Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 250-279).

Thesis (M.S.M.E.)--State University of New York at Binghamton, Watson School of Engineering and Applied Science, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 306-329).

The effects of single-step and two-step aging treatments on the tensile properties of an A1-4.5%Cu-1.4%Mg- 0.5%Ag alloy have been investigated. Results showed that a maximum ultimate tensile strength of 75 ksi can be attained by single-step aging 24 hr at 170°C. The two-step aging treatments consisting of first aging one week at 80°C followed by aging at 160° and 190°C led to lower strength properties than simple one-step aging. Reversion treatments applied to fully age-hardened alloy resulted in an almost progressive loss of strength in the 250° to 375° range.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-10T17:31:45Z No. of bitstreams: 1 FrancinaldoLeite.pdf: 1004818 bytes, checksum: 43aab237ee9ed6aa04ac6e7dc0283c0d (MD5) / Made available in DSpace on 2017-05-10T17:31:45Z (GMT). No. of bitstreams: 1 FrancinaldoLeite.pdf: 1004818 bytes, checksum: 43aab237ee9ed6aa04ac6e7dc0283c0d (MD5) Previous issue date: 2017-03-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / The structures Cu3Agn, with n ranging from 3 to 25, using the Genetic Algorithm (GA) methodology and later the most stable structures (Cu3Ag10, Cu3Ag16 and Cu3Ag19) were studied through the Functional Theory of (DFT) density. The DFT calculations were performed with the SIESTA computational package, with the (PBE / DZP) theory level. In addition, we performed calculations in the Gaussian 09 computational package to verify the fundamental state, as well as to obtain spectroscopic data, where we analyzed PDOS, spin multiplicity and infrared. The results showed that the Cu orbital of the Cu most contributed to form the bond and to the atom of Ag 4p. The lowest energy values in the multiplicities sexteto, dubleto and quarteto, were found respectively for the Cu3Ag10, Cu3Ag16 and Cu3Ag20 clusters. Infrared data revealed that the Cu-Cu bonds showed a wavelength equal to 80 cm -1, Cu-Ag at 160 cm -1 and Ag-Ag at 180 cm -1. Therefore, it is concluded that the electronic and magnetic effects are influenced by the size and omposition of the clusters and that in the proportion Ag is added the gap obtained through HOMO-LUMO tends to decrease. / As estruturas Cu3Agn, com n variando de 3 até 25, usando a metodologia Algoritmo genético (GA) e posteriormente as estruturas dos mais estáveis (Cu3Ag10, Cu3Ag16 e Cu3Ag19) foram estudadas através da Teoria do Funcional da densidade (DFT). Os cálculos de DFT foram realizados com o pacote computacional SIESTA, com o nível de teoria (PBE/DZP). Além disso, realizamos cálculos no pacote computacional Gaussian 09 para verificar o estado fundamental, bem como obter dados espectroscópicos, onde analisou-se PDOS, multiplicidade de spin e infravermelho. Os resultados mostraram que o orbital 3d do Cu foi o que mais contribuiu para formar ligação e para o átomo de Ag o 4p. O menores valores de energia nas multiplicidades sexteto, dubleto e quarteto, foram encontrados respectivamente para os clusters Cu3Ag10, Cu3Ag16 e Cu3Ag20. Os dados obtidos no infravermelho revelaram que as ligações Cu-Cu mostrou-se no comprimento de onda igual a 80 cm-1, Cu-Ag em 160 cm-1 e Ag-Ag em 180 cm-1. Assim sendo, conclui-se que os efeitos eletrônicos e magnéticos são influenciados pelo tamanho e composição dos clusters e que na proporção que se acrescenta Ag o gap obtido por meio do HOMO-LUMO tende a diminuir.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1931. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed February 9, 2010) Includes bibliographical references (p. 38-39).

Nowadays, the requirement to design highly valuable compounds is undoubtedly one of the major challenges in the field of organic and organometallic chemistry. The use of the versatile and efficient N-heterocyclic carbenes (NHCs) combined with transition metals represents a key feature in modern organometallic chemistry and homogeneous catalysis. In the course of this thesis, the straightforward design and synthesis of a library of Pd(0) bearing NHC ligands was achieved. Their catalytic performances (Chapter 1) and their phosphorescence properties in solution (Chapter 2) were disclosed. Currently, cross-couplings are some of the most important types of reaction in palladium catalysis. The formation of highly hindered biaryls substrates is one of the main requirements in cross-coupling chemistry. The design and synthesis of a palladium dimer bearing a bulky NHC ligand can fulfil this proposal (Chapter 4). The development of new classes of ligands is a topic of interest. For this reason, normal, abnormal, remote and mesoionic N-heterocyclic carbenes copper complexes were investigated and their reactivity compared in the [3+2] cycloaddition of azides and alkynes (Chapter 7). Air and moisture stable Cu(I)-NHC species have also been compared to their silver analogues for the alkynylation of ketones (Chapter 9). The different reactivity of the two latter organometallic species (Cu and Ag) with ethyldiazoacetate reagent via the formation of carbenes or C-H activated product is presented in Chapter 8. Recently, the development of a bimetallic catalytic system is strongly considered and has high impact. For this reason, two dual catalytic transformations (Pd-NHC and Cu-NHC) were studied for the C-H arylation (Chapter 5) and the synthesis of substituted alkenes products via a relay or cooperative mechanisms (Chapter 6). The isolation of intermediates and mechanistic studies were examined in each of these studies.

