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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Sintese van amino-arielaldehied verbindings / Marlene Prinsloo

Prinsloo, Marlene January 2015 (has links)
Die soeke na sterk hoë-verrigtingspolimere het gelei tot die idee om ʼn volledig gekonjugeerde polimeer te ontwikkel vir moontlike gebruik in die motorindustrie. Hierdie polimeer moet soortgelyke eienskappe as dié van Kevlar besit, aangesien die beoogde polimeer vir die bakwerk van battery-aangedrewe voertuie gebruik sou kon word. Die selfpolimerisasie van 4,6-diaminobenseen-1,3-dikarbaldehied is as die gewenste gekonjugeerde polimeer beskou. Tydens die studie is daar gefokus op die sintese van die monomeer 4,6-diaminobenseen- 1,3-dikarbaldehied. Die sintese van monomere wat beide funksionele groepe wat aan die polimerisasie deelneem, op dieselfde molekuul besit, was uitdagend, omdat hierdie monomere baie maklik selfpolimerisasie kan ondergaan. Hierdie studie het ook na groener en korter sinteseroetes om 4,6-diaminobenseen-1,3-dikarbaldehied of derivate daarvan te sintetiseer gekyk, aangesien die sintese van 4,6-diaminobenseen-1,3-dikarbaldehied in die verlede met baie lang sinteseroetes en gevaarlike chemikalieë uitgevoer is. Sintese van 1,5-dibromo-2,4-dimetielbenseen (1), 1,5-dibromo-2,4-bis(dibromometiel)- benseen (2), 4,6-dibromobenseen-1,3-dikarbaldehied (3) en 1,3-bis([1,3]dioksolaan)-4,6- dibromobenseen (5) is suksesvol uitgevoer, maar tydens die koper-gekataliseerde Ullmanntipe reaksies om 4,6-diaminobenseen-1,3-dikarbaldehied (4) te sintetiseer, het slegs poeiers gevorm wat nie oplosbaar in organiese oplosmiddels is nie. Om die selfpolimerisasie moontlikhede van 4 uit te skakel is 5 gesintetiseer. ʼn Poging om 1,3-bis([1,3]dioksolaan)- 4,6-diaminobenseen (6a) vanaf 5 te sintetiseer het egter tot geen reaksie gelei nie. Molekuulmodellering van die Ullmann-tipe reaksies om 6a en 4,6-dimetielbenseen-1,3- diamien te sintetiseer is gedoen om die reaksie te ondersoek. Daar is gevind dat ʼn 1,3- diketoonligand wat aan die koperkatalisator bind, nodig is om die reaksie te verbeter. Vanuit die resultate van die studie is ook gevind dat ʼn Ullmann-tipe reaksie nie met 5 sal plaasvind nie, aangesien dit energeties nie so voordelig is nie. Spektroskopiese analise van die poeiers wat tydens die sintese van 4 gevorm het, bevestig dat die poeiers polimere is. Dit blyk egter dat dit nie die voorgestelde rigiede polimeer is wat gevorm het nie, maar dat dit eerder ʼn amorfe kinasolientipe produk is. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015
12

Electostatic plasma edge turbulence and anomalous transport in SOL plasmas

Meyerson, Dmitry 06 November 2014 (has links)
Controlling the scrape-off layer (SOL) properties in order to limit divertor erosion and extend component lifetime will be crucial to successful operation of ITER and devices that follow, where intermittent thermal loads on the order of GW/m² are expected. Steady state transport in the edge region is generally turbulent with large, order unity, fluctuations and is convection dominated. Owing to the success of the past fifty years of progress in magnetically confining hot plasmas, in this work we examine convective transport phenomena in the SOL that occur in the relatively "slow", drift-ordered fluid limit, most applicable to plasmas near MHD equilibrium. Diamagnetic charge separation in an inhomogeneous magnetic field is the principal energy transfer mechanism powering turbulence and convective transport examined in this work. Two possibilities are explored for controlling SOL conditions. In chapter 2 we review basic physics underlying the equations used to model interchange turbulence in the SOL and use a subset of equations that includes electron temperature and externally applied potential bias to examine the possibility of suppressing interchange driven turbulence in the Texas Helimak. Simulated scans in E₀×B₀ flow shear, driven by changes in the potential bias on the endplates appears to alter turbulence levels as measured by the mean amplitude of fluctuations. In broad agreement with experiment negative biasing generally decreases the fluctuation amplitude. Interaction between flow shear and interchange instability appears to be important, with the interchange rate forming a natural pivot point for observed shear rates. In chapter 3 we examine the possibility of resonant magnetic perturbations (RMPs) or more generally magnetic field-line chaos to decrease the maximum particle flux incident on the divertor. Naturally occurring error fields as well as RMPs applied for stability control are known to cause magnetic field-line chaos in the SOL region of tokamaks. In chapter 3 2D simulations are used to investigate the effect of the field-line chaos on the SOL and in particular on its width and peak particle flux. The chaos enters the SOL dynamics through the connection length, which is evaluated using a Poincaré map. The variation of experimentally relevant quantities, such as the SOL gradient length scale and the intermittency of the particle flux in the SOL, is described as a function of the strength of the magnetic perturbation. It is found that the effect of the chaos is to broaden the profile of the sheath-loss coefficient, which is proportional to the inverse connection length. That is, the SOL transport in a chaotic field is equivalent to that in a model where the sheathloss coefficient is replaced by its average over the unperturbed flux surfaces. Both fully chaotic and the flux-surface averaged approximation of RMP application significantly lower maximum parallel particle flux incident on the divertor. / text
13

