A method for the preparation of air stable difluoroboryl acrylamides is reported. In contrast to the ubiquitous organotrifluoroborate salts, difluoroboryl acrylamides are relatively nonpolar and are readily purified by silica gel chromatography. Difluoroboryl acrylamides serve as efficient substrates in cross-coupling reactions to afford the corresponding trisubstituted acrylamides in good to excellent yields. The utility of the difluoroboryl group in various chemical transformations is presented. / A new method for the formation of a unique difluorinated boron-based functional group is reported. In contrast to the commonly observed trifluoronated boron species, the difluoroboryl species is relatively nonpolar, which allows for these compounds to be purified by silica gel chromatography, a convenient method for purification of compounds. Similarly to trifluoroborate salts, difluoroboryl species are capable of undergoing cross-coupling reactions, which form carbon-carbon bonds, in good to excellent yields. Additional examples of chemical reactions using difluoroboryl acrylamides are also presented.

The stochastic dynamics of an array of closely spaced micron scale cantilevers in a viscous fluid is considered. The stochastic cantilever dynamics are due to the constant buffeting of fluid particles by Brownian motion and the dynamics of adjacent cantilevers are correlated due to long range effects of fluid dynamics. The measurement sensitivity of an experimental setup is limited by the magnitude of inherent stochastic motion. However, the magnitude of this noise can be decreased using correlated measurements allowing for improved force resolution. A correlated scheme is proposed using two atomic force microscope cantilevers for the purpose of analyzing the dynamics of single molecules in real time, a regime that is difficult to observe using current technologies. Using a recently proposed thermodynamic approach the hydrodynamic coupling of an array of cantilevers is quantified for precise experimental conditions through deterministic numerical simulations. Results are presented for an array of two readily available micron-scale cantilevers yielding the possible force sensitivity and time resolution of correlated measurements. This measurement scheme is capable of achieving a force resolution that is more than three fold more sensitive than that of a single cantilever when the two cantilevers are separated by 200 nm, with a time scale on the order of tens of microseconds. / Master of Science

