Dissertationen: „Paire of Distribution Function“

1

Lucas, Tim. „Pair distribution function studies of inorganic materials under extreme conditions“. Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4630/.

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This study concentrates on pair distribution function (PDF) analysis of various related systems under extreme conditions using variable temperatures and pressures. The local structure of BaTiO$_3$ (BTO) was investigated using x-rays (xPDF) between 0 and 8.78 GPa and x-rays and neutrons (nPDF) between 100 and 500K. Evidence is presented that indicates that the “Comes model” of Ti disorder is too simplistic to describe the local structure of BTO at variable temperature but results from the high pressure xPDF study are inconclusive due to the inability to observe the very weak first Ti-O peak. The ambient structure of related Ba$_1$$_-$$_x$Bi$_x$Ti$_1$$_-$$_x$Yb$_x$O$_3$ was also investigated using both nPDF and xPDF between x = 0 and 0.15, with PDFs indicating significant local disorder present on both A and B sites. Cubic ZrMo$_2$O$_7$ undergoes pressure induced amorphisation at ~0.7 GPa and this was investigated up to 11.02 GPa using xPDF which showed an increase in Mo coordination with pressure but no significant change around Zr. Iron undergoes a bcc-hcp phase transition between 10 and 20 GPa and xPDF was used to investigate this phase transition and the local structure of the hcp phase up to 50.07 GPa, but texture in the sample at high pressures hindered analysis.

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2

Martinez-Inesta, Maria M. „Pair distribution function as a probe for disorder in molecular sieves“. Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 2.69 Mb., 260 p, 2005. http://proquest.umi.com/pqdlink?did=1037889231&Fmt=7&clientId=8331&RQT=309&VName=PQD.

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3

Takahashi, Masakuni. „Elucidation of the Dominant Factor in Electrochemical Materials Using Pair Distribution Function Analysis“. Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263748.

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京都大学
新制・課程博士
博士(人間・環境学)
甲第23287号
人博第1002号
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授内本喜晴, 教授田部勢津久, 准教授戸﨑充男
学位規則第4条第1項該当
Doctor of Human and Environmental Studies
Kyoto University
DFAM

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4

Masadeh, Ahmad Salah. „Quantitative structure determination of nanostructured materials using the atomic pair distribution function analysis“. Diss., Connect to online resource - MSU authorized users, 2008.

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5

Brickman, Larry A. „Numerical evaluation of the pair-distribution function of dilute suspensions at high Péclet number“. Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11305.

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6

Zheng, Lianqing. „Statistical identification of metabolic reactions catalyzed by gene products of unknown function“. Diss., Kansas State University, 2013. http://hdl.handle.net/2097/15594.

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Doctor of Philosophy
Department of Statistics
Gary L. Gadbury
High-throughput metabolite analysis is an approach used by biologists seeking to identify the functions of genes. A mutation in a gene encoding an enzyme is expected to alter the level of the metabolites which serve as the enzyme’s reactant(s) (also known as substrate) and product(s). To find the function of a mutated gene, metabolite data from a wild-type organism and a mutant are compared and candidate reactants and products are identified. The screening principle is that the concentration of reactants will be higher and the concentration of products will be lower in the mutant than in wild type. This is because the mutation reduces the reaction between the reactant and the product in the mutant organism. Based upon this principle, we suggest a method to screen the possible lipid reactant and product pairs related to a mutation affecting an unknown reaction. Some numerical facts are given for the treatment means for the lipid pairs in each treatment group, and relations between the means are found for the paired lipids. A set of statistics from the relations between the means of the lipid pairs is derived. Reactant and product lipid pairs associated with specific mutations are used to assess the results. We have explored four methods using the test statistics to obtain a list of potential reactant-product pairs affected by the mutation. The first method uses the parametric bootstrap to obtain an empirical null distribution of the test statistic and a technique to identify a family of distributions and corresponding parameter estimates for modeling the null distribution. The second method uses a mixture of normal distributions to model the empirical bootstrap null. The third method uses a normal mixture model with multiple components to model the entire distribution of test statistics from all pairs of lipids. The argument is made that, for some cases, one of the model components is that for lipid pairs affected by the mutation while the other components model the null distribution. The fourth method uses a two-way ANOVA model with an interaction term to find the relations between the mean concentrations and the role of a lipid as a reactant or product in a specific lipid pair. The goal of all methods is to identify a list of findings by false discovery techniques. Finally a simulation technique is proposed to evaluate properties of statistical methods for identifying candidate reactant-product pairs.

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Batchellor, Adam. „STRUCTURE-ACTIVITY RELATIONSHIPS IN NI-FE (OXY)HYDROXIDE OXYGEN EVOLUTION ELECTROCATALYSTS“. Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22268.

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The oxygen evolution reaction (OER) is kinetically slow and hence a significant efficiency loss in electricity-driven water electrolysis. Understanding the relationships between architecture, composition, and activity in high-performing catalyst systems are critical for the development of better catalysts. This dissertation discusses areas both fundamental and applied that seek to better understand how to accurately measure catalyst activity as well as ways to design higher performing catalysts. Chapter I introduces the work that has been done in the field to date. Chapter II compares various methods of determining the electrochemically active surface area of a film. It further discusses how pulsed and continuous electrodepostition techniques effect film morphology and behavior, and shows that using a simple electrodeposition can create high loading films with architectures that outperform those deposited onto inert substrates. The reversibility of the films, a measure of the films transport efficiency, is introduced and shown to correlate strongly with performance. Chapter III uses high energy x-ray scattering to probe the nanocrystalline domains of the largely amorphous NiFe oxyhydroxide catalysts, and shows that significant similarities in the local structure are not responsible for the change in performance for the films synthesized under different conditions. Bond lengths for oxidized and reduced catalysts are determined, and show no significant phase segregation occurs. Chapter IV seeks to optimize the deposition conditions introduced in Chapter II and to provide a physical representation of how tuning each of the parameters affects film morphology. The deposition current density is shown to be the most important factor affecting film performance at a given loading. Chapter V highlights the different design considerations for films being used in a photoelectrochemical cell, and how in situ techniques can provide information that may otherwise be unobtainable. Chapter VI serves as a summary and provides future directions. This dissertation contains previously published coauthored material.

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Ellezam, Laura. „Dopage (Co/Fe) de nanoparticules de RuO2 : synthèse, modélisation et caractérisation structurale“. Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS304.

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Ce travail concerne l’analyse complète des nanoparticules (NPs) de RuO2 dopées au Co ou au Fe. Le défi ici réside dans la taille des systèmes, comprise entre 1 et 2,5nm. Les synthèses sont réalisées par trois voies différentes de chimie douce en solvant aqueux : la voie sol-gel, hydrothermale, et co-précipitation. Le Fe se substitue facilement au Ru, le Co plus difficilement. À l’issue de l’étude de ces méthodes de synthèse, des NPs dopées au Co et au Fe ont été synthétisées. Afin de les caractériser et de comprendre l’influence, notamment structurale, des dopants, les calculs DFT et la caractérisation par l’étude de la fonction de distribution de paires atomiques (PDF) ont été couplés. La construction de modèle bulk puis des modèles de NPs ont été construits et optimisés. Les études de localisation des dopants montrent qu’ils se concentrent préférentiellement en surface, éloignés par des atomes de Ru dans le cas d’un nombre très faible d’atome. En augmentant le nombre d’atomes dopants, une étude préliminaire suggère un regroupement de surface des atomes dopants. À partir de ces modèles, des PDFs sont calculées et comparées aux PDFs expérimentales des NPs synthétisées. Ainsi il est possible d’attribuer en détail les PDFs expérimentales et de décrire l’arrangement local des NPs dopées ainsi que de valider les modèles DFT. Il a donc été mis en place un protocole de caractérisation permettant de décrire l’arrangement locale et de démontrer le dopage, dans des NPs de moins de 5 nm en utilisant la DFT et l’analyse PDF, avec confirmation par des analyses STEM-HAADF-EELS
The aim of this work is the full analysis of RuO2 nanoparticles (NPs) doped with Co or Fe. This is a big challenge because of the size of these systems (1.0 - 2.5 nm). Synthesis were conducted by three different aqueous pathways at low temperature: via sol-gel, hydrothermal and by co-precipitation methods. Fe atoms replaces easily Ru, whereas it is more difficult for Co. Several parameters had to be changed to obtain a successful doping. In order to characterize the local structure of Co or Fe-doped RuO2 nanoparticles, and understand the structural modifications, a coupling between modelling with DFT calculation and analysis by Pair Distribution Function (PDF) was set up. First a bulk model and after a NP model was built and optimized by DFT. It was seen that numerous doping atoms tend to be localized at the surface of the NPs whereas it is more thermodynamically stable to have a good dispersion when the number of doping atom is smaller. From these DFT model, PDF curves were calculated and compared with experimental PDF curves. These comparisons allow to identify the rutile structure, describe the local structure, and to validate DFT models. It also allows the attribution of distances in the structure and shows the need to consider specifically the surface modifications. This PDF/DFT conclusions were validated by high level STEM-HAADF-EELS analysis

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Wood, Suzannah. „Understanding the Formation of Kinetically Stable Compounds and the Development of Thin Film Pair Distribution Function Analysis“. Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22645.

