• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 48
  • 19
  • 17
  • 12
  • 7
  • 4
  • 3
  • 3
  • 3
  • 3
  • 2
  • 2
  • 2
  • Tagged with
  • 138
  • 138
  • 19
  • 17
  • 14
  • 13
  • 13
  • 11
  • 11
  • 10
  • 10
  • 9
  • 9
  • 9
  • 9
  • 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.
51

I. Contorted Polycyclic Aromatic Hydrocarbons: Attempted Synthesis Of [12]circulene Derivatives Ii. Synthesis And Characterization Of Novel [1]benzothieno[3,2-B][1]benzothiophene Derivatives

Hollin, Jonathan 01 January 2019 (has links)
There has been increasing interest in the development of organic materials due to their unique structural and electronic properties. Organic compounds have the advantage of being able to be deposited from solution, leading to low-cost, high-area electronics production. Contorted polycyclic aromatic hydrocarbons have been shown to have potential for use in organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs) due to their supramolecular properties and charge carrier mobilities. Thiophene-based materials have also shown great promise in OFETs due to their high charge carrier mobilities, stability during device operation, solubility in organic solvents, and structural versatility. [n]Circulenes are a class of polycyclic aromatic compounds whose shape depends on the central n-membered ring. These range from bowl-shaped when n < 6, planar when n = 6, and saddle-shaped when n > 6. The shapes of these molecules, especially for the contorted circulenes, imparts interesting and useful properties such as a polarizable π-system and coordination to fullerenes. Using methods developed in our group, synthesis of [12]circulene derivatives was attempted. Synthetic difficulties, results, and a synthetic plan to overcome these problems are presented herein. 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) is a thiophene-based p-type semiconducting material with one of the highest reported OFET mobility to date. Alterations to BTBT have been made to improve device processing and tune the electronic structure. However, structural alterations have generally been limited to functionalization with electron-donating groups and extension of the π-system. The lack of electron deficient derivatives has prevented further tuning of the electronic structure. Additionally, installation of strongly electron-withdrawing substituents could give BTBT n-type character as seen with perylene diimides. Several synthetic strategies to develop BTBTs with electron-withdrawing groups were explored. Limitations to developing electron deficient BTBTs as well as synthesis and characterization of novel imide-functionalized derivatives are described.
52

A Study on the Relationship between the Air-Sea Density Flux and Isopycnal Meridional Overturning Circulation in a Warming Climate

Han, MyeongHee 10 May 2011 (has links)
The Meridional Overturning Circulation (MOC) plays an important part in the Earth's climate, but the mechanisms that determine MOC response to climate change remain unclear. In particular, the relative importance of the adiabatic and diabatic dynamics in MOC is still under debate. This study aims to explore the relationship between the air-sea density flux and isopycnal MOC, and examine the possibility of diagnosing the adiabatic component of MOC from the air-sea density flux. This is done here using the concept of the "push-pull" mode, which consists of the adiabatic push into the deep ocean in the Northern Hemisphere and pull out of the deep ocean in the Southern Hemisphere. The evolutions of the isopycnal MOC and the "push-pull" mode are qualitatively similar. The maximum streamfunctions of the "push-pull" modes and isopycnal MOC both decrease by 3-5 Sv during 100 years, and their decrease is very similar to each other in the deep layers. In particular, the slope of the downward linear trend in the maximum is about -5 Sv per 100 years in both the "push-pull" modes and isopycanl MOC at the equator. The decrease in actual isopycnal MOC is faster at heavier densities than that at lighter densities. The first EOF mode of eigenvectors of the "push-pull" mode explains less percentage of variance than in the case of the isopycnal MOC at the equator. The detection of the global changes in MOC from the surface fluxes alone is feasible, if the surface fluxes are measured with sufficient accuracy.
53

Reducing WIP Inventory of Production Line in AQ Segerström &amp; Svensson AB

Yuvaraj, Vasanth Raj, Zhang, Sifei January 2013 (has links)
The major objective of present study is to find out the sources which cause higher Work in Process (WIP) in the production line. In which a detailed analysis is performed in the area of inventory, reorder point, Takt time, and Kanban. All the analyses are based on the data obtained from the company’s ERP system and have been used to run some scenarios during the analysis.Lots of problems are responsible to cause higher WIP. But current report only focuses and concentrates in leveling the work load, implementing pull system, suggesting reorder point and Takt time.The current situation is described through Value-stream Map (VSM) and the impact cost matrix is used to show the impact of each problem in the production line in terms of costs. In the analysis chapter, root cause method has been used in order to show the cause and effect of higher WIP. Detailed analyses together with explanations are listed by orders. Therefore, three major suggestions are proposed and the future VSM is plotted to show the effect and change of the suggestions which helps to improve the current situation by eliminating the waste.
54

