Analytical model for melting in a semi-infinite PCM storage with an internal fin

The most PCMs with high energy storage density have an unacceptably low heat conductivity and hence internal heat transfer enhancement techniques such as fins or other metal structures are required in latent heat thermal storage (LHTS) applications. Previous work has concentrated on numerical and experimental examination in determining the influence of the fins in melting phase change material. This paper presents a simplified analytical model based on a quasi-linear, transient, thin-fin equation which predicts the solid-liquid interface location and temperature distribution of the fin in the melting process with a constant imposed end-wall temperature. The analytical results are compared to the numerical results and they show good agreement. Due to the assumptions made in the model, the speed of the solid-liquid interface during the melting process is slightly too slow.     

Learning Trajectories,Lesson Planning,Affordances, and Constraints in the Design and Enactment of Mathematics Teaching

Recent reform efforts in mathematics education have stimulated a focus on learning trajectories. At the same time, a global increase in high-stakes testing has influenced instructional practices. This study investigated how four fourth grade teachers within a school planned and enacted lessons to understand what mediated their planning and teaching decisions. Findings reveal that three of these teachers, who were veteran teachers, used a testing trajectory approach with decisions mediated by preparing students for high-stakes tests. The fourth teacher, a novice, attempted to use a learning trajectory approach to support student understanding. Results reveal that high-stakes testing played a crucial role in teachers' instructional decisions. Based on the findings, we provide a framework for a testing trajectory approach that the veteran teachers used to make instructional decisions. Further research is needed to understand how to support teachers to prepare students for testing using effective teaching practices.     

A novel particle sampling system for physico-chemical and toxicological characterization of emissions

Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency.