Mixing is a common feature of stratified fluids. In stratified fluids the density varies with the height. This is true for the most fluids in geophysical environments, like lakes, the atmosphere or the ocean. Turbulent mixing plays a crucial role for the overall energy budget of the earth and has therefore an huge impact on the global climate. By introducing the mixing efficiency, it is possible to quantify mixing. It is defined as the ratio of gain of potential energy to the injection of mechanical energy. In the ocean energy provided by tidal forces leads to turbulence and thus highly dense water is lifted up from the deep sea to the surface. For this process, a mixing efficiency of 0.2 is estimated. Until now it is not completely understood how this high value can be achieved. Thus we measured the mixing efficiency by using a Couette-Taylor system, which can produce steady-state homogeneous turbulence. This is similar to what we find in the ocean. The Couette-Taylor system consists of two concentric cylinders that can be rotated independently. In between a stratified fluid is filled using salt as a stratifying agent. In the laboratory experiment, we obtained mixing efficiencies in the order of 0.001 as a result. Moreover we found that the mixing efficiency decreases with decreasing stratification like previous laboratory experiments have shown. As this value is two orders of magnitude smaller than what we find in the ocean, further studies will be necessary. / text

Gas-liquid, two-phase flow is encountered in a wide variety of industrial equipment. A few examples are steam generators, condensers, oil and gas pipelines, and various components of nuclear reactors. Slug flow is one of the most common and complex flow patterns and it occurs over a broad range of gas and liquid flow rates. In vertical tubes, most of the gas is located in large, bullet-shaped bubbles (Taylor bubbles) which occupy most of the pipe cross section and move with a relatively constant velocity. The objectives of this work are to increase our understanding of slug flow in vertical tubes, to provide reliable data for validation of numerical models developed to predict the behaviour of slug flow, to interpret the behaviour of Taylor bubbles based on knowledge of the velocity field, and to determine the shape of the Taylor bubbles rising in stagnant and upward flowing liquid under various experimental conditions. To achieve these objectives, an experimental facility was designed and constructed to provide instantaneous two-dimensional (2-D) velocity field measurements using particle image velocimetry (PIV) around Taylor bubbles rising in a vertical 25 mm tube containing stagnant or upward moving liquids at Reynolds number based on the superficial liquid velocity (ReL = 250 to 17,800). The working fluids were filtered tap water and mixtures of glycerol and water (µ = 0.0010, 0.0050 and 0.043 Pa•s) and air. Mean axial and radial velocity profiles, axial turbulence intensity profiles, velocity vectors, and streamlines are presented for Taylor bubbles rising in stagnant and upward flowing liquids. The measurements were validated by a mass balance around the nose of the bubble. In stagnant liquids, the size of the primary recirculation zone in the near wake of the Taylor bubble depends on the inverse viscosity. For low viscosity liquid, the length of the primary recirculation zone is 1.23D (D is the tube diameter), for the intermediate viscosity it is 1.2D, and for the high viscosity it is 0.68D. Based on the velocity measurements, the minimum stable liquid slug length (the minimum distance needed to re-establish a fully-developed velocity distribution in the liquid in front of the trailing Taylor bubble) for stagnant cases was found to be in the range of 2~12D. In the flowing liquid, the flow structure of the wake depends on the relative motion between the two phases and the liquid viscosity. The wake is turbulent in all cases except at high viscosity where the wake is transitional. In general, the length of the primary recirculation zone increases with increasing liquid flow rate. For low viscosity cases, in a frame of reference moving at the bubble velocity, the length of the recirculation zone is 1.73D for ReL =9,200 and become essentially constant at 1.90D for ReL ≥ 13,600. For the intermediate viscosity, the length of the recirculation zone is 1.22D for ReL = 1,500. The length of the recirculation zone is increased to 1.34D for ReL = 3,900. For the high viscosity, the length of the recirculation region is elongated to 1.4D for ReL = 260. As the liquid flow rate increases the oscillations of the bottom surface increase and the number of small bubbles shed from the bubble bottom increases. The liquid slug minimum stable length for turbulent upward flowing liquid is around 12D. For laminar flow, the minimum stable length is 10D for ReL = 260 (high viscosity) and > 28D for ReL=1,500 (intermediate viscosity) and depends on the wake flow pattern and the liquid flow rate.

No description available.

