This thesis describes the preparation and thermal rearrangement, via homo-[l,5]-hydrogen migration, of a series of unsymmetrically substituted bicyclic and tricyclic vinylcyclo-propanes (65a)-(67a), (68b), (69), (70), (71a), (72a), (74)-(76) and (77a). In each of these compounds two hydrogen atoms one (H[sub=C]) adjacent to the substituent and the other (H[sub=J]) more distant from it - are suitably disposed to undergo homo-[1,5]-hydrogen migration. It was found that an oxygen substituent retarded the rate of homo-[l,5]-migration of the hydrogen atom (H[sub=C]) adjacent to it relative to that of the other more remote hydrogen atom (H[sub=J]) The retarding effect appeared to be dependent on the structure of the oxy-substituted vinylcyclopropane as well as on the nature of the oxygen substituent. A methyl substituent exerted a negligible, retarding effect on the rate of migration of while phenyl and trimethylsilyl groups accelerated the rate of migration of H[sub=C] relative to that of H[sub=J]. The results are consistent with the proposal that in the transition state for the homo-[1,5]-hydrogen migration the carbon centre bearing the migrating hydrogen atom develops a partial negative charge. / Science, Faculty of / Chemistry, Department of / Graduate

High power circuits, those involving high levels of voltages and currents to produce several kilowatts of power, would possess an optimized efficiency when driven at high frequencies (on the order of MHz). Such an approach would greatly reduce the size of capacitive and magnetic components, and thus ultimately reduce the cost of the power electronic circuits. The problem with this strategy in conventional packaging, however, is that at high frequencies, interconnects between the power devices on one board (such as Power MOSFETs or IGBTs) and components on another board (such as the coasting diodes) suffer from severe parasitic effects, thus affecting the overall electrical performance of the system. A conceivable solution to this problem is the design and construction of a power electronics module which would incorporate all power devices and supporting circuitry into one very simple and compact module. Such an approach would reduce interconnect inductances (thus reducing costly parasitic effects), increase system efficiency and electrical performance, produce a standardization for power electronic modules, and through this standardization, lower overall industry-wide system costs and increase power electronic system reliability. This technology would prove especially valuable for power electronics in industry, where prevalent power systems such as half bridge or full bridge converters would benefit greatly from the large reduction of inductances which currently exist between separate bridge legs. This thesis will discuss a novel multilayer approach towards the described issues. A power module has been designed and fabricated which contains one metallization power layer for the power devices, and a second metallization control layer for the low power signal components. The two layers are separated by a dielectric layer which serves as an electrical separation and as a physical spacer. In addition, issues have been addressed towards optimal physical layout and construction (with regards to thermal dissipation), materials comparisons have been made, and thermal simulations and experimental verifications performed. Issues relating to standardized power electronic module design and the efforts of this researcher at the Microelectronics Laboratories at Virginia Polytechnic Institute and State University to contribute to this quickly evolving field will be discussed. Such topics as power electronic module design, control and driver circuitry design, material issues, and thermal issues will be discussed. / Master of Science

No description available.

Call number: LD2668 .T4 1956 W74 / Master of Science

No description available.

