245 research outputs found
Direct versus noise-induced optimal transitions for a model shear flow
No full textThe transition from laminar to turbulent flow in parallel shear flows like pipe flow or plane Couette flow is not due to a linear instability of the laminar profile but requires finite amplitude perturbations. The perturbations have to be strong enough that they cross the boundary to the basin of attraction of the turbulent regime. We use a 2-dimensional model of the transition to turbulence to explore the underlying phase space structure for optimal perturbations with respect to three different criteria: the energy of the initial condition, the energy dissipation of the initial condition and the amplitude of noise in a noise-induced transition. We find that the optimal transition states are different, but that the scaling with Reynolds number is the same in all three cases. Implications for full simulations will be discussed
Intergenerationale Betreuung von älteren Menschen mit Demenz
No full textCan caring communities address the crisis in health and care? Annalena Eckhardt analyses the practices and models of caring communities. These aim to improve the quality of life of people with dementia through intergenerational support. In a comprehensive literature review, the author analyses the social, emotional and practical aspects of intergenerational care models, including intercultural aspects. She concludes that people with dementia can benefit greatly from social participation and autonomy within communities, but that obstacles such as idealised assumptions and barriers to access still need to be overcome
Stability and exact coherent structures of the asymptotic suction boundary layer with temperature gradient
No full textThe asymptotic suction boundary layer with a temperature gradient is a good point of entry to study the dynamics of thermal boundary layers by means of dynamical systems theory. The laminar flow without heating is parallel and its properties have been studied before. We add a temperature difference between the bottom plate and the free stream flow, and study the stability in dependence on Reynolds, Rayleigh and Prandtl number. In marked contrast to the usual Rayleigh-B\'enard problem, the onset of convection is subcritical. Tracking secondary bifurcations we identify time-periodic, spanwise, and doubly-localized exact coherent states for this flow
Mean field model for turbulence transition in plane Poiseuille flow
No full textIn the pipe flow model of Dwight Barkley the main idea is to model pipe flow as an excitable, bistable medium. Using a one-dimensional FitzHugh-Nagumo-type reaction-advection-diffusion system with two variables the model captures qualitatively a surprising number of features of the turbulence transition in pipe flow. Motivated by this success, we here describe a derivation of a set of two 1+1-dimensional coupled differential equations for the closely related system of plane Poiseuille flow from the Navier-Stokes equation. The model contains terms for the production of turbulent kinetic energy, its transfer between the modes and its dissipation by viscous terms. The model shows a bifurcation to a non-trivial state and reflects some of the complex dynamics observed in direct numerical simulations
Der Schweizer Stiftungsreport 2011
No full textDer Schweizer Stiftungsreport ist eine Informationsquelle für Stiftungsvertreter, Politiker, Medienvertreter, Aufsichtsbehörden und weitere Interessierte und soll dazu dienen, das Verständnis und die Berichterstattung über das Schweizer Stiftungswesen zu verbessern. Last but not least ist er auch eine Bestandsaufnahme mit dem Ziel, als Nachschlagewerk die Entwicklung des Schweizer Stiftungswesens kontinuierlich nachvollziehbar zu machen
Bypass transition in boundary layers as an activated process
No full textWe consider the spatio-temporal aspects of the transition to turbulence in a boundary layer above a flat plate exposed to free-stream turbulence. Combining results from the receptivity to free-stream turbulence with the observation of a double threshold from transition studies in e.g. pipe flow we arrive at a physically motivated prediction for the spatial distribution of nucleation events in boundary layers. We use a cellular automaton to implement a complete model for the spatial and temporal evolution of turbulent patches and show that the model reproduces the statistical features of the boundary layer remarkably well. The success of the modeling shows that bypass transition occurs as a spatiotemporally activated process, where transition is triggered by critical fluctuations imported from the free-stream turbulence
Fully localised edge states in boundary layers
No full textInvestigation of the laminar-turbulent boundary is performed in a boundary-layer flow. Constant homogeneous suction is applied at the wall in order to prevent the spatial growth of the layer, leading to the parallel Asymptotic Suction Boundary Layer (ASBL). Edge tracking is performed in a large computational domain allowing for full spatial localisation of the structures on the laminar-turbulent separatrix. The obtained dynamics of the state goes through calm and bursting phases. During the latter the structure grows in size, shedding vortices downstream of its core which viscously decay during the calm phases. Comparison with the computation in spatially growing boundary layer is made. The influence of the Reynolds number and the path leading from the edge state to turbulent flow are considered
Hedda Sterne and the abstract expressionist context
No full textThis dissertation focuses on the development of Hedda Sterne’s artistic philosophy and practice in the 1940s and 1950s. Over those years Sterne began to develop a concept of her identity as an artist that set her apart from most of her colleagues and fundamentally shaped her unique oeuvre. She defined identity as shifting and relational, influenced by changing contexts and opposed to the aggressively monolithic model of identity that generally prevailed among the abstract expressionists. She also believed in a reciprocal relationship between language and ideas: different communal languages shaped the ideas of their speakers, just as different ideas often required different languages for precise expression. Combining these two strands of her artistic philosophy, Sterne developed a career-long practice of switching styles, and even of using different styles simultaneously, sometimes to express different themes and at other times to articulate the same idea in distinct ways. Even her most abstract styles, however, recorded her changing relationship to the environment around her. This study proposes that her insistence on changing styles paradoxically expresses a coherent artistic philosophy of identity, and constitutes a critical response to the rhetoric, interpretation, and marketing of the abstract expressionism in the late 1940s and 1950s.
This project also tells an institutional and cultural history of the mid-century art world that treats the artist, her work, and the institutions that promoted (or failed to promote) it as inextricably linked. By focusing on specific points at which Sterne’s example proved inassimilable to the dominant narrative of abstract expressionism, this dissertation ultimately suggests the need for a more comprehensive narrative that redefines the essential parameters.Item withdrawn by Mark Zulauf ([email protected]) on 2012-04-17T17:21:52Z
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University of Illinois Theses & Dissertations (ID: 1)
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Imágenes de autor e imágenes de la Patagonia: Trelew de Marcelo Eckhardt
No full textTrelew (1997) of the Argentine writer Marcelo Eckhardt is composed byessays, stories and a novel that they develop in an inserted way. Characterized by the generic mixture, and by a insistent description of the geographic and cultural space of the Patagonia, Trelew develops the mitografìa of the city homonym simultaneously that constructs that of the own author who expands and diversifies his speech in other voices, turning the text in a plural text by the forms and by the voices that form it.Trelew (1997) del escritor argentino Marcelo Eckhardt está compuesto porensayos, relatos y una novela que se desarrollan de modo intercalado. Caracterizado por la mixtura genérica, así como por una insistente descripción del espacio geográfico y cultural de la Patagonia, Trelew despliega la mitografía de la ciudad homónima a la vez que construye la del propio autor que expande y diversifica su enunciación en otras voces, convirtiendo el texto en un texto plural no sólo en cuanto a las formas sino, también, en cuanto a las voces que lo configuran
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