Understanding students’ thinking and learning processes is one of the greatest challenges teachers face in the classroom. Misconceptions and errors have the potential to be a rich source of ...information for identifying students’ thinking and reasoning processes. However, empirical studies show that pre-service teachers (PSTs) and teachers find it challenging to focus their interpretations and pedagogical decisions on students’ thinking processes when they identify students’ mathematical errors.
Based on the theoretical approach of noticing, the study described in this paper examines primary PSTs’ diagnostic competence in error situations before and after they participated in a seminar sequence implemented at several Chilean universities. Our analyses focus on PSTs’ competence with regard to formulating hypotheses about the causes of students’ errors. The proposed hypotheses were categorized into those that attributed errors to students’ lack of conceptual understanding, those that explained errors in terms of lack of procedural understanding, and those that assumed a failure of instructional strategies. In addition, the relationships between PSTs’ diagnostic competence, their beliefs and university learning opportunities were examined. The results indicate that PSTs’ diagnostic competence in error situations and the changes of this competence were related to PSTs’ beliefs, practical experiences, and learning opportunities. Overall, the findings suggest that it is possible to promote changes on PSTs’ diagnostic competence during initial teacher education. The paper concludes with implications for teacher education and future research.
Increasing plastic recycling rates is crucial to tackle plastic pollution and reduce consumption of fossil resources. Recycling routes for post-consumer plastic fractions that are technologically and ...economically feasible remain a challenge. Profitable value chains for recycling mixed film and tray-like plastics have hardly been implemented today, in sharp contrast to recycling of relatively pure fractions such as polyethylene terephthalate and high-density polyethylene bottles.
This study examines the economic feasibility of implementing mechanical recycling for plastic waste such as polypropylene, polystyrene, polyethylene films and mixed polyolefins. In most European countries these plastic fractions are usually incinerated or landfilled whilst in fact technologies exist to mechanically recycle them into regranulates or regrinds.
Results show that the economic incentives for the recycling of plastic packaging depend predominantly on the product price and product yield. At current price levels, the most profitable plastic fraction to be recycled is PS rigids, with an internal rate of return of 14%, whereas the least profitable feed is a mixed polyolefin fraction with a negative internal rate of return in a scenario with steadily rising oil prices. Moreover, these values would be substantially reduced if oil prices, and therefore plastic product prices decrease. Considering a discount rate of 15% for a 15-year period, mechanical recycling is not profitable if no policy changes would be imposed by governments. Clearly low oil prices may jeopardize the mechanical recycling industry, inducing the need for policies that would increase the demand of recycled products such as imposing minimal recycled content targets.
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Mathematics classrooms are typically characterized by considerable heterogeneity with respect to students' knowledge and skills. Mathematics teachers need to be highly attentive to students' ...thinking, learning difficulties, and any misconceptions that they may develop. Identification of potential errors and appropriate ways to approach them is crucial for attaining positive learning outcomes. This paper explores which knowledge and affective-motivational skills teachers most require to effectively identify and approach students' errors.
To address this research question within the German follow-up study of the Teacher Education and Development Study in Mathematics (TEDS-M), 131 primary school mathematics teachers' ability to identify students' errors was assessed based on (a) a digitalized speed test showing different students' solutions in a written notation and (b) three video vignettes that showed different scenes from mathematics classes. These scenes dealt, among other things, with children who struggled with the lesson's mathematical content. Teachers were asked to analyze students' thinking and to determine how best to react. In addition, teachers' mathematics pedagogical content knowledge, mathematical content knowledge, and beliefs were assessed in separate tests and served as predictors for teachers' abilities to identify, analyze, and deal with students' errors.
The results indicate that all components are interrelated. However, path analysis reveals that teachers' ability to deal with students' errors is mainly predicted by their constructivist beliefs while their ability to quickly identify typical students' errors is largely dependent on their mathematics content knowledge.
The results show the central filtering function of beliefs. Teachers who believe that students must shape and create their own learning processes are more successful in perceiving and analyzing student errors in classroom situations. They may understand errors as learning opportunities and - thus - pay specific attention to these occurrences.
•Recycling household plastics shows lower environmental impact than incineration.•Recycling of PS rigid fraction performs best, whereas MPO rigid is the worst.•Contamination of the plastics ...determines the environmental performance of recycling.•Mechanical recycling receives higher credits than thermochemical recycling.•Quality and market uptake of final products requires further investigation.
