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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.
301

Modeling conjugate heat transfer phenomena for multi-physics simulations of combustion applications / Modélisation des transferts de chaleur couplés pour la simulation multi-physique des chambres de combustion

Koren, Chai 04 April 2016 (has links)
Dans un souci d’optimisation des fours industriels et de réduction des émissions de gaz à effet de serre,l’oxy-combustion est considérée comme l’une des solutions d’avenir. Les conditions existantes dans les chambres d’oxycombustion créent une interaction forte entre les différents phénomènes : Combustion,turbulence et transferts de chaleur. Pour mieux dimensionner les configurations futures il est nécessaire de pouvoir étudier la physique qui y règne, et ce pour un coût et un temps de retour raisonnables. De tels études nécessitent l’emploi d’outils de simulation de haute fidélité,et afin de modéliser les interactions inter-phénomènes à un coût acceptable le couplage de codes est utilisé. C’est avec cet objectif que les travaux présentés dans ce manuscrit se concentrent sur la mise au point d’une méthodologie de couplage entre codes d’écoulements réactifs et de transfert de chaleur dans les parois pour la réalisation de simulations de haute-fidélité massivement parallèles prédictives des chambres futures. / Oxycombustion is seen as one mean to attain the wished goals in terms of efficiency optimisation and Greenhouse Effect Gases emissions reduction for industrial furnaces. The extreme operating conditions, high pressure and temperature, lead to a strong interaction between the different phenomena which take place inside the combustion chambe r: Combustion, turbulence and heat transfer. To better design these futur oxyfuel processes, a mean to study the related physics with a reasonable computational cost and return time. Such studies require the use of high-fidelity numerical resolution tools, and in order to model the multi-physics interaction in a cost efficient way, code coupling. The operating conditions being extreme : High pressure and temperature, a strong interaction exists between the different phenomena occuring inside the chamber. To better understand the physics inside oxycombustion chambers,a multiphysics high-fidelity simulation methodology is developped.
302

Modélisation multiphysique de flammes turbulentes suitées avec la prise en compte des transferts radiatifs et des transferts de chaleur pariétaux. / Multi-physics modelling of turbulent sooting flames including thermal radiation and wall heat transfer

