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During this qualitative study on writing anxiety among EFL learners which was done as part of a large scale Ph.D dissertation by the authors, most learners complained about conceptual blockage. They claimed they did not know what to write or how to start. We started to ecologically study the causes of the issue from Bronfenbrenner's perspective. We realized that the learners' causes are mostly related to chronosystem than macro-system or microsystem. The participants were 8 novice EFL tobe teachers and 8 expert EFL teachers of Iranian ministry of education who voluntarily took part in a longitudinal study in three academic semesters. They were interviewed, observed and asked to keep journals; we coded all the data using Nvivo10. The finding confirmed Horwits' idea (1986) that the discrepancy between matured thought and immature language skill is one of the causes of concept blockage. Therefore, besides all the ecological elements and the chronosystem interactions, learners should improve their language skills to get rid of conceptual blockage. Finally, in order to understand and interpret the learners' complex behavior in classroom situations, it is better to study ecologically

This paper reviews the current status of boiling heat transfer modelling, discusses the need for its improvement due to unresolved intriguing experimental findings and emergence of novel technical applications and outlines the directions for an advanced modelling approach. The state-of-the-art of computational boiling heat transfer studies is given for: macro-scale boiling models applied in two-fluid liquid-vapour interpenetrating media approach, micro-, meso-scale boiling computations by interface capturing methods, and nano-scale boiling simulations by molecular dynamics tools. Advantages, limitations and shortcomings of each approach, which originate from its grounding formulations, are discussed and illustrated on results obtained by the boiling model developed in our research group. Based on these issues, we stress the importance of adaptation of a multi-scale approach for development of an advanced boiling predictive methodology. A general road-map is outlined for achieving this challenging goal, which should include: improvement of existing methods for computation of boiling on different scales and development of conceptually new algorithms for linking of individual scale methods. As dramatically different time steps of integration for different boiling scales hinder the application of full multi-scale methodology on boiling problems of practical significance, we emphasise the importance of development of another algorithm for the determination of sub-domains within a macro-scale boiling region, which are relevant for conductance of small-scale simulations. [ABSTRACT FROM AUTHOR]

The physical mechanisms associated with the evolution of a micro-layer beneath a bubble and the transition between contact line and micro-layer regimes are investigated with fully resolved numerical simulations, in the framework of nucleate pool boiling. Capturing the transition between these two regimes has been possible for the first time using very refined grids and parallel computations. Indeed, grids with a cell size under 1 μm must be used in order to capture thermal and dynamical effects in the micro-layer. Such multiscale computations require advanced code capabilities. The present simulations are used to analyse the physical processes involved in the formation and depletion of a micro-layer. A parametric study is carried out to investigate the impact of the main parameters affecting the presence of the micro-layer. From these results, the limit conditions between nucleate boiling in micro-layer and contact line regimes are deduced. Neglecting the micro-layer would lead to erroneous results because it has a strong influence on the overall bubble growth. Therefore the present results could be of major interest for designing models of nucleate pool boiling in larger scales computations, when the micro-layer cannot be resolved. [ABSTRACT FROM AUTHOR]

The equilibrium evaporation of the thin liquid film on a solid substrate is studied by performing molecular dynamics simulation (MD). The evaporation properties are obtained for a simple atomic system in three-phase coexistence and compared with those of the modeling methods based on the disjoining pressure. The thickness of the film is varied and goes down to as small as a few molecular diameters. The MD results show that the evaporation rate of the ultrathin film on a high-energy substrate is smaller than that of a macroscopic film because of the solid molecular potential effective over the film. The comparison with the mean field theory based on the kinetic theory of gases and the classical Hamaker theory of disjoining pressure shows a sizable discrepancy when the film thickness is comparable to the size of the interfacial region. The discrepancy mostly disappears when the disjoining pressure is derived by using the static properties from MD. This indicates that the evaporation modeling on ultrathin film of which the disjoining pressure is an integral part critically requires an accurate representation of the property. [ABSTRACT FROM AUTHOR]

Abstract: The function of gas diffusion layer in the fuel cell electrode is very critical as it acts as a current collector, facilitates the supply of reactants to the catalytic sites, and helps in removal of product water from the catalyst layer. In this paper attempts have been made to improve the dispersion of micro-layer by introducing an organic solvent. The electrodes were made by a screen printing method to improve the homogeneity of the gas diffusion layer. The main focus is on the effect of PTFE content in micro-layer using Ballard Avcarb 1071 carbon cloth as a substrate material. The percentage of PTFE on the substrate is kept constant in all the experiments, at about 18%. However, the percentage of PTFE in the micro-layer carbon is varied from 15 to 40 wt%. The micro-layer carbon loadingis about 3 mg/cm2 for all the electrodes. The Gurley number decreases with increase in concentration of PTFE in the micro-layer. The PEMFC cells were tested at 60 °C and at ambient pressure with relative humidity of hydrogen and air kept at 90% and 70%, respectively. The results were analyzed from the polarization curves. The DC resistances of the electrodes were correlated with concentration of PTFE in the micro-layer. The over potential values were also correlated with the Gurley number. The gas permeability, contact angle of the samples was measured and the results were correlated with performance of the PEMFC. The long-term stability of the electrode was recorded at fixed current density for various concentration of PTFE content in the micro-layer. The detailed results are discussed in this paper. [Copyright &y& Elsevier]

The possibilities of using newly developed nano- and micro-thin films in biomedicine are intensively studied at the present time. Many research institutions are looking for ways to evaluate mechanical properties of these films. One of the most important and frequently studied characteristics is practical adhesion. A very important method for evaluating the practical adhesion strength is scratch test. Often, however, the research teams use a method based on the disunity evaluation of adhesion of biocompatible surface layer. This makes the quantitative comparison of research results impossible. We designed and tested new evaluation method and procedure based on international standards in order to eliminate these problems. This article is aimed at showing the new possibility of using established standards for evaluating adhesion of nano- and micro-thin biocompatible films and at showing the application of the standards to evaluate the often studied DLC biocompatible layers. The thickness of the film was 470 nm. As a substrate a titanium alloy Ti6Al4V was used. [ABSTRACT FROM AUTHOR]

Abstract: The performance of the fuel cell electrode depends on many factors: types of materials and their properties, composition, process parameters and fuel cell operation conditions. In the present paper, cathode electrode performance in a PEM fuel cell as a function of Teflon concentration in the substrate materials and in micro-layer carbon, pore former in the micro-layer, amount of carbon used in the diffusion layer and Platinum & Nafion loading in the catalyst layer are studied. These six factors each at two levels are considered. A full factorial design would have required 26, i.e., 64 experiments to be carried out. With the use of Taguchi method, L12 designs, the number of experiments can be reduced to 12. The electrode current density values are taken as responses for the analysis. Statistical sensitivity analysis (ANOVA analysis) is used to compute the effects and the contributions of the various factors to the fuel cell electrode. Some graphic representations are employed in order to display the results of the statistical analysis made for different current values. The behavior of cathode PEM fuel cell electrode was studied using humidified hydrogen and compressed air. The present paper examines the six main factors and their levels responsible for altering the performance particularly when the fuel is operated under ambient pressure. [Copyright &y& Elsevier]