Ullmann etherification

Cox, Robert John January 2015 (has links)
Formation of the diaryl ether moiety remains a challenging target for organic synthesis despite modern technologies, however, better understanding of older techniques often leads to improvements. The copper-catalysed Ullmann ether synthesis, whilst attractive in many ways, is frequently problematic due to the inherent irreproducibility of the reaction on scale up. Little is yet known about the mechanism of the reaction and conflicting views are rife within the scientific community. In a well-studied example, we show that the potassium iodide formed during the reaction slows catalysis. Additionally, the deprotonation of phenol is complicated by the insolubility of the inorganic base. This results in a beneficial outcome, providing a rate enhancement and reduction of by-products, which can be further exploited to provide lower stoichiometries, improved selectivity and greater functional group tolerance. The development of an improved, more reproducible procedure in combination with reaction calorimetry has allowed the mechanism to be studied in intricate detail. Excellent agreement with a mechanistic model has led to further insight into the enigmatic aryl halide activation and provides good evidence for a single electron transfer mechanism. In addition, evidence for a dynamic catalyst resting state has been observed which adds to the complexity of the mechanism. This, in turn, leads to a fine balance of concentration and electronic effects that prove vital to the rate of reaction.
14

Re-Contextualizing Viktor Ullmann's "Der Kaiser von Atlantis" within Twentieth-Century German Opera

Buckton, Mindy Elicia 14 January 2014 (has links)
Viktor Ullmann’s opera Der Kaiser von Atlantis, composed in the Theresienstadt concentration camp in 1943-44, has received regular performances since its belated first performance in 1975. Research on this opera has largely been restricted to the confines of Theresienstadt, with limited connections made to the outside world. Nevertheless, when Ullmann’s work is viewed within the artistically evolving context of the interwar period – a formative era in Ullmann’s life – new light is shed on his artistic achievements. This era of change between 1919 and 1930 gave rise to new artistic movements such as Neue Sachlichkeit and produced the genres of Zeitoper, Brechtian Epic Theatre,” and Kabarett. Artists of staged works used their artistic freedom to challenge audiences, most obviously with techniques such as Bertolt Brecht’s “Verfremdungseffekt.” In the freedom of the newly established Republics, political commentary and the representation of contemporary life became the source material for libretti. It is within this era that we find the inspiration and source of Ullmann’s representation of Theresienstadt within Der Kaiser von Atlantis. Indeed, examining the opera within the context of the interwar period expands many elements beyond the representation of Theresienstadt. By investigating the inherent symbolisms within the opera to the spirit of the new Republics, we can re-contextualize the modest but growing place Der Kaiser von Atlantis holds in the operatic repertoire. For it is only by combining these two radically contrasting worlds – the freedoms associated with the artistic experiments in liberal democracy typical of the interwar period and the restrictions of detention in Theresienstadt at the hands of the National Socialists – that a robust understanding of the mastery of defiance and irony that is Der Kaiser von Atlantis becomes possible. / Graduate / 0413 / mbuckton@hotmail.com
15

Viktor Ullmann a jeho 3. smyčcový kvartet / Viktor Ullmann and his third string quartet