Orientador: Clóvis Augusto Ribeiro / Banca: Adelino Vieira de Godói Netto / Banca: Mirabel Vieira Cerqueira / Resumo: Aduto (do latin Adductus, "atraidos") é o produto de uma adição direta de duas ou mais moléculas distintas, resultando em um produto de reação simples contendo todos os átomos de todos os componentes, com formação de duas ligações químicas e uma redução na multiplicidade da ligação em pelo menos um dos reagentes. Assim, aduto é uma nova espécie química resultante da união direta de moléculas individuais. A meglumina é um carboidrato que se caracteriza pela sua habilidade em formar adutos altamente solúveis em meio aquoso com ácidos carboxílicos. A indústria farmacêutica foi pioneira em explorar essa propriedade, aplicando-a no aperfeiçoamento de medicamentos já existentes. Diante desse contexto, os ácidos carboxílicos envolvidos na formação de adutos com a meglumina apresentam propriedades farmacológicas, mais especificadamente, pertencem à classe dos anti-inflamatórios não esteroidais (AINEs). Com relação à elucidação estrutural dessas espécies, um único trabalho é descrito na literatura o qual contempla o arranjo cristalino da flunixina-meglumina, primeiro aduto dessa classe a ser comercializado. Neste trabalho a flunixina-meglumina e o diclofenaco-meglumina, este último preparado como proposta do estudo, foram caracterizados a partir das técnicas Espectroscopia de Absorção na Região do Infravermelho (IV) e Ressonância Magnética Nuclear (RMN). O comportamento térmico da flunixina-meglumina e do diclofenaco-meglumina no estado sólido foi avaliado mediante as técnicas termoanalíticas Termogravimetria e Termogravimetria Derivada (TG/DTG); Termogravimetria e Análise Térmica Diferencial Simultânea (TG-DTA) e Calorimetria Exploratória Diferencial (DSC). Foi evidenciado que após a temperatura de fusão das respectivas amostras cristalinas, ocorre a formação de um material com comportamento polimérico sugerindo que os adutos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: An adduct (from the Latin adductus, "drawn toward") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components, with formation of two chemical bonds and a net reduction in bond multiplicity in at least one of the reactants.Thus, an adduct is a new chemical specie that results from the direct union of individual molecules. Meglumine is a carbohidrate characterized by its capability to form soluble adducts in aquous solutions with carboxilic acids. Pharmaceuticals industry was the first to explore this property, with application to enhance drugs that already exists. In this context, carboxylic acids related to adducts formation with meglumine present pharmacological properties and are included in the class of nonsteroidal anti-inflamatory drugs (NSAIDs). Actually, it is not well understood the structural and chemical characteristics about adducts formed by association of meglumine and carboxylic acids. Only one work in the literature describes the cristaline sctructure formed by flunixin-meglumine adducts, the first compound in this class to go to market. In this work, two adducts (flunixin-meglumine and diclofenac-meglumine) were characterized by Infrared Absortion Spectroscopy (IR) and Nuclear Magnetic Resonance (NMR). Results sugest that the adduct formation of carboxylic acid-meglumine occurs by deprotonation of carboxylic acid and protonation of meglumine. Both adducts in solid state studied in this work were analyzed by Thermogravimetry - Differential Thermal Analysis (TG-DTA) and Differential Scanning Calorimetry (DSC). The results for DSC curves presented two cristaline forms for both adducts. Besides, it was noted that after the melting temperature of the respectives cristalines compounds, they present an self-assembly process wich leads to supramolecular polymers... (Complete abstract click electronic access below) / Mestre

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Chemistry in the Faculty of Applied Science at the CAPE PENINSULA UNIVERSITY OF TECHNOLOGY 2014 / Crystal engineering based upon acid: base compounds have been studied in this thesis. Selected phenolic acids such as: vanillic acid (VA), phenylacetic acid (PAA), 4-hydroxyphenylacetic acid (HPAA), 3-chloro-4-hydroxyphenylacetic acid (CHPAA), caffeic acid (CFA), p-coumaric acid (pCA), trans-ferulic acid (tFER), 2-phenylpropionic acid (PPA) and 2-phenylbutyric acid (PBA) were the main compounds investigated. These phenolic acids have formed co-crystals/co-crystal hydrates, salts/salt hydrates and hybrid salt-co-crystals with acridine (ACRI), caffeine (CAF), cinchonidine (CIND), isonicotinamide (INM), isonicotinic acid (INA), nicotinamide (NAM), quinidine (QUID), quinine (QUIN), theobromine (THBR), theophylline (THPH) and urea (U). The two racemic compounds 2-phenylpropionic acid (PPA) and 2-phenylbutyric acid (PBA) were used to study chiral discrimination leading to the understanding of separation enantiomers. Compounds were prepared in different solvents (alcohols, ketone and distilled water) to investigate the relationship between solvents used and the crystalline product obtained. (If there is any effect on the crystalline compound obtained by changing the solvent). The structures were elucidated using single crystal X-ray diffraction. Ground products of obtained compounds were characterized by powder X-ray diffraction (PXRD). Thermal analyses like thermogravimetry (TG), differential scanning calorimetry (DSC) and hot stage microscopy (HSM) were used for the determination of thermal character of the new compounds. IR was also performed to characterize the new compounds. Non-isothermal TG was utilised to obtain kinetic parameters for the water and the methanol release in (pCA−)(QUIN+)•pCA•MeOH•H2O. A selective experiment was done in which quinidine and quinine were used to compete between selected phenolic acids (PAA and HPAA). viii The comparison of the crystal structures determined showed that, changing the phenolic acid while using the same co-crystal former has a significant effect on the type of compounds obtained. The obtained crystal structures were either co-crystal/co-crystal hydrates, salts/salt hydrates or hybrid salt-co-crystals which formed network via means of supramolecular interactions.

