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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.
1

An Improved Genetic Algorithm for Designing Broadband Mushroom-Type EBG Structures

Chen, Chun-hong 19 July 2011 (has links)
Genetic algorithms (GAs) are global optimization methods that can be applied to almost all problems, requiring only proper fitness function to evaluate. However, one problem of general GA is slow convergence. An improved GA is presented to speed up the efficiency of searching for global optimum in this author. The concept of this proposed method uses a few cost to obtain better individuals in initial population, and the evolution of GA is divided into two-stage with the concept of the genetic evolution process, which uses to improve efficiency. An improved GA with finite-difference time-domain (FDTD) will be applied to optimize mushroom-type EBG structures, which can obtain a wide range stop-band by adjusting the position of via with different patch size cascaded without changing via size, then the simulation and measurement results are also compared. In addition, the novel steps will be presented to design broadband mushroom-type EBG structures with smaller size systematically.
2

Textlinguistische Betrachtung von Motivationsschreiben / The Text Analysis of Cover Letter

ŘEHOŘOVÁ, Jiřina January 2017 (has links)
This master thesis deals with the text analysis of cover letter in German and with identifying characteristic text structures of this text type. The theoretical part covers the main concepts of text linguistics. Based on the scientific literature are defined the basic outline for the text analysis. The practical part concerns the analysis of the corpus of 30 cover letters written by Czech candidates in compliance with the criteria for job application in supposed language German. After that, the communication context, textual theme, function and text structures significant for this text type are determined. Finally, the results are compared with the set hypotheses.
3

Baigtinio tipo g- struktūrų vidinės sietys / Intrinsic connections of finite type of G- structures

Balčiūnas, Aidas 02 July 2010 (has links)
Vienas svarbiausių šiuolaikinės diferencialinės geometrijos skyrių yra glodžių G- struktūrų teorija, kuriai pradžią davė klasikinės Rymano erdvės struktūros nagrinėjimas. G- struktūra glodžioje daugdaroje yra gaunama paėmus jos reperių sluoksniuotės redukciją , atitinkantį neišsigimusių matricų grupės pogrupį G. G-struktūros egzistuoja ne bet kurioje daugdaroje. Šiame darbe yra nagrinėjama tik baigtinio tipo G- struktūrų vidinės sietys. Yra įrodoma, kad kiekvieną baigtinio tipo G- struktūrą atitinka baigtinio tipo diferencialinė lygtis ant daugdaros . G- struktūrų geometrija nagrinėjama netradiciniu būdu nagrinėjant jų infinitezimalių simetrijų diferencialines lygtis. Šiuo metodu yra išnagrinėtos G- struktūrų afininės sietys, taip pat ir normalinės sietys. Paskutiniosios G- struktūrų geometrijoje nebuvo iki šiol tyrinėtos. / The most important part of differential geometry in our days is the theory of smooth G- structures, which started with the analyses of clasical construction of Riemannian space. G-structure in smooth manifold is acquired, when we take reduction of its frame bundle corresponding to subgroup G of non-degeneracy matrix group . It‘s important to note, that G- structures do not exist in every manifold. In this paper are considering intrisic connections only of finite type of G- structures. It is proved, that every finite type of G- structure corresponds to finite type of differential equation on the manifold . The Geometry of G- structures is investigated not traditionally while analyzing differential equations of infetisimal simmetrics of G- structures. There are analysed affine connections of G- structures, also and normal connections. The former haven‘t been investigated in geometry of G- structures.
4

Predator Effects of the Invasive Green Crab (Carcinus maenas) and the Native Rock Crab (Cancer irroratus) on Soft-Sediment Macrofauna

