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1
MOSTONI, SILVIA. « From nanosized to single sites zinc-based activators for rubber vulcanization process ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241069.
Texte intégralRésumé :
I nanocompositi di gomma (NC) sono materiali comunemente usati nell’industria degli pneumatici. Le proprietà meccaniche dipendono sia dall’aggiunta delle nanoparticelle (NP) di filler rinforzanti e dal processo di vulcanizzazione. La reazione di vulcanizzazione a base zolfo si basa sulla formazione di un reticolo chimico tra le catene di polimero attraverso ponti mono-, bi- e poli-sulfurei. L’incremento della velocità di reazione e dell’efficienza di reticolazione è consentito da un complesso sistema catalitico, composto da acceleranti (ad esempio sulfenammidi), attivatori (ossidi metallici) e co-attivatori (acidi grassi). L’ossido di zinco (ZnO) è il principale attivatore usato industrialmente; un ruolo fondamentale è assegnato agli ioni zinco, in grado di influenzare aspetti cinetici e meccanicistici, come il processo di accorciamento dei ponti sulfurei nei prodotti di reticolazione (associato a maggiori densità di reticolo). Ciononostante, la bassa dispersione dell’ossido di zinco, dovuta ad una bassa affinità verso il polimero, porta ad un uso ingente di ZnO nelle gomme (3-5 parti per cento di gomma) e a problemi ambientali, connessi al rilascio dello zinco durante il ciclo di vita degli pneumatici.
In questo quadro, lo scopo del progetto di dottorato è stato lo sviluppo di attivatori innovativi a base zinco per il processo di vulcanizzazione, per ridurre il quantitativo di ZnO micro-cristallino nel processo industriale e diminuire il rilascio di zinco, mantenendo un’elevata efficienza del processo. A tal scopo, l’introduzione di siti reattivi di zinco è stata indagata. Partendo da NP di ZnO ancorate sulla superficie della silice (ZnO/SiO2), siti singoli di zinco (Zn/SiO2) dispersi su silice sono stati sintetizzati, sfruttando i vantaggi derivanti da una maggiore dispersione dello zinco nel composito e incrementando la reattività e disponibilità dell’attivatore nella reazione.
Inizialmente, la sintesi dei due materiali e le loro proprietà sono state studiate, tramite analisi strutturali, morfologiche e di superficie. NP di ZnO amorfe, con dimensioni e percentuali di carico su silice variabili, sono state sintetizzate utilizzando una procedura ottimizzata di tipo sol-gel, basata sul fenomeno di idrolisi e condensazione di un precursore di zinco in ambiente basico. Inoltre, centri isolati di zinco (II) sono stati preparati in una reazione a due fasi, in cui la silice è pre-funzionalizzata con un agente ancorante (3-amminopropil)trietossisilano, APTES) e in seguito fatta interagire con un precursore di zinco. La caratterizzazione sperimentale ha suggerito che ogni centro di zinco isolato fosse coordinato con due gruppi amminici e due gruppi labili (idrossidi o nitrati), che potessero promuovere una maggiore reattività.
I test in NC di gomma, comparati con NC preparati con ZnO micro-cristallino, hanno dimostrato maggiori efficienze di vulcanizzazione, migliorate proprietà meccaniche, elevate densità di reticolo e maggiore rinforzo in presenza dei due attivatori, usando metà del quantitativo tradizionale di ZnO. La cinetica di reazione è stata studiata tramite un approccio modello (Model Compound Vulcanization, MCV), evidenziando una migliore cinetica di processo e differenti meccanismi di reazione per ZnO/SiO2 e Zn/SiO2. Inoltre, i centri di zinco isolati hanno dimostrato di comportarsi da siti catalitici eterogenei, con una potenziale riduzione del rilascio di zinco e conseguenze dirette sulla distribuzione della reticolazione nel composito vulcanizzato, evidenziato tramite analisi avanzate di tipo morfologico e meccanico.
Infine, la modulazione dei parametri strutturali degli attivatori e il loro uso in sistemi non convenzionali, che includono compositi rinforzati da filler anisotropici e polimeri modificati organicamente, hanno dimostrato la possibile regolazione della reattività e l’alta versatilità dei due attivatori per applicazioni in diversi sistemi.Rubber nanocomposites (NCs) are commonly used materials in tyres industries. Their mechanical properties are the combined result of the addition of reinforcing filler nanoparticles (NPs) and the vulcanization process. Sulphur vulcanization reaction is based on the formation of a chemical cross-link between polymer chains through mono-, bi- and poly-sulphide bridges. The enhancement of the vulcanization rate and cross-linking efficiency is achieved thanks to a complex catalytic system, composed of accelerators (as sulphenamides), activators (metal oxides) and co-activators (fatty acids). Zinc oxide (ZnO) is the primary industrial activator and a main role is recognized to zinc ions, able to influence both kinetic and mechanistic aspects of the reaction, through the shortening of sulphur bridges in the products (associated to higher cross-linking densities). Nevertheless, some drawbacks are connected to the low dispersion of ZnO, because of the low affinity with the rubber, such as the use of high ZnO amount in rubber (3-5 parts per hundred rubber) and environmental issues, due to zinc release during the lifecycle of tyres. In this scenario, the aim of the PhD project is the development of innovative zinc-based activators for rubber vulcanization process, to reduce the amount of microcrystalline ZnO used in the industrial process and to decrease the zinc leaching during the preparation and use of the material, keeping a high vulcanization efficiency. Thus, the introduction of more active zinc species in the form of reactive sites has been proposed. Starting from nanosized ZnO particles anchored onto surface silica particles (ZnO/SiO2), single zinc sites (Zn/SiO2) dispersed on silica were synthesized, to exploit the advantages derived from the higher distribution, while increasing the availability and reactivity of the activator towards the other vulcanization reagents. In the first part, the syntheses of the materials were studied and their properties deeply investigated, through structural, morphological and surface analyses. The formation of amorphous ZnO NPs with tunable zinc loading and size on silica was achieved exploiting an optimized sol-gel procedure, based on hydrolysis and condensation of a zinc precursor in a basic environment. Besides, isolated zinc(II) centres anchored to silica were synthesized in a two-step reaction, in which silica was pre-functionalized with a grafting agent ((3-aminopropyl)triethoxysilane, APTES) and then reacted with a zinc precursor. The experimental characterization suggested the coordination of each zinc isolated centres to two amine groups and two labile groups (hydroxide or nitrate), promoting a higher reactivity. Both ZnO/SiO2 and Zn/SiO2 were tested as activators in rubber NCs and compared to microcrystalline ZnO; higher vulcanization efficiencies and improved mechanical properties were achieved, with increased cross-linking densities, using half of the conventional amount of ZnO. Lately, the kinetic of the vulcanization reaction was studied thanks to a model approach, called “Model Compound Vulcanization” (MCV). This study highlighted that the vulcanization process proceeded with an improved kinetic and following different reaction mechanisms. In particular, Zn centres were proved to behave as heterogeneous catalytic sites during the reaction, with a potential impact on the reduction of zinc leaching from rubber NCs and a direct consequence on the cross-linking distribution of the vulcanized rubber NCs, evidenced through advanced morphological and mechanical analyses. Finally, the modulation of the structural parameters of the activators and the use into non-conventional systems, including anisotropic NPs reinforced NCs and organically modified polymers, demonstrated the possible modulation of their reactivity and the high versatility of the materials for applications into different systems.
2
Larsson, Chatarina. « Single-molecule Detection in situ ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-98538.
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Dong, Yi. « Single site surface reactions : STM Studies ». Doctoral thesis, Université Laval, 2018. http://hdl.handle.net/20.500.11794/30204.
Texte intégralRésumé :
La demande des composants chimiques énantiopurs dans le secteur pharmaceutique est une des forces qui motive la recherche dans la création des catalyseurs homochiraux à la surface. La catalyse hétérogène est une méthode prometteuse pour la fabrication des produits énantiopurs puisqu'elle porte des avantages tels que la facilité de la séparation des produits désirés, la réutilisation du catalyseur et l'adaptabilité dans différentes conditions de la production en continu. La réaction d'Orito est un des exemples de la réaction hétérogène énantiosélective la plus réussie. Elle concerne l'hydrogénation de α-cétoesters sur des particules de platine modifiées par le cinchona. Il est généralement accepté que des modificateurs cinchona tels que la cinchonidine ou la cinchonine transfère la chiralité en formant des complexes bimoléculaires (complexes 1 :1) avec des réactifs prochiraux sur la surface. La compréhension de la catalyse asymétrique hétérogène au niveau fondamental est insu sante. Par contre, c'est aussi une zone fertile pour la découverte. Du progrès dans le domaine peut être réalisé par des travaux complémentaires en catalyse, en sciences des surfaces et en calcul théorique. Cette thèse décrit les études en science des surfaces inspirées par des rapports dans la littérature sur la réaction d'Orito. En plus des alcaloïdes du cinchona, qui sont des produits naturels, certains nombres de molécules synthétiques sont également des modificateurs chiraux pour la réaction d'Orito. En particulier, Baiker et ses collègues ont enquêté sur la performance du 1-(1-naphtyl)éthylamine (NEA) optiquement pur en tant que modificateur chiral pour l'hydrogénation énantiosélective de cétopantolactone (KPL) en pantolactone sur le Pt/Al2O3.1 Une partie du travail décrit dans cette thèse est l'étude des complexes formés par l'interaction de (R)-NEA et KPL sur la surface de monocristal Pt(111). Le microscope à e et tunnel (STM) est utilisé pour acquérir un grand nombre d'images des complexes KPL/(R)-NEA. Les mesures sont effectuées sur un large rapport de couverture de KPL à (R)-NEA sur la surface. Un algorithme est développé pour accélérer le comptage et la catégorisation de la forme du grand ensemble d'images STM des complexes. L'abondance de plusieurs complexes distincts qui impliquent toute une liaison hydrogène NH···O est déterminée. La prochiralité de KPL dans ces complexes sont attribuées en référant des images STM simulées par théorie de la fonctionnelle de la densité (DFT). Le rapport prochiral global (pr) mesuré dans l'expérience de la surface est comparé au rapport énantiomérique (er) mesuré par Baiker et ses collègues. Un autre algorithme est développé pour l'analyse des événements dynamiques des complexes diastéréomères individuels. Il est appliqué pour tester l'interconversion d'un état à l'autre état pendant la durée de vie de chaque complexe qui est observée par STM. Les résultats sont présentés pour les complexes formés entre 2,2,2-trifluoroacetophenone (TFAP) et (R)-NEA sur le Pt(111). Les complexes TFAP/(R)-NEA montrent des événements dynamiques qui sont décrits comme décomplexation, inversion prochirale sur site et migration intracomplexe. Les résultats sont discutés en référant les barrières énergétiques prédites par DFT pour l'hydrogénation et pour l'inversion prochirale sur site. Un rapport préliminaire présente les données quantitatives sur les interconversions des états aux états des complexes individuels des trois systèmes : TFAP/(R)-NEA, KPL/(R)-NEA et TFAP/8-Me-(R)-NEA. Le dernier modificateur de la surface concerne la substitution d'un méthyle à l'hydrogène à la position 8 du groupe naphtyle du (R)-NEA. Les observations sur les complexes KPL/(R)-NEA et TFAP/(R)-NEA sont résumés dans le contexte des données de science de surface précédemment publiées de notre groupe. La revue met l'accent sur le rôle des interactions secondaires, CH···O et CF···H, dans le contrôle stéréoscopique des molécules prochirales.The demand for enantiopure compounds in the pharmacological sectorsisastrong driving force for research aimed at creating homochiral catalyst surfaces. Heterogeneous catalysts offer potential advantages over homogeneous catalysts including ease of separation of products from the catalyst and greater suitability for operations under continuous ow conditions. One of the most successful examples of a heterogeneous enantioselective reaction is known as the Orito reaction, the hydrogenation of α-ketoesters on cinchona modi ed platinum particles. It is believed that the cinchona modi ers operate chirality transfer by forming bimolecular surface complexes with prochiral reactants. At a fundamental level, heterogeneous asymmetric catalysis is a poorly understood area of surface chemistry. Hence, it is also a fertile area for discovery. Progress in the area can best be made by complementary work in catalysis, surface science and computation. This thesis describes surface science studies that were inspired by reports in the catalysis literature on the Orito reaction. In addition to cinchona alkaloids, which are natural products, a number of synthetic molecules have been shown to be effective chiral modifiers for the Orito reaction. In particular, Baiker and co-workers explored the performance of optically pure 1-(1-naphtyl)-ethylamine (NEA) as a chiral modifier for the enantioselective hydrogenation of ketopantolactone (KPL) to pantolactone on Pt/Al2O3.1 A major part of the work described in this thesis deals with the investigation of surface complexes formed through the interaction of (R)-NEA and KPL on single crystal Pt(111). Scanning tunnelling microscopy (STM) measurements were used to acquire a large number of images of KPL/(R)-NEA complexes. The measurements were performed over a wide ratio KPL to (R)-NEA surface coverage ratios. An algorithm was developed to enable accelerated counting and cataloguing of the large set of STM images of complexes. Therelativeabundancesofmultipledistinctcomplexationstates, allinvolvingNH·· ·O hydrogen bonding, were determined. The prochirality of KPL in these states was assigned by reference to density functional theory (DFT) simulated STM images. The overall prochiral ratio (pr) measured in the surface science experiment was compared to the enantiomeric ratio (er) measured by Baiker and co-workers. An algorithm was developed to investigate uxional events in individual diastereomeric complexes. It was applied to examine state-to-state interconversion occurring during the life times of complexes, as observed using time-lapsed STM measurements. Results are presented for complexes formed by 2,2,2-trifluoroacetophenone (TFAP) interacting with (R)-NEA on Pt(111). The TFAP/(R)-NEA complexes show dynamic events that we describe as decomplexation, on-site prochiral inversion and intracomplex migration. The results are discussed in relation to energy barriers predicted by DFT for hydrogenation and for on-site prochiral inversion. Quantitative data for state-to-state interconversion in single complexes are presented for three systems: TFAP/(R)-NEA, KPL/(R)-NEA and for TFAP interacting with methyl-substituted (R)-NEA. A preliminary analysis of the data is presented. The observations on KPL/(R)-NEA and TFAP/(R)-NEA complexes are reviewed within the context of previously published surface science data from our group. The review emphasizes the role of secondary interactions, CH···O and CF···H bonding, in the stereocontrol of prochiral molecules.
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Montaseri, Majid. « Stochastic investigation of the planning characteristics of within-year and over-year reservoir systems ». Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/586.
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Tran, Phu-Dennis. « Ethen-Norbornen-Copolymerisation durch Single-site-Katalysatoren-MAO ». [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968875459.
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Cotta, Dylan A. « A single-site resolution fermionic quantum-gas microscope ». Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29619.
Texte intégralRésumé :
Quantum-gas microscopes have become an important tool in quantum simulation as they enable direct probing of local quantities by single-atom-resolved detection in optical lattices. Recent years have seen many fascinating results from the bosonic quantum-gas microscopes using 87Rb. However, no such device existed for fermionic species. The goal of this thesis work was to develop and build a quantum-gas microscope setup for fermionic potassium-40. Single-atom-resolved imaging of 40K has proven very challenging due to its smaller mass and smaller excited-state hyperfine splitting compared to 87Rb. In addition, the inverted excited state trapping potential required us to employ electromagnetically induced transparency (EIT) cooling instead of sub-Doppler molasses cooling. EIT cooling occurs when a coherent driving of a three-level system generates a spectrally narrow Fano-like resonance which can be set to favour red-sideband transitions over blue ones of the quantised vibrational levels in the optical lattice potential. During the cooling process, the fluorescence light is collected by a high-NA objective to image the atomic distribution in a two-dimentional square lattice potential. Due to the physical constraints of our apparatus, EIT cooling had to be combined with coupling between different motional axes via Raman transitions to achieve cooling of all degrees of freedom. Our imaging method allowed us to collect about 1,000 fluorescence photons per atom within a 1.5 s exposure time. From the analysis of two distinct subsequent fluorescence images, we found that less than 5% of the atoms hopped or were lost during 1s of EIT cooling. Such fidelity will allow fermionic quantum-gas microscopes to investigate fermionic quantum phases, spin-spin correlations, and out of-equilibrium dynamics of correlated fermionic many-body quantum systems.
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Parsons, Maxwell F. « Probing the Hubbard Model With Single-Site Resolution ». Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493308.
Texte intégralRésumé :
Strongly-correlated electron systems generate some of the richest phenomena and most challenging theoretical problems studied in physics. One approach to understanding these systems is with ultracold fermionic atoms in optical lattices, which can provide a level of control and ways of observing strongly-correlated fermionic systems that are not accessible with conventional materials. This thesis describes the development of an experimental technique where a quantum gas of fermionic 6Li atoms is prepared in a two-dimensional optical lattice and each atom can be frozen in place and imaged with single-site resolution. Combining a vacuum-compatible large numerical aperture microscope with Raman sideband cooling enables site-resolved fluorescence imaging with high fidelity. We observe several phases of the Hubbard model, including band and Mott insulators.
The observed in-situ occupation distributions of atoms in the lattice are compared to theory with unprecedented detail and are used to determine the thermodynamic properties of the system. By combining site-resolved imaging with a spin-removal technique, we observe antiferromagnetic correlations in the Hubbard model with single-site resolution. We observe, for the first time in cold atom systems, beyond-nearest-neighbor magnetic correlations, which provide a direct measurement of the correlation length. We also present detailed measurements of the formation of correlations during lattice loading.Physics
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Milatos, Gerasimos Dionisios. « Evaluation of site effects on a high frequency direction finding single site location system ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA267465.
Texte intégralRésumé :
Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, March 1993.Thesis advisor(s): Adler, Richard W. "March 1993." Includes bibliographical references (p. 111-113). Also available online.
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Lovatt, Stephen Charles. « Anisotropic single-site scattering theory for space-filling potentials ». Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357933.
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Leith, Nadja Alexandra. « Single-site rainfall generation under scenarios of climate change ». Thesis, University College London (University of London), 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527841.
Texte intégralRésumé :
Many hydrological applications require high-resolution rainfall data under scenarios of climate change. This thesis uses numerical climate model output at a coarse spatial resolution to condition simulations of sub-daily rainfall sequences at individual sites. Downscaling techniques based on generalised linear models are employed, along with stochastic models based on Poisson cluster processes. The two model classes are coupled using stable relationships between the properties of observed rainfall sequences at different time scales. It is recognised that projections of future climate can differ widely between climate models and it is therefore necessary to account for climate model uncertainty. A hierarchical statistical model is proposed, and implemented in a Bayesian framework, which provides a logically coherent and interpretable way to describe uncertainty in multivariate sequences of climate model output. A way of dramatically reducing the computing time needed to fit such a model, based on condensing the data via the use of maximum likelihood estimates, is also discussed. The ideas are illustrated by considering the generation of future daily rainfall sequences at sites in the UK, using climate model outputs under the SRES A2 emissions scenario.
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Weibrecht, Irene. « Visualizing Interacting Biomolecules In Situ ». Doctoral thesis, Uppsala universitet, Molekylära verktyg, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-151579.
Texte intégralRésumé :
Intra- and intercellular information is communicated by posttranslational modifications (PTMs) and protein-protein interactions, transducing information over cell membranes and to the nucleus. A cells capability to respond to stimuli by several highly complex and dynamic signaling networks provides the basis for rapid responses and is fundamental for the cellular collaborations required in a multicellular organism. Having received diverse stimuli, being positioned at various stages of the cell cycle or, for the case of cancer, containing altered genetic background, each cell in a population is slightly different from its neighbor. However, bulk analyses of interactions will only reveal an average, but not the true variation within a population. Thus studies of interacting endogenous biomolecules in situ are essential to acquire a comprehensive view of cellular functions and communication. In situ proximity ligation assay (in situ PLA) was developed to investigate individual endogenous protein-protein interactions in fixed cells and tissues and was later applied for detection for PTMs. Progression of signals in a pathway can branch out in different directions and induce expression of different target genes. Hence simultaneous measurement of protein activity and gene expression provides a tool to determine the balance and progression of these signaling events. To obtain this in situ PLA was combined with padlock probes, providing an assay that can interrogate both PTMs and mRNA expression at a single cell level. Thereby different nodes of the signaling pathway as well as drug effects on different types of molecules could be investigated simultaneously. In addition to regulation of gene expression, protein-DNA interactions present a mechanism to manage accessibility of the genomic DNA in an inheritable manner, providing the basis for lineage commitment, via e.g. histone PTMs. To enable analyses of protein-DNA interactions in situ we developed a method that utilizes the proximity dependence of PLA and the sequence selectivity of padlock probes. This thesis presents new methods providing researchers with a set of tools to address cellular functions and communication in complex microenvironments, to improve disease diagnostics and to contribute to hopefully finding cures.
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Pinkney, Justin N. M. « Extending and combining single-molecule fluorescence methods to study site-specific recombination ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:cde8481b-ac4b-4040-bb98-6035b8f43817.
Texte intégralRésumé :
Förster resonance energy transfer (FRET) has become an important tool for studying biochemical reactions at the single-molecule level, despite its increasing maturity there is an on-going effort to improve and expand the technique. This thesis presents methods for extending conventional two-colour single-molecule FRET measurements; by expanding the range and applicability of single-molecule fluorescence methods a greater variety of biological reactions can be studied, in greater detail than previously possible. To circumvent the complexities of multi-colour FRET measurements and extend the range of observable distances I developed and characterised a new single-molecule fluorescence method termed tethered fluorophore motion (TFM). TFM is based on the existing technique of tethered particle motion (TPM) which relies on Brownian motion of a particle, attached to a surface by DNA, to probe the effective length of the DNA tether. TFM takes this concept and applies it at the single-fluorophore level, allowing simultaneous measurement of other fluorescence observables such as FRET and protein induced fluorescence enhancement (PIFE). Having developed TFM I combined it with FRET to study site-specific recombinase proteins at the single-molecule level, in greater detail than possible by either technique alone. Studying the model tyrosine recombinase Cre, I extend and clarify previous ensemble observations regarding the order of DNA strand exchange, as well as uncovering a previously unobserved complex conformation and molecular heterogeneity. Finally, I used TFM-FRET to study the more complex XerCD recombination system and its interaction with the DNA translocase FtsK. I made observations, for the first time, of synaptic complex formation and of recombination at the single-molecule level, and these suggest intriguing and unexpected intermediates in the recombination reaction. I also combine TFM with PIFE to investigate the mechanism of DNA looping by FtsK. The introduction of TFM, and its combination with other fluorescence techniques, allows observation of complex protein-DNA interactions from a variety of perspectives and will help expand the repertoire and applicability of single-molecule biophysical experiments.
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Franchini, Patrick Lorenzo Angelo. « Structure/Function in the CD site of parvalbumin : understanding calcium affinity using synthetic single site EF-hand peptides ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0020/NQ46344.pdf.
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Wang, Haozhu. « Cobalt Phosphide Single Site Electrocatalysts derived from 2D ZIF-8 for Hydrogen Evolution Reaction ». Thesis, University of Sydney, 2021. https://hdl.handle.net/2123/26246.
Texte intégralRésumé :
Hydrogen (H2) is a promising energy carrier due to its high gravimetric energy density and environmental friendliness. Among different approaches of H2 production, hydrogen evolution reaction (HER) via electrochemical water splitting has attracted significant research interests when electricity can be supplied by sustainable energy sources, such as solar, wind, and tidal energy. Electrocatalysts play a crucial role in accelerating HER's kinetics. Platinum (Pt)-based electrocatalysts have excellent catalytic activities for HER due to their optimal adsorption/desorption energy for hydrogen and have been are widely used in industrial water electrolyzers. However, their high cost and poor stability seriously limit their broad adoption. Tremendous research efforts have been devoted to developing electrocatalysts based on earth-abundant transition metals, such as iron (Fe), cobalt (Co), nickel (Ni), and molybdenum (Mo). In this regard, emerging single-atom catalysts (SACs) with maximum atom utilization is considered as one of the most promising solutions.
Here, a new cobalt phosphide single site HER electrocatalyst was synthesized from ultrathin 2D ZIF-8 metal-organic framework (MOF) nanosheets using a mixed solution containing Zn2+, Co2+, 2-methylimidazole. The 2D MOF nanosheets facilitate the phosphating of single atom Co sites rather than forming cobalt phosphide nanoparticles. Structural characterizations indicated that the as-synthesized electrocatalyst (denoted as CoPSS) has a CoN2P2 coordination structure, where Co metal centres coordinate with two P atoms and two N atoms. CoPSS demonstrates an excellent HER performance in an alkaline electrolyte with an overpotential of 117 mV at 10 mA cm-2 and a Tafel slope of 55 mV dec-1. This work provides a facile and cost-effective strategy for preparing high efficient HER electrocatalysts.
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Viscor, Pagès Daniel. « From quantum memories to single-site addressing with three-level atoms ». Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/117482.
Texte intégralRésumé :
El camp de la informació quàntica, que sorgeix de la combinació entre la teoria de la informació i la física quàntica, ha experimentat un enorme progrés durant les darreres dècades, donant lloc a avenços revolucionaris en una àmplia varietat de camps interdisciplinaris, com ara la computació quàntica, la comunicació quàntica, els mesuraments d'alta precisió, i l’estudi fonamental de la teoria quàntica. No obstant això, les ambicioses metes en què la comunitat científica esta centrada, per exemple, la criptografia quàntica, els simuladors quàntics, o fins i tot la computació quàntica, tot just han començat a destacar.En la majoria d'aplicacions de la informació quàntica, per tal d’emmagatzemar i processar la informació s'utilitzen normalment sistemes amb un gran nombre d’àtoms, mentre que la llum s'utilitza com una eina per a manipular i realitzar operacions lògiques, així com per transmetre els bits quàntics entre nodes distants d'una xarxa quàntica. Per tant, la realització d'una interfície adequada entre la llum i els conjunts d’àtoms és essencial en la ciència de la informació quàntica. Quant a la interacció llum-matèria, un dels sistemes més rellevants són els àtoms de tres nivells en interacció amb un parell de camps electromagnètics. Els sistemes de tres nivells mostren una rica varietat de fenòmens quàntics a causa de les interferències produïdes degut a les dues vies d'absorció de la llum. Aquestes interferències quàntiques donen lloc, per exemple, a l’atrapament coherent de població, la transparència induïda electromagnèticament, o el passatge adiabàtic via estimulació Raman, que han trobat aplicacions en moltes àrees de la informació quàntica.Aquesta tesi, que recull el treball d'investigació que he realitzat durant el meu doctorat sota la guia i el suport dels meus supervisors i col•laboradors, se centra principalment en aplicacions de la informació quàntica amb àtoms de tres nivells en interacció amb camps electromagnètics, tant a nivell semi clàssic i com completament quàntic. Els tres primers capítols de l'obra es centren en l'estudi teòric de nous mètodes per implementar memòries quàntiques per qubits de fotons individuals en superposició de dues components, tant de la polarització com de la freqüència. Les memòries quàntiques són dispositius capaços d'emmagatzemar i recuperar a voluntat estats quàntics de la llum amb una alta eficiència i fidelitat, i són components essencials en moltes aplicacions de la informació quàntica, com ara en repetidors quàntics o en fonts de fotons individuals. Així, l'estudi de mètodes per emmagatzemar diferents tipus de codificació de la informació quàntica en fotons és una tasca essencial.D'altra banda, propostes addicionals en el context del processat d'informació quàntica, dutes a terme durant el meu doctorat, es recullen en els capítols finals. En particular, primer ens centrem en el problema de l’adreçament de llocs individuals per àtoms neutres ultra freds en xarxes òptiques amb un àtom per lloc. Aquesta proposta es du a terme mitjançant l'ús d'una tècnica de passatge adiabàtic selectiu segons la posició. A més, en segon lloc ampliem un model teòric capaç de proporcionar prediccions fiables sobre un experiment per a la producció de parells de fotons individuals, d’alta puresa i ample de banda controlat, utilitzant una configuració de conversió paramètrica espontània.Quantum information science, which emerges from the combination of information theory and quantum physics, has experienced an enormous progress during the last decades, leading to revolutionary advances in a wide range of interdisciplinary fields, such as quantum computation, quantum communication, high precision measurements, and fundamental quantum science. However, the ambitious goals at which the scientific community aim, e.g., quantum criptography, quantum simulators, or even quantum computation, have only started to stand out.In most quantum information applications, atomic ensembles are normally used to store and process the information, while light is used as a tool to manipulate and perform logical operations, as well as to transmit the quantum bits between distant nodes of a quantum network. Thus, the realization of a suitable quantum interface between light and atomic ensembles is essential in quantum information science. Regarding light-matter interaction, one of the most relevant systems are three-level atoms in interaction with a pair of electromagnetic fields. Three-level systems exhibit a rich variety of phenomena due to quantum interferences between the two absorption paths for the light. These quantum interferences lead, for instance, to coherent population trapping, electromagnetically induced transparency, or stimulated Raman adiabatic passage, which have found applications in many areas of quantum information. This thesis, which collects the research work that I have performed during my PhD under the guidance and support of my supervisors and collaborators, is mainly focused in quantum information applications using three level atoms in interaction with electromagnetic fields both at the semiclassical and fully quantum levels. The first three chapters of the work are focused on the theoretical study of novel methods to implement quantum memories for single photon qubits in superposition of two components, either polarization or frequency. Quantum memories are devices capable of storing and retrieving on demand quantum states of light with high efficiency and fidelity, and are essential components in many quantum information applications, such as quantum repeaters or single photon sources. Thus, the study of methods to store different kinds of quantum information encoding in photons is an essential task.Moreover, additional work in quantum information processing done during my PhD is collected in the final chapters. In particular, first we focus on the problem of single site addressing of ultracold neutral atoms in optical lattices with one atom per site, by using a position selective adiabatic passage technique. Next, we extend a theoretical model capable of providing reliable predictions for the production of controlled bandwidth and pure single photon pairs experiment, using a spontaneous parametric down-conversion setup.
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Pršlja, Paulina. « Theoretical Studies of Single-Site Catalysts for Efficient Electrochemical CO2 Reduction ». Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/671468.
Texte intégralRésumé :
El desenvolupament de l’electroquímica té el potenciar d’utilizar el CO2 com a matèria primera per a la producció sostenible de compostos i materials i té un gran impacte en la indústria química. El catalitzador “de lloc únic” (single site catalyst) és un material prometedor per aconseguir elevades activitats y selectivitats cap a la formació de CO i hidrocarburs C1. L’estructura única d’aquest catalitzador derivat de carboni redueix la competència d’aquests processos amb d’altres processos catalítics com la hydrogen evolution reaction (HER) perquè el single site catalyst requereix la unió de l’hidrogen a la part superior. En aquesta tesi s’han aplicat mètodes DFT i conceptes electroquímics per tal d’entendre els processos de reducció de CO2. Al tercer capítol es descriu la importància de les característiques estructurals del single site catalyst, juntament amb els conceptes relacionats amb la química de coordinació necessaris per a entendre l’activitat del catalitzador en la reacció electroquímica de reducció del CO2 (eCO2RR). L’objectiu del capítol 4 és establir correlacions experimentals i teòriques entre les propietats fisicoquímiques i catalítiques de la eCO2RR que dona com a producte CO per al catalitzador del MNC. El procés de reconstrucció de les nanopartícules de Ni mitjançant la desintegració de Ni(CO)2 en materials de carboni dopats amb N es descriu al capítol 5. Per últim, en el capítol 6 es descriu la selectivitat dels productes de reducció de CO2 tenint en compte com afecta el potencial i la temperatura sobre el catalitzador modelat de CoTPP/MWCNT.El desarrollo de la electroquímica tiene el potencial de utilizar el CO2 como materia prima para la producción sostenible de compuestos y materiales y tiene un gran impacto en la industria química. El catalizador “de sitio único” (single site catalyst) es un material prometedor para lograr una elevada actividad y selectividad hacia CO e hidrocarburos C1. La estructura única de este catalizador derivado de carbono reduce la competencia de estos procesos con otros procesos catalíticos como la reacción hydrogen evolution reaction (HER) porque el single site catalyst requiere la unión de hidrógeno en la parte superior. En esta tesis, métodos DFT y conceptos electroquímicos computacionales han sido aplicados para entender los procesos de reducción de CO2. En el capítulo 3 se describe la importancia de las características estructurales del single site catalyst, además de los conceptos relacionados con la química de coordinación que se aplican para comprender la actividad del catalizador en la reacción electroquímica de reducción de CO2 (eCO2RR). El objetivo del capítulo 4 es establecer correlaciones experimentales y teóricas entre las propiedades fisicoquímicas y catalíticas para la eCO2RR hacia CO para el catalizador del MNC. El proceso de reconstrucción de las nanopartículas de Ni mediante la desintegración de Ni(CO)2 en materiales de carbono dopados con N se describe en el capítulo 5. Por último, en el capítulo 6 se describe la selectividad de los productos de reducción de CO2 teniendo en cuenta cómo afecta el potencial y la temperatura sobre el catalizador modelado de CoTPP/MWCNT.
The development of electrochemistry has the potential to use CO2 as a feedstock for the sustainable production of chemicals and materials and it has an important impact on the chemical industry. Single site catalyst is a promising new material for achieving high activity and selectivity towards CO and C1 hydrocarbons. The unique structure of carbon-based catalyst makes it a good compressor of competing Hydrogen evolution reaction (HER) because the single site requires an ontop binding of hydrogen. In this thesis, I applied DFT methods and computational electrochemical concepts for understanding the processes of CO2 reduction (eCO2RR). In chapter 3 I described the importance of single-site structural features catalyst, besides the basic concept of the coordination chemistry that is applied to understand eCO2RR activity of the catalyst. The aim of chapter 4 was to establish experimental and theoretical correlations between physicochemical and catalytic properties for the eCO2RR towards CO for MNC catalyst. The process of reconstruction of Ni nanoparticles by the disintegration of Ni(CO)2 on N-doped carbon materials is described in chapter 5. Finally, in chapter 6 I unraveled the selectivity of CO2 reduction products that were influenced by potential and the temperature over modeled CoTPP/MWCNT catalyst.
17
Doherty, P. W. « The curriculum dimensions of student disaffection : a single site case study ». Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364969.
Texte intégral
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Teh, Aun Shih. « In-situ synthesis of single wall carbon nanotubes for electronic devices ». Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612322.
Texte intégral
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Kaczmarska, J. M. « Single-site point process-based rainfall models in a nonstationary climate ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1387820/.
Texte intégralRésumé :
Long series of simulated rainfall are required at point locations for a range of applications, including hydrological studies. Clustered point-process based rainfall models have been used for generating such simulations for many decades. One of their main advantages is the fact that they generate simulations in continuous time, allowing aggregation to different timescales in a consistent way, and such models generally perform well in representing rainfall at hourly to daily timescales. An important disadvantage, however, is their stationarity. Although seasonality can be allowed for by fitting separate models for each calendar month or season, the models are unsuitable in their basic form for climate impact studies. In this thesis we develop new methodology to address this limitation. We extend the current fitting approach by replacing the discrete covariate, calendar month, with continuous covariates which are more directly related to the incidence and nature of rainfall. The covariate-dependent model parameters are estimated for each time interval using a kernel-based nonparametric approach within a Generalised Method of Moments framework. An empirical study using the new methodology is undertaken using a time series of five-minute rainfall data. In addition to addressing the need for temporal non-stationarity, which is our main focus, we also carry out a systematic comparison of a number of key variants of the basic model, in order to identify which features are required for an optimal fit at sub-hourly resolution. This generates some new insights into the models, leading to the development of a new model extension, which introduces dependence between rainfall intensity and duration in a simple way. The new model retains the “rectangular pulses” (i.e. rain cells with a constant intensity) of the original clustered point-process model, which had previously been considered inappropriate for fine-scale data, obviating the need for a computationally more intensive “instantaneous pulse” model.
20
Femino, Andrea M. « Visualization of Single RNA Transcripts in situ : A Dissertation ». eScholarship@UMMS, 2001. http://escholarship.umassmed.edu/gsbs_diss/193.
Texte intégralRésumé :
Fluorescence in situ hybridization (FISH) and digital imaging microscopy were modified to allow detection of single RNA molecules. Oligodeoxynucleotide probes were synthesized with five fluorochromes per molecule and the light emitted by a single probe was calibrated. Points of light in exhaustively deconvolved images of hybridized cells gave fluorescent intensities and distances between probes consistent with single mRNA molecules. Analysis of β-actin transcription sites after serum induction revealed synchronous and cyclical transcription from single genes. The rates of transcription initiation and termination and mRNA processing could be determined by positioning probes along the transcription unit. This approach extends the power of FISH to yield quantitative molecular information on a single cell.
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FREGATTI, PIERO. « No Ink on Ductal Carcinoma in Situ : A Single Centre Experience ». Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1010024.
Texte intégralRésumé :
Abstract
Introduction: The incidence of ductal carcinoma in situ (DCIS) of the breast has greatly increased thanks to the widespread use of screening mammography. The primary aim of surgery is to prevent local recurrence by achieving a clear margin of resection although its extent still represents a controversial issue. Hence, a retrospective analysis of patients undergoing surgery for DCIS was performed in order to assess the association of margin widths of < 1 mm, 1 to 2 mm, and > 2 mm with ipsilateral breast tumor recurrence (IBTR) considering also the potential role of host-, tumor- and treatment-related factors.
Methods: From 2000 to 2016, 388 patients diagnosed with pure DICS undergoing BCS with or without post-operative RT at the Breast Unit of “Ospedale Policlinico San Martino” in Genoa were selected. The pathologic analysis was always performed according to a standardized protocol including the measure of the microscopic distance to the nearest radial margin: positive margins were those with DCIS present at the inked margin; close margins were considered to have tumor between 0.1 to 0.9 mm, or 1 to 1.9 mm, and negative margins were > 2 mm.
Results: At a median follow-up of 90 months there were 26 IBTR (10 invasive and 16 DCIS). In univariate analysis there was a significant difference in IBTR by comparing positive versus close/negative margins of excision (P = 0.05) and the number of re-operations (P = 0.000). On multivariate analysis, both the margin status (P = 0.002) and the number of re-operations (P < 0.001) were still significantly associated with IBTR. The actuarial IBTR rates were significantly different in patients with a positive margin of excision at the primary operation as compared to patients with close/negative margins (log-rank test, P = 0,042) while the stratification by the margin width (0.1-0.9 mm; 1.0-1.9 mm; > 2 mm) was not significant (log-rank test, P = 0,243).
Conclusions: The policy of “no ink on the tumor” that is well accepted for invasive breast cancer can be translated to DCIS, because the actuarial IBTR rates were significantly different only in patients with a positive margin of excision as compared to patients with close/negative margins.
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McKittrick, Michael W. « Single-Site Olefin Polymerization Catalysts via the Molecular Design of Porous Silica ». Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6871.
Texte intégralRésumé :
The major goals of this work were to: develop a new methodology for the preparation of site-isolated catalytic sites on a silica surface, prepare the first truly single-site supported metallocene/CGC polymerization catalyst, and develop structure-reactivity relationships for these new systems.
To synthesize these novel catalysts, the approach taken was to develop a protocol which allows for the synthesis of an aminosilica material with isolated, uniform amine sites. This patterned aminosilica was then used as a scaffold to support a constrained geometry catalyst. These functionalizations occurred at essentially a quantitative level, in stark contrast to previous literature reports. The patterned catalysts were evaluated in the polymerization of ethylene and compared to densely loaded literature materials. Overall, it was found the patterned materials were 5-10 times more active than traditional immobilized CGC catalysts.
The patterned catalysts were also found to be effective catalysts for the copolymerization of norbornenes (including functionalized norbornenes) and ethylene, the first reported use of a tethered CGC for the production of ethylene-norbornene copolymers. The control materials were inactive in these polymerizations, providing further evidence that the patterning protocol allows for the synthesis of unique highly active, isolated catalytic sites.
Various structural components of the immobilized CGC developed in this work were tested for their impact on catalyst synthesis and reactivity in ethylene polymerizations. The results showed the patterned materials in general behaved according to the trends seen in homogeneous CGC polymerizations. These results, while congruent with similar homogeneous CGC studies, are in direct conflict with previous work on supported CGCs reported in the literature. This discrepancy is likely the result of the difference between the isolated, possibly single-site patterned catalysts developed in the course of this work and the multi-sited catalysts prepared by traditional supporting protocols. This also further illustrates the difficulty in developing structure-reactivity relationships when ill-defined solid catalysts are used.
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Hawthorne, Wendy, et n/a. « Classroom encounters and mathematics curriculum change : a single-site school improvement study ». University of Canberra. Education, 1988. http://erl.canberra.edu.au./public/adt-AUC20060720.152732.
Texte intégralRésumé :
In November, 1986, Mrs Lorna Ireland; Principal of Junee Primary School in the
Riverina Region of New South Wales; approached a Senior Lecturer in Mathematics
Education at Riverina-Murray Institute of Higher Education in Wagga Wagga; seeking
his involvement in a project aimed to assist teachers at the school with their
mathematics teaching. In addition to the planned involvement in 1987 of this
mathematics educator, the school was also to be a pilot school for the trialling of a
strand of the New South Wales Education Department's Draft Mathematics Curriculum
and a participating school in the numeracy component of the federal government's
Basic Learning in Primary Schools program.
This study documents the mathematics education activities which involved Junee
Primary School teachers in 1987. It focuses on the RMIHE involvement in the school
but considers this in the context of broader mathematics curriculum activity. The
process of change is described within a theoretical framework derived from a review
of relevant literature.
The research methodology employed is fundamentally ethnographic and relies on the
collection of qualitative data to derive descriptions of people and events. The data
analysis relates to curriculum change, the role of the change agent and the role of
mathematics educators in school mathematics programs. A discussion of outcomes
highlights the strengths of an approach to curriculum change which had its genesis in
the school rather than in some external agency. The generation of problems and issues
and the resolution of these are features of the analysis which tracks the progress
towards professional development autonomy of one group of teachers.
24
Emsley, Margaret W. « A model to optimize single tower crane location within a construction site ». Thesis, Loughborough University, 2001. https://dspace.lboro.ac.uk/2134/7560.
Texte intégralRésumé :
This thesis describes the development of a descriptive mathematical model to determine the optimum position of a single tower crane. The objective function of the model is that of minimization of total travel time necessary to complete all movements from the installation of the crane until it is dismantled and removed. Previous models which have been developed to determine optimum crane selection and location are categorized as simulation models, expert systems and mathematical models and three particular models are credited as making contributions to the problem of tower crane location. However, the model developed here overcomes many of the deficiencies exhibited by these models. In developing a model to determine optimum tower crane location, the characteristics of the construction site in which it will be placed and those of the crane itself must be considered separately. The most challenging and significant problem is in determining the total number of movements which will occur during the time when a particular crane is installed on a particular site. The method adopted was the application of a linear programming technique, the Simplex Method. Once the (computer) model had been developed a wide range of simulations were carried out to see if any general truth concerning the optimum layout could be evinced. The result of these simulations demonstrated that there are potentially significant savings to be made, in terms of the time to complete all movements, by locating the crane in the optimum position rather than in one where the maximum time to complete all movements occurs. Typical savings were in the order of 30% but situations where the time savings were in excess of 100% and even 200% were not uncommon. The layout configuration was shown to have very little influence on the magnitude of the minimum time to complete all movements. And these optimum positions were found to consistently occur at the site perimeter, very often at the corners, whilst the positions associated with the maximum times were consistently located internally. However, when the cost implications of locating the crane at the perimeter, which necessitates the use of a crane with a longer jib than would be necessary were the crane located internally, were taken into account, it was shown that, in terms of cost benefits, the cheaper option is to use the crane with a short a jib as is viable for the purposes of reaching the points the crane is required to service, and locate the crane internally. Finally, neural networks were shown to have potential as a tool to predict optimum crane location, but further work is needed to produce a working model.
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Pettersson, John. « Single Molecule Studies of hGSTA1-1 : Binding Kinetics and Active Site Dynamics ». Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/620.
Texte intégralRésumé :
The human detoxification enzyme glutathione s-transferase alpha 1 (GSTA1-1) is known for its ability to conjugate a variety of different hydrophobic xenobiotics to the tripeptide glutathione. The conjugation can be catalyzed through either a substitution or an addition reaction. Which reaction mechanism is being used affects the cooperativity of the enzyme. GST is also capable of catalyzing isomerization reactions of particular substrates without conjugation to GSH which further extends its repertoire. The C-terminal of the enzyme transitions from a random loop to an α-helix that localizes over the active site as a ligand binds. The α-helix is also involved in product release. We hypothesize that the broad substrate specificity and the catalytic flexibility of GST is a result of a heterogeneous protein population where multiple conformers with different properties coexist. To identify different conformers in a population a single molecule approach is needed. Fluorescently tagged substrates and products of GSTA1-1 have been imaged as they bind immobilized GSTA1-1 using TIRF microscopy. Single molecule binding events can be analyzed to characterize different binding states of the enzyme. The observation of at least two average occupancy times suggests that there are multiple binding states and conformations of the enzyme. One of these binding states is dominating the population and a large number of binding events has to be sampled to pick up the more rare states. To further characterize the behavior of GSTA1-1 FRET and DEER have been used to study the active site dynamics during binding of a ligand. Unlike X-ray crystallography, DEER and FRET provide a distribution in a distance between groups, and not just an average. Our data suggest that binding of S-hexylglutathione does not localize the C-terminal helix which is contrary to what can be observed in the X-ray crystal structure. Glutathione alone is sufficient to localize the helix. This highlights the importance of using proteins in solution to study their conformation.
26
Rodriguez, Sarah Marie Budde. « Sensitivity of Alternaria Species to Ten Single-Site Mode of Action Fungicides ». Diss., North Dakota State University, 2020. https://hdl.handle.net/10365/31815.
Texte intégralRésumé :
Early blight caused by Alternaria solani and brown spot caused by the small-spored Alternaria spp., Alternaria alternata, Alternaria arborescens, and Alternaria tenuissima are observed annually in midwestern potato production areas. The use of foliar fungicides remains a primary management strategy. However, Alternaria spp. have developed reduced-sensitivity and/or resistance to many single-site fungicides such as quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI), and anilinopyrimidines (AP) fungicides in recent years.
Boscalid, fluopyram, solatenol, and adepidyn are EPA-registered SDHI fungicides applied commercially to a variety of crops including potato. High intrinsic activity was observed in fluopyram, solatenol and adepidyn to A. solani isolates. Adepidyn and solatenol reduced disease severity caused by A. solani in field evaluations. Molecular characterization of 2018 A. solani field isolates determined that the frequency of the D123E and H134R SDH mutations increased. In contrast, the H278R/Y and H133R SDH mutations were found at low frequency.
Adepidyn demonstrated the highest intrinsic activity against the small-spored Alternaria spp. but high intrinsic activity was also observed with boscalid, fluopyram, and solatenol. In vivo experiments demonstrated that adepidyn, solatenol, and fluopyram were more effective at managing A. arborescens and A. tenuissima than boscalid. Under greenhouse conditions, adepidyn and solatenol reduced brown spot severity caused by A. alternata to a greater extent than did fluopyram and boscalid. Results of these studies determined that accurate pathogen identification of small-spored Alternaria spp. may be important for brown spot management.
Fludioxonil and cyprodinil exhibited a higher efficacy against of A. solani isolates when compared to pyrimethanil in greenhouse assays. Fludioxonil and cyprodinil were also highly efficacious against the Alternaria spp. evaluated and appear to be a good addition into fungicide rotation programs for early blight and brown spot management. Anilinopyrimidine (AP) (pyrimethanil and cyprodinil) and phenylpyrrole (PP) (fludioxonil) fungicides have demonstrated high intrinsic activity against other pathogens. Determining the efficacy of these fungicides on Alternaria spp. is important to the potato industry.
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Uprety, Bibek. « Site-Specific Metallization of Multiple Metals on a Single DNA Origami Template ». BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/8808.
Texte intégralRésumé :
This work examines the selective deposition of two different metals on the same DNA origami template for nanofabrication. DNA, with adjustable size and shape serves as a suitable template for fabricating metal junctions in the nanometer domain via bottom-up assembly. Bottom-up assembly utilizes the recognition capability of molecules like DNA to self-assemble and form structures. In this regard, DNA origami provides a useful means for forming nanostructures by folding single-stranded DNA into different two and three dimensional shapes. Selective deposition of metal on specific locations of a DNA template is essential for making DNA-templated electronic circuits.Site-specific metallization of DNA origami templates was recently demonstrated, for a single metal at molecularly designated sites. This study addresses the next important step of depositing multiple metals on the same template. Specifically, it is an experimental study to demonstrate the gold-copper metal junction on a DNA origami template, and to understand the challenges associated with junction fabrication. DNA-templated circuit fabrication depends on the ability to deposit multiple components on a DNA template. To achieve this, a section of the DNA template was seeded with Au nanoparticles and electrolessly plated with Au. This Au plated section of the template was then masked with an organic layer to protect it from additional deposition. The remaining section of the same template was subsequently seeded with Pd and plated with copper to form the desired metal junction. This work is the first of its kind to demonstrate metal junctions on a DNA origami template. Metallized origami templates were characterized with the help of SEM imaging and EDX composition data to confirm the presence of the two different metals on the same template. In addition, a chemical “mask” was also used successfully at nanometer resolution to protect previously metallized sites (gold plated) to prevent further metal deposition. The results obtained represent important progress toward the realization of DNA-templated components for nano-circuit fabrication. The work also provides the basis for the next step to make metal-semiconductor junctions on a DNA template.
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Beuzer, Paolo. « Characterization of replication fork barriers at a single site in mammalian cells ». Paris 6, 2013. http://www.theses.fr/2013PA066012.
Texte intégralRésumé :
Les voies de réplication et de réparation de l'ADN coopèrent pour surmonter la présence de barrières au niveau des fourches de réplication (RFB pour Replication Fork Block) qui entravent leur progression. Comprendre les mécanismes permettant de surmonter de telles RFB est particulièrement important compte tenu de l’instabilité génétique et épigénétique qui peuvent en découler. À ce jour, des études ont permis de documenter les RFB endogènes. Ici, nous utilisons les systèmes LacO/LacI et TetO/TetR pour générer des RFB artificielles mais inductibles, dans des cellules de mammifères. Ainsi, nous avons pu montrer que la liaison à l'ADN des protéines LacI et TetR peut bloquer, dans différentes lignées cellulaires de mammifères, la progression des fourches de réplication lorsqu'elle est liée à une série de répétitions insérées dans l’ADN. La liaison de ces protéines à l’ADN au cours de la réplication conduit à une persistance locale des foyers de réplication, à l’activation de la voie de réparation aux dommages à l’ADN (DDR pour DNA Damage Response), et à l'apparition de phénotypes de réplication incomplète comme des micronoyaux et des ponts d'ADN après la mitose. De plus, nous montrons que la DDR provoquée par la liaison de LacI et TetR favorise le recrutement de protéines impliquées dans la réparation de cassures double brin comme TOPBP1 et 53BP1, et la phosphorylation de H2A. X. Dans cette étude nous décrivons une RFB artificielle et inductible dans des cellules de mammifères qui peut ainsi être exploitée pour analyser la mise en place d'une RFB et la manière de la surmonter. Nous discutons ici nos données obtenues grâce à ce modèle unique en fonction de ces deux aspectsDNA replication and repair pathways cooperate to overcome the presence of replication fork barriers (RFBs) that hinder replication fork progression. Understanding the mechanisms of RFB bypass is particularly important given the threat of genetic and epigenetic instability if RFBs are inappropriately handled. To date, studies related to RFBs have documented endogenous RFBs. Here we use the LacO/LacI and TetO/TetR systems to generate an artificial but inducible RFB in mammalian cells. We show that the DNA binding proteins LacI and TetR can block replication fork progression when bound to a series of repeats inserted in different mammalian cell lines. Protein binding during replication causes a prolonged persistence of replication foci at the site, induces a local DNA Damage Repair (DDR) response and the appearance of incomplete replication phenotypes such as micronuclei and DNA bridges after mitosis. We show that the DDR elicited by LacI and TetR binding promotes the recruitment of proteins involved in Double Strand Brake (DSB) repair such as TOPBP1 and 53BP1, and the phosphorylation of H2AX in 30% to 40% of cells. In this study we describe an artificial and inducible RFB in mammalian cells that can be exploited to analyze the establishment of a RFB and the way to overcome it. We discuss here our initial findings on both aspects with this unique model system
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Allan, Charlotte Sarah Moreis. « Computational mechanistic and stereochemical studies of single-site polymerisation catalysts and reactions ». Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/6160.
Texte intégralRésumé :
Computational investigations into four metal-centred polymerisation catalysts are presented. The work investigates how and why the catalysts behave as they do, focusing on specific interactions within the catalyst structure itself and also on the transition states involved in the polymerisation reactions. Density functional theory has been used to examine the effect of the metal, the role of the ligand and the interplay between the two. Each study addresses particular mechanistic and structural questions that have been raised during experimental investigations and that are difficult to answer experimentally. Chapter one provides a general overview of computational techniques used in chemical modelling. The specific methods used in this work are presented as well as a brief review of modern trends. Chapter two investigates an unusual pair of metal-hydrogen interactions in a tin bis(triazenide) complex. We have termed this double M-H interaction “bifurcated” and compared other systems in which this interaction is present (and often unidentified). A variety of computational techniques are used to analyse the nature of the interactions both in qualitative and quantitative terms. The third chapter investigates the mechanism of alkyl transfer in a magnesium bis(imino)pyridine complex. A number of mechanistic pathways are explored to explain the original report of non-electrophilic alkylation at a pyridine nitrogen. We consider in particular how the solvent and the role of other species in the reaction mixture may influence the mechanism. Chapter four describes the inversion of configuration occurring in a pseudo-C3- symmetric zirconium tris(phenolate) complex. Variable temperature NMR spectra and simulations complement DFT calculations to explore the mechanism of inversion. We question the long-held assumption that the inversion process is concerted. In chapter five, the polymerisation of rac-lactide by an aluminium salen-type system is investigated in detail through characterisation of the transition state structures. Specifically, we have aimed to explain the different behaviour of two structurally similar catalytic species’ which produce polymer of different tacticity. Application of a variety of additional computational techniques in a number of these studies supplements the density functional calculations. They provide insight into specific interactions in both starting materials and transition states and detailed information about the reaction mechanisms.
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Williams, Benjamin Deeter. « Uranium contamination of vadose zone sediments from the Hanford U single shell tank farm ». Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Fall2009/B_Williams_112709.pdf.
Texte intégralRésumé :
Thesis (M.S. in environmental science)--Washington State University, December 2009.Title from PDF title page (viewed on Jan. 26, 2010). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 48-51).
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Lorieux, Louis. « Analysis of train ‐ induced vibrations on a single ‐ span composite bridge ». Thesis, KTH, Bro- och stålbyggnad, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37021.
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Carlberg, Konstantin. « In Situ RNA Quality Control : A spatial heat map of RNA integrity with single cell resolution ». Thesis, KTH, Skolan för bioteknologi (BIO), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176873.
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The quality of RNA is of great importance in gene expression studies. It is mostly measured using the RNA integrity number (RIN). Lately it has been shown that samples with low RIN and different fragmentation patterns could affect quality of sequencing data. For such low RIN samples a new approach has been developed by Illumina called the DV200 metric, which is the percentage of fragments >200 nucleotides. For samples with low RIN, DV200 has proved to be a better method to predict if good quality data from RNA sequencing can be generated. However, neither RIN nor DV200 provide spatial infromation on the RNA integrity. Thus, tissues with areas of heterogeneous RNA integrity, where regions of good quality RNA sequencing data could be generated from are missed. We have designed a method to spatially evaluate the RNA integrity in tissue, which we named in situ RNA QC. The method uses three probes with three different fluorophores, each bound to three specific cDNA regions synthesized from the high abundant and well conserved 18S rRNA. With the help of in-house technology from the Spatial Transcriptomics (ST) group at SciLifeLab, we enable creation of heat maps over the RNA integrity to show spatial fragmentation patterns of RNA in tissue. This could reveal the regional quality of transcripts in situ, which is crucial knowledge when selecting samples for further RNA sequencing. The assay has been tried using different tissue fixation methods in order to show a proof of concept that formalin gives shorter cDNA fragments than acetone. The generated heat-map provides a visual overview of RNA integrity in situ; hence this method could be used to select samples for sequencing by evaluation the spatial quality of RNA. For instance from fresh frozen and formalin fixated paraffin embedded (FFPE) tissue (biobanks contain large number of longterm storage FFPE samples). With this assay we will be able to determine which samples are suitable for sequencing.
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Favre, Anne-Catherine. « Single and multi-site modelling of rainfall based on the Neyman-Scott process / ». Lausanne : EPFL, 2001. http://library.epfl.ch/theses/?nr=2320.
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Grundberg, Ida. « Genotyping and Mutation Detection In Situ : Development and application of single-molecule techniques ». Doctoral thesis, Uppsala universitet, Molekylära verktyg, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-149776.
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The human body is composed of trillions of cells closely working together to maintain a functional organism. Every cell is unique in molecular composition and can acquire genetic variations that might cause it to turn pathological. It is essential to develop improved tools to better understand the development of normal and disease tissue, ideally enabling single-cell expression studies in preserved context of complex tissue with single-nucleotide resolution. This thesis presents the development and application of a new in situ method for localized detection and genotyping of individual transcripts directly in cells and tissues. The described technique utilizes padlock probes and target-primed rolling circle amplification and is highly suitable for sensitive in situ analysis. First, a new strategy for directed cleavage of single stranded DNA was investigated, e.g. nucleic acid targets with extended 3´ ends, for successful initiation of rolling circle amplification. The presented cleavage strategy is simple and applicable for subsequent enzymatic reactions, e.g. ligation and polymerization. Specific cleavage of long target overhangs was demonstrated in synthetic oligonucleotides and in genomic DNA and the detection efficiency was substantially increased. For multiplex detection and genotyping of individual transcripts in single cells, a new in situ method was developed. The technique showed a satisfactorily detection efficiency and was later applied as a general mutation analysis tool for detection of KRAS point mutations in complex tumor tissue sections, e.g. formalin-fixed, paraffin-embedded tumor tissues and cytologic tumor imprints. Mutation status was assessed in patient samples by in situ padlock probe detection and results were confirmed by DNA-sequencing. Finally, the method was adapted for simultaneous detection of individual mRNA molecules and endogenous protein modifications in single cells using padlock probes and in situ PLA. This assay will be useful for gene expression analysis and exploration of new drugs with vague effector sites. To our knowledge, no other technique exists today that offers in situ transcript detection with single-nucleotide resolution in heterogeneous tissues. The method will especially be suitable for discrimination of highly similar transcripts, e.g. splice variants, SNPs and point mutations, within gene expression studies and for cancer diagnostics.
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Rice, Gordon L. « Structure and reactivity of silica-supported vanadium and vanadium/titanium single-site catalysts ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0020/NQ46540.pdf.
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Vadhavkar, Sameer S. « Polymerization of methyl acrylate and as comonomer with ethylene using single-site catalysts / ». Online version of thesis, 2008. http://hdl.handle.net/1850/6135.
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Hodson, Mark James. « Use of single molecule methods to reveal the mechanisms of splice site selection ». Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/11072.
Texte intégralRésumé :
Understanding the molecular mechanisms that allow splice site selection is of fundamental importance to the study of alternative splicing. The study presented here has focused on the interactions of two spliceosomal trans-acting factors with pre-mRNA. The U1 snRNP is very important in 5’ splice site selection. However, how binding of U1 snRNP to pre-mRNAs containing multiple 5’ splice sites leads to 5’ splice site selection is unknown. To investigate the role of U1 snRNP in 5’splice site selection, single molecule microscopy was used to determine the number of U1 snRNPs bound to a single molecule of pre-mRNA. In cases where multiple strong 5’ splice sites are competing the furthest downstream 5’ss is used. In these cases, as many U1 snRNPs were observed bound to the pre-mRNA at an early stage of the reaction as there were 5’ splice sites, demonstrating that multiple sites were occupied. However, later pre-spliceosomal complexes contained only one U1 snRNP, indicating that the surplus U1 snRNP had been removed. A novel model of 5’ splice site selection is presented, in which U1snRNP stimulates the binding of SR proteins to the pre-mRNA and thus increases exon rigidity, enforcing use of the downstream 5’ splice site. The U2 Auxiliary Factor (U2AF), binds to the polypyrimidine tract and 3’ splice site of an intron and is a hetrodimer of the U2AF65 and U2AF35 subunits. The length of the polypyrimidine tract has been shown to influence the efficiency with which a 3’splice site is spliced. To investigate the role of polypyrimidine tract length on U2AF binding, experiments have been conducted in which the binding of U2AF65 to pre-mRNAs has been analysed using single molecule microscopy. Through the analysis of constructs derived from the Globin C pre-mRNA, the mechanisms of U2AF65 association with pre-mRNA have been shown to comprise; (i) a non-specific association that occurs with all RNA tested in the absence of ATP, (ii) a U1 snRNP-dependent association with pre-mRNAs in a polypyrimidine tract-independent manner, and (iii) an association with pre-mRNA in a polypyrimidine tract-dependent manner.
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Marmodoro, A. « Beyond single-site disorder effects in first-principles studies of solid state systems ». Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/46881/.
Texte intégralRésumé :
A generalization of the non-local coherent potential approximation (NL-CPA) for the treatment of short range ordering (SRO) effects in complex unit cell solids with different forms of disorder is proposed. The method is discussed with respect to fully first-principles Korringa, Kohn and Rostoker multiple scattering theory, and a tight-binding model hamiltonian. Examples from the context of applications to metallic alloys, diluted magnetic semiconductors, and half-metals in the presence of antisite disorder are discussed.
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Lapen, Thomas J., Minako Righter, Rasmus Andreasen, Anthony J. Irving, Aaron M. Satkoski, Brian L. Beard, Kunihiko Nishiizumi, A. J. Timothy Jull et Marc W. Caffee. « Two billion years of magmatism recorded from a single Mars meteorite ejection site ». AMER ASSOC ADVANCEMENT SCIENCE, 2017. http://hdl.handle.net/10150/623275.
Texte intégralRésumé :
The timing and nature of igneous activity recorded at a single Mars ejection site can be determined from the isotope analyses of Martian meteorites. Northwest Africa (NWA) 7635 has an Sm-Nd crystallization age of 2.403 +/- 0.140 billion years, and isotope data indicate that it is derived from an incompatible trace element-depleted mantle source similar to that which produced a geochemically distinct group of 327-to 574-million-year-old "depleted" shergottites. Cosmogenic nuclide data demonstrate that NWA 7635 was ejected from Mars 1.1 million years ago (Ma), as were at least 10 other depleted shergottites. The shared ejection age is consistent with a common ejection site for these meteorites. The spatial association of 327-to 2403-Ma depleted shergottites indicates >2 billion years of magmatism from a long-lived and geochemically distinct volcanic center near the ejection site.
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Amanov, Ernar [Verfasser]. « Designing a robotic port system for laparo-endoscopic single-site surgery / Ernar Amanov ». Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2019. http://d-nb.info/1219652229/34.
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Lim, Leonard Lik Pueh. « In-situ photocatalytic remediation of organic contaminants in groundwater ». Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/238767.
Texte intégralRésumé :
This research is about the development of a photocatalytic reactor design, Honeycomb, for in-situ groundwater remediation. Photocatalysis, typically a pseudo first order advanced oxidation process, is initiated via the illumination of UVA light on the catalyst, i.e. titanium dioxide (TiO2). In the presence of oxygen, highly reactive oxidising agents are generated such as superoxide (O2-), hydroxyl (OH.-) radicals, and holes (hvb+) on the catalyst surface which can oxidise a wide range of organic compounds. The target contaminant is methyl tert butyl ether (MTBE), a popular gasoline additive in the past three decades, which gives the water an unpleasant taste and odour at 20 μg L-1, making it undrinkable. This research consists of three major parts, i.e. (i) establishing a suitable catalyst immobilisation procedure, (ii) characterisation and evaluation of reactor models and (iii) scale up studies in a sand tank. TiO2 does not attach well onto many surfaces. Therefore, the first step was to determine a suitable immobilisation procedure by preparing TiO2 films using several potential procedures and testing them under the same conditions, at small scale. The coatings were evaluated in terms of photocatalytic activity and adhesion. The photocatalytic activity of the coatings was tested using methylene blue dye (MB), which is a photocatalytic indicator. A hybrid coating, which comprises a sol gel solution enriched with Aeroxide TiO2 P25 powder, on woven fibreglass exhibited the best adhesion and photocatalytic activity among samples evaluated. Thus, it was used to produce immobilised catalyst for this research. Consequently, the immobilisation procedure was scaled up to synthesize TiO2 coatings for the potential photocatalytic reactor design. The photocatalytic activity of the coatings produced from the scaled up immobilisation procedure were reasonably comparable to that produced at small scale. Due to the UVA irradiation and mass transfer limitations, photocatalytic reactors are typically compact in order to maximise their efficiency to accommodate high flows, particularly in water and wastewater treatment. In the case of groundwater, however, the treatment area can span up to meters in width and depth. Groundwater flow is significantly lower than that of water treatment, as the reactor design does not need to be compact. Considering both factors, a photocatalytic reactor design of hexagonal cross-section (Honeycomb) was proposed, in which the structures can be arranged adjacent to each other forming a honeycomb. A model was constructed and tested in a 4 L column (cylindrical) reactor, using the MB test to characterise the reactor performance and operating conditions. This was followed by a hydraulic performance study, which encompasses single and double pass flow studies. The single pass flow study involves the photocatalytic oxidation (PCO) of MB and MTBE, while the double pass flow study was focused on the PCO of MTBE only. The double pass can simulate two serially connected reactors. Single pass flow studies found that the critical hydraulic residence time (HRT) for the PCO of MB and MTBE is approximately 1 day, achieving up to 84 % MTBE removal. Critical HRT refers to the minimum average duration for a batch of contaminant remaining in the reactor in order to maintain the potential efficiency of the reactor. Double pass studies showed the reactor can achieve up to 95 % MTBE removal in 48 hours, and that reactor performance in the field of serially connected reactors can be estimated by sequential order of single pass removal efficiency. In groundwater, there are likely to be other impurities present and the effects of groundwater constituents on the reactor efficiency were studied. The MTBE PCO rate is affected by the presence of organic compounds and dissolved ions mainly due to the competition for hydroxyl radicals and the deactivation of catalyst surface via adsorption of the more strongly adsorbed organic molecules and ions. Despite the presence of organic compounds and dissolved ions, the reactor achieved about 80 % MTBE removal in 48 hours. A double pass flow study showed that the overall efficiency of the photocatalytic reactor in the field can be estimated via sequential order of its efficiency in a single pass flow study using the actual groundwater sample in the laboratory. A sand tank was designed for the simulation of the clean up of an MTBE plume from a point source leakage using the 200 mm i.d. Honeycomb I prototype. Honeycomb I achieved up to 88.1 % MTBE removal when the contaminated groundwater flowed through (single pass) at 14.6 cm d-1. The critical HRT for Honeycomb I was also approximately 1 day, similar to that in the column reactor. The response of MTBE removal efficiency towards flow obtained in the column reactor and sand tank was generic, indicating that the reactor efficiency can be obtained via testing of the model in the column reactor. The presence of toluene, ethylbenzene and o-xylene (TEo-X) decreased the MTBE removal efficiency in both the sand tank and column reactor. The same set of catalyst and 15 W Philips Cleo UVA fluorescent lamp was operated for a total of about 582 h (24 d) out of the cumulative 1039 h (43 d) sand tank experiments, achieving an overall MTBE removal efficiency of about 76.2 %. The experiments in the column reactor and sand tank exhibited the reliability of the immobilised catalyst produced in this research. This research demonstrates the potential of Honeycomb for in-situ groundwater remediation and also proposes its fabrication and installation options in the field.