No description available.

Im Netz der Elektroenergieversorgung werden einzelne Netzkomponenten und Betriebsmittel durch Verbindungen elektrisch zusammengeschaltet. Dabei werden häufig Schraubenverbindungen mit Stromschienen eingesetzt. Diese müssen über mehrere Jahrzehnte zuverlässig hohe Ströme tragen können. Abhängig von der sich einstellenden Temperatur an den Verbindungen altern diese mit der Zeit. Die Alterung wird je nach Verbindungssystem von verschiedenen Mechanismen beeinflusst, die alle parallel ablaufen. Bei ruhenden, stationären elektrotechnischen Verbindungen, deren Kontaktpartner aus verschiedenen Materialien bestehen, können abhängig von der Paarung intermetallische Phasen (IMP) entstehen. Die sich bildenden IMP haben schlechtere elektrische und mechanische Eigenschaften als die reinen Metalle. Daraus resultiert ein höherer Verbindungswiderstand. Die erzeugte Verlustleistung sowie die Temperatur der Verbindung steigen an. Dies kann zum Ausfall der Verbindung führen. In der Elektroenergietechnik werden aufgrund ihrer guten elektrischen Leitfähigkeit häufig die Werkstoffe Aluminium und Kupfer sowie das Beschichtungsmetall Silber bei Temperaturen von üblicherweise 90 °C bis 200 °C eingesetzt. Speziell bei Aluminium-Kupfer-Verbindungen, die nicht langzeitstabil sind, wird als maßgebliche Ausfallursache das Bilden von IMP gesehen. Die IMP des Systems Al-Cu wurden in der Vergangenheit bereits vielfach untersucht. Das Übertragen der Ergebnisse auf die Problematik stromtragender Verbindungen der Elektroenergietechnik ist jedoch nicht ohne Weiteres möglich. Der relevante niedrige Temperaturbereich zwischen 90 °C und 200 °C spielt bei vielen Untersuchungen nur eine untergeordnete Rolle. Zusätzlich können die Eigenschaften der IMP bei unterschiedlichen Herstellungsverfahren voneinander abweichen. Zum System Al-Ag ist in der Literatur nur wenig bekannt. Deshalb wurden für diese Arbeit phasenreine IMP der Systeme Al-Cu und Al-Ag mit unterschiedlichen Herstellungsverfahren bei möglichst identischen Randbedingungen hergestellt. Diese wurden mit einer speziell für diese Proben entwickelten Messeinrichtung elektrisch charakterisiert und der ermittelte spezifische elektrische Widerstand der IMP und ihr Temperaturbeiwert mit Werten aus der Literatur verglichen. An verschiedenen Schraubenverbindungen mit Stromschienen aus Aluminium und Kupfer wurden Langzeitversuche von bis zu 3 Jahren durchgeführt. Der Verbindungswiderstand wurde abhängig von der Zeit ermittelt. An ausgewählten Verbindungen wurde zusätzlich in zwei identischen Versuchen der Einfluss der Belastung mit Dauer- und Wechsellast auf das Langzeitverhalten untersucht. Mithilfe der an den IMP ermittelten elektrischen Eigenschaf-ten wurde deren Einfluss auf den Verbindungswiderstand berechnet. Die Ergebnisse dieser Modellrechnung wurden mit den Ergebnissen aus den Langzeitversuchen verglichen. Ausgewählte Verbindungen wurden dazu mikroskopisch untersucht. Es wurde festgestellt, dass die IMP nicht ausschließlich das Langzeitverhalten stromtragender Verbindungen bestimmen. Es muss mindestens ein weiterer Alterungsmechanismus einen signifikanten Einfluss haben. Die Untersuchungen deuten darauf hin, dass dabei Sauerstoff eine zentrale Rolle spielen könnte. / In electrical power supply networks a huge number of electrical joints are used to connect transmission lines, conductors, switchgears and other components. During operation these joints are aging due to different aging mechanisms. Depending on the type of the joint several aging mechanisms can take place at the same time. For stationary joints with contact partners made of different materials, the formation of intermetallic compounds (IMC) may be an issue. These IMC have worse electrical and mechanical properties compared to the pure metals. Therefore, the presence of IMC in the contact area results in a higher joint re-sistance and the temperature and the thermal power losses increase. Typical temperatures for high current joints are between 90 °C and 200 °C. Due to their good electrical conductivity aluminum and copper are often used as conductor materials and silver as a coating material. Especially bimetal joints made of aluminum and copper are not long term stable. The formation of Al-Cu IMC is held responsible as a cause of failure. The IMC of the System Al-Cu have already been studied by several authors. However, it is difficult to apply the results directly to electrical joints in power supply networks. In many studies the low temperature range between 90 °C and 200 °C is not regarded. In addition, the properties of the IMC may vary due to different preparation processes. There is only little information about the system Al-Ag in the literature. For this work, phase pure IMC of the systems Al-Cu and Al-Ag were prepared by different preparation processes using similar process parameters. These IMC samples were electrically characterized with a specially developed measuring device. The specific electric resistivity and the temperature coefficient of resistance were determined and compared to values taken from the literature. Various combinations of bus bar joints made of aluminum and copper were investigated in long term tests for up to three years. The joint resistance was determined as a function of time. In addition, for selected joints two identic setups were operated with continuous load and alternating load. The long term behavior was investigated with regard to the load ap-plied. Using the results of the electrical characterization of the IMC their influence on the joint resistance was calculated theoretically. The results of the calculation were compared to the results determined in the long term tests. Selected joints were examined microscopi-cally after termination of the long term tests. It was found, that the long term behavior of bimetal electrical joints with the combination Al-Cu and Al-Ag cannot be exclusively described by the growth of IMC. At least there is one further aging mechanism involved. The studies suggest, that oxygen may have a significant influence.