Cheverie, Anne 07 December 2012 (has links)
When multiple predators foraging together have different individual consumption rates than predators foraging in isolation, they exhibit non-independent multiple predator effects on prey. I examined multiple predator effects in a system consisting of invasive green crabs (Carcinus maenas L.), native rock crabs (Cancer irroratus Say) and benthic macrofauna prey. First, I examined multiple predator effects when green crabs and rock crabs forage on soft-shell clams (Mya arenaria L.) in different habitat types (sand, sand with artificial seagrass) and assessed the behavioural mechanisms responsible for the observed predation effects. Independent multiple predator effects on prey were detected for most conspecific and heterospecific pairs in both habitat types. In general, crab foraging behaviours were not affected by the presence of another predator. Interactions between predators did not influence foraging behaviours because encounters were infrequent, short in duration and predominantly non-aggressive. A non-independent multiple predator effect on prey (marginally significant) was observed when green crabs foraged with rock crabs in artificial seagrass. This effect, however, could not be explained by the observed crab behaviours. Second, I investigated multiple predator effects when green crabs and rock crabs forage on a soft-sediment macrofauna community. Because crabs did not have significant predation effects on the community throughout the experiment, I did not evaluate multiple predator effects on prey. It is possible that crab predation was not important in regulating the macrofauna community, in which case multiple predator effects were non-existent. Predation may have been suppressed due to a combination of factors, including interactions between predators, harsh environmental conditions or a sub-optimal prey field. Alternatively, my ability to detect significant predation effects may have been hindered because of prey movement in and out of cages or low statistical power. Overall, results from this thesis demonstrate that multiple predator effects on prey may differ with habitat and highlights the importance of conducting behavioural observations to better understand interactions between predators and the resulting consequences for prey. Multiple predator effects on a soft-sediment community should be re-evaluated to assess the importance of these crab species in regulating benthic macrofauna under natural conditions.
5

Low Temperature Oxygen Mobility Applied to Catalysis / Mobilité de l’oxygène à basse température appliquée à la catalyse