Greffage de molécules 'push-pull' sur germanium: vers la passivation diélectrique

Lefèvre, Xavier 22 October 2012 (has links) (PDF)
Les excellentes propriétés électroniques du germanium limitées par la faible qualité isolante de son oxyde rendent le développement de nouveaux matériaux diélectriques nécessaires. En outre, la sensibilité du germanium requiert la création d'une couche passivante de surface pour le protéger. Bien que de nombreuses études soient réalisées pour le développement de nouveaux diélectriques inorganiques, ce projet de recherche en rupture concerne la conception, la réalisation et le développement de film mince diélectrique organique passivant sur le germanium pour des applications en nanoélectronique. Le travail réalisé porte principalement sur la synthèse de nouvelles molécules " push-pull " (systèmes conjugués linéaires portant de part et d'autres un groupe donneur et un groupe accepteur) et sur la fonctionnalisation du germanium. Plusieurs nouveaux systèmes donneur-accepteur ainsi que des systèmes conjugués linéaires contenant une fonction d'ancrage ont été synthétisés selon de nouvelles voies. En particulier, une série de dérivés azobenzène contenant différents accepteurs (groupes fluorés, pyridinium, nitro) et donneurs (amines, alcoxyl) ainsi que des fonctions d'ancrage variées (thiol, acide carboxylique, sel de diazonium, triazene) a été obtenue. En parallèle, la préparation et la fonctionnalisation de surfaces de germanium ont été étudiées. Un nouveau procédé permettant d'enlever l'oxyde natif de la surface et d'obtenir des surfaces halogénées de faible rugosité a été développé. Les substrats de germanium ont été fonctionnalisés par des thiols mais également par des sels de diazonium. Ce nouveau processus de greffage spontané a permis d'abaisser considérablement le temps de réaction (15 minutes de greffage spontané des sels de diazonium contre 3 jours pour la formation de monocouches auto-assemblées de thiols) tout en travaillant dans des conditions douces. Les films minces ainsi obtenus présentent une stabilité comparable à celles des monocouches de thiols. Des systèmes conjugués linéaires ont été greffés à la fois sous forme de thiol et sous forme de sels de diazonium afin de déterminer l'influence du noyau aromatique sur la formation du film et sur ses propriétés. Enfin, les systèmes " push-pull " ont également été greffés. Des premières études électroniques sur or avec les systèmes conjugués linéaires ont été réalisées. Ces études ont été étendues au germanium et laissent envisager des résultats significatifs avec les molécules " push-pull ".
55

Migration of African-trained physicians abroad : a case study of Saskatchewan, Canada

Kogo, Seraphine 01 June 2009
Several factors inform health professionals decisions to migrate from developing to developed countries to practice their profession. This study explores the Push and Pull factors that informed African-trained physicians decisions to migrate to the province of Saskatchewan, how well they integrated into their new working environments upon arrival and how that might contribute to future migration and retention in Saskatchewan. Based on questionnaire surveys and face-to-face interviews, this study identified differences in the relative importance of precipitating factors for physicans from South, North and Other African nations. Although the majority of African-trained physicians for the study indicated that profession-related push factors were the precipitating factors for their migration, a smaller number did not cite these as important. Most respondents for the study integrated well into the health care system and have remained at their current location of practice because of the support they received from colleagues at their work places.
56