No

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Worldwide, more large antenna arrays are being deployed in areas of science previously dominated by other antenna geometries. Applications for large arrays include Radar, Satellite Communications and Radio Astronomy. Even though the use of large arrays solve some of the difficulties posed by more traditional antennas, new challenges are also faced. One of these challenges is the problem of noise coupling, and how the overall system performance is affected by it. The Focal Plane Array (FPA), which is a new example of a large antenna array, is currently being researched at a number of institutions worldwide for use in Radio Astronomy. As a result, FPA’s were used as an example element to demonstrate the practical importance of this research. In this study, the effect of mutual coupling on the noise performance of FPA’s was illustrated. This was done by calculating the mutual coupling between the elements of the array, and then calculating the noise power received by each element as a result of the mutual coupling. Next, the Active Noise Figure and Active Noise Temperature were calculated. These parameters were introduced to visualise the effect of mutual coupling on the overall noise performance of the array. Since FPA’s are by definition large, conventional brute-force analysis techniques are very resource intensive. Solving the coupling terms using these methods therefore requires the use of computer clusters even during the design phase of the antenna, which is very expensive. A method was therefore developed to calculate the coupling terms of a large array using Periodic Boundary Conditions. The method uses infinite array analysis, which resulted in an improvement in memory usage in orders of magnitude. This improvement comfortably places the memory requirements for the analysis of large arrays within the range of current personal computers. The results also displayed a reasonable amount of accuracy for use during the design phase of an array. The additional noise power on each element as a result of mutual coupling were also calculated. This was achieved by developing an equivalent circuit diagram that represents the system in terms of the noise and transmission parameters of the LNA of each receiver channel, and the coupling terms of the antenna array. Lastly, the active noise temperature and active noise figure are calculated. The theory was implemented by means of a script with a graphical user interface, to provide easy-to-use access to the theory. A quick reference table of estimated noise coupling penalty versus first term coupling and LNA noise temperature was also compiled. The results of an example calculation showed a significant amount of noise coupling in an 8×8 Vivaldi array. The noise coupling resulted in an increase in system noise temperature, Tsys, in the order of 9% of the LNA noise temperature, TLNA. According to the SKA Tsys budget, this results in an approximate Tsys increase of 1.3 Kelvin. In the context of Radio Astronomy, this additional source of noise cannot be ignored, as it can greatly affect the usebility of the telescope for certain areas of research. / AFRIKAANSE OPSOMMING: Groot antennaskikkings word deesdae al hoe meer ingespan in plek van ander tradisionele antennamodelle. Toepassings vir groot antennaskikkings sluit Radar, Satellietkommunikasie en Radioastronomie in. Alhoewel die gebruik van groot antennaskikkings baie van die probleme wat deur ander tradisionele antennamodelle veroorsaak word oplos, word nuwe uitdagings terselfdertyd geskep. Een van hierdie nuwe uitdagins is ruiskoppelling en hoe dit die ruisgedrag van die stelsel as ’n geheel affekteer. ’n Beeldvlakskikking (FPA), is ’n opwindende nuwe voorbeeld van ’n groot antennaskikking en die moontlikheid vir die gebruik daarvan in radioastronomie word tans wêreldwyd nagevors. Om hierdie rede is die FPA gekies as voorbeeldelement om die bruikbaarheid van hierdie navorsing in die praktyk te beklemtoon. In hierdie studie word die effek van wedersydse koppelling op die ruisgedrag van FPA’s geïllustreer. Dit word gedoen deur eers die wedersydse koppelling tussen die elemente van die antennaskikking te bereken en dan die ruisdrywing wat deur elke element ontvang word as gevolg van wedersydse koppelling. Daarna word die Aktiewe Ruistal en die Aktiewe Ruistemperatuur bereken. Hierdie nuwe parameters word bekendgestel om die gevolge van wedersydse koppelling op die ruisgedrag van die stelsel as ’n geheel te visualiseer. Omdat FPA’s per definisie groot is, vereis die analise daarvan deur middel van konvensionele metodes baie rekenaar hulpbronne. Hierdie metodes vereis dus die gebruik van rekenaarbondels of superrekenaars selfs gedurende die ontwerpfase van die antenna, wat baie duur en onprakties is. Daar is dus ’n metode ontwikkel wat gebruik maak van periodiese randvoorwaardes om groot antennaskikkings te analiseer. Die metode benader ’n groot antennaskikking as ’n eindig-opgewekte oneindige skikking van antennas. As gevolg hiervan, word die geheueverbruik met ordegroottes verbeter. Hierdie verbetering plaas dus die analise van groot antennaskikkings binne die vermoëns van huidige persoonlike rekenaars. Die resultate wys ook ’n aanvaarbare graad van akkuraatheid vir gebruik gedurende die ontwerpfase van die skikking. Die bykomende ruisdrwying op elke element as gevolg van wedersydse koppelling is ook bereken. Om dit te vermag, is daar ’n ekwivalente stroombaandiagram ontwikkel wat die gekoppelde stelsel in terme van die ruis- en transmissieparameters van die laeruisversterker (LNA) aan elke ontvangerkanaal en die koppelterme van die antenna skikking voorstel. Laastens word die aktiewe ruistal en die aktiewe ruistermperatuur ook bereken. Die teorie is geïmplimenteer deur gebruik te maak van ’n grafiesegebruikerskoppelvlak (GUI). Die GUI verskaf aan die gebruiker maklike toegang tot die teorie wat onwikkel is in hierdie navorsing. Daar is ook ’n snelnaslaantabel geskep met benaderde waardes van ruiskoppelling vir ’n verskeidenheid waardes van LNA ruistemperature en eerste element koppelling. Die resultate van ’n 8×8 Vivaldiskikking voorbeeld, het ’n beduidende hoeveelheid ruiskoppelling getoon. Die ruiskoppelling het ’n maksimum toename in stelsel ruistemperatuur, Tsys, van ongeveer 9% van die LNA ruistemperatuur tot gevolg gehad. Volgens die huidige Tsys begroting van die SKA, kom dit neer op ’n Tsys toename van byna 1.3 Kelvin. In die konteks van die radioastronomie, kan hierdie toename in ruistemperatuur nie geïgnoreer word nie aangesien dit die bruikbaarheid van die teleskoop vir sekere velde van navorsing nadelig kan beïnvloed.