Rodrigues, Pedro 08 June 2018 (has links)
Les simulations sont utilisées pour concevoir des chambres de combustion industrielles robustes et peu polluantes. Parmi les polluants, l’émission de particules de suies constitue une question sociétale et une priorité politico- industrielle, en raison de leurs impacts néfastes sur la santé et l'environnement. La taille des particules de suies joue un rôle important sur ces effets. Il est donc important de prévoir non seulement la masse totale ou le nombre de particules générées, mais également leur distribution en taille (PSD). De plus, les suies peuvent jouer un rôle important dans le rayonnement thermique. Dans des configurations confinées, la prédiction des transferts de chaleur est une question clé pour augmenter la robustesse des chambres de combustion. Afin de déterminer correctement ces transferts, les flux radiatifs et de conducto-convectifs aux parois doivent être pris en compte. Enfin, la température pariétale est aussi contrôlée par les transferts conjugués de chaleur entre les domaines fluides et solides. L’ensemble de ces transferts thermiques impactent la stabilisation de la flamme, la formation de polluants et la production de suies elle-même. Il existe donc un couplage complexe entre ces phénomènes et la simulation d'un tel problème multiphysique est aujourd'hui reconnu comme un important défi. Ainsi, l'objectif de cette thèse est de développer une modélisation multiphysique permettant la simulation de flammes suitées turbulentes avec le rayonnement thermique et les transferts conjugués de chaleur associés aux parois. Les méthodes retenues sont basées sur la Simulation aux Grandes Échelles (LES), une description en taille des suies, des transferts conjugués et un code Monte Carlo pour le rayonnement. La combinaison de telles approches est réalisable grâce aux ressources de calcul aujourd’hui disponibles afin d’obtenir des résultats de référence. Le manuscrit est organisé en trois parties. La première partie se concentre sur le développement d'un modèle détaillé pour la description de la production de suies dans les flammes laminaires. Pour cela, la méthode sectionnelle est retenue ici car elle permet la description de la PSD. La méthode est validée sur des flammes laminaires éthylène/air. Dans la deuxième partie, un formalisme LES spécifique à la méthode sectionnelle est développé et utilisé pour étudier deux flammes turbulentes : une flamme jet non-prémélangée et une flamme swirlée pressurisée confinée. Les champs de température et de fraction volumique de suies sont comparés aux données expérimentales. De bonnes prédictions sont obtenues et l’évolution des particules de suies dans de telles flammes est analysée à travers l'étude de l’évolution de leur PSD. Dans ces premières simulations, les pertes de chaleur aux parois reposent sur des mesures expérimentales de la température aux parois, et un modèle de rayonnement simple. Dans la troisième partie, une approche Monte Carlo permettant de résoudre l'équation de transfert radiatif avec des propriétés radiatives détaillées des phases gazeuse et solide est utilisée et couplée au solveur LES. Cette approche est appliquée à l'étude de la flamme jet turbulente. La prédiction des flux thermiques est comparée aux données expérimentales et la nature des transferts radiatifs est étudiée. Ensuite, une modélisation couplée de la combustion turbulente prenant en compte la production de suies, les transferts conjugués de chaleur et le rayonnement thermique est proposée en couplant les trois codes dédiés. Cette stratégie est appliquée pour la simulation du brûleur pressurisé confiné. L'approche proposée permet à la fois de prédire la température des parois et la bonne stabilisation de la flamme. Les processus de formation de suies se révèlent être affectés par la modélisation des transferts thermiques. Ceci souligne l’importance d’une description précise de ces transferts thermiques dans les développements futurs de modèles de production de suies et leur validation. / Numerical simulations are used by engineers to design robust and clean industrial combustors. Among pollutants, soot control is an urgent societal issue and a political-industrial priority, due to its harmful impact on health and environment. Soot particles size plays an important role in its negative effect. It is therefore important to predict not only the total mass or number of emitted particles, but also their population distribution as a function of their size. In addition, soot particles can play an important role in thermal radiation. In confined configurations, controlling heat transfer related to combustion is a key issue to increase the robustness and the life cycle of combustors by avoiding wall damages. In order to correctly determine these heat losses, radiative and wall convective heat fluxes must be accounted for. They depend on the wall temperature, which is controlled by the conjugate heat transfer between the fluid and solid domains. Heat transfer impacts the flame stabilization, pollutants formation and soot production itself. Therefore, a complex coupling exists between these phenomena and the simulation of such a multi-physics problem is today recognized as an extreme challenge in combustion, especially in a turbulent flow, which is the case of most industrial combustors. Thus, the objective of this thesis is to develop a multi-physics modeling enabling the simulation of turbulent sooting flames including thermal radiation and wall heat transfer. The retained methods based on Large-Eddy Simulation (LES), a soot sectional model, conjugate heat transfer, a Monte Carlo radiation solver are combined to achieve a stateof- the-art framework. The available computational resources make nowadays affordable such simulations that will yield present-day reference results. The manuscript is organized in three parts. The first part focuses on the definition of a detailed model for the description of soot production in laminar flames. For this, the sectional method is retained here since it allows the description of the particle size distribution (PSD). The method is validated on laminar premixed and diffusion ethylene/air flames before analyzing the dynamics of pulsed diffusion flames. In the second part, an LES formalism for the sectional method is developed and used to investigate two different turbulent flames: a non-premixed jet flame and a confined pressurized swirled flame. Predicted temperature and soot volume fraction levels and topologies are compared to experimental data. Good predictions are obtained and the different soot processes in such flames are analyzed through the study of the PSD evolution. In these first simulations, wall heat losses rely on experimental measurements of walls temperature, and a coarse optically-thin radiation model. In the third part, to increase the accuracy of thermal radiation description, a Monte Carlo approach enabling to solve the Radiative Transfer Equation with detailed radiative properties of gaseous and soot phases is used and coupled to the LES solver. This coupled approach is applied for the simulation of the turbulent jet flame. Quality of radiative fluxes prediction in this flame is quantified and the nature of radiative transfers is studied. Then, a whole coupled modeling of turbulent combustion accounting for soot, conjugate heat transfer and thermal radiation is proposed by coupling three dedicated codes. This strategy is applied for a high-fidelity simulation of the confined pressurized burner. By comparing numerical results with experimental data, the proposed approach enables to predict both the wall temperature and the flame stabilization. The different simulations show that soot formation processes are impacted by the heat transfer description: a decrease of the soot volume fraction is observed with increasing heat losses. This highlights the requirement of accurate description of heat transfer for future developments of soot models and their validation.
303

Desenvolvimento de um método de conjugação entre o polissacarídeo capsular sorotipo 1 de Streptococcus pneumoniae e a proteína de superfície pneumocócica A. / Development of a conjugation method between the capsular polysaccharide serotype 1 of Streptococcus pneumoniae and pneumococcal surface protein A.

