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

Design and Characterization of a Hypervelocity Expansion Tube Facility

We report on the design and characterization of a 152 mm diameter expansion tube capable of accessing a range of high enthalpy test conditions with Mach numbers up to 7.1 for aerodynamic studies. Expansion tubes have the potential to offer a wide range of test flow conditions as gas acceleration is achieved through interaction with an unsteady expansion wave rather than expansion through a fixed area ratio nozzle. However, the range of test flow conditions is in practice limited by a number of considerations such as short test time and large amplitude flow disturbances. We present a generalized design strategy for small-scale expansion tubes. As a starting point, ideal gas dynamic calculations for optimal facility design to maximize test time at a given Mach number test condition are presented, together with a correction for the expansion head reflection through a non-simple region. A compilation of practical limitations that have been identified for expansion tube facilities such as diaphragm rupture and flow disturbance minimization is then used to map out a functional design parameter space. Experimentally, a range of test conditions have been verified through pitot pressure measurements and analysis of schlieren images of flow over simple geometries. To date there has been good agreement between theoretical and experimental results

Occupational commitment from a life span perspective: An integrative review and a research outlook

Purpose – The purpose of this review was to integrate and organize past research findings on affective, normative, and continuance occupational commitment (OC) within an integrative framework based on central life span concepts. Design/methodology/approach – We identified and systematically analyzed 125 empirical articles (including 138 cases) that examined OC with a content valid measure to the here applied definition of OC. These articles provided information on the relationship between OC and four distinct life span concepts: chronological age, career stages, occupational and other life events, and occupational and other life roles. Furthermore, developmental characteristics of OC in terms of construct stability and malleability were reviewed. Findings – The reviewed literature allowed us to draw conclusions about the mentioned life span concepts as antecedents and outcomes of OC. For example, age and tenure is more strongly positively related to continuance OC than to affective and normative OC, nonlinear and moderating influences seem to be relevant in the case of the latter OC types. We describe several other findings within the results sections. Originality/value – OC represents a developmental construct that is influenced by employees’ workand life-related progress, associated roles, as well as opportunities and demands over their career. Analyzing OC from such a life span perspective provides a new angle on the research topic, explaining inconsistencies in past research and giving recommendation for future studies in terms of dynamic career developmental thinking

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

Coupled stalagmite – Alluvial fan response to the 8.2 ka event and early Holocene palaeoclimate change in Greece

We explore the expression of early Holocene climatic change in the terrestrial Mediterranean of southern Greece. A regional palaeoclimate record from stable isotope and trace element geochemical proxies in an early Holocene (~12.4 ka to 6.7 ka) stalagmite is compared to the timing of palaeosol (entisol) development on an early Holocene alluvial fan located <100 km from the stalagmite site. Radiocarbon dated entisol development records fan abandonment surfaces, which can be coupled to the stalagmite climate signal. Variations in δ13C best record the main elements of palaeoclimatic change, more negative values indicating soil carbon input to karst groundwater under wetter conditions. The wettest conditions begin around 10.3 ka, coincident with the start of sapropel 1 deposition in the eastern Mediterranean. The widely documented northern hemisphere ‘8.2 ka event’ of cooler and drier conditions has a muted δ18O climatic signal in common with other stalagmite climate records from the wider Mediterranean. However, less negative δ13C values do record a period of episodic dryness between ~8.8 and ending at 8.2 ka. Wetter conditions re-established after 8.1 ka to the end of the record. The oldest alluvial fan entisols were developing by ~9.5 ka, and a prominent rubified entisol developed ~8.3 to 8.4 ka, indicating pedogenesis within dating error of the 8.2 ka event. The speleothem record of episodic dryness between ~8.8 and 8.2 ka, combined with other regional proxies, is consistent with the notion that precipitation patterns in Greece may have changed from predominantly winter frontal to summer convective during this period. Palaeosol formation on the alluvial fan may have been an allocyclic response to this change. It is plausible that fan-channel incision, driven by temporary development of a ‘flashier’ summer rainfall regime, isolated large areas of the fan surface allowing onset of prolonged pedogenesis there

Do Bad Guys Get Ahead or Fall Behind? Relationships of the Dark Triad of Personality With Objective and Subjective Career Success

This study analyzed incremental effects of single Dark Triad traits (i.e., narcissism, psychopathy, and Machiavellianism) on objective (i.e., salary and leadership position) and subjective (i.e., career satisfaction) career success. We analyzed 793 early career employees representative of age and education from the private industry sector in Germany. Results from multiple and logistic regressions revealed bright and dark sides of the Dark Triad, depending on the specific Dark Triad trait analyzed. After controlling for other relevant variables (i.e., gender, age, job tenure, organization size, education, and work hours), narcissism was positively related to salary, Machiavellianism was positively related to leadership position and career satisfaction, and psychopathy was negatively related to all analyzed outcomes. These results provide evidence that the Dark Triad plays a role in explaining important career outcomes. Implications for personality and career research are derived