Eddy genesis and manipulation in plane laminar shear flow

Eddy formation and presence in a plane laminar shear flow configuration consisting of two infinitely long plates orientated parallel to each other is investigated theoretically. The upper plate, which is planar, drives the flow; the lower one has a sinusoidal profile and is fixed. The governing equations are solved via a full finite element formulation for the general case and semi-analytically at the Stokes flow limit. The effects of varying geometry (involving changes in the mean plate separation or the amplitude and wavelength of the lower plate) and inertia are explored separately. For Stokes flow and varying geometry, excellent agreement between the two methods of solution is found. Of particular interest with regard to the flow structure is the importance of the clearance that exists between the upper plate and the tops of the corrugations forming the lower one. When the clearance is large, an eddy is only present at sufficiently large amplitudes or small wavelengths. However, as the plate clearance is reduced, a critical value is found which triggers the formation of an eddy in an otherwise fully attached flow for any finite amplitude and arbitrarily large wavelength. This is a precursor to the primary eddy to be expected in the lid-driven cavity flow which is formed in the limit of zero clearance between the plates. The influence of the flow driving mechanism is assessed by comparison with corresponding solutions for the case of gravity-driven fluid films flowing over an undulating substrate. When inertia is present, the flow generally becomes asymmetrical. However, it is found that for large mean plate separations the flow local to the lower plate becomes effectively decoupled from the inertia dominated overlying flow if the wavelength of the lower plate is sufficiently small. In such cases the local flow retains its symmetry. A local Reynolds number based on the wavelength is shown to be useful in characterising these large-gap flows. As the mean plate separation is reduced, the form of the asymmetry caused by inertia changes, and becomes strongly dependent on the plate separation. For lower plate wavelengths which do not exhibit a cinematically induced secondary eddy, an inertially induced secondary eddy can be created if the mean plate separation is sufficiently small and the global Reynolds number sufficiently large

Studying Flow Close to an Interface by Total Internal Reflection Fluorescence Cross Correlation Spectroscopy: Quantitative Data Analysis

Total Internal Reflection Fluorescence Cross Correlation Spectroscopy (TIR-FCCS) has recently (S. Yordanov et al., Optics Express 17, 21149 (2009)) been established as an experimental method to probe hydrodynamic flows near surfaces, on length scales of tens of nanometers. Its main advantage is that fluorescence only occurs for tracer particles close to the surface, thus resulting in high sensitivity. However, the measured correlation functions only provide rather indirect information about the flow parameters of interest, such as the shear rate and the slip length. In the present paper, we show how to combine detailed and fairly realistic theoretical modeling of the phenomena by Brownian Dynamics simulations with accurate measurements of the correlation functions, in order to establish a quantitative method to retrieve the flow properties from the experiments. Firstly, Brownian Dynamics is used to sample highly accurate correlation functions for a fixed set of model parameters. Secondly, these parameters are varied systematically by means of an importance-sampling Monte Carlo procedure in order to fit the experiments. This provides the optimum parameter values together with their statistical error bars. The approach is well suited for massively parallel computers, which allows us to do the data analysis within moderate computing times. The method is applied to flow near a hydrophilic surface, where the slip length is observed to be smaller than 10nm, and, within the limitations of the experiments and the model, indistinguishable from zero.Comment: 18 pages, 12 figure

Self-authorship and creative industries workers’ career decision-making

Career decision-making is arguably at its most complex within professions where work is precarious and career calling is strong. This article reports from a study that examined the career decision-making of creative industries workers, for whom career decisions can impact psychological well-being and identity just as much as they impact individuals’ work and career. The respondents were 693 creative industries workers who used a largely open-ended survey to create in-depth reflections on formative moments and career decision-making. Analysis involved the theoretical model of self-authorship, which provides a way of understanding how people employ their sense of self to make meaning of their experiences. The self-authorship process emerged as a complex, non-linear and consistent feature of career decision-making. Theoretical contributions include a non-linear view of self-authorship that exposes the authorship of visible and covert multiple selves prompted by both proactive and reactive identity work

Stable carbon- and hydrogen-isotope ratios of subfossil Oaks in Southern Germany: methodology and application to a composite record for the Holocene

The deltaD and delta(13)C values of tree rings from dendrochronologically dated subfossil Holocene oaks have been studied for palaeoenvironmental and palaeoclimate reconstructions. The wood material mainly originates from fluvial deposits of the river Main and to a lesser extent from the Danube and Rhine regions in southern Germany. The chronology consists of the isotope records of 82 trees that cover a large part of the Holocene. The periods 8230 BC to AD 905 are represented by delta(13)C values; deltaD values exist for the time interval 6470 BC to AD 905. Not all records have the same time resolution and not all of them were prepared in the same way for isotope analysis. However, investigations on the influence of the preparation technique on the isotope values and on the isotope composition of different wood compartments (latewood and earlywood, respectively) allowed us to homogenize the records. The comparison of deltaD values of wood with different cambial ages showed that hydrogen-isotope ratios were affected by growth trends. The uniformity of the trends implies physiological rather than microclimatic causes of these deltaD growth trends. The growth trends were corrected by subtracting a standardized trend curve, which in most cases resulted in a higher conformity in the overlap of tree-ring sequences. The delta(13)C records showed no uniform trends. However, the differences between delta(13)C values of overlapping trees in several cases were markedly offset, making it difficult to interpret the delta(13)C long-term trends in some sections of the chronology. Despite that, there are some characteristics common to both isotope chronologies. Most noticeable is the occurrence of comparatively high values in the interval 4500 to 2000 BC indicating higher temperatures (deltaD) and possibly lower water availability (delta(13)C), and a decrease in both isotope chronologies since about 2000 BC