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Showing 131 to 135 of 135 (0.311 seconds)| 131 |
Étude de l'ébullition sur plaque plane en microgravité, application aux réservoirs cryogéniques des fusées Ariane V / Study of nucleate boiling in microgravity conditions, aplicated to the ArineV cryogenics tanksKannengieser, Olivier 18 December 2009 (has links)
Ce rapport de thèse porte sur une étude expérimentale et théorique de l'ébullition en microgravité. Les expériences furent réalisées en condition de gravité terrestre, en vol parabolique et en fusée-sonde. Les expériences en vol parabolique ont montré l'influence de divers paramètres sur le transfert thermique et ont mis en évidence les mécanismes contrôlant le transfert thermique. De l'écriture des équations gouvernant ces mécanismes et de l'identification des échelles caractéristiques, une corrélation permettant d'estimer le transfert de chaleur lors de l'ébullition en microgravité pour une large gamme de fluide est bâtie. L'expérience en fusée-sonde a permis d'étudier l'influence des gaz incondensables et notamment de la convection Marangoni sur le comportement de l'ébullition et sur le transfert thermique. / Between the different propulsion phases, the Ariane V rocket passes through microgravity periods and solar radiation can induce boiling in its cryogenics tanks. Experiments were performed during 6 parabolic flights and in a sounding rocket to study pool boiling in microgravity. In the parabolic flight experiments, the influence of pressure, subcooling and surface roughness was studied. It is showed that subcooling has a weak effect on microgravity boiling heat transfer, and that roughness is an important factor also in microgravity. Detailed results on the behavior of bubbles and on the superheated liquid layer show that the heat transfer mechanisms can be divided in two groups : the primary mechanisms which directly take energy from the wall and the secondary mechanisms which transport the energy stored in the fluid by the primary mechanisms, from the vicinity of the wall to the bulk liquid. The secondary mechanisms appear not to limit primary mechanism heat transfer which explains the weak influence of gravity on heat transfer. From the study of equations governing primary mechanisms and the definition of new scales, a correlation is built to predict heat transfer in microgravity for a wide variety of fluids. In the sounding rocket experiment, the influence of non-condensable gases was studied. The existence of two regimes of boiling heat transfer with non-condensable gas is established. The temperature in the primary bubble is directly measured and the influences of both Marangoni convection and non-condensable gas on both heat transfer and bubble growth are also considered.
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Matter wave interferometry in microgravityKrutzik, Markus 20 October 2014 (has links)
Quantensensoren auf Basis ultra-kalter Atome sind gegenwärtig auf dem Weg ihre klassischen Pendants als Messintrumente sowohl in Präzision als auch in Genauigkeit zu überholen, obwohl ihr Potential noch immer nicht vollständig ausgeschöpft ist. Die Anwendung von Quantensensortechnologie wie Materiewelleninterferometern im Weltraum wird ihre Sensitivität weiter steigen lassen, sodass sie potentiell die genauesten erdbasierten Systeme um mehrere Grössenordnungen übertreffen könnten. Mikrogravitationsplattformen wie Falltürme, Parabelflugzeuge und Höhenforschungsraketen stellen exzellente Testumgebungen für zukünftge atominterferometrische Experimente im Weltraum dar. Andererseits erfordert ihre Nutzung die Entwicklung von Schlüsseltechnologien, die hohe Standards in Bezug auf mechanische und thermische Robustheit, Autonomie, Miniaturisierung und Redundanz erfüllen müssen. In der vorliegenden Arbeit wurden erste Interferometrieexperimente mit degenerieten Quantengasen in Schwerelosigkeit im Rahmen des QUANTUS Projektes durchgeführt. In mehr als 250 Freifall-Experimenten am Bremer Fallturm konnte die Präparation, freie Entwicklung und Phasenkohärenz eines Rubidium Bose- Einstein Kondensates (BEC) auf makroskopischen Zeitskalen von bis zu 2 s untersucht werden. Dazu wurde ein BEC-Interferometer mittels Bragg-Strahlteilern in einen Atomchip-basierten Aufbau implementiert. In Kombination mit dem Verfahren der Delta-Kick Kühlung (DKC) konnte die Expansionsrate der Kondensate weiter reduziert werden, was zur Beobachtung von effektiven Temperaturen im Bereich von 1 nK führte. In einem Interferometer mit asymetrischer Mach-Zehnder Geometrie konnten Interferenzstreifen mit hohem Kontrast bis zu einer Verweildauer von 2T = 677 ms untersucht werden. / State-of-the-art cold atomic quantum sensors are currently about to outpace their classical counterparts in precision and accuracy, but are still not exploiting their full potential. Utilizing quantum-enhanced sensor technology such as matter wave interferometers in the unique environment of microgravity will tremendously increase their sensitivity, ultimately outperforming the most accurate groundbased systems by several orders of magnitude. Microgravity platforms such as drop towers, zero-g airplanes and sounding rockets are excellent testbeds for advanced interferometry experiments with quantum gases in space. In return, they impose demanding requirements on the payload key technologies in terms of mechanical and thermal robustness, remote control, miniaturization and redundancy. In this work, first interferometry experiments with degenerate quantum gases in zero-g environment have been performed within the QUANTUS project. In more than 250 free fall experiments operated at the drop tower in Bremen, preparation, free evolution and phase coherence of a rubidium Bose-Einstein condensate (BEC) on macroscopic timescales of up to 2 s have been explored. To this end, a BEC interferometer using first-order Bragg diffraction was implemented in an atomchip based setup. Combined with delta-kick cooling (DKC) techniques to further slow down the expansion of the atomic cloud, effective temperatures of about 1 nK have been reached. With an asymmetrical Mach-Zehnder geometry, high-contrast interferometric fringes were observed up to a total time in the interferometer of 2T = 677 ms.
