - 10^5 AGN are predicted to be beyond redshift z = 3 and about 2 000 - 30 000 beyond z = 4, which will potentially include some of the earliest AGN in the Universe. We demonstrate that, given these unique properties, the eRASS-AGN sample will be able to significantly improve our current knowledge of the AGN spatial density as a function of redshift and luminosity over a wide range of cosmic time. Further, we show that it will enable us, for the first time, to perform detailed redshift- and luminosity-resolved studies of the clustering strength of X-ray selected AGN. All these measurements will dramatically improve our understanding of the growth of supermassive black holes over cosmic time and its implications for galaxy evolution. We demonstrate for the first time that, given the breadth and depth of eRASS, it will be possible to use AGN as a cosmological probe via baryon acoustic oscillation (BAO) measurements. We will be able to convincingly detect BAOs in the currently uncharted redshift range of z ~ 1-2, which will improve the constraints on the current cosmological model.
In the second part of this Thesis, we have conducted the most accurate measurement to date of the brightness fluctuations of the unresolved CXB in the 0.5-2.0 keV band for angular scales of < ~17'. For this we used the XBOOTES survey, the currently largest continuous survey of the X-ray telescope Chandra. We find that on small angular scales (< ~2') the observed power spectrum of the brightness fluctuations is broadly consistent with the conventional AGN clustering model, although with a 30% deviation. This deviation nevertheless presents a good opportunity to improve our understanding of clustering properties of unresolved AGN by testing more sophisticated clustering models with our measurement. For angular scales of > ~2' we measure a significant excess with up to an order of magnitude difference in comparison to the standard AGN clustering model. We demonstrate that an instrumental origin can be excluded. However, we also show that the excess can neither be explained with any known X-ray source population by looking at strength of its clustering signal and the shape of its energy spectrum. It might be caused by more than one type of source but the dominant source appears to have extragalactic origin. Finally, we make predictions on how eRASS will be able to advance the studies of the unresolved CXB.
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Chen, B. "X-ray imaging of three-dimensional spatial structure of coatings." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1386117/.
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Coatings, typically painted films, one of the most important and widely-used surface treatment materials, were selected as the subject of this research project. In this dissertation, detailed three-dimensional (3D) spatial structures of three types of coating specimens: silver epoxy adhesive, iron oxide alkyd paint and aluminium epoxy marine coating were obtained by using different 3D X-ray imaging methods and comparative 3D electron imaging means. The shapes and spatial distributions of particles of the main functional ingredients of all these coating specimens were demonstrated. Specifically, for the aluminium epoxy marine coating, the quantitative analysis of the sizes, volumes, orientations and spatial distributions and correlations of the aluminium flakes in the matrix materials of the coating were carried out. Furthermore, the 3D structures of the aluminium epoxy marine coating samples were used for the finite element simulations of the (ion) percolation properties of the coating film. This potentially provides us with a practical method to engineer the efficacy of coatings by modelling their performances based on the actual structures instead of using assumed model structures. This is a new way to evaluate the performance of materials, and also can be an approach for validating their mechanistic assumptions. It could help to shorten the product research and development lifetime, complementing endurance studies of original specimens. The work presented in the dissertation is the first systematic research of 3D spatial structures of coatings and it could help guide coating researchers how to choose the most suitable 3D investigation method for a specific coating specimen. Through comparative experiments, transmission X-ray microscopy (TXM), ptychographic Xray computed tomography (PXCT), X-ray holo-tomography and serial block-face scanning electron microscopy (SBFSEM) have been verified as effective ways to reveal 3D spatial structures of complex industrial specimens. A comparison among these 3D imaging approaches and their advantages and disadvantages are discussed. The wave-front modulation coherent X-ray diffraction imaging was also implemented. It proved to be a capable method of measuring structures of coating samples and reaches similar resolution as TXM. Developing it into a 3D coherent X-ray imaging methodology with capabilities of obtaining a unique image solution from a single diffraction pattern is left as future work.
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Wilson, Claire. "Structure-reactivity relationships through X-ray and neutron diffraction studies." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5314/.
