When children learn to count and acquire a symbolic system for representing numbers, they map these symbols onto a preexisting system involving approximate nonsymbolic representations of quantity. Little is known abou...
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When children learn to count and acquire a symbolic system for representing numbers, they map these symbols onto a preexisting system involving approximate nonsymbolic representations of quantity. Little is known about this mapping process, how it develops, and its role in the performance of formal mathematics. Using a novel task to assess children's mapping ability, we show that children can map in both directions between symbolic and nonsymbolic numerical representations and that this ability develops between 6 and 8 years of age. Moreover, we reveal that children's mapping ability is related to their achievement on tests of school mathematics over and above the variance accounted for by standard symbolic and nonsymbolic numerical tasks. These findings support the proposal that underlying nonsymbolic representations play a role in children's mathematical development. (C) 2009 Elsevier Inc. All rights reserved.
In a questionnaire survey, 94 teachers in Taiwan and 140 in the United States judged which topics among 20 moral issues would be appropriate subjects of study in grade six of the primary school and in the first year o...
In a questionnaire survey, 94 teachers in Taiwan and 140 in the United States judged which topics among 20 moral issues would be appropriate subjects of study in grade six of the primary school and in the first year of the university. The issues related to religion, ethnicity, gender, health care, crime, alcohol, tobacco, gambling, guns, government corruption, birth control, caring for the elderly, and television programming. The results revealed great diversity of opinion within each group of respondents. No single topic was approved by all teachers in either group, nor was any topic rejected by all. Among the 234 teachers, no two offered precisely the same configuration of answers over the 20 topics. Nevertheless, some group trends could be identified for individual topics. For example, in both countries the great majority of respondents would teach about industrial pollution, whereas very few would approve of trying to identify the best religion. In the rationales teachers offered in support of their choices, the four reasons that figured most prominently in both countries were that a topic would contribute to the nation's welfare, would help students to make wise decisions, would be interesting for students, and would represent a peaceful way to face social problems.
The aim of this study was to analyse the changes of Prospero-related homeobox 1 (Prox1) gene expression in rat liver under different experimental conditions of liver injury, regeneration and acute phase reaction, and ...
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The aim of this study was to analyse the changes of Prospero-related homeobox 1 (Prox1) gene expression in rat liver under different experimental conditions of liver injury, regeneration and acute phase reaction, and to correlate it with that of markers for hepatoblasts, hepatocytes, cholangiocytes and oval cells. Gene expression was studied at RNA level by RT-PCR, and at protein level by immunohistochemistry. At embryonal stage of rat liver development (embryonal days (ED) 14-16) hepatoblasts were found to be Prox1(+)/Cytokeratin (CK) 19(+) and alpha-fetoprotein (AFP)(+), at this stage Prox1(-)/CK19(+)/AFP(-) small cells (early cholangiocytes?) were identified. In fetal liver (ED 18-22) hepatoblasts were Prox1(+)/CK19(-)/AFP(+). CK7(+) cholangiocytes were detected at this stage, and they were Prox1(-)/AFP(-). In the adult liver hepatocytes were Prox1(+)/CK19(-)/CK7(-)/AFP(-), cholangiocytes were CK19(+) and/or CK7(+) and AFP(-)/Prox1(-). In models of liver damage and regeneration Prox1 remained a stable marker of hepatocytes. After 2-acetyl-aminofluorene treatment with partial hepatectomy (AAF/PH) the amount of Prox1 specific transcripts was low in the liver, when CK19 and AFP gene expression was high, and at no time point AFP(+)/CK19(+) "oval cells" were found to be Prox1(+). However, a few Prox1(+)/CK19(+) and a few Prox1(+)/CK7(+) cells were identified in the liver of AAF/PH-animals, which may represent precursors of hepatocytes, or a precancerous state.
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