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Zur Bedeutung des Vergleichs in Eichendorffs Erzählwerk : "...ihm war, als spiegelte sich wunderbar sein Leben wie ein Traum noch einmal wieder"Behrens, Ragni January 2005 (has links)
The present dissertation investigates similes and their importance in Eichendorff’s narrative work. The sources of the investigation consist of seven of Eichendorff’s narratives. Their 734 similes make up the corpus, which is presented in its entirety in the appendix. The context of the similes is partly included as well. Initially, I define the concept of “simile” more precisely, partly distancing myself from the definitions found in classical dictionaries of literary terms. After this, I describe my procedure for analysis in detail. This turned out to be necessary, since there was no similar study to be found on this topic in the extensive literature on Eichendorff. The search for models of types of similes brought me back to antique rhetoric as well as to Middle High German epic poems. In the first analysis, the types of similes occurring in the corpus are presented. The syntactic structures of image receivers and image givers are used as criteria. Four structures of similes occurred: a) classical similes and b) similes with image givers, which represent adverbial clauses and c) as / as if – clauses or are d) subject-related. The frequency and the development of frequency of types of similes are presented as well. In the second step of the thesis, I investigate whether similes tend to depict conditions/qualities or procedures/actions. It turned out that similes reflecting conditions/qualities, i.e. epic similes, dominated strongly. The high number of similes could possibly be explained by the functions carried out by epic similes in narrative texts. In the third part, I concern myself with the question whether the similes of the corpus are imaginative representations only and what kind of sensorial perceptions they express. Admittedly, the dominating percentage of the similes proved to be images, but more than fifteen per cent consist of sounds and other sensorial perceptions. Furthermore, imaginative similes, but also sounding similes express motion, so that they illustrate pictures in motion and sounding motion respectively. These come close to synaesthesia, whereas only five similes illustrate „pure“ synaesthesia. In contrast, subject-related similes are perceptions of different sensations and feelings, illustrating the inner life of a character not shared by any other character. Finally, the semantic content of the similes is investigated in order to determine the metamorphosis, i.e. the trope transfer from proprium to improprium. It turned out that only the classical simile originating in antique rhetoric is suitable for a semantic analysis. Above all, there is great variation in the trope transfer. The metamorphosis human being → nature dominates strongly, which makes the narrative text appear as a palimpsest, in which yet another world glimmer in front of the human being behind every character. However, the many trope transfers that convey reality → unreality could be interpreted as transitions and as a “magical code” of Eichendorff. Furthermore, the semantic analysis uncovers content and motives of classical similes. It becomes clear that pre-constructed – and only pre-constructed - content is imitated here. Consequently, it can be asserted that Eichendorff’s great number of similes constitute or at least contribute to the formulaic manner (according to Kohlschmidt) and the intertextuality (according to Nienhaus) in Eichendorff’s narrative work. Above all, the subject-related simile type turns out to be a typical representative of Romanticism because of its subjectivism. Together with its preformed semantic content, it constitutes the “romantic formula” of Eichendorff’s work.