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This thesis is primarily concerned with the investigation of a structure-reactivity relationship in a series of pentacyclic Isodrin derivatives. These compounds undergo a two-hydrogen atom dyotropic rearrangement at vastly differing rates when apparently small structural changes are made. Two pairs of these isomers (with the formulas C(_16)H(_8)Cl(_10) and C(_16)H(_9)Cl(_9) ) have been investigated using both X-ray and neutron single crystal diffraction studies, at ambient and low temperatures. The experimental details of these studies are given for five experiments and the results of the least-squares refinements made using the data from these experiments are reported herein. In addition to conventional crystallographic studies, an experimental charge density study of one of these compounds, C(_16)H(_9)Cl(_9), has been made at 123K. The electron density was modelled using a multipole model which allows explicitly for the aspherical nature of the electron density. The results of this study, including a topological analysis of the charge density are reported in this thesis. The structures of six organometallic, four molybdenum bis(imido) and two half-sandwich niobium imido complexes, are also reported herein. Their structures were determined from single crystal diffraction data. These compounds show the expected structures predicted using the pseudo-isolobal relationship to the Group 4 bent metallocenes of which they may be considered analogues.
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Mayer, Suzanne Marie. "X-ray structure determination of Klebsiella pneumoniae nitrogenase component 1." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323342.
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Crapper, M. D. "X-ray absorption fine structure of adsorbates on metal surfaces." Thesis, University of Warwick, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377093.
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Jenkins, Paul James. "X-ray and neutron scattering studies of starch granule structure." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362925.
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Lunel, Marie Monique France. "Structure characterisation of catalysts using X-ray micro-computed tomography." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5710/.
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Knowledge of internal porous structure is essential in improving the development of a catalytic system and consequently leading to an optimized performance. XRCT has been used to show differences in density and pore distribution and that differences can be related to the process route by which the specimen was prepared. Alumina samples with defects prepared using different conditions have been investigated in order to acquire information on the introduction and development of cracks. Results indicated that cracks became larger when the water content, the ram speed of the extruder and the drying temperature were higher. The calcination process increased the number and the 3-D size of the cracks. Both concentration of the bulk solution and impregnation time appeared to have a significant impact on the metal distribution profile during the impregnation process. Drying had a strong impact on the metal profile, as a redistribution of copper was noticed. The redistribution was observed exclusively in the case of weak adsorption of copper with alumina support. Experiments on the newly established I13 beamline synchrotron in Diamond was carried out in order to gain an understanding of the cracks induction/propagation and of the diffusion of metallic solution inside the catalyst support.
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Schneider, Andrea-Ingrid. "X-ray structure analysis of liquid crystalline copoly(ester carbonates)." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059570165.
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DeRose, Guy Arthur. "X-ray absorption fine structure strain determination in thin films." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1060005230.
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Tsuboi, Chiaki. "X-ray crystal structure analyses of magnetically oriented microcrystalline suspensions." Kyoto University, 2016. http://hdl.handle.net/2433/216190.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第19936号
農博第2186号
新制||農||1044(附属図書館)
学位論文||H28||N5009(農学部図書室)
33022
京都大学大学院農学研究科森林科学専攻
(主査)教授 木村 恒久, 教授 西尾 嘉之, 教授 髙野 俊幸
学位規則第4条第1項該当
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Shorrosh, Raed Saed. "An x-ray absorption fine structure study of semiconductor nanoclusters." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/30867.
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Bisiak, Francesco. "Structural studies of the Roundabout protein family." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAV006/document.