La fusion nucléaire contrôlée par confinement magnétique avec les réacteurs de type Tokamaks et les applications spatiales ont en commun d’utiliser des composants Haute-Fréquence (HF) sous vide à forte puissance. Ces composants peuvent être sujets à l’effet multipactor qui augmente la densité électronique dans le vide au sein des systèmes, ce qui est susceptible d’induire une dégradation des performances des équipements et de détériorer les composants du système. Ces recherches consistent à améliorer la compréhension et la prédiction de ces phénomènes. Dans un premier temps nous avons réalisé une étude de sensibilité de l’effet multipactor au rendement d’émission électronique totale (noté TEEY). Cette étude a permis de montrer que l’effet multipactor est sensible à des variations d’énergies autour de la première énergie critique et dans la gamme d’énergies entre la première énergie critique et l’énergie du maximum. De plus, les composants HF utilisés dans les réacteurs Tokamak et dans le domaine du spatial peuvent être soumis à un champ magnétique continu. Nous avons donc développé un nouveau dispositif expérimental afin d’étudier ce phénomène. Le fonctionnement du dispositif et la méthode de mesure ont été analysées et optimisées à l’aide de modélisations numériques avec le logiciel PIC SPIS. Une fois que l’utilisation du dispositif a été optimisée et que le protocole de mesures a été validé, nous avons étudié l’influence d’un champ magnétique uniforme et continu sur le TEEY du cuivre. Nous avons démontré que le rendement d’émission électronique totale du cuivre est influencé par la présence d’un champ magnétique et par conséquent également l’effet multipactor. / Space communication payload as well as magnetic confinement fusion devices, among other applications, are affected by multipactor effect. This undesirable phenomenon can appear inside high frequency (HF) components under vacuum and lead to increase the electron density in the vacuum within the system. Multipactor effect can thus disturb the wave signal and trigger local temperature increases or breakdowns. This PhD research aims to improve our understanding and the prediction of the multipactor effect. The multipactor phenomenon is a resonant process which can appear above a certain RF power threshold. To determine this power threshold, experimental tests or/and simulations are commonly used. We have made a study to evaluate the multipactor power threshold sensitivity to the TEEY. Two particular critical parameters have been found: first cross-over energy and the energies between the first cross-over and the maximum energies. In some situations, the HF components are submitted to DC magnetic fields which might affect the electron emission properties and hence the multipactor power threshold. Current multipactor simulation codes don’t take into account the effect of the magnetic field on the TEEY. A new experimental setup specially designed to investigate this effect was developed during this work. Our new experimental setup and the associated TEEY measurement technique were analysed and optimized thanks to measurements and SPIS simulations. We used the setup to study the influence of magnetic field perpendicular to the sample surface on the TEEY of copper. We have demonstrated that the magnetic field affects the copper TEEY, and hence multipactor power threshold.