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Navigating the synthesis landscape poses many challenges when developing novel solid state materials. Advancements in both synthesis and characterization are necessary to facilitate the targeting of specific materials. This dissertation discusses the formation of chalcogenide heterostructures and their properties in the first part and the development of thin film pair distribution function analysis (tfPDF) in the second part. The heterostructures were formed by the self-assembly of designed precursors deposited by physical vapor deposition in a modulated elemental reactants approach, which provides the control and predictability to synthesis. Specifically, a series of (BiSe)1+δ(TiSe2)n, where n = 2,3,&4, were synthesized to explore the extent of charge transfer from the BiSe to TiSe2 layers. To further explore the role Bi plays in charge donation, a family of structurally similar compounds, (BixSn1-xSe)1+TiSe2 , where 0≥x≥1, were synthesized and characterized. Electrical measurements show doping efficiency decreases as x increases, correlated with the structural distortion and the formation of periodic antiphase boundaries containing Bi-Bi pairs. The first heterostructures composed of three unique structural types were synthesized and Bi2Se3 layer thickness was used to tune electrical properties and further explore charge transfer. To better understand the potential energy landscape on which these kinetically stable compounds exist, two investigations were undertaken. The first was a study of the formation and subsequent decomposition of [(BiSe)1+δ]n(TiSe2)n compounds, where n= 2&3, the second an investigation of precursor structure for thermodynamically stable FeSb2 and kinetically stable FeSb3. The second section describes the development of thin film pair distribution function analysis, a technique in which total scattering data for pair distribution function (PDF) analysis is obtained from thin films, suitable for local structure analysis. This study illustrates how analysis of the local structure in amorphous precursor films can help to understand the crystallization processes of metastable phases and enables a range of new local structure studies of thin films. tfPDF was then demonstrated on In-Ga-O film materials and compared to traditional powder PDF analysis. This highlights differences between the products, and the utility of tfPDF to determined structural features of amorphous materials. This dissertation includes previously published and unpublished co-authored materials.
10000-01-01

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Owen, Lewis Robert. „The analysis of local structural effects in alloys using total scattering and reverse Monte Carlo techniques“. Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273748.

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Over the years `short-range order' (SRO), whereby the local atomic arrangement differs from that of a random distribution, has been used to explain physical phenomena such as thermodynamic discontinuities, increased strength, anomalous electrical resistivity and magnetic variations in a host of alloys. However, due mainly to experimental difficulties and the complexity of the calculations required for the analysis of diffuse scattering, such work has been largely abandoned and hence quantification and assessment of SRO is notably sparse in the literature. The recent development of reverse Monte-Carlo (RMC) methods for the analysis of total scattering data has opened a promising route for the assessment of a material's local environment and has already provided important insights into a host of complex chemical systems, including liquids, network glasses, nano-materials, functional oxides and metal organic frameworks. The work presented in this thesis focuses on the development of a new methodology for the analysis of local structural effects in metallic systems using total scattering, and the first systematic application to the study of alloys. The simulation of total scattering data from a range of model structures is used to show that the information content of total scattering functions, in particular the pair distribution function (PDF), is sufficiently high to allow the assessment of different types and degrees of short-range order. This is supported by a demonstration of how such orders can be quantified from large box models, produced by fitting total scattering data using the RMC algorithm, with the mathematical analyses outlined. This culminates in a proposed methodology for the analysis of SRO in alloys. Having developed this analytical methodology it is subsequently applied to a number of interesting alloy systems. To demonstrate the efficacy of this methodology it was first applied to the study of a sample of Cu$_{3}$Au - the classically cited case example of a system demonstrating SRO prior to an ordering transition. This experiment provides new insight into this well characterised transition, and also demonstrates the significance of data processing errors on the generation of artefacts in large box modelling. The technique is also applied to the study of the industrially important family of nickel superalloys, assessing ordering in the gamma-phase alloy Ni-Cr and the sublattice orderings occurring in L1$_{2}$ alloys. Next, the use of the technique for the analysis of local strains exhibited in a lattice is presented. A series of models is used to demonstrate how the PDF is expected to change under variations in local strain caused by increased concentration of atomic substitution and variation in atomic radii. This is subsequently used to study the characteristic high-entropy alloy (HEA) CrMnFeCoNi. Through analysis of the PDF, it is demonstrated that the level of local strain exhibited in this alloy is not significantly different from those of other related compositionally simpler alloys. This result is highly significant as it challenges one of the core principles of the field - that the lattices of HEAs are necessarily highly strained. Finally, the energetics of ordering reactions are briefly considered and used to justify some of the observed transformations presented in the earlier work. Together, the body of work in this thesis shows how the total scattering technique can be used to provide valuable insight into a host of interesting local phenomena occurring in alloy systems. It is hoped that this will open up a new field of study into these effects, and ultimately guide the creation of new alloys based on these structure-property relationships.

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Hsieh, Kuan-Ying. „Étude multi-échelle des changements structuraux et leur influence sur les propriétés optiques de complexes photoactifs encapsulés dans des matrices méesoporeuses“. Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0124/document.

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Les matériaux poreux silicatés ont été mis à profit pour encapsuler différents types de molécules, clusters ou nano-objets fonctionnels, donnant lieu à des nanocomposites hybrides organiques-inorganiques à propriétés physiques, chimiques ou biologiques remarquables. Élucider l'organisation structurale à l'échelle moléculaire de tels nanocomposites est indispensable pour l'analyse et la compréhension des propriétés macroscopiques qui en découlent. Ainsi, les techniques de diffusion totale associées à la fois à l'analyse Debye et la Fonction de Distribution de Paires (PDF) sont des méthodes de choix pour la caractérisation des propriétés structurales de matériaux hybrides nano-structurés. Le principal objectif de ce travail consiste à l'utilisation des approches basées sur la diffusion totale de rayons X pour l'analyse structurale complète de molécules photoactives confinées dans des matrices silicatées amorphes avec différentes tailles de pores, afin d'étudier l'influence de l'organisation structurale sur les propriétés optiques et d'explorer également les limites de ces approches d'analyse. Nous avons étudié deux systèmes photoactifs. L'analyse structurale du premier complexe confiné, Na2[Fe(CN)5NO].2H2O (SNP), a été entreprise par une approche multi-échelle combinant la RMN du solide et l'analyse PDF. Cette approche a permis l'identification de la nature des espèces incorporées, l'arrangement des cations et des anions ainsi que la distinction des différentes phases existantes : molécules isolées et nanoparticules. Les analyses Debye et PDF sur le deuxième composé étudié, [NdCl2(H2O)6]Cl, montrent que l'organisation structurale du complexe confiné est différente de celle du matériau massif cristallin. De plus, les cations Nd3+ changent de coordination de 8 à 9 durant le processus d'imprégnation et adoptent ainsi un arrangement structural très similaire à celui en solution aqueuse. Cette modification structurale est en accord avec le changement des propriétés luminescentes de ce complexe
Silica xerogels are versatile host materials for the inclusion of molecules, clusters, or nano-objects yielding host-guest compounds with unique physical, chemical or biological properties. The knowledge of the structural organization of the guest within the host is crucial for the understanding of its properties. Total scattering methods, based on Debye function analysis (DFA) and Pair Distribution Function (PDF), have become powerful tools for structural characterization of nanostructured hybrid materials. The aim of this work is to use the X-ray total scattering method to obtain structural information on photoactive molecules embedded into amorphous silica hosts with different pore sizes, to correlate their structure with the optical properties, and to explore the limitations of the chosen method. Two different photoactive complexes have been investigated. In the first example, the combined PDF and NMR study on Na2[Fe(CN)5NO].2H2O (SNP) embedded into silica matrices allows to extract the nature of the inserted species: quasi-free isolated molecules can be distinguished from nanoparticles and in the former case a model for the arrangement of cation-anion can be proposed from the PDF analysis. In the second example, a luminescent Nd3+ complex, the PDF and DFA analysis reveal that the structural organization of the embedded Nd3+ complexes is different from that of the crystalline material. Furthermore, the Nd3+ cations change the coordination from 8 to 9 during the wet-impregnation doping and adopt very similar structural arrangement as in aqueous solution, which is in agreement with the observed change in the luminescence properties

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Fernández, Martínez Alejandro. „Physics of natural nanoparticles-water interfaces : chemical reactivity and enviromental implications“. Grenoble 1, 2009. http://www.theses.fr/2009GRE10173.

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Les eaux et les plantes des zones volcaniques sont souvent très pauvres en sélénium, alors que les teneurs totales observées dans les sols sont normales. Ceci est très spécifique aux zones volcaniques et semble dû aux argiles des sols qui ne sont pas des phylloaluminosilicates comme dans la plupart des autres régions du globe, mais des aluminosilicates tubulaires, les imogolites. Ces minéraux sont dotés d'une très grande surface spécifique (400-1000 m2 g-1 selon la méthode) et réagissent avec les anions de sélénium en formant des complexes de sphère interne, liées par des liaisons covalentes, qui réduisent la mobilité du sélénium en affectant sa biodisponibilité. D'un autre cote, l'interaction de la surface externe de ces nanotubes d'imogolite, similaire a la surface (001) de la gibbsite, avec l'eau a été étudié par des simulations de dynamique moléculaire. Les simulations décrivent une surface plus hydrophobique que celle de la gibbsite, étant l'hydrophobicite induite par la courbure de la structure. Ce résultat a des importantes implications environnementales, car il peut expliquer la formation de complexes organo-minerales entre les aluminosilicates nanotubulaires ou nanoparticulés. Comme dernier résultat, une structure pour la schwertmannite, un oxyhydroxy-sulphate de fer nanoparticulé, a été décrite a partir de données de diffraction de rayons X de haute énergie et des simulations ab-initio
Precise structural studies of nano-crystalline minerals using diffraction techniques have been hindered by the broad diffraction peaks found in their diffraction patterns. In this thesis, I have applied molecular scale techniques such as High-Energy X-ray Diffraction and Molecular Dynamics simulations to study the structure and reactivity of two nano-minerals of important environmental significance: imogolite and schwertmannite. These minerals have nanotube or channel-like structures, and both are strong anion adsorbers. Imogolite is a nanotubular aluminosilicate present in the clay fraction of volcanic soils. It has high specific surface areas and it is one of the few minerals reactive towards anions and cations, which makes it a very important mineral in soils where it is found. However, the prediction of imogolite chemical reactivity is hindered by its nano-crystalline character. Structural studies up to now have been restricted to X-Ray Diffraction and Electron Diffraction analyses, where the diffraction peaks were used mainly as fingerprints for the identification of the mineral. In this thesis I have performed a detailed structural characterisation of the structure of synthetic imogolite by Transmission Electron Microscopy (TEM), High-Energy X-ray and Molecular Dynamics methods. In addition, the structure of water at the imogolite / water interface has been investigated by theoretical and experimental methods. Using these structural inputs, I have developed a geochemical MUSIC model of imogolite, and compared it to the existing models for Gibbsite (planar equivalent of the external surface of imogolite), evaluating the effect of the curvature on geochemical reactivity. Parameters investigated include, the number of hydrogen bonds per surface adsorption site or the protonation constants of surface hydroxyl groups. Finally, these molecular-scale investigations have been linked to the biogeochemistry of Selenium in volcanic soils (andisols). Andisols are frequently rich in Selenium but controversially often low in bioavailable selenium. At the same time, imogolite is often found in the clay fraction of these soils. The adsorption of Selenium oxyanions at the Imogolite/water interface has been studied using X-ray Absorption Spectroscopy and DFT methods. In contrast to imogolite, schwertmannite structure is thought to be akin to that of akaganeite, with sulphate molecules substituting chlorine atoms in channels. The structure of the octahedral iron frame and the positions of the sulphate molecules within the structure have been object of an intense debate during the last 15 years. I present here a combined Pair-Distribution Function and X-ray Diffraction Study of the structure of schwertmannite. A structural model is proposed and discussed in terms of the retention of oxyanions