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Les systèmes neuronaux et vasculaires nécessitent un réseau complexe pour exécuter correctement leurs fonctions. Les processus impliqués dans la création de ce réseau s'appuient sur des voies coordonnées, souvent activées par des systèmes protéine/récepteur communs, qui conduisent au remodelage du cytosquelette.En général, les cellules neuronales et vasculaires répondent aux stimuli extracellulaires sous forme de protéines solubles sécrétées, qui interagissent avec les récepteurs de surface pour favoriser l'attraction ou la répulsion vers la source des protéines sécrétées. Ce processus, appelé guidage, est régulé par sept familles de récepteurs et leurs ligands respectifs, qui s'influencent les uns sur les autres et peuvent agir sur le système neuronal, le système vasculaire ou les deux ensembles.Cette étude est centrée sur deux récepteurs transmembranaires à passage unique, les membres des familles de protéines Roundabout et UNC5 qui sont principalement impliquées dans l'angiogenèse: Robo4 et UNC5B.L'information structurelle sur la région extracellulaire de plusieurs de ces récepteurs, et comment le signal est relayé à travers la membrane, fait défaut.La déglycosylation enzymatique a confirmé que les domaines extracellulaires de Robo4 et UNC5B sont largement glycosylés avec des glycanes liés en azote du complexe type. La mutagenèse dirigée des sites de glycosylation prédits de Robo4 perturbe son expression, indiquant que ces résidus sont nécessaires pour la stabilité de la protéine et que leur glycosylation, ou leur passage dans la voie de glycosylation, pourrait être nécessaire pour un repliement correct. Les données MALS et SAXS montrent qu'en solution, Robo4 ecto est un monomère flexible de forme allongée. Les domaines ne présentent pas des caractéristiques distinctes dans le modèle construit à partir des données SAXS. Plusieurs Fabs se liant au domaine extracellulaire de Robo4 ont été caractérisés, avec l'espoir d'identifier les Fab qui pourraient inhiber l'interaction Robo4 / UNC5B rapportée pour une caractérisation plus poussée. La formation du complexe a été vérifiée par SEC-MALS et SAXS, et les constantes d'interaction ont été déterminées en utilisant SPR. Des cristaux de certains complexes domaine Fab / domaine extracellulaire Robo4 ont été produits, bien que la structure du complexe n'ait pas pu être résolue à l'heure actuelle.Les expériences de pull-down, SEC-MALS et SPR montrent que Robo4 ecto et UNC5B ecto n'interagissent pas entre elles, malgré une étude par un autre groupe montrant le contraire. Étant donné que différentes lignées cellulaires ont été utilisées, des modèles de glycosylation spécifiques, ou une tierce partie non détectée, pourraient être nécessaires pour l'interaction. En raison de leur implication avec les récepteurs extracellulaires, les héparanes sulfates sont un candidat probable, mais d'autres partenaires devraient être envisagés.La structure cristallographique de l'UNC5B ecto est similaire aux structures existantes de UNC5A et UNC5D. Le haut degré de conservation des domaines del’Ig pourrait être une indication de l'importance de cette région, qui est responsable de la liaison à Netrin. Bien que la région de liaison de Netrin soit connue pour être dans les domaines Ig, le site de liaison précis n'a pas encore été déterminé, mais il pourrait être situé à proximité ou à l'intérieur des surfaces chargées négativement présentes sur les domaines Ig observées dans la structure d’UNC5B.Le travail présenté ici devrait servir de base à une meilleure caractérisation biochimique et structurale des récepteurs extracellulaires Robo4 et UNC5BNeuronal and vascular systems require a complex network to properly perform their functions. The processes involved in creating this network rely on coordinated pathways, often activated through common protein/receptor systems, which lead to cytoskeletal remodelling. In general, neuronal and vascular cells respond to extracellular stimuli in the form of soluble secreted proteins, which interact with surface receptors to mediate attraction or repulsion towards the source of the secreted proteins. This process, called guidance, is regulated by seven families of receptors and their respective ligands, which influence each other and can act on the neuronal system, the vascular system or both.Structural information about the extracellular region of many of these receptors, and how signal is relayed across the membrane, is lacking.This study is focused around the extracellular domain of two single-pass transmembrane receptors of the Roundabout and UNC5 protein families that are majorly involved in angiogenesis: Robo4 and UNC5B.Based on the findings of this study, the Robo4 and UNC5B extracellular domains are extensively glycosylated with N-linked glycans of the complex type. Site-directed mutagenesis of the predicted Robo4 glycosylation sites disrupts protein expression, indicating that they are necessary for protein stability and passage through the glycosylation pathway might be necessary for correct folding. MALS and SAXS data show that in solution the Robo4 extracellular domain is a flexible monomer with extended shape. Several Fabs binding to the extracellular domain of Robo4 were characterised, with the expectation to identify those Fabs that could inhibit the reported Robo4/UNC5B interaction for further characterisation. Complex formation was verified by SEC-MALS and SAXS, and interaction constants were determined using SPR. Crystals of some Robo4 extracellular domain/Fab complexes were produced, although the structure of the complex could not be solved at the present time.Despite a study by another group showing otherwise, pull-down, SEC-MALS and SPR experiments show that the Robo4 and UNC5B extracellular domains do not interact with each other. It is proposed that the difference may be caused by different glycosylation patterns specific to the cell lines used for each study, or by an undetected third party necessary for interaction. This, however, still requires further study. SEC-MALS analysis showed that the UNC5B extracellular domain is a monomer in solution and its crystal structure was solved at 3.4 Å resolution. Comparison to the existing structures of human UNC5A and rat UNC5D shows striking similarities and a high degree of evolutionary conservation of the Ig domains might be indication of the importance of this region, which is responsible for binding to the guidance cue Netrin. Although the Netrin binding region is known to be within the Ig domains, the precise binding site has not yet been determined, but it might be located in proximity, or within, the negatively charged surfaces present on the Ig domains which are observed in the UNC5B structure.It is hoped that the work presented here will give the basis for better biochemical and structural characterisation of these two receptors
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Dent, A. J. "The development of anomalous (resonance) X-ray diffraction techniques for solution." Thesis, University of Bristol, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384555.