Penkala, Bartosz 06 November 2015 (has links)
Accomplir les spécifications des nouvelles réglementations concernant les gaz d'échappement de post-traitement des technologies automobiles, par exemple, TWC, implique la disponibilité et l'utilisation de matériaux catalytiquement actifs et notamment des composés tampons d'oxygène, ce qui peut réversible stocker et libérer de grandes quantités de l'oxygène. Oxyde de cérium dopé présente encore aujourd'hui le seul composé de référence pour un support approprié, en raison de sa grande capacité de stockage de l'oxygène et possibilité de créer facilement des lacunes en ions d'oxygène. Cependant, pour des raisons économiques et de l'abondance naturelle très limitée à quelques pays, la substitution de l'oxyde de cérium semble être obligatoire; Dans ce contexte, nous notons que l'oxyde de cérium est partie de la liste des 13 matières premières économiquement importants qui ont été identifiés par la Commission européenne comme soumis à un risque élevé d'interruption de l'alimentation. Dans ce contexte, les oxydes de type brownmillérite sont d'un intérêt potentiel, car ils révèlent oxygène mobilité ionique jusqu'à la température ambiante. En outre, ils permettent de régler la présence de défauts étendus par exemple frontières anti-phase au cours de conditions de synthèse, et qui se sont avérés diminuer de manière significative l'énergie d'activation pour la diffusion d'oxygène. Nous avons ainsi pu montrer que vice-riche nano-Ca2Fe2O5, traditionnellement connue comme une ligne phase stoechiométrique, peut être oxydé dans des conditions douces à CaFeO3, tandis que l'oxydation de Ca2Fe2O5 ordinaire nécessite généralement des conditions de réaction extrême, soit 1100 ° C et plusieurs GPa pression partielle d'oxygène. Ainsi, l'introduction d'une forte concentration de défauts semble être un concept prometteur pour transformer ligne phases stoechiométriques même traditionnellement connus pour devenir une sorte d'éponge de l'oxygène et de se comporter en tant que composé de stockage / tampon d'oxygène à des températures très modérées. Ce comportement est donc comparable à la capacité de stockage d'oxygène d'oxyde de cérium dopé, et dispose d'un potentiel réel pour l'application dans la catalyse. Par conséquent, le brownmillérite Ca2Fe2O5 semble être un candidat prometteur pour étudier en raison de ses oxygène connue propriétés de conductivité ionique.Objectif principal de ce travail est d'établir la relation fondamentale entre structure / microstructure, propriétés de mobilité de l'oxygène et de l'activité catalytique, simultanément entrepris pour deux systèmes: Ca2Fe2O5 avec la structure brownmillérite-type et CeO2 avec une structure de type fluorite. Nous essentiellement exploré les critères sous-jacents qui régissent leur composition chimique / activité catalytique, utilisant de l'oxygène comportement d'échange des isotopes par TG expériences couples de MS. D'autres études utilisant la spectroscopie Raman essentiellement permis de conclure à partir d'une dynamique de réseau modifiées pour différents isotopes de l'oxygène à la différence entre masse et la participation à l'oxygène de la surface au mécanisme d'oxydation du CO en CO2. Pour une meilleure compréhension mécaniste de l'oxydation de CO, nous avons développé un nouveau test catalytique, par rapport à une variation dynamique de la pression partielle d'oxygène dans le récipient de réaction, ce qui permet de conclure à la fois sur l'activité catalytique du catalyseur et sa libération de l'oxygène / comportement absorption , non accessible par le test d'activité catalytique classique interprétée sous un flux de gaz constant. De cette façon, nous avons eu un nouvel aperçu de différencier la participation de la surface et de l'activité vrac d'oxygène pour les catalyseurs à base d'oxyde de cérium et Ca2Fe2O5 différente. / Accomplishing specifications of new regulations regarding automotive exhaust after-treatment technologies, e.g. TWC, imply the availability and usage of catalytically active materials and especially oxygen buffer compounds, which can reversibly store and release high quantities of the oxygen. Doped cerium oxide presents still today the only reference compound for a suitable support, due to its high oxygen storage capacity and ability to easily create oxygen ion vacancies. However, for economic reasons and very limited natural abundance to a few countries, the substitution of ceria appears to be mandatory; in this context we note that ceria is part of the list of 13 economically important raw materials which were identified by the European Commission as subject to a high risk of supply interruption.In this context, Brownmillerite-type oxides are of potential interest, since they reveal oxygen ion mobility down to ambient temperature. Furthermore, they allow to adjust the presence of extended defects e.g. anti-phase boundaries, during synthesis conditions, and which have been shown to significantly decrease the activation energy for oxygen diffusion. We were thus able to show that defect-rich nano-Ca2Fe2O5, traditionally known as a stoichiometric line-phase, can be oxidized under mild conditions to CaFeO3, while the oxidation of ordinary Ca2Fe2O5 usually requires extreme reaction conditions, i.e. 1100°C and several GPa oxygen partial pressure. Thus, introducing a high concentration of defects seems to be a promising concept to transform even traditionally known stoichiometric line-phases to become a kind of oxygen sponge and behave as oxygen storage/buffer compound at very moderate temperatures. This behavior is thus comparable to the oxygen storage capacity of doped cerium oxide, and offers a true potential for application in the catalysis. Consequently, the Brownmillerite Ca2Fe2O5 appears to be a promising candidate to study due to its known oxygen ion conductivity properties.Primary aim of this work is to establish fundamental relation between structure/microstructure, oxygen mobility properties and catalytic activity, simultaneously undertaken for two systems: Ca2Fe2O5 with Brownmillerite-type structure and CeO2 with Fluorite-type structure. We essentially explored the underlying criteria governing their chemical/catalytic activity, using oxygen isotope exchange behavior by TG couples MS experiments. Further studies using essentially Raman spectroscopy allowed concluding from a modified lattice dynamics for different oxygen isotopes to differentiate between bulk and surface oxygen participation to the oxidation mechanism of CO to CO2. For a deeper mechanistic understanding of the CO oxidation, we developed a new catalytic test, based on a dynamic variation of the oxygen partial pressure in the reaction vessel, allowing to conclude simultaneously on the catalytic activity of the catalyst and its oxygen release/uptake behavior, not accessible by the classical catalytic activity test performed under constant gas flow. In this way we got a new insight to differentiate the participation of surface and bulk oxygen activity for different Ca2Fe2O5 and ceria based catalysts.

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