Petrásek, Daniel January 2016 (has links)
This thesis deals with Viktor Ullmann, a Czech-German composer of Jewish descent, and with his third string quartet. The text is arranged into three chapters. The first part describes Viktor Ullmann's life. His life is divided into two periods. The first period is delienated by the years 1898-1942 and the second one is focused on the last two years of the composer's life, 1942-1944, which he spent in Terezín concentration camp. The second chapter deals with Ullmann's third string quartet, which he composed in Terezín ghetto in the year 1943.
16

The Chemistry of Ynamide and its Application in Organic Synthesis

Siyu, Y., Wu, Na (Anna) 30 March 2021 (has links)
Yes / Ynamide, is an understudied but attractive class of alkynes, activated by the donating ability of the nitrogen adjacent to alkynes. With the nucleophilicity on β-carbon and the electrophilicity on α-carbon of ynamides, this review summarizes the syntheses of ynamides and miscellaneous reactions - oxidation, rearrangement, cyclization, and cycloaddition to construct complicated heterocyclic rings. The synthetic methodologies were further applied into natural products synthesis, e.g. marinoquinolines A and C, aplidiopsamine A, rigidin A, and 7-azaserotonin derivative. / We thank National Science Foundation of China (NSFC) (21462004), State Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources (CMEMR2014-A04), 2015 GXNSFBA (139032), GXNU, and Newton International Fellowship granted by Royal Society.
17

On-surface fabrication of functional molecular nanomaterials

Skidin, Dmitry 05 December 2019 (has links)
Polyzyklische organische Moleküle und deren Derivate sind eine Klasse von Nanostrukturen, die wegen diverser möglicher Anwendungen in molekularer und organischer Elektronik viel Aufmerksamkeit in der Wissenschaft erregt haben. Um ihre einzigartigen Eigenschaften in vollem Umfang auszunutzen, muss man das Verhalten von molekularen Systemen auf der Nanoskala verstehen und eine Reihe von Herstellungsverfahren entwickeln. In dieser Arbeit werden molekulare Nanostrukturen durch den Bottom-Up-Ansatz der Oberflächensynthese erzeugt. Als Untersuchungsmethode gilt Rastertunnelmikroskopie (STM) bei tiefen Temperaturen und im Ultrahochvakuum als Werkzeug der Wahl. Drei verschiedene molekulare Systeme werden ausführlich erforscht, mit dem Ziel organische Nanostrukturen mit gewünschten Eigenschaften und atomarer Präzision zu erzeugen. Im ersten Teil dieser Arbeit wird eine Cyclodehydrierungsreaktion erfolgreich für die Synthese von asymmetrischen Starphen verwendet. Es wird dann gezeigt, dass dieses Molekül als unimolekulares NAND-Logikgatter fungieren kann. Dabei wird die Positionierungsänderung der elektronischen Resonanz nach der Zufügung einzelner Goldatome an die Inputs des Moleküls gemessen. Eine Kombination aus atomarer und molekularer Lateralmanipulation mithilfe der Spitze des Rastertunnelmikroskops sowie Rastertunnelspektroskopie wird verwendet, um dieses Verhalten zu demonstrieren. Die steuerbare Verschiebung von molekularen Resonanzen entsteht wegen der asymmetrischen Form des Starphens und wurde theoretisch vorhergesagt. Molekulare Drähte werden im zweiten Teil der Arbeit durch die oberflächenassistierte Ullmann-Kupplung hergestellt. Ihr Baustein besteht aus abwechselnden Donor- und Akzeptorgruppen und wurde speziell vorgesehen, um leitfähige flexible molekulare Drähte herzustellen. Die Leitfähigkeit wird durch Ziehen einzelner Drähten von der Oberflächen mit der STM-Spitze gemessen. Theoretische Berechnungen der komplexen Bandstruktur der molekularen Drähte bestätigen die experimentellen Ergebnisse und unterstützen dabei die Wichtigkeit der Balance zwischen Akzeptor- und Donorgruppen für die Leitfähigkeit der Drähte. Basierend auf diesen Resultaten werden neue Strukturen zur Herstellung vorgeschlagen. Der letzte Teil befasst sich schließlich mit einer unimolekularen Reaktion, die zur Erzeugung einer anomalen Kombination von Pentagon- und Heptagonringen in einem einzelnen organischen Molekül führt. Solche 5-7-Einheiten sind analog zu Stone-Wales-Defekten in Graphen und können elektronische Eigenschaften beachtlich ändern. Die exakte intramolekulare Struktur der Reaktionsprodukte wird durch hochauflösende STM-Bildgebung mit funktionalisierter Spitze eindeutig zugeordnet und zusätzlich durch DFT-Rechnungen bestätigt. / Polycyclic organic molecules and their derivatives present the class of nanostructures that are currently in the focus of scientific research due to their perspectives for the versatile applications in molecular and organic electronics. To exploit their unique properties to full extent, one has to understand the behavior of molecular systems at the nanoscale and to develop a set of fabrication methods. In this work, molecular nanostructures are fabricated using the bottom-up on-surface synthesis approach, which allows precision of the desired products and control over their properties through careful precursors design. To study the reaction flow and the properties of the formed structures, scanning tunneling microscopy (STM) at low temperature and in ultra-high vacuum is the tool of choice. In this work, three molecular systems are studied in detail, with the focus of fabricating atomically precise nanostructures with tailored properties. A cyclodehydrogenation reaction is successfully applied to synthesize an asymmetric starphene molecule in the first part of the work. It is then shown that this molecule can function as a unimolecular NAND logic gate with its response to the attached single Au atoms measured as the position of the electronic resonance. A combination of the atomic and molecular lateral manipulation with the STM tip and scanning tunneling spectroscopy (STS) is used to demonstrate this behavior. The effect of the controllable shifting of the molecular resonances is due to the asymmetric shape of the starphene molecule and was initially predicted theoretically. More complex structures, molecular wires, are presented in the second part of the work by using the surface-assisted Ullmann coupling reaction. The monomer unit, consisting of the alternant donor and acceptor parts, was specifically designed to achieve highly-conductive flexible molecular wires. The conductance is measured by pulling the single wires with the STM tip off the surface. Theoretical calculations of the complex band structure of the wires confirm the obtained results and support the discussion of the importance of the balance between the strength of acceptor and donor units for the conductance of the resultant wires. Based on this, some model structures are proposed. Finally, the last part deals with a unimolecular reaction to create an anomalous combination of pentagon and heptagon rings in a single organic molecule. Such 5-7 moieties are analogous to the Stone-Wales defects in graphene and may significantly alter the electronic properties. The precise intramolecular structure of the reaction products is unambiguously assigned by high-resolution STM imaging with functionalized tips and further confirmed by DFT calculations.
18

