Dans ce travail, nous représentons des résultats expérimentaux sur la transition vers les rouleaux turbulents dans l’écoulement de Couette-Taylor, l’écoulement produit entre deux cylindres coaxiaux tournant indépendamment l’un par rapport à l’autre. Une fois la géométrie et la nature du fluide sont fixes, l’écoulement est gouverné par deux paramètres de contrôle, les nombres de Reynolds intérieur et extérieur 〖Re〗_o et 〖Re〗_i associés à la rotation des cylindres extérieur et intérieur respectivement. La variation de ces paramètres confère à l’écoulement une variété de régimes, décrits par Coles [7] et par Andereck et al. [13]. Dans le cas de la contra-rotation, nous avons identifié trois régimes principaux sur le diagramme d'Andereck et al. [13] En considérant la variation de 〖Re〗_i pour une valeur fixe de〖 Re〗_o, l’écoulement est laminaire pour des faibles〖 Re〗_i. Il devient instable pour des valeurs plus élevées de〖 Re〗_i. Avant d'atteindre la turbulence, l'écoulement passe par un régime de coexistence laminaire-turbulent [7 13 14 16]. Pour notre série de mesures, nous avons fixé le nombre de Reynolds extérieur à 〖Re〗_o=-4368 et nous avons varié 〖Re〗_i du régime laminaire vers le régime turbulent. Pour 3000 < 〖Re〗_i < 4000, les diagrammes spatio-temporels indiquent la présence de structures cohérentes désordonnées. Ces structures sont bien organisées dans le temps et dans l’espace pour 4000 <〖 Re〗_i < 10000, et deviennent stationnaires pour des 〖Re〗_i plus grands [35]. Cette étude a été réalisée à l’aide d’une technique de visualisations à l'aide du kalliroscope, ainsi que par des mesures de vitesse par PIV stéréoscopique et LDV. Ceci nous permet ensuite de calculer les différentes quantités moyennes (énergie cinétique, contrainte de Reynolds, temps et longueur de corrélation, ...). / In this work we report experimental results on the transition to the turbulent vortices in the Couette-Taylor flow, the flow produced between independently rotating coaxial cylinders. Once the geometry and the nature of the fluid are fixed, the flow is gouverned by two control parameters, the outer and the inner Reynolds numbers 〖Re〗_o and 〖Re〗_i associated with the rotation of the outer and inner cylinders respectively. The variation of these parameters produces a large variety of regimes, which have been described by Coles [7], and Andereck et al. [13]. In the counter-rotating case, we have identified three main regimes on the diagram of Andereck et al. [13] When considering the variation of 〖Re〗_ifor a fixed value of〖 Re〗_o, the flow is laminar for low〖 Re〗_i. It becomes unstable for higher values of 〖Re〗_i. Before reaching turbulence, the flow passes by a regime of laminar-turbulent coexistence [7 13 14 16]. For our series of measurements, we fixed the outer Reynolds number at 〖Re〗_o=-4368, and varied 〖Re〗_ifrom the laminar to the turbulent regime. For 3000 < 〖Re〗_i< 4000, the space-time diagrams indicate the occurrence of disordered coherent structures. These structures are then well organized in time and space for 4000 < 〖Re〗_i< 10000, and become stationnary for the highest 〖Re〗_i [35]. These regimes are studied by visualizations using kalliroscope, as well as measurements of the velocity by stereoscopic PIV and LDV. This later allows us to calculate the various mean quantities (kinetic energy, Reynolds stress, time and length of correlation, etc…).