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Diez, Stefan J. [Verfasser], Neder [Akademischer Betreuer] Reinhard, Neder [Gutachter] Reinhard und Julien [Gutachter] Bachmann. „Pair distribution function analysis applied on weakly scattering nanoparticles ― their structure and surfaces / Stefan J. Diez ; Gutachter: Neder Reinhard, Julien Bachmann ; Betreuer: Neder Reinhard“. Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2020. http://d-nb.info/1223175170/34.

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14

Gebretsadik, Adane Samuel Gebretsadik. „INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION“. Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816.

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15

Coduri, M. „LOCAL DISORDER IN DOPED CERIA: A CRYSTALLOGRAPHIC STUDY“. Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/215536.

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In recent years, doped ceria compounds have attracted increasing attention as electrolytes for application in Solid Oxide Fuel Cell devices, thanks to their high performance at intermediate temperature. In cerium oxide, ionic conductivity is driven by the presence of oxygen vacancies, introduced for charge balance after doping with a lower valent cation. With increasing doping concentration the oxygen diffusion is impeded, probably because of the formation of aggregates that trap oxygen vacancies. Their nature is though still under debate. Owing to the close interplay between transport properties and local structure, an accurate description of the defects on the atomic scale is of the utmost importance for understanding the mechanisms at work in doped ceria. In this study we propose to unveil the complex disorder in doped ceria with a combined powder diffraction study. On the one hand, X-ray and Neutron powder diffraction are joint to couple their potentialities; on the other hand, two different crystallographic approaches are exploited. The conventional crystallographic methods allow to study the long range structure modifications that occur with doping. The Pair Distribution Function is instead employed to study the local structure, in terms of deviations from the long range atomic ordering. The goal of the thesis is to provide a crystallographic description of the atomic rearrangements induced by doping, looking for a relationship between the local structure and the transport properties.

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16

Perversi, Giuditta. „Ordering phenomena in iron-containing spinels“. Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31242.

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The spinel structure (general formula AB2O4) is widely occurring in natural and synthetic materials, and has a marked technological and scientific significance due to its magnetic, electric and multiferroic behaviours. The presence of transition metal cations with multiple oxidation state and the resulting charge, orbital and spin degrees of freedom of the partially occupied d-orbitals lead to uniquely ordered ground states. The coupling of all the three degrees of freedom can result in a structurally distorted ground state where the direct metal-metal interaction forms atomic clusters, or 'orbital molecules'. The Verwey phase of magnetite (Fe3O4), occurring below TV ~ 125 K, is driven by a cooperative bond distortion that forms linear Fe3+-Fe2+-Fe3+ arrangement (trimeron). The effect of non-stoichiometry and chemical modification on this complex structure has been investigated with a variety of samples through microcrystal synchrotron XRD. A mineral sample (Al, Si, Mg and Mn impurities, TV = 119 K) confirms the Verwey phase as the most complex long-range electronic order known to occur naturally; its relevance in space sciences is discussed. Moreover, the structural analysis of two synthetic magnetites (Fe3(1-δ)O4 with 3δ = 0.012 and TV = 102 K, Fe3-xZnxO4 with x = 0.03 and TV = 90 K) univocally confirmed the persistence of the transition, and its first order, at doping level > 1 %, contrary to previous reports. Moreover, the temperature evolution of the trimerons and their persistence above TV was probed through X-ray Pair Distribution Function analysis on pure Fe3O4: the data analysis between 90 K < T < 923 K show that the Verwey phase goes from long-range ordered (T < 125 K) to short-range ordered (T > 850 K). Magnetite can thus only be considered to have a regular cubic spinel structure above the Curie temperature (TC = 858 K). The pyrochlore lattice of B cations in a spinel gives the structure the potential for frustration upon antiferromagnetic ordering. Fe2GeO4 and γ-Fe2SiO4 were synthesised through conventional solid state routes, with the use of high-pressure synthesis for the latter. Magnetometry and heat capacity measurements highlighted two transitions (Tm1 = 8.6 K and Tm2 = 7.2 K, and Tm1 = 11.2 K and Tm2 = 7.5 K respectively). Powder neutron diffraction data between 2 K < T < 25 K showed that both materials stay undistorted below TN. Magnetic Rietveld refinement led to two highly unconventional magnetic structures, with incommensurate propagation vectors and modulation of the moment magnitude. γ-Fe2SiO4 also shows a spin-ice order below Tm2. The results are unique and unusual for transition metal oxides; the models are systematised by proposing a 'frustration wave' model, in which the degree of frustration is a spatial quantity that can be distributed through the structure in order to stabilise the ground state.

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Cooper, Susan. „Understanding Size-Dependent Structure and Properties of Spinel Iron Oxide Nanocrystals Under 10 nm Diameter“. Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24523.

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Iron oxide nanoparticles (NPs) are promising materials for use in many applications, including new cancer treatments and in cleaning water, because they exhibit size-dependent magnetic and absorptive properties. NP properties are caused by structural attributes of the NPs, like surface disorder and cation vacancies. However, NP synthetic methods also impact structure, therefore properties, of NPs. Furthermore, the synthetic method is often changed in order to change the core diameter of NPs. Determining if properties are caused by the dimensions of the NP is impossible if there are also structural features present in the NP caused by the synthetic method, like grain boundaries or polycrystalline shells. In Chapter II of this dissertation, we show a new continuous growth synthesis of spinel iron oxide where the diameter of NPs is changed by the amount of precursor added to the reaction, meaning the only structural feature changing between the NPs is size. Continuous growth, therefore, can be used to probe the impact that size has on NP structure and properties. We report that saturation magnetization of NPs produced from continuous growth is size-dependent and higher in magnitude than NPs of the same core diameter made by other syntheses. In chapter III of this dissertation we determine nanoscale structure by Pair Distribution Function (PDF) analysis of Total X-ray Scattering data of NPs isolated from the reaction with core diameters between 3-10 nm. In Chapter IV of this dissertation we monitored the growth of NPs in situ with Total X-ray Scattering to gain insight on the structures of NPs while forming. In situ measurements of Total X-ray Scattering data gave insights into how precursor oxidation state influences the structures formed during formation of NPs, with more oxidized precursor giving a more oxidized product and a reduced precursor yielding a more reduced product even though the NPs formed by either method are indistinguishable by ex situ analysis. This dissertation includes previously published and unpublished co-authored material.
2021-04-30

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Allieta, M. „DIFFRACTION STUDIES ON STRONGLY CORRELATED PEROVSKITE OXIDES“. Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/168362.

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In recent years, a great interest has been devoted to the so called strongly correlated systems containing perovskite building blocks. These systems exhibit a complex interplay between charge, spin, orbital and lattice degrees of freedom paving the way for very attractive applications. In this work, entitled “Diffraction Studies on Strongly Correlated Perovskite Oxides” the use of x-ray diffraction techniques to investigate the coupling between the structure and the physical properties of several bulk material based on perovskite structure is presented. The thesis is organized in five chapters. Introduction presents a very general overview on strongly correlated perovskite oxides and the scope of the thesis. The first chapter reports technical details of the diffraction techniques involved in all the structural studies performed during the PhD. Chapter 2 reports an accurate investigation performed on the magnetoresistive cobaltite GdBaCo2O5+d (d=0) using single-crystal and synchrotron powder X-ray diffraction. In this work, we assign the correct space group and we demonstrate that a very small tetragonal-to-orthorhombic lattice distortion is coupled to magnetic phase transition. In Chapter 3, we show the study of the temperature induced insulator-to-metal transition for GdBaCo2O5+d (d>0.5). By using a combined approach between electron paramagnetic resonance and powder diffraction techniques we provide new interesting features about the spin – lattice interaction occurring in these systems. Chapter 4 presents synchrotron X-ray powder diffraction study on EuTiO3 system. We show for the first time the existence of a new structural phase transition occurring in EuTiO3 below room temperature. In addition, by performing the atomic pair distribution function analysis of the powder diffraction data, we provide evidence of a mismatch between the local (short-range) and the average crystallographic structures in this material and we propose that the lattice disorder is of fundamental importance to understand the EuTiO3 properties. Finally, beyond the scope of the thesis, in Chapter 5, we review the basic procedure to get the differential pair distribution function obtained by applying the anomalous X-ray diffraction technique to total X- ray scattering method. We show an example of the application of this procedure by presenting the case of gadolinium doped ceria electrolytes. This work will show that use of the powder diffraction techniques provides a powerful tool to unveil the coupling between the structure and the physical properties in strongly correlated perovskite oxides.