Couplage en liquide ionique pour l'accès à des molécules macrocycliques d'intérêt biologique / Coupling in ionic liquid of molecules with biological interest

Jebri, Khouloud 08 December 2016 (has links)
Le présent travail décrit l'utilisation des liquides ioniques comme solvant de réaction dans plusieurs types de couplage permettant la création de liaisons C-C, C-N et C-O. Dans un premier temps, ces solvants ont permis d'effectuer la synthèse des a-oxo gamma-thio-esters via la réaction de condensation de Mukaiyama de l'énoxysilane du pyruvate d'éthyle sur des thioacétals. Dans le cadre d'une stratégie de synthèse multi-étape en liquide ionique, la synthèse des produits de départ a été également menée à bien dans ces solvants. Ensuite, une application des liquides ioniques dans la chimie des peptides a été décrite. Une série de di- et tri-peptides formés essentiellement par des dérivés de la tyrosine a été obtenue avec de bons rendements dans ces milieux ioniques, en ayant recours à des agents de couplage modernes tels que HATU et BOP. Une réactivité différente a été observée dans les liquides ioniques comparée à celle dans les solvants moléculaires classiques. Des sels de cuivre (I) et (II) ont été utilisés pour catalyser la réaction de couplage diaryl éther intermoléculaire dans les liquides ioniques, à partir des dérivés de la tyrosine afin d'obtenir des motifs isodityrosines. Le couplage d'Ullmann n'a pas été efficace à cause de la présence de contraintes électroniques et stériques, tandis que le couplage de Chan-Lam s'est révélé plus intéressant et il a permis d'obtenir les motifs isodityrosines avec des rendements satisfaisants. De plus, celui-ci présente l'avantage d'utiliser des conditions opératoires plus douces. / This thesis describes our studies regarding the organic synthesis in ionic liquids allowing the creation of C-C, C-N and C-O bonds. We describe the synthetic approaches of alpha-oxo gamma-thio-esters via the Mukayaima condensation of the enoxysilane of ethyl pyruvate on thioacetals. In the context of a multi-step synthesis strategy in ionic liquid, the synthesis of the starting materials was also carried out in these solvents. We also present an application of ionic liquids in peptide chemistry: cyclopeptides containing biaryl and biaryl ether linkages. These compounds have attracted considerable interest due to the significant biological activities that most of them exhibit, including antimicrobial and cytotoxic activities. We describe the synthetic approaches of macrocyclic peptides from tyrosine derivatives in ionic liquids. Two main strategies are investigated for the synthesis of macromolecules, peptidic coupling from tyrosine derivatives followed by formation of the biaryl ether bridge as key step and macrolactamization of the preformed biaryl ether, using modern coupling agents such as HATU and BOP. A different reactivity was observed in ionic liquids compared to that in conventional molecular solvents. Copper (I) and (II) salts have been used to catalyze the intermolecular diaryl ether coupling reaction in ionic liquids from tyrosine derivatives to obtain isodityrosine units. Ullmann coupling was not effective due to the presence of electronic and steric constraints, while the Chan-Lam coupling proved to be more advantageous and allowed the formation the isodityrosine units with satisfactory yields . In addition, the Chan-Lam has the advantage of using milder operating conditions.
19