60 Watts Broadband Push Pull RF Power Amplifier Using LTCC Technology

Jundi, Ayman 23 September 2013 (has links)
The continuous increase in wireless usage forces an immense pressure on wireless communication in terms of increased demand and spectrum scarcity. Service providers for communication services had no choice but to allocate new parts of the spectrum and present new communication standards that are more spectrally efficient. Communication is not only limited to mobile phones but recently attention has been given to intelligent transportation systems (ITS) where cars will be given a significant place in the communication network. Vehicular Ad-Hoc Network (VANET) is already assigned a slice of the spectrum at 5.9GHz using the IEEE802.11p standard also known as Dedicated Short-Range Communication (DSRC); however, this assignment will have limited range and functionality at first, and users are expected to depend on existing wireless mobile channels for some services such as video streaming and car entertainment. Therefore, it is essential to integrate existing wireless mobile communication standards into the skeleton of ITS at launch and most probably permanently. An investigation was carried out regarding the existing communication standards including wireless local area networks (WLAN) and it was found that frequency bands from 400MHz up to 6GHz are being used in various regions around the world. It is also noted that current state of the art transceivers are composed of several transmitter front-ends targeting certain bands and standards. However, the more standards to be supported the more components to be added and the higher the cost not to mention the limited space in mobile devices. Multimode Multiband (MMMB) transmitters are therefore proposed as a potential solution to the existing redundancy in the number of front-end paths in modern transmitters. Broadband amplifiers are an essential part of any MMMB transmitter and they are also among the most challenging especially for high power requirements. This work explains why single ended topologies with efficiencies higher than 50% have a fundamental bandwidth limit such that the highest frequency of operation must be lower than twice the lowest frequency of operation. Hence, Push-Pull amplifier topology is being proposed as it was found that it has inherent broadband capabilities exceeding those of other topologies with comparable efficiency. The major advantage of Push-Pull power amplifiers is its capability of isolating the even harmonics present in the even mode operation of a Push-Pull amplifier from the less critical odd mode harmonics and the fundamental frequency. This separation between even and odd signals comes from the inclusion of a Balun at the output of push-pull amplifiers. Such separation makes it possible to operate amplifiers beyond the existing limit of single ended power amplifiers. To prove the concept, several Baluns were designed and tested and a comparison was made between different topologies in terms of balance, bandwidth and odd and even mode performances; moreover, to illustrate the concept a Push-Pull power amplifier design was implemented using the multilayer Low Temperature Co-fired Ceramics (LTCC) technology with a bandwidth ratio of more than 100%.
57

Migration of African-trained physicians abroad : a case study of Saskatchewan, Canada

Kogo, Seraphine 01 June 2009 (has links)
Several factors inform health professionals decisions to migrate from developing to developed countries to practice their profession. This study explores the Push and Pull factors that informed African-trained physicians decisions to migrate to the province of Saskatchewan, how well they integrated into their new working environments upon arrival and how that might contribute to future migration and retention in Saskatchewan. Based on questionnaire surveys and face-to-face interviews, this study identified differences in the relative importance of precipitating factors for physicans from South, North and Other African nations. Although the majority of African-trained physicians for the study indicated that profession-related push factors were the precipitating factors for their migration, a smaller number did not cite these as important. Most respondents for the study integrated well into the health care system and have remained at their current location of practice because of the support they received from colleagues at their work places.
58

60 Watts Broadband Push Pull RF Power Amplifier Using LTCC Technology

Jundi, Ayman 23 September 2013 (has links)
The continuous increase in wireless usage forces an immense pressure on wireless communication in terms of increased demand and spectrum scarcity. Service providers for communication services had no choice but to allocate new parts of the spectrum and present new communication standards that are more spectrally efficient. Communication is not only limited to mobile phones but recently attention has been given to intelligent transportation systems (ITS) where cars will be given a significant place in the communication network. Vehicular Ad-Hoc Network (VANET) is already assigned a slice of the spectrum at 5.9GHz using the IEEE802.11p standard also known as Dedicated Short-Range Communication (DSRC); however, this assignment will have limited range and functionality at first, and users are expected to depend on existing wireless mobile channels for some services such as video streaming and car entertainment. Therefore, it is essential to integrate existing wireless mobile communication standards into the skeleton of ITS at launch and most probably permanently. An investigation was carried out regarding the existing communication standards including wireless local area networks (WLAN) and it was found that frequency bands from 400MHz up to 6GHz are being used in various regions around the world. It is also noted that current state of the art transceivers are composed of several transmitter front-ends targeting certain bands and standards. However, the more standards to be supported the more components to be added and the higher the cost not to mention the limited space in mobile devices. Multimode Multiband (MMMB) transmitters are therefore proposed as a potential solution to the existing redundancy in the number of front-end paths in modern transmitters. Broadband amplifiers are an essential part of any MMMB transmitter and they are also among the most challenging especially for high power requirements. This work explains why single ended topologies with efficiencies higher than 50% have a fundamental bandwidth limit such that the highest frequency of operation must be lower than twice the lowest frequency of operation. Hence, Push-Pull amplifier topology is being proposed as it was found that it has inherent broadband capabilities exceeding those of other topologies with comparable efficiency. The major advantage of Push-Pull power amplifiers is its capability of isolating the even harmonics present in the even mode operation of a Push-Pull amplifier from the less critical odd mode harmonics and the fundamental frequency. This separation between even and odd signals comes from the inclusion of a Balun at the output of push-pull amplifiers. Such separation makes it possible to operate amplifiers beyond the existing limit of single ended power amplifiers. To prove the concept, several Baluns were designed and tested and a comparison was made between different topologies in terms of balance, bandwidth and odd and even mode performances; moreover, to illustrate the concept a Push-Pull power amplifier design was implemented using the multilayer Low Temperature Co-fired Ceramics (LTCC) technology with a bandwidth ratio of more than 100%.
59