Experiments are presented in which the diffuse interface between two gases is made Rayleigh-Taylor unstable by interaction with a rarefaction wave. The apparatus used consists of a test section where the counter-flow of light and heavy gases generates a diffuse, stably stratified interface. A tank attached to the bottom of the apparatus is evacuated, and when an appropriate pressure is reached, the interface is perturbed using either a horizontal or a vertical oscillation technique to produce 2D, 3D, and multi-mode perturbations. A solenoid plunger fires an arrowhead which ruptures a membrane, generating a rarefaction wave that travels upward toward the interface. When the rarefaction wave impacts the interface, the interface accelerates down toward the vacuum tank, and the Rayleigh-Taylor instability and mixing develop in the test section. The instability evolution and mixing are recorded using high-speed CMOS cameras and planar laser Mie scattering of smoke particles seeded in the heavy gas. Additional visualization is undertaken with a high-speed shadowgraph system using three CMOS cameras. Interface diffusion thicknesses are recorded using the Rayleigh scattered light of an unexpanded laser beam. Simulations are conducted using a 1D numerical characteristics code based on the method of Hoskin (Meth. Comp. Physics, 3, 1964), and using the LLNL research hydrodynamics code Miranda (Cook, Phys. Fluids, 19, 2007). This 1D code produces Lagrangian interface trajectories while the 2D and 3D simulations using Miranda calculate the growth of perturbations. The theory of Chandrasekhar (Chandrasekhar, Proc. Camb. Phil. Soc., 51, 1955) is extended to capture the effects of diffuse interfaces while including viscosity, and dispersion curves are solved for numerically using a Riccati technique. These solutions show that the method of Duff et al. (Phys. Fluids, 5, 1962) may not accurately describe the growth of single modes for large wavenumbers. For large wavenumbers, when the interface has a large diffusion thickness, perturbations are found to grow with the linear growth rate n = 2Ag/(√πv₀δk²), where A is the Atwood number, g is the acceleration, v₀ is the average kinematic viscosity, δ is the thickness of the interface, and k is the wavenumber of the perturbation. Flat interface experiments exhibit predictable acceleration profiles, but the tail of the rarefaction wave appears at late times reducing the duration of acceleration. Single-mode experiments are conducted for four Atwood numbers including CO₂/SF₆ with A = 0.49, Air/SF₆ with A = 0.63, He/CO₂ with A = 0.82, and He/SF₆ with A = 0.94. Early time results compare well with linear stability theory when non-constant acceleration and diffusion thickness are accounted for. Simulations show good agreement with experiments into the non-linear growth phase. The CO₂/SF₆ and Air/SF₆ experiments show terminal velocity behavior where buoyancy is balanced by drag, but produce Froude numbers larger than those predicted by the Goncharov model (Phys. Rev. Lett., 88, 2002). Using the Mikaelian model (Phys. Fluids, 21, 2009), improved asymptotic Froude numbers are found. The He/CO₂ and He/SF₆ experiments exhibit free-fall behavior, accelerating freely without external forces, with spike amplitudes proportional to the displacement of the unperturbed interface. Single-mode experiments conducted with 3D perturbations using CO₂/SF₆ and Air/SF₆ show good agreement with linear stability theory when non-constant acceleration and diffusion thickness are accounted for. Simulations and the model of Mikaelian predict the growth of the spikes up until late time, while the 3D bubbles reach a terminal velocity more quickly than in simulations. Multi-mode experiments were conducted using Air/SF₆. Multi-mode experiments exhibit nearly t² growth at early times which decays. Using extraction techniques that account for variable acceleration, alpha values are found between ɑ = 0.02 and ɑ = 0.04. These alpha values are lower than are seen for most experiments, but are similar to ɑ values seen in miscible experiments.

No description available.