<p>This thesis deals with the copper-catalyzed substitution of allylic substrates.</p><p>In the first part of this thesis, the synthesis of a series of metallocenethiolates is described. The thiolates were examined as ligands in the enantioselective copper(I)-catalyzed γ-substitution of allylic acetates.</p><p>The second part describes a study on copper-catalyzed α-substitution of enantiomerically pure secondary allylic esters. It was observed that the degree of chirality transfer is strongly dependent on the reaction temperature. The loss of chiral information is consistent with an equilibration of the allylCu(III) intermediates prior to product formation, which is essential in order to realize a copper-catalyzed dynamic kinetic asymmetric transformation process.</p><p>The third part describes a study on copper-catalyzed stereoselective α-substitution of enantiopure acyclic allylic esters. This method, when combined, with ruthenium and enzyme catalyzed dynamic kinetic resolution of allylic alcohols, provides a straightforward route to pharmaceutically important α-methyl carboxylic acids.</p><p>The fourth part is a mechanistic study on the reaction of perfluoroallyl iodide with organocuprates. Experimental studies as well as theoretical calculations were used to explain the contrasting reactivity of perfluoroallyl iodide vs. allyl iodide in cuprate allylation reactions.</p><p>In the fifth part, the development of a practical and useful method for the preparation of pentasubstituted acylferrocenes is presented.</p>

No description available.

Dans l'industrie aéronautique, la génération d'énergie dépend presque exclusivement de la combustion d'hydrocarbures. La meilleure façon d'améliorer le rendement de ces systèmes et de contrôler leur impact environnemental, est d'optimiser le processus de combustion. Avec la croissance continue du de la puissance des calculateurs, la simulation des systèmes complexes est devenue abordable. Jusqu'à très récemment dans les applications industrielles le rayonnement des gaz et la conduction de chaleur dans les solides ont été négligés. Dans ce travail les outils nécessaires à la résolution couplée des trois modes de transfert de chaleur ont été développés et ont été utilisés pour l'étude d'une chambre de combustion d'hélicoptère. On montre que l'inclusion de tous les modes de transfert de chaleur peut influencer la distribution de température dans le domaine. Les outils numériques et la méthodologie de couplage développés ouvrent maintenant la voie à un bon nombre d'applications tant scientifiques que technologiques. / In the aeronautical industry, energy generation relies almost exclusively in the combustion of hydrocarbons. The best way to improve the efficiency of such systems, while controlling their environmental impact, is to optimize the combustion process. With the continuous rise of computational power, simulations of complex combustion systems have become feasible, but until recently in industrial applications radiation and heat conduction were neglected. In the present work the numerical tools necessary for the coupled resolution of the three heat transfer modes have been developed and applied to the study of an helicopter combustion chamber. It is shown that the inclusion of all heat transfer modes can influence the temperature repartition in the domain. The numerical tools and the coupling methodology developed are now opening the way to a good number of scientific and engineering applications.