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Eger, Karl-Heinz, und Evgeni Borisovich Tsoy. „Robustness of Sequential Probability Ratio Tests in Case of Nuisance Parameters“. Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000949.

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This paper deals with the computation of OC- and ASN-function of sequential probability ratio tests in the multi-parameter case. In generalization of the method of conjugated parameter pairs Wald-like approximations are presented for the OC- and ASN-function. These characteristics can be used describing robustness properties of a sequential test in case of nuisance parameters. As examples tests are considered for the mean and the variance of a normal distribution.

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Khoder, Hassan. „Effet de confinement de l’eau dans les verres bioactifs : relation structure propriétés“. Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0106.

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L’utilisation des matrices mésoporeuses nanostructurées pour le confinement de nano-objets fonctionnels ou des liquides est un domaine de recherche très actif, en vertu des applications potentielles dans divers domaines. Cependant, l’effet de confinement peut affecter les propriétés de ces nanomatériaux et par conséquent leurs potentielles et diverses applications. Cet effet dépend à la fois des liquides utilisés et des propriétés des matériaux hôtes. Dans ce contexte, les verres bioactifs de comblement et de remplacement osseux constituent des systèmes poreux dans lesquels des liquides physiologiques sont confinés. Ces biomatériaux sont de plus en plus étudiés du fait de leur utilisation fréquente en chirurgie orthopédique et en chirurgie réparatrice. Le grand intérêt de ces matériaux provient du fait de leur biocompatibilité et leur réactivité avec les fluides physiologiques, puisqu’au contact avec le milieu vivant, ils développent rapidement une couche d’hydroxyapatite sur leur surface susceptible de combler les pertes osseuses en se liant avec les tissus receveurs.Il est donc important d’étudier l’effet de confinement sur l’organisation structurale des liquides physiologiques véhiculés à travers ces nanomatériaux. Étant donné que les fluides physiologiques sont composés principalement de l’eau, nous avons focalisé nos investigations sur les propriétés structurales de l'eau confinée dans ces systèmes biologiquement actifs. Nous proposons dans ce travail de thèse d’aborder cette problématique par des méthodes expérimentales spécifiques, telle que la diffusion totale des rayons X couplée aux analyses de la fonction de distribution de paires, PDF. Des caractérisations complémentaires par calorimétrie différentielle à balayage (DSC), et des simulations Monte Carlo, corroborent les modèles structuraux obtenus par les analyses PDF. Pour mieux comprendre l’impact de la réduction de taille et l’influence des propriétés texturales des matrices hôtes sur les propriétés structurales et physiques des liquides confinés, nous avons appliqué notre méthode d’analyse multi-échelles à d’autres systèmes modèles tels que le MCM-41, et le SBA-15.Les mesures de diffusion totale des rayons X ont été effectuées en fonction de la température pour les différents matériaux étudiés. En complément, les simulations numériques ont été réalisées à l'aide du code EPSR, Empirical Potential Structure Refinement. Les résultats obtenus montrent une structuration non homogène de l'eau confinée à l'intérieur des pores. Nous avons montré que l’organisation structurale des liquides confinés dépend de la taille des pores, de leur taux de remplissage et des propriétés texturales des nanomatériaux hôtes. De plus, nos résultats des analyses de la fonction de distribution partielle de paires montrent que les liquides confinés dans des pores larges, (diamètre de pore > 5 nm), présentent trois phases. Cependant, une seule phase plus distordue a été observée dans les matrices avec des pores plus étroits
The use of nanostructured mesoporous silica gels for the confinement of functional nano-objects or liquids is a very active area of research with potential applications in various fields. However, the confinement might affect the properties of these nanomaterials and thus their potential applications, depending both on the nature of the liquids used and on the properties of the host materials. In this context, bioactive glasses are porous systems in which physiological fluids are confined. These biomaterials are increasingly studied in view of their frequent application in orthopedic and reconstructive surgery. The biomedical applications of these bioactive glasses are mainly due to their high biocompatibility and high reactivity with the human physiological environment, since the reaction products obtained from these bioactive glasses and the physiological fluids lead to the deposition of a layer of crystalline bone-like carbonate calcium phosphate (Hydroxy-Carbonate Apatite) on their surface shortly after interaction. This hydroxyapatite layer allows the adhesion to the biological substrate, and hence to reconstruct damaged bones.Since these materials are intended to interact with body fluids, the understanding of the impact of confinement on the organization and diffusion of the encapsulated physiological fluids is crucial for improving their properties. Given that the physiological fluids are composed mainly of water, we have focused our investigations to study the structure and properties of water confined in bioactive glasses as model systems. In this thesis work, we propose to tackle this problem by specific experimental methods, primarily by total X-ray scattering coupled with pair distribution function (PDF) analysis. Complementary characterizations by differential scanning calorimetry (DSC) and atomistic simulations based on the Monte Carlo method are used to corroborate the structural models obtained from the PDF analysis. To better understand the impact of size reduction and the influence of host matrix textural properties on the structural and physical properties of confined liquids, we have applied our multi-scale approach to other model systems such as MCM-41, and SBA-15.The total X-ray scattering measurements have been performed as a function of temperature for the different studied nanomaterials while for the numerical simulations the Empirical Potential Structure Refinement (EPSR) code was used. The obtained results indicate a non-homogeneous structuring of the water confined within the silica nanopores. We have shown that the structural organization of confined liquids depends on pore size, water-loading ratio and the textural properties of the host nanomaterials. Furthermore, the partial pair distribution function analysis show that liquids confined in large pores, (pore diameter > 5 nm), have three phases. However, only one distorted phase was observed in the matrices with narrower pores

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CONFALONIERI, GIORGIA. „LOCAL DISORDER IN THE STRUCTURE OF BA(TI,CE)O3 PEROVSKITE BY MEANS OF POWDER DIFFRACTION AND TOTAL SCATTERING. EFFECT OF TEMPERATURE, DOPING CONCENTRATION AND GRAIN SIZE“. Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/478906.

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Nowadays BaTiO3 is considered as one of the most relevant environmental-friend ferroelectric and, thank to the chemical substitutions at the Ba2+ and/or Ti4+ sites, its properties are usually tailor to meet a big variety of devices and performance requirements. A classical example is the solid solution BaTi1-xMIVxO3, where M could be Sn, Zr, Hf, Ce etc., whose ferroelectric behavior shows an almost continuous variation with composition. The study of these compounds is then essential to improve their characteristics and make their suitable in more applications. Considering that their properties are deeply linked to the structure and especially to structural defects, average and local structural analyses are essential to better understand the origins of different polar behaviours and to have a real control on these materials. Despite this need, only BaTi1-xZrxO3 (BTZ) system, which is one of the most popular dielectrics used in multilayer ceramic capacitors, has been investigated in some detail. Although the similarity to BTZ suggests that BaTi1-xCexO3 (BTC) may be promising as lead free actuator materials, studies on this solid solution are almost limited. Thus in this research the BTC solid solution has been structurally investigated in order to provide knowledge lacks. Different ceramic samples with different doping amounts and different polar behaviours (from normal ferroelecric to relaxor via diffuse phase transition) have been investigated at different temperatures. In addition, taking into account the current tendency in miniaturized devices required in microelectronics, also chemical equivalent nano powders have been considered to explore not only doping effects, but also that of size. Pair Distribution Function (PDF) with different type of approaches (as carbox, biphasic and so on) has been employed coupled with TEM analysis and Raman spectroscopy. A complete description of that BaTi1-xCexO3 materials is given underlining links between polar behaviours, temperature, doping and size effects.

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Ortatatlı, Şeyma [Verfasser], Cuenya Beatriz [Gutachter] Roldán und Claudia [Gutachter] Weidenthaler. „Monitoring the structures of inorganic materials by $\textit ex situ/in situ}$ X-Ray powder diffraction and pair distribution function analysis / Şeyma Ortatatlı ; Gutachter: Beatriz Roldán Cuenya, Claudia Weidenthaler ; Fakultät für Physik und Astronomie“. Bochum : Ruhr-Universität Bochum, 2018. http://d-nb.info/1160442223/34.

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Zhang, Ying. „Synthesis and Determination of the Local Structure and Phase Evolution of Unique Boehmite-Derived Mesoporous Doped Aluminas“. BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7105.

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Mesoporous alumina (Al2O3) in the gamma (Î³) phase is widely used as a support in catalytic applications because of its high surface area, large pore volume, acid-base characteristics, and thermal stability. To improve the thermal stability of gamma alumina, dopants such as lanthanum, magnesium, zirconia, and silica are often introduced. Current laboratory-based methods for synthesizing gamma alumina generally involve 10-15 steps and/or use toxic, expensive surfactants and solvents. Industrial methods, while simpler, lack control of pore properties and surface chemistry. In contrast, we have developed an innovative solvent deficient, one-step method that is able to synthesize a wide range of pure and silica-doped aluminas with high surface areas, pore volumes from 0.3 to 1.8 cm3/g, and pore diameters from 5 to 40 nm. More significantly, our silica-doped aluminas are stable up to temperatures as high as 1300<°>C, which is 200<°>C higher than other pure and doped gamma alumina materials.The usefulness of gamma-alumina as a catalyst support is dependent on its favorable combination of textural, thermal, structural, and chemical properties, yet the relationship between structure and these other properties is still not clearly understood due to the poorly crystallized nature of the material. In particular, the mechanism by which the gamma structure is stabilized thermally by so many dopants is still not well understood. Based on our previous PDF experiments on pure and La-doped alumina, we have developed a hypothesis regarding the mechanism by which dopants increase thermal stability. To validate or refute this hypothesis, we collected PDF data on a wider range of laboratory and industrial alumina samples. Herein, we have utilized PDF analysis to study the local to intermediate-range structure of a series of our pure and silica-doped aluminas calcined at 50<°>C intervals between 50 and 1300<°>C as well as pure and silica-doped aluminas from commercial sources and other synthetic methods. This thorough study of alumina local structure will allow us to separate general trends in the local structure from idiosyncrasies based on synthetic method/conditions, and it will help us identify the structural features responsible for improved thermal stability. Having access to these PDF experiments, we have validated our current hypothesis on the nature of stabilization afforded by dopants and, more generally, developed a better understanding of the role structure plays in the properties of aluminas.

