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.     

Validating the effectiveness of EvalAccess when deploying WCAG 2.0 tests

While automatic tools are not intended to replace human judgment, they are crucial in order to develop accessible websites. The release of WCAG 2.0 has caused great expectation, as it is supposed to be precisely testable with automated review tools. Therefore, more effective tools could be developed. However, so far few tools applying WCAG 2.0 have been developed. This paper presents an evaluation framework which has been updated in order to evaluate the new tests. In addition, it describes a validation process carried out in order to verify the effectiveness of the new version of the evaluation tool. The effectiveness is validated by conducting a quantitative and qualitative analysis of the results obtained by applying both versions of the tool (the one implementing WCAG 1.0 and the one implementing WCAG 2.0) to a set of selected web pages, as well as by manual evaluation of an expert for detecting the possible false positives and false negatives produced by each tool.     

Web accessibility awareness in search engine results

The enormous amount of information available on the Internet requires the use of search engines in order to find specific information. As far as web accessibility is concerned, search engines contain two kinds of barriers: on the one hand, the interfaces for making queries and accessing results are not always accessible; on the other hand, web accessibility is not taken into account in information retrieval (IR) processes. Consequently, in addition to interface problems, accessing the items in the list of results tends to be an unsatisfactory experience for people with disabilities. Some groups of users cannot take advantage of the services provided by search engines, as the results are not useful due to their accessibility restrictions. The goal of this paper is to propose the integration of web accessibility measurement into information retrieval processes. Firstly, quantitative accessibility metrics are defined in order to accurately measure the accessibility level of web pages. Secondly, a model to integrate these metrics within IR processes is proposed. Finally, a prototype search engine which re-ranks results according to their accessibility level based on the proposed model is described.     

Entrapment and perceived status in graduate students experiencing a recurrence of major depression.

The present study used a prospective design to test the role of involuntary subordination as a predictor of major depression. Involuntary subordination is a construct derived from social rank theory and has been implicated as a cause of major depression. Its most salient features include feelings of entrapment and unfavourable social comparisons (i.e., low perceived status). An initial sample of 146 graduate students underwent a diagnostic interview to confirm a history of major depression and also completed measures of entrapment and social comparison. After 16 months, participants were assessed for a recurrence of major depression. Participants who experienced a recurrence of depression had significantly higher levels of involuntary subordination (as measured by factor scores of entrapment and social comparison). A logistic regression analysis also showed that involuntary subordination predicted recurrence of depression, even when controlling for current major depression and the number of previous episodes. The present study demonstrates the advantages of adopting a social rank perspective in modeling major depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.     

Effect of daylight saving time on lighting energy use: A literature review

The principal reason for introducing (and extending) daylight saving time (DST) was, and still is, projected energy savings, particularly for electric lighting. This paper presents a literature review concerning the effects of DST on energy use. Simple estimates suggest a reduction in national electricity use of around 0.5%, as a result of residential lighting reduction. Several studies have demonstrated effects of this size based on more complex simulations or on measured data. However, there are just as many studies that suggest no effect, and some studies suggest overall energy penalties, particularly if gasoline consumption is accounted for. There is general consensus that DST does contribute to an evening reduction in peak demand for electricity, though this may be offset by an increase in the morning. Nevertheless, the basic patterns of energy use, and the energy efficiency of buildings and equipment have changed since many of these studies were conducted. Therefore, we recommend that future energy policy decisions regarding changes to DST be preceded by high-quality research based on detailed analysis of prevailing energy use, and behaviours and systems that affect energy use. This would be timely, given the extension to DST underway in North America in 2007.     

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.