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Erskine, Peter Thomas. "X-ray crystallographic studies of 5-aminolaevulinic acid dehydratase." Thesis, Birkbeck (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299090.
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Onifade, Ibrahim. "Internal structure characterization of asphalt concrete using x-ray computed tomography." Thesis, KTH, Väg- och banteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127689.
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This study is carried out to develop the workflow from image acquisition to numerical simulation for asphalt concrete (AC) microstructure. High resolution computed tomography (CT) images are acquired and the image quality is improved using digital image processing (DIP). Non-uniform illumination which results in inaccurate phase segmentation is corrected by applying an illumination profile to correct the background and flat-fields in the image. Distance map based watershed segmentation is used to accurately segment the phases and separate the aggregates. Quantitative analysis of the microstructure is used to determine the phase volumetric relationship and aggregates characteristics. The results of the phase reconstruction and internal structure quantification using this procedure shows a very high level of reliability. Numerical simulations are carried out in Two dimensions (2D) and Three dimensions (3D) on the processed AC microstructure. Finite element analysis (FEM) is used to capture the strength and deformation mechanisms of the AC microstructure. The micromechanical behaviour of the AC is investigated when it is considered as a continuum and when considered as a multi-phase model. The results show that the size and arrangement of aggregates determines the stress distribution pattern in the mix.
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Memola, Elisabetta. "Magnetic jets from accretion disks field structure and X-ray emission /." Phd thesis, [S.l.] : [s.n.], 2002. http://pub.ub.uni-potsdam.de/2002/0014/memola.pdf.
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Martins, Emanuel. "X-ray spectroscopic study of the electronic structure of sulfur compounds." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283717.
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Lane, S. E. "Structure determination by X-ray crystallography of some Group IIIB compounds." Thesis, Lancaster University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355338.
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Sadow, Jennifer Beth Hurley. "The X-ray crystal structure of wheat translation initiation factor eIF4E /." Thesis, Full text (PDF) from UMI/Dissertation Abstracts International, 2002. http://wwwlib.umi.com/cr/utexas/fullcit?p3085056.
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Guo, Meiyuan. "Electronic structure investigations of transition metal complexes through X-ray spectroscopy." Doctoral thesis, Uppsala universitet, Teoretisk kemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-328072.
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Catalysts based on the first-row (3d) transition metals are commonly seen in chemical and biological reactions. To understand the role of the transition metal in the catalyst, the element specific technique core level spectroscopy is used to probe the electronic structure and geometric properties centered around the metal site. Different types of X-ray spectra can be applied to probe the metal 3d character orbitals involved in reactions, which make it possible to identify and characterize the reactive sites of samples in different forms. A detailed interpretation and understanding of the different X-ray spectra requires a unified method which can be used to model different types of X-ray spectra, e.g., soft and hard X-rays. In this thesis, theoretical investigations of the electronic structures of 3d transition metal complexes through X-ray spectroscopy are presented. The restricted active space method (RAS) is used to successfully reproduce different types of X-ray spectra by including all important spectral effects: multiplet structures, spin-orbit coupling, charge-transfer excitations, ligand field splitting and 3d-4p orbital hybridization. Different prototypes of molecules are adopted to test the applicability of the RAS theory. The metal L edge X-ray absorption (XAS) spectra of low spin complexes [Fe(CN)6]n and [Fe(P)(ImH)2]n in ferrous and ferric oxidation state are discussed. The RAS calculations on iron L edge spectra of these comparing complexes have been performed to fingerprint the oxidation states of metal ion, and different ligand environments. The Fe(P) system has several low-lying spin states in the ground state, which is used as a model to identify unknown species by their spectroscopic fingerprints through RAS spectra simulations. To pave the route of understanding the electronic structure of oxygen evolution complex of Mn4CaO5 cluster, the MnII(acac)2 and MnIII(acac)3 are adopted as prototypical Mn-complexes. The 3d partial fluorescence yield-XAS are employed on the Mn L-edge in solution. Combining experiments and RAS calculations, primary questions related to the oxidation state and spin state are discussed. The first application to simulate the metal K pre-edge XAS of mono-iron complexes and iron dimer using RAS method beyond the electric dipole is completed by implementing the approximate origin independent calculations for the intensities. The K pre-edge spectrum of centrosymmetric complex [FeCl6]n– ferrous state is discussed as s and a donor model systems. The intensity of the K pre-edge increases significantly if the centrosymmetric environment is broken, e:g:, when going from a six-coordinate to the four-coordinate site in [FeCl4]n. Distortions from centrosymmetry allow for 3d-4p orbital hybridization, which gives rise to electric dipole-allowed transitions in the K pre-edge region. In order to deliver ample electronic structure details with high resolution in the hard X-ray energy range, the two-photon 1s2p resonant inelastic X-ray scattering process is employed. Upon the above successful applications of one-photon iron L edge and K pre-edge spectra, the RAS method is extended to simulate and interpret the 1s2p resonant inelastic X-ray scattering spectra of [Fe(CN)6]n in ferrous and ferric oxidation states. The RAS applications on X-ray simulations are not restricted to the presented spectra in the thesis, it can be applied to the photon process of interest by including the corresponding core and valence orbitals of the sample.