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Morris, Samuel Alexander. „X-ray studies of zeolites and MOFs“. Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/9891.

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This thesis is largely a study of the ADOR process (assembly-disassembly-organisation-reassembly) when applied to zeolite UTL. The final chapter of this thesis deals with the adsorption of the medical gases NO and CO onto the metal organic framework NiNaSIP. Chapter 4 is devoted to the disassembly and organisation steps of the ADOR process. Calcined UTL was hydrolysed using 0.1 – 12 M HCl solutions from 75 – 95 °C run over 10 mins to 72 hrs. A three step mechanism is proposed, which is comprised of an initial rapid hydrolysis that removes the majority of the interlayer constituents of UTL, causing the silica-rich layers to largely collapse. This is followed by a slow, temperature and molarity dependent, deintercalation process that sees the remainder of the interlayer material removed resulting in the full collapse of the layers to form IPC-1P. The third step is a temperature and molarity dependent rebuilding process, whereby the interlayer region is slowly rebuilt, eventually forming a precursor which upon calcination becomes IPC-2 (OKO). Chapter 5 uses the pair distribution function (PDF) technique to structurally confirm the intermediate of the ADORable zeolite UTL. The intermediate, IPC-1P, is a disordered layered compound formed by the hydrolysis of UTL in 0.1 M HCl. Its structure is unsolvable by traditional X-ray diffraction techniques. The PDF technique was first benchmarked against high-quality synchrotron Rietveld refinements of IPC-2 (OKO) and IPC-4 (PCR) – two end products of IPC-1P condensation that share very similar structural features. An IPC-1P starting model derived from density functional theory was used for the PDF refinement, which yielded a final fit of Rw = 18% and a geometrically reasonable structure. This confirms that the layers do stay intact throughout the ADOR process, and shows that PDF is a viable technique for layered zeolite structure determination. Chapter 6 examines the reassembly stage by following the in-situ calcination of a variety of hydrolysed intermediates into their three-dimensional counterparts. Beamline I11 at Diamond Light Source provided high-quality PXRD patterns as a function of temperature, which were refined against using sequential Pawley refinements to track the unit cell changes. 0.1, 1.75, 2.5 and 12 M hydrolysed lamellar precursor phases were calcined. The largest unit cell changes were observed for 0.1 M, and the smallest for 12 M. This shows that increasing the molarity must prebuild most of the interlayer connections, such that upon calcination, only minimal condensation occurs to fully connect the layers. Chapter 7 probes the uptake of the medical gases CO and NO into the metal organic framework NiNaSIP. An in-situ single-crystal XRD study was undertaken using an environmental gas cell at beamline 11.3.1 at the Advanced Light Source. NiNaSIP was first dehydrated to reveal an open nickel site, which acted as the main site of adsorption for the inputted gases. NO was observed in a bent geometry at an occupancy of 40 % and a Ni – N bond length of 2.166(16) Å. The oxygen was modelled to be disordered over two sites. CO was not fully observed, as only the carbon was able to be modelled with an occupancy of 31.2 % and a Ni – C bond length of 2.27(3) Å.

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Shakur, Shahabi Hamed. „Study of deformation-induced structures in a Zr-based bulk metallic glass via high energy x-ray diffraction“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-198272.

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This PhD thesis employed high energy synchrotron x-ray radiation to reveal atomic scale structural features occurring in plastically deformed Zr52.5Ti5Cu18Ni14.5Al10 (Vit105) bulk metallic glass (BMG). The study is divided into three parts: Strain evolution during in-situ compression, strain distribution maps in mechanically-imprinted BMG, and residual strain around a single shear band. 1. Strain evolution during in-situ compression The structural rearrangements occurring during compressive deformation of a plastically deformable BMG showed that the elastic and plastic deformation of the BMG is correlated to the structural changes at short- (SRO) and medium range order (MRO). In the elastic regime, the atomic distances at SRO vary linearly with macroscopic stress. Analysis of the area under radial distribution function indicates that a small fraction of bonds in the first shell is broken in the loading direction whereas some new bonds are formed in the transverse direction. Atomic bonds at SRO appeared significantly stiffer than the MRO shells. Compared to the macroscopic values of the elastic strain, Young’s modulus and Poisson's ratio, both SRO and MRO appeared significantly stiffer, implying that the elastic behavior of the BMG is not only ruled by simple compression of the atoms/clusters but also is aided by rearrangement of atoms/clusters. The deviation of MRO atomic strain-stress correlation from linearity at the onset of plastic deformation was attributed to the activation of irreversible shear transformation zones. It was demonstrated by a strong shear strain value at the onset of yielding. This value is in good agreement with the reported value of the critical shear strain needed for activation of an irreversible STZ. The length scale of 12.5 Å indicated the largest shear strain and is probably the most effective length scale in the formation of STZs. The atomic pairs at SRO with smallest shear strain have the least contribution to the STZs. It was also indicated that the typical fracture angle of this BMG can be explained by the orientation of maximum shear strain at the onset of catastrophic shear band formation. 2. Strain distribution map in mechanically-imprinted BMG In mechanical imprinting, the BMG plate is loaded between two tools with a regular array of linear teeth and, as a result, a regular pattern of linear imprints is created on the surface of the plate. Mechanically imprinting results in considerable tensile plasticity of brittle Vit105 BMG plate. The distribution of hardness and Young’s modulus values at the transverse cross section of imprinted plate probed via nanoindentation revealed oscillating soft and hard regions beneath the surface. Spatially-resolved strain maps obtained via high-energy nano-size beam X-ray diffraction exhibited that the plastic deformation during imprinting creates a spatially heterogeneous atomic arrangement, consisting of strong compressive and tensile strain fields as well as significant shear strain fields in the cross section. It was shown that the heat treatment diminishes the heterogeneous structure resulting in brittle behavior in tension. The analysis of strain tensor components based on changes in the first diffraction maximum of the structure function, q1, revealed that Ɛx, the strain perpendicular to the loading direction, changes from the compressive at near to the surface to the tensile mode at the center of the imprinted plate. In contrast, the strain component along the loading direction, Ɛy, changes from tensile near the surface to the compressive at the center. Beneath the surface, Ɛx reaches to values about 1.5% under the imprints where there is a negligible Ɛy. The distribution map of principal strains, Ɛ1 and Ɛ2, indicated that large regions with compressive Ɛ1 and Ɛ2 exist under the imprints which can result in blocking of the propagating shear bands in agreement with microstructural observations of shear banding after uniaxial tension. Moreover, the region beneath the border of the imprinted and un-imprinted parts has the highest residual shear strain. Microstructural observations indicated that such regions can nucleate new shear bands upon tensile loading of imprinted BMG plate. 3. Residual strain around a single shear band In order to probe structural changes in the shear-induced zone around a single shear band, the distribution of residual strains at short- and medium-range order around a single shear band was determined in cold-rolled BMG plate using the nano-focused high energy x-ray diffraction. Plastic deformation results in significant residual normal and shear strains at distances of more than 15 μm around the shear band. The residual normal strains exhibit an asymmetric distribution whereas the residual shear strain is distributed symmetrically around the shear band. The large amount of residual atomic shear strain magnitude at the vicinity of the shear band triggers the nucleation of the new shear bands. The coincidence of the direction of the nucleating secondary shear bands from the main shear band with the orientation of the residual shear strain at the vicinity of the mature shear band highlight the dominant role of the shear strain in determining further plastic deformation at regions near the shear band
Im Rahmen dieser Arbeit wird hochenergetische Synchrotron Röntgenstrahlung zum Aufzeigen der strukturellen Veränderungen in plastisch verformtem Zr52.5Ti5Cu18Ni14.5Al10 metallischen Glas verwendet. Die Arbeit gliedert sich in drei Teile: Dehnungsentwicklung während in-situ Druckversuch, Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases, und Restdehnungen in der Umgebung eines einzenen Scherbandes. 1. Dehnungsentwicklung während in-situ Druckversuch Die während der Verformung auftretende strukturelle Neuordnung eines plastisch verformbaren metallischen Glases zeigt die Korrelation der elastischen und plastischen Verformung mit den strukturellen Änderungen in den Größenordnungen der Nah- (SRO) und mittelreichweitigen Ordnung (MRO). Im elastischen Bereich verändern sich die Atomabstände in der SRO linear mit der makroskopisch anliegenden Spannung. Die Untersuchung der Fläche unter der Radialen Verteilungsfunktion (RDF) deutet auf ein Aufbrechen eines geringen Anteils der Bindungen der ersten Schale in Druckspannungsrichtung und deren Neubildung quer dazu. Die atomaren Bindungen in der SRO erscheinen wesentlich steifer als in den MRO Schalen. Vergleicht man die Werte von elastischer Dehnung, E-Modul und Querkontraktionszahl mit ihren makroskopischen Gegenstücken erscheinen beide, SRO und MRO, wesentlich steifer. Dies zeigt, dass die elastische Verformung von metallischen Gläsern nicht nur von der einfachen Stauchung der Atome bzw. Atomgruppen bestimmt, sondern auch durch deren Neuanordnung unterstützt wird. Das Abweichen der Dehnungs-Spannungs-Korrelation vom linearen Verhalten in der MRO am Beginn der plastischen Verformung wird der irreversiblen Bildung von Schertransformations-zonen (STZ) zugeschrieben. Dies zeigt sich zudem in den erhöhten Scherdehnungswerten am Beginn der Dehngrenze, welche mit den in der Literatur berichteten Werten für die kritische Scherdehnung zum Bilden einer STZ übereinstimmen. Bei einem Atomabstand von 12,5 Å tritt der höchste Wert der Scherdehnung auf und markiert den effektivsten Längenbereich der STZ Bildung. Andererseits haben die atomaren Paare in der SRO mit der geringsten Scherdehnung den geringsten Beitrag an der STZ. Es zeigt sich außerdem, dass der typische Bruchwinkel dieses metallischen Glases über die Orientierung der maximalen Scherdehnung am Beginn der kritischen Scherbandbildung erklärt werden kann. 2. Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases Eine Prägung besteht darin, eine Platte metallischen Glases mit zwei Stempel, auf denen eine regelmäßige Anordnung von geradlinigen Kerben angebracht ist, zu belasten. Dadurch wird eine ebenso regelmäßige Anordnung von geradlinigen Kerben auf der Oberfläche des metallischen Glases erzeugt. Die plastische Verformbarkeit der Vit105 Platte im Zugversuch wird durch Prägung im Vergleich zur gegossenen Probe eindeutig verbessert. Die Untersuchung der Härte und des E-Moduls über den Querschnitt der geprägten Probe zeigt die Einbringung von Abwechselnd weichen und harten Regionen an der Oberfläche. Es wurden räumlich aufgelöste Dehnungskarten des geprägten metallischen Glases durch Beugung eines hochenergetischen nanometergroßen Röntgenstrahles erzeugt. Die Ergebnisse offenbaren, dass die durch Prägung eingebrachte plastische Verformung eine räumlich heterogene Atomanordnung erzeugt, welche aus starken Druck- und Zugdehnungsfeldern besteht. Zusätzlich wird eine signifikante Scherdehnung in die Probe eingebracht. Die Wärmebehandlung beseitigt diese heterogene Struktur und führt sie fast auf den Ausgangszustand zurück. Die Analyse der Dehnungstensorkomponenten basierend auf Änderungen im erstem Maximum des Strukturfaktors, q1, zeigt, dass sich Ɛx von der Oberfläche zur Mitte der Platte hin von einer Stauchung in eine Dehnung umwandelt. Im Gegensatz dazu wandelt sich die Komponente Ɛy von der Oberfläche zur Mitte der Platte hin von einer Dehnung in eine Stauchung um. An der Oberfläche unter den Eindrücken, wo Ɛy vernachlässigbar ist, erreicht Ɛx Werte von ca. 1.5 %. Die Verteilungskarten der Hauptdehnungen zeigt, dass beide e1 und e2 unterhalb der Kerben als Stauchungen vorhanden sind. Daraus resultiert das Blockieren und Ablenken der sich ausbreitenden Scherbänder, was an Zugproben im REM beobachtet werden kann. Weiterhin hat der Bereich an der Grenze der geprägten und nicht geprägten Regionen die höchste Restscherdehnung. Mikrostrukturelle Beobachtungen deuten darauf hin, dass solche Bereiche unter Zuglast Keimstellen für neue Scherbänder sind. 3. Restdehnungen in der Umgebung eines einzenen Scherbandes Es wurde ein einzelnes Scherband einer kaltgewalzte Platte mittels Beugung eines hochenergetischen nanometergroßen Röntgenstrahles untersucht. Die strukturellen Unterschiede in der scherinduzierten Zone um ein einzelnes Scherband werden durch die Verteilung der Restdehnungen in SRO und MRO bestimmt. Plastische Verformung führt zu signifikanten Restnormal- und Restscherdehnungen in Entfernungen von mehr als 15 µm um das Scherband. Die Restnormaldehnungen zeigen eine asymmetrische Verteilung, wohingegen die Restscherdehnungen auf beiden Seiten des Scherbandes symmetrisch verteilt sind. Der große Betrag der atomaren Restscherdehnung in der Nähe des Scherbandes führt zur Bildung von neuen Scherbändern. Das Zusammenfallen der Richtung des sich bildenden sekundären Scherbandes und der Orientierung der Restscherdehnung, in der Nähe des primären Scherbandes, demonstriert die dominierende Rolle der Scherdehnung bei weiterer plastischer Verformung in der Nähe des Scherbandes