I denna uppsats undersöks på kvartalsbasis de ekonomiska effekterna av två välkända instrumentregler för Sverige under perioden 1993–2005. Dessa är: Taylor- respektive McCallumregeln. Instrumentet som används i Taylorregeln är den korta styrräntan. McCallumregeln innehåller ett annat instrument för centralbanken, långräntan. För att kunna utvärdera Taylorrespektive McCallumregeln skattas en makromodell. Makromodellen består av två ekvationer, en för aggregerat utbud och en för aggregerad efterfrågan. Skattningarna för makromodellen används sedan för att simulera effekterna på produktionsgapet och inflationen av en penningpolitik betingad på Taylor- respektive McCallumregeln. Slutligen används de simulerade värdena för produktionsgapet och inflationen under respektive regel för att beräkna en samhällsekonomisk förlustfunktion. Resultaten av simuleringarna och förlustfunktionerna tyder på att en tillämpning av Taylorregeln hade varit positiv för Sverige. Motsvarande resultat erhålles inte för McCallumregeln

The publication in 1957 and 1961 of two volumes of Coleridge's Notebooks has opened to all those who are interested in this writer as man, poet, critic, philosopher and psychologist opportunities to study him and his work anew. [...]

Many Indigenous leaders and public figures, as well as scholars of Indigenous culture and history, assert that non-Indigenous ignorance of Indigenous realities has systematically disadvantaged Indigenous peoples in Canada, weakened Canadian society, and makes it impossible to address the conditions of life for Indigenous people in Canada in a sustained or coherent way. Additionally, for many scholars silence and unawareness are deeply linked to colonialism and are implicated in the maintenance of unequal social relations. Drawing from this literature, I contend that in Canada, silence around Indigenous peoples and issues works as a spatial tactic of exclusion. I argue that unawareness is bound up in interests that work to render Indigenous peoples absent from the concerns of modern Canada, and that these interests are deeply intertwined with national and provincial identities such that silences around Indigenous peoples and issues are expressed differently in each Canadian province and territory. This thesis explores the nature of public unawareness of Indigenous realities in Québec. Using the remarkable public voice resource generated by the 2007 Reasonable Accommodation Commission in Québec, a public inquiry into Québec citizens’ opinions about the nature of Québec identity and its relationship to the integration of minorities in the province, I analyze the Commission’s mandate and geographical movements, as well as over 750 written briefs submitted to the Commission. I argue that unawareness of Indigenous realities is widespread in Québec and is unconstrained by participants’ social positions, interests, arguments, or level of engagement with the question of indigeneity in Québec. Though the Commission worked to exclude Indigenous content (and perhaps peoples) from its activities from the outset, eight Indigenous leaders submitted briefs and spoke powerfully and critically of the Commission’s exclusion. These authors point out that the question of Indigenous rights is far from settled, that the Commission’s and Quebecers’ unawareness of Indigenous realities is complicit in a long history of exclusion in Québec and in Canada, and assert that Quebecers will not be able to address their anxiety around immigration in any meaningful or coherent way until Indigenous rights are respected. In my focus on the Reasonable Accommodation Commission, I suggest the particular nature of exclusion in Québec. While exclusion of Indigenous peoples is a Canadian universal, its flavour varies. In this case, the provincial jurisdiction is important. / Thesis (Master, Geography) -- Queen's University, 2012-04-22 18:11:39.47

This thesis attempts to address different problems pertaining to the concept of subject. These problems might appear remote from one another, but their juxtaposition reveals possible interactions that yield rich avenues of research. The ensuing dialogue provides an interesting portrait of the contemporary subject. / Enunciation theories are the point of departure of this thesis. They contend that the subject constructs itself in and by discourse. A link is then made with certain problems put forward by Charles Taylor who also sets the contemporary subject in discourse, seen as essential material for its construction. The elaboration of a personal morality is the foundation of what he calls the self. / The exploration of these problems draws our attention toward some questions which are tackled in the two last chapters. The first question concerns the mode of construction of the subject. In accordance with our modern episteme, the subject constructs itself as narrative. The second question aims at understanding the role of the Other in the construction of the subject. The contact with the Other and the recognition of this difference are the motors of this construction.

Concerned with the state of the self in modernity, Charles Taylor engages in an act of cultural retrieval in order to allow for a meaningful struggle against the pernicious developments of the modern age. To avoid a loss of meaning, rampant instrumentality, and ultimately a loss of freedom, Taylor suggests that we must arrive at a new understanding of the self. To this end Taylor positions himself between contemporary liberals and communitarians, arriving at what he deems holistic individualism or an "ethic of authenticity". He holds that, in order for this notion of authenticity to be realized, we must be in contact with the constitutive goods which underpin western society. After prolonged consideration Taylor arrives at the conclusion that the only publicly available constitutive good in the modern age is religion. Although he is at times hesitant to admit it, Taylor contends that religion is an invaluable source for the self and the only good able to meet the challenges of modernity.