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Oliveira, Felipe Souza. « Crescimento de monocristais do sistema Sr1-xCaxTiO3 e estudo in situ da cinética de desoxigenação ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/97/97135/tde-29032017-103241/.
Texte intégralRésumé :
O titanato de estrôncio é um dielétrico com elevada energia de gap entre a banda de va-lência e a banda de condução, porém quando alguns íons de oxigênio são removidos de sua estrutura cristalina, o composto se torna um semicondutor dopado do tipo n com um regime de ionização de impurezas diferente dos outros semicondutores convencionais. Além disto, o composto exibe uma supercondutividade anômala que diverge da teoria BCS no que diz respeito às interações elétron-fônon. Na medida em que o oxigênio é removido do cristal, a resistividade elétrica diminui no composto, sendo assim, este trabalho tem o objetivo de estudar a evolução do tratamento térmico que transforma o estado isolante em um semicondutor através de medidas de resistividade elétrica in situ durante o tratamento de desoxigenação de monocristais de titanatos de estrôncio crescidos pelo método Floating zone. Com o interesse de estudar as propriedades físicas do sistema Sr1-xCaxTiO3, amostras com diferentes teores de cálcio na faixa entre x = 0 e x = 0,05 foram preparadas e caracteriza-das por difratometria de raios X e medidas de calor específico. A cinética de desoxigena-ção é descrita por modelos matemáticos ajustados sobre pontos experimentais adquiridos nas medidas de resistividade elétrica in situ durante o tratamento térmico. Foi observado que a cinética de desoxigenação é de primeira ordem com energia de ativação de 1,4±0,1 eV, que concorda com os dados previamente reportados na literatura.Strontium titanate is a dielectric material with large energy gap between valence and con-duction bands. However, when some oxygen ions are removed from the crystal structure it becomes n-type semiconductor with an impurity ionization regime which differs from conventional semiconductors. Furthermore, this compound exhibits non-conventional su-perconductivity which can not be described by electron-phonon interaction predicted by BCS theory. When oxygen gets out from the sample electrical resistivity decreases. The goal of this work is study the deoxygenation kinetics during annealing which turns an insulator into a semiconductor using in situ electrical resistivity measurements during the thermal an-nealing of titanate single crystals grown by Floating zone Method. In order to study physical properties of Sr1-xCaxTiO3 system, samples with different cal-cium contents between x = 0 and 0.05 were prepared and characterized by X-ray difratom-etry and heat capacity. Deoxygenation kinetics were analyzed by models with fits the experimental data acquired at in situ electrical resistivity measurements. It was observed that deoxygenation kinetics is of first order with energy activation of 1,4±0,1 eV The estimated value for activation energy agrees with previously reported data.
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Albers, Isabel. « Homo- und Copolymerisation von Ethen und Styrol mit Metallocenen und weiteren Single-site-Katalysatoren ». [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965640922.
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Kusama, R., C. Liu et Y. Itoh. « COMPUTER SIMULATION OF ON-SITE FULL-SCALE TESTS OF SINGLE-SLOPE CONCRETE GUARD FENCES ». CI-PREMIER, 2005. http://hdl.handle.net/2237/18882.
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Schiantarelli, Harry Thornberry. « Performance analysis of high frequency single-site-location antenna arrays using numerical electromagnetic modeling ». Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA240868.
Texte intégralRésumé :
Thesis (M.S. in Electrical Engineering and M.S. in Systems Engineering (Electronic Warfare))--Naval Postgraduate School, September 1990.Thesis Advisor(s): Adler, Richard W. Second Reader: Jauregui, Stephen. "September 1990." Description based on title screen as viewed on December 18, 2009. DTIC Descriptor(s): Electronic Support Measures, Direction Finding, Propagation, Warfare, Models, Performance Tests, Paths, Theses, Reflection, Vertical Orientation, Electromagnetic Radiation, Coordinates, Communication And Radio Systems, Radio Waves, Antenna Arrays, Law Enforcement, Ionospheric Propagation, Triangulation, Mathematical Models, Ionosphere. Author(s) subject terms: Single-Sight-Location, Direction Finding, High Frequency, Numerical Electromagnetics Code. Includes bibliographical references (p. 116). Also available in print.
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Nishijima, Yoshinori. « Effects of single-site and multi-site ventricular pacing on left and right ventricular mechanics and synchrony is there an optimal pacing sequence ? / ». Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1126717344.
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Nikolou, Maria. « In-situ spectroscopic studies of single-walled carbon nanotubes and conjugated polymers in electrochromic devices ». [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012152.
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Theurkauff, Gabriel. « Investigations on the stereoselective polymerization of α-olefins by single-site group IV metal catalysts ». Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S158/document.
Texte intégralRésumé :
Les travaux présentés dans ce manuscrit ont trait à la catalyse de polymérisation des α-oléfines sont présentés en 4 parties distinctes. La première est consacrée à l'étude d'un système catalytique pour la production de polypropylène élastomère. L'analyse poussée des polymères produits et la caractérisation complète des catalyseurs utilisés a permis de montrer la présence de deux homopolymères sous forme de blende. La seconde partie porte sur la copolymérisation de monomères bifonctionnels vinyl-vinylidène avec le propylène. La caractérisation des polymères a permis de révéler la réactivité particulière des liaisons vinylidène et d'étudier l'influence du catalyseur utilisé sur le mécanisme de la polymérisation. La troisième partie s'intéresse à la caractérisation des espèces active en polymérisation et à l'étude des mécanismes d'activation et de désactivation des catalyseurs métallocènes. La synthèse et la caractérisation d'espèces cationiques, l'étude de leur comportement dynamique en solution, ainsi que l'évaluation de leur productivité en polymérisation ont permis d'établir un lien entre les propriétés électrophiles de ces espèces et de leur activité en polymérisation. La dernière partie porte sur l'homopolymérisation d'α-oléfines encombrées. La recherche d'un catalyseur suffisamment productif nous a amené à tester plusieurs catalyseurs présentant des structures différentes. L'absence de catalyseur productif soulève l'hypothèse d'interactions désactivantes entre le catalyseur et le monomèreThe work presented in the manuscript focus on α-olefin polymerization catalysis, and is divided into four distinct parts. The first part is dedicated to the study of catalytic systems for the production of elastomeric polypropylene. The analysis of the produced polymers and the characterization of the catalysts showed the presence of two homopolymers as a blend in the elastomeric polypropylene. The second part focuses on the copolymerization of bifunctionnal vinyl-vinylidene monomers with propylene. The characterization of the polymers revealed the reactivity of the vinylidène bonds and showed different polymerization mechanisms for the different catalysts. The third part reports a study on the activation and deactivation pathways of the active species in polymerization. The characterization of model cationic species and the study of their behavior in solution and in polymerization showed the relationship between the electrophilicity of the species and its productivity in propylene polymerization. The last part is dedicated to the polymerization of hindered α-olefins. The quest for a productive catalyst led to test various single site catalysts with different structures. Deactivating interactions between the monomers and the catalyst are supposed to explain the low productivity of the tested catalysts
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Spriggs, Elizabeth L. « Aneuploidy in human sperm, results of multicolour fluorescence in situ hybridization and single-sperm typing ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq20773.pdf.
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LeBlanc, Michel Joseph. « Interaction mechanics of embedded single-ended optical fibre sensors using novel in-situ measurement techniques ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/NQ41205.pdf.
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