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Shotton, Mark William. "DNA structure investigated using complementary x-ray and neutron fibre diffraction." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245356.
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Seaton, Colin Cormack. "Novel methods of structure determination from X-ray powder diffraction data." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396462.
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The determination of crystal structures from powder diffraction data is a field that is rapidly expanding due to a range of computational and experimental developments. A major driving force of this expansion is the continuing development of direct space methods of structure solution. This work will show the development of the program POSSUM as a suite of direct space structure determination methods and its subsequent successful application to a number of molecular organic and inorganic materials whose crystal structures were previously unknown. Direct space methods utilise global optimisation algorithms to locate the crystal structure. This work describes the successful application of the differential evolution optimisation algorithm to structure determination from powder diffraction. Differential evolution is shown to be a robust and efficient optimisation technique with the limited number of control parameters associated with the method ensuring that optimisation of the searching is easily achieved. Investigation into improving the computer performance of the method also focused on reduction of the time taken to evaluate agreement between experimental and calculated patterns through the application of the discrete wavelet transform. This effectively reduces the number of points in the powder pattern, yet retains the same level of information as the original data set and is shown to illustrate good discrimination between solutions generated in a direct space structure solution.
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Kawaguchi, Tomoya. "Development of x-ray spectroscopy coupling with resonant scattering -toward applications of practical materials-." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199305.
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Nesvizhskii, Alexey I. "Theory and interpretation of L-shell x-ray absorption spectra /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9738.
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Heath, Andrew Edmund. "High pressure structural investigations of solids using X-ray and synchrotron radiation." Thesis, University of Leicester, 1989. http://hdl.handle.net/2381/33731.
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X-ray diffraction has been used to investigate the structure and structural behaviour of several inorganic solids under variable pressure and temperature conditions. A brief description of the diamond anvil cell (d.a.c.) and its applications to the high- pressure investigations is given. A spectroscopic system built for pressure calibration is discussed, plus an account of powder diffraction data analysis including a detailed description of a software package engineered for the specific reduction of powder data obtained under variable pressure. Potassium nitrate (KNO3) has seven polymorphs in the pressure range 0.0-4.0 GPa. This material has been studied with energy dispersive powder diffraction (EDXRD) to 9.3 GPa. The structure of the non-ambient phase IV refined by neutron diffraction at 0.36 GPa has been confirmed, the compressibility of the high-pressure phase measured and found to be anisotropic with axial compression ratios a:b:c = 1.0:0.64:0.50. The valence induced structural transition at 0.8 GPa in EuPd2Si2 has been studied using EDXRD and uni-axial compressibilities calculated. A basic explanation of the electronic theory which accompanies the subtle shortening of the a lattice parameter in the tetragonal asymmetric unit is also given. The structures of two compounds CH3HgX (X = I, Cl) have been investigated using single crystal and angle-dispersive powder techniques respectively. The crystal structure of methyl mercuric iodide is reported. CH3HgCl has been observed above and below the temperature induced I/II phase boundary at 162.5 K. A hypothesis detailing the iso-structural nature of CH3HgCl low temperature phase II and the ambient phase I of the analogous methyl mercuric bromide is also tested.