Synthèse et caractérisation d'assemblages multi-porphyriniques à espaceurs NHC / Synthesis and characterization of multi-porphyrinic scaffolds using NHC linkers

Haumesser, Julien 13 September 2013 (has links)
L'objectif de cette thèse a été de mettre au point l'introduction d'azoles en meso d'une porphyrine par couplage d'Ullmann; Divers azoles ont pu être introduit par cette méthode avec de bons rendements, par formation d'une liaison carbone-azote. il a même été possible avec certains azotes de réaliser des doubles couplages d'Ullmann, conduisant ainsi à des 5.15-diazolyle-porphyrines. De plus, ces même conditions réactionnelles ont été utilisées pour introduire un ou deux dérivés donneurs d'électrons (carbazole, phénoxazine, phénothiazine). L'introduction d'imidazole, de triazole et de benzimidazole en meso a permis, après alkylation, d'obtenir des précurseurs de carbènes N-hétérocycles (NHC). La coordination de deux équivalents de NHC sur un sel de palladium conduit à un dimère de porphyrines via coordination exocyclique. La géométrie de coordination trans-anti autour du palladium a été confirmée par l'obtention de la structure radiocristallographique de deux complexes. Les études par électrochimie de ces complexes ont révélé une communication interporphyrinique à l'état fondamental, mise en évidence par une succession de quatre vagues monoélectroniques en oxydation. / The purpose of this thesis was to functionalize the meso position of a porphyrinWith azoles using the Ullmann coupling. Various azoles were introduced with good yieldsby using this reaction, leading to the formation of a carbon-nitrogen bond. With someazoles a double Ullmann coupling was possible, resulting in the formation of 5,15-diazolyl-porphyrins. Moreover, the same conditions were used to introduce one ortwo electron-donating groups (carbazole, phenoxazine, phenothiazine). The insertionof imidazole, triazole and benzimidazole at the meso position allowed, afteralkylation, their use as N-heterocyclic carbene (NHC). Coordination of twoequivalents of NHC to a palladium salt led to a porphyrin dimer, as a bis-carbene complex. X-Ray structures revealed that the complex’s geometry was trans-anti. Electrochemistry studies of the various dimers showed interactions between the porphyrins, highlighted by four successive oxidation peaks.
20

Kostel sv. Václava v Praze na Smíchově. Otázka historismu a novorenesance. / The Church of St. Wenceslas in Prague-Smíchov. The issues of historicism and Neo-Renaissance

Klinerová, Adéla January 2014 (has links)
This thesis is presenting the church of St. Wenceslas in Prague-Smíchov and also the issues of historicism and Neo-Renaissance, which are directly connected to this religious building. The introductory chapter of the thesis is depicting the historical and urban development of Prague historical suburb Smíchov that contributed to the creation of its church. The main part of the thesis is dedicated to the matter of selecting the architect. This part observes the circumstances of the architectural competition and compares the projects of participating architects. Following part of the thesis is consecrated to the decoration programme of the church of St. Wenceslas. Applied art is included only marginally. The conclusion has the objective of classifying the building of the church of St. Wenceslas into the wider context of central European architecture and religion painting. This thesis would not have been achieved without archival materials and historical sources, including especially architectural plans and the documentation administrated once by the parish office of the church of St. Wenceslas in Smíchov.

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