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[en] COMPARISON AMONG WIDEBAND MOBILE RADIO CHANNEL SOUNDING TECHNIQUES IN THE PRESENCE OF SOUNDER IMPERFECTIONS / [pt] COMPARAÇÃO ENTRE MÉTODOS DE SONDAGEM DO CANAL RÁDIO MÓVEL EM BANDA LARGA NA PRESENÇA DE IMPERFEIÇÕES NAS SONDASCARLOS EDUARDO SALLES FERREIRA 18 July 2018 (has links)
[pt] As características do canal rádio móvel são essenciais ao desenvolvimento de equipamentos e sistemas modernos de telecomunicações sem fio. Para os ambientes nos quais o sistemas operarão, o conhecimento dos principais parâmetros do canal em banda larga é obtido através do uso do conjunto formado por um equipamento transmissor e outro equipamento receptor com suas respectivas antenas. A este conjunto transmissor e receptor atribui-se o nome de sonda. Existem diversas tecnologias sobre as quais as sondas são projetadas e construídas. Em particular mencionam-se as técnicas STDCC (swept time-delay cross-correlation), o Filtro Casado e o OFDM (orthogonal frequency-division multiplexing). Esta tese compara, por simulação, o desempenho de sondas que utilizam estas três técnicas. São propostas alterações nos métodos Filtro Casado e OFDM, de forma que estes proporcionem resultados mais precisos. Além disto, são estudadas imperfeições em dispositivos comuns a todas elas e comparadas sua influência sobre a qualidade das estimações, de forma isolada e combinada. Para o amplificador de potência é considerado o seu principal fator de degradação: suas não linearidades. Para o oscilador local existente no receptor é analisada a contribuição do ruído de fase. O ruído térmico, sempre presente à entrada do receptor em qualquer situação, é variado em uma extensa faixa de valores e o seu efeito sobre a precisão de cada método é analisado. Os resultados obtidos são apresentados na forma de tabelas e gráficos representando, diretamente, o resultado da comparação com o canal de referência ou por meio dos indicadores erro RMS e desvio padrão. / [en] The mobile radio channel characterization is essential to the development of modern wireless telecommunication equipment and systems. The main wideband channel parameters of the environments where these systems will operate are collected by the use of a set comprising a transmitter, a receiver and an aerial system. This set is named sounder. There are many techniques used to project and implement these sounders, such as STDCC (Swept Time-Delay Cross-Correlation), Matched Filter and OFDM (Orthogonal Frequency-Division Multiplexing). This thesis compares, by means of computer simulations, the performance of these three techniques. Some changes are proposed on the Matched Filter and OFDM methods to reach more precise results. Moreover, imperfections in common devices used by all sounders are studied, both independently and jointly, and the impact over the precision of channel estimations is analyzed. The main degradation factor of power amplifiers, which are the nonlinearities, was also considered, as well as the contribution of the phase noise in the receiver local oscillator. The effect of the thermal noise, always present on the receiver input, was also considered, over a large range of values. The results are presented by diagrams and tables showing results of comparisons with a reference channel or by mean of RMS errors and standard deviations.
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銀行聯合貸款業務之經營模式與策略研究-以台灣聯貸市場為例 / The Study of Banking Business Model and Strategy about Syndicated Loan Product – in Taiwan Syndication Market葉美華, Yeh, Mei-Hua Unknown Date (has links)
政府在1990年開放新銀行申請設立、1991年共核准通過15家新銀行籌設，國內銀行自此即進入百家爭鳴的時代，各家銀行惡性競爭的結果，除了利差不斷降低外，授信品質亦不斷惡化，各銀行資本報酬率直直落，為求生存，遂絞盡腦汁不斷推出各種新型商品以促進客戶擴大信用；聯合貸款業務亦不例外，各銀行有鑑於傳統企業授信漸不能達到應有績效之際，紛紛著重於聯貸業務，於是業務競爭日趨白熱化，如何設計符合貸款企業期望的授信方案，是各銀行贏得聯合授信主辦權的重要課題。
因此，企業如何選擇聯合貸款主辦行之影響因素，是各銀行放款經理人亟盼了解的經營知識，而根據這些關鍵影響因素，各銀行為爭取主辦權所擬定的各項經營模式與策略，即是足以決定聯合貸款業務在各銀行未來之發展情形與定位，甚而決定其在聯貸市場所扮演之角色與市場佔有率。
有鑑於此，本研究主要以銀行端的角色來探討各銀行針對聯合貸款業務所為之相關措施及其後續之影響結果，並針對國內主要聯貸銀行做個案分析，以了解各銀行所採取的策略及經營方針。
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