Machado, Luciene Oliveira 23 June 2015 (has links)
Streptococcus pneumoniae é uma bactéria encapsulada causadora de doenças infecciosas como pneumonia, bacteremia e meningite, infecções essas que estão entre as principais causas de morte entre crianças, idosos e imunodeprimidos, indivíduos que constituem o grupo de risco para tais infecções. A vacinação tem sido a mais eficaz forma de conter tais infecções. A vantagem das vacinas conjugadas em comparação às polissacarídicas é a capacidade de indução de uma resposta imune T-dependente o que garante proteção mesmo ao grupo de risco para infecções por S. pneumonia. A proposta do projeto foi estabelecer um protocolo para obtenção de um conjugado constituído pelo polissacarídeo capsular de S. pneumonia sorotipo 1 (PS1) e pela proteína de superfície pneumocócica A (PspA). A síntese do conjugado empregou uma metodologia inédita para o sorotipo 1. A avaliação da resposta imune humoral induzida pelo conjugado mostrou a indução de IgG anti-PS1 gerada pelas imunizações com o conjugado PS1-PspA. / Streptococcus pneumoniae is an encapsulated bacteria causing infectious diseases such as pneumonia, bacteremia and meningitis, these infections are among the leading causes of death among children, elderly and immunocompromised, who constituting individuals of risk group. The vaccination has been the more effective form to counter these infection. The advantage of conjugated vaccines compared to vaccines polysaccharide, is the ability to induce a T-dependent immune response which provides protection even at risk groups for infection by S. pneumoniae. The project proposal was establish a protocol for obtaining a conjugate consisting of the capsular polysaccharide of S. pneumoniae serotype 1 (PS1) and the pneumococcal surface protein A (PspA). The synthesis of conjugate employed a new methodology for serotype 1. The evaluation of humoral immune response induced by the conjugate showed anti-PS1 IgG induction generated by immunization with the PS1-PspA.
304

Synthèse de carbènes N-hétérocycliques chiraux et applications en catalyse asymétrique / Synthesis of new chiral N-heterocyclic carbènes and applications in asymmetric catalysis

Thomasset, Amélia 18 October 2013 (has links)
Ce travail de thèse porte dans un premier temps sur la synthèse de nouveaux sels d’azolinium chiraux précurseurs de carbènes N-hétérocycliques. Deux nouvelles familles de sels ont été préparées à partir de la L-proline. Nous avons pu caractériser les NHC issus de ces sels, par la formation des dimères, des thiones et des complexes de rhodium correspondants. Dans un second temps, ces nouveaux sels d’azolinium ont été évalués dans la réaction d’addition conjuguée de réactifs de Grignard sur des cétones α,β insaturées. Les résultats ont montré de très bonnes activités catalytiques, et de très bonnes régiosélectivités. Les énantiosélectivités obtenues sont encourageantes. Ensuite, ces catalyseurs ont été engagés dans la réaction de substitution allylique. Une bonne activité catalytique a aussi été observée malgré des régiosélectivités et des énantiosélectivités modérées. Enfin, ces sels ont été employés comme précurseurs de NHC pour la réduction asymétrique de cétones aromatiques par transfert d’hydrogène. Les complexes formés se sont montrés actifs mais non énantiosélectifs. / This work deals with, at first, the synthesis of new chiral azolinium precursors to N-heterocyclic carbenes. Two families have been prepared from the L-proline. The structures of some NHC dimmers, thiones and [Rh-NHC] complexes were characterized and confirmed by different analysis methods.Secondly, these new salts were evaluated in the conjugate addition reaction of Grignard reagents to α,β-unsaturated ketones. The results obtained shown very good catalytic activity, excellent regioselectivity with moderate enantioselectivity. They were also involved in the allylic substitution reaction. Good catalytic activity was observed despite moderate regioselectivity and enantioselectivity. Finally, these azolinium salts were employed as NHC precursors for the asymmetric transfer hydrogenation of aromatic ketones. The complexes proved to be active, but non enantioselective.
305

