Rheological study of TBAB hydrate slurries as secondary two-phase refrigerants

In the refrigeration field, the use of ice slurries (suspensions of ice) as secondary refrigerant fluids is spreading. This technology could be extended to air-conditioning systems provided that one can propose a phase-change material (PCM) with melting temperature belonging to the range [+6 °C; +12 °C]. Aqueous solutions of tetra butylammonium bromide, which crystallise under atmospheric pressure and temperatures between 0 and +12 °C, into ice-like compounds (hydrates), seem to be good candidates for air-conditioning applications. We focus here on the rheological properties of TBAB hydrates suspensions and propose an experimental determination of their flow behaviour through flow rate and pressure drop measurements. In laminar regime, we observe Bingham behaviour. Apparent viscosity and yield shear stress are determined for different hydrate contents.

Résumé

Dans le domaine de la réfrigération, l'utilisation de coulis de glace en tant que fluides frigoporteurs connaît un vif intérêt. Cette technologie pourrait être étendue aux systèmes de climatisation dans la mesure où il existe un matériau dont la température de fusion est comprise dans le domaine de fonctionnement usuel des climatisations [6 °C; 12 °C]. D'un point de vue thermodynamique, l'hydrate de bromure de tetra-bultylammonium (TBAB) apparaît bien approprié pour une telle application puisqu'il est stable à pression atmosphérique et pour des températures comprises entre 0 et 12 °C. Nous nous intéressons ici aux propriétés rhéologiques de coulis d'hydrates de TBAB. Nous proposons une méthode expérimentale de l'étude de leur comportement en écoulement à travers des mesures de débits et de pressions différentielles. En écoulement laminaire, les coulis d'hydrates de TBAB présentent un comportement du type fluide de Bingham. Les dépendances de la viscosité et de la contrainte seuil avec la température, et par conséquent la teneur en cristaux d'hydrates, est mise en évidence.     

A density-based cellular automaton model for studying the clustering of noninvasive cells

We investigated whether cluster formation by noninvasive cells can be explained by a global attractive potential. Indices quantifying the persistence of migration in experimental conditions were compared to the same indexes computed from simulations with a density-based cellular automaton. The results indicate that the attractive potential hypothesis must be rejected.     

Comparative analysis of bacterial community composition in bulk tank raw milk by culture-dependent and culture-independent methods using the viability dye propidium monoazide

Microbial diversity of 3 raw milk samples after 72 h of storage at 4°C in a bulk tank was analyzed by culture-dependent and -independent methods. The culture-dependent approach was based on the isolation of bacteria on complex and selective media, chemotaxonomic differentiation of isolates, and subsequent identification by 16S rRNA gene sequencing. The culture-independent approach included the treatment of raw milk with the dye propidium monoazide before direct DNA extraction by mechanic and enzymatic cell lysis approaches, and cloning and sequencing of the 16S rRNA genes. The selective detection of viable bacteria improved the comparability between bacterial compositions of raw milk based on culture-dependent and -independent methods, which was the major objective of this study. Several bacterial species of the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were detected by the culture-dependent method, whereas mainly bacteria of the phylum Proteobacteria as well as low proportions of the phyla Bacteroidetes and Actinobacteria were detected by the culture-independent method. This led to the conclusion that the phylum Firmicutes was strongly discriminated by the culture-independent approach. Generally, species richness detected by the culture-dependent method was higher than that detected by the culture-independent method for all samples. However, few taxa could be detected solely by the direct DNA-based method. In conclusion, the combination of culture-dependent and -independent methods led to the detection of the highest bacterial diversity for the raw milk samples analyzed. It was shown that DNA extraction from raw milk as the essential step in culture-independent methods causes the discrimination of taxa by incomplete cell lysis. Treatment of raw milk with the viability dye propidium monoazide was optimized for the application in raw milk without former removal of milk ingredients and proved to be a suitable tool to ensure comparability of bacterial diversity depicted by both methods.     

The primacy of perceiving: Emotion recognition buffers negative effects of emotional labor.