Author's thesis (Ph. D.)--Technische Universiteit Delft, 2006. / Includes bibliographical references.

Under certain conditions, reactive chemicals may proceed into uncontrolled chemical reaction pathways with rapid and significant increases in temperature, pressure, and/or gas evolution. Reactive chemicals have been involved in many industrial incidents, and have harmed people, property, and the environment. Evaluation of reactive chemical hazards is critical to design and operate safer chemical plant processes. Much effort is needed for experimental techniques, mainly calorimetric analysis, to measure thermal reactivity of chemical systems. Studying all the various reaction pathways experimentally however is very expensive and time consuming. Therefore, it is essential to employ simplified screening tools and other methods to reduce the number of experiments and to identify the most energetic pathways. A systematic approach is presented for the evaluation of reactive chemical hazards. This approach is based on a combination of computational methods, correlations, and experimental thermal analysis techniques. The presented approach will help to focus the experimental work to the most hazardous reaction scenarios with a better understanding of the reactive system chemistry. Computational methods are used to predict reaction stoichiometries, thermodynamics, and kinetics, which then are used to exclude thermodynamically infeasible and non-hazardous reaction pathways. Computational methods included: (1) molecular group contribution methods, (2) computational quantum chemistry methods, and (3) correlations based on thermodynamic-energy relationships. The experimental techniques are used to evaluate the most energetic systems for more accurate thermodynamic and kinetics parameters, or to replace inadequate numerical methods. The Reactive System Screening Tool (RSST) and the Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) were employed to evaluate the reactive systems experimentally. The RSST detected exothermic behavior and measured the overall liberated energy. The APTAC simulated near-adiabatic runaway scenarios for more accurate thermodynamic and kinetic parameters. The validity of this approach was investigated through the evaluation of potentially hazardous reactive systems, including decomposition of di-tert-butyl peroxide, copolymerization of styrene-acrylonitrile, and polymerization of 1,3-butadiene.

Multi-beam bridges made from precast concrete box girders are one of the most common bridge types used in the United States. One problem that affects these bridges is the development of longitudinal or reflective cracks on the road surface because of failure of the shear keys. Some states have attempted to correct this problem by redesigning the shear key or adding post-tensioning, but the problem persists in many new bridges. The purpose of this study is to investigate why these shear key failures are occurring. This project studies two types of box girder designs, the common Precast/Prestressed Concrete Institute (PCI) box girder bridges and the Texas Department of Tranportation (TxDOT) box girder bridge. In the past, reflective cracking has occurred in bridges of both types. The analysis procedure involves finite element analyses of bridge models with realistic support and loading conditions, and comparing the PCI and TxDOT bridges. The results indicate that both PCI and TxDOT box girder have sufficient strength to resist cracking from vehicular loads, but uneven temperature changes and shrinkage strains cause high tensile stresses in the shear key regions and lead to reflective cracking. The analyses showed the highest stresses were often times near the supports, rather than at midspan. Past studies have proposed using larger composite deck slabs, transverse posttensioning, or full-depth shear keys to prevent shear key failure. Composite slabs were the most effective way to reduce high stresses in shear keys, and were effective for all loading cases considered. Post-tensioning and full-depth keys also showed a reduction in shear key stresses, but were less effective.