Global Talent Flow as 'Musical Chairs' : Driving Forces of Young Talents:An Examination of Italy and Lithuania

Hoerstel, Jonas, Jaeger, Patrick January 2018 (has links)
This Master thesis examines the impact of the individual driving forces of young highly educated talents from Italy and Lithuania to apply for a job abroad after the graduation. By investigating the motivations and influences during this decision-making process, we clarify the role of different impulses on the individual’s decision to become part of the phenomenon known as the global talent flow. Within this study, we obtain the actor’s view, while we use an inductive approach to put the construction of meaning of the participants in the center of our study. This aim of our qualitative study is further strengthened by the use of semi-structured interviews and the usage of the phenomenology approach. The data is analyzed and interpreted according to the emerged themes and linked back to the existing theory on‘migration’, the ‘Push-Pull-Mooring’ paradigm, the ‘gravity’ model, and the knowledge flow according to ‘brain gain’, 'brain drain’, and ‘brain circulation’. This study highlights the variety of facets which are of importance to the individuals within the decision-making process of the non-rational phenomenon of the global talent flow. Although the main motivation - the opportunity to grow - is shared among all participants, a clear distinction can be made between the ‘professional’ and the ‘personal’ growth. Furthermore, our study reveals the direct influence of initiatives taken by the European Union (EU), such as the ERASMUS+ Programme on the mobility of young talents and the impact of possible unforeseen side effects such as the ‘brain drain’ in some of the member countries of the EU. Our findings contribute another layer to the understanding of the driving forces of tomorrow’s mobile workforce to apply for a job abroad. This comprehension is fundamental to policymakers, companies, the society at larger, and the young talents themselves, as it becomes crucial to attract this ‘brain’ to secure long-term development of all stakeholders of the global talent flow within the EU.
60

Síntese de butadienos push-pull

Santos, Reginaldo Pereira January 2016 (has links)
Orientador: Prof. Dr. Anderson Orzari Ribeiro / Tese (doutorado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2016. / Este trabalho descreve a sintese de butadienos push-pull. Utilizou-se as reacoes de Vilsmeier-Haack para a obtencao de clorovinilaldeidos e posteriormente a reacao de Knoevenagel, obtendo-se assim os butadienos push-pull, que sao compostos de elevada conjugacao eletronica. Alem dos butadienos push-pull, obteve-se atraves de uma reacao de condensacao aldolica, catalisada por acido, uma nova pentadienona, a 2,6-bis-(4-hidroxi-3-metoxi-benziliden)-cicloexanona e uma tetraen-5-ona, a 9-dicloro-1,9-bis-(3,4-dimetoxi-fenil)-nona-1,3,6,8-tetraen-5-ona. Realizou-se a caracterizacao estrutural de todos esses compostos, confirmando-se assim a estrutura dos mesmos. Testou-se estes compostos a respeito de suas propriedades antioxidantes, bactericidas e fungicidas. O composto 2,6-bis-(4-hidroxi-3-metoxi-benziliden)-cicloexanona demonstrou elevada atividade antioxidante na concentracao de 260 ¿Êg/mL quando comparado com a quercetina, que e um fenol utilizado como padrao no teste de DPPH. Realizou-se dois testes de atividade bactericida e fungicida e os compostos apresentaram halo de inibicao a diversos micro-organismos sendo que o composto 2,6-bis-(4-hidroxi-3-metoxi-benziliden)-cicloexanona demonstrou ser o mais promissor, inibindo o crescimento de 7 das 9 especies de micro-organismos testados. / This work describes the synthesis of push-pull butadienes. The Vilsmeier-Haack reactions were used to obtain chloro-vinyl-aldehydes and later the Knoevenagel reaction to obtain the push-pull butadienes, which are compounds of high electronic conjugation. In addition to push-pull butadiene, applying acid catalyzed aldol condensation, new pentadienones were obtained, like 2,6-bis-(4-hydroxy-3-methoxy-benzylidene)¿cyclohexanone and a 9-dichloro-1,9-bis-(3,4-dimethoxy-phenyl)-1,3,6,8-tetraen-5-one. The structural characterization was carried out, confirming the structure the synthesized compounds. The compounds were tested for their antioxidant, bactericidal and fungicidal properties. The 2,6-bis-(4-hydroxy-3-methoxy-benzylidene) -cyclohexanone showed a high antioxidant activity at 260 ìg/mL when compared to quercetin, which is a phenol used as a standard in the DPPH test. They showed inhibition to several microorganisms and the compound, 2,6-bis- (4-hydroxy-3-methoxy-benzylidene) -cyclohexanone was the most promising, inhibiting the growth of 7 of the 9 species of microorganisms tested.

Page generated in 0.0468 seconds