There is ample empirical evidence for negative effects of emotional labor (surface acting and deep acting) on workers' well-being. This study analyzed to what extent workers' ability to recognize others' emotions may buffer these effects. In a 4-week study with 85 nurses and police officers, emotion recognition moderated the relationship between emotional labor and work engagement: Workers with high emotion recognition engaging in emotional labor did not report lower work engagement after 4 weeks, whereas those with low emotion recognition did. These effects pertained to both surface and deep acting. The results suggest that emotional labor be not necessarily detrimental to workers' engagement. Instead, the impact of emotional labor hinges upon workers' ability to correctly identify interaction partners' emotions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Binding and strategic selection in working memory: A lifespan dissociation.

Working memory (WM) shows a gradual increase during childhood, followed by accelerating decline from adulthood to old age. To examine these lifespan differences more closely, we asked 34 children (10–12 years), 40 younger adults (20–25 years), and 39 older adults (70–75 years) to perform a color change detection task. Load levels and encoding durations were varied for displays including targets only (Experiment 1) or targets plus distracters (Experiment 2, investigating a subsample of Experiment 1). WM performance was lower in older adults and children than in younger adults. Longer presentation times were associated with better performance in all age groups, presumably reflecting increasing effects of strategic selection mechanisms on WM performance. Children outperformed older adults when encoding times were short, and distracter effects were larger in children and older adults than in younger adults. We conclude that strategic selection in WM develops more slowly during childhood than basic binding operations, presumably reflecting the delay in maturation of frontal versus medio-temporal brain networks. In old age, both sets of mechanisms decline, reflecting senescent change in both networks. We discuss similarities to episodic memory development and address open questions for future research. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Group creativity and innovation: A motivated information processing perspective.

The authors review the Motivated Information Processing in Groups Model (De Dreu, Nijstad, & Van Knippenberg, 2008) to understand group creativity and innovation. Although distinct phenomena, group creativity and innovation are both considered a function of epistemic motivation (EM; the degree to which group members tend to systematically process and disseminate information), and prosocial motivation (PSM; the extent to which group members seek collective [rather than personal] gain). EM is considered a function of, for example, time constraints, accountability pressures, preference diversity, openness to experience, and ambiguity aversion. PSM is stronger under, for example, participative decision making, shared social identity, and collective reward schemes. A review of the authors' work, and that of others, supports the prediction that group creativity and innovation is higher when group members combine high EM with a PSM. Avenues for new research and practical implications are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Simulation of synthetic climate at local scale as a mean to assess the impact of climate change on infrastructures

A global modelling approach for estimating the climate influence on corrosion activity in reinforced concrete is developed. It combines: (a) the identification of statistical properties of climates in various temperate regions, and the development of a synthetic simulator able to reproduce its dominant patterns, (b) the identification of an empirical corrosion activity model, based on the analysis of experimental data, highlighting the respective influence of temperature and humidity. Synthetic simulations combining these two models are carried out. They show the complexity of the interactions, since the influence of temperature and humidity may be adverse, and the interest to describe both random fluctuations at daily scale and at seasonal scale. They confirm that monitoring of corrosion must account for this time variability and propose a way to estimate average corrosion even with measurements which would remain limited to a short period. Synthetic simulations are also used for estimating the influence of a global warming scenario on the corrosion activity. A global increase of about 38% of corrosion activity has been estimated in response to an average temperature elevation of 3°C.     

Modelling and simulation of virtual natural lighting solutions with complex views

In situations where daylight is insufficiently available, Virtual Natural Lighting Solutions (VNLS) can be promising to turn currently unused floor space into spaces with enough daylight qualities. This article introduces VNLS models with complex image scenes pasted on a transparent glass surface in front of arrays of small, directional white light sources. The objectives are twofold: the first one is to understand the effect of changing input variables, i.e. beam angle, total luminous flux of the “sky” elements, and image scene itself, on the lighting performance of a reference office space. The second objective is to compare two techniques of modelling the view, i.e. transmissive and emissive approaches, using Radiance. Sensitivity analysis of the simulation results show that under every image scene, the total luminous flux of the “sky” element is largely influential to the space availability, whereas the beam angle of the “sky” element is largely influential to the other output variables, including discomfort glare. The findings lead to a suggestion of preferred elements in the image scene, to ensure large space availability and uniformity. The transmissive approach generally generates smaller values of space availability, and largely depends on the view elements of the image scene. In turn, the average probability of discomfort glare using the transmissive approach is smaller than that using the emissive approach.