Cross-coupling reactions, where a transition metal catalyst facilitates the formation of a new carbon-carbon or carbon-heteroatom bond between two coupling partners, has become one of the most widely used, reliable, and robust family of transformations for the construction of molecules. The Nobel Prize was awarded to pioneers in this field who primarily used aryl iodides, bromides, and triflates as electrophilic coupling partners. The expansion of the reaction scope to non-traditional electrophiles is an ongoing challenge to enable an even greater number of useful products to be made from simple starting materials. The major goal of this thesis research is to improve and expand upon this field by using esters as electrophiles via the activation of the strong C(acyl)−O bond. Esters are particularly robust in comparison to other carboxylic acid derivatives used in cross-coupling reactions. Success on the activation of such inert functional group using catalysis has both fundamental and practical value. By discovering new reaction modes of this abundant functional group, synthetic routes to access novel or industrially important molecules can be improved. Chapter 1 of this thesis describes a literature overview of what has been accomplished in the field of cross coupling reactions using carboxylic acid derivatives as electrophilic coupling partners. Chapter 2 discloses the first palladium Suzuki-Miyaura couplings of phenyl esters to produce ketones. The method is efficient and robust, giving good yields of useful products. The reaction is proposed to proceed via an oxidative addition to the strong C(acyl)−O bond of the ester. In contrast to previous efforts in this field that use traditional catalysts such as Pd(PPh3)4, the developed reaction requires use of an electron-rich, bulky N-heterocyclic carbene ligand, which facilitates the strong bond activation. Furthermore, a palladium-catalyzed cross-coupling between aryl esters and anilines is reported, enabling access to diverse amides. The reaction takes place via a similar activation of the C−O bond by oxidative addition with a Pd−NHC complex, which enables the use of relatively non-nucleophilic anilines that otherwise require stoichiometric activation with strong bases to react. Chapter 3 discloses a nickel-catalyzed amide bond formation using unactivated and abundant esters. In this transformation, an accessible nickel catalyst can facilitate the activation of diverse aliphatic and aromatic esters to enable direct amide bond formation with amines as nucleophiles. No stoichiometric base, acid, or other activating agent is needed, providing exceptional functional group tolerance and producing only methanol as a by-product. This reaction is of both fundamental and practical importance because it is the first to demonstrate that simple conditions can enable Ni to cleave the C–O bond of an ester to make an oxidative addition product, which can be subsequently coupled with amines. This discovery contrasts industrially-common and wasteful methods that still require stoichiometric activating agents or multistep synthesis. Chapter 4 describes the evaluation of different types of cross-coupling reactions using methyl esters as electrophilic coupling partner. A high-throughput screening technique has been applied to this project. A combination between specific ligands, known by their efficiency to activate strong C−O bonds, and literature-based conditions has been designed for the chosen transformations. Using this strategy, two promising hits have been obtained using the same NHC ligand: a decarbonylative Suzuki-Miyaura and a decarbonylative borylation reaction.