Metal mediated mechanisms of drug release

Stenton, Benjamin James January 2018 (has links)
In this thesis will be described research towards the development of bioorthogonal bond-cleavage reactions, and their applications in targeted drug delivery (Figure 1). The first project relates to the development of a palladium mediated bond-cleavage or "decaging" reaction which can cause a propargyl carbamate to decompose and release an amine. This was further developed by the incorporation of a protein modification handle which allowed an amine-bearing drug to be covalently ligated to a protein by a palladium-cleavable linker. This chemistry was demonstrated by the conjugation of the anticancer drug doxorubicin to a tumour targeted anti-HER2 nanobody. The drug could then be delivered to cancer cells upon addition of a palladium complex. The second project relates to the development of a platinum mediated bond-cleavage reaction. This was developed with the aim of using platinum-containing anticancer drugs - such as cisplatin - as a catalyst to cause drug release reactions in tumours. In this reaction an alkyne-containing amide can decompose to release an amine upon addition of platinum complexes, and was applied to the release of prodrugs of the cytotoxins monomethylauristatin E and 5-fluorouracil in cancer cells. A cisplatin-cleavable antibody-drug conjugate was designed and synthesised, and progress towards its biological evaluation will be discussed.
306

Conjugate Heat Transfer and Average Versus Variable Heat Transfer Coefficients

Macbeth, Tyler James 01 March 2016 (has links)
An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.
307

Structure-properties relationships in small pi-conjugated molecules : electrochromism, photovoltaic conversion and mechano-fluorochromism / Relations structure-propriétés dans de petites molécules pi-conjuguées : électrochromisme, conversion photovoltaïque et mécanofluorocromisme

Jiang, Yue 08 September 2015 (has links)
Ce travail porte sur la synthèse et l’évaluation de systèmes pi-conjugués en tant matériaux actifs pour des dispositifs opto(électroniques). Un premier chapitre décrit une série d’oligothiophènes cruciformes et leur évaluation dans des dispositifs électrochromes. Le second chapitre décrit la synthèse d’accepteurs moléculaires à base de benzodithiophène et l’analyse de leur potentialités comme matériaux accepteurs dans des cellules solaires organiques. La plus large part du travail porte sur l’analyse des relations structure-propriétés d’une série de petites molécules push-pull comportant un groupe donneur triphénylamine (TPA) relié à un groupe accepteur par un espaceur thiényl. Une première étape a consisté à remplacer l’un des cycles phényles de la TPA par des groupes aromatiques tels que p-fluorophényle, anthryle et naphtyle. Ces modifications ont peu d’influence sur les propriétés électroniques de la molécule mais induisent de large variations des propriétés de transport de charge et de conversion photovoltaïque des matériaux correspondants. Au cours d’une seconde étape l’un des groupes phényles de la TPA a été remplacé par des chaînes alkyle, perfluoroalkyle et oligo(oxyethylene). Les résultats de diffraction X, spectroscopie d’absorption et de fluorescence, génération de second harmonique et électrochimie démontrent que certaines de ces molécules présentent des propriétés d’émission contrôlées par agrégation tandis que les matériaux correspondants se réorganisent spontanément à l’état solide sous forme d’agrégats H ou J dotés de propriétés de transport de charges et de conversion photovoltaïque fortement améliorées et de propriétés d’absorption, d’émission et de génération de second harmonique mécaniquement modulables. / This work deals with the design, synthesis and evaluation of molecular pi-conjugated systems as active materials for (opto)electronics devices. A short first chapter describes three X-shaped oligothiophenes, thecharacterization of their structure and properties and a first evaluation of their performances in electrochromic devices. The second chapter describes the synthesis of molecular acceptors based on a benzodithiophene and the analysis of their potentialities when combined with molecular donors in organic solar cells.The major part of the work is focused on the analysis of structure-properties relationships of a series of smallpush-pull molecules involving di- or tri-arylamine donorblocks linked to an acceptor group by a thienyl bridge. In a first step, a phenyl ring of triphenylamine (TPA) is replaced by p-fluorophenyl, anthryl and naphtyl groups.Optical and electrochemical results show that substitution has little effect at the molecular level but can markedly affect solid-state properties with in particular an improvement of charge-transport and short-circuit current density of solar cells based on these donor materials.In a second step, a phenyl ring of TPA is replaced by alkyl, perfluoroalkyl and oligo(oxyethylene) chains. Results of X-ray diffraction, absorption and photoluminescence spectroscopies, second harmonic generation, and electrochemistry demonstrate that some of these molecules under go aggregation controlled photoluminescence emission wave length while the corresponding materials spontaneous lyre organize in the solid-state to form either H or Jaggregates with enhanced charge mobility, photovoltaic conversion efficiency and mechanically-induced chromism, fluorochromism and NLO-chromism.
308

