A framework for understanding what algebraic thinking is

In relation to the learning of mathematics, algebra occupies a very special place, both because it is in itself a powerful tool for solving problems and modelling situations, and also because it is essential to the learning of so many other parts of mathematics. On the other hand, the teaching of algebra has proven to be a difficult task to accomplish, to the extent of algebra itself being sometimes considered the border line which separates those who can from those who cannot learn mathematics. A review of the research literature shows that no clear characterisation of the algebraic activity has been available, and that for this reason research has produced only a local understanding of aspects of the learning of algebra. The research problem investigated in this dissertation is precisely to provide a clear characterisation of the algebraic activity. Our research has three parts: (i) a theoretical characterisation of algebraic thinking, which is shown to be distinct from algebra; in our framework we propose that algebraic thinking IS • thinking aritmnetically, • thinking internally, and • thinking analytically. and each of those characteristics are explained and analysed; (ii) a study of the historical development of algebra and of algebraic thinking; in this study it is shown that our characterisation of algebraic thinking provides an adequate framework for understanding the tensions involved in the production of an algebraic knowledge in different historically situated mathematical cultures, and also that the characteristics of the algebraic knowledge of each of those mathematical cultures can only be understood in the context of their broader assumptions, particularly in relation to the concept of number. (iii) an experimental study, in which we examine the models used by secondary school students, both from Brazil and from England, to solve "algebraic verbal problems" and "secret number problems"; it is shown that our characterisation of algebraic thinking provides an adequate framework for distinguishing different types of solutions, as well as for identifying the sources of errors and difficulties in those students' solutions. The key notions elicited by our research are those of: (a) intrasystemic and extrasystemic meaning; (b) different modes of thinking as operating within different Semantical Fields; (c) the development of an algebraic mode of thinking as a process of cultural immersion- both in history and for individual learners; (d) ontological and symbolical conceptions of number, and their relationship to algebraic thinking and other modes of manipulating arithmetical relationships; (e) the arithmetical articulation as a central aspect of algebraic thinking; and, (f) the place and role of algebraic notation in relation to algebraic thinking. The findings of our research show that although it can facilitate the learning of certain early aspects of algebra, the use of non-algebraic models-such as the scale balance or areas-to "explain" particular algebraic facts, contribute, in fact, to the constitution of obstacles to the development of an algebraic mode of thinking; not only because the sources of meaning in those models are completely distinct from those in algebraic thinking, but also because the direct manipulation of numbers as measures, by manipulating the objects measured by the numbers, is deeply conflicting with a symbolic understanding of number, which is a necessary aspect of algebraic thinking

A framework for understanding what algebraic thinking is

In relation to the learning of mathematics, algebra occupies a very special place, both because it is in itself a powerful tool for solving problems and modelling situations, and also because it is essential to the learning of so many other parts of mathematics. On the other hand, the teaching of algebra has proven to be a difficult task to accomplish, to the extent of algebra itself being sometimes considered the border line which separates those who can from those who cannot learn mathematics. A review of the research literature shows that no clear characterisation of the algebraic activity has been available, and that for this reason research has produced only a local understanding of aspects of the learning of algebra. The research problem investigated in this dissertation is precisely to provide a clear characterisation of the algebraic activity. Our research has three parts: (i) a theoretical characterisation of algebraic thinking, which is shown to be distinct from algebra; in our framework we propose that algebraic thinking IS • thinking aritmnetically, • thinking internally, and • thinking analytically. and each of those characteristics are explained and analysed; (ii) a study of the historical development of algebra and of algebraic thinking; in this study it is shown that our characterisation of algebraic thinking provides an adequate framework for understanding the tensions involved in the production of an algebraic knowledge in different historically situated mathematical cultures, and also that the characteristics of the algebraic knowledge of each of those mathematical cultures can only be understood in the context of their broader assumptions, particularly in relation to the concept of number. (iii) an experimental study, in which we examine the models used by secondary school students, both from Brazil and from England, to solve "algebraic verbal problems" and "secret number problems"; it is shown that our characterisation of algebraic thinking provides an adequate framework for distinguishing different types of solutions, as well as for identifying the sources of errors and difficulties in those students' solutions. The key notions elicited by our research are those of: (a) intrasystemic and extrasystemic meaning; (b) different modes of thinking as operating within different Semantical Fields; (c) the development of an algebraic mode of thinking as a process of cultural immersion- both in history and for individual learners; (d) ontological and symbolical conceptions of number, and their relationship to algebraic thinking and other modes of manipulating arithmetical relationships; (e) the arithmetical articulation as a central aspect of algebraic thinking; and, (f) the place and role of algebraic notation in relation to algebraic thinking. The findings of our research show that although it can facilitate the learning of certain early aspects of algebra, the use of non-algebraic models-such as the scale balance or areas-to "explain" particular algebraic facts, contribute, in fact, to the constitution of obstacles to the development of an algebraic mode of thinking; not only because the sources of meaning in those models are completely distinct from those in algebraic thinking, but also because the direct manipulation of numbers as measures, by manipulating the objects measured by the numbers, is deeply conflicting with a symbolic understanding of number, which is a necessary aspect of algebraic thinking