Magnetorotational instability (MRI) is one of the most important and most common instabilities in astrophysics. Today it is widely accepted that it serves as a major source of turbulent viscosity in accretion disks, the most energy efficient objects in the universe. The importance of the MRI for astrophysics has been realized only in recent fifteen years. However, originally it was discovered much earlier, in 1959, in a very different context. Theoretical flow of a conducting liquid confined between differentially rotating cylinders in the presence of an external magnetic field was analyzed. The central conclusion is that the additional magnetic field parallel to the axis of rotation can destabilize otherwise stable flow. Theory of non-magnetized fluid motion between rotating cylinders has much longer history, though. It has been studied already in 1888 and today such setup is usually referred as a Taylor-Couette flow. To prove experimentally the existence of MRI in a magnetized Taylor-Couette flow is a demanding task and different MHD groups around the world try to achieve it. The main problem lies in the fact that laboratory liquid metals which are used in such experiments are characterized by small magnetic Prandtl number. Consequently rotation rates of the cylinders must be extremely large and vast amount of technical problems emerge. One of the most important difficulties is an influence of plates enclosing the cylinders in any experiment. For fast rotation the plates tend to dominate the whole flow and the MRI can not be observed. In this thesis we discuss a special helical configuration of the applied magnetic field which allows the critical rotation rates to be much smaller. If only the axial magnetic field is present, the cylinders must rotate with angular velocities corresponding to Reynolds numbers of order Re ≈ 10^6. With the helical field this number is dramatically reduced to Re ≈ 10^3. The azimuthal component of the magnetic field can be easily generated by letting an electric current through the axis of rotation, In a Taylor-Couette flow the (primary) instability manifests itself as Taylor vortices. The specific geometry of the helical magnetic field leads to a traveling wave solution and the vortices are drifting in a direction determined by rotation and the magnetic field. In an idealized study for infinitely long cylinders this is not a problem. However, if the cylinders have finite length and are bounded vertically by the plates the situation is different. In this dissertation it is shown, with use of numerical methods, that the traveling wave solution also exists for MHD Taylor-Couette flow at finite aspect ratio H/D, H being height of the cylinders, D width of the gap between them. The nonlinear simulations provide amplitudes of fluid velocity which are helpful in designing an experiment. Although the plates disturb the flow, parameters like the drift velocity indicate that the helical MRI operates in this case. The idea of the helical MRI was implemented in a very recent experiment PROMISE. The results provided, for the first time, an evidence that the (helical) MRI indeed exists. Nevertheless, the influence of the vertical endplates was evident and the experiment can be, in principle, improved. Exemplary methods of reduction of the end-effect are here proposed. Near the vertical boundaries develops an Ekman-Hartmann layer. Study of this layer for the MHD Taylor-Couette system as well as its impact on the global flow properties is presented. It is shown that the plates, especially if they are conducting, can disturb the flow far more then previously thought also for relatively slow rotation rates. / Die magnetische Scherinstabilitaet (engl. MRI) ist eine sehr häufig in der Astrophysik anzutreffende Instabilität. Es wird heute weithin angenommen, dass sie die Ursache für die turbulente Viskosität in Akkretionsscheiben ist, den Objekten mit der höchsten Energieeffizienz im Kosmos. Die Bedeutung der MRI ist erst in den letzten fünfzehn Jahren klargeworden. Entdeckt wurde sie jedoch schon viel früher, im Jahre 1959 in einem völlig anderen physikalischen Kontext. Die Strömung in einer leitfähigen Flüssigkeit zwischen differentiell rotierenden Zylindern unter dem Einfluss eines externen Magnetfeldes wurde theoretisch untersucht. Die Schlussfolgerung war, dass das zugesetzte Magnetfeld eine sonst stabile Strömung destabilisieren kann. Die Geschichte der Theorie von Strömungen zwischen Zylindern reicht bis ins Jahr 1888 zurück. Heute wird ein solcher Aufbau üblicherweise als Taylor-Couette-Strömung bezeichnet. Ein System rotierender Zylinder, zwischen denen sich flüssiges Metall befindet, war Gegenstand des kürzlich durchgeführten Experiments PROMISE. Die Ergebnisse belegen zum ersten Mal experimentell die Existenz der MRI. Um die notwendigen Drehzahlen gering zu halten, wurde ein spezielles, helikales Magnetfeld angelegt. Gegenstand dieser Dissertation ist die theoretische Behandlung der magnetohydrodynamischen Taylor-Couette-Strömung, ähnlich der des Experiments PROMISE. Insbesondere der Einfluss der vertikalen Ränder (Deckel) wird untersucht. Es wird gezeigt, dass die MRI auch in Zylindern mit endlicher Höhe und mit begrenzenden Deckeln einsetzt. In der Nähe der vertikalen Ränder bildet sich eine Ekman-Hartmann-Schicht. Die Untersuchung dieser Schicht im Zusammenhang mit dem MHD-Taylor-Couette-System sowie ihr Einfluss auf die globalen Strömungseigenschaften werden vorgestellt. Es wird gezeigt, dass die Deckel - insbesondere wenn sie elektrisch leitend sind - die Strömung stärker beeinflussen können als bisher angenommen, selbst bei den geringen Drehzahlen. Es werden Methoden zur Verringerung dieser unerwünschten Effekte vorgeschlagen.