Synthetic Studies Towards the Tridachione Family of Marine Natural Products

Kasprzyk, Milena, milena.kasprzyk@freehills.com January 2008 (has links)
Since the middle of the 20th century, significant interest has evolved from the scientific community towards the polypropionate family of marine natural products. A number of these compounds have been shown to possess significant biological activity, and this property, as well as their structural complexity, has driven numerous efforts towards their synthesis. The first chapter provides an introduction into the world of polypropionates, with a discussion on synthetic studies into a number of members of the tridachiapyrone family. Fundamental synthetic concepts utilised in this thesis towards the preparation of polyketides are also described, with a focus on their application towards the synthesis of 9,10-deoxytridachione, anti tridachiahydropyrone and syn tridachiahydropyrone. Chapter 2 describes the work undertaken towards the total synthesis of 9,10-deoxytridachione. The novel tandem conjugate addition-Dieckmann condensation of complex enones developed previously in the Perkins group was used to generate anti methylated cyclohexenones as key synthetic intermediates. The conversion of the cyclohexenones into the corresponding cyclohexadienes via allylic alcohols was attempted, utilising a Grignard-mediated reaction to achieve the selective 1,2-reduction. Studies into the Grignard-mediated reduction were also undertaken on seven additional cyclohexenones, in order to investigate the utility and scope of the reaction. The extension of the methodology previously developed for the synthesis of cyclohexenones is the subject of Chapter 3. This section describes investigations into the synthesis of stereochemically-diverse cyclohexenones from complex enones. The conjugate addition-Dieckmann condensation strategy was extended successfully towards the synthesis of a syn methylated cyclohexenone, which allowed the synthesis of the proposed true structure of tridachiahydropyrone to be pursued. The methodology developed in Chapter 3 was utilised in Chapter 4 to synthesise a model system of syn tridachiahydropyrone. A comparative analysis of the NMR data of the syn model, an anti model and anti tridachiahydropyrone with the natural product indicated that the true structure of tridachiahydropyrone may indeed have syn stereochemistry. The synthesis of syn tridachiahydropyrone was attempted, and to this end a suitable cyclohexanone was successfully synthesised. However, the subsequent methylation-elimination cascade failed to furnish the desired syn methylated cyclohexenone, producing only an anti methylated cyclohexanone. The stereochemistry of the methylation was deduced using high and low variable temperature NMR coupled with selective irradiation NOESY.
309

Stereoselective intramolecular Michael addition reactions of pyrrole and their application to natural product syntheses