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Ramezani-Dakhel, Hadi. „Bioengineered Metal Nanoparticles: Shape Control, Structure, and Catalytic Functionality“. University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1426184509.

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Lemarchand, Alex. „Synthèse par chimie douce et étude structurale de nanocristaux d'oxydes métalliques“. Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0110/document.

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Ce travail concerne la synthèse et la caractérisation structurale de nanocristaux de faible taille (~1-3 nm) d’oxydes métalliques simples, à savoir le dioxyde de titane (TiO2), le dioxyde d’étain (SnO2) et le monoxyde de zinc (ZnO). Les synthèses ont été réalisées au moyen de méthodes sol-gel non-aqueuses voire strictement non-hydrolytiques sous contrôle cinétique. La caractérisation structurale s’est principalement appuyée sur la diffraction des rayons X, la microscopie électronique en transmission et la méthode des fonctions de distribution de paires atomiques, obtenues grâce à la diffusion totale des rayons X, couplées à des méthodes de modélisation à l’échelle atomique. Dans le cas de TiO2, des nanoparticules d’anatase bien cristallisées de 4 nm à 8 nm ont été synthétisées. Le ratio molaire de donneur d’oxygène par rapport au titane s’est avéré être un paramètre influençant fortement la taille des particules. Nous avons également mis en évidence la formation d’une phase intermédiaire caractérisée par des nanoparticules faiblement cristallisées de très faible taille dont la structure pourrait s’apparenter à une structure brookite désordonnée. Pour SnO2, des nanocristaux présentant une structure rutile ont été obtenus avec des tailles comprises entre 2 nm et 4 nm. Dans le cas de l’utilisation d’un éther, nous avons mis en évidence la formation concomitante d’une phase organique polymérisée et de nanoparticules primaires dont la structure intermédiaire présente de fortes similitudes avec la structure rutile. L’utilisation de solvants possédant une fonction benzyle en présence de tétrachlorure d’étain a conduit à la formation d’eau dans le système. Dans le cas de ZnO, nous avons montré que l’utilisation d’une base organique pour initier la formation du réseau oxyde dans une solution méthanolique d’acétate de zinc en présence d’un agent complexant du zinc permettait d’obtenir des nanoparticules de l’ordre de 1 nm. Même pour les faibles valeurs de taille, les nanoparticules présentent une structure très proche de la wurtzite avec un désordre croissant au niveau du réseau cationique
The aim of this work was to synthesize small size (~1-3 nm) metal oxide nanocrystals namely titanium dioxide (TiO2), tin dioxide (SnO2) and zinc oxide (ZnO), and to study their structure. Syntheses were conducted via non-aqueous or even strictly non-hydrolytic sol-gel methods under kinetic control. The structural characterization was mainly carried out by X-Ray diffraction methods, transmission electronic microscopy and the study of pair distribution functions, obtained by X Ray total scattering, coupled with atomic scale modelling methods. In the case of TiO2, anatase nanocrystals were obtained with sizes ranging between 4 nm and 8 nm. The molar ratio of the oxygen donor with respect to titanium was shown to be an important parameter to control the nanoparticle size. In peculiar conditions we have been able to isolate an intermediate phase characterized by very small sized and poorly crystallized nanoparticles which the structure can be assimilated to a disordered brookite structure. Concerning SnO2, rutile-type nanocrystals were synthesized with sizes ranging between 2 nm and 4 nm. The use of an ether as oxygen donor led to the simultaneous formation of an organic polymeric phase and of primary nanoparticles characterized by an intermediate structure close but still different from the rutile-type structure. Moreover, the use of benzyl-type solvents in the presence of tin tetrachloride led to the formation of water in the system. Lastly, for ZnO, we have shown that using an organic base to induce the formation of the metal oxide network in a methanolic solution of zinc acetate in the presence of a strong complexing agent of the zinc allowed us to obtain wurtzite nanocrystals of ultrasmall sizes around 1 nm. Even for the smallest sizes, the nanoparticles exhibit a structure very close to that of wurtzite with an increasing disorder of the cationic network

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Auxemery, Aimery. „Étude des mécanismes de stabilisation de nanoparticules de ZrO2 quadratique en milieux fluides supercritiques“. Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0416.

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Afin d’expliquer la stabilisation de nanoparticules de ZrO2 de structure quadratique dans des conditions où seule la structure monoclinique est attendue, l’effet de taille est mis en avant depuis plusieurs décennies. A ce jour, aucun consensus ne préfigure au sein de la communauté scientifique. Nous proposons dans ce travail une nouvelle méthode de synthèse, basée sur le principe du sol-gel non-hydrolytique (N.H.S.G.) dans l’éthanol supercritique, permettant de stabiliser des nanoparticules de ZrO2 dont la taille se situe sous la limite de la « taille critique » généralement admise (< 3 nm). Les qualités des nanoparticules obtenues en synthèse continue supercritique ont été mises en avant à l’aide de techniques de caractérisation ex situ conventionnelles telles que la diffraction des rayons X, les spectroscopies Raman et Infrarouge, ainsi que la microscopie électronique en transmission. Des mesures de diffusion des rayons X aux grands angles ont ensuite été réalisées in situ au synchrotron lors de la formation de nanoparticules de ZrO2 dans l’éthanol, le butanol, le pentanol et l’hexanol supercritiques. L’analyse des fonctions de distributions de paires ont ainsi pu nous éclairer sur les mécanismes prépondérants pour la stabilisation de nanoparticules de ZrO2 quadratiques : les similitudes structurelles et les lacunes en oxygène, dont la présence est liée à l’effet de taille
To gain deeper understanding concerning the stabilization of tetragonal ZrO2 nanoparticles when only monoclinic ZrO2 is expected, the critical size theory has been established many decades ago. However, the theory has not yet found a consensus in the scientific community. We herein propose a new synthesis method, based on non-hydrolytic sol-gel (N.H.S.G.) reactions performed in supercritical alcohols, to stabilize ZrO2 nanoparticles below the critical size limit generally admitted (< 3 nm). Conventional ex situ analysis techniques such as X-ray diffraction, Raman and Infrared spectroscopies and transmission electron microscopy were combined to investigate the crystal structure of ultrafine ZrO2 nanoparticles formed in supercritical continuous flow reactors. Wide angle X-ray scattering measurements were then performed in similar conditions under a high energy X-ray source at a synchrotron to unravel in situ the formation mechanism of ZrO2 nanoparticles in supercritical ethanol, butanol, pentanol and hexanol. Pair distribution function analysis performed on these measurements enabled us to understand the stabilization mechanisms of the tetragonal structure: structural similarities and formation of oxygen vacancies linked to the ZrO2 nanoparticle size

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Torzuoli, Lyna. „Etude de la structure des verres des systèmes TeO2-MxOy (M = Ti, TI) par diffusion totale des rayons X et dynamique moléculaire“. Thesis, Limoges, 2020. http://www.theses.fr/2020LIMO0072.