Mechanical Behavior and Microstructural Development of Low-Carbon Steel and Microcomposite Steel Reinforcement Bars Deformed under Quasi-Static and Dynamic Shear Loading

Reinforcement bars of microcomposite (MC) steel, composed of lath martensite and minor amounts of retained austenite, possess improved strength and corrosion characteristics over low-carbon (LC) steel rebar; however, their performance under shear loading has not previously been investigated at the microstructural level. In this study, LC and MC steel cylinders were compression tested, and specimens machined into a forced-shear geometry were subjected to quasi-static and dynamic shear loading to determine their shear behavior as a function of the strain and strain rate. The as-received and sheared microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Higher-resolution microstructural examinations were performed using transmission electron microscopy (TEM). The influence of the starting microstructure on the shear behavior was found to depend strongly on the strain rate; the MC steel exhibited not only greater strain-rate sensitivity than the LC steel but also a greater resistance to shear localization with load. In both steels, despite differences in the starting microstructure, post-mortem observations were consistent with a continuous mechanism operating within adiabatic shear bands (ASBs), in which subgrains rotated into highly misoriented grains containing a high density of dislocations

Estudo da poluição pontual e difusa na bacia de contribuição do reservatório da usina hidrelétrica de Funil utilizando modelagem espacialmente distribuída em Sistema de Informação Geográfica

RESUMO Este estudo avaliou o potencial poluidor da bacia de contribuição do reservatório de Funil (BCRF), localizado na bacia hidrográfica do rio Paraíba do Sul, considerando a geração da carga de nutrientes, nitrogênio (N) e fósforo (P), por fontes pontuais e difusas, a partir de uma modelagem distribuída utilizando Sistema de Informação Geográfica (SIG). As cargas e concentrações médias anuais desses nutrientes foram geradas a partir do acoplamento de equações empíricas, em SIG, considerando informações espaciais de uso e cobertura do solo, população residente na bacia e vazão média anual de longo período, obtida por equações do tipo chuva vazão. Os resultados indicaram que 80% da carga total de nitrogênio foram provenientes de fontes pontuais e 20% de fontes difusas, enquanto que, da carga total de fósforo, 89,1% foram originadas de fontes pontuais e 10,9% de fontes difusas. As concentrações de nutrientes estimadas pelo modelo empírico apresentaram bons ajustes em relação aos valores observados de fósforo e de nitrogênio no rio Paraíba do Sul, com R²=0,96 (p<0,01) e R²=0,70 (p<0,01), respectivamente. Dessa forma, o modelo foi capaz de detectar, de forma significativa, a tendência das variações nas concentrações de nutrientes ao longo de diferentes trechos da BCRF