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Palma, Joseph John. "X-ray Diffraction Studies of Amorphous Materials." Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/231213.
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PhysicsPh.D.
This thesis presents a study on two types of X-ray diffraction methodologies applied to the characterization of amorphous materials. The purpose of this study was to assess the feasibility of measuring the diffractive spectrum of amorphous materials by Energy-Dispersive X-ray Diffraction (EDXRD) utilizing Cadmium Zinc Telluride detectors. The total scattering intensity (coherent plus incoherent scatter) spectra precisely measured by high-energy Wide-Angle X-ray Scattering (WAXS) were compared to the EDXRD spectra to determine the level of agreement between the two techniques. The EDXRD spectra were constructed by applying a spectra fusing technique which combined the EDXRD spectra collected at different scattering angles rendering a continuous total scattering spectrum. The spectra fusing technique extended the momentum transfer range of the observed scattered spectrum beyond the limitations of the X-ray source and CZT detection efficiencies. Agreement between the WAXS and fused EDXRD spectra was achieved. In addition, this thesis presents the atomic pair correlation functions and coordination numbers of the first coordination shell for four hydrogen peroxide solutions of varying mass concentrations using Empirical Potential Structural Refinement (EPSR). The results are compared to the state-of-the art ad initio quantum mechanical charge field molecular dynamics (QMCF MD) model of the hydrogen peroxide in solution to support the model's predictions on why hydrogen peroxide is stable in water. The EPSR results using the coherent scattering intensity calculated from the WAXS data set predicts a hydration shell of 6.4 molecules of water surrounding hydrogen peroxide. The results also indicate that hydrogen peroxide is more likely to behave as a proton donor than acceptor. These findings are in agreement with QMCF MD model of aqueous hydrogen peroxide.
Temple University--Theses
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Swaraj, Sufal. "Surface chemical characterization of plasma-chemically deposited polymer films by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/273/index.html.
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Zhang, Weizhe, and 张蔚哲. "Development of crystallographic phasing method and structural study ofDscam." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46940996.
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Zhang, Weizhe, and 張蔚哲. "Development of macromolecular phasing methods." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206741.
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X-ray crystallography is a powerful method in determining the structure of both small molecules and macromolecules and is now routinely applied in many scientific fields. However, to apply this method, there is an unavoidable problem to tackle: the Phase Problem, which arises because the phases of a scattered x-ray cannot be measured in diffraction experiment and the original structure cannot be retrieved only with the measurable amplitudes. This thesis presents two approaches in the development of macromolecular phasing methods.
One approach presented here utilizes molecular envelope of NMR structures for molecular replacement (MR) phasing with the program FSEARCH at low resolution (about 6 Å). X-ray crystallography and NMR are complementary tools in structural biology. However, it is often difficult to use NMR structures as search models in MR to phase crystallographic data. For this purpose, in our study, several targets with both crystallographic and NMR structures available have been tested. The test protocol involves four steps: (1) Model preparation, NMR structures were processed into averaged polyalanine model, and centroid NMR models have also been tested; (2) Six-dimensional low resolution search were carried out by FSEARCH to find the best match between observed and calculated structure factors; (3) Apply the solution (4) Model building and refinement. In our tests, FSEARCH was able to find the correct translation and orientation of the search model in the crystallographic unit cell, while conventional MR procedures were unsuccessful.
The other approach presented in this thesis is protein complex structure completion using IPCAS (Iterative Protein Crystal structure Automatic Solution). Protein complexes have been concerned as essential components in almost every cellular process. X-ray crystallography method is quite useful in studying the nature of protein complexes. In this study, we demonstrated a protein complex completion procedure from a partial molecular replacement (MR) solution using IPCAS. IPCAS is a direct-method aided dual-space iterative phasing and model-building procedure. The test cases were carefully selected from a practical perspective and IPCAS could build the whole complex from one or less than one subunit once molecular replacement method could give a partial solution. Before delivering to IPCAS, MR solution model examination and improvement might be necessary. The IPCAS iteration procedure involves (1) real-space model building and refinement; (2) direct-method aided reciprocal-space phase refinement; and (3) phase improvement through density modification. In our tests, IPCAS is able to extend the full length complex from a less than 30% starting model while conventional model building procedure were unsuccessful.published_or_final_version
Physiology
Doctoral
Doctor of Philosophy
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Andrews, Paul. "In situ studies of homogeneous nickel alkene oligomerisation catalysts." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239603.
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