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Ce travail de thèse constitue une contribution à la compréhension de la structure de verres à base de TeO2, notamment au sein des systèmes binaires TeO2-TiO2 et TeO2-Tl2O. La spectroscopie Raman et la diffusion totale des rayons X (extraction des fonctions de distribution de paires) ont permis de déterminer que la structure du verre évolue fortement avec l'ajout de Tl2O tandis que l'ajout de TiO2 n'entraîne pas d'évolution structurale significative. Des simulations par dynamique moléculaire sont réalisées pour la première fois dans le système TeO2-TiO2. Pour cela, nous avons affiné un jeu de potentiels interatomiques Te(IV)-O transférable aux matériaux tellurites, permettant de reproduire les structures des polymorphes de TeO2 ainsi que celles de plus d'une douzaine de composés cristallins à base de TeO2. La structure simulée du verre pur TeO2 est composé majoritairement d'unités TeO4 et TeO3, engendrant une coordinence de l'atome Te de 3,71, inférieure à celle dans les polymorphes de TeO2. L'ajout de TiO2 renforce la connectivité du réseau tellurite via la diminution de la proportion d'atomes O terminaux et la création de ponts Te-O-X (avec X = Te, Ti), ce qui justifierait une amélioration des propriétés mécaniques et thermiques de ces verres
This work aims to improve the structural description of the pure TeO2 glass and to give an insight of the structure of TeO2-MxOy binary glasses (M = Ti, Tl) by means of X-ray total scattering experiments and molecular dynamics (MD) simulations. We were able to determine, via Raman spectroscopy and X-ray total scattering experiments, that Tl2O causes the depolymerization of the glass structure whereas the addition of TiO2 leads to the conservation of Te(IV) environments. The MD simulations of the pure TeO2 glass and glasses within the TeO2-TiO2 system are carried out. First, we refined the Te(IV)-O interatomic potentials allowing us to reproduce TeO2 polymorphs as well as 14 crystalline structures containing TeO2. It was then demonstrated that the TeO2 glass consists largely of TeO4 and TeO3 units, giving a coordination number of 3.71, lower than that in the TeO2 polymorphs. Adding TiO2 tends to reinforce the connectivity within the tellurite framework via the reduction of the number of non-bridging oxygen atoms and the creation of Te-O-X bridges (with X = Te, Ti), which would justify the improvement of mechanical and thermal resistance of these glasses

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Karaliūnaitė, Julija. „Value distribution theorems for the periodic zeta-function“. Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20100915_162405-31358.

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In the thesis, the Atkinson formula for the periodic zeta-function on the critical line and the critical strip, and limit theorems in the sense of weak convergence of probability measures in various spaces are considered. The aim of the thesis is to solve the following problems: 1. To obtain the Atkinson formula on the critical line for the periodic zeta-function. 2. To obtain the Atkinson formula in the critical strip for the periodic zeta-function. 3. To prove limit theorems on the complex plane in the sense of weak convergence for the periodic zeta-function. 4. To prove limit theorems in the space of analytic functions for the periodic zeta-function. To solve them analytical and probabilistic methods are applied. For the proof of Atkinson formula, we use properties of the error term in the Dirichlet divisor problem and classical Voronoi formula. For the proof of limit theorems, the theory of weak convergence of probability measures, in particular, the Prokhorov's theory is applied. All results obtained in the thesis are new. The Atkinson formula for periodic zeta-function was not known. The same is true for limit theorems for periodic zeta-function. The Atkinson formula gives the explicit formula for the error term in the asymptotic formula for the first moment. This result is not only interesting itself but also has a series of applications, for example, in the investigation of higher moments. Probabilistic limit theorems are used for the characterization of... [to full text]
Darbe nagrinėjama periodinės dzeta funkcijos antrojo momento liekamojo nario išreikštinis pavidalas ir šios funkcijos asimptotinio elgesio charakterizacija ribinių teoremų silpnojo tikimybinių matų konvergavimo prasmė įvairiose erdvėse pagalba. Darbo uždaviniai yra šie: 1. Įrodyti Atkinsono formulę periodinai dzeta funkcijai kritinėje tiesėje. 2. Įrodyti Atkinsono formulę periodinai dzeta funkcijai kritinėje juostoje. 3. Įrodyti ribinę teoremą su ribinio mato išreikštiniu pavidalu kompleksinėje plokštumoje periodinei dzeta funkcijai. 4. Įrodyti ribinę teoremą su ribinio mato išreikštiniu pavidalu analizinių funkcijų erdvėje periodinei dzeta funkcijai. Atkinsono formulė duoda momentų asimptotinės formulės liekamojų narių išreikštinį pavidalą. Tai ne tik įdomus, bet ir turintis rimtų pritaikymų, pavyzdžiui, tiriant aukštesniuosius momentus, rezultatas. Tikimybinės ribinės teoremos charakterizuoja dzeta funkcijų asimptotinio elgesio reguliarumą. Be to, buvo pastebėta, kad tokios teoremos yra svarbiausia dzeta funkcijų universalumo įrodymo grandis. Periodinė dzeta funkcija nėra klasikinė, ji yra Rymano (Riemann) dzeta funkcijos apibendrinimas, tačiau ji pasirodo įvairiuose analizinės skaičių teorijos uždaviniuose. Pavyzdžiui, ji įeina į Hurvico (Hurvitz) ir Lercho (Lerch) dzeta funkcijų antrojo momento parametro atžvilgiu asimptotinę formulę. Iš kitos pusės, darbų, skirtų periodinei dzeta funkcijai, yra nedaug, aukščiau minėti autoriai daugiausia dėmesio skyrė... [toliau žr. visą tekstą]

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31

Savidge, Tor C. „Distribution, origin and function of mouse intestinal cells“. Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281994.

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Zareikar, Gita. „The Distribution and Function of Number in Azeri“. Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38044.

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In this dissertation, I study the distribution of number in Azeri within the Exo- Skeletal model of Borer (2005a). I adopt the Exo-Skeletal model's assumption that number marking is a syntactic rather than a lexical process. Following Borer (2005a), I assume that, in order to be counted, nouns need to be individuated by means of a functional category Div. In Borer's model, plural markers and classifiers are argued to be generated in DivP. However, unlike Borer, I propose that the plural marker in Azeri is not an individuator. Instead, it solely marks plurality. Under my proposal, individuation in Azeri is morphologically null. Moreover, I argue that classifiers do not belong to the category of individuators either and their function is to unitize the individuated object. Therefore, I consider classifiers in Azeri to be generated on a cluster head where they contribute to a group formation process. The generation of the plural marker and the classifier on heads other than division derives the conclusion that the individuation in Azeri is morphologically null. Furthermore, I investigate the interpretation of number in the verbal domain, i.e. in TP, in the presence of the viewpoint aspect in both telic and atelic contexts. I argue that the singular interpretation of the Azeri bare noun is linked to the projection of AspQ, where the specific interpretation of the bare noun arises under the effect of the perfective aspect. The presence of AspQ yields a telic interpretation of the event structure, and the DP in the specifier of AspQ is the subject of quantity (Borer, 2005a). Moreover, according to Borer, number ambiguous nouns are generated in atelic structures where AspQ is absent. In this case, the DP does not have to be the subject of quantity and the availability of quantity on the DP remains optional. Nevertheless, (non-)specific interpretation of the noun in telic and atelic contexts in Azeri, I argue to be due to the impact of the viewpoint aspect.

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Matavalam, Roop Kishore R. „Power distribution reliability as a function of weather“. [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006668.

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34

Chatterjee, Haimantee Verfasser], Reinhard [Akademischer Betreuer] Neder, Ana-Sunčana [Gutachter] [Smith und M. Alexander [Gutachter] Schneider. „Atomistic modelling of ligand-capped ZnO nanoparticles against pair distribution functions / Haimantee Chatterjee ; Gutachter: Ana-Suncana Smith, M. Alexander Schneider ; Betreuer: Reinhard Neder“. Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2020. http://d-nb.info/1216704333/34.

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Chatterjee, Haimantee [Verfasser], Reinhard Akademischer Betreuer] Neder, Ana-Sunčana [Gutachter] [Smith und M. Alexander [Gutachter] Schneider. „Atomistic modelling of ligand-capped ZnO nanoparticles against pair distribution functions / Haimantee Chatterjee ; Gutachter: Ana-Suncana Smith, M. Alexander Schneider ; Betreuer: Reinhard Neder“. Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2020. http://d-nb.info/1216704333/34.

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36

Turner, Marianne Teresa. „The function, design and distribution of New Zealand adzes /“. Online version, 2000. http://bibpurl.oclc.org/web/31625.

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37

Amlani, Shahira R. „Intermediate filaments in Sertoli cells : distribution and possible function“. Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27790.