Bwana Tela (1856-1927) alikuja Afrika ya mashriki kutoka Ulaya katika mwaka 1297 wa hijti (mwaka 1880 wa miladi), akakaa kwa muda wa myaka khamustaashara takriban. Ingawa alikuja kutangaza dini ya kiNasara, kazi aliyofanya zaidi Mambasa ilikuwa ni ya mambo ya utaalamu wa lugha ya kiSawahili, na mashairi yake, na utamaduni wa waSawahili. Alipata bahati ya kuwa na marafiki wataalamu wa kiMvita, khaswa Mwalimu Sikujuwa al-Batawi, na Bwana Hemedi al-Mambasi. Nyimbo zake za kiMisheni alizotunga kwa kiSawahili hazikutiwa maanani, lakini mahadhi aliokuwa akiimbiya yalibakiya kwa myaka mingi kwa jina la `mahildhi ya Tela´. Bwana Tela alisaidiana na Mwalimu Sikujuwa kuhifadhi t´ungo za washairi wengi wa kale zisipotee, khaswa t´ungo za Bwana Muyaka. Kadhalika alikusanya mithali ya kiSawahili, zaidi ya sita-mia. Karatasi zake alizoandika mambo ya kiSawahili, nyingi sasa ziko maktaba ya SOAS, London, na ni muhimu katika kutusaidiya kufahamu kiSawahili cha kiSawahili. Si makosa kusema kuwa Bwana Tela ndiye mtaalamu mkubwa wa kiSawahili katika wataalamu wote wa kiNgereza.

This study seeks to describe the theodicy of Scottish theologian Peter Taylor Forsyth. We begin by making some preliminary comments concerning Forsyth’s conception of reality and his understanding of evil. We then examine Forsyth’s methodology of the theologia crucis, which he utilises in his justification of God. Forsyth sees a crucial event taking place at the Cross, “the self-justification of God”, one which constitutes the basis for all human attempts to justify God. We explore his multi-faceted understanding of this event, and how it leads to two outcomes which form the main thrusts of his theodicy. In Chapters 3 and 4, we look at the first such outcome, which is that God moves the world inexorably towards his glorious telos. We also consider here the significance of this first outcome for Forsyth’s theodicy, which is that it imparts to this theodicy a strongly teleological and historical nature. In Chapters 5 and 6, we consider the second outcome of God’s self-justification. This is the revelation that God suffered incomparably in the event of the Cross. We draw out two major implications of this for Forsyth’s theodicy, based upon the idea that God is the chief sufferer and giver in our battle against sin, and the possibility that Christ might serve as our model of faith in times of suffering. We turn, in our final two chapters, to examine Forsyth’s view on the origin of both sin and suffering, his understanding of the God-world relationship, and the significance of these for his theodicy. We conclude that Forsyth’s justification of God constitutes a robust and comprehensive response to the problem of evil, possibly rendering a valuable service to the task of Christian theodicy through its ability to integrate insights from what has hitherto been considered different approaches to the issue.

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Romantic literature's preoccupation with subjectivity, and the nature of the self, is recognised as influential on modern conceptions of consciousness, and in particular as a precursor of psychoanalysis. This thesis examines Coleridge's understanding of consciousness, as expressed in his prose, to demonstrate that he theorised a language of the unconscious; a non-arbitrary, authentic language that remains inaccessible. By comparing this idea with Julia Kristeva's theory of Semiotic language, the thesis will show that this language is indeed recognised in her psychoanalytic theory as a product of the unconscious. Most importantly, it will show that while Coleridge's supernatural poetry laments the inaccessibility of unconscious language, Kristevan theory demonstrates it to be present in that very poetry.

Zugl.: Giessen, Universiẗat, Magisterarbeit.

Mémoire (M.A.)--Université du Québec à Trois-Rivières, 2005. / Comprend des réf. bibliogr.: f. 102-105. Également disponible en format microfiche et PDF.

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