Currently, Belgium is in a transition period after which more household plastic packaging waste will be collected separately in function of increased recycling. The challenge is to identify the most environmentally sound treatment option for the increased selectively collected plastic waste. In this study, mechanical recycling (MR) and thermochemical recycling (TCR) of four newly collected subfractions, being polypropylene (PP), polystyrene (PS), mixed polyolefins (MPO) rigids and polyethylene (PE) films, were investigated through prospective Life Cycle Assessment (LCA), in comparison to incineration with energy recovery. Results showed clear benefits of recycling over incineration with energy recovery. Generally, MR showed a better net environmental impact compared to TCR (for PP, PS, MPO rigids and PE films, respectively, e.g., a global warming impact of 100, -1580, 539 and 101 kg CO2 eq. per ton by TCR, and -1183, -3096, -319 and -1162 kg CO2 eq. per ton by MR, and 2339, 2494, 2108 and 2141 kg CO2 eq. per ton by incineration). This could mainly be explained by the avoided burdens of virgin materials. Whereas TCR avoids the virgin supply of the feedstock for polymer production, MR avoids additionally polymerisation and granulation. MR products, i.e. regranulates or flakes, can be directly used in manufacturing, whereas TCR products require first processes like steam cracking, polymerisation and granulation before being used in manufacturing. As this study assumed a 1:1 substitution ratio between MR regranulates and their virgin alternatives, it presents the most favourable results for MR, which should be kept in mind and further investigated.
To date, atmospheric concentrations of sulfur hexafluoride (SF6) are the most potent among the greenhouse gases identified by the Intergovernmental Panel on Climate Change (IPCC) and are still ...rising. In the EU-28, SF6 has been banned from several applications, however, an important exception is gas-insulated electrical switchgear (GIS) for which cost-effective and environmentally sound alternatives were unavailable when the F-Gas regulation was last revised in 2014. To date, after some recent innovations, we argue that the phasing out of SF6 could spur the accelerated development of alternatives with a lower carbon footprint. In the EU-28, the SF6 amount in switchgear is unclear. In this paper, we estimated the SF6 amount to be between 10,800 and 24,700 t (with a mode at 12,700 t) in 2017, resulting in 68 to 140 t of annual emissions from operational leakage only, corresponding to 1.6 to 3.3 Mt of CO2-eq. We additionally calculated the potential greenhouse gas savings over the lifecycle of one exemplary 145 kV gas-insulated switchgear bay upon replacing SF6 by decafluoro-2-methylbutan-3-one (C5-FK) and heptafluoro-2-methylpropanenitrile (C4-FN) mixtures. Projecting these results over the EU-28, a phase-out scenario starting from 2020 onwards could reduce the carbon footprint by a median of 14 Mt of CO2-eq, over a period of 50 years. Extrapolation to medium voltage could be assumed to be of a similar magnitude.
In recent decades new recycling technologies for mixed plastic waste have emerged. In pyrolysis, the polymer chains are thermally broken (pyrolyzed) to obtain hydrocarbon materials of different ...molecular weights such as naphtha, oil or waxes, whose yields can be controlled by varying the reaction parameters. Naphtha represents a closed-loop recycling process as it is a feedstock for (poly)olefins; while the co-production of waxes, having several applications in e.g. the construction industry, exemplifies an open-loop recycling process. This paper compares the economic performance of the pyrolysis of mixed polyolefin waste in a closed-loop and open-loop scheme, including a probabilistic approach to the most important variables. From an economic perspective, open-loop pyrolysis as presented outperforms closed-loop recycling, due to the high prices of wax. However, the results present a high dispersion caused by the volatility of the prices of crude oil and its derivates. Considering the current oil price projections, our case study analysis showed that for open-loop recycling there is a future probability of almost a 98% of observing positive results and around 57% of probability in the case of closed-loop recycling, under the assumptions made. Yet, in a future scenario where decarbonized electricity would decrease oil prices, the probability of a positive outcome reduces to 57% for the open-loop case and to less than 8% in the case of closed-loop recycling. To make these pathways attractive to investors, the nameplate capacity should be at least 70 kt/year for open-loop recycling and 115 kt/year for closed-loop recycling. A 120 kt/year plant should operate minimally at 80% of its capacity for open-loop recycling, while closed-loop recycling would demand running close to maximum capacity. Security of feedstock supply therefore is required.
•Open-loop recycling has better economic performance than closed-loop recycling.•Oil price variability and CAPEX estimation uncertainty affect the variance.•Technology is profitable for 70 kt/year capacity plants or larger.•Provision of plastic waste feedstock should be ensured.
•Predicts the environmental and economic performance of policy instruments to promote plastic recycling.•Combines equilibrium model (top-down) with techno-economic and life cycle assessment ...(bottom-up).•Policy instruments that do not target a specific technology are more likely to increase thermochemical recycling than mechanical recycling.•Policy instruments should focus on environmental outcomes rather than increasing recycling rates.•Future research should include geographical considerations and asses other circular economy strategies.
The objective of this paper is to examine the recycling rates for mechanical and thermochemical recycling of postconsumer polyethylene flexible packaging after the implementation of different policy instruments. The study uses a supply chain equilibrium model that incorporates market data and techno-economic assessments to simulate market equilibrium. It combines this with a life cycle assessment to explore the environmental implications of implementing different policy instruments. The results show that instruments that do not target a specific technology are more likely to increase thermochemical recycling than mechanical recycling. Furthermore, a higher recycling rate is not equivalent to a better environmental outcome. An increased collection target that ensures a supply of plastic waste would increase the overall recycling rates the most. A recycled content standard for mechanical recycling would lead to the highest increase in mechanical recycling, with top results for environmental indicators, but low results for economic indicators.
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