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The distribution of vimentin intermediate filaments in Sertoli cells during spermatogenesis was observed with immunofluorescence, and was confirmed with electron microscopy. The distribution of vimentin filaments within Sertoli cells changes with changes in the germ cell population. At stages where elongate spermatids reside in crypts located deep within the seminiferous epithelium, groups of eight to twelve intermediate filaments were consistently found at the convex surface of the spermatid heads. Here the filaments are in close association with ectoplasmic specializations. At later stages of spermatogenesis, intermediate filaments are not found in crypt areas. Because of their association with particular stages of developing germ cells, intermediate filaments in Sertoli cells may be involved in the attachment and positioning of developing germ cells within the seminiferous epithelium. Intermedate filaments in general are thought to be involved in anchoring the nucleus and cytoplasmic organelles within a cell. In order to test this hypothesis, acrylamide, a specific perturbant of intermediate filaments in vitro, was perfused through rat and ground squirrel testes in order to perturbate the intermediate filament system within Sertoli cells. No effects of acrylamide on intermediate filaments were observed in vivo at either the light microscopic or ultrastructural level. However, toxic effects were observed upon treatment with high concentrations of acrylamide, indicating that Sertoli cells and associated germ cells were indeed exposed to the perturbant. Based on these studies, one can conclude that: (1) vimentin filaments in Sertoli cells change their distribution during spermatogenesis; (2) vimentin filaments are closely associated with specific stages of developing germ cells, and may be involved in the positioning and attachment of these cells to Sertoli cells within the seminiferous epithelium, and (3) acrylamide has no effect on vimentin filaments in Sertoli cells in vivo.
Medicine, Faculty of
Graduate

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Turner, Marianne. „The function, design and distribution of New Zealand adzes“. Thesis, University of Auckland, 2000. http://hdl.handle.net/2292/26.

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The main objective of this thesis was to understand the function, design and distribution of New Zealand adzes, aspects little studied in Polynesia as a whole. Methodology involved functional and manufacturing replication experiments and comparisons of these results with statistics derived from the analysis of almost 12,000 archaeological adzes. Methodology was guided by technological organization theory which states that technological strategies reflect human behaviours and that artefacts like adzes are physical manifestations of the strategies employed by people to overcome problems posed by environmental and resource conditions. Variability in adze morphology was discovered to be the outcome of ongoing technological adjustments to a range of conditions that were constrained by a set of functionally defined parameters. The nature of the raw material, both for the adzes themselves and to make them, had a major influence on adze technology and morphology within these functional parameters. Four basic functional adze types were identified fi-om distinct and consistent combinations of design attributes not previously recognized explicitly in previous adze typologies. It was found that design attributes previously considered significant like crosssection shape and butt reduction were more heavily influenced by raw material quality than functional specifications. It was also important to recognize that form and function changed over time with use, and because adzes were so valuable due to manufacturing costs, they were intensively curated. The majority of archaeological specimens studied for this thesis had seen major morphological and functional change. This dynamic was included ,in a typology based on 'adze state7 as findings suggested (1) that extending adze use-life and optimizing reworking potential was incorporated in initial design strategies, (2) that intensive curation may have played a major role in changes in adze morphology over time, and (3). that it had a major influence on distribution and discard patterns in the archaeological record. Having identified these influences on adze discard and distribution, two complex production and distribution networks were observed for the North Island based around Tahanga basalt and Nelson~Marlborough argillite. Each was complimentary to the other and involved other major and minor products and materials. Influential factors in the roles different settlements played in distribution included where people and raw materials were in relation to one another and the mode of transportation. The coastal location of early period settlements and important stone sources was an important aspect of these networks.

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Dixon, A. K. „Distribution and function of adenosine receptors in the rat“. Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598553.

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This thesis describes investigations into the tissue distribution of messenger RNAs encoding the four cloned adenosine receptors in the rat, and aspects of adenosine A₁ and A_2a receptor function in the rat central nervous system (CNS). Chapter 1 reviews the literature relating to this field, presenting an overview of adenosine metabolism and adenosine receptor classification, distribution and function. In Chapter 2 the distribution of adenosine A₂ and A₃ receptor gene expression is described. Chapter 3 describes investigations into the possible anatomical association between the adenosine A₁ receptor and members of Kir3.0, a subfamily of inwardly rectifying K⁺ channels. In Chapter 4 adenosine A₁ and A₂ receptor mediated control of proenkephalin and substance P gene expression in the rat striatum was investigated. In Chapter 5 the results of an investigation into interactions between striatal adenosine A₁ and A_2a, receptors, is described. Chapter 6 describes work performed on a related project in which a technique was developed to promote the fusion of cortical synaptosomes, thus rendering them amenable to elctrophysiological examination. The fused entities resulting from this procedure were subsequently characterised. In conclusion, the tissue distribution, at the molecular level, of all four cloned adenosine receptors has been defined. Consequently many novel sites of adenosine receptor gene expression have been identified. Also, certain functional effects of the striatal adenosine A_2a receptor have been demonstrated for the first time, these include an ability to control the activity of both major striatal output pathways and a modulatory interaction with colocalised adenosine A₁ receptors. The latter observations may be of some importance in the development of new therapeutic approaches designed to alleviate the symptoms of Parkinson's disease.

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Robinson, Andrea Keryn. „Microbial zinc metallothioneins : function of SmtA and species distribution“. Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366622.

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41

Garcia-Serrano, Antonio Victor. „Extracting density distribution function models from three-dimensional data“. Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326916.

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42

Woods, Aaron R. „Distribution, Function, And Value Of Parowan Valley Projectile Points“. Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd2905.pdf.

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43

Portillo, Maria Virginia. „Distribution and function of nematode glutamate-gated chloride channels“. Thesis, University of Bath, 2003. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398437.

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44

Bressert, Eli Walter. „The initial distribution of stars“. Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3890.

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The primary focus of my PhD is to quantify the spatial distribution of star-forming environments from optical to radio wavelengths using data from the Hubble Space Telescope, the Very Large Telescope, the Spitzer Space Telescope, the Herschel Space Observatory, and the Caltech Submillimeter Observatory. Towards the end of my PhD study I have developed theoretical models. With these observational and theoretical avenues I have led a series of research projects to (1) quantify the initial spatial structure of pre-stellar cores and proto-stars, (2) test whether massive stars can form in isolation or not, (3) and develop a theoretical model on how young massive clusters form. These research projects have been fruitful as my collaborators and I have shown that pre-stellar cores and stars form in a smooth continuum of surface densities from a few to thousands of stars per pc^2. These two works have important implications on our understanding of what a young stellar cluster is and how star forming environments can evolve to form field star populations or gravitationally bound clusters. In my second study my collaborators and I found evidence for isolated massive star formation in the active star forming region 30 Doradus, in the Large Magellanic Cloud. The result impacts the field of the initial mass function and star formation models. Massive stars forming in isolation is consistent with a stochastically sampled initial mass function. Additionally, the result would put constraints on theoretical models on massive star formation. Continuing my work on massive star forming environments my collaborators and I have developed a theoretical model on how young massive clusters form. From the models we argue that feedback energies can be contained by the gravitational potential well of the massive progenitors. Furthermore, we predict the physical properties the massive cluster progenitors in terms of initial gas mass, radii and flux brightness to enable a search for these objects in Galactic plane surveys and upcoming telescopes. Using the common thread of spatial distribution analysis of star formation I describe my future research plans, which entails studies on extragalactic scales in the conclusion.

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Ashworth, Rachel Jane. „The distribution and function of the TRH-related peptide, pyroglutamylglutamylprolinamide“. Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317630.

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46

Puthiyaveetil, Sujith. „Two-component signalling systems of chloroplasts : function, distribution and evolution“. Thesis, Queen Mary, University of London, 2008. http://qmro.qmul.ac.uk/xmlui/handle/123456789/121.

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Two-component signal transduction, comprising sensor kinases and response regulators, is the predominant signalling mechanism in prokaryotes. This signalling system originated in bacteria, and has spread to the eukaryotic domain of life through symbiotic, lateral gene transfer from the bacterial ancestors of chloroplasts and mitochondria. During the course of their evolution, chloroplasts, with the exception of a few instances in non-green algae, appear to have relinquished all genes encoding two-component systems to their eukaryotic host cell nuclei. In green algae and plants, chloroplast genes for two-component systems were neither known nor were chloroplast two-component proteins shown to exist as products of nuclear genes prior to the work described here. This thesis describes the identification and characterisation of a novel two-component sensor kinase in chloroplasts. This Chloroplast Sensor Kinase (CSK) is the product of a nuclear gene in algae and plants. CSK is synthesised in the cytosol of Arabidopsis thaliana and imported into the chloroplast as a protein precursor. CSK is autophosphorylated and couples photosynthetic electron transport to gene transcription in chloroplasts. The identity of the response regulator partner of CSK reveals an unexpected phylogenetic and functional relatedness of CSK with chloroplast two-component systems of non-green algae. Chloroplast two-component systems are likely to be universal in photosynthetic eukaryotes and they persist in chloroplasts as products of nuclear genes even where chloroplast genomes no longer encode them. Chloroplast twocomponent systems have homologues in extant cyanobacterial lineages, indicating their ancient cyanobacterial origin. The persistence of cyanobacterial two-component systems in chloroplasts and their function in coupling photosynthesis with chloroplast gene expression are central to the premise that chloroplasts retain genes whose expression is regulated by the activity of the photosynthetic electron transport chain, using a mechanism conserved from their cyanobacterial ancestors.

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47

Huang, Yen-Chin. „Empirical distribution function statistics, speed of convergence, and p-variation“. Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12017.

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48

Cronin, Thomas Martin. „Effect Of Fiber Orientation Distribution Function Reconstruction On Probabilistic Tractography“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1327524558.

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49

Ro, Seungil. „SK channels : distribution, function and regulation in mouse colonic myocytes /“. abstract and full text PDF (UNR users only), 2002. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3090879.

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50

Tamang, Bijay. „Tree windbreak function, root distribution and biomass production in Florida“. [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0041134.

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Dissertationen zum Thema „Paire of Distribution Function“

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