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No. of bitstreams: 1 Cristiano Henrique Schuster 2018.pdf: 4202405 bytes, checksum: 730f564dd132126eb49b0f1d88a6ed54 (MD5) Previous issue date: 2018-02-23 / A camada limite estável (CLE) começa a se desenvolver logo após o ocaso, quando a radiação de onda curta proveniente do Sol cessa e a superfície terrestre para de aquecer, nessas condições, devido a grande perda radiativa da superfície terrestre, a turbulência pode ter sua intensidade reduzida em várias ordens de grandeza, em um regime com estas características os níveis verticais estão energicamente desacoplados. Durante uma mesma noite, pode ocorrer alternância entre intervalos em que os níveis verticais estão energicamente desacoplados e momentos em que existe grande mistura turbulenta, a transição entre esses dois estados ocorre em um valor específico da velocidade média do vento, conhecida como velocidade de conexão. Em regimes de baixas turbulência, que é uma característica de um estado de desacoplamento enérgico vertical, o escoamento próximo à superfície passa a ser governado pro fenômenos de maiores escalas, como por exemplo escalas de submeso, dentre os quais pode-se citar o fenômeno de meandro das componentes horizontais do vento, que é caracterizado pela oscilação da direção horizontal do vento. O meandro do ventos exerce papel fundamental na difusão de escalares, além disso, a maioria dos modelos de dispersão falham em representar a influência do meandro, principalmente pelo fato de que o meandro dos ventos ainda não é totalmente entendido e caracterizado, destacando assim a relevância deste trabalho, cujo tema de relaciona a dependência dos parâmetros de identificação do meandro do vento com o acoplamento do escoamento na camada limite atmosférica noturna e tem objetivo relacionar o estado de acoplamento atmosférico com a ocorrência de meandro dos ventos, utilizando a velocidade necessária para o acoplamento (velocidade de conexão) como critério inicial para a identificação do meandro dos ventos. Para tal, dados do experimento Fluxes Over Snow-covered Surfaces II (FLOSSII) serão submetidos a dois métodos para a identificação de parâmetros característicos de meandro, sendo o primeiro o ajuste da autocorrelação dos dados à Função de Autocorrelação (ACF) através do parâmetro de loop (m) e o período do meandro (T*) e o segundo a Transformada de Hilbert-Huang (HHT) utilizando o espectro marginal para determinação do período do meandro (T*). Com os parâmetros característicos de meandro será realizada uma análise estatística utilizando-se o critério clássico de vento fraco (Ū > 1,5 ms-1 ) e a velocidade de conexão (Ūcoup) para encontrar intervalos de um hora em que existe a possibilidade de ocorrência de meandro. Comparando os dois critérios, as análises realizadas mostram que o critério de Ūcoup encontrou aproximadamente 4 vezes mais intervalos, mantendo a mesma porcentagem de casos em que o parâmetro de loop é maior que um, mostrando-se um critério mais adequado para encontrar casos de possível meandro, principalmente para os níveis de medições mais altos. Em sítios que possuem torres de medição com níveis altos i critério de Ū < 1,5 ms-1 pode restringir a maioria dos casos, enquanto que a velocidade de conexão faz a separação natural dos regimes de escoamento. Permitindo assim, que todos os possíveis casos sejam analisados. / The stable boundary layer (CLE) begins to develop after the sunset, when short-wave radiation from the Sun ceases and the Earth’s surface ceases to heat, in these conditions, due to the great radioactive loss of the earth’s surface, turbulence intensity is reduced by several orders of magnitude, in a regime with these characteristics the vertical levels are energetically decoupled. During one night, alternations can occur between intervals in which vertical levels are energetically decoupled and times when there is a large turbulent mixture, the transition between these two states occurs at a specific value of wind speed. In low turbulence regimes, which is a characteristic of a state of vertical energy decoupling, the flow near the surface is governed by phenomena of larger scales, such as submeso scales, among which we can mention the phenomenon of meander of the horizontal components of the wind, which is characterized by oscillation of the horizontal direction of the wind. The meander of the winds plays a fundamental role in the diffusion of scalars cite anfossi2005, in addition, most dispersion models fail to represent the influence of the meander, mainly because the meander of the winds is not yet fully understood and characterized, highlighting the relevance of this work, whose research theme is “Study of the dependence of the wind meander identification parameters with the coupling in the atmospheric nocturnal boundary layer” and has as objective to relate the state of atmospheric coupling with the occurrence of winds meander, using the velocity required for the coupling as the initial criterion for wind meander identification. For this, data from the experiment Fluxes Over Snow-covered Surfaces II (FLOSSII) will be submitted to two methods for the identification of meander characteristic parameters, the first being the adjustment of the autocorrelation of the data to the Autocorrelation Function (ACF) through of the loop parameter (m) and the meander period (T*) and the second the Hilbert-Huang Transform (HHT) using the marginal spectrum for meander period determination (T*). With the characteristic meander parameters, a statistical analysis will be performed using the classical criterion of weak wind (Ū > 1,5 ms-1 ) and the coupling speed (Ūcoup) to find one hour intervals in which there is the possibility of meander occurrence. Comparing the two criteria, the analyses performed show that the Ūcoup criterion found approximately 4 times more intervals, maintaining the same percentage of cases of possible meander, especially for the higher measurement levels. In sites that have high-level measurement towers, the criterion of Ū < 1,5 ms-1 may restrict most cases, while the coupling speed causes the natural separation of flow regimes. Thus allowing all possible cases to be analysed.

In order to investigate the thermal stress and expansion as well as the associated strain effect on material properties caused by high temperature and large temperature gradient, a two-way thermo-mechanical coupling solver is developed. This solver integrates a new structural response module to the Kentucky Aerothermodynamics and Thermal response System (KATS) framework. The structural solver uses a finite volume approach to solve either hyperbolic equations for transient solid mechanics, or elliptic equations for static solid mechanics. Then, based on the same framework, a quasi-static approach is used to couple the structural response and thermal response to estimate the thermal expansion and stress within Thermal Protection System (TPS) materials. To better capture the thermal expansion and study its impacts on material properties such as conductivity and porosity, a moving mesh scheme is also developed and incorporated into the solver. Grid deformation is transferred among different modules in the form of variations of geometric parameters and strain effects. By doing so, a bi-direction information loop is formed to accomplish the two-way strong thermo-mechanical coupling. Results revealed that the thermal stress experienced during atmospheric re-entry concentrates in a banded area at the edge of the pyrolysis zone and its magnitude can be large enough to cause the failure of the TPS. In addition, thermal expansion causes the whole structure to deform and the changes in material properties. Results also indicated that the impacts coming from structural response should not be ignored in thermal response.