Nonlinearities in shadowgraphy experiments on non-equilibrium fluctuations in polymer solutions.

Giant thermal and solutal non-equilibrium fluctuations are observed in shadowgraphy experiments on liquid mixtures subjected to a temperature gradient. For large temperature differences, both the temperature and the composition dependence of the relevant thermophysical parameters and the nonlinear terms in the diffusion equation need to be taken into account, leading to a nonlinear concentration profile. For temperature differences exceeding the inverse of the Soret coefficient, in our example approximately 10 K, the usual data evaluation yields increasingly wrong diffusion and Soret coefficients that are off by almost a factor of two for a temperature difference of 50 K. A local model that treats the measured shadowgraph signal as a superposition of the contributions from every layer of the sample is able to capture the essential trend and yields a good agreement with experimental data. The results are important for the application of shadowgraphy as a tool for the measurement of Soret and diffusion coefficients, where large temperature gradients promise a good signal-to-noise ratio.

Thermal and solutal non-equilibrium fluctuations in a polymer solution.

We have performed shadowgraphy experiments on a dilute polymer solution subjected to a temperature gradient in order to investigate simultaneous thermal and solutal non-equilibrium fluctuations (NEFs). The gravitational quenching of the NEFs at small q-vectors defines the thermal and solutal roll-off wavevectors, which can be extracted from both the static structure function and the time correlation functions. Both methods yield good agreement, and the ∼10% larger static solutal roll-off wavevector coincides with a similar observation reported in the literature. The thermal diffusivity of the solution and the diffusion, thermodiffusion, and Soret coefficients of the polymer can be obtained from the q-dependence of the relaxation times and from the thermal and solutal roll-off wavevectors without explicit knowledge of the optical contrast factors. This provides an alternative route for the measurement of diffusive transport coefficients, albeit with an unfavorable error propagation.

[Psychological stressors, resources and well-being of surgeons in Germany : A cross-sectional study]. / Psychische Belastungen, Ressourcen und Wohlbefinden von Chirurgen in Deutschland : Eine Querschnittsstudie.

BACKGROUND: Psychological stress at work is associated with detrimental and health-impairing consequences for employees. OBJECTIVE: In this study major stress factors and the resource job control at the workplace of surgeons and facets of mental health were examined and compared to benchmark results of a large reference sample. METHOD: Data were collected by a representative online survey among surgeons throughout Germany who were contacted via the Professional Association of German Surgeons. In total 643 surgeons from different organizations and different disciplines completed the questionnaire that was developed using well-validated instruments. RESULTS: Time pressure was the most meaningful stress factor for surgeons. Moreover, the results for medical assistants showed adverse stress combinations of high goal uncertainty and low job control as well as high emotional exhaustion and low job satisfaction. In addition, the results indicated that surgeons in single and group practices as well as in outpatient healthcare centers have less stressors and more job resources. CONCLUSION: The survey results suggest high levels of burnout risk for German surgeons, especially among medical assistants and medical specialists from large hospitals. In order to maintain a high quality in the surgical disciplines, a concerted effort by all players in the healthcare system is necessary.

Particle accumulation and depletion in a microfluidic Marangoni flow.

Thermosolutal and thermocapillary Marangoni convection at a liquid-gas interface in a microchannel structure of approximately 100 × 90 µm2 cross section creates a localized vortex that acts as a trap for micrometer and sub-micrometer sized tracer particles. Next to the vortex, depleted volumes appear that are entirely cleared of particles. This particle redistribution is caused by collisions of the tracers with the meniscus, which push the particles back onto the critical streamline with one particle radius distance to the meniscus. The streamlines between the meniscus and the critical streamline feed the depleted regions. Since the critical streamline depends on the particle radius, the effect leads to a particle fractionation according to their size. Diffusion allows only small particles to escape from the trap. Larger particles are permanently confined and their diffusion is rectified after every revolution at the meniscus, which produces a ratchet effect and increases the particle localization within the vortex.

Modeling workplace bullying using catastrophe theory.

Workplace bullying is defined as negative behaviors directed at organizational members or their work context that occur regularly and repeatedly over a period of time. Employees' perceptions of psychosocial safety climate, workplace bullying victimization, and workplace bullying perpetration were assessed within a sample of nearly 5,000 workers. Linear and nonlinear approaches were applied in order to model both continuous and sudden changes in workplace bullying. More specifically, the present study examines whether a nonlinear dynamical systems model (i.e., a cusp catastrophe model) is superior to the linear combination of variables for predicting the effect of psychosocial safety climate and workplace bullying victimization on workplace bullying perpetration. According to the AICc, and BIC indices, the linear regression model fits the data better than the cusp catastrophe model. The study concludes that some phenomena, especially unhealthy behaviors at work (like workplace bullying), may be better studied using linear approaches as opposed to nonlinear dynamical systems models. This can be explained through the healthy variability hypothesis, which argues that positive organizational behavior is likely to present nonlinear behavior, while a decrease in such variability may indicate the occurrence of negative behaviors at work.

Emotion work and job stressors and their effects on burnout.

Abstract This article reports research on emotion work, organizational as well as social variables as predictors of job burnout. In burnout research, high emotional demands resulting from interactions with clients are seen as a core characteristic of service jobs. However, these emotional demands were seldom measured in a direct manner. It was only recently that emotional demands were included in studies on burnout referring to the concept of emotion work (emotional labor). Emotion work is defined as the requirement to display organizationally desired emotions. A multi-dimensional concept of emotion work was used to analyze the relations of emotion work variables with organizational and social variables and their joint effect on burnout in five samples including employees working in children's homes, kindergartens, hotels, banks and call centers. Emotion work variables correlated with organizational stressors and resources. However, hierarchical multiple regression showed a unique contribution of emotion work variables in the prediction of burnout. Moreover, the analysis of interaction effects of emotional dissonance and organizational and social stressors showed that for service professionals, the coincidence of these stressors led to exaggerated levels of emotional exhaustion and depersonalization.

Social support, social stressors at work, and depressive symptoms: testing for main and moderating effects with structural equations in a three-wave longitudinal study.

This study investigated the moderating effects of social support by supervisors and colleagues relative to social stressors at work and depressive symptoms using a structural equations approach in a 3-wave longitudinal study over 1 year. The analyses were based on a randomly drawn sample (N = 543) of citizens in the area around Dresden in the former East Germany. LISREL analysis with latent moderating effects revealed a moderating effect for supervisor support. This applied only if the time lag was 8 months, but not for longer or shorter lags. Under low-support conditions depressive symptoms were increased by social stressors, whereas, contrary to expectations, social stressors reduced subsequent depressive symptoms under high-support conditions. No moderating effect for colleague support was found. Several mechanisms are discussed that may explain the results.

Longitudinal studies in organizational stress research: a review of the literature with reference to methodological issues.

Demonstrating causal relationships has been of particular importance in organizational stress research. Longitudinal studies are typically suggested to overcome problems of reversed causation and third variables (e.g., social desirability and negative affectivity). This article reviews the empirical longitudinal literature and discusses designs and statistical methods used in these studies. Forty-three longitudinal field reports on organizational stress were identified. Most of the investigations used a 2-wave panel design and a hierarchical multiple regression approach. Six studies with 3 and more waves were found. About 50% of the studies analyzed potential strain-stressor (reversed causation) relationships. In about 33% of the studies there was some evidence of reverse causation. The power of longitudinal studies to rule out third variable explanations was not realized in many studies. Procedures of how to analyze longitudinal data are suggested.