Beck, Daniel Antony Speedie, beckautomatic@gmail.com January 2006 (has links)
Chapter one; “(-)-Rhazinilam and (-)-Rhazinal: Alkaloids with Anti-mitotic Properties Derived from Kopsia teoi”, provides the background information behind the motives that initiated this research project. The plant alkaloid (-)-rhazinilam [(-)-1] and its naturally-occurring derivative (-)-rhazinal [(-)-13] both exhibit potent anti-mitotic activities and, as such, are interesting targets for total synthesis. Chapter one is a review of the literature regarding these two compounds and discusses the occurrence, proposed biosynthetic origins, structural elucidation and biological activites of compound (-)-1 and that of its analogues including alkaloid (-)-13. Previous total syntheses of these two compounds are then examined, concluding with the only reported total synthesis of compound (-)-13. Developed within the Banwell research group, this total synthesis produced the racemic modification of alkaloid (-)-13 due to a lack of any stereocontrol in the key intramolecular Michael addition step. This unprecedented key step, involving cyclisation of the C2 of pyrrole onto an N-tethered and ?,?-disubstituted acrylate to produce a quaternary-carbon stereogenic centre, would be of greatly enhanced utility if it could be achieved in a catalytic-enantioselective fashion. The realisation of this goal is the central aim of the research conducted within this thesis. ¶ Chapter two; “Investigating Asymmetric Induction in the Intramolecular Michael Addition of pyrrole to N-Tethered Acrylates and Related Species”, introduces the model study used to direct research towards achieving the goal of asymmetric induction in the title process. The model is a somewhat simplified version of the original process used in the total synthesis of compound (-)-13 involving cyclisation of the C2 of pyrrole onto an N-tethered and ?-monosubstituted Michael acceptor, to produce a tertiary-carbon stereogenic centre. This simplification allows the rapid synthesis of a broad range of potential substrates for use in the title process, thus enabling the investigation of various different approaches to inducing asymmetry therein. High levels of asymmetric induction are observed with the use of chiral substrates or catalysts, facilitating the synthesis of both 6- and 7-membered rings annulated to pyrrole with construction of the relevant tertiary-carbon stereogenic centre in enantio-enriched form. For the reactions producing a 6-membered ring annulated to pyrrole, unambiguous proof of the absolute sense of asymmetric induction observed in the intramolecular Michael addition event is established using a chemical correlation study involving elaboration of a key indolizine-type cyclisation product, to the plant alkaloid of known absolute stereochemistry, (-)-tashiromine [(-)-75]. For the reaction producing a 7-membered ring annulated to pyrrole, the same information is obtained via X-ray crystallographic analyses of a dibrominated derivative of a key pyrroloazepine-type cyclisation product. ¶ Chapter three “An Enantioselective Total Synthesis of the Alkaloid (-)-Rhazinal: An Anti-mitotic Agent Isolated from Kopsia teoi.”, focuses on the application of methodology developed in the previous chapter, to the original goal of inducing asymmetry in the intramolecular Michael addition reaction, involving cyclisation of the C2 of pyrrole onto an N-tethered and ?,?-disubstituted acrylate to produce a quaternary-carbon stereogenic centre. This is ultimately achieved in a catalytic-enantioselective fashion, resulting in the first such total synthesis of the anti-mitotic alkaloid (-)-rhazinal [(-)-13]. ¶ Chapter four “Extending the Reaction Manifold to the Syntheses of Related Natural Products: A Formal Total Synthesis of (+)-Aspidospermidine and Syntheses of (-)-Rhazinilam and (-)-Leuconolam from (-)-Rhazinal”, describes three extensions to the reaction manifold used in the enantioselective total synthesis of alkaloid (-)-13: The acquisition in an enantioselective manner, of an intermediate previously obtained in racemic form, en route to the racemic modification of the natural product (±)-aspidospermidine [(±)-134], constitutes a formal and enantioselective total synthesis of (+)-aspidospermidine [(+)-134]. The direct deformylation of (-)-rhazinal [(-)-13], is carried out, to produce the parent alkaloid (-)-rhazinilam [(-)-1]. The pyrrole ring present in (-)-rhazinilam [(-)-1] is oxidised, to produce the related natural product (-)-Leuconolam [(-)-12] which has not, hitherto, been prepared by total synthesis. ¶Chapter five contains the experimental procedures and characterisation data associated with compounds described in chapters two to four.
310

Efficient Updating Shortest Path Calculations for Traffic Assignment

Holmgren, Johan January 2004 (has links)
<p>Traffic planning in a modern congested society is an important and time consuming procedure. Finding fast algorithms for solving traffic problems is therefore of great interest for traffic planners allover the world. </p><p>This thesis concerns solving the fixed demand traffic assignment problem (TAP) on a number of different transportation test networks. TAP is solved using the Frank-Wolfe algorithm and the shortest path problems that arise as subproblems to the Frank-Wolfe algorithm are solved using the network simplex algorithm. We evaluate how a number of existing pricing strategies to the network simplex algorithm performs with TAP. We also construct a new efficient pricing strategy, the Bucket Pricing Strategy, inspired by the heap implementation of Dijkstra's method for shortest path problems. This pricing strategy is, together with the actual use of the network simplex algorithm, the main result of the thesis and the pricing strategy is designed to take advantage of the special structure of TAP. In addition to performing tests on the conventional Frank-Wolfe algorithm, we also test how the different pricing strategies perform on Frank-Wolfe algorithms using conjugate and bi-conjugate search directions. </p><p>These test results show that the updating shortest path calculations obtained by using the network simplex outperforms the non-updating Frank-Wolfe algorithms. Comparisons with Bar-Gera's OBA show that our implementation, especially together with the bucket pricing strategy, also outperforms this algorithm for relative gaps down to 10E-6.</p>

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